A Look Back at 2019: Progress Towards the Treatment of Aging as a Medical Condition

It is that time again, an arbitrary midwinter point in the annual pilgrimage around the sun at which we take a look back to summarize some of the high points of the past year. As has been the case for a few years now, progress towards the implementation of rejuvenation therapies is accelerating dramatically, ever faster with each passing year. While far from everyone is convinced that near term progress in addressing human aging is plausible, it is undeniable that we are far further ahead than even a few years ago. Even the public at large is beginning to catch on. While more foresightful individuals of past generations could do little more than predict a future of rejuvenation and extended healthy lives, we are in a position to make it happen.

The State of Funding

A great deal of venture funding is arriving or preparing to arrive to support biotech startups that are working on means to treat aging. This year saw the launch of the Longevity Vision Fund, among others. I can think of three groups presently working to launch new mid-sized longevity-focused venture funds in 2020, and this is as seen from my fairly sedate perch of observation, without any great attempt to reach out and ask folk for a census. This activity will have an beneficial influence on public and private funding available for fundamental science in this part of the field. It also influences non-profit advocacy, as new organizations such as the Academy for Health and Lifespan Research are created. New governmental initiatives are also emerging, such as the Healthy Longevity Global Grand Challenge, and not just in the US: the UK government is putting out position statements on health longevity. Regulators are being petitioned by the scientific community to approve treatment of aging as a recognized goal for medicine. We should expect this trajectory to continue, though beyond the clearance of senescent cells, where development of therapies is very much a going concern, few approaches to rejuvenation are very close to making the leap from laboratory to clinical development.

There is no shortage of new companies targeting aging, many of which are (unfortunately, I think) focused on manipulation of stress responses rather than rejuvenation. BHB Therapeutics works on ketosis mechanisms. Turn.bio aims to produce a safe way to partially reprogram cells in vivo, restoring youthful function. Samsara Therapeutics works on autophagy enhancement. Rejuvenate Bio works on gene therapies to slow aging, initially in dogs. My own company, Repair Biotechnologies, still young, raised a seed round to fund our work on thymic regeneration and reversal of atherosclerosis. The Oisin Biotechnologies spinoff OncoSenX also raised a seed round this year to deploy their suicide gene therapy in cancer patients, and LIfT Biosciences raised funds to develop immune cell transplants that have been shown to do very well against cancer in animal models. Underdog Pharmaceuticals is the SENS Research Foundation spinout targeting 7-ketocholesterol (which may be important in more than just atherosclerosis). They raised a seed round this year and are well on their way. Nanotics has launched a senolytics program based on interfering in mechanisms that senescent cells used to evade immune surveillance. For more you might look at the recently created Aging Biotech Info and its curated list of companies in the longevity industry.

Speaking of funding, the SENS Research Foundation year end fundraiser is coming to a close. More than three quarters of a million dollars were donated last year. I hope that you all did your part and contributed this year - helping this form of research is the most effective form of altruism, given the size of the potential benefits. The SENS Research Foundation remains one of the most important organizations in research aimed at treating aging. Just because senolytics to clear senescent cells are a going concern, we cannot ignore the fact that the rest of the rejuvenation research agenda is nowhere near as advanced. It still needs funding, and near all funding for many of these vital projects remains philanthropic. We fund it. We are the people who make that difference, ensuring that important research projects can advance to the point at which they attract the support of more conservative, mainstream sources of large-scale funding.

Conferences and Community

These days, I'm as often as not out and about in the world raising funding or reporting on progress for a startup biotech company, Repair Biotechnologies. I'm found at many more conferences than would otherwise be the case. Side-effects of the growth of the longevity industry over the past few years include a change in the tenor of existing scientific conferences, as well the addition of new conference series on aging that are focused as much on industry as on academia. This past year, I attended and wrote up a few notes on the following events: the SENS Research Foundation / Juvenescence gathering in San Franscisco held alongside the big JPM Healthcare conference; the first Longevity Therapeutics event, also in San Francisco; the Longevity Leaders conference in London; the vitally important Undoing Aging in Berlin; Biotech Investing in Longevity in San Francisco; the Ending Age-Related Diseases conference organized by LEAF in New York; BASEL Life, Founders Forum, LSX USA, and Giant Health in quick succession later in the year; the Alcor New York Science Symposium; and the Longevity Week events in London coordinated by Jim Mellon and his allies.

Many conference presentations and interviews with members of the growing community have been published over the past year, too many to note each and every one. The few that caught my eye:

Clinical Development

Drug development pipelines are moving forward, though not always smoothly. There is a high failure rate in the development of medical biotechnology. Eidos Therapeutics announced Phase II results for their approach to preventing transthyretin amyloid aggregation. Gensight is presently struggling with phase III for allotopic expression of mitochondrial genes - the mechanism works, the earlier trials passed, and now reaching sufficient efficacy is proving to be a challenge. Intervene Immune published interesting results from their small thymic regeneration trial, while Libella Gene Therapeutics is launching a patient paid trial for telomase gene therapy. The resTORbio approach to inhibition of mTORC1 failed a phase III trial for immunosenescence, which may or may not cast a pall over that part of the industry. The TAME clinical trial for metformin, using a new composite endpoint as a surrogate for aging, was funded this year and will start soon. This despite the point that metformin remains terrible choice of intervention, picked because the FDA couldn't object to it on technical grounds, not because anyone thinks that it will produce meaningful results for patients. Opinions are mixed on this topic.

The first human trials of senolytic therapies to clear senescent cells reported results this year, starting with promising results for lower dose dasatinib and quercetin versus idiopathic pulmonary fibrosis. Data from an as yet incomplete trial of dasatinib and quercetin versus chronic kidney disease has confirmed that these senolytics do clear senescent cells in humans in the same way as in mice. Unity Biotechnology announced results from their first trial of senolytics for osteoarthritis of the knee, and is moving on to phase II. There are those who think that there is still a long road ahead to the clinic. A trial of fisetin by the Mayo Clinic has yet to publish results, but for those who'd like to follow along at home in advance of data, the Forever Healthy Foundation published a risk/benefit analysis covering what is known of fisetin as a senolytic.

Cellular Senescence

Senescent cells accumulate with age and contribute to degenerative disease, despite their many beneficial roles earlier in life. Senolytics to selectively destroy lingering senescent cells continue to show great promise in animal models, and as a class of therapy appear about as close to a panacea as it is possible to be. New supporting evidence published over the course of 2019 offers the potential of effective treatment for a range of conditions: Alzheimer's disease, osteoporosis, osteoarthritis, rheumatoid arthritis, atherosclerosis, cardiac fibrosis and hypertrophy, periodontitis, pulmonary fibrosis, cataracts, aortic aneurysm, acute kidney injury, chronic kidney disease, heart failure, type 1 diabetes, type 2 diabetes, thrombosis, degenerative disc disease, immunosenescence due to changes in hematopoiesis, pulmonary disease resulting from smoking, age-related loss of liver function, neurodegeneration through astrocyte senescence, recovery from heart attack, and recovery from chemotherapy. The accumulation of senescent T cells is an important component of immune aging and chronic inflammation, including some of the issues observed in type 2 diabetes. Visceral fat tissue produces many of its harmful effects via the generation of more senescent cells than would otherwise be created.

Any number of compounds are under evaluation as potential senolytics, though we should always be skeptical of effect size until animal data is in hand, particularly when the compounds include those already in widespread use, as drugs, supplements, or components of diet. Compounds recently examined for senolytic effects include circumin analogs, the fibrate class of drugs used to treat raised blood lipid levels, cardiac glycosides used in treatment of aspects of heart disease, and quercetin coated nanoparticles. Other approaches also exist: exosomes from embryonic stem cells clear senescent cells, and it may be possible to interfere in the mechanisms that senescent cells use to evade the immune system. Further, designed compounds that are transformed into toxins by senescence-associated β-galactosidase, which is upregulated in senescent cells, appear a promising line of attack.

A great deal of research is ongoing into the biochemistry of cellular senescence, not least because any particular mechanism might turn out to be the basis for therapies that meaningfully turn back aging - there is a little of the element of a gold rush to the work. Senescent cells are large because they produce too much protein in expectation of cell division that doesn't occur - or possibly also because they consume neighboring cells. The ceremides found in extracellular vesicles increase senescence. Versican may link the hyperglycemic diabetic metabolism to increased vascular calcification via cellular senescence. The harmful secretions of senescent cells, the senescence-associated secretory phenotype (SASP) depend on certain aspects of the heterochromatin. The activity of L1 retrotransposons also appears relevant to the SASP. Naked mole-rat senescent cells do not exhibit the SASP, which goes a long way towards explaining how this species can exhibit robust good health even while accumulating senescent cells just like other mammals. Meanwhile, researchers are producing a comprehensive map of all of the molecules making up the SASP, many of which are conveyed via exosomes. Another group has published a database of senescence-associated genes. Acute myeloid leukemia turns out to produce senescent cells to aid its own growth. The gene ccna2 is a regulator of the senescent state. Rising levels of aneuploidy may be important in increasing numbers of senescent cells. Upregulation CBX4 or DGCR8 reduces senescence in mice. Melanocytes are the only epidermal cell type to exhibit senescence. Age-related AT1 autoimmunity may spur generation of senescent cells in vascular tissue, and consequent vascular dysfunction.

An important part of the senolytics industry, and one that has so far lagged behind, is the ability to quantify the number of senescent cells in different tissues by age, along with their pace of creation. A start on senescence burden by tissue and age was published this year for mice, accompanied by a good review on the far patchier data for humans. Are these errant cells lingering for years on end, or is turnover and clearance still happening in very old people, and just needs a helping hand? Recent work on topical rapamyin for skin aging and the speed of senescent cell clearance by age suggests that the latter model is more the case. Answering these questions robustly will require better means of quantifying senescence in patients without restoring to a biopsy. This might be achieved via fluorescent reporter genes, or, for senescence in the kidney, by suitable urinalysis. It will likely also require better and more consistent signatures of cellular senescence.

Mitochondria in Aging

Mitochondrial function is clearly important in the progression of aging. Why does it falter consistently in cells throughout the body? Proximate causes appear to involve a loss of fission, leading to worn and damaged mitochondria that are too large to be effectively cleared by mitophagy; this appears to be related to changing expression of PUM2 and MFF, but how that relates to the underlying molecular damage of aging remains a question.

A method of enhancing mitophagy has been shown to improve mitochondrial function in old humans. Other approaches to mitochondrial decline are at various stages of development, such as delivering entire mitochondria that are taken up by cells and put to work. The SENS Research Foundation team continues to work on allotopic expression of mitochondrial genes as a way to prevent certain forms of mitochondrial DNA damage from causing cells to become pathological, and crowdfunded one of the next steps in their program this year.

Efforts to increase NAD+ levels in old mitochondria are enjoying considerable support at present, though it remains to be proven rigorously that they are producing benefits in the many people who are chosen to employ the various supplements. Animal studies and human trials continue, as does the more fundamental research into the biochemistry of NAD+ in mitochondria. An NMNT inhibitor improves NAD+ salvage to increase stem cell function. Nicotinamide riboside improves intestinal stem cell function. The levels of eNAMPT may be important in the way nicotinamide mononucleotide supplementation increases NAD+. Increased NAD+ levels also slows age-related hearing loss in mice.

Nuclear DNA Damage

Random mutations can spread through a tissue when they occur in stem cells or progenitor cells. There are also epigenetic mutations to consider, persistent and aberrant changes in epigenetic markers that alter the production of proteins. Is this damage a meaningful cause of aging beyond its contribution to cancer risk, though? Most mutations happen in genes that are turned off in tissues. There was a discussion earlier this year of the evidence for this sort of clonal expansion of mutations to be involved in neurodegeneration.

The most interesting new work to emerge this year suggests that repair of certain types of DNA damage causes the epigenetic changes observed to take place with age. Since this mechanism doesn't depend on the mutation of specific genes, and the effect arises wherever the DNA damage occurs in the genome, this is viable alternative to explain how mutational damage can contribute to aging in a way that is very similar in every cell, despite the random nature of the damage, and the fact that the damage largely occurs to irrelevant portions of the genome. It also has implications for the viability of epigenetic reprogramming as an intervention. That the pathological outcomes of the DNA repair deficiency Werner syndrome were shown this year to be strongly dependent on mitochondrial dysfunction, which itself emerges from changes in gene expression mediated by epigenetics, might be taken as somewhat supportive of this new line of work.


There has been little further progress towards bringing approaches to cross-link breaking into a new generation of startup companies this year. Revel Pharmaceuticals, spinning out from the Spiegel Lab at Yale, has yet to raise seed funding to progress beyond initial setup - this is taking far too long, for reasons that have little to do with the technical details. An interesting unrelated advance relates to cross-links in the lens of the eye, which are completely different from those in other tissues in the body and thus require a different approach. A cross-link breaker for these forms of cross-link was trialed for age-related presbyopia, and the results were good.


In neurodegenerative research, the concept that failing drainage of cerebrospinal fluid from the brain is an important component of these conditions is gaining support. Cerebrospinal fluid drainage clears metabolic waste from the brain - and this clearance fails with age as the channels are disrupted by tissue dysfunction. Researchers have suggested that hypertension may contribute to the effect, along with age-related declines in lymphatic vessel function, and have provided evidence for reduced flow to correlate with cognitive decline.

Another growing theme in the study of neurodegenerative conditions is the importance of chronic inflammation. This is thought to be the mechanism by which gum disease is linked to Alzheimer's risk, for example. The neuroinflammation model of Alzheimer's disease inverts the first two steps in the amyloid cascade hypothesis: instead of amyloid aggregation causing chronic inflammation, which in turn produces tau aggregation, the chronic inflammation is the whole of the cause of the early stages of the condition, with amyloid as a side-effect. Much the same view is argued for Parkinson's disease and its protein aggregates. The infection hypothesis is a different aspect of this view, in which amyloid aggregation and chronic inflammation both arise from persistent viral infection. A variant of this hypothesis places more emphasis on the way in which infection generates senescent immune cells in the brain, promoting inflammation via that path. In any of these possibilities, dysfunction in glial cells is an important part of the inflammatory process, and depleting these cells reduces inflammation and consequent tau pathology. There is evidence in mice for herpesviruses to accelerate amyloid buildup. Whatever the order of causation, there is good evidence for amyloid and tau aggregates to synergize with one another in degrading neural function.

The evidence for CMV to generate chronic inflammation and otherwise impact immune function suggests that persistent viral infection is harmful in general, not just when it comes to the brain. The immune system and its decline is an important determinant of aging, and chronic inflammation is the proximate cause of a sizable fraction of age-related disease. Complicating matters, chronic inflammation might even contribute to thymic involution, an important cause of immune aging.

The Alzheimer's community is looking for new approaches. There is an increasing focus in the Alzheimer's research community on targeting tau rather than amyloid-β. A variety of methods are under exploration. An existing farnesyltransferase inhibitor drug was found to reverse tau aggregation in a mouse model. Approaches aimed at clearance of amyloid-β have not gone away, of course, and are still very actively developed. The use of affibodies is becoming explored, to pick one example. Clearance of protein aggregates is still a comparatively underutilized approach for other neurodegenerative conditions, however. There is still work taking place, such as small molecule discovery to interfere in α-synuclein aggregation in Parkinson's disease, or catching α-synuclein aggregation in the gut before it spreads to the brain. Researchers are also investigating the heat shock response as a way to direct greater clearance of protein aggregates, as well as the far more promising use of catabodies as pioneered by Covalent Bioscience.

The blood-brain barrier has long been thought important in neurodegeneration. Dysfunction in the barrier is an early leading indicator of larger neurodegeneration, though, confusingly, amyloid aggregation can cause blood-brain barrier leakage. This dysfunction is centered around the tight junction structures of the barrier, and it isn't just neurodegenerative conditions in which this is a factor. Many forms of damage to the brain are characterized by leakage of the blood-brain barrier. Early disruption of the barrier might be due in part to increased levels of acid sphingomyelinase. The primary contribution of blood-brain barrier dysfunction to neurodegeneration may well be that leaking barrier allows the passage of cells and molecules that drive chronic inflammation in brain tissue, such as fibrinogen.

Upregulation of Cell Maintenance

Upregulation of the various cell maintenance processes in order to modestly slow aging, particularly autophagy (a process that shows up everywhere in aging) and the ubiquitin-proteasome system, is an area of active research. Autophagy is known to decline with age for a variety of reasons, such as progressive failure to form autophagosomes. Recent evidence links this decline to aging in skin, and accumulation of senescent cells in the brain.

Strangely, there hasn't been all that much progress towards the clinic over the past decade, despite all of this ongoing activity. Restoration of mitophagy has been proposed as a potential treatment for neurodegenerative conditions. Upregulation of autophagy in general has recent evidence supporting its use in slowing the progression of sarcopenia, memory B cell decline, and atherosclerosis. Researchers have also proposed altering the behavior of the proteasome to target unwanted molecules, such as those altered by misfolding, or achieving a similar effect by binding unwanted proteins to component parts of the autophagosome, ensuring they get dragged along to the lysosome for disassembly. Targeting the GATA transcription factor can upregulate autophagy. The proteasome can be made more active by increasing production of one of its component parts, which is an interesting potential strategy that is gaining some support in the research community. Improving cellular maintenance in intestinal stem cells extends life in flies, a species in which intestinal function is particularly important in aging.

In Vivo Cell Reprogramming

A number of groups are working on in vivo cell reprogramming, applying similar strategies to that used to produce induced pluripotent stem cells, but in a living animal. Turn.bio launched this year to work on a method of partial reprogramming, and another group has demonstrated regeneration from optic nerve injury. The challenge here is cancer risk, and the gains appear at this point to be some combination of restoring more youthful mitochondrial function and epigenetic control of gene expression.


Work on parabiosis continues apace, linking the circulatory systems of an old and young animal and observing the results on each. It is a way to identify factors in young blood and tissue or old blood and tissue that can slow or accelerate aging, for all that the evidence is somewhat confusing and contradictory at this time. The two companies in the space in recent years, Ambrosia and Alkahest have produced only marginal results in human trials. Researchers have found MANF as a possible factor in young blood, associated with liver function. Factors in young blood appear to influence kidney function via upregulated autophagy. It is argued that most of the effects of parabiosis are mediated by the contents of extracellular vesicles, not individually secreted proteins. Beyond parabiosis, there are other approaches that involve introducing young tissue into old animals. Researchers have shown that transplanting young bone marrow into old mice is beneficial, resulting in extended life span.

The Gut Microbiome in Aging

Research into the role of changes in the gut microbiome in aging seems to be hitting its stride. The effect size of the loss of beneficial bacteria and gain in harmful bacteria is an open question, but studies in short-lived animals suggest it might be in the same ballpark as that of exercise. Certainly, healthier older people tend to have more youthful-appearing microbial populations, and this is true for thinner, fitter individuals as well. Changes in the microbiome are shown to contribute to inflammation and vascular dysfunction, as well as neurodegenerative conditions. Further, a number of quite concrete, actionable discoveries have been made in the past few years. The secretion of proprionate improves exercise capacity, and the microbes responsible are found in athletes. Optimizing gut microbial populations for greater butyrate production is beneficial to cognitive function. The populations responsible for providing tryptophan and indole decline precipitously in the mid 30s in humans, indicating supplementation of these metabolites or restoration of the lost microbes will be beneficial when started comparatively early in adult life, well ahead of most signs of aging.

Calorie restriction slows changes in the gut microbiome, but can these age-related changes be reversed? The answer is yes: transplantation of young microbes into old animals has produced good results in animal studies. Fecal microbiota transplantation is an established procedure in human medicine for conditions in which the gut is overtaken with pathological microbes, so perhaps it would not be a huge leap to extend it to improving the elderly gut microbiome. There are other approaches: limiting energy generation by pathological bacteria can diminish these populations; immunization against flagellin causes the immune system to more aggressively cull harmful gut microbes.

Biomarkers of Aging

The measurement of aging is an important goal. Quick, low-cost, reliable assessments that can be used shortly before and shortly after application of a potential rejuvenation therapy would greatly speed development of the field. Epigenetic clocks based on DNA methylation are the best known of present development programs aimed at producing biomarkers of aging. These clocks are multiplying rapidly, and do a fair job of predicting disease risk and mortality. Epigenetic age correlates with cancer risk, for example. The GrimAge clock was announced this year, as was a ribosomal DNA focused clock. In a related part of the field of epigenetic research, it was recently found that CpG site density in the genome correlates with species life span.

The clocks are not without their challenges. We don't know what they are actually measuring, and there is no guarantee that the results will be useful for any given therapy. Troubling results have been reported, the most recent of which include the inability of the clocks to distinguish between sedendary versus active twins, and lack of correlation between telomere length measures and epigenetic clocks.

Epigenetic measures are far from the only area of focus. Other groups are set on constructing biomarkers of aging from algorithmic combinations of simple measures such as grip strength, or from the gut microbiome. In the past year, other researchers have proposed intron retention via alternative splicing, the fundamentals of systems biology, measurement of protein levels in blood, and immune system metrics as potential foundations for a biomarker.


I don't watch cancer research in as much detail as I did in past years. There is a lot of very interesting work taking place, nonetheless, and the outlook is favorable for those of us who are expecting to tackle our own cancers two decades or more in the future - survival rates continue to improve, and the technologies presently in trials or development are considerably better than past therapeutic approaches. Much of the focus these days is on the refinement of ways to unleash the immune system, removing suppression mechanisms that are preventing it from vigorously attacking tumors. For example by interfering in CD47 signaling or the newly discovered similar role for CD24. There are also more speculative early stage approaches such as permanently increasing the number of natural killer cells to reduce cancer risk, or clearing out subsets of tumor associated macrophages that appear to be suppressing anti-tumor immune function.

That said, some more exciting work turns up at early stages, such as a potentially safe way to suppress telomerase activity. All cancers require lengthening of telomeres, via telomerase or ALT. Turning that off could be a universal cancer therapy. On the ALT side of the house, researchers have found that inhibition of FANCM activity is a potential point of intervention.

The Genetics of Longevity

All things genetic continue to attract a great deal of funding. This is an age of low-cost, high-capacity genetic tools - but given a hammer, perhaps too many things start to look like a nail. Studies of recent years have shown over and again that genetic contributions to human variance in aging are near entirely some combination of rare and inconsistent, small in effect size, and overall not all that important. Essentially, we all age in the same way, because of the same causes, and the observed variance is largely down to environment, chance, and choice. Based on this, I predict, and we can come back and look at this prediction in a few years, that the benefits produced by senolytic rejuvenation therapies will be very little affected by human genetic variation, as this form of therapy targets a mechanism in which the size of effect is significantly larger than the variance in that effect.

Regenerative Medicine

Efforts are underway to replace first generation cell therapies of many sorts, some of which were never even deployed to the clinic, with the delivery of extracellular vesicles harvested from those cells. This appears a very promising line of work. Development is underway aimed at skin regeneration, such as via increased collagen production, as well as osteoporosis and thymic regrowth. One can also mix and match: use exosomes to make a cell therapy more effective. Another possible approach to the replacement of cell therapies is reprogramming of cells in situ, such as to make astrocytes or glial cells become neurons in the brain, or turning supporting retinal cells into photoreceptors, heart fibroblasts into cardiomyocytes, or inner ear cells into sensory hair cells to replace losses. There is also considerable interest in rejuvenating stem cell populations in situ via signaling molecules, gene therapies (such as upregulation of GAS1 in muscle stem cells, or Nrf2 for degenerative disc disease), or other strategies.

Cell therapies are of course still very much a going concern, for all that their implementation in the clinic has proven to be challenging. There are some surprising successes in animal models, such as the use of a stem cell therapy to restore lost sense of smell in mice. Researchers are working on ways to replace lost cell populations or influence disease processes in Parkinsons's disease, atherosclerosis, corneal damage, and hearing loss, just to list a small selection of work from the past year. A large part of working towards success in this goal is to ensure that more cells survive and engraft, and that might be achieved by as simple an approach as culling less healthy cells prior to transplant. The march towards more cost-effective means of cell therapy continues, with the creation of cell lines that can be used in every patient being a priority. That reprogramming cells into induced pluripotent stem cells reverses epigenetic signatures of aging seems like a good reason to put more effort into using these cells as a basis for therapy.

In the tissue engineering space, the research and development community continues to move towards the growth of human organs in animals as a source for transplantation. Meanwhile, organoids are being generated for many tissue types; work on the kidney is being carried out by numerous research groups. Further, some organs are simple enough that simpler, artificial versions are useful - artificial lymph nodes, for example, are a popular topic. Or bioprinted corneal tissue. Arguably the biggest advances of the past year have been demonstrations of printed tissue incorporating microvasculature, either directly printing vascular channels, via a form of sacrificial embedded printing, or by providing a mix of cells that generates a vasculature in and of itself, potentially working around the limits to size on engineered tissues. Justifiably, these advances received considerable attention.

Odds and Ends

As is usually the case, a range of scientific work was published this year relating to approaches that could in principle lead to enhancement biotechnologies that would improve health and capabilities for everyone, not just sick people. There is, sadly, near zero chance that most such approaches will be developed to the point of robust function and widespread availability, given the present regulatory environment. To pick a few examples: symbiotic bacteria that increase oxygen availability in tissues; CXCL12 promotes small artery growth, providing alternative paths for the bloodstream that can reduce mortality and harm from heart attacks and similar blood vessel blockages. One of the possible exceptions to the absence of development efforts is delivery of soluable klotho, which has been picked up by Unity Biotechnology to expand their pipeline beyond senolytics.

There are of course any number of other topics I could have discussed at greater length and chose to skip over for the sake of time. Destruction and recreation of the immune system as a way to put autoimmunity into remission continues to be promising, and continues to need a better, safer approach than hematopoietic stem cell transplantation. Age-associated B cells are a good target for more selective destruction, though, as ever, it doesn't fix as many problems as we'd like it to. Being fit is good for you, and in a world without rejuvenation therapies, exercise capacity is a better predictor of mortality than chronological age. Reversal of atherosclerosis is ever an interesting topic, and earlier this year I summarized some of the past work in this part of the field in the context of nattokinase. In this context, it is fascinating that humans seem to need far less cholesterol than we actually have in our bloodstreams, even in a healthy state. Naked mole-rats have a far more effective and resilient metabolism than other mammalian species, and it is possible that improved mitochondrial antioxidants might be a part of that general superiority - though this is a species that thrives under high oxidative stress. There was a sizable debate over whether or not Jeanne Calment was actually aged 122 at death. Late life mortality is in general tough to examine because the data is of a terrible quality, which makes it difficult to debate propositions such as whether or not there is a limit to human longevity in the present environment of slowly increasing life spans. Does obesity actually accelerate aging? Quite likely yes. Declines in the density of microvasculature may be an important mediating process in aging, linking fundamental molecular damage to declining tissue function as a consequence. TDP-43 protein aggregation is a comparatively newly discovered form of proteopathy causing neurodegeneration, and researchers continue to explore the implications. Human cell division rates decrease with age, which might explain why cancer risk actually declines in very late life. Amyloid buildup in the heart correlates with the risk of atrial fibrillation, adding to data from past years showing that amyloid contributes to heart disease and cardiac mortality. Dogs are a possibly underused model for aging research; that underuse might change with the growth of the Dog Aging Project.

Short Articles

As usual, a number of short articles were written over the past year, though it seems I'm doing this less often than used to be the case. Time is ever fleeting.

In Conclusion

A great deal of progress is being made in the matter of treating aging: in advocacy, in funding, in the research and development. It can never be enough, and it can never be fast enough, given the enormous cost in suffering and lost lives. The longevity industry is really only just getting started in the grand scheme of things: it looks vast to those of us who followed the slow, halting progress in aging research that was the state of things a decade or two ago. But it is still tiny compared to the rest of the medical industry, and it remains the case that there is a great deal of work yet to be done at all stages of the development process. Senolytics must reach the clinic and widespread availability, and that will involve the deployment of vast amounts of funding. At the same time, however, numerous other equally important lines of rejuvenation research are still largely stuck in the labs or in preclinial development at best. There is much left to accomplish.

Smooth Muscle Cells in Age-Related Vascular Degeneration and Calcification

Vascular smooth muscle cells are impacted considerably by aging, contributing to detrimental age-related remodeling of blood vessel walls in a number of ways. This includes the structural changes that accompany hypertension and atherosclerosis, as well as arterial stiffness and calcification. Insofar as calcification goes, existing evidence supports a role for the inflammatory signaling of senescent cells in driving vascular cells to behave as though they are in bone tissue, depositing calcium. The overall dysfunction of vascular smooth muscle cells is quite complex, however, and probably involves loss of mitochondrial function and other forms of damage beyond that of an inflammatory environment.

Vascular smooth muscle cells (VSMCs) are connected to a network of elastin and collagen fibers. The capacity of the vessel wall to elastically distend is important to accommodate the volume ejected with each heartbeat and to limit peripheral pressure pulsations. The spatial arrangement of VSMCs may influence the mechanical load on the extracellular matrix (ECM) components and, therefore, modulate vessel diameter and stiffness. Chronic exposure to high blood pressure increases tensile stress to which VSMCs respond by proliferation, resulting in hyperplasia and thickening of the vascular wall. Concomitant activity of matrix metallopeptidases facilitates the structural breakdown of elastin ECM, and VSMCs produce collagen ECM, attempting to preserve stiffness homeostasis. High blood pressure thus aggravates age-related stiffening of arteries. Additional ECM disturbances, such as the presence of calcium crystals, have a further impact on the stiffening of the medial layer.

During aging, it is generally accepted that the number of cells in the vasculature decreases, although the causes of this finding remain to be established. It has been hypothesized that VSMCs become senescent and that cell division rates decrease. The recent literature ignores vessel wall cellularity and often refers to cellular processes, such as apoptosis, inflammation, calcification, and epigenetic effects, all playing a part in vessel wall aging. Additionally, with aging, collagen content in major arterial vasculature increases, whereas elastin content decreases and the number of VSMCs declines. As a consequence, remaining VSMCs are embedded in a collagen-enriched ECM with fewer cellular focal adhesions.

Within arterial vessels, differences exist in the content of elastin to VSMC ratios. Large arteries close to the heart contain more elastin and are therefore called "elastic" arteries. It is particularly elastic arteries that stiffen with age. Large artery stiffening results in decreased arterial compliance, especially in those aged over 60 years. Peripheral vessels contain more VSMCs relative to elastin and are termed "muscular" arteries. In muscular arteries, the relative elastin content increases with age, most likely caused by the decline in the number of VSMCs and decreased collagen content. It should be noted that the absolute amount of ECM proteins in the vasculature decreases with age, but that fat and extracellular material, such as calcium crystals, increase. Taken together, the number of VSMCs within the vasculature strongly correlates with vascular stiffening and the arterial remodeling processes.

Link: https://doi.org/10.3390/ijms20225694

A Fourfold Greater Risk of Cardiovascular Mortality in Women with Poor Fitness

The research results here are a reminder that exercise has a meaningful effect on long-term health. Agreeing with the outcomes from many other epidemiological studies, the data here shows a significantly higher risk of mortality due to cardiovascular disease for individuals possessed of a lesser capacity for exercise. Human studies largely only show correlations between exercise and age-related disease risk, leaving open the question of the direction of causation, but the equivalent animal studies quite comprehensively demonstrate that exercise lowers risk of age-related disease. Regular exercise and maintenance of physical fitness are good for you.

Exercise is good for health and longevity, but information on women is scarce. Women generally live longer than men, so dedicated studies are needed. This study examined exercise capacity and heart function during exercise in women and their links with survival. The study included 4,714 adult women referred for treadmill exercise echocardiography because of known or suspected coronary artery disease. Most study participants were middle aged or older women: the average age was 64 and 80% were between 50 and 75.

Participants walked or ran on a treadmill, gradually increasing the intensity, and continuing until exhaustion. Images of the heart were generated during the test. Fitness was defined as a maximal workload of 10 metabolic equivalents (METs), which is equal to walking fast up four flights of stairs or very fast up three flights, without stopping. Women who achieved 10 METs or more (good exercise capacity) were compared to those achieving less than 10 METs (poor exercise capacity).

During a median follow-up of 4.6 years there were 345 cardiovascular deaths, 164 cancer deaths, and 203 deaths from other causes. After adjusting for factors that could influence the relationship, METs were significantly associated with lower risk of death from cardiovascular disease, cancer, and other causes. The annual rate of death from cardiovascular disease was nearly four times higher in women with poor, compared to good, exercise capacity (2.2% versus 0.6%). Annual cancer deaths were doubled in patients with poor, compared to good, exercise capacity (0.9% versus 0.4%). The annual rate of death from other causes was more than four times higher in those with poor, compared to good, exercise capacity (1.4% vs. 0.3%).

Link: https://www.escardio.org/The-ESC/Press-Office/Press-releases/Women-exercise-and-longevity

A Rate of Living Approach to the Concept of Programmed Aging

A vocal minority of gerontologists consider aging to be a genetic program. In their view, changes in regulation of cellular metabolism that drive aging are selected for in the course of evolution, and these changes cause the observed damage and dysfunction in older individuals. This is the reverse of the more widespread consensus view of aging, in which dysfunction and changes in regulation of cellular metabolism are the result of stochastic molecular damage that is either hard to repair, or gradually overwhelms repair capabilities. In this case, the damage precedes and causes harmful changes in cellular function.

Today, I'll point out a novel take on programmed aging, an open access paper in which the author proposes that the important aspect of aging is that every cell division causes a reduction in mitochondrial function - a very rate-of-living sort of a concept. I can't say that I agree with it, but it is an interesting idea to try to argue one way or another. Further, I do not agree with the author's proposition that failure to date to extend human life span is a failure of the stochastic damage models of aging. No-one has really much tried to repair the damage yet. Senolytic therapies to clear senescent cells are the first approach to aging based on damage repair to have reached the stage of earnest, widespread development efforts. They do very well in the lab, in animal models of age-related disease, but human trials have only just started. The numerous other approaches, aimed at different types of damage, have yet to reach fruition. If anything, the failures of past decades represent a failure on the part of the research and development community to engage seriously with the mechanisms of damage.

In the field of research into aging taken as a whole, there is a pretty good catalog of fundamental forms of molecular damage, and there is a pretty good catalog of age-related diseases and dysfunction. The understanding of how these two are linked is, unfortunately, very poor: knowing exactly how aging progresses would require a complete map of cellular metabolism, something that is decades away from realization at the very least. Thus it is quite easy for any given aspect of aging to be claimed and fit into either programmed aging therapies or stochastic damage theories. Cellular senescence, for example, is clearly important in aging, given that clearing these cells extends life and reverses age-related disease in animal models. Does the burden of senescent cells increase with age due to rising levels of cellular damage and consequent impairment of the immune system in its role of clearing senescent cells? Or does it rises with age because of programmed epigenetic changes that diminish resilience to the senescent state by, e.g. impairing autophagy and mitochondrial function. In areas in which complexity and lack of information makes it quite challenging to produce sound proofs, theorizing is rampant.

There is considerable variation in evolutionary models for how and why a program of detrimental change over time might be selected for. Some, like the hyperfunction theory, look a lot like the standard antagonistic pleiotropy view of why evolution doesn't tend to result in adult organisms that can last indefinitely. Biological systems evolve to do very well in early life, to optimize reproductive fitness right out of the gate, regardless of later consequences. So there are developmental programs that run wild in adult life, or systems that are incapable as constituted of running indefinitely, due to inadequate repair, limited space, or other issues. Other researchers suggest that aging is selected for directly, and invoke group selection arguments to suggest that it enhances fitness in times of environmental change, or acts to reduce the odds of ecosystem collapse due to population growth.

One of the more important advances in aging research made of late may turn out to be the discovery that repair of double strand breaks in nuclear DNA is the cause of shifts in epigenetic regulation characteristic of aging. If validated, it is a mechanism by which stochastic DNA damage, different in every cell, can produce the consistent result observed in old tissues, a detrimental change in metabolism that is much the same in all cells of a given type. That might explain the general decline in mitochondrial function, autophagy, and other processes in which changes in gene expression are the proximate cause. This should also place age-related epigenetic change firmly into the stochastic damage camp of aging, a downstream consequence of molecular damage, rather than being a program of some sort.

The Mechanism of Programed Aging: The Way to Create a Real Remedy for Senescence

Despite the breathtaking progress in all areas of science, especially in biology, and the emergence of powerful new technologies, gerontology has not made any progress in extending the maximum human lifespan. The primary reason for this stagnation is that the basal postulate of the dominant concept of aging states that the genes of longevity cannot exist, while age-related organism degradation is the result of the accumulation of stochastic errors. By now, it has been shown experimentally that genes of longevity exist and that their manipulation can influence the maximal lifespan. But, the obtained empirical data have no convincing substantiation.

It is time to conclude that further research in traditional direction is hopeless and we need to revive the initial ideas of Hippocrates and Weisman, which state that the aging process is programmed via the decline in bioenergetics. All conditions are maturated already for the realization of this way. Compared to the first half of the 20th century, genetics made enormous successes, the machinery of biological energy production has been studied substantially, and a huge amount of different fundamental knowledge has been accumulated.

Since the conception of stochastic errors has been dominant until now, gerontologists have not looked into the physicochemical essence of bioenergetics. Therefore, an age-related decline in bioenergetics is usually expressed by such inexplicit terms as "a decrease [decline] in energy production", "a defect of mitochondrial function", "mitochondrial dysfunction", "a defect in mitochondrial respiration", "a decline in mitochondrial function", or "dysregulated mitochondrial dynamics". A level of bioenergetics at the current time is usually measured by the amount of oxygen absorbed per unit of time. This is enough for resolving of some specific tasks but insufficient for understanding the mechanism of programed aging and resolving the longevity problem. To achieve the main goal, it is necessary to find out what parameter of bioenergetics is directly controlled by the genetic program, what molecular mechanism performs this program.

The ATP/ADP ratio generated by the mitochondrial bioenergetics machine predetermines the capacity of any biological system to work. It is this parameter of bioenergetics that is decreased by a genetic program to drive aging. The performance efficiency of bioenergetics depends on the ATP/ADP ratio rather than the absolute value of ATP or the number of mitochondria in cells. For example, the maximum weight that a weightlifter can lift, having a certain muscle mass, depends on the ATP/ADP ratio in his mitochondria, with the number of mitochondria in muscle cells determining how many times he can lift it. Over the years, the strength decreases, even if the muscle mass and the number of mitochondria in the muscles remain the same. The value of the ATP/ADP ratio is denoted below simply as the "bioenergetics level."

The conventional viewpoint on the mechanism of the Hayflick limit, based on the telomere shortening, is now discredited. Instead, another mechanism has been put forward. According to this proposition, there is a specific checkpoint at the boundary between the G1 and S phases in the cycle of cell division called the restriction point. All normal dividing somatic cells make a cycle suspension here; but, after a certain number of reduplication cycles, this checkpoint becomes impassable and cells enter the non-dividing state. The cyclin-dependent kinase inhibitor p27 prevents passage through this restriction point. There is a special molecular mechanism for its removal, and the efficiency of its work depends on the supply of energy. When bioenergetics levels decrease under a certain threshold, this mechanism stops inhibitor removal while cell division becomes impossible.

This leads to the conclusion that the level of cell bioenergetics, and therefore age, are strictly related to the number of duplications that have elapsed. This provides grounds for concluding that the genetic program reduces the level of cell energetics production intermittently in the process of every mitosis. Thus, the core of the mechanism of programmed aging appears to be very simple: every cell division is followed by a slight decrease in energetics generation which in turn causes some decline in viability. It has been shown that, as stem cells are divided, both in vitro and in vivo, their proliferative potential decreases and they reach the Hayflick limit, i.e., stem cells also grow old. It was concluded: "a living organism is as old as its stem cells." Thus, the bioenergetics aging clock regulates the aging process both in cell culture and in an organism.

Autophagy as a Common Denominator of Age-Slowing Interventions in Animal Models

Most of the interventions shown to slow aging in short-lived laboratory species produce their effects through upregulation of autophagy, a collection of cellular maintenance processes that recycle damaged or unwanted proteins and cell structures. This is an important part of the cellular response to various stresses, from heat to lack of nutrients. Since short-lived species have quite plastic life spans when subjected to this sort of stress, particularly to calorie restriction, and since these mechanisms have many component parts that influence the whole, ways to trigger stress response pathways have tended to be the interventions discovered by screening of compound libraries.

Aging is accompanied by progressive decline of autophagy in many organisms. A reduction in autophagy during aging was demonstrated in a study that carefully examined autophagy in different tissues throughout adulthood of long-lived daf-2 and glp-1 C. elegans mutants, and showed that intestinal autophagy inhibition abolishes longevity only in glp-1 mutants. In mice, neuronal and glial specific deletion of either of essential autophagy genes atg5 and atg7 results in short-lived animals displaying neuronal protein accumulation and neurodegeneration. This highlights the importance of autophagy in removing damaged proteins in non-dividing neuronal tissue, and the potential of therapeutic autophagy enhancement in neurodegenerative disease.

Evidence for the role of autophagy in aging was first shown in daf-2 long-lived worms, where RNAi-mediated downregulation of the autophagy gene bec-1 completely abrogated their pronounced longevity. Since this discovery, dependence on autophagy enhancement has been demonstrated in nearly all longevity-promoting interventions. For instance, lifespan extension by dietary restriction, mTOR inhibition, AMPK up-regulation, mitochondrial mutations, and the above mentioned germline glp-1 mutation, all require functional autophagy for lifespan extension. In all these long-lived mutants, lessening autophagy by RNAi returns lifespan toward wild type levels. However, controls treated with similar autophagy-reducing RNAi interventions do not display altered longevity, suggesting that the residual autophagy levels are sufficient to maintain normal lifespan. It is worth noting that the nutrient-sensing pathways implicated in longevity have pleiotropic effects on metabolism, and often, under conditions when autophagy is up-regulated, this also impacts on other anti-aging processes such translation. It is thus challenging to fully evaluate exact contributions of different down-stream effectors on overall longevity.

Manipulations that increase autophagy directly are valuable but sparse, and complicated by the fact that that numerous autophagy genes are involved in different stages of this multistep process. Moreover, overexpression of only one autophagy gene does not necessarily trigger autophagy. Nevertheless, there are some very valuable exceptions that directly show how important this process is in aging. For instance, overexpression of Atg8a in neurons, as well as Atg1 overexpression in neuronal tissue or muscle, extends lifespan in Drosophila. In addition, mammalian lifespan was extended by an ubiquitous increase of Atg5 in mice, and was accompanied by improved motor function. Further studies of autophagy manipulation in different tissues will help to elucidate further tissue-specific effects and the impact of these on organismal aging. In particular, combining longevity experiments with healthspan parameters, such as motor function, cardiovascular deterioration, neuronal loss, and insulin sensitivity, will facilitate the discovery of pharmacological targets for disease prevention and treatment.

Link: https://doi.org/10.3389/fcell.2019.00308

A Discussion of Relaxin as a Possible Treatment for Heart Failure

The hormone relaxin did well in an early clinical trial as a treatment for heart failure, but failed in a larger trial. Researchers here determine that the benefits observed in animal models and patients are probably due to interactions between relaxin and Wnt signaling, a pathway important in regeneration. The actions of this pathway are very complicated and situational, as is true of most regulators of development and regeneration. Given the presently successful trajectory of Samumed, a regenerative medicine company focused on developing therapeutics based on manipulation of Wnt signaling, it is understandable that numerous other groups have attempted much the same in recent years. Manipulation of pathways central to processes such as regeneration is a road littered with failures, unfortunately, thanks to the complexity of the biochemistry.

Based on intriguing clinical and pre-clinical data, relaxin (RLX) engendered significant enthusiasm as a potential therapy for cardiopulmonary diseases. In the acute heart failure trial RELAX-AHF, RLX treatment improved patient survival by a remarkable 37% in 6 months. These exciting results led the FDA to declare RLX as a "break-through" therapy made all the more significant because the trial included patients with systolic and diastolic HF. Unfortunately, the reduced mortality benefits were not duplicated in a subsequent larger clinical trial sponsored by Novartis.

Detailed analysis of the larger trial has not been reported and the failure of RLX to significantly reduce mortality is not fully understood. A possible explanation is that the control group of patients receiving standard of care for heart failure fared considerably better than in earlier trials but another problem has been the design methodology of a 2-days treatment which has justifiably received substantial criticism. Our previous studies on the effects of RLX in experimental animals provide compelling evidence of significant beneficial effects of the hormone in cardiac physiology. We reported that RLX suppressed atrial fibrillation in aged rats by increasing conduction velocity (CV) of atrial action potentials. These effects were linked to increased expression of the voltage-gated sodium channel (Nav1.5), and a marked decrease in fibrosis, both effects confirmed here in ventricles. At the cellular level, the reversal of fibrosis required more than a week due to the slow turn-over of collagen in the extracellular matrix. Besides electrical and extracellular matrix remodeling, we reported that RLX acted as a potent anti-immune and anti-inflammatory agent in the ventricles of aged animals.

Our results show that RLX's effects in heart tissue are largely mediated by the modulation of canonical Wnt signaling which can act as a master controller of gene expression in heart and other organs. While RLX and Wnt signaling have been investigated in models of cancer, there is no work on the interactions of the RLX and Wnt pathways in adult heart and 'healthy' aging as a precursor of cardiac diseases. Wnt signaling in the heart is complex, and different Wnt ligands have distinct effects. Many details of the mechanism by which RLX modulates canonical Wnt signaling remain to be explored. Nonetheless, these findings demonstrate a close interplay between RLX and Wnt-signaling resulting in myocardial remodeling and reveal a fundamental mechanism of great therapeutic potential.

Link: https://doi.org/10.1038/s41598-019-53867-y

Genetic Variants are not an Important Risk Factor in the Vast Majority of People and Age-Related Conditions

This is an age of genetics, in which the costs of obtaining and working with genetic data have dropped by orders of magnitude, while the capabilities of the tools and technologies have expanded to a similar degree. Give the scientific community a hammer, and a great many parts of the field start to look like a nail. Thus there are innumerable studies of genetics and longevity, genetics and specific age-related diseases, and so forth. There is considerable interest in trying to find out whether there is a genetic contribution to survival to extreme old age, and then using this information to develop therapies.

What the data tells us, however, is that we all age in pretty much the same way. The underlying processes of damage and reactions to damage are the same in everyone. The risk of age-related disease is not all that influenced by genetics for the vast majority of people and vast majority of conditions. Long-lived lineages of humans are a tiny, tiny fraction of the population, and may well exist for cultural rather than genetic reasons. Only a tiny number of genetic variants have been reliably correlated with longevity, and the effect sizes in each case are small, the variants adding only modestly to the odds of living longer.

What has by far the largest effect on variations in human aging? Firstly lifestyle, largely exercise and diet, and secondly environment, largely exposure to pathogens, particularly persistent viral infections. This will remain the case until the first rejuvenation therapies are widely adopted, at which point whether or not one uses them will become the largest contributing cause to variation in aging. Genetics is an enormously valuable branch of the sciences, but not as a direct path to human longevity.

Your DNA is not your destiny - or a good predictor of your health

In most cases, your genes have less than five per cent to do with your risk of developing a particular disease, according to new research. In the largest meta-analysis ever conducted, scientists have examined two decades of data from studies that examine the relationships between common gene mutations, also known as single nucleotide polymorphisms (SNPs), and different diseases and conditions. And the results show that the links between most human diseases and genetics are shaky at best. "Simply put, DNA is not your destiny, and SNPs are duds for disease prediction. The vast majority of diseases, including many cancers, diabetes, and Alzheimer's disease, have a genetic contribution of 5 to 10 per cent at best."

The study also highlights some notable exceptions, including Crohn's disease, celiac disease, and macular degeneration, which have a genetic contribution of approximately 40 to 50 per cent. "Despite these rare exceptions, it is becoming increasingly clear that the risks for getting most diseases arise from your metabolism, your environment, your lifestyle, or your exposure to various kinds of nutrients, chemicals, bacteria, or viruses."

Assessing the performance of genome-wide association studies for predicting disease risk

To date more than 3700 genome-wide association studies (GWAS) have been published that look at the genetic contributions of single nucleotide polymorphisms (SNPs) to human conditions or human phenotypes. Through these studies many highly significant SNPs have been identified for hundreds of diseases or medical conditions. However, the extent to which GWAS-identified SNPs or combinations of SNP biomarkers can predict disease risk is not well known. One of the most commonly used approaches to assess the performance of predictive biomarkers is to determine the area under the receiver-operator characteristic (ROC) curve (AUROC).

Our results indicate that the average AUROC for a typical GWAS-derived biomarker profile is low, just 0.55 with a standard deviation of 0.05. This is significantly lower than what we expected given that (the few) published AUROCs typically report a range between 0.62-0.67. The fact that published GWAS AUROCs tend to be high (~0.65) and unpublished GWAS AUROCs tend to be low (~0.55), suggests that one reason for the paucity of published GWAS AUROCs is that many AUROCs for SNP biomarker profiles are either uninterestingly low (less than 0.55), or not statistically different from those generated by a random predictor.

Welcome to the GWAS-ROCS Database Version 1.0

The GWAS-ROCS Database is a freely available electronic database containing the largest and most comprehensive set of SNP-derived AUROCs. All of the data is either directly from, or derived from, studies accessible through PubMed or GWAS Central - an open-access online repository of summary-level genome-wide association study (GWAS) data. The database currently houses 579 simulated populations (corresponding to 219 different conditions) and SNP data (odds ratio, risk allele frequency, and p-values) for 2886 unique SNPs. Each study simulation record (GR-Card) contains information detailing the original study as well as simulated population data (e.g. ROC curves, AUROCs, SNP-heritability scores) determined from careful population modelling to recreate individual-level GWAS data. All GWAS-ROCS data is downloadable and is intended for applications in genomics, biomarker discovery, and general education.

Type 2 Diabetes as a Simple Condition of Excess Fat

Research of recent years has shown that the triggering mechanism for type 2 diabetes is specifically excess fat in the pancreas. The only way to place that fat into the pancreas, in the normal course of affairs, is to become very overweight - to overload the body with fat to the point that it cannot find places to safely store it. Losing this excess fat through a low calorie diet, and then maintaining a lower weight going forward, is a cure for type 2 diabetes, as demonstrated in clinical trials.

For the first time, scientists have been able to observe people developing type 2 diabetes - and confirmed that fat over-spills from the liver into the pancreas, triggering the chronic condition. The study involved a group of people who previously had type 2 diabetes but had lost weight and successfully reversed the condition as part of the DiRECT trial. The majority remained non-diabetic for the rest of the two year study, however, a small group went on to re-gain the weight and re-developed type 2 diabetes while monitored by the study organizers.

"We saw that when a person accumulates too much fat, which should be stored under the skin, then it has to go elsewhere in the body. The amount that can be stored under the skin varies from person to person, indicating a 'personal fat threshold' above which fat can cause mischief. When fat cannot be safely stored under the skin, it is then stored inside the liver, and over-spills to the rest of the body including the pancreas. This 'clogs up' the pancreas, switching off the genes which direct how insulin should effectively be produced, and this causes type 2 diabetes."

"This means we can now see Type 2 diabetes as a simple condition where the individual has accumulated more fat than they can cope with. Importantly this means that through diet and persistence, patients are able to lose the fat and potentially reverse their diabetes. The sooner this is done after diagnosis, the more likely it is that remission can be achieved."

Link: https://www.ncl.ac.uk/press/articles/latest/2019/12/type2diabetesstudy/

Cynomolgus Macaques and Humans Exhibit Broadly Similar Age-Related Changes in the Gut Microbiome

The relative sizes of gut microbial populations are known to change significantly with age; harmful bacteria become more numerous while beneficial bacteria become less numerous. This results in greater chronic inflammation and a lowered production of beneficial metabolites. Numerous causes are proposed for this shift in the microbiome, from dietary changes characteristic of aging to declining immune function, but it is far from clear as to the relative contribution of each such mechanism. In the years ahead we might expect to see strategies emerge to reverse age-related changes in the microbiome, such as application of fecal microbiota transplantation to providing old people with young microbial populations, or the delivery of beneficial bacterial populations in pill form.

Previous clinical and rodent studies have suggested that age may affect the composition of the gut microbiota. Here, monkeys were used to investigate this issue and this animal model has the following advantages: (i) the microbial composition of monkeys is highly similar to that of humans, which makes it easier to translate these findings into human research; (ii) it can effectively avoid the influences of confounding factors such as living environment and genetic background; (iii) nonhuman primates exhibit similar key life span metrics as humans. Here, we characterized the composition and function of the gut microbiota at three representative age phases, which is a new development in this field.

Our results showed that the diversity of the gut microbiota in cynomolgus macaques was reduced with age, which was consistent with previous human studies. Moreover, we found that the microbial composition of the three groups was significantly different. Firmicutes and Bacteroidetes were the dominant phyla in both humans and cynomolgus macaques. Similar to human studies, we found that, compared with the young and adult groups, the old group showed a slight increase in Firmicutes, whereas Bacteroidetes gradually decreased after youth.

With increased age, the relative abundances of Veillonellaceae and Coriobacteriaceae were significantly increased, and Ruminococcaceae and Rikenellaceae were significantly decreased at the family level. There is evidence to confirm that the family Veillonellaceae is associated with age-related diseases such as atherosclerosis and stroke. Ruminococcaceae play a vital role in the maintenance of gut health through degrading cellulose and hemicellulose components of plant material by CAZymes and transporters. These compounds are fermented and converted into short-chain fatty acids (mainly acetate, butyrate, and propionate), which are absorbed by the host and are important for metabolic and immunological homeostasis. Our finding showed that the relative abundance of Ruminococcaceae was negatively correlated with age. Consistent with our findings, previous studies showed that Ruminococcaceae, one of the core microbiota, becomes less abundant in older people, whereas some taxa associated with unhealthy aging emerge. These findings suggested that Ruminococcaceae may have a positive effect on the aging process.

Link: https://doi.org/10.18632/aging.102541

Berberine as an mTOR Inhibitor that Reduces Generation of Senescent Cells and Extends Life Span in Mice

Today's open access paper is an interesting look at berberine as an mTOR inhibitor and its effects on cellular senescence in cell culture and animal models. This is particularly interesting in the context of recent work on rapamycin, showing low doses to reduce the burden of cellular senescence in aged skin. In both cases this appears to be the result of reducing the pace at which cells become senescent, allowing natural clearance mechanisms to catch up - though there is always the question of whether or not the various protein markers used to identify senescence are reduced because the number of senescent cells are reduced, or are reduced because the drug causes a lowering of expression of these proteins.

Is it a good idea to prevent cells from becoming senescent? Cellular senescence halts replication and encourages programmed cell death or destruction via the immune system. It is way to remove damaged and potentially damaged cells from tissues. If a method of preventing senescence gives cells a chance to repair themselves, then fine, but otherwise it starts to sound like a way to increase cancer risk - to have damaged cells remain active while damaged. To refute that proposition, one has to run life span studies, as the researchers did here. Clearly, in these mice, preventing entry into senescence is beneficial, since it increases life span. This may again be a matter of allowing natural clearance processes a chance to catch up and reduce the overall level of cellular senescence. Or it may be that the harmful inflammatory signals produced by senescent cells are, on balance, far worse that the raised cancer risk resulting from prevention of senescence.

Studies of this nature must lead us to think about the right dosing schedule for senolytic therapies capable of destroying senescent cells. If natural clearance of senescent cells is taking place in late life, and accumulation is a matter of too much creation versus a slowed pace of clearance, then senolytic treatments should be delivered every few months. If, on the other hand, accumulation is a matter of a small fraction of all senescent cells managing to linger for years or more, senolytic treatments can be much less frequent. At present there is all too little evidence, but the evidence that does exist suggests that the former scenario is more likely.

Berberine ameliorates cellular senescence and extends the lifespan of mice via regulating p16 and cyclin protein expression

Cellular senescence is one of the most important in vivo mechanisms related to aging. Senescent cells impair tissue function by irreparable cell damage resulting from acute stress or natural aging, consequently restricting the lifespan. Cellular senescence can be categorized into two groups. The replicative senescence, seen after approximately sixty rounds of cell division in cultures (the Hayflick limit), results from the progressive erosion of telomeres following each cell division. This progressive erosion leads to telomere dysfunction and irreversible cell-cycle arrest.

The second category is defined as premature cellular senescence. It is unrelated to telomere shortening but is related to persistent cellular stress. Thus, replicative stress caused by oxidative DNA damage, activation of oncogenes, and loss of tumor suppressor genes also results in premature senescence. Furthermore, premature senescence includes irreversible impairment of tumor cell reproductive capability via chemotherapy or radiotherapy-induced apoptosis which is defined as a drug or radiation-induced senescence. The in vivo stress-induced premature senescence of normal cells is considered to be a critical mechanism affecting organismal aging and longevity.

Berberine (BBR), a natural alkaloid found in Coptis chinensis, has a long history of medicinal use. Furthermore, BBR possesses anti-cancer, anti-inflammatory, and anti-neurodegenerative properties. Although the biological properties of BBR are well-documented, there is little evidence of its role in anti-aging processes. It was previously observed that BBR inhibited mTOR/S6 signaling concurrent with the reduction in the level of endogenous oxidants and constitutive DNA damage response. Thus, it was hypothesized that BBR, with its potential anti-aging effects, could treat the senescence in aging cells.

This study presents the effects of berberine (BBR) on the aging process resulting in a promising extension of lifespan in model organisms. BBR extended the replicative lifespan, improved the morphology, and boosted rejuvenation markers of replicative senescence in human fetal lung diploid fibroblasts. BBR also rescued senescent cells with late population doubling (PD). Furthermore, the senescence-associated β-galactosidase (SA-β-gal)-positive cell rates of late PD cells grown in the BBR-containing medium were ~72% lower than those of control cells, and its morphology resembled that of young cells. Mechanistically, BBR improved cell growth and proliferation by promoting entry of cell cycles from the G0 or G1 phase to S/G2-M phase.

Most importantly, BBR extended the lifespan of chemotherapy-treated mice and naturally aged mice by ~52% and ~16.49%, respectively. The residual lifespan of the naturally aged mice was extended by 80%, from 85.5 days to 154 days. The oral administration of BBR in mice resulted in significantly improved health span, fur density, and behavioral activity. Therefore, BBR may be an ideal candidate for the development of an anti-aging medicine.

More Visceral Fat and Less Muscle Mass Correlate with Lower Fluid Intelligence in Middle Age

Fluid intelligence is described as the ability to solve novel reasoning problems; high fluid intelligence tends to imply a greater capacity to learn, ability to comprehend, and so forth. Fluid intelligence declines with age, but researchers here suggest that has more to do with the effects of visceral fat tissue and loss of muscle mass than it does with an inexorable aging process in the brain - at least into middle age, if not later in life. Both visceral fat and skeletal muscle are metabolically active tissues, though more is understood about the harms caused by visceral fat than about the protective effects that are lost as muscle declines with age. It is reasonable to think, based on weight of evidence, that chronic inflammation and other forms of immune dysfunction with age are strongly influenced by visceral fat, and that this in turn has an effect on brain function. All of the common neurodegenerative conditions of late life have a strong inflammatory component to their progression.

Researches looked at data from more than 4,000 middle-aged to older UK Biobank participants, both men and women. The researchers examined direct measurements of lean muscle mass, abdominal fat, and subcutaneous fat, and how they were related to changes in fluid intelligence over six years. The researches discovered that people mostly in their 40s and 50s who had higher amounts of fat in their mid-section had worse fluid intelligence as they got older. Greater muscle mass, by contrast, appeared to be a protective factor. These relationships stayed the same even after taking into account chronological age, level of education, and socioeconomic status. "Chronological age doesn't seem to be a factor in fluid intelligence decreasing over time. It appears to be biological age, which here is the amount of fat and muscle."

Generally, people begin to gain fat and lose lean muscle once they hit middle age, a trend that continues as they get older. To overcome this, implementing exercise routines to maintain lean muscle becomes more important. Exercising, especially resistance training, is essential for middle-aged women, who naturally tend to have less muscle mass than men.

The study also looked at whether or not changes in immune system activity could explain links between fat or muscle and fluid intelligence. Previous studies have shown that people with a higher body mass index (BMI) have more immune system activity in their blood, which activates the immune system in the brain and causes problems with cognition. BMI only takes into account total body mass, so it has not been clear whether fat, muscle, or both jump-start the immune system. In this study, in women, the entire link between more abdominal fat and worse fluid intelligence was explained by changes in two types of white blood cells: lymphocytes and eosinophils. In men, a completely different type of white blood cell, basophils, explained roughly half of the fat and fluid intelligence link. While muscle mass was protective, the immune system did not seem to play a role.

Link: https://fshn.hs.iastate.edu/news/2019/12/16/changes-in-the-immune-system-explain-why-belly-fat-is-bad-for-thinking/

Refuting the Link Between Persistent Herpesvirus Infection and Alzheimer's Disease

There is a reasonable mechanism by which persistent viral infections might raise the risk of Alzheimer's disease: amyloid-β is an antimicrobial peptide, a part of the innate immune system. The presence of viral particles will contribute to greater production of amyloid-β, which will accelerate the pace at which amyloid-β might aggregate in older individuals due to an imbalance between production and clearance. The aggregates then cause the usual progression to neural inflammation, damage, and cognitive decline. Does the epidemiological data support a role for persistent herpes viruses in Alzheimer's risk, however? Previous studies suggested yes, but here researchers dismantle and refute one of those studies, while suggesting that people need to be more careful when using statistics. This sequence of events happens more often than you might think in the research community.

Like all types of dementia, Alzheimer's disease is characterized by massive death of brain cells, the neurons. Identifying the reason why neurons begin and continue to die in the brains of Alzheimer's disease patients is an active area of research. One theory that has gained traction in the past year is that certain microbial infections, such as those caused by viruses, can trigger Alzheimer's disease. A 2018 study reported increased levels of human herpesvirus in the postmortem brain tissues of more than 1,000 patients with Alzheimer's disease when compared to the brain tissues of healthy-aging subjects or those suffering from a different neurodegenerative condition.

Surprisingly, when researchers reanalyzed the data sets from the 2018 study using the identical statistical methods with rigorous filtering, as well as four commonly used statistical tools, they were unable to produce the same results. The team was motivated to reanalyze the data from the previous study because they observed that while the p-values (a statistical parameter that predicts the probability of obtaining the observed results of a test, assuming that other conditions are correct) were highly significant, they were being ascribed to data in which the differences were not visually appreciable. Moreover, the p-values did not fit with simple logistic regression - a statistical analysis that predicts the outcome of the data as one of two defined states. In fact, after several types of rigorous statistical tests, they found no link between the abundance of herpes viral DNA or RNA and likelihood of Alzheimer's disease in this cohort.

"As high-throughput 'omics' technologies, which include those for genomics, proteomics, metabolomics and others, become affordable and easily available, there is a rising trend toward 'big data' in basic biomedical research. In these situations, given the massive amounts of data that have to be mined and extracted in a short time, researchers may be tempted to rely solely on p-values to interpret results and arrive at conclusions. Our study highlights one of the potential pitfalls of over-reliance on p-values. While p-values are a very valuable statistical parameter, they cannot be used as a stand-alone measure of statistical correlation - data sets from high-throughput procedures still need to be carefully plotted to visualize the spread of the data. Data sets also have to be used in conjunction with accurately calculated p-values to make gene-disease associations that are statistically correct and biologically meaningful."

Link: https://www.bcm.edu/news/alzheimers-disease/herpes-virus-linked-to-alzheimers

Reviewing What is Known of the Role of Transposable Element Activity in Aging

Transposable elements make up a sizable portions of the genome, capable of copying themselves to other locations in the genome under the right circumstances. This activity is suppressed in youth, but increases in older individuals for reasons that are still being explored. Transposable element activity is thought to contribute to aging in a similar way to the effects of mutational damage to DNA, setting aside the risk of cancer, meaning a growing disarray in cellular metabolism due to altered genes and gene expression. When this occurs in stem cells or progenitor cells, this disarray might propagate to a sizable fraction of cells in a tissue.

It is still a little early to say to what degree transposable element activity is a problem, in comparison to the other contributing mechanisms of aging, and what the best approach to suppress it might be. Nonetheless, it is worth considering the recent research suggesting that the operation of DNA repair processes that address double-strand breaks in the nuclear genome causes epigenetic changes characteristic of aging. The LINE-1 retrotransposons have been shown to increase the pace at which double-strand breaks occur once they become active. Joining the dots, perhaps this is a plausible mechanism for cellular disarray. It is an interesting connection, but one that needs further exploration and validation, however.

The role of transposable elements activity in aging and their possible involvement in laminopathic diseases

Transposable elements (TEs) are mobile genetic elements able to change their position within a genome, often resulting in a duplication of their sequences. There are two main classes of these genetic elements: DNA transposons, which encode a transposase required for a cut-and-paste mechanism of transposition, and retrotransposons, which transpose by reverse transcription of an RNA intermediate. Mobilization of TEs may have deleterious effects on genomes, such as the induction of chromosome rearrangements and, when inserted in the coding region of a gene, the destruction or alteration of the normal gene functions. For this reason, TEs are normally repressed by specific silencing mechanisms guided by small non-coding RNAs (sncRNAs).

Beyond the deleterious effects, TEs have an important impact on genome-wide gene regulation. In fact, TEs and TE-derived sequences represent a consistent part of the genome of eukaryotic cells and comprise about 46% of the human genome. TE-derived sequences act as transcriptional regulatory regions in a substantial proportion of human genes, contributing to determining the regulation of the controlled genes. In fact, there is clear evidence that regulatory regions of TEs in mammalian cells have been domesticated to modulate the regulation of nearby genes. Transposition of TEs can deposit regulatory sequences across the genome, modifying the regulation of genes located nearby. Some of these events seem to have had evolutionary advantages.

The transposon theory of aging proposed that the increased activation of TEs in somatic tissues during the aging process leads to a shortening of the lifespan. Activation of TEs is a consequence of the loss of repressive structure that occurs gradually with aging in constitutive heterochromatin regions. Since TEs are highly enriched in these domains, loss of heterochromatin induces an increase in TE expression and a consequent increase in transposition rate. While there are different studies that confirm the upregulation in the expression of TEs during aging, it is not clear to which extent this activation is associated to production of de novo TE mutations in somatic tissues.

It is possible that the contribution of TEs to aging does not depend only on the production of de novo mutations. In fact, activation of LINE-1 retrotransposons leads to a high level of DNA double-strand breaks (DSB), while the predicted numbers of successful retrotransposition events appears lower. Since DNA damage is considered a cause of aging, the mechanism by which LINE-1 contributes to aging could depend on the significant degree of inefficiency in the LINE-1 integration process, which, however, produces a progressive increase of DSBs. Given these findings, LINE-1 element activation during the lifetime in somatic tissues has been considered a possible key factor in human aging.

Bioprinting Liver Organoids with Patient-Derived Cells

Researchers here report on the use of 3-D printing techniques to generate small, functional liver organoids from patient-derived cells. A cell sample is reprogrammed into induced pluripotent stem cells, and these are then differentiated into liver cell clusters to be used in the printing process. These organoids lack a vasculature, and thus cannot be made larger than a few millimeters in size. Given the progress made by Lygenesis and other groups towards the practical use of liver organoids even without vasculature, however, by implantation into lymph nodes, or into the liver itself, patients may well benefit considerably in the near future.

Using human blood cells, researchers have succeeded in obtaining hepatic organoids ("mini-livers") that perform all of the liver's typical functions, such as producing vital proteins, storing vitamins, and secreting bile, among many others. The innovation permits the production of hepatic tissue in the laboratory in only 90 days and may in the future become an alternative to organ transplantation. This study combined bioengineering techniques, such as cell reprogramming and the cultivation of pluripotent stem cells, with 3D bioprinting. Thanks to this strategy, the tissue produced by the bioprinter maintained hepatic functions for longer than reported by other groups in previous studies.

"More stages have yet to be achieved until we obtain a complete organ, but we're on the right track to highly promising results. In the very near future, instead of waiting for an organ transplant, it may be possible to take cells from the patient and reprogram them to make a new liver in the laboratory. Another important advantage is zero probability of rejection, given that the cells come from the patient." The innovative part of the study resided in how the cells were included in the bioink used to produce tissue in the 3D printer. Instead of printing individualized cells, researchers developed a method of grouping them before printing. These clumps of cells, or spheroids, are what constitute the tissue and maintain its functionality much longer.

The researchers thereby avoided a problem faced by most human tissue bioprinting techniques, namely, the gradual loss of contact among cells and hence loss of tissue functionality. Spheroid formation in this study already occurred in the differentiation process, when pluripotent cells were transformed into hepatic tissue cells (hepatocytes, vascular cells, and mesenchymal cells). Researchers started the differentiation process with the cells already grouped together. They were cultured in agitation, and groups formed spontaneously.

Link: http://agencia.fapesp.br/researchers-create-functional-mini-liver-by-3d-bioprinting/32217/

More Insight into the Relationship Between Cell Size and Cell Senescence

Senescent cells accumulate with age and cause considerable disruption of metabolism and tissue function. This is an important contribution to aging, and there is thus funding and interest for continued research into senescent cell biochemistry. Senescent cells are very different from normal cells in many respects, but one of the more striking is that they are much larger. One group has used this to build a microfluidics platform capable of counting and sorting senescent cells, but we may well ask why exactly it is that senescent cells become large in comparison to normal cells. A hypothesis is offered in this popular science article.

Biologists have known since 1961 that normal human cells will only divide 40 to 60 times before ceasing to replicate - a constraint known as the Hayflick limit. Recent research shows that this limit may be defined by a cell's physical size. When Leonard Hayflick first described this senescence phenomenon, he pointed out that these senescent cells were actually huge. Researchers have shown that when cells below the Hayflick limit are induced to grow larger than they should be, they have all the characteristics of senescent cells.

But why do cells get so large, and why should that increased size cause a cell to senesce and ultimately stop dividing? The explanation is suggested to lie in how cells repair damage to the DNA coiled in their chromosomes. Natural DNA damage occurs constantly, and cells must periodically pause the cell cycle to fix it. However, other processes inside the cell - such as building proteins and other biomolecules - don't pause during DNA repair. As a result, every time the cell cycle stops, the cell gets a little larger. If a cell becomes too large, its own genes can't direct the production of enough protein to sustain the cell's function. Cellular functions decline and the cell becomes senescent.

One clue supporting this connection between size and senescence is that doubling the number of genes inside the cell - which doubles the amount of proteins it builds to sustain itself - reverses the senescence process. Furthermore, when using rapamycin to inhibit cells' ability to manufacture proteins (and thus get larger) while paused to repair DNA damage, the cells stay small and avoid senescence - they don't lose their replicative potential. "We've known for a very long time that DNA damage causes senescence, but nobody could explain it. I think we've come up with a proposal for why this is happening - cells get larger during the time they arrest in the cell cycle to repair the damage, and when they are large they lose their functionality. This appears to be universally true from yeast to humans."

Link: http://spectrum.mit.edu/fall-2019/taking-aim-at-cell-dysfunction/

Towards Small Molecule Therapies to Reverse T Cell Exhaustion

T cells of the adaptive immune system are a vital part of the defense against pathogens and cancers. T cells are not invulnerable, unfortunately. T cell exhaustion is a feature of cancers, persistent viral infections, and aging. Exhausted T cells are characterized by inhibition of replication, reduced secretion of immune signals, and sharply limited activity. The proximate cause is of this state is the expression of immune checkpoint proteins such as PD-1. The cancer research industry has achieved considerable success in the development of checkpoint inhibitors, monoclonal antibodies that bind to and inhibit immune checkpoint proteins. These therapies can effectively reverse T cell exhaustion in the context of cancer, allowing the immune system to more effectively attack tumor cells.

Are there other options? Today's open access paper reports on the development of a screening system to allow a search for small molecules capable of reversing T cell exhaustion. This is again achieved by interfering with the operation of immune checkpoints or their immediately downstream biochemistry. Small molecule therapies might be more appropriate than monoclonal antibodies for the reduction of T cell exhaustion in chronic viral infection or in older people in general, particularly given the relative costs of these two approaches.

Discovery of Small Molecules for the Reversal of T Cell Exhaustion

Immune surveillance for the recognition and removal of unwanted virus infected cells and the detection and attack of malignant cells resides primarily with the activity of cytotoxic T lymphocytes (CTLs). To counteract this response, viruses, and cancers reduce the function of CTLs, exhausting them. This is achieved, in part, by upregulation of inhibitory "checkpoint" receptors (IRs) on the surfaces of CTLs. The importance of this strategy in controlling T cell responses is illuminated by findings that neutralizing IRs such as PD-1 or CTLA-4 on exhausted T cells restores their effector responses. The use of such checkpoint inhibitory therapies has led to remarkable clinical benefits in cancer patients.

However, responses in many patients remain limited, in part, due to insufficient restoration of T cell function. Thus, the discovery of additional targets and pharmacologic drugs is required to overcome the limitations of current checkpoint blockade. Therapeutics with distinct properties could enhance the effectiveness of existing IR blockade agents or achieve responses in patients resistant to existing treatment modalities. Several recent reports examining the synergistic effects of antibody-based blockade strategies by targeting alternative IRs, cytokines, or cytokine signaling pathways have sparked numerous clinical trials. Discovery and utilization of low-molecular-weight therapeutics can complement, and in some cases replace, existing IR blockade biologics.

Functional exhaustion of virus-specific T cells was first described in mice infected with the clone 13 (CL13) variant of lymphocytic choriomeningitis virus (LCMV). CL13 causes a persistent viral infection resulting in varying degrees of suboptimal CD4 and CD8 T cell activity, characterized by reduced to absent cytotoxic capacity of anti-viral CD8 T cells, poor proliferative potential, decreased production of antiviral effector molecules such as interferon γ (IFN-γ) and tumor necrosis factor α (TNF-α), insufficient expression of several homeostatic cytokines, and sustained expression of IRs such as PD-1, LAG-3, and TIM-3 and the immunosuppressive cytokine interleukin-10 (IL-10). T cell exhaustion is progressive and thought to be driven by persistent antigen stimulation. The importance of immunosuppressive pathways that maintain T cell dysfunction was initially demonstrated by the resurrection of T cell activity following PD-1 or IL-10 receptor blockade during persistent LCMV infection.

Here, we report utilizing the in vivo LCMV-CL13 model to construct a platform for in vitro high-throughput screening (HTS) to detect small molecules that reverse T cell exhaustion. We identify 19 compounds from the ReFRAME drug-repurposing collection that restore cytokine production and enhance the proliferation of exhausted T cells. Analysis of our top hit, ingenol mebutate, a protein kinase C (PKC) inducing diterpene ester, reveals a role for this molecule in overriding the suppressive signaling cascade mediated by IR signaling on T cells. Collectively, these results demonstrate a disease-relevant methodology for identifying modulators of T cell function and reveal new targets for immunotherapy.

CD33 Influences Alzheimer's Risk via Regulation of Microglial Functions

Researchers here explore CD33 as a possible target for the development of Alzheimer's disease treatments. The protein suppresses the ability of microglia in the brain to ingest and dispose of amyloid. This, in principle, will cause issues over the long term by promoting the presence of amyloid, leading to neural dysfunction and chronic inflammation in the brain. The work here is also interesting as an illustration of the complexities of trying to model the processes of Alzheimer's disease in mice, a species that doesn't normally suffer any of the relevant underlying mechanisms that produce the condition. Previous research proceeded on the basis that the mouse version of CD33 behaved in much the same way as the human version, which turns out not to be the case.

The strong genetic link between variants of CD33 and Alzheimer's disease (AD) susceptibility suggests that targeting the common risk allele of CD33, which preferentially encodes the longer human isoform of (hCD33M) containing its glycan-binding domain, could be a treatment strategy in neurodegenerative disease. To better understand if targeting CD33 in AD is a viable option, a better grasp is needed on the role CD33 plays in modulating the function of microglia. Our findings demonstrate that expression of the long isoform of hCD33 (hCD33M) alone is sufficient to repress phagocytosis in both monocytes and microglia. We have created transgenic mice expressing hCD33M, and these will be a valuable tool for future studies addressing the role of hCD33 in modulating plaque accumulation as well as pre-clinical testing of therapeutics aimed at targeting hCD33.

Divergent features between human CD33 (hCD33) and mouse CD33 (mCD33) include a unique transmembrane lysine in mCD33 and cytoplasmic tyrosine in hCD33. The functional consequences of these differences in restraining phagocytosis remains poorly understood. Using a new monoclonal antibody, we show that mCD33 is expressed at high levels on neutrophils and low levels on microglia. In mouse derived macrophages and monocytes, uptake of cargo - including aggregated amyloid - is not altered upon genetic ablation of mCD33. Alternatively, deletion of hCD33 in monocytic cell lines increased cargo uptake. Moreover, transgenic mice expressing hCD33 in the microglial cell lineage showed repressed cargo uptake in primary microglia. Therefore, mCD33 and hCD33 have divergent roles in regulating phagocytosis.

Accumulation of aggregated amyloid drives the formation of amyloid plaques and mouse models to study human genetic factors that modulate this process in vivo have been widely used. Our studies suggest that mCD33 may not be an appropriate surrogate for studying hCD33. We demonstrate that transgenic expression of hCD33M in the microglial cell lineage inhibits phagocytosis; these hCD33M transgenic mice should provide a valuable model to test the role of hCD33M in regulating plaque accumulation in vivo, which is currently being tested in ongoing studies in our laboratory. Indeed, establishing a good mouse model to study hCD33 is critical for both better understanding AD pathology and also testing therapeutics aimed at controlling microglial cell function by targeting hCD33M.

Link: https://doi.org/10.1038/s42003-019-0698-6

CpG Site Density in the Genome Predicts Species Maximum Life Span

Researchers investigating epigenetic modifications and their relationship to aging have found that the density of CpG sites, where DNA methylation occurs in order to modify the pace of production of specific proteins, correlates with maximum species life span. This is an interesting finding, but, as for the epigenetic clock used to assess aging in individuals, it will likely require the work of many research groups and many years to build a firm understanding as to why this correlation exists.

Ageing involves the decline of diverse biological functions and the dynamics of this process limit species maximum lifespan. Longevity of individuals is strongly linked to specific alleles in genetic model organisms. Ageing is also associated with several epigenetic changes involving DNA methylation (DNAm). DNAm of cytosine-phosphate-guanosine (CpG) sites, involves a covalent modification to cytosine to form 5-methylcytosine. This modification to DNA has the potential to regulate gene expression, including of genes critical for longevity, without altering the underlying sequence.

The observation that DNAm at promoter CpG sites can accumulate or decline predictably with age, over and above the more random process of epigenetic drift, has enabled the development of "clock like" biomarkers for age. Individual human age, for example, can be predicted with great accuracy in a range of tissues by an epigenetic clock. Similar epigenetic clocks have been created in a range of mammal and bird species.

Maximum lifespans differ greatly among species, even among fairly closely-related species. In vertebrates, species such as the pygmy goby (Eviota sigillata) live for only eight weeks, while the Greenland shark (Somniosus microcephalus) may live for more than 400 years. In mammals, the forest shrew (Myosorex varius) has one of the shortest reported lifespans at 2.1 years, whereas some bowhead whales (Balaena mysticeta) have been reported to be older than 200 years. Despite profound importance, lifespan is poorly characterised for most wild animals because it is difficult to estimate.

Maximum lifespan is believed to be under genetic control, but so far, no gene variants can account for differences in lifespan among species. Because ageing is characterised by changes in gene expression caused by DNAm, another potential controller of lifespan is genomic changes that accommodate DNAm's effects on regulation of gene expression. Specifically, clusters of high density CpG sites, also known as CpG islands, are highly conserved within promoter sequences and well known for regulating gene expression. CpG sites are also prone to mutation and their function in regulating gene expression may make them prime targets for evolutionary pressures to vary lifespans.

Here, we extend observations of the correlation between promoter CpG density and lifespan in mammals to produce a predictive model for lifespan in all vertebrates. We use reference genomes of animals with known lifespans to identify promoters that can be predictive of lifespan. We combined data from major databases including NCBI Genomes, the Eukaryotic Promoter Database (EPD), Animal Ageing and Longevity Database (AnAge) and TimeTree to build a predictive model that estimates lifespan. Our results show CpG density in selected promoters is highly predictive of lifespan across vertebrates. To our knowledge this is the first study which has built a genetic predictive model to estimate the lifespan of vertebrate species from genetic markers.

Link: https://doi.org/10.1038/s41598-019-54447-w

The Quest to Measure Human Biological Aging

Today's open access review article is a discussion of the importance of being able to measure biological aging, easily and robustly. Initially, this is an approach to speed the development of rejuvenation therapies; at present one can only efficiently and quickly assess the results of a potential rejuvenation therapy in the context of its ability to reverse a specific age-related disease. There are scores of important age-related conditions to assess, and animal models of these conditions are usually significantly different from the human condition - different enough for a careful consideration of the details to be needed to determine whether or not the model is useful.

If one wants to assess the overall efficacy of a rejuvenation therapy rigorously, it remains the case that life span studies are the only recourse. At minimum, deliver the treatment to old mice and run the study for six months to a year to see how mortality differs between the treatment and control groups. This is painfully expensive, and just doesn't scale to a world in which the research and development community may want to assess hundreds to thousands of variants of potential rejuvenation therapies at any given time. What is desired here is a way to run a quick study in normal aged animals: take a baseline assessment of the state of aging, deliver the intervention, and then within a week or two redo the assessment to see what has changed.

At present a number of different approaches to the measurement of biological aging are under development to one degree or another. The epigenetic clock is one such approach, which looks for epigenetic reactions to the underlying damage of aging. In this case, the challenge is connecting the epigenetic alterations characteristic of aging back to the underlying processes of damage and dysfunction: it is far from clear that the present clocks measure all of aging, versus part of aging. Another approach would be to take the list of cell and tissue damage that causes aging and measure each portion of it. Until rejuvenation therapies based on repairing this damage are developed, however, it will remain unclear as to the relative contribution of each form of damage to the progression of aging. Further, few of these forms of damage can actually be measured in a practical, non-invasive fashion in human patients. There is much work yet needed here.

Measuring biological aging in humans: A quest

Substantial investment is necessary to develop an estimator of biological aging that is robust, precise, reliable, and sensitive to change. Thus, a fair question is whether such a titanic project is worth the effort and cost. The answer is YES, without hesitation. Developing an index of biological aging is perhaps the most critical milestone required to advance the field of aging research and, especially, to bring relieve from the burden of multimorbidity and disability in an expanding aging population. Ideally, these measures would be obtained by running tests using blood samples without performing a biopsy, preferably quickly and at low cost.

An index of biological aging could be used to empirically address the geroscience hypothesis: "Is biological aging is the cause of the global susceptibility to disease with aging." Data collected longitudinally - ideally in a life course epidemiological study - could then be used to test if individuals that accumulate coexisting diseases faster than in the general population also have accelerated biological aging. Similarly, these data could be used to test if individuals who are biologically "older," independent of chronological age, are at a higher risk of developing different medical or functional conditions that do not share physiological mechanisms. Once validated, the fundamental basis of biological aging can be used to probe deeper into questions related to the mechanisms of aging, such as the following: Are there genetic traits that are associated with faster or slower biological aging? Are there "hallmarks" that are better at capturing biological aging at different stages of life?

Developing a proxy measure of biological aging for humans still requires work but is a very dynamic and promising area of investigation with strong potential for translation. Some of the measures - namely mitochondrial function, DNA methylation, and, to a lesser extent, cellular senescence and autophagy - are ready to be implemented based on several epidemiological studies, although refinements are always possible. Measures of telomere length are hampered by noise and wide longitudinal variations that cannot be explained by health events and at this stage are not useful for measuring biological age. New methods are being developed, some of which are focused on detecting the DNA damage response (a typical marker of critical telomere shortening) may yield better results. Senescence has been studied successfully in T lymphocytes, skin, and intramuscular fat, and high-throughput methods will be available soon. In addition, specific patterns of circulating proteins may exist that indirectly estimate the burden of senescence. Similarly, measures of autophagy are routinely used in mammalian studies and should be applicable to humans.

Multiple lines of evidence suggest that the measures listed above are associated with the severity of multimorbidity but, except for the epigenetic clock, this association has not yet been clearly established. Logically, none of the measures described above represent an exhaustive measure of biological aging and, therefore, new aggregate measures are needed that leverage differences and complementarities of the various biomarkers. To accomplish these goals, the hallmarks of aging should be assessed in a group of individuals that is reasonably sized and enough dispersed across the lifespan to represent the variability of biological age in the general population. Initially, it will be important to evaluate the intercorrelation between these measures.

These questions have immense relevance for geriatric medicine. Despite the rising emphasis on prevention, most current medical care is dedicated to diagnosing and managing diseases that are already symptomatic, which does not address the underlying issues related to geriatric health conditions. By understanding the intrinsic mechanisms of biological aging, including damage and resilience, medical professional will be able to best orient and prescribe therapeutic choices.

Progress in research is not linear. Periods characterized by rates of incremental knowledge are interlaced with "eureka" moments as milestone discoveries suddenly open new possibilities that thrust research and knowledge to a higher level. Galileo's use of the telescope to explore the stars, Kary Mullis's description of polymerase chain reaction, and Edwin Hubble's demonstration that the universe is expanding are just few examples of these moments. The field of aging research is living one of those magical moments. Finding a reference metric for the rate of biological aging is key to understanding the molecular nature of the aging process. Defining and validating this metric in humans opens the door to a new kind of medicine that will overcome the limitation of current disease definitions, approaching health in a global perspective and bringing life course preventative measures to the center of attention.

Age-Related Hyperglycemia as a Cause of Increased Cancer Incidence

Why is cancer an age-related condition? One can propose a range of mechanisms: the spread of stochastic DNA damage through cell populations; rising levels of chronic inflammation; ever more senescent cells turning out disruptive, pro-growth signals; the growing inability of the immune system to promptly destroy errant cells. The authors of this open access paper argue that the metabolic dysfunction of later life that leads to raised blood sugar, hyperglycemia, is also an important contributing factor to cancer risk. Most hyperglycemia is self-inflicted via obesity, but it can manifest in other ways as damage and systems failure accumulates in late life.

Aging can increase cancer incidence because of accumulated mutations that initiate cancer and via compromised body control of premalignant lesions development into cancer. Relative contributions of these two factors are debated. Recent evidence suggests that the latter is rate limiting. In particular, hyperglycemia caused by compromised body control of blood glucose may be a factor of selection of somatic mutation-bearing cells for the ability to use glucose for proliferation. High glucose utilization in aerobic glycolysis is a long known characteristic of cancer.

The new evidence adds to the concepts that have been being developed starting from mid-1970s to suggest that age-related shifts in glucose metabolism and lipid metabolism increase the risk of cancer and compromise prognoses for cancer patients and to propose antidiabetic biguanides, including metformin, for cancer prevention and as an adjuvant means of cancer treatment aimed at the metabolic rehabilitation of patients.

The new evidence is consistent with several effects of glucose contributing to aging and acting synergistically to enhance carcinogenesis. Glucose can affect (i) separate cells (via promoting somatic mutagenesis and epigenetic instability), (ii) cell populations (via being a factor of selection of phenotypic variants in cell populations for higher glucose consumption and, ultimately, for high aerobic glycolysis); (iii) cell microenvironment (via modification of extracellular matrix proteins), and (iv) the systemic levels (via shifting the endocrine regulation of metabolism toward increasing blood lipids and body fat, which compromise immunological surveillance and promote inflammation). Thus, maintenance of youthful metabolic characteristics must be important for cancer prevention and treatment.

Link: https://doi.org/10.18632/oncotarget.27344

Why Doesn't the State of Having High Blood Cholesterol Cause Pain?

Progress in the sciences is as much a matter of finding novel questions to ask as it is a matter of answering existing questions. The novel question here is this: given that high blood cholesterol is harmful over the long term, accelerating the progression towards atherosclerosis, so why haven't we evolved to feel pain and discomfort from being in that state, leading to avoidance? The answer is mostly likely that issues that arise in later life, after reproduction is carried out, are not subject to selection pressure to anywhere near the degree needed to improve the situation for the individual. Evolution optimizes for early life success and reproduction.

To avoid any kind of potential harm to the body, to restore physiological functions when out of balance, and to satisfy the biochemical needs of the organism by giving itself signals that favour respective behaviour. Acknowledging this, one may ask why causal drivers of cardiovascular disease do not prompt the individual to behave in a way that diminishes these risk factors. Why does the insult to the vascular endothelium by smoking, high blood pressure, or high blood sugar not cause discomfort? Why does the vasculature of a person with familial hypercholesterolemia not hurt? Why does a person with high cholesterol not feel antipathy for fatty and high-caloric meals?

From an evolutionary perspective, the mentioned physiological functions preserve the integrity of the body with the ultimate goal to enable the organism to reproduce. Physical harms and unsatisfied physiological needs directly affect the probability of reproductive success and therefore, individuals displaying favourable behaviour in this regard are more likely to pass their genes on to the next generation. Any genetic trait with effects that become relevant only after reproduction does not exert pressure to be sustained. Such traits may even have been beneficial under the circumstances of feast-famine cycles under which they evolved. This explanation why detrimental genetic traits leading to hypercholesterolemia, diabetes mellitus, and obesity, occur with such high prevalence has been called "thrifty gene hypothesis".

Hypercholesterolemia affects one in two individuals in Western societies and is, relying on different lines of evidence, causal for the development of atherosclerotic cardiovascular disease. Genetic traits that favour high blood levels of cholesterol have likely been beneficial long ago to foster energy security and in consequence, lead to early reproduction. It is indisputable that cholesterol is an essential element of the human body, but with 93% of all cholesterol being intracellular and famine episodes being virtually absent today, do we than still need any cholesterol in our bloodstream? Very low levels of LDL cholesterol, due to mutations or aggressive medical treatment, do not appear to have any detrimental effects.

While the question why hypercholesterolemia does not hurt may primarily be of academic interest, the answer provided may be useful for patient care as well. It can explain why cholesterol levels referred to as "normal" by patients and physicians is still associated with subclinical atherosclerosis as precursor of established cardiovascular disease and should be a target of treatment. Since high cholesterol does not hurt, lipid lowering will not confer symptomatic benefit. Therefore, patient discussion - including the principles discussed here - is the key to medication adherence.

Link: https://doi.org/10.18632/aging.102620

A Biomarker of Aging Based on Blood Protein Levels

A robust, reliable, low-cost biomarker of aging that measures the burden of damage that causes aging would be of great value to the field. It would allow rapid testing of potential rejuvenation therapies, given the capacity to show how effective a treatment is in only a short period of time: test once, apply the therapy, test again a few days or a month later. Most of the work aimed at producing and proving such a biomarker is focused on assessment of epigenetic changes that are characteristic of aging. This is not the only approach, however. Research groups are also attempting algorithmic combinations of very simple assessments such as grip strength and skin elasticity, while others, as is the case here, are focused on measuring protein levels in blood samples.

At the end of the day, however, it is still far from clear as to how all of these potential biomarkers relate to the underlying damage that causes aging. It is quite possible that they are strongly dependent on only a fraction of the full range of types of damage, for example. A rejuvenation therapy might not change the biomarker as much as it should. Or perhaps more than it should. Thus proving out biomarkers must proceed in parallel with proving out rejuvenation therapies based on damage repair. At the present time one cannot just blindly use any of the existing biomarkers and assume the results to be useful in the matter of assessing interventions.

One interesting outcome from the work noted here is that it shows staged alterations in the biomarker, rather than a smooth progression of changes. The first such change occurs quite early, in the 30s. One might compare that result with recent work on changes in the gut microbiome that also shows alterations in gut microbe populations that are relevant to health, due to a loss of beneficial compounds produced by these microbes, taking place during the 30s - at exactly the same average age in the mid-30s, in fact, which is most intriguing.

Stanford scientists reliably predict people's age by measuring proteins in blood

Researchers analyzed the levels of proteins circulating in plasma - the cell-free, fluid fraction of blood - from 4,263 people ages 18-95. On measuring the levels of roughly 3,000 proteins in each individual's plasma, researchers identified 1,379 proteins whose levels varied significantly with participants' age. A reduced set of 373 of those proteins was sufficient for predicting participants' ages with great accuracy. In fact, a mere nine proteins were enough to do a passable job, and adding more proteins to the clock improves its prediction accuracy only a bit more.

The study's results suggest that physiological aging does not simply proceed at a perfectly even pace, but rather seems to chart a more herky-jerky trajectory, with three distinct inflection points in the human life cycle. Those three points, occurring on average at ages 34, 60 and 78, stand out as distinct times when the number of different blood-borne proteins that are exhibiting noticeable changes in abundance rises to a crest. This happens because instead of simply increasing or decreasing steadily or staying the same throughout life, the levels of many proteins remain constant for a while and then at one point or another undergo sudden upward or downward shifts. These shifts tend to bunch up at three separate points in a person's life: young adulthood, late middle age and old age.

The investigators built their clock by looking at composite levels of proteins within groups of people rather than in individuals. But the resulting formula proved able to predict individuals' ages within a range of three years most of the time. And when it didn't, there was an interesting upshot: People whose predicted age was substantially lower than their actual one turned out to be remarkably healthy for their age.

Undulating changes in human plasma proteome profiles across the lifespan

Aging is a predominant risk factor for several chronic diseases that limit healthspan. Mechanisms of aging are thus increasingly recognized as potential therapeutic targets. Blood from young mice reverses aspects of aging and disease across multiple tissues, which supports a hypothesis that age-related molecular changes in blood could provide new insights into age-related disease biology. We measured 2,925 plasma proteins from 4,263 young adults to nonagenarians (18-95 years old) and developed a new bioinformatics approach that uncovered marked non-linear alterations in the human plasma proteome with age. Waves of changes in the proteome in the fourth, seventh and eighth decades of life reflected distinct biological pathways and revealed differential associations with the genome and proteome of age-related diseases and phenotypic traits. This new approach to the study of aging led to the identification of unexpected signatures and pathways that might offer potential targets for age-related diseases.

Delivering Adenosine to a Bone Injury Accelerates Regeneration

A very large number of tissue-specific signals are involved in the mechanisms of regeneration, an intricate dance between many different cell types. It has long been the goal of the research community to identify the most important signals in this enormous repertoire and amplify them in a targeted way in order to enhance regeneration from injury or reverse age-related loss of tissue maintenance capacity. The work here is an example of the former goal, in which researchers find that adenosine can be delivered to bone injuries in a targeted way in order to accelerate healing.

Researchers have found that the body naturally floods the area around a new bone injury with the pro-healing adenosine molecules, but those locally high levels are quickly metabolized and don't last long. They wondered if maintaining those high levels for longer would help the healing process. But there was a catch. "Adenosine is ubiquitous throughout the body in low levels and performs many important functions that have nothing to do with bone healing. To avoid unwanted side effects, we had to find a way to keep the adenosine localized to the damaged tissue and at appropriate levels."

The solution was to let the body dictate the levels of adenosine while helping the biochemical stick around the injury a little bit longer. The researchers designed a biomaterial bandage applied directly to the broken bone that contains boronate molecules that grab onto the adenosine. However, the bonds between the molecules do not last forever, which allows a slow release of adenosine from the bandage without accumulating elsewhere in the body. Researchers first demonstrated that porous biomaterials incorporated with boronates were capable of capturing the local surge of adenosine following an injury. The researchers then applied bandages primed to capture the host's own adenosine or bandages preloaded with adenosine to tibia fractures in mice. After more than a week, the mice treated with both types of bandages were healing faster than those with bandages not primed to capture adenosine. After three weeks, while all mice in the study showed healing, those treated with either kind of adenosine-laced bandage showed better bone formation, higher bone volume, and better vascularization.

The results showed that not only do the adenosine-trapping bandages promote healing, they work whether they're trapping native adenosine or are artificially loaded with it, which has important implications in treating bone fractures associated with aging and osteoporosis. "Our previous work has shown that patients with osteoporosis don't produce adenosine when their bones break. These early results indicate that these bandages could help deliver the needed adenosine to repair their injuries while avoiding potential side effects."

Link: https://pratt.duke.edu/about/news/bone-bandage

The Relationships Between Telomeres, Telomerase, and Mitochondrial Function

Telomerase is best known for its role in lengthening telomeres. Telomeres are the caps of repeated DNA sequences at the ends of chromosomes; a little is lost with each cell division, and telomere length is a vital part of the mechanisms of the Hayflick limit on the number of times a somatic cell can replicate. Stem cells and cancer cells use telomerase to maintain long telomeres, allowing for indefinite replication. This is not the only function of telomerase, however. It has been shown to act on mitochondria, but the nature of this relationship is nowhere near as well explored.

The present consensus on beneficial effects on health and life span in mice that result from telomerase gene therapy is that increased telomere length is the central and vital mechanism. Many lines of evidence show declining mitochondrial function to be very important in the aging process, however. To the degree that telomerase improves mitochondrial function directly, independently of effects resulting from telomere length, we might expect this to contribute to health and life span effects. As is usually the case in the matter of aging, picking apart the mechanisms in order to compare effect sizes is a challenging prospect, however.

Mitochondrial functions and telomere functions have mostly been studied independently. In recent years, it, however, has become clear that there are intimate links between mitochondria, telomeres, and telomerase subunits. Mitochondrial dysfunctions cause telomere attrition, while telomere damage leads to reprogramming of mitochondrial biosynthesis and mitochondrial dysfunctions, which has important implications in aging and diseases. In addition, evidence has accumulated that telomere-independent functions of telomerase also exist and that the protein component of telomerase TERT shuttles between the nucleus and mitochondria under oxidative stress.

Our previously published data show that the RNA component of telomerase TERC is also imported into mitochondria, processed, and exported back to the cytosol. Mitochondrial localization of TERT is a cell type-specific event that protects the cells from oxidative stress. What is the exact function of mitochondrion-localized TERT within the mitochondrial matrix, however, remains to be elucidated. This data shows a complex regulation network where telomeres, nuclear genome, and mitochondria are co-regulated by multi-localization and multi-function proteins and RNAs.

Link: https://doi.org/10.3389/fcell.2019.00274

Targeting Aging is the Future of Medicine

The scientific community does in fact engage in advocacy to attempt to generate more interest and funding for specific initiatives in research and development, particularly where public understanding is lagging far behind scientific understanding in a given field. This is very much the case in the matter of treating aging as a medical condition. The scientific establishment is united in the desire to move forward towards therapies that treat aging, albeit quite divided on the topic of what exactly the form those therapies should be. The world at large has yet to catch up to the idea that aging can be slowed or reversed, never mind the very important point that the first rejuvenation therapies already exist, in the form of senolytic drugs that can clear a sizable fraction of senescent cells in old tissues.

The latest issue of the Public Policy and Aging Report journal is an example of scientific advocacy for the treatment of aging. It is undoubtedly the case that the future of medicine will become largely a matter of treating aging, targeting the numerous underlying mechanisms that cause aging. Most diseases are suffered by only a small fraction of the population at any given time, but everyone suffers from aging. The target market for therapies is more or less half of the human race at any given moment in time, everyone much past the age of 40. The vast majority of medical costs are related to aging. The overwhelming majority of deaths in the wealthier parts of the world result from aging. The next few decades will see a transition from a world in which only palliative approaches or small gains are possible in the treatment of age-related disease, to a world in which these diseases will be cured and prevented, as the healthy human life span lengthens dramatically.

Is Targeting Aging the Future of Medicine? Researchers Make the Case

Human life expectancy worldwide rose dramatically over the past century, but people's health spans - the period of life spent free from chronic, age-related disease or disability - have not increased accordingly. "Twenty-first century medicine should adopt the strategy of directly targeting the molecular mechanisms that cause biological aging. Only in this way will it be possible to slow the onset and progression of multiple age-related diseases simultaneously, in order to extend the health span proportionately with the life span." The authors write that aging itself is not a disease, but rather is the biggest risk factor for a wide range of chronic diseases. This is a central tenet of the emerging field of geroscience, which seeks to define the biological mechanisms that underly the diseases of aging - with the goal of slowing human aging to delay or prevent many diseases simultaneously.

It is Time to Embrace 21st-Century Medicine

Biomedical research and clinical practice have traditionally been focused on disease rather than health. We typically wait until people are sick before trying to cure their disease or alleviate their symptoms, rather than actively supporting health and wellbeing in the absence of disease. Current demographic trends toward older populations make this approach problematic. Instead of improving the quality of life, we may be extending the period of morbidity and frailty for millions of people. Twenty-first century medicine should adopt the strategy of directly targeting the molecular mechanisms that cause biological aging. Only in this way will it be possible to slow the onset and progression of multiple age-related diseases simultaneously, in order to extend the healthspan proportionately with the lifespan.

The Longevity Dividend: A Brief Update

The language of the longevity dividend as we know it today originated in 2006, but its intellectual origins are not new. in 1956 Clive McKay suggested the successful life extension that had already been achieved in laboratory animals by then (without knowing whether changes in the healthspan also occurred in these animals) justified the experimental manipulation of the lifespan in humans. A lot has happened in the past 65 years since this idea first appeared and in the 13 years since the term was first used. Just recognizing that aging itself is inherently modifiable, and that interventions derived from aging biology represent a new, more promising form of primary prevention than the usual approach to treating one disease at a time, is sufficient reason to see the value of the modern rise of geroscience and the longevity dividend initiative. The language of these initiatives has now made its way into mainstream medicine, in the form of a preference for "healthspan" over "lifespan", representing a new meme that should permanently change the way in which humanity thinks about what it means to age.

Time for a New Strategy in the War on Alzheimer's Disease

Alzheimer's disease is a growing threat to the economic and social well-being of developed countries around the globe, but efforts to delay, prevent, or cure this disorder have yet to yield success. I believe the lack of progress largely results from approaches that ignore the most important component of Alzheimer's disease: biological aging. Major advances have been made in understanding the molecular mechanisms that link biological aging to disease. These mechanisms have been formalized as nine hallmarks, or pillars, of aging. Here, I discuss the barriers that have impaired progress and propose specific steps that can be taken to overcome these barriers. The time has come to adopt bold new strategies that tackle biological aging as the root cause of Alzheimer's disease.

The Benefits of Calorie Restriction Most Likely Largely Result from Increased Autophagy

Calorie restriction slows aging in near all species and lineages tested to date, though its effects on life span are much larger in short-lived species than in long-lived species such as our own. While calorie restriction produces sweeping changes in near every aspect of metabolism, making it a challenging intervention to analyze, the present consensus is that the bulk of its benefits arise due to an increased operation of the cellular maintenance processes of autophagy. A more efficient clearance of damaged and otherwise unwanted proteins and structures in cells should in principle lead to improved cellular operation and tissue function, and a reduction in downstream consequences of cell damage. Since numerous other means of slowing aging in animal models also exhibit increased autophagy, this seems a reasonable working hypothesis.

Calorie restriction (CR) has been shown to be an established life-extension method regulating age-related diseases as well as aging itself. Although different in methodology (usually 20%-40% less than ad libitum intake, a 40% reduction in most cases), CR showed a prolonged lifespan in a wide range of species from yeast to non-human primates, and supports healthy human aging. Furthermore, CR exerts preventive effects on various age-related conditions such as cancer, neurodegenerative diseases, cardiovascular, and other metabolic diseases. The diverse efficacy of CR in counteracting aging and age-related diseases has made it the golden standard of aging intervention studies.

Although the anti-aging effects of CR are reproducible, the exact mechanisms of how CR exerts its anti-aging effects are debatable, because CR regulates several different aspects of physiology. These changes include modifications in the energy-sensing signaling, oxidative stress, inflammation, and other intercellular and intracellular processes. Among the many changes induced by CR, energy production and utilization is the most directly regulated signaling exerted by CR. Since reduced energy intake and changes in nutritional status following CR may change the molecular signaling pathways associated with energy-sensing mechanisms, other mechanisms may be secondary effects to this process.

Based on the induction mechanism of autophagy and its role during starvation, it was predicted that CR might induce the autophagic process. Indeed, under many different settings of nutrient deprivation conditions, including in CR, autophagy is induced to regulate the organism's homeostasis. Although it is clear that CR represents a strong physiologically autophagic inducer, it is uncertain whether autophagy contributes to the anti-aging effects of CR. Recently, several studies have shown that autophagy induction was essential for the anti-aging effects of CR. CR was shown to promote longevity or protect from hypoxia through a Sirtuin-1-dependent autophagy induction process. Another study also showed that life extension through methionine restriction required autophagy activation. Growing evidence supports the notion that autophagy has a substantial role in the beneficial effects of CR. In addition to research on longevity, other studies have shown that CR robustly induces autophagy under various physiological and pathological conditions, and that it has a protective effect in the maintenance of normal functions in the organism.

Link: https://doi.org/10.3390/nu11122923

Epigenetic Mutations Accumulate with Age, with Uncertain Consequences

Epigenetic markers, such as methylation, determine the production rates of specific proteins in a cell. These epigenetic decorations to DNA change constantly, but many changes are characteristic of aging, which has led to the generation of epigenetic clocks in recent years. Epigenetic mutations are distinct from these changes, being effectively a form of stochastic damage in which methylation is inappropriately applied to a given location in the genome. Does this cause significant issues in aging? That is an open question, and can be considered in a similar way to the question of the effects of mutation to nuclear DNA. In most cases, random methylation won't have much of an effect, as it occurs in a cell that will not replicate extensively, or changes expression of a gene that isn't all that important in the tissue in question. When an epigenetic mutation occurs in stem cells or progenitor cells, it may manage to spread widely in a tissue, however.

Epigenetic processes, among which DNA methylation is one of the most well studied, are fundamental in human aging. Studies on DNA methylation have identified age-associated changes in methylation levels shared by individuals, and have also reported an increasing divergence of methylation levels between individuals with age. While the role of DNA methylation in aging has been widely studied, epigenetic mutations, here defined as aberrant methylation levels compared to the distribution in a population, are less understood.

Epigenetic mutations may be involved in cancer development and important for human aging. Unlike age-associated changes in methylation levels that are shared among individuals, the incidences of epigenetic mutations are rare, stochastic, and inconsistent between individuals. Recently, emerging studies on methylation variability have also identified differentially varied CpG sites associated with cancer field defects. Epigenetic mutations can partly explain the increasing variability of methylation levels between individuals over time, but conversely, highly varied methylation sites do not necessarily contain extreme outliers. The extreme methylation levels may concur stronger biological consequences, such as cancer.

However, the study on epigenetic mutations and aging was based on a cross-sectional study, it needs to be validated in a longitudinal setting, where the accumulation of epigenetic mutations over time can be followed within the same individuals. It is not yet known what the clinical consequences of accumulated epigenetic mutations are, and if individuals with a high burden of epigenetic mutations are prone to develop cancer as previously suggested.

In this study, we analyzed age-related accumulation of epigenetic mutations from a longitudinal perspective in old Swedish twins, using 994 blood samples collected at up to five time points from 375 individuals in old ages. Apart from being exponentially associated with age, epigenetic mutations were also associated with sex, CD19+ B cell count, genetic background, cancer incidence, and technical factors. We showed once mutations are established, they are stable over time. Furthermore, epigenetic mutations are enriched in important regulatory sites, e.g., promoter regions of genes involved in histone modification processes, which could potentially be an explanation to why people who develop cancer have more epigenetic mutations than others do.

We further classified epigenetic mutations into High/Low Methylation Outliers (HMO/LMO) according to their changes in methylation. We also found that biological factors, including B cell compositions and genetic factors, were more strongly associated with frequent HMOs than LMOs, while frequent LMOs were more influenced by technical factors. Moreover, cancer diagnosis was significantly associated with the increase of epigenetic mutations, especially among frequent HMOs, while the same was not true for LMOs. Furthermore, we concluded that the age-related accumulation of epigenetic mutations was not related to genetic factors, hence is driven by stochastic or environmental effects.

Link: https://doi.org/10.1186/s13148-019-0788-9

SQSTM1 Overexpression Extends Life in Nematode Worms

Macroautophagy is a cellular recycling process in which unwanted proteins and cell structures are engulfed by an autophagosome that is then transported to a lysosome, where its contents are broken down. Greater autophagy is a feature of many of the approaches shown to slow aging in laboratory species. In principle this should lead to better cell function and less downstream damage resulting from uncleared issues in cells. Many different approaches to the upregulation of autophagy have been demonstrated in the laboratory, but this class of therapy has yet to make the leap to the clinic. Arguably mTOR inhibition is the closest to realization, but more targeted methods of increasing autophagy are still largely stuck in the laboratory stage of research and development.

As an example of the type, researchers here investigate upregulation of autophagy via increased production of one portion of the protein machinery necessary for the operation of autophagy. This sort of approach has worked well for other cellular maintenance structures, such as the proteasome. The protein SQSTM1, also known as p62, assists in selecting materials to be recycled. Ubiquitination, the decoration of a protein with ubiquitin, is one of the ways in which a cell determines which proteins and structures are targeted for recycling. SQSTM1 binds to ubiquinated proteins in order to shuttle them into an autophagosome. As demonstrated in this research, greater production of SQSTM1 leads to more efficient autophagy, and thus a slowing of degenerative aging in short-lived nematode worms.

Given what is known of calorie restriction in various species, an intervention that functions to improve health and extend life largely via increased autophagy, we should take this research as interesting but not necessarily all that relevant to human life spans. Calorie restriction greatly extends life span in short-lived species, but adds at most a few years to life span in long-lived species such as our own. This pattern of lesser life extension for species with longer life spans is true of all of the stress response mechanisms that influence aging. Nonetheless, calorie restriction does improve human health significantly. Thus we should temper our expectations regarding therapies based on upregulation of autophagy: some degree of improved health is the expected outcome, not meaningfully greater longevity.

The autophagy receptor p62/SQST-1 promotes proteostasis and longevity in C. elegans by inducing autophagy

Macroautophagy (hereafter called autophagy) facilitates degradation and recycling of cytosolic components, referred to as cargo, in response to nutrient deprivation or other stressors. Autophagy is initiated by the nucleation of a double membrane, which forms the phagophore. As the phagophore expands, it begins to sequester cytosolic cargo into the growing vesicle. Upon completion, the autophagosome or amphisome (formed by fusion with vesicles from the endolysosomal compartments) then fuse with acidic lysosomes, resulting in the degradation of the sequestered content by hydrolases.

Autophagy is essential for survival, development, and organismal homeostasis. It occurs at low levels under basal conditions, whereas developmental stimuli or cellular stress, including starvation and heat shock, can induce autophagy. Furthermore, autophagy can protect against pathologies, including neurodegeneration and aging. The regulation of autophagy with age is incompletely understood, but several lines of evidence suggest that autophagy declines with age. Conversely, autophagy genes are essential for lifespan extension in distinct longevity paradigms in S. cerevisiae, C. elegans, and Drosophila. While these observations demonstrate a link between autophagy and aging, it remains unclear how the autophagy process affects longevity and healthspan.

Autophagy was originally described as a 'bulk' turnover process, in which cytosolic components are indiscriminately recycled to provide amino acids and other building blocks during nutrient deprivation and cellular stress. Emerging evidence indicates that selective types of autophagy degrade specific and possibly damaged cytosolic components in a tightly regulated manner. During selective autophagy, autophagosomes recruit specific types of cargo, including mitochondria and protein aggregates, through the action of autophagy receptors that connect the autophagosome to the cargo. The selective autophagic degradation of ubiquitinated protein aggregates, termed aggrephagy, can be facilitated by autophagy receptor p62/SQSTM1 (hereafter referred to as p62).

The degradation of ubiquitinated proteins can occur via autophagy as well as the ubiquitin-proteasome system (UPS), and p62 has been implicated in both processes; i.e., as a selective autophagy receptor, and through the delivery of ubiquitinated proteins for degradation to the proteasome. Consistent with a key role in age-related disease, mice deficient in p62 have reduced lifespan, increased oxidative stress, synaptic deficiencies, and memory impairment. The expression levels of p62 have been shown to decline with age in mice, and reduced expression of p62 correlates with age-related neurodegenerative diseases in humans. Notably, we recently reported that sqst-1 mRNA levels are markedly increased upon heat stress in C. elegans, prompting the hypothesis that SQST-1 may play a role in the heat-shock response, in which heat-shock proteins and molecular chaperones are rapidly and transiently induced to ameliorate the deleterious effects of heat stress.

Since emerging evidence suggests that the degradation of specific cargos by selective autophagy is important for maintaining health, we investigated the role of SQST-1 in hormetic heat shock, lifespan, and proteostasis. Here we demonstrate that sqst-1 is required for autophagy induction as well as organismal benefits conferred by a hormetic heat shock. Furthermore, we show that overexpression of SQST-1 is sufficient to increase longevity in C. elegans. SQST-1 overexpression leads to tissue-specific induction of autophagy. These observations illustrate that overexpression of a selective autophagy receptor is sufficient to induce autophagy and enhance longevity and proteostasis. As p62 plays an important role in many age-related diseases, our findings highlight potential therapeutic opportunities in inducing p62-mediated selective autophagy.

Reprogramming Supporting Cells into Hair Cells in the Inner Ear

Age-related deafness is thought to result from either loss or incapacity of sensory hair cells in the inner ear. One possibly approach to treatment is to stimulate the creation of new hair cells, and their integration with the appropriate nerve pathways to the brain. A number of groups have examined ways to use Wnt and Notch pathways to achieve this end, with an eye to developing drugs that can cause hair cell regeneration, and the work noted here is a recent example.

Despite its prevalence, there remains no available pharmacological therapies to treat hearing loss. Loss of hair cells (HCs), the inner ear sensory cells that detect sound and sense balance, is a major cause of hearing loss and vestibular dysfunction in humans. In lower vertebrates such as birds, fish, and amphibians, HC loss triggers supporting cells (SCs) to re-enter the cell cycle. Proliferating SCs then transdifferentiate into new HCs, resulting in the recovery of hearing and vestibular functions. In contrast, the mature mammalian cochlea completely lacks the capacity to spontaneously proliferate or regenerate HCs, and has very limited regeneration potential in the vestibular system.

In the young mammalian inner ear, SC-to-HC transdifferentiation can be induced by overexpression of HC fate-determining transcription factor, Atoh1. An early study provided evidence that Atoh1 overexpression had limited but similar effects in the adult mammalian cochlea, however, subsequent studies failed to reproduce the essential findings. It is therefore suggested that, in the adult inner ear, overexpression of Atoh1 in SCs alone is inefficient in promoting HC regeneration. To recapture the capacity to respond to HC induction signals, it is likely that mature SCs need to first regain the properties of their younger biological selves.

To identify potential reprogramming factors in the adult mammalian inner ear, we began by studying chick and zebrafish HC regeneration models and uncovered that reactivation of Myc is a major event that leads to cell cycle re-entry. Additional studies have shown that overexpression of Notch1, a receptor important in mammalian inner ear early development and patterning, is sufficient to induce formation of the prosensory domain of the developing mouse otocyst. We hypothesize that the combined action of MYC and NOTCH1 may be sufficient to reprogram adult mouse inner ear cells for cell cycle re-entry and the reprogrammed SCs may regain the properties enabling them to transdifferentiate into HCs in the presence of induction signals.

In this study, by adenovirus-mediated delivery and inducible transgenic mouse models, we demonstrate the proliferation of both HCs and SCs by combined Notch1 and Myc activation in in vitro and in vivo inner ear adult mouse models. These proliferating mature SCs and HCs maintain their respective identities. Moreover, when presented with HC induction signals, reprogrammed adult SCs transdifferentiate into HC-like cells both in vitro and in vivo. Finally, our data suggest that regenerated HC-like cells likely possess functional transduction channels and are able to form connections with adult auditory neurons.

Link: https://doi.org/10.1038/s41467-019-13157-7

Immunization Against Flagellin as a Way to Beneficially Alter Aging Gut Microbiota Populations

The microbial populations of the gut make a significant contribution to health via secreted metabolites and interactions with the immune system. Starting in mid-life, these populations alter for the worse, and this is thought to influence the progression of aging - perhaps primarily as a contributing cause of chronic inflammation. How this effect size compares with those resulting from dietary and exercise choices is an open question, but it isn't unreasonable to suggest it to be in the same ballpark as exercise.

What can be done to improve this situation? Supplementation with metabolites produced in larger amounts in youth, perhaps. Known options include tryptophan, indole, butyrate, and propionate, but there are no doubt many others as yet uncatalogued. Fecal microbiota transplants from young animals to old animals have been shown to reverse age-related changes in microbial populations and consequently extend life in short-lived species. This seems the best option of those on the table. There are others, however. As an example, the work here is quite clever, building upon a point of difference between beneficial and harmful gut microbes in order to steer the immune system to preferentially attack those harmful microbes and thus control their population size and impact on health.

The intestinal tract is colonized by billions of bacteria and other microorganisms that play numerous beneficial roles, but improperly controlled microbiota can lead to chronic inflammatory diseases. Previous studies have shown the intestinal microbiota are associated with inflammatory bowel diseases, such as ulcerative colitis and Crohn's disease, and diseases characterized by low-grade inflammation of the intestinal tract, such as obesity and metabolic syndrome.

Therapeutic options have focused on lessening the inflammatory response and have often overlooked the contribution of the intestinal microbiota. The researchers wanted to determine if a targeted immune response could be used to beneficially shape the intestinal microbiota and protect against inflammatory diseases. Previously, they found that a common feature of microbiotas associated with inflammation is an increased level of expression of flagellin by select microbiota members, a protein that forms the appendage that enables bacterial mobility, which can drive bacteria to penetrate the intestinal mucosa and disrupt homeostasis.

The researchers immunized mice with flagellin to elicit an adaptative immune response and demonstrated targeted immunization against bacterial flagellin is sufficient to beneficially alter the composition and function of the intestinal microbiota. Anti-flagellin antibodies were produced and affected the microbiota by reducing its pro-inflammatory potential and ability to penetrate its host. These alterations were associated with protection against chronic inflammatory diseases.

Link: https://www.eurekalert.org/pub_releases/2019-12/gsu-rda120919.php

External Versus Intrinsic Causes of Hematopoietic Stem Cell Aging

Today I'll point out a pair of open access review papers in which the authors discuss mechanisms involved in the age-related declines and detrimental altered behaviors of hematopoietic stem cells. These stem cells are responsible for generating blood and immune cells, and so are of vital importance to the function of the immune system throughout life. One paper focuses on external contributions, those arising from the surrounding environment, while the other looks at damage and change arising from the stem cells themselves.

This encapsulates the divide in thinking about stem cell aging in general. At least some stem cell populations, such as those supporting skeletal muscle, appear to remain capable of function well into late life. That their output of daughter somatic cells to support tissue function declines is a matter of the cells lapsing into quiescence for ever longer periods, rather than there being too few competent cells remaining. This is probably more a matter of signals from the surrounding environment rather than inherent damage to the stem cells.

In the case of hematopoietic stem cells, evidence suggests more of a role for damage and declining numbers of competent cells than is the case for muscle stem cells, however. In this situation, rejuvenation therapies will almost certainly have to involve the delivery of new patient-matched stem cells capable of engrafting into tissue and continuing the work of their damaged predecessors. This aspect of stem cell therapy has proven to be challenging. It remains the case that most cell therapies, certainly those presently available in clinics, struggle to achieve lasting cell survival. Whatever benefits they produce result from signals released by the transplanted cells in the short time they remain viable. Still, progress has been made, and organizations like AgeX Therapeutics are working towards reliable approaches to the replacement of stem cell populations.

Microenvironmental contributions to hematopoietic stem cell aging

Hematopoietic stem cell (HSC) aging was originally thought to be essentially an HSC-autonomous process. However, studies on the microenvironment that maintains and regulates HSCs (the HSC niche) over the past 20 years have suggested that microenvironmental aging contributes to declined HSC function over time. The HSC niches comprise a complex and dynamic molecular network of interactions across multiple cell types, including endothelial cells, mesenchymal stromal cells (BMSCs), osteoblasts, adipocytes, neuro-glial cells and mature hematopoietic cells.

Upon aging, functional changes in the HSC niches, such as microenvironmental senescence, imbalanced BMSC differentiation, vascular remodeling, changes in adrenergic signaling, and inflammation, coordinately and dynamically influence the fate of HSCs and their downstream progeny. The end result is lymphoid deficiency and myeloid skewing. During this process, aged HSCs and their derivatives remodel the niche to favor myeloid expansion. Therefore, the crosstalk between HSC and the microenvironment is indispensable for the aging of the hematopoietic system and might represent a therapeutic target in age-related pathological disorders.

Understanding intrinsic hematopoietic stem cells aging

Hematopoietic stem cells (HSCs) are sustaining blood production during the whole life of an organism. It is of extreme importance that these cells maintain self-renewal and differentiation potential over time, in order to preserve homeostasis of the hematopoietic system. Many HSC intrinsic aspects are affected by the aging process, leading to the deterioration of the potential of these cells independently of their microenvironment. Here we review recent findings characterizing most of the intrinsic aspects of aged HSCs, ranging from phenotypic to molecular alterations.

Historically, DNA damage was thought to be the main responsible for HSC aging. However, in the last years, many new findings have defined an increasing number of biological processes that are intrinsically changing with age in HSCs. Epigenetics and chromatin architecture together with autophagy, proteostasis, and metabolic changes and how they are interconnected to each other are acquiring growing importance for understanding the intrinsic aging of stem cells. Considering that aging is the primary risk factors for most diseases, understanding HSC aging becomes particularly relevant as well in the context of hematological disorders, such as myelodysplastic syndrome and acute myeloid leukemia. Research on intrinsic mechanisms responsible of HSC aging is and will continue to provide new potential molecular targets to possibly ameliorate or delay aging of the hematopoietic system and consequently improve the outcome of hematological disorders in the elderly.

An Interview with Brian Kennedy of the Center for Healthy Aging in Singapore

Brian Kennedy formerly headed the Buck Institute, but these days can be found leading the Center for Healthy Aging at the National University of Singapore. The Life Extension Advocacy Foundation staff recently had a chance to conduct an interview, and you should read the whole thing. Kennedy has an interesting view of the field, for all that he is largely focused on calorie restriction mimetic approaches that, to my eyes, are not likely to produce large enough benefits to really change the trajectory of human aging.

Do you consider aging to be a disease or, at least, a co-morbid syndrome?

I think you can make an argument that it's a disease, and you can also make an argument that it's a risk factor for disease, but to me, fundamentally, it doesn't matter. It's the biggest driver of chronic diseases, loss of function late in life, and has a huge impact on life quality and health care costs. So we have to do something about aging, whatever you call it, and I don't think it's so important what we call it; it's more important that we all agree that we have to slow down this process.

I think that the regulatory declaration of aging as a disease could certainly have a positive impact, because if aging is a disease, then it's much easier to develop therapies and get reimbursed for therapies, so I'm totally supportive of that effort. I think that, however, we don't call cholesterol a disease, but we treat cholesterol because it's a risk factor, so the FDA does approve interventions on targeted risk factors as well. I think we have to differentiate whether we're discussing this from a conceptual point of view or from a regulatory point of view. Either way, we need the FDA to recognize the fact that aging is driving these other diseases that they care so much about, whether they want to call it a disease or recognize it as a validated risk factor. Either way, something has to happen so that we can develop interventions.

We sometimes hear people say that we don't know enough about aging to do anything about it; however, others argue that we know enough now to start testing interventions and moving forward. Would you agree that we are at the point where we can start doing this?

I'm totally committed to the idea of testing candidate interventions in humans. I think we're totally ready to do that; we have a range of safe interventions that we can test, so we have very low risk of doing harm, and the field will move forward dramatically if we can validate even one or two of these strategies. I believe exercise is more or less already validated, but what I'm talking about are some of the small molecule strategies and other kinds of interventions that are being developed. If we can validate that a couple of those work, I think it'll have a huge positive impact on the field.

Singapore is projected to have a population made up of nearly 50% of senior citizens by 2050; what do you think will be the biggest challenge facing the elder care sector?

I think that we have to change the system. You can't just build hospitals, because there are multiple challenges with that. First of all, you have a lot of sick people on a small island; it's hard to treat all of them. There are not enough doctors and not enough hospitals; there are not enough caregivers to take care of older people. Perhaps most importantly, there are not enough younger workers to keep the economy going to pay for all the costs of the older people. We have to change the paradigm. I don't think there's any solution on Singapore except keeping people healthy longer. We're going to have to raise the retirement age. The people that are working later, they're already doing that, and that's not going to work unless those people are healthy and functional. We think we're trying to provide an essential component of what Singapore and other countries like it need to get through this demographic crisis that's happening in the next 30 or 40 years.

Link: https://www.leafscience.org/brian-kennedy-on-rapamycin-mtor-and-interventions/

High Levels of Blood Triglycerides Trigger Chronic Inflammation

Much of the focus on blood lipid levels is on cholesterol, as higher levels of cholesterol mean higher levels of the oxidized cholesterol that causes atherosclerosis, the formation of fatty lesions that narrow and weaken blood vessels. Methods of lowering cholesterol, such as statins, can slow the progression of atherosclerosis to some degree and reduce risk of a consequent stroke or heart attack occurring when an atherosclerotic lesion ruptures. Researchers here look instead at consequences of high triglyceride levels in the blood, uncovering a mechanism by which this provokes chronic inflammation. Since inflammation drives the progression of all of the common conditions of aging, atherosclerosis included, ways to lower triglyceride levels should also be an area of interest.

It has been known for some time that certain fat molecules in our bloodstream can trigger an inflammatory response. Patients with higher levels of these fats in their blood have a significantly greater chance of dying early from kidney damage or vascular disease. Now a research team was able to show how these fat molecules interact with body cells and how they can mobilize the body's own immune system to damaging effect.

"Our work has involved studying a special group of lipids, the triglycerides. We've been able to show that when these naturally occurring fats are present at elevated concentrations they can alter our defense cells in such a way that the body reacts as if responding to a bacterial infection. This leads to inflammation, which, if it becomes chronic, can damage the kidneys or cause atherosclerosis - the narrowing of arteries due to a build up of deposits on the inner arterial wall. And atherosclerosis is one of the main causes of heart attacks and strokes."

The large-scale study was able to demonstrate that patients with elevated levels of triglycerides in their blood had a significantly higher mortality rate than comparison groups with a similar health history. Blood triglyceride levels rise substantially in people who eat a high-fat diet. As a result of biochemical changes, the triglycerides develop toxic properties that activate the body's innate immune system via the NLRP3 inflammasome. This initiates a series of self-destructive processes including those in which the walls of the arteries are attacked and the blood vessels become occluded, reducing blood flow.

Link: https://www.eurekalert.org/pub_releases/2019-12/su-hhl120919.php

Declan Doogan of Juvenescence Presenting at Investing in the Age of Longevity

Investing in the Age of Longevity was an event held in London earlier this year as a part of the Longevity Week, a chance for Jim Mellon and the rest of the Juvenescence team to present their thesis on the longevity industry to the investor community - that this is an enormous opportunity to both greatly improve the human condition and generate returns on investment. A number of companies were there to present, as examples of the work on slowing and reversing aging presently taking place, and I was graciously invited to discuss the latest developments at Repair Biotechnologies. The presentations from the event have been posted to YouTube, mine among them.

Today I thought I'd focus on Declan Doogan's talk, which you may find interesting for the points on which he chose to focus. Doogan is the Chief Medical Officer of Juvenescence, a position responsible for guiding the clinical development of therapies as they move through the IND process with the FDA and analogous regulators in other parts of the world. Realistically, it is also a position responsible for taking preclinical development companies and shaping them into clinical development companies. These two phases of development are very different from one another, as different as work in a company is from the academic work that preceded it, and require quite the distinct mindset and set of talents to be successful.

Declan Doogan | Investing in the Age of Longevity 2019

Good afternoon, everybody. I'm pleased to be here. I'm a cofounder of Juvenescence, along with Jim Mellon and Greg Bailey. Those two are the ones who put the company together and are raising all of the capital. I'm the one who spends it. We are ambitious: we can have a meaningful impact on health in the context of longevity. As you heard this morning, aging is a disease, and we want to embark on investigating the mechanisms in longevity, learning from what is going on around us, but also looking to solutions - because we're a drug development company. We're raising capital, we've done quite well so far, thanks to Jim and Greg, and thanks to some of the investors in this room. We want to get on with the job.

Now, I'm a physician. I qualified a long time ago, and looking around the room I could be the oldest person here - which is scary. But I'm involved in this because I think it is a huge medical and societal need. What was really of concern to me was when I saw the statistics. Of course we've done well, we're living longer, 30 years longer than a century ago, and that was usually due to public health measures and control of infectious disease, and so on. But longevity is becoming a huge issue because of the number of people living longer. A 60 year old male, if he is doing everything right, can get 13 years more life expectancy than non-healthy people. But we have 10 or 11 years of unhealth at the end of life, which I call disability in this slide. In the US it is about 11.5 years. In the UK and Japan, as you can see here, 10.8 years. As noted this morning, 25% of Medicare costs occur in the last year of life.

So you can see the opportunity here for the research, development, and medical communities do a lot of good. We have done good in terms of managing cardiovascular disease up to now, to a point. But hypertension causes 45% of all cardiovascular deaths, and it is rising. 80% of the elderly have hypertension, and screening is still not good enough, especially outside the US and Europe. We have the drugs: thiazide and ACE inhibitors are particularly good for reducing not just blood pressure, but cardiovascular events and associated mortality. As you know the statins have done pretty well in terms of managing cholesterol and cardiovascular events and mortality.

Now I put up this next slide not to blow a trumpet or anything, but to say that I am a product of two things. Firstly, I went to medical school to learn how to detect and manage disease. Secondly, I entered the drug industry in the small molecule era where we blocked receptors and enzymes because it translated into disease constructs that we could measure. You could drop blood pressure, you could cure bacterial infection, you could treat erectile dysfunction, and also decrease blood cholesterol. So that was terrific at the time, but you also heard this morning about the rise of molecular biology, monoclonal antibodies, and now gene therapy. Where I was is now old school, but it did good, and it is still needed. I've done some other things in terms of small molecules and fatty acids, and the last one is Juvenescence. This is the one thing that will probably be my last hurrah, so to speak, but I'm going to hand off to our wonderful team of young people who are going to take the baton and run with this. They will deliver some of the medicines that we hope we can develop in the not so distant future.

So the first thing I asked myself is this: really, can aging be reversed? I've listened to Aubrey de Grey for a long time, and I'm now persuaded of that. I am also persuaded that aging is a construct that we all, as physicians and drug developers and whomever, should be passionate about fixing. I mean unhealthy aging. There are all these kinds of interventions and technologies that we can access, some of which will be extraordinary, and look like moonshots, while others will be more incremental. As was said this morning, there are other technologies that we need to be participant in: diagnostics, devices, apps, measurement of health management efficiency, and also we need to change our incentives.

In the American healthcare system, where I live, we are activity-based in terms of incentives. We get rewarded for identifying and treating disease. We do not get rewarded for identifying healthy people and keeping them healthy. So we have to change those incentives. Someone might say "where's the money for a drug company in keeping people healthy rather than treating disease?" But we have to migrate to that new model.

There are drugs in development that have been mentioned this morning. I think Reason mentioned the senolytic dasatinib, that has been used and has impact on longevity. A paper from Intervene Immune described the use of growth hormone, DHEA, metformin, and vitamin D to actually increase longevity. And you might say "how do you do that" - well you measure it by the aging clock, the Horvath epigenetic clock. Then Unity Biotechnology is developing a senolytic for osteoarthritis and pulmonary fibrosis. resTORbio is developing a rapalog for the treatment of immunosenescence; our immune system declines in its efficiency as we get older, manifesting in other diseases coming through. What they've done was a very clever thing, they looked at the uptake of flu vaccine in an elderly cohort, there is an antigen response, and showed that it protected more than in the control group in terms of susceptibility to disease. Samumed, working on the Wnt pathway, treating osteoarthritis of the knee. Then we have MitoQ, nicotinamide riboside, and cell therapy with Mike West's AgeX Therapeutics.

But in order to get there, we don't just say "hey, we've got a disease modifier." Or an age-modifier. We actually access it through disease constructs, as Nir Barzilai has for the TAME metformin trial. These are the sorts of areas where I think I can help design programs with the new technologies and measure impact in a biomarker-enabled way. Then we have that dialog with the FDA, and Europeans, and other agencies, to at least get them to buy into the idea that you are doing something that might improve the prospects for patients, that can manifest in a longer but healthier life. My view is that if you can compress that time of disability from even 11 to 10 years, the benefits to society will be massive.

What we're trying to do at Juvenescence is develop these treatments for both prevention and reversal. I wasn't sure that was going to be possible, until I saw some of the preclinical basic data. We really want to build a thriving company; we have a great group of young people - and young to me is something less than 40 - who are embarking on search and diligence, and we've got an emergent drug development team who are expert and experienced in developing drugs in the conventional pharma model. So we know how to deal with regulators and dialog with them, because we've had plenty of experience of what I'll not call misunderstandings, but miscommunication and misalignment of expectations. What we hope to do is to participate with other companies in moving the agenda forward such that the regulators are understanding that we're all trying to do something of merit, and they have got to work with us to regulate in a practicable way.

In the next slide, I think Laura Deming showed the left picture, of middle-aged mice, on how altering the genome can lead to a longer healthy life span and a change in the phenotype of the patient. This on the right is another set of mouse pictures, and this is from a company that we've invested in that actually interacts with the FOXO4-p53 system. And you look, that is an aged mouse, and the treatment perturbed that FOXO4-p53 system, and you do get rejuvenation. So maybe there is one clue to what we might be able to do in humans, and we're developing drugs in that space. I would hope to see that there is at least a modicum of translation from these animal models. Some animal models will not translate, and we'll learn with the passage of time. But these are the experiments that we'll have to do, and we'll learn from one another.

There is another company that we have, Lygenesis, which is probably the most advanced in terms of bringing something to the clinic. This is organ regeneration, a wonderful little company from Pittsburgh. They actually take hepatocytes and inject them into the abdominal lymph nodes. The hepatocytes are engineered and they grow ectopic livers. This has been shown in dogs: it does actually work, and we're preparing to go into the clinic in humans. Why are we doing that? First of all, the number of liver transplants in a year in the US is now about 8,000 and it is about to grow dramatically because of the increased incidence of nonalcoholic steatohepatitis and cirrhosis, and so on. Each transplant costs $700,000. If you multiply that by 8,000, and going up, you have a big price tag that you've got to pay for healthcare. If Lygenesis could mitigate some of those transplants, you will have a benefit that is quite easy to understand. We were showing that this is a company that is barreling along the road to the clinic, and I have to say that they are a fantastic team of people.

Now, just in finishing up, I want to say that we are a drug development company. We have capital, and Jim and Greg are raising more. We see great opportunities. We are, I won't call it agnostic, but we have a very broad purview over technologies that might actually bear fruit. We have a very good search and diligence team, who set a high bar. We don't just take in anything. We have an ecosystem of longevity experts and drug development experts we can bring to bear. When there is a company that we acquire or a technology we acquire, we fill the gaps. So although we've got the capital to invest, we are principally a drug development company.

The other point I mean is that when I was talking about health, in the future we are not talking about patients. I believe that we should be talking about pre-patients. All of you here who don't have a disease, and you want not to get it, there should be some strategy that you adopt for yourselves, and indeed for your family. When do you start? Now is a good time to start managing the parameters that you know predict for ill health. We go to our annual physician checkup - in this country I've been to many of them, and they are not all that good. I think that we really need to up our game in screening. To have broader biomarkers that we actually incorporate into our annual health screening, and which should be personalized. Our genetics are different, so our propensities are different. So a degree of personalized prevention I think is where we should be headed as well, to manage these growing healthcare costs.

Finally, in our company, we are ambitious, we think we can do it. We've got a lot of companies under our purview now, and we're going to acquire more. We'll need more capital and eventually we'll IPO. Thank you very much.

Variants of a Bitter Taste Receptor Gene are More Prevalent in Centenarians

This paper is chiefly interesting for the discussion on possible mechanisms by which variants in a taste receptor gene might be modestly influencing the odds of living a longer, healthier life. Calorie restriction, practiced to even a lesser degree, has such as a strong effect on aging in comparison to most other factors that one has to consider whether alterations in mechanisms of taste can be influential on aging via consequent alterations in dietary preferences.

Yet taste is complicated, and these genes also have other functions that seem clearly relevant to health over the long term. As this paper illustrates, even when provided with a very specific taste-related mechanism to discuss, and data on its prevalence in centenarians versus the rest of the population, it is far from straightforward to arrive at a robust conclusion. Of course it remains the case that, even given that robust conclusion, the size of this effect would not be large enough to care about in a world in which rejuvenation therapies are presently under development.

Bitter taste receptors play crucial roles in detecting bitter compounds not only in the oral cavity, but also in other tissues where they are involved in a variety of non-tasting physiological processes. Disorders or modifications in the sensitivity or expression of these receptors can affect physiological functions. Here we evaluated the role of the bitter receptor TAS2R38 in attainment of longevity, since it has been widely associated with individual differences in taste perception, food preferences, diet, nutrition, immune responses and pathophysiological mechanisms.

Our results show that the genetically homogeneous cohort of subjects ranging in age from 90 to 105 years of an area recognised as one of the world's longevity hot spots, differed based on the genotype distribution and haplotype frequencies of TAS2R38 gene from the two genetically heterogeneous cohorts from the South of Sardinia where the longevity level is distinctly lower. Results show in the centenarian cohort an increased frequency of subjects carrying the homozygous genotype for the functional variant of TAS2R38 (PAV/PAV) and a decreased frequency of those having homozygous genotype for the non-functional form (AVI/AVI), as compared to those determined in the two control cohorts.

A number of studies on human nutrition have suggested that the TAS2R38 variants and the related 6-n-propylthioural (PROP) phenotype may influence dietary behaviour and nutritional status. The possible association between PROP responsiveness and perception and intake of fats has been extensively studied, but with controversial results. The widely accepted hypothesis is that PROP non-tasters, compared to PROP super-tasters, show a reduced ability to perceive dietary fat which could lead them to increase the consumption of high-fat foods to compensate the reduced perception. In agreement with this assumption, the high frequency of the tasting homozygous genotype (PAV/PAV) and the low frequency of the non-tasting one (AVI/AVI), that we found in centenarian subjects, suggest that these individuals may have reached an exceptional longevity because of their genetic predisposition to a low-fat diet.

On the other hand, the extreme bitterness intensity of PROP super-tasters has been shown to be the primary reason for avoiding bitter-tasting fruits and vegetables. Since many bitter-tasting compounds in foods (e.g., flavonoids, phenols, glucosinolates) have benefit effects for health, our results in the centenarian cohort seem to be in contrast with the possibility that TAS2R38 genotype is a genetic factor that favour an adequate intake of fruits and vegetables or other bitter foods recommended for a healthy life. However, only a few studies have investigated the relationship between TAS2R38 variants and vegetable intake obtaining controversial results. The notion that TAS2R38 might serve to govern food intake is interesting, but eating behaviour is a complex phenomenon influenced by a broad range of environmental factors.

In addition, it is known that TAS2R38 receptor serves other genotype-dependent roles which are relevant for health, with the PAV form associated with an efficient immune response, a favourable body composition, as well as with physiological processes. On the contrary, the AVI group is associated with a higher risk to develop many dysfunctions and diseases. Therefore, it is not surprising that we find in the centenarian cohort an increased frequency of homozygous subjects for the functional variant of TAS2R38 (PAV) and above all a decreased frequency of those having homozygous genotype for the non-functional form (AVI).

Link: https://doi.org/10.1038/s41598-019-54604-1

Blood-Brain Barrier Dysfunction Causes Chronic Inflammation and Neurodegeneration

Numerous lines of evidence point to the characteristic increase in chronic inflammation that takes place in old age to be of great importance in the progression of neurodegenerative conditions. A fair degree of that inflammation in the brain results from dysfunction of the blood-brain barrier, a layer of cells lining blood vessels in the central nervous system that normally acts to prevent unwanted and potentially harmful molecules and cells from entering the brain. The work reported here builds on more than a decade of investigation of the age-related decline of the blood-brain barrier, and consequent inflammation in the brain, to build a targeted therapy to damp down one very specific source of inflammatory signaling. This is no doubt far from the only mechanism leading to inflammation, and repairing the blood-brain barrier would be a better way forward than compensating for its decline, mechanism by mechanism through a long list of such mechanisms, but the results are nonetheless interesting.

Scientists report that senile mice given an anti-inflammatory drug had fewer signs of brain inflammation and were better able to learn new tasks, becoming almost as adept as mice half their age. "We tend to think about the aged brain in the same way we think about neurodegeneration: Age involves loss of function and dead cells. But our new data tell a different story about why the aged brain is not functioning well: It is because of this "fog" of inflammatory load. But when you remove that inflammatory fog, within days the aged brain acts like a young brain. It is a really, really optimistic finding, in terms of the capacity for plasticity that exists in the brain. We can reverse brain aging."

The successful treatment in mice supports a radical new view of what causes the confusion and dementia that often accompany aging. More and more research shows that, with age, the filtration system that prevents molecules or infectious organisms in the blood from leaking into the brain - the so-called blood-brain barrier - becomes leaky, letting in chemicals that cause inflammation and a cascade of cell death. After age 70, nearly 60% of adults have leaky blood- brain barriers, according to magnetic resonance imaging (MRI) studies.

An accompanying paper shows that the inflammatory fog induced by a leaky blood-brain barrier alters the mouse brain's normal rhythms, causing microseizure-like events - momentary lapses in the normal rhythm within the hippocampus - that could produce some of the symptoms seen in degenerative brain diseases like Alzheimer's disease. Electroencephalograms (EEGs) revealed similar brain wave disruption, or paroxysmal slow wave events, in humans with epilepsy and with cognitive dysfunction, including Alzheimer's and mild cognitive impairment (MCI).

Scientists have long suspected that a leaky blood-brain barrier causes at least some of the tissue damage after brain injury and some of the mental decline that comes with age. But no one knew how. In 2007, researchers linked these problems to a blood protein, albumin. In 2009, they showed that when albumin leaks into the brain after trauma, it binds to the TGF-β receptor in brain cells called astrocytes. This triggers a cascade of inflammatory responses that damage other brain cells and neural circuits, leading to decreased inhibition and increased excitation of neurons and a propensity toward seizures.

In the new studies, researchers showed that introducing albumin into the brain can, within a week, make the brains of young mice look like those of old mice, in terms of hyperexcitability and their susceptibility to seizures. These albumin-treated mice also navigated a maze as poorly as aged mice. When they genetically engineered mice so that they could knock out the TGF-β receptor in astrocytes after they'd reached old age, the senile mouse brains looked young again. The mice were as resistant to induced seizures as a young mouse, and they learned a maze like a young mouse. Researchers developed a small-molecule drug that blocks the TGF-β receptor in astrocytes only, and that could traverse the blood-brain barrier. When they gave the drug, called IPW, to mice in doses that lowered the receptor activity level to that found in young mice, the brains of the aged mice looked younger, too. They showed young brain-like gene expression, reduced inflammation and improved rhythms - that is, reduced paroxysmal slow wave events - as well as reduced seizure susceptibility. They also navigated a maze or learned a spatial task like a young mouse.

Link: https://news.berkeley.edu/2019/12/04/drugs-that-quell-brain-inflammation-reverse-dementia/

A Large Study of Aspirin Use Finds Reduced Mortality, Contradicting the Recent ASPREE Study Results

The back and forth over whether regular aspirin use is beneficial continues with the publication of results from analysis of a large patient population that show a 15% reduction in all cause mortality in patients using aspirin. This contradicts the much smaller (but still large in and of itself) ASPREE clinical trial, in which patients using aspirin exhibited a small increase in mortality in comparison to their peers. As in that earlier study, the data here strongly suggests that benefits and risks vary with patient characteristics, such as whether or not a patient is overweight.

Aspirin is thought to be a weak calorie restriction mimetic, in that it can produce benefits via upregulation of autophagy to some degree, but it also reduces inflammation and blood clotting, among other effects. That reduction in inflammation is probably the most important benefit. Other studies suggest that the use of NSAIDs like aspirin reduces risk of Alzheimer's disease, which may well be the case for any long-term anti-inflammatory treatment, given the strong role played by chronic inflammation in that condition.

This sort of contradictory evidence is characteristic of medications with small effects. One would imagine that senolytics, capable of producing a larger and more reliable reduction of chronic inflammation in old people via clearance of senescent cells, could be put through much the same sort of clinical trials and emerge on the other side with far less ambiguity in the outcome for patients. We shall see whether or not this is the case in the years ahead, of course. But the point is that large effects tend to lead to consistent data, while inconsistent data is a hallmark of small effects.

Association of Aspirin Use With Mortality Risk Among Older Adult Participants in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial

This cohort study found that aspirin use among individuals 65 years and older was associated with a lower risk of mortality. This observation was consistent across all causes of mortality, i.e., all-cause, cancer, gastrointestinal cancer, and colorectal cancer (CRC); however, the greatest reduction in risk was noted for CRC mortality among individuals who used aspirin 3 or more times per week. Additionally, our exploratory analyses investigating the potential associations among aspirin use, BMI, and mortality risk suggest that the efficacy of aspirin as a cancer preventive agent may be associated with BMI. Participants in the PLCO Cancer Screening Trial who were underweight (i.e., BMI less than 20) had no observable benefit associated with aspirin use, while those with BMI 20 or higher were associated with reduced mortality risk, particularly with aspirin use 3 or more times per week. reduced risk of CRC mortality was only associated with individuals with BMI 20 to 29.9 who reported aspirin use 3 or more times per week.

The efficacy of prophylactic aspirin use for prevention of cancer incidence and mortality has been debated; however, the most evidence from prospective cohorts and secondary analyses from clinical trials indicates a protective association with aspirin use. A 2016 systematic analysis of primary and secondary cardiovascular prevention trials found reduced CRC incidence 10 to 19 years after aspirin use initiation. This association persists among investigations of aspirin use and cancer mortality.

These observations are in contrast with data from the ASPREE trial. However, the interpretation of the ASPREE results is limited owing a lack of an association of aspirin with cancer and CRC incidence and the short duration of follow-up. With additional follow-up, an association of aspirin with lower cancer incidence and death may have emerged. In addition, a 2018 combined analysis of the NIH-AARP Diet and Health Study and the PLCO Cancer Screening Trial reported decreased risk of all-cause, cancer, and cardiovascular mortality associated with daily aspirin use. However, a dosage that exceeded 1 per day was associated with an increased risk of mortality. These data also did not account for effect modifications by BMI on mortality risk. Previous studies have also found that variables, such as BMI, are associated with the efficacy of prophylactic aspirin. In a 2012 study of the Cancer Prevention Study-II Nutrition Cohort, individuals with prediagnostic BMI 30 or higher were associated with increased risk of all-cause and CRC death. A similar association was demonstrated across several other cohort and case-control studies, cancers, and causes of death.

The observation that BMI may be associated with efficacy of aspirin in individuals 65 years and older is notable; however, our findings require further confirmation. Increasing rates of overweight and obesity globally may substantially alter the population-based efficacy of cancer prevention prophylatics. Studies have suggested that aspirin has reduced effectiveness as a primary prevention modality among individuals who are obese owing to decreased bioavailability and antithrombotic efficacy; however, this study did not find an association of overweight or obesity with decreased efficacy. Therefore, although aspirin use is associated with benefit as a cancer preventive agent, the changing characteristics of the global population may alter its efficacy and must be considered along with age and risk of bleeding before recommending aspirin for cancer prevention.

A Review of Efforts to Target Senescent Cells in Order to Treat Age-Related Disease

This review paper looks at the present range of strategies adopted by the research and development communities in their efforts to target senescent cells. The accumulation of senescent cells is a contributing cause of aging; many animal studies have demonstrated reversal of aspects of age-related disease via clearance of senescent cells, particularly for those conditions in which chronic inflammation plays an important role. Senescent cells are comparatively few in number even in later life, but cause harm via secreted signals, a potent mix of proteins and vesicles known as the senescence-associated secretory phenotype (SASP). The SASP drives inflammation, changes the behavior of nearby cells for the worse, and destructively remodels surrounding tissue.

As there is ample evidence placing senescent cells as one of the causes of age-related dysfunctions, it has been considered to be one of the hallmarks of aging. It was recently demonstrated that elimination of senescent cells by genetic or pharmacological approaches delays the onset of aging-related diseases, such as cancer, neurodegenerative disorders, or cardiovascular diseases, among others, showing that the chronic presence of these cells is not essential. Conversely, local injections of senescent cells drive aging-related diseases. This data, together with that obtained from tissues of patients with different diseases and ages, has established causality of senescent cells in some aging-related pathologies.

One option to eliminate the negative effects of chronic senescent cells is to kill them specifically, using compounds called senolytics, which target pathways activated in senescent cells. The list of these senolytic compounds is extensive and continuously growing Senolytics target key proteins mainly involved in apoptosis, such as Bcl-2, Bcl-XL, p21, PI3K, AKT, FOXO4, and p53. Although senolytics are supposed to be specific for senescent cells, there are always unwanted damage/side effects since the administration is not directed. In this regard, a new strategy has been recently described to specifically target senescent cells in mice, using nanocapsules containing toxins (or senolytics). The outer layer of these nanocapsules are composed of substrates for enzymes that are overexpressed in senescent cells. In this way, the toxin (senolytic) will only be released inside senescent cells, killing them.

Another strategy to inhibit the functions of senescent cells is through the specific silencing of SASP, the complex mixture of soluble factors such as cytokines, chemokines, growth factors, proteases, and angiogenic factors that mediates the paracrine and autocrine functions of senescent cells. Senomorphics inhibit SASP functions by targeting pathways such as p38 mitogen-activated protein kinase (MAPK), NF-κB, IL-1α, mTOR, and PI3K/AKT, which act at the level of transcription, translation, or mRNA stabilization. Alternatively, inhibition may be achieved by specific antibodies against individual SASP factors (protein function inhibition), as is the case for IL-1α, IL-8, and IL-6. One doubt about this strategy is how SASP-silenced/attenuated senescent cells would be cleared. Given that some SASP factors are involved in the recruitment of immune cells, SASP inhibition could make senescent cells effectively "invisible" to the immune system, therefore remaining chronically within the tissue.

A third strategy to target senescent cells is to strengthen the immune system for efficient recognition and elimination of these cells, a process termed immunosurveillance. The role of the immune system in the elimination of senescent cells is fundamental, and a decline in immune function is associated with an increase in the number of senescent cells and finally, disease. In this regard, there are two strategies: i) improving the specific anti-senescent cell functions; and ii) general enhancement of immune functions (to avoid senescence of immune cells involved in recognition of senescent cells). Anti-senescent cell functions have been described in NK cells, macrophages, and CD4+ T cells. Since these functions take place through membrane receptors, one option is to increase the binding affinity of the involved receptors. In this sense, the use of chimeric antigen receptor (CAR) T cells to target specific senescent-related molecules would be an attractive approach.

Link: https://doi.org/10.18632/aging.102557

Clearance of Senescent Cells is Fast in Youth, Slow in Aging, Tipping the Balance Towards Accumulation

The accumulation of senescent cells is a cause of aging, which is why a great deal of effort is presently going towards the development of senolytic therapies capable of selectively destroying these unwanted cells. Very little is known about the dynamics of senescent cells in old age, however. We know that older individuals have more senescent cells at any given moment in time, but is this because a small fraction of the many senescent cells created every day manage to linger persistently for years, resistant to the efforts of the immune system to remove them, or because clearance processes, while they will eventually destroy all senescent cells, are slowed to the point at which they cannot keep up? This open access paper suggests the second option to be more plausible. This has implications for therapies, such as how often a senolytic treatment would need to be applied.

In this study, we propose a framework for the dynamics of senescent cell (SnCs) based on rapid turnover that slows with age. Bleomycin-induced SnC half-life is days in young mice and weeks in old mice, causing critical slowing down, which greatly amplifies the differences between individual SnC levels at old age. We theoretically explore the implications of this slowdown in a model in which SnCs cause death when they exceed a threshold. The widening variation in SnC levels with age causes a mortality distribution that follows the Gompertz law of exponentially increasing risk of death.

The rapid removal of SnCs that we observe following bleomycin-induced DNA damage is in line with studies that showed efficient removal of SnCs in vivo following liver fibrosis or induction by senescence by mutant Ras. On the other hand, when senescence was induced in the skin by directly activating the cell-cycle inhibitor p14ARF, which was not associated with an increase in tissue cytokine expression or inflammation, the induced SnCs persisted in the tissue for several weeks. Clearance may thus depend on the tissue, on the method of senescence induction, and on the presence of the senescence-associated secretory phenotype (SASP).

The present analysis of longitudinal p16 trajectories suggests that SnC slow down their own removal rate. This effect may be due to several mechanisms, including SASP, disruption of tissue architecture, or SnC abundance exceeding immune capacity. For the latter effect, SnC abundance at old age needs to be comparable to the abundance of the immune cells that remove them, which make up on the order of 0.1% of the body's cells. Further research is needed to characterize these effects.

Our results suggest that treatments that remove SnCs can therefore have a double benefit: an immediate benefit from a reduced SnC load, and a longer-term benefit from increased SnC removal. Similarly, interventions that increase removal capacity, for example by augmenting the immune surveillance of SnC, are predicted to be an effective approach to reduce SnC levels. More generally, the present combination of experiment and theory can be extended to explore further stochastic processes in aging, in order to bridge between the population-level and molecular-level understanding of aging.

Link: https://doi.org/10.1038/s41467-019-13192-4

Corpora Amylacea in the Clearance of Metabolic Waste from the Brain via Cerebrospinal Fluid Drainage

Age-related neurodegeneration is characterized by rising levels of various protein aggregates in the brain. A few of the many thousands of proteins in the body can become misfolded in ways that encourage other molecules of the same protein to also misfold in the same way, forming structures that spread and precipitate into solid deposits. These aggregates are accompanied by a halo of surrounding biochemistry that is toxic to neurons, disrupting function in the brain and killing vital cells, causing loss of cognitive function and ultimately death.

In recent years, increasing attention has been given to the role of cerebrospinal fluid drainage in maintaining the brain. The circulation of cerebrospinal fluid is not a closed system, but one that drains into the body via a few different routes. This is a path for molecular waste of all sorts to be removed from brain tissue, but unfortunately it deteriorates with age. The company Leucadia Therapeutics is founded on evidence for one such drainage path, through the cribriform plate, to become blocked with age, thereby leading to the early stages of Alzheimer's disease because amyloid-β cannot be cleared as rapidly as is needed. Similarly, other paths through the glymphatic system also deteriorate with age, for different reasons, and with similar consequences for the clearance of molecular waste.

Today's open access paper is of interest in this broader context. It examines one of the mechanisms by which waste can be packaged up into granules, exported from brain tissue into the cerebrospinal fluid, and thereby drained from the brain to be dealt with by immune cells elsewhere in the body.

Corpora amylacea act as containers that remove waste products from the brain

In 1837 the anatomist and physiologist J. E. Purkinje described the presence of some particular granular bodies in the brain of elderly patients. These bodies, named corpora amylacea (CA), were initially considered to have no pathological significance and for a long time were thought to be irrelevant. In recent decades, however, this perception has changed. With the advances in technology, CA have been studied from different perspectives and a large number of theories regarding their nature have been put forward. Unfortunately, none of these theories have been demonstrated conclusively and CA remain intriguing and mysterious bodies. In the present study, several features of CA are described and a vision of their function is proposed which may have implications for clinical practice.

There is a consensus that the main components of CA are polymerized hexoses (primarily glucose). Other components originating in neurons, astrocytes, or oligodendrocytes, from blood or of fungal or viral origin, have also been described. We observed that CA contain glycogen synthase (GS), an indispensable enzyme for polyglucosan formation, and also ubiquitin and protein p62, both associated with processes of elimination of waste substances. The relationship between CA and waste substances is recurrent in the literature. CA functions seem to be directed towards trapping and sequestration of potentially hazardous products of cellular metabolism, principally derived from the aging process, but probably also from any disease state resulting in excessive amounts of potentially harmful metabolic products.

It is well known that CA are located mainly in perivascular, periventricular, and subpial regions of the brain. Since the glymphatic system drains the interstitial fluid (ISF) from the perivascular regions to the cerebrospinal fluid (CSF), and since both periventricular and subpial regions are close to the cavities that contain the CSF (i.e., ventricles and subarachnoid space), it is plausible that CA are expelled from the brain to the CSF. The CSF drains not only via arachnoid granulations, as classically believed, but also via the recently rediscovered meningeal lymphatic system. From meningeal lymphatic vessels and subsequent lymphatic vessels, lymph crosses different cervical lymph nodes before accessing the lymphatic duct or right thoracic duct, which ultimately drain into the brachiocephalic veins.

On this basis, it has been reported that meningeal lymphatic vessels allow the brain to eliminate macromolecules by collecting them from the CSF. Conceivably, in the same way as waste molecules generated in the brain, it is possible that CA released from the brain into the CSF escape from the CSF via the meningeal lymphatic system, reaching the deep cervical lymph nodes or beyond. The lymphatic capillaries are formed by overlapping cells that can act as valves leaving relatively large openings, allowing the passage of macromolecules and even cells, and thus also the passage of CA. Overall, this evidence suggests a mechanism for eliminating residual substances from the brain in which CA act as waste containers that are extruded from the brain to the CSF. Afterward, via the meningeal lymphatic system, CA can reach the cervical lymph nodes, and macrophages located there may play a significant role in their phagocytosis.

This study shows that CA are released from periventricular and subpial regions to the cerebrospinal fluid and are present in the cervical lymph nodes, into which cerebrospinal fluid drains through the meningeal lymphatic system. We also show that CA can be phagocytosed by macrophages. We conclude that CA can act as containers that remove waste products from the brain and may be involved in a mechanism that cleans the brain. Moreover, we postulate that CA may contribute in some autoimmune brain diseases, exporting brain substances that interact with the immune system, and hypothesize that CA may contain brain markers that may aid in the diagnosis of certain brain diseases.

Assessing Late Life Cardiovascular Risk from Mid-Life Cholesterol Levels

Researchers here use data on cholesterol and health assessed in a large patient population over a 40 year period in order to determine how the risk of suffering atherosclerosis by age 75 varies with cholesterol levels assessed in the 30s and 40s. It is no surprise that higher cholesterol levels mean a greater risk of atherosclerosis, the development of fatty lesions that narrow and weaken blood vessels. The condition is one in which the macrophage cells responsible for removing these unwanted lipids from blood vessel walls are made dysfunctional by rising levels of oxidized cholesterol. The more cholesterol in the blood stream, the more oxidized cholesterol, all other things being equal.

Using data for individuals without prevalent cardiovascular disease, we characterised the age-specific and sex-specific long-term association of non-HDL cholesterol with cardiovascular disease. On the basis of this association, we derived and validated a tool specific for age, sex, and cardiovascular risk factors to assess the individual long-term probability of cardiovascular disease by the age of 75 years associated with non-HDL cholesterol. Further, we modelled the potentially achievable long-term cardiovascular disease risk, assuming a 50% reduction of non-HDL cholesterol.

Considerable uncertainty exists about the extent to which slightly increased or apparently normal cholesterol concentrations affect lifetime cardiovascular risk and about which thresholds should be used to merit a treatment recommendation, particularly in young people. Our study extends current knowledge because it suggests that increasing concentrations of non-HDL cholesterol predict long-term cardiovascular risk, particularly in cases of modest increase at a young age.

Results showed a stepwise increase of cardiovascular disease events across increasing concentrations of non-HDL cholesterol. 30-year cardiovascular disease event rates were approximately three-to-four times higher in women and men in the highest non-HDL cholesterol category (≥5.7 mmol/L) than those in the lowest category (less than 2.6 mmol/L; 33.7% vs 7.7% in women and 43.6% vs 12.8% in men). To estimate the long-term probability of a cardiovascular disease event associated with non-HDL cholesterol, we established a model for cardiovascular disease risk up to the age of 75 years. For example, women with non-HDL cholesterol concentrations between 3.7 and 4.8 mmol/L, younger than 45 years, and with at least two additional cardiovascular risk factors had a 15.6% probability of experiencing a non-fatal or fatal cardiovascular disease event by the age of 75 years (28.8% in men with the same characteristics).

We calculated the optimally achievable risk reduction for cardiovascular disease by the age of 75 years assuming a 50% reduction of non-HDL cholesterol. In the population with non-HDL cholesterol of 3.7-4.8 mmol/L, younger than 45 years, and with at least two risk factors, the long-term risk of cardiovascular disease could hypothetically be reduced from 15.6% to 3.6% in women and from 28.8% to 6.4% in men. Absolute risk reductions of cardiovascular disease were more pronounced in individuals with two or more cardiovascular disease risk factors than in those with one or no risk factors, and in men than women.

Link: https://doi.org/10.1016/S0140-6736(19)32519-X

Variation in Early Life Stress Contributes to Differences in Lifespan in Genetically Identical Worms

Why do genetically identical nematode worms raised in the same environment exhibit a distribution in life span? Researchers here suggest that differences in oxidative stress in early life are an important contributing factor, perhaps steering metabolism in some of these simple organisms towards greater resistance to the rising oxidative stress of aging. So a form of hormetic effect, perhaps. Does this have much relevance to higher animals such as our own, however?

It would be challenging to separate out early life effects of this nature from the environmental differences across the whole of life, given the existing human epidemiological data. We might consider lines of research into childhood exposure to persistent viruses such as cytomegalovirus, which hint at an earlier burden of infection leading to a shorter and less healthy later life. Or evidence for greater exposure to solar radiation in utero, via seasonal variation, to produce differences in long-term human health and life expectancy. These are not hormetic effects, but ones in which the burden of increased damage reduces health and longevity. Perhaps hormetic effects do exist, but they would certainly be harder to find in the human data.

Oxidative stress happens when cells produce more oxidants and free radicals than they can deal with. It's part of the aging process, but can also arise from stressful conditions such as exercise and calorie restriction. Examining a type of roundworm called C. elegans, scientists found that worms that produced more oxidants during development lived longer than worms that produced fewer oxidants. Researchers have long wondered what determines variability in lifespan. One part of that is genetics: If your parents are long-lived, you have a good chance for living longer as well. Environment is another part.

That other stochastic factors might be involved becomes clear in the case of C. elegans. These short-lived organisms are a popular model system among aging researchers in part because every hermaphroditic mother produces hundreds of genetically identical offspring. However, even if kept in the same environment, the lifespan of these offspring varies to a surprising extent. "If lifespan was determined solely by genes and environment, we would expect that genetically identical worms grown on the same petri dish would all drop dead at about the same time, but this is not at all what happens. Some worms live only three days while others are still happily moving around after 20 days. The question then is, what is it, apart from genetics and environment, that is causing this big difference in lifespan?"

Researchers found one part of the answer when they discovered that during development, C. elegans worms varied substantially in the amount of reactive oxygen species they produce. Reactive oxygen species, or ROS, are oxidants that every air-breathing organism produces. ROS are closely associated with aging, but instead of having a shorter lifespan, worms that produced more ROS during development actually lived longer. When the researchers exposed the whole population of juvenile worms to external ROS during development, the average lifespan of the entire population increased. Though the researchers don't know yet what triggers the oxidative stress event during development, they were able to determine what processes enhanced the lifespan of these worms.

By separating worms that produced large amounts of ROS from those that produced little amounts of ROS, she showed that the main difference between the two groups was a histone modifier, whose activity is sensitive to oxidative stress conditions. The researchers found that the temporary production of ROS during development caused changes in the histone modifier early in the worm's life. How these changes persist throughout life and how they ultimately affect and extend lifespan is still unknown. What is known, however, is that this specific histone modifier is also sensitive to oxidative stress sensitive in mammalian cells. Additionally, early-life interventions have been shown to extend lifespans in mammalian model systems such as mice.

Link: https://news.umich.edu/u-m-researchers-discover-stress-in-early-life-extends-lifespan/

Ways in Which the Failing Lymphatic System Contributes to Age-Related Disease

The lymphatic system is a parallel circulatory system responsible for moving fluid, immune cells, and a range of vital molecules around the body. It is of particular importance to immune function, allowing components of the immune system to carry messages from place to place in the body, and communicate and coordinate the immune response at the hubs known as lymph nodes. Like all tissues in the body, the lymphatic system is negatively impacted by aging, and this has widespread detrimental effects throughout the body and brain.

For example, lymph nodes become disrupted in structure and function by the presence of senescent cells and consequent fibrosis as tissue maintenance runs awry in the face of the senescence-associated secretory phenotype. The consequences of this are well demonstrated in a recent paper: very old mice and primates suffering from immunosenescence, an immune system with a poor response to pathogens, cannot benefit from the addition of new, functional immune cells. Their lymph nodes are too structurally impacted to allow the new cells to coordinate an effective immune response. Given that fibrosis in a number of tissues has been reversed in animal models via use of senolytics to clear senescent cells and their inflammatory signaling, it is possible that lymph node aging might be reversed to some degree. If the structure cannot be regenerated, however, then there are efforts underway to produce artificial lymph nodes that can be transplanted to integrate with the lymphatic system.

It isn't just a matter of lymph nodes, of course. Lymphatic vessels actively pump their contents, and this pumping function declines and becomes erratic with advancing age. Other forms of degeneration also take place, impairing the ability of immune cells and their signals to move about the body. This is a harder problem to solve, given its distributed nature, and that it probably arises due to contributions from most of the underlying forms of molecular damage that cause aging. It is important for the research community to keep working on means of repair for all forms of damage, not just focus on the approaches, like senolytics, that are closest to practical clinical use.

Reduced lymphatic function contributes to age-related disease

The diverse etiologies of age-related diseases, from osteoarthritis to Alzheimer's disease, all share an impairment, or slow loss, of tissue function. Aging tissue homeostasis shifts towards progressive, low-grade inflammation and a dampened immune response. The lymphatic vasculature is the key regulator of tissue homeostasis in health and disease. Lymphatics transport antigens and other macromolecules, excess interstitial fluid, and activated immune cells during inflammation. Here we highlight how reduced lymphatic function is a key component regulating several age-related diseases.

Lymphatic vessels are structurally quite different from blood vessels, beginning with blind-ended capillaries possessing leaf-like cell junctions that lead to large, unidirectionally-valved collecting vessels. These larger vessels are surrounded by lymphatic muscle cells that provide intrinsic pumping to maintain lymph flow. A recent review focused on lymphatic collecting vessels found that lymphatic muscle contractions are reduced in amplitude and frequency and can become irregular with age. Other researchers have demonstrated altered muscle coverage and function, decreased ion channel activity, limited nitric oxide responsiveness, and reduced antigen trafficking in aged lymphatic vessels: all leading to an impairment of the immune response. They identified that increased mast cell investiture and elevated histamine levels cause heightened basal NF-kB activity in aged lymphatic vessels. This resulted in a blunted inflammatory response both in reduced vessel contractility and limited NF-kB activation. Tissue homeostasis depends on lymphatics and the structural and physiologic decline in lymphatic vessel function likely contributes to age-associated pathologies.

Chronic tissue degeneration is a common feature of age-associated disorders like osteoarthritis (OA). A series of collaborative studies have extensively detailed lymphatic involvement in several models of arthritis. Inflammatory lymphangiogenesis and increased pumping initially facilitate the removal of immune cells and fluid to the draining lymph nodes, but that over time lymphatics regress and collecting lymphatic vessels lose contractility. In their recent study of OA, blocking lymphangiogenesis accelerated joint tissue loss. The team identified increased pro-inflammatory macrophages in the knee joint and increased inflammatory markers expressed by lymphatic endothelial cells. Treatment with the proteasome inhibitor bortezomib significantly improved lymphatic drainage and reduced cartilage loss. The group's arthritis research portfolio has clearly identified that maintaining effective lymphatic drainage reduces inflammation through fluid clearance and immunomodulatory mechanisms. Further elucidating these mechanisms may make modulating lymphatics a strategy to slow OA progression.

Cardiovascular (CV) disease and diabetes are progressive pathologies whose diagnoses increase with age, and the side effects, treatment, and recovery are more difficult to manage in older patients. Lymphatic vessels have demonstrated a critical role and therapeutic potential in several CV pathologies including atherosclerosis, myocardial infarction, hypertension, and diabetes. Atherosclerosis is characterized by chronic cholesterol-rich plaque accumulation and macrophage foam cell residency in the arterial wall. Preventing lymphangiogenesis worsened lesions while increasing lymphatics reduced macrophage numbers and cholesterol content, highlighting the lymphatic route of immune cell and macromolecule. Similarly, following myocardial infarction, functional lymphangiogenesis reduced fluid accumulation and inflammatory fibrosis. We recently demonstrated that the therapeutic induction of lymphangiogenesis specifically in the kidney may target the chronic renal inflammation characteristic of hypertension and prevent an elevation in blood pressure. Similarly, we found that inducing lymphangiogenesis in adipose tissue reduced adipose-associated macrophage accumulation and improved glucose homeostasis in an obese mouse model of diet-induced diabetes. Age-related lymphatic impairment may therefore provide a target to slow the functional decline of CV tissues.

A Survey of Existing Literature on Senescent Cell Burden by Age and Tissue in Humans

Cells enter a state of senescence in response to reaching the Hayflick limit, or to a toxic environment, or potentially cancerous mutational damage. Near all senescent cells self-destruct, or are destroyed by the immune system. Some linger, however, and when present in even comparatively small numbers relative to normal cells, these senescent cells cause considerable harm via their inflammatory secretions. Thus the targeted destruction of senescent cells via senolytic therapies has been shown to extend healthy life and reverse numerous aspects of aging in mice. Human trials of senolytic treatments are presently underway, and have produced promising initial results.

Researchers here do the public service of combing through the existing literature on senescent cells in aging to assemble in one place all that is presently known on the level of cellular senescence in humans by age and tissue type. The data is fairly consistent, in that rising numbers of senescent cells with age appear throughout the body, but present techniques for assessing senescence clearly need to be improved, given that the numbers vary by measurement strategy.

This is the first study to quantify the association between the magnitude of senescence and chronological age across different human tissue types. A qualitative analysis of the literature identifies a largely positive association between cellular senescence and chronological age; however, the strength of the association differed based on the tissue type, subsection of tissue, and the senescence marker used within and between tissues. The observed differences in the strength of the association between senescence and chronological age between tissue types may be explained by the natural cell turnover rate of tissue which is known to vary widely. However, a tissue-specific response to environmental exposures or different defense mechanisms against cytotoxic stress may also explain this variable senescence level within human tissue types. For example, researchers demonstrated higher numbers of senescent cells in patients who have received chemotherapy.

To date, there is little data available on senescence within different organ systems from the same individual. Articles included in this review that investigated the difference in senescence within tissues of the same organ showed that despite higher senescence within these tissues, the magnitude of senescence differed based on the tissue or cell type. Researches also investigated senescence within individuals using tissue samples from different organs (blood and gut) and demonstrated that the magnitude of senescence was not only variable depending on the tissue assessed but also the marker used to define senescence. Thus, in alignment with the findings of this review, the current evidence would suggest that while cellular senescence is likely to increase with chronological age, the magnitude of senescence can vary from tissue to tissue. How this variation in senescence contributes to the onset of age-related disease is yet to be determined.

This analysis did identify some tissue types (adipose, gut, prostate, and thymus) where senescence was not significantly associated with age. The lack of significance in these tissues could be caused by the limited number of studies investigating senescence and age within these tissues and the smaller sample sizes within these articles. Thus, despite positive correlations the relationship between senescence and age within these tissues requires confirmation through additional studies. On the other hand, adipose and thymus tissue are also postmitotic tissue. Senescence within postmitotic cells, such as neurons, adipose, and skeletal muscle, has been largely overlooked in human research, which is reflected in this current review. This is likely due to a lack of evidence as to whether postmitotic cells can become senescent.

In addition to heterogeneity of senescence between and within tissue samples, senescence varied widely depending on the marker used to detect senescence. Notably, correlation of senescence markers and age differed substantially for proliferation and DNA damage markers. This is thought to be caused by the various other cellular processes these markers are involved in, as proliferation and DNA damage are not specific to the senescent phenotype. Furthermore, production of SA-β-gal does not necessarily indicate senescence either: quiescent cells in culture are also known to express SA-β-gal. Thus, the higher expression of any senescent marker within tissue samples as evidence of senescence must be viewed with caution. These observations are supported here by the pronounced heterogeneity of senescence within the same tissue sample, such as skin and eye, using different senescence markers.

Link: https://doi.org/10.1111/acel.13083

Reviewing the Present Development of Biomarkers of Aging

As this open access paper notes, a great deal of the present work on developing biomarkers of aging involves machine learning. Researchers are sifting and arranging health metrics, blood markers, and epigenetic data to find combinations that predict risk of disease and mortality. The aim at the end of the day is to determine a good measure of biological age, one that accounts for all of the burden of cellular and molecular damage that leads to death and dysfunction, and will thus be a good, rapid measure of effectiveness for rejuvenation therapies. The biggest challenge in this line of work at the present time is that researchers don't have a good understanding of what exactly is being measured by many of these potential biomarkers. It is entirely plausible that they are only a measure of some types of the underlying damage of aging, and will thus be of no use in assessing many of the possible approaches to rejuvenation.

The recent hype cycle in artificial intelligence (AI) resulted in substantial investment in machine learning and increase in available talent in almost every industry and country. This wave of increased attention to AI was fueled by the many credible advances in deep learning that allowed machines to outperform humans in multiple tasks. The advantage of deep learning (DL) systems is in their ability to learn and generalize from a large number of examples. DL methods rapidly propagated into the many biomedical applications, starting primarily with the imaging, text, and genomic data. The availability of large volumes of data and new algorithms made it possible to use deep learning to start making predictions about the activity and pharmacological properties of small molecules, identify mimetics of the known geroprotectors, and discover new ones.

There are many biological features that demonstrated correlation with the chronological age such as telomere length, racemization of amino acids in proteins, and others. The epigenetic age predictors were proposed in 2011. But it was not until 2012 when the first epigenetic aging clock was published by Hannum. Hannum's group profiled the methylomes derived from peripheral blood samples of healthy individuals to develop the first epigenetic clock consisting of 71 CpG sites and demonstrated the root mean squared error of 4.9 years on independent data. A more precise and comprehensive multi-tissue aging clock was then published in 2013 by Horvath who coined the terms "DNAm clock" and "epigenetic aging clock" and rapidly gained popularity in the aging research community. Horvath used 353 CpG sites and achieved a median error of 3.6 years on the testing set. These clocks were developed using traditional machine learning approaches - notably linear regression with regularization and the use of a limited number of samples. Similar methylation aging clocks were developed for mice.

With the first deep-neural-network-based aging clocks published in 2016, significant progress has been made the past few years in deep learned biomarkers of human aging. The first DL clock was constructed using 41 blood test values of over 50,000 individuals. Making use of deep neural network abilities to capture nonlinear dependencies between input data and target variable, the initially proposed method was able to achieve mean absolute accuracy of 5.5 years on previously unseen 12,000 individuals. Additionally, this study demonstrated how the deep clock can be used for further interpretations of relations between aging and blood parameters. By employing feature importance analysis they identified top parameters related to age changes.

The deep biomarkers of aging and longevity have a broad range of applications in research and development, medical, insurance, and many other areas. Developing comprehensive granular multi-modal aging clocks will help obtain a better understanding of the aging processes, establish causal relationships, and identify preventative and therapeutic interventions. One of the many promising applications of the deep aging clocks built into the generative adversarial networks is generation of synthetic biological data with age as a generation condition. The deep aging clock research is expected to increase in popularity.

Link: https://doi.org/10.18632/aging.102475

Calorie Restriction as a Way to Slow Harmful Age-Related Changes in the Gut Microbiome

The practice of calorie restriction, eating 20-40% fewer calories while still obtaining an optimal intake of micronutrients, produces sweeping changes in the operation of cellular metabolism. It improves health and extends life span in near all species tested to date, though much more so in short-lived species than in long-lived species. The most important mechanism appears to be a boost to the operation of the cellular housekeeping processes of autophagy, more efficiently clearing out damaged components and unwanted molecular waste before they can cause further issues. That said, near every measure of aging is slowed by calorie restriction, so it is no surprise to see in today's open access paper that this slowing also applies to the detrimental changes to the microbial populations of the gut that are observed to take place with age.

In recent years the research community has been giving ever more attention to the gut microbiome in the context of long-term health and aging. Gut microbes produce a number of compounds that are beneficial, such as tryptophan, indole, butyrate, and propionate, but this production falls off in adult life and into old age. Populations of beneficial bacterial species are replaced by populations of harmful species that interact with tissues and the immune system to cause chronic inflammation. There are many possible contributing causes for age-related changes microbial populations in the gut, such as specific dietary changes, as well as failure of the immune system to control harmful populations. It isn't clear as to which of these are more or less important, however.

While calorie restriction seems to slow this progression, and here again it is hard to say which of the possible mechanisms are the important ones, transplantation of gut microbes appears to be a better approach, one capable of reversing age-related changes. This has been demonstrated with fecal microbiota transplants from young animals to old animals, and this form of treatment is well proven in humans as a therapy for a range of conditions in which the gut is colonized by pathological microbes. It has also been trialed for a range of medical conditions that are suspected to have some inflammatory or other contribution arising from gut microbes, such as Parkinson's disease. So why not the condition of aging as well?

Calorie restriction slows age-related microbiota changes in an Alzheimer's disease model in female mice

The gut-brain axis is an integrated network in which the microbiota and central nervous system communicate via endocrine, immune, and neural signaling pathways. Several translational studies show that transferring microbiota from patients with neurodevelopmental and neurological disorders including autism, multiple sclerosis, and Parkinson's disease can influence behavior, motor dysfunction, and immune responses in relevant animal models. These studies provide evidence that intestinal microbiota may play an etiologic role in diseases that emerge at differing points during the lifespan. Consistent with this notion, Alzheimer's disease (AD) patients have altered gut microbiota compared to age-matched healthy subjects. In established animal models of AD, depleting the microbiota either in germ-free or antibiotic-treated mice served as protection against the pathological hallmark amyloid-beta (Aβ) plaque deposition.

While host genotypes influence AD risk, the most important risk factor is advanced age. In older adults, the microbiota is less diverse, and immunosenescence and age-related changes in host physiology can destabilize the microbiota. An 'aged' microbiota promotes immune dysfunction, including increased systemic inflammation and impaired macrophage phagocytosis, which can be partially restored by transferring microbiota from young to aged mice. Thus, understanding how to slow or reverse age-related changes in the gut microbiota has therapeutic implications for age-related brain diseases, including AD.

Diet is a major environmental factor that modulates the microbiota and has been proposed to prevent age-related changes of the microbiota. Calorie restriction (CR), characterized by 20-40% reduction of total calorie intake without malnutrition, increases the healthspan and lifespan in multiple model organisms. A 30% reduction in calories from carbohydrates activates neuroprotective signatures and suppresses age-related transcriptional changes in the hippocampus in wildtype (WT) mice. In the context of AD, we found that CR prevents Aβ plaque accumulation and modulates the expression of the gamma-secretase complex, the amyloid-beta precursor protein (APP) processing enzymes, in a sex-dependent manner in Tg2576 mice. In addition to effects on host physiology, CR modulates the microbiota and increases abundances of bacteria that positively correlate with lifespan. However, the association between CR, the microbiome, and AD pathogenesis has not been established.

In this study, we investigated the effect of long-term 30% CR compared with ad libitum (AL) feeding on the microbiome in aging. We studied the Tg2576 model, where a mutant variant of the human APP is expressed in transgenic mice. This transgene results in cerebral amyloid accumulation, synaptic loss, and cognitive impairment by 12 months of age. We found that female Tg2576 mice have more substantial age-related microbiome changes compared to wildtype (WT) mice, including an increase in Bacteroides, which were normalized by CR. Specific gut microbiota changes were linked to Aβ levels, with greater effects in females than in males. In the gut, Tg2576 female mice had an enhanced intestinal inflammatory transcriptional profile, which was reversed by CR. Furthermore, we demonstrate that Bacteroides colonization exacerbates Aβ deposition, which may be a mechanism whereby the gut impacts AD pathogenesis. These results suggest that long-term CR may alter the gut environment and prevent the expansion of microbes that contribute to age-related cognitive decline.

Proteasomal Failure as a Contributing Cause of Protein Aggregation in Neurodegenerative Disease

Neurodegenerative diseases are characterized by the formation of protein aggregates, misfolded proteins that encourage other molecules of the same protein to also misfold in the same way, forming solid deposits that damage and destroy brain cells. Researchers here suggest that the age-related decline in proteasomal function is a contributing factor. The proteasome is a structure that breaks down damaged or otherwise unwanted proteins in cells. While this form of cellular housekeeping does decline with age, and there is good evidence in lower animals for increased proteasomal function to slow aging, it is worth bearing in mind that the research here is based on deliberately breaking proteasomes by removing a crucial component protein. It is always difficult to say whether the results of this sort of breakage are relevant to aging - it strongly depends on the details in each case.

Proteasomes are made in the cell body of a neuron and need to be transported over long distances to reach the nerve endings where the neuron connects with other cells - a journey of more than one meter in some cases. When proteasomes fail to reach these critical communication hubs, the cell descends into turmoil. Instead of being degraded, damaged proteins in these sites hang around long enough to interact with other binding partners, form aggregates, and disrupt cell function. Over time, this causes degeneration of nerve fibers and ultimately cell death.

When researchers began investigating the proteasome transportation system in fruit flies, they identified a protein called PI31, which plays a crucial role in loading the proteasomes onto the cellular components that ferry them around. They show that PI31 enhances binding and promotes movement of proteasomes with cellular motors. Without it, transport is halted. This is the case in both fly and mouse neurons, suggesting that the transport mechanism is common between many species. Digging deeper into what happens when PI31 is defective, the scientists generated mice whose PI31 gene was switched off in two groups of brain cells with particularly long extensions. They found that without PI31, proteasomes cannot travel, resulting in abnormal protein levels at the tips of neuronal branches. The PI31-lacking neurons also looked peculiar, both with respect to their branches and to their synapses, the structures where branches from two neurons connect. Notably, these structural changes became progressively more severe with age.

There are other reasons to suspect that the lab's findings could inform the treatment of neurodegenerative diseases. For example, mutations in the PI31 gene have been linked to Alzheimer's disease. The fact that PI31 appears to be involved in the early stages of nerve cell degeneration is especially compelling, as it could mean that drugs blocking this protein might have the potential to halt brain damage early on in the process. The researchers believe the formation of aggregates is likely not the direct disease mechanism, but rather a symptom of bigger problems. "Our work suggests that it really starts with a local defect in proteasomes, resulting in the failure to degrade proteins that are critical for nerve function. These undigested proteins subsequently form aggregates and activate additional damage control pathways. But eventually, these clearance systems are overwhelmed, which causes a slow but steady progression to a detectable disease."

Link: https://www.rockefeller.edu/news/26927-neurodegenerative-diseases-may-caused-molecular-transportation-failures-inside-neurons/

Investigating Circular RNAs in Cellular Senescence

Numerous demonstrations of rejuvenation via clearance of senescent cells in recent years have led to a newfound and considerable enthusiasm for the study of the mechanisms of cellular senescence. Ever more funding in flowing into this part of the life sciences. That any new discovery might lead to a company, valuable intellectual property, a means to treat aging, is a considerable incentive forthe various research and funding ecosystems. The open access research noted here is a representative example of numerous projects presently underway.

Cellular senescence is involved in modulating aging and aging-associated pathologies via the senescence-associated secretory phenotype (SASP). Growing evidence has implicated the accumulation of senescent cells are implicated in chronologic aging of organisms. Several lines of evidence have suggested that cellular senescence is closely associated with age-related diseases. Therefore, characterizing the regulatory mechanisms of cellular senescence may allow us to intervene in aging-related diseases.

Circular RNAs (CircRNA) generated by back-splicing are highly conserved and stable long non-coding RNAs abundant in eukaryotic transcriptomes. Currently, the functions of most CircRNAs remain largely unexplored; however, the known functions include (I) sequestration of microRNAs or proteins; (II) modulation of transcription and splicing; (III) peptide or protein encoding. CircRNAs are also involved in various pathological and physiological processes, including cancer development, cardiovascular disease, and aging. However, molecular mechanisms and functions of CircRNAs in cellular senescence and aging of organisms remain largely unknown.

The present study identified senescence-associated CircRNAs (SAC-RNAs) by the whole-transcriptome sequencing, and revealed that CircCCNB1 is dramatically downregulated in replicative senescence and prematurely senescent fibroblasts. Short hairpin RNA (shRNA)-induced knockdown of circular cyclin B1 (CircCCNB1) led to senescence in proliferating fibroblasts. Mechanistically, CircCCNB1 regulated cyclin E2 (CCNE2) by controlling microRNA 449a (miR-449a) activity. Our data implicated that CircCCNB1-miR-449a-CCNE2 axis in the regulation of cellular senescence. Modulating miRNA activity by targeting SAC-RNAs can influence target protein expression, which may represent a promising strategy for aging and age-related disease interventions.

Link: https://doi.org/10.18632/aging.102449

Cancer Survivors have Double the Risk of Suffering a Later Stroke

Surviving cancer comes with a well known loss of remaining life expectancy, roughly the same as being obese or a lifelong smoker. It is plausible that this is a consequence of the generation of large numbers of lingering senescent cells, resulting from radiotherapy and chemotherapy, still the dominant forms of cancer treatment. An increased burden of cellular senescence is certainly preferable to death by cancer, but these cells secrete a potent mix of inflammatory signals that disrupt tissue maintenance and immune function, encourage fibrosis, and increase the risk of numerous age-related conditions. Given that the accumulation of senescent cells is a cause of aging, increasing their presence might rightfully be regarded as an acceleration of aging.

Researchers here note one of the specific consequences of surviving cancer, its present day therapies, and continuing forward with an increased burden of senescent cells, which is a greatly increased risk of stroke. This and numerous other consequences might be alleviated in large part via the use of senolytic drugs to clear out senescent cells. The development of senolytics is still in its comparative infancy, but some of the existing senolytics compounds are in human trials, are cheap and readily available, have been shown to clear senescent cells in human patients, and there is little other than regulatory barriers to prevent their wider adoption as a treatment for a range of age-related conditions. Consequently, testing their ability to reduce the impact of cancer therapy on patients only requires a trial sponsor, the funds, and the will to get started.

Notably, the authors of this open access paper do not mention cellular senescence in their discussion of potential mechanisms by which cancer might increase risk of stroke, which I think an oversight - senescent cells are known to influence many of the mentioned mechanisms. While much of the research community is embracing the contribution of cellular senescence to aging and age-related disease, there is still a way to go yet.

Stroke among cancer patients

We present a contemporary analysis of risk of fatal stroke among more than 7.5 million cancer patients and report that stroke risk varies as a function of disease site, age, gender, marital status, and time after diagnosis. The risk of stroke among cancer patients is two times that of the general population and rises with longer follow-up time. The relative risk of fatal stroke, versus the general population, is highest in those with cancers of the brain and gastrointestinal tract. The plurality of strokes occurs in patients older than 40 years of age with cancers of the prostate, breast, and colorectum. Patients of any age diagnosed with brain tumors and lymphomas are at risk for stroke throughout life.

Most cancer patients now die of non-cancer causes. The results of the current work suggest that stroke prevention strategies may be aimed at patients treated for brain tumors and lymphomas (particularly children) and older patients (i.e., older than 40 years) diagnosed with cancers of the prostate, breast, and colorectum. Though relatively less common, patients with cancers of the gastrointestinal tract (especially the pancreas, liver, esophagus) are at a relatively high risk to die of stroke at any time after diagnosis. We encourage individual guideline and survivorship committees to incorporate these data into their stroke prevention statements.

Relatively few studies have examined the risk of stroke among cancer patients, and the current analysis is the largest of its kind. Similar to previous analyses, we found that lung, prostate, breast, and colorectal patients experience the plurality of strokes. Although the current analysis does not include patient comorbidities or biomarkers, other studies suggest that D-dimer levels and classic risk factors for stroke (e.g., hypertension) put patients at greatest risk.

The risk factors for stroke in cancer patients are under investigation. A systemic review reported that patients with cancer are subject to the same stroke risk factors as the general population, and atherosclerosis remains the most common cause of stroke in cancer patients. Further, the authors noted that if stroke in cancer patients was caused by the same pathophysiologic mechanisms as in the general population, the distribution of stroke should be identical to the population at large, and there would be a distribution of primary neoplasms proportional to the most common cancers (i.e., lung, breast, and prostate). In their review, there was a relatively wide variability of stroke among tumor types.

Several pathways for increased risk of stroke in cancer patients have been proposed, and there are several cancer-specific types and causes of stroke in cancer patients. Cancer may lead to stroke via several mechanisms. First, certain cancers cause occlusive disease from emboli, compression, or meningeal extension of tumor. Tumor dissemination into the leptomeningeal space can lead to vascular compromise. Patients with leukemia and elevated leukocyte counts may develop intravascular leukostasis, leading to hemorrhagic infarct. Brain tumor metastases may also cause hemorrhage, and this is more common in cancers of the kidneys, thyroid, germ cells, melanoma, and choriocarcinoma. Second, coagulopathies, including non-bacterial thrombotic endocarditis (NBTE), may cause stroke. NBTE, or marantic endocarditis, is characterized by the presence of relatively acellular aggregates of fibrin and platelets attached to normal heart valves. Third, stroke may occur from therapy, such as radiation therapy-induced atherosclerosis, drug-induced thrombocytopenia, and hypercoagulability.

Are Benefits from Cardiac Stem Cell Therapy Due to an Immune Response to Transplanted Cells?

As this article notes, researchers have recently suggested that the benefits to heart function observed over many years of stem cell therapies are not in fact due to any action of the cells themselves, not even cell signaling mechanisms such as release of exosomes, but are rather due to an immune response to the transplanted cells. The study reported here illustrates the point by showing some degree of regeneration of injured heart tissue to take place in mice when the debris of dead cells is transplanted. We might compare these findings with the body of work showing that delivery of exosomes can spur cardiac regeneration; few portions of the field of stem cell therapy are lacking a good supply of contradictory evidence.

For 15 years, scientists have put various stem cells into seriously ill patients' hearts in hopes of regenerating injured muscle and boosting heart function. A new mouse study may finally debunk the idea behind the controversial procedure, showing the beneficial effects of two types of cell therapy are caused not by the rejuvenating properties of stem cells, but by the body's wound-healing response - which can also be triggered by injecting dead cells or a chemical into the heart.

The discovery will have to be repeated and investigated in human tissue, but the emergence of a likely explanation for how heart cell therapy can have modest benefits comes after years of hype, hope and disagreement about stem cells' potential to heal broken hearts. Experimental therapies have been tested in hundreds of patients with heart disease, even as doubts have grown about the underlying scientific rationale. The idea that the cells could regenerate the heart was intuitively attractive and captured a field searching for therapies to offer desperate patients, and many scientists started companies to try to commercialize different cell types. The new work provides a long-awaited explanation - one that some outside scientists argued does not support more trials with the cells.

Five years ago, researchers debunked the idea that one type of heart stem cell, called a cardiac progenitor cell, was a stem cell at all. Contrary to expectations, those cells were not regenerating appreciable amounts of heart muscle after being injected into injured mouse hearts. Some scientists and physicians, many of whom had built careers on the use of cells as therapy, argued that it wasn't the cells themselves doing the repair but, rather, factors that the cells secreted. In the new study, scientists reported that the modest beneficial effects of injecting either cardiac progenitor cells or bone marrow cells into the injured mouse heart don't appear to be specific to the cell therapy. Modest improvements in heart function, the result of the healing of a heart attack scar, can also be triggered by injecting dead cellular debris or a chemical that stimulates the immune system.

"The progression, after we figured out that was wrong, was that people were hoping the cells we inject make a magic soup ... that revitalize the cells. What we did and showed is there is no magic soup. You're injecting cells, they're dying and stimulating an immune response."

Link: https://www.washingtonpost.com/health/2019/11/27/benefits-stem-cell-heart-therapy-may-have-nothing-do-with-stem-cells-mouse-study-suggests/

Low Lymphocyte Levels Correlate with Greater Mortality in Late Life

Lymphopenia is the condition of having lower than normal levels of lymphocytes, a mix of cells of the adaptive and innate immune system, in blood samples. The immune system is of vital importance to health, and this is demonstrated here by data that shows raised mortality in the sizable fraction of older people with degrees of lymphopenia versus those without. Lymophocytes do not just respond to the presence of infectious pathogens, but also attack and destroy senescent cells and cancerous cells, among other important activities. A severely deficient immune system is a real threat to life, and as this work illustrates, even a modestly deficient immune system is something to worry about.

The near future should see the advent of approaches to restore immune function in the elderly. Regrowth of the atrophied thymus, where T cells of the adaptive immune system are trained; restoration of the declining hematopoietic stem cell population responsible for creating immune cells in the bone marrow; clearance of harmful populations of misconfigured, senescent, and exhausted T cells in the aged immune system; regeneration of fibrotic and structurally disrupted lymph nodes. These four approaches, as they are enacted, should go a long way towards ensuring a healthier, longer life for older people.

This study sought to (1) determine the associations among lymphocyte levels, other immunohematologic parameters, and survival and (2) establish the extent to which the associated risk of these variables is additive. In this large cohort of adults, we found that lymphopenia was associated with mortality risk independently of traditional clinical risk factors and other immunohematologic variables (red blood cell distribution width and C-reactive protein level). Individuals with multiple immunohematologic abnormalities had a strikingly high risk of mortality among this generally low-risk population. Approximately 20% of the general US population appears to have a high-risk immunohematologic profile, and these participants' 10-year mortality was 28%, compared with 4% in participants in the present study with a low-risk profile. The risk associated with this immunohematologic pattern is independent of (and thus additive to) traditional clinical risk factors. Together, these data suggest that immunohematologic risk may be viewed as a multidimensional entity and can be estimated using markers commonly available as part of routine clinical care.

We believe the results presented herein add to the growing body of evidence that immune status is associated with cardiovascular and noncardiovascular disease. Previous observational and prospective trials suggest that participants with overt or subacute inflammatory diseases have elevated risk of atherothrombotic disease, heart failure, malignant disease, and death. Comparatively few studies have evaluated absolute lymphocyte count as a prognostic biomarker. Herein, we found that lymphopenia is relatively common in the general population and is associated with reduced longevity independently of age, clinical risk factors, and other immunohematologic parameters. In our fully adjusted analyses, a bimodal relationship between lymphocyte counts and mortality emerged, suggesting that the expansion of lymphocytes may also introduce hazard in the general population.

Because mortality in this population was largely driven by noninfectious causes, these data support the notion that immune status is indeed associated with resilience against cancer and cardiovascular disease, and an adverse immune phenotype may precede clinical manifestations of these illnesses. Whether lymphocyte levels are themselves part of the causal pathways linking lymphopenia to death will require additional study. Cytotoxic T cells can eradicate cells with malignant potential, and thus an optimal absolute lymphocyte count may reflect an immune system capable of providing protection against tumor development. Lymphopenia can also induce compensatory proliferation of antigen-experienced T cells, which could increase the risk of cardiovascular disease. In those with lymphocytosis, dysregulated expansion of memory T cells, whether driven by indolent viral infections (eg, cytomegalovirus) or other mechanisms, may induce a proinflammatory milieu and similarly elevate the risk of incident cardiovascular disease.

Lymphopenia may also reflect adverse inflammatory, metabolic, or neuroendocrine stressors and thus be associated with survival as an epiphenomenon. The administration of tumor necrosis factor, interleukin 1β, or microbial products reduces levels of circulating T cells. Excess levels of cortisol and catecholamine also cause lymphopenia. In these disease and models systems, lymphopenia was caused by redistribution of T cells from the circulation to lymphoid tissues and an increased susceptibility of T cells to apoptosis. Thus, additional study is needed to characterize the immune, metabolic, and neuroendocrine profiles in those with dysregulated T-cell homeostasis and to explore the lines of causation and effect that may contribute to resilience and longevity in the primary prevention setting.

Link: https://doi.org/10.1001/jamanetworkopen.2019.16526

Tryptophan Metabolism and Inflammaging

Today's open access research on tryptophan and its role in age-related immune dysfunction is particularly interesting in the context of ongoing research into the changes that take place in gut microbiota with age. Other recent work has examined the way in which tryptophan production by gut microbes declines precipitously with age, as this is one of a number of compounds produced by bacteria, such as butyrate, indole, and proprionate, that are influential on long term health. It is a slow process, but researchers are uncovering the specific mechanisms linking age-related changes in gut microbe populations with declining health. The overall size of effect of gut microbes on heath might be in the same ballpark as that of exercise, but this is only suggested by the evidence to date, not rigorously established.

Given detrimental changes in gut microbes, declining production of beneficial compounds, and a rise in chronic inflammation due to a rise in the presence of harmful microbes, what might be done about all of this? One possibility is supplementation with the various identified compounds, not all of which can make it past the stomach without some form of protection. Some have been tested, with varying results. Another is fecal microbiota transplant, which has produced some quite eye-opening results on life span and measures of health in short-lived species such as killifish. As a treatment for severe conditions in which pathological microbes have taken hold in a patient's intestine, this approach to therapy has done quite well to date. It has not yet been assessed as a way to restore - even temporarily - a more youthful set of gut microbes in older people, however, as the animal evidence suggests it might.

Tryptophan Metabolism in Inflammaging: From Biomarker to Therapeutic Target

Age-related changes of the innate immune system are common and include shifts in the composition of immune cell populations, paralleled by the development of a chronic inflammatory state referred to as inflammaging. This is characterized by an imbalance between pro- and anti-inflammatory responses and fluctuations of inflammatory cytokines. The rate of inflammaging, quantified by measuring these markers, is strongly associated with age-related disability, disease, and mortality. It is theorized that inflammaging is driven by endogenous ligands released upon age-related tissue damage and can be aggravated by food excess and attenuated by caloric restriction, suggesting relevant cross-talk between metabolic and immune functioning.

Understanding how inflammaging is controlled could aid in the development of diagnostic and therapeutic tools for many age-related diseases associated with inflammation. Tryptophan (Trp) metabolism is associated with aging and produces metabolites that control inflammation, regulate energy homeostasis, and modulate behavior. The essential amino acid Trp fuels the synthesis of kynurenine (Kyn), serotonin (5-HT) and indoles. The Kyn pathway of Trp is the most active pathway of Trp metabolism and produces metabolites including kynurenic acid and nicotinamide adenine dinucleotide (NAD+). While indoleamine 2,3-dioxygenase (IDO) plays a minor role in Trp metabolism under normal circumstances, IDO-dependent Trp metabolism is strongly activated in response to interferons and other cytokines that are released upon inflammation. Inflammation-related IDO activity is often measured by the Kyn/Trp ratio in blood in diseases characterized by excessive or chronic inflammation including infections, autoimmune disorders, cardiovascular disease, and cancer.

Trp metabolism controls hyperinflammation and induces long term immune tolerance. These effects pivot on the ability of IDO to alter the local and systemic Kyn/Trp balance. This balance directly affects metabolic and immune signaling pathways that drive an anti-inflammatory response. The Kyn/Trp ratio, measured in blood, is robustly associated with aging in humans. The fact that this association is already evident in healthy young adults, and persists throughout life, implies that the age-dependent increase in the Kyn/Trp ratio is not secondary to the onset of disease but rather represents a physiological age-related change. Taken together, these observational data suggests that the Kyn/Trp ratio could provide a valuable marker for the rate of (physiological) inflammaging. As inflammaging is involved in the onset of age-related diseases, a marker for inflammaging should also predict the onset of age-related diseases. This is the case for the Kyn/Trp ratio.

Age-related changes to the microbiome were associated with increased expression of enzymes involved in microbial Trp metabolism. This highlights the importance of microbiota-dependent Trp metabolism and suggest that activation of intestinal IDO and age-related changes in microbiome composition can deplete the body of health-promoting indoles while affecting the systemic Kyn/Trp balance. In addition, it provides relevant evidence that links metabolic inflammation to gastrointestinal Trp metabolism and metabolic health.

Reviewing the DNA Damage Response in Aging

Nuclear DNA damage is considered a contributing cause of aging, though at this stage the research community is still proposing and debating processes by which this damage might cause metabolic dysfunction throughout the body. Mutations to nuclear DNA evidently increase cancer risk, but setting this aside, how does random damage to random cells contribute to the declines of age?

There are a few possibilities; firstly that the vast majority of nuclear DNA damage, occurring as it does in somatic cells, or in unusued portions of the genome, is irrelevant. Harms are done when mutations affecting function occur in stem cells and progenitor cells, allowing that mutation to spread widely throughout a tissue. The second possibility, more recently proposed, is that all nuclear DNA damage systemically affects cell function wherever it occurs in the genome, because the processes of DNA repair have the side-effect of causing epigenetic changes characteristic of aging. Thirdly, higher levels of mutational damage may generate a greater burden of cellular senescence. Relative effect sizes of these processes are an open question, and much more work must be done to confirm that they are relevant in each case.

One important aspect of the ageing process is the accumulation of DNA damage through time. While containing the entire genetic information (except for mitochondria-encoded genes), the nuclear genome is constantly threatened by genotoxic insults, with an estimated frequency of the order of tens of thousands per day. These hazards can arise from exogenous or endogenous sources. Exogenous sources are, to some extent, avoidable; these include ultraviolet (UV) and ionizing radiation and a variety of genotoxic chemicals. Endogenous sources, on the other hand, are unavoidable as they include metabolic by-products, such as reactive oxygen species (ROS), and spontaneous chemical reactions that target DNA molecules (including alkylation and hydrolysis of DNA chemical bonds). The lesion type inflicted on the DNA greatly depends on the source of the damage. Lesions caused by endogenous sources tend to arise stochastically at a higher rate.

DNA damage can have distinctive consequences for cells. Persistent nucleotide substitutions, due to erroneous repair followed by misreplication, lead to the accumulation of permanent mutations and chromosomal aberrations, which increase the risk of cancer development. By contrast, bulky types of DNA lesions can block transcription and replication, triggering the arrest of the normal cell cycle, ultimately leading to cell senescence or cell death, both states preventing the cell from transforming into tumour cells but ultimately contributing to ageing. Nuclear DNA requires constant maintenance to be kept intact and error-free in order to avoid the aforementioned consequences. For this, cells evolved intricate, evolutionarily highly conserved machineries mediating cellular responses to DNA damage-termed the DNA damage response (DDR). These highly complex systems include not only several repair pathways specific for different types of lesion but also distinct signalling cascades of damage sensors, signal boosters and effectors responsible for deciding the cell's fate.

This system has two immediate goals: (i) arrest the cell cycle to prevent the propagation of corrupted genetic information, while providing time to repair the damage, and (ii) actually coordinate the repair of the DNA lesion. Depending on the success of these previous steps, the cell's fate is then decided: after lesions are successfully repaired, the DDR signalling ceases, cells survive and return to their original state; however, impossible to repair lesions trigger a persistent DDR signalling which can then engender cellular senescence or apoptosis. Given the harmful consequences of irreparable DNA damage, it is not surprising that defects in DNA repair pathways are associated with severe human pathological conditions.

Research over past decades has elucidated the role of genomic instability as a root cause of ageing. The observed age-dependent accumulation of somatic mutations in the genome and the accelerated ageing phenotypes caused by deficiencies in DNA repair systems provide compelling evidence supporting an active role for intrinsic DNA damage in mediating loss of tissue functionality with ageing. Still, the broad range of phenotypic variability within ageing populations strongly suggests that complex signalling pathways might coordinate specific systemic responses to DNA damage. These systemic responses have become increasingly apparent in multiple species and appear to have a major role not only during the physiological ageing process but also in response to acute stress. Importantly, these responses represent perfect examples of the intricate connection between DNA damage and other hallmarks of ageing, such as cellular senescence, stem cell exhaustion, and altered intercellular communication, which can all occur as a consequence of the DDR. Nevertheless, the interplay between cell-autonomous and these non-cell-autonomous responses is still somewhat poorly understood.

Link: https://doi.org/10.1098/rsob.190168

Evidence for Exercise to Slow Cognitive Decline

A sizable body of evidence, both mechanistic and epidemiological, supports the idea that exercise slows age-related cognitive decline. The report here is an example of the type, noting the results of a study in which some of the participants were assigned to an exercise program. The exercising participants exhibited a slower decline in cognitive function, particularly memory, in comparison to the others. This is a representative result: in general, the consensus in the scientific literature is that regular exercise is beneficial to cognitive function over the long term.

Researchers theorized that the healthy lifestyle behaviors that slow the development of heart disease could reduce heart disease risk and also slow cognitive decline in older adults with cognitive impairment without dementia (CIND). These behaviors include regular exercise and a heart-healthy diet, such as the DASH (Dietary Approaches to Stop Hypertension) diet. Researchers designed a study titled Exercise and Nutritional Interventions for Cognitive and Cardiovascular Health Enhancement (or ENLIGHTEN for short). The goal of the study was to examine the effects of aerobic exercise and the DASH diet on cognitive functioning in older adults with CIND.

The ENLIGHTEN study examined 160 adults 55-years-old or older. The study participants were older adults who didn't exercise and had memory problems, difficulty thinking, and making decisions. They also had at least one additional risk factor for heart disease, such as high blood pressure (also known as hypertension), high cholesterol, diabetes, or other chronic conditions. Participants were randomly assigned to one of four groups: a group doing aerobic exercise alone, a group following the DASH diet alone, a group doing aerobic exercise and following the DASH diet combined, or a group receiving standard health education.

People in the exercise group did 35 minutes of moderate intensity aerobic exercise (including walking or stationary biking) three times per week for six months. They were supervised for three months and then exercised unsupervised at home for three months. Participants in the exercise group did not receive any counseling in the DASH diet and were encouraged to follow their usual diets for six months. The results of the research team's study showed that exercise improved the participants' ability to think, remember, and make decisions compared to non-exercisers, and that combining exercise with the DASH diet improved the ability to think, remember, and make decisions, compared to people who didn't exercise or follow the diet - even though they didn't perfectly follow the programs they were assigned to during the six-month interventions.

Link: https://www.healthinaging.org/blog/aerobic-exercise-and-heart-healthy-diet-may-slow-development-of-memory-problems/

Mesodermal Progenitor Cells Enable the Generation of Vascularized Organoids

Researchers have made considerable progress in the construction of small, functional tissue sections called organoids over the past decade, enabled by a combination of better understanding the mechanisms involved in regeneration and embryonic development of tissues, advances in 3-D bioprinting, guidance of cell behavior via appropriate provision of signal molecules, and the generation of environments that mimic an existing tissue environment. Every tissue requires its own specific recipe of signals and environment in order to form a functional organoid, but researchers have demonstrated the manufacture of organoids for liver, kidney, lung, and thymus, among others.

Organoids are tiny, usually a millimeter or two in size. They are a stepping stone to the generation of patient matched replacement organs on demand, given a cell sample as a starting point. Ever since the first organoids were generated, however, the blocking challenge to scaling up engineered tissue in size has been the inability to generate organoids that incorporate functional blood vessel networks. In cross-sections of natural tissues, several hundred capillaries pass through every square millimeter. Absent this microvasculature, blood (and thus the necessary oxygen and nutrients for cell survival) cannot perfuse through more than a few millimeters into tissues.

Producing vasculature in engineered tissues has proven to be challenging. That it is so challenging is why considerable effort has gone towards establishing decellularization of donor organs and xenotransplantation of genetically engineered pig organs as a basis for expanding the pool of organs available for transplantation. Of late some progress has been made on methods of 3-D printing organoids that contain an initial vasculature that is dense enough to sustain the tissue, albeit short of the natural capillary density. Today's open access paper describes an example of the opposite approach, which is to find a suitable combination of cells, signals, and environment that causes a microvasculature to form within the organoid as it grows.

Generation of complex human organoid models including vascular networks by incorporation of mesodermal progenitor cells

Organoids derived from human induced pluripotent stem cells (hiPSCs) are state of the art cell culture models to study mechanisms of development and disease. The establishment of different tissue models such as intestinal, liver, cerebral, kidney, and lung organoids was published within the last years. These organoids recapitulate the development of epithelial structures in a fascinating manner. However, they remain incomplete as vasculature, stromal components, and tissue resident immune cells are mostly lacking. All these cell types derive from mesenchymal tissue and it is well known that epithelial-mesenchymal interactions play a fundamental role during tissue development.

Recent publications addressed this issue, especially with regard to organoid vascularization. Researchers demonstrated that human blood vessels self-organize and can be grown in vitro. In order to vascularize cerebral organoids, others added endothelial cells to the system. But blood vessels are more complex than an endothelial tube. Larger vessels consist of multiple layers that contain cell types such as endothelial and smooth muscle cells, while even small capillaries rely on the support of pericytes and a basal lamina. Other groups generated vascularized neural organoids consisting of blood vessels and microglia. However, in these cases, the heterologous vessels as well as microglia are host derived and invade the neural organoid after transplantation.

We propose that the directed incorporation of mesodermal progenitor cells (MPCs) into organoids will overcome the aforementioned limitations. In order to demonstrate the feasibility of the method, we generated complex human tumor as well as neural organoids. We show that the formed blood vessels display a hierarchic organization and mural cells are assembled into the vessel wall. Moreover, we demonstrate a typical blood vessel ultrastructure including endothelial cell-cell junctions, a basement membrane as well as luminal caveolae and microvesicles. We observe a high plasticity in the endothelial network, which expands, while the organoids grow and is responsive to anti-angiogenic compounds and pro-angiogenic conditions such as hypoxia. We show that vessels within tumor organoids connect to host vessels following transplantation.

The Latest on Cellular Senescence in Type 2 Diabetes

One of the more unexpected recent findings relating to cellular senescence is that it appears to be an important part of the mechanisms that lead to loss of the pancreatic β-cells responsible for insulin secretion in both type 1 diabetes and type 2 diabetes - which are very different conditions, despite the shared name. The authors of the brief open access commentary noted here discuss the present state of this research.

Age is one of the major risk factors for the development of type 2 diabetes mellitus (T2D). However, the understanding of how cellular aging contributes to diabetes pathogenesis is incomplete and as a result, current therapies do not target this aspect of the disease. In recent work we showed that insulin resistance induced the expression of aging markers, suggesting that β-cell aging could accelerate the progression toward diabetes. Therefore, reversing the hallmarks of cellular aging presents a potential avenue for novel T2D therapies; in particular, transcriptomic analysis of aged β-cells pointed us toward cellular senescence as a promising target.

Senescent cells enter a state of long-term growth inhibition and replicative arrest after exposure to environmental insults, including genomic damage, oncogene activation, and reactive oxygen species. The resulting changes in gene expression impair cell function and proliferation while modifying intercellular signaling through the senescence-associated secretory phenotype (SASP). The potential paracrine effects of senescent β-cells highlight the importance of the β-cell SASP in driving metabolic dysfunction.

Along these lines, we demonstrated that senescent β-cells downregulated hallmark identity genes, upregulated disallowed genes, and secreted proinflammatory cytokines. We established two models of insulin resistance in mice: one using the delivery of the insulin receptor antagonist S961, and the other using a more physiologically representative high fat diet. In both cases, the metabolic stress increased the number of senescent β-cells while impairing glucose tolerance. Aging and SASP genes were also upregulated, but after insulin resistance was stopped, gene expression returned to healthy levels. This suggests that there might be critical windows during which β-cell senescence may be reversible. These results were consistent with experiments on human β-cells, in which senescence increased with age, body mass index, and in the presence of T2D.

Additionally, we found that the targeted deletion of senescent cells, or senolysis, in mice improved β-cell function, reduced blood glucose levels, and restored healthy expression levels of aging and SASP genes. Our findings highlight the transformative therapeutic potential of senolytic drugs in restoring β-cell function among T2D patients. The partial reversibility of β-cell senescence suggests that, consistent with recent publications, this is a non-binary phenomenon. External insults may create subpopulations of aged β-cells activating distinct levels of the senescence-associated regulatory progression.

The progression of damaged β-cells through this regulatory cascade likely accelerates T2D; eventually, the accumulation of senescent β-cells may cross a threshold inducing long-term metabolic dysfunction through the permanent loss of β-cell mass and function. The deletion of senescent β-cells or the reversal of senescence in a targeted subpopulation of aged β-cells may inhibit this cascade of dysfunction. To advance these therapeutic strategies, it is imperative to characterize the distinct subpopulations of senescent β-cells and the temporal expression patterns of senescence genes.

Link: https://doi.org/10.18632/aging.102502

On Making Philanthropy in Support of Rejuvenation Research Attractive to Investors

In this interview, Aubrey de Grey of the SENS Research Foundation talks about how the foundation has sought to make philanthropy in support of the development of rejuvenation therapies an attractive prospect for high net worth investors, people who are usually much more interested in deploying capital into for-profit programs. Since the goal of the SENS community is to move projects from the lab to clinical development, particularly those promising projects in rejuvenation research that have previously lacked funding and moved more slowly than we'd all like, it should be quite compatible with the goals of investors. It makes sense to offer philanthropic support to programs that will later lead to startup biotech companies that are looking for investment.

How did Project 21 come into being?

The name Project 21 was always a bit of a misnomer. It wasn't really a project in any real sense, it was really just an umbrella name that we gave to our fundraising efforts, especially for high net worth donors. Basically, we had come to the conclusion that a very clear majority of the people who were giving us money or making positive noises about doing so tended to be investor types and were more inclined to give money to a benefactor than to charities. So the goal was to try to persuade people who were psychologically investors first and donors second to nevertheless support us. We felt that one thing that we had not emphasised sufficiently over the previous years, was the timeframe proximity of clinical trials - hence the focus on 2021.

How has Project 21 evolved since 2016?

Some of the more significant developments that have occurred are in terms of our business model. In 2016, we had barely started thinking in terms of spinning projects out as start-up companies. But it was in 2016 that Michael Greve came along - a German entrepreneur who made money in the early days of the web. He started giving us a million dollars a year, but he also started investing a million dollars a year in companies that were very much in our space, and was specifically interested in companies coming from our own projects. And that has worked out beautifully - he has now done that for a number of companies as well as a number of companies that are not spinouts from us, but are closely aligned with us.

And he's not been the only one, so now it's accurate to say that our business model is to work on important projects in this rejuvenation space for as long as it takes to get them to a point of sufficient proof of concept that an investor decides they can join the dots. As long as they can see the path from where we are to eventual revenue, and are therefore willing to back an actual for-profit entity. We've done this six or seven times now. But SENS Research Foundation is still a charity - we haven't shut up shop and declared victory yet. And that's because there are still some equally vital projects that have not reached an investable stage, so Project 21 is alive and kicking.

SENS Research Foundation is a charity - so how does the non-profit aspect connect with investors?

There is a big link. I always say to investors that if you're thinking about writing proper sized checks to start-up companies in the space, and you're happy with the really early stage of all of this - high risk, high reward - then you should also want to be donating to the foundation. What you will get for that is as much of my time as you want, which means that you will be in the position of having access to the information that will allow you to be a founding investor in the next start-up, which other people just won't have.

Back in 2015, we had one major donor, a very busy guy and seriously successful businessman, who, twice a year, would take an entire day to come visit us and get as much information as he was able to understand on everything we were doing. One day he turned around and said "Look, this project that you're funding - I think I can make money out of it." So he basically created a company, out of the blue, he took our people, gave us 10% of the company. And although that company was actually not successful, it changed our mindset completely. Since then, we have been aggressively pursuing that way of doing things, and all the other companies that we spun out have been very effective in terms of bringing in initial investment. It's definitely created a pipeline and I would say we are likely to be doing at least one a year, probably closer to two a year, for the foreseeable future.

Link: https://www.longevity.technology/project-21-well-on-track/

The Prospects for Restoring Neurogenesis in the Aging Brain

Today's open access paper is a review of potential approaches that might be used as a basis for therapies to restore a more youthful level of neurogenesis in the aging mammalian brain. Neurogenesis is the process by which new neurons are created by neural stem cell populations and then integrated into neural networks. In adults, neurogenesis is essential to memory, learning, and the limited degree of regeneration that the brain is capable of enacting. Unfortunately, the supply of new neurons declines with age as the underlying stem cells become ever less active. Beyond making the aging brain more resilient, methods of increasing neurogenesis may prove to be enhancement therapies capable of improving cognitive function even in young people.

Any discussion of adult neurogenesis must note the present debate over whether or not it in fact does take place in humans in the same way as it does in mice. It was only in the 1990s that neurogenesis was discovered to take place in some portions of the adult mouse brain, and since then near all work on neurogenesis in general, as well on changes in neurogenesis with age, has focused on mice, given the costs and difficulties inherent in studying human brains and brain tissue. This became a growing concern, careful human studies were undertaken, and in the past few years rigorous evidence has been presented on both sides of the question of adult human neurogenesis, both ruling it out, and demonstrating that it does take place. Considerable debate has taken place over the technical details of these studies and the underlying processes of neurogenesis. Insofar as there is a present weight of evidence, it appears to lean towards the conclusion that humans do in fact exhibit adult neurogenesis.

Rejuvenating subventricular zone neurogenesis in the aging brain

Adult neurogenesis is the generation of new neurons from neural stem cells (NSCs). NSCs are known for their hallmark characteristics of long-term self-renewal and differentiation into neurons and glia. While many noncanonical sites of neurogenesis have been observed in the mammalian brain, the two main stem cell niches studied are the subventricular zone (SVZ) located along the walls of the lateral ventricles (LV) and subgranular zone (SGZ) in the hippocampus. The largest pool of NSCs in rodents lies in the SVZ, where the majority of NSCs are quiescent (qNSCs). These qNSCs undergo activation (aNSC) and proliferate to produce transit amplifying cells (TACs). TACs rapidly proliferate and then differentiate into neuroblasts that migrate in chains along the rostral migratory stream (RMS) to the olfactory bulb (OB) and become synaptically integrated into the existing circuitry.

Neurogenesis in the SVZ results in the functional integration of neurons in the OB. This has been shown to be important in olfactory behavior such as memory and scent/pheromone discrimination. In addition, brain injury, in the form of ischemic stroke, induces NSC proliferation and production of neuroblasts (NBs). These NBs migrate to the site of injury to differentiate into astrocytes and neurons that synaptically integrate into the peri-infarct cortex. Blockade of neuroblast migration results in increased lesion size and worsened behavioral outcomes as SVZ-derived neurons with synaptic function are critical to stroke recovery. Additionally, post-stroke neurogenesis is plastic and can be increased and directed by overuse behavior that mimics current human neurorehabilitation therapies. During aging, neurogenesis is reduced, which contributes to declines in olfactory memory and repair.

Multiple strategies to rejuvenate neurogenesis have come from experiments utilizing blood/plasma exchange between young and aged rodents. Landmark studies utilizing heterochronic parabiosis, where a young and aged mouse are connected surgically to share circulation, showed that young circulating factors can rejuvenate neurogenesis in aged mice vice versa with old circulating factors young mice. The field has since made further progress by identification of circulating rejuvenation factors of NSCs in the SVZ and hippocampus that include GDF11 and TIMP2, as well as the pro-aging factors CCL11, β2-microglobulin, TGF-β, and recently VCAM1.

The dietary interventions caloric restriction (CR) (10-40% reduction in caloric intake) and the fasting mimicking diet (FMD) (50-90% reduction in caloric intake for 4 days twice a month) are perhaps the most robust, pleiotropic, and conserved methods of longevity extension and rejuvenation. In a mouse model of caloric restriction starting at 14-weeks of age, the number of NB and new neurons in the OB were preserved in the aged (12-months to 18-months) and comparable to levels of ad libitum fed young (six-month) mice. This preservation of neurogenesis resulted in olfactory memory in aged mice that was similar to young (six-month) mice.

The two top drugs that have emerged from CR research are rapamycin and metformin, which act primarily through inhibition of the mTOR and activation of the AMPK (downstream inhibition of mTOR) pathways. However, other studies suggest that mTOR signaling is a mediator of TAC proliferation since rapamycin treatment decreases the number of TACs in two-month old mice and mTOR activation decreases with age, concomitant with proliferation. Metformin has been shown to enhance proliferation in the young (three-month) SVZ, but despite interest in using metformin to ameliorate aging phenotypes, research with this drug in the aging SVZ is lacking.

Multiple lines of evidence now point towards an increased age-dependent inflammatory environment within the SVZ. A major source of this inflammation originates from aged microglia and should be a central target for inflammation reduction in future studies. Having identified the neurogenic-inhibiting contribution of aged microglia to NSC proliferation, researchers fed 8-month old mice the anti-inflammatory drug HCT1026. This treatment restored redox/inflammatory balance to the niche, and substantially increased neurogenesis. Increase in senescent cell burden in the aging SVZ has been found in 12-18 month old mice. Avoidance of the senescence program was achieved with p16INK41-/- mice aged to 15-19 months that partially rescued OB neurogenesis. A recent study showed that obesity is associated with increased senescence and reduced neuroblasts in the SVZ of middle-aged (10-13 months) mice and clearance of senescent cells partially rescued the number of neural precursors. Thus, removal of senescent cells in elderly mice, especially using treatments such as Dasatinib + Quercetin that have been used in clinical trials, appear to be favorable routes to rejuvenate neurogenesis but are in need of further study in aged animals to determine long term effects.

The studies gathered here present compelling evidence that aging of the SVZ niche is not a one-way street. Instead, the aging process is not only delayable through early interventions such as CR, but is also reversible by way of systemic interventions started late in life. The possibility of rejuvenation not only sheds light on the mechanisms of NSC aging, but is also an appealing therapeutic avenue for the rapidly increasing elderly human population.

Discovering New Mechanisms of Action for Metformin

Metformin is a terrible approach to slowing aging in comparison to, say, mTOR inhibition. Slowing aging in this way, by manipulating the operation of an aged cellular metabolism without repairing the underlying damage that causes aging, is in turn a terrible approach to the treatment of aging. Yet metformin attracts a great deal of interest. I believe that most people simply don't care about effect size and reliability. Most popular science materials don't discuss these points, thus putting every intervention on the same footing in the minds of much of the public. Yet effect size and reliability are the very heart of the matter.

The animal data on metformin shows it to be unreliable when it comes to effects on life span; results from different studies and different groups are quite varied. The one large human study to examine mortality and life span looked at people with type 2 diabetes, not healthy individuals. It is known that metformin disrupts the operation of mechanisms needed for benefits to health to arise from regular exercise - a significant issue. Lastly, even if taking the human data at face value, the effect size is really just not large enough to care about. Nothing in the research noted here changes any of this.

Previously, the only biochemical pathway that was known to be activated by metformin was the AMPK pathway, which researchers discovered stalls cell growth and changes metabolism when nutrients are scarce, as can occur in cancer. But the scientists believed more pathways than AMPK might be involved. The scientists developed a novel screening platform to examine kinases, the proteins that transfer phosphate groups, which are critical on/off switches in cells and can be rapidly flipped by metformin. Using this technology, the researchers were able to decode hundreds of regulatory "switch-flipping" events that could affect healthy aging.

The results revealed that metformin turns on unexpected kinases and pathways, many independent of AMPK. Two of the activated kinases are called Protein Kinase D and MAPKAPK2. These kinases are poorly understood, but are known to have some relation to cellular stress, which could connect them to the health-span- and life-span-extending effects observed in other studies. In fact, metformin is currently being tested in multiple large-scale clinical trials as a health-span- and life-span-extending drug, but the mechanism for how metformin could affect health and aging has not been clear. The current study indicates that Protein Kinase D and MAPKAPK2 may be two players in providing these therapeutic effects, and identifies new targets and cellular processes regulated by AMPK that may also be critical to metformin's beneficial effects.

"The results broaden our understanding of how metformin induces a mild stress that triggers sensors to restore metabolic balance, explaining some of the benefits previously reported such as extended healthy aging in model organisms taking metformin. The big questions now are what targets of metformin can benefit the health of all individuals, not just type 2 diabetics."

Link: https://www.salk.edu/news-release/diabetes-drug-has-unexpected-broad-implications-for-healthy-aging/

A Demonstration of Small Molecule Inhibition of Tau Aggregation

Researchers here demonstrate a small molecule approach to the inhibition of tau aggregation in neurodegenerative conditions. The tau protein is one of the few in the human body that can become altered in a way that leads to the aggregation of ever more molecules of the protein into solid deposits. These aggregates and their surrounding halo of harmful biochemistry cause cell dysfunction and cell death. Once the aggregation process starts, it spreads from cell to cell like an infection. This form of pathology is characteristic of a number of neurodegenerative conditions, designated as tauopathies, including the late stage of Alzheimer's disease.

Tau oligomers have been shown to transmit tau pathology from diseased neurons to healthy neurons through seeding, tau misfolding, and aggregation that is thought to play an influential role in the progression of Alzheimer's disease (AD) and related tauopathies. To develop a small molecule therapeutic for AD and related tauopathies, we have developed in vitro and cellular assays to select molecules inhibiting the first step in tau aggregation, the self-association of tau into oligomers.

In vivo validation studies of an optimized lead compound were independently performed in the htau mouse model of tauopathy that expresses the human isoforms of tau without inherited tauopathy mutations that are irrelevant to AD. Treated mice did not show any adverse events related to the compound. The lead compound significantly reduced the level of self-associated tau and total and phosphorylated insoluble tau aggregates. The dose response was linear with respect to levels of compound in the brain.

A confirmatory study was performed with male htau mice that gave consistent results. The results validated our screening approach by showing that targeting tau self-association can inhibit the entire tau aggregation pathway by using the selected and optimized lead compound whose activity translated from in vitro and cellular assays to an in vivo model of tau aggregation.

Link: https://doi.org/10.3233/JAD-190465

This Giving Tuesday, Support Rejuvenation Research at the SENS Research Foundation

It is Giving Tuesday today, a prompt for each of to think about the change that we would like to see happen in the world, and then do our parts in making it happen. We can all be philanthropists, we can all support the projects that we believe will improve the human condition. In the sciences, it is largely exactly this sort of motivated philanthropy that funds the most important progress, that which takes place at the cutting edge of research. Public funding for research is near always only awarded after the discovery is made, after the proof of principle is demonstrated. Commercial funding tends to arrive later still. The vital work of generating that proof of principle is, in practice, funded through donations made to researchers and research institutions.

A good example is the progress towards real, working rejuvenation therapies, those based on the SENS model of periodic repair of cell and tissue damage, that has been generated by the SENS Research Foundation and Methuselah Foundation before it. These projects have been near entirely funded by our community over the years, and have led to multiple lines of work making the leap from laboratory to startup company. These are our success stories: we all helped to make this happen by choosing to donate in support of the SENS rejuvenation research projects. We have made a start, but there are still important projects to assist.

The SENS Research Foundation year end fundraiser is running, and this Giving Tuesday give some thought to supporting the work of the foundation on bringing rejuvenation therapies to the clinic. What sort of future do you want to see? One in which we are ever less troubled by the suffering and disease of aging? Then donate to the SENS Research Foundation; it remains the most effective organization in this field when it comes to making progress in the fundamental research of human rejuvenation, advancing the most promising programs from laboratory to clinical development.

Giving Tuesday is a global generosity movement, giving power to individuals for the transformation of their communities and to create a global impact. The idea is simple: do good. Started in 2012, this idea has inspired millions of people to give, collaborate, and celebrate generosity. This year, maximize the good your gift can do by donating to SENS Research Foundation.

For this year's #GivingTuesday event on December 3rd, 2019, we're delighted to announce matching challenges from long-term supporters Christophe Cornuejols and David Chambers. Christophe will match the first $20,000 donated at any time on Giving Tuesday, and David will match the first $10,000. Thanks to their combined generosity, the first $10,000 given will be tripled, and the second $10,000 will be doubled!

Chrisophe said that "it is my strong belief that we are the first generation in history which has the capability to decide to be the last generation to die of aging or be the first not to. The evolution of science and technology gives us that choice. Either we invest in research in this area now, and gain 20, 30, 200 years of healthy life, or we leave it to a future generation. It's just up to us to decide."

David notes that "I've known Aubrey for fifteen years, and witnessed him over that time energise a new field of scientific endeavour. I'm convinced that donations to SRF will realise great improvements in human wellbeing."

Fibrosis as an Important Contributing Cause of Atrial Fibrillation

Researchers here argue that fibrosis of cardiac tissue is an important contribution to the development of atrial fibrillation in older patients. Fibrosis is a feature of many age-related conditions, a dysfunction in tissue maintenance processes that involves the generation of scar-like deposits of collagen by overactive fibroblasts. This scarring disrupts normal tissue structure and function in many organs, including the heart, and there is no good approved therapy to treat the progression of fibrosis: even slowing it is haphazard and unreliable.

This may soon change. Fibrosis appears to be caused to a large degree by the accumulation of lingering senescent cells. These errant cells are highly disruptive to tissue maintenance through inflammatory and other types of signaling. The development of senolytic therapies to selectively destroy senescent cells is well underway, and has been shown to reverse fibrosis in animal models. Some of the first human trials, using a combination of the generic drug dasatinib and supplement quercetin, are focused on fibrotic diseases such as idiopathic pulmonary fibrosis. Given continued success, this senolytic therapy should certainly be trialed as a means to treat fibrosis in other organs.

Atrial fibrillation (AF), the most common cardiac arrhythmia, is associated with high morbidity and mortality. It is well known that both the prevalence and incidence of AF increase sharply with age, particularly after 65 years of age. AF and aging share mutual bidirectional relationships. On the one hand, aging and aging-related underlying diseases result in myocardial remodeling that may lead to cardiac electrical abnormalities which enhance the occurrence or persistence of AF. On the other hand, AF worsens biological aging, specifically at the brain level, causing injuries related to ischemic and non-ischemic events, thereby impairing functional capacity. In addition, handling of AF is challenging in aged patients due to the high prevalence of complex clinical features (i.e. heart failure [HF] and chronic kidney disease) and the progressive AF-mediated aggravation of degenerative processes typical of aging. All these aspects have profound effects on the patient health condition and on the resources provided by the society and national health systems to dedicate to the care of elderly patients.

Even though it is well known that age is the single most important determinant of AF risk, the underlying mechanisms are not completely understood. Some of the mechanisms involved in the aging-AF association may be related with age-dependent left atrial dilation or senile amyloidosis that alter the structure of the myocardial tissue and constitute typical features of the so-called AF substrate. In addition, resting membrane potential depolarization and spontaneous calcium releases from the sarcoplasmic reticulum, among others, might promote afterdepolarization and trigger AF. Since fibrosis is a prominent lesion present in the atria of AF patients and atrial fibrosis can both affect the substrate and induce the trigger, this lesion emerges as a factor that may play a central role in aging-related AF. In particular, by increasing the severity of atrial fibrosis, age may contribute to the development of electrical conduction disturbances and ectopic activity, affecting atrial arrthythmogenity.

Link: https://doi.org/10.18632/aging.102501

IL-15 as an Exercise Mimetic that Improves Wound Healing in Old Mice

Researchers here demonstrate that providing the cytokine IL-15 to older mice improves wound healing. The surrounding context suggests that this is a part of the stress response systems that link exercise to health benefits, acting through at least mitochondrial function, and no doubt other pathways as well. Since the mitochondria in cells throughout the body undergo a series of detrimental changes with age, faltering in their ability to deliver energy store molecules to power cellular processes, most methods of intervening in this decline might be expected to produce some degree of benefit. This is the case even when, as here, the intervention is essentially compensatory, addressing only a proximate cause rather than the underlying accumulation of damage that drives the manifestations of aging.

Impaired wound healing in elderly individuals increases infection risk and prolongs surgical recovery, but current treatment options are limited. Low doses of interleukin 15 (IL-15) that mimic exercise responses in the circulation improve skin structure and increase mitochondria in uninjured aged skin, suggesting that IL-15 is an essential mitochondrial signal for healing that is lost during aging.

Here we used gene microarray analysis of old and young murine epidermal stem cells and demonstrate that aging results in a gene signature characteristic of bioenergetic dysfunction. Intravenous IL-15 treatment rescued chronological aging-induced healing defects and restored youthful wound closure in old, sedentary mice. Additionally, exercise-mediated improvements in the healing of aged skin depend upon circulating IL-15. We show that IL-15 induces signal transducer and activator of transcription 3 (STAT3) signaling characteristic of young animals, reduces markers of growth arrest, and increases keratinocyte and fibroblast growth. Moreover, exercise or exercise-mimicking IL-15 treatment rescued the age-associated decrease in epidermal mitochondrial complex IV activity.

Overall, these results indicate that IL-15 or its analogs represent promising therapies for treating impaired wound healing in elderly patients.

Link: https://doi.org/10.1074/jbc.RA119.010740

The Catalytic Antibody Approach to Amyloid Aggregation

Today's paper is authored by the Covalent Bioscience science team, and is an overview of the science underlying their catalytic antibody (or catabody) approach to clearing amyloids of various sorts from aged tissues. It isn't open access, unfortunately, but the paper is, as usual, available to the world thanks to the ethical civil disobedience of the Sci-Hub team. Amyloids are solid deposits formed by one of the very small number of proteins in the body that can become misfolded or otherwise altered in ways that cause other molecules of the same protein to also alter in the same way. These errant proteins aggregate into structures that are surrounded by a halo of damaging biochemistry that degrades cell function or kills cells, and, once started, this aggregation can spread through tissues over time.

The Covalent Bioscience team believes that natural catalytic antibodies are the primary way by which our biochemistry tries to clear out amyloids - but evidently, amyloid generation overwhelms this mechanism as aging progresses. Catalytic antibodies act as catalysts for reactions that break down amyloids. Because one catalytic antibody can do this for many amyloid molecules, they have the potential to be a highly efficient basis for therapy. The process of development is to identify natural catalytic antibodies specific to a target amyloid, improve on their structure and function, establish ways to manufacture these improved versions at scale, and then deliver them in large numbers as a therapy.

Covalent Bioscience is a fair way into the preclinical development phase of this project for catabodies targeting transthyretin amyloid, a cause of heart disease and other conditions, and the amyloid-β associated with the early stages of Alzheimer's disease. The paper is an interesting read, and recommended if you'd like greater insight into catabodies as a novel form of therapy to remove misfolded proteins.

Catalytic Antibody (Catabody) Platform for Age-Associated Amyloid Disease: From Heisenberg's Uncertainty Principle to the Verge of Medical Interventions

Thirty seven proteins misfold into particulate and soluble aggregates. The misfolding process is accelerated by age-associated metabolic disturbances, for example, increased generation of advanced glycation end products and lipid peroxidation end products. Misfolded self-protein aggregates are a significant cause of aging, exemplified by appearance of lumbar spinal stenosis and carpal tunnel syndrome due to misfolded transthyretin in 40-50% of humans older than 50 years age and cardiac myopathy at a later age. About 15-20% of humans show at least mild cognitive impairment due to Alzheimer disease, thought to be triggered by misfolded amyloid β aggregates starting around age 65 years.

Our studies suggest that specific, constitutively produced catabodies are the primary proteostatic mediators in the blood of humans that destroy the disease-causing misfolded self-protein aggregates. In contrast, text-book portrayals of humoral immunity focus on IgG class antibodies that mature within days to weeks following stimulation with the foreign (non-self) antigens. The observed catabody properties display clear departures from classical immunology rules. Our perspective of constitutive catabodies specific for the disease-causing misfolded self-proteins is conditioned by the organismal survival requirements during Darwinian evolution. As the problem of protein misfolding is an intrinsic organismal weakness that is even more ancient than the threat of extinction due to the external microbes, eliminating amyloid disease at an early age can safely be assumed to serve as a strong selective pressure for evolving a constitutive immune defense against the misfolded proteins, i.e., the specific germline gene-encoded catabodies.

Catabodies outperformed ordinary antibodies in two significant aspects. By definition, a catalyst is re-used again and again to inactivate and destroy large quantities of the harmful target. First, we proved in side-by-side tests that a small catabody amount permanently removes the target with efficacy far superior to an ordinary antibody (which can only bind reversibly to the target on a 1:1 basis). Human IgM catabodies selectively destroyed misfolded but not normally folded transthyretin into non-aggregable fragments without potential for initiating or sustaining systemic amyloid disease. Likewise, human catabody fragments digested amyloid-β into non-toxic and non-aggregable fragments without potential for initiating or sustaining Alzheimer's disease. Second, while ordinary antibodies form stable immune complexes that inevitably induce inflammation, the catabody-substrate complexes are too transient to activate inflammatory cells. Catabodies are particularly valuable if large amounts of the target are to be removed, as is required for effectively treating amyloid diseases. In such diseases, the inflammatory damage induced by an ordinary antibody will be so great that the favorable amyloid removal effect is essentially canceled out.

Many things go wrong in human aging, and if humans live long enough something or the other invariably goes wrong. The phenomenon of constitutive catabodies is not limited to the misfolded transthyretin and amyloid-β disease-causing proteins. We identified catabodies to additional amyloid-forming proteins (misfolded tau, immunoglobulin light chains). Indeed, the value of the Catabody Platform likely extends to virtually any of the innumerable proteins that contribute directly or indirectly in disease and damage to various organ systems in aging, including the protein targets involved in increased susceptibility of humans to microbial infections and autoimmune, neurological, cardiovascular, and neoplastic disease. Specific catabodies can be generated on-demand either from the constitutive or immunogen-induced antibody repertoires.

We subscribe to the view that preventing age-associated dysfunctional processes before they have caused substantial damage is the preferred medical strategy for prolonging healthy lives. Prophylactic vaccines against infectious microbes have improved public health enormously. We suggest that lessons from our vaccine approach for microbes are valuable in developing safe and efficacious anti-amyloid longevity vaccines. The central requirements for such longevity vaccines is inducing long-lasting synthesis of catabodies with epitope specificity suitable for destroying the disease-causing misfolded self-proteins without interfering in the physiological functions of the properly folded conformations of these proteins.

Our vision is to bypass the mechanism-based limitations of ordinary antibodies and vaccines for fulfilling important unmet medical needs: (a) Intrinsic inability of ordinary antibodies to bind the target with stoichiometry greater than 1:1; (b) The inevitable activation of inflammatory pathways upon antibody-target binding that not only cause unacceptable side effects but also reduce efficacy through functional antagonism pathways, as seen in numerous failed trials of antibodies in patients with Alzheimer's disease; and (c) Failure of ordinary vaccines to induce protective immunity to certain protein epitopes because of immune check-point suppressor mechanisms.

The lead products generated from our Catabody Platform have not shown these limitations. Success in early stage human trials of any one lead catabody will make the entire underlying technology more attractive, thus encouraging development of additional catabodies and vaccines for new disease targets. For instance, transthyretin amyloid disease and Alzheimer's disease are but 2 of 56 amyloid diseases caused by misfolded proteins. Our findings suggest that destruction of misfolded proteins by catabodies extends beyond the targets described in this article. The Catabody Platform is enabled to utilize both innate immunity and immunogen-induced acquired immunity for generating catabodies to virtually any target protein.

Potentially Significant Gut Microbiome Changes Occur in Younger Adult Life

Researchers here provide evidence for detrimental changes in the composition of gut microbiota, and thus the compounds they secrete, to occur quite sharply at a threshold age as early as mid-30s. It is well known that the microbial populations of the gut change with age, and there are several identified mechanisms by which compounds secreted by beneficial gut microbes improve health over the long-term, or by which harmful gut microbes can spur chronic inflammation. It has been suggested that supplementation with some of these secreted compounds might be useful, or engineering of the microbial population to minimize harmful microbes and expand beneficial species.

Here, we have compared the proteins associated with the active fraction of the microbiota in infants, adults and elderly individuals. Ageing is associated with the progressive activation of gut bacteria, possibly because bacteria must react to increasing number of factors associated with preserving the health status in response to exposure to an increasing number of environmental conditions that are distinct and greater than the conditions experienced during early life stages. Most importantly, we identified a link between ageing and the microbial pathway associated with tryptophan and indole production and metabolism by the commensal microbiota. The key proteins involved in tryptophan-to-indole metabolism, TnaA and TrpB are both more abundant and expressed in the gut microbiota of infants. Both were expressed at significantly lower levels in adults and at even lower levels or below the detection limit in elderly individuals.

As shown in a recent study, indoles from commensal bacteria extend the healthspan of geriatric worms, flies and mice, and indoles may represent a class of therapeutics that improve the way we age, but not how long we live. The essential amino acid tryptophan, which is the least abundant in terms of its use in proteins, is provided by the diet or produced by gut bacteria, can cross the blood-brain barrier under the influence of the gut microbiota and is a biosynthetic precursor for a large number of complex microbial natural products. Recent in vitro studies have indicated the decreased production, transport, and catabolism of tryptophan in patients with a number of disorders.

Researchers have postulated that a chronological age threshold at which the composition of the microbiota suddenly changes does not exist, and changes occur gradually with time. However, compared with previous investigations, our study suggests a threshold or age at which the microbiota-based metabolism of tryptophan and indole begin to be significantly reduced, which may have health-related consequences on ageing if not treated accordingly. Indeed, based on our results, from the age of 11 years, the human gut microbiota may exhibit a decreased capacity to produce these metabolites, and from the age of 34 years, this capacity may be reduced by more than 90% compared to childhood. The results of this study reinforce the hypothesis that dietary supplementation with indole and tryptophan exert a beneficial effect on elderly individuals because their gut bacteria exhibit an impaired capacity to produce these molecules required for extending the healthspan. This supplement can be administered beginning at the age of 11 years, at which time a 50% decrease in the production of these metabolites occurs, and particularly beginning at the age of 34 years, when a greater than 90% reduction occurs

Link: https://doi.org/10.1111/acel.13063

More Aggressive Control of Blood Pressure Modestly Extends Life in Older People

Hypertension, the widespreak age-related increase in blood pressure, is very damaging. It is one of the major ways in which low-level biochemical damage, leading to stiffening of blood vessels and consequent disruption of the feedback mechanisms that determine blood pressure, gives rise to structural tissue damage throughout the body. Hypertension harms delicate tissues in the brain, kidneys, and elsewhere. Hypertension also speeds the development of atherosclerosis, the formation of fatty lesions in blood vessel walls, and makes it more likely that blood vessels weakened by plaques will rupture, leading to a heart attack or stroke. These and other mechanisms are why control of blood pressure, without controlling the underlying causes of hypertension, has a measurable effect on life expectancy.

Globally, an estimated 1.13 billion people have high blood pressure, or hypertension, which causes about 13% of all deaths, according to the World Health Organization. Almost 1,000 people in the U.S. die each day with high blood pressure as a primary or contributing cause, according to data from the Centers for Disease Control and Prevention. The research into hypertension care and life span found that with more intensive blood pressure control, focused on a target systolic blood pressure of less than 120 mmHg, a 50-year-old could expect to live almost three years longer. In order to achieve the lower blood pressure target, patients adopted healthy lifestyle habits and took blood pressure medications as prescribed.

At age 65, intensive treatment could extend life by more than a year, the research estimated. With intensive treatment, an 80-year-old would be expected to add almost 10 months to his or her life span. The new study builds on the 2015 findings of the landmark Systolic Blood Pressure Intervention Trial, or SPRINT, which tested the value of treating blood pressure intensively to reduce systolic readings to a lower target - below 120 mm Hg, instead of the routinely used target of below 140 mmHg. SPRINT, which followed patients for up to six years, found that the intensive approach reduced patients' risk of cardiovascular events by 25%. These events included heart attack, stroke, heart failure and cardiovascular-related death.

In this analysis, SPRINT data was evaluated to project the full life spans for patients treated intensively to meet the lower blood pressure target of 120 mmHg and for those who received standard care (systolic blood pressure target of less than 140 mmHg). Across age groups, intensive treatment for high blood pressure lengthened patients' remaining life span by 4% to 9%, compared with standard care, the study found.

Link: https://newsroom.heart.org/news/studies-explore-potential-benefits-and-costs-of-increased-treatment-to-achieve-lower-blood-pressure-targets