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- The Old-Fashioned Approach to Delivery and Targeting of Gene Therapy for Arthritis
- An Alternative Approach to Myostatin Inhibition to Increase Muscle Growth
- TIGIT as a Therapeutic Target and Marker of T Cell Senescence and Exhaustion
- Delivery of Extracellular Vesicles as a Potential Basis for Therapies
- Negligible Senescence and Exceptional Genome Maintenance in Naked Mole-Rats
- Even Modest Changes in Calorie Intake and Weight can Ruin any Study of Health
- Evidence for Human Species Longevity to be a Matter of Many Small Adaptations
- Wnt Signaling and p53 in the Progression of Heart Failure
- A Desire for Improved Vaccine Effectiveness as the Spur to Invest in Potential Methods of Immune System Rejuvenation
- Evidence for Clearance of Senescent Glial Cells to Slow Parkinson's Disease
- Amyloid-β May Cause Mitochondrial Dysfunction in Alzheimer's Disease
- A Novel View of How Frail Bones Break
- Considering Various Strategies to Treat the Issue of Mutated Mitochondrial DNA
- Stroke Risk Nearly Halved by Some Combinations of Medications to Lower Blood Pressure and Cholesterol
- Fat Tissue Outside the Heart Plays a Role in the Progression of Heart Failure
The Old-Fashioned Approach to Delivery and Targeting of Gene Therapy for Arthritis
Sometimes the old-fashioned, simple solution is more than sufficient for the task at hand. In today's open access review paper, researchers discuss the delivery and targeting of gene therapies to arthritic joint tissue via the simple expedient of injecting the therapeutic into the joint - the most modern of medical treatments married to a 150-year-old technology. And why not? The alternatives for targeting a therapy to a specific tissue are numerous, but all quite complicated and expensive: magnetic fields to guide metallic nanoparticles attached to the therapeutic; using seeker proteins that preferentially match the surface structure of a given cell type; DNA machinery that checks the internal state of a cell and only triggers the therapeutic if the local environment appears correct; and so forth.
First generation gene therapies are appearing in clinical trials in ever larger numbers, hundreds in recent years, though the term covers a wide range of what are arguably quite distinct approaches and endpoints. Very few of these use CRISPR today; most are older delivery technologies working their way through the last portions of a years-long development pipeline. That story will likely be very different a couple of years from now, given the enthusiasm with which the research community has embraced CRISPR. Today's candidate gene therapies largely have effects that are temporary, as the delivery mechanisms don't successfully transfer their cargo into a large number of cells. Of those that are affected, near all will be somatic cells, limited in their ability to replicate, and thus altered cell lineages in a tissue will die out in a matter of months at most.
Putting aside the more advanced, machine-like, and programmable gene therapy platforms, such as that pioneered by Oisin Biotechnologies, most present day gene therapies in trials are essentially a way to make some cells produce more of a specific protein for some period of time. Each is an indirect two-stage protein delivery system, in effect, using cells as a local manufactory. All cellular machinery is controlled by levels of specific proteins - the amount of a specific protein in circulation in the local environment is a switch, or a dial. The cell is a fantastically complicated collection of these switches and dials, most of which can affect numerous others, forming feedback loops and chains of cause and consequence. Directly altering the amount of a specific protein is better than the use of pharmaceuticals to achieve the same aim, given that even the best drugs have all sorts of side-effects, but it is still a crude approach to obtaining the desired end results. Changing the amount of a protein will have all sorts of downstream effects that may or may not be helpful, in addition to the desired outcome. Future medical technologies will likely become more sophisticated in their control over cellular operations.
Though, ironically, these anti-arthritis gene therapies are conceptually quite crude. They target controlling mechanisms of inflammation in a fairly heavy handed way - following the well-established pharmaceutical industry path for inflammatory conditions, which is to suppress inflammation and the immune response rather than go further in search of the causes of the problem. Yes, there is inflammation, but why is there inflammation? Why not find and target that root cause? The arthritis research community will likely undergo a considerable rearrangement of priorities and leaders in the years ahead, if the results obtained in mice for arthritis and clearance of senescent cells translate into human patients. Senescent cells are one of the root causes of aging, and it appears that their accumulation, and their pro-inflammatory signaling, is a significant cause of at least some types of arthritis.
Gene Delivery to Joints by Intra-Articular Injection
With the exception of rheumatoid arthritis (RA) and related autoimmune conditions, disorders of joints tend to be local and usually affect a small number of joints - often only one. Such circumstances favor intra-articular therapies, where the therapeutic agent is delivered directly to the affected joint. Compared to systemic delivery, this reduces the likelihood of adverse events in non-target organs, maximizes the concentration of the therapeutic at the site of disease, and, by treating a joint instead of the whole body, lowers cost. Joints are discrete, enclosed cavities, and most are readily accessible to intra-articular injection, which is the delivery method of choice.
Although it is a straightforward matter to inject therapeutics into joints, the effectiveness of intra-articular therapy is greatly compromised by the rapidity and efficiency with which material leaves the synovial space. Small molecules diffuse out through the sub-synovial capillaries, while macromolecules and particles leave through the lymphatics. It is thus very difficult to achieve sustained, therapeutic concentrations of drugs in joints. The idea to use gene therapy for joint disorders arose in response to this problem. The original concept was to target gene delivery to the synovium for treating arthritis. This would lead to the sustained synovial synthesis of therapeutic gene products locally within joints. Such a strategy also obviates another problem for treating joints with biologics, namely the restricted access of proteins and other large molecules to the interior of the joint from the circulation.
Intra-articular injection of suspensions of genetically modified cells is unlikely to achieve long-term transgene expression because injected cells are cleared from joints within days to weeks. Persistent intra-articular expression following in vivo gene delivery was only achieved when the importance of the immune system in curtailing transgene expression was fully appreciated. This followed experiments in which vectors were injected into the knee joints of athymic rats. Under these conditions, transduction of the synovium was initially high, but transgene expression then fell as a result of synovial cell turnover, persisting at about 25% of the early level for the rest of the animals' life-span. Similarly extended periods of transgene expression are achieved when immunologically silent vectors are used to deliver autologous gene products in wild-type animals.
Proof of concept has now been achieved for both in vivo and ex vivo gene delivery using a variety of vectors, genes, and cells in several different animal models. There have been a small number of clinical trials for rheumatoid arthritis (RA) and osteoarthritis (OA) using retrovirus vectors for ex vivo gene delivery and adeno-associated virus (AAV) for in vivo delivery. AAV is of particular interest because, unlike other viral vectors, it is able to penetrate deep within articular cartilage and transduce chondrocytes in situ.
Although gene therapy for arthritis and related conditions has been discussed for more than 25 years, progress toward clinical application has been slow. Nevertheless, there have been several clinical trials, and the first product, Invossa, has just received marketing approval in Korea. Phase III human clinical trials of Invossa are projected to begin shortly in the United States. Its approval should stimulate interest in the entire field leading to more rapid development of genetic drugs for conditions that affect joints. Invossa targets OA by the injection of allogeneic chondrocytes that have been transduced with a retrovirus carrying transforming growth factor-β1 cDNA. Meanwhile, two additional Phase I trials are listed, both using AAV. One targets RA by transferring interferon-β, and the other targets OA by transferring interleukin-1 receptor antagonist. The field is thus gaining momentum and promises to improve the treatment of these common and debilitating diseases.
An Alternative Approach to Myostatin Inhibition to Increase Muscle Growth
Today, I'll point out a group that is working on a novel approach to myostatin inhibition in humans. Myostatin is a part of the regulatory system for muscle growth. Its role is to suppresses muscle growth, and thus lowered levels of myostatin result in less fat and more muscle in a variety of mammalian species, including our own. Complete removal of myostatin via genetic engineering or breakage through rare natural mutation has resulted in very heavily muscled mice, dogs, cows, and even a few people. The technical name for the outcome is myostatin-related muscle hypertrophy. There are no obvious downsides - which doesn't mean they there are absolutely no issues, but if they do exist, then they are largely subtle and long-term problems.
Given this, there is considerable interest in building therapies based on myostatin inhibition. Quite aside from the potential market for human enhancement, satisfying the desire for muscles without the need to work for those muscles, therapies of this type should help to compensate somewhat for sarcopenia, the characteristic age-related loss of muscle mass and muscle function. Not all of that loss relates to a simple lack of muscle tissue, but where it does, adjusting the regulator of muscle growth could be useful. To date, researchers have trialed the use of antibodies to reduce the amount of myostatin in circulation. This appears successful, though to a much lesser degree than genetic loss of myostatin. This is to be expected, and is usually the case when comparing genetic alterations to inhibition of proteins produced from the genetic blueprint - the inhibition only removes or suppresses a portion of the protein.
Other groups are looking ahead to human gene therapies to either disable myostatin or increase levels of follistatin, the natural inhibitor of myostatin. Follistatin gene therapy in mice produces a similar level of muscle growth as myostatin knockout, and was the approach pursued by BioViva Sciences when Elizabeth Parrish underwent gene therapy as a proof of concept and wake up call for the world. I think in general that the current delivery systems for gene therapy are not yet good enough or cheap enough to merit widespread use: they don't edit the genome in enough cells, and especially in the stem cell populations that would be needed to produce a life-long effect. That will likely change soon enough, however, as many researchers are working on the problem.
The notes below cover an alternative and more sophisticated inhibitory approach for myostatin that is presently under development at Scholar Rock - that this material is out there now has a lot to do with there being a company involved, and one that has just raised a sizable amount of funding. That tends to be how things work in the attention economy: always consider cui bono, though the useful result of a spread of knowledge also occurs as a side-effect. Instead of destroying, binding, or otherwise globally interfering with myostatin molecules, here the researchers involved suppress the activation of those molecules. A better understanding of how myostatin functions as a regulator shows that it spends much of its time inactive, and that the system of activation can be constructively interfered with in a number of ways. While this approach should be more selective, time - and forthcoming human trials - will tell as to whether it is better or worse than the more standard approaches to inhibition of a specific protein when it comes to producing additional muscle.
Scientists elucidate molecular basis of myostatin activation, key process in muscle health
Myostatin (also known as GDF8) is a key signaling protein that contributes to the regulation of muscle mass and function. Initially produced by muscle in a latent inactive form, myostatin can be activated under certain conditions by sequential enzymatic steps. For the first time, the new study provides an understanding at the molecular level of the structural changes that take place in the protein during this activation process, and the central role of the tolloid enzyme in generating active myostatin. Insight into the activation mechanism of myostatin and other related proteins is central to the drug discovery platform established at Scholar Rock for the development of novel therapies for the treatment of many severe diseases.
"Deploying deep structural understanding of growth factors and their activation is opening a profound new way to intervene in human disease. SRK-015, our clinical candidate for the treatment of muscle atrophy and wasting disorders, exemplifies the strong potential of targeting specific structural states of myostatin with the objective of providing superior therapeutic outcomes."
The proprietary therapeutic antibody, SRK-015, was discovered and designed to selectively and locally target the latent form of myostatin with the ability to specifically block its intramuscular activation. In a variety of preclinical models of muscle atrophy, SRK-015 has demonstrated improvement in muscle function. SRK-015 is initially being developed for the improvement of muscle strength and function in patients with Spinal Muscular Atrophy (SMA) with the treatment of additional neuromuscular diseases to follow.
SRK-015 for Spinal Muscular Atrophy (SMA)
SRK-015 uniquely targets the latent form of myostatin, specifically blocking its activation in muscle. Inhibiting the supracellular activation of myostatin, rather than the traditional approach of blocking already activated, mature myostatin or the myostatin receptor, avoids blocking the activity of other closely-related members of the TGFβ superfamily that may lead to undesirable side effects. Scholar Rock is actively working to advance SRK-015 into clinical trials, which are anticipated to commence in mid-2018. We intend to develop SRK-015 in combination with therapies aimed at correcting the underlying genetic defect in SMA and as monotherapy in patients with certain subtypes of SMA.
Tolloid cleavage activates latent GDF8 by priming the pro-complex for dissociation
Growth differentiation factor 8 (GDF8)/Myostatin is a latent TGF-β family member that potently inhibits skeletal muscle growth. Here, we compared the conformation and dynamics of precursor, latent, and Tolloid-cleaved GDF8 pro-complexes to understand structural mechanisms underlying latency and activation of GDF8. Why some TGF-β family members are active and others are latent as procomplexes is incompletely understood. Here, we ask why GDF8 is latent, and what changes when it becomes activated.
GDF8 and its close relative GDF11 are activated by BMP1/Tolloid (TLD) metalloprotease-mediated cleavage of the prodomain between the straitjacket elements and the arm domain. Tolloid-like protein 2 (TLL2), used in this paper, is among the most active on GDF8 of the four TLD proteases found in mammals, and is the only TLD protease expressed in muscle. While TLD cleavage clearly activates signaling by GDF8, whether the two prodomain fragments rapidly dissociate from GDF8 after cleavage, or remain associated with GDF8 in a "primed" state, is not known. Here, we compare pro-GDF8, the state prior to PC cleavage; latent GDF8, the state after PC cleavage; and primed GDF8, a state after TLD cleavage in which we found the persistence of substantial prodomain-GDF8 association.
TIGIT as a Therapeutic Target and Marker of T Cell Senescence and Exhaustion
In the open access paper here, researchers propose TIGIT as a marker of T cell senescence and exhaustion, also known as anergy, in the aged immune system. Further, this is not just a marker, but also a potential therapeutic target, as an initial test of lowered levels of TIGIT resulted in restoration of some measures of lost function in T cell populations with large degrees of senescence and exhaustion. These two forms of T cell dysfunction are not the same thing, but they do have overlapping features, and seem to be connected in a number of ways. In general, such cells perform poorly and behave badly. They show up to increasing degrees in the aged immune system, and play their part in its inflammatory, weakened state.
Much of the research into immune system aging leads to the conclusion that selectively destroying immune cells is helpful. An old immune system is a zoo of breakage and malfunction: too many senescent and exhausted cells; too many cells uselessly specialized to persistent viruses, particularly cytomegalovirus; autoimmunities of many varieties, outright or subtle, some poorly understood or yet to be recognized; and so forth. These problems are to a very large extent within the immune cells themselves. Thus a clean sweep to start over is not a bad idea, or at the very least removal of the known worst classes of malfunctioning immune cell, but these approaches currently lack an implementation safe enough to be used in older people. The only way of doing this at present is high dose treatments with immunosuppressive drugs, optionally followed by cell therapy to rebuild the immune system more rapidly than would other wise happen. This has been shown to cure the autoimmune condition multiple sclerosis, but bears a significant mortality risk, judging from the studies to date.
Distinctly from considerations of the immune system, the discovery of novel markers of cellular senescence is an interesting topic these days. Senescent cells are firmly identified as a cause of aging, producing general effects such as an increase in chronic inflammation, but also tissue- and type-specific effects that are largely detrimental. Senescent cells do assist in wound healing and cancer suppression, but these are transient duties, and the cells that linger afterwards quickly become a liability. Given a novel marker for cellular senescence, or cellular senescence in a specific cell type, it is a fairly slow and expensive process to figure out a pharmaceutical strategy to target it. But one of the companies in the space, Oisin Biotechnologies, has a programmable gene therapy that can in principle be triggered by high levels of any protein of interest inside a cell. Given this sort of capability, the path towards a successful attack on any new and interesting target can be much shorter than it used to be.
T-cell Immunoglobulin and ITIM Domain Contributes to CD8+ T-cell Immunosenescence
Immunosenescence is the age-associated dysregulation of the immune system, of high clinical relevance, as it contributes to multiple age-related comorbidities, including malignancies, infectious diseases, autoimmune diseases, and degenerative diseases. T cells are important components of the immune system. Age-associated T-cell dysfunction is important for the development of immunosenescence.
T-cell senescence is different from T-cell exhaustion, a hyporesponsiveness associated with chronic infections and cancer. Exhausted T cells are derived from activated T cells that progressively lose function because of persistent antigen stimulation, whereas senescence is cell cycle arrest due to aging. However, emerging evidence indicates that T-cell senescence shares several key features with exhaustion. The upregulation of multiple co-inhibitory receptors is not only a hallmark, but also an important mechanism involved in the development of T-cell exhaustion. Consistently, certain co-inhibitory receptors such as programmed cell death protein 1 (PD-1), T-cell immunoglobulin domain and mucin domain 3 (TIM-3), lymphocyte activation gene 3 (LAG-3), and cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) are upregulated on T cells from aged mice, and blockade of PD-1 partially restores the functional defect of T cells derived from these mice. This finding indicates a pivotal role of T-cell inhibitory receptors in immunosenescence.
T-cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif (ITIM) domain (TIGIT) is a recently identified co-inhibitory receptor that is expressed on activated T cells, regulatory T cells, and natural killer cells. Similar to CTLA-4 and CD28, TIGIT competes with its costimulatory counterpart CD226 for the same ligands (CD155 and CD112) and mediates immune suppression in tumors and chronic infections. Here, we investigated the role of TIGIT in human immunosenescence using blood samples from healthy adults.
As senescent and exhausted T cells exhibit similar features of immune dysfunction, it has been speculated that these two processes share common mechanisms. Studies show that a number of co-inhibitory receptors, including PD-1, TIM-3, LAG-3, and CTLA-4, are associated with impaired T-cell function in aged mice. However, we did not observe a correlation between these co-inhibitory receptors and aging in humans. The discrepancy highlights the limitations associated with the use of animal models in studies of immune senescence. Instead, we found a significant upregulation of TIGIT expression on T cells from elderly healthy donors compared with that from young individuals. The difference was more prominent in CD8+ T cells. TIGIT+ CD8+ T cells expressed high levels of other inhibitory receptors and displayed multiple functional defects, including reduced cytokine production and susceptibility to apoptosis. These data suggest that TIGIT is a biomarker and elucidate a potential mechanism of T-cell senescence. To the best of our knowledge, this is the first evidence linking TIGIT to immunosenescence.
The upregulation of TIGIT in the cohort started early and became worse with age, which indicated that T-cell senescence exists not only in the elderly but also in young individuals. Although senescence is thought to be associated with the physiological aging process, chronic activation, stimulation, or damage may accelerate T-cell senescence. A high percentage of senescent T cells is observed in young patients with chronic viral infections and autoimmune diseases. It remains unclear whether the age-dependent upregulation of TIGIT is associated with a physiological process or pathogenic stimulation. It is possible that TIGIT-associated T-cell senescence is a consequence of physiological stimulation. Moreover, despite TIGIT expression in the young and middle-aged, TIGIT+CD8+ T cells in the elderly were more dysfunctional than the population from the young and middle-aged groups, especially regarding defective cytokine production.
To study a direct effect of TIGIT in T-cell dysfunction, we performed a TIGIT knockdown experiment using siRNA and evaluated the T-cell functions upon TIGIT knockdown. We found a significant increased cytokine release and less apoptosis in CD8+ T cells from elderly subjects upon TIGIT knockdown. This important data demonstrate the suppressive effect of TIGIT in T-cell function in the elderly.
Recent studies demonstrated that TIGIT suppresses antiviral and antitumor CD8 T-cell immunity. Our novel observation that TIGIT is highly expressed on senescent T cells led us to speculate that TIGIT contributes to the functional defect of these T cells and subsequently increases the susceptibility to infection or cancer. In conclusion, the present study demonstrated that TIGIT is a prominent negative immune regulator involved in immunosenescence. This novel finding is highly significant, as targeting TIGIT might be an effective strategy to improve the immune response and decrease age-related comorbidities.
Delivery of Extracellular Vesicles as a Potential Basis for Therapies
Here I'll point out a readable open access review paper on the potential use of extracellular vesicles as a basis for therapy: harvested from, say, some form of stem cell, and then delivered to a patient. One of the ways in which stem cell therapies might branch and evolve in the near future is to discard the cells themselves in favor of the signals produced by those cells. The evidence to date strongly suggests that many of the current forms of cell therapy produce their beneficial effects, such as a reduction in inflammation, via signaling. The cells themselves do not survive for long enough in large enough numbers to be making a difference through other activities.
This is not to say that all cell therapies should be replaced by signals - in most of the cases relevant to human rejuvenation, it is vital to deliver cells that stick around, integrate with tissues, and perform all of the necessary tasks required of them. To augment a failing organ such as the heart that is not naturally regenerative to a great degree, for example, or replace age-related losses in a small but necessary cell population, such as the dopamine generating neurons lost in Parkinson's disease. The present state of biotechnology isn't all that good at achieving this goal of cell survival, unfortunately, but that will improve. So there may be two fields in the future where there is one today, the first focused on delivering cells, the second on delivering cell signals absent the cells. Both can be useful, though only the replacement of lost cells directly addresses a root cause of aging. If we are prepared to accept stem cell therapies as a worthwhile endeavor even if they only work through signaling and fail to address root causes of aging, then we should be as accepting of the delivery of signals alone.
What are extracellular vesicles? These are numerous different forms of membrane-wrapped package that are constructed and released by cells, containing all sorts of proteins and other molecules. Other cells take them up and their behavior adjusts based on the way in which the contents interact with internal cellular machinery. A rough taxonomy of vesicles exist, based on their size - exosomes versus microvesicles, for example. This will no doubt give way to a better taxonomy based on function, given further research. Currently, only a comparatively crude understanding exists of the specific functions that vesicles accomplish, and how that differs between types. So while it is possible to say that stem cells produce beneficial effects via vesicles, and senescent cells produce harmful effects via vesicles, it isn't yet possible to break down that flow of vesicles into its component parts and talk in detail about each part in isolation.
Extracellular vesicles and aging
It is estimated that in the next 20 years, the number of individuals in the United States over the age of 65 will double, numbering more than 70 million individuals. Unfortunately, as we age there is an unavoidable and progressive loss of the ability to maintain tissue homeostasis under stress and an attrition of functional reserve. Over 90% of individuals older than 65 years of age have at least one chronic disease, while more than 70% have at least two. These chronic diseases account for 75% of our healthcare costs, amounting to approximately 3 trillion in costs last year alone. Thus, there is a significant need to understand mechanisms driving aging and to develop novel therapeutics.
There is compelling evidence to support the hypothesis that the underlying cause of aging is the cell autonomous, time-dependent accumulation of stochastic damage to cells, organelles, and macromolecules. However, it is also clear from heterochronic parabiosis and serum transfer studies that cell non-autonomous mechanisms play important roles in suppressing or driving degenerative changes that arise as the consequence of spontaneous, stochastic damage. For example, using heterochronic parabiosis, it was demonstrated that factors in young blood rejuvenate certain cell types and tissues in old mice.
Conversely, factors in old blood can drive aging of certain cell types and tissues in young mice. These blood-borne pro-geronic factors include the chemokine CCL-11 and β-2 microglobulin. In addition to these identified geronic factors, it is likely there are other circulating factors that also play key, cell non-autonomous roles in aging. Indeed, it is likely a combination of loss of anti-geronic factors and an increase in pro-geronic factors that drives aging. Given that almost all cell types release extracellular vesicles (EVs), including stem/progenitor cells and senescent cells, it is likely that subsets of blood-borne EVs play key roles as both anti- and pro-geronic factors.
EVs are comprised of both microvesicles, released from the plasma membrane by shedding, and nanovesicles or exosomes, generated by reverse budding of multivesicular bodies (MVBs). Although their contents likely differ, both small and large EVs are enriched for a subset of diverse proteins, lipids, messenger RNAs (mRNAs), and non-coding RNAs (ncRNAs), such as miRNAs, which are derived from the parental cells. EVs have a variety of reported functions and some of their better-documented activities are associated with some form of immune regulation. EVs derived from stem cells also have significant ability to repair damaged tissue.
Consistent with the regenerative capacities of stem cell EVs, a recent study demonstrated that implantation of healthy hypothalamic stem/progenitor cells into the hypothalamus leads to the slowing of ageing. Moreover, it was demonstrated that the functional hypothalamic stem/progenitor cells release exosomes into the cerebral spinal fluid that likely contribute to slowing aging through transfer of miRNAs. Conversely, it has been demonstrated that senescent cells release more EVs and with a different composition, likely contributing to the senescence-associated secretory phenotype (SASP). These results suggest that functional stem/progenitor cell-derived EVs are able to extend healthspan and lifespan whereas senescent cell-derived EVs could function as pro-geronic factors. Taken together, there is substantial circumstantial evidence that EVs play key roles in aging and that regenerative EVs could be used to extend healthy aging. Finally, given the likely role of EVs in aging, components of EVs could be developed as biomarkers of unhealthy aging.
Negligible Senescence and Exceptional Genome Maintenance in Naked Mole-Rats
Studies of the comparative biology of aging involve mapping the genetics and cellular biochemistry of exceptionally long-lived species in search of significant differences, when compared with both humans and shorter-lived species. The hope is that findings may inform human medical research, and at best could lead to new directions for the development of therapies to address aspects of aging. Species of interest include whales, for longevity and exceptional cancer resistance given their size, elephants, also for unusual cancer resistance, and naked mole-rats, which live far longer than similarly sized rodent species, and are near immune to cancer.
Today I'll point out a couple of recent papers from research groups investigating the naked mole-rat. It has for a while now been generally accepted that naked mole-rats are negligibly senescent. This is a blanket and in practice fairly loosely applied term indicating that members of a species show little signs of aging across most of a life span (for some definition of "little" and "most"), with a sudden and short decline at the end. This is very unlike the human life course, which takes the form of an exponential decline that starts comparatively early, in the middle of life.
Aging in this context has a precise definition: it is the rise in mortality rate over time due to intrinsic causes, the accumulation of cell and tissue damage resulting from the normal operation of cellular metabolism. If mortality rate remains roughly static over time in a population, then its individuals are not aging - which can in principle be the case at any mortality rate, high or low, but agelessness coupled with a high mortality rate seems more of a curiosity than a useful phenomenon, where it does occur. The naked mole-rats exhibit the low mortality option, of course. The first paper below provides evidence to back up the assertion that naked mole-rats don't just seem negligibly senescent, but actually are negligibly senescent.
The second paper looks at stochastic mutation rates across the life span, one of the many areas of biochemistry that researchers believe is important to aging. Mutation incidence is also a determinant of cancer risk - cancer is a numbers game, with every mutation that occurs having a tiny chance to be of a type that can give rise to an unrestrained, cancerous cell. Everything connected to aging looks better in a naked mole-rat, and that includes low mutation rates and highly effective DNA repair. Clearly some of those measures are secondary to the root cause reasons as to why the species ages so lightly until the very end of life - they can't all be root causes.
DNA maintenance may fall into either category, though the present consensus places it a meaningful contributor to the declines of aging. However, it remains the case that definitively determining the relative importance of specific contributions to the outcomes of aging is a challenge. These questions will probably remain open until biotechnology is applied to block or eliminate various likely mechanisms in naked mole-rats, or recreate those same mechanisms in mice, in order to observe the outcome. Theorizing and mapping can only take us so far at the present time.
Naked mole-rat mortality rates defy Gompertzian laws by not increasing with age
The naked mole-rat is a strictly subterranean, mouse-sized rodent and is one of only two known eusocial mammals. The longest-lived rodent, it is recognized as an animal model of biogerontological interest, with a maximal lifespan of more than 30 years in our captive care. This maximum lifespan is five-fold greater than predicted allometrically for a 40g rodent. Beyond lifespan, the physiological declines that accompany advancing age in most mammals fail to manifest in naked mole-rats. Breeding females show no menopause, retaining high fertility even at ages past 30 years. Neurogenesis is also prolonged and may continue for at least two decades, and over a similar time course, no significant changes in cardiac function, body composition, bone quality, and metabolism are evident. Age-associated chronic diseases such as cancer are also rare. Within the cell, proteasome function, as well as mitochondrial mass, gene expression, and protein expression are maintained with age.
The concepts of mortality and physiological decline associated with aging can be connected within the mathematical framework of the Gompertz-Makeham law of mortality. Mortality hazard increases exponentially with age, presumably due to intrinsic age-related physiological declines. While naked mole-rats are already noted as exceptionally long-lived, this status relies on small-sample-based estimates, leaving much uncertainty as to how exceptional their longevity may truly be and how they differ from other mammals with respect to the Gompertz-Makeham aging framework. Here, we compiled a large, historical dataset of naked mole-rat lifespans using records kept throughout the ~35 year maintenance of our collection. With over 3000 data points, we constructed survival curves and performed analyses of age-specific hazard. In these analyses, this mouse-sized rodent exhibited no increase in mortality hazard, that is, no Gompertzian aging, across its full, as-yet-observed, multi-decade lifespan. This life-history trend is unprecedented for mammals.
Genome Stability Maintenance in Naked Mole-Rat
DNA damage caused by environmental stress and normal metabolic processes occur daily at a frequency raging from 1,000 to 1 x 10^6 per living cell. As a result, only 0.00017% of the human genome consisting of 3 x 10^9 base pairs is damaged, but lesions in essential genes, such as the genes that code for tumor-suppressor proteins, can significantly disturb cellular function. The efficient DNA repair mechanisms that counteract DNA damage accumulation substantially contribute to genome stability maintenance, which is one of the crucial cellular functions. Accumulation of DNA lesions and mutations increases the risk of cancer and is related to aging.
Only a few experimental studies have focused on the search for a correlation between the activity of DNA repair systems and maximum lifespan. The complexity of these studies and their controversial findings may stem from both the imperfect methods used for activity assessment and improper selection of model systems. The naked mole-rat (NMR) is one of the most promising models used to study genome maintenance systems, including effective repair of DNA damage. The lifespan of the NMR can reach 32 years, ten times longer than that of the mouse. For most of its lifespan (at least 80%), this animal shows no signs of aging and retains the ability to reproduce. It possesses a very efficient mechanism of resistance to cancer, including cancer induced by different stressors.
The naked mole-rat draws the heightened attention of researchers who study the molecular basis of lengthy lifespan and cancer resistance. Despite the fact that the naked mole-rat lives under genotoxic stress conditions (oxidative, etc.), the main characteristics of its genome and proteome are a high stability and effective functioning. Replicative senescence in the somatic cells of naked mole-rats is missing, while an additional p53/pRb-dependent mechanism of early contact inhibition has been revealed in its fibroblasts, which controls cell proliferation and its mechanism of ARF-dependent aging. The unique traits of phenotypic and molecular adaptations found in the naked mole-rat speak to a high stability and effective functioning of the molecular machinery that counteract damage accumulation in its genome.
Even Modest Changes in Calorie Intake and Weight can Ruin any Study of Health
Calorie restriction has a large beneficial effect on health and longevity in mice, and as a result any number of studies carried out over the past century were ruined - usually without the researchers noticing - because no attempt was made to control for calorie intake and weight. Any treatment that causes nausea in mice, and thus a lower calorie intake, may have mistakenly reported benefits. Any treatment that resulted in mice eating more may have mistakenly missed benefits or reported harms.
The same general principle applies for people running their own self-experiments of treatments that might slow or turn back aging to some degree - something that will become ever more common as the world wakes up to the potential of low-cost senolytic treatments that can remove senescent cells, one of the root causes of aging. As the article here makes clear, all it takes is a short period of changed calorie intake and weight to throw off most of the indirect metrics one might use to assess the results of an early, comparatively crude senolytic treatment. For individuals in the earlier stages of aging, benefits are likely to be subtle and more easily obscured. It is something to think about: consistency in lifestyle, particularly diet, is very important when trying to measure effects.
Gaining and losing weight causes extensive changes in the gut microbiota and in biomarkers related to inflammation and heart disease, researchers report. The researchers monitored subjects' omics profiles as they added extra snacks and beverages to their regular diets. "We were fortunate we got 23 people who would eat extra calories - typically 1,000 if you're male, 750 if you're female - every day for 30 days. They're just a very interested bunch of folks. They have to be to show this kind of dedication to giving samples." The team collected samples before and after the 30 days of eating extra calories, as well as after participants returned to their starting weight, about 60 days after dropping the extra calories, and then three months after that. Of the 23 participants, 13 were insulin resistant and 10 were insulin sensitive at the beginning of the study. Comparisons of baseline profiles showed differences in metabolism, transcript and protein levels, and the microbiota of insulin resistant and insulin sensitive people.
Although subjects only gained an average of about six pounds, the researchers detected considerable changes in molecules related to fat metabolism, inflammation, and dilated cardiomyopathy, a condition where the heart is less able to pump blood, which can lead to heart failure. The team also found differences in the gut microbiota after weight gain. Many of the shifts the scientists observed were less pronounced in the insulin-resistant individuals. For instance, one bacterial species - Akkermansia muciniphila, which is thought to help protect against the development of insulin resistance after weight gain - only appeared in the insulin-sensitive participants. "There is a molecular difference in the way [insulin] resistant and sensitive folks react to gaining weight, and we think it reflects differences in their underlying biochemistry."
Most of the changes went back to baseline after weight loss, but a few - such as molecules associated with folate metabolism - stayed elevated. And while the researchers saw some common responses to weight gain and loss across the group, "you still look more like you than somebody else. That means that our inherent biochemical profiles are pretty stable, at least through weight gain and weight loss."
Evidence for Human Species Longevity to be a Matter of Many Small Adaptations
Why do humans live so much longer than other, short lived species? The researchers here provide evidence to suggest that it is a matter of many small changes, with the specific area of investigation being the the cellular repair mechanisms of autophagy. A world in which differences in longevity between species are the summed contributions from countless small effects is one in which we should discount the possibility that comparative genetic studies - between long-lived and short-lived humans, or between humans and other species - can yield silver bullets, findings that can on their own offer the potential to dramatically improve health and longevity. That expectation, and the sizable mountain of other evidence for the "many tiny contributions" model can be weighed against the recent reports of human PAI-1 mutants with a seven year greater life expectancy than their peers. I wouldn't have wagered on the discovery of such a thing, given what is otherwise known of the genetics of longevity.
Research into the importance of protein called p62 shows that a collection of small adaptations in stress activated proteins, accumulated over millennia of human history, could help to explain our increased natural defences and longer lifespan. Many cells in our body, such as those which make up our brain need to last us a lifetime. To do this our cells have developed ways of protecting themselves. One way is through a process called autophagy, which literally means self-eating, where damaged components are collected together and removed from the cell. "As we age, we accumulate damage in our cells and so it is thought that activating autophagy could help us treat older people suffering from dementia. In order to be able to do this we need to understand how we can induce this cell cleaning."
In the study the authors were able to identify how a protein called p62 is activated to induce autophagy. They found that p62 can be activated by reactive oxygen species (ROS). ROS are by-products of our metabolism that can cause damage in the cell. This ability of p62 to sense ROS allows the cell to remove the damage and to survive this stress. In lower organisms, such as fruit flies, p62 is not able to do this. The team identified the part of the human p62 protein which allows it to sense ROS and created genetically modified fruit flies with 'humanised' p62. These 'humanised' flies survived longer in conditions of stress. "This tells us that abilities like sensing stress and activating protective processes like autophagy may have evolved to allow better stress resistance and a longer lifespan."
Indeed, in the study, the authors found that specific mutations in human p62, which cause a neurodegenerative disease called amyotrophic lateral sclerosis (ALS), can prevent activation of p62 by ROS. These cells are then unable to induce protective autophagy, and this could underlie the premature death of neurons in patients with this devastating age-related disease. The research demonstrates that a collection of small adaptations like that of human p62 could have accumulated over time and these adaptations could underlie our increased natural defences and longer lifespans.
Wnt Signaling and p53 in the Progression of Heart Failure
If at the bottom of aging are root causes, and at the top of aging are end results, meaning organ and tissue failure and age-related disease, then the majority of aging research is focused on the middle layer of the problem in between. This middle layer is made up of the exceptionally complex changes in cellular biochemistry that take place over the course of aging, a snake-pit of long chains of cause and effect, with many feedback loops and interactions. All of this is incompletely investigated, and the links to top and bottom tiers of aging are in many places only tenuously understood or proven. Making progress towards a grand map of cellular metabolism and aging is very slow and very expensive.
The research here is an example of this type of work, illustrating that even the better-studied portions of the cellular biochemistry of aging include collections of contradictory observations and clashing evidence, yet to be explained, and that there is all too little consideration given as to why the observed changes take place. Until more attention to root causes appears on a regular basis in everyday papers such as this one, then the research community will continue to give little attention to those root causes. As a consequence little progress will be made in the matter of preventing and reversing aging. Researchers will remain in the wilderness of the middle layer, eternally cataloging, and never intervening in any effective way.
Heart failure, which is a complex pathophysiological syndrome, is one of the leading causes of mortality in the world. In the cardiovascular area, there is an age-dependent increase in the prevalence of left ventricular hypertrophy, diastolic dysfunction, and atrial fibrillation, which are not necessarily associated with classical risk factors for cardiovascular diseases. There is also an aging-related increase in vascular intimal thickening and vessel stiffness. In addition, maladaptation and/or abnormal response to stress (e,g,. pathological hypertrophy, apoptosis, replacement fibrosis, progression to heart failure) can be aging-related.
Here, we will review the contribution of Wnt/β-catenin signaling and p53 pathway, both of which play an important role in aging, to the progression of cardiac remodeling and dysfunction in the failing heart. Wnt/β-catenin signaling plays critical roles in stem cell self-renewal, development as well as adult homeostasis, and augmented Wnt/β-catenin signaling is also implicated in aging, aging-related phenotypes, and various diseases. Wnt/β-catenin signaling is activated in the failing heart. Circulating C1q was identified as a potent activator of Wnt/β-catenin signaling, promoting systemic aging-related phenotypes including sarcopenia and heart failure.
In a previous report, cardiac-specific overexpression of a positive regulator of Wnt/β-catenin signaling was found to cause extensive hypertrophy, heart failure, and premature death in mice. On the other hand, it was reported that stabilization of β-catenin attenuates adaptive cardiac hypertrophy and leads to impaired cardiac function under angiotensin II treatment. The Wnt1/β-catenin injury response activated cardiac fibroblasts to promote cardiac repair after acute ischemic cardiac injury, preserving cardiac function. In other reports, blocking of Wnt/β-catenin signaling was shown to avert adverse remodeling or improve cardiac function in animal models of myocardial infarction. In spite of such a context-dependency, Wnt/β-catenin signaling is thought to play a pivotal role in the progression of cardiac dysfunction/heart failure.
The p53 pathway also plays an important role in the pathophysiology of heart failure through the induction of aging-related phenotypes. Replicative senescence induced by telomere dysfunction and stress-induced premature senescence are mediated by p53. p53 activates a cellular response to stress signals (e,g,. DNA damage) that leads to a halt in proliferation via apoptosis or senescence. Such a depletion of cells could compromise the structure and function of tissues, which are the processes towards aging-related phenotypes and tumor suppression. In particular, because cardiomyocytes do not proliferate after birth, p53 exerts a pathogenic effect on cardiomyocytes through the induction of apoptosis.
Further investigations with multidisciplinary approaches will be required to fully clarify the molecular mechanisms underlying heart failure.
A Desire for Improved Vaccine Effectiveness as the Spur to Invest in Potential Methods of Immune System Rejuvenation
In the same way that the regenerative medicine field cannot evade addressing the aging of stem cells, the vaccination research community cannot evade addressing the aging of the immune system. The reasons are much the same in both case: all too many of the patients are elderly, and due to the processes of aging, treatments do not work anywhere near as well in older people. Thus effective clinical applications of research will eventually require the relevant effects of aging to be in some way addressed: mitigated or reversed. This is widely understood in the research community. At the present time this understanding largely manifests as efforts to better understand the mechanisms involved. These research communities are large, however, and that means that there are at least a few groups at any point in time whose members are somewhere in the process of moving potential approaches to stem cell or immune system rejuvenation closer towards the clinic.
Vaccines represent one of the most powerful medical interventions against infectious diseases. Effective adult vaccination programs targeting all age groups, including older adults are now more urgent than ever. Changing demographics and the vast increase of aged individuals, necessitates development of efficacious and safe vaccines, suitable for adults and in particular for older adults. While vaccines targeting older populations exist, their performance is often sub-optimal and/or they are under-used. At present, major gaps exist in our knowledge of the mechanisms behind the reduced ability of the aging immune system to respond appropriately to both infections and vaccinations. This hinders our ability to design interventions capable of improving the immune response in older adults and to tailor vaccines better suited for this group.
Aging is characterized by multifaceted changes in the immune system which lead to a progressive reduction of the ability to mount effective antibody and cellular responses against infections and to vaccinations. This phenomenon, referred to as immunosenescence, is multifactorial: it affects both arms of the immune system and can be influenced by genetic factors and extrinsic factors, such as nutrition, physical exercise, co-morbidities, physical and mental stress, previous exposure to microorganisms, toxins, and pharmacological treatments. Consequently, the presenting forms of immunosenescence are protean, varying at population and individual levels.
Therefore the concept of "Bioage" is arising to describe the concept that the real age is not the chronological, but the biological one. The concept of "bio-age" is in line with the observation of the wide variability of immune responses observed in the elderly after vaccination. In addition, it is in line with the increasing evidence that the immunological experience that individuals have during their lives can shape their ability to respond to external stimuli, such as infections or vaccinations. The pro-inflammatory environment of the aging body is a common denominator of aging which is referred to as "inflammaging". Extensive scientific literature has been published on this area and among the many hypothetical potential causes, the most popular is infection with cytomegalovirus (CMV). Indeed, strong CMV seropositivity has been associated with lower antibody and cellular responses to a variety of vaccines. The long-term maintenance of vaccine-specific antibodies seems to be hampered by CMV.
Considering the pleiotropic nature of immunosenescence and its variable expression among older individuals, it is not surprising that, despite the "physiological" decay of the immune responsiveness with age, vaccination remains a vital intervention in the older adults. Several pharmacoeconomic studies have underlined the benefit of influenza vaccines in terms of lives saved and reduced direct and societal costs linked to reducing influenza-related morbidity and mortality. Moreover, failure to vaccinate is associated with excess mortality due to infection and its complications. However, some vaccines have been shown to exhibit sub-optimal efficacy in recipients of advanced age or significant frailty. Differences in bio-age, immunobiography, and trained immunity can reconcile the apparent discrepancy between the reduced response of the elderly to some existing vaccines, and the evident successes that have been obtained recently. There is reason to believe that we can improve on the former by deciphering the mechanisms underlying the latter.
Evidence for Clearance of Senescent Glial Cells to Slow Parkinson's Disease
Senescent cells accumulate with age and are one of the root causes of degenerative aging. Since senescent cells generate chronic inflammation, removing the accumulation of such cells in old tissues should improve matters for all age-related conditions with an inflammatory component. Of course that will vary greatly from condition to condition and between tissue types - there are other contributing causes for the chronic inflammation that characterizes old age, and in any specific case senescent cells may or may not be the most important cause.
Here researchers look at senescent astrocytes in the brain in the context of Parkinson's disease, finding that removing them in a mouse model of astrocyte senescence is beneficial. This line of research has been underway for a few years now, ever since the start of increased interest in cellular senescence in aging. The Alzheimer's research community is paying attention as well. The animal model used here is fairly artificial, disconnected from the real state of affairs in the aging brain, but the evidence gathered at least makes the point that senescent astrocytes are harmful, and that harm can be reversed by destroying them.
One concerning item in all of this research is that the signs of senescence, in terms of the usual marker proteins expressed, such as p16 and SA-β-gal, appear in a sizable fraction of astrocytes in old people. This may or may not reflect actual senescence, but it is a much higher proportion of cells in comparison to other aged tissues examined to date - sufficiently high to raise doubt over whether this is in fact the same phenomenon observed in better characterized types of senescent cells. It may be just as well that early senolytic therapies do not pass through the blood-brain barrier, as if all of those astrocytes are indeed senescent then removing a quarter to a half of them all at once would likely be dangerous at the very least, and possibly fatal.
In work that could open a new front in the war on Parkinson's disease, scientists have shown that they can stave off some of the effects of the neurodegenerative disease by flushing "zombie cells" from the brain. The approach may have benefits far beyond Parkinson's, with other neurodegenerative diseases - and the ageing process more broadly - all being linked to the ill effects of these "senescent" cells, which linger in tissues. "It's a completely new way of looking at neurodegenerative disease and finding potential drugs. For most of these conditions, we don't have any way to counteract them."
Parkinson's disease usually takes hold when certain types of neurons in the brain become impaired or die off completely. The neurons in question produce a substance called dopamine. Scientists suspected that other cells in the brain - the astrocytes which support the dopamine-generating neurons - may be involved in Parkinson's disease. Specifically, they thought astrocytes might cause problems when they became senescent, a state where cells stop dividing but release chemicals that drive up inflammation. This local inflammation could be harming nearby neurons.
Scientists described how brain tissue taken from dead Parkinson's patients had more senescent astrocytes than healthy brain tissue. They also found that exposing human astrocytes to the herbicide paraquat flipped the cells from a healthy state into senescence. The transformation into the zombie-like state forms part of the body's natural defences against cancer: when cells are in danger of uncontrolled growth, the switch to senescence keeps them in check.
To test whether senescent astrocytes might have a downside - and play a role in Parkinson's disease - the scientists exposed six-month-old mice to paraquat, a weedkiller that has been linked to Parkinson's disease in humans. The herbicide produced senescent astrocytes in the animals' brains and tests showed they had physical difficulties moving around. The scientists next looked at what happened when mice exposed to paraquat were injected with a drug that destroys senescent cells. The drug appeared to protect the mice and kept their movement problems at bay. "They are able to move around their cages well. They are almost indistinguishable from the healthy mice."
Amyloid-β May Cause Mitochondrial Dysfunction in Alzheimer's Disease
Researchers recently reported evidence for some of the complex, toxic halo of biochemistry that surrounds amyloid-β to be capable of causing mitochondrial dysfunction. It is the certainly the case that there is plenty of evidence for mitochondrial dysfunction to be very relevant to age-related neurodegenerative conditions such as Alzheimer's disease. The hundreds of mitochondria found in every cell act as power plants, and the brain is an energy-hungry organ. In most research, however, the direction of causation is that declining and disrupted mitochondrial function causes amyloid-β accumulation and the other manifestations of Alzheimer's disease. Causation can be a two-way street, however. That aging and age-related diseases accelerate as they progress indicates the presence of feedback loops, in which dysfunction A causes dysfunction B, while dysfunction B makes dysfunction A worse. It isn't unreasonable to expect that sort of connection between many of the mechanisms of neurodegeneration, especially in the later stages.
Two pathological hallmarks are observed in Alzheimer's disease (AD) brains at autopsy: intracellular neurofibrillary tangles and extracellular senile plaques, which tend to occur in the neocortex, hippocampus, and other subcortical regions crucial for cognitive function. These observations have led to a dominant theory of Alzheimer's causality, known as the amyloid hypothesis. The theory points to accumulations of the sticky protein substance amyloid-β as the critical factor initiating the chain of events leading to development of Alzheimer's disease. While the amyloid hypothesis continues to exert a considerable hold on the field, an increasing consensus among researchers is moving away from the idea of amyloid-β accumulation as the primary event that sets the disease in motion.
In a new study, researchers examined the effects of the disease on the functioning of mitochondria - structures performing a variety of essential tasks, including supplying cells with energy. The new research reveals that a highly toxic form of amyloid-β protein - known as oligomeric amyloid-β (OAβ) - disrupts the normal functioning of mitochondria. The result is a fateful cascade of events that appears early in the development of AD - decades before the onset of clinical symptoms.
The most promising finding in the new study is that human neuronal cells can be protected from OAβ-induced deterioration of their mitochondria when they are pre-treated with a custom-designed compound, suggesting an exciting avenue for future drug targeting. "Mitochondria are the major source of energy in brain cells and deficiencies in energy metabolism have been shown to be one of the earliest events in Alzheimer's disease pathobiology. This study reinforces the toxicity of oligomeric amyloid-β on neuronal mitochondria and stresses the importance for protective compounds to protect the mitochondria from oligomeric amyloid-β toxicity."
In the new study, cells known as pyramidal neurons, extracted from the hippocampus of patients who died of Alzheimer's, display a marked reduction in the expression of a suite of mitochondrial genes, pointing to their degradation by OAβ. The reduction of mitochondrial gene expression was also seen when cells belonging to a human neuroblastoma cell line were exposed to OAβ. The authors stress that not all types of nervous system cells are implicated in the mitochondrial dysfunction brought on by exposure to OAβ. Hippocampal astrocyte and microglia cells taken from the same AD-afflicted brains did not display reduced mitochondrial function.
One problem with the amyloid theory of Alzheimer's disease is its inconsistency. Researchers have reported that some elderly patients, bearing heavy burdens of amyloid plaque in their brains, lack any measurable cognitive deficit, while other patients showing little to no amyloid buildup nevertheless display severe Alzheimer's-like dementia. These facts have led researchers to seek other processes occurring at the earliest stages, which may kick the disease into gear. One of the most promising avenues of new research is the mitochondrial cascade hypothesis, which places these energy-delivering powerhouses of the cell at the center of the action. The hypothesis suggests that mitochondrial function, which declines as a natural feature of aging, may be further impaired in the presence of amyloid-β, in particular, OAβ. The fact that severe metabolic deficit appears as a prominent feature of AD further implicates energy-delivering mitochondria as likely culprits in the early disease process.
A Novel View of How Frail Bones Break
The common wisdom regarding the fractures and breaks that are sadly common in very old individuals is that they result from hard knocks against - and heavy loads placed on - bones that are made fragile by osteoporosis. A younger person would shrug off a fall or a load that will cause catastrophic structural failure in the bones of an individual in the advanced stages of osteoporosis. The research here suggests that this view is subtly wrong in several important details, and that the progressive harm caused by osteoporosis is in fact much worse than thought. It is an interesting and plausible viewpoint, though one that needs corroborating physiological data.
Either way, what can be done about osteoporosis? The proximate cause is an imbalance between the activities of cells that deposit bone, osteoblasts, and cells that break down bone, osteoclasts. Both are constantly active, but the various forms of change and damage that accompany aging cause the activity of osteoblasts to decline relative to the activity of osteoclasts, and thus bone becomes ever weaker. Senescent cell accumulation and chronic inflammation are in the list of deeper causes for osteoporosis, as is true of many other age-related conditions, but they are not alone. There numerous possible avenues by which this balance can be adjusted, and research groups are at various stages in these lines of work. If the balance is turned back, then the age-related weakness and damage of bone should start to reverse.
To better understand why many elderly people are prone to break a bone in a fall (known as bone fragility fractures), perhaps doctors and researchers should look at the human skeleton in much the same way civil engineers analyze buildings and bridges. A team of researchers believes the bones of an older person, say above the age of 50, become more susceptible to a break due to repeated stress from everyday activities such as walking, creating microdamage that affects the quality of the bone. That is in contrast to the common-held belief that bone breaks in the elderly are largely due to one massive impact or force on the bone, such as a fall.
"It really starts with a small microcrack that grows over time under repeated loading. You need to be doing something like just walking or moving, and the crack is slowly propagating. At some point, the remaining cross-section of the bone that is still connected is too small and will break suddenly." In that case, such fractures in the elderly would be the cause of a fall rather than the result of a fall. The theory that "cyclic loading" (repeated and fluctuating loads) might be a bigger contributor to bone breaks is similar to the study of structures and engineered materials. This type of stress in structures and materials resulted in a rise of catastrophic accidents near the turn of the 20th Century and has led to the development of "fracture mechanics."
"In engineered materials and structures, cyclic fatigue is the most ubiquitous mode of failure. Cyclic fatigue accounts for more than 80 percent of all failures, leading to catastrophic and sudden accidents such as the failure of railway axles, the collapse of metallic bridges, the failure of ships and the cracking of aircraft airframes and engines." The research is based on examining not just the bone's mineral density (bone mass) but its quality, specifically how well the collagen that provides the ductility of the bone deforms to resist fractures. And as one gets older, the more microdamage that person accumulates over time and the weaker the bones get.
Considering Various Strategies to Treat the Issue of Mutated Mitochondrial DNA
Mitochondria, the power plants of the cell, are the evolved descendants of symbiotic bacteria. They still carry a remnant of the original bacterial DNA, encoding a few vital genes. That mitochondrial DNA becomes damaged in aging, and based on the various direct and indirect evidence for the size of the influence of mitochondria on life span, this mutational damage and its consequences are a big deal. Some way to revert mitochondrial DNA damage is high on the list of rejuvenation therapies that we would like to see developed in the years ahead.
The open access paper here is largely focused on the treatment of inherited mitochondrial conditions, in which a sizable fraction of mitochondrial DNA in every cell throughout the body is affected by the same specific harmful mutation. It is nonetheless is a useful tour of some of the available tools that researchers might consider adapting in order to attempt to reverse the mitochondrial damage that occurs in aging. It mentions allotopic expression (copying mitochondrial DNA into the cell nucleus as a backup) only briefly, but that is fine: the audience here is no doubt familiar with this favored strategy of the SENS research program, but possibly less familiar with the other options on the table that involve mitochondrial DNA.
Most of those options boil down to either (a) delivering or creating larger amounts of correct mitochondrial DNA or (b) destroying as much broken mitochondrial DNA as possible. Both are viable approaches for inherited mitochondrial disease, but the dynamics are different in the case of aging. The real challenge posed by the most harmful age-related mitochondrial DNA mutations is that they result in mitochondria that are both broken and able to replicate more effectively than their peers. So even a single copy can quickly replicate to take over a cell, and that places tough constraints on the ability to produce benefits through treatments that work through the methods noted above. Adding correct mitochondrial DNA seems non-viable in principle on its own, while methods of destroying broken mitochondrial DNA would have to be exceedingly efficient to make any lasting progress. Still, the latter may be worth testing in order to certain, given that the technology exists to make the attempt.
The human mitochondrial DNA (mtDNA) is a small double stranded circular genome which is maternally inherited. Each mammalian cell contains in average one thousand copies of mtDNA and each molecule contains 37 genes. Defects in the mtDNA, both point mutations and large scale rearrangements, have been associated with severe mitochondrial syndromes. When pathogenic mutations occur in the mtDNA most often both mutant and wild-type copies co-exist within the same cell, a phenomenon known as heteroplasmy, and, in general, only when the mutation load is higher than approximately 80% symptoms manifest.
Currently, there are no effective strategies to cure mitochondrial disease and, in spite of the advances in genetics and biotechnology, there are still some gaps in the understanding of mitochondrial genetics. For instance, we do not know what controls mtDNA copy number, and mechanisms of mtDNA replication are still controversial. During the past 16 years our lab and others have been focusing in the use of endonucleases to target mitochondria and induce double strand breaks (DSB) in the mtDNA. Taking advantage of the fact that mitochondria lack an established DSB repair mechanism, it has been shown that mtDNA is quickly degraded after a DSB. Therefore, heteroplasmy can be manipulated and the mutant genomes can be efficiently eliminated through cleavage of mutant mtDNA and repopulation of the cells with wild-type mtDNA. Recently, a new door has been open regarding translation of these techniques into the clinics by the development of precise DNA editing tools, which can be targeted to mitochondria to promote DSB in the mtDNA.
Because of the high rate of mutations in the mtDNA, new pathogenic mutations are recurrently introduced into the human population. Recently, next-generation sequencing technology has been used to identify and quantify mtDNA mutations. However, these techniques have a high intrinsic error rate when applied to detection of low-level heteroplasmy. Despite all the technological difficulties, it is believed that mtDNA heteroplasmy exists in almost every healthy individual studied, even though at very low levels. These heteroplasmic variants can also be passed down the maternal lineage, raising the possibility that some presumably somatic mutations measured late in life are actually low-level heteroplasmies that have been inherited and somehow clonally expanded.
In contrast to point mutations, primary mitochondrial rearrangements of mtDNA are not inheritable, they are sporadic. Large-scale deletions are typically heteroplasmic and result in disease. To date, roughly 120 different mtDNA deletions have been found in patients with mitochondrial disease. In this case, the heteroplasmic threshold is reported to be lower than the one for point mutations, the patients manifest the disease symptoms with as low as 50-60% heteroplasmic mtDNA levels. Two different models arise to explain deletions in the mtDNA, while one points to replication errors, the other one points to poor and inefficient mtDNA repair mechanisms.
The concept of shifting the balance between healthy and mutated mtDNA as a treatment for heteroplasmic mtDNA disease has been under investigation over the past 20 years. Many publications demonstrated that it is possible to manipulate the mtDNA and shift heteroplasmy, either in vitro or in vivo. By simply reducing the levels of the mutant allele below a certain threshold, an improvement in pathology is achieved. There are currently at least two strategies for applying gene therapy to patients with mtDNA diseases: 1) Allotopic expression of mitochondrial genes; 2) Manipulation of mtDNA heteroplasmy. Allotopic expression of mitochondrial genes which consists in the synthesis of a wild-type version of the mutated protein in the nuclear-cytosolic compartment followed by its import into mitochondria has been a controversial approach because of the high hydrophobicity of mtDNA-encoded proteins and the competition with endogenous counterparts. Nonetheless, clinical trials for Leber's optic neuropathy are currently ongoing. The use of mitochondrial endonucleases is still in its infancy, but hopefully will move into the clinics in the next few years.
To conclude, the manipulation of mtDNA heteroplasmy either by using mito restriction endonucleases, mito zinc-fingers or mitoTALENs could facilitate delivery and increase specificity of mtDNA editing, having the potential to eliminate mutant mitochondrial genomes from germline treated affected patients.
Stroke Risk Nearly Halved by Some Combinations of Medications to Lower Blood Pressure and Cholesterol
The data here gives a fairly good idea of the bounds of the possible and plausible when lowering blood pressure and blood cholesterol, putting some numbers to the degree to which stroke risk can be reduced. Strokes occur due to breakage or blockage of blood vessels, and the roots of that lie in (a) the stiffening of blood vessels that breaks the feedback mechanisms determining blood pressure, and (b) the processes of atherosclerosis that produce fatty plaques in blood vessel walls, narrowing and weakening them.
Blood pressure medications don't address the roots of the problem, but force a lower blood pressure, which reduces the risk of rupture in weakened vessels. Lowered blood cholesterol, such as via statins, or more modern and effective approaches such as PCSK9 inhibition, reduces the pace at which atherosclerosis progresses over time by reducing the amount of damaged cholesterol in the blood stream. Again, it achieves this result not by addressing the root causes of that damage, but through a blanket lowering that happens to include the problem cholesterol molecules that feed the growth of atherosclerotic plaques. Fortunately it appears that we humans don't need anywhere as much cholesterol as we have; it is interesting to speculate on why we seem to have at least ten times as much in our bloodstreams as we need to get by.
Combining medication that lowers blood pressure with medication that lowers cholesterol reduced first-time strokes by 44 percent. Seventy-five percent of strokes are first-time strokes. High blood pressure and high cholesterol both increase the risk for stroke, the fifth leading cause of death in America. Yet it's not known whether combining drugs that lower blood pressure and cholesterol levels can protect individuals from stroke. Now, a study involving 12,705 participants from 21 countries shows that individually, drugs that lower blood pressure or cholesterol do indeed reduce stroke risk, but when combined, they offer even greater protection.
Taking daily doses of two blood pressure drugs (fixed dose candesartan and hydrochlorothiazide) along with a cholesterol-lowering drug (low-dose rosuvastatin), proved to be the most effective, cutting first-time strokes by 44 percent among patients at intermediate risk for heart disease. For those with very high blood pressure - readings 143.5 mm Hg or higher - taking 16 milligrams of candesartan plus 12.5 milligrams of hydrochlorothiazide every day reduced stroke by 42 percent. Compared with a placebo, stroke was reduced by 30 percent among participants taking daily doses of 10 milligrams of rosuvastatin.
The findings come from the Heart Outcomes Prevention Evaluation Study, a large, international study focused on heart disease and stroke prevention. The average age of the participants was 66 years; 46 percent were women, and 166 strokes occurred during an average follow-up of 5.6 years. At the start of the study, the average blood pressure was 138/82 mm Hg. A normal blood pressure reading is around 120/80 mm Hg. Based on these findings, researchers are now looking at developing a single pill that produces the same effects as taking multiple pills that lower both blood pressure and cholesterol.
Fat Tissue Outside the Heart Plays a Role in the Progression of Heart Failure
Researchers here demonstrate the degree to which fat tissue is involved in the progression from hypertension to heart failure, achieving this result by finding a way to sabotage one of the linking mechanisms. Removing a specific gene, ATGL, greatly reduces heart failure in mouse models of the condition. ATGL appears to play an important mediating role in the way in which fat tissue produces altered lipid levels in an aged, dysfunctional heart, and those lipid changes in turn accelerate the decline into heart failure. The full paper is open access, and worth looking over if the topic interests you. It should go without saying that there is already a mountain of research to demonstrate that excess fat tissue is a bad thing: this adds one more item to that lengthy list.
Heart failure is a chronic disease that should not be underestimated. Between one and two thirds of patients with heart failure die of the disease within five years. While researching the molecular causes of heart failure and new ways to treat it, researchers found that changes in adipose (fat) tissue lipid metabolism affect disease development. "We were able to show that the lipid composition of the heart is altered by non-cardiac body fat, and that these changes are likely to affect heart function."
For some time, researchers have suspected that the impact of body fat on heart function also exists on a molecular level. One of the key processes involved is the release of fatty acids from adipose tissue. In order to gain a better understanding of this process, the researchers used an animal model, which allowed them to interfere with the lipid metabolism, and to knock out the gene responsible for the relevant enzyme, adipose triglyceride lipase (ATGL). This resulted in all treated mice developing near-complete protection against heart failure. As part of this study, the researchers also analyzed blood samples from patients with and without heart failure. Some aspects of the changes observed in the lipid composition of blood samples were comparable to those observed in the animal model.
The researchers are now planning to transfer these results into clinical practice. In doing so, they will be guided by one central question: how might a drug-based treatment target the gene responsible for the release of fatty acids and the enzyme ATGL, and how might it do so exclusively in adipose tissue? The researchers are also planning to conduct further analyses of patient samples to confirm their results, and are working to determine the role of adipose tissue in patients with heart failure within the clinical setting. "For patients, this means that we should be starting to pay greater attention to adipose tissue when making diagnostic and treatment decisions, even when our primary aim is to treat heart disease."