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- Can Two Dozen Marginal Ways to Treat Aging be Combined into One Useful Therapy?
- Weaponizing the Biochemistry of Huntington's Disease as a General Cancer Therapy
- Greater Activity Slows the Progression of Age-Related Neurodegeneration
- Development of Exosome Delivery as a Regenerative Therapy Continues Apace
- HDAC3 Knockout Mice Exhibit Greatly Reduced Loss of Memory Function with Age
- There are Many Possible Paths to Immunotherapy for Senescent Cell Destruction
- Jagged-1 as a More Selective Signal to Spur Bone Regrowth
- Inhibition of Wnt Signaling as a Treatment for Osteoarthritis
- Evidence for Tau Accumulation and Failing Cerebrospinal Fluid Clearance to be the Starting Point for Alzheimer's Disease
- DNA Machinery that can Sabotage the Blood Supply of Tumors
- Liver Organoids Come Ever Closer to Natural Liver Tissue
- BACE1 Deletion Eliminates Amyloid Deposits in a Mouse Model of Alzheimer's Disease
- Macrophages Make a Significant Contribution to Heart Failure
- Bacteria Engineered to Deliver CXCL12 Accelerate Wound Healing in Mice
- Further Investigation of the Role of Osteopontin in Hematopoietic Stem Cell Aging
Can Two Dozen Marginal Ways to Treat Aging be Combined into One Useful Therapy?
Comparatively little work on combinations of therapies takes place in the research community. I suspect this to be a matter of regulatory incentives. For example there is little room for commercial entities to be able to make money by combining established treatments owned by other entities. Similarly for researchers, the world of possible approaches is balkanized by intellectual property, while the disposition of the majority of research funding is ultimately guided by the promise of a pot of gold at the end of the road. That pot of gold is much harder to obtain when someone else owns the therapies involved, and all that is being done is to apply them together. The edifice of intellectual property is a great evil, and this is one of many reasons why that is the case.
Given this long-standing state of affairs, there is at present little data to guide our expectations on the bounds of the possible when it comes to combining large numbers of therapies in search of additive and synergistic effects. Some people think that we should forge ahead in the matter of slowing aging: take every intervention with good evidence to date, and run large numbers of them in the same mice to see what happens. Should we believe that various ways of manipulating the operation of cellular metabolism demonstrated to achieve 5-10% life extension in mice can combine to double life span in that species? Intuition suggests not, but I don't think it to be completely out the question. Nor is it unreasonable to try it and see, given a rigorous approach to experimental design. Sadly, no established funding institution would go for this; it would have to be funded through philanthropy.
Why do I think that this is unlikely to produce large enough results to make it worthwhile? Because the evidence to date strongly suggests that the scores of methods of manipulating metabolism to modestly slow aging are operating on just a few core processes, such as autophagy. These are the stress responses that produce the lengthening of life observed in calorie restriction, and we know that these mechanisms don't produce anywhere near the same degree of life extension in humans as they do in short-lived species. Everything is connected to everything else in cellular biochemistry. A given interaction between two proteins can be influenced by adjusting levels of any number of other proteins, with widely varying degrees of effectiveness and side-effects. So most methods of slowing aging are different views into the same mechanism of action. The few combinations of approaches tried to date, involving only two methods, have resulted in mixed outcomes. Calorie restriction and mTOR inhibition may be additive, while growth hormone receptor knockout and mTOR inhibition interfere with one another, for example. That gives little insight as to the rest. It is hard to predict other results, beyond noting that a majority of interventions do appear to function through enhanced autophagy, and thus we might expect them not to combine in an additive way to any great degree.
What of the SENS rejuvenation biotechnology approach to aging, in which independent fundamental forms of cell and tissue damage are repaired? How will repair therapies combine? In this case we should expect additive effects: removing damage should be beneficial in proportion to the amount removed, at least when considered from a fundamental, reliability theory perspective. The mortality risk and longevity of a complex system of many redundant parts is dependent on its current load of damage. At this point we have no idea as to how that will turn out in practice, however. The contributions of different forms of damage may be significantly larger or smaller than one another. The results of two independent root cause forms of damage are not themselves independent: they interact, and probably significantly. Functional decline in one system spurs greater damage and functional decline in others, which is why age-related degeneration accelerates greatly in later life. It is a complex business. It isn't unreasonable to think that in some circumstances the results of rejuvenation therapies A and B will be indistinguishable from A alone, or that B will never achieve a great deal without being combined with C.
Can we envisage a world in which repairing cellular senescence alone produces no extension to life span because other, largely independent chains of damage and consequence are still life-limiting for old humans? That is becoming increasingly hard given the evidence to date for reversal of numerous age-related diseases to result from removal of senescent cells, not to mention the PAI-1 mutants who exhibit increased life span - but we know far more about senescent cell clearance than we do about any of the other SENS strategies. No-one is in a position to do more than make educated guesses about the results of combining senescent cell destruction with removal of mitochondrial DNA damage, or with clearance of specific lysosomal aggregates. Beyond "two should be better than one, but perhaps not in some specific cases" everything else will remain a mystery until the biotechnology is ready and the work is carried out. Making predictions seems a fool's game, given the degree to which the people closest to senescent cell research have been surprised by the scope and size of benefits observed in mice over the past few years.
Weaponizing the Biochemistry of Huntington's Disease as a General Cancer Therapy
An interesting observation that has arisen over the years of epidemiological study of human age-related disease is that there are a number of distinct inverse relationships between incidence of cancer and incidence of some forms of neurodegeneration. This was in the news a few years ago in the case of Alzheimer's disease for example. Why would people with a higher risk of cancer suffer lower rates of Alzheimer's disease, however? We can only speculate at this point, but the more recent discovery I'll point out here adds fuel for that speculation. The Alzheimer's-cancer relationship is modest in size and somewhat complex in detail in comparison to the quite dramatic and straightforward Huntington's-cancer relationship. People with the dysfunctional forms of the huntingtin gene that cause this neurodegenerative condition have a greatly reduced cancer risk.
Why is this the case? Researchers have now discovered that the aberrant huntingtin proteins implicated in Huntington's disease are actually a lot more damaging to cancerous cells than to neurons in the brain. While that is no great comfort to those who suffer the slow deterioration of Huntington's disease, the prospect of turning this discovery into a general cancer therapy is quite real. Something that reliably and rapidly kills all of the cancers it is tested against, while harming neurons only very slowly, is a much better class of candidate treatment than most chemotherapeutics. (And meanwhile, a number of groups are working on gene therapies to address harmful huntingtin gene variants; Huntington's disease - and most other inherited diseases - will vanish from the wealthier parts of the world over the next few decades).
This approach to killing cancerous cells is noteworthy because it appears to be non-specific, reliably attacking many different types of cancer. The only way to make earnest progress in bringing cancer under control is for the research community to focus on treatments that can be applied to many different cancers - or, for preference, to all cancers - with minimal cost of adjustment by cancer type. There are hundreds of types of cancer, and attempting to produce therapies specialized to the molecular peculiarities of a specific type is too inefficient. Too much time and funding has been poured into such approaches, and both of those resources are limited. That is not the way forward. The future of the field of cancer therapeutics lies in treatments that can be applied as-is to defeat near any type of cancer. So we should watch for promising examples such as the research here.
Huntington's disease provides new cancer weapon
Patients with Huntington's disease, a fatal genetic illness that causes the breakdown of nerve cells in the brain, have up to 80 percent less cancer than the general population. Huntington's is caused by an over abundance of a certain type of repeating RNA sequences in one gene, huntingtin, present in every cell. The defect that causes the disease also is highly toxic to tumor cells. These repeating sequences - in the form of so-called small interfering RNAs (siRNA) - attack genes in the cell that are critical for survival. Nerve cells in the brain are vulnerable to this form of cell death, however, cancer cells appear to be much more susceptible.
"This molecule is a super assassin against all tumor cells. We've never seen anything this powerful." To test the super assassin molecule in a treatment situation, researchers delivered the molecule in nanoparticles to mice with human ovarian cancer. The treatment significantly reduced the tumor growth with no toxicity to the mice. Importantly, the tumors did not develop resistance to this form of cancer treatment. The molecule was also used to treat human and mouse ovarian, breast, prostate, liver, brain, lung, skin, and colon cancer cell lines. The molecule killed all cancer cells in both species.
Earlier research had identified an ancient kill-switch present in all cells that destroys cancer. "I thought maybe there is a situation where this kill switch is overactive in certain people, and where it could cause loss of tissues. These patients would not only have a disease with an RNA component, but they also had to have less cancer." The researchers started searching for diseases that have a lower rate of cancer and had a suspected contribution of RNA to disease pathology. Huntington's was the most prominent. When they looked at the repeating sequences in huntingtin, the gene that causes the disease, she saw a similar composition to the earlier kill switch. Both were rich in the C and G nucleotides (molecules that form the building blocks of DNA and RNA). "Toxicity goes together with C and G richness. Those similarities triggered our curiosity. We believe a short-term treatment cancer therapy for a few weeks might be possible, where we could treat a patient to kill the cancer cells without causing the neurological issues that Huntington's patients suffer from."
Small interfering RNAs based on huntingtin trinucleotide repeats are highly toxic to cancer cells
Trinucleotide repeat (TNR) expansions in the genome cause a number of degenerative diseases. A prominent TNR expansion involves the triplet CAG in the huntingtin (HTT) gene responsible for Huntington's disease (HD). Pathology is caused by protein and RNA generated from the TNR regions including small siRNA-sized repeat fragments. An inverse correlation between the length of the repeats in HTT and cancer incidence has been reported for HD patients.
We now show that siRNAs based on the CAG TNR are toxic to cancer cells by targeting genes that contain long reverse complementary TNRs in their open reading frames. Of the 60 siRNAs based on the different TNRs, the six members in the CAG/CUG family of related TNRs are the most toxic to both human and mouse cancer cells. siCAG/CUG TNR-based siRNAs induce cell death in vitro in all tested cancer cell lines and slow down tumor growth in a preclinical mouse model of ovarian cancer with no signs of toxicity to the mice. We propose to explore TNR-based siRNAs as a novel form of anticancer reagents.
Greater Activity Slows the Progression of Age-Related Neurodegeneration
Here I'll point out two papers, one looking at exercise and the aging of grey matter in the brain, the other looking at exercise and the aging of white matter in the brain. It is well known that cardiovascular health is linked to cognitive health. An entire category of neurodegenerative disease is related to the age-related failure of the cardiovascular system to remain intact and supply adequate nutrients to the brain. A sizable portion of cognitive decline is linked to incidences of rupture of tiny blood vessels in the brain, each killing a comparatively small number of cells, but over the years that damage adds up. Further, the cellular biochemistry of the brain is kept separate from the body by the blood brain barrier, a layer of cells that lines the blood vessels of the brain. As blood vessels age, that barrier breaks down, allowing molecules present in the rest of the body to leak into the brain, producing disruption and damage. All in all, the quality of blood vessels matters greatly, just as much as the ability of the heart to pump enough blood to the energy-hungry brain. Scores of studies provide evidence to support a strong link between the cardiovascular system and the brain, with data at every layer of scientific investigation, from epidemiology to physiology to cellular biochemistry.
Since true, actual, working rejuvenation therapies are still very new and limited in scope, the way in which researchers presently observe the effects of cardiovascular health on the aging of the brain is by comparing people with different levels of fitness. Exercise modestly slows the pace at which the corrosive damage of aging harms the function and integrity of the vascular system and the heart, though animal studies suggest that exercise, while beneficial for long-term health, doesn't greatly extend life span. A sizable fraction of declines in measures of cardiovascular function across the middle of life results from a reduction in exercise rather than the intrinsic processes of damage that come to dominate the progression of aging in late life. Yet even in late life, undertaking physical exercise is beneficial - the cell and tissue damage of aging may be the dominant factor in reduced health and increased dysfunction, but exercise still helps to a degree that makes it worth the effort.
Ultimately, we should look at the data from the two studies noted here, and from the many other similar studies carried out over the years, and think: "if a modest positive impact on the biochemistry of the vascular system has this effect, how much better would it be to repair the underlying damage that causes aging?" The decline of the physical structure of the brain - and the mind it supports - will one day be prevented through the advent of rejuvenation therapies after the SENS model: repairing the root causes of aging, the cell and tissue damage that results in loss of function and catastrophic failure of organs and other systems in the body. A world absent aging is something to strive for, and the differences in aging of individuals that we observe today are just a tiny fraction of what will become possible through new medical science in the years ahead.
Poor fitness linked to weaker brain fiber, higher dementia risk
A new study from suggests that the lower the fitness level, the faster the deterioration of vital nerve fibers in the brain. This deterioration results in cognitive decline, including memory issues characteristic of dementia patients. The study published focused on a type of brain tissue called white matter, which is comprised of millions of bundles of nerve fibers used by neurons to communicate across the brain. Researchers enrolled older patients at high risk to develop Alzheimer's disease who have early signs of memory loss, or mild cognitive impairment (MCI). The researchers determined that lower fitness levels were associated with weaker white matter, which in turn correlated with lower brain function.
Unlike previous studies that relied on study participants to assess their own fitness, the new research objectively measured cardiorespiratory fitness with a scientific formula called maximal oxygen uptake. Scientists also used brain imaging to measure the functionality of each patient's white matter. Patients were then given memory and other cognitive tests to measure brain function, allowing scientists to establish strong correlations between exercise, brain health, and cognition.
The study leaves plenty of unanswered questions about how fitness and Alzheimer's disease are intertwined. For instance, what fitness level is needed to notably reduce the risk of dementia? Is it too late to intervene when patients begin showing symptoms? Some of these topics are already being researched through a five-year national clinical trial. The trial, which includes six medical centers across the country, aims to determine whether regular aerobic exercise and taking specific medications to reduce high blood pressure and cholesterol levels can help preserve brain function. It involves more than 600 older adults at high risk to develop Alzheimer's disease.
Everyday Activities Associated with More Gray Matter in Brains of Older Adults
The gray matter in the brain includes regions responsible for controlling muscle movement, experiencing the senses, thinking and feeling, memory and speech and more. The volume of gray matter is a measure of brain health, but the amount of gray matter in the brain often begins to decrease in late adulthood, even before symptoms of cognitive dysfunction appear. "More gray matter is associated with better cognitive function, while decreases in gray matter are associated with Alzheimer's disease and other related dementias."
The study measured the levels of physical activity by 262 older adults in the Memory and Aging Project, an ongoing epidemiological cohort study. Participants in the lifestyle study wore a noninvasive device called an accelerometer continuously for seven to 10 days. The goal was to accurately measure the frequency, duration, and intensity of a participant's activities over that time. The use of accelerometers was only one of the ways in which this analysis differed from some other investigations of the health of older people. Most research that explores the effects of exercise relies on questionnaires. The real problem with questionnaires, though, is that "sometimes, we get really inaccurate reports of activity."
Another departure from some other investigations was the opportunity to assess the effects of exercise on individuals older than 80. In fact, the mean age in this study was 81 years, compared with 70 for other studies used as a reference. The study compared gray matter volumes as seen in participants' MRIs with readings from the accelerometers and other data, which all were obtained during the same year. Analysis found the association between participants' actual physical activity and gray matter volumes remained after further controlling for age, gender, education levels, body mass index and symptoms of depression, all of which are associated with lower levels of gray matter in the brain.
Development of Exosome Delivery as a Regenerative Therapy Continues Apace
If many stem cell therapies produce their benefits largely through the signaling generated by the transplanted cells, in a brief window of time before these cells die, unable to integrate into the local tissue, then why not skip the cells entirely and just deliver the signals? This is made an easier prospect by the fact that a great deal of cell to cell signaling takes the form of extracellular vesicles such as exosomes, tiny membrane-bound packages of various molecules. Thus researchers don't need to completely map and understand the entire set of signals used in order to recreate most of the signaling effects of stem cells. Given a cultured stem cell population, the exosomes that the cells produce can be harvested and then employed as a therapy. Further down the line, after the mapping and the understanding is complete, then manufacture of exosomes from scratch will probably become the standard approach. For now, cells are required for that much, at least.
The research noted here is an illustrative example of present work on exosome-based regenerative therapies; a fair number of research groups are working towards treatments for various tissue types and age-related conditions. As a class, exosome therapies seem about as promising as early stem cell therapies, based on the results to date in animal models, and are arguably more easily controlled and managed than cells. Just considering the logistics of manufacture and storage, the costs should be significantly lower. Scientists are working their way up from mice to larger animal models, and the first human clinical trials for various conditions are on the near horizon. It is a significant shift in focus for the stem cell research community, and it will be interesting to see where this leads in the next few years.
Stem-cell based stroke treatment repairs brain tissue
A team of researchers and ArunA Biomedical, a startup company, have developed a new treatment for stroke that reduces brain damage and accelerates the brain's natural healing tendencies in animal models. The research team created a treatment called AB126 using extracellular vesicles (EV), fluid-filled structures known as exosomes, which are generated from human neural stem cells. Fully able to cloak itself within the bloodstream, this type of regenerative EV therapy appears to be the most promising in overcoming the limitations of many cell therapies - with the ability for exosomes to carry and deliver multiple doses - as well as the ability to store and administer treatment. Small in size, the tiny tubular shape of an exosome allows EV therapy to cross barriers that cells cannot.
Following the administration of AB126, the researchers used MRI scans to measure brain atrophy rates in preclinical, age-matched stroke models, which showed an approximately 35 percent decrease in the size of injury and 50 percent reduction in brain tissue loss - something not observed acutely in previous studies of exosome treatment for stroke. Outside of rodents, the results were replicated using a porcine model of stroke. Based on these pre-clinical results, ArunA Biomedical plans to begin human studies in 2019. The company has plans to expand this initiative beyond stroke for preclinical studies in epilepsy, traumatic brain and spinal cord injuries later this year.
Human Neural Stem Cell Extracellular Vesicles Improve Tissue and Functional Recovery in the Murine Thromboembolic Stroke Model
Over 700 drugs have failed in stroke clinical trials, an unprecedented rate thought to be attributed in part to limited and isolated testing often solely in "young" rodent models and focusing on a single secondary injury mechanism. Here, extracellular vesicles (EVs), nanometer-sized cell signaling particles, were tested in a mouse thromboembolic (TE) stroke model. Neural stem cell (NSC) and mesenchymal stem cell (MSC) EVs derived from the same pluripotent stem cell (PSC) line were evaluated for changes in infarct volume as well as sensorimotor function.
NSC EVs improved cellular, tissue, and functional outcomes in middle-aged rodents, whereas MSC EVs were less effective. Acute differences in lesion volume following NSC EV treatment were corroborated by MRI in 18-month-old aged rodents. NSC EV treatment has a positive effect on motor function in the aged rodent as indicated by beam walk, instances of foot faults, and strength evaluated by hanging wire test. Increased time with a novel object also indicated that NSC EVs improved episodic memory formation in the rodent. The therapeutic effect of NSC EVs appears to be mediated by altering the systemic immune response. These data strongly support further preclinical development of a NSC EV-based stroke therapy and warrant their testing in combination with FDA-approved stroke therapies.
HDAC3 Knockout Mice Exhibit Greatly Reduced Loss of Memory Function with Age
Work on the decline of memory formation with aging was presented at a recent conference and is doing the rounds in the press. The core of it was published and presented last year, so the overall topic isn't particularly new, but I didn't notice it at the time. The scientific group in question is interested in the role of histone deacetylases (HDACs) in memory. This is a long-running thread of research. Looking back in the Fight Aging! archives, inhibition of HDACs in the context of improved neural function was mentioned in 2012, and a trail of publications exists prior and since.
The processes of acetylation and deacetylation of histones are important to gene regulation, a core part of the machinery that controls the packaged state of nuclear DNA in the cell nucleus. Genes must be accessible to the machinery of the cell in order to begin transcription, the first step in the complex operations involved in constructing proteins from their genetic blueprints. Whether a specific gene is accessible or inaccessible is determined by the state of various different histones, among other mechanisms. What does this have to do with memory? The formation of memory requires reliable access to certain genes, and the production of their proteins, but it is apparently the case that access becomes less available with age. One of the histones, HDAC3, becomes overactive, keeping DNA more tightly packaged than was the case in younger individuals.
Researchers have now demonstrated that mice lacking HDAC3 do not seem to suffer much in the way of side-effects, and also do not suffer age-related loss of memory - though this effect differs in detail for the various types of memory tested to date. It is worth considering that these mechanisms are a snapshot of some middle layer of the long chain of cause and effect that stretches between the root causes of aging and the ultimate consequences of age-related disease and organ failure. Why does HDAC3 become more active in older individuals? What underlying process is taking place, and what other harms is that process causing? Leaping to interventions has a way of short-cutting the conversation about deeper causes that should be taking place, especially when the interventions are comparatively easy to implement - there are plenty of approaches to HDAC3 inhibition that might be taken at low cost and in the near future, even given the need to bypass the blood-brain barrier. But what is shut out by taking that path as the primary focus?
Research cracks code to restoring memory creation in older or damaged brains
Aging or impaired brains can once again form lasting memories if an enzyme that applies the brakes too hard on a key gene is lifted. "What we've discovered is that if we free up that DNA again, now the aging brain can form long-term memories normally. In order to form a long-term memory, you have to turn specific genes on. In most young brains, that happens easily, but as we get older and our brain gets older, we have trouble with that." That's because the 6 feet of DNA spooled tightly into every cell in our bodies has a harder time releasing itself as needed. Like many body parts, "it's no longer as flexible as it used to be." The stiffness in this case is due to a molecular brake pad called histone deacetylase 3, or HDAC3, that has become "overeager" in the aged brain and is compacting the material too hard, blocking the release of a gene called Period1. Removing HDAC3 restores flexibility and allows internal cell machinery to access Period1 to begin forming new memories.
Researchers had previously theorized that the loss of transcription and encoding functions in older brains was due to deteriorating core circadian clocks. But it was found that the ability to create lasting memories was linked to a different process - the overly aggressive enzyme blocking the release of Period1 - in the same hippocampus region of the brain. That's potentially good news for developing treatments. "New drugs targeting HDAC3 could provide an exciting avenue to allow older people to improve memory formation."
NIH Summit Examines What Makes a Healthy Aging Brain
Histone deacetylase HDAC3 is expressed predominantly in the brain and represses gene expression. Researchers knocked out the HDAC3 gene in the dorsal hippocampi of mice, then trained them at young or old ages on a novel object-location task. Young mice performed equally well, regardless of whether they expressed HDAC3. In older animals the story was different. Wild-type animals became forgetful, whereas HDAC3-deficient mice remembered just as well as did young mice. This suggests HDAC3 hampers memory as mice age. In keeping with this, long-term potentiation weakened with age in wild-type but not HDAC3 knockout mice. Since knocking out HDAC3 restored hippocampal expression of Period1 (Per1), a master regulator of the cellular circadian clock, HDAC3 might function to help regulate circadian genes in the hippocampus.
Distinct roles for the deacetylase domain of HDAC3 in the hippocampus and medial prefrontal cortex in the formation and extinction of memory
Histone deacetylases (HDACs) are chromatin modifying enzymes that have been implicated as powerful negative regulators of memory processes. HDAC3 has been shown to play a pivotal role in long-term memory for object location as well as the extinction of cocaine-associated memory, but it is unclear whether this function depends on the deacetylase domain of HDAC3. Here, we tested whether the deacetylase domain of HDAC3 has a role in object location memory formation as well as the formation and extinction of cocaine-associated memories. Using a deacetylase-dead point mutant of HDAC3, we found that selectively blocking HDAC3 deacetylase activity in the dorsal hippocampus enhanced long-term memory for object location, but had no effect on the formation of cocaine-associated memory.
When this same point mutant virus of HDAC3 was infused into the prelimbic cortex, it failed to affect cocaine-associated memory formation. With regards to extinction, impairing the HDAC3 deacetylase domain in the infralimbic cortex had no effect on extinction, but a facilitated extinction effect was observed when the point mutant virus was delivered to the dorsal hippocampus. These results suggest that the deacetylase domain of HDAC3 plays a selective role in specific brain regions underlying long-term memory formation of object location as well as cocaine-associated memory formation and extinction.
There are Many Possible Paths to Immunotherapy for Senescent Cell Destruction
Rising numbers of senescent cells are one of the root causes of aging, a process that arises from the normal operation of youthful metabolism, yet results in accumulated damage and failure over time. Senescent cells generate signaling that degrades tissue function, breaks down and remodels tissue structure, spurs chronic inflammation, and alters the behavior of surrounding cells for the worse. Evidence shows their presence to be a contributing cause of a range of common fatal age-related conditions. In a youthful body, near all cells that become senescent and fail to self-destruct as a result are promptly eliminated by the immune system. In an aged body, the immune system is worn and degraded; as a consequence many more senescent cells survive to linger. We are machines of interacting, dependent parts. Damage and failure in one component speeds the onset of damage and decline in others. The age-related failure of the immune system is an important part of the acceleration of functional decline in later life.
Much of the current work on methods to selectively destroy senescent cells, and thus produce a narrow form of rejuvenation, is focused on pharmaceuticals. Given that the immune system is already capable of destroying senescent cells in the normal course of events, why not immunotherapies, however? I'm only aware of the one company working along those lines, SIWA Therapeutics, and I believe that their immunotherapy approach doesn't interact at all with the natural immunosurveillance of senescent cells. Is it possible to do better than this, to build on the existing evolved mechanisms to induce high levels of clearance even in old and damaged immune systems? Alternatively, could the general methods of immune rejuvenation currently under consideration (such as restoring the thymus, destroying malfunctioning or overspecialized immune cells, or inducing greater stem cell production of immune cells) result in youthful levels of senescent cell destruction?
Whilst there is currently little understanding concerning the mechanisms governing macrophage mediated recognition of senescent cells, the processes are probably not specific to senescent cells. Rather, the more characterised molecular mechanisms associated with macrophage recognition during cancer immunosurveillance and apoptotic cell clearance may also be pertinent for senescence surveillance. Apoptotic cells have been shown to preferentially express specific cell surface antigens which can be recognised by naturally occurring antibodies (IgMs) that enable phagocytosis by macrophages. As such, it can be speculated that senescent cells may also express specific cell surface antigens which would not only provide insights into the mechanisms mediating immune clearance, but would also provide a means to specifically identify senescent cells in tissues.
Surface expression of CD47 acts as a "don't eat me" signal, sending inhibitory signals through SIRPα, a receptor expressed on the surface of macrophage, ensuring that healthy cells are not inappropriately phagocytosed. Therefore, the downregulation of CD47 would be required for macrophages to target damaged "self" cells. One study has demonstrated that induction of tumour cell senescence via c-Myc inactivation leads to the downregulation of CD47 which consequently promoted tumour regression. Whether CD47 downregulation in this instance is a specific response to c-Myc inactivation or activation of the senescence program is unclear. It would make biological sense to downregulate CD47 during cell senescence to enable removal of damaged "self" cells, but further research is required.
Immunotherapeutic strategies already in development for combating cancer may one day be repurposed for targeting senescent cells for the alleviation of age-related diseases. In addition, identifying further molecular changes associated with senescent cells, especially cell-type specific alterations, would be advantageous for developing therapeutic approaches for targeting senescent cells. Since senescent cells can also be beneficial in the short term, the elimination of acute senescent cells could be problematic. Therefore, the identification of therapeutic targets specific to chronic senescence which are absent in acute senescent cells would be highly desirable.
One of the mechanisms by which natural killer (NK) cells specifically recognise and kill senescent cells is via the surface expression of NKG2D ligands. Since many tumour cells also express NKG2D ligands, such ligands have been suggested to be a useful target for immunotherapeutic approaches in cancer, and so could be adapted for senescent cell clearance. For example, the use of engineered immune cells such as chimeric antigen receptor (CAR) T cells to target specific molecules on cancer cells has great potential as an anti-cancer therapy. As such, it may be possible to target senescent cells by engineering T cells to express a NKG2D CAR which recognise NKG2D ligands on the surface of senescent cells.
An adaption of cancer vaccines could also be considered for boosting immune clearance of senescent cells. Although a universal biomarker of cell senescence has not been identified, the exposure of senescent cell membranes to immune cells may evoke an immune response to antigens not yet identified. In one approach, senescence vaccines would involve the isolation of senescence specific antigens (SSAs) which are then exposed to dendritic cells, professional antigen presenting cells. In response to SSA uptake, dendritic cells process and express these antigens on their cell surface which can then be recognised by T cells. T cell interaction with these antigens promotes T cell activation, differentiation, and ultimately killing of target cells.
Jagged-1 as a More Selective Signal to Spur Bone Regrowth
Researchers here report on a more selective way to trigger the accelerated or enhanced regeneration of bone tissue, delivering jagged-1 to injuries rather than the bone morphogenetic proteins (BMPs) that have been used in the past. It appears to cause fewer issues related to inappropriate excess bone growth, as it influences mechanisms that are more closely associated with the process of regeneration in response to damage. The delivery of signals rather than cells or pharmaceuticals to produce regeneration will be a growing theme in the years ahead, and the approaches will only grow in sophistication and degree of control. The advance here is a small step in the grand scheme of the possible and the plausible; it will be interesting to see how this part of the industry evolves over the next few decades.
When a patient breaks a bone, there's a possibility the fracture won't heal properly or quickly, and use of a restorative tactic known as bone morphogenetic proteins, or BMPs, is increasingly less likely. Designed to promote spinal fusion and bone repair more than a decade ago, these molecules can overperform, causing excessive or misdirected bone growth, studies have shown. But because bone-healing biological research has often been limited, few other options exist. "Novel therapies have gone underdeveloped because of this assumption that bones heal without problem. The reality is there's a huge number of fractures that occur each year that don't heal very well."
The divide recently inspired scientists to examine a new therapeutic approach. Their method: deliver additional Jagged-1 - a potent osteoinductive protein known to activate the Notch signaling pathway that regulates bone healing - at the spot of a bone injury. "We've hypothesized for many years that by binding the Jagged-1 to a biomaterial and delivering it to a bone injury site, we could enhance healing." The results affirm that hunch: Rodents that received Jagged-1, applied via wet collagen sponge, saw improvements to skull and femoral bone injuries. Rodents treated with BMPs, by contrast, also benefited but developed the same problematic bone hypertrophy associated with human use of those proteins. Those findings suggest that the former therapy could one day benefit people.
It's not fully known why some bones don't heal the way they should - nor do scientists know whether a genetic component plays a role. What researchers have studied for years, meanwhile, is the capacity of the Jagged-1 ligand to promote bone-forming cells. The signaling is unique because this particular ligand typically binds to a delivery cell to activate bone healing in an adjacent cell - a vital trait to help ensure that a supplemental Jagged-1 dose, administered at the spot of injury, stays in place (and on task) to carry out its intended function. As a result, bone will only form where bone is supposed to form. BMPs, by comparison, are soluble, so they can migrate from the site of delivery and settle elsewhere in the body, triggering other cells that aren't supposed to form bone.
Inhibition of Wnt Signaling as a Treatment for Osteoarthritis
Researchers here find that inhibition of Wnt signaling can improve the state of cartilage and joint function in a mouse model of osteoathritis. Wnt and its closely related proteins are a complex topic, but the short version is that they are involved in the regulation of growth, regeneration, and embryonic development. They are also significant in cancer, as well as in other, less dramatic ways in which regeneration can run wild or fail, producing fibrosis and functional problems rather than a useful restoration of tissue. Numerous research groups are investigating ways in which Wnt signaling can be adjusted to produce beneficial effects such as enhanced healing, or a reduction in function damage to tissues following injury. This is a representative example.
Wnt family proteins are a class of morphogens associated with embryonic skeletal formation, tissue repair, fibrosis, and joint homeostasis. Wnts regulate multiple signaling cascades, including the β-catenin-dependent (canonical) pathway. The Wnt/β-catenin pathway, which is typically quiescent in many adult organs, is activated in response to injury. Its role in tissue repair and regeneration is complex and incompletely understood, although an increasing body of data suggests that its activation augments fibrotic repair. Our group recently published studies demonstrating that brief therapeutic Wnt inhibition following both full thickness cutaneous or ischemic cardiac injury resulted in improved regenerative repair with less fibrosis.
Osteoarthritis (OA) is a degenerative joint disease typically characterized by articular cartilage degeneration, bone remodeling, and osteophytosis as well as fibrosis and hyperplasia of the synovial membrane. In OA pathogenesis, activation of canonical Wnt signaling is observed in both articular cartilage and synovium following injury, with increased expression of both Wnt ligands and target genes. Induced overexpression of β-catenin within mature chondrocytes has been shown to exacerbate cartilage degeneration, chondrocyte hypertrophy, and expression of matrix proteases. However, significant or complete ablation of β-catenin in chondrocytes also results in the deleterious effect of chondrocyte apoptosis. Moreover, increased canonical Wnt expression in the synovium resulted in strong induction of cartilage pathology. Although the sum of the published data using genetic modulation of Wnt suggests deleterious effects of Wnt on OA pathogenesis, there is little known about the therapeutic effect of inhibiting the Wnt pathway within the context of disease.
Multiple Wnt inhibitory therapeutics are being investigated at various stages of clinical development due to Wnt pathway activation, not only in fibrotic diseases, but also cancers. We sought to study Wnt signaling and the effect of local therapeutic Wnt inhibition in a murine model of traumatic OA caused by destabilization of the medial meniscus (DMM). To assess the effect of Wnt inhibition on OA progression, we injected the small-molecule Wnt inhibitor, XAV-939, in the intra-articular space. We further studied the cell-specific effects of Wnt modulation in vitro using primary human synovial fibroblasts and chondrocytes in order to understand the cellular basis for the disease-modifying effects.
Our study demonstrated that traumatic joint injury through DMM surgery induced robust activation of canonical Wnt signaling, most striking in the synovium, and this upregulation was downregulated with intermittent (every 10 days), local (intra-articular) treatment using a small-molecule Wnt inhibitor, resulting in amelioration of both synovitis and cartilage loss. An important advantage of identifying therapeutic benefits with local administration is avoiding systemic effects of Wnt inhibition on Wnt-dependent tissues, such as intestinal stem cell/intestinal turnover, hematopoiesis, and bone density. The use of small-molecule Wnt inhibitors bypasses the restrictions of genetic approaches by targeting the entire injury milieu, rather than a particular cell type, as is the case in genetic models. Additionally, since different cell types exhibit different levels of Wnt activation and sensitivity to Wnt inhibition, one can also fine-tune the degree and timing of Wnt inhibition using dosing strategies that are calibrated.
Evidence for Tau Accumulation and Failing Cerebrospinal Fluid Clearance to be the Starting Point for Alzheimer's Disease
Alzheimer's disease might be considered as the consequence of the related, interacting buildup of two primary forms of metabolic waste in the brain, tau and amyloid-β. Either, independently, can cause neurodegeneration, but they have a complicated relationship with one another in which the presence of both makes the pathology worse. Which comes first? There is evidence to suggest that amyloid aggregation leads to tau aggregation, and there is also evidence for things to be the other way around, such as that presented in the research materials here.
Both of these options could be the case, in that either tau or amyloid-β produces disruption that can accelerate aggregation of the other. Or it may be that a third mechanism, such as loss of effective drainage of cerebrospinal fluid, causes aggregation of both, and interactions between the two are less important to the amount present and more important to the damage done. Alzheimer's is a very complex area of study. Until therapies start to make some inroads into improving the condition, thereby quantifying some of the mechanisms and their effects, it is likely that greater understanding of the details of the progression of the condition, and the degree to which different aspects contribute to cognitive decline, will be slow to arrive.
In the commonly held definition of Alzheimer's disease, one type of amyloid-beta (Aβ42) starts to form clumps between nerve cells, injuring them. Worsening injury is then marked by the release and toxic buildup of a second protein called tau. Together, changes in Aβ42 and tau levels represent the standard international measure of a patient's risk for future cognitive decline. A new study found that the build-up in the brain of amyloid beta cannot be the sole trigger of subsequent nerve damage because many relatively younger people who develop disease later do not show signs of the buildup. "Once you stop assuming that the starting point of Alzheimer disease is marked by the buildup of Aβ42 in brain cells, a different picture emerges. By recognizing an earlier disease phase, we may be able to start treating earlier and in tailored ways based on a better understanding of disease biology."
For many years, neuroscientists have sought to predict AD risk by tracking protein levels in the cerebrospinal fluid (CSF) that fills the spaces around brain tissue, and which can be sampled by lumbar puncture as part of a spinal tap. In 1999, researchers started collecting clinical and CSF protein level data from healthy normal subjects every two years. Combining this database with two others, the current study is the largest of its kind to date, including roughly 700 patients. The study found that the best predictor of future AD risk was not, as currently thought, decreased CSF Aβ42 levels with elevated tau. Elevated CSF Aβ42 levels were also found to confer future AD risk.
The results add to the evidence that an increase in CSF tau over a lifetime may be the more relevant, early feature of AD than a drop in CSF Aβ42 (taken as evidence of a buildup in brain cells). While the actual mechanism behind Alzheimer's disease and the trajectory of Aβ42 and tau levels remains obscure, the results provide evidence in support of the "clearance theory." It holds that the pumping of the heart, along with constriction of blood vessels, pushes cerebrospinal fluid through the spaces between brain cells, clearing potentially toxic proteins into the bloodstream. Mid-life cardiovascular changes that bring on heart failure and hypertension may lessen the CSF flow needed to clear tau, and perhaps disease-causing proteins yet to be identified.
Aside from Aβ42 which is readily deposited into the brain, the team found that CSF levels of two other common forms of amyloid beta that are less able to build up, Aβ38 and Aβ40, increase in proportion to rising tau throughout the normal older adult lifespan, even after CSF Aβ42 starts to decrease. This is further evidence of a decline in clearance with age. "Future CSF studies need to follow normal subjects, starting at age 40, for decades to get an unbiased look at the trajectory of CSF proteins and the likelihood of developing cognitive impairment decades later."
DNA Machinery that can Sabotage the Blood Supply of Tumors
Researchers have been building simple molecular machines out of DNA for some years now. This approach to molecular machinery is well suited to applications that involve conditional activation based on the proteins present in the surrounding environment; a lot of the necessary functional parts already exist in DNA and just have to be assembled in the right way. The Oisin Biotechnologies cell-killing technology is a smaller example of the type than the approach here, in which sizable DNA containers are constructed. They carry a cargo that will disrupt local blood flow, and are triggered into opening by cancerous cell surface proteins, thereby sabotaging the nutrient supply to tumors without harming other tissues. It is all quite clever and quite mechanical.
DNA nanorobots that travel the bloodstream, find tumors, and dispense a protein that causes blood clotting can trigger the death of cancer cells in mice. The researchers started with the goal of finding a path to design nanorobots that can be applied to treatment of cancer in humans. They first generated a self-assembling, rectangular, DNA-origami sheet to which they linked thrombin, an enzyme responsible for blood clotting. Then, they used DNA fasteners to join the long edges of the rectangle, resulting in a tubular nanorobot with thrombin on the inside. The authors designed the fasteners to dissociate when they bind nucleolin - a protein specific to the surface of tumor blood-vessel cells - at which point, the tube opens and exposes its cargo.
The scientists next injected the nanorobots intravenously into nude mice with human breast cancer tumors. The robots grabbed onto vascular cells at tumor sites and caused extensive blood clots in the tumors' vessels within 48 hours, but did not cause clotting elsewhere in the animals' bodies. These blood clots led to tumor-cell necrosis, resulting in smaller tumors and a better chance for survival compared to control mice. The team also found that nanorobot treatment increased survival and led to smaller tumors in a mouse model of melanoma, and in mice with xenografts of human ovarian cancer cells. The next step is to investigate any damage - such as undetected clots or immune-system responses - in the host organism, as well as to determine how much thrombin is actually delivered at the tumor sites. The authors showed in the study that the nanorobots didn't cause clotting in major tissues in miniature pigs, which satisfies some safety concerns, but more work is needed.
Liver Organoids Come Ever Closer to Natural Liver Tissue
Tissue engineers continue to improve the quality of their creations. The liver is one of the easier organs to work with, given the much greater regenerative capacity of liver cells. It is, nonetheless, an organ with a complex small-scale internal structure, and getting that right is a process of incremental advances. The tissues created via present state of the art approaches are usually still small, lacking the capillary networks needed to support tissue larger than a few millimeters in depth. The only way to provide those networks is to use decellularized donor organs, the cells destroyed, and the organ thus reduced to the scaffold of the extracellular matrix, complete with blood vessels and chemical cues. If the starting point is a cell sample without such a scaffold, blood vessels remain a challenge. By the time that challenge is reliably solved, however, it seems likely that the research community will be ready to build fairly accurate replicas of at least a couple of different real organs, even without donor tissue to provide a scaffold.
The creation of living mini-organs is a relatively new area of science with the potential to replace animal models that are not always accurate. The liver organoids, made with human cells, are less than one-third inch in diameter. While scientists have already created liver organoids to screen new drugs for liver toxicity, the livers developed in this research represent several "firsts" in the quest to build a functional model of human liver development. To make the organoids, scientists allow fetal liver progenitor cells, an immature cell that is destined to become a specialized liver cell, to self-assemble on a small disc. The discs are made of ferret liver that has been processed to remove all of the animal's cells. The resulting organoids, which assemble within two to three weeks, are the first to model actual human liver development.
The research is significant in two ways. First, the scientists showed that these organoids generated hepatocytes, the main functional cells of the liver. This achievement represents a milestone in work to create truly functional bioengineered liver tissue for transplantation into patients. Second, while other scientists have shown that lab-grown livers can generate bile ducts, this is the first study to show the stepwise maturation of bile ducts exactly as can be observed in the human fetal liver. Bile ducts carry bile, a fluid that is secreted by the liver and collected in the gall bladder to digest fats.
BACE1 Deletion Eliminates Amyloid Deposits in a Mouse Model of Alzheimer's Disease
BACE1 is one of the proteins involved in early stages of the production of amyloid-β, a form of metabolic waste that aggregates into solid deposits in the aging brain, and is characteristic of Alzheimer's disease. Inhibition of BACE1 so as to reduce levels of amyloid-β is a strategy pursued by a number of research groups, though it has to be said that disenchantment with the years of failure in the dominant strategy of clearing amyloid-β appears to be reaching a tipping point these days. While it is clear that amyloid-β is harmful, it may not be the most effective point of intervention. Or perhaps earlier efforts to remove amyloid-β were not going about it in the right way, and different approaches would work. It is very hard to say, as the aging brain is a complex mix of many different, interacting forms of damage and dysfunction.
The research here can be read as strong support for the BACE1 inhibition approach to Alzheimer's disease, given the size of the effect, though the same questions remain as in any other success in reducing amyloid from the mouse models of Alzheimer's disease. If none of the others successfully translated to human therapies, and failed in trials, how confident or hopeful should we be here? A great many people are asking themselves exactly that these days, which is why we can observe the growth of support for the impaired cerebrospinal fluid drainage model of Alzheimer's disease, or the microbial model of the condition, and a range of further theorizing on different causes and different priorities in research and development.
With a large swath of the population entering its senior years, the number of Alzheimer's disease (AD) cases are expected to skyrocket, placing a tremendous burden on the healthcare system. Yet, a glimmer of hope may have just emerged as investigators report that gradually depleting an enzyme called BACE1 completely reverses the formation of amyloid plaques in the brains of mice with AD, subsequently improving the animals' cognitive function. "To our knowledge, this is the first observation of such a dramatic reversal of amyloid deposition in any study of AD mouse models."
One of the earliest events in AD is an abnormal buildup of the beta-amyloid (Aß) peptide, which can form large, amyloid plaques in the brain and disrupt the function of neuronal synapses. Also known as beta-secretase, BACE1 helps produce the Aß peptide by cleaving the amyloid precursor protein (APP). Drugs that inhibit BACE1 are therefore being developed as potential AD treatments but, because BACE1 controls many important processes by cleaving proteins other than APP, these drugs could have serious side effects.
Mice completely lacking BACE1 suffer severe neurodevelopmental defects. To investigate whether inhibiting BACE1 in adults might be less harmful, the research team generated mice that gradually lose this enzyme as they grow older. These mice developed normally and appeared to remain perfectly healthy over time. "To mimic BACE1 inhibition in adults, we generated BACE1 conditional knockout (BACE1fl/fl) mice to induce deletion of BACE1 after passing early developmental stages. Strikingly, sequential and increased deletion of BACE1 in an adult AD mouse model was capable of completely reversing amyloid deposition. This reversal in amyloid deposition also resulted in significant improvement in gliosis and neuritic dystrophy. Moreover, synaptic functions, as determined by long-term potentiation and contextual fear conditioning experiments, were significantly improved, correlating with the reversal of amyloid plaques."
Remarkably, the loss of BACE1 also improved the learning and memory of mice with AD. However, when the researchers made electrophysiological recordings of neurons from these animals, they found that depletion of BACE1 only partially restored synaptic function, suggesting that BACE1 may be required for optimal synaptic activity and cognition.
Macrophages Make a Significant Contribution to Heart Failure
Researchers here implicate the immune cells known as macrophages in the progression of a particularly problematic form of heart failure. Macrophages are very important to the processes of tissue maintenance and regeneration, but they have several different characteristic states, or polarizations: one is inflammatory and aggressive, hindering regeneration, while the other is actively beneficial for regeneration. Researchers are finding that adjusting the proportion of these two states can be beneficial. The situation in heart failure - and a number of other age-related conditions - may well be made worse due to the balance in macrophage populations tipping away from assisting regeneration and towards chronic inflammation. In support of that view, stem cell therapies that have the primary outcome of reducing inflammation have been shown to be helpful in treating the form of heart failure examined here.
Researchers have discovered that the immune cells called macrophages contribute to a type of heart failure for which there currently is no effective treatment, heart failure with preserved ejection fraction (HFpEF). The concept of heart failure traditionally referred to a loss of the organ's pumping capacity, which is called systolic heart failure. But in HFpEF the heart retains the ability to pump or eject blood into the circulation. What is compromised is the ability of the heart muscle to relax and allow blood to flow into the left ventricle, reducing the amount of blood available to pump into the aorta. Symptoms of HFpEF are similar to those of heart failure in general, but since factors contributing to the condition are not well understood, it has been difficult to find promising therapies.
Interactions among cells within the heart - including macrophages - are essential to normal cardiac function but can also contribute to problems. For example, after the heart muscle is damaged by a heart attack, macrophages induce the cells called fibroblasts to generate the connective tissues that help reinforce damaged tissue. But excessive fibroblast activation can lead to the distortion and stiffening of tissues, further reducing cardiac function.
To explore a potential role for macrophages in HFpEF, the team examined cardiac macrophages in two mouse models that develop the sort of diastolic dysfunction - impaired relaxation of the heart muscle - that characterizes HFpEF. Those animals were found to have increased macrophage density in the left ventricle and exhibited elevated levels of a factor called IL-10, which is known to contribute to fibroblast activation. Deletion of IL-10 from cardiac macrophages in one model, in which the development of hypertension is induced, prevented the upregulation of macrophages and reduced the numbers and activation of cardiac fibroblasts. Levels of cardiac macrophages were also elevated in tissue biopsies from human patients with HFpEF, as were levels of circulating monocytes, which are precursors of macrophages.
"Not only were numbers of inflammatory cardiac macrophages increased in both the mice and in humans with HFpEF, but their characteristics and functions were also different from those in a healthy heart. Through their participation in the remodeling of heart tissue, these macrophages increase the production of extracellular matrix, which reduces diastolic relaxation. Our findings regarding the cell-specific knockout of IL-10 are the first to support the contribution of macrophages to HFpEF. Heart muscle cells and fibroblasts have been considered the major contributors to HFpEF. Our identification of the central involvement of macrophages should give us a new focus for drug development."
Bacteria Engineered to Deliver CXCL12 Accelerate Wound Healing in Mice
Researchers here report on an interesting approach used to deliver a therapeutic molecule into wounds, and thereby accelerate regeneration. They engineered a common bacterial species to produce the molecule of interest, CXCL12, which is implicated in the processes of wound healing. Those processes are an intricate dance between various types of immune cell, stem cell, senescent cell and somatic cells in the injured tissue. In recent years researchers have gained an increased understanding of the scope of involvement of immune cells known as macrophages; the participation of the immune system has turned out to be much more important to the quality and pace of regeneration than was thought a few decades ago. Macrophages can adopt different states, or polarizations. Of the two commonly observed polarizations, one is inflammatory and harmful to regeneration, while the other assists regeneration. There appears to be some potential in therapies that adjust the proportions of a macrophage population in injured tissue to favor the second type - and this is one of the goals that the researchers here aimed to achieve in their study.
During the inflammation phase of wound healing, immune cells accumulate in response to alarm signals, cytokines, and chemokines released by injured or activated cells. The chemokine CXCL12 (Stromal cell-Derived Factor 1α) is associated with beneficial effects in models of cutaneous wounds and binds CXCR4 expressed by immune cells and keratinocytes. Macrophages and neutrophils represent the major immune cell populations at the wound site, where they are essential for keeping invading microorganisms at bay and also for fueling the healing process by secreting additional chemokines, growth factors, and matrix digesting enzymes. During the course of healing, macrophages shift phenotype toward an anti-inflammatory one and subsequently promote tissue restitution. This shift is induced by macrophage phagocytosis of cell debris and by microenvironmental signals such as CXCL12.
Chronic wounds are often associated with underlying pathologic processes that increase susceptibility for acquiring wounds (e.g., peripheral neuropathies) and/or reduced healing abilities as seen in persons with arterial or venous insufficiencies. Several experimental and clinical trials have investigated the effects of local application of growth factors alone or coupled to different biomaterials on different types of chronic wounds, but with modest results so far.
This study aimed to accelerate wound healing by targeting the function of immune cells through local bioengineering of the wound microenvironment. To achieve this, a technology optimized to deliver chemokines directly to wounded skin was developed, whereby lactic acid bacteria were used as vectors. Lactobacillus reuteri bacteria were transformed with a plasmid encoding the chemokine CXCL12 previously associated with beneficial effects in models of healing and blood-flow restoration. Bacteria-produced lactic acid reduced the pH in the wound and thereby potentiated the effects of the produced CXCL12 by prolonging its bioavailability. The overall result of topical wound treatment with this on-site chemokine delivery system was strongly accelerated wound closure to an extent not reported before.
Importantly, treatment with CXCL12-delivering Lactobacilli also improved wound closure in mice with hyperglycemia or peripheral ischemia, conditions associated with chronic wounds, and in a human skin wound model. Further, initial safety studies demonstrated that the topically applied transformed bacteria exerted effects restricted to the wound, as neither bacteria nor the chemokine produced could be detected in systemic circulation.
Further Investigation of the Role of Osteopontin in Hematopoietic Stem Cell Aging
The Hematopoietic stem cell population resident in bone marrow is responsible for generating blood cells and immune cells. Like all stem cell populations, their activity alters and declines with aging. This is one of the causes of the progressive disarray of the immune system in older individuals. If we want to rejuvenate the immune system, then restoring the youthful activity of hematopoietic stem cells is one of the items on the to-do list, alongside regrowth of the thymus, and clearing out the accumulation of exhausted, senescent, and misconfigured immune cells.
The protein osteopontin appears to have a sizable role in maintaining the hematopoietic stem cell population, but levels fall in older individuals. Researchers have demonstrated, in mice, that restoring high levels osteopontin can also restore a significant degree of hematopoietic stem cell activity. This is promising because it is comparatively simple to achieve and package as a therapy, but equally it isn't addressing whatever root causes underlie this narrow view of the picture. The open access paper here continues the investigation of osteopontin in the context of hematopoietic aging in mice, adding further evidence for its relevance.
In mammalian tissues that undergo high cell turnover, such as the hematopoietic system, a small population of stem cells maintains organ regeneration throughout the animal's life span. However, the functionality of stem cells declines during aging and can contribute to aging-associated impairments in tissue regeneration. Accumulating evidence indicates that aged hematopoietic stem cells (HSCs) increase in number due to a higher rate of self-renewal cell divisions while displaying reduced ability to reconstitute the immune system.
The phosphorylated glycoprotein osteopontin (OPN) is an extracellular matrix component of the bone marrow with important roles in tissue homeostasis, inflammatory responses, and tumor metastasis. The expression of OPN within the bone marrow is highly restricted to the endosteal surface, a location where HSCs have been found to reside preferentially. OPN binds to cells through integrins or the CD44 receptor, subsequently activating multiple signaling pathways. When HSCs are transplanted into wild-type (WT) or OPN knockout mice, they exhibit aberrant attachment and engraftment, suggesting the dependence of HSCs on OPN in these processes. Moreover, OPN deficiency within the bone marrow microenvironment results in an increase in primitive HSC numbers. More recently it has been reported that osteopontin exposure to aged HSC can attenuate their aging-associated phenotype.
Here, we study the impact of OPN on HSC function during aging using an OPN-knockout mouse model. We show that during aging OPN deficiency is associated with an increase in lymphocytes and a decline in erythrocytes in peripheral blood. In a bone marrow transplantation setting, aged OPN-deficient stem cells show reduced ability to reconstitute the immune system likely due to insufficient differentiation of HSCs into more mature cells. In serial bone marrow transplantation, aged OPN knockout bone marrow cells fail to adequately reconstitute red blood cells and platelets, resulting in severe anemia and thrombocytopenia as well as premature deaths of recipient mice. Thus, OPN has different effects on HSCs in aged and young animals and is particularly important to maintain stem cell function in aging mice.