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- Adjusting Macrophage Proportions as a Basis for the Treatment of Atherosclerosis
- Adjusting Microglia Proportions as a Basis for the Treatment of Parkinson's Disease
- Arguing Against the Appearance of a Limit to Human Life Span in Historical Data
- A Review of the Intersection Between Aging Research and Calorie Restriction Research
- Progress in SENS Rejuvenation Research Over the Past 15 Years
- Arguing a Role for Stochastic Mutation in Stem Cells in Cardiovascular Disease
- Gensight Continues to Forge Ahead with the First Implementation of Allotopic Expression of Mitochondrial Genes
- Oisin Biotechnologies Launches New Website
- Evolutionary Trade-Offs in Stem Cell Populations: Repair Capacity versus Cancer Risk
- Centenarians Suffer from Significantly Lower Rates of Chronic Age-Related Disease than Younger Cohorts
- A Popular Science Overview of Calorie Restriction Research
- Using RNA Regulation to Argue for the Relevance of Transposons in Aging
- The Contribution of Decreasing Cancer Mortality to Gains in Life Expectancy
- Loss of TDP-43 Points to Microglia as a Cause of Lost Synapses in Alzheimer's Disease
- Methuselah Fund Launches New Website
Adjusting Macrophage Proportions as a Basis for the Treatment of Atherosclerosis
The immune cells known as macrophages are involved in debris cleanup and destruction of potentially harmful cells, among other tasks, but in recent years more attention has been drawn to the important role they play in the complex coordination of cellular activities relating to healing and tissue maintenance. It is even thought that a significant portion of the difference between limited human regeneration and proficient regeneration of the sort observed in salamanders might be explained by differences in macrophage behavior between these species.
Further, and possibly a near-future basis for therapies, macrophages involved in regenerative processes appear split into a few different classes with distinct behaviors and protein signatures. Although this is a case of arbitrary dividing lines drawn on a continuous spectrum rather than a case of clearly separate camps, it is a still a useful distinction to make. These types are known as polarizations, and the polarizations of interest in this discussion are M1 and M2. Both play important roles in the bigger picture, but M1 macrophages are generally less helpful in regeneration, spurring inflammation and fibrosis, while M2 macrophages are generally more helpful, suppressing inflammation and generating a supportive environment for regrowth.
Researchers are finding that it is possible to enhance the outcome of regeneration by increasing the ratio of M2 macrophages to M1 macrophages. More M2 macrophages and fewer M1 macrophages produces more rapid, more effective regrowth of tissues, and in some cases induces regrowth that normally doesn't occur with any reliability in mammals. This has been achieved in animal studies of nerve regeneration and bone healing, to pick a few examples. Interestingly, the cancer research community is interested in turning the dial in the opposite direction, generating more of the aggressive, inflammatory M1 macrophages that destroy cancer cells. As I said, both types have their part to play in the bigger picture.
Moving on to the topic at hand here today, the research below covers the impact of polarization on another part of the macrophage task list, that of debris clearance. Atherosclerosis is a condition in which oxidized, fatty metabolic waste enters the blood stream and sufficiently irritates a section of the blood vessel walls for the cells there to take action. Inflammatory signals draw macrophages that attempt to clean up the garbage, but macrophages are unfortunately unexpectedly frail in the face of this sort of fatty debris. Some ingest too much and either die or become senescent, dysfunctional foam cells, further aggravating the situation. Over time, a small irritated portion of a blood vessel wall swells into a self-perpetuating disaster zone of dead and dying macrophages. Eventually this happens somewhere critical, and driven by the hypertension of aging, a blood vessel wall or the fatty mass inside the vessel ruptures to cause a stroke or heart attack. It turns out that here, as elsewhere, it is the case that adjusting the natural balance towards more M2 and fewer M1 macrophages produces better outcomes, but just how useful this is for human medicine remains to be determined with any great certainty.
Mechanism Shown to Reverse Disease in Arteries
A certain immune reaction is the key, not to slowing atherosclerosis as cholesterol-lowering drugs do, but instead to reversing a disease that gradually blocks arteries to cause heart attacks and strokes. The study in mice focuses on reversing the effects of "bad cholesterol," which is deposited into the walls lining blood vessels in levels influenced by both genetics and a person's diet. By the fourth decade of life, and thanks to the chronic reaction to cholesterol, most people have inflamed "wounds" in their arteries, called plaques, which when severe enough can rupture to cause blood clots that block arteries. "Even the latest, most potent cholesterol-lowering drugs, PCSK9 inhibitors, let alone widely used statins, cannot fully reverse damage done to arteries over time. We need the next generation of drugs to go beyond cholesterol lowering to address the immune reaction to accumulated cholesterol, and to dismantle plaques as part of reversing or regressing mature disease."
Once deposited into arteries, bad cholesterol - known to physicians as low density lipoprotein - triggers the body's immune system, which is meant to destroy invading microbes but can drive inflammatory disease in the wrong context. Immune cells in the bloodstream called monocytes swarm to cholesterol deposits, and become either inflammatory or healing cell types based on signals there. In situations where disease is worsening in a plaque, past studies have shown that monocytes become M1 macrophages that amplify immune responses, increase inflammation, and secrete enzymes that gnaw at plaques until they rupture. The current study confirmed that monocytes arriving in plaques where disease is regressing instead become M2 "healing" macrophages, which dampen inflammation and prevent the ruptures that precede clotting.
When mice were engineered to lose the ability of monocytes to become M2 macrophages, they could no longer achieve normal disease regression. By surgically transplanting plaques from diseased mice into the arteries of healthy mice, the research team brought about dramatic drops in cholesterol levels. This drop has been shown to trigger a second benefit in mice, where monocytes automatically become M2 instead of M1 macrophages as plaques rapidly regress. It is not known whether cholesterol lowering alone triggers this M2 switch in humans, but new imaging techniques may soon be able to detect changes in the type and number of macrophages in plaques. In the meantime, if researchers learn how to boost the M2 switch, a number of clinical applications may become possible just as methods arrive that can measure their success. "A race is underway to develop treatments that enhance the decision of human monocytes to become M2 macrophages in cases where the disease has not yet caused clot formation, at which point it becomes irreversible."
Inflammatory Ly6Chi monocytes and their conversion to M2 macrophages drive atherosclerosis regression
Using a number of mouse models of atherosclerosis regression, including the aortic arch transplant used in the present study, we have previously shown that aggressive lipid lowering promotes the resolution of plaque inflammation, which is characterized by a decreased content of macrophages and an increase in the level of markers of the M2 state. We now extend these findings to show that plaque regression and the attendant resolution of inflammation surprisingly require the recruitment of new monocytes, which assume the characteristics of M2 macrophages. Furthermore, contrary to the prevailing paradigm, the newly recruited monocytes are drawn from the Ly6Chi circulating subset, generally considered to be "inflammation-prone" precursors of M1 macrophages.
The characteristic rapid reversal of hyperlipidemia in mouse atherosclerosis regression models is likely to reduce the continuous stimulation of the plaque inflammatory response by atherogenic lipoproteins, but clearly is not sufficient for the resolution of inflammation. Based on our results, M2 enrichment must also occur, and how the change in lipoprotein environment causes this to happen also remains to be determined. Our finding that it depends on STAT6-dependent signaling in the newly recruited monocytes suggests that local factors in the regressing plaque stimulate this signaling pathway. STAT6 is activated by two key cytokines, IL-4 and IL-13. However, which of these cytokines is the main player, as well as their cellular source(s), in promoting plaque regression is unclear.
Though many questions remain, the present results provide insights into the dynamic nature of the inflammatory process and the role of Ly6Chi monocytes in plaques. These cells were previously thought to contribute only to plaque progression and inflammation, but are now shown here to be important in regression and inflammation resolution. One clinically relevant insight raised by our studies is that strategies that promote the accumulation of M2 macrophages in atherosclerotic lesions may be a promising approach toward promoting plaque regression, consistent with recent studies in mice in which treatment with IL-13- or IL-4-based therapy was protective against atherosclerosis progression.
Adjusting Microglia Proportions as a Basis for the Treatment of Parkinson's Disease
The balance between different types of the immune cells known as macrophages is becoming a stronger theme these days, a line of research that falls somewhere into the broad overlap between regeneration, inflammation, and aging. I've seen quite a number of interesting papers on this topic in the past year, which seems to me a leap in the level of interest shown by the research community of late. While possibly oversimplifying a more complicated reality, we can think of macrophages as having a few different types, or polarizations. The M1 polarization tends towards aggressive destruction of problem cells, the creation of inflammation, and hindrance of regeneration. The M2 polarization tends towards suppression of inflammation and other behaviors that encourage regeneration. The cancer research community would like to be able to adjust macrophage populations towards the M1 type, more willing to destroy cancerous cells, while the regenerative medicine community would like to be able to adjust macrophage populations towards the M2 type to spur enhanced regeneration and tissue maintenance.
It may be that the increased interest in macrophage polarization is a function of the emergence of tools that now allow for cost-effective attempts to shift the balance of macrophage types. The infrastructure of biotechnology is advancing rapidly, and progress spurred by falling costs is a common theme in many parts of the field. Today I'll offer up another example of macrophage polarization research, this time involving microglia, a form of macrophage resident in the central nervous system. Changes in microglia have been shown to be important in any number of age-related neurodegenerative conditions: the immune system declines with age in the brain, just as elsewhere in the body, falling into a dysfunctional and inflammatory state. This affects regeneration and tissue maintenance as is the case for macrophages beyond the brain, but microglia also have additional roles in the correct function of neurons and neural connections, an area of our biochemistry that is still comparatively poorly understood. It is possible to achieve benefits for patients by coercing more microglia into the M2, pro-regenerative polarization? In this open access paper, researchers examine the question in the context of Parkinson's disease.
Targeting Microglial Activation States as a Therapeutic Avenue in Parkinson's Disease
A growing body of evidence suggest that neuroinflammation mediated by microglia, the resident macrophage-like immune cells in the brain, play a contributory role in Parkinson's disease (PD) pathogenesis. In the central nervous system (CNS), the innate immune response is predominantly mediated by microglia and astrocytes. Microglia play a vital role in both physiological and pathological conditions. Microglia appear to be involved in several regulatory processes in the brain that are crucial for tissue development, maintenance of the neural environment and, response to injury and promoting repair. Similar to peripheral macrophages, microglia directly respond to pathogens and maintain cellular homeostasis by purging said pathogens, as well as dead cells and pathological gene products.
Microglia participate in both physiological and pathological conditions. In the former, microglia restore the integrity of the central nervous system and, in the latter, they promote disease progression. Microglia acquire different activation states to modulate these cellular functions. When classically activated, microglia acquire the M1 phenotype, characterized by pro-inflammatory and pro-killing functions that serve as the first line of defense. The alternative M2 microglial activation state is involved in various events including immunoregulation, inflammation dampening, and repair and injury resolution.
Upon activation to the M1 phenotype, microglia elaborate pro-inflammatory cytokines and neurotoxic molecules promoting inflammation and cytotoxic responses. In contrast, when adopting the M2 phenotype microglia secrete anti-inflammatory gene products and trophic factors that promote repair, regeneration, and restore homeostasis. Relatively little is known about the different microglial activation states in PD, and the distribution of microglial M1/M2 phenotypes depends on the stage and severity of the disease. Understanding stage-specific switching of microglial phenotypes and the capacity to manipulate these transitions within appropriate time windows might be beneficial for PD therapy. The transition from the M1 pro-inflammatory state to the regulatory or anti-inflammatory M2 phenotype is thought to assist improved functional outcomes and restore homeostasis. The induction of M1 phenotype is a relatively standard response during injury. For peripheral immune cells it is thought that M1 polarization is terminal and the cells die during the inflammatory response. Although a shift from M1 to the M2 phenotype is considered rare for peripheral immune cells, microglia can shift from M1 to M2 phenotype.
To inhibit the pro-inflammatory damage through M1 activation of microglia, its downstream signaling pathways could be targeted. The M1 phenotype is induced by IFN-γ via the JAK/STAT signaling pathway and targeting this pathway may arrest M1 activation. In fact, studies show that inhibition of the JAK/STAT pathway leads to suppression of the downstream M1-associated genes in several disease models. Another approach to suppress M1 activation would be to target the pro-inflammatory cytokines such as TNF-α, IL-1β and IFN-γ, and decrease its ability to interact with its receptors on other cell types. Alternatively, molecules with the capability to activate the anti-inflammatory M2 phenotype or promote the transition of pro-inflammatory M1 phenotype to anti-inflammatory M2 could be useful in the treatment of PD. Anti-inflammatory molecules such as IL-10 and beta interferons produce neuroprotection by altering the M1 and M2 balance.
The critical role of microglia in most neurodegenerative pathologies including PD is increasingly documented through many studies. Until recently, microglial activation in pathological conditions was considered to be detrimental to neuronal survival in the substantia nigra of PD brains. Recent findings highlight the crucial physiological and neuroprotective role of microglia and other glial cells in neuropathological conditions. Studies on anti-inflammatory treatments targeting neuroinflammation in PD and other diseases by delaying or blocking microglial activation failed in many trials due to the lack of a specific treatment approach, possibly the stage of disease and an incorrect understanding of mechanisms underlying microglial activation. With the updated knowledge on different microglial activation states, drugs that can shift microglia from a pro-inflammatory M1 state to anti-inflammatory M2 state could be beneficial for PD. The M1 and M2 microglial phenotypes probably need further characterization, particularly in PD pathological conditions for better therapeutic targeting. We support targeting of microglial cells by modulating their activation states as a novel therapeutic approach for PD.
Arguing Against the Appearance of a Limit to Human Life Span in Historical Data
Today I'll point out the latest paper in a debate over whether there are limits to human life span. As everyone in the audience here is no doubt aware, human life expectancy is gently trending upward. Life expectancy at birth is rising at about two years with every decade, while life expectancy at 60 is rising at about a year with every decade. The evidence in support of this trend is robust, thanks to the enormous demographic databases collected over the past few decades. Is this trend approaching any sort of limit to human life span, however? Can historical data even be used to answer that question? This is a much more challenging proposition, as the available data for the oldest humans, the population of supercentenarians older than 110, is sparse. Very, very few people survive to these ages, to the point at which statistical methods operating on this data become ever more dubious with each additional year of age.
Still, people crunch the numbers and try to extract meaning. You might recall that last year, Jan Vijg's group put forward their argument for the data to show there to be a limit to human life span over the years in which that data was collected. It was coupled to some unexpectedly pessimistic commentary on the future development of longevity science, given that Vijg has for some time been counted among those researchers openly in favor of extending healthy life spans by treating aging as a medical condition. The paper sparked some occasionally heated discussion. I don't think the researchers expressed their argument all that well in their publicity materials, and the popular science press then generated more than the usual degree of mess and confusion when they pitched in.
So to the casual observer, it was a little difficult to see whether Vijg and company were making the obvious point, which is that human life span is effectively limited by the present level of medical technology, or whether some more subtle argument was being made. I think it is hard to disagree with the statement that medical technology determines limits to human life span. Where we can debate, given the sparse nature of the evidence to hand, is whether or not there exists one or more mechanisms of aging that have not been impacted in any meaningful way by improvements in medical technology over the past century, and which, on their own, can produce a very high rate of mortality in late life. That circumstance would look a lot like a limit when examining the consequent demographic data.
One mechanism that springs to mind here is the accumulation of transthyretin amyloid, found in one small study to be the majority cause of death in supercentenarians, but which appears to have only a smaller impact on mortality in younger old age - it is implicated in something like 10% of heart failure cases, for example. Can we argue that advances in medicine and public health over the past century have had little to no impact on the accumulation of misfolded transthyretin deposits in tissues, and thus this mechanism acts as a limit on life span? Or do some of these improvements in fact produce an small, incidental reduction in amyloid burden in later life? I think that the evidence to support any of the possible positions on these questions is presently lacking.
Whatever the state of effective limits on life span today, however, the limits on life span tomorrow are determined by progress towards rejuvenation therapies. There are treatments under development that can clear transthyretin amyloid from tissues, for example. The same is true for many of the other forms of molecular damage and waste accumulation that cause aging. Thus any debate over what the present demographics do or do not show is more academic than it might otherwise be. The natural state of human aging, already largely paved over by medicine, will be buried completely, made irrelevant in the decades ahead by the advent of means to repair the damage, restore youthful function, and eventually to indefinitely postpone all of the symptoms of aging.
No detectable limit to how long people can live
Supercentenarians, such as Jeanne Calment who famously lived to be 122 years old, continue to fascinate scientists and have led them to wonder just how long humans can live. A study published last October concluded that the upper limit of human age is peaking at around 115 years. Now, however, a new study comes to a starkly different conclusion. By analyzing the lifespan of the longest-living individuals from the USA, the UK, France and Japan for each year since 1968, researchers found no evidence for such a limit, and if such a maximum exists, it has yet to be reached or identified.
"We just don't know what the age limit might be. In fact, by extending trend lines, we can show that maximum and average lifespans, could continue to increase far into the foreseeable future." Many people are aware of what has happened with average lifespans. In 1920, for example, the average newborn Canadian could expect to live 60 years; a Canadian born in 1980 could expect 76 years, and today, life expectancy has jumped to 82 years. Maximum lifespan seems to follow the same trend. Some scientists argue that technology, medical interventions, and improvements in living conditions could all push back the upper limit. "It's hard to guess. Three hundred years ago, many people lived only short lives. If we would have told them that one day most humans might live up to 100, they would have said we were crazy."
Many possible maximum lifespan trajectories
A recent analysis of demographic trends led to the claim that there is a biological limit to maximum human lifespan (approximately 115 years). Although this claim is not novel - others have also identified a biological 'barrier' at 115 years - the methodology that the authors used is. Here we show that the analysis does not allow the distinction between the hypothesis that maximum human lifespan is approximately 115 years and the null hypothesis that maximum lifespan will continue to increase. The central difficulty with this exercise is accurately extrapolating onwards from a limited, noisy set of data.
Beyond a plateauing of maximum life span, there are other different trajectories that maximum lifespan could follow over time if the null hypothesis (that maximum lifespan will continue to increase) were true, with maximum lifespans continuing to increase to an eventual future plateau or continuing to increase indefinitely. All three models appear equally consistent with the known maximum lifespan data used. How the authors differentiated between these possibilities is important. Their claim rests on their identification of a plateau in the ages of maximum lifespan beginning around 1995. They separated the data into two groups, 1968-1994 and 1995-2006, and modelled each group using linear regression. While the first partition shows a trend for increasing maximum lifespan, the second partition does not. It is this latter partition upon which their conclusions are largely based. This is problematic, because, even within a dataset showing an overall trend for an increase with time, normal variability can generate apparent plateaus and even temporary decreases over small intervals.
Furthermore, the authors do not describe how they identified the lifespan plateau, nor the partition site, indicating that these were products of casual visual inspection. This is a critical point for the validity of their argument because even slight changes to the assumptions that they made can notably alter the results of their analysis, with markedly different outcomes. In conclusion, the analyses do not permit us to predict the trajectory that maximum lifespans will follow in the future, and hence provide no support for their central claim that the maximum lifespan of humans is "fixed and subject to natural constraints". This is largely a product of the limited data available for analysis, owing to the challenges inherent in collecting and verifying the lifespans of extremely long-lived individuals.
A reply from Jan Vijg's research group
The authors of the accompanying comment disagree with our finding of a limit to human lifespan. Although we thank them for alerting us to other work reporting a limit of around 115 years, we disagree with the arguments presented and remain confident in our results. We feel that the scenarios presented, although imaginative, are not informative. They argue that their three different models (which they extrapolate until the year 2300) are not statistically differentiable based on the data available. We used a data-driven approach to identify the trend in the maximum reported age at death (MRAD) by analysing actual data rather than arbitrary simulations; although the authors criticize us for visually inspecting our data, graphing data in order to evaluate the choice of model has long been acknowledged as a useful and important technique by statisticians. Taken together, and in the absence of solid statistical underpinning of various possible future scenarios, we feel that our interpretation of the data as pointing towards a limit to human lifespan of about 115 years remains valid.
This is, it has to be said, exactly the sort of exchange one might expect to see between researchers who are working with a very sparse set of data. It is always interesting to watch the ongoing efforts to better refine, mine, and interpret this data, but it is of limited relevance to the near future of therapies to treat aging. All of the present well-known demographics of later life will be changed greatly for the better as therapies capable of addressing the causes of aging emerge.
A Review of the Intersection Between Aging Research and Calorie Restriction Research
Below, find linked a very readable review of the intersection between aging research and calorie restriction research. While less so now than a decade ago, it nonetheless remains the case that much of the ongoing research into aging is in fact not concerned with treating aging as a medical condition. It is observational only, an field of programs of investigation and mapping that are quite disconnected from any impetus to improve medical technology. In the other portion of the aging research community, however, the part of more interest to us, in which scientists are aiming at interventions that target the causes of aging, a sizable proportion of funding and initiatives can be traced back to roots in calorie restriction research. This is why this topic shows up so often here and elsewhere.
Interestingly, while interest in calorie restriction research is but a slice of the broader field of aging research, aging has always been a principle focus of calorie restriction research. This came to be an area of interest precisely because calorie restricted laboratory animals reliably live longer, a result first formally published by researchers some eighty years ago. That data languished until the era of genetics and molecular biochemistry arrived, at which point calorie restriction became a tool used to investigate the complexity of cellular metabolism: given two reliably produced states of metabolic operation, a great deal can be learned by looking into the details of the differences. In fact, judging by the behavior of the research community, we should probably consider aging to be viewed as a tool used to investigate the complexity of cellular metabolism. A great deal of the otherwise puzzling reluctance to engage with rejuvenation research, an engineering approach in which comparative ignorance of the progression of aging can be bypassed in order to apply what is already known of the molecular damage that causes aging, might be explained by presuming that most researchers are primarily motivated to produce a comprehensive map of our biochemistry, rather than to produce more effective therapies.
So, given the starting point of calorie restriction, researchers move along chains of cause and effect in cells, mapping proteins and their relationships, comparing old and young, calorie restricted and well fed states. Technologies are spun off as they can be from these investigations, because every research institution is these days embedded in a larger organization that seeks to apply new knowledge in any way possible, but this application is a secondary concern at the point at which new directions are chosen for aging research. Since the primary thrust of the work takes little account of the potential effectiveness of resulting technological applications, we end up with a great deal of effort devoted to developing calorie restriction mimetic drugs that might slightly slow aging, rather than that same effort devoted towards repair technologies capable of rejuvenating the old. This happens because the primary goal for researchers is gathering information about biochemistry, as opposed to bringing aging under medical control. In this, there is a set of fundamental mismatches between the expectations and goals of funding sources, researchers, entrepreneurs, and the public at large.
Aging and Caloric Restriction Research: A Biological Perspective With Translational Potential
The dramatic increase in average life expectancy has led to a rapid rise in the aging population across the globe. Age is a robust and independent risk factor for a range of non-communicable diseases like cancer, diabetes, cardiovascular disease, and neurodegenerative disease, and so it follows that this newfound increase in longevity creates a substantial burden in disease incidence and health care costs. Overwhelming evidence suggests that processes intrinsic to aging contribute to the pathogenesis of age-related diseases. Ongoing international efforts have made great strides in advancing our knowledge of the biology of aging and several "hallmarks" of aging have been identified that may play a causative role in the age-related increase in disease vulnerability.
These last few years have seen a shift in emphasis from the investigation of individual age-related diseases in isolation toward a broader context to define the basic biology of aging. The concept behind the recently coined pursuit of geroscience is that a strategy to delay the aging process itself would decrease vulnerability across the age-related disease spectrum leading to lower morbidity and comorbidity. Indeed the concept that aging might be a suitable drug target in a clinical context is gaining traction and there is considerable effort being applied to bring this idea to fruition. One of the most valuable tools in aging research is caloric restriction (CR), a proven intervention to delay aging and age-related disease. If we could understand what mechanisms are employed by CR to impinge on the aging process we could potentially identify causal networks that contribute to the increase in disease vulnerability as a function of normative aging.
To investigate the translatability of CR's beneficial effects from rodents to primates, three independent rhesus monkey studies were initiated in the late 1980s. The take home message from this joint initiative is that CR delays aging in primates, where lower food intake is associated with improvements in health and survival. The implications of this work are broader, first that aging in primates can be manipulated, supporting the concept that aging is a valuable target for intervention and eventual clinical application, and second, that the mechanisms recruited by CR to impinge on aging will likely have utility in the development of treatments to delay or abrogate age-related disease vulnerability.
With evidence that CR is effective in long-lived species the next question is whether its beneficial effects and mechanistic underpinnings are conserved in humans. The hallmarks of mammalian CR include lower adiposity, increased insulin sensitivity, favorable lipid profiles, and increased levels of the adipose-derived hormone adiponectin. Short-term studies of CR in humans have been conducted as part of the multicenter study CALERIE in 2 phases. In the first phase of CALERIE studies (CALERIE-I), the metabolic effects of 6 or 12 months of CR was evaluated in overweight individuals with a target level of restriction of 20-30%. Favorable changes in body weight, body composition, glucoregulatory function and serum risk factors for cardiovascular disease were reported in CR individuals. These outcomes were consistent with those reported for monkeys on CR. Overall, these studies are highly suggestive that CR's effect on aging is translatable to humans and confirm that nonhuman primates do indeed bridge the gap between human and rodent studies.
CR impinges on multiple signaling pathways that regulate growth, metabolism, oxidative stress response, damage repair, inflammation, autophagy, and proteostasis, to modulate the aging process. The relationship between calorie intake and longevity follows a U-shaped curve, dietary excess and malnutrition both negatively impact survival. Between the extremities there is an inverse linear relationship between lifespan and calorie/energy intake, suggesting that adaptive metabolism is a key component in the response to CR. Caloric restriction as an intervention is likely to be very difficult to implement in humans. Indeed the goal of CR research is to figure out how it works, not to promote it as a lifestyle. In order to gain the beneficial effects of CR without the restriction of calories, a number of nutraceuticals and established drugs are being explored as a means to mimic the effects of CR. The National Institute on Aging (NIA) has created the Interventions Testing Program (ITP) to investigate treatments with the potential to extend lifespan and delay age-related disease and dysfunction. To date several effective compounds have been identified some of which have been used in human clinical applications such as rapamycin (inhibitor of mTOR), metformin (activator of AMPK), and others that are only recently being applied in human studies such as resveratrol (activator of AMPK and SIRT1).
Aging research has entered a very exciting period where traditional scientific approaches to understanding the biology of aging are converging with clinical research and epidemiology. Technological advances in the last few decades have brought aging research to a place that could not even have been imagined back in the days when the establishment of the National Institute on Aging first officially recognized the science of aging. We have already seen the identification of genes and biomarkers associated with healthy aging and exceptional aging, and studies in laboratory animals have laid out a rich framework of factors that have established roles in regulation of longevity.
Outstanding questions include the molecular basis for the role of energy metabolism in aging. How do differences in mitochondrial function create vulnerability to disease? How do defects in mitochondrial efficiency and adaptation arise? To what extent do minor differences in energetic capacity or fuel utilization influence other cellular functions? What networks within the cell are responsive to these relatively small age-related changes? Another important avenue of investigation is the role of lipid metabolism in aging and disease vulnerability. Lipid transport and lipid handling are common themes in human and laboratory aging studies, and differences in lipid metabolism have been strongly implicated in the mechanisms of CR, but how does this translate to a change in disease vulnerability as a function of age?
Taking a broader view, it will be necessary to distinguish between events that are coincident with aging and those that are driving aging. Does aging arise first within discrete systems or is it orchestrated simultaneously across systems? To what extent are failures in individual processes such as repair or induction of senescence responsible for age-related disease vulnerability? To resolve these and other questions future directions must include synergistic collaborative efforts focused on aligning insights from human and laboratory aging studies. Caloric restriction research will also have a role to play, where interdisciplinary approaches can be brought to bear to determine the molecular details of CR's mechanisms and thereby identify the most promising candidate factors for targeted intervention.
Progress in SENS Rejuvenation Research Over the Past 15 Years
Reforming and rebuilding an entire field of medical research and development isn't an easy task, and sadly nor is it something that can be achieved overnight. A comprehensive reformation of the aging research community is nonetheless the goal of the SENS initiative, the Strategies for Engineered Negligible Senescence - a way to build rejuvenation therapies that work by repairing forms of cell and tissue damage that cause aging. SENS came into being precisely because aging research was not heading in the right direction: researchers were not attempting to treat aging as a medical condition, influential figures were in fact actively suppressing any sort of impetus in that direction, and where there were glimmerings of hope in the form of a few scientists interested in intervening in the aging process, these individuals were focused on strategies that could not possibly do more than slightly slow down age-related degeneration.
Over the past fifteen years SENS has progressed from a position statement and a vision for the end of aging, a set of ideas and supporting evidence only, to a modestly sized set of research programs that are now producing results, several non-profit foundations, a web of relationships with a outsized influence on the research community, and the clinical development of the first rejuvenation therapies. SENS has come a long way from the first meetings of a few like-minded researchers and advocates, just after the turn of the century. Now many researchers are openly talking about the causes of aging and the construction of therapies to meaningfully treat aging. The old suppression of this topic has crumbled entirely. It remains the case that most researchers are still stubbornly pursuing approaches that cannot have a large effect on human health and life span, but the initial battle to change the direction of the research community has been fought and won. Now it is just an increasingly vocal and public debate over how best to proceed, and here SENS will win in time as therapies that repair age-related molecular damage are proven to be far cheaper, more effective, and more reliable than other efforts.
We have come a long way, but one of the necessary parts of advocacy that I think that our community does poorly is the presentation of this growth and success of past years. There is so much we can point to, and show where and how we came together to make a difference, to change the course of research, to fund and build new advances, to change minds and gather allies. We don't do a good job when it comes to clearly showing the progression from (1) initial idea to (2) non-profit scientific foundations to (3) philanthropic support of research to (4) broader research community participation to (5) proof of concept technology demonstrations to (6) founding of biotechnology companies to (7) venture fundraising to (8) clinical trials of rejuvenation therapies. That long chain now exists nearly end to end for senescent cell clearance as a rejuvenation treatment, and all of the other potential branches of SENS research are underway in some form.
So with that in mind, the following timeline references some of the important developments and advances in rejuvenation biotechnology since the origin of the SENS program, from the slow and incremental start to the present more rapid pace. It is by design a high-level and sparse overview, as I wanted to capture the bigger picture without getting dragged down into the details. Watching early stage progress in research from year to year can be a frustrating process, but as senescent cell clearance demonstrates, once a field reaches the tipping point of viability and support, things then move very rapidly. Further, given that this all started with a few ideas and a little persuasion, it is certainly the case that mountains have been moved over the years, even if it feels all too slow on a day to day basis. There is much more to be done ahead, but all who have participated in the past should feel rightfully proud of what has been accomplished, and what continues to be accomplished today.
- The first of Aubrey de Grey's collaborative papers, describing SENS as a goal-driven approach to the treatment of aging as a medical condition, is published in the Annals of the New York Academy of Sciences.
- The Methuselah Foundation is created, and the founders launch the Mprize for longevity science, a research prize aiming to spur greater interest in extending healthy life spans.
- The first SENS-focused academic conference is held in the UK under the auspices of the International Association of Biomedical Gerontology.
- The Methuselah Foundation begins to assemble the 300, a core group of donors who go on to be influential in the course of advocacy and development of rejuvenation biotechnology. Their funds power the early work of the foundation, and some start their own initiatives in later years.
- An individual whose identity remains a mystery to this day makes a 1 million donation to the Methuselah Foundation to expand the Mprize purse.
- The Methuselah Foundation begins funding (a) LysoSENS research, searching for enzymes in soil bacteria capable of consuming age-related metabolic waste, and (b) allotopic expression of mitochondrial genes, aiming to remove the consequences of mitochondrial damage in aging.
- The Methuselah Foundation sponsors the Supercentenarian Research Foundation, supporting a program of autopsies of supercentenarians. Over the next few years this demonstrates transthyretin amyloidosis to be the majority cause of death.
- Peter Thiel publicly supports SENS research with a 3.5M grant.
- Researchers first demonstrate the creation of induced pluripotent stem cells, a foundation for much of the future of regenerative medicine to replace cells lost to aging.
- The Methuselah Foundation expands allotopic expression funding to support a French research group that will go on to establish Gensight Biologics on the strength of this work.
- The first US SENS conference is held at UCLA.
- The SENS Research Foundation spins off from the Methuselah Foundation to focus entirely on SENS rejuvenation research.
- GSK and Pentraxin Therapeutics begin a collaboration to develop a therapy capable of clearing transthyretin amyloid.
- The Methuselah Foundation makes its first outside investment in the Organovo tissue printing startup.
- The SENS Research Foundation's yearly budget reaches 1 million. The foundation sets up a laboratory facility in Mountain View, California for ongoing intramural research projects.
- Jason Hope pledges 500,000 to the SENS Research Foundation to start a research program aimed at developing a viable cross-link breaker for glucosepane in humans.
- Researchers find that transplanting a young thymus into an old mouse restores immune function and extends life.
- Aubrey de Grey devotes the majority of his 16.5M net worth to funding SENS research.
- The SENS Research Foundation is funding either in-house or external research projects in all of the seven strands of SENS rejuvenation research. Some are very early stage, focused on building tools or discovery, while others are building the basis for therapies.
- The first demonstration of targeted senescent cell clearance is carried out by an independent research group, producing benefits in mice with an accelerated aging condition.
- The Methuselah Foundation launches the New Organ tissue engineering initiative.
- Gensight Biologics is founded to commercialize allotopic expression of mitochondrial gene ND4, based on the research program supported initially by the Methuselah Foundation, and later the SENS Research Foundation.
- The SENS Research Foundation demonstrates bacterial enzymes that can break down 7-ketocholesterol in cell culture.
- Methuselah Foundation supported tissue printing company Organovo becomes publicly traded on NASDAQ.
- Covalent Bioscience is founded to advance work on catalytic antibodies (or catabodies) to clear the amyloid associated with Alzheimer's disease.
- Gensight Biologics raises a 32M series A round.
- The Methuselah Foundation announces a 1 million research prize for liver tissue engineering as a part of the New Organ initiative. This year the foundation also sponsors organ banking initiatives at the Organ Preservation Alliance.
- The important Hallmarks of Aging position paper is published, the authors taking a cue from the SENS rejuvenation research proposals, but carving out their own view on damage and repair.
- Google Ventures launches Calico, adding a great deal of support to aging research with the size and publicity of the investment. Unfortunately Calico goes on to focus on areas of aging research unrelated to rejuvenation.
- Cenexys is founded to work on the creation of means to selectively destroy senescent cells in aged tissues.
- The Methuselah Foundation and SENS Research Foundation provide seed funding to launch Oisin Biotechnologies, to develop a method of targeted clearance of senescent cells.
- The SENS Research Foundation begins the Rejuvenation Biotechnology conference series, bringing together industry and academia to smooth the path for development of rejuvenation therapies.
- Following the Hallmarks of Aging, leading researchers publish their Seven Pillars of Aging position, again echoing the long-standing SENS view of aging and its treatment.
- The SENS Research Foundation funds development of catabodies to break down transthyretin amyloid, and the work shows considerable promise.
- Human Rejuvenation Technologies is founded to commercialize a treatment for atherosclerosis based on SENS Research Foundation LysoSENS program approaches to clearing metabolic waste compounds.
- The SENS Research Foundation's yearly budget reaches 5 million.
- The Spiegel Lab at Yale announces a method of creating glucosepane, a vital and to this point missing tool needed to develop glucosepane cross-link breaker drugs. This work was funded by the SENS Research Foundation.
- A research team demonstrates the first senolytic drug candidates capable of selectively destroying senescent cells. The number of candidate drugs increases quite quickly after this point.
- Pentraxin Therapeutics announces positive results in a trial of targeted clearance of transthyretin amyloid. Meanwhile, evidence continues to emerge from other groups for transthyretin amyloid to have more of an impact in age-related disease that previously thought.
- SENS Research Foundation work on sabotaging ALT to suppress cancer receives more attention. Meanwhile progress is reported on the other half of telomere extension blockade, interfering in the operation of telomerase, an area in which a number of groups are participating.
- The Methuselah Foundation makes a founding investment in Leucadia Therapeutics in order to pursue a novel approach to the effective treatment of Alzheimer's disease.
- The research program producing catabodies capable of breaking down transthyretin amyloid is transferred to Covalent Bioscience for clinical development.
- Ichor Therapeutics begins commercial development of a method of clearing metabolic waste from the retina, based on technology developed in the SENS Research Foundation LysoSENS program.
- Gensight Biologics demonstrates success in a trial of mitochondrial allotopic expression of ND4 as a way to treat inherited mutations of that gene. The underlying technology is proven. SENS Research Foundation scientists, meanwhile, successfully demonstrate allotopic expression of ATP6 and ATP8.
- After more than a decade of high profile failures, amyloid-β is finally cleared from the brain in a small human study using an immunotherapy approach.
- The SENS Research Foundation crowdfunds a drug discovery program to find candidates that can interfere in ALT, and thus suppress the telomere elongation that cancer depends upon.
- Cenexys is reformed as Unity Biotechnology with a focus on senolytic drugs. The researchers involved show that clearance of senescent cells in normal mice produces 25% extension of median life span. Later in 2016, the company raises 116M in venture funding.
- Other work on removal of senescent cells across the year shows restoration of function in aged lung tissue, and improved vascular health. New evidence reinforces the role of senescent cells in osteoarthritis, as well as in atherosclerosis, immunosenescence, and diabetic retinopathy
- The Methuselah Foundation launches a 500,000 research prize for tissue engineering in collaboration with NASA.
- Michael Greve pledges 10M to fund SENS research and startup biotechnology companies that emerge from that research.
2017, so far...
- There are now nearing ten different senolytic drug candidates with openly published evidence, and more in the pipeline.
- Oisin Biotechnologies announces that their senescent cell clearance technology can also be applied to cancerous cells, reporting successful animal studies for tumor ablation.
- Methuselah Foundation launches the Methuselah Fund to shepherd more rejuvenation-related biotechnology startups towards success.
Arguing a Role for Stochastic Mutation in Stem Cells in Cardiovascular Disease
To what degree does random mutation in nuclear DNA contribute to aging over the present human life span? The present consensus is that this is a cause of disarray in metabolic processes, and that it does reach a significant level of consequence for tissue function. Unfortunately there is little direct evidence for this view - it is hard to split out just nuclear DNA damage from the rest of aging in order to isolate its effects, though there a few lines of research showing promise in this direction. Researchers here take a different approach to the question; they suggest that some forms of random mutational damage that occurs in stem cells will expand throughout that population over time, because the damage in some way confers a replication advantage. In this way it can come to have a significant effect, and it should be feasible to correlate different degrees of the expansion of this sort of mutational damage with specific measures of aging. In this case, the correlation is with cardiovascular disease.
Several explanations have been offered for how age contributes to cardiovascular disease. Aging is associated with the acquisition and exposure duration of other established risk factors for cardiovascular disease, including high systolic blood pressure and increased levels of low-density lipoprotein cholesterol. However, analyses that adjust for the concomitant burden of other risk factors consistently identify age as an independent predictor of cardiovascular disease. Modifiable risk factors account for only about 12% of the age effect in men and 40% in women. Thus, the aging process itself must promote cardiovascular risk, although the mechanisms that are involved are poorly understood.
Researchers now provide new insight into how aging can promote atherosclerosis and cardiovascular events in their investigation of a phenomenon termed clonal hematopoiesis of indeterminate potential, or CHIP. This condition is an age-related disorder characterized by the acquisition of somatic mutations in hematopoietic stem cells that confer on these cells a selective advantage. As a consequence, instead of the normal polyclonal generation of blood cells, mutation-containing clones expand over time and make up an increasing percentage of the stem cells and their progeny and may include granulocytes, lymphocytes, and monocytes. CHIP is rarely found in patients who are younger than 40 years of age, whereas this condition may exist in up to 10% of persons over the age of 70 years. Patients with CHIP have a higher rate of death from noncancer causes (particularly cardiovascular disease) than do age-matched controls without CHIP.
To address the cause of excess cardiovascular mortality, researchers identified CHIP (which they define as clonal dominance of hematopoietic cells bearing pathogenic mutations in any of 74 known driver genes of hematologic cancers) among participants in several studies that ascertained cardiovascular disease. In studies involving participants with a mean age of 60 years or older, carriers of CHIP had nearly twice the risk of coronary heart disease as noncarriers. Among younger participants (below 50 years of age), CHIP carriers had four times the risk of myocardial infarction as noncarriers. Preclinical coronary disease, as assessed on imaging as coronary-artery calcification, was also associated with CHIP. Finally, four of the most commonly mutated genes in CHIP (DNMT3A, TET2, ASXL1, and JAK2) were each individually associated with coronary heart disease.
Collectively, the work supports the hypothesis that CHIP is linked to the clinical events of atherosclerosis and that certain CHIP driver genes are involved in regulating inflammation. Both TET2 and DNMT3A appear to inhibit inflammation, so loss-of-function mutations in these genes could plausibly promote inflammatory responses. Similarly, there is a large body of literature suggesting that JAK2 regulates both inflammation and thrombosis, two important factors in the clinical manifestations of atherosclerosis. Thus, the data is consistent with established paradigms that inflammation is an accelerator of atherosclerosis and coronary heart disease. Moreover, their findings should prompt a discourse about studying the use of anti-inflammatory agents in patients with CHIP to limit the most common cause of death in these patients - cardiovascular disease.
Gensight Continues to Forge Ahead with the First Implementation of Allotopic Expression of Mitochondrial Genes
Mitochondria, the power plants of the cell, bear their own DNA, a small remnant of their origin as symbiotic bacteria. Unfortunately, this DNA is more vulnerable than the DNA found in the cell nucleus, and can become damaged in ways that contribute significantly to the aging process. How to address this problem? Allotopic expression of a mitochondrial gene is a process by which an altered version of the gene is placed into the cell nucleus in order to provide a backup source of the protein encoded by the gene. In this age of genetic engineering, inserting the gene isn't really the challenge, instead the difficulty lies in figuring out how to alter the gene in order for the protein produced to be transported back to the mitochondria where it is needed.
Funded by philanthropic donations, the SENS Research Foundation has been supporting allotopic expression research for a decade now, seeking to accelerate the development of therapies that can remove this contribution to the aging progress. The first programs funded gave rise to Gensight Biologics, a company that is pioneering the use of allotopic expression of the ND4 gene to address an inherited blindness condition in which the gene is mutated and dysfunctional. This effort is well on the way to proving out the technology in human trials and thereby providing a solid foundation for work on the other genes that must be backed up. Three mitochondrial genes are demonstrated so far, including ND4, and there are another ten to go after that. Commercial efforts of this nature are an important part of the overall development process, and it is a good thing to see a company pulling in significant funding for a technology that will become a part of later rejuvenation therapies.
GenSight Biologics has raised €22.5 million to prepare to bring gene therapy GS010 to market in the U.S. and Europe. The financing gives the Novartis-backed biotech enough cash to deliver data from two phase 3 trials next year and gear up for anticipated approvals on both sides of the Atlantic. Paris-based GenSight raised the cash from a mix of new and existing institutional investors, most of which are based in the US. Strong interest from these backers saw GenSight ease past its initial target of €20 million to pull in €22.5 million in the private placement. When added to the €48.8 million GenSight had in the bank at the end of March, management thinks the money moves its runway out to the first quarter of 2019.
That runway covers a critical period for GenSight. Topline 48-week data from two phase 3 trials of GS010 in patients with Leber hereditary optic neuropathy (LHON) are due in the second and third quarters of next year. GenSight is looking to the trials for evidence GS010 improves the clarity of the vision of patients with LHON, a hereditary form of vision loss caused by mitochondrial defects. GS010 is injected into the eye to deliver the human wild-type ND4 gene via an adeno-associated virus to deliver. This gene encodes for a protein typically produced by mitochondria.
One trial is assessing GS010 in patients who started losing their vision in the six months prior to enrolling in the study. The other is recruiting patients whose vision started deteriorating between seven and 12 months ago. Both trials are injecting GS010 into one eye of each participant and pretending to inject it into the other eye. Data from an earlier phase 1/2 trial suggest the gene therapy is most effective in patients whose vision started deteriorating less than two years ago. A recent 96-week update found the treated eyes of such patients had a mean gain of 29 ETDRS letters, as compared to an increase of 15 letters in untreated eyes. ETDRS is the test showing progressively smaller letters opticians use to gauge vision. The performance of GS010 to date has enabled GenSight to secure the support of some big-name backers. Following the latest financing, its biggest shareholders are Novartis, Versant, Abingworth, and Fidelity.
Oisin Biotechnologies Launches New Website
Oisin Biotechnologies is a senescent cell clearance company founded by long-standing members of our community, seed funded by the Methuselah Foundation and SENS Research Foundation, and supported by the investment of a number of folk in the audience here. Targeted removal of senescent cells is a form of narrowly focused rejuvenation, shown to turn back numerous measures of aging in animal studies, and the Oisin team has made great strides in proving out their programmable gene therapy approach. This sort of commercialization project is exact what our community has been working towards all these years, and the faster that implementations reach the clinic, the better off we all are.
Oisin Biotechnologies' ground-breaking research and technology is demonstrating that the solution to mitigating the effects of age-related diseases is to address the damage created by the aging process itself. Our first target is senescent cells. When cells detect that they have been irretrievably damaged, they enter a non-dividing condition known as cell-cycle arrest, or senescence. It's believed this occurs to prevent cells from going rogue and turning cancerous. Ideally, they should die by the process known as apoptosis, but as we age, more and more frequently they don't. They become zombie cells - unable to kill themselves or resume normal function.
Senescent cells secrete molecules that cause inflammation in an effort to attract immune cells that would usually clear them. But for reasons that are not fully known, as we age, persistently senescent cells accumulate, leading to a vast number of age-related diseases. Oisin is developing a highly precise, patent-pending, DNA-targeted intervention to clear these cells. As a recent study has shown, clearing senescent cells both reduces negative effects of aging pathologies and also extends median lifespan and survival.
There are two major challenges to clearing senescent cells using our approach. First is to design and create the DNA construct that recognizes that a cell has become senescent, and then destroys it. Second is to safely and efficiently deliver this construct into cells throughout the body. Both goals have been achieved in our pioneering proof of concept experiments in 2016. We've first demonstrated the ability to transduce cells both in vitro (cell culture) and in vivo (in aged mice). Then we showed that p16 positive senescent cells can be killed on demand in both in vitro and in vivo environments. Now we are embarked on experiments that will show improvements in both healthspan and lifespan in model organisms from mice to primates. And then, everything changes.
Our proprietary technology gives persistently senescent cells a helping hand to "do the right thing." By providing an exogenous apoptotic gene, which is only transiently expressed in cells that already have the p16 gene active, we can precisely induce the senescent cell to commit suicide. Oisin has shown as much as an 80% reduction in senescent cells in cell culture and significant reductions of senescent cell burden in naturally aged mice. SENSOlytics is an Oisin proprietary platform technology that enables precise targeting of a senescent cell based on the DNA expression of the cell, not on surface markers or other characteristics that might be shared with normal, undamaged cells.
Evolutionary Trade-Offs in Stem Cell Populations: Repair Capacity versus Cancer Risk
This open access paper is an interesting companion piece to yesterday's discussion of the potential for expansion of mutations in stem cell populations to contribute to degenerative aging. What evolutionary constraints have led to the present state of stem cell populations in mammals: why are they not larger, with more capacity for tissue maintenance and regeneration in later life, for example?
Multicellular organisms continually accumulate mutations within their somatic tissues, constituting a significant, but poorly quantified, burden on tissue maintenance. To investigate this burden in a specific, well-parameterized context, we model the mammalian intestine and quantify the expected impact of mutation accumulation in stem cell populations. Furthermore, we explore how the population size of the stem cell niche influences mutation accumulation and demonstrate the expected trade-off between the risk of accumulating deleterious mutations, population size, and the risk of tumorigenesis. However, we further characterize how this trade-off can be expected to manifest over the lifetime of two well-studied mammalian systems, mice and humans, by estimating the expected effect of mutation accumulation on cellular homeostasis.
The intestinal epithelium is in constant flux, with populations of stem cells distributed throughout the intestine differentiating into other, transient, cell populations. These stem cells exist within small discrete populations in intestinal crypts, a compartmentalization thought to have evolved as a mechanism to deter tumorigenesis, as cells accumulating mutations that are beneficial to cellular fitness have a physical hindrance to spreading throughout the tissue. However, small populations are subject to significant genetic drift, that is, random changes in allele frequency that eventually lead to fixation or loss, and less effective selection.
The accumulation of damage causing the loss of cellular fitness is a hallmark of aging and is especially relevant when DNA damage occurs in stem cells, compromising their role in tissue renewal. Indeed, several mouse models with the diminished ability to maintain cellular genome integrity succumb to accelerated age-related phenotypes through the loss of tissue homeostasis caused by stem and progenitor cell attrition. Just as stem cell mutations conferring a beneficial fitness effect will increase cell production, mutations conferring a deleterious fitness effect will lead to decreased cell production and the diminished maintenance of healthy tissue.
When mutations confer a selective advantage or disadvantage within the niche, there exists an intermediate crypt size that minimizes the probability that any crypt accumulates the large beneficial mutations necessary to initiate a tumor. By modeling the fixation of mutations drawn from a full distribution of mutational effects and accumulating throughout the populations of the entire intestinal epithelium, we show that a secondary trade-off exists - populations maintained at a size that results in the lowest rate of tumorigenesis are expected to accumulate deleterious mutations that manifest in tissue attrition and contribute to organismal aging.
At small stem cell niche sizes, there exists a large number of crypts to maintain homeostasis, and a higher probability that any one crypt will obtain a rare mutation of large effect that would result in tumorigenesis. As stem cell niche size increases, the number of crypts needed to maintain the same amount of epithelium decreases, and so does the probability of fixing mutations within the crypts, and therefore the chance of fixing a rare mutation of large effect. However, for larger values of stem cell niche size, the strength of selection increases, thus increasing the chance that a fixed mutation was beneficial, leading to higher chances of tumorigenesis. At the observed intermediate population size in mice, the whole tissue size is expected to decline with age as deleterious mutations accumulate in stem cell niches. If selective pressures against tumorigenesis have selected for intermediate stem cell niche population sizes in mammalian species, then it has been at the expense of increasing epithelial attrition.
Centenarians Suffer from Significantly Lower Rates of Chronic Age-Related Disease than Younger Cohorts
Aging is an accumulation of molecular damage and its consequences. The greater the level of damage, the greater the dysfunction in organs and the immune system, then the closer the individual comes to the arbitrary dividing line at which that dysfunction becomes a formal, named age-related disease. Further, the more damage, the higher the mortality rate. Given this view of aging, it should be no great surprise to find that the longest lived people have a history of comparatively little age-related disease: the only ways to become extremely old are to either (a) have accumulated damage at a slower rate that everyone else, most likely through lifestyle choices, or (b) bear genetic variants that increase resistance to some forms of damage and consequence. In either case, cell and tissue damage, aging, longevity, and age-related disease are all linked together, facets of the same whole.
In a large cohort of predominantly male community-dwelling elderly veterans, centenarians had a lower incidence of chronic illness than those in their 80s and 90s. The centenarian population is one of the fastest growing in the country, according to the United States Social Security Administration. They are predicted to exceed one million by the close of this century, little is known about why this generation has achieved such longevity. In a recent study, researchers looked primarily at octogenarians, nonagenarians, and centenarians within the Veterans Affairs medical system. The sample that they studied comprised mostly of white males that had fought in World War II. "Additionally, this generation lived through the Great Depression. It is a wonder, considering the hardships they had faced, that they have achieved such longevity."
A key factor that the research team observed in these individuals is that, due to their military background, many had a developed sense of discipline and therefore were keen to make healthy decisions; many did not smoke or drink. The team also offered the hypothesis of compression of morbidity as a potential explanation for the extended health span in an individual's life span. The hypothesis states that the lifetime burden of illness could be reduced if the onset of chronic illness is postponed until very late in life, or in other words "the older you get, the healthier you have been."
Ninety-seven percent of centenarians were male, 88.0% were white, 31.8% were widowed, 87.5% served in World War II, and 63.9% did not have a service-related disability. The incidence rates of chronic illnesses were higher in octogenarians than centenarians (atrial fibrillation, 15.0% vs 0.6%; heart failure, 19.3% vs 0.4%; chronic obstructive pulmonary disease, 17.9% vs 0.6%; hypertension, 29.6% vs 3.0%; end-stage renal disease, 7.2% vs 0.1%; malignancy, 14.1% vs 0.6%; diabetes mellitus, 11.1% vs 0.4%; stroke, 4.6% vs 0.4%) and in nonagenarians than centenarians (atrial fibrillation, 13.2% vs 3.5%; heart failure, 15.8% vs 3.3%; chronic obstructive pulmonary disease, 11.8% vs 3.5%; hypertension, 27.2% vs 12.8%; end-stage renal disease, 11.9% vs 4.5%; malignancy, 8.6% vs 2.3%; diabetes mellitus, 7.5% vs 2.2%; and stroke, 3.5% vs 1.3%).
A Popular Science Overview of Calorie Restriction Research
This popular science piece covers some of the high points of recent years in the field of calorie restriction research. It is above average for the type, though it has to be said that the bar has been set low by the media in recent years. This long-standing area of research involves quantifying the benefits to health and longevity produced by consuming fewer calories while still obtaining an optimal level of micronutrients, mapping the cellular mechanisms involved, and a search for ways to recreate some of these effects via calorie restriction mimetic drugs rather than diet.
Thanks to advances in medicine and improvements in healthy living, we benefiting from longer lifespans and also experiencing longer "healthspans". So, what do we need to do to enhance the length and quality of our lives even more? Researchers worldwide are pursuing various ideas, but for some researchers, the answer is a simple change in diet. They believe that the key to a better old age may be to reduce the amount of food on our plates, via an approach called "calorie restriction". This diet goes further than cutting back on fatty foods from time-to-time; it's about making gradual and careful reductions in portion size permanently.
Since a foundational study in 1935 in white rats, a dietary restriction of between 30-50% has been shown to extend lifespan, delaying death from age-related disorders and disease. Of course, what works for a rat or any other laboratory organism might not work for a human. Long-term trials, following humans from early adulthood to death, are a rarity. "I don't see a human study of longevity as something that would be a fundable research programme. Even if you start humans at 40 or 50 years old, you're still looking at potentially 40 or 50 more years of study." That's why, in the late 1980s, two independent long-term trials - one at NIA and the other at the University of Wisconsin - were set up to study calorie restriction and ageing in Rhesus monkeys. Not only do we share 93% of our DNA with these primates, we age in the same way too.
They are far from malnourished or starving. Take Sherman, a 43-year-old monkey from NIA. Since being placed on the CR diet in 1987, aged 16, Sherman hasn't shown any overt signs of hunger that are well characterised in his species. Sherman is the oldest Rhesus monkey ever recorded, nearly 20 years older than the average lifespan for his species in captivity. Even into his 30s he would have been considered an old monkey, but he didn't look or act like one. The same is true, to varying extents, for the rest of his experimental troop at NIA. "We have demonstrated that ageing can be manipulated in primates. It kind of gets glossed over because it's obvious, but conceptually that's hugely important; it means that ageing itself is a reasonable target for clinical intervention and medical treatment."
If ageing can be delayed, in other words, all of the diseases associated with it will follow suit. "Going after each disease one at a time isn't going to significantly extend lifespan for people because they'll die of something else. If you cured all cancers, you wouldn't offset death due to cardiovascular disease, or dementia, or diabetes-associated disorders. Whereas if you go after ageing you can offset the lot in one go."
In the Comprehensive Assessment of Long-Term Effects of Reducing Intake of Energy trial, also known as Calerie, over two years, 218 healthy men and women aged between 21 and 50 years were split into two groups. In one, people were allowed to eat as they normally would (ad libitum), while the other ate 25% less (CR). Both had health checks every six months. Unlike in the Rhesus monkey trials, tests over two years can't determine whether CR reduces or delays age-related diseases. There simply isn't enough time for their development. But the Calerie trials tested for the next best thing: the early biological signs of heart disease, cancer, and diabetes. The results after two years were very positive. In the blood of calorie-restricted people, the ratio of "good" cholesterol to "bad" cholesterol had increased, molecules associated with tumour formation - called tumour necrosis factors (TNFs) - were reduced by around 25%, and levels of insulin resistance, a sure sign of diabetes, fell by nearly 40% compared to people who ate their normal diets. Overall, blood pressure was lower.
With less food, is the metabolism forced to be more efficient with what it has? Is there a common molecular switch regulating ageing that is turned on (or off) with fewer calories? Or is there an as of yet unknown mechanism underpinning our lives and deaths? Answers to such questions might be long in coming. "If I cloned 10 of myself and we all worked furiously, I don't think we'd have it solved. The biology is inordinately complicated." It's a worthwhile undertaking - understand how CR works and other treatments could then be used to target that specific part of our biology. Ageing could be treated directly, that is, without the need of calorie restriction.
Using RNA Regulation to Argue for the Relevance of Transposons in Aging
Of late a number of research groups have argued that transposon activity is a contributing cause of dysfunction in aging. Transposons are sections of genetic material that can move around within the genome, and more of this moving around occurs with advancing age, taking place in a more or less random manner within individual cells. The discussion over whether and why this can be a significant cause of aging is similar to that for stochastic mutational damage in nuclear DNA. Here researchers point to a comparative lack of transposon activity in lower organisms such as hydra, species that exhibit exceptional regeneration and minimal aging, as a point to consider in this debate.
Intense investigation in aging research has led to the identification of over five hundred evolutionarily conserved genes, the mutational or RNA interference-mediated inactivation of which slows down the rate of the aging process in divergent eukaryotic species. While many of these genetic interventions can significantly promote longevity, they are unable to halt aging. Even mutant animals with extreme longevity continue to age, albeit at a diminished rate when contrasted with their corresponding controls. A related problem in aging research is that of the mortality rate, which displays an exponential growth throughout the adult life in numerous animal species. As the accumulation of mutations and harmful metabolic factors, such as reactive oxygen species, causing cellular damage, is known to occur at a nearly constant rate during the lifespan, this has bred speculations regarding potential genetic or metabolic components that are likely to be generated exponentially, and to primarily contribute to aging.
Triggered by unrepaired mutations, genomic instability is a key feature of aging cells. Nonaging biological systems however show either no or only limited signs of genome disintegration. Such potentially immortal systems involve the germline that genetically interconnects the subsequent generations, somatic cancer stem cells with indefinite proliferation capacity, and certain organisms from some 'lower' animal taxa, somatic cells of which display stem cell-like features. The term of 'nonaging cells' refers to cells constituting a tissue that traces an essentially immortal lineage. Nonaging tissues display an indefinite renewal capacity. In nonaging cells, genome integrity remains largely stable during the lifespan.
Genomic instability in aging cells progressively increases during adulthood, thereby limiting their capacity to proliferate and survive. A molecular machinery primarily responsible for maintaining the integrity of genetic material is the Piwi-piRNA pathway. This small RNA-based gene regulatory system operates predominantly in nonaging cells. The pathway was originally discovered in the Drosophila male germline, and established to function in repressing the activity of mobile genetic elements, also called transposable elements (TEs), transposons, or 'jumping genes'. In addition planarian flatworms and freshwater hydra somatically express components of the Piwi-piRNA pathway, rendering the self-renewal ability of their somatic cells apparently unlimited.
In the absence of active Piwi-piRNA pathway components, aging somatic cells tend to increasingly lose heterochromatin, which normally maintains TEs under transcriptional repression. Thus, during adulthood, the gradual release of TEs may generate considerable levels of molecular damage that overwhelm the capacity of the cellular maintenance and DNA repair systems. In addition to their increasing mobilization during adult life, TEs can inactivate genes that function in the repair and maintenance systems, further contributing to the age-associated accumulation of cellular damage. In contrast, the Piwi-piRNA pathway protects the germline and nonaging somatic cells from TE-mediated mutagenesis. Occasional mutations generated by chemical and physical mutagens are effectively recognized and eliminated by cellular maintenance and repair mechanisms.
Alternatively, the Piwi-piRNA pathway may have a different, TE-independent, but as of yet unexplored function to ensure genomic integrity in nonaging cells. For example, the pathway may regulate the transcription of certain key genes via modulating chromatin organization. It is also possible that besides the Piwi-piRNA system, another molecular mechanism operates in nonaging cells to preserve the stability of their genomes. Such a mechanism however has not yet been identified. Nevertheless, the activity of the Piwi-piRNA pathway is a shared feature of all nonaging cells identified so far.
The Contribution of Decreasing Cancer Mortality to Gains in Life Expectancy
This study provides an assessment of the impact of improvements in cancer prevention and cancer therapies over the past few decades, based on observed changes in life expectancy. In the opinion of the authors, better prevention is the more important contribution to these results - which doesn't say much for the current high level strategy in cancer research aimed at production of better therapies, given the vast sums devoted to that industry. Because of its focus on cancer, an unusual life expectancy construct is used in this study, considering only ages 40 to 84; cancer has a very low incidence at younger ages, and the risk declines again in late life, both absolutely, and in comparison to other causes of death.
Cancer is surpassing cardiovascular disease (CVD) as the leading cause of death in many high income populations and is projected to become a leading cause of morbidity and mortality worldwide in the coming decades. While substantial progress in reducing mortality from CVD has been shown, equivalent global assessment of cancer remains challenging, requiring a multifaceted and multi-indicator approach. Cancer mortality rates are declining in most highly developed countries, largely due to recent successes in the control of common cancers through programs of effective prevention, early detection, and treatment. In contrast, mortality rates of many types of cancer, including breast cancer and prostate cancer, are still increasing in transitioning countries, or at best stabilizing.
There is a need to quantify and better understand the position of cancer among other leading causes of avoidable death, including CVD, and the specific impact of major cancers as barriers to attaining old age. In this study, we quantify the contributions of changing cancer mortality rates on changes in life expectancy in ages 40-84 (LE40-84) over the period 1981-2010, adjusting for other causes of deaths, while making benchmark comparisons with equivalent gains achieved through the reduction of CVD mortality rates.
Only ages 40-84 were included, as individuals within this age group comprise the majority of cancer cases. In addition, in this age group there is also a lower probability of the causes of death being misreported and the existence of comorbid conditions compared with in those aged 85 or more, reducing bias related to competing causes of deaths. As a sensitivity test, we replicated the analysis for ages 0-39 and found that the contributions of cancer to change in life expectancy are negligible in this age group. Accordingly, LE40-84 throughout this article refers to life expectancy in ages 40-84, the expected number of years lived between ages 40 and 84, whereas we truncated years lived above age 85.
An overall decrease in mortality rates from all causes led to a noticeable increase in LE40-84 over the study period. In particular, very high Human Develpment Index (HDI) populations experienced gains of on average 3.7 and 2.5 years in LE40-84 among men and women, respectively, while respective values for medium and high HDI populations were lower, at 1.1 and 1.4 years. Decline in mortality rates from CVD was the main contributor, accounting for an average of more than 60% and 50% of declines in overall mortality rates in very high and medium and high HDI populations, respectively. Although decreasing overall cancer mortality rates were observed, they were greater in very high HDI populations (declines of 20% and 15% over the 30 year period for men and women, respectively) compared with medium and high HDI populations (4% and 5% decreases, respectively).
The past three decades have been marked by several triumphs in cancer control, which are clearly reflected in our results. For example, the increase in LE40-84 among men can be considered partly the result of corresponding declines in lung cancer mortality rates linked to improved tobacco control measures. Gains in life expectancy from a reduction of stomach cancer mortality rates links socioeconomic advancement to successes in combating infectious diseases through both "unplanned" prevention as well as treatment. In most of the very high HDI populations, the progress seen in terms of reductions in mortality rates from breast, prostate, and colorectal cancer can be related to a broad spectrum of cancer control interventions, including early detection, improved diagnosis, and better access to effective treatment.
Loss of TDP-43 Points to Microglia as a Cause of Lost Synapses in Alzheimer's Disease
The protein TDP-43 acts as a regulator of autophagy, among other things: more of it means less autophagy. The presence of increased amounts of TDP-43 has been investigated in the context of ALS and frontotemporal dementia, where it appears to cause more dysfunction than would be expected just from a loss of the cellular maintenance processes of autophagy. In this recent research, the focus is instead on Alzheimer's disease, where researchers discovered that reducing TDP-43 levels makes the immune cells called microglia more efficiently clear out the β-amyloid associated with this condition. Unfortunately, microglia are also involved in generation and maintenance of synapses, and loss of TDP-43 turns out to ensure that synapses are removed as well as the amyloid. Overall it seems that the amount of TDP-43 in circulation has a narrow safe range; therapies targeting it would have to be more sophisticated than just a blanket reduction or increase via pharmaceuticals. On the plus side, this research adds to the evidence for changes in microglia behavior to be important in neurodegenerative diseases, and there are many other options when it comes to adjusting the activities of these cells.
For the first time, researchers demonstrate a surprising effect of microglia, the scavenger cells of the brain: If these cells lack the TDP-43 protein, they not only remove Alzheimer's plaques, but also synapses. This removal of synapses by these cells presumably leads to neurodegeneration observed in Alzheimer's and other neurodegenerative diseases. Alzheimer's is a disease in which the cognitive abilities of afflicted persons continuously worsen. The reason is the increasing loss of synapses, the contact points of the neurons, in the brain. In the case of Alzheimer's, certain protein fragments, the β-amyloid peptides, are suspected of causing the death of neurons. These protein fragments clump together and form the disease's characteristic plaques.
In an initial step, the researchers looked at the effect that certain risk genes for Alzheimer's have on the production of the β-amyloid peptide. They found no effect in neurons. This led the researchers then to examine the function of these risk genes in microglia cells - and made a discovery: If they turned off the gene for the TDP-43 protein in these scavenger cells, these cells remove β-amyloid very efficiently. This is due to the fact that the lack of TDP-43 protein in microglia led to an increased scavenging activity, called phagocytosis.
In the next step, researchers used mice, which acted as a disease model for Alzheimer's. In this case, as well, they switched off TDP-43 in microglia and observed once more that the cells efficiently eliminated the β-amyloid. Surprisingly, the increased scavenging activity of microglia in mice led also to a significant loss of synapses at the same time. This synapse loss occurred even in mice that do not produce human amyloid. This finding that increased phagocytosis of microglia can induce synapse loss led researchers to hypothesize that perhaps, during aging, dysfunctional microglia could display aberrant phagocytic activity. The results show that the role of microglia cells in neurodegenerative diseases like Alzheimer's has been underestimated. It is not limited to influencing the course of the disease through inflammatory reactions and the release of neurotoxic molecules as previously assumed. Instead, this study shows that they can actively induce neurodegeneration.
Methuselah Fund Launches New Website
The Methuselah Fund is the evolution of the Methuselah Foundation's long-standing activities as an incubator of startups, such as Organovo, Oisin Biotechnologies, and Leucadia Therapeutics. In recent months the community has been invited to invest in expanding these efforts. The fund has just launched its website:
The Methuselah Fund (M Fund) is designed to accelerate results in the longevity field, extending the healthy human lifespan. Our success is measured by financial return on investments and furthering the mission, with the mission being the priority. Our DNA stems from The Methuselah Foundation, which has been working hard during the last 16 years to extend the healthy human lifespan. Our access to the key players in this space is significant and our ability to help our companies thrive is proven.
Our strategies are meant to be accessible to everyone since elegantly simple ideas can move masses. Our portfolio companies are achieving one or more of the our anti-aging strategies. New parts for people: technologies that will create new organs, bones, vasculature (with the probable near-term exception of the brain). Get the crud out: Safely remove senescent and other destructive biological structures, intercellular damage or waste (i.e. amyloid), etc. Restore the rivers: restore the circulatory system to full competence. Debug the code: restore informational integrity and viability of cells. Restock the shelves: replenish building blocks such as stem cells and immune system antibodies. Lust for life: restore the capacity for joy. For instance, rejuvenated senses and athletic competence.
Our portfolio companies include Leucadia Therapeutics and Oisin Biotechnologies. Leucadia Therapeutics has a unique and compelling approach on how to potentially predict, halt and cure early stage Alzheimer's Disease. 25 years of research have focused on plaques and tangles as the cause of Alzheimer's. At Leucadia, it is known that those are pathological effects of a more serious underlying condition. The science allows for the creation of a sophisticated surgical procedure bypassing the small molecule approach that has shown no progress until now. Oisin Biotechnologies' ground-breaking research and technology is demonstrating that one of the solutions to mitigating the effects of age-related diseases is to address the damage resulting from the aging process itself. Oisin is developing a highly precise, DNA-targeting platform to clear senescent cells. Oisin's platform has shown as much as an 80% reduction in senescent cells in cell culture and significant reductions of senescent cell burden in naturally aged mice.