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- Reviewing the Measurement of Biological Age in Humans
- The Degree to which Vascular Stiffness and Hypertension are Secondary Aging
- MicroRNA Inhibition to Enhance Skin Healing
- A High Level View of the State of SENS Rejuvenation Research
- An Angiogenesis Hypothesis of Aging
- Latest Headlines from Fight Aging!
- Modifying Macrophages to Accelerate Healing
- An Interview with James Peyer of Apollo Ventures
- A Potential Target to Prevent One Class of Autoimmune Diseases
- Impaired Insulin Signaling Outside the Nervous System Fails to Produce Life Extension in Mice
- An Example of the Early Stages of Antisenescence Drug Development
- In Search of Ways to Induce Heart Regeneration
- Exercise and Cardiovascular Aging
- Reviewing the Components of Age-Related Immune System Dysfunction
- An Update from Ambrosia on their Paid Plasma Transfusion Study
- Altering the Polarization of Microglia for Therapeutic Benefit
Reviewing the Measurement of Biological Age in Humans
To go along with a recent open access paper on progress in the development of biomarkers of aging, I though I'd point out another top to bottom review of the presently available means to measure aging in humans. This is an especially important topic now the first rejuvenation therapies, those based on targeted removal of senescent cells, are close to availability. Most of the drug candidates are in fact available now to some degree for the adventurous who would like to try self-experimentation. But if you self-experiment with a potential rejuvenation therapy, how do you know that it works? If you cannot answer that question, you should certainly hold back rather than forge ahead.
Since there are a number of distinct root causes of aging, at this stage in the field a given therapy will only target one of them, these first therapies will most likely be only partially effective, and biology is complicated and contrary, it would be entirely possible to try something and experience no obvious immediate outcome, whether or not it worked in the strict sense. Further, while one can measure the outcome appropriate to the therapy, for example the degree to which it does in fact remove lingering senescent cells, proof is still required to show that this outcome did in fact produce rejuvenation. Thus other measures of function and health are needed, and those must be generally agreed upon across the research community to accurately reflect the state of biological age.
While there are plenty of options to form the basis for a generally applicable measure of biological age, ranging from metrics built of a combination of simple measure such as grip strength to characteristic age-related changes in the patterns of DNA methylation, the "generally agreed upon" part of the process has yet to happen. Firstly there is the matter of proving that a given metric is actually useful, something that will probably only happen in conjunction with proving that the first rejuvenation therapies are in fact rejuvenation therapies. Secondly, the research community tends to move very slowly on the matter of establishing standards of any sort, and the more possibilities there are to debate and refine, the slower that progression.
This paper is somewhat illustrative of that point, given the scope and length of work that the authors foresee for the future. I suspect that things will move more rapidly than the future that these researchers envisage, however. My prediction is that the marketplace of biotech companies and clinics will settle on one or more forms of DNA methylation assessments of biological age as good enough at the cost required for their implementation, and move ahead to standardize on them long before the academic research community has finished their more painstaking efforts.
Molecular and physiological manifestations and measurement of aging in humans
In the 20th century, decreased mortality and lengthening of average human lifespan shifted the worldwide demographic structure toward the aged. This shift stemmed initially from treatment of infectious diseases and subsequently cardiovascular disorders. However, an increase in late-life disability has accompanied gains in healthy years lived (health span) and longevity. Biological aging is associated with a reduction in the regenerative potential in tissues and organs. Individuals with the same chronological age and their organs exhibit differential trajectories of age-related decline, and it follows that we should assess biological age distinctly from chronological age. Understanding the molecular and physiological phenomena that drive the complex and multifactorial processes underlying biological aging in humans will inform how researchers assess and investigate health and disease over the life course. In this review, we outline mechanisms of aging, discuss normal human aging at the organ-system level, suggest methods to measure biological age, and propose a framework to integrate molecular and physiological data into a composite score that measures biological aging in humans.
The heritable contribution to aging is limited for most humans, with genetics accounting for only 20-30% of lifespan variability in human twin and founder population family studies. However, heritable factors may represent a significantly larger contribution to lifespan at extreme ages, and the exceptionally aged may offer an opportunity to find rare genetic variants associated with longevity. Inter-related molecular and cellular phenomena occur during normal aging, intensify during accelerated or premature aging, and can be mitigated to increase lifespan. Researchers have proposed nine so-called hallmarks of aging - genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication - that frame mechanisms underlying senescence. As we discuss in this section, many hallmarks suggest potential therapeutic targets to restore age-associated functional decline, although potential therapies are not completely benign. Translation of these hallmarks with surrogate measurements are important to include in a composite biological age score (BAS) because of their direct relationship with the molecular basis of aging.
Physiological aging involves a progressive detrimental change in maximal organ function with differential trajectories across organ systems. Importantly, multiple factors including genetics, environmental conditions, and developmental programming determine maximal organ function, which varies significantly between individuals. Aging affects all organ systems and must be assessed through a variety of physiological measures, as aging varies greatly organ-to-organ and person-to-person and results in impaired reserve capacity and limited ability to respond to stress. While there appears to be an organ-specific or organ-differential resilience and vulnerability of aging, frailty refers to the cumulative decline and increasing homeostatic imbalance that precedes the ultimate consequence of aging: death.
Chronological age offers limited information regarding the complex processes driving biological aging. Individuals with the same chronological age vary greatly in health and in disease and disability prompting the utility of defining a 'biological age'. The conceptualization of such a biological age distinct from chronological age has been proposed by many researchers with measures as crude as functional 'frailty' and as sophisticated as patterns of DNA methylation. While much research has focused on quantification of biological aging, a comprehensive and integrative score incorporating molecular biomarkers and physiological functional parameters is lacking. Current strategies to assess systemic biological age carry significant limitations as individual parameters to accurately reflect an individual's global loss of homeostasis have been elusive. Further, biological plausibility suggests that no single biomarker is likely to suffice given the underlying multisystem nature of the aging process with changes occurring on a molecular and organ-based level underscoring the utility of an aggregate score of biological aging. Scoring systems require careful integration of molecular markers (surrogates of the hallmarks of aging) with longitudinal physiological functional measures, yet little consensus exists regarding optimal methods for creation and evaluation of a composite biological age score (BAS).
We propose a conceptual framework for a composite BAS, which integrates available molecular measurements based on the hallmarks of aging and functional organ physiology measurements across the life course. Comprehensive and repeated assessments over time of existing and emerging molecular biomarkers and organ-specific functional measures in longitudinal epidemiologic cohorts in parallel with the use of sophisticated bioinformatics methodologies are needed to derive a global BAS. In general, components of the BAS should be i) highly correlated with chronological age, ii) predict organ-system and global age-related decline, and iii) be minimally invasive, readily observable, and reliably measured. Investigation into the optimal parameters used to derive a BAS will require collection and analysis of data sets that include successful agers without morbidity as well as accelerated agers with genetic progeroid syndromes, inflammatory pathologic conditions, and disease-related morbidity. Derivation and validation of a BAS will require multiple types of study designs including observational prospective population-based cohorts, leveraging large sample sizes with repeated measures over several decades as well as case-control studies and family-based studies to incorporate less common phenotypes of interest, including successful agers and accelerated agers with nongenetic and genetic conditions.
The Degree to which Vascular Stiffness and Hypertension are Secondary Aging
Today's research results provide data to indicate the degree to which vascular stiffening and hypertension across today's population are the consequences of avoidable lifestyle choices and environmental factors rather than consequences of unavoidable processes of damage. The study suggests that cardiovascular aging can be influenced considerably until a comparatively late age, and in this it may be one of the most malleable of the many distinct aspects of aging. All of aging is some mix of primary and secondary contributions, varying widely between organs and circumstances. One can think of primary aging as the list of cell and tissue damage described in the SENS program, causes of aging that occur as a consequence of the normal, healthy operation of metabolism. Secondary aging, on the other hand, is some mix of being overweight, living a sedentary lifestyle, exposure to a toxic environment that spurs inflammation, exposure to pathogens that wear down the immune system, and so forth. Choices and environment, in other words - things that are optional or at least to some degree avoidable, and which act to accelerate the pace at which fundamental damage accrues.
Raised blood pressure, hypertension, is a good marker for cardiovascular mortality, and lowered blood pressure obtained through pharmacology and lifestyle changes have resulted in a considerable reduction in that rate of death over the past few decades. There is good evidence for hypertension to be largely caused by the stiffening of blood vessels, and the changes that loss of elasticity produces in the systems of feedback that guide blood flow and heart activity. Stiffening of blood vessels in turn is caused by a range of mechanisms, including calcification, the inflammatory activity of senescent cells, and the presence of cross-links in the extracellular matrix of blood vessel walls. Some of these contributing factors are more easily adjusted than others - levels of inflammation, for example. So while on the one hand it is encouraging to see that presently available courses of action can make some difference, on the other hand it all still ends in the same place, at least until such time as rejuvenation therapies after the SENS model of damage repair are developed. The manifestations of aging are produced by damage, and until that damage can be effectively repaired, there is only so far you can go with an optimal approach to secondary aging.
Common artery problems as you age may be avoided or delayed, study shows
Potentially dangerous artery problems considered common as people age may actually be avoided or delayed well into the senior years, according to new research. The risk for high blood pressure and increased blood vessel stiffness, which both increase the risk of heart disease, may be reduced with a healthy lifestyle. There's a catch, though: It takes a lot of work. "What we are showing is that, even in a population acculturated to a Western lifestyle, it is possible to maintain a healthy vasculature over age 70. But it is extremely challenging."
The researchers defined healthy vascular aging as absence of high blood pressure and having vascular stiffness of the arteries of a person 30 years or younger. In a study of nearly 3,200 people ages 50 and older from the Framingham Heart Study, researchers found 566 individuals, or nearly 18 percent, met the requirements for healthy vascular aging. Most were in the youngest group, ages 50 to 59, where about 30 percent had the measures of healthy vascular aging. Among those 70 and older, only 1 percent had the soft arteries of a 30-something. "People with healthy vascular aging were at a 55 percent lower risk of developing cardiovascular disease. Those results are mainly a result of the softness of their arteries." Most importantly, having a low body mass index and being free of diabetes seemed to be associated with healthier arteries into old age. Other factors, including use of lipid-lowering drugs, also made a difference.
Prevalence, Correlates, and Prognosis of Healthy Vascular Aging in a Western Community-Dwelling Cohort
Hypertension and increased vascular stiffness are viewed as inevitable parts of aging. To elucidate whether the age-related decrease in vascular function is avoidable, we assessed the prevalence, correlates, and prognosis of healthy vascular aging (HVA) in 3,196 Framingham Study participants aged ≥50 years. We defined HVA as absence of hypertension and pulse wave velocity of less than 7.6 m/s. Overall, 566 (17.7%) individuals had HVA, with prevalence decreasing from 30.3% in people aged 50 to 59 to 1% in those aged ≥70 years.
In regression models adjusted for physical activity, caloric intake, and traditional cardiovascular disease (CVD) risk factors, we observed that lower age, female sex, lower body mass index, use of lipid-lowering drugs, and absence of diabetes mellitus were cross-sectionally associated with HVA. Although HVA is achievable in individuals acculturated to a Western lifestyle, maintaining normal vascular function beyond 70 years of age is challenging. Although our data are observational, our findings support prevention strategies targeting modifiable factors and behaviors and obesity, in particular, to prevent or delay vascular aging and the associated risk of CVD.
MicroRNA Inhibition to Enhance Skin Healing
These are the opening years of a period of barnstorming and experimentation in the modification of regenerative processes. A growing mountain of knowledge is under construction for all of the most important aspects of regeneration: stem cells, cellular senescence, immune cell activity, and so forth. The cost of tools used in the biotechnology field is falling even as the capabilities of those tools increase dramatically. Exploration of the biochemistry of regeneration has never been as easy and as cheap as it is today. A tipping point has either passed or lies just ahead, with the result being an expanding diversity of ways to adjust the self-repair of tissues - and to perhaps restore a more youthful, healthy degree of healing where it is impaired by aging, by inflammation, or by metabolic diseases such as diabetes.
One of the important challenges found in most areas of modern medical research is targeting. As it becomes possible to edit genes and selectively increase or decrease the amounts of specific proteins inside cells, it is also becoming increasingly important for such changes to be localized. The amount of a given protein in circulation is a switch or a dial in the machinery of cellular metabolism, but the same protein can have radically different roles in different tissue types. So while a global adjustment throughout the body is in many cases quite feasible to achieve today, it is in many cases a bad idea to try it. A beneficial change in one tissue might even prove fatal in another. Thus a wide range of approaches are at various stages of development when it comes to to targeting therapies to specific tissues, as the better and more reliable the targeting mechanism, the more options become available as a basis for medical development. The paper I'll point out today is one example of the type:
New hope for slow-healing wounds
MicroRNAs are small gene fragments which bond onto target structures in cells and in this way prevent certain proteins from forming. As they play a key role in the occurrence and manifestation of various diseases, researchers have developed what are known as antimiRs, which block microRNA function. The disadvantage of this approach is, however, that the blockade can lead to side effects throughout the entire body since microRNAs can perform different functions in various organs. Researchers have now solved this problem.
The researcher have developed antimiRs that can be activated very effectively over a limited local area by using light of a specific wavelength. To this purpose, the antimiRs were locked in a cage of light-sensitive molecules that disintegrate as soon as they are irradiated with light of a specific wavelength. As a means of testing the therapeutic effect of these new antimiRs, the researchers chose microRNA-92a as the target structure. This is frequently found in diabetes patients with slow-healing wounds. They injected the antimiRs in the light-sensitive cage into the skin of mice and then released the therapeutic agent into the tissue with the help of light. Together the research groups were able to prove that pinpointed activation of an antimiR against microRNA-92a helps wounds to heal.
"Apart from these findings, which prove for the first time that wound healing can be improved by using antimiRs to block microRNA-92a, our data also confirms that microRNA-92a function is indeed only locally inhibited. Other organs, such as the liver, were not affected." The researchers now want to see whether they can also expand the use of light-inducible antimiRs to the treatment of other diseases. In particular they want to examine whether toxic antimiRs can attack tumors locally as well.
Light-inducible antimiR-92a as a therapeutic strategy to promote skin repair in healing-impaired diabetic mice
MicroRNAs (miRs) are small non-coding RNAs that post-transcriptionally regulate gene expression by binding to targeted mRNAs and thereby inducing degradation or blocking its translation. MiRs have important functions in different pathophysiological processes and diseases. Therefore, targeting miRs by application of specific miR inhibitors might have great therapeutic potential. MiRs can be inhibited by different types of antisense RNAs (antimiRs). Such antisense oligonucleotides are relatively easily taken up by detoxifying organs such as the liver or kidney, but uptake in other organs such as the muscle or brain tends to be limited. Local delivery or activation may be necessary to augment the biological functions of antimiRs in the target tissue and reduce systemic toxicity. Local activation might also avoid unwanted side effects of antimiRs, since miRs have diverse functions in different tissues.
Several targeting strategies have been experimentally used including the linking of miRs or antimiRs to aptamers, nanoparticle- or microparticle-mediated delivery and cell type-specific delivery by viral vectors as well as attempts of local delivery by mechanical tools, for example, catheters. In addition, we and others have developed photoactivatable antimiRs by attaching photolabile protecting groups (cages) to the nucleobases that temporarily inhibit duplex formation with the target miR, thereby allowing an excellent on/off behaviour upon irradiation.
However, the therapeutic in vivo use of light-activatable antimiRs has been unclear. Therefore, we tested whether light-activatable antimiRs directed against miR-92a can be used to locally augment impaired wound healing in diabetic mice. Inhibition of miR-92a was previously shown to improve angiogenesis and recovery after ischaemia; however, its regulation and function during wound healing, a process that is dependent on the angiogenic response, is unknown. Here we show that light-activatable antimiR-92a efficiently downregulate miR-92a expression leading to target gene derepression in the murine skin, thereby improving diabetic wound healing by stimulating cell proliferation and angiogenesis.
A High Level View of the State of SENS Rejuvenation Research
The Life Extension Advocacy Foundation (LEAF) volunteers caught up with Aubrey de Grey of the SENS Research Foundation at the recent International Longevity and Cryopreservation Summit held in Spain, and hence the publication of the high level view of current progress in SENS rejuvenation research that I'll point out today. The conference was an opportunity for members the overlapping European communities focused on longevity science, cryonics, and transhumanism to present their work, build their networks, and plan future initiatives. When it comes to longevity, the SENS research program looms large: its focus on repair of the known forms of molecular damage that cause aging so far appears to be the only approach to therapies for aging that can plausibly produce significant rejuvenation in our lifetime. Success here, meaning working rejuvenation therapies in the clinic, is conditional on continued growth in funding and support for this part of the field, however, and while a great deal has been accomplished, there is a lot of work yet to be done.
SENS: Where are we now?
RepleniSENS: Cell loss and tissue atrophy
Over the course of decades, long lived tissues like brain, heart and skeletal muscles gradually lose cells and as replacement dwindles their function becomes compromised. The brain also loses neurons which leads to cognitive decline and dementia as well as the loss of fine muscle movements. The immune system also suffers, with the thymus gradually shrinking and losing the ability to produce immune cells, leaving you vulnerable to diseases. Thankfully stem cell research and cell therapy is already a well advanced field. SENS has not needed to get involved in this area as it is well funded and moving along very rapidly. Only this month we have seen hematopoietic stem cells produced for the first time and research in this field is moving forward at a furious rate. It will be plausible in the near future that we will be able to produce every cell type within the body to replace age related losses.
OncoSENS: Cancerous cells
Cancer uses two pathways to uncontrolled growth: hijacking telomerase and using the Alternative Lengthening of Telomeres (ALT) mechanism. Both allow cancer to maintain its telomeres and grow out of control. Therapies that can inhibit these pathways could be combined and are therefore a potential way for us to defeat all cancers. ALT therapies are progressing following a successful fundraiser on Lifespan.io last year. SENS has been developing a high throughput assay for ALT allowing cost effective candidate evaluation for drugs that can inhibit or destroy cancer cells using ALT. Within the next year a company based on ALT should be possible. Telomerase inhibiting therapies are being developed by a number of organizations and companies so the SENS Research Foundation does not need to get involved with this. Therapies that inhibit telomerase in cancer cells are already in clinical trials and are well funded.
MitoSENS: Mitochondrial mutations
As mitochondria produce the chemical energy store ATP they also generate waste products as a byproduct, in this case highly reactive molecules called free radicals. Free radicals can strike and damage parts of the cell including the mitochondrial DNA (mtDNA), which, due to their close proximity to the source of free radicals, are very vulnerable to these damaging strikes. Damaged mutant mitochondria enter an abnormal metabolic state to remain alive. This leads to cells with damaged mitochondria that dump waste into the circulation causing system wide levels of oxidative stress to rise and driving the aging process.
The solution to this problem is gene therapy to move the mtDNA to the cell nucleus where it will have a far greater level of protection from free radical strikes. The SENS Research Foundation successfully fundraised for the MitoSENS project on Lifespan.io back in 2015. They then followed up with a publication in the prestigious Nucleic Acids Research journal showing their results in September 2016. Thanks to the support of the community the MitoSENS project succeeded in migrating not one but two mitochondrial genes to the cell nucleus, a world first. Since then progress has been rapid and they have now almost migrated 4 of the 13 mitochondrial genes. They are currently refining the process into a standardized therapy.
ApoptoSENS: Death-resistant cells
Our cells have a built-in safety device that causes cells that are dysfunctional and damaged to destroy themselves in a process known as apoptosis. However as we age cells increasingly fail to dispose of themselves in this manner and they enter a state known as senescence. As we age more of these cells build up leading to increasingly poor tissue repair and regeneration. There has been a huge level of interest in senescent cell removal therapies in the last year or two and a number of companies are currently developing senolytics. Unity Biotechnology is taking the first generation of senolytics into human clinical trials this year after being successfully funded by a number of big investors. However the heat is on as other companies are following up close behind with potentially more sophisticated approaches for removing senescent cells such as plasmid based solutions from Oisin Biotechnologies and a synthetic biology approach from CellAge who successfully fundraised on Lifespan.io last year.
GlycoSENS: Extracellular matrix stiffening
Blood sugar and other molecules react with structural proteins in tissues and bond with them creating fused crosslinks. Crosslinks bind neighboring proteins together impairing their movement and function. In the case of the artery wall crosslinked collagen prevents the artery from flexing in time with the pulse leading to hypertension and a rise of blood pressure. The SENS Research Foundation proposes to find ways to break down these crosslinks to restore movement to the structural proteins and thus reversing the consequences of their formation. The problem for many years was obtaining enough glucosepane, the primary constituent of human crosslinks, to be able to test therapies on. Thanks to funding by the SENS Research Foundation progress at Yale University now allows the cheap production of glucosepane on demand, this means that researchers can now test directly on it and find antibodies and enzymes to dissolve the accumulated crosslinks. Yale already has some antibodies against glucosepane, it is anticipated that by the end of the year monoclonal antibodies will be available and there is strong evidence for the existence of bacteria with enzymes that can break down glucosepane.
AmyloSENS: Extracellular aggregates
Misfolded proteins produced in the cell are normally broken down and recycled within the cell, but as we age more and more misfolded proteins accumulate to form sticky aggregates. These misshapen proteins impair cell or tissue function with their presence. This extracellular junk is known as amyloid and comes in a number of types. The work SENS Research Foundation funded at UT Houston in Sudhir Paul's lab is now in the hands of his company Covalent Biosciences, hopefully we will hear some news from them in the near future. Fortunately a number of alternatives are in development such as the GAIM system that appears capable of clearing multiple types of amyloids included those associated with Alzheimer's, Parkinson's and amyloidosis. The AdPROM protein targeting system also holds promise for selectively degrading target amyloids and other undruggable proteins to treat age-related diseases.
LysoSENS: Intracellular aggregates
Cells have a number of systems for breaking down unwanted materials, the lysosome is one of them. The lysosome can be considered to be a kind of cellular garbage disposal unit which contains powerful enzymes for breaking down unwanted materials. However, sometimes materials are fused together so well that not even the lysosome can break them down. This leaves the unwanted material sitting there and over time more and more of this material accumulates until it starts to interfere with lysosomal function. The solution to this problem proposed by the SENS Research Foundation is to identify new enzymes able to digest these insoluble wastes and supply macrophages and other cells with them so they can break it down. Ichor Therapeutics is taking SENS Research Foundation technology to market for macular degeneration with a therapy that removes a Vitamin A derivative that accumulates in the eye and causes blindness. Ichor has successfully conducted a seed round and is now undertaking a 15 million series A round. The company is less than a year away from human clinical trials.
It is true that the SENS initiative, the Strategies for Engineered Negligible Senescence, has come a long way from its turn of the century origins as a rallying point, a research proposal, and a few like-minded advocates and researchers. After fifteen years of earnest advocacy, fundraising, scientific work, and persuasion, some lines of SENS research are now in clinical trials and commercial development, numerous independent groups are working on SENS or SENS-like research, a great, sweeping, and positive change in the attitudes of the research community towards aging has taken place, and the SENS Research Foundation has a yearly budget of a few million provided by philanthropic donations - a mix of grassroots support by our community, and the greater material support provided a few high net worth individuals. This progress is a big deal, make no mistake: collectively our community has bootstrapped something from nothing, and that something has made and continues to make a great difference to our odds of living to see aging brought under medical control.
Yet this is still the beginning of the story, the opening of the age of rejuvenation, the very first portion of a much bigger picture. A great deal of necessary growth is yet to be achieved. Wherever we stand on the upward curve of bootstrapping and success, there is still a mountain ahead. The yearly funding needs to be hundreds of millions, not a few million. SENS must become the majority concern in the broader research community, not just a handful of labs and a few dozen lines of research. I believe that is is possible for us to create this future, as success in the SENS approach of senescent cell clearance will be proof enough to direct ever more researchers and funding sources towards repair and rejuvenation as a guiding strategy rather than their current approach of tinkering with metabolism to slightly slow down aging.
In any machine, biological or otherwise, repair will almost always have better and more cost-effective outcomes than trying to alter the way in which the machine operates: remove the rust and replace the worn parts rather than merely changing the oil while hoping for the best. This has already been quite adequately demonstrated in the case of aging: repair in the sense of targeted removal of senescent cells has achieved a greater and more reliable impact on aging in a few short years of animal studies, than has been achieved by the far greater, much more expensive, and longer-lasting efforts devoted to calorie restriction mimetic development.
The potential for SENS rejuvenation research is tremendous, and we are just getting started.
An Angiogenesis Hypothesis of Aging
There are many theories of aging, some with a broader scope, focused on the high level or the evolutionary explanation for aging and all of its variations in pace, and others that are more limited, examining just a few aspects of age-related decline and in search of the principle mechanisms that cause that decline. Today's example is one of the more compact theories of aging, restricting itself to considering the creation and maintenance of the network of capillaries that supplies tissues. The oxygen and nutrients carried by blood cannot perfuse far beyond blood vessels, and so every last cubic millimeter of the body must be reached by the circulatory system, where it branches out into the smallest and most numerous blood vessels, those too small to be discerned by the naked eye.
What does it tell us about aging that capillary density appears to decrease in older mammals? Cardiovascular disease is of course well known to be a major cause of mortality, but much of the focus there is on the stiffening of major blood vessels, hypertension, and dysfunction and remodeling of heart tissue. These are larger-scale phenomenon, undeniably important, but does their importance overwhelm what is going on at the small scale, in the network of capillaries throughout the body? The researchers here argue that the small scale is just as important.
One item to bear in mind when reading the paper here is that mitochondrial dysfunction of a fairly general sort, a global loss of function, is implicated in many aspects of aging. Mitochondria are the power plants of the cell, using nutrients to generate chemical energy store molecules. One might ponder on a connection between reduced capillary coverage and reduced mitochondrial activity due to a lack of nutrients; certainly a great deal of neurodegenerative disease research focuses on vascular dysfunction and consequently reduced delivery of oxygen and nutrients to the brain.
The other principle point made by the authors of this paper is that there may be a short path to therapies that can partially compensate for the loss of capillary density by spurring angiogenesis, the creation of new blood vessels. Angiogenesis has been fairly well studied in the cancer research community and elsewhere, and there are a wide range of targets and drug candidates to either increase or decrease angiogenesis rates. Since testing effectiveness would be a comparatively rapid process, it might be worth trying this approach even though it doesn't address the underlying reasons for the loss of capillary density. As to what those reasons might be, we can speculate; perhaps loss of stem cell activity, perhaps changes in the extracellular matrix, or perhaps chronic inflammation that disrupts the normal processes of regeneration and angiogenesis, to pick a few options for further discussion.
Pro-Angiogenesis Therapy and Aging: A Mini-Review
Elderly persons may experience a range of medical conditions: a fatal disease (cancer, stroke, etc.), chronic afflictions (diabetes, arthritis, atrial fibrillation, etc.), and troubling lesser ailments. The last is a collective term for 5 minor symptoms and signs of old age, which include general muscle weakness, cold intolerance, minor memory lapses, skin wrinkles, and the slow healing of bruises or abrasions in the skin. The lesser ailments of aging (LAA) are the focus of this review and are grouped together here because they may have a common vascular cause and may be treatable, as next explained.
It is well recognized that atherosclerosis in arteries and arterioles leads to major illnesses - stroke, heart disease, and peripheral vascular disease. Later in life, changes occur at the terminal end of the vascular tree, where capillaries develop looping, kinking, and extensive tortuosity. Not commonly appreciated is that capillaries also undergo significant regression in absolute number. Over 40 published studies have reported a reduced capillary density throughout the body of aged animals and people.
The development and maintenance of capillaries depend on angiogenesis - i.e., on genetically programmed levels of angiogenic growth factors (AGFs). During early growth and maturation of the body, the development and function of various organ systems involve rising levels of AGFs and an expanding microcirculation. However, during old age, people and animals show declining levels of such factors in various organ systems, paralleling the reduced capillary density. Thus, old age represents a deficiency condition for angiogenesis factors, much like hormone levels that are decreased in the elderly.
The idea that the lesser ailments may be due in part to age-associated diminished capillary density and AGFs is termed "the angiogenesis hypothesis of aging." Its corollary suggests that treatment with exogenous angiogenic factors should restore reduced capillary density in areas experimentally depleted of capillaries and may improve function in areas of naturally impaired microcirculation. Recombinant angiogenic factors have been shown to induce new capillary formation in ischemic and normoxic tissues within days, as observed in numerous animal studies. Thus, in theory, pro-angiogenesis therapy may ease the LAA after they have appeared or delay their development. This is in contrast to the pathology in the larger blood vessels, where fatty plaques and cholesterol deposits cannot be readily eliminated once acquired but only prevented in the decades before old age by avoiding risk factors - i.e., obesity, diabetes, hypertension, etc.
Countless theories have been advanced to explain aging in people but none has led to a widely accepted treatment based on reversing an underlying cause. Physiological aging is commonly assumed to be due to various causes. Indeed, if aging is the result of several enfeebling influences, then lessening any one might ease its symptoms and signs. Again, there is abundant evidence in the literature that a reduced capillary density and a waning angiogenesis occur during old age. It seems likely that these linked changes influence the physiological state of the aged body - accounting for its fading functions and possibly for the lesser ailments. A reduced cerebral capillary density may contribute to the more profound cognitive problems of old age; e.g., Alzheimer's disease.
Animal studies establish that exogenous AGFs generate new capillaries. While numerous investigators have administered recombinant AGFs to relieve specific conditions of ischemia in the human body, to my knowledge, no gerontologist has proposed pro-angiogenesis therapy for moderating or delaying the widespread reduced microcirculation occurring during old age. Therapeutic pro-angiogenesis seems a tenable consideration for the lesser ailments of the elderly. The extensive data referenced here bring to mind George Orwell's admonition "To see what is in front of one's nose needs a constant struggle."
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Modifying Macrophages to Accelerate Healing
The immune cells called macrophages play an important role in the healing of injuries. Their activities appear to be the key to examples of exceptional regeneration in mammals, for example. This may have something to do with their clearance of the transient senescent cells generated during regeneration, or may be related to other signaling processes. Researchers have in previous years shown that adjusting the behavior of macrophages can alter the pace at which wounds heal, and it is hoped that this might be a compensatory approach capable of reducing the loss of regenerative capacity that occurs with aging. Here is a recent example of work that runs along the same lines:
It has long been known that macrophages play a key role in the normal wound healing process. These cells specialize in major cellular clean-up processes and are essential for tissue repair; they accelerate healing while maintaining a balance between inflammatory and anti-inflammatory reactions. "When a wound doesn't heal, it might be secondary to enhanced inflammation and not enough anti-inflammatory activity. We discovered that macrophage behaviour can be controlled so as to tip the balance toward cell repair by means of a special protein called Milk Fat Globule Epidermal Growth Factor-8, or MFG-E8."
The researchers showed that when there is a skin lesion, MFG-E8 calls for an anti-inflammatory and pro-reparatory reaction in the macrophages. Without this protein, the lesions heal much more slowly. Then the researchers developed a treatment by adoptive cell transfer in order to amplify the healing process. Adoptive cell transfer consists in treating the patient using his or her own cells, which are harvested, treated, then re-injected in order to exert their action on an organ. This immunotherapeutic strategy is usually used to treat various types of cancer. This is the first time it has been shown to also be useful in reprogramming cells to facilitate healing of the skin.
"We used stem cells derived from murine bone marrow to obtain macrophages, which we treated ex vivo with the MFG-E8 protein before re-injecting them into the mice, and we quickly noticed an acceleration of healing. The MFG-E8 protein, by acting directly upon macrophages, can generate cells that will orchestrate accelerated cutaneous healing. The beauty of this therapy is that the patient (in this case the mouse) is not exposed to the protein itself. If we were to inject the MFG-E8 protein directly into the body there could be effects, distant from the wound, upon all the cells that are sensitive to MFG-E8, which could lead to excess repair of the skin causing aberrant scars named keloids. The major advantage of this treatment is that we only administer reprogrammed cells, and we find that they are capable of creating the environment needed to accelerate scar formation."
An Interview with James Peyer of Apollo Ventures
Apollo Ventures is one of the more recent additions to the presently small number of funds focused on investment in the longevity science space, and here I'll point out an interview with one of their founding partners. The Apollo principals are distinguished by being somewhat more vocal than most of their peers, the Methuselah Fund founders aside. To pick one example, the fund has launched the Geroscience online magazine to help advance the position that treating aging as a medical condition is both viable and desirable. As technologies based on the SENS view of achieving rejuvenation through damage repair arrive at the point of commercial viability, it is increasingly important that a healthy venture investment ecosystem exists to fund the biotech startups needed to push therapies towards the clinic.
Last week we talked with James Peyer, a partner at Apollo Ventures, to ask a few questions about how biotech is tackling the anti-aging space. For a long time, the anti-aging field has not seen much innovation, both due to a lack of scientific know-how as well as a lack of confidence on the part of pharma and regulatory agencies. Yet, in the past years, the field has started to turn into one of the most hyped areas in biotech, marked by the launch of companies like Unity Biotechnology, which recently raked in 116M in venture funding or Calico, which was co-founded by Google in 2013. Referring to a review article on the hallmarks of aging, Peyer explains that "within the last 5 years, our understanding has gone from theory and hypothesis-driven to really coalescing a strong data-driven knowledge base. The geroscience space has at least 80 mutations or chemicals that have been shown with some level of conviction to extend the healthy life span of a mouse."
Peyer mentions a group of scientists from Albert Einstein College of Medicine in New York that have been piloting such a preventative medicine study with a 7-year trial, to test whether the generic drug metformin can delay the onset of age-related conditions. "This model of a 7-year clinical trial though, that's not really something that can be easily translated to a commercial model with a patented drug. But what's going to come out of those trials in the next 5-10 years are biomarkers that will give us a hint on whether or not a drug is working to reduce the risk of age-related diseases, and then that biomarker could be used in future trials."
Apollo is following a slightly different path, though. The VC aims to go after geriatric syndromes, such as osteoarthritis, that are actually treatable medical conditions. "You'll be really focused on one indication that's a real clinical opportunity and move that towards the clinic just as you would with a traditional oncology drug or osteoarthritis drug. That's the opportunity that Apollo is really excited about and then, of course, there is the vision in the longer term that those two paths will come together and create a world where we can actually do preventive clinical trials. The big players that are now coming into the area are technology players like Jeff Bezos or Google. The internet space has attracted so much investment but the return profiles in this space actually look much worse compared to biopharma both in the US and the EU."
A Potential Target to Prevent One Class of Autoimmune Diseases
Autoimmune diseases, in which the immune system malfunctions to attack the patient's own tissues, are a challenge to investigate. The immune system is enormously complex, and making a definitive determination of the specific problems in its regulation that cause autoimmunity has yet to be achieved for most forms of autoimmune disease. Fortunately there has been some progress, such as the identification of age-associated B cells as necessary in the development of autoimmunity, and here the determination that JunB is critical to some autoimmune diseases. In both cases, these mechanisms might be targeted to produce broadly effective therapies. Yet even in absence of any useful targets, if there was a way to safely destroy all immune cells - without the use of damaging chemotherapeutic drugs that cause significant side-effects and mortality - then all autoimmune diseases could be cured. Malfunctions are a matter of state, and that state is stored in the immune cells themselves; if they are all removed, and the immune system allowed to repopulate itself from scratch, then this effectively restores a pristine and correctly functioning state.
Most of the current treatments against auto-immune diseases require to shut down major parts of the immune system, inhibiting desirable immune responses and, leaving the patient vulnerable to potentially life-threatening bacterial and viral infections. Such a drastic solution is required because until now scientists had yet not fully identified a different mechanism in these rogue cells they could use as a selective target - the known genetic material was common between healthy and rogue cells. But researchers have reported a previously undiscovered role for a known molecule - named "JunB" - and its associated gene: JunB seems to be essential for a specific type of white blood cell to turn toxic.
The scientists were investigating T Helper white blood cells, which coordinate the immune system response by secreting a diverse range of communication signals in the shape of molecules called interleukins. JunB operates in 'T Helper 17' cells, a subdivision that specifically promotes the initial immune response against an infection. But sometimes, these T Helper 17 cells turns rogue and become toxic for our guts and joints. "We have a lot of T Helper 17 cells in our guts. They have three major impacts on our body: first to maintain a healthy gut and second to deal with bacterial and fungi infections. The third is their toxicity leading to auto-immune diseases, which is something we want to avoid."
The scientists studied the process in which T-Helper 17 cells become toxic. One of the immune system communication molecules - interleukin 23 - is required to "wake up" T-Helper 17 cells during an infection and make it start fighting the invaders. But interleukin 23 is a double-edged sword: it also responsible for sometimes triggering the same T Helper 17 cell to turn rogue. For T helper 17 cells to hear the wake-up call, they need to display interleukin 23 receptors on their surface, which means the corresponding gene - usually switched off - needs to be activated. Finding a way to stop this interleukin 23 receptor gene from being activated is potentially key to shut down the entire process. And this is where JunB, the focus of this research, comes into play.
JunB is a transcription factor, which means it regulates - switches on and/or off - the activity of a gene or a group of genes in the cell's DNA. Researchers identified JunB by systematically checking transcription factors in the T Helper 17 cell DNA. For this purpose, they would "knock down" - meaning disrupt the gene DNA sequence - the genes for each transcription factor one by one. For each knocked down gene, they checked if the T Helper 17 cell still display its interleukin-23 receptors. When they knocked down JunB, they realized the T Helper 17 cells were no longer displaying interleukin 23 receptors and were unable to turn rogue. Moreover, mice in which T Helper cells lacked JunB were incapable of developing T Helper 17-related auto-immune diseases. An exciting part of this research is that T Helper 17 cells deprived of JunB are still able to accumulate in the gut and likely to cope and fight infections. Therefore, if scientists design a drug able to target JunB specifically, it should prevent T Helper 17 cells from turning rogue without impacting the immune system as a whole.
Impaired Insulin Signaling Outside the Nervous System Fails to Produce Life Extension in Mice
This paper might be taken as an interesting sidebar to the large amount of research into the influence of insulin signaling on the pace of aging, a part of the way in which the operation of cellular metabolism determines natural variations in longevity. Many of the methods of slowing aging in laboratory species involve some form of impairment in insulin signaling, usually implemented globally in all tissues and throughout the entire life span via the use of genetic engineering to create an altered lineage of animals. Whether such alterations are global and when in life they occur matters, however. Further, most investigations have taken place in lower species such as flies and worms rather than in mammals. Here, researchers demonstrate that impaired insulin signaling achieved in adulthood and only in tissues other than the nervous system has no positive effect on mammalian life span.
Longevity is determined by a complex interaction between environmental and genetic factors. One of the most successful interventions to delay the onset of aging-associated diseases and increase life expectancy is the chronic reduction in food intake, that is calorie restriction (CR). One of the mechanisms through which CR may extend lifespan is through reduced activation of insulin/IGF1 signalling. Following food intake, insulin is released and acts via the insulin receptor (IR) to facilitate the metabolism of glucose. Altering glucose metabolism via the inhibition of glycolysis or the impairment of insulin/IGF1 signalling consistently extends lifespan in Caenorhabditis elegans and Drosophila melanogaster. However, the effect of insulin/IGF1 signalling cascade inhibition on longevity in mammals is less clear.
In mammals, prenatal complete ablation of the insulin receptor (IR) or IGF1 receptor (IGF1R) globally shortens lifespan, whereas ablation of the IR in some tissues such as the liver and pancreas induces a diabetic phenotype. The IR appears to play a central role in normal development, and central nervous system (CNS) IR expression in adulthood is required for the maintenance of glucose homeostasis. This suggests that the absence of the IR in peripheral tissues during early development, and in the CNS during adulthood may contribute to reduced lifespan and diabetic phenotype seen in some prenatal IR knockout models. Interestingly, deletion of the IR, which primarily targets adipose tissue but may also act on several other nervous system and peripheral tissues, as well as the disruption of the insulin/IGF1 signalling pathway downstream of the IR, is effective in prolonging lifespan in rodents. Furthermore, some genetic variations in the insulin/IGF1 pathway are associated with increased human lifespan expectancy. This is consistent with the requirement of the IR to facilitate metabolism of glucose in peripheral tissue and indicates that some degree of IR signalling is probably required during development and adulthood for normal life expectancy.
In all of these studies, however, the disruptions in insulin signalling were created using systems that were active from early developmental stages, so little is known about the effects of altered insulin signalling on longevity when the alteration is limited to adulthood. We have previously shown that partial disruption of the IR in mammalian cells causes adaptations, and similar adaptations extend the lifespan of C. elegans. In the present study, we determined the effect of partial or complete adult-induced peripheral tissue IR disruption on metabolism and lifespan of mice. Complete peripheral IR disruption resulted in a diabetic phenotype with increased blood glucose and plasma insulin levels in young mice. Although blood glucose levels returned to normal, and fat mass was reduced in aged mice, their lifespan was reduced. By contrast, heterozygous disruption had no effect on lifespan. This was despite young male mice showing reduced fat mass and mild increase in hepatic insulin sensitivity. In conflict with findings in metazoans like Caenorhabditis elegans and Drosophila melanogaster, our results suggest that heterozygous impairment of the insulin signalling limited to peripheral tissues of adult mice fails to extend lifespan despite increased systemic insulin sensitivity, while homozygous impairment shortens lifespan.
An Example of the Early Stages of Antisenescence Drug Development
The presence of senescent cells is a contributing cause of aging; the number of such cells grows over time as a consequence of the normal operation of metabolism, and collectively they cause considerable harm to tissue and organ function. The most important lines of research on cellular senescence aim at the production of senolytic therapies capable of removing these unwanted cells, but a sizable fraction of the researchers involved in this part of the field are more interested in antisenescence treatments, those that minimize the bad behavior of these cells, or reduce the number of cells that become senescent.
It would perhaps be more accurate to say that there is an ongoing reassessment of protein and drug candidate libraries in order to categorize known effects in terms of their influence on cellular senescence; all too much of medical research involves repurposing of existing drugs where there is any small positive outcome rather than building better technologies from first principles. When it comes to looking at existing outcomes from the drug and protein libraries in search of modifications to the behavior of senescent cells, my impression is that this is a road to marginal therapies only, those that slightly reduce the impact of senescent cells rather than solving the problem completely. This is a widespread problem in the research community, in which too many people are devoting resources to projects that are unlikely to have a sizable impact on aging.
Kallistatin, an endogenous protein, protects against vascular injury by inhibiting oxidative stress and inflammation in hypertensive rats and enhancing the mobility and function of endothelial progenitor cells (EPCs). We aimed to determine the role and mechanism of kallistatin in vascular senescence and aging using cultured EPCs, streptozotocin (STZ)-induced diabetic mice, and Caenorhabditis elegans (C. elegans). Human kallistatin significantly decreased TNF-α-induced cellular senescence in EPCs, as indicated by reduced senescence-associated β-galactosidase activity and plasminogen activator inhibitor-1 expression, and elevated telomerase activity. Kallistatin blocked TNF-α-induced superoxide levels, NADPH oxidase activity, and microRNA-21 (miR-21) and p16INK4a synthesis. Kallistatin prevented TNF-α-mediated inhibition of SIRT1, eNOS, and catalase, and directly stimulated the expression of these antioxidant enzymes.
Moreover, kallistatin inhibited miR-34a synthesis, whereas miR-34a overexpression abolished kallistatin-induced antioxidant gene expression and antisenescence activity. Kallistatin via its active site inhibited miR-34a, and stimulated SIRT1 and eNOS synthesis in EPCs, which was abolished by genistein, indicating an event mediated by tyrosine kinase. Moreover, kallistatin administration attenuated STZ-induced aortic senescence, oxidative stress, and miR-34a and miR-21 synthesis, and increased SIRT1, eNOS, and catalase levels in diabetic mice. Furthermore, kallistatin treatment reduced superoxide formation and prolonged wild-type C. elegans lifespan under oxidative or heat stress, although kallistatin's protective effect was abolished in miR-34 or sir-2.1 (SIRT1 homolog) mutant C. elegans. Kallistatin inhibited miR-34, but stimulated sir-2.1 and sod-3 synthesis in C. elegans. These in vitro and in vivo studies provide significant insights into the role and mechanism of kallistatin in vascular senescence and aging by regulating miR-34a-SIRT1 pathway.
In Search of Ways to Induce Heart Regeneration
The heart is one of the least regenerative organs in mammals, but this actually isn't the case in every circumstance; some types of injury and stimulus do produce a greater regenerative response, even if nowhere near as large as desired. The suspicion is that the capacity for greater regenerative exists, but is muted in some way, perhaps by cancer suppression mechanisms such as the ARF gene. Thus researchers are hunting for clues in the biochemistry of more regenerative species, such as zebrafish and salamanders, in order to discover whether or not mammalian heart cells can be adjusted to heal injuries more readily. Another place to look, as illustrated here, is in the biochemistry of the few circumstances in which mammalian hearts are known to regenerate more readily.
In adult mammal hearts, cardiomyoctyes do not proliferate following damage, like that caused by myocardial infarction. However, the inability to proliferate is not true for all animals, and even in mammals, cardiomyocyte proliferation is known. Neonatal cardiomyocytes proliferate, and the cardiomyocytes of zebrafish proliferate through adulthood, for example. However, hearts recover well from myocarditis, suggesting adult cardiomyocytes can proliferate in certain conditions. Myocarditis describes inflammation of the heart, usually in response to a viral infection. Many patients will suffer from cardiac dysfunction but recover naturally, largely because of factors activated by the immune response.
Researchers prepared mice with myocarditis to investigate this recovery under the assumption that proliferation was not the cause. "We hypothesized that immune factors are responsible. STAT3 is a transcription factor with cardioprotective effects. But in our study, we found it also has cardioproliferative effects. In myocarditis, we found that STAT3 was activated and that cardiomyocytes could proliferate. But when we knocked-out STAT3, the proliferation was lost." For cells to proliferate, they must enter the cell cycle. Following birth, mammalian cardiomyoctyes exit the cell cycle. The researchers found that in myocarditis, cardiomyoctyes could reenter the cycle to proliferate and recover heart function.
In myocarditis about 1% of cardiomyocytes express Aurora B, an indicator of cells entering the cell cycle, but in myocardial infarction (heart attacks) only 0.01% of cardiomyocytes expressed Aurora B. The team also found that the activation of STAT3 and expression of cell cycle markers could be stimulated by the immune protein interleukin 11, suggesting a possible cytokine means to initiate the proliferation. "These were very surprising findings. We still have much to learn about how the inflammatory signaling can promote heart regeneration. Medicines that activates these pathways could lead to new cardiac drugs."
Exercise and Cardiovascular Aging
As a companion piece to a recent paper on the degree to which cardiovascular aging can be postponed through lifestyle choices, here researchers review the differences observed in the cardiovascular system between people who do maintain physical activity and people who do not. While the benefits are undeniable, you can't reliably exercise your way to living to 100 in good health - the majority of physically fit people don't make it to 90 given today's level of medical technology, and everyone who lives to 100 is greatly impacted by the damage of aging. However, the fact that we live in an era of accelerating progress in biotechnology and its application to medicine suggests that every extra year counts. The technologies of tomorrow will be far more impressive than those of today. That extra year might mean that you avoid dying too early, or being too frail to benefit from the first generation of rejuvenation therapies that will emerge over the next few decades.
Chronological age is identified as the major risk factor for cardiovascular morbidity and mortality, with older people significantly more likely to have cardiovascular disease. In the absence of hypertension or clinically apparent cardiovascular disease, the cardiovascular system undergoes structural and functional changes with age that compromise cardiac reserve. These age-associated cardiovascular changes lower the threshold for the three major cardiac pathophysiological conditions such as left ventricular hypertrophy, chronic heart failure and atrial fibrillation, all seen with increasing age.
In order to understand the effects of aging on the cardiovascular system, it is important to consider the complex interaction between the heart as a pump and the afterload on the heart imposed by the arterial system. Cardiac aging is associated with progressive loss of myocytes and compensating mild hypertrophy, but also with reduced sensitivity to sympathetic stimuli that compromises myocardial contractility and pumping ability in older people. With advanced aging, the large arteries dilate, their walls become thicker and stiffer due to collagen and calcium deposition and fragmentation of the elastic fibres.
Physical activity, exercise, and associated high level of cardiorespiratory fitness reduce all cause and cardiovascular mortality, the risk of heart failure and myocardial infarction, and age-related arterial and cardiac stiffening. Epidemiologic studies investigating the association of physical activity with cardiovascular disease risk have been conducted for more than six decades now. The earliest studies from the 1950s showed that men who were physically active on the job experienced coronary heart disease mortality rates that were approximately half those of men who were sedentary at work. Following these observations, studies in the 1960s showed that men who died from coronary heart disease were approximately 40% to 50% less likely to be recreationally active, compared with men who remained alive.
Numerous epidemiological studies were published since these early investigations reporting strong association between physical activity in cardiovascular health with 30% to 40% reduction in all-cause and cardiovascular mortality in active men and women of different age. Conversely, low active and sedentary behaviour are associated with 63% greater risk to develop cardiovascular disease. From the evidence available it is now clear that physical activity and exercise can attenuate the age-related cardiovascular changes by improving functional capacity of the cardiovascular system, cardiac function, and metabolism.
Reviewing the Components of Age-Related Immune System Dysfunction
The short open access review paper noted here sketches a high-level picture of the known components of immune system aging, without going into great detail. The progressive failure of the immune system is a significant component of the frailty that accompanies old age; not only are the elderly vulnerable to pathogens that are easily resisted in youth, but the immune system fails to destroy senescent and potentially cancerous cells, increasing their contribution to aging and mortality risk. Some of this decline is the result of molecular damage after the SENS vision for the treatment of aging, but some is a matter of misconfiguration and limits.
The immune system retains a memory of the pathogens it encounters; that memory can become corrupted in a number of ways, and in the end it simply takes up too much of the limited capacity of the immune system. Capacity is limited in part because the thymus atrophies with age, reducing the supply of new immune cells to a low level in comparison to childhood. In old age, there are too many memory cells, most uselessly specialized to persistent but otherwise minor threats such as cytomegalovirus, and too few cells capable of tackling new pathogens. This part of the problem at least might be solved in the near future through selective destruction of misconfigured or damaged immune cells, and their replacement with new cells cultured from a patient blood sample.
Human aging is characterized by both physical and physiological frailty. With progressive age, the immune system and the propensity for abnormal immunity change fundamentally. Aging is associated with a decline in multiple areas of immune function. Aging is associated with a sort of paradox: a state of increased autoimmunity and inflammation coexistent with a state of immunodeficiency. Immunosenescence is a new concept that reflects the immunological changes associated with age. There are three theories that explain the phenomenon of immunosenescence.
According to the autoimmune theory of aging, the immune system tends to lose efficiency and experiences widespread dysfunction, evidenced by autoimmunity (immune reactions against one's own body proteins). Two age-related processes cause autoimmune diseases: (i) different rates of senescent cell accumulation in the immune system and target tissue/organ and heterogeneous accumulation of senescent cells in tissues/organs. Separately or combined, these two processes are at the base of autoimmune diseases. The production of autoantibodies has been hypothesized to be secondary to thymus involution with a decline of naïve T cells and the accumulation of clonal T cells with activation due to "neoantigens" during the aging process.
With advancing age the body is unable to defend itself from pathogens and results in a detrimental harm; this is the focus of immunodeficiency theory. Clinical evidence indicates that with advancing age, immune responses against recall antigens may still be conserved, but the ability to mount primary immune responses against novel antigens declines significantly. The impaired ability to mount immune responses to new antigens may result in a high susceptibility to infectious diseases. The immune responses to novel antigens rely on the availability of naive T cells. Together with the age-related thymic involution, and the consequent age-related decrease of thymic output of naive CD8+ T-cell reservoir, this situation leaves the body practically devoid of naive T cells, and thus likely more prone to a variety of infectious and non infectious diseases.
Ageing is associated with various changes in immune parameters, therefore many authors have postulated that these age-related diseases could be explained, at least in part, by an overall deregulation in the immune system response, leading to a deregulation theory of immune system aging. This is supported by an age-associated disruption to the balance of alternatively expressed isoforms for selected genes, suggesting that a modification of the mRNA processing may be a feature of human aging. The observed down regulation of toll-like receptors (TLRs) and nod-like receptors (NLRs) during the aging process may contribute to the lack of effective recognition of invading pathogens or the commensal flora. This effect results in aberrant secondary immune cell activation and could significantly contribute to morbidity and mortality at an advanced age.
An Update from Ambrosia on their Paid Plasma Transfusion Study
You might recall that Ambrosia was founded to obtain human data on blood plasma transfusions between young and old individuals. There has been the standard grumbling about their efforts being a paid trial without controls, but if one is only concerned with the identification or ruling out of large and reliable effects, that gets the job done. When the necessary millions in funding for formal studies cannot be found, as is often the case, then patient paid studies are a way to make some progress. If compelling enough results are produced, than it will be much easier to fund more rigorous efforts to quantify outcomes.
This recent commentary suggests that none of the results so far are either large enough or extensive enough to definitively be something other than the placebo effect, chance, or other items such as a patient making lifestyle changes. I think there is some skepticism regarding the potential effectiveness of transfusions of young blood in any case; the data is somewhat mixed, and underlying theory on what is going on still in flux. Recent research suggests that the effects observed in parabiosis studies of mice with joined circulatory systems are due to a dilution of harmful factors in old blood rather than a delivery of helpful factors from young blood, for example. If the case, that would mean that transfusions should produce very limited results at best. Still, obtaining data is the important thing, and that is what is being done here. Those complaining the loudest should put in the work to raise funds and run a study they way they would prefer to.
Older people who received transfusions of young blood plasma have shown improvements in biomarkers related to cancer, Alzheimer's disease and heart disease. Since August 2016, Ambrosia has been transfusing people aged 35 and older with plasma - the liquid component of blood - taken from people aged between 16 and 25. So far, 70 people have been treated, all of whom paid Ambrosia to be included in the study. The first results come from blood tests conducted before and a month after plasma treatment, and imply young blood transfusions may reduce the risk of several major diseases associated with ageing.
None of the people in the study had cancer at the time of treatment, however the Ambrosia team looked at the levels of certain proteins called carcinoembryonic antigens. These chemicals are found in the blood of healthy people at low concentrations, but in larger amounts these antigens can be a sign of having cancer. The team detected that the levels of carcinoembryonic antigens fell by around 20 per cent in the blood of people who received the treatment. However, there was no control group or placebo treatment in the study, and it isn't clear whether a 20 per cent reduction in these proteins is likely to affect someone's chances of developing cancer.
The team also saw a 10 per cent fall in blood cholesterol levels. "That was a surprise." This may help explain why a study by a different company last year found that heart health improved in old mice that were given blood from human teenagers. They also report a 20 per cent fall in the level of amyloids - a type of protein that forms sticky plaques in the brains of people with Alzheimer's disease. One participant, a 55-year-old man with early onset Alzheimer's, began to show improvements after one plasma treatment, and his doctors decided he could be allowed to drive a car again. An older woman with more advanced Alzheimer's is reportedly showing slow improvements, but her results have not been as dramatic.
Altering the Polarization of Microglia for Therapeutic Benefit
In past years, researchers have established that the immune cells known as macrophages are involved in wound healing, and are split into groups with different polarizations (M1 and M2) that play different roles in this process. Adjusting the balance between the numbers in each group may enhance regeneration, and a disarray in this balance of numbers appears to take place over the course of aging, perhaps contributing to the decline in regenerative capacity. This polarization and its consequences exist for microglia as well, the predominant immune cell in the brain. These cells are responsible for a great many tasks beyond those of immune cells elsewhere in the body; not just clearing debris and pathogens, but also deeply involved in the correct function of connections between brain cells, for example. In this paper, researchers discuss the potential to obtain therapeutic benefits through adjusting the balance of polarization types in the microglial population.
Microglia, the resident immune cells of the central nervous system (CNS), are highly specialized macrophages that play a fundamental role in neurodegenerative diseases. Microglia have been traditionally classified as either of the following: (1) resting with branched morphology and present in healthy brains or (2) activated with amoeboid morphology and present in diseased brains. Recent microglia classifications are more complex. Activated microglia are now recognized as being heterogeneous and plastic, and exist in various phenotypes in the CNS. Microglia can be divided into at least two types (neurotoxic or neuroprotective) based on their function. Microglia can promote neurotoxicity via the release of several pro-inflammatory mediators, such as nitric oxide, interleukin (IL)-1β, and tumor necrosis factor-alpha (TNF-α). Conversely, they can be neuroprotective and neurosupportive, via several mechanisms under certain conditions. For example, neuroprotective roles of microglia include glutamate uptake, removal of dead cell debris and abnormally accumulated proteins, and production of neurotrophic factors.
The dual nature of microglial functional polarization is consistent with the general classification of macrophages as being either the M1 (classic pro-inflammatory) or M2 (anti-inflammatory) phenotype. Specific environmental cues induce macrophages to adopt a given functionality. For example, stimulation with either lipopolysaccharide (LPS) or interferon (IFN)-γ induces activation of the classical M1 phenotype, whereas stimulation with either IL-4 or IL-13 induces the M2 activation. Microglia are critical to immune response in the CNS, and unsurprisingly, microglial functional polarization has been implicated in almost all CNS disorders, and in the progression of neurodegenerative diseases. Microglia also play key functional roles in recovery from brain injury and in the maintenance of homeostasis in the brain.
Although the specific classification of M1 and M2 functionally polarized microglia remains a topic for debate, the use of functional modulators of microglial phenotypes as potential therapeutic approaches for the treatment of neurodegenerative diseases has garnered considerable attention. The modulation of microglial polarization toward the M2 phenotype may lead to development of future therapeutic and preventive strategies for neuroinflammatory and neurodegenerative diseases.