Antibody Binding Changes with Age and Can be Used to Build an Immune Aging Clock

In recent years, researchers have used omics data to construct an ever broadening variety of clocks that measure biological age. This is a natural consequence of plentiful computing power and its effects on materials science, one outcome of which is a dramatic improvement in the cost and capability of biotechnology, from sequencing DNA to assessing protein levels. The cost of cell data obtained from tissue and blood samples has fallen to the point at which even small labs can make significant contributions to the field.

Epigenetic marks on the genome, alongside mRNA and protein levels, have been used in most of the clocks constructed to date. Any such database covering many individuals at many different ages is raw material for the discovery of correlations between biological data and age. The better clocks tend to reflect mortality rather than age, in that people with a measured clock age older than their real age are in fact more burdened by aging than their peers: suffering greater incidence of age-related disease and greater mortality rate.

The authors of today's open access paper report on a different approach to an aging clock, one based on circulating antibodies and their ability to bind a selection of proteins. It isn't surprising that researchers can establish a clock in this case, as the work to date on epigenetic, transcriptomic, and proteomic clocks suggests that any sufficiently complex system in the body will give rise to data that can be used in this way. What is worthy of note is that autoimmune conditions accelerate age as measured by this clock.

Age-associated changes in the circulating human antibody repertoire are upregulated in autoimmunity

Ageing is associated with broad decline in organ function and increased risk for chronic disease. The immune system undergoes dramatic changes associated with age, including decreased immune response, loss of immune memory, and increased chronic inflammation. Ageing broadly impacts humoral immunity, as antibody affinity and the adaptive immune processes that lead to their production suffer with age. For instance, plasma cells produce less antibody, germinal center B cell selection results in lower affinity antibodies in mouse, and the CD4+ T cell receptor diversity decreases. Additionally, hematopoiesis broadly declines, professional antigen presenting cells reduce expression of peptide-MHC-II complex, and antibody effector cells show decreased functional clearance of IgG-bound pathogens. These age-dependent declines in humoral immunity can be manifested in less effective antibody binding.

To better understand and quantify the impact of ageing on the immune response, we identified age-associated patterns in serum antibody binding profiles. We profiled IgG antibody binding using peptide microarrays in a cohort of 1675 donors. We created a machine learning model that estimates an "immune age" from a donor's antibody binding profile that is highly correlated with chronological age.

The immune age is highly robust with respect to technical parameters, such as reagents, peptide microarray design, and serum handling. The machine learning regression model was validated on an independent donor cohort and longitudinal profiling revealed that a donor's immune age is typically consistent over multiple years suggesting that this could be a robust long-term biomarker of age-associated humoral immune decline. We show that accelerated immune ageing, when a donor has an older immune age than chronological age, is associated with autoimmunity, autoinflammatory disease, and acute disease flares.

In conclusion, the circulating antibody repertoire has increased binding to thousands of peptides in older donors, which can be represented as an immune age. Increased immune age is associated with autoimmune disease, acute inflammatory disease severity, and may be a broadly relevant biomarker of immune function in health, disease, and therapeutic intervention. The immune age has the potential for wide-spread use in clinical and consumer settings.

Reviewing Present Thought on the Cause of Mitochondrial DNA Mutations in Aging

Mitochondria, the power plants of the cell, are the descendants of ancient symbiotic bacteria, and carry a remnant of the original bacterial DNA. This mitochondrial DNA is less well protected and repaired than the DNA found in the cell nucleus, but still encodes a number of vital proteins. Damage to mitochondrial DNA can in some cases produce pathological mitochondria that cause cells to export large numbers of harmful oxidative molecules. This can contribute to the onset and progression of age-related diseases in a number of ways. More generally, mitochondrial DNA damage may produce loss of mitochondrial function with age, but whether or not that is important in comparison to other factors, such as reduced mitophagy, a quality control mechanism that removes damaged mitochondria, is open to question. Why does mitochondrial DNA damage occur? As noted here, opinions on this topic have shifted in recent years.

A major assumption of the free radical theory of aging is that random de novo or somatic mitochondrial DNA (mtDNA) mutations gradually accumulate over time, eventually reaching pathological levels. However, data supports the hypothesis that, rather than gradually accumulating over time, mtDNA turnover can lead to the clonal expansion of pre-existing age-related mutations. Once amplified, these higher frequency mtDNA mutations, that are potentially pathogenic, are referred to as heteroplasmy.

To further understand the potential link between mtDNA mutations and the free radical theory of aging, our group examined aging in the context of tobacco smoking and human immunodeficiency virus (HIV) infection, both believed to accelerate aging. Data suggests that smoking and HIV may distinctly contribute to the accumulation of mtDNA mutations. Indeed, smoking showed an association with increased mtDNA heteroplasmy but not somatic mutations, while the reverse was observed with HIV participants, but only in those with a history of high viremia, reflecting poor control of HIV. These results suggest that the chronic immune activation and subsequent oxidative stress induced by HIV may lead to de novo mtDNA mutations, while oxidative damage associated with exposure to tobacco smoking may promote the clonal amplification of pre-existing mtDNA mutations.

Such a pattern is not consistent with the gradual build-up of random mtDNA mutations. Taken together, our findings do not support the slow accumulation of mtDNA transversion mutations as proposed by the free radical theory of aging. Rather, they suggest that randomly mutated molecules of mtDNA are being clonally amplified to generate unique patterns of heteroplasmy in our participants.

Although the accumulation of mtDNA mutations has been linked to older age and age-associated conditions, several studies have provided new insight that challenge the connection between oxidative damage and mtDNA mutations. For example, the most studied oxidative lesion, 8-oxodG, is one of the 37 major oxidative lesions, and is known to induce transversion mutations (A ↔ C, A ↔ T, C ↔ G, G ↔ T). However, recent studies showing the accumulation of mtDNA mutations with aging did not observe increases in mtDNA transversion mutations, but rather increases in mtDNA transition mutations (A ↔ G, C ↔ T), believed to be the hallmark of mitochondrial polymerase γ errors rather than oxidative damage. Additionally, in our study, although both somatic transition and transversion mutations increased with older age, transition mutations were over 30 times more abundant than transversion mutations, once again suggesting that mtDNA replication errors are the major contributors to mtDNA mutation burden.

In conclusion, recent research support the theory that mtDNA replication errors are the major drivers of cellular mtDNA mutation burden. Nonetheless they do not exclude a comparatively minor role for 8-oxodG-induced transversion mutations, or the many other DNA oxidative lesions that can induce transition mutations. Based on recent findings, an updated understanding regarding the role of free radicals in contemporary theories of mtDNA aging is needed. It seems likely that rather than directly contributing to mtDNA mutations via oxidative lesions, free radicals may affect the mitochondrial polymerase and decrease its fidelity, indirectly increasing somatic transition mutations. Free radicals may also act as a signaling molecule and influence mitochondrial biogenesis and/or mitochondrial turnover via mitophagy, which could in turn promote the clonal expansion of pre-existing mtDNA mutations.


Adjusting Glial Cell Behavior to Promote Axon Regrowth

One of the reasons why injuries to the nervous system are poorly regenerated at best is that the regrowth of axons, long connections between neurons, is hindered by scarring. The formation of neural tissue scarring is mediated by glial cells such as astrocytes. Researchers here demonstrate that it is in principle possible to adjust the behavior of these cells in order to reduce scar formation and promote successful axon regrowth following injury.

Glial cells carry out a variety of support and maintenance functions, and one type in particular - the astrocytic glial cell - has the unique ability to form scar tissue around damaged neurons. The presence of scar tissue is associated with inhibitory effects on the regrowth of mature neurons that are damaged by spinal cord injury. Recent evidence suggests, however, that these inhibitory effects are reversible, and in new work, scientists show that astrocytic glial cells can in fact play a major role in facilitating neuron repair.

The research is the first to establish a link between glucose metabolism in glial cells and functional regeneration of damaged neurons in the central nervous system. Scientists set out to investigate how scar tissue formation induced by glial cells impacts axon regeneration, using both fly and mouse models of axon injury. In initial experiments, they confirmed that the negative effects of glial cell activity on axon regeneration are indeed reversible. But the researchers also found that the switch between positive and negative effects on axon regrowth is directly related to the glial cells' metabolic status.

In follow-up experiments in flies, the researchers focused specifically on glycolysis - the metabolic pathway responsible for the breakdown of glucose - and discovered that upregulating this pathway alone in glial cells was sufficient to promote axon regeneration. This same result was observed in mice. Further investigation in fly and mouse models led to the identification of two glucose metabolites, lactate and hydroxyglutarate, that act as key mediators of the glial switch from an inhibitory reaction to a stimulatory response. "In the fly model, we observed axon regeneration and dramatic improvements in functional recovery when we applied lactate to damaged neuronal tissue. We also found that in injured mice, treatment with lactate significantly improved locomotor ability, restoring some walking capability, relative to untreated animals."

Experiments revealed that when glial cells are activated, they release glucose metabolites, which subsequently attach to molecules known as GABAB receptors on the neuron surface and thereby activate pathways in neurons that stimulate axon growth. "Our findings indicate that GABAB receptor activation induced by lactate can have a critical role in neuronal recovery after spinal cord injury. Moreover, this process is driven by a metabolic switch to aerobic glycolysis, which leads specifically to the production of lactate and other glucose metabolites."


Towards Restoration of Mitophagy to Reverse Mitochondrial Dysfunction in Alzheimer's Disease

Mitochondria are the power plants of the cell, a herd of bacteria-like organelles responsible for packaging energy store molecules used to power the chemistry of life. With age, mitochondria become dysfunctional throughout the body, for reasons that are not yet fully understood, but which clearly contribute to the onset of age-related declines and diseases. There is certainly stochastic damage to mitochondrial DNA that can lead to a small but significant number of pathological cells dumping oxidizing molecules into the surrounding tissue, but the general malaise of mitochondria is more sweeping than this.

One important contribution to this universal mitochondrial dysfunction appears to be a progressive failure of mitophagy. Mitophagy is a specialized form of autophagy, a quality control process responsible for flagging and then destroying worn and damaged mitochondria. Researchers have shown that specific component parts of the autophagy process can become less efficient with age, but the culprit here may be that mitochondria change in structure and size, becoming larger and more resilient to clearance by mitophagy. Why exactly this happens is, again, quite unclear at the detail level. Many of the research groups interested in the mitochondrial contribution to aging are focused on mitophagy, however, so we shall see, given time.

The brain is an energy-hungry organ, and, like muscle tissue, more profoundly affected by loss of mitochondrial function than is the case elsewhere in the body. Loss of mitochondrial function is a prominent feature of many neurodegenerative diseases, and is thought to be a noteworthy contributing cause of these conditions. Today's open access paper discusses this topic in the context of mitophagy, and possible approaches to upregulation of mitophagy in old tissues, in order to better maintain mitochondrial function in later life.

A Glimmer of Hope: Maintain Mitochondrial Homeostasis to Mitigate Alzheimer's Disease

In Alzheimer's disease (AD), mitochondrial dysfunction and the bioenergetic deficit contribute to the amyloid-β (Aβ) and phosphorylated Tau (p-Tau) pathologies; in turn, these two pathologies promote mitochondrial defects. As a consequence, a fundamental characteristic of AD is the impairment of mitochondria. Pharmacological agents, fasting, physical exercise, and caloric restriction can reverse this impairment. The main target of these methods is to enhance autophagy and mitophagy. Mitophagy plays a fundamental role in mitochondrial quality control and homeostasis, and the pathological consequences of its misregulation demonstrate its importance. However, the exact positions of mitophagy in AD etiology are still unclear as multiple steps are affected. Cells regulate mitochondrial degradation not only through control of the mitophagy machinery but also through delicate tuning of mitochondrial fusion and fission. It remains to see whether other cellular processes linked with mitochondria also have a role to play in mitophagy regulation.

Accumulating studies suggest that dysfunctional mitochondria are mainly due to impaired mitophagy in neurons in AD. The 'vicious cycle' hypothesis proposed that loss-of-function mitophagy and Aβ and p-Tau, the biomarkers in AD pathophysiology, strongly influence each other. Moreover, the 'vicious cycle' experiments state that Aβ-dependent neuronal hyperactivity supports circuit dysfunction in the early stages of AD. Recently, researchers successfully stimulated mitophagy and reversed memory impairment using NAD+ supplementation, urolithin A, and action in both Aβ and tau Caenorhabditis elegans models. In human neurons derived from the hippocampus of AD patients and in AD animal models, enhanced mitophagy can even diminish insoluble Aβ and prevent cognitive impairment in AD mouse model through the suppression of neuroinflammation and microglial phagocytosis of Aβ plaques. These findings predict that enhancing mitophagy could be a novel approach to delay or even treat AD. To this end, plentiful pharmacological agents have been examined in preclinical studies.

In the past 20 years, most of the drugs tested in the clinic for AD have targeted the Aβ accumulation; however, none of these anti-Aβ therapies overcome the central problem. Today, a promising alternative option for AD therapeutics is to maintain mitochondrial homeostasis by enhancing autophagy and stimulating mitophagy. Dysfunctional mitophagy can increase Aβ and Tau pathologies, while aggregating Aβ can impair neuronal mitophagy in reverse. These outcomes indicate pivotal roles for mitophagy dysfunction, both upstream and downstream of Aβ and Tau pathways.

Health For All, For Longer

The growing interest in treating aging as a medical condition, in the production of therapies that target the mechanisms of aging and can thus slow or reverse the progression of aging, is reflected by the launch of new scientific journals that cover this topic. The prestigious Lancet is now getting into the game with the launch of Health Longevity. It has been a long road, and a great deal of advocacy and persuasion, to get to this point of enthusiasm for intervention in the aging process. Now that we are here, the next battle is over the strategies adopted, in an attempt to guide more of the research community towards rejuvenation produced by repair of cell and tissue damage, rather than merely tinkering with metabolism to slow aging without addressing that damage.

The coronavirus disease 2019 (COVID-19) pandemic does not affect everyone equally. While anyone can contract COVID-19, accumulating data suggest that older people or those with pre-existing comorbidities are far more likely to have severe complications or die from the disease. While researchers scramble to unravel the mechanisms of action underlying the disease's wide-ranging effects, news that the disease hits older people hardest has been received without demur: it is widely accepted that to be old is to be fragile. Indeed, even in so-called normal times, everyone expects more things break as people age: bones, hearts, brains. In the context of the pandemic, being old is seen as just one more comorbidity. It should not be.

We accept growing old and losing our vitality as an inevitability of life. To do so is to overlook the fact that ageing is, fundamentally, a plastic trait-influenced both by our genetic predispositions and many (controllable) environmental factors. Anecdotally we know this to be true: for some, being in their eighties means being confined to a wheelchair whereas for others, like Eileen Noble, who at 84 years old was the oldest runner in 2019's London Marathon, it decidedly does not. The burgeoning field of biogerontology is now beginning to amass data in support of such observations. Single genetic mutations in evolutionarily conserved pathways across model organisms - ranging from fruit flies to mice - increase lifespan by up to 80%. Crucially, not only do these animals live longer, they also have a longer youthspan - the proportion of their lives in which they retain the trappings of youth such as peak mobility, immunity, and stress resilience. These data show something amazing: the rate of ageing is not fixed. Fragility, vulnerability, and poor health need not necessarily follow advancing age.

This is an unprecedented crossroads in global society, raising fundamental questions about how we live as individuals, and collectively. Will an ageing population mean people experience longer periods of good health, a sustained sense of wellbeing, and extended periods of social engagement and productivity - or will it be associated with a higher burden of illness, disability, and dependence on others? The science suggests that we have a choice.


Proteomic Analysis of Blood Samples Points to the Importance of Inflammation in Aging

Chronic inflammation is a feature of aging, the constant inappropriate overactivation of the immune system. Many of the mechanisms that contribute to this unfortunate state are catalogued and understood to at least some degree, such as growing numbers of senescent cells, excess visceral fat tissue, numerous forms of molecular damage and debris that are interpreted as cues for immune activation, and so forth. While short-term inflammation is necessary to maintain tissue, respond to pathogens, and heal injuries, when unresolved that same signaling and changed cell behavior is very disruptive of tissue maintenance and function. Greater inflammation leads to worse outcomes over time, a more rapid onset and progression of all of the common age-related conditions. Suppression of chronic inflammation, preferably by cleaning up the damage that causes the immune system to respond in this way, is an important goal in the treatment of aging as a medical condition.

The biological bases of longevity are not well understood, and there are limited biomarkers for the prediction of long life. We used a high-throughput, discovery-based proteomics approach to identify serum peptides and proteins that were associated with the attainment of longevity in a longitudinal study of community-dwelling men age ≥65 years. Baseline serum in 1196 men were analyzed using liquid chromatography - ion mobility - mass spectrometry, and lifespan was determined during ~12 years of follow-up. Men who achieved longevity (≥90% expected survival) were compared to those who died earlier.

Rigorous statistical methods that controlled for false positivity were utilized to identify 25 proteins that were associated with longevity. All these proteins were in lower abundance in long-lived men and included a variety involved in inflammation or complement activation. Lower levels of longevity-associated proteins were also associated with better health status, but as time to death shortened, levels of these proteins increased. Pathway analyses implicated a number of compounds as important upstream regulators of the proteins and implicated shared networks that underlie the observed associations with longevity.

Overall, these results suggest that complex pathways, prominently including inflammation, are linked to the likelihood of attaining longevity. This work may serve to identify novel biomarkers for longevity and to understand the biology underlying lifespan.


Another New Senolytic Prodrug is Demonstrated to Reverse Frailty and Loss of Cognitive Function in Old Mice

Today's open access paper reports on the use of a prodrug senolytic strategy to reverse aspects of aging in mice via the selective destruction of senescent cells. A prodrug is a small molecule, usually innocuous, that can be converted into an active drug molecule by the action of specific proteins in the body. For example a drug can be made into a prodrug by the addition of further chemical structure that (a) renders it inert, and (b) is cleaved away by an enzyme inside cells. Ideally, the inactive prodrug is designed such that this conversion to an active drug molecule only takes place where and when the drug is needed.

Senescent cell accumulation with age is an important cause of age-related degeneration and disease. Senescent cells are characterized by high levels of β-Galactosidase, known as senescence-associated β-Galactosidase (SA-β-Gal). Since β-Galactosidase is an enzyme that cleaves glycosidic bonds, it is possible to turn many types of drug into prodrugs that only activate to meaningful levels inside senescent cells by attaching structures that will be removed by β-Galactosidase. Researchers have recently demonstrated that this can be done with the chemotherapeutic drug navitoclax. Navitoclax is the worst of the effective first generation senolytics: it certainly kills senescent cells, and is somewhat specific, but it also kills far too many other cells for comfort. It has significant and unpleasant side-effects, but when it is made into a prodrug, these problems go away.

One doesn't have to use senolytic drugs as a basis for the prodrug. The results below were obtained using a fairly generic cytotoxic chemotherapeutic drug. More or less any cell-killing drug will do, so long as (a) it can be made inert with a structure that will be cleaved away by β-Galactosidase, and (b) the difference in amount of β-Galactosidase between normal cells and senescent cells is enough to make the difference between too few drug molecules to produce any measurable effect and sufficient drug molecules to kill the cell.

Targeted senolytic prodrug is well tolerated and results in amelioration of frailty, muscle regeneration and cognitive functions in geriatric mice

Frailty is connected to cellular aging, which in turn is connected to cellular senescence. Senescent cells are permanently withdrawn from the cell cycle and generally develop a persistent pro-inflammatory phenotype called the senescence-associated secretory phenotype (SASP) which is comprised of proinflammatory cytokines and chemokines. Selective killing of senescent cells with therapeutics (i.e., senolytics) have gained attention as a new therapeutic approach for age-related diseases. Targeting of pro-survival Senescent Cell Anti-apoptotic Pathways (SCAPs) has emerged as the primary strategy for senescent cell killing.

The translational value of many senolytic drugs in vivo is limited due to their chronic toxicity. The identification of agents that selectively kill senescent cells while sparing other cell populations represents a scientific challenge. Current senolytic drugs target molecular pathways shared between senescent and proliferating cells, thus achieving cell killing but not specificity. As a matter of fact, many known senolytic agents were initially developed as cytotoxic anti-cancer agents and subsequently repurposed for 'selective' removal of senescent cell populations.

Senescent cells are characterized by a notable change in biological properties such as an increase in the levels of mitochondria, reactive oxygen species, lysosomal content, and upregulation of many lysosomal proteins, including the lysosomal enzyme senescence-associated β-galactosidase (SA-βGal). Recently, a promising strategy has been proposed based on galactose-derivative prodrugs. These prodrugs are selectively activated in senescent cells upon conversion into the parent active drug by the hydrolase activity of SA-βGal. In particular, specific senotoxic compounds such as duocarmycin, gemcitabine, and navitoclax have been modified into galacto-derivative prodrugs showing increased selectivity in targeting senescence cells and efficacy in treating cancer and aged mouse models.

Here, we report a novel prodrug design to target senescent cells, allowing systemic removal of senescent cells in geriatric mice without noticeable side effects. We took advantage of the senescence-specific activity of SA-βGal in the design of a non-toxic senolytic prodrug derivative of the compound 5-Fluorouridine, a metabolic precursor of the clinically approved anti-cancer medication 5-Fluorouracil. We first tested the specificity of this prodrug on senescent cells in vitro. We then confirmed safety and efficacy of the prodrug in young (5 month-old), aged (22 month old) and in geriatric (30 month old) mice. Importantly, we showed that geriatric mice that received the prodrug treatment for four weeks altogether improved significantly: 1) frailty profile; 2) skeletal muscle function; 3) muscle stem cell function; 4) cognitive function; and 5) survival.

Resting Metabolic Rate in Aging and Age-Related Disease

Resting metabolic rate declines with age, a situation that has evolved for perhaps much the same reasons as loss of stem cell function, in that it is one part of the trade-off between risk of death by cancer on the one hand versus organ failure due to faltering tissue maintenance on the other. Researchers here note that this reduction in resting metabolic rate is attenuated by the presence of age-related diseases. Why would age-related disease cause a relative increase in resting metabolic rate? Perhaps because the body is devoting more energy to fighting the condition, or perhaps the disease processes themselves, such as increased presence of senescent cells, result in greater metabolic activity.

Resting metabolic rate (RMR) changes over the life span and has been related to changes in health status. RMR reflects the energy expended by the human body in a prolonged resting state in the absence of food digestion, physical, or cognitive activities. As such, RMR can be understood as the "cost of living", i.e., the energetic cost of maintaining all physiological processes that preserve homeostatic equilibrium and cognitive alertness and sets the stage for all activities of life. RMR is affected by changes in body size, with greater RMR associated with larger body size, especially large lean body mass. RMR is widely determined by the most metabolically active tissues, such as muscle, heart, brain, and liver, and, as the function and metabolic activity of these organs and tissues decline with aging, RMR also declines with aging.

In an analysis of data from the Baltimore Longitudinal Study of Aging (BLSA), subjects in good health and functional status had lower RMR than those affected by chronic diseases and functional limitations, independent of age, sex and body composition. Also, independent of relevant confounders, higher RMR was cross-sectionally associated with both a higher number of chronic diseases and with significantly higher risk of developing multimorbidity, defined as two or more out of 15 chronic conditions. Similarly, in community-dwelling women 60 years and older, increasing multimorbidity was associated with an increase in RMR independent of body composition and age. Moreover, two studies evaluating the longitudinal association between energy metabolism and mortality found higher RMR and 24 hour energy expenditure (24EE), which are predictive of future negative health outcomes and early mortality.

Overall, these data suggest that while healthy aging is associated with a progressive decline of RMR, independent of changes in body composition, superimposed adverse changes in health and functional status tend to attenuate such decline. This attenuation has been attributed to the potential extra-energetic cost of maintaining homeostasis in response to disease-related processes. However, a comprehensive analysis of how various diseases that ensue with aging affect age-associated changes in RMR is still lacking.

A hypothesis that could explain the increased basal metabolism observed in these conditions is the accumulation of senescent cells. The cell stops replicating, withdrawing from the cell cycle, and develops specific features such as resistance to apoptosis, increased energy metabolism, and production of bioactive molecules globally defined as "Senescence Associated Secretory Phenotype" (SASP). SASP includes several pro-inflammatory proteins that determine damage to tissues and produce a chronic inflammatory environment. We argue that the enhanced metabolic activity we observe in this analysis for some diseases could be attributable to the presence of increasing numbers of metabolically active senescent cells.


Towards a More Sensitive Blood Test for the Earlier Stages of Alzheimer's Disease

The onset of Alzheimer's disease is preceded by years of slowly growing levels of amyloid-β aggregates in the brain. There is an equilibrium between amyloid-β in the brain and amyloid-β in the bloodstream, and so the research community has worked towards blood tests that can determine who is at risk of developing the condition. This goal is complicated by the sensitivity required, given the low levels of amyloid-β in blood samples, but the results here suggest that this problem may be sufficiently well solved to proceed towards an widely used assay. While the failure of clinical trials testing amyloid-clearing immunotherapies strongly suggests that amyloid-β is not the right target for the development of treatments for Alzheimer's disease, it may still be helpful as a biomarker.

Scientists are in the initial stages of development of a method to detect the biomarkers for Alzheimer's disease that is 10 times more sensitive than current blood testing technology. For Alzheimer's disease, doctors most often diagnose patients based on their symptoms. By that time, the patients often already have severe brain damage. Imaging technology such as magnetic resonance imaging and CT scans can also be used to help confirm the disease, but they are not suitable for early stage diagnosis. Occasionally, doctors may test spinal fluid to look for beta-amyloid proteins, markers of the disease, but the process is more invasive than a simple blood test would be.

One common way of testing blood is the ELISA, or enzyme-linked immunosorbent assay, which is used to test for a variety of diseases. The ELISA uses a natural enzyme found in the roots of horseradish that can change color to indicate the presence of disease biomarkers. But, using the technique to detect the beta-amyloid proteins of Alzheimer's is difficult because their levels in the blood are too small.

Last year, researchers created an artificial enzyme using a single-atom architecture that was able to work as efficiently as natural enzymes. Their artificial enzyme, called a nanozyme, is made of single iron atoms embedded in nitrogen-doped carbon nanotubes. For this work, the researchers were able to use their single-atom nanozyme to mimic the active site of a natural enzyme and to detect the Alzheimer's disease proteins at levels 10 times lower than commercially available ELISA tests. The nanozyme was also more robust than natural enzymes, which can degrade in acidic environments or in high temperatures. It is also less expensive and could be stored for long periods of time.


Wnt Signaling in Neurogenesis and the Aging of the Brain

The Wnt signaling pathway is found somewhere in the midst of the exceedingly complicated network of processes that regulate regeneration and stem cell function. This small slice of cellular biochemistry has been an area of interest for researchers for quite some time. Firstly, Wnt signaling changes with age, as regenerative prowess diminishes. Secondly, adjusting Wnt signaling appears to be a practical basis for interventions aimed at tilting the balance of functions in aged tissue back towards greater stem cell activity, maintenance, and regeneration.

To pick a prominent example, the sizable biotech company Samumed is undertaking clinical development of Wnt signaling manipulation therapies to treat a broad range of age-related conditions. Further, as noted here, Wnt signaling is relevant to the maintenance and function of brain tissue via the creation of new neurons, a process known as neurogenesis. This is all very interesting, but it is worth noting that tinkering with Wnt signaling does not address underlying damage and causes of dysfunction: it is a way to force cells to act in more youthful ways despite damage and dysfunction. This can be beneficial where it succeeds, but is likely inferior to successful efforts to repair the underlying damage.

Role of Wnt Signaling in Adult Hippocampal Neurogenesis in Health and Disease

Studies indicate that the Wnt signaling plays multiple roles in adult hippocampal neurogenesis including neural progenitor cell (NPC) proliferation, fate-commitment, development and maturation of newborn neurons. Evidences suggest a stage-specific expression of particular receptors that might activate different Wnt signaling cascades to control the progression of neurogenesis. Although the role of the canonical Wnt co-receptor LRP6 support this notion, the role of other co-receptors that control the activation of non-canonical Wnt signaling remains to be elucidated. The identification of Wnt co-receptors involved in adult neurogenesis is a critical issue that should be addressed to gain a more comprehensive understanding of how canonical and non-canonical Wnt signaling are regulated during adult neurogenesis. In addition, it will be interesting to further study the downstream signaling components and effectors involved in the regulation of adult hippocampal neurogenesis by non-canonical Wnt signaling.

Several studies indicate that Wnt proteins released by hippocampal astrocytes and progenitor cells are crucial components of the subgranular zone (SGZ) neural stem cell niche. In addition, endogenous Wnt inhibitors are also components of the neurogenic microenvironment that dynamically regulate Wnt-mediated neurogenesis under physiological conditions. Considering the increasing number of Wnt regulators identified to date, it will be interesting to further investigate the contribution of these molecules to the dynamic control of neurogenesis.

In agreement with the critical roles of Wnt signaling in adult neurogenesis, evidence indicates that Wnt signaling is associated with the age-dependent decline in neurogenesis. Concomitantly with the decrease in the generation of new neurons, in normal aging there is a reduction in the expression of Wnt proteins, an increase in the expression of Wnt inhibitors, and a decrease in canonical Wnt signaling activity in the dentate gyrus. Wnt dysfunction might also underlie the impairment of neurogenesis observed in Alzheimer's disease (AD).

Interestingly, genetic and pharmacological activation of Wnt signaling was shown to restore adult hippocampal neurogenesis, and also to improve cognitive performance in animal models of AD. Although it is not yet known how neurogenesis contribute to hippocampal function in humans, compelling evidence in animal models suggest that adult-born neurons are important for learning and memory, cognitive flexibility and mood regulation. In addition, recent findings support that neurogenesis impairment contributes to cognitive decline in aging and AD. Therefore, a better understanding on the molecular mechanisms involved in the regulation of neurogenesis may have important therapeutic implications.

Cellular Senescence as an Important Cause of Non-Healing Wounds in Diabetes

One of the many unpleasant complications produced by type 1 and type 2 diabetes is a much reduced ability to heal wounds, leading to ulcers and non-healing injuries. Following the discovery of the importance of senescent cells to degenerative aging, it was found that senescent cell accumulation is important in the pathology of both type 1 and type 2 diabetes. Senescent cells secrete a mix of molecules that provoke chronic inflammation, destructively remodel nearby tissue, and encourage other cells to become senescent, among other outcomes. This signaling, when present for the long term, is harmful to tissue function. Therapies that selectively destroy senescent cells may thus be beneficial for diabetic patients, even while not addressing the root causes of the condition.

Although more than 300 theories have emerged over the years to explain the intrinsic molecular and evolutionary drivers behind organismal aging, the onset of cellular senescence seems to act as a foundational pillar for organ and organismal aging. Diabetes mellitus (DM) is a heterogeneous metabolic disease characterized by chronic hyperglycemia resulting from defects in insulin secretion, insulin action, or both. An intense debate has existed so far addressing whether senescence precedes or follows the onset of chronic inflammation and insulin resistance (IR). Irrespective to "who-precedes-who," diabetic patients experience an obvious accelerated aging process that increases their susceptibility to morbidity and earlier mortality. Hence, diabetes-affected patients have a significantly shorter life expectancy than non-diabetic individuals, while this life expectancy reduction is largely dependent on diabetes duration.

The major clinical challenge of diabetes is the progressive and expansive morbidity and mortality resulting from the long-term secondary complications. Within the constellation of diabetic complications, the delayed and poorness in triggering and progressing along a physiological repair response following wounding is of major clinical significance. Diabetes undermines skin cells physiology and progressively intoxicates the dermal layer by the accumulation of advanced glycation end products (AGEs) and free radicals derivatives. Accordingly, most if not all of the events encompassed within the cutaneous healing process including hemostasis, inflammation, matrix deposition, angiogenesis, contraction, remodeling, and re-epithelialization are somewhat buffeted by diabetes.

Chronic low-grade inflammation and an increased burden of senescent cells are hallmarks of aging in diabetic subjects. Hyperglycemia per se is known to act as a senescence-promoting factor for cultured cells, and steadily precipitates organs complications and functional demise by different mechanistic pathways. The notion that cellular senescence is an imperceptible underlying force in the pathogenesis of wound chronicity and ulcer recurrence has accrued for years. Consequently, we suggest that diabetes-associated wound healing failure and reduced tissue resilience are clinical translations of an "entrenched" wound senescent cell population, with self-perpetuating and propagating abilities.

This population may be fostered by a diabetic archetypal secretome that induces replicative senescence in dermal fibroblasts, endothelial cells, and keratinocytes. Mesenchymal stem cells are also susceptible to major diabetic senescence drivers, which accounts for the inability of these cells to appropriately assist in diabetic wound healing. The senescent cell population and its adjunctive secretome could be an ideal local target to manipulate diabetic ulcers and resolve non-healing wounds.


Magnetic Fields Used to Engineer Better Cartilage with a More Natural Variation in Cell Density

Researchers here demonstrate the use of magnetic fields and fluids to produce a more natural cell density gradient in engineered cartilage tissue. The result is bioartificial cartilage with better structural and mechanical properties than would otherwise be obtained. The approach is quite interesting, and illustrative of a broader area of research into the best way to engineer tissues that must contain variations in cell types, cell density, signal molecules, or supporting structure in order to delivery the desired end result.

Using a magnetic field and hydrogels, a team of researchers have demonstrated a new possible way to rebuild complex body tissues. "We found that we were able to arrange objects, such as cells, in ways that could generate new, complex tissues without having to alter the cells themselves. Others have had to add magnetic particles to the cells so that they respond to a magnetic field, but that approach can have unwanted long-term effects on cell health. Instead, we manipulated the magnetic character of the environment surrounding the cells, allowing us to arrange the objects with magnets."

In humans, tissues like cartilage can often break down, causing joint instability or pain. Often, the breakdown isn't in total, but covers an area, forming a hole. Current fixes are to fill those holes in with synthetic or biologic materials, which can work but often wear away because they are not the same exact material as what was there before. What complicates fixing cartilage or other similar tissues is that their make-up is complex. "There is a natural gradient from the top of cartilage to the bottom, where it contacts the bone. Superficially, or at the surface, cartilage has a high cellularity, meaning there is a higher number of cells. But where cartilage attaches to the bone, deeper inside, its cellularity is low."

With that in mind, the research team found that if they added a magnetic liquid to a three-dimensional hydrogel solution, cells, and other non-magnetic objects including drug delivery microcapsules, could be arranged into specific patterns that mimicked natural tissue through the use of an external magnetic field. After brief contact with the magnetic field, the hydrogel solution (and the objects in it) was exposed to ultraviolet light in a process called "photo crosslinking" to lock everything in place, and the magnetic solution subsequently was diffused out. After this, the engineered tissues maintained the necessary cellular gradient. With this magneto-patterning technique, the team was able to recreate articular cartilage, the tissue that covers the ends of bones.

"These magneto-patterned engineered tissues better resemble the native tissue, in terms of their cell disposition and mechanical properties, compared to standard uniform synthetic materials or biologics that have been produced. By locking cells and other drug delivering agents in place via magneto-patterning, we are able to start tissues on the appropriate trajectory to produce better implants for cartilage repair." While the technique was restricted to in vitro studies, it's the first step toward potential longer-lasting, more efficient fixes in living subjects.


Research into the Mechanisms of Aging is Very Poorly Funded in Comparison to its Importance to Health

Research into aging is sparsely funded in comparison to research into the biochemistry and treatment of any specific common age-related disease, such as atherosclerosis or Alzheimer's disease. Yet these conditions are caused by aging. So we have the strange situation in which the past century of work on treating age-related conditions has produced only small gains, because the research and development communities have steadfastly refused to work on the root cause of these conditions - which is to say the mechanisms of aging, the accumulation of cell and tissue damage that causes degeneration and dysfunction.

This problematic and frustrating state of affairs is slowly changing, and more rapidly in the past few years, but the gains made by patient advocates and the small community of researchers who do work on aging are still incremental. The mechanisms of aging remain a small area of research in comparison to the rest of medicine. This is far out of line, given that age-related disease - the consequence of the mechanisms of aging - is the dominant form of human mortality, by far the greatest medical cost imposed upon individuals, and causes by far the most suffering. Year after year, the priorities for medical research and development remain distant from this reality.

Leonard Hayflick is a retired eminence in the field who happens to hold the completely incorrect view that aging is, in some meaningful way, a consequence of thermodynamics and entropy gain over time. This is easily dismissed: an aging cell or an aging individual is not a closed system, and therefore can certainly lose entropy over time given suitable circumstances. Most of what he has to say about the present poor allocation of resources and attention is quite right, however. Just substitute a focus on molecular damage and persistent metabolic waste after the SENS view of aging for Hayflick's considerations of thermodynamics.

The greatest risk factor for the leading cause of death is ignored

All major United States institutional advocates for research on the biology of aging and for the leading causes of death assert that aging is the greatest risk factor for these deaths. Nevertheless, all fail to support research on the etiology of aging despite having mechanisms to do so. Bordering on scandal, research on the cause of aging in life forms is not a major priority for any organization in this country with "Age" or "Aging" in its title. This neglect is inexplicable because the mantra believed by most physicians, geriatricians and biogerontologists is that "Aging is the greatest risk factor for the leading causes of death." It does not require a great leap of intellect to ask: "Then, why is research on the etiology of the greatest risk factor that increases vulnerability to cancer, cardiovascular disease, stroke, and Alzheimer's disease (AD), ignored?"

The field of aging is the only area of biomedical research where causation is ignored. This inexplicable omission is compounded by the fact that aging is a universal human phenomenon for all who live long enough to experience it. Even for those in good health, that condition is merely the slowest rate of aging and dying. Today, like the former rich and powerful, their modern counterparts have the same goals in the form of funding hundreds of biotech startup companies. Plus ça change, plus c'est la meme chose. In these modern efforts there seems to be little understanding that there is an enormous difference between the molecular biology of what determines the longevity of life forms and what causes their aging. Longevity is determined by anabolic processes and addresses the question, "Why do life forms live as long as they do?" Aging is a catabolic process that addresses the question, "Why do longevity systems eventually fail?"

There is a general failure to understand that manipulating the genome or anabolic processes in living forms which may increase longevity, or cure a disease, tells us nothing about the dysfunctional or missing molecules that characterize the catabolic process of aging. Research on the biogerontology of aging is unique because of the common belief that the goal is to interfere or manipulate the process. The availability of funds for age-associated disease research is several orders of magnitude greater than what is available for research on the fundamental biology of their greatest risk factor. The resolution of any age-associated disease has not in the past, nor will it in the future, improve our understanding of the etiology of aging. A century ago, the leading cause of death in old age was pneumonia, often called "the old man's friend" (with its sexist overtones). Pneumonia is no longer one of the leading causes of death in old age and its resolution did not advance our knowledge of the cause of aging. Nor will the resolution of any other age-associated pathology.

Targeting Aging is the Way to Treat Diseases of Aging

Near all work to date on the treatment of age-related disease has failed to consider or target underlying mechanisms of aging, the molecular damage that accumulates to cause pathology. It has instead involved one or another attempt to manipulate the complicated, disrrayed state of cellular metabolism in late stage disease, chasing proximate causes of pathology that are far downstream of the mechanisms of aging. This strategy has largely failed, and where it has succeeded has produced only modest benefits. Consider that statins, widely thought to be a major success in modern medicine, do no more than somewhat reduce and delay mortality due to atherosclerosis. They are not a cure. The mechanisms of aging are why age-related diseases such as atherosclerosis exist. They are the root cause of these diseases. Attempted therapies that continue to fail to target the mechanisms of aging will continue to fail to deliver meaningful benefits to patients. This must change.

Aging doesn't kill people - diseases kill people. Right? In today's world, and in a country like the United States, most people die of diseases such as heart attack and stroke, cancer, and Alzheimer's. These diseases tend to be complex, challenging, difficult, and extremely ugly to experience. And they are by nature chronic, caused by multifactorial triggers and predispositions and lifestyle choices. What we are only now beginning to understand is that the diseases that ultimately kill us are inseparable from the aging process itself. Aging is the root cause. This means that studying these diseases without taking aging into account could be dangerously misleading ... and worst of all, impede real progress.

Take Alzheimer's disease. To truly treat a disease like Alzheimer's, we would need to identify and understand the biological targets and mechanisms that trigger the beginning of the disease, allowing us to intervene early - ideally, long before the onset of disease, to prevent any symptoms from happening. But in the case of diseases like Alzheimer's, the huge problem is that we actually understand very little about those early targets and mechanisms. The biology underlying such diseases is incredibly complex. We aren't sure what the cause is, we know for sure there isn't only one target to hit, and all prior attempts to hit any targets at all have failed. When you start to think about how much of what we think we know about Alzheimer's comes from very broken models - for example, mice, which don't get Alzheimer's naturally - it becomes totally obvious why we're at a scientific stalemate in developing treatments for the disease, and that we've likely been coming at this from the wrong direction entirely.

The biggest risk factor for Alzheimer's isn't your APOE status; it's your age. People in their twenties don't get Alzheimer's. But after you hit the age of 65, your risk of Alzheimer's doubles every five years, with your risk reaching nearly one out of three by the time you're 85. What if going after this one biggest risk factor is the best vector of attack? Maybe even the only way to truly address it? This isn't about the vanity of staying younger, about holding on to your good looks or your ability to run an 8 minute mile. It's about the only concrete possibility we have to cure these diseases. Instead of choosing targets for a single specific disease, i.e. a specific condition that arises in conjunction with aging, we can get out in front of disease by choosing targets that promote health. And we can identify these by looking at disease through the lens of the biology of aging.


In Vivo Reprogramming Improves Cognitive Function in Old Mice

Reprogramming cells in a living animal, transforming them into induced pluripotent stem cells, has the sound of a bad idea - leading to cancer, damage to structures and tissues, inappropriate signaling, and more. One of the interesting discoveries of recent years is that in vivo reprogramming can be quite beneficial, provided that small enough numbers of cells are transformed, or provided that reprogramming is only partial, halted before it progresses far enough to change cell type. It is possible that modest levels of in vivo reprogramming act much like the effects of a stem cell therapy, producing changes in the signaling environment and cell behavior that improve tissue function. Equally, the effects may be more a case of large numbers of cells undergoing some degree of reprogramming, enough to reverse age-related mitochondrial dysfunction and epigenetic change.

The study here demonstrates that excessive in vivo reprogramming is indeed a bad idea, while also showing that old mice have their cognitive function improved by lesser degrees of reprogramming. This is achieved by using mice engineered to express the Yamanaka factors that reprogram cells, but only conditionally, when exposed to an antibiotic. Mice given the antibiotic continually largely die after a few weeks, the inevitable result of too much disruption, too many vital cells being transformed, in one organ or another. Mice given the antibiotic intermittently instead exhibit improved cognitive function, and suffered no increase in mortality over the course of a four month study.

As organisms age, some epigenetic markers are modified. It has been proposed that the removal of these aging-dependent epigenetic modifications may reverse some features of aging. Temporal expression of Oct4, Sox2, Klf4, and c-Myc (also known as the Yamanaka factors, YFs), used for pluripotency cell reprogramming, can cause this removal of epigenetic marks and subsequent reversal of aging features. Indeed, this approach has been successfully used to improve age-associated hallmarks in peripheral tissues of mice. However, little attention has been given to the therapeutic use of YFs in the central nervous system. Importantly, YF expression must be tightly regulated, since it can lead to aberrant mitogenic stimulation or apoptosis.

In this study, we addressed age-dependent changes in brain structures susceptible to premature degeneration. It has been postulated that age-related brain decline mirrors developmental maturation and, accordingly, brain structures with a late development may be the first to degenerate. This notion was first described as Ribot's law. The dentate gyrus (DG) exemplifies a brain structure that matures after birth and whose functions decline early with age. For example, the DG of 10-month-old mice shows a clear decrease in adult neurogenesis, the process through which functional neurons are generated from adult neural precursors and integrated into existing circuits. In the adult mouse brain, adult neurogenesis occurs at the interface between the DG and hilus, in a region known as the subgranular zone. This type of neurogenesis is involved in learning and memory.

Here, we examined several markers for adult neurogenesis in mice. We found impaired adult hippocampal neurogenesis as the animals aged, thereby supporting previous observations. Our aim here has been to rejuvenate old hippocampal neurons by expressing YFs. However, an extended expression of YFs (continuous protocol) can cause aberrant transcription and cell death. Indeed, around 50% of YF-expressing mice died after 10 days of this protocol. We then tested cyclic induction of YFs. In this protocol, mouse death was prevented. Our results indicate that in mature mice, the expression of YFs results in a partial prevention of those aging-associated changes found in the newborn neurons of adult mice. In addition, YFs show an effect on DG mature neurons that could increase synaptic plasticity in old mice. This increase could explain why mice expressing YFs outperformed same-age wild-type counterparts in a memory test.


The Challenge of Achieving Healthy Human Longevity

The big sea change of the past 10 to 15 years in aging research is that the scientific community is now near entirely behind the idea that aging is a viable target for therapy, and that we should be working towards greater healthy human longevity. Prior to this time, aging was near entirely a "look but don't touch" field, in which any talk of medical intervention in aging was strongly discouraged. Making this change come about was a battle of years of patient advocacy (such as by the SENS Research Foundation and Methuselah Foundation), argument, and incremental advances in the science funded by small sums of hard-to-find research funding. It is perhaps hard for people today to recall how opposed the culture was to the idea of extending healthy life spans.

The present challenge is different: to ensure that the now willing workers and funding institutions direct their attention towards projects that will make a meaningful difference. Near all present work on intervention in the aging process is intended to do no more than modestly slow aging, tinkering with metabolism to slightly slow the accumulation of cell and tissue damage, or slightly blunt the consequences of damage. But the research community can do far better than this; it is possible to repair the damage that causes aging in order to produce rejuvenation. That strategy should be the primary focus on the research and development community, and it is not.

The initiative mentioned here, the Health Longevity Global Competition, is an example of this problem. If one digs in to see what exactly it is that they are supporting, one sees that it near all consists of projects that will clearly make no meaningful difference to the healthy human life span. It is not enough to have the enthusiasm and support of the research community. The strategy must also be correct.

Achieving healthy human longevity: A global grand challenge

Over the past century, major advances in medicine, public health, and socioeconomic development have led to unprecedented extensions of life expectancy worldwide. Global population aging presents both new opportunities and challenges. The COVID-19 pandemic has challenged recent advances in science and medicine and underscored the vulnerability of older populations to emerging diseases, alongside existing age-associated susceptibilities to noncommunicable diseases. Without innovation and adaptation, societal aging is poised to strain health care systems, economies, and social structures worldwide.

Yet, these and other looming stressors are not inevitable and could be mitigated, if not avoided, by accelerating biomedical and technological advancements, as well as socioeconomic infrastructures and policies to keep people healthier throughout their lives. By extending the health span, defined as the healthy years of life, societies can benefit from the tremendous social and economic opportunities that come with an active and vibrant older population. Numerous studies have identified common cellular and molecular mechanisms underlying the aging process, demonstrating that biological aging is modifiable and in some organisms health span or life span can even be extended. Many of the genetic pathways underlying aging and age-related disease - such as the insulin/IGF-1 and mammalian target of rapamycin (mTOR) pathways - play a critical role in maintaining homeostasis in response to environmental modulators such as injury, infection, stress, or food availability.

Other emerging areas of aging research include cellular senescence and senolytic therapy, regenerative medicine, immunoengineering, and genome editing and silencing. Therapies targeting these mechanisms and biological changes associated with aging are now being investigated in clinical trials (1). For example, senolytic compounds that selectively eliminate senescent cells are being studied in human clinical trials for osteoarthritis, glaucoma, and pulmonary fibrosis (2). Likewise, researchers are studying the effects of caloric restriction (3); metformin, a first-line drug for the treatment of type 2 diabetes (4); and rapamycin, an approved drug that inhibits mTOR, on the biology of human aging.

A fundamental question that remains is how interventions that show promise in improving life span or health span in model organisms will be evaluated in humans, where a complex interplay of factors underlies the aging process. Indeed, biological age often differs from chronological age. Some older individuals are less likely to develop age-related diseases than their age would predict, whereas some younger individuals prematurely develop age-related conditions. Thus, scientists have searched for biomarkers or other biological changes associated with aging and age-related declines that might act as "aging clocks."

Despite recent progress, the current research and innovation ecosystem is not poised to deliver the transformative innovations needed to achieve healthy longevity. To achieve major breakthroughs, we need to reexamine our fundamental approach to aging research and innovation. The traditional biomedical research funding model continues to be largely risk averse. Typically, incremental and clearly feasible research is funded, whereas bold, high-risk but high-gain proposals are often less well supported. Similarly, we see a rather conservative approach to drug discovery, which is designed to target, manage, or cure one disease at a time.

For these reasons, the National Academy of Medicine (NAM) has launched the Healthy Longevity Global Competition to catalyze breakthrough research and generate transformative and scalable innovations by mobilizing action across disciplines and sectors - from basic research to technology, care delivery, financing, community development, and social policy. An important goal of this Global Competition is to stimulate worldwide interest from scientists and innovators, thereby creating a global movement to dramatically increase innovation and groundbreaking advances in aging research. In October 2019, NAM and global collaborators launched the Global Competition with the participation of 49 countries and territories. During the first phase of the competition over 3 years, more than 450 Catalyst Awards will be distributed globally, representing over US$30 million in seed funding to attract bold, audacious research ideas. In the second phase, "Accelerator Awards" will provide additional substantial funding or support for projects that have demonstrated proof of concept with potential for commercialization. In the third and final phase, one or more Grand Prizes totaling over US$4 million will reward breakthrough achievements with the promise of global impact.

ELOVL2 in the Aging of the Eye

The development of epigenetic clocks for the assessment of biological age is a popular area of study, but connecting characteristic age-related epigenetic changes at specific CpG sites on the genome to specific underlying mechanisms of aging is slow going at best. There are many such sites and only so many scientists and only so much funding. An example of this sort of work is presented here, illustrative of the complexity involved in this area of research. The gene ELOVL2 is associated with a few sites that are strongly linked to age. There is a lot to say about potentially relevant mechanisms, and a great many gaps left to be filled in, even when just focused down on a single small part of the body, the retina in this case.

Epigenetic aging of tissues and organs has been tightly correlated with global genome DNA methylation changes in specific regions, called CpG islands. A number of recent studies have shown that CpG methylation (CpGme) patterns progressively change during aging in a variety of tissues and cells such as blood, muscle, brain, lung, and colon. One major question is whether these methylation changes merely correlate with aging, or if there any functional role of these epigenetic changes in regulating aging. Interestingly, within the top ten markers predictive of human epigenetic age, four are localized in the CpG islands in the regulatory element of the ELOVL2 gene, accounting for over 70% of the one "methylation clock" model. Consequently, methylation of the ELOVL2 regulatory region has been shown in many studies to correlate strongly with the biological age of individuals, as well as in rodents.

ELOVL2 is an enzyme that elongates long-chain omega-3 and omega-6 polyunsaturated fatty acids (LC-PUFAs), precursors of docosahexaenoic acid (DHA) and very-long-chain PUFAs (VLC-PUFAs), playing important role in retina biology. The fatty acids composition in the retina is unique - the retina is particularly enriched in PUFAs, with DHA constitutes 40-50% of the total fatty acids in the photoreceptor outer disc membranes. PUFAs are well known to play important roles in the retina and deficiency of LC-PUFAs has been shown to be associated with increased risk of the dry form of age-related macular degeneration (AMD), a highly prevalent retinal disease. Recent studies suggest that individuals who self-reported intake of foods rich in omega 3 PUFAs were 30% less likely to develop central geographic atrophy (GA) and 50% less likely to develop AMD than subjects with the lowest self-reported intake.

While methylation of the ELOVL2 promoter is highly correlated with chronological age, whether ELOVL2 protein has a functional role in aging has not been investigated. We observed an age-dependent increase in Elovl2 regulatory region methylation associated with concomitant downregulation of Elovl2 expression on mRNA and protein levels. Next we observed Elovl2 expression in cone and rod photoreceptors, as well as the retinal pigment epithelium. We also observed a significant age-related decline of the expression of the Elovl2 in the eye. The same age-dependent changes of Elovl2 methylation and gene expression were observed in the mouse liver, indicating that age-associated methylation of Elovl2 occurs in multiple tissues in the mouse, similarly to what was observed previously in humans.

Next, we investigated the function of Elovl2 in aging in vivo. As Elovl2 heterozygous mice are infertile, we created a knock-in point mutation using Crispr-Cas9 technology, Elovl2-C234W. Inhibiting Elovl2 accelerates aging in the mouse retina. Using lipidomics, we confirmed that Elovl2-C234W mutation results in loss of ELOVL2-specific function. We further investigated the effect of Elovl2-C234W mice on both anatomic and functional surrogates of aging in the mouse eye. These included autofluorescent (AF) deposits in the fundus, which increases with age, as well as the electroretinogram (ERG), which shows a decrease in the maximum scotopic response with age. In Elovl2-C234W mice, we noticed an increase in AF deposits as well as a decrease in ERG compared to age-matched controls, suggesting that inhibiting Elovl2 accelerates aging in the mouse retina.


Cerebrovascular Disease Prevention as a Priority in Dementia Prevention

Disruption of the blood flow to the brain, either a slow decline in supply due to vascular aging, or following a stroke, is an important contributing factor in the development of dementia. The brain requires a great deal of energy to function, and thus the supply of nutrients and oxygen is even more critical than is the case for other organs. Reductions in that supply have consequences.

Cerebrovascular diseases include a variety of medical conditions that affect the blood vessels of the brain and the cerebral circulation. These include conditions that may cause acute interruption of cerebral circulation and subsequent acute neuronal damage, such as ischaemic or haemorrhagic stroke, and disorders that may cause chronic pathological changes in small vessels and neurological dysfunction, such as cerebral small vessel diseases. Patients with cerebrovascular diseases, both acute and chronic, usually have multidimensional functional impairments to the brain and an increased risk of cognitive impairment and dementia.

Despite cognitive impairment after cerebral small vessel disease being a common cause of impairment of brain function, its underlying pathogenesis and mechanism are poorly understood. Recent studies showed that early impairment of cognition may be induced by disruption of the glio-neuro-vascular unit. Small vessel pathologies due to vascular risk factors may induce breakdown in the integrity of the blood-brain barrier and cerebral blood flow deficits. Although not yet tested in prospective longitudinal studies, structural and functional alterations of cerebral small vessels may trigger the cascade of molecular signals (for example, activation of innate immunity, vascular oxidative stress, and inflammation), leading to disruption of the glio-neuro-vascular unit. Neurovascular dysfunction alters the homeostasis of the brain microenvironment and promotes accumulation of amyloid and tau protein in regions involved in cognition, leading to early vascular and neurodegenerative cognitive impairment.

As cerebrovascular diseases and dementia are so closely interlinked, amelioration of vascular risk and vascular damage offers a new dawn for preventing not only vascular dementia but also mixed and even Alzheimer's dementias, and it may even offer alternative routes to clear amyloid and tau protein aggregation. For example, a substudy of the SPRINT MIND (Systolic Blood Pressure Intervention Trial Memory and Cognition in Decreased Hypertension) trial showed that intensive blood pressure reduction decreased progression of white matter hyperintensities, mild cognitive impairment, and probable dementia. The results of these trials indicated that patients with cerebrovascular disease or vascular risk factors might be a potential target population to prevent dementia.


OneSkin Launches a Topical Senolytic Treatment

Senescent cells are damaging to tissue function and health when they linger and grow in number, as becomes the case with age. They contribute to the chronic inflammation of aging via their signaling, the senescence-associated secretory phenotype. In skin, senescent cells are most likely responsible for a sizable fraction of the more problematic later life skin aging, in the 50s and on. It is less clear and less likely that they have much do to with the changes seen from the late 20s into the 40s.

The primary advantage inherent in targeting the mechanisms of aging specifically in skin is that the regulatory path to market for cosmetic treatments is much, much shorter than the alternative Investigational New Drug option. Thus OneSkin is making available a topical senolytic treatment that selectively destroys senescent cells in skin, and is doing so years in advance of FDA approval of any of the programs aiming to destroy senescent cells throughout the body. (That said, the senolytic treatment of dasatinib and quercetin, shown to destroy senescent cells in humans in a clinical trial, and capable of producing significant reversal of aging and age-related disease in mice, is very much available to any sufficiently motivated individual).

It would be interesting to see concrete data on the size of the effect produced by the OneSkin treatment, but that data isn't available yet. Is this approach definitively better than the suppression of skin senescence achieved via long term topical use of rapamycin, for example? One would hope so, but we'll have to wait and see. This lack of published, detailed data on effects in humans at the time of product launch is fairly characteristic of the supplement and cosmetics industries, and it makes it hard for the public at large to tell the difference between groups that are earnest and addressing a useful mechanism versus those that are not.

OneSkin launches topical senetherapeutic skin treatment

OneSkin is a longevity company on a mission to transform the way we think about skin. Today the company is launching OneSkin, a topical supplement containing a proprietary peptide, OS-01. Designed to reduce skin's biological age, OneSkin claims to improve the skin barrier, support DNA damage repair and prevent the accumulation of senescent cells. OneSkin launched in 2016 as a biotech startup after acceptance into IndieBio, one of the world's leading science accelerators.

"Our goal was to develop a product that extends skinspan, the period of time your skin is healthy and youthful. Our roots are in longevity science and we saw a need to shift the current paradigm. Instead of short-term fixes that focus purely on aesthetics, we're targeting the root cause of aging and optimizing skin health on a molecular level. We believe what we put on our skin should be safe, effective, and help to maximize our human potential."

OneSkin operates end-to-end research and development in-house with a team of experts in stem cell biology, skin regeneration, tissue engineering, biochemistry, bioinformatics, molecular biology, immunology, and aging. They measure skinspan in with MolClock - OneSkin's first skin-specific molecular clock - and with skin aging modelling, using a proprietary technology and lab process which includes growing 3D human skin weekly and measuring how various products and ingredients influence gene expression of the many genes associated with aging and longevity.

"As we age, senescent cells begin to accumulate in our skin tissues. The accumulation of these cells can contribute to an increased presence of wrinkles, susceptibility to skin cancer, and a damaged skin barrier. Beyond its impact on skin, when left to linger, senescent cells send pro-inflammatory signals to the rest of the body, increasing the risk of age-related diseases." Preventing the accumulation of senescent cells reduces skin's biological age as measured via MolClock, as well as leading to increased epidermal thickness, improved skin structure through increased collagen production and hyaluronic acid expression, maintained skin homeostasis and cell vitality.

Obese Individuals Have an Impaired Synaptic Plasticity Response

Researchers here provide initial evidence for obesity to impair synaptic plasticity, albeit a fairly indirect assessment of plasticity in just one area of the brain. Excessive visceral fat tissue is metabolically active and contributes to chronic inflammation, capable of impairing tissue function throughout the body. Being overweight or obese correlates very robustly with the risk of suffering many common conditions, and arguably accelerates the aging process via an increased pace of production of senescent cells.

Obesity is characterised by excessive body fat and is associated with several detrimental health conditions, including cardiovascular disease and diabetes. There is some evidence that people who are obese have structural and functional brain alterations and cognitive deficits. It may be that these neurophysiological and behavioural consequences are underpinned by altered plasticity. This study investigated the relationship between obesity and plasticity of the motor cortex in people who were considered obese (n = 14, nine males, aged 35.4 ± 14.3 years) or healthy weight (n = 16, seven males, aged 26.3 ± 8.5 years).

A brain stimulation protocol known as continuous theta burst transcranial magnetic stimulation was applied to the motor cortex to induce a brief suppression of cortical excitability. The suppression of cortical excitability was quantified using single-pulse transcranial magnetic stimulation to record and measure the amplitude of the motor evoked potential in a peripheral hand muscle. Therefore, the magnitude of suppression of the motor evoked potential by continuous theta burst stimulation was used as a measure of the capacity for plasticity of the motor cortex.

Our results demonstrate that the healthy-weight group had a significant suppression of cortical excitability following continuous theta burst stimulation (cTBS), but there was no change in excitability for the obese group. Comparing the response to cTBS between groups demonstrated that there was an impaired plasticity response for the obese group when compared to the healthy-weight group. This might suggest that the capacity for plasticity is reduced in people who are obese. Given the importance of plasticity for human behaviour, our results add further emphasis to the potentially detrimental health effects of obesity.


COVID-19 Is Only One of the Compelling Arguments for Developing the Means of Immune System Rejuvenation

Infectious disease is a far greater risk for the old than for the young. But then so is cancer. Both are conditions driven by the age-related failure of immune system competence, a growing inability to respond to vaccines and to destroy pathogens and errant cells, a state known as immunosenescence. Further, the failing immune system becomes inappropriately overactive at the same time as losing its efficacy, generating chronic inflammation that disrupts normal tissue function and spurs the development of numerous age-related diseases. Restoring a youthful immune function would be enormously beneficial and greatly reduce mortality and age-related disease across the board in older people. While this is a topic of interest in the research community, nowhere near enough resources are directed to achieving this goal, given the enormous cost and suffering that results from immune aging.

Unlike fine wine, the human body does not improve with age. Hearing fades, skin sags, joints give out. Even the body's immune system loses some of its vigour. This phenomenon, known as immunosenescence, might explain why older age groups are so hard-hit by COVID-19. And there is another troubling implication: vaccines, which incite the immune system to fight off invaders, often perform poorly in older people. The best strategy for quelling the pandemic might fail in exactly the group that needs it most.

The human immune system is mind-bendingly complex, and ageing affects nearly every component. Some types of immune cell become depleted: for example, older adults have fewer naive T cells that respond to new invaders, and fewer B cells, which produce antibodies that latch on to invading pathogens and target them for destruction. Older people also tend to experience chronic, low-grade inflammation, a phenomenon known as inflammageing. Although some inflammation is a key part of a healthy immune response, this constant buzz of internal activation makes the immune system less responsive to external insults. The upshot is a poorer reaction to infections and a dulled response to vaccines, which work by priming the immune system to fight off a pathogen without actually causing disease.

Many of the immune changes that come with ageing lead to the same result: inflammation. So researchers are looking at drugs that will calm this symptom. A class of drug, called senolytics, helps to purge the body of cells that have stopped dividing but won't die. These senescent cells are typically cleared by the immune system, but as the body ages, they begin to accumulate, ramping up inflammation. In August, a team launched a 70-person trial to test whether a senolytic called fisetin can curb progression of COVID-19 in adults aged 60 or older. They also plan to test whether fisetin can prevent COVID-19 infection in nursing-home residents.

In general, developing medications to improve immune function seems like a much smarter strategy than creating vaccines specifically for elderly people. Individual vaccines target specific pathogens, but an immune-boosting medication could be used with any vaccine. "I think the net result of all this will be renewed interest in understanding the defect in the immune response in the elderly. COVID-19 has brought to the front something that a lot of people have ignored."


BMP6 as a Target for Pro-Angiogenic Therapies

Today's research materials are focused on the fine details of angiogenesis, the formation of new blood vessels, and point to BMP6 as a potential target to increase or diminish that process. Angiogenesis is very well studied by the cancer community, in the context of how tumors subvert tissue signaling to support themselves via the generation of blood vessel networks. Angiogenesis is perhaps an underappreciated topic in the study of aging, however, and particularly with regard to the treatment of aging as a medical condition. There is a good argument to be made that the observed loss of capillary density in older individuals is an important aspect of degenerative aging, a downstream consequence of poorly understood chains of cause and effect, that in turn leads to disruption of blood pressure maintenance and feedback systems, and diminished delivery of nutrients to tissues throughout the body.

A few fairly blunt approaches to boosting angiogenesis have been demonstrated in mice. This is largely in the context of cardiovascular disease, however, trying to encourage the creation of additional larger blood vessels that can bypass areas of damage. Growing such additional blood vessels prior to a cardiovascular event would obviously be preferable, and this is a plausible goal for the future of medicine. One strategy is to mobilize hematopoietic and endothelial cells from the bone marrow, using much the same class of treatment that is employed to collect donor cells for hematopoietic stem cell transplantation. These cells are involved in angiogenesis, and when the vasculature is flooded with them, more angiogenesis takes place.

Effects on capillary density have yet to be assessed, unfortunately. This is a part of the field that merits greater attention. For example, an intriguing study showed that mouse life span is extended by a related class of hematopoietic cell mobilizing drug. The mechanism of action was left undetermined, however. It could as well be improved immune function via increased hematopoietic generation of immune cells as improved vascular function via restoration of blood vessel density. This uncertainty following a result in which aging is in some way turned back is exactly why more research is needed on this topic.

New insight into neovessel formation shows promise in future treatment of cardiovascular diseases

Bone morphogenetic proteins, BMPs, are growth factors originally discovered as regulators in bone formation. Later on, their regulatory role on the development and maintenance of a wide range of tissues has become apparent. BMPs have a vital role in the development of the cardiovascular system. In addition, BMPs have been shown to regulate blood vessel formation but their exact mechanisms are unknown. Crosstalk of BMP-signalling with a well-known blood vessel formation regulator, VEGF, and its downstream effectors is poorly understood.

The new study now shows that VEGF gene transfer or oxygen deprivation of the tissue induce the expression of BMPs. Bone morphogenetic factor 6 (BMP6) ligand was further demonstrated, for the first time, to regulate blood vessel formation. BMP6 was shown to act in endothelial cells via VEGFR2 and Hippo signalling pathways by inducing nuclear localization of Hippo signalling pathway mediator TAZ. The findings from this research improve our understanding of multifactorial communication of cell signalling pathways in blood vessel formation. The discoveries related to BMP6 and Hippo signalling can be used in the development of novel treatments for cardiovascular diseases.

BMP6/TAZ-Hippo signaling modulates angiogenesis and endothelial cell response to VEGF

BMP family members are important regulators of both vascular homeostasis and angiogenesis. Synergistic effect of VEGF and BMPs on vasculature have been previously detected in bone formation but their role in angiogenesis, particularly crosstalk with VEGFR2 signaling has remained elusive. Our data demonstrate that BMPs are widely expressed in endothelium of various tissues in hypoxia or normoxia and after VEGF-induced angiogenesis, and that BMP2 and BMP6 regulate VEGFR and Notch signaling. BMP6 was further demonstrated to induce neovessel formation in vivo. This is the first comprehensive data on BMPs in hypoxia, and in angiogenesis in various animal models.

miR-195 Promotes Blood-Brain Barrier Integrity by Suppressing TSP1 Activity

The blood-brain barrier consists of specialized cells that line central nervous system blood vessels, allowing only certain cells and molecules to pass to and from the brain. This barrier becomes leaky with age, and this results in growing inflammation and dysfunction in the brain. Inappropriate molecules find their way through and provoke the immune system of the brain into a damaging, lasting inflammatory reaction. This is an important early stage in the progression towards neurodegeneration and consequent cognitive decline. Researchers here report on their investigations of the biochemistry of blood-brain barrier dysfunction, focusing on TSP1 and its ability to disrupt the blood-brain barrier by breaking down proteins involved in the tight junction structures that link cells together. MicroRNA-195 can block some of this disruption when delivered intravenously, which makes it a potentially interesting basis for treatment.

Blood-brain barrier (BBB) disruption contributes to neurodegenerative diseases. Loss of tight junction (TJ) proteins in cerebral endothelial cells (ECs) is a leading cause of BBB breakdown. We recently reported that miR-195 provides vasoprotection, which urges us to explore the role of miR-195 in BBB integrity. Here, we found cerebral miR-195 levels decreased with age, and BBB leakage was significantly increased in miR-195 knockout mice. Furthermore, exosomes from miR-195-enriched astrocytes increased endothelial TJ proteins and improved BBB integrity.

To decipher how miR-195 promoted BBB integrity, we first demonstrated that TJ proteins were metabolized via autophagic-lysosomal pathway and the autophagic adaptor p62 was necessary to promote TJ protein degradation in cerebral ECs. Next, proteomic analysis of exosomes revealed miR-195-suppressed thrombospondin-1 (TSP1) as a major contributor to BBB disruption. Moreover, TSP1 was demonstrated to activate selective autophagy of TJ proteins by increasing the formation of claudin-5-p62 and ZO1-p62 complexes in cerebral ECs while TSP1 impaired general autophagy.

Delivering TSP1 antibody into the circulation showed dose-dependent reduction of BBB leakage by 20%-40% in 25-month-old mice. Intravenous or intracerebroventricular injection of miR-195 rescued TSP1-induced BBB leakage. Dementia patients with BBB damage had higher levels of serum TSP1 compared to those without BBB damage, while the normal subjects had the lowest TSP1. Taken together, the study implies that TSP1-regulated selective autophagy facilitates the degradation of TJ proteins and weakens BBB integrity. An adequate level of miR-195 can suppress the autophagy-lysosome pathway via a reduction of TSP1, which may be important for maintaining BBB function.


Chromatin Changes in the Aging of Stem Cells

Chromatin is the name given to the packed structure of nuclear DNA and surrounding molecules, tightly coiled in the center of the cell. Chromatin structure and the molecules responsible for regulating that structure are a part of the complex epigenetic systems that determine the pace of protein production, and thus cell behavior. Chromatin changes in characteristic ways with age, a situation that is far from fully mapped and understood, but is particularly important in stem cell aging. Stem cell populations become less active with age, most likely an evolved response to rising levels of tissue damage that acts to limit the incidence of cancer. The cost of that protection is a slow decline into organ failure, disease, and death. Safely restoring youthful function in the scores of different stem cell populations throughout the body is an important goal for the future of medicine.

In most tissues, adult stem cells occupy a rare but powerful functional compartment, capable of differentiating into multiple tissue-specific lineages. Some stem cell types can remain quiescent until environmental signals prompt them to divide whereas other types continuously divide to repopulate lost or injured tissue. This process is critical and is harnessed during injury and disease to enhance tissue repair. Stem cells in adult tissues show dramatic reductions in regenerative capacity with age. Stem cells undergo replicative aging (due to repeat proliferative cycles), chronological aging (due to chronic changes during prolonged quiescent state) and even show senescence or exhaustion phenotypes. Prolonged quiescence can accumulate DNA damage and cause chronological aging due to additive insults and error-prone damage repair mechanisms.

In response to replication signals, stem cells are activated to divide. Two major aspects of stem cell division are self-renewal and differentiation. Studies across multiple organisms and stem cell types have revealed distinct effects of aging on self-renewal capacity and differentiation potential depending on stem cell type. This is manifested in either loss or gain of stem cell numbers, delay in activation kinetics, altered fate, lineage bias and/or compromised function of differentiated cells with age. Ultimately, these changes in aged stem cells eventually lead to physiological disorders and age-dependent pathologies in the organism.

Evidence suggests a reconfiguration of the chromatin state to a global increase in DNA hypermethylation, an imbalanced heterochromatin, a loss of active enhancers, even a disruption of chromosome territories. The consequences of these epigenomic changes are reflected in functional outcomes such as altered self-renewal patterns and/or senescence phenotypes that impact stem cell number. Additionally, there is dramatic change in stem cell potential, lineage bias, delayed activation kinetics and ultimately higher frequencies of disease phenotypes such as cancer.

While "drift" patterns are not necessarily programmed, it may be possible to delay their accumulation or even reverse the changes by late-life epigenetic drug interventions or cellular epigenome reprogramming strategies that "wipe out and start over". Complete reprogramming of aged hematopoietic stem cells (HSCs) into induced pluripotent stem cells - by overexpression of OCT4, SOX2, KLF4, and MYC (OSKM) - followed by blastocyst complementation, re-differentiation into HSCs, and serial transplantation showed remarkable repopulation capacity invariant with young cells. Since the genetic material of the stem cells was unchanged, this type of rejuvenation was attributed to an epigenetic resetting although the exact mechanisms remain to be identified. Partial reprogramming by short-term cyclic expression of OSKM also had positive outcomes in aged mice. There is also evidence from other studies that partial reprogramming can turn back the DNA methylation clock further supporting the notion that reprogramming directly affects the epigenome. However, whether similar changes occur in stem cells remains to be investigated.


Non-Alcoholic Fatty Liver Disease as the Marker of a Lifestyle that Shortens Life Span

If you are overweight, then you will suffer a faster pace of aging, more age-related disease, greater lifetime medical costs, and an earlier death. The more excess weight and the longer that weight is held, the worse the outcome. In at least one sense, being overweight literally accelerates aging, increasing the pace at which harmful senescent cells accumulate in the body. These errant cells secrete signals that produce chronic inflammation, but this isn't the only way in which visceral fat tissue causes unresolved, chronic inflammation, an unwanted overactivation of the immune system that disrupts metabolism and speeds the progression of age-related disease. Fat cells produce signals that mimic those of infected cells, and DNA fragments released from dying fat cells produce a similar outcome.

Whenever one looks at the relationship between mortality and metabolic diseases - such as non-alcoholic fatty liver disease, today's topic - that are usually the product of being overweight, then one is looking at a proxy measure of the progression of mechanisms by which visceral fat tissue accelerates aging. Today's research materials note that even mild non-alcoholic fatty liver disease is linked to increased mortality. This is because the most common cause of mild non-alcoholic fatty liver disease is for an individual to be meaningfully overweight, carrying excessive visceral fat tissue that disrupts metabolism and harms future prospects.

Even mild fatty liver disease is linked to increased mortality

Non-alcoholic fatty liver disease, NAFLD, is often caused by obesity and affects nearly one in four adults in Europe and the US. Earlier research has demonstrated an increased risk of death in patients with NAFLD. Now, researchers show that mortality increases with disease severity, but even mild fatty liver disease is linked to higher mortality. The researchers matched 10,568 individuals with biopsy-confirmed NAFLD to general population controls through Sweden's comprehensive, nationwide registers. They found that all stages of NAFLD were associated with excess mortality risk, even early stages of disease. This risk was driven primarily by deaths from cancer (excluding liver cancer) and cirrhosis, while the risks of cardiovascular mortality or hepatocellular carcinoma (HCC) mortality were relatively modest.

Patients with NAFLD had a 93 percent increased risk of all-cause mortality, but the numbers varied with disease severity. The risk increased progressively from the mildest form of NAFLD (simple steatosis), to non-fibrotic steatohepatitis (NASH), to non-cirrhotic fibrosis, and to severe NAFLD with liver cirrhosis.

Even mild fatty liver disease is linked to increased mortality

This nationwide, matched cohort study included all individuals in Sweden with biopsy-confirmed NAFLD (1966 to 2017; n=10,568). NAFLD was categorised as simple steatosis, non-fibrotic steatohepatitis (NASH), non-cirrhotic fibrosis and cirrhosis. Using Cox regression, we estimated multivariable-adjusted hazard ratios (aHRs).

Over a median of 14.2 years, 4,338 NAFLD patients died. Compared with controls, NAFLD patients had significantly increased overall mortality (aHR=1.93). Compared with controls, significant excess mortality risk was observed with simple steatosis (aHR=1.71), non-fibrotic NASH (aHR=2.14), non-cirrhotic fibrosis (aHR=2.44) and cirrhosis (aHR=3.79). This dose-dependent gradient was similar when simple steatosis was the reference. The excess mortality associated with NAFLD was primarily from extrahepatic cancer (aHR=2.16), followed by cirrhosis (aHR=18.15), cardiovascular disease (aHR=1.35) and hepatocellular carcinoma (HCC) (aHR=11.12).

In conclusion, all NAFLD histological stages were associated with significantly increased overall mortality, and this risk increased progressively with worsening NAFLD histology. Most of this excess mortality was from extrahepatic cancer and cirrhosis, while in contrast, the contributions of cardiovascular disease and HCC were modest.

Myokines Mediate the Effects of Exercise on Health

Mapping mammalian biochemistry is a sizable task, and much of that biochemistry remains poorly understood and categorized. Cell signaling is a vast topic in and of itself. Here researchers discuss myokines, signal molecules generated by muscle cells as a result of exercise. These diverse signals are influential on tissue function and health, and mediate some fraction of the benefits resulting from physical activity. Further, some clearly change in abundance with age, and might therefore be useful targets for interventions intended to better maintain health and function with aging.

In recent decades, it has been discovered that contracting skeletal muscles release various hormone-like substances. These activators are called myokines, which are small proteins and proteoglycan peptides that are produced and secreted by skeletal muscle cells in response to muscle contractions. Various myokines secreted by skeletal muscles during aerobic and anaerobic exercises have been studied in connection with various human diseases. For a long time, skeletal muscles were only recognized as being involved in the physical aspects of exercise. However, with the discovery of exercise-induced myokines, skeletal muscles have been demonstrated to be involved in the maintenance of metabolic homeostasis. Although the detailed mechanisms are not clear, both skeletal muscle contraction and mass maintenance appear to be actively involved in maintaining health and preventing disease development in the elderly, particularly considering the rapid deterioration of muscle physiology with aging.

This review summarizes 13 myokines regulated by physical activity that are affected by aging and aims to understand their potential roles in metabolic diseases. We categorized myokines into two groups based on regulation by aerobic and anaerobic exercise. With aging, the secretion of apelin, β-aminoisobutyric acid (BAIBA), bone morphogenetic protein 7 (BMP-7), decorin, insulin-like growth factor 1 (IGF-1), interleukin-15 (IL-15), irisin, stromal cell-derived factor 1 (SDF-1), sestrin, secreted protein acidic rich in cysteine (SPARC), and vascular endothelial growth factor A (VEGF-A) decreased, while that of IL-6 and myostatin increased. Aerobic exercise upregulates apelin, BAIBA, IL-15, IL-6, irisin, SDF-1, sestrin, SPARC, and VEGF-A expression, while anaerobic exercise upregulates BMP-7, decorin, IGF-1, IL-15, IL-6, irisin, and VEGF-A expression. Myostatin is downregulated by both aerobic and anaerobic exercise.

Although the 13 myokines reviewed are all stimulated by exercise, each has unique characteristics. In brief, apelin is an anti-aging factor and has positive effects on hypertension and ischemia-reperfusion injury when combined with exercise. BAIBA prevents metabolic diseases by acting as an osteocyte survival factor, protecting against mitochondrial breakdown, and attenuating bone and skeletal muscle loss. BMP-7 is an important factor in bone formation and skeletal muscle mass maintenance. Decorin, IGF-1, and SDF-1 have positive effects on tendon strength, bone and tissue development, and skeletal muscle regeneration, respectively. IL-15 facilitates fibroblast collagen synthesis and cell proliferation. IL-6 contributes to the maintenance of glucose homeostasis, obesity regulation, microglial function, and lactate production. Irisin might become a treatment for Alzheimer's disease because of its positive influence on neuron functional impairment. The most interesting is myostatin. Unlike the other myokines, exercise reduces its secretion. It is beneficial in chronic heart failure, chronic kidney disease, and lipidomic abnormalities. Sestrin helps prevent the development of age-associated metabolic diseases and sarcopenia. SPARC, which is increased by aerobic exercise, has potential as a cancer treatment. VEGF-A, which is upregulated by both anaerobic and aerobic exercise, is involved in the growth and survival of skeletal muscle.

The biggest takeaway of our review is that both aerobic and anaerobic exercises exert positive effects on skeletal muscles by releasing various myokines that are beneficial to the elderly. Given that most studies on long term physical activity in the elderly have focused on aerobic exercises, it is worth broadening the scope of research by examining the need for anaerobic exercise.


Phosphate as an Agent of Accelerated Aging

Here find an interesting viewpoint on the role of phosphate in mammalian biochemistry, suggesting that it tilts the playing field in the direction of faster degenerative aging. This emerges from work on the longevity-associated gene klotho and its effects on kidney function and vascular function in aging. As is usually the case in such matters, there is no great debate over whether or not specific mechanisms and contributions to aging and age-related diseases exist. The question is whether or not the size of the effect is large enough to care about, and that is always much harder to answer, given the immense complexity of cellular biochemistry.

During the evolution of skeletons, terrestrial vertebrates acquired strong bones made of calcium-phosphate. By keeping the extracellular fluid in a supersaturated condition regarding calcium and phosphate ions, they created the bone when and where they wanted simply by providing a cue for precipitation. To secure this strategy, they acquired a novel endocrine system to strictly control the extracellular phosphate concentration. In response to phosphate intake, fibroblast growth factor-23 (FGF23) is secreted from the bone and acts on the kidney through binding to its receptor Klotho to increase urinary phosphate excretion, thereby maintaining phosphate homeostasis.

The FGF23-Klotho endocrine system, when disrupted in mice, results in hyperphosphatemia and vascular calcification. Besides, mice lacking Klotho or FGF23 suffer from complex aging-like phenotypes, which are alleviated by placing them on a low-phosphate diet, indicating that phosphate is primarily responsible for the accelerated aging. Phosphate acquires the ability to induce cell damage and inflammation when precipitated with calcium. In the blood, calcium-phosphate crystals are adsorbed by serum protein fetuin-A and prevented from growing into large precipitates. Consequently, nanoparticles that comprised calcium-phosphate crystals and fetuin-A, termed calciprotein particles (CPPs), are generated and dispersed as colloids.

CPPs increase in the blood with an increase in serum phosphate and age. Circulating CPP levels correlate positively with vascular stiffness and chronic non-infectious inflammation, raising the possibility that CPPs may be an endogenous pro-aging factor. Terrestrial vertebrates with the bone made of calcium-phosphate may be destined to age due to calcium-phosphate in the blood.


Interventions Targeting the Aging of the Gut Microbiome

Age-related changes to the microbial populations of the gut, the gut microbiome, appear important in the progression of aging. The effects on long-term health and risk of age-related conditions might be on a par with those of physical activity, and certainly overlap with those of diet. With ageing, beneficial microbes that produce metabolites (such as butyrate) that lead to better tissue function diminish in number, while harmful microbes that spur chronic inflammation grow in number. This may be due to loss of immune system competency, as the immune system gardens the gut microbiome, or it may be due to diminished intestinal barrier efficiency. Changes in diet characteristic of age may also play a role, but it is an open question as to the relative size of these and other potential contributing effects.

The research and medical community may not require a complete understanding prior to taking action, as it is quite clear from animal models that fecal microbiota transplantation from young to old reverses changes in the microbiome, improves health, and extends life span. Fecal microbiota transplantation is already practiced in human medicine, for conditions in which pathological bacteria overtake the intestine - conditions more commonly found in older people. Thus there is a comparatively short path to its use as a way to reverse ordinary, harmful age-related changes in the gut microbiome, given the will and funding to forge ahead.

Gut microbiota and old age: Modulating factors and interventions for healthy longevity

From a healthcare perspective, a longer life does not necessarily mean more health life-years. Unfortunately, aging often manifests itself negatively through frailty. Recent research has suggested that aging may be also associated with a different gut microbiota composition (i.e. a rearrangement) and with the increased presence of certain pathobionts, as compared to younger adults. This may be related to the heightened disease progression (and exposure to medication) and the decrease in immunocompetence in the older population. Most degenerative diseases are affected by our long-term dietary habits and lifestyle. Diet is also one of the most influential factors affecting our gut microbiota composition, diversity and function. Therefore, age-related dietary alterations could negatively impact the gut microbiota health in the older adults, and, consequently, their healthy longevity.

How aging affects the gut microbiota, the effects of the age-related changes on the health status of the host, and possible therapeutic approaches to counteract the negative aspects of dysbiosis have recently received considerable research interest. Although this research area has been expanding tremendously over the past years, there are still major gaps in our understanding of the functional interactions between the complex microbial community and the human host, especially at an advanced age. For example, which are the main factors which negatively influence our gut microbiota diversity and functions? Are they different in the older population as compared to younger adults? Are there specific microbiome signatures for longevity or are they rather reflective of health status? Are short-term effects (e.g. antibiotic exposure) as important as the long-term ones (e.g. food preferences), and which ones are more difficult to counterbalance? Are therapeutic interventions targeting the gut microbiota less effective or less safe in the older adults? Are these interventions suitable for entire populations, or should they be targeted individually (i.e. personalized modulation of the microbiota)?

Over the past two decades, numerous randomized clinical trials have been conducted in various target populations, including the older adults, to investigate the effectiveness of several therapeutic approaches impacting out gut microbiota and improving our health. Among these, supplementation of the human diet with beneficial microorganisms (probiotics), substrates to promote the proliferation of these beneficial microbes (prebiotics), or a combination of both (synbiotics) represent the most investigated health interventions.

Based on the results of several randomized clinical trials showing fecal microbiota transplantation (FMT) as a viable alternative treatment approach against C. difficile infection, current clinical guidelines recommend FMT for "patients with multiple recurrences of C. difficile infection who have failed appropriate antibiotic treatments (strong recommendation, moderate quality of evidence)". C. difficile infection is known to affect the older population disproportionately, mainly due to immunosenescence, increased exposure to healthcare settings, and frequent use of antibiotics and proton-pump inhibitors. FMT proved to be a safe and effective treatment option for C. difficile infection in older adults.

Following the success in C. difficile infection treatment, the potential of FMT has also been investigated against Crohn's disease, irritable bowel syndrome, cirrhosis, and even neurological and behavioral conditions. The results are promising, but still modest. One important aspect in the success of FMT is the diversity and the composition of the stool donor, which plays an essential role in restoring metabolic deficits in recipients.

Our gut microbiota is a dynamic ecosystem, which adapts continuously to changes in lifestyle, nutrition, hygiene, and exposure to medication. Establishing and maintaining positive interactions between us and our gut microbiota are essential for our health. The longer the exposure to certain stressors, the more significant the changes, which may explain why recent research has found that older populations have a less diverse microbiota than younger individuals, and more pathobionts. With advanced age, the prevalence of certain diseases increases as well, which can also contribute to an increased risk of frailty leading to microbiota dysfunctionalities, and therefore, to progression of other metabolic diseases.

Regarding older adults, and especially the residents of long-term care facilities, microbiota-targeted interventions should be made early and often, to attenuate the occurrence of critical conditions such as frailty. Any long-term medication exposure, and especially antibiotic treatments, should be followed by a microbiota restoration therapy, to prevent the occurrence of dangerous infections such as C. difficile and the proliferation of other opportunistic strains.

Molecules Leaking from Damaged Muscle Fibers can Activate Muscle Stem Cells

Declining muscle stem cell function appears likely to be the most important contributing cause of sarcopenia, the characteristic loss of muscle mass and strength with age. Studies of the stem populations that support muscle tissue have suggested that the cells are largely intact and capable, but quiescent. This may be a reaction to changes in signaling resulting from the age-damaged and inflammatory tissue environment, or it may be due to damage and dysfunction in the cells making up the stem cell niche, or both. Beyond the few efforts directed at repairing the underlying damage that causes these issues, such as accumulation of senescent cells, there is some interest in uncovering signals that will force muscle cells to get back to work. The research here is an example of this sort of initiative.

Skeletal muscle is made up of bundles of contracting muscle fibers and each muscle fiber is surrounded by satellite cells - muscle stem cells that can produce new muscle fibers. Thanks to the work of these satellite cells, muscle fibers can be regenerated even after being bruised or torn during intense exercise. Satellite cells also play essential roles in muscle growth during developmental stages and muscle hypertrophy during strength training. However, in refractory muscle diseases like muscular dystrophy and age-related muscular fragility (sarcopenia), the number and function of satellite cells decreases. It is therefore important to understand the regulatory mechanism of satellite cells in muscle regeneration therapy.

Since satellite cells are activated when muscle fibers are damaged, researchers hypothesized that muscle damage itself could trigger activation. However, this is difficult to prove in animal models of muscle injury so they constructed a cell culture model in which single muscle fibers, isolated from mouse muscle tissue, were physically damaged and destroyed. Using this injury model, they found that components leaking from the injured muscle fibers activated satellite cells, and the activated cells entered the G1 preparatory phase of cell division. Further, the activated cells returned to a dormant state when the damaged components were removed, thereby suggesting that the damaged components act as the activation switch.

The research team named the leaking components "Damaged myofiber-derived factors" (DMDFs), after the broken muscle fibers, and identified them using mass spectrometry. Most of the identified proteins were metabolic enzymes, including glycolytic enzymes such as GAPDH, and muscle deviation enzymes that are used as biomarkers for muscle disorders and diseases. GAPDH is known as a "moonlighting protein" that has other roles in addition to its original function in glycolysis, such as cell death control and immune response mediation. The researchers therefore analyzed the effects of DMDFs, including GAPDH, on satellite cell activation and confirmed that exposure resulted in their entry into the G1 phase. Furthermore, the researchers injected GAPDH into mouse skeletal muscle and observed accelerated satellite cell proliferation after subsequent drug-induced muscle damage. These results suggest that DMDFs have the ability to activate dormant satellite cells and induce rapid muscle regeneration after injury.


Targeting NAD+ Metabolism for the Treatment of Cardiovascular Disease

Nicotinamide adenine dinucleotide (NAD+) is important to mitochondrial function, the supply of chemical energy store molecules to power cellular processes, and thus to cell and tissue function. Levels of NAD+ decline with age, a part of the deterioration of mitochondrial function throughout the body:. Too little NAD+ is created, too little NAD+ is recycled after use. This downturn occurs for reasons in which the proximate causes are fairly clear, meaning which of the other molecules required for NAD+ synthesis and recycling come to be in short supply in old tissues, but a map of the deeper connections to the known root causes of aging is lacking.

Various vitamin B3 derived supplements have been shown to increase NAD+ levels in older individuals. Those that have undergone clinical trials were no better in this regard than the effects of structured exercise programs. It seems plausible that this performance can be improved upon, but will that produce better effects than exercise? That remains to be determined. As noted in this open access paper, there are plenty of age-related conditions in which loss of mitochondrial function is important, and either exercise or pharmacological approaches to produce NAD+ upregulation may produce benefits in older individuals by reducing this loss of function.

Nicotinamide adenine dinucleotide or NAD+, is one of the most essential small molecules in mammalian cells. NAD+ interacts with over 500 enzymes and plays important roles in almost every vital aspect in cell biology and human physiology. Dysregulation of NAD+ homeostasis is associated with a number of diseases including cardiovascular diseases (CVD). Particularly, modulation of NAD+ metabolism has been proposed to provide beneficial effects for CVD settings that are highly associated with sudden cardiac death (SCD), such as ischemia/reperfusion injury (I/R injury), heart failure, and arrhythmia.

The heart, along with the kidney and the liver has the highest level of NAD+ among all the organs. In mammalian cells, NAD+ is synthesized via two distinct pathways: the de novo pathway and the salvage pathway. The de novo pathway generates NAD+ from tryptophan through the kynurenine metabolic pathway, or nicotinic acid (NA) through the Preiss-Handler pathway. Nevertheless, most organs other than the liver, including the heart, use the salvage pathway as the main route to generate NAD+. Metabolic profiling of NAD+ biosynthetic routes in mouse tissues was established by measuring the in vitro activity of enzymes, the levels of substrates and products, and revealed that 99.3% of NAD+ in the heart is generated by the salvage pathway. On the other hand, enzymes involved in the de novo pathway are of low expression and low activity in the heart. The salvage pathway generates NAD+ from the NAD+ degradation product nicotinamide (NAM). NAM is converted into an intermediate product nicotinamide mononucleotide (NMN) via NAM phosphoribosyltransferase (NAMPT) - the rate limiting enzyme in the salvage pathway.

Both reductions in NAD+ biosynthesis and activation of NAD+-consuming enzymes can cause NAD+ depletion, which in turn may lead to dysregulation of numerous vital cellular functions. Chronic dysregulation of NAD+-dependent cell functions ultimately results in the development of CVD. An increasing number of studies, particularly in rodent models, have shown that boosting NAD+ is beneficial for CVD. Elevation of NAD+ levels can be achieved by supplementing NAD+, NAD+ precursors or modulating activities of enzymes responsible for NAD+ generation or degradation such as NAMPT, PARP, and CD38.

Human studies have shown that NAD+-boosting therapy can reduce mortality and provide moderate clinical benefits for patients with CAD. However, conflicting results on critical clinical outcomes such as incidence of composite mortality and major vascular events have raised the concern that whether NAD+-boosting therapy can ultimately become a primary treatment for CAD and other CVD. Several important aspects may help overcome these hurdles. First, it is critical to determine the effective dose of NAD+ boosters for each individual patient. Direct measurement for NAD+ level or NAD+ metabolome from accessible samples such as plasma should be considered. Second, the optimal time window for NAD+ booster supplementation remains to be established in human subjects. NAD+-boosting therapy should coordinate with the intrinsic circadian oscillation of NAD+ level in human body so that maximal beneficial effects can be achieved. With a more nuanced understanding of NAD+ biology in the heart and clinical studies designed with more sophistication, we anticipate that NAD+-boosting therapy would ultimately harness its potential for SCD-associated CVD.


Using CRISPR to Remove Mutated Sequences of Nuclear DNA Required by Cancerous Cells

Fusion genes feature in many cancers, a form of mutation in which two genes are joined together, such as through deletion of the DNA sequences that normally separate the two genes. The resulting mutant fusion gene sequence encodes a fusion protein that can have novel effects, or in which both portions remain functional, but are now produced in at inappropriate times and in inappropriate amounts. This change in cell biochemistry can be important in driving cancerous behavior, and this appears to be the case in a meaningful fraction of cancer types.

Today's research materials discuss a clever use of CRISPR DNA editing techniques. CRISPR is used to induce targeted breaks in nuclear DNA at specific points relative to two well known fusion genes, with the result that the gene, if present, is skipped over and removed by the DNA repair mechanisms responsible for reassembling the broken chromosome. This same strategy could well be applied to a range of fusion genes in cancer. The most promising part of this approach is that it is very specific to the cells that exhibit this fusion gene mutation. Thus gene therapy vectors can be used deliver the CRISPR tools into tissues quite generally, with no detrimental effect on normal cells.

Scientists succeed in reprogramming the CRISPR system in mice to eliminate tumour cells without affecting healthy cells

Fusion genes are the abnormal result of an incorrect joining of DNA fragments that come from two different genes, an event that occurs by accident during the process of cell division. If the cell cannot benefit from this error, it will die and the fusion genes will be eliminated. But when the error results in a reproductive or survival advantage, the carrier cell will multiply and the fusion genes and the proteins they encode thus become an event triggering tumour formation. Many chromosomal rearrangements and the fusion genes they produce are at the origin of childhood sarcomas and leukaemias. Fusion genes are also found in among others prostate, breast, lung and brain tumours: in total, in up to 20% of all cancers.

Because they are only present in tumour cells, fusion genes attract a great deal of interest among the scientific community because they are highly specific therapeutic targets, and attacking them only affects the tumour and has no effect on healthy cells. And this is where the CRISPR technology comes into play. With this technology, researchers can target specific sequences of the genome and, as if using molecular scissors, cut and paste DNA fragments and thus modify the genome in a controlled way. In a new study, researchers worked with cell lines and mouse models of Ewing's sarcoma and chronic myeloid leukaemia, in which they managed to eliminate the tumour cells by cutting out the fusion genes causing the tumour.

"Our strategy was to make two cuts in introns, non-coding regions of a gene, located at both ends of the fusion gene. In that way, in trying to repair those breaks on its own, the cell will join the cut ends which will result in the complete elimination of the fusion gene located in the middle." As this gene is essential for the survival of the cell, this repair automatically causes the death of the tumour cell.

In vivo CRISPR/Cas9 targeting of fusion oncogenes for selective elimination of cancer cells

In the context of cancer gene therapy, it is clear that targeting a single gene is often insufficient to eliminate cancer cells - yet, many types of cancers are addicted to the presence of a single oncogenic event that can reprogram cells and initiate tumorigenesis. This is the case for the so-called fusion oncogenes (FOs), which are chimeric genes resulting from in-frame fusions of the coding sequences of two genes involved in a chromosomal rearrangement. While the nature of the FOs may be diverse, they are primarily classified as involving transcription factors or tyrosine kinases. Silencing of FO transcripts has been shown to inhibit tumor cell growth in vitro and in vivo, demonstrating FO addiction in many human cancers.

FOs are ideal therapeutic targets for the development of new directed cancer treatments, owing to their cancer-driving roles, their restriction to cancer cells and the reliance of tumors on them. Unfortunately, FOs are challenging to target directly with candidate drugs. The ability to precisely manipulate cancer cell genomes to correct or eliminate cancer-causing aberrations by highly-efficient CRISPR/Cas9 genome editing opens new possibilities to develop FO-targeted options to eliminate cancer cells. In the present study, we describe a simple and efficient genome editing strategy specifically targeting FOs in cancer cells. Our CRISPR/Cas9-based approach induces two targeted intronic double strand breaks in both genes involved in a FO that, importantly, produces a cancer cell-specific genomic deletion that is dependent on the presence of the FO, and has no effect on wild-type gene expression in non-cancer cells.

Investigating Zebrafish Biochemistry in Search of Mechanisms of Neural Regeneration

Zebrafish are highly regenerative, capable of regrowing organs, and even nervous system tissue such as the retina. Research groups investigate these species in search of specific mechanisms of proficient regeneration, with the hope that they can be ported over to human biochemistry. In the best case scenario, mechanisms of this nature could still exist in mammals, retained in order to conduct embryonic development, but actively suppressed in some way in adults, possibly because such suppression reduces cancer risk. The existing evidence is suggestive that this is the case, and the work here adds further support.

Researchers mapped the genes of animals that have the ability to regenerate retinal neurons. For example, when the retina of a zebrafish is damaged, cells called the Müller glia go through a process known as reprogramming. During reprogramming, the Müller glia cells will change their gene expression to become like progenitor cells, or cells that are used during early development of an organism. Therefore, these now progenitor-like cells can become any cell necessary to fix the damaged retina.

Like zebrafish, people also have Müller glia cells. However, when the human retina is damaged, the Müller glia cells respond with gliosis, a process that does not allow them to reprogram. "After determining the varying animal processes for retina damage recovery, we had to decipher if the process for reprogramming and gliosis were similar. Would the Müller glia follow the same path in regenerating and non-regenerating animals or would the paths be completely different? This was really important, because if we want to be able to use Müller glia cells to regenerate retinal neurons in people, we need to understand if it would be a matter of redirecting the current Müller glia path or if it would require an entirely different process."

The research team found that the regeneration process only requires the organism to "turn back on" its early development processes. Additionally, researchers were able to show that during zebrafish regeneration, Müller glia also go through gliosis, meaning that organisms that are able to regenerate retinal neurons do follow a similar path to animals that cannot. While the network of genes in zebrafish was able to move Müller glia cells from gliosis into the reprogrammed state, the network of genes in a mouse model blocked the Müller glia from reprogramming. From there, researchers were able to modify zebrafish Müller glia cells into a similar state that blocked reprogramming while also having a mouse model regenerate some retinal neurons. Next, the researchers will aim to identify the number of gene regulatory networks responsible for neuronal regeneration and exactly which genes within the network are responsible for regulating regeneration.


More Work on Proteomic Clocks to Measure Biological Age

Researchers are these days producing a fair number of novel metrics capable of measuring age and mortality. Machine learning or similar approaches are used to mine epigenetic, proteomic, and transcriptomic data sets, in order to establish algorithmic combinations of epigenetic marks or expression of specific genes that change in characteristic ways with age. The work here is an example of the type, focused on the proteome, the set of proteins produced by cells, and how it shifts over the course of a lifetime. Unlike first generation epigenetic clocks, this approach appears to be able to pick up the difference to the pace of aging caused by regular exercise and consequent physical fitness, suggesting that it is probably a better class of biomarker, given what is known of the effects of exercise on long-term health.

We previously identified 529 proteins that had been reported by multiple different studies to change their expression level with age in human plasma. In the present study, we measured the q-value and age coefficient of these proteins in a plasma proteomic dataset derived from 4263 individuals. A bioinformatics enrichment analysis of proteins that significantly trend toward increased expression with age strongly implicated diverse inflammatory processes. A literature search revealed that at least 64 of these 529 proteins are capable of regulating life span in an animal model. Nine of these proteins (AKT2, GDF11, GDF15, GHR, NAMPT, PAPPA, PLAU, PTEN, and SHC1) significantly extend life span when manipulated in mice or fish.

By performing machine-learning modeling in a plasma proteomic dataset derived from 3301 individuals, we discover an ultra-predictive aging clock comprised of 491 protein entries. The Pearson correlation for this clock was 0.98 in the learning set and 0.96 in the test set while the median absolute error was 1.84 years in the learning set and 2.44 years in the test set. Using this clock, we demonstrate that aerobic-exercised trained individuals have a younger predicted age than physically sedentary subjects. By testing clocks associated with 1565 different Reactome pathways, we also show that proteins associated with signal transduction or the immune system are especially capable of predicting human age. We additionally generate a multitude of age predictors that reflect different aspects of aging. For example, a clock comprised of proteins that regulate life span in animal models accurately predicts age.


Big Pharma Senolytics Programs are Getting Underway

Biotech startups working in a new and credible field of clinical development only have a few years before large pharmaceutical companies take notice and begin to enter the arena. This shift in the competitive landscape is a good thing for patients, as a great deal more funding will be deployed to expand the space of possible therapies. Further, small companies with viable approaches are more likely to be acquired, increasing the odds that specific programs will continue through to clinical trials. It doesn't solve the problem of the burdensome regulatory system that slows all progress, but it does improve the odds of pushing something through the present roadblocks in the path of progress.

As today's news from Insilico Medicine indicates, this second phase of development, the interest of large pharmaceutical developers, is now underway for the field of senolytic therapies. These are treatments capable of producing rejuvenation via selective destruction of senescent cells in old tissues. Senescent cells secrete signals that disrupt tissue maintenance, structure, and function, generating chronic inflammation that accelerates the progression of aging. They are strongly implicated in the pathology of numerous age-related conditions. In mice, senolytic therapies have produced noteworthy examples of reversal of age-related disease. Biotech startups are presently working on approaches to senescent cell destruction: small molecules; immunotherapies; gene therapies; and so forth.

A few small human clinical trials of first generation senolytic drugs and supplements have taken place or are underway, awaiting publication of results. The results have been mixed. The dasatinib and quercetin combination looks promising for inflammatory lung disease and kidney disease, and has been confirmed to destroy senescent cells in humans in much the same way as it does in mice. A localized injection approach for osteoarthritis did not work, for reasons that are much discussed by the community - a poor choice of strategy, in that senescent cells throughout the body affect the inflammatory environment of joints, or a drug that doesn't do as well in humans as in mice, perhaps.

Looking at the past five years of work on senolytics, one may guess that the amount of effort needed to get Big Pharma interested enough to participate in a new line of work amounts to a few hundred million dollars in venture investment, half a dozen phase I and phase II clinical trials, ten to twenty biotech startups, and a few IPOs either taken place or on the horizon. At that point executives and boards in the pharmaceutical giants start to ask whether there might be something worthy of attention in this new part of the biotech industry.

Insilico partners with Taisho on end-to-end AI-powered senolytic drug discovery

Insilico Medicine announced today that Taisho Pharmaceutical Co., Ltd. and Insilico have entered into a research collaboration to identify novel therapeutics against aging. Insilico Medicine will utilize both the target discovery and generative chemistry parts of its Pharma.AI platform in this collaboration. It will use its proprietary Pandomics Discovery Platform to identify novel targets for senolytic drugs and Chemistry42 platform for a molecular generation. This collaboration brings together Insilico's state-of-art artificial intelligence (AI) technologies in drug discovery with Taisho's expertise in drug development, aimed to extend the human healthspan.

"We're delighted to collaborate with Taisho pharmaceutical, a well-recognized leader in the pharmaceutical industry and healthcare sector. It is believed that aging is a universal phenomenon that we cannot stop. However, emerging scientific evidence has shown that one may be able to reverse some of the age-associated processes. Through this collaboration, we will adopt our AI-powered drug discovery suites together with Taisho's validation platform to explore the new space of anti-aging solutions."

Under the terms of the agreement, Insilico Medicine will receive an upfront payment and milestone payments upon achievement of specified goals. Insilico Medicine will be responsible for early research phase target identification and molecular generation and Taisho will work collaboratively with Insilico in validating the results in various in vitro and in vivo assays. Taisho has the exclusive option to acquire Insilico's co-ownership of the successfully developed programs under agreed payment.

COVID-19 as a Disease of Aging

Researchers are writing a great many papers these days to point out the obvious regarding COVID-19, that the vast majority of SARS-CoV-2 coronavirus mortality occurs in older individuals, particularly those who already suffer age-related disease and thus a high burden of tissue and immune system dysfunction. This process of repeating the obvious seems necessary, given that the public discourse on the topic of the present pandemic presents it as a condition that affects all members of society more or less equally. In fact it is a condition that does little more than inconvenience near all younger people who are infected, while being quite dangerous for the old - along the same lines as influenza and many other common infectious diseases. This is entirely due to the fact that old people have damaged, dysfunctional immune systems. A range of research programs aim at rejuvenation of the immune system, and in a better world they would be receiving a great deal more attention than is presently the case.

Older subjects, men, and those with pre-existing conditions such as hypertension, diabetes, cancer, heart failure, and chronic obstructive pulmonary disease are more prevalent among hospitalized COVID-19 patients. Clinical risk factors for COVID-19-related deaths have been identified using a very large cohort. The most common comorbidities have age as a risk factor and have been described in recent years as age-related diseases. The COVID-19 case fatality rate (CFR), that is, the quotient of deaths to confirmed infections, was shown to be lower in patients below 60 years old (1.4%) compared to those who were 60 years or older (4.5%). The severity of the respiratory illness might be related to age-associated changes in the physical properties of the lung and the decline of the immune function, known as immunosenescence.

In general, the idea that older people are more susceptible to infections is not new. In fact, it has been reported that up to one third of deaths in the elderly is a result of infectious diseases. Persistent viral infections may also trigger monoclonal expansion of T cells, which over the lifetime results in poor variability of memory T cells. In turn, this eventually drives immune exhaustion due to the decline in T-cell diversity, a critical problem when facing novel threats such as SARS-CoV-2.

An additional feature that characterizes the severe cases of COVID-19 is the elevated levels of inflammation that can compromise lung tissue integrity and function, leading to pneumonia. Remarkably, accumulated and exhausted T cells secrete preferentially pro-inflammatory cytokines such as IFN and TNF. These cytokines can contribute, along with the innate immune system, to the low-grade pro-inflammatory background observed in elderly individuals, which may worsen COVID-19 outcomes and explain the elevated levels of inflammation. It is also possible that age-associated clonal hematopoiesis may contribute to the increased inflammation due to hematopoietic stem cell myeloid generation bias of pro-inflammatory macrophages and mast cells, and reduction of lymphoid differentiation.

Moreover, decreased T-cell capacity to properly activate antibody-secreting cells to further elicit effective immune responses may be compromised. Yet, another possible explanation is thymus involution. During aging, the thymus becomes atrophic and is gradually replaced by fibrotic tissue. This results in a reduced number, or even complete abrogation, of exiting naive T cells. Together, all these features may result in the decreased ability of older people to fight viral infections, leading to age-related inflammation and higher susceptibility of the lung, and eventually other organs, to the COVID-19-inflicted damage.

In this work, we revealed a strong link between COVID-19 fatality rate and aging. Based on our analysis, we propose that COVID-19, and more generally deadly respiratory diseases, should be considered as novel and emergent diseases of aging. Understanding that age is a major factor for fatality of COVID-19 may help to design approaches against this disease that target the aging process, along with specific antiviral approaches and those that boost more efficiently the human immune system of the elderly.


Evidence for High Intensity Interval Training to be More Beneficial than Moderate Exercise in the Elderly

Researchers here report on the results five years in to a study comparing the effects of different exercise programs on mortality in older people. While the high intensity interval training group are clearly doing well in comparison to their peers, there is a cautionary tale in study design for the other two groups, in that the control individuals appear to have been inspired by their inclusion in the study to exercise more than the study participants who were assigned to the moderate intensity training group. Taken as a whole, the results nonetheless provide yet more corroborating evidence for exercise to reduce mortality in later life.

Can exercise really give older people a longer and healthier life? Generation 100 is the first major study that can tell us that, and researchers have encouraging news. Among most 70-77-year-olds in Norway, 90% will survive the next five years. In the Generation 100 study, more than 95% of the 1500 participants survived. The Generation 100 study is a cause-and-effect study. This means that all participants were divided completely randomly into three different training groups when the study started in 2012.

One group was assigned to do high-intensity training intervals according to the 4×4 method twice a week, while group two was instructed to train at a steady, moderate intensity for 50 minutes two days a week. The participants could choose whether they wanted to train on their own or participate in group training with instructors. The third group - the control group - was advised to exercise according to the Norwegian health authorities' recommendations. This group was not offered organized training under the auspices of Generation 100, but was called in for regular health checks and fitness assessments.

Both physical and mental quality of life were better in the high-intensity group after five years than in the other two groups. High-intensity interval training also had the greatest positive effect on fitness. "In the interval training group, 3% of the participants had died after five years. The percentage was 6% in the moderate group. The difference is not statistically significant, but the trend is so clear that we believe the results give good reason to recommend high-intensity training for the elderly. Among the participants in the control group, 4.5% had died after five years. One challenge in interpreting our results has been that the participants in the control group trained more than we envisioned in advance. One in five people in this group trained regularly at high intensity and ended up, on average, doing more high-intensity training than the participants in the moderate group. You could say that this is a disadvantage, as far as the research goes. But it may tell us that an annual fitness and health check is all that's needed to motivate older people to become more physically active."


Lower Mitochondrial DNA Copy Number Produces Disease-Related Epigenetic Changes in the Nucleus

Epigenetic marks on nuclear DNA, such as DNA methylation, control the expression of specific genes, and thus the mix of proteins being manufactured by a cell, and thus the behavior of that cell. Epigenetic marks are added and removed constantly in response to changing circumstances inside and outside a cell, and differ between cell types, but some of these marks are quite characteristic of the altered environment of an aged tissue. So much so that epigenetic clocks have been established to produce quite accurate assessments of chronological age, and more importantly biological age, a representation of the burden of molecular damage and cellular dysfunction produced by aging.

A sizable minority of the research community sees epigenetic change as an evolved program, a fundamental cause of aging. A more mainstream view is that epigenetic change is a downstream consequence of deeper causes, various forms of molecular damage to cells and tissues that lead to an altered signaling environment. Some of these epigenetic changes are adaptive and helpful, some maladaptive and harmful. The question of how specific mechanisms and damage cause age-related epigenetic change remains largely open, however. Much of cellular biology remains a poorly explored maze of relationships and mechanisms; there are many, many epigenetic marks to investigate, and only so many researchers in the world.

Some progress has been made towards demonstrating that at least some age-related epigenetic alterations are an unfortunate side-effect of repeated cycles of repair of double strand breaks in DNA. Along the same lines, in today's open access paper, researchers provide evidence for some epigenetic alteration to be driven by loss of mitochondrial function in aging tissues. Mitochondria are the power plants of the cell, involved in many fundamental cellular processes, but their activity declines throughout the body with age. Research into this manifestation of aging, important in numerous age-related conditions, suggests that loss of mitochondrial function results from altered mitochondrial dynamics, an imbalance of fusion and fission of mitochondria that makes it harder for cells to remove and replace damaged mitochondria. That imbalance is in turn is caused by changes in protein levels related to fusion and fission - and those protein levels are controlled by epigenetic marks determining production from their DNA blueprints. Many of the relationships in the cellular biochemistry of aging are two-way streets at the very least, and possibly more complex than that in detail.

Mitochondrial DNA copy number can influence mortality and cardiovascular disease via methylation of nuclear DNA CpGs

Mitochondria are cytoplasmic organelles primarily responsible for cellular metabolism and have pivotal roles in many cellular processes, including aging, apoptosis, and oxidative phosphorylation. Dysfunction of the mitochondria has been associated with complex disease presentation including susceptibility to disease and severity of disease. Mitochondrial DNA copy number (mtDNA-CN), a measure of mitochondrial DNA (mtDNA) levels per cell, while not a direct measure of mitochondrial function, is associated with mitochondrial enzyme activity and adenosine triphosphate production. mtDNA-CN is regulated in a tissue-specific manner and in contrast to the nuclear genome, is present in multiple copies per cell, with the number being highly dependent on cell type. mtDNA-CN estimates can be derived from DNA isolated from blood and is therefore a relatively easily attainable biomarker of mitochondrial function. Cells with reduced mtDNA-CN show reduced expression of vital complex proteins, altered cellular morphology, and lower respiratory enzyme activity. Variation in mtDNA-CN has been associated with numerous diseases and traits, including cardiovascular disease, chronic kidney disease, diabetes, and liver disease. Lower mtDNA-CN has also been found to be associated with frailty and all-cause mortality.

Communication between the mitochondria and the nucleus is bi-directional and it has long been known that crosstalk between nuclear DNA (nDNA) and mtDNA is required for proper cellular functioning and homeostasis. However, the precise relationship between mtDNA and the nuclear epigenome has not been well defined despite a number of reports which have identified a relationship between mitochondria and the nuclear epigenome. For example, mtDNA polymorphisms have been previously demonstrated to be associated with nDNA methylation patterns. Further, mtDNA-CN has been previously associated with changes in nuclear gene expression.

Thus, gene expression changes identified as a result of mitochondrial variation may be mediated, at least in part, by nDNA methylation. Further, given that it has been well-established that mtDNA-CN influences a number of human diseases, we propose that one mechanism by which mtDNA-CN influences disease may be through regulation of nuclear gene expression via the modification of nDNA methylation. To this end, we report the results of cross-sectional analysis of this association between mtDNA-CN and nDNA methylation in 5035 individuals from the Atherosclerosis Risk in Communities (ARIC), Cardiovascular Health Study (CHS), and Framingham Heart Study (FHS) cohorts.

Thirty-four independent CpGs were associated with mtDNA-CN at genome-wide significance. Meta-analysis across all cohorts identified six mtDNA-CN-associated CpGs at genome-wide significance. Additionally, over half of these CpGs were associated with phenotypes known to be associated with mtDNA-CN, including coronary heart disease, cardiovascular disease, and mortality. Experimental modification of mtDNA-CN demonstrated that modulation of mtDNA-CN results in changes in nDNA methylation and gene expression of specific CpGs and nearby transcripts. These results demonstrate that changes in mtDNA-CN influence nDNA methylation at specific loci and result in differential expression of specific genes that may impact human health and disease via altered cell signaling.

A Conservative View on Osteoarthritis, Failing to Mention Senescent Cells

This open access paper provides a conservative view on the state of research and development of osteoarthritis treatments. Some time is spent on the puzzling nature of inflammation in osteoarthritis, and the failure of immunosuppressive therapies used for other conditions to produce meaningful benefits in this case. Yet senescent cells - and their inflammatory signaling, shown in a number of animal studies to contribute to and even directly cause osteoarthritis - are not mentioned at all. This gives some idea of the mindset in evidence here: lines of research arising in the past five to ten years, and that have not yet progressed to later stage clinical trials, are not worthy of note. The clinical community progresses slowly indeed.

Despite an increasing burden of osteoarthritis in developed societies, target discovery has been slow and there are currently no approved disease-modifying osteoarthritis drugs. This lack of progress is due in part to a series of misconceptions over the years: that osteoarthritis is an inevitable consequence of ageing, that damaged articular cartilage cannot heal itself, and that osteoarthritis is driven by synovial inflammation similar to that seen in rheumatoid arthritis. Recent randomised controlled trials, using treatments repurposed from rheumatoid arthritis, have largely been unsuccessful. Genome-wide studies point to defects in repair pathways, which accords well with recent promise using growth factor therapies or Wnt pathway antagonism.

There are many reasons to be optimistic about new therapeutic developments in osteoarthritis. Although it is true that much of what has been learned in the past few years from clinical studies is what not to use in disease, these negative studies have been highly informative in reminding the medical community that osteoarthritis is distinct from inflammatory arthritidies, such as rheumatoid arthritis. Research has shown that inflammation in osteoarthritis is nuanced and that classical immunomodulatory pathways are not good targets, but that there are several other inflammatory pathways awaiting clinical exploration, including those driven by direct mechanical injury of the cartilage (so-called mechanoflammation), complement, and mast cells.

The nature and role of inflammation in osteoarthritis pathogenesis thus remains unclear. Clarification is crucially important, not only so that we can develop appropriate targeted therapies for patients, but also to decide whether patients require stratification before treatment. There has been a popular move to try to phenotype patients, with a view to personalising their treatment to improve the efficacy of a given drug. However, these phenotypes currently lack cohesion, and here is little or no evidence that stratification by any of these features changes the response to treatment.

Clinical successes point towards a focus on regenerative or anabolic pathways rather than inflammatory ones. This suggestion fits well with preclinical studies, although the reciprocal relationship between repair and inflammation in the chondrocyte suggests that targeting one will probably affect the other. Recent large genome-wide association studies in osteoarthritis also support the concept that osteoarthritis is a failure of repair. Several at-risk loci have been attributed to genes in the TGFβ and FGF pathways, and there is a notable absence of loci that predict the regulation of classical inflammatory genes. Newer targets identified by genome studies, including the retinoic acid pathway, also look promising.


A Hydrogel Scaffold to Encourage Peripheral Nerve Regeneration

The nervous system of mammals is poorly regenerative at best. The use of implantable scaffold materials is one of the strategies under development in the tissue engineering community to encourage greater degrees of regrowth following nerve damage. Such materials can be infused with chemical cues to guide cell activity, or provided with other useful properties such as conductivity. The work noted here is an example of this field of research and development, quite similar to many other studies conducted over the past decade or more. As for all medical research in this heavily regulated environment, it is slow to make it to the clinic in any meaningful way.

Injuries in which a peripheral nerve has been completely severed, such as a deep cut from an accident, are difficult to treat. A common strategy, called autologous nerve transplantation, involves removing a section of peripheral nerve from elsewhere in the body and sewing it onto the ends of the severed one. However, the surgery does not always restore function, and multiple follow-up surgeries are sometimes needed. Artificial nerve grafts, in combination with supporting cells, have also been used, but it often takes a long time for nerves to fully recover. Researchers wanted to develop an effective, fast-acting treatment that could replace autologous nerve transplantation. For this purpose, they decided to explore conducting hydrogels - water-swollen, biocompatible polymers that can transmit bioelectrical signals.

The researchers prepared a tough but stretchable conductive hydrogel containing polyaniline and polyacrylamide. The crosslinked polymer had a 3D microporous network that, once implanted, allowed nerve cells to enter and adhere, helping restore lost tissue. The team showed that the material could conduct bioelectrical signals through a damaged sciatic nerve removed from a toad. Then, they implanted the hydrogel into rats with sciatic nerve injuries. Two weeks later, the rats' nerves recovered their bioelectrical properties, and their walking improved compared with untreated rats. Because the electricity-conducting properties of the material improve with irradiation by near-infrared light, which can penetrate tissues, it could be possible to further enhance nerve conduction and recovery in this way.


G3BP1 is Required for the Senescence-Associated Secretory Phenotype

The senescence-associated secretory phenotype (SASP) is how senescent cells cause long-term harm. It is also how senescent cells produce short-term benefits. SASP is the name given to the mix of inflammatory signals, growth factors, and other molecules and vesicles secreted by senescent cells. This is helpful during embryonic development, as well as in wound healing and suppression of cancer. In these cases, a small number of cells become senescent in order to beneficially alter the local signaling environment to provoke immune activity, restructuring, and growth. These helpful senescent cells are soon destroyed by immune cells or via programmed cell death. We age, however, more cells become senescent in response to damage and dysfunction, and the processes of clearance become slower and less effective. Senescent cells accumulate in tissues, and a constant SASP disrupts tissue maintenance, tissue structure, and immune function, giving rise to a state of chronic inflammation.

A number of research groups are working towards ways to modulate or shut down the SASP as an alternative to periodic selective destruction of senescent cells via senolytic therapies. Today's open access paper is a promising step towards turning off the SASP entirely. The challenge inherent in this goal is similar to that in achieving immunosuppression - the SASP is both beneficial and harmful, depending on location, timing, and circumstance. Shutting it down entirely for the long term will have unfortunate side-effects. It isn't just that the SASP is involved in regeneration, but also that it enables the prompt destruction of potentially cancerous cells. Still, in cases where the SASP is raging due to the presence of significant numbers of senescent cells, and the resulting chronic inflammation and pro-growth signaling is accelerating the progression of an established cancer, then shutting down the SASP may well be a useful strategy in combination with other cancer therapies.

G3BP1 controls the senescence-associated secretome and its impact on cancer progression

One of the main promoters of age-related disease, such as cancer, is cellular senescence, a process by which cells enter an irreversible cell cycle arrest in response to various stresses. Generally, these cells undergo profound molecular and biological changes, namely decreased genomic stability, increased markers of DNA damage, and induction of the senescent-associated secretory phenotype (SASP). The SASP is a large group of secreted factors that include cytokines, chemokines, angiogenic factors, extracellular matrix-remodeling proteases, and growth factors (e.g. IL-6, IL-8, and TNFα). Despite the protective role that senescence plays in an organism, the accumulation of senescent cells during aging has been associated with many cancers by enhancing neoplastic cell proliferation and metastasis. The most striking evidence supporting a link between senescence and cancer is the fact that removing senescent cells from mice decreases cancer occurrence throughout their lifespan.

The Ras GTPase-activating protein-binding protein 1 (G3BP1), a key factor in the stress response and stress granule (SG) assembly, is associated with several processes including pro-survival response and cell fate. G3bp1-/- mice exhibit a premature aging phenotype as well as symptoms of pathologies related to aging such as ataxia. Since the loss of G3BP1 is associated with age-related phenotypes, it is possible that G3BP1 modulates these effects by controlling cellular senescence and cancer growth.

In this study, we assessed the role of G3BP1 as a regulator of the deleterious effects of senescent cells. We show that G3BP1 is required for the activation of the senescent-associated secretory phenotype (SASP). During senescence, G3BP1 achieves this effect by promoting the association of the cyclic GMP-AMP synthase (cGAS) with cytosolic chromatin fragments. In turn, G3BP1, through cGAS, activates the NF-κB and STAT3 pathways, promoting SASP expression and secretion. G3BP1 depletion or pharmacological inhibition impairs the cGAS-pathway preventing the expression of SASP factors without affecting cell commitment to senescence. These SASPless senescent cells impair senescence-mediated growth of cancer cells in vitro and tumor growth in vivo. Our data reveal that G3BP1 is required for SASP expression and that SASP secretion is a primary mediator of senescence-associated tumor growth.

A Healthy Lifestyle Correlates with Increased Life Span Even in People with Multiple Age-Related Conditions

This assessment of epidemiological data shows that the gain in life expectancy that accompanies a healthy lifestyle is much the same whether or not an individual suffers from multiple age-related conditions. As always in this sort of study, the question is the degree to which this reflects the point that the onset of more serious conditions renders people less able to be active, versus a matter of good lifestyle choices producing corresponding benefits over time. Animal studies make it quite clear that efforts to maintain good health do in fact make a real difference over the long term, but that sort of certainty is hard to extract from human epidemiological data. That said, the most relevant factors, such as smoking and diet, are much less impacted by disease status than is the case for physical activity.

Whether a healthy lifestyle impacts longevity in the presence of multimorbidity is unclear. We investigated the associations between healthy lifestyle and life expectancy in people with and without multimorbidity. A total of 480,940 middle-aged adults (median age of 58 years, 46% male, 95% white) were analysed in the UK Biobank; this longitudinal study collected data between 2006 and 2010, and participants were followed up until 2016. We extracted 36 chronic conditions and defined multimorbidity as 2 or more conditions. Four lifestyle factors, based on national guidelines, were used: leisure-time physical activity, smoking, diet, and alcohol consumption. A combined weighted score was developed and grouped participants into 4 categories: very unhealthy, unhealthy, healthy, and very healthy. Survival models were applied to predict life expectancy, adjusting for ethnicity, working status, deprivation, body mass index, and sedentary time.

A total of 93,746 (19.5%) participants had multimorbidity. During a mean follow-up of 7 (range 2-9) years, 11,006 deaths occurred. At 45 years, in men with multimorbidity an unhealthy score was associated with a gain of 1.5 additional life years compared to very unhealthy score, though the association was not significant, whilst a healthy score was significantly associated with a gain of 4.5 life years and a very healthy score with 6.3 years. Corresponding estimates in women were 3.5, 6.4, and 7.6 years. Results were consistent in those without multimorbidity and in several sensitivity analyses. For individual lifestyle factors, no current smoking was associated with the largest survival benefit.

In conclusion, we found that regardless of the presence of multimorbidity, engaging in a healthier lifestyle was associated with up to 6.3 years longer life for men and 7.6 years for women; however, not all lifestyle risk factors equally correlated with life expectancy, with smoking being significantly worse than others.


Loss of Sense of Smell as an Early Biomarker for Brain Aging

Alzheimer's disease begins in the olfactory bulb, with evidence suggesting that this is related to failing drainage of cerebrospinal fluid from that part of the brain. It has been noted that a faltering of the sense of smell takes place with aging. This may be a useful way to assess the overall state of the brain on the path towards neurodegenerative conditions, but, considered as a whole, comparatively little work has taken place on this aspect of sensory decline with age.

Olfaction, from an evolutionary aspect, is the oldest of our senses. Across different species, it modulates the interactions between an organism and the surrounding environment even before birth. Nevertheless, the majority of the studies on chemo-sensation have been developed in rodents, with a less rich literature in humans. The incomplete understanding of human olfaction may relate to the complexity of studying the multiple olfactory centers distributed in several brain regions comprising the cortical and the subcortical pathways, e.g., olfactory bulb, piriform and entorhinal cortex, amygdala, orbitofrontal cortex, and hypothalamus. This anatomical heterogeneity implies an extensive connection among the olfactory sensory areas which constitute a complex network essential to associate the olfactory stimulus with other cerebral regions, such as those involved in the processing of memories and emotions and multisensory integration with other senses.

Another challenge facing smell research in humans relates to its minor clinical implication as compared to impairment of vision and hearing: the occurrence of blindness or deafness produces a massive personal and social deficit which severely disrupts someone's life. In line with these observations, the different attention paid to these three senses has been also described, in that older adults in the US received assistance for vision and hearing deficits, whereas no testing for olfactory dysfunction was performed. While vision and hearing have been treated as primary senses for general health, olfaction is gaining increasing importance in clinical settings since its impairment represents an overarching non-invasive biomarker in predicting dementia during aging. With the frequent decline in smell acuity, mostly attributed to the reduced turnover of the olfactory neuroepithelium with aging, the early and pronounced olfactory deficit described in different neurodegenerative diseases, ranging from Alzheimer's to Parkinson's and Huntington's diseases remains yet poorly understood.

In an attempt to put olfaction forward as an early biomarker for pathological brain aging, we draw a comparison with vision and hearing, regarded as more relevant for general health. This perspective article wants to encourage further studies aimed at understanding the mechanisms responsible for the early smell dysfunction in individuals a decade or more before the onset of cognitive symptoms.


Towards Harnessing Growth to Create Rejuvenation

A recent pair of open access papers offer an interesting viewpoint on embryonic development, aging, cancer, and possible approaches to rejuvenation in this era of biotechnology. I'm not sure that I agree with more than half of it, but it does make for a good read, even given that the language is somewhat obtuse in places. Tissue growth is the unifying process, wherein: (a) embryonic development is the epitome of regulated, successful, beneficial growth; (b) aging suppresses and damages the shackled processes of growth that are turned to tissue maintenance; (c) cancer is unfettered and uncontrolled growth; and (d) the research community might achieve rejuvenation by finding a way to harness the vigor of cancer and embryonic development in a controlled way. This is of course an ambitious goal, we most likely stand a long way from it, and there are forms of molecular damage, such as accumulation of metabolic waste in long-lived cells of the central nervous system, that can't be addressed by growth.

Nonetheless, it seems a valid topic for discussion given the present interest in applying reprogramming technologies to living animals (and perhaps people not too many years from now). Reprogramming in this context is the process of turning normal cells into induced pluripotent stem cells, essentially mimicking embryonic stem cells in their behavior. This reverses epigenetic marks of aging and other changes, such as loss of mitochondrial function. Unexpectedly, delivering the Yamanaka factors into mice produces benefits to health, not disruption of tissue function as cells are converted into inappropriate types and behaviors, and not a comprehensive unleashing of cancer, as one might expect to happen. A number of groups are now working on ways to reprogram or partially and temporarily reprogram cells in order to produce rejuvenation in animal models.

From cancer to rejuvenation: incomplete regeneration as the missing link (Part I: the same origin, different outcomes)

There are two major problems: the eradication of cancer and aging. For radical rejuvenation, gerontologists attempt to activate signaling pathways for rejuvenation/pluripotency. Quite often, such attempts result in the formation of tumors. This happens because the only way is to radically rejuvenate and this normally, without special intervention, leads to cancer. At the same time, oncologists are trying to suppress all these signaling pathways of rejuvenation, based on the idea that tumor cells are the enemies and that they should be eliminated by all available means. In short, this strategy can be called a killing strategy (both through direct action and creating conditions unfavorable for cell growth and proliferation). This currently applied killing strategy does not restore tissue and function deficiency but rather exacerbates it. That is why, after some clinical success, this strategy leads to a recurrence of cancer and the formation of cell clones that are resistant to therapy.

In pregnancy, it is the immune privilege of the fetus that ensures the unidirectionality of the vector totipotency to differentiation, or integrating growth (IG). IG is defined here as the submission of potency of single cells composing an organism to the development program and functions of the whole organism. However, in the adult organism, in the absence of immune privilege, this recapitulation is transformed into cancer, or disintegrating growth (DG).

Cancer cells are normal cells with a blocked entry to the normal growth path and redifferentiation, and the last feature is the only marker of malignant growth. It is this blocking and nonlimited execution of a developmental program in reverse order that is the cause of the disintegrative character of its growth or, in other words, the cause that transforms rejuvenation into DG - not the expression of the so-called oncogenes. Oncogene expression does not affect the normal morphogenetic potential of cells. Oncogenes, as genes that cause cancer, do not exist at all. They are normal genes, due to which organisms are developed and due to which they can potentially reach immortality. All properties that are associated with cancer, except blocked redifferentiation, are features of the embryonic pathway recapitulation and self-renewal, and they are inherent for cells at different stages of ontogenesis.

The transformation of normal cells into tumor cells is an adaptive response to a failure in self-restoration and repair capabilities. Due to the rebirth process, complete tissue renewal leading to the elimination of senescence occurs similarly to embryonic tissue development. We propose to use this potential of transformed cells to eliminate senescence. This will make it possible to direct the process of transformation toward an integrated growth path, to prevent the clinical phenomenon of malignancy and to use the potential of transformed cells to initialize the self-renewal program and program of unlimited life for the whole organism.

From cancer to rejuvenation: incomplete regeneration as the missing link (part II: rejuvenation circle)

Aging is a process and a consequence of processes brought about by steadily increasing restriction of the self-renewal ability, limiting life expectancy, and leading to an increase in the probability of death and, inevitable death resulting from the fading of functions, failure of the regulatory mechanisms, occurrence of endogenous disorders and increased susceptibility to exogenous factors. In our opinion, one of the fundamental (systemic) flaws of gerontology is the idea of the existence of a special aging program and the search for the cause of aging, which states that if removed, aging can be eliminated. However, there is only one general program, a program of growth and development (ontogenesis), of which aging is an integral part. The essence of this program is the stabilization of multicellular integrity by submitting the purposes of the constituent parts (cells) to the purposes of the whole (tissues, organs and the body in entirety), through the epigenetic restriction of cell potencies in favor of perfecting (complicating) tissue specialization, for what we pay for with aging, all types of endogenous pathology and, as a result, mortality.

From this, it follows that the 'cause' of aging is not some special mechanism but a program/order, which can be overridden only by implementing another program, a program, of permanent, unlimited, quantitative and qualitative full restoration of structures, functions and functional interconnections. In other words, the linear unidirectionality of ontogenesis, fatally leading to aging and death, can only be overcome with permanent reontogenesis, through the looping of this linearity. This does not require an application of any force against nature, because similar processes were invented by nature itself and because they work in practically immortal multicellular organisms, such as Hydra vulgaris. It is important to note that Hydra does not have cancer as a pathological process. In other words, a periodic return or 'rollback' to the blast state does not cause cancer (disintegrating growth, DG) in those types of immortal organisms.

During ontogenesis, cells such as neurons or myocardiocytes become postmitotic, thus playing an integrative role in the functioning of an organism. The beginning of the ontogenetic program of development includes its own control of division in relation to cells until its complete stop in postmitotic cells, making them one of the main targets for aging processes. To increase the regenerative possibilities of an organism, it is necessary to make postmitotic cells 'build themselves anew'. The main biological ways to accomplish this is full-scale reprogramming that brings cells back to the early stages of pluripotency. It must be emphasized that what later becomes cancer is initially started as spontaneous reprogramming and the goal is to prevent the transformation of this process into carcinogenesis and direct it as rejuvenation. By creating similar conditions in the body, we can apply safe systemic-induced reprogramming in vivo, without fear of resulting in cancer.

To What Degree do Bodily Microbiomes Beyond the Gut Contribute to the Chronic Inflammation of Aging?

Most research on the microbial life of the body in the context of aging is focused on the gut microbiome, though a fair amount of investigation of oral microbial populations also takes place. In both cases, changes occur with age that allow harmful species of microbe to prosper, contributing to the chronic inflammation of aging. In the case of the gut microbiome, fecal microbiota transplantation from young individuals to old individuals has been shown in animal studies to reverse detrimental changes and improve health and life span. This has yet to be earnestly attempted for other microbial populations of the body that plausible contribute meaningfully to health, but the attempt should be made.

The human body and its microbiome represent an integrated meta-organism, which results from million years of reciprocal adaptation and functional integration conferring significant advantages for both parties. All the members of this human microbiota participate in host physiology and change according to development and late in the life contributing to health and fitness. The human immune system is influenced by the microbiota assembly, composition, diversity, and dynamics, and the interaction of all these features plausibly contributes to the process of inflammaging. In the last decades, we experienced an explosion of studies on the role of the gut microbiome in health and disease and the relationship between the gut microbiome and the other organs and tissues also due to an improvement of the sequencing methods that can be applied to the study of microbiota.

The complex relationship between humans and the trillions of bacterial cells that form our microbiome remains largely unexplored. The consequences for medicine are challenging, since it is likely that our multifaceted symbiosis affects each aspect of health. Manipulating the intestinal microbiota and microbiome may be helpful for preserving health and treating disease, particularly among older adults. On the contrary, the relationship between the microbiome of other human ecological niches (i.e., oral cavity, lung, skin, vagina, and genito-urinary tract) and the progress of other clinical diseases that are common among older adults remains an important area of future studies. It is also necessary to consider how biological age (assessed by health status and life expectancy) shapes the microbiota and immune system and vice versa. Moreover, the complexity of the interactions within the microbiome of the different body sites and between microbes and hosts presents a major challenge; a more concerted and predictive theoretical framework is imperative to progress.

Efforts to standardize specimen preparation and analytical protocols and to increase the availability of the growing body of data should be increased. These technical efforts as well as robust clinical research will improve characterization of the variation in the global human microbiomes, functions of redundancy, disease biomarkers, immigration, effect of lifestyles, and trajectories of development, all of which will establish the basis to understand the progression from health to disease and to efficiently discover new preventive strategies and therapies.


Attempting to Make Periodontal Stem Cells More Active in the Inflammatory Conditions of Periodontitis

The state of chronic, unresolved inflammation in the diseased gums of periodontitis drives loss of bone and tissue. This occurs in part due to suppression of the activity of stem cells and other necessary participants in tissue maintenance processes. Researchers here evaluate an approach to forcing stem cells into greater activity under inflammatory conditions, by introducing naturally occurring lipids that are known to act in the mechanisms responsible for resolving inflammation. The work is carried out in cell cultures only, but is nonetheless interesting.

Periodontitis is a chronic inflammatory disease that affects supporting periodontal tissues surrounding the teeth, i.e., cementum, alveolar bone, and periodontal ligament, leading to extensive tooth loss in severe cases and impacting the systemic well-being of the patient. The understanding of chronic inflammatory disorders, including periodontitis, has been limited to the activation of pro-inflammatory mediators through a canonical pathway that is responsible for the exaggerated synthesis of cytokines such as IL-1β and TNF-α. However, it is now appreciated that the physiology of the inflammatory processes also involves a cascade of programmed and receptor-mediated events that determine the synthesis of endogenous specialized pro-resolving lipid mediators (SPMs), and the resolution of inflammation.

Specialized pro-resolving lipid mediators derived from ω-3 polyunsaturated fatty acids, including resolvins and maresins, have a wide array of functions, induce changes in local biofilm composition, reorganize host response, and enhance bacterial phagocytosis and efferocytosis of inflammatory cells during the immunological responses to microbial and inflammatory stimuli. Resolvin E1 (RvE1), which is derived from eicosapentaenoic acid, has been shown to promote periodontal regeneration inducing the formation of new alveolar bone, cementum, and improved fibrogenesis in an experimental model of periodontitis. Maresin MaR1, which is derived from docosahexaenoic acid, has been shown to have potent activity accelerating surgical wound healing in planaria, providing evidence for organ regeneration and tissue healing. Both RvE1 and MaR1 have the potential to stimulate pro-regenerative activities, regulate wound healing, and reverse tissue destruction.

Thus, we measured the impact of MaR1 and RvE1 in an in vitro model of human periodontal ligament stem cells (hPDLSCs) under stimulation with IL-1β and TNF-α. The data showed that the pro-inflammatory milieu suppresses pluripotency, viability, and migration of hPDLSCs; MaR1 and RvE1 both restored regenerative capacity by increasing hPDLSC viability, accelerating wound healing/migration, and up-regulating periodontal ligament markers and cementogenic-osteogenic differentiation. Together, these results demonstrate that MaR1 and RvE1 restore or improve the regenerative properties of highly specialized stem cells when inflammation is present and offer opportunities for direct pharmacologic treatment of lost tissue integrity.


Fecal Microbiota Transplantation from Old Mice to Young Mice Impairs Cognitive Function

The microbiome of the gut changes with age, and this is presently thought to have a meaningful influence over the course of aging. It is perhaps in the same ballpark as the effects of exercise on the pace of aging and risk of age-related disease, and certainly overlaps with the effects of diet, particularly that of calorie restriction. In general, aging is accompanied by a reduction in beneficial microbial species that produce metabolites known to improve cell and tissue function, such as butyrate, propionate, and indoles. Equally, harmful inflammatory microbial species grow in numbers, and contribute to the chronic inflammation that characterizes aging, disrupting tissue maintenance and accelerating the progression towards age-related disease.

Today's open access paper is a representative example of a broad range of present work that attempts to quantify the degree to which age-related changes in the gut microbiome are harmful. There are two ways to go about this, involving fecal microbiota transplantation from either (a) old to young animals and looking for harms, or (b) from young to old animals and looking for benefits. The former is the case here, and researchers quite credibly show that an old microbiome impairs cognitive function in young mice.

What is to be done about the aging of the gut microbiome? The most plausible path forward is to adapt the existing use of fecal microbiota transplantation in human medicine in order to transplant material from young donors into older individuals. In medical conditions in which the intestine is overtaken by harmful pathogens, this treatment can be a lasting cure: the balance of species in the gut is permanently changed in these cases. Lasting reversal of the impaired state of an old microbiome also appears possible via transplantation from a young individual, based on work conducted in short-lived species such as killifish. It is a promising approach, but is not at present receiving the level of interest required for clinical development to move ahead.

Faecal microbiota transplant from aged donor mice affects spatial learning and memory via modulating hippocampal synaptic plasticity- and neurotransmission-related proteins in young recipients

The gut-brain axis and the intestinal microbiota are emerging as key players in health and disease. Shifts in intestinal microbiota composition affect a variety of systems; however, evidence of their direct impact on cognitive functions is still lacking. We tested whether faecal microbiota transplant (FMT) from aged donor mice into young adult recipients altered the hippocampus, an area of the central nervous system (CNS) known to be affected by the ageing process and related functions.

Young adult mice were transplanted with the microbiota from either aged or age-matched donor mice. Following transplantation, characterization of the microbiotas and metabolomics profiles along with a battery of cognitive and behavioural tests were performed. Label-free quantitative proteomics was employed to monitor protein expression in the hippocampus of the recipients. We report that FMT from aged donors led to impaired spatial learning and memory in young adult recipients, whereas anxiety, explorative behaviour, and locomotor activity remained unaffected.

This was paralleled by altered expression of proteins involved in synaptic plasticity and neurotransmission in the hippocampus. Also, a strong reduction of bacteria associated with short-chain fatty acids (SCFAs) production (Lachnospiraceae, Faecalibaculum, and Ruminococcaceae) and disorders of the CNS (Prevotellaceae and Ruminococcaceae) was observed. Finally, the detrimental effect of FMT from aged donors on the CNS was confirmed by the observation that microglia cells of the hippocampus fimbria, acquired an ageing-like phenotype; on the contrary, gut permeability and levels of systemic and local (hippocampus) cytokines were not affected.

These results demonstrate that age-associated shifts of the microbiota have an impact on protein expression and key functions of the CNS. Furthermore, these results highlight the paramount importance of the gut-brain axis in ageing and provide a strong rationale to devise therapies aiming to restore a young-like microbiota to improve cognitive functions and the declining quality of life in the elderly.

Incorporating Microelectronics into Bioartificial Blood Vessels

Researchers here report on an interesting proof of concept, incorporating electronic device capabilities into the flexible biomaterials used as scaffolding for blood vessel tissue engineering. As a next generation technology to potentially replace the use of stents in the treatment of cardiovascular disease, bioartificial blood vessel sections are already promising. Adding to this the programmable ability to alter nearby cell behavior, control delivery of gene-based therapeutics, or report sensory data on cells and blood flow opens up intriguing new vistas for the future.

A variety of tissue-engineered blood vessels (TEBVs) have been created to provide mechanical support for hard-to-treat blockages of tiny blood vessels, but these have limitations, and none "has met the demands of treating cardiovascular diseases. We take the natural blood vessel-mimicking structure and go beyond it by integrating more comprehensive electrical functions that are able to provide further treatments, such as gene therapy and electrical stimulation."

Researchers fabricated a new form of electronic blood vessels using a cylindrical rod to roll up a membrane made from poly(L-lactide-co-ε-caprolactone). In the lab, they showed that electrical stimulation from the blood vessels increased the proliferation and migration of endothelial cells in a wound-healing model, suggesting that electrical stimulation could facilitate the formation of new endothelial blood vessel tissue. They also integrated the flexible circuitry with an electroporation device, which applies an electrical field to make cell membranes more permeable, and observed that this successfully delivered green fluorescent protein DNA into three kinds of blood vessel cells.

A three-month trial in rabbits showed, they say, that the artificial arteries appeared to function just as well as natural ones, with no sign of narrowing, and with no inflammatory response in the host. Part of the next stage is to try to pair the electronic blood vessels with smaller electronics than the electroporation device used in this study.


In Search of Common Transcriptional Regulators of Aging

Are there common regulators of aging to be found among transcription factors? Sweeping, complex, tissue-specific and species-specific changes in gene expression take place over the course of aging. If these are reactions to comparatively straightforward processes of molecular damage at the root of aging, processes that are similar between species, then it is possible that there also exist at least a few regulators that are also comparatively straightforward and similar between species. Where is the leap from simplicity to complexity? Is it that the immediate reaction to damage is complicated, with a hundred different sensors and systems reacting in their own ways? Or is the reaction to damage marshaled by a few controlling systems at the top level, leading to a sea of complexity downstream of those controlling systems? Which of these is the case makes a big difference as to the type of potential rejuvenation therapies that might be useful to attempt - though in either case repairing the damage sounds like a better idea to me.

Here, we measure changes in the transcriptome, histone modifications, and DNA methylome in three metabolic tissues of adult and aged mice. Our main question was whether common regulatory players underlie the seemingly tissue- and species-specific molecular footprint of aging. We show that although the molecular footprint of aging evolves differently across tissues, striking similarities emerge in terms of affected pathways and underlying regulators. For instance, the liver's aging footprint is dominated by changes in transcriptome and DNA methylome. In contrast, transcriptomes of heart and quadriceps are relatively stable but have marked changes in histone modification profiles around genes. Despite all these differences, similar pathways are affected in these distinct layers.

The striking similarity in transcription factor (TF) enrichment between different mouse and human tissues implies that there may be a common and perhaps restricted set of TFs underlying the aging footprint across tissues and species. The ZIC1 motif is highly enriched across multiple tissues and gene-regulatory layers. ZIC1 increases with age in many peripheral human tissues. Although its relationship or possible implication in aging has not been studied extensively, it has been shown that its brown adipose tissue (BAT) expression increases with age and body mass index, concurrently with a decrease in BAT activity. In addition, ZIC1 and ZIC2 transactivate apolipoprotein E (APOE) expression, one of the strongest human longevity determinants. The facts that APOE increases with age and that higher APOE levels correlate with negative outcomes in age-related diseases such as Alzheimer's disease render ZIC1 a prime candidate driver of gene regulatory changes associated with aging.

We also identify other TFs, such as HMGA1, TBP, and CXXC1, as candidate regulators of the aging process. HMGA1 has been linked to mitochondrial function, repair, and maintenance and is implicated in promoting senescence-associated heterochromatic foci, which are associated with transcriptional repression. In addition, it has recently been shown to promote the senescence-associated secretory phenotype (SASP) through its effect on NAD+ metabolism. The TATA box binding protein (TBP) motif is enriched in genes that decrease with age. Although this TF has not been directly linked to aging, it can harbor variations in polyglutamine repeats, which may be relevant in age-related processes such as neuro-muscular degenerative disease. CXXC1, or Cfp1, is a member of the Setd1 H3K4 methyltransferase complex and binds non-methylated DNA of transcriptionally permissive promoters. Given the trend for hypermethylation with age, CXXC1 binding to many promoters may be affected, which may lead to differences in H3K4 methylation. CXXC1 may therefore be an important link between the different molecular layers, which merits further mechanistic investigation, especially given that its motif's enrichment varies in direction in different tissues, suggesting a complex context-dependent relationship with aging.


Lamenting the Incomplete Understanding of Human Immunosenescence

The immune system is inconveniently complicated. Aging is also inconveniently complicated. The overlap between the two is a particularly dark forest for the research community, with few well-tracked paths. The fine details of how exactly the immune system becomes dysfunctional with age, and the sizable variation in those details between individuals, will keep research teams occupied for decades to come. It seems very plausible that here, as elsewhere in the study of aging, effective rejuvenation therapies that turn back immune aging will precede a strong understanding of how they produce benefits.

For example, it is fairly clear that here are harmful populations of immune cells, and that selectively destroying them produces benefits in old individuals. Age-associated B cells accumulate over time to cause numerous issues. When the B cell population is entirely destroyed it is rapidly replaced, even in late life, with new cells that lack the harmful behaviors of their predecessors. Similarly, it is fairly clear that having too few naive T cells capable of tackling new threats is damaging to health. The supply and reserve of such cells diminish with age due to atrophy of the thymus and incapacity of hematopoietic stem cell populations. Restoring the thymus or hematopoietic activity has been shown to improve immune function.

In both of those cases, there is a surrounding halo of unknowns regarding how and why problem cells arise, or the thymus atrophies, or hematopoietic stem cells become damaged and quiescent. The types of treatment proposed are very much engineering solutions: cut the Gordian knot of a lack of knowledge by enacting what appears to be the best solution and examining the consequences. When it works well in animal models, trial it in humans, is the philosophy. The scientific community is made somewhat uncomfortable by this sort of approach, however. The scientific impulse is, correctly, always in the direction of greater knowledge and greater understanding of exactly how a system works, fails, or is repaired. But we cannot let that impulse rule to the exclusion of building rejuvenation therapies that can work now, to the extent that we can do so, in advance of a full and complete understanding of immune aging.

The conundrum of human immune system "senescence"

Here, we consider what we believe to be the especially confused and confusing case of the ageing of the human immune system, commonly referred to as "immunosenescence". But what exactly is meant by this term? It has been used loosely in the literature, resulting in a certain degree of confusion as to its definition and implications. Here, we argue that only those differences in immune parameters between younger and older adults that are associated in some definitive manner with detrimental health outcomes and/or impaired survival prospects should be classed as indicators of immunosenescence in the strictest sense of the word, and that in humans we know remarkably little about their identity.

Demonstrating which changes of immune ageing are in fact associated with detrimental health outcomes and only then trying to restore them to an appropriate level may indeed be theoretically desirable. However, prior to establishing which are truly detrimental, rather than merely different in aged individuals, such intervention would be premature, and in some cases might be dangerous. One has to say that with this in mind most such efforts are indeed premature because we do not know which parameters to take as biomarkers reflecting these changes, and mistakenly attempting to "correct" adaptive changes would be undesirable. Hence, there is an argument in favour of attempts to classify such biomarkers of senescence in ageing in general, and even more challengingly in immunosenescence in particular, in order to generate actionable entities for treatment.

A consensus from published studies delineates one immune parameter consistently reported to be different between younger and older adults, namely the very low absolute and relative counts of naïve CD8+ T cells in the peripheral blood of older adults. This is not to say the older adults actually do possess fewer naïve T cells because data on the presence of immune cells in other organs are mostly lacking and most data pertain only to circulating cells. However, the expectation is that the whole-body number of CD8+ naïve T cells is indeed low, due to markedly reduced thymic output and cell mortality owing to a lifetime´s exposure to pathogens, agreeing with data from animal models. Reciprocally, it would be expected that because antigen-stimulated naïve cells differentiate into effector and memory cells, the latter would be increased in older adults, as also often reported. It is thus somewhat surprising that CD8+ memory cell accumulation in the blood of older adults is not universally reported. It has become apparent in the meantime that the accumulations of late-stage memory cells that are seen in older people are driven by persistent infection with cytomegalovirus (CMV), but apparently not by other herpesviruses or other pathogens. These sometimes disputed findings have been confirmed in systematic reviews.

Despite differences in many immune parameters between men and women, in the few studies examining this issue, the markedly lower levels of circulating CD8+ naïve T cells have been found in both sexes, further emphasising the universality of these findings. Intriguingly, although present, age-associated differences for CD4+ naïve T cells, B cells, and many aspects of innate immunity, especially dendritic cells (DCs) and neutrophils, are much less marked than for CD8+ T cells, one of the enduring mysteries in immunosenescence research. Again, it should be emphasized that the majority of immune cells resides in tissues and not in blood, and that the latter most likely does not reflect patterns of cell subset distribution elsewhere

Immune parameters assessed in cross-sectional studies clearly document multiple differences between younger and older populations. Animal studies as well as some more limited longitudinal studies in humans indicate that many of these differences are indeed likely to be intra-individual age- and environment-associated changes. Some immune signatures established as subject to distinct changes with age can be associated with important health outcomes such as frailty and responses to vaccination, and finally, with mortality. Many others are clearly hallmarks of the adaptation to exposures over the lifespan and continue to play a positive role in maintaining organismal integrity. Many may be informative only in the population in which they were assessed, and the search for truly universal age-associated changes in immune markers is ongoing. Whether these exist as reflections of ageing processes per se is open to question. Thus far, they mostly seem limited to reductions in numbers, proportions and the antigen receptor repertoire of peripheral blood naïve T cells and other immune cells. In turn, this reflects thymic involution at puberty and the degree of residual thymic function in later life, as well as possibly dysfunctional haematopoiesis and the poorly defined detrimental systemic milieu in older individuals which remains mysterious.

Klotho in Aging and the Failing Kidney

Klotho is one of the few longevity-associated genes with robustly demonstrated effects in both directions: reduce its expression and life span is reduced, increase its expression and life span is increased. Klotho levels decline with age, and this decline is strongly associated with loss of cognitive function, but, interestingly, this may be a very indirect effect that exists due to klotho's influence over kidney function in aging. More klotho implies a slower decline in kidney function, and loss of kidney function is also shown to be a contributing factor in cognitive decline. Thus there is some interest in the research community in developing therapies based on delivery of klotho to patients; Unity Biotechnology added klotho to its otherwise senolytics-focused pipeline last year, for example.

Klotho has been recognized as a gene involved in the aging process in mammals for over 30 years, where it regulates phosphate homeostasis and the activity of members of the fibroblast growth factor (FGF) family. The α-Klotho protein is the receptor for Fibroblast Growth Factor-23 (FGF23), regulating phosphate homeostasis and vitamin D metabolism. Phosphate toxicity is a hallmark of mammalian aging and correlates with diminution of Klotho levels with increasing age. As such, modulation of Klotho activity is an attractive target for therapeutic intervention in aging; in particular for chronic kidney disease (CKD), where Klotho has been implicated directly in the pathophysiology.

Klotho expression levels and its circulating level decline during aging. In humans, Klotho deficiency features medial calcification, intima hyperplasia, endothelial dysfunction, arterial stiffening, hypertension, impaired angiogenesis, and vasculogenesis (i.e., characteristics of early vascular aging). As Klotho-deficient phenotypes have been attenuated and rescued by Klotho gene expression, or supplementation, it is suggestive that Klotho has a protective effect with regard to the vasculature.

A range of strategies have been developed to directly or indirectly influence Klotho expression, with varying degrees of success. These include administration of exogenous Klotho, synthetic and natural Klotho agonists, and indirect approaches, via modulation of diet and the gut microbiota. All these approaches have significant potential to mitigate loss of physiological function and resilience accompanying old age and to improve outcomes of aging.


An Example of the Beneficial Role of Senescence in Injury

Researchers here provide an interesting demonstration of the beneficial role of transient cellular senescence in injury. Applying senolytics to selectively destroy senescent cells immediately following traumatic injury greatly worsens the consequences. Senescent cells are harmful when they build up and linger in tissues over the course of later life. The signaling they generate is useful in the short-term, such as by mobilizing the response to injury in numerous cell populations, but very damaging when sustained for the long term. This dynamic is one of the reasons why we should favor infrequent senolytic therapies that destroy only the harmful, lingering senescent cells, rather than continuing treatments that would negatively impact regeneration and other functions by also destroying transient senescent cells.

It's called senescence, when stressed cells can no longer divide to make new cells, and it's considered a factor in aging and in some diseases. Now scientists have some of the first evidence that at a younger age at least, senescent cells show up quickly after a major injury and are protective. Their model is hemorrhagic shock, a significant loss of blood and the essential oxygen and nutrients it delivers that accounts for about 30-40% of trauma-related deaths from things like car accidents and shootings; and their focus the liver, one of the many major organs that can fail in response.

Shortly after hemorrhagic shock occurs, a population of liver cells quickly become senescent. To find out if the rapid movement to senescence they saw for some liver cells was good or bad, researchers gave some of the rats in their studies senolytics, a relatively new class of drugs that target senescent cells for elimination. Laboratory studies of these drugs have shown they can prevent or improve age-related problems like frailty, cataracts, and vascular and heart dysfunction. Early trials in humans have also reported success in reducing the progression of problems like diabetes and kidney related damage.

But when younger rats in hemorrhagic shock were given the drugs as part of the fluids used for resuscitation shortly after blood loss, they all quickly died. When the researchers gave the same senolytics to healthy rats, they were fine. Death of the senescent cells appears to exacerbate the tissue injury resulting from blood loss. Researchers suspect the rapid transition to senescence that occurred in a population of liver cells was an attempt to stabilize after the trauma, and likely transient. While he says you can't generalize that what happens in one tissue, like the liver, will happen in another organ, the researchers expect something similar happens in other organs in the face of serious injury.


Delivery of T Cell Progenitor Cells as an Approach to Thymic Regeneration

The thymus is a small organ in which thymocytes generated in the bone marrow mature to become T cells of the adaptive immune system. Unfortunately, the thymus atrophies with age, its active tissue largely replaced by fat in most people by age 50 or so. Thereafter the adaptive immune system declines into immunosenescence and inflammaging, deprived of a sufficiently large supply of reinforcement cells. Given the importance of the immune system to health, in matters including tissue maintenance, resistance to infection, suppression of cancer, and more, regeneration of the thymus must be an important component of any serious effort to rejuvenate the elderly. Numerous approaches have been proposed, shown to work in mice, and some even attempted or demonstrated in humans, but this isn't yet a solved problem.

One important class of approach to thymic regeneration is the delivery of cells that will home to the thymus. These cells can in principle be delivered via simple intravenous injection, rather than requiring a much more invasive introduction into the thymus directly. Once in the thymus they either directly assist in building new tissue, or deliver signals that encourage native stem cells to stop slacking and regenerate the thymus. An example of the type is the delivery of epithelial progenitor cells, demonstrated to produce thymic growth in mice a few years ago. Another example, as outlined in today's open access paper, is to deliver cells that are somewhere in the lineage that starts with thymocytes and ends at T cells, as these will also home to the thymus, and their signaling encourages greater thymic activity. The cross-talk between hematopoietic cells in the bone marrow and the thymus is likely mediated by these cells and their signals.

Thymic Engraftment by in vitro-Derived Progenitor T Cells in Young and Aged Mice

T cells play a critical role in mediating antigen-specific and long-term immunity against viral and bacterial pathogens, and their development relies on the highly specialized thymic microenvironment. T cell immunodeficiency can be acquired in the form of inborn errors, or can result from perturbations to the thymus due to aging or irradiation/chemotherapy required for cancer treatment. Hematopoietic stem cell (HSC) transplant (HSCT) from compatible donors is a cornerstone for the treatment of hematological malignancies and immunodeficiency. Although it can restore a functional immune system, profound impairments exist in recovery of the T cell compartment. T cells remain absent or low in number for many months after HSCT, depending on a variety of factors including the age of the recipient.

While younger patients have a shorter refractory period, the prolonged T cell recovery observed in older patients can lead to a higher risk of opportunistic infections and increased predisposition to relapse. Thus, strategies for enhancing T cell recovery in aged individuals are needed to counter thymic damage induced by radiation and chemotherapy toxicities, in addition to naturally occurring age-related thymic involution.

Preclinical results have shown that robust and rapid long-term thymic reconstitution can be achieved when progenitor T cells, generated in vitro from HSCs, are co-administered during HSCT. Progenitor T cells appear to rely on lymphostromal crosstalk via receptor activator of NF-κB (RANK) and RANK-ligand (RANKL) interactions, creating chemokine-rich niches within the cortex and medulla that likely favor the recruitment of bone marrow-derived thymus seeding progenitors. Here, we employed preclinical mouse models to demonstrate that in vitro-generated progenitor T cells can effectively engraft involuted aged thymuses, which could potentially improve T cell recovery. The utility of progenitor T cells for aged recipients positions them as a promising cellular therapy for immune recovery and intrathymic repair following irradiation and chemotherapy, even in a post-involution thymus.

Markers of Chronic Inflammation Correlate with Age-Related Loss of Muscle Mass and Strength

Chronic inflammation is a sizable component of aging. The immune system becomes inappropriately overactive, disrupting its normal participation in tissue maintenance, and producing alterations in the signaling environment that change the behavior of other cells for the worse. Inflammation appears to be important in the age-related decline of stem cell activity, for example. It is certainly important in the maintenance of muscle tissue. The study here is far from the only one to show a link between chronic inflammation and the age-related loss of muscle mass and strength, a condition known as sarcopenia.

Skeletal muscle plays an integral role in maintaining homeostasis across organ systems. Skeletal muscle is plastic, changing dynamically in response to physical activity, load, injury, illness, and ageing. The age-related loss of skeletal muscle strength, muscle mass, and physical performance (sarcopenia), has been associated with falls and fractures in older populations, and remains a largely undiagnosed condition. Beyond ageing, sarcopenia is associated with age-related diseases such as dementia, chronic obstructive pulmonary disease, and cardiovascular disease. In older adults, several of these diseases coincide with decline in muscle mass and whether this is caused by ageing or disease is largely unknown. However, a common feature underlying both conditions is inflammation.

Chronic inflammation, characterised by higher systemic cytokine and acute phase protein circulation, is not only linked to ageing 'inflammaging' but also muscle mass loss. Tumor necrosis factor α (TNFα) released from diseased tissues has been shown to exert endocrine effects on skeletal muscle. In vitro studies have shown that TNFα is a key endocrine stimulus for contractile dysfunction in chronic inflammation and that the muscle derived reactive oxygen species (ROS) and nitric oxide (NO) participate in depressing specific force of muscle fibre, which can lead to muscle atrophy. Furthermore Interleukin (IL)-6, a key cytokine involved in low-grade chronic inflammation, has been shown to facilitate muscle atrophy via blunting muscle anabolism and energy homeostasis.

The aim of this systematic review and meta-analysis was to determine the relationship between systemic inflammation, muscle strength, and/or muscle mass in adults. Overall, 168 articles; 149 cross-sectional articles (n = 76,899 participants, 47.0% male) and 19 longitudinal articles (n = 12,295 participants, 31.9% male) met inclusion criteria. Independent of disease state, higher levels of C reactive protein (CRP), Interleukin (IL)-6, and Tumor necrosis factor (TNF)α were associated with lower handgrip and knee extension strength and muscle mass. Furthermore, higher levels of systemic inflammatory markers appeared to be associated with lower muscle strength and muscle mass over time.


Lef1 Enables Skin Regeneration Without Scarring in Mice

To achieve regeneration without scarring is an important goal in the medical research community. Some species are capable of proficient regeneration of even whole limbs or internal organs, but mammalian regeneration is stunted by comparison, sidetracked into the process of scar formation. This is likely a side-effect of processes that act to reduce cancer incidence, but researchers have not yet achieved a sufficiently comprehensive understanding of regeneration in species with different capabilities to be certain. Here, researchers note a demonstration of skin regeneration without scarring, produced by upregulation of the lef1 transcription factor. Studies of this nature can help to focus scientific investigations into more productive directions, narrowing down areas of interest in the cellular biochemistry of regeneration.

Researchers have identified a factor that acts like a molecular switch in the skin of baby mice that controls the formation of hair follicles as they develop during the first week of life. The switch is mostly turned off after skin forms and remains off in adult tissue. When it was activated in specialized cells in adult mice, their skin was able to heal wounds without scarring. The reformed skin even included fur and could make goose bumps, an ability that is lost in adult human scars.

Researchers used a new technique called single cell RNA sequencing to compare genes and cells in developing skin and adult skin. In developing skin, they found a transcription factor - proteins that bind to DNA and can influence whether genes are turned on or off. The factor the researchers identified, called Lef1, was associated with papillary fibroblasts which are developing cells in the papillary dermis, a layer of skin just below the surface that gives skin its tension and youthful appearance.

When the researchers activated the Lef1 factor in specialized compartments of adult mouse skin, it enhanced the skins' ability to regenerate wounds with reduced scarring, even growing new hair follicles that could make goose bumps. Researchers first got the idea to look at early stages of mammalian life for the capacity to repair skin because after emergency life-saving surgery in utero, it was observed that when the babies were born they did not have any scars from the surgery. A lot of work still needs to be done before this latest discovery in mice can be applied to human skin, but it is an important advance.


Targeting Senescent Cells to Reverse the Aging of the Heart

Almost a decade has passed since the first compelling demonstration that clearance of senescent cells in mice could produce rejuvenation. This validated decades of prior evidence, largely ignored in the research community, indicating that accumulation of senescent cells is a significant cause of degenerative aging. It was a wake-up call. Since then, numerous research groups have shown that targeted clearance of senescent cells reverses many age-related conditions and extends healthy life span in mice. It is easy to accomplish in the lab. Near any approach works, to the degree that it can destroy senescent cells without harming normal cells. As a consequence, a new biotech industry has come into being, a range of startups and programs working on clinical development of the first generation of senolytic drugs capable of safely removing senescent cells from aged tissues.

As a result of this field of research, it has been shown that accumulation of senescent cells is an important part of the development of cardiovascular disease. Senescent foam cells accelerate the progression of atherosclerosis, driving the growth of fatty lesions that narrow and weaken blood vessels, leading to stroke and heart attack. Senescent cells drive the calcification of blood vessels, and degrade the function of smooth muscle tissue in blood vessel walls. Senescent cells are a part of the dysfunction that leads to cardiac hypertrophy, the enlargement and weakening of heart muscle that causes heart failure, as well as fibrosis, a disruption of tissue structure by inappropriate collagen deposits. We now know all of this because it is possible to run animal studies in which senolytic treatments remove senescent cells, and then observe the result - a reversal of age-related cardiovascular disease.

Therapeutic Potential of Senolytics in Cardiovascular Disease

The most significant determining factor of cardiovascular health is a person's age, with cardiovascular disease (CVD) being the leading cause of death in 40% of individuals over 65 years. The ageing heart undergoes a process of myocardial remodelling, which is characterised by physiological and molecular alterations that result in endothelial stenosis, vasomotor dysfunction and stiffening, cardiomyocyte hypertrophy, myocardial fibrosis, and inflammation which result in increased ventricular stiffness, impaired cardiac function and can ultimately lead to HF. In particular, HF with preserved ejection fraction (HFpEF), characterised by diastolic ventricular dysfunction with maintained systolic function, is clinically associated with ageing.

The association between senescence and myocardial ageing in humans has been reported for nearly 20 years. More recently it has been demonstrated that senescence contributes directly to age-related myocardial remodelling in mice, as pharmacogenetic elimination of senescent cells, using the p16-INKATTAC model, reduced myocardial fibrosis, and attenuated cardiomyocyte hypertrophy. Elimination of senescent cells from aged p16-INKATTAC mice also increased their survival and reduced the development of cardiac dysfunction following isoproterenol-induced myocardial stress. Following on from this data, we and others have hypothesised that an accumulation of senescence and the expression of a senescence-associated secretory phenotype (SASP) drive age-related myocardial remodelling and have begun to independently investigate if senolytics can eliminate senescent cell populations resident in the aged heart in order to improve myocardial function.

Pharmacological elimination of senescent cells from aged mice could improve myocardial function. Treatment of 24-month-old mice with a single dose of dasatinib and quercetin significantly improved left ventricular (LV) ejection fraction and fractional shortening. This observed change in function was suggested to be a result of a restoration in vascular endothelial function. We have shown in aged mice that senescence occurred primarily within the cardiomyocyte population and led to the expression of a cardiomyocyte-specific SASP with the potential to promote myofibroblast differentiation of fibroblasts and induce cardiomyocytes to hypertrophy in vitro. In vivo, cyclical oral administration of navitoclax reduced the number of senescent cardiomyocytes, attenuated components of the cardiomyocyte SASP and reduced myocardial remodelling as indicated by a reduction in both cardiomyocyte hypertrophy and interstitial fibrosis.

Given the limited regenerative capacity of the heart, there is considerable interest in the potential of regenerative cellular therapies for the treatment of CVD such as myocardial infarction (MI) and age-related HF. For cellular therapies to be effective, the grafted cells must survive, integrate, and function within the surviving myocardium. The data discussed above suggest that older age not only increases the potential for dysfunction in the very populations that are being used for cellular therapies but also increases the hostility of the recipient myocardial environment as a result of SASP mediated inflammation and the bystander effect. This may in part explain the failure of pre-clinical trials to translate clinically into regenerative therapies. Preclinical studies showing successful cell regenerative therapies use young healthy animals, whereas the prevalence of CVD increases linearly with age, and therefore, most patients undergoing cellular therapy are likely to display high levels of myocardial senescence which could create an unfavourable environment impeding incorporation and differentiation of the transplanted cell populations. Senolytic-mediated elimination of senescent cells from aged patients may, therefore, have the potential to improve the outcomes of such regenerative cellular therapies.

Dopaminergenic Neurons Transplanted into Mouse Brains Integrate Into Neural Circuits and Improve Parkinson's Symptoms

Researchers here demonstrate that human dopaminergenic neurons, the class of cell lost in Parkinson's disease, can integrate into neural circuits and improve motor function when transplanted into mice. The challenge with all such cell therapies, in which cell replacement and consequent functional improvement is the goal, is that it is very hard to achieve any significant survival of cells following transplantation. Finding the right methodology has been a challenge, so proof of concept work like this is more important for the precise details of the methodology used - not discussed here - than for the outcome.

Researchers demonstrated a proof-of-concept stem cell treatment in a mouse model of Parkinson's disease. They found that neurons derived from stem cells can integrate well into the correct regions of the brain, connect with native neurons and restore motor functions. The key is identity. By carefully tracking the fate of transplanted stem cells, the scientists found that the cells' identity - dopamine-producing cells in the case of Parkinson's - defined the connections they made and how they functioned. Coupled with an increasing array of methods to produce dozens of unique neurons from stem cells, the scientists say this work suggests neural stem cell therapy is a realistic goal.

To repair damaged neural circuits in the Parkinson's disease mouse model, the researchers began by coaxing human embryonic stem cells to differentiate into dopamine-producing neurons, the kind of cells that die in Parkinson's. They transplanted these new neurons into the midbrains of mice, the brain region most affected by Parkinson's degeneration. Several months later, after the new neurons had time to integrate into the brain, the mice showed improved motor skills. Looking closely, researchers were able to see that the transplanted neurons grew long distances to connect to motor-control regions of the brain. The nerve cells also established connections with regulatory regions of the brain that fed into the new neurons and prevented them from being overstimulated.

Both sets of connections - feeding in and out of the transplanted neurons - resembled the circuitry established by native neurons. To confirm that the transplanted neurons had repaired the Parkinson's-damaged circuits, the researchers inserted genetic on-and-off switches into the stem cells. These switches turn the cells' activity up or down when they are exposed to specialized designer drugs in the diet or through an injection. When the stem cells were shut down, the mice's motor improvements vanished.


The More Time Spent with High Blood Cholesterol, the Greater the Lifetime Risk of Heart Disease

Researchers here suggest that the processes of atherosclerosis, leading to the buildup of fatty deposits that narrow and weaken blood vessels, are cumulative over time. One of the risk factors is high blood cholesterol, and high cholesterol in youth is found to correlate with increased risk in later life, even if blood cholesterol has been restored to normal levels at that time. This is interesting, as the cause of atherosclerosis is less blood cholesterol per se and more the oxidized cholesterol that disrupts the function of macrophage cells responsible for cleaning up cholesterol in blood vessel walls. Those macrophages should be working just fine in genetically normal young people with high cholesterol, as oxidized cholesterol is a feature of aging, and should be only minimally present in the young. This suggests that perhaps the researchers are seeing the ongoing, lifetime effects of the sort of neglect of health that is required to obtain high blood cholesterol when young, rather than a specific disease process.

An ongoing study, funded by the National Heart, Lung, and Blood Institute, began 35 years ago, recruiting 5,000 young adults aged 18 to 30. Researchers have tracked this cohort ever since to understand how individual characteristics, lifestyle, and environmental factors contribute to the development of cardiovascular disease later in life. "We found having an elevated LDL cholesterol level at a young age raises the risk of developing heart disease, and the elevated risk persists even in those who were able to later lower their LDL cholesterol levels. Damage to the arteries done early in life may be irreversible and appears to be cumulative. For this reason, doctors may want to consider prescribing lifestyle changes and also medications to lower high LDL cholesterol levels in young adults in order to prevent problems further down the road."

To conduct the study, the researchers used complex mathematical modeling to understand how cardiovascular risk (heart attack, stroke, blood vessel blockages, and death from cardiovascular disease) rises with increasing cumulative "exposure" to LDL cholesterol over an average of 22 years. They found that the greater the area under the "LDL curve" - which measured time of exposure and level of LDL cholesterol over time - the more likely participants were to experience a major cardiovascular event. While the medical establishment understands the importance of managing high LDL cholesterol levels to lower heart risks, there is little consensus on how aggressively to intervene in young adults who may not experience a heart attack or stroke for decades.


There is No Such Thing as Aging

Today's open access commentary is intended to provoke discussion on the topic of how aging is thought about and presented, particularly at the intersection between the scientific community and the rest of the world, or between scientific disciplines, or between scientists and funding institutions. It is an interesting read, as such commentaries often are.

Aging, of course, exists. It is a useful word that is applied as a bucket to hold a very complicated, ever-changing, and still comparatively poorly defined set of degenerative processes and the consequences of those processes. We age, we decline. That much is evident and right in front of our eyes. So a term will be invented and applied to it; we humans are nothing if not ruthless taxonomists.

In another sense, however, there is no such thing as aging. Aging is a fiction, like all abstractions, and it is frequently counterproductive to try to deal with the bucket rather than the inconveniently complex contents of the bucket. Focusing on an abstraction will lead one astray and distance one from the reality of the situation. That may well have been fine and possibly even helpful in the past, but it could be harmful at a time in which it is becoming possible to address the mechanisms that make up aging, to slow and reverse the consequences of those mechanisms.

What if there's no such thing as "aging"?

Some years ago, it was argued that aging is not a biological phenomenon. The argument - that there are not necessarily common mechanisms underlying the major aging-related chronic diseases, such as cancer, but rather a suite of individual disease processes synchronized via natural selection - would surely find little favor today. Common mechanisms, including inflammaging, mitochondrial dysfunction, and cellular senescence, are now thought to be well established. In retrospect, the argument seems ignorant of aging mechanisms. Here, we argue that this apparently ignorant view is right, but for the wrong reasons: that our more detailed knowledge of aging mechanisms is increasingly showing that there is no unitary phenomenon usefully summarized with the word aging.

What is aging? This question, at the heart of our field, has received a great deal of attention, and many definitions, implicit or explicit, have been proposed. (Here, we use the term "aging," though all our arguments equally apply to the term "senescence," which is favored by some). A coherent definition is even essential for the field: there are intensive efforts to measure aging, to slow aging, and to treat aging, and it will be impossible to know if they are succeeding without a clear definition of the subject of our research. Is it accumulation of molecular damage? Is it loss of function with increasing age? Is it increases in mortality (or decreases in reproductive rate) with age? Underlying the discussion to date is an assumption so basic it goes unnoticed: that there is an underlying biological phenomenon of aging.

We have a word for aging, and therefore we assume that science will accommodate us, providing a phenomenon to match our word. And in a colloquial sense this is certainly the case: no one can doubt that we see ourselves, our relatives, and our friends age. But is this colloquial usage scientifically justified? Is there really a "thing" or a phenomenon we can call aging? We argue here that our understanding of the biology is now sufficient to say definitively that this is not the case, that from a scientific perspective there is no such thing as aging, but rather a collection of disparate phenomena and mechanisms - sometimes interacting with each other - that relate in one way or another to our colloquial sense of the word. Accordingly, our desire to find a single reality of aging has created a great deal of confusion in the field.

We are well aware that not all researchers in our field will like our thesis here: our identity as "aging researchers" is tightly wrapped around the notion that there is a phenomenon of aging. However, we do not believe there is a need to feel any existential threat from this idea, which is in some sense a natural extension of the multi-factorial hallmarks of aging or pillars of aging framework. Rather, we think that being more careful about our underlying assumptions, and how they do or do not conform to biological reality, can only make us better researchers. The field of aging research can still exist, but with a more nuanced understanding that we are not studying a single biological phenomenon, but an assortment of loosely related processes that we find convenient to lump together.

Senolytics as an Arm of Regenerative Medicine for the Elderly

Senolytic therapies are those that selectively destroy the senescent cells that accumulate in tissues with age. These cells secrete a potent mix of signals that produce chronic inflammation and degrade tissue function, particularly the ability of tissues to maintain and repair themselves. While many well known interventions that improve long-term health - exercise, calorie restriction, and so forth - are likely to modestly lower the burden of senescent cells over time, by increasing the pace of destruction or lowering the pace of creation, the senolytic label is reserved for therapies that can be applied to very quickly destroy a significant number of such cells. Animal studies suggest that removing as little as a third of the senescent cells in an old individual, via treatments such as the dasatinib and quercetin combination, is enough to produce quite profound reversal of pathology in numerous age-related diseases. A higher degree of clearance should be better.

Researchers are probing ways to activate the body's regenerative potential to slow the clock on chronic conditions that set in as we age. "We're quite interested in what it is it about aging that compromises the ability of our bodies to rejuvenate. We want to know what it is about the process of aging that leads to the molecular and cellular damage associated with different diseases and geriatric syndromes."

Cell senescence, a state of growth arrest, plays a key role in aging. Damage to cells, and particularly their DNA, due to natural aging processes or environmental factors such as cigarette smoke, causes cells to become senescent. Senescent cells no longer divide and differentiate. They then lose their ability to repair tissue. Senescent cells secrete harmful proteins and chemicals, creating sort of a "toxic soil" locally, if not globally, that disrupts the function of stem cells. That can sap the body's ability to heal from injury. Though senescent cells are relatively few, they accumulate with advancing age. Ultimately, they contribute to disease and failing health.

"What's interesting about a senescent cell, is it is a robust secretory factory, if you will, pumping out cytokines, chemokines, and other factors into the local environment that creates all kinds of havoc. It compromises the health and function of neighboring cells and the surrounding tissue. In the field of aging, we often talk about inflammation as a primary cause of disease. Factors secreted by senescent cells clearly contribute to a state of chronic sterile inflammation, or a smoldering fire, which can burst into a conflagration and drive disease."

"We've published one study that in at least the context of obesity, finds exercise can prevent senescent cell accumulation and, to some extent, clear senescent cells from the body. Exercise has profound effects on our cells and their capacity to repair different aspects of cell damage that are linked to aging and age-related diseases. For example, exercise improves the cells' ability to repair DNA, manage oxidative stress, and turn on the garbage disposal and get rid of old damaged proteins."


Making the Leap from Mice to Humans in the Treatment of Aging

This commentary makes the point that the development of interventions to slow and reverse aging is moving along at some pace in mice, the field expanding year after year, but the translation of this work into human medicine is very definitely lagging behind, yet to come up to speed. This is largely true for any comparatively new and growing field of medicine, given the enormous and excessive cost and delay imposed by regulators, but the study of aging has its own peculiarities in addition to that issue. For example, the lack of a good way to measure the outcome of a treatment on the mechanisms and progression of aging. Or the strong focus on approaches such as upregulation of the stress response mechanisms of autophagy, wherein the effects on aging and life span are much more pronounced in short-lived species, leading to comparatively poor results in humans. There will be a point at which the medical side of the field of aging research catches up, certainly, but exactly when that will start to happen is an open question.

Almost a century has passed since Clive McCay discovered that reducing the food intake of his rats increased their lifespan by up to 40%. Now we know that dozens of interventions extend the lifespan of organisms such as rodents, nematodes, yeast, and fruit flies. Aging is not as static as it once seemed. Clearly, we now know that several conserved molecular changes occur in organisms with age and we have developed interventions in animal models to impact almost all of them. Nevertheless, despite our great push for testing lifespan and healthspan altering molecules and growing knowledge of the underlying causes of aging, we still do not know if most of our interventions will work in humans. Why is that?

A major problem facing the field of aging is measuring the effect of an intervention. In short lived organisms such as fruit flies, nematodes, and yeast, effects are easy to measure simply by investigating how an intervention impacts the lifespan. However, with longer lived organisms this becomes challenging and surrogate markers are therefore needed that reflect biological aging. Ten years ago, the identification of single biomarkers of aging was a grand challenge when considering trials for aging in humans, however, landmark papers have since shown that we can quite accurately measure age by looking at the combined alterations in the epigenetic landscape. We can then use these biomarkers to test if we can reduce or reverse the biological age of an individual. With these tools at our disposal, we have truly moved into an era where biomarkers are no longer an issue.

Concurrent with the recent development in biomarkers the first trials targeting aging in humans are now being started. The need for testing a significant number of individuals have been a limiting factor for trial designs. This has been the case because trials are often designed for mortality endpoints or other relatively rare events for otherwise healthy elderly individuals which necessitates large cohorts. Based on recent trials, it appears that even relatively short treatments may be enough to see signs of epigenetic age-reduction in humans, however. In summary, we have all the tools available to begin transitioning to testing in humans.

Twenty years ago, the NIA funded Interventions Testing Program (ITP) was conceived to test interventions in mice with the specific goal of translating the findings to clinical trials in human. The program, which investigates the lifespan effect of proposed interventions in genetically diverse mice across multiple centers, has been a massive success with numerous groundbreaking findings, perhaps most notoriously the discovery that rapamycin extends the lifespan of mice. Nevertheless, the hope of real translation was never completely carried forward to humans even though some trials have been examining the effect of compounds such as rapamycin on age-associated diseases, but not aging itself. To tackle our grand challenge, I propose that the field funds a human interventions testing program that will investigate promising compounds in humans.


Building the Glucosepane Research Toolkit Continues with the Creation of Anti-Glucosepane Antibodies

Glucosepane is likely the most important form of persistent cross-linking in aging human tissue. There is some remaining uncertainty, but it appears that the vast majority of cross-links in old tissues are based on glucosepane. Cross-links are the consequence of advanced glycation end-products (AGEs), sugary metabolic waste that can bond with the structural molecules of the extracellular matrix. Where two such molecules are linked together by a single AGE (a "cross-link"), it reduces their ability to move relative to one another. The presence of many persistent cross-links thus degrades the structural properties of that tissue. This is particularly true of elasticity, vital to the correct function of skin and, more importantly, blood vessels. Cross-linking is likely an important contribution to arterial stiffening, and the hypertension and cardiovascular disease that follows as a consequence.

The solution to this aspect of aging is to find a way to periodically remove cross-links. That effort has been hampered by the fact that the important cross-links in humans and laboratory species such as mice are completely different. That was well demonstrated by the high profile failure of the cross-link breaker compound alagebrium to perform in humans in the same way that it does in rats. Further, the tools required to work with important human AGEs such as glucosepane have been lacking. Without necessary line items such as animal models, a cheap method of synthesizing glucosepane, and antibodies specific to glucosepane, scientists avoided this part of the field in favor of easier programs of research. Fortunately the SENS Research Foundation started to fund efforts to solve this tooling problem some years ago, and, once started and shown to be productive, that line of work has continued.

Today's paper reports on the development of specific antibodies for glucosepane by the same group that first produced a robust, low-cost method of glucosepane synthesis. Antibodies that are highly specific to the molecules under study are needed for any rigorous program of development, as without them many assays of cells and tissues become questionable or impossible. This paper is an important step forward, just as much so as the synthesis of glucosepane. This part of the field of cross-link study is being opened up, and the more researchers to participate, the sooner we'll see successful trials of cross-link breaking drugs capable of removing glucosepane from the human body. There is at present one startup biotech company working towards that goal, and in a better world there would be a dozen, a mirror of the developing senolytics industry.

Generation and Characterization of Anti-Glucosepane Antibodies Enabling Direct Detection of Glucosepane in Retinal Tissue

Glucosepane is among the most abundant AGEs found in human tissues. It is formed from lysine, arginine, and glucose, and it is over an order of magnitude more abundant than any other AGE crosslink in extracellular matrix (ECM). Notably, glucosepane levels have been shown to correlate with various disease states, including diabetic retinopathy, microalbuminuria, and neuropathy. While the exact mechanisms behind glucosepane-mediated dysfunction remain unclear, it is believed to impair the functional and mechanical properties of proteins in the ECM and interfere with proteolytic degradation of collagen.

To date, the primary method for identifying glucosepane in tissues has required exhaustive enzymatic degradation followed by high pressure liquid chromatography-mass spectrometry (LC/MS). Although these protocols have proven effective in quantifying glucosepane in bulk tissue extracts, they are labor-intensive and the degradation process destroys the tissue architecture, making it difficult to examine the localization of glucosepane.

In recent years, anti-AGE antibodies have emerged as useful tools for studying AGEs and have the advantage of being compatible with the evaluation of intact tissues, enabling immunohistochemical staining and imaging procedures. Several anti-AGE antibodies have been produced by immunization of animals with AGEs generated either from total synthesis or through in vitro glycation methods. Such methods involve the incubation of an immunogenic carrier protein, such as BSA, with glucose or other reactive sugar metabolites. Reaction conditions that generate glucosepane are known also to generate a range of AGE by-products, including carboxymethyllysine. These in vitro preparation methods are unlikely to produce antibodies that are specific for glucosepane, although no such studies have been reported.

To avoid this expected complication, we decided to synthesize homogeneous, synthetic glucosepane immunogens. Herein, we describe the development and characterization of the first antibodies known to selectively recognize glucosepane. To this end, we have created a synthetic glucosepane immunogen that closely resembles glucosepane found in vivo and used it to generate a polyclonal antibody serum that recognizes glucosepane both in vitro and in ex vivo tissue samples. We have demonstrated that the antibodies can bind to glucosepane with high degrees of specificity and sensitivity through ELISA studies and have employed these antibodies in immunohistochemical experiments.

Interestingly, these latter studies demonstrate that glucosepane accumulates within sub-components of the retina, specifically the retinal pigment epithelium (RPE), Bruch's membrane, and choroid, which are anatomic areas highly affected by AMD and diabetic retinopathy.

Fructose Metabolism in Alzheimer's Disease

The degree to which Alzheimer's disease is a lifestyle condition is an interesting question. A good deal of research points to insulin resistance in the brain as important in the progression of Alzheimer's disease, to the point at which one group declared Alzheimer's to be a type 3 diabetes, a condition that should be thought of as primarily metabolic in origin. That idea gained enough traction that when a definitively new type of diabetes was discovered, it had to be named type 4 diabetes to avoid confusion.

Insulin resistance and type 2 diabetes are a consequence of being overweight in the vast majority of patients, but Alzheimer's disease isn't as obviously directly a consequence of excess fat as is the case for type 2 diabetes. Fewer overweight people develop Alzheimer's disease than develop type 2 diabetes - it isn't the same picture at all as the comparatively reliable progression to metabolic syndrome, insulin resistance, and then type 2 diabetes that happens as a result of excessive weight gain. Nonetheless, the disrupted metabolism of overweight people does look compelling as a contributing cause of this form of neurodegenerative condition.

The loss of cognitive function in Alzheimer's disease is pathologically linked with neurofibrillary tangles, amyloid deposition, and loss of neuronal communication. Cerebral insulin resistance and mitochondrial dysfunction have emerged as important contributors to pathogenesis supporting our hypothesis that cerebral fructose metabolism is a key initiating pathway for Alzheimer's disease.

Fructose is unique among nutrients because it activates a survival pathway to protect animals from starvation by lowering energy in cells in association with adenosine monophosphate degradation to uric acid. The fall in energy from fructose metabolism stimulates foraging and food intake while reducing energy and oxygen needs by decreasing mitochondrial function, stimulating glycolysis, and inducing insulin resistance. When fructose metabolism is overactivated systemically, such as from excessive fructose intake, this can lead to obesity and diabetes.

Herein, we present evidence that Alzheimer's disease may be driven by overactivation of cerebral fructose metabolism, in which the source of fructose is largely from endogenous production in the brain. Thus, the reduction in mitochondrial energy production is hampered by neuronal glycolysis that is inadequate, resulting in progressive loss of cerebral energy levels required for neurons to remain functional and viable. In essence, we propose that Alzheimer's disease is a modern disease driven by changes in dietary lifestyle in which fructose can disrupt cerebral metabolism and neuronal function. Inhibition of intracerebral fructose metabolism could provide a novel way to prevent and treat this disease.


Insight into How Loss of Functional TDP-43 Contributes to ALS and Frontotemporal Dementia

TDP-43 is one of a number of proteins that can misfold in ways that cause neurodegeneration, either via aggregation into solid deposits, or via a diminished amount of functional protein in critical cells in the brain. Research into TDP-43 is at an earlier stage than is the case for amyloid-β, α-synuclein, or other better known proteins that exhibit these problems. Important and quite fundamental discoveries related to the way in which TDP-43 causes pathology are still being made, as is the case in this recently announced paper.

Two common neurodegenerative diseases - ALS and frontotemporal lobar degeneration, or FTLD - result from reduced transportation of RNA by the protein TDP-43, which ultimately disrupts neuron function. Because one of the biggest physiological changes in both ALS and FTLD is the disappearance of TDP-43 from the nucleoli of neurons, the team focused their research on finding out what TDP-43 normally does. TDP-43 is known to bind to RNA, and the team's first experiment showed that in neurons, TDP-43 attaches to RNA that codes for pieces of ribosomes, which are necessary for making proteins from RNA code.

"We discovered TDP-43 in axons and that it binds to ribosomal protein messenger RNA. That was strong support for the idea that TDP-43 carries the RNA to the axon where it can be used to make ribosomal proteins. This would allow local synthesis of proteins at ribosomes built in axons." Indeed, further experiments confirmed that hypothesis and showed that when TDP-43 was missing, the RNA in question could not be transported to the axon.

But what happens if the RNA cannot be transported? The researchers examined axon growth in culture as well as in mouse embryos. They found that in both cases, axon extension and outgrowth were stunted when TDP-43 was missing. However, outgrowth could be restored by forcing the neurons to overproduce ribosomal proteins. "Now that we understand TDP-43's role in transporting the ribosomal protein messenger RNA, it should help us develop new strategies and new targets for ALS and FTLD treatments. Our results in reversing stunted axon extension in mouse embryos is promising, but is just a first step."


On the Aging of the Germline and Rejuvenation in Embryos

It is clearly the case that cells and tissues are in principle capable of rejuvenation. Individuals age, but their offspring are born young. The germline in adults is protected in comparison to other cell populations, but it nonetheless accumulates forms of stochastic damage over time. Yet that damage is not apparent by the time later stage embryonic development takes place. Somewhere between conception and that later stage of embryonic development, a form of rejuvenation takes place.

The authors of today's open access paper consider this topic in some detail, and the relevance it might have to future efforts to produce rejuvenation therapies. In recent years, scientists have become interested how and why reprogramming cells into induced pluripotent stem cells turns out to mirror much of what takes place in the developing embryo. Many of the marks of age are removed, and cells are rejuvenated.

An unexpected development in this field of research is that reprogramming cells in vivo appears to be beneficial, rather than very disruptive to tissue structure and function, and this approach is consequently now under development as a form of rejuvenation therapy. This makes it much more interesting to better understand exactly what is going on in the developing embryo.

The Ground Zero of Organismal Life and Aging

One of most profound revelations of recent advances in science is that biological systems can be completely rejuvenated. Indeed, just a few years ago, reversing the deleterious changes that accumulate with age in their entirety was simply unimaginable. Yet, we now know that this is possible, whether we consider the conversion of somatic cells to induced pluripotent stem cells (iPSCs) or the natural reversal of age of the germline with each generation. These two processes converge somewhere during early development at the point here proposed to be termed the 'ground zero.' It is here that both organismal life and aging begin.

It is often discussed that, because the germline is immortal, it does not age; this notion dates to the 19th century, when August Weismann proposed the separation of ageless germline and aging body. However, at the time of conception, the contributing human germline has typically been maintained in a metabolically active state for two or more decades and must have accumulated damage, such as metabolic by-products, epimutations, and modified irreplaceable proteins. In other words, it has become biologically older than its earlier, embryonic state.

Although the germline biological age at the time of conception is expected to be much younger than that of somatic tissues of the same organism, and although some of the accumulated damage may be removed by designated molecular systems, rejuvenation in the prezygotic state could only be partial because, in the absence of cell division (as in the oocyte), there are always more damage forms than the means of protecting against them. Also, although some germ cells may accumulate more damage than others and therefore may lead to early mortality and abnormalities in the offspring (this damage will also increase with the age of the host), all germ cells unavoidably accumulate some damage. Thus, for the new life to begin in the same young state as in the previous generation, the zygote must somehow remove this damage and decrease its biological age to the level of the germline age in the previous generation. In other words, it appears that the germline ages during development and adult life, and then it is rejuvenated in the offspring after conception.

All this leads to a model wherein early embryos are gradually rejuvenated, for example, by extending their telomeres, erasing epigenetic marks, and clearing up and diluting molecular damage, and this continues up to a particular time during early development. Conception represents a starting point for this process, culminating in the state of the lowest biological age, the ground zero of organismal life and aging. In effect, the period from conception to this stage may be viewed as a preparatory stage, which is associated with damage clearance and rejuvenation, for subsequent development of the organism.

The ground zero model extends and modifies Weismann's notion of heritable immortal germline and noninheritable aging body by positing that (i) both body and germline can age; (ii) both body and germline can be rejuvenated; (iii) body and germline can be brought to a common state characterized by the lowest biological age, ground zero; and (iv) age can be reversed without the need to have a separate body and germline. The proposed model is currently based on in vitro experiments and application of epigenetic and other clocks to assess biological age and should be extended to experimental organismal biology. Understanding the nature and mechanisms of rejuvenation, defining the exact point of ground zero, and discovering ways to manipulate the lowest age may provide opportunities for dramatic advances in human biology and medicine

Visceral Fat Tissue is the Major Determinant of Mortality Due to Excess Body Weight

It is the metabolic activity of visceral fat packed around abdominal organs that determines most of the harmful consequences of being overweight, not the subcutaneous fat deposits elsewhere in the body. Excess visceral fat produces chronic inflammation through a variety of mechanisms, such as increased burden of senescent cells, cell signaling that mimics the signals of infected cells, and more cell debris that triggers the immune system into overactivity. That chronic inflammation in turn disrupts normal tissue maintenance and cell behavior, and drives the onset and progression of all of the common age-related conditions. It is fair to say that being overweight literally accelerates aging, and the more visceral fat, the larger the effect.

Two recent comprehensive meta-analyses assessed the association of general adiposity, represented by body mass index, with the risk of all cause mortality in the general population. The results indicated that a U shaped and a J shaped association existed between body mass index and the risk of all cause mortality in the general population. The lowest risk was observed for a body mass index of 22-23 in healthy never smokers. Body mass index is easy to obtain and so is the most frequent anthropometric measure used to investigate obesity-mortality and obesity-morbidity associations.

The validity of body mass index as an appropriate indicator of obesity has been questioned. Research suggests that body mass index does not differentiate between lean body mass and fat mass; therefore, when using body mass index as a measure, inaccurate assessment of adiposity could occur. Additionally, the most important limitation of body mass index is that it does not reflect regional body fat distribution. Existing evidence suggests that central obesity and abdominal deposition of fat is more strongly associated with cardiometabolic risk factors and chronic disease risk than overall obesity.

Taking this evidence into account, indices of central obesity might be more accurate than body mass index when estimating adiposity, and therefore could be more closely and strongly associated with the risk of mortality. We aimed to perform a systematic review and dose-response meta-analysis of prospective cohort studies to investigate the association of indices of central fatness with the risk of all cause mortality in the general population, in never smokers, and in healthy never smokers. The indices of central fatness were waist circumference, hip circumference, thigh circumference, waist-to-hip ratio, waist-to-height ratio, waist-to-thigh ratio, body adiposity index, and A body shape index.

Indices of central fatness including waist circumference, waist-to-hip ratio, waist-to-height ratio, waist-to-thigh ratio, body adiposity index, and A body shape index, independent of overall adiposity, were positively and significantly associated with a higher all cause mortality risk. Larger hip circumference and thigh circumference were associated with a lower risk. The results suggest that measures of central adiposity could be used with body mass index as a supplementary approach to determine the risk of premature death.


Ketone Body β-hydroxybutyrate Inhibits Inflammation to Reduce Alzheimer's Pathology in a Mouse Model

Ketosis is a response to low dietary intake of carbohydrates, and one of the mechanisms by which calorie restriction produces benefits to health and longevity. A ketogenic diet attempts to capture that part of the process by reducing carbohydrate intake without reducing calorie intake. Ketosis results in the production of ketone bodies, metabolites that change cellular behavior for the better throughout the body. One beneficial effect is a reduction in chronic inflammation, via inhibition of the inflammasome as shown here. The sustained inflammation of aging is important in the progression of neurodegenerative conditions such as Alzheimer's disease, and, as demonstrated here, suppression of inflammation improves matters in a mouse model of the condition.

Alzheimer's disease (AD) is a progressive, late-onset dementia with no effective treatment available. Recent studies suggest that AD pathology is driven by age-related changes in metabolism. Alterations in metabolism, such as placing patients on a ketogenic diet, can alter cognition by an unknown mechanism. One of the ketone bodies produced as a result of ketogenesis, β-hydroxybutyrate (BHB), is known to inhibit NLRP3 inflammasome activation. Therefore, we tested if BHB inhibition of the NLRP3 inflammasome reduces overall AD pathology in the 5XFAD mouse model of AD.

Here, we find BHB levels are lower in red blood cells and brain parenchyma of AD patients when compared with non-AD controls. Furthermore, exogenous BHB administration reduced plaque formation, microgliosis, PYCARD speck formation, and caspase-1 activation in the 5XFAD mouse model of AD. Taken together, our findings demonstrate that BHB reduces AD pathology by inhibiting NLRP3 inflammasome activation. Additionally, our data suggest dietary or pharmacological approaches to increase BHB levels as promising therapeutic strategies for AD.