Fight Aging! Newsletter, June 7th 2021

Aging induces broad gene expression changes across diverse mammalian cell types, and these changes have been linked to many of the prominent hallmarks of aging. Cell reprogramming experiments have shown that young animals can develop from adult cells and aging features can be erased through complete reprogramming to pluripotency. Recent reports have further suggested that transient expression of the Yamanaka factors (SOKM) is sufficient to reverse features of aging and improve cell function. However, it was unclear whether these transient reprogramming interventions suppress somatic cell identities, activate late-stage pluripotency programs, or whether alternative reprogramming strategies could restore youthful gene expression.

Here, we investigated these questions using single cell measurements of gene expression to capture the phenotypic trajectory of transient reprogramming and evaluate the impact of alternative reprogramming methods. We found that transient reprogramming suppressed somatic cell identities and upregulated hallmark pluripotency programs, contrary to some previous reports but consistent with timecourse iPSC reprogramming experiments and lineage-tracing studies of transient SOKM expression. By inferring RNA velocity and applying numerical tools from dynamical systems, we also found that transiently reprogrammed cells transition back toward their original gene expression states after transit through an intermediate state. Our single cell profiles therefore revealed transient cell states that were likely masked in previous bulk measurements and support a model in which transient reprogramming suppresses somatic identities that are later reacquired through differentiation. Further experiments profiling single cell populations at multiple time-points during transient reprogramming will be necessary to confirm this hypothesis.

It remains unknown which of the Yamanaka Factors are required to restore youthful gene expression, or which subsets might exhibit distinct effects during transient reprogramming. Previous studies have explored only one set of factors at a time, preventing accurate comparisons to address these questions. Our pooled screens of all possible Yamanaka Factor subsets revealed that combinations of 3-4 Yamanaka Factors have remarkably similar effects, suggesting no single factor is required to restore youthful gene expression. Combinations of two Yamanaka Factors were also more similar to the full SOKM set than to control or single factor perturbations, and all reprogramming factor combinations reduced an aging gene expression score. Our screen demonstrates that no single pluripotency factor is required to mask features of aging and suggest oncogene-free reprogramming strategies may also restore youthful gene expression. Our multipotent reprogramming experiments in myogenic cells further support this suggestion, indicating that youthful gene expression may be restored even without activating the pluripotency factors.

Restoring youthful gene expression can improve tissue function, implying that transient reprogramming may be therapeutic. However, pluripotent reprogramming is well-known to be an oncogenic process, even when Myc is excluded from the reprogramming set. While it has been reported that transient reprogramming does not suppress somatic cell identities based on bulk measurements, our single cell results show that somatic cell identity is suppressed and late-stage pluripotency GRNs are activated in a transitional cell state in multiple cell types. This raises the possibility that even transient reprogramming may be oncogenic. Identifying alternative reprogramming strategies to restore youthful gene expression with lower neoplastic risk is therefore desirable. Toward this aim, we have shown that transient reprogramming with multiple subsets of the Yamanaka Factors induces highly similar transcriptional effects to the full set, and that a distinct multipotent reprogramming system can confer youthful expression. These results suggest the feasibility of disentangling the rejuvenative and pluripotency inducing effects of transient reprogramming and serve as a resource for further interrogation of transient reprogramming effects in aged cells.

Children with progeria have a mutation in the relevant gene; instead of producing lamin A, they produce a defective mutant protein called progerin. The cell tries to build the nuclear lamina out of defective progerin instead of normal lamin A, and as a result the cell nucleus is screwed up and can't maintain a normal shape. So then aging happens? My sources don't seem to have a great explanation of this. The UniProt database says that this "acts to deregulate mitosis and DNA damage signaling, leading to premature cell death and senescence". This paper goes a little further, saying that the screwiness in the nuclear lamina prevents DNA repair proteins from doing their job.

So a unified theory of progeria goes: the lamin mutation causes accumulation of defective protein in the nucleus, preventing DNA repair. This makes people accumulate DNA damage faster, and since DNA damage is a major cause of aging, it makes these people age more quickly. Lornafarnib interferes with the production of the defective progerin protein. All of this suggests lornafarnib shouldn't help prevent normal aging. After all, normal aging is caused by lots of processes including gradual expected accumulation of DNA damage - not just the downstream effects of one weird mutant protein.

...except that in doing this research I kept finding people saying that maybe some of aging is caused by this one weird mutant protein. I don't really get what's going on here. I know that often, as age-related damage degrades DNA, a lot of weird malformed proteins pop up and accumulate. Maybe progerin is one of these proteins and causes some of the problems commonly associated with aging?

At first glance, longevity and immunity appear to be different traits that have not much in common except the fact that the immune system promotes survival upon pathogenic infection. Substantial evidence however points to a molecularly intertwined relationship between the immune system and ageing. Although this link is well-known throughout the animal kingdom, its genetic basis is complex and still poorly understood.

In this review, we combined curation and analysis of orthologs between D. melanogaster, C. elegans, mice, and humans to reveal that genes currently known to be pleiotropically involved in immunity, lifespan, and ageing reside in a few core pathways mediating the immuno-ageing interplay. We identified 7 evolutionarily conserved signalling cascades, the insulin/TOR network, three MAPK (ERK, p38, JNK), JAK/STAT, TGF-β, and Nf-κB pathways that act pleiotropically on ageing and immunity. However, we highlight that these pathways not only cross-talk, but also clearly act pleiotropically to regulate pathogen resistance, lifespan, and ageing among many other physiological processes such as metabolism and stress resistance.

Our review demonstrates that loss of immune homeostasis is a central determinant of ageing across diverse phyla. Yet, whether immunosenescence and the age-associated decline in other traits is a cause or result of ageing remains a fundamental problem difficult to resolve. Knowing the exact time and place of changes related to immunity and ageing would be a huge step in answering this question. Moreover, how environmental effects, including life-long pathogenic challenges, variation in the microbiome, or nutrition affect age-related changes in immunity is poorly understood. To date most studies are restricted in resolution, particularly in terms of analysed tissues, time points, phenotypes, and experimental conditions. Cutting-edge technologies such as single-cell sequencing can be useful in that respect and could be utilized to characterize molecular changes during ageing and infection in specific cell types. In combination with genome-wide CRISPR knockout screens, new immuno-ageing genes can be discovered and the cross-talk between immunity and ageing further deciphered.

Currently, the level of detail needed to solve the causality enigma of ageing is likely not achievable in humans but may be addressed in shorter lived model organisms that are easier to manipulate. Once we understood ageing at this unprecedented level, it will be possible to optimize lifestyle factors and emerging drug therapies treating senescence to facilitate healthy ageing and extend lifespan.

Reprogramming of somatic cells to a pluripotent state by overexpressing the Yamanaka factors (Oct-3/4, Sox2, Klf4, and c-Myc [OSKM]) is a long and complex process. Cellular reprogramming is widely utilized for disease modeling in vitro. However, reprogramming in vivo induces tumor development. Our lab showed that partial reprogramming by short-term expression of reprogramming factors ameliorated aging hallmarks without tumor formation, opening a possible application of this approach in vivo. Recently, other reports have demonstrated rejuvenation of dentate gyrus cells, retinal ganglion cells, chondrocytes, and muscle stem cells using reprogramming factors, reinforcing its potential application in clinical settings. Besides amelioration of cellular aging hallmarks, reprogramming factors promote tissue regeneration in aged mice. However, it is unknown whether OSKM-improved regeneration is solely a result of its rejuvenating effect.

Muscle regeneration is primarily mediated by muscle stem cells, also known as satellite cells (SCs), which reside in a characteristic niche located between the basal lamina and plasma membrane of myofibers. The regenerative capacity of SCs is influenced by both intrinsic modulators and the extrinsic microenvironment. We have shown that partial reprogramming promotes skeletal muscle regeneration in 12-month-old mice, but these studies were performed by expressing OSKM systemically (i.e., in all cell types). It is therefore unclear whether intrinsic or niche-specific factors contributed to the observed improvement in muscle regeneration.

In this work, we generate myofiber- and SC-specific OSKM induction mouse models to investigate the effect of OSKM induction on extrinsic and intrinsic modulators of SCs, respectively. In addition, we chose young mice to investigate whether the improvement of regeneration can be achieved by OSKM induction regardless of its rejuvenating effect. Our data shows that myofiber-specific OSKM induction accelerates muscle regeneration through downregulating the myofiber-secreted niche factor, Wnt4, to induce the activation and proliferation of SCs. In contrast, SC-specific OSKM induction does not improve muscle regeneration in young mice. We conclude that partial reprogramming via OSKM can remodel the SC niche to induce SC activation and proliferation and accelerate muscle regeneration.

The CD4/CD8 T-cell ratio is emerging as a relevant marker of evolution for different pathologies and therapies, including cardiovascular diseases. Immune alterations related to cellular immunosenescence, together with persistent inflammation, are known to be involved in the process of deleterious aging, which underlies the failure to maintain global health status during aging. The CD4/CD8 ratio might be related to cellular immunosenescence, and potential factors affecting the CD4/CD8 ratio in older people have been extensively studied.

Cytomegalovirus infection has been widely reported as the main cause of CD8 T-cell oligoclonal expansion. Additionally, free radicals, which accumulate during aging, may have an impact because subjects with an inverted CD4/CD8 ratio exhibit reduced levels of antioxidant defenses and higher oxidative stress. Hence, factors associated with cumulative cellular senescence and oxidative stress appear to trigger a reduction in the CD4/CD8 ratio; however, the immunological features beyond CD4/CD8 T-cell ratio values require further exploration.

It is reasonable that CD4/CD8 T-cell ratio values, particularly in older people, might reflect different degrees of immune capabilities both for responding to antigens and for preserving health status in this population. Although thymic output is the main regulator of T-cell homeostasis, whether it relates to the CD4/CD8 T-cell ratio in older individuals has not yet been explored. Notably, the thymus undergoes progressive atrophy throughout life, reducing its activity by approximately 3% per year until middle age, when it slows down to less than 1% per year.

Nevertheless, the thymus remains active in adults, contributing to the renewal of the pool of naïve T-cells, even though thymic function is highly variable in older people. In fact, intrathymic CD4+CD8+ double-positive T cells obtained from thymic biopsies correlate not only with age (negative) but also with the frequency of naïve T cells (positive). Interestingly, a relationship between thymic function and the CD4/CD8 T-cell ratio exists in HIV infection, which is a different scenario but shares several immunosenescence traits with aging. On the other hand, it is also reasonable that CD4/CD8 T-cell ratio values might correlate with different inflammatory profiles. To better understand the biological meaning of the CD4/CD8 ratio in the elderly, we explored the phenotypic profiles of both CD4 and CD8 T-cells, as well as the thymic output and several inflammation-related parameters, in a population of older subjects classified according to CD4/CD8 ratio value.

The lower CD4/CD8 ratio group showed a lower thymic output and frequency of naïve T-cells, concomitant with increased mature T-cells. In these subjects, the CD4 T-cell subset was enriched in CD95+ but depleted of CD98+ cells. The regulatory T-cell (Treg) compartment was enriched in CTLA-4+ cells. The CD8 T-cell pool exhibited increased frequencies of CD95+ cells but decreased frequencies of integrin-β7+ cells. Interestingly, in the intermediate CD4/CD8 ratio group, the CD4 pool showed greater differences than the CD8 pool, mostly for cellular senescence.

Regarding inflammation, only high sensitivity CRP was elevated in the lower CD4/CD8 ratio group; however, negative correlations between the CD4/CD8 ratio and β2-microglobulin and soluble CD163 were detected. These subjects displayed trends of more comorbidities and less independence in daily activities. Altogether, our data reveal that different thymic output and immune profiles for T-cells across CD4/CD8 ratio values that can define immune capabilities, affecting health status in older individuals. Thus, the CD4/CD8 ratio may be used as an integrative marker of biological age.

Organ transplantation is the treatment of choice for end-stage-organ failure. The supply of organs, however, is limited, resulting in prolonged waiting times with many patients dying or becoming too ill to be transplanted. Aging demographics have incrementally affected the population of deceased donors, with older donors showing the by far largest proportional increase. Organs from older donors are, at the same time, underutilized, frequently discarded or not even considered.

The most obvious strategy that may close the gap between demand and supply may thus be an optimized utilization of older organs from deceased donors. Increased donor age, at the same time poses a significant risk for adverse outcomes including more frequent rejections due to an augmented immunogenicity in aging. Most relevantly, older organs have shown compromised long-term graft outcomes with inferior graft survival rates in addition to increased rates of chronic allograft dysfunction in kidney, heart, and lung transplantation.

Senescent cells accumulate with aging and have been identified as critical in driving the immunogenicity of older organs linked to the accumulation of cell-free mitochondrial DNA that accelerate alloimmune responses. Recent evidence also suggests that senescent cells can induce a senescent phenotype in adjacent cells, a potential mechanism on how the engraftment of older organs may facilitate the spread of senescence. Depletion of senescent cells, at the same time, has been shown to ameliorate a wide range of age-associated disabilities and diseases.

Characteristically, senescent cells secrete a myriad of pro-inflammatory, soluble molecules as part of their distinct secretory phenotype that have been shown to drive senescence and age-related co-morbidities. Preliminary data show that the transplantation of old organs limits the physical reserve of recipient animals. Here, we introduce potential mechanisms and consequences of prompting bystander senescence and discuss clinically relevant aspects of senescent cell spread when transplanting older organs. Although speculative, age-disparate transplantation may also provide unique opportunities as the transplantation of young organs may contribute to rejuvenation.

The exact mechanisms underlying Alzheimer's disease (AD) remain unclear despite comprehensive attempts to understand its pathophysiology. The most prominent theory postulates that, in AD, tau and amyloid-β negatively affect neuronal cells by compromising energy supply and the antioxidant response, causing mitochondrial and synaptic dysfunction. Neuronal activity is highly energy-dependent, and neurons are particularly sensitive to disruption in mitochondrial function. In addition, mitochondria produce cellular energy (adenosine triphosphate; ATP) and are also involved in many processes that are important for the life and death of the cell, including the control of second messenger levels, such as calcium ions (Ca2+) and reactive oxygen species (ROS).

Importantly, mitochondrial dysfunction contributes to reduced ATP production, Ca2+ dyshomeostasis, and ROS generation. Alterations in mitochondrial dynamics and mitophagy occur in early-stage AD, but the underlying mechanisms are poorly understood. Thus, studies elucidating the mechanisms of mitochondrial abnormalities in AD will facilitate a greater understanding of the pathogenesis of this neurodegenerative disease and potentially contribute to the advancement of therapeutic strategies to protect synaptic activity and subsequent cognitive function. Here, we review studies that suggest a role of mitochondrial dysfunction and the consequent ROS production in AD pathology and provide a context to explain current and future therapeutic approaches. We suggest that improving mitochondrial function should be considered an important therapeutic intervention against AD.

Optogenetics may enable mutation-independent, circuit-specific restoration of neuronal function in neurological diseases. Retinitis pigmentosa is a neurodegenerative eye disease where loss of photoreceptors can lead to complete blindness. In a blind patient, we combined intraocular injection of an adeno-associated viral vector encoding the channelrhodopsin ChrimsonR with light stimulation via engineered goggles. The goggles detect local changes in light intensity and project corresponding light pulses onto the retina in real time to activate optogenetically transduced retinal ganglion cells.

The patient perceived, located, counted and touched different objects using the vector-treated eye alone while wearing the goggles. During visual perception, multichannel electroencephalographic recordings revealed object-related activity above the visual cortex. The patient could not visually detect any objects before injection with or without the goggles or after injection without the goggles. This is the first reported case of partial functional recovery in a neurodegenerative disease after optogenetic therapy.

Daily calorie restriction (CR) and intermittent fasting (IF) enhance longevity and cognition. Despite the positive effects of CR and IF in neurodegenerative and affective conditions, the specific behavioral contributions and mechanisms that differentiate both interventions remain largely unknown. Answering these questions is pivotal to adapting these regimens to human populations, given the challenges of adhering to a long-term CR regimen when compared to the improved adherence to variations of the IF paradigm.

Here, we directly compared the effects of IF to a matched 10% daily CR regimen upon learning and memory in mice. A 10% energy restriction protocol was chosen for the CR group following the observation that IF mice overall consume 10% less calories on a weekly basis. IF improved long-term retention memory to a greater extent than CR and was associated with increased adult hippocampal neurogenesis and upregulation of the longevity gene Klotho. Though klotho protein is produced primarily in the kidney, it is also highly expressed in some brain areas, including the dentate gyrus of the hippocampus and in particular by its mature neurons.

The function of klotho in the brain is still largely unknown but it has been proposed that it plays an important role in cognition because increased serum levels of klotho were associated with increased cognitive ability in humans and rodents. Here, we confirm previous evidence suggesting that Kl is an important regulator of adult hippocampal neurogenesis and propose it as a novel molecular player through which IF may enhance cognitive performance.

Most important factors that are strongly associated with age are also known as the hallmarks of aging and may be, at least in principle, modified pharmacologically. In addition to that, the dynamic properties such as physiological resilience measured as the recovery rate from the organism state perturbations were also associated with mortality and thus may serve as an early warning sign of impending health outcomes.

We conducted a systematic investigation of aging, organism state fluctuations, and gradual loss of resilience in a dataset involving multiple Complete Blood Counts (CBC) measured over short periods of time (a few months) from the same person along the individual aging trajectory. Instead of focusing on individual factors, to simplify the matters, we followed and described the organism state by means of a single variable, henceforth referred to as the dynamic organism state indicator (DOSI) in the form of the all-cause mortality model predictor. First, we observed that early in life the DOSI dynamics quantitatively follows the universal ontogenetic growth trajectory. Once the growth phase is completed, the indicator demonstrated all the expected biological age properties, such as association with age, multiple morbidity, unhealthy lifestyles, mortality and future incidence of chronic diseases.

Late in life, the dynamics of the organism state captured by DOSI along the individual aging trajectories is consistent with that of a stochastic process (random walk) on top of the slow aging drift. The increase in the DOSI variability is approximately linear with age and can be explained by the rise of the organism state recovery time. The latter is thus an independent biomarker of aging and a characteristic of resilience. Our analysis shows that the auto-correlation time of DOSI fluctuations grows (and hence the recovery rate decreases) with age from about 2 weeks to over 8 weeks for cohorts aging from 40 to 90 years. The divergence of the recovery time at advanced ages appeared to be an organism-level phenomenon.

We put forward arguments suggesting that such behavior is typical for complex systems near a bifurcation (disintegration) point and thus the progressive loss of resilience with age may be a dynamic origin of the Gompertz law of mortality. Finally, we noted, by extrapolation, that the recovery time would diverge and hence the resilience would be ultimately lost at the critical point at the age in the range of 120-150 years, thus indicating the absolute limit of human lifespan, absent novel interventions.

The ability of the kidney to regenerate successfully after injury is lost with advancing age, chronic kidney disease, and after irradiation. The factors responsible for this reduced regenerative capacity remain incompletely understood, with increasing interest in a potential role for cellular senescence in determining outcomes after injury. Here, we demonstrated correlations between senescent cell load and functional loss in human aging and chronic kidney diseases including radiation nephropathy.

We dissected the causative role of senescence in the augmented fibrosis occurring after injury in aged and irradiated murine kidneys. In vitro studies on human proximal tubular epithelial cells and in vivo mouse studies demonstrated that senescent renal epithelial cells produced multiple components of the senescence-associated secretory phenotype that include transforming growth factor β1, induced fibrosis, and inhibited tubular proliferative capacity after injury.

Treatment of aged and irradiated mice with the senolytic drug ABT-263 reduced senescent cell numbers and restored a regenerative phenotype in the kidneys with increased tubular proliferation, improved function, and reduced fibrosis after subsequent ischemia-reperfusion injury. Senescent cells are key determinants of renal regenerative capacity in mice and represent emerging treatment targets to protect aging and vulnerable kidneys in man.

Oisín Biotechnologies, a privately held, preclinical biotechnology company focused on mitigating the effects of age-related diseases, today announced it has completed an oversubscribed round raising 5 million in new seed funding. Led by early-stage investing firm Althea Group, LLC, the round brings Oisín's total funding to 9.5 million. Oisín will use the proceeds to advance its preclinical pipeline, including its most advanced investigational therapy aimed at chronic kidney disease (CKD).

"The support for Oisín's novel approach to slowing or halting age-related diseases has been strong. Chronic kidney disease (CKD), our initial therapeutic focus, has seen little in the way of therapeutic advances over the past several decades. We believe Oisín is well positioned to address this unmet medical need and will continue to explore other applications in tandem."

Oisín's highly precise, DNA-based interventions are designed to clear senescent cells, which can trigger aging pathologies and shorten lifespan, from the body. Its proprietary technology is a third-wave innovation that uses a novel proteo-lipid vehicle drug delivery platform to induce a senescent cell to trigger apoptosis without harming surrounding healthy cells. In preclinical studies, Oisín's investigational therapeutics have significantly reduced senescent cell burden in naturally aged mice and extended lifespan by more than 20%, even when the treatment was started in old age.

Oisín expects the first readouts from its preclinical study in CKD later this year. The initial data will inform its next series of studies and eventually, its first proposed clinical trial design. While using this latest funding to accelerate its CKD work, the company is continuing to progress other planned studies in its preclinical program, advance additional pipeline indications and move towards a regulatory filing to begin its first clinical trial.

Although people in industrialized nations have access to modern medical care, they are more sedentary and eat a diet high in saturated fats. In contrast, the Tsimane have little or no access to health care but are extremely physically active and consume a high-fiber diet that includes vegetables, fish and lean meat. "The Tsimane have provided us with an amazing natural experiment on the potentially detrimental effects of modern lifestyles on our health."

The researchers enrolled 746 Tsimane adults, ages 40 to 94, in their study. To acquire brain scans, they provided transportation for the participants from their remote villages to Trinidad, Bolivia, the closest town with CT scanning equipment. That journey could last as long as two full days with travel by river and road. The team used the scans to calculate brain volumes and then examined their association with age for Tsimane. Next, they compared these results to those in three industrialized populations in the U.S. and Europe.

The scientists found that the difference in brain volumes between middle age and old age is 70% smaller in Tsimane than in Western populations. This suggests that the Tsimane's brains likely experience far less brain atrophy than Westerners as they age; atrophy is correlated with risk of cognitive impairment, functional decline, and dementia. The researchers note that the Tsimane have high levels of inflammation, which is typically associated with brain atrophy in Westerners. But their study suggests that high inflammation does not have a pronounced effect upon Tsimane brains.

According to the study authors, the Tsimane's low cardiovascular risks may outweigh their infection-driven inflammatory risk, raising new questions about the causes of dementia. One possible reason is that, in Westerners, inflammation is associated with obesity and metabolic causes. In the Tsimane, however, it is driven by respiratory, gastrointestinal, and parasitic infections. Infectious diseases are the most prominent cause of death among the Tsimane.

Of the seven mammalian sirtuins, SIRT1-7, SIRT1, and SIRT6 protein levels increase upon dietary restriction and fasting in various mouse tissues and human cell lines. Interestingly, whole-body SIRT1 overexpression in mice leads to improvement in parameters reflecting healthspan, but not lifespan. Whereas whole-brain-specific SIRT1 overexpression did not affect lifespan and brain plasticity, hypothalamic SIRT1 overexpression delays aging. However, whole-body SIRT6 overexpression in mice background leads to a significant extension of male lifespan and healthspan, associated with inhibition of IGF-1 signaling.

Here, we show that overexpression of SIRT6, but not SIRT1, extends lifespan in C57BL/6JOlaHsd mice in both sexes. SIRT1 does not synergize with SIRT6 to further increase median or maximal survival. Overexpression of SIRT6 reduced the age-related metabolic decline in energy metabolism pathways and inhibited frailty by preserving hepatic NAD+ levels, gluconeogenesis capacity, and maintenance of normoglycemia, key markers of healthy aging. These results emphasize the potential of targeting SIRT6 for maintaining energy metabolism and reducing age-related frailty.

Exercise is a lifestyle intervention with known antiaging effects capable of counteracting several of the hallmarks of aging including senescence and age-associated inflammation. We propose that 5' adenosine monophosphate-activated protein kinase (AMPK) can orchestrate many of the antiaging effects of exercise through its regulation of diverse cellular pathways in the setting of energetic stress.

Activating AMPK is sufficient to extend lifespan in many organisms. It is naturally activated in response to muscle contraction and nutrient depletion, both of which are components of exercise. Whereas most of the studies supporting AMPK as an antiaging strategy are based in animal models, the use of metformin (an AMPK activator) in clinical trials (TAME) as an antiaging drug is based on its capacity to delay heart disease, cancer, cognitive decline, and death in people with diabetes. These results suggest that the antiaging effects of AMPK are also relevant in humans, but the molecular mechanisms underlying these effects remain to be determined.

A landmark 21-year longitudinal study that followed runners and compared them with a sedentary group, found that those who exercise had a significantly lower risk of dying (15%) during that time frame than the sedentary group (34%) while also having reduced disabilities. It is unclear whether the beneficial effects of exercise in this study were due to a delay in secondary aging or to countering of the effects of sedentarism. Regardless of this limitation, numerous studies have shown that maintaining a minimum quantity and quality of exercise improves cardiorespiratory fitness and muscle function, flexibility, and balance.

Current guidelines recommend a minimum of 150 min/week of moderate intensity aerobic activity for maximum longevity benefits, with higher duration and intensity increasing cardiovascular and metabolic effects. It has been estimated that performing three to five times the recommended physical activity (450-750 min/week) reaches the maximal healthspan benefit that can be achieved with endurance exercise. Strength training should be added to minimize loss of muscle mass that is characteristic of aging and disease.

In summary, exercise is an effective strategy to prevent aging and enhance longevity and health span both on a clinical and a cellular level due to its capacity to modulate all nine hallmarks of aging. Additionally muscle, one of the main systemic effectors of exercise, is recognized as an endocrine organ that produces and releases myokines, implying a complex cross talk between muscles and other tissues. The AMPK pathway, a well-known mediator of exercise effects in muscle could be activated in different tissues and drive many of the health-promoting and lifespan-extending capabilities of exercise. We propose that it is a central effector node able to impact the hallmarks of aging and integrate the effects of exercise on many tissues.