Fight Aging! Newsletter, May 8th 2023

Do we truly know how old we are biologically, that is, more accurately describing the status of our body than our chronological ages? Are some people at higher risk of certain types of age-related diseases, i.e., cardiovascular disorders or neurodegenerative diseases, and how can they be identified? Or how do we know if any of the claimed geroprotective treatments are effective? To answer these questions, we need to establish biomarkers for aging. In a broad aspect, these biomarkers are defined as scientifically measured parameters of the physiological aging process, to measure age-related changes and to predict the transition into a pathological status.

As a biological measurement to qualify aging, a biomarker must be specific, systemic, and serviceable. (i) Specific: aging is such a heterogeneous process that it proceeds at different rates in different individuals and varies in different organs, even in the same individual. Therefore, it is impossible to have one biomarker for the entire organism but different ones or even different sets of biomarkers for different organs for evaluation; vice versa, each biomarker should be able to capture a unique aging signal of the relevant organ. Moreover, aging biomarkers should be predictive of the risk of disease development, which requires a specific threshold for the transition from physiological aging to pathological disorder. (ii) Systemic: aging involves almost every organ system, comprising many interconnected biological processes. Moreover, changes in one organ may elicit compensatory mechanisms or systemic feedback across the body. Therefore, biomarkers should be able to reflect such systemic changes with age, and a collection of biomarkers from multiple dimensions is required for this aspect. (iii) Serviceable: biomarkers collected through non-invasive or minimally invasive methods are particularly suited for translation into clinical practice. As aging is a gradually deteriorating process over time, longitudinal studies are needed, and again, non-invasive measurements are preferred. In larger cohort studies, cost and convenience should be considered when choosing biomarkers. In all, being specific, systemic, and serviceable are as critical to the broad spectrum of aging biomarkers as the three primary colors.

Over the years, various data types and modeling techniques have been used to develop a broad spectrum of aging biomarkers. Based on the nature of these parameters used for aging biomarkers, the collection of alterations with age can be categorized into 6 classes, or 6 pillars, although biomarkers in different categories are often interconnected with each other. There are higher-order types of changes that reflect physiological and functional changes, such as physiological characteristics, imaging traits, and histological features. Additionally, there are more causal or mechanistic driver types of biomarkers, such as cellular alterations and molecular changes. Finally, there are biomarkers serving in between, such as hormones and secretory factors that are detectable in body fluids, such as blood, urine, saliva, and cerebrospinal fluid (CSF), among which those act in a paracrine manner are of particular interest. The latter three types, as they may also serve as hallmarks or drivers of aging, may be targeted to intervene in the aging process.

Aging biomarkers are critical to answer the three major questions in the field of aging: how old are we? Why do we get old? And how can we age slower? In this comprehensive review, we provided an encyclopedia summary of aging biomarkers covering a hierarchy of dimensions at cellular, organ, organismal, and populational aging levels, along with associated ethical and social implications. We hope this re- view serves as a resource for readers in academia, industry and medical practice, broadening our understanding of not only what biomarkers can be used to monitor aging, but also how to use them to assess novel therapies to slow, modify or even reverse aging. As such, we can accelerate the journey of basic science discoveries in the aging field from bench to bedside.

A growing body of evidence suggests that dysbiosis of the human gut microbiota is associated with neurodegenerative diseases like Alzheimer's disease (AD) via neuroinflammatory processes across the microbiota-gut-brain axis. The gut microbiota affects brain health through the secretion of toxins and short-chain fatty acids, which modulates gut permeability and numerous immune functions. Observational studies indicate that AD patients have reduced microbiome diversity, which could contribute to the pathogenesis of the disease. Uncovering the genetic basis of microbial abundance and its effect on AD could suggest lifestyle changes that may reduce an individual's risk for the disease.

Using the largest genome-wide association study of gut microbiota genera from the MiBioGen consortium, we used polygenic risk score (PRS) analyses and determined the genetic correlation between 119 genera and AD in a discovery sample (ADc12 case/control: 1278/1293). To confirm the results from the discovery sample, we next repeated the PRS analysis in a replication sample (GenADA case/control: 799/778) and then performed a meta-analysis with the PRS results from both samples. Finally, we conducted a linear regression analysis to assess the correlation between the PRSs for the significant genera and the APOE genotypes.

In the discovery sample, 20 gut microbiota genera were initially identified as genetically associated with AD case/control status. Of these 20, three genera (Eubacterium fissicatena as a protective factor, Collinsella, and Veillonella as a risk factor) were independently significant in the replication sample. Meta-analysis with discovery and replication samples confirmed that ten genera had a significant correlation with AD, four of which were significantly associated with the APOE rs429358 risk allele in a direction consistent with their protective/risk designation in AD association. Notably, the proinflammatory genus Collinsella, identified as a risk factor for AD, was positively correlated with the APOE rs429358 risk allele in both samples.

Overall, the host genetic factors influencing the abundance of ten genera are significantly associated with AD, suggesting that these genera may serve as biomarkers and targets for AD treatment and intervention. Our results highlight that proinflammatory gut microbiota might promote AD development through interaction with APOE. Larger datasets and functional studies are required to understand their causal relationships.

Microglia are the resident immune cells of the central nervous system (CNS), a tissue-resident macrophage population with specific characteristics to support the CNS environment and health. Microglia have a mesodermal origin and originate from yolk-sac progenitors during embryogenesis; after their early migration and proliferation, they colonize the CNS and self-renew throughout the lifespan.

Microglia perform a variety of critical functions; (a) they support neurogenesis and ensure correct neuronal circuitry by pruning synapses; (b) phagocytose apoptotic neurons; (c) defend against infectious and non-infectious insults; (d) produce extracellular matrix (ECM) components and control its remodeling by secreting ECM-degrading enzymes; (e) maintain myelin health; (f) and remove extracellular protein aggregates, which accumulate in neurodegenerative diseases. Homeostatic adult microglia have a highly ramified morphology, with extended and arborized processes and a small body. However, when responding to stimulation or during aging and CNS pathology, their morphology changes.

With age, microglia alter their function, morphology and phenotype; however, there are still many gaps in our knowledge of how microglia age. Both rodent and human aging microglia are characterized by alterations in morphology, phagocytosis, metabolism, and inflammatory phenotype, which appear to play protective and detrimental roles in maintaining brain homeostasis and preserving their ability to respond to non-sterile and sterile insults.

Furthermore, more recent evidence indicates that environmental factors, such as meningeal lymphatics health and production of metabolites from the gut microbiome, can affect brain homeostasis by affecting microglia reactivity and phenotype. Recent single cell RNA-seq studies suggest that different subsets of microglia already exist in young adults; however, they expand in aging and even more so in neurodegeneration. Nonetheless, we still do not know the full extent of microglia plasticity and how firm these phenotypes are.

A landmark, long-term, prospective, cohort study evaluated the links between leisure-time physical activity duration and intensity with all-cause mortality and cause-specific mortality. The relationships between dose of exercise and risk of death during follow up were distinctly different for vigorous physical activity (VPA) than for moderate physical activity (MPA). First and foremost, very high levels of MPA reduced risk of cardiovascular disease (CVD) mortality and all-cause mortality substantially better than very high levels of VPA. Secondly, the reductions in CVD mortality and all-cause mortality were maximized at ~150 minutes/week of VPA; doses >150 minutes/week of VPA were associated with a plateau in all-cause mortality, and a modest but progressive loss of CVD mortality reduction at higher doses. In contrast, MPA reduced CVD mortality and all-cause mortality in dose-dependent, inverse relationships - the higher the dose of MPA the lower the number of deaths during the study.

For an individual whose goal is to decrease the risk of CVD and boost life expectancy, a routine of MPA appears to be adequate. Although chronically performing very high doses of VPA may attenuate some of the benefits bestowed by less extreme efforts, this is relevant for only about 2.5% of the US adult population. This is not to say that VPA is harmful; it substantially reduces all-cause mortality and CVD mortality compared to a sedentary lifestyle. Yet, the magnitude of the mortality and CVD risk reductions with high doses of VPA do not appear to be as substantial as for high doses of MPA. Chronically doing very high doses of moderate exercise reduced risks of all-cause mortality and CVD mortality at least two-fold better compared to chronically performing very high doses of vigorous exercise.

At the other extreme, a sedentary lifestyle - which affects about half of the U.S. adult population - is associated with worse health outcomes and diminished life expectancy. After sitting more than 60 minutes, the levels of blood glucose, triglycerides, and inflammatory markers begin to rise. Even light or moderate activity mitigates these adverse effects of sedentary behavior without unduly increasing orthopedic injuries or cardiac risks.

Throughout the last three million years of hominin evolution, our ancestors' existence necessitated a very physically active lifestyle. Adults would usually accumulate 14,000 to 16,000 steps/day, mostly in the form of walking three to eight miles, often while carrying objects such as wood, food, water, and children. Hunter-gatherer humans' daily subsistence required large amounts of MPA with smaller doses of interspersed VPA - this is the activity pattern for which we remain genetically adapted. This evolutionary template would seem to be a logical guide to structuring an ideal activity pattern for promoting optimum health and longevity.

In obesity, adipose tissue (AT) undergoes cellular senescence. This involves activation of adipose tissue macrophages (ATMs), which enhances AT remodeling through proinflammatory and profibrotic signaling. Macrophages play a pivotal role in both the induction and resolution of inflammation that results in cellular dysfunction and AT damage. Notably, increased infiltration of proinflammatory macrophages in AT impairs the secreted adipokine profile and contributes to insulin resistance through a senescence-associated secretory phenotype (SASP). Indeed, ATMs are an important source of chemokines, matrix metalloproteinases, and other profibrotic and inflammatory mediators that collectively constitute the SASP.

Macrophages are also critically involved in AT remodeling because they are key to the clearance of obesity-associated senescent or damaged AT cells. Recent observations suggest that senescence initiates tissue remodeling by recruiting immune cells through SASP to allow clearance and regeneration of the damaged tissue. With persistent damage, as occurs in obesity and aging, however, clearance and regeneration may be compromised by senescence-associated macrophage dysfunction.

Interestingly, we have recently established visceral AT (VAT) as the major source of osteopontin (OPN) during aging. OPN is a matricellular protein involved in intracellular and extracellular signaling mediating cell-to-cell interactions, immune cell function, inflammation, and tissue remodeling. Beyond the reported role of OPN in AT proinflammatory status, we identified OPN as an important SASP component among a variety of growth factors, proinflammatory cytokines/chemokines, and adipokines, with a major role in inducing remote cardiac tissue remodeling by modulating fibroblast function. However, the link among age-related OPN production, VAT senescence, and impairment of ATM function is elusive.

Here we show that during chronological aging ATMs acquire several features of senescent cells, which impair ATM function, and contribute to age-related VAT remodeling and dysfunction, a process mediated by OPN. Our findings highlight OPN inhibition as a potential therapeutic intervention to rejuvenate VAT, thus promoting healthy aging.

Dietary oligosaccharides can impact the gut microbiota and confer tremendous health benefits. The aim of this study was to determine the impact of a novel functional oligosaccharide, neoagarotetraose (NAT), on aging in mice. 8-month-old C57BL/6J mice as the natural aging mice model were orally administered with NAT for 12 months. The preventive effect of NAT in Alzheimer's disease (AD) mice was further evaluated. Aging related indicators, neuropathology, gut microbiota and short-chain fatty acids (SCFAs) in cecal contents were analyzed.

NAT treatment extended the lifespan of these mice by up to 33.3%. Furthermore, these mice showed the improved aging characteristics and decreased injuries in cerebral neurons. Dietary NAT significantly delayed DNA damage in the brain, and inhibited reduction of tight junction protein in the colon. A significant increase at gut bacterial genus level (such as Lactobacillus, Butyricimonas, and Akkermansia) accompanied by increasing concentrations of SCFAs in cecal contents was observed after NAT treatment. Functional profiling of gut microbiota composition indicated that NAT treatment regulated the glucolipid and bile acid-related metabolic pathways. Interestingly, NAT treatment ameliorated cognitive impairment, attenuated amyloid-β (Aβ) and Tau pathology, and regulated the gut microbiota composition and SCFAs receptor-related pathway of Alzheimer's disease (AD) mice.

In conclusion, NAT mitigated age-associated cerebral injury in mice through gut-brain axis. The findings provide novel evidence for the effect of NAT on anti-aging, and highlight the potential application of NAT as an effective intervention against age-related diseases.

Life Biosciences (Life Bio), a biotechnology company advancing cellular rejuvenation technologies to reverse diseases of aging and injury and ultimately restore health for patients, today announced preclinical data in nonhuman primates (NHP) for its novel gene therapy candidate which uses a partial epigenetic reprogramming approach to restore visual function. Life Bio's therapy significantly restored visual function in an NHP model of non-arteritic anterior ischemic optic neuropathy (NAION), a disorder similar to a stroke of the eye that is characterized by painless yet sudden loss of vision.

Life Bio's lead platform reprograms the epigenome of older animals to resemble that of younger animals via expression of three Yamanaka factors, Oct4, Sox2, and Klf4, collectively known as OSK. The approach partially reprograms cells to resemble a more youthful state while retaining their original cellular identity. Previous data have shown that treatment with OSK reverses retinal aging and restores vision in old mice in a mouse model of glaucoma. Now, the company has demonstrated restoration of visual function and increased nerve axon survival in an NHP model that mimics human NAION deficits in retinal ganglion cells.

Maintaining lifelong mobility is one aim of healthy aging that allows independence and autonomy. However, falls and fragility fractures, which tend to occur in clusters toward the end of life, represent common hazards for the mobility of the aging population. This period comes with a substantial loss of quality of life and causes an enormous socioeconomic burden for patients and their families. While there has been tremendous progress in our understanding of osteoporosis due to sex hormone deficiency or medications, insights into how cell-intrinsic mechanisms contribute to the aging process of the skeletal system are still limited.

Over the past decade, emerging bone research has focused on the biology of osteocytes, the least accessible yet most common bone-resident cell type. Osteocytes are specialized bone cells that orchestrate skeletal remodeling. Senescent osteocytes are characterized by an activation of cyclin-dependent kinase inhibitor p16Ink4a and have been implicated in the pathogenesis of several bone loss disorders.

Researchers have now shown that systemic removal of senescent cells (termed senolysis) prevented age-related bone loss at the spine and femur and mitigated bone marrow adiposity through a robust effect on osteoblasts and osteoclasts, whereas cell-specific senolysis in osteocytes alone was only partially effective. Surprisingly, transplantation of senescent fibroblasts into the peritoneum of young mice caused host osteocyte senescence associated with bone loss. This refined concept of osteocyte senescence and the effects of remote senolysis may help to develop improved senolytic strategies against multisystem aging in bone and beyond.

Subjective age describes how old people feel, in comparison with how old they actually are chronologically. It is usually assessed with a single-item question (such as "How old do you feel?"). Evidence from nearly 300 studies using this item has shown that most middle-age and older people feel younger than they are, including very old individuals. This phenomenon has been labeled subjective age bias and might reflect an age-group dissociation process ("They are old, but I feel younger") that helps individuals cope with ageism.

Little is known about historical shifts in subjective age. Moving beyond the very few time-lagged cross-sectional cohort comparisons, we examined historical shifts in within-person trajectories of subjective age from midlife to advanced old age. We used cohort-comparative longitudinal data from middle-age and older adults in the German Ageing Survey (N = 14,928; ~50% female) who lived in Germany and were between 40 and 85 years old when entering the study. They provided up to seven observations over 24 years.

Results revealed that being born later in historical time is associated with feeling younger by 2% every birth-year decade and with less intraindividual change toward an older subjective age. Women reported feeling younger than men; this gender gap widened across cohorts. The association of higher education with younger subjective age became weaker across cohorts. This historical trend of feeling younger was observable across all ages in the second half of life, also - contrary to our expectations - in very old age.

In this study, we tested associations of blood-chemistry measures of biological aging with prevalent and incident depression and anxiety among a half-million midlife and older adults in the UK Biobank. The main findings were that adults with more advanced biological age were more likely to experience depression and anxiety at baseline and were at higher risk of depression/anxiety over eight years of follow-up, as compared with peers who were the same chronological age, but who were tested to be biologically younger.

The risk associated with biological age was independent of and additive to genetic risk. The risk was also independent of self-reported history of childhood adversity. This study contributes evidence from a large biobank cohort to support the hypothesis that biological aging might represent a risk factor for depression/anxiety in midlife and older adults.

There is accumulating evidence for a link between mental health problems and biological aging. However, most studies have focused on poor mental health as a risk factor for accelerated aging. The reverse process may also occur. For example, white matter hyperintensities, neuroimaging signatures of small cerebral infarcts, are associated with aging and with the risk of depression, and recently have been linked to measurements of biological aging. The same is true of low-grade systemic inflammation and mitochondrial dysfunction.

Physical fitness is a well-known correlate of health and the aging process and DNA methylation (DNAm) data can capture aging via epigenetic clocks. However, current epigenetic clocks did not yet use measures of mobility, strength, lung, or endurance fitness in their construction. We develop blood-based DNAm biomarkers for fitness parameters gait speed (walking speed), maximum handgrip strength, forced expiratory volume in one second (FEV1), and maximal oxygen uptake (VO2max) which have modest correlation with fitness parameters in five large-scale validation datasets.

We then use these DNAm fitness parameter biomarkers with DNAmGrimAge, a DNAm mortality risk estimate, to construct DNAmFitAge, a new biological age indicator that incorporates physical fitness. DNAmFitAge is associated with low-intermediate physical activity levels across validation datasets, and younger/fitter DNAmFitAge corresponds to stronger DNAm fitness parameters in both males and females. DNAmFitAge is lower and DNAmVO2max is higher in male body builders compared to controls.

Physically fit people have a younger DNAmFitAge and experience better age-related outcomes: lower mortality risk, coronary heart disease risk, and increased disease-free status. These new DNAm biomarkers provide researchers a new method to incorporate physical fitness into epigenetic clocks.

The Phaedon Institute was envisioned by a group of distinguished scientists and entrepreneurs to promote a greater degree of synergy, efficient cooperation, and discussion among longevity industry stakeholders that could set rigorous standards and guidance to support the growing community of the emerging field of longevity sciences. The Phaedon Institute is aimed to distill solid and sound science, support the leaders and talents, recognize the proper regulatory environment and investment opportunities, and transform the aging and longevity industry.

In the past 100 years, we have achieved groundbreaking milestones in disease diagnosis and treatment and extended a healthy life span. A step change in life expectancy will have vast implications for individuals, governments, and society. To ensure that increases in longevity benefit all, a collaborative approach among different stakeholders is required to drive change and create solutions to equip us for this new reality.

The Phaedon Summit is a platform to offer space to the key opinion leaders in the science and therapeutic development to support the growing community of the emerging field of longevity sciences. Phaedon Institute is pleased to introduce the inaugural Seno-Therapeutics Summit 2023 to be held in November 2023 at the beautiful Buck Institute For Research On Aging, Novato, California.

Blood vessels are key conduits for the transport of blood and circulating factors. Abnormalities in blood vessels promote cardiovascular disease (CVD), which has become the most common disease as human lifespans extend. Aging itself is not pathogenic; however, the decline of physiological and biological function owing to aging has been linked to CVD. Although aging is a complex phenomenon that has not been comprehensively investigated, there is accumulating evidence that cellular senescence aggravates various pathological changes associated with aging.

Emerging evidence shows that approaches that suppress or eliminate cellular senescence can preserve vascular function in aging-related CVD. However, most pharmacological therapies for treating age-related CVD are inefficient. Therefore, effective approaches to treat CVD are urgently required. The benefits of exercise for the cardiovascular system have been well documented in basic research and clinical studies; however, the mechanisms and optimal frequency of exercise for promoting cardiovascular health remain unknown.

Accordingly, in this review, we have discussed the changes in senescent endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) that occur in the progress of CVD and the roles of physical activity in CVD prevention and treatment.

Aging is associated with a decline in the regenerative potential of stem cells. In recent years, several clinical trials have been launched in order to evaluate the efficacy of mesenchymal stem cell interventions to slow or reverse normal aging processes (aging conditions).

Information concerning those clinical trials was extracted from national and international databases (United States, EU, China, Japan, and World Health Organization). Mesenchymal stem cell preparations were in development for two main aging conditions: physical frailty and facial skin aging. With regard to physical frailty, positive results have been obtained in phase II studies with intravenous Lomecel-B (an allogeneic bone marrow stem cell preparation), and a phase I/II study with an allogeneic preparation of umbilical cord-derived stem cells was recently completed. With regard to facial skin aging, positive results have been obtained with an autologous preparation of adipose-derived stem cells.

A further sixteen clinical trials for physical frailty and facial skin aging are currently underway. Reducing physical frailty with intravenous mesenchymal stem cell administration can increase healthy life expectancy and decrease costs to the public health system. However, intravenous administration runs the risk of entrapment of the stem cells in the lungs (and could raise safety concerns). In addition to aesthetic purposes, clinical research on facial skin aging allows direct evaluation of tissue regeneration using sophisticated and precise methods. Therefore, research on both conditions is complementary, which facilitates a global vision.

Protein homeostasis, the balance between protein synthesis and degradation, requires the clearance of misfolded and aggregated proteins and is therefore considered to be an essential aspect of establishing a physiologically effective proteome. Aging alters this balance, termed "proteostasis", resulting in the progressive accumulation of misfolded and aggregated proteins. Defective proteostasis leads to the functional deterioration of diverse regulatory processes during aging and is implicated in the etiology of multiple pathological conditions underlying a variety of neurodegenerative diseases and in age-dependent cardiovascular disease.

Detergent-insoluble protein aggregates have been reported by us in both aged and hypertensive hearts. The protein constituents were found to overlap with protein aggregates seen in neurodegenerative diseases such as Alzheimer's disease. Therefore, targeting these protein components of aggregates may be a promising therapeutic strategy for cardiovascular pathologies associated with aging, ischemia, and/or hypertension.