Fight Aging! Newsletter, November 11th 2024

The aging vasculature is associated with endothelial dysfunction, arterial stiffness, increased oxidative stress and chronic inflammation, contributory to higher risks of cardiovascular diseases, such as heart failure and coronary artery disease. 'Dysbiosis' is considered as a new integrative hallmark of aging. During aging, the microbial composition in intestine varies that the homeostatic relationship between the host and gut microbiome deteriorates, contributory to altered immune and inflammatory responses in the elderly. Age-associated dysbiosis also increases the risks of various diseases, particularly cancers, cardiovascular diseases (CVDs), and diabetes, potentially through shift in intestinal microbial composition from providing benefits to causing chronic inflammation, and through alterations in the production of gut-derived substances to influence host nutrient-sensing pathways. However, the comprehensive mechanism of how age-related dysbiosis promotes other recognized hallmarks of aging remains elusive.

Of note, the vasculature serves as the first-line barrier vulnerable to the changes in gut microbiome due to close proximity between the intestine and blood circulation. Besides, the increased intestinal permeability, known as 'leaky gut', during aging further aggravates the vulnerability of vasculature towards dysbiosis. However, whether age-associated dysbiosis promotes host premature aging remains unclear. Previous studies showed that gut microbiome suppression by antibiotics ameliorates endothelial dysfunction in aged mice, and age-associated hyperproduction of harmful gut-derived metabolite (e.g., trimethylamine-N-oxide) drives endothelial dysfunction. It is therefore reasonable to hypothesize that age-associated dysbiosis shall promote vascular aging by triggering aging hallmarks in the vasculature, such as telomere attrition, endothelial dysfunction, and vascular inflammation and oxidative stress.

In this study, we performed fecal microbiome transfer (FMT) from aged to young mice to (i) study whether age-associated dysbiosis causes premature vascular and intestinal dysfunction; (ii) unveil whether such transfer changes the metabolic profiles; (iii) uncover microbiome alterations and underlying mechanism that are potentially critical; and (iv) identify potential interventions that might partially reverse age-related harmful effects. We demonstrated that age-associated dysbiosis, achieved by aged-to-young FMT, caused endothelial dysfunction, telomere dysfunction, inflammation, and oxidative stress in vascular tissues, partially reflective of premature vascular aging. Moreover, aged-to-young FMT also caused metabolic impairment and altered gut microbial profiles in young mice, along with disrupted intestinal integrity. Interestingly, aged-to-young FMT caused telomere dysfunction in both intestinal and aortic tissues. These findings highlight the harmful effects of aged microbiome on intestine and vasculature, providing important insight that gut-vascular connection represents a potential intervention target against age-related cardiometabolic complications.

Accumulation of senescent cells drives aging and age-related diseases. Senolytics, which selectively kill senescent cells, offer a promising approach for treating many age-related diseases. Using a senescent cell-based phenotypic drug discovery approach that combines drug screening and drug design, we developed two novel flavonoid senolytics, SR29384 and SR31133, derived from the senolytic fisetin. These compounds demonstrated enhanced senolytic activities, effectively eliminating multiple senescent cell types, reducing tissue senescence in vivo, and extending healthspan in a mouse model of accelerated aging.

Mechanistic studies utilizing RNA-Seq, machine learning, network pharmacology, and computational simulation suggest that these novel flavonoid senolytics target PARP1, BCL-xL, and CDK2 to induce selective senescent cell death. This phenotype-based discovery of novel flavonoid senolytics, coupled with mechanistic insights, represents a key advancement in developing next-generation senolyticss with potential clinical applications in treating aging and age-related diseases.

Beta cells secrete insulin in response to increases in blood glucose levels to sustain normal glucose homeostasis for an entire lifetime. Several studies have investigated the impact of aging on beta cells and established that aging beta cells have compromised expression of transcription factors (TFs) and re-organization of gene regulatory networks (GRNs) that maintain beta cell identity, accumulation of islet fibrosis, inflammation, and ER stress, reduced KATP channel conductance, loss of coordinated beta cell calcium dynamics, impaired beta cell autophagy and accumulation of beta cell DNA damage, and/or beta cell senescence. When combined with an unhealthy lifestyle during old age, these aging signatures could pre-dispose beta cells to failure and lead to type 2 diabetes (T2D) onset.

Caloric restriction (CR) and CR-mimicking approaches (e.g., time-restricted feeding (TRF)) can prolong organismal longevity and delay aging from yeast to non-human primates. These beneficial effects are associated with improved glucose homeostasis due to prolonged fasting and enhanced peripheral insulin sensitivity, enhanced insulin signaling, lower adiposity, enhanced mitochondrial homeostasis and lower ATP generation, increased autophagy, enhanced protein homeostasis and reduced ER stress and inflammation. In the pancreas, 20-40% CR or CR achieved via TRF are linked to lower islet cell mass in lean mice, whereas in pre-diabetic mice, CR restores normal beta cell secretory function, identity, and preserves beta cell mass in a process dependent on activation of beta cell autophagy via Beclin-2. In patients with a recent T2D diagnosis, the efficacy of extreme CR (average of 835 kcal/day or greater than 50% CR based on a 2000 kcal/day diet) to reverse T2D depends on the capacity of beta cells to recover from previous exposure to a T2D metabolic state. However, how beta cells adapt during CR, and whether CR can delay the hallmarks of beta cell aging remains largely unknown.

We investigated these questions by exposing adult male mice to mild CR (i.e., 20% restriction) for up to 12 months and applied comprehensive in vivo and in vitro metabolic phenotyping of beta cell function followed by single-cell multiomics and multi-modal high-resolution microscopy pipelines. Our data reveals that CR reduces the demand for beta cell insulin release necessary to sustain euglycemia by increasing peripheral insulin sensitivity. Ad-libitum (AL) consumption of a diet with reduced caloric intake failed to trigger a similar phenotype, thus indicating that CR and CR-associated fasting periods are required for this adaptive metabolic response. During CR, the transcriptional architecture of beta cells is re-organized to promote a largely post-mitotic and long-lived phenotype with enhanced cell homeostasis and mitochondrial structure-function. This is associated with reduced onset and/or expression of beta cell aging and senescence signatures. When exposed to a high-fat diet (HFD), CR beta cells upregulate insulin release, however they have a compromised adaptive response due to limited cell proliferation resulting in reduced beta cell mass. Therefore, our results provide a molecular footprint of how CR modulates adult beta cell function and insulin sensitivity to promote beta cell longevity and delay aging in mice.

Ageing is associated with a gradual loss of muscle strength, which in the end may have consequences for survival. Whether muscle strength and mortality risk associate in a gradual or threshold-specific manner remains unclear. This study investigates the prospective association of muscle strength with all-cause mortality in the oldest old. We included 1890 adults aged ≥ 90 years (61.6% women, mean age 91.0 ± 1.5 years) from 27 European countries and Israel participating in the Survey of Health, Ageing and Retirement in Europe (SHARE) study. Muscle strength was assessed using handgrip dynamometry. We determined the prospective association of muscle strength with mortality, controlling for age, sex, smoking, BMI, marital status, education, geographical region, and self-perceived health.

Over a mean follow-up of 4.2 ± 2.4 years, more than half of the participants died (n = 971, 51.4%). The mean handgrip strength was 20.4 ± 8.0 kg for all participants, with men (26.7 ± 7.5 kg) showing significantly higher strength than women (16.4 ± 5.4 kg). Using the median level of muscle strength as reference (18 kg), lower and higher levels were associated in a gradual and curvilinear fashion with higher and lower mortality risk, respectively. The 10th percentile of muscle strength (10 kg) showed a hazard ratio (HR) of 1.27. The 90th percentile (31 kg) showed an HR of 0.69. Stratified for sex, the median levels of muscle strength were 26 kg for men and 16 kg for women. The 10th percentile of muscle strength showed HRs of 1.33 at 15 kg for men and 1.19 at 10 kg for women. The 90th percentile of muscle strength showed HRs of 0.75 at 35 kg for men and 0.75 at 23 kg for women. Sensitivity analyses, which excluded individuals who died within the first 2 years of follow-up, confirmed the main findings.

Rather than a specific threshold, muscle strength is gradually and inversely associated with mortality risk in the oldest old. As muscle strength at all ages is highly adaptive to resistance training, these findings highlight the importance of improving muscle strength in both men and women among the oldest old.

Klebsiella pneumoniae is infamous for hospital-acquired infections and sepsis, which have also been linked to Alzheimer disease (AD)-related neuroinflammatory and neurodegenerative impairment. However, its causative and mechanistic role in AD pathology remains unstudied. Thus a preclinical model of K. pneumoniae enteric infection and colonization is developed in an AD model (3xTg-AD mice) to investigate whether and how K. pneumoniae pathogenesis exacerbates neuropathogenesis via the gut-blood-brain axis.

K. pneumoniae, particularly under antibiotic-induced dysbiosis, was able to translocate from the gut to the bloodstream by penetrating the gut epithelial barrier. Subsequently, K. pneumoniae infiltrated the brain by breaching the blood-brain barrier. Significant neuroinflammatory phenotype was observed in mice with K. pneumoniae brain infection. K. pneumoniae-infected mice also exhibited impaired neurobehavioral function and elevated total tau levels in the brain. Metagenomic analyses revealed an inverse correlation of K. pneumoniae with gut biome diversity and commensal bacteria, highlighting how antibiotic-induced dysbiosis triggers an enteroseptic "pathobiome" signature implicated in gut-brain perturbations.

The findings demonstrate how infectious agents following hospital-acquired infections and consequent antibiotic regimen may induce gut dysbiosis and pathobiome and increase the risk of sepsis, thereby increasing the predisposition to neuroinflammatory and neurobehavioral impairments via breaching the gut-blood-brain barrier.

The actin cytoskeleton is a key determinant of cell structure and homeostasis. However, possible tissue-specific changes to actin dynamics during aging, notably brain aging, are not understood. Actin can be found in two forms: monomeric (G-actin) and filamentous (F-actin). Assembly and disassembly of actin filaments are regulated by a large number of actin-interacting proteins, making maintenance of the actin cytoskeleton highly susceptible to disruption caused by aging. Here, we show that there is an age-related increase in filamentous actin (F-actin) in Drosophila brains, which is counteracted by prolongevity interventions.

Critically, decreasing F-actin levels in aging neurons prevents age-onset cognitive decline and extends organismal healthspan. Mechanistically, we show that autophagy, a recycling process required for neuronal homeostasis, is disabled upon actin dysregulation in the aged brain. Remarkably, disrupting actin polymerization in aged animals with cytoskeletal drugs restores brain autophagy to youthful levels and reverses cellular hallmarks of brain aging. Finally, reducing F-actin levels in aging neurons slows brain aging and promotes healthspan in an autophagy-dependent manner. Our data identify excess actin polymerization as a hallmark of brain aging, which can be targeted to reverse brain aging phenotypes and prolong healthspan.

The drugs mifepristone and rapamycin were compared for their relative ability to increase the life span of mated female Drosophila melanogaster. Titration of rapamycin indicated an optimal concentration of approximately 50 μM, which increased median life span here by average +81%. Meta-analysis of previous mifepristone titrations indicated an optimal concentration of approximately 466 μM, which increased median life span here by average +114%. Combining mifepristone with various concentrations of rapamycin did not produce further increases in life span, and instead reduced life span relative to either drug alone.

Assay of maximum midgut diameter indicated that rapamycin was equally efficacious as mifepristone in reducing mating-induced midgut hypertrophy. The mito-QC mitophagy reporter is a previously described green fluorescent protein (GFP)-mCherry fusion protein targeted to the outer mitochondrial membrane. Inhibition of GFP fluorescence by the acidic environment of the autophagolysosome yields an increased red/green fluorescence ratio indicative of increased mitophagy. Creation of a multi-copy mito-QC reporter strain facilitated assay in live adult flies, as well as in dissected midgut tissue. Mifepristone was equally efficacious as rapamycin in activating the mito-QC mitophagy reporter in the adult female fat-body and midgut. The data suggest that mifepristone and rapamycin act through a common pathway to increase mated female Drosophila life span, and implicate increased mitophagy and decreased midgut hypertrophy in that pathway.

Microglia signatures refer to specific profiles of microglia activity or gene expression. Through a comprehensive analysis of gene and protein expression profiles, we can identify specific genes and proteins that characterize different states of microglial activation, including those associated with pro-inflammatory and anti-inflammatory states. This approach contributes to the knowledge base regarding the dynamics of microglial activation in both physiological and pathological conditions. The question of whether these signatures are a cause or a consequence of microglia-related brain disorders is highly relevant since understanding whether alterations in microglia are a primary cause of brain pathologies (e.g., neurodegenerative diseases such as Alzheimer's disease) or whether they are a secondary response to such pathologies can significantly influence therapeutic strategies.

Microglia can become hyperactive or dysfunctional, releasing inflammatory cytokines and neurotoxic factors that can damage neurons and the extracellular matrix. This may contribute to the pathogenesis of diseases such as Alzheimer's disease and Parkinson's disease. Microglia can have a proactive role in shaping the neuronal environment. If altered, they can negatively affect synaptogenesis, synaptic plasticity, and clearance of cellular debris, leading to brain dysfunction. Microglia interact closely with neurons, astrocytes, and other cell types in the brain. Alterations in these interactions caused by primary diseases may lead to changes in microglia signatures as an adaptive response, which could exacerbate the disease. Microglia may be activated in response to brain damage or other pathologies. In this scenario, alterations in their signatures could be a consequence of the presence of pathogens, abnormal protein deposits, or neuronal damage. In neurodegenerative disorders, neuroinflammation may be a secondary response to primary pathological processes. For example, in Alzheimer's disease, microglia may be activated by amyloid-β deposits.

The relationship between microglia signatures and brain disorders is likely to be bidirectional and dynamic. In some conditions, dysfunctional microglia may actively contribute to disease onset and progression (cause), while in other situations, they may represent an adaptive or maladaptive response to pre-existing damage or pathology (consequence). Understanding this complex interaction requires further research, including longitudinal studies and experimental models that can isolate the various factors involved. Unraveling these dynamics may lead to new and more effective therapeutic strategies for microglia-related brain diseases.

Visceral fat tissue, interspersed with resident immune cells, when activated, increases local or systemic inflammation, leading to the production of cytokines and other immune and pro-inflammatory mediators, promoting insulin resistance, oxidative stress, and altered cell metabolism. Abdominal fat accumulation is associated with changes in glucose metabolism and lipid metabolism, primarily due to insulin resistance, resulting in hyperlipidemia, hypertension, glucose intolerance, and mitochondrial abnormalities in skeletal muscle.

An individual's leanness or corpulence is commonly assessed using the Body Mass Index (BMI), but this measure does not account for fat distribution or differentiate between fat and muscle mass. Therefore, clinicians have explored alternative anthropometric measurements that better reflect body composition and mortality risk, such as waist circumference (WC) and waist-to-hip and waist-to-height ratios. Most of these measures fail to reflect body composition effectively or are easily affected by variations in other body measurements. A new body shape index (A Body Shape Index, ABSI) has been introduced as an anthropometric measure unrelated to BMI, based on waist circumference adjusted for weight and height. ABSI offers a better explanation of how central abdominal adiposity is strongly associated with mortality than other anthropometric measurements, and it captures additional harmful effects not captured by BMI.

This prospective cohort study included 159 volunteers (94 women, aged 60-80 years), recruited in the frame of the "Physical Activity and Nutrition for Great Ageing" (PANGeA) Cross-border Cooperation Program Slovenia-Italy 2007-2013, and followed for 10 years. During the 10-year follow-up, 10 deaths (6.7%) were recorded. ABSI (adjusted for age, smoking, comorbidities, and therapy) was an independent predictor of mortality (hazard ratio = 4.65). Higher ABSI scores were linked to reduced VO2max (r = -0.190) and increased systolic blood pressure (r = 0.262). An ABSI-based predictive model showed strong discriminatory power, and thus ABSI is a reliable predictor of 10-year mortality in active, non-obese elderly individuals and may improve risk stratification in clinical practice.

Aging is associated with a decline in physiological functions and an increased risk of metabolic disorders. The liver, a key organ in metabolism, undergoes significant changes during aging that can contribute to systemic metabolic dysfunction. This study investigates the expression of genes involved in the tricarboxylic acid (TCA) cycle, a critical pathway for energy production, in the aging liver. We analyzed RNA sequencing data from the Genotype-Tissue Expression (GTEx) project to assess age-related changes in gene expression in the human liver. To validate our findings, we conducted complementary studies in young and old mice, examining the expression of key TCA cycle genes using quantitative real-time PCR.

Our analysis of the GTEx dataset revealed a significant reduction in the expression of many genes that are critical for metabolism, including fat mass and obesity associated (FTO) and adiponectin receptor 1 (ADIPOR1). The most overrepresented pathway among the statistically enriched ones was the TCA cycle, with multiple genes exhibiting downregulation in older humans. This reduction was consistent with findings in aging mice, which also showed decreased expression of several TCA cycle genes. These results suggest a conserved pattern of age-related downregulation of TCA cycle, potentially leading to diminished mitochondrial function and energy production in the liver. The reduced expression of TCA cycle genes in the aging liver may contribute to metabolic dysfunction and increased susceptibility to age-related diseases. Understanding the molecular basis of these changes provides new insights into the aging process and highlights potential targets for interventions aimed at promoting healthy aging and preventing metabolic disorders.

To date, the capacity of one life cycle stage to transform back to the preceding stage by morphological reorganization has been regarded as a distinctive and unparallelled feature of cnidarians. This ability for reverse development known for a few cnidarian species was first reported over a century ago and gained wide renown with the discovery of the peculiar life cycle of the so-called immortal jellyfish, Turritopsis dohrnii. This hydrozoan is currently considered the only animal able to repeatedly rejuvenate after sexual reproduction, challenging our understanding of aging and suggesting a potential for biological immortality.

Ctenophores (or comb jellies) are one of the oldest extant animal lineages. Accumulated evidence supporting their phylogenetic position as the sister group to all other animals place them as a pivotal model to study unique evolutionary innovations potentially rooted within the deepest branches of the animal tree of life. Here, we demonstrate that the ctenophore Mnemiopsis leidyi is capable of reversal from mature lobate to early cydippid when fed following a period of stress. Our findings illuminate central aspects of ctenophore development, ecology, and evolution and show the high potential of M. leidyi as a unique model system to study reverse development and rejuvenation.

With advancing age comes an increased risk of disease and disability. As people live longer, they are more likely to develop at least one age-related disease. Aging in people results from the gradual accumulation of defects and damage to the molecules and cells that make up our bodies. Unlike a car, our bodies have built-in mechanisms for repairing this damage. But even these repair mechanisms wear out over time. Eventually, enough damage accumulates to affect the function of whole organs and systems. NIH-funded researchers have been working to better understand aging at the molecular level. They're studying ways to measure differences in how people age before health problems appear. They're also exploring possible ways to slow, or even reverse, aging at the molecular level. This could lead to better approaches to prevent or treat age-related disease and disability.

Before you can tell if a treatment could slow or even reverse aging, you need to know how fast someone is aging in the first place. It's no secret that people age at different rates. Some people remain healthy and disease-free well into their ninth or even tenth decade of life. Others develop age-related diseases, such as cancer, heart disease, and dementia, much earlier. The concept of "biological age" is often used to describe these differences. Biological age reflects the molecular damage that accumulates over the years and eventually leads to disease and disability. Differences in biological age can develop years before age-related diseases appear. So a treatment to slow aging would also need to start well before such diseases appear. Then, to find out if a treatment worked or not, you'd have to track people for the rest of their lives. That's why researchers have been working to develop "aging clocks" to measure a person's biological age.

Age-reversing therapies like these are still some way in the future. Still, there are hints of lifestyle interventions that may have potential to lengthen life and delay aging. One that's been particularly well-studied is calorie restriction (CR). This is where you reduce the total number of calories you consume, but still get enough of the essential nutrients. To find out whether CR might have benefits in humans, too, NIH funded the Comprehensive Assessment of Long-Term Effects of Reducing Intake of Energy (CALERIE) study. More than 200 healthy, middle-aged volunteers were randomly assigned to two groups. Participants in one group were challenged to reduce their daily caloric intake by 25% for two years and given dietary and behavioral strategies for doing so. Those in the other group continued to eat their normal diets. Researchers examined the pace of biological aging in CALERIE participants. Those in the CR group had a much slower pace of aging as measured by clinical blood biomarkers. They also had a small but significant decrease in DunedinPACE, a rate of aging clock, while participants in the other group did not.

The Integrated Stress Response (ISR) is a conserved signaling pathway across species and an important area of focus for Calico because of its possible link to many age-related diseases and its potential as a target for new drug development. Calico is currently developing an ISR inhibitor, Fosigotifator (ABBV-CLS-7262), which is being tested in the clinic as a potential treatment for two neurodegenerative diseases. To gain a deeper understanding of how the ISR controls cell states, the Calico team used a highly specific and tunable cellular model to disentangle the effects of the ISR from other processes that are engaged when cells encounter stress or damage that disrupts them.

A key discovery was the suppression of a process known as the tricarboxylic acid (TCA) cycle which is a series of reactions that are essential for creating energy via cellular respiration. The researchers found that when the ISR is turned on even at low levels, carbon is redirected from mitochondria to make amino acids and glutathione, a key antioxidant that protects cells. This shows how the ISR may help cells adapt to mitochondrial dysfunction or starvation, two common triggers of the pathway, by rewiring their metabolism. Using a synthetic tool researchers also showed that activation of the ISR can lead to the formation of droplets that store fats, also known as lipids. This is interesting because lipid droplets have been linked to neurodegenerative diseases.

This study included 18,815 women and men age 50+ years (dementia-free at baseline) who participated in the Health and Retirement Study (HRS), a nationally representative cohort of US adults. Presence of obstructive sleep apnea (OSA) was defined by self-reported diagnosis or key HRS items that correspond to elements of a validated OSA screening tool (STOP-Bang). Incident dementia cases were identified using a validated, HRS-based algorithm derived from objective cognitive assessments. Survey-weighted regression models based on pseudo-values were utilized to estimate sex- and age-specific differences in cumulative incidence of dementia by OSA status.

Data from 18,815 adults were analyzed, of which 9% of women and 8% of men (weighted proportions) met criteria for incident dementia. Known/suspected OSA was more prevalent in men than in women (weighted proportions 68% vs. 31%). Unadjusted sex-stratified analyses showed that known/suspected OSA was associated with higher cumulative incidence of dementia across ages 60-84 years for women and men. By age 80, relative to adults without known/suspected OSA, the cumulative incidence of dementia was 4.7% higher for women with known/suspected OSA, and 2.5% for men with known/suspected OSA, respectively. Adjusted associations between age-specific OSA and cumulative incidence of dementia attenuated for both women and men but remained statistically significant.

The relationship between genomic characteristics and species traits is of paramount importance for biology. We proposed a novel technique that allows one to determine the relationship between any genomic characteristic and species traits, such as maximal reported lifespan, the body weight of an adult animal, and the related longevity quotient. This technique is exemplified in the physiologically significant genes involved in regulating circadian rhythms, which change quite rapidly during evolution.

Regardless of devising this technique, the study of the genes that are critical for circadian rhythms is of interest on its own. For instance, we thoroughly examined the paralogous genes Fbxl21 and Fbxl3, which are involved in the regulation of circadian rhythms. We found out that the above-mentioned characteristic of the Fbxl21 gene correlates with the maximal reported lifespan and body weight only in two superorders of placental mammals, Euarchontoglires (the clades Euarchonta, Lagomorpha, and Rodentia) and Afrotheria. On the contrary, such a correlation is not observed in other superorders, such as Laurasiatheria and Xenarthra. The presence or absence of the correlation is confirmed statistically with a very high accuracy.

Thus for certain genes (such as Fbxl21), the accumulation of amino acid substitutions up to pseudogenization or gene loss, as well as the preference for certain amino acids in the encoded protein, is an effective way to achieve a significant phylogenetic change. The Fbxl21 gene and the species-specific maximal reported lifespan, together with body weight, are examples of such a phylogenetic change in Euarchontoglires and Afrotheria, which is also observed in relatively small taxonomic groups, as, for example, in anthropoid apes and the Cercopithecidae.