Fight Aging! Newsletter, January 22nd 2024

In advanced aging, innate immune activation has been viewed as an inducer of chronic inflammation, which promotes different signs of aging and age-related diseases. At the same time, numerous examples indicate that the innate immune system contributes to tissue homeostasis and repair. Toll-like receptors (TLRs) are crucial for the innate immune system's response to threats, primarily by regulating inflammation and activating immune responses. The reduction in TLR activity induced by aging leads to a decreased efficiency in immune responses, potentially lowering the body's resistance to infections.

TLR5 is a remarkably versatile receptor found on both epithelial and immune cells, and its functions are distributed throughout the body. One of its critical roles emerges in the respiratory tract, where TLR5 assumes a pivotal position in initiating protective immune responses, particularly when combating infections like Pseudomonas aeruginosa. It is well known that the reduction in TLR activity induced by aging leads to a decreased efficiency in immune responses, potentially lowering the body's resistance to infections. However, in our previous study, we discovered that TLR5 expression and signaling were relatively well-preserved in aged mice and older individuals compared to other TLRs. We also demonstrated that TLR5 effectively enhances vaccine efficacy against pneumonia, leading to increased survival rates from pneumococcal infection in old mice. Unlike other TLRs, TLR5 has been reported not only to induce pro-inflammatory signals essential for vaccine efficacy boosting but also to suppress inflammation in lesions, induce tissue regeneration in major disease models, and strengthen the barrier. This unique functionality underscores the diverse applicability and therapeutic potential of TLR5 in addressing age-related health issues and promoting longevity.

In our study, we show that stimulating toll-like receptor 5 (TLR5) via mucosal delivery of a flagellin-containing fusion protein effectively extends the lifespan and enhances the healthspan of aged mice of both sexes. This enhancement in healthspan is evidenced by diminished hair loss and ocular lens opacity, increased bone mineral density, improved stem cell activity, delayed thymic involution, heightened cognitive capacity, and the prevention of pulmonary fibrosis. Additionally, this fusion protein boosts intestinal mucosal integrity by augmenting the surface expression of TLR5 in a certain subset of dendritic cells and increasing interleukin-22 (IL-22) secretion. In this work, we present observations that underscore the benefits of TLR5-dependent stimulation in the mucosal compartment, suggesting a viable strategy for enhancing longevity and healthspan.

4,4′-dimethoxychalcone (DMC) is a flavonoid previously reported as a small molecule promoting longevity and health. Our previous studies have shown that DMC functions as a ferroptosis inducer in cancer cells. However, there were no report on the function of DMC in senescent cells. Senotherapeutics consist of senolytics and senomorphics, which selectively eliminate senescent cells and reduce the senescence-associated secretory phenotype (SASP), respectively. Many flavonoids are senotherapeutics, and dasatinib + quercetin is so far the most commonly used senolytics. Dasatinib is a tyrosine kinase inhibitor, which inhibits cell proliferation and migration and induces apoptosis. Quercetin is a flavonoid that interacts with Bcl-2 family members to induce apoptosis. In the present study, we found that DMC, DMC + dasatinib, DMC + quercetin have a characteristic of senolytics. To investigate the senolytics effects, we employed replicative senescent cells and a DNA damage-induced senescent cells model. We found that DMC and its combination with dasatinib or quercetin selectively eliminated senescent cells, more effectively than using dasatinib + quercertin alone.

Senescent cells secrete a series of pro-inflammatory cytokines, chemokines, and growth factors, which is called SASP, to cause chronic inflammation and tissue dysfunction. In this study, we found that DMC reduced the SASP level in senescent cells. Furthermore, senescent cells enter irreversible cell cycle arrest, which involves the activation of p53/p21 and Rb/p16. In this study we found that the expression levels of p21 and p16 were decreased after DMC treatment. The downregulation of p21 may be attributed to the decrease of p53. In this study, we found that the mRNA level of p53 was reduced after DMC treatment.

Ferroptosis is an iron-dependent cell death process, which is accompanied by iron accumulation. Our previous study reported an important role of FECH, an enzyme inserts ferrous ion into PPIX, in ferroptosis, and showed that the inhibition of FECH by DMC led to iron accumulation in cancer cells. In this study, we found that the expression level of FECH increased in senescent cells, which may explain the sensitivity of DMC-induced ferroptosis in senescent cells. Senescent cells are associated with impaired ferritinophagy and ferroptosis. Interestingly, in our present study, we found that DMC could induce ferritinophagy, which may underlie DMC-induced ferroptosis in senescent cells.

Inflammasomes are large protein complexes that play a major role in sensing inflammatory signals and triggering the innate immune response. Each inflammasome complex has three major components: an upstream sensor molecule that is connected to a downstream effector protein such as caspase-1 through the adapter protein ASC. Inflammasome formation typically occurs in response to infectious agents or cellular damage. The active inflammasome then triggers caspase-1 activation, followed by the secretion of pro-inflammatory cytokines and pyroptotic cell death. Aberrant inflammasome activation and activity contribute to the development of diabetes, cancer, and several cardiovascular and neurodegenerative disorders.

As a result, recent research has increasingly focused on investigating the mechanisms that regulate inflammasome assembly and activation, as well as the potential of targeting inflammasomes to treat various diseases. Multiple clinical trials are currently underway to evaluate the therapeutic potential of several distinct inflammasome-targeting therapies. Therefore, understanding how different inflammasomes contribute to disease pathology may have significant implications for developing novel therapeutic strategies. In this article, we provide a summary of the biological and pathological roles of inflammasomes in health and disease. We also highlight key evidence that suggests targeting inflammasomes could be a novel strategy for developing new disease-modifying therapies that may be effective in several conditions.

Sarcopenia, characterized by the insidious reduction of skeletal muscle mass and strength, detrimentally affects the quality of life in elderly cohorts. Present therapeutic strategies are confined to physiotherapeutic interventions, signaling a critical need for elucidation of the etiological underpinnings to facilitate the development of innovative pharmacotherapies. Recent scientific inquiries have associated mitochondrial dysfunction and inflammation with the etiology of sarcopenia. Mitochondria are integral to numerous fundamental cellular processes within muscle tissue, including but not limited to apoptosis, autophagy, signaling via reactive oxygen species, and the maintenance of protein equilibrium. Deviations in mitochondrial dynamics, coupled with compromised oxidative capabilities, autophagic processes, and protein equilibrium, result in disturbances to muscular architecture and functionality.

Mitochondrial dysfunction is particularly detrimental as it diminishes oxidative phosphorylation, escalates apoptotic activity, and hinders calcium homeostasis within muscle cells. Additionally, deleterious feedback loops of deteriorated respiration, exacerbated oxidative injury, and diminished quality control mechanisms precipitate the acceleration of muscular senescence. Notably, mitochondria that exhibit deficient energetic metabolism are pivotal in precipitating the shift from normative muscle aging to a pathogenic state.

This analytical review meticulously examines the complex interplay between mitochondrial dysfunction, persistent inflammation, and the pathogenesis of sarcopenia. It underscores the imperative to alleviate inflammation and amend mitochondrial anomalies within geriatric populations as a strategy to forestall and manage sarcopenia. An initial overview provides a succinct exposition of sarcopenia and its clinical repercussions. The discourse then progresses to an examination of the direct correlation between mitochondrial dysfunction and the genesis of sarcopenia. Concomitantly, it accentuates potential synergistic effects between inflammatory responses and mitochondrial insufficiencies during the aging of skeletal muscle, thereby casting light upon emergent therapeutic objectives.

In this study, we discovered that genetic associations with longevity are on average stronger in females than in males through bio-demographic analyses of genome-wide association studies (GWAS) dataset of 2178 centenarians and 2299 middle-age controls of Chinese Longitudinal Healthy Longevity Study (CLHLS). This discovery is replicated across North and South regions of China, and is further confirmed by North-South discovery/replication analyses of different and independent datasets of Chinese healthy aging candidate genes with CLHLS participants who are not in CLHLS GWAS, including 2972 centenarians and 1992 middle-age controls. Our polygenic risk score analyses of eight exclusive groups of sex-specific genes, analyses of sex-specific and not-sex-specific individual genes, and Genome-wide Complex Trait Analysis using all SNPs all reconfirm that genetic associations with longevity are on average stronger in females than in males. Our discovery/replication analyses are based on genetic datasets of in total 5150 centenarians and compatible middle-age controls, which comprises the worldwide largest sample of centenarians.

Our results beg the question of why are genetic associations with longevity on average stronger in females than in males? The fact that females take much more care for childbearing and offspring than males may shed light on answering this question. Studies related to age-specific manifestation of genetic load suggest that fertility serves as the major factor of Darwinian natural selection for the accumulation of genetic mutation driving population survival and growth. The grandmother hypothesis proposed that postmenopausal longevity in human evolved from grandmothers' assistance with childcare, which prolonged females' lifespan.

A study reported that female centenarians were four times more likely to have children in their forties than females who lived only to age 73. Other studies (including analyses based on the CLHLS datasets) also found that females' late childbearing after ages 35 or 40 is positively and significantly associated with longevity. A study indicated that the longevity advantage of females over males may be a by-product of genetic evolution that maximizes the length of time during which females could bear and take care of children and contribute to human reproduction. The reproductive function of females might serve as a driving force for positive selection on the human genome and the related physiological features, such as immune response and metabolism. During periods of stress such as starvation, females use available amino acids to create deposits in the liver to support reproduction; conversely males slow down anabolic pathways and reserve carbohydrate stores for eventual use by the musculature.

Sex differences in genetics also affect innate and adaptive immunity. Various studies have reported a more progressive decline in immunity and dysregulated inflammatory response with increase of age in males than in females. In the current study, our pathway analysis revealed neuronal system, glycosaminoglycan biosynthesis-heparan sulfate, NABA ECM glycoproteins, and cell-cell junction organization are male-specific pathways, and neuroactive ligand receptor interaction is the female-specific pathway. Interestingly, it is previously reported that reductions of heparan sulfate biosynthetic gene function increased lifespan in Drosophila parkin mutants.

Mutations to the TMTC4 gene trigger a molecular domino effect known as the unfolded protein response (UPR), leading to the death of hair cells in the inner ear. Intriguingly, hearing loss from loud noise exposure or drugs such as cisplatin, a common form of chemotherapy, also stems from activation of the UPR in hair cells, suggesting that the UPR may underly several different forms of deafness. There are several drugs that block the UPR - and stop hearing loss - in laboratory animals. The new findings make a stronger case for testing these drugs in people who are at risk of losing their hearing, according to the researchers.

"As mice with TMTC4 mutations grew, we saw that they didn't startle in response to loud noise. They had gone deaf after they had matured." Researchers investigated what was happening to the mice, which looked like an accelerated version of age-related hearing loss in humans. They showed that mutations to TMTC4 primed hair cells in the ear to self-destruct, and loud noise did the same thing. In both cases, hair cells were flooded with excess calcium, throwing off the balance of other cellular signals, including the UPR.

Understanding TMTC4 mutations gives researchers a new way of studying progressive deafness, since it is critical for maintaining the health of the adult inner ear. The mutations mimic damage from noise, aging or drugs like cisplatin. Researchers envision a future where people who must take cisplatin, or who have to be exposed to loud noises for their jobs, take a drug that dampens the UPR and keeps hair cells from withering away, preserving their hearing.

Dysfunctional extracellular matrices (ECM) contribute to aging and disease. Repairing dysfunctional ECM could potentially prevent age-related pathologies. Interventions promoting longevity also impact ECM gene expression. However, the role of ECM composition changes in healthy aging remains unclear. Here we perform proteomics and in-vivo monitoring to systematically investigate ECM composition (matreotype) during aging in C. elegans revealing three distinct collagen dynamics.

Longevity interventions slow age-related collagen stiffening and prolong the expression of collagens that are turned over. These prolonged collagen dynamics are mediated by a mechanical feedback loop of hemidesmosome-containing structures that span from the exoskeletal ECM through the hypodermis, basement membrane ECM, to the muscles, coupling mechanical forces to adjust ECM gene expression and longevity via the transcriptional co-activator YAP-1 across tissues. Our results provide in-vivo evidence that coordinated ECM remodeling through mechanotransduction is required and sufficient to promote longevity, offering potential avenues for interventions targeting ECM dynamics.

Altered composition and function of the gut microbiota play an important role in the pathogenesis of reproductive aging. Experimental and clinical studies have uncovered the relationship between gut dysbiosis and ovarian follicle development, as well as a disturbed immune response. Results from fecal microbiota transplant (FMT) studies provide a new insight to anti-ovarian aging, that is the maintenance of youthful gut microbiota helps to preserve ovarian function and prevent ovarian-related diseases. Microbiota-based intervention to delay or reserve ovarian aging is an appealing approach and may offer new therapeutic strategies for intestinal microbiota regulation to improve female fertility.

Furthermore, investigation of antiaging interventions such as antiaging drugs and calorie restriction may improve the gut microbial imbalance and promote a healthier intestinal ecological environment. However, evidence from the current scientific literature cannot offer any direct conclusions regarding these measures. The majority of the relevant studies were conducted in animal models, which cannot simply apply to human beings. Therefore, future studies should shift from simple correlation analysis to large-scale cohort research and focus on the potential causes and underlying mechanisms to verify the beneficial effects of these interventions in ovarian aging.

Given the wide alterations in the gut microbiota composition and function throughout ovarian aging, it has been suggested that the gut microbiota may be suitable for deciphering the processes of expected and unexpected ovarian aging in women. Imbalance in the gut microbiota may lead to the progression of various ovarian aging-related conditions. Although ovarian aging is unavoidable, maintenance of a balanced gut microbiota is a potential way to delay ovarian aging and subsequent adverse outcomes.

Alzheimer's disease (AD) is heterogenous at the molecular level. Understanding this heterogeneity is critical for AD drug development. Here we define AD molecular subtypes using mass spectrometry proteomics in cerebrospinal fluid (CSF), based on 1,058 proteins, with different levels in individuals with AD (n = 419) compared to controls (n = 187).

These AD subtypes had alterations in protein levels that were associated with distinct molecular processes: subtype 1 was characterized by proteins related to neuronal hyperplasticity; subtype 2 by innate immune activation; subtype 3 by RNA dysregulation; subtype 4 by choroid plexus dysfunction; and subtype 5 by blood-brain barrier impairment. Each subtype was related to specific AD genetic risk variants, for example, subtype 1 was enriched with TREM2 R47H. Subtypes also differed in clinical outcomes, survival times, and anatomical patterns of brain atrophy.

These results indicate molecular heterogeneity in AD and highlight the need for personalized medicine. CSF-based subtyping may be useful to select individuals for a specific therapeutic treatment, either for a priori subject stratification or for responder and side effect analysis in clinical trials.

ALS is caused by the loss of upper motor neurons, located in the brain, and lower motor neurons, which extend from the spinal cord to the muscles. Using a genetically modified mouse model, researchers found that structural changes in the upper neurons occurred prior to disease symptoms. The study suggests that these morphological changes send a signal to microglia and astrocytes, the immune cells of the central nervous system. When they arrive, their effect is protective, but if they stay too long, they become toxic to neurons. This leads to a reduction in synaptic connections between motor neurons in the brain and spinal cord, which in turn results in a reduction in synaptic connections with muscles. These changes lead to atrophy and loss of motor function.

Given this correlation between symptoms and immune response, the research team wondered whether it might be possible to restore synaptic connections by blocking inflammation. They tested a semi-synthetic drug based on Withaferin A, an extract of the Ashwagandha plant. The drug blocks inflammation and allows motor neurons to return to a more normal state. Neurons regenerate in the absence of activated immune cells. The dendrites of motor neurons start to grow and make connections again, increasing the number of synapses between motor neurons and muscles. This seems a promising way of improving ALS symptoms, whether the disease is familial or sporadic, since both types are associated with inflammation.

Neurons in the dorsomedial hypothalamus, produce an important protein - Ppp1r17. When this protein is present in the nucleus, the neurons are active and stimulate the sympathetic nervous system. The neurons in the hypothalamus set off a chain of events that triggers neurons that govern white adipose tissue - a type of fat tissue - stored under the skin and in the abdominal area. The activated fat tissue releases fatty acids into the bloodstream that can be used to fuel physical activity. The activated fat tissue also releases another important protein - an enzyme called eNAMPT - which returns to the hypothalamus and allows the brain to produce fuel for its functions.

This feedback loop is critical for fueling the body and the brain, but it slows down over time. With age, the researchers found that the protein Ppp1r17 tends to leave the nucleus of the neurons, and when that happens, the neurons in the hypothalamus send weaker signals. With less use, the nervous system wiring throughout the white adipose tissue gradually retracts, and what was once a dense network of interconnecting nerves becomes sparse. The fat tissues no longer receive as many signals to release fatty acids and eNAMPT, which leads to fat accumulation, weight gain and less energy to fuel the brain and other tissues. When researchers used genetic methods in old mice to keep Ppp1r17 in the nucleus of the neurons in the hypothalamus, the mice were more physically active - with increased wheel-running - and lived 7% longer than control mice. They also used a technique to directly activate these specific neurons in the hypothalamus of old mice, and they observed similar anti-aging effects.

Researchers are continuing to investigate ways to maintain the feedback loop between the hypothalamus and the fat tissue. One route they are studying involves supplementing mice with eNAMPT, the enzyme produced by the fat tissue that returns to the brain and fuels the hypothalamus, among other tissues. When released by the fat tissue into the bloodstream, the enzyme is packaged inside compartments called extracellular vesicles, which can be collected and isolated from blood. "We can envision a possible anti-aging therapy that involves delivering eNAMPT in various ways. We already have shown that administering eNAMPT in extracellular vesicles increases cellular energy levels in the hypothalamus and extends life span in mice."

Recent findings have identified an exciting potential new link to signs of skin aging - the skin microbiome, the collection of microorganisms that inhabits our skin. To the best of the team's knowledge, the study is the first to isolate microbes associated specifically with signs of skin aging and skin health, rather than chronological age. The study comprehensively examined data collected during 13 past studies, consisting of 16S rRNA amplicon sequence data and corresponding skin clinical data for over 650 female participants, aged 18 - 70. While each of the studies included in the analysis had focused on one particular area of interest - for example, crow's feet wrinkles or moisture loss - this multi-study analysis collated the data to search for trends related to specific microbes while accounting for other variables, such as age.

Two notable trends emerged from the analysis. First, the team found a positive association between skin microbiome diversity and lateral cantonal lines (crow's feet wrinkles), which are generally viewed as one of the key signs of skin aging. Second, they observed a negative correlation between microbiome diversity and transepidermal water loss, which is the amount of moisture that evaporates through the skin. In further exploring the trends, the researchers identified several potential biomarkers that warrant investigation as microorganisms of interest. It would be premature to infer causation or actionable insights, but the study's results have provided researchers with directions on the next steps to hone in on better understanding microbial associations with skin aging.

How cell replication ultimately results in aging and the Hayflick limit are not fully understood. Here we show that clock-like accumulation of DNA G-quadruplexes (G4s) throughout cell replication drives conserved aging mechanisms. G4 stimulates transcription-replication interactions to delay genome replication and impairs DNA re-methylation and histone modification recovery, leading to loss of heterochromatin. This creates a more permissive local environment for G4 formation in subsequent generations.

As a result, G4s gradually accumulate on promoters throughout mitosis, driving clock-like DNA hypomethylation and chromatin opening. In patients and in vitro models, loss-of-function mutations in the G4-resolving enzymes WRN, BLM and ERCC8 accelerate the erosion of the epigenomic landscape around G4. G4-driven epigenomic aging is strongly correlated with biological age and is conserved in yeast, nematodes, insects, fish, rodents, and humans. Our results revealed a universal molecular mechanism of aging and provided mechanistic insight into how G-quadruplex processor mutations drive premature aging.

Using a large proteomic cohort in the UK Biobank, we aimed to develop a proteomic aging clock for all-cause mortality risk as a proxy of biological age (BA). Participants in the UK Biobank Pharma Proteomics Project were included with ages between 39 and 70 years (n = 53,021). We developed a proteomic aging clock (PAC) for all-cause mortality risk as a surrogate of BA using a combination of Least Absolute Shrinkage and Selection Operator (LASSO) penalized Cox regression and Gompertz proportional hazards models. The validation for PAC included assessing its age-adjusted associations with, and predictions for all-cause mortality and 18 incident diseases, and head-to-head comparisons with two biological age measures (PhenoAge and BioAge) and leukocyte telomere length (LTL). Additionally, a functional analysis was performed to identify gene sets and tissues enriched with genes associated with BA deviation, based on different BA measures.

The Spearman correlation between PAC proteomic age and chronological age was 0.76. 10.9% of the combined training and test samples died during a mean follow-up of 13.3 years, with the mean age at death 70.1 years. PAC proteomic age, after controlling for age and other covariates, showed stronger associations than PhenoAge, BioAge, and LTL, with mortality and multiple incident diseases in the test set sample and in disease-free participants, such as mortality, heart failure, pneumonia, delirium, Chronic Obstructive Pulmonary Disease (COPD), and dementia. Additionally, PAC proteomic age showed higher predictive power for the conditions above compared to chronological age, PhenoAge, and BioAge. Proteins associated with PAC proteomic age deviation (from chronological age) are enriched in various hallmarks of biological aging, including immunoinflammatory responses, cellular senescence, extracellular matrix remodeling, cellular response to stressors, and vascular biology.

Dietary restriction (DR) delays aging, but the mechanism remains unclear. We identified polymorphisms in mtd, the fly homolog of OXR1, which influenced lifespan and mtd expression in response to DR. Knockdown in adulthood inhibited DR-mediated lifespan extension in female flies. We found that mtd/OXR1 expression declines with age and it interacts with the retromer, which regulates trafficking of proteins and lipids. Loss of mtd/OXR1 destabilized the retromer, causing improper protein trafficking and endolysosomal defects.

Overexpression of retromer genes or pharmacological restabilization with R55 rescued lifespan and neurodegeneration in mtd-deficient flies and endolysosomal defects in fibroblasts from patients with lethal loss-of-function of OXR1 variants. Multi-omic analyses in flies and humans showed that decreased Mtd/OXR1 is associated with aging and neurological diseases. mtd/OXR1 overexpression rescued age-related visual decline and tauopathy in a fly model. Hence, OXR1 plays a conserved role in preserving retromer function and is critical for neuronal health and longevity.