Frontiers in Aging

BACKGROUNDAlong with advancing age comes declines in physical, cognitive, and cardiovascular function. This diminished capacity may lead to decreased ability to perform activities of daily living, disability onset, and loss of independence. Exercise is a regenerative medicine therapy that can mitigate this loss of function. High intensity interval training (HIIT) is an aerobic exercise paradigm consisting of intense activity periods interspersed with bouts of active recovery. Previously we demonstrated that HIIT preserved physical function in adult, middle-aged, and older male mice. However, whether HIIT preserves physical, cognitive, and cardiovascular function, mitigates frailty, and improves brain and heart health in older adult female mice remains unknown. HYPOTHESISCognitive, physical, and cardiovascular function in older adult female C57BL/6 will be preserved in exercised mice (HIIT) versus sedentary control (SED). METHODSMice (HIIT and SED, both n=9, 24m at end) were tested pre/post-intervention for physical (rotarod, treadmill, grip meter, inverted cling, voluntary wheel running, activity monitor), cognitive (open field, novel object recognition, puzzle box, y-maze), and cardiovascular (blood pressure, echocardiogram) function, body composition, and whole body calorimetry. The mice underwent 14-weeks of HIIT training with progressive volume and intensity. RESULTSHIIT significantly (p<0.05) increased or preserved function in many tests including: aerobic capacity (+71% HIIT versus, vs, no change, NC, in SED), four limb strength/endurance (-67% SED vs -28% HIIT), forelimb strength (-16% SED vs NC HIIT), overall motor function (NC SED vs +39% HIIT), executive function (NC SED vs +73% HIIT), and exploratory behavior, which improved across multiple tests with HIIT while remaining unchanged in SED. HIIT also reduced both systolic blood pressure by 12% (-17 mmHg) and mean arterial pressure by -16 mmHg. In addition, HIIT significantly reduced cardiac fibrosis, increased muscle fiber type 2a percentage, reduced IL-1{beta} expression in the hypothalamus, and mitigated frailty onset. CONCLUSIONHIIT significantly reduced age-related functional loss in all three domains assessed while preventing frailty onset in older adult females and improving markers of brain and heart health.

Autophagy is a hallmark of aging, but autophagy-related proteins have not been exclusively targeted to attenuate the progressive decline in physical function associated with aging. Here, we combined Tat-Beclin1, an autophagy agonist, and endurance training to determine whether Tat-Beclin1 enhances exercise adaptation in old male mice. Tat-Beclin1 was administered intraperitoneally (TB group, 15 mg/kg, 2x/week) as a standalone therapy, or in combination with endurance training (TB+Exe group, 70% of maximal running speed 3x/week) for 1 month in 23-month-old male C57BL/6J mice. Control groups were age-matched cage controls and exercise-only groups. Animals were assessed for grip strength, endurance capacity on a treadmill, and balance and coordination on a rotarod. Gastrocnemius/plantaris (G/P) and tibialis anterior muscles were harvested for western blotting, myofiber typing, and proteomic profiling (G/P only). TB+Exe led to significant increases in grip strength, endurance capacity, and balance and coordination performance beyond those observed in the TB and Exe groups alone. Autophagy markers, including Beclin1, the LC3B-II/I ratio, and p62, did not differ among groups. A proteomic analysis of the G/P muscle revealed that TB upregulated biological processes involved in muscle contraction and adaptation, whereas TB+Exe increased mitochondrial bioenergetic processes and, surprisingly, upregulated acute inflammatory responses, including proteins such as haptoglobin and orosomucoid-1. We conclude that combining Tat-Beclin1 and endurance training may represent a new approach to attenuate aging-related decline in physical function. New & NoteworthyWe show evidence that combining Tat-Beclin1 and endurance training (TB+Exe) resulted in greater improvements in physical function in 24-month-old male mice than either standalone therapy. We also show that TB+Exe upregulates traditional exercise-like biological processes and unexpectedly upregulates acute-inflammatory proteins (e.g., orosomucoid-1), which are thought to improve physical function in preclinical studies. Our study suggests that TB may be a new drug enhancing physical function, especially when combined with endurance training in old male mice.

Autophagy is widely proposed to decline with age; however, direct evidence for this across cell and tissue types in humans remains limited. Furthermore, it remains unknown whether interventions that improve physiological health during aging can modify autophagic activity in humans. Here, we performed transcriptomic and functional autophagy analyses across subject-matched human cell types from a healthy aging cohort spanning the adult lifespan. RNA-seq of primary dermal fibroblasts and induced neurons (iNs) revealed increased transcription of many autophagy-related genes with age, most markedly in fibroblasts. The impact of age on autophagic activity, measured using autophagy flux assays, was cell type- and sex-dependent, and uncoupled from autophagy-gene transcription. Autophagy flux decreased with age in male fibroblasts, was unchanged in female fibroblasts, and increased in female iNs. In freshly isolated peripheral blood mononuclear cells (PBMCs), autophagy flux became more heterogeneous with age and trended higher in older individuals, independent of sex. Although autophagy flux levels did not match across different cell types, higher autophagy flux in all cell types was associated with reduced physical function in older adults ([&ge;]70 years). Importantly, autophagy flux decreased following 12 weeks of mild exercise in parallel with improved physical function. These findings indicate that autophagy is regulated in a cell type-, sex-and physiological function-dependent manner during human aging, and highlight PBMC autophagy flux as a potentially modifiable, blood-accessible readout of physiological state in older adults.

Growing evidence supports a critical role for the gut-brain axis in regulating metabolic health, inflammation,and cognitive function during aging. Age-associated gut dysbiosis has been linked to metabolic dysfunction and cognitive decline, with females exhibiting increased susceptibility to these age-related impairments. Diet is a major determinant of gut microbiome composition and function. Previous studies from our laboratory demonstrated that dietary protein restriction (DPR) induces fibroblast growth factor 21 (FGF21), improves metabolic health, and extends lifespan in male mice. However, the effects of DPR on the gut microbiome and associated health outcomes in aged female mice remain poorly understood. Female mice were assigned at 16 months of age to either a normal-protein (NP) or low-protein (LP) diet for 26 weeks. Metabolic assessments included food intake, fasting glucose concentrations, and glucose tolerance testing. Senescence-associated markers in mesenteric white adipose tissue (mWAT), fecal microbiome composition, and behavioral outcomes were evaluated to determine relationships among dietary protein intake, microbial communities, metabolic health, and cognitive function. Low-protein diet significantly improved metabolic health in aged female mice, as evidenced by improved glucose regulation. Microbiome analyses revealed increased abundance of Akkermansia at 17 months and Faecalibaculum in LP-fed animals at 22 months of age. More so, functional profiling and gene set enrichment analyses indicated enrichment of microbial pathways associated with membrane integrity and metal ion binding. Lastly, LP-fed female mice displayed improved memory performance at 22 months of age compared with age-matched NP-fed controls. Collectively, these findings demonstrate that DPR remodels the gut microbiome and improves metabolic and cognitive health in aged female mice. The observed microbial adaptations may contribute to the beneficial effects of DPR on aging related physiology, highlighting the gut microbiome as a potential mediator of dietary interventions that promote healthy aging.

Background Vaccination programs have greatly reduced the burden of infectious diseases, particularly in childhood. As populations age, however, the burden of respiratory infections such as influenza A, respiratory syncytial virus (RSV), and SARS-CoV-2 increasingly falls on older adults. Because infection fatality rates rise steeply with age, vaccination strategies that alter the age distribution of infections may have complex population-level consequences. We used transmission models to examine how the timing and frequency of vaccination influence infection-induced mortality and years of life lost (YLL) in aging populations. Methods and findings We analyzed age-structured transmission models that incorporate demographic change, age-specific infection fatality rates, and waning immunity after infection or vaccination. We varied the age at first vaccination, vaccination intervals, and coverage across a wide range of pathogen characteristics, including transmissibility and the duration of natural and vaccine-induced immunity. For single-dose vaccination programs with long-lived protection (5-50 years), the age at vaccination minimizing mortality in older adults for pathogens with strongly age-increasing fatality risk typically ranges from 60 to 80 years. The optimal age shifted toward older ages when transmissibility was higher or natural immunity lasted longer. Repeated vaccination produced qualitatively different outcomes. When vaccine-induced immunity was short-lived ($<$5 years), vaccination can shift infections toward the oldest ages where fatality risks are highest, increasing both mortality and YLL compared with no vaccination. This study has limitations. Our analysis used stylized transmission models and assumed vaccines that fully prevent infection, which may overestimate age-shifting effects compared with real-world vaccines that primarily reduce disease severity. Conclusions Optimal adult vaccination strategies depend jointly on pathogen transmissibility, the duration of immunity, and population demography. Vaccination programs that suppress infections earlier in life without protecting individuals into late life may shift infections toward ages with higher fatality risk. These findings highlight the need to evaluate adult vaccination strategies across the full life course and have important implications for vaccination policies against influenza A and other pathogens with strongly age-dependent infection fatality rates.

Age-related reductions in muscle fiber size and contractile function, particularly in fibers expressing fast myosin heavy chains, contribute to declines in whole-muscle power. However, methodological limitations in estimating fiber size during contractile experiments have likely contributed to conflicting findings regarding whether reduced single-fiber force and power in older adults reflects their smaller size and/or impaired intrinsic contractile function. To address this, we coupled single-fiber contractile experiments with 3D-imaging in 7 young (19-40yrs) and 6 older (69-84yrs) males to assess intrinsic contractile function and compare agreement between 3D-derived cross-sectional area (CSA) and CSA estimates obtained either in air or solution. Fast fiber CSA from older males were [~]28-45% smaller across measurement conditions compared with young, whereas slow fiber CSA did not differ. Accordingly, absolute force and power of fast fibers were 41% and 37% lower. When normalized to CSA from measurements in air or 3D-imaging, size-specific force and power either did not differ or were greater in older adults, indicating preserved intrinsic contractile function in both fiber types. This was supported by no age-related differences in the rate of tension redevelopment (ktr), a size-independent measure of intrinsic contractile function. In contrast, size-specific force and power calculated using solution-based CSA estimates were lower in older compared with young adults, and Bland-Altman analyses demonstrated the poorest agreement between solution-based and 3D CSA measurements. These findings indicate that intrinsic contractile function is preserved with aging and suggest that methodological differences in CSA measurement contributes to the disparate findings in the literature.

Skeletal muscle mass and training adaptations decline with aging, yet the proteomic basis of these attenuated responses remains unclear. We hypothesized that aging is accompanied by diminished proteome plasticity in response to resistance training (RT). The soluble proteome of VL biopsies was profiled in 17 younger (21.9 {+/-} 2.5 yr) and 15 older (57.5 {+/-} 6.9 yr) untrained males before and after 10-12 weeks of supervised RT using data-independent acquisition mass spectrometry (2,113 quantified proteins). At baseline, we detected 196 differentially expressed proteins (DEPs) significantly differed between age groups by {Pi}-score (278 by FDR). A 5.6-fold difference in training-responsive was observed in younger vs. older adults (100 vs. 18 {Pi}-score DEPs; 134 vs. 0 FDR-significant). Despite this quantitative attenuation, 61.6% of proteins changed in the same direction in both age groups (Spearman {rho} = 0.284, p = 3.46 x 10-), indicating conserved but amplitude-compressed training responses (median |log2FC|: 0.13 young vs. 0.09 old). RT in older adults partially reversed the aging proteome in that directionally different changes were observed in 75.2% of aging- or training-significant proteins in aging and training contrasts, with ribosomal and translational machinery showing the strongest reversal (cytoplasmic translation NES: -2.90 with aging, +2.60 with training). Ten WGCNA co-expression modules were identified, with age emerging as the dominant organizing principle (Turquoise module r-equiv = +0.59, p < 0.001). Module eigengenes discriminated age groups at the univariate level (Turquoise/Lipid Catabolism AUC = 0.96, q < 0.012), and training-induced module changes correlated with hypertrophic outcomes. Aging markedly attenuates but does not qualitatively alter skeletal muscle proteome plasticity. RT partially reverses aging proteome signatures, with translational machinery being the most responsive and mitochondrial programs the least responsive. Baseline proteomic state constrains adaptive capacity, suggesting that the molecular features distinguishing aging muscle directly may limit its hypertrophic response to RT.

BackgroundThe distinction between healthy and pathological ageing has led to the concept of vitality capacity (VC), which can be understood as the bodys physiological reserve. An individuals VC can be estimated using 12 biomarkers spread across 3 domains: immune and stress response, energy and metabolism and neuromuscular function. Vitality capacity may be preserved by lifelong physical activity. This cross-sectional study aimed to examine the relationship between lifelong aerobic physical activity and VC. MethodsVC of 20 lifelong active and 19 inactive healthy adults aged >55 years was assessed using 12 biomarkers across the three VC domains. Domain-specific z-scores were calculated and averaged to derive a global VC score. Principal component analysis was performed and loadings extracted to estimate domains weight, and multiple correlations were conducted to identify associations among biomarkers, domains and VC scores. ResultsVC was higher in lifelong active participants (+0.2 z-score units, p = 0.006) and correlated with age (r = -0.53, p < 0.001). Neuromuscular domain contributed most to VC variability, and the immune and stress response domain was higher in the active group (+0.4 z-score units, p = 0.001) as energy/metabolism among female participants (+0.5 z-score units, p.adj = 0.006). ConclusionLifelong aerobic physical activity is associated with higher VC in older adults, particularly within the immune and stress response domain. These findings highlight the role of physical activity in preserving the physiological reserve and reinforce the relevance of lifelong aerobic physical activity as a driver of healthy ageing.

The study aimed to evaluate the metabolic flexibility of sedentary elderly women in response to resistance training (RT) plus photobiomodulation therapy (PBMT) or RT alone, after two months of intervention. Nineteen elderly women were allocated into two groups, RT (n = 9, 68.44 {+/-} 5.27 years old) and RT plus PBMT (RTPT) (n = 10, 69.40 {+/-} 5.21 years old). The RTPT group received the PBMT, while for the RT group, the equipment was turned off. An incremental treadmill test together with a gas analyzer was performed to record variables such as heart rate (HR), oxygen consumption (VO2), carbon dioxide production (VCO2) and power output (PO) at the anaerobic threshold (AT), respiratory compensation point (RCP) and maximal oxygen consumption (VO2max), and thus indirectly verify metabolic flexibility. In comparison with baseline RTPT displayed significant differences in VO2max (pre: 18.32 {+/-} 3.01; post: 21.89 {+/-} 2.35), carbohydrate oxidation (CHox) (pre: 1.54 {+/-} 0.61; post: 2.45 {+/-} 0.91), CHox/FFM (fat-free mass) (pre: 36.12 {+/-} 12.28; post: 55.92 {+/-} 16.74) and energy expenditure normalized to FFM, EE/FFM (pre: 147.00 {+/-} 49.95; post: 227.56 {+/-} 68.08) during maximum effort incremental testing, while the RT group did not demonstrate a significant difference in these variables.The intervention with RT plus PBMT seems to result in a positive impact on metabolic variables in sedentary elderly women when compared with RT alone, making this approach a viable alternative to improve VO2max, CHox, CHox/FFM and EE/FFM during maximal effort testing. Author summaryAn aging-related decline in metabolic flexibility may reduce the ability to efficiently use energy during exercise, contributing to lower physical capacity and increased health risks in older adults. Resistance training is widely recommended for elderly populations, but additional strategies may further improve metabolic and physiological adaptations. This study investigated whether combining resistance training with photobiomodulation therapy could improve metabolic responses in sedentary elderly women more effectively than resistance training alone. Participants completed two months of supervised training, and metabolic responses were evaluated during an incremental exercise test. Women who received both resistance training and photobiomodulation therapy showed greater improvements in maximal oxygen consumption, carbohydrate oxidation, and energy expenditure during maximal exercise compared with those who performed resistance training alone. These findings suggest that photobiomodulation therapy may enhance the physiological adaptations associated with resistance training. The results indicate that combining resistance training with photobiomodulation therapy may represent a promising non-invasive strategy to improve exercise metabolism and functional capacity in sedentary elderly women. Further studies with larger samples are needed to confirm these findings and clarify the mechanisms involved.

Aging is associated with a gradual and progressive decline in skeletal muscle mass and strength known as sarcopenia, which has been attributed to chronic low-grade inflammation. Dietary long-chain polyunsaturated fatty acids (LC-PUFAs), including omega-6 arachidonic acid (ARA) and omega-3 docosahexaenoic acid (DHA), are precursors to bioactive lipid mediators that regulate the initiation, propagation, and active resolution of inflammation. While traditionally considered a pro-inflammatory and catabolic factor, the ARA-derived eicosanoid prostaglandin E2 has recently emerged as a potential anti-sarcopenic molecule. DHA-derived specialized pro-resolving mediators may also act as immunomodulatory pro-regenerative molecules in muscle inflammaging. In the current study, we tested the effects of long-term dietary supplementation with either ARA or DHA on muscle health in aging mice. Twenty-two-month-old C57BL/6N mice were fed a control AIN-93M diet, or an AIN-93M diet supplemented with either ARA (0.48% w/w) or DHA (0.48% w/w) for 12 weeks. Both dietary interventions reduced total body weight, but only ARA reduced absolute fat mass and increased the percentage of lean mass. Despite these changes in body composition, ARA supplementation reduced absolute muscle strength and myofiber size. This functional decline was associated with increased neuromuscular junction fragmentation, elevated expression of pro-inflammatory cytokines/protein degradation markers, and suppressed ribosome biogenesis. In contrast, DHA uniquely reduced chronic inflammation of aged muscle and returned c-Myc expression to young levels but did not affect muscle mass or strength. These data demonstrate that long-term dietary intake of ARA and DHA have overall divergent effects on the structure and function of aging muscle.

Skeletal muscle function is central to the preservation of functional mobility. Given global shifts to an increasingly aged population, it is paramount that researchers and clinicians better understand the effectors of age-related functional decline. Muscle fatiguability acutely modifies skeletal muscle mechanics in ways that may affect joint stability. We have previously reported sex-specific reductions in cellular passive stress and modulus with fatigue in young males, but not females. Here, we assess whether older adults, who are more susceptible to fatigue during dynamic contractions, exhibit changes to cellular passive mechanics following fatiguing exercise. Muscle tissue biopsies were collected from 11 young and 11 older adults to measure passive stress and Youngs Modulus at the single fiber and bundle level. Biopsy samples were acquired from rested muscle and immediately following intermittent maximal contractions to task failure. Fatigue was associated with persistent reduction in elastic modulus that was specific to male participants, regardless of age. In muscle fiber bundles, containing both myofibrillar proteins and the extracellular matrix, fatigue-induced changes in modulus were largely negated, with the only significant change observed in young females, who demonstrated enhanced modulus with fatigue. Taken together our findings suggest a preservation of sex-based differences in the acute response to fatigue across the adult lifespan when measured at the myofilament level. However, further research is needed to understand how and whether these findings translate to the whole tissue level. New and noteworthyAcute modifications to muscle tissue mechanics are poorly understood but may have important impacts on functional outcomes in at-risk populations. Our findings suggest myocellular mechanics respond to acute fatigue stress in a sex specific manner that persists across the lifespan.

BackgroundEstrogen-related receptor gamma (ERR{gamma}) drives an exercise mimicking aerobic gene program in the skeletal muscle that could be beneficial in aging. We have investigated the effect of chronic ERR{gamma} activation on minimizing sarcopenia. MethodsExperiments were performed in muscle specific ERR{gamma} transgenic (TG) mice and wild type (WT) littermates, at young (4-5 months) and old (24-26 months) age. In the skeletal muscle, global gene expression changes, as well as myofiber histological changes in fiber type, size, vascular supply and neuromuscular junction (NMJ), and mitochondrial content were measured. Functional analysis was performed using in vivo muscle contraction assay. Exercise fitness was measured using treadmill sprint and endurance test. Gene and protein expression was measured using QPCR and Westerns, respectively. ResultsERR{gamma} activates a pan-ERR aerobic program in the skeletal muscle to increase expression of 574 genes including ERR, mitochondrial homeostasis (e.g. Mfn1, Opa1, Drp1, Fis1, and Tfam), vascularization (e.g. Vegfa, Angpt1, Fgf1), and neuromuscular junction (NMJ) (e.g. Nrp1, Aspa, Ptprm, Cxcr4), simultaneously suppressing the expression of atrophy related genes (e.g. Atrogin1, Traf6, Nedd4, Myd88, p21). ERR{gamma} increases mitochondrial content [Mitochondrial area: old TG vs. WT, 2.00 fold; young TG vs. WT, 1.32 fold], oxidative capacity [NADH-TR activity: old TG vs. WT, 1.20 fold; young TG vs. WT, 1.22 fold] and myofiber type [2a: old TG (687{+/-}258) vs. WT (252{+/-}71); young TG (797{+/-}168) vs. WT (440{+/-}76); 2x: old TG 1348{+/-}87 vs. WT 976{+/-}219; young TG 1131{+/-}135 vs. WT 936{+/-}84; 2b: old TG (798{+/-}103) vs. WT (1628{+/-}148); young TG (967{+/-}133) vs. WT (1623{+/-}189)], and capillarity [capillary-to-myofiber ratio: old TG (3.25{+/-}0.19) vs. WT (2.41{+/-}0.16); young TG (3.41{+/-}0.21) vs WT (2.59{+/-}0.2)] and [NMJ number [old TG (67{+/-}8) vs. WT (40{+/-}9); young TG (77{+/-}11) vs WT (77{+/-}7)], mitigating age-related loss of NMJ and myofiber cross-sectional area [old TG (1570{+/-}147{micro}m2) vs. WT (1692.5{+/-}208{micro}m2) WT; young TG (1828.15{+/-}132.8{micro}m2) vs. WT (2109.7{+/-}296.8{micro}m2)]. ERR{gamma} overexpression preserves muscle contractility with aging [Fatigue resistance: 22.72% reduction in force in old vs. young WT; 3.11% reduction in force between old vs. young TG]. Furthermore, ERR{gamma} maintains exercise fitness in old mice [Running: old TG (2964.52{+/-}405m) vs. old WT (910.75{+/-}6034m); young TG (2232.43{+/-}193.64m) vs. young WT (1366.76{+/-}60.76m)]. ConclusionsERR{gamma} drives a pan-ERR and counter sarcopenic gene program enhancing oxidative myofiber type, mitochondrial content, vasculature, and NMJ in aging muscle. Consequently, ERR{gamma} minimizes myofiber atrophy, preserves contractility, and improves exercise fitness in old mice. Therefore, ERRs are potential translational targets for combating sarcopenia.

ObjectiveLoss of skeletal muscle mass and performance is a hallmark of ageing. Mitochondrial function has been suggested as a critical determinant of skeletal muscle performance. However, mixed results have been reported regarding mitochondrial function in older individuals. Therefore, the primary objective of this systematic review is to determine whether 31P-MRS-derived {tau}PCr, reflecting mitochondrial oxidative capacity, is reduced in ageing skeletal muscle. MethodsA preregistered systematic literature review was performed using the databases MEDLINE, EMBASE, SPORTDiscus, and Cochrane Central Register of Controlled Trials (CENTRAL). Papers were included if they reported {tau}PCr as measured by 31P-MRS; and studied individuals over 65 years of age in combination with a younger control group. Differences between young and older groups were assessed using random effects meta-analysis. ResultsWe included 20 papers in total, of which 2 measured 2 muscles, 5 focused on the tibialis anterior (TA) muscle, 11 on the calf muscles, 5 on the quadriceps, and 1 on the flexor digitorum longus. No statistically-significant differences were found in {tau}PCr between older and younger adults for all muscles combined (Hedges g=0.11 (p=0.487). Inter-study heterogeneity was high ({tau}2=0.36, I2=72.49%, H2=3.64). Sub-analyses for the individual muscles showed longer {tau}PCr in the quadriceps (g=0.65, p<0.001) in older adults, but shorter {tau}PCr in the TA muscle (g=-0.64, p<0.001). For the calf muscles, no differences were detected between older and young individuals (g=0.20, p=0.377). ConclusionNo uniform age-related decline was found for {tau}PCr when comparing all studies together. Substantial heterogeneity was observed between the individual muscles, with {tau}PCr being prolonged in the upper leg muscles in older adults, but shortened in the tibialis anterior. This suggests more work using standardised settings and well-defined cohorts is needed.

Birds provide a unique model for ageing research, as they exhibit higher mass-adjusted metabolic rates and blood glucose levels than other vertebrate groups, yet demonstrate greater longevity and slower senescence compared to mammals of similar body size. This challenges the "pace of life syndrome" hypothesis, which predicts that high metabolic rates and elevated glucose should correlate with shorter lifespans. While the effects of glucose, glycation, and advanced glycation end-products (AGEs) on ageing are well-documented in humans and the conventional models used in biomedical research, their impact on avian physiology and ageing remains poorly understood. Some evidence suggests that birds possess adaptations mitigating the potential detrimental effects of glucose levels, which are much higher than those of all other vertebrate groups. However, previous studies indicate that elevated glucose predicts reduced lifespan, and protein glycation--varying with age--can influence survival and some fitness-related traits. This implies that glycation or AGE accumulation may have relevant effects on avian longevity. In this study, we experimentally investigated how one year of dietary supplementation with glucose or methylglyoxal affects survival and ageing markers (metabolic rate, flying performance, and beak coloration) in captive zebra finches (Taeniopygia guttata). Our results reveal a significant increase in mortality exclusively in glucose-supplemented birds. Although glucose treatment elevated albumin glycation rate and AGE formation--the latter also observed with methylglyoxal supplementation--these variables did not directly explain the increased mortality in glucose-treated birds, which was absent in methylglyoxal-treated individuals despite similar AGE accumulation. Additionally, we observed some effects on the assessed senescence markers, with an age-related constraint on seasonal metabolic adjustment, and a treatment-influenced age decline in secondary sexual traits expression. These findings support the use of these markers as proxies for senescence in zebra finches. We also discuss alternative mechanisms, independent of the glycation cascade, which may contribute to mortality. A seasonal decline in flight performance, particularly during peak mortality periods, suggests a broader deterioration of health. Thus, although we demonstrate glucose supplementation to be more deleterious than methylglyoxal, the underlying mechanisms for the observed increase in mortality induced by the treatment remain unresolved.

Healthspan, the period of life where organisms are without frailty and/or disease, is a major focus of biogerontological research. To understand late-life decline and increased mortality risk, short-lived organisms such as nematode worms are commonly used. Pristionchus nematodes are established models for evolutionary developmental genetics research and show promise as systems for comparative and experimental study of ageing. To support this, we developed phenotypic ageing profiles for the evo-devo model Pristionchus pacificus and its little-studied congener Pristionchus fissidentatus. We find that various life history traits differ between P. pacificus and P. fissidentatus (lifespan, brood size, and reproductive period), demonstrating their utility for studying divergent ageing trajectories. Further, several traits are consistently impacted by age, including intestinal barrier function, body size, and locomotory ability. Additionally, in P. pacificus, rupture avoidance, cuticle integrity, and feeding rate decline with age, indicating dysregulation across many tissue types. Several age-linked patterns resemble those documented for Caenorhabditis elegans despite considerable evolutionary distance, suggesting conserved senescent processes across the Rhabditida family of nematodes. This work highlights similarities and differences in the impact of ageing in two Pristionchus nematodes and supports their development as models for evolutionary genetic study of senescence.

Astrocytes assume multiple phenotypes in the brain in response to stress, injury, inflammation, and aging. Given the complexity of this critical cell type in the CNS, it is important to gain a greater understanding of the differences between these phenotypes and to potentially identify therapeutic approaches to modifying astrocyte function in the context of disease and aging. We compared senescent and reactive astrocytes using a strictly defined paradigm to induce these phenotypes in human astrocytes. Gene expression profiling reveals overlapping but distinct expression profiles. Reactive astrocytes predominantly express genes involved in inflammatory responses while senescent astrocytes express genes and a secretome that suggests a role in synaptic pruning. Unexpectedly, functional analysis in a simplified neurite outgrowth assay suggests that senescent astrocytes retain the ability to support neurite outgrowth while reactive astrocytes lose this capacity. The data suggests that senescent and reactive astrocytes play distinct functional roles in the physiology of the aging brain. However, the overlapping inflammatory nature of senescent and reactive astrocytes makes it difficult to discriminate between them using existing toolsets designed to identify senescent cells.

ObjectivesPrior studies have shown that cyclin D1 regulates diverse aspects of liver metabolism during cell cycle progression. Interestingly, this protein is induced in hepatocytes by feeding, but its function in modulating hepatic postprandial physiology is poorly characterized. The aim of this study was to evaluate the contribution of cyclin D1 to the hepatic response to feeding and to gain insight into its potential non-proliferative roles in other conditions. MethodsMice with or without hepatocyte cyclin D1 (D1fl/fl or D1{Delta}Hep) were fasted and refed a high-carbohydrate diet. Mouse and human liver in the setting of aging and MASLD were analyzed. The C. elegans model was used to evaluate the role of cyclin D1 (CYD-1) in response to overnutrition. ResultsCyclin D1 regulated hepatic gene networks involved in glucose and lipid metabolism, protein synthesis, immune response, and other pathways after feeding. Induction of acute phase response proteins was markedly inhibited in D1{Delta}Hep mice, which was associated with corresponding changes in histone acetylation on key genes. In aged liver, hepatocyte cyclin D1 was induced without associated proliferation; this was markedly pronounced in progeroid Ercc1-deficient mice. Cyclin D1 was upregulated in MASLD and diminished with successful treatment. CYD-1 was induced by overnutrition in the intestine of Caenorhabditis elegans (which performs metabolic functions similar to liver) and regulates key nutrient-responsive proteins. CYD-1 inhibition prolonged lifespan in this setting. ConclusionsCyclin D1 regulates nutrient-mediated physiology in the liver and C. elegans, indicating that it has unexpected and highly conserved metabolic functions. Further study is warranted to define its role in hepatic disease and aging. HighlightsO_LICyclin D1 is induced in hepatocytes with feeding and broadly regulates hepatic gene expression. C_LIO_LIAcute phase response (APR) and senescence-associated secretory phenotype (SASP) proteins are markedly regulated by cyclin D1. C_LIO_LIHepatocyte expression of cyclin D1 is substantially upregulated in aging, premature aging, and MASLD without associated proliferation. C_LIO_LICyclin D1 (CYD-1) regulates nutrient-mediated signaling and lifespan in response to overnutrition in C. elegans. C_LI

Engulfment by macrophages is critical for waste clearance in the vertebrate brain. Understanding clearance mechanisms may open new therapeutic possibilities to counter brain aging and neurodegenerative diseases. However, few in vivo models exist to study engulfment in the brain and characterize this process during aging and across species. Here we present a genetic model for secretion of a fluorescent protein by neurons in the brain of the African turquoise killifish, the shortest-lived vertebrate that can be bred in captivity. We use this model to identify a population of brain macrophages in the killifish responsible for engulfment of material from the brain extracellular space. Intriguingly, many of these cells bear similarities to mammalian border-associated and monocyte-derived macrophages, rare subsets of macrophages in mouse and human brains noted for their engulfment capabilities. We also find that in our model, killifish brain macrophages decline in engulfment capacity with age. This work highlights how vertebrate brain macrophages, particularly those at brain border regions, can play a critical role in clearance and provides an opportunity to test interventions that can boost engulfment by these macrophages to promote brain resilience in old age and disease.

The adult skeletal muscle regenerates robustly upon injury, but this regenerative capacity rapidly declines with age. In this study, we identify the lanthionine synthetase C-Like (LanCL) proteins, mammalian homologs of the bacterial peptide cyclase LanC, as positive regulators of muscle regeneration in middle-aged mice. In a barium chloride-induced injury model, we found the protein levels of LanCL1 and LanCL2 to increase during an early phase of regeneration in middle-aged (12-month-old) but not young adult (4-month-old) mice. Utilizing a mouse line lacking all three LanCL proteins (LanCL triple KO or LTKO), we examined a potential role of LanCL in injury-induced muscle regeneration. Consistent with an age-dependent function of LanCL, we observed a delayed regeneration of the tibialis anterior (TA) muscle after injury, as reflected by reduced sizes of regenerating myofibers in middle-aged (but not young) LTKO compared to age-matched WT mice. Although the pool size of quiescent satellite cells (Pax7+) was comparable between 12-month-old LTKO and WT muscles without injury, the number of Pax7+ cells was significantly higher in regenerating LTKO muscles at day 5 after injury, accompanied by drastically decreased numbers of MyoD+ and MyoG+ cells, as well as increased numbers of proliferating cells. In addition, we detected elevated expression of pro-inflammatory cytokines in regenerating LTKO muscles, while the number of macrophages was similar comparing LTKO and WT muscles. Taken together, our observations suggest that in aging muscles LanCLs are important for proper timing of inflammation resolution and regeneration upon injury. New & NoteworthyPhysiological roles of the mammalian homologs of bacterial LanC, LanCLs, are poorly understood. Our work uncovers a function of LanCLs in post-injury regeneration of aging skeletal muscles. Middle-aged LanCL triple KO mice displayed a delay in satellite cell differentiation and regenerative myofiber formation, as well as persistent inflammatory cytokine expression, suggesting that LanCLs may have an age-dependent role in modulating inflammation in the injured muscles to facilitate regeneration.

Multiple object tracking (MOT) is a core function of dynamic visual attention that relies on the ability to simultaneously monitor several moving objects. Although MOT performance is known to decline with age, and to depend on efficient oculomotor strategies, how these processes interact across the adult lifespan and under degraded visual input remains poorly understood. Here, we examined the effects of aging on MOT under normal and gaze-contingent viewing conditions simulating central and peripheral visual field loss. Sixty participants aged 20-80 years completed a MOT task while eye movements were recorded, enabling characterization of performance and oculomotor behavior across five viewing conditions. Behavioral results revealed a continuous decline in tracking performance across adulthood, indicating a graded rather than categorical effect of age. Performance was strongly reduced by visual-field restrictions, with the largest impairments under central vision occlusion. Eye-tracking analyses showed that better performance was associated with greater reliance on centroid-based gaze strategies, consistent with distributed monitoring of target configurations. Critically, older adults relied more on focal, target-based tracking under conditions simulating peripheral vision loss, and less on centroid-based strategies; this shift was associated with poorer performance. In contrast, oculomotor behavior during full-field viewing was largely preserved across age. Together, these findings suggest that aging affects multiple object tracking through combined sensory, attentional, and oculomotor mechanisms. Beyond a reduction in capacity, age-related decline also reflects systematic changes in visual sampling strategies during dynamic tracking.