Quantifying biological aging and predicting age-related functional decline are increasingly important for reducing the health and socioeconomic burden of population aging. DNA methylation is one of the most extensively studied epigenetic features of aging and underlies epigenetic clocks, promising quantitative biomarkers of biological age. However, the molecular processes driving age-associated DNA methylation changes and the biological signals captured by these clocks remain unclear. A major unresolved issue is the contribution of oxidized 5-methylcytosine (5mC) derivatives to epigenetic remodeling during aging. These derivatives, including 5-hydroxymethylcytosine (5hmC), 5-formylcytosine and 5-carboxylcytosine, are generated through TET-mediated oxidation of 5mC. Although they can act as intermediates of DNA demethylation, they may also represent epigenetic signals with regulatory functions distinct from 5mC. This review summarizes current evidence on oxidized 5mC derivatives in mammalian aging, focusing on 5hmC. Aging is associated with context-dependent changes in global 5hmC levels and genome-wide distribution. Age-associated differentially hydroxymethylated regions occur in genes, regulatory elements, repetitive sequences and transposable elements. 5hmC and 5mC changes often show distinct genomic distributions, suggesting partially independent epigenetic processes. 5hmC may regulate transcriptional stability, cellular identity, inflammation and tissue vulnerability. Understanding the TET/5hmC pathway may improve interpretation of epigenetic aging and support 5hmC-based clocks and healthy-aging strategies.

Aging is a universal biological process signified by a time-dependent decline in physiological activity, driven by molecular and cellular damage, leading to greater susceptibility to diseases and fatal outcomes. Impaired proteostasis is a key aspect of cellular aging in which the cells become less efficient at folding, repairing, and recycling proteins, consequently inducing accumulation of damaged and aggregation-prone proteins. The onset of muscle loss is driven by a reduction in protein synthesis, heightened activation of proteolytic pathways, and elevated ER stress factors, collectively contributing to functional decline and increased vulnerability with aging. Muscle atrophy, whether age-related or driven by chronic illness, represents a major role in defective health, impacting both quality of life and survival. This review explores the intricate and multidimensional nature of proteostasis network regulating protein quality control across skeletal muscles. We examined how the malfunction of components within proteostasis networks during aging contributes to the induction, progression, and chronicity of common age-related muscle wasting. Experimental and clinical studies exploring potential therapeutic strategies for better proteostasis in muscle wasting have been discussed. In this review, we emphasized the increasing demand for effective therapeutic interventions that can slow down or mitigate age-related deterioration in muscle physiology and sustain mobility and quality of life in the elderly. We analyzed the roles of ubiquitin proteasome system, autophagy lysosomal pathway, and unfolded protein response in muscle wasting, highlighting protein loss from synthesis-degradation imbalance as a major driver of muscle atrophy under catabolic conditions. This review outlines key findings with emerging insights to help drive the development of targeted therapies against muscle wasting. Looking ahead, emerging approaches such as PROTACs, extracellular vesicle-based therapies, and artificial intelligence-driven predictive models hold promise for advancing precision interventions in muscle wasting research.

Mitochondria arose from an alphaproteobacterial endosymbiont that became integrated within an archaeal host during eukaryogenesis. The discovery of Asgard archaea has clarified host ancestry and supports reconstructions in which aspects of cytoskeletal and membrane complexity preceded mitochondrial acquisition. Organellogenesis involved genome reduction, gene transfer, protein import, metabolic coupling, and vertical inheritance. These evolutionary principles complement current mitochondrial transplantation recommendations by generating testable predictions about recipient dependence and the duration of rescue. Transplanted mitochondria are mature organelles introduced into cells already equipped to maintain mitochondria; the requirement for transient or durable function must nevertheless be tested for each indication. Aging can modify organelle delivery, recipient quality control, and tissue responses, with particular implications for the neurovascular unit and neuronal function. Extracellular vesicle delivery requires verification of mitochondrial cargo, potency, and compatibility. Measurable criteria distinguish delivery, uptake, cytosolic access, network interaction, persistence, and functional benefit, while separating evidence from aging, acute ischemia, and inherited disease models.

Aging is associated with progressive oxidative stress, chronic inflammation and functional deterioration across multiple organs. Increasing evidence suggests that the gut microbiota plays a pivotal role in regulating aging through the gut-brain axis and systemic immune interactions. The present study investigated the therapeutic potential of fecal microbiota transplantation (FMT) in a D-galactose-induced rat model of accelerated aging. Male rats were allocated into four experimental groups: Healthy control, D-galactose-induced aging, aging treated with FMT and aging treated with antibiotics prior to FMT. Accelerated aging was induced by intraperitoneal administration of D-galactose (150 mg/kg/day). FMT was performed using fecal microbiota obtained from healthy donor rats. Cognitive performance was assessed using the Morris Water Maze (MWM), and histopathological alterations were evaluated in the heart, hippocampus and colon using hematoxylin and eosin staining. D-galactose administration significantly impaired spatial learning and memory and induced marked pathological alterations, including myocardial edema and hemorrhage, neuronal degeneration and vacuolation in the hippocampus, and crypt disruption with inflammatory cell infiltration in the colon. FMT markedly improved behavioral performance and substantially attenuated tissue damage in all examined organs. In contrast, antibiotic pretreatment was associated with less pronounced improvement following FMT, suggesting that the recipient intestinal environment may influence the response to transplantation. These findings provide behavioral and histopathological evidence consistent with beneficial effects of FMT on several features of accelerated aging; however, direct changes in microbial composition, microbial function, and donor engraftment were not assessed.

Inflammaging, a state of chronic low-grade inflammation, is a key contributor to biological aging and diabetes. Traditional inflammatory indices within the interplay between inflammation and epigenetic aging remain insufficiently explored. In addition, novel platelet-based inflammatory indices may perform better than traditional inflammatory indices. This study was a cross-sectional study with survival analysis and analyzed data from 2494 participants in the National Health and Nutrition Examination Survey (NHANES) 1999-2002. In addition to four traditional inflammatory indices (Neutrophil-to-Lymphocyte Ratio [NLR], Systemic Inflammation Response Index [SIRI], Systemic Immune-Inflammation Index [SII], and Pan-Immune-Inflammation Value [PIV]), three novel platelet-based inflammatory indices, including Neutrophil-to-Platelet Ratio (NPR), Monocyte-to-Platelet Ratio (MPR), and Monocyte-Neutrophil-to-Platelet Ratio (MNPR) were used. Biological aging indicators were quantified using seven indicators: six DNA methylation clocks (HorvathAge, HannumAge, SkinBloodAge, PhenoAge, GrimAge2Mort, and DUNEDINPOAM) and one clinical biomarker-based measure (Klemera-Doubal BioAge). For age-based metrics, epigenetic age deviation (EAD) was defined as the residual from regression on chronological age. Multivariate linear regression and restricted cubic spline (RCS) models were used to assess the associations between inflammatory indices and biological aging indicators. Cox proportional hazards models were further applied to evaluate diabetes-specific mortality risk using linked mortality follow-up data through December 31, 2019, with a median follow-up duration of 206.00 months, and mediation analysis was performed to explore the role of metabolic indicators. Traditional inflammatory indices exhibited significant associations with accelerated biological aging across multiple biological aging indicators (all P < 0.05). Compared with traditional inflammatory indices, platelet-based indices showed that the placement of platelets, particularly in the denominator versus the numerator, was associated with differences in aging-related outcomes, suggesting an important role of platelets in inflammation. Further analysis results indicate that the inflammatory indicators with platelets in the denominator perform better in risk stratification prediction. Survival analysis revealed that patients with the "High NPR + Accelerated Aging" phenotype faced the highest risk of diabetes-specific mortality, particularly within the GrimAge2Mort model. Mediation analysis identified the triglyceride-glucose (TyG) index as a critical mediator in the pathway linking epigenetic aging to diabetes-related mortality. Among the evaluated indices, the novel inflammatory index, especially NPR, showed stronger associations with epigenetic aging than traditional inflammatory indices. This study not only elucidates the role of platelets in inflammaging and diabetes, but also offers a novel perspective for prognostic assessment in diabetes management.

Time-to-event models are central to aging research, quantifying both whether and when an event occurs. However, guidance on selecting among traditional statistical and machine learning (ML) methods for prediction modeling remains limited, particularly for epidemiologic aging cohorts with wide assessment intervals. Mobility limitation, as a clinically important aging outcome with such complexities, provides a relevant test case for methodological benchmarking. We conducted a systematic benchmark comparison of 14 statistical and ML time-to-event methods using harmonized data from four longitudinal U.S. aging cohorts (N = 14,821). The outcome was time to incident mobility limitation, defined by self-reported walking difficulty or gait speed < 0.8 m/s. Models were evaluated using 4-fold cross-validation repeated 100 times within cohorts. Performance metrics captured complementary dimensions of predictive quality: discrimination (C-index), accuracy and calibration (Brier score, integrated log loss, calibration index), and computational efficiency (model training time). Prespecified decision rules synthesize results across metrics to identify preferable methods. Across pooled analyses, multiple methods demonstrated comparable discrimination, including penalized Cox models, tree-based ensembles, and boosting approaches. Oblique random survival forest achieved the most favorable overall trade-off, combining high discrimination (C-index 0.673), good calibration (Brier score 0.147), and moderate training time (9.2 min). When computational efficiency was prioritized, penalized regression methods may be preferable, with good discrimination and Brier score. These findings support random forest and penalized regression as strong defaults for time-to-event prediction modeling in gerontologic research and highlight the importance of joint evaluation of discrimination, calibration, and feasibility.