A comparative study of metformin and nicotinamide riboside in alleviating tissue aging in rats

Insights and Interventions in Age-Associated Inflammation

Aging is a systemic, complex, and heterogeneous process characterized by a progressive decline in physiological functions, rendering it a major risk factor for various chronic diseases. Chronic inflammation has emerged as both a hallmark and a driver in this complicated process. This persistent inflammatory state arises from a spectrum of stimuli, ranging from external pathogens to internal cellular remnants, to metabolic dysregulation, and to chronic stress. Here, we examine recent mechanistic advances into the driving forces behind age-related chronic inflammation, explore promising anti-inflammatory strategies to mitigate aging, and address current challenges, proposing future directions to propel this evolving field toward translational breakthrough.

Unraveling aging from transcriptomics

Research into aging constitutes a pivotal endeavor aimed at elucidating the underlying biological mechanisms governing aging and age-associated diseases, as well as promoting healthy longevity. Recent advances in transcriptomic technologies, such as bulk RNA sequencing (RNA-seq), single-cell transcriptomics, and spatial transcriptomics, have revolutionized our ability to study aging at unprecedented resolution and scale. These technologies present novel opportunities for the discovery of biomarkers, elucidation of molecular pathways, and development of targeted therapeutic strategies for age-related disorders. This review surveys recent breakthroughs in different types of transcripts on aging, such as mRNA, long noncoding (lnc)RNA, tRNA, and miRNA, highlighting key findings and discussing their potential implications for future studies in this field.

SIRT5 safeguards against primate skeletal muscle ageing via desuccinylation of TBK1

Ageing-induced skeletal muscle deterioration contributes to sarcopenia and frailty, adversely impacting the quality of life in the elderly. However, the molecular mechanisms behind primate skeletal muscle ageing remain largely unexplored. Here, we show that SIRT5 expression is reduced in aged primate skeletal muscles from both genders. SIRT5 deficiency in human myotubes hastens cellular senescence and intensifies inflammation. Mechanistically, we demonstrate that TBK1 is a natural substrate for SIRT5. SIRT5 desuccinylates TBK1 at lysine 137, which leads to TBK1 dephosphorylation and the suppression of the downstream inflammatory pathway. Using SIRT5 lentiviral vectors for skeletal muscle gene therapy in male mice enhances physical performance and alleviates age-related muscle dysfunction. This study sheds light on the molecular underpinnings of skeletal muscle ageing and presents the SIRT5-TBK1 pathway as a promising target for combating age-related skeletal muscle degeneration.

A multi-omic single-cell landscape of the aging mouse ovary

The ovary is one of the first organs in humans to exhibit age-related functional impairments. As an organ composed of diverse heterogeneous cell types, the ovary exhibits cell-type-specific changes during the aging process, ultimately leading to a decline in female fertility. Investigating the molecular mechanisms of ovarian aging is crucial for understanding age-related fertility dysfunction in females. In this study, we combine scRNA-seq and scATAC-seq from mouse young/aged ovaries to characterize molecular features during ovarian aging. Using the single-cell multi-omic data, we revealed the cell-type-specific transcriptional changes during the aging process in seven major ovarian cell types and identified the cis/trans-regulatory elements governing these transcriptional changes. Specifically, we uncovered the transcriptional alterations of TGF-beta signaling in mesenchymal cells and endoplasmic reticulum stress in granulosa cells of aged mouse ovaries and further identified the potential corresponding cis/trans-regulatory elements. These molecular alterations may contribute to aging-induced functional impairments in mouse ovaries. In summary, this work provides transcriptome and chromatin accessibility landscape of ovarian aging in mice, which serve as a resource for identifying the cell-type-specific molecular mechanisms underlying ovarian aging, aiding in the identification of potential diagnostic biomarkers and treatment strategies.

Advancing Longevity: Exploring Antiaging Pharmaceuticals in Contemporary Clinical Trials Amid Aging Dynamics

Aging is an inevitable biological process that significantly impacts human health, leading to a decline in cellular function and an increase in cellular damage. This study elucidates the burgeoning potential of antiaging pharmaceuticals in mitigating the thriving burden of chronic conditions linked to advancing age. It underscores the pivotal role of these pharmacotherapeutic agents in fostering longevity free from debilitating age-related afflictions, notably cardiovascular disorders, neoplastic processes, and neurodegenerative pathologies. While commendable strides have been made evident in preclinical models, it is crucial to thoroughly investigate their effectiveness and safety in human groups. In addition, ethical concerns about fair access, societal impacts, and careful resource distribution are significant in discussions about developing and using antiaging medications. By approaching the development and utilization of antiaging medications with diligence and foresight, we can strive toward a future where individuals can enjoy extended lifespans free from the debilitating effects of age-related ailments.

Metformin decelerates aging clock in male monkeys

In a rigorous 40-month study, we evaluated the geroprotective effects of metformin on adult male cynomolgus monkeys, addressing a gap in primate aging research. The study encompassed a comprehensive suite of physiological, imaging, histological, and molecular evaluations, substantiating metformin's influence on delaying age-related phenotypes at the organismal level. Specifically, we leveraged pan-tissue transcriptomics, DNA methylomics, plasma proteomics, and metabolomics to develop innovative monkey aging clocks and applied these to gauge metformin's effects on aging. The results highlighted a significant slowing of aging indicators, notably a roughly 6-year regression in brain aging. Metformin exerts a substantial neuroprotective effect, preserving brain structure and enhancing cognitive ability. The geroprotective effects on primate neurons were partially mediated by the activation of Nrf2, a transcription factor with anti-oxidative capabilities. Our research pioneers the systemic reduction of multi-dimensional biological age in primates through metformin, paving the way for advancing pharmaceutical strategies against human aging.

Identification of FOXO1 as a geroprotector in human synovium through single-nucleus transcriptomic profiling

The synovium, a thin layer of tissue that is adjacent to the joints and secretes synovial fluid, undergoes changes in aging that contribute to intense shoulder pain and other joint diseases. However, the mechanism underlying human synovial aging remains poorly characterized. Here, we generated a comprehensive transcriptomic profile of synovial cells present in the subacromial synovium from young and aged individuals. By delineating aging-related transcriptomic changes across different cell types and their associated regulatory networks, we identified two subsets of mesenchymal stromal cells (MSCs) in human synovium, which are lining and sublining MSCs, and found that angiogenesis and fibrosis-associated genes were upregulated whereas genes associated with cell adhesion and cartilage development were downregulated in aged MSCs. Moreover, the specific cell-cell communications in aged synovium mirrors that of aging-related inflammation and tissue remodeling, including vascular hyperplasia and tissue fibrosis. In particular, we identified forkhead box O1 (FOXO1) as one of the major regulons for aging differentially expressed genes (DEGs) in synovial MSCs, and validated its downregulation in both lining and sublining MSC populations of the aged synovium. In human FOXO1-depleted MSCs derived from human embryonic stem cells, we recapitulated the senescent phenotype observed in the subacromial synovium of aged donors. These data indicate an important role of FOXO1 in the regulation of human synovial aging. Overall, our study improves our understanding of synovial aging during joint degeneration, thereby informing the development of novel intervention strategies aimed at rejuvenating the aged joint.

CRL2APPBP2-mediated TSPYL2 degradation counteracts human mesenchymal stem cell senescence

Cullin-RING E3 ubiquitin ligases (CRLs), the largest family of multi-subunit E3 ubiquitin ligases in eukaryotic cells, represent core cellular machinery for executing protein degradation and maintaining proteostasis. Here, we asked what roles Cullin proteins play in human mesenchymal stem cell (hMSC) homeostasis and senescence. To this end, we conducted a comparative aging phenotype analysis by individually knocking down Cullin members in three senescence models: replicative senescent hMSCs, Hutchinson-Gilford Progeria Syndrome hMSCs, and Werner syndrome hMSCs. Among all family members, we found that CUL2 deficiency rendered hMSCs the most susceptible to senescence. To investigate CUL2-specific underlying mechanisms, we then applied CRISPR/Cas9-mediated gene editing technology to generate CUL2-deficient human embryonic stem cells (hESCs). When we differentiated these into hMSCs, we found that CUL2 deletion markedly accelerates hMSC senescence. Importantly, we identified that CUL2 targets and promotes ubiquitin proteasome-mediated degradation of TSPYL2 (a known negative regulator of proliferation) through the substrate receptor protein APPBP2, which in turn down-regulates one of the canonical aging marker-P21waf1/cip1, and thereby delays senescence. Our work provides important insights into how CRL2APPBP2-mediated TSPYL2 degradation counteracts hMSC senescence, providing a molecular basis for directing intervention strategies against aging and aging-related diseases.

Emerging epigenetic insights into aging mechanisms and interventions

Epigenetic dysregulation emerges as a critical hallmark and driving force of aging. Although still an evolving field with much to explore, it has rapidly gained significance by providing valuable insights into the mechanisms of aging and potential therapeutic opportunities for age-related diseases. Recent years have witnessed remarkable strides in our understanding of the epigenetic landscape of aging, encompassing pivotal elements, such as DNA methylation, histone modifications, RNA modifications, and noncoding (nc) RNAs. Here, we review the latest discoveries that shed light on new epigenetic mechanisms and critical targets for predicting and intervening in aging and related disorders. Furthermore, we explore burgeoning interventions and exemplary clinical trials explicitly designed to foster healthy aging, while contemplating the potential ramifications of epigenetic influences.

Stress, epigenetics, and aging: Unraveling the intricate crosstalk

Aging, as a complex process involving multiple cellular and molecular pathways, is known to be exacerbated by various stresses. Because responses to these stresses, such as oxidative stress and genotoxic stress, are known to interplay with the epigenome and thereby contribute to the development of age-related diseases, investigations into how such epigenetic mechanisms alter gene expression and maintenance of cellular homeostasis is an active research area. In this review, we highlight recent studies investigating the intricate relationship between stress and aging, including its underlying epigenetic basis; describe different types of stresses that originate from both internal and external stimuli; and discuss potential interventions aimed at alleviating stress and restoring epigenetic patterns to combat aging or age-related diseases. Additionally, we address the challenges currently limiting advancement in this burgeoning field.

CHIT1-positive microglia drive motor neuron ageing in the primate spinal cord

Ageing is a critical factor in spinal-cord-associated disorders1, yet the ageing-specific mechanisms underlying this relationship remain poorly understood. Here, to address this knowledge gap, we combined single-nucleus RNA-sequencing analysis with behavioural and neurophysiological analysis in non-human primates (NHPs). We identified motor neuron senescence and neuroinflammation with microglial hyperactivation as intertwined hallmarks of spinal cord ageing. As an underlying mechanism, we identified a neurotoxic microglial state demarcated by elevated expression of CHIT1 (a secreted mammalian chitinase) specific to the aged spinal cords in NHP and human biopsies. In the aged spinal cord, CHIT1-positive microglia preferentially localize around motor neurons, and they have the ability to trigger senescence, partly by activating SMAD signalling. We further validated the driving role of secreted CHIT1 on MN senescence using multimodal experiments both in vivo, using the NHP spinal cord as a model, and in vitro, using a sophisticated system modelling the human motor-neuron-microenvironment interplay. Moreover, we demonstrated that ascorbic acid, a geroprotective compound, counteracted the pro-senescent effect of CHIT1 and mitigated motor neuron senescence in aged monkeys. Our findings provide the single-cell resolution cellular and molecular landscape of the aged primate spinal cord and identify a new biomarker and intervention target for spinal cord degeneration.

SGF29 nuclear condensates reinforce cellular aging

Phase separation, a biophysical segregation of subcellular milieus referred as condensates, is known to regulate transcription, but its impacts on physiological processes are less clear. Here, we demonstrate the formation of liquid-like nuclear condensates by SGF29, a component of the SAGA transcriptional coactivator complex, during cellular senescence in human mesenchymal progenitor cells (hMPCs) and fibroblasts. The Arg 207 within the intrinsically disordered region is identified as the key amino acid residue for SGF29 to form phase separation. Through epigenomic and transcriptomic analysis, our data indicated that both condensate formation and H3K4me3 binding of SGF29 are essential for establishing its precise chromatin location, recruiting transcriptional factors and co-activators to target specific genomic loci, and initiating the expression of genes associated with senescence, such as CDKN1A. The formation of SGF29 condensates alone, however, may not be sufficient to drive H3K4me3 binding or achieve transactivation functions. Our study establishes a link between phase separation and aging regulation, highlighting nuclear condensates as a functional unit that facilitate shaping transcriptional landscapes in aging.

Genome-wide CRISPR activation screening in senescent cells reveals SOX5 as a driver and therapeutic target of rejuvenation

Our understanding of the molecular basis for cellular senescence remains incomplete, limiting the development of strategies to ameliorate age-related pathologies by preventing stem cell senescence. Here, we performed a genome-wide CRISPR activation (CRISPRa) screening using a human mesenchymal precursor cell (hMPC) model of the progeroid syndrome. We evaluated targets whose activation antagonizes cellular senescence, among which SOX5 outperformed as a top hit. Through decoding the epigenomic landscapes remodeled by overexpressing SOX5, we uncovered its role in resetting the transcription network for geroprotective genes, including HMGB2. Mechanistically, SOX5 binding elevated the enhancer activity of HMGB2 with increased levels of H3K27ac and H3K4me1, raising HMGB2 expression so as to promote rejuvenation. Furthermore, gene therapy with lentiviruses carrying SOX5 or HMGB2 rejuvenated cartilage and alleviated osteoarthritis in aged mice. Our study generated a comprehensive list of rejuvenators, pinpointing SOX5 as a potent driver for rejuvenation both in vitro and in vivo.

MAVS Antagonizes Human Stem Cell Senescence as a Mitochondrial Stabilizer

Mitochondrial dysfunction is a hallmark feature of cellular senescence and organ aging. Here, we asked whether the mitochondrial antiviral signaling protein (MAVS), which is essential for driving antiviral response, also regulates human stem cell senescence. To answer this question, we used CRISPR/Cas9-mediated gene editing and directed differentiation techniques to generate various MAVS-knockout human stem cell models. We found that human mesenchymal stem cells (hMSCs) were sensitive to MAVS deficiency, as manifested by accelerated senescence phenotypes. We uncovered that the role of MAVS in maintaining mitochondrial structural integrity and functional homeostasis depends on its interaction with the guanosine triphosphatase optic atrophy type 1 (OPA1). Depletion of MAVS or OPA1 led to the dysfunction of mitochondria and cellular senescence, whereas replenishment of MAVS or OPA1 in MAVS-knockout hMSCs alleviated mitochondrial defects and premature senescence phenotypes. Taken together, our data underscore an uncanonical role of MAVS in safeguarding mitochondrial homeostasis and antagonizing human stem cell senescence.

Biomarkers of aging

Aging biomarkers are a combination of biological parameters to (i) assess age-related changes, (ii) track the physiological aging process, and (iii) predict the transition into a pathological status. Although a broad spectrum of aging biomarkers has been developed, their potential uses and limitations remain poorly characterized. An immediate goal of biomarkers is to help us answer the following three fundamental questions in aging research: How old are we? Why do we get old? And how can we age slower? This review aims to address this need. Here, we summarize our current knowledge of biomarkers developed for cellular, organ, and organismal levels of aging, comprising six pillars: physiological characteristics, medical imaging, histological features, cellular alterations, molecular changes, and secretory factors. To fulfill all these requisites, we propose that aging biomarkers should qualify for being specific, systemic, and clinically relevant.

m6A epitranscriptomic regulation of tissue homeostasis during primate aging

How N⁶-methyladenosine (m⁶A), the most abundant mRNA modification, contributes to primate tissue homeostasis and physiological aging remains elusive. Here, we characterize the m⁶A epitranscriptome across the liver, heart and skeletal muscle in young and old nonhuman primates. Our data reveal a positive correlation between m⁶A modifications and gene expression homeostasis across tissues as well as tissue-type-specific aging-associated m⁶A dynamics. Among these tissues, skeletal muscle is the most susceptible to m⁶A loss in aging and shows a reduction in the m⁶A methyltransferase METTL3. We further show that METTL3 deficiency in human pluripotent stem cell-derived myotubes leads to senescence and apoptosis, and identify NPNT as a key element downstream of METTL3 involved in myotube homeostasis, whose expression and m⁶A levels are both decreased in senescent myotubes. Our study provides a resource for elucidating m⁶A-mediated mechanisms of tissue aging and reveals a METTL3-m⁶A-NPNT axis counteracting aging-associated skeletal muscle degeneration.