Understanding Treatments for Aging and Related Diseases

Genomic instability is one of the central mechanisms of aging, which involves DNA sequence changes, accumulation of damage and mutations, and mitochondrial DNA (mtDNA) release. This DNA damage and mutation affect gene expression and function, leading to cell and organ aging. Genomic instability is also closely related to the occurrence and development of aging-related diseases, such as cancer and neurodegenerative diseases.

An increasing number of studies have indicated that telomerase activity and telomere length are strongly linked to aging. Telomere dysfunction can lead to the aging of multiple tissues and organs, as well as the occurrence of age-related disorders,⁵⁵ including AD, Parkinson’s disease (PD), IPF, and age-related macular degeneration. There is a significant negative correlation between telomere length and the aging rate in different species, with some long-lived species having longer telomere lengths and short-lived species having shorter telomere lengths. Normal aging in mammals is accompanied by telomere attrition and the accumulation of shorter telomeres.⁵⁶ The lifespan of organisms can be influenced by interference with telomere length.

Telomere-related DNA damage response (DDR) foci, also known as telomere-induced DNA damage foci, are formed when the DDR is activated at telomeres.⁴³ This leads to a lower efficiency of damage repair at telomeres, which accumulates and accelerates a senescence-like phenotype.⁵⁵ Telomerase activity is regulated by the telomerase reverse transcriptase (TERT) gene. Therapeutically, telomere shortening can be inhibited by activating endogenous TERT expression or inducing telomerase activity. The agents that activate telomerase are considered potent antiaging agents for treating age-related diseases. The TERT activator TAC can upregulate TERT transcription and promote telomere synthesis, thereby delaying aging.⁵⁷ When telomerase is inactive in cells, antigen-presenting cells transfer telomeres to recipient T cells through extracellular vesicles (EVs), which can extend the telomere length of T cells more than 30-fold, thereby protecting recipient T cells from replicative aging and prolonging the lifespan of the immune system.⁵⁸ SIRT6 is known to have chromatin regulatory activity in telomeres, and deletion of SIRT6 causes genomic instability and premature cell senescence in primary human fibroblasts due to telomere dysfunction. SIRT6 also maintains repressive heterochromatin in subtelomeric regions, thereby silencing the transcription of telomere genes.⁵⁹ SIRT6 is critical for maintaining the sustained self-renewal capacity of hematopoietic stem cells (HSCs) and human mesenchymal stem cells (hMSCs).⁶⁰ Importantly, lifestyle regimen including diets rich in vegetables, fruits, legumes, nuts, and other foods rich in fiber and antioxidants is also linked to increased telomere length. While interventions such as telomerase activation have not yet fully overcome safety-related bottlenecks, an in-depth understanding of the telomere-aging axis has provided new directions for precision antiaging strategies and disease prevention. Future research should focus on screening agents that can specifically prolong telomeres and activate telomerase and on means to support telomere maintenance through judicious selection of foods.

Epigenetics refers to the modification of genes without altering the DNA sequence, including DNA and RNA methylation, histone modification, and noncoding RNA.⁶¹ The loss of epigenetic information has proven to be one of the reasons for the aging of mammals.⁶² Increasing evidence suggests that regulating DNA methylation, histone modifications, RNA splicing and noncoding RNAs in epigenetics (Fig. 4) can delay aging phenotypes.^39,61 Strategies that focus on the manipulation of epigenetic processes have reduced aging or extended lifespan in animal models.

Proteostasis refers to the dynamic balance of a complex network of proteins in cells, including protein synthesis, structural and functional maturation, protein quality control, folding modification, localization and transport, functional recovery and degradation.⁸¹ This balance is achieved through the synergistic effects of the molecular chaperone system, ubiquitin-proteasome system (UPS) and autophagy-lysosome system. The imbalance of proteostasis caused by aging is characterized by decreased protein synthesis and folding efficiency, dysfunction of the protein degradation system, and abnormal posttranslational modifications.^81,82 Together, these changes aggravate the accumulation of misfolded or abnormal proteins, triggering cellular dysfunction and even leading to age-related pathological states.

Autophagy is an evolutionarily conserved catabolic homeostatic program for intracellular material turnover in eukaryotes. Autophagy is separated into three types according to the way in which intracellular substrates are transported to lysosomes: macroautophagy, microautophagy, and chaperone-mediated autophagy (CMA)⁹⁶ (Fig. 5). Autophagy directly or indirectly participates in the regulation of aging in various eukaryotes. The function of autophagy gradually weakens with age, and the failure of autophagy gene function further leads to a shortened lifespan of the organism, forming a vicious cycle. Enhancing autophagy (physiological inducers or pharmacological inducers) helps extend the lifespan and healthy lifespan of mammals.⁹⁷

Accumulating evidence indicates that autophagic activity decreases with age in multiple organisms and that the material transport of lysosomes decreases, indicating that damaged autophagy is a canonical characteristic of aging in organisms. The breakdown of protein homeostasis (misfolding, mislocalization, and aggregation of proteins) is a core characteristic of aging. Although age-related protein homeostasis loss has been recorded in many tissues, age-dependent protein aggregation is closely associated with neurodegenerative diseases. By removing harmful misfolded and aggregated proteins, autophagy supports a healthy aging process. In 2003, the autophagy gene bec-1 (mammalian beclin1) was revealed to be indispensable for longevity extension in nematodes with dysfunction in the IIS pathway.⁹⁸ Subsequently, functional analysis of multiple autophagy-related genes revealed the crucial role of autophagy in extending lifespan. Activating autophagy and increasing autophagic flux via nutritional, pharmacologic and genetic manipulations that contribute to the extension of longevity.⁹⁹ Even so, authoritative evidence that enhancing basal autophagy can prolong the healthspan and lifespan of mammals was not discovered until 2018. Specifically, disruption of beclin1-BCL2 binding is associated with increased levels of basal autophagic flux. The decrease in beclin1-BCL2 binding is linked to longevity and improved aging-related phenotypes.¹⁰⁰ Autophagy-related gene (ATG) family members (ATG5, ATG7, ATG8, etc.) are the core components of autophagy and are essential for the initiation and execution of autophagy. Knockout of ATG5 or ATG7 can shorten the lifespan of experimental animals, whereas overexpression of ATG5 can prolong the lifespan.¹⁰¹ As a selective autophagy receptor, p62/SQSTM1, when upregulated in nematodes and Drosophila, can promote protein homeostasis and extend lifespan.¹⁰¹ Transcription factor EB (TFEB, HLH-30 in C. elegans) is a transcriptional regulator of autophagy and lysosome biogenesis, and TFEB nuclear translocation is reduced during aging, resulting in a decrease in lysosomal number and activity. TFEB activators, such as rapamycin, reverse the age-related decline in autophagy-lysosomal function, and overexpression of HLH-30 prolongs the lifespan of C. elegans.¹⁰² Autophagy can delay aging in a variety of organs, including cardiac aging,¹⁰³ vascular aging,¹⁰⁴ brain aging,¹⁰⁵ skin aging,¹⁰⁶ skeletal muscle aging,¹⁰⁷ liver aging,¹⁰⁸ eye aging,¹⁰⁹ and systemic aging.¹¹⁰ Furthermore, other types of autophagy, such as nucleophagy and lipophagy (Fig. 5), have also been found to regulate aging. Nucleolar size is linked to longevity and life-prolonging interventions, and small nucleoli represent a biological signature of longevity.¹¹¹ Abnormal nuclear anchor protein 1 (ANC-1)/nesprin-2 is eliminated and restrict nucleolus size through autophagy. Furthermore, nucleophagy contributes to stress resistance, germline immortality and longevity.¹¹²

CMA is a type of autophagy that selectively degrades substrates carrying KFERQ motifs through lysosomes. CMA activity decreases with age in the majority of tissues and organs, which is due to the decreased stability of lysosomal-associated membrane protein 2A (LAMP2A) on the lysosomal membrane of aging organisms.¹¹³ There are multiple pathways by which CMA dysfunction induces senescence, including the generation of DNA damage, cell cycle arrest (expression of p12/Cdkn1a), and lipid accumulation.¹¹⁴ The first direct evidence of aging amelioration effects by activating CMA was demonstrated in a double transgenic mouse model. CMA enables improvement of intracellular protein disorders and maintenance of hepatic function in aging.¹¹⁵ CA, a small-molecule agonist of CMA, increases LAMP2A receptor levels on lysosomes to improve AD.¹¹⁶ Additionally, caloric restriction can mediate constitutive activation of CMA to improve health and promote healthy aging.¹¹⁷ Considering the core role of CMA in maintaining cellular homeostasis and delaying aging, intervention strategies targeting CMA may provide new strategies for the treatment of age-related diseases.

Compared with those of macroautophagy and CMA, the molecular mechanism and physiological implications of microautophagy are still unclear, but the basic characteristics of microautophagy in aging have been revealed. Microautophagy activity decreases with age and is related to an increase in protein secretion. Serine-threonine kinase 38 (STK38/NDR1) is specifically recruited to damaged lysosomes and, together with gamma-aminobutyric acid receptor-associated protein (GABARAPs), repaired damaged membranes through microautophagy.¹¹⁸ Maintenance of lysosomal integrity through the modulation of microlysophagy by STK38 and GABARAPs presumably contributes to preventing aging.

Given the core role of autophagy in aging and the dependency of many geriatric protective agents on autophagy, identifying direct regulators of autophagy that contribute to delaying aging and prolonging a healthy lifespan is critical. At present, research on agents that target autophagy for antiaging mainly focuses on macroautophagy, whereas few studies have focused on natural products that activate chaperone-mediated autophagy and microautophagy, which need to be further explored.

The nutrient-sensing signaling pathway is highly conserved in different species. It is the ability of cells to perceive and respond to energy metabolism substrates. Extensive evidence has demonstrated that the inhibition of nutrient-sensing pathways contributes to delaying the aging process in organisms. We focus on three key nutrient-sensing pathways, including the mTOR, IGF-1, and adenosine monophosphate (AMP)-activated protein kinase (AMPK) pathways.

As a dynamic biophysical system, mitochondria play a major role in regulating energy metabolism and dominating cell death or survival. Research has demonstrated that mitochondrial dysfunction, mitochondrial biogenesis, mitochondrial quality control (MQC), and mitophagy (Fig. 7a) are related to aging.¹⁴⁹ Mitochondrial dysfunction accelerates T-cell senescence and induces senile changes in metabolic, cognitive and cardiovascular features of aging in mice.¹⁵⁰ Mitophagy contributes to maintaining mitochondrial homeostasis by selectively removing impaired and aged mitochondria. This process reduces excessive accumulation of ROS, thereby interrupting the vicious cycle of cellular senescence.¹⁴⁹

MQC ensures cellular homeostasis by coordinating various processes, including protein homeostasis, biogenesis, dynamics, and mitophagy. Preclinical evidence suggests that modulation of MQC can be used to treat cardiac aging, cardiovascular diseases and skin aging.¹⁵¹ However, either excessive activation or inhibition of MQC can cause the accumulation of oxidized proteins, expedite abnormal energy metabolism, and induce mitochondrial dysfunction to stimulate aging. Mitochondrial UPR is an important part of MQC, which can effectively remove unfolded or misfolded proteins under stress to maintain the stability and health of mitochondria. Dysregulation of mitochondrial protein folding stress is a precipitating factor for HSC and NSC senescence. Reducing mitochondrial protein-folding stress can improve neurogenesis, the cognitive function of NSCs and the regenerative capacity of HSCs.^152,153 Minority mitochondrial outer membrane permeabilization (miMOMP) normally occurs in senescent cells, enhances the secretion of mtDNA into the cytoplasm and stimulates the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway to promote SASP. Inhibition of miMOMP can reduce the expression of inflammatory factors and ameliorate metabolic homeostasis in aging mice.¹⁵⁴ In conclusion, targeted regulation of mitochondria can delay aging.

The mitochondria-ER interaction is the central hub of cellular metabolism and regulates the interchange of lipids and metabolites between organelles. The mitochondria-associated membrane or ER-mitochondria contact sites (ERMCSs), which are regions of tight linkage between the ER and mitochondria, are crucial for both cellular physiology and disease (Fig. 7b).¹⁵⁵ ERMCS are capable of remodeling to satisfy the metabolic requirements of cells in response to alterations in intracellular homeostasis. Disruption of the regional homeostasis of ERMCS affects their remodeling ability, leading to impaired intercellular communication and even the occurrence of ALS.¹⁵⁶ Inflammation and mitochondrial Ca²⁺ may play significant roles in aging. Research has indicated that the mitochondrial Ca²⁺ uptake capacity of macrophages gradually decreases with age.¹⁵⁷ ER-mitochondrion calcium transport contributes to regulating mitochondrial Ca²⁺ homeostasis.¹⁵⁸ Inositol 1,4,5-trisphosphate receptors mediate ER Ca²⁺ release and subsequent mitochondrial Ca²⁺ accumulation, leading to cell senescence.^158–160 In AD, hyperoside reduces Aβ oligomers by regulating the ER-mitochondrial Ca²⁺ signaling cascade, which can improve learning, spatial memory and motor ability in mice.¹⁶¹ At present, there are few studies on such drugs, and the discovery of agents that target interorganelle contacts to delay aging still has much room for exploration.

Cell senescence is largely influenced by the interplay between mitochondria and lysosomes, not merely mitophagy (Fig. 7b). Lysosomal signaling triggers the modulation of mitochondrial activity, which improves metabolic homeostasis, redox homeostasis, and longevity. Mitochondrial-lysosome contacts are mainly involved in organelle dynamics and the exchange of ions and lipids among organelles. In aging-related PD, the number of mitochondrial-lysosomal contacts decreases, and the instability of these contact sites leads to disruption of mitochondrial and lysosomal amino acid homeostasis. These discoveries demonstrate that mitochondrial-lysosomal contact may act as a platform for amino acid transfer between organelles.¹⁶² Thus, directly regulating interorganelle contacts can be a potential therapeutic means to ameliorate age-related nervous system disorders.

In 1961, Hayflick first reported that when cell division reaches its limit, it stops dividing and enters a state of irreversible proliferation arrest and proposed the famous “Hayflick limit”.¹⁰ This is the earliest description of replicative senescent cells. In 2024, the SenNet program summarized nine hallmarks of senescent cells: cell cycle arrest, SASP, nuclear changes, changes in cell surface markers, changes in cell morphology, increases in lysosomal content, metabolic adaptation, DNA damage, and upregulation of antiapoptotic pathway.¹⁶³ A variety of anti-cellular senescence strategies have been developed to address these characteristics. Recent studies have shown that cell cycle arrest is not completely irreversible. By targeting the cell cycle inhibitors Cdkn1a and Ccng2, miR-302b can release cell cycle arrest, restore the proliferation ability of senescent cells, and significantly reverse the aging phenotype of mice.³⁸ This provides a new direction and solution for the treatment of age-related diseases. Unfortunately, cellular senescence can spread not only within the same organ through paracrine signals but also from one organ to another through systemic endocrine signals. Systemic senescence triggered by hepatic senescent cells through transforming growth factor beta (TGFβ) signaling is the main cause of multiple organ dysfunction.¹⁶⁴ Importantly, depletion of p16^Ink4a-positive hepatic senescent macrophages significantly attenuated hepatocyte injury.¹⁶⁵ Blocking TGFβ signaling can effectively mitigate the effects of aging transmission, providing a new direction for the treatment of aging-related diseases.

Senescent cells can aggravate neurodegenerative diseases,¹⁶⁶ cardiovascular diseases,^5,167 atherosclerosis,¹⁶⁸ osteoarthritis,¹⁶⁹ etc. Remarkably, not all senescent cells are detrimental (Fig. 8); senescent cells are still involved in many important physiological processes, such as tumor suppression, embryonic development, wound healing and tissue remodeling.^42,170 Some senescent cells can be inserted into young healthy tissues to defend normal tissues from damage by accelerating adjacent stem cell growth and activating repair.¹⁷¹ The senescent cells of fibroblasts and endothelial cells are able to expedite wound healing by stimulating myofibroblast differentiation.¹⁷² The senescent cells are not replaced after removal but instead disturb the blood-tissue barrier, leading to fibrosis of the liver and perivascular tissues.¹⁷³ Unfortunately, the lack of specificity and severe side effects of existing senolytic therapies limit their potential as therapeutic agents. Although strategies for precise elimination of senescent cells have been reported,¹⁷⁴ they can only distinguish between senescent cells and healthy cells and cannot distinguish beneficial senescent cells. On the basis of this dilemma, recent research has made breakthroughs. A double recombinase-mediated genetic system (Sn-pTracer, Sn-cTracer and Sn-gTracer)¹⁶⁵ was generated on the basis of the cell senescence marker p16^Ink4a. Using this system, it was revealed that depletion of p16^INK4a-positive macrophages significantly alleviated liver injury, whereas depletion of p16^INK4a-positive endothelial cells aggravated liver injury.¹⁶⁵ This system can precisely identify and target cell-type-specific senescent cells, providing insights for the future development of cell type-specific aging therapies. While exciting, the continuous discoveries in the senescence field also highlight that it is necessary to develop superior and more targeted senolytic drugs to eliminate pathological senescent cells while preserving healthy senescent cells. In the future, longevity-extending or antiaging agents should target senescent cells related to diseases rather than regeneration.

The essence of stem cell exhaustion is a reduction in stem cell number, functional degradation and loss of regeneration ability, leading to an imbalance in tissue homeostasis and decreased repair ability. Stem cells can recognize signals released by senescent cells and localize to tissues in need of repair and regeneration, improving the aging state. Hence, the age-dependent decline in the regenerative capacity of stem cells is involved in the aging process. Stem cell exhaustion can lead to the occurrence and development of a variety of age-related diseases. During bone aging, knocking out histone demethylase 4B (KDM4B) in hMSCs induces the formation of age-related heterochromatin foci, thereby impairing the self-renewal of hMSCs and promoting hMSC exhaustion, leading to bone aging and osteoporosis.¹⁷⁵ Satellite cells in hMSCs are functionally reduced during muscle aging, which in turn impairs cell–cell interactions. Epigenetic changes, telomere shortening and DNA damage, proteotoxicity, mitochondrial dysfunction, and changes in intercellular communication and key signaling pathways (MAPK,¹⁷⁶ JAK-STAT3,¹⁷⁷ and Notch¹⁷⁸) all lead to permanent cell cycle arrest and exhaustion of satellite cell pools.¹⁷⁹ Activation of autophagy in aged satellite cells can reverse aging and restore stem cell regenerative function.¹⁸⁰ The escape of hair follicle stem cells (HFSCs) leads to stem cell depletion. The expression of cell adhesion and extracellular matrix genes, which are regulated by Foxc1 and Nfatc1,¹⁸⁰ is decreased in aged HFSCs. The aged HFSC niche shows extensive alterations in extracellular matrix composition and basement membrane stiffness,¹⁸¹ which are central regulators of age-dependent stem cell exhaustion. HSCs are adult stem cells that maintain lifelong hematopoietic function, with self-renewal and multilineage differentiation potential.¹⁸² The senescence and exhaustion of HSCs are the core reasons for the decline in hematopoietic system function, involving multiple mechanisms such as telomere attrition, oxidative stress, inflammatory disorders and epigenetic disorders, which ultimately lead to anemia, immunodeficiency, and an increased risk of hematological diseases.¹⁸³ The main characteristics of HSC senescence include a decrease in self-renewal ability, an imbalance in differentiation bias, and epigenetic abnormalities.¹⁸³

Stem cell-rich umbilical cord blood infusion has shown efficacy and safety as adjuvant therapy for older adults with acute leukemia in a phase 2 clinical trial (ChiCTR-OPC-15006492).¹⁸⁴ Despite the widespread use of stem cell therapy, scientists are still struggling to elucidate the molecular mechanism of stem cell depletion. Recent studies have shown that changes in chromosome structure and gene expression may be important causes of stem cell depletion.⁶⁶ In the future, with the development of stem cell research, we are expected to find effective antiaging methods and even reverse some aging-related diseases.

Intercellular communication is a central mechanism for maintaining tissue homeostasis and an important driving force for pathological changes during aging. With increasing age, the intercellular communication network becomes disturbed, leading to the diffusion of inflammatory factors, metabolic disorders and organ dysfunction. Various interactions, such as those involving EVs and soluble factors, play key roles in aging.

The intricate interplay between chronic inflammation and the aging process has been the subject of extensive scientific inquiry, with this phenomenon formally termed “inflammaging”. Characterized as a low-grade, systemic chronic inflammatory state that progressively accompanies the aging process, inflammaging represents a distinct pathophysiological condition.²⁰⁰ Unlike acute inflammatory responses triggered by infection or injury, this persistent inflammatory phenotype arises from the dynamic interplay of multiple factors, including long-term immune system dysregulation, cellular stress responses, and metabolic derangements. This complex etiology underscores the multifactorial nature of age-related inflammatory processes and their critical role in mediating organismal senescence.

Multiple proinflammatory factors secreted by the SASP have been shown to play key roles in driving aging. IL-11 is a proinflammatory cytokine that plays a crucial role in maintaining human health. Under normal circumstances, IL-11 participates in regulating immune responses, but excessive levels can trigger unnecessary inflammation. As individuals age, the expression of IL-11 increases in cells and tissues, leading to fat accumulation and muscle loss. Anti-IL-11 therapy has been shown to prolong the average lifespan of male and female mice by 22.4% and 25%, respectively. In addition, neutralizing IL-11 antibodies combined with angiotensin-converting enzyme inhibitors synergistically prolong the lifespan of Alport syndrome mice.²⁰¹ Dysregulation of IL-17 signaling disrupts epidermal homeostasis through activation of the NF-κB pathway, concurrently exacerbating systemic inflammatory cascades.²⁰² Targeted suppression of IL-17 signaling in aging models attenuates cutaneous inflammation and delays the progression of age-associated phenotypes.²⁰² Intra-articular injection of an anti-IL-17 neutralizing antibody reduced the expression of Cdkn1a, a marker of joint degeneration and aging.²⁰³ IL-6 signaling can drive cellular senescence through activation of the cGAS-STING-NF-κB pathway.²⁰⁴ In age-related cardiovascular disorders, IL-6 exacerbates mitochondrial dysfunction in vascular endothelial cells, thereby accelerating atherosclerosis progression via oxidative stress and lipid accumulation.²⁰⁵ Notably, the inhibition of IL-6 signaling ameliorates senescence-associated phenotypes in both Hutchinson-Gilford progeria syndrome-derived fibroblasts and progeroid mouse models, highlighting its therapeutic potential in counteracting premature aging.²⁰⁶ In addition, tissue-specific aging processes manifest distinct inflammaging signatures, with IL-17 predominating in cutaneous aging, IL-6 predominating in vascular aging, and TNF-α predominating in immune organ senescence.

The molecular mechanism of chronic inflammation-driven aging involves intricate crosstalk among multiple signaling axes within a distinct pathophysiological context. Recent advancements highlight the central roles of several evolutionarily conserved pathways in inflammaging. In addition to the previously discussed nutrient-sensing and autophagy pathways, the molecular landscape of inflammaging further encompasses several key regulatory signaling pathways: the cGAS-STING, Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathways, Wnt/β-catenin signaling, and Notch signaling.

There is an inseparable relationship between the gut microbiota and host health. Dysbiosis promotes multiple pathological conditions, such as obesity, ulcerative colitis, nervous system diseases and cardiovascular diseases.^39,232 The gut microbiota changes with age, and this change in the microbiota is closely related to age-related cognitive decline. Screening of 3983 Escherichia coli mutants revealed that deletion of 29 bacterial genes extends the lifespan of the host C. elegans.²³³ Colanic acid (capsular isopolysaccharide acid), a common gut bacterial metabolite extracted from five bacterial mutants, has been confirmed to extend the lifespan of nematodes and Drosophila by regulating ER stress and mitochondrial dynamics in host cells.²³³ Transplanting the gut microbiota of elderly mice into young mice can lead to loss of intestinal wall integrity in young mice, thereby promoting the release of microbiota metabolites into the circulatory system, leading to inflammation of the brain and eyes.²³⁴ Conversely, transplanting the gut microbiota of young mice into elderly mice can reverse the aging hallmarks of the gut, eyes, and brain.^234,235 Additionally, fecal microbiota transplantation (FMT) from young mice restores the vitality of aging HSCs by inhibiting inflammation²³⁶ and regulating the availability of iron in the bone marrow.²³⁷ Supplementation of Bifidobacterium longum 68S mediates gut homeostasis, thereby exerting a delaying effect on skin aging,²³⁸ and improving age-related delays in fracture repair.²³⁹ Human progeria patients also exhibit gut dysbiosis, showing a remarkable increase in Verrucomicrobia and a decline in Proteobacteria in centenarians.²³² Compared with older people, centenarians have a unique gut microbiota with special metabolites that can inhibit the growth of intestinal pathogens and reduce inflammation.^240,241 Therefore, targeting the gut microbiota can provide means to delay aging (Fig. 11).

Numerous studies have shown that gut microbiota can be regulated by bioactive compounds through multiple pathways. They can directly suppress or stimulate the growth of certain bacteria, change the composition of the gut microbiota, and restore the balanced gut microbiota, thereby affecting host health. Secondly, they can cause changes in the content of bioactive microbial metabolites. Third, they regulate the secretion of substances by the gut microbiota, sustain the integrity of the intestinal mucosal barrier structure, and indirectly change the diversity of the intestinal microbiota. A variety of compounds, such as daurisoline-d4,²⁴² trilobatin,²⁴³ genistein,²⁴⁴ puerarin,²⁴⁵ and icariin,²⁴⁶ have been shown to regulate intestinal homeostasis and delay aging.

Immunoglobulin G (IgG), the most important type of antibody in the body, has long been considered to be involved primarily in immune defense. However, in recent years, multiple studies have shown that IgG accumulates abnormally during the aging process and become an important factor driving tissue degeneration and metabolic decline. The accumulation of IgG is positively correlated with aging and is conserved in multiple species (including humans and mice),²² suggesting that it may serve as a cross-species hallmark of aging. Through the construction of a gerontological atlas of multiorgan aging, it was found that the accumulation of IgG is closely related to the increase in structural entropy and the loss of cell identity.²² During the aging process in mice and humans, IgG accumulates significantly in multiple organs, especially in metabolic- and immune-related organs such as white adipose tissue, the liver, and the spleen.²⁴⁸ For example, the IgG level in the white adipose tissue of elderly mice is nearly 20-fold higher than that of young mice.²⁴⁸ In addition, IgG can promote the senescence phenotype of macrophages and microglia, release inflammatory factors such as IL-6 and TNF-α, form a systemic chronic inflammatory environment, and accelerate multiorgan aging.²² Interference with IgG accumulation can significantly ameliorate metabolic decline during aging and prolong the healthy lifespan. The intervention strategy on the basis of antisense oligonucleotides reduces the IgG content in mouse tissues and delays multiorgan aging.²⁴⁹ In addition, caloric restriction has also been shown to delay aging by reducing IgG levels.²⁴⁸

In summary, the abnormal accumulation of IgG reveals the central role of the immunometabolic network during aging. The accumulation of IgG promotes systemic inflammation by activating macrophages, which can be attributed to the integrative characteristics of chronic inflammation. Future studies need to clarify the dynamic changes in IgG in different organs and develop therapies to precisely regulate IgG levels. Moreover, by combining spatiotemporal omics and big data models, the interaction between IgG and other aging hallmarks (such as chronic inflammation and stem cell depletion) can be analyzed to provide systematic solutions for delaying aging.

Endogenous retroviruses (ERVs) are the remnants of ancient retroviruses integrated into the host genome, accounting for approximately 8% of the human genome.⁴⁵ Recent studies have shown that the abnormal activation of ERVs is closely related to the aging process, which accelerates the occurrence of aging and related diseases through epigenetic dysregulation, the inflammatory response and intercellular signaling.^250,251 Liu’s group systematically defined and revealed that aging-induced resurrection of endogenous retrovirus can serve as a hallmark of senescence.⁴⁰ During aging, epigenetic regulation (e.g., decreased heterochromatin and disturbed DNA methylation) leads to the activation of otherwise silent ERV elements, the production of viral RNA and proteins, and packaging into viral particles. Their reverse transcription products (such as cDNA) trigger innate immune responses by activating the cGAS-STING pathway, leading to cell senescence and inflammation.^41,252 At the same time, viral particles infect neighboring young cells through paracrine or humoral diffusion, spreading the senescence phenotype to the whole body through the mechanism of “contagious aging”, resulting in a cascade of amplification effects.⁴¹ Consistently, multiple high-throughput omics methods have revealed that the reactivation of ERVs directly leads to hair regeneration disorders and depletion of follicle stem cells.²⁵³ Notably, nucleoside reverse transcriptase inhibitors (abacavir and NRTIs) can alleviate age-related cellular and molecular changes.^252,253 Intervention strategies against ERV provide novel approaches for delaying aging and preventing geriatric diseases. However, its biological complexity and clinical safety still need to be further explored. So does molecular mechanisms of ERV–host interactions.

Centromeres are key structures on chromosomes responsible for chromosome segregation, and their dysfunction is closely related to cell senescence. Centromeric inactivation during aging can lead to chromosome segregation defects, genomic instability and decreased cell proliferation, which has become an important driver of aging.²⁴⁷ In senescent cells, the interaction between centromere protein B and lysine-specific demethylase-1 is increased, inhibiting H3K4me2 enrichment and thus hindering centromeric transcription. The centromere signature histone variant CENP-A and the structural protein CENP-C are significantly reduced.²⁴⁷ This decrease is directly related to abnormal chromosome segregation and increased micronucleus formation, suggesting that inactivation of centromere function is the core cause of mitotic defects in senescent cells. Chromosome missegregation caused by centromere inactivation leads to formation of micronuclei, activation of the cGAS-STING pathway, induction of chronic inflammation (such as the release of IL-6 and TNF-α), and formation of a pro-aging microenvironment.²⁴⁷ In addition, p53 protein levels are elevated in senescent cells and exacerbate centromere inactivation through the negative regulation of CENP-A expression.²⁴⁷ Caloric restriction or its mimetics such as rapamycin can indirectly maintain centromere function by regulating the mTOR pathway. In summary, centromere inactivation accelerates aging through epigenetic disorders, inflammatory cascades, and genomic instability. Intervention strategies targeting centromere inactivation have shown potential in cell models, and in the future, they need to be combined with multiomics analysis and clinical validation to promote the precise development of prolongevity treatments.

Collectively, the advances summarized above for the different hallmarks of aging highlight the importance of understanding the molecular mechanisms by which each hallmark influences aging pathologies and, more importantly, the functional interconnections between different hallmarks. Such an understanding forms the foundation for developing more effective and safer therapeutic interventions to combat these age-associated chronic diseases.

AD is the most common progressive neurodegenerative disorder characterized by cognitive decline and memory loss, and it primarily impacts the hippocampus and cerebral cortex.²⁷⁵ A key hallmark of AD is disrupted proteostasis, which leads to the pathological buildup of misfolded and aggregated proteins. These include amyloid-beta (Aβ) plaques, hyperphosphorylated tau tangles and the transactive response DNA-binding protein of 43 kDa (TDP-43).²⁷⁶ While AD has genetic causes, notably the apolipoprotein E4 (ApoE4) allele, which promotes the accumulation of Aβ plaques through the MAPK signaling pathway,²⁷⁷ the majority of cases are sporadic and strongly age-associated.²⁷⁸ A subaging population consisting of postmenopausal women can experience a sudden decline in estrogen levels, causing the brain to switch from glucose metabolism to lipid metabolism via white matter. This heightens women’s susceptibility to neuronal damage, leading to a higher (than men) incidence of AD as they age.²⁷⁹ Furthermore, aging can drive oxidative stress,²⁸⁰ DNA damage,²⁸¹ epigenetic modifications,²⁸² and mitochondrial dysfunction,²⁸³ which can also contribute to the accumulation of Aβ plaques and tau tangles. This buildup subsequently disrupts proteostasis and autophagy, ultimately hindering the removal of these toxic protein aggregates.

PD, the most prevalent neurodegenerative disorder after AD, is a movement disorder characterized by the accumulation of α-synuclein aggregates,²⁸⁴ known as Lewy bodies, and impaired dopamine neurotransmission in the substantia nigra pars compacta,²⁸⁵ a region that controls movement. Like AD, PD is influenced by several genetic risk factors. Mutations at loci hinder lysosomal and mitochondrial function and obstruct protein clearance, increasing the accumulation of toxic protein aggregates and driving neurodegeneration. Aging accelerates the progression of PD through various mechanisms. Faulty proteolysis and hindered autophagy²⁸⁶ lead to the accumulation of α-syn aggregates, which can trigger disease progression once they exceed a specific threshold. Dysfunction of the PINK1-Parkin pathway in PD can lead to mitochondrial issues by obstructing mitophagy and disrupting ATP metabolism. As a result, the high-energy needs of dopaminergic neurons may be unmet, increasing their vulnerability to oxidative stress, which drives neurodegeneration. Additionally, chronic inflammation due to aging can compromise the immune system, leading to extended activation of glial cells.²⁸⁷ This ongoing activation initiates a detrimental cycle of inflammation in the brain, as these activated glial cells produce increased amounts of inflammatory cytokines. Ultimately, reducing or delaying these risk factors of aging may provide neuroprotection and delay the onset of disease progression.

Amyotrophic lateral sclerosis (ALS) is a swiftly advancing, fatal neurodegenerative disorder linked to mitochondrial dysfunction,²⁸⁸ primarily resulting in the degeneration of motor neurons within the central nervous system (CNS) because of unmet energy demands, leading to muscle weakness and eventually respiratory failure. Approximately 90% of ALS cases are sporadic, although mutations in some genes related to mitochondrial functions, such as HuD, TDP-43, and FUS, can increase the risk of disease progression.²⁸⁹ The incidence of ALS increases with age, peaking at approximately 70 years. In ALS, mutated TDP-43 can disrupt nuclear integrity and hamper the nonhomologous end-joining (NHEJ) pathways crucial for repairing double-strand DNA breaks in neurons.²⁹⁰ With aging, mitochondrial dysfunction and genomic instability can lead to the buildup of oxidative stress and DNA damage, which can disrupt energy production and genomic maintenance in motor neurons, processes implicated in ALS pathogenesis. Moreover, ALS is often further characterized by dysregulated proteostasis and autophagy, which can cause an excess of unfolded proteins, including stress granules, and TDP-43 pathologies.²⁹¹

HD is a hereditary neurodegenerative condition caused by a mutated huntingtin (HTT) gene on chromosome 4.²⁹² In HD, the GABAergic neurons in the striatum and cortex are the most affected, contributing to clinical hallmarks such as chorea, cognitive impairment and nonmotor symptoms.²⁹³ Telomere attrition and increased DNA methylation with aging can accelerate the onset of HD.²⁹⁴ Inhibition of autophagy via TFEB activation can subsequently inhibit calcineurin activity, which is required for neuronal transmission.²⁹⁵ Excessive mutHTT can overwhelm the UPS, dysregulating proteostasis and further promoting mutHTT accumulation.²⁹⁶ The presence of mutHTT and the accumulation of mtDNA mutations caused by inadequate mitophagy and decreased biogenesis impair oxidative phosphorylation, enhance the formation of reactive ROS, and lower ATP production. This leads to inefficient energy generation and heightens the likelihood of neuronal degeneration.²⁹⁷ With HD, senescent neural cells and neurons can arise because mutHTT contributes to chronic neuroinflammation via the secretion of SASP.²⁹⁷

Atherosclerosis is a chronic inflammatory disease characterized by the accumulation of plague made of cholesterol, fat, calcium, dead cell waste components, and immune cells in arterial walls. This can restrict blood flow, depriving vital organs of oxygen.²⁹⁸ It can trigger cardiovascular diseases such as heart attack and strokes. Key risk factors for atherosclerosis include hypertension, obesity, and maternal-fetal blood transfer.²⁹⁹ Poor diets or metabolic conditions can lead to independent atherosclerosis risk factors such as increased ceramide levels.³⁰⁰ Genetic mutations that affect inflammatory pathways, such as the activation of NF-κB, may increase the risk of atherosclerosis.³⁰¹ Aging causes internal and external alterations in blood arteries, usually preceding atherosclerosis.²⁰⁵ Understanding these mechanisms may enable early interventions to lessen the effects of atherosclerosis. Telomere attrition in leukocytes can lead to genomic instability, initiating senescence in vascular smooth muscle cells (VSMCs) and subsequently promoting a proinflammatory environment. Aging may lead to diminished regeneration and functionality of VSMCs, potentially promoting the formation of atherosclerotic plaques and weakening the structural integrity of blood vessel walls.³⁰² The age-related decrease in NRF2 expression may result in a loss of proteostasis and mitochondrial dysfunction. This leads to increased systemic ROS, which can contribute to cardiovascular events and promote atherosclerosis.³⁰³

Heart failure (HF) is a clinical illness characterized by structural impairment of the heart, impairing its capacity to deliver adequate blood to satisfy the metabolic requirements of essential organ functions. Left ventricular HF often results from coronary heart disease, hypertension, or myocardial infarction, whereas right ventricular HF is more commonly linked to pulmonary conditions such as chronic obstructive pulmonary disease (COPD). The role of aging in HF is significant. Aging can impair heart function, leading to disrupted proteostasis. This then drives oligomeric aggregation of proteins in the myocardium and reduced levels of extracellular clusterin, contributing to reduced ejection fraction.³⁰⁴ Elevated concentrations of insulin-like growth factor-binding protein-7 (IGFBP7) are recognized to facilitate cardiac senescence, hindering DNA repair and resulting in ROS production, thus expediting the onset of HF.³⁰⁵ The mitochondrial dysfunction associated with aging can impair the ability of cardiac muscle to fulfill ATP demands. It also disrupts calcium homeostasis, contributing to increased ROS, which can cause proteotoxic damage and lead to cardiomyocyte death. Ultimately, these factors create a vicious cycle that contributes to HF.³⁰⁶

Stroke is a significant cerebrovascular incident that is generally categorized into two types: ischemic and hemorrhagic. Ischemic strokes account for approximately 80% of cases and occur due to blockage of blood flow caused by thrombosis in the vessels. In contrast, hemorrhagic strokes result from ruptured blood vessels caused by increased intracranial pressure due to tumors, injury, or inflammation. Genetic risk factors for ischemic stroke overlap with atrial fibrillation and coronary heart disease, whereas APOE and PMF1 are associated with hemorrhagic stroke.³⁰⁷ After reaching 55 years of age, an individual’s risk of stroke is expected to double every decade.³⁰⁸ This may be associated with aging hallmarks such as telomere shortening.³⁰⁹ A reduction in telomere length can drive cells into a senescent state, which triggers chronic inflammation through the NF-κB pathway. This inflammation can disrupt matrix integrity, resulting in cell fibrosis, endothelial damage, and increased oxidative stress. Moreover, this inflammatory state may lead to a potential loss of proteostasis, autophagy, and mitochondrial dysfunction,³¹⁰ diminishing the ability of cells to repair or regenerate, further exacerbating the pathologies linked to stroke progression.

Type 2 diabetes mellitus, metabolically associated fatty liver disease, neurodegenerative diseases, and cardiovascular diseases are significantly increased by insulin resistance.³¹¹ Global projections indicate that the prevalence of diabetes is expected to reach 11% by 2045, affecting 700 million people, whereas impaired glucose tolerance is anticipated to rise to 9%, impacting 548 million individuals worldwide.³¹² Moreover, age serves as a significant risk factor, with the incidence of diabetes doubling for those over 65 years and increasing fourfold for individuals above 75 years old.³¹³ For instance, a study reported that gut bacteria from the Lachnospiraceae family contribute to insulin resistance by promoting lipid accumulation and chronic inflammation, whereas bacteria in the genus Bacteroides counter insulin resistance.³¹³ As mitochondrial dysfunction increases with age, it can reduce ATP levels and increase oxidative stress in various tissues, including cardiac, hepatic, and pancreatic β-cells. This process can lead to their dysfunction and contribute to insulin resistance.³¹⁴ Hormonal changes associated with aging, such as decreased estrogen during menopause, can increase insulin sensitivity in adipose tissue. As we age, decreasing adiponectin levels may worsen glucose sensitivity and lipid metabolism.³¹⁵ Dysfunctional autophagy in adipose tissues can lead to ER stress and disrupt insulin signaling, contributing to insulin resistance in adipocytes.³¹⁶

Maintaining bone mass requires a delicate balance between osteoblast-mediated bone production and osteoclast-mediated resorption. When this equilibrium is disrupted by excessive bone resorption or impaired bone formation, bones become more porous and brittle. Bone metabolism dysregulation worsens with age. Bone mass decreases steadily by approximately 10 g/Ca annually, with females experiencing accelerated loss postmenopause.³¹⁷ With age, the accumulation of senescent bone marrow mesenchymal stem cells and macrophages (S-MΦs) can activate the secretion of SASP.³¹⁸ SASP, such as TNF-α, IL-1, and IL-6, can increase osteoclast activity, accelerate bone resorption and contribute to decreased bone mineral density.³¹⁹ Additionally, in aging osteoprogenitor cells, telomere attrition, DNA damage, and dysregulation of signaling pathways such as mTORC1 and Nrf2 reduce bone formation.³¹⁹ Mitochondrial dysfunction in bone cells hinders energy generation, increases ROS, and disrupts the balance between osteoblasts and osteoclasts.³²⁰ These interconnected aging mechanisms undermine bone integrity, driving osteoporosis severity and complicating recovery.

Metabolically associated fatty liver disease (MAFLD) encompasses a spectrum of liver diseases not covered by its previous terminology of nonalcoholic fatty liver disease³²¹ MAFLD has become the leading cause of chronic liver disease, affecting approximately 25% of the world’s population as of 2024. Age and MAFLD incidence are correlated, with the median age of the MAFLD population being 50 years.³²² Several aging-related hallmarks have been identified that exacerbate MAFLD, which will be discussed in more detail. Impaired MQC resulting from reduced mitochondrial biogenesis (decreased PGC-1α) and mitophagy (impaired PINK1/Parkin pathway) leads to oxidative stress and free fatty acid buildup in hepatocytes.³²³ Elevated IL-6 levels can reduce insulin signaling and contribute to lipid accumulation and hepatic fibrosis.³²⁴ Furthermore, as we age, gut dysbiosis may reduce the beneficial bacteria responsible for activating pancreatic lipase, which is essential for efficiently breaking down lipids and preventing their accumulation.³²⁵

Hyperuricemia poses a worldwide health issue, impacting 3% to nearly 40% of individuals. Its prevalence is influenced by demographic factors and is linked to painful conditions such as gout and kidney stones.³²⁶ It can be further defined as a serum uric acid level exceeding 6.8 mg/dL (the saturation points for monosodium urate crystal formation). This condition primarily stems from renal underexcretion caused by dysfunctional urate transporters. However, the overproduction of uric acid caused by enzymatic abnormalities, such as deficiency of hypoxanthine-guanine phosphoribosyl transferase in nucleotide metabolism, may also contribute to elevated urate levels. Chronic hyperuricemia promotes the deposition of monosodium urate crystals in joints and renal tubules, leading to gout³²⁷ and kidney stones,³²⁸ respectively. This accumulation activates the innate immune response via NLRP3 inflammasome-mediated IL-1β production, further propagating inflammation.³²⁹ Kidney function diminishes with age, reducing uric acid excretion and increasing serum uric acid levels.³²⁶ Age-related immunosenescence and chronic kidney disease impair immunological clearance and renal regeneration, potentially leading to irreversible renal damage.³³⁰ Furthermore, gut dysbiosis, which involves bacteria that affect purine metabolism, can lead to inflammation and contribute to hyperuricemia and gout.³³¹

RA develops when the immune system targets healthy synovium, causing chronic inflammation and cartilage loss.³³² Age affects genetic and environmental susceptibility by affecting immune regulation and metabolic homeostasis. The lifetime risk of developing RA ranges from 1 to 3%, peaking after the age of 50 years,³³³ with a marked increase in incidence among women.³³⁴ Aging is associated with elevated levels of leptin, an adipokine that accumulates in adipose tissue and is exacerbated by obesity.³³⁵ Leptin stimulates both the innate and adaptive immune systems, promoting the production of proinflammatory cytokines such as IL-1, IL-6, and TNF-α, contributing to systemic and synovial inflammation.³³⁶ As people age, their DNA repair mechanisms weaken, increasing susceptibility to infections. This can result in immune dysregulation and reduced self-tolerance. Consequently, rheumatoid factor and antinuclear antibodies, often found in autoimmune disorders such as RA, may be produced more readily owing to this immunological imbalance.³³⁷ Concurrently, age-related decreases in PINK1/Parkin-mediated mitophagy promote oxidative stress and mitochondrial dysfunction, which can trigger synovial inflammation and reduce the osteoclast activity critical for healthy bone remodeling, thereby contributing to joint damage and motor impairment.³³⁸ The accumulation of ROS further exacerbates cellular stress by inducing genotoxic damage, which can lead to overactivation of the p53 tumor suppressor gene, driving persistent senescence and amplifying inflammatory signaling through increased cytokine and metalloproteinase production, potentially accelerating the onset or progression of RA and other age-related inflammatory conditions.³³⁹

Multiple sclerosis is another autoimmune disease mediated by the activation of self-reactive T cells. While multiple sclerosis can affect children, late-onset multiple sclerosis can occur in individuals older than 50 years because of age-related changes.³⁴⁰ Research has shown that aging exacerbates multiple sclerosis pathology through several biological mechanisms, which span from increased neuroinflammation and a dysregulated immune system to impaired remyelination and gut dysbiosis.³⁴¹ A population-based study revealed that late-onset multiple sclerosis most commonly occurs between the ages of 50 and 55, accounting for approximately 69% of late-onset multiple sclerosis cases.³⁴² Immune senescence, particularly of cytotoxic CD4 + T cells,³⁴³ promotes chronic inflammation and the accumulation of somatic single-nucleotide variants in the CNS.³⁴⁴ These mutations can enhance neuroinflammatory cascades. Chronic inflammation leads to elevated nitric oxide production, which can cause axonal demyelination and downstream mitochondrial dysfunction.³⁴⁵ Dysfunctional mitochondria in demyelinated axons fail to meet the high ATP demands of Na/K-ATPases, thus impairing neurotransmission.³⁴⁶

The production of antinuclear antibodies is a hallmark of the chronic autoimmune disease known as SLE.³⁴⁷ SLE is a clinically heterogeneous disease in which patients experience manifestations ranging from mild cutaneous involvement, such as flashes, to life-threatening organ dysfunctions.³⁴⁸ SLE shares similar risk factors with the other autoimmune diseases mentioned above. These factors can trigger or worsen the autoimmune response when they cause immune dysregulation, impacting both the innate and adaptive immune systems. The accumulation of cellular debris and apoptotic cells may act as a source of autoantigens and cause inflammation. This triggers the adaptive immune response, which activates T cells to release additional inflammatory cytokines to activate B cells. The development of autoimmunity can be promoted by the capacity of these cells to generate specific autoantibodies to target self-antigens.³⁴⁹ According to epidemiological studies, the global burden of SLE varies considerably on the basis of demographic factors. Prevalence estimates range from 13 to over 7000 per 100,000 individuals, whereas incidence rates range from approximately 1.5 to 11 per 100,000 person–years. The prevalence of SLE peaked in the 60- to 64-year-old age range in women,³⁵⁰ suggesting that age may act as a risk factor for SLE. Chronic inflammation caused by senescent T cells can compromise proteostasis and lead to mitochondrial dysfunction, contributing to immunosenescence.³⁵¹ Mitochondrial dysfunction is associated with triggering autoimmune responses because it releases mtDNA that can initiate IFN-I signaling.³⁵²

Senolytic chimeric antigen receptor (CAR)-T (CAR-T) cell therapy is an emerging antiaging strategy that genetically engineers T cells to target senescent cells to delay or reverse aging-related diseases. Studies have revealed that there is a protein marker of urokinase plasminogen activator receptor (uPAR) on the surface of senescent cells and that uPAR-positive senescent cells accumulate during aging.³⁶ On the basis of this marker, a chimeric peptide, E16-uPA24, that specifically targets senescent cells was constructed.³⁹⁴ This small molecule can promote immune cells to recognize and kill senescent cells, thereby effectively eliminating senescent cells. Based on this, an approach based on CAR-T cells has been developed to eliminate senescent cells. uPAR-28z CAR-T cells were generated, and a single injection effectively eliminated senescent cells and improved nonalcoholic fatty liver disease (NASH)-induced liver fibrosis in young mice.³⁷ Further studies have shown that senolytic uPAR-CAR-T-cell therapy can safely and effectively eliminate senescent cells and prolong the lifespan of aged mice.³⁹⁵ In addition, senolytic uPAR-CAR-T-cells have been shown to promote intestinal stem cell regeneration and restore the intestinal niche.³⁹⁶ Notably, natural killer group 2 member D ligands (NKG2DLs) are upregulated in various tissues of aging mice and aging nonhuman primates.³⁹⁷ Accordingly, NKG2D-CAR-T-cell therapy has been developed to selectively target and eliminate senescent NKG2DL-expressing cells in mice and nonhuman primates for the treatment of aging and age-related diseases driven by aging.^397,398 At present, only two validated senescence markers are used for CAR-T-cell therapy, and more specific targets in aging tissues need to be identified in the future. Senolytic CAR-T-cell therapy represents a groundbreaking advancement in geroscience, offering targeted clearance of senescent cells through precision immunotherapy. While challenges persist in cost optimization, safety profiling, and biomarker heterogeneity, its unique advantages of sustained efficacy and systemic action position this modality as a promising candidate for addressing age-related pathologies. Future directions should focus on integrating multiomics platforms (e.g., single-cell transcriptomics and spatial proteomics) to refine target selection paradigms while leveraging engineering innovations to lower translational barriers, ultimately bridging the gap between preclinical validation and clinical implementation.

Owing to the different mechanisms of action of senolytic drugs, the clearance of senescent cells also varies. Additionally, there are multiple problems that need to be solved. First, the ability of senolytics to selectively eliminate senescent cells are not high. Currently, the majority of senolytics still cause damage to normal cells. More importantly, senolytic drugs are unable to distinguish between beneficial aging cells and harmful aging cells in tissue repair. Second, the optimal therapeutic time is uncertain. Senolytic drugs can deplete stem cells after premature therapy, whereas late use can reduce efficacy. Third, the residual decomposition products cannot be removed in time after the senescent cells are eliminated, and the resulting tissue voids cannot be repaired. Finally, the distribution of senescent cells varies in different tissues and organs. How to improve the ability of senolytic drugs to target and penetrate organs remains to be determined.

Rapamycin is also an effective SASP inhibitor that controls the SASP through the regulation of MAPKAPK2 kinase translation by 4EBP1.⁴⁰⁰ Later-life rapamycin feeding increases lifespan by 14% in females and 9% in males,⁴⁰¹ with a sex difference.⁴⁰² However, long-term administration of rapamycin has significant side effects (including skin and metabolic disorders) and inhibits mTORC2.¹⁴⁰ Given the side effects of mTORC1 inhibitors such as rapamycin, dietary restriction has shown superior health and longevity extension performance by inhibiting mTORC1. The breakdown metabolism of branched-chain amino acids (BCAAs) is a noteworthy regulator of physiological aging, and blocking the accumulation of BCAAs can alleviate the SASP by inhibiting mTORC1.⁴⁰³ A protein-restricted (BCAA leucine, isoleucine, and valine) diet prolongs the healthspan and lifespan of mice by reducing mTORC1 activity in male mice.⁴⁰⁴ In addition, ketogenic diets have also been shown to extend the longevity of mice by suppressing mTORC1 activity.^405,406 Drug combinations that target nutrient sensing have shown superior performance in terms of lifespan. The combination of trametinib, the mTORC1 inhibitor rapamycin, and lithium prolongs the lifespan of Drosophila by 48%.⁴⁰⁷ Therefore, the combination of drugs that act simultaneously on different nutrient-sensing signaling factors and rapamycin can synergistically exert their beneficial effects, providing directions for future research on antiaging combinations.

Accumulating evidence suggests that metformin can delay aging in nematodes and mice. Mechanistically, metformin prolongs lifespan mainly by activating AMPK to inhibit the SASP. Dysfunction of AMPK in nematodes can eliminate the longevity-prolonging function caused by metformin. Presenilin enhancer 2 (PEN2) is regarded as the target of metformin.⁴⁰⁸ Metformin binds to PEN2 to activate AMPK and cross-links to the lysosomal glucose-sensing pathway through ATP6AP1, thereby delaying aging.⁴⁰⁸ Metformin can reduce the SASP by enhancing autophagy and mitophagy and improve the aging of VSMCs and auditory cells.⁴⁰⁹ In addition, metformin can enhance the anticancer efficacy of CDK4/6 inhibitors by inhibiting SASP.⁴¹⁰

Lithocholic acid (LCA) is a secondary bile acid that is synthesized mainly in the liver and is produced in the gut through bacterial metabolism. It plays a variety of roles in bile, such as promoting fat digestion and absorption, regulating blood lipids, promoting cell proliferation, inhibiting inflammation and protecting the gastric mucosa. Previous studies have shown that LCA can extend the lifespan of yeast and Drosophila melanogaster.⁴¹¹ Calorie restriction is widely accepted as an approach to prolong life and delay aging. However, long-term dietary restriction is challenging to implement broadly in the elderly population, as it may lead to malnutrition and muscle wasting. Thus, identifying interventions that can extend healthspan and lifespan without requiring caloric restriction has become a key research goal. LCA acts as a caloric restriction mimetic to prolong the lifespan of C. elegans, Drosophila, and mice.²⁵ Mechanistically, LCA targets the protein TULP3 to activate the sirtuin-v-ATPase-AMPK signaling axis, thereby exerting antiaging effects through conserved metabolic regulatory pathways.²⁶ More importantly, unlike caloric restriction, LCA does not induce the adverse effect of muscle loss observed in caloric restriction, offering a superior strategy to enhance healthspan. Notably, long-term administration of high-dose LCA exerts adverse effects on the liver, disrupting phospholipid-sphingolipid homeostasis and thereby inducing cholestasis, which severely impairs hepatic function.⁴¹² Therefore, more rigorous clinical trials are needed before approval can be obtained.

Urolithin A is generated by the metabolism of ellagitannins and ellagic acid via gut microbes and is found mainly in pomegranates, nuts, and some berries. Urolithin A can inhibit the SASP through a variety of pathways, thereby improving aging-related diseases. In the C. elegans model, urolithin A activates the AMPK signaling pathway and significantly promotes mitophagy, which prolongs lifespan by 45.4%.⁴²⁵ Similarly, muscle endurance is increased by 40% in aged mice after urolithin A treatment.⁴²⁵ Defects in mitophagy play important roles in the progression of Duchenne muscular dystrophy (DMD). Therapy with urolithin A restores mitophagy in DMD worms and mice, as well as in primary myoblasts from DMD patients, thereby restoring muscle function and improving survival in the DMD mouse model.⁴²⁶ In an aged mouse model, urolithin A-induced mitophagy weakened cGAS/STING activation and improved neurological deterioration.⁴²⁷ In addition, treatment with urolithin A can improve the mitochondrial function of aging HSCs through promoting mitophagy, thereby restoring these cells to their youthful hematopoietic function levels.⁴²⁸

Spermidine, a naturally occurring polyamine, is widely distributed in plant and animal tissues (e.g., cheese, legumes, mushrooms) and human cells, and its levels are maintained through dietary intake or endogenous synthesis. Spermidine levels decline progressively with age and are closely associated with the development of age-related diseases. Spermidine delays aging through multiple pathways, such as the activation of autophagy, the regulation of epigenetic modifications, the improvement of mitochondrial function and the inhibition of inflammation, and has shown potential for improving healthspan in model organisms (yeasts, Drosophila, nematodes, and mice)⁴²⁹ and humans. By activating mitophagy and enhancing mitochondrial respiration, spermidine mitigates brain aging and improves cognitive function. Mechanistically, dietary spermidine crosses the blood-brain barrier in mice, increasing hypusination of eukaryotic translation initiation factor 5A (EIF5A) and mitochondrial function in the hippocampus while reducing mitochondrial decay.^430,431 This effect requires the autophagy regulator ATG7 as well as the mitophagy mediators PARKIN and PINK1. Inhibition of the enzymes required for EIF5A hypusination abolishes fasting-mediated autophagy enhancement and longevity extension.^430,431 Furthermore, spermidine delays oocyte aging by activating mitophagy and maintaining mitochondrial function, improves the quality of aged oocytes after ovulation, and promotes fertility in aged female mice,^432,433 which can potentially be applied to human-assisted reproductive technology.⁴³³ Overall, spermidine, with its natural origin, few side effects, and convenient access through diet or supplements, is poised to become a pivotal tool for future pro-longevity interventions.

Ergothioneine (EGT) is a natural sulfur-containing amino acid that is widely present in mushrooms (such as shiitakes and Pleurotus edodes), animal livers, and legumes. As humans cannot synthesize EGT endogenously, it must be obtained through diet or supplementation. Characterized by a unique imidazole ring structure, EGT has potent antioxidant and anti-inflammatory properties and selectively accumulates in highly metabolic tissues such as the brain, kidneys, and retina. Notably, circulating EGT levels decline progressively with age, correlating negatively with the risk of age-related diseases.⁴³⁴ In recent years, its antiaging potential has emerged as a hotspot, particularly for extending healthspan, improving mitochondrial function, and regulating oxidative stress pathways. EGT supplementation prolongs the lifespan and promotes healthy aging in C. elegans and mice.⁴³⁵ Importantly, dietary EGT intake inhibits age-related degeneration in multiple organs, including the kidneys, liver and brain, while ameliorating age-associated impairments in learning and memory capabilities. EGT can reduce the damage to hippocampal neurons induced by D-galactose and improve the learning and memory ability of mice by regulating the AMPK/SIRT1/PGC-1α pathway.⁴³⁶ Recent studies have shown that ergothioneine (ET) acts as an alternative substrate for cystathionine γ-lyase, stimulating hydrogen sulfide production.⁴³⁷ This process induces persulfidation of the critical cysteine residue C243 in cytosolic glycerol-3-phosphate dehydrogenase (cGPDH), thereby increasing its catalytic activity.⁴³⁷ The resulting increase in cGPDH activity promotes NAD⁺ regeneration and maintains cellular energy metabolism.⁴³⁷ This explains why EGT mainly enhances exercise endurance, improves metabolic health, and delays the occurrence of aging-related diseases through persulfidation. Dietary supplementation with EGT significantly enhances exercise endurance in mice. Proteome-wide thermal stability analysis revealed that EGT directly binds to and activates the mitochondrial enzyme 3-mercaptopyruvate sulfurtransferase (MPST), thereby increasing mitochondrial respiration and improving exercise performance.⁴³⁸ This is the first physiologically relevant EGT target and establishes the EGT-MPST axis as a regulator of mitochondrial function, ameliorating aging-related diseases. However, the long-term efficacy of caloric restriction mimetics as a geroprotector and their safety require further investigation. Ultimately, the goal is to strike a balance between the benefits of longevity and practicality while developing interventions for aging and health that are both accessible and sustainable.

Although these compounds show potential antiaging properties. There are some negative effects of some of the agents. For example, supplementation of β-nicotinamide mononucleotide/nicotinamide riboside (NMN/NR) in aged mice can increase the level of NAD⁺ and extend the lifespan of mice.⁴³⁹ However, nicotinamide nucleoside NR supplementation increased the incidence of tumors by 27% and increased the incidence of brain metastases by 227.2% compared with controls.⁴⁴⁰ The carcinogenic risk of antiaging drugs is a core contradiction in the field of antiaging medicine, which essentially stems from the deep interweaving of aging and cancer in biological mechanisms. Both share key pathways such as cell proliferation regulation, DNA damage repair, and immune surveillance. Antiaging drugs often work by promoting cell repair and delaying apoptosis, but excessive inhibition of apoptosis or enhanced proliferation may lead to the survival and accumulation of abnormal cells, such as cancer cells. Some drugs delay aging by activating DNA repair pathways, yet abnormal repair mechanisms may mask gene mutations in cancer cells and accelerate tumor development. The immune system can both eliminate senescent cells and recognize and kill cancer cells. If drugs excessively suppress immune inflammation (such as rapamycin), they may weaken the surveillance against cancer cells, resulting in cancer cell metastasis. In addition, telomerase activators delay aging by extending telomeres, but this mechanism inherently carries carcinogenic risks. Activating telomerase may accelerate the proliferation of existing cancer cells or induce the carcinogenesis of normal cells. Like any other therapeutic agents, both safety and efficacy shall be fully studied and the therapeutic windows to be determined before safe dosages can be determined.

Several promising strategies against aging have entered clinical trials with preliminary evidence of safety and efficacy in humans (Table 3). A clinical study (NCT02848131↗) demonstrated that senolytic (D + Q) agents successfully clear senescent cells in diabetic nephropathy patients and significantly relieve the burden of senescent cells in adipose and skin tissues.⁴⁴⁹ Another clinical study (NCT02874989↗) revealed that D + Q improved physical dysfunction in IPF³¹ patients and was well tolerated.⁴⁵⁰ A phase 1 trial (NCT04063124↗) of AD revealed that senolytics (D + Q) are safe, feasible and well tolerated.^33,34 A phase 2 clinical study (NCT04313634↗) using senolytics (D + Q) to treat bone loss in postmenopausal women showed that patients with higher senescent cell burden had a more significant response to D + Q, manifested as a 34% increase in bone formation and an 11% decrease in bone resorption.⁴⁵¹ Fisetin, another natural senolytic drug, has also been studied in the clinical stage (Table 3) for the treatment of age-related diseases, and its use is expected to lead to breakthroughs in the clinical research of senolytics. UBX0101, a p53/MDM2 interaction inhibitor, improves osteoarthritis by eliminating senescent synovial cells in the knee joint.^169,452 Two phase 1 trials from 2018 to 2020 (NCT04229225↗ and NCT03513016↗) revealed that UBX0101 was well tolerated.⁴⁵³ However, a subsequent phase 2 clinical trial (NCT04129944↗) failed to demonstrate the efficacy of single-dose, intra-articular dosing of UBX0101 in patients with painful knee osteoarthritis.⁴⁵⁴ This might be caused by factors such as the method of administration, the expectations of patients or researchers, and gender differences in pain reports. UBX1325 (foselutoclax), a novel antiaging small-molecule BCL-xL inhibitor, was the first senolytic agent evaluated for the treatment of DME. The phase I clinical data (NCT04537884↗) revealed good safety and tolerability, with beneficial and long-lasting effects on visual acuity and macular thickness,³⁵ and were shown to restore outer retinal function.⁴⁵⁵ A subsequent phase 2 (NCT04857996↗) study evaluated the activity of a single intravitreal injection of UBX1325 for the treatment of DME. After 48 weeks of UBX1325 treatment, the best-corrected visual acuity significantly improved, and the central subfield thickness steadily decreased.⁴⁵⁶ Although senolytics have shown preliminary efficacy in clinical studies, long-term evaluation is still lacking. In conclusion, elimination of senescent cells plays a significant role in the treatment of a variety of aging-related pathological states. However, further studies are needed to verify that the underlying senescent cell burden may determine the clinical response to aging.

Unlike senolytics, senomorphics offer a complementary strategy to preserve tissue homeostasis while reducing chronic inflammation. Here, we highlight emerging senomorphics in clinical stages and their translational potential. A phase 1 study (NCT02655393↗) with single or multiple doses over 4 weeks demonstrated favorable safety profiles and improved molecular signatures of mitochondrial and cellular health in healthy sedentary older adults.⁴⁵⁷ Two independent phase 2 clinical studies (NCT03464500↗, NCT03283462↗) of urolithin A supplementation revealed that 4 months of urolithin administration enhanced muscle endurance and offset age-related muscle decline.^458,459 Metformin is the drug of choice for the treatment of type 2 diabetes and has shown definite efficacy in delaying aging in preclinical studies. Mendelian randomization analysis (UK Biobank, n = 321,412) revealed that metformin promoted healthy aging through its targets glycerol-3-phosphate dehydrogenase 1 (GPD1) and AMPKγ2.⁴⁶⁰ A phase 1 trial (NCT03107884↗) revealed that metformin treatment reduced primary muscle fibroadipogenic senescent marker levels of progenitors and decreased type I muscle fiber atrophy.⁴⁶¹ However, metformin may interfere with the improvement of some physiological functional parameters, such as whole-body insulin sensitivity and cardiorespiratory fitness, and may have a negative effect on the hypertrophic response in healthy elderly individuals.⁴⁶² In addition, owing to the heterogeneity of aging, metformin treatment does not improve physical function in the elderly population with sarcopenia and frailty and is poorly tolerated in this population (ISRCTN29932357).⁴⁶³ Hence, further studies are needed before metformin can be widely used as a treatment to delay aging. Clinical studies have shown that mTOR inhibition plays an important role in delaying aging. The phase 2b and phase 3 studies of the mTOR inhibitor RTB101 showed that RTB101 could improve immune function in older adults (NCT03373903↗, ACTRN12619000628145). In a phase 2a study (ACTRN12613001351707), the TORC1 inhibitors BEZ235 and RAD001 showed potential to improve immune function and reduce infection rates in older adults.⁴⁶⁴ In addition, topical rapamycin treatment reduces the levels of aging markers in aged skin tissue and improves skin health (NCT03103893↗).⁴⁶⁵ Although clinical studies of senomorphics have revealed phenotypes associated with delayed aging, there are still some cases with insignificant effects and even negative health effects. Therefore, more rigorous and long-term clinical trials are needed for further verification.

Endogenous metabolites have shown promising longevity potential in preclinical studies. At present, a variety of endogenous metabolites, including α-KG, spermidine and NAD⁺ precursors, have entered the clinical stage for the treatment of aging-related diseases (Table 3). Safety evaluation of a 28-day high-dose (40 mg/d) spermidine supplement in healthy elderly men revealed good safety and tolerability (NCT05459961↗).⁴⁶⁶ There is a robust association between a spermidine-rich nutritional diet and improved survival in humans (NCT03378843↗).⁴⁶⁷ However, a 12-month phase 2b (NCT094546) study of dietary spermidine supplementation revealed no changes in memory or biomarkers in older adults, possibly because of the lower spermidine dose (0.9 mg/day)30.⁴⁶⁸ As an important precursor of NAD⁺, long-term NR supplementation was well tolerated, effectively promoted NAD⁺ metabolism and reduced inflammatory levels (NCT02921659↗, NCT03727646↗).⁴³⁹ In addition, NR supplementation can also increase NAD⁺ levels in the brain and reduce the levels of inflammatory cytokines in the cerebrospinal fluid, and NR can be used as a potential neuroprotective agent for PD (NCT03816020↗, NCT05344404↗).^469,470 A 6-week treatment with NR (NCT04990869↗) increased NAD⁺ levels in whole blood by more than twofold and reduced epigenetic aging in patients with COPD.⁴⁷¹ In elderly patients with mild cognitive impairment, 10 weeks of NR supplementation significantly increased blood NAD⁺ concentrations. However, these clinical trials have a short period and a small number of participants, and more in-depth clinical studies are needed before approval.

Owing to the heterogeneity and individual differences in aging, current clinical drugs cannot precisely target senescent cells and have frequent off-target effects, resulting in poor clinical efficacy. In addition, the clinical dosage, individual variation, insufficient sample size, improper selection of endpoint indicators and short follow-up time may all be potential factors for the failure of antiaging clinical trials. Therefore, critically analyzing negative clinical results is necessary to avoid misleading conclusions, standardize the clinical relevance of endpoint indicators, and promote the rational development of the antiaging field.

In conclusion, it is necessary to explore the synergistic effects of existing natural compounds, reduce the limitations of single therapies, optimize dosing regimens, and carry out large-scale long-term studies. In the future, it is necessary to integrate multiomics data, develop precision delivery technologies, and promote the translation of basic research to clinical application through interdisciplinary cooperation to provide innovative solutions for healthy aging.