Cellular senescence and polycystic ovary syndrome: mechanisms and therapeutic strategies from a new perspective

Abstract

Objective

Cellular senescence is often linked to diseases or states of dysfunction, including reproductive disorders caused by ovarian dysfunction. It plays a significant role in conditions like polycystic ovary syndrome (PCOS). However, the specific effects and potential mechanisms of cellular senescence in PCOS need to be elucidated.

Methods

This review comprehensively consolidates evidence from original research articles and systematic reviews to explore the association between PCOS and cellular senescence, particularly emphasizing cell senescence markers and mechanisms linked to various PCOS phenotypes. In addition, it also covers potential mechanisms and advances in cellular senescence-related treatment methods in PCOS.

Results

Current evidence suggests that cellular senescence might contribute to PCOS through mechanisms such as replicative senescence, stress-induced premature senescence, and immunoinflammatory responses mediated by senescent cells. Key features of senescence, including cell cycle arrest, the senescence-associated secretory phenotype (SASP), epigenetic changes, abnormal cell morphology, oxidative stress, DNA damage from telomere shortening and telomerase inhibition, and overactivation of anti-apoptotic pathways, are all related to PCOS. These mechanisms might especially impair follicular development in obese, hyperandrogenic, or insulin-resistant patients with PCOS, leading to endometrial hyporeceptivity and increased pregnancy complications. Senolytic and senomorphic drugs are valuable clinical treatments for PCOS respectively targeted to immune surveillance mechanisms of senescent cells or mitigated the harmful effects of senescent cells on intercellular communication.

Conclusions

There is a complex correlation mechanism between cellular senescence and PCOS. Studying these cellular senescence markers and mechanisms in PCOS could provide new insights into the pathogenesis, and lay the groundwork for in-depth study and potential application of anti-senescence therapies in treating PCOS.

1. Introduction

Cellular senescence refers to a process in which cells undergo a gradual decline in proliferation, differentiation capacity, and physiological functions over time during their life activities. It is a stable state of cell cycle arrest and an intrinsic change occurring in cells during their life activities [1], characterized by alterations in intracellular biomacromolecules and functional decline of organelles, among other features. Notably, its manifestations vary across different cell types and tissues, exhibiting heterogeneity. This is significantly distinct from the irreversible gradual deterioration or aging of the body’s overall morphological structure and physiological functions over time; the two concepts are fundamentally different and hold distinct physiological significance for the human body [2]. In fact, cellular senescence exhibits a certain degree of reversibility; under specific conditions, the proliferative capacity of some senescent cells can be partially restored through targeted interventions [3].

Cellular senescence is classified into developmental programmed senescence, replicative senescence, and stress-induced senescence [4]. Under physiological conditions, the dynamic balance maintained by the immune system – including the elimination of dead cells and the growth of new cells – serves as the foundation for maintaining normal bodily functions and metabolism, preventing the accumulation of senescent cells, and promoting various physiological processes [5]. Replicative senescence primarily arises from DNA damage caused by severe telomere shortening and/or dysfunction, which results from limited proliferative capacity and growth arrest following multiple cell divisions [6]. On the other hand, stress-induced senescence refers to cell cycle arrest in response to various internal and external stresses, such as oxidative stress, stress from metabolic and inflammatory products, oncogene- and chemotherapy-induced stress, as well as mechanical stress caused by mitochondrial dysfunction, environmental toxic pollution, abnormal gene expression, and DNA damage [7].

Specifically, cellular senescence is typically accompanied by features such as changes in chromatin structure, accumulation of damaged macromolecules, and genomic instability, and plays a crucial role in biological development, tissue repair, tumor suppression, and other processes. Senescent cells exhibit diminished physiological functions, with significantly upregulated cell survival and anti-apoptotic pathways. However, their high exocrine activity leads to the release of large amounts of chemokines, cytokines, growth factors, and proteases, which activates the senescence-associated secretory phenotype (SASP) [8]. This in turn recruits immune cells by transmitting damage signals, triggering immune and inflammatory responses [9]. Additionally, cellular senescence is often associated with reproductive system diseases; for instance, during embryonic development, cellular senescence can regulate cell differentiation and tissue formation [10].

The follicular microenvironment plays a pivotal role in follicular maturation, ovulation, and luteinization. Granulosa cells (GCs) and various immune cells are components of the preovulatory follicular microenvironment, and GCs and oocytes promote follicular growth and development through intercellular communication. Studies have revealed that cellular senescence within the follicular microenvironment may transmit harmful local environmental signals – including SASP – to follicles through intercellular communication, leading to the development of ovulatory disorders, including polycystic ovary syndrome (PCOS) [11]. Moreover, key components of the ovarian stroma – including immune cells, nerves, and ovary-specific components such as ovarian surface epithelium, stem cells, fibroblasts, and extracellular matrix components – also participate in cellular senescence in the ovary by regulating hormones and ovarian stiffness [12,13].

PCOS is a common reproductive endocrine disorder characterized by polycystic ovaries, elevated testosterone levels, and irregular menstruation, and is often accompanied by increased risks such as obesity and insulin resistance (IR). Due to long-term and extensive follicular atresia, the follicles fail to mature and ovulate, which ultimately results in higher levels of anti-Mullerian hormone compared to individuals with normal ovarian function [14], but at the same time, PCOS is often accompanied by apoptosis of GCs within the follicles, which seems to suggest a higher degree of cellular senescence in PCOS. Bioinformatics analyses have identified that LMNB1, a senescence-associated hub gene, exhibits favorable diagnostic properties in PCOS [15]. Senescence-related genes and non-coding RNAs that regulate their functions are intricately linked to cellular senescence pathways in PCOS, potentially associated with abnormal proliferation and apoptosis levels of GCs in PCOS [16], increased ovarian collagen and stiffness caused by fibrosis [17], metabolic and inflammatory stress-induced senescence activated by SASP, and replicative senescence related to telomere length [18]. Notably, compared with age- or BMI-matched control groups, PCOS patients with obesity, or IR exhibit a higher risk of cellular senescence [19], suggesting that these factors may be involved in PCOS-related cellular senescence through certain mechanisms illustrated in Figure 1.

Figure 1.

The association between cellular senescence and polycystic ovary syndrome. This diagram illustrates the mechanism of polycystic ovary syndrome and related complications caused by cellular senescence of ovary, endometrium and placenta, and further emphasizes the effect of obesity and IR on a variety of different senescent markers.

However, given the significant heterogeneity of senescence characteristics across different cells, tissues, and phenotypes, identifying a single marker is prone to false positives. Therefore, identifying senescent cells may require the integration of multiple markers to accurately characterize the state of cellular senescence in PCOS [20]. As an extensive exploratory study, this research aims to lay a foundation for elucidating the pathogenesis of PCOS and improving potential therapeutic strategies in the future.

2. Cellular senescence markers and related research progress in PCOS

2.1. Cell cycle arrest

One of the most fundamental characteristics of cellular senescence is cell cycle arrest or permanent withdrawal from the cell cycle. The p53/p21 signaling pathway is a crucial regulator of cellular senescence and cell cycle control. Sustained activation of p53 during cellular stress and damage promotes p21 expression, and together with p21, inhibits the cell cycle process, leading to the cessation of cell division and senescence [21]. Furthermore, the cyclin-dependent kinase inhibitor 1 A (CDKN1A) gene encodes p21, leading to p21 overexpression in the context of cellular senescence. It has also been found to be associated with levels of cellular fibrosis, reactive oxygen species (ROS), phosphorylated histone H2AX (γ-H2AX), and senescence-associated β-galactosidase (SA-β-gal) in a mouse model of fatty liver disease [22]. In fact, this interaction is part of the cellular senescence process associated with cell cycle arrest. Moreover, bromodomain-containing protein 7 is a regulator of cellular senescence and is also associated with increased activity of p53, p21, and SA-β-gal. Its downregulation or knockout prevents cell cycle arrest through multiple mechanisms, including mitochondrial dysfunction [23]. AT-rich interaction domain 1 A is an intron of the CDKN1A gene, and its overexpression exhibits the ability to inhibit cell proliferation, induce cell cycle arrest, and promote cellular senescence, particularly in an environment with elevated glucose levels [24]. Additionally, mitochondrial DNA (mtDNA) damage also coordinates cell cycle arrest through complex molecular pathways [25].

In PCOS, there is oocyte meiotic arrest, as well as reduced proliferative capacity of GCs caused by steroid hormone synthesis disorders and abnormal cell cycle regulation. Similarly, cellular senescence characterized by cell cycle arrest has been identified in animal models and clinical studies of PCOS. Studies have shown that high-level expression of p16INK4a (p16), p21, p53, and SA-β-gal is observed in testosterone-induced mouse ovaries, suggesting a potential mechanism by which cell cycle arrest in GCs during cellular senescence may contribute to impaired follicular maturation in PCOS [26]; Another study found that in a dihydrotestosterone-induced PCOS mouse model, the expression level of sirtuin 1 (SIRT1), a deacetylase protein, is significantly reduced. As a key protein in reproductive system senescence-related pathways, SIRT1 may be involved in regulating key long non-coding genes associated with cell cycle dynamics, which may represent a pathogenic mechanism underlying cell cycle arrest-related cellular senescence in testosterone-induced PCOS animal models [27].

As for the mechanisms underlying cellular senescence in common metabolic abnormalities associated with PCOS, including obesity and IR, evidence has shown that p21 is directly or indirectly associated with cellular senescence in different cell types in diseases involving glycolipid metabolism disorders. Firstly, p21 can modulate the sensitivity of pancreatic β-cells to endoplasmic reticulum stress, thereby potentially reducing cellular senescence and cell death, and improving diabetic outcomes [28]. Additionally, adipose senescence is also associated with increased IR, and knockout of p21 in adipose tissue enhances insulin sensitivity and glucose tolerance while inhibiting the SASP phenotype [29].

Elevated expression of angiopoietin-like 4 (ANGPTL4) has also been observed in normal-weight reproductive-aged PCOS patients with high testosterone levels and in human cell lines. It enhances CDKN1A expression by blocking the G1/S cell cycle transition in the EGFR/JAK1/STAT3 pathway and the STAT3-dependent CDKN1A promoter, thereby strengthening the inhibition of GCs proliferation and division, which is detrimental to follicular development and maturation. Increased ANGPTL4 levels in serum and follicular fluid from clinical samples confirm the critical role of cell cycle arrest in the mechanism of ovulatory dysfunction in PCOS [30]. Furthermore, bidirectional Mendelian randomization analysis has revealed a potential genetic causal relationship between human mitochondrial DNA copy number and increased risk of PCOS at the genetic level [31]. This analytical method has the advantage of avoiding the influence of confounding factors such as reverse causation and different phenotypes, providing new evidence for the role of cell cycle arrest induced by mitochondrial DNA damage in cellular senescence in PCOS. However, current research on regulatory genes and related mechanisms that determine cellular senescence by arresting cell cycle progression in PCOS, particularly in the context of different PCOS specific phenotypes and metabolic disorder symptoms, remains limited. Further in-depth studies are therefore necessary, especially considering that the chronic low-grade inflammatory state in the body during IR and obesity may form a vicious cycle with cell cycle arrest and interact with each other [32].

2.2. Senescence-associated secretory phenotype (SASP)

Senescent cells secrete various proinflammatory cytokines, chemokines, interleukins, insoluble factors, and other inflammatory molecules, such as IL-6, IL-1α, IL-1β, growth differentiation factor-15 (GDF-15), fibronectin, collagen, transforming growth factor-β (TGF-β1), and interferon-γ (IFN-γ). The accumulation of these molecules generates heterogeneous biomarkers collectively termed the senescence-associated secretory phenotype (SASP). SASP is a hallmark of cellular senescence triggered by various stress responses, including oxidative stress induced by mitochondrial damage [33]. Studies have demonstrated that circulating concentrations of SASP-related factors reflect the senescent cells phenotype by disrupting energy metabolism, augmenting aberrant immune responses, inducing tissue dysfunction, and elevating the risk of chronic diseases, including reproductive system disorders such as PCOS [34].

SASP factors, such as IL-6, have been found to be highly expressed in androgen-induced PCOS mouse models, highlighting the potential mechanism of action of SASP-related factors in polycystic ovary changes and ovulation disorders in PCOS pathogenesis [26]. Previous studies have suggested that androgens are associated with cellular senescence in prostate cancer and androgenetic alopecia, with a potential mechanism involving SASP-mediated immune system activation [35], which offers insights into the pathogenesis of PCOS exhibiting hyperandrogenism or high androgen levels. In addition, SASP factors (such as TNF-α) interfere with GnRH pulse secretion, leading to an imbalance in LH/FSH ratio, further exacerbating hyperandrogenism and ovulation disorders [36].

Furthermore, obesity-induced cellular senescence also contributes to immunosenescence, specifically by influencing inflammatory and immune processes through SASP. Persistent chronic inflammation further impairs insulin metabolism [37], suggesting novel insights into the crosstalk between obesity, IR, and hyperandrogenism in PCOS, distinct from previous perspectives. In addition, other animal studies have found that SASP from senescent cells impairs tissue structure and function, exacerbates cellular senescence and fibrosis [38], and excessive fibrosis is generally recognized as one of the key hallmarks of cellular senescence. PCOS mice induced by exposure to environmental doses (0.1, 1.0, and 10 mg/kg/d) of di-2-ethylhexyl phthalate (DEHP) exhibit ovarian tissue atresia, increased numbers of preantral follicles, and enhanced fibrosis, accompanied by significant oxidative stress damage [39]. These findings provide indirect support for future in-depth exploration of SASP as a biomarker for different types of cellular senescence in PCOS.

GDF-15 is a stress-induced SASP cytokine that may regulate body weight, food intake, and metabolism. Clinical studies have revealed that elevated GDF-15 levels are associated with obesity and IR, which are common in PCOS patients, suggesting that SASP related to oxidative stress induced by mitochondrial damage may be involved in diverse cellular senescence processes under various systemic contexts [40], especially in PCOS patients with carbohydrate metabolism disorders, the levels of GDF-15 may act as predictor about accelerated cellular senescence. Similarly, Mendelian randomization analysis has been employed to avoid the influence of confounding factors, and the findings have preliminarily identified a genetic causal relationship between IL-1α (a component of SASP) and PCOS progression [41]. In human GCs lines, palmitic acid, acting as a cellular senescence inducer, has also been found to induce a significant increase in the concentrations of IL-6 and IL-8 [42]. IL-6 and IL-8 are senescence-associated cytokines that induce self-reinforcing and cross-reinforcing senescence [43], and studies have revealed a positive correlation between these cytokines and fatty acid levels [44], suggesting aberrant SASP in obese PCOS with IR.

Unfortunately, direct animal and clinical evidence linking additional SASP factors under cellular senescence to PCOS remains insufficient. Integrating findings from studies on SASP and cellular senescence in other diseases, we hypothesize that cellular senescence in PCOS may mediate inflammation and secondary senescence of surrounding cells through paracrine signaling, direct intercellular contact, or complex intercellular communication. However, SASP-related cytokines, inflammatory factors, and other such factors not only persist in environments with extensive accumulation of senescent cells but may also be associated with fluctuations caused by abnormal functions and states of other cells in non-senescent states. However, it remains unclear whether these fluctuations are associated with underlying SASP factors, and further in-depth mechanistic studies are required in the future.

2.3. Epigenetic changes

In addition to cell cycle withdrawal and SASP, senescent cells also undergo epigenetic modifications, including chromatin remodeling and DNA methylation. Among these, during cellular senescence, the cell nucleus undergoes prominent structural and functional changes. Nuclear bodies, membraneless biomolecular aggregates rich in proteins and RNA (e.g. nucleoli and nuclear speckles), are involved in various intranuclear cellular processes, respond to cellular stimuli, and regulate local and global chromatin activity [45]. Research teams have used coherent anti-Stokes Raman scattering spectral imaging to visualize nucleolar defects and aggregation caused by unfolded/misfolded proteins in immature cells, thereby providing direct insights into cellular senescence [46]. Furthermore, alterations in the integrity of nuclear peripheral structures also affect chromatin reorganization and may activate SASP factor expression programs through transcription factors such as NF-κB [47]. High-mobility group A1 (HMGA1) and high-mobility group box 1 (HMGB1) are regulators involved in the formation of cytoplasmic chromatin fragments and signal transduction in response to nuclear stress or damage during cellular senescence [48]. Studies have found that histone deacetylase inhibitors induce p16 expression and cell proliferation arrest, while histone acetylation around the p16 transcription start site is associated with cellular senescence caused by mitochondrial dysfunction [49]. As another epigenetic modification, DNA methylation involves the addition of methyl groups to DNA molecules without altering the sequence, and is also closely associated with cellular senescence. Furthermore, DNA methylation also accelerates the global loss and local increase of heterochromatin during cellular senescence [50].

Currently, the role of epigenetics in the pathogenesis and progression of PCOS is receiving increasing attention. Chromatin remodeling, particularly acetylation of histone H3 at lysine 27 (H3K27Ac), has also been found to occur during follicular growth and ovulation in PCOS. In testosterone-induced PCOS mouse models, nuclear translocation of casein kinase 2α is observed, which is associated with increased phosphorylation of histone deacetylase 2, leading to H3K27Ac modification and promoting the inhibition of GCs proliferation in PCOS [51]. Fat mass and obesity-associated protein (FTO), an RNA N6-methyladenosine (m⁶A) demethylase, has been found to be overexpressed in PCOS mice with hyperandrogenism, resulting in decreased m⁶A levels. In vitro experiments have also confirmed that dihydrotestosterone promotes FTO expression and inhibits m⁶A in a dose-dependent manner [52]. In fact, m6A methylation plays a crucial role in cellular senescence [53]. The level of m⁶A methylation is also associated with ovarian inflammation and fibrosis in PCOS, and could serve as a potential biomarker for future studies on different types of cellular senescence in various tissues of PCOS [54].

Similar evidence has also emerged in clinical studies. Transcriptome-wide association studies have shown that after adjusting for BMI, age, and testosterone levels, there is a significant difference in the expression of the ARF-like GTPase 14 effector protein (ARL14EP) gene between PCOS patients and control groups, and ARL14EP acts on chromatin remodeling [55]. These findings indicate the genetic impact of chromatin remodeling on PCOS pathogenesis, while minimizing the interactive interference between other metabolic disorders and PCOS. Furthermore, reduced DNA methyltransferase 1-dependent methylation of the CDKN1A promoter in PCOS can enhance CDKN1A transcription, ultimately leading to the inhibition of GC proliferation and growth [56]. Further studies on the quantity and arrangement of heterochromatin in GC nuclei will facilitate in-depth exploration of the specific mechanisms by which GCs senescence in PCOS leads to impaired follicular maturation and ovulation. The presence of CpG DNA methylation in ovarian GCs of PCOS patients may also be a key factor contributing to reproductive dysfunction, and it may affect multiple protein targets at the microRNA level [57]. Hypomethylation at the CpG4 and CpG7 sites in the TGF-β1 gene promoter has been observed in the peripheral blood of PCOS patients, and the degree of methylation is associated with IR status in PCOS [58]. This emphasizes the importance of extensive research and investigation on PCOS patients exhibiting IR, which may help reveal a novel understanding of pathogenesis predisposed to cellular senescence. As a key component of SASP factors, abnormal methylation of TGF-β1 may also further exacerbate the senescent state of surrounding cells through the influence of senescent cell phenotypes. Notably, bioinformatics analysis has revealed differentially expressed genes related to ferroptosis in PCOS GCs compared with matched control groups, and the transcriptional regulatory network highlights the key role of HMGA1, a cellular senescence regulator, in regulating core ferroptosis genes in PCOS GCs [59]. Ferroptosis has long been recognized to have a complex and complementary relationship with cellular senescence [60]. However, there is insufficient clinical or mechanistic research on cellular senescence and ferroptosi in PCOS, which need further research evidence to support this association. These findings appear to provide potential evidence for the crosstalk or interaction of regulatory factors involved in nuclear chromatin fragmentation between cellular senescence and ferroptosis in PCOS GCs.

2.4. Cell morphology and structure changes

Compared with cells remaining in the mitotic cell cycle, cell cycle-arrested senescent cells typically exhibit an enlarged and flattened morphology, accompanied by nuclear abnormalities, including increased incidences of nuclear alterations, binucleation, nuclear non-disjunction, nuclear malformation, or disproportionately enlarged nuclei [61]. Furthermore, senescent cells typically exhibit expansion of the lysosomal compartment and vacuoles, as well as dilation of the endoplasmic reticulum and mitochondria. This may be attributed to the requirement for compensatory expansion of these organelles to maintain cellular homeostasis; however, newly formed organelles remain susceptible to environmental and functional perturbations induced by the accumulation of factors associated with cellular senescence, which may exacerbate the cellular senescence phenotype [62]. The activity of lysosomal SA-β-gal in senescent cells is significantly positively correlated with lysosomal mass and is currently one of the most widely used senescence biomarkers [63]. Similarly, lipofuscin – a complex composed of lysosomal digests, lipid residues, metals, and misfolded proteins – serves as another sensitive biomarker for senescent cells [64,65]. Notably, cytoskeletal stability, chromosomal integrity, and disruptions in spindle morphology or function (e.g. elongated spindles, missing poles, chromosome misalignment, and abnormal F-actin structures) have been identified as key morphological indicators of oocyte senescence [66,67].

Cellular morphological and structural alterations induced by cellular senescence are also evident in both PCOS specific phenotype and metabolic disorder phenotype. In a PCOS rat model treated with bisphenol A, the number of atretic follicles and immature small follicles in the ovaries was significantly increased, accompanied by a higher proportion of senescent cells and aberrant expression of genes regulating mitochondrial fission and fusion [68]. While a study utilizing a PCOS mouse model with IR induced by palmitic acid demonstrated cellular morphological alterations in metabolic organs, including the liver, spleen, and kidney – with manifestations such as disorganized hepatic lobule structure, vacuolar degeneration, and loose degeneration of hepatocytes. Additionally, significant alterations were observed in the ovaries, including GCs senescence and a marked increase in autophagosomes and lysosomes [42]. As the primary source of lipofuscin, the significant increase and dysfunction of lysosomes may contribute to lipofuscin accumulation; however, relevant evidence is currently lacking, and further investigations are warranted to explore this phenomenon. A meta-analysis revealed that PCOS is significantly associated with elevated levels of free radicals and malondialdehyde (MDA) [69]. Free radicals induce damage to human cells, generate the senescence factor MDA, and further promote lipofuscin accumulation [70] – suggesting a potential link between lysosomal senescence markers and PCOS. Furthermore, lipofuscin elevates mitochondrial oxidative stress levels by impairing lysosomal membrane permeability, thereby contributing to lysosomal dysfunction and further cellular senescence [71,72]. Lipofuscin accumulation, oxidative stress, and cellular senescence may also interact in the pathogenesis and progression of PCOS; thus, more in-depth studies are needed to elucidate the precise mechanisms underlying these interactions.

Currently, the diagnostic potential of markers reflecting cellular morphological and functional alterations in cellular senescence is frequently highlighted in PCOS patients with metabolic disturbances, including fat accumulation and IR [73]. Prospective clinical cohort studies have also demonstrated that SA-β-gal activity in the subcutaneous adipose tissue of severely obese patients is positively correlated with IR markers [74], underscoring the critical role of lysosomes in cellular senescence in PCOS with metabolic disorders.

2.5. Metabolic disorders

Cellular senescence is also characterized by metabolic abnormalities. Mitochondrial DNA (mtDNA) exhibits a higher propensity for mutation and accumulation due to its unique characteristics, including an independent replication cycle and simple structure [75]. Proteins encoded by mtDNA are integral components of mitochondrial respiratory chain complexes; mutations in mtDNA disrupt energy metabolism and reduce cellular sensitivity to oxidative damage, thereby strongly linking mtDNA mutations to cellular senescence. Impaired mitochondrial quality control and disrupted balance of antioxidant defenses in senescent cells lead to deficiencies in oxidative phosphorylation (OXPHOS), elevated ROS, cellular respiratory dysfunction, respiratory chain defects, and reduced ATP production. These conditions subsequently drive an increase in oxidative metabolism to sustain cellular survival [76,77]. However, oxidative stress can be both a cause of mtDNA mutation accumulation and a consequence of such mutations [78]. Increased mitochondrial outer membrane permeability (MOMP) in certain senescent cells is another hallmark of cellular senescence. This increased permeability leads to the release of mtDNA into the cytoplasm, activating the cGAS-STING pathway and promoting the formation of the SASP [79]. Inhibiting MOMP-associated inflammation may represent an effective strategy to counteract cellular senescence. Furthermore, senescent cells exhibit impaired endoplasmic reticulum (ER) function, including reduced protein synthesis capacity and enzyme activity, which is critical for the production of SASP factors. This dysfunction is associated with ROS accumulation generated by ER stress responses triggered by misfolded proteins [80], and further accelerates cellular senescence by influencing cell cycle arrest and DNA damage.

Oxidative stress associated with mitochondrial damage and cellular metabolic abnormalities are also present in PCOS. Elevated ROS levels induce oxidative stress-induced DNA damage, thereby contributing to oocyte and GCs senescence in PCOS patients, as clinical studies have identified an increased proportion of meiotic abnormalities in in vitro matured oocytes from PCOS patients [81]. Targeted metabolomics studies have revealed that abnormal OXPHOS and glycolysis in the follicular fluid of PCOS patients – two primary energy pathways supporting follicular maturation – impair ATP synthesis and generate excessive ROS through dysregulated energy metabolism, subsequently damaging mitochondria and inducing oxidative stress and mitophagy [82]; these processes are associated with impaired follicular growth and maturation in PCOS. Recent studies have identified the level of anti-Müllerian hormone (AMH) and molecular signatures in the follicular fluid of PCOS women associated with GCs glycolysis and mitochondrial dysfunction, which may negatively impact oocyte fertilization potential and represent a key feature of PCOS pathophysiology [83]; this could help further elucidate the mechanisms underlying GCs senescence and impaired oocyte quality.

In fact, compared with non-PCOS women with infertility due to tubal factors or male factors alone, GCs from PCOS patients exhibit significant mitochondrial abnormalities, including morphological changes, altered quantity and distribution, reduced mitochondrial membrane potential, decreased ATP production, elevated mitochondrial ROS, and insufficient OXPHOS. These impairments may be associated with low expression of SIRT3 in GCs [84]. SIRT3 is a key gene in mammalian follicular senescence and is regarded as a critical sensor of metabolic status by targeting mitochondrial enzymes in human GCs and oocytes [85]; its deficiency may be associated with elevated oxidative stress and glucose metabolism defects in PCOS [86]. Furthermore, reduced mtDNA copy number in the blood and GCs of PCOS patients, as well as genetic variations in the coding and non-coding regions of mtDNA, lead to mitochondrial dysfunction, disrupt the electron transport chain, and result in abnormal levels of cellular oxidative stress [87]. Abnormal status of the mitochondrial permeability transition pore (mPTP) in PCOS GCs may also influence cellular senescence by affecting mtDNA release [88]. Excessive oxidative stress accelerates telomere shortening, which is consistent with telomere shortening in cumulus cells of PCOS patients mentioned in a clinical study[89]; as guardians of oocytes, these findings suggest a potential mechanism underlying impaired follicular development and maturation in PCOS. In fact, clinical studies have identified the ability of circulating AMH levels in follicular fluid to serve as a biomarker reflecting oxidative stress levels [90]; future studies combining follicular fluid AMH with oxidative stress in follicular supporting cells will further reveal the heterogeneous cellular senescence status and specific mechanisms in PCOS.

In PCOS patients with IR, mitochondrial genetic variations are more closely associated with mutations in OXPHOS complex components and tRNA genes, which reduce ATP production in GCs, leading to insufficient cellular energy supply and subsequent cellular senescence [91]. Studies have demonstrated that elevated glucose and free fatty acids are associated with excessive ROS production and oxidative stress induced by mitochondrial oxidation [92], while high levels of free fatty acids and androgens in serum and follicular fluid induce mitochondrial damage and ER stress [93]; conversely, intense oxidative stress increases androgen production by affecting the levels of enzymes involved in testosterone synthesis [94]. Reports have indicated that the ER stress pathway is activated in PCOS patients [95], and hyperandrogenism in the follicular microenvironment may act as an activator of the ER stress pathway; hyperandrogenism can induce senescence of GCs in PCOS by activating ER stress [96], The relevant findings highlight a new cross-talk pattern between PCOS specific phenotype manifested by high androgen and metabolic disorder phenotype IR, obesity, thereby providing insights for developing relevant clinical therapeutic strategies.

2.6. DNA damage

Under normal circumstances, upon the occurrence of DNA damage, cells activate the DNA damage response (DDR) to maintain genomic integrity, and failure of repair can induce cellular senescence. The core mechanism of DDR involves the detection and repair of DNA damage by mutated ataxia-telangiectasia mutated, ataxia-telangiectasia and Rad3-related kinases. Activation of these kinases leads to p53 phosphorylation, which influences cell cycle arrest, DNA repair, and cellular senescence [97]. Inability to repair DNA damage accelerates cellular senescence. In senescent cells, impaired transcriptional and repair capacities severely disrupt the biosynthesis of RNA and proteins. The accumulation of these damages further impairs transcriptional quality and exacerbates cellular senescence [98]. Evidence in this regard includes the significant downregulation of genes encoding key components of DNA repair pathways in senescent cells [99], as well as a marked increase in the DDR marker γ-H2AX, which is closely associated with cellular senescence [100]. Sustained DDR can also reactivate the SASP [101]. Studies have found that the expression of γ-H2AX in oocytes of PCOS mice exposed to excessive androgens is significantly increased, indicating that excessive androgens may exacerbate DNA damage in oocytes. This is accompanied by germinal vesicle breakdown and reduced oocyte maturation rate, highlighting the importance of DNA damage, particularly the role of γ-H2AX in impaired follicular development and maturation in PCOS [102]. Consistent findings from clinical studies have shown that the level of DNA damage in oocytes from PCOS patients is higher than that in non-PCOS patients, which may be associated with elevated androgen levels, obesity, ROS accumulation, and chronic inflammation [103]. Polymorphisms in DNA repair genes such as XRCC1, APE1, and XPD are also associated with an increased risk of PCOS [104], suggesting that abnormal DDR may contribute to germ cell senescence in PCOS.

Furthermore, the activation of DDR is influenced by telomere length and telomerase activity. Following DNA damage, telomerase activity decreases, resulting in telomere shortening with each cell division. DDR is subsequently activated due to telomere shortening or damage, leading to telomere dysfunction and thereby promoting cellular senescence or cell death [105]. Telomeric repeat-containing RNA (TERRA) is a long non-coding RNA transcribed from telomeric repeat sequences, which plays a crucial role in regulating and maintaining telomere function. TERRA coordinates telomeric chromatin remodeling, telomerase activity, and homologous directed repair pathways involved in DDR, thereby determining cellular senescence [106]. Telomerase exhibits high activity in the ovary and is the most effective factor in limiting telomere loss and maintaining ovarian reserve. Its high activity enables GCs to undergo multiple replications. However, telomerase activity gradually decreases from preantral follicles to mature follicles [107].

Several studies have suggested an association between the pathogenesis of PCOS and longer telomeres in GCs [108]. However, persistent oxidative stress and inflammatory status in PCOS may lead to increased telomere loss and decreased telomerase activity [109,110]. There is a potential link between telomere dysfunction and limited telomerase activity [111]. Research findings regarding the relationship between telomere length and PCOS are conflicting. Other studies have revealed fluctuations in leukocyte telomere length in PCOS patients, showing age-related significant changes [112], which may be associated with differences in telomerase activity. Furthermore, studies suggest that the existence of tissue-specific telomere dynamics may also contribute to telomere length differences in PCOS, particularly in the ovary where telomerase activity is expressed. Additionally, different mechanistic pathways in immune cells and GCs may also result in different telomere lengths.

In summary, despite conflicting results from different studies – possibly due to the phenotypic heterogeneity of PCOS – clinical studies have shown that after age adjustment, the expression of TERRA in peripheral blood leukocytes of PCOS patients is significantly lower than that in the control group. TERRA regulates leukocyte telomere length and acts as a modulator of abnormal DDR in the context of cellular senescence; its correlation with testosterone levels reflects the potential mechanism underlying cellular senescence in PCOS complicated by hyperandrogenism [113]. Hyperandrogenism may compensate for the harmful effects of PCOS-related inflammatory status and metabolic disorders. Therefore, future studies using the most appropriate telomere measurement methods in larger populations may help further identify and elucidate the impact of telomere homeostasis on cellular senescence in PCOS.

2.7. Abnormal apoptosis signaling pathway

Cellular senescence typically exhibits resistance to apoptosis. Apoptosis constitutes a distinct cellular process from cellular senescence. During cellular senescence, negative regulators of apoptosis – including members of the Bcl-2 family (e.g. Bcl-2, Bcl-w, and Bcl-xL) – are upregulated, thereby conferring resistance to apoptotic signals [114]. Accordingly, detecting the expression of BCL2 family members represents a promising strategy for identifying cellular senescence. Alterations in MOMP are not only linked to apoptosis but also serve as a hallmark of cellular senescence; they induce SASP production by facilitating the release of mtDNA into the cytoplasm, and may further trigger apoptosis in surrounding healthy cells or adjacent senescent cells. Studies have demonstrated that inhibition of MOMP alleviates cellular senescence, indicating that apoptosis and cellular senescence share interconnected mitochondria-dependent regulatory mechanisms [79]. Senescent cells typically display aberrant activation of anti-apoptotic pathways, such as the hyperactivated PI3K/AKT/mTOR pathway in senescent tendon stem cells [115] and the central regulatory TP53/P21 pathway that governs the cell cycle and apoptosis of osteoarticular cells [116]. These pathways hold potential as therapeutic targets and research avenues for mitigating cellular senescence and SASP.

The cGAS/STING/NF-κB pathway represents a well-characterized signaling cascade involved in the regulation of apoptosis [117]. In vitro studies have revealed that stress-induced DNA damage leads to the accumulation of cytoplasmic chromatin fragments in senescent cells with activated cGAS-STING-NF-κB signaling, thereby driving SASP production and cellular senescence; this mechanism is likely linked to impaired lysosomal DNA degradation activity [118]. Murine studies have also identified a therapeutic mechanism whereby inhibition of cellular senescence in pulmonary hypertension is mediated by the cGAS/STING signaling pathway [119]; likewise, cGAS/STING can further accelerate cellular senescence during myocardial infarction by inducing SASP and an inflammatory microenvironment [120].

Studies have shown that elevated testosterone levels in PCOS induce mitochondrial damage, culminating in the release of mitochondrial DNA, which triggers activation of the cGAS/STING/NF-κB pathway in the ovaries of PCOS mice and subsequent GC apoptosis [121]. The cGAS-STING axis is also implicated in cellular senescence in PCOS; research has demonstrated that mPTP inhibits activation of the cGAS-STING axis and subsequent inflammatory responses in PCOS by reducing mtDNA release into the cytoplasm [122]. The ASK1-JNK apoptotic pathway represents another critical pathway in PCOS, linked to GC apoptosis and follicular wall integrity. Inhibition of this pathway effectively reverses the phenotypic manifestations of PCOS [123].

AMPK functions as a master regulator of lipid and glucose metabolism and, through interactions with mTOR and deacetylases, acts as a key modulator of cellular senescence. Hyperactivation of the AMPK/SIRT1 pathway in PCOS provides compelling evidence supporting the occurrence of cellular senescence in PCOS with metabolic disordera [124].

Although many apoptotic signals are believed to act alone in cellular senescence mechanisms in specific phenotypes of PCOS, such as hyperandrogenism, ovulation disorders, polycystic ovary like changes, or metabolic disorders, such as obesity, IR. Current studies have only explored specific pathways, and the same signaling pathway appears to exert pleiotropic regulatory effects. Consequently, further investigations are imperative to fully elucidate these mechanisms.

3. Evidence of cellular senescence in different tissues of PCOS

3.1. Ovary

The ovary is primarily composed of oocytes, granulosa cells, stromal and theca cells, and other cell types; these distinct ovarian cell types influence ovarian senescence through diverse cellular senescence pathways [125].

Folliculogenesis in the ovary largely depends on granulosa cells (GCs) that promote oocyte maturation by providing metabolic support, aiding hormonal signaling, and maintaining structural integrity. Concurrently, oocytes regulate glycolysis, amino acid, and lipid metabolism in GCs, thereby creating an optimal niche for follicular development [126]. GCs are currently the focal point of research on reproductive disorders associated with cellular senescence. Excessive apoptosis and mitochondrial dysfunction of ovarian GCs have been extensively studied in the pathogenesis and progression of PCOS; this represents a critical window for developing therapeutic strategies and may also be implicated in the cellular senescence processes of PCOS [127].

Relevant animal studies have demonstrated that fetal exposure to endocrine-disrupting chemicals (estradiol or diethylstilbestrol) may lead to slow growth of antral follicle reserves in the ovaries of adult PCOS rats, impair the normal function of primordial follicle differentiation into oocytes, and cause arrested meiosis [128]; the specific mechanism may be linked to the pathological features of ovarian GC senescence in PCOS patients. Ovarian mesenchymal stem/stromal cells and other stem cells can facilitate ovarian tissue repair and regeneration by homing to damaged sites and differentiating into oocytes or follicular cells [129]. However, these processes may be impaired by proliferation inhibition induced by GC senescence [130], further hindering the replacement and repair of damaged cells in the ovary, resulting in impaired follicular development and maturation in PCOS, and exacerbating inflammation. A recent systematic review highlighted significant changes in follicular fluid composition in PCOS women undergoing in vitro fertilization (IVF), emphasizing the roles of oxidative stress, inflammation, and growth factors in influencing oocyte quality and reproductive success [131]. In fact, stromal and theca cells may participate in cellular senescence through multiple regulatory pathways, including estrogen signaling, insulin pathways, and circadian rhythms; however, direct research on senescence in stromal and theca cells remains extremely limited. Given the critical role of stromal cells as supporting cells in maintaining ovarian function and microenvironmental homeostasis, research on the mechanisms associated with senescence of stromal and theca cells in PCOS is highly necessary [132]. For example, in the transcriptomic analysis of theca cells in a PCOS rat model, differences in genes and pathways that determine cell cycle arrest and apoptosis were identified [133]. These findings serve as important evidence for gaining an in-depth understanding of the mechanism by which theca cells disrupt follicular development and induce ovarian dysfunction through causing steroidogenesis dysregulation.

Furthermore, telomere length in GCs may also serve as a key predictor of oocyte quality and subsequent embryo quality. In fact, oocyte telomere length itself can also serve as a predictor of oocyte quality, although consistent evidence of changes in telomere length has not been obtained in in vitro matured oocytes from PCOS, possibly due to limitations imposed by the invasiveness of oocyte detection [134]. Additionally, prolonged retention of oocytes in the fallopian tube from ovulation to fertilization, as well as extended in vitro culture and pre-fertilization induction periods, may lead to ‘post-ovulatory aging’ of oocytes, which has been found to accelerate oocyte senescence through aberrant regulation of energy homeostasis, mitochondrial biogenesis, chromatin remodeling, and oxidative stress responses [135].

Currently, studies on cellular senescence and ovarian dysfunction in PCOS encompass multiple phenotypes, including androgen abnormality specific phenotypes, as well as metabolic disorders such as obesity and IR phenotypes. Recent studies have indicated that distinct phenotypes – including polycystic ovaries on ultrasound, clinical and/or biochemical hyperandrogenism, and oligomenorrhea – may involve different underlying mechanisms. For instance, elevated palmitic acid (PA) has been identified in PCOS patients with normal androgen levels [136] and is also significantly elevated in the follicular fluid of PCOS women exhibiting insulin resistance (IR) [137]. Relevant preclinical studies have demonstrated that PA induces ovarian GC senescence by promoting IR, likely because IR disrupts mitochondrial protein homeostasis through the mitochondrial unfolded protein response (UPRmt)/autophagy/lysosomal axis. This disruption further accelerates cellular senescence in the ovary, leading to GC senescence and follicular atresia in PCOS, impairing oocyte development [42]. This suggests a cross correlation between metabolic abnormalities such as obesity and IR in PCOS and disease-specific phenotypes such as hyperandrogenism, ovulation disorders, and polycystic ovary syndrome in terms of cellular senescence mechanisms.

Moreover, lncRNA cyclin L1 (CCNL1) is highly expressed in GCs of PCOS, particularly in those with high androgen levels. In vitro experiments have shown that higher concentrations of dihydrotestosterone (DHT) increase CCNL1 expression and reactive oxygen species (ROS) production. Under hyperandrogenic conditions, CCNL1 affects the expression of forkhead box O1 (FOXO1), regulating cell cycle arrest, apoptosis, and oxidative stress [138]. Unfortunately, current preclinical studies on cellular senescence in PCOS rely primarily on testosterone or DHT to induce experimental models, which limits understanding of senescence-related characteristics in ovarian and other tissue cells across other PCOS phenotypes and those exhibiting additional metabolic disorders such as IR or obesity. To address this issue, future studies should investigate senescence markers and their unique characteristics across a broader range of PCOS phenotypes.

Normal folliculogenesis is accompanied by increased pro-inflammatory cytokines, which are associated with the acquisition of oocyte developmental competence during follicle growth and permit remodeling of the ovarian stroma to weaken the ovarian wall for follicular rupture and participate in post-ovulatory wound repair; ovarian fibrosis is thus considered associated with ovarian senescence [139]. Under this theory, PCOS, particularly in anovulatory patients, might be expected to exhibit lower ovarian fibrosis. But in reality, studies have demonstrated a marked degree of ovarian fibrosis in women with PCOS [140], which may be associated with chronic inflammation-induced fibrosis. Despite the current lack of relevant evidence, existing findings can still serve as supporting evidence for discovering and exploring the mechanisms of cellular senescence in PCOS, particularly in PCOS metabolic disorder phenotypes accompanied by chronic low-grade inflammation, including obesity, IR.

Klotho, a multifunctional anti-aging protein with properties of preventing chronic fibrosis, antioxidation, anti-inflammation, anti-apoptosis, and anti-aging, is widely expressed in the ovary [141]. However, clinical studies have shown that Klotho expression is elevated in the follicular fluid and GCs of PCOS patients with hyperandrogenism, positively correlated with the number of antral follicles but negatively correlated with the number of mature oocytes. In vitro studies have indicated that an association exists between elevated Klotho levels and GC apoptosis, mitochondrial dysfunction, and inflammatory status in PCOS [142]. Klotho also functions as a specific co-receptor for fibroblast growth factor 23 (FGF23). The degree of fibrosis in dysfunctional tissues is associated with FGF23 gene expression [143], and elevated FGF23 levels have been observed in obese PCOS patients [144]. This provides evidence for exploring the link between ovarian tissue fibrosis and germ cell senescence in PCOS patients.

3.2. Endometrium

Following ovulation, the endometrium must exhibit normal morphology and function to support embryo implantation. The decidualization of endometrial stromal cells (ESCs) is a critical preparatory process for successful implantation. Under physiological conditions, there exists a complex interplay between cellular senescence and ESC-specific decidual differentiation. Decidualization is a multistep process. During the implantation window, a sustained acute proinflammatory stress response reprograms the endometrial glandular epithelium, leading to the emergence of stress-resistant decidual cells (DCs) or senescent DCs (sDCs). The balance between these cell populations may determine whether the endometrium successfully transitions to the gestational decidua during embryo implantation. The presence of sDCs promotes the secretion of various implantation-related factors, which induce secondary senescence in adjacent decidual cells; elimination of these sDCs can accelerate the decidualization process to a certain extent [145]. Physiological decidualization is an active adaptive differentiation of ESCs under strict regulation by hormonal and embryonic signals, aimed at establishing endometrial receptivity, supporting placentation, and maintaining pregnancy, and serves as the core physiological basis for successful pregnancy.

However, when ESCs are exposed to sustained stress, they aberrantly activate cellular senescence programs accompanied by a passive pathological process involving SASP. It occurs without a well-defined time window, often accompanied by inadequate or excessive decidualization, ultimately disrupting the pregnancy microenvironment, and represents a potential mechanism underlying pregnancy complications such as recurrent implantation failure, early pregnancy loss, and preeclampsia. Furthermore, proliferative arrest observed in senescent ESCs hinders the endometrial decidualization process, further exacerbating the impact of SASP inflammatory factors on the endometrial microenvironment [146]. Single-cell sequencing results also indicate that aberrant senescence of ESCs and epithelial cells, along with consequent perivascular collagen overdeposition, is associated with endometrial thinning [147].

Due to the effects of oxidative stress, DNA damage, and hormonal disorders, PCOS is often associated with abnormal endometrial decidualization and dysfunction, and exhibits relatively poor endometrial receptivity. Women with PCOS exhibit elevated levels of proinflammatory cytokines, chemokines, and matrix metalloproteinases in the endometrium, particularly in obese individuals [148,149]. Compared with healthy reproductive controls, proteomic analyses of serum and endometrium from PCOS patients have also revealed differential expression of proteins involved in cell cycle regulation, DNA repair, and mitochondrial metabolism [150]. These findings highlight the potential pathogenic significance of the interplay between aberrant SASP-associated senescence of ESCs and DCs and inflammation in PCOS-related endometrial dysfunction. Cellular senescence-related genes and pathways may serve as potential targets for research and therapeutic intervention, aimed at addressing endometrial infertility associated with cellular senescence in PCOS.

3.3. Placenta

The placenta plays a crucial role in maintaining fetal growth by serving as a critical interface between the mother and the fetus. It can secrete antioxidant enzymes and other molecules to counteract excessive free radicals and oxidative stress and maintain its stability. However, elevated levels of oxidative metabolism can also impair placental cell activity and hinder placental development [151]. In PCOS, the placenta is typically characterized by elevated hormone levels and IR, which manifest as excessive oxidative stress and abnormal cell cycle arrest [152]. These conditions may inevitably lead to placental cellular senescence by impairing mitochondrial function and shortening telomeres.

When women with PCOS exhibit high androgen levels, the placenta often exhibits specific histopathological changes, such as immature villi and defects in trophoblast proliferation or invasion [153]. Gestational diabetes mellitus is a common pregnancy complication associated with PCOS, and the trophoblast cells of which display phenotypic characteristics of senescent cells [154]. Animal studies have demonstrated that significant increases in placental dysfunction markers and cell senescence-related protein levels occur simultaneously in PCOS rats, highlighting the potential connection between increased PCOS-related pregnancy complications and cellular senescence in the placenta [155].

The senescence of endometrial and placental cells is accompanied by the release of various inflammatory factors and SASP-related chemokines. In PCOS, the excessive inflammatory state in the uterus, secondary to the release of these inflammatory factors following placental dysfunction and abnormal cellular senescence, exacerbates pre-existing chronic low-grade inflammation, negatively impacts the interaction between the decidua and trophoblast during early pregnancy, and inhibits the interaction between the chorion and decidua in late pregnancy. These disturbances may contribute to pregnancy complications of varying severity, including recurrent miscarriage, preterm birth, and preeclampsia [156]. The results of metabolomic analyses suggest differences in lactate metabolism in the plasma, urine, follicular fluid microenvironment, and intestinal microenvironment of PCOS patients; these differences include changes in lactate levels across different PCOS phenotypes and before and after treatment intervention [157]. Differential lactate levels may be a key factor in promoting cellular senescence across various tissues. Studies suggest that lactic acid may promote trophoblast senescence by modulating epigenetic modifications, potentially contributing to the development of preeclampsia [158].

Furthermore, emerging evidence from large clinical studies and pathophysiological investigations reveals that women with PCOS face an increased risk of developing preeclampsia compared to non-PCOS women [159,160]. While obesity exacerbates these pathways, PCOS itself independently contributes to preeclampsia risk through androgen-mediated oxidative stress, impaired trophoblast invasion, and aberrant expression of angiogenic factors [161,162]. Beyond the excessive uterine inflammation observed in PCOS, these mechanisms may explain some of the pregnancy complications linked to the condition.

4. Therapeutic strategies and potential of PCOS based on cellular senescence

Appropriate elimination of replicative and premature senescent cells is considered beneficial for mitigating related diseases. Currently, drug strategies for targeting senescent cells in humans primarily encompass two categories: senolytic drugs, which selectively eliminate senescent cells by leveraging immune surveillance mechanisms specific to these cells; and senomorphic drugs, which mitigate the harmful effects of senescent cells on intercellular communication by inhibiting the production and secretion of the SASP [1].

4.1. Senolytic drugs

Senolytic drugs are typically developed for specific cell types. Intermittent administration of senolytics – including those targeting anti-apoptotic pathways and SASP inhibitors, can effectively avoid off-target effects potentially induced by continuous use, such as nephrotoxicity, metabolic disorders, and increased susceptibility to infections, particularly for SASP-inhibiting senolytics [163]. However, studies on the clinical application of senescent cell models, preclinical animal models, and anti-aging agents in PCOS with different phenotypes remain scarce, and most research is still in the stage of exploring preclinical application value. More robust and in-depth studies will help uncover additional insights into cellular senescence in the pathogenesis of PCOS.

4.1.1. Dasatinib and quercetin

The combination of dasatinib and quercetin (DQ) is a widely used senolytic agent. Recently, it has been reported that DQ therapy was applied in in vitro testosterone-induced senescent human granulosa cell (GC) models. They observed decreased expression of p16INK4a, p21, p53, γH2AX, SA-β-gal, and senescence-associated secretory phenotype (SASP)-related factors, and these levels were associated with morphological restoration of ovarian senescence [26]. This confirms the therapeutic value of senolytics in targeting GC senescence in PCOS-specific phenotypes with hyperandrogenism, and may be particularly beneficial for improving follicular development and maturation disorders.

In fact, DQ may target additional molecules, including pan-receptor tyrosine kinases and PI3K, which are involved in cell cycle regulation and epigenetic modification. Further related studies will help clarify its pharmacological value. Currently, the mechanisms and application value of DQ in cellular senescence research have been extensively explored in other diseases. In vitro studies have demonstrated that DQ inhibits cellular senescence and enhances osteogenic differentiation by inducing apoptosis in senescent periodontal ligament stem cells [164]. Furthermore, a research group found that DQ therapy alters the chromatin structure of senescent vascular smooth muscle cells, leading to chromatin regeneration and alleviation of age-related characteristics. However, this mechanism may vary by cell type and physiological context, requiring further research for validation [165].

Given the heterogeneity of metabolic disturbances in the PCOS population, particularly when accompanied by clinical phenotypes such as IR and obesity, different genetic characteristics, hormonal fluctuations, and corresponding hormonal changes may significantly affect the response of PCOS patients to these treatments through distinct mechanisms. For instance, animal studies have shown that DQ reduces cellular senescence in metabolic dysfunction-associated fatty liver disease by decreasing adipose deposition and inhibiting the expression of fibrotic genes [166]. Similarly, mouse experiments have demonstrated that DQ combined with other gonadotropin therapies can improve insulin sensitivity in mice with impaired ovarian function [167], which is consistent with another study showing that DQ effectively restores glucose homeostasis and reduces adipose tissue senescence in mice with ovarian cancer [168].

Current DQ-related studies are mostly focused on preclinical experiments and have not yet been extensively conducted in the PCOS population. However, these preclinical findings indicate potential applications and research directions; particularly for PCOS women with obesity-related metabolic disturbances, the efficacy of DQ combination therapy may be more pronounced. Nevertheless, DQ therapy cannot eliminate all types of senescent cells. Given that PCOS-specific phenotypes characterized by hyperandrogenism and metabolic disturbance phenotypes may involve distinct core effector cells, pathways, and molecular mechanisms, it remains unclear whether DQ can improve follicular development disorders and metabolic abnormalities induced by inflammation and oxidative stress in PCOS. This underscores the need for more in-depth research, particularly large-scale clinical cohort studies and trials to validate its therapeutic value.

4.1.2. Fisetin

Fisetin is another PCOS-related senolytic agent that primarily targets regulators of the PI3K/AKT/mTOR pathway. Animal studies have revealed that fisetin exerts preclinical value in PCOS through complex regulation mediated by the AMPK/PI3K/AKT-dependent antioxidant defense mechanism and modulation of the inflammatory signaling pathway NLRP3/NF-κB p65/IL-1β. It effectively reduces IR and cholesterol levels, while also inhibiting hyperandrogenism and promoting ovulation [169], which is also associated with reduced oxidative stress.

Furthermore, high-dose fisetin significantly ameliorates testosterone levels in PCOS rats, which may be attributed to the regulation of the AMPK/SIRT1 signaling pathway [168]. Its therapeutic value is highlighted in the improvement of sex hormone disorders and abnormal follicular development following administration. Additionally, fisetin can exert significant alleviating and protective effects by restoring PCOS-induced alterations in key genes involved in energy homeostasis and antioxidant enzymes [170].

These findings suggest that fisetin appears to have a broader range of targets and therapeutic mechanisms, with therapeutic significance not only in PCOS-specific phenotypes but also in metabolic disturbance phenotypes of PCOS. This indicates the potential future application of fisetin in PCOS patients with concurrent follicular development disorders and glycolipid metabolic disturbances. Numerous in vitro and in vivo studies have preliminarily confirmed its role in improving cellular senescence by influencing inflammation and the cell cycle. However, related clinical trials remain scarce, with fisetin only observed to reduce SASP factors in patients with colorectal cancer [171] and acute ischemic stroke [172]. Whether it possesses more specific and substantial value in PCOS clinical applications, including the regulation of SASP factor levels and epigenetic modifications, requires further population-based studies.

4.1.3. Cordyceps polysaccharide

Cordyceps polysaccharide (CP) is a polymer composed of galactose, mannose, and other compounds. It has been demonstrated to improve glucose and lipid metabolism disorders in a PCOS rat model by inhibiting the TLR4/MyD88/NF-κB inflammatory pathway in the liver and adipose tissue, restoring insulin signaling, and additionally facilitating the recovery of ovarian morphology and hormonal metabolism in PCOS with metabolic disturbance phenotypes [173]. A literature review indicates that the TLR4/MYD88/NF-κB pathway is also crucial for serum-soluble anti-aging factor Klotho to inhibit cardiac cell senescence and may simultaneously regulate immunity and inflammation [174]. Currently, CP has been explored as an agent that enhances lysosomal activity in senescent cells and improves their senescent state. Although its application has been validated and explored in preclinical animal models of PCOS with metabolic disturbances, its potential to alleviate inflammation and metabolic disorders in PCOS patients, as well as its ability to improve follicular development, requires further clinical research. The reduction of senescence markers following the elimination of senescent cells may provide evidence for its future therapeutic applications.

4.1.4. Mitochondrial targeted ferroptosis inducing drugs

Notably, senescent cells exhibit resistance to ferroptosis, a form of programmed cell death. Due to its ability to selectively target and eliminate both primary and paracrine functions of senescent cells, ferroptosis induction has been established as a therapeutic strategy analogous to senolytic agents [60]. Studies have demonstrated that mitochondrial targeting of tamoxifen inhibits mitochondrial function, impairs the integrity of senescent cells, induces ferroptosis activation, accelerates senescent cell death, and promotes tissue regeneration [175]. This mechanism of targeted ferroptosis induced by mitochondria in senescent cells represents a universal therapeutic strategy for senescence, implying a complex interplay between ferroptosis and cellular senescence. Given the aberrant ferroptosis observed in PCOS complicated by metabolic disturbances, further studies are crucial for elucidating the underlying mechanisms of cellular senescence in PCOS with concurrent metabolic disorders and their potential therapeutic relevance.

4.2. Senomorphic drugs

In summary, senomorphic drugs inhibit cellular senescence by targeting multiple markers, offering a promising and effective supplement to the treatment of PCOS. Nevertheless, translating these compounds into clinical practice remains a significant challenge. Creating a simulated environment that closely mimics the senescence of human PCOS cells is essential for achieving widespread clinical application. Additionally, addressing phenotypic differences and genetic variability among PCOS patients and developing personalized treatment models are key challenges. Exploring more combination therapies, including alternative senolytics and senomorphics, could also help improve clinical symptoms in PCOS patients in the future.

4.2.1. Metformin

Commonly used senomorphic drugs typically have distinct targets. Studies have demonstrated that metformin-induced autophagic activation significantly inhibits cellular senescence, with the specific mechanism potentially associated with reduced size and levels of cytoplasmic chromatin fragments and inhibition of the apoptotic cGAS/STING/NF-κB/SASP cascade [118].

Metformin is an important adjuvant therapeutic agent for PCOS patients. It improves soluble interleukin (sIL) levels, increases the expression of insulin-like growth factor-binding protein 1 (IGFBP-1) in the endometrium, and restores decidualization capacity [176]. In vitro studies have also found that metformin can reduce the number of senescent B cells, as well as the levels of SA-β-gal, SASP factors, and other senescent cell markers [177]. Notably, metformin has been shown to exert anti-fibrotic effects on the ovary, which is of great significance for improving ovarian morphology, oxidative stress, and ovarian fibrosis in PCOS [178].

Metformin is a commonly used clinical drug in PCOS. Clinical studies have found that metformin (1500–2000 mg/day) can restore ovulation in obese women with PCOS in some cases [179]. However, there is insufficient clear evidence supporting whether it exerts therapeutic effects on improving ovulatory dysfunction by ameliorating cellular senescence. Preliminary studies have indicated that metformin increases the survival rate of ovarian GCs in PCOS patients by upregulating the expression of LINC00548 and inhibiting the AR/Klotho apoptotic pathway [180]. Metformin is a potentially important therapeutic option for addressing abnormal cellular senescence in PCOS. A systematic review and network meta-analysis of clinical studies on patients undergoing in IVF and intracytoplasmic sperm injection (ICSI) demonstrated that metformin increases the number of mature oocytes, providing preliminary evidence for its efficacy in improving ovarian function. However, its clinical application in PCOS remains challenging. Although this meta-analysis highlighted the potential of metformin to reduce ovarian hyperstimulation [181], several factors limit its widespread use, including different PCOS metabolic disturbance phenotypes characterized by obesity and IR, variations in drug response and efficacy among ovarian stimulation protocols, and the need to balance drug cycle length with the risk of side effects such as gastrointestinal disorders [182]. Additionally, whether metformin improves senescence-related phenotypes in PCOS remains unclear. Therefore, its use as a senomorphic drug in clinical PCOS treatment requires further extensive research and careful consideration to fully explore its potential.

4.2.2. Apigenin

As a natural flavonoid, apigenin has been shown to regulate the activity of SA-β-gal and may exert anti-aging effects via activation of the Nrf2 pathway [173]. Another study highlighted that apigenin can reduce senescence in rectal cancer cells by inducing apoptosis [183] and may suppress the expression and secretion of various SASP factors through pathways such as p38 MAPK and NF-κB [184]. Furthermore, apigenin can ameliorate endoplasmic reticulum stress-induced cell death and IR in diabetic models [185]. It may promote adipose browning in obese mice by activating autophagy mediated by the PI3K-Akt-mTOR pathway, thereby reducing body weight and improving glycolipid metabolic disorders [186].

Apigenin also holds preclinical potential in improving lipid profiles and oxidative metabolism in PCOS rat models. It demonstrates efficacy in reducing ovarian diameter and the accumulation of numerous antral follicles in the ovary, which is associated with the regulation of inflammatory cytokines TNF-α and IL-6 levels [187,188]. Other studies have observed the same trend, where apigenin treatment partially restores follicular development in PCOS rats, reduces cyst count, increases corpus luteum, decreases collagen density in polycystic ovaries, and attenuates ovarian angiogenesis by reducing the number of endothelial and perivascular cells [189]. Additionally, the combination of apigenin and ascorbic acid can effectively reduce intracellular ROS levels and apoptosis in zebrafish ovarian cells [190].

These findings provide important preclinical evidence supporting future clinical studies on the application of apigenin as a senomorphic drug in PCOS patients to improve ovarian morphology, function, and inflammatory status. Clinical studies in patients based on these results will help to better elucidate the clinical value, targets, and pharmacological mechanisms of apigenin in ameliorating ovulatory dysfunction in PCOS.

4.2.3. Resveratrol

A randomized, triple-blind, placebo-controlled clinical trial highlighted the clinical potential of resveratrol in addressing ovarian dysfunction caused by cellular senescence in PCOS. Resveratrol has been shown to delay the premature senescence of GCs by regulating oxidative metabolism levels, mitochondrial function, and biogenesis in follicular fluid, reduce SA-β-gal levels and SASP factors, and significantly affect SIRT1 levels as a SIRT1 agonist to alleviate cellular senescence [191]. Furthermore, it is associated with the activity of RNA methyltransferases and m6A methylation levels in senescent cell models [192], and effectively ameliorates the inflammatory status of PCOS ovaries and various signaling pathways related to cell apoptosis and proliferation [193].

In addition to its effects on ovarian function, some studies have indicated that resveratrol treatment inhibits sDCs during the initial proinflammatory decidual phase of the implantation window in vivo and induces deacetylation of genes critical for decidualization [194], which may reduce endometrial receptivity. Therefore, some researchers suggest that administration of resveratrol after the initial inflammatory stress phase can promote physiological decidualization by inhibiting excessive sDCs [195], highlighting the importance of stage-specific administration of resveratrol to enhance decidualization and endometrial receptivity. This strategy may offer particular benefits to PCOS patients with recurrent embryo implantation failure.

Regarding the mechanism and efficacy of resveratrol in PCOS with concurrent metabolic disturbances, animal studies have found that resveratrol can improve IR and glycolytic abnormalities in PCOS rats by regulating SIRT2, which may be a potential mechanism for alleviating PCOS ovarian damage and IR-related cellular senescence [196]. Furthermore, a meta-analysis of clinical trials on resveratrol in PCOS found that resveratrol has no effect on reducing BMI, triglycerides, high-density lipoprotein, or low-density lipoprotein [197]; however, comprehensive fundamental studies and randomized controlled trials are still warranted to explore its mechanisms and evaluate its clinical efficacy. Additionally, other factors must be considered, such as different cell and tissue types, administration methods, and dosages, to prevent growth arrest and induce cellular senescence or apoptosis [198].

4.3. Inadequacies and limitations

Although numerous drugs potentially associated with cellular senescence in PCOS have been identified, most of their mechanisms and efficacy have been primarily investigated in preclinical studies, i.e. in vitro cell lines and animal models. Large-scale clinical trials that have been completed or are planned are lacking; thus, only evidence supporting senolytic and senomorphic agents as experimental drugs has been obtained to date, and there is a long way to go before they become clinically approved drugs and are widely used in PCOS.

Furthermore, there are certain differences in the pathogenesis of PCOS-specific phenotypes (e.g. ovarian developmental and maturation disorders) and PCOS metabolic disturbance phenotypes (e.g. obesity and IR). For instance, metabolic disturbance phenotypes primarily involve oxidative stress and inflammatory responses associated with adipocytes, pancreatic β cells, and mitochondrial dysfunction; in contrast, cellular senescence mechanisms in follicular developmental disorders are more related to ovarian granulosa cell senescence under hyperandrogenism, granulosa cell apoptosis and ovarian fibrosis induced by SASP factors, and hypothalamic-pituitary axis dysfunction. Although crosstalk and interactions between multiple phenotypes cannot be ignored in practical research, when considering cell senescence-based therapies, it is crucial to select different personalized therapies for animal models and clinical patients that prominently exhibit distinct PCOS-specific phenotypes and metabolic disturbance phenotypes. This may help address potential challenges in translating senolytics/senmorphics into clinical practice.

Additionally, considering that PCOS treatment often needs to cover the reproductive years and even long-term maintenance (e.g. prevention of long-term metabolic complications), data on the long-term application safety and reproductive toxicity of senolytics and senmorphics in PCOS are severely lacking. These agents have limitations in tissue targeting, and the off-target risks of senolytics and dysregulation of senmorphics cannot be ignored [199]. More rigorous clinical trial designs are required to clarify endpoints and target populations, thereby achieving efficient clinical translation and application.

5. Conclusions

In summary, both replicative cellular senescence and premature senescence induced by various stressors may be involved in the pathogenesis and progression of PCOS. The underlying mechanisms may involve abnormal oxidative metabolism caused by DNA damage, epigenetic changes, and mitochondrial dysfunction, leading to cell cycle arrest and promotion of anti-apoptotic pathways. Furthermore, secretion of SASP factors into the surrounding tissues and microenvironment may exacerbate or accelerate the cellular senescence state. This phenomenon has been observed in various conditions associated with PCOS, including PCOS-specific disorders of follicular maturation and ovulation, reduced uterine receptivity due to endometrial dysfunction, and pregnancy complications related to placental tissues. Moreover, obesity and insulin resistance, as common metabolic disturbances in PCOS, may also induce cell cycle arrest, excessive oxidative stress, elevated immune and inflammatory levels, abnormal gene methylation, endoplasmic reticulum stress, DNA damage, and excessive apoptosis.

However, metabolic abnormalities in PCOS (e.g. obesity, IR) often cross-correlate with disease-specific phenotypes (e.g. hyperandrogenism, ovulatory dysfunction, polycystic ovarian changes), making it challenging to attribute cellular senescence-related mechanisms. Some findings related to cellular senescence may be co-influenced by both metabolic abnormalities and PCOS-specific phenotypes (e.g. obesity combined with hyperandrogenism may synergistically promote cellular senescence), which cannot be completely separated for the time being – a limitation of current research. However, we also observe that some PCOS patients exhibit only metabolic abnormalities (e.g. obese PCOS), while others present only with reproductive dysfunction phenotypes (e.g. non-obese PCOS), suggesting that the role of cellular senescence is phenotype-dependent. Future validation is required through stratified cohort studies (e.g. comparison between PCOS patients with matched metabolic status and non-PCOS populations with metabolic abnormalities).

In general, our current work primarily summarizes existing research progress and proposes valuable but limited hypotheses based on available literature. Future efforts should focus on broader and deeper exploration of distinct mechanisms in PCOS-specific phenotypes and metabolic disturbance phenotypes to better understand the heterogeneity of cellular senescence under different conditions. Senolytics/senmorphics provide a new direction for PCOS treatment, but their clinical translation requires overcoming multiple barriers such as heterogeneity, targeting, safety, and trial design. Future clinical studies need to combine technologies such as single-cell sequencing and organoid models to analyze the senescence characteristics of PCOS subtypes, develop targeted drugs with higher specificity, and validate their efficacy and safety through rigorous stratified clinical trials to gradually achieve the leap from basic research to clinical application.

Funding Statement

This work was supported by the National Natural Science Foundation of China [No. 82274573, 81703958], the Natural Science Foundation of Shandong Province [No. ZR2021MH255] aandthe Special Fund of “Taishan Scholars” of Shandong Province [No. tsqn202103182].

Disclosure statement

No potential conflict of interest was reported by the author(s).