Lens epithelial cells senescence in cataract pathogenesis and emerging therapeutic opportunities

Stable and virtually irreversible cell-cycle arrest represents the most fundamental hallmark of cellular senescence. It is widely recognized that senescent cells primarily arrest in the G1 phase of the cell cycle, thereby preventing the replication of damaged DNA. However, some senescent cells may also undergo arrest in the G2 phase to block mitotic entry in the presence of persistent genomic damage (Kumari and Jat, 2021; Ogrodnik et al., 2024). Cyclin-dependent kinases (CDKs) are serine/threonine kinases that form complexes with specific cyclins. These CDK–cyclin complexes promote cell cycle progression by phosphorylating critical substrates required for DNA replication and entry into mitosis (Pellarin et al., 2025). Proper activation and regulation of CDK activity is essential for orderly cell cycle transitions, particularly the progression from G1 to S phase and from G2 to M phase (Pellarin et al., 2025; Sunada et al., 2021). In response to various cellular stressors, LECs activate canonical tumor-suppressive pathways, notably the p53/p21 and p16^INK4a/Rb axes, which enforce a stable blockade of cell cycle progression (Liu H., et al., 2025). A range of signaling pathways converge to modulate this arrest program.

Cell-cycle arrest and proliferative inhibition represent the most prominent hallmarks of LECs senescence. In our previous studies, we demonstrated that heme oxygenase-1 (HO-1) delays LECs senescence by enhancing the antioxidant defense system and suppressing activation of the p53/p21 signaling pathway (Wang et al., 2023). Additionally, biliverdin reductase A (BVRA) exerts cytoprotective effects through multiple mechanisms. It catalyzes the conversion of biliverdin (BV) to bilirubin (BR), upregulates the expression of HO-1, and activates the ERK/Nrf2 signaling pathway. Together, these actions enhance the antioxidant capacity of LECs, thereby delaying the onset of cellular senescence. Moreover, BVRA has been shown to inhibit the activation of the p21 and p16, further contributing to the suppression of stress-induced senescence (Huang et al., 2022). In addition, sirtuin 1 (SIRT1), a key NAD⁺-dependent deacetylase, has been shown to exert anti-senescent effects in LECs. Under oxidative stress, the downregulation of SIRT1 enhances the acetylation of p66Shc, thereby promoting its activation and mitochondrial translocation. This process exacerbates mitochondrial ROS production, establishing a vicious cycle of oxidative damage (Liu H., et al., 2025). Mitochondrial dysfunction not only directly impairs cellular energy metabolism but also activates cell cycle inhibitory pathways, ultimately driving cells into a senescent state (Liu H., et al., 2025). The SIRT1/Nrf2 signaling axis has also been shown to delay cellular senescence by enhancing the intrinsic antioxidant defenses of LECs (Chen Q., et al., 2022). Moreover, SIRT1 has been shown to exert anti-senescent effects by inhibiting the FoxO1/TLR4 signaling pathway (Jiang H., et al., 2025). In diabetic cataract patients, aberrant N6-methyladenosine (m⁶A) modification has been shown to promote the degradation of SIRT1 mRNA, leading to decreased SIRT1 expression. This downregulation subsequently results in the upregulation of the p53/p21 signaling pathway, thereby accelerating cellular senescence in LECs (Dong et al., 2024). In addition, several emerging molecular pathways have recently been identified. Loss of FYVE and FYCO1 has been shown to attenuate oxidative stress-induced senescence by suppressing the PAK1/p21 signaling pathway (Chen S., et al., 2024). In cataract models induced by elevated uric acid, uric acid promotes chronic inflammation by activating the NLRP3 inflammasome. This inflammatory cascade subsequently triggers the p53/p21 pathway, thereby inducing senescence in LECs (Lin et al., 2024). Mechanical strain may also contribute to the senescence of LECs. Under tensile stress, activation of the mechanosensitive ion channel PIEZO1 leads to calcium influx, which in turn triggers the expression of senescence-associated genes (Chen L., et al., 2024). Notably, p21 expression is not always regulated through the canonical p53-dependent pathway. Evidence suggests that p53-independent mechanisms of p21 regulation also exist. For instance, Heat Shock Factor 4 (HSF4) can suppress p21 transcription by recruiting the histone methyltransferase EZH2 to the p21 promoter region, thereby enhancing H3K27me3 modification and silencing p21 expression (Cui et al., 2021).

Beyond stable cell-cycle arrest, one of the most prominent features of senescent cells is the development of a complex and pro-inflammatory secretory program known as the senescence-associated secretory phenotype (SASP). The SASP encompasses a wide array of bioactive molecules, including cytokines, chemokines, matrix metalloproteinases (MMPs), and growth factors (Gorgoulis et al., 2019; Cao et al., 2025). These molecules exert their effects either through autocrine reinforcement of senescence or by modulating the microenvironment via paracrine signaling pathways. Functionally, the SASP constitutes the principal mechanism through which senescent cells exert their effects on the surrounding tissue, actively remodeling the microenvironment and contributing to both physiological and pathological processes (Wang et al., 2024). Although comprehensive studies of SASP in cataract remain limited, existing evidence has observed elevated expression of canonical SASP factors in LECs senescence models, which suggests that SASP may play a meaningful role in LECs aging. Once senescence is established, the SASP can actively reshape the tissue microenvironment, impair the function of neighboring non-senescent LECs, and thereby accelerate the propagation of senescence within the lens epithelium.

Emerging data also implicate SIRT1 in the regulation of SASP production. Specifically, treatment of senescent LECs with resveratrol, a pharmacological activator of SIRT1, has been shown to reduce the secretion of multiple SASP factors, including IL-1β, IL-6, CXCL8, MMP1, and TGF-β. Resveratrol enhances the antioxidant capacity of LECs by activating the SIRT1/Nrf2 signaling pathway, thereby preventing the onset of cellular senescence (Chen Q., et al., 2022). HSF4 has also been implicated in the regulation of SASP (Cui et al., 2021). In addition, another study reported an upregulation of IL-1 expression in senescent LECs. Although this study did not explicitly define the response as SASP, the increased expression of IL-1β, a core component of the SASP, further supports the notion that inflammatory secretory activity is a prominent feature of LEC senescence (Lin et al., 2024). Similarly, TGF-β1 and MMP-9 may also function as components of the SASP, contributing to the senescence process of LECs (Yan et al., 2019).

Autophagy is an evolutionarily conserved lysosome-mediated catabolic process that plays a central role in maintaining cellular homeostasis by degrading and recycling damaged organelles, misfolded proteins, and other cytoplasmic components (Gómez-Virgilio et al., 2022). And under stress, autophagy acts as a crucial adaptive mechanism that allows cells to survive nutrient deprivation, oxidative insults, and other damaging stimuli (Kaushik et al., 2021; Ryteret al., 2013; He, 2022). In the context of lens biology, increasing evidence suggests that autophagy may influence the susceptibility of LECs to senescence, particularly under conditions of chronic stress such as oxidative damage or metabolic imbalance. Our previous research demonstrated that HO-1 delays oxidative stress–induced senescence by promoting the nuclear translocation of transcription factor EB (TFEB), thereby enhancing autophagic flux and lysosomal function (Wang et al., 2023). Similarly, SIRT1 has been shown to attenuate cellular senescence through the regulation of autophagic activity. The SIRT1 activator SIRT1720 increases the number of autophagosomes and restores autophagic flux by upregulating Beclin1 and LC3II/I and downregulating p62. This leads to the reversal of P53 and P21 upregulation (Dong et al., 2024). FYCO1, an autophagy adaptor protein, also contributes to the maintenance of autophagic flux and exerts anti-senescent effects (Chen S., et al., 2024). Conversely, impaired autophagic flux has been linked to the activation of the p38 MAPK/p53 signaling axis, thereby promoting the onset of senescence (Xu et al., 2018). These findings collectively underscore the pivotal role of functional autophagy in maintaining LECs homeostasis under stress conditions.

Among various environmental stressors, UVB radiation is recognized as one of the most prominent exogenous sources of oxidative stress contributing to lens aging. UVB, with a wavelength range of 280–315 nm, can penetrate the cornea and reach the anterior capsule of the lens, exerting direct and cumulative phototoxic effects on LECs (Hamba et al., 2021; MacFarlaneet al., 2024). A growing body of epidemiological and experimental evidence has also linked UVB to an increased risk of cortical age-related cataracts (McCarty et al., 2000; Li et al., 2021). UVB exerts its deleterious effects on LECs primarily through the induction of oxidative stress and DNA damage. At the cellular level, UVB exposure can cause DNA double-strand breaks (DSBs), thereby activating the DNA damage response (DDR) pathway (Mesa and Bassnett, 2013; Liu et al., 2021). Concurrently, UVB-induced photoexcitation leads to the overproduction of ROS, which disrupts redox homeostasis and impairs mitochondrial function. With advancing age, the lens exhibits a diminished capacity to counteract oxidative stress, as evidenced by declining GSH levels and reduced activity of antioxidant enzymes. This impairment renders senescent LECs particularly susceptible to prolonged oxidative damage induced by UVB radiation (Bejarano et al., 2023; Pescosolido et al., 2016). Taken together, these cumulative insults can drive cells into a state of irreversible cell-cycle arrest accompanied by persistent expression of senescence-associated phenotypes, including elevated pro-inflammatory cytokine production. In addition to exogenous ultraviolet radiation, LECs are chronically exposed to endogenous oxidative stress arising from intrinsic metabolic activity throughout lifespan. GSH is significantly reduced in aged individuals and in cataractous lenses (Sweeney and Truscott, 1998; Kamei, 1993). Similarly, enzymatic antioxidant systems such as SOD and catalase show diminished activity with age, compromising the clearance of ROS (Fecondo and Augusteyn, 1983; Rajkumar et al., 2008). Our previous work also identified a marked downregulation of BVRA in cataractous lens tissue. BVRA enzymatic activity was found to decline progressively with cellular senescence (Huang et al., 2022). This dual loss of expression and function may further impair the capacity of LECs to defend against oxidative insults.

Metabolic dysregulation, particularly glucotoxicity induced by chronic hyperglycemia, represents a potent and prototypical source of cellular stress in the pathophysiological aging of the lens. In diabetic cataracts, LECs are chronically exposed to a pathological microenvironment characterized by increased oxidative stress and osmotic imbalance (Guo et al., 2023). This adverse cellular context serves as a key upstream factor driving LECs dysfunction and promoting premature senescence. Mechanistically, high glucose activates multiple stress-associated intracellular pathways. One of the most well-characterized is the polyol pathway, which becomes hyperactivated under hyperglycemic conditions, leading to sorbitol accumulation and consequent osmotic stress (Thorne et al., 2024). Simultaneously, non-enzymatic glycation of proteins and lipids accelerates the formation of advanced glycation end products (AGEs), which bind to their receptor, the receptor for advanced glycation end products (RAGE), and perpetuate inflammatory and oxidative signaling cascades (Cooksley et al., 2024).

Beyond metabolic and oxidative stress, LECs are also subject to a range of other physiological and pathological stressors. Several studies have demonstrated that mechanical stretch activates stress-responsive signaling cascades, inducing ROS generation, cytoskeletal remodeling, and the release of inflammatory mediators (Liang et al., 2019; Chen L., et al., 2024). These findings highlight the potential for biomechanical forces to serve as upstream triggers of cellular senescence in lens epithelium. In addition, systemic metabolic abnormalities, such as hyperuricemia and dysregulated lipid metabolism, can lead to the accumulation of metabolic waste products in the aqueous humor, thereby altering the physicochemical properties of the lens microenvironment (Lin et al., 2024; Wang J., et al., 2022). Recent studies have suggested that certain metabolic byproducts may directly or indirectly trigger oxidative stress in LECs. For example, elevated concentrations of uric acid have been shown to activate the NLRP3 inflammasome, contributing to LECs dysfunction and the secretion of SASP (Lin et al., 2024). The pathological connection between systemic metabolic waste and LECs functional integrity may represent a novel mechanistic axis for understanding how systemic metabolic risk factors contribute to cataractogenesis.

Various animal models have been developed to study the role of LEC senescence in cataract formation. One of the most widely used models involves UVB radiation, which induces oxidative stress and DNA damage in LECs. UVB exposure causes the accumulation of ROS and triggers senescence pathways in LECs, leading to the development of cataracts (Liu H., et al., 2025; Chen S., et al., 2024). Besides, D-galactose and sodium selenite are also used to construct cataract models by inducing LEC senescence through oxidative stress (Wang Y., et al., 2022; Chen Q., et al., 2022). In addition to induced models, naturally aged animals are also used to study cataractogenesis. These models provide a more physiologically relevant system in which LEC senescence naturally accumulates over time, leading to gradual lens opacity (Chen M., et al., 2022). In addition, increased LEC senescence and early cataract onset have been observed in genetic knockout mice, such as those with YAP conditional knockout or AQP5 deficiency, both of which promote LEC senescence (Zhang K., et al., 2023; He et al., 2019). Together, these animal models have been pivotal in advancing our understanding of the molecular mechanisms that drive LEC senescence in cataract formation.

Senolytics refer to a class of small-molecule compounds that selectively induce apoptosis in senescent cells while sparing healthy, proliferating counterparts (Lagoumtzi and Chondrogianni, 2021). Key components of these survival pathways include anti-apoptotic members of the BCL-2 protein family and signaling regulators such as the p53/p21 axis, which together help maintain the viability of senescent cells by inhibiting programmed cell death (Rad and Grillari, 2024; Alum et al., 2025). By selectively disrupting critical nodes within these pathways, senolytic agents effectively dismantle the molecular support systems that sustain senescent cells, thereby reactivating intrinsic apoptotic mechanisms and promoting their clearance.

The concept of senolytic therapy was first proposed by Kirkland and colleagues, who identified the vulnerability senescent cell anti-apoptotic pathways as a therapeutic target. Their work demonstrates that the combination of Dasatinib (a tyrosine kinase inhibitor) and Quercetin (a natural flavonoid) could synergistically eliminate senescent cells without harming normal cells (Zhu et al., 2015). Since then, several other senolytics have been developed. Notably, Navitoclax (ABT-263), a BCL-2 family inhibitor originally designed as an anti-cancer drug, exhibits potent senolytic activity by specifically disrupting Bcl-2/Bcl-xL interactions with pro-death proteins, thereby neutralizing their anti-apoptotic function and triggering senescent cell death (Mylonas and Ferenbach, 2024). In senescent cells, FOXO4 exerts an anti-apoptotic effect by binding to and sequestering the nuclear protein p53, thereby preventing the initiation of apoptosis (Bourgeois and Madl, 2018). Disruption of this interaction has been shown to induce selective apoptosis of senescent cells. For instance, the synthetic peptide FOXO4-D-Retro-Inverso (FOXO4-DRI) competitively inhibits the FOXO4–p53 interaction, thereby reactivating p53-mediated apoptotic signaling and functioning as a senolytic agent (Baar et al., 2017). Additionally, Fisetin, a naturally occurring flavonoid, has also been reported to reduce senescent cell burden in multiple preclinical models (Syed et al., 2016; Zhang L., et al., 2023).

Senomorphics aim to modulate the secretion of the SASP in senescent cells by targeting key signaling pathways responsible for its induction. The goal is to convert senescent cells from a pro-inflammatory, tissue-damaging state into a more quiescent or functionally inert condition. This approach may offer a particularly favorable safety profile in non-regenerative tissues such as the lens epithelium, where cellular clearance could lead to loss of barrier function or impaired structural integrity due to the limited proliferative capacity of neighboring cells.

Rapamycin (also known as sirolimus) is a macrolide compound originally isolated from Streptomyces hygroscopicus (Vézina et al., 1975). It functions by inhibiting TORC1, thereby reducing the phosphorylation of its downstream effectors S6K and 4E-BP, which are critical for translational control of SASP components (Bjedov and Rallis, 2020; Choo et al., 2008). Numerous studies have demonstrated that Rapamycin can suppress both cellular senescence and the expression of SASP, thereby alleviating the chronic inflammatory burden associated with aging (Hoff et al., 2022; Wang et al., 2017). Additionally, Metformin has recently garnered attention for its broader pharmacological properties beyond glycemic control (Abou Zaki and El-Osta, 2024). Among these is its emerging role in ameliorating age-related functional decline. It has been shown to suppress the NF-κB signaling cascade by inhibiting the phosphorylation of IκB and its upstream kinases IKKα/β, thereby attenuating the production of pro-inflammatory SASP factors (Moiseeva et al., 2013). In addition, low-dose Metformin activates the Nrf2–GPx7 signaling axis by promoting Nrf2 nuclear accumulation and upregulating GPx7 expression to delay cellular senescence (Fang et al., 2018). NF-κB is both a central transcriptional regulator of SASP and a pivotal driver of the senescence program itself (Schlett et al., 2023). SR12343, for example, exerts its anti-inflammatory and anti-senescent effects by disrupting the interaction between IKKβ and NEMO, thereby blocking NF-κB activation induced by tumor necrosis factor-α (TNF-α) and lipopolysaccharide (LPS) stimulation (Zhao J. et al., 2018; Zhang et al., 2021). The mitogen-activated protein kinase (MAPK) signaling pathway is a classical and evolutionarily conserved cascade involved in transducing various extracellular stimuli into cellular responses. Upon activation, p38 MAPK translocates these stress signals to the nucleus, where it promotes cell cycle arrest and the synthesis of SASP factors (Odawara et al., 2024). Several p38 MAPK inhibitors, including SB203580, UR13756, and BIRB796, have been shown to reduce SASP secretion and mitigate its deleterious paracrine pro-senescent effects (Kuk et al., 2024; Alimbetov et al., 2016). Moreover, inhibition of MK2 kinase, a key downstream effector of p38 MAPK, has similarly been demonstrated to suppress SASP production (Alimbetov et al., 2016).