Rheumatoid Arthritis (RA) is a chronic autoimmune disease characterized by destructive and debilitating arthritis. Its pathogenesis is complex, involving both genetic and environmental factors that lead to dysregulated immune responses and cytokine-mediated inflammation (Alivernini et al., 2022). Despite substantial advances in understanding the pathogenesis of RA, current treatments are only temporarily effective in some patients, and refractoriness rates remain considerable (Buch et al., 2021). Consequently, research into the disease mechanisms remains essential for developing more effective therapies.

Patients with RA experience features of premature aging more markedly than the general population, primarily due to chronic inflammation, oxidative stress, and cellular senescence (Ao et al., 2025; Choubey and Panchanathan, 2016). This includes telomere shortening (Schmid et al., 2008), increased epigenetic aging (Horvath et al., 2017), premature aging of stem cells (Weyand and Goronzy, 2004), and an increased risk of age-related diseases, functional decline, and reduced life expectancy (Aviña-Zubieta et al., 2011). RA specifically leads to immunosenescence, characterized by decreased thymus function, delayed effector T cell differentiation, and heightened cytokine production, known as the senescence-associated secretory phenotype (SASP). These aspects contribute both to the disease's joint-specific issues (Bauer, 2020) and systemic conditions like osteoporosis, cardiovascular complications, and cognitive impairments.

In RA, senescence-associated T cells (SA-T) are characterized by defective T cell receptor-mediated proliferation and the secretion of abundant atypical proinflammatory cytokines reminiscent of SASP. These cells accumulate and cause persistent inflammation following various insults, including immune complex deposition, metabolic stress, vascular damage, and tumors (Gao et al., 2022). Similarly, age-associated B cells (ABCs) promote RA pathogenesis by affecting tumor necrosis factor-alpha (TNF-alpha)-mediated pathways, interacting with primary fibroblast-like synoviocytes (FLS), and increasing levels of IL-21, IFN-gamma, and IL-10 (Ruan et al., 2022). Although the senescent characteristics of T and B cells are well-described in RA, the molecular mechanisms linking senescence to the inflammatory process leading to joint destruction in inflammatory arthritis, including RA, remain poorly understood.

Rapamycin, also known as sirolimus, is a well-established inhibitor of the mechanistic target of the rapamycin (mTOR) pathway, which has gained prominence for its role in aging and several pathological conditions (Arriola Apelo and Lamming, 2016). In RA, aberrant mTOR activation contributes to synovial hyperplasia, chronic inflammation, and joint destruction. This pathway regulates key cellular functions, including FLS proliferation, apoptosis resistance, inflammatory cytokine production, and osteoclast differentiation, all of which drive cartilage degradation and bone erosion (Soltani et al., 2018; Niu et al., 2020; Cejka et al., 2010; Yin et al., 2015; Karonitsch et al., 2015a). The resulting imbalance fosters a hyperproliferative and pro-inflammatory synovial environment (Xu et al., 2022; Malemud, 2013). In addition, mTOR acts as a sensor of inflammatory cues and influences the activity of various immune and stromal cell types implicated in RA pathogenesis, including T cells, B cells, macrophages, and FLS (Zhang et al., 2023a; Karonitsch et al., 2015b).

Pharmacological inhibition of mTOR with rapamycin has been shown to suppress synovial proliferation, reduce inflammatory signaling, limit cartilage damage, and induce autoimmune tolerance, making it a promising therapeutic option for RA in both experimental and clinical settings (Niu et al., 2020; Zhang et al., 2023a; Laragione and Gulko, 2010; Tchetina et al., 2015; Foroncewicz et al., 2005; Siegmund et al., 2017). Its mechanism includes the downregulation of pro-inflammatory cytokines, such as IL-6, TNF, and IL-1β, thereby alleviating RA symptoms (Shao et al., 2017). However, the mechanism of action of rapamycin, which links it to senescence and inflammation in RA, is still incomplete.

Therefore, this study aimed to investigate the connection between cellular senescence and inflammation in rheumatoid arthritis by analyzing the effects of rapamycin treatment in a murine CIA model. This included comparative transcriptomic profiling of joint tissues, assessment of senescence markers such as β-galactosidase (BGAL), evaluation of NPY and its receptors, and in vitro validation of inflammatory and senescence-associated responses following Npy silencing in FLS.