Rapamycin suppresses rheumatoid arthritis fibroblast synovial cell proliferation and induces apoptosis via the AKT/mTORC1 pathway

Abstract Background Rheumatoid arthritis (RA) is an autoimmune disease characterized by the overproliferation of synovial fibroblast‐like synoviocytes (FLSs) in the lining, leading to chronic inflammation and progressive joint damage. RA pathogenesis involves lymphocyte infiltration, increased synovial cell proliferation, and impaired cell death. This study investigated the effects of rapamycin on RA‐FLSs and explored the underlying molecular mechanisms. Methods The optimal drug concentration and time for rapamycin administration were determined using a cell counting kit‐8 assay. The concentration of rapamycin varied from 1 to 25 nmol/L. The mRNA expression levels of protein kinase B ( AKT ), mammalian target of rapamycin ( mTOR ), B cell lymphoma 2 ( Bcl‐2 ), and Bcl‐2‐associated X protein ( Bax ) were quantified by real‐time polymerase chain reaction. Protein expression (p‐AKT, AKT, p‐mTOR, mTOR, pS6 kinase [S6K], S6K, p‐4E‐binding protein 1 [4EBP1], 4EBP1, Bcl‐2, Bax, caspase 3, caspase 9, cyclin‐dependent kinase 2 [CDK2], and CD1) were detected by Western blotting analysis. Results Rapamycin suppresses RA‐FLS proliferation and induces apoptosis in a dose‐dependent manner. Rapamycin significantly elevated the protein expression of Bax ( p < 0.01), caspase 3 ( p < 0.05), and caspase 9 ( p < 0.001), and downregulated Bcl‐2 expression ( p < 0.01). Rapamycin increased Bax mRNA expression ( p < 0.01) and decreased Bcl‐2 ( p < 0.05), AKT ( p < 0.05), and mTOR ( p < 0.05) expression. Additionally, there was a marked reduction in the expression levels of p‐AKT(Ser473) ( p < 0.01), p‐mTOR (Ser2448) ( p < 0.01), p‐S6K1 ( p < 0.01), and p‐4EBP1, CDK2, and CD1 ( p < 0.01). Conclusions Rapamycin effectively inhibited proliferation and induced apoptosis of RA‐FLSs by targeting the AKT/mTORC1 pathway. These findings underscore the potential of rapamycin as a therapeutic candidate for addressing the dysregulated proliferation and inflammatory characteristics of RA. Further clinical investigations are required to validate its application in the management of RA.