Icariin Protects Against Mitochondrial Damage and Ferroptosis-Related Injury in Synovial Fibroblast-Like Synoviocytes Through SUMO1-Dependent Regulation of SIRT1.

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by persistent synovial inflammation and progressive joint destruction, in which fibroblast-like synoviocytes (FLSs) play a central pathogenic role. Ferroptosis and oxidative stress-driven mitochondrial dysfunction have recently been implicated in synovial cell injury during RA progression. Sirtuin 1 (SIRT1), a nicotinamide adenine dinucleotide-dependent deacetylase, is known to regulate inflammation, redox homeostasis, and cell survival; however, the upstream regulatory mechanisms controlling SIRT1 function and their relevance to ferroptosis in RA remain poorly defined. Primary rat FLSs and a complete Freund's adjuvant (CFA)-induced adjuvant arthritis (AA) rat model were used. SIRT1 transcription, protein expression, subcellular localization, and enzymatic activity were assessed using quantitative real-time PCR, Western blotting, immunofluorescence, and enzymatic assays. Oxidative stress, mitochondrial dysfunction, lipid peroxidation, and ferroptosis-related parameters were evaluated using biochemical assays and fluorescence-based probes. SUMO1 expression was manipulated by knockdown and overexpression approaches, and the interaction between SUMO1 and SIRT1 was examined by co-IP.Inflammatory stimulation with IL-1β impaired SIRT1 transcriptional expression, reduced its nuclear localization, and suppressed its enzymatic activity in FLSs, accompanied by enhanced reactive oxygen species accumulation, mitochondrial dysfunction, lipid peroxidation, and ferroptosis-related changes. ICA treatment restored SIRT1 expression and activity while alleviating oxidative stress and ferroptotic injury. ICA upregulated SUMO1 expression, while Co-IP analysis demonstrated an association between SUMO1 and SIRT1. SUMO1-dependent regulation was associated with increased SIRT1 nuclear localization and enzymatic activity. Disruption of SUMO1 expression or pharmacological inhibition of SIRT1 suppressed the protective effects of ICA in FLSs. Consistent regulatory effects were observed in arthritic rats following ICA administration. These findings support the involvement of SUMO1/SIRT1 regulation in ferroptosis-related injury and mitochondrial dysfunction in RA-associated synovial cells. ICA exerts protective effects by restoring coordinated SIRT1 regulation at multiple functional levels, highlighting SIRT1-centered pathways as potential therapeutic targets for RA.