Stigmasterol mitigates rheumatoid arthritis progression by decreasing Nrf2/NLRP3-mediated pyroptosis in chondrocyte

Abstract Background Rheumatoid arthritis (RA) is a long-lasting inflammatory joint disorder characterized by joint swelling, stiffness, pain, and loss of function in joints. Chondrocyte inflammation and apoptosis are closely associated with cartilage destruction. Stigmasterol (Stig) is a phytosterol with anti-inflammatory and anti-oxidant effects. In the study, we aimed to investigate whether Stig mitigates RA progression by decreasing chondrocyte injury. Methods and Results A mouse RA model was established by injecting intradermally type Ⅱ collagen into the tail roots of mice. Arthritic score and spleen index were measured in RA mice to assess the effects of Stig on RA progression. Lipopolysaccharide (Lps)-treated chondrocytes were applied as the cell model of RA. The roles of Stig in chondrocyte viability, proliferation, migration, inflammation, and injury were tested using cell counting kit-8 (CCK-8), EdU, transwell, quantitative real-time PCR (qRT-PCR), and western blot assays, respectively. Our results demonstrated that Stig exhibited no significant cytotoxicity against CHON-001 chondrocytes, but Stig effectively inhibited Lps-induced decreases in cell viability, proliferation, and migration. Stig also alleviated Lps-evoked pro-inflammatory responses and CHON-001 cell injury. Mechanistically, Stig inhibited Lps-induced nuclear factor erythroid 2-related factor 2 (Nrf2) activation and subsequent NOD-like receptor protein 3 (NLRP3) inflammasome activation, resulting in CHON-001 pyroptosis. Nigericin, a NLRP3 activator, reversed the effects of Stig on mitigating CHON-001 cell injury. Furthermore, the clinical severity in RA mice was improved after Stig treatment. Conclusions In summary, Stig decreases Lps-induced chondrocyte injury and mitigates RA progression by inhibiting Nrf2/NLRP3-mediated pyroptosis, thereby providing the opportunity to treat RA.