IRE1/p‑JNK/NRF2 axis-mediated GPX4 upregulation underlies ferroptosis resistance in rheumatoid arthritis fibroblast-like synoviocytes

BACKGROUND: Rheumatoid arthritis fibroblast‑like synoviocytes (RA‑FLS) exhibit chronic endoplasmic reticulum stress with activation of the IRE1/phospho‑JNK arm of the unfolded protein response; yet, they remain resistant to apoptosis. Although ferroptosis has been implicated in the pathogenesis of rheumatoid arthritis, the mechanisms underlying ferroptosis resistance in RA‑FLS remain poorly understood. METHODS: A total of 17 patients who underwent joint replacement were included (RA n = 9; OA n = 8). Primary fibroblast-like synoviocytes (FLS; ≥3 donors per assay) were analyzed by RT-qPCR and western blotting for IRE1, p-JNK, NRF2 and GPX4. Signaling was modulated with siRNA or inhibitors against ERN1 or NRF2. Ferroptosis was assessed by transmission electron microscopy, lipid peroxidation, Fe²⁺ and glutathione depletion; cell phenotypes were evaluated by invasion, wound-healing and CCK-8 assays. In vivo (≥ 4 per group), a collagen-induced arthritis (CIA) rat model received the IRE1 inhibitor 4µ8c; micro-CT, joint pathology and biochemical markers were evaluated. RESULTS: RA-FLS showed elevated IRE1/p-JNK, increased total and nuclear NRF2, and higher GPX4 versus OA-FLS, and were more resistant to ferroptosis. ERN1 knockdown reduced p-JNK, NRF2 and GPX4 and increased lipid peroxidation, iron accumulation, glutathione loss and ferroptosis. NRF2 inhibition also sensitized RA-FLS to ferroptosis and attenuated aggressive phenotypes. In CIA rats, IRE1 inhibition partially attenuated bone destruction, lowered serum IL-1β/MMP9, and reduced synovial GPX4. CONCLUSION: Sustained IRE1/p-JNK/NRF2 signaling upregulates GPX4, linking ER stress to ferroptosis resistance in RA-FLS. Targeting IRE1 lowers GPX4 and restores ferroptotic sensitivity, suggesting a potential therapeutic strategy for RA.