Myeloid differentiation protein 2 (MD2), a co-receptor of toll-like receptor 4 (TLR4) in the innate immune system, has emerged as a promising target for anti-inflammatory therapies. Rheumatoid arthritis (RA), a chronic autoimmune disorder characterized by persistent synovial inflammation and progressive joint destruction, remains a therapeutic challenge due to the lack of effective treatment options. In this study, we investigated the role of MD2 in the pathogenesis and progression of RA. Our findings show that MD2 is overexpressed in both the whole blood and synovial tissues of RA patients. Furthermore, MD2 expression was upregulated in collagen-induced RA mouse models. MD2 knockout significantly alleviated key symptoms of RA, including improved body weight, reduced paw swelling, and decreased bone destruction and cartilage erosion. Additionally, MD2 deficiency led to a significant reduction in serum levels of inflammatory cytokines and a decrease in the expression of inflammatory protein within synovial tissue. Notably, animal models revealed that genetic ablation of MD2 exerts potent anti-ferroptosis effects in arthritic pathophysiology. This protective effect was recapitulated at the cellular level through pharmacological interventions, where MD2-targeting inhibitors effectively attenuated lipopolysaccharide-induced ferroptotic cell death in murine macrophages, as evidenced by characteristic biomarkers including glutathione depletion and lipid peroxidation. Mechanistically, the reduction in ferroptosis and inflammation following MD2 knockout was associated with the inhibition of mitogen-activated protein kinase (MAPK) and nuclear factor kappa-B (NF-κB) signaling pathways in the synovial tissue. These results suggest that MD2 plays a critical role in both the inflammatory response and ferroptosis, in the context of RA. Consequently, MD2 represents a key mediator of RA pathogenesis and an innovative therapeutic target for the treatment of this debilitating disease. KEY MESSAGES: MD2 expression is upregulated in synovial tissue following the onset of rheumatoid arthritis. MD2 knockout alleviates bone destruction, cartilage erosion, and inflammation in rheumatoid arthritis mice. MD2 deficiency mitigates rheumatoid arthritis in mice by inhibiting ferroptosis induced by the MAPK and NF-κB signaling pathways. MD2 may serve as a potential therapeutic target for rheumatoid arthritis.
