Iron overload reprogramming lipid metabolism through the IRP1–SCAP axis in fibroblast-like synoviocytes aggravates bone destruction in rheumatoid arthritis

Rheumatoid arthritis (RA) is a leading cause of disability globally. Although iron accumulation in arthritic lesions has been observed in patients with RA, its specific contribution to disability outcomes remains unclear. Here we demonstrate a comprehensive multiomics approach to elucidate the impact and underlying mechanisms of iron overload in RA. First, clinical radiology in an RA cohort reveals a positive correlation between elevated ferrous iron levels in synovial fluid and joint damage extent. Iron chelator DFO administration significantly alleviates bone destruction in the K/BxN serum-transfer induced arthritis mice model. In terms of cellular function, we identify the aggressive migration and invasion of fibroblast-like synoviocytes (FLSs) induced by excess iron utilizing a humanized synovitis model. Mechanistically, the multiomics integration of transcriptomics and metabolomics indicates the enriched lipid synthesis pathway in the FLS response to iron exposure. The lipid transcription factor SREBP1 is particularly highly expressed in RA-FLSs, and its genetic ablation or pharmacological inhibition markedly mitigates the pathogenic effects of iron overload both in vitro and in vivo. At the molecular level, iron regulatory protein IRP1 enhances the translation of SREBP1 adapter protein SCAP by disengaging from its mRNA 5' untranslated region upon iron stimulation. This process facilitates SREBP1 cleavage and activation, driving the upregulation of genes involved in fatty acid and cholesterol biosynthesis. Our findings elucidate the IRP1-SCAP axis as a critical modulator of lipid metabolic reprogramming in aggressive FLSs, underscoring its potential as a therapeutic target for RA by modulating the 'iron-lipid' crosstalk.