Immune cell-derived cytokines synergistically interact to drive synovial fibroblast invasive function and metabolic capacity

Rheumatoid Arthritis (RA) is a chronic autoimmune disease, defined by synovial inflammation and joint destruction. A significant proportion of patients still have sub-optimal/no response to current treatments, with recent synovial scRNA-seq studies highlighting the complexity of the inflamed joint. This study investigates synovial-scRNA-seq predicted IL-1β/TGF-β synergistic regulation of RA synovial-fibroblast (FLS) pathogenic function. Synovial bulk RNA-seq analysis demonstrated increased expression of IL-1β and TGF-β signalling components in healthy controls (HC) versus early RA versus established RA, with synovial scRNA-seq demonstrating enrichment in specific RA-FLS clusters. In RA-FLS, IL-1β/TGF-β synergistically increased baseline glycolysis, ECAR:OCR ratio, proton-efflux rate, %PER glycolysis, compensatory glycolysis, and glycolytic genes (GLUT-1, PKM2, PFKFB3). Synergistic dysregulation of mitochondrial function (biogenesis and DRP1 fission protein) and endoplasmic reticulum (ER) stress responses (ER size, stress genes, chaperone protein (PDI)) were also demonstrated. The altered metabolic profile was paralleled by synergistic induction of pro-inflammatory mediators/chemokines including IL-8, MCP-1, MMP-3, and CXCL5 in RA-FLS. IL-1β and non-canonical TGF-β signalling converge on TAK1 activation. Takinib (TAK1-inhibitor) significantly reduced glycolytic and pro-inflammatory responses of RA-FLS. Importantly, in RA ex vivo synovial explants (reflecting the inflamed joint), Takinib reduced spontaneous release of pro-inflammatory mediators and the process of synovial growth. In conclusion, IL-1β/TGF-β synergistically drive a pathogenic RA-FLS phenotype in RA, blockade of which reduces inflammatory and invasive mechanisms.