Target Fibroblast-B cell crosstalk via MIF signaling drives pathogenic B cell differentiation and joint damage in...

B cells play a critical role in knee osteoarthritis (KOA), however, the heterogeneity, activation mechanisms, and their contribution to cartilage damage in KOA joints are still not fully understood.

We performed single-cell RNA sequencing (scRNA-seq) on joint tissues from 9 healthy controls and 21 KOA patients, integrating transcriptomic profiling, pseudotime trajectory analysis, and ligand-receptor interaction mapping. Key findings were validated using immunohistochemistry, Western blotting, in vitro co-culture systems, and a murine KOA model induced by anterior cruciate ligament transection and destabilization of the medial meniscus (ACLT + DMM).

scRNA-seq analysis identified 31 cell clusters, with B cells showing marked enrichment in subchondral bone and synovium of KOA joints, particularly in older and female patients. Re-clustering of B cells revealed eight distinct subgroups, including pathogenic DERL3⁺ and CD79B⁺B cell, which exhibited tissue-specific localization and stage-specific expansion during KOA progression. Pseudotime and regulon analyses highlighted JUN as a key transcription factor driving DERL3 ⁺ B cell differentiation. Fibroblasts emerged as critical regulators of B cell activation via MIF-(CD74 + CXCR4/CD44) signaling. Mechanistically, IL-1β-stimulated fibroblasts secreted MIF, inducing DERL3 expression in naïve B cells and may contribute to chondrocyte catabolic responses (increased MMP13, decreased COL2). Pharmacological inhibition of MIF reversed these effects in vitro and awas associated with reduced joint degeneration and improved gait and bone microarchitecture in KOA mice.

This study unveils a fibroblast-B cell crosstalk axis mediated by MIF signaling in KOA pathogenesis. Targeting MIF signaling may represent a promising therapeutic strategy to mitigate B cell-associated joint inflammation and structural alterations in KOA.