Integrated Single‐Cell and Spatial Transcriptomics Reveal Convergence on a Senescence‐Associated B Cell–MIF Signaling Axis in Joint Aging and Osteoarthritis Progression

Osteoarthritis (OA) involves age-associated structural and immune changes, yet whether senescence-associated B-cell states contribute to cartilage degeneration remains unclear. Integrated single-cell RNA sequencing and spatial transcriptomics of healthy, aged, and OA mouse joints identify reduced B-cell abundance but enrichment of a low-proliferative, inflammatory state with heightened macrophage migration inhibitory factor (MIF) signaling. Cell-cell communication and spatial ligand-receptor analyses identify enhanced predicted MIF-CD74/CD44 interactions in B-cell-associated regions adjacent to cartilage. Constitutive MIF deficiency attenuates senescence-associated B-cell changes, MMP13 induction, and cartilage damage in vivo. Joint-derived B cells from aged and OA mice induce chondrocyte senescence, reduce COL2A1 and HMGB1, and increase FN1 and MMP13 through MIF-dependent paracrine signaling. These effects are suppressed by MIF neutralization and restored by recombinant MIF in MIF-deficient co-cultures. A composite hydrogel carrying quercetin and MIF-siRNA-loaded PLGA microspheres for local co-delivery. The microspheres show gradual siRNA release over 96 h in vitro. In DMM-induced OA, the formulation reduces MIF, P16, and MMP13 signals, restores HMGB1, and preserves cartilage. These findings support a senescence-associated B cell-MIF signaling axis associated with joint aging and chondrocyte dysfunction and provide proof of concept for a local biomaterial-based strategy that attenuates OA-associated changes.