Spatial multi‑omics identifies an SPP1+ macrophage‑driven anti‑apoptotic niche in osteoarthritis synovium via the SPP1‑CD44 axis

Osteoarthritis (OA) progression is driven by chronic synovitis. However, the spatially organized macrophage subsets that sustain unresolved inflammation through evasion of apoptosis remain poorly characterized. The present study investigated the functional subsets and spatial niches of synovial macrophages that regulate apoptotic pathways in OA pathogenesis. Spatial transcriptomics, single‑cell RNA sequencing and in vitro apoptotic models were integrated to characterize macrophage interactions in the OA synovium. The anti‑apoptotic role of SPP1⁺ macrophages was evaluated using adeno‑associated virus‑mediated macrophage‑targeted SPP1 knockdown and CCL3 neutralization in a mouse OA model. In addition, an in silico virtual knockout model was employed to delineate SPP1‑mediated apoptotic regulatory networks and prioritize candidate compounds for future validation. Spatial multi‑omics revealed a TGF‑β‑enriched niche in which SPP1+ macrophages expand adjacent to senescent synovial fibroblasts. Distinct from their reported pro‑fibrotic roles, SPP1⁺ macrophages directly suppressed apoptosis of inflammatory macrophages via the SPP1‑CD44 signaling axis, while recruiting additional myeloid cells through CCL3 secretion. In vivo, targeting SPP1 or neutralizing CCL3 effectively restored macrophage apoptosis, attenuated synovitis and cartilage degeneration. In silico myeloid specific SPP1 knockout delineated apoptotic pathway perturbations. In conclusion, TGF‑β‑induced SPP1⁺ macrophages establish an anti‑apoptotic inflammatory niche in OA synovium by directly inhibiting the apoptosis of inflammatory macrophages via SPP1 signaling and promoting myeloid recruitment. This spatially defined anti‑apoptotic circuit provides critical insight into persistent synovitis.