Synovial osteoclastogenesis mediated by chondrocyte‐secreted TNFα promotes TMJ condylar resorption

Abstract Background Insufficient occlusal support (IOS) frequently causes subchondral bone absorption in temporomandibular joint osteoarthritis, and the underlying mechanism requires further investigation. Methods An IOS model was established by abrading rat molars. Micro‐computed tomography was used to evaluate subchondral bone changes. Osteoclastogenesis of synovium‐derived macrophages (SDMs) was confirmed by TRAP staining. Cartilage‐specific TNFα depletion was achieved by intra‐articular injection of adeno‐associated virus carrying shRNA against murine TNFα under control of collagen type II. In vitro, chondrocytes were mechanically compressed and conditioned medium (CM) was collected to detect its ability to induce osteoclastogenesis of SDMs. Results Synovial osteoclastogenesis and condyle resorption were observed following IOS. TNFα level was elevated in hypertrophic chondrocytes after IOS. Synovial Wnt5a level increased, but Wnt3a level decreased after IOS. Depletion of TNFα in chondrocytes alleviated the synovial osteoclastogenesis and condyle bone resorption. In vitro compression of chondrocytes potentiated TNFα expression and secretion. The CM promoted osteoclastogenesis of SDMs, which were partially prohibited by TNFα neutralizing antibody. Furthermore, inhibition of Wnt3a facilitated osteoclastogenesis, whereas inhibition of Wnt5a partially suppressed osteoclastogenesis, of SDMs cultured in CM. Conclusion Chondrocyte‐secreted TNFα induced by IOS is a critical regulator of synovial osteoclastogenesis and subsequent condylar resorption, partially through non‐canonical Wnt5a pathway.