DPSCs modulate synovial macrophage polarization and efferocytosis via PINK1/Parkin-dependent mitophagy.

backgroundSynovitis is a key factor in temporomandibular joint osteoarthritis (TMJOA) and could be an early sign of the disease. Notably, synovitis and its macrophage component represent a target of interest for developing treatments. Dental pulp stem cells (DPSCs) are derived from the neural crest, coincidentally with maxillofacial tissues, thus attracting significant interest in situ maxillofacial regenerative medicine. However, there is a relative scarcity of studies investigating the role of DPSCs in the temporomandibular joint (TMJ) synovial macrophage.

objectiveThis study aimed to evaluate the regulatory and reparative capabilities of DPSCs on synovitis in TMJOA rat models and to elucidate their specific mechanisms of action on synovial macrophages.

methodIn vivo, three groups were established: the control group, which had neither induction nor treatment; the OA group, consisting of rats with OA but without any treatment; and the DPSCs treatment group, where rats with OA received DPSCs therapy. Progressive TMJOA was induced in rats via intra-articular injection of complete Freund’s adjuvant and sodium iodoacetate. After 2 weeks, DPSCs were injected into the joint cavity as a therapeutic intervention. Meanwhile, normal saline was injected into the joints of rats in both the control and OA groups. Four weeks after treatment, histological analysis was performed to evaluate the repair of synovitis. In addition, an in vitro co-culture system, consisting of macrophages and DPSCs. Each group was assessed using techniques, including mRFP-GFP-LC3 lentivirus transfection, Mito-Tracker Red and Lyso-Tracker Green staining, transmission electron microscopy, and Western blot analysis. Furthermore, apoptotic primary neutrophils were co-cultured with polarized macrophages to observe the phagocytic ability of macrophages towards apoptotic primary neutrophils under different treatments in vitro.

resultsIn the rat model, compared with the OA group, the DPSCs group exhibited reduced cell infiltration and collagen deposition, along with elevated levels of anti-inflammatory CD206 and decreased levels of inflammatory CD86, and enhanced the ability of macrophages to phagocytize apoptotic cells in vivo and in vitro. Notably, DPSCs exhibited enhanced efficacy in upregulating autophagosome expression, promoting co-localization with mitochondria and lysosomes, and modulating the expression of mitochondrial mitophagy proteins. Furthermore, inhibition of mitophagy in M1 macrophages partially attenuated the M2 polarization effect and phagocytosis induced by DPSCs.

conclusionDPSCs significantly mitigate synovitis in TMJOA rats by enhancing M2 polarization and efferocytic functions of macrophages. This study underscores the potential of DPSCs as a therapeutic strategy for TMJOA by modulating synovial macrophage functions through the regulation of mitophagy.