Melatonin Exerts Chondroprotective Effects Against Osteoarthritis by Promoting PI3K/AKT/FoxO3-Mediated Mitophagy

Osteoarthritis (OA) is a prevalent degenerative joint disease. This study combines bioinformatics analysis with in vivo and in vitro experiments to elucidate the molecular mechanisms through which melatonin (MT) regulates mitophagy to alleviate OA. Rat and chondrocyte OA models were established via anterior cruciate ligament transection or interleukin (IL)-1β induction, followed by treatment with MT, Cyclosporine A (a mitophagy inhibitor), and 740Y-P (a phosphatidylinositol-3 kinase [PI3K] activator). Pathological changes in cartilage, histological scores, and cell apoptosis were evaluated alongside chondrocyte viability, apoptosis, mitochondrial morphology, mitochondrial membrane potential, and mitophagy using H&E and Safranin O-fast green staining, Osteoarthritis Research Society International scoring (OARSI), TUNEL staining, CCK-8, flow cytometry, transmission electron microscopy, JC-1 staining, and immunofluorescence. Levels of inflammatory factors and mitophagy-related protein levels were determined by ELISA and western blot. Bioinformatics analysis was applied to investigate the regulatory mechanisms of MT on mitophagy in OA. In vivo, MT mitigated OA by enhancing mitophagy and reducing apoptosis of cartilage cells. In vitro, MT attenuated IL-1β-induced chondrocyte apoptosis through mitophagy activation, and this effect was partially reversed by mitophagy inhibition. Mechanistically, the PI3K/protein kinase B (AKT)/forkhead box O3 (FoxO3) axis appeared to play a central role. MT suppressed PI3K/AKT signaling, thereby upregulating FoxO3 expression and promoting mitophagy, ultimately reducing chondrocyte apoptosis. Collectively, these findings suggest that MT enhances mitophagy via inhibition of the PI3K/AKT pathway, and subsequent upregulation of FoxO3, leading to reduced apoptosis of cartilage cells and attenuation of OA progression in rats.