Exosomes secreted by ADMSCs preserve cartilage integrity in knee osteoarthritis via AMPK-mediated mitochondrial dynamics and apoptosis

Adipose-derived mesenchymal stem cell (ADMSC) exosomes have emerged as promising therapeutic agents for degenerative joint diseases, yet their molecular actions in knee osteoarthritis (KOA) remain inadequately defined. In this study, exosomes were isolated from ADMSCs under both physiological and IL-1β-induced inflammatory conditions and comprehensively characterized by NTA, TEM, and exosome marker expression. Both types of exosomes were efficiently internalized by chondrocytes, with uptake reaching saturation after 12 hours regardless of inflammatory status. Functional assays revealed that while exosomes from healthy ADMSCs (EXOs) significantly enhanced levels of mitochondrial fusion proteins and decreased fission marker in IL-1β-induced chondrocytes after 24 hours, these beneficial effects were absent in exosomes derived from inflamed ADMSCs (IL-1β EXOs). Notably, EXO treatment reduced intracellular ROS accumulation, boosted SOD2 levels, and diminished apoptotic cell rates in chondrocytes. In vivo, administration of EXOs to rats with ACLT-induced KOA markedly alleviated cartilage degeneration, restoration of mitochondrial dynamics, and suppression of inflammatory and matrix-degrading mediators. Transcriptomic analysis showed that EXOs activated gene expression programs related to fatty acid metabolism, oxidative phosphorylation, and AMPK signaling, while IL-1β EXOs enriched inflammatory and apoptotic pathways. Importantly, both genetic knockdown and pharmacological inhibition of AMPK abolished the restorative effects of EXOs on mitochondrial dynamics and on the reduction of apoptotic markers both ex vivo and in vivo. These findings demonstrate that exosomes secreted by ADMSCs preserve cartilage integrity in KOA via AMPK-mediated mitochondrial dynamics. This work supports AMPK-targeted modulation of mitochondrial dynamics by stem cell exosomes as a promising disease-modifying strategy for KOA.