SMSC-EVs restore chondrocyte function through S1PR1-mTORC2-mediated mitochondrial fusion and GPS2-HDAC1-driven epigenetic regulation

In osteoarthritis (OA) treatment, synovial mesenchymal stem cell-derived extracellular vesicles (SMSC-EVs) hold therapeutic potential; however, the mechanisms coordinating mitochondrial and epigenetic repair remain unclear. Chondrocyte proliferation, apoptosis and migration were assessed in vitro. Mitochondrial function was evaluated via membrane potential, oxygen consumption, ATP and reactive oxygen species (ROS) levels and network morphology. RNA sequencing and proteomics identified altered pathways. Key molecules (MFN2, S1PR1, GPS2, mTOR components) were investigated using siRNA knockdown. Protein localisation and interactions were examined by immunofluorescence, co-immunoprecipitation and in silico modelling. Efficacy was validated in a monosodium iodoacetate-induced rat OA model. SMSC-EVs enhanced chondrocyte proliferation, reduced apoptosis and restored mitochondrial fusion and bioenergetics through activation of the S1P-S1PR1-mTORC2 axis, leading to MFN2 upregulation (mean difference: 0.676 [95% CI: 0.572-0.778]). EV treatment also induced GPS2 nuclear translocation (mean difference: 0.403 for GPS2/lamin B [0.318-0.489]), facilitating interaction with HDAC1 and increased HDAC1 expression (mean difference: 0.474 [0.398-0.552]). In vivo, SMSC-EVs mitigated cartilage degradation and improved functional outcomes, reflected by decreased OARSI scores (mean difference: -9.000 [-10.518 to -7.482]). SMSC-EVs ameliorate OA through coordinated mitochondrial and epigenetic mechanisms, restoring mitochondrial integrity via the S1P-S1PR1-mTORC2-MFN2 pathway and promoting proliferation through GPS2-HDAC1-mediated epigenetic regulation. These findings highlight a synergistic therapeutic strategy targeting mitochondrial-epigenetic dysfunction in OA.