Metformin-pretreated synovial mesenchymal stem cell-derived exosomes alleviate osteoarthritis via the miR-1208/METTL3/NLRP3 axis

Osteoarthritis (OA) is a common degenerative joint disease that lacks effective reparative treatment methods. Exosomes derived from synovial mesenchymal stem cells (SMSC) have emerged as a promising acellular therapeutic approach due to their roles in immune modulation and tissue regeneration. Metformin, a commonly used anti-diabetic drug, has been shown to possess anti-inflammatory properties and enhance stem cell functionality. This study aims to explore the therapeutic potential and underlying mechanisms of metformin-pretreated SMSC-derived exosomes (M-EVs) in OA treatment. This study first conducted a retrospective analysis of clinical data from OA patients to evaluate the impact of metformin on joint damage. Subsequently, in vitro experiments were performed to investigate the effects of M-EVs on chondrocyte proliferation, apoptosis, migration, and extracellular matrix (ECM) metabolism. In addition, the in vivo efficacy of M-EVs was assessed in a DMM mouse model. Differentially expressed miRNAs were identified using miRNA arrays, and the role of the miR-1208/METTL3/NLRP3 signaling pathway in the therapeutic effects of M-EVs was further elucidated using luciferase reporter assays, m⁶A measurements, and Western blot analyses. Clinical data indicated that OA patients who had been on long-term metformin therapy exhibited less severe joint structural damage. In vitro experiments demonstrated that M-EVs, enriched in miR-1208, inhibited METTL3 expression and reduced m⁶A modification levels of NLRP3, thereby suppressing NLRP3 inflammasome activation and the release of pro-inflammatory factors. M-EVs significantly promoted chondrocyte proliferation and migration, reduced apoptosis, and improved ECM metabolism. Further animal studies confirmed that M-EVs effectively slowed OA progression, improved cartilage structure, and modulated the inflammatory microenvironment, with the therapeutic effect being dependent on the NLRP3 pathway. Metformin-pretreated SMSCs enhance the anti-inflammatory and chondroprotective properties of their secreted exosomes, primarily through the miR-1208-mediated METTL3/NLRP3 signaling pathway. M-EVs offer an innovative, safe, and potentially translatable acellular therapeutic strategy for OA treatment.