Stem cell-derived small extracellular vesicles containing miR-27b-3p attenuated osteoarthritis through inhibition of leukaemia inhibitory factor.

Mesenchymal stem cell (MSC)-derived small extracellular vesicles (sEVs) have been demonstrated to be an effective Cell-Free Therapy in the treatment of OA, but the precise target cells and response mechanisms are not well characterised. In this study, first, we found that intra-articular injection of human umbilical cord MSC (UCMSC)-derived sEVs (U-sEVs) significantly alleviated mouse OA. Then, U-sEVs were taken up rapidly and preferentially by fibroblast-like synoviocytes (FLSs) as well as cartilage superficial layer cells (SFCs) in a mouse model. Furthermore, significant increase in miR-27b-3p in those two cell types after U-sEV treatment was found by miRNA sequencing, identifying miR-27b-3p as a key cargo of U-sEVs. Bioinformatics and luciferase reporter found that leukaemia inhibitory factor (LIF) is the target gene of miR-27b-3p. Later, single-cell RNA-sequencing (scRNA-seq) and RNA-sequencing revealed that LIF could directly induce synovitis and cartilage erosion, possibly by promoting proinflammatory cytokine and MMPs expression. Based on this, miR-27b-3p-overexpressing U-sEVs inhibit the expression of LIF in both FLSs and SFCs, and accordingly exhibited stronger effects in mitigating synovitis, cartilage degeneration and OA progression compared to control U-sEVs. In conclusion, our results revealed that U-sEVs containing miR-27b-3p play a dominant role in relieving OA, largely by targeting LIF expression in FLSs and SFCs.