Macrophages‐derived small extracellular vesicles regulate chondrocyte proliferation and affect osteoarthritis progression via upregulating Osteopontin expression

Small extracellular vesicles (sEVs) are considered promising gene-delivery vehicles for the treatment of osteoarthritis (OA). This study aimed to explore the molecular mechanism by which M2 macrophage-derived sEVs (M2-sEVs) modulate chondrocyte proliferation and apoptosis, thereby affecting OA progression. M2 macrophages were successfully induced, and M2-sEVs were successfully isolated. The sEVs were small vesicles with diameters ranging from 50 to 150 nm. The exosomal markers, including CD9, CD63, and CD81, were highly expressed, whereas the negative marker calnexin was absent in M2-sEVs. M2-sEVs effectively alleviated OA tissue and chondrocyte damage in both in vivo and in vitro models, evidenced by reduced rat knee joint injury, increased chondrocyte viability, and decreased chondrocyte apoptosis and extracellular matrix (ECM) degradation. Furthermore, M2-sEVs decreased the levels of pro-inflammatory cytokines IL-6 and TNF-α. Osteopontin (OPN) was upregulated within rats with OA and IL-1β-induced chondrocytes. Silencing of OPN exacerbated IL-1β-induced chondrocyte damage and partially abrogated the therapeutic effects of M2-sEVs. Additionally, M2-sEVs enhanced OPN expression and activated CD44 and the PI3K/AKT signaling pathway. In conclusion, M2-sEVs promoted OPN expression to improve knee joint tissue damage in rats with OA and chondrocyte damage. This protective effect of M2-sEVs might be associated with the activation of CD44 and the PI3K/AKT signaling.