Extracellular vesicles from cartilage progenitors stimulate type II collagen expression and wound healing in meniscal cells.

Knee meniscus tearing is a common orthopaedic injury that can heal poorly if left untreated, increasing the risk of post-traumatic Osteoarthritis. Intraarticular injection of human cartilage-derived progenitor cells (CPCs) has been shown to promote meniscus healing after injury. However, the mechanism by which CPCs stimulated this effect was unclear. The purpose of this study was to determine the paracrine effects that CPC-derived extracellular vesicles (EVs) have on native meniscal cells during healing. EVs from human CPCs and marrow-derived stromal cells were isolated via ultracentrifugation. EVs produced by each cell type were quantified, and their sizes were determined via NanoSight. EV protein expression was characterized via western blot. Meniscal fibrochondrocyte cellular metabolic activity (as an indicator of cell viability and proliferation) following treatment with EVs, was quantified using MTT and ATP assays. A 2D wound healing assay was used to determine the effects of treating inner meniscal fibrochondrocytes with EVs in a dose-dependent manner. Gene expression analysis for chondrogenesis genes was performed via RT-qPCR on inner meniscal fibrochondrocytes following treatment with EVs. Our results showed that CPCs produced a wide size range of EVs expressing CD9, CD81, and HSP70. Treatment of inner meniscal fibrochondrocytes with CPC-EVs improved 2D wound healing, in comparison to EVs isolated from marrow-derived stromal cell controls. CPC-EV treatment increased Type II Collagen mRNA expression in inner meniscal fibrochondrocytes. These findings demonstrate that CPC-EVs stimulate chondrogenic matrix production and wound healing in meniscal cells at the optimal dose of 1.0 × 10⁷ particles/mL, significantly outperforming the effects of marrow stromal cell-derived EVs.