Promotion of osteochondral repair through immune microenvironment regulation and activation of endogenous chondrogenesis via the release of apoptotic vesicles from donor MSCs

Utilizing transplanted human umbilical cord mesenchymal stem cells (HUMSCs) for cartilage defects yielded advanced tissue regeneration, but the underlying mechanism remain elucidated. Early after HUMSCs delivery to the defects, we observed substantial apoptosis. The released apoptotic vesicles (apoVs) of HUMSCs promoted cartilage regeneration by alleviating the chondro-immune microenvironment. ApoVs triggered M2 polarization in macrophages while simultaneously facilitating the chondrogenic differentiation of endogenous MSCs. Mechanistically, in macrophages, miR-100-5p delivered by apoVs activated the MAPK/ERK signaling pathway to promote M2 polarization. In MSCs, let-7i-5p delivered by apoVs promoted chondrogenic differentiation by targeting the eEF2K/p38 MAPK axis. Consequently, a cell-free cartilage regeneration strategy using apoVs combined with a decellularized cartilage extracellular matrix (DCM) scaffold effectively promoted the regeneration of osteochondral defects. Overall, new mechanisms of cartilage regeneration by transplanted MSCs were unconcealed in this study. Moreover, we provided a novel experimental basis for cell-free tissue engineering-based cartilage regeneration utilizing apoVs. Schematic summary of our main findings. Intraarticular injection of HUMSCs derived apoEVs delivers the miR-100-5p into macrophages and promotes M2 macrophage polarization by activating MAPK/ERK1/2 and delivers the let-7i-5p into MSCs and promotes chondrogenesis. The apoEVs combined with DCM scaffold facilitating cartilage defect repair. HUMSCs: human umbilical cord-derived mesenchymal stem cells, DCM: decellularized cartilage matrix. • This study provides the first evidence of short-term apoptosis of MSCs after implantion in cartilage defect. • HUMSC-apoVs induce macrophage immunomodulation, promoting MSC chondrogenic differentiation. • TmiR-100-5p in apoVs activated the MAPK/ERK pathway to induce macrophage M2 polarization. • Let-7i-5p in apoVs promoted chondrogenic differentiation by targeting the eEF2K/p38 MAPK axis. • A cell-free strategy of apoVs combined with DCM scaffold promoted cartilage regeneration.