Adipose-derived stem cell-derived extracellular vesicles promote critical-sized bone defect repair by enhancing the homing of bone marrow mesenchymal stem cells

The repair of critical-sized bone defects remains a significant clinical challenge. As a cell-free alternative, extracellular vesicles (EVs) derived from adipose-derived stem cells (ADSCs-EVs) hold promise, yet their precise mechanism in promoting bone repair is remain to be fully elucidated. This study investigated whether ADSCs-EVs enhance bone repair by promoting the homing and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). ADSCs-EVs were isolated and co-cultured with BMSCs to assess proliferation, migration, and osteogenic differentiation in vitro. Key gene expression (e.g., Cxcr4, Runx2) was analyzed. A highly elastic hydrogel was used for sustained EVs delivery in a rat calvarial defect model. mouse bone marrow-derived mesenchymal stem cells (mBMSCs) homing was monitored via live imaging, and bone regeneration was evaluated by micro-CT and histology. Results showed that ADSCs-EVs promoted BMSCs migration and osteogenesis, rapidly upregulating homing-related genes (Ccr7, Cxcr4) and subsequently activating osteogenic genes (Runx2, OPN). In vivo, the ADSCs-EVs/hydrogel complex enhanced the recruitment of BMSCs to the defect site compared with the control group, which was associated with improved new bone formation. This study demonstrates that ADSCs-EVs enhance BMSCs migration and osteogenic differentiation in vitro. Mechanistically, ADSCs-EVs rapidly upregulated homing-related genes (Ccr7, Cxcr4, MMP9) in BMSCs at 12 h, followed by activation of osteogenic genes (Runx2, OPN, OCN) at later time points, revealing a two-stage ‘recruit-and-activate’ mechanism. When delivered via a highly elastic hydrogel, ADSCs-EVs promoted the recruitment of intravenously administered BMSCs to a critical-sized bone defect in vivo, as visualized by bioluminescence imaging. These findings support a strategy that combines EVs-mediated homing enhancement with cell transplantation, while also suggesting potential implications for endogenous cell recruitment.