Exosomes derived from endothelial progenitor cells enhance osteogenesis of mesenchymal stem cells by activating the MAPK dependent pathway

Recent studies have shown that endothelial progenitor cells (EPCs) could enhance osteogenesis of mesenchymal stem cells (MSCs) through multiple paracrine signals. However, the role of EPCs-derived exosomes (EPCs-exos) in osteogenesis has been rarely reported, and little is known regarding their underlying mechanisms. This study attempted to investigate the underlying mechanism by which EPCs-exos promotes osteogenesis of MSCs. EPCs-exos was isolated by supercentrifugation and characterized by western blot, transmission electron microscopy (TEM) and nano particle analysis (NTA). Internalization of EPCs-exos was observed via a laser confocal microscope. The effects of EPCs-exos on the regulation of MSCs biological properties were investigated in vivo and in vitro . The expression of osteogenesis markers and calcium nodule formation was quantified by qRT-PCR, western blotting, alkaline phosphatase (ALP) staining and Alizarin Red staining. Rat critical-sized calvarial bone defects model was used to assess the efficacy of EPCs-exos on bone regeneration. Real-time PCR array and western blotting were performed to explore possible signaling pathways involved in osteogenesis. Results showed that EPCs-exos could be internalized by MSCs, which exhibited greater ALP activity and increased calcium mineral deposition and improved osteogenic markers expression. EPCs-exos combined with MSCs could improve bone regeneration in vivo . These data suggest that EPCs-exos influence the biological function and promote MSCs osteogenic differentiation in vivo and in vitro. Mitogen-activated protein kinase (MAPK) signaling pathway was involved in this process. Activation of the p38MAPK pathway may be the key to enhancing MSCs osteogenic differentiation.