Human Endothelial Progenitor Cell-Derived Exosomes Increase Proliferation and Angiogenesis in Cardiac Fibroblasts by Promoting the Mesenchymal-Endothelial Transition and Reducing High Mobility Group Box 1 Protein B1 Expression.

Myocardial fibrosis is a characteristic feature of cardiomyopathies. However, no effective strategies to attenuate cardiac fibrosis are currently available. Late-stage endothelial progenitor cells (EPCs) are precursors of endothelial cells (ECs) that repair the heart through a paracrine mechanism. In the present study, we tested whether EPC-derived exosomes regulate the differentiation of fibroblasts into ECs. We isolated late-stage EPCs from human peripheral blood (PB) and used immunofluorescence and flow cytometry to confirm their identity. Next, we isolated exosomes from the EPCs and characterized their morphology using electron microscopy and confirmed the expression of exosome-specific marker proteins using Western blots. We then investigated the in vitro effects of exosomes on the proliferation and angiogenesis of cardiac fibroblasts (CFs) and on the expression of the mesenchymal-endothelial transition (MEndT)-related genes and the myocardial fibrosis-regulated protein, high mobility group box 1 protein B1 (HMGB1). We found that human PB-EPC-derived exosomes enhanced the proliferation and angiogenesis of CFs in vitro. Furthermore, CFs stimulated with these exosomes showed increased expression of the EC-specific markers, like cluster of differentiation 31 and vascular endothelial growth factor receptor 2, and decreased expression of proteins involved in fibrosis, like alpha-smooth muscle actin, vimentin, collagen I, transforming growth factor-beta, and tumor necrosis factor-alpha. In addition, CFs stimulated with human PB-EPC-derived exosomes, inhibited the expression of HMGB1. Taken together, our study demonstrated that EPC-derived exosomes promote the proliferation and angiogenesis of CFs by inhibiting MEndT and decreasing the expression of HMGB1.