Exosomes secreted from osteocalcin-overexpressing endothelial progenitor cells promote endothelial cell angiogenesis

Exosome secretion is an important paracrine way of endothelial progenitor cells (EPCs) to modulate resident endothelial cells. The osteocalcin (OCN)-expressing EPCs have been found to be increased in cardiovascular disease patients and are considered to be involved in the process of coronary atherosclerosis. Since OCN has been proven to prevent endothelial dysfunction, this study aimed to evaluate the effect of exosomes derived from OCN-overexpressed EPCs on endothelial cells. Exosomes derived from EPCs (Exos) and OCN-overexpressed EPCs (OCN-Exos) were isolated and incubated with rat aorta endothelial cells (RAOECs) with or without the inhibition of OCN receptor G protein-coupled receptor family C group 6 member A (GPRC6A). The effects of exosomes on the proliferation activity of endothelial cells were evaluated by CCK-8 assay, and the migration of endothelial cells was detected by wound healing assay. A tube formation assay was used to test the influence of exosomes on the angiogenesis performance of endothelial cells. Here, we presented that OCN was packed into Exos and was able to be transferred to the RAOECs via exosome incorporation, which was increased in OCN-Exos groups. Compared with Exos, OCN-Exos had better efficiency in promoting RAOEC proliferation and migration and tube formation. The promoting effects were impeded after the inhibition of GPRC6A expression in RAOECs. These data suggest that exosomes from OCN-overexpressed EPCs have a beneficial regulating effect on endothelial cells, which involved enhanced OCN-GPRC6A signaling.