ARPE-19-derived VEGF-containing exosomes promote neovascularization in HUVEC: the role of the melanocortin receptor 5

ARPE-19 retinal pigment epithelial cells cultured in a medium containing 35 mM D-glucose led to an augmented ROS formation and release of vascular endothelial factor (VEGF)-containing exosomes compared to ARPE-19 cells cultured in a medium containing 5 mM D-glucose (standard medium). Exposing these cells to the melanocortin 5 receptor agonist (MCR 5 ) PG-901 (10 −10 M), for 9 d reduced ROS generation, the number of exosomes released and their VEGF content. In contrast, incubating the cells with the melanocortin receptor MCR 1 agonist BMS-470539 (10 −5  M) or with the mixed MCR 3/4 agonist MTII (0.30 nmol) did not produce any significant decrease in ROS levels. ARPE-19-derived VEGF-containing exosomes promoted neovascularization in human umbilical vein endothelial cells (HUVEC), an effect that was markedly reduced by PG-901 (10 −10 M) but not by the MCR 3/4 agonist MTII (0.30 nmol) or the MCR 1 agonist BMS-470539 (10 −5  M). The MCR 5 -related action in the ARPE-19 cells was accompanied by the increased expression of two coupled factors, cytochrome p4502E1 (CYP2E1) and nuclear factor kappa b (Nf-κB). These are both involved in high glucose signalling, in ROS generation and, interestingly, were reduced by the MCR 5 agonist in the ARPE-19 cells. Altogether, these data suggest that MCR 5 is a modulator of the responses stimulated by glucose in ARPE-19 cells, which might possibly be translated into a modulation of the retinal pigment epithelium response to diabetes in vivo.