Melanocortin receptors involvement in vascular cell homeostasis

The Melanocortin system (MCS) consists of several melanocortin peptides derived from the proopiomelanocortin (POMC) gene, five G-coupled melanocortin receptors (MCR), two endogenous antagonists, and two ancillary proteins. The MCS has well-established roles in the central regulation of energy homeostasis and cardiovascular functions and in the control of inflammation. Interestingly, a locally expressed MCS has been observed in endothelial cells (EC) of the microcirculation. Besides, blood vessel tone appeared to be influenced by NO-cGMP dependent relaxation responses through EC MCR in mice, and treatment with MCR agonists prevented vascular dysfunction and attenuated plaque inflammation in a mouse model of pre-established atherosclerosis. We sought to investigate whether human macrovascular EC express any MCRs and whether melanocortins exert a protective role on EC, whose injury is central to the pathogenesis of atherosclerosis, thrombosis and vascular surgery complications. We showed by real-time PCR, Western-Blot, and immunocytochemistry that human aortic EC express the type 1 MCR (MC1R), but no other MCR nor POMC. We demonstrated by enzyme immunoassay that MC1R stimulation raised intracellular cAMP. Moreover, in vitro wound healing experiments showed that the high-affinity MC1R ligand, the alpha-melanocyte stimulating hormone (α-MSH), was able to accelerate EC migration speed as early as 3h after treatment: the wound area became significantly lower (ranging from -15% to -25%) at 9h (p<0.01) and 12h (p<0.001) in α-MSH-treated cells. Accelerated migration was mediated by the activation of the Ca2+ signaling cascade. This was reversed by an MC1R specific antagonist (153-N). Microarray analysis identified 506 genes whose expression showed a significant median fold change ≥30% over time as an effect of stimulation with α-MSH (padj<0.05). Functional analysis allowed identifying time-dependent dynamic modulation of genes involved in extracellular matrix-receptor interaction, cell adhesion, and vessel development. The co-regulation of these cellular processes appeared to drive the faster closure of the wound. These results provide evidence of a novel function of peripherally expressed MC1R, whose activation may participate in preventing and healing endothelial dysfunction in macrovascular arteries. EC MC1R could represent a target for therapeutic strategies aimed at repairing endothelial injury and denudation in a variety of vascular pathological conditions.