| Neuropeptide Y (NPY) is a 36-amino acid neuropeptide, abundant in the sympathetics, the brain, and the heart. We have discovered previously that NPY is an angiogenic factor by stimulating migration, proliferation, and differentiation of endothelial cells in vitro. We have also shown that NPY enhances post-ischemic angiogenesis in vivo. However, receptor subtypes mediating in vitro effect of NPY on the endothelium, and in vivo angiogenesis were not fully characterized. Our previous findings suggested involvement of Y2 receptor with some contribution from other receptor subtypes. Since endothelial cells were found to express NPY receptor subtypes Y1, Y2, and Y5, sequential activation of these receptors was hypothesized to mediate NPY's angiogenic function in the endothelium.;The broad aim of this study was to delineate the NPY receptors mediating each of the steps: migration, proliferation, and differentiation of endothelial cells induced by NPY. In order to do so, selective NPY receptor agonists and antagonists for each of the Y1, Y2, and Y5 receptors were used in various in vitro assays. In addition, role of Y2 receptor in vivo was assessed using the Y2-knockout mice compared to the wild type in two models of angiogenesis: murine Matrigel plug and mouse model of oxygen-induced retinopathy.;The result of the in vitro studies showed that NPY's effect on the endothelium was bimodal at concentrations of 10 fM to 10 nM. Simultaneous activation of all three NPY receptors Y1, Y2, and Y5 was necessary for migration of endothelial cells to NPY, while proliferation required any two receptors, and differentiation only one. Moreover, expression of Y5 receptor was associated with augmented NPY effect. Y2 knockout studies, also, established Y2 receptor essential for NPY-induced angiogenesis.;Therefore, we conclude that NPY-induced angiogenesis involves participation of Y1, Y2, and Y5 receptor subtypes; with Y5 receptor acting as an enhancer. We propose that these receptors form heteromeric complexes with each other and with other receptors, and the heterotrimeric complex of Y1/Y2/Y5 receptor may be the un-cloned Y3 receptor. Also, impaired NPY-induced angiogenesis in Y receptor knockout mice is due to absence of Y1/Y2/Y5 heteromerization complex. |
