Molecular evolution of the Angiotensin II receptors AT1 and AT2: Specificity of the sodium binding site in amniota

In vertebrates, the octopeptide angiotensin II (AngII) is an important in vivo regulator of the cardiovascular system. It acts mainly through two G protein-coupled receptors, AT1 and AT2. To better understand the interplay between these receptors throughout the evolution of the renin-angiotensin system (RAS), we combined a phylogenetic study to electrostatics computations and molecular dynamics (MD) simulations of AT1 and AT2 receptors from different species. The phylogenetic analysis reveals a mirror evolution of AT1 and AT2 that are both split in two clades, separating fish from terrestrian receptors. It also indicates that the unusual allosteric sodium binding site of human AT1 is specific of amniota. Other AT1 and AT2 receptors display a canonical sodium binding site with a serine at position 7.46 (Ballesteros numbering). Electrostatics computations and MD simulations support maintained sodium binding to human AT1 with ingress from the extracellular side. Comparison of the sodium binding modes in AT1 and AT2 from humans and eels indicates that the allosteric control by sodium in both AT1 and AT2 evolved during the transition from an aqueous to a terrestrial environment. The unusual S7.46N mutation in amniota AT1 is mirrored by a L3.36M mutation in amniota AT2. The S7.46N mutation increases the specificity of AT1 for AngII relative to Ang derivatives, whereas the L3.36M mutation might have the opposite effect on AT2. Both mutations should contribute to the split of the renin-angiotensin system into the classical (AngII/AT1) and counter-regulatory (Ang1-7/AT2, Mas) arms in amniota.

Role of pregnancy on insulin-induced vasorelaxation: the influence of angiotensin II receptors

Pregnancy is characterized by insulin resistance that is associated with increased angiotensin II (AngII) and insulin levels. Therefore, pregnancy may change insulin-induced vasodilation through changes in AngII receptors. Insulin-induced vasorelaxation was evaluated in phenylephrine-precontracted aortic rings of pregnant and non-pregnant rats, using a conventional isolated organ preparation. Experiments were performed in thoracic or abdominal aorta rings with or without endothelium in the presence and absence of L-NAME (10-5 M), losartan (10-7 M) or PD123319 (10-7 M). AT1 and AT2 receptors expression were detected by immunohistochemistry. Insulin-induced vasodilation was endothelium and NO dependent and decreased in the thoracic aorta but increased in the abdominal segment of pregnant rats. Insulin’s vasorelaxant effect was increased by losartan mainly on the thoracic aorta. PD123319 decreased insulin-induced vasorelaxation mainly in the pregnant rat abdominal aorta. AT1 receptors’ expression was decreased while AT2 receptors’ expression was increased by pregnancy. In conclusion, pregnancy changes insulin-induced vasorelaxation. Moreover, insulin vasodilation is tonically inhibited by AT1 receptors, while AT2 receptors appear to have an insulin-sensitizing effect. The role of pregnancy and AngII receptors differ depending on the aorta segment. These results shed light on the role of pregnancy and AngII receptors on the regulation of insulin-mediated vasodilation.