Ang-(1-7) and ET-1 interplay through Mas and ET_B receptor interaction defines a novel vasoprotective mechanism

BACKGROUND:
Ang-(1-7) (angiotensin (1-7)) via MasR (Mas receptor) opposes vaso-injurious actions of Ang II (angiotensin II) as shown in models of pulmonary hypertension. The underlying mechanisms remain unclear. We hypothesized cross talk between Ang-(1-7) and the protective arm of the ET-1 (endothelin-1) system involving MasR and ET_BR (endothelin receptor type B).

METHODS:
To address this, we studied multiple models: in vivo, in a mouse model of ET-1–associated vascular injury (hypoxia-induced pulmonary hypertension); ex vivo, in isolated mouse arteries; and in vitro, in human endothelial cells.

RESULTS:
Pulmonary hypertension mice exhibited pulmonary vascular remodeling, endothelial dysfunction, and ET-1–induced hypercontractility. Ang-(1-7) treatment (14 days) ameliorated these effects and increased the expression of vascular ET_BR. In human endothelial cells, Ang-(1-7)–induced activation of eNOS (endothelial NO synthase)/NO was attenuated by A779 (MasR antagonist) and BQ788 (ET_BR antagonist). A779 inhibited ET-1–induced signaling. Coimmunoprecipitation and peptide array experiments demonstrated the interaction between MasR and ET_BR. Binding sites for ET_BR were mapped to MasR (amino acids 290–314). Binding sites for MasR on ET_BR were identified (amino acids 176–200). Peptides that disrupt MasR:ET_BR prevented Ang-(1-7) and ET-1 signaling. Using high-throughput screening, we identified compounds that enhance MasR:ET_BR interaction, which we termed enhancers. Enhancers increased Ang-(1-7)–induced eNOS activity, NO production, and Ang-(1-7)–mediated vasorelaxation, and reduced contractile responses.

CONCLUSIONS:
We identify cross talk between Ang-(1-7) and ET-1 through MasR:ET_BR interaction as a novel network that is vasoprotective. Promoting coactivity between these systems amplifies Ang-(1-7) signaling, increases ET-1/ET_BR-mediated vascular actions, and attenuates the injurious effects of ET-1. Enhancing Ang-(1-7)/MasR:ET-1/ET_BR signaling may have therapeutic potential in conditions associated with vascular damage.