ENHANCING INTERACTIONS BETWEEN MASR AND ETBR AS A NEW VASOPROTECTIVE STRATEGY

Abstract

Objective: We demonstrated that the MAS and ETB receptors physically interact and may be involved in the protective actions of Ang(1–7) in endothelial cells (ECs). We assessed the biological role of MAS/ETBR interaction in the vasculature, focusing on the NO pathway. Design and method: Human ECs were stimulated with Ang(1–7) (10-7 M) in the presence/absence of A779 (MAS antagonist, 10-5 M), BQ788 (ETBR antagonist, 10-5 M) and MAS/ETBR peptide disruptor (10-5 M). ETBR expression and AKT/eNOS activation were evaluated by immunoblotting and NO production by DAF-FM fluorescence. Results: Ang(1–7) increased ETBR expression (50%), an effect blocked by A779 (p < 0.05 vs control). Ang(1–7) also induced AKT (40%) and eNOS (35%) activation; followed by an increase in NO production (2 fold) (p < 0.05 vs control). These effects were inhibited by A779, BQ788 and the MAS/ETBR disruptor. In a high throughput screening of a 20K protein:protein interaction modulator library, we discovered 23 potential enhancers of the MAS/ETBR interaction, where we tested 4 in ECs (Enh1–4: 10–5 M). All four MAS/ETBR enhancers increased eNOS activation with variable responses (Enh1: 44.2%; Enh2: 65.4%; Enh3: 80.7%; Enh4: 94.9% vs control, p < 0.05), but only treatment with Enh1 and Enh2 increased NO production (Enh1: 109.4%; Enh2: 46.5% vs control, p < 0.05) in ECs. Mesenteric resistance arteries were pre-incubated with Enh1–4 for 30 minutes prior to acetylcholine (Ach) curves, to assess endothelium-dependent relaxation. Enh1 decreased ACh-induced relaxation (Emax: 52.8 ± 2.9 vs Emax control: 70.4 ± 3.3), while Enh4 increased ACh-induced relaxation (Emax: 96.7 ± 4.6 vs Emax control: 70.4 ± 3.3), p < 0.05. Conclusions: Promoting the MAS/ETBR interaction with specific enhancers leads to eNOS activation and vasorelaxation, where Enh1–4 have variable effects. Current studies are focusing on identifying the most sensitive enhancer that will provide vasoprotection, and potentially new strategies in the treatment of vascular disease.