Abstract 20: Endothelial αEnac Subunit is Involved in Shear Stress Sensing and Endothelium Stiffness In Vivo

Abstract

The Epithelial Sodium Channel (ENaC) is a key actor in renal sodium homeostasis. The expression of α β γ ENaC subunits has been shown in the endothelium and vascular smooth muscle, suggesting a role in vascular function. We recently demonstrated that endothelial ENaC is involved in aldosterone-modulated endothelial stiffness. It has been proposed that ENaC may act as a mechanosensor, as a member of the degenerin channel family acting as sensors in C. elegans. We hypothesized that the endothelial αENaC subunit is involved in shear stress sensing in the vascular tree. We used mice with conditional αENaC subunit gene inactivation in the endothelium only (Endo-αENaC Knock Out mice) and their controls. Renal function was explored using metabolic cages. Vascular reactivity was assessed by pressure myograph in mesenteric arteries. Endothelial stiffness was analyzed by Atomic Force Microscopy (AFM) in open aortic rings. Renal function and sodium excretion (in basal state and after 1 mM NaCl acute challenge) were not affected, indicating that endothelial ENaC is not involved in sodium balance. Endothelial stiffness was decreased in aorta by acute incubation with benzamil (15min, 1μM) and by the absence of αENaC expression in the endothelium (Cortical stiffness; WT 0.9±0.15, WT Benzamil 0.6±0.10, KO 0.6±0.12, KO Benzamil 0.6±0.11 pN/nm). Ex vivo vascular contraction induced by phenylephrine and potassium chloride were not modified in Endo-αENaC Knock Out mice, nor the vasodilatory response to acetylcholine. Myogenic tone was also similar between the two groups. However, a striking difference was observed regarding flow-mediated vasodilation that is blunted in Endo-αENaC Knock Out mice. Similar results were observed after acute ex vivo benzamil (1μM) treatment in WT mesenteric arteries. In aorta, phosphorylation of eNOS, Akt and Myosin Light Chain were increased in Endo αENaC KO mice as compared to WT (1.00±0.3 vs 2.28±0.2, 1.00±0.1 vs 1.58±0.3, 1.00±0.3 vs 1.65±0.2). Our results demonstrate that the αENaC subunit in endothelial cells is part of the flow-sensing machinery in the vessel. We also showed that in vivo ENaC inhibition (using genetic or pharmacological approaches) reduces endothelial stiffness. Whether these two findings are linked remain to be explored.