Impaired flow-mediated vasodilatation in mutated estrogen receptor alpha (ERα) mouse reveals a role of unliganted membrane, but not nuclear, ERα in shear stress-dependent mechanotransduction

Abstract

Flow-mediated dilation (FMD) of resistance arteries (RAs) plays a key role in tissue perfusion. A reduced FMD is the hallmark of the endothelium dysfunction occurring early in cardiovascular and metabolic disorders. Estrogen therapy improves FMD in diseased conditions without major effect in healthy subjects. Nevertheless, estrogen receptor alpha (ERα) mutation in a man was associated with severe and selective FMD reduction. Thus, we evaluated the role of ERα in FMD in healthy young male mice. FMD was determined in vitro in mesenteric RAs isolated from mice lacking ERα (ERα−/−), the ERα nuclear activation function AF2 (AF2-ERα−/−) or the ERα palmitoylation site (C451A-ERα−/−, inactivation of the membrane effects or ERα), compared to littermate wild-type (WT or+/+) mice. We found that FMD was significantly reduced in ERα−/− compared to ERα+/+ male and female (ovariectomized or not) mice. Exogenous ERα stimulation or blockade did not affect FMD. FMD was not affected in AF2-ERα−/− mice whereas it was significantly decreased in C451A-ERα−/− mice. NO-synthesis blockade with L-NNA strongly reduced FMD in WT and AF2-ERα−/− mice without major effect in ERα-/- and C451A-ERα−/− mice. Acetylcholine-mediated relaxation, not affected by the absence of ERα was similarly reduced by L-NNA in all groups. After ROS reduction in vivo, NO-dependent FMD was equivalent in C451A-ERα−/− and C451A-ERα+/+ mice. Thus, membrane ERα is important for FMD through activation of eNOS activity and reduction of ROS production, possibly in a ligand-independent manner.