Small resistance arteries regulate peripheral tissue perfusion following variations in arterial pressure and blood flow. An altered flow-mediated dilation (FMD) in response to intraluminal shear stress is the hallmark of early vascular dysfunction. We recently showed that the adaptive flow-dependent arterial remodeling was controlled by the endothelial estrogen receptor alpha (ERa). Our goal was to evaluate the role of ERa in endothelial mechanosensitive mechanisms related to the acute response to flow, by using multiple models of ERa deficiency in male mice, avoiding the hormonal influence of estrogens encountered in females.

Evaluation of the FMD was performed on pressurized mesenteric resistance arteries mounted on an arteriograph following step increase in intraluminal flow (6-100μl/min). Arteries were isolated from wild-type (WT) and ERa genetically modified male mice deficient in either (i) total ERa (ERaKO), (ii) its ligand-dependent transactivation function AF2 (AF2°) and (iii) the plasmic membrane-located ERa following a point mutation of the palmitoylation (C451A) site of the receptor.

We first observed a selective attenuation of FMD, without any major modification in response to vasodilator agonists (acetylcholine), in mice deficient in ERa (% dilation 50μl/min: ERaKO: 41±5 vs. WT: 59±4 p<0.05 two-way ANOVA) or its AF2 function involved in its nuclear action (% dilation 100μl/min: AF2: 33±4 vs. WT: 56±5 p<0.01). Interestingly, the proportion of NO involved in FMD droped markedly with the total loss of ERa as NOS inhibition by LNNA only slightly affected FMD in ERaKO, in contrast to WT and AF2, suggesting a putative compensatory mechanism (% of inhibition at flow 100μl/min: ERaKO: 13%; AF2: 70%; WT: 71%). Ex vivo ligand-dependent modulation of ERa after incubation with its agonist 17beta estradiol (10-8M) or the antagonist ICI 182,780 (10-6M) had no major effect on FMD in WT arteries. However, a default in receptor membrane addressing in C451A male mice markedly altered FMD (% dilation 50μl/min: C451A: 26±4 vs. WT: 53±5; p<0.01) characterizing a major decrease in flow-mediated NO production.

We thus show, for the first time, that membrane ERa contributes to arterial shear-sensing irrespective of the presence of an agonist or an antagonist. ERa at the membrane could contribute to vascular homeostasis and the regulation of its expression should now be studied.