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Estrogen receptor alpha (ERα) activation by estrogens prevents atheroma through its nuclear action, whereas plasma membrane-located ERα accelerates endothelial healing. The genetic deficiency of ERα was associated with a reduction in flow-mediated dilation (FMD) in one man. Here, we evaluated ex vivo the role of ERα on FMD of resistance arteries. FMD, but not agonist (acetylcholine, insulin)-mediated dilation, was reduced in male and female mice lacking ERα (Esr1-/- mice) compared to wild-type mice and was not dependent on the presence of estrogens. In C451A-ERα mice lacking membrane ERα, not in mice lacking AF2-dependent nuclear ERα actions, FMD was reduced, and restored by antioxidant treatments. Compared to wild-type mice, isolated perfused kidneys of C451A-ERα mice revealed a decreased flow-mediated nitrate production and an increased H2O2 production. Thus, endothelial membrane ERα promotes NO bioavailability through inhibition of oxidative stress and thereby participates in FMD in a ligand-independent manner.

Hypertension is associated with excessive reactive oxygen species (ROS) production in vascular cells. Mitochondria undergo fusion and fission, a process playing a role in mitochondrial function. OPA1 is essential for mitochondrial fusion. Loss of OPA1 is associated with ROS production and cell dysfunction. We hypothesized that mitochondria fusion could reduce oxidative stress that defect in fusion would exacerbate hypertension. Using (a) Opa1 haploinsufficiency in isolated resistance arteries from Opa1+/- mice, (b) primary vascular cells from Opa1+/- mice, and (c) RNA interference experiments with siRNA against Opa1 in vascular cells, we investigated the role of mitochondria fusion in hypertension. In hypertension, Opa1 haploinsufficiency induced altered mitochondrial cristae structure both in vascular smooth muscle and endothelial cells but did not modify protein level of long and short forms of OPA1. In addition, we demonstrated an increase of mitochondrial ROS production, associated with a decrease of superoxide dismutase 1 protein expression. We also observed an increase of apoptosis in vascular cells and a decreased VSMCs proliferation. Blood pressure, vascular contractility, as well as endothelium-dependent and -independent relaxation were similar in Opa1+/- , WT, L-NAME-treated Opa1+/- and WT mice. Nevertheless, chronic NO-synthase inhibition with L-NAME induced a greater hypertension in Opa1+/- than in WT mice without compensatory arterial wall hypertrophy. This was associated with a stronger reduction in endothelium-dependent relaxation due to excessive ROS production. Our results highlight the protective role of mitochondria fusion in the vasculature during hypertension by limiting mitochondria ROS production.

Mitochondria are dynamic organelles altering their inner and outer membranes through fission and fusion mechanisms. In response to shear stress, the mitochondria in endothelial cells (ECs) continuously undergo fusion and fission mechanisms. We hypothesized that alteration in mitochondrial dynamics could alter ECs function leading to vascular damages. For that, we investigated the role of OPA1 and DRP1 deficiency in ECs and vascular homeostasis using mice lacking fusion protein OPA1 and fission protein DRP1(heterozygous Opa1 ± & Drp1 ± mice). We investigated mitochondrial dynamics-related proteins expression level in ECs submitted to a disturbed shear stress (evidenced by eNOS down-regulation and endothelin-1 up-regulation) and observed a reduction in fusion protein OPA1 mRNA expression and an increase in fission protein DRP1 mRNA expression level. The opposite was observed in ECs submitted to disturbed shear stress. After acute stimulation of ECs to Histamine, cells lacking OPA1 and DRP1 protein have shown a decreased intracellular Ca2+ release, compared to control cells. Besides, these cells showed a decreased capability of migration compared to control cells. As shear stress determines atherogenesis in large arteries, we investigated mitochondrial dynamics-related proteins in various areas in the mouse aorta. In the areas submitted to low shear stress (inner part of the aortic cross), OPA1 mRNA expression was reduced and DRP1 mRNA expression was increased compared to aortic areas subjected to high shear stress. These observations led to investigate atherosclerosis in Opa1± and Drp1 ± mice. These mice, when crossed with Ldlr−/− mice and fed high fat diet, develop more atherosclerosis in Opa1 ± and less in Drp1 ± mice compared to WT. Thus, disregulation in mitochondrial dynamics proteins altered endothelium dependent functions in atherosclerotic mice, and increasing plaque formation with reduced fusion.