Estrogen receptor alpha (ERα) has been recognized now for several decades as playing a key role in reproduction and exerting functions in numerous nonreproductive tissues. In this review, we attempt to summarize the in vitro studies that are the basis of our current understanding of the mechanisms of action of ERα as a nuclear receptor and the key roles played by its two activation functions (AFs) in its transcriptional activities. We then depict the consequences of the selective inactivation of these AFs in mouse models, focusing on the prominent roles played by ERα in the reproductive tract and in the vascular system. Evidence has accumulated over the two last decades that ERα is also associated with the plasma membrane and activates non-nuclear signaling from this site. These rapid/nongenomic/membrane-initiated steroid signals (MISS) have been characterized in a variety of cell lines, and in particular in endothelial cells. The development of selective pharmacological tools that specifically activate MISS and the generation of mice expressing an ERα protein impeded for membrane localization have begun to unravel the physiological role of MISS in vivo. Finally, we discuss novel perspectives for the design of tissue-selective ER modulators based on the integration of the physiological and pathophysiological roles of MISS actions of estrogens.

Flow-induced changes in vessel caliber tend to restore baseline wall shear stress (WSS) and have been reported to be endothelium-dependent. To investigate the role of endothelium-derived nitric oxide (NO) in the adaptive increase in artery diameter in response to a chronic increase in blood flow, an arteriovenous fistula was constructed between the left common carotid artery (CCA) and the external jugular vein in 22 New Zealand White rabbits, and NO synthesis was inhibited in 14 animals by long-term administration ofN^G-nitro-l-arginine-methyl ester (L-NAME) in drinking water given for 4 weeks. The remaining 8 animals served as controls. Mean arterial blood pressure was not significantly altered by L-NAME treatment (91±2 in control versus 98±3 mm Hg in L-NAME–treated rabbits). Blood flow significantly increased in the left CCA in both groups but was lower in L-NAME–treated than control animals (106.1±10.7 versus 196.2±32.3 mL/min,P<.003). The diameter of the flow-loaded left CCA also increased significantly in both groups compared with the right CCA (2.15±0.12 and 2.54±0.1 mm, respectively,P<.02), but the increase was less in the L-NAME–treated than the control group (3.24±0.09 and 4.64±0.17 mm, respectively,P<.0001). The diameter of the anastomosed veins was also increased but to a much lesser degree in L-NAME–treated animals than in controls (4.14±0.29 versus 7.94±0.51 mm,P<.0001). As a result of artery enlargement, WSS was normalized in the flow-loaded left CCA of the control group (8.87±0.77 dynes/cm²) regardless of blood flow values. In L-NAME–treated animals, however, WSS was only partially regulated, the mean value being significantly increased (18.7±2.2 dynes/cm²,P<.006). Moreover, a highly significant positive correlation between WSS and blood flow was obtained in L-NAME–treated animals (r=.84,P<.0001). We also found remodeling of the artery wall, with a larger increase in the medial cross-sectional area associated with an increased number of smooth muscle cells, in the control group compared with the L-NAME–treated group (0.75±0.09 versus 0.49±0.04 mm²and 4504±722 versus 2717±282 cells/mm²,P<.03). We conclude that NO plays a role in the increase of vessel caliber in response to chronic increase in blood flow. As yet unidentified additional metabolic processes appear to be necessary for a complete regulatory response.

Significance: The in vivo roles of plasma membrane-associated estrogen receptor (ER)α, including cross-talk with nuclear ERα, are poorly understood. We created a mouse with a point mutation of the palmitoylation site of ERα (C451A-ERα) to obtain membrane-specific loss of function. A complementary mouse lacking the ERα activation function AF-2 (ERα-AF2 ⁰ ) provided selective loss of function of nuclear ERα actions. Physiologic studies revealed critical requirements for membrane receptors in ovarian function and thereby in fertility, and in vascular physiology. In contrast, nuclear ERα actions mediate uterine responses to estrogen and genome-wide analysis indicates that membrane-to-nuclear receptor cross-talk in vivo is quite modest in uterus. These findings demonstrate for the first time critical tissue-specific roles for membrane versus nuclear actions of a steroid hormone receptor in vivo.

Objective—: Cardiac damage and vascular dysfunction are major causes of morbidity and mortality in hypertension. In the present study, we explored the beneficial therapeutic effect of endoplasmic reticulum (ER) stress inhibition on cardiac damage and vascular dysfunction in hypertension. Methods and Results—: Mice were infused with angiotensin II (400 ng/kg per minute) with or without ER stress inhibitors (taurine-conjugated ursodeoxycholic acid and 4-phenylbutyric acid) for 2 weeks. Mice infused with angiotensin II displayed an increase in blood pressure, cardiac hypertrophy and fibrosis associated with enhanced collagen I content, transforming growth factor-β1 (TGF-β1) activity, and ER stress markers, which were blunted after ER stress inhibition. Hypertension induced ER stress in aorta and mesenteric resistance arteries (MRA), enhanced TGF-β1 activity in aorta but not in MRA, and reduced endothelial NO synthase phosphorylation and endothelium-dependent relaxation (EDR) in aorta and MRA. The inhibition of ER stress significantly reduced TGF-β1 activity, enhanced endothelial NO synthase phosphorylation, and improved EDR. The inhibition of TGF-β1 pathway improved EDR in aorta but not in MRA, whereas the reduction in reactive oxygen species levels ameliorated EDR in MRA only. Infusion of tunicamycin in control mice induced ER stress in aorta and MRA, and reduced EDR by a TGF-β1–dependent mechanism in aorta and reactive oxygen species–dependent mechanism in MRA. Conclusion—: ER stress inhibition reduces cardiac damage and improves vascular function in hypertension. Therefore, ER stress could be a potential target for cardiovascular diseases.