Reduced vasorelaxation to estradiol and G-1 in aged female and adult male rats is associated with GPR30 downregulation

Estrogen-mediated mechanisms in hypertension and other cardiovascular diseases

Cardiovascular disease (CVD) is the leading cause of death globally for men and women. Premenopausal women have a lower incidence of hypertension and other cardiovascular events than men of the same age, but diminished sex differences after menopause implicates 17-beta-estradiol (E2) as a protective agent. The cardioprotective effects of E2 are mediated by nuclear estrogen receptors (ERα and ERβ) and a G protein-coupled estrogen receptor (GPER). This review summarizes both established as well as emerging estrogen-mediated mechanisms that underlie sex differences in the vasculature during hypertension and CVD. In addition, remaining knowledge gaps inherent in the association of sex differences and E2 are identified, which may guide future clinical trials and experimental studies in this field.

Improvement of Cardiovascular Function in Aging Females by the Prolonged Activation of G Protein-Coupled Estrogen Receptor

Ample evidence suggests that estrogen replacement therapy is associated with beneficial effects with regard to cardiovascular diseases when the therapy is initiated temporally close to menopause but not when it is initiated later. Little is known about the complex interactions between hormone receptors after menopause. Coronary artery function and cardiac function were measured in rats that had either received no treatment or had been pretreated with an androgen receptor (AR) antagonist and/or a GPER agonist G-1. ICI 182,780 was used to block the classical estrogen receptors (ERs) to investigate their complex interactions with GPER. The beneficial effects of GPER were only observed by blocking ARs and classical ERs in aged female rats. The results demonstrate that GPER activation is a potential therapeutic target for the inhibition of age-dependent coronary artery dysfunction and cardiac dysfunction under the condition of blocking ARs and classical ERs after menopause. CLINICAL RELEVANCE: The risk of cardiovascular disease in postmenopausal women significantly increased. The role of sex hormones and their receptors during this process is still complicated. Our present study demonstrated that the imbalance of androgen and estrogen may contribute to the impairment of vascular reactivity and subsequent cardiac function. Treatment with GPER agonist G1 combined with the inhibition of ERα and ERβ could improve vascular function and reduce the myocardial ischemia reperfusion injury. These findings may provide the novel and effective strategy for the treatment of cardiovascular diseases in postmenopausal women.

Sex differences in the participation of endothelial mediators and signaling pathways involved in the vasodilator effect of a selective GPER agonist in resistance arteries of gonadectomized Wistar rats

AIM

Endothelial mechanisms underlying the vascular effects of estrogen modulated by the G protein-coupled estrogen receptor (GPER) are not well understood, especially in gonadal sex hormone deprivation. Thus, we investigated vascular function and endothelial signaling pathways involved in the selective activation of GPER in resistance arteries of gonadectomized rats.

METHODS

Gonadectomy was performed in Wistar rats of both sexes. After 21 days, the animals were euthanized. Concentration-response curves were obtained by cumulative additions of G-1 in third-order mesenteric arteries. The vasodilatory effects of G-1 were evaluated before and after endothelium removal or incubation with pharmacological inhibitors. Tissue protein expression was measured by western blotting. Assays with 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF-FM) and 2',7' dichlorodihydrofluorescein-diacetate (DCF-DA) were performed in the arteries investigated. Immunolocalization was assessed by immunofluorescence.

RESULTS

G-1 induced partially endothelium-dependent relaxation in both sexes. The three isoforms of the enzyme nitric oxide synthase contributed to the production and release of nitric oxide in both gonadectomized groups, but the role of inducible nitric oxide synthase is more expressive in males. The mechanistic pathway by which endothelial nitric oxide synthase is phosphorylated appears to differ between sexes, with the rapid signaling pathway phosphatidylinositol-3-kinase/protein kinase B/endothelial nitric oxide synthase (PI3k-Akt-eNOS) being identified for males and mitogen-activated protein kinase/extracellular signal-regulated kinase/endothelial nitric oxide synthase (MEK-ERK-eNOS) for females. The contribution of hydrogen peroxide as an endothelial relaxation mediator seems to be greater in females.

CONCLUSION

These results provide new insights into the effects of estrogen-induced responses via GPER on vascular function in gonadal sex hormone deprivation.

Activation of G protein-coupled estrogen receptor fine-tunes age-related decreased vascular activities in the aortae of female and male rats

BACKGROUND

Hormone replacement therapy was found to be effective in cardiovascular protection only in younger women, not in older women. In this study, we tested whether G protein-coupled estrogen receptor 1 (GPER) activation improves vascular activities in response to ET-1 and ACh in aging rats.

METHODS

Isometric tension study was applied on aortic rings isolated from young adult (5-7 months) and reproductive senescent middle-aged (10-12 months) female Sprague Dawley rats and age matched males.

RESULTS

The aortic contractile response to ET-1 and the relaxation response to ACh were reduced in the female middle-aged rats compared to the female young adult rats. The presence of G-1, the GPER agonist, normalized the reduced vascular activities. Cyclooxygenase inhibitor, meclofenamate, blocked the increased constriction effect of G-1, but further enhanced relaxation effect of G-1. There was no significant difference in aortic reactivity to either ET-1 or ACh between the male middle-aged and young adult rats. The contractile response to ET-1 was not different within the same age of the two sex groups, but there was a remarkable difference in relaxation response to ACh between young adult females and males with better response in females. GPER activation greatly improved the aortic relaxation of both young adult and middle-aged females, but not the males.

CONCLUSIONS

Endothelial dysfunction occurs earlier in males, but in females, dysfunction delays until middle age. GPER activation improves the vascular activities in females, but not males. It is promising to employ GPER as a potential drug target in cardiovascular disease in women.

G-Protein-Coupled Estrogen Receptor Expression in Rat Uterine Artery Is Increased by Pregnancy and Induces Dilation in a Ca2+ and ERK1/2 Dependent Manner

Increasing levels of estrogens across gestation are partly responsible for the physiological adaptations of the maternal vasculature to pregnancy. The G protein-coupled estrogen receptor (GPER) mediates acute vasorelaxing effects in the uterine vasculature, which may contribute to the regulation of uteroplacental blood flow. The aim of this study was to investigate whether GPER expression and vasorelaxation may occur following pregnancy. Elucidation of the functional signalling involved was also investigated. Radial uterine and third-order mesenteric arteries were isolated from non-pregnant (NP) and pregnant rats (P). GPER mRNA levels were determined and—concentration–response curve to the GPER-specific agonist, G1 (10−10–10−6 M), was assessed in arteries pre-constricted with phenylephrine. In uterine arteries, GPER mRNA expression was significantly increased and vasorelaxation to G1 was significantly enhanced in P compared with NP rats. Meanwhile, in mesenteric arteries, there was a similar order of magnitude in NP and P rats. Inhibition of L-type calcium channels and extracellular signal-regulated kinases 1/2 significantly reduced vasorelaxation triggered by G1 in uterine arteries. Increased GPER expression and GPER-mediated vasorelaxation are associated with the advancement of gestation in uterine arteries. The modulation of GPER is exclusive to uterine arteries, thus suggesting a physiological contribution of GPER toward the regulation of uteroplacental blood flow during pregnancy.

Emerging Roles for G Protein-Coupled Estrogen Receptor 1 in Cardio-Renal Health: Implications for Aging

Cardiovascular (CV) and renal diseases are increasingly prevalent in the United States and globally. CV-related mortality is the leading cause of death in the United States, while renal-related mortality is the 8th. Despite advanced therapeutics, both diseases persist, warranting continued exploration of disease mechanisms to develop novel therapeutics and advance clinical outcomes for cardio-renal health. CV and renal diseases increase with age, and there are sex differences evident in both the prevalence and progression of CV and renal disease. These age and sex differences seen in cardio-renal health implicate sex hormones as potentially important regulators to be studied. One such regulator is G protein-coupled estrogen receptor 1 (GPER1). GPER1 has been implicated in estrogen signaling and is expressed in a variety of tissues including the heart, vasculature, and kidney. GPER1 has been shown to be protective against CV and renal diseases in different experimental animal models. GPER1 actions involve multiple signaling pathways: interaction with aldosterone and endothelin-1 signaling, stimulation of the release of nitric oxide, and reduction in oxidative stress, inflammation, and immune infiltration. This review will discuss the current literature regarding GPER1 and cardio-renal health, particularly in the context of aging. Improving our understanding of GPER1-evoked mechanisms may reveal novel therapeutics aimed at improving cardio-renal health and clinical outcomes in the elderly.

Chronic GPER activation prevents ischemia/reperfusion injury in ovariectomized rats

During menopause women are exposed to an increase in cardiovascular risk. G protein-coupled estrogen receptor (GPER) is known to mediate several of the protective effects of such hormones. G1 was described as a selective and synthetic agonist for GPER. The aim of the present research is to evaluate the effect of a chronic treatment with G1 in ovariectomized (OVX) rats exposed to ischemia/reperfusion (I/R). Considering the hypothesis that an impaired mitochondrial state could be involved in the alterations produced in OVX rats, other objective of this study was to investigate it in an isolated preparation. Three months old rats were assigned to undergo either bilateral ovariectomy or sham operation. The OVX rats were randomly treated during one month with either G1 or vehicle. Cardiac mitochondria from OVX rats showed a depolarized membrane potential and a decreased calcium retention capacity in comparison with Sham rats, which were prevented by chronic G1 treatment. I/R caused a higher decrease of left ventricular developed pressure and a higher increase of left ventricular end diastolic pressure in OVX compared to Sham hearts. These altered mechanical parameters were prevented by G1. The induced infarct size was significantly higher in OVX, which was reduced by G1 treatment. These results indicate that the mitochondrial state in OVX rats is impaired, accompanied by an altered mechanical response after ischemia and reperfusion injury, which was effectively prevented with chronic treatment with G1. The present study may provide further insights for the potential development of a therapy based on the GPER modulation.

Sex Differences, Estrogen Metabolism and Signaling in the Development of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a complex and devastating disease with a poor long-term prognosis. While women are at increased risk for developing PAH, they exhibit superior right heart function and higher survival rates than men. Susceptibility to disease risk in PAH has been attributed, in part, to estrogen signaling. In contrast to potential pathological influences of estrogen in patients, studies of animal models reveal estrogen demonstrates protective effects in PAH. Consistent with this latter observation, an ovariectomy in female rats appears to aggravate the condition. This discrepancy between observations from patients and animal models is often called the "estrogen paradox." Further, the tissue-specific interactions between estrogen, its metabolites and receptors in PAH and right heart function remain complex; nonetheless, these relationships are essential to characterize to better understand PAH pathophysiology and to potentially develop novel therapeutic and curative targets. In this review, we explore estrogen-mediated mechanisms that may further explain this paradox by summarizing published literature related to: (1) the synthesis and catabolism of estrogen; (2) activity and functions of the various estrogen receptors; (3) the multiple modalities of estrogen signaling in cells; and (4) the role of estrogen and its diverse metabolites on the susceptibility to, and progression of, PAH as well as their impact on right heart function.

CRISPR/Cas9 Mediated Deletion of the Angiotensinogen Gene Reduces Hypertension: A Potential for Cure?

[Figure: see text].

Alterations in the estrogen receptor profile of cardiovascular tissues during aging

Estrogen exerts protective effects on the cardiovascular system via three known estrogen receptors: alpha (ERα), beta (ERß), and the G protein-coupled estrogen receptor (GPER). Our laboratory has previously showed the importance of GPER in the beneficial cardiovascular effects of estrogen. Since clinical studies indicate that the protective effects of exogenous estrogen on cardiovascular function are attenuated or reversed 10 years post-menopause, the hypothesis was that GPER expression may be reduced during aging. Vascular reactivity and GPER protein expression were assessed in female mice of varying ages. Physiological parameters, blood pressure, and estrogen receptor transcripts via droplet digital PCR (ddPCR) were assessed in the heart, kidney, and aorta of adult, middle-aged, and aged male and female C57BL/6 mice. Vasodilation to estrogen (E2) and the GPER agonist G-1 were reduced in aging female mice and were accompanied by downregulation of GPER protein. However, ERα and GPER were the predominant receptors in all tissues, whereas ERß was detectable only in the kidney. Female sex was associated with higher mRNA for both ERα and GPER in both the aorta and the heart. Aging impacted receptor transcript in a tissue-dependent manner. ERα transcript decreased in the heart with aging, while GPER expression increased in the heart. These data indicate that aging impacts estrogen receptor expression in the cardiovascular system in a tissue- and sex-specific manner. Understanding the impact of aging on estrogen receptor expression is critical for developing selective hormone therapies that protect from cardiovascular damage.

G protein-coupled estrogen receptor 1 as a novel regulator of blood pressure

The mechanisms underlying hypertension are multifaceted and incompletely understood. New evidence suggests that G protein-coupled estrogen receptor 1 (GPER1) mediates protective actions within the cardiovascular and renal systems. This mini-review focuses on recent advancements in our understanding of the vascular, renal, and cardiac GPER1-mediated mechanisms that influence blood pressure regulation. We emphasize clinical and basic evidence that suggests GPER1 as a novel target to aid therapeutic strategies for hypertension. Furthermore, we discuss current controversies and challenges facing GPER1-related research.

G protein-coupled estrogen receptor activation improves contractile and diastolic functions in rat renal interlobular artery to protect against renal ischemia reperfusion injury

OBJECTIVE

This work aimed to investigate whether G protein-coupled estrogen receptor (GPER) can improve the renal interlobular artery vascular function by increasing the NO content, thereby protecting against renal ischemia-reperfusion (IR) injury.

METHODS

This study classified ovariectomised (OVX) female Sprague-Dawley rats into OVX, OVX + IR, OVX + IR + G1 (the GPER agonist G1), OVX + IR + G1+G15 (GPER blocker) and OVX + IR + G1+L-NAME (eNOS blocker) groups. Enzyme-linked immunosorbent assay was performed to detect the estrogen levels in the body and eliminate interference from endogenous estrogens. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling (TUNEL) and HE staining, renal function test and Paller scoring were performed to identify the successful model and detect the degree of renal and renal interlobular arteries injury. The in vitro microvascular pressure diameter measurement technique was used to detect the contraction and diastolic activities of the renal interlobular arteries in each group. Immunofluorescence technique was used to observe the localisation and expression levels of GPER and eNOS in renal interlobular arteries. The GPER and eNOS protein expression levels in each group were detected by Western blot. The NO content in the serum of each group was detected by the nitrate reductase method.

RESULT

After OVX, the estrogen level in the body decreased significantly (P < 0.01), and TUNEL staining showed a significant increase in the degree of renal tubular epithelial cell apoptosis in the IR group. Serum creatinine (SCr) and blood urea nitrogen (BUN) levels were significantly increased in the IR group (P < 0.01), and the Paller score showed significantly increased kidney damage. When performing drug treatment, the G1 intervention group significantly decreased serum BUN and SCr levels after IR injury (P < 0.01). The Paller score showed significantly decreased the degree of renal injury (P < 0.01). After IR, the renal interlobular artery contraction rate and systolic velocity of blood vessels were significantly decreased (P < 0.01). The G1 intervention group significantly restored contraction rate and systolic velocity of blood vessels (P < 0.01), and G15 and L-NAME partially reversed this effect (P < 0.01). Immunofluorescence technique showed that GPER was expressed in renal interlobular artery smooth muscle and endothelial cells. After IR injury, the GPER protein expression increased, and the eNOS protein expression decreased significantly (P < 0.01). Western blot showed that after IR injury, the GPER protein expression increased, and the eNOS protein expression decreased significantly. After G1 intervention, the GPER content did not change, and the eNOS content increased significantly (P < 0.01). After ischemia and reperfusion, the serum NO content decreased significantly, but it increased after G1 intervention. G15 and L-NAME reversed the effects of G1 to varying degrees (both at P < 0.01).

CONCLUSION

GPER may improve the renal interlobular artery vascular function by increasing the NO content, thereby protecting against renal IR injury.

Bazedoxifene-induced vasodilation and inhibition of vasoconstriction is significantly greater than estradiol

OBJECTIVE

A new strategy for menopausal hormone therapy replaces medroxyprogesterone with the selective estrogen receptor modulator bazedoxifene. While the agonist or antagonist activity of bazedoxifene has been examined in other tissues, the current study explored the impact of bazedoxifene on resistance artery reactivity. We hypothesized that bazedoxifene may induce greater vasoprotective effects than estradiol due to enhanced activation of the G-protein-coupled estrogen receptor.

METHODS

We measured the vasodilation of mesenteric resistance arteries from adult male and female wild-type and G-protein-coupled estrogen receptor knockout mice (n = 58) in response to increasing concentrations of bazedoxifene, medroxyprogesterone, and estradiol, and also the impact of these compounds on the responses to phenylephrine and sodium nitroprusside.

RESULTS

Bazedoxifene-induced vasorelaxation was greater than estradiol and blunted phenylephrine-induced contraction-an effect not observed with estradiol. Neither estradiol nor bazedoxifene altered relaxation to sodium nitroprusside. The combination of bazedoxifene + estradiol promoted greater vasodilation than medroxyprogesterone + estradiol, and opposed phenylephrine-induced contraction, whereas medroxyprogesterone + estradiol failed to attenuate this response. Both bazedoxifene + estradiol and medroxyprogesterone + estradiol enhanced sodium nitroprusside-induced relaxation in females. Vascular responses were similar in both sexes in wild-type and G-protein-coupled estrogen receptor knockout mice.

CONCLUSION

Bazedoxifene and bazedoxifene + estradiol relaxed mesenteric arteries and opposed vasoconstriction to a greater degree than estradiol or medroxyprogesterone + estradiol. These effects were independent of sex and G-protein-coupled estrogen receptor expression. We conclude that bazedoxifene may provide vascular benefits over estrogen alone or estrogen plus progestogen combinations in postmenopausal women.

G Protein-Coupled Estrogen Receptor Protects From Angiotensin II-Induced Increases in Pulse Pressure and Oxidative Stress

Our previous work showed that the G protein-coupled estrogen receptor (GPER) is protective in the vasculature and kidneys during angiotensin (Ang) II-dependent hypertension by inhibiting oxidative stress. The goal of the current study was to assess the impact of GPER deletion on sex differences in Ang II-induced hypertension and oxidative stress. Male and female wildtype and GPER knockout mice were implanted with radiotelemetry probes for measurement of baseline blood pressure before infusion of Ang II (700 ng/kg/min) for 2 weeks. Mean arterial pressure was increased to the same extent in all groups, but female wildtype mice were protected from Ang II-induced increases in pulse pressure, aortic wall thickness, and Nox4 mRNA. In vitro studies using vascular smooth muscle cells found that pre-treatment with the GPER agonist G-1 inhibited Ang II-induced ROS and NADP/NADPH. Ang II increased while G-1 decreased Nox4 mRNA and protein. The effects of Ang II were blocked by losartan and Nox4 siRNA, while the effects of G-1 were inhibited by adenylyl cyclase inhibition and mimicked by phosphodiesterase inhibition. We conclude that during conditions of elevated Ang II, GPER via the cAMP pathway suppresses Nox4 transcription to limit ROS production and prevent arterial stiffening. Taken together with our previous work, this study provides insight into how acute estrogen signaling via GPER provides cardiovascular protection during Ang II hypertension and potentially other diseases characterized by increased oxidative stress.

Attenuation of Microbiotal Dysbiosis and Hypertension in a CRISPR/Cas9 Gene Ablation Rat Model of GPER1

G-protein-coupled estrogen receptor, Gper1, has been implicated in cardiovascular disease, but its mechanistic role in blood pressure control is poorly understood. Here, we demonstrate that genetically salt-sensitive hypertensive rats with complete genomic excision of Gper1 by a multiplexed guide RNA CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)/Cas9 (CRISPR associated proteins) approach present with lower blood pressure, which was accompanied by altered microbiota, different levels of circulating short chain fatty acids, and improved vascular relaxation. Microbiotal transplantation from hypertensive Gper1+/+ rats reversed the cardiovascular protective effect exerted by the genomic deletion of Gper1. Thus, this study reveals a role for Gper1 in promoting microbiotal alterations that contribute to cardiovascular pathology. However, the exact mechanism by which Gper1 regulates blood pressure is still unknown. Our results indicate that the function of Gper1 is contextually dependent on the microbiome, whereby, contemplation of using Gper1 as a target for therapy of cardiovascular disease requires caution.

Effects of the Catechol and Methoxy Metabolites of 17β-Estradiol on Nitric Oxide Production by Ovine Uterine Artery Endothelial Cells

Nitric oxide (NO) production is essential to facilitate rises in uterine blood flow (UBF) during pregnancy. It has been proposed that the metabolites of E₂β, 2-hydroxyestradiol (2-OHE₂), 4-hydroxyestradiol (4-OHE₂), 2-methoxyestradiol (2-ME₂), and 4-methoxyestradiol (4-ME₂) play a role in mediating vasodilation and rises in UBF during pregnancy. We previously showed that the E₂β metabolites stimulate prostacyclin production in pregnancy-derived ovine uterine artery endothelial cells (P-UAECs); however, it is unknown whether the E₂β metabolites also induce NO production. Herein, UAECs derived from nonpregnant and pregnant ewes were used to test the hypothesis that E₂β metabolites stimulate NO production in a pregnancy-specific manner. Specific estrogen receptor (ER) and adrenergic receptor (AR) antagonists were used to determine the roles of ERs or ARs in E₂β metabolite-induced NO production. E₂β and its metabolites increased total nitric oxide metabolites (NOx) levels (NO₂ + NO₃) in P-UAECs, but not in NP-UAECs. Pretreatment with combined 1 µmol/L 1,3-bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy)phenol]-1H-pyrazole dihydrochloride (MPP; ER-α antagonist) and 1 µmol/L 4-[2-phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl]phenol (PHTPP; ER-β antagonist) inhibited the rises in NOx levels stimulated by E₂β and 2-ME₂, but had no effect on 2-OHE₂-, 4-OHE₂-, or 4-ME₂-stimulated rises in NOx levels. Pretreatment with yohimbine (α₂-AR antagonist) and propranolol (β_2,3-AR antagonist) inhibited the rises in NOx levels stimulated by 2-OHE₂, but not by E₂β, 4-OHE₂, 2-ME₂, or 4-ME₂. These data demonstrate that E₂β metabolites stimulate NO synthesis via ERs or ARs in UAECs in a pregnancy-specific manner, suggesting that these metabolites contribute to rises in vasodilation and UBF during pregnancy.

Crosstalk between nuclear and G protein-coupled estrogen receptors

In 2005, two groups independently discovered that the G protein-coupled receptor GPR30 binds estradiol in cultured cells and, in response, initiates intracellular signaling cascades Revankar et al. (2005), Thomas et al. (2005). GPR30 is now referred to as GPER, the G-protein coupled estrogen receptor Prossnitz and Arterburn (2015). While studies in animal models are illuminating GPER function, there is controversy as to whether GPER acts as an autonomous estrogen receptor in vivo, or whether GPER interacts with nuclear estrogen receptor signaling pathways in response to estrogens. Here, we review the evidence that GPER acts as an autonomous estrogen receptor in vivo and discuss experimental approaches to test this hypothesis directly. We propose that the degree to which GPER influences nuclear estrogen receptor signaling likely depends on cell type, developmental stage and pathology.

Photoacoustic imaging for in vivo quantification of placental oxygenation in mice

Accurate analysis of placental and fetal oxygenation is critical during pregnancy. Photoacoustic imaging (PAI) combines laser technology with ultrasound in real time. We tested the sensitivity and accuracy of PAI for analysis of placental and fetal oxygen saturation (sO2) in mice. The placental labyrinth (L) had a higher sO2 than the junctional zone plus decidua region (JZ+D) in C57Bl/6 mice. Changing maternal O2 from 100 to 20% in C57Bl/6 mice lowered sO2 in these regions. C57Bl/6 mice were treated with the NO synthase inhibitor L-NG-nitroarginine methyl ester (L-NAME) from gestational day (GD) 11 to GD18 to induce hypertension. L-NAME decreased sO2 in L and JZ+D at GD14 and GD18 in association with fetal growth restriction and higher blood pressure. Hypoxia-inducible factor 1α immunostaining was higher in L-NAME vs control mice at GD14. Fetal sO2 levels were similar between l-NAME and control mice at GD14 and GD18. In contrast to untreated C57Bl/6, L-NAME decreased placental sO2 at GD14 and GD18 vs GD10 or GD12. Placental sO2 was lower in fetal growth restriction in an angiotensin-converting enzyme 2 knockout mouse model characterized by placental hypoxia. On phantom studies, patterns of sO2 measured directly correlated with those measured by PAI. In summary, PAI enables the detection of placental and fetal oxygenation during normal and pathologic pregnancies in mice.-Yamaleyeva, L. M., Sun, Y., Bledsoe, T., Hoke, A., Gurley, S. B., Brosnihan, K. B. Photoacoustic imaging for in vivo quantification of placental oxygenation in mice.

Estrogenic vascular effects are diminished by chronological aging

The beneficial role of estrogen in the vascular system may be due, in part, through reduction of peripheral vascular resistance. The use of estrogen therapy to prevent cardiovascular disease in post-menopausal women remains contentious. This study investigated the influence of aging and the menopause on the acute vasodilatory effects of estrogen using ex vivo human and murine resistance arteries. Vessels were obtained from young (2.9 ± 0.1 months) and aged (24.2 ± 0.1 and 28.9 ± 0.3 months) female mice and pre- (42.3 ± 0.5 years) and post-menopausal (61.9 ± 0.9 years) women. Aging was associated with profound structural alterations of murine uterine arteries, including the occurrence of outward hypertrophic remodeling and increased stiffness. Endothelial and smooth muscle function were diminished in uterine (and tail) arteries from aged mice and post-menopausal women. The acute vasodilatory effects of 17β-estradiol (non-specific estrogen receptor (ER) agonist), PPT (ERα-specific agonist) and DPN (ERβ-specific agonist) on resistance arteries were attenuated by aging and the menopause. However, the impairment of estrogenic relaxation was evident after the occurrence of age-related endothelial dysfunction and diminished distensibility. The data indicate, therefore, that chronological resistance arterial aging is a prominent factor leading to weakened vasodilatory action of estrogenic compounds.

Rapid estrogen receptor-α signaling mediated by ERK activation regulates vascular tone in male and ovary-intact female mice

Estrogen has been shown to affect vascular reactivity. Here, we assessed the estrogen receptor-α (ERα) dependency of estrogenic effects on vasorelaxation via a rapid nongenomic pathway in both male and ovary-intact female mice. We compared the effect of a primary estrogen, 17β-estradiol (E₂) or 4,4',4″-(4-propyl-[1H]pyrazole-1,3,5-triyl)tris-phenol (PPT; selective ERα agonist). We found that E₂ and PPT induced greater aortic relaxation in female mice than in male mice, indicating ERα mediation, which was further validated by using ERα antagonism. Treatment with 1,3-bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy)phenol]-1H-pyrazole dihydrochloride (MPP dihydrochloride; ERα antagonist) attenuated PPT-mediated vessel relaxation in both sexes. ERα-mediated vessel relaxation was further validated by the absence of significant PPT-mediated relaxation in aortas isolated from ERα knockout mice. Treatment with a specific ERK inhibitor, PD-98059, reduced E₂-induced vessel relaxation in both sexes but to a lesser extent in female mice. Furthermore, PD-98059 prevented PPT-induced vessel relaxation in both sexes. Both E₂ and PPT treatment activated ERK as early as 5-10 min, which was attenuated by PD-98059 in aortic tissue, cultured primary vascular smooth muscle cells (VSMCs), and endothelial cells (ECs). Aortic rings denuded of endothelium showed no differences in vessel relaxation after E₂ or PPT treatment, implicating a role of ECs in the observed sex differences. Here, our results are unique to show estrogen-stimulated rapid ERα signaling mediated by ERK activation in aortic tissue, as well as VSMCs and ECs in vitro, in regulating vascular function by using side-by-side comparisons in male and ovary-intact female mice in response to E₂ or PPT. NEW & NOTEWORTHY Here, we assessed the estrogen receptor-α dependency of estrogenic effects in vasorelaxation of both male and ovary-intact female mice by performing side-by-side comparisons. Also, we describe the connection between estrogen-stimulated rapid estrogen receptor-α signaling and downstream ERK activation in regulating vascular function in male and ovary-intact female mice.

Liuwei Dihuang soft capsules attenuates endothelial cell apoptosis to prevent atherosclerosis through GPR30-mediated regulation in ovariectomized ApoE-deficient mice

ETHNOPHARMACOLOGICAL RELEVANCE

Liuwei Dihuang (LWDH), a classical traditional Chinese medicine prescription, has been widely used to prevent and to treat various diseases with symptoms of 'Kidney-Yin' deficiency syndrome for over 1000 years in China. It is commonly used to treat functional decline associated with senile disease and menopausal syndrome, especially memory decline, insomnia, diabetes and osteoporosis. Modern experimental pharmacological studies indicated that the mechanism of LWDH treatment of menopausal syndrome may be associated with enhanced estrogenic effects. However, little attention has been paid to the potential impact of LWDH on atherosclerosis (AS) associated with female menopause. The aim of this study was to evaluate the preventive effects of LWDH intake on an animal model of female menopause AS and to explore the underlying molecular mechanism.

MATERIALS AND METHODS

ApoE^-/- mice were randomly divided into 4 groups, with C57BN/L6 mice as the control group. All ApoE^-/- mice were ovariectomized (Ovx) one week prior to oral administration and initiation of high-fat diet. C57BL/6 mice were given sham operation and maintained on normal diet. The three administered groups were given simvastatin (4mg/kg via i.g.) and LWDH (4.5, 9.0g/kg via i.g.) every day for 14 weeks. Atherosclerotic lesions in the aortic root were determined by oil red O staining and hematoxylin-eosin staining. α-Actin and CD68 in atherosclerotic lesions were detected by immunohistological assay. Serum lipids and homocysteine (Hcy) levels were measured in the 14th week. The cleaved caspase-3, C/EBP homologous protein (CHOP) and G protein coupled estrogen receptor 30 (GPR30) expressions in the aortic arch endothelium were determined by immunohistochemistry and Western blot. The inhibitory effect of LWDH-medicated (20%, 12h) on Hcy (20%, 24h)-induced apoptosis of human umbilical vein endothelial cells (HUVECs) was examined by flow cytometry and Hoechst 33258 staining. Intracellular ROS production, nitric oxide release, and endothelial NO synthase (eNOS) activity were measured with or without LWDH-medicated serum pretreatment. In addition, CHOP, glucose-regulated protein GPR30, 78 (Grp78), Bcl-2, Bax and cleaved caspase-3 were analyzed by Western blot. Finally, the influence of G15, a specific antagonist of GPR30, on the protective effect of LWDH on endothelial cells was investigated.

RESULTS

In vivo administration of LWDH prevented plaque formation and reduced plasma lipid and Hcy levels. LWDH inhibited CHOP and cleaved caspase-3 expression in vivo and in vitro while maintaining GPR30 expression. In vitro study showed that Hcy-induced HUVECs apoptosis was weakened by LWDH-medicated serum pretreatment. Treatment with LWDH-medicated serum significantly upregulated NO release and eNOS activity in HUVECs. In addition, LWDH-medicated serum treatment optimized the balance between Bax and Bcl-2, and attenuated intracellular ROS production. G15 reversed the protective effect of LWDH on endothelial cells and the changes of apoptosis-related proteins.

CONCLUSIONS

LWDH treatment can significantly reduce plaque formation in an animal model of menopausal AS. The mechanism may be inhibition of Hcy-induced endothelial cell apoptosis by modulating GPR30. Hence, LWDH can potentially be used to prevent AS-related vascular disease in menopausal women.

GPER-novel membrane oestrogen receptor

The recent discovery of the G protein-coupled oestrogen receptor (GPER) presents new challenges and opportunities for understanding the physiology, pathophysiology and pharmacology of many diseases. This review will focus on the expression and function of GPER in hypertension, kidney disease, atherosclerosis, vascular remodelling, heart failure, reproduction, metabolic disorders, cancer, environmental health and menopause. Furthermore, this review will highlight the potential of GPER as a therapeutic target.

Activation of GPER ameliorates experimental pulmonary hypertension in male rats

RATIONALE

Pulmonary hypertension (PH) is characterized by pulmonary vascular remodeling that leads to pulmonary congestion, uncompensated right-ventricle (RV) failure, and premature death. Preclinical studies have demonstrated that the G protein-coupled estrogen receptor (GPER) is cardioprotective in male rats and that its activation elicits vascular relaxation in rats of either sex.

OBJECTIVES

To study the effects of GPER on the cardiopulmonary system by the administration of its selective agonist G1 in male rats with monocrotaline (MCT)-induced PH.

METHODS

Rats received a single intraperitoneal injection of MCT (60mg/kg) for PH induction. Experimental groups were as follows: control, MCT+vehicle, and MCT+G1 (400μg/kg/daysubcutaneous). Animals (n=5pergroup) were treated with vehicle or G1 for 14days after disease onset.

MEASUREMENTS AND MAIN RESULTS

Activation of GPER attenuated exercise intolerance and reduced RV overload in PH rats. Rats with PH exhibited echocardiographic alterations, such as reduced pulmonary flow, RV hypertrophy, and left-ventricle dysfunction, by the end of protocol. G1 treatment reversed these PH-related abnormalities of cardiopulmonary function and structure, in part by promoting pulmonary endothelial nitric oxide synthesis, Ca²⁺ handling regulation and reduction of inflammation in cardiomyocytes, and a decrease of collagen deposition by acting in pulmonary and cardiac fibroblasts.

CONCLUSIONS

G1 was effective to reverse PH-induced RV dysfunction and exercise intolerance in male rats, a finding that have important implications for ongoing clinical evaluation of new cardioprotective and vasodilator drugs for the treatment of the disease.

GPER (GPR30): A Nongenomic Receptor (GPCR) for Steroid Hormones with Implications for Cardiovascular Disease and Cancer

Although the rapid effects of steroids, such as estrogen and aldosterone, were postulated originally to be nongenomic, it is now appreciated that activation of such signaling pathways via a steroid-acting G protein-coupled receptor, the G protein estrogen receptor (GPER), has important transcription-dependent outcomes in the regulation of cell growth and programmed cell death secondary to GPER-regulated second-messenger pathways. GPER is expressed ubiquitously and has diverse biological effects, including regulation of endocrine, immune, neuronal, and cardiovascular functions. Perhaps the most biologically important consequences of GPER activation are the regulation of cell growth, migration, and apoptotic cell death. These cell growth regulatory effects, important in cancer biology, are also relevant in the regulation of cardiac and vascular hypertrophy and in the response to ischemia. This review provides a summary of relevant findings of the impact of GPER regulation by either estradiol or aldosterone in in vitro model systems and extends those findings to in vivo studies of direct clinical relevance for development of GPER-directed agents for treatment of cancer and cardiovascular diseases associated with cellular proliferation.

GPER is required for the age-dependent upregulation of the myocardial endothelin system

AIMS

Cardiac aging is associated with progressive structural changes and functional impairment, such as left ventricular hypertrophy, fibrosis and diastolic dysfunction. Aging also increases myocardial activity of endothelin-1 (ET-1), a multifunctional peptide with growth-promoting and pro-fibrotic activity. Because the G protein-coupled estrogen receptor (GPER) regulates vascular responsiveness to ET-1, we investigated whether GPER also plays a role in the regulation of the myocardial endothelin system with aging.

MAIN METHODS

Young (4month-old) and aged (24month-old) wild-type and Gper-deficient (Gper(-/-)) mice were studied. Gene expression levels of prepro-ET-1, endothelin converting enzymes ECE-1 and ECE-2, and endothelin ETA and ETB receptors were determined by qPCR in left ventricular myocardium.

KEY FINDINGS

Aging markedly increased steady-state mRNA expression levels of ECE-1, ECE-2, ETA and ETB receptors (each p<0.001 vs. young mice). Deletion of Gper inhibited the age-dependent increase in ECE-2 and ETB receptor mRNA levels (57% and 40% reduction, respectively, each p<0.01 vs. wild-type mice), whereas gene expression of prepro-ET-1, ECE-1, and the ETA receptor was unaffected in Gper(-/-) mice.

SIGNIFICANCE

We identified a novel regulatory mechanism through which the endogenous Gper facilitates the age-dependent increase in myocardial expression of ECE-2 and the ETB receptor, which is compatible with an activating role of GPER for the local endothelin system with aging. Targeting GPER signaling by selective antagonists may therefore be considered a new therapeutic approach to reduce age-dependent increased ET-1 activity and the associated development of left ventricular hypertrophy, fibrosis and heart failure.

GPR30 decreases with vascular aging and promotes vascular smooth muscle cells maintaining differentiated phenotype and suppressing migration via activation of ERK1/2

Estrogen receptors, including classic nuclear receptors ERα, ERβ, and membrane receptor GPR30, are expressed in vascular tissues and exert protective actions in vascular diseases. But the expression pattern and functional roles of GPR30 in vascular smooth muscle cells (VSMCs) remain unclear. In this study, we found that ERα, ERβ, and GPR30 were decreased with VSMCs passaging in vitro or growing in vivo and activation of GPR30 promoted ERα expression. Then, we validated that activation of GPR30 significantly decreased migratory capability of VSMCs and suppressed ERα, whereas PDGF-BB (20 ng/mL) treatment caused increase of migration. And activation of GPR30 led to reduction of osteopontin and cellular retinol binding protein 1, enhancement of calponin and 3F8, and upregulation of total and phosphorylated ERK1/2 expression in VSMCs knocked down by GPR30, ERα, and ERβ or treated with PDGF-BB. These data suggest that GPR30 promotes VSMCs reducing migration and maintaining differentiated phenotype via activation of ERK1/2 pathway. Our findings provide novel mechanisms of GPR30 protection of VSMCs as well as a new target for prevention of vascular aging.

Heart Disease in Women: Unappreciated Challenges, GPER as a New Target

Heart disease in women remains underappreciated, underdiagnosed and undertreated. Further, although we are starting to understand some of the social and behavioral determinants for this, the biological basis for the increased rate of rise in atherosclerosis risk in women after menopause remains very poorly understand. In this review we will outline the scope of the clinical issues related to heart disease in women, the emerging findings regarding the biological basis underlying the increased prevalence of atherosclerotic risk factors in postmenopausal women (vs. men) and the role of the G protein-coupled estrogen receptor (GPER) and its genetic regulation as a determinant of these sex-specific risks. GPER is a recently appreciated GPCR that mediates the rapid effects of estrogen and aldosterone. Recent studies have identified that GPER activation regulates both blood pressure. We have shown that regulation of GPER function via expression of a hypofunctional GPER genetic variant is an important determinant of blood pressure and risk of hypertension in women. Further, our most recent studies have identified that GPER activation is an important regulator of low density lipoprotein (LDL) receptor metabolism and that expression of the hypofunctional GPER genetic variant is an important contributor to the development of hypercholesterolemia in women. GPER appears to be an important determinant of the two major risk factors for coronary artery disease-blood pressure and LDL cholesterol. Further, the importance of this mechanism appears to be greater in women. Thus, the appreciation of the role of GPER function as a determinant of the progression of atherosclerotic disease may be important both in our understanding of cardiometabolic function but also in opening the way to greater appreciation of the sex-specific regulation of atherosclerotic risk factors.

Estrogen Replacement Reduces Oxidative Stress in the Rostral Ventrolateral Medulla of Ovariectomized Rats

Cardiovascular disease prevalence rises rapidly after menopause, which is believed to be derived from the loss of estrogen. It is reported that sympathetic tone is increased in postmenopause. The high level of oxidative stress in the rostral ventrolateral medulla (RVLM) contributes to increased sympathetic outflow. The focus of this study was to determine if estrogen replacement reduces oxidative stress in the RVLM and sympathetic outflow in the ovariectomized (OVX) rats. The data of this study showed that OVX rat increased oxidative stress in the RVLM and sympathetic tone; estrogen replacement improved cardiovascular functions but also reduced the level of oxidative stress in the RVLM. These findings suggest that estrogen replacement decreases blood pressure and sympathoexcitation in the OVX rats, which may be associated with suppression in oxidative stress in the RVLM through downregulation of protein expression of NADPHase (NOX4) and upregulation of protein expression of SOD1. The data from this study is beneficial for our understanding of the mechanism of estrogen exerting cardiovascular protective effects on postmenopause.

Adaptive increases in expression and vasodilator activity of estrogen receptor subtypes in a blood vessel-specific pattern during pregnancy

Normal pregnancy is associated with adaptive hemodynamic, hormonal, and vascular changes, and estrogen (E2) may promote vasodilation during pregnancy; however, the specific E2 receptor (ER) subtype, post-ER signaling mechanism, and vascular bed involved are unclear. We tested whether pregnancy-associated vascular adaptations involve changes in the expression/distribution/activity of distinct ER subtypes in a blood vessel-specific manner. Blood pressure (BP) and plasma E2 were measured in virgin and pregnant (day 19) rats, and the thoracic aorta, carotid artery, mesenteric artery, and renal artery were isolated for measurements of ERα, ERβ, and G protein-coupled receptor 30 [G protein-coupled ER (GPER)] expression and tissue distribution in parallel with relaxation responses to E2 (all ERs) and the specific ER agonist 4,4',4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl)-tris-phenol (PPT; ERα), diarylpropionitrile (DPN; ERβ), and G1 (GPER). BP was slightly lower and plasma E2 was higher in pregnant versus virgin rats. Western blots revealed increased ERα and ERβ in the aorta and mesenteric artery and GPER in the aorta of pregnant versus virgin rats. Immunohistochemistry revealed that the increases in ERs were mainly in the intima and media. In phenylephrine-precontracted vessels, E2 and PPT caused relaxation that was greater in the aorta and mesenteric artery but similar in the carotid and renal artery of pregnant versus virgin rats. DPN- and G1-induced relaxation was greater in the mesenteric and renal artery than in the aorta and carotid artery, and aortic relaxation to G1 was greater in pregnant versus virgin rats. The nitric oxide synthase inhibitor N(ω)-nitro-l-arginine methyl ester with or without the cyclooxygenase inhibitor indomethacin with or without the EDHF blocker tetraethylammonium or endothelium removal reduced E2, PPT, and G1-induced relaxation in the aorta of pregnant rats, suggesting an endothelium-dependent mechanism, but did not affect E2-, PPT-, DPN-, or G1-induced relaxation in other vessels, suggesting endothelium-independent mechanisms. E2, PPT, DPN, and G1 caused relaxation of Ca(2+) entry-dependent KCl contraction, and the effect of PPT was greater in the mesenteric artery of pregnant versus virgin rats. Thus, during pregnancy, an increase in ERα expression in endothelial and vascular smooth muscle layers of the aorta and mesenteric artery is associated with increased ERα-mediated relaxation via endothelium-derived vasodilators and inhibition of Ca(2+) entry into vascular smooth muscle, supporting a role of aortic and mesenteric arterial ERα in pregnancy-associated vasodilation. GPER may contribute to aortic relaxation while enhanced ERβ expression could mediate other genomic vascular effects during pregnancy.

What have we learned about GPER function in physiology and disease from knockout mice?

Estrogens, predominantly 17β-estradiol, exert diverse effects throughout the body in both normal and pathophysiology, during development and in reproductive, metabolic, endocrine, cardiovascular, nervous, musculoskeletal and immune systems. Estrogen and its receptors also play important roles in carcinogenesis and therapy, particularly for breast cancer. In addition to the classical nuclear estrogen receptors (ERα and ERβ) that traditionally mediate predominantly genomic signaling, the G protein-coupled estrogen receptor GPER has become recognized as a critical mediator of rapid signaling in response to estrogen. Mouse models, and in particular knockout (KO) mice, represent an important approach to understand the functions of receptors in normal physiology and disease. Whereas ERα KO mice display multiple significant defects in reproduction and mammary gland development, ERβ KO phenotypes are more limited, and GPER KO exhibit no reproductive deficits. However, the study of GPER KO mice over the last six years has revealed that GPER deficiency results in multiple physiological alterations including obesity, cardiovascular dysfunction, insulin resistance and glucose intolerance. In addition, the lack of estrogen-mediated effects in numerous tissues of GPER KO mice, studied in vivo or ex vivo, including those of the cardiovascular, endocrine, nervous and immune systems, reveals GPER as a genuine mediator of estrogen action. Importantly, GPER KO mice have also demonstrated roles for GPER in breast carcinogenesis and metastasis. In combination with the supporting effects of GPER-selective ligands and GPER knockdown approaches, GPER KO mice demonstrate the therapeutic potential of targeting GPER activity in diseases as diverse as obesity, diabetes, multiple sclerosis, hypertension, atherosclerosis, myocardial infarction, stroke and cancer.

Uterine artery dysfunction in pregnant ACE2 knockout mice is associated with placental hypoxia and reduced umbilical blood flow velocity

Angiotensin-converting enzyme 2 (ACE2) knockout is associated with reduced fetal weight at late gestation; however, whether uteroplacental vascular and/or hemodynamic disturbances underlie this growth-restricted phenotype is unknown. Uterine artery reactivity and flow velocities, umbilical flow velocities, trophoblast invasion, and placental hypoxia were determined in ACE2 knockout (KO) and C57Bl/6 wild-type (WT) mice at day 14 of gestation. Although systolic blood pressure was higher in pregnant ACE2 KO vs. WT mice (102.3 ± 5.1 vs. 85.1 ± 1.9 mmHg, n = 5-6), the magnitude of difference was similar to that observed in nonpregnant ACE2 KO vs. WT mice. Maternal urinary protein excretion, serum creatinine, and kidney or heart weights were not different in ACE2 KO vs. WT. Fetal weight and pup-to-placental weight ratio were lower in ACE2 KO vs. WT mice. A higher sensitivity to Ang II [pD2 8.64 ± 0.04 vs. 8.5 ± 0.03 (-log EC50)] and greater maximal contraction to phenylephrine (169.0 ± 9.0 vs. 139.0 ± 7.0% KMAX), were associated with lower immunostaining for Ang II receptor 2 and fibrinoid content of the uterine artery in ACE2 KO mice. Uterine artery flow velocities and trophoblast invasion were similar between study groups. In contrast, umbilical artery peak systolic velocities (60.2 ± 4.5 vs. 75.1 ± 4.5 mm/s) and the resistance index measured using VEVO 2100 ultrasound were lower in the ACE2 KO vs. WT mice. Immunostaining for pimonidazole, a marker of hypoxia, and hypoxia-inducible factor-2α were higher in the trophospongium and placental labyrinth of the ACE2 KO vs. WT. In summary, placental hypoxia and uterine artery dysfunction develop before major growth of the fetus occurs and may explain the fetal growth restricted phenotype.

Diabetes impairs the vascular effects of aldosterone mediated by G protein-coupled estrogen receptor activation

Aldosterone promotes non-genomic effects in endothelial and vascular smooth muscle cells via activation of mineralocorticoid receptors (MR) and G protein-coupled estrogen receptors (GPER). GPER activation is associated with beneficial/protective effects in the vasculature. Considering that vascular dysfunction plays a major role in diabetes-associated complications, we hypothesized that the beneficial effects mediated by vascular GPER activation, in response to aldosterone, are decreased in diabetes. Mesenteric resistance arteries from female, 14-16 weeks-old, control and diabetic (db/db) mice were used. Phenylephrine (PhE)-induced contractions were greater in arteries from db/db vs. control mice. Aldosterone (10 nM) increased maximal contractile responses to PhE in arteries from control mice, an effect elicited via activation of GPER. Although aldosterone did not increase PhE responses in arteries from db/db mice, blockade of GPER, and MR decreased PhE-induced contractile responses in db/db mesenteric arteries. Aldosterone also reduced the potency of acetylcholine (ACh)-induced relaxation in arteries from both control and db/db mice via MR-dependent mechanisms. GPER antagonism further decreased ACh-induced relaxation in the control group, but did not affect ACh responses in the diabetic group. Aldosterone increased extracellular signal-regulated kinase 1/2 phosphorylation in arteries from control and db/db mice by a GPER-dependent mechanism. GPER, but not MR, gene, and protein expression, determined by RT-PCR and immunoblotting/immunofluorescence assays, respectively, were increased in arteries from db/db mice vs. control arteries. These findings indicate that aldosterone activates both vascular MR and GPER and that the beneficial effects of GPER activation are decreased in arteries from diabetic animals. Our results further elucidate the mechanisms by which aldosterone influences vascular function and contributes to vascular dysfunction in diabetes. Financial Support: FAPESP, CNPq, and CAPES, Brazil.

GPER-independent effects of estrogen in rat aortic vascular endothelial cells

GPER (aka GPR30) has been identified as an important mechanism by which estrogen mediates its effects. Previous studies from our laboratories and those of others have demonstrated that GPER activation mediates a range of vascular contractile and growth regulatory responses. However, the importance of GPER in mediating the actions of estradiol (E2) in rat aortic endothelial cells is unclear. Therefore, we sought to determine the importance of GPER vs. the "classical" estrogen receptor (ER) in mediating the endothelial growth regulatory effects of E2. To do this we assessed the effect of E2 in regulating phosphoERK content and apoptotic rates in rat aortic endothelial cells and the role of GPER in mediating these effects. E2 mediated a concentration-dependent inhibition of both ERK phosphorylation and serum deprivation-induced apoptosis with a maximal effect at a concentration of 10 nM. Pretreatment with the ER antagonist ICI 182780 abolished E2-mediated inhibition of both ERK phosphorylation and apoptosis. In contrast, pretreatment with GPER antagonist G15 had no significant effect on E2-mediated inhibition of ERK phosphorylation or on apoptosis. Further, downregulation of GPER expression with a GPER shRNA adenovirus did not block E2-mediated inhibitory effects on ERK phosphorylation and apoptosis. In fact, these inhibitory effects of E2 were further enhanced by GPER downregulation. Downregulation of ERα expression reversed the E2-mediated inhibitory effects to stimulatory effects. E2's phosphoERK and apoptosis stimulatory effects seen with ERα downregulation are attenuated by pretreatment with G15. In conclusion, in rat aortic endothelial cells, E2-mediated endothelial effects are predominantly driven by ER and not by GPER.

Estrogen receptor subtypes mediate distinct microvascular dilation and reduction in [Ca2+]I in mesenteric microvessels of female rat

Estrogen interacts with estrogen receptors (ERs) to induce vasodilation, but the ER subtype and post-ER relaxation pathways are unclear. We tested if ER subtypes mediate distinct vasodilator and intracellular free Ca(2+) concentration ([Ca(2+)]i) responses via specific relaxation pathways in the endothelium and vascular smooth muscle (VSM). Pressurized mesenteric microvessels from female Sprague-Dawley rats were loaded with fura-2, and the changes in diameter and [Ca(2+)]i in response to 17β-estradiol (E2) (all ERs), PPT (4,4',4''-[4-propyl-(1H)-pyrazole-1,3,5-triyl]-tris-phenol) (ERα), diarylpropionitrile (DPN) (ERβ), and G1 [(±)-1-[(3aR*,4S*,9bS*)-4-(6-bromo-1,3-benzodioxol-5-yl)-3a,4,5,9b-tetrahydro:3H-cyclopenta(c)quinolin-8-yl]-ethanon] (GPR30) were measured. In microvessels preconstricted with phenylephrine, ER agonists caused relaxation and decrease in [Ca(2+)]i that were with E2 = PPT > DPN > G1, suggesting that E2-induced vasodilation involves ERα > ERβ > GPR30. Acetylcholine caused vasodilation and decreased [Ca(2+)]i, which were abolished by endothelium removal or treatment with the nitric oxide synthase blocker Nω-nitro-l-arginine methyl ester (L-NAME) and the K(+) channel blockers tetraethylammonium (nonspecific) or apamin (small conductance Ca(2+)-activated K(+) channel) plus TRAM-34 (1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole) (intermediate conductance Ca(2+)-activated K(+) channel), suggesting endothelium-derived hyperpolarizing factor-dependent activation of KCa channels. E2-, PPT-, DPN-, and G1-induced vasodilation and decreased [Ca(2+)]i were not blocked by L-NAME, TEA, apamin plus TRAM-34, iberiotoxin (large conductance Ca(2+)- and voltage-activated K(+) channel), 4-aminopyridine (voltage-dependent K(+) channel), glibenclamide (ATP-sensitive K(+) channel), or endothelium removal, suggesting an endothelium- and K(+) channel-independent mechanism. In endothelium-denuded vessels preconstricted with phenylephrine, high KCl, or the Ca(2+) channel activator Bay K 8644 (1,4-dihydro-2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)phenyl]-3-pyridinecarboxylic acid methyl ester), ER agonist-induced relaxation and decreased [Ca(2+)]i were with E2 = PPT > DPN > G1 and not inhibited by the guanylate cyclase inhibitor ODQ [1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one], and showed a similar relationship between decreased [Ca(2+)]i and vasorelaxation, supporting direct effects on Ca(2+) entry in VSM. Immunohistochemistry revealed ERα, ERβ, and GPR30 mainly in the vessel media and VSM. Thus, in mesenteric microvessels, ER subtypes mediate distinct vasodilation and decreased [Ca(2+)]i (ERα > ERβ > GPR30) through endothelium- and K(+) channel-independent inhibition of Ca(2+) entry mechanisms of VSM contraction.

Membrane estrogen receptors: their role in blood pressure regulation and cardiovascular disease

Hypertension (HTN) is a leading risk factor for cardiovascular disease (CVD) and continues to affect millions of people in industrialized nations. The increasing prevalence of HTN is closely related to the growing prevalence of obesity. Despite heightened awareness of the disease, a significant percentage of patients are uncontrolled and are at higher risk of heart failure, stroke, and chronic kidney disease. Evidence of the cardiovascular protective role of estrogen in pre-menopausal females has brought attention to estrogen receptor activation as a treatment strategy for HTN. Estrogen promotes vasodilation and decreases inflammation and atherosclerosis. It also controls blood pressure via modulation of the activity of the renin-angiotensin-aldosterone system. The effects of estrogen on the vasculature are partly mediated via membrane receptors. Membrane estrogen receptor α and G-protein-coupled GPER-1 have been studied extensively in the vasculature. This review will describe the available evidence supporting the role of estrogen membrane receptors in blood pressure control and CVD.

Estrogen biology: new insights into GPER function and clinical opportunities

Estrogens play an important role in the regulation of normal physiology, aging and many disease states. Although the nuclear estrogen receptors have classically been described to function as ligand-activated transcription factors mediating genomic effects in hormonally regulated tissues, more recent studies reveal that estrogens also mediate rapid signaling events traditionally associated with G protein-coupled receptors. The G protein-coupled estrogen receptor GPER (formerly GPR30) has now become recognized as a major mediator of estrogen's rapid cellular effects throughout the body. With the discovery of selective synthetic ligands for GPER, both agonists and antagonists, as well as the use of GPER knockout mice, significant advances have been made in our understanding of GPER function at the cellular, tissue and organismal levels. In many instances, the protective/beneficial effects of estrogen are mimicked by selective GPER agonism and are absent or reduced in GPER knockout mice, suggesting an essential or at least parallel role for GPER in the actions of estrogen. In this review, we will discuss recent advances and our current understanding of the role of GPER and the activity of clinically used drugs, such as SERMs and SERDs, in physiology and disease. We will also highlight novel opportunities for clinical development towards GPER-targeted therapeutics, for molecular imaging, as well as for theranostic approaches and personalized medicine.

Progress in solving the sex hormone paradox in pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a devastating and progressive disease with marked morbidity and mortality. Even though being female represents one of the most powerful risk factors for PAH, multiple questions about the underlying mechanisms remain, and two "estrogen paradoxes" in PAH exist. First, it is puzzling why estrogens have been found to be protective in various animal models of PAH, whereas PAH registries uniformly demonstrate a female susceptibility to the disease. Second, despite the pronounced tendency for the disease to develop in women, female PAH patients exhibit better survival than men. Recent mechanistic studies in classical and in novel animal models of PAH, as well as recent studies in PAH patients, have significantly advanced the field. In particular, it is now accepted that estrogen metabolism and receptor signaling, as well as estrogen interactions with key pathways in PAH development, appear to be potent disease modifiers. A better understanding of these interactions may lead to novel PAH therapies. It is the purpose of this review to 1) review sex hormone synthesis, metabolism, and receptor physiology; 2) assess the context in which sex hormones affect PAH pathogenesis; 3) provide a potential explanation for the observed estrogen paradoxes and gender differences in PAH; and 4) identify knowledge gaps and future research opportunities. Because the majority of published studies investigated 17β-estradiol and/or its metabolites, this review will primarily focus on pulmonary vascular and right ventricular effects of estrogens. Data for other sex hormones will be discussed very briefly.

Vasodilation by GPER in mesenteric arteries involves both endothelial nitric oxide and smooth muscle cAMP signaling

Our previous work showed that chronic activation of the membrane-bound estrogen receptor GPR30/GPER significantly lowers blood pressure in ovariectomized hypertensive mRen2.Lewis female rats which may, in part, reflect direct vasodilatory actions. The current study assessed the hypothesis that cyclic adenosine monophosphate (cAMP) signaling contributes to GPER-mediated vasorelaxation. In mesenteric resistance arteries from intact Lewis females, relaxation to 17-β-estradiol (E2; 47±3% of phenylephrine contraction vs. vehicle 89±2%, P<0.001) or G-1 (44±8%, P<0.001) was blunted to a similar extent by denuding (P<0.001) or the nitric oxide synthase inhibitor l-NAME (P<0.001). In contrast, the cyclooxygenase inhibitor indomethacin did not alter vasodilation (P>0.05). The cAMP analog Rp-cAMPS partially attenuated vasodilation (65±7%, P<0.001), while the combination of l-NAME and Rp-cAMPS exhibited additive effects to effectively abolish vasorelaxation (P>0.05 vs. vehicle). Pretreatment of endothelium-intact vessels with the adenylyl cyclase inhibitor SQ (63±6%) or the guanylyl cyclase inhibitor ODQ (62±9%) both partially inhibited the response to G-1 (P<0.01), while pretreatment with the both inhibitors completely abolished vasorelaxation (P>0.05 vs. vehicle). In denuded vessels only SQ reduced the response (88±3%, P<0.001). Moreover, G-1 significantly increased intracellular cAMP levels in cultured mesenteric smooth muscle cells (P<0.05). We conclude that GPER-dependent vasorelaxation apparently involves both endothelial release of nitric oxide which activates guanylyl cyclase and smooth muscle cell activation of adenylyl cyclase. Downstream production of cyclic nucleotides and stimulation of protein kinases may phosphorylate proteins to promote vascular smooth muscle cell relaxation. The ability of GPER to initiate these signaling pathways may contribute to the beneficial vascular effects of estrogen.

Role of estrogen in diastolic dysfunction

The prevalence of left ventricular diastolic dysfunction (LVDD) sharply increases in women after menopause and may lead to heart failure. While evidence suggests that estrogens protect the premenopausal heart from hypertension and ventricular remodeling, the specific mechanisms involved remain elusive. Moreover, whether there is a protective role of estrogens against cardiovascular disease, and specifically LVDD, continues to be controversial. Clinical and basic science have implicated activation of the renin-angiotensin-aldosterone system (RAAS), linked to the loss of ovarian estrogens, in the pathogenesis of postmenopausal diastolic dysfunction. As a consequence of increased tissue ANG II and low estrogen, a maladaptive nitric oxide synthase (NOS) system produces ROS that contribute to female sex-specific hypertensive heart disease. Recent insights from rodent models that mimic the cardiac phenotype of an estrogen-insufficient or -deficient woman (e.g., premature ovarian failure or postmenopausal), including the ovariectomized congenic mRen2.Lewis female rat, provide evidence showing that estrogen modulates the tissue RAAS and NOS system and related intracellular signaling pathways, in part via the membrane G protein-coupled receptor 30 (GPR30; also called G protein-coupled estrogen receptor 1). Complementing the cardiovascular research in this field, the echocardiographic correlates of LVDD as well as inherent limitations to its use in preclinical rodent studies will be briefly presented. Understanding the roles of estrogen and GPR30, their interactions with the local RAAS and NOS system, and the relationship of each of these to LVDD is necessary to identify new therapeutic targets and alternative treatments for diastolic heart failure that achieve the cardiovascular benefits of estrogen replacement without its side effects and contraindications.

Mechanisms of estrogen effects on the endothelium: an overview

In this review, we aim to provide an overview of the recent advances in understanding estrogen effects on the vascular endothelium. Epidemiological studies suggest the female sex hormone estrogen mediates the relative protection of premenopausal women against cardiovascular disease, compared with age-matched men. However, results from clinical trials of exogenous estrogen supplementation in postmenopausal women have been disappointing, generating much controversy about the role of estrogen and demonstrating the need for further research in this field. Here we have discussed the roles of different estrogen receptors (ERs) such as ERα, ERβ, and G-protein coupled receptor 30; the complex genomic and nongenomic signalling pathways downstream to ER activation and the factors such as age, menopause, pregnancy, and diabetes that might alter estrogen responses. The common themes of this discussion are the complexity and diversity of endothelial estrogen responses and their modulation by 1 or more coexisting factors. Finally, we summarize the emerging therapeutic options including improved targeting of individual ERs and signalling pathways that might maximize the therapeutic potential of estrogenic compounds while minimizing their harmful side effects.