Activation of GPER Induces Differentiation and Inhibition of Coronary Artery Smooth Muscle Cell Proliferation. PLoS One. 2013;8:e64771. [PMID: 23840305 PMCID: PMC3686788 DOI: 10.1371/journal.pone.0064771]

The G protein-coupled oestrogen receptor GPER in health and disease: an update

Oestrogens and their receptors contribute broadly to physiology and diseases. In premenopausal women, endogenous oestrogens protect against cardiovascular, metabolic and neurological diseases and are involved in hormone-sensitive cancers such as breast cancer. Oestrogens and oestrogen mimetics mediate their effects via the cytosolic and nuclear receptors oestrogen receptor-α (ERα) and oestrogen receptor-β (ERβ) and membrane subpopulations as well as the 7-transmembrane G protein-coupled oestrogen receptor (GPER). GPER, which dates back more than 450 million years in evolution, mediates both rapid signalling and transcriptional regulation. Oestrogen mimetics (such as phytooestrogens and xenooestrogens including endocrine disruptors) and licensed drugs such as selective oestrogen receptor modulators (SERMs) and downregulators (SERDs) also modulate oestrogen receptor activity in both health and disease. Following up on our previous Review of 2011, we herein summarize the progress made in the field of GPER research over the past decade. We will review molecular, cellular and pharmacological aspects of GPER signalling and function, its contribution to physiology, health and disease, and the potential of GPER to serve as a therapeutic target and prognostic indicator of numerous diseases. We also discuss the first clinical trial evaluating a GPER-selective drug and the opportunity of repurposing licensed drugs for the targeting of GPER in clinical medicine.

G Protein-Coupled Estrogen Receptor GPER: Molecular Pharmacology and Therapeutic Applications

The actions of estrogens and related estrogenic molecules are complex and multifaceted in both sexes. A wide array of natural, synthetic, and therapeutic molecules target pathways that produce and respond to estrogens. Multiple receptors promulgate these responses, including the classical estrogen receptors of the nuclear hormone receptor family (estrogen receptors α and β), which function largely as ligand-activated transcription factors, and the 7-transmembrane G protein-coupled estrogen receptor, GPER, which activates a diverse array of signaling pathways. The pharmacology and functional roles of GPER in physiology and disease reveal important roles in responses to both natural and synthetic estrogenic compounds in numerous physiological systems. These functions have implications in the treatment of myriad disease states, including cancer, cardiovascular diseases, and metabolic disorders. This review focuses on the complex pharmacology of GPER and summarizes major physiological functions of GPER and the therapeutic implications and ongoing applications of GPER-targeted compounds.

The emerging role of estrogen's non-nuclear signaling in the cardiovascular disease

Sexual dimorphism exists in the epidemiology of cardiovascular disease (CVD), which indicates the involvement of sexual hormones in the pathophysiology of CVD. In particular, ample evidence has demonstrated estrogen's protective effect on the cardiovascular system. While estrogen receptors, bound to estrogen, act as a transcription factor which regulates gene expressions by binding to the specific DNA sequence, a subpopulation of estrogen receptors localized at the plasma membrane induces activation of intracellular signaling, called "non-nuclear signaling" or "membrane-initiated steroid signaling of estrogen". Although the precise molecular mechanism of non-nuclear signaling as well as its physiological impact was unclear for a long time, recent development of genetically modified animal models and pathway-selective estrogen receptor stimulant bring new insights into this pathway. We review the published experimental studies on non-nuclear signaling of estrogen, and summarize its role in cardiovascular system, especially focusing on: (1) the molecular mechanism of non-nuclear signaling; (2) the design of genetically modified animals and pathway-selective stimulant of estrogen receptor.

Correlation of functional and radioligand binding characteristics of GPER ligands confirming aldosterone as a GPER agonist

Aldosterone exerts some of its effects not by binding to mineralocorticoid receptors, but rather by acting via G protein-coupled estrogen receptors (GPER). To determine if aldosterone binds directly to GPER, we studied the ability of aldosterone to compete for the binding of [3 H] 2-methoxyestradiol ([3 H] 2-ME), a high potency GPER-selective agonist. We used GPER gene transfer to engineer Sf9-cultured insect cells to express GPER. We chose insect cells to avoid interactions with any intrinsic mammalian receptors for aldosterone. [3 H] 2-ME binding was saturable and reversible to a high-affinity population of receptors with Kd  = 3.7 nM and Bmax  = 2.2 pmol/mg. Consistent with agonist binding to G Protein-coupled receptors, [3 H] 2-ME high-affinity state binding was reduced in the presence of the hydrolysis-resistant GTP analog, GppNHp. [3 H] 2-ME binding was competed for by the GPER agonist G1, the GPER antagonist G15, estradiol (E2), as well as aldosterone (Aldo). The order of potency for competing for [3 H] 2-ME binding, namely 2ME > Aldo > E2 ≥ G1, paralleled the orders of potency for inhibition of cell proliferation and inhibition of ERK phosphorylation by ligands acting at GPER. These data confirm the ability of aldosterone to interact with the GPER, consistent with the interpretation that aldosterone likely mediates its GPER-dependent effects by direct binding to the GPER. SIGNIFICANCE STATEMENT: Despite the growing evidence for aldosterone's actions via G protein-coupled estrogen receptors (GPER), there remains significant skepticism that aldosterone can directly interact with GPER. The current studies are the first to demonstrate directly that aldosterone indeed is capable of binding to the GPER and thus likely mediates its GPER-dependent effects by direct binding to the receptor.

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.

GPR30 knockdown weakens the capacity of CAF in promoting prostate cancer cell invasion via reducing macrophage infiltration and M2 polarization

Cancer-associated fibroblasts (CAFs) can promote the development and metastasis of prostate cancer partly by mediating tumor-associated inflammation. An increasing amount of studies have focused on the functional interactions between CAFs and immune cells in the tumor microenvironment (TME). We previously reported that G protein-coupled receptor 30 (GPR30) was highly expressed in prostate CAFs and plays a crucial role in prostate stromal cell activation. However, the effect and underlying mechanism of GPR30 expression in prostate CAFs affecting the interaction between CAFs and tumor-associated macrophages (TAMs) need further elucidation. Here, we found that, compared with CAF-shControl, CAF-shGPR30 inhibited macrophage migration through transwell migration assays, which should be attributed to the decreased expression of C-X-C motif chemokine ligand 12 (CXCL12). In addition, macrophages treated with a culture medium of CAF-shGPR30 exhibited attenuated M2 polarization with downregulated M2-like markers expression. Moreover, macrophages stimulated with a culture medium of CAF-shGPR30 were less efficient in promoting activation of fibroblast cells and invasion of PCa cells. Finally, cocultured CAF-shGPR30 and macrophages suppressed PCa cell invasion compared to cocultured CAF-shControl and macrophages by decreasing interleukin-6 (IL-6) secretion, and this effect could be abrogated with rescue expression of IL-6. Our results pinpoint the function of GPR30 in prostate CAFs on regulating the CAF-TAM interaction in the TME and provide new insights into PCa therapies via regulating TME.

Signalling mechanisms in the cardiovascular protective effects of estrogen: With a focus on rapid/membrane signalling

In modern society, cardiovascular disease remains the biggest single threat to life, being responsible for approximately one third of worldwide deaths. Male prevalence is significantly higher than that of women until after menopause, when the prevalence of CVD increases in females until it eventually exceeds that of men. Because of the coincidence of CVD prevalence increasing after menopause, the role of estrogen in the cardiovascular system has been intensively researched during the past two decades in vitro, in vivo and in observational studies. Most of these studies suggested that endogenous estrogen confers cardiovascular protective and anti-inflammatory effects. However, clinical studies of the cardioprotective effects of hormone replacement therapies (HRT) not only failed to produce proof of protective effects, but also revealed the potential harm estrogen could cause. The "critical window of hormone therapy" hypothesis affirms that the moment of its administration is essential for positive treatment outcomes, pre-menopause (3-5 years before menopause) and immediately post menopause being thought to be the most appropriate time for intervention. Since many of the cardioprotective effects of estrogen signaling are mediated by effects on the vasculature, this review aims to discuss the effects of estrogen on vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) with a focus on the role of estrogen receptors (ERα, ERβ and GPER) in triggering the more recently discovered rapid, or membrane delimited (non-genomic), signaling cascades that are vital for regulating vascular tone, preventing hypertension and other cardiovascular diseases.

The Role of Estrogen Receptors in Cardiovascular Disease

Cardiovascular Diseases (CVDs) are the leading cause of death globally. More than 17 million people die worldwide from CVD per year. There is considerable evidence suggesting that estrogen modulates cardiovascular physiology and function in both health and disease, and that it could potentially serve as a cardioprotective agent. The effects of estrogen on cardiovascular function are mediated by nuclear and membrane estrogen receptors (ERs), including estrogen receptor alpha (ERα), estrogen receptor beta (ERβ), and G-protein-coupled ER (GPR30 or GPER). Receptor binding in turn confers pleiotropic effects through both genomic and non-genomic signaling to maintain cardiovascular homeostasis. Each ER has been implicated in multiple pre-clinical cardiovascular disease models. This review will discuss current reports on the underlying molecular mechanisms of the ERs in regulating vascular pathology, with a special emphasis on hypertension, pulmonary hypertension, and atherosclerosis, as well as in regulating cardiac pathology, with a particular emphasis on ischemia/reperfusion injury, heart failure with reduced ejection fraction, and heart failure with preserved ejection fraction.

Non-genomic Effects of Estrogen on Cell Homeostasis and Remodeling With Special Focus on Cardiac Ischemia/Reperfusion Injury

This review takes into consideration the main mechanisms involved in cellular remodeling following an ischemic injury, with special focus on the possible role played by non-genomic estrogen effects. Sex differences have also been considered. In fact, cardiac ischemic events induce damage to different cellular components of the heart, such as cardiomyocytes, vascular cells, endothelial cells, and cardiac fibroblasts. The ability of the cardiovascular system to counteract an ischemic insult is orchestrated by these cell types and is carried out thanks to a number of complex molecular pathways, including genomic (slow) or non-genomic (fast) effects of estrogen. These pathways are probably responsible for differences observed between the two sexes. Literature suggests that male and female hearts, and, more in general, cardiovascular system cells, show significant differences in many parameters under both physiological and pathological conditions. In particular, many experimental studies dealing with sex differences in the cardiovascular system suggest a higher ability of females to respond to environmental insults in comparison with males. For instance, as cells from females are more effective in counteracting the ischemia/reperfusion injury if compared with males, a role for estrogen in this sex disparity has been hypothesized. However, the possible involvement of estrogen-dependent non-genomic effects on the cardiovascular system is still under debate. Further experimental studies, including sex-specific studies, are needed in order to shed further light on this matter.

The activation of G protein-coupled estrogen receptor induces relaxation via cAMP as well as potentiates contraction via EGFR transactivation in porcine coronary arteries

Estrogen exerts protective effects against cardiovascular diseases in premenopausal women, but is associated with an increased risk of both coronary heart disease and stroke in older postmenopausal women. Studies have shown that activation of the G-protein-coupled estrogen receptor 1 (GPER) can cause either relaxation or contraction of arteries. It is highly likely that these dual actions of GPER may contribute to the seemingly paradoxical effects of estrogen in regulating coronary artery function. The objective of this study was to test the hypothesis that activation of GPER enhances agonist-stimulated porcine coronary artery contraction via epidermal growth factor receptor (EGFR) transactivation and its downstream extracellular signal-regulated kinases (ERK1/2) pathway. Isometric tension studies and western blot were performed to determine the effect of GPER activation on coronary artery contraction. Our findings demonstrated that G-1 caused concentration-dependent relaxation of ET-1-induced contraction, while pretreatment of arterial rings with G-1 significantly enhanced ET-1-induced contraction. GPER antagonist, G-36, significantly inhibited both the G-1-induced relaxation effect and G-1-enhanced ET-1 contraction. Gallein, a Gβγ inhibitor, significantly increased G-1-induced relaxation, yet inhibited G-1-enhanced ET-1-mediated contraction. Similarly, inhibition of EGFR with AG1478 or inhibition of Src with phosphatase 2 further increased G-1-induced relaxation responses in coronary arteries, but decreased G-1-enhanced ET-1-induced contraction. Western blot experiments in porcine coronary artery smooth muscle cells (PCASMC) showed that G-1 increased tyrosine phosphorylation of EGFR, which was inhibited by AG-1478. Furthermore, enzyme-linked immunosorbent assays showed that the level of heparin-binding EGF (HB-EGF) released by ET-1 treatment increased two-fold; whereas pre-incubation with G-1 further increased ET-1-induced HB-EGF release to four-fold over control conditions. Lastly, the role of ERK1/2 was determined by applying the MEK inhibitor, PD98059, in isometric tension studies and detecting phospho-ERK1/2 in immunoblotting. PD98059 potentiated G-1-induced relaxation response, but blocked G-1-enhanced ET-1-induced contraction. By western blot, G-1 treatment decreased phospho-ERK1/2, however, in the presence of the adenylyl cyclase inhibitor, SQ22536, G-1 significantly increased ERK1/2 phosphorylation in PCASMC. These data demonstrate that activation of GPER induces relaxation via cAMP as well as contraction via a mechanism involving transactivation of EGFR and the phosphorylation of ERK1/2 in porcine coronary arteries.

Sex differences in vascular physiology and pathophysiology: estrogen and androgen signaling in health and disease

Sex differences between women and men are often overlooked and underappreciated when studying the cardiovascular system. It has been long assumed that men and women are physiologically similar, and this notion has resulted in women being clinically evaluated and treated for cardiovascular pathophysiological complications as men. Currently, there is increased recognition of fundamental sex differences in cardiovascular function, anatomy, cell signaling, and pathophysiology. The National Institutes of Health have enacted guidelines expressly to gain knowledge about ways the sexes differ in both normal function and diseases at the various research levels (molecular, cellular, tissue, and organ system). Greater understanding of these sex differences will be used to steer future directions in the biomedical sciences and translational and clinical research. This review describes sex-based differences in the physiology and pathophysiology of the vasculature, with a special emphasis on sex steroid receptor (estrogen and androgen receptor) signaling and their potential impact on vascular function in health and diseases (e.g., atherosclerosis, hypertension, peripheral artery disease, abdominal aortic aneurysms, cerebral aneurysms, and stroke).

Inhibition of Endoplasmic Reticulum Stress Apoptosis by Estrogen Protects Human Umbilical Vein Endothelial Cells Through the PI3 Kinase-Akt Signaling Pathway

We aimed to investigate whether the cardioprotective effect of estrogen is mediated by inhibiting the apoptosis induced by endoplasmic reticulum stress (ERS) and to explore the underlying signaling pathway responsible for this effect. The effect of estrogen on ERS apoptosis, the mechanism responsible for that effect, and the ERS signaling pathways were examined in human umbilical vein endothelial cells (HUVECs) and measured using Western blot, Hoechst stains and caspase-3 activity assay. In vitro, 10^-8 mol/l estrogen directly inhibited the up-regulation of the ERS marker glucose-regulated protein 78 (GRP78) and ERS apoptosis marker C/EBP homologous protein (CHOP). ERS was induced using the ERS inducer tunicamycin (TM, 10 µmol/l) or dithiothreitol (DTT, 2 mmol/l) in HUVECs. Estrogen can also decrease the apoptosis cells mediated by ERS, based on the results of Hoechst stains. Protein expression in the three main ERS signaling pathways was upregulated in TM- or DTT-induced HUVEC ERS. Increases in p-PERK/PERK were the most obvious, and estrogen significantly inhibited the upregulation of p-PERK/PERK, p-IRE1/IRE1, and ATF6. These inhibitory effects were abolished by specific estrogen receptor antagonists (ICI182, 780, and G15) and inhibitors of the E₂ post-receptor signaling pathway, including phosphoinositide 3-kinase (PI3K) inhibitor LY294002, p38-mitogen activated protein kinase (p38-MAPK) inhibitor SB203580, c-Jun N-terminal kinase (JNK) inhibitor SP600125 and extracellular signal-regulated kinases1/2 (ERK1/2) inhibitor U0126; of these inhibitors, LY294002 was the most effective. Further experiments showed that when the PI3K pathway was blocked, the inhibitory effect of estrogen on ERS apoptosis was reduced. Estrogen can prevent HUVEC apoptosis by inhibiting the ERS apoptosis triggered by the PERK pathway, which may protect vascular endothelial cells and the cardiovascular system. The main mechanism responsible for ERS inhibition is the activation of the PI3K-Akt pathway for the activated estrogen receptor. J. Cell. Biochem. 118: 4568-4574, 2017. © 2017 Wiley Periodicals, Inc.

Cellular distribution and interaction between extended renin-angiotensin-aldosterone system pathways in atheroma

The importance of the renin-angiotensin-aldosterone system (RAAS) in the development of atherosclerotic has been experimentally documented. In fact, RAAS components have been shown to be locally expressed in the arterial wall and to be differentially regulated during atherosclerotic lesion progression. RAAS transcripts and proteins were shown to be differentially expressed and to interact in the 3 main cells of atheroma: endothelial cells, vascular smooth muscle cells, and macrophages. This review describes the local expression and cellular distribution of extended RAAS components in the arterial wall and their differential regulation during atherosclerotic lesion development.

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 G protein-coupled estrogen receptor 1 induces coronary artery relaxation via Epac/Rap1-mediated inhibition of RhoA/Rho kinase pathway in parallel with PKA

Previously, we reported that cAMP/PKA signaling is involved in GPER-mediated coronary relaxation by activating MLCP via inhibition of RhoA pathway. In the current study, we tested the hypothesis that activation of GPER induces coronary artery relaxation via inhibition of RhoA/Rho kinase pathway by cAMP downstream targets, exchange proteins directly activated by cAMP (Epac) as well as PKA. Our results show that Epac inhibitors, brefeldin A (BFA, 50 μM), or ESI-09 (20 μM), or CE3F4 (100 μM), all partially inhibited porcine coronary artery relaxation response to the selective GPER agonist, G-1 (0.3–3 μM); while concurrent administration of BFA and PKI (5 μM), a PKA inhibitor, almost completely blocked the relaxation effect of G-1. The Epac specific agonist, 8-CPT-2Me-cAMP (007, 1–100 μM), induced a concentration-dependent relaxation response. Furthermore, the activity of Ras-related protein 1 (Rap1) was up regulated by G-1 (1 μM) treatment of porcine coronary artery smooth muscle cells (CASMCs). Phosphorylation of vasodilator-stimulated phosphoprotein (p-VASP) was elevated by G-1 (1 μM) treatment, but not by 007 (50 μM); and the effect of G-1 on p-VASP was blocked by PKI, but not by ESI-09, an Epac antagonist. RhoA activity was similarly down regulated by G-1 and 007, whereas ESI-09 restored most of the reduced RhoA activity by G-1 treatment. Furthermore, G-1 decreased PGF2α-induced p-MYPT1, which was partially reversed with either ESI-09 or PKI; whereas, concurrent administration of ESI-09 and PKI totally prevented the inhibitory effect of G-1. The inhibitory effects of G-1 on p- MLC levels in CASMCs were mostly restored by either ESI-09 or PKI. These results demonstrate that activation of GPER induces coronary artery relaxation via concurrent inhibition of RhoA/Rho kinase by Epac/Rap1 and PKA. GPER could be a potential drug target for preventing and treating cardiovascular diseases.

Extent of Vascular Remodeling Is Dependent on the Balance Between Estrogen Receptor α and G-Protein–Coupled Estrogen Receptor

Estrogens are important regulators of cardiovascular function. Some of estrogen’s cardiovascular effects are mediated by a G-protein–coupled receptor mechanism, namely, G-protein–coupled estrogen receptor (GPER). Estradiol-mediated regulation of vascular cell programmed cell death reflects the balance of the opposing actions of GPER versus estrogen receptor α (ERα). However, the significance of these opposing actions on the regulation of vascular smooth muscle cell proliferation or migration in vitro is unclear, and the significance in vivo is unknown. To determine the effects of GPER activation in vitro, we studied rat aortic vascular smooth muscle cells maintained in primary culture. GPER was reintroduced using adenoviral gene transfer. Both estradiol and G1, a GPER agonist, inhibited both proliferation and cell migration effects that were blocked by the GPER antagonist, G15. To determine the importance of the GPER-ERα balance in regulating vascular remodeling in a rat model of carotid ligation, we studied the effects of upregulation of GPER expression versus downregulation of ERα. Reintroduction of GPER significantly attenuated the extent of medial hypertrophy and attenuated the extent of CD45 labeling. Downregulation of ERα expression comparably attenuated the extent of medial hypertrophy and inflammation after carotid ligation. These studies demonstrate that the balance between GPER and ERα regulates vascular remodeling. Receptor-specific modulation of estrogen’s effects may be an important new approach in modifying vascular remodeling in both acute settings like vascular injury and perhaps in longer term regulation like in hypertension.

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.

GPR30 Promotes Prostate Stromal Cell Activation via Suppression of ERα Expression and Its Downstream Signaling Pathway

Cancer-associated fibroblasts (CAFs) play a vital role in malignant transformation and progression of prostate cancer (PCa), and accumulating evidence suggests an enhancing effect of estrogens on PCa. The present study aimed to investigate the possible origin of prostate CAFs and the effects of estrogen receptors, G protein-coupled receptor 30 (GPR30) and estrogen receptor (ER)-α, on stromal cell activation. High expression of fibroblast activation protein (FAP), CD44, and nonmuscle myosin heavy chain B (SMemb) accompanied by low expression of smooth muscle differentiation markers was found in the stromal cells of PCa tissues and in cultured human prostate CAFs. Additionally, SMemb expression, which is coupled to cell phenotype switching and proliferation, was coexpressed with FAP, a marker of activated stromal cells, and with the stem cell marker CD44 in the stromal cells of PCa tissue. Prostate CAFs showed high GPR30 and low ERα expression. Moreover, GPR30 was coexpressed with FAP, CD44, and SMemb. Furthermore, the study demonstrated that the overexpression of GPR30 or the knockdown of ERα in prostate stromal cells induced the up-regulation of FAP, CD44, Smemb, and the down-regulation of smooth muscle markers. The conditioned medium from these cells promoted the proliferation and migration of LNCaP and PC3 PCa cells. GPR30 knockdown or ERα overexpression showed opposite effects. Finally, we present a novel mechanism whereby GPR30 limits ERα expression via inhibition of the cAMP/protein kinase A signaling pathway. These results suggest that stem-like cells within the stroma are a possible source of prostate CAFs and that the negative regulation of ERα expression by GPR30 is centrally involved in prostate stromal cell activation.

Estrogens and Coronary Artery Disease: New Clinical Perspectives

In premenopausal women, endogenous estrogens are associated with reduced prevalence of arterial hypertension, coronary artery disease, myocardial infarction, and stroke. Clinical trials conducted in the 1990s such as HERS, WHI, and WISDOM have shown that postmenopausal treatment with horse hormone mixtures (so-called conjugated equine estrogens) and synthetic progestins adversely affects female cardiovascular health. Our understanding of rapid (nongenomic) and chronic (genomic) estrogen signaling has since advanced considerably, including identification of a new G protein-coupled estrogen receptor (GPER), which like the "classical" receptors ERα and ERβ is highly abundant in the cardiovascular system. Here, we discuss the role of estrogen receptors in the pathogenesis of coronary artery disease and review natural and synthetic ligands of estrogen receptors as well as their effects in physiology, on cardiovascular risk factors, and atherosclerotic vascular disease. Data from preclinical and clinical studies using nonselective compounds activating GPER, which include selective estrogen receptor modulators such as tamoxifen or raloxifene, selective estrogen receptor downregulators such as Faslodex™ (fulvestrant/ICI 182,780), vitamin B3 (niacin), green tea catechins, and soy flavonoids such as genistein or resveratrol, strongly suggest that activation of GPER may afford therapeutic benefit for primary and secondary prevention in patients with or at risk for coronary artery disease. Evidence from preclinical studies suggest similar efficacy profiles for selective small molecule GPER agonists such as G-1 which are devoid of uterotrophic activity. Further clinical research in this area is warranted to provide opportunities for future cardiovascular drug development.

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.

The Expanding Complexity of Estrogen Receptor Signaling in the Cardiovascular System

Estrogen has important effects on cardiovascular function including regulation of vascular function, blood pressure, endothelial relaxation, and the development of hypertrophy and cardioprotection. However, the mechanisms by which estrogen mediates these effects are still poorly understood. As detailed in this review, estrogen can regulate transcription by binding to 2 nuclear receptors, ERα and ERβ, which differentially regulate gene transcription. ERα and ERβ regulation of gene transcription is further modulated by tissue-specific coactivators and corepressors. Estrogen can bind to ERα and ERβ localized at the plasma membrane as well as G-protein-coupled estrogen receptor to initiate membrane delimited signaling, which enhances kinase signaling pathways that can have acute and long-term effects. The kinase signaling pathways can also mediate transcriptional changes and can synergize with the ER to regulate cell function. This review will summarize the beneficial effects of estrogen in protecting the cardiovascular system through ER-dependent mechanisms with an emphasis on the role of the recently described ER membrane signaling mechanisms.

Women-specific factors to consider in risk, diagnosis and treatment of cardiovascular disease

In the era of individualized medicine, gaps in knowledge remain about sex-specific risk factors, diagnostic and treatment options that might reduce mortality from cardiovascular disease (CVD) and improve outcomes for both women and men. In this review, contributions of biological mechanisms involving the sex chromosomes and the sex hormones on the cardiovascular system will be discussed in relationship to the female-specific risk factors for CVD: hypertensive disorders of pregnancy, menopause and use of hormonal therapies for contraception and menopausal symptoms. Additionally, sex-specific factors to consider in the differential diagnosis and treatment of four prevalent CVDs (hypertension, stroke, coronary artery disease and congestive heart failure) will be reviewed with emphasis on areas where additional research is needed.

The G-protein coupled estrogen receptor, GPER: The inside and inside-out story

GPER possesses structural and functional characteristics shared by members of the G-protein-coupled receptor (GPCR) superfamily, the largest class of plasma membrane receptors. This newly appreciated estrogen receptor is localized predominately within intracellular membranes in most, but not all, cell types and its surface expression is modulated by steroid hormones and during tissue injury. An intracellular staining pattern is not unique among GPCRs, which employ a diverse array of molecular mechanisms that restrict cell surface expression and effectively regulating receptor binding and activation. The finding that GPER displays an intracellular predisposition has created some confusion as the estrogen-inducible transcription factors, ERα and ERβ, also reside intracellularly, and has led to complex suggestions of receptor interaction. GPER undergoes constitutive retrograde trafficking from the plasma membrane to the endoplasmic reticulum and recent studies indicate its interaction with PDZ binding proteins that sort transmembrane receptors to synaptosomes and endosomes. Genetic targeting and selective ligand approaches as well as cell models that express GPER in the absence of ERs clearly supports GPER as a bonafide "stand alone" receptor. Here, the molecular details that regulate GPER action, its cell biological activities and its implicated roles in physiological and pathological processes are reviewed.

Exogenous 17-β estradiol administration blunts progression of established angiotensin II-induced abdominal aortic aneurysms in female ovariectomized mice

Background

Abdominal aortic aneurysms (AAAs) occur predominately in males. However, AAAs in females have rapid growth rates and rupture at smaller sizes. Mechanisms contributing to AAA progression in females are undefined. We defined effects of ovariectomy, with and without 17-β estradiol (E2), on progression of established angiotensin II (AngII)-induced AAAs in female mice.

Methods

We used neonatal testosterone exposures at 1 day of age to promote susceptibility to AngII-induced AAAs in adult female Ldlr^−/− mice. Females were infused with AngII for 28 days to induce AAAs, and then stratified into groups that were sham, ovariectomized (Ovx, vehicle), or Ovx with E2 administration for 2 months of continued AngII infusions. Aortic lumen diameters were quantified by ultrasound and analyzed by linear mixed model, and maximal AAA diameters were analyzed by one-way ANOVA. Atherosclerosis was quantified en face in the aortic arch. AAA tissue sections were analyzed for cellular composition. We quantified effects of E2 on abdominal aortic smooth muscle cell (SMC) growth, α-actin and transforming growth factor-beta (TGF-β) production, and wound healing.

Results

Serum E2 concentrations were increased significantly by E2. Aortic lumen diameters increased over time in sham-operated and Ovx (vehicle) females, but not in Ovx females administered E2. At day 70, E2 administration decreased significantly aortic lumen diameters compared to Ovx vehicle and sham-operated females. Compared to Ovx females (vehicle), maximal AAA diameters were reduced significantly by E2. AAA tissue sections from Ovx females administered E2 exhibited significant increases in α-actin and decreases in neutrophils compared to Ovx females administered vehicle. In abdominal aortic SMCs, E2 resulted in a concentration-dependent increase in α-actin, elevated TGF-β, and more rapid wound healing. E2 administration to Ovx females also significantly reduced atherosclerotic lesions compared to sham-operated females. This effect was accompanied by significant reductions in serum cholesterol concentrations.

Conclusions

E2 administration to Ovx females abolished progressive growth and decreased severity of AngII-induced AAAs. These effects were accompanied by increased SMC α-actin, elevated TGF-β, and reduced neutrophils. Similarly, E2 administration reduced AngII-induced atherosclerosis. These results suggest that loss of E2 in post-menopausal females may contribute to progressive growth of AAAs.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-015-0030-1) contains supplementary material, which is available to authorized users.

Effects of estrogen on growth and smooth muscle differentiation of vascular wall-resident CD34(+) stem/progenitor cells

OBJECTIVES

To investigate the effects of estrogen on growth and smooth muscle cell (SMC)-differentiation of vascular wall-resident CD34(+) stem/progenitor cells (VRS/Pcs).

METHODS AND RESULTS

The existence of CD34(+) VRS/Pcs was confirmed by immunohistochemistry in the adventitia of arteries of young (2-month-old) and old (24-month-old) female SD rats with less CD34(+) adventitial cells detected in the old. The VRS/Pcs isolated from young animals were grown in Stem cell growth medium or induced to differentiate into SMC with PDGF-BB in the presence or absence of 17β-estrodiol (E2). Flow cytometry, RT-qPCR and Western blot showed that E2 promoted Brdu incorporation of the CD34(+) VRS/Pcs growing in Stem cell growth medium; but when the cells were incubated in PDGF-BB, the hormone enhanced their expression of SMC marker SM22. ChIP and IP assays showed that E2 significantly promoted the binding of pELK1-SRF complex to the promoter of c-fos gene in CD34(+) VRS/Pcs growing in the Stem cell growth medium; but when the cells were stimulated with PDGF-BB, an E2-enhanced binding of myocardin-SRF to the promoter of SM22 gene was found with enhanced expression of SRC3 and its binding to myocardin. The effects of E2 above could be blocked by the estrogen receptor antagonist ICI 182,780 or inhibited by SRF-siRNA.

CONCLUSION

Estrogen has dual effects on CD34(+) VRS/Pcs. For the undifferentiated VRS/Pcs, it accelerates their proliferation by enhancing binding of pELK1-SRF complex to c-fos gene; while for the differentiating VRS/Pcs, it promotes their differentiation to SMC through a mechanism of SRC3-mediated interaction of myocardin-SRF complex with SM22 gene.

Emerging roles of GPER in diabetes and atherosclerosis

The G protein-coupled estrogen receptor (GPER) is a 7-transmembrane receptor implicated in rapid estrogen signaling. Originally cloned from vascular endothelial cells, GPER plays a central role in the regulation of vascular tone and cell growth as well as lipid and glucose homeostasis. This review highlights our knowledge of the physiological and pathophysiological functions of GPER in the pancreas, peripheral and immune tissues, and the arterial vasculature. Recent findings on its roles in obesity, diabetes, and atherosclerosis, including GPER-dependent regulation of lipid metabolism and inflammation, are presented. The therapeutic potential of targeting GPER-dependent pathways in chronic diseases such as coronary artery disease and diabetes and in the context of menopause is also discussed.

17β-estradiol inhibits spreading of metastatic cells from granulosa cell tumors through a non-genomic mechanism involving GPER1

Granulosa cell tumor (GCT) is a rare and severe form of sex-cord stromal ovarian tumor that is characterized by its long natural history and tendency to recur years after surgical ablation. Because there is no efficient curative treatment beyond surgery, ~20% of patients die of the consequences of their tumor. However, very little is known of the molecular etiology of this pathology. About 70% of GCT patients present with elevated circulating estradiol (E2). Because this hormone is known to increase tumor growth and progression in a number of cancers, we investigated the possible role of E2 in GCTs. Cell-based studies with human GCT metastases and primary tumor-derived cells, ie KGN and COV434 cells, respectively, aimed at evaluating E2 effect on cell growth, migration and invasion. Importantly, we found that E2 did not affect GCT cell growth, but that it significantly decreased the migration and matrix invasion of metastatic GCT cells. Noteworthy, our molecular studies revealed that this effect was accompanied by the inhibition through non-genomic mechanisms of extracellular signal-regulated kinase 1/2 (ERK1/2), which is constitutively activated in GCTs. By using pharmacological and RNA silencing approaches, we found that E2 action was mediated by G protein-coupled estrogen receptor 1 (GPER1) signaling pathway. Analyses of GPER1 expression on tissue microarrays from human GCTs confirmed its expression in ~90% of GCTs. Overall, our study reveals that E2 would act via non-classical pathways to prevent metastasis spreading in GCTs and also reveals GPER1 as a possible target in this disease.

G protein-coupled estrogen receptor 1 mediates relaxation of coronary arteries via cAMP/PKA-dependent activation of MLCP

Activation of GPER exerts a protective effect in hypertension and ischemia-reperfusion models and relaxes arteries in vitro. However, our understanding of the mechanisms of GPER-mediated vascular regulation is far from complete. In the current study, we tested the hypothesis that GPER-induced relaxation of porcine coronary arteries is mediated via cAMP/PKA signaling. Our findings revealed that vascular relaxation to the selective GPER agonist G-1 (0.3-3 μM) was associated with increased cAMP production in a concentration-dependent manner. Furthermore, inhibition of adenylyl cyclase (AC) with SQ-22536 (100 μM) or of PKA activity with either Rp-8-CPT-cAMPS (5 μM) or PKI (5 μM) attenuated G-1-induced relaxation of coronary arteries preconstricted with PGF2α (1 μM). G-1 also increased PKA activity in cultured coronary artery smooth muscle cells (SMCs). To determine downstream signals of the cAMP/PKA cascade, we measured RhoA activity in cultured human and porcine coronary SMCs and myosin-light chain phosphatase (MLCP) activity in these artery rings by immunoblot analysis of phosphorylation of myosin-targeting subunit protein-1 (p-MYPT-1; the MLCP regulatory subunit). G-1 decreased PGF2α-induced p-MYPT-1, whereas Rp-8-CPT-cAMPS prevented this inhibitory effect of G-1. Similarly, G-1 inhibited PGF2α-induced phosphorylation of MLC in coronary SMCs, and this inhibitory effect was also reversed by Rp-8-CPT-cAMPS. RhoA activity was downregulated by G-1, whereas G36 (GPER antagonist) restored RhoA activity. Finally, FMP-API-1 (100 μM), an inhibitor of the interaction between PKA and A-kinase anchoring proteins (AKAPs), attenuated the effect of G-1 on coronary artery relaxation and p-MYPT-1. These findings demonstrate that localized cAMP/PKA signaling is involved in GPER-mediated coronary vasodilation by activating MLCP via inhibition of RhoA pathway.

Expression of the oestrogen receptor GPER by testicular peritubular cells is linked to sexual maturation and male fertility

Besides the two nuclear oestrogen receptors (ESR1/ESR2), the G protein-coupled oestrogen receptor (GPER) was described in the human testis but little is known about testicular GPER during development or male infertility. We performed an immunohistochemical analysis using human and rhesus monkey testicular samples. The results obtained in adult primate testes showed GPER in interstitial and vascular cells as well as in smooth muscle-like peritubular cells, which build the wall of seminiferous tubules. Expression of GPER was also found in cultured human testicular peritubular cells (HPTCs) by Western blotting and RT-PCR/sequencing. Furthermore, as seen in time-lapse videos of cultured cells, addition of a specific GPER agonist (G1) significantly reduced the numbers of HTPCs within 24 h. A GPER antagonist (G15) prevented this action, implying a role for GPER related to the control of cell proliferation or cell death of peritubular cells. Peritubular cell functions and their phenotype change, for example, during post-natal development and in the cases of male infertility. The study of non-human primate samples revealed that GPER in peritubular cells was detectable only from the time of puberty onwards, while in samples from infantile and prepubertal monkeys only interstitial cells showed immunopositive staining. In testicular biopsies of men with mixed atrophy, a reduction or loss of immunoreactive GPER was found in peritubular cells surrounding those tubules, in which spermatogenesis was impaired. In other cases of impaired spermatogenesis, namely when the tubular wall was fibrotically remodelled, a complete loss of GPER was seen. Thus, the observed inverse relation between the state of fertility and GPER expression by peritubular cells implies that the regulation of primate testicular peritubular cells by oestrogens is mediated by GPER in both, health and disease.

G-protein-coupled estrogen receptor as a new therapeutic target for treating coronary artery disease

Coronary heart disease (CHD) continues to be the greatest mortality risk factor in the developed world. Estrogens are recognized to have great therapeutic potential to treat CHD and other cardiovascular diseases; however, a significant array of potentially debilitating side effects continues to limit their use. Moreover, recent clinical trials have indicated that long-term postmenopausal estrogen therapy may actually be detrimental to cardiovascular health. An exciting new development is the finding that the more recently discovered G-protein-coupled estrogen receptor (GPER) is expressed in coronary arteries-both in coronary endothelium and in smooth muscle within the vascular wall. Accumulating evidence indicates that GPER activation dilates coronary arteries and can also inhibit the proliferation and migration of coronary smooth muscle cells. Thus, selective GPER activation has the potential to increase coronary blood flow and possibly limit the debilitating consequences of coronary atherosclerotic disease. This review will highlight what is currently known regarding the impact of GPER activation on coronary arteries and the potential signaling mechanisms stimulated by GPER agonists in these vessels. A thorough understanding of GPER function in coronary arteries may promote the development of new therapies that would help alleviate CHD, while limiting the potentially dangerous side effects of estrogen therapy.

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.