A critical review of fundamental controversies in the field of GPR30 research

Revising the Roles of Aldosterone in Vascular Physiology and Pathophysiology: From Electocortin to Baxdrostat

Aldosterone was initially identified as a hormone primarily related to regulation of fluid and electrolyte homeostasis. However, over the past 20 years there has been an increasing appreciation of its role in regulation of vascular function and pathophysiology in the setting of hypertension, atherosclerosis, and heart failure. This review highlights recent advances in our understanding the biology of aldosterone as it relates to the pathophysiology and the management of vascular disease-especially related to hypertension. The review focuses on 3 key areas: 1) advances in our understanding of the cellular mechanisms by which aldosterone mediates its cellular effects, 2) identification of the hidden epidemic of aldosteronism as a mediator of hypertension, and 3) appreciating new therapeutic advances in the clinical pharmacology of aldosterone inhibition in cardiovascular and renal disease.

High GPER expression in triple-negative breast cancer is linked to pro-metastatic pathways and predicts poor patient outcomes

Triple-negative breast cancer (TNBC) is a particularly aggressive and heterogeneous disease with few effective targeted therapies and precision therapeutic options over a long period. It is generally considered that TNBC is an estrogen-independent breast cancer, while a new estrogen receptor, namely G protein-coupled estrogen receptor (GPER), is demonstrated to mediate estrogenic actions in TNBC. Based on our transcriptomic analysis, expression of GPER was correlated with clinicopathological variables and survival of 360 TNBC patients. GPER expression at mRNA level was significantly correlated with immunohistochemistry scoring in 12 randomly chosen samples. According to the cutoff value, 26.4% (95/360) of patients showed high GPER expression and significant correlation with the mRNA subtype of TNBC (P = 0.001), total metastatic events (P = 0.019) and liver metastasis (P = 0.011). In quantitative comparison, GPER abundance is correlated with the high-risk subtype of TNBC. At a median follow-up interval of 67.1 months, a significant trend towards reduced distant metastasis-free survival (DMFS) (P = 0.014) was found by Kaplan–Meier analysis in patients with high GPER expression. Furthermore, univariate analysis confirmed that GPER was a significant prognostic factor for DMFS in TNBC patients. Besides, high GPER expression was significantly linked to the worse survival in patients with lymph node metastasis, TNM stage III as well as nuclear grade G3 tumors. Transcriptome-based bioinformatics analysis revealed that GPER was linked to pro-metastatic pathways in our cohort. These results may supply new insights into GPER-mediated estrogen carcinogenesis in TNBC, thus providing a potential strategy for endocrine therapy of TNBC.

Segregation of nuclear and membrane-initiated actions of estrogen receptor using genetically modified animals and pharmacological tools

Estrogen receptor alpha (ERα) and beta (ERβ) are members of the nuclear receptor superfamily, playing widespread functions in reproductive and non-reproductive tissues. Beside the canonical function of ERs as nuclear receptors, in this review, we summarize our current understanding of extra-nuclear, membrane-initiated functions of ERs with a specific focus on ERα. Over the last decade, in vivo evidence has accumulated to demonstrate the physiological relevance of this ERα membrane-initiated-signaling from mouse models to selective pharmacological tools. Finally, we discuss the perspectives and future challenges opened by the integration of extra-nuclear ERα signaling in physiology and pathology of estrogens.

A historical view of estrogen effect on arterial endothelial healing: From animal models to medical implication

Endothelial barrier integrity is required for maintaining vascular homeostasis and fluid balance between the circulation and surrounding tissues. In contrast, abnormalities of endothelial cell function and loss of the integrity of the endothelial monolayer constitute a key step in the onset of atherosclerosis. Endothelial erosion is directly responsible for thrombus formation and cardiovascular events in about one-third of the cases of acute coronary syndromes. Thus, after endothelial injury, the vascular repair process is crucial to restore endothelial junctions and rehabilitate a semipermeable barrier, preventing the development of vascular diseases. Endothelial healing can be modulated by several factors. In particular, 17β-estradiol (E2), the main estrogen, improves endothelial healing, reduces neointimal accumulation of smooth muscle cells and atherosclerosis in several animal models. The aim of this review is to highlight how various experimental models enabled the progress in the cellular and molecular mechanisms underlying the accelerative E2 effect on arterial endothelial healing through the estrogen receptor (ER) α, the main receptor mediating the physiological effects of estrogens. We first summarize the different experimental procedures used to reproduce vascular injury. We then provide an overview of how the combination of transgenic mouse models impacting ERα signalling with pharmacological tools demonstrated the pivotal role of non-genomic actions of ERα in E2-induced endothelial repair. Finally, we describe recent advances in the action of selective estrogen receptor modulators (SERMs) on this beneficial vascular effect, which surprisingly involves different cell types and activates different ERα subfunctions compared to E2.

GPR30 Activation by 17β-Estradiol Promotes p62 Phosphorylation and Increases Estrogen Receptor α Protein Expression by Inducing Its Release from a Complex Formed with KEAP1

Estrogens can elicit rapid cellular responses via the G-protein-coupled receptor 30 (GPR30), followed by estrogen receptor α (ERα/ESR1)-mediated genomic effects. Here, we investigated whether rapid estrogen signaling via GRP30 may affect ESR1 expression, and we examined the underlying molecular mechanisms. The exposure of human endometrial cancer cells to 17β-estradiol promoted p62 phosphorylation and increased ESR1 protein expression. However, both a GPR30 antagonist and GPR30 silencing abrogated this phenomenon. GPR30 activation by 17β-estradiol elicited the SRC/EGFR/PI3K/Akt/mTOR signaling pathway. Intriguingly, unphosphorylated p62 and ESR1 were found to form an intracellular complex with the substrate adaptor protein KEAP1. Upon phosphorylation, p62 promoted ESR1 release from the complex, to increase its protein expression. Given the critical role played by p62 in autophagy, we also examined how this process affected ESR1 expression. The activation of autophagy by everolimus decreased ESR1 by promoting p62 degradation, whereas autophagy inhibition with chloroquine increased ESR1 expression. The treatment of female C57BL/6 mice with the autophagy inhibitor hydroxychloroquine—which promotes p62 expression—increased both phosphorylated p62 and ESR1 expression in uterine epithelial cells. Collectively, our results indicate that 17β-estradiol-mediated GPR30 activation elicits the SRC/EGFR/PI3K/Akt/mTOR signaling pathway and promotes p62 phosphorylation. In turn, phosphorylated p62 increased ESR1 expression by inducing its release from complexes that included KEAP1. Our findings may lead to novel pharmacological strategies aimed at decreasing ESR1 expression in estrogen-sensitive cells.

Genistein Directly Represses the Phosphorylation of STAT5 in Lactating Mammary Epithelial Cells

Genistein is a soy isoflavone and shows various physiological activities, such as affinities for estrogen receptors (ERs) and inhibitory effects on the epidermal growth factor receptor (EGFR) pathway. A previous study reported that genistein downregulates milk production ability in mammary epithelial cells (MECs) while decreasing the phosphorylation of STAT5. The ER and EGFR pathways indirectly regulate STAT5. In this study, the repressing mechanism of genistein against the phosphorylation of STAT5 was investigated using a culture model of mouse MECs with milk production ability. The results revealed that genistein did not influence the behavior of ERα and ERβ, whereas genistein immediately repressed the phosphorylation of ERK1/2. However, the decrease in phosphorylated STAT5 occurred independent of the phosphorylation of EGFR. Genistein repressed new phosphorylation of STAT5 by prolactin without influencing the phosphorylation of JAK2. In conclusion, this study indicates that genistein directly inhibits the phosphorylation of STAT5 in lactating MECs.

Hepatic estrogen-responsive genes relating to oogenesis in cutthroat trout (Oncorhynchus clarki): The transcriptional induction in primary cultured hepatocytes and the in vitro promoter transactivation in responses to estradiol-17β

Estradiol-17β (E2) regulates transcription of estrogen-responsive genes via estrogen receptors (Esr). In many teleost species, choriogenin (chg), vitellogenin (vtg) and esr genes are transactivated by E2 in the liver. This study aimed i) to compare expression properties of all subtypes of these genes (chg: chgHα, chgHβ, chgL; vtg: vtgAs, vtgC; esr: esr1a, esr1b, esr2a, esr2b) in response to estrogen stimulation, and ii) to confirm how each of four Esr subtypes is involved in the transcriptional regulation of these estrogen-responsive genes in cutthroat trout hepatocytes. In hepatocytes in primary culture, all chg and vtg subtype mRNA levels, and those of esr1a, were increased by E2 treatment (10^-6 M) at 24 and 72 h post initiation (hpi), but esr1b, esr2a and esr2b mRNA levels were not. Treatment of hepatocytes with various concentrations of E2 (10^-11-10^-6 M) induced dose-dependent increases in the levels of all chg and vtg subtype mRNAs at 24 and 72 hpi. At both time points, the lowest dose that induced a significant increase in the expression levels of mRNAs (LOEC) for E2 differed among the genes; LOECs were estimated as 10^-11 M for chgHα at 24 hpi, as 10^-9 M for vtgC at 72 hpi, and as 10^-10 M for other mRNAs at both 24 and 72 hpi. Meanwhile, the levels of esr1a mRNA exhibited a dose-dependent increase at 24 and 72 hpi, but the LOEC shifted from 10^-9 M at 24 hpi to 10^-7 M at 72 hpi because of a decrease in mRNA levels at treatment groups exposed to high concentrations of E2. All Esr subtypes transactivated chg, vtg and esr1a promoters in the presence of E2 in vitro. The activation levels indicated that promoter activity of chgHα ≥ vtgAs > chgHβ > chgL ≥ vtgC ≥ esr1a when mediated by Esr1a, chgHβ > chgHα > chgHL > vtgAs ≥ vtgC ≥ esr1a by Esr1b, chgHβ ≥ chgL > chgHα ≥ vtgAs > vtgC > esr1a by Esr2a, and chgHβ ≥ chgHα ≥ vtgAs > chgL ≥ vtgC > esr1a by Esr2b. Collectively, different Esr subtypes were distinctly different in their ability to transactivate estrogen-responsive target genes, resulting in differential expression of chg, vtg and esr1a genes in the estrogen-exposed hepatocytes.

Sex-specific Regulation of Spine Density and Synaptic Proteins by G-protein-coupled Estrogen Receptor (GPER)1 in Developing Hippocampus

G-protein-coupled-estrogen-receptor 1 (GPER1) is a membrane-bound receptor that mediates estrogen signaling via intracellular signaling cascades. We recently showed that GPER1 promotes the distal dendritic enrichment of hyperpolarization activated and cyclic nucleotide-gated (HCN)1 channels in CA1 stratum lacunosum-moleculare (SLM), suggesting a role of GPER1-mediated signaling in neuronal plasticity. Here we studied whether this role involves processes of structural plasticity, such as the regulation of spine and synapse density in SLM. In organotypic entorhino-hippocampal cultures from mice expressing eGFP, we analyzed spine densities in SLM after treatment with GPER1 agonist G1 (20 nM). G1 significantly increased the density of "non-stubby" spines (maturing spines with a spine head and a neck), but did so only in cultures from female mice. In support of this finding, the expression of synaptic proteins was sex-specifically altered in the cultures: G1 increased the protein (but not mRNA) expression of PSD95 and reduced the p-/n-cofilin ratio only in cultures from females. Application of E2 (2 nM) reproduced the sex-specific effect on spine density in SLM, but only partially on the expression of synaptic proteins. Spine synapse density was, however, not altered after G1-treatment, suggesting that the increased spine density did not translate into an increased spine synapse density in the culture model. Taken together, our results support a role of GPER1 in mediating structural plasticity in CA1 SLM, but suggest that in developing hippocampus, this role is sex-specific.

Sexual hormones and diabetes: The impact of estradiol in pancreatic β cell

Diabetes is one of the most prevalent metabolic diseases and its incidence is increasing throughout the world. Data from World Health Organization (WHO) point-out that diabetes is a major cause of blindness, kidney failure, heart attacks, stroke and lower limb amputation and estimated 1.6 million deaths were directly caused by it in 2016. Population studies show that the incidence of this disease increases in women after menopause, when the production of estrogen is decreasing in them. Knowing the impact that estrogenic signaling has on insulin-secreting β cells is key to prevention and design of new therapeutic targets. This chapter explores the role of estrogen and their receptors in the regulation of insulin secretion and biosynthesis, proliferation, regeneration and survival in pancreatic β cells. In addition, delves into the genetic animal models developed and its application for the specific study of the different estrogen signaling pathways. Finally, discusses the impact of menopause and hormone replacement therapy on pancreatic β cell function.

Reduced Vitellogenesis and Female Fertility in Gper Knockout Zebrafish

The role G-protein coupled estrogen receptor (GPER) plays in vertebrate reproduction remains controversial. To investigate GPER's reproductive role, we generated a gper zebrafish mutant line (gper^-/- ) using TALENs. Gper mutant females exhibited reduced fertility with a 40.85% decrease in embryo production which was associated with a significant decrease in the number of Stage V (730-750 μm) ovulated oocytes. Correspondingly, the number of early vitellogenic follicles (Stage III, 400-450 µm) in gper^-/- ovaries was greater than that in wildtypes (wt), suggesting that subsequent follicle development was retarded in the gper^-/- fish. Moreover, plasma vitellogenin levels were decreased in gper^-/- females, and epidermal growth factor receptor (Egfr) expression was lower in Stage III vitellogenic oocytes than in wt counterparts. However, hepatic nuclear estrogen receptor levels were not altered, and estrogen levels were elevated in ovarian follicles. These results suggest that Gper is involved in the control of ovarian follicle development via regulation of vitellogenesis and Egfr expression in zebrafish.

Sex-Specific Determinants of Coronary Artery Disease and Atherosclerotic Risk Factors: Estrogen and Beyond

The way we view coronary artery disease in women has changed dramatically over the past decades. From an initial perspective that coronary artery disease was a male disorder and that women were protected by estrogens, there has been the gradual appreciation that this is an equal opportunity disease. Postmenopausal women are more likely than men to be hypertensive, dyslipidemic, and have multiple risk factors. Beyond the appreciation of estrogen's global effects on cardiovascular and metabolic function, our further advances in the understanding of sex-specific risks and management will be based on a greater understanding of the diversity of estrogen-mediated receptor pathways, including appreciation of the sometimes divergent effects of estrogen when acting either via the classic estrogen receptor or the more recently appreciated G protein-coupled estrogen receptor. In addition, the importance of sex-specific regulation of cardiometabolic processes beyond the sex hormones, specifically via SRY regulation, is only beginning to be understood. Finally, the author summarizes his recent studies demonstrating sex-specific G protein-coupled estrogen receptor regulation of blood pressure and cholesterol metabolism that may serve as a paradigm for the elucidation of sex-specific determinants of cardiovascular risk and the basis for sex-specific management of those risks.

Dorsal Hippocampal Actin Polymerization Is Necessary for Activation of G-Protein-Coupled Estrogen Receptor (GPER) to Increase CA1 Dendritic Spine Density and Enhance Memory Consolidation

Activation of the membrane estrogen receptor G-protein-coupled estrogen receptor (GPER) in ovariectomized mice via the GPER agonist G-1 mimics the beneficial effects of 17β-estradiol (E₂) on hippocampal CA1 spine density and memory consolidation, yet the cell-signaling mechanisms mediating these effects remain unclear. The present study examined the role of actin polymerization and c-Jun N-terminal kinase (JNK) phosphorylation in mediating effects of dorsal hippocampally infused G-1 on CA1 dendritic spine density and consolidation of object recognition and spatial memories in ovariectomized mice. We first showed that object learning increased apical CA1 spine density in the dorsal hippocampus (DH) within 40 min. We then found that DH infusion of G-1 increased both CA1 spine density and phosphorylation of the actin polymerization regulator cofilin, suggesting that activation of GPER may increase spine morphogenesis through actin polymerization. As with memory consolidation in our previous work (Kim et al., 2016), effects of G-1 on CA1 spine density and cofilin phosphorylation depended on JNK phosphorylation in the DH. Also consistent with our previous findings, E₂-induced cofilin phosphorylation was not dependent on GPER activation. Finally, we found that infusion of the actin polymerization inhibitor, latrunculin A, into the DH prevented G-1 from increasing apical CA1 spine density and enhancing both object recognition and spatial memory consolidation. Collectively, these data demonstrate that GPER-mediated hippocampal spinogenesis and memory consolidation depend on JNK and cofilin signaling, supporting a critical role for actin polymerization in the GPER-induced regulation of hippocampal function in female mice.SIGNIFICANCE STATEMENT Emerging evidence suggests that G-protein-coupled estrogen receptor (GPER) activation mimics effects of 17β-estradiol on hippocampal memory consolidation. Unlike canonical estrogen receptors, GPER activation is associated with reduced cancer cell proliferation; thus, understanding the molecular mechanisms through which GPER regulates hippocampal function may provide new avenues for the development of drugs that provide the cognitive benefits of estrogens without harmful side effects. Here, we demonstrate that GPER increases CA1 dendritic spine density and hippocampal memory consolidation in a manner dependent on actin polymerization and c-Jun N-terminal kinase phosphorylation. These findings provide novel insights into the role of GPER in mediating hippocampal morphology and memory consolidation, and may suggest first steps toward new therapeutics that more safely and effectively reduce memory decline in menopausal women.

Molecular mechanism of endocrine-disruptive effects induced by Bisphenol A: The role of transmembrane G-protein estrogen receptor 1 and integrin αvβ3

Bisphenol A (BPA) is one of the highest volume industrial products worldwide and has been widely used to make various products as the intermediates of polycarbonate plastics and epoxy resins. Inevitably, general population has been widely exposed to BPA due to extensive use of BPA-containing products. BPA has similar chemical structure with the natural estrogen and has been shown to induce a variety of estrogen-like endocrine effects on organism in vivo or in vitro. High doses of BPA tend to act as antagonist of estrogen receptors (ERs) by directly regulating the genomic transcription. However, BPA at environmentally relevant low-dose always disrupt the biological function via a non-genomic manner mediated by membrane receptors, rather than ERs. Although some studies had investigated the non-genomic effects of low-dose BPA, the exact molecular mechanism still remains unclear. Recently, we found that membrane G protein-coupled estrogen receptor 1 and integrin αvβ3 and its relative signal pathways participate in the induction of male germ cell proliferation and thyroid transcription disruption by the low-dose BPA. A profound understanding for the mechanism of action of the environmentally relevant BPA exposure not only contributes to objectively evaluate and predict the potential influence to human health, but also provides theoretical basis and methodological support for assessing health effects trigged by other estrogen-like environmental endocrine disruptors. Based mainly on our recent findings, this review outlines the research progress of molecular mechanism on endocrine disrupting effects of environmental low-dose BPA, existing problems and some consideration for future studies.

Role of estrogens in fish immunity with special emphasis on GPER1

It is well accepted that estrogens, the primary female sex hormones, play a key role in modulating different aspects of the immune response. Moreover, estrogens have been linked with the sexual dimorphism observed in some immune disorders, such as chronic inflammatory and autoimmune diseases. Nevertheless, their effects are often controversial and depend on several factors, such as the pool of estrogen receptors (ERs) involved in the response. Their classical mode of action is through nuclear ERs, which act as transcription factors, promoting the regulation of target genes. However, it has long been noted that some of the estrogen-mediated effects cannot be explained by these classical receptors, since they are rapid and mediated by non-genomic signaling pathways. Hence, the interest in membrane ERs, especially in G protein-coupled estrogen receptor 1 (GPER1), has grown in recent years. Although the presence of nuclear ERs, and ER signaling, in immune cells in mammals and fish has been well documented, information on membrane ERs is much scarcer. In this context, the present manuscript aims to review our knowledge concerning the effect of estrogens on fish immunity, with special emphasis on GPER1. For example, the numerous tools developed over recent years allowed us to report for the first time that the regulation of fish granulocyte functions by estrogens through GPER1 predates the split of fish and tetrapods more than 450 million years ago, pointing to the relevance of estrogens as modulators of the immune responses, and the pivotal role of GPER1 in immunity.

Effects of isoflavones on breast tissue and the thyroid hormone system in humans: a comprehensive safety evaluation

Isoflavones are secondary plant constituents of certain foods and feeds such as soy, linseeds, and red clover. Furthermore, isoflavone-containing preparations are marketed as food supplements and so-called dietary food for special medical purposes to alleviate health complaints of peri- and postmenopausal women. Based on the bioactivity of isoflavones, especially their hormonal properties, there is an ongoing discussion regarding their potential adverse effects on human health. This review evaluates and summarises the evidence from interventional and observational studies addressing potential unintended effects of isoflavones on the female breast in healthy women as well as in breast cancer patients and on the thyroid hormone system. In addition, evidence from animal and in vitro studies considered relevant in this context was taken into account along with their strengths and limitations. Key factors influencing the biological effects of isoflavones, e.g., bioavailability, plasma and tissue concentrations, metabolism, temporality (pre- vs. postmenopausal women), and duration of isoflavone exposure, were also addressed. Final conclusions on the safety of isoflavones are guided by the aim of precautionary consumer protection.

Sex Hormones Regulate Innate Immune Cells and Promote Sex Differences in Respiratory Virus Infection

Sex differences in the incidence and severity of respiratory virus infection are widely documented in humans and murine models and correlate with sex biases in numbers and/or functional responses of innate immune cells in homeostasis and lung infection. Similarly, changes in sex hormone levels upon puberty, pregnancy, and menopause/aging are associated with qualitative and quantitative differences in innate immunity. Immune cells express receptors for estrogens (ERα and ERβ), androgens (AR), and progesterone (PR), and experimental manipulation of sex hormone levels or receptors has revealed that sex hormone receptor activity often underlies sex differences in immune cell numbers and/or functional responses in the respiratory tract. While elegant studies have defined mechanistic roles for sex hormones and receptors in innate immune cells, much remains to be learned about the cellular and molecular mechanisms of action of ER, PR, and AR in myeloid cells and innate lymphocytes to promote the initiation and resolution of antiviral immunity in the lung. Here, we review the literature on sex differences and sex hormone regulation in innate immune cells in the lung in homeostasis and upon respiratory virus infection.

Androgen and estrogen actions on male physical activity: a story beyond muscle

Physical inactivity is a pandemic that contributes to several chronic diseases and poses a significant burden on health care systems worldwide. The search for effective strategies to combat sedentary behavior has led to an intensification of the research efforts to unravel the biological substrate controlling activity. A wide body of preclinical evidence makes a strong case for sex steroids regulating physical activity in both genders, albeit the mechanisms implicated remain unclear. The beneficial effects of androgens on muscle as well as on other peripheral functions might play a role in favoring adaptation to exercise. Alternatively or in addition, sex steroids could act on specific brain circuitries to boost physical activity. This review critically discusses the evidence supporting a role for androgens and estrogens stimulating male physical activity, with special emphasis on the possible role of peripheral and/or central mechanisms. Finally, the potential translation of these findings to humans is briefly discussed.

Predominant Role of Nuclear Versus Membrane Estrogen Receptor α in Arterial Protection: Implications for Estrogen Receptor α Modulation in Cardiovascular Prevention/Safety

BACKGROUND

Although estrogen receptor α (ERα) acts primarily as a transcription factor, it can also elicit membrane-initiated steroid signaling. Pharmacological tools and transgenic mouse models previously highlighted the key role of ERα membrane-initiated steroid signaling in 2 actions of estrogens in the endothelium: increase in NO production and acceleration of reendothelialization.

METHODS AND RESULTS

Using mice with ERα mutated at cysteine 451 (ERaC451A), recognized as the key palmitoylation site required for ERα plasma membrane location, and mice with disruption of nuclear actions because of inactivation of activation function 2 (ERaAF20 = ERaAF2°), we sought to fully characterize the respective roles of nuclear versus membrane-initiated steroid signaling in the arterial protection conferred by ERα. ERaC451A mice were fully responsive to estrogens to prevent atheroma and angiotensin II-induced hypertension as well as to allow flow-mediated arteriolar remodeling. By contrast, ERαAF20 mice were unresponsive to estrogens for these beneficial vascular effects. Accordingly, selective activation of nuclear ERα with estetrol was able to prevent hypertension and to restore flow-mediated arteriolar remodeling.

CONCLUSIONS

Altogether, these results reveal an unexpected prominent role of nuclear ERα in the vasculoprotective action of estrogens with major implications in medicine, particularly for selective nuclear ERα agonist, such as estetrol, which is currently under development as a new oral contraceptive and for hormone replacement therapy in menopausal women.

Low expression of G protein-coupled oestrogen receptor 1 (GPER) is associated with adverse survival of breast cancer patients

G protein-coupled oestrogen receptor 1 (GPER), also called G protein-coupled receptor 30 (GPR30), is attracting considerable attention for its potential role in breast cancer development and progression. Activation by oestrogen (17β-oestradiol; E2) initiates short term, non-genomic, signalling events both in vitro and in vivo. Published literature on the prognostic value of GPER protein expression in breast cancer indicates that further assessment is warranted. We show, using immunohistochemistry on a large cohort of primary invasive breast cancer patients (n=1245), that low protein expression of GPER is not only significantly associated with clinicopathological and molecular features of aggressive behaviour but also significantly associated with adverse survival of breast cancer patients. Furthermore, assessment of GPER mRNA levels in the METABRIC cohort (n=1980) demonstrates that low GPER mRNA expression is significantly associated with adverse survival of breast cancer patients. Using artificial neural networks, genes associated with GPER mRNA expression were identified; these included notch-4 and jagged-1. These results support the prognostic value for determination of GPER expression in breast cancer.

Estrogen receptor subcellular localization and cardiometabolism

BACKGROUND

In addition to their crucial role in reproduction, estrogens are key regulators of energy and glucose homeostasis and they also exert several cardiovascular protective effects. These beneficial actions are mainly mediated by estrogen receptor alpha (ERα), which is widely expressed in metabolic and vascular tissues. As a member of the nuclear receptor superfamily, ERα was primarily considered as a transcription factor that controls gene expression through the activation of its two activation functions (ERαAF-1 and ERαAF-2). However, besides these nuclear actions, a pool of ERα is localized in the vicinity of the plasma membrane, where it mediates rapid signaling effects called membrane-initiated steroid signals (MISS) that have been well described in vitro, especially in endothelial cells.

SCOPE OF THE REVIEW

This review aims to summarize our current knowledge of the mechanisms of nuclear vs membrane ERα activation that contribute to the cardiometabolic protection conferred by estrogens. Indeed, new transgenic mouse models (affecting either DNA binding, activation functions or membrane localization), together with the use of novel pharmacological tools that electively activate membrane ERα effects recently allowed to begin to unravel the different modes of ERα signaling in vivo.

CONCLUSION

Altogether, available data demonstrate the prominent role of ERα nuclear effects, and, more specifically, of ERαAF-2, in the preventive effects of estrogens against obesity, diabetes, and atheroma. However, membrane ERα signaling selectively mediates some of the estrogen endothelial/vascular effects (NO release, reendothelialization) and could also contribute to the regulation of energy balance, insulin sensitivity, and glucose metabolism. Such a dissection of ERα biological functions related to its subcellular localization will help to understand the mechanism of action of "old" ER modulators and to design new ones with an optimized benefit/risk profile.

Experimental models for evaluating non-genomic estrogen signaling

Non-genomic effects of estrogen receptor α (ERα) signaling have been described for decades. However, the mechanisms and physiological processes resulting solely from non-genomic signaling are poorly understood. Challenges in studying these effects arise from the strongly nucleophilic tendencies of estrogen receptor, and many approaches to excluding ERα from the nucleus have been explored over the years. In this review, we discuss past strategies for studying ERα's non-genomic action and current models, specifically H2NES ERα, first described by Burns et al. (2011). In vitro and preliminary in vivo data from H2NES ERα and H2NES mice suggest a promising avenue for pinpointing specific non-genomic ERα action.

Reduction of estradiol in human malignant pleural mesothelioma tissues may prevent tumour growth, as implied by in in-vivo and in-vitro models

This study aimed to investigate intratumoural estradiol and estrogen-receptors (ERα, ERβ and GPR30) in malignant pleural mesothelioma (MPM) to understand their function. Here, we report that immunohistochemistry of estradiol showed cytoplasmatic staining in 95% of fifty-seven human MPM samples with a trend toward a negative correlation between estradiol levels and the median post-diagnosis survival time. ERβ was only focally positive in 5.3% of cases, GPR30 and ERα were negative in our cases of MPM. GPR30 was detected mainly in glycosylated form in MPM cells. Moreover, G15, a GPR30 antagonist, induced MPM cell death. Altogether, these data suggest that MPM cells produce E₂ interact with glycosylated forms of GPR30, and this facilitates tumour growth. Estradiol was found in MPM cells and plasma from mice mesothelioma xenografts. Concurrent reduction in tumour mass and plasmatic estradiol levels were observed in the mice treated with exemestane, suggesting that the reduction of E₂ levels inhibit MPM growth. Thus, it appears that agents reducing estradiol levels could be useful to MPM therapy.

Effects of 17β-Estradiol on Mitophagy in the Murine MC3T3-E1 Osteoblast Cell Line is Mediated via G Protein-Coupled Estrogen Receptor and the ERK1/2 Signaling Pathway

Background

Osteoporosis is associated with 17β-estradiol deficiency. The G protein-coupled receptor 30 (GPR30) is known to be an estrogen-responsive receptor, but its role in the degradation of mitochondria in osteoblasts by autophagy, or mitophagy, remains unclear. The aim of this in vitro study was to evaluate the effects of 17β-estradiol, GPR30, and its signaling pathway, on mitophagy in the murine MC3T3-E1 osteoblast cell line.

Material/Methods

In the murine MC3T3-E1 osteoblast cell line, cells were treated with 17β-estradiol, or G15, a selective GPR30 antagonist, or U0126, a mitogen-activated protein (MAP) kinase (ERK1/2) inhibitor, or with vehicle as control. The expression of GPR30 was determined by Western blot, reverse transcription-polymerase chain reaction (RT-PCR), and confocal immunofluorescence imaging. Cell morphology and mitochondrial autophagosomes were identified using transmission electron microscopy (TEM). Phosphorylation of the mitophagy markers, heat shock protein 60 (Hsp60), translocase of outer membrane (Tom)20, and microtubule-associated protein 1A/1B-light chain 3 (LC3) were determined by Western blot, and cell proliferation was determined using the bromodeoxyuridine (BrdU) assay.

Results

The optimum concentration of 17β-estradiol that resulted in GPR30 expression in MC3T3-E1 cells was 10⁻⁷ M, which led to the accumulation of mitochondrial autophagosomes and increased protein phosphorylation levels of Hsp60, Tom20, and LC3. In cells pretreated with G15 or U0126, 17β-estradiol treatment did not increase mitophagy in MC3T3-E1 cells.

Conclusions

In murine osteoblasts cultured in vitro, treatment with 17β-estradiol resulted in the expression of GPR30 and enhanced mitophagy through the GPR30 and ERK1/2 signaling pathway.

GPER1/GPR30 in the brain: Crosstalk with classical estrogen receptors and implications for behavior

The GPER1/GPR30 is a membrane estrogen receptor (mER) that binds 17β-estradiol (17β-E) with high affinity and is thought to play a role in cancer progression and cardiovascular health. Though widespread in the central nervous system, less is known about this receptor's function in the brain. GPER1 has been shown to activate kinase cascades and calcium flux within cells rapidly, thus fitting in with the idea of being a mER that mediates non-genomic signaling by estrogens. Signaling from GPER1 has been shown to improve spatial memory, possibly via release of neurotransmitters and generation of new spines on neurons in the hippocampus. In addition, GPER1 activation contributes to behaviors that denote anxiety and to social behaviors such as social memory and lordosis behavior in mice. In the male hippocampus, GPER1 activation has also been shown to phosphorylate the classical intracellular estrogen receptor (ER)α, suggesting that crosstalk with ERα is important in the display of these behaviors, many of which are absent in ERα-null mice. In this review, we present a number of categories of such crosstalk, using examples from literature. The function of GPER1 as an ERα collaborator or as a mER in different tissues is relevant to understanding both normal physiology and abnormal pathology, mediated by estrogen signaling.

Dual action of neuro-estrogens in the regulation of male sexual behavior

Estrogens derived from brain testosterone aromatization (neuro-estrogens) are critical for the activation of male sexual behavior. Their effects on this behavior are typically associated with long-term changes in circulating levels of testosterone and the transcriptional activity of their liganded nuclear receptors. According to this view, neuro-estrogens would prime the neural circuits controlling the long-term expression of behavior, which would then be acutely regulated by neurotransmitter systems conveying information from the social environment. In parallel, neuro-estrogens are also able to produce much faster effects than previously anticipated. Our recent investigations in Japanese quail revealed an interesting dichotomy in the regulation of male sexual behavior by membrane- and nuclear-initiated estrogen signaling providing respectively an acute modulation of sexual motivation and a long-term control of the capacity to display the copulatory sequence. In parallel, a similar dichotomy applies to the regulation of brain aromatase whose expression depends on the transcriptional activity of testosterone metabolites while its enzymatic activity is rapidly regulated in a region- and context-dependent manner. Recent evidences suggest that rapid changes in sexual motivation result from rapid changes in local estrogen production. Together, these data support the idea that the acute regulation of some aspects of male sexual behavior depends not only on classical neurotransmitter systems, but also on rapid and spatially restricted changes in local estrogen availability. The existing literature suggests that this acute regulation by neuro-estrogens of the motivational aspects of behavior could be generalized to other systems such as singing behavior in songbirds.

Increased Serum G Protein-coupled Estrogen Receptor 1 Levels and Its Diagnostic Value in Drug Naïve Patients with Major Depressive Disorder

Objective

The facts that depression is more prevalent in females than in males and females are exposed to depression more commonly during certain hormonal fluctuating periods indicate the role of sex hormones in physiopathology. Estrogen acts over estrogen receptors alpha and beta and recently identified G protein-coupled estrogen receptor 1 (GPER1). The present study aimed, for the first time, to evaluate serum GPER1 levels in drug-naïve major depressive disorder (MDD) patients.

Methods

The study included 56 newly diagnosed drug-naïve MDD patients aged between 18 and 50 years and 42 age- and gender-matched healthy volunteers. Medical history was obtained and physical examinations, laboratory tests, and the Hamilton Depression Rating Scale (HAM-D), Hamilton Anxiety Rating Scale (HAM-A) were performed. The serum GPER1 levels were measured.

Results

The HAM-D score was significantly higher in the MDD patients than in the controls. The GPER1 level was significantly higher in the MDD patients than in the controls. A positive correlation was found with GPER1 levels and depression scores. The receiver operating characteristic analysis revealed sensitivity, specificity, positive predictive value, and negative predictive value as 82.1%, 90.5%, 92.0%, and 79.2%, respectively, for the presence of depression, when the serum GPER1 value was ≥0.16.

Conclusion

This study demonstrated significantly higher serum GPER1 levels in the MDD patients than in the controls, a positive correlation was found between GPER1 levels and depression scores and serum GPER1 level was valuable in predicting the presence of depression.

G protein-coupled estrogen receptor regulates embryonic heart rate in zebrafish

Estrogens act by binding to estrogen receptors alpha and beta (ERα, ERβ), ligand-dependent transcription factors that play crucial roles in sex differentiation, tumor growth and cardiovascular physiology. Estrogens also activate the G protein-coupled estrogen receptor (GPER), however the function of GPER in vivo is less well understood. Here we find that GPER is required for normal heart rate in zebrafish embryos. Acute exposure to estrogens increased heart rate in wildtype and in ERα and ERβ mutant embryos but not in GPER mutants. GPER mutant embryos exhibited reduced basal heart rate, while heart rate was normal in ERα and ERβ mutants. We detected gper transcript in discrete regions of the brain and pituitary but not in the heart, suggesting that GPER acts centrally to regulate heart rate. In the pituitary, we observed gper expression in cells that regulate levels of thyroid hormone triiodothyronine (T3), a hormone known to increase heart rate. Compared to wild type, GPER mutants had reduced levels of T3 and estrogens, suggesting pituitary abnormalities. Exposure to exogenous T3, but not estradiol, rescued the reduced heart rate phenotype in gper mutant embryos, demonstrating that T3 acts downstream of GPER to regulate heart rate. Using genetic and mass spectrometry approaches, we find that GPER regulates maternal estrogen levels, which are required for normal embryonic heart rate. Our results demonstrate that estradiol plays a previously unappreciated role in the acute modulation of heart rate during zebrafish embryonic development and suggest that GPER regulates embryonic heart rate by altering maternal estrogen levels and embryonic T3 levels.

Estrogen hormones are important for the formation and function of the nervous, reproductive and cardiovascular systems. Here we report that acute exposure to estrogens increases heart rate, a previously unappreciated function of estrogens. Using zebrafish with mutations in genes that respond to estrogens, we found that heart rate is regulated not by the typical molecules that respond to estrogens–the nuclear estrogen receptors–but rather by a different molecule, the G protein-coupled estrogen receptor. We also show that estrogens increase heart rate by increasing levels of thyroid hormone. Our results reveal a new function for the G protein-coupled estrogen receptor and a new connection between estrogens and thyroid hormone. Environmental compounds that mimic estrogens can be harmful because they can influence gonad function. Our results suggest that endocrine disrupting compounds may also influence cardiac function.

Membrane and Nuclear Estrogen Receptor Alpha Actions: From Tissue Specificity to Medical Implications

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

G protein-coupled estrogen receptor 1 (GPER1)/GPR30 increases ERK1/2 activity through PDZ motif-dependent and -independent mechanisms

G protein-coupled receptor 30 (GPR30), also called G protein-coupled estrogen receptor 1 (GPER1), is thought to play important roles in breast cancer and cardiometabolic regulation, but many questions remain about ligand activation, effector coupling, and subcellular localization. We showed recently that GPR30 interacts through the C-terminal type I PDZ motif with SAP97 and protein kinase A (PKA)-anchoring protein (AKAP) 5, which anchor the receptor in the plasma membrane and mediate an apparently constitutive decrease in cAMP production independently of G_i/o Here, we show that GPR30 also constitutively increases ERK1/2 activity. Removing the receptor PDZ motif or knocking down specifically AKAP5 inhibited the increase, showing that this increase also requires the PDZ interaction. However, the increase was inhibited by pertussis toxin as well as by wortmannin but not by AG1478, indicating that G_i/o and phosphoinositide 3-kinase (PI3K) mediate the increase independently of epidermal growth factor receptor transactivation. FK506 and okadaic acid also inhibited the increase, implying that a protein phosphatase is involved. The proposed GPR30 agonist G-1 also increased ERK1/2 activity, but this increase was only observed at a level of receptor expression below that required for the constitutive increase. Furthermore, deleting the PDZ motif did not inhibit the G-1-stimulated increase. Based on these results, we propose that GPR30 increases ERK1/2 activity via two G_i/o-mediated mechanisms, a PDZ-dependent, apparently constitutive mechanism and a PDZ-independent G-1-stimulated mechanism.

Nuclear and Membrane Actions of Estrogen Receptor Alpha: Contribution to the Regulation of Energy and Glucose Homeostasis

Estrogen receptor alpha (ERα) has been demonstrated to play a key role in reproduction but also to exert numerous functions in nonreproductive tissues. Accordingly, ERα is now recognized as a key regulator of energy homeostasis and glucose metabolism and mediates the protective effects of estrogens against obesity and type 2 diabetes. This chapter attempts to summarize our current understanding of the mechanisms of ERα activation and their involvement in the modulation of energy balance and glucose metabolism. We first focus on the experimental studies that constitute the basis of the understanding of ERα as a nuclear receptor and more specifically on the key roles played by its two activation functions (AFs). We depict the consequences of the selective inactivation of these AFs in mouse models, which further underline the prominent role of nuclear ERα in the prevention of obesity and diabetes, as on the reproductive tract and the vascular system. Besides these nuclear actions, a fraction of ERα is associated with the plasma membrane and activates nonnuclear signaling from this site. Such rapid effects, called membrane-initiated steroid signals (MISS), have been characterized in a variety of cell lines and in particular in endothelial cells. The development of selective pharmacological tools that specifically activate MISS as well as the generation of mice expressing an ERα protein impeded for membrane localization has just begun to unravel the physiological role of MISS in vivo and their contribution to ERα-mediated metabolic protection. Finally, we discuss novel perspectives for the design of tissue-selective ER modulators.

Functional expression of G protein-coupled receptor 30 in immature rat epididymal epithelium

The aim of this study is to investigate the functional role of G protein-coupled receptor 30 (GPR30) in the epididymis. We found that GPR30 is expressed in the epithelium of the immature rat epididymis and is involved in chloride secretion into the caudal epididymis lumen. The short-circuit current (Isc) experiments showed that in primary cultured caudal epididymis epithelium, activation of GPR30 by its specific agonist G1 induced a mono-phasic current increase, and G15, the specific antagonist of GPR30, could completely inhibit the current induced by G1. The G1-induced Isc was largely blocked by application of the non-specific chloride channel inhibitor diphenylamine-dicarboxylic acid (DPC), or by the cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor CFTR_inh-172 , suggesting that the current was mainly mediated through CFTR. In addition, after stimulating GPR30 by G1, the intracellular concentration of cAMP in the epithelium was significantly increased, indicating that the cAMP signal pathway is involved and could be responsible for the CFTR activation. Finally, to further investigate the function of GPR30 in vivo, G15 was administrated into rats subcutaneously. The osmotic pressure of the micro perfusion solution from epididymis was measured and the sperms were collected. Results showed that there was an osmotic pressure increase of the perfusion solution from G15 treated rats. When the GPR30 was inhibited by G15 endogenously, the motility of sperms decreased. Our data demonstrated that GPR30 is involved in the formation of caudal epididymis fluid micro-environment thus affecting sperm motility.

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.

17β-Estradiol and Agonism of G-protein-Coupled Estrogen Receptor Enhance Hippocampal Memory via Different Cell-Signaling Mechanisms

The ability of 17β-estradiol (E2) to enhance hippocampal object recognition and spatial memory depends on rapid activation of extracellular signal-regulated kinase (ERK) in the dorsal hippocampus (DH). Although this activation can be mediated by the intracellular estrogen receptors ERα and ERβ, little is known about the role that the membrane estrogen receptor GPER plays in regulating ERK or E2-mediated memory formation. In this study, post-training DH infusion of the GPER agonist G-1 enhanced object recognition and spatial memory in ovariectomized female mice, whereas the GPER antagonist G-15 impaired memory, suggesting that GPER activation, like E2, promotes hippocampal memory formation. However, unlike E2, G-1 did not increase ERK phosphorylation, but instead significantly increased phosphorylation of c-Jun N-terminal kinase (JNK) in the DH. Moreover, DH infusion of the JNK inhibitor SP600125 prevented G-1 from enhancing object recognition and spatial memory, but the ERK inhibitor U0126 did not. These data suggest that GPER enhances memory via different cell-signaling mechanisms than E2. This conclusion was supported by data showing that the ability of E2 to facilitate memory and activate ERK signaling was not blocked by G-15 or SP600125, which demonstrates that the memory-enhancing effects of E2 are not dependent on JNK or GPER activation in the DH. Together, these data indicate that GPER regulates memory independently from ERα and ERβ by activating JNK signaling, rather than ERK signaling. Thus, the findings suggest that GPER in the DH may not function as an estrogen receptor to regulate object recognition and spatial memory.

SIGNIFICANCE STATEMENT

Although 17β-estradiol has long been known to regulate memory function, the molecular mechanisms underlying estrogenic memory modulation remain largely unknown. Here, we examined whether the putative membrane estrogen receptor GPER acts like the classical estrogen receptors, ERα and ERβ, to facilitate hippocampal memory in female mice. Although GPER activation did enhance object recognition and spatial memory, it did so by activating different cell-signaling mechanisms from ERα, ERβ, or 17β-estradiol. These data indicate that 17β-estradiol and GPER independently regulate hippocampal memory, and suggest that hippocampal GPER may not function as an estrogen receptor in the dorsal hippocampus. These findings are significant because they provide novel insights about the molecular mechanisms through which 17β-estradiol modulates hippocampal memory.

Assessment of cell line competence for studies of pharmacological GPR30 modulation

CONTEXT/OBJECTIVE

Cell lines used to study the role of the G protein-coupled receptor 30 (GPR30) or G protein-coupled estrogen receptor (GPER) as a mediator of estrogen responses have yielded conflicting results. This work identified a simple assay to predict cell line competence for pharmacological studies of GPR30.

MATERIALS AND METHODS

The phosphorylation or expression levels of ERK1/2, Akt, c-Fos and eNOS were evaluated to assess GPR30 activation in response to known agonists (17β-estradiol and G-1) in MCF-7 and T-47D breast cancer cell lines and in bovine aortic endothelial cells. GPR30 expression was analyzed by qRT-PCR and Western blot with two distinct antibodies directed at its carboxy and amino terminals.

RESULTS

None of the agonists, at any of the concentrations tested, activated any of those target proteins. Additional experiments excluded the disruption of the signaling pathway, interference of phenol red in the culture medium and constitutive proteasome degradation of GPR30 as possible causes for the lack of response of the three cell lines. Analysis of receptor expression showed the absence of clearly detectable GPR30 species of 44 and 50-55 kDa previously identified in cell lines that respond to 17β-estradiol and G-1.

DISCUSSION AND CONCLUSION

Cells that do not express the 44 and 50-55 kDa species do not respond to GPR30 agonists. Thus, the presence or absence of these GPR30 species is a simple and rapid manner to determine whether a given cell line is suitable for pharmacological or molecular studies of GPR30 modulation.

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.

Why estrogens matter for behavior and brain health

The National Institutes of Health (NIH) has required the inclusion of women in clinical studies since 1993, which has enhanced our understanding of how biological sex affects certain medical conditions and allowed the development of sex-specific treatment protocols. However, NIH's policy did not previously apply to basic research, and the NIH recently introduced a new policy requiring all new grant applications to explicitly address sex as a biological variable. The policy itself is grounded in the results of numerous investigations in animals and humans illustrating the existence of sex differences in the brain and behavior, and the importance of sex hormones, particularly estrogens, in regulating physiology and behavior. Here, we review findings from our laboratories, and others, demonstrating how estrogens influence brain and behavior in adult females. Research from subjects throughout the adult lifespan on topics ranging from social behavior, learning and memory, to disease risk will be discussed to frame an understanding of why estrogens matter to behavioral neuroscience.

Differences in GPR30 Regulation by Chlorotriazine Herbicides in Human Breast Cells

Over 200,000 cases of invasive breast cancer are diagnosed annually; herbicide contaminants in local water sources may contribute to the growth of these cancers. GPR30, a G protein coupled receptor, was identified as a potential orphan receptor that may interact with triazine herbicides such as atrazine, one of the most commonly utilized chlorotriazines in agricultural practices in the United States. Our goal was to identify whether chlorotriazines affected the expression of GPR30. Two breast cancer cell lines, MDA-MB-231 and MCF-7, as well as one normal breast cell line, MCF-10A, were treated with a 100-fold range of atrazine, cyanazine, or simazine, with levels flanking the EPA safe level for each compound. Using real-time PCR, we assessed changes in GPR30 mRNA compared to a GAPDH control. Our results indicate that GPR30 expression increased in breast cancer cells at levels lower than the US EPA drinking water contamination limit. During this treatment, the viability of cells was unaltered. In contrast, treatment with chlorotriazines reduced the expression of GPR30 in noncancerous MCF-10A cells. Thus, our results indicate that cell milieu and potential to metastasize may play a role in the extent of GPR30 response to pesticide exposure.

What's new in estrogen receptor action in the female reproductive tract

Estrogen receptor alpha (ERα) is a critical player in development and function of the female reproductive system. Perturbations in ERα response can affect wide-ranging aspects of health in humans as well as in livestock and wildlife. Because of its long-known and broad impact, ERα mechanisms of action continue to be the focus on cutting-edge research efforts. Consequently, novel insights have greatly advanced understanding of every aspect of estrogen signaling. In this review, we attempt to briefly outline the current understanding of ERα mediated mechanisms in the context of the female reproductive system.

Live-Cell Imaging of the Estrogen Receptor by Total Internal Reflection Fluorescence Microscopy

Trafficking studies of plasma membrane-localized intracellular estrogen receptors have mainly relied on biochemical and histological techniques to locate the receptor before and after estradiol stimulation. More often than not these experiments were performed using postmortem, lysed, or fixed tissue samples, whose tissue or cellular structure is typically severely altered or at times completely lost, making the definitive localization of estrogen receptors difficult to ascertain. To overcome this limitation we began using total internal reflection fluorescence microscopy (TIRFM) to study the trafficking of plasma membrane estrogen receptors. This real-time imaging approach, described in this chapter, permits observation of live, intact cells while allowing visualization of the steps (in time and spatial distribution) involved in receptor activation by estradiol and movements on and near the membrane. TIRFM yields high-contrast real-time images of fluorescently labeled E6BSA molecules on and just below the cell surface and is ideal for studying estrogen receptor trafficking in living cells.

Sex steroid hormones matter for learning and memory: estrogenic regulation of hippocampal function in male and female rodents

Ample evidence has demonstrated that sex steroid hormones, such as the potent estrogen 17β-estradiol (E2), affect hippocampal morphology, plasticity, and memory in male and female rodents. Yet relatively few investigators who work with male subjects consider the effects of these hormones on learning and memory. This review describes the effects of E2 on hippocampal spinogenesis, neurogenesis, physiology, and memory, with particular attention paid to the effects of E2 in male rodents. The estrogen receptors, cell-signaling pathways, and epigenetic processes necessary for E2 to enhance memory in female rodents are also discussed in detail. Finally, practical considerations for working with female rodents are described for those investigators thinking of adding females to their experimental designs.

The Activation Function-1 of Estrogen Receptor Alpha Prevents Arterial Neointima Development Through a Direct Effect on Smooth Muscle Cells

RATIONALE

17β-Estradiol (E2) exerts numerous beneficial effects in vascular disease. It regulates gene transcription through nuclear estrogen receptor α (ERα) via 2 activation functions, AF1 and AF2, and can also activate membrane ERα. The role of E2 on the endothelium relies on membrane ERα activation, but the molecular mechanisms of its action on vascular smooth muscle cells (VSMCs) are not fully understood.

OBJECTIVE

The aim of this study was to determine which cellular target and which ERα subfunction are involved in the preventive action of E2 on neointimal hyperplasia.

METHODS AND RESULTS

To trigger neointimal hyperplasia of VSMC, we used a mouse model of femoral arterial injury. Cre-Lox models were used to distinguish between the endothelial- and the VSMC-specific actions of E2. The molecular mechanisms underlying the role of E2 were further characterized using both selective ERα agonists and transgenic mice in which the ERαAF1 function had been specifically invalidated. We found that (1) the selective inactivation of ERα in VSMC abrogates the neointimal hyperplasia protection induced by E2, whereas inactivation of endothelial and hematopoietic ERα has no effect; (2) the selective activation of membrane ERα does not prevent neointimal hyperplasia; and (3) ERαAF1 is necessary and sufficient to inhibit postinjury VSMC proliferation.

CONCLUSIONS

Altogether, ERαAF1-mediated nuclear action is both necessary and sufficient to inhibit postinjury arterial VSMC proliferation, whereas membrane ERα largely regulates the endothelial functions of E2. This highlights the exquisite cell/tissue-specific actions of the ERα subfunctions and helps to delineate the spectrum of action of selective ER modulators.

Estrogen Effects on Cognitive and Synaptic Health Over the Lifecourse

Estrogen facilitates higher cognitive functions by exerting effects on brain regions such as the prefrontal cortex and hippocampus. Estrogen induces spinogenesis and synaptogenesis in these two brain regions and also initiates a complex set of signal transduction pathways via estrogen receptors (ERs). Along with the classical genomic effects mediated by activation of ER α and ER β, there are membrane-bound ER α, ER β, and G protein-coupled estrogen receptor 1 (GPER1) that can mediate rapid nongenomic effects. All key ERs present throughout the body are also present in synapses of the hippocampus and prefrontal cortex. This review summarizes estrogen actions in the brain from the standpoint of their effects on synapse structure and function, noting also the synergistic role of progesterone. We first begin with a review of ER subtypes in the brain and how their abundance and distributions are altered with aging and estrogen loss (e.g., ovariectomy or menopause) in the rodent, monkey, and human brain. As there is much evidence that estrogen loss induced by menopause can exacerbate the effects of aging on cognitive functions, we then review the clinical trials of hormone replacement therapies and their effectiveness on cognitive symptoms experienced by women. Finally, we summarize studies carried out in nonhuman primate models of age- and menopause-related cognitive decline that are highly relevant for developing effective interventions for menopausal women. Together, we highlight a new understanding of how estrogen affects higher cognitive functions and synaptic health that go well beyond its effects on reproduction.

Molecular mechanisms underlying the memory-enhancing effects of estradiol

This article is part of a Special Issue "Estradiol and cognition". Since the publication of the 1998 special issue of Hormones and Behavior on estrogens and cognition, substantial progress has been made towards understanding the molecular mechanisms through which 17β-estradiol (E2) regulates hippocampal plasticity and memory. Recent research has demonstrated that rapid effects of E2 on hippocampal cell signaling, epigenetic processes, and local protein synthesis are necessary for E2 to facilitate the consolidation of object recognition and spatial memories in ovariectomized female rodents. These effects appear to be mediated by non-classical actions of the intracellular estrogen receptors ERα and ERβ, and possibly by membrane-bound ERs such as the G-protein-coupled estrogen receptor (GPER). New findings also suggest a key role of hippocampally-synthesized E2 in regulating hippocampal memory formation. The present review discusses these findings in detail and suggests avenues for future study.

Osteoprotective effect of combination therapy of low-dose oestradiol with G15, a specific antagonist of GPR30/GPER in ovariectomy-induced osteoporotic rats

Administration of low-dose oestradiol (E2) combining G15, this combination therapy may be an effective supplement of drugs in prevention and treatment for postmenopausal osteoporosis.

Identified and cloned in 1996 for the first time, G protein-coupled oestrogen receptor (ER) 30 (GPR30/GPER) has been a hot spot in the field of sex hormone research till now. In the present study, we examined the effects of low-dose oestradiol (E2) combined with G15, a specific antagonist of GPR30 on ovariectomy (OVX)-induced osteoporosis in rats. Female Sprague–Dawley (SD) rats undergoing OVX were used to evaluate the osteoprotective effect of the drugs. Administration of E2 [35 μg/kg, intraperitoneally (ip), three times/week) combining G15 (160 μg/kg, ip, three times/week) for 6 weeks was found to have prevented OVX-induced effects, including increase in bone turnover rate, decrease in bone mineral content (BMC) and bone mineral density (BMD), damage of bone structure and the aggravation in biomechanical properties of bone. The therapeutic effect of these two drugs in combination was better than that of E2 alone. Meanwhile, the administration of G15 prevented body weight increase or endometrium proliferation in the rats. In conclusion, administration of low-dose E2 combining G15 had a satisfactory bone protective effect for OVX rats, without significant influence on body weight or the uterus. This combination therapy may be an effective supplement of drugs in prevention and treatment for postmenopausal osteoporosis.