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

Exploring the physiological role of the G protein-coupled estrogen receptor (GPER) and its associations with human diseases

Estrogen is a group of hormones that collaborate with the nervous system to impact the overall well-being of all genders. It influences many processes, including those occurring in the central nervous system, affecting learning and memory, and playing roles in neurodegenerative diseases and mental disorders. The hormone's action is mediated by specific receptors. Significant roles of classical estrogen receptors, ERα and ERβ, in various diseases were known since many years, but after identifying a structurally and locationally distinct receptor, the G protein-coupled estrogen receptor (GPER), its role in human physiology and pathophysiology was investigated. This review compiles GPER-related information, highlighting its impact on homeostasis and diseases, while putting special attention on functions and dysfunctions of this receptor in neurobiology and biobehavioral processes. Understanding the receptor modulation possibilities is essential for therapy, as disruptions in receptors can lead to diseases or disorders, irrespective of correct estrogen levels. We conclude that studies on the GPER receptor have the potential to develop therapies that regulate estrogen and positively impact human health.

Therapeutic significance of long noncoding RNAs in estrogen receptor-positive breast cancer

About 70% of cases of breast cancer are compromised by Estrogen-positive breast cancer. Through its regulation of several processes, including cell proliferation, cell cycle progression, and apoptosis, Estrogen signaling plays a pivotal role in the genesis and progression of this particular kind of breast cancer. One of the best treatment strategies for treating Estrogen-positive breast cancer is blocking Estrogen signaling. However, patients' treatment failure is mainly caused by the emergence of resistance and metastases, necessitating the development of novel therapeutic targets. Numerous studies have shown long noncoding RNAs (lncRNAs) to play a role in Estrogen-mediated carcinogenesis. These lncRNAs interact with co-regulators and the Estrogen signaling cascade components, primarily due to Estrogen activation. Vimentin and E-cadherin are examples of epithelial-to-mesenchymal transition markers, and they regulate genes involved in cell cycle progression, such as Cyclins, to affect the growth, proliferation, and metastasis of Estrogen-positive breast cancer. Furthermore, a few of these lncRNAs contribute to developing resistance to chemotherapy, making them more desirable targets for enhancing results. Thus, to shed light on the creation of fresh approaches for treating this cancer, this review attempts to compile recently conducted studies on the relationship between lncRNAs and the advancement of Estrogen-positive breast cancer.

Ovaries of estrogen receptor 1-deficient mice show iron overload and signs of aging

Introduction

Estrogens are crucial regulators of ovarian function, mediating their signaling through binding to estrogen receptors. The disruption of the estrogen receptor 1 (Esr1) provokes infertility associated with a hemorrhagic, cystic phenotype similar to that seen in diseased or aged ovaries. Our previous study indicated the possibility of altered iron metabolism in Esr1-deficient ovaries showing massive expression of lipocalin 2, a regulator of iron homeostasis.

Methods

Therefore, we examined the consequences of depleting Esr1 in mouse ovaries, focusing on iron metabolism. For that reason, we compared ovaries of adult Esr1-deficient animals and age-matched wild type littermates.

Results and discussion

We found increased iron accumulation in Esr1-deficient animals by using laser ablation inductively coupled plasma mass spectrometry. Western blot analysis and RT-qPCR confirmed that iron overload alters iron transport, storage and regulation. In addition, trivalent iron deposits in form of hemosiderin were detected in Esr1-deficient ovarian stroma. The depletion of Esr1 was further associated with an aberrant immune cell landscape characterized by the appearance of macrophage-derived multinucleated giant cells (MNGCs) and increased quantities of macrophages, particularly M2-like macrophages. Similar to reproductively aged animals, MNGCs in Esr1-deficient ovaries were characterized by iron accumulation and strong autofluorescence. Finally, deletion of Esr1 led to a significant increase in ovarian mast cells, involved in iron-mediated foam cell formation. Given that these findings are characteristics of ovarian aging, our data suggest that Esr1 deficiency triggers mechanisms similar to those associated with aging.

Role for Nongenomic Estrogen Signaling in Male Fertility

Estrogen actions are mediated by both nuclear (n) and membrane (m) localized estrogen receptor 1 (ESR1). Male Esr1 knockout (Esr1KO) mice lacking functional Esr1 are infertile, with reproductive tract abnormalities. Male mice expressing nESR1 but lacking mESR1 (nuclear-only estrogen receptor 1 mice) are progressively infertile due to testicular, rete testis, and efferent ductule abnormalities similar to Esr1KO males, indicating a role for mESR1 in male reproduction. The H2NES mouse expresses only mESR1 but lacks nESR1. The goal of this study was to identify the functions of mESR1 alone in mice where nESR1 was absent. Breeding trials showed that H2NES males are fertile, with decreased litter numbers but normal pup numbers/litter. In contrast to Esr1KO mice, H2NES testicular, and epididymal weights were not reduced, and seminiferous tubule abnormalities were less pronounced. However, Esr1KO and H2NES males both had decreased sperm motility and a high incidence of abnormal sperm morphology. Seminiferous tubule and rete testis dilation and decreased efferent ductule epithelial height characteristic of Esr1KO males were reduced in H2NES. Consistent with this, expression of genes involved in fluid transport and ion movement that were reduced in Esr1KO (Aqp1, Car2, Car14, Cftr) were partially or fully restored to wild-type levels in H2NES. In summary, in contrast to Esr1KO males, H2NES males are fertile and have reduced phenotypic and functional abnormalities in the testis and efferent ductules. Thus, mESR1 alone, in the absence of nESR1, can partially regulate male reproductive tract structure and function, emphasizing its importance for overall estrogen action.

GPER/PKA-Dependent Enhancement of Hormone-Sensitive Lipase Phosphorylation in 3T3-L1 Adipocytes by Piceatannol

We previously reported that piceatannol (PIC) had an anti-obesity effect only in ovariectomized (OVX) postmenopausal obesity mice. PIC was found to induce the phosphorylation of hormone-sensitive lipase (pHSL) in OVX mice. To elucidate the mechanism by which PIC activates HSL, we investigated the effect of PIC using 3T3-L1 adipocytes. PIC induced HSL phosphorylation at Ser563 in 3T3-L1 cells, as in vivo experiments showed. pHSL (Ser563) is believed to be activated through the β-adrenergic receptor (β-AR) and protein kinase A (PKA) pathways; however, the addition of a selective inhibitor of β-AR did not inhibit the effect of PIC. The addition of a PKA inhibitor with PIC blocked pHSL (Ser563), suggesting that the effects are mediated by PKA in a different pathway than β-AR. The addition of G15, a selective inhibitor of the G protein-coupled estrogen receptor (GPER), reduced the activation of HSL by PIC. Furthermore, PIC inhibited insulin signaling and did not induce pHSL (Ser565), which represents its inactive form. These results suggest that PIC acts as a phytoestrogen and phosphorylates HSL through a novel pathway that activates GPER and its downstream PKA, which may be one of the inhibitory actions of PIC on fat accumulation in estrogen deficiency.

Estrogen dysregulation, intraocular pressure, and glaucoma risk

Characterized by optic nerve atrophy due to retinal ganglion cell (RGC) death, glaucoma is the leading cause of irreversible blindness worldwide. Of the major risk factors for glaucoma (age, ocular hypertension, and genetics), only elevated intraocular pressure (IOP) is modifiable, which is largely regulated by aqueous humor outflow through the trabecular meshwork. Glucocorticoids such as dexamethasone have long been known to elevate IOP and lead to glaucoma. However, several recent studies have reported that steroid hormone estrogen levels inversely correlate with glaucoma risk, and that variants in estrogen signaling genes have been associated with glaucoma. As a result, estrogen dysregulation may contribute to glaucoma pathogenesis, and estrogen signaling may protect against glaucoma. The mechanism for estrogen-related protection against glaucoma is not completely understood but likely involves both regulation of IOP homeostasis and neuroprotection of RGCs. Based upon its known activities, estrogen signaling may promote IOP homeostasis by affecting extracellular matrix turnover, focal adhesion assembly, actin stress fiber formation, mechanosensation, and nitric oxide production. In addition, estrogen receptors in the RGCs may mediate neuroprotective functions. As a result, the estrogen signaling pathway may offer a therapeutic target for both IOP control and neuroprotection. This review examines the evidence for a relationship between estrogen and IOP and explores the possible mechanisms by which estrogen maintains IOP homeostasis.

The G Protein-Coupled Estrogen Receptor (GPER): A Critical Therapeutic Target for Cancer

Estrogens have been implicated in the pathogenesis of various cancers, with increasing concern regarding the overall rising incidence of disease and exposure to environmental estrogens. Estrogens, both endogenous and environmental, manifest their actions through intracellular and plasma membrane receptors, named ERα, ERβ, and GPER. Collectively, they act to promote a broad transcriptional response that is mediated through multiple regulatory enhancers, including estrogen response elements (EREs), serum response elements (SREs), and cyclic AMP response elements (CREs). Yet, the design and rational assignment of antiestrogen therapy for breast cancer has strictly relied upon an endogenous estrogen-ER binary rubric that does not account for environmental estrogens or GPER. New endocrine therapies have focused on the development of drugs that degrade ER via ER complex destabilization or direct enzymatic ubiquitination. However, these new approaches do not broadly treat all cancer-involved receptors, including GPER. The latter is concerning since GPER is directly associated with tumor size, distant metastases, cancer stem cell activity, and endocrine resistance, indicating the importance of targeting this receptor to achieve a more complete therapeutic response. This review focuses on the critical importance and value of GPER-targeted therapeutics as part of a more holistic approach to the treatment of estrogen-driven malignancies.

Zebrafish as an emerging model to study estrogen receptors in neural development

Estrogens induce several regulatory signals in the nervous system that are mainly mediated through estrogen receptors (ERs). ERs are largely expressed in the nervous system, yet the importance of ERs to neural development has only been elucidated over the last decades. Accumulating evidence shows a fundamental role for estrogens in the development of the central and peripheral nervous systems, hence, the contribution of ERs to neural function is now a growing area of research. The conservation of the structure of the ERs and their response to estrogens make the zebrafish an interesting model to dissect the role of estrogens in the nervous system. In this review, we highlight major findings of ER signaling in embryonic zebrafish neural development and compare the similarities and differences to research in rodents. We also discuss how the recent generation of zebrafish ER mutants, coupled with the availability of several transgenic reporter lines, its amenability to pharmacological studies and in vivo live imaging, could help us explore ER function in embryonic neural development.

Sexual Dimorphism in Cardiometabolic Diseases: The Role of AMPK

Cardiovascular diseases (CVDs) are the leading cause of mortality and disability among both males and females. The risk of cardiovascular diseases is heightened by the presence of a risk factor cluster of metabolic syndrome, covering obesity and obesity-related cardiometabolic risk factors such as hypertension, glucose, and lipid metabolism dysregulation primarily. Sex hormones contribute to metabolic regulation and make women and men susceptible to obesity development in a different manner, which necessitates sex-specific management. Identifying crucial factors that protect the cardiovascular system is essential to enhance primary and secondary prevention of cardiovascular diseases and should be explicitly studied from the perspective of sex differences. It seems that AMP-dependent protein kinase (AMPK) may be such a factor since it has the protective role of AMPK in the cardiovascular system, has anti-diabetic properties, and is regulated by sex hormones. Those findings highlight the potential cardiometabolic benefits of AMPK, making it an essential factor to consider. Here, we review information about the cross-talk between AMPK and sex hormones as a critical point in cardiometabolic disease development and progression and a target for therapeutic intervention in human disease.

G-protein couple receptor (GPER1) plays an important role during ovarian folliculogenesis and early development of the Chinese Alligator

The critical role of the G protein-coupled receptor 1 (GPER1), a member of the seven-transmembrane G protein-coupled receptor family, in the functional regulation of oocytes accumulated abundant theories in the early research on model animals. However, the full-length cDNA encoding GPER1 and its role in the folliculogenesis has not been illustrated in crocodilians. 0.5, 3, and 12 months old Alligator sinensis cDNA samples were used to clone the full-length cDNA encoding GPER1. Immunolocalization and quantitative analysis were performed using Immunofluorescence technique, RT-PCR and Western blot. Simultaneously, studies on GPER1's promoter deletion and cis-acting transcriptional regulation mechanism were conducted. Immunolocalization staining for the germline marker DDX4 and GPER1 demonstrated that DDX4-positive oocytes were clustered tightly together within the nests, whereas scarcely any detectable GPER1 was present in the oocytes nest in Stage I. After that, occasionally GPER1-positive immunosignal was observed in oocytes and somatic cells additional with the primordial follicles, and it was mainly located at the granulosa cells or thecal cells within the early PFs in the Stage III. The single mutation of the putative SP1 motif, double mutating of Ets/SP1 and SP1/CRE binding sites all depressed promoter activities. This result will help to investigate the role of GPER1 in the early folliculogenesis of A. sinensis.

The Role of Female Reproductive Hormones in the Association between Migraine and Breast Cancer: An Unanswered Question

Accumulating epidemiological studies have investigated a possible interconnection between migraine (Mi) and breast cancer (BC) because of the strong link between these diseases and female reproductive hormones. This review aims to consolidate findings from epidemiological studies and explore biologically plausible hypothetical mechanisms related to hormonal pathways. Current evidence suggests a protective role of Mi in BC development, particularly in case-control studies but not in cohort ones. The inconsistency among studies may be due to several reasons, including diagnostic criteria for Mi and the age gap between the development of these two diseases. Furthermore, recent research has challenged the concept of a net beneficial effect of Mi on BC, suggesting a more complex relationship between the two conditions. Many polymorphisms/mutations in hormone-related pathways are involved in at least one of the two conditions. The most promising evidence has emerged for a specific alteration in the estrogen receptor 1 gene (rs2228480). However, the possible specific mutation or polymorphism involved in this association has not yet been identified. Further studies with robust methodologies are needed to validate the protective role of Mi in BC and fully elucidate the precise nature of this causal relationship.

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.

Non-Coding RNAs Modulating Estrogen Signaling and Response to Endocrine Therapy in Breast Cancer

The largest part of human DNA is transcribed into RNA that does not code for proteins. These non-coding RNAs (ncRNAs) are key regulators of protein-coding gene expression and have been shown to play important roles in health, disease and therapy response. Today, endocrine therapy of ERα-positive breast cancer (BC) is a successful treatment approach, but resistance to this therapy is a major clinical problem. Therefore, a deeper understanding of resistance mechanisms is important to overcome this resistance. An increasing amount of evidence demonstrate that ncRNAs affect the response to endocrine therapy. Thus, ncRNAs are considered versatile biomarkers to predict or monitor therapy response. In this review article, we intend to give a summary and update on the effects of microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) on estrogen signaling in BC cells, this pathway being the target of endocrine therapy, and their role in therapy resistance. For this purpose, we reviewed articles on these topics listed in the PubMed database. Finally, we provide an assessment regarding the clinical use of these ncRNA types, particularly their circulating forms, as predictive BC biomarkers and their potential role as therapy targets to overcome endocrine resistance.

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.

Comparative G-Protein-Coupled Estrogen Receptor (GPER) Systems in Diabetic and Cancer Conditions: A Review

For many patients, diabetes Mellitus and Malignancy are frequently encountered comorbidities. Diabetes affects approximately 10.5% of the global population, while malignancy accounts for 29.4 million cases each year. These troubling statistics indicate that current treatment approaches for these diseases are insufficient. Alternative therapeutic strategies that consider unique signaling pathways in diabetic and malignancy patients could provide improved therapeutic outcomes. The G-protein-coupled estrogen receptor (GPER) is receiving attention for its role in disease pathogenesis and treatment outcomes. This review aims to critically examine GPER' s comparative role in diabetes mellitus and malignancy, identify research gaps that need to be filled, and highlight GPER's potential as a therapeutic target for diabetes and malignancy management. There is a scarcity of data on GPER expression patterns in diabetic models; however, for diabetes mellitus, altered expression of transport and signaling proteins has been linked to GPER signaling. In contrast, GPER expression in various malignancy types appears to be complex and debatable at the moment. Current data show inconclusive patterns of GPER expression in various malignancies, with some indicating upregulation and others demonstrating downregulation. Further research should be conducted to investigate GPER expression patterns and their relationship with signaling pathways in diabetes mellitus and various malignancies. We conclude that GPER has therapeutic potential for chronic diseases such as diabetes mellitus and malignancy.

Estrogens: Two nuclear receptors, multiple possibilities

Much is known about estrogen action in experimental animal models and in human physiology. This article reviews the mechanisms of estrogen activity in animals and humans and the role of its two receptors α and β in terms of structure and mechanisms of action in various tissues in health and in relationship with human pathologies (e.g., osteoporosis). Recently, the spectrum of clinical pictures of estrogen resistance caused by estrogen receptors gene variants has been widened by our description of a woman with β-receptor defect, which could be added to the already known descriptions of α-receptor defect in women and men and β-receptor defect in men. The essential role of the β-receptor in the development of the gonad stands out. We summarize the clinical pictures due to estrogen resistance in men and women and focus on long-term follow-up of two women, one with α- and the other with β-receptor resistance. Some open questions remain on the complex interactions between the two receptors on bone metabolism and hypothalamus-pituitary-gonadal axis, which need further deepening and research.

Effects of bisphenol A and estradiol in adult rat testis after prepubertal and pubertal exposure

Over the past few decades, male fertility has been decreasing worldwide. Many studies attribute this outcome to endocrine disruptors exposure such as bisphenol A (BPA), which is a chemical compound used in plastics synthesis and exhibiting estrogenic activity. In order to assess how the window of exposure modulates the effects of BPA on the testis, prepubertal (15 dpp to 30 dpp) and pubertal (60 dpp to 75 dpp) male Sprague-Dawley rats were exposed to BPA (50 µg/kg bw/day), 17-β-estradiol (E2) (20 µg/kg bw/day) as a positive control, or to a combination of these compounds. For both periods of exposure, the rats were sacrificed and their testes were collected at 75 dpp. The histological analysis and the quantification of the gene expression of testis cell markers by RT-qPCR confirmed the complete spermatogenesis in all groups for both periods of exposure. However, our results suggest a deleterious effect of BPA on the blood-testis barrier in adults after pubertal exposure as BPA and BPA+E2 treatments induced a decrease in caveolin-1 and connexin-43 gene expression; which are proteins of the junctional complexes. As none of these effects were found after a prepubertal exposure, these results suggested the reversibility of BPA's effects. Caution must be taken when transposing this finding to humans and further studies are needed in this regard. However, from a regulatory perspective, this study emphasizes the importance of taking into account different periods of exposure, as they present different sensitivities to BPA exposure.

Sex Steroid Receptors in Polycystic Ovary Syndrome and Endometriosis: Insights from Laboratory Studies to Clinical Trials

Polycystic ovary syndrome (PCOS) and endometriosis are reproductive disorders that may cause infertility. The pathology of both diseases has been suggested to be associated with sex steroid hormone receptors, including oestrogen receptors (ER), progesterone receptors (PRs) and androgen receptors (ARs). Therefore, with this review, we aim to provide an update on the available knowledge of these receptors and how their interactions contribute to the pathogenesis of PCOS and endometriosis. One of the main PCOS-related medical conditions is abnormal folliculogenesis, which is associated with the downregulation of ER and AR expression in the ovaries. In addition, metabolic disorders in PCOS are caused by dysregulation of sex steroid hormone receptor expression. Furthermore, endometriosis is related to the upregulation of ER and the downregulation of PR expression. These receptors may serve as therapeutic targets for the treatment of PCOS-related disorders and endometriosis, considering their pathophysiological roles. Receptor agonists may be applied to increase the expression of a specific receptor and treat endometriosis or metabolic disorders. In contrast, receptor antagonist functions to reduce receptor expression and can be used to treat endometriosis and induce ovulation. Understanding PCOS and the pathological roles of endometriosis sex steroid receptors is crucial for developing potential therapeutic strategies to treat infertility in both conditions. Therefore, research should be continued to fill the knowledge gap regarding the subject.

Modulatory Effects of Estradiol and Its Mixtures with Ligands of GPER and PPAR on MAPK and PI3K/Akt Signaling Pathways and Tumorigenic Factors in Mouse Testis Explants and Mouse Tumor Leydig Cells

The present study was designed to evaluate how estradiol alone or in combination with G protein-coupled estrogen receptor (GPER) agonists and GPER and peroxisome proliferator-activated receptor (PPAR) antagonists alter the expression of tumor growth factor β (TGF-β), cyclooxygenase-2 (COX-2), hypoxia inducible factor 1-alpha (HIF-1α), and vascular endothelial growth factor (VEGF) in mouse testis explants and MA-10 mouse tumor Leydig cells. In order to define the hormone-associated signaling pathway, the expression of MAPK and PI3K/Akt was also examined. Tissue explants and cells were treated with estradiol as well as GPER agonist (ICI 182,780), GPER antagonist (G-15), PPARα antagonist (GW6471), and PPARγ antagonist (T00709072) in various combinations. First, we showed that in testis explants GPER and PPARα expressions were activated by the GPER agonist and estradiol (either alone or in mixtures), whereas PPARγ expression was activated only by GPER agonist. Second, increased TGF-β expression and decreased COX-2 expression were found in all experimental groups of testicular explants and MA-10 cells, except for up-regulated COX-2 expression in estradiol-treated cells, compared to respective controls. Third, estradiol treatment led to elevated expression of HIF-1α and VEGF, while their lower levels versus control were noted in the remaining groups of explants. Finally, we demonstrated the up-regulation of MAPK and PI3Kp85/Akt expressions in estradiol-treated groups of both ex vivo and in vitro models, whereas estradiol in mixtures with compounds of agonistic or antagonistic properties either up-regulated or down-regulated signaling kinase expression levels. Our results suggest that a balanced estrogen level and its action together with proper GPER and PPAR signaling play a key role in the maintenance of testis homeostasis. Moreover, changes in TGF-β and COX-2 expressions (that disrupted estrogen pathway) as well as disturbed GPER-PPAR signaling observed after estradiol treatment may be involved in testicular tumorigenesis.

The Regulation of Adipose Tissue Health by Estrogens

Obesity and its' associated metabolic diseases such as type 2 diabetes and cardiometabolic disorders are significant health problems confronting many countries. A major driver for developing obesity and metabolic dysfunction is the uncontrolled expansion of white adipose tissue (WAT). Specifically, the pathophysiological expansion of visceral WAT is often associated with metabolic dysfunction due to changes in adipokine secretion profiles, reduced vascularization, increased fibrosis, and enrichment of pro-inflammatory immune cells. A critical determinate of body fat distribution and WAT health is the sex steroid estrogen. The bioavailability of estrogen appears to favor metabolically healthy subcutaneous fat over visceral fat growth while protecting against changes in metabolic dysfunction. Our review will focus on the role of estrogen on body fat partitioning, WAT homeostasis, adipogenesis, adipocyte progenitor cell (APC) function, and thermogenesis to control WAT health and systemic metabolism.

Implications of estrogen receptor alpha (ERa) with the intersection of organophosphate flame retardants and diet-induced obesity in adult mice

Previously, organophosphate flame retardants (OPFRs) were found to produce intersecting disruptions of energy homeostasis using an adult mouse model of diet-induced obesity. Using the same mixture consisting of 1 mg/kg/day of each triphenyl phosphate, tricresyl phosphate, and tris(1,3-dichloro-2-propyl)phosphate, the current study aimed to identify the role of estrogen receptor alpha (ERα) in OPFR-induced disruption, utilizing ERα knockout (ERαKO) mice fed either a low-fat diet (LFD) or high-fat diet (HFD). Body weight and composition, food intake patterns, glucose and insulin tolerance, circulating peptide hormones, and expression of hypothalamic genes associated with energy homeostasis were measured. When fed HFD, no marked direct effects of OPFR were observed in mice lacking ERα, suggesting a role for ERα in generating previously reported wildtype (WT) findings. Male ERαKO mice fed LFD experienced decreased feeding efficiency and altered insulin tolerance, whereas their female counterparts displayed less fat mass and circulating ghrelin when exposed to OPFRs. These effects were not noted in the previous WT study, indicating that loss of ERα may sensitize animals fed LFD to alternate pathways of endocrine disruption by OFPRs. Collectively, these data demonstrate both direct and indirect actions of OPFRs on ERα-mediated pathways governing energy homeostasis and support a growing body of evidence urging concern for risk of human exposure.

Estradiol Signaling at the Heart of Folliculogenesis: Its Potential Deregulation in Human Ovarian Pathologies

Estradiol (E2) is a major hormone controlling women fertility, in particular folliculogenesis. This steroid, which is locally produced by granulosa cells (GC) within ovarian follicles, controls the development and selection of dominant preovulatory follicles. E2 effects rely on a complex set of nuclear and extra-nuclear signal transduction pathways principally triggered by its nuclear receptors, ERα and ERβ. These transcription factors are differentially expressed within follicles, with ERβ being the predominant ER in GC. Several ERβ splice isoforms have been identified and display specific structural features, which greatly complicates the nature of ERβ-mediated E2 signaling. This review aims at providing a concise overview of the main actions of E2 during follicular growth, maturation, and selection in human. It also describes the current understanding of the various roles of ERβ splice isoforms, especially their influence on cell fate. We finally discuss how E2 signaling deregulation could participate in two ovarian pathogeneses characterized by either a follicular arrest, as in polycystic ovary syndrome, or an excess of GC survival and proliferation, leading to granulosa cell tumors. This review emphasizes the need for further research to better understand the molecular basis of E2 signaling throughout folliculogenesis and to improve the efficiency of ovarian-related disease therapies.

Assessing Estrogenic Activity of Classical Estrogen Receptor-Binding Compounds

The classical estrogen receptor α (ERα) has been a clinical therapeutic target for decades. ERα-targeted drugs have shown great clinical success, in particular as antagonists for the treatment of ERα-positive breast cancers. However, ERα-targeted agonists have also been clinically useful (e.g., for the treatment of osteoporosis). The breast cancer field is regularly identifying novel ERα-binding compounds with the goal of identifying new potential ERα-targeted therapeutics. To determine whether such newly identified ERα-binding compounds have clinical potential, it is important to characterize the estrogenic activity (i.e., both receptor-mediated agonism and/or antagonism) of these compounds. This chapter focuses on methods that allow determination of whether an ERα-binding compound acts as an agonist or antagonist of the receptor and whether the compound induces degradation of the receptor.

Assessment of Metabolic Regulation by Estrogen Receptors

Estrogens, predominantly 17β-estradiol (E2), are a class of steroid hormones critical for diverse functions in the body both during normal physiology and disease. Primary actions of E2 include reproduction and development of secondary sexual characteristics. In addition, E2 action is involved in the nervous, immune, vascular, muscular, skeletal, and endocrine systems, all of which contribute to multiple aspects of metabolism. The actions of E2 have traditionally been attributed to the classical nuclear estrogen receptors (ERα and ERβ) that largely mediate transcriptional/genomic activities. However, over the last decade, the G protein-coupled estrogen receptor (GPER/GPR30) has become recognized as a mediator of rapid as well as transcriptional actions of E2, employing both in vitro and in vivo approaches. Recent evidence strongly supports the role of GPER in metabolic regulation. Murine genetic knockout (KO) models and pharmacological tools (agonists and antagonists) represent important approaches to understand the mechanisms of E2 action in physiology and disease via GPER. Studies in cells and GPER KO mice have revealed functions for GPER in the regulation of body weight and metabolism. This chapter focuses on methods relevant for the evaluation of metabolic parameters in vivo, ex vivo, and in vitro. We have emphasized glucose homeostasis through the determination of glucose and insulin tolerance, pancreatic islet function, and glucose uptake. In addition, we describe methods of adipocyte isolation, differentiation of preadipocytes, and evaluation of mitochondrial function.

Skeletal muscle wasting: the estrogen side of sexual dimorphism

The importance of defining sex differences across various biological and physiological mechanisms is more pervasive now than it has been over the past 15-20 years. As the muscle biology field pushes to identify small molecules and interventions to prevent, attenuate, or even reverse muscle wasting, we must consider the effect of sex as a biological variable. It should not be assumed that a therapeutic will affect males and females with equal efficacy or equivalent target affinities under conditions where muscle wasting is observed. With that said, it is not surprising to find that we have an unclear or even a poor understanding of the effects of sex or sex hormones on muscle wasting conditions. Although recent investigations are beginning to establish experimental approaches that will allow investigators to assess the impact of sex-specific hormones on muscle wasting, the field still needs rigorous scientific tools that will allow the community to address critical hypotheses centered around sex hormones. The focus of this review is on female sex hormones, specifically estrogens, and the roles that these hormones and their receptors play in skeletal muscle wasting conditions. With the overall review goal of assembling the current knowledge in the area of sexual dimorphism driven by estrogens with an effort to provide insights to interested physiologists on necessary considerations when trying to assess models for potential sex differences in cellular and molecular mechanisms of muscle wasting.

Insulin receptor cleavage induced by estrogen impairs insulin signaling

INTRODUCTION

Soluble insulin receptor (sIR), which is the ectodomain of insulin receptor (IR), is present in human plasma. Plasma sIR levels are positively correlated with blood glucose levels and negatively correlated with insulin sensitivity. An in vitro model of IR cleavage shows that extracellular calpain 2 directly cleaves IR, which generates sIR, and sequential cleavage of the IRβ subunit by γ-secretase impairs insulin signaling in a glucose concentration-dependent manner. Nevertheless, sIR levels vary among subjects with normal glucose levels.

RESEARCH DESIGN AND METHODS

We examined sIR levels of pregnant women throughout gestation. Using an in vitro model, we also investigated the molecular mechanisms of IR cleavage induced by estradiol.

RESULTS

In pregnant women, sIR levels were positively correlated with estrogen levels and significantly increased at late pregnancy independent of glucose levels. Using an in vitro model, estrogen elicited IR cleavage and impaired cellular insulin signaling. Estradiol-induced IR cleavage was inhibited by targeting of calpain 2 and γ-secretase. Estrogen exerted these biological effects via G protein-coupled estrogen receptor, and its selective ligand upregulated calpain 2 expression and promoted exosome secretion, which significantly increased extracellular calpain 2. Simultaneous stimulation of estrogen and high glucose levels had a synergic effect on IR cleavage. Metformin prevented calpain 2 release in exosomes and restored insulin signaling impaired by estrogen.

CONCLUSIONS

Estradiol-induced IR cleavage causes cellular insulin resistance, and its molecular mechanisms are shared with those by high glucose levels. sIR levels at late pregnancy are significantly elevated along with estrogen levels. Therefore, estradiol-induced IR cleavage is preserved in pregnant women and could be part of the etiology of insulin resistance in gestational diabetes mellitus and overt diabetes during pregnancy.

Molecular Characterization of Membrane Steroid Receptors in Hormone-Sensitive Cancers

Cancer is one of the most common causes of death worldwide, and its development is a result of the complex interaction of genetic factors, environmental cues, and aging. Hormone-sensitive cancers depend on the action of one or more hormones for their development and progression. Sex steroids and corticosteroids can regulate different physiological functions, including metabolism, growth, and proliferation, through their interaction with specific nuclear receptors, that can transcriptionally regulate target genes via their genomic actions. Therefore, interference with hormones’ activities, e.g., deregulation of their production and downstream pathways or the exposition to exogenous hormone-active substances such as endocrine-disrupting chemicals (EDCs), can affect the regulation of their correlated pathways and trigger the neoplastic transformation. Although nuclear receptors account for most hormone-related biologic effects and their slow genomic responses are well-studied, less-known membrane receptors are emerging for their ability to mediate steroid hormones effects through the activation of rapid non-genomic responses also involved in the development of hormone-sensitive cancers. This review aims to collect pre-clinical and clinical data on these extranuclear receptors not only to draw attention to their emerging role in cancer development and progression but also to highlight their dual role as tumor microenvironment players and potential candidate drug targets.

Hormonal influences in migraine - interactions of oestrogen, oxytocin and CGRP

Migraine is ranked as the second highest cause of disability worldwide and the first among women aged 15-49 years. Overall, the incidence of migraine is threefold higher among women than men, though the frequency and severity of attacks varies during puberty, the menstrual cycle, pregnancy, the postpartum period and menopause. Reproductive hormones are clearly a key influence in the susceptibility of women to migraine. A fall in plasma oestrogen levels can trigger attacks of migraine without aura, whereas higher oestrogen levels seem to be protective. The basis of these effects is unknown. In this Review, we discuss what is known about sex hormones and their receptors in migraine-related areas in the CNS and the peripheral trigeminovascular pathway. We consider the actions of oestrogen via its multiple receptor subtypes and the involvement of oxytocin, which has been shown to prevent migraine attacks. We also discuss possible interactions of these hormones with the calcitonin gene-related peptide (CGRP) system in light of the success of anti-CGRP treatments. We propose a simple model to explain the hormone withdrawal trigger in menstrual migraine, which could provide a foundation for improved management and therapy for hormone-related migraine in women.

The Interface of Nuclear and Membrane Steroid Signaling

Steroid hormones bind receptors in the cell nucleus and in the cell membrane. The most widely studied class of steroid hormone receptors are the nuclear receptors, named for their function as ligand-dependent transcription factors in the cell nucleus. Nuclear receptors, such as estrogen receptor alpha, can also be anchored to the plasma membrane, where they respond to steroids by activating signaling pathways independent of their function as transcription factors. Steroids can also bind integral membrane proteins, such as the G protein-coupled estrogen receptor. Membrane estrogen and progestin receptors have been cloned and characterized in vitro and influence the development and function of many organ systems. Membrane androgen receptors were cloned and characterized in vitro, but their function as androgen receptors in vivo is unresolved. We review the identity and function of membrane proteins that bind estrogens, progestins, and androgens. We discuss evidence that membrane glucocorticoid and mineralocorticoid receptors exist, and whether glucocorticoid and mineralocorticoid nuclear receptors act at the cell membrane. In many cases, integral membrane steroid receptors act independently of nuclear steroid receptors, even though they may share a ligand.

Structure-Activity Relationship of para-Carborane Selective Estrogen Receptor β Agonists

Selective agonism of the estrogen receptor (ER) subtypes, ERα and ERβ, has historically been difficult to achieve due to the high degree of ligand-binding domain structural similarity. Multiple efforts have focused on the use of classical organic scaffolds to model 17β-estradiol geometry in the design of ERβ selective agonists, with several proceeding to various stages of clinical development. Carborane scaffolds offer many unique advantages including the potential for novel ligand/receptor interactions but remain relatively unexplored. We synthesized a series of para-carborane estrogen receptor agonists revealing an ERβ selective structure-activity relationship. We report ERβ agonists with low nanomolar potency, greater than 200-fold selectivity for ERβ over ERα, limited off-target activity against other nuclear receptors, and only sparse CYP450 inhibition at very high micromolar concentrations. The pharmacological properties of our para-carborane ERβ selective agonists measure favorably against clinically developed ERβ agonists and support further evaluation of carborane-based selective estrogen receptor modulators.

G Protein-Coupled Estrogen Receptor Agonist G-1 Inhibits Mantle Cell Lymphoma Growth in Preclinical Models

Mantle cell lymphoma (MCL) is an aggressive form of non-Hodgkin’s B-cell lymphoma with poor prognosis. Despite recent advances, resistance to therapy and relapse remain significant clinical problems. G-protein-coupled estrogen receptor (GPER)-mediated estrogenic rapid signaling is implicated in the development of many cancers. However, its role in MCL is unknown. Here we report that GPER activation with selective agonist G-1 induced cell cycle arrest, DNA damage, mitochondria membrane potential abnormality, and eventually apoptosis of MCL cell lines. We found that G-1 induced DNA damage and apoptosis of MCL cells by promoting the expression of nicotinamide adenine dinucleotide phosphate oxidase and the generation of reactive oxygen species. In addition, G-1 inhibited MCL cell proliferation by inactivation of NF-κB signaling and exhibited anti-tumor functions in MCL xenografted mice. Most significantly, G-1 showed synergistic effect with ibrutinib making it a potential candidate for chemotherapy-free therapies against MCL.

Endocrine Disrupting Chemicals, Hormone Receptors, and Acne Vulgaris: A Connecting Hypothesis

The relationship between endocrine disrupting chemicals (EDCs) and the pathogenesis of acne vulgaris has yet to be explored in the literature. Acne vulgaris is a chronic inflammatory skin disease of the pilosebaceous unit. The pathogenesis of acne involves several hormonal pathways, including androgens, insulin-like growth factor 1(IGF-1), estrogens, and corticosteroids. EDCs influence these pathways primarily through two mechanisms: altering endogenous hormone levels and interfering with hormone receptor function. This review article describes the mechanistic links between EDCs and the development of acne lesions. Highlighted is the contributory role of androgen receptor ligands, such as bisphenol A (BPA) and mono-2-ethylhexyl Phthalate (MEHP), via upregulation of lipogenic genes and resultant exacerbation of cholesterol synthesis. Additionally discussed is the protective role of phytoestrogen EDCs in counteracting androgen-induced sebocyte maturation through attenuation of PPARy transcriptional activity (i.e., resveratrol) and restoration of estrogen-regulated TGF-B expression in skin cells (i.e., genistein). Examination of the relationship between EDCs and acne vulgaris may inform adjunctive avenues of treatment such as limiting environmental exposures, and increasing low-glycemic, plant-rich foods in the diet. With a better understanding of the cumulative role that EDCs play in acne, clinicians can be better equipped to treat and ultimately improve the lives of their patients.

Role of G Protein-Coupled Estrogen Receptor in Digestive System Carcinomas: A Minireview

Digestive system carcinomas are one of the leading causes of cancer-related deaths worldwide. G protein-coupled estrogen receptor (GPER), a novel estrogen receptor, has been recognized as an important mediator in numerous cancer types. Recently, the function and clinical significance of GPER in digestive system carcinomas has been a subject of interest. Increasing evidence has revealed that GPER plays an important role as a potential biomarker in digestive system carcinomas. This work summarizes the recent literature and focuses on the emerging functional role of GPER in digestive system carcinomas, including gastric cancer, hepatocellular carcinoma, pancreatic cancer, and colorectal cancer. The potential application of GPER in novel strategies for the diagnosis and treatment of digestive system carcinomas is discussed and highlighted.

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.

Estrogens and development of the rete testis, efferent ductules, epididymis and vas deferens

Estrogen has always been considered the female hormone and testosterone the male hormone. However, estrogen's presence in the testis and deleterious effects of estrogen treatment during development have been known for nearly 90 years, long before estrogen receptors (ESRs) were discovered. Eventually it was learned that testes actually synthesize high levels of estradiol (E2) and sequester high concentrations in the reproductive tract lumen, which seems contradictory to the overwhelming number of studies showing reproductive pathology following exogenous estrogen exposures. For too long, the developmental pathology of estrogen has dominated our thinking, even resulting in the "estrogen hypothesis" as related to the testicular dysgenesis syndrome. However, these early studies and the development of an Esr1 knockout mouse led to a deluge of research into estrogen's potential role in and disruption of development and function of the male reproductive system. What is new is that estrogen action in the male cannot be divorced from that of androgen. This paper presents what is known about components of the estrogen pathway, including its synthesis and target receptors, and the need to achieve a balance between androgen- and estrogen-action in male reproductive tract differentiation and adult functions. The review focuses on what is known regarding development of the male reproductive tract, from the rete testis to the vas deferens, and examines the expression of estrogen receptors and presence of aromatase in the male reproductive system, traces the evidence provided by estrogen-associated knockout and transgenic animal models and discusses the effects of fetal and postnatal exposures to estrogens. Hopefully, there will be enough here to stimulate discussions and new investigations of the androgen:estrogen balance that seems to be essential for development of the male reproductive tract.

Targeting the G protein-coupled estrogen receptor (GPER) in obesity and diabetes

Obesity has become a global epidemic in the modern world with the numbers of obese individuals having risen at alarming rates in the last decades. Obesity represents a serious medical condition that can lead to multiple complications, such as diabetes, dyslipidemia, cardiovascular disease including hypertension and atherosclerosis, stroke and increases in the risk of many types of cancer. Very few effective options exist to treat obesity, with many removed from the market due to associated complications. Obesity and metabolic syndrome display a sexual dichotomy, with (premenopausal) females displaying protection from weight gain and metabolic dysfunction compared to men. These beneficial effects are generally attributed to a class of female ovarian hormone, estrogens, which exert pleiotropic effects in multiple metabolic tissues, such as adipose, skeletal muscle, liver and pancreas. Multiple receptors mediate the actions of estrogens, including the classical nuclear estrogen receptors (ER α and ER β) and the G protein-coupled estrogen receptor (GPER). While the roles of nuclear ERs are more established, evidence of GPER function in metabolic homeostasis is still emerging. In this review, we will discuss the latest advances concerning the contributions of GPER towards obesity and metabolism utilizing GPER-selective pharmacological (agonists or antagonists) or genetic (GPER knock out mice or cells) tools. We present evidence that GPER regulates body weight, fat distribution, inflammation and glucose and lipid homeostasis via effects on metabolic tissues. Selective agonism of GPER by its agonist G-1 can alleviate symptoms of obesity and metabolic dysfunction in multiple murine models, thereby limiting weight gain, reducing insulin resistance and inflammation and improving glucose and lipid homeostasis in vivo. Thus, GPER represents a novel therapeutic target, with G-1 a first-in-class therapeutic agent, to treat obesity and its associated comorbidities, including diabetes.

Decreasing myocardial estrogen receptors and antioxidant activity may be responsible for increasing ischemia- and reperfusion-induced ventricular arrhythmia in older female rats

AIMS

This study aimed to investigate the relationship between ischemia- and reperfusion-induced arrhythmia and blood serum estrogen levels, myocardial estrogen receptor levels, antioxidant enzyme activities, and the effects of the estrogen receptor blocker, fulvestrant (ICI 182 780).

MAIN METHODS

A total of 102 female Sprague-Dawley rats of different ages (2-3, 6-7, 14-15, and 20-21 months) were used in this study. Myocardial ischemia was produced by ligation of the descending branch of the left anterior descending coronary artery, and reperfusion was produced by releasing this artery. An electrocardiogram (ECG) and blood pressure were recorded for 6 min of ischemia and 6 min of reperfusion. The levels of superoxide dismutase (SOD), malondialdehyde (MDA), catalase (CAT), estrogen receptor α (ERα), and estrogen receptor β (ERβ) in myocardial tissue and 17 beta-estradiol (E2) in blood serum were measured via enzyme-linked immunosorbent assay (ELISA). The results were compared using a Mann-Whitney U test, one-way analysis of variance (ANOVA), and a student's t-test.

KEY FINDINGS

It is not the changes in serum estrogen levels but the decreasing myocardial estrogen receptors and antioxidant activities that could be responsible for the occurrence of more severe arrhythmia in response to reperfusion in older female rats.

SIGNIFICANCE

The death rate due to a heart attack in younger men is higher than in women. However, it equalizes after the menopausal stage in women. In this study, the reason for the increasing sudden post-menopausal death rate in women was investigated experimentally.

BIO 300: a promising radiation countermeasure under advanced development for acute radiation syndrome and the delayed effects of acute radiation exposure

INTRODUCTION

There are no radioprotectors currently approved by the United States Food and Drug Administration (US FDA) for either the hematopoietic acute radiation syndrome (H-ARS) or for the acute radiation gastrointestinal syndrome (GI-ARS). There are currently, however, three US FDA-approved medicinals that serve to mitigate acute irradiation-associated hematopoietic injury.

AREA COVERED

We present the current status of a promising radiation countermeasure, BIO 300 (a genistein-based agent), that has been extensively investigated in murine models of H-ARS and models of the delayed effects of acute radiation exposure (DEARE) and is currently being evaluated in large animal models. It is also being developed for the prevention of radiation-induced toxicities associated with solid tumor radiotherapy and is the subject of two active Investigational New Drug (IND) applications. We have included a listing and brief review of significant investigations of this promising medical countermeasure.

EXPERT OPINION

BIO 300 is a leading radioprotector under advanced development for H-ARS and DEARE, as well as for select oncologic indication(s). Efficacy following oral administration (po), lack of clinical side effects, storage at ambient temperature, and intended dual use makes BIO 300 an ideal candidate for military and civilian use as well as for storage in the Strategic National Stockpile.

Characterization of G protein-coupled estrogen receptors in Japanese medaka, Oryzias latipes

The G protein-coupled estrogen receptor 1 (Gper1) is a membrane-bound estrogen receptor that mediates non-genomic action of estrogens. A Gper1-mediating pathway has been implicated in reproductive activities in fish, including oocyte growth, but Gper1 has been characterized in only a very limited number of fish species. In this study, we cloned and characterized two genes encoding medaka (Oryzias latipes) Gper1s, namely, Gper1a and Gper1b, and phylogenic and synteny analyses suggest that these genes originate through a teleost-specific whole genome duplication event. We found that Gper1a induced phosphorylation of mitogen-activated protein kinase (MAPK) in 293T cells transfected with medaka Gper1s on exposure to the natural estrogen, 17β-estradiol (E2) and a synthetic Gper1 agonist (G-1), and treatment with both E2 and G-1 also decreased the rate of spontaneous maturation in medaka oocytes. These findings show that the processes for oocyte growth and maturation are sensitive to estrogens and are possibly mediated through Gper1a in medaka. We also show that 17α-ethinylestradiol (EE2), one of the most potent estrogenic endocrine-disrupting chemicals, and bisphenol A (BPA, a weak environmental estrogen) augmented phosphorylation of MAPK through medaka Gper1s in 293T cells. Interestingly, however, treatment with EE2 or BPA did not attenuate maturation of medaka oocytes. Our findings support that Gper1-mediated effects on oocytes are conserved among fish species, but effects of estrogenic endocrine-disrupting chemicals on oocytes acting through Gper1 may be divergent among fish species.

Therapeutic Perspectives on the Modulation of G-Protein Coupled Estrogen Receptor, GPER, Function

Estrogens exert their physiological and pathophysiological effects via cellular receptors, named ERα, ERβ, and G-protein coupled estrogen receptor (GPER). Estrogen-regulated physiology is tightly controlled by factors that regulate estrogen bioavailability and receptor sensitivity, while disruption of these control mechanisms can result in loss of reproductive function, cancer, cardiovascular and neurodegenerative disease, obesity, insulin resistance, endometriosis, and systemic lupus erythematosus. Restoration of estrogen physiology by modulating estrogen bioavailability or receptor activity is an effective approach for treating these pathological conditions. Therapeutic interventions that block estrogen action are employed effectively for the treatment of breast and prostate cancer as well as for precocious puberty and anovulatory infertility. Theoretically, treatments that block estrogen biosynthesis should prevent estrogen action at ERs and GPER, although drug resistance and ligand-independent receptor activation may still occur. In addition, blockade of estrogen biosynthesis does not prevent activation of estrogen receptors by naturally occurring or man-made exogenous estrogens. A more complicated scenario is provided by anti-estrogen drugs that antagonize ERs since these drugs function as GPER agonists. Based upon its association with metabolic dysregulation and advanced cancer, GPER represents a therapeutic target with promise for the treatment of several critical health concerns facing Western society. Selective ligands that specifically target GPER have been developed and may soon serve as pharmacological agents for treating human disease. Here, we review current forms of estrogen therapy and the implications that GPER holds for these therapies. We also discuss existing GPER targeted drugs, additional approaches towards developing GPER-targeted therapies and how these therapies may complement existing modalities of estrogen-targeted therapy.

Membrane Estrogen Receptor (GPER) and Follicle-Stimulating Hormone Receptor (FSHR) Heteromeric Complexes Promote Human Ovarian Follicle Survival

Classically, follicle-stimulating hormone receptor (FSHR)-driven cAMP-mediated signaling boosts human ovarian follicle growth and oocyte maturation. However, contradicting in vitro data suggest a different view on physiological significance of FSHR-mediated cAMP signaling. We found that the G-protein-coupled estrogen receptor (GPER) heteromerizes with FSHR, reprogramming cAMP/death signals into proliferative stimuli fundamental for sustaining oocyte survival. In human granulosa cells, survival signals are missing at high FSHR:GPER ratio, which negatively impacts follicle maturation and strongly correlates with preferential Gαs protein/cAMP-pathway coupling and FSH responsiveness of patients undergoing controlled ovarian stimulation. In contrast, FSHR/GPER heteromers triggered anti-apoptotic/proliferative FSH signaling delivered via the Gβγ dimer, whereas impairment of heteromer formation or GPER knockdown enhanced the FSH-dependent cell death and steroidogenesis. Therefore, our findings indicate how oocyte maturation depends on the capability of GPER to shape FSHR selective signals, indicating hormone receptor heteromers may be a marker of cell proliferation.

•

G-protein-coupled estrogen receptor (GPER) interacts with FSH receptor (FSHR)

•

FSHR/GPER heteromers reprogram FSH-induced death signals to proliferative stimuli

•

Anti-apoptotic signaling of heteromers is via a GPER-Gαs inhibitory complex and Gβγ

•

Heteromer formation impacts follicle maturation and FSH responses of IVF patients

Natural bioactive compounds as a new source of promising G protein-coupled estrogen receptor (GPER) modulators: comprehensive in silico approach

Cancer ranks in second place among the cause of death worldwide. Cancer progress in multiple stages of carcinogenesis and metastasis programs through complex pathways. Sex hormones and their receptors are the major factors in promoting cancer progression. Among them, G protein-coupled estrogen receptor-1 (GPER) has shown to mediate cellular signaling pathways and cancer cell proliferation. However, the lack of GPER protein structure limited the search for new modulators. In this study, we curated an extensive database of natural products to discover new potential GPER modulators. We used a combination of virtual screening techniques to generate a homology model of GPER and subsequently used that for the screening of 30,926 natural products from a public database to identify potential active modulators of GPER. The best hits were further screened through the ADMET filter and confirmed by docking analysis. Moreover, molecular dynamics simulations of best hits were also carried out to assess the stability of the ligand-GPER complex. This study predicted several potential GPER modulators with novel scaffolds that could be further investigated and used as the core for the development of novel GPER modulators.Communicated by Ramaswamy H. Sarma.

Preclinical efficacy of the GPER-selective agonist G-1 in mouse models of obesity and diabetes

Human obesity has become a global health epidemic, with few safe and effective pharmacological therapies currently available. The systemic loss of ovarian estradiol (E2) in women after menopause greatly increases the risk of obesity and metabolic dysfunction, revealing the critical role of E2 in this setting. The salutary effects of E2 are traditionally attributed to the classical estrogen receptors ERα and ERβ, with the contribution of the G protein-coupled estrogen receptor (GPER) still largely unknown. Here, we used ovariectomy- and diet-induced obesity (DIO) mouse models to evaluate the preclinical activity of GPER-selective small-molecule agonist G-1 (also called Tespria) against obesity and metabolic dysfunction. G-1 treatment of ovariectomized female mice (a model of postmenopausal obesity) reduced body weight and improved glucose homeostasis without changes in food intake, fuel source usage, or locomotor activity. G-1-treated female mice also exhibited increased energy expenditure, lower body fat content, and reduced fasting cholesterol, glucose, insulin, and inflammatory markers but did not display feminizing effects on the uterus (imbibition) or beneficial effects on bone health. G-1 treatment of DIO male mice did not elicit weight loss but prevented further weight gain and improved glucose tolerance, indicating that G-1 improved glucose homeostasis independently of its antiobesity effects. However, in ovariectomized DIO female mice, G-1 continued to elicit weight loss, reflecting possible sex differences in the mechanisms of G-1 action. In conclusion, this work demonstrates that GPER-selective agonism is a viable therapeutic approach against obesity, diabetes, and associated metabolic abnormalities in multiple preclinical male and female models.

Non-alcoholic Fatty Liver Disease as a Canonical Example of Metabolic Inflammatory-Based Liver Disease Showing a Sex-Specific Prevalence: Relevance of Estrogen Signaling

There is extensive evidence supporting the interplay between metabolism and immune response, that have evolved in close relationship, sharing regulatory molecules and signaling systems, to support biological functions. Nowadays, the disruption of this interaction in the context of obesity and overnutrition underlies the increasing incidence of many inflammatory-based metabolic diseases, even in a sex-specific fashion. During evolution, the interplay between metabolism and reproduction has reached a degree of complexity particularly high in female mammals, likely to ensure reproduction only under favorable conditions. Several factors may account for differences in the incidence and progression of inflammatory-based metabolic diseases between females and males, thus contributing to age-related disease development and difference in life expectancy between the two sexes. Among these factors, estrogens, acting mainly through Estrogen Receptors (ERs), have been reported to regulate several metabolic pathways and inflammatory processes particularly in the liver, the metabolic organ showing the highest degree of sexual dimorphism. This review aims to investigate on the interaction between metabolism and inflammation in the liver, focusing on the relevance of estrogen signaling in counteracting the development and progression of non-alcoholic fatty liver disease (NAFLD), a canonical example of metabolic inflammatory-based liver disease showing a sex-specific prevalence. Understanding the role of estrogens/ERs in the regulation of hepatic metabolism and inflammation may provide the basis for the development of sex-specific therapeutic strategies for the management of such an inflammatory-based metabolic disease and its cardio-metabolic consequences.

Mouse testicular transcriptome after modulation of non-canonical oestrogen receptor activity

The aims of this study were to shed light on the role of G-protein-coupled membrane oestrogen receptor (GPER) and oestrogen-related receptor (ERR) in mouse testis function at the gene expression level, as well as the involvement of GPER and ERR in cellular and molecular processes. Male mice were injected (50µg kg-1,s.c.) with the GPER antagonist G-15, the ERRα inverse agonist XCT790 or the ERRβ/ERRγ agonist DY131. Next-generation sequencing (RNA-Seq) was used to evaluate gene expression. Bioinformatic analysis of read abundance revealed that 50, 86 and 171 transcripts were differentially expressed in the G-15-, XCT790- and DY131-treated groups respectively compared with the control group. Annotated genes and their protein products were categorised regarding their associated biological processes and molecular functions. In the XCT790-treated group, genes involved in immunological processes were upregulated. In the DY131-treated group, genes with increased expression were primarily engaged in protein modification (protein folding and small protein conjugation). In addition, the expression of genes recognised as oncogenes, such as BMI1 proto-oncogene, polycomb ring finger (Bmi1) and nucleophosphin 1 (Npm1), was significantly increased in all experimental groups. This study provides detailed information regarding the genetic changes in the testicular transcriptome of the mouse in response to modulation of non-canonical oestrogen receptor activity.

Sex differences in murine myocutaneous flap revascularization

Sex differences in susceptibility to ischemia/reperfusion injury have been documented in humans. Premenopausal women have a lower risk of ischemic heart disease than age-matched men, whereas after menopause, the risk is similar or even higher in women. However, little is known about the effects of sex on myocutaneous ischemia/reperfusion. To explore sex differences in wound revascularization, we utilized a murine myocutaneous flap model of graded ischemia. A cranial-based, peninsular-shaped, myocutaneous flap was surgically created on the dorsum of male and female mice. Physiological, pathological, immunohistochemical, and molecular parameters were analyzed. Flaps created on female mice were re-attached to the recipient site resulting in nearly complete viability at post-operative day 10. In contrast, distal full-thickness myocutaneous necrosis was evident at 10 days post-surgery in male mice. Over the 10 day study interval, laser speckle imaging documented functional revascularization in all flap regions in female mice, but minimal distal flap reperfusion in male mice. Day 10 immunostained histologic sections confirmed significant increases in distal flap vessel count and vascular surface area in female compared to male mice. RT-PCR demonstrated significant differences in growth factor and metabolic gene expression between female and male mice at day 10. In conclusion, in a graded-ischemia wound healing model, flap revascularization was more effective in female mice. The recognition and identification of sex-specific wound healing differences may lead to a better understanding of the underlying mechanisms of myocutaneous revascularization and drive novel discovery to improve soft tissue wound healing following tissue transfer for traumatic injury and cancer resection.

Estrogenic control of mitochondrial function

Sex-based differences in human disease are caused in part by the levels of endogenous sex steroid hormones which regulate mitochondrial metabolism. This review updates a previous review on how estrogens regulate metabolism and mitochondrial function that was published in 2017. Estrogens are produced by ovaries and adrenals, and in lesser amounts by adipose, breast stromal, and brain tissues. At the cellular level, the mechanisms by which estrogens regulate diverse cellular functions including reproduction and behavior is by binding to estrogen receptors α, β (ERα and ERβ) and G-protein coupled ER (GPER1). ERα and ERβ are transcription factors that bind genomic and mitochondrial DNA to regulate gene transcription. A small proportion of ERα and ERβ interact with plasma membrane-associated signaling proteins to activate intracellular signaling cascades that ultimately alter transcriptional responses, including mitochondrial morphology and function. Although the mechanisms and targets by which estrogens act directly and indirectly to regulate mitochondrial function are not fully elucidated, it is clear that estradiol regulates mitochondrial metabolism and morphology via nuclear and mitochondrial-mediated events, including stimulation of nuclear respiratory factor-1 (NRF-1) transcription that will be reviewed here. NRF-1 is a transcription factor that interacts with coactivators including peroxisome proliferator-activated receptor gamma, coactivator 1 alpha (PGC-1α) to regulate nuclear-encoded mitochondrial genes. One NRF-1 target is TFAM that binds mtDNA to regulate its transcription. Nuclear-encoded miRNA and lncRNA regulate mtDNA-encoded and nuclear-encoded transcripts that regulate mitochondrial function, thus acting as anterograde signals. Other estrogen-regulated mitochondrial activities including bioenergetics, oxygen consumption rate (OCR), and extracellular acidification (ECAR), are reviewed.

GPER as a Receptor for Endocrine-Disrupting Chemicals (EDCs)

Endocrine-disrupting chemicals (EDCs) are exogenous chemicals that interfere with endogenous hormonal systems at various levels, resulting in adverse health effects. EDCs belong to diverse chemical families and can accumulate in the environment, diet and body fluids, with different levels of persistence. Their action can be mediated by several receptors, including members of the nuclear receptor family, such as estrogen and androgen receptors. The G protein-coupled estrogen receptor (GPER), a seven-transmembrane domain receptor, has also attracted attention as a potential target of EDCs. This review summarizes our current knowledge concerning GPER as a mediator of EDCs' effects.

Does GPER Really Function as a G Protein-Coupled Estrogen Receptor in vivo?

Estrogen can elicit pleiotropic cellular responses via a diversity of estrogen receptors (ERs)-mediated genomic and rapid non-genomic mechanisms. Unlike the genomic responses, where the classical nuclear ERα and ERβ act as transcriptional factors following estrogen binding to regulate gene transcription in estrogen target tissues, the non-genomic cellular responses to estrogen are believed to start at the plasma membrane, leading to rapid activation of second messengers-triggered cytoplasmic signal transduction cascades. The recently acknowledged ER, GPR30 or GPER, was discovered in human breast cancer cells two decades ago and subsequently in many other cells. Since its discovery, it has been claimed that estrogen, ER antagonist fulvestrant, as well as some estrogenic compounds can directly bind to GPER, and therefore initiate the non-genomic cellular responses. Various recently developed genetic tools as well as chemical ligands greatly facilitated research aimed at determining the physiological roles of GPER in different tissues. However, there is still lack of evidence that GPER plays a significant role in mediating endogenous estrogen action in vivo. This review summarizes current knowledge about GPER, including its tissue expression and cellular localization, with emphasis on the research findings elucidating its role in health and disease. Understanding the role of GPER in estrogen signaling will provide opportunities for the development of new therapeutic strategies to strengthen the benefits of estrogen while limiting the potential side effects.