Rapid, nongenomic estrogen actions protect pancreatic islet survival

G Protein-Coupled Estrogen Receptor (GPER) and ERs Are Modulated in the Testis-Epididymal Complex in the Normal and Cryptorchid Dog

There is growing evidence by the literature that the unbalance between androgens and estrogens is a relevant condition associated with a common canine reproductive disorder known as cryptorchidism. The role of estrogens in regulating testicular cell function and reproductive events is supposedly due to the wide expression of two nuclear estrogen receptors (ERs), ER-alpha and ER-beta and a trans-membrane G protein-coupled estrogen receptor (GPER) in the testis. In this study, immunohistochemistry, Western blotting and qRT-PCR were used to assess the distribution and expression of GPER in the testis-epididymal complex in the normal and cryptorchid dog. ER-alpha and ER-beta were also evaluated to better characterize the relative abundances of all three receptors. In addition, in these tissues, the expression level of two proteins as SOD1 and Nrf2 normally associated with oxidative stress was investigated to evaluate a possible relationship with ERs. Our data revealed changes in the distribution and expression of the GPER between the normal and cryptorchid dog. In particular, dogs affected by cryptorchidism showed an upregulation of GPER at level of the examined reproductive tract. Also considering the obtained result of a modulation of SOD1 and Nrf2 expression, we could hypothesize the involvement of GPER in the cryptorchid condition. Further studies are, however, necessary to characterize the role of GPER and its specific signaling mechanisms.

Naringenin protects pancreatic β cells in diabetic rat through activation of estrogen receptor β

Naringenin is a citrus flavonoid that potently improves metabolic parameters in animal models of metabolic disorders, such as type 2 diabetes. Estrogen receptor (ER) activation promotes β cell function and survival, thereby improving systemic glucose metabolism. In this study, we used a luciferase reporter assay, isolated rat islets and a diabetic rat model to investigate the effects of naringenin on ER signaling and the underlying mechanism of naringenin-mediated improvement of islet function in diabetes. Naringenin specifically activated ERβ without affecting the activity of ERα, G protein-coupled estrogen receptor (GPER) or estrogen-related receptor (ERR) α/β/γ. Additionally, treatment with naringenin enhanced glucose-stimulated insulin secretion in isolated rat islets. This effect was abrogated by PHTPP, an ERβ antagonist. Transcriptomic analysis revealed that naringenin upregulated the expression of genes, such as Pdx1 and Mafa, which are closely linked to improved β-cell function. In consistence, single administration of naringenin to normal rats elevated plasma insulin levels and improved glucose responses. These beneficial effects were blocked by PHTPP. In streptozocin-nicotinamide induced diabetic rats, treatment for 2 weeks with naringenin alone, but not in combination with PHTPP, significantly restored pancreatic β cell mass and improved glucose metabolism. Collectively, these data support that naringenin specifically activate ERβ to improve insulin secretion in the primary rat islets. Furthermore, naringenin administration also protected β cell function and reversed glucose dysregulation in diabetic rats. These beneficial effects are at least partially dependent on the ERβ pathway.

Timing Matters: Effects of Early and Late Estrogen Replacement Therapy on Glucose Metabolism and Vascular Reactivity in Ovariectomized Aged Wistar Rats

Cardiovascular disease incidence increases after menopause due to the loss of estrogen cardioprotective effects. However, there are conflicting data regarding the timing of estrogen therapy (ERT) and its effect on vascular dysfunction associated with impaired glucose metabolism. The aim of this work was to evaluate the effect of early and late ERT on blood glucose/insulin balance and vascular reactivity in aged ovariectomized Wistar rats. Eighteen-month-old female Wistar rats were randomized as follows: (1) sham, (2) 10-week postovariectomy (10 w), (3) 10 w postovariectomy+early estradiol therapy (10 w-early E2), (4) 20-week postovariectomy (20 w), and (5) 20-week postovariectomy+late estradiol therapy (20 w-late E2). Early E2 was administered 3 days after ovariectomy and late therapy after 10 weeks, in both groups. 17β-Estradiol (E2) was administered daily for 10 weeks (5 μg/kg/day). Concentration-response curves to angiotensin II, KCl, and acetylcholine (ACh) were performed. Heart rate (HR), diastolic and systolic blood pressure (DBP and SBP), glucose, insulin, HOMA-IR, and nitric oxide (NO) levels were determined. Higher glucose levels were found in all groups compared to the sham group, except the 20 w-late E2 group. Insulin was increased in all ovariectomized groups compared to sham. The HOMA-IR index showed insulin resistance in all ovariectomized groups, except for the 10 w-early E2 group. The 10 w-early E2 group increased NO levels vs. the 10 w group. After 10 w postovariectomy, the vascular response to KCl and Ach increases, despite early E2 administration. Early and late E2 treatment decreased vascular reactivity to Ang II. At 20-week postovariectomy, DBP increased, even with E2 administration, while SBP and HR remained unchanged. The effects of E2 therapy on blood glucose/insulin balance and vascular reactivity depend on the timing of therapy. Early ERT may provide some protective effects on insulin resistance and vascular function, whereas late ERT may not have the same benefits.

Role of estrogen in the regulation of central and peripheral energy homeostasis: from a menopausal perspective

Estrogen plays a prominent role in regulating and coordinating energy homeostasis throughout the growth, development, reproduction, and aging of women. Estrogen receptors (ERs) are widely expressed in the brain and nearly all tissues of the body. Within the brain, central estrogen via ER regulates appetite and energy expenditure and maintains cell glucose metabolism, including glucose transport, aerobic glycolysis, and mitochondrial function. In the whole body, estrogen has shown beneficial effects on weight control, fat distribution, glucose and insulin resistance, and adipokine secretion. As demonstrated by multiple in vitro and in vivo studies, menopause-related decline of circulating estrogen may induce the disturbance of metabolic signals and a significant decrease in bioenergetics, which could trigger an increased incidence of late-onset Alzheimer's disease, type 2 diabetes mellitus, hypertension, and cardiovascular diseases in postmenopausal women. In this article, we have systematically reviewed the role of estrogen and ERs in body composition and lipid/glucose profile variation occurring with menopause, which may provide a better insight into the efficacy of hormone therapy in maintaining energy metabolic homeostasis and hold a clue for development of novel therapeutic approaches for target tissue diseases.

Association between sex steroid hormones and subsequent hyperglycemia during pregnancy

Objective

Sex steroid hormones may play a role in insulin resistance and glucose dysregulation. However, evidence regarding associations between early-pregnancy sex steroid hormones and hyperglycemia during pregnancy is limited. The primary objective of this study was to assess the relationships between first trimester sex steroid hormones and the subsequent development of hyperglycemia during pregnancy; with secondary evaluation of sex steroid hormones levels in mid-late pregnancy, concurrent with and subsequent to diagnosis of gestational diabetes.

Methods

Retrospective analysis of a prospective pregnancy cohort study was conducted. Medically low-risk participants with no known major endocrine disorders were recruited in the first trimester of pregnancy (n=319). Sex steroid hormones in each trimester, including total testosterone, free testosterone, estrone, estradiol, and estriol, were assessed using high-performance liquid chromatography and tandem mass spectrometry. Glucose levels of the 1-hour oral glucose tolerance test and gestational diabetes diagnosis were abstracted from medical records. Multivariable linear regression models were fitted to assess the associations of individual first trimester sex steroids and glucose levels.

Results

In adjusted models, first trimester total testosterone (β=5.24, 95% CI: 0.01, 10.46, p=0.05) and free testosterone (β=5.98, 95% CI: 0.97, 10.98, p=0.02) were positively associated with subsequent glucose concentrations and gestational diabetes diagnosis (total testosterone: OR=3.63, 95% CI: 1.50, 8.78; free testosterone: OR=3.69; 95% CI: 1.56, 8.73). First trimester estrone was also positively associated with gestational diabetes (OR=3.66, 95% CI: 1.56, 8.55). In mid-late pregnancy, pregnant people with gestational diabetes had lower total testosterone levels (β=-0.19, 95% CI: -0.36, -0.02) after adjustment for first trimester total testosterone.

Conclusion

Early-pregnancy sex steroid hormones, including total testosterone, free testosterone, and estrone, were positively associated with glucose levels and gestational diabetes in mid-late pregnancy. These hormones may serve as early predictors of gestational diabetes in combination with other risk factors.

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.

The Role of Estrogen Signaling in Cellular Iron Metabolism in Pancreatic β Cells

ABSTRACT

Several lines of evidence suggest that estrogen (17-β estradiol; E2) protects against diabetes mellitus and plays important roles in pancreatic β-cell survival and function. Mounting clinical and experimental evidence also suggest that E2 modulates cellular iron metabolism by regulating the expression of several iron regulatory genes, including hepcidin (HAMP), hypoxia-inducible factor 1-α, ferroportin (SLC40A1), and lipocalin (LCN2). However, whether E2 regulates cellular iron metabolism in pancreatic β cells and whether the antidiabetic effects of E2 can be, at least partially, attributed to its role in iron metabolism is not known. In this context, pancreatic β cells express considerable levels of conventional E2 receptors (ERs; mainly ER-α) and nonconventional G protein-coupled estrogen receptors and hence responsive to E2 signals. Moreover, pancreatic islet cells require significant amounts of iron for proper functioning, replication and survival and, hence, well equipped to manage cellular iron metabolism (acquisition, utilization, storage, and release). In this review, we examine the link between E2 and cellular iron metabolism in pancreatic β cells and discuss the bearing of such a link on β-cell survival and function.

Estrogens and the regulation of glucose metabolism

The main estrogens: estradiol, estrone, and their acyl-esters have been studied essentially related to their classical estrogenic and pharmacologic functions. However, their main effect in the body is probably the sustained control of core energy metabolism. Estrogen nuclear and membrane receptors show an extraordinary flexibility in the modulation of metabolic responses, and largely explain gender and age differences in energy metabolism: part of these mechanisms is already sufficiently known to justify both. With regard to energy, the estrogen molecular species act essentially through four key functions: (1) Facilitation of insulin secretion and control of glucose availability; (2) Modulation of energy partition, favoring the use of lipid as the main energy substrate when more available than carbohydrates; (3) Functional protection through antioxidant mechanisms; and (4) Central effects (largely through neural modulation) on whole body energy management. Analyzing the different actions of estrone, estradiol and their acyl esters, a tentative classification based on structure/effects has been postulated. Either separately or as a group, estrogens provide a comprehensive explanation that not all their quite diverse actions are related solely to specific molecules. As a group, they constitute a powerful synergic action complex. In consequence, estrogens may be considered wardens of energy homeostasis.

Growth Hormone/Insulin Growth Factor Axis in Sex Steroid Associated Disorders and Related Cancers

To date, almost all solid malignancies have implicated insulin-like growth factor (IGF) signalling as a driver of tumour growth. However, the remarkable level of crosstalk between sex hormones, the IGF-1 receptor (IGF-1R) and its ligands IGF-1 and 2 in endocrine driven cancers is incompletely understood. Similar to the sex steroids, IGF signalling is essential in normal development as well as growth and tissue homoeostasis, and undergoes a steady decline with advancing age and increasing visceral adiposity. Interestingly, IGF-1 has been found to play a compensatory role for both estrogen receptor (ER) and androgen receptor (AR) by augmenting hormonal responses in the absence of, or where low levels of ligand are present. Furthermore, experimental, and epidemiological evidence supports a role for dysregulated IGF signalling in breast and prostate cancers. Insulin-like growth factor binding protein (IGFBP) molecules can regulate the bioavailability of IGF-1 and are frequently expressed in these hormonally regulated tissues. The link between age-related disease and the role of IGF-1 in the process of ageing and longevity has gained much attention over the last few decades, spurring the development of numerous IGF targeted therapies that have, to date, failed to deliver on their therapeutic potential. This review will provide an overview of the sexually dimorphic nature of IGF signalling in humans and how this is impacted by the reduction in sex steroids in mid-life. It will also explore the latest links with metabolic syndromes, hormonal imbalances associated with ageing and targeting of IGF signalling in endocrine-related tumour growth with an emphasis on post-menopausal breast cancer and the impact of the steroidal milieu.

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.

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.

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.

Chronic GPER1 Activation Protects Against Oxidative Stress-Induced Cardiomyoblast Death via Preservation of Mitochondrial Integrity and Deactivation of Mammalian Sterile-20-Like Kinase/Yes-Associated Protein Pathway

Introduction: Estrogen (17β-estradiol, E2) is well-known to induce cardioprotective effects against ischemia/reperfusion (I/R) injury. We recently reported that acute application of E2 at the onset of reperfusion in vivo induces cardioprotective effects against I/R injury via activation of its non-steroidal receptor, G protein-coupled estrogen receptor 1 (GPER1). Here, we investigated the impact and mechanism underlying chronic GPER1 activation in cultured H9c2 rat cardiomyoblasts. Methods: H9c2 rat cardiomyoblasts were cultured and pretreated with the cytotoxic agent H₂O₂ for 24 h and incubated in the presence of vehicle (control), GPER1 agonists E2 and G1, or GPER1 agonists supplemented with G15 (GPER1 antagonist) for 48 or 96 h. After treatment, cells were collected to measure the rate of cell death and viability using flow cytometry and Calcein AM assay or MTT assay, respectively. The resistance to opening of the mitochondrial permeability transition pore (mPTP), the mitochondrial membrane potential, and ATP production was assessed using fluorescence microscopy, and the mitochondrial structural integrity was observed with electron microscopy. The levels of the phosphorylation of mammalian sterile-20-like kinase (MST1) and yes-associated protein (YAP) were assessed by Western blot analysis in whole-cell lysate, while the expression levels of mitochondrial biogenesis genes, YAP target genes, and proapoptotic genes were measured by qRT-PCR. Results: We found that after H₂O₂ treatment, chronic E2/G1 treatment decreased cell death effect was associated with the prevention of the S phase of the cell cycle arrest compared to control. In the mitochondria, chronic E2/G1 activation treatment preserved the cristae morphology, and increased resistance to opening of mPTP, but with little change to mitochondrial fusion/fission. Additionally, chronic E2/G1 treatment predominantly reduced phosphorylation of MST1 and YAP, as well as increased MST1 and YAP protein levels. E2 treatment also upregulated the expression levels of TGF-β and PGC-1α mRNAs and downregulated PUMA and Bim mRNAs. Except for ATP production, all the E2 or G1 effects were prevented by the cotreatment with the GPER1 antagonist, G15. Conclusion: Together, these results indicate that chronic GPER1 activation with its agonists E2 or G1 treatment protects H9c2 cardiomyoblasts against oxidative stress-induced cell death and increases cell viability by preserving mitochondrial structure and function as well as delaying the opening of mPTP. These chronic GPER1 effects are associated with the deactivation of the non-canonical MST1/YAP mechanism that leads to genetic upregulation of cell growth genes (CTGF, CYR61, PGC-1α, and ANKRD1), and downregulation of proapoptotic genes (PUMA and Bim).

Recent progress in porcine islet isolation, culture and engraftment strategies for xenotransplantation

PURPOSE OF REVIEW

Xenotransplantation of porcine islets is a realistic option to restore β-cell function in type 1 diabetic patients. Among other factors, such as islet donor age (fetal, neonatal and adult) and genotype (wild type and genetically modified), choice of the transplantation site, and immune protection of the islets, efficient strategies for islet isolation, culture and engraftment are critical for the success of islet xenotransplantation.

RECENT FINDINGS

Neonatal porcine islets (NPIs) are immature at isolation and need to be matured in vitro or in vivo before they become fully functional. Recent developments include a scalable protocol for isolation of clinically relevant batches of NPIs and a stepwise differentiation protocol for directed maturation of NPIs. In addition, different sources of mesenchymal stem cells were shown to support survival and functional maturation of NPIs in vitro and in various transplantation models in vivo.

SUMMARY

A plethora of different culture media and supplements have been tested; however, a unique best culture system for NPIs is still missing. New insights, for example from single-cell analyses of islets or from stem cell differentiation toward β cells may help to optimize culture of porcine islets for xenotransplantation in an evidence-based manner.

Tamoxifen suppresses pancreatic β-cell proliferation in mice

Tamoxifen is a mixed agonist/antagonist estrogen analogue that is frequently used to induce conditional gene deletion in mice using Cre-loxP mediated gene recombination. Tamoxifen is routinely employed in extremely high-doses relative to typical human doses to induce efficient gene deletion in mice. Although tamoxifen has been widely assumed to have no influence upon β-cells, the acute developmental and functional consequences of high-dose tamoxifen upon glucose homeostasis and adult β-cells are largely unknown. We tested if tamoxifen influences glucose homeostasis in male mice of various genetic backgrounds. We then carried out detailed histomorphometry studies of mouse pancreata. We also performed gene expression studies with islets of tamoxifen-treated mice and controls. Tamoxifen had modest effects upon glucose homeostasis of mixed genetic background (F1 B6129SF1/J) mice, with fasting hyperglycemia and improved glucose tolerance but without overt effects on fed glucose levels or insulin sensitivity. Tamoxifen inhibited proliferation of β-cells in a dose-dependent manner, with dramatic reductions in β-cell turnover at the highest dose (decreased by 66%). In sharp contrast, tamoxifen did not reduce proliferation of pancreatic acinar cells. β-cell proliferation was unchanged by tamoxifen in 129S2 mice but was reduced in C57Bl6 genetic background mice (decreased by 59%). Gene expression studies revealed suppression of RNA for cyclins D1 and D2 within islets of tamoxifen-treated mice. Tamoxifen has a cytostatic effect on β-cells, independent of changes in glucose homeostasis, in mixed genetic background and also in C57Bl6 mice. Tamoxifen should be used judiciously to inducibly inactivate genes in studies of glucose homeostasis.

The Role of Sexual Hormones on the Enteroinsular Axis

Sex steroid estrogens, androgens, and progesterone, produced by the gonads, which have long been considered as endocrine glands, are implicated in sexual differentiation, puberty, and reproduction. However, the impact of sex hormones goes beyond these effects through their role on energy metabolism. Indeed, sex hormones are important physiological regulators of glucose homeostasis and, in particular, of the enteroinsular axis. In this review, we describe the roles of estrogens, androgens, and progesterone on glucose homeostasis through their effects on pancreatic α- and β-cells, as well as on enteroendocrine L-cells, and their implications in hormonal biosynthesis and secretion. The analysis of their mechanisms of action with the dissection of the receptors implicated in the several protective effects could provide some new aspects of the fine-tuning of hormonal secretion under the influence of the sex. This knowledge paves the way to the understanding of transgender physiology and new potential therapeutics in the field of type 2 diabetes.

Tamoxifen Improves Glucose Tolerance in a Delivery-, Sex-, and Strain-Dependent Manner in Mice

Tamoxifen, a selective estrogen-receptor modulator, is widely used in mouse models to temporally control gene expression but is also known to affect body composition. We report that tamoxifen has significant and sustained effects on glucose tolerance, independent of effects on insulin sensitivity, in mice. IP, but not oral, tamoxifen delivery improved glucose tolerance in three inbred mouse strains. The extent and persistence of tamoxifen-induced effects were sex and strain dependent. These findings highlight the need to revise commonly used tamoxifen-based protocols for gene manipulation in mice by including longer chase periods after injection, oral delivery, and the use of tamoxifen-treated littermate controls.

Estrogens Promote Misfolded Proinsulin Degradation to Protect Insulin Production and Delay Diabetes

Conjugated estrogens (CE) delay the onset of type 2 diabetes (T2D) in postmenopausal women, but the mechanism is unclear. In T2D, the endoplasmic reticulum (ER) fails to promote proinsulin folding and, in failing to do so, promotes ER stress and β cell dysfunction. We show that CE prevent insulin-deficient diabetes in male and in female Akita mice using a model of misfolded proinsulin. CE stabilize the ER-associated protein degradation (ERAD) system and promote misfolded proinsulin proteasomal degradation. This involves activation of nuclear and membrane estrogen receptor-α (ERα), promoting transcriptional repression and proteasomal degradation of the ubiquitin-conjugating enzyme and ERAD degrader, UBC6e. The selective ERα modulator bazedoxifene mimics CE protection of β cells in females but not in males.

The Role of Estrogens in Pancreatic Islet Physiopathology

In rodent models of insulin-deficient diabetes, 17β-estradiol (E2) protects pancreatic insulin-producing β-cells against oxidative stress, amyloid polypeptide toxicity, gluco-lipotoxicity, and apoptosis. Three estrogen receptors (ERs)-ERα, ERβ, and the G protein-coupled ER (GPER)-have been identified in rodent and human β-cells. This chapter describes recent advances in our understanding of the role of ERs in islet β-cell function, nutrient homeostasis, survival from pro-apoptotic stimuli, and proliferation. We discuss why and how ERs represent potential therapeutic targets for the maintenance of functional β-cell mass.

G-Protein-Coupled Estrogen Receptor (GPER) and Sex-Specific Metabolic Homeostasis

Obesity and metabolic syndrome display disparate prevalence and regulation between males and females. Human, as well as rodent, females with regular menstrual/estrous cycles exhibit protection from weight gain and associated chronic diseases. These beneficial effects are predominantly attributed to the female hormone estrogen, specifically 17β-estradiol (E2). E2 exerts its actions via multiple receptors, nuclear and extranuclear estrogen receptor (ER) α and ERβ, and the G-protein-coupled estrogen receptor (GPER, previously termed GPR30). The roles of GPER in metabolic homeostasis are beginning to emerge but are complex and remain unclear. The discovery of GPER-selective pharmacological agents (agonists and antagonists) and the availability of GPER knockout mice have significantly enhanced our understanding of the functions of GPER in normal physiology and disease. GPER action manifests pleiotropic effects in metabolically active tissues such as the pancreas, adipose, liver, and skeletal muscle. Cellular and animal studies have established that GPER is involved in the regulation of body weight, feeding behavior, inflammation, as well as glucose and lipid homeostasis. GPER deficiency leads to increased adiposity, insulin resistance, and metabolic dysfunction in mice. In contrast, pharmacologic stimulation of GPER in vivo limits weight gain and improves metabolic output, revealing a promising novel therapeutic potential for the treatment of obesity and diabetes.

Estrogen receptor α protects pancreatic β-cells from apoptosis by preserving mitochondrial function and suppressing endoplasmic reticulum stress

Estrogen receptor α (ERα) action plays an important role in pancreatic β-cell function and survival; thus, it is considered a potential therapeutic target for the treatment of type 2 diabetes in women. However, the mechanisms underlying the protective effects of ERα remain unclear. Because ERα regulates mitochondrial metabolism in other cell types, we hypothesized that ERα may act to preserve insulin secretion and promote β-cell survival by regulating mitochondrial-endoplasmic reticulum (EndoRetic) function. We tested this hypothesis using pancreatic islet-specific ERα knockout (PERαKO) mice and Min6 β-cells in culture with Esr1 knockdown (KD). We found that Esr1-KD promoted reactive oxygen species production that associated with reduced fission/fusion dynamics and impaired mitophagy. Electron microscopy showed mitochondrial enlargement and a pro-fusion phenotype. Mitochondrial cristae and endoplasmic reticulum were dilated in Esr1-KD compared with ERα replete Min6 β-cells. Increased expression of Oma1 and Chop was paralleled by increased oxygen consumption and apoptosis susceptibility in ERα-KD cells. In contrast, ERα overexpression and ligand activation reduced both Chop and Oma1 expression, likely by ERα binding to consensus estrogen-response element sites in the Oma1 and Chop promoters. Together, our findings suggest that ERα promotes β-cell survival and insulin secretion through maintenance of mitochondrial fission/fusion-mitophagy dynamics and EndoRetic function, in part by Oma1 and Chop repression.

Nitrate induces a type 1 diabetic profile in alligator hatchlings

Type 1 diabetes (T1D) is a chronic autoimmune disease that affects 1 in 300 children by age 18. T1D is caused by inflammation-induced loss of insulin-producing pancreatic beta cells, leading to high blood glucose and a host of downstream complications. Although multiple genes are associated with T1D risk, only 5% of genetically susceptible individuals actually develop clinical disease. Moreover, a growing number of T1D cases occur in geographic clusters and among children with low risk genotypes. These observations suggest that environmental factors contribute to T1D etiology. One potential factor, supported primarily by epidemiological studies, is the presence of nitrate and nitrite in drinking water. To test this hypothesis, female hatchling alligators were exposed to environmentally relevant concentrations of nitrate in their tank water (reference, 10mg/L, or 100mg/L NO₃-N) from hatch through 5 weeks or 5 months of age. At each time point, endpoints related to T1D were investigated: plasma levels of glucose, triglycerides, testosterone, estradiol, and thyroxine; pancreas, fat body, and thyroid weights; weight gain or loss; presence of immune cells in the pancreas; and pancreatic beta cell number, assessed by antibody staining of nkx6.1 protein. Internal dosing of nitrate was confirmed by measuring plasma and urine nitrate levels and whole blood methemoglobin. Cluster analysis indicated that high nitrate exposure (most animals exposed to 100mg/L NO3-N and one alligator exposed to 10mg/L NO3-N) induced a profile of endpoints consistent with early T1D that could be detected after 5 weeks and was more strongly present after 5 months. Our study supports epidemiological data correlating elevated nitrate with T1D onset in humans, and highlights nitrate as a possible environmental contributor to the etiology of T1D, possibly through its role as a nitric oxide precursor.

Use of additives, scaffolds and extracellular matrix components for improvement of human pancreatic islet outcomes in vitro: A systematic review

Pancreatic islet transplantation is an established treatment to restore insulin independence in type 1 diabetic patients. Its success rates have increased lately based on improvements in immunosuppressive therapies and on islet isolation and culture. It is known that the quality and quantity of viable transplanted islets are crucial for the achievement of insulin independence and some studies have shown that a significant number of islets are lost during culture time. Thus, in an effort to improve islet yield during culture period, researchers have tested a variety of additives in culture media as well as alternative culture devices, such as scaffolds. However, due to the use of different categories of additives or devices, it is difficult to draw a conclusion on the benefits of these strategies. Therefore, the aim of this systematic review was to summarize the results of studies that described the use of medium additives, scaffolds or extracellular matrix (ECM) components during human pancreatic islets culture. PubMed and Embase repositories were searched. Of 5083 articles retrieved, a total of 37 articles fulfilled the eligibility criteria and were included in the review. After data extraction, articles were grouped as follows: 1) "antiapoptotic/anti-inflammatory/antioxidant," 2) "hormone," 3) "sulphonylureas," 4) "serum supplements," and 5) "scaffolds or ECM components." The effects of the reviewed additives, ECM or scaffolds on islet viability, apoptosis and function (glucose-stimulated insulin secretion - GSIS) were heterogeneous, making any major conclusion hard to sustain. Overall, some "antiapoptotic/anti-inflammatory/antioxidant" additives decreased apoptosis and improved GSIS. Moreover, islet culture with ECM components or scaffolds increased GSIS. More studies are needed to define the real impact of these strategies in improving islet transplantation outcomes.

Discovery at the interface: Toward novel anti-proliferative agents targeting human estrogen receptor/S100 interactions

Estrogen Receptor Alpha (ER) is expressed in about 70% of breast cancer and mediates various cellular signaling events including cell cycle. The antiestrogen tamoxifen is currently administered to patients in order to induce regression of the tumor growth of estrogen receptor positive (ER+) breast cancer. However, upon continued administration, patients develop resistance to tamoxifen. In addition, calcium binding proteins (EF-hand proteins) such as, Calmodulin and S100, are significantly overexpressed in breast cancer cells, can activate transcription of target genes by directly binding to ER in lieu of estrogen. Calmodulin antagonists (w7 and melatonin) have been shown to significantly inhibit ER mediated activities including cell proliferation and transcriptional activity. Furthermore, S100P is shown to mediate tamoxifen resistance and cell migration capacity in MCF-7 breast cancer cells. Molecules targeting specific ER-EF hand protein interfaces could potentially provide an alternative therapeutic strategy to combat these scenarios. Using theoretical 3D models of ER-S100 protein we identified ER conformation-sensing regions of the interacting EF hand proteins and evaluated their ability to bind to ER in silico and to inhibit breast cancer cell proliferation and viability in vitro. The recognition motif of the binding interface was sensitive to small changes in partner orientation as evidenced by significant anti cell proliferative activity of the short peptide derived from S100P residues 74-78, when compared with a longer peptide with altered orientation of the recognition motif derived from S100P 74-81. Structural clues and pharmacophores from peptide-ER interactions can be used to design novel anti-cancer agents.

High T Gives β Cells a Boost

Androgen deficiency in men is associated with metabolic syndrome and diabetes, which has been attributed to actions of androgens upon insulin target tissues. In this issue of Cell Metabolism, Navarro et al. (2016) report a role for androgens and their receptor in the regulation of insulin secretion in β cells.

Potential efficiency of antioxidants to prevent pressure ulcers. A neglected hypothesis

Pressure ulcers are necrotic lesions mainly due to capillary hypoperfusion. It is well known that hypoxia and also subsequent oxygenation at reperfusion provoke the formation of reactive oxygen species (ROS) responsible for cell death. The hypothesis of their participation in the pathogenesis of pressure ulcers has already been tested; several antioxidants have the capacity to inhibit skin necrosis in animal models but their efficiency in preventing bedsores has never been demonstrated in patients. The failure of clinical trials to show the protective activity of some antioxidants does not rule out the involvement of ROS in ischemic ulcers and the potential efficacy of other antioxidants in preventing their formation remains possible.

Inter-organ communication and regulation of beta cell function

The physiologically predominant signal for pancreatic beta cells to secrete insulin is glucose. While circulating glucose levels and beta cell glucose metabolism regulate the amount of released insulin, additional signals emanating from other tissues and from neighbouring islet endocrine cells modulate beta cell function. To this end, each individual beta cell can be viewed as a sensor of a multitude of stimuli that are integrated to determine the extent of glucose-dependent insulin release. This review discusses recent advances in our understanding of inter-organ communications that regulate beta cell insulin release in response to elevated glucose levels.

Impaired estrogen receptor action in the pathogenesis of the metabolic syndrome

Considering the current trends in life expectancy, women in the modern era are challenged with facing menopausal symptoms as well as heightened disease risk associated with increasing adiposity and metabolic dysfunction for up to three decades of life. Treatment strategies to combat metabolic dysfunction and associated pathologies have been hampered by our lack of understanding regarding the biological underpinnings of these clinical conditions and our incomplete understanding of the effects of estrogens and the tissue-specific functions and molecular actions of its receptors. In this review we provide evidence supporting a critical and protective role for the estrogen receptor α specific form in the maintenance of metabolic homeostasis and insulin sensitivity. Studies identifying the ER-regulated pathways required for disease prevention will lay the important foundation for the rational design of targeted therapeutics to improve women's health while limiting complications that have plagued traditional hormone replacement interventions.

Estrogen: an emerging regulator of insulin action and mitochondrial function

Clinical trials and animal studies have revealed that loss of circulating estrogen induces rapid changes in whole body metabolism, fat distribution, and insulin action. The metabolic effects of estrogen are mediated primarily by its receptor, estrogen receptor-α; however, the detailed understanding of its mechanisms is incomplete. Recent investigations suggest that estrogen receptor-α elicits the metabolic effects of estrogen by genomic, nongenomic, and mitochondrial mechanisms that regulate insulin signaling, substrate oxidation, and energetics. This paper reviews clinical and experimental studies on the mechanisms of estrogen and the current state of knowledge regarding physiological and pathobiological influences of estrogen on metabolism.

Endocrine disruptors: new players in the pathophysiology of type 2 diabetes?

The prevalence of type 2 diabetes (T2D) has dramatically increased worldwide during the last few decades. While lifestyle factors, such as decreased physical activity and energy-dense diets, together with genetic predisposition, are well-known actors in the pathophysiology of T2D, there is accumulating evidence suggesting that the increased presence of endocrine-disrupting chemicals (EDCs) in the environment, such as bisphenol A, phthalates and persistent organic pollutants, may also explain an important part in the incidence of metabolic diseases (the metabolic syndrome, obesity and T2D). EDCs are found in everyday products (including plastic bottles, metal cans, toys, cosmetics and pesticides) and used in the manufacture of food. They interfere with the synthesis, secretion, transport, activity and elimination of natural hormones. Such interferences can block or mimic hormone actions and thus induce a wide range of adverse effects (developmental, reproductive, neurological, cardiovascular, metabolic and immune). In this review, both in vivo and in vitro experimental data and epidemiological evidence to support an association between EDC exposure and the induction of insulin resistance and/or disruption of pancreatic β-cell function are summarized, while the epidemiological links with disorders of glucose homoeostasis are also discussed.

Association of tamoxifen use and increased diabetes among Asian women diagnosed with breast cancer

Background:

We conducted a population-based cohort study to assess whether tamoxifen treatment is associated with an increased incidence of diabetes.

Methods:

Data obtained from the Taiwanese National Health Insurance Research Database were used for a population-based cohort study. The study cohort included 22 257 breast cancer patients diagnosed between 1 January 2000 and 31 December 2004. Among them, 15 210 cases received tamoxifen treatment and 7047 did not. Four subjects without breast cancer were frequency-matched by age and index year as the control group. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using multivariate Cox proportional hazards regression analysis.

Results:

Breast cancer patients exhibited a 14% higher rate of developing diabetes (adjusted HR=1.14, 95% CI=1.08–1.20) compared with non-breast cancer controls, but the significant difference was limited to tamoxifen users. In addition, tamoxifen users exhibited a significantly increased risk of diabetes compared with non-tamoxifen users among women diagnosed with breast cancer (adjusted HR=1.31, 95% CI=1.19–1.45). Stratification by age groups indicated that both younger and older women diagnosed with breast cancer exhibited a significantly higher risk of diabetes than the normal control subjects did, and tamoxifen users consistently exhibited a significantly higher diabetes risk than non-tamoxifen users or normal control subjects did, regardless of age. Both recent and remote uses of tamoxifen were associated with an increased likelihood of diabetes.

Conclusions:

The results of this population-based cohort study suggested that tamoxifen use in breast cancer patients might increase subsequent diabetes risk. The underlying mechanism remains unclear and further larger studies are mandatory to validate our findings.

Endothelial function and insulin resistance in early postmenopausal women with cardiovascular risk factors: importance of ESR1 and NOS3 polymorphisms

Cardiovascular benefits from estradiol activation of nitric oxide endothelial production may depend on vascular wall and on estrogen receptor alpha (ESR1) and nitric oxide synthase (NOS3) polymorphisms. We have evaluated the microcirculation in vivo through nailfold videocapillaroscopy, before and after acute nasal estradiol administration at baseline and after increased sheer stress (postocclusive reactive hyperemia response) in 100 postmenopausal women, being 70 controls (healthy) and 30 simultaneously hypertensive and diabetic (HD), correlating their responses to PvuII and XbaI ESR1 polymorphisms and to VNTR, T-786C and G894T NOS3 variants. In HD women, C variant allele of ESR1 Pvull was associated to higher vasodilatation after estradiol (1.72 vs 1.64 mm/s, p = 0.01 compared to TT homozygotes) while G894T and T-786C NOS3 polymorphisms were connected to lower increment after shear stress (15% among wild type and 10% among variant alleles, p = 0.02 and 0.04). The G variant allele of ESR1 XbaI polymorphism was associated to higher HOMA-IR (3.54 vs. 1.64, p = 0.01) in HD and higher glucose levels in healthy women (91.8 vs. 87.1 mg/dl, p = 0.01), in which increased waist and HOMA-IR were also related to the G allele in NOS3 G894T (waist 93.5 vs 88.2 cm, p = 0.02; HOMA-IR 2.89 vs 1.48, p = 0.05). ESR1 Pvull, NOS3 G894T and T-786C polymorphism analysis may be considered in HD postmenopausal women for endothelial response prediction following estrogen therapy but were not discriminatory for endothelial response in healthy women. ESR1 XbaI and G894T NOS3 polymorphisms may be useful in accessing insulin resistance and type 2 diabetes risks in all women, even before menopause and occurrence of metabolic disease.

The islet estrogen receptor-α is induced by hyperglycemia and protects against oxidative stress-induced insulin-deficient diabetes

The female steroid, 17β-estradiol (E2), is important for pancreatic β-cell function and acts via at least three estrogen receptors (ER), ERα, ERβ, and the G-protein coupled ER (GPER). Using a pancreas-specific ERα knockout mouse generated using the Cre-lox-P system and a Pdx1-Cre transgenic line (PERαKO^−/−), we previously reported that islet ERα suppresses islet glucolipotoxicity and prevents β-cell dysfunction induced by high fat feeding. We also showed that E2 acts via ERα to prevent β-cell apoptosis in vivo. However, the contribution of the islet ERα to β-cell survival in vivo, without the contribution of ERα in other tissues is still unclear. Using the PERαKO^−/− mouse, we show that ERα mRNA expression is only decreased by 20% in the arcuate nucleus of the hypothalamus, without a parallel decrease in the VMH, making it a reliable model of pancreas-specific ERα elimination. Following exposure to alloxan-induced oxidative stress in vivo, female and male PERαKO^−/− mice exhibited a predisposition to β-cell destruction and insulin deficient diabetes. In male PERαKO^−/− mice, exposure to E2 partially prevented alloxan-induced β-cell destruction and diabetes. ERα mRNA expression was induced by hyperglycemia in vivo in islets from young mice as well as in cultured rat islets. The induction of ERα mRNA by hyperglycemia was retained in insulin receptor-deficient β-cells, demonstrating independence from direct insulin regulation. These findings suggest that induction of ERα expression acts to naturally protect β-cells against oxidative injury.

The role of estrogens in control of energy balance and glucose homeostasis

Estrogens play a fundamental role in the physiology of the reproductive, cardiovascular, skeletal, and central nervous systems. In this report, we review the literature in both rodents and humans on the role of estrogens and their receptors in the control of energy homeostasis and glucose metabolism in health and metabolic diseases. Estrogen actions in hypothalamic nuclei differentially control food intake, energy expenditure, and white adipose tissue distribution. Estrogen actions in skeletal muscle, liver, adipose tissue, and immune cells are involved in insulin sensitivity as well as prevention of lipid accumulation and inflammation. Estrogen actions in pancreatic islet β-cells also regulate insulin secretion, nutrient homeostasis, and survival. Estrogen deficiency promotes metabolic dysfunction predisposing to obesity, the metabolic syndrome, and type 2 diabetes. We also discuss the effect of selective estrogen receptor modulators on metabolic disorders.

17β-Estradiol and 17α-estradiol induce rapid changes in cytoskeletal organization in cultured oligodendrocytes

Dramatic changes in the cytoskeleton and the morphology of oligodendrocytes (OLs) occur during various stages of the myelination process. OLs in culture produce large membrane sheets containing cytoskeletal veins of microtubules and actin filaments. We recently showed that estrogen receptors (ER) related to ERα/β were expressed in the membrane sheets of mature OLs in culture. Ligation of these or other membrane ERs in OLs with both 17β- and 17α-estradiol mediated rapid non-genomic signaling. Here, we show that estrogens also mediate rapid non-genomic remodeling of the cytoskeleton in mature OLs in culture. 17β-Estradiol caused a rapid loss of microtubules and the actin cytoskeleton in the OL membrane sheets. It also increased phosphorylation of the actin filament-severing protein cofilin, thus inactivating it. Staining for actin barbed ends with rhodamine-actin showed that it decreased the amount of actin barbed ends. 17α-Estradiol, on the other hand, increased the percentage of cells with abundant staining of actin filaments and actin barbed ends, suggesting that it stabilized and/or increased the dynamics of the actin cytoskeleton. The specific ERα and ERβ agonists, 4,4',4″-(4-propyl-(1H)-pyrazole-1,3,5-triyl) trisphenol (PPT) and diarylpropionitrile 2,3-bis(4-hydroxy-phenyl)-propionitrile (DPN), respectively, also caused the rapid phosphorylation of cofilin. Estrogen-induced phosphorylation of cofilin was inhibited by Y-27632, a specific inhibitor of the Rho-associated protein serine/threonine kinase (ROCK). The Rho/ROCK/cofilin pathway is therefore implicated in actin rearrangement via estrogen ligation of membrane ERs, which may include forms of ERα and ERβ. These results indicate a role for estrogens in modulation of the cytoskeleton in mature OLs, and thus in various processes required for myelinogenesis.

Importance of oestrogen receptors to preserve functional β-cell mass in diabetes

Protecting the functional mass of insulin-producing β cells of the pancreas is a major therapeutic challenge in patients with type 1 (T1DM) or type 2 diabetes mellitus (T2DM). The gonadal hormone 17β-oestradiol (E2) is involved in reproductive, bone, cardiovascular and neuronal physiology. In rodent models of T1DM and T2DM, treatment with E2 protects pancreatic β cells against oxidative stress, amyloid polypeptide toxicity, lipotoxicity and apoptosis. Three oestrogen receptors (ERs)--ERα, ERβ and the G protein-coupled ER (GPER)--have been identified in rodent and human β cells. Whereas activation of ERα enhances glucose-stimulated insulin biosynthesis, reduces islet toxic lipid accumulation and promotes β-cell survival from proapoptotic stimuli, activation of ERβ increases glucose-stimulated insulin secretion. However, activation of GPER protects β cells from apoptosis, raises glucose-stimulated insulin secretion and lipid homeostasis without affecting insulin biosynthesis. Oestrogens are also improving islet engraftment in rodent models of pancreatic islet transplantation. This Review describes developments in the role of ERs in islet insulin biosynthesis and secretion, lipid homeostasis and survival. Moreover, we discuss why and how enhancing ER action in β cells without the undesirable effect of general oestrogen therapy is a therapeutic avenue to preserve functional β-cell mass in patients with diabetes mellitus.

Rapid insulinotropic action of low doses of bisphenol-A on mouse and human islets of Langerhans: role of estrogen receptor β

Bisphenol-A (BPA) is a widespread endocrine-disrupting chemical (EDC) used as the base compound in the manufacture of polycarbonate plastics. It alters pancreatic β-cell function and can be considered a risk factor for type 2 diabetes in rodents. Here we used ERβ-/- mice to study whether ERβ is involved in the rapid regulation of K(ATP) channel activity, calcium signals and insulin release elicited by environmentally relevant doses of BPA (1 nM). We also investigated these effects of BPA in β-cells and whole islets of Langerhans from humans. 1 nM BPA rapidly decreased K(ATP) channel activity, increased glucose-induced [Ca(2+)](i) signals and insulin release in β-cells from WT mice but not in cells from ERβ-/- mice. The rapid reduction in the K(ATP) channel activity and the insulinotropic effect was seen in human cells and islets. BPA actions were stronger in human islets compared to mouse islets when the same BPA concentration was used. Our findings suggest that BPA behaves as a strong estrogen via nuclear ERβ and indicate that results obtained with BPA in mouse β-cells may be extrapolated to humans. This supports that BPA should be considered as a risk factor for metabolic disorders in humans.

Obesity, insulin resistance and diabetes: sex differences and role of oestrogen receptors

Obesity increases the risk of coronary artery disease through insulin resistance, diabetes, arterial hypertension and dyslipidemia. The prevalence of obesity has increased worldwide and is particularly high among middle-aged women and men. After menopause, women are at an increased risk to develop visceral obesity due to the loss of endogenous ovarian hormone production. Effects of oestrogens are classically mediated by the two nuclear oestrogen receptors (ERs) α and β. In addition, more recent research has shown that the intracellular transmembrane G-protein-coupled oestrogen receptor (GPER) originally designated as GPR30 also mediates some of the actions attributed to oestrogens. Oestrogen and its receptors are important regulators of body weight and insulin sensitivity not only in women but also in men as demonstrated by ER mutations in rodents and humans. This article reviews the role of sex hormones and ERs in the context of obesity, insulin sensitivity and diabetes as well as the related clinical issues in women and men.

The G-protein-coupled estrogen receptor GPER in health and disease

Estrogens mediate profound effects throughout the body and regulate physiological and pathological processes in both women and men. The low prevalence of many diseases in premenopausal women is attributed to the presence of 17β-estradiol, the predominant and most potent endogenous estrogen. In addition to endogenous estrogens, several man-made and plant-derived molecules, such as bisphenol A and genistein, also exhibit estrogenic activity. Traditionally, the actions of 17β-estradiol are ascribed to two nuclear estrogen receptors (ERs), ERα and ERβ, which function as ligand-activated transcription factors. However, 17β-estradiol also mediates rapid signaling events via pathways that involve transmembrane ERs, such as G-protein-coupled ER 1 (GPER; formerly known as GPR30). In the past 10 years, GPER has been implicated in both rapid signaling and transcriptional regulation. With the discovery of GPER-selective ligands that can selectively modulate GPER function in vitro and in preclinical studies and with the use of Gper knockout mice, many more potential roles for GPER are being elucidated. This Review highlights the physiological roles of GPER in the reproductive, nervous, endocrine, immune and cardiovascular systems, as well as its pathological roles in a diverse array of disorders including cancer, for which GPER is emerging as a novel therapeutic target and prognostic indicator.

The G protein-coupled receptor 30 is up-regulated by hypoxia-inducible factor-1alpha (HIF-1alpha) in breast cancer cells and cardiomyocytes

GPR30, also known as GPER, has been suggested to mediate rapid effects induced by estrogens in diverse normal and cancer tissues. Hypoxia is a common feature of solid tumors involved in apoptosis, cell survival, and proliferation. The response to low oxygen environment is mainly mediated by the hypoxia-inducible factor named HIF-1α, which activates signaling pathways leading to adaptive mechanisms in tumor cells. Here, we demonstrate that the hypoxia induces HIF-1α expression, which in turn mediates the up-regulation of GPER and its downstream target CTGF in estrogen receptor-negative SkBr3 breast cancer cells and in HL-1 cardiomyocytes. Moreover, we show that HIF-1α-responsive elements located within the promoter region of GPER are involved in hypoxia-dependent transcription of GPER, which requires the ROS-induced activation of EGFR/ERK signaling in both SkBr3 and HL-1 and cells. Interestingly, the apoptotic response to hypoxia was prevented by estrogens through GPER in SkBr3 cells. Taken together, our data suggest that the hypoxia-induced expression of GPER may be included among the mechanisms involved in the anti-apoptotic effects elicited by estrogens, particularly in a low oxygen microenvironment.

Estrogen and androgen receptors: regulators of fuel homeostasis and emerging targets for diabetes and obesity

Because of increasing life expectancy, the contribution of age-related estrogen or androgen deficiency to obesity and type 2 diabetes will become a new therapeutic challenge. This review integrates current concepts on the mechanisms through which estrogen receptors (ERs) and androgen receptor (AR) regulate energy homeostasis in rodents and humans. In females, estrogen maintains energy homeostasis via ERα and ERβ, by suppressing energy intake and lipogenesis, enhancing energy expenditure, and ameliorating insulin secretion and sensitivity. In males, testosterone is converted to estrogen and maintains fuel homeostasis via ERs and AR, which share related functions to suppress adipose tissue accumulation and improve insulin sensitivity. We suggest that ERs and AR could be potential targets in the prevention of age-related metabolic disorders.

Extranuclear estrogen receptor-alpha stimulates NeuroD1 binding to the insulin promoter and favors insulin synthesis

Estrogen receptors (ERs) protect pancreatic islet survival in mice through rapid extranuclear actions. ERalpha also enhances insulin synthesis in cultured islets. Whether ERalpha stimulates insulin synthesis in vivo and, if so, through which mechanism(s) remain largely unknown. To address these issues, we generated a pancreas-specific ERalpha knockout mouse (PERalpha KO(-/-)) using the Cre-loxP strategy and used a combination of genetic and pharmacologic tools in cultured islets and beta cells. Whereas 17beta-estradiol (E2) treatment up-regulates pancreatic insulin gene and protein content in control ERalpha lox/lox mice, these E2 effects are abolished in PERalpha KO(-/-) mice. We find that E2-activated ERalpha increases insulin synthesis by enhancing glucose stimulation of the insulin promoter activity. Using a knock-in mouse with a mutated ERalpha eliminating binding to the estrogen response elements (EREs), we show that E2 stimulation of insulin synthesis is independent of the ERE. We find that the extranuclear ERalpha interacts with the tyrosine kinase Src, which activates extracellular signal-regulated kinases(1/2), to increase nuclear localization and binding to the insulin promoter of the transcription factor NeuroD1. This study supports the importance of ERalpha in beta cells as a regulator of insulin synthesis in vivo.

Minireview: Estrogenic protection of beta-cell failure in metabolic diseases

The prevalence of diabetes is lower in premenopausal women, especially diabetic syndromes with insulin deficiency, suggesting that the female hormone 17beta-estradiol protects pancreatic beta-cell function. In classical rodent models of beta-cell failure, 17beta-estradiol at physiological concentrations protects pancreatic beta-cells against lipotoxicity, oxidative stress, and apoptosis. In this review, we integrate evidence showing that estrogens and their receptors have direct effects on islet biology. The estrogen receptor (ER)-alpha, ER beta, and the G-protein coupled ER are present in beta-cells and enhance islet survival. They also improve islet lipid homeostasis and insulin biosynthesis. We also discuss evidence that ERs modulate insulin sensitivity and energy homeostasis, which indirectly alter beta-cell biology in diabetic and obese conditions.