Estrogen signaling through the transmembrane G protein-coupled receptor GPR30

Neuroprotective actions of estradiol and novel estrogen analogs in ischemia: translational implications

This review highlights our investigations into the neuroprotective efficacy of estradiol and other estrogenic agents in a clinically relevant animal model of transient global ischemia, which causes selective, delayed death of hippocampal CA1 neurons and associated cognitive deficits. We find that estradiol rescues a significant number of CA1 pyramidal neurons that would otherwise die in response to global ischemia, and this is true when hormone is provided as a long-term pretreatment at physiological doses or as an acute treatment at the time of reperfusion. In addition to enhancing neuronal survival, both forms of estradiol treatment induce measurable cognitive benefit in young animals. Moreover, estradiol and estrogen analogs that do not bind classical nuclear estrogen receptors retain their neuroprotective efficacy in middle-aged females deprived of ovarian hormones for a prolonged duration (8weeks). Thus, non-feminizing estrogens may represent a new therapeutic approach for treating the neuronal damage associated with global ischemia.

Mechanisms of estradiol-induced insulin secretion by the G protein-coupled estrogen receptor GPR30/GPER in pancreatic beta-cells

Sexual dimorphism and supplementation studies suggest an important role for estrogens in the amelioration of glucose intolerance and diabetes. Because little is known regarding the signaling mechanisms involved in estradiol-mediated insulin secretion, we investigated the role of the G protein-coupled receptor 30, now designated G protein-coupled estrogen receptor (GPER), in activating signal transduction cascades in β-cells, leading to secretion of insulin. GPER function in estradiol-induced signaling in the pancreatic β-cell line MIN6 was assessed using small interfering RNA and GPER-selective ligands (G-1 and G15) and in islets isolated from wild-type and GPER knockout mice. GPER is expressed in MIN6 cells, where estradiol and the GPER-selective agonist G-1 mediate calcium mobilization and activation of ERK and phosphatidylinositol 3-kinase. Both estradiol and G-1 induced insulin secretion under low- and high-glucose conditions, which was inhibited by pretreatment with GPER antagonist G15 as well as depletion of GPER by small interfering RNA. Insulin secretion in response to estradiol and G-1 was dependent on epidermal growth factor receptor and ERK activation and further modulated by phosphatidylinositol 3-kinase activity. In islets isolated from wild-type mice, the GPER antagonist G15 inhibited insulin secretion induced by estradiol and G-1, both of which failed to induce insulin secretion in islets obtained from GPER knockout mice. Our results indicate that GPER activation of the epidermal growth factor receptor and ERK in response to estradiol treatment plays a critical role in the secretion of insulin from β-cells. The results of this study suggest that the activation of downstream signaling pathways by the GPER-selective ligand G-1 could represent a novel therapeutic strategy in the treatment of diabetes.

Estrogen receptor α signaling in T lymphocytes is required for estradiol-mediated inhibition of Th1 and Th17 cell differentiation and protection against experimental autoimmune encephalomyelitis

Estrogen treatment exerts a protective effect on experimental autoimmune encephalomyelitis (EAE) and is under clinical trial for multiple sclerosis therapy. Estrogens have been suspected to protect from CNS autoimmunity through their capacity to exert anti-inflammatory as well as neuroprotective effects. Despite the obvious impacts of estrogens on the pathophysiology of multiple sclerosis and EAE, the dominant cellular target that orchestrates the anti-inflammatory effect of 17β-estradiol (E2) in EAE is still ill defined. Using conditional estrogen receptor (ER) α-deficient mice and bone marrow chimera experiments, we show that expression of ERα is critical in hematopoietic cells but not in endothelial ones to mediate the E2 inhibitory effect on Th1 and Th17 cell priming, resulting in EAE protection. Furthermore, using newly created cell type-specific ERα-deficient mice, we demonstrate that ERα is required in T lymphocytes, but neither in macrophages nor dendritic cells, for E2-mediated inhibition of Th1/Th17 cell differentiation and protection from EAE. Lastly, in absence of ERα in host nonhematopoietic tissues, we further show that ERα signaling in T cells is necessary and sufficient to mediate the inhibitory effect of E2 on EAE development. These data uncover T lymphocytes as a major and nonredundant cellular target responsible for the anti-inflammatory effects of E2 in Th17 cell-driven CNS autoimmunity.

Diacylglycerol kinase α mediates 17-β-estradiol-induced proliferation, motility, and anchorage-independent growth of Hec-1A endometrial cancer cell line through the G protein-coupled estrogen receptor GPR30

Increased levels of endogenous and/or exogenous estrogens are one of the well known risk factors of endometrial cancer. Diacylglycerol kinases (DGKs) are a family of enzymes which phosphorylate diacylglycerol (DAG) to produce phosphatidic acid (PA), thus turning off and on DAG-mediated and PA-mediated signaling pathways, respectively. DGK α activity is stimulated by growth factors and oncogenes and is required for chemotactic, proliferative, and angiogenic signaling in vitro. Herein, using either specific siRNAs or the pharmacological inhibitor R59949, we demonstrate that DGK α activity is required for 17-β-estradiol (E2)-induced proliferation, motility, and anchorage-independent growth of Hec-1A endometrial cancer cell line. Impairment of DGK α activity also influences basal cell proliferation and growth in soft agar of Hec-1A, while it has no effects on basal cell motility. Moreover, we show that DGK α activity induced by E2, as well as its observed effects, are mediated by the G protein-coupled estrogen receptor GPR30 (GPER). These findings suggest that DGK α may be a potential target in endometrial cancer therapy.

Induction of interleukin-10 in the T helper type 17 effector population by the G protein coupled estrogen receptor (GPER) agonist G-1

Interleukin-10 (IL-10) is a potent suppressor of the immune system, commonly produced by CD4(+) T cells to limit ongoing inflammatory responses minimizing host damage. Many autoimmune diseases are marked by large populations of activated CD4(+) T cells within the setting of chronic inflammation; therefore, drugs capable of inducing IL-10 production in CD4(+) T cells would be of great therapeutic value. Previous reports have shown that the small molecule G-1, an agonist of the membrane-bound G-protein-coupled estrogen receptor GPER, attenuates disease in an animal model of autoimmune encephalomyelitis. However, the direct effects of G-1 on CD4(+) T-cell populations remain unknown. Using ex vivo cultures of purified CD4(+) T cells, we show that G-1 elicits IL-10 expression in T helper type 17 (Th17) -polarized cells, increasing the number of IL-10(+) and IL-10(+) IL-17A(+) cells via de novo induction of IL-10. T-cell cultures differentiated in the presence of G-1 secreted threefold more IL-10, with no change in IL-17A, tumour necrosis factor-α, or interferon-γ. Moreover, inhibition of extracellular signal-regulated kinase (but not p38 or Jun N-terminal kinase) signalling blocked the response, while analysis of Foxp3 and RORγt expression demonstrated increased numbers of IL-10(+) cells in both the Th17 (RORγt(+)) and Foxp3(+) RORγt(+) hybrid T-cell compartments. Our findings translated in vivo as systemic treatment of male mice with G-1 led to increased IL-10 secretion from splenocytes following T-cell receptor cross-linking. These results demonstrate that G-1 acts directly on CD4(+) T cells, and to our knowledge provide the first example of a synthetic small molecule capable of eliciting IL-10 expression in Th17 or hybrid T-cell populations.

The Effects of 17β-estradiol in Cancer are Mediated by Estrogen Receptor Signaling at the Plasma Membrane

Two different isoforms of the estrogen receptors (i.e., ERα and ERβ) mediate pleiotropic 17β-estradiol (E2)-induced cellular effects. The ERs are principally localized in the nucleus where they act by globally modifying the expression of the E2-target genes. The premise that E2 effects are exclusively mediated through the nuclear localized ERs has been rendered obsolete by research over the last 15 years demonstrating that ERα and ERβ proteins are also localized at the plasma membranes and in other extra-nuclear organelles. The E2 modulation of cancer cell proliferation represents a good example of the impact of membrane-initiated signals on E2 effects. In fact, E2 via ERα elicits rapid signals driving cancer cells to proliferation (e.g., in breast cancer cells), while E2-induced ERβ rapid signaling inhibits proliferation (e.g., in colon cancer cells). In this review we provide with an overview of the complex system of E2-induced signal transduction pathways, their impact on E2-induced cancer cell proliferation, and the participation of E2-induced membrane-initiated signals in tumor environment.

Lactogens and estrogens in breast cancer chemoresistance

Tumor resistance to chemotherapy in advanced breast cancer is a major impediment to treatment success. Resistance can be induced by the drugs themselves or result from the action of internal factors. The role of hormones in chemoresistance has received little attention. This article focuses on two classes of hormones: lactogens and estrogens. Lactogens include prolactin, growth hormone and placental lactogen, all of which can activate the prolactin receptor. Estrogens include endogenous steroids and nonsteroidal compounds from the environment termed endocrine disruptors, all of which can activate 'classical' estrogen receptors (ERα and ERβ), as well as other types of receptors. Both lactogens and estrogens antagonize cytotoxicity of multiple chemotherapeutic agents through complementary mechanisms. The implications of chemoresistance by these hormones to patients with breast cancer, and the potential benefits of developing combinatorial anti-lactogen/anti-estrogen treatment regimens, are discussed.

Controls of meiotic signaling by membrane or nuclear progestin receptor in zebrafish follicle-enclosed oocytes

Both membrane progestin receptors (mPRs) and the nuclear progestin receptor (nPR or Pgr) decode the non-genomic progestin signaling (NGPS) in vertebrates. However, the receptor for deciphering extracellular NGPS and initiating meiosis resumption in vertebrate oocytes is still contested hotly. We studied the roles of nPR and mPRs by determining their localization, changes of expression, and activation of NGPS during final oocyte maturation (FOM) in zebrafish. The nPR transcript and protein were expressed abundantly in follicular cells that were surrounding stage IV oocytes, but nPR transcript appeared absent within stage IV oocytes. The most significant daily changes of nPR transcript were observed in stage IV follicular cells, with the highest level observed just prior to ovulation. In contrast, the expressions of mPRα and mPRβ transcripts and proteins were abundant and increased significantly in late stage denuded oocytes prior to oocyte maturation, consistent with the purported role of mPRs in interpreting NGPS. Moreover, over-expression of mPRα in follicle-enclosed oocytes significantly increased the activity of MAPK, the production of cyclin B protein, and the number of oocytes that underwent FOM without exogenous progestin, while over-expression of mPRβ or nPR alone had no such effect. Intriguingly, significant acceleration of FOM was observed when follicle-enclosed oocytes were incubated with the maturation inducing steroid, 4-pregnen-17, 20β-diol-3-one (DHP) following over-expression of nPR or mPRα. Interestingly, this acceleration in oocyte maturation was observed approximately 1h later in oocytes over-expressing nPR compared to those over-expressing mPRα. Importantly, the acceleration of maturation in the nPR injected group was blocked by treatment with the transcription inhibitor actinomycin D, implying a requirement of the genomic signaling pathway, while the same treatment did not affect the accelerated rate of maturation in mPRα injected oocytes. Taken together, these results imply that nPR and mPRβ are unlikely receptors for inducing FOM, while mPRα is the long-sought-after nongenomic progestin receptor that deciphers extracellular NGPS to initiate meiosis resumption in follicle-enclosed zebrafish oocytes.

The ovarian hormone estradiol plays a crucial role in the control of food intake in females

Despite a strong male bias in both basic and clinical research, it is becoming increasingly accepted that the ovarian hormone estradiol plays an important role in the control of food intake in females. Estradiol's feeding inhibitory effect occurs in a variety of species, including women, but the underlying mechanism has been studied most extensively in rats and mice. Accordingly, much of the data reviewed here is derived from the rodent literature. Adult female rats display a robust decrease in food intake during estrus and ovariectomy promotes hyperphagia and weight gain, both of which can be prevented by a physiological regimen of estradiol treatment. Behavioral analyses have demonstrated that the feeding inhibitory effect of estradiol is mediated entirely by a decrease in meal size. In rats, estradiol appears to exert this action indirectly via interactions with peptide and neurotransmitter systems implicated in the direct control of meal size. Here, I summarize research examining the neurobiological mechanism underlying estradiol's anorexigenic effect. Central estrogen receptors (ERs) have been implicated and activation of one ER subtype in particular, ERα, appears both sufficient and necessary for the estrogenic control of food intake. Future studies are necessary to identify the critical brain areas and intracellular signaling pathways responsible for estradiol's anorexigenic effect. A clearer understanding of the estrogenic control of food intake is prerequisite to elucidating the biological factors that contribute to obesity and eating disorders, both of which are more prevalent in women, compared to men.

Estrogen receptor activation and cardioprotection in ischemia reperfusion injury

Premenopausal females have a comparably lower incidence of cardiovascular disease than their male counterparts. Although estrogen and activation of estrogen receptors (ERs) have been found to contribute to female protection, the complex mechanisms involved are unclear. Besides altering gene transcription, estrogen could elicit its cardioprotective effect via ER-mediated nongenomic signaling pathways. In addition to the two classic nuclear ER isoforms, ERα and ERβ, a G-protein coupled ER (GPR30 or GPER) has been found to be expressed in cardiomyocytes and plays an acute cardioprotective role in ischemia reperfusion injury. By using isoform-specific ER knockout mouse models and/or their specific modulators, the mechanisms of the different ERs involved in cardioprotection have been explored. In this review, we will focus on the signaling pathways leading to cardioprotection in ischemia reperfusion injury after ER activation and discuss the possibility and promise of specific ER modulators to treat ischemic heart diseases.

Allosteric modulation of ATP-gated P2X receptor channels

Seven mammalian purinergic receptor subunits, denoted P2X1-P2X7, and several spliced forms of these subunits have been cloned. When heterologously expressed, these cDNAs encode ATP-gated non-selective cation channels organized as trimers. All activated receptors produce cell depolarization and promote Ca(2+) influx through their pores and indirectly by activating voltage-gated calcium channels. However, the biophysical and pharmacological properties of these receptors differ considerably, and the majority of these subunits are also capable of forming heterotrimers with other members of the P2X receptor family, which confers further different properties. These channels have three ATP binding domains, presumably located between neighboring subunits, and occupancy of at least two binding sites is needed for their activation. In addition to the orthosteric binding sites for ATP, these receptors have additional allosteric sites that modulate the agonist action at receptors, including sites for trace metals, protons, neurosteroids, reactive oxygen species and phosphoinositides. The allosteric regulation of P2X receptors is frequently receptor-specific and could be a useful tool to identify P2X members in native tissues and their roles in signaling. The focus of this review is on common and receptor-specific allosteric modulation of P2X receptors and the molecular base accounting for allosteric binding sites.

GPR30 deficiency causes increased bone mass, mineralization, and growth plate proliferative activity in male mice

Estrogen regulation of the male skeleton was first clearly demonstrated in patients with aromatase deficiency or a mutation in the ERα gene. Estrogen action on the skeleton is thought to occur mainly through the action of the nuclear receptors ERα and ERβ. Recently, in vitro studies have shown that the G protein-coupled receptor GPR30 is a functional estrogen receptor (ER). GPR30-deficient mouse models have been generated to study the in vivo function of this protein; however, its in vivo role in the male skeleton remains underexplored. We have characterized size, body composition, and bone mass in adult male Gpr30 knockout (KO) mice and their wild-type (WT) littermates. Gpr30 KO mice weighed more and had greater nasal-anal length (p < .001). Both lean mass and percent body fat were increased in the KO mice. Femur length was greater in Gpr30 KO mice, as was whole-body, spine, and femoral areal bone mineral density (p < .01). Gpr30 KO mice showed increased trabecular bone volume (p < .01) and cortical thickness (p < .001). Mineralized surface was increased in Gpr30 KO mice (p < .05). Bromodeoxyuridine (BrdU) labeling showed greater proliferation in the growth plate of Gpr30 KO mice (p < .05). Under osteogenic culture conditions, Gpr30 KO femoral bone marrow cells produced fewer alkaline phosphatase-positive colonies in early differentiating osteoblast cultures but showed increased mineralized nodule deposition in mature osteoblast cultures. Serum insulin-like growth factor 1 (IGF-1) levels were not different. These data suggest that in male mice, GPR30 action contributes to regulation of bone mass, size, and microarchitecture by a mechanism that does not require changes in circulating IGF-1.

GPR30 co-localizes with cholinergic neurons in the basal forebrain and enhances potassium-stimulated acetylcholine release in the hippocampus

GPR30 is a novel, membrane-bound, G-protein coupled estrogen receptor (Filardo et al., 2002; Prossnitz et al., 2008). We hypothesize that GPR30 may mediate effects of estradiol (E2) on basal forebrain cholinergic neurons and cognitive performance. Recently we showed that G-1, a selective GPR30 agonist, enhances the rate of acquisition on a delayed matching-to-position (DMP) T-maze task (Hammond et al., 2009). In the present study, we examined the distribution of GPR30 in the rat forebrain, and the effects of G-1 on potassium-stimulated acetylcholine release in the hippocampus. GPR30-like immunoreactivity was detected in many regions of the forebrain including the hippocampus, frontal cortex, medial septum/diagonal band of Broca, nucleus basalis magnocellularis and striatum. GPR30 mRNA also was detected, with higher levels in the hippocampus and cortex than in the septum and striatum. Co-localization studies revealed that the majority (63-99%) of cholinergic neurons in the forebrain expressed GPR30-like immunoreactivity. A far lower percentage (0.4-42%) of GABAergic (parvalbumin-containing) cells also contained GPR30. Sustained administration of either G-1 or E2 (5 μg/day) to ovariectomized rats produced a nearly 3-fold increase in potassium-stimulated acetylcholine release in the hippocampus relative to vehicle-treated controls. These data demonstrate that GPR30 is expressed by cholinergic neurons in the basal forebrain, and suggest that activation of GPR30 enhances cholinergic function in the hippocampus similar to E2. This may account for the effects of G-1 on DMP acquisition previously reported.

GPR30 expression is required for the mineralocorticoid receptor-independent rapid vascular effects of aldosterone

It has been increasingly appreciated that steroids elicit acute vascular effects through rapid, so-called nongenomic signaling pathways. Though aldosterone, for example, has been demonstrated to mediate rapid vascular effects via both mineralocorticoid receptor-dependent and -independent pathways, the mechanism(s) of this mineralocorticoid receptor-independent effect of aldosterone is yet to be determined. For estrogen, its rapid effects have been reported to be, at least in part, mediated via the 7-transmembrane-spanning, G protein-coupled receptor GPR30. Previous studies have demonstrated common response outcomes in response to both aldosterone and estrogen on GPR30 expression, ie, activation of phosphatidylinositol 3-kinase-dependent contraction and extracellular signal-regulated kinase activation in vascular smooth muscle cells. The present studies were undertaken to test the hypothesis that the rapid response to aldosterone in smooth muscle is dependent on the availability of a GPR30-dependent signaling pathway. These findings not only reconcile differences in the literature for aldosterone response in freshly isolated versus cultured aortic smooth muscle cells but also suggest alternative therapeutic strategies for modulating aldosterone actions on the vasculature in vivo.

Estrogen receptor-α but not -β or GPER inhibits high glucose-induced human VSMC proliferation: potential role of ROS and ERK

CONTEXT

The decreased incidence of cardiovascular disease in premenopausal women has been attributed, at least partially, to protective effects of estrogens. However, premenopausal women with diabetes mellitus are no longer selectively protected. High-glucose (HG) conditions have previously been shown to abolish the antimitogenic effects of 17β-estradiol (E(2)) in vascular smooth muscle cells (VSMCs).

OBJECTIVE

Because E(2) mediates its action via different estrogen receptor (ER) subtypes, we hypothesized that different subtypes may have different, if not opposing, effects on HG-induced VSMC proliferation.

METHODS AND RESULTS

Treatment of human aortic VSMCs isolated from premenopausal women with the selective ERα agonist, 4,4',4'-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol, but not with E(2), the selective ERβ agonist 2,3-bis(4-hydroxyphenyl)-propionitrile, or the selective G protein-coupled ER agonist G-1 completely prevented increased HG-induced VSMC proliferation. Under these conditions, ERα activation selectively prevented increased hydrogen peroxide (H(2)O(2)) and total intracellular reactive oxygen species (ROS) production, caused up-regulation of manganese superoxide dismutase protein and activity, and inhibited prolonged ERK phosphorylation. The latter was mediated by ROS, and ROS inhibition reversed HG-induced ERK-dependent VSMC proliferation. The selective coactivation of ERβ reversed the antimitogenic and antioxidative effects of ERα as well as the up-regulation of manganese superoxide dismutase protein expression.

CONCLUSION

Selective activation of ERα is required for reducing oxidative stress and the consequent hyperproliferation of VSMCs under HG. Our results may further suggest that ERα activation inhibits HG-induced proliferation by down-regulating ROS-mediated ERK activation and may explain why antimitogenic effects of E(2) are abolished under HG. Pharmacological activation of ERα may thus have therapeutic potential for treating cardiovascular dysregulation associated with diabetes.

G protein-coupled estrogen receptor 1/G protein-coupled receptor 30 localizes in the plasma membrane and traffics intracellularly on cytokeratin intermediate filaments

G protein-coupled receptor 30 [G protein-coupled estrogen receptor 1 (GPER1)], has been introduced as a membrane estrogen receptor and a candidate cancer biomarker and therapeutic target. However, several questions surround the subcellular localization and signaling of this receptor. In native cells, including mouse myoblast C(2)C(12) cells, Madin-Darby canine kidney epithelial cells, and human ductal breast epithelial tumor T47-D cells, G-1, a GPER1 agonist, and 17β-estradiol stimulated GPER1-dependent cAMP production, a defined plasma membrane (PM) event, and recruitment of β-arrestin2 to the PM. Staining of fixed and live cells showed that GPER1 was localized both in the PM and on intracellular structures. One such intracellular structure was identified as cytokeratin (CK) intermediate filaments, including those composed of CK7 and CK8, but apparently not endoplasmic reticulum, Golgi, or microtubules. Reciprocal coimmunoprecipitation of GPER1 and CKs confirmed an association of these proteins. Live staining also showed that the PM receptors constitutively internalize apparently to reach CK filaments. Receptor localization was supported using FLAG- and hemagglutinin-tagged GPER1. We conclude that GPER1-mediated stimulation of cAMP production and β-arrestin2 recruitment occur in the PM. Furthermore, the PM receptors constitutively internalize and localize intracellularly on CK. This is the first observation that a G protein-coupled receptor is capable of associating with intermediate filaments, which may be important for GPER1 regulation in epithelial cells and the relationship of this receptor to cancer.

Role of GPR30 in endometrial pathology after tamoxifen for breast cancer

OBJECTIVE

This study was undertaken to evaluate the potential role of G-protein-coupled estrogen receptor in endometrial pathology associated with tamoxifen treatment of breast cancer patients.

STUDY DESIGN

We investigated whether G-protein-coupled estrogen receptor plays a role in mediating proliferating effect of tamoxifen in endometrial carcinoma cells. These results were compared with the G-protein-coupled estrogen receptor expression pattern in endometrial tissue from a cohort of 95 breast cancer patients, who received tamoxifen or another adjuvant therapy.

RESULTS

In vitro tamoxifen significantly stimulated the mitogen-activated protein kinase phosphorylation and cell proliferation of endometrial cell lines via G-protein-coupled estrogen receptor. In vivo, there was a significant correlation between G-protein-coupled estrogen receptor expression and the tamoxifen-induced endometrial pathology (P = .006). Moreover, G-protein-coupled estrogen receptor positivity was predictive of an earlier development of symptoms, such as bleeding or suspect endometrial thickness, induced by tamoxifen therapy (P = .019).

CONCLUSION

G-protein-coupled estrogen receptor plays an important role in tamoxifen-induced endometrial abnormalities.

Synthesis and functional analysis of novel bivalent estrogens

The steroid hormone estrogen plays a critical role in female development and homeostasis. Estrogen mediates its effects through binding and activation of specific estrogen receptors alpha (ERalpha) and beta (ERbeta), members of the steroid/nuclear receptor family of ligand-induced transcription factors. Due to their intimate roles in genomic and nongenomic signaling pathways, these hormones and their receptors have been also implicated in the pathologies of a variety of cancers and metabolic disorders, and have been the target of large therapeutic development efforts. The binding of estrogen to its respective receptors initiates a cascade of events that include receptor dimerization, nuclear localization, DNA binding and recruitment of co-regulatory protein complexes. In this manuscript, we investigate the potential for manipulating steroid receptor gene expression activity through the development of bivalent steroid hormones that are predicted to facilitate hormone receptor dimerization events. Data are presented for the development and testing of novel estrogen dimers, linked through their C-17 moiety, that can activate estrogen receptor alpha (ERalpha)-mediated transcription events with efficacy and potency equal to or greater than that of ERalpha's cognate ligand, 17beta-estradiol. These bivalent estrogen structures open the door to the development of a variety of steroid therapeutics that could dramatically impact future drug development in this area.

Attenuation of salt-induced cardiac remodeling and diastolic dysfunction by the GPER agonist G-1 in female mRen2.Lewis rats

INTRODUCTION

The G protein-coupled estrogen receptor (GPER) is expressed in various tissues including the heart. Since the mRen2.Lewis strain exhibits salt-dependent hypertension and early diastolic dysfunction, we assessed the effects of the GPER agonist (G-1, 40 nmol/kg/hr for 14 days) or vehicle (VEH, DMSO/EtOH) on cardiac function and structure.

METHODS

Intact female mRen2.Lewis rats were fed a normal salt (0.5% sodium; NS) diet or a high salt (4% sodium; HS) diet for 10 weeks beginning at 5 weeks of age.

RESULTS

Prolonged intake of HS in mRen2.Lewis females resulted in significantly increased blood pressure, mildly reduced systolic function, and left ventricular (LV) diastolic compliance (as signified by a reduced E deceleration time and E deceleration slope), increased relative wall thickness, myocyte size, and mid-myocardial interstitial and perivascular fibrosis. G-1 administration attenuated wall thickness and myocyte hypertrophy, with nominal effects on blood pressure, LV systolic function, LV compliance and cardiac fibrosis in the HS group. G-1 treatment significantly increased LV lusitropy [early mitral annular descent (e')] independent of prevailing salt, and improved the e'/a' ratio in HS versus NS rats (P<0.05) as determined by tissue Doppler.

CONCLUSION

Activation of GPER improved myocardial relaxation in the hypertensive female mRen2.Lewis rat and reduced cardiac myocyte hypertrophy and wall thickness in those rats fed a high salt diet. Moreover, these advantageous effects of the GPER agonist on ventricular lusitropy and remodeling do not appear to be associated with overt changes in blood pressure.

A component of Premarin(®) enhances multiple cognitive functions and influences nicotinic receptor expression

In women, ovarian hormone loss at menopause has been related to cognitive decline, and some studies suggest that estrogen-containing hormone therapy (HT) can mitigate these effects. Recently, the Women's Health Initiative study found that conjugated equine estrogens, the most commonly prescribed HT, do not benefit cognition. Isolated components of conjugated equine estrogens (tradename Premarin(®)) have been evaluated in vitro, with delta(8,9)-dehydroestrone (∆(8)E1) and equilin showing the strongest neuroprotective profiles. It has not been evaluated whether ∆(8)E1 or equilin impact cognition or the cholinergic system, which is affected by other estrogens and known to modulate cognition. Here, in middle-aged, ovariectomized rats, we evaluated the effects of ∆(8)E1 and equilin treatments on a cognitive battery and cholinergic nicotinic receptors (nAChR). Specifically, we used (125)I-labeled epibatidine binding to assay brain nicotinic receptor containing 4α and 2β subunits (α4β2-nAChR), since this nicotinic receptor subtype has been shown previously to be sensitive to other estrogens. ∆(8)E1 enhanced spatial working, recent and reference memory. ∆(8)E1 also decreased hippocampal and entorhinal cortex α4β2-nAChR expression, which was related to spatial reference memory performance. Equilin treatment did not affect spatial memory or rat α4β2-nAChR expression, and neither estrogen impacted (86)Rb(+) efflux, indicating lack of direct action on human α4β2 nAChR function. Both estrogens influenced vaginal smear profiles, uterine weights, and serum luteinizing hormone levels, analogous to classic estrogens. The findings indicate that specific isolated Premarin(®) components differ in their ability to affect cognition and nAChR expression. Taken with the works of others showing ∆(8)E1-induced benefits on several dimensions of health-related concerns associated with menopause, this body of research identifies ∆(8)E1 as a new avenue to be investigated as a potential component of HT that may benefit brain health and function during aging.

Impact of estrogen receptor alpha and beta agonists on delayed alternation in middle-aged rats

Estrogens act in the adult brain to modulate cognition, enhancing performance on some learning tests and impairing performance on others. Our previous research has revealed an impairing effect of chronic 17β-estradiol treatment in young and aged rats on a prefrontally-mediated working memory task, delayed spatial alternation (DSA). Little is known about the mechanisms of these impairing effects. The current study examined the effects of selective estrogen receptor (ER) α or ERβ activation on DSA performance in middle-aged female rats. Ovariectomized 12 month old Long-Evans (LE) rats were treated by subcutaneous injection with the ERα agonist propyl pyrazole triol (PPT) or the ERβ agonist diarylpropionitrile (DPN) at 0.02, 0.08, or 0.20mg/kg/day, or with oil vehicle and tested on an operant variable delay DSA task. A 17β-estradiol group (10% in cholesterol) was included as a positive control group. We replicated our previous finding of a 17β-estradiol induced deficit on DSA performance and this effect was paralleled by low dose (0.02mg/kg/day) DPN treatment. Higher doses of DPN failed to produce a significant change in performance. The highest dose of PPT (0.20mg/kg/day) also impaired performance, but this effect was subtle and limited to the longest delay during the final block of testing. These data confirm our earlier findings that chronic 17β-estradiol treatment has an impairing effect on the DSA task, and suggest that ERβ activation may underlie the deficit.

GPR30/GPER-1 mediates rapid decreases in TLR4 expression on murine macrophages

Studies to define the effects of estrogens on immune function have yielded conflicting results. The recent demonstration that GPR30 can mediate rapid non-genomic events and may function as a novel transmembrane estrogen receptor could provide a mechanism underlying such findings. In this study, we have investigated the ability of GPR30 to regulate cell-surface expression of Toll-like receptor 4 (TLR4), a key molecule in the perception of bacterial lipopolysaccharide (LPS) by immune cells. We show that 17beta-estradiol or GPR30-specific agonists decrease TLR4 expression on macrophages within 10-60 min and such effects were abolished following GPR30 knockdown. Importantly, GPR30 ligation significantly reduces sensitivity of these immune cells to LPS challenge as determined by reductions in inflammatory mediator production. Based on these findings, we suggest that estrogen may utilize this non-classical estrogen receptor to limit potentially lethal acute inflammatory responses without compromising long-term host defense.

Synaptic estrogen receptor-alpha levels in prefrontal cortex in female rhesus monkeys and their correlation with cognitive performance

In rat hippocampus, estrogen receptor-α (ER-α) can initiate nongenomic signaling mechanisms that modulate synaptic plasticity in response to either circulating or locally synthesized estradiol (E). Here we report quantitative electron microscopic data demonstrating that ER-α is present within excitatory synapses in dorsolateral prefrontal cortex (dlPFC) of young and aged ovariectomized female rhesus monkeys with and without E treatment. There were no treatment or age effects on the percentage of excitatory synapses containing ER-α, nor were there any group differences in distribution of ER-α within the synapse. However, the mean size of synapses containing ER-α was larger than that of unlabeled excitatory synapses. All monkeys were tested on delayed response (DR), a cognitive test of working memory that requires dlPFC. In young ovariectomized monkeys without E treatment, presynaptic ER-α correlated with DR accuracy across memory delays. In aged monkeys that received E treatment, ER-α within the postsynaptic density (30-60 nm from the synaptic membrane) positively correlated with DR performance. Thus, although the lack of group effects suggests that ER-α is primarily in synapses that are stable across age and treatment, synaptic abundance of ER-α is correlated with individual performance in two key age/treatment groups. These data have important implications for individual differences in the cognitive outcome among menopausal women and promote a focus on cortical estrogen receptors for therapeutic efficacy with respect to cognition.

Metabolic impact of estrogen signalling through ERalpha and ERbeta

Estrogens, acting on both estrogen receptors alpha (ERalpha) and beta (ERbeta) are recognized as important regulators of glucose homeostasis and lipid metabolism. ERs belong to the family of nuclear hormone receptors which mainly act as ligand activated transcription factors. Both ERs are expressed in metabolic tissue such as adipose tissue, skeletal muscle, liver and pancreas, as well as in the central nervous system. Expression pattern of both ERs differ between species, sexes, and specific tissues. The present review will focus on the key effects of ERs on glucose- and lipid metabolism. It appears that ERalpha mainly mediates beneficial metabolic effects of estrogens such as anti-lipogenesis, improvement of insulin sensitivity and glucose tolerance, and reduction of body weight/fat mass. In contrast, ERbeta activation seems to be detrimental for the maintenance of regular glucose and lipid homeostasis. Metabolic actions of both receptors in relevant tissues will be discussed.

Expression of GPR30 and GPR43 in oral tissues: deriving new hypotheses on the role of diet in animal physiology and the development of oral cancers

Food components and salivary hormones modulate the function of various tissues in the oral cavity. However, the mechanisms underlying such interactions are poorly understood. This study aimed at the detection of GPR30 and GPR43 in oral epithelia. Although unknown yet, the expression of these receptors is hypothesized to be fundamental for the actions of salivary oestrogens, dietary isoflavones and short chain fatty acids (SCFA) in the oral environment. Either immunoblotting or RT-PCR techniques were used for receptor detection in bovine and primate oral tissues. Here we show for the first time that mRNA of the G-protein-coupled oestrogen receptor, GPR30, and the short chain fatty acid receptor, GPR43, are expressed in bovine parotid glands. Furthermore, GPR30 protein is expressed in bovine parotid gland and the tongue of the primate Theropithecus gelada. With GPR30 being a target for dietary isoflavones and GPR43 being a suggested target for short chain fatty acids, we propose new hypotheses concerning the receptors' roles in salivary gland physiology and pathology. Our findings may trigger more detailed studies on GPRs to unravel their role in regulatory mechanisms in the oral cavity as well as in cancer development in relation to diets or biologically active compounds like soy isoflavones.

Discovery of selective probes and antagonists for G-protein-coupled receptors FPR/FPRL1 and GPR30

Recent technological advances in flow cytometry provide a versatile platform for high throughput screening of compound libraries coupled with high-content biological testing and drug discovery. The G protein-coupled receptors (GPCRs) constitute the largest class of signaling molecules in the human genome with frequent roles in disease pathogenesis, yet many examples of orphan receptors with unknown ligands remain. The complex biology and potential for drug discovery within this class provide strong incentives for chemical biology approaches seeking to develop small molecule probes to facilitate elucidation of mechanistic pathways and enable specific manipulation of the activity of individual receptors. We have initiated small molecule probe development projects targeting two distinct families of GPCRs: the formylpeptide receptors (FPR/FPRL1) and G protein-coupled estrogen receptor (GPR30). In each case the assay for compound screening involved the development of an appropriate small molecule fluorescent probe, and the flow cytometry platform provided inherently biological rich assays that enhanced the process of identification and optimization of novel antagonists. The contributions of cheminformatics analysis tools, virtual screening, and synthetic chemistry in synergy with the biomolecular screening program have yielded valuable new chemical probes with high binding affinity, selectivity for the targeted receptor, and potent antagonist activity. This review describes the discovery of novel small molecule antagonists of FPR and FPRL1, and GPR30, and the associated characterization process involving secondary assays, cell based and in vivo studies to define the selectivity and activity of the resulting chemical probes.

Oleuropein and hydroxytyrosol inhibit MCF-7 breast cancer cell proliferation interfering with ERK1/2 activation

The growth of many breast tumors is stimulated by estradiol (E2), which activates a classic mechanism of regulation of gene expression and signal transduction pathways inducing cell proliferation. Polyphenols of natural origin with chemical similarity to estrogen have been shown to interfere with tumor cell proliferation. The aim of this study was to investigate whether hydroxytyrosol (HT) and oleuropein (OL), two polyphenols contained in extra-virgin olive oil, can affect breast cancer cell proliferation interfering with E2-induced molecular mechanisms. Both HT and OL inhibited proliferation of MCF-7 breast cancer cells. Luciferase gene reporter experiments, using a construct containing estrogen responsive elements able to bind estrogen receptor alpha (ERalpha) and the study of the effects of HT or OL on ERalpha expression, demonstrated that HT and OL are not involved in ERalpha-mediated regulation of gene expression. However, further experiments pointed out that both OL and HT determined a clear inhibition of E2-dependent activation of extracellular regulated kinase1/2 belonging to the mitogen activating protein kinase family. Our study demonstrated that HT and OL can have a chemo-preventive role in breast cancer cell proliferation through the inhibition of estrogen-dependent rapid signals involved in uncontrolled tumor cell growth.

In vivo treatments with fulvestrant and anastrozole differentially affect gene expression in the rat efferent ductules

Estrogen plays a key role in maintaining the morphology and function of the efferent ductules. We previously demonstrated that the antiestrogen fulvestrant markedly affected gene expression in the rat efferent ductules. The mechanism of fulvestrant action to modulate gene expression may involve not only the blockade of ESR1 and ESR2 estrogen receptors, but also the activation of ESR1 and ESR2 when the receptors are tethered to AP-1 or SP1 transcription factors, or the activation of the G protein-coupled estrogen receptor 1. We therefore compared the effects of two strategies to interfere with estrogen action in the rat efferent ductules: treatment with fulvestrant or with the aromatase inhibitor anastrozole. Whereas fulvestrant markedly increased Mmp7 and Spp1, and reduced Nptx1 mRNA levels, no changes were observed with anastrozole. Fulvestrant caused changes in epithelial morphology that were not seen with anastrozole. Fulvestrant shifted MMP7 immunolocalization in the epithelial cells from the supranuclear to the apical region; this effect was less pronounced with anastrozole. In vitro studies of (35)S-methionine incorporation showed that protein release was increased, whereas tissue protein content in the efferent ductules of fulvestrant-treated rats was decreased. Although fulvestrant markedly affected gene expression, no changes were observed on AP-1 and SP1 DNA-binding activity. The blockade of ESRs seems to be the major reason explaining the differences between both treatments. At least some of the effects of fulvestrant appear to result from compensatory mechanisms activated by the dramatic changes caused by ESR1 blockade.

Co-expression of GPR30 and ERbeta and their association with disease progression in uterine carcinosarcoma

OBJECTIVE

We sought to evaluate the expression of G protein-coupled receptor 30 (GPR30) and estrogen receptor (ER)beta in uterine carcinosarcoma (CS).

STUDY DESIGN

Immunohistochemistry was performed using antibodies to GPR30, ERbeta, ERalpha, and progesterone receptor (PR). The staining intensity and percentage of positive cells were scored for each tissue section. Expression levels were compared using the Wilcoxon rank sum test. Correlation was evaluated by Spearman rho and logistic regression.

RESULTS

Compared with normal endometrium, CS had lower ERalpha and PR expression (both P < .01) but higher GPR30 epithelial expression (P = .03). Advanced-stage CS had higher GPR30 (P < .01) and ERbeta (P = .02) epithelial expression compared with early-stage CS. Expression of GPR30 and ERbeta correlated with each other (P < .01), and not with ERalpha or PR.

CONCLUSION

In uterine CS, GPR30 and ERbeta are coordinately overexpressed and expression levels increase in advanced-stage disease, supporting the involvement of alternative ERs in disease progression.

Neuroscientists as cartographers: mapping the crossroads of gonadal hormones, memory and age using animal models

Cognitive function is multidimensional and complex, and research in multiple species indicates it is considerably impacted by age and gonadal hormone milieu. One domain of cognitive function particularly susceptible to age-related decrements is spatial memory. Gonadal hormones can alter spatial memory, and they are potent modulators of brain microstructure and function in many of the same brain areas affected by aging. In this paper, we review decades of animal and human literature to support a tertiary model representing interactions between gonadal hormones, spatial cognition and age given that: 1) gonadal hormones change with age, 2) age impacts spatial learning and memory, and 3) gonadal hormones impact spatial learning and memory. While much has been discovered regarding these individual tenets, the compass for future aging research points toward clarifying the interactions that exist between these three points, and understanding mediating variables. Indeed, identifying and aligning the various components of the complex interactions between these tenets, including evaluations using basic science, systems, and clinical perspectives, is the optimal approach to attempt to converge the many findings that may currently appear contradictory. In fact, as discoveries are being made it is becoming clear that the findings across studies that appear contradictory are not contradictory at all. Rather, there are mediating variables that are influencing outcome and affecting the extent, and even the direction, of the effects that gonadal hormones have on cognition during aging. These mediating variables are just starting to be understood. By aligning basic scientific discoveries with clinical interpretations, we can maximize the opportunities for discoveries and subsequent interventions to allow individuals to "optimize their aging" and find their own map to cognitive health as aging ensues.

LIM kinase mediates estrogen action on the actin depolymerization factor Cofilin

The ovarian hormone estrogen increases the axospinous synapse density in the hippocampal CA1 region of young female rats but fails to do so in aged rats. This estrogen-mediated alteration of spine synapse structures suggests the coincident requirement for the structural reorganization of the underlying actin cytoskeleton network. Actin reorganization is known to require the deactivation of Cofilin, an actin depolymerization factor. Cofilin is deactivated by LIM kinase (LIMK), and LIMK activity is modulated by the phosphorylation of specific residues. We have previously demonstrated that estrogen is able to increase phosphorylated LIMK (pLIMK) immunoreactivity (IR) in the hippocampus in vivo and that this estrogen-stimulated pLIMK-IR is decreased in the aged brain. Because Cofilin phosphorylation allows for actin filament elongation and spine synapse growth, we sought to determine if estrogen acts through Cofilin and if such estrogen action requires the observed LIMK activity. Using both hippocampal neurons and the NG108-15 neuroblastoma cell line, we demonstrate here that estrogen stimulates the phosphorylation of Cofilin in vitro. Furthermore, this estrogen action on Cofilin requires LIMK. Lastly, while initiating the phosphorylation of LIMK and Cofilin, estrogen can also stimulate the formation of filopodial extensions, an early step in the formation of nascent spines, demonstrating that estrogen can alter the actin-dependent neuronal morphology. This linkage of estrogen communication to Cofilin via LIMK provides the functionality to the age-sensitive pLIMK-IR that we have observed in vivo.

Signaling via GPR30 protects the myocardium from ischemia/reperfusion injury

BACKGROUND

Estrogen may protect against the development of cardiovascular disease. Recently, a receptor known as GPR30 that seems to mediate estrogen's nongenomic effects has been identified. We hypothesized that the activation of GPR30 protects cardiac function and decreases myocardial inflammation after global ischemia/reperfusion (I/R).

METHODS

Hearts from male Sprague-Dawley rats were perfused via Langendorff and treated with either (1) vehicle; (2) 10 nm of the GPR30 agonist, G-1; or (3) 100 nm of G-1; they then were subjected to 25 minutes of ischemia and 40 minutes of reperfusion. Cardiac functional parameters were measured continuously. Ventricular tissue was analyzed for tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-6.

RESULTS

At end-reperfusion, the left ventricular developed pressure in the 100-nm G-1 group was improved compared with vehicle (26% +/- 12% equilibrium vs 54% +/- 9% equilibrium; P < .05). Similar findings were noted when comparing the 100-nm G-1 group with the vehicle in terms of +dP/dt (53% +/- 12% equilibrium vs 26% +/- 19%, respectively; P < .05) and -dP/dt (56% +/- 15% equilibrium vs 22% +/- 16% equilibrium, respectively; P < .05). TNF-alpha, IL-1beta, and IL-6 levels were lower in myocardium of the 100-nm G-1 group compared with the vehicle (P < .05).

CONCLUSION

The GPR30 agonist, G-1, improves functional recovery and decreases myocardial inflammation after global I/R. GPR30 may play an important role in estrogen's ability to protect the heart against I/R injury.

G protein-coupled receptor 30 in tumor development

Estrogen plays several important physiological and pathological functions in not only reproductive system but many other systems as well. Its transcriptional activation has been traditionally described as being mediated by classic nuclear estrogen receptors (ERs). It is however established recently that a novel functional estrogen transmembrane receptor, G protein-coupled receptor 30 (GPR30), modulates both rapid non-genomic events and genomic transcriptional events of estrogen. It has been demonstrated that GPR30 promotes the progress of estrogen-related tumors through mitogen-activated protein kinase (MAPK) signaling pathways. Effects mediated by GPR30 are maintained when classic ERs are absent or blocked. In addition, GPR30 is involved in drug resistance, which is often occurring during cancer treatments. All these new findings strongly imply that GPR30 may be an important therapeutic target for estrogen-related tumors. Simultaneously blocking both GPR30 and classic ERs may be a better strategy for the treatment of estrogen-related tumors.

Effect of Estradiol-17beta on protein synthesis and degradation rates in fused bovine satellite cell cultures

Although androgenic and estrogenic steroids are widely used to enhance muscle growth and increase feed efficiency in feedlot cattle, their mechanism of action is not well understood. Further, in vivo studies indicate that estradiol (E2) affects muscle protein synthesis and/or degradation, but in vitro results are inconsistent. We have examined the effects of E2 treatment on protein synthesis and degradation rates in fused bovine satellite cell (BSC) cultures. Additionally, to learn more about the mechanisms involved in E2-enhanced muscle growth, we have examined the effects of compounds that interfere with binding of E2 or insulin-like growth factor (IGF)-1 to their respective receptors on E2-induced alterations in protein synthesis and degradation rates in BSC cultures. Treatment of fused BSC cultures with E2 results in a concentration-dependent increase (P < 0.05) in protein synthesis rate and a decrease (P < 0.05) in protein degradation rate. The pure estrogen antagonist ICI 182 780 suppresses (P < 0.05) E2-induced alterations in protein synthesis and degradation in fused BSC cultures. The G-protein coupled receptor (GPR)-30 agonist G1 does not affect either synthesis or degradation rate, which establishes that GPR30 does not play a role in E2-induced alterations in protein synthesis or degradation. JB1, a competitive inhibitor of IGF-1 binding to the Type 1 insulin-like growth factor receptor (IGFR-1), suppresses (P < 0.05) E2-induced alterations in protein synthesis and degradation. In summary, our data show that E2 treatment directly alters both protein synthesis and degradation rates in fused BSC cultures via mechanisms involving both the classical estrogen receptor (ER) and IGFR-1.

Estrogen receptor signaling and its relationship to cytokines in systemic lupus erythematosus

Dysregulation of cytokines is among the main abnormalities in Systemic Lupus Erythematosus (SLE). However, although, estrogens, which are known to be involved in lupus disease, influence cytokine production, the underlying molecular mechanisms remain poorly defined. Recent evidence demonstrates the presence of estrogen receptor in various cell types of the immune system, while divergent effects of estrogens on the cytokine regulation are thought to be implicated. In this paper, we provide an overview of the current knowledge as to how estrogen-induced modulation of cytokine production in SLE is mediated by the estrogen receptor while simultaneously clarifying various aspects of estrogen receptor signaling in this disease. The estrogen receptor subtypes, their structure, and the mode of action of estrogens by gene activation and via extranuclear effects are briefly presented. Results regarding the possible correlation between estrogen receptor gene polymorphisms and quantitative changes in the receptor protein to SLE pathology and cytokine production are reviewed.

Aromatase, oestrogens and human male reproduction

In most mammalian species aromatase is encoded by a single gene (Cyp19), which contains 18 exons, nine of them being translated. In man, the presence of a biologically active aromatase and oestrogen receptors (ERalpha and ERbeta) has been reported in Leydig cells, and also in immature germ cells and ejaculated spermatozoa. Concerning aromatase, the amount of transcript and enzymatic activity are decreased in immotile compared with motile sperm. We have amplified aromatase mRNA by real-time polymerase chain reaction in spermatozoa from asthenospermic, teratospermic and asthenoteratospermic men and recorded, respectively, 44, 52 and 67 per cent decreases of the amount of transcripts compared with fertile donors. A high degree of correlation (r = -0.64) between the abnormal spermatozoa (especially microcephaly and acrosome malformations) and aromatase/GAPDH transcript ratio has been observed. Idiopathic infertility is a wide health problem and no treatment is currently available. In humans, even if the role of oestrogens in spermatogenesis is still a matter of debate, the observations of decreased sperm number and motility in men genetically deficient in aromatase, together with our data and those reported in the literature, may suggest a role for aromatase/oestrogens not only during the development and maintenance of spermatogenesis but also in the final maturation of spermatozoa.

Diurnal in vivo and rapid in vitro effects of estradiol on voltage-gated calcium channels in gonadotropin-releasing hormone neurons

A robust surge of gonadotropin-releasing hormone (GnRH) release triggers the luteinizing hormone surge that induces ovulation. The GnRH surge is attributable to estradiol feedback, but the mechanisms are incompletely understood. Voltage-gated calcium channels (VGCCs) regulate hormone release and neuronal excitability, and may be part of the surge-generating mechanism. We examined VGCCs of GnRH neurons in brain slices from a model exhibiting daily luteinizing hormone surges. Mice were ovariectomized (OVX), and a subset was treated with estradiol implants (OVX+E). OVX+E mice exhibit negative feedback in the A.M. and positive feedback in the P.M. GnRH neurons express prominent high-voltage-activated (HVA) and small low-voltage-activated (LVA) macroscopic (whole-cell) Ca currents (I(Ca)). LVA-mediated currents were not altered by estradiol or time of day. In contrast, in OVX+E mice, HVA-mediated currents varied with time of day; HVA currents in cells from OVX+E mice were lower than those in cells from OVX mice in the A.M. but were higher in the P.M. These changes were attributable to diurnal alternations in L- and N-type components. There were no diurnal changes in any aspect of HVA-mediated I(Ca) in OVX mice. Acute in vitro treatment of cells from OVX and OVX+E mice with estradiol rapidly increased HVA currents primarily through L- and R-type VGCCs by activating estrogen receptor beta and GPR30, respectively. These results suggest multiple mechanisms contribute to the overall feedback regulation of HVA-mediated I(Ca) by estradiol. In combination with changes in synaptic inputs to GnRH neurons, these intrinsic changes in GnRH neurons may play critical roles in estradiol feedback.

Estriol acts as a GPR30 antagonist in estrogen receptor-negative breast cancer cells

Estrogens are structurally related steroids that regulate important physiological processes. 17beta-estradiol (E2) is reversibly oxidized to estrone (E1) and both E2 and E1 can be irreversibly converted to estriol (E3), which also originates directly from androstenedione. The action of E2 has been traditionally explained by the binding to the estrogen receptor (ER) alpha and ER beta, however the G protein-coupled receptor (GPR) 30 has been recently involved in the rapid signaling triggered by estrogens. Although the role of E2 in the development of breast cancer has been largely documented, the contribution of E3 still remains to be completely evaluated. Here, we demonstrate for the first time that E3 acts as a GPR30 antagonist since it was able to inhibit the GPR30-mediated responses such as the rapid ERK activation, the up-regulation of target genes like c-fos and connective tissue growth factor, the proliferative effects observed in ER-negative SkBr3 cells.

Activation of G protein-coupled receptor 30 modulates hormone secretion and counteracts cytokine-induced apoptosis in pancreatic islets of female mice

The role of the newly discovered estrogen receptor GPR30 in islet physiology and pathophysiology is unclear. We examined GPR30 expression in relation to hormone secretion and possible anti-apoptotic effects in isolated mouse islets using the synthetic GPR30 ligand G-1. The mRNA and protein expression of GPR30 was analyzed by qPCR, Western blot and confocal microscopy. Hormone secretion and cAMP content were determined with RIA and apoptosis in islet cells with the Annexin-V method. GPR30 mRNA and protein expression was markedly higher in islets from females compared to male. This gender difference was not found for the genomic estrogen receptors ER alpha and ER beta, the ER alpha expression being 10-fold higher than ER beta in both genders. Confocal microscopy revealed abounden GPR30 expression in insulin, glucagon and somatostatin cells. Dose-response studies of G-1 vs 17beta-estradiol in isolated islets at 1 or 12 mM glucose showed an almost identical pattern in that both compounds increased insulin and inhibited glucagon and somatostatin secretion. ICI-182,780 and EM-652, potent antagonists of the 17beta-estradiol receptors (ER alpha and ER beta) did not influence the amplifying effect of G-1 or 17beta-estradiol on cAMP content or insulin secretion from isolated islets. Cytokine-induced (IL-1 beta+TNFalpha+INF gamma) apoptosis in islets, cultured for 24h at 5mM glucose, was almost abolished by G-1 or 17beta-estradiol treatment. Addition of ICI-182,780 or EM-652 did not affect this beneficial effect of G-1 or 17beta-estradiol. Taken together, our findings show that GPR30 is expressed in most islet endocrine cells. The synthetic GPR30 ligand G-1 mimics the non-genomic effects of 17beta-estradiol on islet hormone secretion, cAMP content in islets and its anti-apoptotic effects. G-1 or analogs thereof might be new potential candidates in the therapeutic strategy for type 2 diabetes in women.

Estradiol inhibits chondrogenic differentiation of mesenchymal stem cells via nonclassic signaling

OBJECTIVE

We undertook this study to examine the effects of estradiol on chondrogenesis of human bone marrow-derived mesenchymal stem cells (MSCs), with consideration of sex-dependent differences in cartilage repair.

METHODS

Bone marrow was obtained from the iliac crest of young men. Density-gradient centrifugation-separated human MSCs proliferated as a monolayer in serum-containing medium. After confluence was achieved, aggregates were created and cultured in a serum-free differentiation medium. We added different concentrations of 17beta-estradiol (E2) with or without the specific estrogen receptor inhibitor ICI 182.780, membrane-impermeable E2-bovine serum albumin (E2-BSA), ICI 182.780 alone, G-1 (an agonist of G protein-coupled receptor 30 [GPR-30]), and G15 (a GPR-30 antagonist). After 21 days, the aggregates were analyzed histologically and immunohistochemically; we quantified synthesized type II collagen, DNA content, sulfated glycosaminoglycan (sGAG) concentrations, and type X collagen and matrix metalloproteinase 13 (MMP-13) expression.

RESULTS

The existence of intracellular and membrane-associated E2 receptors was shown at various stages of chondrogenesis. Smaller aggregates and significantly lower type II collagen and sGAG content were detected after treatment with E2 and E2-BSA in a dose-dependent manner. Furthermore, E2 enhanced type X collagen and MMP-13 expression. Compared with estradiol alone, the coincubation of ICI 182.780 with estradiol enhanced suppression of chondrogenesis. Treatment with specific GPR-30 agonists alone (G-1 and ICI 182.780) resulted in a considerable inhibition of chondrogenesis. In addition, we found an enhancement of hypertrophy by G-1. Furthermore, the specific GPR-30 antagonist G15 reversed the GPR-30-mediated inhibition of chondrogenesis and up-regulation of hypertrophic gene expression.

CONCLUSION

The experiments revealed a suppression of chondrogenesis by estradiol via membrane receptors (GPR-30). The study opens new perspectives for influencing chondrogenesis on the basis of classic and nonclassic estradiol signaling.

New hypotheses and opportunities in endocrine therapy: amplification of oestrogen-induced apoptosis

AIMS

To outline the progress being made in the understanding of acquired resistance to long term therapy with the selective oestrogen receptor modulators (SERMs, tamoxifen and raloxifene) and aromatase inhibitors. The question to be addressed is how we can amplify the new biology of oestrogen-induced apoptosis to create more complete responses in exhaustively antihormone treated metastatic breast cancer.

METHODS AND RESULTS

Three questions are posed and addressed. (1) Do we know how oestrogen works? (2) Can we improve adjuvant antihormonal therapy? (3) Can we enhance oestrogen-induced apoptosis? The new player in oestrogen action is GPR30 and there are new drugs specific for this target to trigger apoptosis. Similarly, anti-angiogenic drugs can be integrated into adjuvant antihormone therapy or to enhance oestrogen-induced apoptosis in Phase II antihormone resistant breast cancer. The goal is to reduce the development of acquired antihormone resistance or undermine the resistance of breast cancer cells to undergo apoptosis with oestrogen respectively. Finally, drugs to reduce the synthesis of glutathione, a subcellular molecule compound associated with drug resistance, can enhance oestradiol-induced apoptosis.

CONCLUSIONS

We propose an integrated approach for the rapid testing of agents to blunt survival pathways and amplify oestrogen-induced apoptosis and tumour regression in Phase II resistant metastatic breast cancer. This Pharma platform will provide rapid clinical results to predict efficacy in large scale clinical trials.

Bisphenol A in combination with TNF-alpha selectively induces Th2 cell-promoting dendritic cells in vitro with an estrogen-like activity

Bisphenol A (BPA) is a monomer used in manufacturing a wide range of chemical products, including epoxy resins and polycarbonate. BPA, an important endocrine disrupting chemical that exerts estrogen-like activities, is detectable at nanomolar levels in human serum worldwide. The pregnancy associated doses of 17beta-estradiol (E2) plus tumor-necrosis factor-alpha (TNF-alpha) induce distorted maturation of human dendritic cells (DCs) that result in an increased capacity to induce T helper (Th) 2 responses. The current study demonstrated that the presence of BPA during DC maturation influences the function of human DCs, thereby polarizing the subsequent Th response. In the presence of TNF-alpha, BPA treatment enhanced the expression of CC chemokine ligand 1 (CCL1) in DCs. In addition, DCs exposed to BPA/TNF-alpha produced higher levels of IL-10 relative to those of IL-12p70 on CD40 ligation, and preferentially induced Th2 deviation. BPA exerts the same effect with E2 at the same dose (0.01-0.1 microM) with regard to DC-mediated Th2 polarization. These findings imply that DCs exposed to BPA will provide one of the initial signals driving the development and perpetuation of Th2-dominated immune response in allergic reactions.

Estrogen therapy and cognition: a review of the cholinergic hypothesis

The pros and cons of estrogen therapy for use in postmenopausal women continue to be a major topic of debate in women's health. Much of this debate focuses on the potential benefits vs. harm of estrogen therapy on the brain and the risks for cognitive impairment associated with aging and Alzheimer's disease. Many animal and human studies suggest that estrogens can have significant beneficial effects on brain aging and cognition and reduce the risk of Alzheimer's-related dementia; however, others disagree. Important discoveries have been made, and hypotheses have emerged that may explain some of the inconsistencies. This review focuses on the cholinergic hypothesis, specifically on evidence that beneficial effects of estrogens on brain aging and cognition are related to interactions with cholinergic projections emanating from the basal forebrain. These cholinergic projections play an important role in learning and attentional processes, and their function is known to decline with advanced age and in association with Alzheimer's disease. Evidence suggests that many of the effects of estrogens on neuronal plasticity and function and cognitive performance are related to or rely upon interactions with these cholinergic projections; however, studies also suggest that the effectiveness of estrogen therapy decreases with age and time after loss of ovarian function. We propose a model in which deficits in basal forebrain cholinergic function contribute to age-related changes in the response to estrogen therapy. Based on this model, we propose that cholinergic-enhancing drugs, used in combination with an appropriate estrogen-containing drug regimen, may be a viable therapeutic strategy for use in older postmenopausal women with early evidence of mild cognitive decline.

Involvement of estrogen receptor variant ER-alpha36, not GPR30, in nongenomic estrogen signaling

Accumulating evidence suggested that an orphan G protein-coupled receptor (GPR)30, mediates nongenomic responses to estrogen. The present study was performed to investigate the molecular mechanisms underlying GPR30 function. We found that knockdown of GPR30 expression in breast cancer SK-BR-3 cells down-regulated the expression levels of estrogen receptor (ER)-alpha36, a variant of ER-alpha. Introduction of a GPR30 expression vector into GPR30 nonexpressing cells induced endogenous ER-alpha36 expression, and cotransfection assay demonstrated that GPR30 activated the promoter activity of ER-alpha36 via an activator protein 1 binding site. Both 17beta-estradiol (E2) and G1, a compound reported to be a selective GPR30 agonist, increased the phosphorylation levels of the MAPK/ERK1/2 in SK-BR-3 cells, which could be blocked by an anti-ER-alpha36-specific antibody against its ligand-binding domain. G1 induced activities mediated by ER-alpha36, such as transcription activation activity of a VP16-ER-alpha36 fusion protein and activation of the MAPK/ERK1/2 in ER-alpha36-expressing cells. ER-alpha36-expressing cells, but not the nonexpressing cells, displayed high-affinity, specific E2 and G1 binding, and E2- and G1-induced intracellular Ca(2+) mobilization only in ER-alpha36 expressing cells. Taken together, our results demonstrated that previously reported activities of GPR30 in response to estrogen were through its ability to induce ER-alpha36 expression. The selective G protein-coupled receptor (GPR)30 agonist G1 actually interacts with ER-alpha36. Thus, the ER-alpha variant ER-alpha36, not GPR30, is involved in nongenomic estrogen signaling.