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

2-Methoxyestradiol causes matrix metalloproteinase 9-mediated transactivation of epidermal growth factor receptor and angiotensin type 1 receptor downregulation in rat aortic smooth muscle cells

Studies have demonstrated the therapeutic potential of estrogen metabolite 2-methoxyestradiol (2ME2) in several cardiovascular disorders, including hypertension. However, the exact mechanism(s) remains unknown. In this study, primary rat aortic smooth muscle cells (RASMCs) were exposed to 2ME2, and angiotensin type 1 receptor (AT1R) expression, function, and associated signaling pathways were evaluated. In RASMCs, 2ME2 downregulated AT1R expression in a concentration- and time-dependent manner, which was correlated with reduced mRNA expression. The 2ME2 effect was through G protein-coupled receptor 30 (GPR30) that inhibits second messenger cAMP. Moreover, 2ME2 exposure phosphorylated ERK1/2 that was sensitive to MEK inhibitor PD98059. Selective epidermal growth factor receptor (EGFR) inhibitor AG1478 blocked 2ME2-induced EGFR transactivation and attenuated subsequent phosphorylation of ERK1/2 preventing AT1R downregulation. The transactivation was dependent on 2ME2-induced release of matrix metalloproteinase 9 (MMP9) and epidermal growth factor demonstrated by ELISA. Furthermore, transfection with small interfering (si) RNA targeting MMP9 impeded ERK1/2 activation and AT1R downregulation in response to 2ME2 and G1 stimulation. Interestingly, under similar conditions, stimulation of GPR30 with the selective agonist G1 elicited similar signaling pathways and downregulated the AT1R expression that was reversed by GPR30 antagonist G15. Furthermore, 2ME2 and G1 inhibited angiotensin II (ANG II) induced Ca2+ release, a response consistent with AT1R downregulation. Collectively, our study demonstrates for the first time that 2ME2 binding to GPR30 induces MMP9 specific transactivation of EGFR that mediates ERK1/2-dependent downregulation of AT1R in RASMCs. The study provides critical insights into the newly discovered role and signaling pathways of 2ME2 in the regulation of AT1R in vascular cells and its potential to be developed as a therapeutic agent that ameliorates hypertension.

GPCRs in context: sexual dimorphism in the cardiovascular system

Cardiovascular disease (CVD) remains the largest cause of mortality worldwide, and there is a clear gender gap in disease occurrence, with men being predisposed to earlier onset of CVD, including atherosclerosis and hypertension, relative to women. Oestrogen may be a driving factor for female-specific cardioprotection, though androgens and sex chromosomes are also likely to contribute to sexual dimorphism in the cardiovascular system (CVS). Many GPCR-mediated processes are involved in cardiovascular homeostasis, and some exhibit clear sex divergence. Here, we focus on the G protein-coupled oestrogen receptor, endothelin receptors ET_A and ET_B and the eicosanoid G protein-coupled receptors (GPCRs), discussing the evidence and potential mechanisms leading to gender dimorphic responses in the vasculature. The use of animal models and pharmacological tools has been essential to understanding the role of these receptors in the CVS and will be key to further delineating their sex-specific effects. Ultimately, this may illuminate wider sex differences in cardiovascular pathology and physiology.

LINKED ARTICLES

This article is part of a themed section on Molecular Pharmacology of GPCRs. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.21/issuetoc.

Genomic and rapid effects of aldosterone: what we know and do not know thus far

Aldosterone is the most known mineralocorticoid hormone synthesized by the adrenal cortex. The genomic pathway displayed by aldosterone is attributed to the mineralocorticoid receptor (MR) signaling. Even though the rapid effects displayed by aldosterone are long known, our knowledge regarding the receptor responsible for such event is still poor. It is intense that the debate whether the MR or another receptor-the "unknown receptor"-is the receptor responsible for the rapid effects of aldosterone. Recently, G protein-coupled estrogen receptor-1 (GPER-1) was elegantly shown to mediate some aldosterone-induced rapid effects in several tissues, a fact that strongly places GPER-1 as the unknown receptor. It has also been suggested that angiotensin receptor type 1 (AT1) also participates in the aldosterone-induced rapid effects. Despite this open question, the relevance of the beneficial effects of aldosterone is clear in the kidneys, colon, and CNS as aldosterone controls the important water reabsorption process; on the other hand, detrimental effects displayed by aldosterone have been reported in the cardiovascular system and in the kidneys. In this line, the MR antagonists are well-known drugs that display beneficial effects in patients with heart failure and hypertension; it has been proposed that MR antagonists could also play an important role in vascular disease, obesity, obesity-related hypertension, and metabolic syndrome. Taken altogether, our goal here was to (1) bring a historical perspective of both genomic and rapid effects of aldosterone in several tissues, and the receptors and signaling pathways involved in such processes; and (2) critically address the controversial points within the literature as regarding which receptor participates in the rapid pathway display by aldosterone.

Effects of Estrogen on the Gastrointestinal Tract

Estrogen is a kind of steroid compound that has extensive biologic activities. The effect of estrogen is pleiotropic, affecting multiple systems in the body. There is accumulating evidence that estrogen has important effects on the gastrointestinal tract. Longer exposure to estrogen may decrease the risk of gastric cancer. Use of the anti-estrogen drug tamoxifen might increase the risk of gastric adenocarcinoma. Estrogen receptor β may serve as a target for colorectal cancer prevention. In addition, estrogen has been reported to be closely related to the mucosal barrier, gastrointestinal function and intestinal inflammation. However, the role of estrogen in the gastrointestinal tract has not been systematically summarized. In this review, we aim to provide an overview of the role of estrogen in the gastrointestinal tract and evaluate it from various aspects, including estrogen receptors, the mucosal barrier, intestinal inflammation and gastrointestinal tract tumors, which may provide the basis for the development of therapeutic strategies to manage gastrointestinal diseases.

Primary Adrenal Insufficiency: Managing Mineralocorticoid Replacement Therapy

CONTEXT

Mineralocorticoid (MC) replacement therapy in patients with primary adrenal insufficiency (PAI) was introduced more than 60 years ago. Still, there are limited data on how MC substitution should be optimized, because MC dosing regimens have only been systematically investigated in a few studies. We review the management of current standard MC replacement therapy in PAI and its plausible impact on outcome.

DESIGN

Using PubMed, we conducted a systematic review of the literature from 1939 to 2017, with the following keywords: adrenal insufficiency, MC deficiency, aldosterone, cardiovascular disease, hypertension, and heart failure.

RESULTS

The current standard treatment consists of fludrocortisone (FC) given once daily in the morning, aiming at normotension, normokalemia, and plasma renin activity in the upper normal range. Available data suggest that patients with PAI may be underreplaced with FC as symptoms and signs indicating chronic MC underreplacement, such as salt craving and postural dizziness persist, in many treated patients with PAI. Data acquired from large registry-based studies show that glucocorticoid doses for replacement in PAI are higher than those estimated from endogenous production. Glucocorticoid overreplacement may reduce the need of MC replacement but may also be a consequence of inadequate MC replacement.

CONCLUSIONS

The commonly used MC replacement in PAI may not be adequate in some patients. Insufficient MC substitution may be responsible for poor cardiometabolic outcome and the failure to restore well-being adequately in patients with PAI. Well-designed studies oriented at optimizing MC replacement therapy are urgently needed.

Rapid actions of aldosterone revisited: Receptors in the limelight

Steroid hormones like aldosterone have been conclusively shown to elicit both late genomic and rapid, nongenomically initiated responses. Aldosterone was among the first for which rapid, clinically relevant effects were even shown in humans. Yet, after over 30 years of research, the nature of receptors involved in rapid actions of aldosterone is still unclear. Such effects may be assigned to the classical, intracellular steroid receptors, in this case mineralocorticoid receptors (MR, class IIa action Mannheim classification). They typically disappear in knockout models and are blocked by MR-antagonists such as spironolactone, as shown for several cellular and physiological, e.g. renal or cardiovascular effects. In contrast, there is also consistent evidence suggesting type IIb effects involving structurally different receptors ("membrane receptors") being insensitive to classic antagonists and persistent in knockout models; IIb effects have lately even been confirmed by atomic force detection of surface receptors which bind aldosterone but not spironolactone. Type IIa and b may coexist in the same cell with IIa often augmenting early IIb effects. So far cloning of IIb receptors was unsuccessful; therefore results on G-protein coupled estrogen receptor 1 (GPER1) being potentially involved in rapid aldosterone action raised considerable interest. Surprisingly, GPER1 does not bind aldosterone. Though under these circumstances GPER1 should not yet be considered as IIb-receptor, it might be an intermediary signaling enhancer of mineralocorticoid action as shown for epithelial growth factor receptors reconciling those results. We still seem to be left without IIb-receptors whose identification would however be highly desirable and essential for clinical translation.

Does Aldosterone Play a Significant Role for Regulation of Vascular Tone?

Besides the well-known renal effects of aldosterone, the hormone is now known to have direct vascular effects. Clinical observations underline substantial adverse effects of aldosterone on cardiovascular function. The source of systemic circulating aldosterone is the adrenal gland zona glomerulosa cells through stimulus-secretion coupling involving depolarization, opening of L- and T-type calcium channels and aldosterone synthase activation. Local formation and release in peripheral tissues such as perivascular fat is recognized. Where does aldosterone affect the vasculature? Mineralocorticoid receptors (MRs) are present in endothelial and vascular smooth muscle cells, and MR-independent pathways are also involved. The vascular effects of aldosterone are complex, both concentration and temporal and spatial aspects are relevant. The acute response includes vasodilation through endothelial nitric oxide formation and vasoconstrictor effects through endothelial-contracting cyclooxygenase-derived factors and a changed calcium handling. The response to aldosterone can change within the same blood vessels depending on the exposure time and status of the endothelium. Chronic responses involve changed levels of reactive oxygen radicals, endothelial Na-influx and smooth muscle calcium channel expression. Furthermore, perivascular cells for example mast cells have also been suggested to participate in the chronic response. Moreover, the vascular effect of aldosterone depends on the status of the endothelium which is likely the cause of the very different responses to aldosterone and MR treatment observed in human studies going from increased to decreased flow depending on whether the patient had prior cardiovascular disease with endothelial dysfunction or not. A preponderance of constrictor versus dilator responses to aldosterone could therefore be involved in the detrimental vascular actions of the hormone in the setting of endothelial dysfunction and contribute to explain the beneficial action of MR blockers on blood pressure and target organ injury.

30 YEARS OF THE MINERALOCORTICOID RECEPTOR: Nongenomic effects via the mineralocorticoid receptor

The mineralocorticoid receptor (MR) belongs to the steroid hormone receptor family and classically functions as a ligand-dependent transcription factor. It is involved in water-electrolyte homeostasis and blood pressure regulation but independent from these effects also furthers inflammation, fibrosis, hypertrophy and remodeling in cardiovascular tissues. Next to genomic effects, aldosterone elicits very rapid actions within minutes that do not require transcription or translation and that occur not only in classical MR epithelial target organs like kidney and colon but also in nonepithelial tissues like heart, vasculature and adipose tissue. Most of these effects can be mediated by classical MR and its crosstalk with different signaling cascades. Near the plasma membrane, the MR seems to be associated with caveolin and striatin as well as with receptor tyrosine kinases like EGFR, PDGFR and IGF1R and G protein-coupled receptors like AT1 and GPER1, which then mediate nongenomic aldosterone effects. GPER1 has also been named a putative novel MR. There is a close interaction and functional synergism between the genomic and the nongenomic signaling so that nongenomic signaling can lead to long-term effects and support genomic actions. Therefore, understanding nongenomic aldosterone/MR effects is of potential relevance for modulating genomic aldosterone effects and may provide additional targets for intervention.

Unsung renal receptors: orphan G-protein-coupled receptors play essential roles in renal development and homeostasis

Recent studies have shown that orphan GPCRs of the GPR family are utilized as specialized chemosensors in various tissues to detect metabolites, and in turn to activate downstream pathways which regulate systemic homeostasis. These studies often find that such metabolites are generated by well-known metabolic pathways, implying that known metabolites and chemicals may perform novel functions. In this review, we summarize recent findings highlighting the role of deorphanized GPRs in renal development and function. Understanding the role of these receptors is critical in gaining insights into mechanisms that regulate renal function both in health and in disease.

Mineralocorticoid regulation of cell function: the role of rapid signalling and gene transcription pathways

The mineralocorticoid receptor (MR) and mineralocorticoids regulate epithelial handling of electrolytes, and induces diverse effects on other tissues. Traditionally, the effects of MR were ascribed to ligand-receptor binding and activation of gene transcription. However, the MR also utilises a number of intracellular signalling cascades, often by transactivating unrelated receptors, to change cell function more rapidly. Although aldosterone is the physiological mineralocorticoid, it is not the sole ligand for MR. Tissue-selective and mineralocorticoid-specific effects are conferred through the enzyme 11β-hydroxysteroid dehydrogenase 2, cellular redox status and properties of the MR itself. Furthermore, not all aldosterone effects are mediated via MR, with implication of the involvement of other membrane-bound receptors such as GPER. This review will describe the ligands, receptors and intracellular mechanisms available for mineralocorticoid hormone and receptor signalling and illustrate their complex interactions in physiology and disease.

The role of GRIP1 and ephrin B3 in blood pressure control and vascular smooth muscle cell contractility

Several erythropoietin-producing hepatocellular receptor B family (EPHB) and their ligands, ephrinBs (EFNBs), are involved in blood pressure regulation in animal models. We selected 528 single nucleotide polymorphisms (SNPs) within the genes of EPHB6, EFNB2, EFNB3 and GRIP1 in the EPH/EFN signalling system to query the International Blood Pressure Consortium dataset. A SNP within the glutamate receptor interacting protein 1 (GRIP1) gene presented a p-value of 0.000389, approaching the critical p-value of 0.000302, for association with diastolic blood pressure of 60,396 individuals. According to echocardiography, we found that Efnb3 gene knockout mice showed enhanced constriction in the carotid arteries. In vitro studies revealed that in mouse vascular smooth muscle cells, siRNA knockdown of GRIP1, which is in the EFNB3 reverse signalling pathway, resulted in increased contractility of these cells. These data suggest that molecules in the EPHB/EFNB signalling pathways, specifically EFNB3 and GRIP1, are involved blood pressure regulation.

Aldosterone induces rapid sodium intake by a nongenomic mechanism in the nucleus tractus solitarius

The purpose of this study was to determine whether aldosterone has a rapid action in the nucleus tractus solitarius (NTS) that increases sodium intake, and to examine whether this effect of aldosterone, if present, is mediated by G protein-coupled estrogen receptor (GPER). Adult male Sprague-Dawley rats with a stainless-steel cannula in the NTS were used. Aldosterone was injected into the NTS at the doses of 1, 5, 10 and 20 ng 0.1 μl⁻¹. A rapid dose-related increase of 0.3 M NaCl intake was induced within 30 min and this increase was not suppressed by the mineralocorticoid receptor (MR) antagonist spironolactone (10 ng 0.1 μl⁻¹). Water intake was not affected by aldosterone. The GPER agonist G-1 produced a parallel and significant increase in sodium intake, while pre-treatment with GPER antagonist G15 (10 ng 0.1 μl⁻¹) blocked the G-1 or aldosterone-induced rapid sodium intake. In addition, sodium intake induced by sodium depletion or low-sodium diet fell within 30 min after injection into the NTS of the MR antagonist spironolactone, while G15 had no effect. Our results confirm previous reports, and support the hypothesis that aldosterone evokes rapid sodium intake through a non-genomic mechanism involving GPER in NTS.

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

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

GPER (GPR30): A Nongenomic Receptor (GPCR) for Steroid Hormones with Implications for Cardiovascular Disease and Cancer

Although the rapid effects of steroids, such as estrogen and aldosterone, were postulated originally to be nongenomic, it is now appreciated that activation of such signaling pathways via a steroid-acting G protein-coupled receptor, the G protein estrogen receptor (GPER), has important transcription-dependent outcomes in the regulation of cell growth and programmed cell death secondary to GPER-regulated second-messenger pathways. GPER is expressed ubiquitously and has diverse biological effects, including regulation of endocrine, immune, neuronal, and cardiovascular functions. Perhaps the most biologically important consequences of GPER activation are the regulation of cell growth, migration, and apoptotic cell death. These cell growth regulatory effects, important in cancer biology, are also relevant in the regulation of cardiac and vascular hypertrophy and in the response to ischemia. This review provides a summary of relevant findings of the impact of GPER regulation by either estradiol or aldosterone in in vitro model systems and extends those findings to in vivo studies of direct clinical relevance for development of GPER-directed agents for treatment of cancer and cardiovascular diseases associated with cellular proliferation.

Third-generation Mineralocorticoid Receptor Antagonists: Why Do We Need a Fourth?

The first mineralocorticoid receptor (MR) antagonist, spironolactone, was developed almost 60 years ago to treat primary aldosteronism and pathological edema. Its use waned in part because of its lack of selectivity. Subsequently, knowledge of the scope of MR function was expanded along with clinical evidence of the therapeutic importance of MR antagonists to prevent the ravages of inappropriate MR activation. Forty-two years elapsed between the first and MR-selective second generation of MR antagonists. Fifteen years later, despite serious shortcomings of the existing antagonists, a third-generation antagonist has yet to be marketed. Progress has been slowed by the lack of appreciation of the large variety of cell types that express the MR and its diverse cell-type-specific actions, and also its unique complex interaction actions at the molecular level. New MR antagonists should preferentially target the inflammatory and fibrotic effects of MR and perhaps its excitatory effects on sympathetic nervous system, but not the renal tubular epithelium or neurons of the cortex and hippocampus. This review briefly describes efforts to develop a third-generation MR antagonist and why fourth generation antagonists and selective agonists based on structural determinants of tissue and ligand-specific MR activation should be contemplated.

Aldosterone Synthase Inhibition Improves Glucose Tolerance in Zucker Diabetic Fatty (ZDF) Rats

Plasma aldosterone is elevated in type 2 diabetes and obesity in experimental and clinical studies and can act to inhibit both glucose-stimulated insulin secretion by the β-cell and insulin signaling. Currently mineralocorticoid receptor antagonism is the best characterized treatment to ameliorate aldosterone-mediated effects. A second alternative is inhibition of aldosterone synthase, an approach with protective effects on end-organ damage in heart or kidney in animal models. The effect of aldosterone synthase inhibition on metabolic parameters in type 2 diabetes is not known. Therefore, male Zucker diabetic fatty (ZDF) rats were treated for 11 weeks with the aldosterone synthase inhibitor FAD286, beginning at 7 weeks of age. Results were compared with the mineralocorticoid receptor antagonist eplerenone. Plasma aldosterone was abolished by FAD286 and elevated more than 9-fold by eplerenone. The area under the curve calculated from an oral glucose tolerance test (OGTT) was lower and overall insulin response during OGTT was increased by FAD286. In contrast, eplerenone elevated blood glucose levels and blunted insulin secretion during the OGTT. Fasting glucose was lowered and fasting insulin was increased by FAD286 in the prediabetic state. Glycated hemoglobin was lowered by FAD286, whereas eplerenone showed no effect. We conclude that aldosterone synthase inhibition, in contrast to mineralocorticoid receptor antagonism, has the potential for beneficial effects on metabolic parameters in type 2 diabetes.

Mineralocorticoid Receptor (MR) trans-Activation of Inflammatory AP-1 Signaling: DEPENDENCE ON DNA SEQUENCE, MR CONFORMATION, AND AP-1 FAMILY MEMBER EXPRESSION

Glucocorticoids are commonly used to treat inflammatory disorders. The glucocorticoid receptor (GR) can tether to inflammatory transcription factor complexes, such as NFκB and AP-1, and trans-repress the transcription of cytokines, chemokines, and adhesion molecules. In contrast, aldosterone and the mineralocorticoid receptor (MR) primarily promote cardiovascular inflammation by incompletely understood mechanisms. Although MR has been shown to weakly repress NFκB, its role in modulating AP-1 has not been established. Here, the effects of GR and MR on NFκB and AP-1 signaling were directly compared using a variety of ligands, two different AP-1 consensus sequences, GR and MR DNA-binding domain mutants, and siRNA knockdown or overexpression of core AP-1 family members. Both GR and MR repressed an NFκB reporter without influencing p65 or p50 binding to DNA. Likewise, neither GR nor MR affected AP-1 binding, but repression or activation of AP-1 reporters occurred in a ligand-, AP-1 consensus sequence-, and AP-1 family member-specific manner. Notably, aldosterone interactions with both GR and MR demonstrated a potential to activate AP-1. DNA-binding domain mutations that eliminated the ability of GR and MR to cis-activate a hormone response element-driven reporter variably affected the strength and polarity of these responses. Importantly, MR modulation of NFκB and AP-1 signaling was consistent with a trans-mechanism, and AP-1 effects were confirmed for specific gene targets in primary human cells. Steroid nuclear receptor trans-effects on inflammatory signaling are context-dependent and influenced by nuclear receptor conformation, DNA sequence, and the expression of heterologous binding partners. Aldosterone activation of AP-1 may contribute to its proinflammatory effects in the vasculature.

Aldosterone Upregulates Transient Receptor Potential Melastatin 7 (TRPM7)

Transient receptor potential melastatin 7 (TRPM7) is a ubiquitously expressed Mg(2+)-permeable ion channel fused to a C-terminal α-kinase domain. Recently, aldosterone was shown to increase intracellular Mg(2+) levels and alter inflammatory signaling in TRPM7-expressing HEK293 cells. This study was undertaken to assess whether these effects were related to an aldosterone-mediated increase of TRPM7 current and/or plasma membrane localization. Using HEK293 cells stably expressing WT-TRPM7, we found that 18-h application of aldosterone significantly increased TRPM7 current and TRPM7 plasma membrane protein expression by 48% and 34%, respectively. The aldosterone-mediated increase of TRPM7 current was inhibited by eplerenone, a mineralocorticoid receptor (MR) blocker, and GSK-650394, an inhibitor of the serum- and glucocorticoid-regulated kinase 1 (SGK1). SGK1 blockade also prevented the aldosterone-induced increase of TRPM7 plasma membrane protein. It was further determined that K1648R-TRPM7, the phosphotransferase-inactive TRPM7 mutant, was unresponsive to aldosterone. Therefore, chronic aldosterone treatment increases the plasma membrane expression of TRPM7, which is associated with an increase of TRPM7 current. This process occurs via an MR-dependent, genomic signaling cascade involving SGK1 and a functioning TRPM7 α-kinase domain. We suggest that this mechanism may be of general relevance when interpreting the effects of aldosterone because the MR receptor is found in multiple tissues, and TRPM7 and SGK1 are ubiquitously expressed.

Not lost in translation: Emerging clinical importance of the G protein-coupled estrogen receptor GPER

It has been 20years that the G protein-coupled estrogen receptor (GPER) was cloned as the orphan receptor GPR30 from multiple cellular sources, including vascular endothelial cells. Here, I will provide an overview of estrogen biology and the historical background leading to the discovery of rapid vascular estrogen signaling. I will also review the recent advances in the understanding of the mechanisms underlying GPER function, its role in physiology and disease, some of the currently available GPER-targeting drugs approved for clinical use such as SERMs (selective estrogen receptor modulators) and SERDs (selective estrogen receptor downregulators). Many of currently used drugs such as tamoxifen, raloxifene, or faslodex™/fulvestrant were discovered targeting GPER many years after they had been introduced to the clinics for entirely different purposes. This has important implications for the clinical use of these drugs and their modes of action, which I have termed 'reverse translational medicine'. In addition, environmental pollutants known as 'endocrine disruptors' have been found to bind to GPER. This article also discusses recent evidence in these areas as well as opportunities in translational clinical medicine and GPER research, including medical genetics, personalized medicine, prevention, and its theranostic use.

Estrogens and Coronary Artery Disease: New Clinical Perspectives

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

Role of the Renin-Angiotensin-Aldosterone System beyond Blood Pressure Regulation: Molecular and Cellular Mechanisms Involved in End-Organ Damage during Arterial Hypertension

Arterial hypertension is a common condition worldwide and an important predictor of several complicated diseases. Arterial hypertension can be triggered by many factors, including physiological, genetic, and lifestyle causes. Specifically, molecules of the renin-angiotensin-aldosterone system not only play important roles in the control of blood pressure, but they are also associated with the genesis of arterial hypertension, thus constituting a need for pharmacological interventions. Chronic high pressure generates mechanical damage along the vascular system, heart, and kidneys, which are the principal organs affected in this condition. In addition to mechanical stress, hypertension-induced oxidative stress, chronic inflammation, and the activation of reparative mechanisms lead to end-organ damage, mainly due to fibrosis. Clinical trials have demonstrated that renin-angiotensin-aldosterone system intervention in hypertensive patients lowers morbidity/mortality and inflammatory marker levels as compared to placebo patients, evidencing that this system controls more than blood pressure. This review emphasizes the detrimental effects that a renin-angiotensin-aldosterone system (RAAS) imbalance has on health considerations above and beyond high blood pressure, such as fibrotic end-organ damage.

Rapid steroid hormone actions via membrane receptors

Steroid hormones regulate a wide variety of physiological and developmental functions. Traditional steroid hormone signaling acts through nuclear and cytosolic receptors, altering gene transcription and subsequently regulating cellular activity. This is particularly important in hormonally-responsive cancers, where therapies that target classical steroid hormone receptors have become clinical staples in the treatment and management of disease. Much progress has been made in the last decade in detecting novel receptors and elucidating their mechanisms, particularly their rapid signaling effects and subsequent impact on tumorigenesis. Many of these receptors are membrane-bound and lack DNA-binding sites, functionally separating them from their classical cytosolic receptor counterparts. Membrane-bound receptors have been implicated in a number of pathways that disrupt the cell cycle and impact tumorigenesis. Among these are pathways that involve phospholipase D, phospholipase C, and phosphoinositide-3 kinase. The crosstalk between these pathways has been shown to affect apoptosis and proliferation in cardiac cells, osteoblasts, and chondrocytes as well as cancer cells. This review focuses on rapid signaling by 17β-estradiol and 1α,25-dihydroxy vitamin D3 to examine the integrated actions of classical and rapid steroid signaling pathways both in contrast to each other and in concert with other rapid signaling pathways. This new approach lends insight into rapid signaling by steroid hormones and its potential for use in targeted drug therapies that maximize the benefits of traditional steroid hormone-directed therapies while mitigating their less desirable effects.

The cardiac electrogenic sodium/bicarbonate cotransporter (NBCe1) is activated by aldosterone through the G protein-coupled receptor 30 (GPR 30)

The sodium/bicarbonate cotransporter (NBC) transports extracellular Na⁺ and HCO₃^- into the cytoplasm upon intracellular acidosis, restoring the acidic pH_i to near neutral values. Two different NBC isoforms have been described in the heart, the electroneutral NBCn1 (1Na⁺:1HCO₃^-) and the electrogenic NBCe1 (1Na⁺:2HCO₃^-). Certain non-genomic effects of aldosterone (Ald) were due to an orphan G protein-couple receptor 30 (GPR30). We have recently demonstrated that Ald activates GPR30 in adult rat ventricular myocytes, which transactivates the epidermal growth factor receptor (EGFR) and in turn triggers a reactive oxygen species (ROS)- and PI3K/AKT-dependent pathway, leading to the stimulation of NBC. The aim of this study was to investigate the NBC isoform involved in the Ald/GPR30-induced NBC activation. Using specific NBCe1 inhibitory antibodies (a-L3) we demonstrated that Ald does not affect NBCn1 activity. Ald was able to increase NBCe1 activity recorded in isolation. Using immunofluorescence and confocal microscopy analysis we showed in this work that both NBCe1 and GPR30 are localized in t-tubules. In conclusion, we have demonstrated that NBCe1 is the NBC isoform activated by Ald in the heart.

Roles of aldosterone in vascular calcification: An update

Both clinical and experimental studies have demonstrated that vascular calcification (VC) is a common pathology shared in many chronic diseases such as chronic kidney disease (CKD) and diabetes. It's an independent risk factor for cardiovascular events. Since the pathogenesis of VC is complicated, current therapies have limited effects on the regression of VC. Therefore, it is urgent to investigate the potential mechanisms and find new targets for the treatment of VC. Aldosterone (Aldo), a mineralocorticoid hormone, is the metabolite of renin-angiotensin-aldosterone system (RAAS) activation, which can exert genomic and non-genomic effects on the cardiovascular system. Recent data suggests that Aldo can promote VC. Here, we summarized the roles of Aldo in the process of VC and a series of findings indicated that Aldo could act as a potentially therapeutic target for treating VC.

Heart Disease in Women: Unappreciated Challenges, GPER as a New Target

Heart disease in women remains underappreciated, underdiagnosed and undertreated. Further, although we are starting to understand some of the social and behavioral determinants for this, the biological basis for the increased rate of rise in atherosclerosis risk in women after menopause remains very poorly understand. In this review we will outline the scope of the clinical issues related to heart disease in women, the emerging findings regarding the biological basis underlying the increased prevalence of atherosclerotic risk factors in postmenopausal women (vs. men) and the role of the G protein-coupled estrogen receptor (GPER) and its genetic regulation as a determinant of these sex-specific risks. GPER is a recently appreciated GPCR that mediates the rapid effects of estrogen and aldosterone. Recent studies have identified that GPER activation regulates both blood pressure. We have shown that regulation of GPER function via expression of a hypofunctional GPER genetic variant is an important determinant of blood pressure and risk of hypertension in women. Further, our most recent studies have identified that GPER activation is an important regulator of low density lipoprotein (LDL) receptor metabolism and that expression of the hypofunctional GPER genetic variant is an important contributor to the development of hypercholesterolemia in women. GPER appears to be an important determinant of the two major risk factors for coronary artery disease-blood pressure and LDL cholesterol. Further, the importance of this mechanism appears to be greater in women. Thus, the appreciation of the role of GPER function as a determinant of the progression of atherosclerotic disease may be important both in our understanding of cardiometabolic function but also in opening the way to greater appreciation of the sex-specific regulation of atherosclerotic risk factors.

Characterisation of Signalling by the Endogenous GPER1 (GPR30) Receptor in an Embryonic Mouse Hippocampal Cell Line (mHippoE-18)

Estrogen can modulate neuronal development and signalling by both genomic and non-genomic pathways. Many of its rapid, non-genomic effects on nervous tissue have been suggested to be mediated via the activation of the estrogen sensitive G-protein coupled receptor (GPER1 or GPR30). There has been much controversy over the cellular location, signalling properties and endogenous activators of GPER1. Here we describe the pharmacology and signalling properties of GPER1 in an immortalized embryonic hippocampal cell line, mHippoE-18. This cell line does not suffer from the inherent problems associated with the study of this receptor in native tissue or the problems associated with heterologously expression in clonal cell lines. In mHippoE-18 cells, 17β-Estradiol can mediate a dose-dependent rapid potentiation of forskolin-stimulated cyclic AMP levels but does not appear to activate the ERK1/2 pathway. The effect of 17β-Estradiol can be mimicked by the GPER1 agonist, G1, and also by tamoxifen and ICI 182,780 which activate GPER1 in a variety of other preparations. The response is not mimicked by the application of the classical estrogen receptor agonists, PPT, (an ERα agonist) or DPN, (an ERβ agonist), further suggesting that this effect of 17β-Estradiol is mediated through the activation of GPER1. However, after exposure of the cells to the GPER1 specific antagonists, G15 and G36, the stimulatory effects of the above agonists are replaced by dose-dependent inhibitions of forskolin-stimulated cyclic AMP levels. This inhibitory effect is mimicked by aldosterone in a dose-dependent way even in the absence of the GPER1 antagonists. The results are discussed in terms of possible "Biased Antagonism" whereby the antagonists change the conformation of the receptor resulting in changes in the agonist induced coupling of the receptor to different second messenger pathways.

Role of Nox2 and p22phox in Persistent Postoperative Hypertension in Aldosterone-Producing Adenoma Patients after Adrenalectomy

Adrenal aldosterone-producing adenoma (APA), producing the salt-retaining hormone aldosterone, commonly causes secondary hypertension, which often persists after unilateral adrenalectomy. Although persistent hypertension was correlated with residual hormone aldosterone, the in vivo mechanism remains unclear. NADPH oxidase is the critical cause of aldosterone synthesis in vitro. Nox2 and p22phox comprise the NADPH oxidase catalytic core, serving to initiate a reactive oxygen species (ROS) cascade that may participate in the pathology. mRNAs of seven NADPH oxidase isoforms in APA were evaluated by RT-PCR and Q-PCR and their proteins by immunohistochemistry and Western blotting. NADPH oxidase activity was also detected. Nox2 and p22phox were especially abundant in APA. Particularly higher Nox2 and p22phox gene and protein levels were seen in APA than controls. Significant correlations between Nox2 mRNA and aldosterone synthase (CYP11B2) mRNA (R = 0.66, P < 0.01) and Nox2 protein and baseline plasma aldosterone concentration (PAC) (R = 0.503, P < 0.01) were detected in APA; however, none were found between p22phox mRNA, CYP11B2 mRNA, p22phox protein, and baseline PAC. Importantly, we found that Nox2 localized specifically in hyperplastic zona glomerulosa cells. In conclusion, our results highlight that Nox2 and p22phox may be directly involved in pathological aldosterone production and zona glomerulosa cell proliferation after APA resection.

Rapid effects of aldosterone in primary cultures of cardiomyocytes - do they suggest the existence of a membrane-bound receptor?

Aldosterone acts on its target tissue through a classical mechanism or through the rapid pathway through a putative membrane-bound receptor. Our goal here was to better understand the molecular and biochemical rapid mechanisms responsible for aldosterone-induced cardiomyocyte hypertrophy. We have evaluated the hypertrophic process through the levels of ANP, which was confirmed by the analysis of the superficial area of cardiomyocytes. Aldosterone increased the levels of ANP and the cellular area of the cardiomyocytes; spironolactone reduced the aldosterone-increased ANP level and cellular area of cardiomyocytes. Aldosterone or spironolactone alone did not increase the level of cyclic 3',5'-adenosine monophosphate (cAMP), but aldosterone plus spironolactone led to increased cAMP level; the treatment with aldosterone + spironolactone + BAPTA-AM reduced the levels of cAMP. These data suggest that aldosterone-induced cAMP increase is independent of mineralocorticoid receptor (MR) and dependent on Ca(2+). Next, we have evaluated the role of A-kinase anchor proteins (AKAP) in the aldosterone-induced hypertrophic response. We have found that St-Ht31 (AKAP inhibitor) reduced the increased level of ANP which was induced by aldosterone; in addition, we have found an increase on protein kinase C (PKC) and extracellular signal-regulated kinase 5 (ERK5) activity when cells were treated with aldosterone alone, spironolactone alone and with a combination of both. Our data suggest that PKC could be responsible for ERK5 aldosterone-induced phosphorylation. Our study suggests that the aldosterone through its rapid effects promotes a hypertrophic response in cardiomyocytes that is controlled by an AKAP, being dependent on ERK5 and PKC, but not on cAMP/cAMP-dependent protein kinase signaling pathways. Lastly, we provide evidence that the targeting of AKAPs could be relevant in patients with aldosterone-induced cardiac hypertrophy and heart failure.

The acute prothrombotic effect of aldosterone in rats is partially mediated via angiotensin II receptor type 1

INTRODUCTION

We showed previously that the prothrombotic effect of one hour aldosterone (ALDO) infusion in rats was only partially mediated by the mineralocorticoid receptor (MR). Bearing in mind that ALDO potentiates the effects of angiotensin II (Ang II), in the present study we investigated the role of Ang II receptor type 1 - AT1 in acute ALDO prothrombotic action.

MATERIALS AND METHODS

The experiments were performed in a stasis-induced venous thrombosis model in male Wistar, normotensive rats. ALDO (30μg/kg) was infused for 1h. Valsartan (VAL; 10mg/kg), a selective AT1 receptor antagonist, was administered in a single bolus injection before ALDO infusion. Eplerenone (EPL, 100mg/kg), a selective MR receptor antagonist, was administered per os before ALDO. Thrombus weight and incidences of thrombosis were assayed. Bleeding time and platelet adhesion to collagen were evaluated as primary hemostasis parameters. The plasma levels of some coagulation and fibrinolysis parameters, and plasma NO metabolite levels were assayed.

RESULTS

AT1 blockade with valsartan significantly reduced ALDO-induced thrombosis expressed as a reduced thrombus mass (p<0.05 vs ALDO) and diminished the incidence of thrombosis. Valsartan reduced the ALDO-induced changes in bleeding time and platelet adhesion, as well as in coagulation, fibrinolysis, and NO metabolite levels. The effect of AT1 blockade in ALDO-induced thrombosis was similar to the effect of MR blockade. However, dual blockade of AT1 and MR showed no additional benefit.

CONCLUSIONS

ALDO prothrombotic action is partially mediated via AT1 receptor in the mechanism involving enhanced platelet activation, induced coagulation, impaired fibrinolysis and reduced NO bioavailability.

Copernicus Revisited: Overturning Ptolemy's View of the GPER Universe

Whether aldosterone activates the G-protein-coupled estrogen receptor (GPER) has been questioned, recently, in the name of Copernicus. However, for G-protein-coupled receptors (GPCRs) multiple hormone activators are common. Further, studies in mineralocorticoid receptor (MR)-deficient systems, with pharmacological GPER-selective antagonists or regulation of GPER expression, consistently show that some aldosterone effects can be GPER mediated.

Aldosterone stimulates the cardiac sodium/bicarbonate cotransporter via activation of the g protein-coupled receptor gpr30

Some cardiac non-genomic effects of aldosterone (Ald) are reported to be mediated through activation of the classic mineralocorticoid receptor (MR). However, in the last years, it was proposed that activation of the novel G protein-coupled receptor GPR30 mediates certain non-genomic effects of Ald. The aim of this study was to elucidate if the sodium/bicarbonate cotransporter (NBC) is stimulated by Ald and if the activation of GPR30 mediates this effect. NBC activity was evaluated in rat cardiomyocytes perfused with HCO3(-)/CO2 solution in the continuous presence of HOE642 (sodium/hydrogen exchanger blocker) during recovery from acidosis using intracellular fluorescence measurements. Ald enhanced NBC activity (% of ΔJHCO3(-); control: 100±5.82%, n=7 vs Ald: 151.88±11.02%, n=5; P<0.05), which was prevented by G15 (GPR30 blocker, 90.53±7.81%, n=7). Further evidence for the involvement of GPR30 was provided by G1 (GPR30 agonist), which stimulated NBC (185.13±18.28%, n=6; P<0.05) and this effect was abrogated by G15 (124.19±10.96%, n=5). Ald- and G1-induced NBC stimulation was abolished by the reactive oxygen species (ROS) scavenger MPG and by the NADPH oxidase inhibitor apocynin. In addition, G15 prevented Ald- and G1-induced ROS production. Pre-incubation of myocytes with wortmannin (PI3K-AKT pathway blocker) prevented Ald- or G1-induced NBC stimulation. In summary, Ald stimulates NBC by GPR30 activation, ROS production and AKT stimulation.

Nicolaus Copernicus and the rapid vascular responses to aldosterone

For decades, rapid steroid responses initiated by membrane receptors have been a primary research focus. G protein-coupled estrogen receptor (GPER) is activated by 17β-estradiol and participates in functional crosstalk with other steroid receptors. With reference to the physician and astronomer Nicolaus Copernicus (1473-1543), who used rigorous scientific approaches to shift paradigms and change dogma, we discuss whether GPER can also be considered an aldosterone receptor.

Cooperative Role of Mineralocorticoid Receptor and Caveolin-1 in Regulating the Vascular Response to Low Nitric Oxide-High Angiotensin II-Induced Cardiovascular Injury

Aldosterone interacts with mineralocorticoid receptor (MR) to stimulate sodium reabsorption in renal tubules and may also affect the vasculature. Caveolin-1 (cav-1), an anchoring protein in plasmalemmal caveolae, binds steroid receptors and also endothelial nitric oxide synthase, thus limiting its translocation and activation. To test for potential MR/cav-1 interaction in the vasculature, we investigated if MR blockade in cav-1-replete or -deficient states would alter vascular function in a mouse model of low nitric oxide (NO)-high angiotensin II (AngII)-induced cardiovascular injury. Wild-type (WT) and cav-1 knockout mice (cav-1(-/-)) consuming a high salt diet (4% NaCl) received Nω-nitro-l-arginine methyl ester (L-NAME) (0.1-0.2 mg/ml in drinking water at days 1-11) plus AngII (0.7-2.8 mg/kg per day via an osmotic minipump at days 8-11) ± MR antagonist eplerenone (EPL) 100 mg/kg per day in food. In both genotypes, blood pressure increased with L-NAME + AngII. EPL minimally changed blood pressure, although its dose was sufficient to block MR and reverse cardiac expression of the injury markers cluster of differentiation 68 and plasminogen activator inhibitor-1 in L-NAME+AngII treated mice. In aortic rings, phenylephrine and KCl contraction was enhanced with EPL in L-NAME+AngII treated WT mice, but not cav-1(-/-) mice. AngII-induced contraction was not different, and angiotensin type 1 receptor expression was reduced in L-NAME + AngII treated WT and cav-1(-/-) mice. In WT mice, acetylcholine-induced relaxation was enhanced with L-NAME + AngII treatment and reversed with EPL. Acetylcholine relaxation in cav-1(-/-) mice was greater than in WT mice, not modified by L-NAME + AngII or EPL, and blocked by ex vivo L-NAME, 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ), or endothelium removal, suggesting the role of NO-cGMP. Cardiac endothelial NO synthase was increased in cav-1(-/-) versus WT mice, further increased with L-NAME + AngII, and not affected by EPL. Vascular relaxation to the NO donor sodium nitroprusside was increased with L-NAME + AngII in WT mice but not in cav-1(-/-) mice. Plasma aldosterone levels increased and cardiac MR expression decreased in L-NAME + AngII treated WT and cav-1(-/-) mice and did not change with EPL. Thus, during L-NAME + AngII induced hypertension, MR blockade increases contraction and alters vascular relaxation via NO-cGMP, and these changes are absent in cav-1 deficiency states. The data suggest a cooperative role of MR and cav-1 in regulating vascular contraction and NO-cGMP-mediated relaxation during low NO-high AngII-dependent cardiovascular injury.

Effects of sex and gender on adaptations to space: reproductive health

In this report, sex/gender research relevant to reproduction on Earth, in conjunction with the extant human and animal observations in space, was used to identify knowledge gaps and prioritize recommendations for future sex- and gender-specific surveillance and monitoring of male and female astronauts. With overall increased durations of contemporary space missions, a deeper understanding of sex/gender effects on reproduction-related responses and adaptations to the space environment is warranted to minimize risks and insure healthy aging of the men and women who travel into space.

International Union of Basic and Clinical Pharmacology. XCVII. G Protein-Coupled Estrogen Receptor and Its Pharmacologic Modulators

Estrogens are critical mediators of multiple and diverse physiologic effects throughout the body in both sexes, including the reproductive, cardiovascular, endocrine, nervous, and immune systems. As such, alterations in estrogen function play important roles in many diseases and pathophysiological conditions (including cancer), exemplified by the lower prevalence of many diseases in premenopausal women. Estrogens mediate their effects through multiple cellular receptors, including the nuclear receptor family (ERα and ERβ) and the G protein-coupled receptor (GPCR) family (GPR30/G protein-coupled estrogen receptor [GPER]). Although both receptor families can initiate rapid cell signaling and transcriptional regulation, the nuclear receptors are traditionally associated with regulating gene expression, whereas GPCRs are recognized as mediating rapid cellular signaling. Estrogen-activated pathways are not only the target of multiple therapeutic agents (e.g., tamoxifen, fulvestrant, raloxifene, and aromatase inhibitors) but are also affected by a plethora of phyto- and xeno-estrogens (e.g., genistein, coumestrol, bisphenol A, dichlorodiphenyltrichloroethane). Because of the existence of multiple estrogen receptors with overlapping ligand specificities, expression patterns, and signaling pathways, the roles of the individual receptors with respect to the diverse array of endogenous and exogenous ligands have been challenging to ascertain. The identification of GPER-selective ligands however has led to a much greater understanding of the roles of this receptor in normal physiology and disease as well as its interactions with the classic estrogen receptors ERα and ERβ and their signaling pathways. In this review, we describe the history and characterization of GPER over the past 15 years focusing on the pharmacology of steroidal and nonsteroidal compounds that have been employed to unravel the biology of this most recently recognized estrogen receptor.

Role of Nongenomic Signaling Pathways Activated by Aldosterone During Cardiac Reperfusion Injury

Aldosterone (Aldo) activates both genomic and nongenomic signaling pathways in the cardiovascular system. Activation of genomic signaling pathways contributes to the adverse cardiac actions of Aldo during reperfusion injury; however, the extent nongenomic signaling pathways contribute has been difficult to identify due to lack of a specific ligand that activates only nongenomic signaling pathways. Using a pegylated aldosterone analog, aldosterone-3-carboxymethoxylamine-TFP ester conjugated to methoxypegylated amine (Aldo-PEG), we are able for the first time to distinguish between nongenomic and genomic cardiac actions of Aldo. We confirm Aldo-PEG activates phosphorylation of ERK1/2 in rat cardiomyocyte H9c2 cells similar to Aldo and G protein-coupled receptor 30 (GPR30 or GPER) agonist G1. GPER antagonist, G36, but not mineralocorticoid receptor (MR) antagonist spironolactone, prevented ERK1/2 phosphorylation by Aldo, Aldo-PEG, and G1. The selective nongenomic actions of Aldo-PEG are confirmed, with Aldo-PEG increasing superoxide production in H9c2 cells to similar levels as Aldo but having no effect on subcellular localization of MR. Striatin serves as a scaffold for GPER and MR, with GPER antagonist G36, but not spironolactone, restoring MR-striatin complexes. Aldo-PEG had no effect on MR-dependent transcriptional activation, whereas Aldo increased transcript levels of serum-regulated kinase 1 and plasminogen activator inhibitor-1. Using our ex vivo experimental rat model of myocardial infarction, we found aggravated infarct size and apoptosis by Aldo but not Aldo-PEG. Our studies confirm that in the heart, activation of nongenomic signaling pathways alone are not sufficient to trigger the deleterious effects of aldosterone during myocardial reperfusion injury.

Estradiol and GPER Activation Differentially Affect Cell Proliferation but Not GPER Expression in the Hippocampus of Adult Female Rats

Estradiol increases cell proliferation in the dentate gyrus of the female rodent but it is not known whether the G protein-coupled estrogen receptor (GPER), a membrane receptor, is involved in this process, nor whether there are regional differences in estradiol’s effects on cell proliferation. Thus, we investigated whether estradiol exerts its effects on cell proliferation in the dorsal and ventral dentate gyrus through GPER, using the GPER agonist, G1, and antagonist, G15. Ovariectomized adult female rats received a single injection of either: 17β-estradiol (10 μg), G1 (0.1, 5, 10 μg), G15 (40 μg), G15 and estradiol, or vehicle (oil, DMSO, or oil+DMSO). After 30 min, animals received an injection of bromodeoxyuridine (BrdU) and were perfused 24 h later. Acute treatment with estradiol increased, while the GPER agonist G1 (5 μg) decreased, the number of BrdU+ cells in the dentate gyrus relative to controls. The GPER antagonist, G15 increased the number of BrdU+ cells relative to control in the dorsal region and decreased the number of BrdU+ cells in the ventral region. However, G15 treatment in conjunction with estradiol partially eliminated the estradiol-induced increase in cell proliferation in the dorsal dentate gyrus. Furthermore, G1 decreased the expression of GPER in the dentate gyrus but not the CA1 and CA3 regions of the hippocampus. In summary, we found that activation of GPER decreased cell proliferation and GPER expression in the dentate gyrus of young female rats, presenting a potential and novel estrogen-independent role for this receptor in the adult hippocampus.

Hypertension: renin-angiotensin-aldosterone system alterations

Blockers of the renin-angiotensin-aldosterone system (RAAS), that is, renin inhibitors, angiotensin (Ang)-converting enzyme (ACE) inhibitors, Ang II type 1 receptor antagonists, and mineralocorticoid receptor antagonists, are a cornerstone in the treatment of hypertension. How exactly they exert their effect, in particular in patients with low circulating RAAS activity, also taking into consideration the so-called Ang II/aldosterone escape that often occurs after initial blockade, is still incompletely understood. Multiple studies have tried to find parameters that predict the response to RAAS blockade, allowing a personalized treatment approach. Consequently, the question should now be answered on what basis (eg, sex, ethnicity, age, salt intake, baseline renin, ACE or aldosterone, and genetic variance) a RAAS blocker can be chosen to treat an individual patient. Are all blockers equal? Does optimal blockade imply maximum RAAS blockade, for example, by combining ≥2 RAAS blockers or by simply increasing the dose of 1 blocker? Exciting recent investigations reveal a range of unanticipated extrarenal effects of aldosterone, as well as a detailed insight in the genetic causes of primary aldosteronism, and mineralocorticoid receptor blockers have now become an important treatment option for resistant hypertension. Finally, apart from the deleterious ACE-Ang II-Ang II type 1 receptor arm, animal studies support the existence of protective aminopeptidase A-Ang III-Ang II type 2 receptor and ACE2-Ang-(1 to 7)-Mas receptor arms, paving the way for multiple new treatment options. This review provides an update about all these aspects, critically discussing the many controversies and allowing the reader to obtain a full understanding of what we currently know about RAAS alterations in hypertension.

Primary aldosteronism: challenges in diagnosis and management

Primary aldosteronism (PA) is the main cause of endocrine hypertension, present in approximately 10% of hypertensive patients; about one-third is secondary to aldosterone-producing adenomas. Cardiovascular and renal morbidity are out of proportion to the degree of hypertension. Physicians have compelling rationale to correctly identify and treat PA. Physicians are challenged with patient selection for screening with the aldosterone/renin ratio (ARR), interpretation of ARR, and selecting a confirmatory test. Adrenal vein sampling is performed for subtype differentiation. The treatment depends on the disease subtype and results in control of hypertension and reversal of associated excess morbidity.

Extra sensory perception: the role of Gpr receptors in the kidney

PURPOSE OF REVIEW

This review will summarize recent literature highlighting the roles of sensory Gpr receptors and their roles in renal function.

RECENT FINDINGS

Chemoreceptors play important roles in renal physiology wherein they modulate renal function in response to ligands from a variety of sources.

SUMMARY

As specialized chemical detectors, chemoreceptors in the kidney monitor the level of a variety of chemical ligands in the body and adjust renal function accordingly. In addition to olfactory receptors and taste receptors, G-protein coupled receptors of the orphan Gpr family are now being found to play a 'sensory' role in renal physiology. Identifying the physiological roles of these receptors and elucidating the cell biology underlying these signaling pathways can give us novel insights into renal function.

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

OBJECTIVES

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

METHODS AND RESULTS

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

CONCLUSION

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

Emerging roles of GPER in diabetes and atherosclerosis

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