Position paper: The membrane estrogen receptor GPER--Clues and questions

Rapid signaling of estrogen involves membrane estrogen receptors (ERs), including membrane subpopulations of ERα and ERβ. In the mid-1990s, several laboratories independently reported the cloning of an orphan G protein-coupled receptor from vascular and cancer cells that was named GPR30. Research published between 2000 and 2005 provided evidence that GPR30 binds and signals via estrogen indicating that this intracellular receptor is involved in rapid, non-genomic estrogen signaling. The receptor has since been designated as the G protein-coupled estrogen receptor (GPER) by the International Union of Pharmacology. The availability of genetic tools such as different lines of GPER knock-out mice, as well as GPER-selective agonists and antagonists has advanced our understanding, but also added some confusion about the new function of this receptor. GPER not only binds estrogens but also other substances, including SERMs, SERDs, and environmental ER activators (endocrine disruptors; xenoestrogens) and also interacts with other proteins. This article represents a summary of a lecture given at the 7(th) International Meeting on Rapid Responses to Steroid Hormones in September 2011 in Axos, Crete, and reviews the current knowledge and questions about GPER-dependent signaling and function. Controversies that have complicated our understanding of GPER, including interactions with human ERα-36 and aldosterone as a potential ligand, will also be discussed.

The future of endothelin research: scientific mentoring and beyond

Endothelium-dependent regulation of vascular tone was one of the key discoveries in physiology in the 1980s, including the characterization of endothelium-derived vasoactive factors such as endothelin. Young investigators, often while starting research as part of their PhD degree, have been instrumental in carrying out the work that led some of the most important discoveries in the endothelin field. This article reviews the importance of mentoring for research in general and for endothelin research in particular, including examples of outstanding young investigators that have been instrumental in some of the key discoveries in the endothelin field. Recognizing scientific excellence among young investigators has a long tradition in the history of the International Conferences on Endothelin. Winners of "Young Investigator Awards" of the past five endothelin conferences (ET-8, ET-9, ET-10, ET-11, and ET-12) are presented, as well as recipients of the "ET-12 Best Presentation Awards" established on the occasion of the Twelfth International Conference on Endothelin ET-12 in Cambridge in September 2011.

Is it beneficial to increase the provision of thrombolysis?-- a discrete-event simulation model

BACKGROUND

Although Thrombolysis has been licensed in the UK since 2003, it is still administered only to a small percentage of eligible patients.

AIM

We consider the impact of investing the impact of thrombolysis on important acute stroke services, and the effect on quality of life. The concept is illustrated using data from the Northern Ireland Stroke Service.

DESIGN

Retrospective study.

METHODS

We first present results of survival analysis utilizing length of stay (LOS) for discharge destinations, based on data from the Belfast City Hospital (BCH). None of these patients actually received thrombolysis but from those who would have been eligible, we created two initial groups, the first representing a scenario where they received thrombolysis and the second comprising those who do not receive thrombolysis. On the basis of the survival analysis, we created several subgroups based on discharge destination. We then developed a discrete event simulation (DES) model, where each group is a patient pathway within the simulation. Coxian phase type distributions were used to model the group LOS. Various scenarios were explored focusing on cost-effectiveness across hospital, community and social services had thrombolysis been administered to these patients, and the possible improvement in quality of life, should the proportion of patients who are administered thrombolysis be increased. Our aim in simulating various scenarios for this historical group of patients is to assess what the cost-effectiveness of thrombolysis would have been under different scenarios; from this we can infer the likely cost-effectiveness of future policies.

RESULTS

The cost of thrombolysis is offset by reduction in hospital, community rehabilitation and institutional care costs, with a corresponding improvement in quality of life.

CONCLUSION

Our model suggests that provision of thrombolysis would produce moderate overall improvement to the service assuming current levels of funding.

Antimicrobial susceptibilities and resistance genes in Campylobacter strains isolated from poultry and pigs in Australia

AIMS

To evaluate the phenotypic and genotypic profiles of Campylobacter spp. from poultry faecal samples from free range or intensively raised meat chickens and free range egg layers. In addition, a case-comparison study of antibiotic resistance genes from different groups of poultry and some pig strains previously collected was carried out.

METHODS

Resistance to different antibiotics was assessed using the agar dilution method. In addition, all the strains were tested for ampicillin (bla(OXA-61) ), erythromycin (aph-3-1), tetracycline tet(O), streptomycin (aadE), and the energy-dependent multi-drug efflux pump (cmeB) resistance genes using multiplex polymerase chain reaction.

RESULTS

The evaluation of phenotypic resistance revealed all of the strains from poultry were sensitive to ciprofloxacin, gentamicin, erythromycin or tylosin. But, widespread resistance to lincomycin (51-100%), extensive resistance to ampicillin (33·3-60·2%) and less resistance to tetracycline (5·6-40·7%) were observed in the different groups of chickens. Antibiotic resistance genes bla(OXA-61,) cmeB and tet(O) were found in 82·6-92·7%, 80·3-89% and 22·3-30·9% Camp. coli isolates from pigs, whilst 59-65·4% and 19·2-40·7% Camp. jejuni from chickens were found to encode bla(OXA-61) and tet(O), respectively.

CONCLUSION

No significant difference between isolates from free range egg layers and meat chickens (P < 0·05) was found. However, there were significant differences between the pig strains and all the groups of poultry strains (P < 0·05) with regard to carriage of resistance genes. In addition, pulsed field gel electrophoresis of selected resistant isolates from the poultry and pig revealed closely related clonal groups.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results suggest the resistant strains are persisting environmental isolates that have been acquired by the different livestock species. Furthermore, the different treatment practices in poultry and pigs have resulted in differences in resistance profiles in Campylobacter isolates.

GPER regulates endothelin-dependent vascular tone and intracellular calcium

AIMS

An increase in intracellular vascular smooth muscle cell calcium concentration (VSMC [Ca(2+)](i)) is essential for endothelin-1 (ET-1)-induced vasoconstriction. Based on previous findings that activation of the G protein-coupled estrogen receptor (GPER) inhibits vasoconstriction in response to ET-1 and regulates [Ca(2+)](i) in cultured VSMC, we investigated whether endogenous GPER regulates ET-1-induced changes in VSMC [Ca(2+)](i) and constriction of intact arteries.

MAIN METHODS

Pressurized carotid arteries of GPER-deficient (GPER(0)) and wildtype (WT) mice were loaded with the calcium indicator fura 2-AM. Arteries were stimulated with the GPER-selective agonist G-1 or solvent followed by exposure to ET-1. Changes in arterial diameter and VSMC [Ca(2+)](i) were recorded simultaneously. Vascular gene expression levels of ET(A) and ET(B) receptors were determined by qPCR.

KEY FINDINGS

ET-1-dependent vasoconstriction was increased in arteries from GPER(0) compared to arteries from WT mice. Despite the more potent vasoconstriction to ET-1, GPER deficiency was associated with a marked reduction in the ET-1-stimulated VSMC [Ca(2+)](i) increase, suggesting an increase in myofilament force sensitivity to [Ca(2+)](i). Activation of GPER by G-1 had no effect on vasoconstriction or VSMC [Ca(2+)](i) responses to ET-1, and expression levels of ET(A) or ET(B) receptor were unaffected by GPER deficiency.

SIGNIFICANCE

These results demonstrate that endogenous GPER inhibits ET-1-induced vasoconstriction, an effect that may be associated with reduced VSMC Ca(2+) sensitivity. This represents a potential mechanism through which GPER could contribute to protective effects of endogenous estrogen in the cardiovascular system.

Obesity and risk of vascular disease: importance of endothelium-dependent vasoconstriction

Obesity has become a serious global health issue affecting both adults and children. Recent devolopments in world demographics and declining health status of the world's population indicate that the prevalence of obesity will continue to increase in the next decades. As a disease, obesity has deleterious effects on metabolic homeostasis, and affects numerous organ systems including heart, kidney and the vascular system. Thus, obesity is now regarded as an independent risk factor for atherosclerosis-related diseases such as coronary artery disease, myocardial infarction and stroke. In the arterial system, endothelial cells are both the source and target of factors contributing to atherosclerosis. Endothelial vasoactive factors regulate vascular homeostasis under physiological conditions and maintain basal vascular tone. Obesity results in an imbalance between endothelium-derived vasoactive factors favouring vasoconstriction, cell growth and inflammatory activation. Abnormal regulation of these factors due to endothelial cell dysfunction is both a consequence and a cause of vascular disease processes. Finally, because of the similarities of the vascular pathomechanisms activated, obesity can be considered to cause accelerated, 'premature' vascular aging. Here, we will review some of the pathomechanisms involved in obesity-related activation of endothelium-dependent vasoconstriction, the clinical relevance of obesity-associated vascular risk, and therapeutic interventions using 'endothelial therapy' aiming at maintaining or restoring vascular endothelial health.

LINKED ARTICLES

This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.

Endothelin and the podocyte

In the past decade, research has advanced our understanding how endothelin contributes to proteinuria and glomerulosclerosis. Data from pre-clinical and clinical studies now provide evidence that proteinuric diseases such as focal segmental glomerulosclerosis and diabetic nephropathy as well as hypertension nephropathy are sensitive to treatment with endothelin receptor antagonists (ERAs). Like blockade of the renin-angiotensin system, ERA treatment-under certain conditions-may even cause disease regression, effects that could be achieved on top of renin-angiotensin-aldosterone system blockade, suggesting independent therapeutic mechanisms by which ERAs convey nephroprotection. Beneficial effects of ERAs on podocyte function, which is essential to maintain the glomerular filtration barrier, have been identified as one of the key mechanisms by which inhibition of the endothelin ETA receptor ameliorates renal structure and function. In this article, we will review pre-clinical studies demonstrating a causal role for endothelin in proteinuric chronic kidney disease (with a particular focus on functional and structural integrity of podocytes in vitro and in vivo). We will also review the evidence suggesting a therapeutic benefit of ERA treatment on the functional integrity of podocytes in humans.

Deletion of G protein-coupled estrogen receptor increases endothelial vasoconstriction

Endogenous estrogens mediate protective effects in the cardiovascular system, affecting both endothelium-dependent and endothelium-independent mechanisms. Previous studies have suggested that nonselective estrogen receptor agonists such as endogenous estrogens inhibit endothelium-dependent vasoconstriction; however, the role of estrogen receptors in this response has not yet been clarified. This study investigated whether the intracellular transmembrane G protein-coupled estrogen receptor (GPER) regulates vascular reactivity in mice. Effects of chronic deficiency (using mice lacking the GPER gene) and acute inhibition (using the GPER-selective antagonist G15) on endothelium-dependent and endothelium-independent vascular reactivity, and the effects of GPER deficiency on vascular gene expression and structure were investigated. We found that chronic GPER deficiency is associated with increased endothelial prostanoid-mediated vasoconstriction but has no effect on endothelial nitric oxide bioactivity, gene expression of endothelial nitric oxide synthase and thromboxane prostanoid (TP) receptor, or vascular structure. GPER deletion also increases TP receptor-mediated contraction. Acute GPER blockade enhances endothelium-dependent contractions and reduces endothelial nitric oxide bioactivity. Contractions in response to TP receptor activation are unaffected by G15. In conclusion, this study identifies GPER as the first estrogen receptor with inhibitory activity on endothelium-dependent contractility. These findings may be important for understanding and treating diseases associated with increased endothelial vasoconstrictor prostanoid activity such as hypertension and obesity.

GPER/GPR30 and Regulation of Vascular Tone and Blood Pressure

Natural estrogens such as 17β-estradiol are endogenous vasodilators and have been implicated in the gender differences of hypertension. These hormones activate estrogen receptors ERα and ERβ, which mediate part of estrogen-dependent vasodilation. In addition, a novel G protein-coupled estrogen-binding receptor termed GPER/GPR30 has been identified that is expressed in the cardiovascular system. Using knock-out animals or drugs selectively targeting GPER/GPR30, a significant role for this receptor as a mediator of acute estrogen-dependent vasodilation involving nitric oxide (NO) and blood pressure-lowering activity has been demonstrated. The accumulating evidence that GPER/GPR30 is responsible for control of vascular tone indicates that this receptor may represent a novel drug target for pharmacologic treatment of hypertension in postmenopausal women and possibly also men.

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

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

Endothelin antagonists in clinical trials: lessons learned

Over the past 20 years, a large number of endothelin receptor antagonists (ERAs) have been developed, many of which underwent clinical testing. Yet, today only two ERAs are approved for the treatment of only two clinical indications, namely pulmonary arterial hypertension and scleroderma-related digital ulcers. Clinical development of ERAs has been hampered by problems with dosing, with the makeup of study cohorts, and adverse events. More recently, a number of studies evaluated the potential of ERA treatment for proteinuric renal disease. Although several ERAs were found to reduce proteinuria in patients with nephropathy, clinical testing was stopped for all but one drug. The reasons for the failure of some of these studies and general considerations about how to move forward with clinical studies involving ERAs in renal disease are discussed in this chapter.

Endothelin and podocyte injury in chronic kidney disease

The identification of patients at increased risk for chronic kidney disease offers the potential to prevent or delay end-stage renal disease and the associated cardiovascular events. Data from recently completed controlled clinical trials of endothelin (ET) receptor blockers confirmed their potent antiproteinuric effect after a number of preclinical studies. A spectrum of proteinuric glomerular diseases results from podocyte abnormalities and, in return, impact podocyte structure and function. Because podocytes are cells in the glomerulus that form a crucial component of the glomerular filtration barrier, contributing to size selectivity and maintaining a large filtration surface, we focus on evidence that suggest ET-1 may promote podocyte injury thereby aggravating albumin urinary loss and alteration of the glomerular microvasculature. Systematic confrontation of animal models and studies in human subjects should help decipher pathophysiological mechanisms whereby the local renal ET system promotes podocyte injury and chronic kidney disease in specific pathophysiological contexts. Current evidence suggests that more experimental and clinical attention should be paid to conditions with increased vascular or endocapillary ET-1 production on the one hand, and in diseases with altered podocyte phenotype and survival such as focal segmental glomerulosclerosis and crescentic glomerulonephritis on the other. These conclusions may assist clinicians in creating optimal clinical trials for patients at increased risk for or with overt chronic kidney disease.

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

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

The G protein-coupled estrogen receptor GPER/GPR30 as a regulator of cardiovascular function

Endogenous estrogens are important regulators of cardiovascular homeostasis in premenopausal women and delay the development of hypertension and coronary artery disease. These hormones act via three different estrogen receptors affecting both gene transcription and rapid signaling pathways in a complex interplay. In addition to the classical estrogen receptors ERα and ERβ, which are known mediators of estrogen-dependent vascular effects, a G protein-coupled estrogen receptor termed GPER that is expressed in the cardiovascular system has recently been identified. Endogenous human 17β-estradiol, selective estrogen receptor modulators (SERMs) including tamoxifen and raloxifene, and selective estrogen receptor downregulators (SERDs) such as ICI 182,780 are all agonists of GPER, which has been implicated in the regulation of vasomotor tone and protection from myocardial ischemia/reperfusion injury. As a result, understanding the individual role of ERα, ERβ, and GPER in cardiovascular function has become increasingly complex. With accumulating evidence that GPER is responsible for a variety of beneficial cardiovascular effects of estrogens, this receptor may represent a novel target to develop effective strategies for the treatment of cardiovascular diseases by tissue-specific, selective activation of estrogen-dependent molecular pathways devoid of side effects seen with conventional hormone therapy.

Apparatus for dimensional characterization of fused silica fibers for the suspensions of advanced gravitational wave detectors

Detection of gravitational waves from astrophysical sources remains one of the most challenging problems faced by experimental physicists. A significant limit to the sensitivity of future long-baseline interferometric gravitational wave detectors is thermal displacement noise of the test mass mirrors and their suspensions. Suspension thermal noise results from mechanical dissipation in the fused silica suspension fibers suspending the test mass mirrors and is therefore an important noise source at operating frequencies between ∼10 and 30 Hz. This dissipation occurs due to a combination of thermoelastic damping, surface and bulk losses. Its effects can be reduced by optimizing the thermoelastic and surface loss, and these parameters are a function of the cross sectional dimensions of the fiber along its length. This paper presents a new apparatus capable of high resolution measurements of the cross sectional dimensions of suspension fibers of both rectangular and circular cross section, suitable for use in advanced detector mirror suspensions.

'GAP' in radiotherapy services in Australia and New Zealand in 2009

AIM

In this study we estimated (a) the number of linear accelerators required in Australia and New Zealand to achieve a 52.3% treatment rate; (b) the 'GAP' between the actual and required number of linear accelerators; c) the number of persons not treated (PNT), premature deaths (PD) and years of life lost (YLL) as a result of the 'GAP'; and (d) to review the actions being taken by health jurisdictions in Australia and in New Zealand to address the 'GAP' and reach the 52.3% treatment rate.

MATERIAL AND METHODS

The actual number of fully staffed and operating linear accelerators (A) in Australian and New Zealand was obtained from a survey of radiotherapy facilities in December 2009. The required number of linear accelerators (R) was calculated from the projected cancer incidence figures for 2009 and was based on 1.6 linear accelerators being required per 1000 new cancer patients. The 'GAP' in Radiotherapy services (G) was R minus A. The maximum treatment capacity (MTC) was the ratio of A over R multiplied by 52.3%, assuming that all linear accelerators were operating at 100% capacity. As each linear accelerator can treat 331 new patients each year, the number of new cancer PNT is G x 331. The estimated 5-year survival benefit from radiotherapy is 16%, and the average survival for all patients receiving radiotherapy (radical and palliative) is 0.76 year. Hence, the number of PD attributed to the 'GAP' is PNT x 16%, and the YLL to cancer is PNT x 0.76. A literature search and local knowledge of health department Radiotherapy Plans in all jurisdictions were used to determine the action being taken to achieve a 52.3% treatment rate.

RESULTS

In 2009, the 'GAP' was 50 linear accelerators in Australia and the MTC was 38%, the same as it was in 1999, but there has been an increase in PNT each year from 7419 in 1999 to 16,550 in 2009, and PD each year increased from 1187 in 1999 to 2649 in 2009, and YLL each year increased from 5638 in 1999 to 12,585 in 2009. In New Zealand in 2009, the 'GAP' was nine linear accelerators and the MTC was 38%. An estimated 3310 persons did not receive radiotherapy in 2009 in New Zealand, and as a result, there were 523 PD and 2266 YLL. The review showed that new and replacement machines were being installed in all jurisdictions in Australia and in New Zealand. Only Victoria and Queensland have a Radiotherapy Plan beyond 2010, but both have underestimated the projected cancer incidence.

CONCLUSION

Urgent action is needed by health departments and governments on both sides of the Tasman to improve access and equity to this essential cancer treatment. There is merit in the Baume Report recommendation of establishing a national body to oversee radiotherapy services in all jurisdictions in Australia. A similar central body should also be considered for New Zealand.

Management of skin toxicity during radiation therapy: a review of the evidence

Acute skin toxicity occurs in the majority of the patients undergoing radical radiotherapy. While a variety of topical agents and dressing are used to ameliorate side effects, there is minimal evidence to support their use. The aims of this study were to systematically review evidence on acute skin toxicity management and to assess the current practices in ANZ. A systematic review of the literature was conducted on studies published between 1980 and 2008. A meta-analysis was performed on articles on clinical trials reporting grade II or greater toxicity. Analyses were divided into breast (the most common site) and other sites. A survey of Radiation Oncology departments across ANZ was conducted to identify patterns of practices and compare these with the published evidence. Twenty-nine articles were reviewed. Only seven articles demonstrated statistically significant results for management of side-effects. These were for topical corticosteroids, hyaluronic acid, sucralfate, calendula, Cavilon cream (3M, St Paul, Minnesota, USA) and silver leaf dressing. Meta-analysis demonstrated statistical significance for the prophylactic use of topical agents in the management acute toxicity. The survey of departments had a low response rate but demonstrated variation in skin care practices across ANZ. A considerable number of these practices were based only on anecdotal evidence. Lack of evidence in the literature for the care of radiation skin reactions was associated with variation in practice. Only a limited number of studies have demonstrated a significant benefit of specific topical agents. There is a need for objective and prospective recording of skin toxicity to collect meaningful comparative data on which to base recommendations for practice.

Exploring beyond viral load testing for EBV lymphoproliferation: role of serum IL-6 and IgE assays as adjunctive tests

We examined serum IL-6 and IgE assays as adjuncts to VL monitoring for PTLD. Paediatric solid organ transplant recipients were followed with VL monitoring. VL, IL-6, and IgE assays were compared between PTLD cases and non-cases at <3, 3-6 and >6 months after transplantation. Median IL-6 levels in PTLD cases were 15.5 (2.0-87.1) and 23.3 (2.1-276) pg/mL compared with 3.25 (0.92-114) and 3.5 (0.75-199.25) pg/mL in non-cases at 3-6 and >6 months, respectively (p = 0.006 and p = 0.005). At >6 months, IL-6 levels correlated with VL and PTLD occurrence (Spearman's coefficients = 0.40; p = 0.001 and 0.32; p = 0.003) in univariate analyses. No benefit was derived from performance of IgE levels. The sensitivity and specificity of high VL as a test of PTLD were 76.3% and 92.5%, while the negative predictive value and PPV of VL were 94.9% and 68.4%, respectively. Combining elevated IL-6 with high VL increased the PPV and specificity to 80% and 96.2%, respectively, and improved the receiver operating characteristic curve. Serum IL-6 levels can improve the clinician's ability to identify PTLD, among patients with elevated EBV viral loads.