Cloning and expression of a cDNA encoding an endothelin receptor

Taming the "sleeping giant": the role of endothelin-1 in the regulation of skeletal muscle blood flow and arterial blood pressure during exercise

The cardiovascular response to exercise is governed by a combination of vasodilating and vasoconstricting influences that optimize exercising muscle perfusion while protecting mean arterial pressure (MAP). The degree to which endogenous endothelin (ET)-1, the body's most potent vasoconstrictor, participates in this response is unknown. Thus, in eight young (24 ± 2 yr), healthy volunteers, we examined leg blood flow, MAP, tissue oxygenation, heart rate, leg arterial-venous O(2) difference, leg O(2) consumption, pH, and net ET-1 and lactate release at rest and during knee extensor exercise (0, 5, 10, 15, 20, and 30 W) before and after an intra-arterial infusion of BQ-123 [ET subtype A (ET(A)) receptor antagonist]. At rest, BQ-123 did not evoke a change in leg blood flow or MAP. During exercise, net ET-1 release across the exercising leg increased approximately threefold. BQ-123 increased leg blood flow by ~20% across all work rates (changes of 113 ± 76, 176 ± 83, 304 ± 108, 364 ± 130, 502 ± 117, and 570 ± 178 ml/min at 0, 5, 10, 15, 20, and 30 W, respectively) and attenuated the exercise-induced increase in MAP by ~6%. The increase in leg blood flow was accompanied by a ~9% increase in leg O(2) consumption with an unchanged arterial-venous O(2) difference and deoxyhemoglobin, suggesting a decline in intramuscular efficiency after ET(A) receptor blockade. Together, these findings identify a significant role of the ET-1 pathway in the cardiovascular response to exercise, implicating vasoconstriction via the ET(A) receptor as an important mechanism for both the restraint of blood flow in the exercising limb and maintenance of MAP in healthy, young adults.

The novel ETA receptor antagonist HJP-272 prevents cerebral microvascular hemorrhage in cerebral malaria and synergistically improves survival in combination with an artemisinin derivative

AIM

To investigate the association between vasculopathy and survival during experimental cerebral malaria (ECM), and to determine whether targeting the endothelin-1 (ET-1) pathway alone or in combination with the anti-malaria drug artemether (a semi-synthetic derivative of artemisinin) will improve microvascular hemorrhage and survival.

MAIN METHODS

C57BL/6 mice infected with Plasmodium berghei ANKA (PbA) were randomly assigned to four groups: no treatment, artemether treated, ET(A) receptor antagonist (HJP-272) treated, or HJP-272 and artemether treated. The uninfected control mice were treated with HJP-272 and artemether. We analyzed survival, cerebral hemorrhage, weight change, blood glucose levels and parasitemia.

KEY FINDINGS

Our studies demonstrated decreased brain hemorrhage in PbA-infected (ECM) mice treated when HJP-272, a 1,3,6-trisubstituted-2-carboxy-quinol-4-one novel ET(A) receptor antagonist synthesized by our group, is used in conjunction with artemether, an anti-malarial agent. In addition, despite adversely affecting parasitemia and weight in non-artemether treated infected mice, HJP-272, seemed to confer some survival benefit when used as adjunctive therapy, though this did not reach significance.

SIGNIFICANCE

Previous studies demonstrate that the endothelin pathway is associated with vasculopathy, neuronal injury and inflammation in ECM. As demonstrated here, components of the ET-1 pathway may be important targets for adjunctive therapy in ECM, and may help in preventing hemorrhage and in improving survival when used as adjunctive therapy during malaria infection. The data presented suggest that our novel agent, HJP-272, may ameliorate alterations in the vasculature which can potentially lead to inflammation, neurological dysfunction, and subsequent death in mice with ECM.

Defining the affinity and receptor sub-type selectivity of four classes of endothelin antagonists in clinically relevant human cardiovascular tissues

AIMS

We have compared the endothelin receptor subtype affinity (K(D)) and selectivity of four structural classes of antagonists (peptide, sulphonamide-based, carboxylic acid-based, myceric acid-based) in human cardiovascular tissues to determine whether these are predicted by values reported for human cloned receptors. Additionally, affinities (K(B)) for these antagonists, determined in ET-1-mediated vasoconstriction assays in human blood vessels, were used to identify discrepancies between K(B) and K(D) determined in the same tissues.

MAIN METHODS

Competition binding experiments were carried out in sections of human left ventricle, coronary artery and homogenates of saphenous vein to determine K(D) values for structurally different ET(A)-selective (FR139317, BMS 182874, S97-139, sitaxentan, ambrisentan) and mixed (PD142893, Ro462005, bosentan, L-749329, SB209670) antagonists. Schild-derived values of antagonist affinity were obtained in vascular functional studies.

KEY FINDINGS

When compared with previously reported data in human cloned endothelin receptors, those antagonists reported to be ET(A)-selective exhibited even greater ET(A) selectivity in human ventricle (BMS 182874, sitaxentan, ambrisentan) that expressed both receptor subtypes. Those antagonists reported to have <100 fold selectivity in cloned receptors (PD142893, Ro-462005, bosentan, SB209670, L-749329) did not distinguish between receptor subtypes in human left ventricle. For antagonists where we determined affinity in vascular functional and binding assays (Ro462005, bosentan, BMS 182874, L-749329, SB209670) there was no correlation between the degree of discrepancy in K(B) and K(D) and structural class.

SIGNIFICANCE

For an antagonist to retain ET(A)-selectivity in vivo it may be necessary to identify those compounds that have at least 1000 fold ET(A):ET(B) selectivity in in vitro assays.

Apolipoprotein B is a new target of the GDNF/RET and ET-3/EDNRB signalling pathways

BACKGROUND

GDNF/RET and Endothelin-3 (ET-3)/EDNRB regulate survival, differentiation, migration, and proliferation of neural crest-derived cells. Although several RET and EDNRB signalling mediators have been characterized, most of the genes targeted by these two pathways are still largely unknown. We focused our study on apolipoprotein B (APOB) as a novel target gene of the RET and EDNRB pathways, based on previous data obtained using a Caenorhabditis elegans strain mutant for the homologue of mammalian ECE1.

METHODS

Molecular and cellular studies of Apob were performed in the murine Neuro2a cells, an in vitro model for studying neural crest-derived cell development, along with a mouse knock-in for the Hirschsprung-associated mutation Ret(C620R). Silencing for Apob and Ret has been performed via shRNA.

KEY RESULTS

GDNF/RET and ET-3/EDNRB cooperated in inducing neuronal differentiation resulting in Apob activation in Neuro2a cell line. Apob expression was downregulated in mouse embryos homozygous for the Ret(C620R) mutation and presenting a severe Hirschsprung phenotype. Ret silencing prevented Apob expression increase. MAPK P38 kinase activation evoked Apob expression via GDNF/RET signalling in Neuro2a cells. A p53-dependent repressor element in Apob promoter resulted in a reduced Apob expression. Silencing of Apob reduced HuD protein expression.

CONCLUSIONS & INFERENCES

Apob is a novel downstream target of the RET/EDNRB pathways with a role in neuronal survival and maintenance, as indicated by its effect on HuD expression. Our data provide a conceptual framework to investigate and establish the role of APOB gene in severe gut dysmotility.

The role of the neuro-astro-vascular unit in the etiology of ataxia telangiectasia

The growing recognition that brain pathologies do not affect neurons only but rather are, to a large extent, pathologies of glial cells as well as of the vasculature opens to new perspectives in our understanding of genetic disorders of the CNS. To validate the role of the neuron-glial-vascular unit in the etiology of genome instability disorders, we report about cell death and morphological aspects of neuroglia networks and the associated vasculature in a mouse model of Ataxia Telangiectasia (A-T), a human genetic disorder that induces severe motor impairment. We found that A-T-mutated protein deficiency was consistent with aberrant astrocytic morphology and alterations of the vasculature, often accompanied by reactive gliosis. Interestingly similar findings could also be reported in the case of other genetic disorders. These observations bolster the notion that astrocyte-specific pathologies, hampered vascularization and astrocyte-endothelium interactions in the CNS could play a crucial role in the etiology of genome instability brain disorders and could underlie neurodegeneration.

Placental expression and localization of endothelin-1 system and nitric oxide synthases during bovine pregnancy

This study aimed to investigate mRNA expression of the endothelin-1 (EDN1) system (preproEDN1; precursor, ECE-1; converting enzyme, EDNRA and EDNRB; receptor subtypes A and B) and endothelial and inducible nitric oxide synthases (eNOS and iNOS) in the bovine utero-placental unit during pregnancy. We also investigated the cellular localization of mRNA and protein of components of the EDN1 system in the placentome. The bovine utero-placental unit on Day 60, 100, 150, 200 and 250 of gestation was separated into carunclar areas (CAR), intercaruncular areas (ICAR), cotyledonary villi (COT) and intercotyledonary areas (ICOT). PreproEDN1, ECE1, EDNRA, EDNRB, eNOS and iNOS mRNA expression was determined by real-time quantitative RT-PCR. In situ hybridization and immunohistochemistry were performed using placentomes on Day 94 or Day 250 of gestation. PreproEDN1 and ECE1 mRNA expression was higher on Day 100 than on other gestation days. The mRNA expression for EDNRA in COT and ICOT and eNOS in COT, CAR and ICAR were higher on Day 150 than on other gestation days. EDNRB mRNA expression increased from Day 60 to Day 150 then decreased. iNOS mRNA expression in COT and CAR was higher on Day 250 than on other gestation days. PreproEDN1, ECE1 and EDNRA mRNA was localized in the caruncular epithelial cells (CEs) and the COT. EDNRB mRNA was found in the CEs and the trophoblast binucleate giant cells (BNCs). PreproEDN1, EDNRA and EDNRB proteins were detected in COT and CEs, whereas ECE-1 was found in the BNCs. Our results demonstrate that differential cell-specific and spatiotemporal expression of the EDN1 system and NOS in the bovine utero-placental unit may be associated with regulation of vascular and cellular functions during pregnancy.

Clinical trials with endothelin receptor antagonists: what went wrong and where can we improve?

In the early 1990s, within three years of cloning of endothelin receptors, orally active endothelin receptor antagonists (ERAs) were tested in humans and the first clinical trial of ERA therapy in humans was published in 1995. ERAs were subsequently tested in clinical trials involving heart failure, pulmonary arterial hypertension, resistant arterial hypertension, stroke/subarachnoid hemorrhage and various forms of cancer. The results of most of these trials - except those for pulmonary arterial hypertension and scleroderma-related digital ulcers - were either negative or neutral. Problems with study design, patient selection, drug toxicity, and drug dosing have been used to explain or excuse failures. Currently, a number of pharmaceutical companies who had developed ERAs as drug candidates have discontinued clinical trials or further drug development. Given the problems with using ERAs in clinical medicine, at the Twelfth International Conference on Endothelin in Cambridge, UK, a panel discussion was held by clinicians actively involved in clinical development of ERA therapy in renal disease, systemic and pulmonary arterial hypertension, heart failure, and cancer. This article provides summaries from the panel discussion as well as personal perspectives of the panelists on how to proceed with further clinical testing of ERAs and guidance for researchers and decision makers in clinical drug development on where future research efforts might best be focused.

The endothelin axis in uterine leiomyomas: new insights

The endothelin axis, comprising endothelin-1 (ET-1) and its receptors (ETA and ETB), is involved in the pathophysiology of different human tumors. Here we review conventional approaches and gene expression profiling indicating the association of ET-1 and its cognate receptors with human and rat leiomyomas, the most common benign tumors of myometrium. Specifically, ET-1/ETA interactions affect human and rat leiomyoma cell proliferation through protein kinase C and mitogen-activated protein kinase-dependent signaling pathways. Recent experiments demonstrate that the ET-1 axis exerts a potent antiapoptotic effect involving sphingolipid metabolism and prostaglandin-endoperoxide synthase 2/prostaglandin system in the rat Eker leiomyoma tumor-derived ELT3 cell line. Evidence supports that steroid hormones, growth factors, and extracellular matrix are key regulators of the leiomyoma growth. Interestingly, the ET-1 axis is under steroid hormones and can cooperate with these growth factors. Therefore, ET-1 alone or in association with these factors could contribute to the complex regulation of uterine tumor growth, such as proliferation, survival, and extracellular matrix production. This review summarizes current knowledge and emerging data on ET-1 in uterine leiomyoma pathology.

c-Src-dependent EGF receptor transactivation contributes to ET-1-induced COX-2 expression in brain microvascular endothelial cells

Background

Endothelin-1 (ET-1) is elevated and participates in the regulation of several brain inflammatory disorders. The deleterious effects of ET-1 on endothelial cells may aggravate brain inflammation mediated through the upregulation of cyclooxygenase-2 (COX-2) gene expression. However, the signaling mechanisms underlying ET-1-induced COX-2 expression in brain microvascular endothelial cells remain unclear.

Objective

The goal of this study was to examine whether ET-1-induced COX-2 expression and prostaglandin E₂ (PGE₂) release were mediated through a c-Src-dependent transactivation of epidermal growth factor receptor (EGFR) pathway in brain microvascular endothelial cells (bEnd.3 cells).

Methods

The expression of COX-2 induced by ET-1 was evaluated by Western blotting and RT-PCR analysis. The COX-2 regulatory signaling pathways were investigated by pretreatment with pharmacological inhibitors, short hairpin RNA (shRNA) or small interfering RNA (siRNA) transfection, chromatin immunoprecipitation (ChIP), and promoter activity reporter assays. Finally, we determined the PGE₂ level as a marker of functional activity of COX-2 expression.

Results

First, the data showed that ET-1-induced COX-2 expression was mediated through a c-Src-dependent transactivation of EGFR/PI3K/Akt cascade. Next, we demonstrated that ET-1 stimulated activation (phosphorylation) of c-Src/EGFR/Akt/MAPKs (ERK1/2, p38 MAPK, and JNK1/2) and then activated the c-Jun/activator protein 1 (AP-1) via G_q/i protein-coupled ET_B receptors. The activated c-Jun/AP-1 bound to its corresponding binding sites within COX-2 promoter, thereby turning on COX-2 gene transcription. Ultimately, upregulation of COX-2 by ET-1 promoted PGE₂ biosynthesis and release in bEnd.3 cells.

Conclusions

These results demonstrate that in bEnd.3 cells, c-Src-dependent transactivation of EGFR/PI3K/Akt and MAPKs linking to c-Jun/AP-1 cascade is essential for ET-1-induced COX-2 upregulation. Understanding the mechanisms of COX-2 expression and PGE₂ release regulated by ET-1/ET_B system on brain microvascular endothelial cells may provide rational therapeutic interventions for brain injury and inflammatory diseases.

Docosahexaenoic acid monoacylglyceride decreases endothelin-1 induced Ca(2+) sensitivity and proliferation in human pulmonary arteries

BACKGROUND

Pulmonary artery vasoconstriction and vascular remodeling contribute to a sustained elevation of pulmonary vascular resistance and pressure in patients with pulmonary arterial hypertension (PH), an often fatal hemodynamic disease. The effect of docosahexaenoic acid monoacylglyceride (MAG-DHA) and the role of the 17 kDa protein kinase C-potentiated inhibitor protein (CPI-17) were determined on vasoconstriction and smooth muscle cell proliferation of human pulmonary arteries (HPA).

METHODS

HPA were obtained from 16 patients undergoing lung resection for carcinoma. The mechanical tension and Ca(2+) sensitivity were measured on arterial rings treated with endothelin-1 (ET-1) in the absence or presence of MAG-DHA. The effect of MAG-DHA on the level of proliferation of smooth muscle cells isolated from HPA was evaluated in order to determine the role of CPI-17 protein.

RESULTS

MAG-DHA treatment decreased the reactivity and Ca(2+) sensitivity induced by ET-1 in HPA. MAG-DHA treatment also decreased the expression of vascular endothelial growth factor (VEGF) induced by ET-1. Moreover, both VEGF inhibitor and MAG-DHA treatments reduced Ca(2+) hypersensitivity induced by ET-1, which was associated to a reduction in CPI-17 and myosin-binding subunit of the myosin light chain phosphatase (MYPT-1) phosphorylation levels. Proliferation of ET-1-stimulated HPA smooth muscle cells (PASMc) was also decreased following CPI-17 small interfering RNA transfection and MAG-DHA treatments. Western blot analyses revealed that MAG-DHA treatment resulted in decreased phosphorylation levels of CPI-17 and extracellular signal-regulated kinases (ERK) in PASMc treated with ET-1.

CONCLUSIONS

We have demonstrated that VEGF interacts with CPI-17 signaling pathway resulting in an increase in Ca(2+) sensitivity and proliferation of PASMc, whereas MAG-DHA treatment reversed these effects.

The association of an adenine insertion variant in the 5'UTR of the endothelin-1 gene with hypertension and orthostatic hypotension

INTRODUCTION

An adenine insertion polymorphism in the 5' untranslated region of the endothelin-1 gene is functional and increases the expression of endothelin mRNA and protein in the insertion homozygote. In the present study we hypothesized that this functional polymorphism might be associated with hypertension and/or orthostatic hypotension.

MATERIAL AND METHODS

The adenine insertion polymorphism was genotyped in 381 untreated hypertensive patients and 298 normotensive subjects, all of whom underwent an upright posture study for orthostatic blood pressure measurements. Orthostatic hypotension was defined as a drop in blood pressure of 20/10 mm Hg or more within 3 min of assuming the upright posture.

RESULTS

The allele frequency of the adenine insertion was similar in hypertensive and normotensive subjects (15.2% vs. 15.3%, p > 0.05). After adjustment for age, sex and body mass index, blood pressure levels did not differ significantly among the genotypes in both hypertensives and normotensives. No associations were found between the distribution of the adenine insertion genotypes and the risk of orthostatic hypotension in both hypertensive patients and normotensive subjects even after adjustment for demographic parameters and supine systolic or diastolic blood pressure. Neither hypertensive nor normotensive subjects showed significant differences in orthostatic systolic or diastolic blood pressure changes among the genotype groups (all p > 0.05).

CONCLUSIONS

We concluded that the functional adenine insertion polymorphism in the endothelin-1 gene is not associated with either hypertension or orthostatic hypotension risk in Chinese.

Reactive oxygen and nitrogen species in pulmonary hypertension

Pulmonary vascular disease can be defined as either a disease affecting the pulmonary capillaries and pulmonary arterioles, termed pulmonary arterial hypertension, or a disease affecting the left ventricle, called pulmonary venous hypertension. Pulmonary arterial hypertension (PAH) is a disorder of the pulmonary circulation characterized by endothelial dysfunction, as well as intimal and smooth muscle proliferation. Progressive increases in pulmonary vascular resistance and pressure impair the performance of the right ventricle, resulting in declining cardiac output, reduced exercise capacity, right-heart failure, and ultimately death. While the primary and heritable forms of the disease are thought to affect over 5000 patients in the United States, the disease can occur secondary to congenital heart disease, most advanced lung diseases, and many systemic diseases. Multiple studies implicate oxidative stress in the development of PAH. Further, this oxidative stress has been shown to be associated with alterations in reactive oxygen species (ROS), reactive nitrogen species (RNS), and nitric oxide (NO) signaling pathways, whereby bioavailable NO is decreased and ROS and RNS production are increased. Many canonical ROS and NO signaling pathways are simultaneously disrupted in PAH, with increased expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases and xanthine oxidoreductase, uncoupling of endothelial NO synthase (eNOS), and reduction in mitochondrial number, as well as impaired mitochondrial function. Upstream dysregulation of ROS/NO redox homeostasis impairs vascular tone and contributes to the pathological activation of antiapoptotic and mitogenic pathways, leading to cell proliferation and obliteration of the vasculature. This paper will review the available data regarding the role of oxidative and nitrosative stress and endothelial dysfunction in the pathophysiology of pulmonary hypertension, and provide a description of targeted therapies for this disease.

Purification and characterization of recombinant human endothelin receptor type A

Human endothelin receptor type A (ET(A)) is a G-protein coupled receptor that mediates vasoconstriction of blood vessels. To determine the structural characteristics and signaling mechanism of ET(A), we have expressed recombinant ET(A) as a fusion protein with p9 envelope protein from phi6 bacteriophage. The His-tag-labeled p9-ET(A) fusion protein was highly expressed in the membrane fraction of Escherichia coli and purified to homogeneity by single affinity chromatography after solubilization with detergents. Purified p9-ET(A) appeared as an oligomer and presented mainly as an α-helical structure. The protein also showed specific binding to endothelin-1 (ET-1) and the alpha subunit of G(q) protein with apparent K(D) values of 17 and 20 nM, respectively. An antagonist of ET(A), bosentan, prevented the interaction between p9-ET(A) and ET-1 in a concentration-dependent manner. These results indicate that recombinant p9-ET(A) has a competent conformation for interactions with ET-1 and the alpha subunit of G(q) protein.

Endothelin and endothelin receptors in the renal and cardiovascular systems

Endothelin-1 (ET-1) is a multifunctional hormone which regulates the physiology of the cardiovascular and renal systems. ET-1 modulates cardiac contractility, systemic and renal vascular resistance, salt and water renal reabsorption, and glomerular function. ET-1 is responsible for a variety of cellular events: contraction, proliferation, apoptosis, etc. These effects take place after the activation of the two endothelin receptors ET(A) and ET(B), which are present - among others - on cardiomyocytes, fibroblasts, smooth muscle and endothelial cells, glomerular and tubular cells of the kidney. The complex and numerous intracellular pathways, which can be contradictory in term of functional response depending on the receptor type, cell type and physiological situation, are described in this review. Many diseases share an enhanced ET-1 expression as part of the pathophysiology. However, the use of endothelin blockers is currently restricted to pulmonary arterial hypertension, and more recently to digital ulcer. The complexity of the endothelin system does not facilitate the translation of the molecular knowledge to clinical applications. Endothelin antagonists can prevent disease development but secondary undesirable effects limit their usage. Nevertheless, the increasing understanding of the effects of ET-1 on the cardiac and renal physiology maintains the endothelin system as a promising therapeutic target.

Endothelin ET(B) receptors are involved in the relaxation to the pig urinary bladder neck

AIMS

The involvement of endothelin receptors in the contraction of the lower urinary tract smooth muscle is well established. There is scarce information, however, about endothelin receptors mediating relaxation of the bladder outlet region. The current study investigates the possible existence of endothelin ET(B) receptors involved in the relaxation of pig bladder neck.

METHODS

ET(B) receptor expression was determined by immunohistochemistry and urothelium-denuded bladder neck strips were mounted in organ baths for isometric force recording.

RESULTS

ET(B) -immunoreactivity (ET(B) -IR) was observed within nerve fibers among smooth muscle bundles and urothelium. BQ3020 (0.01-300 nM), an ET(B) receptor agonist, produced concentration-dependent relaxations which were reduced by BQ788, an ET(B) receptor antagonist, and by inhibitors of protein kinase A (PKA) and large (BK(Ca) )- or small (SK(Ca) )-conductance Ca(2+) -activated K(+) channels. Pretreatment with BK(Ca) or SK(Ca) channel inhibitors plus PKA blocking did not cause further inhibition compared with that exerted by inhibiting BK(Ca) or SK(Ca) channels only. BQ3020-induced relaxation was not modified by blockade of either nitric oxide (NO) synthase, guanylyl cyclase, cyclooxygenase (COX) or of intermediate-conductance Ca(2+) -activated-(IK(Ca) ), ATP-dependent-(K(ATP) ), or voltage-gated-(K(v) ) K(+) channels. Under non-adrenergic non-cholinergic (NANC) conditions, electrical field stimulation (0.5-16 Hz) evoked frequency-dependent relaxations, which were reduced by BQ788 and potentiated by threshold concentrations of BQ3020.

CONCLUSIONS

These results suggest that BQ3020 produces relaxation of the pig bladder neck via activation of muscle endothelin ET(B) receptors, NO/cGMP- and COX-independent-, cAMP-PKA pathway-dependent-mechanisms, and involving BK(Ca) and SK(Ca) channel activation. ET(B) receptors are also involved in the NANC inhibitory neurotransmission.

Comparison of human ETA and ETB receptor signalling via G-protein and β-arrestin pathways

AIMS

To determine the pharmacology of ET(A)- and ET(B)-mediated β-arrestin recruitment and compare this to established human pharmacology of these receptors to identify evidence for endothelin receptor biased signalling and pathway specific blockade by antagonists.

MAIN METHODS

The ability of ET-1, ET-2, ET-3, sarafotoxin 6b and sarafotoxin 6c to activate ET(A) and ET(B)-mediated β-arrestin recruitment was determined in CHO-K1 cells. Affinities were obtained for ET(A) selective (BQ123, sitaxentan, ambrisentan), ET(B) selective (BQ788) and mixed (bosentan) antagonists using ET-1 and compared to affinities obtained in competition experiments in human heart and by Schild analysis in human saphenous vein. Agonist dependence of affinities was compared for BQ123 and BQ788 in the ET(A) and ET(B) β-arrestin assays respectively.

KEY FINDINGS

For β-arrestin recruitment, order of potency was as expected for the ET(A) (ET-1≥ET-2>>ET-3) and ET(B) (ET-1=ET-2=ET-3) receptors. However, at the ET(A) receptor sarafotoxin 6b and ET-3 were partial agonists. Antagonism of ET peptides by selective and mixed antagonists appeared non-competitive. BQ123, but not BQ788, exhibited agonist-dependent affinities. Bosentan was significantly more effective an inhibitor of β-arrestin recruitment mediated by ET(A) compared to the ET(B) receptor. In the ET(A) vasoconstrictor assay, ET-1, ET-2 and S6b were equipotent, full agonists and antagonists tested behaved in a competitive manner, although affinities were lower than predicted from the competition binding experiments in left ventricle.

SIGNIFICANCE

These data suggest that the pharmacology of ET(A) and ET(B) receptors linked to G-protein- and β-arrestin mediated responses was different and bosentan appeared to show bias, preferentially blocking ET(A) mediated β-arrestin recruitment.

Relationships among hyperuricemia, endothelial dysfunction and cardiovascular disease: molecular mechanisms and clinical implications

Uric acid is the end product of purine metabolism. Its immediate precursor, xanthine, is converted to uric acid by an enzymatic reaction involving xanthine oxidoreductase. Uric acid has been formerly considered a major antioxidant in human plasma with possible beneficial anti-atherosclerotic effects. In contrast, studies in the past two decades have reported associations between elevated serum uric acid levels and cardiovascular events, suggesting a potential role for uric acid as a risk factor for atherosclerosis and related diseases. In this paper, the molecular pattern of uric acid formation, its possible deleterious effects, as well as the involvement of xanthine oxidoreductase in reactive oxygen species generation are critically discussed. Reactive oxygen species contribute to vascular oxidative stress and endothelial dysfunction, which are associated with the risk of atherosclerosis. Recent studies have renewed attention to the xanthine oxidoreductase system, since xanthine oxidoreductase inhibitors, such as allopurinol and oxypurinol, would be capable of preventing atherosclerosis progression by reducing endothelial dysfunction. Also, beneficial effects could be obtained in patients with congestive heart failure. The simultaneous reduction in uric acid levels might contribute to these effects, or be a mere epiphenomenon of the drug action. The molecular mechanisms involved are discussed.

Endothelin B receptor is not required but necessary for finite regulation of ovulation

AIMS

In the ovary, endothelins regulate a variety of ovarian functions that include but not limited to folliculogenesis, steroidogenesis, oocyte maturation, ovulation and corpus luteum (CL) function. Two cognate receptors, EDNRA and EDNRB are constitutively expressed in the ovary, and mediate the regulatory endothelin actions. However, the physiological significance of the presence of the two receptors that often elicit opposite responses upon activation by an endothelin is yet to be determined. This study was proposed to test the hypothesis that both receptors are present in the ovary to lend an endothelin a finite regulation of ovulation.

MAIN METHODS

A rescued EDNRB knockout (rEDNRB-KO) mouse that is deficient of EDNRB expression in all cells but adrenergic cell lineage was used to test the impact of the loss of function of EDNRB on ovulation. The EDNRB gene deletion and its confirmation at mRNA level were assessed by molecular biology techniques, and the number and size of corpus lutea was determined by ovarian histology.

KEY FINDINGS

Female rEDNRB-KO mice had larger litter sizes (numbers of pups per birth) and their ovaries contained more corpora lutea than wild type littermates.

SIGNIFICANCE

This result shows that without EDNRB excessive ovulation occurs, suggesting a role of EDNRB in having the extent of ovulation confined.

Endothelin-1 plasma levels and vascular endothelial dysfunction in primary open angle glaucoma

AIMS

To assess the relationship between endothelial dysfunction, endothelin 1 (ET-1) plasma levels and subclinical inflammation in primary open angle glaucoma (POAG) patients.

MAIN METHODS

We enrolled 40 POAG patients with progressive visual field damage, although well controlled intraocular pressure (IOP) and compared to age and sex matched healthxy subjects. Each patient underwent an ophthalmological examination, a standard achromatic perimetry (SAP), blood sampling to assess ET-1 plasma levels, an objective assessment of cellularity within the anterior chamber (FLARE) and measurement of flow mediated dilation (FMD) with high resolution 2-dimensional ultrasonographic imaging of the brachial artery.

KEY FINDINGS

At baseline, POAG patients, compared to healthy controls, showed an increase of ET-1 plasma levels: 2.83 ± 0.28 pg/ml vs. 1.75 ± 0.25 pg/ml (p<0.001), lower FMD values 4.46 ± 1.28% vs. 13.18 ± 2.80% (p<0.001) and increased FLARE values 9.98 ± 0.97 photons/ms vs. 5.87 ± 0.64 photons/ms (p<0.001). A follow up after 1 year revealed a further increase of ET-1 plasma levels (to 3.68 ± 0.60; p<0.001) and decrease of FMD (3.52 ± 1.28; p>0.001).

SIGNIFICANCE

The increase of ET-1 in POAG patients is related to vascular dysfunction (r=0.942; p=0.001) and vascular dysfunction is related to sub-clinical intraocular inflammation (r=0.968; p=0.001). Thus ET-1 and vascular dysfunction related to sub-clinical inflammation may play a key role in determining a progressive visual field damage in POAG patients who present a well-controlled IOP.

Aminoguanidine normalizes ET-1-induced aortic contraction in type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats by suppressing Jab1-mediated increase in ET(A)-receptor expression

Circulating levels of endothelin (ET)-1 are increased in the diabetic state, as is endogenous ET(A)-receptor-mediated vasoconstriction. However, the responsible mechanisms remain unknown. We hypothesized that ET-1-induced vasoconstriction is augmented in type 2 diabetes with hyperglycemia through an increment in advanced glycation end-products (AGEs). So, we investigated whether treatment with aminoguanidine (AG), an inhibitor of AGEs, would normalize the ET-1-induced contraction induced by ET-1 in strips of thoracic aortas isolated from OLETF rats at the chronic stage of diabetes. In such aortas (vs. those from age-matched genetic control LETO rats): (1) the ET-1-induced contraction was enhanced, (2) the levels of HIF1α/ECE1/plasma ET-1 and plasma CML-AGEs were increased, (3) the ET-1-stimulated ERK phosphorylation mediated by ET(A)-R was increased, (4) the expression level of Jab1-modified ET(A)-R protein was reduced, and (5) the expression level of O-GlcNAcylated ET(A)-R protein was increased. Aortas isolated from such OLETF rats that had been treated with AG (50mg/kg/day for 10 weeks) exhibited reduced ET-1-induced contraction, suppressed ET-1-stimulated ERK phosphorylation accompanied by down-regulation of ET(A)-R, and increased modification of ET(A)-R by Jab1. Such AG-treated rats exhibited normalized plasma ET-1 and CML-AGE levels, and their aortas exhibited decreased HIF1α/ECE1 expression. However, such AG treatment did not alter the elevated levels of plasma glucose or insulin, or systolic blood pressure seen in OLETF rats. These data from the OLETF model suggest that within the timescale studied here, AG normalizes ET-1-induced aortic contraction by suppressing ET(A)-R/ERK activities and/or by normalizing the imbalance between Jab1 and O-GlcNAc in type 2 diabetes.

Sexual dimorphism in endothelin-1 induced mechanical hyperalgesia in the rat

While the onset of mechanical hyperalgesia induced by endothelin-1 was delayed in female rats, compared to males, the duration was much longer. Given that the repeated test stimulus used to assess nociceptive threshold enhances hyperalgesia, a phenomenon we have referred to as stimulus-induced enhancement of hyperalgesia, we also evaluated for sexual dimorphism in the impact of repeated application of the mechanical test stimulus on endothelin-1 hyperalgesia. In male and female rats, endothelin-1 induced hyperalgesia is already maximal at 30 min. At this time stimulus-induced enhancement of hyperalgesia, which is observed only in male rats, persisted for 3-4h. In contrast, in females, it develops only after a very long (15 day) delay, and is still present, without attenuation, at 45 days. Ovariectomy eliminated these differences between male and female rats. These findings suggest marked, ovarian-dependent sexual dimorphism in endothelin-1 induced mechanical hyperalgesia and its enhancement by repeated mechanical stimulation.

Gene duplication of endothelin 3 is closely correlated with the hyperpigmentation of the internal organs (Fibromelanosis) in silky chickens

During early development in vertebrates, pluripotent cells are generated from the neural crest and migrate according to their presumptive fate. In birds and mammals, one of the progeny cells, melanoblasts, generally migrate through a dorsolateral route of the trunk region and differentiate to melanocytes. However, Silky is an exceptional chicken in which numerous melanoblasts travel via a ventral pathway and disperse into internal organs. Finally, these ectopic melanocytes induce heavy dermal and visceral melanization known as Fibromelanosis (Fm). To identify the genetic basis of this phenotype, we confirmed the mode of inheritance of Fm as autosomal dominant and then performed linkage analysis with microsatellite markers and sequence-tagged site markers. Using 85 backcross progeny from crossing Black Minorca chickens (BM-C) with F(1) individuals between White Silky (WS) and BM-C Fm was located on 10.2-11.7 Mb of chicken chromosome 20. In addition, we noticed a DNA marker that all Silky chickens and the F(1) individuals showed heterozygous genotyping patterns, suggesting gene duplication in the Fm region. By quantitative real-time PCR assay, Silky line-specific gene duplication was detected as an ~130-kb interval. It contained five genes including endothelin 3 (EDN3), which encoded a potent mitogen for melanoblasts/melanocytes. EDN3 with another three of these duplicated genes in Silky chickens expressed almost twofold of those in BM-C. Present results strongly suggest that the increase of the expression levels resulting from the gene duplication in the Fm region is the trigger of hypermelanization in internal organs of Silky chickens.

Modulatory Role of Nitric Oxide/cGMP System in Endothelin-1-Induced Signaling Responses in Vascular Smooth Muscle Cells

Nitric oxide (NO) is an important vasoprotective molecule that serves not only as a vasodilator but also exerts antihypertrophic and antiproliferative effects in vascular smooth muscle cells (VSMC). The precise mechanism by which the antihypertrophic and antiproliferative responses of NO are mediated remains obscure. However, recent studies have suggested that one of the mechanisms by which this may be achieved includes the attenuation of signal transduction pathways responsible for inducing the hypertrophic and proliferative program in VSMC. Endothelin-1 is a powerful vasoconstrictor peptide with mitogenic and growth stimulatory properties and exerts its effects by activating multiple signaling pathways which include ERK 1/2, PKB and Rho-ROCK. Both cGMP-dependent and independent events have been reported to mediate the effect of NO on these pathways leading to its vasoprotective response. This review briefly summarizes some key studies on the modulatory effect of NO on these signaling pathways and discusses the possible role of cGMP system in this process.

Endothelin-mediated in vivo pressor responses following TRPV1 activation

Transient receptor potential vanilliod 1 (TRPV1) channels have recently been postulated to play a role in the vascular complications/consequences associated with diabetes despite the fact that the mechanisms through which TRPV1 regulates vascular function are not fully known. Accordingly, our goal was to define the mechanisms by which TRPV1 channels modulate vascular function and contribute to vascular dysfunction in diabetes. We subjected mice lacking TRPV1 [TRPV1(−/−)], db/ db, and control C57BLKS/J mice to in vivo infusion of the TRPV1 agonist capsaicin or the α-adrenergic agonist phenylephrine (PE) to examine the integrated circulatory actions of TRPV1. Capsaicin (1, 10, 20, and 100 μg/kg) dose dependently increased MAP in control mice (5.7 ± 1.6, 11.7 ± 2.1, 25.4 ± 3.4, and 51.6 ± 3.9%), which was attenuated in db/db mice (3.4 ± 2.1, 3.9 ± 2.1, 7.0 ± 3.3, and 17.9 ± 6.2%). TRPV1(−/−) mice exhibited no changes in MAP in response to capsaicin, suggesting the actions of this agonist are specific to TRPV1 activation. Immunoblot analysis revealed decreased aortic TRPV1 protein expression in db/db compared with control mice. Capsaicin-induced responses were recorded following inhibition of endothelin A and B receptors (ETA /ETB). Inhibition of ETA receptors abolished the capsaicin-mediated increases in MAP. Combined antagonism of ETA and ETB receptors did not further inhibit the capsaicin response. Cultured endothelial cell exposure to capsaicin increased endothelin production as shown by an endothelin ELISA assay, which was attenuated by inhibition of TRPV1 or endothelin-converting enzyme. TRPV1 channels contribute to the regulation of vascular reactivity and MAP via production of endothelin and subsequent activation of vascular ETA receptors. Impairment of TRPV1 channel function may contribute to vascular dysfunction in diabetes.

Endothelin B receptor contribution to peripheral microvascular function in women with polycystic ovary syndrome

Endothelin-1 is elevated in women with polycystic ovary syndrome (PCOS), and may play a role in the endothelial dysfunction associated with PCOS. Endothelin-1 binds two receptor subtypes, endothelin A (ET-A) and endothelin B (ET-B). We hypothesized that ET-A mediates vasoconstriction in the cutaneous microvasculature in women with and without PCOS. We further hypothesized that while the ET-B receptors mediate vasodilatation in both groups of women, this response would be blunted in women with PCOS. During local skin warming, we used laser Doppler flowmetry combined with intradermal microdialysis to measure skin blood flow (SkBF) during graded ET-A (BQ-123) and ET-B (BQ-788) antagonist infusions in women with (n = 6) and without (n = 8) PCOS. In both groups, SkBF increased during local heating. The percentage of maximal SkBF-[BQ123] sigmoidal dose-response curve indicated a vasodilatory response as the concentration of the antagonist increased (Hill slope 4.96 ± 4.77, 4.74 ± 5.01; logED(50) 2.53 ± 0.09, 2.49 ± 0.09 nm, for PCOS and Control, respectively). In contrast, the % max SkBF-[BQ788] curve indicated a vasoconstrictive response (Hill slope -4.69 ± 3.85, -4.03 ± 3.85; logED(50), 2.56 ± 0.09, 2.41 ± 0.12 nm, in PCOS and Control). Moreover, the SkBF-[BQ788] curve shifted to the right in women with PCOS, suggesting attenuated ET-B receptor mediated vasodilatation during local skin warming compared to Controls. Thus, the endothelium located ET-B receptors function similarly in women with and without PCOS, although with blunted responsiveness in women with PCOS. Our studies suggest that the lower ET-B receptor responsiveness associated with PCOS may reflect lower endothelial-mediated vasodilatation independent of generally lower vascular reactivity.

Endothelin type A receptor (ETA) expression is regulated by HOXA10 in human endometrial stromal cells

Endothelin type A receptor (ET(A)) is a member of the superfamily of G protein-coupled receptors. Our laboratory conducted a microarray screen that identified ET(A) as target of HOXA10 transcriptional control in endometrium. Here, we confirm HOXA10-regulated ET(A) expression in endometrium. Endometrial biopsies were obtained from fertile reproductive-age individuals, and first trimester decidual samples were obtained at the time of elective termination. Immunohistochemistry (IHC) was used to identify ET(A) protein in endometrium as well as first trimester decidua. ET(A) was expressed in endometrial stromal cells throughout the menstrual cycle. ET(A) was also highly expressed in first trimester decidual cells. The regulatory relationship between HOXA10 and ET(A) was established by transient transfection analysis. The human endometrial stromal cell line (HESC) and the human endometrial epithelial cell line (Ishikawa) were transfected with pcDNA/HOXA10, HOXA10 small interfering RNA (siRNA), or respective controls. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) was performed to determine expression levels of HOXA10 and ET(A) in each group. ET(A) gene expression increased 9-fold (P < .05) after pcDNA/HOXA10 transfection of HESC. ET(A) was not regulated by HOXA10 in Ishikawa cells. We conclude that ET(A) is expressed in normal endometrium and decidua. Expression of this receptor is regulated by an essential mediator of endometrial receptivity, HOXA10. ET(A) may enhance the proliferative potential of endometrial cells in a manner similar to that seen in vascular smooth muscle cells. ET( A) likely acts as a molecular mechanism by which HOXA10 promotes stromal cell growth and prostaglandin production in both the implantation window and decidua.

Endothelin-1 reduces glucose uptake in human skeletal muscle in vivo and in vitro

OBJECTIVE

Endothelin (ET)-1 is a vasoconstrictor and proinflammatory peptide that may interfere with glucose uptake. Our objective was to investigate whether exogenous ET-1 affects glucose uptake in the forearm of individuals with insulin resistance and in cultured human skeletal muscle cells.

RESEARCH DESIGN AND METHODS

Nine male subjects (aged 61 ± 3 years) with insulin resistance (M value <5.5 mg/kg/min or a homeostasis model assessment of insulin resistance index >2.5) participated in a protocol using saline infusion followed by ET-1 infusion (20 pmol/min) for 2 h into the brachial artery. Forearm blood flow (FBF), endothelium-dependent vasodilatation, and endothelium-independent vasodilatation were assessed. Molecular signaling and glucose uptake were determined in cultured skeletal muscle cells.

RESULTS

ET-1 decreased forearm glucose uptake (FGU) by 39% (P < 0.05) after the 2-h infusion. ET-1 reduced basal FBF by 36% after the 2-h infusion (P < 0.05) and impaired both endothelium-dependent vasodilatation (P < 0.01) and endothelium-independent vasodilatation (P < 0.05). ET(A) and ET(B) receptor expression was detected on cultured skeletal muscle cells. One-hour ET-1 incubation increased glucose uptake in cells from healthy control subjects but not from type 2 diabetic patients. Incubation with ET-1 for 24 h reduced glucose uptake in cells from healthy subjects. ET-1 decreased insulin-stimulated Akt phosphorylation and increased phosphorylation of insulin receptor substrate-1 serine 636.

CONCLUSIONS

ET-1 not only induces vascular dysfunction but also acutely impairs FGU in individuals with insulin resistance and in skeletal muscle cells from type 2 diabetic subjects. These findings suggest that ET-1 may contribute to the development of insulin resistance in skeletal muscle in humans.

Insights into ET(A) subtype selectivity of benzodiazepine endothelin receptor antagonists by 3D-QSAR approaches

ET(A) subtype selective antagonists constitute a novel and potentially important class of agents for the treatment of pulmonary hypertension, heart failure, and other pathological conditions. In this paper, 60 benzodiazepine derivatives displaying potent activities against ET(A) and ET(B) subtypes of endothelin receptor were selected to establish the 3D-QSAR models using CoMFA and CoMSIA approaches. These models show excellent internal predictability and consistency, external validation using test-set 19 compounds yields a good predictive power for antagonistic potency. Statistical parameters of models were obtained with CoMFA-ET(A) (q (2) = 0.787, r (2) = 0.935, r (2) ( pred ) = 0.901), CoMFA-ET(B) (q (2) = 0.842, r (2) = 0.984, r (2) ( pred ) = 0.941), CoMSIA-ET(A) (q (2) = 0.762, r (2) = 0.971, r (2) ( pred ) = 0.958) and CoMSIA-ET(B) (q (2) = 0.771, r (2) = 0.974, r (2) ( pred ) = 0.953) respectively. Field contour maps (CoMFA and CoMSIA) corresponding to the ET(A) and ET(B) subtypes reflects the characteristic similarities and differences between these types. The results of this paper provide valuable information to facilitate structural modifications of the title compounds to increase the inhibitory potency and subtype selectivity of endothelin receptor.

Pediatric pulmonary arterial hypertension: current and emerging therapeutic options

INTRODUCTION

Pulmonary arterial hypertension (PAH) is a rare disease in neonates, infants and children that is associated with significant morbidity and mortality. An adequate understanding of the controlling pathophysiologic mechanisms is lacking and although mortality has decreased as therapeutic options have increased over the past several decades, outcomes remain unacceptable.

AREAS COVERED

This review summarizes the currently available therapies for neonates, infants and children with PAH and describes emerging therapies in the context of what is known about the underlying pathophysiology of the disease.

EXPERT OPINION

All of the currently approved PAH therapies impact one of three endothelial-based pathways: nitric oxide-guanosine-3'-5'cyclic monophosphate, prostacyclin or endothelin-1. The beneficial effects of these agents may relate to their impact on pulmonary vascular tone, and/or their antiproliferative and antithrombotic properties. Fundamental advances in PAH therapy are likely to relate to: i) a better understanding of PAH subpopulations, allowing for therapies to be better tailored to individual patients and pathophysiologic processes; and ii) therapies that promote the regression of advanced structural remodeling.

ET-1 induced Elevation of intracellular calcium in clonal neuronal and embryonic kidney cells involves endogenous endothelin-A receptors linked to phospholipase C through Gα(q/11)

Endothelin-1 (ET-1) is a pain mediator, elevated in skin after injury, which potentiates noxious thermal and mechanical stimuli (hyperalgesia) through the activation of ET(A) (and, perhaps, ET(B)) receptors on pain fibers. Part of the mechanism underlying this effect has recently been shown to involve potentiation of neuronal TRPV1 by PKCɛ. However, the early steps of this pathway, which are recapitulated in HEK 293 cells co-expressing TRPV1 and ET(A) receptors, remain unexplored. To clarify these steps, we investigated the pharmacological profile and signaling properties of native endothelin receptors in immortalized cell lines including HEK 293 and ND7 model sensory neurons. Previously we showed that in ND7/104, a dorsal root ganglia-derived cell line, ET-1 elicits a rise in intracellular calcium ([Ca(2+)](in)) which is blocked by BQ-123, an ET(A) receptor antagonist, but not by BQ-788, an ET(B) receptor antagonist, suggesting that ET(A) receptors mediate this effect. Here we extend these findings to HEK 293T cells. Examination of the expression of ET(A) and ET(B) receptors by RT-PCR and [(125)I]-ET-1 binding experiments confirms the slight predominance of ET(A) receptor binding sites and messenger RNA in both ND7/104 and HEK 293T cells. In addition, selective agonists of the ET(B) receptor (sarafotoxin 6c, BQ-3020 or IRL-1620) do not induce a transient increase in [Ca(2+)](in). Furthermore, reduction of ET(B) mRNA levels by siRNA does not abrogate calcium mobilization by ET-1 in HEK 293T cells, corroborating the lack of an ET(B) receptor role in this response. However, in HEK 293 cells with low endogenous ET(A) mRNA levels, ET-1 does not induce a transient increase in [Ca(2+)](in). Observation of the [Ca(2+)](in) elevation in ND7/104 and HEK 293T cells in the absence of extracellular calcium suggests that ET-1 elicits a release of calcium from intracellular stores, and pretreatment of the cells with pertussis toxin or a selective inhibitor of phospholipase C (PLC) point to a mechanism involving Gαq/11 coupling. These results are consistent with the hypothesis that a certain threshold of ET(A) receptor expression is necessary to drive a transient [Ca(2+)](in) increase in these cells and that this process involves release of calcium from intracellular stores following Gαq/11 activation.

BQ-153, a novel endothelin (ET)A antagonist, attenuates the renal vascular effects of endothelin-1

Endothelin (ET)-l, leukotriene D4 and the thromboxane analogue, U-44069, were all shown to produce dose-dependent reductions in renal blood flow after direct injection into the renal artery of anaesthetized pigs. The effects of ET-1 differed from the other two mediators in that ET-1 caused a transient vasodilator followed by a prolonged vasoconstrictor response. The pressor response was not mediated by the secondary release of either leukotriene D4 or thromboxane A2 as evidenced by the lack of effect of appropriate receptor antagonist MK571 (3-{-2(7-chloro-2 quinolinyl) ethenyl}phenyl{3-(dimethylamino-3-oxopropyl)thio}methyl thio propionic acid) and L-670,596 respectively. This response, however, could be inhibited in a dose-dependent fashion by the selective ETA antagonist, BQ-153 (cyclo-d-sulphalanine-l-Pro-d-Val-l-Leu-d-Trp-). Following blockade by BQ-153 the vasodilator response was unaffected and a residual pressor response remained, suggesting that either or both of these effects were mediated either through an ETB or a novel, as yet undefined, endothelin receptor.

Physiology of endothelin and the kidney

Since its discovery in 1988 as an endothelial cell-derived peptide that exerts the most potent vasoconstriction of any known endogenous compound, endothelin (ET) has emerged as an important regulator of renal physiology and pathophysiology. This review focuses on how the ET system impacts renal function in health; it is apparent that ET regulates multiple aspects of kidney function. These include modulation of glomerular filtration rate and renal blood flow, control of renin release, and regulation of transport of sodium, water, protons, and bicarbonate. These effects are exerted through ET interactions with almost every cell type in the kidney, including mesangial cells, podocytes, endothelium, vascular smooth muscle, every section of the nephron, and renal nerves. In addition, while not the subject of the current review, ET can also indirectly affect renal function through modulation of extrarenal systems, including the vasculature, nervous system, adrenal gland, circulating hormones, and the heart. As will become apparent, these pleiotropic effects of ET are of fundamental physiologic importance in the control of renal function in health. In addition, to help put these effects into perspective, we will also discuss, albeit to a relatively limited extent, how alterations in the ET system can contribute to hypertension and kidney disease.

Mitogen-activated protein kinase in endothelin-1-induced cardiac differentiation of mouse embryonic stem cells

Endothelin-1(ET-1) is a potent vasoconstrictor involved in the development of cardiovascular diseases and is an important regulator of heart development. However, the role of ET-1 in cardiac differentiation of mouse embryonic stem cells (mESCs) and the underlying molecular mechanisms remain poorly understood. In the present study, we showed that ET-1 significantly up-regulated gene expression of the cardiac specific transcriptional factors Nkx2.5, GATA4, and conduction system specific marker CX40, with no affect on the gene expression of α-MHC and β-MHC in cardiac differentiation of mESCs. The percentage of beating embryoid bodies (EB) and the Troponin T (TnT) positive area in total EBs was unchanged following ET-1 treatment, while the percentage of spindle cells that stained positively with TnT was increased in the presence of ET-1. Further investigation indicated that the percentage of beating EBs and the TnT positive area were decreased by the extracellular signal-related kinases (ERK)-1/2 inhibitor U0126 and the p38 inhibitor SB203580, but not by the Jun amino-terminal kinases (JNK) inhibitor SP600125. Inhibition of ERK1/2, p38, and JNK pathways also blocked the up-regulation of Nkx2.5 and GATA4 by ET-1, however only inhibition of the ERK1/2 pathway had negatively effects on the increase in CX40 expression in response to ET-1. ET-1 induced an increase in the percentage of spindle cells was also inhibited by U0126. Our results suggest that ET-1 plays a significant role in the cardiac differentiation of mESCs, especially in those cells committed to the conduction system, with the ERK1/2 pathway playing a critical role in this process.