Quantitative analysis of endothelin-1 and vasoactive intestinal contractor/endothelin-2 gene expression in rats by real-time reverse transcriptase polymerase chain reaction

Expression of endothelin type B receptors in uterine artery smooth muscle cells from pregnant Guinea pigs

INTRODUCTION

It is well established that upregulation of endothelin type B (ET_B) receptors in vascular smooth muscle cells plays a role in pathophysiological artery remodeling as response to ischemia and atherosclerosis. This study aimed to investigate the ET_B receptors function and localization under normal physiological remodeling. Specifically, in the guinea pig uterine arteries during pregnancy.

METHODS

Uterine artery contractility was assessed with sarafotoxin 6c and endothelin-1 in wire-myography in uterine arteries from non-pregnant and pregnant guinea pigs at gestational day 37 ± 5. Localization of ET_B receptors, proliferation marker Ki-67, and SMC differentiation marker SM22α in uterine arteries were investigated with immunohistochemistry.

RESULTS

Uterine arteries from pregnant guinea pigs showed significantly increased ET_B receptor-mediated vasoconstriction compared to uterine arteries from non-pregnant and to coronary arteries from pregnant guinea pigs (p < 0.001), suggesting that ET_B-receptor upregulation in uterine artery SMCs is a normal physiological mechanism taking place during remodeling. Furthermore, uterine arteries from pregnant guinea pigs showed enhanced expression of ET_B receptors, high density of Ki-67 positive SMCs and sparse SM22α staining in SMCs localized in the outer layer of the vessel wall.

DISCUSSION

Our results suggest that ET_B receptors are expressed in dedifferentiated proliferating SMCs of uterine arteries in pregnant guinea pigs. This study provides novel insight into the function and expression of ET_B receptors in uterine vascular remodeling during pregnancy.

Endothelin-1 and Endothelin-3 Regulate Endothelin Receptor Expression in Rat Coronary Arteries

In ischaemic hearts, endothelin (ET) levels are increased, and vasoconstrictor responses to ET-1 are greatly enhanced. We previously reported that ETB receptors are up-regulated in the smooth muscle layer of coronary arteries after myocardial ischaemia-reperfusion and that the MEK-ERK1/2 signalling pathway is involved in ETB receptor up-regulation. Whether ETs are directly involved in receptor regulation has not been determined. We suggest that ET-1 and ET-3 alter the expression/activity of ET receptors in coronary vascular smooth muscle cells. Vasoconstrictor responses were studied in endothelium-denuded coronary artery segments from rats that were subjected to experimental ischaemia-reperfusion or in organ-cultured segments. Post-ischaemic and cultured coronary arteries exhibited similar increased sensitivity to ET-3. ETA receptor-mediated vasoconstriction was dominant in fresh and non-ischaemic arteries. Organ culture significantly up-regulated ETB receptors and down-regulated ETA receptor expression. Co-incubation with ET-1 (1 nM) or ET-3 (100 nM) induced further down-regulation of the ETA receptor mRNA, while the function and protein level of ETA remained unchanged. ET-3 (100 nM) further up-regulated ETB receptor mRNA and proteins but abolished ETB receptor-mediated vasoconstriction, suggesting a desensitization of ETB receptors that was not observed with ET-3 (1 nM). In conclusion, ET-1, which is the most prevalent isoform in the cardiovascular system, induces down-regulation of ETA receptor expression without changing ETA or ETB receptor function or protein levels. Intermediate concentrations of ET-3 had an effect that was similar to that of ET-1, such that high concentrations of ET-3 (100 nM) up-regulated the ETB receptor at the gene and protein levels but switched off the function of the ETB receptors via desensitization.

Generation and characterization of an endothelin-2 iCre mouse

A novel transgenic mouse line that expresses codon-improved Cre recombinase (iCre) under regulation of the Endothelin-2 gene (edn2) promoter was developed for the conditional deletion of genes in Endothelin-2 lineage cells and for the spatial and temporal localization of Endothelin-2 expression. Endothelin-2 (EDN2, ET-2, previously VIC) is a transcriptionally regulated 21 amino acid peptide implicated in vascular homeostasis, and more recently in female reproduction, gastrointestinal function, immunology, and cancer pathogenesis that acts through membrane receptors and G-protein signaling. A cassette (edn2-iCre) was constructed that contained iCre, a polyadenylation sequence, and a neomycin selection marker in front of the endogenous start codon of the edn2 gene in a mouse genome BAC clone. The cassette was introduced into the C57BL/6 genome by pronuclear injection, and two lines of edn2-iCre positive mice were produced. The edn2-iCre mice were bred with ROSA26-lacZ and Ai9 reporter mice to visualize areas of functional iCre expression. Strong expression was seen in the periovulatory ovary, stomach and small intestine, and colon. Uniquely, we report punctate expression in the corneal epithelium, the liver, the lung, the pituitary, the uterus, and the heart. In the embryo, expression is localized in developing hair follicles and the dermis. Therefore, edn2-iCre mice will serve as a novel line for conditional gene deletion in these tissues.

Endothelin-2, the forgotten isoform: emerging role in the cardiovascular system, ovarian development, immunology and cancer

Endothelin-2 [ET-2; also known as vasoactive intestinal contractor (VIC), in rodents] differs from endothelin-1 (ET-1) by only two amino acids, and unlike the third isoform, endothelin-3 (ET-3), it has the same affinity as ET-1 for both ET(A) and ET(B) receptors. It is often assumed that ET-2 would mimic the actions of the more abundant ET-1 and current pharmacological interventions used to inhibit the ET system would also block the actions of ET-2. These assumptions have focused research on ET-1 with ET-2 studied in much less detail. Recent research suggests that our understanding of the ET family requires re-evaluation. Although ET-2 is very similar in structure as well as pharmacology to ET-1, and may co-exist in the same tissue compartments, there is converging evidence for an important and distinct ET-2 pathway. Specifically is has been demonstrated that ET-2 has a key role in ovarian physiology, with ET-2-mediated contraction proposed as a final signal facilitating ovulation. Furthermore, ET-2 may also have a pathophysiological role in heart failure, immunology and cancer. Comparison of ET-2 versus ET-1 mRNA expression suggests this may be accomplished at the level of gene expression but differences may also exist in peptide synthesis by enzymes such as endothelin converting enzymes (ECEs) and chymase, which may allow the two pathways to be distinguished pharmacologically and become separate drug targets. LINKED ARTICLES This article is part of a themed section on Endothelin. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.168.issue-1.

High doses of ultraviolet-C irradiation increases vasoactive intestinal contractor/endothelin-2 expression in keratinocytes of the newborn mouse epidermis

We examined the expression profiles of vasoactive intestinal contractor/endothelin-2 (VIC/ET-2) at both gene and peptide level in skin irradiated with different ultraviolet wavelengths. We found that VIC/ET-2 gene expression is sensitive only to ultraviolet-C (UVC) irradiation and has an immediate response. These results provide direct evidence that high doses of UVC irradiation induce an increase in gene expression and protein production of VIC/ET-2 and endothelin (ET) receptors in a dose-dependent manner in epidermal keratinocytes. We suggest that VIC/ET-2 can play an essential role in the maintenance, protection and hyperpigmentation of the epidermis exposed to UVC irradiation from artificial or natural sources.

Elevated endothelin-1 expression in dogs with heartworm disease

We explored the involvement of endothelin-1 (ET-1) in the pathophysiology of dog dirofilariasis (heartworm disease caused by Dirofilaria immitis) by analyzing mRNA levels of preproendothelin-1 (PPET-1), the precursor form of ET-1, in cardiopulmonary organs as well as ET-1 peptide levels in plasma. To determine the cDNA sequence and primary protein structure of dog PPET-1, we performed molecular cloning of the full-length cDNA. Based on the determined sequence information, comparative expression analysis of PPET-1 mRNA was carried out by real-time polymerase chain reaction on cardiopulmonary organs from healthy (n=5) and filarial (n=5) dogs. Filarial dogs showed a significantly (p<0.05) higher mRNA expression level in the heart (about one hundred times) and lung (about ten times) than healthy dogs. Analysis of plasma ET-1 levels in healthy (n=10) and filarial (n=10) dogs showed that filarial dogs (6.9+/-2.7 pg/ml) have significantly (p<0.01) increased plasma ET-1 levels compared with healthy dogs (1.4+/-0.3 pg/ml). To assess the pathophysiological significance of ET-1 in dirofilariasis relative to other cardiopulmonary disorders, plasma ET-1 levels determined in dogs diagnosed with mitral regurgitation (n=10), tricuspid regurgitation (n=5), ventricular septal defect (n=5), and patent ductus arteriosus (n=5) were compared to plasma ET-1 levels in filarial dogs. Filarial dogs, which commonly develop serious pulmonary hypertension, exhibited by far the highest ET-1 levels of the disease states examined. Based on the fact that ET-1 is a potent bioactive mediator that induces vasoconstriction and promotes vascular remodeling, these findings suggest that ET-1 plays an important role in the pathophysiology of dog dirofilariasis as an aggravating factor by inducing pulmonary hypertension.

Cloning of bovine preproendothelin-2 cDNA and organ distribution of transcripts

Endothelin-2 (ET2), which was originally identified in human, is a bioactive peptide of 21 amino acids with strong vasoconstrictive and pressor effects. Here we report the cDNA cloning and characterization of bovine preproendothelin-2 (PPET2), the precursor form of ET2. The bovine cDNA encodes 177 amino acids of the PPET2 polypeptide, in which a 21-amino acid mature ET2 peptide and a 16-amino acid ET2-like peptide as well as a 23-amino acid putative signal peptide were found. The bovine ET2-like peptide sequence was missing a dibasic amino acid pair at the C-terminal, in contrast to human, mouse and rat, for which the ET2-like sequence is flanked by dibasic pairs at both the N- and C-terminals. Gene expression analysis by RT-PCR showed that the transcript is expressed in various organs including heart, lung, liver, kidney, gastrointestinal tract, uterus and ovary, but not in spleen. Within the gastrointestinal tract, gene expression was detected in rumen, a ruminant-specific digestive organ, as well as stomach, duodenum and colon.

Increased gene expression of endothelin-1 and vasoactive intestinal contractor/endothelin-2 in the mammary gland of lactating mice

In an attempt to understand the roles of endothelin-1 (ET-1) and vasoactive intestinal contractor/endothelin-2 (VIC/ET-2), we have studied the genes for both peptides to be expressed in the mammary gland of lactating mice. We observed through real-time PCR analysis that ET-1 and VIC/ET-2 gene expression gradually increase after parturition and that ET-1 gene expression is significantly higher than that of VIC/ET-2. The distribution of ET-1 peptide was found to be localized mainly in the epithelial cells of the mammary gland at 14th day of lactation. ET-1 gene expression increases significantly, parallel to the increase in beta-casein gene expression, in epithelial cell lines (HC11) of mouse mammary gland after hormonal stimulation by addition of dexamethazone and prolactin. The observed increase in ET-1 expression in differentiated epithelial cells suggests physiological roles for ET-1, including milk production and secretion in the mammary gland of lactating mice.