Association between diastolic blood pressure and variants of the endothelin-1 and endothelin-2 genes

A novel missense variant in endothelin-2 (EDN2) causes a growth and respiratory lethal syndrome in bovine

The high level of fragmentation of the Spanish Lidia cattle breed, divided into lineages called ‘castas’ and into herds within lineages based on reproductive isolation, increases the risk of homozygosity and the outbreak of recessive genetic defects. Since 2004, an increasing number of calves have been identified in a Lidia herd with signs of severe growth retardation, respiratory alterations and juvenile lethality, which constitutes a novel inherited syndrome in cattle and was subsequently termed growth and respiratory lethal syndrome. We performed a genome‐wide association study on a cohort of 13 affected calves and 24 putative non‐carrier parents, mapping the disease to a wide 6 cM region on bovine chromosome 3 (p < 10⁻⁷). Whole genome re‐sequencing of three affected calves and three putative non‐carrier parents identified a novel missense variant (c.149G>A|p.Cys50Tyr) in exon 2 of the endothelin 2 (EDN2) gene. Bioinformatic analyses of p.Cys50Tyr effects predicted them to be damaging for both the structure and the function of the edn2 protein, and to create a new site of splicing that may also affect the pattern of pre‐mRNA splicing and exon definition. Sanger sequencing of this variant on the rest of the sample set confirmed the segregation pattern obtained with whole genome re‐sequencing. The identification of the causative variant and the development of a diagnostic genetic test enable the efficient design of matings to keep the effective population size as high as possible, as well as providing insights into the first EDN2‐associated hereditary disease in cattle or other species.

Associations of + 138 Ins/del A and + 5665 G/T polymorphisms of endothelin-1 gene with hypertension in Burmese people in Magway, Myanmar

Background

Hypertension is one of the major public health problems worldwide, and is one of the recognized causes of premature deaths every year in the world. The purpose of this study was to investigate the associations between the + 138 insertion/deletion of adenine (Ins/del A) and + 5665 guanine-to-thymine (G/T) polymorphisms of the endothelin-1 gene and hypertension in the residents of Magway Township, Myanmar.

Methods

This study was a cross-sectional comparative study including 60 hypertensive patients and 60 control subjects in Magway Township, Myanmar. The inclusion criterion for hypertension was blood pressure ≥ 140/90 mmHg or previous diagnosis by a physician as hypertension and/or taking antihypertensive drugs. The control group had blood pressure < 140/90 mmHg and no previous diagnosis of hypertension. The genotyping was done by polymerase chain reaction and restriction fragment length polymorphism method.

Results

In this study, the genotype distribution of the + 138 Ins/del A variant was significantly different between hypertensive patients and the control group, especially in the 3A4A genotype (odds ratio [OR], 2.451; 95% confidence interval [CI], 1.138–5.280; P = 0.022). Adenine insertion genotypes (3A4A and 4A4A) were significantly associated with hypertension in the dominant model (OR, 2.494; 95% CI, 1.179–5.276; P = 0.017). In addition, there was a significant association between the 4A allele and hypertension (OR, 1.771; 95% CI, 1.026–3.056; P = 0.040). The genotype and allelic distributions of the + 5665 G/T polymorphism were not significantly different between the hypertensive patients and the control group (P > 0.05). In this study, there was no significant association between the genotype and allele frequency, and hypertension (P > 0.05). The linkage disequilibrium was weak between the + 138 Ins/del A and + 5665 G/T loci (D’ = 0.108, r² = 0.009).

Conclusions

This study provides evidence that the + 138 Ins/del A rather than + 5665 G/T polymorphism is associated with hypertension in Burmese people.

Dissecting genetic factors affecting phenylephrine infusion rates during anesthesia: a genome-wide association study employing EHR data

BACKGROUND

The alpha-adrenergic agonist phenylephrine is often used to treat hypotension during anesthesia. In clinical situations, low blood pressure may require prompt intervention by intravenous bolus or infusion. Differences in responsiveness to phenylephrine treatment are commonly observed in clinical practice. Candidate gene studies indicate genetic variants may contribute to this variable response.

METHODS

Pharmacological and physiological data were retrospectively extracted from routine clinical anesthetic records. Response to phenylephrine boluses could not be reliably assessed, so infusion rates were used for analysis. Unsupervised k-means clustering was conducted on clean data containing 4130 patients based on phenylephrine infusion rate and blood pressure parameters, to identify potential phenotypic subtypes. Genome-wide association studies (GWAS) were performed against average infusion rates in two cohorts: phase I (n = 1205) and phase II (n = 329). Top genetic variants identified from the meta-analysis were further examined to see if they could differentiate subgroups identified by k-means clustering.

RESULTS

Three subgroups of patients with different response to phenylephrine were clustered and characterized: resistant (high infusion rate yet low mean systolic blood pressure (SBP)), intermediate (low infusion rate and low SBP), and sensitive (low infusion rate with high SBP). Differences among clusters were tabulated to assess for possible confounding influences. Comorbidity hierarchical clustering showed the resistant group had a higher prevalence of confounding factors than the intermediate and sensitive groups although overall prevalence is below 6%. Three loci with P < 1 × 10^-6 were associated with phenylephrine infusion rate. Only rs11572377 with P = 6.09 × 10^-7, a 3'UTR variant of EDN2, encoding a secretory vasoconstricting peptide, could significantly differentiate resistant from sensitive groups (P = 0.015 and 0.018 for phase I and phase II) or resistant from pooled sensitive and intermediate groups (P = 0.047 and 0.018).

CONCLUSIONS

Retrospective analysis of electronic anesthetic records data coupled with the genetic data identified genetic variants contributing to variable sensitivity to phenylephrine infusion during anesthesia. Although the identified top gene, EDN2, has robust biological relevance to vasoconstriction by binding to endothelin type A (ET_A) receptors on arterial smooth muscle cells, further functional as well as replication studies are necessary to confirm this association.

Association of endothelin receptor type A rs5333 gene polymorphism with steroid response in Egyptian children with idiopathic nephrotic syndrome

Aim: To investigate ENDRA rs5333 gene polymorphism distribution in idiopathic nephrotic syndrome (INS) and to analyze their association with response to steroid therapy, and biochemical markers of INS. Subjects & methods: The PCR-restriction fragment length polymorphism was used to analyze ENDRA rs5333 polymorphism in 100 children with idiopathic nephrotic syndrom (INS) and 100 healthy children. Plasma endothelin-1 were measured by ELISA. Results: The ENDRA rs5333 gene polymorphism was not associated with risk of INS. The frequency of minor allele (C) was significantly higher in the steroid resistant nephrotic syndrome group than the steroid sensitive group. The CC and TC mutant variants were associated with higher plasma levels of cholesterol, albumin, urea and 24-h urinary protein, but were not associated with risk of hypertension. The endothelin-1 plasma level was higher in INS than control and in steroid resistant nephrotic syndrome group when compared with steroid sensitive group cases. Conclusion: The ENDRA rs5333 gene polymorphism may be associated with genetic predisposition to steroid resistance in INS Egyptian children.

Endothelin-1 Pathway Polymorphisms and Outcomes in Pulmonary Arterial Hypertension

RATIONALE

Pulmonary arterial hypertension (PAH) is a progressive fatal disease. Variable response and tolerability to PAH therapeutics suggests that genetic differences may influence outcomes. The endothelin pathway is central to pulmonary vascular function, and several polymorphisms and/or mutations in the genes coding for endothelin (ET)-1 and its receptors correlate with the clinical manifestations of other diseases.

OBJECTIVES

To examine the interaction of ET-1 pathway polymorphisms and treatment responses of patients with PAH treated with ET receptor antagonists (ERAs).

METHODS

A total of 1,198 patients with PAH were prospectively enrolled from 45 U.S. and Canadian pulmonary hypertension centers or retrospectively from global sites participating in the STRIDE (Sitaxsentan To Relieve Impaired Exercise) trials. Comprehensive objective measures including a 6-minute-walk test, Borg dyspnea score, functional class, and laboratory studies were completed at baseline, before the initiation of ERAs, and repeated serially. Single-nucleotide polymorphisms from ET-1 pathway candidate genes were selected from a completed genome-wide association study performed on the study cohort.

MEASUREMENTS AND MAIN RESULTS

Patient efficacy outcomes were analyzed for a relationship between ET-1 pathway polymorphisms and clinical efficacy using predefined, composite positive and negative outcome measures in 715 European descent samples. A single-nucleotide polymorphism (rs11157866) in the G-protein alpha and gamma subunits gene was significantly associated, accounting for multiple testing, with a combined improvement in functional class and 6-minute-walk distance at 12 and 18 months and marginally significant at 24 months.

CONCLUSIONS

ET-1 pathway associated polymorphisms may influence the clinical efficacy of ERA therapy for PAH. Further prospective studies are needed.

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.

Endothelin Type A Receptor Genotype is a Determinant of Quantitative Traits of Metabolic Syndrome in Asian Hypertensive Families: A SAPPHIRe Study

Co-heritability of hypertension and insulin resistance (IR) within families not only implies genetic susceptibility may be responsible for these complex traits but also suggests a rational that biological candidate genes for hypertension may serve as markers for features of the metabolic syndrome (MetS). Thus we determined whether the T323C polymorphism (rs5333) of endothelin type A (ETA) receptor, a predominant receptor evoking potent vasoconstrictive action of endothelin-1, contributes to susceptibility to IR-associated hypertension in 1694 subjects of Chinese and Japanese origins. Blood pressures (BPs) and biochemistries were measured. Fasting insulin level, insulin-resistance homeostasis model assessment (HOMAIR) score, and area under curve of insulin concentration (AUCINS) were selected for assessing insulin sensitivity. Genotypes were obtained by methods of polymerase chain reaction-restriction fragment length polymorphism. Foremost findings were that minor allele frequency of the T323C polymorphism was noticeable lower in our overall Asian subjects compared to multi-national population reported in gene database; moreover both the genotypic and allelic frequencies of the polymorphism were significantly different between the two ethnic groups we studied. The genotype distributions at TT/TC/CC were 65, 31, 4% in Chinese and 51, 41, 8% in Japanese, respectively (p < 0.0001). Additionally, carriers of the C homozygote revealed characteristics of IR, namely significantly higher levels of fasting insulin, HOMAIR score, and AUCINS at 29.3, 35.3, and 39.3%, respectively, when compared to their counterparts with TT/TC genotypes in Chinese. Meanwhile, the CC genotype was associated with a higher level of high density lipoprotein cholesterol in Japanese. No association of the polymorphism with BP was observed. This study demonstrated for the first time that T323C polymorphism of ETA receptor gene was associated with an adverse insulin response in Chinese and a favorite atherogenic index in Japanese.

Differential genetic basis for pre-menopausal and post-menopausal salt-sensitive hypertension

Essential hypertension affects 75% of post-menopausal women in the United States causing greater cardiovascular complications compared with age-matched men and pre-menopausal women. Hormone replacement and current anti-hypertensive therapies do not correct this post-menopausal increased risk suggesting a distinct pathogenic framework. We investigated the hypothesis that distinct genetic determinants might underlie susceptibility to salt sensitive hypertension in pre-menopausal and post-menopausal states. To determine whether distinct genetic loci contribute to post-menopausal salt-sensitive hypertension, we performed a genome-wide scan for quantitative trait loci (QTLs) affecting blood pressure (BP) in 16-month old post-menopausal F2 (Dahl S×R)-intercross female rats characterized for blood pressure by radiotelemetry. Given identical environments and high salt challenge, post-menopausal BP levels were significantly higher than observed in pre-menopausal (post-menopausal versus pre-menopausal SBP, P<0.0001) and ovariectomized (post-menopausal versus ovariectomized SBP, P<0.001) F2-intercross female rats. We detected four significant to highly significant BP-QTLs (BP-pm1 on chromosome 13, LOD 3.78; BP-pm2 on chromosome 11, LOD 2.76; BP-pm3 on chromosome 2, LOD 2.61; BP-pm4 on chromosome 4, LOD 2.50) and two suggestive BP-QTLs (BP-pm5 on chromosome 15, LOD 2.37; BP-f1 on chromosome 5, LOD 1.65), four of which (BP-pm2, BP-pm3, BP-pm4, BP-pm5) were unique to this post-menopausal cohort. These data demonstrate distinct polygenic susceptibility underlying post-menopausal salt-sensitive hypertension providing a pathway towards the identification of mechanism-based therapy for post-menopausal hypertension and ensuing target-organ complications.

Dahl (S x R) congenic strain analysis confirms and defines a chromosome 5 female-specific blood pressure quantitative trait locus to <7 Mbp

The detection of multiple sex-specific blood pressure (BP) quantitative trait loci (QTLs) in independent total genome analyses of F2 (Dahl S x R)-intercross male and female rat cohorts confirms clinical observations of sex-specific disease cause and response to treatment among hypertensive patients, and mandate the identification of sex-specific hypertension genes/mechanisms. We developed and studied two congenic strains, S.R5A and S.R5B introgressing Dahl R-chromosome 5 segments into Dahl S chromosome 5 region spanning putative BP-f1 and BP-f2 QTLs. Radiotelemetric non-stressed 24-hour BP analysis at four weeks post-high salt diet (8% NaCl) challenge, identified only S.R5B congenic rats with lower SBP (−26.5 mmHg, P = 0.002), DBP (−23.7 mmHg, P = 0.004) and MAP (−25.1 mmHg, P = 0.002) compared with Dahl S female controls at four months of age confirming BP-f1 but not BP-f2 QTL on rat chromosome 5. The S.R5B congenic segment did not affect pulse pressure and relative heart weight indicating that the gene underlying BP-f1 does not influence arterial stiffness and cardiac hypertrophy. The results of our congenic analysis narrowed BP-f1 to chromosome 5 coordinates 134.9–141.5 Mbp setting up the basis for further fine mapping of BP-f1 and eventual identification of the specific gene variant accounting for BP-f1 effect on blood pressure.

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.

Systematic Analysis of Sequence Variability of the Endothelin-1 Gene: A Prerequisite for Association Studies

We analyzed allele frequencies and pairwise linkage disequilibria of 13 variants in the EDN1 gene of 298 young males, the majority of German ancestry. Our analysis comprises all common variants in the five exons and flanking intronic regions, as well as known polymorphisms in the promoter sequence. In addition to previously analyzed polymorphisms, our haplotype reconstruction included five recently described variants and was done by using three different algorithms to allow inference of result stability. More than 30 haplotypes were predicted. All haplotypes with frequencies > or = 1% were inferred by all three methods and can be described by seven haplotype tagging single-nucleotide polymorphisms (htSNPs), reducing the genotyping load to 65%. Three of these haplotypes with frequencies of about 11%, 9%, and 4% had been mistaken for one haplotype in the previous analysis, which included only six polymorphisms, some of them not being htSNPs. Systematic analysis of sequence variability and comprehensive haplotype analysis of the EDN1 gene determined a substantial part of its genetic variability for further association studies and helped to reduce the genotyping load for common phenotypes.

Genetic variation in the endothelin system: do polymorphisms affect the therapeutic strategies?

Endothelin-1 (ET-1) exerts multiple biological effects, including vasoconstriction and the stimulation of cell proliferation in tissues both within and outside of the cardiovascular system. ET-1 is synthesized by ET-converting enzymes (ECE), chymases (CMAs), and non-ECE metalloproteases through a process regulated in an autocrine fashion in vascular and nonvascular cells. ET-1 acts through the activation of G(i)protein-coupled receptors. ET(A) receptors mediate vasoconstriction and cell proliferation, whereas ET(B) receptors are important for aldosterone secretion, endothelial cell (EC) migration, the release of nitric oxide (NO) and prostacyclin, the clearance of ET-1, and the inhibition of ECE-1. ET is activated in scleroderma, hypertension, atherosclerosis, restenosis, heart failure, idiopathic cardiomyopathy, and renal failure. Tissue concentrations more reliably reflect the activation of the ET system because of the predominantly abluminal secretion of the peptide. Experimental studies and clinical trials have demonstrated that ET-1 plays a major role in normal cardiovascular homeostasis and in the functional and structural changes observed in arterial and pulmonary hypertension, glomerulosclerosis, atherosclerosis, and heart failure. Accordingly, ET antagonists are promising new agents in the treatment of cardiovascular diseases. Single nucleotide polymorphisms (SNPs) of the genes of preproET-1, ECE-1, CMA, ET(A) and ET(B) receptors have been identified and can be important for their functional regulation. However, for most of them the association with disease conditions and the evidence for a functional role remain controversial. Thus, even though ET antagonists are being used for the treatment of pulmonary hypertension, there is no convincing evidence for a role of SNPs in affecting the therapeutic strategies.

The Lack of Relationship between an Endothelin-1 Gene Polymorphism (Ala288Ser) and Incidence of Hypertension: A Retrospective Cohort Study among Japanese Workers

BACKGROUND

Some case-control association studies revealed the relationship between some endothelin-1 (ET-1) gene polymorphisms and blood pressure. Because no report was available about the relationship between any ET-1 gene polymorphism and incidence of hypertension, we examined the relationship between novel ET-1 gene polymorphism (G862T / Ala288Ser in exon 5) and incidence of hypertension by a retrospective cohort study.

METHODS

The subjects were Japanese workers at a company in Shimane Prefecture in Japan. The polymorphism with genome DNA extracted from the blood of the workers was analyzed using the polymerase chain reaction confronting two pair primers method. According to the results of two regular health checkups with a 6-year interval, the study population was divided into two groups by blood pressure and antihypertensive treatment in 1998, after excluding people who had hypertension in 1992.

RESULTS

There were 133 (93 males and 40 females) incidences of hypertension observed among the study population of 922 (540 males and 382 females). In the univariate analysis, odds ratios of Ala/Ser and Ser/Ser against Ala/Ala were 0.98 (95% confidence interval [CI]): 0.7-1.4) and 0.79 (95% CI: 0.4-1.6), respectively. In the multivariate analysis adjusted for sex, age, body mass index, serum total cholesterol, fasting blood sugar, and smoking and drinking habits, odds ratios for Ala/Ser and Ser/Ser against Ala/Ala were 0.97 (95% CI: 0.7-1.4) and 0.75 (95% CI: 0.4-1.5), respectively.

CONCLUSIONS

The ET-1 gene polymorphism in this study did not seem to be associated with the incidence of hypertension among the Japanese workers.