Interactive association of five candidate polymorphisms in Apelin/APJ pathway with coronary artery disease among Chinese hypertensive patients

A Comparison of Apelin Rs56204867 and Apelin Receptor Rs11544374 Gene Polymorphisms and Their Association with Risk of Preeclampsia in Southeast Iran

Background

Pre-eclampsia (PE) is a severe pregnancy condition with genetic and environmental factors affecting the placental function and vascular changes. Genetic variants in the apelinergic system may influence preeclampsia risk and birth outcomes. Therefore, this study aimed to compare apelin (APLN) rs56204867 and apelin receptor (APLNR) rs11544374 gene polymorphisms and to investigate their association with mothers' body mass index and infant's birth weight among women with preeclampsia and control group in southeast Iran.

Methods

A total of 123 PE patients and 125 age- and gender-matched control subjects were enrolled in the study. The PCR-RFLP method was employed to genotype the APLN rs56204867 and APLNR rs11544374 gene polymorphisms.

Results

There was no significant association between the genotypes of the rs11544374 variant and the PE risk. The incidence of the AG genotype of the rs54204867 variant in the control group was considerably greater than in the PE group. Also, a significant relationship was found between the body mass profile of patients with PE and the APLN rs54204867 gene polymorphism.

Conclusions

It was observed that the APLN rs54204867 gene polymorphism could affect the PE risk. No significant difference was found between the PE group and the control group in terms of the genotypes of the APLNR rs11544374 variant. It was not statistically significant between mothers' BMI and rs11544374 of the APLNR gene, whereas an obvious link was observed between mothers' BMI and rs54204867 of the APLN gene.

Apelin Association with Hepatic Fibrosis and Esophageal Varices in Patients with Chronic Hepatitis C Virus

Portal hypertension and esophageal varices complicating hepatitis C virus (HCV)-related chronic liver diseases are some of the most devastating sequelae. Angiogenesis is the hallmark of their pathogenesis. Apelin is one of the recently identified angiogenic and fibrogenic peptides. We studied apelin gene expression, apelin (rs3761581) single-nucleotide polymorphism (SNP), and serum apelin level in patients with chronic HCV, and their association with liver fibrosis and esophageal varices in 112 patients with HCV-related chronic liver disease (40 with liver cirrhosis [LC]/low-grade varices, 33 with LC/high-grade varices, and 39 with fibrotic non-cirrhotic liver/no varices) and 80 healthy control subjects. Real-time polymerase chain reaction was used for apelin gene expression assay and apelin rs3761581 SNP analysis in peripheral blood samples. The serum apelin level was measured by ELISA. Apelin gene expression was undetectable in the studied samples. The SNP analysis revealed a greater frequency of the C (mutant) allele among patients compared with control subjects (P = 0.012; odds ratio, 3.67). The serum apelin level was significantly greater in patients with LC/varices (median, 31.6 ng/L) compared with patients without LC/varices (median, 2.9 ng/L; P < 0.001). A serum apelin level cutoff value of 16.55 ng/L predicted the presence of varices, with an area under the receiver operating characteristic curve value of 0.786. A positive correlation was found between serum apelin level and grade of liver fibrosis (r = 0.346, P < 0.001) and portal hypertension (r = 0.438, P < 0.001). In conclusion, the apelin rs3761581-C allele may be associated with the progression of HCV-related chronic liver disease and varices formation, and can be considered a potential therapeutic target to control fibrosis progression. The serum apelin level provided an accurate prediction of the presence of esophageal varices.

The microRNA-204-5p inhibits APJ signalling and confers resistance to cardiac hypertrophy and dysfunction

BACKGROUND

MicroRNAs regulate cardiac hypertrophy development, which precedes and predicts the risk of heart failure. microRNA-204-5p (miR-204) is well expressed in cardiomyocytes, but its role in developing cardiac hypertrophy and cardiac dysfunction (CH/CD) remains poorly understood.

METHODS

We performed RNA-sequencing, echocardiographic, and molecular/morphometric analysis of the heart of mice lacking or overexpressing miR-204 five weeks after trans-aortic constriction (TAC). The neonatal rat cardiomyocytes, H9C2, and HEK293 cells were used to determine the mechanistic role of miR-204.

RESULTS

The stretch induces miR-204 expression, and miR-204 inhibits the stretch-induced hypertrophic response of H9C2 cells. The mice lacking miR-204 displayed a higher susceptibility to CH/CD during pressure overload, which was reversed by the adeno-associated virus serotype-9-mediated cardioselective miR-204 overexpression. Bioinformatic analysis of the cardiac transcriptomics of miR-204 knockout mice following pressure overload suggested deregulation of apelin-receptor (APJ) signalling. We found that the stretch-induced extracellular signal-regulated kinase 1/2 (ERK1/2) activation and hypertrophy-related genes expression depend on the APJ, and both of these effects are subject to miR-204 levels. The dynamin inhibitor dynasore inhibited both stretch-induced APJ endocytosis and ERK1/2 activation. In contrast, the miR-204-induced APJ endocytosis was neither inhibited by dynamin inhibitors (dynasore and dyngo) nor associated with ERK1/2 activation. We find that the miR-204 increases the expression of ras-associated binding proteins (e.g., Rab5a, Rab7) that regulate cellular endocytosis.

CONCLUSIONS

Our results show that miR-204 regulates trafficking of APJ and confers resistance to pressure overload-induced CH/CD, and boosting miR-204 can inhibit the development of CH/CD.

Maternal serum Apelin 13 and APLN gene promoter variant -1860T > C in preeclampsia

OBJECTIVE

To evaluate the apelin (APLN) -1860 T > C (rs56204867) polymorphism and maternal serum apelin 13 levels in preeclampsia and its association with blood pressure.

METHODS

This case-control study was conducted in department of Biochemistry, Sri Devaraj Urs Medical College, Karnataka, India. A total of 181 subjects were enrolled in the study from department of Department of Obstetrics and Gynecology. The recruited women were grouped as: Group-I (n = 91) cases with preeclampsia and Group-II (n = 90) normotensive healthy pregnant women as controls. Under aseptic conditions, the collected 5 mL blood was distributed for serum separation (3 mL) and genetic analysis (2 mL). Serum was stored at -80 °C after centrifugation at 3000 rpm for 10 min. The collected five mL urine sample was used for urinary protein analysis by dipstick method. The APLN gene -1860 T > C polymorphism and Apelin 13 levels were analyzed by molecular methods and ELISA technique respectively. Birth weight and demographic details were recorded.

RESULTS

In the present study, no significant difference was observed for mean gestational age and maternal age. Systolic (158.7 ± 14.0 mmHg) and diastolic (104.9 ± 10.7 mmHg) blood pressure, and mean arterial pressure (MAP) (123.0 ± 11.1 mmHg) (p-value .001) were significantly increased in preeclamptic women compared with healthy pregnant women. Birth weight (2.4 ± 0.5 kg) (p-value .001) was significantly decreased in babies born to preeclamptic mothers. Birth weights were also expressed in centiles, according to Fenton Chart. Number of small for gestational age (SGA) babies were more in preeclampsia (n = 55) than healthy pregnant women (n = 28). Mean maternal serum apelin 13 (239.4 ± 126.3 pg/mL) (p-value .001) concentrations were significantly lower in preeclampsia compared with healthy controls. Maternal serum apelin 13 concentration in preeclampsia was negatively correlated with systolic blood pressure (r = -0.235), diastolic blood pressure (r= -0.172) and mean arterial pressure (r = -0. 206). However, maternal serum apelin 13 levels showed insignificant positive correlation with age, gestational age and birth weight. The genotype and allele frequencies of APLN gene were found significant between study groups as in preeclampsia (χ² = 11.69; df = 2; p = .0028 and χ2 = 14.27; df = 1; p = .00013 respectively). CC genotype and C allele of APLN - 1860 T > C site was high in preeclampsia.

CONCLUSION

Study concludes that preeclamptic women have low level of serum apelin 13 and -1860 T > C polymorphism at APLN gene promoter site with increased allelic frequency of CC genotype and C allele compared to normotensive pregnant women. And this evidence may link to cardiac complications in preeclamptic women after delivery in later stage.

Association of genetic defects in the apelin-AGTRL1 system with myocardial infarction risk in Han Chinese

We aimed to test the hypothesis that apelin (APLN) and its receptor AGTRL1 (APLNR) genes may contribute to the pathogenesis of myocardial infarction in Han Chinese. This is a hospital-based, case-control association study, involving 1067 patients with myocardial infarction and 942 healthy controls. Myocardial infarction is diagnosed by electrocardiogram or anatomopathological examination. Eight polymorphisms in APLN gene and 5 in APLNR gene were genotyped using the TaqMan assay. Risk was summarized as odds ratio (OR) and 95% confidence interval (CI). In males, rs56204867-G allele (adjusted OR, 95% CI, p: 0.21, 0.08-0.55, 0.002) and rs2235309-T allele (0.60, 0.42-0.84, 0.004) was associated with a significantly reduced risk of myocardial infarction, and the mutations of rs2235310 was associated with an increased risk (1.41, 1.06-2.52, 0.021), as well as for rs948847-GG genotype (1.85, 1.23-2.91, 0.007). In females, the presence of rs56204867-AG and -GG genotypes was significantly associated with 44% and 50% reduced risk (0.56 and 0.50, 0.40-8.04 and 0.29-0.86, 0.007 and 0.036), respectively; for rs2235310, CC genotype was associated with 72% increased risk (1.72, 1.09-3.22, 0.016), and the odds of myocardial infarction was 3.47 for rs9943582-TT genotype (95% CI: 1.53-7.57, 0.009). The gender-specific association of APLN and APLNR genes with myocardial infarction was reinforced by further linkage and haplotype analyses. Finally, nomograms based on significant polymorphisms are satisfactory, with the C-indexes over 80% for both genders. Taken together, our findings indicate that APLN and APLNR genes are potential candidates in the pathogenesis of myocardial infarction in Han Chinese, and importantly their contribution is gender-dependent.

International Union of Basic and Clinical Pharmacology. CVII. Structure and Pharmacology of the Apelin Receptor with a Recommendation that Elabela/Toddler Is a Second Endogenous Peptide Ligand

The predicted protein encoded by the APJ gene discovered in 1993 was originally classified as a class A G protein-coupled orphan receptor but was subsequently paired with a novel peptide ligand, apelin-36 in 1998. Substantial research identified a family of shorter peptides activating the apelin receptor, including apelin-17, apelin-13, and [Pyr1]apelin-13, with the latter peptide predominating in human plasma and cardiovascular system. A range of pharmacological tools have been developed, including radiolabeled ligands, analogs with improved plasma stability, peptides, and small molecules including biased agonists and antagonists, leading to the recommendation that the APJ gene be renamed APLNR and encode the apelin receptor protein. Recently, a second endogenous ligand has been identified and called Elabela/Toddler, a 54-amino acid peptide originally identified in the genomes of fish and humans but misclassified as noncoding. This precursor is also able to be cleaved to shorter sequences (32, 21, and 11 amino acids), and all are able to activate the apelin receptor and are blocked by apelin receptor antagonists. This review summarizes the pharmacology of these ligands and the apelin receptor, highlights the emerging physiologic and pathophysiological roles in a number of diseases, and recommends that Elabela/Toddler is a second endogenous peptide ligand of the apelin receptor protein.

The association between apelin polymorphisms and hypertension in China: A meta-analysis

INTRODUCTION:

Apelin plays an important part in regulating blood pressure, metabolism, and the development of cancer. Recent studies have investigated the association of apelin polymorphisms and hypertension risk, but no meta-analysis has been conducted.

MATERIALS AND METHODS:

Five studies were included in this meta-analysis in total. The pooled odds ratio and its corresponding 95% confidence interval were calculated by the random-effect model.

RESULTS:

The overall pooled odds ratio of the distribution of rs3761581 G allelic frequency was 0.90 (95% confidence interval: 0.82-1.00). In female participants, the pooled odds ratio of the frequency of G allele was 1.01 (95% confidence interval: 0.89-1.14). For males, the pooled odds ratio of the frequency of G allele was 0.69 (95% confidence interval: 0.46-1.03). As for rs56204867, the overall pooled odds ratio of the frequency of G allele was 1.09 (95% confidence interval: 0.86-1.37). In females, the pooled odds ratio of the frequencies of the G allele was 1.05 (95% confidence interval: 0.86-1.29). In male participants, the frequency of G allele did not show significant correlation with hypertension (pooled odds ratio=1.21 95% confidence interval: 0.81-1.79).

CONCLUSION:

This meta-analysis revealed that there was no correlation between apelin polymorphisms, rs3761581 and rs56204867, and the prevalence of hypertension.

Association study of apelin-APJ system genetic polymorphisms with incident metabolic syndrome in a Chinese population: a case-control study

Objectives: Apelin-APJ system has been implicated in the regulation of metabolic homeostasis. This study aimed to explore the genetic predisposition of the apelin-APJ system to metabolic syndrome.

Materials And Methods: 1005 subjects were enrolled, including 448 metabolic syndrome patients and 557 controls. Seven single nucleotide polymorphisms, including rs909656, rs5975126, and rs3115757 of the apelin gene and rs7119375, rs10501367, rs9943582 and rs11544374 of the APJ gene, were genotyped.

Results: For males, apelin-36 were higher in metabolic syndrome subjects compared with controls (p < 0.05). Apelin-36 were significantly lower in those with TT genotype of rs10501367 than those with CC and CT genotypes (p < 0.05), and fasting plasma glucose were higher in T allele carriers of rs10501367 and A allele carriers of rs7119375 compared with non-carriers (both p < 0.05). A significant difference in genotype distribution between diabetes mellitus patients and controls existed for both rs10501367 and rs7119375 (both p < 0.05). However, the association between apelin-APJ system genetic polymorphisms and metabolic syndrome was nonsignificant.

For females, apelin-36 were higher in metabolic syndrome subjects compared with controls (p < 0.05). The association between apelin-APJ system genetic polymorphisms and apelin-36, fasting plasma glucose and diabetes mellitus was nonsignificant. However, carrying A allele in rs7119375 was associated with lower metabolic syndrome risk compared with non-carriers of A allele (odds ratio: 0.646, 95% confidence interval: 0.420–0.994, p = 0.043).

Conclusions: The current findings revealed a gender-specific association of apelin-APJ system genetic polymorphisms with metabolic syndrome and glucose homeostasis disorders in a Han Chinese population.

Association of polymorphisms of leptin, leptin receptor and apelin receptor genes with susceptibility to coronary artery disease and hypertension

AIMS

Apelin and leptin are factors which have a potential physiological and pathological role in cardiovascular homoeostasis. Apelin receptor (APLNR), leptin receptor (LEPR) and leptin variants may affect the vascular tone in heart or peripheral circulation, thereby predisposing patients to hypertension and coronary artery disease (CAD). The aim of the present study was to evaluate four single nucleotide polymorphisms (SNPs) of APLNR genes (rs11544374 and rs948847), LEPR (rs1137101) and leptin (rs7799039) gene in patients with CAD and hypertension.

MATERIALS AND METHODS

This case-control study was carried out on 286 CAD-suspected patients. The participants were divided into four subgroups including: CAD patients with no hypertension (H^-CAD⁺), hypertensive patients with no CAD (H⁺CAD^-), CAD patients with hypertension (H⁺CAD⁺) and non-hypertensive non-CAD subjects as control group (H^-CAD^-). Genomic DNA from whole blood was extracted and four SNPs were assessed using PCR-RFLP.

KEY FINDINGS

A significant difference was found in the genotype frequency of APLNR rs11544374 gene in H⁺CAD⁺ and H^-CAD⁺ groups compared to control subjects (P < 0.001 for both comparisons). Regarding the rs1137101, the prevalence of A allele compared to G allele was significantly different among the four groups (P = 0.02). Results of multinomial regression analysis indicated that G allele carriers in the recessive genetic model (AA vs. AG + GG) of rs11544374 had a significantly protective effect compared to H^-CAD⁺ and H⁺CAD⁺after adjustment (OR = 0.12; 95% CI = 0.02-0.61; P = 0.01 and OR = 0.40; 95% CI = 0.17-0.98; P = 0.04, respectively).

SIGNIFICANCE

The findings of present study revealed that the APLNR rs11544374 gene polymorphism might serve as predisposing factor in CAD.

Recognition of the polycistronic nature of human genes is critical to understanding the genotype-phenotype relationship

Technological advances promise unprecedented opportunities for whole exome sequencing and proteomic analyses of populations. Currently, data from genome and exome sequencing or proteomic studies are searched against reference genome annotations. This provides the foundation for research and clinical screening for genetic causes of pathologies. However, current genome annotations substantially underestimate the proteomic information encoded within a gene. Numerous studies have now demonstrated the expression and function of alternative (mainly small, sometimes overlapping) ORFs within mature gene transcripts. This has important consequences for the correlation of phenotypes and genotypes. Most alternative ORFs are not yet annotated because of a lack of evidence, and this absence from databases precludes their detection by standard proteomic methods, such as mass spectrometry. Here, we demonstrate how current approaches tend to overlook alternative ORFs, hindering the discovery of new genetic drivers and fundamental research. We discuss available tools and techniques to improve identification of proteins from alternative ORFs and finally suggest a novel annotation system to permit a more complete representation of the transcriptomic and proteomic information contained within a gene. Given the crucial challenge of distinguishing functional ORFs from random ones, the suggested pipeline emphasizes both experimental data and conservation signatures. The addition of alternative ORFs in databases will render identification less serendipitous and advance the pace of research and genomic knowledge. This review highlights the urgent medical and research need to incorporate alternative ORFs in current genome annotations and thus permit their inclusion in hypotheses and models, which relate phenotypes and genotypes.

A promoter polymorphism in APJ gene is significantly associated with blood pressure changes and hypertension risk in Chinese women

The aim of this study was to interrogate the gender-specific association of 5 well-defined polymorphisms in apelin/APJ system with both blood pressure changes and hypertension risk in a northeastern Chinese population. This is a population-based case-control study, including 650 hypertensive patients and 645 normotensive controls. Data were analyzed by STATA and Haplo.Stats. The genotype distributions of 5 study polymorphisms were in Hardy-Weinberg equilibrium in both genders. The rs7119375 and rs10501367 were completely linked. The genotypes (P = 0.001) and alleles (P < 0.001) of rs7119375 differed significantly between patients and controls in women. Carriers of rs7119375-AA genotype had significant higher systolic blood pressure (SBP) than carriers of rs7119375-GG genotype in both patients and controls of female gender (P < 0.01). Moreover, carriers of rs7119375-A allele were 1.80 times more likely to develop hypertension relative to carriers of rs7119375-GG genotype after adjusting for age, body mass index and glucose (odds ratio: 1.80; 95% confidence interval: 1.03–3.16; P = 0.040). Further allele combination analysis supported the leading contribution of rs7119375 to hypertension risk. Our findings demonstrated that the mutation of promoter polymorphism rs7119375 in APJ gene was significantly associated with elevated SBP and increased hypertension risk in Chinese women.

Apelinergic System Structure and Function

Apelin and apela (ELABELA/ELA/Toddler) are two peptide ligands for a class A G-protein-coupled receptor named the apelin receptor (AR/APJ/APLNR). Ligand-AR interactions have been implicated in regulation of the adipoinsular axis, cardiovascular system, and central nervous system alongside pathological processes. Each ligand may be processed into a variety of bioactive isoforms endogenously, with apelin ranging from 13 to 55 amino acids and apela from 11 to 32, typically being cleaved C-terminal to dibasic proprotein convertase cleavage sites. The C-terminal region of the respective precursor protein is retained and is responsible for receptor binding and subsequent activation. Interestingly, both apelin and apela exhibit isoform-dependent variability in potency and efficacy under various physiological and pathological conditions, but most studies focus on a single isoform. Biophysical behavior and structural properties of apelin and apela isoforms show strong correlations with functional studies, with key motifs now well determined for apelin. Unlike its ligands, the AR has been relatively difficult to characterize by biophysical techniques, with most characterization to date being focused on effects of mutagenesis. This situation may improve following a recently reported AR crystal structure, but there are still barriers to overcome in terms of comprehensive biophysical study. In this review, we summarize the three components of the apelinergic system in terms of structure-function correlation, with a particular focus on isoform-dependent properties, underlining the potential for regulation of the system through multiple endogenous ligands and isoforms, isoform-dependent pharmacological properties, and biological membrane-mediated receptor interaction. © 2018 American Physiological Society. Compr Physiol 8:407-450, 2018.

Association of apelin and apelin receptor with the risk of coronary artery disease: a meta-analysis of observational studies

It is well established that apelin-APLNR (apelin receptor) pathway plays a central role in cardiovascular system. In this meta-analysis, we summarized published results on circulating apelin concentration in association with coronary artery disease (CAD), apelin and APLNR genetic polymorphism(s) in predisposition to CAD risk and circulating apelin changes after surgical treatment for CAD. The results from 15 articles were pooled. Two authors independently took charge of literature search, article selection and information collection. Overall, circulating apelin concentration was significantly lower in CAD patients (N=1021) than in controls (N=654) (weighted mean difference [WMD]: -1.285 ng/mL, 95% confidence interval [CI]: -1.790 to -0.780, P<0001), with significant heterogeneity (I²=99.3%) but without publication bias. For the association of APLNR gene rs9943582 polymorphism with CAD (patients/controls: 5975/4717), the mutant T allele was associated with a 5.2% increased risk relative to the wild C allele (odds ratio: 1.052, 95% CI: 0.990 to 1.117, P=0.100), without heterogeneity (I²=0.0%) or publication bias. Circulating apelin was increased significantly after surgical treatment for CAD (N=202) (WMD: 2.011 ng/mL, 95% CI: 0.541 to 3.481, P=0.007), with significant heterogeneity (I²=98.0%). Stratified analyses showed that circulating apelin was significantly reduced in studies with age- and sex-matched patients and controls (WMD: -1.881 ng/mL, 95% CI: -2.457 to -1.304, P<0.001) and with total sample size ≥125 (WMD: -1.657 ng/mL, 95% CI: -2.378 to -0.936, P<0.001), relative to studies without matching reports and with total sample size <125. In brief, our results suggested that circulating apelin was a prominent athero-protective marker against the development of CAD.

Biochemical and genetic role of apelin in essential hypertension and acute coronary syndrome

BACKGROUND

Apelin-APJ pathway has emerged as a potent regulator of blood pressure (BP) and blood flow in vasculature and heart. Variants in apelin gene may affect the vascular tone in peripheral circulation or heart, thereby predisposing to cardiovascular diseases. The aim of our study was to investigate the association of two apelin gene polymorphisms rs3761581 and rs2235312, and apelin levels in patients with essential hypertension (EH) and acute coronary syndrome (ACS).

METHODS

The study comprised of three groups namely, (1) 118 healthy control subjects, (2) 92 EH patients, and (3) 60 ACS patients. DNA was extracted from peripheral blood leukocytes and genotyping was performed by SNaPshot method. Plasma apelin 13 levels were estimated using ELISA.

RESULTS

EH and ACS patients had a significantly lower level of apelin 13, regardless of gender (p=0.003, p=0.017, respectively). Interestingly, the female EH and ACS patients had lower levels of apelin 13 than their male counterparts. The G allele of rs3761581 was more apparent in patients especially in ACS than the controls.

CONCLUSION

Reduced apelin levels may enhance vasoconstriction to influence high BP and heart's workload in EH and ACS. Genetic involvement of apelin needs to be established in well-defined larger sample size.

Search for Genetic Variant in the Apelin Gene by Resequencing and Association Study in European Subjects

AIMS

Apelin is a peptide produced and secreted by white adipose tissue. It is synthesized as preproapelin, a protein containing 77 aminoacids which is then cleaved to shorter active fragments. As an adipokine, apelin plays a role in the regulation of many biological functions, including body energy homeostasis and glucose metabolism, water balance, and immunity. We have recently demonstrated that subjects with type 2 diabetes (T2D) have significantly higher serum apelin levels compared with controls, and that these levels associate with fasting glucose, basal disposition index, age, and diagnosis of T2D. The first aim of this study was to search for sequence variants in the apelin gene (APLN), located on chromosome Xq25-q26.1 that may associate with serum levels of apelin. The second aim was to analyze the possible association between diabetes and diabetes-related traits and APLN variants.

METHODS

We designed a two-step genetic association study. Step one consisted of an initial screen of 100 individuals selected from the extremes of the apelin distribution levels wherein we sequenced the APLN gene to identify common variants. In step two, the rs181301686 with a minor allele frequency >0.2 was genotyped in 917 individuals to explore its association with T2D and diabetes-related traits.

RESULTS

Five sequence variations were found across the APLN gene. To test for association with apelin levels, the rs181301686 and rs2281069 single-nucleotide polymorphisms were genotyped in 256 subjects for whom serum apelin levels were available. No significant differences were observed in apelin levels between genotypes. Association analysis in 917 individuals did not show significant differences between APLN genotypes and diabetes and diabetes-related traits.

CONCLUSIONS

Resequencing of the apelin gene in subjects stratified by low or high apelin levels identified five APLN variants in an European population. No association was found between the most frequent variant, diabetes, and metabolic parameters.

APJ receptor A445C gene polymorphism in Turkish patients with coronary artery disease

Coronary artery disease (CAD) is a disease in which a waxy substance called plaque builds up inside the coronary arteries. Apelin is a novel endogenous peptide with inotropic and vasodilatory properties and is the ligand for the angiotensin receptor-like 1 (APJ) receptor. We aimed to determine genotype and allele frequencies of APJ receptor A445C gene polymorphism in Turkish patients with CAD and healthy controls by RFLP-PCR. This study was performed on 159 unrelated CAD patients and 62 healthy controls. We obtained AA, AC and CC genotype frequencies in CAD patients as 41.5%, 49.1% and 9.4%, respectively. In the control group, frequencies of genotypes were found as 35.5% for AA, 48.4% for AC and 16.1% for CC. We did not observe difference in APJ receptor A445C polymorphism between CAD patients and healthy controls (χ(2) = 2.178; df = 2; P = 0.336). The A allele was encountered in 66% (210) of the CAD and 59.7% (74) of the controls. The C allele was seen in 34% (108) of the CAD and 40.3% (50) of the controls. Allele frequencies of interested genes were not significantly different between groups (χ(2) = 1.57; df = 1; p = 0.225). The frequencies of APJ receptor A445C genotype were not significantly different between control and patients. None of the three APJ receptor A445C genotypes, AA, AC and CC displayed significant difference in CAD patients. We did not find any difference in the clinical parameters except for weight and diastolic blood pressure levels in the AA, AC and CC genotypes of patients. Individuals with CC genotypes had significantly higher weight, systolic and diastolic blood pressure levels and systolic blood pressure than other genotypes, P ≤ 0.05. In addition, HDL-C level was found decreased, but this reduction was not statistically significant. Contrarily, the low levels of weight, SBP, DBP and TC were statistically significant in the subjects with AA genotype in CAD. In conclusion, CC genotype carriers may have more risk than other genotypes in the development of hypertension in CAD, but not AAgenotype carriers. We suggest that this polymorphism may not be a marker of CAD, but it may cause useful in function of the apelin/APJ system and may be a genetic predisposing factor for diagnostic processes and can be helpfull in finding new treatment strategies. We think that it is required to further comprehensive studies in order to make clear this situation in CAD.

MicroRNA-765 influences arterial stiffness through modulating apelin expression

The present study aims to discover single nucleotide polymorphisms (SNPs) at the apelin gene (APLN) in relation to arterial stiffness, and to explore its molecular mechanisms. A two-step genetic association study was conducted using 799 and 937 subjects in the screening and validation data, respectively. Four tagging SNPs of APLN were tested. SNP rs3115757 was significantly associated with stiffness parameters (β, Ep and PWV) in women, but not in men. The function of rs3115757 was tagged by rs3115758 which is located in miR-765 binding site in the 3' untranslated region of APLN. The reporter assay confirmed that different alleles of rs3115758 interfered with miR-765 binding and then modified APLN expression. Over-expression of miR-765 in endothelial cells decreased mRNA and protein levels of APLN, which further inhibited the phosphorylation of eNOS and ERK/Akt/AMPK signaling. Collectively, our data showed that rs3115758 accounts for the susceptibility of arterial stiffening through miR-765-induced APLN repression.

Genetic differences and aberrant methylation in the apelin system predict the risk of high-altitude pulmonary edema

Hypoxia-inducible factor stimulates the expression of apelin, a potent vasodilator, in response to reduced blood arterial oxygen saturation. However, aberrations in the apelin system impair pulmonary vascular function, potentially resulting in the development of high-altitude (HA)-related disorders. This study aimed to elucidate the genetic and epigenetic regulation of apelin, apelin receptor (APLNR), and endothelial nitric oxide synthase (NOS3) in HA adaptation and HA pulmonary edema (HAPE). A genome-wide association study and sequencing identified variants of apelin, APLNR, and NOS3 that were validated in a larger sample size of HAPE-patients (HAPE-p), HAPE-free controls (HAPE-f), and healthy highland natives (HLs). Apelin-13 and nitrite levels and apelin and NOS3 expression were down-regulated in HAPE-p (P < 0.001). Among the several studied polymorphisms, apelin rs3761581, rs2235312, and rs3115757; APLNR rs11544374 and rs2282623; and NOS3 4b/4a, rs1799983, and rs7830 were associated with HAPE (P < 0.03). The risk allele rs3761581G was associated with a 58.6% reduction in gene expression (P = 0.017), and the risk alleles rs3761581G and rs2235312T were associated with low levels of apelin-13 and nitrite (P < 0.05). The latter two levels decreased further when both of these risk alleles were present in the patients (P < 0.05). Methylation of the apelin CpG island was significantly higher in HAPE-p at 11.92% than in HAPE-f and HLs at ≤ 7.1% (P < 0.05). Moreover, the methylation effect was 9% stronger in the 5' UTR and was associated with decreased apelin expression and apelin-13 levels. The rs3761581 and rs2235312 polymorphisms and methylation of the CpG island influence the expression of apelin in HAPE.

The assessment of the relationship between variations in the apelin gene and coronary artery disease in Turkish population

Objective:

Apelin is a novel endogenous peptide with inotropic and vasodilatory properties and is the ligand for the angiotensin receptor-like 1 (APJ) receptor. The aim of the study was to investigate the association of 2 single-nucleotide polymorphisms (SNPs) in the apelin gene with susceptibility to coronary artery disease (CAD) in the Turkish population.

Methods:

The present observational case-control study consisted of 244 subjects (134 angiographically proven CAD patients and 110 healthy controls) aged 30-65 years. The association of 2 SNPs (rs3115758 and rs3115759) in the apelin gene and CAD risk was investigated. Real-time polymerase chain reaction (RT-PCR) was used to analyze the 2 SNPs in both the CAD and the healthy subjects. Allele and genotype frequencies between patients and control groups were compared using the Chi-square (χ²) test. The relationships of the 2 polymorphisms with the presence of CAD were determined with multiple binary logistic regression analysis after adjustment for CAD risk factors.

Results:

TT and AA risk genotypes of the rs3115758 and rs3115759 variants in the apelin gene were found to be significantly related with the risk of CAD with the same power (OR: 6.36, 95% CI: 1.41-28.6) (p=0.007). After adjustments for traditional CAD risk factors, the homozygous TT genotype for rs3115758 and AA genotype for rs3115759 increased the CAD risk, both with an OR of 5.91.

Conclusion:

Genetic variants in the apelin gene are significantly associated with the risk of CAD in the Turkish population.

Association of 5 Well-Defined Polymorphisms in the Gene Encoding Transforming Growth Factor-β1 With Coronary Artery Disease Among Chinese Patients With Hypertension

We assessed the association between 5 well-defined polymorphisms of the transforming growth factor-β1 (TGFB1) gene and coronary artery disease (CAD) among patients with hypertension from northeast China. All study participants were classified into patients with CAD (n = 679) and controls (n = 686) according to angiographic results. Genotyping was carried out with the ligase detection reaction method. In single-locus analysis, only genotypes of rs1800469 differed significantly between patients with CAD and controls ( P = .001); patients carrying the mutant allele of rs1800469 exhibited a 73% increased risk of CAD ( P < .001). Haplotype analysis indicated that haplotype A-T-T-C-C (alleles in the order of rs1800468, rs1800469, rs1800470, rs1800471, and rs1800472) was associated with a 1.49-fold increased risk ( P = .003). Interaction analysis identified an overall best 3-locus model including rs1800469, rs1800468, and rs1800471 ( P = .003). Taken together, we identified a synergistic interaction between TGFB1 gene multiple polymorphisms that entailed greater risk of CAD in Chinese patients.

Adipose tissue and vascular inflammation in coronary artery disease

Obesity has become an important public health issue in Western and developing countries, with well known metabolic and cardiovascular complications. In the last decades, evidence have been growing about the active role of adipose tissue as an endocrine organ in determining these pathological consequences. As a consequence of the expansion of fat depots, in obese subjects, adipose tissue cells develope a phenotypic modification, which turns into a change of the secretory output. Adipocytokines produced by both adipocytes and adipose stromal cells are involved in the modulation of glucose and lipid handling, vascular biology and, moreover, participate to the systemic inflammatory response, which characterizes obesity and metabolic syndrome. This might represent an important pathophysiological link with atherosclerotic complications and cardiovascular events. A great number of adipocytokines have been described recently, linking inflammatory mileu and vascular pathology. The understanding of these pathways is crucial not only from a pathophysiological point of view, but also to a better cardiovascular disease risk stratification and to the identification of possible therapeutic targets. The aim of this paper is to review the role of Adipocytokines as a possible link between obesity and vascular disease.

Elevated blood pressure: Our family's fault? The genetics of essential hypertension

AIM

To provide an updated review on current genetic aspects possibly affecting essential hypertension (EH), and to further elucidate their role in EH.

METHODS

We searched for genetic and epigenetic factors in major studies associated with EH between Jan 2008-Oct 2013 using PubMed. We limited our search to reviews that discussed mostly human studies, and were accessible through the university online resource. We found 11 genome wide association studies (GWAS), as well as five methylation and three miRNA studies that fit our search criteria. A distinction was not made between genes with protective effects or negative effects, as this article is only meant to be a summary of genes associated with any aspect of EH.

RESULTS

We found 130 genes from the studies that met our inclusion/exclusion criteria. Of note, genes with multiple study references include: STK39, CYP17A1, MTHFR-NPPA, MTHFR-NPPB, ATP2B1, CSK, ZNF652, UMOD, CACNB2, PLEKHA7, SH2B3, TBX3-TBX5, ULK4, CSK-ULK3, CYP1A2, NT5C2, CYP171A, PLCD3, SH2B3, ATXN2, CACNB2, PLEKHA7, SH2B3, TBX3-TBX5, ULK4, and HFE. The following genes overlapped between the genetic studies and epigenetic studies: WNK4 and BDKRB2. Several of the identified genes were found to have functions associated with EH. Many epigenetic factors were also correlated with EH. Of the epigenetic factors, there were no articles discussing siRNA and its effects on EH that met the search criteria, thus the topic was not included in this review. Among the miRNA targets found to be associated with EH, many of the genes involved were also identified in the GWAS studies.

CONCLUSION

Genetic hypertension risk algorithms could be developed in the future but may be of limited benefit due to the multi-factorial nature of EH. With emerging technologies, like next-generation sequencing, more direct causal relationships between genetic and epigenetic factors affecting EH will likely be discovered creating a tremendous potential for personalized medicine using pharmacogenomics.

The contributory role of angiotensin receptor-like 1 gene multiple polymorphisms in hypertension among northeastern Han Chinese

Background and Objective

Via direct sequencing, we have recently identified six common polymorphisms in angiotensin receptor-like 1 (AGTRL1) gene, and found only two polymorphisms were significantly associated with hypertension in a family-based analysis on 1,015 southern Han Chinese. Extending our previous work and considering the ubiquity of epistasis in determining disease susceptibility, we, in this study, sought to explore the potential interaction of AGTRL1 gene six polymorphisms with hypertension in a large northeastern Han Chinese population.

Methods and Results

This was a case-control study involving 1,009 sporadic hypertensive patients and 756 normotensive controls. Data were analyzed by Haplo.Stats and multifactor dimensionality reduction (MDR) softwares. There were no deviations from Hardy-Weinberg equilibrium for all polymorphisms. The genotypes and alleles of rs7119675 and rs11544374 differed significantly between the two groups (P<0.0005), even after the Bonferroni correction. Under three genetic models, significant association was consistently observed for rs7119675 and rs11544374, and this association was independent of confounding factors. Taking rs7119375 as an example, the odds of having hypertension was 2.46 (95% confidence interval (95% CI): 2.06–2.94), 2.82 (95% CI: 2.29–3.46) and 3.97 (95% CI: 2.37–6.64) under additive, dominant and recessive models (P<0.001), respectively, whereas the adjusted risk estimates were slightly attenuated but still significant. The frequencies of most derived haplotypes differed significantly between patients and controls. Haplotype-phenotype analyses indicated marginal association for triglyceride (P_Sim = 0.011) and total cholesterol (P_Sim = 0.025) in patients and for triglyceride in controls (P_Sim = 0.023). The overall best MDR model included rs11544374, rs7119375 and rs948847 with the maximal testing accuracy of 0.737 and cross-validation consistency of 10 out of 10 (P<0.0001). Further interaction entropy graph suggested that the interaction of rs7119375 with rs11544374 and rs948847 was strongly antagonized.

Conclusions

Our findings demonstrate that AGTRL1 genetic polymorphisms might contribute to the development of hypertension independently and/or through complex interaction.

Replication of the top 10 most significant polymorphisms from a large blood pressure genome-wide association study of northeastern Han Chinese East Asians

The replication of genome-wide significant association signals in independent populations is a practical approach for characterizing gene-disease relationships. Therefore, we sought to explore the top 10 polymorphisms from a large blood pressure genome-wide association study of northeastern Han Chinese East Asians. This was a hospital-based study involving 1009 patients with essential hypertension and 756 normotensive controls from Qiqihar city, China. Genotyping was conducted with a polymerase chain reaction-ligase detection reaction method. All polymorphisms except for rs6825911 satisfied Hardy-Weinberg equilibrium. Overall, the genotype differences between the patients and controls were significant for rs35444 (P<0.001), rs11191548 (P=0.017) and rs17249754 (P=0.017). The per-minor-allele odds ratios of rs35444, rs11191548 and rs17249754 were 0.54 (95% confidence interval (95% CI): 0.46-0.62; P<0.01), 1.23 (95% CI: 1.07-1.43; P=0.005) and 1.23 (95% CI: 1.07-1.41; P=0.004), respectively. Similarly, the carriers of minor homozygotes had a significant reduction in adjusted systolic and diastolic blood pressure for rs35444 (P<0.01) but an increase for both rs11191548 (P<0.01) and rs17249754 (P<0.04). Further application of the genetic risk score method indicated that subjects with risk scores of 8, 10 and 12-16 had 1.66-fold (95% CI: 1.01-2.72), 1.72-fold (95% CI: 1.03-2.86) and 1.97-fold (95% CI: 1.12-3.46) increases, respectively, in the odds of developing hypertension, and similar increases were also observed for blood pressure. Taken together, our findings demonstrate that although only three of the top 10 polymorphisms were successfully validated in the northeastern Han Chinese population, the genetic risk score analyses led us to more profound insights into the possible joint effects of multiple polymorphisms on hypertension risk and blood pressure variation.