Genes and hypertension

Investigation of epigenetics insights of hypertension: A bibliometric analysis

PURPOSE

Hypertension remains a major risk factor for myocardial infarction, heart failure, end-stage renal disease, and stroke. Multiple genes are involved in the process of hypertension with an additional dimension of interaction with the environment. This study conducted a bibliometric analysis of publications in the field of hypertension and epigenetics over the past 10 years to summarize the current status of the field and analyze the trends in the field.

METHODS

On February 5, 2023, we chose the web of science core collection database as the study data source. VOS viewer 1.6.18 and Cite Space 6.1.6 were used to examine publications of research on hypertension and epigenetics that were published between 2013 and 2022. We looked through the papers for journals, organizations, nations and regions, authors, and key terms.

RESULTS

This analysis covered a total of 1535 papers on studies into hypertension and epigenetics. There were 7279 authors, 83 nations, 1983 organizations, and 606 journals in all of the articles. In the USA, 540 publications were the most. The institution with the most publications was Harvard Medical School. The author with the most articles was Zhao Lubo.

CONCLUSION

This study summarizes the global research trends in hypertension and epigenetics. Publications in this field have increased year by year in the last decade and the field of research on hypertension and epigenetics has good prospects for growth.

Summary of Known Genetic and Epigenetic Modification Contributed to Hypertension

Hypertension is a multifactorial disease due to a complex interaction among genetic, epigenetic, and environmental factors. Characterized by raised blood pressure (BP), it is responsible for more than 7 million deaths per annum by acting as a leading preventable risk factor for cardiovascular disease. Reports suggest that genetic factors are estimated to be involved in approximately 30 to 50% of BP variation, and epigenetic marks are known to contribute to the initiation of the disease by influencing gene expression. Consequently, elucidating the genetic and epigenetic mediators associated with hypertension is essential for better discernment of its pathophysiology. By deciphering the unprecedented molecular hypertension basis, it could help to unravel an individual's inclination towards hypertension which eventually could result in an arrangement of potential strategies for prevention and therapy. In the present review, we discuss known genetic and epigenetic drivers that contributed to the hypertension development and summarize the novel variants that have currently been identified. The effect of these molecular alterations on endothelial function was also presented.

Epigenetic Mechanisms Involved in Inflammaging-Associated Hypertension

PURPOSE OF REVIEW

This review summarizes the involvement of inflammaging in vascular damage with focus on the epigenetic mechanisms by which inflammaging-induced hypertension is triggered.

RECENT FINDINGS

Inflammaging in hypertension is a complex condition associated with the production of inflammatory mediators by the immune cells, enhancement of oxidative stress, and tissue remodeling in vascular smooth muscle cells and endothelial cells. Cellular processes are numerous, including inflammasome assembly and cell senescence which may involve mitochondrial dysfunction, autophagy, DNA damage response, dysbiosis, and many others. More recently, a series of noncoding RNAs, mainly microRNAs, have been described as possessing epigenetic actions on the regulation of inflammasome-related hypertension, emerging as a promising therapeutic strategy. Although there are a variety of pharmacological agents that effectively regulate inflammaging-related hypertension, a deeper understanding of the epigenetic events behind the control of vessel deterioration is needed for the treatment or even to prevent the disease onset.

CYP17A1-ATP2B1 SNPs and Gene-Gene and Gene-Environment Interactions on Essential Hypertension

Background: The association between the CYP17A1 and ATP2B1 SNPs and essential hypertension (referred to as hypertension) is far from being consistent. In addition to the heterogeneity of hypertension resulting in inconsistent results, gene–gene and gene–environment interactions may play a major role in the pathogenesis of hypertension rather than a single gene or environmental factor.

Methods: A case–control study consisting of 1,652 individuals (hypertension, 816; control, 836) was conducted in Maonan ethnic minority of China. Genotyping of the four SNPs was performed by the next-generation sequencing technology.

Results: The frequencies of minor alleles and genotypes of four SNPs were different between the two groups (p < 0.001). According to genetic dominance model analysis, three (rs1004467, rs11191548, and rs17249754) SNPs and two haplotypes (CYP17A1 rs1004467G-rs11191548C and ATP2B1 rs1401982G-rs17249754A) were negatively correlated, whereas rs1401982 SNP and the other two haplotypes (CYP17A1 rs1004467A-rs11191548T and ATP2B1 rs1401982A-rs17249754G) were positively associated with hypertension risk (p ≤ 0.002 for all). Two best significant two-locus models were screened out by GMDR software involving SNP–environment (rs11191548 and BMI ≥ 24 kg/m²) and haplotype–environment (CYP17A1 rs1004467G-rs11191548C and BMI ≥ 24 kg/m²) interactions (p ≤ 0.01). The subjects carrying some genotypes increased the hypertension risk.

Conclusions: Our outcomes implied that the rs1004467, rs11191548, and rs17249754 SNPs and CYP17A1 rs1004467G-rs11191548C and ATP2B1 rs1401982G-rs17249754A haplotypes have protective effects, whereas the rs1401982 SNP and CYP17A1 rs1004467A-rs11191548T and ATP2B1 rs1401982A-rs17249754G haplotypes showed adverse effect on the prevalence of hypertension. Several SNP–environment interactions were also detected.

Association Between TLR4 Gene Polymorphisms and Risk of Preeclampsia: Systematic Review and Meta-Analysis

BACKGROUND Toll-like receptor 4 (TLR4) plays a pivotal role in the innate immune response and is hyperactivated in preeclampsia (PE). Several researchers have published conflicting evidence for TLR4 rs4986790 and rs4986791 single nucleotide polymorphisms (SNPs) as risk factors for PE. The present meta-analysis was conducted to obtain a more definitive conclusion about the effects of these SNPs on PE susceptibility. MATERIAL AND METHODS To determine the correlation between rs4986790 and rs4986791 polymorphisms in the TLR4 gene and susceptibility to PE, the PubMed, Web of Science, EMBASE, Chinese National Knowledge Infrastructure, and Chinese WANFANG databases were searched for eligible articles. Statistical analysis was performed with STATA software, version 12.0. Pooled odds ratios with corresponding 95% confidence intervals (CIs) were extracted for assessment of correlation strength. RESULTS We identified 5 studies including 578 cases and 631 controls for the rs4986790 SNP and 4 studies including 469 cases and 457 controls for the rs4986791 SNP, mainly from a White population. The pooled analyses showed no statistical relationship between the polymorphisms rs4986790 and rs4986791 and PE susceptibility in 5 genetic models (all P>0.05). Moreover, the allelic and dominant gene models of rs4986790 and the allelic, heterozygous, and dominant gene models of rs4986791 had high heterogeneity. The sensitivity analysis explored potential sources of heterogeneity and confirmed the findings of this meta-analysis. CONCLUSIONS TLR4 rs4986790 and rs4986791 polymorphisms may not be implicated in PE susceptibility, primarily in a White population. More high-quality studies of genetic associations with PE are warranted.

Exploration of CYP21A2 and CYP17A1 polymorphisms and preeclampsia risk among Chinese Han population: a large-scale case-control study based on 5021 subjects

BACKGROUND

Several genome-wide association studies have identified single-nucleotide polymorphisms (SNPs), such as rs4409766, rs1004467, and rs3824755 in CYP17A1 and rs2021783 in CYP21A2, as new hypertension susceptibility genetic variants in the Chinese population. This study aimed to look into the relationship between preeclampsia (PE) and these SNPs in Chinese Han women.

METHODS

Overall, 5021 unrelated pregnant women were recruited, including 2002 patients with PE and 3019 normal healthy controls. The real-time PCR (TaqMan) method was applied to genotype these four polymorphisms.

RESULTS

A statistically obvious difference in the allelic frequencies was observed in CYP21A2 rs2021783 between cases and controls (χ2 = 7.201, Pc = 0.028 by allele), and the T allele was associated with the occurrence and development of PE (OR = 1.151, 95% CI 1.039-1.275). We also found a significant association between rs2021783 and the development of early-onset PE (Pc = 0.008 by genotype, Pc = 0.004 by allele). For rs1004467 and rs3824755, the distribution of allelic frequencies differed markedly between mild PE and control groups (χ2 = 6.843, Pc = 0.036; χ2 = 6.869, Pc = 0.036), and patients with the TT genotype of rs1004467 were less easy to develop mild PE than were those carrying the CT or CC genotype (χ2 = 7.002, Pc = 0.032, OR = 1.306, 95% CI 1.071-1.593). The GG genotype of rs3824755 appeared to a protective effect on the occurrence of mild PE (OR = 0.766, 95% CI 0.629-0.934).

CONCLUSIONS

CYP21A2 rs2021783 appears to be closely related to PE susceptibility, and CYP17A1 rs1004467 and rs3824755 seem to be closely associated with mild PE in Han women.

The CYP17A1 gene polymorphisms are associated with hypercholesterolemia in Han Chinese

BACKGROUND

The CYP17A1 gene has been identified to associate with hypertension in Chinese population. However, the association between CYP17A1 polymorphisms and hypertension-related factors is unclear. The present study aimed to investigate the relation between CYP17A1 single nucleotide polymorphisms (SNPs) and serum lipid profiles.

METHODS

In total, 1350 participants were included in the study. Six SNPs in or near CYP17A1 gene were genotyped in a Han Chinese population in two stages.

RESULTS

There was a statistically significant association of rs1004467 (adjusted odds ratio = 0.783, 95% confidence interval = 0.667-0.919, p < 0.05) and rs11191548 (adjusted odds ratio = 0.788, 95% confidence interval = 0.672-0.925, p < 0.05) with hypercholesterolemia after adjustment for potential factors. Additionally, the rs1004467 minor G-allele and the rs11191548 minor C-allele were significantly associated with the lower serum total cholesterol levels (p < 0.05 for all).

CONCLUSIONS

The rs1004467 and rs11191548 in the CYP17A1 gene are associated with a decreased risk of hypercholesterolemia and lower serum TC levels in Han Chinese.

A system view and analysis of essential hypertension

OBJECTIVES

The goal of this study was to investigate genes associated with essential hypertension from a system perspective, making use of bioinformatic tools to gain insights that are not evident when focusing at a detail-based resolution.

METHODS

Using various databases (pathways, Genome Wide Association Studies, knockouts etc.), we compiled a set of about 200 genes that play a major role in hypertension and identified the interactions between them. This enabled us to create a protein-protein interaction network graph, from which we identified key elements, based on graph centrality analysis. Enriched gene regulatory elements (transcription factors and microRNAs) were extracted by motif finding techniques and knowledge-based tools.

RESULTS

We found that the network is composed of modules associated with functions such as water retention, endothelial vasoconstriction, sympathetic activity and others. We identified the transcription factor SP1 and the two microRNAs miR27 (a and b) and miR548c-3p that seem to play a major role in regulating the network as they exert their control over several modules and are not restricted to specific functions. We also noticed that genes involved in metabolic diseases (e.g. insulin) are central to the network.

CONCLUSION

We view the blood-pressure regulation mechanism as a system-of-systems, composed of several contributing subsystems and pathways rather than a single module. The system is regulated by distributed elements. Understanding this mode of action can lead to a more precise treatment and drug target discovery. Our analysis suggests that insulin plays a primary role in hypertension, highlighting the tight link between essential hypertension and diseases associated with the metabolic syndrome.

The Association of ADRB1 and CYP2D6 Polymorphisms With Antihypertensive Effects and Analysis of Their Contribution to Hypertension Risk

BACKGROUND

Genetic factors have a vital influence on the pathogenesis of hypertension. In this retrospective study, we aimed to evaluate the association of ADRB1 and CYP2D6 polymorphisms with antihypertensive effects and perform an analysis of their contribution to hypertension risk.

METHODS

A total of 261 healthy individuals and 261 essential hypertension patients treated with metoprolol for 12 weeks were enrolled. ADRB1 and CYP2D6 genotypes were identified by xTAG liquid chip technology. We used multivariate logistic regression and a generalized linear mixed model to assess hypertension-related risk factors.

RESULTS

The allele frequencies of ADRB1 and CYP2D6 variants were 59.8% and 64.6% in the essential hypertension group and 70.3% and 65.9% in the controls, respectively. The genotype and allele distribution of ADRB1 were significantly different between the 2 groups (P < 0.05), but there was no significant difference in CYP2D6 distribution (P = 0.91 and 0.88). By logistic regression analysis, high fasting plasma glucose, smoking, high triglyceride and the Gly/Gly polymorphism in Arg389Gly ADRB1 all emerged as independent risk factors for hypertension. Additionally, the ADRB1 genotype played a major role in the antihypertensive effect of metoprolol and the patients with the Gly389Gly genotype showed a significantly better response to metoprolol than did those with a heterozygous ADRB1 mutation (Arg389Gly) (P = 0.027).

CONCLUSIONS

The results demonstrate that Gly/Gly polymorphism in Arg389Gly ADRB1 was an independent risk factor together with high fasting plasma glucose, smoking and high triglyceride; moreover, the patients who carried the Gly389Gly genotype had a significantly improved metoprolol antihypertensive effect than those with ADRB1.

Common variant rs11191548 near the CYP17A1 gene is associated with hypertension and the serum 25(OH) D levels in Han Chinese

The CYP17A1 gene, which encodes17α-hydroxylase and 17,20-lyase, has been identified as a common hypertension susceptibility locus in a European population. However, the association between CYP17A1 polymorphisms and hypertension is unclear in the Chinese population as well as in the role of serum 25(OH) D levels. Six single nucleotide polymorphisms (SNPs) in CYP17A1 were genotyped in two stages in a Han Chinese population, and the serum 25(OH) D levels were measured. Analysis in stage 1 showed that the rs1004467 minor G-allele and rs11191548 minor C-allele in CYP17A1 were significantly associated with a decreased risk of hypertension and higher serum 25(OH) D levels (all P < 0.05). The larger sample in stage 2 also showed that a mutation in rs11191548 was significantly associated with a decreased risk of hypertension (adjusted OR = 0.707, 95% CI: 0.553-0.904, P = 0.006). The rs11191548 minor C-allele was associated with higher serum 25(OH) D levels in hypertensive subjects (βadj ± SEM = 0.094 ± 0.949, P = 0.003) and controls (βadj ± SEM = 0.128 ± 1.025, P < 0.001). In conclusion, the rs11191548 CYP17A1 gene mutation was associated with hypertension and the serum 25(OH) D levels in Han Chinese.

Association of CYP17A1 Genetic Polymorphisms and Susceptibility to Essential Hypertension in the Southwest Han Chinese Population

Background

The CYP17A1 gene encodes for cytochrome P450 enzyme CYP17A1, which is involved with the steroidogenic pathway including mineralocorticoids. The CYP17A1 polymorphisms might affect enzyme activity, then leading to a state of mineralocorticoid 11-deoxycorticosterone excess characterized by hypertension, suppressed plasma renin activity, and low aldosterone concentrations. The aim of this study was to investigate the contribution of CYP17A1 polymorphisms in inducing the susceptibility to essential hypertension among the Southwest Han Chinese population.

Material/Methods

Eight single nucleotide polymorphisms of CYP17A1 were genotyped in a case-control study for samples by polymerase chain reaction-restriction fragment length polymorphism analysis.

Results

The polymorphisms rs11191548 and rs4919687 were significantly associated with hypertension risk, which was confirmed by systolic and diastolic blood pressure distribution analyses between different genotype groups, and these two polymorphisms were found in linkage disequilibrium. The rs4919687 polymorphism was estimated to cause the destruction of exonic splicing silencer (ESR and Motif 3) sites and to transform the transcription factor AREB6 binding site, respectively, in the bioinformatics analyses. The haplotypes rs4919686A-rs3740397G -rs4919687C-rs743572C-rs11191548C and rs4919686A-rs3740397G-rs4919687T-rs743572C- rs11191548T were found to be susceptible to essential hypertension.

Conclusions

Our findings suggest that the CYP17A1 polymorphisms could be a genetic risk factor for essential hypertension among the Yunnan Han Chinese population, which would have implications for the treatment of this complex disorder.

Animal models for the study of primary and secondary hypertension in humans

Hypertension is a significant cause of morbidity and mortality worldwide. It is defined as systolic and diastolic blood pressures (SBP/DBP) >140 and 90 mmHg, respectively. Individuals with an SBP between 120 and 139, or DBP between 80 and 89 mmHg, are said to exhibit pre-hypertension. Hypertension can have primary or secondary causes. Primary or essential hypertension is a multifactorial disease caused by interacting environmental and polygenic factors. Secondary causes are renovascular hypertension, renal disease, endocrine disorders and other medical conditions. The aim of the present review article was to examine the different animal models that have been generated for studying the molecular and physiological mechanisms underlying hypertension. Their advantages, disadvantages and limitations will be discussed.

Phenylethanolamine N-methyltransferase gene expression in adrenergic neurons of spontaneously hypertensive rats

Epinephrine is synthesised by the catecholamine biosynthetic enzyme, phenylethanolamine N-methyltransferase (PNMT), primarily in chromaffin cells of the adrenal medulla and secondarily in brainstem adrenergic neurons of the medulla oblongata. Epinephrine is an important neurotransmitter/neurohormone involved in cardiovascular regulation; however, overproduction is detrimental with negative outcomes such as cellular damage, cardiovascular dysfunction, and hypertension. Genetic mapping studies have linked elevated expression of PNMT to hypertension. Adrenergic neurons are responsible for blood pressure regulation and are the only PNMT containing neurons in the brainstem. The purpose of the current study was to determine whether elevated blood pressure found in adult spontaneously hypertensive rats (SHR) is associated with altered regulation of the PNMT gene in catecholaminergic neurons. C1, C2, and C3 adrenergic regions of 16 week old Wistar Kyoto (WKY) and SHR rats were excised using micropunch microdissection for mRNA expression analyses. Results from the current study confirm high PNMT mRNA expression in all three brainstem adrenergic regions (C1: 2.96-fold; C2: 2.17-fold; C3 1.20-fold) of the SHR compared to normotensive WKY rats. Furthermore, the immediate early gene transcription factor (Egr-1) mRNA was elevated in the C1 (1.84-fold), C2 (8.57-fold) and C3 (2.41-fold) regions in the brainstem of the SHR. Low mRNA expression for transcription factors Sp1 and GR was observed, while no change was observed for AP-2. The findings presented propose that alterations in the PNMT gene regulation in the brainstem contribute to enhanced PNMT production and epinephrine synthesis in the SHR, a genetic model of hypertension.

Endothelial nitric oxide synthase gene polymorphisms are associated with cardiovascular risks in prehypertensives

Though endothelial nitric oxide synthase (eNOS) gene polymorphism is documented in the causation of hypertension, its role in prehypertension has not been investigated. The present study was conducted in 172 subjects divided into prehypertensives (n = 57) and normotensives (n = 115). Cardiovascular (CV) parameters including baroreflex sensitivity (BRS) by continuous BP variability assessment and sympathovagal imbalance (SVI) by heart rate variability analysis were recorded. Biochemical parameters for insulin resistance (homeostatic model for assessment of insulin resistance), oxidative stress, lipid risk factors, renin, and inflammatory parameters were measured. Genotyping for eNOS polymorphisms rs1799983 (298G>T) and rs2070744 (-786T>C) was performed by polymerase chain reaction-restriction fragment length polymorphism method. Multiple regression analysis was done to assess the association between SVI and metabolic markers, and multivariate logistic regression was done to determine the prediction of prehypertension status by genotype, BRS, and ratio of low-frequency to high-frequency in these subjects. The BP variability, heart rate variability, and biochemical parameters were significantly altered in prehypertensives. The eNOS polymorphisms were found to be associated with prehypertension. BRS, the marker of SVI, was significantly associated with BP, homeostatic model for assessment of insulin resistance, and tumor necrosis factor alpha in 298GG genotype of prehypertensive population. The eNOS gene polymorphisms appear to be associated with prehypertension. 298G>T and -786T>C contribute to SVI in young prehypertensives attributed by insulin resistance and inflammation. The CV risks were associated with prehypertension status in prehypertensives expressing both 298GG and -786TT genotypes. Association of CV risks with SVI appears to be stronger in prehypertensives expressing GG genotype.

Molecular genetics of essential hypertension

Hypertension is a major public health problem in the developing as well as in developed countries due to its high prevalence and its association with coronary heart disease, renal disease, stroke, peripheral vascular disease, and related disorders. Essential hypertension (EH) is the most common diagnosis in this disease, suggesting that a monocausal etiology has not been identified. However, a number of risk factors associated with EH have also been identified such as age, sex, demographic, environmental, genetic, and vascular factors. Recent advances in molecular biological research had achieved clarifying the molecular basis of Mendelian hypertensive disorders. Molecular genetic studies have now identified mutations in several genes that cause Mendelian forms of hypertension in humans. However, none of the single genetic variants has emerged from linkage or association analyses as consistently related to the blood pressure level in every sample and in all populations. Besides, a number of polymorphisms in candidate genes have been associated with differences in blood pressure. The most prominent candidate has been the polymorphisms in the renin-angiotensin-aldosterone system. In total, EH is likely to be a polygenic disorder that results from inheritance of a number of susceptibility genes and involves multiple environmental determinants. These determinants complicate the study of blood pressure variations in the general population. The complex nature of the hypertension phenotype makes large-scale studies indispensable, when screening of familial and genetic factors was intended. In this review, recent genetic studies exploring the molecular basis of EH, including different molecular pathways, are highlighted.

Associations between ADRB1 and CYP2D6 gene polymorphisms and the response to β-blocker therapy in hypertension

OBJECTIVE

To investigate the associations between β1-adrenergic receptor (ADRB1) and cytochrome P450 2D6 (CYP2D6) gene polymorphisms and β-blocker treatment outcomes in patients with hypertension.

METHODS

Chinese patients with essential hypertension were treated with the β-blocker metoprolol and followed up for 12 weeks. xTAG® liquid-chip technology was used for CYP2D6 100 C > T and ADRB1 1165G > C genotyping. Associations between gene polymorphisms and antihypertensive therapy outcomes were assessed by generalized linear model fitting. A decrease of ≥ 10 mmHg in systolic blood pressure indicated an effective treatment outcome.

RESULTS

A total of 93 patients were included in the study. Mutant allele frequencies of 61.29% and 58.60% were obtained for ADRB1 and CYP2D6, respectively. There was no significant interaction between the effects of ADRB1 and CYP2D6 gene polymorphisms on treatment outcome. Patients homozygous for the mutant ADRB1 genotype (CC) had better treatment outcomes than those heterozygous for the mutation (GC). Interestingly, β-blocker treatment duration was an independent factor associated with treatment outcome.

CONCLUSIONS

The ADRB1 1165G > C gene polymorphism and β-blocker treatment duration are independent factors associated with β-blocker treatment outcome. These findings suggest that the selection of antihypertensive therapy should take into consideration the patient's genotype.

Association of polymorphisms in prolylcarboxypeptidase and chymase genes with essential hypertension in the Chinese Han population

INTRODUCTION

The prolylcarboxypeptidase (PRCP) gene encodes a membrane protein that acts on angiotensin II (Ang II) and kallikrein to release vasoactive peptides. The chymase (CMA1) gene is important for Ang II generation. Therefore, the two genes might be involved in the pathogenesis of essential hypertension (EH).

MATERIALS AND METHODS

Eleven tag single nucleotide polymorphisms (SNPs) in the PRCP gene and four tag SNPs and G-1903A (rs1800875) polymorphism in the CMA1 gene were genotyped in the Chinese Han population (n=1020) using a polymerase chain reaction-restriction fragment length polymorphism method.

RESULTS

In the PRCP gene, single site analyses indicated that the rs7104980 G allele was a susceptible factor for EH (adjusted odds ratio (OR)=1.98, 95% confidence interval (CI) 1.62-2.43, p=0.3×10(-10)). The protective effect of Hap3 GAGCACTAACA was observed without carrying the susceptible rs7104908 G allele (OR=0.67, 95% CI 0.56-0.81, p=0.3×10(-4)) by haplotype analyses. In the case of the CMA1 gene, no associations with EH were found through single site analyses. However, haplotype analyses showed that Hap16 TTTA significantly increased the risk of EH with OR=3.15 (p=0.0002) which may be driven by interaction with a nearby SNP combination.

CONCLUSIONS

The present results indicated PRCP rs7104980 can be considered as a marker for EH and Hap3 GAGCACTAACA (PRCP) and Hap16 TTTA (CMA1) might be associated with EH in Chinese Han population.

Muscle sympathetic response to arousal predicts neurovascular reactivity during mental stress

Mental stress often begins with a sudden sensory (or internal) stimulus causing a brief arousal reaction, and is followed by a more long lasting stress phase. Both arousal and stress regularly induce blood pressure (BP) increases whereas effects on muscle sympathetic nerve activity (MSNA) are variable. Here we have compared responses of MSNA and BP during arousal induced by an electrical skin stimulus and mental stress evoked by a 3 min paced auditory serial arithmetic test (PASAT) in 30 healthy males aged 33 ± 10 years. In addition, recordings were made of ECG, respiratory movements, electrodermal activity and perceived stress. We also monitored corresponding effects of a cold test (CT: 2 min immersion of a hand in ice water). The arousal stimulus evoked significant inhibition of one or two MSNA bursts in 16 subjects, who were classified as responders; the remaining 14 subjects were non-responders. During mental stress responders showed a significant decrease of MSNA and a lesser BP increase compared to non-responders. In non-responders MSNA was unchanged or increased. Perceived stress was higher in non-responders (P = 0.056), but other measures were similar in the two groups. In non-responders mental stress and the cold test induced increases of BP that lasted throughout the subsequent rest period. During the cold test MSNA and BP increased equally in responders and non-responders. In the whole group of subjects, there was a significant correlation (r = 0.80, P < 0.001) between MSNA responses induced by arousal and by mental stress but not between responses evoked by arousal and the cold test (r < 0.1, P > 0.6). Additionally arousal-induced MSNA change was positively correlated with blood pressure changes during MS (systolic BP: r = 0.48; P < 0.01; diastolic BP: r = 0.42; P < 0.05) but not with blood pressure changes during CT. We conclude that in males the MSNA response to arousal predicts the MSNA and BP responses to mental stress.

Genome-Wide Linkage Analysis of Hemodynamic Parameters Under Mental and Physical Stress in Extended Omani Arab Pedigrees: The Oman Family Study

Background:We performed a genome-wide scan in a homogeneous Arab population to identify genomic regions linked to blood pressure (BP) and its intermediate phenotypes during mental and physical stress tests.Methods:The Oman Family Study subjects (N= 1277) were recruited from five extended families of ~10 generations. Hemodynamic phenotypes were computed from beat-to-beat BP, electrocardiography and impedance cardiography. Multi-point linkage was performed for resting, mental (word conflict test, WCT) and cold pressor (CPT) stress and their reactivity scores (s), using variance components decomposition-based methods implemented in SOLAR.Results:Genome-wide scans for BP phenotypes identified quantitative trait loci (QTLs) with significant evidence of linkage on chromosomes 1 and 12 for WCT-linked cardiac output (LOD = 3.1) and systolic BP (LOD = 3.5). Evidence for suggestive linkage for WCT was found on chromosomes 3, 17 and 1 for heart rate (LOD = 2.3), DBP (LOD = 2.4) and left ventricular ejection time (LVET), respectively. For △WCT, suggestive QTLs were detected for CO on chr11 (LOD = 2.5), LVET on chr3 (LOD = 2.0) and EDI on chr9 (LOD = 2.1). For CPT, suggestive QTLs for HR and LVET shared the same region on chr22 (LOD 2.3 and 2.8, respectively) and on chr9 (LOD = 2.3) for SBP, chr7 (LOD = 2.4) for SV and chr19 (LOD = 2.6) for CO. For △CPT, CO and TPR top signals were detected on chr15 and 10 (LOD; 2.40, 2.08) respectively. Conclusion: Mental stress revealed the largest number of significant and suggestive loci for normal BP reported to date. The study of BP and its intermediate phenotypes under mental and physical stress may help reveal the genes involved in the pathogenesis of essential hypertension.

Vascular endothelial growth factor (VEGF) +405 C/G polymorphism is associated with essential hypertension in a population from Tehran of Iran

Vascular endothelial growth factor (VEGF) has long been recognized as a hypotensive mediator. Little is known regarding the contribution of polymorphisms in VEGF gene to essential hypertension (EH), however. We aimed to investigate the association between +405 VEGF C/G single nucleotide polymorphism (SNP) and occurrence of EH in a sample of patients with diabetes. A study population of 474 subjects with diabetes of which 45.6% (216) had EH was enrolled in this study. Interviews and physical examinations were performed in a clinical setting. Subjects were matched in baseline anthropometric and biochemical characteristics except for total cholesterol. Genotyping of +405 VEGF C/G (rs2010963) SNP was carried out using polymerase chain reaction-restriction fragment length polymorphism. The allelic distribution of the sample did not violate Hardy-Weinberg equilibrium. Subjects with EH had a higher frequency of G allele (P = 0.005). Additionally, those with EH had a significantly higher frequency of GG genotype (P = 0.015). In multivariate logistic regression models controlling for possible confounders, having GG against CC genotype was associated with an odds ratio of 2.51 (95% CI: 1.44-4.38; P = 0.001). Moreover, presence of each G allele was linked to a 1.58-fold increase in risk of having EH (95% CI: 1.200-2.086; P = 0.001). In conclusion, +405 VEGF C/G SNP is associated with EH in patients with diabetes, suggesting presence of G allele and GG or CG genotype confer susceptibility towards EH.

Epigenetics and hypertension

Epigenetics refers to mechanisms for environment-gene interactions (mainly by methylation of DNA and modification of histones) that do not alter the underlying base sequence of the gene. This article reviews evidence for epigenetic contributions to hypertension. For example, DNA methylation at CpG islands and histone acetylation pathways are known to limit nephron development, thereby unmasking hypertension associated with exposure to a high-salt diet. Maternal water deprivation and protein deficiency are shown to increase expression of renin-angiotensin system genes in the offspring. The methylation pattern of a serine protease inhibitor gene in human placentas is shown to be a marker for preeclampsia-associated hypertension. Mental stress induces phenylethanolamine n-methyltransferase, which may act as a DNA methylase and mimic the gene-silencing effects of methyl CpG binding protein-2 on the norepinephrine transporter gene, which, in turn, may exaggerate autonomic responsiveness. A disrupter of telomeric silencing (Dot1) is known to modulate the expression of a connective-tissue growth-factor gene associated with blood vessel remodeling, which could alter vascular compliance and elastance. Dot1a also interacts with the Af9 gene to produce high sodium channel permeability and silences the hydroxysteroid dehydrogenase-11β2 gene, thereby preventing metabolism of cortisol to cortisone and overstimulating aldosterone receptors. These findings indicate targets for environment-gene interactions in various hypertensive states and in essential hypertension.

Common variants in or near FGF5, CYP17A1 and MTHFR genes are associated with blood pressure and hypertension in Chinese Hans

OBJECTIVES

Recent genome-wide association studies have identified a number of variants influencing blood pressure. We aimed to examine whether these associations can be replicated in Chinese.

METHODS

We genotyped eight of these variants (in or near FGF5, CYP17A1, MTHFR, ZNF652, PLCD3, ATP2B1, c10orf107) in a population-based cohort of Chinese Hans (N = 3210). Logistics regression and generalized linear analyses were applied to test for association of each variant with hypertension risk and blood pressure (BP), BMI, waistline and high-sensitivity C-reactive protein (hsCRP), respectively.

RESULTS

Six variants showed directionally consistent association with blood pressure and risk of hypertension, of which four (FGF5, two in CYP17A1, MTHFR) reached significance. The associations were most pronounced for FGF5-rs16998073 [SBP: β = 1.97 mmHg/allele, P = 0.0006; DBP: β = 0.95 mmHg/allele, P = 0.0008, hypertension: odds ratio (OR) 1.36/allele, P = 0.0001]. Effect size of FGF5-rs16998073 on SBP and hypertension were significantly more pronounced in Han Chinese compared to white Europeans. None of these variants was associated with BMI, waistline or hsCRP that are the well established risk factors for hypertension. The genetic risk score, calculated as the sum of BP-increasing alleles of FGF5-rs16998073, CYP17A1-rs11191548, CYP17A1-rs1004467 and MTHFR-rs17367504, was significantly associated with increased SBP (1.16 mmHg/allele, P = 9.01E-5), DBP (0.51 mmHg/allele, P = 4.40E-4) and hypertension risk (OR = 1.22/allele, P = 2.74E-7).

CONCLUSION

Variants in or near FGF5, CYP17A1 and MTHFR contributed to variation in BP and hypertension risk. Effect sizes of these three loci tended to be larger in Chinese than in white Europeans, but more studies with larger sample size are required for a definitive conclusion.

Angiotensin II type 1 receptor gene polymorphism and telomere shortening in essential hypertension

Several genetic studies were carried out among hypertensive patients to assess allelic association at the 1166 position of the 3' untranslated region of angiotensin II type 1 receptor gene. In addition, attempts have also been made to find out whether telomere length attrition is associated with hypertension. The main aim of this study was to examine the association of A1166C polymorphism of angiotensin II type 1 receptor and telomere length with essential hypertension in Egyptian people. Angiotensin II type 1 genotyping and relative telomere length were investigated by PCR in 40 patients of essential hypertension and 15 healthy controls. The homozygous AA1166 allele frequency was 92.8% among the studied subjects. There was no intergroup variation in A allele frequency in normotensive group. The frequency of homozygous A allele was significantly higher in hypertensive than normotensive subjects (97.5 and 80%, respectively) with higher frequencies in male patients. The average telomere length ratio was significantly shorter in hypertensive than in normal subjects (1.08 ± 0.3 and 1.54 ± 0.18, respectively). No correlation was observed between telomere length ratio and body mass index. This study suggests that the homozygous A1166 allele of angiotensin II type 1 and short telomeres may be predisposing factors for essential hypertension in Egyptians and may be involved in the pathogenesis of the disease. Further strategies for treating high-risk patients could result in prevention or delay of end organ damage.

The Renin-Angiotensin System in the Development of Salt-Sensitive Hypertension in Animal Models and Humans

Hypertension is still one of the major causes of death from cardiovascular failure. Increased salt intake may aggravate the rise in blood pressure and the development of consequential damage of the heart, the vessels and other organs. The general necessity of restricted salt intake regardless of blood pressure or salt sensitivity has been a matter of debate over the past decades. This review summarizes the main pathogenic mechanisms of hypertension and salt sensitivity in rat models, particularly in the spontaneously hypertensive rat (SHR), and in patients with essential hypertension (EH). Although SHRs are commonly considered to be salt-resistant, there is much evidence that salt loading may deteriorate blood pressure and cardiovascular function even in these animals. Similarly, EH is not a homogenous disorder - some patients, but not all, exhibit pronounced salt sensitivity. The renin-angiotensin system (RAS) plays a key role in the regulation of blood pressure and salt and fluid homeostasis and thus is one of the main targets of antihypertensive therapy. This review focuses on the contribution of the RAS to the pathogenesis of salt-sensitive hypertension in SHRs and patients with EH.

Angiotensin II type 1 receptor gene A1166C polymorphism and essential hypertension in Chinese: a meta-analysis

Introduction. We performed a meta-analysis with the aim of assessing the association of the angiotensin II type 1 (AT1) receptor gene A1166C polymorphism with essential hypertension in Chinese case-control studies. Methods. Studies were searched from the Chinese Biomedicine Database, the China National Knowledge Infrastructure platform, Pubmed and Medline, using the search terms ‘hypertension’, ‘angiotensin II type 1 receptor’, ‘AT1R’, ‘polymorphism’, ‘China’ and ‘Chinese’, without limiting to any specific language. The strength of the association between the A1166C polymorphism and hypertension was evaluated by the odds ratio (OR) with the corresponding 95% confidence interval (CI). The analyses were performed with Cochrane RevMan software version 4.2.

Results. Overall, the variant genotype AC/CC was associated with a statistically increased essential hypertension risk with the pooled OR 1.48 (95% CI: 1.20—1.83). In the subgroup analyses, the association was also significant among studies using Northern populations, Southern populations, Han Chinese and hospital-based controls. The age did not influence the relationship between the AT 1 receptor A1166C polymorphism and hypertension in the subgroup analyses.

Conclusions. The present meta-analysis suggests that the AT1 receptor 1166 AC/CC genotype is associated with susceptibility to hypertension in the Chinese population.

Non-synonymous single-nucleotide polymorphisms associated with blood pressure and hypertension

In this study, we determined the association of 1180 non-synonymous single-nucleotide polymorphisms (SNPs) with systolic blood pressure (SBP) and hypertensive status. A total of 8842 subjects were taken from two community-based cohorts--Ansung (n=4183) and Ansan (n=4659), South Korea--which had been established for genome-wide association studies (GWAS). Five SNPs (rs16835244, rs2286672, rs6265, rs17237198 and rs7312017) were significantly associated (P-values: 0.003-0.0001, not corrected for genome-wide significance) with SBP in both cohorts. Of these SNPs, rs16835244 and rs2286672 correlated with risk for hypertension. The rs16835244 SNP replaces Ala288 in arginine decarboxylase (ADC) with serine, and rs2286672 replaces Arg172 in phospholipase D2 (PLD2) with cysteine. A comparison of peptide sequences between vertebrate homologues revealed that the SNPs identified occur at conserved amino-acid residues. In silico analysis of the protein structure showed that the substitution of a polar residue, serine, for a non-polar alanine at amino-acid residue 288 affects a conformational change in ADC, and that Arg172 in PLD2 resides in the PX domain, which is important for membrane trafficking. These results provide insights into the function of these non-synonymous SNPs in the development of hypertension. The study investigating non-synonymous SNPs from GWAS not only by statistical association analysis but also by biological relevance through the protein structure might be a good approach for identifying genetic risk factors for hypertension, in addition to discovering causative variations.

Microsatellites and SNPs linkage analysis in a Sardinian genetic isolate confirms several essential hypertension loci previously identified in different populations

Background

A multiplicity of study designs such as gene candidate analysis, genome wide search (GWS) and, recently, whole genome association studies have been employed for the identification of the genetic components of essential hypertension (EH). Several genome-wide linkage studies of EH and blood pressure-related phenotypes demonstrate that there is no single locus with a major effect while several genomic regions likely to contain EH-susceptibility loci were validated by multiple studies.

Methods

We carried out the clinical assessment of the entire adult population in a Sardinian village (Talana) and we analyzed 16 selected families with 62 hypertensive subjects out of 267 individuals. We carried out a double GWS using a set of 902 uniformly spaced microsatellites and a high-density SNPs map on the same group of families.

Results

Three loci were identified by both microsatellites and SNP scans and the obtained linkage results showed a remarkable degree of similarity. These loci were identified on chromosome 2q24, 11q23.1–25 and 13q14.11–21.33. Further support to these findings is their broad description present in literature associated to EH or related phenotypes. Bioinformatic investigation of these loci shows several potential EH candidate genes, several of whom already associated to blood pressure regulation pathways.

Conclusion

Our search for major susceptibility EH genetic factors evidences that EH in the genetic isolate of Talana is due to the contribution of several genes contained in loci identified and replicated by earlier findings in different human populations.

Genetic effect on blood pressure is modulated by age: the Hypertension Genetic Epidemiology Network Study

Genome-wide linkage analysis was performed for systolic and diastolic blood pressures in the Hypertension Genetic Epidemiology Network. We investigated the role of gene-age interactions using a recently developed variance components method that incorporates age variation in genetic effects. Substantially improved linkage evidence, in terms of both the number of linkage peaks and their significance levels, was observed. Twenty-six linkage peaks were identified with maximum logarithm of odds scores ranging between 3.0 and 4.6, 15 of which were cross-validated by the literature. The chromosomal region 1p36 that showed the highest logarithm of odds score in our study was found to be supported by evidence from 3 studies. The new method also led to vastly improved validation across ethnic groups. Ten of the 15 supported linkage peaks were cross-validated between 2 different ethnic groups, and 2 peaks on chromosomal region 1q31 and 16p11 were validated in 3 ethnic groups. In conclusion, this investigation demonstrates that genetic effects on blood pressure vary by age. The improved genetic linkage results presented here should help to identify the specific genetic variants that explain the observed results.

Homozygosity by descent mapping of blood pressure in the Old Order Amish: evidence for sex specific genetic architecture

BACKGROUND

High blood pressure is a well established risk factor for morbidity and mortality acting through heart disease, stroke and cardiovascular disease. Genome wide scans have linked regions of nearly every human chromosome to blood pressure related traits. We have capitalized on beneficial qualities of the Old Order Amish of Lancaster, PA, a closed founder population with a relatively small number of founders, to perform a genome wide homozygosity by descent mapping scan. Each individual in the study has a non zero probability of consanguinity. Systolic and diastolic blood pressures are shown to have appreciable dominance variance components.

RESULTS

Areas of two chromosomes were identified as suggestive of linkage to SBP and 5 areas to DBP in either the overall or sex specific analyses. The strongest evidence for linkage in the overall sample was to Chromosome 18q12 (LOD = 2.6 DBP). Sex specific analyses identified a linkage on Chromosome 4p12-14 (LOD in men only = 3.4 SBP). At Chromosome 2q32-33, an area where we previously reported significant evidence for linkage to DBP using a conventional identity by descent approach, the LOD was 1.4; however an appreciable sex effect was observed with men accounting for most of the linkage (LOD in men only = 2.6).

CONCLUSION

These results add evidence to a sex specific genetic architecture to blood pressure related traits, particularly in regions of linkage on chromosome 2, 4 and 18.

Multiple genes for essential-hypertension susceptibility on chromosome 1q

Essential hypertension, defined as elevated levels of blood pressure (BP) without any obvious cause, is a major risk factor for coronary heart disease, stroke, and renal disease. BP levels and susceptibility to development of essential hypertension are partially determined by genetic factors that are poorly understood. Similar to other efforts to understand complex, non-Mendelian phenotypes, genetic dissection of hypertension-related traits employs genomewide linkage analyses of families and association studies of patient cohorts, to uncover rare and common disease alleles, respectively. Family-based mapping studies of elevated BP cover the large intermediate ground for identification of genes with common variants of significant effect. Our genomewide linkage and candidate-gene-based association studies demonstrate that a replicated linkage peak for BP regulation on human chromosome 1q, homologous to mouse and rat quantitative trait loci for BP, contains at least three genes associated with BP levels in multiple samples: ATP1B1, RGS5, and SELE. Individual variants in these three genes account for 2-5-mm Hg differences in mean systolic BP levels, and the cumulative effect reaches 8-10 mm Hg. Because the associated alleles in these genes are relatively common (frequency >5%), these three genes are important contributors to elevated BP in the population at large.

Association of genetic polymorphisms of ACADSB and COMT with human hypertension

OBJECTIVES

Genetically hypertensive rats provide an excellent model to investigate the genetic mechanisms of hypertension. We previously identified three differentially expressed genes, Acadsb (short/branched chain acyl-CoA dehydrogenase), Comt (catecholamine-O-methyltransferase), and Pnpo (pyridoxine 5'-phosphate oxidase), in hypertensive and normotensive rat kidneys as potential susceptibility genes for rat hypertension. We examined the association of human homologues of these genes with human hypertension.

METHODS

We sequenced three genes using samples from 48 or 96 hypertensive patients, identified single nucleotide polymorphisms, and genotyped them in a population-based sample of 1818 Japanese individuals (771 hypertensive individuals and 1047 controls).

RESULTS

After adjustments for age, body mass index, present illness (hyperlipidaemia, diabetes mellitus), and lifestyle (smoking, alcohol consumption), multivariate logistic regression analysis revealed that -512A>G in ACADSB was associated with hypertension in women (AA vs AG + GG: odds ratio = 0.70, 95% confidence interval = 0.53-0.94). This single nucleotide polymorphism was in tight linkage disequilibrium with -254G>A. Furthermore, -1187G>C in COMT was associated with hypertension in men (GG vs CG + CC: odds ratio = 0.69, 95% confidence interval = 0.52-0.93) and was in tight linkage disequilibrium with 186C>T. After adjustments described above, -512 A>G and -254G>A in ACADSB were associated with variations in systolic blood pressure. ACADSB was in tight linkage disequilibrium with MGC35392 across a distance of 18.3 kb. COMT was not in linkage disequilibrium with any adjacent genes. Analysis indicated that two haplotypes of COMT were significantly associated with hypertension in men.

CONCLUSION

Our study suggests the possible involvement of genetic polymorphisms in ACADSB and COMT in essential hypertension in the Japanese population.

The molecular basis of pediatric hypertension

Blood pressure, the product of cardiac output and peripheral vascular resistance, follows a circadian rhythm and is altered by a host of circulating and local substances and by many physiologic events. The number of genes, signaling pathways, and systems involved in blood pressure regulation is enormous, and dissecting those factors that are most important in hypertension has proven challenging. This article discusses molecular mechanisms of hypertension in several conditions in which mutations in a single gene give rise to hypertension and then considers the contribution of these and other genes to essential hypertension.

Access to exercise and its relation to cardiovascular health and gene expression in laboratory animals

The interaction between genes and environment can influence cardiovascular disease (CVD). This 16 month study investigated if genes associated with cardiovascular (CV) regulation were expressed differently in animals having: 1) no access to physical activity or exercise (SED), 2) access to hour-long, twice weekly activity (PA), and 3) access every-other-day to a running wheel (EX). Out of 31,000 genes, a CV subset comprising 44 genes was investigated. Ten genes from this subset were expressed differently in EX compared with SED, and 34 genes were expressed differently in PA compared with SED (p<0.05). Total cholesterol (70+/-8 vs. 101+/-9 mg dl(-1)), triglycerides (104+/-8 vs. 127+/-4 mg dl(-1)), resting systolic blood pressure (130+/-3 vs. 141+/-3 mmHg), mean arterial pressure (110+/-2 vs. 120+/-2 mmHg) and heart rate (380+/-6 vs. 405+/-9 beats min(-1)) were lower in EX compared with SED (p<0.05), but intracellular adhesion molecule levels did not differ among groups. Mean gene expressions for Gja1, Fdft1, Edn1, Cd36, and Hmgb2 differed in animals according to access to physical activity. These genes play roles in heart rate, cholesterol biosynthesis, blood pressure, cell adhesion, and transcription and neurogenesis regulation, respectively. In conclusion, a total of 44 CV genes were expressed differently in SED compared to PA and EX; and SED showed more physiological evidence of CVD.

Protection from angiotensin II-induced cardiac hypertrophy and fibrosis by systemic lentiviral delivery of ACE2 in rats

Angiotensin converting enzyme 2 (ACE2), a newly discovered member of the renin-angiotensin system (RAS), is a potential therapeutic target for the control of cardiovascular disease owing to its key role in the formation of vasoprotective peptides from angiotensin II. The aim of the present study was to evaluate whether overexpression of ACE2 could protect the heart from angiotensin II-induced hypertrophy and fibrosis. Lentiviral vector encoding mouse ACE2 (lenti-mACE2) or GFP was injected intracardially in 5-day-old Sprague-Dawley rats. This resulted in expression of mACE2 in cardiac tissue for the duration of the study. Infusion of 200 ng kg-1 min-1 angiotensin II for 4 weeks resulted in an 80 mmHg increase in systolic blood pressure, a significant increase in the heart weight to body weight ratio (HW:BW), and marked myocardial fibrosis in control rats. Transduction with lenti-mACE2 resulted in significant attenuation of the increased HW:BW and myocardial fibrosis induced by angiotensin II infusion. These observations demonstrate that ACE2 overexpression results in protective effects on angiotensin II-induced cardiac hypertrophy and fibrosis.

Genomics, proteomics and integrative "omics" in hypertension research

PURPOSE OF REVIEW

During the past few years, genomics, proteomics and other "omics" fields have been applied extensively to several areas of biomedical research. This review provides an overview and summarizes the current status of applications of these omics fields to essential and secondary hypertension. Some perspectives of these fields for future hypertension research are discussed.

RECENT FINDINGS

Genome-wide scans applying to essential hypertension have demonstrated numerous chromosomal regions with significant and/or suggestive evidence of linkage. The consistency of these results among several different studies is, however, problematic; probably because of the variability in number of families, ethnicity, family types, phenotyping strategy, study design and statistical analyses in those studies. Findings from such studies will be more valuable when more-complete sets of data and their integration are available. Proteomics is in its early phase in hypertension research, but has shown some significant data on the pathophysiology of hypoxia-induced and renovascular hypertension. Recently, integrative omics and systems biology have been emerging and seem to be the ideal approach for future hypertension research.

SUMMARY

Genomics, proteomics and integrative omics have demonstrated their potential in hypertension research to better understand the pathogenesis and pathophysiology of hypertension. In addition, they may contribute to identification of new therapeutic targets, biomarker discovery, prediction of therapeutic response, personalized treatment regimens, better therapeutic outcome and ultimately prevention of the disease.

Blood pressure demographics: nature or nurture ... ... genes or environment?

Hypertension is a growing worldwide problem associated with an increased risk of cardiovascular morbidity and mortality. However, the rates of prevalence of hypertension are higher in some populations than others. Although ethnic and genetic factors have been implied in the past to explain this, the environmental influence and psychosocial factors may play a more important role than is widely accepted. Examining the non-genetic influences in future hypertension research may be necessary in order to clearly define the local blood pressure demographics and the global hypertensive disease burden.