Angiotensin II type 2 receptor gene polymorphism and cardiovascular phenotypes: the GLAECO and GLAOLD studies

Renin Angiotensin Blockers and Cardiac Protection: From Basis to Clinical Trials

Despite a similar beneficial effect on blood pressure lowering observed with angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II type 1 receptor (AT1R) blocker (ARBs), several clinical trials and meta-analyses have reported higher cardiovascular mortality and lower protection against myocardial infarction with ARBs when compared with ACEIs. The European guidelines for the management of coronary syndromes and European guidelines on diabetes recommend using ARBs in patients who are intolerant to ACEIs. We reviewed the main pharmacological differences between ACEIs and ARBs, which could provide insights into the differences in the cardiac protection offered by these 2 drug classes. The effect of ACEIs on the tissue and plasma levels of bradykinin and on nitric oxide production and bioavailability is specific to the mechanism of action of ACEIs; it could account for the different effects of ACEIs and ARBs on endothelial function, atherogenesis, and fibrinolysis. Moreover, chronic blockade of AT1 receptors by ARBs induces a significant and permanent increase in plasma angiotensin II and an overstimulation of its still available receptors. In animal models, AT4 receptors have vasoconstrictive, proliferative, and inflammatory effects. Moreover, in models with kidney damage, atherosclerosis, and/or senescence, activation of AT2 receptors could have deleterious fibrotic, vasoconstrictive, and hypertrophic effects and seems prudent and reasonable to reserve the use of ARBs for patients who have presented intolerance to ACE inhibitors.

Association between polymorphisms of genes involved in the Renin-Angiotensin-Aldosterone System and the adaptive morphological and functional responses to essential hypertension

Hypertensive cardiac remodeling is illustrated by increased left ventricular (LV) mass index values and/or relative wall thickness (RWT) values >0.42, and functionally by isolated alteration of LV diastole (abnormal relaxation). The aim of the present study was to establish differentiated models of anatomical and functional adaptation to essential hypertension (EHT), in relation to the genetic variants of genes involved in the Renin-Angiotensin-Aldosterone System (RAAS). The M235T-AGT, I/D-ACE, A1166C-R1AngII, A3123C-R2AngII and G83A-REN genotypes were determined using PCR-Restriction Fragment Length Polymorphism in 139 hypertensive subjects. The relationship between the studied RAAS gene polymorphisms with morphological and functional cardiac remodeling was assessed by multiple logistic regression analysis. Patients carrying the C/C, A/C genotypes (A3123C-R2AngII polymorphism) had a 2.72-fold (P=0.033) increased risk of exhibiting an RWT value <0.42; in the multivariate model the risk was 4.02-fold higher (P=0.008). Analysis of LV diastolic dysfunction (LVDD) revealed that hypertensive patients carrying the T/T, M/T genotypes (M235T-AGT polymorphism) had a 2.24-fold (P=0.037) increased risk of developing LVDD and a 2.42-fold increased risk (P=0.039) after adjustment for confounders. Similarly, carriers of the G/G, A/G genotypes (G83A-REN) had a 2.32-fold (P=0.021) increased risk of developing LVDD, and this remained an independent risk factor based on the multivariate model (P=0.033). The results of the present study showed that no particular gene was associated with increased LV mass, but the A3123C-R2AngII polymorphism was associated with a non-concentric type of cardiac response in hypertensive patients. Conversely, the M235T-AGT and G83A-REN polymorphisms were found to be statistically significantly associated with LVDD when assessing abnormal relaxation.

Exploring AT2R and its polymorphism in different diseases: An approach to develop AT2R as a drug target beyond hypertension

The Angiotensin II type 2 receptor (AT2R) is one of the critical components of the renin-angiotensin system (RAS), which performs diverse functions like inhibiting cell differentiation, cell proliferation, vasodilatation, reduces oxidative stress and inflammation. AT2R is relatively less studied in comparison to other components of RAS despite its uniqueness (sex-linked) and diverse functions. The AT2R is differentially expressed in different tissues, and its gene polymorphisms are associated with several diseases. The molecular mechanism behind the association of AT2R and its gene polymorphisms with the diseases remains to be fully understood, which hinders the development of AT2R as a drug target. Single nucleotide polymorphisms (SNPs) in AT2R are found at different locations (exons, introns, promoter, and UTR regions) and were studied for association with different diseases. There may be different mechanisms behind these associations as some AT2R SNP variants were associated with differential expression, the SNPs (A1675G/A1332G) affect the alternate splicing of AT2R mRNA, A1332G genotype results in shortening of the AT2R mRNA and subsequently defective protein. Few SNPs were found to be associated with the diseases in either females (C4599A) or males (T1334C). Several other SNPs were expected to be associated with other similar/related diseases, but studies have not been done yet. The present review emphasizes on the significance of AT2R and its polymorphisms associated with the diseases to explore the precise role of AT2R in different diseases and the possibility to develop AT2R as a potential drug target.

Association of renin-angiotensin system genetic polymorphisms and aneurysmal subarachnoid hemorrhage

OBJECTIVE

Renin-angiotensin system (RAS) genetic polymorphisms are thought to play a role in cerebral aneurysm formation and rupture. The Cerebral Aneurysm Renin-Angiotensin System (CARAS) study prospectively evaluated common RAS polymorphisms and their relation to aneurysmal subarachnoid hemorrhage (aSAH).

METHODS

The CARAS study prospectively enrolled aSAH patients and controls at 2 academic centers in the United States. A blood sample was obtained from all patients for genetic evaluation and measurement of plasma angiotensin-converting enzyme (ACE) concentration. Common RAS polymorphisms were detected using 5′ exonuclease (TaqMan) genotyping assays and restriction fragment length polymorphism analysis.

RESULTS

Two hundred forty-eight patients were screened, and 149 aSAH patients and 50 controls were available for analysis. There was a recessive effect of the C allele of the angiotensinogen (AGT) C/T single-nucleotide polymorphism (SNP) (OR 1.94, 95% CI 0.912–4.12, p = 0.0853) and a dominant effect of the G allele of the angiotensin II receptor Type 2 (AT2) G/A SNP (OR 2.11, 95% CI 0.972–4.57, p = 0.0590) on aSAH that did not reach statistical significance after adjustment for potential confounders. The ACE level was significantly lower in aSAH patients with the II genotype (17.6 ± 8.0 U/L) as compared with the ID (22.5 ± 12.1 U/L) and DD genotypes (26.6 ± 14.2 U/L) (p = 0.0195).

CONCLUSIONS

The AGT C/T and AT2 G/A polymorphisms were not significantly associated with aSAH after controlling for potential confounders. However, a strong trend was identified for a dominant effect of the G allele of the AT2 G/A SNP. Downregulation of the local RAS may contribute to the formation of cerebral aneurysms and subsequent presentation with aSAH. Further studies are required to elucidate the relevant pathophysiology and its potential implication in treatment of patients with aSAH.

Blood pressure, arterial stiffness and endogenous lithium clearance in relation to AGTR1 A1166C and AGTR2 G1675A gene polymorphisms

Introduction:

Although recently a matter of epidemiologic controversy, sodium overload and its interaction with genetic factors predispose to hypertension and related target organ complications.

Methods:

In 131 (66 male) treated hypertensives, we measured peripheral and central arterial pressures and pulse wave augmentation indexes (AIx_P, AIx_C1, AIx_C2), pulse wave velocity (PWV), daily urinary sodium excretion and did genetic studies of AGTR1 A1166C and AGTR2 G1675A polymorphisms. Proximal (FE_Li) and distal (FDR_Na) sodium reabsorption measurements were performed using endogenous lithium clearance.

Results:

In men, we found interaction between FDR_Na and AGTR2 G1675A polymorphism with respect to AIx_C1 (p_INT=0.01), AIx_C2 (p_INT=0.05) and AIx_P (p_INT=0.006). Arterial stiffness increased with higher sodium reabsorption in the distal tubule, in the presence of AGTR2 G allele with the opposite tendency in A allele carriers. In the subgroup with FDR_Na below median, as compared to those with FDR_Na above median, the AIx_C1 (139.6±3.8 vs 159.1±5.7%; p=0.009), AIx_C2 (26.3±1.8 vs 33.3±1.7%; p=0.016) and AIx_P (83.4±2.5 vs 96.5±2.6%; p<0.0001) were lower, in the G allele carrying men and GG homozygous women.

Conclusions:

The relation between sodium reabsorption in the distal tubule and the development of arterial stiffness depends on the AGTR2 G1675A polymorphism in blood pressure independent fashion.

Association of angiotensin II type I and type II receptor genes polymorphisms with the presence of premature coronary disease and metabolic syndrome

Premature coronary artery disease (PCAD) is known to have a particularly strong genetic component. We aimed to investigate the association between angiotensin II receptor type 1 (ATR1) or type II (ATR2) genes polymorphisms and PCAD with or without metabolic syndrome in males. 132 male patients with PCAD and 132 controls were included in the study. ATR1 and ATR2 genes polymorphisms were analyzed by polymerase chain reaction. The present study revealed that ATR1 CC genotype and ATR2 G allele increased the risk of PCAD by 2.9 and 1.3 respectively as well as they increased susceptibility to metabolic syndrome by 4.5 and 2.3 respectively. The present study proved that diabetes, smoking, obesity, total cholesterol, triglycerides, LDLc and HDLc were independent risk factors for the development of PCAD. We concluded that ATR1 CC genotype and ATR2 G allele increased the susceptibility of Egyptian males to have PCAD. The increased susceptibility to have metabolic syndrome could be one of the mechanisms leading to the development of PCAD in subjects carrying one or both of these polymorphisms.

AT2R -1332 G:A polymorphism and diabetic nephropathy in type 2 diabetes mellitus patients

Introduction: The rennin-angiotensin system (RAS) plays a central role in the regulation of sodium metabolism, vascular tone, blood pressure, renal hemodynamics, and vascular modeling and is activated by hyperglycemiaObjectives: In the present study the influence of AT2R -1332 G:A polymorphism on the risk of T2DM and its complications in a population from Western Iran has been investigated.

Patients and Methods: In a case-control study, 70 individuals with type 2 diabetes mellitus (T2DM) including normo-, micro- and macro-albuminuric patients and 112 healthy subjects from the Kermanshah province were studied to investigate the association between the angiotensin type 2 receptor (AT2R) -1332 G:A variants with the risk of T2DM and its complications. The genotypes of the AT2R were detected using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Analysis of AT2R -1332 G:A polymorphism indicated the absence of association between this polymorphism with T2DM and diabetic nephropathy.

Results: Analysis of AT2R -1332 G:A polymorphism indicated the absence of association between this polymorphism with T2DM and diabetic nephropathy. In females with diabetic nephropathy a significantly higher frequency of AA genotype (50%) was detected compared to those without nephropathy (13.3%, p=0.015). The presence of A allele of AT2R was associated with significantly (p=0.029) increased risk of coronary artery disease (CAD) in diabetic patients without nephropathy.

Conclusion: Our study indicated an association between the AT2R -1332 G:A polymorphism and the risk of diabetic nephropathy in females only. Also, the A allele was associated with the risk of CAD in those diabetic patients without nephropathy.

Association of polymorphisms in angiotensin II receptor genes with aldosterone-producing adenoma

This study examined the association of polymorphisms in angiotensin II receptor genes (AT (1) R and AT (2) R) with the risk for aldosterone-producing adenoma (APA) in a Chinese Han population. Four polymorphisms including rs5182 (573T/C) in exon 4, rs5186 (1166A/C) in 3'-untranslated region (3'-UTR) in AT (1) R gene and rs5194 (2274G/A) in 3'-UTR, rs1403543 (1675G/A) in intron 1 in AT (2) R gene were detected in 148 APA patients and 192 normal subjects (serving as control) by using a MGB-Taqman probe. The distribution of genotypes of each locus was in accordance with Hardy-Weinberg Equilibrium (HWE) in the APA and control groups (P>0.05). The allele A frequency at rs5194 was significantly higher in the APA group (0.49) than in the control group (0.35) (χ (2)=12.08, P=0.001). Subjects with homozygotic genotype AA and heterozygotic genotype GA were at an increased risk for APA as compared to those with GG genotype (OR=2.66, 95% CI=1.45-4.87; OR=1.67, 95% CI=1.02-2.74). Furthermore, rs5194 single-nucleotide polymorphism (SNP) at AT (2) R gene was significantly associated with APA in additive (OR=1.64, 95% CI=1.21-2.20, P=0.001), dominant (OR=1.94, 95% CI=1.23-3.06, P=0.003), and recessive model (OR=2.01, 95% CI=1.17-3.45, P=0.01). It was concluded that rs5194 polymorphism at AT (2) R gene was associated with the risk for APA, which may constitute a genetic marker of APA.

Genetic variation in angiotensin II type 2 receptor gene influences extent of left ventricular hypertrophy in hypertrophic cardiomyopathy independent of blood pressure

Introduction. Hypertrophic cardiomyopathy (HCM), an inherited primary cardiac disorder mostly caused by defective sarcomeric proteins, serves as a model to investigate left ventricular hypertrophy (LVH). HCM manifests extreme variability in the degree and distribution of LVH, even in patients with the same causal mutation. Genes coding for renin—angiotensin—aldosterone system components have been studied as hypertrophy modifiers in HCM, with emphasis on the angiotensin (Ang) II type 1 receptor (AT1R). However, Ang II binding to Ang II type 2 receptors (AT2R) also has hypertrophy-modulating effects.

Methods. We investigated the effect of the functional +1675 G/A polymorphism (rs1403543) and additional single nucleotide polymorphisms in the 3’ untranslated region of the AT2R gene ( AGTR2) on a heritable composite hypertrophy score in an HCM family cohort in which HCM founder mutations segregate.

Results. We find significant association between rs1403543 and hypertrophy, with each A allele decreasing the average wall thickness by ~0.5 mm, independent of the effects of the primary HCM causal mutation, blood pressure and other hypertrophy covariates ( p = 0.020).

Conclusion. This study therefore confirms a hypertrophy-modulating effect for AT2R also in HCM and implies that +1675 G/A could potentially be used in a panel of markers that profile a genetic predisposition to LVH in HCM.

The angiotensin II receptor type 2 polymorphism influences haemodynamic function and circulating RAS mediators in normotensive humans

BACKGROUND

The haemodynamic responses to angiotensin II type 1 (AT1) receptor blockade may be mediated in part by interactions between angiotensin II and the angiotensin II type 2 receptor (AT2R). An AT2R G1675A gene polymorphism has been described, but the functional effects of this polymorphism are unknown.

METHODS

Haemodynamic function, circulating renin-angiotensin system mediators and norepinephrine were measured in young healthy subjects at baseline and at 2 and 4 weeks after treatment with irbesartan. Subjects were divided into two groups on the basis of the AT2R G1675A gene polymorphism: GG subjects (n = 12) and AA/GA subjects (n = 22).

RESULTS

AA/AG subjects exhibited hypotensive and renal vasodilatory responses to irbesartan at 4 weeks, but GG subjects did not. In accord with haemodynamic effects, circulating aldosterone levels were suppressed in AA/AG, while circulating norepinephrine levels were augmented only in GG subjects. In contrast, increases in circulating renin, angiotensin II and plasma renin activity after irbesartan were exaggerated in AA/AG subjects.

CONCLUSIONS

The AT2R G1675A polymorphism is a determinant of haemodynamic responses to AT1 receptor blockade, an effect that may be due to influences on aldosterone escape.

Genetic polymorphism on type 2 receptor of angiotensin II, modifies cardiovascular risk and systemic inflammation in hypertensive males

BACKGROUND

Angiotensin type 2 receptor (AT2R), plays a crucial role in blood pressure regulation and atherogenesis. AT2R gene is located on chromosome X and the biological effect of polymorphism A1675G in this gene needs to be further specified. We examined the impact of A1675G on the risk and the severity of coronary artery disease (CAD), and the expression of proatherogenic inflammatory molecules in hypertensive patients.

METHODS

The study population consisted of 146 with CAD (102 with hypertension) and 266 age-matched individuals without CAD (114 with hypertension). The presence of A1675G polymorphism on AT2R gene was determined by PCR. Serum levels of C-reactive protein (CRP), fibrinogen, interleukin-6 (IL-6) and soluble vascular cell adhesion molecule-1 (sVCAM-1) were measured in all the participants.

RESULTS

The G allele was associated with decreased risk of CAD among hypertensives (odds ratio (OR) (95% confidence interval (CI))): 0.4 (0.2-0.9), P = 0.01) and less aggressive angiographic CAD (P < 0.001). The G allele was associated with lower IL-6 (median (25-75th percentile): 1.4 (0.6-3.8)), sVCAM-1 (621 (476-799)), CRP (1.2 (0.6-1.7)), and fibrinogen (369 (320-416)) vs. A allele (IL-6: 2.4 (1.1-4.5) P < 0.01, sVCAM-1: 702 (548-925) P < 0.05, CRP: 3.5 (2.0-6.1) P < 0.001, and fibrinogen: 407 (348-514) P < 0.01). The effect of A1675G on serum IL-6, sVCAM-1, and fibrinogen was driven by its effect among hypertensives (IL-6 3.1 (2.1-5.6 in A vs. 1.2 (0.3-3.4) in G P < 0.001, sVCAM-1: 890 (560-1000) in A vs. 556 (377-788) in G P < 0.01, and fibrinogen: 408 (354-510) in A vs. 369 (324-418) in G P < 0.001) whereas it had no effect among nonhypertensives.

CONCLUSIONS

Genetic polymorphism A1675G on AT2R gene affects cardiovascular risk and the severity of atherosclerosis by modifying systemic inflammation, especially in hypertensive males.

Angiotensin II type 2 receptor gene polymorphisms in cardiovascular disease

Considerable progress in our understanding of the role of the angiotensin II type 2 (AT(2)) receptor in the development of cardiac hypertrophy and coronary artery disease has been achieved using in vitro and in vivo animal models. Our understanding in humans, however, has been hindered by the lack of availability of specific AT(2) receptor agonists and antagonists suitable for human study. Nevertheless, an alternative approach involving genotyping humans for a functional polymorphism within the AT(2) receptor gene (-1332G/A) has been used in several association studies to elucidate the pathogenic role of the AT(2) receptor in cardiovascular disease. Both the A allele and the G allele have independently been associated with left ventricular remodelling. However, the methods of measuring left ventricular mass, sodium balance, age and degree of remodelling appear to influence the outcome. An association of carriers of the G allele and premature coronary artery disease has also been established, particularly in males presenting with stenotic atherosclerosis requiring revascularisation. At the molecular level, it remains unclear as to whether carriers of the G allele express more or fewer AT(2) receptors when compared to carriers of the A allele. Consequently, it is presently not possible to definitively interpret the role of the AT(2) receptor in human cardiovascular disease from these association studies.

Genetics of the human renin angiotensin system

The genes coding for the renin angiotensin system have been extensively studied. During the last 15 years, informative markers and functional polymorphisms have been identified, and numerous linkage and association studies have been performed in cardiovascular diseases, especially human hypertension. This mini-review aims to summarize the main findings observed for each component of this enzymatic cascade taken alone or in combination, with an emphasis on the most recent or innovative studies.

High sodium intake modulates left ventricular mass in patients with G expression of +1675 G/A angiotensin II receptor type 2 gene

OBJECTIVES

In patients with hypertension left ventricular hypertrophy (LVH) is associated with genetic variations of the angiotensin type 2 receptor (AT2R). Hypertension and LVH are often aggravated by salt intake. Our objective was to assess the relationship between AT2R gene variation and salt intake and their impact on left ventricular mass (LVM).

METHODS AND RESULTS

In 205 subjects with normal or mildly elevated blood pressure, we assessed sodium intake and left ventricular structure and function by echocardiography. Intronic +1,675 G/A polymorphism of the AT2R gene was investigated. A-allele carriers had a greater LVM (P = 0.049) than G-allele carriers. Independent of diet, septal wall thickness was higher in A-allele carriers (P = 0.001). Fractional fibre shortening was greater in A-allele carriers (P = 0.034), and the velocity of circumferential fibre shortening tended to be greater in A-allele carriers (P = 0.057). When the two groups were stratified according to their salt intake, only G-allele carriers displayed a modulating effect of salt intake on LVM. Covariance analysis revealed that there was a trend towards a modulating effect of salt intake on LVM, even after taking blood pressure into account (P = 0.054).

CONCLUSION

Our data clearly support the notion that LVM is influenced by AT2R polymorphisms. Furthermore, G-allele carriers in particular appear to be susceptible to a modifying effect of increased salt intake on LVM.

X-linked angiotensin II type 2 receptor gene polymorphism -1332A/G in male patients with essential hypertension

BACKGROUND

The role of AT2R in regulation of blood pressure (BP) was mainly investigated in animal models. It is proposed to be a negative regulator of BP. X-linked AT2R -1332 A/G polymorphism has been denoted as functional. This polymorphism was associated with certain cardiovascular phenotypes in hypertensive patients, but it was poorly investigated in essential hypertension. The aim of our study was to evaluate possible association of -1332 A/G gene polymorphism with essential hypertension in males from Serbian population.

METHODS

The study group included 304 men of Caucasian origin, 190 normotensive (NT) and 114 hypertensive (HT), free of cardiovascular disorders. Genotyping was done by PCR RFLP method.

RESULTS

G/- genotype was in association with HT (OR 1.6, CI=1.0-2.6, p=0.04). Stratification by age (<40 years, mean 31.65+/-5.29 and >40 years, mean 51.36+/-8.32) pronounced significance only in older males (OR 2.4, CI=1.2-5.0, p=0.02). After adjustment for confounding factors the OR for hypertension remained unchanged and significant (adjusted OR 2.3, CI=1.0-5.4, p=0.04).

CONCLUSION

Hemizygosity for the G allele was found to be susceptibility factor for hypertension in males. Still, clarifying the role of AT2R in development of human hypertension requires further replication studies in larger and different populations.

The AT2 gene may have a gender-specific effect on kidney function and pulse pressure in type I diabetic patients

Diabetic nephropathy shows a higher incidence in male subjects, which may in part be owing to genetic factors. The angiotensin II type 2 receptor (AT2), present in the renal glomerulus, may oppose the deleterious effects of the type I receptor (AT1) through vasodilatation and growth inhibition. We determined whether the functional intronic G1675A or A1818T polymorphism of the X-chromosomal AT2 gene is associated with blood pressure levels or with kidney function. We genotyped 996 (538 female/458 male subjects) Finnish patients with type I diabetes from the FinnDiane-study in a cross-sectional study. DNA samples were amplified using standard polymerase chain reaction protocol and the genotypes were determined by the minisequencing method. Male patients with the AA haplotype had a lower glomerular filtration rate (83 +/- 32 vs 94 +/- 34 ml min(-1) 1.73 m(-2), P = 0.008) and a higher pulse pressure (PP) (62 +/- 18 vs 57 +/- 15 mm Hg, P = 0.002; P < 0.05 after adjustment for age) than did those with the GT haplotype. No differences between the genotypes or haplotypes and these variables were evident in females. In males, the G1675A was also an independent variable in a linear regression analysis with PP (r(2) = 0.16, coefficient=3.64, s.e.m.=1.38, P < 0.01) as the dependent variable. These data suggest a gender-specific association between the AT2 gene and kidney function and premature aging of the arterial tree in patients with type I diabetes.

Angiotensin II type 2 receptor gene polymorphisms and cardioprotective role in essential hypertension

Angiotensin II type 2 receptor (AT2R) has been proved to be involved in a cardioprotective role, but only a few studies have addressed the association of AT2R-genotype with this role. Whether the AT2R genotype is associated with hypertension is controversial. The aim of the study was to explore the information of single-nucleotide polymorphisms (SNPs) of the AT2R gene in Cantonese, an essential subpopulation of Chinese, and study the association of SNPs in the AT2R gene with hypertension, and to detect the genotypes that indicate a cardioprotective role. Two hundred and sixty-two patients with essential hypertension and 75 normotensive subjects were enrolled for a case-control study. All of the subjects were Cantonese. Sixteen individuals were chosen to sequence the AT2R gene and 16 SNPs were acquired. G/T rs5193 and G/A rs5194 were two SNPs in the 3' untranslated region which were focused on the association of the AT2R-genotype and phonotype. Polymerase chain reaction was performed to amplify the fragment spanning the two SNPs. Genotype and haplotype were identified by dot blot hybridization. Four haplotypes in males (G-G, G-A, T-A, T-G) and eight haplotype combinations in females (G-G/G-G, G-A/G-A, G-G/G-A, G-G/T-A, G-G/T-G, T-A/T-A, T-G/T-G, and T-A/T-G) were detected. G-G and G-A haplotype were predominant, while T-A and T-G were rare in Cantonese. None of these was associated with hypertension. T-A carriers with essential hypertension indicated lower levels of left ventricular mass (LVM) and left ventricular hypertrophy index (LVHI). The levels of LVM and LVHI were still significantly lower in T-A carriers with hypertension adjusted for age or body mass index for men and women separately. No episodes of coronary heart disease and heart failure were detected in T-A carriers with hypertension. Haplotypes of G/T rs5193-G/A rs5194 are not associated with essential hypertension. Among these haplotypes, T-A may be implicated in a cardioprotective role to protect hypertense subjects from left ventricular hypertrophy.

Sodium excretion as a modulator of genetic associations with cardiovascular phenotypes in the European Project on Genes in Hypertension

Hypertension is a chronic age-related disorder, affecting nearly 20% of all adult Europeans. This disease entails debilitating cardiovascular complications and is the leading cause for drug prescriptions in Europeans older than 50 years. Intensive research over the past two decades has so far failed to identify common genetic polymorphisms with a major impact on blood pressure or associated cardiovascular phenotypes, suggesting that multiple genes each with a minor impact, along with gene-gene and gene-environment interactions, play a role. The European Project on Genes in Hypertension (EPOGH) is a large-scale, family-based study in which participants from seven different populations were phenotyped and genotyped according to standardized procedures. This review article summarizes the initial 5-year findings and puts these observations into perspective against other published studies. The EPOGH demonstrated that phenotype-genotype relations strongly depend on host factors such as gender and lifestyle, in particular salt intake as reflected by the 24-h urinary excretion of sodium. The EPOGH therefore highlights the concept that phenotype-genotype relations can only be studied within a defined ecogenetic context.

Intronic enhancement of angiotensin II type 2 receptor transgene expression in vitro and in vivo

The angiotensin II type 2 receptor (AT2R) can influence a variety of intracellular signaling molecules and cellular functions. However, its physiological functions and the roles of introns in the regulation of its expression have not been well determined. We first demonstrated that both intron 1 and intron 2 of AT2R could significantly enhance AT2R overexpression. Thus, we have provided some new prerequisites for further studies on the mechanisms that control AT2R gene expression. Next, we established a highly efficient method of delivering this receptor in vitro and in vivo using an AT2R recombinant adenoviral vector containing two introns of the AT2R. The vector may be useful in helping to uncover AT2R physiological functions and also for gene therapy related to AT2R. Moreover, we determined the important role of introns in gene expression cassettes and the inconsistency of expression between the targeted gene and the reporter gene.

Intronic ANG II type 2 receptor gene polymorphism 1675 G/A modulates receptor protein expression but not mRNA splicing

The X-linked ANG II type 2 receptor (AT2) is supposed to be involved in cardiovascular disorders. Two studies associated the A allele of the AT2 gene polymorphism (PM) 1675 G/A with left ventricular hypertrophy in men and coronary ischemia in women. Because the PM is located in the short intron 1 of the AT2 gene within a sequence motif similar to the splice branch site consensus, we tested whether it might affect pre-mRNA splicing and/or modulate AT2 receptor expression. We first analyzed the AT2 mRNA splice pattern by RT-PCR in myocardial samples from 12 explanted human hearts and compared it with the respective genotypes. All 12 patients, 10 hemizygous males (7 A, 3 G allele carriers) and 2 homozygous females (2 G/G allele carriers), exhibited the same myocardial AT2 splice pattern with a relative abundance of transcript exon 1/2/3 compared with exon 1/3. Next, AT2 minigene constructs were cloned from both alleles, comprising the core promoter and the complete transcribed region up to the translation start codon, upstream of a luciferase reporter gene. These constructs were transfected into human (HT1080) and rat (PC12W) cell lines and rat vascular smooth muscle cells, and luciferase activities were assessed, as well as the splice patterns of the chimeric AT2/luciferase mRNAs. In all transfected cell types, the mRNA expressed from the AT2 constructs was spliced like the endogenous myocardial AT2 mRNA. However, luciferase activities driven by the G allele construct were significantly higher than those expressed from the A allele. Taken together, these data indicate that individuals carrying the G allele may express higher levels of AT2 receptor protein, which may be protective during the development of ventricular hypertrophy and coronary ischemia.

AT1 receptor A1166C and AT2 receptor -1332A/G gene polymorphisms: efficient genotyping by single-tube PCR

Angiotensin II type 1 receptor (AT1) and angiotensin II type 2 receptor (AT2) genes have been investigated in recent years as potential etiologic candidates for cardiovascular and renal diseases. The pathogenic implications of AT1 A1166C and AT2 A-1332G gene polymorphisms have been shown. Here we describe a rapid and reliable method for detecting both AT1 and AT2 gene polymorphisms by a single-tube PCR, to reduce analysis time and simplify the genotyping procedure. In contrast to previously described methods, our method does not require hybridization, primer extension, or nested PCR for genotyping. In most previous studies concerning gene polymorphisms of RAS, both AT1 and AT2 receptor gene polymorphisms were investigated. The advantage of our method is that it makes it possible to detect both of these polymorphisms in a duplex PCR. The procedure described is convenient for routine laboratory use with manual sample processing, and offers the potential for further automation as well. Its simplicity makes it practical for large-scale screening of individuals and families at risk for cardiovascular or renal diseases.

Genetic polymorphisms and heart failure

Heart failure is a complex clinical syndrome. There is evidence for a genetic contribution to the pathophysiology of heart failure. Considering the fundamental role of neurohormonal factors in the pathophysiology and progression of cardiac dysfunction and hypertrophy, variants of genes involved in this system are logical candidate genes in heart failure. In this report, genetic polymorphisms of the major neurohormonal systems in heart failure will be discussed. Studies on polymorphisms of the renin-angiotensin-aldosterone system (RAAS), adrenergic receptor polymorphisms, endothelin (receptor) polymorphisms, and a group of miscellaneous polymorphisms that may be involved in the development or phenotypic expression of heart failure will be reviewed. Research on left ventricular hypertrophy is also included. The majority of genetic association studies focused on the ACE I/D polymorphism. Initial genetic associations have often been difficult to replicate, mainly due to problems in study design and lack of power. Promising results have been obtained with genetic polymorphisms of the RAAS and sympathetic system. Considering the evidence so far, a modifying role for these polymorphisms seems more likely than a role of these variants as susceptibility genes. Besides the need for larger studies to examine the effects of single nucleotide polymorphisms and haplotypes, future studies also need to focus on the complexity of these systems and study gene-gene interactions and gene-environment interactions.

The clinical significance of a common, functional, X-linked angiotensin II type 2-receptor gene polymorphism (-1332 G/A) in a cohort of 509 families with premature coronary artery disease

AIMS

To assess, in families with premature coronary artery disease (CAD), the possible association, with linkage, of the X-linked AT2 receptor (-1332 G/A) gene polymorphism and premature CAD.

METHODS AND RESULTS

We investigated 509 families with a history of premature CAD that consisted of one sibling affected with premature CAD and two unaffected siblings. Genotyping of subjects was performed using a restriction enzyme digestion of an initial 310 bp polymerase chain reaction fragment that included the AT2 (-1332 G/A) locus. The mean age of the 611 individuals affected by premature CAD at the time of event was 49.5 +/- 8.1 years. Conditional logistic regression analysis confirmed a significant predictive value of premature CAD for the covariates of hypertension, diabetes, dyslipidaemia, history of smoking, and male gender. The genetic data were analysed for these families using the X-linked sibling transmission/deletion test (XS-TDT) statistics program. In hemizygous men we observed evidence for association in the presence of linkage, for the AT2 (-1332 G/A) locus and premature CAD (P-exact value = 0.024) and also a trend towards association, in the presence of linkage, for this polymorphism and hypertension (P-exact value = 0.08).

CONCLUSIONS

We have observed evidence of association between the presence of linkage for the X-linked AT2 (-1332 G/A) polymorphism and premature CAD in hemizygous males.

Left ventricular mass in relation to genetic variation in angiotensin II receptors, renin system genes, and sodium excretion

BACKGROUND

In the European Project On Genes in Hypertension (EPOGH), we investigated in 3 populations to what extent left ventricular mass (LVM) was associated with genetic variation in the angiotensin II receptors type 1 (AGTR1 A1166C) and type 2 (AGTR2 G1675A) while accounting for possible gene-gene interactions with the angiotensin-converting enzyme (ACE D/I) and angiotensinogen (AGT -532C/T) polymorphisms.

METHODS AND RESULTS

We randomly recruited 221 nuclear families (384 parents, 431 offspring) in Cracow (Poland), Novosibirsk (Russia), and Mirano (Italy). Echocardiographic LVM was indexed to body surface area, adjusted for covariates, and subjected to multivariate analyses using generalized estimating equations and quantitative transmission disequilibrium tests in a population-based and family-based approach, respectively. For AGTR1 and AGTR2, there was no heterogeneity in the phenotype-genotype relations across populations. LVM index was unrelated to the AGTR1 A1166C polymorphism. In men, in the population- and family-based analyses, the allelic effects of the AGTR2 polymorphism on LVM index differed (P=0.01) according to sodium excretion. In women, this gene-environment interaction did not reach statistical significance. In untreated men, LVM index (4.2 g/m2 per 100 mmol) and left ventricular internal diameter (0.73 mm/100 mmol) increased (P<0.02) with higher sodium excretion in the presence of the G allele with an opposite tendency in A allele carriers. The ACE D/I polymorphism, together with the ACE genotype-by-sodium interaction term, significantly and independently improved the models relating LVM index to the AGTR2 polymorphism and the AGTR2 genotype-by-sodium interaction.

CONCLUSIONS

The present findings support the hypothesis that in men the AGTR2 G1675A and the ACE D/I polymorphisms independently influence LVM and that salt intake modulates these genetic effects.

Left Ventricle Mass Index and the Common, Functional, X-Linked Angiotensin II Type-2 Receptor Gene Polymorphism (−1332 G/A) in Patients With Systemic Hypertension

A common intronic polymorphism, (-1332 G/A) of the angiotensin type-2 receptor gene, located on the X-chromosome, has been reported to be functional. The aim of our study was to evaluate this polymorphism for an association with left ventricular hypertrophy. Left ventricle (LV) mass was measured in 197 patients with systemic hypertension and 60 normal volunteers using a 1.5-Tesla Philips MRI system. Genotyping was performed using a restriction enzyme digestion of an initial 310-bp polymerase chain reaction product that included the angiotensin type-2 (-1332 G/A) locus. The mean LV mass index for the male patients was 94.3+/-19.6 g/m2 (n=125) and for the female patients was 71.2+/-12.0 g/m2 (n=72). Seventy-three (37.1%) of all patients had an elevated LV mass index, defined as the mean LV mass index for normal volunteers plus 2 SD (males 77.8+/-9.1 g/m2, n=30; females 61.5+/-7.5 g/m2, n=30). Comparison of LV mass index of the A_/AA genotype (mean LV mass index=82.4+/-21.1 g/m2; n=123) against that of the G_/GG genotype (mean LV mass index=88.1+/-19.0 g/m2; n=89) as a continuous variable was significant by ANOVA (P=0.044). chi2 Comparison between subjects with and subjects without left ventricular hypertrophy revealed an excess of the G_/GG genotype among the group with LV hypertrophy (P=0.031). We observed an association between the angiotensin type-2 receptor (-1332 G) allele and the presence of left ventricular hypertrophy in hypertensive subjects.