Angiotensin II (type-1) receptor locus: CA repeat polymorphism and genetic mapping

MicroRNA and vascular smooth muscle cells

Vascular smooth muscle cells (VSMCs) exhibit extraordinary plasticity during postnatal development. Vascular injury initiates VSMC phenotypic switch from the contractile to proliferative phenotype, which plays a central role in vascular lesion formation and diverse vascular diseases. MicroRNAs (miRNAs) regulate gene expression posttranscriptionally by either degrading target mRNAs or repressing their translation. Emerging evidence has revealed miRNAs are critical regulators in VSMC differentiation from stem cells, phenotypic switch, and various vascular pathogenesis. Here, we review recent advances regarding functions of specific miRNAs in vasculature and discuss possible mechanisms by which miRNAs affect VSMC biology.

Association between the angiotensin-converting enzyme (insertion/deletion) and angiotensin II type 1 receptor (A1166C) polymorphisms and breast cancer among Brazilian women

Introduction.We evaluated the association between components of the renin-angiotensin system and the development of breast cancer in a case-control study by means of angiotensin-converting enzyme (ACE) insertion/deletion (I/D) and angiotensin II type 1 (AT 1)-receptor A1166C polymorphisms.

Methods. Genotyping was performed by PCR-RFLP (restriction fragment length polymorphism) or PCR (polymerase chain reaction) using genomic DNA extracted from buccal cells of subjects with (101 cases) or without (307 controls) breast cancer.

Results.The frequencies of genotypes for ACE were: DD, ID and II (in %: cases: 60; 20; 20; controls: 46; 37; 17; p=0.019, χ2); and for AT1receptor were:AA,AC and CC (in %: cases: 65; 30; 5; controls: 51; 44; 5; p=0.114, χ 2).The results suggested that the A1166C polymorphism was not associated with breast cancer risk. On the other hand, for the ACE (I/D), there seemed to be different risks for cancer between cases and controls.

Conclusions.The ID genotype was less frequently associated with the disease than were the DD or II; that is, women with the ID genotype were 3.1 times less likely to develop breast cancer than those with the other genotypes.The ID genotype might be protective against breast cancer and the ACE (I/D) polymorphism a possible target for developing genetic markers for breast cancer.

The effect of polymorphisms in the renin-angiotensin-aldosterone system on diabetic nephropathy risk

OBJECTIVES

The risk of diabetic nephropathy (DN) can be increased by elevated intraglomerular pressure and glomerular filtration rate, leading to glomerular damage. This can be controlled by the renin-angiotensin-aldosterone (RAA) system, which has an important function regulating both systemic and intrarenal blood pressure. Smoking increases the risk of DN, but not all diabetic patients who smoke develop DN. There is a possibility that smoking has different effects depending on the different genotypes of the individual. We investigated the association of DN with seven polymorphisms in the RAA system and their possible interaction with smoking.

SUBJECTS AND METHODS

In the present case-control study, type 1 diabetic patients with diabetes duration > or =20 years, without albuminuria and without antihypertensive treatment (n=197), were included as controls. An albumin excretion rate (AER) of 20-200 microg/min (n=73) was considered as incipient DN, and an AER >200 microg/min was considered as overt DN (n=48). Smoking habits were obtained from questionnaires.

RESULTS

Homozygosity for the A allele, of the angiotensin II type 1 receptor (AGTR1) A1166C polymorphism, was associated with increased risk of overt DN (OR=3.04; 99% CI=1.02-9.06), independently of the other associated variables: age, duration of diabetes, ever smoking, HbA1c, and sex. The effect of the AA genotype was enhanced to a four times risk increase among ever-smoking patients. Two alleles of the microsatellite marker adjacent to the angiotensinogen gene were less common among nephropathy cases than among controls, but this was not significant when controlling for the same variables as above.

CONCLUSIONS

The risk of having overt DN was increased in patients homozygous for the A1166 allele, and smoking seemed to enhance the effect of the AGTR1 genotype.

Angiotensin II type 1 receptor polymorphisms and susceptibility to hypertension: a HuGE review

The angiotensin II type 1 receptor (AGTR1) plays an integral role in blood pressure control, and is implicated in the pathogenesis of hypertension. Polymorphisms within this gene have been extensively studied in association with hypertension; however, findings are conflicting. To clarify these data, we conducted a systematic review of association studies of AGTR1 polymorphisms and hypertension, and performed a meta-analysis of the rs5186 variant. Results show that the currently available literature is too heterogeneous to draw meaningful conclusions. The definition of hypertension and gender composition of individual studies helps to explain this heterogeneity. Although the structure and splicing pattern of AGTR1 would suggest a likely effect of polymorphisms within the promoter region on gene function, few studies have been conducted thus far. In conclusion, there is insufficient evidence that polymorphisms in the AGTR1 gene are risk factors for hypertension. However, most studies are inadequately powered, and larger well-designed studies of haplotypes are warranted.

Confirmation of a susceptibility locus for diabetic nephropathy on chromosome 3q23-q24 by association study in Russian type 1 diabetic patients

Family-based studies and segregation analyses suggest that inherited factors play a significant role in susceptibility to diabetic nephropathy (DN). Moczulski et al. [Diabetes 47 (1998) 1164-1169] found a susceptibility locus for DN in type 1 diabetes covering a 20cM region on chromosome 3q, with a peak of linkage close to the angiotensin II type 1 receptor (AT1) gene. We examined eight polymorphic markers (D3S1512, D3S1550, D3S1557, D3S1744, D3S2326, D3S3599, D3S3694, and a (CA)(n) dinucleotide repeat polymorphism in the 3' flanking region of the AT1 gene) spanning about 6.2 megabases (Mb) in the region of maximal linkage with DN on chromosome 3q23-q24. The markers were used to genotype a total of 381 Russian type 1 diabetic subjects, 195 of whom had DN and 186 had no clinical nephropathy. Four of the markers tested, D3S1512, D3S1550, D3S2326, and D3S3599, showed an association with DN in type 1 diabetes mellitus. These markers are located within a 1.0Mb interval that starts about 4.4Mb centromeric to the AT1 gene. Thus, our results suggest the existence of the DN susceptibility locus previously described by Moczulski et al. on chromosome 3q.

A method for developing high-density SNP maps and its application at the type 1 angiotensin II receptor (AGTR1) locus

Evaluating the potential genetic components of complex disease will likely be aided through the use of dense polymorphism maps. Previously, we reported evidence for linkage with diabetic nephropathy on chromosome 3q in a region encompassing the type 1 angiotensin II receptor (AGTR1) gene. To further investigate any role for this gene in disease onset, we set out to design a dense polymorphism map spanning the AGTR1 locus for the purpose of association studies. Toward this goal, we have developed a technique for rapid identification of polymorphisms in long stretches of genomic DNA. This approach uses long-range PCR, DNA pooling, and transposon-based DNA sequencing. Using this technique, we efficiently validated and genotyped 18 polymorphisms spanning the 60.5-kb AGTR1 locus. Our panel of polymorphisms has an average spacing of 3.2 kb and an average minor allele frequency of 24%.

Genome-wide scan of predisposing loci for increased diastolic blood pressure in Finnish siblings

OBJECTIVES

To review, on a genome-wide scale, a linkage result obtained in an earlier candidate gene analysis in this same study sample, and to look for other possible contributing genetic loci predisposing to hypertension in this population.

DESIGN

An affected sibpair linkage study with highly polymorphic genetic markers spanning the genome at an average intermarker density of 10 cM.

PARTICIPANTS

A total of 47 families with two affected siblings (mostly dizygotic twins) and all available additional family members from the genetic isolate of Finland. The families were identified through the Finnish Twin Cohort Study, the total number of this follow-up cohort being 13,888. The study sample was selected on the basis of early-onset hypertension with minimal presence of other phenotypic risk factors such as obesity.

RESULTS

The AT1 locus stood out as the most significant locus in this population (maximum likelihood score 4.04). Some evidence for linkage was also detected with markers on chromosomes 2q (maximum likelihood score 2.96), 22q (2.07), and Xp (2.41).

CONCLUSIONS

Our results establish the role of the AT1 locus, on a genome-wide scale, as a major contributing locus to essential hypertension in this study sample.

RAS genes influence exercise-induced left ventricular hypertrophy: an elite athletes study

PURPOSE

The association of ACE I/D polymorphism with changes in LV mass in response to physical training has been observed, but no association has been found with AT1R A1166C polymorphism. We investigated the ACE I/D, AT1R A1166C, and AT1R CA microsatellite polymorphisms genotype distribution in elite athletes and whether the presence of AT1R C1166 variant, in addition to ACE D allele affects the training-induced LV mass alterations in elite trained athletes.

METHODS

The study population comprised 28 healthy players recruited from an Italian elite male soccer team and 155 healthy male subjects. LV mass, LV mass adjusted for body surface area, septal thickness, posterior wall, end-diastolic and end-systolic ventricular dimension, and ejection fraction were determined by echocardiography in pretrained period, at rest and 7 months later during the training. All subjects were genotyped for ACE I/D, AT1R A1166C, and CA microsatellite polymorphisms.

RESULTS

Training induced an LV mass increase in all but six athletes. The percentage of athletes in whom an increase of LV mass was found after training was statistically different in relation to the ACE D allele: no increase was observed in three of 24 D allele carriers and in three of four II genotype players (Fisher's exact test, P = 0.02). As AT1R is concerned, no increase was observed in 4 of 15 C allele carriers and in 2 of 13 AA genotype athletes (Fisher's exact test, P > 0.05). The contemporary presence of ACE D and AT1R C allele did not affect the changes after training. No difference has been observed in the CA microsatellite marker allele frequencies between athletes and controls (P = 0.46).

CONCLUSION

In this study, we provide the evidence that soccer play does not select athletes on genotype basis. Training-induced LV mass changes in male elite athletes are significantly associated with the presence of ACE D allele, but not of AT1R C allele.

Distortion of maternal-fetal angiotensin II type 1 receptor allele transmission in pre-eclampsia

OBJECTIVE

To investigate the fetal angiotensin II type 1 receptor genotype in pre-eclampsia.

DESIGN

Case-control study.

POPULATION

Forty-one maternal-fetal pairs from pre-eclamptic pregnancies and 80 maternal-fetal pairs from normotensive pregnancies.

METHODS

Maternal and fetal DNA was genotyped at three diallelic polymorphisms, at nucleotides 573, 1062, and 1166, in the coding exon of the angiotensin II type 1 receptor gene, and at a dinucleotide repeat polymorphism in its 3' flanking region.

RESULTS

Allele and genotype frequencies at the four polymorphic regions investigated did not differ between pre-eclamptic and normotensive groups, in either fetal or maternal samples. Mothers heterozygous for the dinucleotide repeat allele designated A4 transmitted this allele to the fetus in 15 of 18 informative pre-eclamptic pregnancies and in eight of 26 normotensive pregnancies. This was greater than the expected probability in pre-eclamptic pregnancies (p=0.04) and less than expected in normotensive pregnancies (p<0.005). The 573T variant, which is in partial linkage disequilibrium with the A4 allele, showed a similar distortion of maternal-fetal transmission.

CONCLUSION

Angiotensin II type 1 receptor gene expression in the fetus may contribute to the aetiology of pre-eclampsia. It is unclear whether susceptibility is conferred by the fetal genotype acting alone, or by allele sharing by mother and fetus. Possible mechanisms for the effect of the angiotensin II type 1 receptor gene are suggested by the association of the 573T variant with low levels of surface receptor expression on platelets. If receptor expression is similarly genetically determined in the placenta, responsiveness to angiotensin II may be affected, with the potential to influence placentation or placental prostaglandin secretion.

Variation in the region of the angiotensin-converting enzyme gene influences interindividual differences in blood pressure levels in young white males

BACKGROUND

The renin-angiotensin system regulates blood pressure through its effects on vascular tone, renal hemodynamics, and renal sodium and fluid balance.

METHODS AND RESULTS

Using data from a large population-based sample of 1488 siblings having a mean age of 14.8 years and belonging to the youngest generation of 583 randomly ascertained three-generation pedigrees from Rochester, Minn, we carried out variance components-based linkage analyses to evaluate the contribution of variation in four renin-angiotensin system gene regions (angiotensinogen, renin, angiotensin I-converting enzyme, and angiotensin II receptor type 1) to interindividual variation in systolic, diastolic, and mean arterial pressure. We rejected the null hypothesis that allelic variation in the region of the angiotensin-converting enzyme (ACE) gene does not contribute to interindividual blood pressure variability. After conditioning on measured covariates, variation in this region accounted for 0%, 13% (P=0.04), and 16% (P=0.04) of the interindividual variance in systolic, diastolic, and mean arterial pressures, respectively. These estimates were even greater in a subset of subjects with a positive family history of hypertension (0%, 29% [P=0.005], and 32% [P<0.005], respectively). In sex-specific analyses, genetic variation in the region of the ACE gene significantly influenced interindividual blood pressure variation in males (37% for SBP [P=0.03], 38% for DBP [P=0.04], and 53% for MAP [P<0.005]) but not in females.

CONCLUSIONS

Although it is possible that variation in a gene near the ACE gene may explain the observed results, knowledge about the physiological involvement of ACE in blood pressure regulation supports the proposition that the ACE gene itself influences blood pressure variability in a sex-specific manner.

Functional and genetic studies of the angiotensin II type 1 receptor in pre-eclamptic and normotensive pregnant women

OBJECTIVE

To examine and compare angiotensin II type 1 receptor genotype and its relationship to platelet angiotensin II binding for pre-eclamptic and normotensive pregnant women.

DESIGN

In a case-control study, 43 pre-eclamptic women and 83 normotensive women were genotyped at the angiotensin II type 1 receptor gene locus. Platelet angiotensin II binding was measured for a subset of 11 pre-eclamptic and 57 normotensive pregnant women. We genotyped 162 healthy blood donors also, to examine the allelic background and patterns of linkage disequilibrium in the Nottingham population.

METHODS

Patients were recruited during pregnancy using a rigorous definition of pre-eclampsia. DNA was extracted from peripheral venous blood and genotyped at six previously described diallelic polymorphisms in the angiotensin II type 1 receptor gene, using competitive allele-specific oligonucleotide hybridization, and at a dinucleotide repeat polymorphism in the 3' flanking region of the gene. Platelet angiotensin II binding and plasma angiotensin II concentrations were determined for peripheral venous blood.

RESULTS

Normotensive pregnant women homozygous for cytosine at nucleotide 573 had significantly higher levels of platelet angiotensin II binding than did heterozygous women and women homozygous for thymidine at this site. Pre-eclamptic women had significantly higher levels of platelet angiotensin II binding than did normotensive pregnant women. The frequencies of allelic variants did not differ significantly between normotensive and pre-eclamptic women.

CONCLUSION

The physiological regulation of platelet angiotensin II type 1 receptor expression in normal pregnancy is determined in part by angiotensin II type 1 receptor genotype. There was no evidence that the polymorphisms in the angiotensin II type 1 receptor gene were associated with pre-eclampsia.

Synergistic effect of angiotensin II type 1 receptor genotype and poor glycaemic control on risk of nephropathy in IDDM

We investigated the contribution of polymorphisms in the angiotensin II type 1 receptor gene (AGTR1) to renal complications in an inception cohort of 152 insulin-dependent diabetic (IDDM) patients examined 15-21 years after diabetes onset. This nested case-control study included 79 normoalbuminuric control subjects and 73 cases with evidence of nephropathy ranging from microalbuminuria to overt proteinuria. Subjects were genotyped for two AGTR1 polymorphisms (T573-->C and A1166-->C), and an adjacent CA repeat microsatellite. Allele C1166 and the 140 bp allele of the microsatellite were more frequent among nephropathy cases than normoalbuminuric control subjects (0.322 vs 0.247, and 0.618 vs 0.521, respectively), but these differences were not statistically significant. Although not significant by themselves, the AGTR1 polymorphisms contributed significantly to the risk of diabetic nephropathy when accompanied by poor glycaemic control. Among patients with frequent severe hyperglycaemia during the first decade of diabetes, the relative risk of nephropathy among allele C1166 carriers was 12.1 (95% CI: 3.7-39.8), whereas it was only 1.4 (95% CI: 0.6-3.5) among allele A1166 homozygotes. The difference between relative risks was highly significant (chi(2) = 8.25, p = 0.004 with 1 df). A similar pattern of higher risk of microalbuminuria, specifically among those carriers of allele C1166 who had poor glycaemic control was also found in an independent study of a cross-sectional sample of 551 IDDM individuals, although the effect was smaller in magnitude. We conclude that DNA sequence differences in the AGTR1 gene may modify the noxious effects of hyperglycaemia on the kidney. Allele C1166 carriers might especially benefit from nephropathy prevention programmes.

Association analysis of six candidate genes in a sample of Australian hypertensive patients

1. Essential hypertension is characterized by increased vascular resistance due to narrowing of the small arterioles. This may be influenced by vasoactive substances, cell growth and vascular remodelling. 2. A sample of Australian hypertensive and normotensive subjects was investigated for association with genetic markers which are candidates for a role in blood pressure (BP) regulation due to potential effects on vascular diameter. 3. The six markers used were for genes encoding vasoconstrictors, growth factors and a structural protein of the extracellular matrix. 4. No significant association of any of the markers used was found with BP status in this sample of patients.

Association between an angiotensinogen microsatellite marker in children and coronary events in their grandparents

BACKGROUND

Recently we found that the deletion (D) allele of the insertion/deletion (I/D) polymorphism of the ACE gene in 404 children was associated with a history of coronary artery disease (CAD) in their grandparents. This led us to explore polymorphisms in other genes of the renin-angiotensin system in this same population.

METHODS AND RESULTS

We determined the genotypes for three microsatellite markers located near or in the angiotensinogen, angiotensin II (type-1) receptor, and renin genes in the children and related the allele frequencies to grandparental CAD. We found a significant association between the angiotensinogen marker in children and grandparental CAD (chi2 = 42.2, P = .00001) with these children having an excess of the 125-bp and 129-bp alleles (odds ratio, 2.5; 95% confidence interval, 1.7 to 3.7). Greatest grandparental risk was when their grandchildren had the 125-bp/125-bp, 129-bp/129-bp, or 125-bp/129-bp genotypes (odds ratio, 7.75; 95% confidence interval, 2.2 to 27). There was no association between the microsatellites at either the angiotensin II (type-1) receptor (P = .8) or renin (P = .2) genes in children and grandparental CAD and none between the angiotensinogen and ACE polymorphisms in relation to CAD family history.

CONCLUSIONS

This study identifies a significant association between an angiotensinogen marker in children and grandparental CAD. There was no association between the microsatellites at either the angiotensin II (type-1) receptor or renin genes and CAD in this population. We conclude that the angiotensinogen polymorphism as well as the ACE polymorphism may explain a part of the risk related to a family history of CAD.

Genetic variants of proteins from the renin angiotensin system are associated with pressure load cardiac hypertrophy

1. The relationship between the angiotensinogen (AGT) T174M, angiotensin converting enzyme (ACE) insertion/deletion (I/D) and the angiotensin II type 1 receptor (AT1) genetic markers and left ventricular hypertrophy was examined in normal subjects and those with aortic stenosis. 2. Subjects with aortic stenosis had higher left ventricular systolic pressure and relative wall thickness (RWT) compared with normal. However, within aortic stenosis subjects, left ventricular RWT did not correlate with left ventricular systolic pressure or with aortic valve area. 3. In subjects with aortic stenosis, left ventricular RWT was higher in those with ACE DD (P < 0.05) or AGT T174M (P < 0.06) compared with those with the ACE II or ID genotype or AGT TT174 genotype. No relationship was observed with any of the AT1 alleles. The ACE and AGT genetic markers independently predicted left ventricular RWT in aortic stenosis. No association was observed between these genotypes and left ventricular RWT in normal subjects. 4. The data suggest that the AGT T174M and ACE I/D genotypes may act together to influence the degree of hypertrophy in subjects with aortic stenosis. 5. In patients with aortic stenosis, genetic variants of proteins from the renin angiotensin system may be at least as important as left ventricular systolic pressure in determining the degree of left ventricular hypertrophy and could therefore explain the clinical variation observed in the progression to cardiac dysfunction.

Angiotensin II type 1 receptor gene polymorphisms in human essential hypertension

We conducted the present study to determine whether the angiotensin II type I receptor (AT1) gene might be implicated in human essential hypertension by using case-control and linkage studies. The entire coding and 3' untranslated regions of the AT1 receptor gene (2.2 kb) were amplified by polymerase chain reaction and submitted to single-strand conformation polymorphism in 60 hypertensive subjects with a familial susceptibility. We identified five polymorphisms (T573-->C, A1062-->G, A1166-->C, G1517-->T, and A1878-->G). However, no mutations that alter the encoded amino acid sequence were detected. A case-control study performed on white hypertensive (n = 206; blood pressure, 168 +/- 16/103 +/- 9 mm Hg) and normotensive (n = 298; blood pressure, 122 +/- 10/75 +/- 9 mm Hg) subjects using three of five polymorphisms showed a significant increase in allelic frequency of C1166 in hypertensive subjects (0.36 versus 0.28 for normotensive subjects, chi 2 = 6.8, P < .01). Frequencies for the alleles of the other two polymorphisms (T573-->C, A1878-->G) were similar in both groups. We performed a linkage study using the affected sib pair method and a highly polymorphic marker of the AT1 receptor gene. There was no evidence for linkage in 267 sib pairs analyzed from 138 pedigrees. These findings would be compatible with a common variant of the AT1 receptor imparting a small effect on blood pressure; further studies will be needed to address this possibility.