A molecular variant of angiotensinogen associated with preeclampsia

Polymorphism in oestrogen response element associated with variation in plasma angiotensinogen concentrations in healthy pregnant women

OBJECTIVE

To investigate the hypothesis that the genotype at nucleotide A(-20)C in the 5' flanking region of the angiotensinogen gene, which lies within a sequence with high homology to an oestrogen response element, affects plasma angiotensinogen levels in pregnancy.

DESIGN

Prospective observational study

METHODS

Seventy-two healthy pregnant women were recruited in the second half of pregnancy from hospital and primary care antenatal clinics in Nottingham, UK. Plasma angiotensinogen concentrations were measured by radioimmunoassay of angiotensin I generated from endogenous angiotensinogen in the presence of excess human renin. DNA was extracted from peripheral venous blood, and angiotensinogen genotype determined at A(-20)C, G(-6)A and Met235Thr. Associations between genotype and plasma angiotensinogen concentration were assessed by analysis of variance.

RESULTS

Women homozygous for the -20C allele had the lowest mean plasma angiotensinogen concentration of 1.7 +/- 0.3micromol/l. Women homozygous for -20A had significantly higher plasma angiotensinogen concentrations (2.6 +/- 0.1 micromol/l), and intermediate levels (2.0 +/- 0.1 micromol/l) were observed in women heterozygous for A(-20)C (P = 0.002, ANOVA). The polymorphisms at nucleotide -6 and codon 235 were in almost complete linkage disequilibrium, and nucleotide -20C was found only in a subset of -6A/235Thr alleles. Conclusion The low plasma angiotensinogen levels associated with the -20C/-6A/235Thr haplotype in pregnant women contrast with the high concentrations associated with the 235Thr allele in the non-pregnant state. A possible explanation lies in the presence of a motif with high homology to an oestrogen response element between the TATA box and transcription initiation site. Previous in vitro studies of reporter gene constructs have demonstrated thatthe A(-20)C polymorphism affects oestrogen responsiveness. The results of this study support the hypothesis that the oestrogen response element of the angiotensinogen gene is of functional importance in pregnancy, and that oestrogen responsiveness in pregnancy is influenced by the genotype at nucleotide - 20.

Genetics of kidney disease

Perhaps nothing in the fields of medicine and nephrology is moving more rapidly than genetics. From this movement are opportunities for discovery, new therapy, and better counseling for patients. At a level of basic science, renal medicine has been a consistent contributor to this emerging discipline, but our current approach to training in the methods and uses of human genetics probably will not keep up with the technology, nor the needs of the modern bedside practitioner. The facile use of genetics in the next century will require the construction and exploration of new disease models, rededication to human informatics, and teaching the language of molecular and population genomics.

The eNOS gene: a candidate for the preeclampsia susceptibility locus?

OBJECTIVE

To investigate the endothelial cell nitric oxide synthase (eNOS) gene as a candidate for susceptibility to preeclampsia.

METHODS

Twenty-six Australian families containing 11 eclamptics, 59 severe preeclamptics, and 27 mild preeclamptics were used to test for linkage between the eNOS gene region and preeclampsia. Two microsatellite markers (D7S483 and D7S505) in the proximity of the eNOS gene were used.

MAIN OUTCOME MEASURES

Logarithm of odds (LOD) scores were used to examine the cosegregation of alleles with the disease under a variety of inheritance models. Model-independent analysis, affected pedigree member method (AFFPED), and pairwise haplotype sharing between affected sibs were also used.

RESULTS

Two-point LOD score analysis gave no evidence of linkage between preeclampsia and two markers in close proximity to the eNOS gene (LOD scores < 1) for any of the inheritance models investigated, with no evidence of heterogeneity between pedigrees. The AFFPED and the pairwise haplotype sharing test on affected sibs also gave no evidence of linkage (p-values > 0.05).

CONCLUSION

This study provides no evidence for linkage between two markers in close proximity to the eNOS gene and preeclampsia in these families. These results do not support the recent suggestion that eNOS could be a familial pregnancy-induced hypertension gene (Arngrimsson R, et al., Am J Hum Genet 1997;61:354-62). Distinguishing preeclampsia from other hypertensive disorders in pregnancy is difficult. Hypertension appears to be a consequence, rather than a primary cause of preeclampsia. Given the vasodilatory role of the eNOS gene product, it is possible that the linkage recently reported for eNOS reflects its relationship with hypertension rather than preeclampsia.

[Role of the angiotensinogen gene for essential hypertension]

Essential hypertension is a complex disease influenced by different genetic and environmental factors. The renin-angiotensin system (RAS) is implicated in blood pressure regulation. Angiotensinogen (AGT) is the precursor of the biologically active angiotensin II (Ang II). Initial studies on hypertensive siblings and case-control studies indicated the important role of the angiotensinogen gene (AGT) for the predisposition to essential hypertension, preeclampsia and obesity-related hypertension. Recently, different AGT polymorphisms had been identified and analyzed in case-control studies. The aim of present studies is the analysis of potentially functional AGT variants (C-532T, G-6A), which might be responsible for the regulation of gene expression and therefore AGT generation. The A-6 allele is in complete linkage disequilibrium with the T235 allele and is associated with higher AGT expression in vitro. Segregation linkage analysis demonstrated that the C-532T polymorphism influences plasma AGT variability more significantly than the G-6A variant. Since the C-532T polymorphism is located within a AP-2 consensus element, functional promoter analyses are required. The understanding of the molecular basis of RAS in essential hypertension may provide us with new and more specific pharmacological agents and perhaps the ability to individualize antihypertensive treatment.

Preeclampsia: what we know and what we do not know

Preeclampsia remains a major health problem for mothers and infants. Studying the entire pathophysiology of preeclampsia rather than "pregnancy-induced hypertension" has greatly expanded our knowledge of the disorder. Current thinking approaches preeclampsia as a 2 stage disorder: reduced placental perfusion usually secondary to abnormal implantation and a consequent maternal disorder characterized by endothelial dysfunction and subsequent pathophysiological changes. We know much about the 2 stages and less about their linkage. It is evident that reduced placental perfusion is not sufficient to account for the pathophysiology. Reduced perfusion and abnormal implantation occur in other conditions (intrauterine growth restriction and preterm labor) without the maternal syndrome. This leads to the hypothesis that reduced placental perfusion must interact with maternal constitutional factors to generate the systemic pathophysiology of preeclampsia. The similarities of these risk factors and metabolic alterations between preeclampsia and atherosclerosis suggest a common pathophysiology. Oxidative stress is postulated as the genesis of endothelial dysfunction in atherosclerosis. The author proposes that oxidative stress secondary to reduced placental perfusion leads to endothelial dysfunction, linking the 2 stages of the syndrome.

The L10F mutation of angiotensinogen is rare in pre-eclampsia

BACKGROUND

A mutation in the gene for angiotensinogen, changing the leucine residue at position 10 to a phenylalanine (L10F), has been reported in a patient with proteinuric pre-eclampsia. In vitro enzymatic studies suggest this mutation would increase production of the vasoactive peptide, angiotensin II in vivo, and therefore explain the etiology of the maternal hypertension.

OBJECTIVE

To determine whether mutation of codon 10 of angiotensinogen is common in pre-eclampsia, and therefore likely to be involved in disease susceptibility.

DESIGN

We collected a cohort of 32 women with 'true' pre-eclampsia. All were normotensive prior to the 20th week of pregnancy, developed blood pressures consistently above 140/90 mmHg and had proteinuria of greater than 300 mg/day during the third trimester. All had blood pressures that returned to normal within 1 month of delivery; 31 women were primigravida. Genomic DNA was isolated from their peripheral blood lymphocytes for genetic analyses.

METHODS

A polymerase chain reaction-restriction enzyme-based assay was devised to screen for mutation of codon 10 of the angiotensinogen gene. In addition, we determined the frequency of a threonine residue at position 235 in the angiotensinogen gene, given previous controversial findings of association of this polymorphism with disease.

CONCLUSIONS

We detected no mutation of codon 10 in angiotensinogen in any of the 32 women studied, indicating that this mutation is not commonly associated with proteinuric pre-eclampsia. Furthermore, there was no increased frequency of threonine 235 in the affected individuals studied compared with respective normotensive Caucasian-American and African-American populations.

Genetic control of fertility and embryonic waste in the mouse: A rolefor angiotensinogen

The purpose of this study was to evaluate the impact of angiotensinogen gene (Agt) deficiency on reproductive fitness in a rodent model. Mice with 0 (Agt(-/-)), 1 (Agt(-/+)), and 2 (Agt(+/+)) copies of Agt were bred according to the following schemes: 1) Agt(-/-) x Agt(-/-), 2) Agt(-/+) x Agt(-/+), 3) Agt(+/+) x Agt(+/+), and 4) Agt(+/+) female symbol x Agt(-/+) male symbol. There were 4 breeding pairs per scheme. Breedings were time mated. Mice and litters were weighed daily. Southern blotting was used for genotyping. We found that Agt(-/-) breeding pairs had fewer litters (2 [range 1-2] vs. 4 [range 3-5]; P = 0.01), fewer pups per litter (4 [range 1-7] vs. 6 [range 1-10]; P = 0.006), and longer interpregnancy intervals (43 days [range 31-44] vs. 35.5 days [range 22-58]; P = 0.04) compared to wild-type controls. The ratio of postcoital plugs to subsequent litters was 4.0 and 1.2 for Agt(-/-) and Agt(+/+) breedings, respectively (P = 0.03). Median maternal weights during all trimesters of pregnancy were significantly lower for Agt-deficient mice compared to wild-type controls. Among Agt(-/+) x Agt(-/+) breedings, the proportions of Agt(+/+) (n = 17), Agt(-/+) (n = 38), and Agt(-/-) (n = 4) offspring differed significantly from the expected 1:2:1 Mendelian inheritance pattern (P = 0.03). Neonatal survival among the offspring derived from the Agt(-/-) x Agt(-/-) breeding scheme was significantly reduced (P = 0. 001). We conclude that Agt deficiency is associated with an in utero lethal effect, decreased fertility, and impaired neonatal survival.

Synergistic effect of angiotensin-converting enzyme and angiotensinogen gene on cardiac hypertrophy

AIMS

There are controversies concerning the association of angiotensin-converting enzyme (ACE) insertion/deletion (I/D) polymorphism with left ventricular hypertrophy (LVH), and the unclear association between angiotensinogen (ATG) M235T polymorphism and LVH. We investigated both the separate and interactive effects of these two genes on LVH in patients (N=396) with cardiovascular disease and normal healthy volunteers (N=133).

RESULTS

Frequency of DD genotype of ACE gene was significantly (P<0.05) higher in patients with LVH than patients without LVH or normal controls. Frequency of IT genotype of ATG gene in patients with LVH was significantly (P<0.01) greater than that in normal controls or marginally (P=0.1) higher than that in patients without LVH. These findings were also observed in normotensive patients and normal controls after excluding hypertensive patients. Only in patient group, the frequency of DD genotype in the highest quartile of LVMI was significantly greater than that in the lowest quartile (P<0.05). The higher tendency of TT genotype in the highest quartile patients compared with that in the lowest, did not reach statistical significance. In combined genotype analysis, there was a remarkable difference in LVMI between the two extreme double homozygotes only in patient group (156+/-25 versus 109+/-25 g/m2 for TT+DD versus MM+II) (P<0.01). In ANCOVA, the interaction term composed of ACE and ATG genotype was a significant independent variable for LVMI only in the male patient group (P<0.01).

CONCLUSION

The D-allele of ACE and T-allele of ATG gene exert a synergistic effect on cardiac hypertrophy in male patients with cardiovascular diseases, but not in normal healthy population.

Is angiotensinogen gene polymorphism associated with hypertension in pregnancy?

OBJECTIVE

To determine whether a state of hypertension in pregnancy in the Japanese can be predicted in the early period based on detection of the M235T variant of the angiotensinogen gene, alone or with other factors.

METHODS

A total of 313 Japanese pregnant women were divided into 3 groups on the basis of their angiotensinogen genotype: TT, MT, and MM. Hypertension in pregnancy was diagnosed for 33 patients in all. For each group, we sought to determine what factors increased the risk of the disease.

MAIN OUTCOME MEASURES

The angiotensinogen M235T variant, mean arterial pressure (MAP) before the 12th gestational week, body mass index (BMI) before pregnancy, age at delivery, parity, a familial history of hypertension, and development of preeclampsia or gestational hypertension were considered.

RESULTS

The frequencies of the allele T were the same among preeclampsia, gestational hypertension, and normal subjects. In TT subjects, a high incidence of gestational hypertension was found for women with MAP > or = 90 mm Hg, high or low BMI before pregnancy > or = 22.0 or < 18.0, and maternal history of hypertension. In MT subjects, women who showed MAP > or = 90 mm Hg or who were above 36 years old at delivery had a high incidence of gestational hypertension. Preeclampsia could not be predicted in either group.

CONCLUSIONS

Hypertension in pregnancy cannot be predicted on the basis of the M235T variant of angiotensinogen gene alone. However, gestational hypertension is associated with combinations of other factors. In contrast, it is virtually impossible to predict the development of preeclampsia.

Regulated expression of human angiotensinogen gene by hepatocyte nuclear factor 4 and chicken ovalbumin upstream promoter-transcription factor

We previously identified various upstream and downstream regulatory elements and factors important for hepatic expression of the human angiotensinogen (ANG) gene, the precursor of vasoactive octapeptide angiotensin II. In the present study, to further investigate the molecular mechanism of human ANG transcriptional regulation, we generated transgenic mice carrying the fusion gene composed of the 1. 3-kilobase promoter of the human ANG gene, its downstream enhancer, and the chloramphenicol acetyltransferase reporter gene. Because expression of the chloramphenicol acetyltransferase gene was observed strongly in the liver and weakly in the kidney, we suspected that hepatocyte nuclear factor (HNF) 4 with a tissue expression pattern similar to that of the reporter gene would regulate ANG transcription. In vitro assays indicated that HNF4 bound to the promoter elements and strongly activated the ANG transcription, but that chicken ovalbumin upstream promoter transcription factor (COUP-TF), a transcriptional repressor, dramatically repressed human ANG transcription through the promoter elements and the downstream enhancer core elements. Furthermore, COUP-TF dramatically decreased the human ANG transcription in the mouse liver by the Helios Gene Gun system in vivo. These results suggest that an interplay between HNF4 and COUP-TF could be important in hepatic human ANG transcription.

Hypertension in pregnancy: new recommendations for management

Hypertension in pregnancy is a frequent complication that has substantial adverse perinatal outcomes. Hypertension may be preexisting (chronic) essential or secondary hypertension; a second entity is pregnancy induced (gestational hypertension, preeclampsia). Recent advances have identified newer markers for pregnancy hypertension: several potential candidate genes may explain the apparent family inheritance of preeclampsia, and some thrombophilic markers have been associated with the condition. Management options for mild to moderate hypertension include a short hospital stay to exclude ongoing severe hypertension and to ascertain fetal well-being. Outpatient care with appropriate maternal and fetal surveillance, including umbilical artery doppler velocimetry, is recommended for better perinatal outcomes. Acute care for severe hypertension includes the use of magnesium sulfate to prevent eclampsia and antihypertensive medication. Expeditious delivery is recommended when the maternal or fetal states cannot be stabilized. Follow-up after delivery allows the uncovering of any other coexisting hypertensive or cardiovascular disorder.

Primordial prevention of cardiovascular disease through applied genetics

Primordial prevention might be considered prevention of the development of disease at its earliest stages or early intervention on risk factors to eliminate increased risk in the first place. In this review we consider how knowledge of genetic causes of early cardiovascular disease can lead to directed screening and better treatment of high risk individuals. While gene therapy would be the most "primordial" approach to prevention of some diseases such as familial hypercholesterolemia, its practical application remains on the horizon. Nevertheless, there is much we can do now to prevent early deaths in genetically high risk patients. Here we consider epidemiology as the parent discipline for applied genetics and as integral to primordial prevention. With new knowledge of special susceptibility and new understanding of the interaction of genetics and exposures, prevention of individual high-risk in the first place is realizable. We summarize here the known and candidate genes influencing atherosclerosis, hypertension, and thrombosis; their diagnosis; and some useful preventive approaches. MEDPED, an international scheme for detection of risk in medical pedigrees, is described, along with the cost and social implications of its application as a preventive strategy.

Transgenic and knockout models in renin-angiotensin system

The renin-angiotensin system, composed of enzymatic and signal-transduction cascades, plays a key role in the regulation of arterial blood pressure and in the development of certain forms of experimental and human hypertension. The products of this system, angiotensin peptides, exert a wide range of physiologically important effects on many tissues, including those of the cardiovascular systems, through their actions on angiotensin receptors. Molecular genetic and transgenic studies have begun to implicate some of the genes encoding components of the renin-angiotensin system in the development of cardiovascular diseases. Recently, we succeeded in generating transgenic mice with chronic hypertension and with inducible hypertension during pregnancy and in creating mice homozygous for a targeted disruption of the angiotensinogen gene (the only known precursor of angiotensins), resulting in the complete loss of angiotensin signals in vivo. Here, we will review recent advances related to the functional analysis of the renin-angiotensin system, in particular by focusing on transgenic approaches including gene targeting.

No mutations found in candidate genes for dystocia

Dystocia is a disorder characterized by prolonged or dysfunctional labour. Delivery that starts late or not at all, leads to an increased risk for Caesarean section, infant morbidity and mortality. Familial aggregations of dystocia suggest a polygenic background. We have studied three candidate genes for dystocia, i.e. the genes for testosterone 5-alpha reductase type 1, prostaglandin F2alpha receptor and endothelin 1 and performed mutational screening in 23 women with dystocia, of which 12 have affected relatives. No mutations were found, making it unlikely that any of these genes represent a major cause of dystocia in man.

Association of a variant of the angiotensinogen gene with pure type of hypertension in pregnancy in the Japanese: implication of a racial difference and significance of an age factor

The contribution of genetic factors to hypertension in pregnancy, including pre-eclampsia, has been well documented. The association with a common molecular variant of the angiotensinogen (AGT) gene, in which methionine (M235) is substituted for threonine (T235) at residue 235, has been reported in both Caucasians and Japanese. In the present study, we examined 115 cases of pure type of hypertension in pregnancy (PHP) and 381 normal pregnant controls in order to look for subgroups in which the AGT gene is the major factor in the PHP pathogenesis. By classification of PHP cases according to the clinical diagnosis, gravidity, and maternal age, we found significantly higher frequencies of T235 in both all PHP patients and preeclampsia/eclampsia patients than in normal controls. These results are discordant with those reported for Caucasian subjects where only a group of preeclamptic primigravidae was associated with the AGT variant, possibly indicating the existence of a racial difference. We also found that the variant frequency was significantly higher in the PHP subgroup with maternal age of 20-34 years (0.93) than in a subgroup of multigravid PHP patients age 35 years or older (0.77, P < 0.05) or in normal controls of age 20-34 years (0.76, P < 0.001). The result indicates that the AGT variant plays a significant role in hypertension in the age group 20-34 years.

A genome-wide scan reveals a maternal susceptibility locus for pre-eclampsia on chromosome 2p13

Pre-eclampsia is a common and serious disease and a major cause of maternal and infant mortality. Antenatal care systems world-wide screen for signs of the disease such as hypertension and proteinuria. Unlike most other human disorders it impacts two individuals, the mother and the child, both of whom can be severely affected. The pathophysiology of the disorder is incompletely understood, but familial clustering of the disease is apparent. Here we report the results of a genome-wide screen of Icelandic families representing 343 affected women. Including those patients with non-proteinuric pre-eclampsia (gestational hypertension), proteinuric pre-eclampsia and eclampsia, we detected a significant locus on 2p13 with a lod score of 4.70 (single point P < 3.49 x 10(-6)). This is the first reported locus for pre-eclampsia meeting the criteria for genome-wide significance.

Lipoprotein-genotype associations in Trinidadian neonates

OBJECTIVES

We hypothesized that common variation in the angiotensinogen (AGT), beta-3-adrenergic receptor, intestinal fatty acid-binding protein, serum paraoxonase, paraoxonase-2, hepatic lipase, apolipoprotein E (APOE), and Werner helicase (WRN) genes would be associated with variation in biochemical phenotypes in a previously unstudied neonatal sample.

DESIGN AND METHODS

We examined associations of both nongenetic and genetic variables with plasma lipoprotein traits in neonates from Trinidad.

RESULTS

Among nongenetic variables, we found significant associations between plasma concentrations of: 1) lipoprotein(a) [Lp(a)] and both ethnicity (p = 0.037) and birth weight (p = 0.001); 2) total cholesterol and gender (p = 0.010); 3) triglyceride and birth weight (p = 0.035); and 4) apolipoprotein AI and gender (p = 0.016). Among genetic variables, we found that: 1) common variation on chromosome 1q in AGT codon 235 was significantly associated with variation in plasma apolipoproteins AI (p<0.0001) and B (p = 0.013); 2) common variation in WRN at codon 1367 was significantly associated with variation in plasma Lp(a) (p<0.0001); and 3) common variation in APOE at codons 112 and 158 was significantly associated with variation in plasma triglycerides (p = 0.013).

CONCLUSIONS

The associations with AGT and WRN are novel and may have resulted either from a direct influence of the genetic variants or through linkage disequilibrium with other functional loci, such as the familial combined hyperlipidemia locus on chromosome 1q in the case of AGT. Despite the fact that there are some limitations in making determinations from cord blood, the results suggest that there may be genetic determinants of plasma lipoproteins in neonates.

Novel mechanism of hypertension revealed by cell-specific targeting of human angiotensinogen in transgenic mice

We tested the hypothesis that the tissue-specific intrarenal renin-angiotensin system (RAS) can participate in the regulation of blood pressure independently of its endocrine counterpart, by generating two transgenic models that differ in their tissue-specific expression of human angiotensinogen (AGT). Human AGT expression was driven by its endogenous promoter in the systemic model and by the kidney androgen-regulated protein promoter in the kidney-specific model. Using molecular, biochemical, and physiological measurements, we demonstrate that human AGT mRNA and protein are restricted to the kidney in the kidney-specific model. Plasma ANG II was elevated in the systemic model but not in the kidney-specific model. Nevertheless, blood pressure was markedly elevated in both the systemic and kidney-specific transgenic mice. Acute administration of the selective ANG II AT-1 receptor antagonist losartan lowered blood pressure in the systemic model but not in the kidney-specific model. These results provide evidence for the potential importance of the intrarenal RAS in blood pressure regulation by showing that expression of AGT specifically in the kidney leads to chronic hypertension independently of the endocrine RAS.

Factor V Leiden and thermolabile methylenetetrahydrofolate reductase gene variants in an East Anglian preeclampsia cohort

Preeclampsia is a heritable condition that develops as a result of widespread vascular endothelial dysfunction. The thrombotic tendency in this condition has suggested a number of candidate genes, and there have been recent reports of positive association with the Leiden variant of factor V and the thermolabile variant of methylenetetrahydrofolate reductase. We attempted to reproduce these results in a large cohort of well-characterized women with preeclampsia, recruited prospectively within the East Anglian region of the United Kingdom. Women in the preeclampsia cohort (n=283) were genotyped for both the Leiden variant (G1691A) of factor V and the thermolabile variant (C677T) of methylenetetrahydrofolate reductase. Genotype and allele frequencies were compared with those of 2 control groups, one consisting of women recruited prospectively (n=100) from the same maternity hospital as the subjects and another consisting of normotensive women (n=100) from East Anglia. No significant differences were detected. Specifically, the carrier rate for the Leiden variant was 5.3% in the preeclampsia group and 5. 5% in the combined control group. T677 homozygotes for methylenetetrahydrofolate reductase were 11% and 11.5% in the 2 groups, respectively. We conclude that there is no evidence of association of preeclampsia with either of these 2 polymorphisms in our study population.

Seven lessons from two candidate genes in human essential hypertension: angiotensinogen and epithelial sodium channel

The candidate gene approach to understanding the genetics of human essential hypertension is discussed by analyzing the contribution of 2 genes, angiotensinogen (AGT) and epithelial amiloride-sensitive sodium channel (ENaC). From a large series of studies conducted in humans and animals, it appears that the AGT gene plays a significant but modest role in human blood pressure variance. Mutations of the beta- and gamma-ENaC subunits are responsible for Liddle's syndrome, but the implication of the 3 ENaC subunits in essential hypertension is still questionable. Several lessons can be learned from these studies and applied to other candidate genes in essential hypertension: (1) Many linkage or association studies have a limited statistical power; (2) The genetic findings may vary greatly according to the populations studied; (3) There is a need for better phenotyping of the hypertensive population; (4) The causal relationship between molecular variants and hypertension is and will be difficult to establish firmly; (5) The contribution of genetic studied in rodents to the molecular genetics of human hypertension must be re-examined; (6) Most molecular variants lead to a low attributable risk in the population or a low individual effect at the individual level; and (7) It is too early to propose dietary recommendations and specific drug treatment according to patients' genotypes.

Transcriptional regulation of angiotensinogen gene expression

The renin--angiotensin system (RAS) is an extracellular hormonal system implicated in acute, homeostatic control of peripheral vascular resistance and electrolyte homeostasis. In this tightly regulated system, physiological regulators of blood pressure and fluid balance induce the production of the potent vasoactive angiotensin peptides by sequential proteolysis of the angiotensinogen (AGT) prohormone. AGT is the only known precursor of the angiotensin peptides, whose circulating concentrations influence the tonic activity of the RAS. AGT abundance is regulated at the transcriptional level through hormonal and cell-type specific regulators. In this review, we will discuss the identified mechanisms controlling AGT expression separately for the rodent and human genes. The most intensively investigated gene (rodent AGT) is regulated constitutively by multiple positive- and negative-acting cis factors that function in a cell-type dependent fashion. Inducible rodent AGT expression is mediated through a multihormone-inducible enhancer that integrates signals from steroid and cytokine hormones into AGT transcription. We review recent advances in understanding the mechanism of the nuclear factor-kappa B (NF-kappa B) family in mediating cytokine-induced AGT expression and our recent discoveries on the existence of differentially inducible pools of cytoplasmic NF-kappa B. Constitutive control of the human AGT gene will be discussed; there is surprisingly little information on the cis- and trans-acting regulators controlling inducible expression of human AGT. Finally, we will explore some of the recent developments in gene linkage studies where human AGT alleles have been associated with hypertensive phenotypes through a mechanism that may involve enhanced transcription. These studies have provided a molecular explanation for a subset of heritable hypertensive disorders in humans.

Renin-angiotensin system component gene polymorphism in Japanese bronchial asthma patients

The influence of renin-angiotensin system (RAS) component gene polymorphism in the pathogenesis of bronchial asthma was investigated in an association study involving 119 bronchial asthma patients and 208 control subjects. The selected RAS polymorphisms were angiotensinogen (Agt) T235/M235 and angiotensin I-converting enzyme (ACE) insertion/deletion (I/D). The control allelic frequencies of the Agt T235/M235 (0.84/0.16) and ACE I/D (0.63/0.37) in this study were similar to the previous reports in Japanese normal population. The allelic frequencies of the Agt T235/M235 (0.84/0.16) and ACE I/D (0.65/ 0.35) among the asthma patients were not significantly different from those among the control subjects. There was no association between severity of bronchial asthma and the selected RAS component gene polymorphism. From these data, we conclude that in the Japanese population, the RAS component gene polymorphism is not associated with increased risk for bronchial asthma.

Patients with preeclampsia develop agonistic autoantibodies against the angiotensin AT1 receptor

Immune mechanisms and the renin-angiotensin system are implicated in preeclampsia. We investigated 25 preeclamptic patients and compared them with 12 normotensive pregnant women and 10 pregnant patients with essential hypertension. Antibodies were detected by the chronotropic responses to AT1 receptor-mediated stimulation of cultured neonatal rat cardiomyocytes coupled with receptor-specific antagonists. Immunoglobulin from all preeclamptic patients stimulated the AT1 receptor, whereas immunoglobulin from controls had no effect. The increased autoimmune activity decreased after delivery. Affinity-column purification and anti-human IgG and IgM antibody exposure implicated an IgG antibody directed at the AT1 receptor. Peptides corresponding to sites on the AT1 receptor's second extracellular loop abolished the stimulatory effect. Western blotting with purified patient IgG and a commercially obtained AT1 receptor antibody produced bands of identical molecular weight. Furthermore, confocal microscopy of vascular smooth muscle cells showed colocalization of purified patient IgG and AT1 receptor antibody. The protein kinase C (PKC) inhibitor calphostin C prevented the stimulatory effect. Our results suggest that preeclamptic patients develop stimulatory autoantibodies against the second extracellular AT1 receptor loop. The effect appears to be PKC-mediated. These novel autoantibodies may participate in the angiotensin II-induced vascular lesions in these patients.

Maternal and fetal angiotensinogen gene allele sharing in pre-eclampsia

OBJECTIVE

To compare the angiotensinogen genotypes in normotensive and pre-eclamptic pregnancies in maternal and fetal samples.

DESIGN

Prospective observational study.

SETTING

University Hospital, Queen's Medical Centre, Nottingham.

POPULATION

Forty-three women with pre-eclampsia and 84 normotensive pregnant women. Fetal samples were available for genotyping from 96% of the pregnancies.

METHODS

Maternal and fetal DNA was genotyped at angiotensinogen codon 235 and at a dinucleotide repeat polymorphism in the 3' flanking region of the gene. Angiotensinogen and renin concentrations were measured in maternal plasma by radioimmunoassay.

RESULTS

In contrast to earlier studies, no association was demonstrated between the angiotensinogen 235 Thr variant and pre-eclampsia. Normotensive pregnant women homozygous for this variant had significantly lower plasma angiotensinogen concentrations (median 2.2 ng AI/mL; IQR 1.8-3.0) than women homozygous for the 235 Met allele (3.6 ng AI/mL; IQR 2.5-4.1; P = 0.04). In pre-eclamptic pregnancies, 79% (11/14) of mothers heterozygous for the dinucleotide repeat allele designated A9 transmitted this allele to the fetus, more frequently than would be expected by chance (P = 0.02). The A9 allele was associated with low plasma angiotensinogen concentrations (P = 0.001) and high renin concentrations (P = 0.02) in normotensive women.

CONCLUSIONS

There is no evidence that the angiotensinogen 235 Thr allele is associated with pre-eclampsia in the Nottingham population. The angiotensinogen 235 Thr allele is associated with low plasma angiotensinogen concentrations in normotensive pregnant women, in contrast to the high levels associated with this variant in non-pregnant women, suggesting that regulation of angiotensinogen expression in normal pregnancy may differ significantly from that in the non-pregnant state. There is preliminary evidence that maternal-fetal transmission of an angiotensinogen allele associated with low plasma angiotensinogen concentrations is associated with pre-eclampsia. Impaired generation of angiotensin II at the maternal-fetal interface may be a factor in the pathogenesis of pre-eclampsia.

Orphan receptor Arp-1 binds to the nucleotide sequence located between TATA box and transcriptional initiation site of the human angiotensinogen gene and reduces estrogen induced promoter activity

Human angiotensinogen gene contains a C/A polymorphism at 20 bases upstream from the transcriptional initiation site. This sequence binds to the estrogen receptor when nucleoside A is present at this site and reporter constructs containing human angiotensinogen gene promoter with nucleoside A at -20 are transactivated on co-transfection of estrogen receptor in HepG2 cells followed by estrogen treatment. We show here that orphan receptor, Arp-1, which belongs to the COUP family of transcription factors also binds to this sequence. Co-transfection of Arp-1 reduces estrogen induced promoter activity of reporter constructs containing human angiotensinogen gene promoter. On the other hand co-transfection of Arp-1 does not have a significant effect on estrogen induced promoter activity of reporter constructs containing rat angiotensinogen gene promoter. Our data suggests that human and rat angiotensinogen genes are regulated in a different manner by estrogens.

Prediction of preeclampsia

The onset of preeclampsia at or near to term is associated with low maternal and neonatal morbidity and mortality. In contrast, those patients (1%) who suffer early onset preeclampsia engender significant maternal and perinatal morbidity and mortality. Therefore, because of the lack of proven prophylaxis for preeclampsia, prediction of risk or identification of subclinical disease is desirable to identify patients for more intensive observation. There are certain at-risk groups of patients such as those with chronic hypertension, pregestational diabetes, multifetal gestation, and previous preeclampsia. These patients account for the majority of cases of preeclampsia in multiparas, yet only account for 14% of preeclampsia in nulliparous women. Thus, the majority of cases of preeclampsia arises from nulliparous women without medical complications at low risk. Differences in the time of onset, severity, and organ system involvement suggest there may be different underlying etiologies that ultimately lead to preeclampsia manifested as the triad of maternal hypertension, proteinuria, and edema. Distinct markers therefore may identify subgroups of at-risk patients with separate underlying causes. These markers ultimately could be used for diagnosis of disease before the clinical appearance of maternal disease (hypertension, proteinuria, and edema). Based on data from patients with established disease, with the involvement of various organ systems, potential candidate markers would include renal function (kallikrein-creatinine); coagulation and fibrinolytic systems and platelet activation (platelet volume); markers of vascular function (fibronectin, prostacyclin, thromboxane) and oxidant stress (lipid peroxides, 8-isoprostane, antioxidants, anticardiolipin antibodies, hemoglobin, iron, transferrin, homocysteine, hypertriglyceridemia, albumin isoforms); placental peptide hormones (CRH, CRHbp, activin, inhibin, hCG); vascular resistance (uteroplacental flow velocity waveforms); genetic markers; insulin resistance; and glucose intolerance. Although cross-sectional studies have identified these potential markers, they need to be evaluated in prospective longitudinal studies with rigorous definition of outcome to determine if they are useful in predicting preeclampsia and whether they can identify different subgroups of patients.

Angiotensinogen variants and human hypertension

The research on molecular genetics of human hypertension aims to identify the loci involved in the regulation of blood pressure, detect gene variants within the identified loci, associate them with intermediate phenotypes, and ultimately estimate their quantitative effects on blood pressure level and their interaction with main environmental factors. So far, the angiotensinogen (AGT) gene is one of the few candidate genes that has been investigated using these multiple statistical, clinical, and biochemical strategies. A highly polymorphic dinucleotide GT repeat (80% heterozygosity) has been used in several linkage studies. Other diallelic polymorphisms, located in the 5' regulatory region of the gene in intronic and exonic sequences, have been described, which were then used in association studies in different clinical settings. Positive associations between the M235T and the G-6A polymorphisms and plasma angiotensinogen levels indicates a pathway by which the AGT locus could be involved in essential hypertension.

New insights into the genetics of preeclampsia

Preeclampsia is familial. Pedigree analyses suggest that one or more common alleles may act as "preeclampsia susceptibility genes." The authors speculate that genes involved in blood pressure control, volume regulation, placental health, vascular disease, and vascular remodeling, underlie familial susceptibility to preeclampsia. Several candidate genes have been examined. These data suggest that a common mutation in the angiotensinogen promoter, A(-6), leads to elevated expression of this gene and pleiotropic effects, including abnormal spiral artery remodeling and failed hypervolemia of pregnancy. The factor V Leiden mutation, which predisposes women to thromboembolic disorders during pregnancy, has been implicated as another preeclampsia susceptibility gene. New insights into the genetics of preeclampsia will contribute to the understanding of this disease and should ultimately lead to improved diagnosis and treatment.

Ionizing radiation and genetic risks. VI. Chronic multifactorial diseases: a review of epidemiological and genetical aspects of coronary heart disease, essential hypertension and diabetes mellitus

This paper provides a broad overview of the epidemiological and genetical aspects of common multifactorial diseases in man with focus on three well-studied ones, namely, coronary heart disease (CHD), essential hypertension (EHYT) and diabetes mellitus (DM). In contrast to mendelian diseases, for which a mutant gene either in the heterozygous or homozygous condition is generally sufficient to cause disease, for most multifactorial diseases, the concepts of genetic susceptibility' and risk factors' are more appropriate. For these diseases, genetic susceptibility is heterogeneous. The well-studied diseases such as CHD permit one to conceptualize the complex relationships between genotype and phenotype for chronic multifactorial diseases in general, namely that allelic variations in genes, through their products interacting with environmental factors, contribute to the quantitative variability of biological risk factor traits and thus ultimately to disease outcome. Two types of such allelic variations can be distinguished, namely those in genes whose mutant alleles have (i) small to moderate effects on the risk factor trait, are common in the population (polymorphic alleles) and therefore contribute substantially to the variability of biological risk factor traits and (ii) profound effects, are rare in the population and therefore contribute far less to the variability of biological risk factor traits. For all the three diseases considered in this review, a positive family history is a strong risk factor. CHD is one of the major contributors to mortality in most industrialized countries. Evidence from epidemiological studies, clinical correlations, genetic hyperlipidaemias etc., indicate that lipids play a key role in the pathogenesis of CHD. The known lipid-related risk factors include: high levels of low density lipoprotein cholesterol, low levels of high density lipoprotein cholesterol, high apoB levels (the major protein fraction of the low density lipoprotein particles) and elevated levels of Lp(a) lipoprotein. Among the risk factors which are not related to lipids are: high levels of homocysteine, low activity of paraoxonase and possibly also elevated plasma fibrinogen levels. In addition to the above, hypertension, diabetes and obesity (which themselves have genetic determinants) are important risk factors for CHD. Among the environmental risk factors are: high dietary fat intake, smoking, stress, lack of exercise etc. About 60% of the variability of the plasma cholesterol is genetic in origin. While a few genes have been identified whose mutant alleles have large effects on this trait (e.g., LDLR, familial defective apoB-100), variability in cholesterol levels among individuals in most families is influenced by allelic variation in many genes (polymorphisms) as well as environmental exposures. A proportion of this variation can be accounted for by two alleles of the apoE locus that increase (&epsi;4) and decrease (&epsi;2) cholesterol levels, respectively. A polymorphism at the apoB gene (XbaI) also has similar effects, but is probably not mediated through lipids. High density lipoprotein cholesterol levels are genetically influenced and are related to apoA1 and hepatic lipase (LIPC) gene functions. Mutations in the apoA1 gene are rare and there are data which suggest a role of allelic variation at or linked LIPC gene in high density lipoprotein cholesterol levels. Polymorphism at the apoA1--C3 loci is often associated with hypertriglyceridemia. The apo(a) gene which codes for Lp(a) is highly polymorphic, each allele determining a specific number of multiple tandem repeats of a unique coding sequence known as Kringle 4. The size of the gene correlates with the size of the Lp(a) protein. The smaller the size of the Lp(a) protein, the higher are the Lp(a) levels. (ABSTRACT TRUNCATED)

M235T angiotensinogen gene polymorphism and cardiovascular renal risk

OBJECTIVE

In this meta-analysis, we attempted to derive pooled estimates for the putative associations between various cardiovascular-renal disorders and the M235T polymorphism of the angiotensinogen gene.

METHODS

Case-control studies were combined, using the Mantel and Haenszel approach. Joint P values for continuous variables were calculated by Stouffer's method. Continuous measurements reported in different units were expressed on a percentage scale using the intrastudy mean of the MM genotype as denominator.

RESULTS

The computerized database used for this analysis included 69 reports with an overall sample size of 27,906 subjects. Overall, possession of the T allele was associated with an increased risk of hypertension. In comparison with the MM reference group (number of studies, n = 32), the excess risk was 31% (P = 0.001) in TT homozygotes and 11% (P = 0.03) in TM heterozygotes. The sensitivity analysis showed that this association was present only in whites (T allelic frequency, f = 42.2%), but not in blacks (f = 77.0%) or Asians (f = 78.0%). Atherosclerotic complications (n = 12), renal microvascular disorders (n = 13), cardiomyopathy (n = 2) or diabetic retinopathy (n = 3) were not correlated with the M235T polymorphism. Publication bias was observed for hypertension, but not for coronary heart disease, including myocardial infarction, and for microvascular nephropathy. Furthermore, in comparison with the MM control group, the circulating angiotensinogen levels (n = 8) were raised by 11 and 7% (P = 0.01) in TT and TM subjects, respectively. In contrast, plasma levels of the angiotensin I converting enzyme (n = 4) and body mass index (n = 15) were not associated with the T allele.

CONCLUSION

The T allele encoding angiotensinogen is not associated with atherosclerotic or microvascular complications, but in Caucasians behaves as a marker for hypertension. This association, which may have been inflated by publication bias, does not necessarily imply causality.

Role of C/A polymorphism at -20 on the expression of human angiotensinogen gene

-Angiotensinogen is the glycoprotein precursor of 1 of the most potent vasoactive hormones, angiotensin II. Human angiotensinogen gene contains a C/A polymorphism at -20 located between the TATA box and transcriptional initiation site. We show here that when nucleoside A is present at -20, this sequence binds to the estrogen receptor. We also show that transcriptional activity of reporter constructs containing human angiotensinogen gene promoter with nucleoside A at -20 is increased on cotransfection of an expression vector containing human estrogen receptor-alpha coding sequence in human hepatoma cells (HepG2) followed by estrogen treatment. On the other hand, adenoviral major late transcription factor binds preferentially to this region of the promoter when nucleoside C is present at -20. We also show that reporter constructs containing human angiotensinogen gene promoter with nucleoside C at -20 have increased basal promoter activity on transient transfection in HepG2 cells as compared with reporter constructs with nucleoside A at -20. Our data suggest that C/A polymorphism at -20 may modulate the expression of human angiotensinogen gene in a sex-specific manner.

Angiotensinogen Thr235 variant is associated with abnormal physiologic change of the uterine spiral arteries in first-trimester decidua

OBJECTIVE

The angiotensinogen Thr235 polymorphism associated with preeclampsia is tightly linked to a mutation in the angiotensinogen promoter A(-6), which may lead to elevated expression in decidual spiral arteries. We hypothesize that locally elevated angiotensin II levels play a role in failed physiologic change leading to preeclampsia. Our objective was to determine whether spiral artery morphologic characteristics were different in first-trimester decidual samples from women homozygous for the angiotensinogen Thr235 allele and women homozygous for the normal angiotensinogen Met235 allele.

STUDY DESIGN

We used quantitative histologic analysis to study 1266 spiral artery cross-sections in decidual samples obtained from normal pregnancies (n = 53) terminated at 8 weeks' gestation. To define vessel characteristics before pregnancy-induced remodeling, we also examined 60 arteries in nonpregnant endometrial control samples (n = 5). We measured the aspect ratio, media area, and external diameter of each cross-section with Image-Pro plus software. Maternal angiotensinogen genotypes were determined by means of mutagenically separated polymerase chain reaction. Average spiral artery morphologic measurements were compared between genotypes with the Student t test.

RESULTS

The media area/external diameter ratio was lower in decidual samples than in endometrial samples (P <.0001), consistent with pregnancy-induced physiologic changes. Women homozygous for the angiotensinogen Thr235 allele (n = 11) had a greater area/diameter ratio than did women homozygous for the normal angiotensinogen Met235 allele (n = 11, P <.05). Samples from heterozygous women (n = 31) had intermediate values.

CONCLUSION

Our results suggest that the angiotensinogen Thr235 allele predisposes women toward abnormal physiologic change, potentially beginning the cascade of events leading to preeclampsia.

Role of cysteine residues in human angiotensinogen. Cys232 is required for angiotensinogen-pro major basic protein complex formation

The M235T polymorphism of human angiotensinogen is associated with essential and pregnancy-induced hypertension. A covalent complex is formed between angiotensinogen and the proform of the eosinophil major basic protein (proMBP) during pregnancy. The sequence of human angiotensinogen contains four cysteines. Their function was analyzed. Presence of free cysteines was demonstrated by their alkylation with iodo[14C]acetic acid. A disulfide bond between Cys18 and Cys138 using a fully N-deglycosylated mutant of human angiotensinogen was identified by tryptic digestion and mass spectrometry. We produced angiotensinogen. proMBP complex by co-transfection of COS-7 cells and by co-culturing transfected CHO-K1 cells. Experiments with 8 mutated recombinant angiotensinogen, in which one or more of the four cysteines were replaced by alanine, demonstrated that Cys232 is involved in complex formation and could interact with the M235T variant. The angiotensinogen.proMBP complex was isolated by molecular sieving. Hydrolysis of the complex by human renin was 7 times slower than hydrolysis of monomeric form, whatever the M235T genotype. The complex:monomeric angiotensinogen ratio was greater for Met235 (72%) than for Thr235 (58%) angiotensinogen. These data suggest a new pathophysiological explanation for the genetic association between M235T angiotensinogen polymorphism and pregnancy-induced hypertension.

Exon-I is involved in positive as well as negative regulation of human angiotensinogen gene expression

Angiotensinogen is the glycoprotein precursor of one of the most potent vasoactive hormones, angiotensin-II. Angiotensinogen gene is primarily expressed in the liver, and this gene locus is linked with human essential hypertension. We show here that a mutation in exon-I reduces the basal expression of the human angiotensinogen gene in liver cells. We also show that a nucleotide sequence in exon-I binds to liver-enriched transcription factor HNF-3 and a ubiquitous factor AP4. Our studies also show that transient transfection of an expression vector containing AP4 coding sequence downregulates the expression of reporter constructs containing human angiotensinogen gene promoter. By contrast, co-transfection of an expression vector containing HNF-3beta coding sequence increases the expression of these reporter constructs. The human angiotensinogen gene has a C/A polymorphism located at -20, and we have shown that estrogen receptor-alpha binds to this sequence when nucleoside A is present at this site. We show here that co-transfection of an expression vector containing AP4 coding sequence reduces estrogen-induced promoter activity of reporter constructs containing human angiotensinogen gene promoter (with nucleoside A at -20) attached to the CAT gene. These studies partly explain the molecular mechanisms involved in tissue-specific expression of the human angiotensinogen gene.

A polymorphism of angiotensinogen gene codon 174 and coronary artery disease in Japanese subjects

The relationship between coronary artery disease (CAD) and polymorphisms of genes encoding angiotensinogen (AGT) and angiotensin converting enzyme (ACE) was analyzed in Japanese subjects. One hundred and four patients with CAD and 170 healthy subjects were enrolled in the study. CAD was defined as having a luminal diameter stenosis > or =50% in at least one of three major coronary arteries by coronary angiography. The genotypes (determined by polymerase chain reaction) of AGT gene codon 174 were not significantly associated with CAD in the total study population. However, the frequency of T/T homozygotes of AGT codon 174 was significantly higher in CAD patients compared to controls in each of three subgroups: 1) body mass index (BMI) below the median value of 24.1 kg/m2; 2) not more than two CAD risk factors out of five (hypercholesterolemia, hypertension, diabetes mellitus, smoking, and family history of CAD); and 3) the ACE I/I genotype. The M/M genotype of AGT codon 235 was negatively associated, and the ACE D/D genotype was positively associated, with CAD in the total study population. Our results indicate that the T/T genotype of AGT codon 174 may be a risk factor for CAD in Japanese individuals with low BMI, lesser CAD risk factors, or ACE I/I genotype.

Etiology and pathogenesis of preeclampsia: current concepts

The etiology of preeclampsia is unknown. At present, 4 hypotheses are the subject of extensive investigation, as follows: (1) Placental ischemia-Increased trophoblast deportation, as a consequence of ischemia, may inflict endothelial cell dysfunction. (2) Very low-density lipoprotein versus toxicity-preventing activity-In compensation for increased energy demand during pregnancy, nonesterified fatty acids are mobilized. In women with low albumin concentrations, transporting extra nonesterified fatty acids from adipose tissues to the liver is likely to reduce albumin's antitoxic activity to a point at which very-low density lipoprotein toxicity is expressed. (3) Immune maladaptation-Interaction between decidual leukocytes and invading cytotrophoblast cells is essential for normal trophoblast invasion and development. Immune maladaptation may cause shallow invasion of spiral arteries by endovascular cytotrophoblast cells and endothelial cell dysfunction mediated by an increased decidual release of cytokines, proteolytic enzymes, and free radical species. (4) Genetic imprinting-Development of preeclampsia-eclampsia may be based on a single recessive gene or a dominant gene with incomplete penetrance. Penetrance may be dependent on fetal genotype. The possibility of genetic imprinting should be considered in future genetic investigations of preeclampsia.

DBP binds to the proximal promoter and regulates liver-specific expression of the human angiotensinogen gene

Angiotensinogen is the glycoprotein precursor of one of the most potent vasoactive hormones, angiotensin-II. It has been shown recently that an ATF like element (ALE) located between bases -102 and -87 of the human angiotensinogen gene plays an important role in liver specific expression of this gene and binds to CREB/ATF family of transcription factors and a novel factor (ALF). We show here that this sequence binds to the liver enriched transcription factor DBP and cotransfection of expression vector CMV-DBP increases the expression of reporter constructs containing this sequence. In addition, we show that transcription factor C/EBP-delta binds to this sequence and an expression vector containing C/EBP-delta coding region increases the expression of reporter constructs containing this sequence. Since DBP is involved in circadian rhythm, our studies suggest that this sequence may be involved in circadian expression of the human angiotensinogen gene.

Human spiral artery renin-angiotensin system

Pregnancy induces uterine spiral arteries to remodel into dilated uteroplacental vessels by an unknown mechanism called "physiological change." In women who develop preeclampsia, however, many spiral arteries remain unchanged or develop medial hyperplasia and atherosis. We recently demonstrated that angiotensinogen is expressed by remodeling spiral arteries in first-trimester decidua. We hypothesize that a local spiral artery renin-angiotensin system mediates pregnancy-induced remodeling of these vessels. In this study we tested for expression of renin, angiotensin-converting enzyme, and angiotensin II type 1 receptor genes in the first-trimester uterus using reverse-transcription polymerase chain reaction. Expression was localized by in situ hybridization and immunohistochemistry. Renin, angiotensin-converting enzyme, and the angiotensin II type 1 receptor are all expressed in and around remodeling spiral arteries. These observations suggest that a local spiral artery renin-angiotensin system may play a role in pregnancy-induced remodeling of these vessels. Elevated angiotensinogen expression in women homozygous for the A(-6) variant in the angiotensinogen promoter may promote abnormal remodeling, whereas relatively lower levels in women homozygous for G(-6) may permit enough normal remodeling to protect these women from preeclampsia.

Associations of angiotensinogen gene mutations with hypertension and myocardial infarction in a gulf population

To date, the human angiotensinogen (AGT) gene and some of its variants represent the best examples of genetic influences that are involved in the determination of essential hypertension (EH) and associated cardiovascular diseases (CVDs). To assess the value of genotyping AGT in a genetically homogeneous population, we carried out a retrospective, case control study of variants M235T and T174M for putative correlations with CVDs among nationals from the United Arab Emirates (Emirati)--an ethnic group characterized by no alcohol intake and no cigarette smoking. We investigated a sample population of 229 Emirati (119 males and 110 females), comprising groups of controls and patients with clinical diagnoses of EH, left ventricular hypertrophy (LVH), ischaemic heart disease (IHD) and myocardial infarction (MI). M235T and T174M alleles were determined via assays based on the polymerase chain reaction. T174M showed no correlation with any of the four clinical entities included in this study. T235 alleles, however, occurred more frequently in the EH group and less frequently in the group of MI survivors. We also found that T235 allele frequencies decreased with age, indicating that in the Emirati population, T235 alleles are associated with a reduced life span and that this effect could occur through independent mechanisms underlying genetic susceptibilities to both EH and MI.

Transgenesis and Gene Targeting in the Mouse

As more effort is made to identify genes responsible for hypertension in human populations and genetically hypertensive animal models, the need for experimental systems in which the functional significance of genes, gene variants, and quantitative trait loci (QTL) can be determined is becoming increasingly important. Over the past five years, transgenic and gene-targeting technology has been utilized to study the cardiovascular effects of over-expression or ablation of genes which have been considered candidates in the genetic basis of hypertension. This review focuses on the most recent major advances in this area, and how this technology aids in our understanding of the molecular mechanisms by which newly discovered genes or gene variants affect blood pressure in the whole organism. We also discuss the potential use of transgenic models in refining the location of a QTL, and discuss some of the limitations and potential pitfalls in the application of these tools to the field of hypertension research. The coupling of genetic manipulations afforded by transgenesis and gene targeting, along with advances in our ability to assess the cardiovascular phenotype in the mouse, provides us with a powerful system for examining the genes responsible for causing essential hypertension.

T235 variant of the angiotensinogen gene and blood pressure in the Chilean population

BACKGROUND

The angiotensinogen gene has recently been linked to essential hypertension. A variant within this gene, encoding threonine rather than methionine at amino acid position 235, was associated with essential hypertension. However, results of new studies have not confirmed this association, suggesting that ethnic differences may explain the different results.

OBJECTIVE

To evaluate whether the T235 variant is associated with a higher incidence of essential hypertension among Hispanics (a group that has scarcely been evaluated) and to determine whether T235 is associated with variations in the plasma renin activity or the serum aldosterone level.

PATIENTS AND METHOD

We studied 64 patients with essential hypertension and 62 normotensives, matched for age and sex. We obtained samples for determinations of plasma renin activity, serum aldosterone level and genome DNA from all subjects. The genomic DNA was amplified using the polymerase chain reaction technique and digested by the restriction enzyme streptococcus faecalis (Sfa NI) which cuts M235 only, not T235.

RESULTS

The patients with essential hypertension had a higher prevalence of the risk variant T235 (alleles 77/128 = 60.2%) than did the normotensive controls (alleles 65/124 = 52.4%), but the difference was not statistically significant (chi2=1.53, P=0.22). The plasma renin activity levels in hypertensives were not statistically different for homozygous T235, heterozygous and homozygous M235 (1.0 +/- 0.96, 2.0 +/- 2.25 and 1.55 +/- 1.49 ng/ml per h, respectively, P=0.5 1). However, when we considered those hypertensives with low plasma renin activity levels (< 1 ng/ml per h), we found a high prevalence (72.7%) of subjects homozygous for the T235 variant. We found no association between the T235 variant and the serum aldosterone levels in hypertensive and normotensive subjects.

CONCLUSIONS

We demonstrated that there is a high prevalence of T235 variant in our Hispanic population. The slight difference between prevalences of T235 variant among hypertensive and normotensive subjects that we found was not statistically significant and did not permit us to establish an association between T235 variant and essential hypertension. We believe that only studying a larger cohort of subjects could show whether there is a quantitative effect of the T allele on plasma renin activity levels.

Decidual spiral artery remodelling begins before cellular interaction with cytotrophoblasts

Endometrial arteries undergo structural alterations during pregnancy to increase blood flow to the intervillous space. It is hypothesized that physiologic change in decidual arteries is similar to vascular remodelling seen in other organs. Histologic features of spiral arteries in secretory endometrial biopsies were compared blindly to decidual arteries from elective abortions. Similar sections were stained for trophoblastic and vascular antigens. Spiral arteries in endometrium from ectopic (tubal) and intrauterine pregnancies were compared also. Evidence of decidual endothelial activation was sought using antibodies to vascular cell adhesion molecule (VCAM-1). As expected, decidual arteries were significantly different than arteries in secretory endometrium: there was more endothelial basophilia, vacuolation, and arterial dilation in early pregnancy. Some vessels had disorganized or hypertrophied smooth muscle layers. Similar structural alterations were seen in endometrium of ectopic pregnancies, and in the decidua parietalis of intrauterine pregnancies. Immunohistochemical studies confirmed that these alterations occurred in the absence of cellular interaction with extravillous cytotrophoblasts. Independently of trophoblasts, decidual endothelial cells expressed VCAM-1. It is concluded that the initial stages of physiologic change are characterized by vascular remodelling, which occur in the absence of trophoblast invasion of the spiral arteries. Arterial modifications in decidua begin as a maternal response to pregnancy.

Hypertension: genes and environment

Hypertension can be classified as either Mendelian hypertension or essential hypertension, on the basis of the mode of inheritance. The Mendelian forms of hypertension develop as a result of a single gene defect, and as such are inherited in a simple Mendelian manner. In contrast, essential hypertension occurs as a consequence of a complex interplay of a number of genetic alterations and environmental factors, and therefore does not follow a clear pattern of inheritance, but exhibits familial aggregation of cases. In this review, we discuss recent advances in understanding the pathogenesis of both types of hypertension. We review the causal gene defects identified in several monogenic forms of hypertension, and we discuss their possible relevance to the development of essential hypertension. We describe the current approaches to identifying the genetic determinants of human essential hypertension and rat genetic models of hypertension, and summarise the results obtained to date using these methods. Finally, we discuss the significance of environmental factors, such as stress and diet, in the pathogenesis of hypertension, and we describe their interactions with specific hypertension susceptibility genes.

Pre-eclampsia--still a disease of theories?

The pathophysiology of pre-eclampsia remains poorly understood. Moreover, there is no reliable predictive test and no effective prophylactic therapy for this disease. Advances have, however, recently been made in our understanding of the genetics of pre-eclampsia and in the processes which lead to abnormal trophoblastic invasion in pre-eclampsia. Prediction and prevention are intimately linked, and both problems will only be solved by further unravelling of the complex pathophysiology of pre-eclampsia.

Angiotensin-converting enzyme and angiotensinogen gene polymorphisms and heart rate variability in twins

Decreased heart rate variability (HRV) is associated with congestive heart failure, post-myocardial infarction, ventricular arrhythmias, sudden cardiac death, and advancing age. A deletion/insertion polymorphism in the angiotensin-converting enzyme (ACE) gene and a substitution (M235T) in the angiotensinogen gene have been associated with risk for heart disease. The aim of this study was to determine the heritability of HRV and related parameters in monozygotic and dizygotic twins and to assess the influence of ACE and angiotensinogen polymorphisms. We studied 95 MZ pairs and 46 DZ pairs. We measured HRV and related parameters, ACE and angiotensinogen levels, plasma norepinephrine, ACE, and angiotensinogen genotypes. We found that HRV and related parameters were significantly influenced by genetic variability, although nonshared genetic effects were also important. Angiotensinogen and plasma norepinephrine were generally correlated with decreased HRV, whereas ACE was correlated with perturbances of normal rhythmic HRV. Nevertheless, the DD ACE genotype was associated with increased HRV (p <0.05), whereas angiotensinogen polymorphisms had no effect. We conclude that HRV and related parameters are in part heritable. Interestingly, the DD ACE genotype is associated with increased HRV.

Polymorphisms at the angiotensinogen (AGT) and angiotensin II type 1 receptor (AT1R) loci and normal blood pressure

The M235T polymorphism at the angiotensinogen (AGT) locus and the A1166C polymorphism at the angiotensin II type 1 receptor (AT1R) locus have been reported to be associated with hypertension in several populations. We examined these polymorphisms in three samples of healthy Norwegians with respect to normal blood pressure (BP) levels. None of the genotypes defined by the polymorphisms or their combinations were associated with systolic (S) BP (SBP) or diastolic (D) BP (DBP) level. However, there was a trend in all three series that individuals carrying the C allele of the A1166C polymorphism at the AT1R locus (homozygotes as well as heterozygotes) had higher SBP, than AA homozygous individuals. The observation did not reach statistical significance in any of the series. When examining these two polymorphisms with respect to possible variability gene effects on BP in two series of monozygote (MZ) twin pairs, no such effect was detected. We could not detect any interaction between the loci studied with respect to BP level or variability. Thus, neither the AGT locus nor AT1R locus, separately analysed or together, seem to have variability gene effects or definite level gene effects on normal BP.