A molecular variant of angiotensinogen associated with preeclampsia

Antisense inhibition of hypertension in the spontaneously hypertensive rat

Phosphorothioated antisense oligodeoxynucleotide (ASODN) targeted to angiotensinogen mRNA was administered intracerebroventricularly in spontaneously hypertensive rats to test whether angiotensinogen reduction would lower their hypertensive blood pressures. The ASODN lowers hypertensive blood pressures to normotensive levels in spontaneously hypertensive rats; sense oligodeoxynucleotide had no effect. Administration of phosphorothioated ASODN produced a prolonged duration of lowered blood pressure. Injections of ASODN at the same dose that decreased hypertension when administered centrally did not result in blood pressure decreases when administered intra-arterially. Furthermore, angiotensinogen production was decreased in the brain stem and significantly decreased in the hypothalamus of the ASODN-treated rats (P < .05), supporting the concept of centrally mediated regulation of hypertension by an overactive brain angiotensin system. To determine the distribution of centrally administered oligodeoxynucleotides, fluorescein isothiocyanate-conjugated oligodeoxynucleotides were injected directly into the lateral ventricles. One hour later, oligodeoxynucleotides were distributed throughout the lateral and third ventricles, with tissue and cellular uptake observed in discrete cells at the injection site. This indicates that the oligodeoxynucleotides are taken up rapidly by brain cells and that they permeate the areas surrounding brain nuclei involved in central blood pressure regulation and volume homeostasis. The results confirm and extend our previous study with phosphodiester ASODN and show that phosphorothioation modification increases the duration of the response and is taken up in vivo. We conclude that with modification, ASODN inhibition of angiotensinogen mRNA translation can be used for a prolonged, profound decrease in mean arterial pressure in the spontaneously hypertensive rat through a central mechanism.

Molecular variant of angiotensinogen gene is associated with coronary atherosclerosis

BACKGROUND

A positive association was previously reported between angiotensin-converting enzyme (ACE) gene polymorphism and several cardiovascular diseases, such as myocardial infarction, left ventricular hypertrophy, and restenosis after percutaneous transluminal coronary angioplasty. Plasma ACE activity and carotid-wall thickening measured by ultrasonography were related, and it was postulated that long-term exposure to high levels of plasma ACE could be involved in structural changes of the arterial wall. In addition, angiotensinogen gene mutation was recently reported to be associated with essential hypertension and preeclampsia. There exists a possibility that the renin-angiotensin system plays an important role in the progress of cardiovascular diseases in humans. Therefore, we examined the association between the molecular variant of the angiotensin gene and coronary atherosclerosis.

METHODS AND RESULTS

This study included 82 patients who had coronary atherosclerosis and 160 control subjects; all study participants were Japanese. All patients with coronary atherosclerosis had at least one coronary artery with > 25% luminal diameter obstruction on average according to multiple coronary angiographic views. Angiotensinogen gene molecular variants were designated AA, Aa, and aa. The a allele indicated thymine-cytosine transition at nucleotide 704 in exon 2. Genomic DNA was extracted from peripheral blood leukocytes. Polymerase chain reaction was performed to amplify the concerned region of the angiotensinogen gene. After restriction enzyme digestion, it was possible to distinguish the molecular variant of the angiotensinogen gene. The frequencies of these genotypes were 7.3%, 26.8%, and 65.9% in the patients and 18.8%, 31.9%, and 49.3% in the control subjects for the AA, Aa, and aa alleles, respectively. There was an excess in the a allele among patients (P < .01).

CONCLUSIONS

We found a significant association between coronary atherosclerosis and a molecular variant of the angiotensin gene. The results suggested that the molecular variant of the angiotensinogen gene could be a new risk factor for coronary atherosclerosis.

What do dysfunctional serpins tell us about molecular mobility and disease?

Proteinase inhibitors of the serpin family have a unique ability to regulate their activity by changing the conformation of their reactive-centre loop. Although this may explain their evolutionary success, the dependence of function on structural mobility makes the serpins vulnerable to the effects of mutations. Here, we describe how studies of dysfunctional variants, together with crystal structures of serpins in different forms, provide insights into the molecular functions and remarkable folding properties of this family. In particular, comparisons of variants affecting different serpins allow us to define the domains which control this folding and show how spontaneous but inappropriate changes in conformation cause diverse diseases.

Rapid detection and prevalence of the variants of the angiotensinogen gene in patients with essential hypertension

OBJECTIVES

The angiotensinogen (AGT) gene has been implicated as a candidate gene of high blood pressure. However, because the variants of the AGT gene are point mutations, it is difficult to detect them in large scale population studies. The aims of this study were to develop a rapid screening method for the point mutations and, using this method, to determine the possible role of the AGT gene variant in high blood pressure in the Japanese population.

DESIGN AND SUBJECTS

A rapid screening method for the point mutations by means of primer-specified restriction map modification is described here. Using this method, the distribution of two variants of the AGT gene, M235T and T174M, was determined in 80 patients with essential hypertension (EHT) and 100 normotensive controls (control).

RESULT

The hypertensive group showed a significantly (P < 0.05) higher frequency for the T174M variant but the same frequency for the M235T variant.

CONCLUSION

These data provide evidence in favour of an association between hypertension and a genetic variant of AGT in human EHT, and a marked ethnic difference in the AGT gene.

Genetic determinants of myocardial infarction

There is a strong familial and genetic nature of CAD and predisposing metabolic disorders. This should encourage health care workers to focus additional attention on the younger members of affected families, particularly the families of patients with MI prior to age 55. This should take the form of genetic counseling as well as patient education and follow-up with respect to hygienic measures of proven efficacy, and aggressive treatment of metabolic disorders that prove resistant to changes in lifestyle. In certain cases, as discussed in this review, genetic testing may prove helpful.

Diagnosis and the new genetics

The rapid pace of gene discovery has led to new opportunities for clinical diagnosis using molecular genetic technologies. Recent achievements include the culmination of the 10-year search for the Huntington's disease gene, the identification of predisposing genes for certain familial colon cancers, and the characterization of potential genetic risk indicators for Alzheimer's disease, hypertension, and coronary heart disease. These advances, coupled with the previous discoveries of important disease genes (e.g. those for cystic fibrosis, Duchenne muscular dystrophy, and fragile X syndrome) have quickly expanded the capacity of genetic analysis, allowing the design of enhanced and novel approaches for diagnostic testing. The transfer of molecular technology to the area of clinical genetic analysis, although associated with many potential benefits, has raised some concern regarding the possible misuse of genetic tests and information, particularly with regard to presymptomatic diagnosis of disease and population screening.

Angiotensinogen gene in human hypertension. Lack of an association of the 235T allele among African Americans

The frequency of the 235T and 174M alleles of the angiotensinogen gene, previously reported to be associated with hypertension in Caucasians and Japanese, was compared between 57 hypertensive African Americans and 130 normotensive African Americans sampled as part of a community survey of hypertension in the Chicago area. The frequency of the 235T allele was unrelated to hypertension status (cases, 83%, control subjects, 82%), as was true for the 174M allele. Compared with Caucasians, the frequency of the 235T allele was twice as high in this African American population, while the frequency of the 174M allele was similar. Even higher frequencies of the 235T allele (93%) were noted in a sample of 122 Nigerians. It appears that the 235T allele is very common in populations of West African origin, although we found no evidence that it confers risk of hypertension.

A polymorphism of the angiotensinogen gene associated with variation in blood pressure in a genetic isolate

BACKGROUND

The Hutterite Brethren are a genetic isolate characterized by high indices of relatedness and a communal agrarian lifestyle. We hypothesized that variation of the angiotensinogen (AGT) and angiotensin-converting enzyme (ACE) genes would be associated with variation in resting blood pressure in this group. We also hypothesized that the association would depend on the sex of the subjects.

METHODS AND RESULTS

In 741 Hutterites, we measured blood pressure in quadruplicate and analyzed DNA for genotypes of an insertion/deletion (I/D) polymorphism of ACE and of two protein polymorphisms of AGT, namely, M235T and T174M. We tested for association between variation in systolic and diastolic blood pressures and genotypic class. We observed that genotypes of AGT codon 174 were significantly associated with variation in systolic blood pressure. We also tested for an interaction between the AGT genotype and sex. We observed that genotypes of AGT codon 174 were significantly associated with variation in systolic blood pressure only in men. The AGT codon 174 polymorphism accounted for 3.1% of the total variation in systolic blood pressure in men.

CONCLUSIONS

The association of AGT variation with resting blood pressure in men is consistent with the existence of important structural elements within, flanking, or proximal to the AGT gene, whose functional impact might be related to differences in sex.

Diverse factors influencing angiotensin metabolism during ACE inhibition: insights from molecular biology and genetic studies

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Single fetal demise in twin gestation resulting in the resolution of severe pre-eclampsia

A primigravida presenting with a twin pregnancy and severe pre-eclampsia which developed during early pregnancy is described. Complete resolution of symptoms and signs of pre-eclampsia were evident following the death of a growth-retarded single fetus. Pregnancy continued successfully until 35 weeks of gestation, when a single healthy infant was delivered. Few such cases of complete resolution of pre-eclampsia following the death of a single fetus are reported in the literature. The possibility that genetic susceptibility to pre-eclampsia is conferred by homozygosity for the same single recessive gene expressed by both mother and fetus is discussed.

Evidence for single gene contributions to hypertension and lipid disturbances: definition, genetics, and clinical significance

Several large family studies are reviewed to identify results suggesting single gene traits contributing to the occurrence of hypertension in humans. Segregation analysis in families has suggested major gene effects for several highly heritable traits associated with hypertension. These include recessively segregating high sodium-lithium countertransport (major gene H2 = 34%), additively segregating low urinary kallikrein excretion (major gene H2 = 51%), and recessively segregating hyperinsulinemia (major gene H2 = 33%). In some families, hypertension and metabolic abnormalities (dyslipidemia, hyperinsulinemia, and obesity) seem to be related to several candidate genes studied but not conclusively proven (LPL deficiency mutations, dense LDL subfractions, or NIDDM with hyperinsulinemia). More recently, DNA markers have identified genes promoting hypertension. Glucocorticoid-remediable aldosteronism (GRA) promotes a rare but unusual form of hypertension that is unresponsive to ordinary medications but very responsive to glucocorticoid medications. GRA has been found in hypertensive persons with a specific mutation of the 11 beta-hydroxylase gene on chromosome 8q21. Many persons with essential hypertension carry a common "susceptibility gene" at the angiotensinogen locus (chromosome 1q4) identified using linkage studies in siblings, association studies, and in studies of preeclampsia and hypertension in pregnant women. These first two well-established genetic loci promoting human hypertension represent two ends of a broad spectrum. The rare "determinant" gene for GRA by itself seems to produce severe hypertension and early strokes. The angiotensinogen (AGT) "susceptibility" gene is very common (30% of Utah Caucasians) and seems to predispose to hypertension but probably requires other genetic and environmental influences to be fully expressed.(ABSTRACT TRUNCATED AT 250 WORDS)

Linkage of the angiotensinogen gene to essential hypertension

BACKGROUND

The renin-angiotensin system is a powerful pressor system with a major influence on salt and water homeostasis. Angiotensinogen (also called renin substrate) is a key component of this system; it is cleaved by renin to yield angiotensin I, which is then cleaved by angiotensin-converting enzyme to yield angiotensin II. The observation that plasma angiotensinogen levels correlate with blood pressure and track through families suggests that angiotensinogen may have a role in essential hypertension. We therefore investigated whether there is linkage between the angiotensinogen gene on chromosome 1q42-43 and essential hypertension.

METHODS

Samples of DNA from 63 white European families in which two or more members had essential hypertension were tested for linkage of the angiotensinogen gene to this disorder. Affected cousins, nephews, nieces, and half-siblings were included when possible. To test for linkage, we used as a marker a dinucleotide-repeat sequence flanking this gene, and we employed the affected-pedigree-member method of linkage analysis. Two molecular variants of the angiotensinogen gene, one encoding threonine instead of methionine at position 235 (M235T) and the other encoding methionine rather than threonine at position 174 (T174M), were also tested for possible association with essential hypertension.

RESULTS

We found significant linkage (t = 5.00, P < 0.001) and association (chi-square = 53.3, P < 0.001) of the angiotensinogen-gene locus to essential hypertension in the 63 multiplex families. This linkage was consistently maintained in the subgroup of subjects with diastolic pressure above 100 mm Hg and in the subgroups classified according to sex. It has been proposed previously that T174M and M235T are associated with essential hypertension. However, we found no association in our population between either polymorphism and this disorder.

CONCLUSIONS

This study provides strong and consistent support for the linkage to essential hypertension of regions within or close to the angiotensinogen gene. Precisely how mutations in this region may result in hypertension remains to be determined.

Volume homeostasis in normal pregnancy and pre-eclampsia: physiology and clinical implications

The pieces of the jigsaw puzzle of volume homeostasis in human pregnancy are being put together gradually. This chapter has focused on recent advances in our understanding of factors controlling extracellular fluid volume in normal pregnancy and their disturbance in women who develop pre-eclampsia. We have explored the clinical implications of these guidelines for management of patients with pre-eclampsia. Clearly there is still much to be learned. Studies of the cellular and subcellular handling of sodium are still in their infancy and will add much to our understanding of the physiology of volume homeostasis in normal pregnancy and its disturbance in pre-eclampsia and other causes of hypertension in pregnancy.

Molecular mechanism of transcriptional activation of angiotensinogen gene by proximal promoter

Angiotensinogen is shown to be produced by the liver and the hepatoma cell line HepG2. As a first step for understanding the molecular relationship between the transcriptional regulation of the angiotensinogen gene and the pathogenesis of hypertension, we have analyzed the basal promoter of the angiotensinogen gene. Chloramphenicol acetyltransferase (CAT) assays with 5'-deleted constructs showed that the proximal promoter region from -96 to +22 of the transcriptional start site was enough to express HepG2-specific CAT activity. Electrophoretic mobility shift assay and DNase I footprinting demonstrated that the liver- and HepG2-specific nuclear factor (angiotensinogen gene-activating factor [AGF2]) and ubiquitous nuclear factor (AGF3) bound to the proximal promoter element from -96 to -52 (angiotensinogen gene-activating element [AGE2]) and to the core promoter element from -6 to +22 (AGE3), respectively. The site-directed disruption of either AGE2 or AGE3 decreased CAT expression, and the sequential titration of AGF3 binding by in vivo competition remarkably suppressed HepG2-specific CAT activity. Finally, the heterologous thymidine kinase promoter assay showed that AGE2 and AGE3 synergistically conferred HepG2-specific CAT expression. These results suggest that the synergistic interplay between AGF2 and AGF3 is important for the angiotensinogen promoter activation.

Angiotensinogen as a risk factor for essential hypertension in Japan

A common molecular variant of angiotensinogen (AGT), the precursor of the potent vasoactive hormone angiotensin II, has been incriminated as a marker for a genetic predisposition to essential hypertension in Caucasians (Jeunemaitre, X., F. Soubrier, Y. V. Kotelevtsev, R. P. Lifton, C. S. Williams, A. Charru, S. C. Hunt, P. N. Hopkins, R. R. Williams, J. M. Lalouel, and P. Corvol. 1992. Cell. 71:169-180). We now show that the same variant, T235, is associated with essential hypertension in Japanese patients. The observation of this association in a distinct, ethnically homogeneous population further substantiates an involvement of angiotensinogen in the pathogenesis of essential hypertension and has physiological, epidemiological, and evolutionary implications.

Gene mapping of the mammalian genome: the CEPH and Genethon initiative

Over the past four years, the CEPH (Jean Dausset Foundation) has expanded its linkage mapping effort to include physical mapping and, in 1990, co-founded the Genethon to ensure that a combined physical and genetic map of the entire human genome would be achieved. The Genethon has applied methods developed at CEPH on an industrial scale to accomplish the colossal task of constructing an integrated map. It is the role of such an integrated map to accelerate the search for the genes responsible for inherited diseases, and the results of the past 12 months encourage our optimism that this goal will be realized rapidly. These discoveries are providing not only an approach to the diagnosis of genetically based disease but also some of the first breakthroughs in the area of gene therapy.

Genetic approaches to common diseases

Combined molecular and epidemiological studies are advancing our understanding of the genetic basis of multifactorial diseases. Several of the results obtained during the past year highlight methodological issues associated with these approaches. For example, the affected sib-pair method has been applied successfully to detect linkage between the angiotensinogen gene and susceptibility to hypertension, and a large multi-centre epidemiological study has demonstrated association of a polymorphism of the angiotensin-converting enzyme gene with increased risk of myocardial infarction. The study of Mendelian forms of multifactorial diseases has also led to many new results. These include the characterization of mutations in the glucokinase gene in maturity onset diabetes of the young, localization to chromosome 2 of a gene involved in familial colon cancer, and localization to chromosome 19 of a gene responsible for hemiplegic migraine. New insights have been provided into the genetics of multifactorial disorders such as diabetes and hypertension through the study of animal models. Localization of susceptibility loci in such models has recently led to the identification of new candidate genes that may be implicated in disease.