市原 佐保子

Background - The roles of angiotensin II (Ang II) in the regulation of heart function under normal and pathological conditions have been well documented. Although 2 types of Ang II receptor (AT(1) and AT(2)) are found in various proportions, most studies have focused on AT(1)-coupled events. In the present study, we examined the hypothesis that signaling by AT(2) is important to the development of left ventricular hypertrophy and cardiac fibrosis by Ang II infusion in mice lacking the AT(2) gene (Agtr2-/T). Methods and Results - Male Agrt2-/Y and age-matched wild-type (WT) mice were treated long-term with Ang II, infused at a rate of 4.2 ng (.) kg(-1 .) min(-1)for 3 weeks. Ang II elevated systolic blood pressure to comparable levels in Agtr2-/Y and WT mice. WT mice developed prominent concentric cardiac hypertrophy, prominent fibrosis, and impaired diastolic relaxation after Ang II infusion. In contrast, there was no cardiac hypertrophy in Agtr2-/Y mice. Agtr2-/Y mice, however, did not show signs of heart failure or impairment of ventricular relaxation and only negligible fibrosis after Ang II infusion. The absence of fibrosis may be a clue to the absence of impairment in ventricular relaxation and account for the normal left ventricular systolic and diastolic performances in Agtr2-/Y mice. Conclusions - Chronic loss of AT(2) by gene targeting abolished left ventricular hypertrophy and cardiac fibrosis in mice with Ang II-induced hypertension.

The pathophysiological roles of the angiotensin II type 2 receptor (AT(2)) in cardiac hypertrophy remain unclear. By the targeted deletion of mouse AT(2) we mere able to prevent the left ventricular hypertrophy resulting From pressure overload, while cardiac contractile functions remained normal. This implies that AT(2) is a mediator of cardiac hypertrophy in response to increased blood pressure. The effects of AT(2) deletion were independent of activation of embryonic genes for cardiac hypertrophy. However, p70(S6k), one of the key factors in cardiac hypertrophy, was markedly and specifically reduced in the ventricles of Agtr2(-)/Y mice. We propose that p70(S6k) plays a major role in AT(2)-mediated ventricular hypertrophy.

Background-Transforming growth factor-beta (TGF-beta) is an important regulator of vascular remodeling and is involved in the pathogenesis of atherosclerosis, A T-->C transition at nucleotide 29 of the TGF-beta 1 gene results in a Leu-->Pro substitution at amino acid 10 of the signal peptide. We have now examined a possible association of TCF-beta 1 genotype with myocardial infarction (MI) in a Japanese population. Methods and Results-TGF-beta 1 genotype was determined in 315 Japanese patients (234 men and 81 women) with MI and 591 control subjects (289 men and 302 women). We found that age, body mass index, and incidence of habitual smoking, hypertension, diabetes mellitus, and hypercholesterolemia did not differ between the 2 groups for either men or women. Multivariable logistic regression analysis, however, demonstrated the frequency of the T allele to be significantly higher in male subjects with MI than in controls (TT + TC versus CC; P<0.0001, odds ratio 3.5, 95% CI 2.0 to 63). In contrast, the T allele was not associated with the prevalence of MI in women. In both male MI patients and controls, the serum concentration of TGF-beta 1 was significantly higher in individuals with the CC genotype than in subjects with the TT or TC genotype. Conclusions-Findings suggest that the T allele at nucleotide 29 in the TGF-beta 1 gene is a risk factor for genetic susceptibility to MI, at least in middle-aged Japanese men.

Mutation of the cardiac troponin T (cTnT) gene is a genetic determinant of familiar hypertrophic cardiomyopathy (HCM). A Japanese family of 14 individuals, including 6 with HCM, was subjected to genetic and clinical assessment, Five exons of the cTnT gene were sequenced in all family members, A heterozygous or homozygous T-340-->A (phe(110)-Ile) mutation in exon 9 of the cTnT gene was detected in 11 subjects. Morphological and functional evaluation of the left and right ventricles by echocardiography revealed that 4 of 9 individuals heterozygous for the mutant allele exhibited HCM with moderate cardiac hypertrophy, Cardiac hypertrophy and other clinical features in the 2 subjects homozygous for the mutation were more severe than were those in heterozygous individuals with HCM, Thus, the clinical features of HCM due to the Phe(110)-Ile mutation in the cTnT gene appear to be modified by a gene dosage effect, Copyright (C) 2000 S. Karger AG, Basel.

Angiotensin II (Ang II) is now believed to play a critical role in the pathogenesis of hypertrophy and/or hyperplasia of vascular smooth muscle cells (VSMCs). Several G(i)- and G(q)-coupled receptors, including the Ang II type 1 (AT(1)) receptor, activate Rho and Rho-associated kinase in Swiss 3T3 cells and cardiac myocytes. However, little is known about the role of Rho-kinase in Ang II-induced vascular hypertrophy in VSMCs. In the present study, we explored the role of Rho and Rho-kinase in Ang II-induced protein synthesis in VSMCs. In unstimulated cells, RhoA was observed predominantly in the cytosolic fraction, but it was translocated in part to the particulate fraction in response to Ang II (100 nmol/L). This effect was completely blocked by the AT(1) receptor blocker candesartan but not by the Ang II type 2 (AT(2)) receptor antagonist PD123319. Botulinum C-3 exoenzyme, which inactivated RhoA, attenuated Ang II-induced [H-3]leucine incorporation. The specific Rho-kinase inhibitor, Y-27632, dose-dependently abolished Ang II-induced protein synthesis and also suppressed Ang II-induced c-fos mRNA expression. On the other hand, Y-27632 had no effect on Ang II-stimulated phosphorylation of p70 S6 kinase and extracellular signal-regulated kinase 1/2, which are reported to be involved in Ang II-induced protein synthesis, nor had it any effect on the Ang II-induced phosphorylation of PHAS-I, a heat- and acid-stable eIF-4E-binding protein. The phosphorylation of PHAS-I is regulating for translation initiation. These observations suggest that the Rho, Rho-kinase, and c-fos pathways may play a role in Ang II-induced hypertrophic changes of VSMCs through a novel pathway.

Platelet-activating factor (PAF) acetylhydrolase may play important roles in the pathophysiology of thrombosis and atherosclerosis related to its catalytic action in the degradation of PAF and oxidized phospholipids. A missense mutation (G --> T transversion at nucleotide 994) in the plasma PAF acetylhydrolase gene results in a Val --> Phe substitution at amino acid 279 of the mature protein and a consequent loss of catalytic activity. However, the role of a deficiency or low activity of this enzyme caused by the missense mutation in the etiology of coronary artery disease (CAD) has not been determined, The relation between this mutation and the incidence of CAD in the Japanese population is investigated herein, The genotype of plasma PAF acetylhydrolase (MM, normal; Mm, heterozygote; and mm, deficient homozygote) was determined with a polymerase chain reaction (PCR) assay for 454 patients with myocardial infarction (MI) and 602 control subjects, The frequency of the m allele was significantly higher in male patients with MI (odds ratio, 1.8) than in controls, an association that was more marked in a low-risk subgroup (odds ratio, 2.3). In contrast, the m allele was not associated with MI in women, These results indicate that the G(994) --> T missense mutation in exon 9 of the plasma PAF acetylhydrolase gene is an independent risk factor for CAD in Japanese men, especially low-risk individuals, but not in women. Copyright (C) 1998 by W.B. Saunders Company.

We investigated the association between variations in the endothelial constitutive nitric oxide synthase (ecNOS) gene and the presence of myocardial infarction. The results indicate that the mutant allele (ecNOS'4a) is an independent risk factor for myocardial infarction in the Japanese population, especially in those lacking other conventional risk factors.

The renin-angiotensin system is important in cardiovascular remodeling. Although a variant of the angiotensinogen gene is associated with an increased generation of angiotensinogen, it is unclear how this genetic variant might influence the activity of the renin-angiotensin system and thereby contribute to the predisposition to coronary artery disease (CAD). The relation between genetic polymorphisms in the gene-encoding angiotensinogen and the risk of CAD in middle-aged Japanese men was investigated. Two polymorphisms in exon 2 of the angiotensinogen gene, M235T and T174M, were analyzed in 327 patients with CAD and 352 matched control subjects. The genotype distribution of both polymorphisms did not differ between patients with CAD and control subjects. No combination of genotypes of the two polymorphisms was associated with CAD. Results indicate that the M235T and T174M variants of the angiotensinogen gene are not associated with CAD in Japanese men.

Although several genes or genetic loci that are either responsible for or confer susceptibility to familial hypertrophic cardiomyopathy (HCM) or dilated cardiomyopathy (DCM) have been identified, genetic defects that underlie nonfamilial HCM or DCM remain to be characterized. An allelic association study for the angiotensin converting enzyme (ACE) and angiotensinogen genes has now been performed with 71 patients with nonfamilial HCM, 88 patients with nonfamilial DCM, and 122 healthy control subjects in the Japanese population. The distribution of ACE genotypes for an insertion/deletion (I/D) polymorphism in intron 16 did not differ significantly among control subjects and patients with HCM or DCM. Similarly, the distributions of angiotensinogen genotypes for methionine-235-threonine (M235T) and threonine-174-methionine (T174M) polymorphisms did not differ significantly among the three groups. Echocardiographic parameters that are indicators of the severity or progression of disease did not differ significantly among ACE I/D or angiotensinogen M235T and T174M genotypes in the two patient groups. Finally, no additive or synergistic effect of any combined genotypes or haplotypes of the ACE and angiotensinogen polymorphisms on the association with HCM or DCM was detected. Results indicate that the ACE I/D and angiotensinogen M235T and T174M polymorphisms are not related to HCM or DCM in the Japanese population, and that variants of these polymorphisms do not contribute to the genesis or progression of these cardiomyopathies. (C) 1997 American Journal of Hypertension, Ltd.

The aim of this study was to clarify that the depressed mechanoenergetics in patients with idiopathic dilated cardiomyopathy (DCM) resulted from compensation for the decreased contractility. The study population consisted of eight control subjects, with normal left ventricular size and ejection fraction and 31 patients with DCM. Left ventricular end-systolic elastance (Ees), effective arterial elastance (Ea), external work (EW), and the pressure-volume area (PVA) were measured, using a dual-field volume conductance catheter equipped with a micromanometer-tipped catheter. Ea/Ees was evaluated as ventriculoarterial coupling. Normal hearts worked at almost optimal condition (defined as Ea/Ees = 1/2), while ventriculoarterial coupling was far from the optimum (Ea > Ees) in patients with DCM. Ees in patients with DCM was less than that in control subjects; however, Ea was similar in the two groups. The mismatch of Ea/Ees observed in DCM leads to depressed mechanoenergetics as a result of the compensatory response to maintain adequate blood pressure. Volume enlargement plays an important role in maintaining adequate blood pressure and cardiac output in the course of chronic deterioration of contractility.