Noboru Kajiyama

Endothelial Nitric Oxide Synthase Gene Is Positively Associated With Essential Hypertension

Essential hypertension has a genetic basis. Accumulating evidence, including findings of elevation of arterial blood pressure in mice lacking the endothelial nitric oxide synthase (eNOS) gene, strongly suggests that alteration in NO metabolism is implicated in hypertension. There are, however, no reports indicating that polymorphism in the eNOS gene is associated with essential hypertension. We have identified a missense variant, Glu298Asp, in exon 7 of the eNOS gene and demonstrated that it is associated with both coronary spastic angina and myocardial infarction. To explore the genetic involvement of the eNOS gene in essential hypertension, we examined the possible association between essential hypertension and several polymorphisms including the Glu298Asp variant, variable number tandem repeats in intron 4 (eNOS4b/4a), and two polymorphisms in introns 18 and 23. We performed a large-scale study of genetic association using two independent populations from Kyoto (n=458; 240 normotensive versus 218 hypertensive subjects) and Kumamoto (n=421; 223 normotensive versus 187 hypertensive subjects), Japan. In both groups, a new coding variant, Glu298Asp, showed a strong association with essential hypertension (Kyoto: odds ratio, 2.3 [95% confidence interval, 1.4 to 3.9]; Kumamoto: odds ratio, 2.4 [95% confidence interval, 1.4 to 4.0]). The allele frequencies of 298Asp in hypertensive subjects were significantly higher than those in normotensive subjects in both groups (Kyoto: 0.103 versus 0.050, P<0.0017; Kumamoto: 0.120 versus 0.058, P<0.0013, respectively). No such disequilibrium between genotypes was significantly associated with any other polymorphisms we examined; the Glu298Asp variant was also not linked to any other polymorphisms. In conclusion, the Glu298Asp missense variant was significantly associated with essential hypertension, which suggests that it is a genetic susceptibility factor for essential hypertension.

THE EFFECTS OF THE SELECTIVE ROCK INHIBITOR, Y27632, ON ET-1-INDUCED HYPERTROPHIC RESPONSE IN NEONATAL RAT CARDIAC MYOCYTES : POSSIBLE INVOLVEMENT OF RHO/ROCK PATHWAY IN CARDIAC MUSCLE CELL HYPERTROPHY

A small GTPase, Rho, participates in agonist‐induced cytoskeletal organization and gene expression in many cell types including cardiac myocytes. However, little is known about the functions of Rhos downstream targets in cardiac myocytes. We examined the role of ROCK, a downstream target of Rho, in ET‐1‐induced hypertrophic response. Y27632, a selective ROCK inhibitor, inhibited ET‐1‐induced increases in natriuretic peptide production, cell size, protein synthesis, and myofibrillar organization. In addition, a dominant‐negative mutant of p160ROCK suppressed ET‐1‐induced transcription of the BNP gene. These findings suggest that the Rho/ROCK pathway is an important component of ET‐1‐induced hypertrophic signals in cardiac myocytes.

Involvement of Cardiotrophin-1 in Cardiac Myocyte-Nonmyocyte Interactions During Hypertrophy of Rat Cardiac Myocytes In Vitro

BACKGROUND The mechanism responsible for cardiac hypertrophy is currently conceptualized as having 2 components, mediated by cardiac myocytes and nonmyocytes, respectively. The interaction between myocytes and nonmyocytes via growth factors and/or cytokines plays an important role in the development of cardiac hypertrophy. We found that cardiac myocytes showed hypertrophic changes when cocultured with cardiac nonmyocytes. Cardiotrophin-1 (CT-1), a new member of the interleukin-6 family of cytokines, was identified by its ability to induce hypertrophic response in cardiac myocytes. In this study, we used the in vitro coculture system to examine how CT-1 is involved in the interaction between cardiac myocytes and nonmyocytes during the hypertrophy process. METHODS AND RESULTS RNase protection assay revealed that CT-1 mRNA levels were 3. 5 times higher in cultured cardiac nonmyocytes than in cultured cardiac myocytes. We developed anti-CT-1 antibodies and found that they significantly inhibited the increased atrial and brain natriuretic peptide secretion and protein synthesis characteristic of hypertrophic changes of myocytes in the coculture. In addition, non-myocyte-conditioned medium rapidly elicited tyrosine phosphorylation of STAT3 and induced an increase in natriuretic peptide secretion and protein synthesis in cultured cardiac myocytes; these effects were partially suppressed by anti-CT-1 antibodies. Finally, the hypertrophic effects of CT-1 and endothelin-1, which we had previously implicated in the hypertrophic activity in the coculture, were additive in cardiac myocytes. CONCLUSIONS These results show that CT-1 secreted from cardiac nonmyocytes is significantly involved in the hypertrophic changes of cardiac myocytes in the coculture and suggest that CT-1 is an important local regulator in the process of cardiac hypertrophy.

Interaction of myocytes and nonmyocytes is necessary for mechanical stretch to induce ANP/BNP production in cardiocyte culture

In cardiac hypertrophy or ventricular remodeling, enlargement of myocytes and interstitial or perivascular fibrosis are observed simultaneously, which suggests an interaction between cardiac myocytes and fibroblasts. In this study we examined the mechanism of cyclic mechanical stretch-induced myocytic hypertrophy, focusing on the interaction between myocytes and cardiac nonmyocytes, mostly fibroblasts. Ventricular myocytes (MCs) and cardiac nonmyocytes (NMCs) were separately extracted from neonatal rat ventricles by the discontinuous Percoll gradient method and primary cultures of cardiac cells were prepared. When MCs were co-cultured with NMCs, the size of MCs and the ANP/BNP secretion were significantly increased. This hypertrophic change of MCs in the co-culture was significantly suppressed by BQ-123, an endothelin-A (ETA) receptor antagonist. Cyclic stretch did not induce hypertrophic responses in MC culture. However, it further increased ANP/BNP production in MC-NMC co-culture (2.2-fold and 2.1-fold increases vs. non-stretch group after 48-h incubation). This increase in ANP/BNP production in the co-culture was significantly suppressed by CV-11974, an angiotensin II (Ang II) type 1 receptor antagonist. This study raises the possibility that NMCs regulate cardiocyte hypertrophy via secretion of endothelin-1 and that Ang II is involved in the interaction between MCs and NMCs during the course of hypertrophic response of cardiocytes to mechanical stretch.

A heart-specific increase in cardiotrophin-1 gene expression precedes the establishment of ventricular hypertrophy in genetically hypertensive rats

OBJECTIVE Cardiotrophin-1 is a cytokine, a novel member of the interleukin-6 superfamily, which is isolated from mouse embryoid bodies. It is known to bind a gp130/ leukemia inhibitory factor (LIF) receptor heterodimer and to induce myocyte hypertrophy. Accumulating evidence indicates that a gp130 signaling pathway is involved in cardiac development and ventricular hypertrophy. METHODS In order to elucidate the pathophysiologic significance of cardiotrophin-1 in ventricular hypertrophy associated with hypertension, we examined the level of cardiotrophin-1 mRNA in the ventricle of spontaneously hypertensive rats/Izm stroke-prone (SHRSP/Izm) in neonates, and at 4-, 12- and 20-weeks of age by Northern blot analysis. We also examined the gene expression of LIF by Northern blot and reverse transcription-polymerase chain reaction analyses. RESULTS No significant difference was observed in the level of cardiotrophin-1 mRNA in the ventricle between SHRSP/ Izm and Wistar-Kyoto/Izm (WKY/Izm) neonates. However, the level of cardiotrophin-1 mRNA in the ventricle was significantly augmented in 4-week-old SHRSP/Izm, which did not yet show overt ventricular hypertrophy, and its augmented expression lasted for the duration of the experimental period. The difference in the level of cardiotrophin-1 mRNA between the two strains was most prominent at the age of 4 weeks. This augmented expression of the cardiotrophin-1 gene was not related to the severity of left ventricular hypertrophy. The level of cardiotrophin-1 mRNA in other organs, including the kidney and lung, showed no significant change with aging and was not different between the two strains. After long-term treatment with lisinopril, levels of cardiotrophin-1 mRNA were not changed, although it morphologically prevented the development of left ventricular hypertrophy. LIF mRNA was not detected in any ventricles examined by Northern blot analysis. CONCLUSIONS The present study demonstrates that the expression of cardiotrophin-1 mRNA is increased in the early stage of ventricular hypertrophy in SHRSP/Izm and it remains elevated after hypertrophy has been established. However, it is unlikely that cardiotrophin-1 plays a mechanistic role in the development and maintenance of left ventricular hypertrophy in SHRSP/Izm. The present study also suggests that cardiotrophin-1, but not LIF, is a possible candidate for natural ligand of a gp130 signaling pathway in the heart.

Fibronectin signaling stimulates BNP gene transcription by inhibiting neuron-restrictive silencer element-dependent repression

OBJECTIVE Brain natriuretic peptide (BNP) is a cardiac hormone mainly synthesized in ventricles and its expression is markedly increased in ventricular hypertrophy that involves the accumulation of extracellular matrix proteins, such as fibronectin (Fn). We recently reported that Fn signaling stimulated BNP secretion accompanied by hypertrophic responses in vitro. METHODS To elucidate the regulatory mechanism for BNP gene transcription, we examined cis-acting elements downstream of Fn signaling in rat ventricular myocytes transfected with either the -1812 human BNP-luciferase reporter gene (-1812hBNP/Luc) or one of several truncated forms. RESULTS A strong cis-repressor element was identified between -552 and -522 in myocytes plated on uncoated dishes. This region contains a neuron-restrictive silencer element (NRSE)-like element (NRSE(BNP)) that is 90% homologous with the NRSE consensus sequence. Neuron-restrictive silencer factor (NRSF) is known to bind to NRSE and to silence transcription of genes containing NRSE. Deletion of NRSE(BNP) and dominant negative NRSF markedly increased the reporter activity in transfected cells, suggesting that the NRSE/NRSF system silences basal BNP gene transcription. When myocytes were cultured on Fn-coated dishes, the reporter activity of -1812hBNP/Luc was increased by approximately 600% compared with that on uncoated dishes. Interestingly, truncation from -552 to -522 reduced the Fn-inducible reporter activity. Moreover, deletion of NRSE(BNP) and dominant negative NRSF also inhibited the Fn-inducible reporter activity. Electrophoretic mobility shift assays showed that Fn signaling inhibited the binding activity of NRSF to NRSE(BNP). CONCLUSION These results suggest that Fn-induced BNP up-regulation in rat ventricular myocytes is due to inhibition of NRSE(BNP)-dependent repression of BNP gene transcription.