Kazuo Niwano

Increased Connective Tissue Growth Factor Relative to Brain Natriuretic Peptide as a Determinant of Myocardial Fibrosis

Excessive fibrosis contributes to an increase in left ventricular stiffness. The goal of the present study was to investigate the role of connective tissue growth factor (CCN2/CTGF), a profibrotic cytokine of the CCN (Cyr61, CTGF, and Nov) family, and its functional interactions with brain natriuretic peptide (BNP), an antifibrotic peptide, in the development of myocardial fibrosis and diastolic heart failure. Histological examination on endomyocardial biopsy samples from patients without systolic dysfunction revealed that the abundance of CTGF-immunopositive cardiac myocytes was correlated with the excessive interstitial fibrosis and a clinical history of acute pulmonary congestion. In a rat pressure overload cardiac hypertrophy model, CTGF mRNA levels and BNP mRNA were increased in proportion to one another in the myocardium. Interestingly, relative abundance of mRNA for CTGF compared with BNP was positively correlated with diastolic dysfunction, myocardial fibrosis area, and procollagen type 1 mRNA expression. Investigation with conditioned medium and subsequent neutralization experiments using primary cultured cells demonstrated that CTGF secreted by cardiac myocytes induced collagen production in cardiac fibroblasts. Further, G protein-coupled receptor ligands induced expression of the CTGF and BNP genes in cardiac myocytes, whereas aldosterone and transforming growth factor-&bgr; preferentially induced expression of the CTGF gene. Finally, exogenous BNP prevented the production of CTGF in cardiac myocytes. These data suggest that a disproportionate increase in CTGF relative to BNP in cardiac myocytes plays a central role in the induction of excessive myocardial fibrosis and diastolic heart failure.

Transcriptional stimulation of the eNOS gene by the stable prostacyclin analogue beraprost is mediated through cAMP-responsive element in vascular endothelial cells: Close link between PGI2 signal and NO pathways

Abstract— Beraprost sodium (BPS), an orally active prostacyclin analogue, has been reported to be beneficial in the treatment of primary pulmonary hypertension and obstructive peripheral arterial disease. Although BPS was originally described for its effects on platelet aggregation and vasodilatory response, the effect on endothelial cells has been poorly understood. In this study, we examined the effects of BPS on the eNOS gene expression in mouse aorta and cultured human and bovine aortic endothelial cells. Treatment of these cells with BPS increased the eNOS expression as assessed by Northern blots, Western blots, and NO production by NO-specific fluorescence (DAF2-DA) and by the Griess method. Standard mRNA decay assays showed that BPS increases the stability of eNOS mRNA. In addition, BPS increased the promoter activity of the human eNOS gene, as determined by luciferase assays of the eNOS promoter gene. Progressive 5′-deletion and site-specific mutation analyses defined the BPS-responsive sequences as cAMP-responsive elements (CRE) located at −733 and −603. By using the oligonucleotide probe containing this CRE sequence in electrophoretic mobility shift assays, we showed that the phosphorylated form of CRE-binding protein is a major constituent of the complex in BPS-treated cells. Western blot analyses indicate that BPS but not endogenous prostacyclin phosphorylates CRE-binding protein. The presence of functional CRE sites within human eNOS promoter may represent a novel mechanism for regulating eNOS gene expression.

Plasma connective tissue growth factor is a novel potential biomarker of cardiac dysfunction in patients with chronic heart failure.

Connective tissue growth factor (CTGF) has been recently reported as a mediator of myocardial fibrosis; however, the significance of plasma CTGF concentration has not been evaluated in patients with heart failure. The aim of this study was to investigate the clinical utility of plasma CTGF concentration for the diagnosis of heart failure.

Lentiviral Vector–mediated SERCA2 Gene Transfer Protects Against Heart Failure and Left Ventricular Remodeling After Myocardial Infarction in Rats

Reduced expression of the SERCA2 gene impairs the calcium-handling and contractile functions of the heart. We developed an SERCA2 gene transfer system using lentiviral vectors, and examined the long-term effect of SERCA2 gene transfer in the rat ischemic heart failure model. A lentiviral vector containing the SERCA2 gene was infused into a rat heart by hypothermic intracoronary delivery 2 weeks after myocardial infarction (MI). The transduction efficiency was approximately 40%. Six months after transduction, echocardiogram and pressure-volume measurements revealed that the SERCA2 gene transfer had significantly protected against left ventricular (LV) dilation, and had improved systolic and diastolic function, resulting in reduction in mortality rates. The brain natriuretic peptide mRNA level showed a significantly decrease and the phosphorylation level of serine residue of phospholamban (PLN) showed an increase in the Lenti-SERCA2-transduced heart. Further, DNA microarray analysis disclosed that SERCA2 gene transfer had increased cardioprotective gene expression and lowered the expression of genes that are known to exacerbate heart failure. The SERCA2 gene was successfully integrated into the host heart, induced favorable molecular remodeling, prevented LV geometrical remodeling, and improved the survival rate. These results suggest that a strategy to compensate for reduced SERCA2 gene expression by lentiviral vectors serves as a positive inotropic, lucitropic, and cardioprotective therapy for post-MI heart failure.

Competitive Binding of CREB and ATF2 to cAMP/ATF Responsive Element Regulates eNOS Gene Expression in Endothelial Cells

Objective—Expression of endothelial nitric oxide synthase (eNOS) is a critical determinant for vascular homeostasis. We examined the effects of Beraprost sodium (BPS), a stable analogue of prostacyclin, on the eNOS gene expression in the presence of inflammatory cytokine interleukin (IL)-1β in cultured endothelial cells. Method and Results—Exposure of human and bovine endothelial cells to IL-1β decreased eNOS expression. Western blot analysis using phospho-specific antibodies showed that IL-1β stimulated p38 MAP kinase and phosphorylated ATF2. BPS inhibited these effects via protein kinase A (PKA)/cAMP-responsive element binding protein (CREB) activation. Transfection assays using site-specific mutation constructs showed that CRE/ATF elements located at −733 and −603 within the human eNOS promoter are necessary for full IL-1β responsiveness. BPS attenuated the IL-1β–mediated decrease in eNOS promoter activity and the expression of eNOS gene through PKA pathway. Electrophoretic gel mobility shift assays showed that IL-1β increased the binding of phosphorylated ATF2 to CRE/ATF. On treatment with BPS, phosphorylated CREB predominantly bound to CRE/ATF. Conclusions—These results indicate that IL-1β and BPS antagonistically regulates the eNOS expression through the activation of p38 and PKA, respectively. Furthermore, the ability to bind both CREB and ATF2 implicates the CRE/ATF sequence as a potential target for multiple signaling pathways in the regulation of the eNOS gene transcription.

Mitochondrial transcription factors TFAM and TFB2M regulate Serca2 gene transcription.

AIMS Sarco(endo)plasmic reticulum Ca²(+)-ATPase 2a (SERCA2a) transports Ca²(+) by consuming ATP produced by mitochondrial respiratory chain enzymes. Messenger RNA (mRNA) for these enzymes is transcribed by mitochondrial transcription factors A (TFAM) and B2 (TFB2M). This study examined whether TFAM and TFB2M coordinately regulate the transcription of the Serca2 gene and mitochondrial genes. METHODS AND RESULTS Nuclear localization of TFAM and TFB2M was demonstrated by immunostaining in rat neonatal cardiac myocytes. Chromatin immunoprecipitation assay and fluorescence correlation spectroscopy revealed that TFAM and TFB2M bind to the -122 to -114 nt and -122 to -117 nt regions of the rat Serca2 gene promoter, respectively. Mutation of these sites resulted in decreased Serca2 gene transcription. In a rat myocardial infarction model, Serca2a mRNA levels significantly correlated with those of Tfam (r = 0.54, P < 0.001) and Tfb2m (r = 0.73, P < 0.001). Overexpression of TFAM and TFB2M blocked hydrogen peroxide- and norepinephrine-induced decreases in Serca2a mRNA levels. In addition, overexpression of TFAM and TFB2M increased the mitochondrial DNA (mtDNA) copy number and mRNA levels of mitochondrial enzymes. CONCLUSION Although TFAM and TFB2M are recognized as mtDNA-specific transcription factors, they also regulate transcription of nuclear DNA, i.e. the Serca2 gene. Our findings suggest a novel paradigm in which the transcription of genes for mitochondrial enzymes that produce ATP and the gene for SERCA2a that consumes ATP is coordinately regulated by the same transcription factors. This mechanism may contribute to maintaining proper cardiac function.