Shinji Yasuno

NRSF regulates the fetal cardiac gene program and maintains normal cardiac structure and function

Reactivation of the fetal cardiac gene program is a characteristic feature of hypertrophied and failing hearts that correlates with impaired cardiac function and poor prognosis. However, the mechanism governing the reversible expression of fetal cardiac genes remains unresolved. Here we show that neuron‐restrictive silencer factor (NRSF), a transcriptional repressor, selectively regulates expression of multiple fetal cardiac genes, including those for atrial natriuretic peptide, brain natriuretic peptide and α‐skeletal actin, and plays a role in molecular pathways leading to the re‐expression of those genes in ventricular myocytes. Moreover, transgenic mice expressing a dominant‐negative mutant of NRSF in their hearts exhibit dilated cardiomyopathy, high susceptibility to arrhythmias and sudden death. We demonstrate that genes encoding two ion channels that carry the fetal cardiac currents If and ICa,T, which are induced in these mice and are potentially responsible for both the cardiac dysfunction and the arrhythmogenesis, are regulated by NRSF. Our results indicate NRSF to be a key transcriptional regulator of the fetal cardiac gene program and suggest an important role for NRSF in maintaining normal cardiac structure and function.

Angiotensin II type 2 receptor deficiency exacerbates heart failure and reduces survival after acute myocardial infarction in mice.

Background—Angiotensin II plays a prominent role in the progression of heart failure after acute myocardial infarction (AMI). Although both angiotensin type 1 (AT1) and type 2 (AT2) receptors are known to be present in the heart, comparatively little is known about the latter. We therefore examined the role played by AT2 receptors in post-AMI heart failure. Methods and Results—In wild-type mice subjected to AMI by coronary artery ligation, AT2 receptor immunoreactivity is upregulated in the infarct and border areas. Among AT2 receptor-null (−/−) mice, the 7-day survival rate after AMI was significantly lower than among wild-type mice (43% versus 67%;P <0.05). All sham-operated animals of both genotypes survived through the study. Ventricular mRNA levels for brain natriuretic peptide were elevated in both genotypes 24 hours after coronary occlusion, with levels in AT2−/− significantly higher than in wild-type mice, as were their lung weights, and histological examination revealed marked pulmonary congestion in the AT2−/− mice. Cardiac function was significantly decreased in AT2−/− mice 2 days after AMI. Conclusions—AT2 receptor deficiency exacerbates short-term death rates and heart failure after experimental AMI in mice. The AT2 receptor may thus exert a protective effect on the heart after AMI.

T-type Ca2+ channel blockade prevents sudden death in mice with heart failure.

Background— Pharmacological interventions for prevention of sudden arrhythmic death in patients with chronic heart failure remain limited. Accumulating evidence suggests increased ventricular expression of T-type Ca2+ channels contributes to the progression of heart failure. The ability of T-type Ca2+ channel blockade to prevent lethal arrhythmias associated with heart failure has never been tested, however. Methods and Results— We compared the effects of efonidipine and mibefradil, dual T- and L-type Ca2+ channel blockers, with those of nitrendipine, a selective L-type Ca2+ channel blocker, on survival and arrhythmogenicity in a cardiac-specific, dominant-negative form of neuron-restrictive silencer factor transgenic mice (dnNRSF-Tg), which is a useful mouse model of dilated cardiomyopathy leading to sudden death. Efonidipine, but not nitrendipine, substantially improved survival among dnNRSF-Tg mice. Arrhythmogenicity was dramatically reduced in dnNRSF-Tg mice treated with efonidipine or mibefradil. Efonidipine acted by reversing depolarization of the resting membrane potential otherwise seen in ventricular myocytes from dnNRSF-Tg mice and by correcting cardiac autonomic nervous system imbalance. Moreover, the R(−)-isomer of efonidipine, a recently identified, highly selective T-type Ca2+ channel blocker, similarly improved survival among dnNRSF-Tg mice. Efonidipine also reduced the incidence of sudden death and arrhythmogenicity in mice with acute myocardial infarction. Conclusions— T-type Ca2+ channel blockade reduced arrhythmias in a mouse model of dilated cardiomyopathy by repolarizing the resting membrane potential and improving cardiac autonomic nervous system imbalance. T-type Ca2+ channel blockade also prevented sudden death in mice with myocardial infarction. Our findings suggest T-type Ca2+ channel blockade is a potentially useful approach to preventing sudden death in patients with heart failure.

Role of Natriuretic Peptide Receptor Guanylyl Cyclase-A in Myocardial Infarction Evaluated Using Genetically Engineered Mice

Although plasma levels of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are elevated early after myocardial infarction (MI), the significance is not fully understood. We therefore investigated the function of natriuretic peptides after induction of MI in knockout (KO) mice lacking the natriuretic peptide receptor guanylyl cyclase-A, the receptor for ANP and BNP. KO and wild-type (WT) mice were subjected to left coronary artery ligation and then followed up for 4 weeks. Irrespective of genotype, almost all deaths occurred within 1 week after induction of MI. KO mice showed significantly higher mortality because of a higher incidence of acute heart failure, which was associated with diminished water and sodium excretion and with higher cardiac levels of mRNAs encoding ANP, BNP, transforming growth factor-&bgr;1, and type I collagen. By 4 weeks after infarction, left ventricular remodeling, including myocardial hypertrophy and fibrosis, and impairment of left ventricular systolic function were significantly more severe in KO than WT mice. Notably, the enhanced myocardial fibrosis seen in KO mice was virtually absent in infarcted double-KO mice, lacking guanylyl cyclase-A and angiotensin II type 1a receptors, although there was no improvement in survival and no attenuation of cardiac hypertrophy. Thus, guanylyl cyclase-A activation by endogenous cardiac natriuretic peptides protects against acute heart failure and attenuates chronic cardiac remodeling after MI. These beneficial effects are mediated partly through inhibition of the renin-angiotensin system (RAS), although RAS-independent protective actions of guanylyl cyclase-A are also suggested.

Reciprocal expression of MRTF-A and myocardin is crucial for pathological vascular remodelling in mice

Myocardin‐related transcription factor (MRTF)‐A is a Rho signalling‐responsive co‐activator of serum response factor (SRF). Here, we show that induction of MRTF‐A expression is key to pathological vascular remodelling. MRTF‐A expression was significantly higher in the wire‐injured femoral arteries of wild‐type mice and in the atherosclerotic aortic tissues of ApoE−/− mice than in healthy control tissues, whereas myocardin expression was significantly lower. Both neointima formation in wire‐injured femoral arteries in MRTF‐A knockout (Mkl1−/−) mice and atherosclerotic lesions in Mkl1−/−; ApoE−/− mice were significantly attenuated. Expression of vinculin, matrix metallopeptidase 9 (MMP‐9) and integrin β1, three SRF targets and key regulators of cell migration, in injured arteries was significantly weaker in Mkl1−/− mice than in wild‐type mice. In cultured vascular smooth muscle cells (VSMCs), knocking down MRTF‐A reduced expression of these genes and significantly impaired cell migration. Underlying the increased MRTF‐A expression in dedifferentiated VSMCs was the downregulation of microRNA‐1. Moreover, the MRTF‐A inhibitor CCG1423 significantly reduced neointima formation following wire injury in mice. MRTF‐A could thus be a novel therapeutic target for the treatment of vascular diseases.

Intra-abdominal fat area is a predictor for new onset of individual components of metabolic syndrome: MEtabolic syndRome and abdominaL ObesiTy (MERLOT study)

Objective: To investigate the significance of intra-abdominal fat area (IAFA) on new onset of individual components of the metabolic syndrome: high blood pressure, dyslipidemia, or hyperglycemia. Methods: We conducted a longitudinal study using checkup data of a hospital from 1994 to 2010. Of 25,255 subjects, we examined 1,380 Japanese, who underwent computed tomography to measure IAFA and had no metabolic syndrome components at baseline. Results: During 3.6 years of the mean follow-up period, one of metabolic syndrome components occurred in 752 subjects. Of three components, high blood pressure was more prevalent. The multiple Cox regression analysis disclosed that IAFA is significantly associated with onset of metabolic syndrome components (HR: 1.05 per 10 cm2, 95%CI: 1.03–1.07). This finding was independent of BMI, and significant even in non-obese individuals with body mass index <25 kg/m2. Conclusions: MERLOT study demonstrates that IAFA is an independent predictor for new onset of individual components of the metabolic syndrome, even in non-obese healthy Japanese.

Clinical significance of left ventricular hypertrophy and changes in left ventricular mass in high-risk hypertensive patients: a subanalysis of the Candesartan Antihypertensive Survival Evaluation in Japan trial.

Objective To evaluate the associations of left ventricular hypertrophy (LVH) and its changes with the incidence of cardiovascular events and the time-course of serum creatinine (sCr) levels in high-risk hypertensive patients who participated in the Candesartan Antihypertensive Survival Evaluation in Japan trial. Methods We analysed data of 1447 patients who underwent echocardiography at enrolment as an observational study irrespective of allocation. According to the left ventricular mass index (LVMI) at the baseline, they were divided into two groups (without LVH, LVMI < 125 g/m2; n = 607 and with LVH, LVMI ≥ 125 g/m2; n = 840) and four categories on the basis of LVMI at the baseline and 1 year: absence of LVH (n = 285), development of LVH (n = 97), regression of LVH (n = 155), and persistence of LVH (n = 418). Results During 3.3 ± 0.8 years, cardiovascular events occurred in 20 (3.3%) patients without LVH and in 67 (8.0%) patients with LVH (hazard ratio: 2.58; 95% confidence interval: 1.54–4.33; P < 0.001). Among the four categories, absence of LVH was associated with lower risk of cardiovascular events than persistence of LVH (hazard ratio: 0.30; 95% confidence interval: 0.13–0.71; P = 0.006), but development or regression of LVH was not. Only in persistence of LVH did the sCr level significantly increase over time (baseline vs. 3 years; 0.92 vs. 1.02 mg/dl, P < 0.001). Adjusted sCr level of absence and regression of LVH at 3 years was significantly lower than that of persistence of LVH (0.89 and 0.90 vs. 0.97 mg/dl, P < 0.001, P = 0.002, respectively), but that of development of LVH was not. Conclusion Protection against LVH is associated with a reduced risk of cardiovascular events and may be related to the preservation of renal function in high-risk hypertensive patients.

Increased Expression of HCN Channels in the Ventricular Myocardium Contributes to Enhanced Arrhythmicity in Mouse Failing Hearts

Background The efficacy of pharmacological interventions to prevent sudden arrhythmic death in patients with chronic heart failure remains limited. Evidence now suggests increased ventricular expression of hyperpolarization‐activated cation (HCN) channels in hypertrophied and failing hearts contributes to their arrythmicity. Still, the role of induced HCN channel expression in the enhanced arrhythmicity associated with heart failure and the capacity of HCN channel blockade to prevent lethal arrhythmias remains undetermined. Methods and Results We examined the effects of ivabradine, a specific HCN channel blocker, on survival and arrhythmicity in transgenic mice (dnNRSF‐Tg) expressing a cardiac‐specific dominant‐negative form of neuron‐restrictive silencer factor, a useful mouse model of dilated cardiomyopathy leading to sudden death. Ivabradine (7 mg/kg per day orally) significantly reduced ventricular tachyarrhythmias and improved survival among dnNRSF‐Tg mice while having no significant effect on heart rate or cardiac structure or function. Ivabradine most likely prevented the increase in automaticity otherwise seen in dnNRSF‐Tg ventricular myocytes. Moreover, cardiac‐specific overexpression of HCN2 in mice (HCN2‐Tg) made hearts highly susceptible to arrhythmias induced by chronic β‐adrenergic stimulation. Indeed, ventricular myocytes isolated from HCN2‐Tg mice were highly susceptible to β‐adrenergic stimulation‐induced abnormal automaticity, which was inhibited by ivabradine. Conclusions HCN channel blockade by ivabradine reduces lethal arrhythmias associated with dilated cardiomyopathy in mice. Conversely, cardiac‐specific overexpression of HCN2 channels increases arrhythmogenicity of β‐adrenergic stimulation. Our findings demonstrate the contribution of HCN channels to the increased arrhythmicity seen in failing hearts and suggest HCN channel blockade is a potentially useful approach to preventing sudden death in patients with heart failure.

Angiotensin II type 1a receptor signalling directly contributes to the increased arrhythmogenicity in cardiac hypertrophy

Angiotensin II has been implicated in the development of various cardiovascular ailments, including cardiac hypertrophy and heart failure. The fact that inhibiting its signalling reduced the incidences of both sudden cardiac death and heart failure in several large‐scale clinical trials suggests that angiotensin II is involved in increased cardiac arrhythmogenicity during the development of heart failure. However, because angiotensin II also promotes structural remodelling, including cardiomyocyte hypertrophy and cardiac fibrosis, it has been difficult to assess its direct contribution to cardiac arrhythmogenicity independently of the structural effects.

p300 Plays a Critical Role in Maintaining Cardiac Mitochondrial Function and Cell Survival in Postnatal Hearts

Rationale: It is known that the transcriptional coactivator p300 is crucially involved in the differentiation and growth of cardiac myocytes during development. However, the physiological function of p300 in the postnatal hearts remains to be characterized. Objective: We have now investigated the physiological function of p300 in adult hearts. Methods and Results: We analyzed transgenic mice exhibiting cardiac-specific overexpression of a dominant-negative p300 mutant lacking the C/H3 domain (p300&Dgr;C/H3 transgenic [TG] mice). p300&Dgr;C/H3 significantly inhibited p300-induced activation of GATA- and myocyte enhancer factor 2–dependent promoters in cultured ventricular myocytes, and p300&Dgr;C/H3-TG mice showed cardiac dysfunction that was lethal by 20 weeks of age. The numbers of mitochondria in p300&Dgr;C/H3-TG myocytes were markedly increased, but the mitochondria were diminished in size. Moreover, cardiac mitochondrial gene expression, mitochondrial membrane potential and ATP contents were all significantly disrupted in p300&Dgr;C/H3-TG hearts, suggesting that mitochondrial dysfunction contributes to the progression of the observed cardiomyopathy. Transcription of peroxisome proliferator-activated receptor &ggr; coactivator (PGC)-1&agr;, a master regulator of mitochondrial gene expression, and its target genes was significantly downregulated in p300&Dgr;C/H3-TG mice, and p300&Dgr;C/H3 directly repressed myocyte enhancer factor 2C-dependent PGC-1&agr; promoter activity and disrupted the transcriptional activity of PGC-1&agr; in cultured ventricular myocytes. In addition, myocytes showing features of autophagy were observed in p300&Dgr;C/H3-TG hearts. Conclusions: Collectively, our findings suggest that p300 is essential for the maintenance of mitochondrial integrity and for myocyte survival in the postnatal left ventricular myocardium.