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 neuronrestrictive silencer factor (NRSF), a transcriptional repressor, selectively regulates expression of multiple fetal cardiac genes, including those for atrial natriuretic peptide, brain natriuretic peptide and a-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 I f and I Ca,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.

Rationale: Atrial and brain natriuretic peptides (ANP and BNP, respectively) exert antihypertrophic effects in the heart via their common receptor, guanylyl cyclase (GC)-A, which catalyzes the synthesis of cGMP, leading to activation of protein kinase (PK)G. Still, much of the network of molecular mediators via which ANP/BNP-GC-A signaling inhibit cardiac hypertrophy remains to be characterized. Objective: We investigated the effect of ANP-GC-A signaling on transient receptor potential subfamily C (TRPC)6, a receptor-operated Ca 2؉ channel known to positively regulate prohypertrophic calcineurin-nuclear factor of activated T cells (NFAT) signaling. Methods and Results: In cardiac myocytes, ANP induced phosphorylation of TRPC6 at threonine 69, the PKG phosphorylation site, and significantly inhibited agonist-evoked NFAT activation and Ca 2؉ influx, whereas in HEK293 cells, it dramatically inhibited agonist-evoked TRPC6 channel activity. These inhibitory effects of ANP were abolished in the presence of specific PKG inhibitors or by substituting an alanine for threonine 69 in TRPC6. In model mice lacking GC-A, the calcineurin-NFAT pathway is constitutively activated, and BTP2, a selective TRPC channel blocker, significantly attenuated the cardiac hypertrophy otherwise seen. Conversely, overexpression of TRPC6 in mice lacking GC-A exacerbated cardiac hypertrophy. BTP2 also significantly inhibited angiotensin II-induced cardiac hypertrophy in mice. Conclusions: Collectively, these findings suggest that TRPC6 is a critical target of antihypertrophic effects elicited via the cardiac ANP/BNP-GC-A pathway and suggest TRPC6 blockade could be an effective therapeutic strategy for preventing pathological cardiac remodeling. (Circ Res. 2010;106:1849-1860.)Key Words: natriuretic peptides Ⅲ calcium Ⅲ ion channels Ⅲ hypertrophy I n response to pathological stimuli such as prolonged mechanical stress, massive tissue injury, or abnormal neurohumoral activation, hearts show hypertrophic growth and remodeling, which is characterized by an increase in myocyte cell size, assembly of sarcomere proteins, interstitial fibrosis, and reexpression of fetal cardiac genes. Although the hypertrophic response is initially compensatory, it ultimately causes heart failure, which is now a leading cause of morbidity and mortality around the world. Diverse intracellular signaling pathways exerting pro-or antihypertrophic effects have been shown to play important roles in the complex processes of cardiac remodeling, 1,2 but the details of the molecular mechanisms mediating the crosstalk among these signaling pathways remain uncertain. Unraveling those details should give us a better understanding of the molecular processes underlying the establishment of cardiac hypertro- phy and heart failure, which could ultimately lead to the discovery of novel therapeutic targets for prevention of pathological cardiac remodeling. The heart regulates cardiovascular homeostasis in part by secreting 2 peptide mediators, atrial natriuretic peptide (ANP) and brain n...

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.

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Background-Recent clinical trials have shown that systemic infusion of nesiritide, a recombinant human brain natriuretic peptide (BNP), improves hemodynamic parameters in acutely decompensated hearts. This suggests that BNP exerts a direct cardioprotective effect and might thus be a useful therapeutic agent with which to treat acute myocardial infarction (MI). In the present study, we used BNP-transgenic (BNP-Tg) mice with elevated plasma BNP to determine whether and how BNP contributes to left ventricular remodeling and healing after MI. Methods and Results-We examined the accumulation of neutrophils and the expression and activation of matrix metalloproteinase (MMP)-9 in the ventricles of male BNP-Tg mice and their nontransgenic (non-Tg) littermates during the early phase after acute MI. The numbers of neutrophils infiltrating the infarcted area were significantly increased in BNP-Tg mice 3 days after MI. In addition, both the gene expression and zymographic activity of MMP-9, but not MMP-2, were significantly higher in BNP-Tg than non-Tg mice. Double immunostaining revealed that neutrophils are the main source of the MMP-9, although doxycycline, an MMP inhibitor, had no effect on neutrophil infiltration of the infarcted area in BNP-Tg mice. Conclusions-These results demonstrate that elevated plasma BNP facilitates neutrophil infiltration of the infarcted area after MI and increases the activity of the MMP-9 they produce. This suggests that BNP plays a key role in the processes of extracellular matrix remodeling and wound-healing during the early phase after acute MI.