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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BackgroundThe 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 ResultsWe 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.ConclusionsHCN 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.

Ability to drive an automobile was evaluated in 16 patients with well compensated liver cirrhosis. Four tests were performed, namely the emergency reaction test, the continuous emergency reaction test, the signal confirmation test and the accelerator reaction test. Test scores were compared to those of a group of age-matched healthy volunteers. 31% of patients were found to be unfit to drive. Alcoholic cirrhotics fared as poorly as non-alcoholic cirrhotics. In patients with subclinical hepatic encephalopathy (defined by neuropsychologic testing), 44% were unfit to drive. Routine testing of cirrhotic patients for ability to drive could have a major impact on motor vehicle accident rates.

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 Ca 2ϩ channels contributes to the progression of heart failure. The ability of T-type Ca 2ϩ 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 Ca 2ϩ channel blockers, with those of nitrendipine, a selective L-type Ca 2ϩ 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(Ϫ)-isomer of efonidipine, a recently identified, highly selective T-type Ca 2ϩ 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 Ca2ϩ 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 Ca 2ϩ channel blockade also prevented sudden death in mice with myocardial infarction. Our findings suggest T-type Ca 2ϩ channel blockade is a potentially useful approach to preventing sudden death in patients with heart failure. Key Words: ion channels Ⅲ nervous system, autonomic Ⅲ heart failure Ⅲ calcium Ⅲ arrhythmia A s many as 50% of deaths among heart failure patients are sudden and unexpected, presumably the result of lethal arrhythmias. 1 Despite recent progress in nonpharmacological therapy, pharmacological interventions for the treatment and prevention of lethal arrhythmias associated with chronic heart failure remain limited. A prerequisite for the development of new pharmacological approaches is to identify potential targets based on knowledge of the molecular basis of arrhythmogenesis in failing hearts. Clinical Perspective on p 752Compelling evidence implicates T-type Ca 2ϩ channels in the progression of heart failure. 2,3 During development, T-type Ca 2ϩ channels are abundantly expressed in the embryonic ventricle, but their expression is suppressed in the adult ventricle, so that it is restricted to the conduction system. 4,5 However, T-type Ca 2ϩ channels are reexpressed in hypertrophied and failing ventricles, 4,6 -9 and the resultant T-type Ca 2ϩ currents (I Ca,T ) are thought to be involved in the pathologica...

BackgroundRecent studies have shown that in addition to brain (or B-type) natriuretic peptide (BNP) and the N-terminal proBNP fragment, levels of intact proBNP are also increased in heart failure. Moreover, present BNP immunoassays also measure proBNP, as the anti-BNP antibody cross-reacts with proBNP. It is important to know the exact levels of proBNP in heart failure, because elevation of the low-activity proBNP may be associated with the development of heart failure.Methodology/Principal FindingsWe therefore established a two-step immunochemiluminescent assay for total BNP (BNP+proBNP) and proBNP using monoclonal antibodies and glycosylated proBNP as a standard. The assay enables measurement of plasma total BNP and proBNP within only 7 h, without prior extraction of the plasma. The detection limit was 0.4 pmol/L for a 50-µl plasma sample. Within-run CVs ranged from 5.2%–8.0% in proBNP assay and from 7.0%–8.4% in total BNP assay, and between-run CVs ranged from 5.3–7.4% in proBNP assay and from 2.9%–9.5% in total BNP assay, respectively. The dilution curves for plasma samples showed good linearity (correlation coefficients = 0.998–1.00), and analytical recovery was 90–101%. The mean total BNP and proBNP in plasma from 116 healthy subjects were 1.4±1.2 pM and 1.0±0.7 pM, respectively, and were 80±129 pM and 42±70 pM in 32 heart failure patients. Plasma proBNP levels significantly correlate with age in normal subjects.Conclusions/SignificanceOur immunochemiluminescent assay is sufficiently rapid and precise for routine determination of total BNP and proBNP in human plasma.

We previously reported the secretion of C-type natriuretic peptide (CNP) from vascular endothelial cells and proposed the existence of a vascular natriuretic peptide system composed of endothelial CNP and smooth muscle guanylyl cyclase-B (GC-B), the CNP receptor, and involved in the regulation of vascular tone, remodeling, and regeneration. In this study, we assessed the functional significance of this system in the regulation of blood pressure in vivo using vascular endothelial cell–specific CNP knockout and vascular smooth muscle cell–specific GC-B knockout mice. These mice showed neither the skeletal abnormality nor the early mortality observed in systemic CNP or GC-B knockout mice. Endothelial cell–specific CNP knockout mice exhibited significantly increased blood pressures and an enhanced acute hypertensive response to nitric oxide synthetase inhibition. Acetylcholine-induced, endothelium-dependent vasorelaxation was impaired in rings of mesenteric artery isolated from endothelial cell–specific CNP knockout mice. In addition, endothelin-1 gene expression was enhanced in pulmonary vascular endothelial cells from endothelial cell–specific CNP knockout mice, which also showed significantly higher plasma endothelin-1 concentrations and a greater reduction in blood pressure in response to an endothelin receptor antagonist than their control littermates. By contrast, vascular smooth muscle cell–specific GC-B knockout mice exhibited blood pressures similar to control mice, and acetylcholine-induced vasorelaxation was preserved in their isolated mesenteric arteries. Nonetheless, CNP-induced acute vasorelaxation was nearly completely abolished in mesenteric arteries from vascular smooth muscle cell–specific GC-B knockout mice. These results demonstrate that endothelium-derived CNP contributes to the chronic regulation of vascular tone and systemic blood pressure by maintaining endothelial function independently of vascular smooth muscle GC-B.