Sarcoplasmic reticulum adenosine triphosphatase overexpression in the L-type Ca2+ channel mouse results in cardiomyopathy and Ca2+ -induced arrhythmogenesis

Identifying ion channel genes related to cardiomyopathy using a novel decision forest strategy

Ion channels play many crucial functions in life. Their dysfunction may lead to a number of diseases, such as arrhythmia and beta cell dysfunction. In this study, we firstly selected the ion channel gene expression profiles using a dimensionality reduction method. After that, we applied a novel decision forest strategy to mine cardiomyopathy related ion channel genes. The novel proposed Zi integrated the information of the decision trees' height and the frequency at which a gene was located in the tree. It achieved a much higher ability of feature selection. In the result, 26 cardiomyopathy related ion channel genes were identified. Their Zi were higher than the threshold Z*. Furthermore, most of these genes had been reported to have relationships with cardiomyopathies. In conclusion, our proposed decision forest strategy had a better classification performance. Our result can provide a theoretical basis for cardiovascular researchers.

Testosterone suppresses ventricular remodeling and improves left ventricular function in rats following myocardial infarction

Men with congestive heart failure (CHF) have relatively low testosterone levels. Several studies demonstrated that testosterone treatment increases cardiac output and reduces peripheral vascular resistance. However, the effects of testosterone on heart function, cardiomyocyte apoptosis and ventricular remodeling have not been fully elucidated. This study was conducted to investigate the effects of testosterone on heart function, cardiomyocyte apoptosis and ventricular remodeling in male rats post-myocardial infarction. A total of 86 male rats were randomly assigned to undergo ligation of the coronary artery (n=70) or pseudosurgery (n=16). After 6 weeks, a left ventricular ejection fraction (LVEF) of ≤45% was defined as a successful model of CHF. The model rats were randomly assigned to 3 groups, namely low-dose testosterone (TU), high-dose TU and placebo (PL) groups. After treatment for 12 weeks, the expression of several mRNA transcripts in myocardial tissue was measured by quantitative polymerase chain reaction. Immunofluorescence was used to measure myocardial caspase-3 expression. Compared to the PL group, LVEF was significantly improved in the TU treatment groups. Moreover, the mRNA expression of atrial natriuretic peptide, brain natriuretic peptide, matrix metalloproteinase-2 and sarcoendoplasmic reticulum Ca²⁺-ATPase 2a was significantly reduced, while the mRNA expression of glycogen synthase kinase 3β and tissue inhibitor of metalloproteinase-2 was markedly increased in the TU groups. TU treatment also significantly reduced caspase-3 expression. Therefore, different doses of TU suppressed ventricular remodeling and improved left ventricular function, reduced apoptosis and prevented mortality in a CHF rat model.

Calcium handling abnormalities in atrial fibrillation as a target for innovative therapeutics

Atrial electrical and structural alterations (remodeling) have emerged as key elements in the development of the atrial fibrillation (AF) substrate. Evidence points to abnormalities in intracellular Ca (calcium) handling as crucial links in AF-initiating focal activity and in perpetuation by rapidly firing foci and reentry. This review focuses on the molecular basis of altered Ca handling in AF, with the goal of providing new insights into molecular effective antiarrhythmic therapy.

Limited functional and metabolic improvements in hypertrophic and healthy rat heart overexpressing the skeletal muscle isoform of SERCA1 by adenoviral gene transfer in vivo

Adenoviral gene transfer of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA)2a to the hypertrophic heart in vivo has been consistently reported to lead to enhanced myocardial contractility. It is unknown if the faster skeletal muscle isoform, SERCA1, expressed in the whole heart in early failure, leads to similar improvements and whether metabolic requirements are maintained during an adrenergic challenge. In this study, Ad.cmv.SERCA1 was delivered in vivo to aortic banded and sham-operated Sprague-Dawley rat hearts. The total SERCA content increased 34%. At 48-72 h posttransfer, echocardiograms were acquired, hearts were excised and retrograded perfused, and hemodynamics were measured parallel to NMR measures of the phosphocreatine (PCr)-to-ATP ratio (PCr/ATP) and energy substrate selection at basal and high workloads (isoproterenol). In the Langendorff mode, the rate-pressure product was enhanced 27% with SERCA1 in hypertrophic hearts and 10% in shams. The adrenergic response to isoproterenol was significantly potentiated in both groups with SERCA1. 31P NMR analysis of PCr/ATP revealed that the ratio remained low in the hypertrophic group with SERCA1 overexpression and was not further compromised with adrenergic challenge. 13C NMR analysis revealed fat and carbohydrate oxidation were unaffected at basal with SERCA1 expression; however, there was a shift from fats to carbohydrates at higher workloads with SERCA1 in both groups. Transport of NADH-reducing equivalents into the mitochondria via the alpha-ketoglutamate-malate transporter was not affected by either SERCA1 overexpression or adrenergic challenge in both groups. Echocardiograms revealed an important distinction between in vivo versus ex vivo data. In contrast to previous SERCA2a studies, the echocardiogram data revealed that SERCA1 expression compromised function (fractional shortening) in the hypertrophic group. Shams were unaffected. While our ex vivo findings support much of the earlier cardiomyocyte and transgenic data, the in vivo data challenge previous reports of improved cardiac function in heart failure models after SERCA intervention.

Multiple downstream proarrhythmic targets for calmodulin kinase II: Moving beyond an ion channel-centric focus

The multifunctional Ca(2+) calmodulin-dependent protein kinase II (CaMKII) has emerged as a pro-arrhythmic signaling molecule. CaMKII can participate in arrhythmia signaling by effects on ion channel proteins, intracellular Ca(2+) uptake and release, regulation of cell death, and by activation of hypertrophic signaling pathways. The pleuripotent nature of CaMKII is reminiscent of another serine-threonine kinase, protein kinase A (PKA), which shares many of the same protein targets and is the downstream kinase most associated with beta-adrenergic receptor stimulation. The ability of CaMKII to localize and coordinate activity of multiple protein targets linked to Ca(2+) signaling set CaMKII apart from other "traditional" arrhythmia drug targets, such as ion channel proteins. This review will discuss some of the biology of CaMKII and focus on work that has been done on molecular, cellular, and whole animal models that together build a case for CaMKII as a pro-arrhythmic signal and as a potential therapeutic target for arrhythmias and structural heart disease.