Reversible protein phosphorylation is an essential regulatory mechanism in many cellular functions. In contrast to protein kinases, the role and regulation of protein phosphatases has remained ambiguous. To address this issue, we generated transgenic mice that overexpress the catalytic subunit ␣ of protein phosphatase 2A (PP2A) (PP2Ac␣) in the heart driven by the ␣-myosin heavy chain promoter. Overexpression of the PP2Ac␣ gene in the heart led to increased levels of the transgene both at RNA and protein levels. This was accompanied by a significant increase of PP2A enzyme activity in the myocardium. Morphological analysis revealed isles of necrosis and fibrosis. The phosphorylation state of phospholamban, troponin inhibitor, and eukaryotic elongation factor 2 was reduced significantly. The expression of junctional (calsequestrin) and free SR proteins (SERCA and phospholamban) was not altered. Whereas no increase in morbidity or mortality was noted, transgenic mice developed cardiac hypertrophy and reduced contractility of the heart, as well as cardiac dilatation as shown by biplane echocardiography. Taken together, these findings are indicative of the fundamental role of PP2A in cardiac function and imply that disturbances in protein phosphatases expression and activity may cause or aggravate the course of cardiac diseases.

Background-Survivin inhibits apoptosis and regulates cell division in many organs, but its function in the heart is unknown. Methods and Results-We show that cardiac-specific deletion of survivin resulted in premature cardiac death. The underlying cause was a dramatic reduction in total cardiomyocyte numbers as determined by a stereological method for quantification of cells per organ. The resulting increased hemodynamic load per cell led to progressive heart failure as assessed by echocardiography, magnetic resonance imaging, positron emission tomography, and invasive catheterization. The reduction in total cardiomyocyte number in ␣-myosin heavy chain (MHC)-survivin Ϫ/Ϫ mice was due to an Ϸ50% lower mitotic rate without increased apoptosis. This occurred at the expense of DNA accumulation because survivin-deficient cardiomyocytes displayed marked DNA polyploidy indicative of consecutive rounds of DNA replication without cell division. Survivin small interfering RNA knockdown in neonatal rat cardiomyocytes also led to polyploidization and cell cycle arrest without apoptosis. Adenoviral overexpression of survivin in cardiomyocytes inhibited doxorubicin-induced apoptosis, induced DNA synthesis, and promoted cell cycle progression. The phenotype of the ␣MHC-survivin Ϫ/Ϫ mice also allowed us to determine the minimum cardiomyocyte number sufficient for normal cardiac function. In human cardiomyopathy, survivin was potently induced in the failing heart and downregulated again after hemodynamic support by a left ventricular assist device. Its expression positively correlated with the mean cardiomyocyte DNA content. Conclusions-We suggest that the ontogenetically determined cardiomyocyte number may be an independent factor in the susceptibility to cardiac diseases. Through its profound impact on both cardiomyocyte replication and apoptosis, survivin may emerge as a promising new target for myocardial regeneration.

This review summarizes the current knowledge on essential vitamins B1, B2, B3, and B5. These B-complex vitamins must be taken from diet, with the exception of vitamin B3, that can also be synthetized from amino acid tryptophan. All of these vitamins are water soluble, which determines their main properties, namely: they are partly lost when food is washed or boiled since they migrate to the water; the requirement of membrane transporters for their permeation into the cells; and their safety since any excess is rapidly eliminated via the kidney. The therapeutic use of B-complex vitamins is mostly limited to hypovitaminoses or similar conditions, but, as they are generally very safe, they have also been examined in other pathological conditions. Nicotinic acid, a form of vitamin B3, is the only exception because it is a known hypolipidemic agent in gram doses. The article also sums up: (i) the current methods for detection of the vitamins of the B-complex in biological fluids; (ii) the food and other sources of these vitamins including the effect of common processing and storage methods on their content; and (iii) their physiological function.

The transcriptional activation mediated by cAMP-response element (CRE) and transcription factors of the CRE-binding protein (CREB)/CRE modulator (CREM) family represents an important mechanism of cAMP-dependent gene regulation possibly implicated in detrimental effects of chronic ␤-adrenergic stimulation in end-stage heart failure. We studied the cardiac role of CREM in transgenic mice with heart-directed expression of CREM-Ib⌬C-X, a human cardiac CREM isoform. Transgenic mice displayed atrial enlargement with atrial and ventricular hypertrophy, developed atrial fibrillation, and died prematurely. In vivo hemodynamic assessment revealed increased contractility of transgenic left ventricles probably due to a selective up-regulation of SERCA2, the cardiac Ca 2؉ -ATPase of the sarcoplasmic reticulum. In transgenic ventricles, reduced phosphorylation of phospholamban and of the CREB was associated with increased activity of serine-threonine protein phosphatase 1. The density of ␤ 1 -adrenoreceptor was increased, and messenger RNAs encoding transcription factor dHAND and small G-protein RhoB were decreased in transgenic hearts as compared with wild-type controls. Our results indicate that heart-directed expression of CREM-Ib⌬C-X leads to complex cardiac alterations, suggesting CREM as a central regulator of cardiac morphology, function, and gene expression.The transcriptional activation mediated by the cAMP-response element (CRE) 1 and transcription factors of the CREbinding protein (CREB)/CRE modulator (CREM) family represents an important mechanism of cAMP-responsive gene control (1). CREB and CREM bind as homo-or heterodimers to the CRE, a palindromic consensus element in gene promoters of numerous target genes. One mechanism of CRE-mediated transcriptional activation is the cAMP-dependent protein kinase A (PKA)-dependent phosphorylation of a critical serine in activating isoforms of CREB or CREM, finally leading to activation of the transcriptional complex (2). Inhibitory CREM or CREB isoforms lack functional domains that mediate transcriptional activation or regulation by phosphorylation. Those repressors bind to the CRE as homodimers or as heterodimers in combination with other activating or inhibitory isoforms and suppress transcriptional activation by displacing functionally active dimers from the CRE.Several studies suggested that CRE-mediated transcriptional regulation plays an important role in cardiac gene regulation contributing to the pathophysiology of heart failure: (i) CREB and CREM are both expressed in human heart (3, 4); (ii) transgenic mice with heart-directed expression of a nonphosphorylatable, dominant-negative CREB isoform (dnCREB) (5) or of ATF3 (6), another repressor of CRE-mediated transcriptional activation, developed cardiac hypertrophy and signs of heart failure; and (iii) CREM-deficient mice (general knockout) displayed left ventricular dysfunction in the absence of hypertrophy and premature death (7,8).Here, we tested the role of CREM-Ib⌬C-X, a CREM isoform previously isolated from ...