Altered Ca 2؉ homeostasis is a salient feature of heart disease, where the calcium release channel ryanodine receptor (RyR) plays a major role. Accumulating data support the notion that neuronal nitric oxide synthase (NOS1) regulates the cardiac RyR via Snitrosylation. We tested the hypothesis that NOS1 deficiency impairs RyR S-nitrosylation, leading to altered Ca 2؉ homeostasis. Diastolic Ca 2؉ levels are elevated in NOS1 ؊/؊ and NOS1/NOS3 ؊/؊ but not NOS3 ؊/؊ myocytes compared with wild-type (WT), suggesting diastolic Ca 2؉ leakage. Measured leak was increased in NOS1 ؊/؊ and NOS1/NOS3 ؊/؊ but not in NOS3 ؊/؊ myocytes compared with WT. Importantly, NOS1 ؊/؊ and NOS1/NOS3 ؊/؊ myocytes also exhibited spontaneous calcium waves. Whereas the stoichiometry and binding of FK-binding protein 12.6 to RyR and the degree of RyR phosphorylation were not altered in NOS1 ؊/؊ hearts, RyR2 S-nitrosylation was substantially decreased, and the level of thiol oxidation increased. Together, these findings demonstrate that NOS1 deficiency causes RyR2 hyponitrosylation, leading to diastolic Ca 2؉ leak and a proarrhythmic phenotype. NOS1 dysregulation may be a proximate cause of key phenotypes associated with heart disease.heart ͉ nitric oxide ͉ excitation-contraction coupling ͉ oxidative stress ͉ heart failure T he cardiac myocyte has emerged as a prototypic example of the manner in which nitric oxide (NO) signaling occurs in a spatially confined manner. Although neuronal (NOS1) and endothelial (NOS3) isoforms of nitric oxide synthase are located extremely close to one another within the cell on opposite sides of the dyad, they exert opposite effects on myocardial contractility (1). The mechanism(s) for this effect remains controversial. One explanation derived from in vitro observations is that NOS3 inhibits the sarcolemmal L-type calcium channel on the sarcolemmal aspect of the dyad, whereas NOS1 modulates ryanodine receptor (RyR) activity on the sarcoplasmic reticulum (SR) (1-3). Although this paradigm explains many facets of NO activity within the heart, other studies suggest that in the myocyte, NOS1 may bind to and/or regulate other ion channels or effectors, including the plasma membrane calcium/calmodulin-dependent calcium ATPase (4), sarcoplamic reticulum Ca 2ϩ -ATPase (SERCA) (5), and possibly phospholamban (PLB). In addition, there is support for the notion that this effect is mediated by a direct protein posttranslational modification; but again, this assertion is controversial (6).Another facet of NO cardiobiology has emerged that further motivates the importance of understanding the direct NOS effector molecules. In heart failure and/or other states of cardiac injury, NOS1 levels within the heart rise, and NOS1 effectively translocates from the SR to the plasma membrane (2,7,8). Because this phenomenon could have either deleterious effects or adaptive consequences, it is imperative to address definitively the physiologic role of NOS1 in the heart.To address these issues, we tested the hypothesis that the cardiac RyR i...

Although protein S-nitrosylation is increasingly recognized as mediating nitric oxide (NO) signaling, roles for protein denitrosylation in physiology remain unknown. Here, we show that S-nitrosoglutathione reductase (GSNOR), an enzyme that governs levels of S-nitrosylation by promoting protein denitrosylation, regulates both peripheral vascular tone and β-adrenergic agonist-stimulated cardiac contractility, previously ascribed exclusively to NO/cGMP. GSNOR-deficient mice exhibited reduced peripheral vascular tone and depressed β-adrenergic inotropic responses that were associated with impaired β-agonist-induced denitrosylation of cardiac ryanodine receptor 2 (RyR2), resulting in calcium leak. These results indicate that systemic hemodynamic responses (vascular tone and cardiac contractility), both under basal conditions and after adrenergic activation, are regulated through concerted actions of NO synthase/GSNOR and that aberrant denitrosylation impairs cardiovascular function. Our findings support the notion that dynamic S-nitrosylation/denitrosylation reactions are essential in cardiovascular regulation.excitation-contraction coupling | nitroso-redox imbalance G uanosine 3′,5′-cyclic monophosphate (cGMP)-dependent and -independent signaling by nitric oxide (NO) has been described in many organ systems, including the cardiovascular (CV) system (1, 2). Accumulating evidence indicates that the principal non-cGMP signal is effected by the covalent attachment of NO to the thiol group of cysteine (Cys) residues (Snitrosylation) (3) and that this posttranslational modification may influence cardiac contractility (4) and peripheral vascular resistance (5) through effects on ion channels (6) and adrenergic receptors (7). Because deletion or inhibition of NO synthase (NOS) diminishes all forms of NO bioactivity and thus impairs both cGMP and S-nitrosylation signaling, it has been difficult to elucidate the exact roles of S-nitrosylation vs. cGMP in CV regulation.Investigation of the role of S-nitrosylation in cellular signaling has been aided by discovery of enzymes that metabolize Snitrosothiols (SNOs) without affecting NOS activity or levels of NO itself (mammalian enzymes that directly metabolize NO have not been identified) (8-10). In particular, S-nitrosoglutathione reductase (GSNOR), an enzyme involved in the removal of NO groups from Cys thiols in proteins (SNO-proteins) through metabolism of S-nitrosoglutathione (GSNO, which is in equilibrium with SNO-proteins), has been ascribed an indispensable role in regulating S-nitrosylation in the CV system (9). Although GSNOR does not affect baseline blood pressure, it mitigates hypotension induced by anesthetics and infectious agents (5) and plays an essential role in regulating both β-adrenergic receptor expression and responsiveness in the heart (7). These studies suggest that SNOs may exert physiological roles in the control of systemic hemodynamics and cardiac contractility.In the CV system, endothelial NOS (NOS3, eNOS) and neuronal NOS (NOS1, nNOS) subserve endothe...

Rational The regenerative capacity of the heart is markedly diminished shortly after birth coinciding with overall withdrawal of cardiomyocytes from cell cycle. Consequently, the adult mammalian heart has limited capacity to regenerate after injury. The discovery of factors that can induce cardiomyocyte proliferation is therefore of high interest and has been the focus of extensive investigation over the past years. Objective We have recently identified C3orf58 as a novel Hypoxia and Akt induced Stem cell Factor (HASF) secreted from mesenchymal stem cells that can promote cardiac repair through cytoprotective mechanisms. Here, we tested the hypothesis that HASF can also contribute to cardiac regeneration by stimulating cardiomyocyte division and proliferation. Methods and Results Neonatal ventricular cardiomyocytes were stimulated in culture for seven days with purified recombinant HASF protein. Compared to control untreated cells, HASF-treated neonatal cardiomyocytes exhibited 60% increase in DNA synthesis as measured by BrdU incorporation. These results were confirmed by immunofluorescence confocal microscopy showing a 50–100% increase in the number of cardiomyocytes in the mitotic and cytokinesis phases. Importantly, in vivo cardiac overexpression of HASF in a transgenic mouse model resulted in enhanced level of DNA synthesis and cytokinesis in neonatal and adult cardiomyocytes. These proliferative effects were modulated by a PI3K-AKT-CDK7 pathway as revealed by the use of PI3K pathway specific inhibitors and silencing of the Cdk7 gene. Conclusion Our studies support the hypothesis that HASF induces cardiomyocyte proliferation via a PI3K-AKT-CDK7 pathway. The implications of this finding may be significant for cardiac regeneration biology and therapeutics.

Wnt signaling has recently emerged as an important regulator of cardiac progenitor cell proliferation and differentiation, but the exact mechanisms by which Wnt signaling modulates these effects are not known. Understanding these mechanisms is essential for advancing our knowledge of cardiac progenitor cell biology and applying this knowledge to enhance cardiac therapy. Here, we explored the effects of Sfrp2, a canonical Wnt inhibitor, in adult cardiac progenitor cell (CPC) differentiation and investigated the molecular mechanisms involved. Our data show that Sfrp2 treatment can promote differentiation of CPCs after ischemia-reperfusion injury. Treatment of CPCs with Sfrp2 inhibited CPC proliferation and primed them for cardiac differentiation. Sfrp2 binding to Wnt6 and inhibition of Wnt6 canonical pathway was essential for the inhibition of CPC proliferation. This inhibition of Wnt6 canonical signaling by Sfrp2 was important for activation of the non-canonical Wnt/Planar Cell Polarity (PCP) pathway through JNK, which in turn induced expression of cardiac transcription factors and CPC differentiation. Taken together, these results demonstrate a novel role of Sfrp2 and Wnt6 in regulating the dynamic process of CPC proliferation and differentiation, as well as providing new insights into the mechanisms of Wnt signaling in cardiac differentiation.