Exercise training provides cardioprotection by activating and coupling endothelial nitric oxide synthase via a ß3-adrenergic receptor-AMP-activated protein kinase signaling pathway.

Exercise training confers sustainable protection against ischemia/reperfusion injury. However, the mechanism by which this process occurs is not fully understood. Previously, it was shown that ß3-adrenergic receptors (ß3-ARs) play a critical role in regulating the activation of endothelial nitric oxide synthase (eNOS) in response to exercise and play a critical role in exercise-mediated cardioprotection. Intriguingly, a deficiency in ß3-ARs led to increased myocardial injury following exercise training. The purpose of the current study was to determine mechanisms by which ß3-ARs are linked to eNOS activation and to determine the mechanism responsible for the exacerbated ischemia/reperfusion injury displayed by ß3-AR deficient (ß3-AR KO) mice after exercise training. Wild-type (n = 37) and ß3-AR KO (n = 40) mice were subjected to voluntary wheel running for 4 weeks. Western blot analysis revealed that neither protein kinase B nor protein kinase A linked ß3-ARs to eNOS following exercise training. However, analysis revealed a role for AMP-activated protein kinase (AMPK). Specifically, exercise training increased the phosphorylation of AMPK in the hearts of wild-type mice, but failed to do so in the hearts of ß3-AR KO mice. Additional studies revealed that exercise training rendered eNOS less coupled and increased NOS-dependent superoxide levels in ß3-AR KO mice. Finally, supplementing ß3-AR KO mice with the eNOS coupler, tetrahydrobiopterin, during the final week of exercise training reduced myocardial infarction. These findings provide important information that exercise training protects the heart in the setting of myocardial ischemia/reperfusion injury by activating and coupling eNOS via the stimulation of a ß3-AR-AMPK signaling pathway.

Sodium Sulfide Attenuates Ischemic-Induced Heart Failure by Enhancing Proteasomal Function in an Nrf2-Dependent Manner.

BACKGROUND: Therapeutic strategies aimed at increasing hydrogen sulfide (H2S) levels exert cytoprotective effects in various models of cardiovascular injury. However, the underlying mechanism(s) responsible for this protection remain to be fully elucidated. Nuclear factor E2-related factor 2 (Nrf2) is a cellular target of H2S and facilitator of H2S-mediated cardioprotection after acute myocardial infarction. Here, we tested the hypothesis that Nrf2 mediates the cardioprotective effects of H2S therapy in the setting of heart failure. METHODS AND RESULTS: Mice (12 weeks of age) deficient in Nrf2 (Nrf2 KO; C57BL/6J background) and wild-type littermates were subjected to ischemic-induced heart failure. Wild-type mice treated with H2S in the form of sodium sulfide (Na2S) displayed enhanced Nrf2 signaling, improved left ventricular function, and less cardiac hypertrophy after the induction of heart failure. In contrast, Na2S therapy failed to provide protection against heart failure in Nrf2 KO mice. Studies aimed at evaluating the underlying cardioprotective mechanisms found that Na2S increased the expression of proteasome subunits, resulting in an increased proteasome activity and a reduction in the accumulation of damaged proteins. In contrast, Na2S therapy failed to enhance the proteasome and failed to attenuate the accumulation of damaged proteins in Nrf2 KO mice. Additionally, Na2S failed to improve cardiac function when the proteasome was inhibited. CONCLUSIONS: These findings indicate that Na2S therapy enhances proteasomal activity and function during the development of heart failure in an Nrf2-dependent manner and that this enhancement leads to attenuation in cardiac dysfunction.

Hydrogen sulfide attenuates high fat diet-induced cardiac dysfunction via the suppression of endoplasmic reticulum stress.

Diabetic cardiomyopathy is a significant contributor to the morbidity and mortality associated with diabetes and metabolic syndrome. However, the underlying molecular mechanisms that lead to its development have not been fully elucidated. Hydrogen sulfide (H2S) is an endogenously produced signaling molecule that is critical for the regulation of cardiovascular homeostasis. Recently, therapeutic strategies aimed at increasing its levels have proven cardioprotective in models of acute myocardial ischemia-reperfusion injury and heart failure. The precise role of H2S in the pathogenesis of diabetic cardiomyopathy has not yet been established. Therefore, the goal of the present study was to evaluate circulating and cardiac H2S levels in a murine model of high fat diet (HFD)-induced cardiomyopathy. Diabetic cardiomyopathy was produced by feeding mice HFD (60% fat) chow for 24 weeks. HFD feeding reduced both circulating and cardiac H2S and induced hallmark features of type-2 diabetes. We also observed marked cardiac dysfunction, evidence of cardiac enlargement, cardiac hypertrophy, and fibrosis. H2S therapy (SG-1002, an orally active H2S donor) restored sulfide levels, improved some of the metabolic perturbations stemming from HFD feeding, and attenuated HFD-induced cardiac dysfunction. Additional analysis revealed that H2S therapy restored adiponectin levels and suppressed cardiac ER stress stemming from HFD feeding. These results suggest that diminished circulating and cardiac H2S levels play a role in the pathophysiology of HFD-induced cardiomyopathy. Additionally, these results suggest that H2S therapy may be of clinical importance in the treatment of cardiovascular complications stemming from diabetes.

ß-adrenergic receptor-mediated cardiac contractility is inhibited via vasopressin type 1A-receptor-dependent signaling.

BACKGROUND: Enhanced arginine vasopressin levels are associated with increased mortality during end-stage human heart failure, and cardiac arginine vasopressin type 1A receptor (V1AR) expression becomes increased. Additionally, mice with cardiac-restricted V1AR overexpression develop cardiomyopathy and decreased ß-adrenergic receptor (ßAR) responsiveness. This led us to hypothesize that V1AR signaling regulates ßAR responsiveness and in doing so contributes to development of heart failure. METHODS AND RESULTS: Transaortic constriction resulted in decreased cardiac function and ßAR density and increased cardiac V1AR expression, effects reversed by a V1AR-selective antagonist. Molecularly, V1AR stimulation led to decreased ßAR ligand affinity, as well as ßAR-induced Ca(2+) mobilization and cAMP generation in isolated adult cardiomyocytes, effects recapitulated via ex vivo Langendorff analysis. V1AR-mediated regulation of ßAR responsiveness was demonstrated to occur in a previously unrecognized Gq protein-independent/G protein receptor kinase-dependent manner. CONCLUSIONS: This newly discovered relationship between cardiac V1AR and ßAR may be informative for the treatment of patients with acute decompensated heart failure and elevated arginine vasopressin.

Discoveries of hydrogen sulfide as a novel cardiovascular therapeutic.

Hydrogen sulfide (H2S) is an endogenously produced gaseous signaling molecule that elicits a number of cytoprotective effects in mammalian species. H2S was originally considered toxic at elevated levels, but 15 years ago the labile molecule was discovered in mammalian tissue and termed a gasotransmitter, thus opening the door for research aimed towards understanding its physiologic nature. Since then, novel findings have depicted the beneficial aspects of H2S therapy, such as vasodilation, antioxidant upregulation, inflammation inhibition, and activation of anti-apoptotic pathways. These cytoprotective alterations effectively treat multiple forms of cardiac injury at the preclinical level of research. The field has progressed towards instituting novel H2S donors that prove more effective at activating the subsequent cardioprotective enhancements over longer time periods. As more findings explore the efficacy of H2S, research focused on detection of sulfhydrated targets is on the rise. Understanding the molecular mechanisms that stem from H2S treatment may lead the field towards powerful therapeutics in the clinical setting. This review will discuss the cytoprotective and cardioprotective effects of H2S therapy, provide analysis on the molecular alterations that lead to these enhancements, and explore recently developed therapeutics that may bring this gasotransmitter into the clinic in the near future.

Imatinib activates pathological hypertrophy by altering myocyte calcium regulation.

BACKGROUND: Imatinib mesylate is a selective tyrosine-kinase inhibitor used in the treatment of multiple cancers, most notably chronic myelogenous leukemia. There is evidence that imatinib can induce cardiotoxicity in cancer patients. Our hypothesis is that imatinib alters calcium regulatory mechanisms and can contribute to development of pathological cardiac hypertrophy. METHODS AND RESULTS: Neonatal rat ventricular myocytes (NRVMs) were treated with clinical doses (low: 2 µM; high: 5 µM) of imatinib and assessed for molecular changes. Imatinib increased peak systolic Ca(2+) and Ca(2+) transient decay rates and Western analysis revealed significant increases in phosphorylation of phospholamban (Thr-17) and the ryanodine receptor (Ser-2814), signifying activation of calcium/calmodulin-dependent kinase II (CaMKII). Imatinib significantly increased NRVM volume as assessed by Coulter counter, myocyte surface area, and atrial natriuretic peptide abundance seen by Western. Imatinib induced cell death, but did not activate the classical apoptotic program as assessed by caspase-3 cleavage, indicating a necrotic mechanism of death in myocytes. We expressed AdNFATc3-green fluorescent protein in NRVMs and showed imatinib treatment significantly increased nuclear factor of activated T cells translocation that was inhibited by the calcineurin inhibitor FK506 or CaMKII inhibitors. CONCLUSION: These data show that imatinib can activate pathological hypertrophic signaling pathways by altering intracellular Ca(2+) dynamics. This is likely a contributing mechanism for the adverse cardiac effects of imatinib.

Ca(2+) influx through L-type Ca(2+) channels and transient receptor potential channels activates pathological hypertrophy signaling.

Common cardiovascular diseases such as hypertension and myocardial infarction require that myocytes develop greater than normal force to maintain cardiac pump function. This requires increases in [Ca(2+)]. These diseases induce cardiac hypertrophy and increases in [Ca(2+)] are known to be an essential proximal signal for activation of hypertrophic genes. However, the source of "hypertrophic" [Ca(2+)] is not known and is the topic of this study. The role of Ca(2+) influx through L-type Ca(2+) channels (LTCC), T-type Ca(2+) channels (TTCC) and transient receptor potential (TRP) channels on the activation of calcineurin (Cn)-nuclear factor of activated T cells (NFAT) signaling and myocyte hypertrophy was studied. Neonatal rat ventricular myocytes (NRVMs) and adult feline ventricular myocytes (AFVMs) were infected with an adenovirus containing NFAT-GFP, to determine factors that could induce NFAT nuclear translocation. Four millimolar Ca(2+) or pacing induced NFAT nuclear translocation. This effect was blocked by Cn inhibitors. In NRVMs Nifedipine (Nif, LTCC antagonist) blocked high Ca(2+)-induced NFAT nuclear translocation while SKF-96365 (TRP channel antagonist) and Nickel (Ni, TTCC antagonist) were less effective. The relative potency of these antagonists against Ca(2+) induced NFAT nuclear translocation (Nif>SKF-96365>Ni) was similar to their effects on Ca(2+) transients and the LTCC current. Infection of NRVM with viruses containing TRP channels also activated NFAT-GFP nuclear translocation and caused myocyte hypertrophy. TRP effects were reduced by SKF-96365, but were more effectively antagonized by Nif. These experiments suggest that Ca(2+) influx through LTCCs is the primary source of Ca(2+) to activate Cn-NFAT signaling in NRVMs and AFVMs. While TRP channels cause hypertrophy, they appear to do so through a mechanism involving Ca(2+) entry via LTCCs.