Stimulation of IP3Rs with ET-1 induces Ca(2+ )release from the SR which is tunnelled to mitochondria via mitochondrial RyR leading to stimulation of mitochondrial ATP production.

Background-We previously demonstrated that conditional overexpression of neuronal nitric oxide synthase (nNOS) inhibited L-type Ca 2ϩ channels and decreased myocardial contractility. However, nNOS has multiple targets within the cardiac myocyte. We now hypothesize that nNOS overexpression is cardioprotective after ischemia/reperfusion because of inhibition of mitochondrial function and a reduction in reactive oxygen species generation. Methods and Results-Ischemia/reperfusion injury in wild-type mice resulted in nNOS accumulation in the mitochondria.Similarly, transgenic nNOS overexpression caused nNOS abundance in mitochondria. nNOS translocation into the mitochondria was dependent on heat shock protein 90. Ischemia/reperfusion experiments in isolated hearts showed a cardioprotective effect of nNOS overexpression. Infarct size in vivo was also significantly reduced. nNOS overexpression also caused a significant increase in mitochondrial nitrite levels accompanied by a decrease of cytochrome c oxidase activity. Accordingly, O 2 consumption in isolated heart muscle strips was decreased in nNOS-overexpressing nNOS ϩ /␣MHC-tTA ϩ mice already under resting conditions. Additionally, we found that the reactive oxygen species concentration was significantly decreased in hearts of nNOS-overexpressing nNOS ϩ /␣MHC-tTA ϩ mice compared with noninduced nNOS ϩ /␣MHC-tTA ϩ animals. Conclusion-We demonstrated that conditional transgenic overexpression of nNOS resulted in myocardial protection after ischemia/reperfusion injury. Besides a reduction in reactive oxygen species generation, this might be caused by nitrite-mediated inhibition of mitochondrial function, which reduced myocardial oxygen consumption already under baseline conditions. (Circulation. 2010;122:1588-1603.)

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Background-E193, a heterozygous truncating mutation in the human transcription cofactor Eyes absent 4 (Eya4), causes hearing impairment followed by dilative cardiomyopathy. Methods and Results-In this study, we first show Eya4 and E193 alter the expression of p27 kip1 in vitro, suggesting Eya4 is a negative regulator of p27. Next, we generated transgenic mice with cardiac-specific overexpression of Eya4 or E193. Luciferase and chromatin immunoprecipitation assays confirmed Eya4 and E193 bind and regulate p27 expression in a contradictory manner. Activity and phosphorylation status of the downstream molecules casein kinase-2α and histone deacetylase 2 were significantly elevated in Eya4-but significantly reduced in E193-overexpressing animals compared with wild-type littermates. Magnetic resonance imaging and hemodynamic analysis indicate Eya4-overexpression results in an age-dependent development of hypertrophy already under baseline conditions with no obvious functional effects, whereas E193 animals develop onset of dilative cardiomyopathy as seen in human E193 patients. Both cardiac phenotypes were aggravated on pressure overload. Finally, we identified a new heterozygous truncating Eya4 mutation, E215, which leads to similar clinical features of disease and a stable myocardial expression of the mutant protein as seen with E193. Conclusions-Our

Background: The calcineurin (Cn)/NF-AT signaling cascade plays a crucial role during T-cell activation and development of myocardial hypertrophy. We previously demonstrated that, in addition to NF-AT, Cn is translocated to the nucleus. We also developed a synthetic peptide (IBP) which inhibited the nuclear import of Cn without affecting calcineurin phosphatase activity. The antihypertrophic effect of IBP on the rat myocardium was shown in vivo and in vitro . Here we extended our studies on a potential use of IBP in the prevention of transplant rejection. Methods and results: Coimmunoprecipitation experiments revealed that the synthetic IBP peptide, which is identical to the nuclear localization sequence of calcineurin, disrupts importin/calcineurin interaction. We further demonstrated that inhibition of the importin/calcineurin interaction by the small competitive peptide (IBP) is sufficient to inactivate the calcineurin/NF-AT signaling cascade. Inhibitory effects of IBP on T-cell activation were analyzed by [H 3 ]-thymidine incorporation (7135 ± 2503 vs. 2957 ± 1161 [%]) in activated T-cells in vitro (dentritic cells were used as antigen stimulation). To verify immunosuppressive effect of IBP in vitro , heterotopic heart transplantations were performed on rats. Following transplantation rats were treated with IBP (i.p. 130mg/kg/d) or peanut oil as control (i.p. 1 ml peanut oil/d) for 14 days. Time until transplant rejection was significantly prolonged in IBP treated animals compared to control group (15.2 ± 1.5 day vs. 4 ± 2.8 day; n = 8; p < 0.05). Immunohistochemical studies from transplanted hearts demonstrated that the synthetic calcineurin inhibitory peptide IBP prevented calcineurin nuclear translocation in infiltrating T cells in the donor hearts. Conclusions: The synthetic inhibitory peptide IBP disrupts the calcineurin/NF-AT cascade by inhibition of Cn nuclear import. This suppresses T-cell activation in vitro and in vivo, thereby revealing a potential use of IBP as novel agent to protect donor organs from rejection.

Background: Recent evidence demonstrates that not only NFAT, but also calcineurin is translocated into the nucleus upon hypertrophic stimulation. Previously it was also demonstrated that calpain-mediated degradation caused a constitutive active calcineurin. We hypothesised that nuclear calcineurin is an intranuclear Ca 2+ sensor hypertrophied myocardium and that inhibition of nuclear translocation of calcineurin is a therapeutic strategy to prevent hypertrophy. Methods: Employing a transgene mouse model with conditional calpastatin overexpression (”tet-off”, resulting in calpain inhibition), different adenoviral calcineurin mutants and confocal microscopy in isolated adult cardiac myocytes we investigated calcineurin translocation and nuclear Ca 2+ transients. Assessment of cardiac function if transgenic animals was performed by 7T MRI. Results: We could demonstrate that chronic Ang II stimulation of mice caused calpain-mediated degradation of calcineurin resulting in a constitutive active calcineurin with nuclear translocation. The constitutive active calcineurin in the nucleus escaped further degradation by the UPS and sustained an ongoing hypertrophic response, even after removal of Ang II. Inhibition of nuclear translocation of activated calcineurin by a small inhibitory peptide prevented myocardial hypertrophy in vivo. Transgenic inhibition of calpain activity by calpastatin overexpression prevented proteolysis of calcineurin and allowed for relocation of calcineurin from the nucleus back to the cytosol and regression hypertrophy after removal of Ang II. We were also able to demonstrate that Ang II increases nuclear Ca 2+ transients via InsP3 receptors and that calcineurin is able to act as nuclear Ca 2+ sensor detecting local Ca 2+ release from the nuclear envelope via InsP3R. Nuclear calcineurin mutants that are defective for Ca 2+ activation failed to activate NFAT dependent transcription. Conclusion: This provides an explanation how Ca 2+ and calcineurin can regulate transcription in cardiomyocytes in response to neurohumoral signals apart from Ca 2+ changes in contraction regulation.

Inhibition of nuclear translocation of CnA is a novel approach to inhibit the activation of the CnA/NFAT signaling cascade. Further studies have to demonstrate the long-term use of this principle in vivo.

Introduction: Eyes absent 4 (Eya4) is a transcription cofactor involved in a number of cellular and developmental processes. We have previously shown that a mutation in Eya4 (E193) leads to late-onset familial dilated cardiomyopathy and heart failure. A precise role for Eya4 in the myocardium has not yet been identified. It appears to regulate the cyclin dependent kinase inhibitor p27 kip1 (p27), a protein shown to regulate hypertrophic responses in the adult cardiomyocyte. This study was aimed to explore the role of Eya4 in induced cardiac hypertrophy. Methods and results: We generated transgenic mice with cardiac-specific overexpression of HA-tagged Eya4 or E193 to elucidate the function of these proteins in the development of heart failure in vivo . These and wildtype littermates were challenged with angiotensin II (ATII) or subjected to transaortic constriction (TAC). Magnetic resonance imaging to visualize cardiac structures in detail showed that in response to sustained ATII stimulation and TAC, Eya4 mice exhibited a phenotype with significantly increased parameters of hypertrophy compared to WT and E193 overexpressing animals as judged by increases in heart weight and LV free wall diameter, cross-sectional cell surface areas and fibrosis. MRI also showed mild cardiac hypertrophy in Eya4 transgenic mice already under baseline conditions in an age dependent fashion. Moreover, Eya4 overexpression induced a significant suppression of p27 protein expression and resulted in increased levels of phosphorylated histone deacetylase 2 (HDAC2). E193 overexpression induced age dependent wall thinning and ventricular dilation under baseline conditions with no obvious structural or functional defects. ATII or TAC induced significant changes in HW/BW ratio, IVS, fibrosis, hemodynamic and cell size measurements, albeit to a lesser extent than seen with Eya4 mice. p27 expression and pHDAC2 levels were only slightly altered. Conclusion: In summary, we have demonstrated a mutation in Eya4 to disturb cardiac physiology. We now provide evidence that Eya4 is also involved in forms of acquired heart disease. It seems to suppress p27, which leads to phosphorylation and activation of HDAC2 and results in the development of cardiac hypertrophy.