AKAP121 downregulation impairs protective cAMP signals, promotes mitochondrial dysfunction, and increases oxidative stress.

AIMS: The aim of the present study was to determine the function and the role of the scaffold protein AKAP121, tethering cAMP dependent protein kinase A to the outer wall of mitochondria, in neonatal ventricular myocytes and the heart. METHODS AND RESULTS: Competitive peptides displacing AKAP121 from mitochondria in the tissue and in the cells were used to investigate the role of AKAP121 in mitochondrial function, reactive oxygen species (ROS) generation, and cell survival. Displacement of AKAP121 from mitochondria by synthetic peptides triggers the death program in cardiomyocytes. Under pathological conditions in vivo, in a rat model of cardiac hypertrophy induced by ascending aorta banding, the levels of AKAP121 are significantly down-regulated. Disappearance of AKAP121 is associated with mitochondrial dysfunction, high oxidative stress, and apoptosis. In vivo delocalization of AKAP121 by competitive peptides replicates some of the molecular signatures induced by pressure overload: mitochondrial dysfunction, increased mitochondrial ROS, and apoptosis. CONCLUSION: These data suggest that AKAP121 regulates the response to stress in cardiomyocytes, and therefore AKAP121 downregulation might represent an important event contributing to the development of cardiac dysfunction.

Tumor necrosis factor-alpha mediates hemolysis-induced vasoconstriction and the cerebral vasospasm evoked by subarachnoid hemorrhage.

Hypertension can lead to subarachnoid hemorrhage and eventually to cerebral vasospasm. It has been suggested that the latter could be the result of oxidative stress and an inflammatory response evoked by subarachnoid hemorrhage. Because an unavoidable consequence of hemorrhage is lysis of red blood cells, we first tested the hypothesis on carotid arteries that the proinflammatory cytokine tumor necrosis factor-alpha contributes to vascular oxidative stress evoked by hemolysis. We observed that hemolysis induces a significant increase in tumor necrosis factor-alpha both in blood and in vascular tissues, where it provokes Rac-1/NADPH oxidase-mediated oxidative stress and vasoconstriction. Furthermore, we extended our observations to cerebral vessels, demonstrating that tumor necrosis factor-alpha triggered this mechanism on the basilar artery. Finally, in an in vivo model of subarachnoid hemorrhage obtained by the administration of hemolyzed blood in the cisterna magna, we demonstrated, by high-resolution ultrasound analysis, that tumor necrosis factor-alpha inhibition prevented and resolved acute cerebral vasoconstriction. Moreover, tumor necrosis factor-alpha inhibition rescued the hemolysis-induced brain injury, evaluated with the method of 2,3,5-triphenyltetrazolium chloride and by the histological analysis of pyknotic nuclei. In conclusion, our results demonstrate that tumor necrosis factor-alpha plays a crucial role in the onset of hemolysis-induced vascular injury and can be used as a novel target of the therapeutic strategy against cerebral vasospasm.

Nebivolol induces nitric oxide release in the heart through inducible nitric oxide synthase activation.

Nebivolol is a beta1-adrenergic receptor antagonist that also reduces blood pressure by evoking endothelial NO production and vasodilation. We aimed at assessing whether nebivolol induces NO production also in the heart and delineating the molecular mechanisms involved. Using the fluorescent probe diaminofluorescein, we found that nebivolol induces a dose-dependent NO production in the heart, statistically significant already at 10(-7) mol/L. It is not an effect because of the blockade of beta1-adrenergic receptor, because this effect is not shared by another drug of the same class, atenolol. Because nebivolol has been reported to act as an agonist on other beta-adrenergic receptors, we tested NO production in the presence of receptor antagonists. Nebivolol was not able to induce NO production in presence of the beta3-antagonist SR59230A, indicating a fundamental role for beta3-adrenergic receptors in cardiac NO production by nebivolol. Moreover, inducible NO synthase inhibition abolishes NO release in the heart, indicating that nebivolol induces NO production by acting on the inducible isoform of the enzyme. The action of nebivolol on inducible NO synthase was confirmed by real-time PCR experiments, showing cardiac overexpression of inducible NO synthase but not neuronal NO synthase or endothelial NO synthase, after 5 hours of treatment with nebivolol. In conclusion, our study demonstrates that nebivolol also stimulates NO production in the heart. This action of nebivolol is exerted via a signaling pathway starting from the activation of beta3-adrenergic receptors and leading to overexpression of inducible NO synthase. Cardiac NO production by nebivolol could participate in the cardiovascular effects of nebivolol treatment in patients affected by hypertension and heart failure.