Protein Kinase G Transmits the Cardioprotective Signal From Cytosol to Mitochondria

Abstract

Abstract-Ischemic and pharmacological preconditioning can be triggered by an intracellular signaling pathway in which G i -coupled surface receptors activate a cascade including phosphatidylinositol 3-kinase, endothelial nitric oxide synthase, guanylyl cyclase, and protein kinase G (PKG). Activated PKG opens mitochondrial K ATP channels (mitoK ATP ) which increase production of reactive oxygen species. Steps between PKG and mitoK ATP opening are unknown. We describe effects of adding purified PKG and cGMP on K ϩ transport in isolated mitochondria. Light scattering and respiration measurements indicate PKG induces opening of mitoK ATP similar to K ATP channel openers like diazoxide and cromakalim in heart, liver, and brain mitochondria. This effect was blocked by mitoK ATP inhibitors 5-hydroxydecanoate, tetraphenylphosphonium, and glibenclamide, PKG-selective inhibitor KT5823, and protein kinase C (PKC) inhibitors chelerythrine, Ro318220, and PKC-⑀ peptide antagonist ⑀V 1-2 . MitoK ATP are opened by the PKC activator 12-phorbol 13-myristate acetate. We conclude PKG is the terminal cytosolic component of the trigger pathway; it transmits the cardioprotective signal from cytosol to inner mitochondrial membrane by a pathway that includes PKC-⑀. (Circ Res. 2005;97:329-336.)Key Words: ATP-sensitive K ϩ channel Ⅲ cGMP Ⅲ preconditioning Ⅲ protein kinase C Ⅲ protein kinase G I schemic (IPC) and pharmacological preconditioning by ligands such as acetylcholine and bradykinin initiates a signaling cascade that opens mitochondrial ATP-sensitive K ϩ channels (mitoK ATP ). Many components of this signaling pathway have been identified. 1 Surface receptors activate phosphatidylinositol 3-(PI3-) kinase by transactivation of epidermal growth factor receptors (EGFRs). A signaling complex composed of transactivated EGFR, Src kinase, and PI3-kinase causes phosphorylation of phosphatidylinositol bisphosphate, which in turn activates the phosphatidylinositol-dependent kinases (PDKs). 2 The PDKs then phosphorylate Akt 3 which activates the remainder of the cytosolic signaling pathway (Figure 1) including phosphorylation of endothelial nitric oxide synthase (eNOS), production of NO, stimulation of guanylyl cyclase, generation of cGMP, and activation of protein kinase G (PKG).cGMP and presumably PKG activation are important during preconditioning. Delayed preconditioning by diazoxide involves NO, 4 and cGMP accumulation after inhibition of cGMP-specific phosphodiesterase by sildenafil induces acute and delayed preconditioning. 5 Direct activation of PKG increases generation of reactive oxygen species (ROS) in cardiomyocytes, and this effect depends on mitoK ATP opening. 3 Whereas PKG antagonists abort ROS generation by PKG activators, they have no effect on ROS triggered by diazoxide, a direct opener of mitoK ATP , indicating PKG is upstream of mitoK ATP . A direct activator of PKG mimics IPC in intact hearts. 6 We hypothesized that PKG opens mitoK ATP by causing its phosphorylation, 7 and that the open channel increases generation of mi...

Sildenafil and cardiomyocyte-specific cGMP signaling prevent cardiomyopathic changes associated with dystrophin deficiency

“…Such a mechanism would appear to reconcile many findings. Indeed, it has been reported that augmented cGMP signaling prevents mitochondria-mediated cell death through reduced opening of the mitochondrial permeability transition pore (24). The opening of this pore was recently shown to be associated with dysregulated ␤-adrenergic receptor signaling and Ca 2ϩ handling (25).…”

Statin and resveratrol in combination induces cardioprotection against myocardial infarction in hypercholesterolemic rat

“…It has been demonstrated that activation of Akt induces phosphorylation and inhibition of GSK-3β, which inhibits mitochondrial permeability transiton pore opening, a primary step for apoptotic and necrotic cell death [22]. On the other hand, activation of eNOS generates NO and activates mitochondrial K ATP channels in a cGMP dependent manner, leading to acute cardioprotection [23]. Again, the following study suggests possible involvement of increased β-catenin translocation followed by VEGF expression in the resveratrol and combination groups after myocardial infarction which might be one of the positive effect of β-catenin and its angiogenic property that leads to chronic cardioprotection.…”

Remote Ischemic Preconditioning and Renoprotection

“…11 The current concept of signal transduction in IPC suggests activation of the signaling cascades through the phosphoinositide 3-kinase/Akt/endothelial nitric oxide synthase (NOS)/cyclic guanosine monophosphate/PKG pathways, eventually leading to the opening of the ATP-dependent mitochondrial potassium (K ATP ) channel, which is believed to be a downstream target of PKG/PKC activation. 10,12,13 The activated mitochondrial K ATP channels have the ability to limit the opening of mitochondrial permeability transition pores, thus causing a marked improvement in cell survival. 14 Nitric oxide (NO) is emerging as an important cytoprotective agent and may play a pivotal role in rIPC both as a trigger and mediator of rIPC.…”