cGMP signalling in pre- and post-conditioning: The role of mitochondria

Abstract

Much of cell death from ischaemia/reperfusion in heart and other tissues is generally thought to arise from mitochondrial permeability transition (MPT) in the first minutes of reperfusion. In ischaemic pre-conditioning, agonist binding to Gi protein-coupled receptors prior to ischaemia triggers a signalling cascade that protects the heart from MPT. We believe that the cytosolic component of this trigger pathway terminates in activation of guanylyl cyclase resulting in increased production of cGMP and subsequent activation of protein kinase G (PKG). PKG phosphorylates a protein on the mitochondrial outer membrane (MOM), which then causes the mitochondrial KATP channel (mitoKATP) on the mitochondrial inner membrane to open, leading to increased production of reactive oxygen species (ROS) by the mitochondria. This implies that the protective signal is somehow transmitted from the MOM to its inner membrane. This is accomplished by a series of intermembrane signalling steps that includes protein kinase C (PKCε) activation. The resulting ROS then activate a second PKC pool which, through another signal transduction pathway termed the mediator pathway, causes inhibition of MPT and reduction in cell death. Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2007.