The roles of PKCδ and ϵ isoenzymes in the regulation of myocardial ischaemia/reperfusion injury

Reperfusion of ischaemic cardiac tissue is associated with increased apoptosis and oncosis, resulting in diminished heart function. Short bouts of ischaemia before the prolonged ischaemic event (ischaemic preconditioning) protect the heart from injury mediated by reperfusion. The PKC (protein kinase C) family of serine/threonine kinases are involved in many different signalling processes. Two calcium-insensitive isoforms of the novel PKC subfamily, PKCδ and ϵ, play opposing roles in ischaemia/reperfusion injury. Activation of PKCδ during reperfusion induces cell death through the regulation of mitochondrial function and induction of apoptosis and oncosis. In contrast, activation of PKCϵ before ischaemia protects mitochondrial function and diminishes apoptosis and oncosis. How can two highly homologous PKC isoenzymes play such opposing roles through the regulation of mitochondrial function? This review will highlight what is known about PKCδ and ϵ function during ischaemia/reperfusion injury and will suggest a novel regulatory pathway which determines the fate of the cell following ischaemic stress.