Increased particulate partitioning of PKCε reverses susceptibility of phospholamban knockout hearts to ischemic injury

Cytosolic Ca²⁺ overload is a critical mediator of myocardial damage following cardiac ischemia-reperfusion. It has therefore been proposed that normalization of sarcoplasmic reticulum Ca²⁺ cycling through inhibition or ablation of the Ca²⁺ ATP-ase inhibitor phospholamban (PLN), which shows promise as a treatment for heart failure, could be beneficial in ischemic heart disease. However, a recent study has shown that globally ischemic PLN-deficient hearts exhibit increased ischemic injury, with impaired contractile, ATP, and phosphocreatine recoveries, compared to wild-type hearts. Since protein kinase C (PKC) family members are widely recognized as mediators of both post-ischemic injury and ischemic preconditioning, we assessed PKC levels in PLN-deficient hearts. Compared to genetically normal hearts, PLN-deficient hearts exhibited diminished particulate partitioning of PKCε, a known cardioprotective PKC isoform, without alterations in the levels of membrane-associated PKCδ nor PKCα. To determine if decreased particulate partitioning of cardioprotective PKCε was a cause of increased ischemic injury in PLN-deficient hearts, PLN-deficient mice were mated with mice expressing a myocardial-specific PKCε translocation activator peptide, pseudo-epsilon receptor for activated kinase C (ψεRACK). In ψεRACK/PLN knockout (KO) hearts, PKCε translocation to membranous cellular structures was augmented and this was associated with a significant acceleration of post-ischemic contraction and relaxation rates, as well as reduction of creatine phosphokinase release, compared to PLN-deficient hearts. Importantly, post-ischemic functional recovery reached pre-ischemic hyperdynamic values in ψεRACK/PLN KO hearts, indicating super-rescue by the combination of PLN ablation and ψεRACK expression. These findings suggest that diminished PKCε particulate partitioning in PLN-deficient hearts is associated with attenuated contractile recovery upon ischemia-reperfusion and that increased translocation of PKCε to membranous cellular structures confers full cardioprotection.