Local delivery of PKCε-activating peptide mimics ischemic preconditioning in aged hearts through GSK-3β but not F₁-ATPase inactivation

In adult heart, selective PKCε activation limits ischemia (I)-reperfusion (R) damage and mimics the protection associated with ischemic preconditioning. We sought to determine whether local delivery of PKCε activator peptide ψε-receptor for activated C-kinase (ψε-RACK) is sufficient to produce a similarly protected phenotype in aged hearts. Langendorff-perfused hearts isolated from adult (5 mo; n = 9) and aged (24 mo; n = 9) male Fisher 344 rats were perfused with ψε-RACK conjugated to Tat (500 nM) or Tat only (500 nM) for 10 min before global 31-min ischemia. Western blotting was used to measure mitochondrial targeting of PKCε, PKCδ, phospho (p)-GSK-3β (Ser⁹) and GSK-3β in hearts snap-frozen during I. Recovery of left ventricular developed pressure was significantly improved by ψε-RACK (P < 0.01) and infarct size reduced in 24-mo rats vs. age-matched controls (60% vs. 34%; P < 0.01). Mitochondrial PKCε levels were 30% greater during I with ψε-RACK in aged vs. control rats (P < 0.01). Interestingly, mitochondrial GSK-3β levels were threefold greater in aged vs. adult rats during I, and ψε-RACK prevented this increase (P < 0.01). Mitochondrial p-GSK-3β levels were also greater in aged rats after ψε-RACK (P < 0.01), and subsequent inhibition of GSK-3β with SB-216763 (3 μM) before I/R elicited protection similar to that of ψε-RACK (n = 3/group). Mitochondrial proteomic analysis further identified group differences in the F ₁-ATPase β-subunit, and coimmunoprecipitation studies revealed a novel interaction with PKCε. F₁-ATPase-PKCε association was affected by ψε-RACK in adult but not aged rats. Our results provide evidence, for the first time, for PKCε-mediated protection in aged rat heart after I/R and suggest a central role for mitochondrial GSK-3β but not F₁-ATPase as a potential target of PKCε to limit I/R damage with aging.