Attenuation of the hypoxia-induced protein kinase Cδ interaction with the ‘d’ subunit of F₁F_o-ATP synthase in neonatal cardiac myocytes: implications for energy preservation and survival

The F₁F_o-ATP synthase provides most of the heart's energy, yet events that alter its function during injury are poorly understood. Recently, we described a potent inhibitory effect on F₁F_o-ATP synthase function mediated by the interaction of PKCδ (protein kinase Cδ) with dF₁F_o (‘d’ subunit of the F₁F_o-ATPase/ATP synthase). We have now developed novel peptide modulators which facilitate or inhibit the PKCδ–dF₁F_o interaction. These peptides include HIV-Tat (transactivator of transcription) protein transduction and mammalian mitochondrial-targeting sequences. Pre-incubation of NCMs (neonatal cardiac myocyte) with 10 nM extracellular concentrations of the mitochondrial-targeted PKCδ–dF₁F_o interaction inhibitor decreased Hx (hypoxia)-induced co-IP (co-immunoprecipitation) of PKCδ with dF₁F_o by 40±9%, abolished Hx-induced inhibition of F₁F_o-ATPase activity, attenuated Hx-induced losses in F₁F_o-derived ATP and protected against Hx- and reperfusion-induced cell death. A scrambled-sequence (inactive) peptide, which contained HIV-Tat and mitochondrial-targeting sequences, was without effect. In contrast, the cell-permeant mitochondrial-targeted PKCδ–dF₁F_o facilitator peptide, which we have shown previously to induce the PKCδ–dF₁F_o co-IP, was found to inhibit F₁F_o-ATPase activity to an extent similar to that caused by Hx alone. The PKCδ–dF₁F_o facilitator peptide also decreased ATP levels by 72±18% under hypoxic conditions in the presence of glycolytic inhibition. None of the PKCδ–dF₁F_o modulatory peptides altered the inner mitochondrial membrane potential. Our studies provide the first evidence that disruption of the PKCδ–dF₁F_o interaction using cell-permeant mitochondrial-targeted peptides attenuates cardiac injury resulting from prolonged oxygen deprivation.