PKC-ε-dependent survival signals in diabetic hearts

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Abstract
Diabetes mellitus is complicated by the development of a primary cardiomyopathy, which contributes to the excess morbidity and mortality of this disorder. The protein kinase C (PKC) family of isozymes plays a key role in the cardiac phenotype expressed during postnatal development and in response to pathological stimuli. Hyperglycemia is an activating signal for cardiac PKC isozymes that modulate a myriad of cell events including cell death and survival. The ε-isozyme of the PKC family transmits a powerful survival signal in cardiac muscle cells. Accordingly, to test the hypothesis that endogenous activation of cardiac PKC-ε will protect against hyperglycemic cell injury and left ventricular dysfunction, diabetes mellitus was induced using streptozotocin in genetically engineered mice with cardiac-specific expression of the PKC-ε translocation activator [ψε-receptors for activated C kinase (ψε-RACK)]. The results demonstrate a striking PKC-ε cardioprotective phenotype in diabetic ψε-RACK (ε-agonist) mice that is characterized by inhibition of the hyperglycemia apoptosis signal, attenuation of hyperglycemia-mediated oxidative stress, and preservation of parameters of left ventricular pump function. Hearts of diabetic ε-agonist mice exhibited selective trafficking of PKC-ε to membrane and mitochondrial compartments, phosphorylation/inactivation of the mitochondrial Bad protein, and inhibition of cytochrome c release. We conclude that activation of endogenous PKC-ε in hearts of diabetic ε-agonist mice promotes the survival phenotype, attenuates markers of oxidative stress, and inhibits the negative inotropic properties of chronic hyperglycemia.