Endothelin receptor antagonist CPU0213 and vitamin E reverse downregulation of FKBP12.6 and SERCA2a: A role of hyperphosphorylation of PKCε

Downregulation of FKBP12.6 and sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) contributes to sudden cardiac death and heart failure. We aimed to test the hypothesis that (i) downregulation of FKBP12.6 and SERCA2a can be taken as molecular markers for drug interventions and (ii) such downregulation is produced by crosstalk between endothelin-reactive oxygen species and β-adrenoceptors stimulation, mediated by hyperphosphorylation of protein kinase Cɛ (PKCɛ). Rat cardiomyocytes were incubated with isoproterenol (1 μM), endothelin-1 (0.1 μM) or hydrogen peroxide (10 μM) for 18 h, resulting in downregulation of mRNA and protein of FKBP12.6 and SERCA2a, as well as upregulation of PKCɛ mRNA and phosphorylated PKCɛ protein. These changes were reversed by an application of either propranolol (1 μM), endothelin receptor antagonist CPU0213 (1 μM) or vitamin E (1 μM). As indicated by the fluorescent dye Fluo3, diastolic [Ca2+]i in rat ventricular myocytes was increased after incubation with isoproterenol (0.1 μM). The increased [Ca2+]i in diastole was dramatically decreased by CPU0213. Thus, the downregulation of FKBP12.6 and SERCA2a, and hyperphosphorylation of PKCɛ, appear to be related to crosstalk between over-activated endothelin-reactive oxygen species and a β-adrenoceptor pathway. CPU0213 is beneficial in treating cardiac insufficiency and preventing cardiac arrhythmias possibly by normalizing hyperphosphorylation of PKCɛ and abnormal FKBP12.6 and SERCA2a. The antioxidant activity of vitamin E was sufficient to normalize the levels of FKBP12.6 and SERCA2a and phosphorylation of PKCɛ. Thus by testing with biomarkers FKBP12.6 and SERCA2a, we have shown that the endothelin receptor antagonist CPU0213 and the antioxidant vitamin E may relieve risk of lethal arrhythmias and heart failure by suppressing PKCɛ.