Pharmacological- and gene therapy-based inhibition of protein kinase Cα/β enhances cardiac contractility and attenuates heart failure

Background - The conventional protein kinase C ( PKC) isoform alpha functions as a proximal regulator of Ca2+ handling in cardiac myocytes. Deletion of PKC alpha in the mouse results in augmented sarcoplasmic reticulum Ca2+ loading, enhanced Ca2+ transients, and augmented contractility, whereas overexpression of PKC alpha in the heart blunts contractility. Mechanistically, PKC alpha directly regulates Ca2+ handling by altering the phosphorylation status of inhibitor-1, which in turn suppresses protein phosphatase-1 activity, thus modulating phospholamban activity and secondarily, the sarcoplasmic reticulum Ca2+ ATPase. Methods and Results - In the present study, we show that short-term inhibition of the conventional PKC isoforms with Ro-32-0432 or Ro-31-8220 significantly augmented cardiac contractility in vivo or in an isolated work-performing heart preparation in wild-type mice but not in PKC alpha-deficient mice. Ro-32-0432 also increased cardiac contractility in 2 different models of heart failure in vivo. Short-term or long-term treatment with Ro-31-8220 in a mouse model of heart failure due to deletion of the muscle lim protein gene significantly augmented cardiac contractility and restored pump function. Moreover, adenovirus-mediated gene therapy with a dominant-negative PKC alpha cDNA rescued heart failure in a rat model of postinfarction cardiomyopathy. PKC alpha was also determined to be the dominant conventional PKC isoform expressed in the adult human heart, providing potential relevance of these findings to human pathophysiology. Conclusions - Pharmacological inhibition of PKC alpha, or the conventional isoforms in general, may serve as a novel therapeutic strategy for enhancing cardiac contractility in certain stages of heart failure.