Cardiac remodeling is triggered in response to mechanical stress and various neurohumoral factors. We have recently discovered that protein kinase D (PKD), which has been scarcely studied in cardiomyocytes, plays a significant role to regulate cardiac hypertrophy and remodeling in the downstream of Gq-coupling receptor (GqPCR) -protein kinase C (PKC) signaling. Furthermore, we have identified that a muscle restricted PDZ-3LIM protein, ENH1, has a unique function to selectively and directly bind to PKC and PKD and segregate this kinase complex to cardiac Z-disc, which has been thought as a central machinery of mechanical stress signaling. Based on these observations, we hypothesize that the PKCr ENH1-PKD1 complex plays a critical role in the regulation of cardiac hypertrophy and remodeling by integrating GqPCR signaling and mechanical stress signaling. In this proposal, we will test this hypothesis using a combinatory strategy of genetically modified mouse models and in vivo physiological analysis. The research focuses on in vivo analysis of the relationship between the mechanical stress-induced cardiac remodeling and the PKC-ENH1-PKD1 signal complex. Accordingly, our specific aims are: 1) to characterize in vivo activation of PKD in the process of cardiac remodeling in animal models of cardiac hypertrophy and failure, 2) to generate and characterize cardiac transgenic mice with constitutive active and dominant negative mutants of PKD, 3) to test ENH-null hearts and cardiomyocytes to define the physiological roles of ENH in cardiac mechanical stress signaling, and 4) to examine potential downstream target molecules of PKC-ENH-PKD signaling in cardiac remodeling. We anticipate that the outcome of these studies will assist our better understanding of molecular mechanisms that determine the fate of stressed cardiomyocytes and help to design new drug to induce favorable remodeling in diseased hearts.
