Abstract 1402: Ras Induced Gαi Signaling in Cardiac Dysfunction and Arrhythmias
Background: Diastolic dysfunction and arrhythmia are common features of hypertrophic cardiomyopathy. Tamoxifen-induced cardiac-specific Ras activation in adult transgenic mice led to hypertrophic cardiomyopathy and marked induction of arrhythmia, suggesting that Ras mediated signaling plays a contributing role to the onset of diastolic dysfunction and arrhythmia in hypertrophic cardiomyopathy hearts. However, the underlying molecular and cellular mechanisms are unknown and are the focus of current study.
Aims: To further investigate the molecular and cellular mechanisms of Ras induced arrhythmia and diastolic dysfunction.
Methods and Results: As demonstrated by chronic monitoring using surface EKG, the cardiac-specific Ras activated transgenic animals developed polymorphic arrhythmia which was first detectable at 7 days post-Ras induction and markedly worsened at later time points. Cellular and molecular studies showed that the onset of cardiac arrhythmia was correlated with significant prolongation of action potential duration, SR calcium defects and loss of PKA phosphorylation of phospholamban. Using cDNA microarray analysis, we detected a significant induction of Gαi 1 mRNA in Ras transgenic hearts compared to wild-type controls, which was subsequently confirmed by real-time qPCR and immunoblot. The functional relevance of Gai1 induction was tested in vivo by pertussis toxin (PTX, a specific inhibitor of Gαi, 30mg/kgBW ip, single) treatment in Ras transgenic animals. PTX markedly reduced arrhythmic activities in Ras transgenic hearts and restored action potential in isolated ventricular myocytes to the same level as the wildtype cells. PTX treatment also enhanced basal PKA phosphorylation of phospholamban in Ras transgenic hearts.
Conclusions: Our study revealed that a novel role of Gαi signaling as a major downstream event in Ras mediated signaling in adult heart. Enhanced Gαi activity had a critical contribution to the electrophysiological and intracellular calcium defects in ventricular myocytes, and diastolic dysfunction and arrhythmia in intact heart. Our study suggests that inhibition of Gαi mediated signaling may ameliorate arrhythmias and contractile dysfunction in hypertrophic cardiomyopathy.