Enhancement of β-catenin/T-cell factor 4 signaling causes susceptibility to cardiac arrhythmia by suppressing Na_V1.5 expression in mice

Background: β-Catenin/T-cell factor 4 (TCF4) signaling is enhanced in ischemic heart disease in which ventricular tachycardia (VT)/ventricular fibrillation occurs frequently. How this signaling links to arrhythmogenesis remains unclear. Objective: The purpose of this study was to investigate the role of β-catenin gain of function in the development of arrhythmia. Methods: A mouse model with a conditional deletion of CTNNB1 exon 3 resulting in cardiac exon 3–deleted and stabilized β-catenin (β-catΔE3) was used to determine the role of β-catenin gain of function in the regulation of cardiac rhythm. Results: Western blotting showed β-catΔE3 expression and significantly decreased Na_V1.5 protein in CTNNB1 E3^−/− and CTNNB1 E3^+/− mouse hearts. Real-time qRT-PCR revealed significantly decreased Na_V1.5 messenger RNA with no changes in Na⁺ channel β1 to β4 expression in these hearts. Immunofluorescence revealed accumulation of β-catΔE3 in the nuclei of CTNNB1 E3^−/− cardiomyocytes. Immunohistochemistry demonstrated nuclear localization of β-catenin in cardiomyocytes, which was associated with significantly decreased Na_V1.5 messenger RNA in human ischemic hearts. Immunoprecipitation revealed that β-catΔE3 interacted with TCF4 in CTNNB1 E3^−/− cardiomyocytes. Whole-cell recordings showed that Na⁺ currents and depolarization and amplitude of action potentials were significantly decreased in CTNNB1 E3^−/− ventricular myocytes. Electrocardiographic recordings demonstrated that in mice with cardiac CTNNB1 E3^−/−, the QRS complex was prolonged and VT was induced by the Na⁺ channel blocker flecainide. However, cardiac function, as determined by echocardiography and heart/body weight ratios, remained unchanged. Conclusion: Enhancement of β-catenin/TCF4 signaling led to the prolongation of the QRS complex and increase in susceptibility to VT by suppression of Na_V1.5 expression and Na⁺ channel activity in mice.