Direct and Indirect Suppression of Scn5a Gene Expression Mediates Cardiac Na+ Channel Inhibition by Wnt Signalling

Abstract

Background: Myocardial infarction and heart failure are associated with reduced voltage-gated Na⁺ current (I_Na) that promotes arrhythmias and sudden deaths. We have previously shown that the Wnt/β-catenin signalling (Wnt signalling), which is active in heart disease, reduces cardiac I_Na, suggesting that Wnt signalling may be a potential therapeutic target. However, because Wnt signalling is required for the homeostasis of many noncardiac tissues, administration of Wnt inhibitors to heart patients would cause significant side effects. The present study aims to elucidate the molecular mechanisms of cardiac I_Na inhibition by Wnt, which would identify cardiac-specific therapeutic targets.

Methods: Wnt signalling was activated in neonatal rat ventricular myocytes by Wnt3a protein. Adenovirus expressing Wnt3a was injected into the adult rat ventricle. CRISPR/Cas9 and chromatin immunoprecipitation were used for mechanistic studies.

Results: Wnt signalling activation in neonatal rat ventricular myocytes reduced Na_v1.5 protein and Scn5a mRNA, but increased Tbx3, a known suppressor of Scn5a. Chromatin immunoprecipitation showed that Wnt signalling inhibits Scn5a expression through downstream mediator (TCF4) binding to both Tbx3 and Scn5a promoters. Overexpression or knockdown of Tbx3 directly modified Na_v1.5 and I_Na, whereas CRISPR/Cas9-induced mutations at TCF4 binding sites within the Scn5a promoter attenuated Wnt inhibition of Scn5a and Na_v1.5. In adult rat hearts, adenovirus expressing Wnt3a reduced Na_v1.5, increased QRS duration in electrocardiogram, and increased the susceptibility to ventricular tachycardia.

Conclusions: Wnt signalling inhibits the Na⁺ channel by direct and indirect (via Tbx3) suppression of Scn5a transcription. Strategies to block TCF4 binding to the Tbx3 and Scn5a promoters would represent novel strategies for cardiac-specific inhibition of the Wnt pathway to rescue I_Na and prevent sudden cardiac deaths.