Inhibition of Wnt/β-catenin signaling upregulates Nav1.5 channels in Brugada syndrome iPSC-derived cardiomyocytes

The voltage--gated Na(v)1.5 channels mediate the fast Na+ current (I-Na) in cardiomyocytes initiating action potentials and cardiac contraction. Downregulation of INa, as occurs in Brugada syndrome (BrS), causes ventricular arrhythmias. The present study investigated whether the Wnt/beta-catenin signaling regulates Na(v)1.5 in human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). In healthy male and female iPSC-CMs, activation of Wnt/beta-catenin signaling by CHIR-99021 reduced (p < 0.01) both Na(v)1.5 protein and SCN5A mRNA. In iPSC-CMs from a BrS patient, both Na(v)1.5 protein and peak INa were reduced compared to those in healthy iPSC-CMs. Treatment of BrS iPSC-CMs with Wnt-C59, a small-molecule Wnt inhibitor, led to a 2.1-fold increase in Na(v)1.5 protein (p = 0.0005) but surprisingly did not affect SCN5A mRNA (p = 0.146). Similarly, inhibition of Wnt signaling using shRNA-mediated beta-catenin knockdown in BrS iPSC-CMs led to a 4.0-fold increase in Na(v)1.5, which was associated with a 4.9-fold increase in peak INa but only a 2.1-fold increase in SCN5A mRNA. The up regulation of Na(v)1.5 by beta-catenin knockdown was verified in iPSC-CMs from a second BrS patient. This study demonstrated that Wnt/beta-catenin signaling inhibits Na(v)1.5 expression in both male and female human iPSC-CMs, and inhibition of Wnt/beta-catenin signaling upregulates Na(v)1.5 in BrS iPSC-CMs through both transcriptional and posttranscriptional mechanisms.