Inhibition of Wnt/β‐catenin signaling upregulates Na(v)1.5 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 I (Na), as occurs in Brugada syndrome (BrS), causes ventricular arrhythmias. The present study investigated whether the Wnt/β‐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/β‐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 I (Na) 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 β‐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 I (Na) but only a 2.1‐fold increase in SCN5A mRNA. The upregulation of Na(v)1.5 by β‐catenin knockdown was verified in iPSC‐CMs from a second BrS patient. This study demonstrated that Wnt/β‐catenin signaling inhibits Na(v)1.5 expression in both male and female human iPSC‐CMs, and inhibition of Wnt/β‐catenin signaling upregulates Na(v)1.5 in BrS iPSC‐CMs through both transcriptional and posttranscriptional mechanisms.