Inhibition of Wnt/β-catenin signaling upregulates Na 1.5 channels in Brugada syndrome iPSC-derived cardiomyocytes.

The voltage-gated Na 1.5 channels mediate the fast Na current (I ) in cardiomyocytes initiating action potentials and cardiac contraction. Downregulation of I , as occurs in Brugada syndrome (BrS), causes ventricular arrhythmias. The present study investigated whether the Wnt/β-catenin signaling regulates Na 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 1.5 protein and SCN5A mRNA. In iPSC-CMs from a BrS patient, both Na 1.5 protein and peak I 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 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 1.5, which was associated with a 4.9-fold increase in peak I but only a 2.1-fold increase in SCN5A mRNA. The upregulation of Na 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 1.5 expression in both male and female human iPSC-CMs, and inhibition of Wnt/β-catenin signaling upregulates Na 1.5 in BrS iPSC-CMs through both transcriptional and posttranscriptional mechanisms.