REGULATION OF VOLTAGE-GATED SODIUM CURRENT BY WNT SIGNALLING IN HEALTHY AND BRUGADA SYNDROME HUMAN CARDIOMYOCYTES
CCC ePoster Gallery. Liang W. 10/26/19; 280310; 252
Wenbin Liang
Wenbin Liang
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BACKGROUND: Both inherited arrhythmogenic diseases (such as Brugada Syndrome) and heart failure are associated with reduced voltage-gated Na+ current (INa) which promotes lethal arrhythmias and sudden deaths. We and others have shown that Wnt/beta-catenin signaling (Wnt signaling), which is active in heart disease, inhibits INa in rat and mouse cardiomyocytes. But whether Wnt signaling regulates INa in human cardiomyocytes and represents a novel therapeutic target is unknown. This study aims to investigate if Wnt signaling inhibits INa in human cardiomyocytes, to elucidate the underlying mechanisms, and to test if blocking Wnt signaling can rescue INa in Brugada syndrome patient cardiomyocytes.

METHODS AND RESULTS: Cardiomyocytes were differentiated from human induced pluripotent stem cells (hiPSC-CMs) that were derived from healthy volunteers or a Brugada Syndrome patient. Whole-cell patch-clamp technique was used for INa measurement. Activation of Wnt signaling in healthy hiPSC-CMs led to a 69% reduction in INa amplitude (peak current at -20 mV: -10.5±2.8 pA/pF, n=9 cells vs. control -33.6±4.1 pA/pF, n=6 cells, p < 0.01) by reducing SCN5A mRNA (encoding the pore-forming α subunit of INa, Nav1.5). In addition, Wnt signaling also reduced Nav1.5 glycosylation causing a depolarizing shift of INa activation curve (a mechanism found in human, but not in rodent, cardiomyocytes). Blocking Wnt signaling in Brugada hiPSC-CMs with shRNA-mediated b-catenin knockdown led to a 13-fold increase in INa amplitude (p < 0.01, n=9 cells), offsetting the fundamental genetic defect. Consistent with increased INa, blocking Wnt signaling also upregulated SCN5A mRNA and Nav1.5 protein, without affecting expression of other cardiac ion channels in Brugada hiPSC-CMs.

CONCLUSION: This study demonstrated Wnt-inhibition of human cardiac INa and, using Brugada Syndrome as an example, demonstrated that blocking Wnt signaling is a novel therapeutic strategy to rescue INa in heart disease. Translational Perspective: Downregulation of INa is a key defect causing malignant ventricular arrhythmias and sudden cardiac death (SCD) in heart failure and J-wave Syndrome (including Brugada Syndrome and Early Repolarization (ER) Syndrome). The high SCD rate in these patients reflects a lack of disease-specific therapies due to our poor understanding of the mechanisms regulating INa. The present study demonstrated, for the first time, that inhibition of Wnt/β-catenin signalling is a valid and novel strategy to restore INa in Brugada patient cardiomyocytes, and may also be potentially applicable to heart failure and ER Syndrome.
BACKGROUND: Both inherited arrhythmogenic diseases (such as Brugada Syndrome) and heart failure are associated with reduced voltage-gated Na+ current (INa) which promotes lethal arrhythmias and sudden deaths. We and others have shown that Wnt/beta-catenin signaling (Wnt signaling), which is active in heart disease, inhibits INa in rat and mouse cardiomyocytes. But whether Wnt signaling regulates INa in human cardiomyocytes and represents a novel therapeutic target is unknown. This study aims to investigate if Wnt signaling inhibits INa in human cardiomyocytes, to elucidate the underlying mechanisms, and to test if blocking Wnt signaling can rescue INa in Brugada syndrome patient cardiomyocytes.

METHODS AND RESULTS: Cardiomyocytes were differentiated from human induced pluripotent stem cells (hiPSC-CMs) that were derived from healthy volunteers or a Brugada Syndrome patient. Whole-cell patch-clamp technique was used for INa measurement. Activation of Wnt signaling in healthy hiPSC-CMs led to a 69% reduction in INa amplitude (peak current at -20 mV: -10.5±2.8 pA/pF, n=9 cells vs. control -33.6±4.1 pA/pF, n=6 cells, p < 0.01) by reducing SCN5A mRNA (encoding the pore-forming α subunit of INa, Nav1.5). In addition, Wnt signaling also reduced Nav1.5 glycosylation causing a depolarizing shift of INa activation curve (a mechanism found in human, but not in rodent, cardiomyocytes). Blocking Wnt signaling in Brugada hiPSC-CMs with shRNA-mediated b-catenin knockdown led to a 13-fold increase in INa amplitude (p < 0.01, n=9 cells), offsetting the fundamental genetic defect. Consistent with increased INa, blocking Wnt signaling also upregulated SCN5A mRNA and Nav1.5 protein, without affecting expression of other cardiac ion channels in Brugada hiPSC-CMs.

CONCLUSION: This study demonstrated Wnt-inhibition of human cardiac INa and, using Brugada Syndrome as an example, demonstrated that blocking Wnt signaling is a novel therapeutic strategy to rescue INa in heart disease. Translational Perspective: Downregulation of INa is a key defect causing malignant ventricular arrhythmias and sudden cardiac death (SCD) in heart failure and J-wave Syndrome (including Brugada Syndrome and Early Repolarization (ER) Syndrome). The high SCD rate in these patients reflects a lack of disease-specific therapies due to our poor understanding of the mechanisms regulating INa. The present study demonstrated, for the first time, that inhibition of Wnt/β-catenin signalling is a valid and novel strategy to restore INa in Brugada patient cardiomyocytes, and may also be potentially applicable to heart failure and ER Syndrome.
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