The Brugada Syndrome Susceptibility Gene HEY2 Modulates Cardiac Transmural Ion Channel Patterning and Electrical Heterogeneity

Abstract

Rationale: Genome-wide association studies previously identified an association of rs9388451 at chromosome 6q22.3 (near HEY2 ) with Brugada syndrome. The causal gene and underlying mechanism remain unresolved. Objective: We used an integrative approach entailing transcriptomic studies in human hearts and electrophysiological studies in Hey2 +/− ( Hey2 heterozygous knockout) mice to dissect the underpinnings of the 6q22.31 association with Brugada syndrome. Methods and Results: We queried expression quantitative trait locus data acquired in 190 human left ventricular samples from the genotype-tissue expression consortium for cis -expression quantitative trait locus effects of rs9388451, which revealed an association between Brugada syndrome risk allele dosage and HEY2 expression (β=+0.159; P =0.0036). In the same transcriptomic data, we conducted genome-wide coexpression analysis for HEY2 , which uncovered KCNIP2 , encoding the β-subunit of the channel underlying the transient outward current ( I to ), as the transcript most robustly correlating with HEY2 expression (β=+1.47; P =2×10 −34 ). Transcript abundance of Hey2 and the I to subunits Kcnip2 and Kcnd2 , assessed by quantitative reverse transcription–polymerase chain reaction, was higher in subepicardium versus subendocardium in both left and right ventricles, with lower levels in Hey2 +/− mice compared with wild type. Surface ECG measurements showed less prominent J waves in Hey2 +/− mice compared with wild-type. In wild-type mice, patch-clamp electrophysiological studies on cardiomyocytes from right ventricle demonstrated a shorter action potential duration and a lower V max in subepicardium compared with subendocardium cardiomyocytes, which was paralleled by a higher I to and a lower sodium current ( I Na ) density in subepicardium versus subendocardium. These transmural differences were diminished in Hey2 +/− mice because of changes in subepicardial cardiomyocytes. Conclusions: This study uncovers a role of HEY2 in the normal transmural electrophysiological gradient in the ventricle and provides compelling evidence that genetic variation at 6q22.31 (rs9388451) is associated with Brugada syndrome through a HEY2 -dependent alteration of ion channel expression across the cardiac ventricular wall.

Coexistence of atrioventricular accessory pathways and drug‐induced type 1 Brugada pattern

“…Genetic variants in proteins in the signaling pathways and/or transcription factors can potentially cause DI‐type 1 BrP or BrS . Loss‐of‐function mutation in Tbx5 (G145R) has been shown to cause BrS in humans .…”

“…Tbx5 and Tbx3 have been also shown to regulate the BrS susceptibility genes “SCN5A‐SCN10A” locus and effect the expression of SCN5A . Hey2 has been recently shown to be a BrS susceptibility gene by modulating cardiac transmural ion channel patterning and electrical heterogeneity . In addition, activation of canonical Wnt signaling has been shown to decrease SCN5A mRNA levels, Na v 1.5 protein and Na + current density in rat ventricular myocytes …”

“…33 Hey2 has been recently shown to be a BrS susceptibility gene by modulating cardiac transmural ion channel patterning and electrical heterogeneity. 32 In addition, activation of canonical Wnt signaling has been shown to decrease SCN5A mRNA levels, Na v 1.5 protein and Na + current density in rat ventricular myocytes. 34 The putative mutations in BrS susceptibility genes (e.g., SCN5A, SCN10A, SCN4A, SCNN1A, KCNJ8, and KCND3) identified in this study likely contribute to the DI-type 1 BrP, although further study is needed to reach this conclusion.…”

“…30 Genetic variants in proteins in the signaling pathways and/or transcription factors can potentially cause DI-type 1 BrP or BrS. 31,32 Lossof-function mutation in Tbx5 (G145R) has been shown to cause BrS in humans. 31 Tbx5 and Tbx3 have been also shown to regulate the BrS susceptibility genes "SCN5A-SCN10A" locus and effect the expression of SCN5A.…”

Dissecting the Genetic Basis of the ECG as a Means of Understanding Mechanisms of Arrhythmia

“…Other transcriptomic approaches, such as coexpression analysis as recently implemented by us in a functional follow up study of a locus identified for Brugada syndrome, may also provide functional hypotheses to be tested experimentally. 20 The progress being made in recent years in dissecting genetic factors contributing to AF, both by means of genetic studies in large cohorts of AF 10 and by the intermediate phenotype approach, is remarkable. With their large collaborative study on P wave indices as intermediate phenotypes, Christophersen et al 6 have made another important contribution along a journey that will eventually lead us through the maze of AF.…”