The Brugada Syndrome Susceptibility Gene <i>HEY2</i> Modulates Cardiac Transmural Ion Channel Patterning and Electrical Heterogeneity.

Abstract

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