Abstract 17134: Variation Within a Left Ventricle-Specific Hand1 Enhancer Impairs Gata Transcription Factor Binding and Disrupts Ventricular Conduction System Development

Abstract

The ventricular conduction system (VCS), composed of the His bundle, the left and right bundle branches, and the Purkinje fiber network, rapidly propagates electrical impulses through the ventricles to coordinate chamber contraction. An ECG depicts VCS-mediated ventricular depolarization as the QRS interval. Disorders of the VCS may manifest as arrhythmias, and are associated with increased risk of sudden cardiac death and overall mortality. The genetic and developmental mechanisms underlying VCS dysfunction are poorly understood. Genome-wide association studies have identified multiple single nucleotide polymorphisms (SNPs) associated with VCS arrhythmias. A majority of these SNPs occur outside of coding domains, within intergenic or intronic regions. We hypothesize that such pathogenic SNPs may impact VCS development and function by altering the expression of critical genes. Two intergenic SNPs associated with QRS prolongation occur near the bHLH cardiac transcription factor HAND1 . We have identified a left ventricle (LV) enhancer, located between these two SNPs, that is necessary and sufficient for LV cis -regulatory activity. Two evolutionarily conserved GATA transcription factor consensus-binding sites within this enhancer are bound by GATA4 and necessary for cis -regulatory activity. CRISPR-mediated deletion of this enhancer dramatically reduced Hand1 expression solely within the LV. Mice homozygous for this deleted enhancer displayed dysregulated LV gene expression, morphologically abnormal His bundles and left bundle branches, and a VCS phenotype consistent with right bundle branch block. Genome-wide association analyses of human patients with QRS prolongation revealed additional, linked SNPs, one of which overlaps with a critical GATA cis -regulatory element within the LV-specific Hand1 enhancer. This SNP disrupts GATA4 binding. Ongoing studies of mice that genetically mimic these minor SNP variants will assess reduced Hand1 expression and impaired VCS function. We conclude that a LV-specific Hand1 enhancer is necessary for VCS development and a SNP associated with QRS prolongation directly influences GATA4 binding to a critical cis -regulatory element within this enhancer.