Drug-Sensitized Zebrafish Screen Identifies Multiple Genes, Including GINS3 , as Regulators of Myocardial Repolarization

Abstract

Background-Cardiac repolarization, the process by which cardiomyocytes return to their resting potential after each beat, is a highly regulated process that is critical for heart rhythm stability. Perturbations of cardiac repolarization increase the risk for life-threatening arrhythmias and sudden cardiac death. Although genetic studies of familial long-QT syndromes have uncovered several key genes in cardiac repolarization, the major heritable contribution to this trait remains unexplained. Identification of additional genes may lead to a better understanding of the underlying biology, aid in identification of patients at risk for sudden death, and potentially enable new treatments for susceptible individuals. Methods and Results-We extended and refined a zebrafish model of cardiac repolarization by using fluorescent reporters of transmembrane potential. We then conducted a drug-sensitized genetic screen in zebrafish, identifying 15 genes, including GINS3, that affect cardiac repolarization. Testing these genes for human relevance in 2 concurrently completed genome-wide association studies revealed that the human GINS3 ortholog is located in the 16q21 locus, which is strongly associated with QT interval. Conclusions-This sensitized zebrafish screen identified 15 novel myocardial repolarization genes. Among these genes isGINS3, the human ortholog of which is a major locus in 2 concurrent human genome-wide association studies of QT interval. These results reveal a novel network of genes that regulate cardiac repolarization. (Circulation. 2009;120:553-559.) Key Words: electrophysiology Ⅲ genes Ⅲ ion channels Ⅲ myocardial repolarization T he ECG QT interval duration is a predictor of mortality in familial long QT (LQT) syndromes 1 and in a wide range of acquired heart diseases. 2,3 QT prolongation by drugs can lead to fatal arrhythmias and has been a major cause of the withdrawal of medications from the market in the last decade. 4 Virtually all drugs that cause this adverse effect inhibit the rapid component of the delayed rectifier current, I Kr . 5 Clinical Perspective on p 559The QT interval, a summation of individual cellular action potential (AP) durations (APDs), is known to depend on the function of multiple ion channels and their accessory proteins. Much of our current understanding of cardiac repolarization comes from study of LQT syndromes. 6,7 These disorders are marked by abnormal cardiac repolarization and a high incidence of sudden death. 8 Although the majority of LQT disorders result from mutation of ion channel genes, there is increasing recognition of the role of non-ion channel mechanisms such as ankyrin B 9 and the caveolar scaffolding protein caveolin 3. 10 The zebrafish has been shown to recapitulate much of the complexity of higher vertebrates 11 yet retains the potential for exploring integrative physiology on a genomic scale. 12,13 Here, we studied cardiac repolarization as a complex trait using a functional screen to identify novel genetic determinants. Received September 11, 2008; accept...

The regenerative capacity of zebrafish reverses cardiac failure caused by genetic cardiomyocyte depletion

“…The wavefront fractionation might also represent intercalation of noncoupled epicardial cells into the myocardium with resultant conduction block and delayed subepicardial impulse propagation. In addition to the conduction findings, the prolongation of action potential duration and diminution of peak action potential upstroke velocities recapitulate the electrical phenotypes of less differentiated cardiomyocytes (Milan et al, 2009;Panakova et al, 2010). Such changes in action potential upstroke velocity probably represent an increased dependence of depolarization on calcium channel conductance and a reduced role for sodium channel conductance (Chopra et al, 2010;Milan et al, 2009;Panakova et al, 2010).…”

Drug-Induced Long QT Syndrome

“…The genome-wide association scan approach to normal QT has also implicated common variants in cLQTS disease genes (SCN5A, KCNJ2, KCNQ1, and KCNH2), other genes thought to play a role in cardiac electrophysiology (e.g., phospholamban, a regulator of intracellular calcium), and entirely new loci. One of 776 these includes GINS3, which has also been implicated as a modulator of heart-rate response to dofetilide challenge in zebrafish (Milan et al, 2009).…”

Congenital heart disease protein 5 associates with CASZ1 to maintain myocardial tissue integrity

“…Recent work in mice investigating congenital heart disease in individuals with DS exclude Chd5 from the minimal region that induces congenital heart disease upon duplication (Liu et al, 2011a). By contrast, a recent screen in zebrafish identified CHD5 as a regulator of myocardial repolarization (Milan et al, 2009), and subsequent work in the medaka fish demonstrated that CHD5-depleted hearts had general looping and chamber defects (Murata et al, 2009). Our results demonstrate for the first time a mechanism by which CHD5 functions during cardiac development via interaction with a cardiac transcription factor and demonstrate cardiac defects in CHD5-depleted embryos.…”

“…CHD5, initially identified in a screen for genes within a restricted region of chromosome 21 associated with heart disease in individuals with DS, was found to be expressed in fetal hearts and shown to localize predominately to the nuclei of cells of cardiac origin (Egeo et al, 1998). CHD5 was also identified in a drug-sensitized screen in zebrafish as a regulator of myocardial repolarization (Milan et al, 2009) and depletion of CHD5 in medaka fish has been reported to be associated with general cardiac defects of unknown etiology (Murata et al, 2009). In addition to these findings, CHD5 has also been reported to be localized to the membrane of the endoplasmic reticulum (ER), where it is proposed to function as a receptor to transport charged proteins across the ER membrane (Ando and Suzuki, 2005;Vilardi et al, 2011).…”