Cardiac repolarization, assessed in myocytes as action potential (AP) duration and on the electrocardiogram as the QT interval, requires the tightly regulated function of multiple ion channels and their accessory proteins. In the last decade, perturbations of repolarization have been directly implicated in the genesis of drug-induced arrhythmias and sudden cardiac death (SCD). While QT interval is a predictor of arrhythmias and sudden death, it is clear that a prolonged QT interval by itself is insufficient to cause such catastrophic events;additional environmental insults are usually required. There are several identified triggers including, myocardial ischemia, electrolyte imbalances (especially hypokalemia), and elevated catecholamine states, but perhaps the greatest environmental challenge to cardiac repolarization comes in the form of prescribed drugs. In the past decade, the single most common cause of the withdrawal or restriction of drugs that have already been marketed has been undesired QT prolongation. While the QT interval is a heritable quantitative trait, the genes that influence the QT interval as well as the response to QT prolonging drugs remain unknown. Common variants have long been thought to play a significant role in this complex trait and there are now several novel loci associated with QT interval through recent genome-wide association studies. Along with the power to identify novel loci, genome wide association studies do have limitations: they cannot distinguish which gene at a given locus is causal, nor do they reveal mechanistic insights. As we begin to unravel the discoveries of GWA studies, the first step will be to identify the functional gene(s) at each associated locus. We propose the use of a tractable zebrafish model that faithfully recapitulates key features of human myocardial repolarization. Using an approach that allows translation of human genetic discoveries into a tractable relevant model, we will test the hypothesis that gene knockdown in zebrafish will confirm candidate genes for each of five novel human repolarization loci. Once novel repolarization genes are identified, they will be tested for gene x drug interactions in our model. We propose the following specific aims:
Aim 1 : Validate candidate myocardial repolarization genes from five recently discovered novel genetic loci in a zebrafish model of cardiac repolarization. This will involve targeted knockdown of genes from these five loci and determination of effects on myocardial repolarization using optical voltage mapping.
Aim 2 : Quantitatively identify gene x drug interactions in myocardial repolarization. The most clinically important environmental exposures to myocardial repolarization are QT prolonging drugs. All 25 candidate repolarization genes will be tested for interactions in gene x drug experiments with QT prolonging drugs.

Public Health Relevance

The QT interval on the electrocardiogram is a predictor of cardiac rhythm problems and sudden death, but the genes that govern this process remain largely unknown. Recently, large population-based studies have narrowed the search for these genes, identifying five genetic neighborhoods where these genes lie. We propose to use a zebrafish model to systematically knockdown the genes in these neighborhoods and measure the impact on the equivalent of the QT interval;we hope to conclusively identify the genes that modify the QT interval and achieve a better understanding of heart rhythm problems and sudden death.

Agency
National Institute of Health (NIH)
Institute
National Institute on Drug Abuse (NIDA)
Type
Exploratory/Developmental Grants (R21)
Project #
1R21DA026982-01
Application #
7708608
Study Section
Special Emphasis Panel (ZDA1-GXM-A (03))
Program Officer
Wideroff, Louise
Project Start
2009-09-30
Project End
2011-08-31
Budget Start
2009-09-30
Budget End
2010-08-31
Support Year
1
Fiscal Year
2009
Total Cost
$449,829
Indirect Cost
Name
Massachusetts General Hospital
Department
Type
DUNS #
073130411
City
Boston
State
MA
Country
United States
Zip Code
02199
Mahida, Saagar; Mills, Robert W; Tucker, Nathan R et al. (2014) Overexpression of KCNN3 results in sudden cardiac death. Cardiovasc Res 101:326-34
Kokel, David; Cheung, Chung Yan J; Mills, Robert et al. (2013) Photochemical activation of TRPA1 channels in neurons and animals. Nat Chem Biol 9:257-63
den Hoed, Marcel (see original citation for additional authors) (2013) Identification of heart rate-associated loci and their effects on cardiac conduction and rhythm disorders. Nat Genet 45:621-31
Wu, Sean M; Milan, David J (2012) Reprogramming the beat: kicking it up a notch. Circulation 126:1009-11
Chen, Jenny X; Krane, Markus; Deutsch, Marcus-Andre et al. (2012) Inefficient reprogramming of fibroblasts into cardiomyocytes using Gata4, Mef2c, and Tbx5. Circ Res 111:50-5
Mahida, Saagar; Lubitz, Steven A; Rienstra, Michiel et al. (2011) Monogenic atrial fibrillation as pathophysiological paradigms. Cardiovasc Res 89:692-700
Peal, David S; Mills, Robert W; Lynch, Stacey N et al. (2011) Novel chemical suppressors of long QT syndrome identified by an in vivo functional screen. Circulation 123:23-30
Ellinor, Patrick T; Lunetta, Kathryn L; Glazer, Nicole L et al. (2010) Common variants in KCNN3 are associated with lone atrial fibrillation. Nat Genet 42:240-4
Milan, David J; Melman, Yonathan F; Ellinor, Patrick T (2010) Rare ion channel polymorphisms: separating signal from noise. Heart Rhythm 7:920-1
Milan, David J; Lubitz, Steven A; Kääb, Stefan et al. (2010) Genome-wide association studies in cardiac electrophysiology: recent discoveries and implications for clinical practice. Heart Rhythm 7:1141-8