Cardiac calsequestrin (CASQ2), and its binding partners junctin and triadin-1 (TRDN), are key regulators of sarcoplasmic reticulum (SR) Ca storage and release. In humans, CASQ2 mutations cause the syndrome of catecholaminergic polymorphic ventricular tachycardia (CPVT) and sudden cardiac death. During the previous funding period, we have generated and studied Casq2 null (Casq2-/-) mice to determine the mechanisms whereby CASQ2 mutations cause electrophysiological instability. We found that despite a lack of Casq2 protein, these mice maintain near normal SR Ca storage, Ca release and contractile function, likely as a result of an expansion of SR volume and drastic reductions in the Casq2 binding proteins triadin-1 and junctin. Casq2-/- mice exhibit the CPVT phenotype, i.e. they develop polymorphic ventricular tachycardia with catecholamine infusion or exercise. Our current concept is that the loss of Ca release refractoriness and premature SR Ca release under conditions of high SR Ca load, results in delayed after-depolarizations, triggered beats and polymorphic ventricular tachycardia. However, if the trigger originates from ventricular myocytes or from specialized cells of the conduction system, the Purkinje cells, is unresolved. Experimental data from a RyR2 mutant mouse model and theoretical considerations favor the Purkinje network. Furthermore, biochemical, electron microscopy and confocal studies show that Casq2 is only found in the terminal cisternae of the junctional SR in close contact with RyR2 Ca release channels. Thus, we hypothesize that the reduced presence of Casq2 near the RyR2 in ventricular myocytes and/or Purkinje cells is a fundamental defect that causes premature SR Ca release and increases arrhythmia susceptibility. This is applicable to inherited syndromes (e.g., Casq2-linked CPVT;
Aims 1 +2) and potentially acquired heart disease due to defects in the trafficking to and/or retention of Casq2 near the RyR2 (Aim 3).
Aim 1. To test the hypothesis that restoration of Casq2 rescues the CPVT phenotype of Casq2-/- mice.
Aim 2. To test the hypothesis that loss of Casq2 in Purkinje cells is both necessary and sufficient to cause CPVT Aim 3. To test the hypothesis that Casq2 is reduced near RyR2 Ca release channels in cardiac muscle surviving after myocardial infarction

Public Health Relevance

The proposed work will study the causes for certain inherited heart diseases associated with arrhythmia (irregular heartbeats) and a high risk for sudden and premature deaths. The studies will also examine the benefit of gene therapy in an animal model, which will provide important information for new therapies for patients with inherited arrhythmia disorders.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL088635-06
Application #
8403766
Study Section
Electrical Signaling, Ion Transport, and Arrhythmias Study Section (ESTA)
Program Officer
Krull, Holly
Project Start
2007-04-15
Project End
2015-12-31
Budget Start
2013-01-01
Budget End
2013-12-31
Support Year
6
Fiscal Year
2013
Total Cost
$371,280
Indirect Cost
$133,280
Name
Vanderbilt University Medical Center
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
004413456
City
Nashville
State
TN
Country
United States
Zip Code
37212
Flores, Daniel J; Duong, ThuyVy; Brandenberger, Luke O et al. (2018) Conditional ablation and conditional rescue models for Casq2 elucidate the role of development and of cell-type specific expression of Casq2 in the CPVT2 phenotype. Hum Mol Genet 27:1533-1544
Ho, Hsiang-Ting; Thambidorai, Senthil; Knollmann, Björn C et al. (2018) Accentuated vagal antagonism paradoxically increases ryanodine receptor calcium leak in long-term exercised Calsequestrin2 knockout mice. Heart Rhythm 15:430-441
Wang, Lili; Kim, Kyungsoo; Parikh, Shan et al. (2018) Hypertrophic cardiomyopathy-linked mutation in troponin T causes myofibrillar disarray and pro-arrhythmic action potential changes in human iPSC cardiomyocytes. J Mol Cell Cardiol 114:320-327
Wang, Lili; Kryshtal, Dmytro O; Kim, Kyungsoo et al. (2017) Myofilament Calcium-Buffering Dependent Action Potential Triangulation in Human-Induced Pluripotent Stem Cell Model of Hypertrophic Cardiomyopathy. J Am Coll Cardiol 70:2600-2602
Parikh, Shan S; Blackwell, Daniel J; Gomez-Hurtado, Nieves et al. (2017) Thyroid and Glucocorticoid Hormones Promote Functional T-Tubule Development in Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes. Circ Res 121:1323-1330
Gomez-Hurtado, Nieves; Blackwell, Daniel Jesse; Knollmann, Bjorn Christian (2017) Modelling human calmodulinopathies with induced pluripotent stem cells: progress and challenges. Cardiovasc Res 113:437-439
Kannankeril, Prince J; Moore, Jeremy P; Cerrone, Marina et al. (2017) Efficacy of Flecainide in the Treatment of Catecholaminergic Polymorphic Ventricular Tachycardia: A Randomized Clinical Trial. JAMA Cardiol 2:759-766
Knollmann, Björn C (2017) Cardiac regulatory mechanisms: new concepts and challenges. J Physiol 595:3683-3684
Yang, Zhenjiang; Prinsen, Joseph K; Bersell, Kevin R et al. (2017) Azithromycin Causes a Novel Proarrhythmic Syndrome. Circ Arrhythm Electrophysiol 10:
Raucci Jr, Frank J; Shoemaker, M Benjamin; Knollmann, Bjorn C (2017) Clinical phenotype of HCN4-related sick sinus syndrome. Heart Rhythm 14:725-726

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