Sudden death resulting from cardiac arrhythmias is the most common consequence of cardiac disease and is oftena result of abnormal impulse formation. Such triggered activity are associated with abnormal Ca2+ release from the sarcoplasmic reticulum (SR) and are a hallmark of catecholaminergic polymorphic ventricular tachycardia (CPVT). CPVT-associated mutations in the ryanodine receptors (RyR2) or calsequestrin (Casq2), the major intra-SR Ca2+ binding protein render the RyR2 leaky and predispose these patients to arrhythmias. Atrial fibrillation is an another common finding in CPVT, indicating that Ca2+ mishandling in CPVT is not isolated to the ventricles. Despite high response of CPVT to Ca2+ channel- and/or beta-blockers, refractory cases often require Na+ channel inhibitor based therapy. However, the relationship between Na+ influx and disturbances in Ca2+ handling immediately preceding arrhythmias in CPVT remains poorly understood. The applicant has developed an experimental system using various murine models of CPVT that integrates information of Ca2+ handling at the cellular level with the electrophysiologic phenotype in tissue. The applicant plans to investigate the hypothesis that subpopulation of Na+ channels (neuronal Na+ channels; nNav) contribute to arrhythmogenic aberrant Ca2+ release through the microdomain Na+/Ca2+ signaling. Specifically the proposal will address the following aims during the mentored phase (K99): 1) Elucidate the molecular and subcellular consequences of subdomain-specific Na+/Ca2+ signaling on aberrant Ca2+ release in the genesis of Ca2+ -dependent atrial and ventricular arrhythmias. Here we will test the hypothesis that subdomain-specific Na+/Ca2+ signaling contributes to arrhythmogenic aberrant Ca2+ release while attempting to identify the molecular determinants of local Na+/Ca2+ subdomain signaling. 2) Define the role of Na+/Ca2+ signaling in tissue wide aberrant Ca2+ release synchronization. These translational studies will test the hypothesis that subdomain-specific Na+/Ca2+ signaling facilitates myocardial synchronization of aberrant Ca2+ release and promotes subsequent ectopic activity in intact ventricular tissue. 3) Validate the applicability of Na+/Ca2+ signaling to in vivo settings. During the independent phase (R00) the proposal will: 1) Investigate the role of subdomain-specific Na+/Ca2+ signaling on aberrant Ca2+ release in the genesis of atrial arrhythmias. 2) Examine the regional heterogeneities of the subdomain-specific Na+/Ca2+ signaling in atrial aberrant Ca2+ release synchronization. 3) Validate the therapeutic potential of perturbation of Na+/Ca2+ signaling in settings of atrial arrhythmias and translate the applicability to animal models of acquired Ca2+-mediated arrhythmias. The mechanistic and pharmacological insights gained on the cellular as well as on tissue levels will offer a mechanism-based therapeutic approach that will be tested in vivo. Furthermore, these studies will determine whether such arrhythmogenic mechanism(s) is/are applicable to a clinically-relevant model of Ca2+-mediated arrhythmias. A long term goal of this study is to better understand the cellular and molecular mechanisms of Ca2+-mediated arrhythmogenesis.

Public Health Relevance

Aberrant diastolic Ca2+ release is involved in the pathophysiology of catecholaminergic polymorphic ventricular tachycardia (CPVT); however, the mechanism(s) underlying aberrant Ca2+ release genesis in cell and its synchronization in tissue is elusive. We preliminarily identify a distinct microdomain, where a specific subpopulation of Na+ channels are localized near Ca2+ cycling proteins, and serve as the functional unit underlying arrhythmogenic aberrant Ca2+ release. Our preliminary findings suggest that the unique interplay between Na+ and Ca2+ handling is key to the process and disrupting it via selective inhibition of neuronal Na+ channels effectively suppressed arrhythmias in myocytes, tissue as well as in CPVT mice. Thus our study may reveal a novel arrhythmogenic mechanism, its structural underpinnings and identifie a novel mechanism-based antiarrhythmic therapy.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Transition Award (R00)
Project #
5R00HL127299-05
Application #
9764456
Study Section
Special Emphasis Panel (NSS)
Program Officer
Balijepalli, Ravi C
Project Start
2017-09-01
Project End
2020-08-31
Budget Start
2019-09-01
Budget End
2020-08-31
Support Year
5
Fiscal Year
2019
Total Cost
Indirect Cost
Name
Ohio State University
Department
Type
DUNS #
832127323
City
Columbus
State
OH
Country
United States
Zip Code
43210
Veeraraghavan, Rengasayee; Radwa?ski, Przemys?aw B (2018) Sodium channel clusters: harmonizing the cardiac conduction orchestra. J Physiol 596:549-550
Koleske, Megan; Bonilla, Ingrid; Thomas, Justin et al. (2018) Tetrodotoxin-sensitive Navs contribute to early and delayed afterdepolarizations in long QT arrhythmia models. J Gen Physiol 150:991-1002
Radwa?ski, Przemys?aw B; Johnson, Christopher N; Györke, Sándor et al. (2018) Cardiac Arrhythmias as Manifestations of Nanopathies: An Emerging View. Front Physiol 9:1228
Veeraraghavan, Rengasayee; Györke, Sándor; Radwa?ski, Przemys?aw B (2017) Neuronal sodium channels: emerging components of the nano-machinery of cardiac calcium cycling. J Physiol 595:3823-3834