Evolutionarily, voltage-gated sodium channels are fundamental to the organization of most complex excitable tissues where they are crucial to ensure the sharp initiation dynamics and proper propagation of the action potential and are at the center of cellular excitability. Hence, mutations in voltage-gated sodium channel genes have been linked to a whole host of diseases including cardiac arrhythmias. Modification in Na+ current (INa) is known to contribute to both cardiac arrhythmias from acquired heart diseases and inherited cardiac arrhythmias. Since the original cloning of the genes encoding for voltage-gated sodium channels and the recording of its function by patch-clamping over 30 years ago, the ?-subunit of the sodium channel was thought to be a monomer. However, during the previous funding period our studies of mutations found in SCN5A linked to several different arrhythmic syndromes led us to question the traditional idea of the sodium channel forming a monomer. In fact, we and others have shown that several Brugada Syndrome (BrS) mutations display dominant- negative effects (DN-effect), which could only be attributed to interaction between ?-subunits within multimeric complexes. Similarly, we have shown that the defects of several BrS or LQT3 SCN5A mutations could be rescued by different SCN5A polymorphisms expressed on a separate construct, again supporting the idea of an ????subunit interaction. Finally, we also reported the presence of atypical BrS mutations that do not present defects when expressed alone but lead to reduced current amplitudes when co-expressed with WT, again supporting an interaction of the ??subunits. Therefore, multiple lines of evidence challenged the conventional wisdom that sodium channels exist in complexes containing a single ??subunit. We thus sought to investigate the stoichiometry of sodium channel ??subunits. We demonstrated using different experimental approaches that sodium channels form functional dimers. We also identified the region modulating the dimerization and found that this physical dimerization results in coupled gating of the sodium channels and involves 14-3-3. Our findings shifted conventional paradigms in regards to sodium channel assembly, structure, and function. Our overall hypothesis for this renewal is that the physical dimerization of sodium channels leads to dimerization-dependent channel activity (i.e. channel gating and trafficking) with implication for normal physiology and for cardiac pathologies linked to dysregulation of the sodium current.
In aim 1 we will study the biophysical coupling and determine if this is dynamically modulated.
In aim 2 we will explore trafficking of the sodium channel and the involvement of 14-3-3. Finally in aim 3 we will determine the role of posttranslational modification in the dimerization of sodium channels. Understanding of the mechanisms involved in channel dimerization, trafficking and functional biophysical coupling could open the door to new approaches and targets to treat and/or prevent sodium channelopathies and dysregulation of INa in heart failure.

Public Health Relevance

Voltage-gated sodium channels are fundamental to cardiac excitability. Hence, modifications in sodium currents are known to contribute to cardiac arrhythmias. Since the original cloning of the genes encoding for voltage- gated sodium channels, the ?-subunit of the sodium channel was thought to be a monomer. However, during the previous funding period we demonstrated that sodium channels form functional dimers. In this renewal we will explore how the physical dimerization of sodium channels leads to dimerization-dependent channel activity with implication for normal physiology and for cardiac pathologies.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL094450-07
Application #
10013280
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Balijepalli, Ravi C
Project Start
2010-03-15
Project End
2023-07-31
Budget Start
2020-08-01
Budget End
2021-07-31
Support Year
7
Fiscal Year
2020
Total Cost
Indirect Cost
Name
Ohio State University
Department
Physiology
Type
Schools of Medicine
DUNS #
832127323
City
Columbus
State
OH
Country
United States
Zip Code
43210
Chatterjee, Soumili; Vyas, Rajan; Chalamalasetti, Sreevatsa V et al. (2018) The voltage-gated sodium channel pore exhibits conformational flexibility during slow inactivation. J Gen Physiol 150:1333-1347
Nassal, Michelle M J; Wan, Xiaoping; Dale, Zack et al. (2017) Mild hypothermia preserves myocardial conduction during ischemia by maintaining gap junction intracellular communication and Na+channel function. Am J Physiol Heart Circ Physiol 312:H886-H895
Clatot, Jérôme; Hoshi, Malcolm; Wan, Xiaoping et al. (2017) Voltage-gated sodium channels assemble and gate as dimers. Nat Commun 8:2077
Sattayaprasert, Prasongchai; Nassal, Drew M; Wan, Xiaoping et al. (2016) Mesenchymal stem cells suppress cardiac alternans by activation of PI3K mediated nitroso-redox pathway. J Mol Cell Cardiol 98:138-45
Hoshi, Malcolm; Liu, Haiyan; Kaufman, Elizabeth S et al. (2015) Polygenic Case of Long QT Syndrome Confirmed through Functional Characterization Informs the Interpretation of Genetic Screening Results. HeartRhythm Case Rep 1:201-205
Plummer, Bradley N; Liu, Haiyan; Wan, Xiaoping et al. (2015) Targeted antioxidant treatment decreases cardiac alternans associated with chronic myocardial infarction. Circ Arrhythm Electrophysiol 8:165-73
Hoshi, Malcolm; Du, Xi X; Shinlapawittayatorn, Krekwit et al. (2014) Brugada syndrome disease phenotype explained in apparently benign sodium channel mutations. Circ Cardiovasc Genet 7:123-31
Ziyadeh-Isleem, Azza; Clatot, Jérôme; Duchatelet, Sabine et al. (2014) A truncating SCN5A mutation combined with genetic variability causes sick sinus syndrome and early atrial fibrillation. Heart Rhythm 11:1015-1023
Jehle, J; Ficker, E; Wan, X et al. (2013) Mechanisms of zolpidem-induced long QT syndrome: acute inhibition of recombinant hERG K(+) channels and action potential prolongation in human cardiomyocytes derived from induced pluripotent stem cells. Br J Pharmacol 168:1215-29
Clatot, Jerome; Ziyadeh-Isleem, Azza; Maugenre, Svetlana et al. (2012) Dominant-negative effect of SCN5A N-terminal mutations through the interaction of Na(v)1.5 ýý-subunits. Cardiovasc Res 96:53-63

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