Voltage-Gated Sodium Channel Nav1.6 S-Palmitoylation Regulates Channel Functions and Neuronal Excitability

Abstract

The voltage-gated sodium channels (VGSCs) are critical determinants of neuronal excitability. They set the threshold for action potential generation. The VGSC isoform Nav1.6 participates in various physiological processes and contributes to distinct pathological conditions, but how Nav1.6 function is differentially regulated in different cell types and subcellular locations is not clearly understood. Some VGSC isoforms are subject to S-palmitoylation and exhibit altered functional properties in different S-palmitoylation states. This dissertation investigates the role of S-palmitoylation in Nav1.6 regulation and explores the consequences of S-palmitoylation in modulating neuronal excitability in physiological and pathological conditions. The aims of this dissertation were to 1) provide biochemical and electrophysiological evidence of Nav1.6 regulation by S-palmitoylation and identify specific S-palmitoylation sites in Nav1.6 that are important for excitability modulation, 2) determine the biophysical consequences of epilepsy-associated mutations in Nav1.6 and employ computational models for excitability prediction and 3) test the modulating effects of S-palmitoylation on aberrant Nav1.6 activity incurred by epilepsy mutations. To address these aims, an acyl-biotin exchange assay was used for Spalmitoylation detection and whole-cell electrophysiology was used for channel characterization and excitability examination. The results demonstrate that 1) Nav1.6 is biochemically modified and functionally regulated by S-palmitoylation in an isoform- and site-specific manner and altered S-palmitoylation status of the channel results in substantial changes of neuronal excitability, 2) epilepsy associated Nav1.6 mutations affect different aspects of channel function, but may all converge to gain-of-function alterations with enhanced resurgent currents and increased neuronal excitability and 3) S-palmitoylation can target specific Nav1.6 properties and could possibly be used to rescue abnormal channel function in diseased conditions. Overall, this dissertation reveals S-palmitoylation as a new mechanism for Nav1.6 regulation. This knowledge is critical for understanding the potential role of S-palmitoylation in isoform-specific regulation for VGSCs and providing potential targets for the modulation of excitability disorders.