Pharmacologically Targeting the Fibroblast Growth Factor 14 Interaction Site on the Voltage-Gated Na+ Channel 1.6 Enables Isoform-Selective Modulation.

Nolan M Dvorak,Jia Zhou,Cynthia M Tapia,Haiying Chen,Paul A Wadsworth,Aditya K Singh,Fernanda Laezza,Timothy J Baumgartner,Pingyuan Wang

doi:10.3390/ijms222413541

Abstract

Voltage-gated Na+ (Nav) channels are the primary molecular determinant of the action potential. Among the nine isoforms of the Nav channel α subunit that have been described (Nav1.1-Nav1.9), Nav1.1, Nav1.2, and Nav1.6 are the primary isoforms expressed in the central nervous system (CNS). Crucially, these three CNS Nav channel isoforms display differential expression across neuronal cell types and diverge with respect to their subcellular distributions. Considering these differences in terms of their localization, the CNS Nav channel isoforms could represent promising targets for the development of targeted neuromodulators. However, current therapeutics that target Nav channels lack selectivity, which results in deleterious side effects due to modulation of off-target Nav channel isoforms. Among the structural components of the Nav channel α subunit that could be pharmacologically targeted to achieve isoform selectivity, the C-terminal domains (CTD) of Nav channels represent promising candidates on account of displaying appreciable amino acid sequence divergence that enables functionally unique protein–protein interactions (PPIs) with Nav channel auxiliary proteins. In medium spiny neurons (MSNs) of the nucleus accumbens (NAc), a critical brain region of the mesocorticolimbic circuit, the PPI between the CTD of the Nav1.6 channel and its auxiliary protein fibroblast growth factor 14 (FGF14) is central to the generation of electrical outputs, underscoring its potential value as a site for targeted neuromodulation. Focusing on this PPI, we previously developed a peptidomimetic derived from residues of FGF14 that have an interaction site on the CTD of the Nav1.6 channel. In this work, we show that whereas the compound displays dose-dependent effects on the activity of Nav1.6 channels in heterologous cells, the compound does not affect Nav1.1 or Nav1.2 channels at comparable concentrations. In addition, we show that the compound correspondingly modulates the action potential discharge and the transient Na+ of MSNs of the NAc. Overall, these results demonstrate that pharmacologically targeting the FGF14 interaction site on the CTD of the Nav1.6 channel is a strategy to achieve isoform-selective modulation, and, more broadly, that sites on the CTDs of Nav channels interacted with by auxiliary proteins could represent candidates for the development of targeted therapeutics.

Highlights

In excitable cells, voltage-gated Na+ (Nav) channels enable the initiation and propagation of the action potential [1,2]
Despite representing novel pharmacological targets for neuromodulation, such protein–protein interactions (PPIs) have historically proven difficult to appreciably modulate using conventional small molecules [53,54,55,56]. As this challenge largely arises from the large size of PPI interfaces making it difficult to identify druggable motifs that could confer functionally relevant modulation of the intermolecular interaction, efforts to map PPI interfaces using chemical probes, such as those employed in the present investigation, are a necessary pre-requisite for the development of small molecule modulators of PPIs
In our previous work [37], we showed that PW201 modulated fibroblast growth factor 14 (FGF14):Nav1.6 complex assembly, displayed direct binding to the C-terminal domains (CTD) of the Nav1.6 channel, modulated Nav1.6mediated INa in heterologous cells, and docked well with residues that are interacted with by the β8/9 loop of FGF14

Summary

Introduction

Voltage-gated Na+ (Nav) channels enable the initiation and propagation of the action potential [1,2]. In addition to displaying unique electrophysiological profiles, Nav1.1, Nav1.2, and Nav1.6 channels vary with respect to their distributions across neuronal cell types [3,4,5,6,7] and their subcellular distributions [8,9]. Given this heterogeneity of localization, isoform-selective targeting of one of the isoforms could enable targeted neuromodulatory effects. The identification of less highly conserved structural regions that are amenable to pharmacological modulation is a necessary prerequisite to fully actualize the potential of Nav channels as targets for neurologic and neuropsychiatric disorders [11]

Methods

Results

Conclusion