RT Journal Article
SR Electronic
T1 Cellular and behavioral effects of altered Na<sub>V</sub>1.2 sodium channel ion permeability in <em>Scn2a<sup>K1422E</sup></em> mice
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 2021.07.19.452930
DO 10.1101/2021.07.19.452930
A1 Dennis M. Echevarria-Cooper
A1 Nicole A. Hawkins
A1 Sunita N. Misra
A1 Alexandra Huffman
A1 Tyler Thaxton
A1 Christopher H. Thompson
A1 Roy Ben-Shalom
A1 Andrew D. Nelson
A1 Anna M. Lipkin
A1 Alfred L. George, Jr.
A1 Kevin J. Bender
A1 Jennifer A. Kearney
YR 2021
UL http://biorxiv.org/content/early/2021/07/19/2021.07.19.452930.abstract
AB Genetic variants in SCN2A, encoding the NaV1.2 voltage-gated sodium channel, are associated with a range of neurodevelopmental disorders with overlapping phenotypes. Some variants fit into a framework wherein gain-of-function missense variants that increase neuronal excitability lead to infantile epileptic encephalopathy, while loss-of-function variants that reduce neuronal excitability lead to developmental delay and/or autism spectrum disorder with or without co- morbid seizures. One unique case less easily classified using this binary paradigm is the de novo missense variant SCN2A p.K1422E, associated with infant-onset developmental delay, infantile spasms, and features of autism spectrum disorder. Prior structure-function studies demonstrated that K1422E substitution alters ion selectivity of NaV1.2, conferring Ca2+ permeability, lowering overall conductance, and conferring resistance to tetrodotoxin (TTX). Based on heterologous expression of K1422E, we developed a compartmental neuron model that predicted mixed effects on channel function and neuronal activity. We also generated Scn2aK1422E mice and characterized effects on neurons and neurological/neurobehavioral phenotypes. Dissociated neurons from heterozygous Scn2aK1422E/+ mice exhibited a novel TTX-resistant current with a reversal potential consistent with mixed ion permeation. Cortical slice recordings from Scn2aK1442E/+ tissue demonstrated impaired action potential initiation and larger Ca2+ transients at the axon initial segment during the rising phase of the action potential, suggesting mixed effects on channel function. Scn2aK1422E/+ mice exhibited rare spontaneous seizures, interictal EEG abnormalities, altered response to induced seizures, reduced anxiety-like behavior and alterations in olfactory-guided social behavior. Overall, Scn2aK1422E/+ mice present with phenotypes similar yet distinct from Scn2a knockout models, consistent with mixed effects of K1422E on NaV1.2 channel function.Significance Statement The early-onset epilepsy variant SCN2A-p.K1422E displays unique biophysical properties in vitro. To model the impact of this rare variant, we generated Scn2aK1422E mice. Neurons from heterozygous Scn2aK1422E/+ mice showed functional deficits similar to the loss-of-function effects observed in the Scn2a haploinsufficiency model, as well as gain-of-function effects specific to the K1422E variant. There is also some overlap in neurobehavioral phenotypes between Scn2aK1422E/+ and Scn2a haploinsufficient mice. However, Scn2aK1422E/+ mice exhibited unique epilepsy-related phenotypes, including epileptiform events and seizures. Scn2aK1422E/+ mice serve as a useful platform to investigate phenotypic complexity of SCN2A-associated disorders.Competing Interest StatementALG receives grant support from Tevard Biosciences, Inc. and is a paid consultant for Praxis Precision Medicines, Inc. JAK serves on the scientific advisory board of the FamilieSCN2A foundation and receives grant support from Praxis Precision Medicines, Inc. The remaining authors declare no competing interests.