Biology subjects

Misra, S. N.

Publications and source records attributed to Misra, S. N..

3 recordsLinked to original sources

bioRxiv2021

Cellular and behavioral effects of altered NaV1.2 sodium channel ion permeability in Scn2aK1422E mice

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 StatementThe 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.

neuroscience↗

bioRxiv2019

Epilepsy and neurobehavioral abnormalities in mice with a KCNB1 pathogenic variant that alters conducting and non-conducting functions of KV2.1

Developmental and epileptic encephalopathies (DEE) are a group of severe epilepsies that usually present with intractable seizures, developmental delay and are at a higher risk for premature mortality. Numerous genes have been identified as a monogenic cause of DEE, including KCNB1. The voltage-gated potassium channel KV2.1, encoded by KCNB1, is primarily responsible for delayed rectifier potassium currents that are important regulators of excitability in electrically excitable cells, including neurons and cardiomyocytes. The de novo pathogenic variant KCNB1-p.G379R was identified in an infant with epileptic spasms, atonic, focal and tonic-clonic seizures that were refractory to treatment with standard antiepileptic drugs. Previous work demonstrated deficits in potassium conductance, but did not assess non-conducting functions. To determine if the G379R variant affected clustering at endoplasmic reticulum-plasma membrane junctions KV2.1-G379R was expressed in HEK293T cells. KV2.1-G379R expression did not induce formation of endoplasmic reticulum-plasma membrane junctions, and co-expression of KV2.1-G379R with KV2.1-WT lowered induction of these structures relative to KV2.1-WT alone, suggesting a dominant negative effect. To model this variant in vivo, we introduced Kcnb1G379R into mice using CRISPR/Cas9 genome editing. We characterized neurological and neurobehavioral phenotypes of Kcnb1G379R/+ (Kcnb1R/+) and Kcnb1G379R/G379R (Kcnb1R/R) mice, and screened for cardiac abnormalities. Immunohistochemistry studies on brains from Kcnb1+/+ (WT), Kcnb1R/+ and Kcnb1R/R mice revealed genotype-dependent differences in the levels and subcellular localization of KV2.1, with reduced plasma membrane expression of the KV2.1-G379R protein, consistent with in vitro data. Kcnb1R/+ and Kcnb1R/R mice displayed profound hyperactivity, repetitive behaviors, impulsivity and reduced anxiety. In addition, both Kcnb1R/+ and Kcnb1R/R mice exhibited abnormal interictal EEG abnormalities, including isolated spike and slow waves. Spontaneous seizure events were observed in Kcnb1R/R mice during exposure to novel environments and/or handling, while both Kcnb1R/+ and Kcnb1R/R mutants were more susceptible to induced seizures. Kcnb1R/+ and Kcnb1R/R mice exhibited prolonged rate-corrected QT interval on surface ECG recording. Overall, the Kcnb1G379R mice recapitulate many features observed in individuals with DEE due to pathogenic variants in KCNB1. This new mouse model of KCNB1 associated DEE will be valuable for improving the understanding of the underlying pathophysiology and will provide a valuable tool for the development of therapies to treat this pharmacoresistant DEE.

neuroscience↗

bioRxiv2019

High throughput Characterization of KCNB1 variants Associated with Developmental and Epileptic Encephalopathy

Pathogenic variants in KCNB1, encoding the voltage-gated potassium channel Kv2.1, are associated with developmental and epileptic encephalopathies (DEE). Previous functional studies on a limited number of KCNB1 variants indicated a range of molecular mechanisms by which variants affect channel function, including loss of voltage sensitivity, loss of ion selectivity, and reduced cell-surface expression. We evaluated a series of 17 KCNB1 variants associated with DEE or neurodevelopmental disorder (NDD) to rapidly ascertain channel dysfunction using high-throughput functional assays. Specifically, we investigated the biophysical properties and cell-surface expression of variant Kv2.1 channels expressed in heterologous cells using high-throughput automated electrophysiology and immunocytochemistry-flow cytometry. Pathogenic variants exhibited diverse functional defects, including altered current density and shifts in the voltage-dependence of activation and/or inactivation, as homotetramers or when co-expressed with wild-type Kv2.1. Quantification of protein expression also identified variants with reduced total Kv2.1 expression or deficient cell-surface expression.\n\nOur study establishes a platform for rapid screening of functional defects of KCNB1 variants associated with DEE and other NDDs, which will aid in establishing KCNB1 variant pathogenicity and may enable discovery of targeted strategies for therapeutic intervention based on molecular phenotype.

genetics↗