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Solé L, Wagnon JL, Tamkun MM. Functional analysis of three Na v1.6 mutations causing early infantile epileptic encephalopathy. Biochim Biophys Acta Mol Basis Dis 2020; 1866:165959. [PMID: 32916281 DOI: 10.1016/j.bbadis.2020.165959] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Revised: 08/21/2020] [Accepted: 09/03/2020] [Indexed: 11/24/2022]
Abstract
The voltage-gated sodium channel Nav1.6 is associated with more than 300 cases of epileptic encephalopathy. Nav1.6 epilepsy-causing mutations are spread over the entire channel's structure and only 10% of mutations have been characterized at the molecular level, with most of them being gain of function mutations. In this study, we analyzed three previously uncharacterized Nav1.6 epilepsy-causing mutations: G214D, N215D and V216D, located within a mutation hot-spot at the S3-S4 extracellular loop of Domain1. Voltage clamp experiments showed a 6-16 mV hyperpolarizing shift in the activation mid-point for all three mutants. V216D presented the largest shift along with decreased current amplitude, enhanced inactivation and a lack of persistent current. Recordings at hyperpolarized potentials indicated that all three mutants presented gating pore currents. Furthermore, trafficking experiments performed in cultured hippocampal neurons demonstrated that the mutants trafficked properly to the cell surface, with no significant differences regarding surface expression within the axon initial segment or soma compared to wild-type. These trafficking data suggest that the disease-causing consequences are due to only changes in the biophysical properties of the channel. Interestingly, the patient carrying the V216D mutation, which is the mutant with the greatest electrophysiological changes as compared to wild-type, exhibited the most severe phenotype. These results emphasize that these mutations will mandate unique treatment approaches, for normal sodium channel blockers may not work given that the studied mutations present gating pore currents. This study emphasizes the importance of molecular characterization of disease-causing mutations in order to improve the pharmacological treatment of patients.
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Affiliation(s)
- Laura Solé
- Molecular, Cellular and Integrative Neurosciences Graduate Program, Colorado State University, Fort Collins, CO 80523, USA; Department of Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA
| | - Jacy L Wagnon
- Department of Neuroscience, Wexner Medical Center, The Ohio State University, Columbus, OH 43210, USA
| | - Michael M Tamkun
- Molecular, Cellular and Integrative Neurosciences Graduate Program, Colorado State University, Fort Collins, CO 80523, USA; Department of Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA; Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523, USA.
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2
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Hossain MM, Weig B, Reuhl K, Gearing M, Wu LJ, Richardson JR. The anti-parkinsonian drug zonisamide reduces neuroinflammation: Role of microglial Na v 1.6. Exp Neurol 2018; 308:111-9. [PMID: 30017881 DOI: 10.1016/j.expneurol.2018.07.005] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2018] [Revised: 06/22/2018] [Accepted: 07/11/2018] [Indexed: 11/23/2022]
Abstract
Parkinson's disease (PD), the second most common age-related progressive neurodegenerative disorder, is characterized by dopamine depletion and the loss of dopaminergic (DA) neurons with accompanying neuroinflammation. Zonisamide is an-anti-convulsant drug that has recently been shown to improve clinical symptoms of PD through its inhibition of monoamine oxidase B (MAO-B). However, zonisamide has additional targets, including voltage-gated sodium channels (Nav), which may contribute to its reported neuroprotective role in preclinical models of PD. Here, we report that Nav1.6 is highly expressed in microglia of post-mortem PD brain and of mice treated with the parkinsonism-inducing neurotoxin MPTP. Administration of zonisamide (20 mg/kg, i.p. every 4 h × 3) following a single injection of MPTP (12.5 mg/kg, s.c.) reduced microglial Nav 1.6 and microglial activation in the striatum, as indicated by Iba-1 staining and mRNA expression of F4/80. MPTP increased the levels of the pro-inflammatory cytokine TNF-α and gp91phox, and this was significantly reduced by zonisamide. Together, these findings suggest that zonisamide may reduce neuroinflammation through the down-regulation of microglial Nav 1.6. Thus, in addition to its effects on parkinsonian symptoms through inhibition of MAO-B, zonisamide may have disease modifying potential through the inhibition of Nav 1.6 and neuroinflammation.
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Barker BS, Nigam A, Ottolini M, Gaykema RP, Hargus NJ, Patel MK. Pro-excitatory alterations in sodium channel activity facilitate subiculum neuron hyperexcitability in temporal lobe epilepsy. Neurobiol Dis 2017; 108:183-94. [PMID: 28860087 DOI: 10.1016/j.nbd.2017.08.018] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2017] [Revised: 08/07/2017] [Accepted: 08/26/2017] [Indexed: 11/23/2022] Open
Abstract
Temporal lobe epilepsy (TLE) is a common form of adult epilepsy involving the limbic structures of the temporal lobe. Subiculum neurons act to provide a major output from the hippocampus and consist of a large population of endogenously bursting excitatory neurons. In TLE, subiculum neurons are largely spared, become hyperexcitable and show spontaneous epileptiform activity. The basis for this hyperexcitability is unclear, but is likely to involve alterations in the expression levels and function of various ion channels. In this study, we sought to determine the importance of sodium channel currents in facilitating neuronal hyperexcitability of subiculum neurons in the continuous hippocampal stimulation (CHS) rat model of TLE. Subiculum neurons from TLE rats were hyperexcitable, firing a higher frequency of action potentials after somatic current injection and action potential (AP) bursts after synaptic stimulation. Voltage clamp recordings revealed increases in resurgent (INaR) and persistent (INaP) sodium channel currents and pro-excitatory shifts in sodium channel activation and inactivation parameters that would facilitate increases in AP generation. Attenuation of INaR and INaP currents with 4,9-anhydro-tetrodotoxin (4,9-ah TTX; 100nM), a toxin with increased potency against Nav1.6 channels, suppressed neuronal firing frequency and inhibited AP bursting induced by synaptic stimulation in TLE neurons. These findings support an important role of sodium channels, particularly Nav1.6, in facilitating subiculum neuron hyperexcitability in TLE and provide further support for the importance of INaR and INaP currents in establishing epileptiform activity of subiculum neurons.
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Jones JM, Dionne L, Dell'Orco J, Parent R, Krueger JN, Cheng X, Dib-Hajj SD, Bunton-Stasyshyn RK, Sharkey LM, Dowling JJ, Murphy GG, Shakkottai VG, Shrager P, Meisler MH. Single amino acid deletion in transmembrane segment D4S6 of sodium channel Scn8a (Nav1.6) in a mouse mutant with a chronic movement disorder. Neurobiol Dis 2016; 89:36-45. [PMID: 26807988 PMCID: PMC4991781 DOI: 10.1016/j.nbd.2016.01.018] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2015] [Revised: 01/06/2016] [Accepted: 01/20/2016] [Indexed: 02/08/2023] Open
Abstract
Mutations of the neuronal sodium channel gene SCN8A are associated with lethal movement disorders in the mouse and with human epileptic encephalopathy. We describe a spontaneous mouse mutation, Scn8a(9J), that is associated with a chronic movement disorder with early onset tremor and adult onset dystonia. Scn8a(9J) homozygotes have a shortened lifespan, with only 50% of mutants surviving beyond 6 months of age. The 3 bp in-frame deletion removes 1 of the 3 adjacent isoleucine residues in transmembrane segment DIVS6 of Nav1.6 (p.Ile1750del). The altered helical orientation of the transmembrane segment displaces pore-lining amino acids with important roles in channel activation and inactivation. The predicted impact on channel activity was confirmed by analysis of cerebellar Purkinje neurons from mutant mice, which lack spontaneous and induced repetitive firing. In a heterologous expression system, the activity of the mutant channel was below the threshold for detection. Observations of decreased nerve conduction velocity and impaired behavior in an open field are also consistent with reduced activity of Nav1.6. The Nav1.6Δ1750 protein is only partially glycosylated. The abundance of mutant Nav1.6 is reduced at nodes of Ranvier and is not detectable at the axon initial segment. Despite a severe reduction in channel activity, the lifespan and motor function of Scn8a(9J/9J) mice are significantly better than null mutants lacking channel protein. The clinical phenotype of this severe hypomorphic mutant expands the spectrum of Scn8a disease to include a recessively inherited, chronic and progressive movement disorder.
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Affiliation(s)
- Julie M Jones
- Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109, United States
| | - Louise Dionne
- The Jackson Laboratory, Bar Harbor, ME 04609, United States
| | - James Dell'Orco
- Department of Neurology, University of Michigan, Ann Arbor, MI 48109, United States
| | - Rachel Parent
- Department of Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI 48109, United States
| | - Jamie N Krueger
- Department of Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI 48109, United States
| | - Xiaoyang Cheng
- Department of Neurology and Centre for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06516, United States.
| | - Sulayman D Dib-Hajj
- Department of Neurology and Centre for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06516, United States
| | | | - Lisa M Sharkey
- Department of Neurology, University of Michigan, Ann Arbor, MI 48109, United States
| | - James J Dowling
- Department of Neurology, University of Michigan, Ann Arbor, MI 48109, United States
| | - Geoffrey G Murphy
- Department of Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI 48109, United States; Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109, United States
| | - Vikram G Shakkottai
- Department of Neurology, University of Michigan, Ann Arbor, MI 48109, United States
| | - Peter Shrager
- Department of Neurobiology & Anatomy, University of Rochester Medical Center, Rochester, NY 14642, United States
| | - Miriam H Meisler
- Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109, United States.
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Horvath GA, Demos M, Shyr C, Matthews A, Zhang L, Race S, Stockler-Ipsiroglu S, Van Allen MI, Mancarci O, Toker L, Pavlidis P, Ross CJ, Wasserman WW, Trump N, Heales S, Pope S, Cross JH, van Karnebeek CDM. Secondary neurotransmitter deficiencies in epilepsy caused by voltage-gated sodium channelopathies: A potential treatment target? Mol Genet Metab 2016; 117:42-8. [PMID: 26647175 DOI: 10.1016/j.ymgme.2015.11.008] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/03/2015] [Revised: 11/16/2015] [Accepted: 11/16/2015] [Indexed: 12/26/2022]
Abstract
We describe neurotransmitter abnormalities in two patients with drug-resistant epilepsy resulting from deleterious de novo mutations in sodium channel genes. Whole exome sequencing identified a de novo SCN2A splice-site mutation (c.2379+1G>A, p.Glu717Gly.fs*30) resulting in deletion of exon 14, in a 10-year old male with early onset global developmental delay, intermittent ataxia, autism, hypotonia, epileptic encephalopathy and cerebral/cerebellar atrophy. In the cerebrospinal fluid both homovanillic acid and 5-hydroxyindoleacetic acid were significantly decreased; extensive biochemical and genetic investigations ruled out primary neurotransmitter deficiencies and other known inborn errors of metabolism. In an 8-year old female with an early onset intractable epileptic encephalopathy, developmental regression, and progressive cerebellar atrophy, a previously unreported de novo missense mutation was identified in SCN8A (c.5615G>A; p.Arg1872Gln), affecting a highly conserved residue located in the C-terminal of the Nav1.6 protein. Aside from decreased homovanillic acid and 5-hydroxyindoleacetic acid, 5-methyltetrahydrofolate was also found to be low. We hypothesize that these channelopathies cause abnormal synaptic mono-amine metabolite secretion/uptake via impaired vesicular release and imbalance in electrochemical ion gradients, which in turn aggravate the seizures. Treatment with oral 5-hydroxytryptophan, l-Dopa/Carbidopa, and a dopa agonist resulted in mild improvement of seizure control in the male case, most likely via dopamine and serotonin receptor activated signal transduction and modulation of glutamatergic, GABA-ergic and glycinergic neurotransmission. Neurotransmitter analysis in other sodium channelopathy patients will help validate our findings, potentially yielding novel treatment opportunities.
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Affiliation(s)
- Gabriella A Horvath
- Division of Biochemical Diseases, Dept of Pediatrics, B.C. Children's Hospital, University of British Columbia, Vancouver, Canada
| | - Michelle Demos
- Div. of Pediatric Neurology, Dept of Pediatrics, B.C. Children's Hospital, University of British Columbia, Vancouver, Canada
| | - Casper Shyr
- Center for Molecular Medicine and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, Canada; Department of Medical Genetics, University of British Columbia, Vancouver, Canada
| | - Allison Matthews
- Center for Molecular Medicine and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, Canada; Department of Medical Genetics, University of British Columbia, Vancouver, Canada
| | - Linhua Zhang
- Center for Molecular Medicine and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, Canada
| | - Simone Race
- Division of Biochemical Diseases, Dept of Pediatrics, B.C. Children's Hospital, University of British Columbia, Vancouver, Canada
| | - Sylvia Stockler-Ipsiroglu
- Division of Biochemical Diseases, Dept of Pediatrics, B.C. Children's Hospital, University of British Columbia, Vancouver, Canada
| | - Margot I Van Allen
- Department of Medical Genetics, University of British Columbia, Vancouver, Canada
| | - Ogan Mancarci
- Department of Psychiatry and Michael Smith Laboratories, University of British Columbia, Vancouver, Canada
| | - Lilah Toker
- Department of Psychiatry and Michael Smith Laboratories, University of British Columbia, Vancouver, Canada
| | - Paul Pavlidis
- Department of Psychiatry and Michael Smith Laboratories, University of British Columbia, Vancouver, Canada
| | - Colin J Ross
- Department of Medical Genetics, University of British Columbia, Vancouver, Canada
| | - Wyeth W Wasserman
- Center for Molecular Medicine and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, Canada; Department of Medical Genetics, University of British Columbia, Vancouver, Canada
| | - Natalie Trump
- Molecular Genetics, Great Ormond Street Hospital for Children, London, United Kingdom
| | - Simon Heales
- Neurometabolic Unit, National Hospital, Queen Square, London, United Kindgdom; Chemical Pathology, Great Ormond Street Hospital, UCL Institute of Child Health, London, United Kingdom
| | - Simon Pope
- Neurometabolic Unit, National Hospital, Queen Square, London, United Kindgdom
| | - J Helen Cross
- Developmental Neurosciences Programme, UCL Institute of Child Health, and Great Ormond Street Hospital for Children, London, United Kingdom
| | - Clara D M van Karnebeek
- Division of Biochemical Diseases, Dept of Pediatrics, B.C. Children's Hospital, University of British Columbia, Vancouver, Canada; Center for Molecular Medicine and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, Canada.
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Makinson CD, Dutt K, Lin F, Papale LA, Shankar A, Barela AJ, Liu R, Goldin AL, Escayg A. An Scn1a epilepsy mutation in Scn8a alters seizure susceptibility and behavior. Exp Neurol 2015; 275 Pt 1:46-58. [PMID: 26410685 DOI: 10.1016/j.expneurol.2015.09.008] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2015] [Revised: 09/03/2015] [Accepted: 09/12/2015] [Indexed: 11/26/2022]
Abstract
Understanding the role of SCN8A in epilepsy and behavior is critical in light of recently identified human SCN8A epilepsy mutations. We have previously demonstrated that Scn8a(med) and Scn8a(med-jo) mice carrying mutations in the Scn8a gene display increased resistance to flurothyl and kainic acid-induced seizures; however, they also exhibit spontaneous absence seizures. To further investigate the relationship between altered SCN8A function and epilepsy, we introduced the SCN1A-R1648H mutation, identified in a family with generalized epilepsy with febrile seizures plus (GEFS+), into the corresponding position (R1627H) of the mouse Scn8a gene. Heterozygous R1627H mice exhibited increased resistance to some forms of pharmacologically and electrically induced seizures and the mutant Scn8a allele ameliorated the phenotype of Scn1a-R1648H mutants. Hippocampal slices from heterozygous R1627H mice displayed decreased bursting behavior compared to wild-type littermates. Paradoxically, at the homozygous level, R1627H mice did not display increased seizure resistance and were susceptible to audiogenic seizures. We furthermore observed increased hippocampal pyramidal cell excitability in heterozygous and homozygous Scn8a-R1627H mutants, and decreased interneuron excitability in heterozygous Scn8a-R1627H mutants. These results expand the phenotypes associated with disruption of the Scn8a gene and demonstrate that an Scn8a mutation can both confer seizure protection and increase seizure susceptibility.
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Affiliation(s)
| | - Karoni Dutt
- Department of Microbiology and Molecular Genetics, University of California Irvine, Irvine, CA 92697, USA
| | - Frank Lin
- The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332, USA
| | - Ligia A Papale
- Department of Human Genetics, Emory University, Atlanta, GA 30022, USA
| | - Anupama Shankar
- Department of Human Genetics, Emory University, Atlanta, GA 30022, USA
| | - Arthur J Barela
- Department of Microbiology and Molecular Genetics, University of California Irvine, Irvine, CA 92697, USA
| | - Robert Liu
- Department of Biology, Emory University, Atlanta, GA 30022, USA
| | - Alan L Goldin
- Department of Microbiology and Molecular Genetics, University of California Irvine, Irvine, CA 92697, USA.
| | - Andrew Escayg
- Department of Human Genetics, Emory University, Atlanta, GA 30022, USA.
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Makinson CD, Tanaka BS, Lamar T, Goldin AL, Escayg A. Role of the hippocampus in Nav1.6 (Scn8a) mediated seizure resistance. Neurobiol Dis 2014; 68:16-25. [PMID: 24704313 DOI: 10.1016/j.nbd.2014.03.014] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2013] [Revised: 03/13/2014] [Accepted: 03/25/2014] [Indexed: 10/25/2022] Open
Abstract
SCN1A mutations are the main cause of the epilepsy disorders Dravet syndrome (DS) and genetic epilepsy with febrile seizures plus (GEFS+). Mutations that reduce the activity of the mouse Scn8a gene, in contrast, are found to confer seizure resistance and extend the lifespan of mouse models of DS and GEFS+. To investigate the mechanism by which reduced Scn8a expression confers seizure resistance, we induced interictal-like burst discharges in hippocampal slices of heterozygous Scn8a null mice (Scn8a(med/+)) with elevated extracellular potassium. Scn8a(med/+) mutants exhibited reduced epileptiform burst discharge activity after P20, indicating an age-dependent increased threshold for induction of epileptiform discharges. Scn8a deficiency also reduced the occurrence of burst discharges in a GEFS+ mouse model (Scn1a(R1648H/+)). There was no detectable change in the expression levels of Scn1a (Nav1.1) or Scn2a (Nav1.2) in the hippocampus of adult Scn8a(med/+) mutants. To determine whether the increased seizure resistance associated with reduced Scn8a expression was due to alterations that occurred during development, we examined the effect of deleting Scn8a in adult mice. Global Cre-mediated deletion of a heterozygous floxed Scn8a allele in adult mice was found to increase thresholds to chemically and electrically induced seizures. Finally, knockdown of Scn8a gene expression in the adult hippocampus via lentiviral Cre injection resulted in a reduction in the number of EEG-confirmed seizures following the administration of picrotoxin. Our results identify the hippocampus as an important structure in the mediation of Scn8a-dependent seizure protection and suggest that selective targeting of Scn8a activity might be efficacious in patients with epilepsy.
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Affiliation(s)
| | - Brian S Tanaka
- Departments of Microbiology and Molecular Genetics and Anatomy and Neurobiology, University of California, Irvine, CA 92697
| | - Tyra Lamar
- Department of Human Genetics, Emory University, Atlanta, GA 30322
| | - Alan L Goldin
- Departments of Microbiology and Molecular Genetics and Anatomy and Neurobiology, University of California, Irvine, CA 92697
| | - Andrew Escayg
- Department of Human Genetics, Emory University, Atlanta, GA 30322
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