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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] [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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The MAP1B Binding Domain of Na v1.6 Is Required for Stable Expression at the Axon Initial Segment. J Neurosci 2019; 39:4238-4251. [PMID: 30914445 DOI: 10.1523/jneurosci.2771-18.2019] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Revised: 03/14/2019] [Accepted: 03/17/2019] [Indexed: 12/22/2022] Open
Abstract
Nav1.6 (SCN8A) is a major voltage-gated sodium channel in the mammalian CNS, and is highly concentrated at the axon initial segment (AIS). As previously demonstrated, the microtubule associated protein MAP1B binds the cytoplasmic N terminus of Nav1.6, and this interaction is disrupted by the mutation p.VAVP(77-80)AAAA. We now demonstrate that this mutation results in WT expression levels on the somatic surface but reduced surface expression at the AIS of cultured rat embryonic hippocampal neurons from both sexes. The mutation of the MAP1B binding domain did not impair vesicular trafficking and preferential delivery of Nav1.6 to the AIS; nor was the diffusion of AIS inserted channels altered relative to WT. However, the reduced AIS surface expression of the MAP1B mutant was restored to WT levels by inhibiting endocytosis with Dynasore, indicating that compartment-specific endocytosis was responsible for the lack of AIS accumulation. Interestingly, the lack of AIS targeting resulted in an elevated percentage of persistent current, suggesting that this late current originates predominantly in the soma. No differences in the voltage dependence of activation or inactivation were detected in the MAP1B binding mutant relative to WT channel. We hypothesize that MAP1B binding to the WT Nav1.6 masks an endocytic motif, thus allowing long-term stability on the AIS surface. This work identifies a critical and important new role for MAP1B in the regulation of neuronal excitability and adds to our understanding of AIS maintenance and plasticity, in addition to identifying new target residues for pathogenic mutations of SCN8A SIGNIFICANCE STATEMENT Nav1.6 is a major voltage-gated sodium channel in human brain, where it regulates neuronal activity due to its localization at the axon initial segment (AIS). Nav1.6 mutations cause epilepsy, intellectual disability, and movement disorders. In the present work, we show that loss of interaction with MAP1B within the Nav1.6 N terminus reduces the steady-state abundance of Nav1.6 at the AIS. The effect is due to increased Nav1.6 endocytosis at this neuronal compartment rather than a failure of forward trafficking to the AIS. This work confirms a new biological role of MAP1B in the regulation of sodium channel localization and will contribute to future analysis of patient mutations in the cytoplasmic N terminus of Nav1.6.
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Erickson A, Deiteren A, Harrington AM, Garcia‐Caraballo S, Castro J, Caldwell A, Grundy L, Brierley SM. Voltage-gated sodium channels: (Na V )igating the field to determine their contribution to visceral nociception. J Physiol 2018; 596:785-807. [PMID: 29318638 PMCID: PMC5830430 DOI: 10.1113/jp273461] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2017] [Accepted: 01/02/2018] [Indexed: 12/19/2022] Open
Abstract
Chronic visceral pain, altered motility and bladder dysfunction are common, yet poorly managed symptoms of functional and inflammatory disorders of the gastrointestinal and urinary tracts. Recently, numerous human channelopathies of the voltage-gated sodium (NaV ) channel family have been identified, which induce either painful neuropathies, an insensitivity to pain, or alterations in smooth muscle function. The identification of these disorders, in addition to the recent utilisation of genetically modified NaV mice and specific NaV channel modulators, has shed new light on how NaV channels contribute to the function of neuronal and non-neuronal tissues within the gastrointestinal tract and bladder. Here we review the current pre-clinical and clinical evidence to reveal how the nine NaV channel family members (NaV 1.1-NaV 1.9) contribute to abdominal visceral function in normal and disease states.
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Affiliation(s)
- Andelain Erickson
- Visceral Pain Research Group, Human Physiology, Centre for Neuroscience, College of Medicine and Public HealthFlinders UniversityBedford ParkSouth Australia5042Australia
- Centre for Nutrition and Gastrointestinal Diseases, Discipline of Medicine, University of AdelaideSouth Australian Health and Medical Research Institute (SAHMRI)North TerraceAdelaideSouth Australia 5000Australia
| | - Annemie Deiteren
- Visceral Pain Research Group, Human Physiology, Centre for Neuroscience, College of Medicine and Public HealthFlinders UniversityBedford ParkSouth Australia5042Australia
- Centre for Nutrition and Gastrointestinal Diseases, Discipline of Medicine, University of AdelaideSouth Australian Health and Medical Research Institute (SAHMRI)North TerraceAdelaideSouth Australia 5000Australia
| | - Andrea M. Harrington
- Visceral Pain Research Group, Human Physiology, Centre for Neuroscience, College of Medicine and Public HealthFlinders UniversityBedford ParkSouth Australia5042Australia
- Centre for Nutrition and Gastrointestinal Diseases, Discipline of Medicine, University of AdelaideSouth Australian Health and Medical Research Institute (SAHMRI)North TerraceAdelaideSouth Australia 5000Australia
| | - Sonia Garcia‐Caraballo
- Visceral Pain Research Group, Human Physiology, Centre for Neuroscience, College of Medicine and Public HealthFlinders UniversityBedford ParkSouth Australia5042Australia
- Centre for Nutrition and Gastrointestinal Diseases, Discipline of Medicine, University of AdelaideSouth Australian Health and Medical Research Institute (SAHMRI)North TerraceAdelaideSouth Australia 5000Australia
| | - Joel Castro
- Visceral Pain Research Group, Human Physiology, Centre for Neuroscience, College of Medicine and Public HealthFlinders UniversityBedford ParkSouth Australia5042Australia
- Centre for Nutrition and Gastrointestinal Diseases, Discipline of Medicine, University of AdelaideSouth Australian Health and Medical Research Institute (SAHMRI)North TerraceAdelaideSouth Australia 5000Australia
| | - Ashlee Caldwell
- Visceral Pain Research Group, Human Physiology, Centre for Neuroscience, College of Medicine and Public HealthFlinders UniversityBedford ParkSouth Australia5042Australia
- Centre for Nutrition and Gastrointestinal Diseases, Discipline of Medicine, University of AdelaideSouth Australian Health and Medical Research Institute (SAHMRI)North TerraceAdelaideSouth Australia 5000Australia
| | - Luke Grundy
- Visceral Pain Research Group, Human Physiology, Centre for Neuroscience, College of Medicine and Public HealthFlinders UniversityBedford ParkSouth Australia5042Australia
- Centre for Nutrition and Gastrointestinal Diseases, Discipline of Medicine, University of AdelaideSouth Australian Health and Medical Research Institute (SAHMRI)North TerraceAdelaideSouth Australia 5000Australia
| | - Stuart M. Brierley
- Visceral Pain Research Group, Human Physiology, Centre for Neuroscience, College of Medicine and Public HealthFlinders UniversityBedford ParkSouth Australia5042Australia
- Centre for Nutrition and Gastrointestinal Diseases, Discipline of Medicine, University of AdelaideSouth Australian Health and Medical Research Institute (SAHMRI)North TerraceAdelaideSouth Australia 5000Australia
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Li Z, Yang X, Song X, Ma H, Zhang P. Chitosan Oligosaccharide Reduces Propofol Requirements and Propofol-Related Side Effects. Mar Drugs 2016; 14:md14120234. [PMID: 28009824 PMCID: PMC5192471 DOI: 10.3390/md14120234] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2016] [Revised: 11/24/2016] [Accepted: 11/29/2016] [Indexed: 12/18/2022] Open
Abstract
Propofol is one of the main sedatives but its negative side effects limit its clinical application. Chitosan oligosaccharide (COS), a kind of natural product with anti-pain and anti-inflammatory activities, may be a potential adjuvant to propofol use. A total of 94 patients receiving surgeries were evenly and randomly assigned to two groups: 10 mg/kg COS oral administration and/or placebo oral administration before being injected with propofol. The target-controlled infusion of propofol was adjusted to maintain the values of the bispectral index at 50. All patients’ pain was evaluated on a four-point scale and side effects were investigated. To explore the molecular mechanism for the functions of COS in propofol use, a mouse pain model was established. The activities of Nav1.7 were analyzed in dorsal root ganglia (DRG) cells. The results showed that the patients receiving COS pretreatment were likely to require less propofol than the patients pretreated with placebo for maintaining an anesthetic situation (p < 0.05). The degrees of injection pain were lower in a COS-pretreated group than in a propofol-pretreated group. The side effects were also more reduced in a COS-treated group than in a placebo-pretreated group. COS reduced the activity of Nav1.7 and its inhibitory function was lost when Nav1.7 was silenced (p > 0.05). COS improved propofol performance by affecting Nav1.7 activity. Thus, COS is a potential adjuvant to propofol use in surgical anesthesia.
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Affiliation(s)
- Zhiwen Li
- Department of Anesthesiology, the First Hospital of Jilin University, Changchun 130021, China.
| | - Xige Yang
- Department of Anesthesiology, the First Hospital of Jilin University, Changchun 130021, China.
| | - Xuesong Song
- Department of Anesthesiology, the First Hospital of Jilin University, Changchun 130021, China.
| | - Haichun Ma
- Department of Anesthesiology, the First Hospital of Jilin University, Changchun 130021, China.
| | - Ping Zhang
- Department of Hepatobiliary and Pancreatic Surgery, the First Hospital of Jilin University, Changchun 130021, China.
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Luo J, Zhang Y, Gong M, Lu S, Ma Y, Zeng X, Liang S. Molecular surface of JZTX-V (β-Theraphotoxin-Cj2a) interacting with voltage-gated sodium channel subtype NaV1.4. Toxins (Basel) 2014; 6:2177-93. [PMID: 25055801 PMCID: PMC4113750 DOI: 10.3390/toxins6072177] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2014] [Revised: 06/24/2014] [Accepted: 07/03/2014] [Indexed: 12/11/2022] Open
Abstract
Voltage-gated sodium channels (VGSCs; NaV1.1–NaV1.9) have been proven to be critical in controlling the function of excitable cells, and human genetic evidence shows that aberrant function of these channels causes channelopathies, including epilepsy, arrhythmia, paralytic myotonia, and pain. The effects of peptide toxins, especially those isolated from spider venom, have shed light on the structure–function relationship of these channels. However, most of these toxins have not been analyzed in detail. In particular, the bioactive faces of these toxins have not been determined. Jingzhaotoxin (JZTX)-V (also known as β-theraphotoxin-Cj2a) is a 29-amino acid peptide toxin isolated from the venom of the spider Chilobrachys jingzhao. JZTX-V adopts an inhibitory cysteine knot (ICK) motif and has an inhibitory effect on voltage-gated sodium and potassium channels. Previous experiments have shown that JZTX-V has an inhibitory effect on TTX-S and TTX-R sodium currents on rat DRG cells with IC50 values of 27.6 and 30.2 nM, respectively, and is able to shift the activation and inactivation curves to the depolarizing and the hyperpolarizing direction, respectively. Here, we show that JZTX-V has a much stronger inhibitory effect on NaV1.4, the isoform of voltage-gated sodium channels predominantly expressed in skeletal muscle cells, with an IC50 value of 5.12 nM, compared with IC50 values of 61.7–2700 nM for other heterologously expressed NaV1 subtypes. Furthermore, we investigated the bioactive surface of JZTX-V by alanine-scanning the effect of toxin on NaV1.4 and demonstrate that the bioactive face of JZTX-V is composed of three hydrophobic (W5, M6, and W7) and two cationic (R20 and K22) residues. Our results establish that, consistent with previous assumptions, JZTX-V is a Janus-faced toxin which may be a useful tool for the further investigation of the structure and function of sodium channels.
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Affiliation(s)
- Ji Luo
- The key Laboratory of Protein Chemistry and Developmental Biology of Ministry of Education, College of Life Science, Hunan Normal University, Changsha 410081, China.
| | - Yiya Zhang
- The key Laboratory of Protein Chemistry and Developmental Biology of Ministry of Education, College of Life Science, Hunan Normal University, Changsha 410081, China.
| | - Mengting Gong
- The key Laboratory of Protein Chemistry and Developmental Biology of Ministry of Education, College of Life Science, Hunan Normal University, Changsha 410081, China.
| | - Shanshan Lu
- The key Laboratory of Protein Chemistry and Developmental Biology of Ministry of Education, College of Life Science, Hunan Normal University, Changsha 410081, China.
| | - Yifeng Ma
- The key Laboratory of Protein Chemistry and Developmental Biology of Ministry of Education, College of Life Science, Hunan Normal University, Changsha 410081, China.
| | - Xiongzhi Zeng
- The key Laboratory of Protein Chemistry and Developmental Biology of Ministry of Education, College of Life Science, Hunan Normal University, Changsha 410081, China.
| | - Songping Liang
- The key Laboratory of Protein Chemistry and Developmental Biology of Ministry of Education, College of Life Science, Hunan Normal University, Changsha 410081, China.
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Oliva MK, McGarr TC, Beyer BJ, Gazina E, Kaplan DI, Cordeiro L, Thomas E, Dib-Hajj SD, Waxman SG, Frankel WN, Petrou S. Physiological and genetic analysis of multiple sodium channel variants in a model of genetic absence epilepsy. Neurobiol Dis 2014; 67:180-90. [PMID: 24657915 DOI: 10.1016/j.nbd.2014.03.007] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2014] [Accepted: 03/11/2014] [Indexed: 10/25/2022] Open
Abstract
In excitatory neurons, SCN2A (NaV1.2) and SCN8A (NaV1.6) sodium channels are enriched at the axon initial segment. NaV1.6 is implicated in several mouse models of absence epilepsy, including a missense mutation identified in a chemical mutagenesis screen (Scn8a(V929F)). Here, we confirmed the prior suggestion that Scn8a(V929F) exhibits a striking genetic background-dependent difference in phenotypic severity, observing that spike-wave discharge (SWD) incidence and severity are significantly diminished when Scn8a(V929F) is fully placed onto the C57BL/6J strain compared with C3H. Examination of sequence differences in NaV subunits between these two inbred strains suggested NaV1.2(V752F) as a potential source of this modifier effect. Recognising that the spatial co-localisation of the NaV channels at the axon initial segment (AIS) provides a plausible mechanism for functional interaction, we tested this idea by undertaking biophysical characterisation of the variant NaV channels and by computer modelling. NaV1.2(V752F) functional analysis revealed an overall gain-of-function and for NaV1.6(V929F) revealed an overall loss-of-function. A biophysically realistic computer model was used to test the idea that interaction between these variant channels at the AIS contributes to the strain background effect. Surprisingly this modelling showed that neuronal excitability is dominated by the properties of NaV1.2(V752F) due to "functional silencing" of NaV1.6(V929F) suggesting that these variants do not directly interact. Consequent genetic mapping of the major strain modifier to Chr 7, and not Chr 2 where Scn2a maps, supported this biophysical prediction. While a NaV1.6(V929F) loss of function clearly underlies absence seizures in this mouse model, the strain background effect is apparently not due to an otherwise tempting Scn2a variant, highlighting the value of combining physiology and genetics to inform and direct each other when interrogating genetic complex traits such as absence epilepsy.
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Affiliation(s)
- M K Oliva
- The Florey Institute for Neuroscience and Mental Health, The University of Melbourne, Australia
| | - T C McGarr
- The Jackson Laboratory, Bar Harbor, ME, USA
| | - B J Beyer
- The Jackson Laboratory, Bar Harbor, ME, USA
| | - E Gazina
- The Florey Institute for Neuroscience and Mental Health, The University of Melbourne, Australia
| | - D I Kaplan
- The Florey Institute for Neuroscience and Mental Health, The University of Melbourne, Australia
| | - L Cordeiro
- The Florey Institute for Neuroscience and Mental Health, The University of Melbourne, Australia
| | - E Thomas
- The Florey Institute for Neuroscience and Mental Health, The University of Melbourne, Australia
| | - S D Dib-Hajj
- Department for Neurology, Center for Neuroscience and Regeneration Research, Yale University, New Haven, USA
| | - S G Waxman
- Department for Neurology, Center for Neuroscience and Regeneration Research, Yale University, New Haven, USA
| | | | - S Petrou
- The Florey Institute for Neuroscience and Mental Health, The University of Melbourne, Australia; The Centre for Neural Engineering, The University of Melbourne, Australia.
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Abstract
Voltage-gated sodium channels (VGSCs) are integral membrane proteins. They are essential for normal neurologic function and are, currently, the most common recognized cause of genetic epilepsy. This review summarizes the neurobiology of VGSCs, their association with different epilepsy syndromes, and the ways in which we can experimentally interrogate their function. The most important sodium channel subunit of relevance to epilepsy is SCN1A, in which over 650 genetic variants have been discovered. SCN1A mutations are associated with a variety of epilepsy syndromes; the more severe syndromes are associated with truncation or complete loss of function of the protein. SCN2A is another important subtype associated with epilepsy syndromes, across a range of severe and less severe epilepsies. This subtype is localized primarily to excitatory neurons, and mutations have a range of functional effects on the channel. SCN8A is the other main adult subtype found in the brain and has recently emerged as an epilepsy gene, with the first human mutation discovered in a severe epilepsy syndrome. Mutations in the accessory β subunits, thought to modulate trafficking and function of the α subunits, have also been associated with epilepsy. Genome sequencing is continuing to become more affordable, and as such, the amount of incoming genetic data is continuing to increase. Current experimental approaches have struggled to keep pace with functional analysis of these mutations, and it has proved difficult to build associations between disease severity and the precise effect on channel function. These mutations have been interrogated with a range of experimental approaches, from in vitro, in vivo, to in silico. In vitro techniques will prove useful to scan mutations on a larger scale, particularly with the advance of high-throughput automated patch-clamp techniques. In vivo models enable investigation of mutation in the context of whole brains with connected networks and more closely model the human condition. In silico models can help us incorporate the impact of multiple genetic factors and investigate epistatic interactions and beyond.
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Affiliation(s)
- Megan Oliva
- Florey Neuroscience Institutes, University of Melbourne, Melbourne, Victoria, Australia
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8
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Mao Q, Jia F, Zhang XH, Qiu YM, Ge JW, Bao WJ, Luo QZ, Jiang JY. The up-regulation of voltage-gated sodium channel Nav1.6 expression following fluid percussion traumatic brain injury in rats. Neurosurgery 2010; 66:1134-9; discussion 1139. [PMID: 20421839 DOI: 10.1227/01.neu.0000369612.31946.a2] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The influx of Na and the depolarization mediated by voltage-gated sodium channels (VGSCs) is an early event in traumatic brain injury (TBI) induced cellular abnormalities and is therefore well positioned as an upstream target for pharmacologic modulation of the pathological responses to TBI. Alteration in the expression of the VGSC alpha-subunit has occurred in a variety of neuropathological states including focal cerebral ischemia, spinal injury, and epilepsy. OBJECTIVE In this study, changes in Nav1.6 mRNA and protein expression were investigated in rat hippocampus after TBI. METHODS Forty-eight adult male Sprague Dawley rats were randomly assigned to control or TBI groups. TBI was induced with a lateral fluid percussion device. Expression of mRNA and protein for Nav1.6 in the bilateral hippocampus was examined at 2, 12, 24, and 72 hours after injury by real-time quantitative polymerase chain reaction and Western blot. Immunofluorescence was performed to localize the expression of Nav1.6 protein in the hippocampus. RESULTS Expression of >Nav1.6 mRNA was significantly up-regulated in the bilateral hippocampus at 2 and 12 hours post-TBI. Significant up-regulation of Nav1.6 protein was identified in the ipsilateral hippocampus from 2 to 72 hours post-TBI and in the contralateral hippocampus from 2 to 24 hours post-TBI. Expression of Nav1.6 occurred predominantly in neurons in the hippocampus. CONCLUSION Results of the study showed significant up-regulation of mRNA and protein for Nav1.6 in rat hippocampal neurons after TBI.
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Affiliation(s)
- Qing Mao
- Department of Neurosurgery, Shanghai RenJi hospital, Shanghai Jiaotong University, School of Medicine, People's Republic of China
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Abstract
Mutations in a number of genes encoding voltage-gated sodium channels cause a variety of epilepsy syndromes in humans, including genetic (generalized) epilepsy with febrile seizures plus (GEFS+) and Dravet syndrome (DS, severe myoclonic epilepsy of infancy). Most of these mutations are in the SCN1A gene, and all are dominantly inherited. Most of the mutations that cause DS result in loss of function, whereas all of the known mutations that cause GEFS+ are missense, presumably altering channel activity. Family members with the same GEFS+ mutation often display a wide range of seizure types and severities, and at least part of this variability likely results from variation in other genes. Many different biophysical effects of SCN1A-GEFS+ mutations have been observed in heterologous expression systems, consistent with both gain and loss of channel activity. However, results from mouse models suggest that the primary effect of both GEFS+ and DS mutations is to decrease the activity of GABAergic inhibitory neurons. Decreased activity of the inhibitory circuitry is thus likely to be a major factor contributing to seizure generation in patients with GEFS+ and DS, and may be a general consequence of SCN1A mutations.
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Affiliation(s)
- Andrew Escayg
- Department of Human Genetics, Emory University, Atlanta, Georgia 30322, USA.
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10
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Dib‐Hajj SD, Yang Y, Waxman SG. Chapter 4 Genetics and Molecular Pathophysiology of Nav1.7‐Related Pain Syndromes. ADVANCES IN GENETICS 2008; 63:85-110. [DOI: 10.1016/s0065-2660(08)01004-3] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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Burbidge SA, Dale TJ, Powell AJ, Whitaker WRJ, Xie XM, Romanos MA, Clare JJ. Molecular cloning, distribution and functional analysis of the NA(V)1.6. Voltage-gated sodium channel from human brain. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 2002; 103:80-90. [PMID: 12106694 DOI: 10.1016/s0169-328x(02)00188-2] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
We have cloned and expressed the full-length human Na(V)1.6 sodium channel cDNA. Northern analysis showed that the hNa(V)1.6 gene, like its rodent orthologues, is abundantly expressed in adult brain but not other tissues including heart and skeletal muscle. Within the adult brain, hNa(V)1.6 mRNA is widely expressed with particularly high levels in the cerebellum, occipital pole and frontal lobe. When stably expressed in human embryonic kidney cells (HEK293), the hNa(V)1.6 channel was found to be very similar in its biophysical properties to human Na(V)1.2 and Na(V)1.3 channels [Eur. J. Neurosci. 12 (2000) 4281-4289; Pflügers Arch. 441 (2001) 425-433]. Only relatively subtle differences were observed, for example, in the voltage dependence of gating. Like hNa(V)1.3 channels, hNa(V)1.6 produced sodium currents with a prominent persistent component when expressed in HEK293 cells. These persistent currents were similar to those reported for the rat Na(V)1.2 channel [Neuron 19 (1997) 443-452], although they were not dependent on over-expression of G protein betagamma subunits. These data are consistent with the proposal that Na(V)1.6 channels may generate the persistent currents observed in cerebellar Purkinje neurons [J. Neurosci. 17 (1997) 4157-4536]. However, in our hNa(V)1.6 cell line we have been unable to detect the resurgent currents that have also been described in Purkinje cells. Although Na(V)1.6 channels have been implicated in producing these resurgent currents [Neuron 19 (1997) 881-891], our data suggest that this may require modification of the Na(V)1.6 alpha subunit by additional factors found in Purkinje neurons but not in HEK293 cells.
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Affiliation(s)
- Stephen A Burbidge
- Migraine and Stroke Research, Neurology Centre of Excellence for Drug Discovery, GlaxoSmithKline, North Frontiers Science Park, harlow, Essex CM19 5AW, UK. steve a
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12
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Abstract
A variety of isoforms of mammalian voltage-gated sodium channels have been described. Ten genes encoding sodium channel alpha subunits have been identified, and nine of those isoforms have been functionally expressed in exogenous systems. The alpha subunit is associated with accessory beta subunits in some tissues, and three genes encoding different beta subunits have been identified. The alpha subunit isoforms have distinct patterns of development and localization in the nervous system, skeletal and cardiac muscle. In addition, many of the isoforms demonstrate subtle differences in their functional properties. However, there are no clear subfamilies of the channels, unlike the situation with potassium and calcium channels. The subtle differences in the functional properties of the sodium channel isoforms result in unique conductances in specific cell types, which have important physiological effects for the organism. Small alterations in the electrophysiological properties of the channel resulting from mutations in specific isoforms cause human diseases such as periodic paralysis, long QT syndrome, and epilepsy.
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Affiliation(s)
- A L Goldin
- Department of Microbiology and Molecular Genetics, University of California Irvine, California 92697-4025, USA.
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Whitaker WR, Faull RL, Waldvogel HJ, Plumpton CJ, Emson PC, Clare JJ. Comparative distribution of voltage-gated sodium channel proteins in human brain. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 2001; 88:37-53. [PMID: 11295230 DOI: 10.1016/s0169-328x(00)00289-8] [Citation(s) in RCA: 123] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Antisera directed against unique peptide regions from each of the human brain voltage-gated sodium channel alpha subunits were generated. In immunoblots these were found to be highly specific for the corresponding recombinant polypeptides and to recognise the native holoprotein in human brain membrane preparations. These antisera were used to perform a comparative immunohistochemical distribution analysis of all four brain sodium channel subtypes in selected human CNS regions. Distinct but heterogeneous distribution patterns were observed for each of the alpha subunits. In general, these were complimentary to that previously shown for the corresponding human mRNAs. A high degree of conservation with respect to the distribution found in rat was also evident. The human alpha subunit proteins exhibited distinct subcellular localisation patterns. Types I, III and VI immunoreactivity was predominantly in neuronal cell bodies and proximal processes, whereas type II was concentrated along axons. This is similar to rat brain and suggests the different the sodium channel subtypes have distinct functions which are highly conserved between human and rodents. A notable difference was that the type III protein was detected in all human brain regions examined, unlike in rat brain where expression in adults is very restricted. Also in contrast to rat brain, the human type VI protein was not detected in axons of unmyelinated neurons. These differences may reflect true species variation and could have important implications for understanding the function of the sodium channel subtypes and their roles in human disease.
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Affiliation(s)
- W R Whitaker
- Department of Neurobiology, The Babraham Institute, Babraham, Cambridge CB2 4AT, UK
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