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Alrashdi B, Dawod B, Tacke S, Kuerten S, Côté PD, Marshall JS. Mice Heterozygous for the Sodium Channel Scn8a (Nav1.6) Have Reduced Inflammatory Responses During EAE and Following LPS Challenge. Front Immunol 2021; 12:533423. [PMID: 33815353 PMCID: PMC8017164 DOI: 10.3389/fimmu.2021.533423] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2020] [Accepted: 03/03/2021] [Indexed: 11/16/2022] Open
Abstract
Voltage gated sodium (Nav) channels contribute to axonal damage following demyelination in experimental autoimmune encephalomyelitis (EAE), a rodent model of multiple sclerosis (MS). The Nav1.6 isoform has been implicated as a primary contributor in this process. However, the role of Nav1.6 in immune processes, critical to the pathology of both MS and EAE, has not been extensively studied. EAE was induced with myelin oligodendrocyte (MOG35-55) peptide in Scn8admu/+ mice, which have reduced Nav1.6 levels. Scn8admu/+ mice demonstrated improved motor capacity during the recovery and early chronic phases of EAE relative to wild-type animals. In the optic nerve, myeloid cell infiltration and the effects of EAE on the axonal ultrastructure were also significantly reduced in Scn8admu/+ mice. Analysis of innate immune parameters revealed reduced plasma IL-6 levels and decreased percentages of Gr-1high/CD11b+ and Gr-1int/CD11b+ myeloid cells in the blood during the chronic phase of EAE in Scn8admu/+ mice. Elevated levels of the anti-inflammatory cytokines IL-10, IL-13, and TGF-β1 were also observed in the brains of untreated Scn8admu/+ mice. A lipopolysaccharide (LPS) model was used to further evaluate inflammatory responses. Scn8admu/+ mice displayed reduced inflammation in response to LPS challenge. To further evaluate if this was an immune cell-intrinsic difference or the result of changes in the immune or hormonal environment, mast cells were derived from the bone marrow of Scn8admu/+ mice. These mast cells also produced lower levels of IL-6, in response to LPS, compared with those from wild type mice. Our results demonstrate that in addition to its recognized impact on axonal damage, Nav1.6 impacts multiple aspects of the innate inflammatory response.
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Affiliation(s)
- Barakat Alrashdi
- Department of Biology, Dalhousie University, Halifax, NS, Canada
| | - Bassel Dawod
- Department of Pathology, Dalhousie University, Halifax, NS, Canada
| | - Sabine Tacke
- Department of Anatomy and Cell Biology, Institute of Anatomy, Friedrich-Alexander-University Erlangen-Nuremberg (FAU), Erlangen, Germany
| | - Stefanie Kuerten
- Department of Anatomy and Cell Biology, Institute of Anatomy, Friedrich-Alexander-University Erlangen-Nuremberg (FAU), Erlangen, Germany
| | - Patrice D. Côté
- Department of Biology, Dalhousie University, Halifax, NS, Canada
- Department of Ophthalmology and Visual Sciences, Dalhousie University, Halifax, NS, Canada
| | - Jean S. Marshall
- Department of Pathology, Dalhousie University, Halifax, NS, Canada
- Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada
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Smith BJ, Côté PD, Tremblay F. Voltage-gated sodium channel-dependent retroaxonal modulation of photoreceptor function during post-natal development in mice. Dev Neurobiol 2021; 81:353-365. [PMID: 33248000 DOI: 10.1002/dneu.22793] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Revised: 11/16/2020] [Accepted: 11/17/2020] [Indexed: 11/11/2022]
Abstract
Juvenile (postnatal day 16) mice lacking Nav 1.6 channels (null-mutant Scn8admu ) have reduced photoreceptor function, which is unexpected given that Nav channels have not been detected in mouse photoreceptors and do not contribute appreciably to photoreceptor function in adults. We demonstrate that acute block of Nav channels with intravitreal TTX in juvenile (P16) wild-type mice has no effect on photoreceptor function. However, reduced light activity by prolonged dark adaptation from P8 caused significant reduction in photoreceptor function at P16. Injecting TTX into the retrobulbar space at P16 to specifically block Nav channels in the optic nerve also caused a reduction in photoreceptor function comparable to that seen at P16 in null-mutant Scn8a mice. In both P16 null-mutant Scn8admu and retrobulbar TTX-injected wild-type mice, photoreceptor function was restored following intravitreal injection of the TrkB receptor agonist 7,8-dihydroxyflavone, linking Nav -dependent retrograde transport to TrkB-dependent neurotrophic factor production pathways as a modulatory influence of photoreceptor function at P16. We also found that in Scn8admu mice, photoreceptor function recovers by P22-25 despite more precarious general health of the animal. Retrobulbar injection of TTX in the wild type still reduced the photoreceptor response at this age but to a lesser extent, suggesting that Nav -dependent modulation of photoreceptor function is largely transient, peaking soon after eye opening. Together, these results suggest that the general photosensitivity of the retina is modulated following eye opening by retrograde transport through activity-dependent retinal ganglion cell axonal signaling targeting TrkB receptors.
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Affiliation(s)
- Benjamin J Smith
- Department of Biology, Dalhousie University, Halifax, NS, Canada
| | - Patrice D Côté
- Department of Biology, Dalhousie University, Halifax, NS, Canada.,Department of Ophthalmology and Visual Sciences, Dalhousie University, Halifax, NS, Canada
| | - François Tremblay
- Department of Ophthalmology and Visual Sciences, Dalhousie University, Halifax, NS, Canada.,Department of Physiology and Biophysics, Dalhousie University, Halifax, NS, Canada.,Izaak Walton Killam Health Centre, Halifax, NS, Canada
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Glial Reaction in the Spinal Cord of the Degenerating Muscle Mouse (Scn8a dmu ). Neurochem Res 2014; 40:124-9. [DOI: 10.1007/s11064-014-1475-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2014] [Revised: 09/24/2014] [Accepted: 11/04/2014] [Indexed: 12/21/2022]
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Smith BJ, Tremblay F, Côté PD. Voltage-gated sodium channels contribute to the b-wave of the rodent electroretinogram by mediating input to rod bipolar cell GABAc receptors. Exp Eye Res 2013; 116:279-90. [DOI: 10.1016/j.exer.2013.09.006] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2013] [Revised: 08/23/2013] [Accepted: 09/10/2013] [Indexed: 11/26/2022]
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Zabouri N, Haverkamp S. Calcium channel-dependent molecular maturation of photoreceptor synapses. PLoS One 2013; 8:e63853. [PMID: 23675510 PMCID: PMC3652833 DOI: 10.1371/journal.pone.0063853] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2012] [Accepted: 04/08/2013] [Indexed: 01/08/2023] Open
Abstract
Several studies have shown the importance of calcium channels in the development and/or maturation of synapses. The CaV1.4(α1F) knockout mouse is a unique model to study the role of calcium channels in photoreceptor synapse formation. It features abnormal ribbon synapses and aberrant cone morphology. We investigated the expression and targeting of several key elements of ribbon synapses and analyzed the cone morphology in the CaV1.4(α1F) knockout retina. Our data demonstrate that most abnormalities occur after eye opening. Indeed, scaffolding proteins such as Bassoon and RIM2 are properly targeted at first, but their expression and localization are not maintained in adulthood. This indicates that either calcium or the CaV1.4 channel, or both are necessary for the maintenance of their normal expression and distribution in photoreceptors. Other proteins, such as Veli3 and PSD-95, also display abnormal expression in rods prior to eye opening. Conversely, vesicle related proteins appear normal. Our data demonstrate that the CaV1.4 channel is important for maintaining scaffolding proteins in the ribbon synapse but less vital for proteins related to vesicular release. This study also confirms that in adult retinae, cones show developmental features such as sprouting and synaptogenesis. Overall we present evidence that in the absence of the CaV1.4 channel, photoreceptor synapses remain immature and are unable to stabilize.
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Affiliation(s)
- Nawal Zabouri
- Neuroanatomy, Max-Planck-Institute for Brain Research, Frankfurt am Main, Germany.
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Smith BJ, Côté PD. Reduced Retinal Function in the Absence of Na(v)1.6. PLoS One 2012; 7:e31476. [PMID: 22355369 PMCID: PMC3280295 DOI: 10.1371/journal.pone.0031476] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2010] [Accepted: 01/12/2012] [Indexed: 11/19/2022] Open
Abstract
Background Mice with a function-blocking mutation in the Scn8a gene that encodes Nav1.6, a voltage-gated sodium channel (VGSC) isoform normally found in several types of retinal neurons, have previously been found to display a profoundly abnormal dark adapted flash electroretinogram. However the retinal function of these mice in light adapted conditions has not been studied. Methodology/Principal Findings In the present report we reveal that during light adaptation these animals are shown to have electroretinograms with significant decreases in the amplitude of the a- and b-waves. The percent decrease in the a- and b-waves substantially exceeds the acute effect of VGSC block by tetrodotoxin in control littermates. Intravitreal injection of CoCl2 or CNQX to isolate the a-wave contributions of the photoreceptors in littermates revealed that at high background luminance the cone-isolated component of the a-wave is of the same amplitude as the a-wave of mutants. Conclusions/Significance Our results indicate that Scn8a mutant mice have reduced function in both rod and the cone retinal pathways. The extent of the reduction in the cone pathway, as quantified using the ERG b-wave, exceeds the reduction seen in control littermates after application of TTX, suggesting that a defect in cone photoreceptors contributes to the reduction. Unless the postreceptoral component of the a-wave is increased in Scn8a mutant mice, the reduction in the b-wave is larger than can be accounted for by reduced photoreceptor function alone. Our data suggests that the reduction in the light adapted ERG of Scn8a mutant mice is caused by a combination of reduced cone photoreceptor function and reduced depolarization of cone ON bipolar cells. This raises the possibility that Nav1.6 augments signaling in cone bipolar cells.
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Affiliation(s)
- Benjamin J. Smith
- Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Patrice D. Côté
- Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada
- Department of Ophthalmology and Visual Sciences, Dalhousie University, Halifax, Nova Scotia, Canada
- * E-mail:
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Noujaim SF, Kaur K, Milstein M, Jones JM, Furspan P, Jiang D, Auerbach DS, Herron T, Meisler MH, Jalife J. A null mutation of the neuronal sodium channel NaV1.6 disrupts action potential propagation and excitation-contraction coupling in the mouse heart. FASEB J 2011; 26:63-72. [PMID: 21948246 DOI: 10.1096/fj.10-179770] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Evidence supports the expression of brain-type sodium channels in the heart. Their functional role, however, remains controversial. We used global Na(V)1.6-null mice to test the hypothesis that Na(V)1.6 contributes to the maintenance of propagation in the myocardium and to excitation-contraction (EC) coupling. We demonstrated expression of transcripts encoding full-length Na(V)1.6 in isolated ventricular myocytes and confirmed the striated pattern of Na(V)1.6 fluorescence in myocytes. On the ECG, the PR and QRS intervals were prolonged in the null mice, and the Ca(2+) transients were longer in the null cells. Under patch clamping, at holding potential (HP) = -120 mV, the peak I(Na) was similar in both phenotypes. However, at HP = -70 mV, the peak I(Na) was smaller in the nulls. In optical mapping, at 4 mM [K(+)](o), 17 null hearts showed slight (7%) reduction of ventricular conduction velocity (CV) compared to 16 wild-type hearts. At 12 mM [K(+)](o), CV was 25% slower in a subset of 9 null vs. 9 wild-type hearts. These results highlight the importance of neuronal sodium channels in the heart, whereby Na(V)1.6 participates in EC coupling, and represents an intrinsic depolarizing reserve that contributes to excitation.
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Affiliation(s)
- Sami F Noujaim
- Center for Arrhythmia Research, University of Michigan, Ann Arbor, MI 48108, USA
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Increase of CGRP Expression in Motor Endplates Within Fore and Hind Limb Muscles of the Degenerating Muscle Mouse (Scn8a dmu ). Cell Mol Neurobiol 2010; 31:155-61. [DOI: 10.1007/s10571-010-9601-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2010] [Accepted: 09/08/2010] [Indexed: 11/25/2022]
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Ichikawa H, Kano M, Shimizu Y, Suzuki T, Sawada E, Ono W, Chu LWG, Côté PD. Increase of c-Fos and c-Jun Expression in Spinal and Cranial Motoneurons of the Degenerating Muscle Mouse (Scn8a dmu ). Cell Mol Neurobiol 2010; 30:737-42. [DOI: 10.1007/s10571-010-9498-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2009] [Accepted: 01/13/2010] [Indexed: 01/08/2023]
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Ben-Ari Y. Neuro-archaeology: pre-symptomatic architecture and signature of neurological disorders. Trends Neurosci 2008; 31:626-36. [DOI: 10.1016/j.tins.2008.09.002] [Citation(s) in RCA: 108] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2008] [Revised: 09/26/2008] [Accepted: 09/26/2008] [Indexed: 01/16/2023]
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O'Brien BJ, Caldwell JH, Ehring GR, Bumsted O'Brien KM, Luo S, Levinson SR. Tetrodotoxin-resistant voltage-gated sodium channels Na(v)1.8 and Na(v)1.9 are expressed in the retina. J Comp Neurol 2008; 508:940-51. [PMID: 18399542 DOI: 10.1002/cne.21701] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Voltage-gated sodium channels (VGSCs) are one of the fundamental building blocks of electrically excitable cells in the nervous system. These channels are responsible for the generation of action potentials that are required for the communication of neuronal signals over long distances within a cell. VGSCs are encoded by a family of nine genes whose products have widely varying biophysical properties. In this study, we have detected the expression of two atypical VGSCs (Na(v)1.8 and Na(v)1.9) in the retina. Compared with more common VGSCs, Na(v)1.8 and Na(v)1.9 have unusual biophysical and pharmacological properties, including persistent sodium currents and resistance to the canonical sodium channel blocker tetrodotoxin (TTX). Our molecular biological and immunohistochemical data derived from mouse (Mus musculus) retina demonstrate expression of Na(v)1.8 by retinal amacrine and ganglion cells, whereas Na(v)1.9 is expressed by photoreceptors and Müller glia. The fact that these channels exist in the central nervous system (CNS) and exhibit robust TTX resistance requires a re-evaluation of prior physiological, pharmacological, and developmental data in the visual system, in which the diversity of VGSCs has been previously underestimated.
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Affiliation(s)
- Brendan J O'Brien
- Department of Optometry & Vision Science, University of Auckland, Private Bag 92019, Auckland, New Zealand.
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Rosker C, Lohberger B, Hofer D, Steinecker B, Quasthoff S, Schreibmayer W. The TTX metabolite 4,9-anhydro-TTX is a highly specific blocker of the Nav1.6 voltage-dependent sodium channel. Am J Physiol Cell Physiol 2007; 293:C783-9. [PMID: 17522141 DOI: 10.1152/ajpcell.00070.2007] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The blocking efficacy of 4,9-anhydro-TTX (4,9-ah-TTX) and TTX on several isoforms of voltage-dependent sodium channels, expressed in Xenopus laevis oocytes, was tested (Nav1.2, Nav1.3, Nav1.4, Nav1.5, Nav1.6, Nav1.7, and Nav1.8). Generally, TTX was 40–231 times more effective, when compared with 4,9-ah-TTX, on a given isoform. An exception was Nav1.6, where 4,9-ah-TTX in nanomole per liter concentrations sufficed to result in substantial block, indicating that 4,9-ah-TTX acts specifically at this peculiar isoform. The IC50 values for TTX/4,9-ah-TTX were as follows (in nmol/l): 7.8 ± 1.3/1,260 ± 121 (Nav1.2), 2.8 ± 2.3/341 ± 36 (Nav1.3), 4.5 ± 1.0/988 ± 62 (Nav1.4), 1,970 ± 565/78,500 ± 11,600 (Nav1.5), 3.8 ± 1.5/7.8 ± 2.3 (Nav1.6), 5.5 ± 1.4/1,270 ± 251 (Nav1.7), and 1,330 ± 459/>30,000 (Nav1.8). Analysis of approximal half-maximal doses of both compounds revealed minor effects on voltage-dependent activation only, whereas steady-state inactivation was shifted to more negative potentials by both TTX and 4,9-ah-TTX in the case of the Nav1.6 subunit, but not in the case of other TTX-sensitive ones. TTX shifted steady-state inactivation also to more negative potentials in case of the TTX-insensitive Nav1.5 subunit, where it also exerted profound effects on the time course of recovery from inactivation. Isoform-specific interaction of toxins with ion channels is frequently observed in the case of proteinaceous toxins. Although the sensitivity of Nav1.1 to 4,9-ah-TTX is not known, here we report evidence on a highly isoform-specific TTX analog that may well turn out to be an invaluable tool in research for the identification of Nav1.6-mediated function, but also for therapeutic intervention.
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Affiliation(s)
- Christian Rosker
- Institute for Biophysics, Center for Physiological Medicine, Medical University of Graz, Harrachgasse 21/4, Graz, Austria
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