1
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Sopacua M, Hoeijmakers JGJ, van der Kooi AJ, Merkies ISJ, Faber CG. Pain triangle phenomenon in possible association with
SCN9A
: A case report. Mol Genet Genomic Med 2022; 10:e2026. [PMID: 36114697 PMCID: PMC9544215 DOI: 10.1002/mgg3.2026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2021] [Revised: 05/04/2022] [Accepted: 07/19/2022] [Indexed: 11/12/2022] Open
Abstract
Background Voltage‐gated sodium channels are essential for the generation and conduction of electrical impulses in excitable cells. Sodium channel Nav1.7, encoded by the SCN9A‐gene, has been of special interest in the last decades because missense gain‐of‐function mutations have been linked to a spectrum of neuropathic pain conditions, including inherited erythermalgia (IEM), paroxysmal extreme pain disorder (PEPD), and small fiber neuropathy (SFN). Methods In this case report, we present a 61‐year‐old woman who was referred to our tertiary referral center in a standard day care setting with suspicion of SFN. We performed additional investigations: skin biopsy to determine the intra‐epidermal nerve fiber density (IENFD), quantitative sensory testing (QST), and blood examination (including DNA analysis) for possible underlying conditions. Results The patient showed a clinical picture that fulfilled the criteria of IEM, PEPD, and SFN. DNA analysis revealed the heterozygous variant c.554G > A in the SCN9A‐gene (OMIM 603415). This variant has already been described in all three human pain conditions separately, but never in one patient having symptoms of all three conditions. Because its pathogenicity has never been functionally confirmed, the variant is classified as a variance of unknown significance (VUS)/risk factor. This suggests that another genetic and/or environmental substrate plays a role in the development of neuropathic conditions like described. Conclusion We have described this as the SCN9A‐pain triangle phenomenon. Treatment should focus on pain management, genetic counseling, and improving/maintaining quality of life by treating symptoms and, if indicated, starting a rehabilitation program.
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Affiliation(s)
- Maurice Sopacua
- Department of Neurology, School of Mental Health and Neuroscience Maastricht University Medical Center+ Maastricht The Netherlands
- Department of Rehabilitation Medicine Libra Revalidatie & Audiologie Eindhoven The Netherlands
| | - Janneke G. J. Hoeijmakers
- Department of Neurology, School of Mental Health and Neuroscience Maastricht University Medical Center+ Maastricht The Netherlands
| | | | - Ingemar S. J. Merkies
- Department of Neurology, School of Mental Health and Neuroscience Maastricht University Medical Center+ Maastricht The Netherlands
- Department of Neurology Curaçao Medical Center Willemstad Curaçao
| | - Catharina G. Faber
- Department of Neurology, School of Mental Health and Neuroscience Maastricht University Medical Center+ Maastricht The Netherlands
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2
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Mancino AS, Glass WG, Yan Y, Biggin PC, Bowie D. Spliced isoforms of the cardiac Nav1.5 channel modify channel activation by distinct structural mechanisms. J Gen Physiol 2022; 154:213074. [PMID: 35297947 PMCID: PMC8939363 DOI: 10.1085/jgp.202112906] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2021] [Revised: 02/02/2022] [Accepted: 02/22/2022] [Indexed: 12/19/2022] Open
Abstract
Alternative splicing is an important cellular mechanism that fine tunes the gating properties of both voltage- and ligand-gated ion-channels. The cardiac voltage-gated sodium channel, Nav1.5, is subject to alternative splicing of the DI S3–S4 linker, which generates two types of channels with different activation properties. Here, we show that the gating differences between the adult (mH1) and neonatal (Nav1.5e) isoforms of Nav1.5 are mediated by two amino acid residues: Thr/Ser at position 207 and Asp/Lys at position 211. Electrophysiological experiments, in conjunction with molecular dynamics simulations, revealed that each residue contributes equally to the overall gating shifts in activation, but that the underlying structural mechanisms are different. Asp/Lys at position 211 acts through electrostatic interactions, whereas Thr/Ser at position 207 is predicted to alter the hydrogen bond network at the top of the S3 helix. These distinct structural mechanisms work together to modify movement of the voltage-sensitive S4 helix to bring about channel activation. Interestingly, mutation of the homologous Asp and Thr residues of the skeletal muscle isoform, Nav1.4, to Lys and Ser, respectively, confers a similar gating shift in channel activation, suggesting that these residues may fulfill a conserved role across other Nav channel family members.
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Affiliation(s)
- Adamo S Mancino
- Integrated Program in Neuroscience, McGill University, Montréal, Quebec, Canada.,Department of Pharmacology and Therapeutics, McGill University, Montréal, Quebec, Canada
| | - William G Glass
- Department of Biochemistry, University of Oxford, Oxford, UK
| | - Yuhao Yan
- Integrated Program in Neuroscience, McGill University, Montréal, Quebec, Canada.,Department of Pharmacology and Therapeutics, McGill University, Montréal, Quebec, Canada
| | - Philip C Biggin
- Department of Biochemistry, University of Oxford, Oxford, UK
| | - Derek Bowie
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Quebec, Canada
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3
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Sodium ion channels as potential therapeutic targets for cancer metastasis. Drug Discov Today 2021; 26:1136-1147. [PMID: 33545383 DOI: 10.1016/j.drudis.2021.01.026] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2020] [Revised: 07/31/2020] [Accepted: 01/27/2021] [Indexed: 12/28/2022]
Abstract
Is it possible to develop drugs for the treatment of a specific type of metastatic cancer by targeting sodium ion channels?
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4
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Sopacua M, Hoeijmakers JGJ, Merkies ISJ, Lauria G, Waxman SG, Faber CG. Small‐fiber neuropathy: Expanding the clinical pain universe. J Peripher Nerv Syst 2019; 24:19-33. [DOI: 10.1111/jns.12298] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Revised: 11/27/2018] [Accepted: 12/14/2018] [Indexed: 12/11/2022]
Affiliation(s)
- Maurice Sopacua
- Department of Neurology, School of Mental Health and NeuroscienceMaastricht University Medical Centre+ Maastricht The Netherlands
| | - Janneke G. J. Hoeijmakers
- Department of Neurology, School of Mental Health and NeuroscienceMaastricht University Medical Centre+ Maastricht The Netherlands
| | - Ingemar S. J. Merkies
- Department of Neurology, School of Mental Health and NeuroscienceMaastricht University Medical Centre+ Maastricht The Netherlands
- Department of NeurologySt. Elisabeth Hospital Willemstad Curaçao
| | - Giuseppe Lauria
- Neuroalgology UnitIRCCS Foundation, “Carlo Besta” Neurological Institute Milan Italy
- Department of Biomedical and Clinical Sciences “Luigi Sacco”University of Milan Milan Italy
| | - Stephen G. Waxman
- Department of NeurologyYale University School of Medicine New Haven Connecticut
- Center for Neuroscience and Regeneration ResearchVA Connecticut Healthcare System West Haven Connecticut
| | - Catharina G. Faber
- Department of Neurology, School of Mental Health and NeuroscienceMaastricht University Medical Centre+ Maastricht The Netherlands
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5
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Gonçalves TC, Benoit E, Partiseti M, Servent D. The Na V1.7 Channel Subtype as an Antinociceptive Target for Spider Toxins in Adult Dorsal Root Ganglia Neurons. Front Pharmacol 2018; 9:1000. [PMID: 30233376 PMCID: PMC6131673 DOI: 10.3389/fphar.2018.01000] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2018] [Accepted: 08/14/2018] [Indexed: 12/11/2022] Open
Abstract
Although necessary for human survival, pain may sometimes become pathologic if long-lasting and associated with alterations in its signaling pathway. Opioid painkillers are officially used to treat moderate to severe, and even mild, pain. However, the consequent strong and not so rare complications that occur, including addiction and overdose, combined with pain management costs, remain an important societal and economic concern. In this context, animal venom toxins represent an original source of antinociceptive peptides that mainly target ion channels (such as ASICs as well as TRP, CaV, KV and NaV channels) involved in pain transmission. The present review aims to highlight the NaV1.7 channel subtype as an antinociceptive target for spider toxins in adult dorsal root ganglia neurons. It will detail (i) the characteristics of these primary sensory neurons, the first ones in contact with pain stimulus and conveying the nociceptive message, (ii) the electrophysiological properties of the different NaV channel subtypes expressed in these neurons, with a particular attention on the NaV1.7 subtype, an antinociceptive target of choice that has been validated by human genetic evidence, and (iii) the features of spider venom toxins, shaped of inhibitory cysteine knot motif, that present high affinity for the NaV1.7 subtype associated with evidenced analgesic efficacy in animal models.
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Affiliation(s)
- Tânia C Gonçalves
- Sanofi R&D, Integrated Drug Discovery - High Content Biology, Paris, France.,Service d'Ingénierie Moléculaire des Protéines, CEA de Saclay, Université Paris-Saclay, Gif-sur-Yvette, France
| | - Evelyne Benoit
- Service d'Ingénierie Moléculaire des Protéines, CEA de Saclay, Université Paris-Saclay, Gif-sur-Yvette, France.,Institut des Neurosciences Paris-Saclay, UMR CNRS/Université Paris-Sud 9197, Gif-sur-Yvette, France
| | - Michel Partiseti
- Sanofi R&D, Integrated Drug Discovery - High Content Biology, Paris, France
| | - Denis Servent
- Service d'Ingénierie Moléculaire des Protéines, CEA de Saclay, Université Paris-Saclay, Gif-sur-Yvette, France
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6
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Liavas A, Lignani G, Schorge S. Conservation of alternative splicing in sodium channels reveals evolutionary focus on release from inactivation and structural insights into gating. J Physiol 2017. [PMID: 28621020 PMCID: PMC5811987 DOI: 10.1113/jp274693] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Key points Sodium channels are critical for supporting fast action potentials in neurons; even mutations which cause small changes in sodium channel activity can have devastating consequences for the function of the nervous system. Alternative splicing also changes the activity of sodium channels, and while it is highly conserved, it is not known whether the functional role of this splicing is also conserved. Our data reveal that splicing has a highly conserved impact on the availability of sodium channels during trains of rapid stimulations, and suggest that in one mammalian channel, Nav1.1 encoded by SCN1A, the increased availability of one splice variant is detrimental. A model reproducing the effects of splicing on channel behaviour suggests that the voltage sensor in the first domain is a rate limiting step for release of the inactivation domain, and highlights the functional specialization of channel domains.
Abstract Voltage‐gated sodium channels are critical for neuronal activity, and highly intolerant to variation. Even mutations that cause subtle changes in the activity these channels are sufficient to cause devastating inherited neurological diseases, such as epilepsy and pain. However, these channels do vary in healthy tissue. Alternative splicing modifies sodium channels, but the functional relevance and adaptive significance of this splicing remain poorly understood. Here we use a conserved alternate exon encoding part of the first domain of sodium channels to compare how splicing modifies different channels, and to ask whether the functional consequences of this splicing have been preserved in different genes. Although the splicing event is highly conserved, one splice variant has been selectively removed from Nav1.1 in multiple mammalian species, suggesting that the functional variation in Nav1.1 is less well tolerated. We show for three human channels (Nav1.1, Nav1.2 and Nav1.7) that splicing modifies the return from inactivated to deactivated states, and the differences between splice variants are occluded by antiepileptic drugs that bind to and stabilize inactivated states. A model based on structural data can replicate these changes, and indicates that splicing may exploit a distinct role of the first domain to change channel availability, and that the first domain of all three sodium channels plays a role in determining the rate at which the inactivation domain dissociates. Taken together, our data suggest that the stability of inactivated states is under tight evolutionary control, but that in Nav1.1 faster recovery from inactivation is associated with negative selection in mammals. Sodium channels are critical for supporting fast action potentials in neurons; even mutations which cause small changes in sodium channel activity can have devastating consequences for the function of the nervous system. Alternative splicing also changes the activity of sodium channels, and while it is highly conserved, it is not known whether the functional role of this splicing is also conserved. Our data reveal that splicing has a highly conserved impact on the availability of sodium channels during trains of rapid stimulations, and suggest that in one mammalian channel, Nav1.1 encoded by SCN1A, the increased availability of one splice variant is detrimental. A model reproducing the effects of splicing on channel behaviour suggests that the voltage sensor in the first domain is a rate limiting step for release of the inactivation domain, and highlights the functional specialization of channel domains.
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Affiliation(s)
- A Liavas
- Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, London, WC1N 3BG, UK
| | - G Lignani
- Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, London, WC1N 3BG, UK
| | - S Schorge
- Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, London, WC1N 3BG, UK
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7
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Vetter I, Deuis JR, Mueller A, Israel MR, Starobova H, Zhang A, Rash LD, Mobli M. NaV1.7 as a pain target – From gene to pharmacology. Pharmacol Ther 2017; 172:73-100. [DOI: 10.1016/j.pharmthera.2016.11.015] [Citation(s) in RCA: 80] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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8
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Donaldson LF, Beazley-Long N. Alternative RNA splicing: contribution to pain and potential therapeutic strategy. Drug Discov Today 2016; 21:1787-1798. [PMID: 27329269 PMCID: PMC5405051 DOI: 10.1016/j.drudis.2016.06.017] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2016] [Revised: 05/31/2016] [Accepted: 06/14/2016] [Indexed: 12/19/2022]
Abstract
Alternative pre-mRNA splicing generates multiple proteins from a single gene. Control of alternative splicing is a likely therapy in cancer and other disorders. Key molecules in pain pathways – GPCRs and channels – are alternatively spliced. It is proposed that alternative splicing may be a therapeutic target in pain.
Since the sequencing of metazoan genomes began, it has become clear that the number of expressed proteins far exceeds the number of genes. It is now estimated that more than 98% of human genes give rise to multiple proteins through alternative pre-mRNA splicing. In this review, we highlight the known alternative splice variants of many channels, receptors, and growth factors that are important in nociception and pain. Recently, pharmacological control of alternative splicing has been proposed as potential therapy in cancer, wet age-related macular degeneration, retroviral infections, and pain. Thus, we also consider the effects that known splice variants of molecules key to nociception/pain have on nociceptive processing and/or analgesic action, and the potential for control of alternative pre-mRNA splicing as a novel analgesic strategy.
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Affiliation(s)
- Lucy F Donaldson
- School of Life Sciences and Arthritis Research UK Pain Centre, University of Nottingham, Nottingham NG7 2UH, UK.
| | - Nicholas Beazley-Long
- School of Life Sciences and Arthritis Research UK Pain Centre, University of Nottingham, Nottingham NG7 2UH, UK
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9
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Zhou Y, Fang FH, Liu ZR, Ji YH. Dissection of voltage-gated sodium channels in developing cochlear sensory epithelia. Protein Cell 2016; 6:458-62. [PMID: 25937544 PMCID: PMC4444814 DOI: 10.1007/s13238-015-0157-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Affiliation(s)
- You Zhou
- Laboratory of Neuropharmacology and Neurotoxicology, Shanghai University, Shanghai, 200436, China
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10
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Barbosa C, Cummins TR. Unusual Voltage-Gated Sodium Currents as Targets for Pain. CURRENT TOPICS IN MEMBRANES 2016; 78:599-638. [PMID: 27586296 DOI: 10.1016/bs.ctm.2015.12.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Pain is a serious health problem that impacts the lives of many individuals. Hyperexcitability of peripheral sensory neurons contributes to both acute and chronic pain syndromes. Because voltage-gated sodium currents are crucial to the transmission of electrical signals in peripheral sensory neurons, the channels that underlie these currents are attractive targets for pain therapeutics. Sodium currents and channels in peripheral sensory neurons are complex. Multiple-channel isoforms contribute to the macroscopic currents in nociceptive sensory neurons. These different isoforms exhibit substantial variations in their kinetics and pharmacology. Furthermore, sodium current complexity is enhanced by an array of interacting proteins that can substantially modify the properties of voltage-gated sodium channels. Resurgent sodium currents, atypical currents that can enhance recovery from inactivation and neuronal firing, are increasingly being recognized as playing potentially important roles in sensory neuron hyperexcitability and pain sensations. Here we discuss unusual sodium channels and currents that have been identified in nociceptive sensory neurons, describe what is known about the molecular determinants of the complex sodium currents in these neurons. Finally, we provide an overview of therapeutic strategies to target voltage-gated sodium currents in nociceptive neurons.
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Affiliation(s)
- C Barbosa
- Indiana University School of Medicine, Indianapolis, IN, United States
| | - T R Cummins
- Indiana University School of Medicine, Indianapolis, IN, United States
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11
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Genes, molecules and patients--emerging topics to guide clinical pain research. Eur J Pharmacol 2013; 716:188-202. [PMID: 23500200 PMCID: PMC3793871 DOI: 10.1016/j.ejphar.2013.01.069] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2012] [Revised: 12/20/2012] [Accepted: 01/09/2013] [Indexed: 01/23/2023]
Abstract
This review selectively explores some areas of pain research that, until recently, have been poorly understood. We have chosen four topics that relate to clinical pain and we discuss the underlying mechanisms and related pathophysiologies contributing to these pain states. A key issue in pain medicine involves crucial events and mediators that contribute to normal and abnormal pain signaling, but remain unseen without genetic, biomarker or imaging analysis. Here we consider how the altered genetic make-up of familial pains reveals the human importance of channels discovered by preclinical research, followed by the contribution of receptors as stimulus transducers in cold sensing and cold pain. Finally we review recent data on the neuro-immune interactions in chronic pain and the potential targets for treatment in cancer-induced bone pain.
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12
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Farmer C, Cox JJ, Fletcher EV, Woods CG, Wood JN, Schorge S. Splice variants of Na(V)1.7 sodium channels have distinct β subunit-dependent biophysical properties. PLoS One 2012; 7:e41750. [PMID: 22911851 PMCID: PMC3404004 DOI: 10.1371/journal.pone.0041750] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2012] [Accepted: 06/25/2012] [Indexed: 12/13/2022] Open
Abstract
Genes encoding the α subunits of neuronal sodium channels have evolutionarily conserved sites of alternative splicing but no functional differences have been attributed to the splice variants. Here, using NaV1.7 as an exemplar, we show that the sodium channel isoforms are functionally distinct when co-expressed with β subunits. The gene, SCN9A, encodes the α subunit of the NaV1.7 channel, and contains both sites of alternative splicing that are highly conserved. In conditions where the intrinsic properties of the NaV1.7 splice variants were similar when expressed alone, co-expression of β1 subunits had different effects on channel availability that were determined by splicing at either site in the α subunit. While the identity of exon 5 determined the degree to which β1 subunits altered voltage-dependence of activation (P = 0.027), the length of exon 11 regulated how far β1 subunits depolarised voltage-dependence of inactivation (P = 0.00012). The results could have a significant impact on channel availability, for example with the long version of exon 11, the co-expression of β1 subunits could lead to nearly twice as large an increase in channel availability compared to channels containing the short version. Our data suggest that splicing can change the way that NaV channels interact with β subunits. Because splicing is conserved, its unexpected role in regulating the functional impact of β subunits may apply to multiple voltage-gated sodium channels, and the full repertoire of β subunit function may depend on splicing in α subunits.
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Affiliation(s)
- Clare Farmer
- UCL Institute of Neurology, Queen Square, London, United Kingdom
| | - James J. Cox
- UCL Wolfson Institute of Biomedical Research, London, United Kingdom
| | - E. V. Fletcher
- UCL Institute of Neurology, Queen Square, London, United Kingdom
| | - C. Geoffrey Woods
- Department of Medical Genetics, Cambridge Institute for Medical Research, Addenbrooke’s Hospital, Cambridge, United Kingdom
| | - John N. Wood
- UCL Wolfson Institute of Biomedical Research, London, United Kingdom
| | - Stephanie Schorge
- UCL Institute of Neurology, Queen Square, London, United Kingdom
- * E-mail:
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13
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Fletcher EV, Kullmann DM, Schorge S. Alternative splicing modulates inactivation of type 1 voltage-gated sodium channels by toggling an amino acid in the first S3-S4 linker. J Biol Chem 2011; 286:36700-8. [PMID: 21890636 PMCID: PMC3196094 DOI: 10.1074/jbc.m111.250225] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Voltage-gated sodium channels underlie the upstroke of action potentials and are fundamental to neuronal excitability. Small changes in the behavior of these channels are sufficient to change neuronal firing and trigger seizures. These channels are subject to highly conserved alternative splicing, affecting the short linker between the third transmembrane segment (S3) and the voltage sensor (S4) in their first domain. The biophysical consequences of this alternative splicing are incompletely understood. Here we focus on type 1 sodium channels (Nav1.1) that are implicated in human epilepsy. We show that the functional consequences of alternative splicing are highly sensitive to recording conditions, including the identity of the major intracellular anion and the recording temperature. In particular, the inactivation kinetics of channels containing the alternate exon 5N are more sensitive to intracellular fluoride ions and to changing temperature than channels containing exon 5A. Moreover, Nav1.1 channels containing exon 5N recover from inactivation more rapidly at physiological temperatures. Three amino acids differ between exons 5A and 5N. However, the changes in sensitivity and stability of inactivation were reproduced by a single conserved change from aspartate to asparagine in channels containing exon 5A, which was sufficient to make them behave like channels containing the complete exon 5N sequence. These data suggest that splicing at this site can modify the inactivation of sodium channels and reveal a possible interaction between splicing and anti-epileptic drugs that stabilize sodium channel inactivation.
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Affiliation(s)
- Emily V Fletcher
- Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, London WC1N 3BG, United Kingdom
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14
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Thompson CH, Kahlig KM, George AL. SCN1A splice variants exhibit divergent sensitivity to commonly used antiepileptic drugs. Epilepsia 2011; 52:1000-9. [PMID: 21453355 DOI: 10.1111/j.1528-1167.2011.03040.x] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
PURPOSE A common genetic variant (rs3812718) in a splice donor consensus sequence within the neuronal sodium channel gene SCN1A (encoding Na(V) 1.1) modulates the proportion of transcripts incorporating either the canonical (5A) or alternative (5N) exon 5. A pharmacogenetic association has been reported whereby increased expression of exon 5N containing Na(V) 1.1 transcripts correlated with lower required doses of phenytoin in epileptics. We tested the hypothesis that SCN1A alternative splicing affects the pharmacology of Na(V) 1.1 channels. METHODS To directly examine biophysical and pharmacologic differences between the exon 5 splice variants, we performed whole-cell patch clamp recording of tsA201 cells transiently coexpressing either Na(V) 1.1-5A or Na(V) 1.1-5N with the β1 and β2 accessory subunits. We examined tonic inhibition and use-dependent inhibition of Na(V) 1.1 splice isoforms by phenytoin, carbamazepine, and lamotrigine. We also examined the effects of phenytoin and lamotrigine on channel biophysical properties and determined concentration-response relationships for both splice variants. KEY FINDINGS We observed no significant differences in voltage dependence of activation, steady-state inactivation, and recovery from inactivation between splice variants. However, Na(V) 1.1-5N channels exhibited enhanced tonic block by phenytoin and lamotrigine compared to Na(V) 1.1-5A. In addition, Na(V) 1.1-5N exhibited enhanced use-dependent block by phenytoin and lamotrigine across a range of stimulation frequencies and concentrations. Phenytoin and lamotrigine induced shifts in steady-state inactivation and recovery from fast inactivation for both splice isoforms. No splice isoform differences were observed for channel inhibition by carbamazepine. SIGNIFICANCE These results suggest Na(V) 1.1 channels containing exon 5N are more sensitive to the commonly used antiepileptic drugs phenytoin and lamotrigine.
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15
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Abstract
Mendelian heritable pain disorders have provided insights into human pain mechanisms and suggested new analgesic drug targets. Interestingly, many of the heritable monogenic pain disorders have been mapped to mutations in genes encoding ion channels. Studies in transgenic mice have also implicated many ion channels in damage sensing and pain modulation. It seems likely that aberrant peripheral or central ion channel activity underlies or initiates many pathological pain conditions. Understanding the mechanistic basis of ion channel malfunction in terms of trafficking, localization, biophysics, and consequences for neurotransmission is a potential route to new pain therapies.
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Affiliation(s)
- Ramin Raouf
- Molecular Nociception Group, Wolfson Institute for Biomedical Research, University College London, UK.
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16
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Lampert A, O'Reilly AO, Reeh P, Leffler A. Sodium channelopathies and pain. Pflugers Arch 2010; 460:249-63. [PMID: 20101409 DOI: 10.1007/s00424-009-0779-3] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2009] [Revised: 12/13/2009] [Accepted: 12/18/2009] [Indexed: 12/19/2022]
Abstract
Chronic pain often represents a severe, debilitating condition. Up to 10% of the worldwide population are affected, and many patients are poorly responsive to current treatment strategies. Nociceptors detect noxious conditions to produce the sensation of pain, and this signal is conveyed to the CNS by means of action potentials. The fast upstroke of action potentials is mediated by voltage-gated sodium channels, of which nine pore-forming alpha-subunits (Nav1.1-1.9) have been identified. Heterogeneous functional properties and distinct expression patterns denote specialized functions of each subunit. The Nav1.7 and Nav1.8 subunits have emerged as key molecules involved in peripheral pain processing and in the development of an increased pain sensitivity associated with inflammation and tissue injury. Several mutations in the SCN9A gene encoding for Nav1.7 have been identified as important cellular substrates for different heritable pain syndromes. This review aims to cover recent progress on our understanding of how biophysical properties of mutant Nav1.7 translate into an aberrant electrogenesis of nociceptors. We also recapitulate the role of Nav1.8 for peripheral pain processing and of additional sodium channelopathies which have been linked to disorders with pain as a significant component.
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Affiliation(s)
- Angelika Lampert
- Department of Physiology and Pathophysiology, Friedrich-Alexander University Erlangen-Nuremberg, Universitätsstrasse 17, 91054, Erlangen, Germany.
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