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Molecular correlates of muscle spindle and Golgi tendon organ afferents. Nat Commun 2021; 12:1451. [PMID: 33649316 PMCID: PMC7977083 DOI: 10.1038/s41467-021-21880-3] [Citation(s) in RCA: 33] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Accepted: 02/18/2021] [Indexed: 12/16/2022] Open
Abstract
Proprioceptive feedback mainly derives from groups Ia and II muscle spindle (MS) afferents and group Ib Golgi tendon organ (GTO) afferents, but the molecular correlates of these three afferent subtypes remain unknown. We performed single cell RNA sequencing of genetically identified adult proprioceptors and uncovered five molecularly distinct neuronal clusters. Validation of cluster-specific transcripts in dorsal root ganglia and skeletal muscle demonstrates that two of these clusters correspond to group Ia MS afferents and group Ib GTO afferent proprioceptors, respectively, and suggest that the remaining clusters could represent group II MS afferents. Lineage analysis between proprioceptor transcriptomes at different developmental stages provides evidence that proprioceptor subtype identities emerge late in development. Together, our data provide comprehensive molecular signatures for groups Ia and II MS afferents and group Ib GTO afferents, enabling genetic interrogation of the role of individual proprioceptor subtypes in regulating motor output. Coordinated movement critically depends on sensory feedback from muscle spindles (MSs) and Golgi tendon organs (GTOs) but the afferents supplying this proprioceptive feedback have remained genetically inseparable. Here the authors use single cell transcriptome analysis to reveal the molecular basis of MS (groups Ia and II) and GTO (group Ib) afferent identities in the mouse.
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2
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Tu NH, Katano T, Matsumura S, Funatsu N, Pham VM, Fujisawa JI, Ito S. Na + /K + -ATPase coupled to endothelin receptor type B stimulates peripheral nerve regeneration via lactate signalling. Eur J Neurosci 2017; 46:2096-2107. [PMID: 28700113 DOI: 10.1111/ejn.13647] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2017] [Revised: 07/07/2017] [Accepted: 07/07/2017] [Indexed: 12/22/2022]
Abstract
We have recently demonstrated that endothelin (ET) is functionally coupled to Nax , a Na+ concentration-sensitive Na+ channel for lactate release via ET receptor type B (ETB R) and is involved in peripheral nerve regeneration in a sciatic nerve transection-regeneration mouse model. Nax is known to interact directly with Na+ /K+ -ATPase, leading to lactate production in the brain. To investigate the role of Na+ /K+ -ATPase in peripheral nerve regeneration, in this study, we applied ouabain, a Na+ /K+ -ATPase inhibitor, to the cut site for 4 weeks with an osmotic pump. While functional recovery and nerve reinnervation to the toe started at 5 weeks after axotomy and were completed by 7 weeks, ouabain delayed them by 2 weeks. The delay by ouabain was improved by lactate, and its effect was blocked by α-cyano-4-hydroxy-cinnamic acid (CIN), a broad monocarboxylate transporter (MCT) inhibitor. In primary cultures of dorsal root ganglia, neurite outgrowth of neurons and lactate release into the culture medium was inhibited by ouabain. Conversely, lactate enhanced the neurite outgrowth, which was blocked by CIN, but not by AR-C155858, a MCT1/2-selective inhibitor. ET-1 and ET-3 increased neurite outgrowth of neurons, which was attenuated by an ETB R antagonist, ouabain and 2 protein kinase C inhibitors. Taken together with the finding that ETB R was expressed in Schwann cells, these results demonstrate that ET enhanced neurite outgrowth of neurons mediated by Na+ /K+ -ATPase via ETB R in Schwann cells. This study suggests that Na+ /K+ -ATPase coupled to the ET-ETB R system plays a critical role in peripheral nerve regeneration via lactate signalling.
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Affiliation(s)
- Nguyen H Tu
- Department of Medical Chemistry, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, 573-1010, Japan
| | - Tayo Katano
- Department of Medical Chemistry, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, 573-1010, Japan
| | - Shinji Matsumura
- Department of Medical Chemistry, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, 573-1010, Japan
| | - Nobuo Funatsu
- Department of Medical Chemistry, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, 573-1010, Japan
| | - Vuong Minh Pham
- Department of Medical Chemistry, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, 573-1010, Japan
| | - Jun-Ichi Fujisawa
- Department of Microbiology, Kansai Medical University, Hirakata, Japan
| | - Seiji Ito
- Department of Medical Chemistry, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, 573-1010, Japan
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3
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Qi FH, Zhou YL, Xu GY. Targeting voltage-gated sodium channels for treatment for chronic visceral pain. World J Gastroenterol 2011; 17:2357-64. [PMID: 21633634 PMCID: PMC3103787 DOI: 10.3748/wjg.v17.i19.2357] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/14/2010] [Revised: 03/16/2011] [Accepted: 03/23/2011] [Indexed: 02/06/2023] Open
Abstract
Voltage-gated sodium channels (VGSCs) play a fundamental role in controlling cellular excitability, and their abnormal activity is related to several pathological processes, including cardiac arrhythmias, epilepsy, neurodegenerative diseases, spasticity and chronic pain. In particular, chronic visceral pain, the central symptom of functional gastrointestinal disorders such as irritable bowel syndrome, is a serious clinical problem that affects a high percentage of the world population. In spite of intense research efforts and after the dedicated decade of pain control and research, there are not many options to treat chronic pain conditions. However, there is a wealth of evidence emerging to give hope that a more refined approach may be achievable. By using electronic databases, available data on structural and functional properties of VGSCs in chronic pain, particularly functional gastrointestinal hypersensitivity, were reviewed. We summarize the involvement and molecular bases of action of VGSCs in the pathophysiology of several organic and functional gastrointestinal disorders. We also describe the efficacy of VGSC blockers in the treatment of these neurological diseases, and outline future developments that may extend the therapeutic use of compounds that target VGSCs. Overall, clinical and experimental data indicate that isoform-specific blockers of these channels or targeting of their modulators may provide effective and novel approaches for visceral pain therapy.
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4
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Salazar BC, Castaño S, Sánchez JC, Romero M, Recio-Pinto E. Ganglioside GD1a increases the excitability of voltage-dependent sodium channels. Brain Res 2004; 1021:151-8. [PMID: 15342262 DOI: 10.1016/j.brainres.2004.06.055] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/10/2004] [Indexed: 11/30/2022]
Abstract
The effect of the negatively charged ganglioside GD1a, one of the major brain gangliosides [H. Beitinger, W. Probst, R. Hilbig, H. Rahmann, Seasonal variability of sialo-glycoconjugates in the brain of the Djungarian hamster (Phodopus sungorus). Comp. Biochem. Physiol., B 86 (1987) 377-384] on the function of brain derived BTX-modified voltage-dependent sodium channel was studied using the planar lipid bilayer system. Bilayers were formed either with a mixture of neutral phospholipids (4 phosphoethanolamine (PE):1 phosphocholine (PC)) alone or with one containing 6% of the disialoganglioside GD1a. The permeation and activation properties of the channels were measured in the presence of symmetrical 200 mM NaCl. We found that the single channel conductance was not affected by GD1a, whereas the steady-state activation curve displayed a hyperpolarizing shift in the presence of GD1a. Since the lipid distribution in these membranes is symmetrical, then the GD1a effect on sodium channels may result either from an induction of channel conformational changes or from an asymmetrical interaction between the channel (extracellular vs. intracellular channel aspect) and GD1a. Regardless of the mechanism, the data indicate that differences in ganglioside content in neuronal cells may contribute to the previously observed sodium channel functional variability within (soma, dentritic, axon hillock) and between neuronal cells as well as to excitability changes in those physiological and pathological conditions where changes in the neuronal ganglioside content occur.
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Affiliation(s)
- Blanca C Salazar
- Centro de Estudios Cerebrales, Universidad del Valle, Calle 4B No.36-00, Barrio San Fernando, Cali, Colombia.
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5
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Castillo C, Thornhill WB, Zhu J, Recio-Pinto E. The permeation and activation properties of brain sodium channels change during development. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2003; 144:99-106. [PMID: 12888221 DOI: 10.1016/s0165-3806(03)00164-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
BTX-modified sodium channels from 15-day embryonic (E15) rat forebrains were studied in planar lipid bilayers. Compared to postnatal sodium channels, E15 channels had a lower maximal single channel conductance, whereas their permeation pathway sensed a comparable surface charge density and had a similar apparent binding affinity for sodium ions. The steady-state activation curve of E15 channels was significantly more hyperpolarized and had a shallower slope than postnatal channels. The apparent BTX binding affinity was significantly lower for E15 channels than for postnatal channels. Finally, E15 channel alpha-subunits displayed a lower apparent molecular weight, and a lower sialylation level than postnatal sodium channel alpha-subunits. Together with previous studies, our data suggested that the observed functional differences between E15 and postnatal voltage-dependent sodium channels cannot be explained solely by the observed differences in channel sialylation, and hence they also appeared to reflect the presence of other channel structural differences.
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Affiliation(s)
- Cecilia Castillo
- Instituto de Estudios Avanzados, Apartado 17606, 1015-A, Caracas, Venezuela.
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6
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Baker MD. Electrophysiology of mammalian Schwann cells. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2002; 78:83-103. [PMID: 12429109 DOI: 10.1016/s0079-6107(02)00007-x] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Schwann cells are the satellite cell of the peripheral nervous system, and they surround axons and motor nerve terminals. The review summarises evidence for the ion channels expressed by mammalian Schwann cells, their molecular nature and known or speculated functions. In addition, the recent evidence for gap junctions and cytoplasmic diffusion pathways within the myelin and the functional consequences of a lower-resistance myelin sheath are discussed. The main types of ion channel expressed by Schwann cells are K(+) channels, Cl(-) channels, Na(+) channels and Ca(2+) channels. Each is represented by a variety of sub-types. The molecular and biophysical characteristics of the cation channels expressed by Schwann cells are closely similar or identical to those of channels expressed in peripheral axons and elsewhere. In addition, Schwann cells express P(2)X ligand-gated ion channels. Possible in vivo roles for each ion channel type are discussed. Ion channel expression in culture could have a special function in driving or controlling cell proliferation and recent evidence indicates that some Ca(2+) channel and Kir channel expression in culture is dependent upon the presence of neurones and local electrical activity.
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Affiliation(s)
- Mark D Baker
- Molecular Nociception Group, Department of Biology, University College London, Gower Street, London WC1E 6BT, UK.
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7
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Abstract
Na(v)2/NaG is a putative sodium channel, whose physiological role has long been an enigma. We generated Na(v)2 gene-deficient mice by inserting the lacZ gene. Analysis of the targeted mice allowed us to identify Na(v)2-producing cells by examining the lacZ expression. Besides in the lung, heart, dorsal root ganglia, and Schwann cells in the peripheral nervous system, Na(v)2 was expressed in neurons and ependymal cells in restricted areas of the CNS, particularly in the circumventricular organs, which are involved in body-fluid homeostasis. Under water-depleted conditions, c-fos expression was markedly elevated in neurons in the subfornical organ and organum vasculosum laminae terminalis compared with wild-type animals, suggesting a hyperactive state in the Na(v)2-null mice. Moreover, the null mutants showed abnormal intakes of hypertonic saline under both water- and salt-depleted conditions. These findings suggest that the Na(v)2 channel plays an important role in the central sensing of body-fluid sodium level and regulation of salt intake behavior.
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8
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COWARD K, MOSAHEBI A, PLUMPTON C, FACER P, BIRCH R, TATE S, BOUNTRA C, TERENGHI G, ANAND P. Immunolocalisation of sodium channel NaG in the intact and injured human peripheral nervous system. J Anat 2001; 198:175-80. [PMID: 11273042 PMCID: PMC1468209 DOI: 10.1046/j.1469-7580.2001.19820175.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The voltage-gated 'glial' sodium channel NaG belongs to a distinct molecular class within the multi-gene family of mammalian sodium channels. Originally found in central and peripheral glia, NaG has since been detected in neurons in rat dorsal root ganglia (DRG) and may play a role in Schwann cell-axon interactions. We have studied the presence of NaG-like immunoreactivity in the intact and injured human peripheral nervous system using a specific affinity-purified antibody. Nerve fibres in normal and injured peripheral nerves and normal skin exhibited intense NaG-immunoreactivity. Numerous NaG-immunoreactive nerve fibres surrounded neuronal cell bodies within postmortem control DRG, and in DRG avulsed from the spinal cord (i.e. after traumatic central axotomy). There were no significant differences in the pattern of NaG immunostaining between control and avulsed DRG, or with delay after injury. Generally, the neuronal cell bodies were only very weakly immunoreactive to NaG, indicating that the NaG immunoreactivity was predominantly in Schwann cells/myelin. In accord, we demonstrated NaG immunostaining in cultured human and rat Schwann cells, and in distal nerve after wallerian degeneration. NaG thus appears to be a useful new marker for Schwann cells in the human PNS, and a role in neuropathy deserves investigation.
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Affiliation(s)
- K.
COWARD
- Peripheral Neuropathy Unit, Imperial College School of Medicine, Hammersmith Hospital Campus, London
| | - A.
MOSAHEBI
- Blond McIndoe Laboratories, University Department of Surgery, Royal Free and University College Medical School, Royal Free Campus, London
| | - C.
PLUMPTON
- Molecular Pharmacology, GlaxoWellcome Research & Development, Medicines Research Centre, Stevenage, Hertfordshire
| | - P.
FACER
- Peripheral Neuropathy Unit, Imperial College School of Medicine, Hammersmith Hospital Campus, London
| | - R.
BIRCH
- Peripheral Nerve Injury Unit, Royal National Orthopaedic Hospital, Stanmore, Middlesex, UK
| | - S.
TATE
- Molecular Pharmacology, GlaxoWellcome Research & Development, Medicines Research Centre, Stevenage, Hertfordshire
| | - C.
BOUNTRA
- Neurosciences Unit, GlaxoWellcome Research & Development, Medicines Research Centre, Stevenage, Hertfordshire
| | - G.
TERENGHI
- Blond McIndoe Laboratories, University Department of Surgery, Royal Free and University College Medical School, Royal Free Campus, London
| | - P.
ANAND
- Peripheral Neuropathy Unit, Imperial College School of Medicine, Hammersmith Hospital Campus, London
- Correspondence to Professor P. Anand, Peripheral Neuropathy Unit, Imperial College School of Medicine, Hammersmith Hospital, Du Cane Road, London, W12 ONN, UK. Tel.: 020 8383 3309/19; fax: 020 8383 3363/4; e-mail:
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9
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Abstract
Functional and molecular analysis of glial voltage- and ligand-gated ion channels underwent tremendous boost over the last 15 years. The traditional image of the glial cell as a passive, structural element of the nervous system was transformed into the concept of a plastic cell, capable of expressing a large variety of ion channels and neurotransmitter receptors. These molecules might enable glial cells to sense neuronal activity and to integrate it within glial networks, e.g., by means of spreading calcium waves. In this review we shall give a comprehensive summary of the main functional properties of ion channels and ionotropic receptors expressed by macroglial cells, i.e., by astrocytes, oligodendrocytes and Schwann cells. In particular we will discuss in detail glial sodium, potassium and anion channels, as well as glutamate, GABA and ATP activated ionotropic receptors. A majority of available data was obtained from primary cell culture, these results have been compared with corresponding studies that used acute tissue slices or freshly isolated cells. In view of these data, an active glial participation in information processing seems increasingly likely and a physiological role for some of the glial channels and receptors is gradually emerging.
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Affiliation(s)
- A Verkhratsky
- School of Biological Sciences, The University of Manchester, Oxford Road, Manchester, UK.
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10
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Waxman SG. The neuron as a dynamic electrogenic machine: modulation of sodium-channel expression as a basis for functional plasticity in neurons. Philos Trans R Soc Lond B Biol Sci 2000; 355:199-213. [PMID: 10724456 PMCID: PMC1692729 DOI: 10.1098/rstb.2000.0559] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Neurons signal each other via regenerative electrical impulses (action potentials) and thus can be thought of as electrogenic machines. Voltage-gated sodium channels produce the depolarizations necessary for action potential activity in most neurons and, in this respect, lie close to the heart of the electrogenic machinery. Although classical neurophysiological doctrine accorded 'the' sodium channel a crucial role in electrogenesis, it is now clear that nearly a dozen genes encode distinct sodium channels with different molecular structures and functional properties, and the majority of these channels are expressed within the mammalian nervous system. The transcription of these sodium-channel genes, and the deployment of the channels that they encode, can change significantly within neurons following various injuries. Moreover, the transcription of these genes and the deployment of various types of sodium channels within neurons of the normal nervous system can change markedly as neurons respond to changing milieus or physiological inputs. As a result of these changes in sodium-channel expression, the membranes of neurons may be retuned so as to alter their transductive and/or encoding properties. Neurons within the normal and injured nervous system can thus function as dynamic electrogenic machines with electroresponsive properties that change not only in response to pathological insults, but also in response to shifting functional needs.
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Affiliation(s)
- S G Waxman
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06510, USA.
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11
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Poiraud E, Gruszczynski C, Porteu A, Cambier H, Escurat M, Koulakoff A, Kahn A, Berwald-Netter Y, Gautron S. The Na-G ion channel is transcribed from a single promoter controlled by distinct neuron- and Schwann cell-specific DNA elements. J Neurochem 1999; 73:2575-85. [PMID: 10582621 DOI: 10.1046/j.1471-4159.1999.0732575.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Na-G is a putative sodium (or cationic) channel expressed in neurons and glia of the PNS, in restricted neuronal subpopulations of the brain, and in several tissues outside the nervous system, like lung and adrenal medulla. To analyze the mechanisms underlying tissue-specific expression of this channel, we isolated the 5' region of the corresponding gene and show that Na-G mRNA transcription proceeds from a single promoter with multiple initiation sites. By transgenic mice studies, we demonstrate that 600 bp containing the Na-G proximal promoter region and the first exon are sufficient to drive the expression of a beta-galactosidase reporter gene in neurons of both CNS and PNS, whereas expression in Schwann cells depends on more remote DNA elements lying in the region between -6,500 and -1,050 bp upstream of the main transcription initiation sites. Crucial elements for lung-specific expression seem to be located in the region between -1,050 and -375 bp upstream of the promoter. Using in vivo footprint experiments, we demonstrate that several sites of the Na-G proximal promoter region are bound specifically by nuclear proteins in dorsal root ganglion neurons, as compared with nonexpressing hepatoma cells.
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MESH Headings
- Animals
- Base Sequence
- Central Nervous System/metabolism
- DNA Footprinting
- DNA, Complementary/genetics
- Exons/genetics
- Ganglia, Spinal/metabolism
- Genes, Reporter
- Liver/metabolism
- Lung/metabolism
- Mice
- Mice, Transgenic
- Molecular Sequence Data
- Muscles/metabolism
- Nerve Tissue Proteins/biosynthesis
- Nerve Tissue Proteins/genetics
- Neurons/metabolism
- Neurons, Afferent/metabolism
- Nuclear Proteins/metabolism
- Organ Specificity
- Peripheral Nervous System/metabolism
- Promoter Regions, Genetic
- RNA, Messenger/biosynthesis
- Rats
- Rats, Inbred F344
- Recombinant Fusion Proteins/biosynthesis
- Regulatory Sequences, Nucleic Acid
- Schwann Cells/metabolism
- Sodium Channels/biosynthesis
- Sodium Channels/genetics
- Transcription, Genetic
- Voltage-Gated Sodium Channels
- beta-Galactosidase/biosynthesis
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Affiliation(s)
- E Poiraud
- Biochimie Cellulaire, CNRS UPR 9065, Collège de France, Paris
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12
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Waxman SG. The molecular pathophysiology of pain: abnormal expression of sodium channel genes and its contributions to hyperexcitability of primary sensory neurons. Pain 1999; Suppl 6:S133-S140. [PMID: 10491982 DOI: 10.1016/s0304-3959(99)00147-5] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Although hyperexcitability and/or increased baseline sensitivity of primary sensory neurons following nerve injury can lead to abnormal burst activity associated with pain, the molecular mechanisms that contribute to it are not fully understood. Early studies demonstrated that, following axonal injury, neurons can display changes in excitability suggesting increased sodium channel expression. Consistent with this, abnormal accumulations of sodium channels have been observed at the tips of injured axons. But we now know that nearly a dozen distinct sodium channels are encoded by different genes, raising the question, what types of sodium channels underlie hyperexcitability of primary sensory neurons following injury? My laboratory has used molecular, electrophysiological, and pharmacological techniques to answer this question. Our studies have demonstrated that multiple sodium channels, with distinct physiological properties, are expressed within small dorsal root ganglion (DRG) neurons, which include nociceptive cells. Several DRG and trigeminal neuron-specific sodium channels have now been cloned and sequenced. There is a dramatic change in sodium channel expression in DRG neurons, with down-regulation of the SNS/PN3 and NaN sodium channel genes and up-regulation of previously silent Type III sodium channel gene, following injury to the axons of these cells. These changes in sodium channel gene expression can produce electrophysiological changes in DRG neurons which poise them to fire spontaneously or at inappropriate high frequencies. We have also observed changes in sodium channel gene expression in experimental models of inflammatory pain. The dynamic nature of sodium channel gene expression in DRG neurons, and the changes which occur in sodium channel and sodium current expression in these cells following axonal injury and in inflammatory pain models, suggest that abnormal expression of sodium channels contributes to the molecular pathophysiology of pain.
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Affiliation(s)
- Stephen G Waxman
- Department of Neurology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06510 and PVA/EPVA Neuroscience Research Center and Rehabilitation Research Center, VA Medical Center, West Haven, CT 06516, USA
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13
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Abstract
Although it is well established that hyperexcitability and/or increased baseline sensitivity of primary sensory neurons can lead to abnormal burst activity associated with pain, the underlying molecular mechanisms are not fully understood. Early studies demonstrated that, after injury to their axons, neurons can display changes in excitability, suggesting increased sodium channel expression, and, in fact, abnormal sodium channel accumulation has been observed at the tips of injured axons. We have used an ensemble of molecular, electrophysiological, and pharmacological techniques to ask: what types of sodium channels underlie hyperexcitability of primary sensory neurons after injury? Our studies demonstrate that multiple sodium channels, with distinct electrophysiological properties, are encoded by distinct mRNAs within small dorsal root ganglion (DRG) neurons, which include nociceptive cells. Moreover, several DRG neuron-specific sodium channels now have been cloned and sequenced. After injury to the axons of DRG neurons, there is a dramatic change in sodium channel expression in these cells, with down-regulation of some sodium channel genes and up-regulation of another, previously silent sodium channel gene. This plasticity in sodium channel gene expression is accompanied by electrophysiological changes that poise these cells to fire spontaneously or at inappropriate high frequencies. Changes in sodium channel gene expression also are observed in experimental models of inflammatory pain. Thus, sodium channel expression in DRG neurons is dynamic, changing significantly after injury. Sodium channels within primary sensory neurons may play an important role in the pathophysiology of pain.
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Affiliation(s)
- S G Waxman
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06510, USA
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14
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Dib-Hajj SD, Tyrrell L, Black JA, Waxman SG. NaN, a novel voltage-gated Na channel, is expressed preferentially in peripheral sensory neurons and down-regulated after axotomy. Proc Natl Acad Sci U S A 1998; 95:8963-8. [PMID: 9671787 PMCID: PMC21185 DOI: 10.1073/pnas.95.15.8963] [Citation(s) in RCA: 407] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Although physiological and pharmacological evidence suggests the presence of multiple tetrodotoxin-resistant (TTX-R) Na channels in neurons of peripheral nervous system ganglia, only one, SNS/PN3, has been identified in these cells to date. We have identified and sequenced a novel Na channel alpha-subunit (NaN), predicted to be TTX-R and voltage-gated, that is expressed preferentially in sensory neurons within dorsal root ganglia (DRG) and trigeminal ganglia. The predicted amino acid sequence of NaN can be aligned with the predicted structure of known Na channel alpha-subunits; all relevant landmark sequences, including positively charged S4 and pore-lining SS1-SS2 segments, and the inactivation tripeptide IFM, are present at predicted positions. However, NaN exhibits only 42-53% similarity to other mammalian Na channels, including SNS/PN3, indicating that it is a novel channel, and suggesting that it may represent a third subfamily of Na channels. NaN transcript levels are reduced significantly 7 days post axotomy in DRG neurons, consistent with previous findings of a reduction in TTX-R Na currents. The preferential expression of NaN in DRG and trigeminal ganglia and the reduction of NaN mRNA levels in DRG after axonal injury suggest that NaN, together with SNS/PN3, may produce TTX-R currents in peripheral sensory neurons and may influence the generation of electrical activity in these cells.
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Affiliation(s)
- S D Dib-Hajj
- Department of Neurology, LCI 707, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06510, USA
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15
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Fjell J, Dib-Hajj S, Fried K, Black JA, Waxman SG. Differential expression of sodium channel genes in retinal ganglion cells. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 1997; 50:197-204. [PMID: 9406935 DOI: 10.1016/s0169-328x(97)00187-3] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Action potential electrogenesis in the axons of retinal ganglion cells is supported by voltage-gated sodium channels, and a tetrodotoxin (TTX)-inhibitable sodium conductance participates in anoxic injury of these axons within the optic nerve. However, the subtypes of sodium channels expressed in retinal ganglion cells have not been identified. In this study, we used reverse transcription-polymerase chain reaction (RT-PCR) and restriction enzyme mapping, together with in situ hybridization, to examine the expression of transcripts for sodium channel alpha-subunits I, II, III, NaG, Na6, hNE/PN1 and SNS, and beta-subunits 1 and 2, in the retina of the adult rat. RT-PCR yielded high levels of amplification of I, II, III, Na6, beta1 and beta2 transcripts. In situ hybridization demonstrated the presence of all these mRNAs in the cell bodies of retinal ganglion cells. Retinal ganglion cells thus express multiple sodium channel mRNAs, suggesting that they deploy several different types of sodium channels.
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Affiliation(s)
- J Fjell
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06510, USA
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