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Caldito EG, Kaul S, Caldito NG, Piette W, Mehta S. Erythromelalgia. Part I: Pathogenesis, clinical features, evaluation, and complications. J Am Acad Dermatol 2024; 90:453-462. [PMID: 37364617 DOI: 10.1016/j.jaad.2023.02.071] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Revised: 01/27/2023] [Accepted: 02/12/2023] [Indexed: 06/28/2023]
Abstract
Erythromelalgia is a rare pain disorder that is underrecognized and difficult-to-treat. It is characterized by episodes of extremity erythema and pain that can be disabling; it may be genetic, related to an underlying systemic disease, or idiopathic. Considering the prominent cutaneous features characteristic of the condition, dermatologists can play an important role in early recognition and limitation of morbidity. The first article in this 2-part continuing medical education series reviews the epidemiology, pathogenesis, clinical manifestations, evaluation, and complications.
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Affiliation(s)
| | - Subuhi Kaul
- Division of Dermatology, John H Stroger Hospital of Cook County, Chicago, Illinois
| | | | - Warren Piette
- Division of Dermatology, John H Stroger Hospital of Cook County, Chicago, Illinois; Department of Dermatology, Rush University Medical Center, Chicago, Illinois
| | - Shilpa Mehta
- Division of Dermatology, John H Stroger Hospital of Cook County, Chicago, Illinois.
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Nájera-Chávez BC, Seeber L, Goldhahn K, Panzer A. Use of Sodium Channel Blockers in the Thr226Met Pathologic Variant of SCN1A: A Case Report. Neuropediatrics 2023; 54:417-421. [PMID: 37467773 PMCID: PMC10643020 DOI: 10.1055/a-2133-5343] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/04/2022] [Accepted: 03/09/2023] [Indexed: 07/21/2023]
Abstract
The Thr226Met pathologic variant of the SCN1A gene has been associated with the clinical development of an early infantile developmental and epileptic encephalopathy (EIDEE) different from Dravet's syndrome. The electrophysiological mechanisms of the mutated channel lead to a paradoxical gain and loss of function. The use of sodium channel blockers (SCB) that counteract this gain of function has been described in previous studies and they can be safely administered to patients carrying mutations in other sodium channel subtypes without causing a worsening of seizures. We report the use of SCB in a child harboring the Thr226Met pathologic variant of SCN1A with early-onset pharmaco-resistant migrating seizures, as well as developmental delay. Lacosamide led to a dramatic reduction in seizure frequency; however, only a mild improvement in the epileptic activity depicted by electroencephalography (EEG) was achieved. The introduction of carbamazepine as an add-on therapy led to a notable reduction in epileptic activity via EEG and to an improvement in sensorimotor development. Despite the overall clinical improvement, the patient developed febrile seizures and a nonepileptic jerking of the right hand. In this case of EIDEE with the Thr226Met variant, we demonstrate a beneficial pharmacological intervention of SCB in contrast to findings described in current literature. Our report encourages the cautious use of SCB at early stages of the disease in patients carrying this pathologic variant.
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Affiliation(s)
| | - Lea Seeber
- Epilepsy Center - Neuropediatrics, DRK Kliniken Berlin, Westend, Germany
| | - Klaus Goldhahn
- Epilepsy Center - Neuropediatrics, DRK Kliniken Berlin, Westend, Germany
| | - Axel Panzer
- Epilepsy Center - Neuropediatrics, DRK Kliniken Berlin, Westend, Germany
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Fu M, Ji X, Zhong L, Wu Q, Li H, Wang N. [Expression changes of Na V channel subunits correlate with developmental maturation of electrophysiological characteristics of rat cerebellar Purkinje neurons]. Nan Fang Yi Ke Da Xue Xue Bao 2023; 43:1102-1109. [PMID: 37488792 PMCID: PMC10366519 DOI: 10.12122/j.issn.1673-4254.2023.07.06] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 07/26/2023]
Abstract
OBJECTIVE To investigate the variations in the expression of voltage-gated sodium (Nav) channel subunits during development of rat cerebellar Purkinje neurons and their correlation with maturation of electrophysiological characteristics of the neurons. METHODS We observed the changes in the expression levels of NaV1.1, 1.2, 1.3 and 1.6 during the development of Purkinje neurons using immunohistochemistry in neonatal (5-7 days after birth), juvenile (12-14 days), adolescent (21-24 days), and adult (42-60 days) SD rats. Using whole-cell patch-clamp technique, we recorded the spontaneous electrical activity of the neurons in ex vivo brain slices of rats of different ages to analyze the changes of electrophysiological characteristics of these neurons during development. RESULTS The expression of NaV subunits in rat cerebellar Purkinje neurons showed significant variations during development. NaV1.1 subunit was highly expressed throughout the developmental stages and increased progressively with age (P < 0.05). NaV1.2 expression was not detected in the neurons in any of the developmental stages (P > 0.05). The expression level of NaV1.3 decreased with development and became undetectable after adolescence (P < 0.05). NaV1.6 expression was not detected during infancy, but increased with further development (P < 0.05). NaV1.1 and NaV1.3 were mainly expressed in the early stages of development. With the maturation of the rats, NaV1.3 expression disappeared and NaV1.6 expression increased in the neurons. NaV1.1 and NaV1.6 were mainly expressed after adolescence. The total NaV protein level increased gradually with development (P < 0.05) and tended to stabilize after adolescence. The spontaneous frequency and excitability of the Purkinje neurons increased gradually with development and reached the mature levels in adolescence. The developmental expression of NaV subunits was positively correlated with discharge frequency (r=0.9942, P < 0.05) and negatively correlated with the excitatory threshold of the neurons (r=0.9891, P < 0.05). CONCLUSION The changes in the expression levels of NaV subunits are correlated with the maturation of high frequency electrophysiological properties of the neurons, suggesting thatmature NaV subunit expressions is the basis of maturation of electrophysiological characteristics of the neurons.
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Affiliation(s)
- M Fu
- Department of Physiology, School of Basic Medical Sciences, Southern Medical University, Guangzhou 510515, China
| | - X Ji
- Department of Quality Management, Nanfang Hospital, Southern Medical University, Guangzhou 510515, China
| | - L Zhong
- Disease Control Department, 74th Army Group Hospital of PLA, Guangzhou 510300, China
| | - Q Wu
- Department of Basic Medicine, Guangdong Jiangmen Chinese Medicine College, Jiangmen 529000, China
| | - H Li
- Department of Mathematical Physics, School of Biomedical Engineering, Southern Medical University, Guangzhou 510515, China
| | - N Wang
- Department of Physiology, School of Basic Medical Sciences, Southern Medical University, Guangzhou 510515, China
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Montero-Dominguez PA, Corzo G. Characterization of the coupling mechanism of scorpion β-neurotoxins on the voltage-gated sodium channel hNav1.6. J Biomol Struct Dyn 2023; 41:14419-14427. [PMID: 36812246 DOI: 10.1080/07391102.2023.2181629] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2022] [Accepted: 02/12/2023] [Indexed: 02/24/2023]
Abstract
Scorpion β-neurotoxins represent a pharmacological group that affects voltage-gated sodium channels (Nav). Despite knowing the electrophysiological effect of these toxins on Nav channels, the molecular mechanism by which the union is carried out is still undetermined. In this study, computational techniques such as modeling, docking and molecular dynamics were used to elucidate the mechanism of interaction between scorpion β-neurotoxins using the neurotoxin nCssII and its recombinant variant CssII-RCR, which bind to the site-4, an extracellular receptor, of the human sodium channel hNav1.6. Different modes of interaction were observed for both toxins, where the main distinguishing feature was the interaction generated by the residue E15 on such site-4; that is, E15 in nCssII exhibits an interaction with the voltage-sensing domain II, and the same residue E15 of CssII-RCR exhibits an interaction with domain III. Despite this difference in interaction by E15, it is seen that both neurotoxins interact with similar regions of the voltage sensing domain such as the S3-S4 connecting loop (L834-E838) of the hNav1.6. Our simulations present a first approach to the mode of interaction of scorpion beta-neurotoxins in toxin-receptor complexes, being able to explain at the molecular level the phenomenon of voltage sensor entrapment generated by these toxins.Communicated by Ramaswamy H. Sarma.
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Affiliation(s)
- Pavel Andrei Montero-Dominguez
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca Mor, México
| | - Gerardo Corzo
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca Mor, México
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Williams J, Cowlishaw R, Sanou A, Ranson H, Grigoraki L. In vivo functional validation of the V402L voltage gated sodium channel mutation in the malaria vector An. gambiae. Pest Manag Sci 2022; 78:1155-1163. [PMID: 34821465 DOI: 10.1002/ps.6731] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Revised: 11/19/2021] [Accepted: 11/25/2021] [Indexed: 06/13/2023]
Abstract
BACKGROUND Pyrethroids are the most widely used insecticides for the control of malaria transmitting Anopheles gambiae mosquitoes and rapid increase in resistance to this insecticide class is of major concern. Pyrethroids target the Voltage Gated Sodium Channels (VGSCs), that have a key role in the normal function of the mosquitoes' nervous system. VGSC mutations L995F and L995S have long been associated with pyrethroid resistance and screening for their presence is routine in insecticide resistance management programs. Recently, a VGSC haplotype containing two amino acid substitutions associated with resistance in other species, V402L and I1527T, was identified. These two VGSC mutations are found in tight linkage and are mutually exclusive to the classical L995F/S mutations. RESULTS We identify the presence of the V402L-I1527T haplotype in resistant An. coluzzii colonized strains and in field populations from Burkina Faso, at frequencies higher than previously reported; in some cases almost reaching fixation. Functional validation of V402L in insecticide resistance using a CRISPR/Cas9 genome modified line showed that it confers reduced mortality after exposure to all tested pyrethroids and DDT, but at lower levels compared to L995F. In contrast to L995F however, no fitness costs were identified for mosquitoes carrying V402L under laboratory conditions. CONCLUSION The V402L substitution confers pyrethroid resistance in An. gambiae in the absence of any other VGSC substitution and/or alternative resistance mechanisms. The lower fitness cost associated with this kdr mutation may provide a selective advantage over the classical kdr in some settings and genotyping at this locus should be added in the list of resistant alleles for routine screening.
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Affiliation(s)
- Jessica Williams
- Vector Biology Department, Liverpool School of Tropical Medicine, Liverpool, UK
| | - Ruth Cowlishaw
- Vector Biology Department, Liverpool School of Tropical Medicine, Liverpool, UK
| | - Antoine Sanou
- Service Scientifique et Technique, Centre National de Recherche et de Formation sur le Paludisme, Ouagadougou, Burkina Faso
| | - Hilary Ranson
- Vector Biology Department, Liverpool School of Tropical Medicine, Liverpool, UK
| | - Linda Grigoraki
- Vector Biology Department, Liverpool School of Tropical Medicine, Liverpool, UK
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Horváth B, Hézső T, Kiss D, Kistamás K, Magyar J, Nánási PP, Bányász T. Late Sodium Current Inhibitors as Potential Antiarrhythmic Agents. Front Pharmacol 2020; 11:413. [PMID: 32372952 PMCID: PMC7184885 DOI: 10.3389/fphar.2020.00413] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2019] [Accepted: 03/18/2020] [Indexed: 12/19/2022] Open
Abstract
Based on recent findings, an increased late sodium current (INa,late) plays an important pathophysiological role in cardiac diseases, including rhythm disorders. The article first describes what is INa,late and how it functions under physiological circumstances. Next, it shows the wide range of cellular mechanisms that can contribute to an increased INa,late in heart diseases, and also discusses how the upregulated INa,late can play a role in the generation of cardiac arrhythmias. The last part of the article is about INa,late inhibiting drugs as potential antiarrhythmic agents, based on experimental and preclinical data as well as in the light of clinical trials.
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Affiliation(s)
- Balázs Horváth
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
- Faculty of Pharmacy, University of Debrecen, Debrecen, Hungary
| | - Tamás Hézső
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Dénes Kiss
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Kornél Kistamás
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - János Magyar
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
- Division of Sport Physiology, University of Debrecen, Debrecen, Hungary
| | - Péter P. Nánási
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
- Department of Dental Physiology and Pharmacology, Faculty of Dentistry, University of Debrecen, Debrecen, Hungary
| | - Tamás Bányász
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
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Silva JJ, Scott JG. Conservation of the voltage-sensitive sodium channel protein within the Insecta. Insect Mol Biol 2020; 29:9-18. [PMID: 31206812 DOI: 10.1111/imb.12605] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2019] [Revised: 06/04/2019] [Accepted: 06/10/2019] [Indexed: 06/09/2023]
Abstract
The voltage-sensitive sodium channel (VSSC) is essential for the generation and propagation of action potentials. VSSC kinetics can be modified by producing different splice variants. The functionality of VSSC depends on features such as the voltage sensors, the selectivity filter and the inactivation loop. Mutations in Vssc conferring resistance to pyrethroid insecticides are known as knockdown resistance (kdr). We analysed the conservation of VSSC in both a broad scope and a narrow scope by three approaches: (1) we compared conservation of sequences and of differential exon use across orders of the Insecta; (2) we determined which kdr mutations were possible with a single nucleotide mutation in nine populations of Aedes aegypti; and (3) we examined the individual VSSC variation that exists within a population of Drosophila melanogaster. There is an increasing amount of transcript diversity possible from Diplura towards Diptera. The residues of the voltage sensors, selectivity filter and inactivation loop are highly conserved. The majority of exon sequences were >88.6% similar. Strain-specific differences in codon constraints exist for kdr mutations in nine strains of A. aegypti. Three Vssc mutations were found in one population of D. melanogaster. This study shows that, overall, Vssc is highly conserved across Insecta and within a population of an insect, but that important differences do exist.
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Affiliation(s)
- Juan J Silva
- Department of Entomology, Comstock Hall, Cornell University, Ithaca, NY, USA
| | - Jeffrey G Scott
- Department of Entomology, Comstock Hall, Cornell University, Ithaca, NY, USA
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Abstract
Erythromelalgia (EM) is a rare disorder characterized by erythematous, warm, painful extremities, which is often precipitated by cold conditions. The pathophysiology of EM is incompletely understood. Recent investigations have identified sodium channelopathy as a genetic cause for this pain condition, classified as primary inherited EM. Other subtypes are idiopathic EM and secondary EM. The management of pain in EM is challenging as no single therapy has been found to be effective. There is varying response to pharmacotherapy and significant variability within this clinical population, resulting in a stepwise trial and error approach. Consequently, EM is often associated with poorer health-related quality of life with higher morbidity. There is currently no consensus or guidelines on management of pain in EM. This is a review of the literature on management of pain using pharmacologic, procedural intervention and nonpharmacologic treatment in children and adults with EM.
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Affiliation(s)
- See Wan Tham
- Seattle Children's Research Institute, Seattle, WA, USA,
- Department of Anesthesiology and Pain Medicine, University of Washington School of Medicine, Seattle, WA, USA,
| | - Marian Giles
- Seattle Children's Research Institute, Seattle, WA, USA,
- Department of Anesthesiology and Pain Medicine, University of Washington School of Medicine, Seattle, WA, USA,
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Hockley JRF, González-Cano R, McMurray S, Tejada-Giraldez MA, McGuire C, Torres A, Wilbrey AL, Cibert-Goton V, Nieto FR, Pitcher T, Knowles CH, Baeyens JM, Wood JN, Winchester WJ, Bulmer DC, Cendán CM, McMurray G. Visceral and somatic pain modalities reveal Na V 1.7-independent visceral nociceptive pathways. J Physiol 2017; 595:2661-2679. [PMID: 28105664 DOI: 10.1113/jp272837] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2016] [Accepted: 01/16/2017] [Indexed: 12/17/2022] Open
Abstract
KEY POINTS Voltage-gated sodium channels play a fundamental role in determining neuronal excitability. Specifically, voltage-gated sodium channel subtype NaV 1.7 is required for sensing acute and inflammatory somatic pain in mice and humans but its significance in pain originating from the viscera is unknown. Using comparative behavioural models evoking somatic and visceral pain pathways, we identify the requirement for NaV 1.7 in regulating somatic (noxious heat pain threshold) but not in visceral pain signalling. These results enable us to better understand the mechanisms underlying the transduction of noxious stimuli from the viscera, suggest that the investigation of pain pathways should be undertaken in a modality-specific manner and help to direct drug discovery efforts towards novel visceral analgesics. ABSTRACT Voltage-gated sodium channel NaV 1.7 is required for acute and inflammatory pain in mice and humans but its significance for visceral pain is unknown. Here we examine the role of NaV 1.7 in visceral pain processing and the development of referred hyperalgesia using a conditional nociceptor-specific NaV 1.7 knockout mouse (NaV 1.7Nav1.8 ) and selective small-molecule NaV 1.7 antagonist PF-5198007. NaV 1.7Nav1.8 mice showed normal nociceptive behaviours in response to intracolonic application of either capsaicin or mustard oil, stimuli known to evoke sustained nociceptor activity and sensitization following tissue damage, respectively. Normal responses following induction of cystitis by cyclophosphamide were also observed in both NaV 1.7Nav1.8 and littermate controls. Loss, or blockade, of NaV 1.7 did not affect afferent responses to noxious mechanical and chemical stimuli in nerve-gut preparations in mouse, or following antagonism of NaV 1.7 in resected human appendix stimulated by noxious distending pressures. However, expression analysis of voltage-gated sodium channel α subunits revealed NaV 1.7 mRNA transcripts in nearly all retrogradely labelled colonic neurons, suggesting redundancy in function. By contrast, using comparative somatic behavioural models we identify that genetic deletion of NaV 1.7 (in NaV 1.8-expressing neurons) regulates noxious heat pain threshold and that this can be recapitulated by the selective NaV 1.7 antagonist PF-5198007. Our data demonstrate that NaV 1.7 (in NaV 1.8-expressing neurons) contributes to defined pain pathways in a modality-dependent manner, modulating somatic noxious heat pain, but is not required for visceral pain processing, and advocate that pharmacological block of NaV 1.7 alone in the viscera may be insufficient in targeting chronic visceral pain.
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Affiliation(s)
- James R F Hockley
- Neuroscience and Pain Research Unit, Pfizer Ltd., The Portway Building, Granta Science Park, Cambridge, CB21 6GS, UK
| | - Rafael González-Cano
- Department of Pharmacology, Biomedical Research Centre (CIBM) and Institute of Neuroscience, Faculty of Medicine, University of Granada, Granada, Spain
| | - Sheridan McMurray
- Neuroscience and Pain Research Unit, Pfizer Ltd., The Portway Building, Granta Science Park, Cambridge, CB21 6GS, UK
| | - Miguel A Tejada-Giraldez
- Department of Pharmacology, Biomedical Research Centre (CIBM) and Institute of Neuroscience, Faculty of Medicine, University of Granada, Granada, Spain
| | - Cian McGuire
- National Centre for Bowel Research and Surgical Innovation, Blizard Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, London, E1 2AT, UK
| | - Antonio Torres
- Department of Biochemistry, Biomedical Research Centre (CIBM) and Institute of Neuroscience, Faculty of Medicine, University of Granada, Granada, Spain
| | - Anna L Wilbrey
- Neuroscience and Pain Research Unit, Pfizer Ltd., The Portway Building, Granta Science Park, Cambridge, CB21 6GS, UK
| | - Vincent Cibert-Goton
- National Centre for Bowel Research and Surgical Innovation, Blizard Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, London, E1 2AT, UK
| | - Francisco R Nieto
- Department of Pharmacology, Biomedical Research Centre (CIBM) and Institute of Neuroscience, Faculty of Medicine, University of Granada, Granada, Spain
| | - Thomas Pitcher
- Neuroscience and Pain Research Unit, Pfizer Ltd., The Portway Building, Granta Science Park, Cambridge, CB21 6GS, UK
| | - Charles H Knowles
- National Centre for Bowel Research and Surgical Innovation, Blizard Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, London, E1 2AT, UK
| | - José Manuel Baeyens
- Department of Pharmacology, Biomedical Research Centre (CIBM) and Institute of Neuroscience, Faculty of Medicine, University of Granada, Granada, Spain
| | - John N Wood
- Molecular Nociception Group, Department of Biology, University College London, Gower Street, London, WC1E 6BT, UK
| | - Wendy J Winchester
- Neuroscience and Pain Research Unit, Pfizer Ltd., The Portway Building, Granta Science Park, Cambridge, CB21 6GS, UK
| | - David C Bulmer
- National Centre for Bowel Research and Surgical Innovation, Blizard Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, London, E1 2AT, UK
| | - Cruz Miguel Cendán
- Department of Pharmacology, Biomedical Research Centre (CIBM) and Institute of Neuroscience, Faculty of Medicine, University of Granada, Granada, Spain
| | - Gordon McMurray
- Neuroscience and Pain Research Unit, Pfizer Ltd., The Portway Building, Granta Science Park, Cambridge, CB21 6GS, UK
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Leterrier C, Clerc N, Rueda-Boroni F, Montersino A, Dargent B, Castets F. Ankyrin G Membrane Partners Drive the Establishment and Maintenance of the Axon Initial Segment. Front Cell Neurosci 2017; 11:6. [PMID: 28184187 PMCID: PMC5266712 DOI: 10.3389/fncel.2017.00006] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2016] [Accepted: 01/12/2017] [Indexed: 11/13/2022] Open
Abstract
The axon initial segment (AIS) is a highly specialized neuronal compartment that plays a key role in neuronal development and excitability. It concentrates multiple membrane proteins such as ion channels and cell adhesion molecules (CAMs) that are recruited to the AIS by the scaffold protein ankyrin G (ankG). The crucial function of ankG in the anchoring of AIS membrane components is well established, but a reciprocal role of membrane partners in ankG targeting and stabilization remained elusive. In rat cultured hippocampal neurons and cortical organotypic slices, we found that shRNA-mediated knockdown of ankG membrane partners (voltage-gated sodium channels (Nav) or neurofascin-186) led to a decrease of ankG concentration and perturbed the AIS formation and maintenance. These effects were rescued by expressing a recombinant AIS-targeted Nav or by a minimal construct containing the ankyrin-binding domain of Nav1.2 and a membrane anchor (mABD). Moreover, overexpressing mABD in mature neurons led to ankG mislocalization. Altogether, these results demonstrate that a tight and precocious association of ankG with its membrane partners is a key step for the establishment and maintenance of the AIS.
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Affiliation(s)
| | - Nadine Clerc
- CNRS, CRN2M, Aix Marseille University Marseille, France
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Venkatesan K, Liu Y, Goldfarb M. Fast-onset long-term open-state block of sodium channels by A-type FHFs mediates classical spike accommodation in hippocampal pyramidal neurons. J Neurosci 2014; 34:16126-39. [PMID: 25429153 DOI: 10.1523/JNEUROSCI.1271-14.2014] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Classical accommodation is a form of spike frequency adaptation in neurons whereby excitatory drive results in action potential output of gradually decreasing frequency. Here we describe an essential molecular component underlying classical accommodation in juvenile mouse hippocampal CA1 pyramidal neurons. A-type isoforms of fibroblast growth factor homologous factors (FHFs) bound to axosomatic voltage-gated sodium channels bear an N-terminal blocking particle that drives some associated channels into a fast-onset, long-term inactivated state. Use-dependent accumulating channel blockade progressively elevates spike voltage threshold and lengthens interspike intervals. The FHF particle only blocks sodium channels from the open state, and mutagenesis studies demonstrate that this particle uses multiple aliphatic and cationic residues to both induce and maintain the long-term inactivated state. The broad expression of A-type FHFs in neurons throughout the vertebrate CNS suggests a widespread role of these sodium channel modulators in the control of neural firing.
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Xiao M, Bosch MK, Nerbonne JM, Ornitz DM. FGF14 localization and organization of the axon initial segment. Mol Cell Neurosci 2013; 56:393-403. [PMID: 23891806 DOI: 10.1016/j.mcn.2013.07.008] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Revised: 06/26/2013] [Accepted: 07/21/2013] [Indexed: 01/26/2023] Open
Abstract
The axon initial segment (AIS) is highly enriched in the structural proteins ankyrin G and βIV-spectrin, the pore-forming (α) subunits of voltage-gated sodium (Nav) channels, and functional Nav channels, and is critical for the initiation of action potentials. We previously reported that FGF14, a member of the intracellular FGF (iFGF) sub-family, is expressed in cerebellar Purkinje neurons and that the targeted inactivation of Fgf14 in mice (Fgf14(-/-)) results in markedly reduced Purkinje neuron excitability. Here, we demonstrate that FGF14 immunoreactivity is high in the AIS of Purkinje neurons and is distributed in a decreasing, proximal to distal, gradient. This pattern is evident early in the postnatal development of Purkinje neurons and is also observed in many other types of central neurons. In (Scn8a(med)) mice, which are deficient in expression of the Nav1.6 α subunit, FGF14 immunoreactivity is markedly increased and expanded in the Purkinje neuron AIS, in parallel with increased expression of the Nav1.1 (Scn1a) α subunit and expanded expression of βIV-spectrin. Although Nav1.1, FGF14, and βIV-spectrin are affected, ankyrin G immunoreactivity at the AIS of Scn8a(med) and wild type (WT) Purkinje neurons was not significantly different. In Fgf14(-/-) Purkinje neurons, βIV-spectrin and ankyrin G immunoreactivity at the AIS were also similar to WT Purkinje neurons, although both the Nav1.1 and Nav1.6 α subunits are modestly, but significantly (p<0.005), reduced within sub-domains of the AIS, changes that may contribute to the reduced excitability of Fgf14(-/-) Purkinje neurons.
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Affiliation(s)
- Maolei Xiao
- Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO 63110, USA
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Sandalon S, Könnecke B, Levkovitch-Verbin H, Simons M, Hein K, Sättler MB, Bähr M, Ofri R. Functional and structural evaluation of lamotrigine treatment in rat models of acute and chronic ocular hypertension. Exp Eye Res 2013; 115:47-56. [PMID: 23810807 DOI: 10.1016/j.exer.2013.06.018] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2013] [Revised: 06/08/2013] [Accepted: 06/17/2013] [Indexed: 10/26/2022]
Abstract
Voltage gated sodium channels (Nav), are proposed mediators of neuronal damage in ischemic and excitotoxicity disease models. We evaluated the neuroprotective effects of lamotrigine, a Nav blocker, in the acute and chronic rat ocular hypertension models. Additionally, expression of the main Nav subtypes in the optic nerve (ON) was assessed to test whether their upregulation plays a role in the pathogenesis of ocular hypertension induced optic neuropathy. Unilateral intraocular pressure (IOP) elevation was induced for 60 min (80 mmHg) and 14-21 days (670-859 mmHg*day) in the acute and chronic models, respectively. Lamotrigine was administered at dosages of 10 mg/kg twice daily and 12.5 mg/kg once daily in the acute (n = 9) and chronic (n = 11) trials, respectively. Treatment began 2 days prior to IOP elevation until sacrifice. Outer and inner retinal function was evaluated with dark- and light-adapted flash electroretinography and pattern electroretinography, respectively, 6 and 14 days post acute IOP elevation and 13, 28 and 48 days post chronic IOP elevation. Retinal ganglion cell and axon densities and inflammatory reaction were evaluated through Fluorogold, Bielschowsky's silver impregnation and ED1 labeling respectively. Immunohistochemistry for Nav1.1, 1.2 and 1.6 was performed in ONs of untreated rats 7 and 15 days post IOP elevation in the acute model and after 7, 28 and 50 days in the chronic model. In the acute model, no differences were found in the a-wave amplitudes between lamotrigine-treated and vehicle-treated rats. B-wave amplitudes decreased by 40-66% in both treatment groups 6 days post IOP elevation, with no significant difference between groups (p = 0.38). However, a partial recovery of b-wave amplitudes was found in lamotrigine-treated rats between day 6 and day 14 post procedure (p < 0.05). No differences were found in any other parameter tested in this model. Similarly, lamotrigine treatment did not result in any beneficial effect in structural parameters of the chronic model. Functional evaluation of this model was inconclusive due to super-normal values in the hypertensive eyes. Up-regulation of Nav1.1 and 1.2 expression was found in both models, beginning by day 7; an increase of the former continued in a time-dependent manner in the chronic model. Nav1.6 labeling was inconclusive. In conclusion we found lamotrigine treatment to be mostly ineffective in both acute and chronic ocular hypertension models.
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Affiliation(s)
- Shai Sandalon
- Koret School of Veterinary Medicine, The R.H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel
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