1
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Wu C, Wang M, Wang X, Li W, Li S, Chen B, Niu S, Tai H, Pan H, Zhang Z. The genetic and phenotypic spectra of adult genetic leukoencephalopathies in a cohort of 309 patients. Brain 2023; 146:2364-2376. [PMID: 36380532 PMCID: PMC10232248 DOI: 10.1093/brain/awac426] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Revised: 09/30/2022] [Accepted: 11/01/2022] [Indexed: 08/12/2023] Open
Abstract
Genetic leukoencephalopathies (gLEs) are a highly heterogeneous group of rare genetic disorders. The spectrum of gLEs varies among patients of different ages. Distinct from the relatively more abundant studies of gLEs in children, only a few studies that explore the spectrum of adult gLEs have been published, and it should be noted that the majority of these excluded certain gLEs. Thus, to date, no large study has been designed and conducted to characterize the genetic and phenotypic spectra of gLEs in adult patients. We recruited a consecutive series of 309 adult patients clinically suspected of gLEs from Beijing Tiantan Hospital between January 2014 and December 2021. Whole-exome sequencing, mitochondrial DNA sequencing and repeat analysis of NOTCH2NLC, FMR1, DMPK and ZNF9 were performed for patients. We describe the genetic and phenotypic spectra of the set of patients with a genetically confirmed diagnosis and summarize their clinical and radiological characteristics. A total of 201 patients (65%) were genetically diagnosed, while 108 patients (35%) remained undiagnosed. The most frequent diseases were leukoencephalopathies related to NOTCH3 (25%), NOTCH2NLC (19%), ABCD1 (9%), CSF1R (7%) and HTRA1 (5%). Based on a previously proposed pathological classification, the gLEs in our cohort were divided into leukovasculopathies (35%), leuko-axonopathies (31%), myelin disorders (21%), microgliopathies (7%) and astrocytopathies (6%). Patients with NOTCH3 mutations accounted for 70% of the leukovasculopathies, followed by HTRA1 (13%) and COL4A1/2 (9%). The leuko-axonopathies contained the richest variety of associated genes, of which NOTCH2NLC comprised 62%. Among myelin disorders, demyelinating leukoencephalopathies (61%)-mainly adrenoleukodystrophy and Krabbe disease-accounted for the majority, while hypomyelinating leukoencephalopathies (2%) were rare. CSF1R was the only mutated gene detected in microgliopathy patients. Leukoencephalopathy with vanishing white matter disease due to mutations in EIF2B2-5 accounted for half of the astrocytopathies. We characterized the genetic and phenotypic spectra of adult gLEs in a large Chinese cohort. The most frequently mutated genes were NOTCH3, NOTCH2NLC, ABCD1, CSF1R and HTRA1.
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Affiliation(s)
- Chujun Wu
- Department of Neurology, Beijing Tiantan Hospital, Capital Medical University, 100070 Beijing, China
- China National Clinical Research Centre for Neurological Disease, Beijing Tiantan Hospital, Capital Medical University, 100070 Beijing, China
| | - Mengwen Wang
- Department of Neurology and Institute of Neurology of First Affiliated Hospital, Institute of Neuroscience, and Fujian Key Laboratory of Molecular Neurology, Fujian Medical University, 350005 Fuzhou, China
| | - Xingao Wang
- Department of Neurology, Beijing Tiantan Hospital, Capital Medical University, 100070 Beijing, China
- China National Clinical Research Centre for Neurological Disease, Beijing Tiantan Hospital, Capital Medical University, 100070 Beijing, China
| | - Wei Li
- Department of Neurology, Beijing Tiantan Hospital, Capital Medical University, 100070 Beijing, China
- China National Clinical Research Centre for Neurological Disease, Beijing Tiantan Hospital, Capital Medical University, 100070 Beijing, China
| | - Shaowu Li
- Department of Neurology, Beijing Tiantan Hospital, Capital Medical University, 100070 Beijing, China
- China National Clinical Research Centre for Neurological Disease, Beijing Tiantan Hospital, Capital Medical University, 100070 Beijing, China
| | - Bin Chen
- Department of Neurology, Beijing Tiantan Hospital, Capital Medical University, 100070 Beijing, China
- China National Clinical Research Centre for Neurological Disease, Beijing Tiantan Hospital, Capital Medical University, 100070 Beijing, China
| | - Songtao Niu
- Department of Neurology, Beijing Tiantan Hospital, Capital Medical University, 100070 Beijing, China
- China National Clinical Research Centre for Neurological Disease, Beijing Tiantan Hospital, Capital Medical University, 100070 Beijing, China
| | - Hongfei Tai
- Department of Neurology, Beijing Tiantan Hospital, Capital Medical University, 100070 Beijing, China
- China National Clinical Research Centre for Neurological Disease, Beijing Tiantan Hospital, Capital Medical University, 100070 Beijing, China
| | - Hua Pan
- Department of Neurology, Beijing Tiantan Hospital, Capital Medical University, 100070 Beijing, China
- China National Clinical Research Centre for Neurological Disease, Beijing Tiantan Hospital, Capital Medical University, 100070 Beijing, China
| | - Zaiqiang Zhang
- Department of Neurology, Beijing Tiantan Hospital, Capital Medical University, 100070 Beijing, China
- China National Clinical Research Centre for Neurological Disease, Beijing Tiantan Hospital, Capital Medical University, 100070 Beijing, China
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2
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Kaur S, Zhang X, Patel S, Rodriguez YA, Luther KJ, Alghafli G, Lang RM, Abrams CK, Dobrowsky RT. Pharmacologic Targeting of the C-Terminus of Heat Shock Protein 90 Improves Neuromuscular Function in Animal Models of Charcot Marie Tooth X1 Disease. ACS Pharmacol Transl Sci 2023; 6:306-319. [PMID: 36798471 PMCID: PMC9926526 DOI: 10.1021/acsptsci.2c00223] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Indexed: 01/22/2023]
Abstract
Charcot-Marie-Tooth X1 (CMTX1) disease is an inherited peripheral neuropathy that arises from loss-of-function mutations in the protein connexin 32 (Cx32). CMTX1 currently lacks a pharmacologic approach toward disease management, and we have previously shown that modulating the expression of molecular chaperones using novologue therapy may provide a viable disease-modifying approach to treat metabolic and demyelinating neuropathies. Cemdomespib is an orally bioavailable novologue that manifests neuroprotective activity by modulating the expression of heat shock protein 70 (Hsp70). We examined if 1 to 5 months of daily cemdomespib therapy may improve neuropathic symptoms in three mouse models of CMTX1 (Cx32 deficient (Cx32def), T55I-Cx32def, and R75W-Cx32 mice). Daily drug therapy significantly improved motor nerve conduction velocity (MNCV) and grip strength in all three models, but the compound muscle action potential was only improved in Cx32def mice. Drug efficacy required Hsp70 as improvements in MNCV, and the grip strength was abrogated in Cx32def × Hsp70 knockout mice. Five months of novologue therapy was associated with improved neuromuscular junction morphology, femoral motor nerve myelination, reduction in foamy macrophages, and a decrease in Schwann cell c-jun levels. To determine if c-jun may be downstream of Hsp70 and necessary for drug efficacy, c-jun expression was specifically deleted in Schwann cells of Cx32def mice. While the deletion of c-jun worsened the neuropathy, cemdomespib therapy remained effective in improving MNCV and grip strength. Our data show that cemdomespib therapy improves CMTX1-linked neuropathy in an Hsp70-dependent but a c-jun-independent manner and without regard to the nature of the underlying Cx32 mutation.
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Affiliation(s)
- Sukhmanjit Kaur
- Department
of Pharmacology and Toxicology, University
of Kansas, Lawrence, Kansas 66045, United States
| | - Xinyue Zhang
- Department
of Pharmacology and Toxicology, University
of Kansas, Lawrence, Kansas 66045, United States
| | - Sugandha Patel
- Department
of Pharmacology and Toxicology, University
of Kansas, Lawrence, Kansas 66045, United States
| | - Yssa A. Rodriguez
- Department
of Pharmacology and Toxicology, University
of Kansas, Lawrence, Kansas 66045, United States
| | - Kylie J. Luther
- Department
of Pharmacology and Toxicology, University
of Kansas, Lawrence, Kansas 66045, United States
| | - Ghufran Alghafli
- Department
of Pharmacology and Toxicology, University
of Kansas, Lawrence, Kansas 66045, United States
| | - Ryan M. Lang
- Department
of Pharmacology and Toxicology, University
of Kansas, Lawrence, Kansas 66045, United States
| | - Charles K. Abrams
- Department
of Neurology and Rehabilitation and Biomedical Engineering, College
of Medicine, University of Illinois Chicago, Chicago, Illinois 60612, United States
| | - Rick T. Dobrowsky
- Department
of Pharmacology and Toxicology, University
of Kansas, Lawrence, Kansas 66045, United States
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3
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Abrams CK, Lancaster E, Li JJ, Dungan G, Gong D, Scherer SS, Freidin MM. Knock-in mouse models for CMTX1 show a loss of function phenotype in the peripheral nervous system. Exp Neurol 2023; 360:114277. [PMID: 36403785 DOI: 10.1016/j.expneurol.2022.114277] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Revised: 10/28/2022] [Accepted: 11/16/2022] [Indexed: 11/20/2022]
Abstract
The X-linked form of Charcot-Marie-Tooth disease (CMTX1) is the second most common form of CMT. In this study we used CRISPR/Cas9 to develop new "knock-in" models of CMTX1 that are more representative of the spectrum of mutations seen with CMTX1 than the Cx32 knockout (KO) mouse model used previously. We compared mice of four genotypes - wild-type, Cx32KO, p.T55I, and p.R75W. Sciatic motor conduction velocity slowing was the most robust electrophysiologic indicator of neuropathy, showing reductions in the Cx32KO by 3 months and in the p.T55I and p.R75W mice by 6 months. At both 6 and 12 months, all three mutant genotypes showed reduced four limb and hind limb grip strength compared to WT mice. Performance on 6 and 12 mm width balance beams revealed deficits that were most pronounced at on the 6 mm balance beam at 6 months of age. There were pathological changes of myelinated axons in the femoral motor nerve in all three mutant lines by 3 months of age, and these became more pronounced at 6 and 12 months of age; sensory nerves (femoral sensory and the caudal nerve of the tail) appeared normal at all ages examined. Our results demonstrate that mice can be used to show the pathogenicity of human GJB1 mutations, and these new models for CMTX1 should facilitate the preclinical work for developing treatments for CMTX1.
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Affiliation(s)
- Charles K Abrams
- Department of Neurology and Rehabilitation, College of Medicine, University of Illinois at Chicago, 912 South Wood Street, Chicago, IL 60657, USA; Richard and Loan Hill Department of Biomedical Engineering, University of Illinois at Chicago, USA.
| | - Eunjoo Lancaster
- Department of Neurology, The Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA..
| | - Jian J Li
- Department of Neurology, The Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA..
| | - Gabriel Dungan
- Department of Neurology and Rehabilitation, College of Medicine, University of Illinois at Chicago, 912 South Wood Street, Chicago, IL 60657, USA
| | - David Gong
- Richard and Loan Hill Department of Biomedical Engineering, University of Illinois at Chicago, USA.
| | - Steven S Scherer
- Department of Neurology, The Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA..
| | - Mona M Freidin
- Department of Neurology and Rehabilitation, College of Medicine, University of Illinois at Chicago, 912 South Wood Street, Chicago, IL 60657, USA.
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4
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Chu F, Xu J, Wang Y, Li Y, Wang Y, Liu Z, Li C. Novel mutations in GJB1 trigger intracellular aggregation and stress granule formation in X-linked Charcot-Marie-Tooth Disease. Front Neurosci 2022; 16:972288. [PMID: 36225735 PMCID: PMC9548587 DOI: 10.3389/fnins.2022.972288] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2022] [Accepted: 09/05/2022] [Indexed: 11/16/2022] Open
Abstract
X-linked Charcot-Marie-Tooth Disease type 1(CMT1X) is the second most common form of inherited peripheral neuropathy that is caused by mutations in the gap junction beta-1 (GJB1) gene. Using targeted exome-sequencing, we investigated four CMT families from central-southern China and identified two novel missense variants (p.F31S and p.W44G) and two previously reported variants (p.R220Pfs*23 and p.R164Q) of GJB1. All four probands presented typical early-onset peripheral neuropathy, of which the R220Pfs*23 carrier also had neurologic manifestations in the central nervous system. We then constructed GJB1 expression vectors and performed cell biological analysis in vitro. Expression of FLAG-tagged GJB1 at various time points after transfection revealed evident protein aggregation with both wild-type and mutant forms, indicated with immunostaining and immunoblotting. Detergent-based sequential fractionation confirmed that all mutants were higher expressed and more prone to aggregate than the wild-type, whereas the R220Pfs*23 mutant showed the greatest amount of SDS-soluble multimers and monomers among groups. Moreover, intracellular aggregation probably occurs in the endoplasmic reticulum compartment rather than the Golgi apparatus. Gap junction plaques were present in all groups and were only compromised in frameshift mutant. Further evidence reveals significant intracellular stress granule formation induced by mutated GJB1 and impaired cell viability indicative of cytotoxicity of self-aggregates. Together, our findings demonstrate novel GJB1 variants-induced cell stress and dysfunction and provide insights into understanding the pathomechanisms of GJB1-CMTX1 and other related disorders.
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Affiliation(s)
- Fan Chu
- Department of Medical Genetics, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Jiaming Xu
- Department of Neurology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Yong Wang
- Department of Neurology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Yingjie Li
- Department of Medical Genetics, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Yaling Wang
- Department of Neurology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Zhijun Liu
- Department of Neurology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Chuanzhou Li
- Department of Medical Genetics, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
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5
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Activation of the unfolded protein response by Connexin47 mutations associated with Pelizaeus-Merzbacher-like disease. Mol Cell Neurosci 2022; 120:103716. [PMID: 35276347 DOI: 10.1016/j.mcn.2022.103716] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Revised: 02/26/2022] [Accepted: 02/28/2022] [Indexed: 11/23/2022] Open
Abstract
Pelizaeus-Merzbacher-like disease type 1 (PMLD1) is a hypomyelinating disorder arising in patients with mutations in GJC2, encoding Connexin47 (Cx47). PMLD1 causes nystagmus, cerebellar ataxia, spasticity and changes in CNS white matter detected by MRI. At least one mutation (p.I33M) yields a much milder phenotype, spastic paraplegia type 44 (SPG44). Cx47 contributes to gap junction communication channels between oligodendrocytes (OLs), the myelinating cells in the central nervous system (CNS), and between OLs and astrocytes. Prior studies in cell lines have shown that PMLD1 mutants such as p.P87S display defective protein trafficking, intracellular retention in the ER and loss-of-function. Here we show that when expressed in primary OLs, three PMLD1 associated mutants (p.P87S, p.Y269D and p.M283T) show ER retention of Cx47 and evidence of activation of the cellular stress (unfolded protein response, UPR) and apoptotic pathways. On the other hand, the milder SPG44 associated mutation p.I33M shows a wild-type-like subcellular distribution and no activation of the UPR or apoptotic pathways. These studies provide new insight into a potential element of toxic gain of function underlying the mechanism of PMLD1 that should help guide future therapeutic approaches.
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6
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Abstract
Demyelinating forms of Charcot-Marie-Tooth disease (CMT) are genetically and phenotypically heterogeneous and result from highly diverse biological mechanisms including gain of function (including dominant negative effects) and loss of function. While no definitive treatment is currently available, rapid advances in defining the pathomechanisms of demyelinating CMT have led to promising pre-clinical studies, as well as emerging clinical trials. Especially promising are the recently completed pre-clinical genetic therapy studies in PMP-22, GJB1, and SH3TC2-associated neuropathies, particularly given the success of similar approaches in humans with spinal muscular atrophy and transthyretin familial polyneuropathy. This article focuses on neuropathies related to mutations in PMP-22, MPZ, and GJB1, which together comprise the most common forms of demyelinating CMT, as well as on select rarer forms for which promising treatment targets have been identified. Clinical characteristics and pathomechanisms are reviewed in detail, with emphasis on therapeutically targetable biological pathways. Also discussed are the challenges facing the CMT research community in its efforts to advance the rapidly evolving biological insights to effective clinical trials. These considerations include the limitations of currently available animal models, the need for personalized medicine approaches/allele-specific interventions for select forms of demyelinating CMT, and the increasing demand for optimal clinical outcome assessments and objective biomarkers.
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Affiliation(s)
- Vera Fridman
- Department of Neurology, University of Colorado Anschutz Medical Campus, 12631 E 17th Avenue, Mailstop B185, Room 5113C, Aurora, CO, 80045, USA.
| | - Mario A Saporta
- Department of Neurology, University of Miami Miller School of Medicine, Miami, FL, USA
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7
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Liu X, Duan X, Zhang Y, Sun A, Fan D. Cross-Sectional Study in a Large Cohort of Chinese Patients With GJB1 Gene Mutations. Front Neurol 2020; 11:690. [PMID: 32903794 PMCID: PMC7438869 DOI: 10.3389/fneur.2020.00690] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2020] [Accepted: 06/09/2020] [Indexed: 11/24/2022] Open
Abstract
Charcot-Marie-Tooth (CMT) disease is a clinically and genetically heterogeneous group of inherited neuropathies. The GJB1 gene is the pathogenic gene of CMTX1. In this study, we screened a cohort of 465 unrelated Chinese CMT patients from years 2007 to 2019 and 650 controls by direct Sanger sequencing in GJB1 gene or targeted next-generation sequencing (NGS) or whole-exome sequencing (WES). A bidirectional Sanger sequencing would be performed on the 600 bases in the upstream promoter region and 30 bases in the 3′ untranslated region (UTR), if no mutation was found in the coding region of GJB1 of the patient. According to the results, 24 missense mutations, 4 nonsense mutation, 1 entire deletion, 1 intronic mutation, and 4 frameshift mutations in GJB1 were identified. Three of them were novel mutations (c.104 T>C, c.658-659 ins C, and c.811 del G). Moreover, central nervous system involvement was observed in five patients carrying mutations of R15W, V95M, R142W, R164W, and E186K. Our findings expand the mutational spectrum of the GJB1 gene in CMT patients. We also explored the genotype–phenotype correlation according to the collected information in this study. NGS panels for detecting inherited neuropathy should cover the non-coding region of GJB1.
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Affiliation(s)
- Xiaoxuan Liu
- Department of Neurology, Peking University Third Hospital, Beijing, China
| | - Xiaohui Duan
- Department of Neurology, China-Japan Friendship Hospital, Beijing, China
| | - Yingshuang Zhang
- Department of Neurology, Peking University Third Hospital, Beijing, China
| | - Aping Sun
- Department of Neurology, Peking University Third Hospital, Beijing, China
| | - Dongsheng Fan
- Department of Neurology, Peking University Third Hospital, Beijing, China.,Key Laboratory for Neuroscience, Ministry of Education/National Health Commission, Peking University, Beijing, China
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8
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Papaneophytou C, Georgiou E, Kleopa KA. The role of oligodendrocyte gap junctions in neuroinflammation. Channels (Austin) 2020; 13:247-263. [PMID: 31232168 PMCID: PMC6602578 DOI: 10.1080/19336950.2019.1631107] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
Gap junctions (GJs) provide channels for direct cell-to-cell connectivity serving the homeostasis in several organs of vertebrates including the central (CNS) and peripheral (PNS) nervous systems. GJs are composed of connexins (Cx), which show a highly distinct cellular and subcellular expression pattern. Oligodendrocytes, the myelinating cells of the CNS, are characterized by extensive GJ connectivity with each other as well as with astrocytes. The main oligodendrocyte connexins forming these GJ channels are Cx47 and Cx32. The importance of these channels has been highlighted by the discovery of human diseases caused by mutations in oligodendrocyte connexins, manifesting with leukodystrophy or transient encephalopathy. Experimental models have provided further evidence that oligodendrocyte GJs are essential for CNS myelination and homeostasis, while a strong inflammatory component has been recognized in the absence of oligodendrocyte connexins. Further studies revealed that connexins are also disrupted in multiple sclerosis (MS) brain, and in experimental models of induced inflammatory demyelination. Moreover, induced demyelination was more severe and associated with higher degree of CNS inflammation in models with oligodendrocyte GJ deficiency, suggesting that disrupted connexin expression in oligodendrocytes is not only a consequence but can also drive a pro-inflammatory environment in acquired demyelinating disorders such as MS. In this review, we summarize the current insights from human disorders as well as from genetic and acquired models of demyelination related to oligodendrocyte connexins, with the remaining challenges and perspectives.
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Affiliation(s)
- Christos Papaneophytou
- a Neuroscience Laboratory, The Cyprus Institute of Neurology and Genetics and Cyprus School of Molecular Medicine , Nicosia , Cyprus.,b Department of Life and Health Sciences, School of Sciences and Engineering , University of Nicosia , Nicosia , Cyprus
| | - Elena Georgiou
- a Neuroscience Laboratory, The Cyprus Institute of Neurology and Genetics and Cyprus School of Molecular Medicine , Nicosia , Cyprus
| | - Kleopas A Kleopa
- a Neuroscience Laboratory, The Cyprus Institute of Neurology and Genetics and Cyprus School of Molecular Medicine , Nicosia , Cyprus.,c Neurology Clinics , the Cyprus Institute of Neurology and Genetics, and the Cyprus School of Molecular Medicine , Nicosia , Cyprus
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9
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Gouvea SP, Tomaselli PJ, Barretto LS, Perina KCB, Nyshyama FS, Nicolau N, Lourenço CM, Marques W. New novel mutations in Brazilian families with X-linked Charcot-Marie-Tooth disease. J Peripher Nerv Syst 2019; 24:207-212. [PMID: 31119804 DOI: 10.1111/jns.12327] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2019] [Revised: 05/20/2019] [Accepted: 05/20/2019] [Indexed: 11/29/2022]
Abstract
Mutations in the GJB1 gene are the second most frequent cause of Charcot-Marie-Tooth disease (CMT), accounting for approximately 10% of CMT cases worldwide. We retrospectively analyzed detailed clinical and neurophysiological data on four Brazilian families carrying novel mutations of the GJB1 gene. Mutations were identified by bidirectional Sanger sequence analysis on the GJB1 coding region. We identified a total of 12 subjects from four different kindred. There was no male-to-male transmission, and their clinical pictures were within the expected spectrum for GJB1-related neuropathy. Males were more severely affected than females. Five out of the eight females only had subclinical neuropathy. Nerve conduction velocities were in the intermediate range in the male patients and higher in the females affected. These mutations increase the genotypic variability associated with GJB1.
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Affiliation(s)
- Silmara P Gouvea
- Neurogenetics, Department of Neurosciences and Behavioral Sciences, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil
| | - Pedro J Tomaselli
- Neuromuscular Section, University Hospital of Ribeirão Preto, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil
| | - Luiza S Barretto
- Neuromuscular Section, University Hospital of Ribeirão Preto, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil
| | - Keity C B Perina
- Neurogenetics, Department of Neurosciences and Behavioral Sciences, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil
| | - Fulviana S Nyshyama
- Neurogenetics, Department of Neurosciences and Behavioral Sciences, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil
| | - Nilson Nicolau
- Institute of Genetics and Biochemistry, Federal University of Uberlândia, Uberlândia, Brazil
| | - Charles M Lourenço
- Neurogenetics, Department of Neurosciences and Behavioral Sciences, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil
- Neuromuscular Section, University Hospital of Ribeirão Preto, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil
| | - Wilson Marques
- Neurogenetics, Department of Neurosciences and Behavioral Sciences, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil
- Neuromuscular Section, University Hospital of Ribeirão Preto, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil
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10
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Luo S, Jin H, Chen J, Zhang L. A Novel Variant in Non-coding Region of GJB1 Is Associated With X-Linked Charcot-Marie-Tooth Disease Type 1 and Transient CNS Symptoms. Front Neurol 2019; 10:413. [PMID: 31068899 PMCID: PMC6491636 DOI: 10.3389/fneur.2019.00413] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2018] [Accepted: 04/04/2019] [Indexed: 11/27/2022] Open
Abstract
X-linked Charcot-Marie-Tooth disease type 1 (CMTX1) is a dominantly inherited peripheral neuropathy and is caused by mutations in gap junction beta 1 gene (GJB1). Here, a novel variant of c.-170T>G in GJB1 was identified in a large Chinese CMTX1 pedigree. The proband presented transient “stroke-like” episodes in addition to the peripheral neuropathy. At the time of episode, he had transient hyperthyroidism. To our knowledge, this is the first variant found in non-coding region associated with transient central nervous system (CNS) symptoms and in this case, thyroid dysfunction might contribute to the episode. The mechanism of CMTX1 as well as the transient CNS symptoms waits to be elucidated.
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Affiliation(s)
- Si Luo
- Department of Neurology, China-Japan Union Hospital of Jilin University, Changchun, China
| | - Hui Jin
- Department of Neurology, China-Japan Union Hospital of Jilin University, Changchun, China
| | - Jiajun Chen
- Department of Neurology, China-Japan Union Hospital of Jilin University, Changchun, China
| | - Lei Zhang
- Department of Neurology, China-Japan Union Hospital of Jilin University, Changchun, China
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11
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Diseases of connexins expressed in myelinating glia. Neurosci Lett 2019; 695:91-99. [DOI: 10.1016/j.neulet.2017.05.037] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2017] [Revised: 05/15/2017] [Accepted: 05/19/2017] [Indexed: 11/23/2022]
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12
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Coelho JPL, Stahl M, Bloemeke N, Meighen-Berger K, Alvira CP, Zhang ZR, Sieber SA, Feige MJ. A network of chaperones prevents and detects failures in membrane protein lipid bilayer integration. Nat Commun 2019; 10:672. [PMID: 30737405 PMCID: PMC6368539 DOI: 10.1038/s41467-019-08632-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Accepted: 01/22/2019] [Indexed: 12/20/2022] Open
Abstract
A fundamental step in membrane protein biogenesis is their integration into the lipid bilayer with a defined orientation of each transmembrane segment. Despite this, it remains unclear how cells detect and handle failures in this process. Here we show that single point mutations in the membrane protein connexin 32 (Cx32), which cause Charcot-Marie-Tooth disease, can cause failures in membrane integration. This leads to Cx32 transport defects and rapid degradation. Our data show that multiple chaperones detect and remedy this aberrant behavior: the ER-membrane complex (EMC) aids in membrane integration of low-hydrophobicity transmembrane segments. If they fail to integrate, these are recognized by the ER-lumenal chaperone BiP. Ultimately, the E3 ligase gp78 ubiquitinates Cx32 proteins, targeting them for degradation. Thus, cells use a coordinated system of chaperones for the complex task of membrane protein biogenesis, which can be compromised by single point mutations, causing human disease.
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Affiliation(s)
- João P L Coelho
- Center for Integrated Protein Science at the Department of Chemistry, Technical University of Munich, Lichtenbergstr. 4, 85748, Garching, Germany
| | - Matthias Stahl
- Center for Integrated Protein Science at the Department of Chemistry, Technical University of Munich, Lichtenbergstr. 4, 85748, Garching, Germany
- SciLifeLab, Department of Oncology-Pathology, Karolinska Institutet, Box 1031, 171 21 Solna, Stockholm, Sweden
| | - Nicolas Bloemeke
- Center for Integrated Protein Science at the Department of Chemistry, Technical University of Munich, Lichtenbergstr. 4, 85748, Garching, Germany
| | - Kevin Meighen-Berger
- Center for Integrated Protein Science at the Department of Chemistry, Technical University of Munich, Lichtenbergstr. 4, 85748, Garching, Germany
| | - Carlos Piedrafita Alvira
- Center for Integrated Protein Science at the Department of Chemistry, Technical University of Munich, Lichtenbergstr. 4, 85748, Garching, Germany
| | - Zai-Rong Zhang
- Interdisciplinary Research Center on Biology and Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai, 201210, China
| | - Stephan A Sieber
- Center for Integrated Protein Science at the Department of Chemistry, Technical University of Munich, Lichtenbergstr. 4, 85748, Garching, Germany
| | - Matthias J Feige
- Center for Integrated Protein Science at the Department of Chemistry, Technical University of Munich, Lichtenbergstr. 4, 85748, Garching, Germany.
- Institute for Advanced Study, Technical University of Munich, Lichtenbergstr. 2a, 85748, Garching, Germany.
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13
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Koutsis G, Breza M, Velonakis G, Tzartos J, Kasselimis D, Kartanou C, Karavasilis E, Tzanetakos D, Anagnostouli M, Andreadou E, Evangelopoulos ME, Kilidireas C, Potagas C, Panas M, Karadima G. X linked Charcot-Marie-Tooth disease and multiple sclerosis: emerging evidence for an association. J Neurol Neurosurg Psychiatry 2019; 90:187-194. [PMID: 30196252 DOI: 10.1136/jnnp-2018-319014] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/13/2018] [Revised: 07/31/2018] [Accepted: 08/11/2018] [Indexed: 11/03/2022]
Abstract
OBJECTIVE X linked Charcot-Marie-Tooth disease (CMTX) is a hereditary neuropathy caused by mutations in GJB1 coding for connexin-32, a gap junction protein expressed in Schwann cells, but also found in oligodendrocytes. Four patients with CMTX developing central nervous system (CNS) demyelination compatible with multiple sclerosis (MS) have been individually published. We presently sought to systematically investigate the relationship between CMTX and MS. METHODS Over 20 years, 70 consecutive patients (36 men) with GJB1 mutations were identified at our Neurogenetics Unit, Athens, Greece, and assessed for clinical features suggestive of MS. Additionally, 18 patients with CMTX without CNS symptoms and 18 matched controls underwent brain MRI to investigate incidental findings. Serum from patients with CMTX and MS was tested for CNS immunoreactivity. RESULTS We identified three patients with CMTX who developed clinical features suggestive of inflammatory CNS demyelination fulfilling MS diagnostic criteria. The resulting 20-year MS incidence (4.3%) differed significantly from the highest background 20-year MS incidence ever reported from Greece (p=0.00039). The search for incidental brain MRI findings identified two CMTX cases (11%) with lesions suggestive of focal demyelination compared with 0 control. Moreover, 10 cases in the CMTX cohort had hyperintensity in the splenium of the corpus callosum compared with 0 control (p=0.0002). No specific CNS-reactive humoral factors were identified in patients with CMTX and MS. CONCLUSIONS We have demonstrated a higher than expected frequency of MS in patients with CMTX and identified incidental focal demyelinating lesions on brain MRI in patients with CMTX without CNS symptoms. This provides circumstantial evidence for GJB1 mutations acting as a possible MS risk factor.
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Affiliation(s)
- Georgios Koutsis
- Neurogenetics Unit, 1st Department of Neurology, School of Medicine, Eginition Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - Marianthi Breza
- Neurogenetics Unit, 1st Department of Neurology, School of Medicine, Eginition Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - Georgios Velonakis
- 2nd Department of Radiology, Medical School, Attikon Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - John Tzartos
- Demyelinating Diseases Unit, 1st Department of Neurology, School of Medicine, Eginition Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - Dimitrios Kasselimis
- Neuropsychology and Speech Pathology Unit, 1st Department of Neurology, School of Medicine, Eginition Hospital, National and Kapodistrian University of Athens, Athens, Greece
- Division of Psychiatry and Behavioral Sciences, School of Medicine, University of Crete, Crete, Greece
| | - Chrisoula Kartanou
- Neurogenetics Unit, 1st Department of Neurology, School of Medicine, Eginition Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - Efstratios Karavasilis
- 2nd Department of Radiology, Medical School, Attikon Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - Dimitrios Tzanetakos
- Demyelinating Diseases Unit, 1st Department of Neurology, School of Medicine, Eginition Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - Maria Anagnostouli
- Demyelinating Diseases Unit, 1st Department of Neurology, School of Medicine, Eginition Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - Elisavet Andreadou
- Demyelinating Diseases Unit, 1st Department of Neurology, School of Medicine, Eginition Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - Maria-Eleftheria Evangelopoulos
- Demyelinating Diseases Unit, 1st Department of Neurology, School of Medicine, Eginition Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - Constantinos Kilidireas
- Demyelinating Diseases Unit, 1st Department of Neurology, School of Medicine, Eginition Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - Constantin Potagas
- Neuropsychology and Speech Pathology Unit, 1st Department of Neurology, School of Medicine, Eginition Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - Marios Panas
- Neurogenetics Unit, 1st Department of Neurology, School of Medicine, Eginition Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - Georgia Karadima
- Neurogenetics Unit, 1st Department of Neurology, School of Medicine, Eginition Hospital, National and Kapodistrian University of Athens, Athens, Greece
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14
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Yuan JH, Sakiyama Y, Hashiguchi A, Ando M, Okamoto Y, Yoshimura A, Higuchi Y, Takashima H. Genetic and phenotypic profile of 112 patients with X-linked Charcot-Marie-Tooth disease type 1. Eur J Neurol 2018; 25:1454-1461. [PMID: 29998508 DOI: 10.1111/ene.13750] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2018] [Accepted: 07/10/2018] [Indexed: 12/22/2022]
Abstract
BACKGROUND AND PURPOSE X-linked Charcot-Marie-Tooth disease type 1 (CMTX1), caused by mutations in gap junction protein beta 1 (GJB1), is characterized by various central nervous system symptoms and gender differences of clinical severity. The aim of this study was to identify the frequency and mutation spectrum of CMTX1 patients in Japan and to demonstrate their phenotypic diversities. METHODS Using three high-throughput sequencing systems, targeted gene panel sequencing on 1483 unrelated index patients with suspected Charcot-Marie-Tooth (CMT) disease was performed. The peripheral and central nervous system involvements of all patients with GJB1 variants were assessed retrospectively and a detailed gender comparison was conducted with the CMT examination score. RESULTS Twenty-three novel and 36 described GJB1 variants were identified from 88 pedigrees, in which 34 female and 78 male patients were enrolled. Mean age at onset of the male patients was much younger than the females, 21.56 ± 17.63 years vs. 35.53 ± 23.72 years (P = 0.007). Male patients presented with more severe phenotypes in every examination item, but statistical differences were observed only in motor dysfunctions of the lower extremities and vibration sensation. No significant sensory difference was identified between genders, either clinically or electrophysiologically. Central nervous system dysfunctions were found in 15 patients from 12 pedigrees. Therein, six patients developed stroke-like phenotypes, with dysarthria as the leading symptom. CONCLUSIONS A relatively lower frequency of CMTX1 (5.9%) was demonstrated and a broad mutation spectrum of GJB1 was described. Detailed clinical differences between genders and various central nervous system symptoms were also illustrated, even in the same pedigree.
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Affiliation(s)
- J-H Yuan
- Department of Neurology and Geriatrics, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan
| | - Y Sakiyama
- Department of Neurology and Geriatrics, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan
| | - A Hashiguchi
- Department of Neurology and Geriatrics, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan
| | - M Ando
- Department of Neurology and Geriatrics, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan
| | - Y Okamoto
- Department of Neurology and Geriatrics, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan
| | - A Yoshimura
- Department of Neurology and Geriatrics, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan
| | - Y Higuchi
- Department of Neurology and Geriatrics, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan
| | - H Takashima
- Department of Neurology and Geriatrics, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan
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15
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Abrams CK, Peinado A, Mahmoud R, Bocarsly M, Zhang H, Chang P, Botello-Smith WM, Freidin MM, Luo Y. Alterations at Arg 76 of human connexin 46, a residue associated with cataract formation, cause loss of gap junction formation but preserve hemichannel function. Am J Physiol Cell Physiol 2018; 315:C623-C635. [PMID: 30044662 DOI: 10.1152/ajpcell.00157.2018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The connexins are members of a family of integral membrane proteins that form gap junction channels between apposed cells and/or hemichannels across the plasma membranes. The importance of the arginine at position 76 (Arg76) in the structure and/or function of connexin 46 (Cx46) is highlighted by its conservation across the entire connexin family and the occurrence of pathogenic mutations at this (or the corresponding homologous) residue in a number of human diseases. Two mutations at Arg76 in Cx46 are associated with cataracts in humans, highlighting the importance of this residue. We examined the expression levels and macroscopic and single-channel properties of human Cx46 and compared them with those for two pathogenic mutants, namely R76H and R76G. To gain further insight into the role of charge at this position, we generated two additional nonnaturally occurring mutants, R76K (charge conserving) and R76E (charge inverting). We found that, when expressed exogenously in Neuro2a cells, all four mutants formed membrane hemichannels, inducing membrane permeability at levels comparable to those recorded in cells expressing the wild-type Cx46. In contrast, the number of gap-junction plaques and the magnitude of junctional coupling were reduced by all four mutations. To gain further insight into the role of Arg76 in the function of Cx46, we performed homology modeling of Cx46 and in silico mutagenesis of Arg76 to Gly, His, or Glu. Our studies suggest that the loss of interprotomeric interactions has a significant effect on the extracellular domain conformation and dynamics, thus affecting the hemichannel docking required for formation of cell-cell channels.
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Affiliation(s)
- Charles K Abrams
- Department of Neurology and Rehabilitation, University of Illinois at Chicago College of Medicine , Chicago, Illinois
- Department of Neurology State University of New York Downstate Medical Center , Brooklyn New York
| | - Alejandro Peinado
- Department of Neurology and Rehabilitation, University of Illinois at Chicago College of Medicine , Chicago, Illinois
| | - Rola Mahmoud
- Department of Neurology State University of New York Downstate Medical Center , Brooklyn New York
| | - Matan Bocarsly
- Department of Neurology State University of New York Downstate Medical Center , Brooklyn New York
| | - Han Zhang
- Department of Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences , Pomona, California
| | - Paul Chang
- Department of Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences , Pomona, California
| | - Wesley M Botello-Smith
- Department of Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences , Pomona, California
| | - Mona M Freidin
- Department of Neurology and Rehabilitation, University of Illinois at Chicago College of Medicine , Chicago, Illinois
- Department of Neurology State University of New York Downstate Medical Center , Brooklyn New York
| | - Yun Luo
- Department of Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences , Pomona, California
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16
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Alaei SR, Abrams CK, Bulinski JC, Hertzberg EL, Freidin MM. Acetylation of C-terminal lysines modulates protein turnover and stability of Connexin-32. BMC Cell Biol 2018; 19:22. [PMID: 30268116 PMCID: PMC6162937 DOI: 10.1186/s12860-018-0173-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2018] [Accepted: 09/17/2018] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND The gap junction protein, Connexin32 (Cx32), is expressed in various tissues including liver, exocrine pancreas, gastrointestinal epithelium, and the glia of the central and peripheral nervous system. Gap junction-mediated cell-cell communication and channel-independent processes of Cx32 contribute to the regulation of physiological and cellular activities such as glial differentiation, survival, and proliferation; maintenance of the hepatic epithelium; and axonal myelination. Mutations in Cx32 cause X-linked Charcot-Marie-Tooth disease (CMT1X), an inherited peripheral neuropathy. Several CMT1X causing mutations are found in the cytoplasmic domains of Cx32, a region implicated in the regulation of gap junction assembly, turnover and function. Here we investigate the roles of acetylation and ubiquitination in the C-terminus on Cx32 protein function. Cx32 protein turnover, ubiquitination, and response to deacetylase inhibitors were determined for wild-type and C-terminus lysine mutants using transiently transfected Neuro2A (N2a) cells. RESULTS We report here that Cx32 is acetylated in transfected N2a cells and that inhibition of the histone deacetylase, HDAC6, results in an accumulation of Cx32. We identified five lysine acetylation targets in the C-terminus. Mutational analysis demonstrates that these lysines are involved in the regulation of Cx32 ubiquitination and turnover. While these lysines are not required for functional Cx32 mediated cell-cell communication, BrdU incorporation studies demonstrate that their relative acetylation state plays a channel-independent role in Cx32-mediated control of cell proliferation. CONCLUSION Taken together these results highlight the role of post translational modifications and lysines in the C-terminal tail of Cx32 in the fine-tuning of Cx32 protein stability and channel-independent functions.
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Affiliation(s)
- Sarah R. Alaei
- Department of Molecular Genetics & Microbiology, Stony Brook University, Stony Brook, NY 11794 USA
| | - Charles K. Abrams
- Department of Neurology & Rehabilitation, University of Illinois at Chicago, Chicago, IL 60612 USA
| | - J. Chloë Bulinski
- Department of Cell & Molecular Biology, Columbia University, New York, NY 10032 USA
| | - Elliot L. Hertzberg
- Department of Cell & Molecular Biology, Columbia University, New York, NY 10032 USA
| | - Mona M. Freidin
- Department of Neurology & Rehabilitation, University of Illinois at Chicago, Chicago, IL 60612 USA
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17
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Bortolozzi M. What's the Function of Connexin 32 in the Peripheral Nervous System? Front Mol Neurosci 2018; 11:227. [PMID: 30042657 PMCID: PMC6048289 DOI: 10.3389/fnmol.2018.00227] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Accepted: 06/11/2018] [Indexed: 12/26/2022] Open
Abstract
Connexin 32 (Cx32) is a fundamental protein in the peripheral nervous system (PNS) as its mutations cause the X-linked form of Charcot–Marie–Tooth disease (CMT1X), the second most common form of hereditary motor and sensory neuropathy and a demyelinating disease for which there is no effective therapy. Since mutations of the GJB1 gene encoding Cx32 were first reported in 1993, over 450 different mutations associated with CMT1X including missense, frameshift, deletion and non-sense ones have been identified. Despite the availability of a sizable number of studies focusing on normal and mutated Cx32 channel properties, the crucial role played by Cx32 in the PNS has not yet been elucidated, as well as the molecular pathogenesis of CMT1X. Is Cx32 fundamental during a particular phase of Schwann cell (SC) life? Are Cx32 paired (gap junction, GJ) channels in myelinated SCs important for peripheral nerve homeostasis? The attractive hypothesis that short coupling of adjacent myelin layers by Cx32 GJs is required for efficient diffusion of K+ and signaling molecules is still debated, while a growing body of evidence is supporting other possible functions of Cx32 in the PNS, mainly related to Cx32 unpaired channels (hemichannels), which could be involved in a purinergic-dependent pathway controlling myelination. Here we review the intriguing puzzle of findings about Cx32 function and dysfunction, discussing possible directions for future investigation.
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Affiliation(s)
- Mario Bortolozzi
- Department of Physics and Astronomy G. Galilei, University of Padua, Padua, Italy.,Venetian Institute of Molecular Medicine (VIMM), Padua, Italy.,Padova Neuroscience Center (PNC), Padua, Italy
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18
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Carrer A, Leparulo A, Crispino G, Ciubotaru CD, Marin O, Zonta F, Bortolozzi M. Cx32 hemichannel opening by cytosolic Ca2+ is inhibited by the R220X mutation that causes Charcot-Marie-Tooth disease. Hum Mol Genet 2018; 27:80-94. [PMID: 29077882 DOI: 10.1093/hmg/ddx386] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2017] [Accepted: 10/17/2017] [Indexed: 11/15/2022] Open
Abstract
Mutations of the GJB1 gene encoding connexin 32 (Cx32) cause the X-linked form of Charcot-Marie-Tooth disease (CMTX1), a demyelinating peripheral neuropathy for which there is no cure. A growing body of evidence indicates that ATP release through Cx32 hemichannels in Schwann cells could be critical for nerve myelination, but it is unknown if CMTX1 mutations alter the cytosolic Ca2+-dependent gating mechanism that controls Cx32 hemichannel opening and ATP release. The current study uncovered that loss of the C-terminus in Cx32 (R220X mutation), which causes a severe CMTX1 phenotype, inhibits hemichannel opening during a canonical IP3-mediated increase in cytosolic Ca2+ in HeLa cells. Interestingly, the gating function of R220X hemichannels was completely restored by both the intracellular and extracellular application of a peptide that mimics the Cx32 cytoplasmic loop. All-atom molecular dynamics simulations suggest that loss of the C-terminus in the mutant hemichannel triggers abnormal fluctuations of the cytoplasmic loop which are prevented by binding to the mimetic peptide. Experiments that stimulated R220X hemichannel opening by cell depolarization displayed reduced voltage sensitivity with respect to wild-type hemichannels which was explained by loss of subconductance states at the single channel level. Finally, experiments of intercellular diffusion mediated by wild-type or R220X gap junction channels revealed similar unitary permeabilities to ions, signalling molecules (cAMP) or larger solutes (Lucifer yellow). Taken together, our findings support the hypothesis that paracrine signalling alteration due to Cx32 hemichannel dysfunction underlies CMTX1 pathogenesis and suggest a candidate molecule for novel studies investigating a therapeutic approach.
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Affiliation(s)
- Andrea Carrer
- Venetian Institute of Molecular Medicine (VIMM), Padua 35129, Italy
- Department of Physics and Astronomy "G. Galilei", University of Padua, Padua 35131, Italy
| | - Alessandro Leparulo
- Venetian Institute of Molecular Medicine (VIMM), Padua 35129, Italy
- Department of Physics and Astronomy "G. Galilei", University of Padua, Padua 35131, Italy
| | - Giulia Crispino
- Venetian Institute of Molecular Medicine (VIMM), Padua 35129, Italy
- Department of Physics and Astronomy "G. Galilei", University of Padua, Padua 35131, Italy
| | | | - Oriano Marin
- Department of Biomedical Sciences, University of Padua, Padua 35131, Italy
| | - Francesco Zonta
- Shanghai Institute for Advanced Immunochemical Studies, ShanghaiTech University, Shanghai 201210, China
- Italian National Research Council (CNR), Institute of Cell Biology and Neurobiology, Monterotondo 00015, Italy
| | - Mario Bortolozzi
- Venetian Institute of Molecular Medicine (VIMM), Padua 35129, Italy
- Department of Physics and Astronomy "G. Galilei", University of Padua, Padua 35131, Italy
- Italian National Research Council (CNR), Institute of Protein Biochemistry, Naples 80131, Italy
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