1
|
Krokengen OC, Touma C, Mularski A, Sutinen A, Dunkel R, Ytterdal M, Raasakka A, Mertens HDT, Simonsen AC, Kursula P. The cytoplasmic tail of myelin protein zero induces morphological changes in lipid membranes. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2024; 1866:184368. [PMID: 38971517 DOI: 10.1016/j.bbamem.2024.184368] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2024] [Revised: 06/24/2024] [Accepted: 07/01/2024] [Indexed: 07/08/2024]
Abstract
The major myelin protein expressed by the peripheral nervous system Schwann cells is protein zero (P0), which represents 50% of the total protein content in myelin. This 30-kDa integral membrane protein consists of an immunoglobulin (Ig)-like domain, a transmembrane helix, and a 69-residue C-terminal cytoplasmic tail (P0ct). The basic residues in P0ct contribute to the tight packing of myelin lipid bilayers, and alterations in the tail affect how P0 functions as an adhesion molecule necessary for the stability of compact myelin. Several neurodegenerative neuropathies are related to P0, including the more common Charcot-Marie-Tooth disease (CMT) and Dejerine-Sottas syndrome (DSS) as well as rare cases of motor and sensory polyneuropathy. We found that high P0ct concentrations affected the membrane properties of bicelles and induced a lamellar-to-inverted hexagonal phase transition, which caused bicelles to fuse into long, protein-containing filament-like structures. These structures likely reflect the formation of semicrystalline lipid domains with potential relevance for myelination. Not only is P0ct important for stacking lipid membranes, but time-lapse fluorescence microscopy also shows that it might affect membrane properties during myelination. We further describe recombinant production and low-resolution structural characterization of full-length human P0. Our findings shed light on P0ct effects on membrane properties, and with the successful purification of full-length P0, we have new tools to study the role of P0 in myelin formation and maintenance in vitro.
Collapse
Affiliation(s)
- Oda C Krokengen
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | - Christine Touma
- Faculty of Biochemistry and Molecular Medicine & Biocenter Oulu, University of Oulu, Oulu, Finland
| | - Anna Mularski
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense, Denmark
| | - Aleksi Sutinen
- Faculty of Biochemistry and Molecular Medicine & Biocenter Oulu, University of Oulu, Oulu, Finland
| | - Ryan Dunkel
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | - Marie Ytterdal
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | - Arne Raasakka
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | - Haydyn D T Mertens
- European Molecular Biology Laboratory EMBL, Hamburg Site, c/o DESY, Hamburg, Germany
| | - Adam Cohen Simonsen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense, Denmark
| | - Petri Kursula
- Department of Biomedicine, University of Bergen, Bergen, Norway; Faculty of Biochemistry and Molecular Medicine & Biocenter Oulu, University of Oulu, Oulu, Finland.
| |
Collapse
|
2
|
Bremer J, Meinhardt A, Katona I, Senderek J, Kämmerer‐Gassler EK, Roos A, Ferbert A, Schröder JM, Nikolin S, Nolte K, Sellhaus B, Popzhelyazkova K, Tacke F, Schara‐Schmidt U, Neuen‐Jacob E, de Groote CC, de Jonghe P, Timmerman V, Baets J, Weis J. Myelin protein zero mutation-related hereditary neuropathies: Neuropathological insight from a new nerve biopsy cohort. Brain Pathol 2024; 34:e13200. [PMID: 37581289 PMCID: PMC10711263 DOI: 10.1111/bpa.13200] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Accepted: 07/19/2023] [Indexed: 08/16/2023] Open
Abstract
Myelin protein zero (MPZ/P0) is a major structural protein of peripheral nerve myelin. Disease-associated variants in the MPZ gene cause a wide phenotypic spectrum of inherited peripheral neuropathies. Previous nerve biopsy studies showed evidence for subtype-specific morphological features. Here, we aimed at enhancing the understanding of these subtype-specific features and pathophysiological aspects of MPZ neuropathies. We examined archival material from two Central European centers and systematically determined genetic, clinical, and neuropathological features of 21 patients with MPZ mutations compared to 16 controls. Cases were grouped based on nerve conduction data into congenital hypomyelinating neuropathy (CHN; n = 2), demyelinating Charcot-Marie-Tooth (CMT type 1; n = 11), intermediate (CMTi; n = 3), and axonal CMT (type 2; n = 5). Six cases had combined muscle and nerve biopsies and one underwent autopsy. We detected four MPZ gene variants not previously described in patients with neuropathy. Light and electron microscopy of nerve biopsies confirmed fewer myelinated fibers, more onion bulbs and reduced regeneration in demyelinating CMT1 compared to CMT2/CMTi. In addition, we observed significantly more denervated Schwann cells, more collagen pockets, fewer unmyelinated axons per Schwann cell unit and a higher density of Schwann cell nuclei in CMT1 compared to CMT2/CMTi. CHN was characterized by basal lamina onion bulb formation, a further increase in Schwann cell density and hypomyelination. Most late onset axonal neuropathy patients showed microangiopathy. In the autopsy case, we observed prominent neuromatous hyperinnervation of the spinal meninges. In four of the six muscle biopsies, we found marked structural mitochondrial abnormalities. These results show that MPZ alterations not only affect myelinated nerve fibers, leading to either primarily demyelinating or axonal changes, but also affect non-myelinated nerve fibers. The autopsy case offers insight into spinal nerve root pathology in MPZ neuropathy. Finally, our data suggest a peculiar association of MPZ mutations with mitochondrial alterations in muscle.
Collapse
Affiliation(s)
- Juliane Bremer
- Institute of NeuropathologyRWTH Aachen University HospitalAachenGermany
| | - Axel Meinhardt
- Institute of NeuropathologyRWTH Aachen University HospitalAachenGermany
| | - Istvan Katona
- Institute of NeuropathologyRWTH Aachen University HospitalAachenGermany
| | - Jan Senderek
- Friedrich Baur Institute at the Department of NeurologyUniversity Hospital, LMU MunichMunichGermany
| | | | - Andreas Roos
- Institute of NeuropathologyRWTH Aachen University HospitalAachenGermany
- Department of NeuropaediatricsUniversity of EssenEssenGermany
| | | | | | - Stefan Nikolin
- Institute of NeuropathologyRWTH Aachen University HospitalAachenGermany
| | - Kay Nolte
- Institute of NeuropathologyRWTH Aachen University HospitalAachenGermany
| | - Bernd Sellhaus
- Institute of NeuropathologyRWTH Aachen University HospitalAachenGermany
| | | | - Frank Tacke
- Department of Hepatology and Gastroenterology, Charité—Universitätsmedizin BerlinCampus Virchow‐Klinikum (CVK) and Campus Charité Mitte (CCM)BerlinGermany
| | | | - Eva Neuen‐Jacob
- Department of NeuropathologyUniversity Hospital, Heinrich‐Heine University DüsseldorfDüsseldorfGermany
| | - Chantal Ceuterick de Groote
- Laboratory of Neuromuscular Pathology, Institute Born‐Bunge, and Translational Neurosciences, Faculty of MedicineUniversity of AntwerpBelgium
| | - Peter de Jonghe
- Laboratory of Neuromuscular Pathology, Institute Born‐Bunge, and Translational Neurosciences, Faculty of MedicineUniversity of AntwerpBelgium
- Department of NeurologyUniversity Hospital AntwerpAntwerpBelgium
| | - Vincent Timmerman
- Laboratory of Neuromuscular Pathology, Institute Born‐Bunge, and Translational Neurosciences, Faculty of MedicineUniversity of AntwerpBelgium
- Peripheral Neuropathy Research Group, Department of Biomedical SciencesUniversity of AntwerpAntwerpBelgium
| | - Jonathan Baets
- Laboratory of Neuromuscular Pathology, Institute Born‐Bunge, and Translational Neurosciences, Faculty of MedicineUniversity of AntwerpBelgium
- Department of NeurologyUniversity Hospital AntwerpAntwerpBelgium
| | - Joachim Weis
- Institute of NeuropathologyRWTH Aachen University HospitalAachenGermany
| |
Collapse
|
3
|
Sakakura M, Tanabe M, Mori M, Takahashi H, Mio K. Structural bases for the Charcot-Marie-Tooth disease induced by single amino acid substitutions of myelin protein zero. Structure 2023; 31:1452-1462.e4. [PMID: 37699394 DOI: 10.1016/j.str.2023.08.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2023] [Revised: 07/28/2023] [Accepted: 08/17/2023] [Indexed: 09/14/2023]
Abstract
Myelin protein zero (MPZ or P0) is a transmembrane protein which functions to glue membranes in peripheral myelin. Inter-membrane adhesion is mediated by homophilic interactions between the extracellular domains (ECDs) of MPZ. Single amino acid substitutions in an ECD cause demyelinating neuropathy, Charcot-Marie-Tooth disease (CMT), with unknown mechanisms. In this study, by using a novel assay system "nanomyelin," we revealed that a stacked-rings-like ECD-8-mer is responsible for membrane adhesion. Two inter-ECD interactions, cis and head-to-head, are essential to constituting the 8-mer and to gluing the membranes. This result was reinforced by the observation that the CMT-related N87H substitution at the cis interface abolished membrane-adhesion activity. In contrast, the CMT-related D32G and E68V variants retained membrane-stacking activity, whereas their thermal stability was lower than that of the WT. Reduced thermal stability may lead to impairment of the long-term stability of ECD and the layered membranes of myelin.
Collapse
Affiliation(s)
- Masayoshi Sakakura
- Graduate School of Medical Life Science, Yokohama City University, Yokohama 230-0045, Japan.
| | - Mikio Tanabe
- Structural Biology Research Center, Institute of Materials Structure Science, KEK/High Energy Accelerator Research Organization, Tsukuba 305-0801, Japan
| | - Masaki Mori
- Graduate School of Medical Life Science, Yokohama City University, Yokohama 230-0045, Japan
| | - Hideo Takahashi
- Graduate School of Medical Life Science, Yokohama City University, Yokohama 230-0045, Japan
| | - Kazuhiro Mio
- Graduate School of Medical Life Science, Yokohama City University, Yokohama 230-0045, Japan; AIST-UTokyo Advanced Operando-Measurement Technology Open Innovation Laboratory (OPERANDO-OIL), National Institute of Advanced Industrial Science and Technology (AIST), Kashiwa 277-0882, Japan
| |
Collapse
|
4
|
Qin S, Tian Z. Gain-of-glycosylation in breast multi-drug-resistant MCF-7 adenocarcinoma cells and cancer stem cells characterized by site- and structure-specific N-glycoproteomics. Anal Chim Acta 2023; 1252:341029. [PMID: 36935145 DOI: 10.1016/j.aca.2023.341029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2022] [Revised: 02/16/2023] [Accepted: 02/26/2023] [Indexed: 03/06/2023]
Abstract
N-linked glycosylation (N-glycosylation) is a common protein post-translational modification, occurring on more than half of mammalian proteins; in striking contract with small molecule modifications (such as methylation, phosphorylation) with only single structures, N-glycosylation has multiple dimensional structural features (monosaccharide composition, sequence, linkage, anomer), which generates enormous N-glycan structures; and these structures widely regulate protein structure and functions. For the modification site, N-glycosylation occurs on the Asn residue among the consensus N-X-S/T/C (X≠P) motif; mutation-originated amino acid change may lead to loss of such an original motif and thus loss-of-glycosylation (LoG) or gain of such a new motif and thus gain-of-glycosylation (GoG). Both LoG and GoG generates new structures and functions of glycoproteins, which has been observed in the S protein of SARS-Cov-2 as well as malignant diseases. Here we report our glycoproteome-wide qualitative N-glycoproteomics characterization of GoGs in breast cancer Adriamycin drug resistance (ADR) cells (MCF-7/ADR) and cancer stem cells (MCF-7/ADR CSCs); comprehensive N-glycosite and N-glycan structure information at the intact N-glycopeptide level were reported.
Collapse
Affiliation(s)
- Suideng Qin
- School of Chemical Science & Engineering, Shanghai Key Laboratory of Chemical Assessment and Sustainability, Tongji University, Shanghai, 200092, China
| | - Zhixin Tian
- School of Chemical Science & Engineering, Shanghai Key Laboratory of Chemical Assessment and Sustainability, Tongji University, Shanghai, 200092, China.
| |
Collapse
|
5
|
Lei L, Xiaobo L, Zhiqiang L, Yongzhi X, Shunxiang H, Huadong Z, Beisha T, Ruxu Z. Genotype-phenotype characteristics and baseline natural history of Chinese myelin protein zero gene related neuropathy patients. Eur J Neurol 2023; 30:1069-1079. [PMID: 36692866 DOI: 10.1111/ene.15700] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Revised: 12/24/2022] [Accepted: 12/30/2022] [Indexed: 01/25/2023]
Abstract
BACKGROUND AND PURPOSE The aim was to characterize the phenotypic and genotypic features of myelin protein zero (MPZ) related neuropathy and provide baseline data for longitudinal natural history studies or drug clinical trials. METHOD Clinical, neurophysiological and genetic data of 37 neuropathy patients with MPZ mutations were retrospectively collected. RESULTS Nineteen different MPZ mutations in 23 unrelated neuropathy families were detected, and the frequency of MPZ mutations was 5.84% in total. Mutations c.103_104InsTGGTTTACACCG, c.513dupG, c.521_557del and c.696_699delCAGT had not been reported previously. Hot spot mutation p.Thr124Met was detected in four unrelated families, and seven patients carried de novo mutations. The onset age indicated a bimodal distribution: prominent clustering in the first and fourth decades. The infantile-onset group included 12 families, the childhood-onset group consisted of two families and the adult-onset group included nine families. The Charcot-Marie-Tooth Disease Neuropathy Score ranged from 3 to 25 with a mean value of 15.85 ± 5.88. Mutations that changed the cysteine residue (p.Arg98Cys, p.Cys127Trp, p.Ser140Cys and p.Cys127Arg) in the extracellular region were more likely to cause severe early-onset Charcot-Marie-Tooth disease type 1B (CMT1B) or Dejerine-Sottas syndrome. Nonsense-mediated mRNA decay mutations p.Asp35delInsVVYTD, p.Leu174Argfs*66 and p.Leu172Alafs*63 were related to severe infantile-onset CMT1B or Dejerine-Sottas syndrome; however, mutation p.Val232Valfs*19 was associated with a relatively milder childhood-onset CMT1 phenotype. CONCLUSION Four novel MPZ mutations are reported that expand the genetic spectrum. De novo mutations accounted for 30.4% and were most related to a severe infantile-onset phenotype. Genetic and clinical data from this cohort will provide the baseline data necessary for clinical trials and natural history studies.
Collapse
Affiliation(s)
- Liu Lei
- Health Management Center, Third Xiangya Hospital, Central South University, Changsha, China
| | - Li Xiaobo
- Department of Neurology, Third Xiangya Hospital, Central South University, Changsha, China
| | - Lin Zhiqiang
- Department of Neurology, Third Xiangya Hospital, Central South University, Changsha, China
| | - Xie Yongzhi
- Department of Neurology, Third Xiangya Hospital, Central South University, Changsha, China
| | - Huang Shunxiang
- Department of Neurology, Third Xiangya Hospital, Central South University, Changsha, China
| | - Zhao Huadong
- Department of Neurology, Third Xiangya Hospital, Central South University, Changsha, China
| | - Tang Beisha
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, China
| | - Zhang Ruxu
- Department of Neurology, Third Xiangya Hospital, Central South University, Changsha, China
| |
Collapse
|
6
|
Nowacki JC, Fields AM, Fu MM. Emerging cellular themes in leukodystrophies. Front Cell Dev Biol 2022; 10:902261. [PMID: 36003149 PMCID: PMC9393611 DOI: 10.3389/fcell.2022.902261] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2022] [Accepted: 06/30/2022] [Indexed: 11/18/2022] Open
Abstract
Leukodystrophies are a broad spectrum of neurological disorders that are characterized primarily by deficiencies in myelin formation. Clinical manifestations of leukodystrophies usually appear during childhood and common symptoms include lack of motor coordination, difficulty with or loss of ambulation, issues with vision and/or hearing, cognitive decline, regression in speech skills, and even seizures. Many cases of leukodystrophy can be attributed to genetic mutations, but they have diverse inheritance patterns (e.g., autosomal recessive, autosomal dominant, or X-linked) and some arise from de novo mutations. In this review, we provide an updated overview of 35 types of leukodystrophies and focus on cellular mechanisms that may underlie these disorders. We find common themes in specialized functions in oligodendrocytes, which are specialized producers of membranes and myelin lipids. These mechanisms include myelin protein defects, lipid processing and peroxisome dysfunction, transcriptional and translational dysregulation, disruptions in cytoskeletal organization, and cell junction defects. In addition, non-cell-autonomous factors in astrocytes and microglia, such as autoimmune reactivity, and intercellular communication, may also play a role in leukodystrophy onset. We hope that highlighting these themes in cellular dysfunction in leukodystrophies may yield conceptual insights on future therapeutic approaches.
Collapse
|
7
|
Veneri FA, Prada V, Mastrangelo R, Ferri C, Nobbio L, Passalacqua M, Milanesi M, Bianchi F, Del Carro U, Vallat JM, Duong P, Svaren J, Schenone A, Grandis M, D’Antonio M. A novel mouse model of CMT1B identifies hyperglycosylation as a new pathogenetic mechanism. Hum Mol Genet 2022; 31:4255-4274. [PMID: 35908287 PMCID: PMC9759335 DOI: 10.1093/hmg/ddac170] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2022] [Revised: 07/19/2022] [Accepted: 07/20/2022] [Indexed: 01/21/2023] Open
Abstract
Mutations in the Myelin Protein Zero gene (MPZ), encoding P0, the major structural glycoprotein of peripheral nerve myelin, are the cause of Charcot-Marie-Tooth (CMT) type 1B neuropathy, and most P0 mutations appear to act through gain-of-function mechanisms. Here, we investigated how misglycosylation, a pathomechanism encompassing several genetic disorders, may affect P0 function. Using in vitro assays, we showed that gain of glycosylation is more damaging for P0 trafficking and functionality as compared with a loss of glycosylation. Hence, we generated, via CRISPR/Cas9, a mouse model carrying the MPZD61N mutation, predicted to generate a new N-glycosylation site in P0. In humans, MPZD61N causes a severe early-onset form of CMT1B, suggesting that hyperglycosylation may interfere with myelin formation, leading to pathology. We show here that MPZD61N/+ mice develop a tremor as early as P15 which worsens with age and correlates with a significant motor impairment, reduced muscular strength and substantial alterations in neurophysiology. The pathological analysis confirmed a dysmyelinating phenotype characterized by diffuse hypomyelination and focal hypermyelination. We find that the mutant P0D61N does not cause significant endoplasmic reticulum stress, a common pathomechanism in CMT1B, but is properly trafficked to myelin where it causes myelin uncompaction. Finally, we show that myelinating dorsal root ganglia cultures from MPZD61N mice replicate some of the abnormalities seen in vivo, suggesting that they may represent a valuable tool to investigate therapeutic approaches. Collectively, our data indicate that the MPZD61N/+ mouse represents an authentic model of severe CMT1B affirming gain-of-glycosylation in P0 as a novel pathomechanism of disease.
Collapse
Affiliation(s)
- Francesca A Veneri
- Biology of Myelin Unit, Division of Genetics and Cell Biology, IRCCS Ospedale San Raffaele, 20132 Milan, Italy,Department of Neuroscience, Rehabilitation, Ophthalmology, Genetics, Maternal and Child Health (DINOGMI), University of Genova, IRCCS AOU San Martino-IST, 16132 Genova, Italy
| | - Valeria Prada
- Department of Neuroscience, Rehabilitation, Ophthalmology, Genetics, Maternal and Child Health (DINOGMI), University of Genova, IRCCS AOU San Martino-IST, 16132 Genova, Italy
| | - Rosa Mastrangelo
- Biology of Myelin Unit, Division of Genetics and Cell Biology, IRCCS Ospedale San Raffaele, 20132 Milan, Italy
| | - Cinzia Ferri
- Biology of Myelin Unit, Division of Genetics and Cell Biology, IRCCS Ospedale San Raffaele, 20132 Milan, Italy
| | - Lucilla Nobbio
- Department of Neuroscience, Rehabilitation, Ophthalmology, Genetics, Maternal and Child Health (DINOGMI), University of Genova, IRCCS AOU San Martino-IST, 16132 Genova, Italy
| | - Mario Passalacqua
- Department of Experimental Medicine, University of Genova, 16132 Genova, Italy
| | - Maria Milanesi
- Experimental Oncology and Immunology, Department of Molecular and Translational Medicine, University of Brescia, 25123 Brescia, Italy
| | - Francesca Bianchi
- Movement Disorders Unit, Division of Neuroscience, IRCCS Ospedale San Raffaele, 20132 Milan, Italy
| | - Ubaldo Del Carro
- Movement Disorders Unit, Division of Neuroscience, IRCCS Ospedale San Raffaele, 20132 Milan, Italy
| | - Jean-Michel Vallat
- Department and Laboratory of Neurology, National Reference Center for ‘Rare Peripheral Neuropathies’, University Hospital of Limoges (CHU Limoges), Dupuytren Hospital, 87000 Limoges, France
| | - Phu Duong
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin–Madison, Madison, WI 53706, USA
| | - John Svaren
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin–Madison, Madison, WI 53706, USA
| | - Angelo Schenone
- Department of Neuroscience, Rehabilitation, Ophthalmology, Genetics, Maternal and Child Health (DINOGMI), University of Genova, IRCCS AOU San Martino-IST, 16132 Genova, Italy,Department of Neurology, IRCCS Ospedale Policlinico San Martino, 16132 Genova, Italy
| | - Marina Grandis
- To whom correspondence should be addressed at: Department of Neurology, IRCCS Ospedale Policlinico San Martino, Largo Daneo 3, 16132 Genova, Italy. Tel: +39 010 3537562; (M.G.); San Raffaele Scientific Institute, DIBIT, via Olgettina 58, 20132 Milan, Italy. Tel: +39 02 26435307; (M.D.)
| | - Maurizio D’Antonio
- To whom correspondence should be addressed at: Department of Neurology, IRCCS Ospedale Policlinico San Martino, Largo Daneo 3, 16132 Genova, Italy. Tel: +39 010 3537562; (M.G.); San Raffaele Scientific Institute, DIBIT, via Olgettina 58, 20132 Milan, Italy. Tel: +39 02 26435307; (M.D.)
| |
Collapse
|
8
|
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.
Collapse
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
| |
Collapse
|
9
|
Animal Models as a Tool to Design Therapeutical Strategies for CMT-like Hereditary Neuropathies. Brain Sci 2021; 11:brainsci11091237. [PMID: 34573256 PMCID: PMC8465478 DOI: 10.3390/brainsci11091237] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2021] [Revised: 09/05/2021] [Accepted: 09/07/2021] [Indexed: 02/07/2023] Open
Abstract
Since ancient times, animal models have provided fundamental information in medical knowledge. This also applies for discoveries in the field of inherited peripheral neuropathies (IPNs), where they have been instrumental for our understanding of nerve development, pathogenesis of neuropathy, molecules and pathways involved and to design potential therapies. In this review, we briefly describe how animal models have been used in ancient medicine until the use of rodents as the prevalent model in present times. We then travel along different examples of how rodents have been used to improve our understanding of IPNs. We do not intend to describe all discoveries and animal models developed for IPNs, but just to touch on a few arbitrary and paradigmatic examples, taken from our direct experience or from literature. The idea is to show how strategies have been developed to finally arrive to possible treatments for IPNs.
Collapse
|
10
|
Howard P, Feely SME, Grider T, Bacha A, Scarlato M, Fazio R, Quattrini A, Shy ME, Previtali SC. Loss of function MPZ mutation causes milder CMT1B neuropathy. J Peripher Nerv Syst 2021; 26:177-183. [PMID: 33960567 DOI: 10.1111/jns.12452] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Revised: 04/29/2021] [Accepted: 05/01/2021] [Indexed: 02/06/2023]
Abstract
Mutations in Myelin Protein Zero (MPZ) cause CMT1B, the second leading cause of CMT1. Many of the >200 mutations cause neuropathy through a toxic gain of function by the mutant protein such as ER retention, activation of the Unfolded Protein Response (UPR) or disruption of myelin compaction. While there is extensive literature on the loss of function consequences of MPZ in heterozygous Mpz +/- null mice, there is little known of the consequences of MPZ haploinsufficiency in humans. We identified six patients from different families with p.Tyr68Ter or p.Asp104fs heterozygous mutations of MPZ that are predicted to cause a premature termination and nonsense mediated decay of the mutant allele. Five patients were evaluated in Milan and one in Iowa City; all should be haploinsufficient for MPZ. Patients were evaluated clinically and by electrophysiology. Sensory ataxia dominated the clinical presentation with only mild weakness present in five of the six patients. Symptoms presented in adulthood in all patients and only one individual had a CMTNSv2 >5. Deep tendon reflexes were absent in all patients. Patients with likely MPZ loss of function due to mutations that cause haplodeficiency in MPZ have a mild, predominantly large fiber sensory neuropathy that serves as a human equivalent to the neuropathy observed in heterozygous Mpz null mice. Successful therapeutic approaches in treating Mpz deficient mice may be candidates for trials in these and similar patients.
Collapse
Affiliation(s)
- Paige Howard
- Roy and Lucille Carver College of Medicine, University of Iowa, Iowa City, Iowa, USA
| | | | - Tiffany Grider
- University of Iowa Healthcare Neurology, Iowa City, Iowa, USA
| | - Alexa Bacha
- Roy and Lucille Carver College of Medicine, University of Iowa, Iowa City, Iowa, USA
| | - Marina Scarlato
- Institute of Experimental Neurology (InSpe) and Division of Neuroscience, IRCCS Ospedale San Raffaele, Milano, Italy
| | - Raffaella Fazio
- Institute of Experimental Neurology (InSpe) and Division of Neuroscience, IRCCS Ospedale San Raffaele, Milano, Italy
| | - Angelo Quattrini
- Institute of Experimental Neurology (InSpe) and Division of Neuroscience, IRCCS Ospedale San Raffaele, Milano, Italy
| | - Michael E Shy
- Roy and Lucille Carver College of Medicine, University of Iowa, Iowa City, Iowa, USA
| | - Stefano C Previtali
- Institute of Experimental Neurology (InSpe) and Division of Neuroscience, IRCCS Ospedale San Raffaele, Milano, Italy
| |
Collapse
|
11
|
How Does Protein Zero Assemble Compact Myelin? Cells 2020; 9:cells9081832. [PMID: 32759708 PMCID: PMC7465998 DOI: 10.3390/cells9081832] [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: 05/11/2020] [Revised: 07/21/2020] [Accepted: 07/30/2020] [Indexed: 02/06/2023] Open
Abstract
Myelin protein zero (P0), a type I transmembrane protein, is the most abundant protein in peripheral nervous system (PNS) myelin—the lipid-rich, periodic structure of membrane pairs that concentrically encloses long axonal segments. Schwann cells, the myelinating glia of the PNS, express P0 throughout their development until the formation of mature myelin. In the intramyelinic compartment, the immunoglobulin-like domain of P0 bridges apposing membranes via homophilic adhesion, forming, as revealed by electron microscopy, the electron-dense, double “intraperiod line” that is split by a narrow, electron-lucent space corresponding to the extracellular space between membrane pairs. The C-terminal tail of P0 adheres apposing membranes together in the narrow cytoplasmic compartment of compact myelin, much like myelin basic protein (MBP). In mouse models, the absence of P0, unlike that of MBP or P2, severely disturbs myelination. Therefore, P0 is the executive molecule of PNS myelin maturation. How and when P0 is trafficked and modified to enable myelin compaction, and how mutations that give rise to incurable peripheral neuropathies alter the function of P0, are currently open questions. The potential mechanisms of P0 function in myelination are discussed, providing a foundation for the understanding of mature myelin development and how it derails in peripheral neuropathies.
Collapse
|
12
|
Mutation update for myelin protein zero-related neuropathies and the increasing role of variants causing a late-onset phenotype. J Neurol 2019; 266:2629-2645. [DOI: 10.1007/s00415-019-09453-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2019] [Revised: 06/21/2019] [Accepted: 06/26/2019] [Indexed: 01/18/2023]
|
13
|
Bai Y, Wu X, Brennan KM, Wang DS, D'Antonio M, Moran J, Svaren J, Shy ME. Myelin protein zero mutations and the unfolded protein response in Charcot Marie Tooth disease type 1B. Ann Clin Transl Neurol 2018; 5:445-455. [PMID: 29687021 PMCID: PMC5899917 DOI: 10.1002/acn3.543] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Revised: 01/24/2018] [Accepted: 01/29/2018] [Indexed: 12/13/2022] Open
Abstract
Objective To determine the prevalence of MPZ mutations that cause Charcot Marie Tooth neuropathy type 1B (CMT1B) and activate the unfolded protein Response (UPR). Background CMT1B is caused by >200 heterozygous mutations in MPZ, the major protein in peripheral nerve myelin. Mutations Ser63del MPZ and Arg98Cys MPZ cause the mutant protein to be retained in the ER and activate the generally adaptive UPR. Treatments that modulate UPR activation have improved cellular and rodent models of CMT1B raising the possibility that other MPZ mutations that activate the UPR would also respond favorably to similar treatment. The prevalence of MPZ mutations that activate the UPR is unknown. Methods We developed a dual luciferase reporter assay of Xbp1 splicing using stably transfected RT4 Schwann cells to assay the ability of cDNA constructs bearing 46 distinct MPZ mutations to activate the UPR. Constructs also carried an HA tag to permit detection of ER retention of mutant proteins. UPR activation and ER retention were correlated with clinical phenotypes. Results Eighteen mutations demonstrated ER retention and UPR activation to a similar degree as Ser63del and Arg98Cys MPZ. Thirty‐five of the mutations activated the UPR > 1.5 fold compared to that of wild‐type MPZ. Correlation was high between firefly and Nano‐luciferase reporters and between both reporters and ER localization. UPR activity did not correlate with clinical onset or severity. Conclusion Many CMT1B causing mutations activate the UPR and may be susceptible to therapeutic efforts to facilitate UPR function.
Collapse
Affiliation(s)
- Yunhong Bai
- Department of Neurology, Neuromuscular and Neurogenetics Divisions University of Iowa Hospitals and Clinics Iowa City Iowa
| | - Xingyao Wu
- Department of Neurology, Neuromuscular and Neurogenetics Divisions University of Iowa Hospitals and Clinics Iowa City Iowa
| | - Kathryn M Brennan
- Department of Neurology, Neuromuscular and Neurogenetics Divisions University of Iowa Hospitals and Clinics Iowa City Iowa
| | - David S Wang
- Department of Neurology, Neuromuscular and Neurogenetics Divisions University of Iowa Hospitals and Clinics Iowa City Iowa
| | - Maurizio D'Antonio
- Biology of Myelin Unit San Raffaele Scientific Institute DIBIT Milano Italy
| | - John Moran
- Waisman Center University of Wisconsin Madison Wisconsin.,Department of Comparative Biosciences University of Wisconsin Madison Wisconsin
| | - John Svaren
- Waisman Center University of Wisconsin Madison Wisconsin.,Department of Comparative Biosciences University of Wisconsin Madison Wisconsin
| | - Michael E Shy
- Department of Neurology, Neuromuscular and Neurogenetics Divisions University of Iowa Hospitals and Clinics Iowa City Iowa
| |
Collapse
|
14
|
Molecular mechanisms of missense mutations that generate ectopic N-glycosylation sites in coagulation factor VIII. Biochem J 2018; 475:873-886. [PMID: 29444815 DOI: 10.1042/bcj20170884] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Revised: 02/07/2018] [Accepted: 02/14/2018] [Indexed: 11/17/2022]
Abstract
N-glycosylation is a common posttranslational modification of secreted and membrane proteins, catalyzed by the two enzymatic isoforms of the oligosaccharyltransferase, STT3A and STT3B. Missense mutations are the most common mutations in inherited diseases; however, missense mutations that generate extra, non-native N-glycosylation sites have not been well characterized. Coagulation factor VIII (FVIII) contains five consensus N-glycosylation sites outside its functionally dispensable B domain. We developed a computer program that identified hemophilia A mutations in FVIII that can potentially create ectopic glycosylation sites. We determined that 18 of these ectopic sites indeed become N-glycosylated. These sites span the domains of FVIII and are primarily associated with a severe disease phenotype. Using STT3A and STT3B knockout cells, we determined that ectopic glycosylation exhibited different degrees of dependence on STT3A and STT3B. By separating the effects of ectopic N-glycosylation from those due to underlying amino acid changes, we showed that ectopic glycans promote the secretion of some mutants, but impair the secretion of others. However, ectopic glycans that enhanced secretion could not functionally replace a native N-glycan in the same domain. Secretion-deficient mutants, but not mutants with elevated secretion levels, show increased association with the endoplasmic reticulum chaperones BiP (immunoglobulin heavy chain-binding protein) and calreticulin. Though secreted to different extents, all studied mutants exhibited lower relative activity than wild-type FVIII. Our results reveal differential impacts of ectopic N-glycosylation on FVIII folding, trafficking and activity, which highlight complex disease-causing mechanisms of FVIII missense mutations. Our findings are relevant to other secreted and membrane proteins with mutations that generate ectopic N-glycans.
Collapse
|
15
|
García-Mateo N, Pascua-Maestro R, Pérez-Castellanos A, Lillo C, Sanchez D, Ganfornina MD. Myelin extracellular leaflet compaction requires apolipoprotein D membrane management to optimize lysosomal-dependent recycling and glycocalyx removal. Glia 2017; 66:670-687. [PMID: 29222871 DOI: 10.1002/glia.23274] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2017] [Revised: 11/09/2017] [Accepted: 11/17/2017] [Indexed: 11/07/2022]
Abstract
To compact the extracellular sides of myelin, an important transition must take place: from membrane sliding, while building the wraps, to membrane adhesion and water exclusion. Removal of the negatively charged glycocalyx becomes the limiting factor in such transition. What is required to initiate this membrane-zipping process? Knocking-out the Lipocalin Apolipoprotein D (ApoD), essential for lysosomal functional integrity in glial cells, results in a specific defect in myelin extracellular leaflet compaction in peripheral and central nervous system, which results in reduced conduction velocity and suboptimal behavioral outputs: motor learning is compromised. Myelination initiation, growth, intracellular leaflet compaction, myelin thickness or internodal length remain unaltered. Lack of ApoD specifically modifies Plp and P0 protein expression, but not Mbp or Mag. Late in myelin maturation period, ApoD affects lipogenic and growth-related, but not stress-responsive, signaling pathways. Without ApoD, the sialylated glycocalyx is maintained and ganglioside content remains high. In peripheral nervous system, Neu3 membrane sialidase and lysosomal Neu1 are coordinately expressed with ApoD in subsets of Schwann cells. ApoD-KO myelin becomes depleted of Neu3 and enriched in Fyn, a kinase with pivotal roles in transducing axon-derived signals into myelin properties. In the absence of ApoD, partial permeabilization of lysosomes alters Neu1 location as well. Exogenous ApoD rescues ApoD-KO hypersialylated glycocalyx in astrocytes, demonstrating that ApoD is necessary and sufficient to control glycocalyx composition in glial cells. By ensuring lysosomal functional integrity and adequate subcellular location of effector and regulatory proteins, ApoD guarantees the glycolipid recycling and glycocalyx removal required to complete myelin compaction.
Collapse
Affiliation(s)
- Nadia García-Mateo
- Instituto de Biología y Genética Molecular-Departamento de Bioquímica y Biología Molecular y Fisiología, Universidad de Valladolid-CSIC, Valladolid, Spain
| | - Raquel Pascua-Maestro
- Instituto de Biología y Genética Molecular-Departamento de Bioquímica y Biología Molecular y Fisiología, Universidad de Valladolid-CSIC, Valladolid, Spain
| | - Alberto Pérez-Castellanos
- Instituto de Biología y Genética Molecular-Departamento de Bioquímica y Biología Molecular y Fisiología, Universidad de Valladolid-CSIC, Valladolid, Spain
| | - Concepción Lillo
- Instituto de Neurociencias de Castilla y León, IBSAL, Universidad de Salamanca, Salamanca, Spain
| | - Diego Sanchez
- Instituto de Biología y Genética Molecular-Departamento de Bioquímica y Biología Molecular y Fisiología, Universidad de Valladolid-CSIC, Valladolid, Spain
| | - Maria D Ganfornina
- Instituto de Biología y Genética Molecular-Departamento de Bioquímica y Biología Molecular y Fisiología, Universidad de Valladolid-CSIC, Valladolid, Spain
| |
Collapse
|
16
|
Volpi VG, Touvier T, D'Antonio M. Endoplasmic Reticulum Protein Quality Control Failure in Myelin Disorders. Front Mol Neurosci 2017; 9:162. [PMID: 28101003 PMCID: PMC5209374 DOI: 10.3389/fnmol.2016.00162] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2016] [Accepted: 12/16/2016] [Indexed: 12/24/2022] Open
Abstract
Reaching the correct three-dimensional structure is crucial for the proper function of a protein. The endoplasmic reticulum (ER) is the organelle where secreted and transmembrane proteins are synthesized and folded. To guarantee high fidelity of protein synthesis and maturation in the ER, cells have evolved ER-protein quality control (ERQC) systems, which assist protein folding and promptly degrade aberrant gene products. Only correctly folded proteins that pass ERQC checkpoints are allowed to exit the ER and reach their final destination. Misfolded glycoproteins are detected and targeted for degradation by the proteasome in a process known as endoplasmic reticulum-associated degradation (ERAD). The excess of unstructured proteins in the ER triggers an adaptive signal transduction pathway, called unfolded protein response (UPR), which in turn potentiates ERQC activities in order to reduce the levels of aberrant molecules. When the situation cannot be restored, the UPR drives cells to apoptosis. Myelin-forming cells of the central and peripheral nervous system (oligodendrocytes and Schwann cells) synthesize a large amount of myelin proteins and lipids and therefore are particularly susceptible to ERQC failure. Indeed, deficits in ERQC and activation of ER stress/UPR have been implicated in several myelin disorders, such as Pelizaeus-Merzbacher and Krabbe leucodystrophies, vanishing white matter disease and Charcot-Marie-Tooth neuropathies. Here we discuss recent evidence underlying the importance of proper ERQC functions in genetic disorders of myelinating glia.
Collapse
Affiliation(s)
- Vera G Volpi
- Biology of Myelin Unit, Division of Genetics and Cell Biology, San Raffaele Scientific Institute, DIBIT Milan, Italy
| | - Thierry Touvier
- Biology of Myelin Unit, Division of Genetics and Cell Biology, San Raffaele Scientific Institute, DIBIT Milan, Italy
| | - Maurizio D'Antonio
- Biology of Myelin Unit, Division of Genetics and Cell Biology, San Raffaele Scientific Institute, DIBIT Milan, Italy
| |
Collapse
|
17
|
Dwyer CA, Esko JD. Glycan susceptibility factors in autism spectrum disorders. Mol Aspects Med 2016; 51:104-14. [PMID: 27418189 DOI: 10.1016/j.mam.2016.07.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Accepted: 07/06/2016] [Indexed: 11/16/2022]
Abstract
Idiopathic autism spectrum disorders (ASDs) are neurodevelopmental disorders with unknown etiology. An estimated 1:68 children in the U.S. are diagnosed with ASDs, making these disorders a substantial public health issue. Recent advances in genome sequencing have identified numerous genetic variants across the ASD patient population. Many genetic variants identified occur in genes that encode glycosylated extracellular proteins (proteoglycans or glycoproteins) or enzymes involved in glycosylation (glycosyltransferases and sulfotransferases). It remains unknown whether "glycogene" variants cause changes in glycosylation and whether they contribute to the etiology and pathogenesis of ASDs. Insights into glycan susceptibility factors are provided by studies in the normal brain and congenital disorders of glycosylation, which are often accompanied by ASD-like behaviors. The purpose of this review is to present evidence that supports a contribution of extracellular glycans and glycoconjugates to the etiology and pathogenesis of idiopathic ASDs and other types of pervasive neurodevelopmental disorders.
Collapse
Affiliation(s)
- Chrissa A Dwyer
- Department of Cellular and Molecular Medicine, Glycobiology Research and Training Center, University of California, San Diego, La Jolla, CA 92093, USA
| | - Jeffrey D Esko
- Department of Cellular and Molecular Medicine, Glycobiology Research and Training Center, University of California, San Diego, La Jolla, CA 92093, USA.
| |
Collapse
|
18
|
Prada V, Capponi S, Ursino G, Alberti A, Callegari I, Passalacqua M, Marotta R, Mandich P, Bellone E, Schenone A, Grandis M. Sural nerve biopsy and functional studies support the pathogenic role of a novelMPZmutation. Neuropathology 2014; 35:254-9. [DOI: 10.1111/neup.12179] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2014] [Accepted: 09/30/2014] [Indexed: 01/01/2023]
Affiliation(s)
- Valeria Prada
- Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal Child Health; Section of Neurology; University of Genova; Genova Italy
| | - Simona Capponi
- Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal Child Health; Section of Medical Genetics; University of Genova; Genova Italy
| | - Giulia Ursino
- Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal Child Health; Section of Neurology; University of Genova; Genova Italy
| | - Antonia Alberti
- Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal Child Health; Section of Neurology; University of Genova; Genova Italy
| | - Ilaria Callegari
- Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal Child Health; Section of Neurology; University of Genova; Genova Italy
| | - Mario Passalacqua
- Department of Experimental Medicine; Section of Biochemistry; University of Genova; Genova Italy
| | - Roberto Marotta
- Nanochemistry Department; Istituto Italiano di Tecnologia (IIT); Electron Microscopy Facility; Genova Italy
| | - Paola Mandich
- Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal Child Health; Section of Medical Genetics; University of Genova; Genova Italy
| | - Emilia Bellone
- Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal Child Health; Section of Medical Genetics; University of Genova; Genova Italy
| | - Angelo Schenone
- Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal Child Health; Section of Neurology; University of Genova; Genova Italy
| | - Marina Grandis
- Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal Child Health; Section of Neurology; University of Genova; Genova Italy
| |
Collapse
|
19
|
Sedzik J, Jastrzebski JP, Grandis M. Glycans of myelin proteins. J Neurosci Res 2014; 93:1-18. [PMID: 25213400 DOI: 10.1002/jnr.23462] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2014] [Revised: 06/19/2014] [Accepted: 07/07/2014] [Indexed: 01/04/2023]
Abstract
Human P0 is the main myelin glycoprotein of the peripheral nervous system. It can bind six different glycans, all linked to Asn(93) , the unique glycosylation site. Other myelin glycoproteins, also with a single glycosylation site (PMP22 at Asn(36) , MOG at Asn(31) ), bind only one glycan. The MAG has 10 glycosylation sites; the glycoprotein OMgp has 11 glycosylation sites. Aside from P0, no comprehensive data are available on other myelin glycoproteins. Here we review and analyze all published data on the physicochemical structure of the glycans linked to P0, PMP22, MOG, and MAG. Most data concern bovine P0, whose glycan moieties have an MW ranging from 1,294.56 Da (GP3) to 2,279.94 Da (GP5). The pI of glycosylated P0 protein varies from pH 9.32 to 9.46. The most charged glycan is MS2 containing three sulfate groups and one glucuronic acid; whereas the least charged one is the BA2 residue. All glycans contain one fucose and one galactose. The most mannose rich are the glycans MS2 and GP4, each of them has four mannoses; OPPE1 contains five N-acetylglucosamines and one sulfated glucuronic acid; GP4 contains one sialic acid. Furthermore, human P0 variants causing both gain and loss of glycosylation have been described and cause peripheral neuropathies with variable clinical severity. In particular, the substitution T(95) →M is a very common in Europe and is associated with a late-onset axonal neuropathy. Although peripheral myelin is made up largely of glycoproteins, mutations altering glycosylation have been described only in P0. This attractive avenue of research requires further study.
Collapse
Affiliation(s)
- Jan Sedzik
- Royal Institute of Technology, Department of Chemical Engineering, Protein Crystallization Facility, Stockholm, Sweden; National Institute of Physiological Sciences, Department of Neuroscience and Bioinformatics, Okazaki, Japan
| | | | | |
Collapse
|