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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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Moss KR, Bopp TS, Johnson AE, Höke A. New evidence for secondary axonal degeneration in demyelinating neuropathies. Neurosci Lett 2021; 744:135595. [PMID: 33359733 PMCID: PMC7852893 DOI: 10.1016/j.neulet.2020.135595] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2020] [Revised: 10/31/2020] [Accepted: 12/19/2020] [Indexed: 12/28/2022]
Abstract
Development of peripheral nervous system (PNS) myelin involves a coordinated series of events between growing axons and the Schwann cell (SC) progenitors that will eventually ensheath them. Myelin sheaths have evolved out of necessity to maintain rapid impulse propagation while accounting for body space constraints. However, myelinating SCs perform additional critical functions that are required to preserve axonal integrity including mitigating energy consumption by establishing the nodal architecture, regulating axon caliber by organizing axonal cytoskeleton networks, providing trophic and potentially metabolic support, possibly supplying genetic translation materials and protecting axons from toxic insults. The intermediate steps between the loss of these functions and the initiation of axon degeneration are unknown but the importance of these processes provides insightful clues. Prevalent demyelinating diseases of the PNS include the inherited neuropathies Charcot-Marie-Tooth Disease, Type 1 (CMT1) and Hereditary Neuropathy with Liability to Pressure Palsies (HNPP) and the inflammatory diseases Acute Inflammatory Demyelinating Polyneuropathy (AIDP) and Chronic Inflammatory Demyelinating Polyneuropathy (CIDP). Secondary axon degeneration is a common feature of demyelinating neuropathies and this process is often correlated with clinical deficits and long-lasting disability in patients. There is abundant electrophysiological and histological evidence for secondary axon degeneration in patients and rodent models of PNS demyelinating diseases. Fully understanding the involvement of secondary axon degeneration in these diseases is essential for expanding our knowledge of disease pathogenesis and prognosis, which will be essential for developing novel therapeutic strategies.
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Affiliation(s)
- Kathryn R Moss
- Department of Neurology, Neuromuscular Division, Johns Hopkins School of Medicine, Baltimore, MD, United States
| | - Taylor S Bopp
- Department of Neurology, Neuromuscular Division, Johns Hopkins School of Medicine, Baltimore, MD, United States
| | - Anna E Johnson
- Department of Neurology, Neuromuscular Division, Johns Hopkins School of Medicine, Baltimore, MD, United States
| | - Ahmet Höke
- Department of Neurology, Neuromuscular Division, Johns Hopkins School of Medicine, Baltimore, MD, United States.
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Zimmer SE, Kowalczyk AP. The desmosome as a model for lipid raft driven membrane domain organization. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1862:183329. [PMID: 32376221 DOI: 10.1016/j.bbamem.2020.183329] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2019] [Revised: 04/20/2020] [Accepted: 04/23/2020] [Indexed: 01/14/2023]
Abstract
Desmosomes are cadherin-based adhesion structures that mechanically couple the intermediate filament cytoskeleton of adjacent cells to confer mechanical stress resistance to tissues. We have recently described desmosomes as mesoscale lipid raft membrane domains that depend on raft dynamics for assembly, function, and disassembly. Lipid raft microdomains are regions of the plasma membrane enriched in sphingolipids and cholesterol. These domains participate in membrane domain heterogeneity, signaling and membrane trafficking. Cellular structures known to be dependent on raft dynamics include the post-synaptic density in neurons, the immunological synapse, and intercellular junctions, including desmosomes. In this review, we discuss the current state of the desmosome field and put forward new hypotheses for the role of lipid rafts in desmosome adhesion, signaling and epidermal homeostasis. Furthermore, we propose that differential lipid raft affinity of intercellular junction proteins is a central driving force in the organization of the epithelial apical junctional complex.
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Affiliation(s)
- Stephanie E Zimmer
- Graduate Program in Biochemistry, Cell and Developmental Biology, Emory University, Atlanta, GA 30322, United States of America; Department of Cell Biology, Emory University, Atlanta, GA 30322, United States of America
| | - Andrew P Kowalczyk
- Department of Cell Biology, Emory University, Atlanta, GA 30322, United States of America; Department of Dermatology, Emory University, Atlanta, GA 30322, United States of America.
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Caress JB, Lewis JA, Pinyan CW, Lawson VH. A charcot-marie-tooth type 1B kindred associated with hemifacial spasm and trigeminal neuralgia. Muscle Nerve 2019; 60:62-66. [PMID: 30920665 DOI: 10.1002/mus.26478] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/24/2019] [Indexed: 01/30/2023]
Abstract
INTRODUCTION Charcot-Marie-Tooth (CMT) phenotypes can be distinguished by electrophysiology and genetic analysis but few can be identified by their clinical characteristics. Distinctive phenotypes are useful in identifying affected individuals and providing additional clues about the mechanism of the neuropathy. Cranial neuropathies are uncommon features of CMT, and few reports of familial hemifacial spasm (HFS) and trigeminal neuralgia (TN) have been published. METHODS Sixty-three members of a large CMT 1B kindred were assessed for signs of peripheral neuropathy and cranial neuropathies then tested for the G163R mutation in the myelin protein zero (MPZ) gene. RESULTS Of 27 individuals with the G163R mutation in MPZ, 10 had HFS or TN. Co-existing HFS and TN were found in 3 of these and 4 had bilateral HFS or TN. CONCLUSIONS This kindred exhibits a distinct CMT phenotype characterized by the development of HFS or TN decades after clinical signs of hereditary neuropathy are manifest. Muscle Nerve, 2019.
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Affiliation(s)
- James B Caress
- Department of Neurology, Wake Forest School of Medicine, Medical Center Boulevard, Winston-Salem, North Carolina 27157, USA
| | | | - Clark W Pinyan
- Wake Forest School of Medicine, Winston-Salem, North Carolina, USA
| | - Victoria H Lawson
- Dartmouth Hitchcock Medical Center, Geisel School of Medicine at Dartmouth, Lebanon, New Hampshire, USA
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Werheid F, Azzedine H, Zwerenz E, Bozkurt A, Moeller MJ, Lin L, Mull M, Häusler M, Schulz JB, Weis J, Claeys KG. Underestimated associated features in CMT neuropathies: clinical indicators for the causative gene? Brain Behav 2016; 6:e00451. [PMID: 27088055 PMCID: PMC4782242 DOI: 10.1002/brb3.451] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Revised: 01/25/2016] [Accepted: 02/02/2016] [Indexed: 12/15/2022] Open
Abstract
INTRODUCTION Charcot-Marie-Tooth neuropathy (CMT) is a genetically heterogeneous group of peripheral neuropathies. In addition to the classical clinical phenotype, additional features can occur. METHODS We studied a wide range of additional features in a cohort of 49 genetically confirmed CMT patients and performed a systematic literature revision. RESULTS Patients harbored a PMP22 gene alteration (n = 28) or a mutation in MPZ (n = 11), GJB1 (n = 4), LITAF (n = 2), MFN2 (n = 2), INF2 (n = 1), NEFL (n = 1). We identified four novel mutations (3 MPZ, 1 GJB1). A total of 88% presented at least one additional feature. In MPZ patients, we detected hypertrophic nerve roots in 3/4 cases that underwent spinal MRI, and pupillary abnormalities in 27%. In our cohort, restless legs syndrome (RLS) was present in 18%. We describe for the first time RLS associated with LITAF or MFN2 and predominant upper limb involvement with LITAF. Cold-induced hand cramps occurred in 10% (PMP22,MPZ,MFN2), and autonomous nervous system involvement in 18% (PMP22,MPZ, LITAF,MFN2). RLS and respiratory insufficiency were mostly associated with severe neuropathy, and pupillary abnormalities with mild to moderate neuropathy. CONCLUSIONS In CMT patients, additional features occur frequently. Some of them might be helpful in orienting genetic diagnosis. Our data broaden the clinical spectrum and genotype-phenotype associations with CMT.
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Affiliation(s)
- Friederike Werheid
- Department of Neurology University Hospital RWTH Aachen Aachen Germany; Institute of Neuropathology University Hospital RWTH Aachen Aachen Germany
| | - Hamid Azzedine
- Institute of Neuropathology University Hospital RWTH Aachen Aachen Germany
| | - Eva Zwerenz
- Department of Neurology University Hospital RWTH Aachen Aachen Germany; Institute of Neuropathology University Hospital RWTH Aachen Aachen Germany
| | - Ahmet Bozkurt
- Department of Plastic and Reconstructive Surgery Hand Surgery-Burn Center University Hospital RWTH Aachen Aachen Germany; Department of Plastic & Aesthetic, Reconstructive & Hand Surgery Center for Reconstructive Microsurgery and Peripheral Nerve Surgery (ZEMPEN) Agaplesion Markus Hospital Frankfurt am Main Germany
| | - Marcus J Moeller
- Section Immunology and Nephrology Department of Internal Medicine University Hospital RWTH Aachen Aachen Germany
| | - Lilian Lin
- Department of Neurology University Hospital RWTH Aachen Aachen Germany; Institute of Neuropathology University Hospital RWTH Aachen Aachen Germany
| | - Michael Mull
- Department of Neuroradiology University Hospital RWTH Aachen Aachen Germany
| | - Martin Häusler
- Division of Neuropediatrics and Social Pediatrics Department of Pediatrics University Hospital RWTH Aachen Aachen Germany
| | - Jörg B Schulz
- Department of Neurology University Hospital RWTH Aachen Aachen Germany; JARA - Translational Brain Medicine Aachen Germany
| | - Joachim Weis
- Institute of Neuropathology University Hospital RWTH Aachen Aachen Germany
| | - Kristl G Claeys
- Department of Neurology University Hospital RWTH Aachen Aachen Germany; Institute of Neuropathology University Hospital RWTH Aachen Aachen Germany; Department of Neurology University Hospitals Leuven and University of Leuven (KU Leuven) Leuven Belgium
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Sanmaneechai O, Feely S, Scherer SS, Herrmann DN, Burns J, Muntoni F, Li J, Siskind CE, Day JW, Laura M, Sumner CJ, Lloyd TE, Ramchandren S, Shy RR, Grider T, Bacon C, Finkel RS, Yum SW, Moroni I, Piscosquito G, Pareyson D, Reilly MM, Shy ME. Genotype-phenotype characteristics and baseline natural history of heritable neuropathies caused by mutations in the MPZ gene. Brain 2015; 138:3180-92. [PMID: 26310628 DOI: 10.1093/brain/awv241] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2015] [Accepted: 06/30/2015] [Indexed: 11/14/2022] Open
Abstract
We aimed to characterize genotype-phenotype correlations and establish baseline clinical data for peripheral neuropathies caused by mutations in the myelin protein zero (MPZ) gene. MPZ mutations are the second leading cause of Charcot-Marie-Tooth disease type 1. Recent research makes clinical trials for patients with MPZ mutations a realistic possibility. However, the clinical severity varies with different mutations and natural history data on progression is sparse. We present cross-sectional data to begin to define the phenotypic spectrum and clinical baseline of patients with these mutations. A cohort of patients with MPZ gene mutations was identified in 13 centres of the Inherited Neuropathies Consortium - Rare Disease Clinical Research Consortium (INC-RDCRC) between 2009 and 2012 and at Wayne State University between 1996 and 2009. Patient phenotypes were quantified by the Charcot-Marie-Tooth disease neuropathy score version 1 or 2 and the Charcot-Marie-Tooth disease paediatric scale outcome instruments. Genetic testing was performed in all patients and/or in first- or second-degree relatives to document mutation in MPZ gene indicating diagnosis of Charcot-Marie-Tooth disease type 1B. There were 103 patients from 71 families with 47 different MPZ mutations with a mean age of 40 years (range 3-84 years). Patients and mutations were separated into infantile, childhood and adult-onset groups. The infantile onset group had higher Charcot-Marie-Tooth disease neuropathy score version 1 or 2 and slower nerve conductions than the other groups, and severity increased with age. Twenty-three patients had no family history of Charcot-Marie-Tooth disease. Sixty-one patients wore foot/ankle orthoses, 19 required walking assistance or support, and 10 required wheelchairs. There was hearing loss in 21 and scoliosis in 17. Forty-two patients did not begin walking until after 15 months of age. Half of the infantile onset patients then required ambulation aids or wheelchairs for ambulation. Our results demonstrate that virtually all MPZ mutations are associated with specific phenotypes. Early onset (infantile and childhood) phenotypes likely represent developmentally impaired myelination, whereas the adult-onset phenotype reflects axonal degeneration without antecedent demyelination. Data from this cohort of patients will provide the baseline data necessary for clinical trials of patients with Charcot-Marie-Tooth disease caused by MPZ gene mutations.
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Affiliation(s)
- Oranee Sanmaneechai
- 1 Department of Neurology, University of Iowa Hospitals and Clinics, Iowa, IA, USA 2 Division of Neurology, Department of Pediatrics, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - Shawna Feely
- 1 Department of Neurology, University of Iowa Hospitals and Clinics, Iowa, IA, USA
| | - Steven S Scherer
- 3 The Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - David N Herrmann
- 4 Department of Neurology, University of Rochester Medical Center, Rochester, NY, USA
| | - Joshua Burns
- 5 Arthritis and Musculoskeletal Research Group, University of Sydney / Paediatric Gait Analysis Service of NSW, Children's Hospital at Westmead, Sydney / Neuromuscular Research Group, Murdoch Childrens Research Institute, Melbourne, Australia
| | - Francesco Muntoni
- 6 University College London Institute of Child Health and Great Ormond Street Hospital, London, UK
| | - Jun Li
- 7 Department of Neurology, Vanderbilt University, Nashville, TN, USA
| | - Carly E Siskind
- 8 Department of Neurology, Stanford University, Stanford, CA, USA
| | - John W Day
- 8 Department of Neurology, Stanford University, Stanford, CA, USA
| | - Matilde Laura
- 9 MRC Centre for Neuromuscular Diseases, University College London Institute of Neurology, London, UK
| | - Charlotte J Sumner
- 10 Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Thomas E Lloyd
- 10 Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | | | - Rosemary R Shy
- 1 Department of Neurology, University of Iowa Hospitals and Clinics, Iowa, IA, USA
| | - Tiffany Grider
- 1 Department of Neurology, University of Iowa Hospitals and Clinics, Iowa, IA, USA
| | - Chelsea Bacon
- 1 Department of Neurology, University of Iowa Hospitals and Clinics, Iowa, IA, USA
| | | | - Sabrina W Yum
- 3 The Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA 13 Neuromuscular Program, Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - Isabella Moroni
- 14 Departments of Child Neurology, IRCCS Foundation, Carlo Besta Neurological Institute, Milan, Italy
| | - Giuseppe Piscosquito
- 15 Departments of Clinical Neurosciences, IRCCS Foundation, Carlo Besta Neurological Institute, Milan, Italy
| | - Davide Pareyson
- 15 Departments of Clinical Neurosciences, IRCCS Foundation, Carlo Besta Neurological Institute, Milan, Italy
| | - Mary M Reilly
- 9 MRC Centre for Neuromuscular Diseases, University College London Institute of Neurology, London, UK
| | - Michael E Shy
- 1 Department of Neurology, University of Iowa Hospitals and Clinics, Iowa, IA, USA
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Strøm TB, Laerdahl JK, Leren TP. Mutation p.L799R in the LDLR, which affects the transmembrane domain of the LDLR, prevents membrane insertion and causes secretion of the mutant LDLR. Hum Mol Genet 2015. [PMID: 26220972 DOI: 10.1093/hmg/ddv304] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Mutations in the low-density lipoprotein receptor (LDLR) gene cause familial hypercholesterolemia (FH). The mechanism by which mutations in the LDLR affecting the transmembrane domain of the receptor cause FH has not been thoroughly investigated. In this study, we have selected 12 naturally occurring mutations affecting the transmembrane domain and studied their effect on the LDLR. The main strategy has been to transiently transfect HepG2 cells with mutant LDLR plasmids and to study the mutant LDLRs in cell lysates and in media by western blot analysis. The most striking finding was that mutation p.L799R led to secretion of the entire 160 kDa mature L799R-LDLR. Residue 799Leu is in the middle of the 22-residue transmembrane domain, and introduction of a basic residue in the hydrophobic core of the transmembrane domain could prevent L799R-LDLR from being correctly recognized and integrated in the membrane by the Sec61 translocon complex. This would then lead to translocation of the entire L799R-LDLR into the lumen of the endoplasmic reticulum. Mutation p.L799R should be considered a member of a separate class of FH-causing mutations that affects the insertion of the LDLR in the cell membrane.
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Affiliation(s)
- Thea Bismo Strøm
- Unit for Cardiac and Cardiovascular Genetics, Department of Medical Genetics
| | - Jon K Laerdahl
- Department of Microbiology and Bioinformatics Core Facility, University of Oslo and Oslo University Hospital, Oslo, Norway
| | - Trond P Leren
- Unit for Cardiac and Cardiovascular Genetics, Department of Medical Genetics,
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Mutation G805R in the transmembrane domain of the LDL receptor gene causes familial hypercholesterolemia by inducing ectodomain cleavage of the LDL receptor in the endoplasmic reticulum. FEBS Open Bio 2014; 4:321-7. [PMID: 24918045 PMCID: PMC4048843 DOI: 10.1016/j.fob.2014.03.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2014] [Revised: 03/14/2014] [Accepted: 03/14/2014] [Indexed: 11/22/2022] Open
Abstract
Mutation G805R is in the transmembrane domain of the LDLR. A polar residue in the transmembrane domain induced metalloproteinase cleavage. Mutation G805R caused reduced amounts of the precursor LDLR. Reduced amounts of precursor LDLR led to reduced amounts of the mature LDLR. Mutation G805R prevented γ-secretase cleavage within the transmembrane domain.
More than 1700 mutations in the low density lipoprotein receptor (LDLR) gene have been found to cause familial hypercholesterolemia (FH). These are commonly divided into five classes based upon their effects on the structure and function of the LDLR. However, little is known about the mechanism by which mutations in the transmembrane domain of the LDLR gene cause FH. We have studied how the transmembrane mutation G805R affects the function of the LDLR. Based upon Western blot analyses of transfected HepG2 cells, mutation G805R reduced the amounts of the 120 kDa precursor LDLR in the endoplasmic reticulum. This led to reduced amounts of the mature 160 kDa LDLR at the cell surface. However, significant amounts of a secreted 140 kDa G805R-LDLR ectodomain fragment was observed in the culture media. Treatment of the cells with the metalloproteinase inhibitor batimastat largely restored the amounts of the 120 and 160 kDa forms in cell lysates, and prevented secretion of the 140 kDa ectodomain fragment. Together, these data indicate that a metalloproteinase cleaved the ectodomain of the 120 kDa precursor G805R-LDLR in the endoplasmic reticulum. It was the presence of the polar Arg805 and not the lack of Gly805 which led to ectodomain cleavage. Arg805 also prevented γ-secretase cleavage within the transmembrane domain. It is conceivable that introducing a charged residue within the hydrophobic membrane lipid bilayer, results in less efficient incorporation of the 120 kDa G805R-LDLR in the endoplasmic reticulum membrane and makes it a substrate for metalloproteinase cleavage.
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Ng DP, Poulsen BE, Deber CM. Membrane protein misassembly in disease. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:1115-22. [PMID: 21840297 DOI: 10.1016/j.bbamem.2011.07.046] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2011] [Revised: 07/28/2011] [Accepted: 07/29/2011] [Indexed: 11/19/2022]
Abstract
Helix-helix interactions play a central role in the folding and assembly of integral α-helical membrane proteins and are fundamentally dictated by the amino acid sequence of the TM domain. It is not surprising then that missense mutations that target these residues are often linked to disease. In this review, we focus on the molecular mechanisms through which missense mutations lead to aberrant folding and/or assembly of these proteins, and then discuss pharmacological approaches that may potentially mitigate or reverse the negative effects of these mutations. Improving our understanding of how missense mutations affect the interactions between TM α-helices will increase our capability to develop effective therapeutic approaches to counter the misassembly of these proteins and, ultimately, disease. This article is part of a Special Issue entitled: Protein Folding in Membranes.
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Affiliation(s)
- Derek P Ng
- Division of Molecular Structure & Function, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada
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Hubert P, Sawma P, Duneau JP, Khao J, Hénin J, Bagnard D, Sturgis J. Single-spanning transmembrane domains in cell growth and cell-cell interactions: More than meets the eye? Cell Adh Migr 2010; 4:313-24. [PMID: 20543559 PMCID: PMC2900628 DOI: 10.4161/cam.4.2.12430] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2010] [Accepted: 05/20/2010] [Indexed: 01/28/2023] Open
Abstract
As a whole, integral membrane proteins represent about one third of sequenced genomes, and more than 50% of currently available drugs target membrane proteins, often cell surface receptors. Some membrane protein classes, with a defined number of transmembrane (TM) helices, are receiving much attention because of their great functional and pharmacological importance, such as G protein-coupled receptors possessing 7 TM segments. Although they represent roughly half of all membrane proteins, bitopic proteins (with only 1 TM helix) have so far been less well characterized. Though they include many essential families of receptors, such as adhesion molecules and receptor tyrosine kinases, many of which are excellent targets for biopharmaceuticals (peptides, antibodies, et al.). A growing body of evidence suggests a major role for interactions between TM domains of these receptors in signaling, through homo and heteromeric associations, conformational changes, assembly of signaling platforms, etc. Significantly, mutations within single domains are frequent in human disease, such as cancer or developmental disorders. This review attempts to give an overview of current knowledge about these interactions, from structural data to therapeutic perspectives, focusing on bitopic proteins involved in cell signaling.
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Affiliation(s)
- Pierre Hubert
- LISM UPR 9027, CNRS-Aix-Marseille University, Marseille, France.
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Finsterer J, Miltenberger G, Rauschka H, Janecke A. Novel C59T leader peptide mutation in the MPZ gene associated with late-onset, axonal, sensorimotor polyneuropathy. Eur J Neurol 2006; 13:1149-52. [PMID: 16987171 DOI: 10.1111/j.1468-1331.2006.01479.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The objective of this study was to report a novel exon-1 mutation in the myelin protein zero (MPZ) gene, resulting in axonal Charcot-Marie-Tooth neuropathy with recurrent hyper-CK-emia. In a 64-year-old woman slowly progressive distal lower limb weakness, muscle cramps in the lower limb muscles, and stocking-type numbness had developed from the age of 61. Neurologic examination revealed discrete hip flexor weakness, weakness for foot extension, diffuse wasting of the distal lower limb muscles, reduced patella tendon reflexes, and absent Achilles tendon reflexes. There was recurrently elevated creatine kinase with a maximum of 607 U/l (n, <145 U/l). Stimulation of the peroneal and tibial nerves did not evoke a muscular response. Electromyography was neurogenic. Biopsy of the right sural nerve showed diffuse axonal degeneration and loss of axons of all diameters. Muscle biopsy showed increased fiber-size variability, angulated fibers, internalized nuclei, accumulations of nuclei, grouped atrophic muscle fibers, and fiber splitting. Molecular genetic analysis by PCR and direct nucleotide sequencing revealed the heterozygous C59T exon-1 MPZ gene mutation, resulting in the amino acid exchange S20F of the MPZ signal protein domain (leader peptide). The novel C59T mutation in the leader peptide of the MPZ gene is pathogenic and manifests as severe, late-onset, axonal, symmetric sensorimotor polyneuropathy (CMT2) and hyper-CK-emia.
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Affiliation(s)
- J Finsterer
- Krankenanstalt Rudolfstiftung, Vienna, Austria.
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