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Mayer JA, Griffiths IR, Goldman JE, Smith CM, Cooksey E, Radcliff AB, Duncan ID. Modeling the natural history of Pelizaeus-Merzbacher disease. Neurobiol Dis 2015; 75:115-30. [PMID: 25562656 PMCID: PMC4492172 DOI: 10.1016/j.nbd.2014.12.023] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2014] [Revised: 12/10/2014] [Accepted: 12/23/2014] [Indexed: 11/27/2022] Open
Abstract
Major gaps in our understanding of the leukodystrophies result from their rarity and the lack of tissue for the interdisciplinary studies required to extend our knowledge of the pathophysiology of the diseases. This study details the natural evolution of changes in the CNS of the shaking pup (shp), a model of the classical form of the X-linked disorder Pelizaeus-Merzbacher disease, in particular in glia, myelin, and axons, which is likely representative of what occurs over time in the human disease. The mutation in the proteolipid protein gene, PLP1, leads to a delay in differentiation, increased cell death, and a marked distension of the rough endoplasmic reticulum in oligodendrocytes. However, over time, more oligodendrocytes differentiate and survive in the spinal cord leading to an almost total recovery of myelination, In contrast, the brain remains persistently hypomyelinated. These data suggest that shp oligodendrocytes may be more functional than previously realized and that their early recruitment could have therapeutic value.
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Affiliation(s)
- Joshua A Mayer
- Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Ian R Griffiths
- Department of Veterinary Clinical Studies, University of Glasgow, Bearsden, Glasgow G61 1QH, Scotland
| | - James E Goldman
- Department of Pathology & Cell Biology, Columbia University, New York, NY 10027, USA
| | - Chelsey M Smith
- Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Elizabeth Cooksey
- Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Abigail B Radcliff
- Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Ian D Duncan
- Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI 53706, USA.
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Mayer CA, Macklin WB, Avishai N, Balan K, Wilson CG, Miller MJ. Mutation in the myelin proteolipid protein gene alters BK and SK channel function in the caudal medulla. Respir Physiol Neurobiol 2009; 169:303-14. [PMID: 19808102 DOI: 10.1016/j.resp.2009.09.013] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2009] [Revised: 09/24/2009] [Accepted: 09/25/2009] [Indexed: 12/31/2022]
Abstract
Proteolipid protein (Plp) gene mutation in rodents causes severe CNS dysmyelination, early death, and lethal hypoxic ventilatory depression (Miller et al., 2004). To determine if Plp mutation alters neuronal function critical for control of breathing, the nucleus tractus solitarii (nTS) of four rodent strains were studied: myelin deficient rats (MD), myelin synthesis deficient (Plp(msd)), and Plp(null) mice, as well as shiverer (Mbp(shi)) mice, a myelin basic protein mutant. Current-voltage relationships were analyzed using whole-cell patch-clamp in 300 microm brainstem slices. Voltage steps were applied, and inward and outward currents quantified. MD, Plp(msd), and Plp(null), but not Mbp(shi) neurons exhibited reduced outward current in nTS at P21. Apamin blockade of SK calcium-dependent currents and iberiotoxin blockade of BK calcium-dependent currents in the P21 MD rat demonstrated reduced outward current due to dysfunction of these channels. These results provide evidence that Plp mutation specifically alters neuronal excitability through calcium-dependent potassium channels in nTS.
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Affiliation(s)
- Catherine A Mayer
- Department of Pediatrics, Case Western Reserve University, 11100 Euclid Ave, Cleveland, OH 44106, United States.
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Southwood C, Olson K, Wu CY, Gow A. Novel alternatively spliced endoplasmic reticulum retention signal in the cytoplasmic loop of Proteolipid Protein-1. J Neurosci Res 2007; 85:471-8. [PMID: 17171701 PMCID: PMC4606141 DOI: 10.1002/jnr.21153] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Increased awareness about the importance of protein folding and trafficking to the etiology of gain-of-function diseases has driven extensive efforts to understand the cell and molecular biology underlying the life cycle of normal secretory pathway proteins and the detrimental effects of abnormal proteins. In this regard, the quality-control machinery in the endoplasmic reticulum (ER) has emerged as a major mechanism by which cells ensure that secreted and transmembrane proteins either adopt stable secondary, tertiary, and quaternary structures or are retained in the ER and degraded. Here we examine cellular and molecular aspects of ER retention in transfected fibroblasts expressing missense mutations in the Proteolipid Protein-1 (PLP1) gene that cause mild or severe forms of neurodegenerative disease in humans. Mild mutations cause protein retention in the ER that is partially dependent on the presence of a cytoplasmically exposed heptapeptide, KGRGSRG. In contrast, retention associated with severe mutations occurs independently of this peptide. Accordingly, the function of this novel heptapeptide has a significant impact on pathogenesis and provides new insight into the functions of the two splice isoforms encoded by the PLP1 gene, PLP1 and DM-20.
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Affiliation(s)
- Cherie Southwood
- Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, Michigan
| | - Kevin Olson
- Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, Michigan
| | - Chia-Yen Wu
- Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, Michigan
| | - Alexander Gow
- Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, Michigan
- Carman and Ann Adams Department of Pediatrics, Wayne State University School of Medicine, Detroit, Michigan
- Department of Neurology, Wayne State University School of Medicine, Detroit, Michigan
- Correspondence to: Dr. Alexander Gow, Center for Molecular Medicine and Genetics, 3216 Scott Hall, 540 E. Canfield Ave, Wayne State University School of Medicine, Detroit, MI 48201.
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Hurst S, Garbern J, Trepanier A, Gow A. Quantifying the carrier female phenotype in Pelizaeus-Merzbacher disease. Genet Med 2006; 8:371-8. [PMID: 16778599 DOI: 10.1097/01.gim.0000223551.95862.c3] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
PURPOSE Pelizaeus-Merzbacher disease and spastic paraplegia type 2 are allelic X-linked disorders that principally affect males and are caused by mutations in the proteolipid protein 1 gene. Neurologic symptoms are occasionally observed in carrier females, and anecdotal evidence suggests that these clinical signs are more likely in families with affected males. We analyze 40 pedigrees to determine whether such a link exists. METHODS From a chart review of patients from Wayne State University, we categorize patients according to disease severity and type of genetic lesion within the proteolipid protein 1 gene. We then analyze the clinical data using nonparametric t tests and analyses of variance. RESULTS Our analyses formally demonstrate the link between mild disease in males and symptoms in carrier female relatives. Conversely, mutations causing severe disease in males rarely cause clinical signs in carrier females. The greatest risk of disease in females is found for nonsense/indel or null mutations. Missense mutations carry moderate risk. The lowest risk, which represents the bulk of families with Pelizaeus-Merzbacher disease, is associated with proteolipid protein 1 gene duplications. CONCLUSIONS Effective genetic counseling of Pelizaeus-Merzbacher disease and spastic paraplegia carrier females must include an assessment of disease severity in affected male relatives.
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Affiliation(s)
- Stephanie Hurst
- Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, Michigan 48201, USA
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Song J, Goetz BD, Duncan ID. His36Pro point-mutated proteolipid protein retained in the endoplasmic reticulum of oligodendrocytes in theShaking pup. Glia 2005; 53:257-65. [PMID: 16265668 DOI: 10.1002/glia.20279] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The shaking pup (shp) is a canine mutation that affects the myelin protein proteolipid protein (PLP) and its smaller and less abundant isoform, DM20, with proline replacing histidine(36), resulting in a severe myelin deficiency in the central nervous system. We present evidence that the mutation leads to disrupted trafficking of the shp PLP/DM20 within oligodendrocytes. Immunohistochemical studies revealed significantly reduced levels of PLP/DM20 and other major myelin components such as myelin basic protein (MBP), myelin associated glycoprotein (MAG), and 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) in shp myelin. The distribution of shp PLP/DM20 proteins were altered and mostly retained in perinuclear cytoplasm and proximal processes, which co-localized with distended rough endoplasmic reticulum (RER) within oligodendrocytes. No abnormal accumulation of MAG, MBP, or CNP in the cell body was found. These results suggest that mutated PLP/DM20 in the shp could be selectively retained in RER, causing disruption of their translocation to the periphery to myelinate axons.
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Affiliation(s)
- Jonathan Song
- Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin, Madison, Wisconsin 53706, USA.
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Abstract
Intracellular trafficking of membranes plays an essential role in the biogenesis and maintenance of myelin. The requisite proteins and lipids are transported from their sites of synthesis to myelin via vesicles. Vesicle transport is tightly coordinated with synthesis of lipids and proteins. To maintain the structural and functional organization of oligodendrocytes it is essential synchronize the various pathways of vesicle transport and to coordinate vesicle transport with reorganization of cytoskeleton. The systems that regulate the targeting of protein to myelin by vesicle transport are now being described. Here we review the current knowledge of these systems including those involved in (a) protein folding, (b) protein sorting and formation of carrier vesicles, (c) vesicle transport along elements of the cytoskeleton, and (d) vesicle targeting/fusion.
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Affiliation(s)
- J N Larocca
- Department of Neurology/Neuroscience, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
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Baumann N, Pham-Dinh D. Biology of oligodendrocyte and myelin in the mammalian central nervous system. Physiol Rev 2001; 81:871-927. [PMID: 11274346 DOI: 10.1152/physrev.2001.81.2.871] [Citation(s) in RCA: 1203] [Impact Index Per Article: 52.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Oligodendrocytes, the myelin-forming cells of the central nervous system (CNS), and astrocytes constitute macroglia. This review deals with the recent progress related to the origin and differentiation of the oligodendrocytes, their relationships to other neural cells, and functional neuroglial interactions under physiological conditions and in demyelinating diseases. One of the problems in studies of the CNS is to find components, i.e., markers, for the identification of the different cells, in intact tissues or cultures. In recent years, specific biochemical, immunological, and molecular markers have been identified. Many components specific to differentiating oligodendrocytes and to myelin are now available to aid their study. Transgenic mice and spontaneous mutants have led to a better understanding of the targets of specific dys- or demyelinating diseases. The best examples are the studies concerning the effects of the mutations affecting the most abundant protein in the central nervous myelin, the proteolipid protein, which lead to dysmyelinating diseases in animals and human (jimpy mutation and Pelizaeus-Merzbacher disease or spastic paraplegia, respectively). Oligodendrocytes, as astrocytes, are able to respond to changes in the cellular and extracellular environment, possibly in relation to a glial network. There is also a remarkable plasticity of the oligodendrocyte lineage, even in the adult with a certain potentiality for myelin repair after experimental demyelination or human diseases.
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Affiliation(s)
- N Baumann
- Institut National de la Santé et de la Recherche Médicale U. 495, Biology of Neuron-Glia Interactions, Salpêtrière Hospital, Paris, France.
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Southwood C, Gow A. Molecular pathways of oligodendrocyte apoptosis revealed by mutations in the proteolipid protein gene. Microsc Res Tech 2001; 52:700-8. [PMID: 11276122 DOI: 10.1002/jemt.1054] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
A decade after the genetic link was established between mutations in the proteolipid protein gene and two leukodystrophies, Pelizaeus-Merzbacher disease and spastic paraplegia, the molecular mechanisms underlying pathogenesis are beginning to come to light. Data from animal models of these diseases suggest that the absence of proteolipid protein gene products in the central nervous system confers a relatively mild phenotype while missense mutations in and duplications of this gene give rise to mild or severe forms of disease. Previously, we have interpreted the disease process in terms of the accumulation of the mutant proteins in the secretory pathway and, herein, we review the evidence in favor of such a cellular mechanism. Furthermore, on the basis of recent data we suggest that the unfolded protein response may be involved in the pathogenesis of Pelizaeus-Merzbacher disease and spastic paraplegia through a kinase signaling cascade that links the accumulation of mutant proteins in the endoplasmic reticulum of oligodendrocytes with changes in gene regulation, protein synthesis, and possibly apoptosis.
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Affiliation(s)
- C Southwood
- Brookdale Center for Developmental and Molecular Biology, Mount Sinai School of Medicine, New York, NY 10029, USA
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Palaniyar N, Semotok JL, Wood DD, Moscarello MA, Harauz G. Human proteolipid protein (PLP) mediates winding and adhesion of phospholipid membranes but prevents their fusion. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1415:85-100. [PMID: 9858696 DOI: 10.1016/s0005-2736(98)00180-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
Proteolipid protein (PLP or lipophilin) is a highly conserved, strongly hydrophobic, integral membrane protein, and is the major protein component of central nervous system myelin. Although PLP has been implicated in many functions, its in vivo role is still uncertain. Here, we report the investigation of PLP's putative adhesive function using purified PLP and reconstituted phospholipid vesicles made of either 100% phosphatidylcholine (PC), or a mixture of 92% PC and 8% phosphatidylserine (PS), by weight. PLP-induced changes in the phospholipid bilayer surfaces were directly examined by transmission electron microscopy. We found that upon the introduction of PLP, larger lipid vesicles became smaller and unilamellar. At the PLP:lipid molar ratio of 1:20, vesicle membranes rolled onto themselves forming 'croissant'-like structures that subsequently adhered to each other. The phenomena of PLP-induced bilayer rolling and adhesion were dependent on the concentration of PLP and the period of incubation, but were independent of the presence of calcium and types of phospholipids (PC or PC:PS). Furthermore, the presence of PLP in the lipid bilayers prevented the fusion of membranes. These findings show that PLP can induce membrane 'winding' while preventing the fusion of adjacent lipid bilayers. Hence, our data provide direct evidence for PLP's suspected function of membrane adhesion, and also suggest that PLP could potentially play a role in the formation of the myelin sheath.
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Affiliation(s)
- N Palaniyar
- Department of Molecular Biology and Genetics, The University of Guelph, 50 Stone Road East, Guelph, Ont. N1G 2W1, Canada
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Gow A, Southwood CM, Lazzarini RA. Disrupted proteolipid protein trafficking results in oligodendrocyte apoptosis in an animal model of Pelizaeus-Merzbacher disease. J Cell Biol 1998; 140:925-34. [PMID: 9472043 PMCID: PMC2141744 DOI: 10.1083/jcb.140.4.925] [Citation(s) in RCA: 175] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Pelizaeus-Merzbacher disease (PMD) is a dysmyelinating disease resulting from mutations, deletions, or duplications of the proteolipid protein (PLP) gene. Distinguishing features of PMD include pleiotropy and a range of disease severities among patients. Previously, we demonstrated that, when expressed in transfected fibroblasts, many naturally occurring mutant PLP alleles encode proteins that accumulate in the endoplasmic reticulum and are not transported to the cell surface. In the present communication, we show that oligodendrocytes in an animal model of PMD, the msd mouse, accumulate Plp gene products in the perinuclear region and are unable to transport them to the cell surface. Another important aspect of disease in msd mice is oligodendrocyte cell death, which is increased by two- to threefold. We demonstrate in msd mice that this death occurs by apoptosis and show that at the time oligodendrocytes die, they have differentiated, extended processes that frequently contact axons and are expressing myelin structural proteins. Finally, we define a hypothesis that accounts for pathogenesis in most PMD patients and animal models of this disease and, moreover, can be used to develop potential therapeutic strategies for ameliorating the disease phenotype.
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Affiliation(s)
- A Gow
- Brookdale Center for Developmental and Molecular Biology, Mount Sinai School of Medicine, New York 10029-6574, USA
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