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Abstract
Haploinsufficiency of peripheral myelin protein 22 (PMP22) causes hereditary neuropathy with liability to pressure palsies, a peripheral nerve lesion induced by minimal trauma or compression. As PMP22 is localized to cholesterol-enriched membrane domains that are closely linked with the underlying actin network, we asked whether the myelin instability associated with PMP22 deficiency could be mediated by involvement of the protein in actin-dependent cellular functions and/or lipid raft integrity. In peripheral nerves and cells from mice with PMP22 deletion, we assessed the organization of filamentous actin (F-actin), and actin-dependent cellular functions. Using in vitro models, we discovered that, in the absence of PMP22, the migration and adhesion capacity of Schwann cells and fibroblasts are similarly impaired. Furthermore, PMP22-deficient Schwann cells produce shortened myelin internodes, and display compressed axial cell length and collapsed lamellipodia. During early postnatal development, F-actin-enriched Schmidt-Lanterman incisures do not form properly in nerves from PMP22(-/-) mice, and the expression and localization of molecules associated with uncompacted myelin domains and lipid rafts, including flotillin-1, cholesterol, and GM1 ganglioside, are altered. In addition, we identified changes in the levels and distribution of cholesterol and ApoE when PMP22 is absent. Significantly, cholesterol supplementation of the culture medium corrects the elongation and migration deficits of PMP22(-/-) Schwann cells, suggesting that the observed functional impairments are directly linked with cholesterol deficiency of the plasma membrane. Our findings support a novel role for PMP22 in the linkage of the actin cytoskeleton with the plasma membrane, likely through regulating the cholesterol content of lipid rafts.
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2
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Baburina YL, Krestinina OV, Azarashvili TS. 2′,3′-cyclic nucleotide phosphodiesterase (CNPase) as a target in neurodegenerative diseases. NEUROCHEM J+ 2013. [DOI: 10.1134/s1819712412040034] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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3
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The association of white matter volume in psychotic disorders with genotypic variation in NRG1, MOG and CNP: a voxel-based analysis in affected individuals and their unaffected relatives. Transl Psychiatry 2012; 2:e167. [PMID: 23032943 PMCID: PMC3565820 DOI: 10.1038/tp.2012.82] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
We investigated the role of variation in putative psychosis genes coding for elements of the white matter system by examining the contribution of genotypic variation in three single-nucleotide polymorphisms (SNPs) neuregulin 1 (NRG1) SNP8NRG221533, myelin oligodendrocytes glycoprotein (MOG) rs2857766 and CNP (rs2070106) and one haplotype HAP(ICE) (deCODE) to white matter volume in patients with psychotic disorder and their unaffected relatives. Structural magnetic resonance imaging and blood samples for genotyping were collected on 189 participants including patients with schizophrenia (SZ) or bipolar I disorder (BDI), unaffected first-degree relatives of these patients and healthy volunteers. The association of genotypic variation with white matter volume was assessed using voxel-based morphometry in SPM5. The NRG1 SNP and the HAP(ICE) haplotype were associated with abnormal white matter volume in the BDI group in the fornix, cingulum and parahippocampal gyrus circuit. In SZ the NRG1 SNP risk allele was associated with lower white matter volume in the uncinate fasciculus (UF), right inferior longitudinal fasciculus and the anterior limb of the internal capsule. Healthy G-homozygotes of the MOG SNP had greater white matter volume in areas of the brainstem and cerebellum; this relationship was absent in those with a psychotic disorder and the unaffected relatives groups. The CNP SNP did not contribute to white matter volume variation in the diagnostic groups studied. Variation in the genes coding for structural and protective components of myelin are implicated in abnormal white matter volume in the emotion circuitry of the cingulum, fornix, parahippocampal gyrus and UF in psychotic disorders.
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Horiuchi M, Maezawa I, Itoh A, Wakayama K, Jin LW, Itoh T, DeCarli C. Amyloid β1-42 oligomer inhibits myelin sheet formation in vitro. Neurobiol Aging 2012; 33:499-509. [PMID: 20594620 PMCID: PMC3013291 DOI: 10.1016/j.neurobiolaging.2010.05.007] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2010] [Revised: 04/30/2010] [Accepted: 05/09/2010] [Indexed: 01/26/2023]
Abstract
Accumulating evidence indicates that white matter degeneration contributes to the neural disconnections that underlie Alzheimer's disease pathophysiology. Although this white matter degeneration is partly attributable to axonopathy associated with neuronal degeneration, amyloid β (Aβ) protein-mediated damage to oligodendrocytes could be another mechanism. To test this hypothesis, we studied effects of soluble Aβ in oligomeric form on survival and differentiation of cells of the oligodendroglial lineage using highly purified oligodendroglial cultures from rats at different developmental stages. Aβ oligomer at 10 μM or higher reduced survival of mature oligodendrocytes, whereas oligodendroglial progenitor cells (OPCs) were relatively resistant to the Aβ oligomer-mediated cytotoxicity. Further study revealed that Aβ oligomer even at 1 μM accelerated 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) formazan exocytosis in mature oligodendrocytes, and, more significantly, inhibited myelin sheet formation after induction of in vitro differentiation of OPCs. These results imply a novel pathogenetic mechanism underlying Aβ oligomer-mediated white matter degeneration, which could impair myelin maintenance and remyelination by adult OPCs, resulting in accumulating damage to myelinating axons thereby contributing to neural disconnections.
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Affiliation(s)
- Makoto Horiuchi
- Department of Neurology, University of California Davis, School of Medicine, Sacramento, CA, United States
- Institute for Pediatric Regenerative Medicine, Shriners Hospitals for Children Northern California, Sacramento, CA, United States
| | - Izumi Maezawa
- M.I.N.D. Institute and Department of Pathology, Department of Internal Medicine, University of California Davis Cancer Center, University of California Davis, Sacramento, CA, United States
| | - Aki Itoh
- Department of Neurology, University of California Davis, School of Medicine, Sacramento, CA, United States
- Institute for Pediatric Regenerative Medicine, Shriners Hospitals for Children Northern California, Sacramento, CA, United States
| | - Kouji Wakayama
- Department of Neurology, University of California Davis, School of Medicine, Sacramento, CA, United States
- Institute for Pediatric Regenerative Medicine, Shriners Hospitals for Children Northern California, Sacramento, CA, United States
| | - Lee-Way Jin
- M.I.N.D. Institute and Department of Pathology, Department of Internal Medicine, University of California Davis Cancer Center, University of California Davis, Sacramento, CA, United States
| | - Takayuki Itoh
- Department of Neurology, University of California Davis, School of Medicine, Sacramento, CA, United States
- Institute for Pediatric Regenerative Medicine, Shriners Hospitals for Children Northern California, Sacramento, CA, United States
| | - Charles DeCarli
- Department of Neurology, University of California Davis, School of Medicine, Sacramento, CA, United States
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The multiple roles of myelin protein genes during the development of the oligodendrocyte. ASN Neuro 2010; 2:e00027. [PMID: 20017732 PMCID: PMC2814326 DOI: 10.1042/an20090051] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2009] [Revised: 12/14/2009] [Accepted: 12/17/2009] [Indexed: 11/22/2022] Open
Abstract
It has become clear that the products of several of the earliest identified myelin protein genes perform functions that extend beyond the myelin sheath. Interestingly, these myelin proteins, which comprise proteolipid protein, 2′,3′-cyclic nucleotide 3′-phosphodiesterase and the classic and golli MBPs (myelin basic proteins), play important roles during different stages of oligodendroglial development. These non-myelin-related functions are varied and include roles in the regulation of process outgrowth, migration, RNA transport, oligodendrocyte survival and ion channel modulation. However, despite the wide variety of cellular functions performed by the different myelin genes, the route by which they achieve these many functions seems to converge upon a common mechanism involving Ca2+ regulation, cytoskeletal rearrangements and signal transduction. In the present review, the newly emerging functions of these myelin proteins will be described, and these will then be discussed in the context of their contribution to oligodendroglial development.
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Hinman JD, Chen CD, Oh SY, Hollander W, Abraham CR. Age-dependent accumulation of ubiquitinated 2′,3′-cyclic nucleotide 3′-phosphodiesterase in myelin lipid rafts. Glia 2008; 56:118-33. [DOI: 10.1002/glia.20595] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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8
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Behbehani GR, Saboury AA, Baghery AF. A Thermodynamic Study on the Binding of Calcium Ion with Myelin Basic Protein. J SOLUTION CHEM 2007. [DOI: 10.1007/s10953-007-9181-y] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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9
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Hill CMD, Libich DS, Harauz G. Assembly of tubulin by classic myelin basic protein isoforms and regulation by post-translational modification. Biochemistry 2006; 44:16672-83. [PMID: 16342957 DOI: 10.1021/bi050646+] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Myelin basic protein (MBP), a highly cationic protein that maintains the structure of the myelin sheath, associates with tubulin in vivo. The in vitro assembly of tubulin by MBP was examined here using several assays. The unmodified C1 component of 18.5 kDa bovine MBP (bC1) assembled tubulin into microtubules in a dose-dependent manner via filamentous intermediates, and was able simultaneously to promote the formation of microtubule bundles. The critical tubulin concentration in the presence of bC1 was 0.69 +/- 0.05 microM. The effects of post-translational modifications (such as deamidation and phosphorylation) were assayed by comparing the bC1-bC6 components of 18.5 kDa bovine MBP; an increasing level of modification enhanced the ability of MBP to assemble tubulin. The effects of charge reduction via deimination were examined using recombinant murine isoforms emulating the unmodified C1 and deiminated C8 isoforms of 18.5 kDa MBP; both rmC1 and rmC8 exhibited a comparable ability to assemble tubulin. The effects of alternate exon recombination of the classic MBP variants were tested using the recombinant murine 21.5, 17.22, and 14 kDa isoforms. The isoforms containing regions derived from exon II of the classic MBP gene, 21.5 and 17.22 kDa MBP, showed no substantial difference in the extent of tubulin polymerization and bundling when compared to those of 18.5 kDa MBP. The 14 kDa isoform and two terminal deletion mutants of rmC1 were able to induce microtubule polymerization, but not bundling, to the same degree as the longer proteins. Finally, bC1 was shown to disrupt and aggregate planar sheets of crystalline tubulin stabilized by paclitaxel, establishing that these structures are not suitable substrates for the formation of MBP cocrystals.
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Affiliation(s)
- Christopher M D Hill
- Department of Molecular and Cellular Biology and Biophysics Interdepartmental Group, University of Guelph, 50 Stone Road East, Guelph, Ontario, Canada N1G 2W1
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Loers G, Aboul-Enein F, Bartsch U, Lassmann H, Schachner M. Comparison of myelin, axon, lipid, and immunopathology in the central nervous system of differentially myelin-compromised mutant mice: a morphological and biochemical study. Mol Cell Neurosci 2005; 27:175-89. [PMID: 15485773 DOI: 10.1016/j.mcn.2004.06.006] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2004] [Revised: 05/27/2004] [Accepted: 06/08/2004] [Indexed: 01/06/2023] Open
Abstract
The present study was carried out to compare different myelin-compromised mouse mutants with regard to myelin morphology in relation to axon-, lipid-, and immunopathology as a function of age. Mouse mutants deficient in the myelin-associated glycoprotein (MAG) and myelin basic protein (MBP) display subtle and severe myelin pathologies in the central nervous system (CNS), respectively. Animals doubly deficient in MAG and the neural cell adhesion molecule (NCAM) show defects similar to those present in MAG single mutants while mice deficient in MAG and the nonreceptor type tyrosine kinase Fyn are severely hypomyelinated, in addition to the MAG-specific myelin abnormalities. These mutant mice showed distinct myelin pathologies in different regions of the central nervous system and generally displayed a decrease in axonal integrity with age. Myelin pathology did not correlate locally with axon transection and with an involvement of the immune system as seen by numbers of CD3-positive lymphocytes and MAC-3-positive macrophages. Interestingly, the degree of these cellular abnormalities also did not correlate with abnormalities in levels of phospholipids, arachidonic acid, cholesterol, and apolipoprotein E (apoE). Moreover, these changes in lipid metabolism, including immune system-related arachidonic acid, preceded cellular pathology. The combined observations point to differences, but also similarities in the relation of myelin, axon, and immunopathology with genotype, and to a common aggravation of the phenotype with age.
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Affiliation(s)
- Gabriele Loers
- Zentrum für Molekulare Neurobiologie Hamburg, Universität Hamburg, D-20251 Hamburg, Germany
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11
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Harauz G, Ishiyama N, Hill CMD, Bates IR, Libich DS, Farès C. Myelin basic protein-diverse conformational states of an intrinsically unstructured protein and its roles in myelin assembly and multiple sclerosis. Micron 2004; 35:503-42. [PMID: 15219899 DOI: 10.1016/j.micron.2004.04.005] [Citation(s) in RCA: 189] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The 18.5 kDa isoform of myelin basic protein (MBP) is a major component of the myelin sheath in the central nervous system of higher vertebrates, and a member of a larger family of proteins with a multiplicity of forms and post-translational modifications (PTMs). The 18.5 kDa protein is the exemplar of the family, being most abundant in adult myelin, and thus the most-studied. It is peripherally membrane-associated, but has generally been investigated in isolated form. MBP is an 'intrinsically unstructured' protein with a high proportion (approximately 75%) of random coil, but postulated to have core elements of beta-sheet and alpha-helix. We review here the properties of the MBP family, especially of the 18.5 kDa isoform, and discuss how its three-dimensional (3D) structure may be resolved by direct techniques available to us, viz., X-ray and electron crystallography, and solution and solid-state NMR spectrometry. In particular, we emphasise that creating an appropriate environment in which the protein can adopt a physiologically relevant fold is crucial to such endeavours. By solving the 3D structure of 18.5 kDa MBP and the effects of PTMs, we will attain a better understanding of myelin architecture, and of the molecular mechanisms that transpire in demyelinating diseases such as multiple sclerosis.
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Affiliation(s)
- George Harauz
- Department of Molecular Biology and Genetics, Biophysics Interdepartmental Group, University of Guelph, Room 230, Axelrod Building, 50 Stone Road East, Guelph, Ont., Canada N1G 2W1.
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12
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Abstract
Phenylketonuria is caused by specific mutations in the phenylalanine hydroxylase gene and is characterized by elevated blood phenylalanine levels, hypomyelination in forebrain structures, reduced dopamine levels, and cognitive difficulties. To determine whether brain tyrosine levels and/or myelination play a role in the up-regulation of dopamine, phenylketonuric mice were placed on a low phenylalanine diet for 4 weeks and as blood phenylalanine levels dropped to normal, the relationships between phenylalanine, tyrosine, dopamine, myelin proteins, and axonal proteins in frontal cortex and striatum were determined using gas chromatography mass spectrometry, histology, and western blotting techniques. Blood phenylalanine rapidly decreased from an eight-fold elevation to near control levels, and blood tyrosine gradually rose from about 50% to near normal values. In frontal cortex and striatum, phenylalanine levels dropped to 2- and 1.5-fold elevations above control, respectively, and tyrosine levels increased but remained less than 70% of control in both structures. In frontal cortex, increases in dopamine and myelin basic protein occurred in a similar biphasic pattern, reaching near normal levels by week 4. In striatum, dopamine and MBP dramatically increased to near normal levels in the first week. Myelination was confirmed histologically and by western blot quantification of phosphorylated neurofilaments. In summary, our results showed: (i) an increase in dopamine despite low brain tyrosine levels and (ii) similar recovery patterns for myelination and dopamine. Since myelin/axonal interactions trigger signaling pathways that result in axonal maturation, we speculate that this interaction also may trigger signals that up-regulate neurotransmitter synthesis.
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Affiliation(s)
- Bernadin Joseph
- Department of Neurology, The University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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Libich DS, Hill CM, Bates IR, Hallett FR, Armstrong S, Siemiarczuk A, Harauz G. Interaction of the 18.5-kD isoform of myelin basic protein with Ca2+ -calmodulin: effects of deimination assessed by intrinsic Trp fluorescence spectroscopy, dynamic light scattering, and circular dichroism. Protein Sci 2003; 12:1507-21. [PMID: 12824496 PMCID: PMC2323942 DOI: 10.1110/ps.0303603] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The effects of deimination (conversion of arginyl to citrullinyl residues) of myelin basic protein (MBP) on its binding to calmodulin (CaM) have been examined. Four species of MBP were investigated: unmodified recombinant murine MBP (rmMBP-Cit(0)), an engineered protein with six quasi-citrullinyl (i.e., glutaminyl) residues per molecule (rmMBP-qCit(6)), human component C1 (hMBP-Cit(0)), and human component C8 (hMBP-Cit(6)), both obtained from a patient with multiple sclerosis (MS). Both rmMBP-Cit(0) and hMBP-Cit(0) bound CaM in a Ca(2+)-dependent manner and primarily in a 1:1 stoichiometry, which was verified by dynamic light scattering. Circular dichroic spectroscopy was unable to detect any changes in secondary structure in MBP upon CaM-binding. Inherent Trp fluorescence spectroscopy and a single-site binding model were used to determine the dissociation constants: K(d) = 144 +/- 76 nM for rmMBP-Cit(0), and K(d) = 42 +/- 15 nM for hMBP-Cit(0). For rmMBP-qCit(6) and hMBP-Cit(6), the changes in fluorescence were suggestive of a two-site interaction, although the dissociation constants could not be accurately determined. These results can be explained by a local conformational change induced in MBP by deimination, exposing a second binding site with a weaker association with CaM, or by the existence of several conformers of deiminated MBP. Titration with the collisional quencher acrylamide, and steady-state and lifetime measurements of the fluorescence at 340 nm, showed both dynamic and static components to the quenching, and differences between the unmodified and deiminated proteins that were also consistent with a local conformational change due to deimination.
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Affiliation(s)
- David S. Libich
- Department of Molecular Biology and Genetics, and Biophysics Interdepartmental Group, and
| | - Christopher M.D. Hill
- Department of Molecular Biology and Genetics, and Biophysics Interdepartmental Group, and
| | - Ian R. Bates
- Department of Molecular Biology and Genetics, and Biophysics Interdepartmental Group, and
| | - F. Ross Hallett
- Department of Physics, and Biophysics Interdepartmental Group, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Souzan Armstrong
- Photon Technology International, London, Ontario N6E 2S8, Canada
| | | | - George Harauz
- Department of Molecular Biology and Genetics, and Biophysics Interdepartmental Group, and
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14
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Libich DS, Harauz G. Interactions of the 18.5-kDa isoform of myelin basic protein with Ca(2+)-calmodulin: in vitro studies using fluorescence microscopy and spectroscopy. Biochem Cell Biol 2003; 80:395-406. [PMID: 12234092 DOI: 10.1139/o02-020] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The interactions of the 18.5-kDa isoform of myelin basic protein (MBP) with calmodulin (CaM) in vitro have been investigated using fluorescence microscopy and spectroscopy. Two forms of MBP were used: the natural bovine C1 charge isomer (bMBP/C1) and a hexahistidine-tagged recombinant murine product (rmMBP), with only minor differences in behaviour being observed. Fragments of each protein generated by digestion with cathepsin D (EC 3.4.23.5) were also evaluated. Using fluorescence microscopy, it was shown that MBP and CaM interacted in the presence of Ca2+ under a variety of conditions, including high urea and salt concentrations, indicating that the interaction was specific and not merely electrostatic in nature. Using cathepsin D digestion fragments of MBP, it was further shown that the carboxyl-terminal domain of MBP interacted with Ca(2+)-CaM, consistent with our theoretical prediction. Spectroscopy of the intrinsic fluorescence of the sole Trp residue of MBP showed that binding was cooperative in nature. The dissociation constants for formation of a 1:1 MBP-Ca(2+)-CaM complex were determined to be 2.1 +/- 0.1 and 2.0 +/- 0.2 microM for bMBP/C1 and rmMBP, respectively. Fluorescence spectroscopy using cathepsin D digestion fragments indicated also that the carboxyl-terminal region of each protein interacted with Ca(2+)-CaM, with dissociation constants of 1.8 +/- 0.2 and 2.8 +/- 0.9 microM for the bMBP/C1 and rmMBP fragments, respectively. These values show a roughly 1000-fold lower affinity of MBP for CaM than other CaM-binding peptides, such as myristoylated alanine-rich C-kinase substrate, that are involved in signal transduction.
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Affiliation(s)
- David S Libich
- Department of Molecular Biology and Genetics, University of Guelph, ON, Canada
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15
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Kaur J, Libich DS, Campagnoni CW, Wood DD, Moscarello MA, Campagnoni AT, Harauz G. Expression and properties of the recombinant murine Golli-myelin basic protein isoform J37. J Neurosci Res 2003; 71:777-84. [PMID: 12605403 DOI: 10.1002/jnr.10547] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
A recombinant form of the murine Golli-myelin basic protein (MBP) isoform J37 (rmJ37) has been expressed in Escherichia coli and isolated to 95% purity via metal chelation and ion exchange chromatography. The protein did not aggregate lipid vesicles containing acidic phospholipids, unlike the 18.5 kDa isoform of MBP. This result is consistent with J37 having a functional role prior to the assembly of compact myelin. Circular dichroic spectroscopy showed that rmJ37 had a large proportion of random coil in aqueous solution but gained alpha-helix and beta-sheet in the presence of monosialoganglioside G(M1) and PI(4)P. Thus, like "classic" MBP, J37 is intrinsically unstructured, and its conformation depends on its environment and bound ligands. Analyses of the amino acid sequence of rmJ37 predicted an N-terminal calmodulin (CaM)-binding site. It was determined via a gel-shift assay and fluorescence spectroscopy that rmJ37 and CaM interacted in a 1:1 ratio in a Ca(2+)-dependent manner. However, the interaction was weak compared with 18.5 kDa MBP.
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Affiliation(s)
- Jaspreet Kaur
- Department of Molecular Biology and Genetics, and Biophysics Interdepartmental Group, University of Guelph, Guelph, Ontario, Canada
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Paz Soldán MM, Warrington AE, Bieber AJ, Ciric B, Van Keulen V, Pease LR, Rodriguez M. Remyelination-promoting antibodies activate distinct Ca2+ influx pathways in astrocytes and oligodendrocytes: relationship to the mechanism of myelin repair. Mol Cell Neurosci 2003; 22:14-24. [PMID: 12595235 DOI: 10.1016/s1044-7431(02)00018-0] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
Our laboratory has identified mouse and human monoclonal antibodies that promote myelin repair in multiple models of demyelinating disease. We have proposed that these antibodies promote remyelination by directly activating central nervous system glia. Intracellular calcium concentration was monitored using a Fura2 ratiometric assay. Repair-promoting antibodies induced distinct Ca2+ signals in both astrocytes and oligodendrocytes. Astrocyte Ca2+ signaling is mediated by a phospholipase C-dependent pathway while oligodendrocyte Ca2+ signaling is mediated via AMPA-sensitive glutamate receptors. An antibody's ability to induce Ca2+ signals is statistically correlated with promotion of myelin repair. These findings support the hypothesis that remyelination-promoting antibodies are acting directly at the surface of glial cells to induce calcium-dependent physiologic reparative function.
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MESH Headings
- Animals
- Animals, Newborn
- Antibodies, Monoclonal/immunology
- Antibodies, Monoclonal/pharmacology
- Antigens, Surface/drug effects
- Antigens, Surface/immunology
- Astrocytes/drug effects
- Astrocytes/immunology
- Astrocytes/metabolism
- Calcium/metabolism
- Calcium Signaling/drug effects
- Calcium Signaling/immunology
- Cells, Cultured
- Demyelinating Diseases/drug therapy
- Demyelinating Diseases/immunology
- Demyelinating Diseases/metabolism
- Disease Models, Animal
- Endoplasmic Reticulum/drug effects
- Endoplasmic Reticulum/metabolism
- Female
- Glial Fibrillary Acidic Protein/metabolism
- Humans
- Mice
- Mice, Inbred Strains
- Myelin Sheath/immunology
- Myelin Sheath/metabolism
- Oligodendroglia/drug effects
- Oligodendroglia/immunology
- Oligodendroglia/metabolism
- Protein Binding/immunology
- Protein Structure, Tertiary/physiology
- Rats
- Rats, Sprague-Dawley
- Receptors, AMPA/antagonists & inhibitors
- Receptors, AMPA/metabolism
- Signal Transduction/drug effects
- Signal Transduction/immunology
- Up-Regulation/drug effects
- Up-Regulation/immunology
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Affiliation(s)
- M Mateo Paz Soldán
- Program in Molecular Neuroscience, Mayo Medical and Graduate Schools, 200 First Street SW, Rochester, MN 55905, USA
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Abstract
The goal of this overview is to propose a novel structure/function model of central nervous system myelin. Although myelin is known to be a compact multilamellar structure that wraps around axons, the biologic role this structure plays in the nervous system remains an enigma. One means of ascertaining myelin's biologic role is by analyzing its structure. The recent discovery of tight junctions in myelin may be the key that unlocks the mysterious black box of myelin structure/function. Tight junctions in other cell types are invariably adjacent to adherens junctions, with both of these junctional plaques playing critical roles in paracellular barrier function, i.e., adhesion of cell membranes, signal transduction, and fluid movement between cells via aqueous pores and channels. The application of current knowledge about junctional plaques to myelin is an original concept. This knowledge, taken together with evidence from studies of normal and pathologic myelin, supports the possibility that a primary function of junctional plaques in myelin is to perfuse the periaxonal space.
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Affiliation(s)
- Charissa A Dyer
- The Children's Hospital of Philadelphia, 502A Abramson Research Center, 3615 Civic Center Blvd., Philadelphia, Pennsylvania 19104, USA.
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Ishiyama N, Bates IR, Hill CM, Wood DD, Matharu P, Viner NJ, Moscarello MA, Harauz G. The effects of deimination of myelin basic protein on structures formed by its interaction with phosphoinositide-containing lipid monolayers. J Struct Biol 2001; 136:30-45. [PMID: 11858705 DOI: 10.1006/jsbi.2001.4421] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The recombinant 18.5-kDa charge isoform of murine myelin basic protein (rmMBP) is unmodified posttranslationally and was used to study the effects of deimination, i.e., the conversion of arginyl to citrullinyl residues, on the protein's interactions with itself and with lipids. The unmodified species rmMBP-Cit(0) (i.e., containing no citrullinyl residues) interacted with binary monolayers containing acidic (phosphatidylinositol) and nickel-chelating lipids to form paracrystalline arrays with 4.8-nm spacing. A sample of protein was deiminated to an average of 9 citrullinyl residues per molecule of protein, yielding rmMBP-Cit(9). Under both low- and high-salt conditions, this species formed better-ordered domains than rmMBP-Cit(0), viz., planar crystalline assemblies. Thus, deimination of MBP resulted in a significant alteration of its lipid-organizing and self-interaction properties that might be operative in myelin in vivo, especially in progression of the autoimmune disease multiple sclerosis. Comparisons of amino acid sequences indicated significant similarities of MBP with filaggrin, a protein that is deiminated in another autoimmune disease, rheumatoid arthritis, suggesting that comparable epitopes could be targeted in both pathologies. In contrast, binary lipid monolayers consisting of phosphatidylinositol-4-phosphate (or phosphatidylinositol-4,5-bisphosphate) and a nickel-chelating lipid formed helical tubular vesicular structures, which appeared to be induced and/or stabilized by rmMBP, especially in its deiminated form. Sequence comparisons with other actin- and phosphoinositide-binding proteins (vinculin, ActA, MARCKS) suggested that the carboxyl-terminal segment of MBP could form an amphipathic alpha helix and was the phosphoinositide binding site.
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Affiliation(s)
- N Ishiyama
- Department of Molecular Biology and Genetics, University of Guelph, 50 Stone Road East, Guelph, Ontario, N1G 2W1, Canada
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Shefer S, Tint GS, Jean-Guillaume D, Daikhin E, Kendler A, Nguyen LB, Yudkoff M, Dyer CA. Is there a relationship between 3-hydroxy-3-methylglutaryl coenzyme a reductase activity and forebrain pathology in the PKU mouse? J Neurosci Res 2000; 61:549-63. [PMID: 10956425 DOI: 10.1002/1097-4547(20000901)61:5<549::aid-jnr10>3.0.co;2-0] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Previous reports have suggested that elevated levels of phenylalanine inhibit cholesterol synthesis. The goals of this study were to investigate if perturbations in cholesterol synthesis exist in the PAH(enu2) genetic mouse model for phenylketonuria (PKU), and if so, initiate studies determining if they might underlie the white matter pathology that exists in PKU forebrain. Gross sections and electron microscopy showed that select tracts were hypomyelinated in adult PKU mouse forebrain but not hindbrain. The activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), the rate controlling enzyme in the cholesterol biosynthetic pathway, was examined in isolated microsomes from forebrain, hindbrain, and liver to assess if perturbations in cholesterol biosynthesis were occurring. HMGR activity was normal in unaffected PKU hindbrain and was increased 2-4-fold in PKU liver compared to control. HMGR activity in the forebrain, however, was decreased by 30%. Because normal numbers of MBP-expressing glia (oligodendrocytes) were present, but the number of glia expressing HMGR was reduced by 40% in the hypomyelinated tracts, the decreased HMGR activity seemed to result from a down-regulation of HMGR expression in affected oligodendrocytes. Exposure of an oligodendrocyte-like glioma cell line to physiologically relevant elevated levels of Phe resulted in a 30% decrease in cholesterol synthesis, a 28% decrease in microsomal HMGR activity, and a 28% decrease in HMGR protein levels. Measurement of HMGR activity after addition of exogenous Phe to control brain microsomes revealed that Phe is a noncompetitive inhibitor of HMGR; physiologically relevant elevated levels of exogenous Phe inhibited HMGR activity by 30%. Taken together, these data suggest that HMGR is moderately inhibited in the PKU mouse. Unlike other cell types in the body, a subset of oligodendrocytes in the forebrain seems to be unable to overcome this inhibition. We speculate that this may be the cause of the observed pathology in PKU brain.
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Affiliation(s)
- S Shefer
- Department of Medicine/Liver Center, UMDNJ-New Jersey Medical School, Newark, NJ, USA
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