Structure and developmental regulation of Golli-mbp, a 105-kilobase gene that encompasses the myelin basic protein gene and is expressed in cells in the oligodendrocyte lineage in the brain

Lymphopenia-induced proliferation is a potent activator for CD4+ T cell-mediated autoimmune disease in the retina

To study retinal immunity in a defined system, a CD4+ TCR transgenic mouse line (betagalTCR) specific for beta-galactosidase (betagal) was created and used with transgenic mice that expressed betagal in retinal photoreceptor cells (arrbetagal mice). Adoptive transfer of resting betagalTCR T cells, whether naive or Ag-experienced, into arrbetagal mice did not induce retinal autoimmune disease (experimental autoimmune uveoretinitis, EAU) and gave no evidence of Ag recognition. Generation of betagalTCR T cells in arrbetagal mice by use of bone marrow grafts, or double-transgenic mice, also gave no retinal disease or signs of Ag recognition. Arrbetagal mice were also resistant to EAU induction by adoptive transfer of in vitro-activated betagalTCR T cells, even though the T cells were pathogenic if the betagal was expressed elsewhere. In vitro manipulations to increase T cell pathogenicity before transfer did not result in EAU. The only strategy that induced a high frequency of severe EAU was transfer of naive, CD25-depleted, betagalTCR T cells into lymphopenic arrbetagal recipients, implicating regulatory T cells in the T cell inoculum, as well as in the recipients, in the resistance to EAU. Surprisingly, activation of the CD25-depleted betagalTCR T cells before transfer into the lymphopenic recipients reduced EAU. Taken together, the results suggest that endogenous regulatory mechanisms, as well as peripheral induction of regulatory T cells, play a role in the protection from EAU.

Different development of myelin basic protein agonist- and antagonist-specific human TCR transgenic T cells in the thymus and periphery

Myelin basic protein (MBP)-specific T cells are thought to play a role in the development of multiple sclerosis. MBP residues 111-129 compose an immunodominant epitope cluster restricted by HLA-DRB1*0401. The sequence of residues 111-129 of MBP (MBP(111-129)) differs in humans (MBP122:Arg) and mice (MBP122:Lys) at aa 122. We previously found that approximately 50% of human MBP(111-129) (MBP122:Arg)-specific T cell clones, including MS2-3C8 can proliferate in response to mouse MBP(111-129) (MBP122:Lys). However, the other half of T cell clones, including HD4-1C2, cannot proliferate in response to MBP(111-129) (MBP122:Lys). We found that MBP(111-129) (MBP122:Lys) is an antagonist for HD4-1C2 TCR, therefore, MS2-3C8 and HD4-1C2 TCRs are agonist- and antagonist-specific TCRs in mice, respectively. Therefore, we examined the development of HD4-1C2 TCR and MS2-3C8 TCR transgenic (Tg) T cells in the thymus and periphery. We found that dual TCR expression exclusively facilitates the development of MBP(111-129) TCR Tg T cells in the periphery of HD4-1C2 TCR/HLA-DRB1*0401 Tg mice although it is not required for their development in the thymus. We also found that MS2-3C8 TCR Tg CD8(+) T cells develop along with MS2-3C8 TCR Tg CD4(+) T cells, and that dual TCR expression was crucial for the development of MS2-3C8 TCR Tg CD4(+) and CD8(+) T cells in the thymus and periphery, respectively. These results suggest that thymic and peripheral development of MBP-specific T cells are different; however, dual TCR expression can facilitate their development.

Presentation of a determinant by MHC class II can be prevented through competitive capture by a flanking determinant on a multideterminant peptide

Competitive capture is a process by which different determinants of an unfolding antigen compete for binding to the same MHC class II molecule. The "winning" determinant is then dominantly displayed. For self antigens, T cells with specificity for dominantly displayed determinants will be subject to strong tolerance induction. With this in mind we set out to characterize the determinant hierarchy of the junctional region of the Golli-MBP complex. Within this region the MBP 1-9 determinant is known to be a strong inducer of experimental autoimmune encephalomyelitis. We found that the Golli-MBP junctional region contains a triad of three overlapping determinants: LDVM1-5, MBP 1-9, and MBP 7-20. We demonstrate that these three determinants are unique and compete for binding to I-A(u) and that a determinant hierarchy exists with MBP 7-20 being the most dominantly displayed determinant. Because of the prevention of MBP1-9 access to MHC-II, the residual T cell repertoire to this determinant remains complete, thereby permitting its highest affinity members to drive the response, and to convert MBP1-9 into a dominant determinant, despite its poor MHC binding capacity.

Backbone dynamics of the 18.5 kDa isoform of myelin basic protein reveals transient alpha-helices and a calmodulin-binding site

The 18.5 kDa isoform of myelin basic protein (MBP) is the predominant form in adult human central nervous system myelin. It is an intrinsically disordered protein that functions both in membrane adhesion, and as a linker connecting the oligodendrocyte membrane to the underlying cytoskeleton; its specific interactions with calmodulin and SH3-domain containing proteins suggest further multifunctionality in signaling. Here, we have used multidimensional heteronuclear nuclear magnetic resonance spectroscopy to study the conformational dependence on environment of the protein in aqueous solution (100 mM KCl) and in a membrane-mimetic solvent (30% TFE-d(2)), particularly to analyze its secondary structure using chemical shift indexing, and to investigate its backbone dynamics using (15)N spin relaxation measurements. Collectively, the data revealed three major segments of the protein with a propensity toward alpha-helicity that was stabilized by membrane-mimetic conditions: T33-D46, V83-T92, and T142-L154 (murine 18.5 kDa sequence numbering). All of these regions corresponded with bioinformatics predictions of ordered secondary structure. The V83-T92 region comprises a primary immunodominant epitope that had previously been shown by site-directed spin labeling and electron paramagnetic resonance spectroscopy to be alpha-helical in membrane-reconstituted systems. The T142-L154 segment overlapped with a predicted calmodulin-binding site. Chemical shift perturbation experiments using labeled MBP and unlabeled calmodulin demonstrated a dramatic conformational change in MBP upon association of the two proteins, and were consistent with the C-terminal segment of MBP being the primary binding site for calmodulin.

A microarray gene expression study of the molecular pharmacology of lithium carbonate on mouse brain mRNA to understand the neurobiology of mood stabilization and treatment of bipolar affective disorder

OBJECTIVES

Lithium is the most widely prescribed and effective mood-stabilizing drug used for the treatment of bipolar affective disorder. To understand how lithium produces changes in the brain, we studied brain mRNA from 10 mice after treatment with lithium and compared them with 10 untreated controls.

METHODS

We used the MAS 5.0, Smudge miner, GC-RMA and FDR-AME packages of software (Bioconductor, Seattle, Washington, USA) to determine gene expression changes using Affymetrix MOE430E 2.0 microarrays after 2 weeks of lithium treatment.

RESULTS

We used both a false discovery rate (FDR-AME) assessment of significance and the Bonferroni method to correct for the possibility of false-positive changes in gene expression among the 39,000 genes present in each array. Our primary method of analysis was to use t-tests on normalized gene expression intensities. By using a Bonferroni correction of P<1.28x10(-6), we found that 121 genes showed significant changes in expression. The three genes with the most changed mRNA expression were alanine-glyoxylate aminotransferase 2-like 1 (Agxt2l1), c-mer proto-oncogene tyrosine kinase (Mertk) and sulfotransferase family 1A phenol-preferring member 1 (Sult1a1). Also among the group of 121 genes with significant changes in gene expression that survived Bonferroni correction () were the genes encoding the Per2 period gene (Per2 P=1.33x10(-8), 2.47-fold change), the metabotropic glutamate receptor (Grm3, P=9.48x10(-7), 0.7-fold change) and secretogranin II (Scg2, P=9.48x10(-7), 1.28-fold change) as well as several myelin-related genes and protein phosphatases. By taking a significance value of P<0.05 without Bonferroni or FDR-AME correction, we identified a total of 4474 genes showing changed mRNA expression in response to lithium. FDR-AME analysis showed that 1027 out of these 4474 genes were significantly changed in expression. Among the mRNAs that were significantly changed with t-tests and FDR-AME were several that had already been implicated in response to lithium such as increased brain-derived neurotrophic factor mRNA ( t-test P=0.0008-0.0005, FDR-AME P=0.0396-0.0393, 1.44-fold change) beta-phosphatidylinositol transfer protein (Pitpnb, t-test P<0.0000, FDR-AME P=0.003, 1.26-fold change) and inositol (myo)-1(or 4)-monophosphatase 1(Impa1, t test P<0.0000, FDR-AME P=0.004, 1.22-fold change). Of interest in relation to the side effect of hypothyroidism, which is caused by long-term lithium treatment was the fact that we observed changes in mRNA expression in five genes related to thyroxine metabolism. These included deiodinase (Dio2 t-test P=0.000003-0.004, FDR-AME P=0.0048-0.061, 1.53-fold change) and thyroid hormone receptor interactor 12 (Trip12, t-test P=0.003, FDR-AME P=0.075, 1.19-fold change). Of relevance to multiple sclerosis was the observed upregulation of the long isoform of myelin basic protein (t-test P=0.00013, FDR-AME P=0.0169). Changes in mRNA expression were found in 45 genes related to phosphatidylinositol metabolism using uncorrected t-tests but only 13 genes after FDR-AME. Thus, our work confirms the considerable previous research implicating this system. Gene ontology analysis showed that lithium significantly affected a cluster of processes associated with nucleotide and nucleoside metabolism. The analysis showed that there were 170 genes expressing RNA described as having ATP-binding or ATPase activity that had changed mRNA expression. The changes found have been discussed in relation to previous experimental work on the pharmacology of lithium.

The BG21 isoform of Golli myelin basic protein is intrinsically disordered with a highly flexible amino-terminal domain

The genes of the oligodendrocyte lineage (Golli) encode a family of developmentally regulated isoforms of myelin basic protein. The "classic" MBP isoforms arise from transcription start site 3, whereas Golli-specific isoforms arise from transcription start site 1, and comprise both Golli-specific and classic MBP sequences. The Golli isoform BG21 has been suggested to play roles in myelination and T cell activation pathways. It is an intrinsically disordered protein, thereby presenting a large effective surface area for interaction with other proteins such as Golli-interacting protein. We have used multidimensional heteronuclear NMR spectroscopy to achieve sequence-specific resonance assignments of the recombinant murine BG21 in physiologically relevant buffer, to analyze its secondary structure using chemical shift indexing (CSI), and to investigate its backbone dynamics using 15N spin relaxation measurements. We have assigned 184 out of 199 residues unambiguously. The CSI analysis revealed little ordered secondary structure under these conditions, with only some small fragments having a slight tendency toward alpha-helicity, which may represent putative recognition motifs. The 15N relaxation and NOE measurements confirmed the general behavior of the protein as an extended polypeptide chain, with the N-terminal Golli-specific portion (residues S5-T69) being exceptionally flexible, even in comparison to other intrinsically disordered proteins that have been studied this way. The high degree of flexibility of this N-terminal region may be to provide additional plasticity, or conformational adaptability, in protein-protein interactions. Another highly mobile segment, A126-S127-G128-G129, may function as a hinge.

Purification and spectroscopic characterization of the recombinant BG21 isoform of murine golli myelin basic protein

A recombinant form of the murine Golli-myelin basic protein (MBP) isoform BG21 (rmBG21) has been expressed in E. coli, and isolated to 96% purity via metal chelation chromatography. Characteristic yields were 6-8 mg protein per liter of culture in either minimal M9 or standard Luria-Bertani media. Circular dichroism spectroscopy showed that rmBG21 had a large proportion of random coil in aqueous solution, but gained alpha-helix in the presence of monosialoganglioside G(M1) and PI(4)P, as well as in the membrane-mimetic solvent trifluoroethanol. Bioinformatics analyses of the amino acid sequence of rmBG21 predicted an N-terminal calmodulin (CaM)-binding site. It was determined by fluorescence spectroscopy and dynamic light scattering that rmBG21 and CaM interacted weakly in a 1:1 ratio in a Ca(2+)-dependent manner. Solution NMR spectra of uniformly [(13)C(15)N]-labeled protein in aqueous buffer were consistent with it being an extended protein; spectral quality was independent of temperature. Thus, like "classic" MBP and the Golli-MBP isoform J37, rmBG21 is intrinsically disordered, implying multi functionality, and that its conformation depends on its environment and bound ligands.

Inhibition of familial cerebral amyloid angiopathy mutant amyloid beta-protein fibril assembly by myelin basic protein

Deposition of fibrillar amyloid beta-protein (Abeta) in the brain is a prominent pathological feature of Alzheimer disease and related disorders, including familial forms of cerebral amyloid angiopathy (CAA). Mutant forms of Abeta, including Dutch- and Iowa-type Abeta, which are responsible for familial CAA, deposit primarily as fibrillar amyloid along the cerebral vasculature and are either absent or present only as diffuse non-fibrillar plaques in the brain parenchyma. Despite the lack of parenchymal fibril formation in vivo, these CAA mutant Abeta peptides exhibit a markedly increased rate and extent of fibril formation in vitro compared with wild-type Abeta. Based on these conflicting observations, we sought to determine whether brain parenchymal factors that selectively interact with and modulate CAA mutant Abeta fibril assembly exist. Using a combination of immunoaffinity chromatography and mass spectrometry, we identified myelin basic protein (MBP) as a prominent brain parenchymal factor that preferentially binds to CAA mutant Abeta compared with wild-type Abeta. Surface plasmon resonance measurements confirmed that MBP bound more tightly to Dutch/Iowa CAA double mutant Abeta than to wild-type Abeta. Using a combination of biochemical and ultrastructural techniques, we found that MBP inhibited the fibril assembly of CAA mutant Abeta. Together, these findings suggest a possible role for MBP in regulating parenchymal fibrillar Abeta deposition in familial CAA.

Molecular "negativity" may underlie multiple sclerosis: role of the myelin basic protein family in the pathogenesis of MS

Myelin basic protein (MBP) binds to negatively charged lipids on the cytosolic surface of oligodendrocyte membranes and is responsible for adhesion of these surfaces in the multilayered myelin sheath. The pattern of extensive posttranslational modifications of MBP is dynamic during normal central nervous system development and during myelin degeneration in multiple sclerosis (MS), affecting its interactions with the myelin membranes and other proteins. In particular, the degree of deimination (or citrullination) of MBP is correlated with the severity of MS, and may represent a primary defect that precedes neurodegeneration due to autoimmune attack. That MBP deimination also affects topological accessibility of an otherwise partially buried immunodominant epitope of the protein indicates that this modification may play a major role in the autoimmune pathogenesis of the disease. In this chapter, we describe the structural and functional consequences of MBP deimination in healthy and diseased myelin.

Partitioning of myelin basic protein into membrane microdomains in a spontaneously demyelinating mouse model for multiple sclerosisThis paper is one of a selection of papers published in this Special Issue, entitled CSBMCB — Membrane Proteins in Health and Disease

We have characterized the lipid rafts in myelin from a spontaneously demyelinating mouse line (ND4), and from control mice (CD1 background), as a function of age and severity of disease. Myelin was isolated from the brains of CD1 and ND4 mice at various ages, and cold lysed with 1.5% CHAPS (3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulphonate). The lysate was separated by low-speed centrifugation into supernatant and pellet fractions, which were characterized by Western blotting for myelin basic protein (MBP) isoforms and their post-translationally modified variants. We found that, with maturation and with disease progression, there was a specific redistribution of the 14–21.5 kDa MBP isoforms (classic exon-II-containing vs exon-II-lacking) and phosphorylated forms into the supernatant and pellet. Further fractionation of the supernatant to yield detergent-resistant membranes (DRMs), representing coalesced lipid rafts, showed these to be highly enriched in exon-II-lacking MBP isoforms, and deficient in methylated MBP variants, in mice of both genotypes. The DRMs from the ND4 mice appeared to be enriched in MBP phosphorylated by MAP kinase at Thr95 (murine 18.5 kDa numbering). These studies indicate that different splice isoforms and post-translationally modified charge variants of MBP are targeted to different microdomains in the myelin membrane, implying multifunctionality of this protein family in myelin maintenance.

Minireview: expression and function of golli protein in immune system

In this minireview, the author briefly reviews the development of our understanding on the immunological function of golli proteins. In the immune system, in addition to serving as autoantigens, golli proteins have been recently found to regulate T-cell activation directly, thus modulating EAE induction. The evidence that golli proteins function as signal molecules is summarized.

T(2)-weighted microMRI and evoked potential of the visual system measurements during the development of hypomyelinated transgenic mice

Our objective was to follow the course of a dysmyelinating disease followed by partial recovery in transgenic mice using non-invasive high-resolution (117 x 117 x 70 microm) magnetic resonance (microMRI) and evoked potential of the visual system (VEP) techniques. We used JOE (for J37 golli overexpressing) transgenic mice engineered to overexpress golli J37, a product of the Golli-mbp gene complex, specifically in oligodendrocytes. Individual JOE transgenics and their unaffected siblings were followed from 21 until 75-days-old using non-invasive in vivo VEPs and 3D T2-weighted microMRI on an 11.7 T scanner, performing what we believe is the first longitudinal study of its kind. The microMRI data indicated clear, global hypomyelination during the period of peak myelination (21-42 days), which was partially corrected at later ages (>60 days) in the JOE mice compared to controls. These microMRI data correlated well with [Campagnoni AT (1995) "Molecular biology of myelination". In: Ransom B, Kettenmann H (eds) Neuroglia--a Treatise. Oxford University Press, London, pp 555-570] myelin staining, [Campagnoni AT, Macklin WB (1988) Cellular and molecular aspects of myelin protein gene-expression. Mol Neurobiol 2:41-89] a transient intention tremor during the peak period of myelination, which abated at later ages, and [Lees MB, Brostoff SW (1984) Proteins in myelin. In: Morell (ed) Myelin. Plenum Press, New York and London, pp 197-224] VEPs which all indicated a significant delay of CNS myelin development and persistent hypomyelination in JOE mice. Overall these non-invasive techniques are capable of spatially resolving the increase in myelination in the normally developing and developmentally delayed mouse brain.

A Tale of Two Citrullines—Structural and Functional Aspects of Myelin Basic Protein Deimination in Health and Disease

Myelin basic protein (MBP) binds to negatively charged lipids on the cytosolic surface of oligodendrocyte membranes and is responsible for adhesion of these surfaces in the multilayered myelin sheath. The pattern of extensive post-translational modifications of MBP is dynamic during normal central nervous system (CNS) development and during myelin degeneration in multiple sclerosis (MS), affecting its interactions with the myelin membranes and with other molecules. In particular, the degree of deimination (or citrullination) of MBP is correlated with the severity of MS, and may represent a primary defect that precedes neurodegeneration due to autoimmune attack. That the degree of MBP deimination is also high in early CNS development indicates that this modification plays major physiological roles in myelin assembly. In this review, we describe the structural and functional consequences of MBP deimination in healthy and diseased myelin.

Golli protein negatively regulates store depletion-induced calcium influx in T cells

Calcium influx is crucial for T cell activation and differentiation. The detailed regulation of this process remains unclear. We report here that golli protein, an alternatively spliced product of the myelin basic protein gene, plays a critical role in regulating calcium influx in T cells. Golli-deficient T cells were hyperproliferative and showed enhanced calcium entry upon T cell receptor stimulation. We further found that golli regulates calcium influx in T cells through the inhibition of the store depletion-induced calcium influx. Mutation of the myristoylation site on golli disrupted its association with the plasma membrane and reversed its inhibitory action on Ca2+ influx, indicating that membrane association of golli was essential for its inhibitory action. These results indicate that golli functions in a unique way to regulate T cell activation through a mechanism involving the modulation of the calcium homeostasis.

Interaction between microglia and oligodendrocyte cell progenitors involves Golli proteins

Multiple sclerosis (MS) is an autoimmune and chronic inflammatory disease characterized by plaques, areas of destroyed myelin sheaths in the CNS, which results in multiple disabilities for patients. In addition to demyelinated plaques, pathophysiological studies have shown "shadow plaques" that represent areas of partial remyelination. New myelin can be made by oligodendrocytes (OLs) generated from oligodendrocyte progenitor cells (OPCs) that pre-exist in the demyelinated area or recruited from surrounding areas. To successfully repopulate the demyelinated area, OPCs have to proliferate, migrate, and differentiate into mature OLs capable of forming myelin. Identifying factors that influence remyelination is a current topic in developmental neurobiology. Previously, we showed that Golli proteins, which have a broad distribution in the nervous and immune systems, are present both in OPCs and activated microglia around MS lesions. We hypothesized that in response to inflammation, Golli proteins may promote proliferation of OPCs through microglial cells. To test this, we established neonatal mouse brain slice and cell cultures and used lipopolysaccharide (LPS) to induce inflammation. In LPS-treated brain slices, Golli proteins displayed increased expression in the cortical subventricular zone. Furthermore, Golli proteins were demonstrated only in the conditioned medium from LPS-treated microglial cell cultures (LPS-MCM), and were absent in either conditioned medium from LPS-treated astrocytes or control media. Finally, proliferation of purified OPCs was promoted with LPS-MCM or Golli proteins, but not with LPS alone. In summary, these results demonstrate that activated microglia are beneficial for proliferation of OPCs and suggest possible involvement of Golli proteins as one of mediators in this process.

Expression of myelin basic protein in two oligodendroglial cell lines is modulated by apotransferrin through different transcription factors

We have shown that apotransferrin (aTf) promotes the differentiation of two oligodendroglial cell (OLGc) lines, N19 and N20.1, representing different stages of OLGc maturation. Although in both cell lines aTf promoted myelin basic protein (MBP) expression, an increase in cAMP levels and CREB phosphorylation was observed only in the less mature cells (N19), suggesting that the maturation induced by aTf is achieved probably through different signaling pathways. We transfected both cell lines with the proximal region of the human MBP promoter fused to the lacZ reporter gene. In both transfected cell lines, addition of aTf produced an activation of the promoter. To elucidate the mechanisms involved in this action, Western blot analysis, EMSAs, and RT-PCR were performed for different transcription factors involved in mbp regulation. In the N20.1 line, treatment with aTf increased the expression and the DNA-binding capacity of thyroid hormone (TH) receptors, Sp1, and nuclear factor-kappaB (NFkappaB). For these cells we found that an inductor of NFkappaB (tumor necrosis factor-alpha) promoted MBP messenger synthesis, whereas mithramycin, a specific inibitor of Sp1, and a cAMP analog (db-cAMP) inhibited its transcription. In the N19 cell line, aTf stimulated NF-I and NFkappaB activation, but, aside from aTf, only db-cAMP induced mbp transcription. These data suggest that, depending on the OLGc maturational stage, aTf modulates MBP expression and OLGc differentiation through different signaling pathways and different transcription factors.

The pathobiology of myelin mutants reveal novel biological functions of the MBP and PLP genes

Substantial biological data indicate that the myelin basic protein (MBP) and myelin proteolipid protein (PLP/DM20) genes produce products with functions beyond that of serving as myelin structural proteins. Much of this evidence comes from studies on naturally-occurring and man-made mutations of these genes in mice and other species. This review focuses upon recent evidence showing the existence of other products of these genes that may account for some of these other functions, and recent studies providing evidence for alternative biological functions of PLP/DM20. The MBP and PLP/DM20 genes each encode the classic MBP and PLP isoforms, as well as a second family of proteins that are not involved in myelin structure. The biological roles of these other products of the genes are becoming clarified. The non-classic MBP gene products appear to be components of transcriptional complexes in the nucleus, and they also may be involved in signaling pathways in T-cells and in neural cells. The non-classic PLP/DM20 gene products appear to be components of intracellular transport vesicles in oligodendrocytes. There is evidence for other functions of the classic PLP/DM20 proteins, including a role in neural cell death mechanisms, autocrine and paracrine regulation of oligodendrocytes and neurons, intracellular transport and oligodendrocyte migration.

Production of CETD transgenic mouse line allowing ablation of any type of specific cell population

Diphtheria toxin A-chain (DT-A) is a potent inhibitor of protein synthesis. As little as a single molecule of DT-A can result in cell death. DT-A gene driven by a tissue-specific promoter is used to achieve genetic ablation of a particular cell lineage. However, this transgenic approach often results in aberrant depletion of unrelated cells. To avoid this, we established a method for specific depletion of a cell population by controlled expression of the DT-A gene via the Cre-loxP system. We produced five transgenic mice carrying CETD construct containing loxP-flanked enhanced green fluorescent protein (EGFP) cDNA and the DT-A gene. Transfection of primary cultured cells derived from CETD transgenic fetus with Cre expression plasmid resulted in extensive cell loss, as expected. Bigenic (double transgenic) offspring obtained by crossbreeding between CETD and MNCE transgenic mice in which Cre expression is controlled by the myelin basic protein (MBP) promoter exhibited embryonic lethality, suggesting expression of Cre at embryonic stages. Intravenous injection of Cre expression vector to CETD mice led to generation of glomerular lesions, probably due to predominant depletion of glomerular epithelial cells. This Cre-loxP-based cell ablation technology is powerful and convenient method of generating mice lacking any chosen cell population.

Autoimmune CD4+ T cell memory: lifelong persistence of encephalitogenic T cell clones in healthy immune repertoires

We embedded green fluorescent CD4(+) T cells specific for myelin basic protein (MBP) (T(MBP-GFP) cells) in the immune system of syngeneic neonatal rats. These cells persisted in the animals for the entire observation period spanning >2 years without affecting the health of the hosts. They maintained a memory phenotype with low levels of L-selectin and CD45RC, but high CD44. Although persisting in low numbers (0.01-0.1% of lymph node cells) they were sufficient to raise susceptibility toward clinical autoimmune disease. Immunization with MBP in IFA induced CNS inflammation and overt clinical disease in animals carrying neonatally transferred T(MBP-GFP) cells, but not in controls. The onset of the clinical disease coincided with mass infiltration of T(MBP-GFP) cells into the CNS. In the periphery, following the amplification phase a rapid contraction of the T cell population was observed. However, elevated numbers of fully reactive T(MBP-GFP) cells remained in the peripheral immune system after acute experimental autoimmune encephalomyelitis mediating reimmunization-induced disease relapses.

Lipopolysaccharide affects Golli expression and promotes proliferation of oligodendrocyte progenitors

Proliferation of oligodendrocyte progenitor cells (OPCs) is important for initial myelination as well as for remyelination in demyelinating diseases. Previously, we showed that numerous OPCs and activated microglia, are present around multiple sclerosis lesions, and that they accumulate Golli proteins. Golli proteins, present in both neuronal and immune cells, might have a role in the immune processes, as well as in development of neurons and oligodendrocytes. We hypothesize that Golli proteins, generated by microglia in response to inflammation, promote proliferation of OPCs. To test this hypothesis, we induced inflammation in neonatal mouse brain slice culture with bacterial endotoxin lipopolysaccharide (LPS). Treated slices showed an increase in the number of OPCs. Several results support the notion that this effect of LPS is conveyed through activation of microglia and upregulation of Golli proteins. First, LPS-treated brain slices have increased expression of Golli proteins observed by immunofluorescence and Western blot analysis. Second, Golli proteins were demonstrated only in the conditioned medium from LPS-treated microglial cell cultures (LPS-MCM), and were absent in either the conditioned media from LPS-treated astrocytes or the control media. Third, proliferation of purified OPCs was promoted with LPS-MCM or Golli proteins, but not with LPS alone. Taken together, these results demonstrate that microglia and/or microglia secreted factors, are necessary for the LPS-promoted proliferation of OPCs and suggest possible involvement of Golli proteins as one of mediators in this process.

Electron paramagnetic resonance spectroscopy and molecular modelling of the interaction of myelin basic protein (MBP) with calmodulin (CaM)—diversity and conformational adaptability of MBP CaM-targets

The classic 18.5 kDa isoform of murine myelin basic protein (mMBP) has been shown to bind calmodulin (CaM) strongly and specifically in vitro. Here, we have used site-directed spin labelling (SDSL) and electron paramagnetic resonance (EPR) spectroscopy to map more precisely the sites of interaction of recombinant mMBP (rmMBP) with CaM. On the basis of these and previous experimental data, and the predictions of CaM-binding motifs using the Calmodulin Target Database (), three main segments of MBP were suggested for the interaction. The first site is located at the C-terminus; the second one lies in the central portion of the protein and forms an amphipathic alpha-helix in reconstituted myelin-mimetic systems; the third is quite close to the N-terminus. The murine Golli-MBP isoform J37 has also been shown to bind CaM in vitro, and an interaction site was predicted in the N-terminal Golli-specific portion of the protein. From these four segments, we selected peptide fragments of 12-14 residues in length, chosen on the bases of their amphipathicity and CaM-target characteristics. We modelled each of these peptides as alpha-helices, and performed docking simulations to investigate their interactions with the CaM peptide-binding tunnel. Different yet almost equally favourable CaM-binding modes were found for each of them. The experimental SDSL/EPR and theoretical modelling results were in good agreement, and supported the conjecture that there are several plausible CaM-binding sites in MBP, that could be induced into an alpha-helical conformation by their interaction with CaM and account for strong immobilisation of spin-labeled residues in all three segments. Phosphorylation and deimination were also emulated and simulated for known sites of MBP post-translational modification. The results obtained confirmed the appropriate utilisation of simple residue substitutions to mimic the natural modifications, and demonstrated molecular mechanisms by which MBP-CaM interactions could be modulated in vivo.

The magnitude and encephalogenic potential of autoimmune response to MOG is enhanced in MOG deficient mice

Myelin oligodendrocyte glycoprotein (MOG) is a minor component of central nervous system myelin presumably implicated in the pathogenesis of Multiple Sclerosis (MS). Immunization with MOG leads to the development of Experimental Autoimmune Encephalomyelitis (EAE), the experimental model of MS. It has been suggested that its encephalitogenic potential may be due to the lack of MOG self-immune tolerance. To clarify this, we have generated a MOG deficient mouse (MOG(-/-)) strain. Surprisingly, MOG(35-55)specific proliferation and Th1-type cytokine production were markedly enhanced in MOG(-/-)mice compared to wild type control. Furthermore, adoptive transfer of MOG(35-55)specific T cells, isolated from MOG deficient mice, into wild-type recipients resulted in the development of a more severe disease, indicating a high capacity of MOG(-/-)T cells to initiate effector responses. Interestingly, T cell reactivity to overlapping MOG peptides in MOG(-/-)mice did not reveal new potential immunodominant epitopes in H-2(b)mice. Taken together, our data suggests that MOG self-tolerance modulates the encephalitogenic potential of autoreactive MOG T cells in the periphery.

Autoantibody repertoires to brain tissue in autism nuclear families

The hypothesis of an immune dysfunction in autism spectrum disorders has previously been put forward without, however, compelling evidence of a direct relation to its etiology or pathogenesis. To further understand if autoimmunity could play a significant role in autism, we analyzed autoantibody repertoires to brain tissue extract in the plasma of 171 autism children, their parents, and 54 controls, by quantitative immunoblotting. Multiparametric analysis revealed significant differences between patients and controls, and showed that one single reactivity in Section 32 of the blot had the most power to discriminate between these samples. Family correlation coefficients and heritability estimates did not provide any evidence that this reactivity was genetically determined. While the molecular weight of the target protein suggested that it might be an isoform of Myelin Basic Protein (MBP), inhibition assays with human MBP argued against this hypothesis. The study evidences the widespread occurrence of autoreactivities to brain tissue in autism patients, which may represent the immune system's neuroprotective response to a previous brain injury occurred during neurodevelopment. The molecular identification of the target protein in Section 32 will contribute to the understanding of the role of immune responses against brain antigens in autistic patients.

The golli-myelin basic protein negatively regulates signal transduction in T lymphocytes

Protein kinase C (PKC) plays a critical role in signal transduction controlling T lymphocyte activation. Both positive and negative regulation of signal transduction is needed for proper control of T lymphocyte activation. We have found that a golli product of the myelin basic protein (MBP) gene can serve as a negative regulator of signaling pathways in the T lymphocyte, particularly the PKC pathway. Increased expression of golli BG21 in Jurkat T cells strongly inhibits anti-CD3-induced IL-2-luciferase activity, an indicator of T lymphocyte activation. Golli BG21 can be phosphorylated by PKC in vitro and its phosphorylation increases in PMA-activated Jurkat cells. BG21 inhibits the PMA-induced increase in AP-1 or NF-kappaB activation, consistent with golli acting in a PKC-mediated cellular event. Golli BG21 inhibition of the PKC pathway is not due to a direct action on PKC activation but in the cascade following PKC activation, since BG21 neither reduces PKC enzyme activity nor blocks the membrane association of PKCtheta brought on by T lymphocyte activation. The inhibitory function of BG21 is independent of its phosphorylation by PKC because a mutant BG21, in which the PKC sites have been mutated, is as effective as the wild type BG21 in inhibiting the PMA-induced AP-1 activation. Structure-function assays indicate that BG21 inhibitory activity resides in the golli domain rather than in MBP domain of the molecule. These results reveal a novel role for MBP gene products in T lymphocytes within the immune system.

Apotransferrin promotes the differentiation of two oligodendroglial cell lines

We have previously shown that addition of apotransferrin (aTf) accelerates maturation of oligodendroglial cells (OLGcs) in primary cultures. In this work, we examined the effect of aTf on two conditionally immortalized cell lines: N19 and N20.1. These cells proliferate at 34 degrees C and differentiate into mature OLGcs at 39 degrees C. In vitro addition of aTf to both cell lines at the differentiation temperature for 7 days showed increased expression of galactocerebroside, O4, and myelin basic protein (MBP) and a drop in the percentage of BrdU+ cells. The effect on MBP expression was particularly interesting in the less mature N19 cells. These cells do not express either MBP mRNAs or proteins, so aTf induced, rather than modulated, MBP expression in this cell line. In addition, even though MBP mRNAs for all four isoforms were induced, only the 17 and 21.5 kDa appeared to be translated. OLGc differentiation has been shown to be stimulated by the cAMP-CREB pathway. In N19 cells, following a pulse of aTf, there was a 10-fold increase in cAMP levels accompanied by elevated levels of pCREB. In the more mature N20.1 cells, there were no changes in cAMP levels. We conclude that addition of aTf to immature OLGc lines can enhance their expression of differentiated markers, such as MBP. The action of aTf on MBP gene expression in the least mature line is likely to be mediated by the cAMP pathway. In the N20.1 cells, it appears that different signals and/or mechanisms are involved in modulating myelin lipid and MBP expression. The results suggest that aTf can influence OLGc gene expression and differentiation through multiple mechanisms depending on the maturation of the cell.

CD8+ T cells maintain tolerance to myelin basic protein by 'epitope theft'

Myelin basic protein-specific CD8(+) T cells can induce central nervous system autoimmunity; however, immune tolerance prevents these autoreactive cells from causing disease. To define the mechanisms that mediate tolerance, we developed two T cell receptor-transgenic mouse lines with different affinities for the H-2K(k)-restricted myelin basic protein epitope consisting of amino acids 79-87 (MBP(79-87)). We observed both thymic deletion and peripheral tolerance in the lower-affinity T cells. The higher-affinity T cells, however, showed no evidence of tolerance induction and were able to prevent tolerance of the lower-affinity T cells by removing H-2K(k)-MBP(79-87) complexes from antigen-presenting cells without proliferating. This form of immune regulation could limit responses of self-reactive T cells that escape other tolerance mechanisms.

Identification of a protein that interacts with the golli-myelin basic protein and with nuclear LIM interactor in the nervous system

The myelin basic protein (MBP) gene encodes the classic MBPs and the golli proteins, which are related structurally to the MBPs but are not components of the myelin sheath. A yeast two-hybrid approach was used to identify molecular partners that interact with the golli proteins. A mouse cDNA was cloned that encoded a protein of 261 amino acids and called golli-interacting protein (GIP). Database analysis revealed that GIP was the murine homolog of human nuclear LIM interactor-interacting factor (NLI-IF), a nuclear protein whose function is just beginning to be understood. It is a member of a broad family of molecules, found in species ranging from yeast to human, that contain a common domain of approximately 100 amino acids. Immunocytochemical and Northern blot analyses showed co-expression of GIP and golli in several neural cell lines. GIP and golli also showed a similar developmental pattern of mRNA expression in brain, and immunohistochemical staining of GIP and golli showed co-expression in several neuronal populations and in oligodendrocytes in the mouse brain. GIP was localized predominantly in nuclei. GIP co-immunoprecipitated with golli in several in vitro assays as well as from PC12 cells under physiologic conditions. GIP was the first member of this family shown to interact with nuclear LIM interactor (NLI). NLI co-immunoprecipitated with GIP and golli from lysates of N19 cells transfected with NLI, further confirming an interaction between golli, GIP, and NLI. The ability of GIP to interact with both golli and NLI, and the nuclear co-localization of GIP and golli in many cells, indicates a role for the golli products of the MBP gene in NLI- associated regulation of gene expression.

The requirement of ammonium or other cations linked with p-cresol sulfate for cross-reactivity with a peptide of myelin basic protein

Urinary myelin basic protein-like material (MBPLM), so designated because of its immunoreactivity with a polyclonal antibody directed against a cryptic epitope located in residues 83-89 of myelin basic protein (MBP), exists in humans normally but increases in concentration in patients with multiple sclerosis who have progressive disease. Given its possible role in reflecting events of neural tissue destruction occurring in multiple sclerosis, urinary MBPLM is a candidate surrogate marker for this phase of the disease. Previously, it has been demonstrated that p-cresol sulfate (PCS) is the dominant component of MBPLM; however, another component(s) was essential in enabling p-cresol sulfate to have molecular mimicry with MBP peptide 83-89 detected by immunoreactivity. In the present investigation, this remaining component(s) was characterized by a combination of high performance size exclusion chromatography followed by nuclear magnetic resonance spectroscopy and shown to be ammonium. The monovalent cation ammonium could be substituted in vitro by several different monovalent and divalent cations, most notably zinc, in restoring to deprotonated p-cresol sulfate its immunoreactivity as MBPLM. These findings indicate the basis for the unexpected molecular mimicry between an epitope of an encephalitogenic protein and a complex containing a small organic molecule, p-cresol sulfate. Furthermore, the reaction of either ammonium or other cations with p-cresol sulfate may represent an in vivo process directly related to damage of axonal membranes.

STOP proteins

Microtubules assembled from purified tubulin in vitro are labile, rapidly disassembling when exposed to a variety of depolymerizing conditions such as cold temperature. In contrast, in many cell types, microtubules seem to be unaffected when the cell is exposed to the cold. This resistance of microtubules to the cold has been intriguing because the earliest and by far most studied microtubule-associated proteins such as MAP2 and tau are devoid of microtubule cold stabilizing activity. Over the past several years, it has been shown that resistance of microtubules to the cold is largely due to polymer association with a class of microtubule-associated proteins called STOPs. STOPs are calmodulin-binding and calmodulin-regulated proteins which, in mammals, are encoded by a single gene but exhibit substantial cell specific variability due to mRNA splicing and alternative promoter use. STOP microtubule stabilizing activity has been ascribed to two classes of new bifunctional calmodulin- and microtubule-binding motifs, with distinct microtubule binding properties in vivo. STOPs seem to be restricted to vertebrates and are composed of a conserved domain split by the apparent insertion of variable sequences that are completely unrelated among species. Recently, STOP suppression in mice has been found to induce synaptic defects associated with neuroleptic-sensitive behavioral disorders. Thus, STOPs are important for synaptic plasticity. Additionally, STOP-deficient mice may yield a pertinent model for the study of neuroleptics in illnesses such as schizophrenia, currently thought to result from defects in synapse function.

Identification and characterisation of a cDNA encoding a 17-kDa isoform of rat myelin basic protein

The myelin basic proteins (MBPs) are the major proteins of the myelin membrane. Multiple MBP mRNAs and protein isoforms are generated by alternative RNA splicing. Here we describe the isolation and characterisation of a cDNA clone encoding a 17-kDa MBP isoform from the rat (Rattus norvegicus). The isoform is a 158-amino acid protein consisting of exons 1, 3, 4, 6 and 7 of the MBP gene. RT-PCR analysis of brain mRNA showed that transcripts encoding the 17-kDa isoform were expressed at higher levels early in post-natal development, up to 7 days post-partum.

Cloning and characterization of the rat myelin basic protein gene promoter

Expression of myelin basic protein in differentiating oligodendrocytes is mainly regulated at the transcriptional level. To better understand the regulation of myelin basic protein gene expression in mammalian cells, we cloned and characterized the rat myelin basic protein promoter by a genome walking technique. Extensive sequence homology has been found among mouse, rat and human MBP promoters. Alignment of the proximal core promoter of mouse and rat reveals highly conserved cis-elements that are important for regulating myelin basic protein gene transcription. One major transcription start site along with two minor sites have been identified in both mouse and rat myelin basic protein gene promoters using RNA ligase-mediated rapid amplification of 5' cDNA ends. The amplified rat myelin basic protein promoter was cloned into a luciferase reporter construct. Transient transfection experiments show that both mouse and rat myelin basic protein promoters yield increased expression when oligodendrocytes differentiate. The sequence and characterization of the rat MBP promoter provide a useful tool to investigate MBP gene regulation in mammalian cells.

Overlap of promoter and coding sequences in the mouse STOP gene (Mtap6)

The microtubule-associated proteins STOP are essential for synaptic plasticity and integrated brain function. The STOP gene (Mtap6) is composed of 4 exons and presents different developmental and tissue specific alternative transcripts resulting in the neuronal isoforms E- and N-STOP, and in the fibroblastic F-STOP isoform. We now characterize the transcription initiation sites for neuronal and non neuronal STOP transcripts. Our results show that there is a single neuronal specific promoter for transcription of E- and N-STOP mRNAs. F-STOP mRNA transcription is regulated by a distinct promoter. A remarkable feature of this promoter is that it lies within coding sequences expressed in neuronal E- and N-STOP isoforms.

Autoreactive T cells can be protected from tolerance induction through competition by flanking determinants for access to class II MHC

It is not clear why the N-terminal autoantigenic determinant of myelin basic protein (MBP), Ac1-9, is dominant in the B1O.PL (H-2(u)) mouse, given its weak I-A(u)-MHC binding affinity. Similarly, how do high-affinity T cells specific for this determinant avoid negative selection? Because the MBP:1-9 sequence is embryonically expressed uniquely in the context of Golli-MBP, determinants were sought within the contiguous N-terminal "Golli" region that could out-compete MBP:1-9 for MHC binding, and thereby prevent negative selection of the public response to Ac1-9, shown here to be comprised of a V beta 8.2J beta 2.7 and a V beta 8.2J beta 2.4 expansion. Specifically, we demonstrate that Ac1-9 itself can be an effective inducer of central tolerance induction; however, in the context of Golli-MBP, Ac1-9 is flanked by determinants which prevent its display to autoreactive T cells. Our data support competitive capture as a means of protecting high-affinity, autoreactive T cells from central tolerance induction.

Expression and properties of the recombinant murine Golli-myelin basic protein isoform J37

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.

Two separate domains in the golli myelin basic proteins are responsible for nuclear targeting and process extension in transfected cells

The golli products of the myelin basic protein (MBP) gene are expressed in neurons and oligodendrocytes (OLs). In certain neuronal populations, golli proteins undergo translocation between the nucleus and cytoplasm/processes during development. The proteins consist of two domains, a golli domain of 133 amino acids and an MBP domain of variable length. One objective of this study was to identify the sequences responsible for nuclear targeting. Site-directed mutagenesis and deletion analyses were used to generate a series of golli-green fluorescent protein (GFP) DNA constructs that were transfected into OL and neuronal cell lines to follow localization by confocal microscopy. The results indicated that a 36-residue stretch in the MBP domain is essential for nuclear targeting, and the sequence appears to be a nontraditional localization signal motif. The studies also revealed that overexpression of golli proteins could induce dramatic changes in cell morphology. In OL lines, overexpression of intact golli proteins, or golli peptide alone, caused an increase in the length and number of processes, and the elaboration of membrane sheets. In the neuronal lines, there was a dramatic increase in number and length of extensions. The results, consistent with the timing of golli expression in cells during neural development, suggest that golli proteins may be involved in process formation/extension in OLs and neurons during development. These studies have defined two functional domains in the golli protein. Sequences in the MBP domain target the protein into the nucleus and sequences within the golli domain induce process sheet extension in OLs and neurons.

The myelin basic protein gene is expressed in differentiated blood cell lineages and in hemopoietic progenitors

Myelin basic proteins (MBP) are major constituents of the myelin sheath of oligodendrocytes and Schwann cells in the central nervous system and the peripheral nervous system, respectively. We previously showed that MBP-related transcripts are present in the bone marrow and the immune system. These mRNAs are transcribed from a region called 0', consisting of three exons, located upstream of the classical MBP exons; these three exons belong to the long MBP gene otherwise called "Golli-MBP." The most abundant of these mRNAs, now called HMBP (hemopoietic MBP), encompasses the sequence encoded by the region 0' plus exon 1 and part of intron 1 of the classic MBP gene. Antisera to recombinant HMBP proteins are immunoreactive with proteins of about 26-28 kDa in brain, thymus, and spleen. This report demonstrates that HMBP proteins are present in the vast majority (>95%) of thymic T cells, which express the corresponding transcripts, as do mature T cells from lymph nodes and spleen. HMBP mRNAs and proteins are also manifest in the majority of spleen B lymphocytes and in B cell lines. In addition to lymphoid cells, HMBP proteins are in all types of myeloid lineage cells, i.e., macrophages, dendritic cells, and granulocytes, as well as in megakaryocytes and erythroblasts. Finally, HMBP proteins are present in CD34+ bone marrow cells, and, furthermore, in highly proliferative cultures, these CD34+ cells express HMBP RNAs and proteins. Thus, MBP gene products are present both in the nervous system and in the entire hemopoietic system.

Expression of Golli proteins in adult human brain and multiple sclerosis lesions

It has been suggested that Golli proteins, structurally related to myelin basic proteins (MBPs), have a role in autoimmune processes. We studied the expression of these proteins in multiple sclerosis (MS) and determined that the number of Golli-immunoreactive (ir) cells was significantly higher around lesions of chronic MS than in control white matter. Golli proteins were expressed in the adult oligodendrocyte precursor cells (OPCs), activated microglia/macrophages, and some demyelinated axons around MS lesions. Their expression in adult OPCs indicates remyelination attempts, whereas the expression in the subpopulation of microglia/macrophages suggests roles in the immune processes of MS. In addition, Golli proteins may be markers of axonal transection, which is characteristic for MS.

Study of expression of myelin basic proteins (MBPs) in developing rat brain using a novel antibody reacting with four major isoforms of MBP

Myelin basic proteins (MBPs) are the major protein components of myelin. MBP isoforms are known to have different expression patterns. In order to distinguish the different expression patterns on myelination, we have developed a novel antibody reacting with the four major isoforms of MBPs with molecular masses of 21.5 kDa, 18.5 kDa, 17.0 kDa, and 14.0 kDa. These MBPs were initially separated by acid urea gel and sodium dodecyl sulfate polyacrylamide gel electrophoreses and detected with the luminol reaction. Then the antibody developed was used to determine the relative amounts of MBP isoforms. The MBPs of oligodendrocytes were detected by the enhanced luminol reaction using Renaissance (Dupont NEN, Boston, MA). From the immunological aspect, the MBP monoclonal antibody (Sires et al. [1981] Science 214:87-89) was revealed to recognize MBPs with molecular masses of 21.5 kDa and 18.5 kDa. Furthermore, we found that Ile-166 in the rat 18.5-kDa MBP isomers was replaced by methionine. The 14.0-kDa and 18.5-kDa isoforms of MBP are the most abundant MBP species and comprise more than 70% of the total MBPs in 3.5-and 24-month-old rats. MBPs are expressed during development and the compositions of MBPs in mature (3.5 months old) and aged (24 months old) rats were almost the same. The expression of the 14.0-kDa and 18.5-kDa MBPs occurred earlier in the cerebellum and the spinal cord than in the cerebrum by approximately 1 week. MBPs are also expressed upon oligodendrocyte maturation by interacting with astrocytes. The above results suggest that the regulation of MBP isoforms during development and oligodendrocyte differentiation may indicate the point of occurrence of both the unique patterns of isoform expression and the shift in intracellular localization of MBPs with the maturation of oligodendrocytes.

Paclitaxel (Taxol) attenuates clinical disease in a spontaneously demyelinating transgenic mouse and induces remyelination

Treatment with paclitaxel by four intraperitoneal injections (20 mg/kg) 1 week apart attenuated clinical signs in a spontaneously demyelinating model, if given with onset of clinical signs. If given at 2 months of age (1 month prior to clinical signs), disease was almost completely prevented The astrogliosis, prominent in our model, was reversed by paditaxel as determined by astrocyte counts and quantitation of GFAP. Electron microscopic examination of affected regions at 2.5 months demonstrated that the myelin was generally normal. By 4 months of age, demyelination was common in the superior cerebellar peduncle, maximal at 6 months, but continued to 8 months. In addition to myelin vacuolation and nude axons, the presence of many thin myelin sheaths suggested remyelination or partial demyelination. Although no evidence of oligodendrocyte loss was seen, nuclear changes were observed. To substantiate that remyelination was occurring, we measured MBP (18.5 kDa), MBP-exon II, Golli-MBP, TP8, Golli-MBP-J37, platelet-derived growth factor alpha (PDGFR alpha) and sonic hedgehog (SHH). Of these TP8, PDGFR alpha and SHH were up-regulated in the untreated transgenic. After paditaxel treatment, MBP-Exon II, TP8, PDGFR alpha and SHH were further up-regulated. We concluded that some of the effects of paditaxel were to stimulate proteins involved in early myelinating events possibly via a signal transduction mechanism.

Expression and regulation of golli products of myelin basic protein gene during in vitro development of oligodendrocytes

The myelin basic protein (MBP) gene produces two families of proteins, the classic MBPs, important for myelination of the CNS, and the golli proteins, whose biological role in oligodendrocytes (OLs) is still unknown. The goals of this work were to study the in vitro pattern of expression of the golli products during OL differentiation and to compare it with that of the classic MBP products of the gene. Mouse primary glial cultures were analyzed at the mRNA and protein levels with an array of techniques. We found that OLs express golli mRNA primarily during intermediate stages of differentiation, which was confirmed by immunocytochemical analysis. Golli expression was low in proliferating OL progenitors as well as in terminally mature OLs. Golli proteins were found associated with the OL cell soma and nuclei and, to a lesser extent, with the cellular processes. We also found that golli proteins are not targeted to myelin in vitro and in vivo, in contrast to the classic MBPs. Finally, we found that golli expression is regulated during OL development and can be manipulated by growth factors such as basic fibroblast growth factor, neurotrophin-3, and retinoic acid.

Effect of cyclic AMP on the expression of myelin basic protein species and myelin proteolipid protein in committed oligodendrocytes: differential involvement of the transcription factor CREB

Our previous results support the idea that CREB (cyclic AMP-response element binding protein) may be a mediator of neuroligand and growth factor signals that, coupled to different signal transduction pathways, play different roles at specific stages of oligodendrocyte development. In the early stages, when cells are immature precursors, CREB may play a role as a mediator of protein kinase C (PKC)/mitogen-activated protein kinase (MAPK) pathways regulating cell proliferation. In contrast, at a later stage, when cells are already committed oligodendrocytes, CREB seems to play an important role as a mediator in the stimulation of myelin basic protein (MBP) expression by cyclic AMP (cAMP). In this study, we have investigated whether cAMP and CREB play a role in regulating the expression of all or on the other hand particular MBP isoforms. The results indicated that treatment of committed oligodendrocytes with the cAMP analogue db-cAMP results in a pattern of expression of MBP-related polypeptides that most closely resembles the pattern of MBPs observed in cerebra from adult animals. Experiments in which CREB expression was inhibited using a CREB antisense oligonucleotide, suggested that CREB is involved in the cAMP-dependent stimulation of all the MBP isoforms. In contrast, we have found that db-cAMP stimulates the expression of myelin proteolipid protein (PLP) in a process that occurs despite inhibition of CREB expression. These results support the idea that cAMP stimulates the maturation of oligodendrocytes and stress the fact multiple mechanisms may convey the action of this second messenger modulating oligodendrocyte differentiation and myelination.

Expression of Golli mRNA during development in primary immune lymphoid organs of the rat

The gene-of-the-oligodendrocyte lineage (Golli)-MBP transcription unit contains three Golli-specific exons together with eight exons of the "classical" myelin basic protein (MBP) gene, yielding alternatively spliced proteins which share amino acid sequence with MBP. Unlike MBP, a late antigen expressed only in the nervous system, Golli gene products are expressed pre- and post-natally at many sites. In this study, we determined the sequence of Golli in rat by RT-PCR and 5' RACE and showed that Golli sequences are expressed in primary lymphoid organs as early as e16.5, which could explain the anergic rat T cell response we previously observed in Golli-induced meningitis.

"Classic" myelin basic proteins are expressed in lymphoid tissue macrophages

"Classic" myelin basic proteins (MBPs) are demonstrated in lymph nodes of SJL mice by western blot and RT-PCR. Interestingly, expression of these "classic" MBPs was increased during the late relapsing phase of adoptive experimental autoimmune encephalomyelitis (EAE). When splenocytes from SJL mice were separated into macrophage versus B lymphocyte-enriched populations, intact MBP isoforms were demonstrated in the macrophage-enriched population while undetectable in the B lymphocyte-enriched population. RT-PCR demonstrated "classic" MBP transcripts in splenic macrophages, as well as in a macrophage cell line (RAW). The expression of "classic" MBPs in lymphoid tissue macrophages raises the possibility that MBP-specific T cells may be exposed to autoantigen outside the central nervous system (CNS).

Biology of oligodendrocyte and myelin in the mammalian central nervous system

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.

Age-dependent T cell tolerance and autoimmunity to myelin basic protein

Experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis, is induced by activating a subset of myelin basic protein (MBP)-specific T cells that have escaped tolerance induction. Here, we define the tolerance mechanisms that eliminate the majority of MBP-specific T cells from the periphery. We show that MBP-specific T cells undergo central tolerance mediated by bone marrow-derived antigen-presenting cells presenting exogenously derived MBP epitopes. The efficiency of tolerance is age dependent, reflecting the developmentally regulated expression of MBP. Dependence of tolerance on the amount of MBP expressed in vivo results in an age window of susceptibility to EAE in mice that peaks during puberty. These results suggest that factors regulating expression of self-antigens in vivo can influence susceptibility to autoimmunity.

Expression of myelin basic protein (MBP) epitopes in human non-neural cells revealed by two anti-MBP IgM monoclonal antibodies

Two monoclonal antibodies (1H6.2 and 45.30) were raised against MBP purified from human brain under experimental conditions that allowed MBP to retain binding to surrounding myelin lipids (human lipid-bound MBP (hLB-MBP)). 1H6.2 and 45.30 MoAbs were selected on the basis of their different binding properties to: hLB-MBP, human lipid-free-MBP (hLF-MBP) and bovine lipid-free-MBP (bLF-MBP). Although the isotype of both MoAbs was IgM, their specificity, as tested in ELISA assays against chemical haptens and unrelated protein antigens, was restricted to MBP. 1H6.2 and 45.30 MoAbs stained MBP from human brain white matter tissue extracts, as well as bLF-MBP, in Western blot assays. Both MoAbs stained oligodendrocytes and myelin in immunohistochemical analysis of white matter from human brain. Tissue sections from human peripheral nerves were labelled by 1H6.2 only, however, demonstrating that the MoAbs recognize two different epitopes. Epitopes recognized by 1H6.2 and 45.30 MoAbs were also expressed by a wide array of human non-neural cells of either normal or pathological origin, as evidenced by cytofluorimetric assays. In particular, MBP epitopes (MEs) were expressed by lymphoid cells as well as by cells which play a pivotal role in immune homeostasis and in the immune response, such as thymic epithelial cells and professional antigen-presenting cells. Both MoAbs were efficiently internalized by cells from a human B cell line, suggesting trafficking of MEs along the endocytic pathways. These findings support hypotheses regarding the role of MEs expressed by non-neural cells in establishing self-tolerance and/or in triggering the immune response against MBP antigen.

Thymocytes express the golli products of the myelin basic protein gene and levels of expression are stage dependent

The golli products of the myelin basic protein gene have been shown to be expressed in mouse thymus and brain. The full repertoire of thymic cell types expressing golli products has not yet been determined, although immunoreactivity has been found in some macrophages. We have analyzed the cellular expression of golli mRNAs and proteins in the thymus. The results showed that MTS5(+) cortical/MTS10(+) medullary epithelial cells and NLDC145(+) dendritic cells did not express golli, while some macrophages did exhibit strong immunoreactivity. GOLLI: mRNAs were not detected in macrophages by in situ hybridization. Thymocytes expressed significant levels of golli mRNAs and proteins by in situ hybridization and immunohistochemistry. Interestingly, golli immunoreactivity varied with thymocyte stage of differentiation. For example, CD4(-)CD8(-) (double-negative) thymocytes expressed relatively high levels of golli. Upon further differentiation into CD4(-)CD8(-) (double-positive) thymocytes, golli protein expression declined dramatically. When thymocytes developed into CD8(-) or CD4(+) (single-positive) thymocytes, golli protein expression increased again, but it never achieved the levels found in double-negative thymocytes. Thus, the altered levels of expression of golli proteins in developing thymocytes correlated with the transitions from double-negative to double-positive and double-positive to single-positive stages. The lack of significant golli expression in thymic stromal cells may offer an alternative explanation for the mechanism of inefficient negative selection of those autoreactive thymocytes with specificity for myelin basic proteins.

Gene expression in the rat supraoptic nucleus induced by chronic hyperosmolality versus hyposmolality

Magnocellular neurons of the hypothalamo-neurohypophysial system play a fundamental role in the maintenance of body homeostasis by secreting vasopressin and oxytocin in response to systemic osmotic perturbations. During chronic hyperosmolality, vasopressin and oxytocin mRNA levels increase twofold, whereas, during chronic hyposmolality, these mRNA levels decrease to 10-20% of that of normoosmolar control animals. To determine what other genes respond to these osmotic perturbations, we have analyzed gene expression during chronic hyper- versus hyponatremia. Thirty-seven cDNA clones were isolated by differentially screening cDNA libraries that were generated from supraoptic nucleus tissue punches from hyper- or hyponatremic rats. Further analysis of 12 of these cDNAs by in situ hybridization histochemistry confirmed that they are osmotically regulated. These cDNAs represent a variety of functional classes and include cytochrome oxidase, tubulin, Na(+)-K(+)-ATPase, spectrin, PEP-19, calmodulin, GTPase, DnaJ-like, clathrin-associated, synaptic glycoprotein, regulator of GTPase stimulation, and gene for oligodendrocyte lineage-myelin basic proteins. This analysis therefore suggests that adaptation to chronic osmotic stress results in global changes in gene expression in the magnocellular neurons of the supraoptic nucleus.

Enhanced T cell responsiveness to citrulline-containing myelin basic protein in multiple sclerosis patients

Myelin basic protein (MBP), a candidate autoantigen in multiple sclerosis (MS), exists in different isoforms and charge isomers generated by differential splicing of exons and by a combination of posttranslational modifications, respectively. These various isoforms and charge isomers of MBP vary in abundance and most likely serve different functions during myelinogenesis and remyelination. The least cationic among the charge isomers of MBP is citrullinated and is referred to as MBP-C8. MBP-C8 is relatively increased in the population of MBP isomers in more developmentally immature myelin and in MS brain tissue. In a previous study, we found that MBP-C8-reactive T cells could be detected in CD4+ T cell lines (TCL) generated with MBP from both MS patients and normal controls. Here, we examined the frequency and peptide specificity of MBP-C8-specific TCL generated with MBP-C8 in MS patients and controls. Ten subjects grouped in five sets, each an MS patient and a control, were studied. In all cases, the MS patient had either a higher overall number of MBP-C8-responding lines, responded with greater sensitivity to the MBP-C8 antigen or both. Few lines responded to the MBP-C8 peptides but, if they did, they appeared to be specific to the carboxyl-half of the MBP-C8 molecule. Given the large amounts of citrullinated MBP in MS brain tissue, a preferential T cell response to MBP-C8 may be involved in the induction and perpetuation of this disease. Multiple Sclerosis (2000) 6 220 - 225

Identification of a novel silencer that regulates the myelin basic protein gene in neural cells

The myelin basic protein gene produces two families of proteins, the golli proteins and the 'classic' myelin basic proteins from three transcription start sites (tsp). The golli proteins are expressed from the first tsp, and little is known about genetic elements that control its activity. We have examined elements that may regulate the expression of the golli products produced from this promoter in neural cell lines with constructs containing upstream portions of the first tsp by transient transfection assays. Three putative regulatory elements were identified, among them a 345bp novel silencer region, termed the golli silencer region (GSR), which was characterized in detail. This silencer was responsible for a significant (approx. 60%) inhibition of luciferase expression in PC12 cells. It was orientation-dependent and a double dose of this GSR completely abolished expression of the luciferase reporter activity. Transfections with deleted constructs identified three critical sites that bind at least two repressor proteins. We postulate that the silencer activity is the result of synergistic interactions between these repressor proteins and might involve the formation of a high-ordered protein-DNA structure.