A new form of myelin basic protein found in human brain

Influence of high level of antibodies to myelin basic protein in female mice on the postnatal development and behavioral reactions of the progeny

Physical development, behavioral reactions, and training capacity were studied in the progeny of female BALB/c mice with high levels of antibodies to myelin basic protein. The proposed protocol of immunization ensures high levels of antibodies to myelin basic protein in this mouse strain. High level of antibodies to myelin basic protein in pregnant females causes an increase in the blood level of these antibodies in the progeny. Inhibitory effect of antibodies to myelin basic protein on physical development, training process, and memory in mouse pups was detected.

The effects of citrullination or variable amino-terminus acylation on the encephalitogenicity of human myelin basic protein in the PL/J mouse

The post-translational modifications of myelin basic protein (MBP) in the form of citrullination and varying length of amino-terminus acylation may modify the biological functions and immunological features of MBP. Both modifications influence the reaction of antibodies and specific T cells recognizing MBP. The present study was undertaken to compare the encephalitogenicity of the citrullinated isomer of MBP (MBP-C8) with the unmodified isomer of MBP (MBP-C1) and to determine if the length of amino-terminal acylation of MBP peptide 1-21 altered an encephalitogenic epitope. MBP-C8, whether from patients with or without multiple sclerosis (MS), and MBP-C1 could induce active experimental allergic encephalomyelitis (EAE) in PL/J mice. A trend of reduced severity of EAE was observed in MBP-C8-injected animals. An increase in the length of amino-terminus fatty acid decreased the encephalitogenicity of MBP peptide 1-21 for both active and adoptive EAE in PL/J mice. Only lymph node cells sensitive to MBP peptide acetyl 1-21 and butyl 1-21 could transfer clinical EAE. In adoptive EAE, MBP peptides hexyl and octyl 1-21 induced moderate histopathological but no clinical change, whereas MBP peptide decyl 1-21 caused neither. A broadening in the antibody response could be detected in the sera of mice with active EAE induced by MBP-acylated peptides 1-21. Our findings demonstrate that encephalitogenicity is retained in the presence of citrullination but that the length of amino-terminus acylation diminishes the encephalitogenicity of MBP in the PL/J mouse.(ABSTRACT TRUNCATED AT 250 WORDS)

Three isoforms of human myelin basic protein: purification and structure

Myelin basic protein (MBP) occurs in multiple forms. Three of these isoforms from human MBP (HMBP) have been highly purified. HMBP, component 1 (18.5 kDa HMBP-1), was purified by ion-exchange chromatography at pH 10.6 in 2 M urea. During this ion-exchange chromatography, a fraction (Fraction 3), which contained HMBP component 3 (monophosphorylated or deamidated 18.5 kDa) and 17.2 kDa HMBP, was collected and further purified by fast protein liquid chromatography, which separated 17.2 kDa HMBP and HMBP component 3. When the latter was subjected to limited thrombic digestion, all of HMBP component 3 not phosphorylated at theonine 98 was cleaved. This digestion mixture was separated on Sephadex, and yielded pure component 3, monophosphorylated at theonine 98 (HMBP 3pT98), for which phosphate analysis yielded approximately 1 mole P/mole protein, and NMR showed only one phosphorylation site present. Circular dichroism (CD) studies were carried out on dilute solutions of HMBP-1 (18.5 kDa), 17.2 kDa HMBP, and HMBP3pT98 (phosphorylated 18.5 kDa). The CD spectrum of HMBP-1 was similar to that reported for rabbit MBP-1 and bovine MBP-1, but the spectra of 17.2 kDa HMBP and HMBP 3pT98 were distinctly different from HMBP-1. When analyzed by best-fit computations, 17.2 kDa HMBP showed about a 9% increase of ordered structure, and a greater increase, about 12%, was estimated for HMBP3pT98, attributable to beta-structure and beta turn.

Reactivity of normal T-cell lines to MBP isolated from normal and multiple sclerosis white matter

T-cell reactivity to human myelin basic protein (MBP) has been extensively studied using T-cell lines and clones generated from both peripheral blood and cerebrospinal fluid, from normal controls and multiple sclerosis (MS) patients. These studies have largely utilized myelin basic protein isolated from control human adult white matter. In our study, we used MBP reactive T-cell lines as a probe to investigate antigenic differences in a series of MBP preparations isolated from either control human white matter or white matter from the central nervous system (CNS) of MS patients. Autologous peripheral blood derived mononuclear cells were used as antigen presenting cells (APC). Although the majority of T-cells were found to react equally well with all preparations of MBP isolated from both control and MS white matter, we were also able to identify T-cell lines which reacted well with all preparations of MBP isolated from controls but failed to react with MBP isolated from MS white matter. These differences were unlikely to reflect differences in degradation products or excess peptides present in the MS brain since SDS-PAGE and HPLC did not show any difference in the MS samples compared to the controls, and the concentration response curves for a human T-cell clone specific for the 84-102 region of MBP were similar for all the MBP preparations. We did not detect differences in amino acid content amongst MBP preparations although single amino acid substitutions cannot be ruled out. These results raise the possibility that MBP isolated from MS brain may differ in charge microheterogeneity which would affect antigenic determinants.(ABSTRACT TRUNCATED AT 250 WORDS)

Myelin in multiple sclerosis is developmentally immature

The etiology of multiple sclerosis (MS) is considered to involve genetic, environmental, infective, and immunological factors which affect the integrity of a normally assembled myelin sheath, either directly or indirectly resulting in demyelination. In a correlative study involving protein chemical, mass spectrometric, and electron microscopic techniques we have determined that myelin obtained from victims of MS is arrested at the level of the first growth spurt (within the first 6 yr of life) and is therefore developmentally immature. The data supporting this conclusion include (a) the pattern of microheterogeneity of myelin basic protein (MBP); (b) the NH2-terminal acylation of the least cationic component of MBP ("C-8"); (c) the phase transition temperature (Tc) of myelin isolated from victims of MS correlated with the increased proportion of the least cationic component of MBP; and (d) immunogold electron microscopy using an antibody specific for "C-8" showed that the distribution of gold particles in a 2-yr-old infant was similar to the distribution found in a victim of MS. We postulate that this developmentally immature myelin is more susceptible to degradation by one or a combination of factors mentioned above, providing the initial antigenic material to the immune system.

Myelin basic protein stimulates insulin and glucagon secretion from rat pancreatic islets in vitro and in vivo

The effect of myelin basic protein on insulin and glucagon secretion from rat pancreatic islets was studied in vivo and in vitro. The myelin basic proteins isolated from bovine, human and rat brains all stimulated insulin secretion in a similar fashion. In a static incubation of isolated pancreatic islets, myelin basic protein at doses of 15.6-250 micrograms in a 0.5-ml reaction volume (1.7 X 10(-6) to 2.7 X 10(-5) M) significantly stimulated hormone release. Maximal stimulation, obtained at the 250-micrograms dose, was 6.5-fold greater than control for insulin secretion and 6.7-fold greater than control for glucagon secretion. In the case of glucagon no saturation was observed, but saturation was obvious for insulin release at doses of myelin basic protein of 62.5-250 micrograms, larger doses causing permeabilization of the islet membranes as indicated by leakage of acid phosphatase. At a 100-micrograms dose the time course of insulin secretion induced by myelin basic protein indicated a fast initial release, and after the first 2 h only a little more insulin was released. At the lower doses of myelin basic protein (11 and 33 micrograms) the secretion rate was nearly constant after the first hour. Significant stimulation of glucagon release by myelin basic protein was seen after 60 min, the rate of release being roughly constant at 33- and 100-micrograms doses thereafter. At the 11-micrograms dose significant stimulation of hormone release was observed only after a 4-h incubation.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for multiple human T cell recognition sites on myelin basic protein

Myelin basic protein (BP)-specific T cell clones were used to study human T cell recognition sites on the BP molecule. Proliferation assays performed with a panel of xenogeneic BPs of known amino acid sequence and with large peptide fragments of human and guinea pig BPs demonstrated ten different patterns of reactivity. The data provide evidence for at least four different human T cell epitopes within the C-terminal half of the BP molecule, three within the N-terminal half, and three located within the central portion of the molecule. The results indicate that attempts to inhibit anti-BP responses in vivo in an antigen-specific manner will require the suppression of multiple T cell populations.

Cellular and molecular aspects of myelin protein gene expression

The cellular and molecular aspects of myelin protein metabolism have recently been among the most intensively studied in neurobiology. Myelination is a developmentally regulated process involving the coordination of expression of genes encoding both myelin proteins and the enzymes involved in myelin lipid metabolism. In the central nervous system, the oligodendrocyte plasma membrane elaborates prodigious amounts of myelin over a relatively short developmental period. During development, myelin undergoes characteristic biochemical changes, presumably correlated with the morphological changes during its maturation from loosely-whorled bilayers to the thick multilamellar structure typical of the adult membrane. Genes encoding four myelin proteins have been isolated, and each of these specifies families of polypeptide isoforms synthesized from mRNAs derived through alternative splicing of the primary gene transcripts. In most cases, the production of the alternatively spliced transcripts is developmentally regulated, leading to the observed protein compositional changes in myelin. The chromosomal localizations of several of the myelin protein genes have been mapped in mice and humans, and abnormalities in two separate genes appear to be the genetic defects in the murine dysmyelinating mutants, shiverer and jimpy. Insertion of a normal myelin basic protein gene into the shiverer genome appears to correct many of the clinical and cell biological abnormalities associated with the defect. Most of the dysmyelinating mutants, including those in which the genetic defect is established, appear to exhibit pleiotropy with respect to the expression of other myelin genes. Post-translational events also appear to be important in myelin assembly and metabolism. The major myelin proteins are synthesized at different subcellular locations and follow different routes of assembly into the membrane. Prevention of certain post-translational modifications of some myelin proteins can result in the disruption of myelin structure, reminiscent of naturally occurring myelin disorders. Studies on the expression of myelin genes in tissue culture have shown the importance of epigenetic factors (e.g., hormones, growth factors, and cell-cell interactions) in modulating myelin protein gene expression. Thus, myelinogenesis has proven to be very useful system in which to examine cellular and molecular mechanisms regulating the activity of a nervous system-specific process.

Electroimmunoblotting of myelin basic protein peptides: a novel approach to the rapid characterisation of antigenic specificities of monoclonal and polyclonal anti-MBP antibodies

A rapid and sensitive method for the identification of antigenic determinants recognised by monoclonal and polyclonal antibodies directed against myelin basic protein (MBP) is described. By electroimmunoblotting a series of overlapping peptides covering the entire MBP molecule with monoclonal anti-MBP antibodies, the binding pattern of immunoreactive peptides can be rapidly determined and the reactive antigenic determinant identified. This procedure, which can be performed with both native and synthetic peptides, can also with appropriate modification, be applied to the analysis of naturally occurring or experimentally induced polyclonal anti-MBP autoantibodies.

Identification of a cDNA coding for a fifth form of myelin basic protein in mouse

The primary sequences of four molecular mass variants (14, 17, 18.5, and 21.5 kDa) of the mouse myelin basic protein (MBP) have recently been determined through analysis of cDNA clones of their mRNAs. The mRNAs coding for the four MBP variants are thought to arise by differential splicing of two exons (exons 2 and 6) from a single gene. In contrast, exons 2 and 5 may be spliced out in the posttranscriptional processing of the human MBP gene. To investigate the possibility that a third exon (exon 5) may also be differentially spliced out in the processing of the mouse MBP gene transcript, a mouse cDNA library was screened to search for cDNAs missing exon 5. A MBP cDNA was isolated whose coding region specified a fifth mouse MBP variant with a molecular mass of approximately equal to 17 kDa. The mass of this variant (17,257 Da) is so close to that of the other 17-kDa mouse MBP (17,224 Da) that the two would be indistinguishable on NaDodSO4/polyacrylamide gels. Analysis of the sequence of the cDNA clone indicates that excision of exons 2 and 5 of the mouse MBP gene would produce the mRNA encoding this newly described 17-kDa MBP, whereas excision of exon 6 would produce the mRNA for the other 17-kDa MBP variant. Thus, the "17-kDa" mouse MBP consists of at least two molecular forms with very similar molecular masses but markedly different primary sequences. Of five full-length or near full-length cDNAs representing 17-kDa MBPs, one was missing exons 2 and 5 and four were missing exon 6.

Evidence for the expression of four myelin basic protein variants in the developing human spinal cord through cDNA cloning

Four human myelin basic protein (MBP) variants with molecular masses of 21.5, 20.2, 18.5, and 17.3 kilodaltons (kDa) have been identified in the developing human spinal cord and their structures determined through an analysis of cDNA clones of their mRNAs. The 20.2-kDa MBP mRNA encoded a novel MBP variant, the structure of which has not been reported in any species. Its amino acid sequence was identical with that of the 21.5-kDa MBP except for a deletion of 11 amino acid residues encoded by exon 5 of the MBP gene. All four human MBP variants were identical except for the insertion of deletion of two peptide fragments corresponding to those encoded by exons 2 and 5 of the MBP gene. In this study, no mature human MBP cDNAs missing exon 6 sequences were identified. This suggests that, unlike the mouse, the four human MBP mRNAs encoding these MBP variants arise by the alternative splicing of only exons 2 and 5 from the primary MBP gene transcript. This indicates that the predominant MBP splicing pathways in human and mouse are different. Immunoblots of human fetal spinal cords (11-21 weeks) indicated that MBP expression turned on abruptly between 14 and 16 weeks. Expression of the 20.2-kDa MBP variant was most evident at 16 weeks and its relative proportion declined thereafter, suggesting that its expression was developmentally regulated.