Lectin receptors in central nervous system myelin

Identification of the glycosylation pattern of meat proteins in tissues from bovine myelin

A variant form of Creutzfeld-Jacob disease in humans is associated with the consumption of food contaminated with the bovine central neural system. This has focused attention on the need for procedures to detect tissues of the neural system in meat and meat products. A method was developed for the identification of myelin glycoproteins in bovine neural tissue. The glycosylated structures of glycoproteins in different protein mixtures from central nervous system (CNS) and peripheral nervous system (PNS) isolated from bovine myelin were identified by the specific lectin-glycoprotein reactions. Digoxigenin-labeled lectins bonded to the terminal glycoconjugate sequences of nine CNS glycoproteins ranging from 15 to 200 kDa and four PNS glycoproteins ranging from 22 to 105 kDa. Datura stramonium (DSA) recognized the epitope Galbeta1-4GlcNAc by two CNS and three PNS glycoproteins. Maackia amurensis (MAA) recognized the epitope NeuAcalpha2-3Gal by four CNS and two PNS glycoproteins. The peanut Arachis hypogaea (PNA) reacted with the high molecular CNS glycoprotein (200 kDa) with the sequence Galbeta1-3GalNAc. Galanthus nivalis (GNA) bonded to mannose subunits linked alpha1-3 and alpha1-6 by six CNS glycoproteins with molecular weights between 17 and 200 kDa. Four of these glycoproteins were recognized from monoclonal antibodies against the "HNK-1 epitope".

Monoclonal antibody detects oligodendroglial cell surface protein exhibiting temporal regulation during development

As tools to study stage-specific surface molecules expressed during the development of oligodendrocytes, we have generated monoclonal antibodies against peanut agglutinin (PNA)-binding glycoproteins isolated by affinity chromatography from the oligodendroglial precursor cell line Oli-neu. In this paper we report the characterization of the monoclonal antibody 7D10. The 7D10 antibody recognizes a 145-kD cell surface glycoprotein expressed by postmitotic multibranched cells of the oligodendroglial lineage. The antigen stains subpopulations of myelin-associated glycoprotein (MAG) and O4-positive cells and is subsequently down-regulated during further differentiation in vitro. The 7D10 antigen is also expressed by a subpopulation of astroglial cells but not by neurons. A truncated form of the protein is released by antigen-expressing cells into the culture supernatant.

Lectin-binding properties of oligodendrocyte lineage cells aid in defining functionally important surface proteins

Oligodendrocytes are the myelin-forming cells of the central nervous system. They develop from migratory and proliferative precursor cells, which differentiate to mature myelinating cells. As a first step toward investigating the expression of cell surface glycoproteins by oligodendrocyte lineage cells, we tested 14 different lectins for their binding to oligodendrocyte lineage cells. Peanut agglutinin (PNA) was the only lectin used that showed a differentiation stage-dependent binding to oligodendrocytes. PNA-binding molecules are specifically expressed by oligodendrocyte precursor cells, downregulated with differentiation, and reexpressed by mature oligodendrocytes. It was additionally observed that PNA stimulates the proliferation of oligodendrocyte precursor cells. PNA may therefore be a useful tool for isolating and characterizing important cell surface glycoproteins expressed by oligodendrocyte lineage cells.

Purification and partial structural and functional characterization of mouse myelin/oligodendrocyte glycoprotein

The myelin/oligodendrocyte glycoprotein (MOG) is found exclusively in the CNS, where it is localized on the surface of myelin and oligodendrocyte cytoplasmic membranes. The monoclonal antibody 8-18C5 identifies MOG. Several studies have shown that anti-MOG antibodies can induce demyelination, thus inferring an important role in myelin stability. In this study, we demonstrate that MOG consists of two polypeptides, with molecular masses of 26 and 28 kDa. This doublet becomes a single 25-kDa band after deglycosylation with trifluoromethanesulfonic acid or peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase, indicating that there are no or few O-linked sugars and that the doublet band represents differential glycosylation. Partial trypsin cleavage, which also gave a doublet band of lower molecular weight, confirmed this idea. MOG was purified by polyacrylamide gel electrophoresis, followed by electroelution. Three N-terminal sequences of eight to 26 amino acids were obtained. By western blot analysis, no binding was found between MOG and cerebellar soluble lectin. MOG does not seem to belong to the signal-transducing GTP-binding proteins. Reduced MOG concentrations were observed in jimpy and quaking dysmyelinating mutant mice, giving further support to its localization in compact myelin of the CNS.

The endogenous lectin cerebellar soluble lectin and its ligands in central nervous system myelin of myelin-deficient (mld) mutant mice

The myelin-deficient (mld) mutation is autosomal recessive mutation in the murine CNS exhibiting severe hypomyelination. The primary defect results in a drastic reduction of myelin basic protein synthesis caused by a duplication of the myelin basic protein gene with partial inversion of the upstream gene copy. The severe deficit of myelin basic protein is responsible for the absence of the major dense line but cannot explain the heterogeneity of myelin compaction found in mld. We have tested the hypothesis that the endogenous cerebellar soluble lectin (CSL) and/or its endogenous glycoprotein ligands could be involved in myelin abnormalities in the dysmyelinating mutant, mld. Immunocytochemical and immunoblotting techniques showed that the CSL level was not reduced significantly in the mld mutant. Furthermore, two ligands of CSL, the myelin-associated glycoprotein and an axonal glycoprotein, with a relative molecular mass of 31 kDa, were not decreased in level in the purified myelin fraction isolated from mld mice. In contrast, three minor glycoprotein ligands of CSL of relative molecular mass of 23, 18, and 16 kDa were greatly reduced in content. The reduced concentration of these low-molecular-mass glycoproteins in mld myelin suggests that they are constituents of compact myelin. Furthermore, the observation that CSL is specifically localized in vivo in regions where mld myelin is more compact and absent from regions devoid of myelin compaction may suggest that the endogenous CSL lectin, as well as its minor glycoprotein ligands, plays a role in the stabilization of the myelin sheath.

Chronic experimental autoimmune encephalomyelitis in the guinea pig. Presence of anti-M2 antibodies in central nervous system tissue and the possible role of M2 autoantigen in the induction of the disease

Experimental autoimmune encephalomyelitis (EAE) can be transferred adoptively with T cells sensitized to the basic protein of myelin (BP). However, in the guinea pig, the chronic form of EAE has not been found to be inducible with BP alone, nor has it been adoptively transferred. An antibody response to the central nervous system (CNS) myelin autoantigens was looked for in serum and target CNS tissue in S13 guinea pigs with isologous CNS tissue-induced chronic EAE. Antibody activity was estimated by an immunoenzymatic technique and by autoradiography, using immunoprecipitated and electrophoresed relevant radiolabelled antigens. In serum, IgG antibody response to BP and M2 reached its maximum level 30 to 40 d after immunization and then declined progressively until it became undetectable. On the other hand, while anti-BP antibodies were seldom detected in CNS tissue acid extract, anti-M2 IgG antibodies were always present in CNS tissue of chronic EAE animals, and the amount of these antibodies were related to the severity of symptoms and lesions. No antibody response to proteolipid or to galactocerebroside was detected in serum or CNS tissue. BP-immunized controls showed no chronic EAE and no response to M2 in their serum or CNS tissue. Inasmuch as M2 has been shown to be a glycoprotein of CNS myelin, and anti-M2 antibodies to have a demyelinating property, the latter would be responsible for CNS tissue demyelination in chronic EAE. A shared role of BP and M2 in the induction of chronic EAE in the guinea pig is suggested.

A phorbol ester-sensitive kinase catalyzes the phosphorylation of P0 glycoprotein in myelin

The proposed structural protein of peripheral nerve myelin, P0, has been shown to have several covalent modifications. In addition to being glycosylated, sulfated, and acylated, P0 is phosphorylated, with the intracellular site of this latter addition being in question. By employing nerve injury models that exhibit different levels of P0 biosynthesis in the absence and presence of myelin assembly, we have examined the cellular location of P0 phosphorylation. It is demonstrated that there is comparable P0 phosphorylation in both normal and crush-injured adult rat sciatic nerves, although the level of biosynthesis of P0 differs between these myelin maintaining and actively myelinating nerve models, respectively. The glycoprotein does not appear to be phosphorylated readily in the transected adult sciatic nerve, a preparation in which P0 biosynthesis is observed but that lacks myelin membrane. These observations suggest that the modification is not associated with the biosynthesis or maturation of P0 in the endoplasmic reticulum or Golgi, but that it instead occurs after myelin assembly. That P0 phosphorylation occurs in the normal nerve even when translation is inhibited by cycloheximide treatment lends further support to this conclusion. P0 is shown to be phosphorylated on one or more serine residues, with all or most of the phosphate group(s) being labile as evidenced by pulse-chase analysis. Addition of a biologically active phorbol ester, 12-O-tetradecanoylphorbol-13-acetate or 4 beta-phorbol 12,13-dibutyrate, substantially increases the extent of [32P]orthophosphate incorporation into the glycoprotein of normal and crushed nerve but not transected nerve. Biologically inactive 4 alpha-phorbol 12,13-didecanoate has no effect on P0 phosphorylation. Similarly, the addition of the cyclic AMP analog 8-bromo-cyclic AMP causes no appreciable changes in P0 labeling. These findings indicate that the phorbol ester-sensitive enzyme, protein kinase C, may be responsible for the phosphorylation of P0 within the myelin membrane.

Isolation of an integral membrane glycoprotein by chloroform-methanol extraction and C3-reversed-phase high-performance liquid chromatography

Methodology is presented for the isolation of integral membrane proteins and applied to the purification of the major myelin glycoprotein, P0. This isolation scheme depends on the detergent solubilization of an isoosmotically extracted membrane fraction from sciatic nerve endoneurium, followed by the removal of lipids and detergent by chloroform/methanol extraction. The resulting membrane proteins are readily dissolved in acetic acid/water (1/1) and directly analyzed by reversed-phase high-performance liquid chromatography. The hydrophobic nature of the intrinsic membrane protein mixture results in strong binding to a C8 stationary phase, leading to poor resolution and yields. These problems can be eliminated by employing a C3 alkylsilane column, thereby allowing separation of the protein components and the isolation of P0. The purified P0 has an amino-terminal sequence that matches that predicted from nucleotide sequencing, and the glycoprotein contains the expected amount of sialic acid. This latter finding indicates that the isolation procedure is not detrimental to the complex-type oligosaccharide structure of P0 and should make the methodology readily applicable to the purification of other integral membrane proteins and glycoproteins.

Autolytic changes of human white matter: an electron microscopic and electrophoretic study

The effect of autolysis on the electrophoretic pattern of the 3H-labeled membrane glycoproteins derived from human brain white matter (WM) was investigated and correlated with electron microscopic findings. Samples were taken from the WM of outer zones of routine surgical specimens sent for pathologist's examination. The WM samples were incubated at +4 and +25 degrees C for 6 and 24 hr and analyzed by electron microscopy and by galactose oxidase labeling with subsequent SDS-polyacrylamide gradient gel electrophoresis. The effect of freezing and thawing was also studied. In electron microscopic examination myelin was found to have degenerated after an incubation of 24 hr at +4 and +25 degrees C, and it was severely disrupted after 24 hr at +25 degrees C, when a periaxonal network-like change was observed. The major labeled membrane glycoprotein band with an estimated molecular weight (MW) of 138,000 was stable during the first 24 hr of incubations at both +4 and +25 degrees C. No marked changes were noticed in the electrophoretic pattern of all of the WM membrane proteins labeled by [3H]acetic anhydride technique. In frozen and thawed specimens there was an increase in the intensity of the band with a MW of 86,500 and a new band appeared at the MW region of 25,000. The present results suggest that despite the apparent stability of the major glycoprotein band during the first 24 hr of autolysis, there are ultrastructural abnormalities in the myelin sheath, which should be taken into consideration during interpretation of changes in pathologic conditions.

A comparison of the glycoproteins and the proteins from multiple sclerosis and normal brain tissue

Two highly sensitive techniques were used to identify glycoproteins and proteins in several tissue fractions from two normal brains and five brains from multiple sclerosis (MS) patients. Comparison of glycoproteins and proteins in white and gray matter, myelin and a myelin-related fraction between normal and MS brains not only showed the presence in all fractions of many more minor components than has previously been reported, but also subtle differences in some of these components. However, no change was unequivocally MS-specific. This provides additional evidence that MS is a demyelinating rather than a dysmyelinating disorder and may lead to some insight into the etiology and/or progression of this disease. Moreover, this study has served to characterize further the proteins and glycoproteins of human brain tissue.

Proliferation of astroglia and oligodendroglia in response to human T cell-derived factors

Human T lymphocytes transformed by human T cell leukemia-lymphoma viruses or activated by lectins were found to produce stimulating factors that promoted both proliferation and maturation of oligodendroglial and astroglial cells in vitro.

Schwann cell expression of a major myelin glycoprotein in the absence of myelin assembly

Quiescent Schwann cells in the distal segment of the permanently transected nerve produced basal levels of the major myelin glycoprotein, P0, in the absence of myelin assembly. Low levels of P0 could be detected at 35 days after transection by autoradiographic analysis of radioiodinated lectin binding after protein separation by high-resolution sodium dodecyl sulfate pore gradient electrophoresis and by fluorographic analysis after electrophoresis of [3H]fucose- and [3H]mannose-labeled glycoproteins after incorporation into endoneurial slices. Immunoreactivity to P0 in the transected nerve could also be demonstrated with antisera against P0 as evaluated by direct "immune overlay" after electrophoresis. These results indicate that the requirement for continuing signals from appropriate axons to make detectable amounts of myelin-specific proteins and glycolipids is not absolute. Schwann cells, therefore, like oligodendrocytes, can synthesize myelin components in the absence of neuronal influence, although information from neuronal elements probably is required for myelin assembly by Schwann cells and for myelin compaction by oligodendrocytes.

Regulation of myelination: biosynthesis of the major myelin glycoprotein by Schwann cells in the presence and absence of myelin assembly

Schwann cell biosynthesis of the major myelin glycoprotein, P0, was investigated in the crush-injured adult rat sciatic nerve, where there is myelin assembly, and in the permanently transected nerve, where there is no myelin assembly. Endoneurial fractions from desheathed rat sciatic nerves distal to the crush were compared with similar fractions from the permanently transected nerves at 7, 14, 21, 28, and 35 days after injury. The Schwann cell expression of this asparagine-linked glycoprotein was evaluated after sodium dodecyl sulfate-pore gradient electrophoresis by Coomassie Blue and silver stain and by autoradiography after direct overlay of radioiodinated lectins [wheat germ agglutinin, gorse agglutinin, and concanavalin A (Con A)]. As evaluated by these parameters, the concentration of P0 after crush decreased and subsequently increased as a function of time after injury, corresponding to the events of demyelination and remyelination. After permanent transection, the P0 concentration decreased following the same time course found after crush. At subsequent time points, P0 could not be detected with Coomassie Blue stain, silver stain, or wheat germ agglutinin. Both gorse agglutinin and Con A, however, showed binding to P0. Radioactive precursor incorporation studies with [3H]fucose or [3H]-mannose into endoneurial slices at 35 days posttransection revealed active oligosaccharide processing of P0 glycoprotein by Schwann cells in this permanent transection model. Compared with other Schwann cell glycoproteins in the transected nerve, the highest level of incorporation of [3H]mannose was found in P0 which accounted for 42.7% of the incorporated label. In contrast, incorporation of [3H]mannose into endoneurial slices at 35 days after crush accounted for only 13.3% in P0. In addition, higher levels of Con A binding were observed in P0 in the transected nerve compared with the contralateral control or the crushed nerve. Both the [3H]fucose incorporation and gorse agglutinin binding to P0 in the transected nerve suggest posttranslational processing of this glycoprotein in the Golgi apparatus; however, the absence of wheat germ agglutinin binding, the high level of mannose incorporation, and the high level of binding by Con A imply that additional processing steps are required prior to its assembly into myelin.

Demyelinating and myelination-inhibiting factors induced by chloroform-methanol insoluble proteins of myelin

A host of proteins was seen when the chloroform-methanol insoluble protein (CMIP) fraction of bovine brain myelin was transferred from polyacrylamide gels to cellulose nitrate sheets. Inoculation of rabbits with the CMIP fraction generated a number of antibodies which were demonstrated by the immunoblot technique. These antisera against CMIP contained antibodies which induced demyelination and inhibited myelin formation in central nervous system cultures. The demyelinating factor was specific for centrally myelinated fibers, and did not demyelinate peripherally myelinated axons.

Peripheral nervous system myelin and Schwann cell glycoproteins: identification by lectin binding and partial purification of a peripheral nervous system myelin-specific 170,000 molecular weight glycoprotein

Radioiodinated lectins were used to detect glycoproteins of peripheral nervous system (PNS) myelin (rat, human, bovine) and cultured rat Schwann cells. Proteins were resolved by sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis and transferred to nitrocellulose filters. The filters were overlaid with radioiodinated lectins of known saccharide affinities. These included concanavalin A, Helix pomatia, Limulus polyphemus, Maclura pomifera, peanut, soybean, Ulex europaeus, and wheat germ agglutinins. Inclusion of the appropriate monosaccharide in the overlay solution (0.2 M) inhibited lectin binding to the nitrocellulose-fixed proteins. Fluorography permitted identification of 26 myelin glycoproteins and many more in Schwann cells. All lectins labeled a band present in myelin, but not Schwann cells, corresponding to the major PNS myelin protein, P0. Our attention focused on a high-molecular-weight myelin glycoprotein [apparent molecular weight (Mr) 170,000], which appeared abundant by Coomassie Blue staining and which was heavily labeled by all lectins except concanavalin A. A protein with approximately this Mr and lectin-binding pattern was present in human and bovine PNS myelin as well, but not detected in rat Schwann cells, CNS myelin, liver and fibroblast homogenates, or cultured bovine oligodendroglia. Hence this 170,000 Mr glycoprotein is apparently unique to PNS myelin.

Myelin membrane from adrenoleukodystrophy brain white matter--biochemical properties

Adrenoleukodystrophy (ALD) is an X-linked progressive neurological disorder characterized by the accumulation of saturated very-long-chain fatty acids (C24 to C30) in lipids, especially cholesterol esters of the brain white matter and adrenal cortex. In the present study we have investigated the localization of accumulated cholesterol esters in brain white matter. During isolation of purified myelin membrane from regions of active demyelination, significant enrichment in cholesterol ester was found in two fractions, mainly in a low-density floating fraction and to a lesser degree in the purified myelin preparation. The fatty acid composition of cholesterol esters from both the ALD floating and myelin fractions was enriched approximately 10-fold in saturated very-long-chain fatty acids (greater than or equal to C24) compared with control preparations.

Lectin-reactive components in white matter membranes from normal and multiple sclerosis brains

Polypeptides derived from human white matter membranes reacted with the radioiodinated lectins concanavalin A, Lens culinaris phytohemagglutinin, Ricinus communis agglutinin and wheat germ agglutinin after electrophoresis in polyacrylamide pore gradient gels. The molecular weights of these lectin-reactive bands were estimated by comparison with radioiodinated protein standards by using the linear relationship between log of the molecular weight and log of the gel concentration reached by the protein after electrophoresis in a polyacrylamide gradient gel. The molecular weight estimates for components reactive with concanavalin A were 176,800, 141,200, 72,800, 52,800, 44,700, 40,000, 24,800 and 23,900. The molecular weights of the bands reactive with both wheat germ agglutinin and Lens culinaris phytohemagglutinin were 138,000, 113,500, 92,100, 52,800, 44,700, 24,800 and 23,900. Wheat germ agglutinin was bound also to a band with a molecular weight of 72,800. Ricinus communis agglutinin bound to bands with estimated molecular weights of 138,000, 72,800, 52,800, 44,700, 24,800 and 23,900. The electrophoretic pattern of lectin-reactive polypeptides derived from normal-appearing white matter of multiple sclerosis brains was not qualitatively different from the lectin-binding pattern of control brain membrane polypeptides.

Glycoprotein biosynthesis in peripheral nervous system myelin: effect of tunicamycin

The effect of an inhibitor of N-glycosylation of glycoproteins, tunicamycin, on synthesis of PNS myelin proteins was investigated in vitro by using chopped sciatic nerves or spinal roots of 21-day-old Wistar rats. Tunicamycin when incubated with these nerves in the presence of 3H-labeled fucose, mannose, or glucosamine inhibited the uptake of radioactivity into myelin proteins including some high-molecular-weight proteins, P0, 23K protein, and 19K protein by amounts ranging from 42 to 79%. Uptake of 14C amino acid mixture was inhibited much less by tunicamycin, but a new radioactive protein peak appeared when the protein mixtures had been separated by electrophoresis on polyacrylamide gels in the presence of sodium dodecyl sulfate. This protein ran directly in front of the P0 peak, did not correspond to any bands stained by Fast green, and was not labeled by fucose. This peak appeared in increasing larger proportions with progressive time of incubation of nerves with 3H amino acids in the presence of tunicamycin. The new protein, which cross-reacts with P0 antiserum, was tentatively identified as a nonglycosylated P0 protein that appears to be almost as well incorporated as P0 into the subcellular fraction containing myelin. At this time it is not possible to determine whether the unglycosylated P0 is actually assembled into a site and configuration like that of P0.

Biochemical studies of the late infantile form of metachromatic leukodystrophy

Biochemical studies from a patient with the late infantile form of metachromatic leukodystrophy are presented. Since the autopsy was performed soon after death, viable cells were isolated from brain. The purified cells had altered densities and unusual appearances. The cells when placed in culture were able to incorporate radiolabeled substrates into cerebrosides, indicating that some of the cells were of oligodendroglial origin. Myelin was isolated using several different methods, and the degree of abnormality appeared to be dependent upon the method of isolation. Nonetheless, MLD myelin, while still retaining its characteristic-morphology, had increased levels of sulfatides (two to four times that normally found). Other membrane subfractions were isolated that were not present in control tissue and that were more abnormal in composition than myelin. Finally, the glycoproteins in MLD tissue also appeared to be altered. There were losses in MLD myelin glycoproteins that bind to Concanavalin A (Con A) and additional prominent glycoproteins that bind to wheat germ agglutinin.

Sonication-enhanced histochemistry of wheat germ agglutinin binding to intracellular sites of rat layer V cortical neurons and spinal motoneurons

Cellular surface carbohydrates have been studied extensively in relation to cell interactions. However, the presence of intracellular carbohydrates not associated with cell surface membranes has not been well-defined histochemically. We describe a technique for the ultrastructural localization of intracytoplasmic carbohydrates using a wheat germ agglutinin peroxidase conjugate. The ultrastructural aspects of wheat germ agglutinin (WGA) binding to intracellular structures of rat somatomotor cortex layer V neurons and spinal cord motoneurons were examined using sonication to enhance penetration of the lectin-peroxidase conjugate. In addition to the membrane-associated structures previously described by others, WGA binding was observed on neuronal nuclear chromatin, nuclear pores, ribosomes, microtubules, vesicular organelles, and to synaptic complexes, primarily in the presynaptic bouton. The results support data indicating that complex carbohydrates may be important in neuronal molecular processing.

Central nervous system myelin proteins and glycoproteins in vertebrates: a phylogenetic study

CNS myelin was isolated by a conventional method from a wide range of vertebrate classes and analyzed by SDS-PAGE for proteins (Coomassie blue) and glycoproteins (concanavalin A (Con-A)-peroxidase). Mammalian, avian and reptilian myelin shared similar protein patterns (basic protein, BP; intermediate protein, DM-20; proteolipid protein, PLP; Wolfgram protein, W). Amphibians lacked DM-20 but were characterized by specific activities of 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) higher than those of the other classes examined. The Con A-binding profiles were similar in the high molecular weight (HMW) regions of the classes listed above, while the typical myelin proteins in the low molecular weight (LMW) regions were devoid of Con A-binding properties. In teleost myelin a putative BP band ran well ahead of rat small basic protein (SBP), whereas the region corresponding to rat PLP was covered by several closely spaced bands, most of which bound Con A. In elasmobranch myelin, apart from bands corresponding to BP, Con A-binding glycoproteins were detected migrating in the region of rat DM-20 and PLP as well as with mammalian PNS P0 protein. Cyclostomates yielded only very small amounts of material in the myelin preparation and displayed undifferentiated Coomassie blue- and Con A-binding in the HMW region, while typical LMW myelin proteins were absent. These results demonstrate that CNS myelin from bony and cartilaginous fishes is characterized by containing several major Con A-binding proteins of low molecular weight. This is in striking contrast to myelin from phylogenetically higher classes.

Developmental regulation of the carbohydrate composition of glycoproteins associated with central nervous system myelin

Glycoproteins from central nervous system myelin were evaluated for developmental alterations in their carbohydrate composition by autoradiographic analysis of radioiodinated lectin binding after separation by high-resolution sodium dodecyl sulfate-pore gradient slab gel electrophoresis (SDS-PGE). Sixteen lectin-binding components were assessed in highly purified myelin preparations from 15-day, 18-day, and adult rat brains, using the lectins Triticum vulgaris (wheat germ agglutinin) and Ulex europeus (gorse agglutinin I). Developmental changes in lectin binding for individual glycoproteins were evaluated semiquantitatively by comparing densitometric scans of the autoradiographs. Both increases and decreases in lectin binding for individual components were observed as a consequence of development, as well as the appearance and disappearance of lectin binding to three low-molecular-weight components. No changes in electrophoretic mobility and hence glycoprotein molecular weight were observed in any components when using these lectins. These developmental changes in lectin binding suggest that increases in glycoprotein (receptor) density occur, as well as an elaboration of oligosaccharide branching for individual glycoproteins. In addition, the appearance of a new glycoprotein in the adult myelin membrane could imply a new functional role not present in the immature membrane. These observations suggest that dynamic alterations of myelin-associated glycoproteins occur during development. Such developmental regulation of membrane glycoproteins increases the significance of their potential role in myelination and myelin maintenance.

Myelin proteins, glycoproteins, and myelin-related enzymes in experimental demyelination of the rabbit optic nerve: sequence of events

Wallerian degeneration of the rabbit optic nerve was investigated by the technique of retinal ablation which precludes edema, hemorrhage, or macrophage infiltration. After 8 days of degeneration, marked degradation of axons and some myelin abnormalities appeared in the optic nerve, optic chiasma, and optic tract. Myelin lesions were maximal 32 days after retinal destruction. The amount of material stained with a myelin dye decreased drastically between 32 and 90 days after the operation. Biochemical parameters gave the following sequence of events. The concentration of the major periodic acid--Schiff staining glycoproteins was decreased after 2 days, and 6 days later the presence of cholesterol esters was detected in the optic tissue. After 16 days of Wallerian degeneration, the specific activity of 2',3'-cyclic nucleotide 3'-phosphodiesterase not associated with myelin decreased, indicating a possible de-differentiation of oligodendrocytes. Degradation of myelin basic protein became significant at 32 days and the amount of myelin isolated decreased later. The loss of myelin basic protein coincided with a reduction of myelin periodicity as measured in purified fractions by electron microscopy. These results show that secondary myelin destruction in the absence of edema, hemorrhage, or macrophages is a very slow process, and in this situation myelin undergoes a selective and sequential loss of its constituents.

Demonstration of five major glycoproteins in myelin and myelin subfractions

Myelin was found to contain five major glycoproteins with molecular weights of 120000, 95000, 88000, 43000 and 38000. Light myelin contained only 5-7% of the amount of these glycoproteins in whole myelin, whereas heavy myelin and the membrane fraction contained amounts nearly identical with whole myelin. Since all the major and minor glycoproteins, with the exception of 120000-mol-wt. glycoprotein, were detected only after treating the myelin membrane with neuraminidase, N-acetylneuraminic acid is a terminal sugar residue in these glycoproteins.

The glycoprotein composition of peripheral nervous system myelin subfractions

Two fractions were isolated by continuous density gradient centrifugation from total particulate matter of rabbit sciatic nerves: a minor fraction, B, consisting of small-sized membrane fragments and a major fraction, C, of characteristic multilayered myelin figures, with maxima at 0.33 and 0.58 M-sucrose, respectively. In comparison with C, fraction B was enriched in CNPase and alkaline phosphatase activities and the P0, 23K and Z proteins, but was virtually devoid of basic protein. The glycoprotein composition of all fractions was examined with four fluorescein isothiocyanate-labelled lectins (WGA, Con A, RCA-60, U.E.). These revealed the presence of six glycoproteins in all fractions with similar lectin binding capacities and molecular weights ranging from 35,500 to 16,000, of which P0 was the predominant component. Material found on the heavy side of fraction C was characterized by the presence of a multitude of glycoproteins which bound variable proportions of the four different lectins, suggesting substantial variations in their carbohydrate moieties. Their absence from the central portion of fraction C points to a location other than that of compact PNS myelin.

Galactose oxidase labeling of membrane proteins from human brain white matter

The use of galactose oxidase (EC 1.1.3.9) and tritiated sodium borohydride for labeling of membrane glycoproteins, described by Gahmberg and Hakomori, has previously been applied to the study of myelin glycoproteins of experimental animals. Rat brain myelin glycoproteins have been studied by sequential lectin affinity of chromatography and recently the lectin-binding capacity of rat central nervous system myelin glycoproteins has been characterized. Complex heterogeneity of the glycoprotein pattern of rat central nervous system myelin has been reported, and so a variety of glycoproteins can be expected to exist in human white matter membranes. Application of the galactose oxidase procedure to the study of human brain membranes could be useful in research concerning certain neurological diseases if the properties of autopsy brain material are taken into account. In this study, membrane proteins of human autopsy brain white matter were subjected to the galactose oxidase/NaB3H4 labeling procedure and the membrane labeled by this method or by the [3H]acetic anhydride techniques were studied by lectin affinity chromatography using Lens culinaris phytohemagglutinin (lentil lectin) attached to Sepharose 4B beads.

5'-nucleotidase in rat brain myelin

Rat brain myelin showed substantial activity of 5'-nucleotidase. The specific activity in myelin was enriched two- to threefold over that in rat brain homogenates, and the total activity in myelin accounted for approximately 24% of the activity in the homogenates. The 5'-nucleotidase in the homogenates and in isolated myelin had optimum activity at pH 7.5--9.0, was stimulated by Mg2+ and Mn2+, and was inhibited by Co2+, Zn2+, EDTA, and EGTA. 5'-AMP, 5'-UMP, and 5'-CMP were the preferred substrates, and 5'-GMP was hydrolyzed at approximately one-half the rate of the other mononucleotides. The very low rates of cleavage of beta-glycerophosphate and 2'-AMP ruled out any significant contribution of nonspecific phosphatase to the observed 5'-nucleotidase activity in myelin. The 5'-nucleotidase was inhibited by concanavalin A and was protected by alpha-methyl-D-mannoside against inhibited by that lectin, suggesting that this enzyme in the CNS is a glycoprotein. It is concluded from these data, and from histochemical observations made in other laboratories, that the myelin sheath is one major locus of 5'-nucleotidase in the rat brain.