A novel myelin-associated glycoprotein defined by a mouse monoclonal antibody

A novel myelin antigen has been defined by a mouse monoclonal antibody (8-18C5) raised against rat cerebellar glycoproteins. By immunohistochemistry, the antigen was detected in white matter tracts of the central nervous system, but was absent from peripheral myelin. Western blotting followed by immunostaining revealed that the antigen was a glycoprotein of Mr 51 000 daltons which was degraded on storage to cross-reacting products of 20-26 000 daltons. Antigen was detected in central but not peripheral nervous system samples. Products of identical Mr were obtained by affinity chromatography of iodinated cerebellar glycoproteins on a column of immobilised 8-18C5.     

Externally disposed polypeptides of chick brain mitochondria

Externally disposed polypeptides of chick brain synaptic and non-synaptic mitochondria were identified using lactoperoxidase-catalyzed iodination and galactose oxidase—sodium boro [³H]hydride labeling (with or without neurominidase pretreatment). After surface labeling, polypeptides were separated by electrophoresis on sodium dodecyl sulfate—polyacrylamide gels and incorporation was detected by liquid scintillation counting. When intact synaptic or non-synaptic mitochondria were iodinated they gave quite similar labeling patterns with 10 major radioactive peaks. Most of the surface-incorporated iodine was removable by trypsin. Iodination of microsomes or synaptosomes gave incorporation profiles different from that of mitochondria.Without neuraminidase pretreatment, galactose oxidase labeling of mitochondria gave only near background incorporation. After neuraminidase treatment, galactose oxidase and sodium borotritide labeling of both synaptic and non-synaptic mitochondria produced 12 major radioactive polypeptides. Four were not iodinatable by lactoperoxidase while two components iodinated by lactoperoxidase showed only minor radioactivity peaks after galactose oxidase-sodium borotritide labeling.These results suggest that (a) chick brain mitochondrial membranes have a complex mixture of glycoproteins which are highly sialiated, (b) at least 14 polypeptides are exposed on the exterior surface of brain mitochondria, (c) the functional differences between synaptic and non-synaptic mitochondria are not reflected by the similarities of their major externally disposed polypeptides. Thus, surface labeled components may represent structural polypeptides common to both mitochondrial types.     

Synaptosomal plasma membrane glycoproteins. II. Isolation of fucosyl-glycoproteins by affinity chromatography on the Ulex europeus lectin specific for L-fucose

After solubilization in sodium dodecyl sulphate, almost 90% of synaptosomal plasma membrane glycoproteins were separated from the bulk of synaptosomal plasma membrane proteins by sequential affinity chromatography on two immobilized lectins: concanavalin A and the Ulex europeus lectin specific for L-fucose. Four fractions were obtained and their sugar composition and electrophoretic patterns were determined. Fucosyl-glycoproteins contain more than 26% of protein and 85% of the protein-bound sugar of synaptosomal plasma membrane; hence they constitute a major class of glycoproteins in these membranes. The presence of some glucose in glycoproteins fractions obtained after affinity chromatography on the two lectins suggests that this sugar could be a structural component of some brain glycoproteins. Polyacrylamide gel electrophoresis revealed at least 28 major bands in fucosylglycoprotein fractions, and 11 in other fractions. Several of these major bands appear to contain more than one glycoprotein each. This heterogeneity appears to be mostly the result of the heterogeneity of the neuronal population in the central nervous system. Microheterogeneity of glycoprotein sugar chains and possible contamination of synaptosomal plasma membranes play, in our opinion, only a minor role.     

Abnormal brain MRI signal in 18q-syndrome not due to dysmyelination

Background

18q-Syndrome is a chromosomal disorder exhibiting various symptoms arising from the central nervous system. Brain magnetic resonance imaging (MRI) of patients with this syndrome usually demonstrates abnormal white matter intensities. This is widely believed to be due to impaired myelin formation because this syndrome involves the deletion of the myelin basic protein (MBP) gene in 18q23. However, this hypothesis has not been confirmed by actual pathology because early death is unusual and autopsy rarely performed.

Patient

A 6-year-old boy with ring chromosome 18 syndrome was examined by genetic analysis for the MBP gene, brain MRI, and autopsy.

Results

Haploinsufficiency of the MBP gene was confirmed. T₂-weighted MRI revealed diffuse high intensities throughout the cerebral white matter. Pathological examination showed the cerebral white matter to be uniformly stained by Klüver–Barrera and MBP immunohistochemical staining. Oligodendrocytes were immunoreactive for proteolipid protein and ferritin but not MBP. Electron microscopy revealed clusters of axons wrapped in compact myelin sheaths with distinct major dense lines. Holzer and immunohistochemical staining for glial fibrillary acidic protein showed extensive staining of the white matter and an increased number of glial filaments.

Conclusions

This pathological study demonstrated that in this disorder, the brain was well myelinated, contrary to established hypotheses about this disorder. The MRI signal abnormalities in 18q-syndrome could be attributed to gliosis and not to dysmyelination.     

HPC-7: A novel oligodendrocyte lineage protein which appears prior to galactocerebroside

The identification of cell type-specific molecules expressed at different developmental stages can help to elucidate the regulatory mechanisms governing the survival, differentiation, and development of cells in the central nervous system (CNS). A cell surface protein, HPC-7, was detected on rat oligodendrocytes (OL) in culture by a monoclonal antibody generated against adult rat hippocampal membranes. Adult rat brain and sciatic nerve sections showed selective labeling of white matter and other myelinated fibers in both the CNS and peripheral nervous system (PNS). Double-labeling of secondary cultures of OL, O-2A, and type-2 astrocytes and primary cultures of type-1 astrocytes with independent cell type-specific antibodies confirmed that HPC-7 was expressed only by the OL lineage. By using a series of OL stage-specific antigenic markers (A2B5, O4, OL-1, galactocerebroside, myelin basic protein) HPC-7 was found to appear at the time when OL precursors became A2B5 negative and began their terminal differentiation in OL. On immunoblots, anti-HPC-7 antibody recognized a single 66 kDa band in rat OL and a single band at 100 kDa in adult myelin. N-glycosidase treatment showed that the HPC-7 protein did not contain substantial amounts of N-linked carbohydrate. Thus, HPC-7 appears to be a cell surface protein of the OL lineage that marks the important transition from proliferative precursor to postmitotic OL. GLIA 23:169–179, 1998. © 1998 Wiley-Liss, Inc.     

Selective effects of LSD and hyperthemia on the synthesis of synaptic proteins and glycoproteins

Protein synthesis in rabbit brain was inhibited following the intravenous injection of LSD. The incorporation of [³⁵S]methionine into brain microsomal and synaptic fractions was decreased by 35–45% relative to control values. A selective increase was observed, however, in the relative labeling of a protein of molecular weight 75,000. Our previous studies have shown that LSD induces an increase in body temperature (i.e. hyperthermia) in rabbits. When LSD-induced hyperthermia was blocked the general reduction in labeling of microsomal and synaptic proteins was still apparent but the selective increase in relative labeling of the 75,000 dalton protein was not. Induction of hyperthermia by means other than LSD (i.e. elevation of ambient temperature) produced selective increases in the relative labeling of microsomal and synaptic proteins of molecular weight 75,000 and 95,000. These proteins are similar in molecular weight to two of the major ‘heat shock’ proteins whose synthesis is induced in several cultured cell lines following elevation of ambient temperature. Fractionation of [³⁵S]methionine-labeled synaptic membranes by lectin affinity chromatography and analysis of [³⁵H]fucose labeling patterns indicated that, in contrast to the general reduction in labeling of brain proteins, the synthesis of synaptic glycoproteins was not altered by LSD. The synthesis of glycosylated proteins present in other subcellular fractions was, however, reduced. These results suggest that LSD induced selective changes in the synthesis of brain proteins and that the synthesis of synaptic glycoproteins may be relatively resistant to drug administration.     

Characterization of two subcellular fractions isolated from myelinated axons

Myelin and a heavy membrane fraction ( fraction) were isolated from rabbit white matter by a slight modification of the procedure for bovine CNS. The specific activities of acetylcholinesterase and Na⁺, K⁺-ATPase were higher in the fraction than in myelin. In contrast, the cerebroside content and 2′, 3′-cyclic nucleotide 3′-phosphohydrolase activity in the fraction were 4.5 and 3.4 times lower than in myelin. Total lipids accounted for only 30% of the fraction's dry weight; for myelin, they represented 70%. Polacrylamide gel electrophoresis showed the presence of many high molecular weight proteins and glycoproteins in the fraction but myelin components were practically missing. Cytochrome c oxidase and NADPH-cytochrome c reductase activities suggested about 15% contamination in the fraction but less than 5% for myelin. In electron micrographs of the fraction, there were many membraneous profiles that varied in size, some mitochondrial fragments, and only a few lamellar whorls of compact myelin. The results suggest that the fraction is different from other myelin-related fractions and is probably enriched in axolemma.     

Maintenance of high proteolipid protein level in adult central nervous system myelin is required to preserve the integrity of myelin and axons

Proteolipid protein (PLP) is the most abundant integral membrane protein in central nervous system (CNS) myelin. Expression of the Plp-gene in oligodendrocytes is not essential for the biosynthesis of myelin membranes but required to prevent axonal pathology. This raises the question whether the exceptionally high level of PLP in myelin is required later in life, or whether high-level PLP expression becomes dispensable once myelin has been assembled. Both models require a better understanding of the turnover of PLP in myelin in vivo. Thus, we generated and characterized a novel line of tamoxifen-inducible Plp-mutant mice that allowed us to determine the rate of PLP turnover after developmental myelination has been completed, and to assess the possible impact of gradually decreasing amounts of PLP for myelin and axonal integrity. We found that 6 months after targeting the Plp-gene the abundance of PLP in CNS myelin was about halved, probably reflecting that myelin is slowly turned over in the adult brain. Importantly, this reduction by 50% was sufficient to cause the entire spectrum of neuropathological changes previously associated with the developmental lack of PLP, including myelin outfoldings, lamellae splittings, and axonal spheroids. In comparison to axonopathy and gliosis, the infiltration of cytotoxic T-cells was temporally delayed, suggesting a corresponding chronology also in the genetic disorders of PLP-deficiency. High-level abundance of PLP in myelin throughout adult life emerges as a requirement for the preservation of white matter integrity.     

Astrocyte‐mediated infantile‐onset leukoencephalopathy mouse model

Astrocytes have recently been shown to provide physiological support for various brain functions, although little is known about their involvement in white matter integrity. Several inherited infantile‐onset leukoencephalopathies, such as Alexander disease and megalencephalic leukoencephalopathy with subcortical cysts (MLC), implicate astrocytic involvement in the formation of white matter. Several mouse models of MLC had been generated by knocking out the Mlc1 gene; however, none of those models was reported to show myelin abnormalities prior to formation of the myelin sheath. Here we generated a new Mlc1 knockout mouse and a Mlc1 overexpressing mouse, and demonstrate that astrocyte‐specific Mlc1 overexpression causes infantile‐onset abnormalities of the white matter in which astrocytic swelling followed by myelin membrane splitting are present, whereas knocking out Mlc1 does not, and only shows myelin abnormalities after 12 months of age. Biochemical analyses demonstrated that MLC1 interacts with the Na⁺/K⁺ ATPase and that overexpression of Mlc1 results in decreased activity of the astrocytic Na⁺/K⁺ pump. In contrast, no changes in Na⁺/K⁺ pump activity were observed in Mlc1 KO mice, suggesting that the reduction in Na⁺/K⁺ pump activity resulting from Mlc1 overexpression causes astrocytic swelling. Our infantile‐onset leukoencephalopathy model based on Mlc1 overexpression may provide an opportunity to further explore the roles of astrocytes in white matter development and structural integrity. We established a novel mouse model for infantile‐onset leukoencephalopathy by the overexpression of Mlc1. Mlc1 overexpression reduced activity of the astrocytic sodium pump, which may underlie white matter edema followed by myelin membrane splitting. GLIA 2016 GLIA 2017;65:150–168     

Distribution and age-dependent concentration in brain tissue of glycoproteins containing N-acetylgalactosamine.

Glycoproteins that yield non-dialyzable, alkali-labile, N-acetylgalactosamine-containing heteropolysaccharides upon proteolytic digestion show a threefold enrichment in white matter relative to gray matter. Approximately 50% of these glycoproteins appear in soluble extracts prepared from rat brain. This distribution contrasts with that of the predominant alkali-stable sialoglycopeptides, which account for 60% of the total brain glycoprotein-carbohydrate. The latter glycopeptides showed a twofold enrichment in gray matter compared with white, and only about 10% of the glycoproteins that yield these glycopeptides could be solubilized by extraction with aqueous solvents. The concentration of the N-acetylgalactosamine-containing glycoproteins in the 3-year-old cerebral gray matter from human brain was respectively 7-15 and 15-30 times greater than in 8- and 72-year-old tissue. Electrophoretic analysis of the non-dialyzable, alkali-stable, acidic glycopeptides that contain NANA, fucose, mannose, galactose, and N-acetylglucosamine, obtained from the microsomal and synaptosomal fractions, revealed that the composition of these glycopeptides in the two fractions was identical.     

Short‐ and long‐term functional plasticity of white matter induced by oligodendrocyte depolarization in the hippocampus

Plastic changes in white matter have received considerable attention in relation to normal cognitive function and learning. Oligodendrocytes and myelin, which constitute the white matter in the central nervous system, can respond to neuronal activity with prolonged depolarization of membrane potential and/or an increase in the intracellular Ca²⁺ concentration. Depolarization of oligodendrocytes increases the conduction velocity of an action potential along axons myelinated by the depolarized oligodendrocytes, indicating that white matter shows functional plasticity, as well as structural plasticity. However, the properties and mechanism of oligodendrocyte depolarization‐induced functional plastic changes in white matter are largely unknown. Here, we investigated the functional plasticity of white matter in the hippocampus using mice with oligodendrocytes expressing channelrhodopsin‐2. Using extracellular recordings of compound action potentials at the alveus of the hippocampus, we demonstrated that light‐evoked depolarization of oligodendrocytes induced early‐ and late‐onset facilitation of axonal conduction that was dependent on the magnitude of oligodendrocyte depolarization; the former lasted for approximately 10 min, whereas the latter continued for up to 3 h. Using whole‐cell recordings from CA1 pyramidal cells and recordings of antidromic action potentials, we found that the early‐onset short‐lasting component included the synchronization of action potentials. Moreover, pharmacological analysis demonstrated that the activation of Ba²⁺‐sensitive K⁺ channels was involved in early‐ and late‐onset facilitation, whereas 4‐aminopyridine‐sensitive K⁺ channels were only involved in the early‐onset component. These results demonstrate that oligodendrocyte depolarization induces short‐ and long‐term functional plastic changes in the white matter of the hippocampus and plays active roles in brain functions. GLIA 2014;62:1299–1312     

Metabolism of a myelin-associated glycoprotein in developing rat brain

The amount of the major myelin-associated glycoprotein/mg of total myelin protein remained nearly constant between 14 days and 60 days of postnatal age in the rat. When 13-day-old rats were injected with [³H]fucose, the total amount of radioactivity recovered in the myelin-associated glycoproteins increased 4–10 fold between 1 day and 3 weeks after injection, at a time when glycoproteins in other structures in the brain were turning over and losing radioactivity. A similar prolonged period of incorporation into myelin occurred when 13-day-old rats were injected with [¹⁴C]glucose, a more general precursor of lipids and proteins. However, when 35-day-old rats were injected with [³H] fucose the amount of radioactivity recovered in the myelin fraction 3 weeks after injection was only 60% of that present 1 day after injection. The results provide additional evidence that a glycoprotein is associated with myelinin situ. The existence of a membranous precursor of myelin in immature brain and reutilization of metabolites are discussed as possible explanations for the long tlme course of myelin labeling after the injection of 13-day-old rats.     

ATPase activities in myelin and oligodendrocytes isolated from the brains of developing rats and from bovine brain white matter

Of the Na, K-ATPase activity in brain homogenates from 20-, 60-, and 120-day-old rats, 1.4 to 2.6% was recovered in myelin. The relative specific activities, at 0.2 to 0.3 times the specific activities in the rat brain homogenates, did not decrease during development, and myelin from bovine brain white matter had a similar relative specific activity. Oligodendrocytes from rat brains and bovine white matter had approximately one third the Na, K-ATPase specific activities found in myelin from the respective sources. The Mg-ATPase activity in rat brain myelin decreased during development and, in myelin from adult rats, was much lower than the Na, K-ATPase activity. Notably, oligodendrocytes from both the forebrains of 10- to 120-day-old rats and from bovine white matter had high Mg-ATPase activities. Whereas Na, K-ATPase may be intrinsic to certain regions of the myelin sheath, the Mg-ATPase in isolated myelin probably arises from fragments of oligodendrocyte membranes.     

Immunohistochemical localization of citrullinated proteins in adult rat brain

By using hybridoma technology, an IgM monoclonal antibody (F95) against multiple citrullinated synthetic and natural peptides was recently developed and used to stain immunohistochemically subsets of astrocytes and myelin basic protein (MBP) from selected regions of human brain (Nicholas and Whitaker [2002] Glia 37:328-336). With this antibody, the present study provides a more detailed localization of citrullinated epitopes in the central nervous system (CNS) by examining immunohistochemical staining patterns for F95 in the normal adult rat brain. Thus, immunohistochemical labeling for citrullinated epitopes was seen in white matter areas consistent with myelin staining; however, in general, it was more prominent and uniform in the caudal CNS (spinal cord, medulla oblongata, pons, and cerebellum) than in more rostral areas. F95 staining was also seen in cells and fibers often intimately associated with blood vessels and/or ventricular surfaces. By using dual-color immunofluorescence, the vast majority of this latter staining was colocalized within a subset of astrocytes also immunoreactive for glial fibrillary acidic protein (GFAP). By using Western blot analysis of rat brain proteins, multiple GFAP- and MBP-immunoreactive proteins and peptide fragments were seen, and many of them were also reactive with the F95 antibody. Thus, the present study not only demonstrates that citrullinated epitopes in normal rat brain are most concentrated in subsets of myelin and astrocytes but also provides evidence that GFAP, like MBP, may be present as multiple citrullinated isoforms.     

Amyloid precursor protein is enriched in axolemma and periaxolemmal-myelin and associated clathrin-coated vesicles

The amyloid precursor protein (APP) is widely distributed within the CNS, where it is expressed in both neurons and glia. We have isolated axolemma and periaxolemmal-myelin from rat brain and have determined by Western blot that APPs, Mr 100–110 kDa, are major constituents of these membrane. Isolation of axolemma, periaxolemmal-myelin, and compact myelin show that while APP represents 1 and 0.6% of the proteins of these respective membranes, it is absent from compact myelin. These results indicate that APP transported down the axon is deposited at sites in the axolemma as well as the synapse, and that within the myelin complex, APP is targeted to the periaxolemmal domain. Both axolemma and periaxolemmal-myelin contained a 10.5 kDa APP peptide which, based on reactivity with anti-C-terminal APP antibodies but not with anti-N-terminal antibody, appears to be a membrane-associated C-terminal fragment. Western blots with antibodies to Alzheimer precursor-like proteins (APLP) indicate that APP immune reactivity is not a result of cross reactivity with APLPs. Isolation of axolemma from human autopsy material showed nearly identical results with a clear enrichment, relative to homogenate, of APP Mr 100–100 and the 10.5 kDa C-terminal peptide. The demonstration of APP in axolemma and periaxolemmal-myelin was replicated in membrane isolated from bovine brain. Bovine studies were extended to analysis of white matter clathrin-coated vesicles; these data show that coated vesicles isolated from white matter, under conditions that previous studies indicate are largely endocytic vesicles, contain levels of APP comparable to that found in axolemma and periaxolemmal-myelin. In addition, these vesicles contain cysteinly and aspartyl proteases. Incubation of axolemma with cathepsin B at pH 6.0 caused a rapid loss in the immune reactivity of APP Mr 100–110 and Mr 10.5 when analyzed with antibodies to APP_672–695. This appears to be the result of hydrolysis within the epitope and not proteolysis of APP or the C-terminal peptide, since no loss of reactivity was observed when analyzed with antibodies to sites more distal to the C-terminus. Thus, cathepsin B hydrolyses membrane bound APP close to the C-terminus and may be a useful tool for altering C-terminal APP function. © 1994 Wiley-Liss, Inc.     

Vascular changes in the cerebral cortex in HIV-1 infection

In human immunodeficiency virus 1 (HIV-1)-infected patients, a hypoperfusion is seen by SPECT analyses in different brain regions but a specific pattern for the predominance of a specific brain region has not been found. The vessels of the cerebral cortex of the frontal, temporal, parietal, and occipital lobes of acquired immunodeficiency syndrome (AIDS) brains and control brains were analyzed by immunohistochemistry and lectin histochemistry. Immunohistochemistry was performed for collagen IV, laminin (basal lamina), and factor VIII (endothelial cell) and lectin histochemistry [Ricinus communis agglutinin (RCA-I), Ulex europaeus agglutinin (UEA-I), wheatgerm agglutinin (WGA) and soybean agglutinin (SBA)] was used to study changes of glycoproteins in the endothelial cell membrane. Vessels were counted in the gray and white matter, and their staining intensity for the different antibodies and lectins was rated using a three-point scale. Immunoreactivity for collagen IV was reduced in AIDS brains, which may be related to thinning of the basal lamina of cerebral vessels, as has previously been shown by electron microscopy. Lectin histochemistry with SBA, UEA-I and WGA indicated loss of glycoproteins in the membrane of endothelial cells. The data from the present study show morphological changes of the endothelial cells and of the basal lamina in the brain of individuals with AIDS, and might represent the morphological sequelae of a disturbed blood-brain barrier, or may account for the hypoperfusion seen in SPECT analyses. Received: 17 February 1995 / Revised, accepted: 7 December 1995     

Characterization of a polyclonal antibody to the μ opioid receptor

Active opioid receptors have been solubilized from bovine striatal synaptosomal membranes and purified approximately 4000-fold using a combination of affinity and hydroxyapatite chromatography. The affinity column was constructed by attaching hybromet, a newly synthesized opioid ligand with high affinity for the μ receptor, to a solid support matrix. A polyclonal antibody was generated to opioid receptors by injection of the purified receptor preparation into female New Zealand rabbits. The specificity of the antiserum was demonstrated by receptor competition and immunoprecipitation studies. Immunological titration of opioid binding activity from rat brain showed that the antibody was able to displace specific binding of [³H]etorphine (universal opioid) and [³H]dihydromorphine (μ opioid) from rat membranes, but was ineffective against the binding of [³H]ethylketocyclazocine (κ opioid), [³H]d-Ala²,d-Leu⁵-enkephalin (δ opioid) or [³H]phencyclidine (phencyclidine/σ receptor ligand). The antibody was able to precipitate the M_r 94 000 component of the ¹²⁵I-labeled affinity-purified receptor, a finding which suggests that this subunit may be an opioid recognition component. By indirect immunofluorescence, the antibody was shown to bind specifically to the plasma membranes of the neurotumor cell line NCB-20 (neuroblastoma × Chinese hamster brain hybrid cells), which has high affinity opioid receptors. The observed fluorescence in the neuroblastoma cells was prevented by pre-adsorption of the antibody with purified receptor from rat brain. These results indicate that the antibody is specific for opioid receptors and may prove useful in the precise localization of opioid receptors in the central and peripheral nervous systems by immunohistochemical procedures.     

An autopsy case of adult-onset hereditary spastic paraplegia type 2 with a novel mutation in exon 7 of the proteolipid protein 1 gene

We report an autopsy case of rare adult-onset spastic paraplegia type 2 (SPG2) with a novel missense mutation in exon 7 of the proteolipid protein 1 gene (PLP1). The patient was a 67-year-old man whose elder brother had died of a similar disease with onset in his 40s. Thirty-three years before death at the age of 35, he noticed difficulty in walking. He gradually became abasic over a period of 6 years. He also developed progressive dementia and eventually became bed-ridden by 28 years after onset. At autopsy, gross inspection revealed diffuse, moderate atrophy of the cerebrum with a dilated ventricular system and softening of the white matter throughout the central nervous system (CNS). Histopathologically, the CNS showed widespread myelin pallor in the white matter. By contrast, the gray matter and peripheral nerves were well preserved. Some white matter tracts, including the corticospinal tracts, were preferentially affected, and severe axonal degeneration was observed in these tracts. Genetic analysis revealed a novel mutation, p.Tyr263Cys, in exon 7 of PLP1. This case represents an adult-onset SPG2 patient with one of the oldest ages of onset reported to date. The late onset and long clinical course suggest that this novel mutation does not affect the maturation of oligodendrocytes, but is related to insufficient maintenance of myelin.     

Histopathology, electrodiagnostic testing, and magnetic resonance imaging show significant peripheral and central nervous system myelin abnormalities in the cat model of alpha-mannosidosis

Alpha-mannosidosis is a disease caused by the deficient activity of alpha-mannosidase, a lysosomal hydrolase involved in the degradation of glycoproteins. The disease is characterized by the accumulation of mannose-rich oligosaccharides within lysosomes. The purpose of this study was to characterize the peripheral nervous system (PNS) and central nervous system (CNS) myelin abnormalities in cats from a breeding colony with a uniform mutation in the gene encoding alpha-mannosidase. Three affected cats and 3 normal cats from 2 litters were examined weekly from 4 to 18 wk of age. Progressively worsening neurological signs developed in affected cats that included tremors, loss of balance, and nystagmus. In the PNS, affected cats showed slow motor nerve conduction velocity and increased F-wave latency. Single nerve fiber teasing revealed significant demyelination/remyelination in affected cats. Mean G-ratios of nerves showed a significant increase in affected cats compared to normal cats. Magnetic resonance imaging of the CNS revealed diffuse white matter signal abnormalities throughout the brain of affected cats. Quantitative magnetization transfer imaging showed a 8%-16% decrease in the magnetization transfer ratio in brain white matter of affected cats compared to normal cats, consistent with myelin abnormalities. Histology confirmed myelin loss throughout the cerebrum and cerebellum. Thus, histology, electrodiagnostic testing, and magnetic resonance imaging identified significant myelination abnormalities in both the PNS and CNS that have not been described previously in alpha-mannosidosis.     

Oligodendrocyte pathology in fetal alcohol spectrum disorders

The pathology of fetal alcohol syndrome and the less severe fetal alcohol spectrum disorders includes brain dysmyelination.Recent studies have shed light on the molecular mechanisms underlying these white matter abnormalities.Rodent models of fetal alcohol syndrome and human studies have shown suppressed oligodendrocyte differentiation and apoptosis of oligodendrocyte precursor cells.Ethanol exposure led to reduced expression of myelin basic protein and delayed myelin basic protein expression in rat and mouse models of fetal alcohol syndrome and in human histopathological specimens.Several studies have reported increased expression of many chemokines in dysmyelinating disorders in central nervous system,including multiple sclerosis and fetal alcohol syndrome.Acute ethanol exposure reduced levels of the neuroprotective insulin-like growth factor-1 in fetal and maternal sheep and in human fetal brain tissues,while ethanol increased the expression of tumor necrosis factor α in mouse and human neurons.White matter lesions have been induced in the developing sheep brain by alcohol exposure in early gestation.Rat fetal alcohol syndrome models have shown reduced axon diameters,with thinner myelin sheaths,as well as reduced numbers of oligodendrocytes,which were also morphologically aberrant oligodendrocytes.Expressions of markers for mature myelination,including myelin basic protein,also were reduced.The accumulating knowledge concerning the mechanisms of ethanol-induced dysmyelination could lead to the development of strategies to prevent dysmyelination in children exposed to ethanol during fetal development.Future studies using fetal oligodendrocyte-and oligodendrocyte precursor cell-derived exosomes isolated from the mother's blood may identify biomarkers for fetal alcohol syndrome and even implicate epigenetic changes in early development that affect oligodendrocyte precursor cell and oligodendrocyte function in adulthood.By combining various imaging modalities with molecular studies,it may be possible to determine which fetuses are at risk and to intervene therapeutically early in the pregnancy.