Increased myelination related enzymatic activities in neuron-glial heterokarya

Two enzymatic activities associated with myelination were determined in a neuron-glial heterokaryon system. Significant increases of 2′,3′-cyclic nucleotide-3′-phosphohydrolase (CNP) and UDP-galactose-ceramide galactosyl transferase (CGalt) activities were noted in heterokarya produced in vitro between 17-day-old rat cerebral neurons and differentiated cultured rat glioma (C₆) cells; rat cerebral neurons and calf brain white matter glial cells or differentiated neuroblastoma 2a cells and differentiated C₆ cells. Morphological expression of differentiation, such as neurite extension, was also noted in the heterokarya. Findings suggest that the glial expression of myelination related enzymatic activities could be under a neuronal regulatory control and further suggest that the interaction of neurons and glia is necessary for myelinogenesis and maintenance of the myelin sheath components.     

Enzyme and protein studies of demyelination in diabetes.

Neuropathological evidence of demyelination was found in the brain and sciatic nerve of diabetic patients at autopsy. The activity of acid proteinase was somewhat increased in the white matter but decreased in the gray matter of diabetic patients. No increase was observed in the activity of neutral proteinase in diabetic white and gray matter. The activities of beta-glucuronidase and 2',3'-cyclic nucleotide-3'-phosphohydrolase (CNP) were of the same level as those of the controls. The activities of all 4 enzymes appeared to be increased in the diabetic nerve, with the possible exception of CNP which was measured from only 1 nerve. Furthermore, the amount of total protein was markedly decreased in diabetic peripheral myelin. The encephalitogenic basic protein of diabetic brain myelin was normal in the disc gel electrophoretic patterns of brain myelin proteins. However, the basic proteins of peripheral myelin were reduced in a number of diabetic patients. The present biochemical findings for diabetic white and gray matter were largely normal. Instead, the increased activities of at least the proteinases and beta-glucuronidase in diabetic peripheral nerve, together with the loss of basic proteins, indicate extensive biochemical damage of the peripheral nervous system in diabetes. They suggest that demyelination and other phenomena observed in diabetic peripheral nerve are not caused only by angiopathy and impaired circulation.     

Digitized image analysis reveals diffuse abnormalities in normal-appearing white matter during acute experimental autoimmune encephalomyelitis

Demyelination of the central nervous system is a hallmark of multiple sclerosis and its widely used animal model, experimental autoimmune encephalomyelitis (EAE). Recent studies using magnetic resonance imaging and spectroscopy on multiple sclerosis patients have revealed abnormalities of central nervous system normal-appearing white matter suggesting that micro-demyelination and/ or extensive membrane turnover accompanies and perhaps precedes the appearance of manifest inflammatory lesions. In the present study, we induced EAE in SWXJ mice and analyzed digitized images of immunocytochemically stained spinal cord for detection of myelin proteolipid protein (PLP). We found that digitized image analysis is a highly sensitive, objective methodology for measuring the extent of myelin loss during EAE. Our data show that two-thirds of the measured reduction of myelin PLP occurring in EAE spinal cord could be attributed to a loss of myelin in normal-appearing white matter. The marked decrease in detection of PLP was accompanied by a corresponding decrease in PLP mRNA in the central nervous system. Our results indicate that during acute EAE, diffuse myelin abnormalities extend far beyond visibly detectable inflammatory foci and are characterized by a global decrease in the expression of myelin genes and their encoded proteins. J. Neurosci. Res. 54:364–372, 1998. © 1998 Wiley-Liss, Inc.     

Experimental autoimmune encephalomyelitis: Antigen-induced inhibition of biochemical and immunohistological alterations

A comprehensive biochemical, immunological, and histological study was undertaken during suppression of experimental autoimmune encephalomyelitis (EAE) induced by antigen-specific inhibition of the immune response. Pretreatment of Wistar rats by intraperitoneal administration of low doses of saline-soluble bovine myelin or myelin basic protein (MBP) but not with ovalbumin suppresses the appearance of the clinical symptoms of EAE induced by sensitization with bovine myelin in complete Freund's adjuvant. Analysis of the central nervous system (CNS) of animals pretreated with MBP or whole myelin shows inhibition of the diminution of MBP and 2′,3′-cyclic nucleotide 3′-phosphohydrolase (CNPase) activity observed in the EAE animals or in rats pretreated with ovalbumin. With respect to the CNS lipid content, these suppressive treatments abolish the increase in esterified cholesterol and partially revert the diminution in the content of cerebrosides and total cholesterol characteristic of the acute stage of the disease. Concomitantly, meningeal and parenchymal infiltration with mononuclear cells and deposits of immunoglobulins in the infiltrated regions as well as in spinal cord motor neurons were reduced. Analysis of the humoral response to myelin antigens shows that all EAE as well as treated animals developed antibodies to MBP and other myelin proteins. However, a higher incidence and level of these antibodies was observed in nontreated EAE animals and MBP- and ovalbumin-treated rats, while rats treated with total bovine myelin showed a highly reduced humoral response. The present results indicate that intraperitoneal treatment with soluble forms of myelin antigens, concomitant with the suppression of the clinical symptoms of the disease, markedly reduces the biochemical and histological alterations occurring in EAE animals and produces changes in the autoimmune humoral response. © 1996 Wiley-Liss, Inc.     

Age-dependent accumulation of ubiquitinated 2',3'-cyclic nucleotide 3'-phosphodiesterase in myelin lipid rafts

Changes in brain white matter are prominent features of the aging brain and include glial cell activation, disruption of myelin membranes with resultant reorganization of the molecular components of the node of Ranvier, and loss of myelinated fibers associated with inflammation and oxidative stress. In previous studies, overexpression of CNP, a key myelin protein, was implicated in age-related changes in myelin and axons. Here we examine the extent of CNP accumulation in brain white matter and isolated myelin of aged rhesus monkeys and its relationship to CNP degradation and partitioning in myelin. With age, excess CNP is found in myelin and throughout brain white matter accompanied by proteolytic fragments of CNP. These increases occur in the absence of changes in CNP mRNA levels. Using a combination of 2D electrophoresis, immunoprecipitation, and mass spectrometry analysis, ubiquitinated CNP was demonstrable in the Triton X-100 insoluble lipid raft associated fractions of myelin isolated from rhesus monkeys. Further, using ubiquitin-mediated fluorescence complementation (UbFC), ubiquitinated CNP was visualized by microscopy in both COS-7 and MO3.13 cells and by immunoblot in MO3.13 cells and appears to at least partially localize within lipid rafts. The findings suggest that incomplete degradation of CNP due to failure of the proteasomal system and aberrant degradation by calpain-1 leads to age-related CNP accumulation and proteolysis. In sum, we suspect these phenomena result in age-related dysfunction of CNP in the lipid raft, which may lead to myelin and axonal pathology.     

Treatment with chimeric anti-human CD40 antibody suppresses MRI-detectable inflammation and enlargement of pre-existing brain lesions in common marmosets affected by MOG-induced EAE

Common marmosets, a Neotropical monkey species, are protected against clinical and neuropathological consequences of experimentally induced autoimmune encephalomyelitis (EAE) by prophylactic treatment with ch5D12, a humanized antagonist antibody against human CD40. In the current study we have tested whether ch5D12 acts therapeutically against the enlargement and inflammatory activity of existing (brain) white matter lesions using serial magnetic resonance imaging (MRI). The results show in all PBS treated monkeys (n=4) a rapid enlargement of T2 lesions together with an increment of the T2 signal intensity due to inflammatory edema. Treatment with ch5D12 delayed the enlargement of T2 lesions in 2 out of 3 tested monkeys while in 3 out of 3 monkeys the T2 signal increment of lesions was suppressed. In conjunction with previously published data on the clinical benefit of anti-CD40 treatment in the marmoset EAE model, the current findings support antibody-mediated blockade of CD40 interaction with its ligand CD154 as a potential treatment of MS.     

Dirty-appearing white matter in multiple sclerosis Preliminary observations of myelin phospholipid and axonal loss

“Dirty-appearing white matter” (DAWM) in multiple sclerosis (MS) is defined as a region(s) with ill-defined borders of intermediate signal intensity between that of normal-appearing white matter (NAWM) and that of plaque on T₂-weighted and proton density imaging. To delineate the histopathology of DAWM, four formalin-fixed cerebral hemisphere slices of three MS patients with DAWM were scanned with T₂- weighted and proton density sequences. The myelin water fraction (MWF) was obtained by expressing the short T₂ component as a fraction of the total T₂ distribution. Hemispheric sections were then stained with Luxol fast blue (LFB) for myelin phospholipids, for myelin basic protein (MBP) and 2’,3’-cyclic nucleotide 3’-phosphohydrolase (CNP) for myelin; Bielschowsky silver impregnation for axons; and for glial fibrillary acidic protein (GFAP) for astrocytes. Compared to NAWM, DAWM showed reduction in MWF, corresponding to a reduction of LFB staining. DAWM also showed reduced Bielschowsky staining. Quantitatively, the change in MWF in DAWM most consistently correlated with the change in LFB staining. The findings of this preliminary study suggest that DAWM is characterized by loss of myelin phospholipids, detected by the short T₂ component, and axonal reduction. † Deceased     

Arrested development of myelin in chick optic tectum following deaferrentation

(1)

The levels of both an enzyme associated with myelin (2′,3′-cyclic nucleotide 3′-phosphohydrolase) and of a lipid constituent of myelin (galactocerebrosides) rise markedly in the chick optic lobe during the maturation of the newly hatched bird.     

Ultrastructural alterations in synaptic boutons of Quaking mice: dense clusters of small vesicles

Synaptosomes were prepared from rat cortex by subjecting a washed crude mitochondrial pellet to centrifugation first on discontinuous Ficoll-isotonic sucrose gradients and then on discontinuous sucrose gradients. The synaptosome fraction, collected from the 7.5–14% Ficoll band (II), was further separated into two additional fractions, designated IIA and IIB, which band at the 0.32–1.05 M and at the 1.05–1.6 M sucrose interfaces, respectively. Electron microscopic analysis showed that fraction IIB contained synaptosomes and extra terminal mitochondria and was essentially free of membrane fragments. Further characterization showed that IIB contained 69% of the protein and 83% of the lactic dehydrogenase activity of fraction II and had a specific activity of a 2′,3′-cyclic nucleotide 3′-phosphohydrolase approximately 1% of that obtained with myelin. Fraction IIA had approximately 50% the specific activity of the 2′,3′-cyclic nucleotide 3′-phosphohydrolase found in myelin. Synaptic plasma membranes were prepared by lysing fraction IIB in 1 mM sodium phosphate, 0.1 mM EDTA at pH 8.5 and subjecting this preparation to centrifugation on a discontinuous sucrose density gradient. Enzymatic analysis indicated that membranes banding at the 0.6–0.8 M sucrose interface had highgh specific activities of plasma membrane enzymes (e.g. acetylcholinesterase, ATPase, 5′-nucleotidase). The specific activity of the (Na⁺ + K⁺)-ATPase in the purified membrane preparation was 8-fold higher than that in the original homogenate. Specific activities of various marker enzymes indicated that the composition of these membrane preparations for the most part was synaptic plasma membranes, approximately 7% mitochondrial outer membranes and 3% a membrane containing 2′,3′-cyclic nucleotide 3′-phosphohydrolase activity. The polypeptide compositions of three possible contaminating membranes and of synaptic membranes were compared by electrophoresis in 6–20% gradient polyacrylamide gels in the presence of sodium dodecyl sulfate. Whereas mitochondrial and myelin membranes had distinct compositions, the compositions of the microsomal and synaptosomal plasma membranes were similar. Synaptic plasma membranes contained at least 27 polypeptides; the three major polypeptdes had molecular weights of 103,000; 54,000; and 50,000. The major polypeptides of soluble synaptosomal proteins had molecular weights of 54,000 and 42,000.     

Rapid upregulation of the Pi isoform of glutathione-S-transferase in mouse brains after withdrawal of the neurotoxicant, cuprizone

Cuprizone intoxication has been used as a model for reversible demyelination in the CNS. During the course of cuprizone intoxication, the glutathione-S-transferase isoform, Pi, normally an oligodendrocytic marker, appears in reactive astrocytes (Cammer and Zhang, 1993). The present experiments address the changes in expression of Pi after removal of cuprizone from the diet of the affected mice. In order to localize Pi message, a riboprobe was prepared andin situ hybridization (ISH) performed. Western blots and immunocytochemistry were used to examine Pi protein and other glial cell markers. The data indicated that Pi protein increased during the first 2 d after withdrawal of the toxicant, when the level of the myelin marker, 2′, 3′-cyclic nucleotide-3′-phosphohydrolase, remained minimal. Results of ISH suggested that levels of Pi message in the corpus striatum decreased during cuprizone feeding and began to recover within 2 d after withdrawal of the toxicant. Both microglia and astrocytes appeared during the first week of cuprizone administration and persisted during two to three additional weeks on cuprizone. Reactive astrocytes remained in the tissue for at least 6 wk after cuprizone was withdrawn, while microglia receded within days. The findings suggest that astrocytes continue to express Pi after withdrawal of cuprizone.     

Noncoordinate regulation of myelinogenic parameters in primary cultures of dissociated fetal rat brain

The developmental regulation of sulfogalactosylceramide (sulfatide) synthesis, 2′,3′-cyclic nucleotide-3′-phosphohydrolase activity (CNP), and myelin basic protein (MBP) accumulation, three markers characteristic of myelinogenesis, were observed in dispersed cultures of fetal rat brain in spite of the absence of the formation of compact, multilamellar myelin. Sulfatide synthetic rate and CNP activity began to increase by 8 days in vitro (DIV) (approximately comparable to days post-natal) and reached their maxima by 20 DIV. MBP began to accumulate after 14 DIV and reached a maximum by 38 DIV. Thus, the temporal regulation of the onset of expression of these parameters, which is coordinate in vivo, has been dissociated into two sequential periods in vitro. Similarly, the regulatory mechanisms controlling the subsequent decline of the net expression of these three parameters were dissociated. Whereas, the increase in the net CNP activity ceased on schedule, the decline of sulfatide synthetic rate was delayed 20 days, and the accumulation of MBP underwent a net loss. These data suggest that there are multiple parallel but separate mechanisms of temporal regulation controlling myelinogenic gene expression, and that, among them, those factors that control MBP accumulation are more sensitive to disruption by the rigors of dissociated culture.     

Passive transfer of experimental autoimmune encephalomyelitis in Wistar rats: dissociation of clinical symptoms and biochemical alterations

We have used passive transfer of myelin-reactive lymphocytes in the Wistar rat model of experimental autoimmune encephalomyelitis (EAE) to investigate the nature of the central nervous system immunopathological alterations induced by these cells. Mononuclear cells from lymph nodes or spleen from sick myelin/complete Freund's adjuvant-immunized donors did not transfer clinical disease. However, depending on the previous treatment of the transferred cells, recipients develop central nervous system biochemical and histological alterations. Fresh cells from lymph nodes immediately transferred after procurement from the sick EAE donor rat were capable of inducing the most significant diminution in the content of myelin basic protein, sulfatides, and 2',3'-cyclic nucleotide-3'-phosphohydrolase activity, with concomitant inflammatory infiltrations of white matter, principally in spinal cord and cerebellar lobules. Similar alterations were observed when animals were injected with spleen mononuclear cells activated in the presence of a nonspecific mitogen as concanavalin A. However, antigen-specific activated spleen cells generated by culturing in the presence of bovine myelin induced alterations to a lesser degree. Results point to a dissociation of the clinical disease from the central nervous system biochemical and histopathological lesions occurring in the EAE-transferred Wistar rats and indicate that these alterations in EAE are induced principally by T cells activated in vivo rather than by cells activated in vitro by myelin antigens. Therefore, these findings suggest a possible participation of lymphocytes unlike the encephalitogenic T cells in the induction of the described alterations and provide a useful model to explore further the subclinical responses to this experimental disease.     

Antisera to different glycolipids induce myelin alterations in mouse spinal cord tissue cultures

To study the demyelinative effects of antibodies to glycolipids, well-myelinated cultures of mouse spinal cord tissue were exposed to antisera against galactocerebroside and two gangliosides (GM₁ and GM₄), as well as to anti-white matter antiserum. The demyelinative process was evaluated by morphologic and biochemical techniques. Cultures exposed to anti-white matter and anti-galactocerebroside antisera showed the most marked changes. These consisted of a decrease in the number of oligodendroglial cells and dissolution and phagocytosis of myelin. Concomitantly, the activity of 2′,3′-cyclic nucleotide-3′-phosphohydrolase (CNPase) was decreased by 60–70%. This occured within 24 h of exposure to a relatively low concentration of serum (10%). Cultures exposed to anit-GM₁ and anti-GM₄ antisera showed similar changes but to a lasser degree. The CNPase activity was decreased about 30% within 48 h of exposure to a 25% concentration of these antisera. This diminution represents about a 20% loss of myelin, an observation corroborated by electron microscopy where myelin but not oligodendroglial cell was observed. Therefore, in addition to anti-galactocerebroside activity, which was previously found to be the major antibody responsible for the demyelinating activity induced by anti-whole CNS tissue antiserum, these data suggest that antibodies to gangliosides like GM₁ and GM₄ might also play a role in immune-mediated demyelination, including perhaps, the human demyelinating diseases.     

Effects of prenatal and neonatal nutritional deficiencies on the 2′,3′-cyclic nucleotide-3′-phosphohydrolase activity in the brain and spinal cord of rats

Studies were made of the effects of deficiencies of protein, vitamin A, and pantothenic acid in the maternal diet during gestation and lactation on the activity of 2′,3′-cyclic nucleotide-3′-phosphohydrolase, a myelin marker, in the brain and spinal cord of the progeny. Neonatal and combined prenatal and neonatal protein deficiencies were continued to 14 days of age. At 14 and 21 days of age there was a significant decrease in body, brain, and spinal cord weights. Brain phosphohydrolase activity was significantly decreased in protein- and vitamin A-deficient rats at 21 days of age. However, there was no change in spinal cord activity in any of the experimental manipulations at this age. Protein deficiency at 14 days resulted in a significant decrease in spinal cord and a slight decrease in brain phosphohydrolase activity. Comparison of the control values of phosphohydrolase activity in brain and spinal cord at these ages showed that the spinal cord has a higher activity than the brain.     

Myelin and Microsomes from Rhesus Monkey Spinal Cord: Isolation and Effects of Trauma

Dispersions of rhesus monkey spinal cord and brain were separated into large particle (crude mitochondrial plus nuclear) and small particle (crude microsomal) fractions; myelin was isolated from each of these preparative fractions. In brain preparations, almost all myelin was found in the large particle fraction; in contrast, almost half the myelin from spinal cord preparations was found in the small particle fraction. In addition, much larger amounts of partially degraded myelin were found in the fraction floating on 0.32 M sucrose and in the cytosol fraction of the spinal cord preparation in comparison to those of the brain preparations. These results suggest that rhesus monkey spinal cord myelin is more fragile than brain myelin; upon dispersion of spinal cord, more small myelin vesicles (isolated from the crude microsomal fraction) and more 0.32 M sucrose floating fraction (partially degraded myelin) are formed. After trauma of the spinal cord, the proportion of small vesicle myelin was increased at the expense of large vesicle myelin, lending further support to the hypothesis that spinal cord myelin is more fragile than brain myelin. Although the lipid compositions were similar, spinal cord myelin had a lower protein content and a lower 2′,3′-cyclic nucleotide phosphodiesterase specific activity than did brain myelin. The lipid composition of microsomes from brain differed somewhat from that of spinal cord microsomes.     

Stimulation of in vitro myelin synthesis by microglia

Central nervous system myelin is elaborated by oligodendrocytes, which have been studied extensively in cell culture. Dissociated brain cultures allow in vitro analysis of events in myelinogenesis, including cell-cell interactions. Microglia, the primary phagocytic cell of the central nervous system, appear in developing fiber tracts prior to the onset of myelination in vivo. To gain insight into potential oligodendrocytemicroglial interactions during development, these cells were co-cultured and various parameters of myelin synthesis were measured. In co-culture, microglia stimulated the synthesis of sulfatide, a myelin-specific galactolipid, in oligodendrocytes, as well as the expression of the myelin-specific proteins myelin basic protein and proteolipid protein. Activity of the oligodendrocyte cytoplasm-specific enzyme 2′,3′-cyclic nucleotide 3′-phosphohydrolase was not elevated, suggesting that the effects of microglia were not due to stimulation of oligodendrocyte proliferation. This was confirmed by the inability of microglia to induce significant DNA synthesis. Conditioned medium from cultured microglia provided a similar stimulatory activity, suggesting that the increase in myelin synthesis does not require contact between oligodendrocytes and microglia. These findings suggest a stimulatory role for microglia during myelinogenesis. © 1994 Wiley-Liss, Inc.     

实验性变应性猴脑脊髓炎的超微结构改变

目的探讨自身免疫性中枢神经系统（ＣＮＳ）脱髓鞘的病理特点和发病过程。方法建立猴实验性变态反应性脑脊髓炎（ＥＡＥ）的模型，并从病情不同阶段进行病理取材和电镜观察。结果（１）ＥＡＥ脱髓鞘最早的靶是少突胶质细胞（ＯＤＣ），而不是髓鞘本身；（２）无论急性期还是慢性期，脱髓鞘病灶内只有极少的炎细胞浸入；（３）急性期髓鞘改变轻微，以变性为主，ＯＤＣ肿胀显著，轴突相对完整。远离髓鞘变性区有大量炎细胞浸入；（４）慢性期病变区髓鞘脱失明显，ＯＤＣ严重变性或部分丢失，继发性轴突变性，边缘可见少量薄的髓鞘再生，血脑屏障破坏。结论ＥＡＥ的ＣＮＳ脱髓鞘过程首先累及ＯＤＣ。     

Induction of allergic encephalomyelitis in rhesus monkeys treated with anti monkey thymocyte sera.

Treatment with rabbit anti-moneky thymus cell sera whether limited (3 days) or extensive (15 days), did not alter the development of experimental allergic encephalomyelitis (EAE) in rhesus monkeys challenged with myelin basic protein or central nervous system tissue (CNS) when compared to similarly challenged control monkeys treated with normal rabbit serum. No consistent difference in disease incidence or intensity as measured by incubation period, neurologic signs or CNS pathology was observed between experimental and control monkeys. This finding is in contrast to previous reports on the efficacy of ATS treatment in prevention of EAE in rodents.     

Virus-induced demyelination. Production by a viral temperature-sensitive mutant.

Infection of mice with a temperature-sensitive (ts) mutant of Chandipura virus (CV) ts472 CV, induced a slower disease than the respective parental virus and white matter lesions characterized by perivascular mononuclear infiltrates accompanied by primary demyelination. The pattern of these lesions was very similar to that in EAE, a prototypic autoimmune disease and in Theiler's virus infection in which an immunopathologic mechanism of myelin injury is strongly suggested. Results obtained in nude mice supported the possible immunopathological nature of myelin injury in ts472 CV infection. No inflammatory response was elicited in either grey or white matter. However, whereas grey matter presented extensive necrosis, no alterations were present in white matter. Such data suggest that whereas grey matter lesions are produced by direct viral cytolytic activity, white matter pathology is probably dependent on the host immune response for its development. The finding of additional models of virus-induced demyelination with a possible immunopathologic mechanism of myelin injury is significant as it suggests that this type of virus-induced myelin degeneration is not restricted to a single virus like Theiler's, but it may represent a more general mechanism of virus-induced demyelination.     

Concentric sclerosis (Baló): Morphometric and in situ hybridization study of lesions in six patients

Brain tissues from 6 patients with concentric sclerosis (Baló) were examined by in situ hybridization, immunocytochemistry, morphometry, and histological methods. The patients were 24 to 48 years old and had progressive cerebral symptoms and signs that lasted 15 to 100 days. Large demyelinative lesions, most frequent in the frontal white matter, contained alternating bands of demyelinated and partly myelinated white matter that were arranged in concentric or mosaic patterns. In the areas of demyelination, axons were relatively well preserved and there were perivascular inflammatory infiltrates. In 2 specimens, lesions contained regions with the characteristic appearance of actively demyelinating multiple sclerosis plaques. Oligodendroglial densities were highest in normal-appearing white matter, lower in partially myelinated areas, and lowest in demyelinated areas, which also contained many hypertrophic astrocytes closely associated with oligodendroglia. Messenger RNA levels for myelin-related proteins followed the same pattern; they were lowest in demyelinated areas, higher in partially myelinated areas, and highest in normal-appearing white matter beyond lesion margins. Our findings suggest that concentric sclerosis is a variant of multiple sclerosis, that oligodendroglial loss is important in the pathogenesis of demyelination, and that partially myelinated areas probably represent stages of ongoing myelin breakdown rather than remyelination of previously demyelinated areas.