Axon-Myelin Unit Blistering as Early Event in MS Normal Appearing White Matter.

OBJECTIVE: Multiple sclerosis (MS) is a chronic neuroinflammatory and neurodegenerative disease of unknown etiology. Although the prevalent view regards a CD4+ -lymphocyte autoimmune reaction against myelin at the root of the disease, recent studies propose autoimmunity as a secondary reaction to idiopathic brain damage. To gain knowledge about this possibility we investigated the presence of axonal and myelinic morphological alterations, which could implicate imbalance of axon-myelin units as primary event in MS pathogenesis. METHODS: Using high resolution imaging histological brain specimens from patients with MS and non-neurological/non-MS controls, we explored molecular changes underpinning imbalanced interaction between axon and myelin in normal appearing white matter (NAWM), a region characterized by normal myelination and absent inflammatory activity. RESULTS: In MS brains, we detected blister-like swellings formed by myelin detachment from axons, which were substantially less frequently retrieved in non-neurological/non-MS controls. Swellings in MS NAWM presented altered glutamate receptor expression, myelin associated glycoprotein (MAG) distribution, and lipid biochemical composition of myelin sheaths. Changes in tethering protein expression, widening of nodes of Ranvier and altered distribution of sodium channels in nodal regions of otherwise normally myelinated axons were also present in MS NAWM. Finally, we demonstrate a significant increase, compared with controls, in citrullinated proteins in myelin of MS cases, pointing toward biochemical modifications that may amplify the immunogenicity of MS myelin. INTERPRETATION: Collectively, the impaired interaction of myelin and axons potentially leads to myelin disintegration. Conceptually, the ensuing release of (post-translationally modified) myelin antigens may elicit a subsequent immune attack in MS. ANN NEUROL 2021;89:711-725.

Expression of membrane progesterone receptors (mPRs) in rat peripheral glial cell membranes and their potential role in the modulation of cell migration and protein expression.

The role played by progestogens in modulating Schwann cell pathophysiology is well established. Progestogens exert their effects in these cells through both classical genomic and non-genomic mechanisms, the latter mediated by the GABA-A receptor. However, there is evidence that other receptors may be involved. Membrane progesterone receptors (mPRs) are novel 7-transmembrane receptors coupled to G proteins that have been characterized in different tissues and cells, including the central nervous system (CNS). The mPRs were shown to mediate some of progestogens' neuroprotective effects in the CNS, and to be upregulated in glial cells after traumatic brain injury. Based on this evidence, this paper investigated the possible involvement of mPRs in mediating progestogen actions in S42 Schwann cells. All five mPR isoforms and progesterone receptor membrane component 1 (PGRMC1) were detected in Schwann cells, and were present on the cell membrane. Progesterone and the mPR-specific agonist, Org-OD-02-0 (02) bound to these membranes, indicating the presence of functional mPRs. The mPR agonist 02 rapidly increased cell migration in an in vitro assay, suggesting a putative role of mPRs in the nerve regeneration process. Treatment with pertussis toxin and 8-Br-cAMP blocked 02-induced cell migration, suggesting this progestogen action is mediated by activation of an inhibitory G protein, leading to a decrease in intracellular cAMP levels. In contrast, long-term mPR activation led to increased expression levels of myelin associated glycoprotein (MAG). Taken together, these findings show that mPRs are present and active in Schwann cells and have a role in modulating their physiological processes.

High-affinity heterotetramer formation between the large myelin-associated glycoprotein and the dynein light chain DYNLL1.

The close association of myelinated axons and their myelin sheaths involves numerous intercellular molecular interactions. For example, myelin-associated glycoprotein (MAG) mediates myelin-to-axon adhesion and signalling via molecules on the axonal surface. However, knowledge about intracellular binding partners of myelin proteins, including MAG, has remained limited. The two splice isoforms of MAG, S- and L-MAG, display distinct cytoplasmic domains and spatiotemporal expression profiles. We used yeast two-hybrid screening to identify interaction partners of L-MAG and found the dynein light chain DYNLL1 (also termed dynein light chain 8). DYNLL1 homodimers are known to facilitate dimerization of target proteins. L-MAG and DYNLL1 associate with high affinity, as confirmed with recombinant proteins in vitro. Structural analyses of the purified complex indicate that the DYNLL1-binding segment is localized close to the L-MAG C terminus, next to the Fyn kinase Tyr phosphorylation site. The crystal structure of the complex between DYNLL1 and its binding segment on L-MAG shows 2 : 2 binding in a parallel arrangement, indicating a heterotetrameric complex. The homology between L-MAG and previously characterized DYNLL1-ligands is limited, and some details of binding site interactions are unique for L-MAG. The structure of the complex between the entire L-MAG cytoplasmic domain and DYNLL1, as well as that of the extracellular domain of MAG, were modelled based on small-angle X-ray scattering data, allowing structural insights into L-MAG interactions on both membrane surfaces. Our data imply that DYNLL1 dimerizes L-MAG, but not S-MAG, through the formation of a specific 2 : 2 heterotetramer. This arrangement is likely to affect, in an isoform-specific manner, the functions of MAG in adhesion and myelin-to-axon signalling. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/. Read the Editorial Highlight for this article on page 712.

Differential Contributions of Alcohol and Nicotine-Derived Nitrosamine Ketone (NNK) to White Matter Pathology in the Adolescent Rat Brain.

AIM: Epidemiologic studies have demonstrated high rates of smoking among alcoholics, and neuroimaging studies have detected white matter atrophy and degeneration in both smokers and individuals with alcohol-related brain disease (ARBD). These findings suggest that tobacco smoke exposure may be a co-factor in ARBD. The present study examines the differential and additive effects of tobacco-specific nitrosamine (NNK) and ethanol exposures on the structural and functional integrity of white matter in an experimental model. METHODS: Adolescent Long Evans rats were fed liquid diets containing 0 or 26% ethanol for 8 weeks. In weeks 3-8, rats were treated with nicotine-derived nitrosamine ketone (NNK) (2 mg/kg, 3×/week) or saline by i.p. injection. In weeks 7-8, the ethanol group was binge-administered ethanol (2 g/kg; 3×/week). RESULTS: Ethanol, NNK and ethanol + NNK caused striking degenerative abnormalities in white matter myelin and axons, with accompanying reductions in myelin-associated glycoprotein expression. Quantitative RT-PCR targeted array and heatmap analyses demonstrated that ethanol modestly increased, whereas ethanol + NNK sharply increased expression of immature and mature oligodendroglial genes, and that NNK increased immature but inhibited mature oligodendroglial genes. In addition, NNK modulated expression of neuroglial genes in favor of growth cone collapse and synaptic disconnection. Ethanol- and NNK-associated increases in FOXO1, FOXO4 and NKX2-2 transcription factor gene expression could reflect compensatory responses to brain insulin resistance in this model. CONCLUSION: Alcohol and tobacco exposures promote ARBD by impairing myelin synthesis, maturation and integrity via distinct but overlapping mechanisms. Public health measures to reduce ARBD should target both alcohol and tobacco abuses.

Adenomatous polyposis coli regulates oligodendroglial development.

The expression of the gut tumor suppressor gene adenomatous polyposis coli (Apc) and its role in the oligodendroglial lineage are poorly understood. We found that immunoreactive APC is transiently induced in the oligodendroglial lineage during both normal myelination and remyelination following toxin-induced, genetic, or autoimmune demyelination murine models. Using the Cre/loxP system to conditionally ablate APC from the oligodendroglial lineage, we determined that APC enhances proliferation of oligodendroglial progenitor cells (OPCs) and is essential for oligodendrocyte differentiation in a cell-autonomous manner. Biallelic Apc disruption caused translocation of ß-catenin into the nucleus and upregulated ß-catenin-mediated Wnt signaling in early postnatal but not adult oligodendroglial lineage cells. The results of conditional ablation of Apc or Ctnnb1 (the gene encoding ß-catenin) and of simultaneous conditional ablation of Apc and Ctnnb1 revealed that ß-catenin is dispensable for postnatal oligodendroglial differentiation, that Apc one-allele deficiency is not sufficient to dysregulate ß-catenin-mediated Wnt signaling in oligodendroglial lineage cells, and that APC regulates oligodendrocyte differentiation through ß-catenin-independent, as well as ß-catenin-dependent, mechanisms. Gene ontology analysis of microarray data suggested that the ß-catenin-independent mechanism involves APC regulation of the cytoskeleton, a result compatible with established APC functions in neural precursors and with our observation that Apc-deleted OPCs develop fewer, shorter processes in vivo. Together, our data support the hypothesis that APC regulates oligodendrocyte differentiation through both ß-catenin-dependent and additional ß-catenin-independent mechanisms.

Ablation of neuronal ceramide synthase 1 in mice decreases ganglioside levels and expression of myelin-associated glycoprotein in oligodendrocytes.

Ceramide synthase 1 (CerS1) catalyzes the synthesis of C18 ceramide and is mainly expressed in the brain. Custom-made antibodies to a peptide from the C-terminal region of the mouse CerS1 protein yielded specific immunosignals in neurons but no other cell types of wild type brain, but the CerS1 protein was not detected in CerS1-deficient mouse brains. To elucidate the biological function of CerS1-derived sphingolipids in the brain, we generated CerS1-deficient mice by introducing a targeted mutation into the coding region of the cers1 gene. General deficiency of CerS1 in mice caused a foliation defect, progressive shrinkage, and neuronal apoptosis in the cerebellum. Mass spectrometric analyses revealed up to 60% decreased levels of gangliosides in cerebellum and forebrain. Expression of myelin-associated glycoprotein was also decreased by about 60% in cerebellum and forebrain, suggesting that interaction and stabilization of oligodendrocytic myelin-associated glycoprotein by neuronal gangliosides is due to the C18 acyl membrane anchor of CerS1-derived precursor ceramides. A behavioral analysis of CerS1-deficient mice yielded functional deficits including impaired exploration of novel objects, locomotion, and motor coordination. Our results reveal an essential function of CerS1-derived ceramide in the regulation of cerebellar development and neurodevelopmentally regulated behavior.

Hippocampal expression of myelin-associated inhibitors is induced with age-related cognitive decline and correlates with deficits of spatial learning and memory.

Impairment of cognitive functions including hippocampus-dependent spatial learning and memory affects nearly half of the aged population. Age-related cognitive decline is associated with synaptic dysfunction that occurs in the absence of neuronal cell loss, suggesting that impaired neuronal signaling and plasticity may underlie age-related deficits of cognitive function. Expression of myelin-associated inhibitors (MAIs) of synaptic plasticity, including the ligands myelin-associated glycoprotein, neurite outgrowth inhibitor A, and oligodendrocyte myelin glycoprotein, and their common receptor, Nogo-66 receptor, was examined in hippocampal synaptosomes and Cornu ammonis area (CA)1, CA3 and dentate gyrus subregions derived from adult (12-13 months) and aged (26-28 months) Fischer 344 × Brown Norway rats. Rats were behaviorally phenotyped by Morris water maze testing and classified as aged cognitively intact (n = 7-8) or aged cognitively impaired (n = 7-10) relative to adults (n = 5-7). MAI protein expression was induced in cognitively impaired, but not cognitively intact, aged rats and correlated with cognitive performance in individual rats. Immunohistochemical experiments demonstrated that up-regulation of MAIs occurs, in part, in hippocampal neuronal axons and somata. While a number of pathways and processes are altered with brain aging, we report a coordinated induction of myelin-associated inhibitors of functional and structural plasticity only in cognitively impaired aged rats. Induction of MAIs may decrease stimulus-induced synaptic strengthening and structural remodeling, ultimately impairing synaptic mechanisms of spatial learning and memory and resulting in cognitive decline.

Expression and function of myelin-associated proteins and their common receptor NgR on oligodendrocyte progenitor cells.

Nogo-A, oligodendrocyte myelin glycoprotein (OMgp) and myelin-associated glycoprotein (MAG) are known as myelin-associated proteins that inhibit axon growth by binding a common receptor, the Nogo66 receptor (NgR). In the CNS, Nogo-A, OMgp and MAG are predominantly expressed by oligodendrocytes. As our previous study revealed that oligodendrocyte progenitor cells (OPCs) did not inhibit neurite outgrowth, it is not clear whether these myelin-associated proteins are expressed in OPCs, and what functions they perform if they are expressed in OPCs. In the present study, with OPCs induced from neural precursor cells (NPCs) derived from rat embryonic spinal cord, and oligodendrocytes differentiated from OPCs, we have observed the expression patterns of Nogo-A, OMgp, MAG and NgR in NPCs, OPCs and oligodendrocytes by immunostaining and western blot assay. We found that Nogo-A could be detected in all tested cells; OMgp could be detected in OPCs and oligodendrocytes, but not in NPCs; MAG was only detected in oligodendrocytes; while NgR could be detected in NPCs and OPCs, but not in oligodendrocytes. These results indicated that the expression pattern of MAG and NgR in OPCs was totally different from that of oligodendrocytes, which might be one of the factors that led to the discrepancy between the two cells in promoting neurite outgrowth. By respectively blocking Nogo-A, OMgp and NgR expressed on OPCs with their corresponding antibodies, we further investigated their roles in the proliferation and differentiation of OPCs, as well as the possible signal pathways involved in. Our results showed that when OPCs were cultured under proliferation condition, blocking Nogo-A, OMgp or NgR did not affect the proliferation of OPCs, but could all significantly prolong their processes. And this effect on OPC processes might involve the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway. When OPCs were cultured under differentiation condition (containing tri-iodothyronine, T3), blocking Nogo-A, OMgp or NgR could all inhibit the differentiation of OPCs, and this effect might involve the extracellular signal-regulated kinases1/2 (Erk1/2) signaling pathway. These results suggested that under proliferation environment, the functions of Nogo-A, OMgp and NgR expressed in OPCs might be to control the length of processes, thus maintaining the morphology of OPCs. While in differentiation environment, the functions of Nogo-A, OMgp and NgR expressed in OPCs turned to promote the differentiation of OPCs, thus facilitating the maturation of oligodendrocytes. And NgR, as the common receptor for Nogo-A and OMgp, might be the main molecule that mediated these functions in OPCs.

[Dynamics of blood concentration of neurospecific proteins and risk of neuropathy development in the conditions of 105-day confinement].

Six male volunteers (aged 25 to 40 years) were subjects in all-round psychophysiological, hormonal and immunological studies before, in and after 105-day isolation and confinement. Blood was drawn and the 16-factorial Cattell personality inventory was filled out every 30 days. Concentrations of blood hormones, neurospecific proteins and cytokines point to a close interrelation between antibody titers to myelin-associated glycoprotein and changes in the parameters of metabolism and reproduction-related hormones, as well as cytokines and individual psychophysiology (extra-introversion, dominance, intropunitiveness, social contact selectivity, etc.), and suggest a minimum risk of demyelinizing neuropathy due to exposure to the conditions of isolation and confinement.

The expression patterns of Nogo-A, myelin associated glycoprotein and oligodendrocyte myelin glycoprotein in the retina after ocular hypertension: the expression of myelin proteins in the retina in glaucoma.

Nogo-A, a major myelin inhibitory protein, inhibits axon growth and synaptic function in the central nervous system. Glaucoma is a progressive neuropathy as a result of retinal ganglion cell (RGC) death. Synaptic degeneration is thought to be an early pathology of neurodegeneration in glaucoma and precedes RGC loss. Here experimental ocular hypertension model was induced in adult rats with laser coagulation of the episcleral and limbal veins. The expression of Nogo-A, myelin-associated glycoprotein (MAG) and oligodendrocyte myelin glycoprotein (OMgp) in the retina was investigated using immunohistochemistry and Western blotting. We found that Nogo-A was expressed in the RGCs and upregulated after the induction of ocular hypertension. OMgp was only expressed in the inner plexiform layer. There was no MAG expression in the retina. Our data provided, for the first time, the expression patterns of three myelin proteins in the adult retina and suggested an important role of Nogo-A in the RGC death and synaptic degeneration in glaucoma.

Resident B cells regulate thymic expression of myelin oligodendrocyte glycoprotein.

Thymic B cells represent a numerically minor cell population located primarily at the cortico-medullary junction. Their biological role is unclear. B cell-deficient µMT mice exhibited reduced medullary thymic epithelial cell (mTEC) numbers and reduced MOG and insulin mRNA expression. Lymphotoxin produced by B cells was critical for normal tissue restricted antigen (TRA) expression, suggesting that B cells regulate self-antigens through their production of LT. These results reveal an unexpected role of B cells in mTEC maintenance and expression of TRAs through their production of LT.

Corticotrophin-releasing hormone (CRH) facilitates axon outgrowth.

OBJECTIVE: To evaluate the role of corticotrophin-releasing hormone (CRH) in facilitating axon outgrowth. BACKGROUND: Injured neural tissue is difficult to regenerate; the mechanism has not been fully understood. METHODS: A rat model of spinal cord transection injury was developed. Levels of BDNF, CRH and oligodendrocyte glycoprotein (OMgp) in injured spinal cord were monitored dynamically after surgery. Cellular interaction among rat dorsal root ganglia (DRG) cells, oligocondrocytes and microglial cells was observed with a coculture model. The axon outgrowth from DRG cells was examined by confocal microscopy. RESULTS: After spinal cord transection, levels of BDNF and CRH increased the next day and decreased afterward, whereas OMgp levels increased from day 3. Administration with BDNF suppressed the levels of OMgp in vitro. The results from a coculture model showed that CRH increased microglial cells to release BDNF; BDNF inhibited OMgp levels in oligodendrocytes and enhanced the axon outgrowth from DRG cells. CONCLUSIONS: This study shows that CRH has the ability to facilitate the outgrowth of axon in spinal neurons, which has therapeutic potential in the treatment of spinal cord injury.

Expression of the tyrosine kinase discoidin domain receptor 1 (DDR1) in human central nervous system myelin.

During development of the mouse brain, the protein kinase discoidin domain receptor 1 (DDR1) is present prenatally in neurons of the proliferative areas, and postnatally, DDR1 expression is no longer detected in neurons, but a spatial-temporal expression pattern in oligodendrocytes that overlaps with the dynamics of the myelination process is detected. Notably, oligodendrocytic DDR1 expression is upregulated in mice during experimentally induced remyelination. Recently, we demonstrated that DDR1 expression is high in human brain and that there is an association between the gene and schizophrenia in a case-control study. However, data regarding expression of DDR1 in the human brain are scarce. Here, we describe the expression pattern of DDR1 in the human adult cerebral cortex. Using several immunohistological techniques and in situ hybridization, we identified DDR1 in the following: a) myelin, b) capillary endothelial cells in the gray as well as white matter, and c) in the soma of some oligodendrocytes and astrocytes in the white matter. The most important overall finding in this study was that DDR1 is present in myelin and is expressed by oligodendrocyte cells. We detected the presence of DDR1 mRNA and protein in myelin and observed that DDR1 co-localized with the classical myelin basic protein (MBP). Moreover, we found a strong positive correlation between expression levels of DDR1 and two myelin-associated genes, myelin-associated glycoprotein (MAG) and oligodendrocyte transcription factor 2 (OLIG2). These observations suggest that DDR1 could be an important constituent of myelin. Because defects in myelination are linked to several mental disorders such as schizophrenia, the function of DDR1 in the process of myelination warrants further investigation.

Developmental expression of the oligodendrocyte myelin glycoprotein in the mouse telencephalon.

The oligodendrocyte myelin glycoprotein is a glycosylphosphatidylinositol-anchored protein expressed by neurons and oligodendrocytes in the central nervous system. Attempts have been made to identify the functions of the myelin-associated inhibitory proteins (MAIPs) after axonal lesion or in neurodegeneration. However, the developmental roles of some of these proteins and their receptors remain elusive. Recent studies indicate that NgR1 and the recently discovered receptor PirB restrict cortical synaptic plasticity. However, the putative factors that trigger these effects are unknown. Because Nogo-A is mostly associated with the endoplasmic reticulum and myelin associated glycoprotein appears late during development, the putative participation of OMgp should be considered. Here, we examine the pattern of development of OMgp immunoreactive elements during mouse telencephalic development. OMgp immunoreactivity in the developing cortex follows the establishment of the thalamo-cortical barrel field. At the cellular level, we located OMgp neuronal membranes in dendrites and axons as well as in brain synaptosome fractions and axon varicosities. Lastly, the analysis of the barrel field in OMgp-deficient mice revealed that although thalamo-cortical connections were formed, their targeting in layer IV was altered, and numerous axons ectopically invaded layers II-III. Our data support the idea that early expressed MAIPs play an active role during development and point to OMgp participating in thalamo-cortical connections.

Lysophosphatidic acid can support the formation of membranous structures and an increase in MBP mRNA levels in differentiating oligodendrocytes.

During development, differentiating oligodendrocytes progress in distinct maturation steps from premyelinating to myelinating cells. Such maturing oligodendrocytes express both the receptors mediating signaling via extracellular lysophosphatidic acid (LPA) and the major enzyme generating extracellular LPA, namely phosphodiesterase-Ialpha/autotaxin (PD-Ialpha/ATX). However, the biological role of extracellular LPA during the maturation of differentiating oligodendrocytes is currently unclear. Here, we demonstrate that application of exogenous LPA induced an increase in the area occupied by the oligodendrocytes' process network, but only when PD-Ialpha/ATX expression was down-regulated. This increase in network area was caused primarily by the formation of membranous structures. In addition, LPA increased the number of cells positive for myelin basic protein (MBP). This effect was associated by an increase in the mRNA levels coding for MBP but not myelin oligodendrocyte glycoprotein (MOG). Taken together, these data suggest that LPA may play a crucial role in regulating the later stages of oligodendrocyte maturation.

Reduction of oligodendrocyte myelin glycoprotein expression following facial nerve transection.

Oligodendrocyte myelin glycoprotein (OMgp) has been thought to be expressed in the oligodendrocytes and inhibit the regeneration of the nerves by binding to the Nogo receptor expressed in neurons in the central nervous system (CNS). However, OMgp is expressed in the CNS in the neurons as well as oligodendrocytes. In order to help understanding the physiological role of neuronal OMgp, we examined the change of OMgp expression in the facial nucleus after the facial nerve transection. Real-time RT-PCR and Western blot analysis showed a down-regulation of OMgp expression in the facial nucleus 5-7 (mRNA) or 5-14 (protein) days after transection. Thereafter, expression of OMgp returned to the control level at 28 days after axotomy. Subsequent analysis using in situ hybridization histochemistry and immunohistochemistry established that the decrease of OMgp expression was attributable to the expression in facial motoneurons, but not in oligodendrocytes. These findings suggest a possibility that the change of neuronal OMgp expression might be involved in reconnection of neural circuit between axotomized facial neuron and upper motor neuron after transection.

Gene expression profiling of nonhuman primates exposed to aerosolized Venezuelan equine encephalitis virus.

Host responses to Venezuelan equine encephalitis viruses (VEEV) were studied in cynomolgus macaques after aerosol exposure to the epizootic virus. Changes in global gene expression were assessed for the brain, lungs, and spleen. In the brain, major histocompatibility complex (MHC) class I transcripts were induced, while the expression of S100b, a factor associated with brain injury, was inhibited, as was expression of the encephalitogenic gene MOG. Cytokine-mediated signals were affected by infection, including those involving IFN-mediated antiviral activity (IRF-7, OAS, and Mx transcripts), and the increased transcription of caspases. Induction of a few immunologically relevant genes (e.g. IFITM1 and STAT1) was common to all tested tissues. Herein, both tissue-specific and nontissue specific transcriptional changes in response to VEEV are described, including induction of IFN-regulated transcripts and cytokine-induced apoptotic factors, in addition to cellular factors in the brain that may be descriptive of the health status of the brain during the infectious process. Altogether, this work provides novel information on common and tissue-specific host responses against VEEV in a nonhuman primate model of aerosol exposure.

Alternative isoforms of myelin/oligodendrocyte glycoprotein with variable cytoplasmic domains are expressed in human brain.

The human myelin/oligodendrocyte glycoprotein (MOG) gene is encoded by 10 exons that exhibit a complex pattern of alternative splicing. This report demonstrates that several MOG-specific alternative splice variants are indeed expressed in human oligodendrocytes (OLs) and myelin during perinatal development and are retained through adulthood. While all forms possess the common extracellular Ig-like domain, these alternative MOG structures differ significantly in their respective cytoplasmic domains. Peptide-specific antibodies were generated to facilitate detection of these different MOG moieties. The fidelity of these antibodies is shown using N20 OLs expressing individual MOG variants. These antibodies also only co-localize with another well-characterized marker of OLs and myelin--PLP/DM20 proteins. Among the human tissue samples tested, very limited expression occurred by 36 weeks gestation for 2-3 MOG variants, and the remaining MOG isoforms were not evident until shortly after birth. This study represents the first evidence of alternative translation products from the MOG gene. To date, it is believed that alternative splicing of MOG is limited to primates. Recent completion of various genome projects has revealed that alternative splicing is much more prevalent than originally estimated, and species-specific alternative splicing is now being shown to be highly relevant to expanding proteomic diversity.

p38 MAP kinase regulation of oligodendrocyte differentiation with CREB as a potential target.

Despite a substantial understanding of the factors regulating oligodendrocyte differentiation, the signaling mechanisms involved in this process are not well-understood. This study elaborates on the findings (Bhat NR, Zhang P (1997) FASEB J 11:A925; Baron W, Metz B, Bansal R, Hoekstra D, de Vries H (2000) Mol Cell Neurosci 15:314-329) of a role for p38 MAP kinase signaling in oligodendrocyte differentiation and myelin gene expression. When proliferating oligodendrocyte progenitors were switched to a growth factor-free differentiation medium, there was a rapid activation of p38 kinase that correlated with an increased phosphorylation of CREB, a down-stream target and a factor involved in oligodendrocyte differentiation. Addition of forskolin, a known inducer of intracellular c-AMP and of oligodendrocyte differentiation, also stimulated CREB phosphorylation in a p38 kinase dependent way. Pharmacological inhibition of p38 interfered with the morphological and antigenic changes associated with differentiating oligodendrocytes as well as with the developmental and forskolin-induced expression of myelin basic protein, thereby supporting an essential role for p38 MAPK pathway in oligodendrocyte differentiation.

Overexpression of myelin-associated glycoprotein after axotomy of the perforant pathway.

Myelin-associated glycoprotein (MAG) contributes to the prevention of axonal regeneration in the adult central nervous system (CNS). However, changes in MAG expression following lesions and the involvement of MAG in the failure of cortical connections to regenerate are still poorly understood. Here, we show that MAG expression is differently regulated in the entorhinal cortex (EC) and the hippocampus in response to axotomy of the perforant pathway. In the EC, MAG mRNA is transiently overexpressed by mature oligodendrocytes after lesion. In the hippocampus, MAG overexpression is accompanied by an increase in the number of MAG-expressing cells. Lastly, the participation of MAG in preventing axonal regeneration was tested in vitro, where neuraminidase treatment of axotomized entorhino-hippocampal cultures potentiates axonal regeneration. These results demonstrate that MAG expression is regulated in response to cortical axotomy, and indicate that it may limit axonal regeneration after CNS injury.