Decrease in oligodendrocyte carbonic anhydrase activity preceding myelin degeneration in cuprizone induced demyelination

mTOR Signaling Regulates Metabolic Function in Oligodendrocyte Precursor Cells and Promotes Efficient Brain Remyelination in the Cuprizone Model

In demyelinating diseases, such as multiple sclerosis, primary loss of myelin and subsequent neuronal degeneration throughout the CNS impair patient functionality. While the importance of mechanistic target of rapamycin (mTOR) signaling during developmental myelination is known, no studies have yet directly examined the function of mTOR signaling specifically in the oligodendrocyte (OL) lineage during remyelination. Here, we conditionally deleted Mtor from adult oligodendrocyte precursor cells (OPCs) using Ng2-CreERT in male adult mice to test its function in new OLs responsible for remyelination. During early remyelination after cuprizone-induced demyelination, mice lacking mTOR in adult OPCs had unchanged OL numbers but thinner myelin. Myelin thickness recovered by late-stage repair, suggesting a delay in myelin production when Mtor is deleted from adult OPCs. Surprisingly, loss of mTOR in OPCs had no effect on efficiency of remyelination after lysophosphatidylcholine lesions in either the spinal cord or corpus callosum, suggesting that mTOR signaling functions specifically in a pathway dysregulated by cuprizone to promote remyelination efficiency. We further determined that cuprizone and inhibition of mTOR cooperatively compromise metabolic function in primary rat OLs undergoing differentiation. Together, our results support the conclusion that mTOR signaling in OPCs is required to overcome the metabolic dysfunction in the cuprizone-demyelinated adult brain.SIGNIFICANCE STATEMENT Impaired remyelination by oligodendrocytes contributes to the progressive pathology in multiple sclerosis, so it is critical to identify mechanisms of improving remyelination. The goal of this study was to examine mechanistic target of rapamycin (mTOR) signaling in remyelination. Here, we provide evidence that mTOR signaling promotes efficient remyelination of the brain after cuprizone-mediated demyelination but has no effect on remyelination after lysophosphatidylcholine demyelination in the spinal cord or brain. We also present novel data revealing that mTOR inhibition and cuprizone treatment additively affect the metabolic profile of differentiating oligodendrocytes, supporting a mechanism for the observed remyelination delay. These data suggest that altered metabolic function may underlie failure of remyelination in multiple sclerosis lesions and that mTOR signaling may be of therapeutic potential for promoting remyelination.

Dysregulation in Subcellular Localization of Myelin Basic Protein mRNA Does Not Result in Altered Myelination in Amyotrophic Lateral Sclerosis

Pathological hallmarks of amyotrophic lateral sclerosis (ALS), including protein misfolding, are well established in oligodendrocytes. More recently, an RNA trafficking deficit of key myelin proteins has been suggested in oligodendrocytes in ALS but the extent to which this affects myelination and the relative contribution of this to disease pathogenesis is unclear. ALS autopsy research findings showing demyelination contrasts with the routine clinical-pathological workup of ALS cases where it is rare to see white matter abnormalities other than simple Wallerian degeneration secondary to widespread neuronal loss. To begin to address this apparent variance, we undertook a comprehensive evaluation of myelination at an RNA, protein and structural level using human pathological material from sporadic ALS patients, genetic ALS patients (harboring C9orf72 mutation) and age- and sex-matched non-neurological controls. We performed (i) quantitative spatial profiling of the mRNA transcript encoding myelin basic protein (MBP), (ii) quantification of MBP protein and (iii) the first quantitative structural assessment of myelination in ALS post-mortem specimens by electron microscopy. We show no differences in MBP protein levels or ultrastructural myelination, despite a significant dysregulation in the subcellular trafficking of MBP mRNA in ALS patients compared to controls. We therefore confirm that whilst there are cell autonomous mRNA trafficking deficits affecting oligodendrocytes in ALS, this has no effect on myelin structure.

Animal Models of Multiple Sclerosis

Animal models with high translational validity are essential tools in understanding disease pathogenesis and in the development of therapeutic strategies. Multiple sclerosis (MS) is an autoimmune demyelinating disease of the central nervous system characterized by progressive neurological deficits and socioeconomic burden. Experimental autoimmune encephalomyelitis (EAE) is the most extensively utilized animal model of MS, with well-characterized rodent and non-human primate variants. The EAE model is typically induced by either active immunization with myelin-derived proteins or peptides in adjuvant or by passive transfer of activated myelin-specific CD4⁺ T lymphocytes. To date, the EAE model has been an essential tool in the development of at least seven U.S. Food and Drug Administration (FDA)-approved immunomodulatory drugs for the treatment of MS, including glatiramer acetate, fingolimod, and natalizumab. However, the translational validity of the EAE model is frequently compromised due to poor study design, inconsistent clinical scoring endpoints, and inappropriate statistical calculations. No single animal model accurately reflects the complexity of human MS pathogenesis. Beyond EAE, multiple additional animal models are described, including Theiler's murine encephalomyelitis virus and cuprizone-induced demyelination, which facilitate the study of pathogen-induced CNS autoimmunity and remyelination, respectively. This overview summarizes several of the most frequently used animal models of MS and highlights key factors that significantly influence the experimental outcome and affect translational validity. © 2021 Wiley Periodicals LLC.

Class switching of carbonic anhydrase isoforms mediates remyelination in CA3 hippocampal neurons during chronic hypoxia

Chronic exposure to hypoxia results in cerebral white matter hyperintensities, increased P300 latency, delayed response and impairment in working memory. Despite burgeoning evidence on role of myelination in nerve conduction, the effect of chronic hypoxia on myelination of hippocampal neurons has been less studied. The present study provides novel evidence on alterations in myelination of hippocampal CA3 neurons following chronic hypoxic exposure. Sprague Dawley rats exposed to global hypobaric hypoxia simulating altitude of 25,000 ft showed progressive demyelination in CA3 hippocampal neurons on 14 days followed by remyelination on 21 and 28 days. The demyelination of CA3 neurons was associated with increased apoptosis of both oligodendrocyte precursor cells (OPCs) and mature oligodendrocytes (OLs), peroxidation of myelin lipids, and nitration induced reduced expression of Carbonic Anhydrase II (CAII). Prolonged hypoxic exposure of 21 and 28 days on the other hand resulted in peroxisome proliferator-activated receptor alpha (PPARα) induced upregulation of Carbonic Anhydrase IV (CAIV) expression in mature oligodendrocytes through iNOS mediated mechanisms along with reduction in lipid peroxidation and remyelination. Inhibition of carbonic anhydrase activity on the other hand prevented remyelination of CA3 neurons. Based on these findings we propose a novel iNOS mediated mechanism for regulation of myelination in hypoxic hippocampal neurons through class switching of carbonic anhydrases.

Revisiting the Pathoetiology of Multiple Sclerosis: Has the Tail Been Wagging the Mouse?

Multiple Sclerosis (MS) is traditionally considered an autoimmune-mediated demyelinating disease, the pathoetiology of which is unknown. However, the key question remains whether autoimmunity is the initiator of the disease (outside-in) or the consequence of a slow and as yet uncharacterized cytodegeneration (oligodendrocytosis), which leads to a subsequent immune response (inside-out). Experimental autoimmune encephalomyelitis has been used to model the later stages of MS during which the autoimmune involvement predominates. In contrast, the cuprizone (CPZ) model is used to model early stages of the disease during which oligodendrocytosis and demyelination predominate and are hypothesized to precede subsequent immune involvement in MS. Recent studies combining a boost, or protection, to the immune system with disruption of the blood brain barrier have shown CPZ-induced oligodendrocytosis with a subsequent immune response. In this Perspective, we review these recent advances and discuss the likelihood of an inside-out vs. an outside-in pathoetiology of MS.

Suppression of the Peripheral Immune System Limits the Central Immune Response Following Cuprizone-Feeding: Relevance to Modelling Multiple Sclerosis

Cuprizone (CPZ) preferentially affects oligodendrocytes (OLG), resulting in demyelination. To investigate whether central oligodendrocytosis and gliosis triggered an adaptive immune response, the impact of combining a standard (0.2%) or low (0.1%) dose of ingested CPZ with disruption of the blood brain barrier (BBB), using pertussis toxin (PT), was assessed in mice. 0.2% CPZ(±PT) for 5 weeks produced oligodendrocytosis, demyelination and gliosis plus marked splenic atrophy (37%) and reduced levels of CD4 (44%) and CD8 (61%). Conversely, 0.1% CPZ(±PT) produced a similar oligodendrocytosis, demyelination and gliosis but a smaller reduction in splenic CD4 (11%) and CD8 (14%) levels and no splenic atrophy. Long-term feeding of 0.1% CPZ(±PT) for 12 weeks produced similar reductions in CD4 (27%) and CD8 (43%), as well as splenic atrophy (33%), as seen with 0.2% CPZ(±PT) for 5 weeks. Collectively, these results suggest that 0.1% CPZ for 5 weeks may be a more promising model to study the ‘inside-out’ theory of Multiple Sclerosis (MS). However, neither CD4 nor CD8 were detected in the brain in CPZ±PT groups, indicating that CPZ-mediated suppression of peripheral immune organs is a major impediment to studying the ‘inside-out’ role of the adaptive immune system in this model over long time periods. Notably, CPZ(±PT)-feeding induced changes in the brain proteome related to the suppression of immune function, cellular metabolism, synaptic function and cellular structure/organization, indicating that demyelinating conditions, such as MS, can be initiated in the absence of adaptive immune system involvement.

Pericytes in Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune inflammatory demyelinating disease that affects the central nervous system (CNS), particularly, in young adults. Current MS treatments aim to reduce demyelination; however, these have limited efficacy, display side effects and lack of regenerative activities. Oligodendrocyte progenitor cells (OPCs) represents the major source for new myelin. Upon demyelination, OPCs get activated, proliferate, migrate towards the lesion, and differentiate into remyelinating oligodendrocytes. Although myelin repair (remyelination) represents a robust response to myelin damage, during MS, this regenerative phenomenon decays in efficiency or even fails. CNS-resident pericytes (CNS-PCs) are essential for vascular homeostasis regulating blood-brain barrier (BBB) permeability and stability as well as endothelial cells (ECs) function during angiogenesis and neovascularization. Recent studies indicate that CNS-PCs also play a crucial role regulating OPC function during remyelination, and very importantly, these cells are substantially affected in MS. This chapter summarizes important aspects of MS and CNS remyelination as well as it provides new insights supporting the contribution of CNS-PCs to myelin regeneration and to MS pathology. Currently, there is evidence arguing in favor of CNS-PCs as novel therapeutic targets for the development of future treatments for MS.

Conditional Deletion of the L-Type Calcium Channel Cav1.2 in NG2-Positive Cells Impairs Remyelination in Mice

Exploring the molecular mechanisms that drive the maturation of oligodendrocyte progenitor cells (OPCs) during the remyelination process is essential to developing new therapeutic tools to intervene in demyelinating diseases such as multiple sclerosis. To determine whether L-type voltage-gated calcium channels (L-VGCCs) are required for OPC development during remyelination, we generated an inducible conditional knock-out mouse in which the L-VGCC isoform Cav1.2 was deleted in NG2-positive OPCs (Cav1.2^KO). Using the cuprizone (CPZ) model of demyelination and mice of either sex, we establish that Cav1.2 deletion in OPCs leads to less efficient remyelination of the adult brain. Specifically, Cav1.2^KO OPCs mature slower and produce less myelin than control oligodendrocytes during the recovery period after CPZ intoxication. This reduced remyelination was accompanied by an important decline in the number of myelinating oligodendrocytes and in the rate of OPC proliferation. Furthermore, during the remyelination phase of the CPZ model, the corpus callosum of Cav1.2^KO animals presented a significant decrease in the percentage of myelinated axons and a substantial increase in the mean g-ratio of myelinated axons compared with controls. In addition, in a mouse line in which the Cav1.2^KO OPCs were identified by a Cre reporter, we establish that Cav1.2^KO OPCs display a reduced maturational rate through the entire remyelination process. These results suggest that Ca²⁺ influx mediated by L-VGCCs in oligodendroglial cells is necessary for normal remyelination and is an essential Ca²⁺ channel for OPC maturation during the remyelination of the adult brain.SIGNIFICANCE STATEMENT Ion channels implicated in oligodendrocyte differentiation and maturation may induce positive signals for myelin recovery. Voltage-gated Ca²⁺ channels (VGCCs) are important for normal myelination by acting at several critical steps during oligodendrocyte progenitor cell (OPC) development. To determine whether voltage Ca²⁺ entry is involved in oligodendrocyte differentiation and remyelination, we used a conditional knockout mouse for VGCCs in OPCs. Our results indicate that VGCCs can modulate oligodendrocyte maturation in the demyelinated brain and suggest that voltage-gated Ca²⁺ influx in OPCs is critical for remyelination. These findings could lead to novel approaches for obtaining a better understanding of the factors that control OPC maturation in order to stimulate this pool of progenitors to replace myelin in demyelinating diseases.

Heterogeneity in oligodendroglia: Is it relevant to mouse models and human disease?

There are many lines of evidence indicating that oligodendrocyte progenitor cells and oligodendrocyte populations in the central nervous system (CNS) are heterogeneous based on their developmental origins as well as from morphological and molecular criteria. Whether these distinctions reflect functional heterogeneity is less clear and has been the subject of considerable debate. Recent findings, particularly from knockout mouse models, have provided new evidence for regional variations in myelination phenotypes, particularly between brain and spinal cord. These data raise the possibility that oligodendrocytes in these regions have different functional capacities and/or ability to compensate for loss of a specific gene. The goal of this review is to briefly revisit the evidence for oligodendrocyte heterogeneity and then to present data from transgenic and demyelinating mouse models suggesting functional heterogeneity in myelination, demyelination, and remyelination in the CNS and, finally, to discuss the implications of these findings for human diseases. © 2016 Wiley Periodicals, Inc.

Paving the way for adequate myelination: The contribution of galectin-3, transferrin and iron

Considering the worldwide incidence of well characterized demyelinating disorders such as Multiple Sclerosis (MS) and the increasing number of pathologies recently found to involve hypomyelinating factors such as micronutrient deficits, elucidating the molecular basis of central nervous system (CNS) demyelination, remyelination and hypomyelination becomes essential to the development of future neuroregenerative therapies. In this context, this review discusses novel findings on the contribution of galectin-3 (Gal-3), transferrin (Tf) and iron to the processes of myelination and remyelination and their potentially positive regulation of oligodendroglial precursor cell (OPC) differentiation. Studies were conducted in cuprizone (CPZ)-induced demyelination and iron deficiency (ID)-induced hypomyelination, and the participation of glial and neural stem cells (NSC) in the remyelination process was evaluated by means of both in vivo and in vitro assays on primary cell cultures.

Animal models of Multiple Sclerosis

Multiple Sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS) which involves a complex interaction between immune system and neural cells. Animal modeling has been critical for addressing MS pathogenesis. The three most characterized animal models of MS are (1) the experimental autoimmune/allergic encephalomyelitis (EAE); (2) the virally-induced chronic demyelinating disease, known as Theiler׳s murine encephalomyelitis virus (TMEV) infection and (3) the toxin-induced demyelination. All these models, in a complementary way, have allowed to reach a good knowledge of the pathogenesis of MS. Specifically, EAE is the model which better reflects the autoimmune pathogenesis of MS and is extremely useful to study potential experimental treatments. Furthermore, both TMEV and toxin-induced demyelination models are suitable for characterizing the role of the axonal injury/repair and the remyelination process in MS. In conclusion, animal models, despite their limitations, remain the most useful instrument for implementing the study of MS.

Glial response during cuprizone-induced de- and remyelination in the CNS: lessons learned

Although astrogliosis and microglia activation are characteristic features of multiple sclerosis (MS) and other central nervous system (CNS) lesions the exact functions of these events are not fully understood. Animal models help to understand the complex interplay between the different cell types of the CNS and uncover general mechanisms of damage and repair of myelin sheaths. The so called cuprizone model is a toxic model of demyelination in the CNS white and gray matter, which lacks an autoimmune component. Cuprizone induces apoptosis of mature oligodendrocytes that leads to a robust demyelination and profound activation of both astrocytes and microglia with regional heterogeneity between different white and gray matter regions. Although not suitable to study autoimmune mediated demyelination, this model is extremely helpful to elucidate basic cellular and molecular mechanisms during de- and particularly remyelination independently of interactions with peripheral immune cells. Phagocytosis and removal of damaged myelin seems to be one of the major roles of microglia in this model and it is well known that removal of myelin debris is a prerequisite of successful remyelination. Furthermore, microglia provide several signals that support remyelination. The role of astrocytes during de- and remyelination is not well defined. Both supportive and destructive functions have been suggested. Using the cuprizone model we could demonstrate that there is an important crosstalk between astrocytes and microglia. In this review we focus on the role of glial reactions and interaction in the cuprizone model. Advantages and limitations of as well as its potential therapeutic relevance for the human disease MS are critically discussed in comparison to other animal models.

Alterations of brain eicosanoid synthetic pathway in multiple sclerosis and in animal models of demyelination: role of cyclooxygenase-2

Inflammation is a physiological response to exogenous and endogenous stimuli and, together with demyelination and immune system activation, is one of the key features of multiple sclerosis (MS). Arachidonic acid (AA) metabolism by cyclooxygenase (COX) and lipoxygenase (LO) enzymes leads to the production of proinflammatory eicosanoids, and stimulates cytokine production and activation of microglia and astrocytes, thereby contributing to MS pathology. Current therapies target the immune system but do not specifically target AA-related inflammatory pathway. Corticosteroids and non-steroidal anti-inflammatory drugs (NSAIDs) are frequently associated with immunomodulatory therapies to treat flu-like adverse effects. Few clinical and mounting preclinical data in MS show that AA metabolism contributes to immune system activation, demyelination and motor disabilities, and administration of NSAIDs reduces these symptoms. The beneficial effect of NSAIDs seems to be a prerogative of COX-2 selective inhibitors and suggests that NSAIDs selective for COX-2 may be more effective than mixed COX-1/2 inhibitors.

Cuprizone [bis(cyclohexylidenehydrazide)] is selectively toxic for mature oligodendrocytes

Cuprizone [bis(cyclohexylidenehydrazide)]-induced toxic demyelination is an experimental animal model commonly used to study de- and remyelination in the central nervous system. In this model, mice are fed with the copper chelator cuprizone which leads to oligodendrocyte death with subsequent demyelination. The underlying mechanisms of cuprizone-induced oligodendrocyte death are still unknown, and appropriate in vitro investigations to study these mechanisms are not available. Thus, we studied cuprizone effects on rat primary glial cell cultures and on the neuroblastoma cell line SH-SY5Y. Treatment of cells with different concentrations of cuprizone failed to show effects on the proliferation and survival of SH-SY5Y cells, microglia, astrocytes, and oligodendrocyte precursor cells (OPC). In contrast, differentiated mature oligodendrocytes (OL) were found to be significantly affected by cuprizone treatment. This was accompanied by a reduced mitochondrial potential in cuprizone-treated OL. These results demonstrate that the main toxic target for cuprizone is mature OL, whilst other glial cells including OPC are not or only marginally affected. This explains the selective demyelination induced by cuprizone in vivo.

Golli myelin basic proteins stimulate oligodendrocyte progenitor cell proliferation and differentiation in remyelinating adult mouse brain

Golli myelin basic proteins are necessary for normal myelination, acting via voltage and store-dependent Ca(2+) entry at multiple steps during oligodendrocyte progenitor cell (OPC) development. To date nothing is known regarding the role of golli proteins in demyelination or remyelination events. Here the effects of golli ablation and overexpression in myelin loss and recovery were examined using the cuprizone (CPZ) model of demyelination/remyelination. We found severe demyelination in the corpus callosum (CC) of golli-overexpressing mice (JOE) during the CPZ treatment, which was accompanied by an increased number of reactive astrocytes and activation of microglia/macrophages. During demyelination of JOE brains, a significant increase in the number of proliferating OPCs was found in the CC as well as in the subventricular zone, and our data indicate that these progenitors matured and fully remyelinated the CC of JOE animals after CPZ withdrawal. In contrast, in the absence of golli (golli-KO mice) delayed myelin loss associated with a smaller immune response, and a lower number of OPCs was found in these mice during the CPZ treatment. Furthermore, incomplete remyelination was observed after CPZ removal in large areas of the CC of golli-KO mice, reflecting irregular recovery of the oligodendrocyte population and subsequent myelin sheath formation. Our findings demonstrate that golli proteins sensitize mature oligodendrocytes to CPZ-induced demyelination, while at the same time stimulate the proliferation/recruitment of OPCs during demyelination, resulting in accelerated remyelination.

Changes in the striatal proteome of YAC128Q mice exhibit gene-environment interactions between mutant huntingtin and manganese

Huntington's disease (HD) is a neurodegenerative disorder caused by expansion of a CAG repeat within the Huntingtin (HTT) gene, though the clinical presentation of disease and age-of-onset are strongly influenced by ill-defined environmental factors. We recently reported a gene-environment interaction wherein expression of mutant HTT is associated with neuroprotection against manganese (Mn) toxicity. Here, we are testing the hypothesis that this interaction may be manifested by altered protein expression patterns in striatum, a primary target of both neurodegeneration in HD and neurotoxicity of Mn. To this end, we compared striatal proteomes of wild-type and HD (YAC128Q) mice exposed to vehicle or Mn. Principal component analysis of proteomic data revealed that Mn exposure disrupted a segregation of WT versus mutant proteomes by the major principal component observed in vehicle-exposed mice. Identification of altered proteins revealed novel markers of Mn toxicity, particularly proteins involved in glycolysis, excitotoxicity, and cytoskeletal dynamics. In addition, YAC128Q-dependent changes suggest that axonal pathology may be an early feature in HD pathogenesis. Finally, for several proteins, genotype-specific responses to Mn were observed. These differences include increased sensitivity to exposure in YAC128Q mice (UBQLN1) and amelioration of some mutant HTT-induced alterations (SAE1, ENO1). We conclude that the interaction of Mn and mutant HTT may suppress proteomic phenotypes of YAC128Q mice, which could reveal potential targets in novel treatment strategies for HD.

The cuprizone animal model: new insights into an old story

Multiple sclerosis (MS) is a chronic, inflammatory, demyelinating disease that affects the central nervous system and represents the most common neurological disorder in young adults in the Western hemisphere. There are several well-characterized experimental animal models that allow studying potential mechanisms of MS pathology. While experimental allergic encephalomyelitis is one of the most frequently used models to investigate MS pathology and therapeutic interventions, the cuprizone model reflects a toxic experimental model. Cuprizone-induced demyelination in animals is accepted for studying MS-related lesions and is characterized by degeneration of oligodendrocytes rather than by a direct attack on the myelin sheet. The present article reviews recent data concerning the cuprizone model and its relevance for MS. Particular focus is given to the concordance and difference between human MS patterns (types I-IV lesions) and cuprizone-induced histopathology, including a detailed description of the sensitive brain regions extending the observations to different white and grey matter structures. Similarities between pattern III lesions and cuprizone-induced demyelination and dissimilarities, such as inflamed blood vessels or the presence of CD3+ T cells, are outlined. We also aim to distinguish acute and chronic demyelination under cuprizone including processes such as spontaneous remyelination during acute demyelination. Finally, we point at strain and gender differences in this animal model and highlight the contribution of some growth factors and cytokines during and after cuprizone intoxication, including LIF, IGF-1, and PDGFalpha.

Differential changes in axonal conduction following CNS demyelination in two mouse models

Transgenic and disease model mice have been used to investigate the molecular mechanisms of demyelinating diseases. However, less attention has been given to elucidating changes in nerve conduction in these mice. We established an experimental system to measure the response latency of cortical neurons and examined changes in nerve conduction in cuprizone-induced demyelinating mice and in myelin basic protein-deficient shiverer mice. Stimulating and recording electrodes were placed in the right and left sensori-motor cortices, respectively. Electrical stimulation of the right cortex evoked antidromic responses in left cortical neurons with a latency of 9.38 +/- 0.31 ms (n = 107; mean +/- SEM). While response latency was longer in mice at 7 days and 4 weeks of cuprizone treatment (12.35 +/- 0.35 ms, n = 102; 11.72 +/- 0.29 ms, n = 103, respectively), response latency at 7 days and 4 weeks after removal of cuprizone was partially restored (10.72 +/- 0.45 ms, n = 106; 10.27 +/- 0.34 ms, n = 107, respectively). Likewise, electron microscopy showed cuprizone-induced demyelination in the corpus callosum and nearly complete remyelination after cuprizone removal. We also examined whether the myelin abnormalities in shiverer mice affected their response latencies. But there were no significant differences in response latencies in shiverer (9.83 +/- 0.24 ms, n = 103) and wild-type (9.33 +/- 0.22 ms, n = 112) mice. The results of these electrophysiological assessments imply that different demyelinating mechanisms, differentially affecting axon conduction, are present in the cuprizone-treated and shiverer mice, and may provide new insights to understanding the pathophysiology of demyelination in animal models in the CNS.

SJL mice exposed to cuprizone intoxication reveal strain and gender pattern differences in demyelination

The role of mouse strain and the influence of gender on demyelination were explored for the first time in SJL mice using the cuprizone intoxication model. We document here that SJL mice display a unique pattern of demyelination that did not follow the profile that is well-characterized in C57BL/6 mice. The SJL mice did not readily demyelinate at the midline within the corpus callosum but showed greater demyelination immediately lateral to midline. During continuous exposure to cuprizone, demyelination was not complete and appeared to plateau after week 7. Importantly, female mice were partially resistant to demyelination, whereas male mice were more severely demyelinated. Differences in the number of mature oligodendrocytes were consistent with the extent of demyelination; however, microglia, astrocyte and oligodendrocyte precursor cell populations did not differ between male and female mice. Thus, genetic factors and gender influence susceptibility to demyelinating disease in the cuprizone model, which may provide additional insights into the variability observed in human demyelinating diseases such as multiple sclerosis.

Implications of protease M/neurosin in myelination during experimental demyelination and remyelination

Protease M/neurosin is a serine protease expressed by oligodendrocytes (OLGs) in the central nervous system (CNS). To investigate the role of protease M/neurosin during experimental demyelination and remyelination, mice were fed cuprizone (bis-cyclohexanon oxaldihydrazone). Semi-quantitative RT-PCR analysis and immunohistochemistry revealed that the expressions of protease M/neurosin mRNA and protein were rapidly reduced in demyelination, whereas the expression of protease M/neurosin was increased in pi form of glutathione-S-transferases (GST-pi)-positive OLGs during remyelination. Cultured primary OLGs displayed a strong correlation between protease M/neurosin and myelin basic protein (MBP). After tumor necrosis factor-alpha (TNF-alpha) and IFN-gamma stimulation, these proteins showed colocalization in the oligodendroglial process. The suppression of protease M/neurosin using RNAi reduced the level of MBP mRNA in cultured OLGs. In contrast, the reduced level of protease M/neurosin was not associated with oligodendroglial cell death or differentiation in cultured OLGs. This study identifies that protease M/neurosin in OLGs is closely associated with the expression of the MBP and the PLP gene. Our data emphasize that the maintenance of myelination is an important function of protease M/neurosin in OLGs, suggesting its relation to the oligodendroglial response to myelin disorders.

Remyelination after cuprizone-induced demyelination in the rat is stimulated by apotransferrin

Twenty-one-day-old Wistar rats were fed a diet containing 0.6% cuprizone for 2 weeks. Studies carried out after withdrawal of cuprizone showed histological evidences of marked demyelination in the corpus callosum. Biochemical studies of isolated myelin showed a marked decrease in myelin proteins, phospholipids, and galactocerebrosides as well as a marked decrease in myelin yield. Treatment of these animals with a single intracranial injection of 350 ng of apotransferrin at the time of withdrawal of cuprizone induced a marked increase in myelin deposition resulting in a significantly improved remyelination, evaluated by histological, immunocytochemical, and biochemical parameters, in comparison to what was observed in spontaneous recovery. Immunocytochemical studies of cryotome sections to analyze developmental parameters of the oligodendroglial cell population at the time of termination of cuprizone and at different times thereafter showed that in the untreated animals, there was a marked increase in the number of NG2-BrdU-positive precursor cells together with a marked decrease in MBP expression at the peak of cuprizone-induced demyelination. As expected, the amount of precursor cells decreased markedly during spontaneous remyelination and was accompanied by an increase in MBP reactivity. In the apotransferrin-treated animals, these phenomena occurred much faster, and remyelination was much more efficient than in the untreated controls. The results of this study suggest that apotransferrin is a very active promyelinating agent which could be important for the treatment of certain demyelinating conditions.

Two temporal stages of oligodendroglial response to excitotoxic lesion in the gray matter of the adult rat brain

Excitotoxic lesions in the gray matter induce profuse demyelination of passage and afferent fibers in areas of neuronal loss, independent of Wallerian degeneration. The time course of this phenomenon, which extends over weeks after the excitotoxin injection, suggests that demyelination is not related only to a direct effect of the toxin. In order to define mechanisms at work, a parallel study of myelin and oligodendrocytes was carried out following kainate injections into the adult rat thalamus. Within the 1st day postlesion, myelin alteration appeared throughout the area exhibiting neuronal loss, while the number of oligodendrocytes fell by 45%. No apoptotic oligodendrocytes were identified at that time. Over the following 2 days, there was no further loss of myelin and oligodendrocytes, but there was an increase in the number of oligodendrocytes displaying typical signs of apoptosis as revealed with TUNEL-end-labeled nuclei, Hoechst-labeled condensed chromatin bodies, or bax immunoreactivity. This resulted in a second, progressive loss of both myelin and oligodendrocytes leading to their almost complete disappearance 2 weeks postlesion. These results demonstrate two temporal stages of oligodendroglial cell death. The excitotoxin injection resulted in the rapid destruction of a first oligodendroglial population, most probably by necrosis. A second population died in a delayed manner from apoptosis. This second wave of death coincided with an activated microglia/macrophage invasion of the lesion, suggesting that delayed oligodendroglial death results from toxic microglia/macrophage effects. In addition, the longest surviving oligodendrocytes were located next to reactive astrocytes, suggesting the existence of trophic interactions between these two glial populations.

Absence of macrophage-inflammatory protein-1alpha delays central nervous system demyelination in the presence of an intact blood-brain barrier

Chemokines are small chemotactic cytokines that modulate leukocyte recruitment and activation during inflammation. Here, we describe the role of macrophage inflammatory protein-1alpha (MIP-1alpha) during cuprizone intoxication, a model where demyelination of the CNS features a large accumulation of microglia/macrophage without T cell involvement or blood-brain barrier disruption. RNase protection assays showed that mRNA for numerous chemokines were up-regulated during cuprizone treatment in wild-type, C57BL/6 mice. RANTES, inflammatory protein-10, and monocyte chemoattractant protein-1 showed greatest expression with initiation of insult at 1-2 wk of treatment, whereas MIP-1alpha and beta increased later at 4-5 wk, coincident with peak demyelination and cellular accumulation. The function of MIP-1alpha during demyelination was tested in vivo by exposing MIP-1alpha knockout mice (MIP-1alpha(-/-)) to cuprizone and comparing pathology to wild-type mice. Demyelination at 3.5 wk of treatment was significantly decreased in MIP-1alpha(-/-) mice ( approximately 36% reduction), a result confirmed by morphology at the electron microscopic level. The delay in demyelination was correlated to apparent decreases in microglia/macrophage and astrocyte accumulation and in TNF-alpha protein levels. It was possible that larger effects of the MIP-1alpha deficiency were being masked by other redundant chemokines. Indeed, RNase protection assays revealed increased expression of several chemokine transcripts in both untreated and cuprizone-treated MIP-1alpha(-/-) mice. Nonetheless, despite this possible compensation, our studies show the importance of MIP-1alpha in demyelination in the CNS and highlight its effect, particularly on cellular recruitment and cytokine regulation.

Microglial/macrophage accumulation during cuprizone-induced demyelination in C57BL/6 mice

To study microglial/macrophage infiltration, a cuprizone-induced model for demyelination in C57BL/6 mice was established. Cuprizone is known to cause demyelination in Swiss mice, however, cuprizone-induced demyelination in C57BL/6 mice has not been previously described. Induction of demyelination in C57BL/6 mice enables examination of the function of microglia/macrophage through comparative analyses of syngeneic mice with various targeted genetic mutations. In this report, cuprizone-induced demyelination is easily inducible, localized, and predictable. Concurrent with the initiation of demyelination, we noted microglial/macrophage accumulation and changes in astrocyte morphology. Astrogliosis promptly followed microglia/macrophage recruitment. These observations suggested that microglia/macrophage actively contribute to the demyelination process.

Gene expression in brain during cuprizone-induced demyelination and remyelination

When C57BL/6J mice, 8 weeks of age, received 0.2% Cuprizone in their diet, extensive demyelination in corpus callosum was detectable after 3 weeks, and there was massive demyelination by 4 weeks. As expected, the accumulation of phagocytically active microglia/macrophages correlated closely with demyelination. When Cuprizone was removed from the diet, remyelination was soon initiated; after 6 weeks of recovery, myelin levels were near-normal and phagocytic cells were no longer prominent. Steady-state levels of mRNA for myelin-associated glycoprotein, myelin basic protein, and ceramide galactosyltransferase were already profoundly depressed after 1 week of Cuprizone exposure and were only 10-20% of control values after 2 weeks. Unexpectedly, upregulation of mRNA for these myelin genes did not correlate with initiation of remyelination but rather with accumulation of microglia/macrophages. After 6 weeks of exposure to Cuprizone, mRNA levels were at control levels or higher-in the face of massive demyelination. This suggests that in addition to effecting myelin removal, microglia/macrophages may simultaneously push surviving oligodendroglia or their progenitors toward myelination.

Multiple restricted origin of oligodendrocytes

The plp gene encodes the proteolipid protein and its alternatively spliced product DM-20, major proteins of CNS myelin. In the mouse, plp/dm-20 transcripts are expressed beginning at embryonic day 9.5 (E9.5) by restricted foci of germinative neuroepithelial cells. To determine the identity of the neural precursors expressing plp/dm- 20, a zeomycin resistance gene fused to the lacZ reporter was expressed in transgenic mice under the control of the plp regulatory sequences. In the three different lines generated, the pattern of beta-galactosidase expression was similar and superimposable on the expression pattern of endogenous plp/dm-20. Both in vivo and in vitro, the transgene was expressed by O4(+) pre-oligodendrocytes, and later by RIP+ differentiated oligodendrocytes, but not by neuronal cells, astrocytes, or radial glial cells. After zeomycin selection, a dramatic enrichment in O4(+) pre-oligodendrocytes was observed in cultures derived from E12.5 transgenic embryos. This enrichment indicates the oligodendroglial specification of neural precursors that continuously express plp/dm-20. Early plp/dm-20-expressing precursors, however, appear to be a separate population from previously described PDGFRalpha oligodendrocyte precursors, as shown by the striking differences in their (1) patterns of distribution and (2) responsiveness to PDGF. These data suggest that oligodendrocytes have a plural origin and that early plp/dm-20 defines one of the neural lineages generating oligodendrocytes.

Biochemical subtypes of oligodendrocyte in the anterior medullary velum of the rat as revealed by the monoclonal antibody Rip

Oligodendrocytes were studied in the anterior medullary velum (AMV) of the rat using the monoclonal antibody Rip, an oligodendrocyte marker of unknown function. Confocal microscopic imaging of double immunofluorescent labelling with antibodies to Rip and carbonic anhydrase II (CAII) revealed two biochemically and morphologically distinct populations of oligodendrocyte which were either Rip+CAII+ or Rip+CAII-. Double immunofluorescent labelling with Rip and myelin basic protein (MBP) or glial fibrillary acidic protein (GFAP) provided direct evidence that Rip-labelled cells were phenotypically oligodendrocytes and confirmed that Rip did not recognise astrocytes. Oligodendrocytes which were Rip+CAII+ supported numerous myelin sheaths for small diameter axons, whilst Rip+CAII- oligodendrocytes supported fewer myelin sheaths for large diameter axons. Morphologically, Rip+CAII+ oligodendrocytes corresponded to types I or II of classical nomenclature, whilst Rip+CAII- oligodendrocytes corresponded to types III and IV. The results demonstrated a biochemical difference between oligodendrocytes which myelinated small and large diameter fibres.

Atypical localization of the oligodendrocytic isoform (PI) of glutathione-S-transferase in astrocytes during cuprizone intoxication

Immunocytochemical staining for the Pi and Mu isoforms of glutathione-S-transferase was used to investigate changes in the glial cells in the mouse forebrain. During early development in mouse forebrains the localizations of carbonic anhydrase, Pi and Mu were similar to the respective cellular localizations that had been observed in neonatal rat brain. That is, Pi was found in oligodendrocyte precursors, Mu in astrocytes, and carbonic anhydrase in both oligodendrocyte precursors and astrocytes. In forebrains of 6-week-old mice the neurotoxicant, cuprizone, induced oligodendrocyte degeneration, gliosis, and partial demyelination. Degeneration, gliosis, and partial demyelination. Degeneration of oligodendrocytes, and astrocytosis, began during the initial week of cuprizone feeding, and by the end of the eighth week some demyelination was observed. After mice were fed cuprizone for 4 to 7 weeks, Pi appeared in some of the reactive astrocytes, and Pi-positive astrocytes were present for at least 7 additional weeks. Normally, Pi appeared only in oligodendrocytes. Very few Pi-positive oligodendrocytes remained after the second week. During the eighth week healthy-looking carbonic anhydrase-positive oligodendrocytes reappeared and began to accumulate, and a few small patches of Pi-positive oligodendrocytes were also observed. In summary, some novel findings about glial cells were the observation of an enzyme (Pi) that is lost earlier from oligodendrocytes than is carbonic anhydrase, the apparently unique shift in Pi expression from oligodendrocytes to astrocytes and the greater temporal dissociation between loss of oligodendrocytes and demyelination in the older mice.

Insulin-like growth factor I gene expression is induced in astrocytes during experimental demyelination

To investigate insulin-like growth factor I (IGF-I) and IGF-I receptor gene expression during experimental demyelination and myelin regeneration, young mice were fed cuprizone (( bis(cyclohexanone) oxaldihydrazone )). This copper-chelating agent produces demyelination in the corpus callosum and superior cerebellar peduncles, and when treatment is stopped, there is rapid remyelination. At intervals during cuprizone treatment and recovery, brain sections were hybridized with specific probes and immunostained with antibodies to determine the localization and relative amounts of IGF-I and IGF-I receptor mRNAs and peptides. In untreated littermates, IGF-I and IGF-I receptor mRNAs and peptides were not detected in white matter. In cuprizone-treated mice, high levels of both IGF-I mRNA and peptide were expressed by astrocytes in areas of myelin breakdown. Astrocyte IGF-I expression decreased rapidly during recovery and oligodendroglial expression of myelin-related genes increased. In severely demyelinated areas, immature oligodendroglia exhibited a transient increase in IGF-I receptor mRNA and peptide immunoreactivity during early recovery. This highly specific pattern of IGF-I induction in astrocytes during demyelination and the expression of the IGF-I receptor in regenerating oligodendrocytes during recovery suggest that IGF-I functions in the regulation of oligodendrocyte and myelin metabolism in vivo.

Induction of myelin-associated glycoprotein mRNA in experimental remyelination

Two forms of myelin-associated glycoprotein (MAG) mRNA are produced by alternative splicing of the exon 12 portion. Expression of the two forms of MAG mRNA was studied here in experimentally introduced demyelination and remyelination by Cuprizone intoxication. During the demyelinating stage, both forms of MAG mRNA decreased markedly. When feeding with Cuprizone was stopped, MAG mRNA began to increase. One form of MAG mRNA without the exon 12 portion, which appears in normal development at the period of active myelination, was characteristically induced during the remyelinating stage. The other form containing the exon 12 portion was also induced but recovered only to the level in normal development.

Immunocytochemical characterization of primary glial cell cultures from normal adult human brain

Primary cultures were established from autopsy or biopsy samples of normal adult human brain and characterized by immunocytochemical techniques. Initially, macrophages were the predominant cell type adhering to the substratum, but as their number fell that of glial cells increased. Oligodendrocytes comprised 30% of the glial population in white matter cultures, and their perikarya and elongated processes were immunostained with antibodies directed against galactocerebroside and four myelin proteins. In white and grey matter cultures, process-bearing astrocytes and small numbers of polygonal astrocytes were stained with antibodies against glial fibrillary acidic protein and glutamine synthetase. Fibroblasts started to appear at 3 weeks and proliferated to form a monolayer beneath glial cells by 5 weeks. Glia began to die in the 6th week. These primary cell cultures of white or grey matter can be used to study the properties of glial cells from normal or pathological adult human brain.