Lack of cuprizone-induced demyelination in the murine spinal cord despite oligodendroglial alterations substantiates the concept of site-specific susceptibilities of the central nervous system

Orosomucoid-1 Arises as a Shared Altered Protein in Two Models of Multiple Sclerosis

Multiple sclerosis (MS) is a complex autoimmune and neurodegenerative disorder that affects the central nervous system (CNS). It is characterized by a heterogeneous disease course involving demyelination and inflammation. In this study, we utilized two distinct animal models, cuprizone (CPZ)-induced demyelination and experimental autoimmune encephalomyelitis (EAE), to replicate various aspects of the disease. We aimed to investigate the differential CNS responses by examining the proteomic profiles of EAE mice during the peak disease (15 days post-induction) and cuprizone-fed mice during the acute phase (38 days). Specifically, we focused on two different regions of the CNS: the dorsal cortex (Cx) and the entire spinal cord (SC). Our findings revealed varied glial, synaptic, dendritic, mitochondrial, and inflammatory responses within these regions for each model. Notably, we identified a single protein, Orosomucoid-1 (Orm1), also known as Alpha-1-acid glycoprotein 1 (AGP1), that consistently exhibited alterations in both models and regions. This study provides insights into the similarities and differences in the responses of these regions in two distinct demyelinating models.

Immunofluorescence assay for demyelination, remyelination, and proliferation in an acute cuprizone mouse model

Here, we present a protocol to assess demyelination in the corpus callosum of an acute cuprizone mouse model, which is routinely used to induce demyelination for studying myelin regeneration in the rodent brain. We describe the tracing of neural stem cells via intraperitoneal injection of tamoxifen into adult Gli1CreERT2;Ai9 mice and the induction of demyelination with cuprizone diet. We also detail EdU administration, cryosectioning of the mouse brain, EdU labeling, and immunofluorescence staining to examine proliferation and myelination. For complete details on the use and execution of this protocol, please refer to Radecki et al. (2020).1.

Motor Behavioral Deficits in the Cuprizone Model: Validity of the Rotarod Test Paradigm

Multiple Sclerosis (MS) is a neuroinflammatory disorder, which is histopathologically characterized by multifocal inflammatory demyelinating lesions affecting both the central nervous system’s white and grey matter. Especially during the progressive phases of the disease, immunomodulatory treatment strategies lose their effectiveness. To develop novel progressive MS treatment options, pre-clinical animal models are indispensable. Among the various different models, the cuprizone de- and remyelination model is frequently used. While most studies determine tissue damage and repair at the histological and ultrastructural level, functional readouts are less commonly applied. Among the various overt functional deficits, gait and coordination abnormalities are commonly observed in MS patients. Motor behavior is mediated by a complex neural network that originates in the cortex and terminates in the skeletal muscles. Several methods exist to determine gait abnormalities in small rodents, including the rotarod testing paradigm. In this review article, we provide an overview of the validity and characteristics of the rotarod test in cuprizone-intoxicated mice.

Lipocalin 2 attenuates oligodendrocyte loss and immune cell infiltration in mouse models for multiple sclerosis

Multiple sclerosis (MS) is a central nervous system disease characterized by both degenerative and inflammatory processes. Various mediators are involved in the interplay of degeneration and innate immunity on one hand and peripheral adaptive immunity on the other hand. The secreted protein lipocalin 2 (LCN2) is an inflammatory modulator in a variety of pathologies. Although elevated intrathecal levels of LCN2 have been reported in MS patients, it's functional role is widely unknown. Here, we identified a subpopulation of astrocytes as a source of LCN2 in MS lesions and respective animal models. We investigated the functional role of LCN2 for both autoimmune and degenerative aspects in three MS mouse models including both wild type (WT) and Lcn2^-/- mouse strains. While the experimental autoimmune encephalomyelitis (EAE) model reflects primary autoimmunity, the cuprizone model reflects selective oligodendrocyte loss and demyelination. In addition, we included a combinatory Cup/EAE model in which primary cytodegeneration is followed by inflammatory lesions within the forebrain. While in the EAE model, the disease outcome was comparable in between the two mouse strains, cuprizone intoxicated Lcn2^-/- animals showed an increased loss of oligodendrocytes. In the Cup/EAE model, Lcn2^-/- animals showed increased inflammation when compared to WT mice. Together, our results highlight LCN2 as a potentially protective molecule in MS lesion formation, which might be able to limit loss of oligodendrocytes immune-cell invasion. Despite these findings, it is not yet clear which glial cell phenotype (and to which extent) contributes to the observed neuroprotective effects, that is, microglia and/or astroglia or even endothelial cells in the brain.

Cuprizone-mediated demyelination reversibly degrades voiding behavior in mice while sparing brainstem reflex

Multiple sclerosis (MS) is a chronic, progressively debilitating demyelinating disease of the central nervous system (CNS). Nearly 80% of MS patients experience lower urinary tract dysfunction early in their diagnosis. This significantly affects the quality of life, and in latter stages of disease is a leading cause of hospitalization. Previously, animal models have shown that inflammatory demyelination in the CNS causes profound bladder dysfunction, but the confounding influence of systemic inflammation limits the potential interpretation of the contribution of CNS demyelination to bladder dysfunction. Since the micturition circuit has myelinated neuronal connections in the cortex, brainstem, and spinal cord, we examined alterations in bladder function in the cuprizone model characterized by demyelinating lesions in the cortex and corpus callosum that are independent of T-cell-mediated autoimmunity. Herein, we report that a 4-week dietary cuprizone treatment in C57Bl/6J mice induced alterations in voiding behavior with increased micturition frequency and reduced volume voided, similar to human MS bladder dysfunction. Subsequently, recovery from cuprizone treatment restored normal bladder function. Demyelination and remyelination were confirmed by Luxol Fast Blue staining of the corpus callosum. Additionally, we also determined that an 8-week cuprizone treatment, resulting in chronic demyelination lacking spontaneous remyelination potential, is associated with an exacerbated voiding phenotype. Interestingly, while cuprizone-induced CNS demyelination severely affected conscious (cortical) urinary behavior, the brainstem and spinal cord reflex remained unchanged, as confirmed by urethane-anesthetized cystometry. This is the first study to show that cortical demyelination independent of inflammation can negatively impact urinary function.

Visual Evoked Potentials to Monitor Myelin Cuprizone-Induced Functional Changes

The visual system is one of the most accessible routes to study the central nervous system under pathological conditions, such as in multiple sclerosis (MS). Non-invasive visual evoked potential (VEP) and optical coherence tomography (OCT) were used to assess visual function and neuroretinal thickness in C57BL/6 taking 0.2% cuprizone for 7 weeks and at 5, 8, 12, and 15 days after returning to a normal diet. VEPs were significantly delayed starting from 4 weeks on cuprizone, with progressive recovery off cuprizone, becoming significant at day 8, complete at day 15. In contrast, OCT and neurofilament staining showed no significant axonal thinning. Optic nerve histology indicated that whilst there was significant myelin loss at 7 weeks on the cuprizone diet compared with healthy mice, at 15 days off cuprizone diet demyelination was significantly less severe. The number of Iba 1⁺ cells was found increased in cuprizone mice at 7 weeks on and 15 days off cuprizone. The combined use of VEPs and OCT allowed us to characterize non-invasively, in vivo, the functional and structural changes associated with demyelination and remyelination in a preclinical model of MS. This approach contributes to the non-invasive study of possible effective treatments to promote remyelination in demyelinating pathologies.

The mechanistic target of rapamycin as a regulator of metabolic function in oligodendroglia during remyelination

Despite evidence for prominent metabolic dysfunction within multiple sclerosis (MS) lesions, the mechanisms controlling metabolic shifts in oligodendroglia are poorly understood. The cuprizone model of demyelination and remyelination is a valuable tool for assessing metabolic insult during oligodendrocyte death and myelin degradation, closely resembling the distal oligodendrogliopathy seen in Pattern III MS lesions. In this review we discuss how metabolic processes in oligodendrocytes are disrupted in both MS and the cuprizone model, as well as the evidence for mechanistic target of rapamycin (mTOR) signaling as a key regulator of oligodendroglial metabolic function and efficient remyelination.

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.

What Guides Peripheral Immune Cells into the Central Nervous System?

Multiple sclerosis (MS), an immune-mediated demyelinating disease of the central nervous system (CNS), initially presents with a relapsing-remitting disease course. During this early stage of the disease, leukocytes cross the blood–brain barrier to drive the formation of focal demyelinating plaques. Disease-modifying agents that modulate or suppress the peripheral immune system provide a therapeutic benefit during relapsing-remitting MS (RRMS). The majority of individuals with RRMS ultimately enter a secondary progressive disease stage with a progressive accumulation of neurologic deficits. The cellular and molecular basis for this transition is unclear and the role of inflammation during the secondary progressive disease stage is a subject of intense and controversial debate. In this review article, we discuss the following main hypothesis: during both disease stages, peripheral immune cells are triggered by CNS-intrinsic stimuli to invade the brain parenchyma. Furthermore, we outline the different neuroanatomical routes by which peripheral immune cells might migrate from the periphery into the CNS.

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.

Amelioration of clinical course and demyelination in the cuprizone mouse model in relation to ketogenic diet

Ketogenic diet (KD) is defined as a high-fat, low-carbohydrate diet with appropriate amounts of protein, which has broad neuroprotective effects. However, the mechanisms of ameliorating the demyelination and of the neuroprotective effects of KD have not yet been completely elucidated. Therefore, the present study investigated the protection mechanism of KD treatment in the cuprizone (bis-cyclohexanone oxalydihydrazone, CPZ)-induced demyelination mice model, with special emphasis on neuroinflammation. After the KD treatment, an increased ketone body level in the blood of mice was detected, and a significant increase in the distance traveled within the central area was observed in the open field test, which reflected the increased exploration and decreased anxiety of mice that received CPZ. The results of Luxol fast blue and myelin basic protein (MBP) immunohistochemistry staining for the evaluation of the myelin content within the corpus callosum revealed a noticeable increase in the number of myelinated fibers and myelin score after KD administration in these animals. Concomitant, the protein expressions of glial fibrillary acidic protein (GFAP, an astrocyte marker), ionized calcium-binding adaptor molecule 1 (Iba-1, a microglial marker), CD68 (an activated microglia marker) and CD16/32 (a M1 microglial marker) were down-regulated, while the expression of oligodendrocyte lineage transcription factor 2 (OLIG2, an oligodendrocyte precursor cells marker) was up-regulated by the KD treatment. In addition, the KD treatment not only reduced the level of the C-X-C motif chemokine 10 (CXCL10), which is correlated to the recruitment of activated microglia, but also inhibited the production of proinflammatory cytokines, including interleukin 1β (IL-1β) and tumor necrosis factor-α (TNF-α), which are closely correlated to the M1 phenotype microglia. It is noteworthy, that the expression levels of histone deacetylase 3 (HADC3) and nod-like receptor pyrin domain containing 3 (NLRP3) significantly decreased after KD administration. In conclusion, these data demonstrate that KD decreased the reactive astrocytes and activated the microglia in the corpus callosum, and that KD inhibited the HADC3 and NLRP3 inflammasome signaling pathway in CPZ-treated mice. This suggests that the inhibition of the HADC3 and NLRP3 signaling pathway may be a novel mechanism by which KD exerts its protective actions for the treatment of demyelinating diseases.

PART 2: Mouse models for multiple sclerosis research

Lower urinary tract symptoms and dysfunction (LUTS/LUTD) contribute to loss of quality of life, morbidity, and need for medical intervention in most patients with multiple sclerosis (MS). Although MS is an inflammatory neurodegenerative disease, clinical manifestations including continence control disorders have traditionally been attributed to the loss of neural signaling due to neurodegeneration. Clinical approaches to MS-LUTS/LUTD have focused on addressing symptoms in the context of urodynamic dysfunctions as pathophysiologic understandings are incomplete. The mouse model provides a useful research platform for discovery of more detailed molecular, cellular, and tissue-level knowledge of the disease and its clinical manifestations. The aim of this two-part review is to provide a state-of-the-art update on the use of the mouse model for MS research, with a focus on lower urinary tract symptoms. Part I presents a summary of current understanding of MS pathophysiology, the impact on lower urinary tract symptoms, and briefly introduces the types of mouse models available to study MS. Part II presents the common animal models that are currently available to study MS, their mechanism, relevance to MS-LUTS/LUTD and their urinary pathophysiology, advantages and disadvantages.

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.

Behavioural and histological changes in cuprizone-fed mice

Feeding cuprizone (CPZ) to mice causes demyelination and reactive gliosis in the central nervous system (CNS), hallmarks of some neurodegenerative diseases like multiple sclerosis. However, relatively little is known regarding the behavioural deficits associated with CPZ-feeding and much of what is known is contradictory. This study investigated whether 37 days oral feeding of 0.2% CPZ to young adult mice evoked sensorimotor behavioural changes. Behavioural tests included measurements of nociceptive withdrawal reflex responses and locomotor tests. Additionally, these were compared to histological analysis of the relevant CNS regions by analysis of neuronal and glial cell components. CPZ-fed mice exhibited more foot slips in walking ladder and beam tests compared to controls. In contrast, no changes in nociceptive thresholds to thermal or mechanical stimuli occurred between groups. Histological analysis showed demyelination throughout the CNS, which was most prominent in white matter tracts in the cerebrum but was also elevated in areas such as the hippocampus, basal ganglia and diencephalon. Profound demyelination and gliosis was seen in the deep cerebellar nuclei and brain stem regions associated with the vestibular system. However, in the spinal cord changes were minimal. No loss of oligodendrocytes, neurons or motoneurons occurred but a significant increase in astrocyte staining ensued throughout the white matter of the spinal cord. The results suggest that CPZ differentially affects oligodendrocytes throughout the CNS and induces subtle motor changes such as ataxia. This is associated with deficits in CNS regions associated with motor and balance functions such as the cerebellum and brain stem.

Cognitive disturbances in the cuprizone model of multiple sclerosis

Cognitive problems frequently accompany neurological manifestations of multiple sclerosis (MS). However, during screening of preclinical candidates, assessments of behaviour in mouse models of MS typically focus on locomotor activity. In the present study, we analysed cognitive behaviour of 9 to 10-week-old female C57Bl/6J mice orally administered with the toxin cuprizone that induces demyelination, a characteristic feature of MS. Animals received 400 mg/kg cuprizone daily for 2 or 4 weeks, and their performance was compared with that of vehicle-treated mice. Cuprizone-treated animals showed multiple deficits in short touchscreen-based operant tasks: they responded more slowly to visual stimuli, rewards and made more errors in a simple rule-learning task. In contextual/cued fear conditioning experiments, cuprizone-treated mice showed significantly lower levels of contextual freezing than vehicle-treated mice. Diffusion tensor imaging showed treatment-dependent changes in fractional anisotropy as well as in axial and mean diffusivities in different white matter areas. Lower values of fractional anisotropy and axial diffusivity in cuprizone-treated mice indicated developing demyelination and/or axonal damage. Several diffusion tensor imaging measurements correlated with learning parameters. Our results show that translational touchscreen operant tests and fear conditioning paradigms can reliably detect cognitive consequences of cuprizone treatment. The suggested experimental approach enables screening novel MS drug candidates in longitudinal experiments for their ability to improve pathological changes in brain structure and reverse cognitive deficits.

The Cuprizone Model: Dos and Do Nots

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system. Various pre-clinical models with different specific features of the disease are available to study MS pathogenesis and to develop new therapeutic options. During the last decade, the model of toxic demyelination induced by cuprizone has become more and more popular, and it has contributed substantially to our understanding of distinct yet important aspects of the MS pathology. Here, we aim to provide a practical guide on how to use the cuprizone model and which pitfalls should be avoided.

Behavioural phenotypes in the cuprizone model of central nervous system demyelination

The feeding of cuprizone (CPZ) to animals has been extensively used to model the processes of demyelination and remyelination, with many papers adopting a narrative linked to demyelinating conditions like multiple sclerosis (MS), the aetiology of which is unknown. However, no current animal model faithfully replicates the myriad of symptoms seen in the clinical condition of MS. CPZ ingestion causes mitochondrial and endoplasmic reticulum stress and subsequent apoptosis of oligodendrocytes leads to central nervous system demyelination and glial cell activation. Although there are a wide variety of behavioural tests available for characterizing the functional deficits in animal models of disease, including that of CPZ-induced deficits, they have focused on a narrow subset of outcomes such as motor performance, cognition, and anxiety. The literature has not been systematically reviewed in relation to these or other symptoms associated with clinical MS. This paper reviews these tests and makes recommendations as to which are the most important in order to better understand the role of this model in examining aspects of demyelinating diseases like MS.

Behavioural alterations and morphological changes are attenuated by the lack of TRPA1 receptors in the cuprizone-induced demyelination model in mice

We have recently reported that the Transient Receptor Potential Ankyrin 1 (TRPA1) receptor deficiency significantly attenuated cuprizone-induced demyelination by reducing the apoptosis of mature oligodendrocytes. The aim of the present study was to gather additional data on the role of TRPA1 by investigating the time course of behavioural alterations and morphological changes in cuprizone-treated TRPA1 receptor gene-deficient mice. Demyelination was induced by feeding male wild-type (WT) and TRPA1 gene-deleted (TRPA1 KO) mice with 0.2% cuprizone for 6 weeks. Behavioural tests were performed once per week to follow cuprizone-induced functional changes. Mechanonociceptive thresholds were investigated by a dynamic plantar aesthesiometer and von Frey filaments. Motor performance was assessed by accelerating RotaRod and horizontal grid tests. For the study of spontaneous activity, the open field test was used. The time course of corpus callosum demyelination was also followed weekly by magnetic resonance imaging (MRI). Histological analysis of myelin loss was performed with Luxol Fast Blue (LFB) staining at week 3 and electron microscopy (EM) at week 6. Astrocyte and microglia accumulation at week 3 was assessed by immunohistochemistry (IHC). Cuprizone treatment induced no changes in mechanonociception or motor performance. In the open arena, cuprizone-treated mice spent more time with locomotion, their mean velocity was significantly higher and the distance they travelled was longer than untreated mice. No statistical difference was detected between WT and TRPA1 KO mice in these parameters. On the other hand, significantly increased rearing behaviour was induced in WT mice compared to TRPA1 KO animals. Morphological changes detected with MRI, LFB, IHC and EM analysis revealed reduced damage of the myelin and attenuated accumulation of astrocytes and microglia in cuprizone-treated TRPA1 KO animals, at each examined time point. Our recent data further suggest that inhibition of TRPA1 receptors could be a promising therapeutic approach to limit central nervous system damage in demyelinating diseases.

Cuprizone Intoxication Induces Cell Intrinsic Alterations in Oligodendrocyte Metabolism Independent of Copper Chelation

Cuprizone intoxication is a common animal model used to test myelin regenerative therapies for the treatment of diseases such as multiple sclerosis. Mice fed this copper chelator develop reversible, region-specific oligodendrocyte loss and demyelination. While the cellular changes influencing the demyelinating process have been explored in this model, there is no consensus about the biochemical mechanisms of toxicity in oligodendrocytes and about whether this damage arises from the chelation of copper in vivo. Here we have identified an oligodendroglial cell line that displays sensitivity to cuprizone toxicity and performed global metabolomic profiling to determine biochemical pathways altered by this treatment. We link these changes with alterations in brain metabolism in mice fed cuprizone for 2 and 6 weeks. We find that cuprizone induces widespread changes in one-carbon and amino acid metabolism as well as alterations in small molecules that are important for energy generation. We used mass spectrometry to examine chemical interactions that are important for copper chelation and toxicity. Our results indicate that cuprizone induces global perturbations in cellular metabolism that may be independent of its copper chelating ability and potentially related to its interactions with pyridoxal 5'-phosphate, a coenzyme essential for amino acid metabolism.

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.

Acute axonal damage in three different murine models of multiple sclerosis: A comparative approach

Axonal damage has been identified as a significant contributor to permanent clinical disability in multiple sclerosis. In the context of demyelinating disorders, this destructive event can be the result of inflammation, demyelination and/or the activation of innate defense cells such as microglia or monocytes. The relative contribution of each of these variables to acute axonal injury is, however, unknown. In the present study, we compared the extent of acute axonal damage in three different murine demyelination models using anti-amyloid precursor protein (APP) immunohistochemistry. T cell dependent (MOG_35-55-induced experimental autoimmune encephalomyelitis (EAE)) as well as T cell independent demyelination models (cuprizone- and lysolecithin-induced demyelination) were used. APP⁺ spheroids were present in all three experimental demyelination models. The number of APP⁺ spheroids was highest within LPC-induced lesions. Equal amounts were found in the spinal cord of MOG_35-55-EAE animals and the corpus callosum of cuprizone-intoxicated animals. Moreover, we detected increased immunoreactivity of the pre-synaptic protein vesicular glutamate transporter 1 (VGluT1) in demyelinated foci. VGluT1-staining revealed long stretched, ovoid-like axonal structures which co-localized with APP. In summary, we showed that acute axonal damage is evident under various experimental demyelination paradigms. Furthermore, disturbed axonal transport mechanisms, which are responsible for intra-axonal APP accumulation, do not only disturb APP, but also the transport of other synaptic proteins. These results indicate that, despite differences in their characteristics, all three models may serve as valid and suitable systems for investigating responsible mechanisms of axonal damage and potential protective strategies.

Characterization of Periodic Acid-Schiff-Positive Granular Deposits in the Hippocampus of SJL/J Mice

Periodic acid-Schiff (PAS)-positive granular deposits in the hippocampus have been reported previously in certain inbred mouse strains such as C57BL/6 and the senescent-accelerated mouse prone-8. Here, we report for the first time that similar PAS-positive granules age dependently occur in SJL/J mice, a mouse strain, for instance, used for central nervous system disease research. Moreover, similar granules stained intensely positive with a polyclonal antibody directed against p75 neurotrophin receptor (p75(NTR)). Granular deposits were absent in young mice and developed with aging in CA1 and CA2 regions of the hippocampus. Interestingly, granules significantly diminished in SJL/J mice previously treated with cuprizone, a copper chelator, which is a useful model for toxic demyelination. The presented data support the idea that granules might be the result of an imbalance of redox-active metals and/or a dysregulation of complementary mechanisms that regulate their homeostasis in astrocyte-neuron coupling, respectively. It remains to be determined whether the unsuspected immunoreactivity for p75(NTR) represents a false-positive reaction or whether p75(NTR) is crucially involved in the pathogenesis of age-related hippocampal granular deposits in mice.

Transcriptomic meta-analysis of multiple sclerosis and its experimental models

Background

Multiple microarray analyses of multiple sclerosis (MS) and its experimental models have been published in the last years.

Objective

Meta-analyses integrate the information from multiple studies and are suggested to be a powerful approach in detecting highly relevant and commonly affected pathways.

Data sources

ArrayExpress, Gene Expression Omnibus and PubMed databases were screened for microarray gene expression profiling studies of MS and its experimental animal models.

Study eligibility criteria

Studies comparing central nervous system (CNS) samples of diseased versus healthy individuals with n >1 per group and publically available raw data were selected.

Material and Methods

Included conditions for re-analysis of differentially expressed genes (DEGs) were MS, myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (EAE) in rats, proteolipid protein-induced EAE in mice, Theiler’s murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD), and a transgenic tumor necrosis factor-overexpressing mouse model (TNFtg). Since solely a single MS raw data set fulfilled the inclusion criteria, a merged list containing the DEGs from two MS-studies was additionally included. Cross-study analysis was performed employing list comparisons of DEGs and alternatively Gene Set Enrichment Analysis (GSEA).

Results

The intersection of DEGs in MS, EAE, TMEV-IDD, and TNFtg contained 12 genes related to macrophage functions. The intersection of EAE, TMEV-IDD and TNFtg comprised 40 DEGs, functionally related to positive regulation of immune response. Over and above, GSEA identified substantially more differentially regulated pathways including coagulation and JAK/STAT-signaling.

Conclusion

A meta-analysis based on a simple comparison of DEGs is over-conservative. In contrast, the more experimental GSEA approach identified both, a priori anticipated as well as promising new candidate pathways.

Regional heterogeneity of cuprizone-induced demyelination: topographical aspects of the midline of the corpus callosum

The cuprizone model is a suitable animal model of de- and remyelination secondary to toxin-induced oligodendrogliopathy. From a pharmaceutical point of view, the cuprizone model is a valuable tool to study the potency of compounds which interfere with toxin-induced oligodendrocyte cell death or boost/inhibit remyelinating pathways and processes. The aim of this study was to analyze the vulnerability of neighboring white mater tracts (i.e., the fornix and cingulum) next to the midline of the corpus callosum which is the region of interest of most studies using this model. Male mice were fed cuprizone for various time periods. Different white matter areas were analyzed for myelin (anti-PLP), microglia (anti-IBA1), and astrocyte (anti-GFAP) responses by means of immunohistochemistry. Furthermore, Luxol fast blue-periodic acid Schiff stains were performed to validate loss of myelin-reactive fibers in the different regions. Cuprizone induced profound demyelination of the midline of the corpus callosum and medial parts of the cingulum that was paralleled by a significant astrocyte and microglia response. In contrast, lateral parts of the corpus callosum and the cingulum, as well as the fornix region which is just beneath the midline of the corpus callosum appeared to be resistant to cuprizone exposure. Furthermore, resistant areas displayed reduced astrogliosis and microgliosis. This study clearly demonstrates that neighboring white matter tracts display distinct vulnerability to toxin-induced demyelination. This important finding has direct relevance for evaluation strategies in this frequently used animal model for multiple sclerosis.

Matrix metalloproteinase-12 deficiency ameliorates the clinical course and demyelination in Theiler's murine encephalomyelitis

Matrix metalloproteinases (MMPs) are a family of extracellular proteases involved in the pathogenesis of demyelinating diseases like multiple sclerosis (MS). The aim of the present study was to investigate whether MMPs induce direct myelin degradation, leukocyte infiltration, disruption of the blood-brain barrier (BBB), and/or extracellular matrix remodeling in the pathogenesis of Theiler's murine encephalomyelitis (TME), a virus-induced model of MS. During the demyelinating phase of TME, the highest transcriptional upregulation was detected for Mmp12, followed by Mmp3. Mmp12 (-/-) mice showed reduced demyelination, macrophage infiltration, and motor deficits compared with wild-type- and Mmp3 knock-out mice. However, BBB remained unaltered, and the amount of extracellular matrix deposition was similar in knock-out mice and wild-type mice. Furthermore, stereotaxic injection of activated MMP-3, -9, and -12 into the caudal cerebellar peduncle of adult mice induced a focally extensive primary demyelination prior to infiltration of inflammatory cells, as well as a reduction in the number of oligodendrocytes and a leakage of BBB. All these results demonstrate that MMP-12 plays an essential role in the pathogenesis of TME, most likely due to its primary myelin- or oligodendrocyte-toxic potential and its role in macrophage extravasation, whereas there was no sign of BBB damage or alterations to extracellular matrix remodeling/deposition. Thus, interrupting the MMP-12 cascade may be a relevant therapeutic approach for preventing chronic progressive demyelination.

Cuprizone inhibits demyelinating leukomyelitis by reducing immune responses without virus exacerbation in an infectious model of multiple sclerosis

Multiple sclerosis is one of the most common demyelinating central nervous system diseases in young adults. Theiler's murine encephalomyelitis (TME) is a widely used virus-induced murine model for human myelin disorders. Immunosuppressive approaches generally reduce antiviral immunity and therefore increase virus dissemination with clinical worsening. In the present study, the progressive course of TME was significantly delayed due to a five-week cuprizone feeding period. Cuprizone was able to minimize demyelinating leukomyelitis without virus exacerbation. This phenomenon is supposed to be a consequence of selective inhibition of detrimental inflammatory responses with maintained protective immunity against the virus.