De- and remyelination in the CNS white and grey matter induced by cuprizone: the old, the new, and the unexpected

Magnetic resonance metrics for identification of cuprizone-induced demyelination in the mouse model of neurodegeneration: a review

Neurodegenerative disorders, including Multiple Sclerosis (MS), are heterogenous disorders which affect the myelin sheath of the central nervous system (CNS). Magnetic Resonance Imaging (MRI) provides a non-invasive method for studying, diagnosing, and monitoring disease progression. As an emerging research area, many studies have attempted to connect MR metrics to underlying pathophysiological presentations of heterogenous neurodegeneration. Most commonly, small animal models are used, including Experimental Autoimmune Encephalomyelitis (EAE), Theiler's Murine Encephalomyelitis (TMEV), and toxin models including cuprizone (CPZ), lysolecithin, and ethidium bromide (EtBr). A contrast and comparison of these models is presented, with focus on the cuprizone model, followed by a review of literature studying neurodegeneration using MRI and the cuprizone model. Conventional MRI methods including T1 Weighted (T1W) and T2 Weighted (T2W) Imaging are mentioned. Quantitative MRI methods which are sensitive to diffusion, magnetization transfer, susceptibility, relaxation, and chemical composition are discussed in relation to studying the CPZ model. Overall, additional studies are needed to improve both the sensitivity and specificity of MRI metrics for underlying pathophysiology of neurodegeneration and the relationships in attempts to clear the clinico-radiological paradox. We therefore propose a multiparametric approach for the investigation of MR metrics for underlying pathophysiology.

Endogenous Sox8 is a critical factor for timely remyelination and oligodendroglial cell repletion in the cuprizone model

Genome-wide association studies identified a single nucleotide polymorphism (SNP) downstream of the transcription factor Sox8, associated with an increased risk of multiple sclerosis (MS). Sox8 is known to influence oligodendrocyte terminal differentiation and is involved in myelin maintenance by mature oligodendrocytes. The possible link of a Sox8 related SNP and MS risk, along with the role of Sox8 in oligodendrocyte physiology prompted us to investigate its relevance during de- and remyelination using the cuprizone model. Sox8-/- mice and wildtype littermates received a cuprizone diet for 5 weeks (wk). Sox8-/- mice showed reduced motor performance and weight compared to wildtype controls. Brains were histologically analysed at the maximum of demyelination (wk 5) and on two time points during remyelination (wk 5.5 and wk 6) for oligodendroglial, astroglial, microglial and myelin markers. We identified reduced proliferation of oligodendrocyte precursor cells at wk 5 as well as reduced numbers of mature oligodendrocytes in Sox8-/- mice at wk 6. Moreover, analysis of myelin markers revealed a delay in remyelination in the Sox8-/- group, demonstrating the potential importance of Sox8 in remyelination processes. Our findings present, for the first time, compelling evidence of a significant role of Sox8 in the context of a disease model.

NOX4-derived ROS are neuroprotective by balancing intracellular calcium stores

Hyperexcitability is associated with neuronal dysfunction, cellular death, and consequently neurodegeneration. Redox disbalance can contribute to hyperexcitation and increased reactive oxygen species (ROS) levels are observed in various neurological diseases. NOX4 is an NADPH oxidase known to produce ROS and might have a regulating function during oxidative stress. We, therefore, aimed to determine the role of NOX4 on neuronal firing, hyperexcitability, and hyperexcitability-induced changes in neural network function. Using a multidimensional approach of an in vivo model of hyperexcitability, proteomic analysis, and cellular function analysis of ROS, mitochondrial integrity, and calcium levels, we demonstrate that NOX4 is neuroprotective by regulating ROS and calcium homeostasis and thereby preventing hyperexcitability and consequently neuronal death. These results implicate NOX4 as a potential redox regulator that is beneficial in hyperexcitability and thereby might have an important role in neurodegeneration.

The Effects of Cuprizone on Murine Subventricular Zone-Derived Neural Stem Cells and Progenitor Cells Grown as Neurospheres

Despite the extensive use of the cuprizone (CPZ) demyelination animal model, there is little evidence regarding the effects of CPZ on a cellular level. Initial studies have suggested that oligodendrocytes (OL) are the main cell targets for CPZ toxicity. However, recent data have revealed additional effects on neural stem cells and progenitor cells (NSC/NPC), which constitute a reservoir for OL regeneration during brain remyelination. We cultured NSC/NPC as neurospheres to investigate CPZ effects on cell mechanisms which are thought to be involved in demyelination and remyelination processes in vivo. Proliferating NSC/NPC cultures exposed to CPZ showed overproduction of intracellular reactive oxygen species and increased progenitor migration at the expense of a significant inhibition of cell proliferation. Although NSC/NPC survival was not affected by CPZ in proliferative conditions, we found that CPZ-treated cultures undergoing cell differentiation were more prone to cell death than controls. The commitment and cell differentiation towards neural lineages did not seem to be affected by CPZ, as shown by the conserved proportions of OL, astrocytes, and neurons. Nevertheless, when CPZ treatment was performed after cell differentiation, we detected a significant reduction in the number and the morphological complexity of OL, astrogliosis, and neuronal damage. We conclude that, in addition to damaging mature OL, CPZ also reduces NSC/NPC proliferation and activates progenitor migration. These results shed light on CPZ direct effects on NSC proliferation and the progression of in vitro differentiation.

Reaction of different cell types of the brain on neurotoxin cuprizone and hormone melatonin treatment in young and aging mice

Introduction

The brain myelin and neurons destruction in multiple sclerosis may be associated with the production of neuroinflammatory cells (macrophages, astrocytes, T-lymphocytes) of pro-inflammatory cytokines and free radicals. The age-associated changes of the above cells can influence on the response of nervous system cells to toxic damaging and regulatory factors of humoral/endocrine nature, in particular pineal hormone melatonin. The study aim was (1) to evaluate changes of the brain macrophages, astrocytes, T-cells, neural stem cells, neurons, and central nervous system (CNS) functioning in the neurotoxin cuprizone-treated mice of different age; and (2) to assess in such mice the effects of exogenous melatonin and possible courses of its action.

Methods

A toxic demyelination and neurodegeneration model was induced in 129/Sv mice aged 3-5 and 13-15 months by adding cuprizone neurotoxin to their food for 3 weeks. From the 8th day of the cuprizone treatment, melatonin was injected intraperitoneally at 6 p.m. daily, at a dose of 1 mg/kg. The brain GFPA + -cells were evaluated by immunohistochemical method, the proportion of CD11b+, CD3+CD11b+, CD3+, CD3+CD4+, CD3+CD8+, Nestin+-cells was determined via flow cytometry. Macrophage activity was evaluated by their ability to phagocytose latex beads Morphometric analysis of the brain neurons and the behavioral reactions ("open field" and rotarod tests) were performed. To assess the involvement of the bone marrow and thymus in the action of melatonin, the amount of granulocyte/macrophage colony-forming cells (GM-CFC), and blood monocytes and thymic hormone thymulin were evaluated.

Results and discussion

The numbers of the GFAP+-, CD3+-, CD3+CD4+, CD3+CD8+, CD11b+, CD3+CD11b+, Nestin+-cells and macrophages phagocytic latex beads and malondialdehyde (MDA) content were increased in the brain of young and aging mice under cuprizone influence. The proportion of undamaged neurons within the brain, motor, affective, and exploratory activities, and muscle tone decreased in mice of both ages. Introducing melatonin to mice of any age reduced the number of GFAP+-, CD3+- cells and their subpopulations, macrophage activation, and MDA content. At the same time, the percentage of brain neurons that were unchanged increased as the number of Nestin+ cells decreased. The behavioral responses were also improved. Besides, the number of bone marrow GM-CFC and the blood level of monocytes and thymulin increased. The effects of both neurotoxin and melatonin on the brain astrocytes, macrophages T-cells, and immune system organs as well as the structure and functioning of neurons were more pronounced in the young mice.

Conclusion

We have observed the involvement of the astrocytes, macrophages, T-cells, neural stem cells, and neurons in the brain reaction of mice different age after administration of neurotoxin cuprizone and melatonin. The brain cell composition reaction has the age features. The neuroprotective effects of melatonin in cuprizone-treated mice have been realized through an improvement of the brain cell composition and oxidative stress factors and functioning of bone marrow and thymus.

Cuprizone feeding induces swollen astrocyte endfeet

The cuprizone model is a widely used model to study the pathogenesis of multiple sclerosis (MS). Due to the selective loss of mature oligodendrocytes and myelin, it is mainly being used to study demyelination and the mechanisms of remyelination, as well as the efficiency of compounds or therapeutics aiming at remyelination. Although early investigations using high dosages of cuprizone reported the occurrence of hydrocephalus, it has long been assumed that cuprizone feeding at lower dosages does not induce changes at the blood-brain barrier (BBB). Here, by analyzing BBB ultrastructure with high-resolution electron microscopy, we report changes at astrocytic endfeet surrounding vessels in the brain parenchyma. Particularly, edema formation around blood vessels and swollen astrocytic endfeet already occurred after feeding low dosages of cuprizone. These findings indicate changes in BBB function that will have an impact on the milieu of the central nervous system (CNS) in the cuprizone model and need to be considered when studying the mechanisms of de- and remyelination.

CAQK, a peptide associating with extracellular matrix components targets sites of demyelinating injuries

The destruction of the myelin sheath that encircles axons leads to impairments of nerve conduction and neuronal dysfunctions. A major demyelinating disorder is multiple sclerosis (MS), a progressively disabling disease in which immune cells attack the myelin. To date, there are no therapies to target selectively myelin lesions, repair the myelin or stop MS progression. Small peptides recognizing epitopes selectively exposed at sites of injury show promise for targeting therapeutics in various pathologies. Here we show the selective homing of the four amino acid peptide, cysteine-alanine-lysine glutamine (CAQK), to sites of demyelinating injuries in three different mouse models. Homing was assessed by administering fluorescein amine (FAM)-labeled peptides into the bloodstream of mice and analyzing sites of demyelination in comparison with healthy brain or spinal cord tissue. FAM-CAQK selectively targeted demyelinating areas in all three models and was absent from healthy tissue. At lesion sites, the peptide was primarily associated with the fibrous extracellular matrix (ECM) deposited in interstitial spaces proximal to reactive astrocytes. Association of FAM-CAQK was detected with tenascin-C although tenascin depositions made up only a minor portion of the examined lesion sites. In mice on a 6-week cuprizone diet, FAM-CAQK peptide crossed the nearly intact blood-brain barrier and homed to demyelinating fiber tracts. These results demonstrate the selective targeting of CAQK to demyelinating injuries under multiple conditions and confirm the previously reported association with the ECM. This work sets the stage for further developing CAQK peptide targeting for diagnostic and therapeutic applications aimed at localized myelin repair.

Characterization of Glial Populations in the Aging and Remyelinating Mouse Corpus Callosum

Cells in the white matter of the adult brain have a characteristic distribution pattern in which several cells are contiguously connected to each other, making a linear array (LA) resembling pearls-on-a-string parallel to the axon axis. We have been interested in how this pattern of cell distribution changes during aging and remyelination after demyelination. In the present study, with a multiplex staining method, semi-quantitative analysis of the localization of oligodendrocyte lineage cells (oligodendrocyte progenitors, premyelinating oligodendrocytes, and mature oligodendrocytes), astrocytes, and microglia in 8-week-old (young adult) and 32-week-old (aged) corpus callosum showed that young adult cells still include immature oligodendrocytes and that LAs contain a higher proportion of microglia than isolated cells. In aged mice, premyelinating oligodendrocytes were decreased, but microglia continued to be present in the LAs. These results suggest that the presence of microglia is important for the characteristic cell localization pattern of LAs. In a cuprizone-induced demyelination model, we observed re-formation of LAs after completion of cuprizone treatment, concurrent with remyelination. These re-formed LAs again contained more microglia than the isolated cells. This finding supports the hypothesis that microglia contribute to the formation and maintenance of LAs. In addition, regardless of the distribution of cells (LAs or isolated cells), astrocytes were found to be more abundant than in the normal corpus callosum at 24 weeks after cuprizone treatment when remyelination is completed. This suggests that astrocytes are involved in maintaining the functions of remyelinated white matter.

Effects of Axonal Demyelination, Inflammatory Cytokines and Divalent Cation Chelators on Thalamic HCN Channels and Oscillatory Bursting

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system that is characterized by the progressive loss of oligodendrocytes and myelin and is associated with thalamic dysfunction. Cuprizone (CPZ)-induced general demyelination in rodents is a valuable model for studying different aspects of MS pathology. CPZ feeding is associated with the altered distribution and expression of different ion channels along neuronal somata and axons. However, it is largely unknown whether the copper chelator CPZ directly influences ion channels. Therefore, we assessed the effects of different divalent cations (copper; zinc) and trace metal chelators (EDTA; Tricine; the water-soluble derivative of CPZ, BiMPi) on hyperpolarization-activated cyclic nucleotide-gated (HCN) channels that are major mediators of thalamic function and pathology. In addition, alterations of HCN channels induced by CPZ treatment and MS-related proinflammatory cytokines (IL-1β; IL-6; INF-α; INF-β) were characterized in C57Bl/6J mice. Thus, the hyperpolarization-activated inward current (I_h) was recorded in thalamocortical (TC) neurons and heterologous expression systems (mHCN2 expressing HEK cells; hHCN4 expressing oocytes). A number of electrophysiological characteristics of I_h (potential of half-maximal activation (V_0.5); current density; activation kinetics) were unchanged following the extracellular application of trace metals and divalent cation chelators to native neurons, cell cultures or oocytes. Mice were fed a diet containing 0.2% CPZ for 35 days, resulting in general demyelination in the brain. Withdrawal of CPZ from the diet resulted in rapid remyelination, the effects of which were assessed at three time points after stopping CPZ feeding (Day1, Day7, Day25). In TC neurons, I_h was decreased on Day1 and Day25 and revealed a transient increased availability on Day7. In addition, we challenged naive TC neurons with INF-α and IL-1β. It was found that I_h parameters were differentially altered by the application of the two cytokines to thalamic cells, while IL-1β increased the availability of HCN channels (depolarized V_0.5; increased current density) and the excitability of TC neurons (depolarized resting membrane potential (RMP); increased the number of action potentials (APs); produced a larger voltage sag; promoted higher input resistance; increased the number of burst spikes; hyperpolarized the AP threshold), INF-α mediated contrary effects. The effect of cytokine modulation on thalamic bursting was further assessed in horizontal slices and a computational model of slow thalamic oscillations. Here, IL-1β and INF-α increased and reduced oscillatory bursting, respectively. We conclude that HCN channels are not directly modulated by trace metals and divalent cation chelators but are subject to modulation by different MS-related cytokines.

Astroglial and oligodendroglial markers in the cuprizone animal model for de- and remyelination

Myelin loss with consecutive axon degeneration and impaired remyelination are the underlying causes of progressive disease in patients with multiple sclerosis. Astrocytes are suggested to play a major role in these processes. The unmasking of distinct astrocyte identities in health and disease would help to understand the pathophysiological mechanisms in which astrocytes are involved. However, the number of specific astrocyte markers is limited. Therefore, we performed immunohistochemical studies and analyzed various markers including GFAP, vimentin, S100B, ALDH1L1, and LCN2 during de- and remyelination using the toxic murine cuprizone animal model. Applying this animal model, we were able to confirm overlapping expression of vimentin and GFAP and highlighted the potential of ALDH1L1 as a pan-astrocytic marker, in agreement with previous data. Only a small population of GFAP-positive astrocytes in the corpus callosum highly up-regulated LCN2 at the peak of demyelination and S100B expression was found in a subset of oligodendroglia as well, thus S100B turned out to have a limited use as a particular astroglial marker. Additionally, numerous GFAP-positive astrocytes in the lateral corpus callosum did not express S100B, further strengthening findings of heterogeneity in the astrocytic population. In conclusion, our results acknowledged that GFAP, vimentin, LCN2, and ALDH1L1 serve as reliable marker to identify activated astrocytes during cuprizone-induced de- and remyelination. Moreover, there were clear regional and temporal differences in protein and mRNA expression levels and patterns of the studied markers, generally between gray and white matter structures.

News and Views on Polysialic Acid: From Tumor Progression and Brain Development to Psychiatric Disorders, Neurodegeneration, Myelin Repair and Immunomodulation

Polysialic acid (polySia) is a sugar homopolymer consisting of at least eight glycosidically linked sialic acid units. It is a posttranslational modification of a limited number of proteins with the neural cell adhesion molecule NCAM being the most prominent. As extensively reviewed before, polySia-NCAM is crucial for brain development and synaptic plasticity but also modulates tumor growth and malignancy. Functions of polySia have been attributed to its polyanionic character, its spatial expansion into the extracellular space, and its modulation of NCAM interactions. In this mini-review, we first summarize briefly, how the modulation of NCAM functions by polySia impacts tumor cell growth and leads to malformations during brain development of polySia-deficient mice, with a focus on how the latter may be linked to altered behaviors in the mouse model and to neurodevelopmental predispositions to psychiatric disorders. We then elaborate on the implications of polySia functions in hippocampal plasticity, learning and memory of mice in light of recently described polySia changes related to altered neurogenesis in the aging human brain and in neurodegenerative disease. Furthermore, we highlight recent progress that extends the range of polySia functions across diverse fields of neurobiology such as cortical interneuron development and connectivity, myelination and myelin repair, or the regulation of microglia activity. We discuss possible common and distinct mechanisms that may underlie these seemingly divergent roles of polySia, and provide prospects for new therapeutic approaches building on our improved understanding of polySia functions.

Regenerative Effects of CDP-Choline: A Dose-Dependent Study in the Toxic Cuprizone Model of De- and Remyelination

Inflammatory attacks and demyelination in the central nervous system (CNS) are the key factors responsible for the damage of neurons in multiple sclerosis (MS). Remyelination is the natural regenerating process after demyelination that also provides neuroprotection but is often incomplete or fails in MS. Currently available therapeutics are affecting the immune system, but there is no substance that might enhance remyelination. Cytidine-S-diphosphate choline (CDP-choline), a precursor of the biomembrane component phospholipid phosphatidylcholine was shown to improve remyelination in two animal models of demyelination. However, the doses used in previous animal studies were high (500 mg/kg), and it is not clear if lower doses, which could be applied in human trials, might exert the same beneficial effect on remyelination. The aim of this study was to confirm previous results and to determine the potential regenerative effects of lower doses of CDP-choline (100 and 50 mg/kg). The effects of CDP-choline were investigated in the toxic cuprizone-induced mouse model of de- and remyelination. We found that even low doses of CDP-choline effectively enhanced early remyelination. The beneficial effects on myelin regeneration were accompanied by higher numbers of oligodendrocytes. In conclusion, CDP-choline could become a promising regenerative substance for patients with multiple sclerosis and should be tested in a clinical trial.

Exploratory study on neurochemical effects of low-intensity pulsed ultrasound in brains of mice

There is now a relatively large body of evidence suggesting a relationship between dysfunction of myelin and oligodendrocytes and the etiology of several neuropsychiatric disorders, including depression and schizophrenia, and also suggesting that ultrasound methods may alleviate some of the symptoms of depression. We have applied low-intensity pulsed ultrasound (LIPUS) to the brains of mice treated with the demyelinating drug cuprizone, a drug that has been used as the basis for a rodent model relevant to a number of psychiatric and neurologic disorders including depression, schizophrenia, and multiple sclerosis. Prior to conducting the studies in mice, preliminary studies were carried out on the effects of LIPUS in vitro in neuron-like SH-SY5Y cells and primary glial cells. In subsequent studies in mice, female C57BL/6 mice were restrained in plastic tubes for 20 min daily with the ultrasound transducer near the end of the tube directly above the mouse's head. LIPUS was used at an intensity of 25 mW/cm² once daily for 22 days in control mice and in mice undergoing daily repetitive restraint stress (RRS). Behavioral or neurochemical studies were done on the mice or the brain tissue obtained from them. The studies in vitro indicated that LIPUS stimulation at an intensity of 15 mW/cm² delivered for 5 min daily for 3 days in an enclosed sterile cell culture plate in an incubator increased the viability of SH-SY5Y and primary glial cells. In the studies in mice, LIPUS elevated levels of doublecortin, a marker for neurogenesis, in the cortex compared to levels in the RRS mice and caused a trend in elevation of brain levels of brain-derived neurotrophic factor in the hippocampus relative to control levels. LIPUS also increased sucrose preference (a measure of the attenuation of anhedonia, a common symptom of several psychiatric disorders) in the RRS model in mice. The ability of LIPUS administered daily to rescue damaged myelin and oligodendrocytes was studied in mice treated chronically with cuprizone for 35 days. LIPUS increased cortex and corpus callosum levels of myelin basic protein, a protein marker for mature oligodendrocytes, and neural/glial antigen 2, a protein marker for oligodendrocyte precursor cells, relative to levels in the cuprizone + sham animals. These results of this exploratory study suggest that future comprehensive time-related studies with LIPUS on brain chemistry and behavior related to neuropsychiatric disorders are warranted. Exploratory Study on Neurochemical Effects of Low Intensity Pulsed Ultrasound in Brains of Mice. Upper part of figure: LIPUS device and in-vitro cell experimental set-up. The center image is the LIPUS generating box; the image in the upper left shows the cell experiment set-up; the image in the upper right shows a zoomed-in sketch for the cell experiment; the image in the lower left shows the set-up of repetitive restraint stress (RRS) with a mouse; the image in the lower middle shows the set-up of LIPUS treatment of a mouse; the image in the lower right shows a zoomed-in sketch for the LIPUS treatment of a mouse.

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.

Effect and Mechanism of Catalpol on Remyelination via Regulation of the NOTCH1 Signaling Pathway

Promoting the differentiation of oligodendrocyte precursor cells (OPCs) is important for fostering remyelination in multiple sclerosis. Catalpol has the potential to promote remyelination and exert neuroprotective effects, but its specific mechanism is still unclear. Recent studies have shown that the NOTCH1 signaling pathway is involved in mediating OPC proliferation and differentiation. In this study, we elucidated that catalpol promoted OPC differentiation in vivo and vitro and explored the regulatory role of catalpol in specific biomolecular processes. Following catalpol administration, better and faster recovery of body weight and motor balance was observed in mice with cuprizone (CPZ)-induced demyelination. Luxol fast blue staining (LFB) and transmission electron microscopy (TEM) showed that catalpol increased the myelinated area and improved myelin ultrastructure in the corpus callosum in demyelinated mice. In addition, catalpol enhanced the expression of CNPase and MBP, indicating that it increased OPC differentiation. Additionally, catalpol downregulated the expression of NOTCH1 signaling pathway-related molecules, such as JAGGED1, NOTCH1, NICD1, RBPJ, HES5, and HES1. We further demonstrated that in vitro, catalpol enhanced the differentiation of OPCs into OLs and inhibited NOTCH1 signaling pathway activity. Our data suggested that catalpol may promote OPC differentiation and remyelination through modulation of the NOTCH1 pathway. This study provides new insight into the mechanism of action of catalpol in the treatment of multiple sclerosis.

Deciphering the heterogeneity of myeloid cells during neuroinflammation in the single-cell era

Multiple sclerosis (MS) is a disabling neuroinflammatory disease, which is little understood and lacks a sufficient therapeutic regimen. Myeloid cells have repeatedly shown to play a pivotal role in the disease progression. During homeostasis, only the CNS‐resident microglia and CNS‐associated macrophages are present in the CNS. Neuroinflammation causes peripheral immune cells to infiltrate the CNS contributing to disease progression and neurological sequelae. The differential involvement of the diverse peripheral and resident myeloid cell subsets to the disease pathogenesis and outcome are highly debated and difficult to assess. However, novel technological advances (new mouse models, single‐cell RNA‐Sequencing, and CYTOF) have improved the depth of immune profiling, which allows the characterization of distinct myeloid subsets. This review provides an overview of current knowledge on the phenotypes and roles of these different myeloid subsets in neuroinflammatory disease and their therapeutic relevance.

Ferroptosis Mediates Cuprizone-Induced Loss of Oligodendrocytes and Demyelination

Multiple sclerosis (MS) is a chronic demyelinating disease of the CNS. Cuprizone (CZ), a copper chelator, is widely used to study demyelination and remyelination in the CNS, in the context of MS. However, the mechanisms underlying oligodendrocyte (OL) cell loss and demyelination are not known. As copper-containing enzymes play important roles in iron homeostasis and controlling oxidative stress, we examined whether chelating copper leads to disruption of molecules involved in iron homeostasis that can trigger iron-mediated OL loss. We show that giving mice (male) CZ in the diet induces rapid loss of OL in the corpus callosum by 2 d, accompanied by expression of several markers for ferroptosis, a relatively newly described form of iron-mediated cell death. In ferroptosis, iron-mediated free radicals trigger lipid peroxidation under conditions of glutathione insufficiency, and a reduced capacity to repair lipid damage. This was further confirmed using a small-molecule inhibitor of ferroptosis that prevents CZ-induced loss of OL and demyelination, providing clear evidence of a copper-iron connection in CZ-induced neurotoxicity. This work has wider implications for disorders, such as multiple sclerosis and CNS injury.SIGNIFICANCE STATEMENT Cuprizone (CZ) is a copper chelator that induces demyelination. Although it is a widely used model to study demyelination and remyelination in the context of multiple sclerosis, the mechanisms mediating demyelination is not fully understood. This study shows, for the first time, that CZ induces demyelination via ferroptosis-mediated rapid loss of oligodendrocytes. This work shows that chelating copper with CZ leads to the expression of molecules that rapidly mobilize iron from ferritin (an iron storage protein), that triggers iron-mediated lipid peroxidation and oligodendrocyte loss (via ferroptosis). Such rapid mobilization of iron from cellular stores may also play a role in cell death in other neurologic conditions.

Effects of Lactobacillus casei Strain T2 (IBRC-M10783) on the Modulation of Th17/Treg and Evaluation of miR-155, miR-25, and IDO-1 Expression in a Cuprizone-Induced C57BL/6 Mouse Model of Demyelination

Multiple sclerosis (MS) is a complex inflammatory disease in which demyelination occurs in the central nervous system affecting approximately 2.5 million people worldwide. Recent reports have shown that the gut microbiome plays a crucial role in the functioning of the immune system in inflammatory diseases such as MS. In this study, the cuprizone-induced demyelination mouse model was used to investigate the effect of Lactobacillus casei strain T2 (IBRC-M10783) on the alleviation of these mice. Female C57BL/6 mice (8-10 weeks old) were divided into 6 groups: group 1, normal control; group 2, cuprizone control (oral administration of cuprizone 0.2% w/w for 4 weeks); group 3, probiotic control (oral administration of 1 × 10⁹ CFU/ml probiotic for 4 weeks); group 4, treatment 1 (probiotic for 4 weeks then cuprizone for 4 weeks); group 5, treatment 2 (cuprizone for 4 weeks then probiotic for 4 weeks); and group 6, treatment 3 (cuprizone for 4 weeks then probiotic for 4 weeks with vitamin D₃ at a dose of 20 IU/day). Then, TGF-β and IL-17 were measured by ELISA, and the expression of miR-155, miR-25, and IDO-1 was evaluated by real-time PCR. Among the measured microRNAs, the results showed that there was a significant decrease in miR-155 expression between the treatment 1 group and the cuprizone group. In the case of IL-17, the results also showed a significant reduction between the three treatment groups and the cuprizone group. These observations suggest that L. casei can reduce proinflammatory cytokines and reduce demyelinating symptoms in the mouse model.

The Protective Effect of Kolaviron on Molecular, Cellular, and Behavioral Characterization of Cerebellum in the Rat Model of Demyelinating Diseases

INTRODUCTION

This study aimed at assessing the protective mechanisms of Kolaviron (KV) on the cerebellum in a rat model of demyelination.

METHODS

Twenty-eight male Wistar rats were used in the present study. They were randomly divided into 4 groups of 7 rats. Group A (control) received corn oil (0.5 mL/kg/d); group B received 0.2% Cuprizone (CPZ); group C was treated with 200 mg/kg/d of KV, and group D received 0.2% CPZ and 200 mg/kg/d KV for 6 weeks. CPZ powder was mixed with the regular diet while KV was dissolved in corn oil and administered orally. A behavioral test was conducted at the termination of the experiment. Thereafter, the animals were sacrificed and their brains were removed with the excision of the cerebellum. A part of the cerebelli underwent tissue processing with a series of 5 μm thick sections cut from paraffin blocks for histological and immunohistochemical assessment. Besides, the remaining cerebellar tissues were homogenized for the spectrophotometric assays of Oxidative Stress (OS) parameters.

RESULTS

The current research findings revealed minimal weight gain following CPZ treatment, but significant weight increase in KV-treated rats. CPZ treatment was associated with a reduction in the number of the line crossed, rearing frequency, rearing duration, center square entry, and center square duration; however, it increased the freezing time, i.e. significantly reversed in the KV-treated animals. Oxidative markers, such as Superoxide Dismutase (SOD) and GPx were reduced in CPZ-treated rats with elevated MDA levels. However, these data were significantly reversed by the co-administration of CPZ and KV. At the tissue level, the cerebellar cortex was characterized by poorly defined layers, cryptic granules, as well as chromatolysis and pyknotic Purkinje cells with the evidence of hypertrophic astrogliosis.

CONCLUSION

CPZ treatment significantly depressed locomotor and exploratory activities. Furthermore, it increased OS and cerebellar toxicity. However, KV intervention significantly enhanced behavioral functions and ameliorated CPZ-induced cerebellar degeneration. Moreover, it considerably regulated OS markers in the cerebellum of the rat model of demyelinating diseases.

Raman Probes for In Situ Molecular Analyses of Peripheral Nerve Myelination

The myelinating activity of living Schwann cells in coculture with neuronal cells was examined in situ in a Raman microprobe spectroscope. The Raman label-free approach revealed vibrational fingerprints directly related to the activity of Schwann cells' metabolites and identified molecular species peculiar to myelinating cells. The identified chemical species included antioxidants, such as hypotaurine and glutathione, and compartmentalized water, in addition to sphingolipids, phospholipids, and nucleoside triphosphates also present in neuronal and nonmyelinating Schwann cells. Raman maps at specific frequencies could be collected, which clearly visualized the myelinating action of Schwann cells and located the demyelinated ones. An important finding was the spectroscopic visualization of confined water in the myelin structure, which exhibited a quite pronounced Raman signal at ∼3470 cm^-1. This peculiar signal, whose spatial location precisely corresponded to a low-frequency fingerprint of hypotaurine, was absent in unmyelinating cells and in bulk water. Raman enhancement was attributed to frustration in the hydrogen-bond network as induced by interactions with lipids in the myelin sheaths. According to a generally accepted morphological model of myelin, an explanation was offered of the peculiar Raman scattering of water confined in intraperiod lines, according to an ordered hydrogen bonding structure. The possibility of concurrently mapping antioxidant molecules and compartmentalized water structure with high spectral accuracy and microscopic spatial resolution enables probing myelinating activity and might play a key-role in future studies of neuronal pathologies. Compatible with life, Raman microprobe spectroscopy with the newly discovered probes could be suitable for developing advanced strategies in the reconstruction of injured nerves and nerve terminals at neuromuscular junctions.

Myelination- and immune-mediated MR-based brain network correlates

Background

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS), characterized by inflammatory and neurodegenerative processes. Despite demyelination being a hallmark of the disease, how it relates to neurodegeneration has still not been completely unraveled, and research is still ongoing into how these processes can be tracked non-invasively. Magnetic resonance imaging (MRI) derived brain network characteristics, which closely mirror disease processes and relate to functional impairment, recently became important variables for characterizing immune-mediated neurodegeneration; however, their histopathological basis remains unclear.

Methods

In order to determine the MRI-derived correlates of myelin dynamics and to test if brain network characteristics derived from diffusion tensor imaging reflect microstructural tissue reorganization, we took advantage of the cuprizone model of general demyelination in mice and performed longitudinal histological and imaging analyses with behavioral tests. By introducing cuprizone into the diet, we induced targeted and consistent demyelination of oligodendrocytes, over a period of 5 weeks. Subsequent myelin synthesis was enabled by reintroduction of normal food.

Results

Using specific immune-histological markers, we demonstrated that 2 weeks of cuprizone diet induced a 52% reduction of myelin content in the corpus callosum (CC) and a 35% reduction in the neocortex. An extended cuprizone diet increased myelin loss in the CC, while remyelination commenced in the neocortex. These histologically determined dynamics were reflected by MRI measurements from diffusion tensor imaging. Demyelination was associated with decreased fractional anisotropy (FA) values and increased modularity and clustering at the network level. MRI-derived modularization of the brain network and FA reduction in key anatomical regions, including the hippocampus, thalamus, and analyzed cortical areas, were closely related to impaired memory function and anxiety-like behavior.

Conclusion

Network-specific remyelination, shown by histology and MRI metrics, determined amelioration of functional performance and neuropsychiatric symptoms. Taken together, we illustrate the histological basis for the MRI-driven network responses to demyelination, where increased modularity leads to evolving damage and abnormal behavior in MS. Quantitative information about in vivo myelination processes is mirrored by diffusion-based imaging of microstructural integrity and network characteristics.

Loss of TMEM106B leads to myelination deficits: implications for frontotemporal dementia treatment strategies

Genetic variants that define two distinct haplotypes at the TMEM106B locus have been implicated in multiple neurodegenerative diseases and in healthy brain ageing. In frontotemporal dementia (FTD), the high expressing TMEM106B risk haplotype was shown to increase susceptibility for FTD with TDP-43 inclusions (FTD-TDP) and to modify disease penetrance in progranulin mutation carriers (FTD-GRN). To elucidate the biological function of TMEM106B and determine whether lowering TMEM106B may be a viable therapeutic strategy, we performed brain transcriptomic analyses in 8-month-old animals from our recently developed Tmem106b-/- mouse model. We included 10 Tmem106b+/+ (wild-type), 10 Tmem106b+/- and 10 Tmem106-/- mice. The most differentially expressed genes (153 downregulated and 60 upregulated) were identified between Tmem106b-/- and wild-type animals, with an enrichment for genes implicated in myelination-related cellular processes including axon ensheathment and oligodendrocyte differentiation. Co-expression analysis also revealed that the most downregulated group of correlated genes was enriched for myelination-related processes. We further detected a significant loss of OLIG2-positive cells in the corpus callosum of Tmem106b-/- mice, which was present already in young animals (21 days) and persisted until old age (23 months), without worsening. Quantitative polymerase chain reaction revealed a reduction of differentiated but not undifferentiated oligodendrocytes cellular markers. While no obvious changes in myelin were observed at the ultrastructure levels in unchallenged animals, treatment with cuprizone revealed that Tmem106b-/- mice are more susceptible to cuprizone-induced demyelination and have a reduced capacity to remyelinate, a finding which we were able to replicate in a newly generated Tmem106b CRISPR/cas9 knock-out mouse model. Finally, using a TMEM106B HeLa knock-out cell line and primary cultured oligodendrocytes, we determined that loss of TMEM106B leads to abnormalities in the distribution of lysosomes and PLP1. Together these findings reveal an important function for TMEM106B in myelination with possible consequences for therapeutic strategies aimed at lowering TMEM106B levels.

Delayed Demyelination and Impaired Remyelination in Aged Mice in the Cuprizone Model

To unravel the failure of remyelination in multiple sclerosis (MS) and to test promising remyelinating treatments, suitable animal models like the well-established cuprizone model are required. However, this model is only standardized in young mice. This does not represent the typical age of MS patients. Furthermore, remyelination is very fast in young mice, hindering the examination of effects of remyelination-promoting agents. Thus, there is the need for a better animal model to study remyelination. We therefore aimed to establish the cuprizone model in aged mice. 6-month-old C57BL6 mice were fed with different concentrations of cuprizone (0.2–0.6%) for 5–6.5 weeks. De- and remyelination in the medial and lateral parts of the corpus callosum were analyzed by immunohistochemistry. Feeding aged mice 0.4% cuprizone for 6.5 weeks resulted in the best and most reliable administration scheme with virtually complete demyelination of the corpus callosum. This was accompanied by a strong accumulation of microglia and near absolute loss of mature oligodendrocytes. Subsequent remyelination was initially robust but remained incomplete. The remyelination process in mature adult mice better represents the age of MS patients and offers a better model for the examination of regenerative therapies.

The effect of the demyelinating agent cuprizone on binge-like eating of sweetened palatable food in female and male C57BL/6 substrains

Binge eating is a heritable symptom of eating disorders with an unknown genetic etiology. Rodent models for binge-like eating (BLE) of palatable food permit the study of genetic and biological mechanisms. We previously genetically mapped a coding mutation in Cyfip2 associated with increased BLE of sweetened palatable food in the C57BL/6NJ versus C57BL/6J substrain. The increase in BLE in C57BL/6NJ mice was associated with a decrease in transcription of genes enriched for myelination in the striatum. Here, we tested the hypothesis that decreasing myelin levels with the demyelinating agent cuprizone would enhance BLE. Mice were treated with a 0.3% cuprizone home cage diet for two weeks. Cuprizone induced similar weight loss in both substrains and sexes that recovered within 48 h after removal of cuprizone. Following a three-week recovery period, mice were trained for BLE in an intermittent, limited access procedure. Surprisingly, cuprizone significantly reduced BLE in male but not female C57BL/6NJ mice while having no effect in C57BL/6J mice. Cuprizone also reduced myelin basic protein (MBP) at seven weeks post-cuprizone removal while having no effect on myelin-associated glycoprotein at this time point. C57BL/6NJ mice also showed less MBP than C57BL/6J mice. There were no statistical interactions of Treatment with Sex on MBP levels, indicating that differences in MBP reduction are unlikely to account for sex differences in BLE. To summarize, cuprizone induced an unexpected, significant reduction in BLE in C57BL/6NJ males, which could indicate genotype-dependent sex differences in the biological mechanisms of BLE.

CD8 T-cell Recruitment Into the Central Nervous System of Cuprizone-Fed Mice: Relevance to Modeling the Etiology of Multiple Sclerosis

Cuprizone (CPZ)-feeding in mice induces atrophy of peripheral immune organs (thymus and spleen) and suppresses T-cell levels, thereby limiting its use as a model for studying the effects of the immune system in demyelinating diseases such as Multiple Sclerosis (MS). To investigate whether castration (Cx) can protect the peripheral immune organs from CPZ-induced atrophy and enable T-cell recruitment into the central nervous system (CNS) following a breach of the blood-brain barrier (BBB), three related studies were carried out. In Study 1, Cx prevented the dose-dependent reductions (0.1% < 0.2% CPZ) in thymic and splenic weight, size of the thymic medulla and splenic white pulp, and CD4 and CD8 (CD4/8) levels remained comparable to gonadally intact (Gi) control males. Importantly, 0.1% and 0.2% CPZ were equipotent at inducing central demyelination and glial activation. In Study 2, combining Cx with 0.1% CPZ-feeding and BBB disruption with pertussis toxin (PT) enhanced CD8⁺ T-cell recruitment into the CNS. The increased CD8⁺ T-cell level observed in the parenchyma of the cerebrum, cerebellum, brainstem and spinal cord were confirmed by flow cytometry and western blot analyses of CNS tissue. In Study 3, PT+0.1% CPZ-feeding to Gi female mice resulted in similar effects on the peripheral immune organs, CNS demyelination, and gliosis comparable to Gi males, indicating that testosterone levels alone were not responsible for the immune response seen in Study 2. The combination of Cx+0.1% CPZ-feeding+PT indicates that CPZ-induced demyelination can trigger an “inside-out” immune response when the peripheral immune system is spared and may provide a better model to study the initiating events in demyelinating conditions such as MS.

The active contribution of OPCs to neuroinflammation is mediated by LRP1

Oligodendrocyte progenitor cells (OPCs) account for about 5% of total brain and spinal cord cells, giving rise to myelinating oligodendrocytes that provide electrical insulation to neurons of the CNS. OPCs have also recently been shown to regulate inflammatory responses and glial scar formation, suggesting functions that extend beyond myelination. Low-density lipoprotein receptor-related protein 1 (LRP1) is a multifaceted phagocytic receptor that is highly expressed in several CNS cell types, including OPCs. Here, we have generated an oligodendroglia-specific knockout of LRP1, which presents with normal myelin development, but is associated with better outcomes in two animal models of demyelination (EAE and cuprizone). At a mechanistic level, LRP1 did not directly affect OPC differentiation into mature oligodendrocytes. Instead, animals lacking LRP1 in OPCs in the demyelinating CNS were characterized by a robust dampening of inflammation. In particular, LRP1-deficient OPCs presented with impaired antigen cross-presentation machinery, suggesting a failure to propagate the inflammatory response and thus promoting faster myelin repair and neuroprotection. Our study places OPCs as major regulators of neuroinflammation in an LRP1-dependent fashion.

Imaging and Quantification of Myelin Integrity After Injury With Spectral Confocal Reflectance Microscopy

Developing a high-throughput approach to quantify the extent of myelin integrity in preclinical models of demyelinating diseases will enhance our capacity to identify novel therapies for myelin repair. In light of the technical limitations of electron microscopy and immunohistochemical analyses of myelination, we have utilized a novel imaging technique, spectral confocal reflectance (SCoRe) microscopy. SCoRe takes advantage of the optically reflective properties of compact myelin, allowing the integrity of compact myelin to be quantified over the course of the cuprizone-induced model of central demyelination. We applied SCoRe imaging on fixed frozen brain sections. SCoRe analysis of control mice identified an increase in corpus callosum myelination during the period of cuprizone administration and recovery, suggesting that the normal developmental processes of myelination are ongoing at this time. Importantly, analysis of mice subjected to cuprizone identified a significant reduction in compact myelin in both rostral and caudal corpus callosum compared to age-matched control mice. SCoRe microscopy also allowed the visualization and quantification of the amount of myelin debris in demyelinating lesions. Combining SCoRe imaging with immunohistochemistry, we quantified the amount of myelin debris within IBA-1+ microglia and found that 11% of myelin debris colocalized in microglia irrespective of the callosal regions, with the vast majority of debris outside of microglia. In summary, we have demonstrated that SCoRe microscopy is an effective and powerful tool to perform both quantitative and qualitative analyses of compact myelin integrity in health or after injury in vivo, demonstrating its future application in high-throughput assessments and screening of the therapeutic efficacy of myelin repair therapies in preclinical animal models of demyelinating diseases.

The emerging role of galectins in (re)myelination and its potential for developing new approaches to treat multiple sclerosis

Multiple sclerosis (MS) is an inflammatory, demyelinating and neurodegenerative disease of the central nervous system with unknown etiology. Currently approved disease-modifying treatment modalities are immunomodulatory or immunosuppressive. While the applied drugs reduce the frequency and severity of the attacks, their efficacy to regenerate myelin membranes and to halt disease progression is limited. To achieve such therapeutic aims, understanding biological mechanisms of remyelination and identifying factors that interfere with remyelination in MS can give respective directions. Such a perspective is given by the emerging functional profile of galectins. They form a family of tissue lectins, which are potent effectors in processes as diverse as adhesion, apoptosis, immune mediator release or migration. This review focuses on endogenous and exogenous roles of galectins in glial cells such as oligodendrocytes, astrocytes and microglia in the context of de- and (re)myelination and its dysregulation in MS. Evidence is arising for a cooperation among family members so that timed expression and/or secretion of galectins-1, -3 and -4 result in modifying developmental myelination, (neuro)inflammatory processes, de- and remyelination. Dissecting the mechanisms that underlie the distinct activities of galectins and identifying galectins as target or tool to modulate remyelination have the potential to contribute to the development of novel therapeutic strategies for MS.

Quantitative Imaging of White and Gray Matter Remyelination in the Cuprizone Demyelination Model Using the Macromolecular Proton Fraction

Macromolecular proton fraction (MPF) has been established as a quantitative clinically-targeted MRI myelin biomarker based on recent demyelination studies. This study aimed to assess the capability of MPF to quantify remyelination using the murine cuprizone-induced reversible demyelination model. MPF was measured in vivo using the fast single-point method in three animal groups (control, cuprizone-induced demyelination, and remyelination after cuprizone withdrawal) and compared to quantitative immunohistochemistry for myelin basic protein (MBP), myelinating oligodendrocytes (CNP-positive cells), and oligodendrocyte precursor cells (OPC, NG2-positive cells) in the corpus callosum, caudate putamen, hippocampus, and cortex. In the demyelination group, MPF, MBP-stained area, and oligodendrocyte count were significantly reduced, while OPC count was significantly increased as compared to both control and remyelination groups in all anatomic structures (p < 0.05). All variables were similar in the control and remyelination groups. MPF and MBP-stained area strongly correlated in each anatomic structure (Pearson’s correlation coefficients, r = 0.80–0.90, p < 0.001). MPF and MBP correlated positively with oligodendrocyte count (r = 0.70–0.84, p < 0.01 for MPF; r = 0.81–0.92, p < 0.001 for MBP) and negatively with OPC count (r = −0.69–−0.77, p < 0.01 for MPF; r = −0.72–−0.89, p < 0.01 for MBP). This study provides immunohistological validation of fast MPF mapping as a non-invasive tool for quantitative assessment of de- and remyelination in white and gray matter and indicates the feasibility of using MPF as a surrogate marker of reparative processes in demyelinating diseases.

Effects of enhanced environment and induced depression on cuprizone mouse model of demyelination

Impairment in cognition and motor activity are commonly encountered in patients affected by multiple sclerosis (MS), and depression is believed to be a contributing factor. The aim of the present study was to investigate the impact of induced depression on a cuprizone mouse model of demyelination and the effectiveness of enhanced environment (EE) as a method of intervention. C57BL/6 male mice were divided into five groups: Cuprizone only (Cup-O), cuprizone undergoing depression (Cup-Dep), cuprizone housed in EE (Cup-EE), cuprizone housed in EE and undergoing depression (Cup-ED) and the control (n=9-10 per group). Depression was induced by repeated open-space forced swim. Neurobehavioral tests were conducted following a 6-week period of 0.2% cuprizone-enriched diet. The Cup-EE group performed significantly better in terms of cognition and motor functions, when compared with the Cup-O group, as evidenced by the Morris water maze (MWM; P<0.001) and rotarod performance test (P<0.05) results. Conversely, the Cup-Dep group exhibited a significant decline in performance in the MWM (P<0.001) and rotarod performance test (P<0.05), when compared with the Cup-O group. The Cup-ED group had comparable results to those of the Cup-O group, indicating a reversal of the induced depression effects. Open field test results failed to show an anxiety-like behavior in the cuprizone mouse model. It was therefore concluded that EE can improve MS-associated cognitive and motor deficits. Insights gained from these results facilitate the exploration of non-medical modes of intervention as an emerging adjuvant therapy in MS.

Structural adaption of axons during de- and remyelination in the Cuprizone mouse model

Multiple Sclerosis is an autoimmune disorder causing neurodegeneration mostly in young adults. Thereby, myelin is lost in the inflammatory lesions leaving unmyelinated axons at a high risk to degenerate. Oligodendrocyte precursor cells maintain their regenerative capacity into adulthood and are able to remyelinate axons if they are properly activated and differentiate. Neuronal activity influences the success of myelination indicating a close interplay between neurons and oligodendroglia. The myelination profile determines the distribution of voltage-gated ion channels along the axon. Here, we analyze the distribution of the sodium channel subunit Nav1.6 and the ultrastructure of axons after cuprizone-induced demyelination in transgenic mice expressing GFP in oligodendroglial cells. Using this mouse model, we found an increased number of GFP-expressing oligodendroglial cells compared to untreated mice. Analyzing the axons, we found an increase in the number of nodes of Ranvier in mice that had received cuprizone. Furthermore, we found an enhanced portion of unmyelinated axons showing vesicles in the cytoplasm. These vesicles were labeled with VGlut1, indicating that they are involved in axonal signaling. Our results highlight the flexibility of axons towards changes in the glial compartment and depict the structural changes they undergo upon myelin removal. These findings might be considered if searching for new neuroprotective therapies that aim at blocking neuronal activity in order to avoid interfering with the process of remyelination.

Astrocyte ablation induced by La-aminoadipate (L-AAA) potentiates remyelination in a cuprizone demyelinating mouse model

Chronic demyelination in the central nervous system (CNS) is accompanied by an increase in the number of reactive astrocytes and astrogliosis. There are controversial issues regarding astrocytes and their roles in demyelinating diseases in particular for multiple sclerosis (MS). We aimed to evaluate possible roles for pharmacologic astrocyte ablation strategy using La-aminoadipate (L-AAA) on remyelination in a cuprizone model of demyelination. Male C57BL/6 mice were fed with 0.2% cuprizone for 12 weeks followed by 2-week administration of L-AAA through a cannula inserted 1 mm above the corpus callosum. Rotarod test showed a significant decrease in the range of motor coordination deficits after ablation of astrocytes in mice receiving cuprizone. Results of Luxol fast blue (LFB) and transmission electron microscopy (TEM) for evaluation of myelin content within the corpus callosum revealed a noticeable rise in the percentage of myelinated areas and in the number of myelinated fibers after L-AAA administration in the animals. Astrocyte ablation reduced protein expressions for GFAP (an astrocyte marker) and Iba-1 (a microglial marker), but increased expression of Olig2 (an oligodendrocyte marker) assessed by immunofluorescence. Finally, expression of genes related to recruitment of microglia (astrocyte chemokines CXCL10 and CXCL12) and suppression of oligodendrocyte progenitor cell (OPC) differentiation (astrocyte peptides ET-1 and EDNRB) showed a considerable decrease after administration of L-AAA (for all p < 0.05). These results are indicative of improved remyelination after ablation of astrocytes possibly through hampering microgliosis and astrogliosis and a further rise in the number of matured Olig2⁺ cells.

Genetic Elimination of Connective Tissue Growth Factor in the Forebrain Affects Subplate Neurons in the Cortex and Oligodendrocytes in the Underlying White Matter

Connective tissue growth factor (CTGF) is a secreted extracellular matrix-associated protein, which play a role in regulating various cellular functions. Although the expression of CTGF has been reported in the cortical subplate, its function is still not clear. Thus, to explore the significance of CTGF in the brain, we created a forebrain-specific Ctgf knockout (FbCtgf KO) mouse model. By crossing Ctgf^fl/fl mice with Emx1-Cre transgenic mice, in which the expression of Cre is prenatally initiated, the full length Ctgf is removed in the forebrain structures. In young adult (2–3 months old) FbCtgf KO mice, subplate markers such as Nurr1 and Cplx3 are still expressed in the cortical layer VIb; however, the density of the subplate neurons is increased. Interestingly, in these mutants, we found a reduced structural complexity in the subplate neurons. The distribution patterns of neurons and glial cells, examined by immunohistochemistry, are comparable between genotypes in the somatosensory cortex. However, increased densities of mature oligodendrocytes, but not immature ones, were noticed in the external capsule underneath the cortical layer VIb in young adult FbCtgf KO mice. The features of myelinated axons in the external capsule were then examined using electron microscopy. Unexpectedly, the thickness of the myelin sheath was reduced in middle-aged (>12 months old), but not young adult FbCtgf KO mice. Our results suggest a secretory function of the subplate neurons, through the release of CTGF, which regulates the density and dendritic branching of subplate neurons as well as the maturation and function of nearby oligodendrocytes in the white matter.

Connexin 43/47 channels are important for astrocyte/ oligodendrocyte cross-talk in myelination and demyelination

The gap junctions (GJs), which form intercellular communicating channels between two apposing cells or form hemichannel with extracellular environment, perform crucial functions to maintain small molecule homeostasis. The central nervous system (CNS) GJs are important for maintenance of myelin sheath and neuronal activity. Connexin (Cx) proteins are building blocks of GJs. Recent cell-biological investigations show that amongst the CNS specific Cxs, the most abundant Cx protein, Cx43 and its oligodendrocytic coupling partner Cx47 primarily important for maintenance of CNS myelin. Recent investigations elucidate that the expression of Cx43 and Cx47 is very important to maintain K+ buffering and nutrient homeostasis in oligodendrocytes, CNS myelin and oligodendrocyte function. The investigations on Multiple Sclerosis (MS) patient samples and EAE hypothesized that the functional loss of Cx43/Cx47 could be associated with spread of chronic MS lesions. Exploring the mechanism of initial GJ alteration and its effect on demyelination in this model of MS might play a primary role to understand the basis of altered CNS homeostasis, observed during MS. In this review, we mainly discuss the role of CNS GJs, specifically the Cx43/Cx47 axis in the perspective of demyelination.

Interferon β-Mediated Protective Functions of Microglia in Central Nervous System Autoimmunity

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) leading to demyelination and axonal damage. It often affects young adults and can lead to neurological disability. Interferon β (IFNβ) preparations represent widely used treatment regimens for patients with relapsing-remitting MS (RRMS) with therapeutic efficacy in reducing disease progression and frequency of acute exacerbations. In mice, IFNβ therapy has been shown to ameliorate experimental autoimmune encephalomyelitis (EAE), an animal model of MS while genetic deletion of IFNβ or its receptor augments clinical severity of disease. However, the complex mechanism of action of IFNβ in CNS autoimmunity has not been fully elucidated. Here, we review our current understanding of the origin, phenotype, and function of microglia and CNS immigrating macrophages in the pathogenesis of MS and EAE. In addition, we highlight the emerging roles of microglia as IFNβ-producing cells and vice versa the impact of IFNβ on microglia in CNS autoimmunity. We finally discuss recent progress in unraveling the underlying molecular mechanisms of IFNβ-mediated effects in EAE.

Five Decades of Cuprizone, an Updated Model to Replicate Demyelinating Diseases

INTRODUCTION

Demyelinating diseases of the central nervous system (CNS) comprise a group of neurological disorders characterized by progressive (and eventually irreversible) loss of oligodendrocytes and myelin sheaths in the white matter tracts. Some of myelin disorders include: Multiple sclerosis, Guillain-Barré syndrome, peripheral nerve polyneuropathy and others. To date, the etiology of these disorders is not well known and no effective treatments are currently available against them. Therefore, further research is needed to gain a better understand and treat these patients. To accomplish this goal, it is necessary to have appropriate animal models that closely resemble the pathophysiology and clinical signs of these diseases. Herein, we describe the model of toxic demyelination induced by cuprizone (CPZ), a copper chelator that reduces the cytochrome and monoamine oxidase activity into the brain, produces mitochondrial stress and triggers the local immune response. These biochemical and cellular responses ultimately result in selective loss of oligodendrocytes and microglia accumulation, which conveys to extensive areas of demyelination and gliosis in corpus callosum, superior cerebellar peduncles and cerebral cortex. Remarkably, some aspects of the histological pattern induced by CPZ are similar to those found in multiple sclerosis. CPZ exposure provokes behavioral changes, impairs motor skills and affects mood as that observed in several demyelinating diseases. Upon CPZ removal, the pathological and histological changes gradually revert. Therefore, some authors have postulated that the CPZ model allows to partially mimic the disease relapses observed in some demyelinating diseases.

CONCLUSION

for five decades, the model of CPZ-induced demyelination is a good experimental approach to study demyelinating diseases that has maintained its validity, and is a suitable pharmacological model for reproducing some key features of demyelinating diseases, including multiple sclerosis.

Brain-Derived Neurotrophic Factor in Central Nervous System Myelination: A New Mechanism to Promote Myelin Plasticity and Repair

Brain-derived neurotrophic factor (BDNF) plays vitally important roles in neural development and plasticity in both health and disease. Recent studies using mutant mice to selectively manipulate BDNF signalling in desired cell types, in combination with animal models of demyelinating disease, have demonstrated that BDNF not only potentiates normal central nervous system myelination in development but enhances recovery after myelin injury. However, the precise mechanisms by which BDNF enhances myelination in development and repair are unclear. Here, we review some of the recent progress made in understanding the influence BDNF exerts upon the myelinating process during development and after injury, and discuss the cellular and molecular mechanisms underlying its effects. In doing so, we raise new questions for future research.

Connexin 43/47 channels are important for astrocyte/ oligodendrocyte cross-talk in myelination and demyelination

The gap junctions (GJs), which form intercellular communicating channels between two apposing cells or form hemichannel with extracellular environment, perform crucial functions to maintain small molecule homeostasis. The central nervous system (CNS) GJs are important for maintenance of myelin sheath and neuronal activity. Connexin (Cx) proteins are building blocks of GJs. Recent cell-biological investigations show that amongst the CNS specific Cxs, the most abundant Cx protein, Cx43 and its oligodendrocytic coupling partner Cx47 primarily important for maintenance of CNS myelin. Recent investigations elucidate that the expression of Cx43 and Cx47 is very important to maintain K? buffering and nutrient homeostasis in oligodendrocytes, CNS myelin and oligodendrocyte function. The investigations on Multiple Sclerosis (MS) patient samples and EAE hypothesized that the functional loss of Cx43/Cx47 could be associated with spread of chronic MS lesions. Exploring the mechanism of initial GJ alteration and its effect on demyelination in this model of MS might play a primary role to understand the basis of altered CNS homeostasis, observed during MS. In this review, we mainly discuss the role of CNS GJs, specifically the Cx43/Cx47 axis in the perspective of demyelination.

TRPV4 Inhibition Improved Myelination and Reduced Glia Reactivity and Inflammation in a Cuprizone-Induced Mouse Model of Demyelination

The inhibition of demyelination and the promotion of remyelination are both considerable challenges in the therapeutic process for many central nervous system (CNS) diseases. Increasing evidence has demonstrated that neuroglial activation and neuroinflammation are responsible for myelin sheath damage during demyelinating disorders. It has been revealed that the nonselective cation channel transient receptor potential vanilloid 4 (TRPV4) profoundly affects a variety of physiological processes, including inflammation. However, its roles and mechanisms in demyelination have remained unclear. Here, for the first time, we found that there was a significant increase in TRPV4 in the corpus callosum in a demyelinated mouse model induced by cuprizone (CPZ). RN-1734, a TRPV4-antagonist, clearly alleviated demyelination and inhibited glial activation and the production of tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β) without altering the number of olig2-positive cells. In vitro, RN-1734 treatment clearly inhibited the influx of calcium and decreased the levels of IL-1β and TNF-α in lipopolysaccharide (LPS)-activated microglial cells by suppressing NF-κB P65 phosphorylation. Apoptosis of oligodendrocyte induced by LPS-activated microglia was also alleviated by RN-1734. The results suggest that activation of TRPV4 in microglia is involved in oligodendrocyte apoptosis through the activation of the NF-κB signaling pathway, thus revealing a new mechanism of CNS demyelination.

Copper signalling: causes and consequences

Copper-containing enzymes perform fundamental functions by activating dioxygen (O2) and therefore allowing chemical energy-transfer for aerobic metabolism. The copper-dependence of O2 transport, metabolism and production of signalling molecules are supported by molecular systems that regulate and preserve tightly-bound static and weakly-bound dynamic cellular copper pools. Disruption of the reducing intracellular environment, characterized by glutathione shortage and ambient Cu(II) abundance drives oxidative stress and interferes with the bidirectional, copper-dependent communication between neurons and astrocytes, eventually leading to various brain disease forms. A deeper understanding of of the regulatory effects of copper on neuro-glia coupling via polyamine metabolism may reveal novel copper signalling functions and new directions for therapeutic intervention in brain disorders associated with aberrant copper metabolism.

Orthologous proteins of experimental de- and remyelination are differentially regulated in the CSF proteome of multiple sclerosis subtypes

OBJECTIVE

Here, we applied a multi-omics approach (i) to examine molecular pathways related to de- and remyelination in multiple sclerosis (MS) lesions; and (ii) to translate these findings to the CSF proteome in order to identify molecules that are differentially expressed among MS subtypes.

METHODS

To relate differentially expressed genes in MS lesions to de- and remyelination, we compared transcriptome of MS lesions to transcriptome of cuprizone (CPZ)-induced de- and remyelination. Protein products of the overlapping orthologous genes were measured within the CSF by quantitative proteomics, parallel reaction monitoring (PRM). Differentially regulated proteins were correlated with molecular markers of inflammation by using MesoScale multiplex immunoassay. Expression kinetics of differentially regulated orthologous genes and proteins were examined in the CPZ model.

RESULTS

In the demyelinated and remyelinated corpus callosum, we detected 1239 differentially expressed genes; 91 orthologues were also differentially expressed in MS lesions. Pathway analysis of these orthologues suggested that the TYROBP (DAP12)-TREM2 pathway, TNF-receptor 1, CYBA and the proteasome subunit PSMB9 were related to de- and remyelination. We designed 129 peptides representing 51 orthologous proteins, measured them by PRM in 97 individual CSF, and compared their levels between relapsing (n = 40) and progressive MS (n = 57). Four proteins were differentially regulated among relapsing and progressive MS: tyrosine protein kinase receptor UFO (UFO), TIMP-1, apolipoprotein C-II (APOC2), and beta-2-microglobulin (B2M). The orthologous genes/proteins in the mouse brain peaked during acute remyelination. UFO, TIMP-1 and B2M levels correlated inversely with inflammation in the CSF (IL-6, MCP-1/CCL2, TARC/CCL17). APOC2 showed positive correlation with IL-2, IL-16 and eotaxin-3/CCL26.

CONCLUSIONS

Pathology-based multi-omics identified four CSF markers that were differentially expressed in MS subtypes. Upregulated TIMP-1, UFO and B2M orthologues in relapsing MS were associated with reduced inflammation and reflected reparatory processes, in contrast to the upregulated orthologue APOC2 in progressive MS that reflected changes in lipid metabolism associated with increased inflammation.

Deregulation of the endocannabinoid system and therapeutic potential of ABHD6 blockade in the cuprizone model of demyelination

Multiple sclerosis (MS) is a chronic demyelinating disease of unknown etiology in which tissue pathology suggests both immune-dependent attacks to oligodendroglia and primary oligodendrocyte demise. The endocannabinoid system has been crucially involved in the control of autoimmune demyelination and cannabinoid-based therapies exhibit therapeutic potential, but also limitations, in MS patients. In this context, growing evidence suggests that targeting the hydrolysis of the main endocannabinoid 2-arachidonoylglycerol (2-AG) may offer a more favorable benefit-to-risk balance in MS than existing cannabinoid medicines. Here we evaluated the modulation of endocannabinoid signaling and the therapeutic potential of targeting the 2-AG hydrolytic enzyme alpha/beta-hydrolase domain-containing 6 (ABHD6) in the cuprizone model of non-immune dependent demyelination. The concentrations of N-arachidonoylethanolamine (anandamide, AEA) and its congener N-palmitoylethanolamine (PEA) were reduced following 6 weeks of cuprizone feeding. Deregulation of AEA and PEA levels was not due to differences in the expression of the hydrolytic and biosynthetic enzymes fatty acid amide hydrolase and N-acylphosphatidylethanolamine-phospholipase D, respectively. Conversely, we measured elevated transcript levels of 2-AG hydrolytic enzymes monoacylglycerol lipase, ABHD6 and ABHD12 without changes in bulk 2-AG concentration. Upregulated CB₁ and CB₂ receptors expression, ascribed in part to microglia, was also detected in the brain of cuprizone-treated mice. Administration of an ABHD6 inhibitor partially attenuated myelin damage, astrogliosis and microglia/macrophage reactivity associated to cuprizone feeding. However, ABHD6 blockade was ineffective at engaging protective or differentiation promoting effects in oligodendrocyte cultures. These results show specific alterations of the endocannabinoid system and modest beneficial effects resulting from ABHD6 inactivation in a relevant model of primary demyelination.

Procyanidin B2 mitigates behavioral impairment and protects myelin integrity in cuprizone-induced schizophrenia in mice

Numerous studies have suggested that neuropathological changes in schizophrenia may be related to damage to white matter or demyelination. Procyanidin B2, which is a constituent of many fruits such as grapes and strawberries, has various biological activities such as anti-inflammatory and anti-tumor activity, as has been reported. This study aimed to estimate the effects of procyanidin B2 on behavioral impairment and the protection of myelin integrity in a cuprizone-induced schizophrenia model. Mice were exposed to cuprizone (0.2% w/w in chow) for five weeks to induce schizophrenia-like behavioral changes and demyelination. Procyanidin B2 (20 or 100 mg kg⁻¹ day⁻¹) or vehicle was administered orally to mice after withdrawal from cuprizone. Behavioral impairment was detected with an open-field test, a rotarod test and a Morris water maze. Myelin integrity was assessed using LFB staining and MBP expression, including immunofluorescence and western blotting. In addition, enhancements in the expression of HO-1 and NQO1 suggested that procyanidin B2 may regulate oxidative homeostasis via promoting the translation of Nrf2 to the nucleus. Data indicated that procyanidin B2 could mitigate behavioral impairment and protect myelin integrity in the cuprizone-induced model via regulating oxidative stress by activating Nrf2 signaling.

Numerous studies have suggested that neuropathological changes in schizophrenia may be related to damage to white matter or demyelination.

Protective potential of dimethyl fumarate in a mouse model of thalamocortical demyelination

Alterations in cortical cellular organization, network functionality, as well as cognitive and locomotor deficits were recently suggested to be pathological hallmarks in multiple sclerosis and corresponding animal models as they might occur following demyelination. To investigate functional changes following demyelination in a well-defined, topographically organized neuronal network, in vitro and in vivo, we focused on the primary auditory cortex (A1) of mice in the cuprizone model of general de- and remyelination. Following myelin loss in this model system, the spatiotemporal propagation of incoming stimuli in A1 was altered and the hierarchical activation of supra- and infragranular cortical layers was lost suggesting a profound effect exerted on neuronal network level. In addition, the response latency in field potential recordings and voltage-sensitive dye imaging was increased following demyelination. These alterations were accompanied by a loss of auditory discrimination abilities in freely behaving animals, a reduction of the nuclear factor-erythroid 2-related factor-2 (Nrf-2) protein in the nucleus in histological staining and persisted during remyelination. To find new strategies to restore demyelination-induced network alteration in addition to the ongoing remyelination, we tested the cytoprotective potential of dimethyl fumarate (DMF). Therapeutic treatment with DMF during remyelination significantly modified spatiotemporal stimulus propagation in the cortex, reduced the cognitive impairment, and prevented the demyelination-induced decrease in nuclear Nrf-2. These results indicate the involvement of anti-oxidative mechanisms in regulating spatiotemporal cortical response pattern following changes in myelination and point to DMF as therapeutic compound for intervention.

Changes in the axo-glial junctions of the optic nerves of cuprizone-treated mice

Demyelination induced by cuprizone in mice has served a useful model system for the study of demyelinating diseases, such as multiple sclerosis. Severity of demyelination by cuprizone, however, varies across different regions of the central nervous system; the corpus callosum is sensitive, while the optic nerves are resistant. Here, we investigated the effects of cuprizone on optic nerves, focusing on the axo-glial junctions. Immunostaining for sodium channels, contactin-associated protein, neurofascins, and potassium channels revealed that there were no massive changes in the density and morphology of the axo-glial junctions in cuprizone-treated optic nerves. However, when we counted the number of incomplete junctional complexes, we observed increased numbers of isolated paranodes. These isolated paranodes were immunopositive for both axonal and glial membrane proteins, indicating that they were the contact sites between axons and glia. These were not associated with sodium channels or potassium channels, suggesting the absence of physiological functions. When teased axons from cuprizone-treated optic nerves were immunostained, the isolated paranodes were found at the internode region of the myelin. From these observations, we conclude that cuprizone induces new contacts between axons and myelins at the internode region.

Microglial Phenotypes and Functions in Multiple Sclerosis

Microglia are the resident immune cells that constantly survey the central nervous system. They can adapt to their environment and respond to injury or insult by altering their morphology, phenotype, and functions. It has long been debated whether microglial activation is detrimental or beneficial in multiple sclerosis (MS). Recently, the two opposing yet connected roles of microglial activation have been described with the aid of novel microglial markers, RNA profiling, and in vivo models. In this review, microglial phenotypes and functions in the context of MS will be discussed with evidence from both human pathological studies, in vitro and in vivo models. Microglial functional diversity-phagocytosis, antigen presentation, immunomodulation, support, and repair-will also be examined in detail. In addition, this review discusses the emerging evidence for microglia-related targets as biomarkers and therapeutic targets for MS.

Myelin injury induces axonal transport impairment but not AD-like pathology in the hippocampus of cuprizone-fed mice

Both multiple sclerosis (MS) and Alzheimer's disease (AD) are progressive neurological disorders with myelin injury and memory impairment. However, whether myelin impairment could cause AD-like neurological pathology remains unclear. To explore neurological pathology following myelin injury, we assessed cognitive function, the expression of myelin proteins, axonal transport-associated proteins, axonal structural proteins, synapse-associated proteins, tau and beta amyloid and the status of neurons, using the cuprizone mouse model of demyelination. We found the mild impairment of learning ability in cuprizone-fed mice and the decreased expression of myelin basic protein (MBP) in the hippocampus. And anti-LINGO-1 improved learning ability and partly restored MBP level. Furthermore, we also found kinesin light chain (KLC), neurofilament light chain (NFL) and neurofilament heavy chain (NF200) were declined in demyelinated hippocampus, which could be partly improved by treatment with anti-LINGO-1. However, we did not observe the increased expression of beta amyloid, hyperphosphorylation of tau and loss of neurons in demyelinated hippocampus. Our results suggest that demyelination might lead to the impairment of neuronal transport, but not cause increased level of hyperphosphorylated tau and beta amyloid. Our research demonstrates remyelination might be an effective pathway to recover the function of neuronal axons and cognition in MS.

Toll-Like Receptor 2-Mediated Glial Cell Activation in a Mouse Model of Cuprizone-Induced Demyelination

Multiple sclerosis (MS) is a chronic degenerative disease of the central nervous system that is characterized by myelin abnormalities, oligodendrocyte pathology, and concomitant glia activation. The factors triggering gliosis and demyelination are currently not well characterized. New findings suggest an important role of the innate immune response in the initiation and progression of active demyelinating lesions. Especially during progressive disease, aberrant glia activation rather than the invasion of peripheral immune cells is accountable for progressive neuronal injury. The innate immune response can be induced by pathogen-associated or danger-associated molecular patterns, which are identified by pattern recognition receptors (PRRs), including the Toll-like receptors (TLRs). In this study, we used the cuprizone model in mice to investigate the expression of TLR2 during the course of cuprizone-induced demyelination. In addition, we used TLR2-deficient mice to analyze the functional role of TLR2 activation during cuprizone-induced demyelination and reactive gliosis. We show a significantly increased expression of TLR2 in the corpus callosum and hippocampus of cuprizone-intoxicated mice. The absence of receptor signaling in TLR2-deficient mice resulted in less severe reactive astrogliosis in the corpus callosum and cortex. In addition, microglia activation was ameliorated in the corpus callosum of TLR2-deficient mice, but augmented in the cortex compared to wild-type littermates. Extent of demyelination and loss of mature oligodendrocytes was comparable in both genotypes. These results suggest that the TLR2 orchestrates glia activation during gray and white matter demyelination in the presence of an intact blood-brain barrier. Future studies now have to address the underlying mechanisms of the region-specific TLR2-mediated glia activation.

An Alternative Cuprizone-Induced Demyelination and Remyelination Mouse Model

The cuprizone model is a well-established and investigated paradigm to study demyelination and remyelination in rodents. Cuprizone is usually administrated by mixing in the powdered or pelleted rodent chow. However, since cuprizone is sensitive to the environment and the consumption of it varies between different animals, the major issue is the discrepancy in demyelination of the animals. This study reports the development of the cuprizone model by gavage administrations in mice. Following testing a series of doses of cuprizone, 400 mg/kg/day was found to be the best dosage to induce dramatic and consistent demyelination after 5 weeks of administration; while remyelination quickly occurred after 9 days of cuprizone withdrawal. The advantage of this alternative model is that the consumption of cuprizone could be well controlled, and the mice were exposed to the same dose of cuprizone. Thus, the variation in demyelination was minimized. This alternative cuprizone dosing regime minimizes the interanimal variability on demyelination and hence provides a consistent model for pharmacological evaluations, in addition to reducing the number of animals used in the experiments.

Advances in noninvasive myelin imaging

Myelin is important for the normal development and healthy function of the nervous system. Recent developments in MRI acquisition and tissue modeling aim to provide a better characterization and more specific markers for myelin. This allows for specific monitoring of myelination longitudinally and noninvasively in the healthy brain as well as assessment of treatment and intervention efficacy. Here, we offer a nontechnical review of MRI techniques developed to specifically monitor myelin such as magnetization transfer (MT) and myelin water imaging (MWI). We further summarize recent studies that employ these methods to measure myelin in relation to development and aging, learning and experience, and neuropathology and psychiatric disorders. © 2017 The Authors. Developmental Neurobiology Published by Wiley Periodicals, Inc. Develop Neurobiol 78: 136–151, 2018