Cuprizone-induced graded oligodendrocyte vulnerability is regulated by the transcription factor DNA damage-inducible transcript 3

Titration of cuprizone induces reliable demyelination

Multiple Sclerosis (MS) is a chronic inflammatory disease of the central nervous system. Cuprizone-induced demyelination, wherein mice are fed a diet containing the copper chelator cuprizone, is a well-established model that replicates key features of demyelination and remyelination. However, the dose-response relationship of cuprizone is complex; high concentrations can induce toxicity, whereas low doses may fail to produce reliable demyelination across subjects. This study aimed to investigate whether titration of the cuprizone concentration results in reliable acute demyelination and weight stabilization. To this end, experimental animals were intoxicated with cuprizone over a period of 5 weeks to induce acute demyelination. In one group, during the first 10 days, the initial cuprizone dose was gradually reduced until the experimental animals showed stable weights. Another group was subjected to a continuous cuprizone intoxication protocol without adaptions. Histological analyses were performed to quantify the extent of demyelination and glia activation. Animals of both groups experienced significant weight loss. Histological analyses revealed, despite adopting the cuprizone concentration, substantial demyelination of various brain regions, including the corpus callosum. This pattern was consistent across multiple staining methods, including anti-proteolipid protein (PLP), anti-myelin basic protein (MBP), and luxol-fast-blue (LFB) stains. Additionally, grey matter regions, specifically the neocortex, demonstrated significant demyelination. Accompanying these changes, there was notable activation and accumulation of microglia and astrocytes in white and grey matter regions. These histopathological changes were comparably pronounced in both cuprizone-treated groups. In summary, we demonstrate that titration of cuprizone is a reliable approach to induce acute demyelination in the mouse forebrain. This work represents a significant step toward refining animal models of MS, contributing to the broader effort of understanding and treating this complex disease.

A Morphological and Behavioral Study of Demyelination and Remyelination in the Cuprizone Model: Insights into APLNR and NG2+ Cell Dynamics

Multiple sclerosis (MS) is a chronic neurodegenerative disorder involving demyelination. The cuprizone model is commonly used to study MS by inducing oligodendrocyte stress and demyelination. The subventricular zone (SVZ) plays a key role in neurogenesis, while the neuronal/glial antigen 2 (NG2) is a marker for immature glial cells, involved in oligodendrocyte differentiation. The apelin receptor (APLNR) is linked to neurogenesis and behavior modulation. This study explores the role of APLNR in NG2-positive cells during de- and remyelination phases in the experimental cuprizone mouse model. Thirty male C57BL/6 mice were divided into control (not treated), demyelination (5 weeks cuprizone administration), and remyelination (5 weeks cuprizone administration + 5 weeks recovery) groups. Histological examinations, immunohistochemistry, and immunofluorescence on serial coronal sections were conducted to evaluate corpus callosum (CC) morphology and APLNR and NG2 expression in the SVZ, in addition to behavioral assessments. The histological analysis showed a significant reduction in the CC's thickness and area after five weeks of cuprizone exposure, followed by recovery five weeks post-exposure. During the demyelination phase, APLNR-expressing cells peaked while NG2-positive cells decreased. In the remyelination phase, APLNR-expressing cells declined, and NG2-positive cells increased. Confocal microscopy confirmed the co-localization of NG2 and APLNR markers. Statistically significant differences were observed across experimental groups. Correlation analyses highlighted associations between APLNR/NG2 cell counts and CC changes. Behavioral tests revealed impaired motor coordination and memory during demyelination, with gradual recovery during remyelination. Significant changes in the CC structure and the number of APLNR and NG2-positive cells were observed during de- and remyelination, suggesting that NG2-positive cells expressing APLNR may play a key role in remyelination.

Galectin-3 alleviates demyelination by modulating microglial anti-inflammatory polarization through PPARγ-CD36 axis

Demyelination is characterized by disruption of myelin sheath and disorders in myelin formation. Currently, there are no effective therapeutic treatments available. Microglia, especially anti-inflammatory phenotype microglia are critical for remyelination. Galectin-3 (Gal-3), which is known to modulate microglia activation, is correlated with myelination. In this study, we aimed to elucidate the roles of Gal-3 during myelin formation and explore the efficiency and mechanism of rGal-3 administration in remyelination. We enrolled Gal-3 knockout (Lgals3 KO) mice and demonstrated Lgals3 KO causes demyelination during spontaneous myelinogenesis. We performed a cuprizone (CPZ) intoxication model and found Lgals3 KO aggravates demyelinated lesions and favors microglial pro-inflammatory phenotype polarization. Recombinant Gal-3 (rGal-3) administration alleviates CPZ intoxication and drives microglial towards anti-inflammatory phenotype. Additionally, RNA sequencing results reveal the correlation between Gal-3 and the PPARγ-CD36 axis. Thus, we performed SSO and GW9662 administration to inhibit the activation of the PPARγ-CD36 axis and found that rGal-3 administration modulates microglial phenotype polarization by regulating the PPARγ-CD36 axis. Together, our findings highlight the importance of Gal-3 in myelination and provide insights into rGal-3 administration for modulating microglial anti-inflammatory phenotype polarization through the PPARγ-CD36 axis.

Evidence for TGF-β1/Nrf2 Signaling Crosstalk in a Cuprizone Model of Multiple Sclerosis

Multiple sclerosis (MS) is a chronic and degenerative disease that impacts central nervous system (CNS) function. One of the major characteristics of the disease is the presence of regions lacking myelin and an oxidative and inflammatory environment. TGF-β1 and Nrf2 proteins play a fundamental role in different oxidative/inflammatory processes linked to neurodegenerative diseases such as MS. The evidence from different experimental settings has demonstrated a TGF-β1-Nrf2 signaling crosstalk under pathological conditions. However, this possibility has not been explored in experimental models of MS. Here, by using the cuprizone-induced demyelination model of MS, we report that the in vivo pharmacological blockage of the TGF-β1 receptor reduced Nrf2, catalase, and TGFβ-1 protein levels in the demyelination phase of cuprizone administration. In addition, ATP production, locomotor function and cognitive performance were diminished by the treatment. Altogether, our results provide evidence for a crosstalk between TGF-β1 and Nrf2 signaling pathways under CNS demyelination, highlighting the importance of the antioxidant cellular response of neurodegenerative diseases such as MS.

The comparative effects of bone marrow mesenchymal stem cells and supernatant transplantation on demyelination and inflammation in cuprizone model

BACKGROUND

Multiple sclerosis (MS) is a chronic demyelinating disease of the central nervous system (CNS) with inflammation and immune dysfunction.

OBJECTIVES

We compared the remyelination and immunomodulation properties of mesenchymal stem cells (MSCs) with their conditioned medium (CM) in the cuprizone model.

METHODS

Twenty-four C57BL/ 6 mice were divided into four groups. After cuprizone demyelination, MSCs and their CM were injected into the right lateral ventricle of mice. The expression level of IL-1β, TNF-α, and BDNF genes was evaluated using the qRT-PCR. APC antibody was used to assess the oligodendrocyte population using the immunofluorescent method. The remyelination and axonal repair were studied by specific staining of the LFB and electron microscopy techniques.

RESULTS

Transplantation of MSCs and CM increased the expression of the BDNF gene and decreased the expression of IL-1β and TNF-α genes compared to the cuprizone group, and these effects in the cell group were more than CM. Furthermore, cell transplantation resulted in a significant improvement in myelination and axonal repair, which was measured by luxol fast blue and transmission electron microscope images. The cell group had a higher number of oligodendrocytes than other groups.

CONCLUSIONS

According to the findings, injecting MSCs intraventricularly versus cell-conditioned medium can be a more effective approach to improving chronic demyelination in degenerative diseases like MS.

Physiological aging and inflammation-induced cellular senescence may contribute to oligodendroglial dysfunction in MS

Aging affects all cell types in the CNS and plays an important role in CNS diseases. However, the underlying molecular mechanisms driving these age-associated changes and their contribution to diseases are only poorly understood. The white matter in the aging brain as well as in diseases, such as Multiple sclerosis is characterized by subtle abnormalities in myelin sheaths and paranodes, suggesting that oligodendrocytes, the myelin-maintaining cells of the CNS, lose the capacity to preserve a proper myelin structure and potentially function in age and certain diseases. Here, we made use of directly converted oligodendrocytes (dchiOL) from young, adult and old human donors to study age-associated changes. dchiOL from all three age groups differentiated in an comparable manner into O4 + immature oligodendrocytes, but the proportion of MBP + mature dchiOL decreased with increasing donor age. This was associated with an increased ROS production and upregulation of cellular senescence markers such as CDKN1A, CDKN2A in old dchiOL. Comparison of the transcriptomic profiles of dchiOL from adult and old donors revealed 1324 differentially regulated genes with limited overlap with transcriptomic profiles of the donors' fibroblasts or published data sets from directly converted human neurons or primary rodent oligodendroglial lineage cells. Methylome analyses of dchiOL and human white matter tissue samples demonstrate that chronological and epigenetic age correlate in CNS white matter as well as in dchiOL and resulted in the identification of an age-specific epigenetic signature. Furthermore, we observed an accelerated epigenetic aging of the myelinated, normal appearing white matter of multiple sclerosis (MS) patients compared to healthy individuals. Impaired differentiation and upregulation of cellular senescence markers could be induced in young dchiOL in vitro using supernatants from pro-inflammatory microglia. In summary, our data suggest that physiological aging as well as inflammation-induced cellular senescence contribute to oligodendroglial pathology in inflammatory demyelinating diseases such as MS.

CNS Resident Innate Immune Cells: Guardians of CNS Homeostasis

Although the CNS has been considered for a long time an immune-privileged organ, it is now well known that both the parenchyma and non-parenchymal tissue (meninges, perivascular space, and choroid plexus) are richly populated in resident immune cells. The advent of more powerful tools for multiplex immunophenotyping, such as single-cell RNA sequencing technique and upscale multiparametric flow and mass spectrometry, helped in discriminating between resident and infiltrating cells and, above all, the different spectrum of phenotypes distinguishing border-associated macrophages. Here, we focus our attention on resident innate immune players and their primary role in both CNS homeostasis and pathological neuroinflammation and neurodegeneration, two key interconnected aspects of the immunopathology of multiple sclerosis.

Glycine disrupts myelin, glutamatergic neurotransmission, and redox homeostasis in a neonatal model for non ketotic hyperglycinemia

Non ketotic hyperglycinemia (NKH) is an inborn error of glycine metabolism caused by mutations in the genes encoding glycine cleavage system proteins. Classic NKH has a neonatal onset, and patients present with severe neurodegeneration. Although glycine accumulation has been implicated in NKH pathophysiology, the exact mechanisms underlying the neurological damage and white matter alterations remain unclear. We investigated the effects of glycine in the brain of neonatal rats and MO3.13 oligodendroglial cells. Glycine decreased myelin basic protein (MBP) and myelin-associated glycoprotein (MAG) in the corpus callosum and striatum of rats on post-natal day (PND) 15. Glycine also reduced neuroglycan 2 (NG2) and N-methyl-d-aspartate receptor subunit 1 (NR1) in the cerebral cortex and striatum on PND15. Moreover, glycine reduced striatal glutamate aspartate transporter 1 (GLAST) content and neuronal nucleus (NeuN), and increased glial fibrillary acidic protein (GFAP) on PND15. Glycine also increased DCFH oxidation and malondialdehyde levels and decreased GSH concentrations in the cerebral cortex and striatum on PND6, but not on PND15. Glycine further reduced viability but did not alter DCFH oxidation and GSH levels in MO3.13 cells after 48- and 72-h incubation. These data indicate that impairment of myelin structure and glutamatergic system and induction of oxidative stress are involved in the neuropathophysiology of NKH.

Interleukin-6 Inhibits Expression of miR-204-5p, a Regulator of Oligodendrocyte Differentiation: Involvement of miR-204-5p in the Prevention of Chemical-Induced Oligodendrocyte Impairment

Oligodendrocytes (OLs) form myelin sheaths around axons in the central nervous system (CNS) facilitate the propagation of action potentials. The studies have shown that the differentiation and maturation of OLs involve microRNA (miR) regulation. The recent findings have addressed that miR-204 regulates OL differentiation in culture. In this study, through in situ hybridization in combination with immunohistochemistry, we showed that microRNA-204-5p in the corpus callosum was mainly expressed in OLs immunoreactive with adenomatous polyposis coli (APC), an OL marker. We also found miR-204-5p expression in mature OLs was suppressed by the addition of interleukin-6 (IL-6). Moreover, IL-6-induced inhibition of miR-204-5p expression was blocked by the addition of the inhibitors specific for p38 mitogen-activated protein kinase (p38MAPK) or phosphatidylinositol 3-kinase (PI3K) pathway. We further utilized a rat model by feeding cuprizone (CPZ)-containing diet for 3 weeks to induce demyelination and gliosis in the corpus callosum, as well as the upregulation of IL-6 gene expression significantly. Despite that miR-204-5p expression in the corpus callosum was not altered after feeding by CPZ for 3 weeks, its expression was increased and IL-6 transcription was decreased in the corpus callosum of the recovery group that was fed by CPZ for the first 2 weeks and by the regular diet for one more week. Our data demonstrate that miR-204-5p expression in OLs declined under the influence of the inflamed microenvironment. The findings that an increase in miR-204-5p and declined IL-6 expression observed in the recovery group might be involved with OL repair in the corpus callosum, and also shed light on a potential role for miR-204-5p in OL homeostasis following the white matter injury.

Oligodendrocyte Maturation Alters the Cell Death Mechanisms That Cause Demyelination

Myelinating oligodendrocytes die in human disease and early in aging. Despite this, the mechanisms that underly oligodendrocyte death are not resolved and it is also not clear whether these mechanisms change as oligodendrocyte lineage cells are undergoing differentiation and maturation. Here, we used a combination of intravital imaging, single-cell ablation, and cuprizone-mediated demyelination, in both female and male mice, to discover that oligodendrocyte maturation dictates the dynamics and mechanisms of cell death. After single-cell phototoxic damage, oligodendrocyte precursor cells underwent programmed cell death within hours, differentiating oligodendrocytes died over several days, while mature oligodendrocytes took weeks to die. Importantly cells at each maturation stage all eventually died but did so with drastically different temporal dynamics and morphological features. Consistent with this, cuprizone treatment initiated a caspase-3-dependent form of rapid cell death in differentiating oligodendrocytes, while mature oligodendrocytes never activated this executioner caspase. Instead, mature oligodendrocytes exhibited delayed cell death which was marked by DNA damage and disruption in poly-ADP-ribose subcellular localization. Thus, oligodendrocyte maturation plays a key role in determining the mechanism of death a cell undergoes in response to the same insult. This means that oligodendrocyte maturation is important to consider when designing strategies for preventing cell death and preserving myelin while also enhancing the survival of new oligodendrocytes in demyelinating conditions.

How to Use the Cuprizone Model to Study De- and Remyelination

Multiple sclerosis (MS) is an autoimmune and inflammatory disorder affecting the central nervous system whose cause is still largely unknown. Oligodendrocyte degeneration results in demyelination of axons, which can eventually be repaired by a mechanism called remyelination. Prevention of demyelination and the pharmacological support of remyelination are two promising strategies to ameliorate disease progression in MS patients. The cuprizone model is commonly employed to investigate oligodendrocyte degeneration mechanisms or to explore remyelination pathways. During the last decades, several different protocols have been applied, and all have their pros and cons. This article intends to offer guidance for conducting pre-clinical trials using the cuprizone model in mice, focusing on discovering new treatment approaches to prevent oligodendrocyte degeneration or enhance remyelination.

Astrocytes: Lessons Learned from the Cuprizone Model

A diverse array of neurological and psychiatric disorders, including multiple sclerosis, Alzheimer's disease, and schizophrenia, exhibit distinct myelin abnormalities at both the molecular and histological levels. These aberrations are closely linked to dysfunction of oligodendrocytes and alterations in myelin structure, which may be pivotal factors contributing to the disconnection of brain regions and the resulting characteristic clinical impairments observed in these conditions. Astrocytes, which significantly outnumber neurons in the central nervous system by a five-to-one ratio, play indispensable roles in the development, maintenance, and overall well-being of neurons and oligodendrocytes. Consequently, they emerge as potential key players in the onset and progression of a myriad of neurological and psychiatric disorders. Furthermore, targeting astrocytes represents a promising avenue for therapeutic intervention in such disorders. To gain deeper insights into the functions of astrocytes in the context of myelin-related disorders, it is imperative to employ appropriate in vivo models that faithfully recapitulate specific aspects of complex human diseases in a reliable and reproducible manner. One such model is the cuprizone model, wherein metabolic dysfunction in oligodendrocytes initiates an early response involving microglia and astrocyte activation, culminating in multifocal demyelination. Remarkably, following the cessation of cuprizone intoxication, a spontaneous process of endogenous remyelination occurs. In this review article, we provide a historical overview of studies investigating the responses and putative functions of astrocytes in the cuprizone model. Following that, we list previously published works that illuminate various aspects of the biology and function of astrocytes in this multiple sclerosis model. Some of the studies are discussed in more detail in the context of astrocyte biology and pathology. Our objective is twofold: to provide an invaluable overview of this burgeoning field, and, more importantly, to inspire fellow researchers to embark on experimental investigations to elucidate the multifaceted functions of this pivotal glial cell subpopulation.

Loss of the Novel Myelin Protein CMTM5 in Multiple Sclerosis Lesions and Its Involvement in Oligodendroglial Stress Responses

This study comprehensively addresses the involvement of the protein CKLF-like Marvel transmembrane domain-containing family member 5 (CMTM5) in the context of demyelination and cytodegenerative autoimmune diseases, particularly multiple Sclerosis (MS). An observed reduction in CMTM5 expression in post-mortem MS lesions prompted further investigations in both in vitro and in vivo animal models. In the cuprizone animal model, we detected a decrease in CMTM5 expression in oligodendrocytes that is absent in other members of the CMTM protein family. Our findings also confirm these results in the experimental autoimmune encephalomyelitis (EAE) model with decreased CMTM5 expression in both cerebellum and spinal cord white matter. We also examined the effects of a Cmtm5 knockdown in vitro in the oligodendroglial Oli-neu mouse cell line using the CRISPR interference technique. Interestingly, we found no effects on cell response to thapsigargin-induced endoplasmic reticulum (ER) stress as determined by Atf4 activity, an indicator of cellular stress responses. Overall, these results substantiate previous findings suggesting that CMTM5, rather than contributing to myelin biogenesis, is involved in maintaining axonal integrity. Our study further demonstrates that the knockdown of Cmtm5 in vitro does not modulate oligodendroglial responses to ER stress. These results warrant further investigation into the functional role of CMTM5 during axonal degeneration in the context of demyelinating conditions.

Korean Red Ginseng and Rb1 facilitate remyelination after cuprizone diet-induced demyelination

Background

Demyelination has been observed in neurological disorders, motivating researchers to search for components for enhancing remyelination. Previously we found that Rb1, a major ginsenoside in Korean Red Ginseng (KRG), enhances myelin formation. However, it has not been studied whether Rb1 or KRG function in remyelination after demyelination in vivo.

Methods

Mice were fed 0.2% cuprizone-containing chow for 5 weeks and returned to normal chow with daily oral injection of vehicle, KRG, or Rb1 for 3 weeks. Brain sections were stained with luxol fast blue (LFB) staining or immunohistochemistry. Primary oligodendrocyte or astrocyte cultures were subject to normal or stress condition with KRG or Rb1 treatment to measure gene expressions of myelin, endoplasmic reticulum (ER) stress, antioxidants and leukemia inhibitory factor (LIF).

Results

Compared to the vehicle, KRG or Rb1 increased myelin levels at week 6.5 but not 8, when measured by the LFB⁺ or GST-pi⁺ area within the corpus callosum. The levels of oligodendrocyte precursor cells, astrocytes, and microglia were high at week 5, and reduced afterwards but not changed by KRG or Rb1. In primary oligodendrocyte cultures, KRG or Rb1 increased expression of myelin genes, ER stress markers, and antioxidants. Interestingly, under cuprizone treatment, elevated ER stress markers were counteracted by KRG or Rb1. Under rotenone treatment, reduced myelin gene expressions were recovered by Rb1. In primary astrocyte cultures, KRG or Rb1 decreased LIF expression.

Conclusion

KRG and Rb1 may improve myelin regeneration during the remyelination phase in vivo, potentially by directly promoting myelin gene expression.

Impact of the Voltage-Gated Calcium Channel Antagonist Nimodipine on the Development of Oligodendrocyte Precursor Cells

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS). While most of the current treatment strategies focus on immune cell regulation, except for the drug siponimod, there is no therapeutic intervention that primarily aims at neuroprotection and remyelination. Recently, nimodipine showed a beneficial and remyelinating effect in experimental autoimmune encephalomyelitis (EAE), a mouse model of MS. Nimodipine also positively affected astrocytes, neurons, and mature oligodendrocytes. Here we investigated the effects of nimodipine, an L-type voltage-gated calcium channel antagonist, on the expression profile of myelin genes and proteins in the oligodendrocyte precursor cell (OPC) line Oli-Neu and in primary OPCs. Our data indicate that nimodipine does not have any effect on myelin-related gene and protein expression. Furthermore, nimodipine treatment did not result in any morphological changes in these cells. However, RNA sequencing and bioinformatic analyses identified potential micro (mi)RNA that could support myelination after nimodipine treatment compared to a dimethyl sulfoxide (DMSO) control. Additionally, we treated zebrafish with nimodipine and observed a significant increase in the number of mature oligodendrocytes (* p≤ 0.05). Taken together, nimodipine seems to have different positive effects on OPCs and mature oligodendrocytes.

Remyelination in Multiple Sclerosis: Findings in the Cuprizone Model

Remyelination therapies, which are currently under development, have a great potential to delay, prevent or even reverse disability in multiple sclerosis patients. Several models are available to study the effectiveness of novel compounds in vivo, among which is the cuprizone model. This model is characterized by toxin-induced demyelination, followed by endogenous remyelination after cessation of the intoxication. Due to its high reproducibility and ease of use, this model enjoys high popularity among various research and industrial groups. In this review article, we will summarize recent findings using this model and discuss the potential of some of the identified compounds to promote remyelination in multiple sclerosis patients.

Siponimod ameliorates metabolic oligodendrocyte injury via the sphingosine-1 phosphate receptor 5

Multiple sclerosis (MS), an autoimmune-driven, inflammatory demyelinating disease of the central nervous system (CNS), causes irreversible accumulation of neurological deficits to a variable extent. Although there are potent disease-modifying agents for its initial relapsing-remitting phase, immunosuppressive therapies show limited efficacy in secondary progressive MS (SPMS). Although modulation of sphingosine-1 phosphate receptors has proven beneficial during SPMS, the underlying mechanisms are poorly understood. In this project, we followed the hypothesis that siponimod, a sphingosine-1 phosphate receptor modulator, exerts protective effects by direct modulation of glia cell function (i.e., either astrocytes, microglia, or oligodendrocytes). To this end, we used the toxin-mediated, nonautoimmune MS animal model of cuprizone (Cup) intoxication. On the histological level, siponimod ameliorated cuprizone-induced oligodendrocyte degeneration, demyelination, and axonal injury. Protective effects were evident as well using GE180 translocator protein 18-kDa (TSPO) imaging with positron emission tomography (PET)/computed tomography (CT) imaging or next generation sequencing (NGS). Siponimod also ameliorated the cuprizone-induced pathologies in Rag1-deficient mice, demonstrating that the protection is independent of T and B cell modulation. Proinflammatory responses in primary mixed astrocytes/microglia cell cultures were not modulated by siponimod, suggesting that other cell types than microglia and astrocytes are targeted. Of note, siponimod completely lost its protective effects in S1pr5-deficient mice, suggesting direct protection of degenerating oligodendrocytes. Our study demonstrates that siponimod exerts protective effects in the brain in a S1PR5-dependent manner. This finding is not just relevant in the context of MS but in other neuropathologies as well, characterized by a degeneration of the axon-myelin unit.

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.

Nimodipine Exerts Beneficial Effects on the Rat Oligodendrocyte Cell Line OLN-93

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS). Therapy is currently limited to drugs that interfere with the immune system; treatment options that primarily mediate neuroprotection and prevent neurodegeneration are not available. Here, we studied the effects of nimodipine on the rat cell line OLN-93, which resembles young mature oligodendrocytes. Nimodipine is a dihydropyridine that blocks the voltage-gated L-type calcium channel family members Cav1.2 and Cav1.3. Our data show that the treatment of OLN-93 cells with nimodipine induced the upregulation of myelin genes, in particular of proteolipid protein 1 (Plp1), which was confirmed by a significantly greater expression of PLP1 in immunofluorescence analysis and the presence of myelin structures in the cytoplasm at the ultrastructural level. Whole-genome RNA sequencing additionally revealed the upregulation of genes that are involved in neuroprotection, remyelination, and antioxidation pathways. Interestingly, the observed effects were independent of Cav1.2 and Cav1.3 because OLN-93 cells do not express these channels, and there was no measurable response pattern in patch-clamp analysis. Taking into consideration previous studies that demonstrated a beneficial effect of nimodipine on microglia, our data support the notion that nimodipine is an interesting drug candidate for the treatment of MS and other demyelinating diseases.

Cuprizone feed formulation influences the extent of demyelinating disease pathology

Cuprizone is a copper-chelating agent that induces pathology similar to that within some multiple sclerosis (MS) lesions. The reliability and reproducibility of cuprizone for inducing demyelinating disease pathology depends on the animals ingesting consistent doses of cuprizone. Cuprizone-containing pelleted feed is a convenient way of delivering cuprizone, but the efficacy of these pellets at inducing demyelination has been questioned. This study compared the degree of demyelinating disease pathology between mice fed cuprizone delivered in pellets to mice fed a powdered cuprizone formulation at an early 3 week demyelinating timepoint. Within rostral corpus callosum, cuprizone pellets were more effective than cuprizone powder at increasing astrogliosis, microglial activation, DNA damage, and decreasing the density of mature oligodendrocytes. However, cuprizone powder demonstrated greater protein nitration relative to controls. Furthermore, mice fed control powder had significantly fewer mature oligodendrocytes than those fed control pellets. In caudal corpus callosum, cuprizone pellets performed better than cuprizone powder relative to controls at increasing astrogliosis, microglial activation, protein nitration, DNA damage, tissue swelling, and reducing the density of mature oligodendrocytes. Importantly, only cuprizone pellets induced detectable demyelination compared to controls. The two feeds had similar effects on oligodendrocyte precursor cell (OPC) dynamics. Taken together, these data suggest that demyelinating disease pathology is modelled more effectively with cuprizone pellets than powder at 3 weeks. Combined with the added convenience, cuprizone pellets are a suitable choice for inducing early demyelinating disease pathology.

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.

Ectopic lymphoid follicles in progressive multiple sclerosis: From patients to animal models

Ectopic lymphoid follicles (ELFs), resembling germinal centre‐like structures, emerge in a variety of infectious and autoimmune and neoplastic diseases. ELFs can be found in the meninges of around 40% of the investigated progressive multiple sclerosis (MS) post‐mortem brain tissues and are associated with the severity of cortical degeneration and clinical disease progression. Of predominant importance for progressive neuronal damage during the progressive MS phase appears to be meningeal inflammation, comprising diffuse meningeal infiltrates, B‐cell aggregates and compartmentalized ELFs. However, the absence of a uniform definition of ELFs impedes reproducible and comparable neuropathological research in this field. In this review article, we will first highlight historical aspects and milestones around the discovery of ELFs in the meninges of progressive MS patients. In the next step, we discuss how animal models may contribute to an understanding of the mechanisms underlying ELF formation. Finally, we summarize challenges in investigating ELFs and propose potential directions for future research.

Proteomics of Multiple Sclerosis: Inherent Issues in Defining the Pathoetiology and Identifying (Early) Biomarkers

Multiple Sclerosis (MS) is a demyelinating disease of the human central nervous system having an unconfirmed pathoetiology. Although animal models are used to mimic the pathology and clinical symptoms, no single model successfully replicates the full complexity of MS from its initial clinical identification through disease progression. Most importantly, a lack of preclinical biomarkers is hampering the earliest possible diagnosis and treatment. Notably, the development of rationally targeted therapeutics enabling pre-emptive treatment to halt the disease is also delayed without such biomarkers. Using literature mining and bioinformatic analyses, this review assessed the available proteomic studies of MS patients and animal models to discern (1) whether the models effectively mimic MS; and (2) whether reasonable biomarker candidates have been identified. The implication and necessity of assessing proteoforms and the critical importance of this to identifying rational biomarkers are discussed. Moreover, the challenges of using different proteomic analytical approaches and biological samples are also addressed.

Neuroprotective effect of newly synthesized 4-aminopyridine derivatives on cuprizone-induced demyelination in mice-a behavioral and immunohistochemical study

The aim of this study was to assess the effect of newly synthesized derivatives of 4-aminopyridine (4-AP) on cuprizone-induced model of brain demyelination in mice. 4-AP is already approved for the treatment of walking difficulties in patients with multiple sclerosis. The model of demyelination was carried out by the administration of cuprizone to the drinking water of the experimental mice. Besides cuprizone, 4-AP derivatives and 4-AP were administered to the groups in order to assess their protective effect on the demyelination. We used immunohistochemistry for visualization of changes in corpus callosum. Memory storage processes were also assessed with the passive avoidance test on the last two days of the experiment. The experimental mice treated with compounds 4b and 4c increased significantly their latency time on the second day in comparison to the control group which indicated an improved memory process. The number of mature oligodendrocytes in the groups treated with compounds 4b, 4c and 4-AP is closer to those in the control group. The results of our studies showed that the newly synthesized compounds 4b and 4c reverse the effect of cuprizone. These groups also showed increased latency time in the passive avoidance test in comparison to the control group.

Novel Tools and Investigative Approaches for the Study of Oligodendrocyte Precursor Cells (NG2-Glia) in CNS Development and Disease

Oligodendrocyte progenitor cells (OPCs), also referred to as NG2-glia, are the most proliferative cell type in the adult central nervous system. While the primary role of OPCs is to serve as progenitors for oligodendrocytes, in recent years, it has become increasingly clear that OPCs fulfil a number of other functions. Indeed, independent of their role as stem cells, it is evident that OPCs can regulate the metabolic environment, directly interact with and modulate neuronal function, maintain the blood brain barrier (BBB) and regulate inflammation. In this review article, we discuss the state-of-the-art tools and investigative approaches being used to characterize the biology and function of OPCs. From functional genetic investigation to single cell sequencing and from lineage tracing to functional imaging, we discuss the important discoveries uncovered by these techniques, such as functional and spatial OPC heterogeneity, novel OPC marker genes, the interaction of OPCs with other cells types, and how OPCs integrate and respond to signals from neighboring cells. Finally, we review the use of in vitro assay to assess OPC functions. These methodologies promise to lead to ever greater understanding of this enigmatic cell type, which in turn will shed light on the pathogenesis and potential treatment strategies for a number of diseases, such as multiple sclerosis (MS) and gliomas.

Focal white matter lesions induce long-lasting axonal degeneration, neuroinflammation and behavioral deficits

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) with episodes of inflammatory demyelination and remyelination. While remyelination has been linked with functional recovery in MS patients, there is evidence of ongoing tissue damage despite complete myelin repair. In this study, we investigated the long-term consequences of an acute demyelinating white matter CNS lesion. For this purpose, acute demyelination was induced by 5-week-cuprizone intoxication in male C57BL/6 J mice, and the tissues were examined after a 7-month recovery period. While myelination and oligodendrocyte densities appeared normal, ongoing axonal degeneration and glia cell activation were found in the remyelinated corpus callosum. Neuropathologies were paralleled by subtle gait abnormalities evaluated using DigiGait™ high speed ventral plane videography. Gene array analyses revealed increased expression levels of various inflammation related genes, among protein kinase c delta (PRKCD). Immunofluorescence stains revealed predominant microglia/macrophages PRKCD expression in both, cuprizone tissues and post-mortem MS lesions. These results support the hypothesis that chronic microglia/macrophages driven tissue injury represents a key aspect of progressive neurodegeneration and functional decline in MS.

Oligodendrocyte Lineage Marker Expression in eGFP-GFAP Transgenic Mice

Oligodendrocytes, the myelinating cells of the central nervous system, orchestrate several key cellular functions in the brain and spinal cord, including axon insulation, energy transfer to neurons, and, eventually, modulation of immune responses. There is growing interest for obtaining reliable markers that can specifically label oligodendroglia and their progeny. In many studies, anti-CC1 antibodies, presumably recognizing the protein adenomatous polyposis coli (APC), are used to label mature, myelinating oligodendrocytes. However, it has been discussed whether anti-CC1 antibodies could recognize as well, under pathological conditions, other cell populations, particularly astrocytes. In this study, we used transgenic mice in which astrocytes are labeled by the enhanced green fluorescent protein (eGFP) under the control of the human glial fibrillary acidic protein (GFAP) promoter. By detailed co-localization studies we were able to demonstrate that a significant proportion of eGFP-expressing cells co-express markers of the oligodendrocyte lineage, such as the transcription factor Oligodendrocyte Transcription Factor 2 (OLIG2); the NG2 proteoglycan, also known as chrondroitin sulfate proteoglycan 4 (CSPG4); or APC. The current finding that the GFAP promoter drives transgene expression in cells of the oligodendrocyte lineage should be considered when interpreting results from co-localization studies.

Guanabenz modulates microglia and macrophages during demyelination

Multiple sclerosis (MS) is an autoimmune disease characterized by infiltration of peripheral immune cells into the central nervous system, demyelination, and neuronal damage. There is no cure for MS, but available disease-modifying therapies can lessen severity and delay progression. However, current therapies are suboptimal due to adverse effects. Here, we investigate how the FDA-approved antihypertensive drug, guanabenz, which has a favorable safety profile and was recently reported to enhance oligodendrocyte survival, exerts effects on immune cells, specifically microglia and macrophages. We first employed the experimental autoimmune encephalomyelitis (EAE) model and observed pronounced immunomodulation evident by a reduction in pro-inflammatory microglia and macrophages. When guanabenz was administered in the cuprizone model, in which demyelination is less dependent upon immune cells, we did not observe improvements in remyelination, oligodendrocyte numbers, and effects on microglial activation were less dramatic. Thus, guanabenz may be a promising therapeutic to minimize inflammation without exerting severe off-target effects.

Aquaporin-4 Expression during Toxic and Autoimmune Demyelination

The water channel protein aquaporin-4 (AQP4) is required for a normal rate of water exchange across the blood–brain interface. Following the discovery that AQP4 is a possible autoantigen in neuromyelitis optica, the function of AQP4 in health and disease has become a research focus. While several studies have addressed the expression and function of AQP4 during inflammatory demyelination, relatively little is known about its expression during non-autoimmune-mediated myelin damage. In this study, we used the toxin-induced demyelination model cuprizone as well as a combination of metabolic and autoimmune myelin injury (i.e., Cup/EAE) to investigate AQP4 pathology. We show that during toxin-induced demyelination, diffuse AQP4 expression increases, while polarized AQP4 expression at the astrocyte endfeet decreases. The diffuse increased expression of AQP4 was verified in chronic-active multiple sclerosis lesions. Around inflammatory brain lesions, AQP4 expression dramatically decreased, especially at sites where peripheral immune cells penetrate the brain parenchyma. Humoral immune responses appear not to be involved in this process since no anti-AQP4 antibodies were detected in the serum of the experimental mice. We provide strong evidence that the diffuse increase in anti-AQP4 staining intensity is due to a metabolic injury to the brain, whereas the focal, perivascular loss of anti-AQP4 immunoreactivity is mediated by peripheral immune cells.

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.

High fat diet consumption results in mitochondrial dysfunction, oxidative stress, and oligodendrocyte loss in the central nervous system

Metabolic syndrome is a key risk factor and co-morbidity in multiple sclerosis (MS) and other neurological conditions, such that a better understanding of how a high fat diet contributes to oligodendrocyte loss and the capacity for myelin regeneration has the potential to highlight new treatment targets. Results demonstrate that modeling metabolic dysfunction in mice with chronic high fat diet (HFD) consumption promotes loss of oligodendrocyte progenitors across the brain and spinal cord. A number of transcriptomic and metabolomic changes in ER stress, mitochondrial dysfunction, and oxidative stress pathways in HFD-fed mouse spinal cords were also identified. Moreover, deficits in TCA cycle intermediates and mitochondrial respiration were observed in the chronic HFD spinal cord tissue. Oligodendrocytes are known to be particularly vulnerable to oxidative damage, and we observed increased markers of oxidative stress in both the brain and spinal cord of HFD-fed mice. We additionally identified that increased apoptotic cell death signaling is underway in oligodendrocytes from mice chronically fed a HFD. When cultured under high saturated fat conditions, oligodendrocytes decreased both mitochondrial function and differentiation. Overall, our findings show that HFD-related changes in metabolic regulators, decreased mitochondrial function, and oxidative stress contribute to a loss of myelinating cells. These studies identify HFD consumption as a key modifiable lifestyle factor for improved myelin integrity in the adult central nervous system and in addition new tractable metabolic targets for myelin protection and repair strategies.

Nrf2 deficiency increases oligodendrocyte loss, demyelination, neuroinflammation and axonal damage in an MS animal model

Oxidative stress is a pathophysiological hallmark of many CNS diseases, among multiple sclerosis (MS). Accordingly, boosting the astrocytic transcription factor nuclear factor E2-related factor 2 (Nrf2) system in an MS mouse model efficiently ameliorates oligodendrocyte loss, neuroinflammation and axonal damage. Moreover, Dimethylfumarate, an efficient activator of Nrf2, has recently been approved as therapeutic option in MS treatment. Here, we use the cuprizone mouse model of MS to induce oxidative stress, selective oligodendrocyte loss, microglia and astrocyte activation as well as axonal damage in both wild type and Nrf2-deficient mice. We found increased oligodendrocyte apoptosis and loss, pronounced neuroinflammation and higher levels of axonal damage in cuprizone-fed Nrf2-deficient animals when compared to wild type controls. In addition, Nrf2-deficient animals showed a higher susceptibility towards cuprizone within the commissura anterior white matter tract, a structure that is relatively insensitive to cuprizone in wild type animals. Our data highlight the cuprizone model as a suitable tool to study the complex interplay of oxidative stress, neuroinflammation and axonal damage. Further studies will have to show whether distinct expression patterns of Nrf2 are involved in the variable susceptibility towards cuprizone in the mouse.

Laquinimod Supports Remyelination in Non-Supportive Environments

Inflammatory demyelination, which is a characteristic of multiple sclerosis lesions, leads to acute functional deficits and, in the long term, to progressive axonal degeneration. While remyelination is believed to protect axons, the endogenous-regenerative processes are often incomplete or even completely fail in many multiple sclerosis patients. Although it is currently unknown why remyelination fails, recurrent demyelination of previously demyelinated white matter areas is one contributing factor. In this study, we investigated whether laquinimod, which has demonstrated protective effects in active multiple sclerosis patients, protects against recurrent demyelination. To address this, male mice were intoxicated with cuprizone for up to eight weeks and treated with either a vehicle solution or laquinimod at the beginning of week 5, where remyelination was ongoing. The brains were harvested and analyzed by immunohistochemistry. At the time-point of laquinimod treatment initiation, oligodendrocyte progenitor cells proliferated and maturated despite ongoing demyelination activity. In the following weeks, myelination recovered in the laquinimod- but not vehicle-treated mice, despite continued cuprizone intoxication. Myelin recovery was paralleled by less severe microgliosis and acute axonal injury. In this study, we were able to demonstrate that laquinimod, which has previously been shown to protect against cuprizone-induced oligodendrocyte degeneration, exerts protective effects during oligodendrocyte progenitor differentiation as well. By this mechanism, laquinimod allows remyelination in non-supportive environments. These results should encourage further clinical studies in progressive multiple sclerosis patients.

Stereological Investigation of Regional Brain Volumes after Acute and Chronic Cuprizone-Induced Demyelination

Brain volume measurement is one of the most frequently used biomarkers to establish neuroprotective effects during pre-clinical multiple sclerosis (MS) studies. Furthermore, whole-brain atrophy estimates in MS correlate more robustly with clinical disability than traditional, lesion-based metrics. However, the underlying mechanisms leading to brain atrophy are poorly understood, partly due to the lack of appropriate animal models to study this aspect of the disease. The purpose of this study was to assess brain volumes and neuro-axonal degeneration after acute and chronic cuprizone-induced demyelination. C57BL/6 male mice were intoxicated with cuprizone for up to 12 weeks. Brain volume, as well as total numbers and densities of neurons, were determined using design-based stereology. After five weeks of cuprizone intoxication, despite severe demyelination, brain volumes were not altered at this time point. After 12 weeks of cuprizone intoxication, a significant volume reduction was found in the corpus callosum and diverse subcortical areas, particularly the internal capsule and the thalamus. Thalamic volume loss was accompanied by glucose hypermetabolism, analyzed by [¹⁸F]-fluoro-2-deoxy-d-glucose (18F-FDG) positron-emission tomography. This study demonstrates region-specific brain atrophy of different subcortical brain regions after chronic cuprizone-induced demyelination. The chronic cuprizone demyelination model in male mice is, thus, a useful tool to study the underlying mechanisms of subcortical brain atrophy and to investigate the effectiveness of therapeutic interventions.

Animal Weight Is an Important Variable for Reliable Cuprizone-Induced Demyelination

An elegant model to study mechanisms operant during oligodendrocyte degeneration and subsequent demyelination is the cuprizone model. In that model, mice are intoxicated with the copper chelation agent cuprizone which results in early oligodendrocyte stress, oligodendrocyte apoptosis, and, finally, demyelination. Here, we systematically investigated to what extent the animals' weight at the beginning of the cuprizone intoxication period is critical for the reproducibility of the cuprizone-induced pathology. We can demonstrate that a negative correlation exists between the two variables "extent of cuprizone-induced demyelination" and "starting weight." Demyelination and microglia activation were more severe in low weight compared to heavy weight mice. These findings are highly relevant for the experimental design using the cuprizone model.

Mechanism of Siponimod: Anti-Inflammatory and Neuroprotective Mode of Action

Multiple sclerosis (MS) is a neuroinflammatory disorder of the central nervous system (CNS), and represents one of the main causes of disability in young adults. On the histopathological level, the disease is characterized by inflammatory demyelination and diffuse neurodegeneration. Although on the surface the development of new inflammatory CNS lesions in MS may appear consistent with a primary recruitment of peripheral immune cells, questions have been raised as to whether lymphocyte and/or monocyte invasion into the brain are really at the root of inflammatory lesion development. In this review article, we discuss a less appreciated inflammation-neurodegeneration interplay, that is: Neurodegeneration can trigger the formation of new, focal inflammatory lesions. We summarize old and recent findings suggesting that new inflammatory lesions develop at sites of focal or diffuse degenerative processes within the CNS. Such a concept is discussed in the context of the EXPAND trial, showing that siponimod exerts anti-inflammatory and neuroprotective activities in secondary progressive MS patients. The verification or rejection of such a concept is vital for the development of new therapeutic strategies for progressive MS.