Astrocytes regulate myelin clearance through recruitment of microglia during cuprizone-induced demyelination

Herpes Simplex Virus type 1 inhibits autophagy in glial cells but requires ATG5 for the success of viral replication

Herpes Simplex Virus type 1 (HSV-1) 1 is a neurotropic virus that has been associated with neurodegenerative disorders. The dysregulation of autophagy by HSV-1 has been proposed as a potential cause of neurodegeneration. While studies have extensively tackled the interaction between autophagy and HSV-1 in neurons, research in glial cells is currently limited. Our studies demonstrate that HSV-1 inhibits, but not completely blocks, the formation of autophagosomes in human oligodendroglioma- and astrocytoma- derived cell lines. These findings have been confirmed in murine oligodendrocyte precursor cells (OPCs). Finally, this study investigates the impact of autophagy on HSV-1 infection in glial cells. While the lack of basal autophagy in LC3B knockout glial cells does not have a significant effect on viral infection, cells without the autophagy-related protein ATG5 exhibit reduced viral production. The absence of ATG5 leads to a decrease in the transcription and replication of viral genes, as well as a delay in the initial stages of the formation of HSV-1 replication compartments. These findings indicate that while autophagy may not play a significant role in antiviral defense in glial cells, HSV-1 may be inhibiting autophagy to exploit non-canonical functions of certain components of the autophagic machinery, such as ATG5, to benefit its lifecycle.

Human post-mortem organotypic brain slice cultures: a tool to study pathomechanisms and test therapies

Human brain experimental models recapitulating age- and disease-related characteristics are lacking. There is urgent need for human-specific tools that model the complex molecular and cellular interplay between different cell types to assess underlying disease mechanisms and test therapies. Here we present an adapted ex vivo organotypic slice culture method using human post-mortem brain tissue cultured at an air-liquid interface to also study brain white matter. We assessed whether these human post-mortem brain slices recapitulate the in vivo neuropathology and if they are suitable for pathophysiological, experimental and pre-clinical treatment development purposes, specifically regarding leukodystrophies. Human post-mortem brain tissue and cerebrospinal fluid were obtained from control, psychiatric and leukodystrophy donors. Slices were cultured up to six weeks, in culture medium with or without human cerebrospinal fluid. Human post-mortem organotypic brain slice cultures remained viable for at least six weeks ex vivo and maintained tissue structure and diversity of (neural) cell types. Supplementation with cerebrospinal fluid could improve slice recovery. Patient-derived organotypic slice cultures recapitulated and maintained known in vivo neuropathology. The cultures also showed physiologic multicellular responses to lysolecithin-induced demyelination ex vivo, indicating their suitability to study intrinsic repair mechanisms upon injury. The slice cultures were applicable for various experimental studies, as multi-electrode neuronal recordings. Finally, the cultures showed successful cell-type dependent transduction with gene therapy vectors. These human post-mortem organotypic brain slice cultures represent an adapted ex vivo model suitable for multifaceted studies of brain disease mechanisms, boosting translation from human ex vivo to in vivo. This model also allows for assessing potential treatment options, including gene therapy applications. Human post-mortem brain slice cultures are thus a valuable tool in preclinical research to study the pathomechanisms of a wide variety of brain diseases in living human tissue.

Engineered PDGFA-ligand-modified exosomes delivery T3 for demyelinating disease targeted therapy

Demyelination is a proper syndrome in plenty of central nervous system (CNS) diseases, which is the main obstacle to recovery and still lacks an effective treatment. To overcome the limitations of the brain-blood barrier on drug permeability, we modified an exosome secreted by neural stem cells (NSCs), which had transfected with lentivirus armed with platelet-derived growth factors A (PDGFA)-ligand. Through the in vivo and in vitro exosomes targeting test, the migration ability to the lesion areas and OPCs significantly improved after ligand modification. Furthermore, the targeted exosomes loaded with 3,5, 30-L-triiodothyronine (T3) have a critical myelination ability in CNS development, administrated to the cuprizone animal model treatment. The data shows that the novel drug vector loaded with T3 significantly promotes remyelination compared with T3 alone. At the same time, it improved the CNS microenvironment by reducing astrogliosis, inhibiting pro-inflammatory microglia, and alleviating axon damage. This investigation provides a straightforward strategy to produce a targeting exosome and indicates a possible therapeutic manner for demyelinating disease.

Galectin-3 Plays a Role in Neuroinflammation in the Visual Pathway in Experimental Optic Neuritis

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS) featuring numerous neuropathologies, including optic neuritis (ON) in some patients. However, the molecular mechanisms of ON remain unknown. Galectins, β-galactoside-binding lectins, are involved in various pathophysiological processes. We previously showed that galectin-3 (gal-3) is associated with the pathogenesis of experimental autoimmune encephalomyelitis (EAE), an animal model of MS. In the current study, we investigated the expression of gal-3 in the visual pathway in EAE mice to clarify its role in the pathogenesis of ON. Immunohistochemical analysis revealed upregulation of gal-3 in the visual pathway of the EAE mice during the peak stage of the disease, compared with naïve and EAE mice during the chronic stage. Gal-3 was detected mainly in microglia/macrophages and astrocytes in the visual pathway in EAE mice. In addition, gal-3+/Iba-1+ cells, identified as phagocytic by immunostaining for cathepsin D, accumulated in demyelinating lesions in the visual pathway during the peak disease stage of EAE. Moreover, NLRP3 expression was detected in most gal-3+/Iba-1+ cells. These results strongly suggest that gal-3 regulates NLRP3 signaling in microglia/macrophages and neuroinflammatory demyelination in ON. In astrocytes, gal-3 was expressed from the peak to the chronic disease stages. Taken together, our findings suggest a critical role of gal-3 in the pathogenesis of ON. Thus, gal-3 in glial cells may serve as a potential therapeutic target for ON.

Automated analysis of gray matter damage in aged mice reveals impaired remyelination in the cuprizone model

Multiple sclerosis is a chronic autoimmune disease of the central nervous system characterized by myelin loss, axonal damage, and glial scar formation. Still, the underlying processes remain unclear, as numerous pathways and factors have been found to be involved in the development and progression of the disease. Therefore, it is of great importance to find suitable animal models as well as reliable methods for their precise and reproducible analysis. Here, we describe the impact of demyelination on clinically relevant gray matter regions of the hippocampus and cerebral cortex, using the previously established cuprizone model for aged mice. We could show that bioinformatic image analysis methods are not only suitable for quantification of cell populations, but also for the assessment of de- and remyelination processes, as numerous objective parameters can be considered for reproducible measurements. After cuprizone-induced demyelination, subsequent remyelination proceeded slowly and remained incomplete in all gray matter areas studied. There were regional differences in the number of mature oligodendrocytes during remyelination suggesting region-specific differences in the factors accounting for remyelination failure, as, even in the presence of oligodendrocytes, remyelination in the cortex was found to be impaired. Upon cuprizone administration, synaptic density and dendritic volume in the gray matter of aged mice decreased. The intensity of synaptophysin staining gradually restored during the subsequent remyelination phase, however the expression of MAP2 did not fully recover. Microgliosis persisted in the gray matter of aged animals throughout the remyelination period, whereas extensive astrogliosis was of short duration as compared to white matter structures. In conclusion, we demonstrate that the application of the cuprizone model in aged mice mimics the impaired regeneration ability seen in human pathogenesis more accurately than commonly used protocols with young mice and therefore provides an urgently needed animal model for the investigation of remyelination failure and remyelination-enhancing therapies.

Neurobehavioral deficits, histoarchitectural alterations, parvalbumin neuronal damage and glial activation in the brain of male Wistar rat exposed to Landfill leachate

Concerns about inappropriate disposal of waste into unsanitary municipal solid waste landfills around the world have been on the increase, and this poses a public health challenge due to leachate production. The neurotoxic effect of Gwagwalada landfill leachate (GLL) was investigated in male adult Wistar rats. Rats were exposed to a 10% concentration of GLL for 21 days. The control group received tap water for the same period of the experiment. Our results showed that neurobehavior, absolute body and brain weights and brain histomorphology as well as parvalbumin interneurons were severely altered, with consequent astrogliosis and microgliosis after 21 days of administrating GLL. Specifically, there was severe loss and shrinkage of Purkinje cells, with their nucleus, and severe diffused vacuolations of the white matter tract of GLL-exposed rat brains. There was severe cell loss in the granular layer of the cerebellum resulting in a reduced thickness of the layer. Also, there was severe loss of dendritic arborization of the Purkinje cells in GLL-exposed rat brains, and damage as well as reduced populations of parvalbumin-containing fast-spiking GABAergic interneurons in various regions of the brain. In conclusion, data from the present study demonstrated the detrimental effects of Gwagwalada landfill leachate on the brain which may be implicated in neuropsychological conditions.

Role of MAPK and PI3K-Akt signaling pathways in cuprizone-induced demyelination and cognitive impairment in mice

This study aimed to find the genes and signaling pathways underlying cuprizone-induced demyelination and cognitive impairments in mice. We used the cuprizone-exposed mice as an animal model of schizophrenia and assessed cognitive function in mice. Total RNA was extracted from mouse brain tissues for RNA sequencing. The DESeq2 R package was utilized to analyze the differentially expressed genes (DEGs). Functional and pathway enrichment analyses were performed simultaneously. We also constructed a protein-protein interaction (PPI) network to screen potential hub genes, and quantitative real-time polymerase chain reaction (qRT-PCR) was employed to validate the screened genes. After 6 weeks of cuprizone treatment, the cognitive function of mice was impaired. Compared to the controls, the cuprizone-exposed mice contained 351 DEGs, including 167 upregulated and 184 downregulated genes. Enrichment analysis showed that the DEGs were enriched in some biological processes involved in demyelination, including the MAPK pathway. Functional pathway analysis revealed that the DEGs were significantly enriched in the PI3K-Akt signaling pathway, which may be associated with cognitive impairments. MBP, IGF1, GFAP, PTPRC, CD14, CD68, ITGB2, LYN, TLR2, TLR4, VAV1, and PLEK were considered as potential hub genes. Except for MBP, all genes were upregulated in the cuprizone models, as verified by qRT-PCR. We suggest that the MAPK and PI3K-Akt signaling pathways may be associated with demyelination and cognitive impairments, respectively. GFAP and IGF-1 expression levels increased in cuprizone-exposed mice, suggesting that astrocytes may play a role in protecting the myelin sheath following treatment with cuprizone.

Astrocyte signaling and interactions in Multiple Sclerosis

Multiple Sclerosis (MS) is a common cause of impairment in working-aged adults. MS is characterized by neuroinflammation and infiltration of peripheral immune cells to the brain, which cause myelin loss and death of oligodendrocytes and neurons. Many studies on MS have focused on the peripheral immune sources of demyelination and repair. However, recent studies revealed that a glial cell type, the astrocytes, undergo robust morphological and transcriptomic changes that contribute significantly to demyelination and myelin repair. Here, we discuss recent findings elucidating signaling modalities that astrocytes acquire or lose in MS and how these changes alter the interactions of astrocytes with other nervous system cell types.

Transforming growth factor-β1 protects against white matter injury and reactive astrogliosis via the p38 MAPK pathway in rodent demyelinating model

In central nervous system (CNS), demyelination is a pathological process featured with a loss of myelin sheaths around axons, which is responsible for the diseases of multiple sclerosis, neuromyelitis optica, and so on. Transforming growth factor-beta1 (TGF-β1) is a multifunctional cytokine participating in abundant physiological and pathological processes in CNS. However, the effects of TGF-β1 on CNS demyelinating disease and its underlying mechanisms are controversial and not well understood. Herein, we evaluated the protective potential of TGF-β1 in a rodent demyelinating model established by lysophosphatidylcholine (LPC) injection. It was identified that supplement of TGF-β1 evidently rescued the cognitive deficit and motor dysfunction in LPC modeling mice assessed by novel object recognition and balance beam behavioral tests. Besides, quantified by luxol fast blue staining, immunofluorescence, and western blot, administration of TGF-β1 was found to significantly ameliorate the demyelinating lesion and reactive astrogliosis by suppressing p38 MAPK pathway. Mechanistically, the results of in vitro experiments indicated that treatment of TGF-β1 could directly promote the differentiation and migration of cultured oligodendrocytes. Our study revealed that modulating TGF-β1 activity might serve as a promising and innovative therapeutic strategy in CNS demyelinating diseases.

The beneficial role of autophagy in multiple sclerosis: Yes or No?

Multiple sclerosis (MS) is a chronic progressive demyelinating disease of the central nervous system (CNS) due to an increase of abnormal peripherally auto-reactive T lymphocytes which elicit autoimmunity. The main pathophysiology of MS is myelin sheath damage by immune cells and a defect in the generation of myelin by oligodendrocytes. Macroautophagy/autophagy is a critical degradation process that eliminates dysfunctional or superfluous cellular components. Autophagy has the property of a double-edged sword in MS in that it may have both beneficial and detrimental effects on MS neuropathology. Therefore, this review illustrates the protective and harmful effects of autophagy with regard to this disease. Autophagy prevents the progression of MS by reducing oxidative stress and inflammatory disorders. In contrast, over-activated autophagy is associated with the progression of MS neuropathology and in this case the use of autophagy inhibitors may alleviate the pathogenesis of MS. Furthermore, autophagy provokes the activation of different immune and supporting cells that play an intricate role in the pathogenesis of MS. Autophagy functions in the modulation of MS neuropathology by regulating cell proliferation related to demyelination and remyelination. Autophagy enhances remyelination by increasing the activity of oligodendrocytes, and astrocytes. However, autophagy induces demyelination by activating microglia and T cells. In conclusion, specific autophagic activators of oligodendrocytes, and astrocytes, and specific autophagic inhibitors of dendritic cells (DCs), microglia and T cells induce protective effects against the pathogenesis of MS.Abbreviations: ALS: amyotrophic lateral sclerosis; APCs: antigen-presenting cells; BBB: blood-brain barrier; CSF: cerebrospinal fluid; CNS: central nervous system; DCs: dendritic cells; EAE: experimental autoimmune encephalomyelitis; ER: endoplasmic reticulum; LAP: LC3-associated phagocytosis; MS: multiple sclerosis; NCA: non-canonical autophagy; OCBs: oligoclonal bands; PBMCs: peripheral blood mononuclear cells; PD: Parkinson disease; ROS: reactive oxygen species; UPR: unfolded protein response.

Astrocytic TIMP-1 regulates production of Anastellin, an inhibitor of oligodendrocyte differentiation and FTY720 responses

Astrocyte activation is associated with neuropathology and the production of tissue inhibitor of metalloproteinase-1 (TIMP1). TIMP1 is a pleiotropic extracellular protein that functions both as a protease inhibitor and as a growth factor. Astrocytes that lack expression of Timp1 do not support rat oligodendrocyte progenitor cell (rOPC) differentiation, and adult global Timp1 knockout (Timp1KO) mice do not efficiently remyelinate following a demyelinating injury. Here, we performed an unbiased proteomic analysis and identified a fibronectin-derived peptide called Anastellin (Ana) that was unique to the Timp1KO astrocyte secretome. Ana was found to block rOPC differentiation in vitro and enhanced the inhibitory influence of fibronectin on rOPC differentiation. Ana is known to act upon the sphingosine-1-phosphate receptor 1, and we determined that Ana also blocked the pro-myelinating effect of FTY720 (or fingolimod) on rOPC differentiation in vitro. Administration of FTY720 to wild-type C57BL/6 mice during MOG35-55-experimental autoimmune encephalomyelitis ameliorated clinical disability while FTY720 administered to mice lacking expression of Timp1 (Timp1KO) had no effect. Analysis of Timp1 and fibronectin (FN1) transcripts from primary human astrocytes from healthy and multiple sclerosis (MS) donors revealed lower TIMP1 expression was coincident with elevated FN1 in MS astrocytes. Last, analyses of proteomic databases of MS samples identified Ana peptides to be more abundant in the cerebrospinal fluid (CSF) of human MS patients with high disease activity. A role for Ana in MS as a consequence of a lack of astrocytic TIMP-1 production could influence both the efficacy of fingolimod responses and innate remyelination potential in the MS brain.

Repurposing of pexidartinib for microglia depletion and renewal

Pexidartinib (PLX3397) is a small molecule receptor tyrosine kinase inhibitor of colony stimulating factor 1 receptor (CSF1R) with moderate selectivity over other members of the platelet derived growth factor receptor family. It is approved for treatment of tenosynovial giant cell tumors (TGCT). CSF1R is highly expressed by microglia, which are macrophages of the central nervous system (CNS) that defend the CNS against injury and pathogens and contribute to synapse development and plasticity. Challenged by pathogens, apoptotic cells, debris, or inflammatory molecules they adopt a responsive state to propagate the inflammation and eventually return to a homeostatic state. The phenotypic switch may fail, and disease-associated microglia contribute to the pathophysiology in neurodegenerative or neuropsychiatric diseases or long-lasting detrimental brain inflammation after brain, spinal cord or nerve injury or ischemia/hemorrhage. Microglia also contribute to the growth permissive tumor microenvironment of glioblastoma (GBM). In rodents, continuous treatment for 1-2 weeks via pexidartinib food pellets leads to a depletion of microglia and subsequent repopulation from the remaining fraction, which is aided by peripheral monocytes that search empty niches for engraftment. The putative therapeutic benefit of such microglia depletion or forced renewal has been assessed in almost any rodent model of CNS disease or injury or GBM with heterogeneous outcomes, but a tendency of partial beneficial effects. So far, microglia monitoring e.g. via positron emission imaging is not standard of care for patients receiving Pexidartinib (e.g. for TGCT), so that the depletion and repopulation efficiency in humans is still largely unknown. Considering the virtuous functions of microglia, continuous depletion is likely no therapeutic option but short-lasting transient partial depletion to stimulate microglia renewal or replace microglia in genetic disease in combination with e.g. stem cell transplantation or as part of a multimodal concept in treatment of glioblastoma appears feasible. The present review provides an overview of the preclinical evidence pro and contra microglia depletion as a therapeutic approach.

Microglia regulation of central nervous system myelin health and regeneration

Microglia are resident macrophages of the central nervous system that have key functions in its development, homeostasis and response to damage and infection. Although microglia have been increasingly implicated in contributing to the pathology that underpins neurological dysfunction and disease, they also have crucial roles in neurological homeostasis and regeneration. This includes regulation of the maintenance and regeneration of myelin, the membrane that surrounds neuronal axons, which is required for axonal health and function. Myelin is damaged with normal ageing and in several neurodegenerative diseases, such as multiple sclerosis and Alzheimer disease. Given the lack of approved therapies targeting myelin maintenance or regeneration, it is imperative to understand the mechanisms by which microglia support and restore myelin health to identify potential therapeutic approaches. However, the mechanisms by which microglia regulate myelin loss or integrity are still being uncovered. In this Review, we discuss recent work that reveals the changes in white matter with ageing and neurodegenerative disease, how this relates to microglia dynamics during myelin damage and regeneration, and factors that influence the regenerative functions of microglia.

Microglia in Central Control of Metabolism

Beyond their role as brain immune cells, microglia act as metabolic sensors in response to changes in nutrient availability, thus playing a role in energy homeostasis. This review highlights the evidence and challenges of studying the role of microglia in metabolism regulation.

Gasdermin D activation in oligodendrocytes and microglia drives inflammatory demyelination in progressive multiple sclerosis

Neuroinflammation coupled with demyelination and neuro-axonal damage in the central nervous system (CNS) contribute to disease advancement in progressive multiple sclerosis (P-MS). Inflammasome activation accompanied by proteolytic cleavage of gasdermin D (GSDMD) results in cellular hyperactivation and lytic death. Using multiple experimental platforms, we investigated the actions of GSDMD within the CNS and its contributions to P-MS. Brain tissues from persons with P-MS showed significantly increased expression of GSDMD, NINJ1, IL-1β, and -18 within chronic active demyelinating lesions compared to MS normal appearing white matter and nonMS (control) white matter. Conditioned media (CM) from stimulated GSDMD+/+ human macrophages caused significantly greater cytotoxicity of oligodendroglial and neuronal cells, compared to CM from GSDMD-/- macrophages. Oligodendrocytes and CNS macrophages displayed increased Gsdmd immunoreactivity in the central corpus callosum (CCC) of cuprizone (CPZ)-exposed Gsdmd+/+ mice, associated with greater demyelination and reduced oligodendrocyte precursor cell proliferation, compared to CPZ-exposed Gsdmd-/- animals. CPZ-exposed Gsdmd+/+ mice exhibited significantly increased G-ratios and reduced axonal densities in the CCC compared to CPZ-exposed Gsdmd-/- mice. Proteomic analyses revealed increased brain complement C1q proteins and hexokinases in CPZ-exposed Gsdmd-/- animals. [18F]FDG PET imaging showed increased glucose metabolism in the hippocampus and whole brain with intact neurobehavioral performance in Gsdmd-/- animals after CPZ exposure. GSDMD activation in CNS macrophages and oligodendrocytes contributes to inflammatory demyelination and neuroaxonal injury, offering mechanistic and potential therapeutic insights into P-MS pathogenesis.

Bruton's tyrosine kinase-bearing B cells and microglia in neuromyelitis optica spectrum disorder

BACKGROUND

Neuromyelitis optica spectrum disorder (NMOSD) is an inflammatory autoimmune disease of the central nervous system that involves B-cell receptor signaling as well as astrocyte-microglia interaction, which both contribute to evolution of NMOSD lesions.

MAIN BODY

Through transcriptomic and flow cytometry analyses, we found that Bruton's tyrosine kinase (BTK), a crucial protein of B-cell receptor was upregulated both in the blood and cerebrospinal fluid of NMOSD patients. Blockade of BTK with zanubrutinib, a highly specific BTK inhibitor, mitigated the activation and maturation of B cells and reduced production of causal aquaporin-4 (AQP4) autoantibodies. In a mouse model of NMO, we found that both BTK and pBTK expression were significantly increased in microglia. Transmission electron microscope scan demonstrated that BTK inhibitor ameliorated demyelination, edema, and axonal injury in NMO mice. In the same mice colocalization of GFAP and Iba-1 immunofluorescence indicated a noticeable increase of astrocytes-microglia interaction, which was alleviated by zanubrutinib. The smart-seq analysis demonstrated that treatment with BTK inhibitor instigated microglial transcriptome changes including downregulation of chemokine-related genes and genes involved in the top 5 biological processes related to cell adhesion and migration, which are likely responsible for the reduced crosstalk of microglia and astrocytes.

CONCLUSIONS

Our results show that BTK activity is enhanced both in B cells and microglia and BTK inhibition contributes to the amelioration of NMOSD pathology. These data collectively reveal the mechanism of action of BTK inhibition and corroborate BTK as a viable therapeutic target.

Astrocytic phagocytosis of myelin debris and reactive characteristics in vivo and in vitro

BACKGROUND INFORMATION

Persistent myelin debris can inhibit axonal regeneration, thereby hindering remyelination. Effective removal of myelin debris is essential to eliminate the interference of myelin debris in oligodendrocyte progenitor cell (OPC) activation, recruitment to demyelinating sites and/or differentiation into mature oligodendrocytes (OLs). In addition to microglia, it has been reported that astrocytic phagocytosis of myelin debris is a feature of early demyelination.

RESULTS

In the present study, astrocytes effectively phagocytized myelin debris in vitro and in vivo. On the 5th day after injecting myelin debris into the brain, astrocytes were enriched in the area injected with myelin debris compared with microglia, and their ability to engulf myelin debris was stronger than that of microglia. When exposed to myelin debris, astrocytes phagocytizing myelin debris triggered self-apoptosis, accompanied by the activation of NF-κB, down-regulation of Nrf2, and the increase of ciliary neurotrophic factor (CNTF) and basic fibroblast growth factor (bFGF). However, the activation of astrocytic NF-κB did not influence the inflammatory cytokines IL-1β, IL-6, and TNF-α, and the anti-inflammatory factor IL-10. The proliferation of astrocytes and mobilization of OPCs in the subventricular zone were elevated on the 5th day after intracerebral injection of myelin debris.

CONCLUSIONS

The results suggested that myelin phagocytosis of astrocytes should help improve the microenvironment and promote myelin regeneration by increasing CNTF and bFGF within the central nervous system.

SIGNIFICANCE

However, the molecular interaction of astrocytes acting as phagocytes remains to be further explored. Therefore, an improvement of astrocytes to phagocytize myelin debris may be a promising treatment measure to prevent demyelination and promote remyelination in MS and other diseases with prominent myelin injury.

The Roles of Caloric Restriction Mimetics in Central Nervous System Demyelination and Remyelination

The dysfunction of myelinating glial cells, the oligodendrocytes, within the central nervous system (CNS) can result in the disruption of myelin, the lipid-rich multi-layered membrane structure that surrounds most vertebrate axons. This leads to axonal degeneration and motor/cognitive impairments. In response to demyelination in the CNS, the formation of new myelin sheaths occurs through the homeostatic process of remyelination, facilitated by the differentiation of newly formed oligodendrocytes. Apart from oligodendrocytes, the two other main glial cell types of the CNS, microglia and astrocytes, play a pivotal role in remyelination. Following a demyelination insult, microglia can phagocytose myelin debris, thus permitting remyelination, while the developing neuroinflammation in the demyelinated region triggers the activation of astrocytes. Modulating the profile of glial cells can enhance the likelihood of successful remyelination. In this context, recent studies have implicated autophagy as a pivotal pathway in glial cells, playing a significant role in both their maturation and the maintenance of myelin. In this Review, we examine the role of substances capable of modulating the autophagic machinery within the myelinating glial cells of the CNS. Such substances, called caloric restriction mimetics, have been shown to decelerate the aging process by mitigating age-related ailments, with their mechanisms of action intricately linked to the induction of autophagic processes.

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.

Methyl-CpG-Binding Protein 2 Emerges as a Central Player in Multiple Sclerosis and Neuromyelitis Optica Spectrum Disorders

MECP2 and its product methyl-CpG binding protein 2 (MeCP2) are associated with multiple sclerosis (MS) and neuromyelitis optica spectrum disorders (NMOSD), which are inflammatory, autoimmune, and demyelinating disorders of the central nervous system (CNS). However, the mechanisms and pathways regulated by MeCP2 in immune activation in favor of MS and NMOSD are not fully understood. We summarize findings that use the binding properties of MeCP2 to identify its targets, particularly the genes recognized by MeCP2 and associated with several neurological disorders. MeCP2 regulates gene expression in neurons, immune cells and during development by modulating various mechanisms and pathways. Dysregulation of the MeCP2 signaling pathway has been associated with several disorders, including neurological and autoimmune diseases. A thorough understanding of the molecular mechanisms underlying MeCP2 function can provide new therapeutic strategies for these conditions. The nervous system is the primary system affected in MeCP2-associated disorders, and other systems may also contribute to MeCP2 action through its target genes. MeCP2 signaling pathways provide promise as potential therapeutic targets in progressive MS and NMOSD. MeCP2 not only increases susceptibility and induces anti-inflammatory responses in immune sites but also leads to a chronic increase in pro-inflammatory cytokines gene expression (IFN-γ, TNF-α, and IL-1β) and downregulates the genes involved in immune regulation (IL-10, FoxP3, and CX3CR1). MeCP2 may modulate similar mechanisms in different pathologies and suggest that treatments for MS and NMOSD disorders may be effective in treating related disorders. MeCP2 regulates gene expression in MS and NMOSD. However, dysregulation of the MeCP2 signaling pathway is implicated in these disorders. MeCP2 plays a role as a therapeutic target for MS and NMOSD and provides pathways and mechanisms that are modulated by MeCP2 in the regulation of gene expression.

Dynamics of reactive astrocytes fosters tissue regeneration after cuprizone-induced demyelination

Demyelination in the central nervous system (CNS) is a hallmark of many neurodegenerative diseases such as multiple sclerosis (MS) and others. Here, we studied astrocytes during de- and remyelination in the cuprizone mouse model. To this end, we exploited the ribosomal tagging (RiboTag) technology that is based on Cre-mediated cell type-selective HA-tagging of ribosomes. Analyses were performed in the corpus callosum of GFAP-Cre+/- Rpl22HA/wt mice 5 weeks after cuprizone feeding, at the peak of demyelination, and 0.5 and 2 weeks after cuprizone withdrawal, when remyelination and tissue repair is initiated. After 5 weeks of cuprizone feeding, reactive astrocytes showed inflammatory signatures with enhanced expression of genes that modulate leukocyte migration (Tlr2, Cd86, Parp14) and they produced the chemokine CXCL10, as verified by histology. Furthermore, demyelination-induced reactive astrocytes expressed numerous ligands including Cx3cl1, Csf1, Il34, and Gas6 that act on homeostatic as well as activated microglia and thus potentially mediate activation and recruitment of microglia and enhancement of their phagocytotic activity. During early remyelination, HA-tagged cells displayed reduced inflammatory response signatures, as indicated by shutdown of CXCL10 production, and enhanced expression of osteopontin (SPP1) as well as of factors that are relevant for tissue remodeling (Timp1), regeneration and axonal repair. During late remyelination, the signatures shifted towards resolving inflammation by active suppression of lymphocyte activation and differentiation and support of glia cell differentiation. In conclusion, we detected highly dynamic astroglial transcriptomic signatures in the cuprizone model, which reflects excessive communication among glia cells and highlights different astrocyte functions during neurodegeneration and regeneration.

Brain Stiffness Follows Cuprizone-Induced Variations in Local Myelin Content

Brain maturation and neurological diseases are intricately linked to microstructural changes that inherently affect the brain's mechanical behavior. Animal models are frequently used to explore relative brain stiffness changes as a function of underlying microstructure. Here, we are using the cuprizone mouse model to study indentation-derived stiffness changes resulting from acute and chronic demyelination during a 15-week observation period. We focus on the corpus callosum, cingulum, and cortex which undergo different degrees of de- and remyelination and, therefore, result in region-specific stiffness changes. Mean stiffness of the corpus callosum starts at 1.1 ± 0.3 kPa in untreated mice, then cuprizone treatment causes stiffness to drop to 0.6 ± 0.1 kPa by week 3, temporarily increase to 0.9 ± 0.3 kPa by week 6, and ultimately stabilize around 0.7 ± 0.1 kPa by week 9 for the rest of the observation period. The cingulum starts at 3.2 ± 0.9 kPa, then drops to 1.6 ± 0.4 kPa by week 3, and then gradually stabilizes around 1.4 ± 0.3 kPa by week 9. Cortical stiffness exhibits less stiffness variations overall; it starts at 4.2 ± 1.3 kPa, drops to 2.4 ± 0.6 kPa by week 3, and stabilizes around 2.7 ± 0.9 kPa by week 6. We also assess the impact of tissue fixation on indentation-based mechanical tissue characterization. On the one hand, fixation drastically increases untreated mean tissue stiffness by a factor of 3.3 for the corpus callosum, 2.9 for the cingulum, and 3.6 for the cortex; on the other hand, fixation influences interregional stiffness ratios during demyelination, thus suggesting that fixation affects individual brain tissues differently. Lastly, we determine the spatial correlation between stiffness measurements and myelin density and observe a region-specific proportionality between myelin content and tissue stiffness. STATEMENT OF SIGNIFICANCE: Despite extensive work, the relationship between microstructure and mechanical behavior in the brain remains mostly unknown. Additionally, the existing variation of measurement results reported in literature requires in depth investigation of the impact of individual cell and protein populations on tissue stiffness and interregional stiffness ratios. Here, we used microindentation measurements to show that brain stiffness changes with myelin density in the cuprizone-based demyelination mouse model. Moreover, we explored the impact of tissue fixation prior to mechanical characterization because of conflicting results reported in literature. We observe that fixation has a distinctly different impact on our three regions of interest, thus causing region-specific tissue stiffening and, more importantly, changing interregional stiffness ratios.

The role of astrocytes response triggered by hyperglycaemia during spinal cord injury

Objective: This manuscript aimed to provide a comprehensive overview of the physiological, molecular, and cellular mechanisms triggered by reactive astrocytes (RA) in the context of spinal cord injury (SCI), with a particular focus on cases involving hyperglycaemia.Methods: The compilation of articles related to astrocyte responses in neuropathological conditions, with a specific emphasis on those related to SCI and hyperglycaemia, was conducted by searching through databases including Science Direct, Web of Science, and PubMed.Results and Conclusions: This article explores the dual role of astrocytes in both neurophysiological and neurodegenerative conditions within the central nervous system (CNS). In the aftermath of SCI and hyperglycaemia, astrocytes undergo a transformation into RA, adopting a distinct phenotype. While there are currently no approved therapies for SCI, various therapeutic strategies have been proposed to alleviate the detrimental effects of RAs following SCI and hyperglycemia. These strategies show promising potential in the treatment of SCI and its likely comorbidities.

Nicotinamide enhances myelin production after demyelination through reduction of astrogliosis and microgliosis

Caloric restriction is the chronic reduction of total caloric intake without malnutrition and has attracted a lot of attention as, among multiple other effects, it attenuates demyelination and stimulates remyelination. In this study we have evaluated the effect of nicotinamide (NAM), a well-known caloric restriction mimetic, on myelin production upon demyelinating conditions. NAM is the derivative of nicotinic acid (vitamin B3) and a precursor of nicotinamide adenine dinucleotide (NAD+), a ubiquitous metabolic cofactor. Here, we use cortical slices ex vivo subjected to demyelination or cultured upon normal conditions, a lysolecithin (LPC)-induced focal demyelination mouse model as well as primary glial cultures. Our data show that NAM enhances both myelination and remyelination ex vivo, while it also induces myelin production after LPC-induced focal demyelination ex vivo and in vivo. The increased myelin production is accompanied by reduction in both astrogliosis and microgliosis in vivo. There is no direct effect of NAM on the oligodendrocyte lineage, as no differences are observed in oligodendrocyte precursor cell proliferation or differentiation or in the number of mature oligodendrocytes. On the other hand, NAM affects both microglia and astrocytes as it decreases the population of M1-activated microglia, while reducing the pro-inflammatory phenotype of astrocytes as assayed by the reduction of TNF-α. Overall, we show that the increased myelin production that follows NAM treatment in vivo is accompanied by a decrease in both astrocyte and microglia accumulation at the lesion site. Our data indicate that NAM influences astrocytes and microglia directly, in favor of the remyelination process by promoting a less inflammatory environment.

Localized Increased Permeability of Blood-Brain Barrier for Antibody Conjugates in the Cuprizone Model of Demyelination

The development of new neurotherapeutics depends on appropriate animal models being chosen in preclinical studies. The cuprizone model is an effective tool for studying demyelination and remyelination processes in the brain, but blood-brain barrier (BBB) integrity in the cuprizone model is still a topic for debate. Several publications claim that the BBB remains intact during cuprizone-induced demyelination; others demonstrate results that could explain the increased BBB permeability. In this study, we aim to analyze the permeability of the BBB for different macromolecules, particularly antibody conjugates, in a cuprizone-induced model of demyelination. We compared the traditional approach using Evans blue injection with subsequent dye extraction and detection of antibody conjugates using magnetic resonance imaging (MRI) and confocal microscopy to analyze BBB permeability in the cuprizone model. First, we validated our model of demyelination by performing T2-weighted MRI, diffusion tensor imaging, quantitative rt-PCR to detect changes in mRNA expression of myelin basic protein and proteolipid protein, and Luxol fast blue histological staining of myelin. Intraperitoneal injection of Evans blue did not result in any differences between the fluorescent signal in the brain of healthy and cuprizone-treated mice (IVIS analysis with subsequent dye extraction). In contrast, intravenous injection of antibody conjugates (anti-GFAP or non-specific IgG) after 4 weeks of a cuprizone diet demonstrated accumulation in the corpus callosum of cuprizone-treated mice both by contrast-enhanced MRI (for gadolinium-labeled antibodies) and by fluorescence microscopy (for Alexa488-labeled antibodies). Our results suggest that the methods with better sensitivity could detect the accumulation of macromolecules (such as fluorescent-labeled or gadolinium-labeled antibody conjugates) in the brain, suggesting a local BBB disruption in the demyelinating area. These findings support previous investigations that questioned BBB integrity in the cuprizone model and demonstrate the possibility of delivering antibody conjugates to the corpus callosum of cuprizone-treated mice.

Transcription factor combinations that define human astrocyte identity encode significant variation of maturity and function

Increasing evidence indicates that cellular identity can be reduced to the distinct gene regulatory networks controlled by transcription factors (TFs). However, redundancy exists in these states as different combinations of TFs can induce broadly similar cell types. We previously demonstrated that by overcoming gene silencing, it is possible to deterministically reprogram human pluripotent stem cells directly into cell types of various lineages. In the present study we leverage the consistency and precision of our approach to explore four different TF combinations encoding astrocyte identity, based on previously published reports. Analysis of the resulting induced astrocytes (iAs) demonstrated that all four cassettes generate cells with the typical morphology of in vitro astrocytes, which expressed astrocyte-specific markers. The transcriptional profiles of all four iAs clustered tightly together and displayed similarities with mature human astrocytes, although maturity levels differed between cells. Importantly, we found that the TF cassettes induced iAs with distinct differences with regards to their cytokine response and calcium signaling. In vivo transplantation of selected iAs into immunocompromised rat brains demonstrated long term stability and integration. In conclusion, all four TF combinations were able to induce stable astrocyte-like cells that were morphologically similar but showed subtle differences with respect to their transcriptome. These subtle differences translated into distinct differences with regards to cell function, that could be related to maturation state and/or regional identity of the resulting cells. This insight opens an opportunity to precision-engineer cells to meet functional requirements, for example, in the context of therapeutic cell transplantation.

Remyelination in animal models of multiple sclerosis: finding the elusive grail of regeneration

Remyelination biology and the therapeutic potential of restoring myelin sheaths to prevent neurodegeneration and disability in multiple sclerosis (MS) has made considerable gains over the past decade with many regeneration strategies undergoing tested in MS clinical trials. Animal models used to investigate oligodendroglial responses and regeneration of myelin vary considerably in the mechanism of demyelination, involvement of inflammatory cells, neurodegeneration and capacity for remyelination. The investigation of remyelination in the context of aging and an inflammatory environment are of considerable interest for the potential translation to progressive multiple sclerosis. Here we review how remyelination is assessed in mouse models of demyelination, differences and advantages of these models, therapeutic strategies that have emerged and current pro-remyelination clinical trials.

The Cuprizone Mouse Model: A Comparative Study of Cuprizone Formulations from Different Manufacturers

The Cuprizone mouse model is widely used in studies on de- and remyelination. In the hands of different experimenters, the Cuprizone concentrations that lead to comparable levels of demyelination differ considerably. The reasons for this variability are unknown. In this study, we tested whether different Cuprizone formulations from different vendors and manufacturers influenced Cuprizone-induced histopathological hallmarks. We intoxicated male C57BL/6 mice with six Cuprizone powders that differed in their manufacturer, vendor, and purity. After five weeks, we analyzed the body weight changes over the course of the experiment, as well as the demyelination, astrogliosis, microgliosis and axonal damage by histological LFB-PAS staining and immunohistochemical labelling of PLP, IBA1, GFAP and APP. All Cuprizone formulations induced demyelination, astrogliosis, microgliosis, axonal damage and a moderate drop in body weight at the beginning of the intoxication period. In a cumulative evaluation of all analyses, two Cuprizone formulations performed weaker than the other formulations. In conclusion, all tested formulations did work, but the choice of Cuprizone formulation may have been responsible for the considerable variability in the experimental outcomes.

Astrocyte-oligodendrocyte interaction regulates central nervous system regeneration

Failed regeneration of myelin around neuronal axons following central nervous system damage contributes to nerve dysfunction and clinical decline in various neurological conditions, for which there is an unmet therapeutic demand. Here, we show that interaction between glial cells - astrocytes and mature myelin-forming oligodendrocytes - is a determinant of remyelination. Using in vivo/ ex vivo/ in vitro rodent models, unbiased RNA sequencing, functional manipulation, and human brain lesion analyses, we discover that astrocytes support the survival of regenerating oligodendrocytes, via downregulation of the Nrf2 pathway associated with increased astrocytic cholesterol biosynthesis pathway activation. Remyelination fails following sustained astrocytic Nrf2 activation in focally-lesioned male mice yet is restored by either cholesterol biosynthesis/efflux stimulation, or Nrf2 inhibition using the existing therapeutic Luteolin. We identify that astrocyte-oligodendrocyte interaction regulates remyelination, and reveal a drug strategy for central nervous system regeneration centred on targeting this interaction.

Therapeutic administration of mouse mast cell protease 6 improves functional recovery after traumatic spinal cord injury in mice by promoting remyelination and reducing glial scar formation

Traumatic spinal cord injury (SCI) most often leads to permanent paralysis due to the inability of axons to regenerate in the adult mammalian central nervous system (CNS). In the past, we have shown that mast cells (MCs) improve the functional outcome after SCI by suppressing scar tissue formation at the lesion site via mouse mast cell protease 6 (mMCP6). In this study, we investigated whether recombinant mMCP6 can be used therapeutically to improve the functional outcome after SCI. Therefore, we applied mMCP6 locally via an intrathecal catheter in the subacute phase after a spinal cord hemisection injury in mice. Our findings showed that hind limb motor function was significantly improved in mice that received recombinant mMCP6 compared with the vehicle-treated group. In contrast to our previous findings in mMCP6 knockout mice, the lesion size and expression levels of the scar components fibronectin, laminin, and axon-growth-inhibitory chondroitin sulfate proteoglycans were not affected by the treatment with recombinant mMCP6. Surprisingly, no difference in infiltration of CD4+ T cells and reactivity of Iba-1+ microglia/macrophages at the lesion site was observed between the mMCP6-treated mice and control mice. Additionally, local protein levels of the pro- and anti-inflammatory mediators IL-1β, IL-2, IL-4, IL-6, IL-10, TNF-α, IFNγ, and MCP-1 were comparable between the two treatment groups, indicating that locally applied mMCP6 did not affect inflammatory processes after injury. However, the increase in locomotor performance in mMCP6-treated mice was accompanied by reduced demyelination and astrogliosis in the perilesional area after SCI. Consistently, we found that TNF-α/IL-1β-astrocyte activation was decreased and that oligodendrocyte precursor cell (OPC) differentiation was increased after recombinant mMCP6 treatment in vitro. Mechanistically, this suggests effects of mMCP6 on reducing astrogliosis and improving (re)myelination in the spinal cord after injury. In conclusion, these data show for the first time that recombinant mMCP6 is therapeutically active in enhancing recovery after SCI.

The Diversity of Astrocyte Activation during Multiple Sclerosis: Potential Cellular Targets for Novel Disease Modifying Therapeutics

Neuroglial cells, and especially astrocytes, constitute the most varied group of central nervous system (CNS) cells, displaying substantial diversity and plasticity during development and in disease states. The morphological changes exhibited by astrocytes during the acute and chronic stages following CNS injury can be characterized more precisely as a dynamic continuum of astrocytic reactivity. Different subpopulations of reactive astrocytes may be ascribed to stages of degenerative progression through their direct pathogenic influence upon neurons, neuroglia, the blood-brain barrier, and infiltrating immune cells. Multiple sclerosis (MS) constitutes an autoimmune demyelinating disease of the CNS. Despite the previously held notion that reactive astrocytes purely form the structured glial scar in MS plaques, their continued multifaceted participation in neuroinflammatory outcomes and oligodendrocyte and neuronal function during chronicity, suggest that they may be an integral cell type that can govern the pathophysiology of MS. From a therapeutic-oriented perspective, astrocytes could serve as key players to limit MS progression, once the integral astrocyte-MS relationship is accurately identified. This review aims toward delineating the current knowledge, which is mainly focused on immunomodulatory therapies of the relapsing-remitting form, while shedding light on uncharted approaches of astrocyte-specific therapies that could constitute novel, innovative applications once the role of specific subgroups in disease pathogenesis is clarified.

Central nervous system demyelinating diseases: glial cells at the hub of pathology

Inflammatory demyelinating diseases (IDDs) are among the main causes of inflammatory and neurodegenerative injury of the central nervous system (CNS) in young adult patients. Of these, multiple sclerosis (MS) is the most frequent and studied, as it affects about a million people in the USA alone. The understanding of the mechanisms underlying their pathology has been advancing, although there are still no highly effective disease-modifying treatments for the progressive symptoms and disability in the late stages of disease. Among these mechanisms, the action of glial cells upon lesion and regeneration has become a prominent research topic, helped not only by the discovery of glia as targets of autoantibodies, but also by their role on CNS homeostasis and neuroinflammation. In the present article, we discuss the participation of glial cells in IDDs, as well as their association with demyelination and synaptic dysfunction throughout the course of the disease and in experimental models, with a focus on MS phenotypes. Further, we discuss the involvement of microglia and astrocytes in lesion formation and organization, remyelination, synaptic induction and pruning through different signaling pathways. We argue that evidence of the several glia-mediated mechanisms in the course of CNS demyelinating diseases supports glial cells as viable targets for therapy development.

Transcriptomic atlas and interaction networks of brain cells in mouse CNS demyelination and remyelination

Demyelination is a hallmark of multiple sclerosis, leukoencephalopathies, cerebral vasculopathies, and several neurodegenerative diseases. The cuprizone mouse model is widely used to simulate demyelination and remyelination occurring in these diseases. Here, we present a high-resolution single-nucleus RNA sequencing (snRNA-seq) analysis of gene expression changes across all brain cells in this model. We define demyelination-associated oligodendrocytes (DOLs) and remyelination-associated MAFBhi microglia, as well as astrocytes and vascular cells with signatures of altered metabolism, oxidative stress, and interferon response. Furthermore, snRNA-seq provides insights into how brain cell types connect and interact, defining complex circuitries that impact demyelination and remyelination. As an explicative example, perturbation of microglia caused by TREM2 deficiency indirectly impairs the induction of DOLs. Altogether, this study provides a rich resource for future studies investigating mechanisms underlying demyelinating diseases.

Activation of TRPV1 receptor facilitates myelin repair following demyelination via the regulation of microglial function

The transient receptor potential vanilloid 1 (TRPV1) is a non-selective cation channel that is activated by capsaicin (CAP), the main component of chili pepper. Despite studies in several neurological diseases, the role of TRPV1 in demyelinating diseases remains unknown. Herein, we reported that TRPV1 expression was increased within the corpus callosum during demyelination in a cuprizone (CPZ)-induced demyelination mouse model. TRPV1 deficiency exacerbated motor coordinative dysfunction and demyelination in CPZ-treated mice, whereas the TRPV1 agonist CAP improved the behavioral performance and facilitated remyelination. TRPV1 was predominantly expressed in Iba1+ microglia/macrophages in human brain sections of multiple sclerosis patients and mouse corpus callosum under demyelinating conditions. TRPV1 deficiency decreased microglial recruitment to the corpus callosum, with an associated increase in the accumulation of myelin debris. Conversely, the activation of TRPV1 by CAP enhanced the recruitment of microglia to the corpus callosum and potentiated myelin debris clearance. Using real-time live imaging we confirmed an increased phagocytic function of microglia following CAP treatment. In addition, the expression of the scavenger receptor CD36 was increased, and that of the glycolysis regulators Hif1a and Hk2 was decreased. We conclude that TRPV1 is an important regulator of microglial function in the context of demyelination and may serve as a promising therapeutic target for demyelinating diseases such as multiple sclerosis.

The Tryptophan-Kynurenine Metabolic System Is Suppressed in Cuprizone-Induced Model of Demyelination Simulating Progressive Multiple Sclerosis

Progressive multiple sclerosis (MS) is a chronic disease with a unique pattern, which is histologically classified into the subpial type 3 lesions in the autopsy. The lesion is also homologous to that of cuprizone (CPZ) toxin-induced animal models of demyelination. Aberration of the tryptophan (TRP)-kynurenine (KYN) metabolic system has been observed in patients with MS; nevertheless, the KYN metabolite profile of progressive MS remains inconclusive. In this study, C57Bl/6J male mice were treated with 0.2% CPZ toxin for 5 weeks and then underwent 4 weeks of recovery. We measured the levels of serotonin, TRP, and KYN metabolites in the plasma and the brain samples of mice at weeks 1, 3, and 5 of demyelination, and at weeks 7 and 9 of remyelination periods by ultra-high-performance liquid chromatography with tandem mass spectrometry (UHPLC-MS/MS) after body weight measurement and immunohistochemical analysis to confirm the development of demyelination. The UHPLC-MS/MS measurements demonstrated a significant reduction of kynurenic acid, 3-hydoxykynurenine (3-HK), and xanthurenic acid in the plasma and a significant reduction of 3-HK, and anthranilic acid in the brain samples at week 5. Here, we show the profile of KYN metabolites in the CPZ-induced mouse model of demyelination. Thus, the KYN metabolite profile potentially serves as a biomarker of progressive MS and thus opens a new path toward planning personalized treatment, which is frequently obscured with immunologic components in MS deterioration.

The roles of microglia and astrocytes in myelin phagocytosis in the central nervous system

Myelination is an important process in the central nervous system (CNS). Oligodendrocytes (OLs) extend multiple layers to densely sheath on axons, composing the myelin to achieve efficient electrical signal conduction. The myelination during developmental stage maintains a balanced state. However, numerous CNS diseases including neurodegenerative and cerebrovascular diseases cause demyelination and disrupt the homeostasis, resulting in inflammation and white matter deficits. Effective clearance of myelin debris is needed in the region of demyelination, which is a key step for remyelination and tissue regeneration. Microglia and astrocytes are the major resident phagocytic cells in the brain, which may play different or collaborative roles in myelination. Microglia and astrocytes participate in developmental myelination through engulfing excessive unneeded myelin. They are also involved in the clearance of degenerated myelin debris for accelerating remyelination, or engulfing healthy myelin sheath for inhibiting remyelination. This review focuses on the roles of microglia and astrocytes in phagocytosing myelin in the developmental brain and diseased brain. In addition, the interaction between microglia and astrocytes to mediate myelin engulfment is also summarized.

Deletion of Nox4 enhances remyelination following cuprizone-induced demyelination by increasing phagocytic capacity of microglia and macrophages in mice

NOX4 is a major reactive oxygen species-producing enzyme that modulates cell stress responses. We here examined the effect of Nox4 deletion on demyelination-remyelination, the most common pathological change in the brain. We used a model of cuprizone (CPZ)-associated demyelination-remyelination in wild-type and Nox4-deficient (Nox4^-/- ) mice. While the CPZ-induced demyelination in the corpus callosum after 4 weeks of CPZ intoxication was slightly less pronounced in Nox4^-/- mice than that in wild-type mice, remyelination following CPZ withdrawal was significantly enhanced in Nox4^-/- mice with an increased accumulation of IBA1-positive microglia/macrophages in the demyelinating corpus callosum. Consistently, locomotor function, as assessed by the beam walking test, was significantly better during the remyelination phase in Nox4^-/- mice. Nox4 deletion did not affect autonomous growth of primary-culture oligodendrocyte precursor cells. Although Nox4 expression was higher in cultured macrophages than in microglia, Nox4^-/- microglia and macrophages both showed enhanced phagocytic capacity of myelin debris and produced increased amounts of trophic factors upon phagocytosis. The expression of trophic factors was higher, in parallel with the accumulation of IBA1-positive cells, in the corpus callosum in Nox4^-/- mice than that in wild-type mice. Nox4 deletion suppressed phagocytosis-induced increase in mitochondrial membrane potential, enhancing phagocytic capacity of macrophages. Treatment with culture medium of Nox4^-/- macrophages engulfing myelin debris, but not that of Nox4^-/- astrocytes, enhanced cell growth and expression of myelin-associated proteins in cultured oligodendrocyte precursor cells. Collectively, Nox4 deletion promoted remyelination after CPZ-induced demyelination by enhancing microglia/macrophage-mediated clearance of myelin debris and the production of trophic factors leading to oligodendrogenesis.

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.

How does neurovascular unit dysfunction contribute to multiple sclerosis?

Multiple sclerosis is an inflammatory demyelinating disease of the central nervous system (CNS) and the most common non-traumatic cause of neurological disability in young adults. Multiple sclerosis clinical care has improved considerably due to the development of disease-modifying therapies that effectively modulate the peripheral immune response and reduce relapse frequency. However, current treatments do not prevent neurodegeneration and disease progression, and efforts to prevent multiple sclerosis will be hampered so long as the cause of this disease remains unknown. Risk factors for multiple sclerosis development or severity include vitamin D deficiency, cigarette smoking and youth obesity, which also impact vascular health. People with multiple sclerosis frequently experience blood-brain barrier breakdown, microbleeds, reduced cerebral blood flow and diminished neurovascular reactivity, and it is possible that these vascular pathologies are tied to multiple sclerosis development. The neurovascular unit is a cellular network that controls neuroinflammation, maintains blood-brain barrier integrity, and tightly regulates cerebral blood flow, matching energy supply to neuronal demand. The neurovascular unit is composed of vessel-associated cells such as endothelial cells, pericytes and astrocytes, however neuronal and other glial cell types also comprise the neurovascular niche. Recent single-cell transcriptomics data, indicate that neurovascular cells, particular cells of the microvasculature, are compromised within multiple sclerosis lesions. Large-scale genetic and small-scale cell biology studies also suggest that neurovascular dysfunction could be a primary pathology contributing to multiple sclerosis development. Herein we revisit multiple sclerosis risk factors and multiple sclerosis pathophysiology and highlight the known and potential roles of neurovascular unit dysfunction in multiple sclerosis development and disease progression. We also evaluate the suitability of the neurovascular unit as a potential target for future disease modifying therapies for multiple sclerosis.

Astrocytic TIMP-1 regulates production of Anastellin, a novel inhibitor of oligodendrocyte differentiation and FTY720 responses

Astrocyte activation is associated with neuropathology and the production of tissue inhibitor of metalloproteinase-1 (TIMP1). TIMP1 is a pleiotropic extracellular protein that functions both as a protease inhibitor and as a growth factor. We have previously demonstrated that murine astrocytes that lack expression of Timp1 do not support rat oligodendrocyte progenitor cell (rOPC) differentiation, and adult global Timp1 knockout ( Timp1 KO ) mice do not efficiently remyelinate following a demyelinating injury. To better understand the basis of this, we performed unbiased proteomic analyses and identified a fibronectin-derived peptide called anastellin that is unique to the murine Timp1 KO astrocyte secretome. Anastellin was found to block rOPC differentiation in vitro and enhanced the inhibitory influence of fibronectin on rOPC differentiation. Anastellin is known to act upon the sphingosine-1-phosphate receptor 1 (S1PR1), and we determined that anastellin also blocked the pro-myelinating effect of FTY720 (or fingolimod) on rOPC differentiation in vitro . Further, administration of FTY720 to wild-type C57BL/6 mice during MOG 35-55 -EAE ameliorated clinical disability while FTY720 administered to mice lacking expression of Timp1 in astrocytes ( Timp1 cKO ) had no effect. Analysis of human TIMP1 and fibronectin ( FN1 ) transcripts from healthy and multiple sclerosis (MS) patient brain samples revealed an inverse relationship where lower TIMP1 expression was coincident with elevated FN1 in MS astrocytes. Lastly, we analyzed proteomic databases of MS samples and identified anastellin peptides to be more abundant in the cerebrospinal fluid (CSF) of human MS patients with high versus low disease activity. The prospective role for anastellin generation in association with myelin lesions as a consequence of a lack of astrocytic TIMP-1 production could influence both the efficacy of fingolimod responses and the innate remyelination potential of the the MS brain.

Significance Statement

Astrocytic production of TIMP-1 prevents the protein catabolism of fibronectin. In the absence of TIMP-1, fibronectin is further digested leading to a higher abundance of anastellin peptides that can bind to sphingosine-1-phosphate receptor 1. The binding of anastellin with the sphingosine-1-phosphate receptor 1 impairs the differentiation of oligodendrocytes progenitor cells into myelinating oligodendrocytes in vitro , and negates the astrocyte-mediated therapeutic effects of FTY720 in the EAE model of chronic CNS inflammation. These data indicate that TIMP-1 production by astrocytes is important in coordinating astrocytic functions during inflammation. In the absence of astrocyte produced TIMP-1, elevated expression of anastellin may represent a prospective biomarker for FTY720 therapeutic responsiveness.

Genetic models of cleavage-reduced and soluble TREM2 reveal distinct effects on myelination and microglia function in the cuprizone model

Triggering receptor expressed on myeloid cells 2 (TREM2) is a cell-surface immunoreceptor expressed on microglia, osteoclasts, dendritic cells and macrophages. Heterozygous loss-of-function mutations in TREM2, including mutations enhancing shedding form the cell surface, have been associated with myelin/neuronal loss and neuroinflammation in neurodegenerative diseases, such as Alzheimer`s disease and Frontotemporal Dementia. Using the cuprizone model, we investigated the involvement of soluble and cleavage-reduced TREM2 on central myelination processes in cleavage-reduced (TREM2-IPD), soluble-only (TREM2-sol), knockout (TREM2-KO) and wild-type (WT) mice. The TREM2-sol mouse is a new model with selective elimination of plasma membrane TREM2 and a reduced expression of soluble TREM2. In the acute cuprizone model demyelination and remyelination events were reflected by a T2-weighted signal intensity change in magnetic resonance imaging (MRI), most prominently in the external capsule (EC). In contrast to WT and TREM2-IPD, TREM2-sol and TREM2-KO showed an additional increase in MRI signal during the recovery phase. Histological analyses of TREM2-IPD animals revealed no recovery of neuroinflammation as well as of the lysosomal marker LAMP-1 and displayed enhanced cytokine/chemokine levels in the brain. TREM2-sol and, to a much lesser extent, TREM2-KO, however, despite presenting reduced levels of some cytokines/chemokines, showed persistent microgliosis and astrocytosis during recovery, with both homeostatic (TMEM119) as well as activated (LAMP-1) microglia markers increased. This was accompanied, specifically in the EC, by no myelin recovery, with appearance of myelin debris and axonal pathology, while oligodendrocytes recovered. In the chronic model consisting of 12-week cuprizone administration followed by 3-week recovery TREM2-IPD displayed sustained microgliosis and enhanced remyelination in the recovery phase. Taken together, our data suggest that sustained microglia activation led to increased remyelination, whereas microglia without plasma membrane TREM2 and only soluble TREM2 had reduced phagocytic activity despite efficient lysosomal function, as observed in bone marrow-derived macrophages, leading to a dysfunctional phenotype with improper myelin debris removal, lack of remyelination and axonal pathology following cuprizone intoxication.

Oligodendrogenesis and myelination tracing in a CRISPR/Cas9-engineered brain microphysiological system

Introduction

Oligodendrocytes (OLs) are the myelin-forming cells of the central nervous system (CNS). Although OLs can be differentiated from human-induced pluripotent stem cells (hiPSCs), the in vitro modeling of axon myelination in human cells remains challenging. Brain microphysiological systems (bMPS, e.g. organoids) are complex three-dimensional (3D) cultures that offer an ideal system to study this process as OLs differentiate in a more in vivo-like environment; surrounded by neurons and astrocytes, which support the myelination of axons.

Methods

Here, we take advantage of CRISPR/Cas9 technology to generate a hiPSC line in which proteolipid protein 1 (PLP1), an OLs marker, is tagged with super-fold GFP (sfGFP). While generating the PLP1-sfGFP reporter, we used reverse transfection and obtained higher Knock-In (KI) efficiency compared to forward transfection (61-72 vs. 46%).

Results

After validation of the KI and quality control of the PLP1-sfGFP line, selected clones were differentiated into bMPS, and the fidelity, specificity, and function of the tagged PLP protein were verified in this model. We tracked different stages of oligodendrogenesis in the verified lines based on PLP1-sfGFP+ cells' morphology, and the presence of PLP1-sfGFP surrounding axons during bMPS' differentiation. Finally, we challenged the bMPS with cuprizone and quantified changes in both the percentage of PLP1-sfGFP expressing cells and the intensity of GFP expression.

Discussion

This work demonstrates an efficient method for generating hiPSC KI lines and the description of a new 3D model to study OL differentiation, migration, and maturation both during in vitro neurodevelopment as well as in response to environmental chemicals or disease-associated stressors.

Glial aging and its impact on central nervous system myelin regeneration

Aging is a major risk factor for several neurodegenerative diseases and is associated with cognitive decline. In addition to affecting neuronal function, the aging process significantly affects the functional phenotype of the glial cell compartment, comprising oligodendrocyte lineage cells, astrocytes, and microglia. These changes result in a more inflammatory microenvironment, resulting in a condition that is favorable for neuron and synapse loss. In addition to facilitating neurodegeneration, the aging glial cell population has negative implications for central nervous system remyelination, a regenerative process that is of particular importance to the chronic demyelinating disease multiple sclerosis. This review will discuss the changes that occur with aging in the three main glial populations and provide an overview of the studies documenting the impact these changes have on remyelination.

Combination Therapy of Mesenchymal Stem Cell Transplantation and Astrocyte Ablation Improve Remyelination in a Cuprizone-Induced Demyelination Mouse Model

Astrocytes display an active, dual, and controversial role in multiple sclerosis (MS), a chronic inflammatory demyelination disorder. However, mesenchymal stem cells (MSCs) can affect myelination in demyelinating disorders. This study aimed to investigate the effect of single and combination therapies of astrocyte ablation and MSC transplantation on remyelination in the cuprizone (CPZ) model of MS. C57BL/6 mice were fed 0.2% CPZ diet for 12 weeks. Astrocytes were ablated twice by L-a-aminoadipate (L-AAA) at the beginning of weeks 13 and 14 whereas MSCs were injected in the corpus callosum at the beginning of week 13. Motor coordination and balance were assessed through rotarod test whereas myelin content was evaluated by Luxol-fast blue (LFB) staining and transmission electron microscopy (TEM). Glial cells were assessed by immunofluorescence staining while mRNA expression was evaluated by quantitative real-time PCR. Combination treatment of ablation of astrocytes and MSC transplantation (CPZ + MSC + L-AAA) significantly decreased motor coordination deficits better than single treatments (CPZ + MSCs or CPZ + L-AAA), in comparison to CPZ mice. In addition, L-AAA and MSCs treatment significantly enhanced remyelination compared to CPZ group. Moreover, combination therapy caused a significant decrease in the number of GFAP⁺ and Iba-1⁺ cells, whereas oligodendrocytes were significantly increased in comparison to CPZ mice. Finally, MSC administration resulted in a significant upregulation of BDNF and NGF mRNA expression levels. Our data indicate that transient ablation of astrocytes along with MSCs treatment improve remyelination through enhancing oligodendrocytes and attenuating gliosis in a chronic demyelinating mouse model of MS.

Opposing effects of apoE2 and apoE4 on microglial activation and lipid metabolism in response to demyelination

BACKGROUND

Abnormal lipid accumulation has been recognized as a key element of immune dysregulation in microglia whose dysfunction contributes to neurodegenerative diseases. Microglia play essential roles in the clearance of lipid-rich cellular debris upon myelin damage or demyelination, a common pathogenic event in neuronal disorders. Apolipoprotein E (apoE) plays a pivotal role in brain lipid homeostasis; however, the apoE isoform-dependent mechanisms regulating microglial response upon demyelination remain unclear.

METHODS

To determine how apoE isoforms impact microglial response to myelin damage, 2-month-old apoE2-, apoE3-, and apoE4-targeted replacement (TR) mice were fed with normal diet (CTL) or 0.2% cuprizone (CPZ) diet for four weeks to induce demyelination in the brain. To examine the effects on subsequent remyelination, the cuprizone diet was switched back to regular chow for an additional two weeks. After treatment, brains were collected and subjected to immunohistochemical and biochemical analyses to assess the myelination status, microglial responses, and their capacity for myelin debris clearance. Bulk RNA sequencing was performed on the corpus callosum (CC) to address the molecular mechanisms underpinning apoE-mediated microglial activation upon demyelination.

RESULTS

We demonstrate dramatic isoform-dependent differences in the activation and function of microglia upon cuprizone-induced demyelination. ApoE2 microglia were hyperactive and more efficient in clearing lipid-rich myelin debris, whereas apoE4 microglia displayed a less activated phenotype with reduced clearance efficiency, compared with apoE3 microglia. Transcriptomic profiling revealed that key molecules known to modulate microglial functions had differential expression patterns in an apoE isoform-dependent manner. Importantly, apoE4 microglia had excessive buildup of lipid droplets, consistent with an impairment in lipid metabolism, whereas apoE2 microglia displayed a superior ability to metabolize myelin enriched lipids. Further, apoE2-TR mice had a greater extent of remyelination; whereas remyelination was compromised in apoE4-TR mice.

CONCLUSIONS

Our findings provide critical mechanistic insights into how apoE isoforms differentially regulate microglial function and the maintenance of myelin dynamics, which may inform novel therapeutic avenues for targeting microglial dysfunctions in neurodegenerative diseases.

Myelin repair is fostered by the corticosteroid medrysone specifically acting on astroglial subpopulations

Background

Multiple sclerosis is characterised by inflammation, oligodendrocyte loss and axonal demyelination and shows an additional impact on astrocytes, and their polarization. Although a certain degree of spontaneous myelin repair can be observed, disease progression, and aging impair regeneration efforts highlighting the need to better understand glial cell dynamics to establish specific regenerative treatments.

Methods

Applying a chronic demyelination model, we here analysed demyelination and remyelination related effects on astrocytes and stem cell niches and studied the consequences of medrysone application on myelin repair, and astrocyte polarization.

Findings

Medrysone induced recovery of mature oligodendrocytes, myelin expression and node formation. In addition, C3d/S100a10 co-expression in astrocytes was enhanced. Moreover, Timp1 expression in C3d positive astrocytes revealed another astrocytic phenotype with a myelination promoting character.

Interpretation

Based on these findings, specific astrocyte subpopulations are suggested to act in a myelin regenerative way and manner the regulation of which can be positively modulated by this corticosteroid.

Funding

This work was supported by the Jürgen Manchot Stiftung, the Research Commission of the medical faculty of the Heinrich-Heine-University of Düsseldorf, the Christiane and Claudia Hempel Foundation for clinical stem cell research and the James and Elisabeth Cloppenburg, Peek and Cloppenburg Düsseldorf Stiftung.

Neuroecotoxicology: Effects of environmental heavy metal exposure on the brain of African giant rats and the contribution of vanadium to the neuropathology

Increased exploitation of minerals has led to pollution of confined environments as documented in Nigeria Niger Delta. Information on the effects on brain of such exposure is limited. Due to its exploratory activities, the African giant rat (Cricetomys gambianus) (AGR) provides a unique model for neuroecotoxicological research to determine levels of animal and human exposure to different pollutants. This study aims to unravel neuropathological features of AGR sampled from three agro-ecological zones of Nigeria. Fifteen AGR were sampled according to previously determined data on heavy metal exposure: high vanadium, high lead, and low metals. Eighteen AGR were collected from low metal zone and divided into two groups. Control group received vehicle while SMV exposed group received 3 mg/kg sodium metavanadate (SMV) intraperitoneally for 14days. Brain immunohistochemical analyses were conducted, and ultrastructural changes were studied in experimentally exposed group. Results showed significant loss of tyrosin hydroxylase, parvalbumin, orexin-A and melanin concentration hormone containing neuronal populations in brains obtained from high vanadium and high lead zones and in experimentally intoxicated SMV groups. Similarly, significant decrease numbers of dendritic arborations; extracellular matrix density, perineuronal nets; astrocytes and microglia activations are documented in same groups. Ultrastructural studies revealed mass denudation, cilia loss, disintegration of ependymal layer and intense destructions of myelin sheaths in SMV exposed group. These are the first "neuroecotoxicological" findings in distinct neuronal cells. The implications of these findings are highly relevant for human population living in these areas, not only in Nigeria but also in similarly polluted areas elsewhere in the world.

Human Primary Astrocytes Differently Respond to Pro- and Anti-Inflammatory Stimuli

For a long time, astrocytes were considered a passive brain cell population. However, recently, many studies have shown that their role in the central nervous system (CNS) is more active. Previously, it was stated that there are two main functional phenotypes of astrocytes. However, nowadays, it is clear that there is rather a broad spectrum of these phenotypes. The major goal of this study was to evaluate the production of some inflammatory chemokines and neurotrophic factors by primary human astrocytes after pro- or anti-inflammatory stimulation. We observed that only astrocytes induced by inflammatory mediators TNFα/IL-1a/C1q produced CXCL10, CCL1, and CXCL13 chemokines. Unstimulated astrocytes and those cultured with anti-inflammatory cytokines (IL-4, IL-10, or TGF-β1) did not produce these chemokines. Interestingly, astrocytes cultured in proinflammatory conditions significantly decreased the release of neurotrophic factor PDGF-A, as compared to unstimulated astrocytes. However, in response to anti-inflammatory cytokine TGF-β1, astrocytes significantly increased PDGF-A production compared to the medium alone. The production of another studied neurotrophic factor BDNF was not influenced by pro- or anti-inflammatory stimulation. The secretory response was accompanied by changes in HLA-DR, CD83, and GFAP expression. Our study confirms that astrocytes differentially respond to pro- and anti-inflammatory stimuli, especially to inflammatory cytokines TNF-α, IL-1a, and C1q, suggesting their role in leukocyte recruitment.

Hybrid 18F-florbetapir PET/MRI for assessing myelin recovery in GFAP-A patients

Glial fibrillary acidic protein astrocytopathy (GFAP-A) is a rare autoimmune disease of the central nervous system that was newly reported in 2016. Previous studies have speculated that the pathological mechanism and clinical outcome of GFAP-A lie in the demyelination of the central nervous system, but due to the limitations of MR, this conclusion has not been further confirmed from the perspective of neuroimaging. A non-invasive, quantitative measurement of demyelination would be clinically valuable, given its critical role in mediating GFAP-A. Here, we report a case in which we use ¹⁸F-florbetapir positron emission tomography-magnetic resonance imaging (PET/MRI) to evaluate myelin recovery with follow-up in the patient with GFAP-A. Our patient displayed a decreased uptake of PET tracer ¹⁸F-florbetapir in the brain lesions and lower distribution volume ratio in the damaged white matter lesions compared to the normal-appearing white matter, indicating significant intracranial demyelination. After treatment, the ¹⁸F-florbetapir PET/MRI examination showed a significant increase in the uptake of ¹⁸F-florbetapir in the brain lesions, along with a reduced Expanded Disability Status Scale score. Although only a small number of patients have been validated, this case first reported ¹⁸F-florbetapir PET/MRI could quantitatively and non-invasively assess the myelin recovery in GFAP-A patients, which may lead to improvements in the early diagnosis and long-term prognosis.

Different Methods for Evaluating Microglial Activation Using Anti-Ionized Calcium-Binding Adaptor Protein-1 Immunohistochemistry in the Cuprizone Model

Microglia play an important role in the pathology of various central nervous system disorders, including multiple sclerosis (MS). While different methods exist to evaluate the extent of microglia activation, comparative studies investigating the sensitivity of these methods are missing for most models. In this study, we systematically evaluated which of the three commonly used histological methods (id est, quantification of microglia density, densitometrically evaluated staining intensity, or cellular morphology based on the determination of a ramification index, all measured in anti-ionized calcium-binding adaptor protein-1 (IBA1) immunohistochemical stains) is the most sensitive method to detect subtle changes in the microglia activation status in the context of MS. To this end, we used the toxin-induced cuprizone model which allows the experimental induction of a highly reproducible demyelination in several central nervous system regions, paralleled by early microglia activation. In this study, we showed that after 3 weeks of cuprizone intoxication, all methods reveal a significant microglia activation in the white matter corpus callosum. In contrast, in the affected neocortical grey matter, the evaluation of anti-IBA1 cell morphologies was the most sensitive method to detect subtle changes of microglial activation. The results of this study provide a useful guide for future immunohistochemical evaluations in the cuprizone and other neurodegenerative models.