The benefits and detriments of macrophages/microglia in models of multiple sclerosis. Clin Dev Immunol. 2013;2013:948976. [PMID: 23840244 PMCID: PMC3694375 DOI: 10.1155/2013/948976]

Multiple sclerosis risk gene Mertk is required for microglial activation and subsequent remyelination

In multiple sclerosis (MS) and other neurological diseases, the failure to repair demyelinated lesions contributes to axonal damage and clinical disability. Here, we provide evidence that Mertk, a gene highly expressed by microglia that alters MS risk, is required for efficient remyelination. Compared to wild-type (WT) mice, Mertk-knockout (KO) mice show impaired clearance of myelin debris and remyelination following demyelination. Using single-cell RNA sequencing, we characterize Mertk-influenced responses to cuprizone-mediated demyelination and remyelination across different cell types. Mertk-KO brains show an attenuated microglial response to demyelination but an elevated proportion of interferon (IFN)-responsive microglia. In addition, we identify a transcriptionally distinct subtype of surviving oligodendrocytes specific to demyelinated lesions. The inhibitory effect of myelin debris on remyelination is mediated in part by IFNγ, which further impedes microglial clearance of myelin debris and inhibits oligodendrocyte differentiation. Together, our work establishes a role for Mertk in microglia activation, phagocytosis, and migration during remyelination.

Peroxisome Proliferator-Activated Receptor-δ Deficiency in Microglia Results in Exacerbated Axonal Injury and Tissue Loss in Experimental Autoimmune Encephalomyelitis

Peroxisome proliferator-activated receptor (PPAR)-δ is a nuclear receptor that functions to maintain metabolic homeostasis, regulate cell growth, and limit the development of excessive inflammation during immune responses. Previously, we reported that PPAR-δ-deficient mice develop a more severe clinical course of experimental autoimmune encephalomyelitis (EAE); however, it was difficult to delineate the role that microglia played in this disease phenotype since PPAR-δ-deficient mice exhibited a number of immune defects that enhanced CNS inflammation upstream of microglia activation. Here, we specifically investigated the role of PPAR-δ in microglia during EAE by using mice where excision of a floxed Ppard allele was driven by expression of a tamoxifen (TAM)-inducible CX3C chemokine receptor 1 promoter-Cre recombinase transgene (Cx3cr1^CreERT2: Ppard^fl/fl). We observed that by 30 days of TAM treatment, Cx3cr1^CreERT2: Ppard^fl/fl mice exhibited Cre-mediated deletion primarily in microglia and this was accompanied by efficient knockdown of Ppard expression in these cells. Upon induction of EAE, TAM-treated Cx3cr1^CreERT2: Ppard^fl/fl mice presented with an exacerbated course of disease compared to TAM-treated Ppard^fl/fl controls. Histopathological and magnetic resonance (MR) studies on the spinal cord and brains of EAE mice revealed increased Iba-1 immunoreactivity, axonal injury and CNS tissue loss in the TAM-treated Cx3cr1^CreERT2: Ppard^fl/fl group compared to controls. In early EAE, a time when clinical scores and the infiltration of CD45⁺ leukocytes was equivalent between Cx3cr1^CreERT2: Ppard^fl/fl and Ppard^fl/fl mice, Ppard-deficient microglia exhibited a more reactive phenotype as evidenced by a shorter maximum process length and lower expression of genes associated with a homeostatic microglia gene signature. In addition, Ppard-deficient microglia exhibited increased expression of genes associated with reactive oxygen species generation, phagocytosis and lipid clearance, M2-activation, and promotion of inflammation. Our results therefore suggest that PPAR-δ has an important role in microglia in limiting bystander tissue damage during neuroinflammation.

Neuregulin-1 beta 1 is implicated in pathogenesis of multiple sclerosis

Multiple sclerosis is characterized by immune mediated neurodegeneration that results in progressive, life-long neurological and cognitive impairments. Yet, the endogenous mechanisms underlying multiple sclerosis pathophysiology are not fully understood. Here, we provide compelling evidence that associates dysregulation of neuregulin-1 beta 1 (Nrg-1β1) with multiple sclerosis pathogenesis and progression. In the experimental autoimmune encephalomyelitis model of multiple sclerosis, we demonstrate that Nrg-1β1 levels are abated within spinal cord lesions and peripherally in the plasma and spleen during presymptomatic, onset and progressive course of the disease. We demonstrate that plasma levels of Nrg-1β1 are also significantly reduced in individuals with early multiple sclerosis and is positively associated with progression to relapsing-remitting multiple sclerosis. The functional impact of Nrg-1β1 downregulation preceded disease onset and progression, and its systemic restoration was sufficient to delay experimental autoimmune encephalomyelitis symptoms and alleviate disease burden. Intriguingly, Nrg-1β1 therapy exhibited a desirable and extended therapeutic time window of efficacy when administered prophylactically, symptomatically, acutely or chronically. Using in vivo and in vitro assessments, we identified that Nrg-1β1 treatment mediates its beneficial effects in EAE by providing a more balanced immune response. Mechanistically, Nrg-1β1 moderated monocyte infiltration at the blood-CNS interface by attenuating chondroitin sulphate proteoglycans and MMP9. Moreover, Nrg-1β1 fostered a regulatory and reparative phenotype in macrophages, T helper type 1 (Th1) cells and microglia in the spinal cord lesions of EAE mice. Taken together, our new findings in multiple sclerosis and experimental autoimmune encephalomyelitis have uncovered a novel regulatory role for Nrg-1β1 early in the disease course and suggest its potential as a specific therapeutic target to ameliorate disease progression and severity.

Adoptive transfer of immunomodulatory M2 macrophages suppresses experimental autoimmune encephalomyelitis in C57BL/6 mice via blockading NF-κB pathway

Macrophages play important roles in multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE), and M2 macrophage may have anti-inflammatory effects. In this study, we elucidated the roles of M1 and M2 macrophages in the pathogenesis of EAE and the effects of treatment with M2 macrophages that target certain proinflammatory cytokines and with immunomodulatory preparations that beneficially influence the disease course. We found macrophages increased at the onset of clinical signs in the EAE group, consistent with an increased proportion of M1 macrophages and low numbers of M2 macrophages. As the disease progressed and the symptoms worsened, M1 macrophages decreased and M2 macrophages gradually increased until the peak. In the recovery stage, M2 macrophages gradually decreased. Treatment with M2 macrophages inhibited the nuclear factor kappa B (NF-κB) pathway, alleviated the symptoms of EAE, reduced inflammatory cell infiltration and demyelination in the central nervous system and decreased the numbers of macrophages in the spleens. BAY-11-7082, an NF-κB blocking agent, could reduce the total number of macrophages both in vivo and in vitro, effectively prevented EAE development and significantly inhibited EAE symptoms in mice. Our study demonstrates that macrophages may play a crucial role in the pathogenesis of EAE, while M2 macrophages have anti-inflammatory effects. Transfer of M2 macrophages to EAE mice can block the NF-κB pathway successfully and relieve EAE symptoms. Application of NF-κB blockers is useful in the prevention and treatment of EAE.

Promoting remyelination in multiple sclerosis

The greatest unmet need in multiple sclerosis (MS) are treatments that delay, prevent or reverse progression. One of the most tractable strategies to achieve this is to therapeutically enhance endogenous remyelination; doing so restores nerve conduction and prevents neurodegeneration. The biology of remyelination-centred on the activation, migration, proliferation and differentiation of oligodendrocyte progenitors-has been increasingly clearly defined and druggable targets have now been identified in preclinical work leading to early phase clinical trials. With some phase 2 studies reporting efficacy, the prospect of licensed remyelinating treatments in MS looks increasingly likely. However, there remain many unanswered questions and recent research has revealed a further dimension of complexity to this process that has refined our view of the barriers to remyelination in humans. In this review, we describe the process of remyelination, why this fails in MS, and the latest research that has given new insights into this process. We also discuss the translation of this research into clinical trials, highlighting the treatments that have been tested to date, and the different methods of detecting remyelination in people.

Go-sha-jinki-Gan Alleviates Inflammation in Neurological Disorders via p38-TNF Signaling in the Central Nervous System

Go-sha-jinki-Gan (GJG) is a traditional Japanese herbal medicine. In clinical practice, GJG is effective against neuropathic pain and hypersensitivity induced by chemotherapy or diabetes. In our previous study using a chronic constriction injury mouse model, we showed that GJG inhibited microglia activation by suppressing the expression of tumor necrosis factor-α (TNF-α) and p38 mitogen-activated protein kinase (p38 MAPK) in the peripheral nervous system. To investigate whether GJG can suppress inflammation in the central nervous system (CNS) in the context of neurological disorders, we examined the effect of GJG on the activation of resident glial cells and on p38-TNF signaling in two mouse models of neurological disorders: the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis and the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinson's disease. GJG administration relieved the severity of clinical EAE symptoms and MPTP-induced inflammation by decreasing the number of microglia and the production of TNF-α in the spinal cord of EAE mice and the substantia nigra of MPTP-treated mice. Accordingly, GJG suppressed the phosphorylation of p38 in glial cells of these two mouse models. We conclude that GJG attenuates inflammation of the CNS by suppressing glial cell activation, followed by a decrease in the production of TNF-α via p38-TNF signaling.

Continuous and interval training attenuate encephalomyelitis by separate immunomodulatory mechanisms

BACKGROUND

Studies have reported beneficial effects of exercise training on autoimmunity, and specifically on multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). However, it is unknown whether different training paradigms affect disease course via shared or separate mechanisms.

OBJECTIVE

To compare the effects and mechanism of immune modulation of high intensity continuous training (HICT) versus high intensity interval training (HIIT) on systemic autoimmunity in EAE.

METHODS

We used the proteolipid protein (PLP)-induced transfer EAE model to examine training effects on the systemic autoimmune response. Healthy mice performed HICT or HIIT by running on a treadmill. Lymph-node (LN)-T cells from PLP-immunized trained- versus sedentary donor mice were transferred to naïve recipients and EAE clinical and pathological severity were assessed. LN cells derived from donor trained and sedentary PLP-immunized mice were analyzed in vitro for T-cell activation and proliferation, immune cell profiling, and cytokine mRNA levels and cytokine secretion measurements.

RESULTS

Both HICT and HIIT attenuated the encephalitogenicity of PLP-reactive T cells, as indicated by reduced EAE clinical severity and inflammation and tissue pathology in the central nervous system, following their transfer into recipient mice. HICT caused a marked inhibition of PLP-induced T-cell proliferation without affecting the T-cell profile. In contrast, HIIT did not alter T-cell proliferation, but rather inhibited polarization of T cells into T-helper 1 and T-helper 17 autoreactive populations.

INTERPRETATION

HICT and HIIT attenuate systemic autoimmunity and T cell encephalitogenicity by distinct immunomodulatory mechanisms.

Oleacein Attenuates the Pathogenesis of Experimental Autoimmune Encephalomyelitis through Both Antioxidant and Anti-Inflammatory Effects

Oxidative stress and proinflammatory cytokines are factors affecting multiple sclerosis (MS) disease progression. Oleacein (OLE), an olive secoiridoid, possesses powerful antioxidant and anti-inflammatory activities, which suggests its potential application to treat neuroinflammatory disorders. Herein, we investigated the impact of OLE on the main clinic-pathological features of experimental autoimmune encephalomyelitis (EAE), an animal model for MS, including paralysis, demyelination, central nervous system (CNS) inflammation/oxidative stress and blood-brain barrier (BBB) breakdown.

METHODS

Mice were immunized with the myelin oligodendrocyte glycoprotein peptide, MOG_35-55, to induce EAE, and OLE was administrated from immunization day. Serum, optic nerve, spinal cord and cerebellum were collected to evaluate immunomodulatory activities at a systemic level, as well as within the CNS. Additionally, BV2 microglia and the retinal ganglion cell line RGC-5 were used to confirm the direct effect of OLE on CNS-resident cells.

RESULTS

We show that OLE treatment effectively reduced clinical score and histological signs typical of EAE. Histological evaluation confirmed a decrease in leukocyte infiltration, demyelination, BBB disruption and superoxide anion accumulation in CNS tissues of OLE-treated EAE mice compared to untreated ones. OLE significantly decreased expression of proinflammatory cytokines (IL-13, TNFα, GM-CSF, MCP-1 and IL-1β), while it increased the anti-inflammatory cytokine IL-10. Serum levels of anti-MOG_35-55 antibodies were also lower in OLE-treated EAE mice. Further, OLE significantly diminished the presence of oxidative system parameters, while upregulated the ROS disruptor, Sestrin-3. Mechanistically, OLE prevented NLRP3 expression, phosphorylation of p65-NF-κB and reduced the synthesis of proinflammatory mediators induced by relevant inflammatory stimuli in BV2 cells. OLE did not affect viability or the phagocytic capabilities of BV2 microglia. In addition, apoptosis of RGC-5 induced by oxidative stressors was also prevented by OLE.

CONCLUSION

Altogether, our results show that the antioxidant and anti-inflammatory OLE has neuroprotective effects in the CNS of EAE mice, pointing out this natural product as a candidate to consider for research on MS treatments.

Demyelinating processes in aging and stroke in the central nervous system and the prospect of treatment strategy

Demyelination occurs in response to brain injury and is observed in many neurodegenerative diseases. Myelin is synthesized from oligodendrocytes in the central nervous system, and oligodendrocyte death‐induced demyelination is one of the mechanisms involved in white matter damage after stroke and neurodegeneration. Oligodendrocyte precursor cells (OPCs) exist in the brain of normal adults, and their differentiation into mature oligodendrocytes play a central role in remyelination. Although the differentiation and maturity of OPCs drive endogenous efforts for remyelination, the failure of axons to remyelinate is still the biggest obstacle to brain repair after injury or diseases. In recent years, studies have made attempts to promote remyelination after brain injury and disease, but its cellular or molecular mechanism is not yet fully understood. In this review, we discuss recent studies examining the demyelination process and potential therapeutic strategies for remyelination in aging and stroke. Based on our current understanding of the cellular and molecular mechanisms underlying remyelination, we hypothesize that myelin and oligodendrocytes are viable therapeutic targets to mitigate brain injury and to treat demyelinating‐related neurodegeneration diseases.

Beneficial Roles of Microglia and Growth Factors in MS, a Brief Review

Microglia are the brain resident immune cells; they can produce a large variety of growth factors (GFs) to prevent neuronal damages and promote recovery. In neurodegenerative diseases, microglia can play both benefic and deleterious roles, depending on different factors and disease context. In multiple sclerosis, microglia are involved in both demyelination (DM) and remyelination (RM) processes. Recent studies suggest a beneficial role of microglia in regenerative processes. These include the regenerative development of myelin after DM. This review gives an overlook of how microglia and GFs can influence the RM properties.

Repurposing of Secukinumab as Neuroprotective in Cuprizone-Induced Multiple Sclerosis Experimental Model via Inhibition of Oxidative, Inflammatory, and Neurodegenerative Signaling

Multiple sclerosis (MS) is a chronic, inflammatory, and neurodegenerative autoimmune disease. MS is a devastating disorder that is characterized by cognitive and motor deficits. Cuprizone-induced demyelination is the most widely experimental model used for MS. Cuprizone is a copper chelator that is well characterized by microgliosis and astrogliosis and is reproducible for demyelination and remyelination. Secukinumab (SEC) is a fully human monoclonal anti-human antibody of the IgG1/kappa isotype that selectively targets IL-17A. Expression of IL-17 is associated with MS. Also, IL-17 stimulates microglia and astrocytes resulting in progression of MS through chemokine production and neutrophil recruitment. This study aimed to investigate the neuroprotective effects of SEC on cuprizone-induced demyelination with examining the underlying mechanisms. Locomotor activity, short-term spatial memory function, staining by Luxol Fast Blue, myelin basic protein, gliasosis, inflammatory, and oxidative-stress markers were assessed to evaluate neuroprotective, anti-inflammatory and antioxidant effects. Moreover, the safety profile of SEC was evaluated. The present study concludes the efficacy of SEC in Cup-induced demyelination experimental model. Interestingly, SEC had neuroprotective and antioxidant effects besides its anti-inflammatory effect in the studied experimental model of MS. Graphical abstract.

Tyrosine Kinase Receptors Axl and MerTK Mediate the Beneficial Effect of Electroacupuncture in a Cuprizone-Induced Demyelinating Model

Electroacupuncture has been shown to promote remyelination in a demyelinating model of multiple sclerosis (MS) through enhanced microglial clearance of degraded myelin debris. However, the mechanisms involved in this process are yet to be clearly elucidated. It has been revealed that TAM receptor tyrosine kinases (Tyro3, Axl, and MerTK) play pivotal roles in regulating multiple features of microglia, including the phagocytic function and myelin clearance. Therefore, the aim of this study is to further confirm whether electroacupuncture improves functional recovery in this model and to characterise the involvement of the TAM receptor during this process. In addition to naive control mice, a cuprizone-induced demyelinating model was established, and long-term electroacupuncture treatment was administrated. To evaluate the efficiency of functional recovery following demyelination, we performed beam-walking test and rotarod performance test; to objectify the degree of remyelination, we performed transmission electron microscopy and protein quantification of mature oligodendrocyte markers. Oil Red O staining was used to evaluate the deposit of myelin debris. We confirmed that, in cuprizone-treated mice, electroacupuncture significantly ameliorates motor-coordinative dysfunction and counteracts demyelinating processes, with less deposit of myelin debris accumulating in the corpus callosum. Surprisingly, mRNA expression of TAM receptors was significantly upregulated after electroacupuncture treatment, and we further confirmed an increased protein expression of Axl and MerTK after electroacupuncture treatment, indicating their involvement during electroacupuncture treatment. Finally, LDC1267, a selective TAM kinase inhibitor, abolished the therapeutic effect of electroacupuncture on motor-coordinative dysfunction. Overall, our data demonstrate that electroacupuncture could mitigate the progression of demyelination by enhancing the TAM receptor expression to facilitate the clearance of myelin debris. Our results also suggest that electroacupuncture may be a potential curative treatment for MS patients.

SeXX Matters in Multiple Sclerosis

Multiple sclerosis (MS) is the most common chronic inflammatory and neurodegenerative disease of the central nervous system (CNS). An interesting feature that this debilitating disease shares with many other inflammatory disorders is that susceptibility is higher in females than in males, with the risk of MS being three times higher in women compared to men. Nonetheless, while men have a decreased risk of developing MS, many studies suggest that males have a worse clinical outcome. MS exhibits an apparent sexual dimorphism in both the immune response and the pathophysiology of the CNS damage, ultimately affecting disease susceptibility and progression differently. Overall, women are predisposed to higher rates of inflammatory relapses than men, but men are more likely to manifest signs of disease progression and worse CNS damage. The observed sexual dimorphism in MS may be due to sex hormones and sex chromosomes, acting in parallel or combination. In this review, we outline current knowledge on the sexual dimorphism in MS and discuss the interplay of sex chromosomes, sex hormones, and the immune system in driving MS disease susceptibility and progression.

Neutrophils: Underestimated Players in the Pathogenesis of Multiple Sclerosis (MS)

Neutrophils are the most abundant circulating and first-responding innate myeloid cells and have so far been underestimated in the context of multiple sclerosis (MS). MS is the most frequent, immune-mediated, inflammatory disease of the central nervous system. MS is treatable but not curable and its cause(s) and pathogenesis remain elusive. The involvement of neutrophils in MS pathogenesis has been suggested by the use of preclinical animal disease models, as well as on the basis of patient sample analysis. In this review, we provide an overview of the possible mechanisms and functions by which neutrophils may contribute to the development and pathology of MS. Neutrophils display a broad variety of effector functions enabling disease pathogenesis, including (1) the release of inflammatory mediators and enzymes, such as interleukin-1β, myeloperoxidase and various proteinases, (2) destruction and phagocytosis of myelin (as debris), (3) release of neutrophil extracellular traps, (4) production of reactive oxygen species, (5) breakdown of the blood-brain barrier and (6) generation and presentation of autoantigens. An important question relates to the issue of whether neutrophils exhibit a predominantly proinflammatory function or are also implicated in the resolution of chronic inflammatory responses in MS.

Alendronate alleviates the symptoms of experimental autoimmune encephalomyelitis

Nitrogen-containing bisphosphonates, such as alendronate, have been widely used to treat osteoporosis because they may target multiple signals in the mevalonate cascade. The present study evaluated the therapeutic effects of alendronate on experimental autoimmune encephalomyelitis (EAE), which is a prototypical autoimmune disease model. EAE was induced in C57BL/6 mice by immunization with myelin oligodendrocyte glycoprotein (MOG)_35-55 peptide. The mice were checked daily for clinical symptoms, such as paralysis, and the levels of inflammatory cytokines were analyzed using ELISA, western blot analyses, and immunohistochemistry. The daily oral administration of alendronate to EAE-induced mice significantly reduced the severity of paralysis and lowered T cell proliferation. Additionally, histopathological examinations confirmed that alendronate mitigated inflammation in the spinal cord after EAE induction, suppressed the infiltration of CD68-positive inflammatory cells, and reduced the production of various pro-inflammatory cytokines, including interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ, as well as inducible nitric oxide synthase (iNOS). Furthermore, the alendronate-treated group exhibited a decrease in the number of iNOS-positive inflammatory cells compared to the vehicle-treated group. Taken together, the present results suggest that alendronate alleviated neuro-inflammation in the spinal cords of EAE-induced mice, which is an animal model of multiple sclerosis, possibly by inhibiting the downstream effects of the mevalonate cascade.

p38MAPK/SGK1 signaling regulates macrophage polarization in experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is characterized with multifocal demyelination resulting from activation and infiltration of inflammatory cells into the central nerve system. Recent reports suggest that p38 mitogen-activated protein kinase (MAPK) / serum- and glucocorticoid-inducible protein kinase 1 (SGK1) signaling pathway contributes to the pathology of MS through regulation of immunity. However, the role of this signaling pathway in MS-related macrophage activation and polarization has not been studied. Here, we used an experimental autoimmune encephalomyelitis (EAE) model for MS to study the role of p38MAPK/SGK1 signaling in the macrophage polarization and its effects on the development and severity of EAE. Here, we found that p38MAPK/SGK1 signaling is required for IL4-induced M2 macrophage polarization in vitro. Chitin-induced M2 macrophage polarization reduces the severity of EAE in mice. Generation of an adeno-associated virus (AAV) carrying sh-p38 or sh-SGK1 under the control of a CD68 promoter successfully knockdown p38 or SGK1 levels in vitro and in vivo. Treatment with AAV-sh-p38 or AAV-sh-SGK1 abolished the effects of Chitin on macrophage polarization and the severity of EAE. Thus, our data suggest that p38MAPK/SGK1 signaling induces M2 macrophage polarization, which reduces the severity of EAE, a model for MS.

Role of Macrophage Colony-Stimulating Factor Receptor on the Proliferation and Survival of Microglia Following Systemic Nerve and Cuprizone-Induced Injuries

Microglia are the innate immune cells of the CNS and their proliferation, activation, and survival have previously been shown to be highly dependent on macrophage colony-stimulating factor receptor (CSF1R). Here we investigated the impact of the receptor in such processes using two different models of nerve injuries, namely hypoglossal axotomy and cuprizone-induced demyelination. Both models are associated with a robust microgliosis. The role of CSF1R was investigated using the gene deletion Cre/Lox system, which allows the conditional knock-out following tamoxifen administration. We found that after 5 weeks of cuprizone diet that CSF1R suppression caused a significant impairment of microglia function. A reduced microgliosis was detected in the corpus collosum of CSF1R knock-out mice compared to controls. In contrast to cuprizone model, the overall number of Iba1 cells was unchanged at all the times evaluated following hypoglossal axotomy in WT and cKO conditions. After nerve lesion, a tremendous proliferation was noticed in the ipsilateral hypoglossal nucleus to a similar level in both knock-out and wild-type groups. We also observed infiltration of bone-marrow derived cells specifically in CSF1R-deficient mice, these cells tend to compensate the CSF1R signaling pathway suppression in resident microglia. Taking together our results suggest a different role of CSF1R in microglia depending on the model. In the pathologic context of cuprizone-induced demyelination CSF1R signaling pathway is essential to trigger proliferation and survival of microglia, while this is not the case in a model of systemic nerve injury. M-CSF/CSF1R is consequently not the unique system involved in microgliosis following nerve damages.

Connexin 43 deletion in astrocytes promotes CNS remyelination by modulating local inflammation

As the most abundant gap junction protein in the central nervous system (CNS), astrocytic connexin 43 (Cx43) maintains astrocyte network homeostasis, affects oligodendroglial development and participates in CNS pathologies as well as injury progression. However, its role in remyelination is not yet fully understood. To address this issue, we used astrocyte-specific Cx43 conditional knockout (Cx43 cKO) mice generated through the use of a hGFAP-cre promoter, in combination with mice carrying a floxed Cx43 allele that were subjected to lysolecithin so as to induce demyelination. We found no significant difference in the demyelination of the corpus callosum between Cx43 cKO mice and their non-cre littermate controls, while the remyelination process in Cx43 cKO mice was accelerated. Moreover, an increased number of mature oligodendrocytes and an unaltered number of oligodendroglial lineage cells were found in Cx43 cKO mouse lesions. This indicates that oligodendrocyte precursor cell (OPC) differentiation was facilitated by astroglial Cx43 depletion as remyelination progressed. Underlying the latter, there was a down-regulated glial activation and modulated local inflammation as well as a reduction of myelin debris in Cx43 cKO mice. Importantly, 2 weeks of orally administrating boldine, a natural alkaloid that blocks Cx hemichannel activity in astrocytes without affecting gap junctional communication, obviously modulated local inflammation and promoted remyelination. Together, the data suggest that the astrocytic Cx43 hemichannel is negatively involved in the remyelination process by favoring local inflammation. Consequently, inhibiting Cx43 hemichannel functionality may be a potential therapeutic approach for demyelinating diseases in the CNS.

Neuroinflammation as a Factor of Neurodegenerative Disease: Thalidomide Analogs as Treatments

Neuroinflammation is initiated when glial cells, mainly microglia, are activated by threats to the neural environment, such as pathogen infiltration or neuronal injury. Although neuroinflammation serves to combat these threats and reinstate brain homeostasis, chronic inflammation can result in excessive cytokine production and cell death if the cause of inflammation remains. Overexpression of tumor necrosis factor-α (TNF-α), a proinflammatory cytokine with a central role in microglial activation, has been associated with neuronal excitotoxicity, synapse loss, and propagation of the inflammatory state. Thalidomide and its derivatives, termed immunomodulatory imide drugs (IMiDs), are a class of drugs that target the 3'-untranslated region (3'-UTR) of TNF-α mRNA, inhibiting TNF-α production. Due to their multi-potent effects, several IMiDs, including thalidomide, lenalidomide, and pomalidomide, have been repurposed as drug treatments for diseases such as multiple myeloma and psoriatic arthritis. Preclinical studies of currently marketed IMiDs, as well as novel IMiDs such as 3,6'-dithiothalidomide and adamantyl thalidomide derivatives, support the development of IMiDs as therapeutics for neurological disease. IMiDs have a competitive edge compared to similar anti-inflammatory drugs due to their blood-brain barrier permeability and high bioavailability, with the potential to alleviate symptoms of neurodegenerative disease and slow disease progression. In this review, we evaluate the role of neuroinflammation in neurodegenerative diseases, focusing specifically on the role of TNF-α in neuroinflammation, as well as appraise current research on the potential of IMiDs as treatments for neurological disorders.

Serum Exosome MicroRNAs Predict Multiple Sclerosis Disease Activity after Fingolimod Treatment

We and others have previously demonstrated the potential for circulating exosome microRNAs to aid in disease diagnosis. In this study, we sought the possible utility of serum exosome microRNAs as biomarkers for disease activity in multiple sclerosis patients in response to fingolimod therapy. We studied patients with relapsing-remitting multiple sclerosis prior to and 6 months after treatment with fingolimod. Disease activity was determined using gadolinium-enhanced magnetic resonance imaging. Serum exosome microRNAs were profiled using next-generation sequencing. Data were analysed using univariate/multivariate modelling and machine learning to determine microRNA signatures with predictive utility. Accordingly, we identified 15 individual miRNAs that were differentially expressed in serum exosomes from post-treatment patients with active versus quiescent disease. The targets of these microRNAs clustered in ontologies related to the immune and nervous systems and signal transduction. While the power of individual microRNAs to predict disease status post-fingolimod was modest (average 77%, range 65 to 91%), several combinations of 2 or 3 miRNAs were able to distinguish active from quiescent disease with greater than 90% accuracy. Further stratification of patients identified additional microRNAs associated with stable remission, and a positive response to fingolimod in patients with active disease prior to treatment. Overall, these data underscore the value of serum exosome microRNA signatures as non-invasive biomarkers of disease in multiple sclerosis and suggest they may be used to predict response to fingolimod in future clinical practice. Additionally, these data suggest that fingolimod may have mechanisms of action beyond its known functions.

Promotion of microglial phagocytosis by tuftsin stimulates remyelination in experimental autoimmune encephalomyelitis

Microglia were once thought to serve a pathogenic role in demyelinating diseases, particularly in multiple sclerosis (MS). However, it has recently been shown that in the experimental autoimmune encephalomyelitis (EAE) model of MS, microglia could serve a protective role by promoting remyelination via the efficient removal of apoptotic cells, the phagocytosis of debris and the support of myelinating oligodendrocytes. The aim of the present study was to determine if the effect of microglia could promote the recovery of EAE and attenuate symptoms in EAE. The severity of EAE was assessed by clinical scores, pathologic changes revealed by luxol fast blue staining and immunohistochemical techniques. The results suggested that microglia reduced clinical scores in mice, suppressed ongoing severe EAE and promoted remyelination and recovery in EAE mice. In addition, following induction with tuftsin, the M1/M2 cytokine balance was shifted, downregulating the proinflammatory M1 response and upregulating the anti-inflammatory M2 response. Generally, microglia can stimulate remyelination, which serves a protective role in different phases of EAE and may represent a potential therapeutic strategy for the treatment of MS.

A Systematic Review of the Impact of Dietary Sodium on Autoimmunity and Inflammation Related to Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system. Current research into potential causes, risk factors, and treatment is largely based around the immune response involved in the pathophysiology of the disease, including factors that contribute to the augmentation of this immune response. This review aimed to determine the role of sodium as a risk factor for increased autoimmunity and inflammation in relation to MS pathogenesis. This systematic review searched the Scopus, MEDLINE, and PubMed scientific databases for studies related to MS and sodium. Studies were included if they addressed sodium intake and MS but were not limited to a disease type or to a study design. Study quality was assessed through the use of the quality rating checklist of the Academy of Nutrition and Dietetics. A total of 12 studies were included in the review, including human, animal, and cellular studies. The studies related to the proinflammatory effect of sodium, the blood-brain barrier, and an effect on autoimmunity. The data presented throughout this review provide insight into the emerging evidence base for sodium intake as a risk factor for MS disease progression and potentially onset of disease. More studies are needed to determine if the influence of sodium is as a single nutrient or has a combined effect as part of an overall eating pattern. This review was registered at PROSPERO as CRD42016039174.

Innate Immune Cells: Monocytes, Monocyte-Derived Macrophages and Microglia as Therapeutic Targets for Alzheimer's Disease and Multiple Sclerosis

The immune system provides protection in the CNS via resident microglial cells and those that traffic into it in the course of pathological challenges. These populations of cells are key players in modulating immune functions that are involved in disease outcomes. In this review, we briefly summarize and highlight the current state of knowledge of the differential contributions of microglia and monocytes in Alzheimer’s disease and multiple sclerosis. The role of innate immunity is frequently seen as a Yin and Yang in both diseases, but this depends on the environment, pre-clinical disease models and the type of cells involved.

ERβ-selective agonist alleviates inflammation in a multiple sclerosis model via regulation of MHC II in microglia

Multiple sclerosis (MS) is an autoimmune, demyelinating, and neurodegenerative disease of the central nervous system (CNS) that affects 2-2.5 million people worldwide. Although the etiology of MS is not well known, MS is widely considered to be an autoimmune disease. Currently approved MS drugs reduce relapse rates but fail to reverse or prevent neurodegeneration and disability progression. Increasing evidence indicates that microglia and major histocompatibility complex class II (MHC II) expression in these cells play important roles in the pathophysiology of MS. For a T cell to contribute to CNS pathogenesis, it must be reactivated by antigen-presenting cells within the CNS parenchyma. Susceptibility to MS is associated with MHC II genes, suggesting that presentation of antigens on MHC II plays an important role in CD4+ T-cell reactivation and disease initiation. An ERβ-selective agonist was previously reported to suppress reactivation of T cells invading the spinal cord, thereby reducing the severity of symptoms and decreasing mortality in the first 2 weeks after disease onset. However, the mechanism by which the expression of MHC II in microglia is regulated by ERβ-selective agonists is still unclear. Therefore, we hypothesize that ERβ-selective agonists inhibit MHC II expression in microglia via inhibition of class II trans-activator (CIITA) expression by a mechanism involving inhibition of the translocation of IFNγ regulatory factor (IRF-1) to the nucleus, thereby inhibiting the inflammatory response and symptoms in the MS model.

Effects of lipoic acid on primary murine microglial cells

The anti-oxidant lipoic acid (LA) is beneficial in murine models of multiple sclerosis (MS) and has recently been shown to slow brain atrophy in secondary progressive MS. The mechanism of these effects by LA is incompletely understood but may involve effects on microglia. The objective of this study is to understand how LA affects microglial cells. We cultured primary microglial cells from C57BL/6 adult mice brains and stimulated the cells with lipopolysaccharide (LPS) and interferon gamma (IFN-γ) in the presence or absence of LA. We demonstrate the inhibition of phagocytosis, rearrangement of actin, and formation of membrane blebs in stimulated microglia in the presence of LA. These experiments suggest that LA causes changes in microglial actin, which may lead to alterations in phagocytosis, mobility, and migration.

Differential neuro-immune patterns in two clinically relevant murine models of multiple sclerosis

Background

The mechanisms driving multiple sclerosis (MS), the most common cause of non-traumatic disability in young adults, remain unknown despite extensive research. Especially puzzling are the underlying molecular processes behind the two major disease patterns of MS: relapsing-remitting and progressive. The relapsing-remitting course is exemplified by acute inflammatory attacks, whereas progressive MS is characterized by neurodegeneration on a background of mild-moderate inflammation. The molecular and cellular features differentiating the two patterns are still unclear, and the role of inflammation during progressive disease is a subject of active debate.

Methods

We performed a comprehensive analysis of the intrathecal inflammation in two clinically distinct mouse models of MS: the PLP_139-151-induced relapsing experimental autoimmune encephalomyelitis (R-EAE) and the chronic progressive, Theiler’s murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD). Microarray technology was first used to examine global gene expression changes in the spinal cord.

Inflammation in the spinal cord was further assessed by immunohistochemical image analysis and flow cytometry. Levels of serum and cerebrospinal fluid (CSF) immunoglobulin (Ig) isotypes and chemokines were quantitated using Luminex Multiplex technology, whereas a capture ELISA was used to measure serum and CSF albumin levels. Finally, an intrathecal Ig synthesis index was established with the ratio of CSF and serum test results corrected as a ratio of their albumin concentrations.

Results

Microarray analysis identified an enrichment of B cell- and Ig-related genes upregulated in TMEV-IDD mice. We also demonstrated an increased level of intrathecal Ig synthesis as well as a marked infiltration of late differentiated B cells, including antibody secreting cells (ASC), in the spinal cord of TMEV-IDD, but not R-EAE mice. An intact blood-brain barrier in TMEV-IDD mice along with higher CSF levels of CXCL13, CXCL12, and CCL19 provides evidence for an intrathecal synthesis of chemokines mediating B cell localization to the central nervous system (CNS).

Conclusions

Overall, these findings, showing increased concentrations of intrathecally produced Igs, substantial infiltration of ASC, and the presence of B cell supporting chemokines in the CNS of TMEV-IDD mice, but not R-EAE mice, suggest a potentially important role for Igs and ASC in the chronic progressive phase of demyelinating diseases.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1501-9) contains supplementary material, which is available to authorized users.

Enhanced remyelination during late pregnancy: involvement of the GABAergic system

Pregnant women with MS experience fewer relapses, especially during the third trimester. In this study, we explore the cellular and molecular events that bring about the protective effect of late pregnancy on the course of de/remyelination in rats. Using cellular, molecular, and ultrastructural methods, we explored remyelination in response to a focal demyelination in the corpus callosum of late pregnant, virgin, and postpartum rats. We further explored the role of GABAA receptor (GABAAR) in the promyelinating effect observed during late pregnancy. Remyelination in response to a gliotoxin-induced demyelination in the corpus callosum was enhanced in late pregnant rats when compared to that seen in virgin and postpartum rats. This pregnancy-associated promyelinating effect was lost when either the GABAAR was blocked or when 5α-reductase, the rate limiting enzyme for the endogenous GABAAR activator allopregnanolone, was inhibited. Taken together, these data suggest that the pregnancy-associated pro-myelination operates, at least in part, through a GABAergic activated system.

Oestrogen receptor β ligand acts on CD11c+ cells to mediate protection in experimental autoimmune encephalomyelitis

Oestrogen treatments are neuroprotective in a variety of neurodegenerative disease models. Selective oestrogen receptor modifiers are needed to optimize beneficial effects while minimizing adverse effects to achieve neuroprotection in chronic diseases. Oestrogen receptor beta (ERβ) ligands are potential candidates. In the multiple sclerosis model chronic experimental autoimmune encephalomyelitis, ERβ-ligand treatment is neuroprotective, but mechanisms underlying this neuroprotection remain unclear. Specifically, whether there are direct effects of ERβ-ligand on CD11c+ microglia, myeloid dendritic cells or macrophages in vivo during disease is unknown. Here, we generated mice with ERβ deleted from CD11c+ cells to show direct effects of ERβ-ligand treatment in vivo on these cells to mediate neuroprotection during experimental autoimmune encephalomyelitis. Further, we use bone marrow chimeras to show that ERβ in peripherally derived myeloid cells, not resident microglia, are the CD11c+ cells mediating this protection. CD11c+ dendritic cell and macrophages isolated from the central nervous system of wild-type experimental autoimmune encephalomyelitis mice treated with ERβ-ligand expressed less iNOS and T-bet, but more IL-10, and this treatment effect was lost in mice with specific deletion of ERβ in CD11c+ cells. Also, we extend previous reports of ERβ-ligand’s ability to enhance remyelination through a direct effect on oligodendrocytes by showing that the immunomodulatory effect of ERβ-ligand acting on CD11c+ cells is necessary to permit the maturation of oligodendrocytes. Together these results demonstrate that targeting ERβ signalling pathways in CD11c+ myeloid cells is a novel strategy for regulation of the innate immune system in neurodegenerative diseases. To our knowledge, this is the first report showing how direct effects of a candidate neuroprotective treatment on two distinct cell lineages (bone marrow derived myeloid cells and oligodendrocytes) can have complementary neuroprotective effects in vivo.awx315media15688130498001.

Phenotypic Screening-Based Identification of 3,4-Disubstituted Piperidine Derivatives as Macrophage M2 Polarization Modulators: An Opportunity for Treating Multiple Sclerosis

Multiple sclerosis (MS) is a disease of the autoimmune-mediated disorder in the central nervous system, for which no effective therapeutic agent is currently available. The regulation of macrophage polarization toward M2 is a general benefit for treating MS. The gene biomarker-based phenotypic screening approach was developed, and 3,4-disubstituted piperidine derivative S-28 was identified as a lead compound modulating macrophage M2 polarization. Further SAR studies resulted in the discovery of the most potent modulator D11 that showed good oral bioavailability and significant in vivo therapeutic effects. Mechanistic studies demonstrated that the M2 polarization macrophages modulated by D11 mainly functioned through inhibiting the proliferation of T-cells and activating the phosphorylation of Stat3 and Akt. Therefore, the gene biomarker-based phenotypic screening was demonstrated as a promising tool for the discovery of novel macrophage M2 polarization modulators. Compound D11 may serve as a promising starting point for the development of therapeutics to treat MS.

Effect of cornel iridoid glycoside on microglia activation through suppression of the JAK/STAT signalling pathway

The effect of cornel iridoid glycoside (CIG), main component extracted from Cornus officinalis, on microglia activation has not been elucidated so far. We induced a mouse model of multiple sclerosis (MS), namely, the experimental autoimmune encephalomyelitis (EAE) model by immunization subcutaneously with the MOG_35-55 peptide, which causes neuroinflammation and microglia activation. Our data demonstrated that CIG delayed the onset of the EAE, ameliorated the severity of the symptoms and inhibited the activation of microglia in different brain regions. In addition, we also found that CIG has therapeutic potential by modulating microglia polarization by reducing the expression and release of proinflammatory cytokines, chemokines and inhibiting phosphorylation in the JAK/STAT cell signalling pathway. Based on our findings, CIG might be a promising candidate for the prevention of neurological disorders such as multiple sclerosis (MS).

Effect of the CSF1R inhibitor PLX3397 on remyelination of corpus callosum in a cuprizone-induced demyelination mouse model

Multiple sclerosis (MS) is a chronic inflammatory disease affecting the central nervous system (CNS). Despite introducing multiple immunomodulatory approaches for MS, there are still major concerns about possible ways for improving remyelination in this disease. Microglia exert essential roles in regulation of myelination processes, and interaction between colony-stimulating factor 1 (CSF1) with its receptor CSF1R is considered as a key regulator of microglial differentiation and survival. The aim of this study was to investigate possible roles for a CSF1R inhibitor PLX3397 in recovery of central myelination processes. Chronic demyelination was induced in mice by addition of 0.2% cuprizone to the chow for 12 weeks. Next, animals were undergoing a diet containing 290 mg/kg PLX3397 to induce microglial ablation. The PLX3397 treatment caused a significant decrease in the rate of expression for the CSF1/CSF1R axis, and a reduction in the protein expressions for the microglial marker Iba-1 and for the oligodendrocyte marker Olig-2. Findings from Luxol fast blue (LFB) staining and transmission electron microscopy (TEM) showed an increase in the rate of myelination for the mice receiving PLX3397. The rate of destruction in the nerve fibers and the extent of the gaps formed between layers of myelin sheaths was also reduced after the treatment with PLX3397. In addition, animals experienced an improvement in recovery of motor deficit after receiving PLX3397 (for all P < 0.05). It could be concluded that PLX3397 could retain myelination in the MS model possibly through regulation of the myelin environment.

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

INTRODUCTION

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

CONCLUSION

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

Immune cell derived BDNF does not mediate neuroprotection of the murine anti-CD52 antibody in a chronic autoimmune mouse model

The murine anti-CD52 antibody, an equivalent of the humanized antibody alemtuzumab, which is successfully used in the treatment of multiple sclerosis, was used to explore a potential neuroprotective effect driven by immune cell derived brain-derived neurotrophic factor (BDNF). Therefore, lineage specific constitutive knock-out mice with a BDNF deficiency in T cells and macrophages were used and compared to treated wildtype mice. Neither therapeutic nor preventive application of the murine anti-CD52 antibody in an animal model of multiple sclerosis, the MOG_35-55 EAE, revealed a beneficial contribution of immune cell derived BDNF to the disease outcome. Furthermore, preventive application of the murine anti-CD52 antibody worsened the clinical EAE disease course and could only be overcome by a prolonged recovery phase after treatment and before disease induction.

Microglia polarization by methylprednizolone acetate accelerates cuprizone induced demyelination

Glucocorticoids (GC) are known as inflammatory drugs, which are used in neuroinflammatory diseases. Unlike the classic picture, recent studies have revealed that some GC drugs exacerbate inflammatory responses in their acute and prolonged administration. Multiple sclerosis (MS) is a demyelinating inflammatory disorder, in which reactive M1 microglia phenotype play a central role. Since methylprednisolone (MP), as a synthetic GC, are commonly used by MS patients, in this study, we evaluated the effect of long-term administration of MP on microglia polarization in cuprizone (CPZ)-induced MS model. The immunostaining results showed that chronic exposure to MP in the CPZ treated mice increased the number of Iba-1 positive microglia, which significantly expressed IP10 as M1 marker than arginase as M2 marker. MP treatment induced significant amplification in the transcript levels of iNOS and TNF-α (M1-related markers) in the corpus callosum of the MS mice, whereas no change detected in the expression of IL-10 (M2-related marker) between the groups. In addition, evaluation of myelin by luxol fast blue staining and transmission electron microscopy revealed that prolonged MP administration increased demyelination in comparison to the CPZ group. In conclusion, our results show that chronic MP therapy in the CPZ-induced demyelination model of MS polarized microglia to M1 pro-inflammatory phenotype.

Age Influences Microglial Activation After Cuprizone-Induced Demyelination

Multiple sclerosis (MS) is a chronic inflammatory CNS disease, which causes demyelinated lesions and damages white and gray matter regions. Aging is a significant factor in the progression of MS, and microglia, the immune cells of the CNS tissue, play an important role in all disease stages. During aging, microglia are functionally altered. These age-related changes probably already begin early and might influence the progression of CNS pathologies. The aim of the present study was to investigate whether microglia in the middle-aged CNS already react differently to demyelination. For this purpose, several microglia markers (ionized calcium binding adaptor molecule 1 (Iba-1), P2RY12, F4/80, CD68, major histocompatibility complex II (MHCII), macrophage receptor with collagenous structure (Marco), Translocator protein 18 kD (TSPO), CD206, and CD163) were analyzed in the acute cuprizone demyelination model in young (2-month-old) and middle-aged (10-month-old) mice. In addition, microglial proliferation was quantified using double-labeling with proliferating cell nuclear antigen (PCNA) and bromodeoxyuridine (BrdU), which was injected with the onset of remyelination. To compare age-related microglial changes during de- and remyelination in both gray and white matter, the hilus of the dorsal hippocampal dentate gyrus (DG) and the splenium of the corpus callosum (CC) were analyzed in parallel. Age-related changes in microglia of healthy controls were more pronounced in the analyzed gray matter region (higher levels of F4/80 and Marco as well as lower expression of CD68 in middle-aged mice). During de- and remyelination, a stronger increase of the microglial markers Iba-1, CD68 and TSPO was observed in the splenium of the younger groups. There was a significant reduction of P2RY12 during demyelination, however, this was age- and region-dependent. The induction of the anti-inflammatory markers CD206 and CD163 was stronger in the middle-aged group, but also differed between the two analyzed regions. De- and remyelination led to a significant increase in PCNA⁺ microglia only in young groups within the white matter region. The number of BrdU⁺ microglia was not changed during de- or remyelination. These results clearly show that microglia are already altered during middle-age and also react differently to CNS demyelination, however, this is highly region-dependent.

Absence of infiltrating peripheral myeloid cells in the brains of mouse models of lysosomal storage disorders

Approximately 70 lysosomal storage diseases are currently known, resulting from mutations in genes encoding lysosomal enzymes and membrane proteins. Defects in lysosomal enzymes that hydrolyze sphingolipids have been relatively well studied. Gaucher disease is caused by the loss of activity of glucocerebrosidase, leading to accumulation of glucosylceramide. Gaucher disease exhibits a number of subtypes, with types 2 and 3 showing significant neuropathology. Sandhoff disease results from the defective activity of β-hexosaminidase, leading to accumulation of ganglioside GM2. Niemann-Pick type C disease is primarily caused by the loss of activity of the lysosomal membrane protein, NPC1, leading to storage of cholesterol and sphingosine. All three disorders display significant neuropathology, accompanied by neuroinflammation. It is commonly assumed that neuroinflammation is the result of infiltration of monocyte-derived macrophages into the brain; for instance, cells resembling lipid-engorged macrophages ('Gaucher cells') have been observed in the brain of Gaucher disease patients. We now review the evidence that inflammatory macrophages are recruited into the brain in these diseases and then go on to provide some experimental data that, at least in the three mouse models tested, monocyte-derived macrophages do not appear to infiltrate the brain. Resident microglia, which are phenotypically distinct from infiltrating macrophages, are the only myeloid population present in significant numbers within the brain parenchyma in these authentic mouse models, even during the late symptomatic stages of disease when there is substantial neuroinflammation. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/. This article is part of the Special Issue "Lysosomal Storage Disorders".

Minocycline plus N-acteylcysteine induces remyelination, synergistically protects oligodendrocytes and modifies neuroinflammation in a rat model of mild traumatic brain injury

Mild traumatic brain injury afflicts over 2 million people annually and little can be done for the underlying injury. The Food and Drug Administration-approved drugs Minocycline plus N-acetylcysteine (MINO plus NAC) synergistically improved cognition and memory in a rat mild controlled cortical impact (mCCI) model of traumatic brain injury.³ The underlying cellular and molecular mechanisms of the drug combination are unknown. This study addressed the effect of the drug combination on white matter damage and neuroinflammation after mCCI. Brain tissue from mCCI rats given either sham-injury, saline, MINO alone, NAC alone, or MINO plus NAC was investigated via histology and qPCR at four time points (2, 4, 7, and 14 days post-injury) for markers of white matter damage and neuroinflammation. MINO plus NAC synergistically protected resident oligodendrocytes and decreased the number of oligodendrocyte precursor cells. Activation of microglia/macrophages (MP/MG) was synergistically increased in white matter two days post-injury after MINO plus NAC treatment. Patterns of M1 and M2 MP/MG were also altered after treatment. The modulation of neuroinflammation is a potential mechanism to promote remyelination and improve cognition and memory. These data also provide new and important insights into how drug treatments can induce repair after traumatic brain injury.

mCSF-Induced Microglial Activation Prevents Myelin Loss and Promotes Its Repair in a Mouse Model of Multiple Sclerosis

A pathological hallmark of multiple sclerosis (MS) is myelin loss in brain white matter accompanied by compromised remyelination. Demyelinated lesions are deeply associated with oligodendrocyte apoptosis and a robust inflammatory response. Although various studies point towards a noxious role of inflammation in MS, others emphasize a positive role for the innate immune cells in disease progression. A cytokine well-known to stimulate cell survival, proliferation and differentiation of myeloid cells, macrophage colony-stimulating factor (mCSF), was administered to mice during a 5 week-long cuprizone diet. Treated mice exhibited reduced myelin loss during the demyelination phase, together with an increased number of microglia and oligodendrocyte precursor cells in lesion sites. Tamoxifen-induced conditional deletion of the mCSF receptor in microglia from cuprizone-fed mice caused aberrant myelin debris accumulation in the corpus callosum and reduced microglial phagocytic response. mCSF therefore plays a key role in stimulating myelin clearance by the brain innate immune cells, which is a prerequisite for proper remyelination and myelin repair processes.

Superparamagnetic iron oxide nanocolloids in MRI studies of neuroinflammation

Iron oxide (IO) nanocolloids are being increasingly used to image cellular contribution to neuroinflammation using MRI, as these particles are capable of labeling circulating cells with phagocytic activity, allowing to assess cell trafficking from the blood to neuroinflammation sites. The use of IOs relies on the natural phagocytic properties of immune cells, allowing their labeling either in vitro or directly in vivo, following intravenous injection. Despite concerns on the specificity of the latter approach, the widespread availability and relatively low cost of these techniques, coupled to a sensitivity that allows to reach single cell detection, have promoted their use in several preclinical and clinical studies. In this review, we discuss the results of currently available preclinical and clinical IO-enhanced MRI studies of immune cell trafficking in neuroinflammation, examining the specificity of the existing findings, in view of the different possible mechanisms underlying IO accumulation in the brain. From this standpoint, we assess the implications of the temporal and spatial differences in the enhancement pattern of IOs, compared to gadolinium-based contrast agents, a clinically established MRI marker blood-brain barrier breakdown. While concerns on the specificity of cell labeling obtained using the in-vivo labeling approach still need to be fully addressed, these techniques have indeed proved able to provide additional information on neuroinflammatory phenomena, as compared to conventional Gadolinium-enhanced MRI.

Molecular Mechanisms of Oligodendrocyte Regeneration in White Matter-Related Diseases

Even in adult brains, restorative mechanisms are still retained to maintain the microenvironment. Under the pathological conditions of central nervous system (CNS) diseases, several immature cells in the brain would be activated as a compensative response. As the concept of the neurovascular unit emphasizes, cell-cell interactions play important roles in this restorative process. White matter damage and oligodendrocyte loss are representative characteristics for many neurodegenerative diseases. In response to oligodendrocyte damage, residual oligodendrocyte precursor cells (OPCs) initiate their proliferation and differentiation for the purpose of remyelination. Although mechanisms of oligodendrogenesis and remyelination in CNS diseases are still mostly unknown and understudied, accumulated evidence now suggests that support from neighboring cells is necessary for OPC proliferation and differentiation. In this review, we first overview basic mechanisms of interaction between oligodendrocyte lineage cells and neighboring cells, and then introduce how oligodendrogenesis occurs under the conditions of neurodegenerative diseases, focusing on vascular cognitive impairment syndrome, Alzheimer’s disease, and multiple sclerosis.

Distinct Gene Profiles of Bone Marrow-Derived Macrophages and Microglia During Neurotropic Coronavirus-Induced Demyelination

Multiple Sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) characterized by demyelination and axonal loss. Demyelinating lesions are associated with infiltrating T lymphocytes, bone marrow-derived macrophages (BMDM), and activated resident microglia. Tissue damage is thought to be mediated by T cell produced cytokines and chemokines, which activate microglia and/or BMDM to both strip myelin and produce toxic factors, ultimately damaging axons and promoting disability. However, the relative contributions of BMDM and microglia to demyelinating pathology are unclear, as their identification in MS tissue is difficult due to similar morphology and indistinguishable surface markers when activated. The CD4 T cell-induced autoimmune murine model of MS, experimental autoimmune encephalitis (EAE), in which BMDM are essential for demyelination, has revealed pathogenic and repair-promoting phenotypes associated with BMDM and microglia, respectively. Using a murine model of demyelination induced by a gliatropic coronavirus, in which BMDM are redundant for demyelination, we herein characterize gene expression profiles of BMDM versus microglia associated with demyelination. While gene expression in CNS infiltrating BMDM was upregulated early following infection and subsequently sustained, microglia expressed a more dynamic gene profile with extensive mRNA upregulation coinciding with peak demyelination after viral control. This delayed microglia response comprised a highly pro-inflammatory and phagocytic profile. Furthermore, while BMDM exhibited a mixed phenotype of M1 and M2 markers, microglia repressed the vast majority of M2-markers. Overall, these data support a pro-inflammatory and pathogenic role of microglia temporally remote from viral control, whereas BMDM retained their gene expression profile independent of the changing environment. As demyelination is caused by multifactorial insults, our results highlight the plasticity of microglia in responding to distinct inflammatory settings, which may be relevant for MS pathogenesis.

Progress in understanding the pathophysiology of multiple sclerosis

Multiple sclerosis (MS) arises in people who have a genetic susceptibility to environmental factors and events, which ultimately trigger the disease. It is thought that peripheral immune cells are mobilized and enter the CNS through the impaired blood-brain barrier in the subarachnoid space, as acute lesions show large numbers of macrophages and CD8+ T cells and, to a lesser extent, CD4+ T cells, B cells and plasma cells. Demyelination is mostly localized to focal lesions in early relapsing-remitting (RR) MS, whereas other areas of white matter appear normal. Over time, T-cell and B-cell infiltration becomes more diffuse and axonal injury more widespread, leading to self-perpetuating atrophy in both white and gray matter. With disease progression, inflammatory processes are predominantly driven by the action of CNS resident microglia cells. In addition, there is evidence that meningeal lymphoid-like structures can form and contribute to late-stage inflammation. In general, however, despite dynamic changes over time in MS pathology, lesions do not appear to differ significantly in the different classic forms of MS already identified. While all treatments approved for MS management target inflammatory components of RRMS, the B-cell-depleting antibody ocrelizumab is the first such treatment approved recently for primary progressive (PP) MS. However, recent pathological and imaging findings have prompted reconsideration of the clinical phenotypes of MS patients proposed by Lublin's 2013 classification, including clinical and MRI signs of activity, and new imaging biomarkers of remyelination are now being investigated for new strategies of MS management.

The roles of macrophages and microglia in multiple sclerosis and experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an autoimmune and neurodegenerative disorder characterized by chronic inflammation, demyelination, as well as axonal and neuronal loss in the central nervous system (CNS). Macrophages and microglia are important components of the innate immune system. They participate in the primary response to microorganisms and play a role in inflammatory responses, homeostasis, and tissue regeneration. In the initial phase of MS and experimental autoimmune encephalomyelitis (EAE), an animal model of MS, macrophages from peripheral tissues infiltrate into the CNS and, together with residential microglia, contribute to the pathogenesis of MS. In the early stages, microglia and macrophages are expressed as the M1 phenotype, which can release proinflammatory cytokines, leading to tissue damage in the CNS. However, in the later stage, the M2 phenotype, which is the phenotype that is associated with resolving inflammation and tissue repair, becomes predominant in the CNS. Therefore, it is hypothesized that the M1/M2 phenotype balance plays an important role in disease progression and that the transition from the proinflammatory M1 phenotype to the regulatory or anti-inflammatory M2 phenotype can lead to restoration of homeostasis and improved functional outcomes. This review of recent literature focuses on the discussion of the M1/M2 phenotypes of microglia and macrophages as well as their relevance in the pathophysiology and treatment of MS and EAE. Furthermore, the possibility of directing the polarization of microglia and macrophages toward the M2 phenotype as a therapeutic and preventative strategy for MS is discussed.