Role of microglia in CNS autoimmunity

Microglial Sirtuin 2 Shapes Long-Term Potentiation in Hippocampal Slices

Microglial cells have emerged as crucial players in synaptic plasticity during development and adulthood, and also in neurodegenerative and neuroinflammatory conditions. Here we found that decreased levels of Sirtuin 2 (Sirt2) deacetylase in microglia affects hippocampal synaptic plasticity under inflammatory conditions. The results show that long-term potentiation (LTP) magnitude recorded from hippocampal slices of wild type mice does not differ between those exposed to lipopolysaccharide (LPS), a pro-inflammatory stimulus, or BSA. However, LTP recorded from hippocampal slices of microglial-specific Sirt2 deficient (Sirt2^–) mice was significantly impaired by LPS. Importantly, LTP values were restored by memantine, an antagonist of N-methyl-D-aspartate (NMDA) receptors. These results indicate that microglial Sirt2 prevents NMDA-mediated excitotoxicity in hippocampal slices in response to an inflammatory signal such as LPS. Overall, our data suggest a key-protective role for microglial Sirt2 in mnesic deficits associated with neuroinflammation.

Inhibition of leucine-rich repeats and calponin homology domain containing 1 accelerates microglia-mediated neuroinflammation in a rat traumatic spinal cord injury model

BACKGROUND

Spinal cord injury (SCI) triggers the primary mechanical injury and secondary inflammation-mediated injury. Neuroinflammation-mediated insult causes secondary and extensive neurological damage after SCI. Microglia play a pivotal role in the initiation and progression of post-SCI neuroinflammation.

METHODS

To elucidate the significance of LRCH1 to microglial functions, we applied lentivirus-induced LRCH1 knockdown in primary microglia culture and tested the role of LRCH1 in microglia-mediated inflammatory reaction both in vitro and in a rat SCI model.

RESULTS

We found that LRCH1 was downregulated in microglia after traumatic SCI. LRCH1 knockdown increased the production of pro-inflammatory cytokines such as IL-1β, TNF-α, and IL-6 after in vitro priming with lipopolysaccharide and adenosine triphosphate. Furthermore, LRCH1 knockdown promoted the priming-induced microglial polarization towards the pro-inflammatory inducible nitric oxide synthase (iNOS)-expressing microglia. LRCH1 knockdown also enhanced microglia-mediated N27 neuron death after priming. Further analysis revealed that LRCH1 knockdown increased priming-induced activation of p38 mitogen-activated protein kinase (MAPK) and Erk1/2 signaling, which are crucial to the inflammatory response of microglia. When LRCH1-knockdown microglia were adoptively injected into rat spinal cords, they enhanced post-SCI production of pro-inflammatory cytokines, increased SCI-induced recruitment of leukocytes, aggravated SCI-induced tissue damage and neuronal death, and worsened the locomotor function.

CONCLUSION

Our study reveals for the first time that LRCH1 serves as a negative regulator of microglia-mediated neuroinflammation after SCI and provides clues for developing novel therapeutic approaches against SCI.

A primary neural cell culture model to study neuron, astrocyte, and microglia interactions in neuroinflammation

Background

Interactions between neurons, astrocytes, and microglia critically influence neuroinflammatory responses to insult in the central nervous system. In vitro astrocyte and microglia cultures are powerful tools to study specific molecular pathways involved in neuroinflammation; however, in order to better understand the influence of cellular crosstalk on neuroinflammation, new multicellular culture models are required.

Methods

Primary cortical cells taken from neonatal rats were cultured in a serum-free “tri-culture” medium formulated to support neurons, astrocytes, and microglia, or a “co-culture” medium formulated to support only neurons and astrocytes. Caspase 3/7 activity and morphological changes were used to quantify the response of the two culture types to different neuroinflammatory stimuli mimicking sterile bacterial infection (lipopolysaccharide (LPS) exposure), mechanical injury (scratch), and seizure activity (glutamate-induced excitotoxicity). The secreted cytokine profile of control and LPS-exposed co- and tri-cultures were also compared.

Results

The tri-culture maintained a physiologically relevant representation of neurons, astrocytes, and microglia for 14 days in vitro, while the co-cultures maintained a similar population of neurons and astrocytes, but lacked microglia. The continuous presence of microglia did not negatively impact the overall health of the neurons in the tri-culture, which showed reduced caspase 3/7 activity and similar neurite outgrowth as the co-cultures, along with an increase in the microglia-secreted neurotrophic factor IGF-1 and a significantly reduced concentration of CX3CL1 in the conditioned media. LPS-exposed tri-cultures showed significant astrocyte hypertrophy, increase in caspase 3/7 activity, and the secretion of a number of pro-inflammatory cytokines (e.g., TNF, IL-1α, IL-1β, and IL-6), none of which were observed in LPS-exposed co-cultures. Following mechanical trauma, the tri-culture showed increased caspase 3/7 activity, as compared to the co-culture, along with increased astrocyte migration towards the source of injury. Finally, the microglia in the tri-culture played a significant neuroprotective role during glutamate-induced excitotoxicity, with significantly reduced neuron loss and astrocyte hypertrophy in the tri-culture.

Conclusions

The tri-culture consisting of neurons, astrocytes, and microglia more faithfully mimics in vivo neuroinflammatory responses than standard mono- and co-cultures. This tri-culture can be a useful tool to study neuroinflammation in vitro with improved accuracy in predicting in vivo neuroinflammatory phenomena.

The role of glia in Parkinson's disease: Emerging concepts and therapeutic applications

Originally believed to primarily affect neurons, Parkinson's disease (PD) has recently been recognized to also affect the functions and integrity of microglia and astroglia, two cell categories of fundamental importance to brain tissue homeostasis, defense, and repair. Both a loss of glial supportive-defensive functions and a toxic gain of glial functions are implicated in the neurodegenerative process. Moreover, the chronic treatment with L-DOPA may cause maladaptive glial plasticity favoring a development of therapy complications. This chapter focuses on the pathophysiology of PD from a glial point of view, presenting this rapidly growing field from the first discoveries made to the most recent developments. We report and compare histopathological and molecular findings from experimental models of PD and human studies. We moreover discuss the important role played by astrocytes in compensatory adaptations taking place during presymptomatic disease stages. We finally describe examples of potential therapeutic applications stemming from an increased understanding of the important roles of glia in PD.

The effect of high mobility group box-1 protein on cerebral edema, blood-brain barrier, oxidative stress and apoptosis in an experimental traumatic brain injury model

Traumatic brain injury (TBI) is one of the important reason of morbidity and mortality. While the primary injury due to mechanical impact is unavoidable, the secondary injury which is formed as a result of primary injury and thought to occur due to neuroinflammation in the forefront can be prevented and by this way mortality and morbidity can be reduced. High mobility group box-1 (HMGB1) is a protein that triggers the neuroinflammatory process by being released from the nucleus of necrotic tissues after primary injury. The aim of this study is to investigate the effects of HMGB1 on its receptors TLR4 and RAGE, cerebral edema, blood-brain barrier, oxidative stress and apoptosis causing secondary damage in an experimental traumatic brain injury model. Weighing between 280-320 g, 10 to 12 weeks-old, a total of 30 adult male Sprague-Dawley rats were used for the experiments. The rats were randomly assigned to 3 groups: 1) Control, 2) TBI and 3) TBI + ethyl pyruvate group (n = 10 per group). Right parietal cortical contusion was made by using a weight-dropping TBI method. Brain samples were harvested from pericontusional area at 24 h after TBI. HMGB1, TLR4, RAGE, occludin, claudin-5, ZO-1 levels are investigated by western blot analyses and immunohistochemistry examinations. HMGB-1, TLR4 and RAGE expressions increased after TBI. Major tight junction proteins in the blood-brain barrier: occludin, claudin-5 and ZO-1 expressions decreased after TBI. Brain edema increased after TBI. Also, proapoptotic bax and active caspase 3 expressions increased, antiapoptotic bcl-2 levels decreased after TBI. Total oxidant status and oxidative stress increased, total antioxidant status decreased after TBI. HMGB-1 protein plays a key role in the pathophysiology of traumatic brain injury.

Microglia in neuropathology caused by protozoan parasites

Involvement of the central nervous system (CNS) is the most severe consequence of some parasitic infections. Protozoal infections comprise a group of diseases that together affect billions of people worldwide and, according to the World Health Organization, are responsible for more than 500000 deaths annually. They include African and American trypanosomiasis, leishmaniasis, malaria, toxoplasmosis, and amoebiasis. Mechanisms underlying invasion of the brain parenchyma by protozoa are not well understood and may depend on parasite nature: a vascular invasion route is most common. Immunosuppression favors parasite invasion into the CNS and therefore the host immune response plays a pivotal role in the development of a neuropathology in these infectious diseases. In the brain, microglia are the resident immune cells active in defense against pathogens that target the CNS. Beside their direct role in innate immunity, they also play a principal role in coordinating the trafficking and recruitment of other immune cells from the periphery to the CNS. Despite their evident involvement in the neuropathology of protozoan infections, little attention has given to microglia-parasite interactions. This review describes the most prominent features of microglial cells and protozoan parasites and summarizes the most recent information regarding the reaction of microglial cells to parasitic infections. We highlight the involvement of the periphery-brain axis and emphasize possible scenarios for microglia-parasite interactions.

Loss of IL-10 Promotes Differentiation of Microglia to a M1 Phenotype

Microglia represent the primary resident immune cells of the central nervous system (CNS) and modulate local immune responses. Depending on their physiological functions, microglia can be classified into pro- (M1) and anti-inflammatory (M2) phenotype. Interleukin (IL)-10 is an important modulator of neuronal homeostasis, with anti-inflammatory and neuroprotective functions, and can be released by microglia. Here, we investigated how IL-10 deficiency affected the M1/2 polarization of primary microglia upon lipopolysaccharide (LPS) stimulation in vitro. Microglia phenotypes were analyzed via flow cytometry. Cytokine and chemokine secretion were examined by ELISA and bead-based multiplex LEGENDplex^TM. Our results showed that genetic depletion of IL-10 led to elevated M1 like phenotype (CD86+ CD206−) under pro-inflammatory conditions associated with increased frequency of IL-6+, TNF-α+ cells and enhanced release of several pro-inflammatory chemokines. Absence of IL-10 led to an attenuated M2 like phenotype (CD86− CD206+) and a reduced secretion of TGF-β1 upon LPS stimulation. In conclusion, IL-10 deficiency may promote the polarization of microglia into M1-prone phenotype under pro-inflammatory conditions.

Role of Chronic Administration of Antidepressant Drugs in the Prenatal Stress-Evoked Inflammatory Response in the Brain of Adult Offspring Rats: Involvement of the NLRP3 Inflammasome-Related Pathway

Evidence indicates that adverse experiences in early life may be a factor for immune disturbances leading to the depression in adulthood. Recently, a pivotal role in the pathogenesis of depression has been assigned to the activation of the brain Nod-like receptor pyrin-containing 3 (NLRP3) inflammasome. We investigated the impact of chronic treatment with antidepressant drugs on the behavioral disturbances and the levels of proinflammatory factors in the hippocampus and frontal cortex of adult male rats after prenatal stress exposure. Next, we explored the involvement of the NLRP3 inflammasome-related pathways in the mechanism of antidepressant action. Our study confirmed that chronic antidepressant treatment attenuated depression-like disturbances and exerted an anxiolytic action. All antidepressants diminished the prenatal stress-induced increase in IL-1β in both brain areas, while IL-18 only in the hippocampus. Moreover, tianeptine administration diminished the increase in CCR2 levels in both brain areas, while in the hippocampus, tianeptine, along with venlafaxine CCL2 and iNOS levels. Next, we observed that in the hippocampus, tianeptine and fluoxetine suppressed upregulation of TLR4. Furthermore, venlafaxine suppressed NFкB p65-subunit phosphorylation, while fluoxetine enhanced the IкB level. Importantly, in the hippocampus, all antidepressants normalized evoked by stress changes in caspase-1 level, while tianeptine and venlafaxine also affect the levels of ASC and NLRP3 subunits. Our results provide new evidence that chronic administration of antidepressants exerts anti-inflammatory effects more pronounced in the hippocampus, through suppression of the NLRP3 inflammasome activation. These effects are accompanied by an improvement in the behavioral dysfunctions evoked by prenatal stress.

DOCK8 is expressed in microglia, and it regulates microglial activity during neurodegeneration in murine disease models

Dedicator of cytokinesis 8 (DOCK8) is a guanine nucleotide exchange factor whose loss of function results in immunodeficiency, but its role in the central nervous system (CNS) has been unclear. Microglia are the resident immune cells of the CNS and are implicated in the pathogenesis of various neurodegenerative diseases, including multiple sclerosis (MS) and glaucoma, which affects the visual system. However, the exact roles of microglia in these diseases remain unknown. Herein, we report that DOCK8 is expressed in microglia but not in neurons or astrocytes and that its expression is increased during neuroinflammation. To define the role of DOCK8 in microglial activity, we focused on the retina, a tissue devoid of infiltrating T cells. The retina is divided into distinct layers, and in a disease model of MS/optic neuritis, DOCK8-deficient mice exhibited a clear reduction in microglial migration through these layers. Moreover, neuroinflammation severity, indicated by clinical scores, visual function, and retinal ganglion cell (RGC) death, was reduced in the DOCK8-deficient mice. Furthermore, using a glaucoma disease model, we observed impaired microglial phagocytosis of RGCs in DOCK8-deficient mice. Our data demonstrate that DOCK8 is expressed in microglia and regulates microglial activity in disease states. These findings contribute to a better understanding of the molecular pathways involved in microglial activation and implicate a role of DOCK8 in several neurological diseases.

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.

MicroRNAs in Neuroinflammation: Implications in Disease Pathogenesis, Biomarker Discovery and Therapeutic Applications

The central nervous system can respond to threat via the induction of an inflammatory response. Under normal circumstances this response is tightly controlled, however uncontrolled neuroinflammation is a hallmark of many neurological disorders. MicroRNAs are small non-coding RNA molecules that are important for regulating many cellular processes. The ability of microRNAs to modulate inflammatory signaling is an area of ongoing research, which has gained much attention in recent years. MicroRNAs may either promote or restrict inflammatory signaling, and either exacerbate or ameliorate the pathological consequences of excessive neuroinflammation. The aim of this review is to summarize the mode of regulation for several important and well-studied microRNAs in the context of neuroinflammation, including miR-155, miR-146a, miR-124, miR-21 and let-7. Furthermore, the pathological consequences of miRNA deregulation during disorders that feature neuroinflammation are discussed, including Multiple Sclerosis, Alzheimer’s disease, Parkinson’s disease, Prion diseases, Japanese encephalitis, Herpes encephalitis, ischemic stroke and traumatic brain injury. There has also been considerable interest in the use of altered microRNA signatures as biomarkers for these disorders. The ability to modulate microRNA expression may even serve as the basis for future therapeutic strategies to help treat pathological neuroinflammation.

Neuregulin-1 Fosters Supportive Interactions between Microglia and Neural Stem/Progenitor Cells

Microglia play diverse roles in homeostasis and pathology of the central nervous system (CNS). Their response to injury or insult is critical for initiating neuroinflammation and tissue damage as well as resolution of inflammation and wound healing. Changes to the microenvironment of microglia appear to be a key determinant of their phenotype and their role in the endogenous repair process in the injured or diseased CNS. Our recent findings have identified a positive role for neuregulin-1 (Nrg-1) in regulating immune response in spinal cord injury and focal demyelinating lesions. We show that increasing the tissue availability of Nrg-1 after injury can promote endogenous repair by modulating neuroinflammation. In the present study, we sought to elucidate the specific role of Nrg-1 in regulating microglial activity and more importantly their influence on the behavior of neural stem/progenitor cells (NPCs). Using injury-relevant in vitro systems, we demonstrate that Nrg-1 attenuates the expression of proinflammatory mediators in activated microglia. Moreover, we provide novel evidence that availability of Nrg-1 can restore the otherwise suppressed phagocytic ability of proinflammatory microglia. Interestingly, the presence of Nrg-1 in the microenvironment of proinflammatory microglia mitigates their inhibitory effects on NPC proliferation. Nrg-1 treated proinflammatory microglia also augment mobilization of NPCs, while they had no influence on their suppressive effects on NPC differentiation. Mechanistically, we show that Nrg-1 enhances the interactions of proinflammatory microglia and NPCs, at least in part, through reduction of TNF-α expression in microglia. These findings provide new insights into the endogenous regulation of microglia-NPC interactions and identify new potential targets for optimizing this important crosstalk during the regenerative process after CNS injury and neuroinflammatory conditions.

Evaluating the Role of Microglial Cells in Clearance of Aβ from Alzheimer's Brain

Ever increasing incidence of Alzheimer's diseases (AD) has been reported all over the globe, and practically no drug is currently available for its treatment. In the past 15 years, not a single drug came out of clinical trials. The researchers have yet to discover a drug that could specifically target AD; in fact, the drugs that are about to launch in the global market either belong to natural compounds or are already approved drugs targeting other diseases. So, we need to shift our focus on finding novel targets which are more specific and could either detect or inhibit the disease progression at a very early stage. Microglia are the only resident innate immune cells of the brain that are originated from erythromyeloid progenitors. They migrate to the brain during early embryonic development, although their number is less (∼5 to 10%), but they could act as guardians of the brain. It has been shown that the extracellular deposits of Aβ are continuously phagocytosed by microglia in healthy individuals, but this ability would decrease with age and lead to development of AD. In this review, we have explored the possibility of whether microglial cells could be utilized as an early predictor of the AD progression. Here, we discuss the innate immune response of microglial cells, the factors affecting microglia response, microglial receptors to which Aβ could bind, and microglial phenotype markers. Last, we conclude with a list of available AD therapeutics along with their mechanism.

Molecular Imaging of Immune Cell Dynamics During De- and Remyelination in the Cuprizone Model of Multiple Sclerosis by [18F]DPA-714 PET and MRI

Background: Activation and dysregulation of innate, adaptive and resident immune cells in response to damage determine the pathophysiology of demyelinating disorders. Among the plethora of involved cells, microglia/macrophages and astrocytes play an important role in the pathogenesis of demyelinating disorders. The in-depth investigation of the spatio-temporal profile of these cell types in vivo may inform about the exact disease state and localization as well as may allow to monitor therapeutic modulation of the components of the neuroinflammatory response during the course of multiple sclerosis (MS). In this study, we aimed to non-invasively decipher the degree and temporal profile of neuroinflammation (TSPO - [18F]DPA-714 PET) in relation to selected magnetic resonance imaging (MRI) parameters (T2 maps) in the cuprizone (CPZ)-induced model of demyelination. Methods: C57Bl6 (n=30) mice were fed with a standard chow mixed with 0.2% (w/w) CPZ for 4 (n=10; demyelination) and 6 weeks (n=10; spontaneous remyelination). The degree of neuroinflammation at de- and remyelination was assessed by [18F]DPA-714 PET, multi-echo T2 MRI, autoradiography and immunohistochemistry. Results: CPZ-induced brain alterations were confirmed by increase of T2 relaxation times in both white and grey matter after 3 and 5 weeks of CPZ. Peak [18F]DPA-714 was found in the corpus callosum (CC, white matter), the hippocampus (HC, grey matter) and thalamus (grey matter) after 4 weeks of CPZ treatment and declined after 6 weeks of CPZ. Ex vivo autoradiography and dedicated immunofluorescence showed demyelination/remyelination with corresponding increased/decreased TSPO levels in the CC and hippocampus, confirming the spatial distribution of [18F]DPA-714 in vivo. The expression of TSPO microglia and astrocytes is time-dependent in this model. Microglia predominantly express TSPO at demyelination, while the majority of astrocytes express TSPO during remyelination. The combination of PET- and MRI-based imaging biomarkers demonstrated the regional and temporal development of the CPZ model-associated neuroinflammatory response in grey and white matter regions. Conclusions: The combination of [18F]DPA-714 PET and T2 mapping may allow to further elucidate the regional and temporal profile of inflammatory signals depending on the myelination status, although the underlying inflammatory microenvironment changes. A combination of the described imaging biomarkers may facilitate the development of patient-tailored strategies for immunomodulatory and neuro-restorative therapies in MS.

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

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

Combination Therapy of Intravenously Injected Microglia and Radiation Therapy Prolongs Survival in a Rat Model of Spontaneous Malignant Glioma

PURPOSE

The aim of this study was to investigate the efficacy of combination therapy with intravenously injected microglia (MI) and radiation therapy (RT) for malignant glioma in rats.

METHODS AND MATERIALS

Transgenic rats expressing v-erbB and spontaneously developing malignant glioma were used. The rats were divided into 4 groups: control (n = 19), RT alone (n = 10), MI alone (n = 9), and combination MI and RT (MI + RT) (n = 10). Cranial x-ray irradiation (8 Gy per fraction; once per week) was performed at 50 and 51 weeks of age. Cultured rat microglial cells (5 × 10⁶ cells/rat) were intravenously injected via the tail vein within 30 minutes after RT.

RESULTS

No evidence of side effects, including thrombosis or graft-versus-host disease, was noted. Rats treated with RT alone, MI alone, MI + RT, and control survived 60.9, 56.3, 66.0, and 56.1 weeks, respectively. The survival period of MI + RT was significantly longer than that of control (P = .014), MI alone (P = .027), and RT alone (P = .049). Immunohistochemical analysis showed a significantly higher number of tumor-infiltrated MI in the RT alone (P = .041) and MI + RT groups (P = .014) compared with the control. Significantly more CD8-positive lymphocytes were observed in the MI + RT group (P = .049) compared with the control. A positive correlation was found between the number of MI and CD8-positive lymphocytes (R² = 0.556). A positive correlation was also found between CD8-positive lymphocytes and survival periods (R² = 0.460).

CONCLUSIONS

MI + RT increased infiltrated MI and CD8-positive T cells and prolonged survival in transgenic rats that spontaneously developed malignant glioma. Combined immunocellular therapy and RT may provide a novel treatment strategy for malignant glioma.

Low-level laser therapy modulates demyelination in mice

There are no effective therapies for remyelination. Low-level laser therapy (LLLT) has been found advantageous in neurogenesis promotion, cell death prevention, and modulation of inflammation in central and peripheral nervous system models. The purpose of this study was to analyse LLLT effects on cuprizone-induced demyelination. Mice were randomly distributed into three groups: Control Laser (CTL), Cuprizone (CPZ), and Cuprizone Laser (CPZL). Mice from CPZ and CPZL groups were exposed to a 0.2% cuprizone oral diet for four complete weeks. Six sessions of transcranial laser irradiation were applied on three consecutive days, during the third and fourth weeks, with parameters of 36 J/cm², 50 mW, 0.028 cm² spot area, continuous wave, 1 J, 20 s, 1.78 W/cm² in a single point equidistant between the eyes and ears of CTL and CPZL mice. Motor coordination was assessed by the rotarod test. Twenty-four hours after the last laser session, all animals were euthanized, and brains were extracted. Serum was obtained for lactate dehydrogenase toxicity testing. Histomorphological analyses consisted of Luxol Fast Blue staining and immunohistochemistry. The results showed that laser-treated animals presented motor performance improvement, attenuation of demyelination, increased number of oligodendrocyte precursor cells, modulated microglial and astrocytes activation, and a milder toxicity by cuprizone. Although further studies are required, it is suggested that LLLT represents a feasible therapy for demyelinating diseases.

Mir223 restrains autophagy and promotes CNS inflammation by targeting ATG16L1

Microglia are innate immune cells in the central nervous system (CNS), that supplies neurons with key factors for executing autophagosomal/lysosomal functions. Macroautophagy/autophagy is a cellular catabolic process that maintains cell balance in response to stress-related stimulation. Abnormal autophagy occurs with many pathologies, such as cancer, and autoimmune and neurodegenerative diseases. Hence, clarification of the mechanisms of autophagy regulation is of utmost importance. Recently, researchers presented microRNAs (miRNAs) as novel and potent modulators of autophagic activity. Here, we found that Mir223 deficiency significantly ameliorated CNS inflammation, demyelination and the clinical symptoms of experimental autoimmune encephalomyelitis (EAE) and increased resting microglia and autophagy in brain microglial cells. In contrast, the autophagy inhibitor 3-methylademine (3-MA) aggravated the clinical symptoms of EAE in wild-type (WT) and Mir223-deficienct mice. Furthermore, it was confirmed that Mir223 deficiency in mice increased the protein expression of ATG16L1 (autophagy related 16-like 1 [S. cerevisiae]) and LC3-II in bone marrow-derived macrophage cells compared with cells from WT mice. Indeed, the cellular level of Atg16l1 was decreased in BV2 cells upon Mir223 overexpression and increased following the introduction of antagomirs. We also showed that the 3’ UTR of Atg16l1 contained functional Mir223-responsive sequences and that overexpression of ATG16L1 returned autophagy to normal levels even in the presence of Mir223 mimics. Collectively, these data indicate that Mir223 is a novel and important regulator of autophagy and that Atg16l1 is a Mir223 target in this process, which may have implications for improving our understanding of the neuroinflammatory process of EAE.

Abbreviations: 3-MA: 3-methylademine; ACTB/β-actin: actin, beta; ATG: autophagy related; ATG16L1: autophagy related 16-like 1 (S. cerevisiae); BECN1: beclin 1, autophagy related; CNR2: cannabinoid receptor 2 (macrophage); CNS: central nervous system; CQ: chloroquine; EAE: experimental autoimmune encephalomyelitis; FOXO3: forkhead box O3; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; H&E: hematoxylin and eosin; ITGAM: integrin alpha M; LPS: lipoplysaccharide; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; miRNAs: microRNAs; MS: multiple sclerosis; PPARG: peroxisome proliferator activated receptor gamma; PTPRC: protein tyrosine phosphatase, receptor type, C; RA: rheumatoid arthritis; SQSTM1: sequestosome 1; TB: tuberculosis; TIMM23: translocase of inner mitochondrial membrane 23; TLR: toll-like receptor.

MicroRNA signature of central nervous system-infiltrating dendritic cells in an animal model of multiple sclerosis

Innate immune cells are integral to the pathogenesis of several diseases of the central nervous system (CNS), including multiple sclerosis (MS). Dendritic cells (DCs) are potent CD11c+ antigen-presenting cells that are critical regulators of adaptive immune responses, particularly in autoimmune diseases such as MS. The regulation of DC function in both the periphery and CNS compartment has not been fully elucidated. One limitation to studying the role of CD11c+ DCs in the CNS is that microglia can upregulate CD11c during inflammation, making it challenging to distinguish bone marrow-derived DCs (BMDCs) from microglia. Selective expression of microRNAs (miRNAs) has been shown to distinguish populations of innate cells and regulate their function within the CNS during neuro-inflammation. Using the experimental autoimmune encephalomyelitis (EAE) murine model of MS, we characterized the expression of miRNAs in CD11c+ cells using a non-biased murine array. Several miRNAs, including miR-31, were enriched in CD11c+ cells within the CNS during EAE, but not LysM+ microglia. Moreover, to distinguish CD11c+ DCs from microglia that upregulate CD11c, we generated bone marrow chimeras and found that miR-31 expression was specific to BMDCs. Interestingly, miR-31-binding sites were enriched in mRNAs downregulated in BMDCs that migrated into the CNS, and a subset was confirmed to be regulated by miR-31. Finally, miR-31 was elevated in DCs migrating through an in vitro blood-brain barrier. Our findings suggest miRNAs, including miR-31, may regulate entry of DCs into the CNS during EAE, and could potentially represent therapeutic targets for CNS autoimmune diseases such as MS.

Increased expression of colony-stimulating factor-1 in mouse spinal cord with experimental autoimmune encephalomyelitis correlates with microglial activation and neuronal loss

Microglia contribute to pathophysiology at all stages of multiple sclerosis. Colony-stimulating factor-1 (CSF1) is crucial for microglial proliferation and activation. In this study we measured the CSF1 levels and studied its cellular expression in the mouse spinal cords with experimental autoimmune encephalomyelitis (EAE) to explore the potential contribution of CSF1 in neuronal death. ELISA data showed that CSF1 levels were significantly higher in the spinal cords with acute and chronic EAE than those of normal and adjuvant-injected mice. Immunohistochemical studies demonstrated that CSF1 was expressed in astrocytes and neurons in normal mouse spinal cord. In acute EAE, CSF1 expression was significantly increased, especially in astrocytes in peripheral white matter and large motoneurons. High density of activated microglia was observed in the gray matter where motoneurons expressed high-level CSF1 in acute EAE. Significant large motoneuron loss was seen in chronic EAE and the remaining motoneurons with high-level CSF1 were enwrapped by microglia. Viral vector mediated over-expression of CSF1 in spinal neurons induced profound proliferation and activation of microglia at the injection site and microglia enwrapped CSF1-transduced neurons and their neurites. Significant loss of large CSF1-transduced neurons was seen at 2 and 3 weeks post-viral injection. Demyelination in the CSF1-transduced areas was also significant. These results implicate that CSF1 upregulation in CNS may play an important role in the proliferation and activation of microglia in EAE, contributing to neuroinflammation and neurodegeneration. © 2018 Wiley Periodicals, Inc.

Targeting the NLRP3 Inflammasome-Related Pathways via Tianeptine Treatment-Suppressed Microglia Polarization to the M1 Phenotype in Lipopolysaccharide-Stimulated Cultures

An increasing body of evidence postulates that microglia are the main mediators of inflammation-related disorders, including depression. Since activated microglia produce a wide range of pro- and anti-inflammatory factors, the modulation of M1/M2 microglial polarization by antidepressants may be crucial in the treatment of depression. The current paper aimed to investigate the impact of tianeptine on the microglia’s viability/death parameters, and on M1/M2 microglial activation in response to lipopolysaccharide (LPS) stimulation. Furthermore, the molecular mechanisms via which tianeptine affected the LPS-evoked changes were investigated. The results revealed that tianeptine had partially protective effects on the changes in microglia viability/death evoked by LPS. Tianeptine attenuated microglia activation by decreasing the expression of cluster of differentiation 40 (CD40), and major histocompatibility complex class II (MHC II) markers, as well as the release of pro-inflammatory factors: interleukin (IL)-1β, IL-18, IL-6, tumor necrosis factor alpha (TNF-α), and chemokine CC motif ligand 2 (CCL2), and the production of nitric oxide and reactive oxygen species. In contrast, we did not observe an impact of tianeptine on M2 microglia measured by IL-4, IL-10, TGF-β, and insulin-like growth factor 1 (IGF-1) expression. Moreover, we demonstrated an inhibitory effect of tianeptine on the LPS-induced activation of the nucleotide-binding oligomerization domain-like (NOD-like) receptor pyrin-containing 3 inflammasome (NLRP3) inflammasome subunits, NLRP3 and caspase-1, as well as the ability of tianeptine to reduce Toll-like receptor 4 (TLR4) levels, as well as the phosphorylation of extracellular signal-related kinases 1 and 2 (ERK1/2) and of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). Collectively, we demonstrated that tianeptine has protective properties and inhibits M1 polarization, thus attenuating the production of inflammatory mediators. Moreover, we found that M1 microglia suppression may be related to the NLRP3 inflammasome and TLR4 signaling. These findings suggest that a better understanding of the multifaceted mechanisms of tianeptine action on microglia may increase the effectiveness of therapy, where inflammation is a central hallmark.

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.

Evaluating Macrophages in Immunotoxicity Testing

Macrophages are a heterogeneous group of cells that have a multitude of functions depending on their differentiation state. While classically known for their phagocytic and antigen presentation abilities, it is now evident that these cells fulfill homeostatic functions beyond the elimination of invading pathogens. In addition, macrophages have also been implicated in the downregulation of inflammatory responses following pathogen removal, tissue remodeling, repair, and angiogenesis. Alterations in macrophage differentiation and/or activity due to xenobiotic exposure can have grave consequences on organismal homeostasis, potentially contributing to disease due to immunosuppression or chronic inflammatory responses, depending upon the pathways affected. In this chapter, we provide an overview of the macrophages subtypes, their origin and a general discussion of several different assays used to assess their functional status.

Anti-neuroinflammatory effects of Ginkgo biloba extract EGb761 in LPS-activated primary microglial cells

BACKGROUND

Neuroinflammation is a key factor of Alzheimer's disease (AD) and other neurodegenerative conditions. Microglia are the resident mononuclear immune cells of the central nervous system (CNS). They play an essential role in the maintenance of homeostasis and responses to neuroinflammation. Ginkgo biloba extract EGb 761 is one of the most commonly used natural medicines owing to its established efficacy and remarkable biological activities especially in respect to CNS diseases. However, only few studies have addressed the effects and mechanisms of Ginkgo biloba extract in microglia activation.

METHODS

We measured the production of pro-inflammatory mediators and cytokines by ELISA and analyzed gene expressions by qRT-PCR and Western Blot in LPS treated cultured primary rat microglia.

RESULTS

The Ginkgo biloba extract EGb 761 significantly inhibited the release of prostaglandin E₂ (PGE₂) and differentially regulated the levels of pro-inflammatory cytokines. The inhibition of LPS-induced PGE₂ release in primary microglia was partially dependent on reduced protein synthesis of mPGES-1 and the reduction in the activation of cytosolic phospholipase A2 (cPLA2) without altering COX-2 enzymatic activity, inhibitor of kappa B alpha (IkappaBalpha) degradation, and the activation of multiple mitogen activated protein kinases (MAPKs). Altogether, we showed that EGb 761 reduces neuro-inflammatory activation in primary microglial cells by targeting PGE₂ release and cytokines.

CONCLUSION

Ginkgo biloba extract EGb 761 displayed anti-neuroinflammatory activity in LPS-activated primary microglia cells. EGb 761 was able to reduce neuroinflammatory activation by targeting the COX/PGE₂ pathway. This effect might contribute to the established clinical cognitive efficacy in Alzheimer's disease, vascular and mixed dementia.

Microglial immune checkpoint mechanisms

Microglia differentiate from progenitors that infiltrate the nascent CNS during early embryonic development. They then remain in this unique immune-privileged environment throughout life. Multiple immune mechanisms, which we collectively refer to as microglial checkpoints, ensure efficient and tightly regulated microglial responses to perturbations in the CNS milieu. Such mechanisms are essential for proper CNS development and optimal physiological function. However, in chronic disease or aging, when a robust immune response is required, such checkpoint mechanisms may limit the ability of microglia to protect the CNS. Here we survey microglial checkpoint mechanisms and their roles in controlling microglial function throughout life and in disease, and discuss how they may be targeted therapeutically.

Dimethyl fumarate attenuates reactive microglia and long-term memory deficits following systemic immune challenge

Background

Systemic inflammation is associated with increased cognitive decline and risk for Alzheimer’s disease. Microglia (MG) activated during systemic inflammation can cause exaggerated neuroinflammatory responses and trigger progressive neurodegeneration. Dimethyl fumarate (DMF) is a FDA-approved therapy for multiple sclerosis. The immunomodulatory and anti-oxidant properties of DMF prompted us to investigate whether DMF has translational potential for the treatment of cognitive impairment associated with systemic inflammation.

Methods

Primary murine MG cultures were stimulated with lipopolysaccharide (LPS) in the absence or presence of DMF. MG cultured from nuclear factor (erythroid-derived 2)-like 2-deficient (Nrf2^−/−) mice were used to examine mechanisms of DMF actions. Conditioned media generated from LPS-primed MG were used to treat hippocampal neuron cultures. Adult C57BL/6 and Nrf2^−/− mice were subjected to peripheral LPS challenge. Acute neuroinflammation, long-term memory function, and reactive astrogliosis were examined to assess therapeutic effects of DMF.

Results

DMF suppressed inflammatory activation of MG induced by LPS. DMF suppressed NF-κB activity through Nrf2-depedent and Nrf2-independent mechanisms in MG. DMF treatment reduced MG-mediated toxicity towards neurons. DMF suppressed brain-derived inflammatory cytokines in mice following peripheral LPS challenge. The suppressive effect of DMF on neuroinflammation was blunted in Nrf2^−/− mice. Importantly, DMF treatment alleviated long-term memory deficits and sustained reactive astrogliosis induced by peripheral LPS challenge. DMF might mitigate neurotoxic astrocytes associated with neuroinflammation.

Conclusions

DMF treatment might protect neurons against toxic microenvironments produced by reactive MG and astrocytes associated with systemic inflammation.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1125-5) contains supplementary material, which is available to authorized users.

Significance and In Vivo Detection of Iron-Laden Microglia in White Matter Multiple Sclerosis Lesions

Microglia are resident immune cells that fulfill protective and homeostatic functions in the central nervous system (CNS) but may also promote neurotoxicity in the aged brain and in chronic disease. In multiple sclerosis (MS), an autoimmune demyelinating disease of the CNS, microglia and macrophages contribute to the development of white matter lesions through myelin phagocytosis, and possibly to disease progression through diffuse activation throughout myelinated white matter. In this review, we discuss an additional compartment of myeloid cell activation in MS, i.e., the rim and normal adjacent white matter of chronic active lesions. In chronic active lesions, microglia and macrophages may contain high amounts of iron, express markers of proinflammatory polarization, are activated for an extended period of time (years), and drive chronic tissue damage. Iron-positive myeloid cells can be visualized and quantified with quantitative susceptibility mapping (QSM), a magnetic resonance imaging technique. Thus, QSM has potential as an in vivo biomarker for chronic inflammatory activity in established white matter MS lesions. Reducing chronic inflammation associated with iron accumulation using existing or novel MS therapies may impact disease severity and progression.

Microglia and CNS Interleukin-1: Beyond Immunological Concepts

Activation of microglia and expression of the inflammatory cytokine interleukin-1 (IL-1) in the CNS have become almost synonymous with neuroinflammation. In numerous studies, increased CNS IL-1 expression and altered microglial morphology have been used as hallmarks of CNS inflammation. A central concept of how CNS IL-1 and microglia influence functions of the nervous system was derived from the notion initially generated in the peripheral immune system: IL-1 stimulates monocyte/macrophage (the peripheral counterparts of microglia) to amplify inflammation. It is increasingly clear, however, CNS IL-1 acts on other targets in the CNS and microglia participates in many neural functions that are not related to immunological activities. Further, CNS exhibits immunological privilege (although not as absolute as previously thought), rendering amplification of inflammation within CNS under stringent control. This review will analyze current literature to evaluate the contribution of immunological and non-immunological aspects of microglia/IL-1 interaction in the CNS to gain insights for how these aspects might affect health and disease in the nervous tissue.

LED enhances anti-inflammatory effect of luteolin (3',4',5,7-tetrahydroxyflavone) in vitro

Neuroinflammation is a complex pathological process usually results from abnormal microglial activation, thus, intervention in a microglial stimulation pathway could be a promising approach for the treatment of neurodegenerative diseases. Luteolin is an important bioflavonoid possesses anti-inflammatory properties, which is widely studied over these years. Light emitting diode (LED) therapy is reported to be a potential therapeutic strategy for many diseases including neurodegenerative diseases. However, little is known about the anti-inflammatory effect of LED therapy on activated microglial cells, even less is known whether there is a synergistic anti-inflammatory effect exist in LED and luteolin therapy. In this study, we aimed to confirm the anti-inflammatory effect of luteolin and LED combination therapy in lipopolysaccharide (LPS)-stimulated BV2 microglial cells. We showed that luteolin inhibited LPS-induced cytotoxicity, tumor necrosis factor alpha (TNFα) and interleukin-6 (IL-6) production through modulation of p38 and extracellular signal-regulated kinase (ERK) signaling in BV2 cells. In addition, LED therapy enhanced the anti-inflammatory effect of luteolin. These results suggest that a synergistic effect between luteolin and LED could be a new effective therapy in relieving neuroinflammation.

Alzheimer's Disease: The Role of Microglia in Brain Homeostasis and Proteopathy

Brain aging is central to late-onset Alzheimer's disease (LOAD), although the mechanisms by which it occurs at protein or cellular levels are not fully understood. Alzheimer's disease is the most common proteopathy and is characterized by two unique pathologies: senile plaques and neurofibrillary tangles, the former accumulating earlier than the latter. Aging alters the proteostasis of amyloid-β peptides and microtubule-associated protein tau, which are regulated in both autonomous and non-autonomous manners. Microglia, the resident phagocytes of the central nervous system, play a major role in the non-autonomous clearance of protein aggregates. Their function is significantly altered by aging and neurodegeneration. This is genetically supported by the association of microglia-specific genes, TREM2 and CD33, and late onset Alzheimer's disease. Here, we propose that the functional characterization of microglia, and their contribution to proteopathy, will lead to a new therapeutic direction in Alzheimer's disease research.

Both classic Gs-cAMP/PKA/CREB and alternative Gs-cAMP/PKA/p38β/CREB signal pathways mediate exenatide-stimulated expression of M2 microglial markers

GLP-1 receptor agonists, exenatide and GLP-1, promoted M2 type polarization in monocytes/macrophages and microglial cells. This study explored the signal basis underlying exenatide-stimulated expression of M2 microglia-specific genes, including the cytoplasmic marker Arg 1, surface marker CD206, and secretion protein marker IL-4. Treatment with exenatide in cultured primary microglial cells concentration dependently stimulated the expression of Arg 1, CD206 and IL-4, but did not significantly alter LPS-stimulated expression of TNF-α, IL-1β and IL-6. The stimulatory effects of exenatide were completely prevented by the GLP-1 receptor antagonist exendin(9-39), but not altered by application of LPS. Furthermore, the adenylyl cyclase inhibitor DDA, PKA inhibitor H89 and CREB inhibitor KG501 completely blocked exenatide-induced overexpression of Arg 1, CD206 and IL-4. In addition, exenatide-stimulated expression of Arg 1 and CD206 was totally blocked by the p38 MAPK inhibitor SB203580 and gene silencer siRNA/p38β (but not siRNA/p38α), whereas the expressed IL-4 was not significantly altered by the p38 inhibitor or other MAPK subtype inhibitors. These findings revealed that both classic Gs-cAMP/PKA/CREB and alternative Gs-cAMP/PKA/p38β/CREB mediated GLP-1 receptor agonism-induced overexpression of M2 microglial biomarkers.

Strain specificities in age-related changes in mechanisms promoting and controlling rat spinal cord damage in experimental autoimmune encephalomyelitis

The study investigated strain specificities in age-related differences in CD8+ T cell- and microglial cell-mediated mechanisms implicated in induction/perpetuation and/or control of neuroinflammation in experimental autoimmune encephalomyelitis (EAE) in Albino Oxford (AO) and Dark Agouti (DA) rats exhibiting age-related changes in the susceptibility to EAE in the opposite direction (increase in relatively resistant AO rats vs decrease in DA rats). In the inductive phase of EAE, the greater number of fully differentiated effector CD8+ T lymphocytes was found in draining lymph nodes (dLNs) from aged rats of both strains than in strain-matched young rats, but this was particularly prominent in AO rats, which exhibited milder EAE of prolonged duration compared with their DA counterparts. Consistently, dLN IFN-γ+ and IL-17+ CD8+ T cell counts were greater in aged AO than in DA rats. Additionally, the magnitudes of myelin basic protein (MBP)-induced rise in the frequency of IFN-γ+ and IL-17+ CD8+ T cells (providing important help to neuroantigen-specific CD4+ T cells in EAE models characterized by clinically mild disease) were greater in dLN cell cultures from aged AO rats. Consistently, the magnitudes of MBP-induced rise in the frequency of both IFN-γ+ and IL-17+ CD8+ T cells were greater in spinal cord mononuclear cell cultures from aged AO rats compared with their DA counterparts. Besides, with aging CD4+CD25+Foxp3+/CD8+CD25+Foxp3+ regulatory T cell ratio changed in spinal cord in the opposite direction. Consequently, in aged AO rats it was shifted towards CD8+CD25+Foxp3+ regulatory T cells (exhibiting lower suppressive capacity) when compared with DA rats. Moreover, the frequency of CX3CR1+ cells among microglia changed with aging and the disease development. In aged rats, in the effector phase of EAE it was lower in AO than in DA rats. This was accompanied by higher frequency of cells expressing IL-1β (whose down-regulation is central for CX3CR1-mediated neuroprotection), but lower that of phagocyting cells among microglia from aged AO compared their DA counterparts. The study indicates the control points linked with strain differences in age-related changes in EAE pathogenesis.

Co-Culture of Neurons and Microglia

Microglia, the resident immune cells of the brain, have been implicated in numerous neurodegenerative and neurodevelopmental diseases. Activation of microglia by a variety of stimuli induces the release of factors, including pro- and anti-inflammatory cytokines and reactive oxygen species, that contribute to modulating neuro-inflammation and oxidative stress, two crucial processes linked to disorders of the central nervous system. The in vitro techniques described here will provide a set of protocols for the isolation and plating of primary cerebellar granule neurons, primary cortical microglia from a mixed glia culture, and methods for co-culturing both cell types. These methods allow the study of how microglia and the factors they release in this shared environment mediate the effects of toxicants on neuronal function and survival. The protocols presented here allow for flexibility in experimental design, the study of numerous toxicological endpoints, and the opportunity to explore neuroprotective strategies. © 2017 by John Wiley & Sons, Inc.

Central Administration of 5Z-7-Oxozeaenol Protects Experimental Autoimmune Encephalomyelitis Mice by Inhibiting Microglia Activation

Transforming growth factor β-activated kinase 1 (TAK1), a vital upstream integrator of multiple pro-inflammatory signaling pathways, mediates the production of pro-inflammatory cytokines, chemokines, and adhesion molecules. Investigations targeting TAK1 provide new therapeutic options for chronic inflammatory disorders, autoimmune diseases, and cancer. However, the role and mechanism of the TAK1 inhibitor 5Z-7-oxozeaenol in treating autoimmune demyelinating diseases remain unclear. This work aimed to identify whether 5Z-7-oxozeaenol exerts neuroprotective effects on experimental autoimmune encephalomyelitis (EAE) in mice. Here, we demonstrate that 5Z-7-oxozeaenol efficiently alleviates the symptoms of EAE by decreasing the levels of pro-inflammatory cytokines in splenocytes and central nervous system, diminishing the number of activated microglia and inhibiting the p38MAPK, JNK, and ERK signaling pathways. Furthermore, we demonstrate that administration during the symptomatic time window is required for 5Z-7-oxozeaenol efficacy. These results suggest that TAK1 inhibition may provide a potent approach toward treating autoimmune demyelinating diseases.

Systemic inflammation combined with neonatal cerebellar haemorrhage aggravates long-term structural and functional outcomes in a mouse model

BACKGROUND

Despite the increased recognition of cerebellar injury in survivors of preterm birth, the neurodevelopmental consequences of isolated cerebellar injury have been largely unexplored and our current understanding of the functional deficits requires further attention in order to translate knowledge to best practices. Preterm infants are exposed to multiple stressors during their postnatal development including perinatal cerebellar haemorrhage (CBH) and postnatal infection, two major risk factors for neurodevelopmental impairments.

METHODS

We developed a translational mouse model of CBH and/or inflammation to measure the short- and long-term outcomes in cerebellar structure and function.

RESULTS

Mice exposed to early combined insults of CBH and early inflammatory state (EIS) have a delay in grasping acquisition, neonatal motor deficits and deficient long-term memory. CBH combined with late inflammatory state (LIS) does not induce neonatal motor problems but leads to poor fine motor function and long-term memory deficits at adulthood. Early combined insults result in poor cerebellar growth from postnatal day 15 until adulthood shown by MRI, which are reflected in diminished volumes of cerebellar structures. There are also decreases in volumes of gray matter and hippocampus. Cerebellar microgliosis appears 24h after the combined insults and persists until postnatal day 15 in the cerebellar molecular layer and cerebellar nuclei in association with a disrupted patterning of myelin deposition, a delay of oligodendrocyte maturation and reduced white matter cerebellar volume.

CONCLUSIONS

Together, these findings reveal poor outcomes in developing brains exposed to combined cerebellar perinatal insults in association with cerebellar hypoplasia, persistence of microgliosis and alterations of cerebellar white matter maturation and growth.

Effectors of Th1 and Th17 cells act on astrocytes and augment their neuroinflammatory properties

Background

Autoreactive Th1 and Th17 cells are believed to mediate the pathology of multiple sclerosis in the central nervous system (CNS). Their interaction with microglia and astrocytes in the CNS is crucial for the regulation of the neuroinflammation. Previously, we have shown that only Th1 but not Th17 effectors activate microglia. However, it is not clear which cells are targets of Th17 effectors in the CNS.

Methods

To understand the effects driven by Th17 cells in the CNS, we induced experimental autoimmune encephalomyelitis in wild-type mice and CD4⁺ T cell-specific integrin α4-deficient mice where trafficking of Th1 cells into the CNS was affected. We compared microglial and astrocyte response in the brain and spinal cord of these mice. We further treated astrocytes with supernatants from highly pure Th1 and Th17 cultures and assessed the messenger RNA expression of neurotrophic factors, cytokines and chemokines, using real-time PCR. Data obtained was analyzed using the Kruskal-Wallis test.

Results

We observed in α4-deficient mice weak microglial activation but comparable astrogliosis to that of wild-type mice in the regions of the brain populated with Th17 infiltrates, suggesting that Th17 cells target astrocytes and not microglia. In vitro, in response to supernatants from Th1 and Th17 cultures, astrocytes showed altered expression of neurotrophic factors, pro-inflammatory cytokines and chemokines. Furthermore, increased expression of chemokines in Th1- and Th17-treated astrocytes enhanced recruitment of microglia and transendothelial migration of Th17 cells in vitro.

Conclusion

Our results demonstrate the delicate interaction between T cell subsets and glial cells and how they communicate to mediate their effects. Effectors of Th1 act on both microglia and astrocytes whereas Th17 effectors preferentially target astrocytes to promote neuroinflammation.

Electronic supplementary material

The online version of this article (10.1186/s12974-017-0978-3) contains supplementary material, which is available to authorized users.

Multifaceted Role of Neuropilins in the Immune System: Potential Targets for Immunotherapy

Neuropilins (NRPs) are non-tyrosine kinase cell surface glycoproteins expressed in all vertebrates and widely conserved across species. The two isoforms, such as neuropilin-1 (NRP1) and neuropilin-2 (NRP2), mainly act as coreceptors for class III Semaphorins and for members of the vascular endothelial growth factor family of molecules and are widely known for their role in a wide array of physiological processes, such as cardiovascular, neuronal development and patterning, angiogenesis, lymphangiogenesis, as well as various clinical disorders. Intriguingly, additional roles for NRPs occur with myeloid and lymphoid cells, in normal physiological as well as different pathological conditions, including cancer, immunological disorders, and bone diseases. However, little is known concerning the molecular pathways that govern these functions. In addition, NRP1 expression has been characterized in different immune cellular phenotypes including macrophages, dendritic cells, and T cell subsets, especially regulatory T cell populations. By contrast, the functions of NRP2 in immune cells are less well known. In this review, we briefly summarize the genomic organization, structure, and binding partners of the NRPs and extensively discuss the recent advances in their role and function in different immune cell subsets and their clinical implications.

Inflammation and mitochondrial dysfunction: A vicious circle in neurodegenerative disorders?

Experimental evidence supports an intricate association between inflammation and mitochondrial dysfunction as main contributors of neurological diseases. Inflammatory mediators produced by activated microglia and infiltrated immune cells trigger intracellular signalling cascades that can alter cellular mitochondrial metabolism. Cytokines, particularly tumor necrosis factor-alpha, impede mitochondrial oxidative phosphorylation and associated ATP production and instigate mitochondrial reactive oxygen species production. This culminates in mitochondrial membrane permeabilization, altered mitochondrial dynamics and might ultimately result in cell death. When severely injured mitochondria are not appropriately removed by mitophagy they can release their contents into the cytosol and extracellular environment and thereby amplify the inflammatory process. Here we provide a comprehensive overview on how inflammatory mediators impair mitochondrial metabolism and discuss how defective mitochondria can elicit and potentiate an inflammatory response.

Myeloid Cells in the Central Nervous System

The central nervous system (CNS) and its meningeal coverings accommodate a diverse myeloid compartment that includes parenchymal microglia and perivascular macrophages, as well as choroid plexus and meningeal macrophages, dendritic cells, and granulocytes. These myeloid populations enjoy an intimate relationship with the CNS, where they play an essential role in both health and disease. Although the importance of these cells is clearly recognized, their exact function in the CNS continues to be explored. Here, we review the subsets of myeloid cells that inhabit the parenchyma, meninges, and choroid plexus and discuss their roles in CNS homeostasis. We also discuss the role of these cells in various neurological pathologies, such as autoimmunity, mechanical injury, neurodegeneration, and infection. We highlight the neuroprotective nature of certain myeloid cells by emphasizing their therapeutic potential for the treatment of neurological conditions.

Expression profiles of cholesterol metabolism-related genes are altered during development of experimental autoimmune encephalomyelitis in the rat spinal cord

Increased evidence suggests that dysregulation of cholesterol metabolism may be a key event contributing to progression of multiple sclerosis (MS). Using an experimental autoimmune encephalomyelitis (EAE) model of MS we revealed specific changes in the mRNA and protein expression of key molecules involved in the maintaining of cholesterol homeostasis in the rat spinal cord: 3-hydroxy-3-methylglutaryl-coenzyme-A reductase (HMGCR), apolipoprotein E (ApoE) and cholesterol 24-hydroxylase (CYP46A1) during the course of disease. The presence of myelin lipid debris was seen only at the peak of EAE in demyelination loci being efficiently removed during the recovery period. Since CYP46A1 is responsible for removal of cholesterol excess, we performed a detailed profiling of CYP46A1 expression and revealed regional and temporal specificities in its distribution. Double immunofluorescence staining demonstrated CYP46A1 localization with neurons, infiltrated macrophages, microglia and astrocytes in the areas of demyelination, suggesting that these cells play a role in cholesterol turnover in EAE. We propose that alterations in the regulation of cholesterol metabolism at the onset and peak of EAE may add to the progression of disease, while during the recovery period may have beneficial effects contributing to the regeneration of myelin sheath and restoration of neuronal function.

GYF-21, an Epoxide 2-(2-Phenethyl)-Chromone Derivative, Suppresses Innate and Adaptive Immunity via Inhibiting STAT1/3 and NF-κB Signaling Pathways

Multiple sclerosis is a chronic inflammatory autoimmune disease of the central nervous system characterized by demyelinating plaques and axonal loss. Inhibition on over activation of innate and adaptive immunity provides a rationale strategy for treatment of multiple sclerosis. In the present study, we investigated the inhibitory effects of GYF-21, an epoxide 2-(2-phenethyl)-chromone derivative isolated from Chinese agarwood, on innate and adaptive immunity for revealing its potential to treat multiple sclerosis. The results showed that GYF-21 markedly inhibited the activation of microglia, and dendritic cells as well as neutrophils, all of which play important roles in innate immunity. Furthermore, GYF-21 significantly suppressed adaptive immunity via inhibiting the differentiation of naive CD4⁺ T cells into T helper 1 (Th1) and T helper 17 (Th17) cells, and suppressing the activation, proliferation, and IFN-γ secretion of CD8⁺ T cells. The mechanism study showed that GYF-21 evidently inhibited the activation of STAT1/3 and NF-κB signaling pathways in microglia. In conclusion, we demonstrated that GYF-21 can significantly inhibit innate and adaptive immunity via suppressing STAT1/3 and NF-κB signaling pathways, and has potential to be developed into therapeutic drug for multiple sclerosis.

Exosomes from NSC-34 Cells Transfected with hSOD1-G93A Are Enriched in miR-124 and Drive Alterations in Microglia Phenotype

Amyotrophic lateral sclerosis (ALS) is a fatal adult-onset neurodegenerative disorder affecting motor neurons (MNs). Evidences indicate that ALS is a non-cell autonomous disease in which glial cells participate in both disease onset and progression. Exosomal transfer of mutant copper-zinc superoxide dismutase 1 (mSOD1) from cell-to-cell was suggested to contribute to disease dissemination. Data from our group and others showed that exosomes from activated cells contain inflammatory-related microRNAs (inflamma-miRNAs) that recapitulate the donor cell. While glia-derived exosomes and their effects in neurons have been addressed by several studies, only a few investigated the influence of motor neuron (MN)-derived exosomes in other cell function, the aim of the present study. We assessed a set of inflamma-miRs in NSC-34 MN-like cells transfected with mutant SOD1(G93A) and extended the study into their derived exosomes (mSOD1 exosomes). Then, the effects produced by mSOD1 exosomes in the activation and polarization of the recipient N9 microglial cells were investigated. Exosomes in coculture with N9 microglia and NSC-34 cells [either transfected with either wild-type (wt) human SOD1 or mutant SOD1(G93A)] showed to be transferred into N9 cells. Increased miR-124 expression was found in mSOD1 NSC-34 cells and in their derived exosomes. Incubation of mSOD1 exosomes with N9 cells determined a sustained 50% reduction in the cell phagocytic ability. It also caused a persistent NF-kB activation and an acute generation of NO, MMP-2, and MMP-9 activation, as well as upregulation of IL-1β, TNF-α, MHC-II, and iNOS gene expression, suggestive of induced M1 polarization. Marked elevation of IL-10, Arginase 1, TREM2, RAGE, and TLR4 mRNA levels, together with increased miR-124, miR-146a, and miR-155, at 24 h incubation, suggest the switch to mixed M1 and M2 subpopulations in the exosome-treated N9 microglial cells. Exosomes from mSOD1 NSC-34 MNs also enhanced the number of senescent-like positive N9 cells. Data suggest that miR-124 is translocated from the mSOD1 MNs to exosomes, which determine early and late phenotypic alterations in the recipient N9-microglial cells. In conclusion, modulation of the inflammatory-associated miR-124, in mSOD1 NSC-34 MNs, with potential benefits in the cargo of their exosomes may reveal a promising therapeutic strategy in halting microglia activation and associated effects in MN degeneration.

Alterations in CD200-CD200R1 System during EAE Already Manifest at Presymptomatic Stages

In the brain of patients with multiple sclerosis, activated microglia/macrophages appear in active lesions and in normal appearing white matter. However, whether they play a beneficial or a detrimental role in the development of the pathology remains a controversial issue. The production of pro-inflammatory molecules by chronically activated microglial cells is suggested to contribute to the progression of neurodegenerative processes in neurological disease. In the healthy brain, neurons control glial activation through several inhibitory mechanisms, such as the CD200-CD200R1 interaction. Therefore, we studied whether alterations in the CD200-CD200R1 system might underlie the neuroinflammation in an experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis. We determined the time course of CD200 and CD200R1 expression in the brain and spinal cord of an EAE mouse model from presymptomatic to late symptomatic stages. We also assessed the correlation with associated glial activation, inflammatory response and EAE severity. Alterations in CD200 and CD200R1 expression were mainly observed in spinal cord regions in the EAE model, mostly a decrease in CD200 and an increase in CD200R1 expression. A decrease in the expression of the mRNA encoding a full CD200 protein was detected before the onset of clinical signs, and remained thereafter. A decrease in CD200 protein expression was observed from the onset of clinical signs. By contrast, CD200R1 expression increased at EAE onset, when a glial reaction associated with the production of pro- and anti-inflammatory markers occurred, and continued to be elevated during the pathology. Moreover, the magnitude of the alterations correlated with severity of the EAE mainly in spinal cord. These results suggest that neuronal-microglial communication through CD200-CD200R1 interaction is compromised in EAE. The early decreases in CD200 expression in EAE suggest that this downregulation might also occur in the initial phases of multiple sclerosis, and that this early neuronal dysfunction might facilitate the development of neuroinflammation. The increased CD200R1 expression in the EAE model highlights the potential use of targeted agonist molecules as therapeutic tools to control neuroinflammation. In summary, the CD200-CD200R1 system is a potential therapeutic target in multiple sclerosis, and CD200R1 agonists are molecules that may be worth developing in this context.