Immune response by microglia in the spinal cord

Vitamin D-An Effective Antioxidant in an Animal Model of Progressive Multiple Sclerosis

Vitamin D (VD) is the most discussed antioxidant supplement for multiple sclerosis (MS) patients and many studies suggest correlations between a low VD serum level and onset and progression of the disease. While many studies in animals as well as clinical studies focused on the role of VD in the relapsing-remitting MS, knowledge is rather sparse for the progressive phase of the disease and the development of cortical pathology. In this study, we used our established rat model of cortical inflammatory demyelination, resembling features seen in late progressive MS, to address the question about whether VD could have positive effects on reducing cortical pathology, oxidative stress, and neurofilament light chain (NfL) serum levels. For this purpose, we used male Dark Agouti (DA) rats, with one group being supplemented with VD (400 IE per week; VD+) from the weaning on at age three weeks; the other group received standard rodent food. The rat brains were assessed using immunohistochemical markers against demyelination, microglial activation, apoptosis, neurons, neurofilament, and reactive astrocytes. To evaluate the effect of VD on oxidative stress and the antioxidant capacity, we used two different oxidized lipid markers (anti- Cu++ and HOCl oxidized LDL antibodies) along with colorimetric methods for protective polyphenols (PP) and total antioxidative capacity (TAC). NfL serum levels of VD+ and VD- animals were analyzed by fourth generation single-molecule array (SIMOA) analysis. We found significant differences between the VD+ and VD- animals both in histopathology as well as in all serum markers. Myelin loss and microglial activation is lower in VD+ animals and the number of apoptotic cells is significantly reduced with a higher neuronal survival. VD+ animals show significantly lower NfL serum levels, a higher TAC, and more PP. Additionally, there is a significant reduction of oxidized lipid markers in animals under VD supplementation. Our data thus show a positive effect of VD on cellular features of cortical pathology in our animal model, presumably due to protection against reactive oxygen species. In this study, VD enhanced remyelination and prevented neuroaxonal and oxidative damage, such as demyelination and neurodegeneration. However, more studies on VD dose relations are required to establish an optimal response while avoiding overdosing.

Severity- and Time-Dependent Activation of Microglia in Spinal Cord Injury

A spinal cord injury (SCI) initiates a number of cascades of biochemical reactions and intercellular interactions, the outcome of which determines the regenerative potential of the nervous tissue and opens up capacities for preserving its functions. The key elements of the above-mentioned processes are microglia. Many assumptions have been put forward, and the first evidence has been obtained, suggesting that, depending on the severity of SCI and the post-traumatic period, microglia behave differently. In this regard, we conducted a study to assess the microglia behavior in the model of mild, moderate and severe SCI in vitro for various post-traumatic periods. We reported for the first time that microglia make a significant contribution to both anti- and pro-inflammatory patterns for a prolonged period after severe SCI (60 dpi), while reduced severities of SCI do not lead to prolonged activation of microglia. The study also revealed the following trend: the greater the severity of the SCI, the lower the proliferative and phagocytic activity of microglia, which is true for all post-traumatic periods of SCI.

Endocannabinoid signaling in microglia

Microglia, the innate immune cells of the central nervous system (CNS), execute their sentinel, housekeeping and defense functions through a panoply of genes, receptors and released cytokines, chemokines and neurotrophic factors. Moreover, microglia functions are closely linked to the constant communication with other cell types, among them neurons. Depending on the signaling pathway and type of stimuli involved, the outcome of microglia operation can be neuroprotective or neurodegenerative. Accordingly, microglia are increasingly becoming considered cellular targets for therapeutic intervention. Among signals controlling microglia activity, the endocannabinoid (EC) system has been shown to exert a neuroprotective role in many neurological diseases. Like neurons, microglia express functional EC receptors and can produce and degrade ECs. Interestingly, boosting EC signaling leads to an anti-inflammatory and neuroprotective microglia phenotype. Nonetheless, little evidence is available on the microglia-mediated therapeutic effects of EC compounds. This review focuses on the EC signals acting on the CNS microglia in physiological and pathological conditions, namely on the CB1R, CB2R and TRPV1-mediated regulation of microglia properties. It also provides new evidence, which strengthens the understanding of mechanisms underlying the control of microglia functions by ECs. Given the broad expression of the EC system in glial and neuronal cells, the resulting picture is the need for in vivo studies in transgenic mouse models to dissect the contribution of EC microglia signaling in the neuroprotective effects of EC-derived compounds.

Full spectrum of vitamin D immunomodulation in multiple sclerosis: mechanisms and therapeutic implications

Vitamin D deficiency has been associated with the risk of multiple sclerosis, disease activity and progression. Results from in vitro experiments, animal models and analysis of human samples from randomized controlled trials provide comprehensive data illustrating the pleiotropic actions of Vitamin D on the immune system. They globally result in immunomodulation by decreasing differentiation of effector T and B cells while promoting regulatory subsets. Vitamin D also modulates innate immune cells such as macrophages, monocytes and dendritic cells, and acts at the level of the blood–brain barrier reducing immune cell trafficking. Vitamin D exerts additional activity within the central nervous system reducing microglial and astrocytic activation. The immunomodulatory role of Vitamin D detected in animal models of multiple sclerosis has suggested its potential therapeutic use for treating multiple sclerosis. In this review, we focus on recent published data describing the biological effects of Vitamin D in animal models of multiple sclerosis on immune cells, blood–brain barrier function, activation of glial cells and its potential neuroprotective effects. Based on the current knowledge, we also discuss optimization of therapeutic interventions with Vitamin D in patients with multiple sclerosis, as well as new technologies allowing in-depth analysis of immune cell regulations by vitamin D.

A new method for primary culture of microglia in rats with spinal cord injury

At present, the primary culture method of microglia is complicated, and the culture of spinal cord microglia is rare, so we will explore to establish a new and efficient primary culture method of microglia in rats with spinal cord injury (SCI). The SCI model of SD rats was established by modified A11en's method, and the model of SCI was performed on 1 d, 3 d, 7 d and 14 d respectively. Then the injured spinal cord was removed, mechanically separated and filtered. The morphology of microglia was observed the next day and its purity was identified by CD11b and Iba1 immunofluorescence labeling. According to the above results, the morphological changes of microglia after 3 d of SCI were observed at 1 d, 2 d and 4 d. The results showed that the purity of microglia was 98%. The number of microglia after 3 d of SCI was the most. After SCI, the migration ability of microglia was enhanced, the number of microglia in the injured area increased, and the number was the highest at 3 d, then gradually decreased. In addition, the microglia after SCI would gradually change from active state to resting state with the passage of time. Therefore, we can use a simple and efficient mechanical separation method to extract primary microglia, which provides the basis for the study of microglia.

Attenuation in Proinflammatory Factors and Reduction in Neuronal Cell Apoptosis and Cerebral Vasospasm by Minocycline during Early Phase after Subarachnoid Hemorrhage in the Rat

Background

Subarachnoid hemorrhage (SAH) is an important subcategory of stroke due to its high mortality rate as well as severe complications such as neurological deficit. It has been suggested that cerebral inflammation is a major factor in advanced brain injury after SAH. Microglia and astrocytes are known supporting cells in the development and maintenance of inflammation in central nervous system. However, the role of microglia and astrocytes in the development of inflammation and neuronal cell apoptosis during the early phase after SAH has not been thoroughly investigated.

Materials and Methods

Sprague-Dawley rats were divided into 4 groups (n = 6/group): sham group, animals subjected to SAH without treatment, SAH animals pretreated with the microglia inhibitor minocycline (50 mg/kg, ip), and SAH animals pretreated with the astrocyte inhibitor fluorocitrate (50 mg/kg, ip). SAH was induced by injecting autologous blood (1 ml/kg) into the cistern magna on day 0. Pretreatment with minocycline or fluorocitrate was given three days prior to the induction of SAH. Rats were sacrificed 6 hr after SAH, and their cerebral spinal fluids were used to measure protein levels of neuroinflammatory cytokines IL-1β, IL-6, and TNF-α by ELISA. In addition, the cerebral cortex was utilized to determine the levels of caspase-3 by western blot and to evaluate neuronal cell apoptosis by immunohistochemistry staining and detect microglia and astrocyte by immunofluorescence staining for Iba-1 and GFAP. In this study, all SAH animals were given an injection of autologous blood and SAH rats treated with minocycline or fluorocitrate received ip injections on day 1, 2, and 3 before inducing SAH. Neurological outcome was assessed by ambulation and placing/stepping reflex responses on day 7.

Results

Immunofluorescence staining showed that SAH induced proliferation of microglia and astrocyte and minocycline inhibited the proliferation of both microglia and astrocyte. However, fluorocitrate inhibited only the proliferation of astrocyte. ELISA analysis showed that SAH upregulated TNF-α and IL-1β, but not IL-6 at 6 hr after SAH. Minocycline, but not fluorocitrate, attenuated the upregulation of TNF-α and IL-1β. Western blot analysis and immunohistochemistry staining showed that SAH induced neuronal cell apoptosis. Pretreatment with minocycline, but not fluorocitrate, decreased SAH-induced neuronal death and cerebral vasospasm. Furthermore, significant improvements in neurobehavioral outcome were seen in the minocycline treatment group, but not in animals treated with fluorocitrate.

Conclusions

Microglia may play an important role to regulate neuronal cell apoptosis and cerebral vasospasm through inhibiting inflammation at an early phase after SAH in the rat.

Autophagy of Spinal Microglia Affects the Activation of Microglia through the PI3K/AKT/mTOR Signaling Pathway

Delayed paralysis occurs within some patients suffered from ischemic spinal cord injury (ISCI) due to the aorta occlusion during the repair surgery of thoracic and thoracoabdominal aortic aneurysms. Although mild hypothermia has been reported to improve ISCI and prolong the tolerance of rats to ISCI without inducing immediate paralysis, the mechanism remains unclear. Herein, the study revealed that the mild hypothermia treatment indeed partially improved the ISCI in rats caused by cross-clamping at the descending aorta. ISCI induced the excessive activation of microglia and moderate autophagy in the spinal cord tissues of rats, while mild hypothermia significantly induced autophagy and reversed the excessive activation of microglia in the spinal cord tissues of rats. In OGD-stimulated mouse microglia BV-2 cells, the excessive activation of microglia and moderate autophagy were also observed; in the rapamycin-treated OGD model in BV-2 cells, autophagy was significantly enhanced whereas the excessive activation of microglia was reversed. In both in vivo ISCI model in rats and in vitro OGD model in BV-2 cells, the PI3K/AKT/mTOR pathway showed to be inhibited, whereas the PI3K/AKT/mTOR pathway was further inhibited by mild hypothermia in ISCI rats or rapamycin treatment in OGD-stimulated BV-2 cells. In conclusion, enhanced autophagy might be the mechanism of inhibited microglia activation by hypothermia treatment in ISCI rats and by rapamycin treatment in OGD-stimulated BV-2 cells. Autophagy could be enhanced through inhibiting the PI3K/AKT/mTOR pathway.

Microglial heterogeneity in chronic pain

In this review, we report existing preclinical evidence on how the CNS compartment as well as sex affect microglia functions in health. We highlight that recent advances in transcriptomics analyses have led to thorough characterization of disease-associated microglial states in mice and humans. We then consider the specific scenario of peripheral nerve or tissue injury which induce expression of a specific subset of genes in microglia in the dorsal horn of the spinal cord. We suggest the intriguing possibility that future studies may disclose the existence of a unique microglia transcriptional profile that is associated with chronic pain conditions. We also collect evidence that microglial activation in pain-related areas of the brain can be observed in models of neuropathic pain in agreement with recent neuroimaging studies in chronic pain patients. Based on the evidence discussed here, we predict that future studies on the neuroimmune interactions in chronic pain should complement our current understanding of microglia functions, but also adventure in using novel approaches such as scRNA-seq, spatial transcriptomics, CYTOF and transmission electron microscopy to provide a more complete characterization of the function, transcriptome and structure of microglia in chronic pain.

Ncx3-Induced Mitochondrial Dysfunction in Midbrain Leads to Neuroinflammation in Striatum of A53t-α-Synuclein Transgenic Old Mice

The exact mechanism underlying selective dopaminergic neurodegeneration is not completely understood. The complex interplay among toxic alpha-synuclein aggregates, oxidative stress, altered intracellular Ca²⁺-homeostasis, mitochondrial dysfunction and disruption of mitochondrial integrity is considered among the pathogenic mechanisms leading to dopaminergic neuronal loss. We herein investigated the molecular mechanisms leading to mitochondrial dysfunction and its relationship with activation of the neuroinflammatory process occurring in Parkinson’s disease. To address these issues, experiments were performed in vitro and in vivo in mice carrying the human mutation of α-synuclein A53T under the prion murine promoter. In these models, the expression and activity of NCX isoforms, a family of important transporters regulating ionic homeostasis in mammalian cells working in a bidirectional way, were evaluated in neurons and glial cells. Mitochondrial function was monitored with confocal microscopy and fluorescent dyes to measure mitochondrial calcium content and mitochondrial membrane potential. Parallel experiments were performed in 4 and 16-month-old A53T-α-synuclein Tg mice to correlate the functional data obtained in vitro with mitochondrial dysfunction and neuroinflammation through biochemical analysis. The results obtained demonstrated: 1. in A53T mice mitochondrial dysfunction occurs early in midbrain and later in striatum; 2. mitochondrial dysfunction occurring in the midbrain is mediated by the impairment of NCX3 protein expression in neurons and astrocytes; 3. mitochondrial dysfunction occurring early in midbrain triggers neuroinflammation later into the striatum, thus contributing to PD progression during mice aging.

Research progress on the regulatory role of microRNAs in spinal cord injury

Spinal cord injury (SCI) is a severe CNS injury that results in abnormalities in, or loss of, motor, sensory and autonomic nervous function. miRNAs belong to a new class of noncoding RNA that regulates the production of proteins and biological function of cells by silencing translation or interfering with the expression of target mRNAs. Following SCI, miRNAs related to oxidative stress, inflammation, autophagy, apoptosis and many other secondary injuries are differentially expressed, and these miRNAs play an important role in the progression of secondary injuries after SCI. The purpose of this review is to elucidate the differential expression and functional roles of miRNAs after SCI, thus providing references for further research on miRNAs in SCI.

Multiple Sclerosis: Lipids, Lymphocytes, and Vitamin D

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system. We review the two core MS features, myelin instability, fragmentation, and remyelination failure, and dominance of pathogenic CD4+ Th17 cells over protective CD4+ Treg cells. To better understand myelin pathology, we describe myelin biosynthesis, structure, and function, then highlight stearoyl-CoA desaturase (SCD) in nervonic acid biosynthesis and nervonic acid's contribution to myelin stability. Noting that vitamin D deficiency decreases SCD in the periphery, we propose it also decreases SCD in oligodendrocytes, disrupting the nervonic acid supply and causing myelin instability and fragmentation. To better understand the distorted Th17/Treg cell balance, we summarize Th17 cell contributions to MS pathogenesis, then highlight how 1,25-dihydroxyvitamin D3 signaling from microglia to CD4+ T cells restores Treg cell dominance. This signaling rapidly increases flux through the methionine cycle, removing homocysteine, replenishing S-adenosyl-methionine, and improving epigenetic marking. Noting that DNA hypomethylation and inappropriate DRB1*1501 expression were observed in MS patient CD4+ T cells, we propose that vitamin D deficiency thwarts epigenetic downregulation of DRB1*1501 and Th17 cell signature genes, and upregulation of Treg cell signature genes, causing dysregulation within the CD4+ T cell compartment. We explain how obesity reduces vitamin D status, and how estrogen and vitamin D collaborate to promote Treg cell dominance in females. Finally, we discuss the implications of this new knowledge concerning myelin and the Th17/Treg cell balance, and advocate for efforts to address the global epidemics of obesity and vitamin D deficiency in the expectation of reducing the impact of MS.

Microglial regional heterogeneity and its role in the brain

Microglia have been recently shown to manifest a very interesting phenotypical heterogeneity across different regions in the mammalian central nervous system (CNS). However, the underlying mechanism and functional meaning of this phenomenon are currently unclear. Baseline diversities of adult microglia in their cell number, cellular and subcellular structures, molecular signature as well as relevant functions have been discovered. But recent transcriptomic studies using bulk RNAseq and single-cell RNAseq have produced conflicting results on region-specific signatures of microglia. It is highly speculative whether such spatial heterogeneity contributes to varying sensitivities of individual microglia to the same physiological and pathological signals in different CNS regions, and hence underlie their functional relevance for CNS disease development. This review aims to thoroughly summarize up-to-date knowledge on this specific topic and provide some insights on the potential underlying mechanisms, starting from microgliogenesis. Understanding regional heterogeneity of microglia in the context of their diverse neighboring neurons and other glia may provide an important clue for future development of innovative therapies for neuropsychiatric disorders.

Differences of Microglia in the Brain and the Spinal Cord

Microglia were previously regarded as a homogenous myeloid cell lineage in the mammalian central nervous system (CNS). However, accumulating evidences show that microglia in the brain and SC are quite different in development, cellular phenotypes and biological functions. Although this is a very interesting phenomenon, the underlying mechanisms and its significance for neurological diseases in association with behavioral and cognitive changes are still unclear. How microglia differ between these two regions and whether such diversity may contribute to CNS development and functions as well as neurological diseases will be discussed in this Perspective.

Neurodegeneration, demyelination, and astrogliosis in rat spinal cord by chronic lead treatment

Early exposure to lead (Pb) has been associated with an elevated risk of developing neurodegenerative diseases. There is evidence that neuronal damage in chronic Pb exposure can be caused by the convergence of glial damage. Apoptosis may be a possible mechanism of Pb-induced cell death in the central nervous system. We tested cellular damage and apoptosis in the spinal cord of Wistar rats treated with Pb. Twelve rats were divided into two groups (n = 6): the control group was treated with only drinking water and the other group received 500 ppm of Pb acetate. After 3 months of Pb treatment, all animals were euthanized and spinal cords were extracted. Morphology was evaluated by Nissl and Kluver-Barrera stainings. Apoptosis was detected by terminal deoxynucleotidyl transferase dUTP nick end labeling assay. Specific antibodies were used to evaluate Pb damage in oligodendrocytes, astrocytes, and microglia. A large number of apoptotic bodies was observed in the white matter of the Pb-treated group. The Pb-treated group also showed a reduced number of neurons and oligodendrocytes but had an increased number of astrocytes compared with the nontreated group. Our results demonstrate that chronic Pb treatment induces neurodegeneration, demyelination, and astrogliosis in the rat spinal cord.

Neuroprotective mechanism involved in spinal cord stimulation postconditioning

OBJECTIVES

Delayed paraplegia developed postoperatively after thoracoabdominal aneurysm surgery is primarily associated with spinal cord ischemia/reperfusion injury. Our previous study suggested that spinal cord stimulation postconditioning protected the spinal cord from ischemia/reperfusion injury through microglia inhibition. In this study, we further investigated whether α7 nicotinic acetylcholine receptors were involved in the neuroprotective mechanism of spinal cord stimulation.

METHODS

Rabbits were randomly assigned to sham, control, 2 Hz, α-bungarotoxin, and 2 Hz-α-bungarotoxin groups (n = 24/group). Transient spinal cord ischemia was performed on all rabbits except rabbits in the sham group. Rabbits in the control group received no further intervention, rabbits in the 2 Hz group were given 2 Hz spinal cord stimulation, rabbits in the α-bungarotoxin group received prescribed intrathecal α-bungarotoxin (α-bungarotoxin, a specific α7 nicotinic acetylcholine receptor antagonist) injections, and rabbits in the 2 Hz-α-bungarotoxin group received both α-bungarotoxin injections and 2 Hz spinal cord stimulation. Hind-limb neurologic function was assessed, and spinal cord histologic examination, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining, and microglia staining were performed at 8 hours, 1 day, 3 days, and 7 days of reperfusion.

RESULTS

Rabbits in the 2 Hz group had significantly better neurologic functions, more α-motor neurons, and lower terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling-positive neuron rates and microglia area/anterior horn area ratios (microglia area ratios) than the control group. The neurologic functions of the α-bungarotoxin group were significantly worse than those of the control group, whereas other results were not significantly different from the control group. The results of the 2 Hz-α-bungarotoxin group were insignificant to the control group except for the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling-positive neuron rates, which were significantly lower than in the control group.

CONCLUSIONS

The neuroprotective effects of spinal cord stimulation postconditioning against spinal cord ischemia/reperfusion injury were partially mediated by activating α7 nicotinic acetylcholine receptors.

Virus-triggered spinal cord demyelination is followed by a peripheral neuropathy resembling features of Guillain-Barré Syndrome

Theiler’s murine encephalomyelitis virus (TMEV)-induces a demyelinating disease in the spinal cord (SC) of susceptible but not in resistant (B6) mouse strains. The aim of the present study was to induce SC demyelination and a peripheral neuropathy in resistant mice by switching the infection site from cerebrum to SC. B6 mice were intraspinally inoculated with TMEV. Infected mice showed clinical signs starting at 7 days post infection (dpi). Histopathology revealed a mononuclear myelitis, centred on the injection site at 3 dpi with subsequent antero- and retrograde spread, accompanied by demyelination and axonal damage within the SC. Virus protein was detected in the SC at all time points. SC inflammation decreased until the end of the investigation period (28 dpi). Concurrent with the amelioration of SC inflammation, the emergence of a peripheral neuropathy, characterized by axonal damage, demyelination and macrophage infiltration, contributing to persistent clinical sings, was observed. Intraspinal TMEV infection of resistant mice induced inflammation, demyelination and delayed viral clearance in the spinal cord and more interestingly, subsequent, virus-triggered inflammation and degeneration within the PN associated with dramatic and progressive clinical signs. The lesions observed in the PN resemble important features of Guillain-Barré syndrome, especially of acute motor/motor-sensory axonal forms.

3D Organotypic Spinal Cultures: Exploring Neuron and Neuroglia Responses Upon Prolonged Exposure to Graphene Oxide

Graphene-based nanomaterials are increasingly engineered as components of biosensors, interfaces or drug delivery platforms in neuro-repair strategies. In these developments, the mostly used derivative of graphene is graphene oxide (GO). To tailor the safe development of GO nanosheets, we need to model in vitro tissue responses, and in particular the reactivity of microglia, a sub-population of neuroglia that acts as the first active immune response, when challenged by GO. Here, we investigated central nervous system (CNS) tissue reactivity upon long-term exposure to GO nanosheets in 3D culture models. We used the mouse organotypic spinal cord cultures, ideally suited for studying long-term interference with cues delivered at controlled times and concentrations. In cultured spinal segments, the normal presence, distribution and maturation of anatomically distinct classes of neurons and resident neuroglial cells are preserved. Organotypic explants were developed for 2 weeks embedded in fibrin glue alone or presenting GO nanosheets at 10, 25 and 50 μg/mL. We addressed the impact of such treatments on premotor synaptic activity monitored by patch clamp recordings of ventral interneurons. We investigated by immunofluorescence and confocal microscopy the accompanying glial responses to GO exposure, focusing on resident microglia, tested in organotypic spinal slices and in isolated neuroglia cultures. Our results suggest that microglia reactivity to accumulation of GO flakes, maybe due to active phagocytosis, may trim down synaptic activity, although in the absence of an effective activation of inflammatory response and in the absence of neuronal cell death.

Delayed xenon post-conditioning mitigates spinal cord ischemia/reperfusion injury in rabbits by regulating microglial activation and inflammatory factors

The neuroprotective effect against spinal cord ischemia/reperfusion injury in rats exerted by delayed xenon post-conditioning is stronger than that produced by immediate xenon post-conditioning. However, the mechanisms underlying this process remain unclear. Activated microglia are the main inflammatory cell type in the nervous system. The release of pro-inflammatory factors following microglial activation can lead to spinal cord damage, and inhibition of microglial activation can relieve spinal cord ischemia/reperfusion injury. To investigate how xenon regulates microglial activation and the release of inflammatory factors, a rabbit model of spinal cord ischemia/reperfusion injury was induced by balloon occlusion of the infrarenal aorta. After establishment of the model, two interventions were given: (1) immediate xenon post-conditioning—after reperfusion, inhalation of 50% xenon for 1 hour, 50% N₂/50%O₂ for 2 hours; (2) delayed xenon post-conditioning—after reperfusion, inhalation of 50% N₂/50%O₂ for 2 hours, 50% xenon for 1 hour. At 4, 8, 24, 48 and 72 hours after reperfusion, hindlimb locomotor function was scored using the Jacobs locomotor scale. At 72 hours after reperfusion, interleukin 6 and interleukin 10 levels in the spinal cord of each group were measured using western blot assays. Iba1 levels were determined using immunohistochemistry and a western blot assay. The number of normal neurons at the injury site was quantified using hematoxylin-eosin staining. At 72 hours after reperfusion, delayed xenon post-conditioning remarkably enhanced hindlimb motor function, increased the number of normal neurons at the injury site, decreased Iba1 levels, and inhibited interleukin-6 and interleukin-10 levels in the spinal cord. Immediate xenon post-conditioning did not noticeably affect the above-mentioned indexes. These findings indicate that delayed xenon post-conditioning after spinal cord injury improves the recovery of neurological function by reducing microglial activation and the release of interleukin-6 and interleukin-10.

Maternal immune activation results in complex microglial transcriptome signature in the adult offspring that is reversed by minocycline treatment

Maternal immune activation (MIA) during pregnancy has been linked to an increased risk of developing psychiatric pathologies in later life. This link may be bridged by a defective microglial phenotype in the offspring induced by MIA, as microglia have key roles in the development and maintenance of neuronal signaling in the central nervous system. The beneficial effects of the immunomodulatory treatment with minocycline on schizophrenic patients are consistent with this hypothesis. Using the MIA mouse model, we found an altered microglial transcriptome and phagocytic function in the adult offspring accompanied by behavioral abnormalities. The changes in microglial phagocytosis on a functional and transcriptional level were similar to those observed in a mouse model of Alzheimer's disease hinting to a related microglial phenotype in neurodegenerative and psychiatric disorders. Minocycline treatment of adult MIA offspring reverted completely the transcriptional, functional and behavioral deficits, highlighting the potential benefits of therapeutic targeting of microglia in psychiatric disorders.

Spinal versus brain microglial and macrophage activation traits determine the differential neuroinflammatory responses and analgesic effect of minocycline in chronic neuropathic pain

Substantial evidence indicates involvement of microglia/macrophages in chronic neuropathic pain. However, the temporal-spatial features of microglial/macrophage activation and their pain-bound roles remain elusive. Here, we evaluated microglia/macrophages and the subtypes in the lumbar spinal cord (SC) and prefrontal cortex (PFC), and analgesic-anxiolytic effect of minocycline at different stages following spared nerve injury (SNI) in rats. While SNI enhanced the number of spinal microglia/macrophages since post-operative day (POD)3, pro-inflammatory MHCII⁺ spinal microglia/macrophages were unexpectedly less abundant in SNI rats than shams on POD21. By contrast, less abundant anti-inflammatory CD172a (SIRPα)⁺ microglia/macrophages were found in the PFC of SNI rats. Interestingly in naïve rats, microglial/macrophage expression of CD11b/c, MHCII and MHCII⁺/CD172a⁺ ratio were higher in the SC than the cortex. Consistently, multiple immune genes involved in anti-inflammation, phagocytosis, complement activation and M2 microglial/macrophage polarization were upregulated in the spinal dorsal horn and dorsal root ganglia but downregulated in the PFC of SNI rats. Furthermore, daily intrathecal minocycline treatment starting from POD0 for two weeks alleviated mechanical allodynia most robustly before POD3 and attenuated anxiety on POD9. Although minocycline dampened spinal MHCII⁺ microglia/macrophages until POD13, it failed to do so on cortical microglia/macrophages, indicating that dampening only spinal inflammation may not be enough to alleviate centralized pain at the chronic stage. Taken together, our data provide the first evidence that basal microglial/macrophage traits underlie differential region-specific responses to SNI and minocycline treatment, and suggest that drug treatment efficiently targeting not only spinal but also brain inflammation may be more effective in treating chronic neuropathic pain.

Sex Differences in Pain

Females greatly outnumber males as sufferers of chronic pain. Although social and psychological factors certainly play a role in the differences in prevalence and incidence, biological differences in the functioning of the immune system likely underlie these observed effects. This Review examines the current literature on biological sex differences in the functioning of the innate and adaptive immune systems as they relate to pain experience. With rodent models, we and others have observed that male mice utilize microglia in the spinal cord to mediate pain, whereas females preferentially use T cells in a similar manner. The difference can be traced to differences in cell populations, differences in suppression by hormones, and disparate cellular responses in males and females. These sex differences also translate into human cellular responses and may be the mechanism by which the disproportionate chronic pain experience is based. Recognition of the evidence underlying sex differences in pain will guide development of treatments and provide better options for patients that are tailored to their physiology. © 2016 Wiley Periodicals, Inc.

Neuroinflammation and virus replication in the spinal cord of simian immunodeficiency virus-infected macaques

Studies of neurologic diseases induced by simian immunodeficiency virus (SIV) in Asian macaques have contributed greatly to the current understanding of human immunodeficiency virus pathogenesis in the brain and peripheral nervous system. Detailed investigations into SIV-induced alterations in the spinal cord, a critical sensorimotor relay point between the brain and the peripheral nervous system, have yet to be reported. In this study, lumbar spinal cords from SIV-infected pigtailed macaques were examined to quantify SIV replication and associated neuroinflammation. In untreated SIV-infected animals, there was a strong correlation between amount of SIV RNA in the spinal cord and expression of the macrophage marker CD68 and the key proinflammatory mediators tumor necrosis factor and CCL2. We also found a significant correlation between SIV-induced alterations in the spinal cord and the degree of distal epidermal nerve fiber loss among untreated animals. Spinal cord changes (including elevated glial fibrillary acidic protein immunostaining and enhanced CCL2 gene expression) also were present in SIV-infected antiretroviral drug-treated animals despite SIV suppression. A fuller understanding of the complex virus and host factor dynamics in the spinal cord during human immunodeficiency virus infection will be critical in the development of new treatments for human immunodeficiency virus-associated sensory neuropathies and studies aimed at eradicating the virus from the central nervous system.

Blockade of gap junction hemichannel protects secondary spinal cord injury from activated microglia-mediated glutamate exitoneurotoxicity

We previously demonstrated that activated microglia release excessive glutamate through gap junction hemichannels and identified a novel gap junction hemichannel blocker, INI-0602, that was proven to penetrate the blood-brain barrier and be an effective treatment in mouse models of amyotrophic lateral sclerosis and Alzheimer disease. Spinal cord injury causes tissue damage in two successive waves. The initial injury is mechanical and directly causes primary tissue damage, which induces subsequent ischemia, inflammation, and neurotoxic factor release resulting in the secondary tissue damage. These lead to activation of glial cells. Activated glial cells such as microglia and astrocytes are common pathological observations in the damaged lesion. Activated microglia release glutamate, the major neurotoxic factor released into the extracellular space after neural injury, which causes neuronal death at high concentration. In the present study, we demonstrate that reduction of glutamate-mediated exitotoxicity via intraperitoneal administration of INI-0602 in the microenvironment of the injured spinal cord elicited neurobehavioral recovery and extensive suppression of glial scar formation by reducing secondary tissue damage. Further, this intervention stimulated anti-inflammatory cytokines, and subsequently elevated brain-derived neurotrophic factor. Thus, preventing microglial activation by a gap junction hemichannel blocker, INI-0602, may be a promising therapeutic strategy in spinal cord injury.

The systemic response to CNS injury

Inflammation within the brain or spinal cord has the capacity to damage neurons and is known to contribute to long-term disability in a spectrum of central nervous system (CNS) pathologies. However, there is a more profound increase in the recruitment of potentially damaging populations of leukocytes to the spinal cord than to the brain after equivalent injuries. Increased levels of inflammatory cytokines and chemokines in the spinal cord underpin this dissimilarity after injury, which also appears to be very sensitive to processes that operate within organs distant from the primary injury site such as the liver, lung and spleen. Indeed, CNS injury per se can generate profound changes in gene expression and the cellularity of these organs, which, as a consequence, gives rise to secondary organ damage. Our understanding of the local inflammatory processes that can damage neurons is becoming clearer, but our understanding of how the peripheral immune system coordinates the response to CNS injury and how any concomitant infections or injury might impact on the outcome of CNS injury is not so well developed. It is clear that the orientation of the response to peripheral challenges, be it a pro- or anti-inflammatory effect, appears to be dependent on the nature and timing of events. Here, the importance of the inter-relationship between inflammation in the CNS and the consequent inflammatory response in peripheral tissues is highlighted.

Reduced inflammatory phenotype in microglia derived from neonatal rat spinal cord versus brain

Microglia are the primary immune cells of the central nervous system (CNS). Membrane bound sensors on their processes monitor the extracellular environment and respond to perturbations of the CNS such as injury or infection. Once activated, microglia play a crucial role in determining neuronal survival. Recent studies suggest that microglial functional response properties vary across different regions of the CNS. However, the activation profiles of microglia derived from the spinal cord have not been evaluated against brain microglia in vitro. Here, we studied the morphological properties and secretion of inflammatory and trophic effectors by microglia derived from the brain or spinal cord of neonatal rats under basal culture conditions and after activation with lipopolysaccharide (LPS). Our results demonstrate that spinal microglia assume a less inflammatory phenotype after LPS activation, with reduced release of the inflammatory effectors tumor necrosis factor alpha, interleukin-1 beta, and nitric oxide, a less amoeboid morphology, and reduced phagocytosis relative to brain-derived microglia. Phenotypic differences between brain and spinal microglia are an important consideration when evaluating anti-inflammatory or immunomodulatory therapies for brain versus spinal injury.

Culturing microglia from the neonatal and adult central nervous system

Microglia are the resident macrophage-like cells of the central nervous system (CNS) and, as such, have critically important roles in physiological and pathological processes such as CNS maturation in development, multiple sclerosis, and spinal cord injury. Microglia can be activated and recruited to action by neuronal injury or stimulation, such as axonal damage seen in MS or ischemic brain trauma resulting from stroke. These immunocompetent members of the CNS are also thought to have roles in synaptic plasticity under non-pathological conditions. We employ protocols for culturing microglia from the neonatal and adult tissues that are aimed to maximize the viable cell numbers while minimizing confounding variables, such as the presence of other CNS cell types and cell culture debris. We utilize large and easily discernable CNS components (e.g. cortex, spinal cord segments), which makes the entire process feasible and reproducible. The use of adult cells is a suitable alternative to the use of neonatal brain microglia, as many pathologies studied mainly affect the postnatal spinal cord. These culture systems are also useful for directly testing the effect of compounds that may either inhibit or promote microglial activation. Since microglial activation can shape the outcomes of disease in the adult CNS, there is a need for in vitro systems in which neonatal and adult microglia can be cultured and studied.

Development and treatments of inflammatory cells and cytokines in spinal cord ischemia-reperfusion injury

During aortic surgery, interruption of spinal cord blood flow might cause spinal cord ischemia-reperfusion injury (IRI). The incidence of spinal cord IRI after aortic surgery is up to 28%, and patients with spinal cord IRI might suffer from postoperative paraplegia or paraparesis. Spinal cord IRI includes two phases. The immediate spinal cord injury is related to acute ischemia. And the delayed spinal cord injury involves both ischemic cellular death and reperfusion injury. Inflammation is a subsequent event of spinal cord ischemia and possibly a major contributor to spinal cord IRI. However, the development of inflammatory mediators is incompletely demonstrated. And treatments available for inflammation in spinal cord IRI are insufficient. Improved understanding about spinal cord IRI and the development of inflammatory cells and cytokines in this process will provide novel therapeutic strategies for spinal cord IRI. Inflammatory cytokines (e.g., TNF-α and IL-1) may play an important role in spinal cord IRI. For treatment of several intractable autoimmune diseases (e.g., rheumatoid arthritis), where inflammatory cytokines are involved in disease progression, anti-inflammatory cytokine antagonist is now available. Hence, there is great potential of anti-inflammatory cytokine antagonist for therapeutic use of spinal cord IRI. We here review the mediators and several possibilities of treatment in spinal cord IRI.

Management strategies for acute spinal cord injury: current options and future perspectives

PURPOSE OF REVIEW

Spinal cord injury is a devastating acute neurological condition with loss of function and poor long-term prognosis. This review summarizes current management strategies and innovative concepts on the horizon.

RECENT FINDINGS

The routine use of steroids in patients with spinal cord injuries has been largely abandoned and considered a 'harmful standard of care'. Prospective trials have shown that early spine stabilization within 24  h results in decreased secondary complication rates. Neuronal plasticity and axonal regeneration in the adult spinal cord are limited due to myelin-associated inhibitory molecules, such as Nogo-A. The experimental inhibition of Nogo-A ameliorates axonal sprouting and functional recovery in animal models.

SUMMARY

General management strategies for acute spinal cord injury consist of protection of airway, breathing, oxygenation and control of blood loss with maintenance of blood pressure. Unstable spine fractures should be stabilized early to allow unrestricted mobilization of patients with spinal cord injuries and to decrease preventable complications. Steroids are largely considered obsolete and have been abandoned in clinical guidelines. Nogo-A represents a promising new pharmacological target to promote sprouting of injured axons and restore function. Prospective clinical trials of Nogo-A inhibition in patients with spinal cord injuries are currently under way.

Myelin antigen load influences antigen presentation and severity of central nervous system autoimmunity

This study was designed to understand the impact of self-antigen load on manifestation of organ specific autoimmunity. Using a transgenic mouse model characterized by CNS hypermyelination, we show that larger myelin content results in greater severity of experimental autoimmune encephalomyelitis attributable to an increased number of microglia within the hypermyelinated brain. We conclude that a larger self-antigen load affects an increase in number of tissue resident antigen presenting cells (APCs) most likely due to compensatory antigen clearance mechanisms thereby enhancing the probability of productive T cell-APC interactions in an antigen abundant environment and results in enhanced severity of autoimmune disease.

The role of pro- and anti-inflammatory cytokines in the pathogenesis of spontaneous canine CNS diseases

Dogs are comparatively frequently affected by various spontaneously occurring inflammatory and degenerative central nervous system (CNS) conditions, and immunopathological processes are a hallmark of the associated neuropathology. Due to the low regenerative capacity of the CNS a sophisticated understanding of the underlying molecular basis for disease initiation, progression and remission in canine CNS diseases represents a prerequisite for the development of novel therapeutical approaches. In addition, as many spontaneous canine CNS diseases share striking similarities with their human counterpart, knowledge about the immune pathogenesis may in part be translated for a better understanding of certain human diseases. In addition to cytokine-driven differentiation of peripheral leukocytes including different subsets of T cells recent research suggests a pivotal role of these mediators also in phenotype polarization of resident glial cells. Cytokines thus represent the key mediators of the local and systemic immune response in CNS diseases and their orchestration significantly decides on either lesion progression or remission. The aim of the present review is to summarize the growing number of data focusing on the molecular basis of the immune response during spontaneous canine CNS diseases and to detail the effect of cytokines on the immune pathogenesis of selected idiopathic, infectious, and traumatic canine CNS diseases. Steroid-responsive meningitis arteritis (SRMA) represents a unique idiopathic disease of leptomeningeal blood vessels characterized by excessive IgA secretion into the cerebrospinal fluid. Recent reports have given sophisticated insights into the cytokine-driven, immune-mediated pathogenesis of SRMA that is characterized by a biased T helper 2 cell response. Canine distemper associated leukoencephalitis represents an important spontaneously occurring disease that allows investigations on the basic pathogenesis of immune-mediated myelin loss. It is characterized by an early virus-induced up-regulation of pro-inflammatory cytokines with chronic bystander immune-mediated demyelinating processes. Lastly, canine spinal cord injury (SCI) shares many similarities with the human counterpart and most commonly results from intervertebral disk disease. The knowledge of its pathogenesis is largely restricted to experimental studies in rodents, and the impact of immune processes that accompany secondary injury is discussed controversially. Recent investigations on canine SCI highlight the pivotal role of pro-inflammatory cytokine expression that is paralleled by a dominating reaction of microglia/macrophages potentially indicating a polarization of these immune cells into a neurotoxic and harmful phenotype. This report will review the role of cytokines in the immune processes of the mentioned representative canine CNS diseases and highlight the importance of cytokine/cytokine interaction as a useful therapeutic target in canine CNS diseases.

Parkinson's disease

Parkinson's disease (PD) is the most common age-related motoric neurodegenerative disease initially described in the 1800's by James Parkinson as the 'Shaking Palsy'. Loss of the neurotransmitter dopamine was recognized as underlying the pathophysiology of the motor dysfunction; subsequently discovery of dopamine replacement therapies brought substantial symptomatic benefit to PD patients. However, these therapies do not fully treat the clinical syndrome nor do they alter the natural history of this disorder motivating clinicians and researchers to further investigate the clinical phenotype, pathophysiology/pathobiology and etiology of this devastating disease. Although the exact cause of sporadic PD remains enigmatic studies of familial and rare toxicant forms of this disorder have laid the foundation for genome wide explorations and environmental studies. The combination of methodical clinical evaluation, systematic pathological studies and detailed genetic analyses have revealed that PD is a multifaceted disorder with a wide-range of clinical symptoms and pathology that include regions outside the dopamine system. One common thread in PD is the presence of intracytoplasmic inclusions that contain the protein, α-synuclein. The presence of toxic aggregated forms of α-synuclein (e.g., amyloid structures) are purported to be a harbinger of subsequent pathology. In fact, PD is both a cerebral amyloid disease and the most common synucleinopathy, that is, diseases that display accumulations of α-synuclein. Here we present our current understanding of PD etiology, pathology, clinical symptoms and therapeutic approaches with an emphasis on misfolded α-synuclein.

Macrophage migration inhibitory factor activates cyclooxygenase 2-prostaglandin E2 in cultured spinal microglia

In our previous study, peripheral inflammatory stimulation evoked production of macrophage migration inhibitory factor (MIF) in the spinal cord and found spinal microglia are the major source of MIF in this context. Given the contribution of the activated-microglia to the inflammatory neuropathy plus the role for upregulated COX 2 expression and PGE(2) production in the severity of clinical manifestations of these neuroinflammatory conditions, we herein tested the hypothesis that in vitro MIF stimulation to spinal microglia could result in an activation of COX 2-PGE(2) system by MIF-CD74 interaction. We found MIF played roles in evoking COX 2 mRNA and protein expression in a dose-dependent manner correspondingly in changes in PGE(2) level in the cultured rat microglia, but these changes could be inhibited by genetic deletion of CD74. Finally, MIF-induced COX 2-PGE(2) activation could be blocked by selective inhibitors of p44/p42 and p38 MAPKs. These data highlight MIF/CD74 interaction induces upregulation of COX 2 expression and PGE(2) secretion in primary rodent microglia, and further this effect is associated with downstream activation of p38 and p44/p42 signaling cascades, and favors the role of MIF as a novel pathway for microglia-associated neuroinflammation.

Unconjugated bilirubin contributes to early inflammation and edema after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a stroke subtype with significant mortality and morbidity. The role of unconjugated bilirubin (UBR) in ICH brain injury is not well understood. Therefore, we studied the effects of UBR on brain injury markers and inflammation, as well as mechanisms involved therein. We induced ICH in mice by infusion of autologous whole blood with vehicle (dimethyl sulfoxide) or UBR. We found that UBR led to an increase in edema (P≤0.05), but a decrease in nitrate/nitrite formation (7.0±0.40  nmol/mg versus 5.2±0.70  nmol/mg protein, P≤0.05) and no change in protein carbonyls. Unconjugated bilirubin was also associated with an increase in neutrophil infiltration compared with ICH alone, as determined by both immunofluorescence and flow cytometry (36%±3.2% versus 53%±1.3% of CD45(+) cells, P≤0.05). In contrast, we observed reduced perihematomal microglia immunoreactivity in animals receiving UBR (P≤0.05). Using in vitro techniques, we show neutrophil activation by UBR and also show that protein kinase C participates in this signaling pathway. Finally, we found that UBR was associated with an increased expression of the leukocyte adhesion molecule intercellular adhesion molecule-1. Our results suggest that UBR possesses complex immune-modulatory and antioxidant effects.

Early graft of neural precursors in spinal cord compression reduces glial cyst and improves function

OBJECTIVE

Spinal cord injury (SCI) often results in irreversible and permanent neurological deficits below the injury site and is considered a pathological state of functional damage to local neurons and axon fibers. There are several experimental treatments to minimize tissue damage, and recently cell transplantation has emerged as a promising approach in spinal cord repair. The authors undertook this study to evaluate grafting of neural tube precursors as a possible therapeutic strategy in a model of spinal cord compression in the mouse.

METHODS

Compression SCI was induced at the T-13 level in adult male mice. Immediately after injury, neural precursor cells (NPs) were transplanted into the SCI lesion cavity in 18 mice; the remaining 19 mice received saline injections into the lesion cavity and were used as controls. Spinal cords were examined 12, 19, and 26 days postinjury to investigate the survival of the NPs and their effects on the cellular environment, glial scar and glial cyst formation, astrogliosis, and microglial activation.

RESULTS

Grafted NPs survived well and integrated into the host spinal cord tissue. Some NPs had differentiated into cells expressing glial and neuronal markers at all 3 end points. Analysis of glial cyst volume showed a lesion volume reduction of 63.2% in the NP-treated mice compared with volume in the injured but untreated mice. There appeared to be no difference in astroglial and microglial activation between untreated mice and treated ones. Sensory and motor tests demonstrated that transplantation of NPs promoted improvement in injured and treated animals compared with controls.

CONCLUSIONS

These results support the therapeutic potential of NPs, demonstrating that they can survive for a long time, differentiate, integrate into the injured spinal cord, and promote functional recovery after SCI.