Number Of Microglia Research Articles

Deletion of Socs3 in LysM+ cells and Cx3cr1 resulted in age-dependent development of retinal microgliopathy

BackgroundWe generated a mouse model of primary microglial dysfunction by deleting two negative immune regulatory genes, Cx3cr1 and Socs3 (in LysM+ cells). This study aimed to understand how primary microglial dysfunction impacts retinal neurons during aging.MethodsThe LysMCre-Socs3fl/flCx3cr1gfp/gfp double knockout (DKO), LysMCre-Socs3fl/fl, Cx3cr1gfp/gfp and Socs3fl/fl mice were maintained up to 12 months. Eyes were collected and processed for immunohistochemistry of IBA-1, cone arrestin, secretagogin, PKCα and GABA. Brain microglia from DKO and WT mice were stimulated with LPS + IFN-γ or IL-4. The expression of TNF-α, IL-1β, IL-6, iNOS, IL-12p40, IL-23p19, CCL2, CCL5, CXCL2, IL-10, CD206 and Arg1 were examined by qRT-PCR and protein production was measured by Luminex assay. Retinal explants from C57BL/6 J mice were co-cultured with microglia from DKO or WT mice for 24 h, after which the number of cone arrestin+ cells in retinal flatmount were quantified.ResultsIn 3–5 month old mice, the number of microglia in retinal ganglion cell layer (GCL) and inner plexiform layer (IPL) were comparable in all strains of mice. The DKO mice had a significantly higher number of microglia in the outer plexiform layer (OPL) but significantly lower numbers of cone arrestin+, secretagogin+ and GABA+ cells compared to Socs3fl/fl and single KO mice. During aging, 57% of the DKO mice died before 12 months old. The 10–12 months old DKO mice had significantly higher numbers of microglia in GCL/IPL and OPL than age-matched Socs3fl/fl and single KO mice. The aged DKO mice developed retinal pigment epithelial (RPE) dysmorphology accompanied by subretinal microglial accumulation. The number of photoreceptors, bipolar cells (Secretagogin+ or PKCα+) and GABA+ amacrine cells was significantly lower in aged DKO mice compared to age-matched Socs3fl/fl and single KO mice. Microglia from DKO mice showed significantly higher levels of phagocytic activity and produced higher levels of TNF-α, IL-6, CCL2, CCL5, CXCL2 and CXCL10 compared to microglia from Socs3fl/fl mice. Co-culture of retinal explants with LPS + IFN-γ or IL-4 pre-treated DKO microglia significantly reduced cone photoreceptor survival.ConclusionsThe LysMCre-Socs3fl/flCx3cr1gfp/gfp DKO mice displayed primary microglial dysfunction and developed age-related retinal microgliopathy characterized by aggragated microglial activation and multiple retinal neuronal and RPE degeneration.Trial registrationNot applicable. The article does not contain any results from human participants.

Partial microglial depletion is associated with impaired hippocampal synaptic and cognitive function in young and aged rats.

The role of microglia in mediating age-related changes in cognition and hippocampal synaptic function was examined by microglial depletion and replenishment using PLX3397. We observed age-related differences in microglial number and morphology, as well as increased Iba-1 expression, indicating microglial activation. PLX3397 treatment decreased microglial number, with aged rats exhibiting the lowest density. Young rats exhibited increased expression of pro-inflammatory cytokines during depletion and repopulation and maintenance of Iba-1 levels despite reduced microglial number. For aged rats, several cytokines increased with depletion and recovered during repopulation; however, aged rats did not fully recover microglial cell number or Iba-1 expression during repopulation, with a recovery comparable to young control levels rather than aged controls. Hippocampal CA3-CA1 synaptic transmission was impaired with age, and microglial depletion was associated with decreased total synaptic transmission in young and aged rats. A robust decline in N-methyl-d-aspartate-receptor-mediated synaptic transmission arose in young depleted rats specifically. Microglial replenishment normalized depletion-induced synaptic function to control levels; however, recovery of aged animals did not mirror young. Microglial depletion was associated with decreased context-object discrimination memory in both age groups, which recovered with microglial repopulation. Aged rats displayed impaired contextual and cued fear memory, and microglial replenishment did not recover their memory to the level of young. The current study indicates that cognitive function and synaptic transmission benefit from the support of aged microglia and are hindered by removal of these cells. Replenishment of microglia in aging did not ameliorate age-related cognitive impairments or senescent synaptic function.

Oligodeoxynucleotides containing unmethylated cytosine-guanine motifs are effective immunostimulants against pneumococcal meningitis in the immunocompetent and neutropenic host

BackgroundBacterial meningitis is a fatal disease with a mortality up to 30% and neurological sequelae in one fourth of survivors. Available vaccines do not fully protect against this lethal disease. Here, we report the protective effect of synthetic oligodeoxynucleotides containing unmethylated cytosine-guanine motifs (CpG ODN) against the most frequent form of bacterial meningitis caused by Streptococcus pneumoniae.MethodsThree days prior to the induction of meningitis by intracerebral injection of S. pneumoniae D39, wild-type and Toll-like receptor (TLR9)−/− mice received an intraperitoneal injection of 100 μg CpG ODN or vehicle. To render mice neutropenic, anti-Ly-6G monoclonal antibody was daily administrated starting 4 days before infection with a total of 7 injections. Kaplan-Meier survival analyses and bacteriological studies, in which mice were sacrificed 24 h and 36 h after infection, were performed.ResultsPre-treatment with 100 μg CpG ODN prolonged survival of immunocompetent and neutropenic wild-type mice but not of TLR9−/− mice. There was a trend towards lower mortality in CpG ODN-treated immunocompetent and neutropenic wild-type mice. CpG ODN caused an increase of IL-12/IL-23p40 levels in the spleen and serum in uninfected animals. The effects of CpG ODN on bacterial concentrations and development of clinical symptoms were associated with an increased number of microglia in the CNS during the early phase of infection. Elevated concentrations of IL-12/IL-23p40 and MIP-1α correlated with lower bacterial concentrations in the blood and spleen during infection.ConclusionsPre-conditioning with CpG ODN strengthened the resistance of neutropenic and immunocompetent mice against S. pneumoniae meningitis in the presence of TLR9. Administration of CpG ODN decreased bacterial burden in the cerebellum and reduced the degree of bacteremia. Systemic administration of CpG ODN may help to prevent or slow the progression to sepsis of bacterial CNS infections in healthy and immunocompromised individuals even after direct inoculation of bacteria into the intracranial compartments, which can occur after sinusitis, mastoiditis, open head trauma, and surgery, including placement of an external ventricular drain.

Aging and Microglial Response following Systemic Stimulation with Escherichia coli in Mice.

Systemic infection is an important risk factor for the development cognitive impairment and neurodegeneration in older people. Animal experiments show that systemic challenges with live bacteria cause a neuro-inflammatory response, but the effect of age on this response in these models is unknown. Young (2 months) and middle-aged mice (13–14 months) were intraperitoneally challenged with live Escherichia coli (E. coli) or saline. The mice were sacrificed at 2, 3 and 7 days after inoculation; for all time points, the mice were treated with ceftriaxone (an antimicrobial drug) at 12 and 24 h after inoculation. Microglial response was monitored by immunohistochemical staining with an ionized calcium-binding adaptor molecule 1 (Iba-1) antibody and flow cytometry, and inflammatory response by mRNA expression of pro- and anti-inflammatory mediators. We observed an increased microglial cell number and moderate morphologically activated microglial cells in middle-aged mice, as compared to young mice, after intraperitoneal challenge with live E. coli. Flow cytometry of microglial cells showed higher CD45 and CD11b expressions in middle-aged infected mice compared to young infected mice. The brain expression levels of pro-inflammatory genes were higher in middle-aged than in young infected mice, while middle-aged infected mice had similar expression levels of these genes in the systemic compartment. We conclude that systemic challenge with live bacteria causes an age-dependent neuro-inflammatory and microglial response. Our data show signs of an age-dependent disconnection of the inflammatory transcriptional signature between the brain and the systemic compartment.

Glial activation and inflammation in the NTS in a rat model after exposure to diesel exhaust particles

Airway pollution can affect the central nervous system, but whether this causes glial activation and inflammation in the nucleus of solitary tract (NTS) remains unclear. We used a rat model with exposure to diesel exhaust particulate matter (DEP) at 200 μg/m3 (low exposure) and 1000 μg/m3 (high exposure) for 14 days. Activation of microglia and astrocytes in the NTS was assessed using Iba-1 and glial fibrillary acidic protein (GFAP) staining. The expression of neurotrophic factors including brain-derived neurotrophic factor (BDNF), glial-derived neurotrophic factor (GDNF), and nerve growth factor (NGF) in the NTS were evaluated by immunofluorescence. Changes in the intracellular structure of NTS neurons were observed via electron microscopy. Inflammatory cytokines and oxidant stress levels in the medulla were also measured. Exposure to DEP can cause NTS inflammation as well as airway inflammation, especially in the H-exposure group. We showed that the numbers of microglia and astrocytes in the NTS, as well as NGF expression in the NTS, were significantly higher in both exposure groups than in controls, but BDNF or GDNF expression was not detected. Exposure to DEP induced ultrastructural changes in NTS neurons as reflected by endoplasmic reticulum dilation, ribosomal loss, mitochondrial vacuolization, and a sparse myelin sheath. Medulla inflammation and an imbalance of oxidants and antioxidants also resulted from exposure to DEP. The H-exposure group showed an imbalance of oxidants and antioxidants with decreased levels of SOD and GSH and increased levels of MDA and ROS compared to the control group (both p < 0.01) in the medulla. Inflammatory cytokines (IL-1β, IL-6, and TNF-α) were also significantly increased in the H-exposure group. Fourteen days of exposure to DEP can affect the NTS neurons in rat. Glial activation and inflammation may play important roles in the response of the NTS to DEP.

Microglial deletion and inhibition alleviate behavior of post-traumatic stress disorder in mice

BackgroundAlteration of immune status in the central nervous system (CNS) has been implicated in the development of post-traumatic stress disorder (PTSD). However, the nature of overall changes in brain immunocyte landscape in PTSD condition remains unclear.MethodsWe constructed a mouse PTSD model by electric foot-shocks followed by contextual reminders and verified the PTSD-related symptoms by behavior test (including contextual freezing test, open-field test, and elevated plus maze test). We examined the immunocyte panorama in the brains of the naïve or PTSD mice by using single-cell mass cytometry. Microglia number and morphological changes in the hippocampus, prefrontal cortex, and amygdala were analyzed by histopathological methods. The gene expression changes of those microglia were detected by quantitative real-time PCR. Genetic/pharmacological depletion of microglia or minocycline treatment before foot-shocks exposure was performed to study the role of microglia in PTSD development and progress.ResultsWe found microglia are the major brain immune cells that respond to PTSD. The number of microglia and ratio of microglia to immunocytes was significantly increased on the fifth day of foot-shock exposure. Furthermore, morphological analysis and gene expression profiling revealed temporal patterns of microglial activation in the hippocampus of the PTSD brains. Importantly, we found that genetic/pharmacological depletion of microglia or minocycline treatment before foot-shock exposure alleviated PTSD-associated anxiety and contextual fear.ConclusionOur results demonstrated a critical role for microglial activation in PTSD development and a potential therapeutic strategy for the clinical treatment of PTSD in the form of microglial inhibition.

Comparing the Effects of Long-term Exposure to Extremely Low-frequency Electromagnetic Fields With Different Values on Learning, Memory, Anxiety, and β-amyloid Deposition in Adult Rats.

Introduction:Extremely Low-Frequency Electromagnetic Fields (ELF-EMFs) have gathered significant consideration for their possible pathogenicity. However, their effects on the nervous system’s functions were not fully clarified. This study aimed to assay the impact of ELF-EMFs with different intensities on memory, anxiety, antioxidant activity, β-amyloid (Aβ) deposition, and microglia population in rats.Methods:Fifty male adult rats were randomly separated into 5 groups; 4 were exposed to a flux density of 1, 100, 500, and 2000 microtesla (μT), 50 Hz frequency for one h/day for two months, and one group as a control group. The control group was without ELF-EMF stimulation. After 8 weeks, passive avoidance and Elevated Plus Maze (EPM) tests were performed to assess memory formation and anxiety-like behavior, respectively. Total free thiol groups and the index of lipid peroxidation were evaluated. Additionally, for detection of Aβ deposition and stained microglia in the brain, anti-β-amyloid and anti-Iba1 antibodies were used.Results:The step-through latency in the retention test in ELF-EMF exposure groups (100500 & 2000 μT) was significantly greater than the control group (P<0.05). Furthermore, the frequency of the entries into the open arms in ELF-EMF exposure groups (especially 2000 μT) decreased than the control group (P<0.05). No Aβ depositions were detected in the hippocampus of different groups. An increase in microglia numbers in the 100, 500, and 2000 μT groups was observed compared to the control and one μT group.Conclusion:Exposure to ELF-EMF had an anxiogenic effect on rats, promoted memory, and induced oxidative stress. No Aβ depositions were detected in the brain. Moreover, the positive impact of ELF-EMF was observed on the microglia population in the brain.HighlightsELF-EMFs have gathered significant consideration for their possible pathogenicity.ELF-EMFs’ effects on the nervous system’s functions were not clarified yet.Positive impact of ELF-EMF was observed on the microglia population in the brain.Plain Language SummaryELF-EMFs effects on human health are a considerable concern. Studies revealed the adverse effects of ELF-EMF in neurological disorders such as Alzheimer's Disease (AD). Anxiety could be an early manifestation of AD. There is a correlation between occupational exposure to ELF-EMF and AD. Recently the researchers interested in the study of the effects of ELF-EMFs on the human body. Some studies examined the molecular mechanisms and the influence of ELF-EMFs on the biologic mechanisms in the body. Also, Microglia act in the Central Nervous system (CNS) immune responses; over-activated microglia can be responsible for devastating and progressive neurotoxic consequences in neurodegenerative disorders. This study aimed to evaluate the memory, anxiety, antioxidant activity, β-amyloid deposition, and frequency of the microglial cells exposed to microtesla (μT) and 2000 (μT) ELF-EMFs.

Leptin enhances adult neurogenesis and reduces pathological features in a transgenic mouse model of Alzheimer’s disease

Alzheimer’s disease (AD) is the most common dementia worldwide and is characterized by the presence of senile plaques by amyloid-beta (Aβ) and neurofibrillary tangles of hyperphosphorylated Tau protein. These changes lead to progressive neuronal degeneration and dysfunction, resulting in severe brain atrophy and cognitive deficits. With the discovery that neurogenesis persists in the adult mammalian brain, including brain regions affected by AD, studies of the use of neural stem cells (NSCs) for the treatment of neurodegenerative diseases to repair or prevent neuronal cell loss have increased. Here we demonstrate that leptin administration increases the neurogenic process in the dentate gyrus of the hippocampus as well as in the subventricular zone of lateral ventricles of adult and aged mice. Chronic treatment with leptin increased NSCs proliferation with significant effects on proliferation and differentiation of newborn cells. The expression of the long form of the leptin receptor, LepRb, was detected in the neurogenic niches by reverse qPCR and immunohistochemistry. Moreover, leptin modulated astrogliosis, microglial cell number and the formation of senile plaques. Additionally, leptin led to attenuation of Aβ-induced neurodegeneration and superoxide anion production as revealed by Fluoro-Jade B and dihydroethidium staining. Our study contributes to the understanding of the effects of leptin in the brain that may lead to the development of new therapies to treat Alzheimer’s disease.

Single nuclear RNA sequencing reveals microglia diversity associated with cognitive resilience in the AD‐BXD mouse model of human Alzheimer’s disease

AbstractBackgroundAn individual’s genetic background plays an important role in governing the risk (or resilience) to developing Alzheimer’s disease (AD) dementia. The goal of this study was to identify the molecular pathways and cell‐types conferring individual differences in cognitive resilience to human familial AD (FAD) mutations that drive high amyloid.MethodA large set of genetically diverse mice harboring familial AD mutations (AD‐BXDs) and their non‐transgenic littermates (Ntg‐BXDs) were tested for short‐ and long‐term memory using contextual fear conditioning at 6m (AD‐BXD n=180, Ntg‐BXD n=174) and 14m (AD‐BXD n=121, Ntg‐BXD n=137). A subset of 14 AD mutation carriers that exhibited extreme resilience (n=7) or susceptibility (n=7) to cognitive decline were selected for hippocampal molecular profiling, along with their Ntg‐BXD littermates, at both 6m and 14m. Data from all hippocampi were aggregated and batch‐corrected using Harmony, and Seurat clustering was employed using the top 2000 variable genes. Known marker genes were used to associate clusters with cell‐types. The fraction of nuclei per sample (cluster composition) and within cell‐type differential gene expression were performed to determine changes in cell quantity and molecular profiles as a function of age, AD mutation carrier status, and resiliency to cognitive decline.ResultThere were no clusters that showed significant change in composition as a function of age. However, AD‐BXD individuals had significantly fewer astrocytes and more microglia than their Ntg‐BXD counterparts. We also found that resilient AD‐BXDs had fewer microglia than susceptible individuals, and the number of microglia at 6m was significantly negatively correlated with cognitive decline in AD‐BXD individuals. Additionally, microglia from resilient individuals showed up‐regulation of mitochondrial respiration and protein translation genes, proposing two pathways that dictate resilience in a microglia‐specific manner.ConclusionOur findings further implicate non‐neuronal cell‐types such as microglia in promoting resilience to cognitive decline in AD, and suggest several pathways by which microglia may be altered in resilient compared to susceptible individuals. We believe that by altering these microglia pathways within susceptible individuals, we can improve how non‐neuronal cells interact with CNS neurons to improve AD cognitive resilience.

Metformin treatment attenuates tau seeding in neuritic plaques

AbstractBackgroundAlzheimer’s disease (AD) is characterized by deposition of amyloid‐β (Aβ) plaques, neurofibrillary tangles. Metformin has been reported to decrease Aβ plaque load , reduce spatial memory deficit in APP/PS1 mice and reduce tau phosphorylation in the P301S mutant human tau (P301S) transgenic mouse. However, the effect of metformin on Aβ plaque‐associated tau pathogies remains unclear.MethodFemale 9‐month‐old APPswe/PS1DE9(APP/PS1) mice were used. Mice in the treatment group received 4 mg/ml metformin in the drinking water for 2 months. Brain extract containing tau aggregates isolated from P301S transgenic mouse brain was unilaterally injected into the right hippocampus and overlying cerebral cortex two weeks after the initial administration of metformin. Tau pathology, its effect on Aβ pathology and plaque‐associated microgliosis were assessed by immunohistochemical staining and immunofluorescence analysis 50 days after infusion.ResultWe observed seeded tau aggregates in dystrophic neurites surrounding Aβ plaques(NP tau) throughout the ipsilateral hippocmapus as well as spread to the contralateral hippocmapus in seeded mice using this experimental paradigm. NP tau aggregation was reduced after metformin administration. We found a decrease in the number of microglia around Aβ plaques in hippocampus of seeded mice and an increase of Aβ load in the bilateral cortex and the ipsilateral dentate gyrus of hippocampus in seeded mice. Metformin administration enhanced the activation of microglia around Aβ plaques and attenuates the Aβ load in the seeded mice.ConclusionThese findings indicate that metformin can enhance plaque‐associated microgliosis, attenuate Aβ load and peri‐plaque tau pathologies, making it a potential therapeutic treatment for AD.

Tanshinone IIA Promotes M2 Microglia by ERβ/IL-10 Pathway and Attenuates Neuronal Loss in Mouse TBI Model.

PurposeTraumatic brain injury (TBI) is a major cause of morbidity and mortality worldwide. Increasing evidence indicates that activated microglia play an important role in the inflammatory response in TBI. Inhibiting M1 and stimulating M2 activated microglia have protective effects in several animal models of central nervous system (CNS) disorders. In the present study, we investigated whether tanshinone IIA (TNA) protects neurons by shifting microglia polarization in a mouse TBI model and further investigated the mechanism in vitro.Materials and MethodsForty C57BL/6 mice were used to investigate the effect of TNA on microglia polarization in TBI. BV-2 cells were used to examine the mechanism of TNA in regulating microglia polarization.ResultsNormal saline (NS), TNA and the combination of TNA with ICI 182,780 (ICI, an estrogen receptor antagonist) were used to treat the TBI mice. After TBI, mice from each group demonstrated functional improvement. The improvement rate in mice treated with TNA was faster than other groups. ICI partially reversed the benefits from TNA treatment. TNA treatment significantly reduced TBI-induced neuronal loss. The number of microglia after TBI was not significantly changed by TNA treatment. However, TNA treatment significantly decreased M1 macrophage markers (iNOS, TNFα and IL-1β) and increased M2 macrophage markers (CD206, arginase 1 and Ym1). This effect was partially abolished by ICI. TNA treatment downregulated M1 macrophage markers and upregulated M2 macrophage markers in BV-2 cells under LPS stimulation. IL-10 was significantly increased by TNA treatment without a significantly change of IL-4 and IL-13 expression. IL-10 knockdown completely abolished the effect of TNA on microglial M2 polarization.ConclusionTaken together, our data demonstrated that TNA attenuates neuronal loss in mouse TBI model and promotes M2 microglia by ERβ/IL-10 pathway. Thus, TNA could be a potential drug for TBI and/or the disorders that caused by microglial over-activation in CNS.

Acute and non-resolving inflammation associate with oxidative injury after human spinal cord injury.

Traumatic spinal cord injury is a devastating insult followed by progressive cord atrophy and neurodegeneration. Dysregulated or non-resolving inflammatory processes can disturb neuronal homeostasis and drive neurodegeneration. Here, we provide an in-depth characterization of innate and adaptive inflammatory responses as well as oxidative tissue injury in human traumatic spinal cord injury lesions compared to non-traumatic control cords. In the lesion core, microglia were rapidly lost while intermediate (co-expressing pro- as well as anti-inflammatory molecules) blood-borne macrophages dominated. In contrast, in the surrounding rim, TMEM119+ microglia numbers were maintained through local proliferation and demonstrated a predominantly pro-inflammatory phenotype. Lymphocyte numbers were low and mainly consisted of CD8+ T cells. Only in a subpopulation of patients, CD138+/IgG+ plasma cells were detected, which could serve as candidate cellular sources for a developing humoral immunity. Oxidative neuronal cell body and axonal injury was visualized by intracellular accumulation of amyloid precursor protein (APP) and oxidized phospholipids (e06) and occurred early within the lesion core and declined over time. In contrast, within the surrounding rim, pronounced APP+/e06+ axon-dendritic injury of neurons was detected, which remained significantly elevated up to months/years, thus providing mechanistic evidence for ongoing neuronal damage long after initial trauma. Dynamic and sustained neurotoxicity after human spinal cord injury might be a substantial contributor to (i) an impaired response to rehabilitation; (ii) overall failure of recovery; or (iii) late loss of recovered function (neuro-worsening/degeneration).

Valproic Acid Labeled Chitosan Nanoparticles Promote the Proliferation and Differentiation of Neural Stem Cells After Spinal Cord Injury.

Chitosan nanoparticles and valproic acid are demonstrated as the protective agents in the treatment of spinal cord injury (SCI). However, the effects of valproic acid-labeled chitosan nanoparticles (VA-CN) on endogenous spinal cord neural stem cells (NSCs) following SCI and the underlying mechanisms involved remain to be elucidated. In this study, the VA-CN was constructed and the effects of VA-CN on NSCs were assessed in a rat model of SCI. We found VA-CN treatment promoted recovery of the tissue and locomotive function following SCI. Moreover, administration of VA-CN significantly enhanced neural stem cell proliferation and the expression levels of neurotrophic factors following SCI. Furthermore, administration of VA-CN led to a decrease in the number of microglia following SCI. In addition, VA-CN treatment significantly increased the Tuj 1- positive cells in the spinal cord of the SCI rats, suggesting that VA-CN could enhance the differentiation of NSCs following SCI. In conclusion, these results demonstrated that VA-CN could improve the functional and histological recovery through promoting the proliferation and differentiation of NSCs following SCI, which would provide a newly potential therapeutic manner for the treatment of SCI.

Xenon treatment after severe traumatic brain injury improves locomotor outcome, reduces acute neuronal loss and enhances early beneficial neuroinflammation: a randomized, blinded, controlled animal study

BackgroundTraumatic brain injury (TBI) is a major cause of morbidity and mortality, but there are no clinically proven treatments that specifically target neuronal loss and secondary injury development following TBI. In this study, we evaluate the effect of xenon treatment on functional outcome, lesion volume, neuronal loss and neuroinflammation after severe TBI in rats.MethodsYoung adult male Sprague Dawley rats were subjected to controlled cortical impact (CCI) brain trauma or sham surgery followed by treatment with either 50% xenon:25% oxygen balance nitrogen, or control gas 75% nitrogen:25% oxygen. Locomotor function was assessed using Catwalk-XT automated gait analysis at baseline and 24 h after injury. Histological outcomes were assessed following perfusion fixation at 15 min or 24 h after injury or sham procedure.ResultsXenon treatment reduced lesion volume, reduced early locomotor deficits, and attenuated neuronal loss in clinically relevant cortical and subcortical areas. Xenon treatment resulted in significant increases in Iba1-positive microglia and GFAP-positive reactive astrocytes that was associated with neuronal preservation.ConclusionsOur findings demonstrate that xenon improves functional outcome and reduces neuronal loss after brain trauma in rats. Neuronal preservation was associated with a xenon-induced enhancement of microglial cell numbers and astrocyte activation, consistent with a role for early beneficial neuroinflammation in xenon’s neuroprotective effect. These findings suggest that xenon may be a first-line clinical treatment for brain trauma.

Aicardi-Goutières syndrome-like encephalitis in mutant mice with constitutively active MDA5.

MDA5 is a cytoplasmic sensor of viral RNA, triggering type I interferon (IFN-I) production. Constitutively active MDA5 has been linked to autoimmune diseases such as systemic lupus erythematosus, Singleton-Merten syndrome (SMS) and Aicardi-Goutières syndrome (AGS), a genetically determined inflammatory encephalopathy. However, AGS research is challenging due to the lack of animal models. We previously reported lupus-like nephritis and SMS-like bone abnormalities in adult mice with constitutively active MDA5 (Ifih1G821S/+), and herein demonstrate that these mice also exhibit high lethality and spontaneous encephalitis with high IFN-I production during the early postnatal period. Increases in the number of microglia were observed in MDA5/MAVS signaling- and IFN-I-dependent manners. Furthermore, microglia showed an activated state with an increased phagocytic capability and reduced expression of neurotrophic factors. Although multiple auto-antibodies including lupus-related ones were detected in the sera of the mice as well as AGS patients, Ifih1G821S/+Rag2-/- mice also exhibited up-regulation of IFN-I, astrogliosis and microgliosis, indicating that auto-antibodies or lymphocytes are not required for the development of the encephalitis. The IFN-I signature without lymphocytic infiltration observed in Ifih1G821S/+ mice is a typical feature of AGS. Collectively, our results suggest that the Ifih1G821S/+ mice are a model recapitulating AGS and that microglia are a potential target for AGS therapy.

BALB/c female subjected to valproic acid during gestational period exhibited greater microglial and behavioral changes than male mice: A significant contra intuitive result.

Most animal model studies of autism spectrum disorders (ASD) were performed in males. Thus, little is known about the mechanisms underlying disease progression in females. Here, we searched for potential influences of sex and environment on gestational valproic acid-induced behavioral abnormalities using hippocampal-dependent tasks, and on number and morphometry of microglia of the molecular layer of the dentate gyrus (Mol-DG). We compared male and females BALB/c control mice with BALB/c mice gestationally exposed to VPA with regards to exploratory activity and risk assessment in novel environments. Pregnant females and males on gestational day 12.5 received VPA in saline (600mg/kg body weight) or an equal volume of saline by gavage. After weaning, female and male offspring were housed separately either in standard laboratory cages (SE) or enriched cages (EE). At 5months of age, these mice underwent behavioral testing and had their brains processed for microglia IBA1 immunolabeling. Compared with control mice, VPA-exposed mice exhibited abnormal behavior in exploring novel environments and assessing risk, and these effects were significantly greater in females than in males and less intense among mice from enriched cages. Three-way ANOVA revealed that environment, sex and valproic acid conditions interacted and altered the behavior results. Microglia number and volume of the Mol-DG were significantly higher in VPA-exposed groups raised in standard cages. The results of counting the intersects of microglia branching on Sholl's circles analyzed with permutational MANOVA, demonstrated that in comparison with males, there was a greater reduction in the number of intersections in females raised in standard cages. These findings suggest that the increased microglia and morphological changes might be associated with behavioral dysfunction in ASD. Moreover, the somatomotor and cognitive stimulation of environmental enrichment started at weaning may be beneficial for reducing behavioral abnormalities and reduction of microglia response in adulthood.

Lateral septum microglial changes and behavioral abnormalities of mice exposed to valproic acid during the prenatal period

Most animal model studies of autism spectrum disorder (ASD) have been performed in males, which may be a reflex of the 3-times higher prevalence in boys than in girls. For this reason, little is known about the mechanisms underlying disease progression in females, and nothing is known about potential associations between microglial changes in the lateral septum (LS) and adult female cognition. Prenatal exposure to valproic acid (VPA) in mice has been widely used as an experimental model of autism-like behaviors associated with cellular changes. However, no study has reported the influence of VPA exposure in utero and its consequences on limbic system-dependent tasks or the microglial response in the LS in adult female mice. We compared the exploratory activity and risk assessment in novel environments of BALB/c control mice to mice exposed in utero to VPA and estimated the total number of microglia in the LS using an optical fractionator. On day 12.5 of pregnancy, females received diluted VPA or saline by gavage. After weaning, VPA exposed or control pups were separately housed in standard laboratory cages. At 5 months of age, all mice underwent behavioral testing and their brain sections were immunolabelled using IBA-1 antibody. In the open field test, VPA group showed a greater distance traveled, which was accompanied by less immobility, less time spent on the periphery and a greater number, crossed lines. Similar findings were found in the elevated plus maze test, where VPA mice traveled greater distances, immobility was significantly higher than that of control and VPA group spent less time on the closed arms of apparatus. Stereological analysis demonstrated higher microglial total number and density in the LS of VPA mice, as the cell count was greater, but the volume was similar. Therefore, we suggest that an increase in microglia in the LS may be part of the cellular changes associated with behavioral dysfunction in the VPA model of ASD.

Tenascin-C preserves microglia surveillance and restricts leukocyte and, more specifically, T cell infiltration of the ischemic brain

As an endogenous activator of toll-like receptor-4 (Tlr4), the extracellular matrix glycoprotein tenascin-C (TnC) regulates chemotaxis, phagocytosis and proinflammatory cytokine production in microglia. The role of TnC for ischemic brain injury, post-ischemic immune responses and stroke recovery has still not been evaluated. By comparing wild type and TnC−/− mice exposed to transient intraluminal middle cerebral artery occlusion (MCAO), we examined the effects of TnC deficiency for ischemic injury, neurological deficits, microglia/macrophage activation and brain leukocyte infiltration using behavioural tests, histochemical studies, Western blot, polymerase chain reaction and flow cytometry. Histochemical studies revealed that TnC was de novo expressed in the ischemic striatum, which contained the infarct core, and overlapped with the area of strongest accumulation of Iba1 + microglia/macrophages. TnC deficiency increased overall Iba1 immunoreactivity in the perilesional cortex, suggesting that TnC might restrict the distribution of microglial cells to the infarct core. By analysing microglial morphology in 3D we found that the post-ischemic loss of microglial cell territory, branching and volume at 3 and 7 days post-ischemia was amplified in the brains of TnC deficient compared with wild type mice. Microglial cell number was not different between genotypes. Hence, TnC deficiency reduced tissue surveillance by microglial cells. Concomitantly, the number of infiltrating leukocytes and, more specifically, T cells was increased in the ischemic brain parenchyma of TnC deficient compared with wild type mice. Ischemic injury and neurological deficits were not affected by TnC deficiency. We propose that the reduced microglia surveillance in TnC deficient mice might favour leukocyte accumulation in the ischemic brain.

The voltage-gated proton channel Hv1 contributes to neuronal injury and motor deficits in a mouse model of spinal cord injury

Traumatic injury to the spinal cord initiates a series of pathological cellular processes that exacerbate tissue damage at and beyond the original site of injury. This secondary damage includes oxidative stress and inflammatory cascades that can lead to further neuronal loss and motor deficits. Microglial activation is an essential component of these secondary signaling cascades. The voltage-gated proton channel, Hv1, functionally expressed in microglia has been implicated in microglia polarization and oxidative stress in ischemic stroke. Here, we investigate whether Hv1 mediates microglial/macrophage activation and aggravates secondary damage following spinal cord injury (SCI). Following contusion SCI, wild-type (WT) mice showed significant tissue damage, white matter damage and impaired motor recovery. However, mice lacking Hv1 (Hv1−/−) showed significant white matter sparing and improved motor recovery. The improved motor recovery in Hv1−/− mice was associated with decreased interleukin-1β, reactive oxygen/ nitrogen species production and reduced neuronal loss. Further, deficiency of Hv1 directly influenced microglia activation as noted by decrease in microglia numbers, soma size and reduced outward rectifier K+ current density in Hv1−/− mice compared to WT mice at 7 d following SCI. Our results therefore implicate that Hv1 may be a promising potential therapeutic target to alleviate secondary damage following SCI caused by microglia/macrophage activation.

Intrinsic DNA damage repair deficiency results in progressive microglia loss and replacement.

The DNA excision repair protein Ercc1 is important for nucleotide excision, double strand DNA break, and interstrand DNA crosslink repair. In constitutive Ercc1‐knockout mice, microglia display increased phagocytosis, proliferation and an enhanced responsiveness to lipopolysaccharide (LPS)‐induced peripheral inflammation. However, the intrinsic effects of Ercc1‐deficiency on microglia are unclear. In this study, Ercc1 was specifically deleted from Cx3cr1‐expressing cells and changes in microglia morphology and immune responses at different times after deletion were determined. Microglia numbers were reduced with approximately 50% at 2–12 months after Ercc1 deletion. Larger and more ramified microglia were observed following Ercc1 deletion both in vivo and in organotypic hippocampal slice cultures. Ercc1‐deficient microglia were progressively lost, and during this period, microglia proliferation was transiently increased. Ercc1‐deficient microglia were gradually replaced by nondeficient microglia carrying a functional Ercc1 allele. In contrast to constitutive Ercc1‐deficient mice, microglia‐specific deletion of Ercc1 did not induce microglia activation or increase their responsiveness to a systemic LPS challenge. Gene expression analysis suggested that Ercc1 deletion in microglia induced a transient aging signature, which was different from a priming or disease‐associated microglia gene expression profile.