Regulation Of Microglial Activation Research Articles

Meningeal Type-2 Innate Lymphoid Cells Emerge as Novel Regulators of Microglial Activation and Blood-Brain Barrier Stability: A Central Role for IL-10

Innate lymphoid cell (ILC) cytokine signatures mirror those of T helper subsets, but ILCs differ substantially as far as biological role. Tissue-resident and antigen-independent, ILCs mediate induction and resolution of inflammation, tissue homeostasis, and barrier maintenance. Although extensively character-ized in periphery, ILCs were newly identified as resident in central nervous system (CNS) meninges, and are less well-understood within this novel context. Here we show that ILC-deficient mice exhibit enhanced microglial reactivity, amplified neuroinflammatory responses and blood-brain barrier (BBB) permeability. Accordingly, transcriptomic and functional examination revealed meningeal ILC2s as vigorous interleukin (IL)-10 producers. Mechanistic relevance was demonstrated by amelioration of neuroinflammation following meningeal engraftment of adoptively-transferred wild type — but not IL-10-deficient — ILC2s. Notably, ILC2s from murine bone marrow and human blood also showed IL-10 competency, suggesting a previously-unappreciated immunoregulatory role for canonical ILC2s. Collectively, these findings reveal meningeal ILC2s as suppressors of neuroinflammation — suggesting potential for ILC2-based cell therapies in CNS pathology.

The pro-remyelination properties of microglia in the central nervous system.

Microglia are resident macrophages of the CNS that are involved in its development, homeostasis and response to infection and damage. Microglial activation is a common feature of neurological disorders, and although in some instances this activation can be damaging, protective and regenerative functions of microglia have been revealed. The most prominent example of the regenerative functions is a role for microglia in supporting regeneration of myelin after injury, a process that is critical for axonal health and relevant to numerous disorders in which loss of myelin integrity is a prevalent feature, such as multiple sclerosis, Alzheimer disease and motor neuron disease. Although drugs that are intended to promote remyelination are entering clinical trials, the mechanisms by which remyelination is controlled and how microglia are involved are not completely understood. In this Review, we discuss work that has identified novel regulators of microglial activation - including molecular drivers, population heterogeneity and turnover - that might influence their pro-remyelination capacity. We also discuss therapeutic targeting of microglia as a potential approach to promoting remyelination.

Peli1 controls the survival of dopaminergic neurons through modulating microglia-mediated neuroinflammation

Chronic neuroinflammation is known to contributes to the toxicity of neurodegeneration of Parkinson’s disease (PD). However, the molecular and cellular mechanisms controlling inflammatory responses in the central nervous system remain poorly understood. Here we found that a E3 ubiquitin ligase Peli1 is dramatically induced only in the substantia nigra (SN) of the human and mouse PD brains. The ablation of Peli1 significantly suppressed LPS-induced production of neurotoxic mediators and proinflammatory cytokines in SN and in primary microglia, whereas Peli1 is dispensable for the inflammatory responses in astrocyte. Accordingly, Peli1 deficiency markedly inhibited neuron death induced by the conditioned medium from LPS-stimulated microglia. Mechanistical study suggested that Peli1 acts as a positive regulator of inflammatory response in microglia through activation of NF-κB and MAP kinase. Our results established Peli1 as a critical mediator in the regulation of microglial activation and neuroinflammation-induced death of dopaminergic neurons during PD pathogenesis, suggesting that targeting Peli1 may have therapeutic effect in neuroinflammation.

Dl-3-n-Butylphthalide Exerts Dopaminergic Neuroprotection Through Inhibition of Neuroinflammation.

Microglia-mediated neuroinflammation contributes to multiple neurodegenerative disorders, including PD. Therefore, the regulation of microglial activation probably has the therapeutic potential. This study is aimed to determine whether NBP could suppress microglial activation and protect dopaminergic neurons from excessive neuroinflammation. In the present study, MPTP-induced PD model was established to explore the neuroprotective and anti-inflammatory effect of NBP. We assessed motor deficits, dopaminergic neurodegeneration and microglial activation in PD mice. In vitro, the anti-inflammatory activity of NBP was confirmed by cell viability assay of SH-SY5Y cells after being treated with conditioned medium from LPS-stimulated BV-2 cells and from 1-Methyl-4-phenylpyridinium iodide (MPP+)-stimulated BV-2 cells. The expression of pro-inflammatory molecules was determined by RT-PCR, Western Blot and ELISA assay. The generation of NO and ROS were also assessed. The involvement of signaling pathways such as MAPK, NF-κB, and PI3k/Akt were further investigated by Western Blot and immunofluorescence assay. The neuroprotective effect of NBP was demonstrated in vivo as shown by the improvement of dopaminergic neurodegeneration, motor deficits and microglial activation in MPTP-induced mouse model of PD. The expression of pro-inflammatory mediators was also reduced by NBP administration. In vitro, NBP also protected dopaminergic neurons from neurotoxicity induced by activated microglia. NBP pretreatment not only reduced pro-inflammatory molecules, but also suppressed NO release and ROS generation in BV-2 cells. Further mechanism research suggested that the inactivation of MAPK, NF-κB and PI3K/Akt may involve in anti-neuroinflammation role of NBP. In conclusion, our results revealed that NBP exerted dopaminergic neuroprotection through inhibition of microglia-mediated neuroinflammation, suggesting the promising therapeutic effect of NBP for PD.

P2Y12 regulates microglia activation and excitatory synaptic transmission in spinal lamina II neurons during neuropathic pain in rodents

Peripheral nerve injury causes neuropathic pain and microglia activation. P2Y12 receptors on microglia are thought to be a key player in the surveillance of the local environment, but whether or how these receptors are engaged in the cross-talk between microglia and neurons of the dorsal horn remain ambiguous. Using a rodent model of nerve injury-induced pain, we investigated the roles of P2Y12 in microglia activation, excitatory synaptic transmission, and nociceptive allodynia. We found that spinal nerve ligation (SNL) significantly increased the level of P2Y12 receptors specifically in the microglia of the ipsilateral dorsal horn. Injections of P2Y12 antagonists (MRS2395 or clopidogrel) attenuated microglia activation and increased the paw withdrawal latency in response to thermal stimuli on the ipsilateral side without affecting the basal threshold on the contralateral side. These effects on pain behaviors were replicated in P2Y12 knockout mice. Patch-clamp recordings further revealed that partial sciatic nerve ligation (PSNL)-induced excessive miniature excitatory postsynaptic currents (mEPSCs) were significantly attenuated in P2Y12 knockout mice. Moreover, we found that SNL activates the GTP-RhoA/ROCK2 signaling pathway and elevates the level of phosphorylated p38 mitogen-activated protein kinase (MAPK), which was inhibited by the P2Y12 antagonist. The phosphorylation of p38 MAPK was inhibited by a ROCK inhibitor, but not vice versa, suggesting that p38 MAPK is downstream of ROCK activation. Our findings suggest that nerve injury engages the P2Y12 receptor-dependent GTP-RhoA/ROCK2 signaling pathway to upregulate excitatory synaptic transmission in the dorsal horn. This cross-talk ultimately participates in the manifestation of nociceptive allodynia, implicating P2Y12 receptor as a potential target for alleviating neuropathic pain.

Melatonin decreases M1 polarization via attenuating mitochondrial oxidative damage depending on UCP2 pathway in prorenin-treated microglia.

Accumulating evidence suggests that neuroinflammation and oxidative stress in cardiovascular center contribute to the pathological processes underlying hypertension. Microglia activation triggers the inflammation and oxidative stress. Melatonin is a documented potent anti-inflammatory regent and antioxidant, the underlying roles of melatonin in regulating microglia activation via mitochondria remain unclear. In present study, we investigated the protective role of melatonin in decreasing M1 phenotype switching via attenuating mitochondrial oxidative damage in dependence on uncoupling protein 2 (UCP2) pathway in microglia. Prorenin (20 nmol/L; 24 hr) was used to induce inflammation in cultured microglia. Mitochondrial morphology was detected by transmission electron microscope. The reactive oxygen species (ROS) production by using DCFH-DA fluorescence imaging and mitochondrial membrane potential (MMP, ΔΨm) was evaluated by JC-1 staining. The indicator of the redox status as the ratio of the amount of total NADP+ to total NADPH, and the expression of 6 subunits of NADPH oxidase is measured. The pro-inflammatory cytokines releasing was measured by qPCR. UCP2 and activated AMPKα (p-AMPKα) expression were examined by immunoblot. Melatonin (100 μM) markedly alleviated the M1 microglia phenotype shifting and abnormal mitochondria morphology. Melatonin attenuated prorenin-induced ΔΨm increasing and ROS overproduction. Melatonin decreased the redox ratio (NADP+/NADPH) and the p47phox and gp91phox subunits of NADPH oxidase expression in prorenin-treated microglia. These effects were reversed in the presence of UCP2 siRNA. Our results suggested that the protective effect of melatonin against prorenin-induced M1 phenotype switching via attenuating mitochondrial oxidative damage depending on UCP2 upregulation in prorenin-treated microglia.

Abstract # 3119 I am woman, watch me soar: females protected from cosmic ray-induced behavioral deficits, microglia activation and synaptic loss

Interplanetary exploration will be humankind’s most ambitious expedition and the journey required to do so, is as intimidating as it is intrepid. One major obstacle for successful deep space travel is the negative effects of galactic cosmic radiation (GCR) exposure. Here, we investigate how GCR impacts long-term behavioral and cellular responses in male and female mice. We find that a single exposure to GCR can induce long-term behavioral deficits in male cohorts, characterized by diminished social interaction, increased anxiety-like phenotype and impaired recognition memory. Remarkably, we find that the female cohorts did not display any behavioral deficits caused by GCR exposure. Mechanistically, we identify that the maladaptive behavioral responses in the male, GCR-exposed cohorts correspond with microglia activation and synaptic loss in the hippocampus, a brain region involved in the cognitive domains reported here. Furthermore, we measured reductions in AMPA expressing synaptic terminals measured in the hippocampus. Taken together these findings suggest that GCR exposure can regulate microglia activity and alter synaptic architecture which in turn leads to a range of cognitive alterations. These novel results identify sex-dependent differences in cognitive domains revealing promising cellular and molecular intervention targets to reduce GCR-induced chronic cognitive deficits. Improved understanding of these differences boosts chances of success for humans in deep space missions such as the upcoming Mars voyage.

Effects of Silibinin Against Prothrombin Kringle-2-Induced Neurotoxicity in the Nigrostriatal Dopaminergic System In Vivo.

Parkinson's disease (PD) and Alzheimer's disease exhibit common features of neurodegenerative diseases and can be caused by numerous factors. A common feature of these diseases is neurotoxic inflammation by activated microglia, indicating that regulation of microglial activation is a potential mechanism for preserving neurons in the adult brain. Recently, we reported that upregulation of prothrombin kringle-2 (pKr-2), one of the domains that make up prothrombin and which is cleaved and generated by active thrombin, induces nigral dopaminergic (DA) neuronal death through neurotoxic microglial activation in the adult brain. In this study, we show that silibinin, a flavonoid found in milk thistle, can suppress the production of inducible nitric oxide synthase and neurotoxic inflammatory cytokines, such as interleukin-1β and tumor necrosis factor-α, after pKr-2 treatment by downregulating the extracellular signal-regulated kinase signaling pathway in the mouse substantia nigra. Moreover, as demonstrated by immunohistochemical staining, measurements of the dopamine and metabolite levels, and open-field behavioral tests, silibinin treatment protected the nigrostriatal DA system resulting from the occurrence of pKr-2-triggered neurotoxic inflammation in vivo. Thus, we conclude that silibinin may be beneficial as a natural compound with anti-inflammatory effects against pKr-2-triggered neurotoxicity to protect the nigrostriatal DA pathway and its properties, and thus, may be applicable for PD therapy.

Manipulation of miR-124 expression on neuronal APP-SWE cells results in different microglial polarization through paracrine signaling

Event Abstract Back to Event Manipulation of miR-124 expression on neuronal APP-SWE cells results in different microglial polarization through paracrine signaling Gonçalo Garcia1, Adelaide Fernandes1, 2 and Dora Brites1, 2* 1 Research Institute for Medicines (iMed.ULisboa), Portugal 2 Faculdade de Farmácia, Universidade de Lisboa, Portugal Neuronal expression of miR-124 is associated to brain regeneration and glial signaling. We found miR-124 overexpression in SH-SY5Y cells transfected with the Swedish mutation APP695 (APP-Swe), as a model of Alzheimer’s disease (AD) [1]. Our recent data suggest that miR-124 upregulation in APP-Swe cells, rather than being pathological, sustains neuronal morphology and inhibits inflammatory-miRNA dissemination via exosomes (unpublished). However, whether/how such miR-124 overexpression by neurons impacts on microglia immunoregulatory properties remains unclear. Here, we investigated the inflammatory dynamic signaling between human AD neurons up-/down-regulated for miR-124 and the activated microglia, as well as the acquired phenotypic diversity. miR-124 modulation in APP-Swe cells was done by transfection with anti/pre-miR-124. Activation of human CHME-3 microglia into the M1-phenotype was performed by IFN-γ stimulation. APP-Swe+CHME-3 co-cultures were maintained for 2, 12 and 24 h. Microglial mRNA/miRNA expression of inflammatory markers was accessed by RT-qPCR. Metalloproteinase activity was determined by gelatin zymography and nitric oxide (NO) by the Griess reaction. IFN-γ induced a classical M1 phenotype on CHME-3 microglia, with consistent overexpression of classical inflammatory-associated markers like RAGE, HMGB1, TNF-α and MHC-II, as well as up-regulation of miR-21, miR146a and miR-155. When IFN-γ-stimulated microglia were co-cultured with miR-124 downregulated APP-Swe cells, we observed an early overexpression of M1-markers, followed by reduction of the M2-markers Arginase-1 and IL-10, as well as of miR-124 and miR-125b. Contrariwise, the co-culture of APP-Swe cells overexpressing miR-124 with IFN-γ-stimulated microglia led to an initial repression of HMGB1 and MHC-II transcription before their recovery at 24h. At this time point, upregulation of neuronal miR-124 led to iNOS, TNF-α, miR-21 and miR-146a repression in microglia. Noteworthy, APP-Swe cells overexpressing miR-124 also inhibited the release of NO and metalloproteinases 2 and 9 into cell media by IFN-γ-stimulated microglia. More than the beneficial effects observed on APP-Swe cells, overexpression of neuronal miR-124 results in a strong paracrine signaling and regulation of microglia activation, by counteracting pro-inflammatory cascades and inducing a regenerative/repairing polarization. It remains to be understood how effectively these microglia benefit bystander cells and counteract neurodegeneration, the major bottleneck in the development of efficient therapies for AD. Acknowledgements EU-JPND project (grant Nº643417 to DB); Fundação para a Ciência e a Tecnologia (JPco-fuND/0003/2015 to DB; UID/DTP/04138/2013 to iMed.ULisboa and SFRH/BD/128738/2017 to GG).

The Neuroprotective Effects of Exercise: Maintaining a Healthy Brain Throughout Aging.

Physical activity plays an essential role in maintaining a healthy body, yet it also provides unique benefits for the vascular and cellular systems that sustain a healthy brain. While the benefit of exercise has been observed in humans of all ages, the availability of preclinical models has permitted systematic investigations into the mechanisms by which exercise supports and protects the brain. Over the past twenty-five years, rodent models have shown that increased physical activity elevates neurotrophic factors in the hippocampal and cortical areas, facilitating neurotransmission throughout the brain. Increased physical activity (such as by the voluntary use of a running wheel or regular, timed sessions on a treadmill) also promotes proliferation, maturation and survival of cells in the dentate gyrus, contributing to the process of adult hippocampal neurogenesis. In this way, rodent studies have tremendous value as they demonstrate that an ‘active lifestyle’ has the capacity to ameliorate a number of age–related changes in the brain, including the decline in adult neurogenesis. Moreover, these studies have shown that greater physical activity may protect the brain health into advanced age through a number of complimentary mechanisms: in addition to upregulating factors in pro-survival neurotrophic pathways and enhancing synaptic plasticity, increased physical activity promotes brain health by supporting the cerebrovasculature, sustaining the integrity of the blood–brain barrier, increasing glymphatic clearance and proteolytic degradation of amyloid beta species, and regulating microglia activation. Collectively, preclinical studies demonstrate that exercise initiates diverse and powerful neuroprotective pathways that may converge to promote continued brain health into old age. This review will draw on both seminal and current literature that highlights mechanisms by which exercise supports the functioning of the brain, and aids in its protection.

Astrocyte-targeted IL-10 production decreases proliferation and induces a downregulation of activated microglia/macrophages after PPT.

When central nervous system (CNS) homeostasis is altered, microglial cells become rapidly activated, proliferate and release a broad range of molecules. Among the plethora of molecules involved in the regulation of microglial activation, cytokines are considered crucial. Although production of interleukin-10 (IL-10) has been demonstrated after different types of CNS injuries and associated with protective functions, the specific role played by IL-10 modulating microglial cells remains unclear. Hence, the objective of this study was to evaluate the effects of transgenic astrocyte IL-10 production on microglial activation associated with axonal anterograde degeneration. To address it, the hippocampal area subjected to perforant pathway transection (PPT) was analyzed by immunohistochemistry (IHC), flow cytometry and protein microarray in transgenic (GFAP-IL10Tg) mice and their corresponding wild types (WT) littermates. Our results demonstrated increased microglial/macrophages density in nonlesioned and PPT-lesioned GFAP-IL10Tg animals when compared with nonlesioned and lesioned WT, respectively. This increase was not due to proliferation, as GFAP-IL10Tg mice showed a reduced proliferation of microglial cells, but was related to an increased population of CD11b+/CD45high monocyte/macrophages. Despite this higher number, the microglia/macrophage population in transgenic animals displayed a downregulated phenotype characterized by lower MHCII, ICOSL, and CD11c. Moreover, a sustained T-cell infiltration was found in transgenic animals. We strongly suggest these modifications must be associated with indirect effects derived from the influence of IL-10 on astrocytes and/or neurons, which express IL-10R. We finally suggested that TGF-β produced by astrocytes, along with IL-2 and CXCL10 might be crucial molecules mediating the effects of transgenic IL-10.

EriB targeted inhibition of microglia activity attenuates MPP+ induced DA neuron injury through the NF-\u03baB signaling pathway

Accumulating evidence indicates that microglia activation is associated with an increased risk for developing Parkinson’s disease (PD). With the progressive and selective degeneration of dopaminergic (DA) neurons, proinflammatory cytokines are elevated in the substantia nigra (SN) of PD patients. Thus, anti-inflammation has become one of the therapeutic strategies of PD. Eriocalyxin B (EriB), a diterpenoid isolated from Isodoneriocalyx, was previously reported to have anti-inflammatory effects. MPTP mouse model and MPP+ cell model were prepared to detect the role of EriB in regulating microglia activation and neuron protection. Midbrain tissue and primary cultured microglia and neuron were used to examine microglia activation and neuron damage by immunofluorescence, real-time PCR, western-blot and Elisa assay. Open field activity test was to evaluate the changes of behavioral activity in MPTP-induced PD mouse model. EriB was efficacious in protecting DA neurons by inhibiting microglia activation in PD mice model. Treatment with EriB led to amelioration of disordered sports of PD mice model, which correlated with reduced microglia-associated inflammation and damaged DA neurons. EriB treatment abolished MPP+ induced microglia activation damages to DA neurons in a microglia and DA neurons co-culture system. The underlying mechanism of EriB-induced protective effects involved inhibition of microglia associated proinflammatory cytokines production through the phenotypic shift of microglial cells as well as activator of transcription and nuclear factor-κB (NF-κB) signaling pathways. These findings demonstrate that EriB exerts potent anti-inflammatory effects through selective modulation of microglia activation by targeting NF-κB signaling pathways, thus exerting the protective effect against on MPP+-induced DA neurons injury. This study may provide insights into the promising therapeutic role of EriB for PD.

Neuronal EphA4 Regulates OGD/R-Induced Apoptosis by Promoting Alternative Activation of Microglia.

Accumulating evidence indicates that post-injury inflammation characterized by activated microglia contributes much to the neuropathology of ischemic injury. Several studies have demonstrated that microglia exhibit two entirely different functional activation states, referred to as classically activated (M1) and alternatively activated (M2) phenotype. Promoting microglial phenotype to switch from M1 dominant to M2 dominant might be a promising approach for handling ischemic injury. However, the comprehensive mechanism that underlines microglia polarization in ischemic brain remains unclear. Neuronal erythropoietin-producing human hepatocellular carcinoma cell receptor 4 (EphA4), the richest Eph receptor in the central nervous system (CNS), upregulate after ischemia and may have the potential to regulate microglia activation. We hypothesized that modulating EphA4/ephrin signaling could affect ischemic injury through controlling microglia polarization. We therefore knocked down neuronal EphA4 with short hairpin RNA (shRNA) and determined the role of EphA4/ephrin signaling in oxygen-glucose deprivation and reperfusion (OGD/R)-induced injury. We found that EphA4 shRNA treatment attenuated OGD/R-induced apoptosis and microglia proliferation. Neuronal EphA4 knockdown also promoted microglial M2 polarization, which reduced pro-inflammatory mediators and released anti-inflammatory cytokines as well as neurotrophic factors. We further revealed that EphA4 shRNA treatment functioned through RhoA/Rho-associated kinase 2 (ROCK2) signaling, a key mediator of microglia alternative activation. Together, these data suggested that blockage of EphA4/ephrin signaling between neuron and microglia decreased OGD/R-induced injury by promoting alternative activation of microglia via RhoA/ROCK2 signaling.

Type I Interferon Receptor Signaling of Neurons and Astrocytes Regulates Microglia Activation during Viral Encephalitis

SummaryIn sterile neuroinflammation, a pathological role is proposed for microglia, whereas in viral encephalitis, their function is not entirely clear. Many viruses exploit the odorant system and enter the CNS via the olfactory bulb (OB). Upon intranasal vesicular stomatitis virus instillation, we show an accumulation of activated microglia and monocytes in the OB. Depletion of microglia during encephalitis results in enhanced virus spread and increased lethality. Activation, proliferation, and accumulation of microglia are regulated by type I IFN receptor signaling of neurons and astrocytes, but not of microglia. Morphological analysis of myeloid cells shows that type I IFN receptor signaling of neurons has a stronger impact on the activation of myeloid cells than of astrocytes. Thus, in the infected CNS, the cross talk among neurons, astrocytes, and microglia is critical for full microglia activation and protection from lethal encephalitis.

Lactobacillus plantarum C29‐Fermented Soybean (DW2009) Alleviates Memory Impairment in 5XFAD Transgenic Mice by Regulating Microglia Activation and Gut Microbiota Composition

The study aims to determine whether Lactobacillus plantarum C29-fermented defatted soybean (FDS, DW2009) can attenuate memory impairment in 5XFAD transgenic (Tg) mice. Oral administration of FDS or C29 increases cognitive function in Tg mice in passive avoidance, Y-maze, novel object recognition, and Morris water maze tasks. FDS or C29 treatment significantly suppresses amyloid-β, β/γ-secretases, caspase-3 expression, and NF-κB activation, and activates microglia and apoptotic neuron cell populations, and increases BDNF expression in the brain. FDS or C29 treatment suppresses blood and fecal lipopolysaccharide levels and Enterobacteriaceae population and increases lactobacilli/bifidobacteria populations. FDS and C29 alleviates the decrease in cognitive function and inhibited amyloid-β expression in Tg mice by regulating microglia activation and gut microbiota composition.

Bacteriophage-derived dsRNA of natural origin alters functional profile of rat microglial cells exposed to hypoxia in vitro: Evaluation of metabolic and phenotypic markers

BackgroundMicroglial cells (MC) are thought to be major innate immune cells in the central nervous system. Hypoxia can cause pro- and anti-inflammatory MC activation. Toll-like receptors (TLRs) play an important role in the regulation of microglia activity and can skew metabolic profile of resting and activated MC. However, the data concerning the effect of TLR agonists on metabolic profile of MC activated by hypoxia are controversial and sparse. Larifan is a pharmaceutical product containing a heterogeneous population of natural origin double-stranded RNA (dsRNA). This study was aimed to investigate the effect of the treatment with Larifan on functional profile of rat MC exposed to hypoxia in vitro. MethodsRat MC were cultured under normoxic (21% O2) or hypoxic (3% O2) conditions for 24 h. After this, cells were treated with Larifan (200 μg/mL) for 18 h. To characterize MC functional profile, reactive oxygen species (ROS) generation, phagocytic activity, arginine metabolism as well as CD206 and CD14 expression were examined. ResultsHypoxic MC were characterized by sharply increased ROS generation, moderately boosted phagocytic activity, arginine metabolism was skewed towards increased arginase activity, CD14+ and CD206+ cell fractions were higher than those in normoxic cells. Treatment MC with Larifan resulted in further increase ROS generation along with the decrease of phagocytic activity that is characteristic for the acquisition of antigen-presenting properties by these cells. The level of CD206 expression was lowered in treated hypoxic MC. ConclusionLarifan promotes transition of hypoxic MC to the state of mature pro-inflammatory APC in vitro.

Cannabinoid 1 Receptor Signaling on Hippocampal GABAergic Neurons Influences Microglial Activity.

Microglia, the resident immune cells of the brain, play important roles in defending the brain against pathogens and supporting neuronal circuit plasticity. Chronic or excessive pro-inflammatory responses of microglia damage neurons, therefore their activity is tightly regulated. Pharmacological and genetic studies revealed that cannabinoid type 1 (CB1) receptor activity influences microglial activity, although microglial CB1 receptor expression is very low and activity-dependent. The CB1 receptor is mainly expressed on neurons in the central nervous system (CNS)—with an especially high level on GABAergic interneurons. Here, we determined whether CB1 signaling on this neuronal cell type plays a role in regulating microglial activity. We compared microglia density, morphology and cytokine expression in wild-type (WT) and GABAergic neuron-specific CB1 knockout mice (GABA/CB1−/−) under control conditions (saline-treatment) and after 3 h, 24 h or repeated lipopolysaccharide (LPS)-treatment. Our results revealed that hippocampal microglia from saline-treated GABA/CB1−/− mice resembled those of LPS-treated WT mice: enhanced density and larger cell bodies, while the size and complexity of their processes was reduced. No further reduction in the size or complexity of microglia branching was detected after LPS-treatment in GABA/CB1−/− mice, suggesting that microglia in naïve GABA/CB1−/− mice were already in an activated state. This result was further supported by correlating the level of microglial tumor necrosis factor α (TNFα) with their size. Acute LPS-treatment elicited in both genotypes similar changes in the expression of pro-inflammatory cytokines (TNFα, interleukin-6 (IL-6) and interleukin 1β (IL-1β)). However, TNFα expression was still significantly elevated after repeated LPS-treatment in WT, but not in GABA/CB1−/− mice, indicating a faster development of tolerance to LPS. We also tested the possibility that the altered microglia activity in GABA/CB1−/− mice was due to an altered expression of neuron-glia interaction proteins. Indeed, the level of fractalkine (CX3CL1), a neuronal protein involved in the regulation of microglia, was reduced in hippocampal GABAergic neurons in GABA/CB1−/− mice, suggesting a disturbed neuronal control of microglial activity. Our result suggests that CB1 receptor agonists can modulate microglial activity indirectly, through CB1 receptors on GABAergic neurons. Altogether, we demonstrated that GABAergic neurons, despite their relatively low density in the hippocampus, have a specific role in the regulation of microglial activity and cannabinoid signaling plays an important role in this arrangement.

Female mice are protected from space radiation-induced maladaptive responses

Interplanetary exploration will be humankind’s most ambitious expedition and the journey required to do so, is as intimidating as it is intrepid. One major obstacle for successful deep space travel is the possible negative effects of galactic cosmic radiation (GCR) exposure. Here, we investigate for the first time how combined GCR impacts long-term behavioral and cellular responses in male and female mice. We find that a single exposure to simulated GCR induces long-term cognitive and behavioral deficits only in the male cohorts. GCR exposed male animals have diminished social interaction, increased anxiety-like phenotype and impaired recognition memory. Remarkably, we find that the female cohorts did not display any cognitive or behavioral deficits after GCR exposure. Mechanistically, the maladaptive behavioral responses observed only in the male cohorts correspond with microglia activation and synaptic loss in the hippocampus, a brain region involved in the cognitive domains reported here. Furthermore, we measured reductions in AMPA expressing synaptic terminals in the hippocampus. No changes in any of the molecular markers measured here are observed in the females. Taken together these findings suggest that GCR exposure can regulate microglia activity and alter synaptic architecture, which in turn leads to a range of cognitive alterations in a sex dependent manner. These results identify sex-dependent differences in behavioral and cognitive domains revealing promising cellular and molecular intervention targets to reduce GCR-induced chronic cognitive deficits thereby boosting chances of success for humans in deep space missions such as the upcoming Mars voyage.

Microglial TREM2/DAP12 Signaling: A Double-Edged Sword in Neural Diseases.

Microglia are activated after neuronal injury and in neurodegenerative diseases, and trigger neuroinflammation in the central nervous system (CNS). Microglia-derived neuroinflammation has both beneficial and detrimental effects on neurons. Because the timing and magnitude of microglial activation is thought to be a critical determinant of neuronal fate, understanding the molecular mechanisms underlying microglial activation is required to enable establishment of microglia-targeted therapies for neural diseases. Plasma membrane receptors play primary roles as activators of microglia and in this review, we focus on a receptor complex involving triggering receptor expressed on myeloid cells 2 (TREM2) and DNAX-activating protein of 12 kDa (DAP12), both of which are causative genes for Nasu-Hakola disease, a dementia with bone cysts. Recent transcriptome approaches demonstrated TREM2/DAP12 signaling as the principal regulator that transforms microglia from a homeostatic to a neural disease-associated state. Furthermore, animal model studies revealed critical roles for TREM2/DAP12 in the regulation of microglial activity, including survival, phagocytosis, and cytokine production, not only in Alzheimer's disease but also in other neural diseases, such as Parkinson's disease, demyelinating disease, ischemia, and peripheral nerve injury. Intriguingly, while TREM2/DAP12-mediated microglial activation is detrimental for some diseases, including peripheral nerve injury, it is beneficial for other diseases. As the role of activated microglia differs among disease models, TREM2/DAP12 signaling may result in different outcomes in different diseases. In this review we discuss recent perspectives on the role of TREM2/DAP12 in microglia and their contribution to neural diseases.

A20 critically controls microglia activation and inhibits inflammasome-dependent neuroinflammation

Microglia, the mononuclear phagocytes of the central nervous system (CNS), are important for the maintenance of CNS homeostasis, but also critically contribute to CNS pathology. Here we demonstrate that the nuclear factor kappa B (NF-κB) regulatory protein A20 is crucial in regulating microglia activation during CNS homeostasis and pathology. In mice, deletion of A20 in microglia increases microglial cell number and affects microglial regulation of neuronal synaptic function. Administration of a sublethal dose of lipopolysaccharide induces massive microglia activation, neuroinflammation, and lethality in mice with microglia-confined A20 deficiency. Microglia A20 deficiency also exacerbates multiple sclerosis (MS)-like disease, due to hyperactivation of the Nlrp3 inflammasome leading to enhanced interleukin-1β secretion and CNS inflammation. Finally, we confirm a Nlrp3 inflammasome signature and IL-1β expression in brain and cerebrospinal fluid from MS patients. Collectively, these data reveal a critical role for A20 in the control of microglia activation and neuroinflammation.