Microglial Priming Research Articles

Silencing of TGF\u03b2 signalling in microglia results in impaired homeostasis

TGFβ1 has been implicated in regulating functional aspects of several distinct immune cell populations including central nervous system (CNS) resident microglia. Activation and priming of microglia have been demonstrated to contribute to the progression of neurodegenerative diseases and, thus, underlie stringent control by endogenous regulatory factors including TGFβ1. Here, we demonstrate that deletion of Tgfbr2 in adult postnatal microglia does neither result in impairment of the microglia-specific gene expression signatures, nor is microglial survival and maintenance affected. Tgfbr2-deficient microglia were characterised by distinct morphological changes and transcriptome analysis using RNAseq revealed that loss of TGFβ signalling results in upregulation of microglia activation and priming markers. Moreover, protein arrays demonstrated increased secretion of CXCL10 and CCL2 accompanied by activation of immune cell signalling as evidenced by increased phosphorylation of TAK1. Together, these data underline the importance of microglial TGFβ signalling to regulate microglia adaptive changes.

Microglia priming by interleukin-6 signaling is enhanced in aged mice

During peripheral infection, excessive production of pro-inflammatory cytokines in the aged brain from primed microglia induces exaggerated behavioral pathologies. While the pro-inflammatory cytokine IL-6 increases in the brain with age, its role in microglia priming is not known. This study examined the functional role of IL-6 signaling on microglia priming. Our hypothesis is that IL-6 signaling mediates primed states of microglia in the aged. An initial study assessed age-related alteration in IL-6 signaling molecules; sIL-6R and sgp130 were measured in cerebrospinal fluid of young and aged wild-type animals. Subsequent studies of isolated microglia from C57BL6/J (IL-6+/+) and IL-6 knock-out (IL-6−/−) mice showed significantly less MHC-II expression in aged IL-6−/− compared to IL-6+/+ counterparts. Additionally, adult and aged IL-6+/+ and IL-6−/− animals were administered lipopolysaccharide (LPS) to simulate a peripheral infection; sickness behaviors and hippocampal cytokine gene expression were measured over a 24 h period. Aged IL-6−/− animals were resilient to LPS-induced sickness behaviors and recovered more quickly than IL-6+/+ animals. The age-associated baseline increase of IL-1β gene expression was ablated in aged IL-6−/− mice, suggesting IL-6 is a key driver of cytokine activity from primed microglia in the aged brain. We employed in vitro studies to understand molecular mechanisms in priming factors. MHC-II and pro-inflammatory gene expression (IL-1β, IL-10, IL-6) were measured after treating BV.2 microglia with sIL-6R and IL-6 or IL-6 alone. sIL-6R enhanced expression of both pro-inflammatory genes and MHC-II. Taken together, these data suggest IL-6 expression throughout life is involved in microglia priming and increased amounts of IL-6 following peripheral LPS challenge are involved in exaggerated sickness behaviors in the aged.

The Impact of Non-Neurotropic Influenza Strains on the Brain: A Role for Microglial Priming?

This year marks the 100th anniversary of the great influenza pandemic of 1918. The “Spanish Flu”, as it came to be known, was one of the deadliest and most widespread in modern history, with fatalities estimated in the tens of millions ([Kristensson, 2006][1]). In the wake of the pandemic, an

Immunization with Mycobacterium vaccae induces an anti-inflammatory milieu in the CNS: Attenuation of stress-induced microglial priming, alarmins and anxiety-like behavior

Exposure to stressors induces anxiety- and depressive-like behaviors, which are mediated, in part, by neuroinflammatory processes. Recent findings demonstrate that treatment with the immunoregulatory and anti-inflammatory bacterium, Mycobacterium vaccae (M. vaccae), attenuates stress-induced exaggeration of peripheral inflammation and stress-induced anxiety-like behavioral responses. However, the effects of M. vaccae on neuroimmune processes have largely been unexplored. In the present study, we examined the effect of M. vaccae NCTC11659 on neuroimmune regulation, stress-induced neuroinflammatory processes and anxiety-like behavior. Adult male rats were immunized 3× with a heat-killed preparation of M. vaccae (0.1 mg, s.c.) or vehicle. M. vaccae induced an anti-inflammatory immunophenotype in hippocampus (increased interleukin (Il)4, Cd200r1, and Mrc1 mRNA expression) and increased IL4 protein 8 d after the last immunization. Central administration of recombinant IL4 recapitulated the effects of M. vaccae on Cd200r1 and Mrc1 mRNA expression. M. vaccae reduced basal levels of genes (Nlrp3 and Nfkbia) involved in microglial priming; thus, we explored the effects of M. vaccae on stress-induced hippocampal microglial priming and HMGB1, which mediates priming. We found that M. vaccae blocked stress-induced decreases in Cd200r1, increases in the alarmin HMGB1, and priming of the microglial response to immune challenge. Furthermore, M. vaccae prevented stress-induced increases in anxiety-like behavior. The present findings suggest that M. vaccae enhances immunomodulation in the CNS and mitigates the neuroinflammatory and behavioral effects of stress, which may underpin its capacity to impart a stress resilient phenotype.

Microglial priming in Alzheimer's disease.

Alzheimer's disease (AD) is a chronic and progressive neurodegenerative disease of central nervous system (CNS). Nowadays, increasing evidence suggests that immune system plays a significant role in the mechanisms of AD's onset and progression. Microglia, the main participator in the immune system of CNS, is always regarded as a protector of our brain in a healthy state and also has a beneficial role in maintaining the homeostasis of CNS microenvironment. However, chronic and sustained stimulation can push microglia into the state termed priming. Primed microglia can induce the production of amyloid β (Aβ), tau pathology, neuroinflammation and reduce the release of neurotrophic factors, resulting in loss of normal neurons in quantity and function that has immense relationship with AD. The therapeutic strategies mainly aimed at modulating the microenvironment and microglial activity in CNS to delay progression and alleviate pathogenesis of AD. Overall, in this review, we highlight the mechanism of microglial priming, and discuss the profound relationship between microglial priming and AD. Besides, we also pay attention to the therapeutic strategies targeting at microglial priming.

Abstract WP101: Progesterone Counteracts Stress-Induced Microglial Priming by Reducing NLRP3 Inflammasome Activation After Ischemic Injury

Introduction: Cerebral ischemia, a consequence of cardiac arrest and stroke, is a leading cause of death and disability in the U.S. To improve translational studies, STAIR recommends augmenting animal models with comorbidities that “better reproduce the pathophysiological state” of stroke patients. Therefore, we incorporated social stress into our ischemia model (Espinosa-Garcia et al., 2017). Prior exposure to social stress upregulates the inflammatory status of microglia. They become primed—sensitized to activation by subsequent ischemia—worsening outcome. Such potentiated activation may result from the release of danger signals in the brain, such as HMGB-1, which binds to TLR4 receptors and activates inflammasomes. The NLRP3 inflammasome consists of a sensor molecule, NLRP3, the ASC adaptor, and caspase-1, whose activation leads to pro-inflammatory IL-1β production. We hypothesized that progesterone (P4) administration will reduce NLRP3 inflammasome activation, one of the molecular mechanisms underlying P4’s neuroprotective effects against ischemia combined with stress. Methods: Adult male rats were exposed to social defeat stress for 8 days and then subjected to global ischemia. P4 was administered 2 and 6h after occlusion and then daily for 7 days. Animals were killed at 7 or 14 days post-ischemia and their hippocampi dissected for western blots. The hippocampus is highly sensitive to stress and selectively vulnerable to global ischemia. Results: Consistent with previous reports, stress primed microglia and increased ( p <0.05) HMGB1 and NLRP3 levels, with no changes in IL-1β production in non-ischemic controls. Stressed ischemic animals showed potentiated ( p <0.05) NLRP3 inflammasome activation and increased IL-1β production. P4 treatment robustly reduced ( p <0.05) HMGB1, TLR4, phospho-IκB, NLRP3, ASC, cleaved caspase-1, and IL-1β levels in both stressed and non-stressed ischemic animals. Conclusion: Our data show that P4 can modulate stress-induced microglial priming to subsequent ischemic injury by counteracting NLRP3 inflammasome activation in the hippocampus. P4 may thus prove a promising neuroprotective agent to reduce inflammation associated with poor outcome in stroke patients with comorbid stress.

Immunoexcitotoxicity as the central mechanism of etiopathology and treatment of autism spectrum disorders: A possible role of fluoride and aluminum.

Our review suggests that most autism spectrum disorder (ASD) risk factors are connected, either directly or indirectly, to immunoexcitotoxicity. Chronic brain inflammation is known to enhance the sensitivity of glutamate receptors and interfere with glutamate removal from the extraneuronal space, where it can trigger excitotoxicity over a prolonged period. Neuroscience studies have clearly shown that sequential systemic immune stimulation can activate the brain's immune system, microglia, and astrocytes, and that with initial immune stimulation, there occurs CNS microglial priming. Children are exposed to such sequential immune stimulation via a growing number of environmental excitotoxins, vaccines, and persistent viral infections. We demonstrate that fluoride and aluminum (Al3+) can exacerbate the pathological problems by worsening excitotoxicity and inflammation. While Al3+ appears among the key suspicious factors of ASD, fluoride is rarely recognized as a causative culprit. A long-term burden of these ubiquitous toxins has several health effects with a striking resemblance to the symptoms of ASD. In addition, their synergistic action in molecules of aluminofluoride complexes can affect cell signaling, neurodevelopment, and CNS functions at several times lower concentrations than either Al3+ or fluoride acting alone. Our review opens the door to a number of new treatment modes that naturally reduce excitotoxicity and microglial priming.

Stress disinhibits microglia via down-regulation of CD200R: A mechanism of neuroinflammatory priming

Exposure to stressors primes the neuroinflammatory and microglial proinflammatory response to subsequent immune challenges, suggesting that stress might attenuate immunoregulatory mechanisms in the CNS microenvironment. CD200:CD200R is a key immunoregulatory signaling dyad that constrains microglial activation, and disruption of CD200:CD200R signaling primes microglia to subsequent immune challenges. Therefore, the present study examined the mediating role of CD200:CD200R signaling in stress-induced microglial priming. Here, we found that exposure to an acute stressor reduced CD200R expression across sub-regions of the hippocampus, amygdala as well as in isolated hippocampal microglia. A transcriptional suppressor of CD200R, CAAT/Enhancer Binding Proteinβ, was induced by stress and inversely associated with CD200R expression. To examine whether disrupted CD200:CD200R signaling plays a mediating role in stress-induced microglial priming, a soluble fragment of CD200 (mCD200Fc) was administered intra-cisterna magna prior to stressor exposure and stress-induced microglia priming assessed ex vivo 24 h later. Treatment with mCD200Fc blocked the stress-induced priming of the microglial pro-inflammatory response. Further, treatment with mCD200R1Fc recapitulated the effects of stress on microglial priming. We previously found that stress increases the alarmin high mobility group box-1 (HMGB1) in hippocampus, and that HMGB1 mediates stress-induced priming of microglia. Thus, we examined whether stress-induced increases in hippocampal HMGB1 are a consequence of disrupted CD200:CD200R signaling. Indeed, treatment with mCD200Fc prior to stress exposure blocked the stress-induced increase in hippocampal HMGB1. The present study suggests that stress exposure disrupts immunoregulatory mechanisms in the brain, which typically constrain the immune response of CNS innate immune cells. This attenuation of immunoregulatory mechanisms may thus permit a primed activation state of microglia to manifest.

Microglial recruitment of monocytes to the brain underlies reoccurring anxiety in stress-sensitized mice

Repeated social defeat (RSD) is a murine stress model that promotes long-term “stress-sensitization”, in which exposure to sub-threshold stress causes re-establishment of anxiety. We previously reported that RSD-induced anxiety depends on trafficking of monocytes to fear and threat appraisal brain regions. We hypothesize that RSD drives the production of inflammatory monocytes that are recruited to the brain by microglia, and these monocytes augment pro-inflammatory signaling that reinforces activation of threat circuitry. To address this, we used the CSF-1R inhibitor, PLX5622, to deplete microglia. Subsequent removal of the inhibitor allows microglia to rapidly repopulate. Here, we show that elimination of microglia after RSD prevented the recruitment of monocytes to the brain and recall of anxiety in stress-sensitized mice. Furthermore, microglia were depleted prior to RSD and allowed to repopulate. The phenotype of microglia was assessed by measuring behavioral and cytokine reactivity to peripheral LPS administered 24 days after RSD. We report that mice exposed to RSD displayed a prolonged reduction in social interaction to peripheral LPS and exaggerated pro-inflammatory cytokine expression from microglia. Importantly, repopulating microglia in mice exposed to RSD normalized social interaction and reduced microglial pro- inflammatory cytokine expression to levels similar to non-stressed mice. These data demonstrate that microglia depletion/repopulation can be used to prevent microglial priming. Collectively, microglial priming may underlie monocyte recruitment to the brain and re-establishment of anxiety in stress-sensitized mice.

Suppression of neuroinflammation by matrix metalloproteinase-8 inhibitor in aged normal and LRRK2 G2019S Parkinson's disease model mice challenged with lipopolysaccharide

Microglial priming is caused by aging and neurodegenerative diseases, and is characterized by an exaggerated microglial inflammatory response to secondary and sub-threshold challenges. In the present study, we examined the effects of the matrix metalloproteinase-8 (MMP-8) inhibitor (M8I) on the brain of aged normal and leucine-rich repeat kinase 2 (LRRK2) G2019S Parkinson's disease (PD) model mice systemically stimulated with lipopolysaccharide (LPS). The results indicated that Iba-1 positive microglia and GFAP-positive astrocytes, which were increased by LPS, significantly decreased by M8I in aged normal and PD model mice. M8I also decreased the expression of pro-inflammatory markers in the hippocampus and midbrain of aged normal and PD model mice challenged with LPS, while it also improved the motor coordination of aged normal mice after LPS challenge in rotor rod test and the general crossing locomotor activities of LPS-treated LRRK2G2019S PD mice after LPS challenge in open field test. To assess the effects of M8I in an in vitro priming model, BV2 microglia were pretreated with macrophage colony-stimulating factor (CSF)-1 or interleukin (IL)-34, and subsequently stimulated with LPS or polyinosinic-polycytidylic acid (poly[I:C]). M8I inhibited the LPS- or poly(I:C)-induced production of the tumor necrosis factor-α and nitric oxide, alone or in combination with CSF-1 or IL-34. Collectively, the data suggested that M8I has a therapeutic potential in treating neurodegenerative diseases that are aggravated by systemic inflammation.

Microglia turnover with aging and in an Alzheimer's model via long-term in vivo single-cell imaging.

To clarify the role of microglia in brain homeostasis and disease, an understanding of their maintenance, proliferation and turnover is essential. The lifespan of brain microglia, however, remains uncertain, and reflects confounding factors in earlier assessments that were largely indirect. We genetically labeled single resident microglia in living mice and then used multiphoton microscopy to monitor these cells over time. Under homeostatic conditions, we found that neocortical resident microglia were long-lived, with a median lifetime of well over 15 months; thus, approximately half of these cells survive the entire mouse lifespan. While proliferation of resident neocortical microglia under homeostatic conditions was low, microglial proliferation in a mouse model of Alzheimer's β-amyloidosis was increased threefold. The persistence of individual microglia throughout the mouse lifespan provides an explanation for how microglial priming early in life can induce lasting functional changes and how microglial senescence may contribute to age-related neurodegenerative diseases.

The role of the immunoproteasome in interferon-\u03b3-mediated microglial activation

Microglia regulate the brain microenvironment by sensing damage and neutralizing potentially harmful insults. Disruption of central nervous system (CNS) homeostasis results in transition of microglia to a reactive state characterized by morphological changes and production of cytokines to prevent further damage to CNS tissue. Immunoproteasome levels are elevated in activated microglia in models of stroke, infection and traumatic brain injury, though the exact role of the immunoproteasome in neuropathology remains poorly defined. Using gene expression analysis and native gel electrophoresis we characterize the expression and assembly of the immunoproteasome in microglia following interferon-gamma exposure. Transcriptome analysis suggests that the immunoproteasome regulates multiple features of microglial activation including nitric oxide production and phagocytosis. We show that inhibiting the immunoproteasome attenuates expression of pro-inflammatory cytokines and suppresses interferon-gamma-dependent priming of microglia. These results imply that targeting immunoproteasome function following CNS injury may attenuate select microglial activity to improve the pathophysiology of neurodegenerative conditions or the progress of inflammation-mediated secondary injury following neurotrauma.

Social interaction modulates the neuroinflammatory response to global cerebral ischemia in male mice

Social isolation is a risk factor for cardiovascular and cerebrovascular diseases, although the underlying mechanisms remain underspecified. Considering the potential of microglia to become sensitized by stressors and their role in neuroinflammation, we hypothesized that social isolation primes microglia, resulting in an exaggerated neuroimmune response to experimental cerebral ischemia. First, major histocompatibility complex II (MHC II) gene expression, an indicator of microglial priming, was compared between mice that were socially isolated or pair-housed. MHC II increased in the hippocampus and cortex of socially isolated mice, which is suggestive of isolation-induced microglial priming. In experiment 2, isolated and pair-housed mice underwent ∼8min of global cerebral ischemia. Hippocampal mRNA expression of tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) was significantly increased among both isolated and pair-housed ischemia groups relative to sham controls. Hippocampal expression of interleukin 1 beta (IL-1β) and cortical TNF-α, IL-1β and IL-6, were significantly increased 24-h post ischemia in isolated mice, but not pair-housed mice, relative to controls. Ischemia-induced increases in microglial cell body area and percent area fraction of ionized calcium binding adaptor molecule 1 (Iba-1) positive staining were also observed in isolated, but not pair-housed mice, relative to controls. For experiment 3, brain sections from socially isolated and pair-housed mice underwent 15min of oxygen glucose deprivation (OGD), an ex vivo model of cerebral ischemia. IL-6 gene expression was significantly elevated following OGD only in hippocampi from mice that had been socially isolated, indicating that isolation prior to ischemia is sufficient to modulate the neuroinflammatory response. Together, these data suggest microglial priming as a possible mechanism underlying the detrimental effects of social isolation on cerebral ischemia outcome.

Sleep Loss Promotes Astrocytic Phagocytosis and Microglial Activation in Mouse Cerebral Cortex.

We previously found that Mertk and its ligand Gas6, astrocytic genes involved in phagocytosis, are upregulated after acute sleep deprivation. These results suggested that astrocytes may engage in phagocytic activity during extended wake, but direct evidence was lacking. Studies in humans and rodents also found that sleep loss increases peripheral markers of inflammation, but whether these changes are associated with neuroinflammation and/or activation of microglia, the brain's resident innate immune cells, was unknown. Here we used serial block-face scanning electron microscopy to obtain 3D volume measurements of synapses and surrounding astrocytic processes in mouse frontal cortex after 6-8 h of sleep, spontaneous wake, or sleep deprivation (SD) and after chronic (∼5 d) sleep restriction (CSR). Astrocytic phagocytosis, mainly of presynaptic components of large synapses, increased after both acute and chronic sleep loss relative to sleep and wake. MERTK expression and lipid peroxidation in synaptoneurosomes also increased to a similar extent after short and long sleep loss, suggesting that astrocytic phagocytosis may represent the brain's response to the increase in synaptic activity associated with prolonged wake, clearing worn components of heavily used synapses. Using confocal microscopy, we then found that CSR but not SD mice show morphological signs of microglial activation and enhanced microglial phagocytosis of synaptic elements, without obvious signs of neuroinflammation in the CSF. Because low-level sustained microglia activation can lead to abnormal responses to a secondary insult, these results suggest that chronic sleep loss, through microglia priming, may predispose the brain to further damage.SIGNIFICANCE STATEMENT We find that astrocytic phagocytosis of synaptic elements, mostly of presynaptic origin and in large synapses, is upregulated already after a few hours of sleep deprivation and shows a further significant increase after prolonged and severe sleep loss, suggesting that it may promote the housekeeping of heavily used and strong synapses in response to the increased neuronal activity of extended wake. By contrast, chronic sleep restriction but not acute sleep loss activates microglia, promotes their phagocytic activity, and does so in the absence of overt signs of neuroinflammation, suggesting that like many other stressors, extended sleep disruption may lead to a state of sustained microglia activation, perhaps increasing the brain's susceptibility to other forms of damage.

Abnormal microglia activation and neuroinflammation in the aging brain

Background Neuroinflammation is implicated in the development of chronic neurodegenerative diseases in aging population, including postoperative cognitive dysfunction(POCD), Azheimer′s disease (AD), Parkinson′s disease(PD), and so on. The exact mechanisms, however, remain unclear. Objective To review the altered neuroinflammation and microglia activation in the aging brain. Content The activation of microglia appears in the aging brain, showing neuroinflammation, POCD, and neurodegeneration. The phenomenon is related to age-associated priming of microglia which increases its vulnerability and damages its function. Trend Suppressing microglia activation is one of the promising strategies to combat age-related neurodegenerative diseases. Key words: Aging; Brain; Microglia; Neurodegeneration

Transcriptomic evidence of a para-inflammatory state in the middle aged lumbar spinal cord

BackgroundWe have previously reported elevated expression of multiple pro-inflammatory markers in the lumbar spinal cord (LSC) of middle-aged male rats compared to young adults suggesting a para-inflammatory state develops in the LSC by middle age, a time that in humans is associated with the greatest pain prevalence and persistence. The goal of the current study was to examine the transcriptome-wide gene expression differences between young and middle aged LSC.MethodsYoung (3 month) and middle-aged (17 month) naïve Fisher 344 rats (n = 5 per group) were euthanized, perfused with heparinized saline, and the LSC were removed.Results~70% of 31,000 coding sequences were detected. After normalization, ~ 1100 showed statistically significant differential expression. Of these genes, 353 middle-aged annotated genes differed by > 1.5 fold compared to the young group. Nearly 10% of these genes belonged to the microglial sensome. Analysis of this subset revealed that the principal age-related differential pathways populated are complement, pattern recognition receptors, OX40, and various T cell regulatory pathways consistent with microglial priming and T cell invasion and modulation. Many of these pathways substantially overlap those previously identified in studies of LSC of young animals with chronic inflammatory or neuropathic pain.ConclusionsUp-modulation of complement pathway, microglial priming and activation, and T cell/antigen-presenting cell communication in healthy middle-aged LSC was found. Taken together with our previous work, the results support our conclusion that an incipient or para-inflammatory state develops in the LSC in healthy middle-aged adults.

NF‐kB, but not HIF‐1a, Inhibition Gene‐specifically Blocks Hypoxia‐induced Microglial Priming

The innate immune system has the capacity for “memory,” the ability to change future cellular responses based on prior experiences. Previous studies in our lab have shown that chronic intermittent hypoxia (IH), a hallmark of sleep‐disordered breathing, can induce cellular memory in both adult and neonatal microglia, CNS resident immune cells. When the immune system is challenged with lipopolysaccharide (LPS) the day following the last IH exposure, LPS‐induced microglial gene expression is augmented, indicating that IH pre‐exposure primes the microglial immune response. Hypoxia‐induced priming of microglial inflammatory gene responses are associated with upregulation of histone 3 lysine 4 trimethylation (H3K4me3) at gene promoters/enhancers, supporting an epigenetic role in microglial memory following hypoxia exposure. To begin to address the signaling mechanisms underlying IH‐induced priming, and the subsequent changes in H3K4me3, we developed an in vitro model of hypoxia which mirrors the microglial responses to IH observed in vivo. Using this model, we tested the hypothesis that hypoxia‐induced potentiation of inflammatory gene expression in microglia requires the activation of the hypoxia‐responsive transcription factors HIF‐1a and NF‐kB, key modulators of inflammatory gene expression. Immortalized N9 microglia were treated overnight with echinomycin (HIF‐1a inhibitor, 1 nM) or BOT‐64 (NF‐kB inhibitor, 3 μM) during the hypoxia exposure period (1.5% O2 for 16 hrs), after which time the cells were washed and stimulated with LPS (100 ng/mL; 3 hrs). We used qRT‐PCR to assess the gene expression of two inflammatory molecules that are potentiated by hypoxia pre‐exposure: inducible nitrogen oxide synthase (iNOS) and interleukin‐1 beta (IL‐1B). We found that while HIF‐1a inhibition did not attenuate the hypoxia‐induced potentiation of iNOS nor IL‐1B, NF‐kB inhibition had gene‐specific effects. Specifically, BOT‐64 blocked the potentiation of iNOS, but not IL‐1B. These results suggest that hypoxia‐induced priming of microglia involves the activation of NF‐kB, as well as at least one other unidentified pathway, to influence microglial gene expression. Ongoing studies are examining if NF‐kB inhibition also attenuates upregulation of H3K4me3 in inflammatory gene regulatory regions to provide insights into the mechanism whereby NF‐kB may regulate hypoxia‐induced microglial priming. Because this form of cellular memory augments the microglial inflammatory response, it may be associated with exacerbated CNS damage during sleep disordered breathing.Support or Funding InformationThis work was supported by NIH R01 NS085226.

Towards an Integrated View of Early Molecular Changes Underlying Vulnerability to Social Stress in Psychosis.

Psychotic disorders are heterogeneous and complex, involving many putative causal factors interacting along the course of disease development. Many of the factors implicated in the pathogenesis of psychosis also appear to be involved in disease onset and subsequent neuroprogression. Herein, we highlight the pertinent literature implicating inflammation and oxidative stress in the pathogenesis of psychosis, and the potential contribution of N-methyl-D-aspartate receptors (NMDARs). We also emphasize the role of peripubertal social stress in psychosis, and the ways in which hippocampal dysfunction can mediate dysregulation of the hypothalamic-pituitary-adrenal axis and cortisol release. Finally, we propose a model wherein inflammation and oxidative stress act as a first hit, producing altered parvalbumin interneuron development, NMDAR hypofunction, microglial priming, and sensitivity to a second hit of peripubertal social stress. With a greater understanding of how these factors interact, it may be possible to detect, prevent, and treat psychosis more effectively.

System xc- and neuro-inflammaging

Event Abstract Back to Event System xc- and neuro-inflammaging Lise Verbruggen1*, Eduard Bentea1, Lauren Deneyer1, Giulia Albertini2, Ilse J. Smolders2, Hideyo Sato3 and Ann Massie1 1 Vrije Universiteit Brussel, Pharmaceutical Biotechnology and Molecular Biology, Belgium 2 Pharmaceutical Chemistry and Drug Analysis, Belgium 3 Department of Medical Technology, Niigata University, Japan, Japan System xc- is a mainly glial cystine/glutamate antiporter (specific subunit xCT) that imports cystine in exchange for glutamate. Cystine is intracellularly reduced to cysteine, a building block of the major brain antioxidant glutathione. Cystine uptake is obligatory coupled to glutamate release which can, given the extrasynaptic localization of system xc-, activate both extrasynaptic metabotropic glutamate receptors (leading to modulation of synaptic glutamatergic transmission) and extrasynaptic NMDA receptors (possibly leading to excitotoxicity). Recently, system xc- was shown to also modulate neuroinflammation, with the absence of system xc- favoring the anti-inflammatory (M2) over the pro-inflammatory (M1) microglial phenotype [1]. As system xc- can provide glutathione to the cell, the expression of xCT is increased in conditions of oxidative stress and neuroinflammation [2] . The involvement of system xc- in the process of brain aging has never been investigated. Although it was reported that the plasma of xCT-/- mice (mice lacking functional system xc-) is in a more oxidized state [3], possibly leading to accelerated aging, we could observe a significantly increased life-span in xCT-/- vs xCT+/+ mice and we previously reported absence of any signs of accelerated brain aging after genetic loss of xCT [4]. Since increased levels of reactive oxygen species and inflammation are hallmarks of normal brain aging, we hypothesized that in the aging brain enhancement of system xc- could modulate the threshold for glutamate toxicity and drive neuroinflammation. As such, inhibition of system xc- might delay age-related diseases by reducing the build-up of several types of damage and thus making cells more resistant to a range of typical age-related stressors. To gain more insight into the role that system xc- fulfills in the process of brain aging, we investigated both the effect of aging on system xc- and the effect of loss of system xc- on age-induced neuroinflammation. xCT protein expression was unaltered in hippocampus, cortex and striatum of adult (3-5 months) versus aged (20-25 months) xCT+/+ mice. Absence of system xc- did not affect the age-related changes in number or shape of astrocytes in dentate gyrus as evidenced by immunohistochemistry for GFAP on sections of adult and aged xCT+/+ as well as xCT-/- mice. Astrocyte number decreased in the dentate gyrus of aged mice compared to adult mice, independent of genotype. Convex closure of astrocytic processes, cell body area and diameter remained stable between different groups. As for microglia, we observed absence of age-induced microglial proliferation in the dentate gyrus of xCT-/- mice compared to their xCT+/+ littermates, as evidenced by Iba1 immunohistochemistry. Also, the age-induced increase in microglial cell body area that was seen in xCT+/+ mice, was absent in xCT-/- mice. Finally, the genotype-effects that were seen on microglial cells in adult and aged dentate gyrus, were absent in substantia nigra. Yet, age-induced microglial priming might still be affected in substantia nigra of xCT-/- mice, as we observed reduced susceptibility to lactacystin-induced neurodegeneration accompanied by lack of nigral microglial activation in aged xCT-/- mice compared to age-matched xCT+/+ littermates. Taken together, the current (preliminary) findings suggest that the brain of xCT-/- mice ages healthier with reduced levels of hippocampal neuroinflammation and protection against toxin-induced neurodegeneration.

Differential response of microglia to distinct alpha-synuclein assemblies

Event Abstract Back to Event Differential response of microglia to distinct alpha-synuclein assemblies Anke Van Der Perren1*, Géraldine Gelders1, Francesca Macchi1, Wouter Peelaerts1, Luc Bousset2, Chris Van Den Haute1, Ronald Melki2 and Veerle Baekelandt1 1 KU Leuven, Neurosciences, Belgium 2 Laboratoire d’Enzymologie et Biochimie Structurales, CNRS, France Misfolded protein aggregates are a critical aspect of several neurodegenerative diseases. There is emerging evidence that these protein aggregates can adopt distinct conformations characterized by noticeable differences in phenotypic features. The discovery of the prion-like transmissible nature of these proteins suggests a pathogenic trigger which propagate throughout the nervous system underlying the progression of the disease. In addition, there is mounting evidence that neuroinflammatory processes are closely linked to neurodegeneration during ageing. In the present study, we investigated the immunological properties of different alpha-synuclein assemblies to define the role of the innate immune system in Parkinson’s disease. We examined the microglia cell response to different recombinant alpha-synuclein assemblies via exogenous addition to primary microglia cultures. We studied uptake and degradation of the different alpha-synuclein assemblies in our primary microglial cultures by confocal microscopy and western blot. The microglial status was analyzed using qPCR and ELISA. Next, we added the microglial supernatant to primary neurons to investigate the impact of microglial priming by specific alpha-synuclein assemblies on neuronal toxicity. We showed that distinct fibrillar alpha-synuclein assemblies promote a pro-inflammatory activation of microglia, however differences between fibrillar assemblies could be observed. Oligomeric species, thought to be the primary species responsible for the disease, were unable to trigger the same cascades. These results support our hypothesis that distinct fibrillar alpha-synuclein assemblies drive the pro-inflammatory activity of microglia and represent the toxic species contributing to the disease. Keywords: alpha-Synuclein, Microglia, Parkinson's disease, Neuroinflammation, synucleinopathies Conference: 12th National Congress of the Belgian Society for Neuroscience, Gent, Belgium, 22 May - 22 May, 2017. Presentation Type: Poster Presentation Topic: Integrative Systems: Neuroendocrinology, Neuroimmunology, and Homeostatic Challenge Citation: Van Der Perren A, Gelders G, Macchi F, Peelaerts W, Bousset L, Van Den Haute C, Melki R and Baekelandt V (2019). Differential response of microglia to distinct alpha-synuclein assemblies. Front. Neurosci. Conference Abstract: 12th National Congress of the Belgian Society for Neuroscience. doi: 10.3389/conf.fnins.2017.94.00095 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 21 Apr 2017; Published Online: 25 Jan 2019. * Correspondence: PhD. Anke Van Der Perren, KU Leuven, Neurosciences, Leuven, Belgium, anke.vanderperren@med.kuleuven.be Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Anke Van Der Perren Géraldine Gelders Francesca Macchi Wouter Peelaerts Luc Bousset Chris Van Den Haute Ronald Melki Veerle Baekelandt Google Anke Van Der Perren Géraldine Gelders Francesca Macchi Wouter Peelaerts Luc Bousset Chris Van Den Haute Ronald Melki Veerle Baekelandt Google Scholar Anke Van Der Perren Géraldine Gelders Francesca Macchi Wouter Peelaerts Luc Bousset Chris Van Den Haute Ronald Melki Veerle Baekelandt PubMed Anke Van Der Perren Géraldine Gelders Francesca Macchi Wouter Peelaerts Luc Bousset Chris Van Den Haute Ronald Melki Veerle Baekelandt Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.