Epigenetic priming of immune/inflammatory pathways activation and abnormal activity of cell cycle pathway in a perinatal model of white matter injury

Prenatal inflammatory insults accompany prematurity and provoke diffuse white matter injury (DWMI), which is associated with increased risk of neurodevelopmental pathologies, including autism spectrum disorders. DWMI results from maturation arrest of oligodendrocyte precursor cells (OPCs), a process that is poorly understood. Here, by using a validated mouse model of OPC maturation blockade, we provide the genome-wide ID card of the effects of neuroinflammation on OPCs that reveals the architecture of global cell fate issues underlining their maturation blockade. First, we find that, in OPCs, neuroinflammation takes advantage of a primed epigenomic landscape and induces abnormal overexpression of genes of the immune/inflammatory pathways: these genes strikingly exhibit accessible chromatin conformation in uninflamed OPCs, which correlates with their developmental, stage-dependent expression, along their normal maturation trajectory, as well as their abnormal upregulation upon neuroinflammation. Consistently, we observe the positioning on DNA of key transcription factors of the immune/inflammatory pathways (IRFs, NFkB), in both unstressed and inflamed OPCs. Second, we show that, in addition to the general perturbation of the myelination program, neuroinflammation counteracts the physiological downregulation of the cell cycle pathway in maturing OPCs. Neuroinflammation therefore perturbs cell identity in maturing OPCs, in a global manner. Moreover, based on our unraveling of the activity of genes of the immune/inflammatory pathways in prenatal uninflamed OPCs, the mere suppression of these proinflammatory mediators, as currently proposed in the field, may not be considered as a valid neurotherapeutic strategy

Neuroprotective effects of dexmedetomidine against glutamate agonist-induced neuronal cell death are related to increased astrocyte brain-derived neurotrophic factor expression

Abstract Background: Brain-derived neurotrophic factor (BDNF) plays a prominent role in neuroprotection against perinatal brain injury. Dexmedetomidine, a selective agonist of α2-adrenergic receptors, also provides neuroprotection against glutamate-induced damage. Because adrenergic receptor agonists can modulate BDNF expression, our goal was to examine whether dexmedetomidine’s neuroprotective effects are mediated by BDNF modulation in mouse perinatal brain injury. Methods: The protective effects against glutamate-induced injury of BDNF and dexmedetomidine alone or in combination with either a neutralizing BDNF antibody or an inhibitor of the extracellular signal-regulated kinase pathway (PD098059) were compared in perinatal ibotenate-induced cortical lesions (n = 10–20 pups/groups) and in mouse neuronal cultures (300 μm of ibotenate for 6 h). The effect of dexmedetomidine on BDNF expression was examined in vivo and in vitro with cortical neuronal and astrocyte isolated cultures. Results: Both BDNF and dexmedetomidine produced a significant neuroprotective effect in vivo and in vitro. Dexmedetomidine enhanced Bdnf4 and Bdnf5 transcription and BDNF protein cortical expression in vivo. Dexmedetomidine also enhanced Bdnf4 and Bdnf5 transcription and increased BDNF media concentration in isolated astrocyte cultures but not in neuronal cultures. Dexmedetomidine’s protective effect was inhibited with BDNF antibody (mean lesion size ± SD: 577 ± 148 μm vs. 1028 ± 213 μm, n = 14–20, P &amp;lt; 0.001) and PD098059 in vivo but not in isolated neuron cultures. Finally, PD098059 inhibited the increased release of BDNF induced by dexmedetomidine in astrocyte cultures. Conclusion: These results suggest that dexmedetomidine increased astrocyte expression of BDNF through an extracellular signal-regulated kinase-dependent pathway, inducing subsequent neuroprotective effects. </jats:sec

Contribution of mast cells to injury mechanisms in a mouse model of pediatric traumatic brain injury

The cognitive and behavioral deficits caused by traumatic brain injury (TBI) to the immature brain are more severe and persistent than injuries to the adult brain. Understanding this developmental sensitivity is critical because children under 4 years of age of sustain TBI more frequently than any other age group. One of the first events after TBI is the infiltration and degranulation of mast cells (MCs) in the brain, releasing a range of immunomodulatory substances; inhibition of these cells is neuroprotective in other types of neonatal brain injury. This study investigates for the first time the role of MCs in mediating injury in a P7 mouse model of pediatric contusion-induced TBI. We show that various neural cell types express histamine receptors and that histamine exacerbates excitotoxic cell death in primary cultured neurons. Cromoglycate, an inhibitor of MC degranulation, altered the inflammatory phenotype of microglia activated by TBI, reversing several changes but accentuating others, when administered before TBI. However, without regard to the time of cromoglycate administration, inhibiting MC degranulation did not affect cell loss, as evaluated by ventricular dilatation or cleaved caspase-3 labeling, or the density of activated microglia, neurons, or myelin. In double-heterozygous cKit mutant mice lacking MCs, this overall lack of effect was confirmed. These results suggest that the role of MCs in this model of pediatric TBI is restricted to subtle effects and that they are unlikely to be viable neurotherapeutic targets. © 2016 Wiley Periodicals, Inc

Pro-epileptogenic effects of viral-like inflammation in both mature and immature brains

International audienceAbstractBackgroundInfectious encephalitides are most often associated with acute seizures during the infection period and are risk factors for the development of epilepsy at later times. Mechanisms of viral encephalitis-induced epileptogenesis are poorly understood. Here, we evaluated the contribution of viral encephalitis-associated inflammation to ictogenesis and epileptogenesis using a rapid kindling protocol in rats. In addition, we examined whether minocycline can improve outcomes of viral-like brain inflammation.MethodsTo produce viral-like inflammation, polyinosinic-polycytidylic acid (PIC), a toll-like receptor 3 (TLR3) agonist, was applied to microglial/macrophage cell cultures and to the hippocampus of postnatal day 13 (P13) and postnatal day 74 (P74) rats. Cell cultures permit the examination of the inflammation induced by PIC, while the in vivo setting better suits the analysis of cytokine production and the effects of inflammation on epileptogenesis. Minocycline (50 mg/kg) was injected intraperitoneally for 3 consecutive days prior to the kindling procedure to evaluate its effects on inflammation and epileptogenesis.ResultsPIC injection facilitated kindling epileptogenesis, which was evident as an increase in the number of full limbic seizures at both ages. Furthermore, in P14 rats, we observed a faster seizure onset and prolonged retention of the kindling state. PIC administration also led to an increase in interleukin 1β (IL-1β) levels in the hippocampus in P14 and P75 rats. Treatment with minocycline reversed neither the pro-epileptogenic effects of PIC nor the increase of IL-1β in the hippocampus in both P14 and P75 rats.ConclusionsHippocampal injection of PIC facilitates rapid kindling epileptogenesis at both P14 and P75, suggesting that viral–induced inflammation increases epileptogenesis irrespective of brain maturation. Minocycline, however, was unable to reverse the increase of epileptogenesis, which might be linked to its absence of effect on hippocampal IL-1β levels at both ages

Role of microglia in a mouse model of paediatric traumatic brain injury

AbstractThe cognitive and behavioural deficits caused by traumatic brain injury (TBI) to the immature brain are more severe and persistent than TBI in the mature brain. Understanding this developmental sensitivity is critical as children under four years of age sustain TBI more frequently than any other age group. Microglia (MG), resident immune cells of the brain that mediate neuroinflammation, are activated following TBI in the immature brain. However, the type and temporal profile of this activation and the consequences of altering it are still largely unknown.In a mouse model of closed head weight drop paediatric brain trauma, we characterized i) the temporal course of total cortical neuroinflammation and the phenotype of ex vivo isolated CD11B-positive microglia/macrophage (MG/MΦ) using a battery of 32 markers, and ii) neuropathological outcome 1 and 5days post-injury. We also assessed the effects of targeting MG/MΦ activation directly, using minocycline a prototypical microglial activation antagonist, on these processes and outcome.TBI induced a moderate increase in both pro- and anti-inflammatory cytokines/chemokines in the ipsilateral hemisphere. Isolated cortical MG/MΦ expressed increased levels of markers of endogenous reparatory/regenerative and immunomodulatory phenotypes compared with shams. Blocking MG/MΦ activation with minocycline at the time of injury and 1 and 2days post-injury had only transient protective effects, reducing ventricular dilatation and cell death 1day post-injury but having no effect on injury severity at 5days.This study demonstrates that, unlike in adults, the role of MG/MΦ in injury mechanisms following TBI in the immature brain may not be negative. An improved understanding of MG/MΦ function in paediatric TBI could support translational efforts to design therapeutic interventions

Characterization of phenotype markers and neuronotoxic potential of polarised primary microglia in vitro

AbstractMicroglia mediate multiple facets of neuroinflammation, including cytotoxicity, repair, regeneration, and immunosuppression due to their ability to acquire diverse activation states, or phenotypes. Modulation of microglial phenotype is an appealing neurotherapeutic strategy but a comprehensive study of classical and more novel microglial phenotypic markers in vitro is lacking. The aim of this study was to outline the temporal expression of a battery of phenotype markers from polarised microglia to generate an in vitro tool for screening the immunomodulatory potential of novel compounds. We characterised expression of thirty-one macrophage/microglial phenotype markers in primary microglia over time (4, 12, 36, and 72h), using RT-qPCR or multiplex protein assay. Firstly, we selected Interleukin-4 (IL-4) and lipopolysaccharide (LPS) as the strongest M1–M2 polarising stimuli, from six stimuli tested. At each time point, markers useful to identify that microglia were M1 included iNOS, Cox-2 and IL-6 and a loss of M2a markers. Markers useful for quantifying M2b-immunomodulatory microglia included, increased IL-1RA and SOCS3 and for M2a-repair and regeneration, included increased arginase-1, and a loss of the M1 and M2b markers were discriminatory. Additional markers were regulated at fewer time points, but are still likely important to monitor when assessing the immunomodulatory potential of novel therapies. Further, to facilitate identification of how novel immunomodulatory treatments alter the functional affects of microglia, we characterised how the soluble products from polarised microglia affected the type and rate of neuronal death; M1/2b induced increasing and M2a-induced decreasing neuronal loss. We also assessed any effects of prior activation state, to provide a way to identify how a novel compound may alter phenotype depending on the stage of injury/insult progression. We identified generally that a prior M1/2b reduced the ability of microglia to switch to M2a. Altogether, we have characterised a profile of phenotype markers and a mechanism of assessing functional outcome that we can use as a reference guide for first-line screening of novel immunomodulatory therapies in vitro in the search for viable neuroprotectants

Epigenome and transcriptome landscapes highlight dual roles of proinflammatory players in a perinatal model of white matter injury

Premature birth is the commonest cause of death and disability in young children. Diffuse white matter injury (DWMI), provoked by inflammatory insults accompanying prematurity, is associated with increased risk of neurodevelopmental disorders – such as autism spectrum disorders – and is due to maturation arrest in oligodendrocyte precursors (OPCs). The lack of therapeutic solutions is a strong impetus to unveil the molecular mechanisms underlying neuroinflammation impact on OPC cell fate. We used a validated mouse model of DWMI, induced by systemic- and neuro-inflammation – as observed in preterm infants – and based on interleukin-1B administration from postnatal day P1 to P5. Using integrated genome-wide approaches we showed that neuroinflammation induced limited epigenomic disturbances in OPCs, but marked transcriptomic alterations of genes of the immune/inflammatory pathways. We found that these genes were expressed in control OPCs and physiologically downregulated between P3-P10, as part of the OPC normal developmental trajectory. We observed that transcription factors of the inflammatory pathways occupied DNA both in unstressed and inflamed OPCs. Thus, rather than altering genome-wide chromatin accessibility, neuroinflammation takes advantage of open chromatin regions and deeply counteracts the stage-dependent downregulation of these active transcriptional programs by the sustained upregulation of transcript levels. The intricate dual roles – stress-responsive and potentially developmental – of these proinflammatory mediators strongly suggest that the mere suppression of these inflammatory mediators, as currently proposed, may not be a valid neurotherapeutic strategy. Our study provides new insights for the future development of more targeted approaches to protect the preterm brain

Additional file 1: of Pro-epileptogenic effects of viral-like inflammation in both mature and immature brains

Blood cytokine levels 24 h after PIC injection measured by Multiplex cytokine assay. Cytokines profile (IL1β, IL6, IL10, TNFα) in the blood 24 h after intrahippocampal injection (saline i.h (white bar) or PIC i.h. (10 μg/rat) (black bar) in P14 and in P75 rats. Data are presented as mean ± SEM. We did not find any difference between the groups. (DOCX 9451 kb

Axl mediates ZIKA virus entry in human glial cells and modulates innate immune responses

International audienceZIKA virus (ZIKV) is an emerging pathogen responsible for neurological disorders and congenital microcephaly. However, the molecular basis for ZIKV neurotropism remains poorly understood. Here, we show that Axl is expressed in human microglia and astrocytes in the developing brain and that it mediates ZIKV infection of glial cells. Axl-mediated ZIKV entry requires the Axl ligand Gas6, which bridges ZIKV particles to glial cells. Following binding, ZIKV is internalized through clathrin-mediated endocytosis and traffics to Rab5+ endosomes to establish productive infection. During entry, the ZIKV/Gas6 complex activates Axl kinase activity, which downmodulates interferon signaling and facilitates infection. ZIKV infection of human glial cells is inhibited by MYD1, an engineered Axl decoy receptor, and by the Axl kinase inhibitor R428. Our results highlight the dual role of Axl during ZIKV infection of glial cells: promoting viral entry and modulating innate immune responses. Therefore, inhibiting Axl function may represent a potential target for future antiviral therapies