Microglia and inflammation: impact on developmental brain injuries

Gastrodin Regulates the Notch-1 Signal Pathway via Renin-Angiotensin System in Activated Microglia

Notch-1 and renin angiotensin system (RAS) are involved in microglia activation. It has been reported that gastrodin inhibited inflammatory responses mediated by activated microglia. This study explored the possible interaction between this two pathways, and to determine whether gastrodin would exert its effects on both of them. Expression of RAS, Notch-1 signaling and proinflammatory mediators in lipopolysaccharide (LPS) activated BV-2 microglia subjected to various treatments was determined by Western blot and immunofluorescence. The protein expression of RAS, Notch-1 pathway and TNF-α and IL-1β was significantly increased in activated microglia. Exogenous Ang II markedly enhanced the expression of these biomarkers. Meanwhile, Azilsartan [a specific inhibitor of AT₁ (AT₁I)] inhibited the expression of Notch-1 pathway and proinflammatory cytokines. When Notch-1 signaling was inhibited with DAPT, ACE and AT₁ expression remained unaffected, indicating that RAS can regulate the Notch-1 pathway in activated microglia but not reciprocally. Additionally, we showed here that gastrodin inhibited the RAS, Notch-1 pathway and inflammatory response. Remarkably, gastrodin did not exert any effect on expression of Notch-1 signaling when RAS was blocked by AT₁I, suggesting that gastrodin acts on the RAS directly, not through the Notch-1 pathway. Furthermore, TNF-α and IL-1β expression was significantly increased in activated microglia treated with exogenous Ang II; the expression, however, was suppressed by gastrodin. Of note, expression of proinflammatory cytokines was further decreased in gastrodin and AT₁I combination treatment. The results suggest that gastrodin acts via the RAS which regulates the Notch-1 signaling and inflammation in LPS-induced microglia.

Chlorogenic Acid Prevents Microglia-Induced Neuronal Apoptosis and Oxidative Stress under Hypoxia-Ischemia Environment by Regulating the MIR497HG/miR-29b-3p/SIRT1 Axis

Background

Chlorogenic acid (CGA) is a polyphenolic compound with antioxidant and anti-inflammatory properties. CGA has been shown to improve neuroinflammation. This study is aimed at elucidating the exact mechanism by which CGA reduces neuroinflammation.

Methods

Oxygen and glucose deprivation (OGD) was utilized to treat BV2 microglia and HT-22 hippocampal neurons to engineer an in vitro model of hypoxic ischemia reperfusion. The levels of inflammatory factors (IL-1β, IL-6, TNF-α, IL-4, and IL-10) and oxidative stress factors (MDA, SOD, and GSH-PX) in microglia were determined by ELISA kits. The neuron proliferation was assessed by CCK-8 assay, and LDH kit was used to determine LDH release in neurons. The fluorescent dye DCF-DA was employed to measure ROS levels in neurons. Correlation of MIR497HG, miR-29b-3p, and SIRT1/NF-κB in neurons and microglia was determined by qRT-PCR. Expressions of inflammatory proteins (COX2, iNOS), oxidative stress pathways (Nrf2, HO-1), and apoptosis-related proteins (Bcl-2, Bax, caspase3, caspase8, and caspase9) in microglia or neurons were determined by western blot. The interactions between MIR497HG and miR-29b-3p, as well as between miR-29b-3p and SIRT1, were determined by dual luciferase assay and RIP assay.

Results

CGA attenuated OGD-mediated inflammation and oxidative stress in microglia and inhibited microglia-mediated neuronal apoptosis. CGA increased the levels of MIR497HG and SIRT1 and suppressed the levels of miR-29b-3p in BV2 and HT-22 cells. MIR497HG knockdown, miR-29b-3p upregulation, and SIRT1 inhibition inhibited CGA-mediated anti-inflammatory and neuronal protective functions. There is a targeting correlation between MIR497HG, miR-29b-3p, and Sirt1. MIR497HG sponges miR-29b-3p to regulate SIRT1 expression in an indirect manner.

Conclusion

CGA upregulates MIR497HG to curb miR-29b-3p expression, hence initiating the SIRT1/NF-κB signaling pathway and repressing OGD-elicited inflammation, oxidative stress, and neuron apoptosis.

Inter-alpha Inhibitor Proteins Ameliorate Brain Injury and Improve Behavioral Outcomes in a Sex-Dependent Manner After Exposure to Neonatal Hypoxia Ischemia in Newborn and Young Adult Rats

Hypoxic-ischemic (HI) brain injury is a major contributor to neurodevelopmental morbidities. Inter-alpha inhibitor proteins (IAIPs) have neuroprotective effects on HI-related brain injury in neonatal rats. However, the effects of treatment with IAIPs on sequential behavioral, MRI, and histopathological abnormalities in the young adult brain after treatment with IAIPs in neonates remain to be determined. The objective of this study was to examine the neuroprotective effects of IAIPs at different neurodevelopmental stages from newborn to young adults after exposure of neonates to HI injury. IAIPs were given as 11-sequential 30-mg/kg doses to postnatal (P) day 7-21 rats after right common carotid artery ligation and exposure to 90 min of 8% oxygen. The resulting brain edema and injury were examined by T2-weighted magnetic resonance imaging (MRI) and cresyl violet staining, respectively. The mean T2 values of the ipsilateral hemisphere from MRI slices 6 to 10 were reduced in IAIP-treated HI males + females on P8, P9, and P10 and females on P8, P9, P10, and P14. IAIP treatment reduced hemispheric volume atrophy by 44.5 ± 29.7% in adult male + female P42 rats and improved general locomotor abilities measured by the righting reflex over time at P7.5, P8, and P9 in males + females and males and muscle strength/endurance measured by wire hang on P16 in males + females and females. IAIPs provided beneficial effects during the learning phase of the Morris water maze with females exhibiting beneficial effects. IAIPs confer neuroprotection from HI-related brain injury in neonates and even in adult rats and beneficial MRI and behavioral benefits in a sex-dependent manner.

Anti-inflammatory effects of N-cyclooctyl-5-methylthiazol-2-amine hydrobromide on lipopolysaccharide-induced inflammatory response through attenuation of NLRP3 activation in microglial cells

Microglial activation is closely associated with neuroinflammatory pathologies. The nucleotide-binding and oligomerization domain-like receptor containing a pyrin domain 3 (NLRP3) inflammasomes are highly organized intracellular sensors of neuronal alarm signaling. NLRP3 inflammasomes activate nuclear factor kappa-B (NF-κB) and reactive oxygen species (ROS), which induce inflammatory responses. Moreover, NLRP3 dysfunction is a common feature of chronic inflammatory diseases. The present study investigated the effect of a novel thiazol derivative, N-cyclooctyl-5-methylthiazol-2-amine hydrobromide (KHG26700), on inflammatory responses in lipopolysaccharide (LPS)-treated BV-2 microglial cells. KHG26700 significantly attenuated the expression of several pro-inflammatory cytokines, including tumor necrosis factor-α, interleukin-1β, and interleukin-6, in these cells, as well as the LPS-induced increases in NLRP3, NF-κB, and phospho-IkBα levels. KHG26700 also suppressed the LPS-induced increases in protein levels of autophagy protein 5 (ATG5), microtubule-associated protein 1 light chain 3 (LC3), and beclin-1, as well as downregulating the LPS-enhanced levels of ROS, lipid peroxidation, and nitric oxide. These results suggest that the anti-inflammatory effects of KHG26700 may be due, at least in part, to the regulation of the NLRP3-mediated signaling pathway during microglial activation.

Amide proton transfer (APT) imaging-based study on the correlation between brain pH and voltage-gated proton channels in piglets after hypoxic-ischemic brain injury

Background

The normal regulation of brain pH is particularly critical for protein structure and enzymatic catalysis in the brain. This study aimed to investigate the regulation mechanism of brain pH after hypoxic-ischemic brain injury (HIBI) through the combination of amide proton transfer (APT) imaging, the analysis of brain pH levels, and the analysis of voltage-gated proton channel (Hv1) expression in piglets with HIBI.

Methods

A total of 59 healthy piglets (age range, 3-5 days after birth; body weight, 1-1.5 kg) were selected. Six piglets were excluded due to death, modeling failure, or motion artifacts, leaving a total of 10 animals in the control group and 43 animals in the HIBI model group. At different time points (0-2, 2-6, 6-12, 12-24, 24-48, and 48-72 hours) after HIBI, brain pH, Hv1 expression, and APT values were measured and analyzed. The statistical analysis of data was performed using the independent samples t-test, analysis of variance, and Spearman rank correlation analysis. A P value less than 0.05 indicated statistical significance.

Results

As shown by the immunofluorescent staining results after HIBI, Hv1 protein expression in the basal ganglia reached a peak value at 0-2 hours, with a statistically significant difference between 0-2 hours and other time points (P<0.001). In piglets, the APT value reached a trough at 0-2 hours after HIBI, and subsequently, it gradually increased, and there was a significant difference between the control group and all HIBI model subgroups (P<0.001) except for the 2-6 hours subgroup (P=0.602). Brain pH decreased after HIBI and reached a trough at 0-2 hours, then gradually increased. Hv1 protein expression, pH, and APT values were all correlated (P<0.001).

Conclusions

After HIBI, values of brain pH, APT, and the expression of Hv1 changed over time and had a linear correlation. This suggests that there was a shift in brain hydrogen ions (H⁺) in the neural network and a change in brain pH after hypoxic-ischemic (HI) injury.

Altered distributions and functions of natural killer T cells and γδ T cells in neonates with neonatal encephalopathy, in school-age children at follow-up, and in children with cerebral palsy

We enumerated conventional and innate lymphocyte populations in neonates with neonatal encephalopathy (NE), school-age children post-NE, children with cerebral palsy and age-matched controls. Using flow cytometry, we demonstrate alterations in circulating T, B and natural killer cell numbers. Invariant natural killer T cell and Vδ2⁺ γδ T cell numbers and frequencies were strikingly higher in neonates with NE, children post-NE and children with cerebral palsy compared to age-matched controls, whereas mucosal-associated invariant T cells and Vδ1 T cells were depleted from children with cerebral palsy. Upon stimulation ex vivo, T cells, natural killer cells and Vδ2 T cells from neonates with NE more readily produced inflammatory cytokines than their counterparts from healthy neonates, suggesting that they were previously primed or activated. Thus, innate and conventional lymphocytes are numerically and functionally altered in neonates with NE and these changes may persist into school-age.

Synthesis of 4-(3-oxo-3-phenylpropyl)morpholin-4-ium chloride analogues and their inhibitory activities of nitric oxide production in lipopolysaccharide-induced BV2 cells

Based on our previous report that 3-morpholino-1-phenylpropan-1-one 2, one of the fluoxetine's simplified morpholino analogue, inhibited nitric oxide (NO) production, in this paper, various substituted benzene analogues with morpholine hydrochloride of 2 were synthesized and their inhibitory effects on NO production in lipopolysaccharide (LPS)-induced BV2 cells were tested. Among the synthesized compounds, 2-trifluoromethyl analogue 16n (IC₅₀ = 8.6 μM) showed a significantly higher inhibitory activity than that of the parent compound 2a (IC₅₀ > 50 μM) and suppressed NO production dose-dependently without cytotoxicity. Compound 16n also inhibited iNOS expression in LPS-induced BV2 cells at 2, 10 and 20 μM concentrations. These results suggest that compound 16n inhibited NO production by suppressing the expression of iNOS and can be used as a lead structure for developing new inhibitor of NO production.

PDE inhibition in distinct cell types to reclaim the balance of synaptic plasticity

Synapses are the functional units of the brain. They form specific contact points that drive neuronal communication and are highly plastic in their strength, density, and shape. A carefully orchestrated balance between synaptogenesis and synaptic pruning, i.e., the elimination of weak or redundant synapses, ensures adequate synaptic density. An imbalance between these two processes lies at the basis of multiple neuropathologies. Recent evidence has highlighted the importance of glia-neuron interactions in the synaptic unit, emphasized by glial phagocytosis of synapses and local excretion of inflammatory mediators. These findings warrant a closer look into the molecular basis of cell-signaling pathways in the different brain cells that are related to synaptic plasticity. In neurons, intracellular second messengers, such as cyclic guanosine or adenosine monophosphate (cGMP and cAMP, respectively), are known mediators of synaptic homeostasis and plasticity. Increased levels of these second messengers in glial cells slow down inflammation and neurodegenerative processes. These multi-faceted effects provide the opportunity to counteract excessive synapse loss by targeting cGMP and cAMP pathways in multiple cell types. Phosphodiesterases (PDEs) are specialized degraders of these second messengers, rendering them attractive targets to combat the detrimental effects of neurological disorders. Cellular and subcellular compartmentalization of the specific isoforms of PDEs leads to divergent downstream effects for these enzymes in the various central nervous system resident cell types. This review provides a detailed overview on the role of PDEs and their inhibition in the context of glia-neuron interactions in different neuropathologies characterized by synapse loss. In doing so, it provides a framework to support future research towards finding combinational therapy for specific neuropathologies.

Microglia Susceptibility to Free Bilirubin Is Age-Dependent

Increased concentrations of unconjugated bilirubin (UCB), namely its free fraction (Bf), in neonatal life may cause transient or definitive injury to neurons and glial cells. We demonstrated that UCB damages neurons and glial cells by compromising oligodendrocyte maturation and myelination, and by activating astrocytes and microglia. Immature neurons and astrocytes showed to be especially vulnerable. However, whether microglia susceptibility to UCB is also age-related was never investigated. We developed a microglia culture model in which cells at 2 days in vitro (2DIV) revealed to behave as the neonatal microglia (amoeboid/reactive cells), in contrast with those at 16DIV microglia that performed as aged cells (irresponsive/dormant cells). Here, we aimed to unveil whether UCB-induced toxicity diverged from the young to the long-cultured microglia. Cells were isolated from the cortical brain of 1- to 2-day-old CD1 mice and incubated for 24 h with 50/100 nM Bf levels, which were associated to moderate and severe neonatal hyperbilirubinemia, respectively. These concentrations of Bf induced early apoptosis and amoeboid shape in 2DIV microglia, while caused late apoptosis in 16DIV cells, without altering their morphology. CD11b staining increased in both, but more markedly in 2DIV cells. Likewise, the gene expression of HMGB1, a well-known alarmin, as well as HMGB1 and GLT-1–positive cells, were enhanced as compared to long-maturated microglia. The CX3CR1 reduction in 2DIV microglia was opposed to the 16DIV cells and suggests a preferential Bf-induced sickness response in younger cells. In conformity, increased mitochondrial mass and NO were enhanced in 2DIV cells, but unchanged or reduced, respectively, in the 16DIV microglia. However, 100 nM Bf caused iNOS gene overexpression in 2DIV and 16DIV cells. While only arginase 1/IL-1β gene expression levels increased upon 50/100 nM Bf treatment in long-maturated microglia, MHCII/arginase 1/TNF-α/IL-1β/IL-6 (>10-fold) were upregulated in the 2DIV microglia. Remarkably, enhanced inflammatory-associated microRNAs (miR-155/miR-125b/miR-21/miR-146a) and reduced anti-inflammatory miR-124 were found in young microglia by both Bf concentrations, while remained unchanged (miR/21/miR-125b) or decreased (miR-155/miR-146a/miR-124) in aged cells. Altogether, these findings support the neurodevelopmental susceptibilities to UCB-induced neurotoxicity, the most severe disabilities in premature babies, and the involvement of immune-inflammation neonatal microglia processes in poorer outcomes.

Lipopolysaccharide-induced changes in the neurovascular unit in the preterm fetal sheep brain

Background

Exposure to inflammation during pregnancy can predispose to brain injury in premature infants. In the present study, we investigated the effects of prolonged exposure to inflammation on the cerebrovasculature of preterm fetal sheep.

Methods

Chronically instrumented fetal sheep at 103–104 days of gestation (full term is ~ 147 days) received continuous low-dose lipopolysaccharide (LPS) infusions (100 ng/kg over 24 h, followed by 250 ng/kg/24 h for 96 h plus boluses of 1 μg LPS at 48, 72, and 96 h) or the same volume of normal saline (0.9%, w/v). Ten days after the start of LPS exposure at 113–114 days of gestation, the sheep were killed, and the fetal brain perfused with formalin in situ. Vessel density, pericyte and astrocyte coverage of the blood vessels, and astrogliosis in the cerebral cortex and white matter were determined using immunohistochemistry.

Results

LPS exposure reduced (P < 0.05) microvascular vessel density and pericyte vascular coverage in the cerebral cortex and white matter of preterm fetal sheep, and increased the activation of perivascular astrocytes, but decreased astrocytic vessel coverage in the white matter.

Conclusions

Prolonged exposure to LPS in preterm fetal sheep resulted in decreased vessel density and neurovascular remodeling, suggesting that chronic inflammation adversely affects the neurovascular unit and, therefore, could contribute to long-term impairment of brain development.

Effects of α-lipoic acid on LPS-induced neuroinflammation and NLRP3 inflammasome activation through the regulation of BV-2 microglial cells activation

Microglial cells are known as the main immune cells in the central nervous system, both regulating its immune response and maintaining its homeostasis. Furthermore, the antioxidant α-lipoic acid (LA) is a recognized therapeutic drug for diabetes because it can easily invade the blood–brain barrier. This study investigated the effect of α-LA on the inflammatory response in lipopolysaccharide (LPS)-treated BV-2 microglial cells. Our results revealed that α-LA significantly attenuated several inflammatory responses in BV-2 microglial cells, including pro-inflammatory cytokines, such as tumor necrosis factor-α and interleukin (IL)-6, and other cytotoxic molecules, such as nitric oxide and reactive oxygen species. In addition, α-LA inhibited the LPS-induced phosphorylation of ERK and p38 and its pharmacological properties were facilitated via the inhibition of the nuclear factor kappa B signaling pathway. Moreover, α-LA suppressed the activation of NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasomes, multiprotein complexes consisting of NLRP3 and caspase-1, which are involved in the innate immune response. Finally, α-LA decreased the genes accountable for the M1 phenotype, IL-1β and ICAM1, whereas it increased the genes responsible for the M2 phenotype, MRC1 and ARG1. These findings suggest that α-LA alleviates the neuroinflammatory response by regulating microglial polarization.

Effect of Glycine on BV-2 Microglial Cells Treated with Interferon-γ and Lipopolysaccharide

Microglia are first-line defense antigen-presenting phagocytes in the central nervous system. Activated microglial cells release pro-inflammatory cytokines and can trigger an oxidative burst. The amino acid glycine exerts anti-inflammatory, immunomodulatory and cytoprotective effects and influences cell volume regulation. This study aimed to investigate the role of glycine in the modulation of inflammatory processes in mouse BV-2 microglial cells. Inflammatory stress was induced by lipopolysaccharide/interferon-γ (LPS/IFN-γ) treatment for 24 h in the absence or presence of 1 or 5 mM glycine. Cells were analyzed by flow cytometry for cell volume, side scatter, apoptosis/necrosis and expression of activation-specific surface markers. Apoptosis progression was monitored by life cell imaging. Reduced glutathione/oxidized glutathione (GSH/GSSG) ratios and release of the pro-inflammatory cytokines IL-6 and TNF-α were measured using luminescence-based assays and ELISA, respectively. We found that LPS/IFN-γ-induced apoptosis was decreased and the fraction of living cells was increased by glycine. Expression of the surface markers CD11b, CD54 and CD80 was dose-dependently increased, while IL-6 and TNF-α release was not altered compared to LPS/IFN-γ-treated cells. We showed that in BV-2 microglial cells glycine improves viability and counteracts deleterious responses to LPS/IFN-γ, which might be relevant in neurodegenerative processes associated with inflammation, like Alzheimer’s or Parkinson’s disease.

Apigenin exhibits anti-inflammatory effects in LPS-stimulated BV2 microglia through activating GSK3β/Nrf2 signaling pathway

Objective: Apigenin is a natural flavonoid compound extracted from Matricaria chamomilla. We evaluated the anti-inflammatory effects of apigenin in this study using the Lipopolysaccharide (LPS)-stimulated BV2 microglia.Methods: BV2 cells were treated with apigenin for 1 h and then treated with LPS. The inflammatory cytokine productions were tested by qRT-PCR and ELISA. The expression of GSK3β, Nrf2, and NF-κB signaling pathways were measured by western blot analysis.Results: Apigenin significantly attenuated LPS-induced TNF-α, IL-1β, and IL-6 production. Apigenin suppressed LPS-induced NF-κB activation. Furthermore, GSK3β, Nrf2, and HO-1 were concentration-dependently increased by apigenin. The suppression of apigenin on LPS-induced inflammatory response and NF-κB activation were prevented when Nrf2 was knocked out or by GSK3β inhibitor.Conclusions: Collectively, apigenin suppressed LPS-induced microglia activation via activating GSK3β/Nrf2 signaling pathway.

Effects of α-lipoic acid on LPS-induced neuroinflammation and NLRP3 inflammasome activation through the regulation of BV-2 microglial cells activation

Microglial cells are known as the main immune cells in the central nervous system, both regulating its immune response and maintaining its homeostasis. Furthermore, the antioxidant α-lipoic acid (LA) is a recognized therapeutic drug for diabetes because it can easily invade the blood-brain barrier. This study investigated the effect of α-LA on the inflammatory response in lipopolysaccharide (LPS)-treated BV-2 microglial cells. Our results revealed that α-LA significantly attenuated several inflammatory responses in BV-2 microglial cells, including pro-inflammatory cytokines, such as tumor necrosis factor-α and interleukin (IL)-6, and other cytotoxic molecules, such as nitric oxide and reactive oxygen species. In addition, α-LA inhibited the LPS-induced phosphorylation of ERK and p38 and its pharmacological properties were facilitated via the inhibition of the nuclear factor kappa B signaling pathway. Moreover, α-LA suppressed the activation of NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasomes, multiprotein complexes consisting of NLRP3 and caspase-1, which are involved in the innate immune response. Finally, α-LA decreased the genes accountable for the M1 phenotype, IL-1β and ICAM1, whereas it increased the genes responsible for the M2 phenotype, MRC1 and ARG1. These findings suggest that α-LA alleviates the neuroinflammatory response by regulating microglial polarization. [BMB Reports 2019; 52(10): 613-618].

Microglia: Brain cells on the move

In the last decade, tremendous progress has been made in understanding the biology of microglia - i.e. the fascinating immigrated resident immune cell population of the central nervous system (CNS). Recent literature reviews have largely dealt with the plentiful functions of microglia in CNS homeostasis, development and pathology, and the influences of sex and the microbiome. In this review, the intriguing aspect of their physical plasticity during CNS development will get specific attention. Microglia move around (mobility) and reshape their processes (motility). Microglial migration into and inside the CNS is most prominent throughout development and consequently most of the data described in this review concern mobility and motility in the changing environment of the developing brain. Here, we first define microglia based on their highly specialized age- and region-dependent gene expression signature and associated functional heterogeneity. Next, we describe their origin, the migration route of immature microglial cells towards the CNS, the mechanisms underlying their invasion of the CNS, and their spatiotemporal localization and surveying behaviour inside the developing CNS. These processes are dependent on microglial mobility and motility which are determined by the microenvironment of the CNS. Therefore, we further zoom in on the changing environment during CNS development. We elaborate on the extracellular matrix and the respective integrin receptors on microglia and we discuss the purinergic and molecular signalling in microglial mobility. In the last section, we discuss the physiological and pathological functions of microglia in which mobility and motility are involved to stress the importance of microglial 'movement'.

Endotoxin-induced cerebral pathophysiology: differences between fetus and newborn

As the comparative pathophysiology of perinatal infection in the fetus and newborn is uncertain, this study contrasted the cerebral effects of endotoxemia in conscious fetal sheep and newborn lambs. Responses to intravenous bacterial endotoxin (lipopolysaccharide, LPS) or normal saline were studied on three consecutive days in fetal sheep (LPS 1 μg/kg, n = 5; normal saline n = 5) and newborn lambs (LPS 2 μg/kg, n = 10; normal saline n = 5). Cerebro-vascular function was assessed by monitoring cerebral blood flow (CBF) and cerebral vascular resistance (CVR) over 12 h each day, and inflammatory responses were assessed by plasma TNF alpha (TNF-α), nitrate and nitrite concentrations. Brain injury was quantified by counting both resting and active macrophages in the caudate nucleus and periventricular white matter (PVWM). An acute cerebral vasoconstriction (within 1 h of LPS injection) occurred in both the fetus (ΔCVR +53%) and newborn (ΔCVR +63%); subsequently prolonged cerebral vasodilatation occurred in the fetus (ΔCVR -33%) in association with double plasma nitrate/nitrite concentrations, but not in the newborn. Abundant infiltration of activated macrophages was observed in both CN and PVWM at each age, with the extent being 2-3 times greater in the fetus (P < 0.001). In conclusion, while the fetus and newborn experience a similar acute disruption of the cerebral circulation after LPS, the fetus suffers a more prolonged circulatory disruption, a greater infiltration of activated macrophages, and an exaggerated susceptibility to brain injury.

Directed glial differentiation and transdifferentiation for neural tissue regeneration

Glial cells which are indispensable for the central nervous system development and functioning, are proven to be vulnerable to a harmful influence of pathological cues and tissue misbalance. However, they are also highly sensitive to both in vitro and in vivo modulation of their commitment, differentiation, activity and even the fate-switch by different types of bioactive molecules. Since glial cells (comprising macroglia and microglia) are an abundant and heterogeneous population of neural cells, which are almost uniformly distributed in the brain and the spinal cord parenchyma, they all create a natural endogenous reservoir of cells for potential neurogenerative processes required to be initiated in response to pathophysiological cues present in the local tissue microenvironment. The past decade of intensive investigation on a spontaneous and enforced conversion of glial fate into either alternative glial (for instance from oligodendrocytes to astrocytes) or neuronal phenotypes, has considerably extended our appreciation of glial involvement in restoring the nervous tissue cytoarchitecture and its proper functions. The most effective modulators of reprogramming processes have been identified and tested in a series of pre-clinical experiments. A list of bioactive compounds which are potent in guiding in vivo cell fate conversion and driving cell differentiation includes a selection of transcription factors, microRNAs, small molecules, exosomes, morphogens and trophic factors, which are helpful in boosting the enforced neuro-or gliogenesis and promoting the subsequent cell maturation into desired phenotypes. Herein, an issue of their utility for a directed glial differentiation and transdifferentiation is discussed in the context of elaborating future therapeutic options aimed at restoring the diseased nervous tissue.

In Vivo MRI of Functionalized Iron Oxide Nanoparticles for Brain Inflammation

Microglia are intrinsic components of the brain immune system and are activated in many central nervous system disorders. The ability to noninvasively image these cells would provide valuable information for both research and clinical applications. Today, most imaging probes for activated microglia are mainly designed for positron emission tomography (PET) and target translocator proteins that also reside on other cerebral cells. The PET images obtained are not specific for microglia-driven inflammation. Here, we describe a potential PET/MRI multimodal imaging probe that selectively targets the scavenger receptor class A (SR-A) expressed on activated microglia. These sulfated dextran-coated iron oxide (SDIO) nanoparticles are avidly taken up by microglia and appear to be nontoxic when administered intravenously in a mouse model. Intravenous administration of this SDIO demonstrated visualization by T₂^∗-weighted MRI of microglia activated by intracerebral administration of tumor necrosis factor alpha (TNF-α). The contrast was significantly enhanced by SDIO, whereas there was little to no contrast change in animals treated with nontargeted nanoparticles or untreated controls. Thus, SR-A targeting represents a promising strategy to image activated microglia in the brain.

Anti-Cytokine Therapy to Attenuate Ischemic-Reperfusion Associated Brain Injury in the Perinatal Period

Perinatal brain injury is a major cause of morbidity and long-standing disability in newborns. Hypothermia is the only therapy approved to attenuate brain injury in the newborn. However, this treatment is unfortunately only partially neuroprotective and can only be used to treat hypoxic-ischemic encephalopathy in full term infants. Therefore, there is an urgent need for adjunctive therapeutic strategies. Post-ischemic neuro-inflammation is a crucial contributor to the evolution of brain injury in neonates and constitutes a promising therapeutic target. Recently, we demonstrated encouraging neuroprotective capacities of anti-cytokine monoclonal antibodies (mAbs) in an ischemic-reperfusion (I/R) model of brain injury in the ovine fetus. The purpose of this review is to summarize the current knowledge regarding the inflammatory response in the perinatal sheep brain after I/R injury and to review our recent findings regarding the beneficial effects of treatment with anti-cytokine mAbs.

Systemic infusions of anti-interleukin-1β neutralizing antibodies reduce short-term brain injury after cerebral ischemia in the ovine fetus

Perinatal hypoxic-ischemic reperfusion (I/R)-related brain injury is a leading cause of neurologic morbidity and life-long disability in children. Infants exposed to I/R brain injury develop long-term cognitive and behavioral deficits, placing a large burden on parents and society. Therapeutic strategies are currently not available for infants with I/R brain damage, except for hypothermia, which can only be used in full term infants with hypoxic-ischemic encephalopathy (HIE). Moreover, hypothermia is only partially protective. Pro-inflammatory cytokines are key contributors to the pathogenesis of perinatal I/R brain injury. Interleukin-1β (IL-1β) is a critical pro-inflammatory cytokine, which has been shown to predict the severity of HIE in infants. We have previously shown that systemic infusions of mouse anti-ovine IL-1β monoclonal antibody (mAb) into fetal sheep resulted in anti-IL-1β mAb penetration into brain, reduced I/R-related increases in IL-1β expression and blood-brain barrier (BBB) dysfunction in fetal brain. The purpose of the current study was to examine the effects of systemic infusions of anti-IL-1β mAb on short-term I/R-related parenchymal brain injury in the fetus by examining: 1) histopathological changes, 2) apoptosis and caspase-3 activity, 3) neuronal degeneration 4) reactive gliosis and 5) myelin basic protein (MBP) immunohistochemical staining. The study groups included non-ischemic controls, placebo-treated ischemic, and anti-IL-1β mAb treated ischemic fetal sheep at 127days of gestation. The systemic intravenous infusions of anti-IL-1β mAb were administered at fifteen minutes and four hours after in utero brain ischemia. The duration of each infusion was two hours. Parenchymal brain injury was evaluated by determining pathological injury scores, ApopTag® positive cells/mm², caspase-3 activity, Fluoro-Jade B positive cells/mm², glial fibrillary acidic protein (GFAP) and MBP staining in the brains of fetal sheep 24h after 30min of ischemia. Treatment with anti-IL-1β mAb reduced (P<0.05) the global pathological injury scores, number of apoptotic positive cells/mm², and caspase-3 activity after ischemia in fetal sheep. The regional pathological scores and Fluoro-Jade B positive cells/mm² did not differ between the placebo- and anti-IL-1β mAb treated ischemic fetal sheep. The percent of the cortical area stained for GFAP was lower (P<0.05) in the placebo ischemic treated than in the non-ischemic group, but did not differ between the placebo- and anti-IL-1β mAb treated ischemic groups. MBP immunohistochemical expression did not differ among the groups. In conclusion, infusions of anti-IL-1β mAb attenuate short-term I/R-related histopathological tissue injury, apoptosis, and reduce I/R-related increases in caspase-3 activity in ovine fetal brain. Therefore, systemic infusions of anti-IL-1β mAb attenuate short-term I/R-related parenchymal brain injury in the fetus.

Impact of Inflammation on the Blood-Neural Barrier and Blood-Nerve Interface: From Review to Therapeutic Preview

A number of nervous system disorders are characterized by a state of inflammation (neuroinflammation) in which members of the innate immune system, most notably mast cells and microglia-acting as single entities and in unison-produce inflammatory molecules that play major roles. A neuroinflammatory environment can weaken not only blood-nerve and blood-brain barrier (BBB) integrity but also that of the blood-spinal cord barrier. Mast cells, with their distribution in peripheral nerves and the central nervous system, are positioned to influence blood-nerve barrier characteristics. Being close also to the perivasculature and on the brain side of the BBB, the mast cell is well positioned to disrupt BBB function. Interestingly, tissue damage and/or stress activates homeostatic mechanisms/molecules expressed by mast cells and microglia, and includes N-acylethanolamines. Among the latter, N-palmitoylethanolamine has distinguished itself as a key component in supporting homeostasis of the organism against external stressors capable of provoking inflammation. This review will discuss the pathobiology of neuroinflammation with emphasis on mast cells and microglia, their roles in BBB health, and novel therapeutic opportunities, including nanoscale delivery for targeting these immune cells with a view to maintain the BBB.

Hypertonic saline attenuates expression of Notch signaling and proinflammatory mediators in activated microglia in experimentally induced cerebral ischemia and hypoxic BV-2 microglia

Background

Ischemic stroke is a major disease that threatens human health in ageing population. Increasing evidence has shown that neuroinflammatory mediators play crucial roles in the pathophysiology of cerebral ischemia injury. Notch signaling is recognized as the cell fate signaling but recent evidence indicates that it may be involved in the inflammatory response in activated microglia in cerebral ischemia. Previous report in our group demonstrated hypertonic saline (HS) could reduce the release of interleukin-1 beta and tumor necrosis factor-alpha in activated microglia, but the underlying molecular and cellular mechanisms have remained uncertain. This study was aimed to explore whether HS would partake in regulating production of proinflammatory mediators through Notch signaling.

Results

HS markedly attenuated the expression of Notch-1, NICD, RBP-JK and Hes-1 in activated microglia both in vivo and in vitro. Remarkably, HS also reduced the expression of iNOS in vivo, while the in vitro levels of inflammatory mediators Phos-NF-κB, iNOS and ROS were reduced by HS as well.

Conclusion

Our results suggest that HS may suppress of inflammatory mediators following ischemia/hypoxic through the Notch signaling which operates synergistically with NF-κB pathway in activated microglia. Our study has provided the morphological and biochemical evidence that HS can attenuate inflammation reaction and can be neuroprotective in cerebral ischemia, thus supporting the use of hypertonic saline by clinicians in patients with an ischemia stroke.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-017-0351-6) contains supplementary material, which is available to authorized users.

Pterostilbene ameliorates intracerebroventricular streptozotocin induced memory decline in rats

There is strong evidence that mitochondrial dysfunction mediated oxidative stress results in aging and energy metabolism deficits thus playing a prime role in pathogenesis of Alzheimer's disease, neuronal death and cognitive dysfunction. Evidences accrued in empirical studies suggest the antioxidant, anticancer and anti-inflammatory activities of the phytochemical pterostilbene (PTS). PTS also exhibits favourable pharmacokinetic attributes compared to other stilbenes. Hence, in the present study, we explored the neuroprotective role of PTS in ameliorating the intracerebroventricular administered streptozotocin (STZ) induced memory decline in rats. PTS at doses of 10, 30 and 50 mg/kg, was administered orally to STZ administered Sprague-Dawley (SD) rats. The learning and memory tests, Morris water maze test and novel object recognition test were performed which revealed improved cognition on PTS treatment. Further, there was an overall improvement in brain antioxidant parameters like elevated catalase and superoxide dismutase activities, GSH levels, lowered levels of nitrites, lipid peroxides and carbonylated proteins. There was improved cholinergic transmission as evident by decreased acetylcholinesterase activities. The action of ATPases (Na+ K+, Ca2+ and Mg2+) indicating the maintenance of cell membrane potential was also augmented. mRNA expression of battery of genes involved in cellular mitochondrial biogenesis and inflammation showed variations which extrapolate to hike in mitochondrial biogenesis and abated inflammation. The histological findings corroborated the effective role of PTS in countering STZ induced structural aberrations in brain.

Spirulina and C-phycocyanin reduce cytotoxicity and inflammation-related genes expression of microglial cells

OBJECTIVE

Our aim was to investigate the effects of Spirulina on BV-2 microglial cell cytotoxicity and inflammatory genes expression.

METHODS

BV-2 microglial cells were treated with lipopolysaccharide (LPS) (1 µg/ml) and various concentrations of Spirulina platensis water extract or its active component (C-phycocyanin (C-PC)) for 24 hours. Cytotoxicity (lactate dehydrogenase (LDH) release) and expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) mRNAs were assayed.

RESULTS

LPS increased LDH production and up-regulated expression of iNOS, COX-2, TNF-α, and IL-6 by BV-2 microglial cells. However, Spirulina platensis water extract and C-PC significantly reduced LPS-induced LDH release, and expression of iNOS, COX-2, TNF-α, and IL-6 mRNAs.

CONCLUSION

Spirulina can reduce the cytotoxicity and inhibit expression of inflammation-related genes of LPS-stimulated BV-2 microglial cells.

Expression of microRNAs miR21, miR146a, and miR155 in tuberous sclerosis complex cortical tubers and their regulation in human astrocytes and SEGA-derived cell cultures

Tuberous sclerosis complex (TSC) is a genetic disease presenting with multiple neurological symptoms including epilepsy, mental retardation, and autism. Abnormal activation of various inflammatory pathways has been observed in astrocytes in brain lesions associated with TSC. Increasing evidence supports the involvement of microRNAs in the regulation of astrocyte-mediated inflammatory response. To study the role of inflammation-related microRNAs in TSC, we employed real-time PCR and in situ hybridization to characterize the expression of miR21, miR146a, and miR155 in TSC lesions (cortical tubers and subependymal giant cell astrocytomas, SEGAs). We observed an increased expression of miR21, miR146a, and miR155 in TSC tubers compared with control and perituberal brain tissue. Expression was localized in dysmorphic neurons, giant cells, and reactive astrocytes and positively correlated with IL-1β expression. In addition, cultured human astrocytes and SEGA-derived cell cultures were used to study the regulation of the expression of these miRNAs in response to the proinflammatory cytokine IL-1β and to evaluate the effects of overexpression or knockdown of miR21, miR146a, and miR155 on inflammatory signaling. IL-1β stimulation of cultured glial cells strongly induced intracellular miR21, miR146a, and miR155 expression, as well as miR146a extracellular release. IL-1β signaling was differentially modulated by overexpression of miR155 or miR146a, which resulted in pro- or anti-inflammatory effects, respectively. This study provides supportive evidence that inflammation-related microRNAs play a role in TSC. In particular, miR146a and miR155 appear to be key players in the regulation of astrocyte-mediated inflammatory response, with miR146a as most interesting anti-inflammatory therapeutic candidate.

CXCL5 signaling is a shared pathway of neuroinflammation and blood-brain barrier injury contributing to white matter injury in the immature brain

Background

In very preterm infants, white matter injury is a prominent brain injury, and hypoxic ischemia (HI) and infection are the two primary pathogenic factors of this injury. Microglia and microvascular endothelial cells closely interact; therefore, a common signaling pathway may cause neuroinflammation and blood–brain barrier (BBB) damage after injury to the immature brain. CXC chemokine ligand 5 (CXCL5) is produced in inflammatory and endothelial cells by various organs in response to insults. CXCL5 levels markedly increased in the amniotic cavity in response to intrauterine infection and preterm birth in clinical studies. The objective of this study is to determine whether CXCL5 signaling is a shared pathway of neuroinflammation and BBB injury that contributes to white matter injury in the immature brain.

Methods

Postpartum day 2 (P2) rat pups received lipopolysaccharide (LPS) followed by 90-min HI. Immunohistochemical analyses were performed to determine microglial activation, neutrophil infiltration, BBB damage, and myelin basic protein and glial fibrillary acidic protein expression. Immunofluorescence experiments were performed to determine the cellular distribution of CXCL5. Pharmacological tests were performed to inhibit or enhance CXCL5 activity.

Results

On P2, predominant increases in microglial activation and BBB damage were observed 24 h after LPS-sensitized HI induction, and white matter injury (decreased myelination and increased astrogliosis) was observed on P12 compared with controls. Immunohistochemical analyses revealed increased CXCL5 expression in the white matter 6 and 24 h after insult. Immunofluorescence experiments revealed upregulated CXCL5 expression in the activated microglia and endothelial cells 24 h after insult. CXCL5 inhibition by SB225002, a selective nonpeptide inhibitor of CXCR2, significantly attenuated microglial activation and BBB damage, increased myelination, and reduced astrogliosis in the white matter after LPS-sensitized HI. In addition, CXCL5-sensitized HI or CXCL5 alone significantly induced BBB damage and white matter injury in association with different neuroinflammation mechanisms. CXCL5-sensitized HI-induced microglial activation and neutrophil infiltration, whereas CXCL5 alone predominately caused neutrophil infiltration.

Conclusions

CXCL5 is a potential biomarker for white matter injury in preterm infants. Pharmacological blockade of CXCL5 signaling that attenuates dysregulated neuroinflammation can be used a therapeutic strategy against white matter injury in the immature brain.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0474-6) contains supplementary material, which is available to authorized users.

Effects of Acute Systemic Hypoxia and Hypercapnia on Brain Damage in a Rat Model of Hypoxia-Ischemia

Therapeutic hypercapnia has the potential for neuroprotection after global cerebral ischemia. Here we further investigated the effects of different degrees of acute systemic hypoxia in combination with hypercapnia on brain damage in a rat model of hypoxia and ischemia. Adult wistar rats underwent unilateral common carotid artery (CCA) ligation for 60 min followed by ventilation with normoxic or systemic hypoxic gas containing 11%O2,13%O2,15%O2 and 18%O2 (targeted to PaO2 30-39 mmHg, 40-49 mmHg, 50-59 mmHg, and 60-69 mmHg, respectively) or systemic hypoxic gas containing 8% carbon dioxide (targeted to PaCO2 60-80 mmHg) for 180 min. The mean artery pressure (MAP), blood gas, and cerebral blood flow (CBF) were evaluated. The cortical vascular permeability and brain edema were examined. The ipsilateral cortex damage and the percentage of hippocampal apoptotic neurons were evaluated by Nissl staining and terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate-biotin nick end labeling (TUNEL) assay as well as flow cytometry, respectively. Immunofluorescence and western blotting were performed to determine aquaporin-4 (AQP4) expression. In rats treated with severe hypoxia (PaO2 < 50 mmHg), hypercapnia augmented the decline of MAP with cortical CBF and damaged blood-brain barrier permeability (p < 0.05). In contrast, in rats treated with mild to moderate hypoxia (PaO2 > 50 mmHg), hypercapnia protected against these pathophysiological changes. Moreover, hypercapnia treatment significantly reduced brain damage in the ischemic ipsilateral cortex and decreased the percentage of apoptotic neurons in the hippocampus after the CCA ligated rats were exposed to mild or moderate hypoxemia (PaO2 > 50 mmHg); especially under mild hypoxemia (PaO2 > 60 mmHg), hypercapnia significantly attenuated the expression of AQP4 protein with brain edema (p < 0.05). Hypercapnia exerts beneficial effects under mild to moderate hypoxemia and augments detrimental effects under severe hypoxemia on brain damage in a rat model of hypoxia-ischemia.

Co-ultramicronized Palmitoylethanolamide/Luteolin in the Treatment of Cerebral Ischemia: from Rodent to Man

Acute ischemic stroke, the most frequent cause of permanent disability in adults worldwide, results from transient or permanent reduction in regional cerebral blood flow and involves oxidative stress and inflammation. Despite the success of experimental animal models of stroke in identifying anti-inflammatory/neuroprotective compounds, translation of these putative neuroprotectants to human clinical trials has failed to produce a positive outcome. Tissue injury and stress activate endogenous mechanisms which function to restore homeostatic balance and prevent further damage by upregulating the synthesis of lipid signaling molecules, including N-palmitoylethanolamine (PEA or palmitoylethanolamide). PEA exerts neuroprotection and reduces inflammatory secondary events associated with brain ischemia reperfusion injury (middle cerebral artery occlusion (MCAo)). Here, we examined the neuroprotective potential of a co-ultramicronized composite containing PEA and the antioxidant flavonoid luteolin (10:1 by mass), nominated co-ultraPEALut. The study consisted of two arms. In the first, rats subjected to MCAo and treated with co-ultraPEALut post-ischemia showed reduced edema and brain infract volume, improved neurobehavioral functions, and reduced expression of pro-inflammatory markers and astrocyte markers. In the second arm, a cohort of 250 stroke patients undergoing neurorehabilitation on either an inpatient or outpatient basis were treated for 60 days with a pharmaceutical preparation of co-ultraPEALut (Glialia). At baseline and after 30 days of treatment, all patients underwent a battery of evaluations to assess neurological status, impairment of cognitive abilities, the degree of spasticity, pain, and independence in daily living activities. All indices showed statistically significant gains at study end. Despite its observational nature, this represents the first description of co-ultraPEALut administration to human stroke patients and clinical improvement not otherwise expected from spontaneous recovery. Further, controlled trials are warranted to confirm the utility of co-ultraPEALut to improve clinical outcome in human stroke.

Acute Blockage of Notch Signaling by DAPT Induces Neuroprotection and Neurogenesis in the Neonatal Rat Brain After Stroke

Notch signaling is critically involved in various biological events. Notch undergoes cleavage by the γ-secretase enzyme to release Notch intracellular domain that will translocate into nucleus to result in expression of target gene. γ-Secretase inhibitors have been developed as potential treatments for neurological degenerative diseases, but its effects against ischemic injury remain relatively uncertain. In the present study, we demonstrated that N-[N-(3, 5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT), a γ-secretase inhibitor not only rescued the cerebral hypoperfusion or ischemia neonatal rats from death, reduced apoptosis in penumbra, but also reduced brain infarct size. Furthermore, DAPT elicited some morphologic hallmarks such as neurogenesis and angiogenesis that related to the brain repair and functional recovery after stroke: increased accumulations of newborn cells in the peri-infarct region with a higher fraction of them adopting immature neuronal and glial markers instead of microglial markers on 5 days, enhanced vascular densities in penumbra at 14 days, and evident regulations of the gene profiles associated with neurogenesis in penumbral tissues. The current results suggest that DAPT is a potential neuroprotectants against ischemic injury in immature brain, and future treatment strategies such as clinical trials using γ-secretase inhibitors would be an attractive therapy for perinatal ischemia.

Immunity and Inflammation in Epilepsy

This review reports the available evidence on the activation of the innate and adaptive branches of the immune system and the related inflammatory processes in epileptic disorders and the putative pathogenic role of inflammatory processes developing in the brain, as indicated by evidence from experimental and clinical research. Indeed, there is increasing knowledge supporting a role of specific inflammatory mediators and immune cells in the generation and recurrence of epileptic seizures, as well as in the associated neuropathology and comorbidities. Major challenges in this field remain: a better understanding of the key inflammatory pathogenic pathways activated in chronic epilepsy and during epileptogenesis, and how to counteract them efficiently without altering the homeostatic tissue repair function of inflammation. The relevance of this information for developing novel therapies will be highlighted.

Low-dose ribavirin treatments attenuate neuroinflammatory activation of BV-2 Cells by interfering with inducible nitric oxide synthase

Microglia play a key role in defending central nervous system from various internal and external threats. However, their excessive and/or chronic activation is associated with deleterious effects in a variety of neurodegenerative diseases. Previously, we have shown that ribavirin when applied in clinically relevant dosage (10 μM) modulates activated microglia in complex fashion inducing both anti- and proinflammatory effects, simultaneously causing cytotoxicity. Here, we examined potential of low-dose ribavirin (0.1 and 1 μM) to modulate activated BV-2 microglia. Morphological and functional activation of BV-2 cells was achieved with lipopolysaccharide (LPS) stimulation. Our results demonstrated that low-dose ribavirin did not induce cell death, while 10 μM ribavirin promoted LPS induced apoptosis. We determined that 1 μM ribavirin was equally efficient in deactivation of LPS induced morphological changes as 10 μM ribavirin treatment. Ribavirin showed halfway success in reducing markers of functional activation of microglia. Namely, none of the doses had effect on LPS triggered production of proinflammatory cytokine tumor necrosis factor alpha. On the other hand, low-dose ribavirin proved its effectiveness in reduction of another inflammatory mediator, nitric oxide, by inhibiting inducible form of nitric oxide synthase. Our results imply that low-dose ribavirin may alleviate nitrosative stress during neuroinflammation.

TNFR1-JNK signaling is the shared pathway of neuroinflammation and neurovascular damage after LPS-sensitized hypoxic-ischemic injury in the immature brain

Background

Hypoxic-ischemia (HI) and inflammation are the two major pathogenic mechanisms of brain injury in very preterm infants. The neurovascular unit is the major target of HI injury in the immature brain. Systemic inflammation may worsen HI by up-regulating neuroinflammation and disrupting the blood–brain barrier (BBB). Since neurons and oligodendrocytes, microvascular endothelial cells, and microglia may closely interact with each other, there may be a common signaling pathway leading to neuroinflammation and neurovascular damage after injury in the immature brain. TNF-α is a key pro-inflammatory cytokine that acts through the TNF receptor (TNFR), and c-Jun N-terminal kinases (JNK) are important stress-responsive kinases.

Objective

To determine if TNFR1-JNK signaling is a shared pathway underlying neuroinflammation and neurovascular injury after lipopolysaccharide (LPS)-sensitized HI in the immature brain.

Methods

Postpartum (P) day-5 mice received LPS or normal saline (NS) injection before HI. Immunohistochemistry, immunoblotting and TNFR1- and TNFR2-knockout mouse pups were used to determine neuroinflammation, BBB damage, TNF-α expression, JNK activation, and cell apoptosis. The cellular distribution of p-JNK, TNFR1/TNFR2 and cleaved caspase-3 were examined using immunofluorescent staining.

Results

The LPS + HI group had significantly greater up-regulation of activated microglia, TNF-α and TNFR1 expression, and increases of BBB disruption and cleaved caspase-3 levels at 24 hours post-insult, and showed more cortical and white matter injury on P17 than the control and NS + HI groups. Cleaved caspase-3 was highly expressed in microvascular endothelial cells, neurons, and oligodendroglial precursor cells. LPS-sensitized HI also induced JNK activation and up-regulation of TNFR1 but not TNFR2 expression in the microglia, endothelial cells, neurons, and oligodendrocyte progenitors, and most of the TNFR1-positive cells co-expressed p-JNK. Etanercept (a TNF-α inhibitor) and AS601245 (a JNK inhibitor) protected against LPS-sensitized HI brain injury. The TNFR1-knockout but not TNFR2-knockout pups had significant reduction in JNK activation, attenuation of microglial activation, BBB breakdown and cleaved caspase-3 expression, and showed markedly less cortical and white matter injury than the wild-type pups after LPS-sensitized HI.

Conclusion

TNFR1-JNK signaling is the shared pathway leading to neuroinflammation and neurovascular damage after LPS-sensitized HI in the immature brain.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-014-0215-2) contains supplementary material, which is available to authorized users.

Anti-inflammatory mechanisms of N-adamantyl-4-methylthiazol-2-amine in lipopolysaccharide-stimulated BV-2 microglial cells

The activation of microglia is crucially associated with the neurodegeneration observed in many neuroinflammatory pathologies, such as multiple sclerosis, Parkinson's disease, and Alzheimer's disease. We have examined various thiazole derivatives with the goal of developing new anti-neuroinflammatory drugs. Thiazole derivatives are attractive candidates for drug development, because they are efficiently synthesized and active against a number of disease organisms and conditions, including neurodegenerative disorders. The present study investigated the effects of a new compound, N-adamantyl-4-methylthiazol-2-amine (KHG26693), against lipopolysaccharide (LPS)-induced inflammation in cultured BV-2 microglial cells. KHG26693 suppressed several inflammatory responses in LPS-activated cells, as evidenced by decreased levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), hydrogen peroxide (H(2)O(2)), reactive oxygen species (ROS), nitric oxide (NO), and lipid peroxidation. These anti-inflammatory/antioxidative actions occurred as a result of the downregulation of NADPH oxidase (NOX), inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2) content, but not as a result of the upregulation of superoxide dismutase (SOD) or catalase activity. The pharmacological properties of KHG26693 were also facilitated via inhibition of both the cluster of differentiation 14 (CD14)/toll-like receptor 4 (TLR4)-dependent nuclear factor kappa B (NF-κB) signaling pathway and extracellular signal-regulated kinase (ERK) phosphorylation. Furthermore, KHG26693 successfully blocked the migration of LPS-activated microglia, most likely by modulating the ERK pathway. Taken together, these results demonstrate that the anti-inflammatory and antioxidative actions of KHG26693 are mediated, at least in part, through the control of microglial activation.

TLR4-mediated brain inflammation halts neurogenesis: impact of hormonal replacement therapy

Experimental and epidemiological data show that the severity and the duration of brain inflammation are attenuated in females compared to males. This attenuated brain inflammation is ascribed to 17β-estradiol. However, several studies suggest that 17β-estradiol is also endowed with proinflammatory properties. The aim of the present study is to assess the effect of hormonal replacement therapies on lipopolysaccharide (LPS)-induced brain inflammation and its consequent effect on newly born neurons. Bilaterally ovariectomized rats received intrastriatal injection of LPS (250 ng/μl) and were subsequently given daily subcutaneous injections of either vehicle, 17β-estradiol (25 μg/kg) or 17β-estradiol and progesterone (5 mg/kg). Microglial activation and newly born neurons in the rostral migratory stream were monitored using double immunofluorescence. Nuclear factor κB (NFκB) signaling pathway and its target inflammatory proteins were assessed by either western blot [cyclooxygenase-2 (COX-2) and interleukin-6 (IL-6)] or enzyme-linked immunosorbent assay [tumor necrosis factor-α (TNF-α)]. LPS-induced activation of microglia, promoted NFκB signaling pathway and enhanced the production of proinflammatory proteins (TNF-α and COX-2). These proinflammatory responses were not attenuated by 17β-estradiol injection. Supplementation of 17β-estradiol with progesterone significantly dampened these proinflammatory processes. Interestingly, LPS-induced brain inflammation dampened the number of newly born neurons in the rostral migratory stream. Administration of combined 17β-estradiol and progesterone resulted in a significantly higher number of newly born neurons when compared to those seen in rats given either vehicle or 17β-estradiol alone. These data strongly suggest that combined 17β-estradiol and progesterone, and not 17β-estradiol alone, rescues neurogenesis from the deleterious effect of brain inflammation likely via the inhibition of the signaling pathways leading to the activation of proinflammatory genes.

Mast cells, glia and neuroinflammation: partners in crime?

Glia and microglia in particular elaborate pro-inflammatory molecules that play key roles in central nervous system (CNS) disorders from neuropathic pain and epilepsy to neurodegenerative diseases. Microglia respond also to pro-inflammatory signals released from other non-neuronal cells, mainly those of immune origin such as mast cells. The latter are found in most tissues, are CNS resident, and traverse the blood-spinal cord and blood-brain barriers when barrier compromise results from CNS pathology. Growing evidence of mast cell-glia communication opens new perspectives for the development of therapies targeting neuroinflammation by differentially modulating activation of non-neuronal cells that normally control neuronal sensitization - both peripherally and centrally. Mast cells and glia possess endogenous homeostatic mechanisms/molecules that can be up-regulated as a result of tissue damage or stimulation of inflammatory responses. Such molecules include the N-acylethanolamine family. One such member, N-palmitoylethanolamine is proposed to have a key role in maintenance of cellular homeostasis in the face of external stressors provoking, for example, inflammation. N-Palmitoylethanolamine has proven efficacious in mast-cell-mediated experimental models of acute and neurogenic inflammation. This review will provide an overview of recent progress relating to the pathobiology of neuroinflammation, the role of microglia, neuroimmune interactions involving mast cells and the possibility that mast cell-microglia cross-talk contributes to the exacerbation of acute symptoms of chronic neurodegenerative disease and accelerates disease progression, as well as promoting pain transmission pathways. We will conclude by considering the therapeutic potential of treating systemic inflammation or blockade of signalling pathways from the periphery to the brain in such settings.

Transcription-related element gene expression pattern differs between microglia and macrophages during inflammation

OBJECTIVE AND DESIGN

Microglia and macrophages play an important role in the innate and adaptive immune systems. Although the resident location of these cells is different, their functions during the polarization response due to various stimuli are very similar. The present study aimed to analyze differences in microglial and macrophage gene expression during inflammation.

METHODS

Mouse microglial BV-2 cells were exposed to LPS (10 ng/ml). The levels of gene expression were measured using real-time RT-PCR and whole transcriptome shotgun sequencing.

RESULTS

The level of Jmjd3 gene expression in activated microglia showed a similar pattern to that of macrophages. In both cell types, genes associated with the inflammation response were generally increased whereas genes associated with metabolic and biosynthetic processes were decreased. However, the expression of transcription-related elements other than genes encoding histone modification enzymes showed a significantly different pattern between microglia and macrophages.

CONCLUSION

Although the function and the gene expression levels of histone modification enzymes showed a similar pattern in microglia and macrophages during inflammation, the expression of transcription-related elements in both cell types showed a completely different pattern.

Neuroinflammation and neuroimmune dysregulation after acute hypoxic-ischemic injury of developing brain

Hypoxic-ischemic (HI) injury to developing brain results from birth asphyxia in neonates and from cardiac arrest in infants and children. It is associated with varying degrees of neurologic sequelae, depending upon the severity and length of HI. Global HI triggers a series of cellular and biochemical pathways that lead to neuronal injury. One of the key cellular pathways of neuronal injury is inflammation. The inflammatory cascade comprises activation and migration of microglia - the so-called "brain macrophages," infiltration of peripheral macrophages into the brain, and release of cytotoxic and proinflammatory cytokines. In this article, we review the inflammatory and immune mechanisms of secondary neuronal injury after global HI injury to developing brain. Specifically, we highlight the current literature on microglial activation in relation to neuronal injury, proinflammatory and anti-inflammatory/restorative pathways, the role of peripheral immune cells, and the potential use of immunomodulators as neuroprotective compounds.

The inflammatory cellular constituents of foetal and infant leptomeninges: a survey of hospital-based autopsies without trauma

OBJECTIVES

Notwithstanding the lack of definitive evidence from studies conducted to date, inflammatory infiltrates and iron deposition in the leptomeninges are routinely used as forensic markers of traumatic brain injury. We investigated the presence of these forensic markers of trauma in neonates and infants, with the objective of determining their suitability for use in forensic cases.

METHODS

Leptomeninges derived from non-traumatic deaths were studied. Thirty-three cases were divided into groups 1 and 2, according to set age groups. Inflammatory cells and iron in these groups were quantified.

RESULTS

CD45, CD68 and CD163 positive inflammatory cells were identified in the leptomeninges of sections of the cerebellum, brain stem and cortex of all 33 cases of non-traumatic infant deaths surveyed in this study. There were no significant differences between the two groups. Iron was found in the leptomeninges in several cases, even those without recent haemorrhage. Overall within the two subgroups, the numbers of inflammatory cells and iron containing cells were not significantly different.

CONCLUSION

These findings demonstrate that inflammatory cells and iron in the leptomeninges can be found in natural and non-traumatic conditions. Further, two cases with no reported neuropathology demonstrated the presence of inflammatory cells and iron. Thus, cautious interpretation of the presence of inflammatory cells and iron containing cells in forensic paediatric cases is recommended.

Lipoic acid treatment after brain injury: study of the glial reaction

After trauma brain injury, oxidative substances released to the medium provoke an enlargement of the initial lesion, increasing glial cell activation and, occasionally, an influx of immune cells into the central nervous system, developing the secondary damage. In response to these stimuli, microglia are activated to perform upregulation of intracellular enzymes and cell surface markers to propagate the immune response and phagocytosis of cellular debris. The phagocytosis of debris and dead cells is essential to limit the inflammatory reaction and potentially prevent extension of the damage to noninjured regions. Lipoic acid has been reported as a neuroprotectant by acting as an antioxidant and anti-inflammatory agent. Furthermore, angiogenic effect promoted by lipoic acid has been recently shown by our group as a crucial process for neural regeneration after brain injury. In this work, we focus our attention on the lipoic acid effect on astroglial and microglial response after brain injury.

Entada africana fraction CH₂Cl₂/MEOH 5% inhibits inducible nitric oxide synthase and pro-inflammatory cytokines gene expression induced by lipopolysaccharide in microglia

Background

Inflammatory response in the CNS mediated by microglia cells play an important role in host defense and is implicated in the pathology of neurodegenerative diseases. We investigated the capacity of Entada africana to protect microglia from inflammatory insults by exploring the effect of the CH₂Cl₂/MEOH 5% fraction (Ea5) on pro-inflammatory cytokines mRNA expression. Finally, we studied the effect of Ea5 on the inhibition of p38 MAPK Kinase. The results were compared to those obtained with Baicalin, a well reported anti-inflammatory flavonoid.

Methods

Barks from E. africana were harvested in 2010, in the west region of Cameroon. A crude extract was prepared using CH₂Cl₂/MEOH 1:1 V/V. The crude extract obtained was further fractionated by flash chromatography. A mouse microglia cell line (N9) was stimulated by LPS with or without different concentrations of Baicalin and Ea5. The release of NO was evaluated using the Griess method. The expression of pro-inflammatory cytokines mRNA (TNFα, IL-1β, IL-6) and iNOS/NO were measured by RT- PCR. The inhibition of p38 MAPK Kinase was assessed using ELISA.

Results

We found that Ea5, as well as Baicalin inhibited LPS-induced NO production in a dose dependent manner. Ea5 was most active in term of NO inhibition (87.07%), in comparison to Baicalin (70.85%). The expression of TNFα, IL-1β, IL-6 and iNOS was strongly suppressed by Ea5 in microglia. Ea5 also inhibited the activity of p38MAPK Kinase, up to 30% for the concentrations tested, whereas a prominent inhibition was obtained with Baicalin.

Conclusion

These results suggest that E. africana may contain promising compounds useful for the treatment of diseases cause by over-activation of microglia such as Alzheimer disease and other neurological diseases.

JNK and NADPH oxidase involved in fluoride-induced oxidative stress in BV-2 microglia cells

Excessive fluoride may cause central nervous system (CNS) dysfunction, and oxidative stress is a recognized mode of action of fluoride toxicity. In CNS, activated microglial cells can release more reactive oxygen species (ROS), and NADPH oxidase (NOX) is the major enzyme for the production of extracellular superoxide in microglia. ROS have been characterized as an important secondary messenger and modulator for various mammalian intracellular signaling pathways, including the MAPK pathways. In this study we examined ROS production and TNF-α, IL-1β inflammatory cytokines releasing, and the expression of MAPKs in BV-2 microglia cells treated with fluoride. We found that fluoride increased JNK phosphorylation level of BV-2 cells and pretreatment with JNK inhibitor SP600125 markedly reduced the levels of intracellular O₂^·− and NO. NOX inhibitor apocynin and iNOS inhibitor SMT dramatically decreased NaF-induced ROS and NO generations, respectively. Antioxidant melatonin (MEL) resulted in a reduction in JNK phosphorylation in fluoride-stimulated BV-2 microglia. The results confirmed that NOX and iNOS played an important role in fluoride inducing oxidative stress and NO production and JNK took part in the oxidative stress induced by fluoride and meanwhile also could be activated by ROS in fluoride-treated BV-2 cells.

Glucocorticosteroids in nano-sterically stabilized liposomes are efficacious for elimination of the acute symptoms of experimental cerebral malaria

Cerebral malaria is the most severe complication of Plasmodium falciparum infection, and a leading cause of death in children under the age of five in malaria-endemic areas. We report high therapeutic efficacy of a novel formulation of liposome-encapsulated water-soluble glucocorticoid prodrugs, and in particular β-methasone hemisuccinate (BMS), for treatment of experimental cerebral malaria (ECM), using the murine P. berghei ANKA model. BMS is a novel derivative of the potent steroid β-methasone, and was specially synthesized to enable remote loading into nano-sterically stabilized liposomes (nSSL), to form nSSL-BMS. The novel nano-drug, composed of nSSL remote loaded with BMS, dramatically improves drug efficacy and abolishes the high toxicity seen upon administration of free BMS. nSSL-BMS reduces ECM rates in a dose-dependent manner and creates a survival time-window, enabling administration of an antiplasmodial drug, such as artemisone. Administration of artemisone after treatment with the nSSL-BMS results in complete cure. Treatment with BMS leads to lower levels of cerebral inflammation, demonstrated by changes in cytokines, chemokines, and cell markers, as well as diminished hemorrhage and edema, correlating with reduced clinical score. Administration of the liposomal formulation results in accumulation of BMS in the brains of sick mice but not of healthy mice. This steroidal nano-drug effectively eliminates the adverse effects of the cerebral syndrome even when the treatment is started at late stages of disease, in which disruption of the blood-brain barrier has occurred and mice show clear signs of neurological impairment. Overall, sequential treatment with nSSL-BMS and artemisone may be an efficacious and well-tolerated therapy for prevention of CM, elimination of parasites, and prevention of long-term cognitive damage.

Glia and mast cells as targets for palmitoylethanolamide, an anti-inflammatory and neuroprotective lipid mediator

Glia are key players in a number of nervous system disorders. Besides releasing glial and neuronal signaling molecules directed to cellular homeostasis, glia respond also to pro-inflammatory signals released from immune-related cells, with the mast cell being of particular interest. A proposed mast cell-glia communication may open new perspectives for designing therapies to target neuroinflammation by differentially modulating activation of non-neuronal cells normally controlling neuronal sensitization-both peripherally and centrally. Mast cells and glia possess endogenous homeostatic mechanisms/molecules that can be upregulated as a result of tissue damage or stimulation of inflammatory responses. Such molecules include the N-acylethanolamines, whose principal family members are the endocannabinoid N-arachidonoylethanolamine (anandamide), and its congeners N-stearoylethanolamine, N-oleoylethanolamine, and N-palmitoylethanolamine (PEA). A key role of PEA may be to maintain cellular homeostasis when faced with external stressors provoking, for example, inflammation: PEA is produced and hydrolyzed by microglia, it downmodulates mast cell activation, it increases in glutamate-treated neocortical neurons ex vivo and in injured cortex, and PEA levels increase in the spinal cord of mice with chronic relapsing experimental allergic encephalomyelitis. Applied exogenously, PEA has proven efficacious in mast cell-mediated experimental models of acute and neurogenic inflammation. This fatty acid amide possesses also neuroprotective effects, for example, in a model of spinal cord trauma, in a delayed post-glutamate paradigm of excitotoxic death, and against amyloid β-peptide-induced learning and memory impairment in mice. These actions may be mediated by PEA acting through "receptor pleiotropism," i.e., both direct and indirect interactions of PEA with different receptor targets, e.g., cannabinoid CB2 and peroxisome proliferator-activated receptor-alpha.

Mast cell-glia axis in neuroinflammation and therapeutic potential of the anandamide congener palmitoylethanolamide

Communication between the immune and nervous systems depends a great deal on pro-inflammatory cytokines. Both astroglia and microglia, in particular, constitute an important source of inflammatory mediators and may have fundamental roles in central nervous system (CNS) disorders from neuropathic pain and epilepsy to neurodegenerative diseases. Glial cells respond also to pro-inflammatory signals released from cells of immune origin. In this context, mast cells are of particular relevance. These immune-related cells, while resident in the CNS, are able to cross a compromised blood-spinal cord and blood-brain barrier in cases of CNS pathology. Emerging evidence suggests the possibility of mast cell-glia communication, and opens exciting new perspectives for designing therapies to target neuroinflammation by differentially modulating the activation of non-neuronal cells normally controlling neuronal sensitization-both peripherally and centrally. This review aims to provide an overview of recent progress relating to the pathobiology of neuroinflammation, the role of glia, neuro-immune interactions involving mast cells and the possibility that glia-mast cell interactions contribute to exacerbation of acute symptoms of chronic neurodegenerative disease and accelerated disease progression, as well as promotion of pain transmission pathways. Using this background as a starting point for discussion, we will consider the therapeutic potential of naturally occurring fatty acid ethanolamides, such as palmitoylethanolamide in treating systemic inflammation or blockade of signalling pathways from the periphery to the brain in such settings.

Oligodendroglial alterations and the role of microglia in white matter injury: relevance to schizophrenia

Schizophrenia is a chronic and debilitating mental illness characterized by a broad range of abnormal behaviors, including delusions and hallucinations, impaired cognitive function, as well as mood disturbances and social withdrawal. Due to the heterogeneous nature of the disease, the causes of schizophrenia are very complex; its etiology is believed to involve multiple brain regions and the connections between them, and includes alterations in both gray and white matter regions. The onset of symptoms varies with age and severity, and there is some debate over a degenerative or developmental etiology. Longitudinal magnetic resonance imaging studies have detected progressive gray matter loss in the first years of disease, suggesting neurodegeneration; but there is also increasing recognition of a temporal association between clinical complications at birth and disease onset that supports a neurodevelopmental origin. Presently, neuronal abnormalities in schizophrenia are better understood than alterations in myelin-producing cells of the brain, the oligodendrocytes, which are the predominant constituents of white matter structures. Proper white matter development and its structural integrity critically impacts brain connectivity, which affects sensorimotor coordination and cognitive ability. Evidence of defective white matter growth and compromised white matter integrity has been found in individuals at high risk of psychosis, and decreased numbers of mature oligodendrocytes are detected in schizophrenia patients. Inflammatory markers, including proinflammatory cytokines and chemokines, are also associated with psychosis. A relationship between risk of psychosis, white matter defects and prenatal inflammation is being established. Animal models of perinatal brain injury are successful in producing white matter damage in the brain, typified by hypomyelination and/or dysmyelination, impaired motor coordination and prepulse inhibition of the acoustic startle reflex, recapitulating structural and functional characteristics observed in schizophrenia. In addition, elevated expression of inflammation-related genes in brain tissue and increased production of cytokines by blood cells from patients with schizophrenia indicate immunological dysfunction and abnormal inflammatory responses, which are also important underlying features in experimental models. Microglia, resident immune defenders of the central nervous system, play important roles in the development and protection of neural cells, but can contribute to injury under pathological conditions. This article discusses oligodendroglial changes in schizophrenia and focuses on microglial activity in the context of the disease, in neonatal brain injury and in various experimental models of white matter damage. These include disorders associated with premature birth, and animal models of perinatal bacterial and viral infection, oxygen deprivation (hypoxia) and excess (hyperoxia), and elevated systemic proinflammatory cytokine levels. We briefly review the effects of treatment with antipsychotic and anti-inflammatory agents in models of perinatal brain injury, and comment on the therapeutic potential of these strategies. By understanding the neurobiological basis of oligodendroglial abnormalities in schizophrenia, it is hoped that patients will benefit from the availability of targeted and more efficacious treatment options.

JNK signaling is the shared pathway linking neuroinflammation, blood-brain barrier disruption, and oligodendroglial apoptosis in the white matter injury of the immature brain

BACKGROUND

White matter injury is the major form of brain damage in very preterm infants. Selective white matter injury in the immature brain can be induced by lipopolysaccharide (LPS)-sensitized hypoxic-ischemia (HI) in the postpartum (P) day 2 rat pups whose brain maturation status is equivalent to that in preterm infants less than 30 weeks of gestation. Neuroinflammation, blood-brain barrier (BBB) damage and oligodendrocyte progenitor apoptosis may affect the susceptibility of LPS-sensitized HI in white matter injury. c-Jun N-terminal kinases (JNK) are important stress-responsive kinases in various forms of insults. We hypothesized that LPS-sensitized HI causes white matter injury through JNK activation-mediated neuroinflammation, BBB leakage and oligodendroglial apoptosis in the white matter of P2 rat pups.

METHODS

P2 pups received LPS (0.05 mg/kg) or normal saline injection followed by 90-min HI. Immunohistochemistry and immunoblotting were used to determine microglia activation, TNF-α, BBB damage, cleaved caspase-3, JNK and phospho-JNK (p-JNK), myelin basic protein (MBP), and glial fibrillary acidic protein (GFAP) expression. Immunofluorescence was performed to determine the cellular distribution of p-JNK. Pharmacological and genetic approaches were used to inhibit JNK activity.

RESULTS

P2 pups had selective white matter injury associated with upregulation of activated microglia, TNF-α, IgG extravasation and oligodendroglial progenitor apoptosis after LPS-sensitized HI. Immunohistochemical analyses showed early and sustained JNK activation in the white matter at 6 and 24 h post-insult. Immunofluorescence demonstrated upregulation of p-JNK in activated microglia, vascular endothelial cells and oligodendrocyte progenitors, and also showed perivascular aggregation of p-JNK-positive cells around the vessels 24 h post-insult. JNK inhibition by AS601245 or by antisense oligodeoxynucleotides (ODN) significantly reduced microglial activation, TNF-α immunoreactivity, IgG extravasation, and cleaved caspase-3 in the endothelial cells and oligodendrocyte progenitors, and also attenuated perivascular aggregation of p-JNK-positive cells 24 h post-insult. The AS601245 or JNK antisense ODN group had significantly increased MBP and decreased GFAP expression in the white matter on P11 than the vehicle or scrambled ODN group.

CONCLUSIONS

LPS-sensitized HI causes white matter injury through JNK activation-mediated upregulation of neuroinflammation, BBB leakage and oligodendrocyte progenitor apoptosis in the immature brain.