Poly(I:C) increases the expression of mPGES-1 and COX-2 in rat primary microglia

Activation of the COX-2/mPGES-1/PGE-2 cascade through the NLRP3 inflammasome contributes to Angiostrongylus cantonensis-induced eosinophilic meningoencephalitis

Prostaglandin E2 (PGE-2) is synthesised by cyclooxygenase-2 (COX-2) and microsomal prostaglandin E synthase 1 (mPGES-1). PGE-2 exhibits pro-inflammatory properties in inflammatory conditions. However, there remains limited understanding of the COX-2/mPGES-1/PGE-2 pathway in Angiostrongylus cantonensis-induced meningoencephalitis. This study revealed several key findings regarding the activation of the COX-2/mPGES-1/PGE-2 pathway and its correlation with eosinophilic meningoencephalitis induced by A. cantonensis infection. Immunostaining revealed an increase in the expression of COX-2 and mPGES-1 in the subarachnoid space and glial cells compared to control subjects. Inhibition of the NLRP3 inflammasome by small interfering RNA (siRNA) blocked extracellular secretory proteins (ESPs) stimulated COX-2, mPGES-1 and PGE-2 in microglia. MCC950, an NLRP3 inhibitor, inhibited the levels of the COX-2, mPGES-1, and PGE-2 proteins induced by A. cantonensis in mice. Treatment of mice infected with A. cantonensis with the COX-2 inhibitor NS398 significantly reduced the levels of mPGES-1, PGE-2, and matrix metalloproteinase-9 (MMP-9) levels. Similarly, the mPGES-1 inhibitor MF63 significantly reduced PGE-2 and MMP-9 levels in A. cantonensis-infected mice. Administration of MCC950, NS398, or MF63 resulted in marked attenuation of blood-brain barrier (BBB) permeability and eosinophil counts in A. cantonensis-infected mice. These findings highlight the critical role of the COX-2/mPGES-1/PGE-2 pathway and its regulation by the NLRP3 inflammasome in the pathogenesis of eosinophilic meningoencephalitis induced by A. cantonensis infection. Furthermore, pharmacological interventions targeting this pathway, such as MCC950, NS398, and MF63, show promising therapeutic potential in mitigating associated inflammatory responses and disruption of the BBB. The results indicate that blocking NLRP3 using pharmacological (MCC950) and gene silencing (siNLRP3) methods emphasised the crucial involvement of NLRP3 in the COX-2/mPGES-1/PGE-2 pathway. This suggests that the activation of the COX-2/mPGES-1/PGE-2 axis in response to A. cantonensis infection may be mediated through a mechanism involving the NLRP3 inflammasome.

Inhibition of Kv1.1 channels ameliorates Cu(II)-induced microglial activation and cognitive impairment in mice

Microglia-mediated neuroinflammation plays a critical role in neuronal damage in neurodegenerative disorders such as Alzheimer's disease. Evidence shows that voltage-gated potassium (Kv) channels regulate microglial activation. We previously reported that copper dyshomeostasis causes neuronal injury via activating microglia. This study was designed to explore the role of Kv1.1 channels in copper-evoked microglial neuroinflammation. BV-2 microglial cells were treated with Cu(II). DiBAC4(3) was used to measure membrane potential. Microglial activation and neuronal loss were detected by enzyme-linked immunosorbent assay, Western blotting, and immunostaining. Learning and memory function was assessed with Morris water maze task. Cu(II) caused a hyperpolarized membrane potential in microglial cells, an effect abolished by functional Kv1.1 blockade. Blockade of Kv1.1 and knock-down of Kv1.1 with small interfering RNA repressed Cu(II)-induced microglial production of pro-inflammatory mediators. Also, Kv1.1 inhibition attenuated activation of PI3K/Akt-ERK1/2 signaling pathway and production of mitochondrial reactive oxidative species as well as nuclear factor-κB activation in Cu(II)-stimulated microglia. Moreover, the Cu(II)-caused, microglia-mediated neurotoxicity (indicated by reduced neuronal survival and increased dendritic loss) was attenuated by Kv1.1 knock-down. In an in vivo mouse model, hippocampal injection of Cu(II) caused elevated Kv1.1 mRNA (but not other Kv1 channels) expression and enhanced microglial Kv1.1 immunoreactivity in the hippocampus. Furthermore, blockade of Kv1.1 attenuated Cu(II)-induced microglial activation and neuronal dendritic loss in the hippocampus and learning and memory dysfunction. These findings suggest that inhibition of Kv1.1 ameliorates Cu(II)-induced microglial activation and cognitive impairment. Thus, it might represent a potential molecular target for anti-inflammatory therapy of neurodegenerative disorders.

Characterizing Microglial Signaling Dynamics During Inflammation Using Single-Cell Mass Cytometry

Microglia play a critical role in maintaining central nervous system (CNS) homeostasis and display remarkable plasticity in their response to inflammatory stimuli. However, the specific signaling profiles that microglia adopt during such challenges remain incompletely understood. Traditional transcriptomic approaches provide valuable insights, but fail to capture dynamic post-translational changes. In this study, we utilized time-resolved single-cell mass cytometry (CyTOF) to measure distinct signaling pathways activated in microglia upon exposure to bacterial and viral mimetics-lipopolysaccharide (LPS) and polyinosinic-polycytidylic acid (Poly(I:C)), respectively. Furthermore, we evaluated the immunomodulatory role of astrocytes on microglial signaling in mixed cultures. Microglia or mixed cultures derived from neonatal mice were treated with LPS or Poly(I:C) for 48 h. Cultures were stained with a panel of 33 metal-conjugated antibodies targeting signaling and identity markers. High-dimensional clustering analysis was used to identify emergent signaling modules. We found that LPS treatment led to more robust early activation of pp38, pERK, pRSK, and pCREB compared to Poly(I:C). Despite these differences, both LPS and Poly(I:C) upregulated the classical reactivity markers CD40 and CD86 at later time points. Strikingly, the presence of astrocytes significantly blunted microglial responses to both stimuli, particularly dampening CD40 upregulation. Our studies demonstrate that single-cell mass cytometry effectively captures the dynamic signaling landscape of microglia under pro-inflammatory conditions. This approach may pave the way for targeted therapeutic investigations of various neuroinflammatory disorders. Moreover, our findings underscore the necessity of considering cellular context, such as astrocyte presence, in interpreting microglial behavior during inflammation.

TLR3-mediated Astrocyte Responses in High and Normal Glucose Adaptation Differently Regulated by Metformin

Toll-like receptors 3 (TLR3) are innate immune receptors expressed on a wide range of cell types, including glial cells. Inflammatory responses altered by hyperglycemia highlight the need to explore the molecular underpinnings of these changes in cellular models. Therefore, here we estimated TLR3-mediated response of astrocytes cultured at normal (NG, 5 mM) and high (HG, 22.5 mM) glucose concentrations for 48 h before stimulation with polyinosinic:polycytidylic acid Poly(I:C) (PIC) for 6 h. Seahorse Extracellular Flux Analyzer (Seahorse XFp) was used to estimate the extracellular acidification rate (ECAR) and oxygen consumption rate (OCR). Although adaptation to HG affected ECAR and OCR, the stimulation of cells with PIC had no effect on ECAR. PIC reduced maximal OCR, but this effect disappeared upon adaptation to HG. PIC-stimulated release of cytokines IL-1β, IL-10 was reduced, and that of IL-6 and iNOS was increased in the HG model. Adaptation to HG reduced PIC-stimulated synthesis of COX-derived oxylipins measured by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Adaptation to HG did not alter PIC-stimulated p38 activity, ERK mitogen-activated protein kinase, STAT3 and ROS production. Metformin exhibited anti-inflammatory activity, reducing PIC-stimulated synthesis of cytokines and oxylipins. Cell adaptation to high glucose concentration altered the sensitivity of astrocytes to TLR3 receptor activation, and the hypoglycemic drug metformin may exert anti-inflammatory effects under these conditions.

DCPIB Attenuates Ischemia-Reperfusion Injury by Regulating Microglial M1/M2 Polarization and Oxidative Stress

The inflammatory response plays an indispensable role in ischemia-reperfusion injury, the most significant of which is the inflammatory response caused by microglial polarization. Anti-inflammatory therapy is also an important remedial measure after failed vascular reconstruction. Maintaining the internal homeostasis of the brain is a crucial measure for suppressing the inflammatory response. The mechanism underlying the relationship between DCPIB, a selective blocker of volume-regulated anion channels (VRAC), and inflammation induced by cerebral ischemia-reperfusion injury is currently unclear. The purpose of this study was to investigate the relationship between DCPIB and microglial M1/M2 polarization-mediated inflammation after cerebral ischemia-reperfusion injury. C57BL/6 mice were subjected to transient middle cerebral artery occlusion (tMCAO). DCPIB was administered by a lateral ventricular injection within 5 min after reperfusion. Behavioral assessments were conducted at 1, 3, and 7 days after tMCAO/R. Pathological injuries were evaluated using TTC assay, HE and Nissl staining, brain water content measurement, and immunofluorescence staining. The levels of inflammatory cytokines were analyzed using qPCR and ELISA. Additionally, the phenotypic variations of microglia were examined using immunofluorescence staining. In mouse tMCAO/R model, DCPIB administration markably reduced mortality, improved behavioral performance, and alleviated pathological injury. DCPIB treatment significantly inhibited the inflammatory response, promoted the conversion of M1 microglia to M2 microglia via the MAPK signaling pathway, and ultimately protected neurons from the microglia-mediated inflammatory response. In addition, DCPIB inhibited oxidative stress induced by cerebral ischemia-reperfusion injury. In conclusion, DCPIB attenuates cerebral ischemia-reperfusion injury by regulating microglial M1/M2 polarization and oxidative stress.

Anti-Inflammatory Effects of GPR55 Agonists and Antagonists in LPS-Treated BV2 Microglial Cells

Chronic inflammation is driven by proinflammatory cytokines such as interleukin 6 (IL-6), tumor necrosis factor-α (TNF-α), and chemokines, such as c-c motif chemokine ligand 2 (CCL2), CCL3, C-X-C motif chemokine ligand 2 (CXCL2), and CXCL10. Inflammatory processes of the central nervous system (CNS) play an important role in the pathogenesis of various neurological and psychiatric disorders like Alzheimer's disease, Parkinson's disease, and depression. Therefore, identifying novel anti-inflammatory drugs may be beneficial for treating disorders with a neuroinflammatory background. The G-protein-coupled receptor 55 (GPR55) gained interest due to its role in inflammatory processes and possible involvement in different disorders. This study aims to identify the anti-inflammatory effects of the coumarin-based compound KIT C, acting as an antagonist with inverse agonistic activity at GPR55, in lipopolysaccharide (LPS)-stimulated BV2 microglial cells in comparison to the commercial GPR55 agonist O-1602 and antagonist ML-193. All compounds significantly suppressed IL-6, TNF-α, CCL2, CCL3, CXCL2, and CXCL10 expression and release in LPS-treated BV2 microglial cells. The anti-inflammatory effects of the compounds are partially explained by modulation of the phosphorylation of p38 mitogen-activated protein kinase (MAPK), p42/44 MAPK (ERK 1/2), protein kinase C (PKC) pathways, and the transcription factor nuclear factor (NF)-κB, respectively. Due to its potent anti-inflammatory properties, KIT C is a promising compound for further research and potential use in inflammatory-related disorders.

Differential regulation of innate immune system in frontal cortex and hippocampus in a "double-hit" neurodevelopmental model in rats

Neurodevelopmental disorders (NDs) are neuropsychiatric conditions affecting central nervous system development, characterized by cognitive and behavioural alterations. Inflammation has been recently linked to NDs. Animal models are essential for understanding their pathophysiology and identifying therapeutic targets. Double-hit models can reproduce neurodevelopmental and neuroinflammatory impairments. Sixty-seven newborn rats were assigned to four groups: Control, Maternal deprivation (MD, 24-h-deprivation), Isolation (Iso, 5 weeks), and Maternal deprivation ​+ ​Isolation (MD ​+ ​Iso, also known as double-hit). Cognitive dysfunction was assessed using behavioural tests. Inflammasome, MAPKs, and TLRs inflammatory elements expression in the frontal cortex (FC) and hippocampus (HP) was analysed through western blot and qRT-PCR. Oxidative/nitrosative (O/N) evaluation and corticosterone levels were measured in plasma samples. Double-hit group was affected in executive and working memory. Most inflammasomes and TLRs inflammatory responses were increased in FC compared to the control group, whilst MAPKs were downregulated. Conversely, hippocampal inflammasome and inflammatory components were reduced after the double-hit exposure, while MAPKs were elevated. Our findings reveal differential regulation of innate immune system components in FC and HP in the double-hit group. Further investigations on MAPKs are necessary to understand their role in regulating HP neuroinflammatory status, potentially linking our MAPKs results to cognitive impairments through their proliferative and anti-inflammatory activity.

Mechanism of baixiangdan capsules on anti-neuroinflammation: combining dry and wet experiments

Neuroinflammation plays an important role in the pathogenesis of neurological disorders, and despite intensive research, treatment of neuroinflammation remains limited. BaiXiangDan capsule (BXD) is widely used in clinical practice. However, systematic studies on the direct role and mechanisms of BXD in neuroinflammation are still lacking. We systematically evaluated the potential pharmacological mechanisms of BXD on neuroinflammation using network pharmacological analysis combined with experimental validation. Multiple databases are used to mine potential targets for bioactive ingredients, drug targets and neuroinflammation. GO and KEGG pathway analysis was also performed. Interactions between active ingredients and pivotal targets were confirmed by molecular docking. An experimental model of neuroinflammation was used to evaluate possible therapeutic mechanisms for BXD. Network pharmacological analysis revealed that Chrysoeriol, Kaempferol and Luteolin in BXD exerted their anti-neuroinflammatory effects mainly by acting on targets such as NCOA2, PIK3CA and PTGS2. Molecular docking results showed that their average affinity was less than -5 kcal/mol, with an average affinity of -8.286 kcal/mol. Pathways in cancer was found to be a potentially important pathway, with involvement of PI3K/AKT signaling pathways. In addition, in vivo experiments showed that BXD treatment ameliorated neural damage and reduced neuronal cell death. Western blotting, RT-qPCR and ELISA analysis showed that BXD inhibited not only the expression of IL-1β, TNF-α and NO, but also NF-κB, MMP9 and PI3K/AKT signaling pathways. This study applied network pharmacology and in vivo experiments to explore the possible mechanisms of BXD against neuroinflammation, providing insight into the treatment of neuroinflammation.

Update on the pathological roles of prostaglandin E2 in neurodegeneration in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by selective degeneration of upper and lower motor neurons. The pathogenesis of ALS remains largely unknown; however, inflammation of the spinal cord is a focus of ALS research and an important pathogenic process in ALS. Prostaglandin E₂ (PGE₂) is a major lipid mediator generated by the arachidonic-acid cascade and is abundant at inflammatory sites. PGE₂ levels are increased in the postmortem spinal cords of ALS patients and in ALS model mice. Beneficial therapeutic effects have been obtained in ALS model mice using cyclooxygenase-2 inhibitors to inhibit the biosynthesis of PGE₂, but the usefulness of this inhibitor has not yet been proven in clinical trials. In this review, we present current evidence on the involvement of PGE₂ in the progression of ALS and discuss the potential of microsomal prostaglandin E synthase (mPGES) and the prostaglandin receptor E-prostanoid (EP) 2 as therapeutic targets for ALS. Signaling pathways involving prostaglandin receptors mediate toxic effects in the central nervous system. In some situations, however, the receptors mediate neuroprotective effects. Our recent studies demonstrated that levels of mPGES-1, which catalyzes the final step of PGE₂ biosynthesis, are increased at the early-symptomatic stage in the spinal cords of transgenic ALS model mice carrying the G93A variant of superoxide dismutase-1. In addition, in an experimental motor-neuron model used in studies of ALS, PGE₂ induces the production of reactive oxygen species and subsequent caspase-3-dependent cytotoxicity through activation of the EP2 receptor. Moreover, this PGE₂-induced EP2 up-regulation in motor neurons plays a role in the death of motor neurons in ALS model mice. Further understanding of the pathophysiological role of PGE₂ in neurodegeneration may provide new insights to guide the development of novel therapies for ALS.

Role of Microglia in Psychostimulant Addiction

The use of psychostimulant drugs can modify brain function by inducing changes in the reward system, mainly due to alterations in dopaminergic and glutamatergic transmissions in the mesocorticolimbic pathway. However, the etiopathogenesis of addiction is a much more complex process. Previous data have suggested that microglia and other immune cells are involved in events associated with neuroplasticity and memory, which are phenomena that also occur in addiction. Nevertheless, how dependent is the development of addiction on the activity of these cells? Although the mechanisms are not known, some pathways may be involved. Recent data have shown psychoactive substances may act directly on immune cells, alter their functions and induce various inflammatory mediators that modulate synaptic activity. These could, in turn, be involved in the pathological alterations that occur in substance use disorder. Here, we extensively review the studies demonstrating how cocaine and amphetamines modulate microglial number, morphology, and function. We also describe the effect of these substances in the production of inflammatory mediators and a possible involvement of some molecular signaling pathways, such as the toll-like receptor 4. Although the literature in this field is scarce, this review compiles the knowledge on the neuroimmune axis that is involved in the pathogenesis of addiction, and suggests some pharmacological targets for the development of pharmacotherapy.

The Key Drivers of Brain Injury by Systemic Inflammatory Responses after Sepsis: Microglia and Neuroinflammation

Sepsis is a leading cause of intensive care unit admission and death worldwide. Most surviving patients show acute or chronic mental disorders, which are known as sepsis-associated encephalopathy (SAE). Although accumulating studies in the past two decades focused on the pathogenesis of SAE, a systematic review of retrospective studies which exclusively focuses on the inflammatory mechanisms of SAE has been lacking yet. This review summarizes the recent advance in the field of neuroinflammation and sheds light on the activation of microglia in SAE. Activation of microglia predominates neuroinflammation. As the gene expression profile changes, microglia show heterogeneous characterizations throughout all stages of SAE. Here, we summarize the systemic inflammation following sepsis and also the relationship of microglial diversity and neuroinflammation. Moreover, a collection of neuroinflammation-related dysfunction has also been reviewed to illustrate the possible mechanisms for SAE. In addition, promising pharmacological or non-pharmacological therapeutic strategies, especially those which target neuroinflammation or microglia, are also concluded in the final part of this review. Collectively, clarification of the vital relationship between neuroinflammation and SAE-related mental disorders would significantly improve our understanding of the pathophysiological mechanisms in SAE and therefore provide potential targets for therapies of SAE aimed at inhibiting neuroinflammation.

Human repair-related Schwann cells adopt functions of antigen-presenting cells in vitro

The plastic potential of Schwann cells (SCs) is increasingly recognized to play a role after nerve injury and in diseases of the peripheral nervous system. Reports on the interaction between immune cells and SCs indicate their involvement in inflammatory processes. However, the immunocompetence of human SCs has been primarily deduced from neuropathies, but whether after nerve injury SCs directly regulate an adaptive immune response is unknown. Here, we performed comprehensive analysis of immunomodulatory capacities of human repair-related SCs (hrSCs), which recapitulate SC response to nerve injury in vitro. We used our well-established culture model of primary hrSCs from human peripheral nerves and analyzed the transcriptome, secretome, and cell surface proteins for pathways and markers relevant in innate and adaptive immunity, performed phagocytosis assays, and monitored T-cell subset activation in allogeneic co-cultures. Our findings show that hrSCs are phagocytic, which is in line with high MHCII expression. Furthermore, hrSCs express co-regulatory proteins, such as CD40, CD80, B7H3, CD58, CD86, and HVEM, release a plethora of chemoattractants, matrix remodeling proteins and pro- as well as anti-inflammatory cytokines, and upregulate the T-cell inhibiting PD-L1 molecule upon pro-inflammatory stimulation with IFNγ. In contrast to monocytes, hrSC alone are not sufficient to trigger allogenic CD4+ and CD8+ T-cells, but limit number and activation status of exogenously activated T-cells. This study demonstrates that hrSCs possess features and functions typical for professional antigen-presenting cells in vitro, and suggest a new role of these cells as negative regulators of T-cell immunity during nerve regeneration.

Urolithin A Inactivation of TLR3/TRIF Signaling to Block the NF-κB/STAT1 Axis Reduces Inflammation and Enhances Antioxidant Defense in Poly(I:C)-Induced RAW264.7 Cells

Urolithin A is an active compound of gut-microbiota-derived metabolites of polyphenol ellagic acid that has anti-aging, antioxidative, and anti-inflammatory effects. However, the effects of urolithin A on polyinosinic acid-polycytidylic acid (poly(I:C))-induced inflammation remain unclear. Poly(I:C) is a double-stranded RNA (dsRNA) similar to a virus and is recognized by Toll-like receptor-3 (TLR3), inducing an inflammatory response in immune cells, such as macrophages. Inflammation is a natural defense process of the innate immune system. Therefore, we used poly(I:C)-induced RAW264.7 cells and attenuated the inflammation induced by urolithin A. First, our data suggested that 1–30 μM urolithin A does not reduce RAW264.7 cell viability, whereas 1 μM urolithin A is sufficient for antioxidation and the decreased production of tumor necrosis factor-α (TNF-α), monocyte chemoattractant protein-1 (MCP-1), and C-C chemokine ligand 5. The inflammation-related proteins cyclooxygenase-2 and inducible nitric oxide synthase were also downregulated by urolithin A. Next, 1 μM urolithin A inhibited the levels of interferon (INF)-α and INF-β. Urolithin A was applied to investigate the blockade of the TLR3 signaling pathway in poly(I:C)-induced RAW264.7 cells. Moreover, the TLR3 signaling pathway, subsequent inflammatory-related pathways, and antioxidation pathways showed changes in nuclear factor-κB (NF-κB) signaling and blocked ERK/mitogen-activated protein kinase (MAPK) signaling. Urolithin A enhanced catalase (CAT) and superoxide dismutase (SOD) activities, but decreased malondialdehyde (MDA) levels in poly(I:C)-induced RAW264.7 cells. Thus, our results suggest that urolithin A inhibits TLR3-activated inflammatory and oxidative-associated pathways in macrophages, and that this inhibition is induced by poly(I:C). Therefore, urolithin A may have antiviral effects and could be used to treat viral-infection-related diseases.

Prenatal disruption of blood-brain barrier formation via cyclooxygenase activation leads to lifelong brain inflammation

Gestational maternal immune activation (MIA) in mice induces persistent brain microglial activation and a range of neuropathologies in the adult offspring. Although long-term phenotypes are well documented, how MIA in utero leads to persistent brain inflammation is not well understood. Here, we found that offspring of mothers treated with polyriboinosinic–polyribocytidylic acid [poly(I:C)] to induce MIA at gestational day 13 exhibit blood–brain barrier (BBB) dysfunction throughout life. Live MRI in utero revealed fetal BBB hyperpermeability 2 d after MIA. Decreased pericyte–endothelium coupling in cerebral blood vessels and increased microglial activation were found in fetal and 1- and 6-mo-old offspring brains. The long-lasting disruptions result from abnormal prenatal BBB formation, driven by increased proliferation of cyclooxygenase-2 (COX2; Ptgs2)-expressing microglia in fetal brain parenchyma and perivascular spaces. Targeted deletion of the Ptgs2 gene in fetal myeloid cells or treatment with the inhibitor celecoxib 24 h after immune activation prevented microglial proliferation and disruption of BBB formation and function, showing that prenatal COX2 activation is a causal pathway of MIA effects. Thus, gestational MIA disrupts fetal BBB formation, inducing persistent BBB dysfunction, which promotes microglial overactivation and behavioral alterations across the offspring life span. Taken together, the data suggest that gestational MIA disruption of BBB formation could be an etiological contributor to neuropsychiatric disorders.

Differential Effects of Toll-Like Receptor Activation and Differential Mediation by MAP Kinases of Immune Responses in Microglial Cells

Microglial activation is believed to play a role in many psychiatric and neurodegenerative diseases. Based largely on evidence from other cell types, it is widely thought that MAP kinase (ERK, JNK and p38) signalling pathways contribute strongly to microglial activation following immune stimuli acting on toll-like receptor (TLR) 3 or TLR4. We report here that exposure of SimA9 mouse microglial cell line to immune mimetics stimulating TLR4 (lipopolysaccharide-LPS) or TLR7/8 (resiquimod/R848), results in marked MAP kinase activation, followed by induction of nitric oxide synthase, and various cytokines/chemokines. However, in contrast to TLR4 or TLR7/8 stimulation, very few effects of TLR3 stimulation by poly-inosine/cytidine (polyI:C) were detected. Induction of chemokines/cytokines at the mRNA level by LPS and resiquimod were, in general, only marginally affected by MAP kinase inhibition, and expression of TNF, Ccl2 and Ccl5 mRNAs, along with nitrite production, were enhanced by p38 inhibition in a stimulus-specific manner. Selective JNK inhibition enhanced Ccl2 and Ccl5 release. Many distinct responses to stimulation of TLR4 and TLR7 were observed, with JNK mediating TNF protein induction by the latter but not the former, and suppressing Ccl5 release by the former but not the latter. These data reveal complex modulation by MAP kinases of microglial responses to immune challenge, including a dampening of some responses. They demonstrate that abnormal levels of JNK or p38 signalling in microglial cells will perturb their profile of cytokine and chemokine release, potentially contributing to abnormal inflammatory patterns in CNS disease states.

NSP2 Is Important for Highly Pathogenic Porcine Reproductive and Respiratory Syndrome Virus to Trigger High Fever-Related COX-2-PGE2 Pathway in Pigs

In 2006, atypical porcine reproductive and respiratory syndrome (PRRS) caused by a highly pathogenic PRRSV (HP-PRRSV) strain broke out in China. Atypical PRRS is characterized by extremely high fever and high mortality in pigs of all ages. Prostaglandin E2 (PGE2) derived from arachidonic acid through the activation of the rate-limiting enzyme cyclooxygenase type 1/2 (COX-1/2) plays an important role in fever. Here, we showed that HP-PRRSV infection increased PGE2 production in microglia via COX-2 up-regulation depending on the activation of MEK1-ERK1/2-C/EBPβ signaling pathways. Then, we screened HP-PRRSV proteins and demonstrated that HP-PRRSV nonstructural protein 2 (NSP2) activated MEK1-ERK1/2-C/EBPβ signaling pathways by interacting with 14-3-3ζ to promote COX-2 expression, leading to PGE2 production. Furthermore, we identified that the amino acid residues 500-596 and 658-777 in HP-PRRSV NSP2 were essential to up-regulate COX-2 expression and PGE2 production. Finally, we made mutant HP-PRRS viruses with the deletion of residues 500-596 and/or 658-777, and found out that these viruses had impaired ability to up-regulate COX-2 and PGE2 production in vitro and in vivo. Importantly, pigs infected with the mutant viruses had relieved fever, clinical symptoms, and mortality. These data might help us understand the molecular mechanisms underlying the high fever and provide clues for the development of HP-PRRSV attenuated vaccines.

Robust COX-2-mediated prostaglandin response may drive arthralgia and bone destruction in patients with chronic inflammation post-chikungunya

Patients following infection by chikungunya virus (CHIKV) can suffer for months to years from arthralgia and arthritis. Interestingly, methotrexate (MTX) a major immune-regulatory drug has proved to be of clinical benefit. We have previously shown that CHIKV can persist in the joint of one patient 18 months post-infection and plausibly driving chronic joint inflammation but through ill-characterized mechanisms. We have pursued our investigations and report novel histological and in vitro data arguing for a plausible role of a COX-2-mediated inflammatory response post-CHIKV. In the joint, we found a robust COX-2 staining on endothelial cells, synovial fibroblasts and more prominently on multinucleated giant cells identified as CD11c+ osteoclasts known to be involved in bone destruction. The joint tissue was also strongly stained for CD3, CD8, CD45, CD14, CD68, CD31, CD34, MMP2, and VEGF (but not for NO synthase and two B cell markers). Dendritic cells were rarely detected. Primary human synovial fibroblasts were infected with CHIKV or stimulated either by the synthetic molecule polyriboinosinic:polyribocytidylic acid (PIC) to mimic chronic viral infection or cytokines. First, we found that PIC and CHIKV enhanced mRNA expression of COX-2. We further found that PIC but not CHIKV increased the mRNA levels of cPLA2α and of mPGES-1, two other central enzymes in PGE2 production. IFNβ upregulated cPLA2α and COX-2 transcription levels but failed to modulated mPGES-1 mRNA expression. Moreover, PIC, CHIKV and IFNβ decreased mRNA expression of the PGE2 degrading enzyme 15-PGDH. Interestingly, MTX failed to control the expression of all these enzymes. In sharp contrast, dexamethasone was able to control the capacity of pro-inflammatory cytokines, IL-1β as well as TNFα, to stimulate mRNA levels of cPLA2α, COX-2 and mPGES-1. These original data argue for a concerted action of CHIKV (including viral RNA) and cytokines plausibly released from recruited leukocytes to drive a major COX-2-mediated PGE2 proinflammatory responses to induce viral arthritis.

It is important to have a better understanding of the immuno-pathogenesis of Chikungunya virus (CHIKV) and particularly focusing on the chronic phase associated to arthralgia and arthritis. Benefiting from our prospective cohort studies, we herein provide novel in vivo data identifying for the first time the implication of COX-2 and several other enzymes involved in prostaglandin biosynthesis and the persistence of the virus on the joint. Prostaglandin has major activities in inflammation and joint destruction. In vitro, we have used a model of human synovial fibroblasts to decipher the regulatory mechanisms of prostaglandin biosynthesis pathway. We have made important observations showing that the virus itself as well as major inflammatory cytokines can dramatically control the expression of all enzymes involved in the metabolism of prostaglandin. Interestingly, pharmacological investigations further revealed that dexamethasone, but not methotrexate (currently used to treat patients with chikungunya) may be of clinical values.

Microglia: Agents of the CNS Pro-Inflammatory Response

The pro-inflammatory immune response driven by microglia is a key contributor to the pathogenesis of several neurodegenerative diseases. Though the research of microglia spans over a century, the last two decades have increased our understanding exponentially. Here, we discuss the phenotypic transformation from homeostatic microglia towards reactive microglia, initiated by specific ligand binding to pattern recognition receptors including toll-like receptor-4 (TLR4) or triggering receptors expressed on myeloid cells-2 (TREM2), as well as pro-inflammatory signaling pathways triggered such as the caspase-mediated immune response. Additionally, new research disciplines such as epigenetics and immunometabolism have provided us with a more holistic view of how changes in DNA methylation, microRNAs, and the metabolome may influence the pro-inflammatory response. This review aimed to discuss our current knowledge of pro-inflammatory microglia from different angles, including recent research highlights such as the role of exosomes in spreading neuroinflammation and emerging techniques in microglia research including positron emission tomography (PET) scanning and the use of human microglia generated from induced pluripotent stem cells (iPSCs). Finally, we also discuss current thoughts on the impact of pro-inflammatory microglia in neurodegenerative diseases.

Dihydroartemisinin ameliorates LPS-induced neuroinflammation by inhibiting the PI3K/AKT pathway

Neuroinflammation can cause multiple neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD). Recent studies have shown that the artemisinin derivative dihydroartemisinin (DHA) can be used as an immunomodulatory, anti-inflammatory and anti-tumor agent. The anti-neuroinflammatory effects of DHA were evaluated in our study, and the underlying mechanisms were explored using the Morris water maze test (MWMT), Open-field test (OFT) and Closed-field test (CFT), Elevated plus maze test (EPMT), Nissl Staining, Immunofluorescence analysis, RT-PCR, and Western Blot. Our results show that DHA significantly inhibits LPS-induced inflammation and attenuates LPS-induced behavioral and memory disorders. 1. Behavioral test results: 1) in the water maze test, the mice in the LPS group showed increased escape latency and length of the movement path on the third day; they also had a decreased number of crossings of the target quadrant after the platform was removed on the 5th day and remained in the target quadrant for less time; 2) in the open- and closed-field experiment, the number of activities and activities in the open-field were significantly reduced; 3) in the elevated cross maze experiment, LPS-treated mice exhibited a significant reduction in the number of times and the time to enter the open arm; the above behavior was reversed after DHA treatment. 2. Nissl staining results: compared with the Control group, the LPS group showed significant damage, and the number of damaged cells in the hippocampal CA1, CA2, CA3 and DG regions was increased; DHA treatment reduced cell damage. 3. RT-PCR results: compared with the Control group, the LPS group showed increased expression of IL-1β and IL-6 but decreased expression after DHA treatment. 4. GFAP fluorescent staining: compared with the control group, the corresponding reactivity of positive cells in the LPS-induced group was increased in the CA1-CA3 and DG regions of the hippocampus; compared with the LPS-induced mice, cells in the LPS + DHA group showed significantly reduced reactivity (GFAP). 5. Western blot results: compared with the Control group, the LPS group showed increased expression of P-PI3K/PI3K, P-AKT/AKT, IL-6 and TNFα and a decreased expression of P-PI3K/PI3K, IL-6, TNF and P-AKT/AKT after DHA treatment. Our findings provide direct evidence for the potential use of DHA in the treatment of neuroinflammatory diseases.

Pinjari O, Teixeira AL, Petronilho F, Macêdo D, Quevedo J, Barichello T. Clozapine Prevents Poly (I:C) Induced Inflammation by Modulating NLRP3 Pathway in Microglial Cells

Schizophrenia is a complex psychiatric disorder that exhibits an interconnection between the immune system and the brain. Experimental and clinical studies have suggested the presence of neuroinflammation in schizophrenia. In the present study, the effect of antipsychotic drugs, including clozapine, risperidone, and haloperidol (10, 20 and 20 μM, respectively), on the production of IL-1α, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-10, IL-17, IL-18, INF-γ, and TNF-α was investigated in the unstimulated and polyriboinosinic-polyribocytidilic acid [poly (I:C)]-stimulated primary microglial cell cultures. In the unstimulated cultures, clozapine, risperidone, and haloperidol did not influence the cytokine levels. Nevertheless, in cell cultures under strong inflammatory activation by poly (I:C), clozapine reduced the levels of IL-1α, IL-1β, IL-2, and IL-17. Risperidone and haloperidol both reduced the levels of IL-1α, IL-1β, IL-2, and IL-17, and increased the levels of IL-6, IL-10, INF-γ, and TNF-α. Based on the results that were obtained with the antipsychotic drugs and observing that clozapine presented with a more significant anti-inflammatory effect, clozapine was selected for the subsequent experiments. We compared the profile of cytokine suppression obtained with the use of NLRP3 inflammasome inhibitor, CRID3 to that obtained with clozapine, to test our hypothesis that clozapine inhibits the NLRP3 inflammasome. Clozapine and CRID3 both reduced the IL-1α, IL-1β, IL-2, and IL-17 levels. Clozapine reduced the level of poly (I:C)-activated NLRP3 expression by 57%, which was higher than the reduction thay was seen with CRID3 treatment (45%). These results suggest that clozapine might exhibit anti-inflammatory effects by inhibiting NLRP3 inflammasome and this activity is not typical with the use of other antipsychotic drugs under the conditions of strong microglial activation.

Bifenthrin insecticide promotes oxidative stress and increases inflammatory mediators in human neuroblastoma cells through NF-kappaB pathway

The extensive application of bifenthrin (BF) insecticide in agriculture has raised serious concerns with regard to increased risks of developing neurodegenerative diseases. Recently, our group showed that BF exposure in rodent models induced oxidative stress and inflammation markers in various regions of the brain (frontal cortex, striatum and hippocampus) and this was associated with behavioral changes. This study aimed to confirm such inflammatory and oxidative stress in an in vitro cell culture model of SK-N-SH human neuroblastoma cells. Markers of oxidative stress (ROS, NO, MDA, H₂O₂), antioxidant enzyme activities (CAT, GPx, SOD) and inflammatory response (TNF-α, IL-6, PGE₂) were analyzed in SK-N-SH cells after 24 h of exposure to different concentrations of BF (1-20 μM). Protein synthesis and mRNA expression of the enzymes implicated in the synthesis of PGE₂ were also measured (COX-2, mPGES-1) as well as nuclear factor κappaB (NF-κBp65) and antioxidant nuclear erythroid-2 like factor-2 (Nrf-2). Cell viability was analyzed by MTT-tetrazolio (MTT) and lactate dehydrogenase (LDH) assays. Exposure of SK-N-SH cells to BF resulted in a concentration-dependent reduction in the number of viable cells (reduction of MTT and increase in LDH activity). There was also a BF concentration-dependent increase in oxidative stress markers (ROS release, NO, MDA and H₂O₂) and decrease in the activity of antioxidant enzymes (CAT and GPx activities). There was further a concentration-dependent increase in pro-inflammatory cytokines (TNF-α and IL-6) and inflammatory mediator PGE₂, increase in protein synthesis and mRNA expression of inflammatory markers (COX-2, mPGES-1 and NF-κBp65) and decrease in protein synthesis and mRNA expression of antioxidant Nrf-2. Our data shows that BF induces various oxidative stress and inflammatory markers in SK-N-SH human neuroblastoma cells as well as the activation of NF-κBp65 signaling pathway. This is in line with prior results in brain regions of rodents exposed in vivo to BF showing increased oxidative stress in response to BF exposure, occurring in pro-inflammatory conditions and likely activating programmed cell death.

Anti- inflammatory effect of Prunus tomentosa Thunb total flavones in LPS-induced RAW264.7 cells

In this research, we investigated possible anti-inflammatory roles of Prunus tomentosa Thunb Total Flavones (PTTTF) in LPS-induced RAW264.7 cells. PTTTF (4μg/ml and 40μg/ml) was applied to RAW264.7 cells induced with 1μg/ml LPS to test the impact of these flavones on neutrophil phagocytosis in vitro. Levels of prostaglandin E2 (PGE2) and two pro-inflammatory interleukin cytokines (i.e. IL-6 and IL-1β) in the supernatant fraction were tested via Enzyme-linked immunosorbent assays (ELISA). Expression of cyclooxygenases COX-1 and COX-2 was detected via RT-PCR. Superoxide dismutase (SOD) content was determined with a spectrophotometric assay (Micromethod). The results revealed that PTTTF at doses higher than 4μg/ml reduces the content of IL-6, IL-1β and PGE2 (P < 0.05), and elevates the activity of SOD in LPS-induced RAW264.7 cells significantly (P < 0.05). PTTTF at 40μg/ml showed no significant effect on the expression of COX-1(P>0.05) but resulted in a significant inhibition of COX-2 in LPS-induced RAW264.7 cells (P<0.05). In summary, PTTTF had a substantial potential anti-inflammatory effect through the alteration of the synthesis of some cytokines and other mediators of the process of inflammation. Novelty statement - Prunus tomentosa Thunb Total Flavones (PTTTF) have known roles in the treatment of diabetes, but here we show that they are also potential anti-inflammatory agents. Our results show that PTTTF exhibited anti-inflammatory effects through altering the synthesis of some cytokines and other mediators of the inflammatory process.

The mTOR kinase inhibitor rapamycin enhances the expression and release of pro-inflammatory cytokine interleukin 6 modulating the activation of human microglial cells

Emerging evidence suggests the potential use of rapamycin in treatment of several neurological disorders. The drug readily crosses the blood brain barrier and may exert direct immunomodulatory effects within the brain. Microglia are the main innate immune cells of the brain, thus critically involved in the initiation and development of inflammatory processes at this level. However, there are conflicting data from rodent studies about the pharmacological effects of rapamycin on microglial inflammatory responses. Considering that rodent microglia display relevant biochemical and pharmacological differences compared to human microglia, in the present study we studied the effects of rapamycin in an experimental model of human microglia, the human microglial clone 3 (HMC3) cell line. Rapamycin was tested in the nM range both under basal conditions and in cells activated with a pro-inflammatory cytokine cocktail, consisting in a mixture of interferon-γ and interleukin-1β (II). The drug significantly increased II stimulatory effect on interleukin-6 (IL-6) expression and release in the HMC3 cells, while reducing the production of free oxygen radicals (ROS) both under basal conditions and in cells activated with II. Consistently with its known molecular mechanism of action, rapamycin reduced the extent of activation of the so-called 'mechanistic' target of rapamycin complex 1 (mTORC1) kinase and the total amount of intracellular proteins. In contrast to rodent cells, rapamycin did not alter human microglial cell viability nor inhibited cell proliferation. Moreover, rapamycin did not exert any significant effect on the morphology of the HMC3 cells. All together these data suggest that the inhibition of mTORC1 in human microglia by rapamycin results in complex immunomodulatory effects, including a significant increase in the expression and release of the pro-inflammatory IL-6.

Role of Microglia TLRs in Neurodegeneration

Toll-like receptors (TLRs) are a group of receptors widely distributed in the organism. In the central nervous system, they are expressed in neurons, astrocytes and microglia. Although their involvement in immunity is notorious, different articles have demonstrated their roles in physiological and pathological conditions, including neurodegeneration. There is increasing evidence of an involvement of TLRs, especially TLR2, 4 and 9 in neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and amyotrophic lateral sclerosis (ALS). In this sense, their expression in microglia might modulate the activity of these cells, which in turn, lead to protective or deleterious effects over neurons and other cells. Therefore, TLRs might mediate the link between inflammation and neurodegenerative diseases. However, further studies have to be performed to elucidate the role of the other TLRs in these diseases and to further prove and confirm the pathophysiological role of all TLRs in neurodegeneration. In this article, we revise and summarize the current knowledge regarding the role of TLRs in neurodegeneration with the focus on the possible functions of these receptors in microglia.

Pyrethroid bifenthrin induces oxidative stress, neuroinflammation, and neuronal damage, associated with cognitive and memory impairment in murine hippocampus

Exposure to synthetic pyrethroid (SPs) pesticides such as bifenthrin (BF) has been associated with adverse neurodevelopmental outcomes and cognitive impairments, but the underlying neurobiological mechanism is poorly understood so far. The present study has been designed to evaluate changes in behavior and in biomarkers of oxidative stress and neuroinflammation in the hippocampus of rats subchronically treated with BF. Rats exposed daily to BF at doses of 0.6 and 2.1 mg/kg b. w. for 60 days exhibited spatial and cognitive impairments as well as memory dysfunction after 60 days. This repeated BF treatment also significantly increased mRNA expression of pro-inflammatory cytokines tumor necrosis factor (TNF-α), interleukin (IL-1β), (IL-6), nuclear factor erythroid-2 (Nrf2), cyclooxygenase-2 (COX-2), nuclear factor-kappaB pathway (NF-kappaB), and prostaglandin E₂ (PGE₂) in the hippocampus. It further resulted in a significant increase in protein levels of Nrf2, COX-2, microsomal prostaglandin synthase-1 (mPGES-1) and NF-kappaB. This was accompanied by oxidative/nitrosative stress in the hippocampus of treated rats, as shown by increased levels of malondialdehyde (MDA), protein carbonyls (PCO), and nitric oxide (NO), and reduced levels of enzymatic (catalase, superoxide dismutase, and glutathione peroxidase) and non-enzymatic (reduced glutathione) antioxidants. The data are in line with those obtained in organotypic hippocampal slice cultures (OHSCs) isolated from mouse brain and exposed to BF for 72 h, showing neuronal death only at the high dose of 20 μM when compared to controls. These findings suggest that exposure to BF induces neuronal damage, alters redox state, and causes neuroinflammation in the hippocampus, which might lead to cognitive and memory impairment.

Inflammatory and oxidative mechanisms potentiate bifenthrin-induced neurological alterations and anxiety-like behavior in adult rats

Bifenthrin (BF) is a synthetic pyrethroid pesticide widely used in several countries to manage insect pests on diverse agricultural crops. Growing evidence indicates that BF exposure is associated with an increased risk of developing neurodegenerative disorders. However, the mechanisms by which BF induces neurological and anxiety alterations in the frontal cortex and striatum are not well known. The present in vivo study was carried out to determine whether reactive oxygen species (ROS)-mediated oxidative stress (OS) and neuroinflammation are involved in such alterations. Thirty-six Wistar rats were thus randomly divided into three groups and were orally administered with BF (0.6 and 2.1 mg/kg body weight, respectively) or the vehicle (corn oil), on a daily basis for 60 days. Results revealed that BF exposure in rats enhanced anxiety-like behavior after 60 days of treatment, as assessed with the elevated plus-maze test by decreases in the percentage of time spent in open arms and frequency of entries into these arms. BF-treated rats also exhibited increased oxidation of lipids and carbonylated proteins in the frontal cortex and striatum, and decreased glutathione levels and antioxidant enzyme activities including superoxide dismutase, catalase and glutathione peroxidase. Treatment with BF also increased protein synthesis and mRNA expression of the inflammatory mediators cyclooxygenase-2 (COX-2), microsomal prostaglandin synthase-1 (mPGES-1) and nuclear factor-kappaBp65 (NF-kBp65), as well as the production of tumor necrosis factor-α (TNF-α) and ROS. Moreover, BF exposure significantly decreased protein synthesis and mRNA expression of nuclear factor erythroid-2 (Nrf2) and acetylcholinesterase (AChE), as well as gene expression of muscarinic-cholinergic receptors (mAchR) and choline acetyltransferase (ChAT) in the frontal cortex and striatum. These data suggest that BF induced neurological alterations in the frontal cortex and striatum of rats, and that this may be associated with neuroinflammation and oxidative stress via the activation of Nrf2/NF-kBp65 pathways, which might promote anxiety-like behavior.

Inflammatory and cytotoxic effects of bifenthrin in primary microglia and organotypic hippocampal slice cultures

BACKGROUND

Pyrethroids, such as bifenthrin (BF), are among the most widely used class of insecticides that pose serious risks to human and wildlife health. Pyrethroids are proposed to affect astrocytic functions and to cause neuron injury in the central nervous system (CNS). Microglia are key cells involved in innate immune responses in the CNS, and microglia activation has been linked to inflammation and neurotoxicity. However, little information is known about the effects of BF-induced toxicity in primary microglial cells as well as in organotypic hippocampal slice cultures (OHSCs).

METHODS

Oxidative stress and inflammatory responses induced by BF were evaluated in primary microglial cells and OHSCs incubated with different concentrations of BF (1-20 μM) for 4 and 24 h. mRNA and protein synthesis of cyclooxygenase-2 (COX-2), tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), nuclear erythroid-2 like factor-2 (Nrf-2), and microsomal prostaglandin synthase-1 (mPGES-1) was also studied by qPCR and Western blot. Cell viability was analyzed by MTT-tetrazolio (MTT) and lactate dehydrogenase (LDH) assays. Neurotoxicity in OHSCs was analyzed by propidium iodide (PI) staining and confocal microscopy.

RESULTS

Exposure of microglial cells to BF for 24 h resulted in a dose-dependent reduction in the number of viable cells. At sub-cytotoxic concentrations, BF increased reactive oxygen species (ROS), TNF-alpha synthesis, and prostaglandin E2 (PGE2) production, at both 4- and 24-h time points, respectively. Furthermore, BF incubation decreased superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities and increased lipid peroxidation, protein oxidation, and H2O2 formation. In addition, BF significantly induced protein synthesis and mRNA expression of oxidative and inflammatory mediators after 4 and 24 h, including Nrf-2, COX-2, mPGES-1, and nuclear factor kappaB (NF-kappaB). A 24-h exposure of OHSCs to BF also increased neuronal death compared to untreated controls. Furthermore, depletion of microglia from OHSCs potently enhanced neuronal death induced by BF.

CONCLUSIONS

Overall, BF exhibited cytotoxic effects in primary microglial cells, accompanied by the induction of various inflammatory and oxidative stress markers including the Nrf-2/COX-2/mPGES-1/NF-kappaB pathways. Moreover, the study provided evidence that BF induced neuronal death in OHSCs and suggests that microglia exert a protective function against BF toxicity.

Anti-neuroinflammatory effects of Ginkgo biloba extract EGb761 in LPS-activated primary microglial cells

BACKGROUND

Neuroinflammation is a key factor of Alzheimer's disease (AD) and other neurodegenerative conditions. Microglia are the resident mononuclear immune cells of the central nervous system (CNS). They play an essential role in the maintenance of homeostasis and responses to neuroinflammation. Ginkgo biloba extract EGb 761 is one of the most commonly used natural medicines owing to its established efficacy and remarkable biological activities especially in respect to CNS diseases. However, only few studies have addressed the effects and mechanisms of Ginkgo biloba extract in microglia activation.

METHODS

We measured the production of pro-inflammatory mediators and cytokines by ELISA and analyzed gene expressions by qRT-PCR and Western Blot in LPS treated cultured primary rat microglia.

RESULTS

The Ginkgo biloba extract EGb 761 significantly inhibited the release of prostaglandin E₂ (PGE₂) and differentially regulated the levels of pro-inflammatory cytokines. The inhibition of LPS-induced PGE₂ release in primary microglia was partially dependent on reduced protein synthesis of mPGES-1 and the reduction in the activation of cytosolic phospholipase A2 (cPLA2) without altering COX-2 enzymatic activity, inhibitor of kappa B alpha (IkappaBalpha) degradation, and the activation of multiple mitogen activated protein kinases (MAPKs). Altogether, we showed that EGb 761 reduces neuro-inflammatory activation in primary microglial cells by targeting PGE₂ release and cytokines.

CONCLUSION

Ginkgo biloba extract EGb 761 displayed anti-neuroinflammatory activity in LPS-activated primary microglia cells. EGb 761 was able to reduce neuroinflammatory activation by targeting the COX/PGE₂ pathway. This effect might contribute to the established clinical cognitive efficacy in Alzheimer's disease, vascular and mixed dementia.

AM404, paracetamol metabolite, prevents prostaglandin synthesis in activated microglia by inhibiting COX activity

Background

N-arachidonoylphenolamine (AM404), a paracetamol metabolite, is a potent agonist of the transient receptor potential vanilloid type 1 (TRPV1) and low-affinity ligand of the cannabinoid receptor type 1 (CB1). There is evidence that AM404 exerts its pharmacological effects in immune cells. However, the effect of AM404 on the production of inflammatory mediators of the arachidonic acid pathway in activated microglia is still not fully elucidated.

Method

In the present study, we investigated the effects of AM404 on the eicosanoid production induced by lipopolysaccharide (LPS) in organotypic hippocampal slices culture (OHSC) and primary microglia cultures using Western blot, immunohistochemistry, and ELISA.

Results

Our results show that AM404 inhibited LPS-mediated prostaglandin E₂ (PGE₂) production in OHSC, and LPS-stimulated PGE₂ release was totally abolished in OHSC if microglial cells were removed. In primary microglia cultures, AM404 led to a significant dose-dependent decrease in the release of PGE₂, independent of TRPV1 or CB1 receptors. Moreover, AM404 also inhibited the production of PGD₂ and the formation of reactive oxygen species (8-iso-PGF₂ alpha) with a reversible reduction of COX-1- and COX-2 activity. Also, it slightly decreased the levels of LPS-induced COX-2 protein, although no effect was observed on LPS-induced mPGES-1 protein synthesis.

Conclusions

This study provides new significant insights about the potential anti-inflammatory role of AM404 and new mechanisms of action of paracetamol on the modulation of prostaglandin production by activated microglia.

Electronic supplementary material

The online version of this article (10.1186/s12974-017-1014-3) contains supplementary material, which is available to authorized users.

Activation of EP2 receptor suppresses poly(I: C) and LPS-mediated inflammation in primary microglia and organotypic hippocampal slice cultures: Contributing role for MAPKs

Brain inflammation is a critical factor involved in neurodegeneration. Recently, the prostaglandin E₂ (PGE₂ ) downstream members were suggested to modulate neuroinflammatory responses accompanying neurodegenerative diseases. In this study, we investigated the protective effects of prostaglandin E₂ receptor 2 (EP₂ ) during TLR3 and TLR4-driven inflammatory response using in vitro primary microglia and ex vivo organotypic hippocampal slice cultures (OHSCs). Depletion of microglia from OHSCs differentially affected TLR3 and TLR4 receptor expression. Poly(I:C) induced the production of prostaglandin E₂ in OHSCs by increasing cyclooxygenase (COX-2) and microsomal prostaglandin E synthase (mPGES)-1. Besides, stimulation of OHSCs and microglia with Poly(I:C) upregulated EP₂ receptor expression. Co-stimulation of OHSCs and microglia with the EP₂ agonist butaprost reduced inflammatory mediators induced by LPS and Poly(I:C). In Poly(I:C) challenged OHSCs, butaprost almost restored microglia ramified morphology and reduced Iba1 immunoreactivity. Importantly, microglia depletion prevented the induction of inflammatory mediators following Poly(I:C) or LPS challenge in OHSCs. Activation of EP₂ receptor reversed the Poly(I:C)/LPS-induced phosphorylation of the mitogen activated protein kinases (MAPKs) ERK, p38 MAPK and c-Jun N-terminal kinase (JNK) in microglia. Collectively, these data identify an anti-inflammatory function for EP₂ signaling in diverse innate immune responses, through a mechanism that involves the mitogen-activated protein kinases pathway.

Juglanin ameliorates LPS-induced neuroinflammation in animal models of Parkinson's disease and cell culture via inactivating TLR4/NF-κB pathway

Parkinson's disease (PD) is a common neuro-degenerative disorder, and novel therapeutic targets are required for the treatment of PD. Juglanin is a natural compound extracted from the crude Polygonum aviculare, exhibiting anti-inflammatory, anti-oxidant and anti-cancer activities. In our study, PD in mice was induced by systemic LPS treatment as evidenced by enhanced α-synuclein and reduced tyrosine hydroxylase (TH), which were reversed by juglanin treatment. Moreover, juglanin administration attenuated LPS-caused behavioral and memory impairments and reduced LPS-induced enhancement of neuro-degenerative markers, including amyloid β (Aβ) and p-Tau. Additionally, juglanin ameliorated synaptic functionality through promoting the expression of synaptic markers, such as SYP, PSD-95 and SNAP-25. Toll-like receptor 4 (TLR4) signaling in brain regulates neuroinflammation, contributing to neurodegenerative diseases. Furthermore, LPS induced neuroinflammation through the acceleration of various pro-inflammatory cytokines, including interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), interleukin-18 (IL-18) and Cyclooxygenase-2 (COX-2), via activating TLR4/nuclear factor (NF)-κB pathway in hippocampus of mice and microglia cells. Juglanin significantly reduced LPS-induced production of pro-inflammatory cytokines and blocked TLR4/NF-κB pathway. We also found that LPS-induced astrocytes (AST) activity was prevented by juglanin through down-regulating glial fibrillary acidic protein (GFAP) and Iba1 in vivo and in vitro. Together, our results indicated that juglanin ameliorated neuroinflammation-related memory impairment, and neurodegeneration through impeding TLR4/NF-κB, indicating its potential for PD prevention.

Alleviation of Microglial Activation Induced by p38 MAPK/MK2/PGE2 Axis by Capsaicin: Potential Involvement of other than TRPV1 Mechanism/s

Exaggerated inflammatory responses in microglia represent one of the major risk factors for various central nervous system’s (CNS) associated pathologies. Release of excessive inflammatory mediators such as prostaglandins and cytokines are the hallmark of hyper-activated microglia. Here we have investigated the hitherto unknown effects of capsaicin (cap) - a transient receptor potential vanilloid 1 (TRPV1) agonist- in murine primary microglia, organotypic hippocampal slice cultures (OHSCs) and human primary monocytes. Results demonstrate that cap (0.1–25 µM) significantly (p < 0.05) inhibited the release of prostaglandin E₂ (PGE₂)_, 8-iso-PGF_2α, and differentially regulated the levels of cytokines (TNF-α, IL-6 & IL-1β). Pharmacological blockade (via capsazepine & SB366791) and genetic deficiency of TRPV1 (TRPV1^−/−) did not prevent cap-mediated suppression of PGE₂ in activated microglia and OHSCs. Inhibition of PGE₂ was partially dependent on the reduced levels of PGE₂ synthesising enzymes, COX-2 and mPGES-1. To evaluate potential molecular targets, we discovered that cap significantly suppressed the activation of p38 MAPK and MAPKAPK2 (MK2). Altogether, we demonstrate that cap alleviates excessive inflammatory events by targeting the PGE₂ pathway in in vitro and ex vivo immune cell models. These findings have broad relevance in understanding and paving new avenues for ongoing TRPV1 based drug therapies in neuroinflammatory-associated diseases.

Neuroprotective effects of intrastriatal injection of rapamycin in a mouse model of excitotoxicity induced by quinolinic acid

Background

The mammalian target of rapamycin (mTOR) is a kinase involved in a variety of physiological and pathological functions. However, the exact role of mTOR in excitotoxicity is poorly understood. Here, we investigated the effects of mTOR inhibition with rapamycin against neurodegeneration, and motor impairment, as well as inflammatory profile caused by an excitotoxic stimulus.

Methods

A single and unilateral striatal injection of quinolinic acid (QA) was used to induce excitotoxicity in mice. Rapamycin (250 nL of 0.2, 2, or 20 μM; intrastriatal route) was administered 15 min before QA injection. Forty-eight hours after QA administration, rotarod test was performed to evaluate motor coordination and balance. Fluoro-Jade C, Iba-1, and GFAP staining were used to evaluate neuronal cell death, microglia morphology, and astrocytes density, respectively, at this time point. Levels of cytokines and neurotrophic factors were measured by ELISA and Cytometric Bead Array 8 h after QA injection. Striatal synaptosomes were used to evaluate the release of glutamate.

Results

We first demonstrated that rapamycin prevented the motor impairment induced by QA. Moreover, mTOR inhibition also reduced the neurodegeneration and the production of interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α induced by excitotoxic stimulus. The lowest dose of rapamycin also increased the production of IL-10 and prevented the reduction of astrocyte density induced by QA. By using an in vitro approach, we demonstrated that rapamycin differently alters the release of glutamate from striatal synaptosomes induced by QA, reducing or enhancing the release of this neurotransmitter at low or high concentrations, respectively.

Conclusion

Taken together, these data demonstrated a protective effect of rapamycin against an excitotoxic stimulus. Therefore, this study provides new evidence of the detrimental role of mTOR in neurodegeneration, which might represent an important target for the treatment of neurodegenerative diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-017-0793-x) contains supplementary material, which is available to authorized users.

Apocynin inhibits Toll-like receptor-4-mediated activation of NF-κB by suppressing the Akt and mTOR pathways

Microbial product lipopolysaccharide has been shown to be involved in the pathogenesis of inflammatory skin diseases. Apocynin has demonstrated to have an anti-inflammatory effect. However, the effect of apocynin on the Toll-like receptor-4-dependent activation of Akt, mammalian target of rapamycin (mTOR), and nuclear factor (NF)-κB pathway, which is involved in productions of inflammatory mediators in keratinocytes, has not been studied. Using human keratinocytes, we investigated the effect of apocynin on the inflammatory mediator production in relation to the Toll-like receptor-4-mediated-Akt/mTOR and NF-κB pathways, which regulates the transcription genes involved in immune and inflammatory responses. Apocynin, Akt inhibitor SH-5, Bay 11-7085 and N-acetylcysteine each attenuated the lipopolysaccharide-induced production of cytokines, PGE₂, and chemokines, changes in the levels of Toll-like receptor-4, p-Akt, mTOR, and NF-κB, and production of reactive oxygen species in keratinocytes. The results show that apocynin appears to attenuate the lipopolysaccharide-stimulated production of inflammatory mediators in keratinocytes by suppressing the Toll-like receptor-4-mediated activation of the Akt, mTOR, and NF-κB pathways. The effect of apocynin appears to be attributed to its inhibitory effect on the production of reactive oxygen species. Apocynin appears to attenuate the microbial product-mediated inflammatory skin diseases.

Neuroprotective effects of the anticancer drug NVP-BEZ235 (dactolisib) on amyloid-β 1-42 induced neurotoxicity and memory impairment

Alzheimer's Disease (AD) is a progressive neurodegenerative disease and the main cause of dementia. Substantial evidences indicate that there is over-activation of the PI3K/Akt/mTOR axis in AD. Therefore, the aim of the present study was to investigate the effects of NVP-BEZ235 (BEZ; dactolisib), a dual PI3K/mTOR inhibitor that is under phase I/II clinical trials for the treatment of some types of cancer, in hippocampal neuronal cultures stimulated with amyloid-β (Aβ) 1-42 and in mice injected with Aβ 1-42 in the hippocampus. In cell cultures, BEZ reduced neuronal death induced by Aβ. BEZ, but not rapamycin, a mTOR inhibitor, or LY294002, a PI3K inhibitor that also inhibits mTOR, reduced the memory impairment induced by Aβ. The effect induced by Aβ was also prevented in PI3Kγ(-/-) mice. Neuronal death and microgliosis induced by Aβ were reduced by BEZ. In addition, the compound increased IL-10 and TNF-α levels in the hippocampus. Finally, BEZ did not change the phosphorylation of Akt and p70s6K, suggesting that the involvement of PI3K and mTOR in the effects induced by BEZ remains controversial. Therefore, BEZ represents a potential strategy to prevent the pathological outcomes induced by Aβ and should be investigated in other models of neurodegenerative conditions.