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Microglia-driven neuroinflammation plays an important role in the development of Alzheimers disease. Microglia activation is accompanied by the formation and chronic expression of TLR4 inflammarafts, defined as enlarged and cholesterol-rich lipid rafts serving as an assembly platform for TLR4 dimers and complexes of other inflammatory receptors. The secreted apoA-I binding protein (APOA1BP or AIBP) binds TLR4 and selectively targets cholesterol depletion machinery to TLR4 inflammaraft-expressing inflammatory, but not homeostatic microglia. Here we demonstrated that amyloid-beta (Aβ) induced formation of TLR4 inflammarafts in microglia in vitro and in the brain of APP/PS1 mice. Mitochondria in Apoa1bp-/- APP/PS1 microglia were hyperbranched and cupped, which was accompanied by increased reactive oxygen species and the dilated endoplasmic reticulum. The size and number of Aβ plaques and neuronal cell death were significantly increased, and the animal survival was decreased in Apoa1bp-/-APP/PS1 compared to APP/PS1 female mice. These results suggest that AIBP exerts control of TLR4 inflammarafts and mitochondrial dynamics in microglia and plays a protective role in Alzheimers disease associated oxidative stress and neurodegeneration.

Abstract Microglia-driven neuroinflammation plays an important role in the development of Alzheimer’s disease. Microglia activation is accompanied by the formation and chronic expression of TLR4 inflammarafts, defined as enlarged and cholesterol-rich lipid rafts serving as an assembly platform for TLR4 dimers and complexes of other inflammatory receptors. The secreted apoA-I binding protein (APOA1BP or AIBP) binds TLR4 and selectively targets cholesterol depletion machinery to TLR4 inflammaraft-expressing inflammatory, but not homeostatic microglia. Here we demonstrated that amyloid-beta (Aβ) induced formation of TLR4 inflammarafts in microglia in vitro and in the brain of APP/PS1 mice. Mitochondria in Apoa1bp −/− APP/PS1 microglia were hyperbranched and cupped, which was accompanied by increased reactive oxygen species and the dilated endoplasmic reticulum. The size and number of Aβ plaques and neuronal cell death were significantly increased, and the animal survival was decreased in Apoa1bp −/− APP/PS1 compared to APP/PS1 female mice. These results suggest that AIBP exerts control of TLR4 inflammarafts and mitochondrial dynamics in microglia and plays a protective role in Alzheimer’s disease associated oxidative stress and neurodegeneration.

Abstract Luteolin is a flavonoid found in high concentrations in celery and green pepper, and acts as a neuroprotectant. PSMC5 (proteasome 26S subunit, ATPase 5) protein levels were reduced after luteolin stimulation in activated microglia. We aimed to determine whether regulating PSMC5 expression could inhibit neuroinflammation, and investigate the underlying mechanisms.BV2 microglia were transfected with siRNA PSMC5 before the addition of LPS (lipopolysaccharide, 1.0 µg/ml) for 24 h in serum free DMEM. A mouse model of LPS-induced cognitive and motor impairment was established to evaluate the neuroprotective effects of shRNA PSMC5. Intracerebroventricular administration of shRNA PSMC5 was commenced 7 days prior to i.p. injection of LPS (750 μg/kg). Treatments and behavioral experiments were performed once daily for 7 consecutive days. Behavioral tests and pathological/biochemical assays were performed to evaluate LPS-induced hippocampal damage. Molecular dynamics simulation was used to confirm the interaction between PSMC5 and TLR4 (Toll-like receptor 4) in LPS-stimulated BV2 microglia. SiRNA PSMC5 inhibited BV2 microglial activation, and suppressed the release of inflammatory factors (IL-1β, COX-2, PGE2, TNF-α, and iNOS) upon after LPS stimulation in BV2 microglia. LPS increased IκB-α and p65 phosphorylation, which was attenuated by siRNA PSMC5. Behavioral tests and pathological/biochemical assays showed that shRNA PSMC5 attenuated LPS-induced cognitive and motor impairments, and restored synaptic ultrastructure and protein levels in mice. ShRNA PSMC5 reduced pro-inflammatory cytokine (TNF-α, IL-1β, PGE2, and NO) levels in the serum and brain, and relevant protein factors (iNOS and COX-2) in the brain. Furthermore, shRNA PSMC5 upregulated the anti-inflammatory mediators interleukin IL-4 and IL-10 in the serum and brain, and promoted a pro-inflammation-to-anti-inflammation phenotype shift in microglial polarization. Mechanistically, shRNA PSMC5 significantly alleviated LPS-induced TLR4 expression. The polarization of LPS-induced microglial pro-inflammation phenotype was abolished by TLR4 inhibitor and in the TLR-4−/− mouse, as in shRNA PSMC5 treatment. PSMC5 interacted with TLR4 via the amino sites Glu284, Met139, Leu127, and Phe283. PSMC5 site mutations attenuated neuroinflammation and reduced pro-inflammatory factors by reducing TLR4-related effects, thereby reducing TLR4-mediated MyD88 (myeloid differentiation factor 88)-dependent activation of NF-κB. PSMC5 could be an important therapeutic target for treatment of neurodegenerative diseases involving neuroinflammation-associated cognitive deficits and motor impairments induced by microglial activation. Graphical Abstract

Abstract Chronic activation and dysfunction of microglia have been implicated in the pathogenesis and progression of many neurodegenerative disorders, including Huntington’s disease (HD). HD is a genetic condition caused by a mutation that affects the folding and function of huntingtin (HTT). Signs of microglia activation have been observed in HD patients even before the onset of symptoms. It is unclear, however, whether pro-inflammatory microglia activation in HD results from cell-autonomous expression of mutant HTT, is the response of microglia to a diseased brain environment, or both. In this study, we used primary microglia isolated from HD knock-in (Q140) and wild-type (Q7) mice to investigate their response to inflammatory conditions in vitro in the absence of confounding effects arising from brain pathology. We show that naïve Q140 microglia do not undergo spontaneous pro-inflammatory activation and respond to inflammatory triggers, including stimulation of TLR4 and TLR2 and exposure to necrotic cells, with similar kinetics of pro-inflammatory gene expression as wild-type microglia. Upon termination of the inflammatory insult, the transcription of pro-inflammatory cytokines is tapered off in Q140 and wild-type microglia with similar kinetics. However, the ability of Q140 microglia to develop tolerance in response to repeated inflammatory stimulations is partially impaired in vitro and in vivo, potentially contributing to the establishment of chronic neuroinflammation in HD. We further show that ganglioside GM1, a glycosphingolipid with anti-inflammatory effects on wild-type microglia, not only decreases the production of pro-inflammatory cytokines and nitric oxide in activated Q140 microglia, but also dramatically dampen microglia response to re-stimulation with LPS in an experimental model of tolerance. These effects are independent from the expression of interleukin 1 receptor associated kinase 3 (Irak-3), a strong modulator of LPS signaling involved in the development of innate immune tolerance and previously shown to be upregulated by immune cell treatment with gangliosides. Altogether, our data suggest that external triggers are required for HD microglia activation, but a cell-autonomous dysfunction that affects the ability of HD microglia to acquire tolerance might contribute to the establishment of neuroinflammation in HD. Administration of GM1 might be beneficial to attenuate chronic microglia activation and neuroinflammation.

Luteolin is a flavonoid found in high concentrations in celery and green pepper, and acts as a neuroprotectant. PSMC5 (proteasome 26S subunit, ATPase 5) protein levels were reduced after luteolin stimulation in activated microglia. We aimed to determine whether regulating PSMC5 expression could inhibit neuroinflammation, and investigate the underlying mechanisms.BV2 microglia were transfected with siRNA PSMC5 before the addition of LPS (lipopolysaccharide, 1.0 µg/ml) for 24 h in serum free DMEM. A mouse model of LPS-induced cognitive and motor impairment was established to evaluate the neuroprotective effects of shRNA PSMC5. Intracerebroventricular administration of shRNA PSMC5 was commenced 7 days prior to i.p. injection of LPS (750 μg/kg). Treatments and behavioral experiments were performed once daily for 7 consecutive days. Behavioral tests and pathological/biochemical assays were performed to evaluate LPS-induced hippocampal damage. Molecular dynamics simulation was used to confirm the interaction between PSMC5 and TLR4 (Toll-like receptor 4) in LPS-stimulated BV2 microglia. SiRNA PSMC5 inhibited BV2 microglial activation, and suppressed the release of inflammatory factors (IL-1β, COX-2, PGE2, TNF-α, and iNOS) upon after LPS stimulation in BV2 microglia. LPS increased IκB-α and p65 phosphorylation, which was attenuated by siRNA PSMC5. Behavioral tests and pathological/biochemical assays showed that shRNA PSMC5 attenuated LPS-induced cognitive and motor impairments, and restored synaptic ultrastructure and protein levels in mice. ShRNA PSMC5 reduced pro-inflammatory cytokine (TNF-α, IL-1β, PGE2, and NO) levels in the serum and brain, and relevant protein factors (iNOS and COX-2) in the brain. Furthermore, shRNA PSMC5 upregulated the anti-inflammatory mediators interleukin IL-4 and IL-10 in the serum and brain, and promoted a pro-inflammation-to-anti-inflammation phenotype shift in microglial polarization. Mechanistically, shRNA PSMC5 significantly alleviated LPS-induced TLR4 expression. The polarization of LPS-induced microglial pro-inflammation phenotype was abolished by TLR4 inhibitor and in the TLR-4−/− mouse, as in shRNA PSMC5 treatment. PSMC5 interacted with TLR4 via the amino sites Glu284, Met139, Leu127, and Phe283. PSMC5 site mutations attenuated neuroinflammation and reduced pro-inflammatory factors by reducing TLR4-related effects, thereby reducing TLR4-mediated MyD88 (myeloid differentiation factor 88)-dependent activation of NF-κB. PSMC5 could be an important therapeutic target for treatment of neurodegenerative diseases involving neuroinflammation-associated cognitive deficits and motor impairments induced by microglial activation. [ABSTRACT FROM AUTHOR]

Chronic activation and dysfunction of microglia have been implicated in the pathogenesis and progression of many neurodegenerative disorders, including Huntington's disease (HD). HD is a genetic condition caused by a mutation that affects the folding and function of huntingtin (HTT). Signs of microglia activation have been observed in HD patients even before the onset of symptoms. It is unclear, however, whether pro-inflammatory microglia activation in HD results from cell-autonomous expression of mutant HTT, is the response of microglia to a diseased brain environment, or both. In this study, we used primary microglia isolated from HD knock-in (Q140) and wild-type (Q7) mice to investigate their response to inflammatory conditions in vitro in the absence of confounding effects arising from brain pathology. We show that naïve Q140 microglia do not undergo spontaneous pro-inflammatory activation and respond to inflammatory triggers, including stimulation of TLR4 and TLR2 and exposure to necrotic cells, with similar kinetics of pro-inflammatory gene expression as wild-type microglia. Upon termination of the inflammatory insult, the transcription of pro-inflammatory cytokines is tapered off in Q140 and wild-type microglia with similar kinetics. However, the ability of Q140 microglia to develop tolerance in response to repeated inflammatory stimulations is partially impaired in vitro and in vivo, potentially contributing to the establishment of chronic neuroinflammation in HD. We further show that ganglioside GM1, a glycosphingolipid with anti-inflammatory effects on wild-type microglia, not only decreases the production of pro-inflammatory cytokines and nitric oxide in activated Q140 microglia, but also dramatically dampen microglia response to re-stimulation with LPS in an experimental model of tolerance. These effects are independent from the expression of interleukin 1 receptor associated kinase 3 (Irak-3), a strong modulator of LPS signaling involved in the development of innate immune tolerance and previously shown to be upregulated by immune cell treatment with gangliosides. Altogether, our data suggest that external triggers are required for HD microglia activation, but a cell-autonomous dysfunction that affects the ability of HD microglia to acquire tolerance might contribute to the establishment of neuroinflammation in HD. Administration of GM1 might be beneficial to attenuate chronic microglia activation and neuroinflammation. [ABSTRACT FROM AUTHOR]

BackgroundRecent clinical and basic research implicated a strong correlation between NAFLD/NASH phenotypes with ectopic manifestations including neuroinflammation and neurodegeneration, but the mediators and critical pathways involved are not well understood. Lipocalin 2 (Lcn2) is one of the important mediators exclusively produced in the liver and circulation during NASH pathology.MethodsUsing murine model of NASH, we studied the role of Lcn2 as a potent mediator of neuroinflammation and neurodegeneration in NASH pathology via the liver-brain axis.ResultsResults showed that high circulatory Lcn2 activated 24p3R (Lipocalin2 receptor) in the brain and induced the release of high mobility group box 1 (HMGB1) preferably from brain cells. Released HMGB1 acted as a preferential ligand to toll-like receptor 4 (TLR4) and induced oxidative stress by activation of NOX-2 signaling involving activated p65 protein of the NF-κB complex. Further, the HMGB1-derived downstream signaling cascade activated NLRP3 inflammasome and release of proinflammatory cytokines IL-6 and IL-1β from brain cells. In addition, to advance our present understanding, in vitro studies were performed in primary brain endothelial cells where results showed high circulatory Lcn2 influenced HMGB1 secretion. Mechanistically, we also showed that elevated Lcn2 level in underlying NASH might be a likely cause for induction of blood-brain barrier dysfunction since the adipokine decreased the expression of tight junction protein Claudin 5 and caused subsequent elevation of pro-inflammatory cytokines IL-6 and IL-1β.ConclusionIn conclusion, the NASH-induced brain pathology might be because of increased Lcn2-induced release of HMGB1 and accompanying neuroinflammation.

Abstract Background Metabolic syndrome (MS) is defined as a low-grade proinflammatory state in which abnormal metabolic and cardiovascular factors increase the risk of developing cardiovascular disease and neuroinflammation. Events, such as the accumulation of visceral adipose tissue, increased plasma concentrations of free fatty acids, tissue hypoxia, and sympathetic hyperactivity in MS may contribute to the direct or indirect activation of Toll-like receptors (TLRs), specifically TLR4, which is thought to be a major component of this syndrome. Activation of the innate immune response via TLR4 may contribute to this state of chronic inflammation and may be related to the neuroinflammation and neurodegeneration observed in MS. In this study, we investigated the role of TLR4 in the brain microcirculation and in the cognitive performance of high-fat diet (HFD)-induced MS mice. Methods Wild-type (C3H/He) and TLR4 mutant (C3H/HeJ) mice were maintained under a normal diet (ND) or a HFD for 24 weeks. Intravital video-microscopy was used to investigate the functional capillary density, endothelial function, and endothelial–leukocyte interactions in the brain microcirculation. Plasma concentrations of monocyte chemoattractant protein-1 (MCP-1), adipokines and metabolic hormones were measured with a multiplex immunoassay. Brain postsynaptic density protein-95 and synaptophysin were evaluated by western blotting; astrocytic coverage of the vessels, microglial activation and structural capillary density were evaluated by immunohistochemistry. Results The HFD-induced MS model leads to metabolic, hemodynamic, and microcirculatory alterations, as evidenced by capillary rarefaction, increased rolling and leukocyte adhesion in postcapillary venules, endothelial dysfunction, and less coverage of astrocytes in the vessels, which are directly related to cognitive decline and neuroinflammation. The same model of MS reproduced in mice deficient for TLR4 because of a genetic mutation does not generate such changes. Furthermore, the comparison of wild-type mice fed a HFD and a normolipid diet revealed differences in inflammation in the cerebral microcirculation, possibly related to lower TLR4 activation. Conclusions Our results demonstrate that TLR4 is involved in the microvascular dysfunction and neuroinflammation associated with HFD-induced MS and possibly has a causal role in the development of cognitive decline.

Abstract Background Traumatic brain injury (TBI) is a significant cause of death and disability worldwide. The TLR4-NFκB signaling cascade is the critical pro-inflammatory activation pathway of leukocytes after TBI, and modulating this signaling cascade may be an effective therapeutic target for treating TBI. Previous studies indicate that recombinant annexin A2 (rA2) might be an interactive molecule modulating the TLR4-NFκB signaling; however, the role of rA2 in regulating this signaling pathway in leukocytes after TBI and its subsequent effects have not been investigated. Methods C57BL/6 mice were subjected to TBI and randomly divided into groups that received intraperitoneal rA2 or vehicle at 2 h after TBI. The peripheral leukocyte activation and infiltrating immune cells were examined by flow cytometry, RT-qPCR, and immunostaining. The neutrophilic TLR4 expression on the cell membrane was examined by flow cytometry and confocal microscope, and the interaction of annexin A2 with TLR4 was assessed by co-immunoprecipitation coupled with Western blotting. Neuroinflammation was measured via cytokine proteome profiler array and RT-qPCR. Neurodegeneration was determined by Western blotting and immunostaining. Neurobehavioral assessments were used to monitor motor and cognitive function. Brain tissue loss was assessed via MAP2 staining. Results rA2 administration given at 2 h after TBI significantly attenuates neutrophil activation and brain infiltration at 24 h of TBI. In vivo and in vitro data show that rA2 binds to and reduces TLR4 expression on the neutrophil surface and suppresses TLR4/NFκB signaling pathway in neutrophils at 12 h after TBI. Furthermore, rA2 administration also reduces pro-inflammation of brain tissues within 24 h and neurodegeneration at 48 h after TBI. Lastly, rA2 improves long-term sensorimotor ability and cognitive function, and reduces brain tissue loss at 28 days after TBI. Conclusions Systematic rA2 administration at 2 h after TBI significantly inhibits activation and brain infiltration of peripheral leukocytes, especially neutrophils at the acute phase. Consequently, rA2 reduces the detrimental brain pro-inflammation-associated neurodegeneration and ultimately ameliorates neurological deficits after TBI. The underlying molecular mechanism might be at least in part attributed to rA2 bindings to pro-inflammatory receptor TLR4 in peripheral leukocytes, thereby blocking NFκB signaling activation pathways following TBI.

Background: Metabolic syndrome (MS) is defined as a low-grade proinflammatory state in which abnormal metabolic and cardiovascular factors increase the risk of developing cardiovascular disease and neuroinflammation. Events, such as the accumulation of visceral adipose tissue, increased plasma concentrations of free fatty acids, tissue hypoxia, and sympathetic hyperactivity in MS may contribute to the direct or indirect activation of Toll-like receptors (TLRs), specifically TLR4, which is thought to be a major component of this syndrome. Activation of the innate immune response via TLR4 may contribute to this state of chronic inflammation and may be related to the neuroinflammation and neurodegeneration observed in MS. In this study, we investigated the role of TLR4 in the brain microcirculation and in the cognitive performance of high-fat diet (HFD)-induced MS mice.Methods: Wild-type (C3H/He) and TLR4 mutant (C3H/HeJ) mice were maintained under a normal diet (ND) or a HFD for 24 weeks. Intravital video-microscopy was used to investigate the functional capillary density, endothelial function, and endothelial-leukocyte interactions in the brain microcirculation. Plasma concentrations of monocyte chemoattractant protein-1 (MCP-1), adipokines and metabolic hormones were measured with a multiplex immunoassay. Brain postsynaptic density protein-95 and synaptophysin were evaluated by western blotting; astrocytic coverage of the vessels, microglial activation and structural capillary density were evaluated by immunohistochemistry.Results: The HFD-induced MS model leads to metabolic, hemodynamic, and microcirculatory alterations, as evidenced by capillary rarefaction, increased rolling and leukocyte adhesion in postcapillary venules, endothelial dysfunction, and less coverage of astrocytes in the vessels, which are directly related to cognitive decline and neuroinflammation. The same model of MS reproduced in mice deficient for TLR4 because of a genetic mutation does not generate such changes. Furthermore, the comparison of wild-type mice fed a HFD and a normolipid diet revealed differences in inflammation in the cerebral microcirculation, possibly related to lower TLR4 activation.Conclusions: Our results demonstrate that TLR4 is involved in the microvascular dysfunction and neuroinflammation associated with HFD-induced MS and possibly has a causal role in the development of cognitive decline. [ABSTRACT FROM AUTHOR]

Abstract Background While the etiology remains elusive, macrophages and T cells in peripheral nerves are considered as effector cells mediating autoimmune peripheral neuropathy (APN), such as Guillain-Barre syndrome. By recognizing both pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) signals, TLRs play a central role in the initiation of both innate and adaptive immune responses. In this study, we aimed to understand the involvement of TLR4 in the pathogenesis of APN and explore the potential of TLR4 as a drug target for therapeutic use. Methods APN was induced by a partial ligation on one of the sciatic nerves in B7.2 (L31) transgenic mice which possess a predisposed inflammatory background. APN pathology and neurological function were evaluated on the other non-injured sciatic nerve. Results TLR4 and its endogenous ligand HMGB1 were highly expressed in L31 mice, in circulating immune cells and in peripheral nerves. Enhanced TLR4 signaling was blocked with TAK 242, a selective TLR4 inhibitor, before and after disease onset. Intraperitoneal administration of TAK 242 not only inhibited monocyte, macrophage and CD8+ T cell activation, but also reduced the release of pro-inflammatory cytokines. TAK 242 protected mice from severe myelin and axonal loss, resulting in a remarkable improvement in mouse motor and sensory functions. TAK 242 was effective in alleviating the disease in both preventive and reversal paradigms. Conclusion The study identified the critical contribution of TLR4-mediated macrophage activation in disease course and provided strong evidence to support TLR4 as a useful drug target for treating inflammatory autoimmune neuropathy.

Abstract Background Microglia, the principal sentinel immune cells of the central nervous system (CNS), play an extensively vital role in neuroinflammation and perioperative neurocognitive disorders (PND). Histamine, a potent mediator of inflammation, can both promote and prevent microglia-related neuroinflammation by activating different histamine receptors. Rat microglia express four histamine receptors (H1R, H2R, H3R, and H4R), among which the histamine 1 and 4 receptors can promote microglia activation, whereas the role and cellular mechanism of the histamine 2 and 3 receptors have not been elucidated. Therefore, we evaluated the effects and potential cellular mechanisms of histamine 2/3 receptors in microglia-mediated inflammation and PND. Methods This study investigated the role of histamine 2/3 receptors in microglia-induced inflammation and PND both in vivo and in vitro. In the in vivo experiments, rats were injected with histamine 2/3 receptor agonists in the right lateral ventricle and were then subjected to exploratory laparotomy. In the in vitro experiments, primary microglia were pretreated with histamine 2/3 receptor agonists before stimulation with lipopolysaccharide (LPS). Cognitive function, microglia activation, proinflammatory cytokine production, NF-κb expression, M1/M2 phenotypes, cell migration, and Toll-like receptor-4 (TLR4) expression were assessed. Results In our study, the histamine 2/3 receptor agonists inhibited exploratory laparotomy- or LPS-induced cognitive decline, microglia activation, proinflammatory cytokine production, NF-κb expression, M1/M2 phenotype transformation, cell migration, and TLR4 expression through the PI3K/AKT/FoxO1 pathway. Conclusion Based on our findings, we conclude that histamine 2/3 receptors ameliorate PND by inhibiting microglia activation through the PI3K/AKT/FoxO1 pathway. Our results highlight histamine 2/3 receptors as potential therapeutic targets to treat neurological conditions associated with PND.

Abstract Background Recent clinical and basic research implicated a strong correlation between NAFLD/NASH phenotypes with ectopic manifestations including neuroinflammation and neurodegeneration, but the mediators and critical pathways involved are not well understood. Lipocalin 2 (Lcn2) is one of the important mediators exclusively produced in the liver and circulation during NASH pathology. Methods Using murine model of NASH, we studied the role of Lcn2 as a potent mediator of neuroinflammation and neurodegeneration in NASH pathology via the liver-brain axis. Results Results showed that high circulatory Lcn2 activated 24p3R (Lipocalin2 receptor) in the brain and induced the release of high mobility group box 1 (HMGB1) preferably from brain cells. Released HMGB1 acted as a preferential ligand to toll-like receptor 4 (TLR4) and induced oxidative stress by activation of NOX-2 signaling involving activated p65 protein of the NF-κB complex. Further, the HMGB1-derived downstream signaling cascade activated NLRP3 inflammasome and release of proinflammatory cytokines IL-6 and IL-1β from brain cells. In addition, to advance our present understanding, in vitro studies were performed in primary brain endothelial cells where results showed high circulatory Lcn2 influenced HMGB1 secretion. Mechanistically, we also showed that elevated Lcn2 level in underlying NASH might be a likely cause for induction of blood-brain barrier dysfunction since the adipokine decreased the expression of tight junction protein Claudin 5 and caused subsequent elevation of pro-inflammatory cytokines IL-6 and IL-1β. Conclusion In conclusion, the NASH-induced brain pathology might be because of increased Lcn2-induced release of HMGB1 and accompanying neuroinflammation.

Abstract Background Cannabinoid-2 receptor (CB2R) plays an important role in the cascading inflammation following ischemic injury. The toll-like receptors 4 (TLR4)/matrix metalloproteinase 9 (MMP9) signal pathway is involved in blood-brain barrier dysfunction induced by ischemia stroke. The aim of this study is to investigate the roles of exogenous activation of CB2R on attenuating neurological deficit and blood-spinal cord barrier (BSCB) disruption during rat spinal cord ischemia reperfusion (I/R) injury, through modulation of the TLR4/MMP9 axis. Methods Animals were intraperitoneally pretreated with TLR4 inhibitor TAK-242, CB2R agonist JWH-133 with or without CB2R antagonist AM630, or equivalent volume of vehicle 1 h before undergoing 14-min occlusion of descending aorta or sham operation. One, two, three, and 7 days after reperfusion, hindlimb locomotor function was evaluated with Basso, Beattie, and Bresnahan (BBB) Locomotor Scale, BSCB integrity was detected by measurement of Evans blue (EB) extravasation and spinal cord edema. The protein expression levels of CB2R, tight junction protein Zonula occluden-1 (ZO-1), TLR4, MMP9, MyD88, NF-κB p65, and NF-κB p-p65 were determined by western blot. The MMP9 activity was analyzed by gelatin zymography. Double immunofluorescence staining was used to identify the perivascular localization of CB2R, TLR4, MMP9, and reactive astrocytes, as well as the colocalization of CB2R, TLR4, and MMP9 with reactive astrocytes. Results JWH-133 pretreatment attenuated hindlimb motor functional deficit and BSCB leakage, along with preventing downregulation of ZO-1 and upregulation of TLR4/MMP9, similar to the effects of TAK-242 preconditioning. JWH-133 or TAK-242 pretreatment reduced the perivascular expression of TLR4/MMP9 and reactive astrocytes following injury. JWH-133 pretreatment also downregulated MyD88/NF-κB level, MMP9 activity, and the astrocytic TLR4/MMP9 after I/R injury. Conclusions Exogenous activation of CB2R by JWH-133 attenuated neurological deficit and BSCB disruption after spinal cord I/R injury via inhibition of TLR4/MMP9 expression.

Background: Traumatic brain injury (TBI) is a significant cause of death and disability worldwide. The TLR4-NFκB signaling cascade is the critical pro-inflammatory activation pathway of leukocytes after TBI, and modulating this signaling cascade may be an effective therapeutic target for treating TBI. Previous studies indicate that recombinant annexin A2 (rA2) might be an interactive molecule modulating the TLR4-NFκB signaling; however, the role of rA2 in regulating this signaling pathway in leukocytes after TBI and its subsequent effects have not been investigated.Methods: C57BL/6 mice were subjected to TBI and randomly divided into groups that received intraperitoneal rA2 or vehicle at 2 h after TBI. The peripheral leukocyte activation and infiltrating immune cells were examined by flow cytometry, RT-qPCR, and immunostaining. The neutrophilic TLR4 expression on the cell membrane was examined by flow cytometry and confocal microscope, and the interaction of annexin A2 with TLR4 was assessed by co-immunoprecipitation coupled with Western blotting. Neuroinflammation was measured via cytokine proteome profiler array and RT-qPCR. Neurodegeneration was determined by Western blotting and immunostaining. Neurobehavioral assessments were used to monitor motor and cognitive function. Brain tissue loss was assessed via MAP2 staining.Results: rA2 administration given at 2 h after TBI significantly attenuates neutrophil activation and brain infiltration at 24 h of TBI. In vivo and in vitro data show that rA2 binds to and reduces TLR4 expression on the neutrophil surface and suppresses TLR4/NFκB signaling pathway in neutrophils at 12 h after TBI. Furthermore, rA2 administration also reduces pro-inflammation of brain tissues within 24 h and neurodegeneration at 48 h after TBI. Lastly, rA2 improves long-term sensorimotor ability and cognitive function, and reduces brain tissue loss at 28 days after TBI.Conclusions: Systematic rA2 administration at 2 h after TBI significantly inhibits activation and brain infiltration of peripheral leukocytes, especially neutrophils at the acute phase. Consequently, rA2 reduces the detrimental brain pro-inflammation-associated neurodegeneration and ultimately ameliorates neurological deficits after TBI. The underlying molecular mechanism might be at least in part attributed to rA2 bindings to pro-inflammatory receptor TLR4 in peripheral leukocytes, thereby blocking NFκB signaling activation pathways following TBI. [ABSTRACT FROM AUTHOR]

Abstract Background Neuraminidase (NA) is a sialidase present, among various locations, in the envelope/membrane of some bacteria/viruses (e.g., influenza virus), and is involved in infectiveness and/or dispersion. The administration of NA within the brain lateral ventricle represents a model of acute sterile inflammation. The relevance of the Toll-like receptors TLR2 and TLR4 (particularly those in microglial cells) in such process was investigated. Methods Mouse strains deficient in either TLR2 (TLR2-/-) or TLR4 (TLR4-/-) were used. NA was injected in the lateral ventricle, and the inflammatory reaction was studied by immunohistochemistry (IBA1 and IL-1β) and qPCR (cytokine response). Also, microglia was isolated from those strains and in vitro stimulated with NA, or with TLR2/TLR4 agonists as positive controls (P3C and LPS respectively). The relevance of the sialidase activity of NA was investigated by stimulating microglia with heat-inactivated NA, or with native NA in the presence of sialidase inhibitors (oseltamivir phosphate and N-acetyl-2,3-dehydro-2-deoxyneuraminic acid). Results In septofimbria and hypothalamus, IBA1-positive and IL-1β-positive cell counts increased after NA injection in wild type (WT) mice. In TLR4-/- mice, such increases were largely abolished, while were only slightly diminished in TLR2-/- mice. Similarly, the NA-induced expression of IL-1β, TNFα, and IL-6 was completely blocked in TLR4-/- mice, and only partially reduced in TLR2-/- mice. In isolated cultured microglia, NA induced a cytokine response (IL-1β, TNFα, and IL-6) in WT microglia, but was unable to do so in TLR4-/- microglia; TLR2 deficiency partially affected the NA-induced microglial response. When WT microglia was exposed in vitro to heat-inactivated NA or to native NA along with sialidase inhibitors, the NA-induced microglia activation was almost completely abrogated. Conclusions NA is able to directly activate microglial cells, and it does so mostly acting through the TLR4 receptor, while TLR2 has a secondary role. Accordingly, the inflammatory reaction induced by NA in vivo is partially dependent on TLR2, while TLR4 plays a crucial role. Also, the sialidase activity of NA is critical for microglial activation. These results highlight the relevance of microbial NA in the neuroinflammation provoked by NA-bearing pathogens and the possibility of targeting its sialidase activity to ameliorate its impact.

Abstract Background Toll-like receptor 4 (TLR4) is well known for activating the innate immune system; however, it is also highly expressed in adaptive immune cells, such as CD4+ T-helper 17 (Th17) cells, which play a key role in multiple sclerosis (MS) pathology. However, the function and governing mechanism of TLR4 in Th17 remain unclear. Methods The changes of TLR4 in CD4+ T cells from MS patients and experimental autoimmune encephalomyelitis (EAE) mice were tested. TLR4-deficient (TLR4−/−) naïve T cells were induced in vitro and transferred into Rag1−/− mice to measure Th17 differentiation and EAE pathology. DNA sequence analyses combining with deletion fragments and mutation analyses, chromatin immunoprecipitation (ChIP), and electrophoretic mobility shift assay (EMSA) were used to explore the mechanism of TLR4 signaling pathway in regulating Th17 differentiation. Results The levels of TLR4 were increased in CD4+ Th17 cells both from MS patients and EAE mice, as well as during Th17 differentiation in vitro. TLR4−/− CD4+ naïve T cells inhibited their differentiation into Th17, and transfer of TLR4−/− CD4+ naïve T cells into Rag1−/− mice was defective in promoting EAE, characterized by less demyelination and Th17 infiltration in the spinal cord. TLR4 signal enhanced Th17 differentiation by activating RelA, downregulating the expression of miR-30a, a negative regulator of Th17 differentiation. Inhibition of RelA activity increased miR-30a level, but decreased Th17 differentiation rate. Furthermore, RelA directly regulated the expression of miR-30a via specific binding to a conserved element of miR-30a gene. Conclusions TLR4−/− CD4+ naïve T cells are inadequate in differentiating to Th17 cells both in vitro and in vivo. TLR4-RelA-miR-30a signal pathway regulates Th17 differentiation via direct binding of RelA to the regulatory element of miR-30a gene. Our results indicate modulating TLR4-RelA-miR-30a signal in Th17 may be a therapeutic target for Th17-mediated neurodegeneration in neuroinflammatory diseases.

Abstract Background Baicalin, which is isolated from Radix Scutellariae, possesses strong biological activities including an anti-inflammation property. Recent studies have shown that the anti-inflammatory effect of baicalin is linked to toll-like receptor 4 (TLR4), which participates in pathological changes of central nervous system diseases such as depression. In this study, we explored whether baicalin could produce antidepressant effects via regulation of TLR4 signaling in mice and attempted to elucidate the underlying mechanisms. Methods A chronic unpredictable mild stress (CUMS) mice model was performed to explore whether baicalin could produce antidepressant effects via the inhibition of neuroinflammation. To clarify the role of TLR4 in the anti-neuroinflammatory efficacy of baicalin, a lipopolysaccharide (LPS) was employed in mice to specially activate TLR4 and the behavioral changes were determined. Furthermore, we used LY294002 to examine the molecular mechanisms of baicalin in regulating the expression of TLR4 in vivo and in vitro using western blot, ELISA kits, and immunostaining. In the in vitro tests, the BV2 microglia cell lines and primary microglia cultures were pretreated with baicalin and LY292002 for 1 h and then stimulated 24 h with LPS. The primary microglial cells were transfected with the forkhead transcription factor forkhead box protein O 1 (FoxO1)-specific siRNA for 5 h and then co-stimulated with baicalin and LPS to investigate whether FoxO1 participated in the effect of baicalin on TLR4 expression. Results The administration of baicalin (especially 60 mg/kg) dramatically ameliorated CUMS-induced depressive-like symptoms; substantially decreased the levels of interleukin-1 beta (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-α) in the hippocampus; and significantly decreased the expression of TLR4. The activation of TLR4 by the LPS triggered neuroinflammation and evoked depressive-like behaviors in mice, which were also alleviated by the treatment with baicalin (60 mg/kg). Furthermore, the application of baicalin significantly increased the phosphorylation of phosphatidylinositol 3-kinase (PI3K), protein kinase B (AKT), and FoxO1. The application of baicalin also promoted FoxO1 nuclear exclusion and contributed to the inhibition of the FoxO1 transactivation potential, which led to the downregulation of the expression of TLR4 in CUMS mice or LPS-treated BV2 cells and primary microglia cells. However, prophylactic treatment of LY294002 abolished the above effects of baicalin. In addition, we found that FoxO1 played a vital role in baicalin by regulating the TLR4 and TLR4-mediating neuroinflammation triggered by the LPS via knocking down the expression of FoxO1 in the primary microglia. Conclusion Collectively, these results demonstrate that baicalin ameliorated neuroinflammation-induced depressive-like behaviors through the inhibition of TLR4 expression via the PI3K/AKT/FoxO1 pathway.

Abstract Background Amyotrophic lateral sclerosis (ALS) is a fatal and rapidly progressing neurodegenerative disease without effective treatment. The receptor for advanced glycation end products (RAGE) and the toll-like receptor (TLR) system are major components of the innate immune system, which have been implicated in ALS pathology. Extracellularly released high-mobility group box 1 (HMGB1) is a pleiotropic danger-associated molecular pattern (DAMP), and is an endogenous ligand for both RAGE and TLR4. Methods The present study examined the effect of HMGB1 inhibition on disease progression in the preclinical SOD1G93A transgenic mouse model of ALS using a potent anti-HMGB1 antibody (2G7), which targets the extracellular DAMP form of HMGB1. Results We found that chronic intraperitoneal dosing of the anti-HMGB1 antibody to SOD1G93A mice transiently improved hind-limb grip strength early in the disease, but did not extend survival. Anti-HMGB1 treatment also reduced tumour necrosis factor α and complement C5a receptor 1 gene expression in the spinal cord, but did not affect overall glial activation. Conclusions In summary, our results indicate that therapeutic targeting of an extracellular DAMP, HMGB1, improves early motor dysfunction, but overall has limited efficacy in the SOD1G93A mouse model of ALS.

Background: While the etiology remains elusive, macrophages and T cells in peripheral nerves are considered as effector cells mediating autoimmune peripheral neuropathy (APN), such as Guillain-Barre syndrome. By recognizing both pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) signals, TLRs play a central role in the initiation of both innate and adaptive immune responses. In this study, we aimed to understand the involvement of TLR4 in the pathogenesis of APN and explore the potential of TLR4 as a drug target for therapeutic use.Methods: APN was induced by a partial ligation on one of the sciatic nerves in B7.2 (L31) transgenic mice which possess a predisposed inflammatory background. APN pathology and neurological function were evaluated on the other non-injured sciatic nerve.Results: TLR4 and its endogenous ligand HMGB1 were highly expressed in L31 mice, in circulating immune cells and in peripheral nerves. Enhanced TLR4 signaling was blocked with TAK 242, a selective TLR4 inhibitor, before and after disease onset. Intraperitoneal administration of TAK 242 not only inhibited monocyte, macrophage and CD8+ T cell activation, but also reduced the release of pro-inflammatory cytokines. TAK 242 protected mice from severe myelin and axonal loss, resulting in a remarkable improvement in mouse motor and sensory functions. TAK 242 was effective in alleviating the disease in both preventive and reversal paradigms.Conclusion: The study identified the critical contribution of TLR4-mediated macrophage activation in disease course and provided strong evidence to support TLR4 as a useful drug target for treating inflammatory autoimmune neuropathy. [ABSTRACT FROM AUTHOR]

Abstract Background Depression is one of the most common mental disorders characterized mainly by low mood and loss of interest or pleasure. About a third of patients with depression do not respond to classic antidepressant treatments. Recent evidence suggests that Mrp8/14 (myeloid-related protein 8/14) plays a crucial role in cognitive dysfunction and neuroinflammatory diseases, yet its role in mood regulation remains largely uninvestigated. In the present work, we explored the potential role of Mrp8/14 in the progression of depression. Methods After 4 weeks of chronic unpredictable mild stress (CUMS), depressive-like symptoms and Mrp8/14 were determined. To verify the effects of Mrp8/14 on depressive-like behaviors, the inhibitor TAK-242 and recombinant Mrp8/14 were used. Furthermore, the molecular mechanisms in Mrp8/14-induced behavioral and biological changes were examined in vivo and ex vivo. Results Four-week CUMS contributed to the development of depressive symptoms. Mrp8 and Mrp14 were upregulated in the hippocampus and serum after exposure to CUMS. Pharmacological inhibition of Mrp14 attenuated CUMS-induced TLR4/NF-κB signaling activation and depressive-like behaviors. Furthermore, central administration of recombinant Mrp8, Mrp14, and Mrp8/14 resulted in neuroinflammation and depressive-like behaviors. Mrp8/14-provoked proinflammatory effects and depressive-like behaviors were improved by pretreatment with a TLR4 inhibitor. Moreover, pharmacological inhibition of TLR4 reduced the release of nitric oxide and reactive oxygen species in Mrp8/14-activated BV2 microglia. Conclusions These data suggest that the hippocampal Mrp8/14-TLR4-mediated neuroinflammation contributes to the development of depressive-like behaviors. Targeting the Mrp8/14 may be a novel promising antidepressant approach.

Abstract Background The steroid hormone estrogen (17-β-estradiol, E2) provides neuroprotection against cerebral ischemic injury by activating estrogen receptors. The novel estrogen receptor G protein-coupled receptor 30 (GPR30) is highly expressed in the brain and provides acute neuroprotection against stroke. However, the underlying mechanisms remain unclear. Methods In this study, ovariectomized female mice were subjected to middle cerebral artery occlusion (MCAO), and E2, G1, and ICI182780 were administered immediately upon reperfusion. The infarction volume, neurological scores, and neuronal injuries were examined. Primary microglial cells were subjected to oxygen-glucose deprivation (OGD), and the drugs were administered immediately upon reintroduction. The pro-inflammatory cytokines TNF-α, IL-1β, and IL-6 in penumbra and microglia were assessed by ELISA. The cell viability and lactose dehydrogenase (LDH) release of neurons co-cultured with microglia were analyzed using cell counting kit-8 (CCK8) and LDH release assays. Microglial activation as well as GPR30, Iba1, and Toll-like receptor 4 (TLR4) protein expression and TLR4 mRNA expression were detected. Additionally, NF-κB activity was detected in lipopolysaccharide (LPS)-activated microglia after the activation of GPR30. Results GPR30 was highly expressed in microglia and significantly increased after ischemic injury. The activation of GPR30 significantly reduced the infarction volume, improved the neurological deficit, and alleviated neuronal injuries. Moreover, GPR30 activation significantly reduced the release of TNF-α, IL-1β, and IL-6 from ischemic penumbra and microglia subjected to OGD and alleviated neuronal injury as assessed using the CCK8 and LDH assays. Finally, the activation of GPR30 relieved microglial activation, reduced Iba1 and TLR4 protein expression and TLR4 mRNA levels, and inhibited NF-κB activity. Conclusions Microglial GPR30 exerts acute neuroprotective effects by inhibiting TLR4-mediated microglial inflammation, which indicates that GPR30 may be a potential target for the treatment of ischemic stroke.

Abstract Background Porphyromonas gingivalis lipopolysaccharide (P. gingivalis-LPS) is one of the major pathogenic factors of chronic periodontitis (CP). Few reports on the correlation between P. gingivalis-LPS and cognitive function exist. Thus, the present study aimed to investigate the effects of P. gingivalis-LPS on cognitive function and the associated underlying mechanism in C57BL/6 mice. Methods The C57BL/6 mice were injected with P. gingivalis-LPS (5 mg kg−1) either with or without Toll-like receptor 4 (TLR4) inhibitor (TAK-242, 5 mg kg−1). After 7 days, behavioral alterations were assessed with the open field test (OFT), Morris water maze (MWM) test, and passive avoidance test (PAT). The activation of astrocytes and microglia in the cerebral cortex and hippocampus of mice was observed by immunohistochemistry. The expression of inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-8), TLRs (TLR2, TLR3, and TLR4), and CD14 and the activation of the NF-κB signaling pathway (IRAK1, p65, and p-p65) in the cerebral cortex of the mice were evaluated by RT-PCR, ELISA, and western blot. Results The OFT showed that P. gingivalis-LPS did not affect the initiative and activity of mice. Administration of P. gingivalis-LPS significantly impaired spatial learning and memory during the MWM test and attenuated the ability of passive avoidance learning during the PAT. Both astrocytes and microglia were activated in the cortex and hippocampus. The messenger RNA (mRNA) and protein expression of inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-8) was upregulated by P. gingivalis-LPS in the cortex. In addition, the TLR4/NF-κB signaling pathway was activated (TLR4, CD14, IRAK1, and p-p65). These effects were effectively alleviated by TAK-242. Conclusions Administration of P. gingivalis-LPS can lead to learning and memory impairment in C57BL/6 mice. This impairment is mediated by activation of the TLR4 signaling pathway. Our study suggests that P. gingivalis-LPS-induced neuroinflammation plays an important role in cognitive impairment. It also reveals that endotoxins of periodontal pathogens could represent a risk factor for cognitive disorders.

Background: Microglia, the principal sentinel immune cells of the central nervous system (CNS), play an extensively vital role in neuroinflammation and perioperative neurocognitive disorders (PND). Histamine, a potent mediator of inflammation, can both promote and prevent microglia-related neuroinflammation by activating different histamine receptors. Rat microglia express four histamine receptors (H1R, H2R, H3R, and H4R), among which the histamine 1 and 4 receptors can promote microglia activation, whereas the role and cellular mechanism of the histamine 2 and 3 receptors have not been elucidated. Therefore, we evaluated the effects and potential cellular mechanisms of histamine 2/3 receptors in microglia-mediated inflammation and PND.Methods: This study investigated the role of histamine 2/3 receptors in microglia-induced inflammation and PND both in vivo and in vitro. In the in vivo experiments, rats were injected with histamine 2/3 receptor agonists in the right lateral ventricle and were then subjected to exploratory laparotomy. In the in vitro experiments, primary microglia were pretreated with histamine 2/3 receptor agonists before stimulation with lipopolysaccharide (LPS). Cognitive function, microglia activation, proinflammatory cytokine production, NF-κb expression, M1/M2 phenotypes, cell migration, and Toll-like receptor-4 (TLR4) expression were assessed.Results: In our study, the histamine 2/3 receptor agonists inhibited exploratory laparotomy- or LPS-induced cognitive decline, microglia activation, proinflammatory cytokine production, NF-κb expression, M1/M2 phenotype transformation, cell migration, and TLR4 expression through the PI3K/AKT/FoxO1 pathway.Conclusion: Based on our findings, we conclude that histamine 2/3 receptors ameliorate PND by inhibiting microglia activation through the PI3K/AKT/FoxO1 pathway. Our results highlight histamine 2/3 receptors as potential therapeutic targets to treat neurological conditions associated with PND. [ABSTRACT FROM AUTHOR]

Background: Cannabinoid-2 receptor (CB2R) plays an important role in the cascading inflammation following ischemic injury. The toll-like receptors 4 (TLR4)/matrix metalloproteinase 9 (MMP9) signal pathway is involved in blood-brain barrier dysfunction induced by ischemia stroke. The aim of this study is to investigate the roles of exogenous activation of CB2R on attenuating neurological deficit and blood-spinal cord barrier (BSCB) disruption during rat spinal cord ischemia reperfusion (I/R) injury, through modulation of the TLR4/MMP9 axis.Methods: Animals were intraperitoneally pretreated with TLR4 inhibitor TAK-242, CB2R agonist JWH-133 with or without CB2R antagonist AM630, or equivalent volume of vehicle 1 h before undergoing 14-min occlusion of descending aorta or sham operation. One, two, three, and 7 days after reperfusion, hindlimb locomotor function was evaluated with Basso, Beattie, and Bresnahan (BBB) Locomotor Scale, BSCB integrity was detected by measurement of Evans blue (EB) extravasation and spinal cord edema. The protein expression levels of CB2R, tight junction protein Zonula occluden-1 (ZO-1), TLR4, MMP9, MyD88, NF-κB p65, and NF-κB p-p65 were determined by western blot. The MMP9 activity was analyzed by gelatin zymography. Double immunofluorescence staining was used to identify the perivascular localization of CB2R, TLR4, MMP9, and reactive astrocytes, as well as the colocalization of CB2R, TLR4, and MMP9 with reactive astrocytes.Results: JWH-133 pretreatment attenuated hindlimb motor functional deficit and BSCB leakage, along with preventing downregulation of ZO-1 and upregulation of TLR4/MMP9, similar to the effects of TAK-242 preconditioning. JWH-133 or TAK-242 pretreatment reduced the perivascular expression of TLR4/MMP9 and reactive astrocytes following injury. JWH-133 pretreatment also downregulated MyD88/NF-κB level, MMP9 activity, and the astrocytic TLR4/MMP9 after I/R injury.Conclusions: Exogenous activation of CB2R by JWH-133 attenuated neurological deficit and BSCB disruption after spinal cord I/R injury via inhibition of TLR4/MMP9 expression. [ABSTRACT FROM AUTHOR]

Abstract Background It has been shown that chronic stress-induced depression is associated with exaggerated inflammatory response in the brain. Alpha7 nicotinic acetylcholine receptors (α7nAChRs) regulate the cholinergic anti-inflammatory pathway, but the role of cholinergic signaling and α7nAChR in chronic stress has not yet been examined. Methods In this study, we used a well-documented model of depression in which mice were exposed to 6 h of restraint stress for 21 consecutive days. Components of cholinergic signaling and TLR4 signaling were analyzed in the hippocampus. The main targets of neuroinflammation and neuronal damage were also evaluated after a series of tests for depression-like behavior. Results Chronic restraint stress (CRS) induced alterations in components of central cholinergic signaling in hippocampus, including increases in choline acetyltransferase protein expression and decreases in nuclear STAT3 signaling. CRS also increased TLR4 signaling activity, interleukin-1β, and tumor necrosis factor-α expression, microglial activation, and neuronal morphologic changes. Cholinergic stimulation with the α7nAChR agonist DMXBA significantly alleviated CRS-induced depressive-like behavior, neuroinflammation, and neuronal damage, but these effects were abolished by the selective α7nAChR antagonist α-bungarotoxin. Furthermore, activation of α7nAChRs restored the central cholinergic signaling function, inhibited TLR4-mediated inflammatory signaling and microglial activity, and increased the number of regulatory T cells in the hippocampus. Conclusions These findings provide evidence that α7nAChR activation mitigates CRS-induced neuroinflammation and cell death, suggesting that α7nAChRs could be a new therapeutic target for the prevention and treatment of depression.

Abstract Background Long-term use of morphine induces analgesic tolerance, which limits its clinical efficacy. Evidence indicated morphine-evoked neuroinflammation mediated by toll-like receptor 4 (TLR4) - NOD-like receptor protein 3 (NLRP3) inflammasome was important for morphine tolerance. In our study, we investigated whether other existing alternative pathways caused morphine-induced activation of TLR4 in microglia. We focused on heat shock protein 70 (HSP70), a damage-associated molecular pattern (DAMP), which was released from various cells upon stimulations under the control of KATP channel and bound with TLR4-inducing inflammation. Glibenclamide, a classic KATP channel blocker, can improve neuroinflammation by inhibiting the activation of NLRP3 inflammasome. Our present study investigated the effect and possible mechanism of glibenclamide in improving morphine tolerance via its specific inhibition on the release of HSP70 and activation of NLRP3 inflammasome induced by morphine. Methods CD-1 mice were used for tail-flick test to evaluate morphine tolerance. The microglial cell line BV-2 and neural cell line SH-SY5Y were used to investigate the pharmacological effects and the mechanism of glibenclamide on morphine-induced neuroinflammation. The activation of microglia was accessed by immunofluorescence staining. Neuroinflammation-related cytokines were measured by western blot and real-time PCR. The level of HSP70 and related signaling pathway were evaluated by western blot and immunofluorescence staining. Results Morphine induced the release of HSP70 from neurons. The released HSP70 activated microglia and triggered TLR4-mediated inflammatory response, leading to the phosphorylation of p38 mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) p65 and the activation of NLRP3 inflammasome. Moreover, anti-HSP70 neutralizing antibody partly attenuated chronic morphine tolerance. The secretion of HSP70 was under the control of MOR/AKT/KATP/ERK signal pathway. Glibenclamide as a classic KATP channel blocker markedly inhibited the release of HSP70 induced by morphine and suppressed HSP70-TLR4-NLRP3 inflammasome-mediated neuroinflammation, which consequently attenuated morphine tolerance. Conclusions Our study indicated that morphine-induced extracellular HSP70 was an alternative way for the activation of TLR4-NLRP3 in analgesic tolerance. The release of HSP70 was regulated by MOR/AKT/KATP/ERK pathway. Our study suggested a promising target, KATP channel and a new leading compound, glibenclamide, for treating morphine tolerance.

Abstract Background The primary cilium is an organelle that can act as a master regulator of cellular signaling. Despite the presence of primary cilia in hippocampal neurons, their function is not fully understood. Recent studies have demonstrated that the primary cilium influences interleukin (IL)-1β-induced NF-κB signaling, ultimately mediating the inflammatory response. We, therefore, investigated ciliary function and NF-κB signaling in lipopolysaccharide (LPS)-induced neuroinflammation in conjunction with ciliary length analysis. Methods Since TLR4/NF-κB signaling is a well-known inflammatory pathway, we measured ciliary length and inflammatory mediators in wild type (WT) and TLR4−/− mice injected with LPS. Next, to exclude the effects of microglial TLR4, we examined the ciliary length, ciliary components, inflammatory cytokine, and mediators in HT22 hippocampal neuronal cells. Results Primary ciliary length decreased in hippocampal pyramidal neurons after intracerebroventricular injection of LPS in WT mice, whereas it increased in TLR4−/− mice. LPS treatment decreased primary ciliary length, activated NF-κB signaling, and increased Cox2 and iNOS levels in HT22 hippocampal neurons. In contrast, silencing Kif3a, a key protein component of cilia, increased ARL13B ciliary protein levels and suppressed NF-κB signaling and expression of inflammatory mediators. Conclusions These data suggest that LPS-induced NF-κB signaling and inflammatory mediator expression are modulated by cilia and that the blockade of primary cilium formation by Kif3a siRNA regulates TLR4-induced NF-κB signaling. We propose that primary cilia are critical for regulating NF-κB signaling events in neuroinflammation and in the innate immune response.

Abstract Background Inflammation during brain development participates in the pathogenesis of early brain injury and cognitive dysfunctions. Prenatal ethanol exposure affects the developing brain and causes neural impairment, cognitive and behavioral effects, collectively known as fetal alcohol spectrum disorders (FASD). Our previous studies demonstrate that ethanol activates the innate immune response and TLR4 receptor and causes neuroinflammation, brain damage, and cognitive defects in the developmental brain stage of adolescents. We hypothesize that by activating the TLR4 response, maternal alcohol consumption during pregnancy triggers the release of cytokines and chemokines in both the maternal sera and brains of fetuses/offspring, which impairs brain ontogeny and causes cognitive dysfunction. Methods WT and TLR4-KO female mice treated with or without 10% ethanol in the drinking water during gestation and lactation were used. Cytokine/chemokine levels were determined by ELISA in the amniotic fluid, maternal serum, and cerebral cortex, as well as in the offspring cerebral cortex. Microglial and neuronal markers (evaluated by western blotting), myelin proteins (immunohistochemical and western blotting) and synaptic parameters (western blotting and electron microscopy) were assessed in the cortices of the WT and TLR4-KO pups on PND 0, 20, and 66. Behavioral tests (elevated plus maze and passive avoidance) were performed in the WT and TLR4-KO mice on PND 66 exposed or not to ethanol. Results We show that alcohol intake during gestation and lactation increases the levels of several cytokines/chemokines (IL-1β, IL-17, MIP-1α, and fractalkine) in the maternal sera, amniotic fluid, and brains of fetuses and offspring. The upregulation of cytokines/chemokines is associated with an increase in activated microglia markers (CD11b and MHC-II), and with a reduction in some synaptic (synaptotagmin, synapsin IIa) and myelin (MBP, PLP) proteins in the brains of offspring on days 0, 20, and 66 (long-term effects). These changes are associated with long-term behavioral impairments, in the 66-day-old alcohol-exposed pups. TLR4-deficient mice are protected against ethanol-induced cytokine/chemokine production in alcohol-treated dams and offspring, along with synaptic and myelin alterations, and the log-term behavioral dysfunction induced by ethanol in offspring. Conclusions These results suggest that the immune system activation, through the TLR4 response, might play an important role in the neurodevelopmental defects in FASD.

Abstract Background Exposure to traffic-related air pollution (TRAP) is associated with accelerated cognitive aging and higher dementia risk in human populations. Rodent brains respond to TRAP with activation of astrocytes and microglia, increased inflammatory cytokines, and neurite atrophy. A role for Toll-like receptor 4 (TLR4) was suggested in mouse TLR4-knockouts, which had attenuated lung macrophage responses to air pollution. Methods To further analyze these mechanisms, we examined mixed glial cultures (astrocytes and microglia) for RNA responses to nanoscale particulate matter (nPM; diameter

Background: Inflammation during brain development participates in the pathogenesis of early brain injury and cognitive dysfunctions. Prenatal ethanol exposure affects the developing brain and causes neural impairment, cognitive and behavioral effects, collectively known as fetal alcohol spectrum disorders (FASD). Our previous studies demonstrate that ethanol activates the innate immune response and TLR4 receptor and causes neuroinflammation, brain damage, and cognitive defects in the developmental brain stage of adolescents. We hypothesize that by activating the TLR4 response, maternal alcohol consumption during pregnancy triggers the release of cytokines and chemokines in both the maternal sera and brains of fetuses/offspring, which impairs brain ontogeny and causes cognitive dysfunction.Methods: WT and TLR4-KO female mice treated with or without 10% ethanol in the drinking water during gestation and lactation were used. Cytokine/chemokine levels were determined by ELISA in the amniotic fluid, maternal serum, and cerebral cortex, as well as in the offspring cerebral cortex. Microglial and neuronal markers (evaluated by western blotting), myelin proteins (immunohistochemical and western blotting) and synaptic parameters (western blotting and electron microscopy) were assessed in the cortices of the WT and TLR4-KO pups on PND 0, 20, and 66. Behavioral tests (elevated plus maze and passive avoidance) were performed in the WT and TLR4-KO mice on PND 66 exposed or not to ethanol.Results: We show that alcohol intake during gestation and lactation increases the levels of several cytokines/chemokines (IL-1β, IL-17, MIP-1α, and fractalkine) in the maternal sera, amniotic fluid, and brains of fetuses and offspring. The upregulation of cytokines/chemokines is associated with an increase in activated microglia markers (CD11b and MHC-II), and with a reduction in some synaptic (synaptotagmin, synapsin IIa) and myelin (MBP, PLP) proteins in the brains of offspring on days 0, 20, and 66 (long-term effects). These changes are associated with long-term behavioral impairments, in the 66-day-old alcohol-exposed pups. TLR4-deficient mice are protected against ethanol-induced cytokine/chemokine production in alcohol-treated dams and offspring, along with synaptic and myelin alterations, and the log-term behavioral dysfunction induced by ethanol in offspring.Conclusions: These results suggest that the immune system activation, through the TLR4 response, might play an important role in the neurodevelopmental defects in FASD. [ABSTRACT FROM AUTHOR]

Background: Exposure to traffic-related air pollution (TRAP) is associated with accelerated cognitive aging and higher dementia risk in human populations. Rodent brains respond to TRAP with activation of astrocytes and microglia, increased inflammatory cytokines, and neurite atrophy. A role for Toll-like receptor 4 (TLR4) was suggested in mouse TLR4-knockouts, which had attenuated lung macrophage responses to air pollution.Methods: To further analyze these mechanisms, we examined mixed glial cultures (astrocytes and microglia) for RNA responses to nanoscale particulate matter (nPM; diameter <0.2 μm), a well-characterized nanoscale particulate matter subfraction of TRAP collected from a local freeway (Morgan et al. Environ Health Perspect 2011; 119,1003-1009, 2011). The nPM was compared with responses to the endotoxin lipopolysaccharide (LPS), a classic TLR4 ligand, using Affymetrix whole genome microarray in rats. Expression patterns were analyzed by significance analysis of microarrays (SAM) for fold change and by weighted gene co-expression network analysis (WGCNA) to identify modules of shared responses between nPM and LPS. Finally, we examined TLR4 activation in hippocampal tissue from mice chronically exposed to nPM.Results: SAM and WGCNA analyses showed strong activation of TLR4 and NF-κB by both nPM and LPS. TLR4 siRNA attenuated TNFα and other inflammatory responses to nPM in vitro, via the MyD88-dependent pathway. In vivo, mice chronically exposed to nPM showed increased TLR4, MyD88, TNFα, and TNFR2 RNA, and decreased NF-κB and TRAF6 RNA TLR4 and NF-κB responses in the hippocampus.Conclusions: These results show TLR4 activation is integral in brain inflammatory responses to air pollution, and warrant further study of TLR4 in accelerated cognitive aging by air pollution. [ABSTRACT FROM AUTHOR]

Background: Pleiotrophin (PTN) is a cytokine found highly upregulated in the brain in different disorders characterized by overt neuroinflammation such as neurodegenerative diseases, drug addiction, traumatic injury, and ischemia. In the present work, we have explored whether PTN modulates neuroinflammation and if Toll-like receptor 4 (TLR4), crucial in the initiation of an immune response, is involved.Methods: In immunohistochemistry assays, we studied lipopolysaccharide (LPS, 7.5 mg/kg i.p.)-induced changes in glial fibrillary acidic protein (GFAP, astrocyte marker) and ionized calcium-binding adaptor molecule 1 (Iba1, microglia marker) expression in the prefrontal cortex (PFC) and striatum of mice with transgenic PTN overexpression in the brain (PTN-Tg) and in wild-type (WT) mice. Cytokine protein levels were assessed in the PFC by X-MAP technology. The influence of TLR4 signaling in LPS effects in both genotypes was assessed by pretreatment with the TLR4 antagonist (TAK-242, 3.0 mg/kg i.p.). Murine BV2 microglial cells were treated with PTN (0.5 μg/ml) and LPS (1.0 μg/ml) and assessed for the release of nitric oxide (NO).Results: We found that LPS-induced microglial activation is significantly increased in the PFC of PTN-Tg mice compared to that of WT mice. The levels of TNF-α, IL-6, and MCP-1 in response to LPS were significantly increased in the PFC of PTN-Tg mice compared to that of WT mice. Pretreatment with TAK-242 efficiently blocked increases in cytokine contents in a similar manner in both genotypes. Concomitant incubation of BV2 cells with LPS and PTN significantly potentiated the production of NO compared to cells only treated with LPS.Conclusions: Our findings identify for the first time that PTN is a novel and potent regulator of neuroinflammation. Pleiotrophin potentiates LPS-stimulated microglia activation. Our results suggest that regulation of the PTN signaling pathways may constitute new therapeutic opportunities particularly in those neurological disorders characterized by increased PTN cerebral levels and neuroinflammation. [ABSTRACT FROM AUTHOR]

Background: Toll-like receptors (TLRs) are transmembrane pattern-recognition receptors of the innate immune system recognizing diverse pathogen-derived and tissue damage-related ligands. It has been suggested that TLR signaling contributes to the pathogenesis of age-related, neurodegenerative diseases, including Alzheimer's disease (AD). AD is associated to oligomers of the amyloid β peptide (Aβo) that cause intracellular Ca2+ dishomeostasis and neuron cell death in rat hippocampal neurons. Here we assessed the interplay between inflammation and Aβo in long-term cultures of rat hippocampal neurons, an in vitro model of neuron aging and/or senescence.Methods: Ca2+ imaging and immunofluorescence against annexin V and TLR4 were applied in short- and long-term cultures of rat hippocampal neurons to test the effects of TLR4-agonist LPS and Aβo on cytosolic [Ca2+] and on apoptosis as well as on expression of TLR4.Results: LPS increases cytosolic [Ca2+] and promotes apoptosis in rat hippocampal neurons in long-term culture considered aged and/or senescent neurons, but not in short-term cultured neurons considered young neurons. TLR4 antagonist CAY10614 prevents both effects. TLR4 expression in rat hippocampal neurons is significantly larger in aged hippocampal cultures. Treatment of aged hippocampal cultures with Aβo increases TLR4 expression and enhances LPS-induced Ca2+ responses and neuron cell death.Conclusions: Aging and amyloid β oligomers, the neurotoxin involved in Alzheimer's disease, enhance TLR4 expression as well as LPS-induced Ca2+ responses and neuron cell death in rat hippocampal neurons aged in vitro. [ABSTRACT FROM AUTHOR]

Background: Accumulating evidence suggest that the enteric nervous system (ENS) plays important roles in gastrointestinal inflammatory responses, which could be in part mediated by Toll-like receptor (TLR) activation. The aim of this study was to characterise the expression and functionality of TLR2/4/9 in the ENS.Methods: TLR2/4/9 expression was assessed in the plexuses of adult rats and embryonic ENS cultures by immunofluorescence and quantitative PCR. Following stimulation with TLR2/4/9 ligands or their combinations, activation of NF-kB, production of TNF-α, IL-6 and MCP-1 and chemoattraction of RAW264.7 macrophages were evaluated by means of Western blot, ELISA, immunofluorescence and migration assays in transwell inserts.Results: TLR2/4/9 staining colocalised with enteric neuronal markers, whereas their presence in enteroglial processes was low to inexistent. Stimulation of ENS cultures with selective ligands induced NF-kB activation and release of cytokines and chemokines by neurons and resident immunocytes. TLR2 neutralisation before lipopolysaccharide (LPS) challenge reduced production of inflammatory mediators, whereas combination of TLR2/4 ligands promoted macrophage migration. Combined stimulation of cultures with LPS and the CpG oligonucleotide 1826 (TLR4/9 ligands) caused a synergic increase in chemoattraction and cytokine production.Conclusions: Our results suggest that the ENS, and particularly enteric neurons, can integrate a variety of microbial signals and respond in a relatively selective fashion, depending on the particular TLRs stimulated. These findings additionally suggest that the ENS is capable of initiating a defensive response against pathogens and expanding inflammation. [ABSTRACT FROM AUTHOR]

Background: Harmful effects of activated microglia are due, in part, to the formation of peroxynitrite radicals, which is attributable to the upregulation of inducible nitric oxide (NO) synthase (NOS2). Because NOS2 expression is determined by Ca(2+)-sensitive calcineurin (CN) dephosphorylating nuclear factor of activated T cells (NFAT), and because Sur1-Trpm4 channels are crucial for regulating Ca(2+) influx, we hypothesized that, in activated microglia, Sur1-Trpm4 channels play a central role in regulating CN/NFAT and downstream target genes such as Nos2.Methods: We studied microglia in vivo and in primary culture from adult rats, and from wild type, Abcc8-/- and Trpm4-/- mice, and immortalized N9 microglia, following activation of Toll-like receptor 4 (TLR4) by lipopolysaccharide (LPS), using in situ hybridization, immunohistochemistry, co-immunoprecipitation, immunoblot, qPCR, patch clamp electrophysiology, calcium imaging, the Griess assay, and chromatin immunoprecipitation.Results: In microglia in vivo and in vitro, LPS activation of TLR4 led to de novo upregulation of Sur1-Trpm4 channels and CN/NFAT-dependent upregulation of Nos2 mRNA, NOS2 protein, and NO. Pharmacological inhibition of Sur1 (glibenclamide), Trpm4 (9-phenanthrol), or gene silencing of Abcc8 or Trpm4 reduced Nos2 upregulation. Inhibiting Sur1-Trpm4 increased the intracellular calcium concentration ([Ca(2+)]i), as expected, but also decreased NFAT nuclear translocation. The increase in [Ca(2+)]i induced by inhibiting or silencing Sur1-Trpm4 resulted in phosphorylation of Ca(2+)/calmodulin protein kinase II and of CN, consistent with reduced nuclear translocation of NFAT. The regulation of NFAT by Sur1-Trpm4 was confirmed using chromatin immunoprecipitation.Conclusions: Sur1-Trpm4 constitutes a novel mechanism by which TLR4-activated microglia regulate pro-inflammatory, Ca(2+)-sensitive gene expression, including Nos2. [ABSTRACT FROM AUTHOR]

Background: IL-1β, also known as "the master regulator of inflammation", is a potent pro-inflammatory cytokine secreted by activated microglia in response to pathogenic invasions or neurodegeneration. It initiates a vicious cycle of inflammation and orchestrates various molecular mechanisms involved in neuroinflammation. The role of IL-1β has been extensively studied in neurodegenerative disorders; however, molecular mechanisms underlying inflammation induced by IL-1β are still poorly understood. The objective of our study is the comprehensive identification of molecular circuitry involved in IL-1β-induced inflammation in microglia through protein profiling.Methods: To achieve our aim, we performed the proteomic analysis of N9 microglial cells with and without IL-1β treatment at different time points. Expression of HSP60 in response to IL-1β administration was checked by quantitative real-time PCR, immunoblotting, and immunofluorescence. Interaction of HSP60 with TLR4 was determined by co-immunoprecipitation. Inhibition of TLR4 was done using TLR4 inhibitor to reveal its effect on IL-1β-induced inflammation. Further, effect of HSP60 knockdown and overexpression were assessed on the inflammation in microglia. Specific MAPK inhibitors were used to reveal the downstream MAPK exclusively involved in HSP60-induced inflammation in microglia.Results: Total 21 proteins were found to be differentially expressed in response to IL-1β treatment in N9 microglial cells. In silico analysis of these proteins revealed unfolded protein response as one of the most significant molecular functions, and HSP60 turned out to be a key hub molecule. IL-1β induced the expression as well as secretion of HSP60 in extracellular milieu during inflammation of N9 cells. Secreted HSP60 binds to TLR4 and inhibition of TLR4 suppressed IL-1β-induced inflammation to a significant extent. Our knockdown and overexpression studies demonstrated that HSP60 increases the phosphorylation of ERK, JNK, and p38 MAPKs in N9 cells during inflammation. Specific inhibition of p38 by inhibitors suppressed HSP60-induced inflammation, thus pointed towards the major role of p38 MAPK rather than ERK1/2 and JNK in HSP60-induced inflammation. Furthermore, silencing of upstream modulator of p38, i.e., MEK3/6 also reduced HSP60-induced inflammation.Conclusions: IL-1β induces expression of HSP60 in N9 microglial cells that further augments inflammation via TLR4-p38 MAPK axis. [ABSTRACT FROM AUTHOR]

Background: Amyotrophic lateral sclerosis (ALS) is a devastating late onset neurodegenerative disorder that is characterised by the progressive loss of upper and lower motor neurons. The mechanisms underlying ALS pathogenesis are unclear; however, there is emerging evidence the innate immune system, including components of the toll-like receptor (TLR) system, may drive disease progression. For example, toll-like receptor 4 (TLR4) antagonism in a spontaneous 'wobbler mouse' model of ALS increased motor function, associated with a decrease in microglial activation. This study therefore aimed to extend from these findings and determine the expression and function of TLR4 signalling in hSOD1G93A mice, the most widely established preclinical model of ALS. Findings: TLR4 and one of its major endogenous ligands, high-mobility group box 1 (HMGB1), were increased during disease progression in hSOD1G93A mice, with TLR4 and HMGB1 expressed by activated microglia and astrocytes. hSOD1G93A mice lacking TLR4 showed transient improvements in hind-limb grip strength and significantly extended survival when compared to TLR4-sufficient hSOD1G93A mice. Conclusion: These results suggest that enhanced glial TLR4 signalling during disease progression contributes to end-stage ALS pathology in hSOD1G93A mice. [ABSTRACT FROM AUTHOR]

Background: Despite the availability of several antihypertensive medications, the morbidity and mortality caused by hypertension is on the rise, suggesting the need for investigation of novel signaling pathways involved in its pathogenesis. Recent evidence suggests the role of toll-like receptor (TLR) 4 in various inflammatory diseases, including hypertension. The role of the brain in the initiation and progression of all forms of hypertension is well established, but the role of brain TLR4 in progression of hypertension has never been explored. Therefore, we investigated the role of TLR4 within the paraventricular nucleus (PVN; an important cardioregulatory center in the brain) in an animal model of human essential hypertension. We hypothesized that a TLR4 blockade within the PVN causes a reduction in mean arterial blood pressure (MAP), inflammatory cytokines and sympathetic drive in hypertensive animals. Methods: Spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats were administered either a specific TLR4 blocker, viral inhibitory peptide (VIPER), or control peptide in their PVN for 14 days. MAP was recorded continuously by radiotelemetry. PVN and blood were collected for the measurement of pro-inflammatory cytokines (Tumor Necrosis Factor (TNF)-α, interleukin (IL)-1β), anti-inflammatory cytokine IL-10, inducible nitric oxide synthase (iNOS), TLR4, nuclear factor (NF) κB activity and plasma norepinephrine (NE) and high mobility group box (HMGB)1 expression, respectively. Results: Hypertensive rats exhibited significantly higher levels of TLR4 in the PVN. TLR4 inhibition within the PVN attenuated MAP, improved cardiac hypertrophy, reduced TNF-α, IL-1β, iNOS levels, and NFκB activity in SHR but not in WKY rats. These results were associated with a reduction in plasma NE and HMGB1 levels and an increase in IL-10 levels in SHR. Conclusions: This study demonstrates that TLR4 upregulation in PVN plays an important role in hypertensive response. Our results provide mechanistic evidence that hypertensive response in SHR are mediated, at least in part, by TLR4 in the PVN and that inhibition of TLR4 within the PVN attenuates blood pressure and improves inflammation, possibly via reduction in sympathetic activity. [ABSTRACT FROM AUTHOR]