Lipopolysaccharide In Microglia Research Articles

The activation impact of lactobacillus-derived extracellular vesicles on lipopolysaccharide-induced microglial cell

Perioperative neurocognitive dysfunction (PND) emerges as a common postoperative complication among elderly patients. Currently, the mechanism of PND remains unclear, but there exists a tendency to believe that inflammation plays a significant role in PND. Alterations in the abundance of intestinal microbiota can increase the permeability of the intestinal mucosal barrier and incite extraintestinal inflammatory responses. Metabolites from these microbiota can be absorbed by the intestinal mucosa into the bloodstream, exerting influence upon the central nervous system (CNS). Lactobacillus (Lac), serving as an intestinal probiotic bacterium, possesses the capacity to modulate emotional behavior and cognitive functions. Extracellular vesicles (EVs) are recognized as novel therapeutic carriers for targeted delivery to regulate physiology and pathogenesis. While the mechanism governing the primary function of Lac-EVs in the CNS remains uncertain. Therefore, we established an in vitro neuroinflammation model to induce PND and then treated the mice with Lac-EVs to observe the effect of these EVs on neuroinflammation, particularly on microglial (MG) polarization. Our research unveils that Lac-EVs reduced inflammation induced by LPS in microglia and the activation of related proteins, including the mRNA expression of M1 labeled protein (iNOS). Moreover, the mRNA expression of M2-labeled protein (Arg1) increased. In addition, flow cytometry revealed that the ratio of M1/M2 microglia also changed significantly. Therefore, Lac-EVs promoted the differentiation of M2 microglia by inducing the preferential expression of specific markers related to M2 macrophages and inflammation. In terms of inflammatory cytokine expression, Lac-EVs decreased the secretion of proinflammatory cytokines (IL-1β and IL-6) and increased IL-10 production after lipopolysaccharide (LPS) stimulation. Therefore, Lac-EVs induce the activation of M2 microglial cells without inducing cellular harm in vitro, and they demonstrate anti-inflammatory effects against lipopolysaccharide-induced neuroinflammation. This finding suggested that it is an effective anti-inflammatory strategy for alleviating inflammation-driven PNDs.

Levistilide A Exerts a Neuroprotective Effect by Suppressing Glucose Metabolism Reprogramming and Preventing Microglia Polarization Shift: Implications for Parkinson's Disease.

The microglia, displaying diverse phenotypes, play a significant regulatory role in the development, progression, and prognosis of Parkinson's disease. Research has established that glycolytic reprogramming serves as a critical regulator of inflammation initiation in pro-inflammatory macrophages. Furthermore, the modulation of glycolytic reprogramming has the potential to reverse the polarized state of these macrophages. Previous studies have shown that Levistilide A (LA), a phthalide component derived from Angelica sinensis, possesses a range of pharmacological effects, including anti-inflammatory, antioxidant, and neuroprotective properties. In our study, we have examined the impact of LA on inflammatory cytokines and glucose metabolism in microglia induced by lipopolysaccharide (LPS). Furthermore, we explored the effects of LA on the AMPK/mTOR pathway and assessed its neuroprotective potential both in vitro and in vivo. The findings revealed that LA notably diminished the expression of M1 pro-inflammatory factors induced by LPS in microglia, while leaving M2 anti-inflammatory factor expression unaltered. Additionally, it reduced ROS production and suppressed IκB-α phosphorylation levels as well as NF-κB p65 nuclear translocation. Notably, LA exhibited the ability to reverse microglial glucose metabolism reprogramming and modulate the phosphorylation levels of AMPK/mTOR. In vivo experiments further corroborated these findings, demonstrating that LA mitigated the death of TH-positive dopaminergic neurons and reduced microglia activation in the ventral SNpc brain region of the midbrain and the striatum. In summary, LA exhibited neuroprotective benefits by modulating the polarization state of microglia and altering glucose metabolism, highlighting its therapeutic potential.

Analysis of Alzheimer’s disease‐related synaptic alterations using microfluidic microglia/neuron co‐cultures

AbstractBackgroundMicroglial cells are resident macrophages of the central nervous system. Genome‐wide association studies identified numerous Alzheimer’s disease (AD) risk genes highly or exclusively expressed in microglia, supporting their role as major players in AD pathogenesis. We aim to describe the effect of microglia activation on synaptic connectivity and its potential modulation by AD risk genes.MethodWe developed a microfluidic co‐culture device where fluidically isolated, mature neuronal synapses are brought in contact with microglia, enabling exclusive genetic and pharmacological interventions to neurons and microglia. We cultured cortical neurons from WT embryonic mice in pre‐ and postsynaptic chambers for 7 days, after which primary microglia from 10‐month‐old WT and APP (hAPPJ20, PDGFAPPSw,Ind) mice were added into the synapse chamber. Microglia morphology and synaptic connectivity near microglia were analyzed via immunocytochemistry and confocal microscopy.ResultExposure to lipopolysaccharide (LPS) activated microglia as evidenced by increased surface area and circularity. Morphological changes were correlated with Interleukin‐1 concentration in the medium, indicative of an inflammatory response. We observed a higher reactivity to LPS in microglia from APP mice compared to WT mice, suggesting that genotype‐related differences in microglia reactivity could also be applicable to pathologically relevant stimuli, such as exposure to amyloid‐β oligomers. On‐going work is focused on the synapse pruning process via live‐cell recordings of fluorescent microglia and neurons expressing fluorescently‐tagged synaptic proteins. This model will be used to characterize the dynamic response of microglia to amyloid‐β and include microglia harvested from mice carrying mutations for microglia‐related AD risk genes.ConclusionOur microfluidic co‐culture device enables specific modulation and high‐content analysis of microglial activity and synaptic connectivity in physiological and AD pathological conditions.

Cyclooxygenase‑2 contributes to the hypoxia‑induced aggravation of the neuroinflammation response stimulated by lipopolysaccharide in microglia.

Hypoxia and neuroinflammation are key risk factors involved in various pathophysiological neural disorders. Hypoxia can aggravate neuroinflammation in vitro and in vivo; however, the underlying mechanisms remain unknown. In the present study, hypoxia [either 3 or 1% oxygen (O2)] increased lipopolysaccharide (LPS)-induced expression of the IL-6, IL-1β and TNF-α proinflammatory cytokines in BV2 cells. At the molecular level, both hypoxia and FG-4592, an hypoxia inducible factor 1 pathway activator, effectively induced cyclooxygenase-2 (COX-2) expression. The COX-2 inhibitor celecoxib significantly reduced the expression of cytokines induced by LPS under hypoxic conditions. Additionally, the administration of celecoxib inhibited the activation of microglia as well as cytokine expression in mice administered with hypoxia exposure and LPS injection. The present data demonstrated that COX-2 is involved in the hypoxia-induced aggravation of neuroinflammation stimulated by LPS.

Pinitol Prevents Lipopolysaccharide (LPS)-Induced Inflammatory Responses in BV2 Microglia Mediated by TREM2.

Microglia-involved neuroinflammation in the central nervous system (CNS) has been shown to aggravate brain damage and is associated with the pathogenesis of various neurodegenerative diseases. Thus, suppression of microglial activity has the potential to be a strategy for the treatment of neurodegenerative diseases. Pinitol, a methylated product of D-chiro-inositol, has been used as a treatment for blood-sugar metabolism and as an anti-tumor agent via its anti-inflammatory effects in cancer. However, whether or not pinitol can inhibit microglia-associated neuroinflammation is still unknown. This study aims to determine the effects of pinitol on inflammatory responses in BV2 microglia induced by LPS. Here, we found that the presence of pinitol ameliorates LPS-induced oxidative stress by reducing the production of ROS. Pinitol suppresses the expression and secretion of pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-6. Notably, pinitol prevents the production of NO and PGE2 by inhibiting the expression of iNOS and COX-2. Mechanistically, our findings demonstrate that pinitol inhibits the phosphorylation and degradation of IκBα and subsequent activation of NF-κB. Furthermore, we show that pinitol increases the expression of TREM2 in BV2 microglia, and silencing of TREM2 abolished the anti-inflammatory effects of pinitol. These findings suggest that TREM2 mediates the protective effects of pinitol against LPS in microglia. In summary, our results display that pinitol possesses a robust and beneficial effect against the LPS-induced inflammatory response in microglia.

Abstract # 3175 Mycobacterium vaccae immunization protects aged rats from surgery-elicited neuroinflammation and cognitive dysfunction

Advanced age is a major risk factor for developing postoperative cognitive dysfunction (POCD). Age-related neuroinflammatory “priming” may contribute to POCD: peripheral immune stimuli (e.g., infection or surgery) cause exaggerated pro-inflammatory responses in the aged brain that can elicit pathology. Exposure to micro-organisms with immunoregulatory and anti-inflammatory properties may be a promising strategy to quell neuroinflammatory priming. We hypothesized that immunization with Mycobacterium vaccae (M. vaccae; NCTC11659) would reduce neuroinflammation and cognitive impairments in aged rats post-surgery. Aged (24mos) and adult (3mos) male F344XBN rats received subcutaneous injections of heat-killed M. vaccae (3 injections, once per week) and then 5 days following the final M. vaccae injection rats underwent a laparotomy or sham (anesthesia control) procedure. Three days post-surgery, rats were trained in a fear conditioning paradigm or tissue was collected. Aged (but not young) rats showed post-operative memory deficits. Prophylactic treatment with M. vaccae protected aged rats from surgery induced-cognitive impairments. Furthermore, M. vaccae treatment shifted the aged pro-inflammatory hippocampal microenvironment (increased IL-1beta and NFKBIA) towards an anti-inflammatory phenotype (increased IL-4 and Arg1). Microglia may mediate the anti-inflammatory effects of M. vaccae in the brain: prior in vivo treatment with M. vaccae reduced hyperinflammatory responses to ex vivo lipopolysaccharide in microglia isolated from aged rats. Overall, our novel data suggest that M. vaccae can re-direct a primed neuroimmune environment in aged rats and prevent POCD.

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

BackgroundInflammatory response in the CNS mediated by microglia cells play an important role in host defense and is implicated in the pathology of neurodegenerative diseases. We investigated the capacity of Entada africana to protect microglia from inflammatory insults by exploring the effect of the CH2Cl2/MEOH 5% fraction (Ea5) on pro-inflammatory cytokines mRNA expression. Finally, we studied the effect of Ea5 on the inhibition of p38 MAPK Kinase. The results were compared to those obtained with Baicalin, a well reported anti-inflammatory flavonoid.MethodsBarks from E. africana were harvested in 2010, in the west region of Cameroon. A crude extract was prepared using CH2Cl2/MEOH 1:1 V/V. The crude extract obtained was further fractionated by flash chromatography. A mouse microglia cell line (N9) was stimulated by LPS with or without different concentrations of Baicalin and Ea5. The release of NO was evaluated using the Griess method. The expression of pro-inflammatory cytokines mRNA (TNFα, IL-1β, IL-6) and iNOS/NO were measured by RT- PCR. The inhibition of p38 MAPK Kinase was assessed using ELISA.ResultsWe found that Ea5, as well as Baicalin inhibited LPS-induced NO production in a dose dependent manner. Ea5 was most active in term of NO inhibition (87.07%), in comparison to Baicalin (70.85%). The expression of TNFα, IL-1β, IL-6 and iNOS was strongly suppressed by Ea5 in microglia. Ea5 also inhibited the activity of p38MAPK Kinase, up to 30% for the concentrations tested, whereas a prominent inhibition was obtained with Baicalin.ConclusionThese results suggest that E. africana may contain promising compounds useful for the treatment of diseases cause by over-activation of microglia such as Alzheimer disease and other neurological diseases.

Potential Role of Heme Oxygenase-1 in Neuroinflammation Caused By Manganese

Potential Role of Heme Oxygenase-1 in Neuroinflammation Caused By Manganese

Inhibitory Effects of Ketamine on Lipopolysaccharide-Induced Microglial Activation

Microglia activated in response to brain injury release neurotoxic factors including nitric oxide (NO) and proinflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). Ketamine, an anesthetic induction agent, is generally reserved for use in patients with severe hypotension or respiratory depression. In this study, we found that ketamine (100 and 250 μM) concentration-dependently inhibited lipopolysaccharide (LPS)-induced NO and IL-1β release in primary cultured microglia. However, ketamine (100 and 250 μM) did not significantly inhibit the LPS-induced TNF-α production in microglia, except at the higher concentration (500 μM). Further study of the molecular mechanisms revealed that ketamine markedly inhibited extracellular signal-regulated kinase (ERK1/2) phosphorylation but not c-Jun N-terminal kinase or p38 mitogen-activated protein kinase stimulated by LPS in microglia. These results suggest that microglial inactivation by ketamine is at least partially due to inhibition of ERK1/2 phosphorylation.

Inhibitory Effects of Lycopene on the Induction of NO, Cytokines, and Mitogen-Activated Protein Kinase Expression by Lipopolysaccharide in Primary Cultured Microglia

Microglia are activated in response to brain injury and release neurotoxic factors including nitric oxide (NO) and proinflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). Lycopene, a potent antioxidant, is known to inhibit brain injury. In this study, we found that lycopene (5–20 μ M) significantly inhibited lipopolysaccharide (LPS)-induced NO release in primary cultured microglia. Lycopene (5–20 μM) also concentration-dependently diminished the LPS-induced production of proinflammatory cytokines such as TNF-α and IL-1β in microglia. Further study of the molecular mechanisms revealed that lycopene markedly inhibited extracellular signal-regulated kinase (ERK1/2) but not c-Jun N-terminal kinase (JNK1/2) or p38 mitogen-activated protein kinase (MAPK) phosphorylation stimulated by LPS in microglia. These results suggest that microglial inactivation by lycopene is at least partially due to activation of ERK1/2 phosphorylation Therefore, inhibition of NO and proinflammatory cytokine production in activated microglia by lycopene may represent a powerful and potential therapeutic strategy for various neurodegenerative diseases including ischemia-reperfusion cerebral infarction.

Cyclic ADP‐ribose is a second messenger in the lipopolysaccharide‐stimulated activation of murine N9 microglial cell line

Lipopolysaccharide, the main component of the cell wall of Gram-negative bacteria, is known to activate microglial cells following its interaction with the CD14/Toll-like receptor complex (TLR-4). The activation pathway triggered by lipopolysaccharide in microglia involves enhanced basal levels of intracellular calcium ([Ca2+]i) and terminates with increased generation of cytokines/chemokines and nitric oxide. Here we demonstrate that in lipopolysaccharide-stimulated murine N9 microglial cells, cyclic ADP-ribose, a universal and potent Ca2+ mobiliser generated from NAD+ by ADP-ribosyl cyclases (ADPRC), behaves as a second messenger in the cell activation pathway. Lipopolysaccharide induced phosphorylation, mediated by multiple protein kinases, of the mammalian ADPRC CD38, which resulted in significantly enhanced ADPRC activity and in a 1.7-fold increase in the concentration of intracellular cyclic ADP-ribose. This event was paralleled by doubling of the basal [Ca2+]i levels, which was largely prevented by the cyclic ADP-ribose antagonists 8-Br-cyclic ADP-ribose and ryanodine (by 75% and 88%, respectively). Both antagonists inhibited, although incompletely, functional events downstream of the lipopolysaccharide-induced microglia-activating pathway, i.e. expression of inducible nitric oxide synthase, overproduction and release of nitric oxide and of tumor necrosis factor alpha. The identification of cyclic ADP-ribose as a key signal metabolite in the complex cascade of events triggered by lipopolysaccharide and eventually leading to enhanced generation of pro-inflammatory molecules may suggest a new therapeutic target for treatment of neurodegenerative diseases related to microglia activation.

Microglial apolipoprotein E and astroglial apolipoprotein J expression in vitro: opposite effects of lipopolysaccharide.

Apolipoprotein E (apoE) and apoJ are lipid carriers produced in the brain primarily by glial cells. A variety of glial-activating stimuli induce a parallel upregulation of both apolipoproteins expression in vivo and in vitro. To further characterize the cell type and mechanisms by which apoE and apoJ expression are upregulated in activated glia, mixed glial cultures from neonatal rat cortex were treated with the endotoxin lipopolysaccharide (LPS). LPS induced dose-dependent increases in apoJ and decreases in apoE expression and secretion with maximum effects at 1-10 ng/mL and 0.1-1 microg/mL, respectively. Experiments with enriched astroglial and microglial cultures demonstrated that apoE and apoJ expression are predominantly microglial and astroglial, respectively. Given the pivotal role that nuclear factor-kappa B (NF-kappa B) plays in glial activation, we assessed its possible role in mediating apoE and apoJ expression by activated glia. LPS robustly increased NF-kappa B activation in mixed glial cultures. Two NF-kappa B inhibitors, aspirin (10 mM) and MG-132 (0.1 microM), blocked basal apoE and apoJ secretion as well as LPS-induced apoJ secretion. These data demonstrate that glial apoE and apoJ expression are independently regulated by LPS in microglia and astroglia, respectively, and that activated microglia are the predominant source of apoE in mixed glial cultures. The transcription factor NF-kappa B appears to be a critical mediator of LPS-stimulated apoJ expression from astroglia.

Expression and Function of Outward K+ Channels Induced by Lipopolysaccharide in Microglia

Expression and Function of Outward K+ Channels Induced by Lipopolysaccharide in Microglia