title: Interactive role of the toll-like receptor 4 and reactive oxygen species in LPS-induced microglia activation.
abstract: Microglia are activated by lipopolysaccharide (LPS) to produce neurotoxic pro-inflammatory factors and reactive oxygen species (ROS). While a multitude of LPS receptors and corresponding pathways have been identified, the detailed mechanisms mediating the microglial response to LPS are unclear. Using mice lacking a functional toll-like receptor 4 (TLR4), we demonstrate that TLR4 and ROS work in concert to mediate microglia activation, where the contribution from each pathway is dependent on the concentration of LPS. Immunocytochemical staining of microglia in neuron-glia cultures with antibodies against F4/80 revealed that while TLR4(+/+) microglia were activated the low concentration of 1 ng/ml of LPS, TLR4(-/-) microglia exhibit activated morphology in response to LPS only at higher concentrations (100-1,000 ng/ml). Additionally, tumor necrosis factor-alpha (TNF-alpha) was only produced from higher concentrations (100-1,000 ng/ml) of LPS in TLR4(-/-) enriched microglia cultures. Diphenylene iodonium (DPI), an inhibitor of NADPH oxidase, reduced TNF-alpha production from TLR4(-/-) microglia. The influence of TLR4 on LPS-induced superoxide production was tested in rat enriched microglia cultures, where the presence or absence of serum failed to show any effect on the superoxide production. Further, both TLR4(-/-) and TLR4(+/+) microglia showed a similar increase in extracellular superoxide production when exposed to LPS (1-1,000 ng/ml). These data indicate that LPS-induced superoxide production in microglia is independent of TLR4 and that ROS derived from the production of extracellular superoxide in microglia mediates the LPS-induced TNF-alpha response of both the TLR4-dependent and independent pathway.
authors.affiliation: Neuropharmacology Section, Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA.
authors.forename: Liya
authors.initials: L
authors.lastname: Qin
authors.forename: Guorong
authors.initials: G
authors.lastname: Li
authors.forename: Xun
authors.initials: X
authors.lastname: Qian
authors.forename: Yuxin
authors.initials: Y
authors.lastname: Liu
authors.forename: Xuefei
authors.initials: X
authors.lastname: Wu
authors.forename: Bin
authors.initials: B
authors.lastname: Liu
authors.forename: Jau-Shyong
authors.initials: JS
authors.lastname: Hong
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Block
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D018920:Coculture Techniques; D004305:Dose-Response Relationship, Drug; D004660:Encephalitis / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005911:Gliosis / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D018836:Inflammation Mediators / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000187:drug effects / Q000378:metabolism*; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019636:Neurodegenerative Diseases / Q000378:metabolism / Q000503:physiopathology; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology; D051381:Rats; D011916:Rats, Inbred F344; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000235:genetics*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D018836:Inflammation Mediators; D008070:Lipopolysaccharides; D017382:Reactive Oxygen Species; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; D013481:Superoxides; D019255:NADPH Oxidases