title: Oxidative Stress Increases Surface Toll-Like Receptor 4 Expression in Murine Macrophages Via Ceramide Generation.
abstract: Multiorgan failure is a major cause of late mortality following trauma. Oxidative stress generated during shock/resuscitation contributes to tissue injury by priming the immune system for an exaggerated response to subsequent inflammatory stimuli, such as lipopolysaccharide (LPS). We recently reported that oxidative stress causes rapid recruitment of the LPS receptor Toll-like receptor 4 (TLR4) to membrane lipid rafts, thus increasing LPS responsiveness and cellular priming. We hypothesized that activation of Src family kinases by oxidants might contribute to these events. We utilized microscopy, flow cytometry, Western blotting, and thin-layer chromatography methods. Using hydrogen peroxide in vitro and hemorrhagic shock/resuscitation in vivo, oxidant-induced TLR4 translocation in macrophages occurred in an Src-dependent manner. Approaches supporting this conclusion included pharmacologic inhibition of the Src family kinases by PP2, Src inhibition by a molecular approach of cell transfection with Csk, and genetic inhibition of all Src kinases relevant to the monocyte/macrophage lineage in hckfgrlyn triple knockout mice. To evaluate the upstream molecules involved in Src activation, we evaluated the ability of oxidative stress to activate the bioactive lipid molecule ceramide. Oxidants induced ceramide generation in macrophages both in vitro and in vivo, an effect that appears to be due to activation of the acid sphingomyelinase. Using pharmacological approaches, ceramide was shown to be both necessary and sufficient to mediate TLR4 translocation to the plasma membrane in an Src-dependent manner. This study identifies a hierarchy of signaling molecules following oxidative stress that might represent novel targets for therapy in critical illness and organ injury.
authors.affiliation: Department of Surgery, University of Toronto, and the Keenan Research Centre for Biomedical Science of St Michael's Hospital, Toronto, Ontario, Canada.
authors.forename: Patrick S
authors.initials: PS
authors.lastname: Tawadros
authors.forename: Kinga A
authors.initials: KA
authors.lastname: Powers
authors.forename: Menachem
authors.initials: M
authors.lastname: Ailenberg
authors.forename: Simone E
authors.initials: SE
authors.lastname: Birch
authors.forename: John C
authors.initials: JC
authors.lastname: Marshall
authors.forename: Katalin
authors.initials: K
authors.lastname: Szaszi
authors.forename: Andras
authors.initials: A
authors.lastname: Kapus
authors.forename: Ori D
authors.initials: OD
authors.lastname: Rotstein
mesh_terms: D000818:Animals; D002460:Cell Line; D002518:Ceramides / Q000096:biosynthesis*; D002855:Chromatography, Thin Layer; D019852:Diacylglycerol Kinase / Q000378:metabolism; D005434:Flow Cytometry; D005786:Gene Expression Regulation; D006861:Hydrogen Peroxide / Q000737:chemistry; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D018384:Oxidative Stress; D010100:Oxygen / Q000737:chemistry; D021381:Protein Transport; D012151:Resuscitation; D012769:Shock; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D002518:Ceramides; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D006861:Hydrogen Peroxide; D019852:Diacylglycerol Kinase; D019061:src-Family Kinases; D010100:Oxygen