title: An endothelial TLR4-VEGFR2 pathway mediates lung protection against oxidant-induced injury.
abstract: TLR4 deficiency causes hypersusceptibility to oxidant-induced injury. We investigated the role of TLR4 in lung protection, using used bone marrow chimeras; cell-specific transgenic modeling; and lentiviral delivery in vivo to knock down or express TLR4 in various lung compartments; and lung-specific VEGF transgenic mice to investigate the effect of TLR4 on VEGF-mediated protection. C57/BL6 mice were exposed to 100% oxygen in an enclosed chamber and assessed for survival and lung injury. Primary endothelial cells were stimulated with recombinant VEGF and exposed to hyperoxia or hydrogen peroxide. Endothelium-specific expression of human TLR4 (as opposed to its expression in epithelium or immune cells) increased the survival of TLR4-deficent mice in hyperoxia by 24 h and decreased LDH release and lung cell apoptosis after 72 h of exposure by 30%. TLR4 expression was necessary and sufficient for the protective effect of VEGF in the lungs and in primary endothelial cells in culture. TLR4 knockdown inhibited VEGF signaling through VEGF receptor 2 (VEGFR2), Akt, and ERK pathways in lungs and primary endothelial cells and decreased the availability of VEGFR2 at the cell surface. These findings demonstrate a novel mechanism through which TLR4, an innate pattern receptor, interacts with an endothelial survival pathway.
authors.affiliation: *Section of Pulmonary, Critical Care, and Sleep Medicine, and Department of Pathology, Yale University School of Medicine, New Haven, Connecticut, USA; and Veterans Affairs Connecticut Healthcare System, New Haven, Connecticut, USA seyedtaghi.takyar@yale.edu patty.lee@yale.edu.
authors.forename: Seyedtaghi
authors.initials: S
authors.lastname: Takyar
authors.affiliation: *Section of Pulmonary, Critical Care, and Sleep Medicine, and Department of Pathology, Yale University School of Medicine, New Haven, Connecticut, USA; and Veterans Affairs Connecticut Healthcare System, New Haven, Connecticut, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: *Section of Pulmonary, Critical Care, and Sleep Medicine, and Department of Pathology, Yale University School of Medicine, New Haven, Connecticut, USA; and Veterans Affairs Connecticut Healthcare System, New Haven, Connecticut, USA.
authors.forename: Maria
authors.initials: M
authors.lastname: Haslip
authors.affiliation: *Section of Pulmonary, Critical Care, and Sleep Medicine, and Department of Pathology, Yale University School of Medicine, New Haven, Connecticut, USA; and Veterans Affairs Connecticut Healthcare System, New Haven, Connecticut, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Jin
authors.affiliation: *Section of Pulmonary, Critical Care, and Sleep Medicine, and Department of Pathology, Yale University School of Medicine, New Haven, Connecticut, USA; and Veterans Affairs Connecticut Healthcare System, New Haven, Connecticut, USA.
authors.forename: Peiying
authors.initials: P
authors.lastname: Shan
authors.affiliation: *Section of Pulmonary, Critical Care, and Sleep Medicine, and Department of Pathology, Yale University School of Medicine, New Haven, Connecticut, USA; and Veterans Affairs Connecticut Healthcare System, New Haven, Connecticut, USA.
authors.forename: Xuchen
authors.initials: X
authors.lastname: Zhang
authors.affiliation: *Section of Pulmonary, Critical Care, and Sleep Medicine, and Department of Pathology, Yale University School of Medicine, New Haven, Connecticut, USA; and Veterans Affairs Connecticut Healthcare System, New Haven, Connecticut, USA seyedtaghi.takyar@yale.edu patty.lee@yale.edu.
authors.forename: Patty J
authors.initials: PJ
authors.lastname: Lee
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000494:pharmacology; D018496:Hyperoxia / Q000378:metabolism*; D008168:Lung / Q000187:drug effects / Q000378:metabolism*; D055370:Lung Injury / Q000139:chemically induced / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic / Q000378:metabolism; D016877:Oxidants / Q000009:adverse effects; D010100:Oxygen / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism*
chemical_list: D016877:Oxidants; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D042461:Vascular Endothelial Growth Factor A; D006861:Hydrogen Peroxide; C000592875:Kdr protein, mouse; D040301:Vascular Endothelial Growth Factor Receptor-2; D051057:Proto-Oncogene Proteins c-akt; D010100:Oxygen
keywords: HALI; TLR4; VEGF; lung injury