title: Activation of endothelial toll-like receptor 3 impairs endothelial function.
abstract: BACKGROUND
  Endothelial dysfunction and atherosclerosis are chronic inflammatory diseases characterized by activation of the innate and acquired immune system. Specialized protein receptors of the innate immune system recognize products of microorganisms and endogenous ligands such as nucleic acids. Toll-like receptor 3 (TLR3), for example, detects long double-stranded RNA and is abundantly expressed in endothelial cells. Whether innate immunity contributes to atherogenic mechanisms in endothelial cells is poorly understood.
  
  
  OBJECTIVE
  We sought to determine the effects of TLR3 activation in endothelial cells.
  
  
  RESULTS
  We first investigated whether stimulation of TLR3 influences endothelial biology in mice. Intravenous injection of polyinosine polycytidylic acid, a synthetic double-stranded RNA analog and TLR3 ligand, impaired endothelium-dependent vasodilation, increased vascular production of reactive oxygen species, and reduced reendothelialization after carotid artery injury in wild-type mice compared with controls but had no effect in TLR3(-/-) animals. TLR3 stimulation not only induced endothelial dysfunction but also enhanced the formation of atherosclerotic plaques in apolipoprotein E-deficient mice. In vitro incubation of endothelial cells with polyinosine polycytidylic acid induced production of the proinflammatory cytokines interleukin-8 and interferon-γ-induced protein 10, increased formation of reactive oxygen species, diminished proliferation, and increased apoptosis, which suggests that endothelial cells are able to directly detect and respond to TLR3 ligands. Neutralization of interleukin-8 and interferon-γ-induced protein 10 antagonizes the observed negative effects of polyinosine polycytidylic acid. We found elevated levels of circulating endothelial progenitor cells in polyinosine polycytidylic acid-treated mice, although they displayed increased endothelial dysfunction. Stimulation of TLR3 in cultured endothelial progenitor cells, however, led to increased formation of reactive oxygen species, increased apoptosis, and reduced migration. Injection of endothelial progenitor cells that had been incubated with polyinosine polycytidylic acid ex vivo hindered reendothelialization after carotid artery injury. Therefore, endothelial progenitor cell function was affected by TLR3 stimulation. Finally, apolipoprotein E-deficient/TLR3-deficient mice exhibited improved endothelial function compared with apolipoprotein E-deficient/TLR3(+/+) littermates.
  
  
  CONCLUSIONS
  Immunorecognition of long double-stranded RNA by endothelial cells may be an important mechanism involved in endothelial cell activation and development of endothelial dysfunction.
authors.affiliation: Medizinische Klinik und Poliklinik II, Universitätsklinikum Bonn, Sigmund Freud Straße 25, D-53105 Bonn, Germany. sebastian.zimmer@ukb.uni-bonn.de.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Zimmer
authors.forename: Martin
authors.initials: M
authors.lastname: Steinmetz
authors.forename: Tobias
authors.initials: T
authors.lastname: Asdonk
authors.forename: Inga
authors.initials: I
authors.lastname: Motz
authors.forename: Christoph
authors.initials: C
authors.lastname: Coch
authors.forename: Evelyn
authors.initials: E
authors.lastname: Hartmann
authors.forename: Winfried
authors.initials: W
authors.lastname: Barchet
authors.forename: Sven
authors.initials: S
authors.lastname: Wassmann
authors.forename: Gunther
authors.initials: G
authors.lastname: Hartmann
authors.forename: Georg
authors.initials: G
authors.lastname: Nickenig
mesh_terms: D000818:Animals; D001057:Apolipoproteins E / Q000235:genetics; D050197:Atherosclerosis / Q000276:immunology / Q000378:metabolism* / Q000503:physiopathology; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000276:immunology / Q000378:metabolism*; D007113:Immunity, Innate / Q000502:physiology; D007369:Interferon Inducers / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D011070:Poly I-C / Q000494:pharmacology; D012330:RNA, Double-Stranded / Q000276:immunology / Q000378:metabolism*; D051196:Toll-Like Receptor 3 / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D014657:Vasculitis / Q000276:immunology / Q000378:metabolism* / Q000503:physiopathology
chemical_list: D001057:Apolipoproteins E; D007369:Interferon Inducers; D012330:RNA, Double-Stranded; C519703:TLR3 protein, mouse; D051196:Toll-Like Receptor 3; D011070:Poly I-C