title: TLR4-MD-2 complex is negatively regulated by an endogenous ligand, globotetraosylceramide.
abstract: Although endogenous ligands for Toll-like receptor (TLR)4-myeloid differentiation factor 2 (MD2) have not been well-understood, we here report that a globo-series glycosphingolipid, globotetraosylceramide (Gb4), attenuates the toxicity of lipopolysaccharides (LPSs) by binding to TLR4-MD-2. Because α1,4-galactosyltransferase (A4galt)-deficient mice lacking globo-series glycosphingolipids showed higher sensitivity to LPS than wild-type mice, we examined mechanisms by which globo-series glycosphingolipids attenuate LPS toxicity. Cultured endothelial cells lacking A4galt showed higher expression of LPS-inducible genes upon LPS treatment. In turn, introduction of A4galt cDNA resulted in the neo expression of Gb4, leading to the reduced expression of LPS-inducible genes. Exogenous Gb4 induced similar effects. As a mechanism for the suppressive effects of Gb4 on LPS signals, specific binding of Gb4 to the LPS receptor TLR4-MD-2 was demonstrated by coprecipitation of Gb4 with recombinant MD-2 and by native PAGE. A docking model also supported these data. Taken together with colocalization of TLR4-MD-2 with Gb4 in lipid rafts after LPS stimulation, it was suggested that Gb4 competes with LPS for binding to TLR4-MD-2. Finally, administration of Gb4 significantly protected mice from LPS-elicited mortality. These results suggest that Gb4 is an endogenous ligand for TLR4-MD-2 and is capable of attenuating LPS toxicity, indicating the possibility for its therapeutic application in endotoxin shock.
authors.affiliation: Department of Biochemistry II, Nagoya University Graduate School of Medicine, Nagoya 466-0065, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kondo
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Ikeda
authors.forename: Noriyo
authors.initials: N
authors.lastname: Tokuda
authors.forename: Chiaki
authors.initials: C
authors.lastname: Nishitani
authors.forename: Umeharu
authors.initials: U
authors.lastname: Ohto
authors.forename: Sachiko
authors.initials: S
authors.lastname: Akashi-Takamura
authors.forename: Yasutomo
authors.initials: Y
authors.lastname: Ito
authors.forename: Makoto
authors.initials: M
authors.lastname: Uchikawa
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Kuroki
authors.forename: Ryo
authors.initials: R
authors.lastname: Taguchi
authors.forename: Kensuke
authors.initials: K
authors.lastname: Miyake
authors.forename: Qing
authors.initials: Q
authors.lastname: Zhang
authors.forename: Keiko
authors.initials: K
authors.lastname: Furukawa
authors.forename: Koichi
authors.initials: K
authors.lastname: Furukawa
mesh_terms: D000818:Animals; D005700:Galactosyltransferases / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics / Q000276:immunology; D005915:Globosides / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D008070:Lipopolysaccharides / Q000633:toxicity; D051218:Lymphocyte Antigen 96 / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D021962:Membrane Microdomains / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D051379:Mice; D008817:Mice, Mutant Strains; D046912:Multiprotein Complexes / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D011485:Protein Binding; D012772:Shock, Septic / Q000139:chemically induced / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000276:immunology* / Q000378:metabolism
chemical_list: D005915:Globosides; D008070:Lipopolysaccharides; C411728:Ly96 protein, mouse; D051218:Lymphocyte Antigen 96; D046912:Multiprotein Complexes; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; C024032:globotetraosylceramide; D005700:Galactosyltransferases