title: Molecular mechanisms of the inhibitory effects of bovine lactoferrin on lipopolysaccharide-mediated osteoclastogenesis.
abstract: Lactoferrin (LF) is an important modulator of the immune response and inflammation. It has also been implicated in the regulation of bone tissue. In our previous study we demonstrated that bovine LF (bLF) reduces LPS-induced bone resorption through a reduction of TNF-α production in vivo. However, it was not known how bLF inhibits LPS-mediated TNF-α and RANKL (receptor activator of nuclear factor κB ligand) production in osteoblasts. In this study we show that bLF impairs LPS-mediated TNF-α and RANKL production. bLF inhibited LPS-mediated osteoclastogenesis via osteoblasts in a co-culture system. Furthermore, bLF pretreatment inhibited LPS-induced NFκB DNA binding activity as well as IκBα and IKKβ (IκB kinase β) phosphorylation. MAP kinase activation was also inhibited by bLF pretreatment. However, bLF pretreatment failed to block the degradation of IRAK1 (interleukin-1 receptor-associated kinase 1), which is an essential event after its activation. Remarkably, we found that bLF pretreatment inhibited LPS-mediated Lys-63-linked polyubiquitination of TNF receptor-associated factor 6 (TRAF6). We also found that bLF is mainly endocytosed through LRP1 (lipoprotein receptor-related protein-1) and intracellular distributed bLF binds to endogenous TRAF6. In addition, bLF inhibited IL-1β- and flagellin-induced TRAF6-dependent activation of the NFκB signaling pathway. Collectively, our findings demonstrate that bLF inhibits NFκB and MAP kinase activation, which play critical roles in chronic inflammatory disease by interfering with the TRAF6 polyubiquitination process. Thus, bLF could be a potent therapeutic agent for inflammatory diseases associated with bone destruction, such as periodontitis and rheumatoid arthritis.
authors.affiliation: Department of Oral and Maxillofacial Pathobiology, Hiroshima University Graduate School of Biomedical Sciences, Hiroshima 734-8553, Japan.
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Inubushi
authors.forename: Aki
authors.initials: A
authors.lastname: Kawazoe
authors.forename: Mutsumi
authors.initials: M
authors.lastname: Miyauchi
authors.forename: Yasusei
authors.initials: Y
authors.lastname: Kudo
authors.forename: Min
authors.initials: M
authors.lastname: Ao
authors.forename: Atsushi
authors.initials: A
authors.lastname: Ishikado
authors.forename: Taketoshi
authors.initials: T
authors.lastname: Makino
authors.forename: Takashi
authors.initials: T
authors.lastname: Takata
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001854:Bone Marrow Cells / Q000166:cytology / Q000378:metabolism; D002417:Cattle; D002460:Cell Line; D002478:Cells, Cultured; D018920:Coculture Techniques; D015870:Gene Expression / Q000187:drug effects; D053592:Interleukin-1 Receptor-Associated Kinases / Q000378:metabolism; D007781:Lactoferrin / Q000494:pharmacology*; D018950:Lipopolysaccharide Receptors / Q000235:genetics / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology*; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010012:Osteogenesis / Q000187:drug effects*; D010766:Phosphorylation / Q000187:drug effects; D053245:RANK Ligand / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D011973:Receptors, LDL / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D048029:TNF Receptor-Associated Factor 6 / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism; D054875:Ubiquitination / Q000187:drug effects
chemical_list: D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D026503:Low Density Lipoprotein Receptor-Related Protein-1; C486645:Lrp1 protein, mouse; D016328:NF-kappa B; D053245:RANK Ligand; D011973:Receptors, LDL; D048029:TNF Receptor-Associated Factor 6; C505689:Tnfsf11 protein, mouse; D014409:Tumor Necrosis Factor-alpha; D025521:Tumor Suppressor Proteins; D053592:Interleukin-1 Receptor-Associated Kinases; C507769:Irak1 protein, mouse; D007781:Lactoferrin