title: Toll-like receptors and their adaptors are regulated in macrophages after phagocytosis of lipopolysaccharide-coated titanium particles.
abstract: Macrophages phagocytose metallic wear particles and produce mediators, which can induce cellular host response and aseptic implant loosening. Lipopolysaccharide (LPS) on the wear debris can stimulate macrophages via Toll-like receptor 4 (TLR4) and enhance the response. However, the precise functional role and interaction of TLRs and their adaptor molecules is still unclear. Rat bone marrow macrophages were stimulated with titanium particle (Ti) coated by LPS (Ti/LPS+) and LPS-free Ti (Ti/LPS-). mRNA levels of cytokines, TLRs and their adaptor molecules were measured using real time PCR. mRNA levels of TNF-α, IL-1β, and IL-6 increased in Ti/LPS+ than Ti/LPS-. In contrast, mRNA levels of TLR4, TLR5, and TLR9 decreased in Ti/LPS+ compared to Ti/LPS-. mRNA levels of MyD88, IRAK1, IRAK4 decreased gradually, and TRAF6 underwent an initial transient increase, followed by suppression in Ti/LPS+. However, mRNA levels of TLR2 and IRAK2 increased after phagocytosis of Ti/LPS+ than Ti/LPS-. The increased expressions of proinflammatory cytokines found in Ti/LPS+ indicated that their productions cytokines could be enhanced by phagocytosis of LPS-coated particles. Subsequent down-regulation of TLR4, TLR5, TLR9, MyD88, IRAK1, and IRAK4 suggests that self-protective mechanisms to regulate excessive host responses are activated in macrophages. Increase of TLR2 and IRAK2 and a transient increase of TRAF6 in Ti/LPS+ suggest that another possible pathway to modulate TLR-mediated cellular response to prolong inflammatory response in foreign body reaction of aseptic loosening. This down- and/or up-regulation of the potential TLR-mediated responses to LPS-coated particles reflects the proactive behavior of effector cells.
authors.affiliation: Department of Orthopaedic Surgery, Yamagata University School of Medicine, 2-2-2 Iida Nishi, Yamagata 990-9585, Japan. t.hirayama@med.id.yamagata-u.ac.jp
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Hirayama
authors.forename: Yasunobu
authors.initials: Y
authors.lastname: Tamaki
authors.forename: Yuya
authors.initials: Y
authors.lastname: Takakubo
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Iwazaki
authors.forename: Kan
authors.initials: K
authors.lastname: Sasaki
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Ogino
authors.forename: Stuart B
authors.initials: SB
authors.lastname: Goodman
authors.forename: Yrjö T
authors.initials: YT
authors.lastname: Konttinen
authors.forename: Michiaki
authors.initials: M
authors.lastname: Takagi
mesh_terms: D000818:Animals; D019643:Arthroplasty, Replacement / Q000009:adverse effects; D001854:Bone Marrow Cells / Q000166:cytology / Q000187:drug effects / Q000276:immunology; D002478:Cells, Cultured; D053592:Interleukin-1 Receptor-Associated Kinases / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D008070:Lipopolysaccharides / Q000276:immunology* / Q000493:pharmacokinetics; D008264:Macrophages / Q000166:cytology / Q000187:drug effects* / Q000276:immunology; D053594:Myeloid Differentiation Factor 88 / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D010587:Phagocytosis / Q000187:drug effects / Q000276:immunology; D011475:Prosthesis Failure / Q000209:etiology*; D051381:Rats; D017208:Rats, Wistar; D014025:Titanium / Q000276:immunology* / Q000493:pharmacokinetics; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D051198:Toll-Like Receptor 5 / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D051217:Toll-Like Receptor 9 / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D051193:Toll-Like Receptors / Q000235:genetics / Q000276:immunology* / Q000378:metabolism
chemical_list: D008070:Lipopolysaccharides; C507781:Myd88 protein, rat; D053594:Myeloid Differentiation Factor 88; C495347:Tlr4 protein, rat; C489640:Tlr9 protein, rat; D051197:Toll-Like Receptor 4; D051198:Toll-Like Receptor 5; D051217:Toll-Like Receptor 9; D051193:Toll-Like Receptors; D014025:Titanium; C547807:IRAK1 protein, rat; D053592:Interleukin-1 Receptor-Associated Kinases