title: Peptidoglycan and lipopolysaccharide synergistically enhance bone resorption and osteoclastogenesis.
abstract: OBJECTIVE
  Peptidoglycan (PGN) and lipopolysaccharide (LPS) are bacterial cell wall constituents that are able to induce bone resorption by stimulating Toll-like receptor (TLR) 2 and TLR4, respectively. The fragments of PGN also stimulate inflammatory responses via nucleotide-binding oligomerization domain (NOD) 1 and NOD2, although there are differences in the NOD-stimulatory activities between gram-positive and gram-negative PGNs. The TLR and NOD signaling pathways are known to engage in cross-talk to enhance the production of inflammatory cytokines. In the present study, we investigated the effects of gram-negative and gram-positive PGNs on bone resorption and osteoclastogenesis in the presence or absence of LPS.
  
  
  METHODS
  We injected Escherichia coli PGN or Staphylococcus aureus PGN with or without LPS into mouse gingiva, and histopathologically assessed alveolar bone resorption by tartrate-resistant acid phosphatase staining. We also stimulated osteoclast precursors from mouse bone marrow macrophages with these PGNs in vitro and assessed osteoclastogenesis. The cells were also stimulated with synthetic ligands for NOD1; γ-D-glutamyl-meso-DAP NOD2; muramyl dipeptide or TLR2; Pam(3) CSK(4) with or without LPS to analyse the signaling cross-talk.
  
  
  RESULTS
  S. aureus PGN, but not E. coli PGN, induced alveolar bone resorption, as did LPS. However, PGN from both sources significantly enhanced the bone resorption in the mice co-injected with LPS. Both types of PGNs induced osteoclastogenesis and accelerated osteoclastogenesis when the cells were co-stimulated with LPS in vitro. All synthetic ligands synergistically induced osteoclastogenesis by co-stimulation with LPS.
  
  
  CONCLUSIONS
  Gram-positive or gram-negative PGN worked synergistically with LPS to induce bone resorption and osteoclastogenesis, possibly by co-ordinating the effects of TLR2, NOD1, NOD2 and TLR4 signaling.
authors.affiliation: Department of Periodontology, Unit of Translational Medicine, Course of Medical and Dental Sciences, Nagasaki University Graduate School of Biomedical Sciences, Sakamoto, Nagasaki, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Kishimoto
authors.forename: T
authors.initials: T
authors.lastname: Kaneko
authors.forename: T
authors.initials: T
authors.lastname: Ukai
authors.forename: M
authors.initials: M
authors.lastname: Yokoyama
authors.forename: R
authors.initials: R
authors.lastname: Ayon Haro
authors.forename: Y
authors.initials: Y
authors.lastname: Yoshinaga
authors.forename: A
authors.initials: A
authors.lastname: Yoshimura
authors.forename: Y
authors.initials: Y
authors.lastname: Hara
mesh_terms: D016301:Alveolar Bone Loss / Q000378:metabolism* / Q000382:microbiology*; D000818:Animals; D002454:Cell Differentiation; D004926:Escherichia coli / Q000737:chemistry; D005881:Gingiva / Q000382:microbiology; D008070:Lipopolysaccharides / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D053474:Nod1 Signaling Adaptor Protein / Q000502:physiology; D053473:Nod2 Signaling Adaptor Protein / Q000502:physiology; D010010:Osteoclasts / Q000166:cytology / Q000378:metabolism*; D010457:Peptidoglycan / Q000378:metabolism*; D020239:Receptor Cross-Talk; D013211:Staphylococcus aureus / Q000737:chemistry; D051195:Toll-Like Receptor 2 / Q000502:physiology; D051197:Toll-Like Receptor 4 / Q000502:physiology
chemical_list: D008070:Lipopolysaccharides; D053474:Nod1 Signaling Adaptor Protein; D053473:Nod2 Signaling Adaptor Protein; D010457:Peptidoglycan; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4