title: S100A8 enhances osteoclastic bone resorption in vitro through activation of Toll-like receptor 4: implications for bone destruction in murine antigen-induced arthritis.
abstract: OBJECTIVE
  Rheumatoid arthritis, which is associated with elevated levels of S100A8 and S100A9, is characterized by severe bone erosions caused by enhanced osteoclast formation and activity. The aim of the present study was to investigate the role of S100A8 and S100A9 in osteoclastic bone destruction in murine antigen-induced arthritis (AIA).
  
  
  METHODS
  Bone destruction was analyzed in the arthritic knee joints of S100A9-deficient mice in which S100A8 protein expression was also lacking, and in wild-type (WT) controls. Osteoclast precursors from S100A9-deficient and WT mice were differentiated into osteoclasts in vitro. Additionally, precursors were stimulated with S100A8, S100A9, or S100A8/A9 during osteoclastogenesis. Receptor involvement was investigated using an anti-receptor for advanced glycation end products (anti-RAGE)-blocking antibody, soluble RAGE, or Toll-like receptor 4 (TLR-4)-deficient osteoclast precursors. The formation of osteoclasts and actin rings, the regulation of osteoclast markers, and bone resorption were analyzed.
  
  
  RESULTS
  Bone erosions and cathepsin K staining were significantly suppressed in S100A9-deficient mice after AIA induction. However, osteoclast precursors from S100A9-deficient mice developed normally into functional osteoclasts, which excludes a role for intrinsic S100A8/A9. In contrast to the results observed with S100A9 and S100A8/A9, the addition of S100A8 during osteoclastogenesis resulted in stimulation of osteoclast formation in conjunction with enhanced actin ring formation and increased bone resorption. Analysis of the putative receptor for S100A8 in osteoclastogenesis revealed that osteoclast differentiation and function could not be inhibited by blocking RAGE, whereas the increase in osteoclast numbers and enhanced bone resorption were completely abrogated using TLR-4-deficient osteoclast precursors.
  
  
  CONCLUSIONS
  These results demonstrate that S100A8 stimulated osteoclast formation and activity and suggest that both S100A8 and TLR-4 are important factors in mediating osteoclastic bone destruction in experimental arthritis.
authors.affiliation: Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands. LGrevers@reuma.umcn.nl
authors.forename: Lilyanne C
authors.initials: LC
authors.lastname: Grevers
authors.forename: Teun J
authors.initials: TJ
authors.lastname: de Vries
authors.forename: Thomas
authors.initials: T
authors.lastname: Vogl
authors.forename: Shahla
authors.initials: S
authors.lastname: Abdollahi-Roodsaz
authors.forename: Annet W
authors.initials: AW
authors.lastname: Sloetjes
authors.forename: Pieter J M
authors.initials: PJ
authors.lastname: Leenen
authors.forename: Johannes
authors.initials: J
authors.lastname: Roth
authors.forename: Vincent
authors.initials: V
authors.lastname: Everts
authors.forename: Wim B
authors.initials: WB
authors.lastname: van den Berg
authors.forename: Peter L E M
authors.initials: PL
authors.lastname: van Lent
mesh_terms: D000818:Animals; D001169:Arthritis, Experimental / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D001862:Bone Resorption / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D001842:Bone and Bones / Q000276:immunology / Q000378:metabolism; D040501:Calgranulin A / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D056657:Cathepsin K / Q000276:immunology / Q000378:metabolism; D007719:Knee Joint / Q000276:immunology / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D010010:Osteoclasts / Q000276:immunology / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000276:immunology / Q000378:metabolism*
chemical_list: D040501:Calgranulin A; D051197:Toll-Like Receptor 4; D056657:Cathepsin K