title: Alarmins S100A8 and S100A9 elicit a catabolic effect in human osteoarthritic chondrocytes that is dependent on Toll-like receptor 4.
abstract: OBJECTIVE
  S100A8 and S100A9 are two Ca(2+)  binding proteins classified as damage-associated molecular patterns or alarmins that are found in high amounts in the synovial fluid of osteoarthritis (OA) patients. The purpose of this study was to investigate whether S100A8 and/or S100A9 can interact with chondrocytes from OA patients to increase catabolic mediators.
  
  
  METHODS
  Using immunohistochemistry, we stained for S100A8 and S100A9 protein, matrix metalloproteinases (MMPs), and a cartilage-breakdown epitope specific for MMPs (VDIPEN) in cartilage from OA donors. Isolated chondrocytes or explants from OA and non-OA donors were stimulated with S100A8 and/or S100A9. Messenger RNA and protein levels of MMPs, cytokines, and cartilage matrix molecules were determined with quantitative reverse transcription-polymerase chain reaction and Luminex techniques, respectively. For receptor blocking studies, specific inhibitors for Toll-like receptor 4 (TLR-4), receptor for advanced glycation end products (RAGE), and carboxylated glycans were used.
  
  
  RESULTS
  In cartilage from OA patients, the expression of S100A8 and S100A9 protein close to chondrocytes was associated with proteoglycan depletion and expression of MMP-1, MMP-3, and VDIPEN. Stimulation of chondrocytes with S100A8 and S100A9 caused a strong up-regulation of catabolic markers (MMPs 1, 3, 9, and 13, interleukin-6 [IL-6], IL-8, and monocyte chemotactic protein 1) and down-regulation of anabolic markers (aggrecan and type II collagen), thereby favoring cartilage breakdown. Blocking TLR-4, but not carboxylated glycans or RAGE, inhibited the S100 effect. The catabolic S100 effect was significantly more pronounced in chondrocytes from OA patients as compared to those from non-OA patients, possibly due to higher TLR-4 expression.
  
  
  CONCLUSIONS
  S100A8 and S100A9 have a catabolic effect on human chondrocytes that is TLR-4 dependent. OA chondrocytes are more sensitive than normal chondrocytes to S100 stimulation.
authors: Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors: Rik F P
authors: RF
authors: Schelbergen
authors: Arjen B
authors: AB
authors: Blom
authors: Martijn H J
authors: MH
authors: van den Bosch
authors: Annet
authors: A
authors: Slöetjes
authors: Shahla
authors: S
authors: Abdollahi-Roodsaz
authors: B Wim
authors: BW
authors: Schreurs
authors: John S
authors: JS
authors: Mort
authors: Thomas
authors: T
authors: Vogl
authors: Johannes
authors: J
authors: Roth
authors: Wim B
authors: WB
authors: van den Berg
authors: Peter L E M
authors: PL
authors: van Lent
mesh_terms: D015415:Biomarkers / Q000378:metabolism; D040501:Calgranulin A / Q000008:administration & dosage / Q000378:metabolism*; D040502:Calgranulin B / Q000378:metabolism* / Q000494:pharmacology; D064236:Cartilage Oligomeric Matrix Protein; D002358:Cartilage, Articular / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D002478:Cells, Cultured; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D000939:Epitopes / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D064235:Matrilin Proteins; D020782:Matrix Metalloproteinases / Q000235:genetics / Q000378:metabolism; D009842:Oligopeptides / Q000378:metabolism; D010003:Osteoarthritis / Q000378:metabolism* / Q000473:pathology; D010446:Peptide Fragments / Q000378:metabolism; D000067759:Receptor for Advanced Glycation End Products; D011971:Receptors, Immunologic / Q000037:antagonists & inhibitors; D011994:Recombinant Proteins; D051197:Toll-Like Receptor 4 / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D015415:Biomarkers; D040501:Calgranulin A; D040502:Calgranulin B; D064236:Cartilage Oligomeric Matrix Protein; D016207:Cytokines; D000939:Epitopes; D016326:Extracellular Matrix Proteins; D006023:Glycoproteins; D064235:Matrilin Proteins; D009842:Oligopeptides; D010446:Peptide Fragments; D000067759:Receptor for Advanced Glycation End Products; D011971:Receptors, Immunologic; D011994:Recombinant Proteins; C495345:TLR4 protein, human; C577553:TSP5 protein, human; D051197:Toll-Like Receptor 4; C093378:peptide VDIPEN; D020782:Matrix Metalloproteinases