title: Soluble biglycan: a potential mediator of cartilage degradation in osteoarthritis.
abstract: BACKGROUND
  Soluble biglycan (sBGN) and soluble decorin (sDCN), are two closely related essential components of extracellular matrix which both have been shown to possess proinflammatory properties. We studied whether sBGN or sDCN were present in synovial fluid (SF) of osteoarthritis (OA) or rheumatoid arthritis (RA) patients and studied sBGN or sDCN potential role in the degradation of OA cartilage.
  
  
  METHODS
  SF obtained from meniscus tear, OA, and RA patients were analysed for sBGN and sDCN using enzyme-linked immunosorbent assays. OA chondrocytes and cartilage explants were stimulated for 48 h with 5 μg/ml sBGN or 1 μg/ml lipopolysaccharide. Messenger RNA (mRNA) levels of Toll-like receptors (TLRs), proteinases and cartilage matrix molecules were determined using quantitative real-time polymerase chain reaction. Protein levels of matrix metalloproteinases (MMPs) and cytokines were measured using Luminex xMap technology. Production of nitric oxide (NO), release of proteoglycans and soluble collagen were measured from conditioned culture media using biochemical assays. OA cartilage explant proteoglycans were stained for Safranin O and quantified using image analysis. TLR4 activation by sBGN and sDCN was studied in engineered HEK-293 cells with TLR4 signalling genes inserted together with a reporter gene.
  
  
  RESULTS
  sBGN was found in meniscus tear SF (14 ± 2 ng/ml), OA SF (582 ± 307 ng/ml) and RA SF (1191 ± 482 ng/ml). Low levels of sDCN could also be detected in SF of meniscus tear (51 ± 4) ng/ml, OA (52 ± 3 ng/ml), and RA (49 ± 4 ng/ml). Stimulation of chondrocytes with sBGN increased significantly the mRNA and protein expression of catabolic MMPs, including MMP1, MMP9 and MMP13, and of inflammatory cytokines interleukin (IL)-6 and IL-8, whereas the expression of anabolic markers aggrecan and collagen type II was decreased. sBGN induced release of proteoglycans, collagen and NO from chondrocytes and cartilage explants. The catabolic response in explants was dependent of OA cartilage degradation stage. The mechanism of action of sBGN was mainly mediated through the TLR4-nuclear factor-κB pathway.
  
  
  CONCLUSIONS
  High levels of sBGN was found in advanced OA and RA SF. sBGN activates chondrocytes mainly via TLR4, which results in net loss of cartilage. Thus, sBGN can be a mediator of OA cartilage degradation and also a potential biomarker for arthritis.
authors.affiliation: Department of Internal Medicine and Rehabilitation, University of Helsinki and Helsinki University (Central) Hospital, Biomedicum 1, PO Box 63, FIN-00290, Helsinki, Finland. goncalo.barreto@helsinki.fi.
authors.forename: Goncalo
authors.initials: G
authors.lastname: Barreto
authors.affiliation: ORTON Orthopaedic Hospital, Helsinki, Finland. antti.soininen@orton.fi.
authors.forename: Antti
authors.initials: A
authors.lastname: Soininen
authors.affiliation: ORTON Orthopaedic Hospital, Helsinki, Finland. pekka.ylinen@orton.fi.
authors.forename: Pekka
authors.initials: P
authors.lastname: Ylinen
authors.affiliation: ORTON Orthopaedic Hospital, Helsinki, Finland. jerker.sandelin@orton.fi.
authors.forename: Jerker
authors.initials: J
authors.lastname: Sandelin
authors.affiliation: Department of Internal Medicine and Rehabilitation, University of Helsinki and Helsinki University (Central) Hospital, Biomedicum 1, PO Box 63, FIN-00290, Helsinki, Finland.|ORTON Orthopaedic Hospital, Helsinki, Finland.
authors.forename: Yrjö T
authors.initials: YT
authors.lastname: Konttinen
authors.affiliation: Department of Internal Medicine and Rehabilitation, University of Helsinki and Helsinki University (Central) Hospital, Biomedicum 1, PO Box 63, FIN-00290, Helsinki, Finland. dan.norsdtrom@hus.fi.
authors.forename: Dan C
authors.initials: DC
authors.lastname: Nordström
authors.affiliation: Department of Rheumatology, University of Helsinki and Helsinki University (Central) Hospital, Helsinki, Finland. kari.eklund@hus.fi.
authors.forename: Kari K
authors.initials: KK
authors.lastname: Eklund
mesh_terms: D000368:Aged; D001172:Arthritis, Rheumatoid / Q000378:metabolism; D058578:Biglycan / Q000378:metabolism*; D015415:Biomarkers / Q000032:analysis*; D002358:Cartilage, Articular / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D060888:Real-Time Polymerase Chain Reaction; D013582:Synovial Fluid / Q000737:chemistry / Q000276:immunology / Q000378:metabolism
chemical_list: C546884:BGN protein, human; D058578:Biglycan; D015415:Biomarkers