title: Expression of osteopontin messenger RNA and protein in rheumatoid arthritis: effects of osteopontin on the release of collagenase 1 from articular chondrocytes and synovial fibroblasts.
abstract: OBJECTIVE
  Osteopontin (OPN) is an extracellular matrix protein that has been implicated in the interactions between tumor cells and host matrix, including those involved in invasion and spread of tumor cells. Because joint destruction in rheumatoid arthritis (RA) is mediated by the invasive growth of synovial tissue through its attachment to cartilage, we examined the expression of OPN in the synovia of patients with RA and the effect of OPN on the production of collagenase 1 in rheumatoid synovial fibroblasts and articular chondrocytes.
  
  
  METHODS
  The expression of OPN messenger RNA (mRNA) and protein in synovia from 10 RA patients was examined by in situ hybridization and immunohistochemistry. Synovial fibroblasts from RA patients and articular chondrocytes from patients without joint disease were cultured in the presence of various concentrations of OPN, and levels of collagenase 1 in the culture supernatants were measured by enzyme-linked immunosorbent assay.
  
  
  RESULTS
  The expression of OPN mRNA and protein was observed in 9 of 10 specimens obtained from patients with RA. OPN was expressed in the synovial lining and sublining layer and at the interface of cartilage and invading synovium. Double labeling revealed that the majority of OPN-expressing cells were positive for the fibroblast-specific enzyme prolyl 4-hydroxylase and negative for the macrophage marker CD68, while only a few, single OPN-expressing cells were positive for CD68 at sites of synovial invasion into cartilage. OPN staining was not observed in lymphocytic infiltrates or leukocyte common antigen (CD45)-positive cells. Three of 3 cultures of human articular chondrocytes secreted detectable basal amounts of collagenase, with a dose-dependent increase upon OPN stimulation, while synovial fibroblast cultures produced much lower levels of collagenase, with only 2 of 4 fibroblast cultures responding in a dose-dependent manner.
  
  
  CONCLUSIONS
  These findings suggest that OPN produced by synovial fibroblasts in the synovial lining layer and at sites of cartilage invasion not only mediates attachment of these cells to cartilage, but also contributes to matrix degradation in RA by stimulating the secretion of collagenase 1 in articular chondrocytes.
authors.affiliation: University Hospital, Zurich, Switzerland.
authors.forename: P K
authors.initials: PK
authors.lastname: Petrow
authors.forename: K M
authors.initials: KM
authors.lastname: Hummel
authors.forename: J
authors.initials: J
authors.lastname: Schedel
authors.forename: J K
authors.initials: JK
authors.lastname: Franz
authors.forename: C L
authors.initials: CL
authors.lastname: Klein
authors.forename: U
authors.initials: U
authors.lastname: Müller-Ladner
authors.forename: J
authors.initials: J
authors.lastname: Kriegsmann
authors.forename: P L
authors.initials: PL
authors.lastname: Chang
authors.forename: C W
authors.initials: CW
authors.lastname: Prince
authors.forename: R E
authors.initials: RE
authors.lastname: Gay
authors.forename: S
authors.initials: S
authors.lastname: Gay
mesh_terms: D000368:Aged; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D015214:Antigens, Differentiation, Myelomonocytic / Q000378:metabolism; D001172:Arthritis, Rheumatoid / Q000378:metabolism* / Q000473:pathology; D002478:Cells, Cultured; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D005260:Female; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008297:Male; D020781:Matrix Metalloproteinase 1 / Q000378:metabolism; D008875:Middle Aged; D053495:Osteopontin; D011393:Procollagen-Proline Dioxygenase / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins; D012795:Sialoglycoproteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D013583:Synovial Membrane / Q000187:drug effects / Q000473:pathology; D000097382:CD68 Molecule
chemical_list: D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D020781:Matrix Metalloproteinase 1; D053495:Osteopontin; D011393:Procollagen-Proline Dioxygenase; D012333:RNA, Messenger; D011994:Recombinant Proteins; D012795:Sialoglycoproteins; C067980:CD68 antigen, human; D000097382:CD68 Molecule; C506895:SPP1 protein, human; C506897:Spp1 protein, rat