title: Human osteoarthritic chondrocytes are impaired in matrix metalloproteinase-13 inhibition by IFN-gamma due to reduced IFN-gamma receptor levels.
abstract: OBJECTIVE
  Human osteoarthritic (OA) cartilage type-II collagen is preferentially cleaved by the proinflammatory cytokine-induced matrix metalloproteinases-13 (MMP-13). Interferon-gamma (IFN-gamma) potently inhibits interleukin-1 (IL-1)-induced MMP-13 expression in healthy chondrocytes. Our goal was to study the previously unknown impact of IFN-gamma on MMP-13 in OA and compare the levels and functional activity of IFN-gamma receptor (IFN-gammaR1) in healthy and OA chondrocytes.
  
  
  METHODS
  Chondrocytes were obtained from OA patients and non-arthritic control subjects and treated with IL-1+ or- IFN-gamma. MMP-13 mRNA and protein expression were measured by reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting. IFN-gammaR1 expression was assessed by flow cytometry, immunoprecipitation and immunohistochemistry with fluorescein-labeled antibody. IFN-gammaR1 was neutralized with its antibody and signal transducer and activator of transcription 1 (STAT1) phosphorylation analyzed by Western blotting. OA chondrocytes were also transfected with control and IFN-gammaR1 expression vectors.
  
  
  RESULTS
  OA chondrocytes displayed a drastically impaired MMP-13 suppression by IFN-gamma compared to control cells. IFN-gammaR1 levels were significantly decreased in OA chondrocytes as assessed by flow cytometry, immunoprecipitation and immunohistochemistry. Consequently, IFN-gamma-stimulated STAT1 phosphorylation mediated by IFN-gammaR1 was also considerably reduced in OA patient chondrocytes. IFN-gammaR1 overexpression in OA cells restored MMP-13 suppression by IFN-gamma.
  
  
  CONCLUSIONS
  Ability of IFN-gamma to suppress IL-1-induced MMP-13 expression is diminished in OA chondrocytes due to decreased IFN-gammaR1 levels, activity and impaired downstream signal transduction. Therefore, IFN-gammaR1 modulation and weakened endogenous IFN-gamma response may be important mechanisms in OA pathogenesis and cartilage degradation.
authors.affiliation: Département de Médecine, Université de Montréal, Centre de recherche du CHUM Hôpital Notre-Dame, Montreal, Quebec H2L 4M1, Canada.
authors.forename: R
authors.initials: R
authors.lastname: Ahmad
authors.forename: M
authors.initials: M
authors.lastname: El Mabrouk
authors.forename: J
authors.initials: J
authors.lastname: Sylvester
authors.forename: M
authors.initials: M
authors.lastname: Zafarullah
mesh_terms: D002478:Cells, Cultured; D019902:Chondrocytes / Q000378:metabolism; D024043:Collagen Type II / Q000378:metabolism*; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007371:Interferon-gamma / Q000378:metabolism*; D008297:Male; D053509:Matrix Metalloproteinase 13 / Q000378:metabolism; D008875:Middle Aged; D010003:Osteoarthritis / Q000473:pathology*; D017471:Receptors, Interferon / Q000378:metabolism*; D000096743:Interferon gamma Receptor
chemical_list: D024043:Collagen Type II; D007371:Interferon-gamma; D053509:Matrix Metalloproteinase 13; D017471:Receptors, Interferon; D000096743:Interferon gamma Receptor