Human osteoarthritic chondrocytes are impaired in matrix metal loproteinase-13 inhibition by IFN-γ due to reduced IFN-γ receptor levels

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-gamma R1) 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-gamma R1 expression was assessed by flow cytometry, immunoprecipitation and immunohistochemistry with fluorescein-labeled antibody. IFN-gamma R1 was neutralized with its antibody and signal transducer and activator of transcription 1 (STAT-1) phosphorylation analyzed by Western blotting. OA chondrocytes were also transfected with control and IFN-gamma RI expression vectors. Results: OA chondrocytes displayed a drastically impaired MMP-13 suppression by IFN-gamma compared to control cells. IFN-gamma R1 levels were significantly decreased in OA chondrocytes as assessed by flow cytometry, immunoprecipitation and immunohistochemistry. Consequently, IFN-gamma-stimulated STAT1 phosphorylation mediated by IFN-gamma R1 was also considerably reduced in OA patient chondrocytes. IFN-gamma R1 overexpression in CA 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-gamma R1 levels, activity and impaired downstream signal transduction. Therefore, IFN-gamma R1 modulation and weakened endogenous IFN-gamma response may be important mechanisms in CA pathogenesis and cartilage degradation. (C) 2009 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.