Interleukin-18 induces apoptosis in human articular chondrocytes
T. John1, B. Kohl1, A. Mobasheri2, W. Ertel1 and M. Shakibaei3
1Department of Trauma and Reconstructive Surgery, Charité University Medical School, Campus Benjamin Franklin, Berlin, Germany, 2The School of Veterinary Medicine and Science, The University of Nottingham, Sutton Bonington Campus, Sutton Bonington, United Kingdom and 3Ludwig-Maximilians-University Munich, Faculty of Medicine, Institute of Anatomy, Musculoskeletal Research Group, Münich, Germany
Offprint requests to: Thilo John, MD, Department of Trauma Surgery, Charite, Campus Benjamin Franklin, Universitátsmedizin Berlin, Hindenburgdamm 30, 12203 Berlin, Germany. e-mail: thilo.john@charite.de
Summary. Elevated levels of the pro-inflammatory cytokine, interleukin-18 (IL-18) have recently been demonstrated in osteoarthritic cartilage. However, the effects of IL-18 on chondrocyte signalling and matrix biosynthesis are poorly understood. Therefore, the present study was undertaken to further characterize the impact of IL-18 on human articular chondrocyte in vitro.
Human articular chondrocytes were stimulated with various concentrations of recombinant human IL-18 (1, 10, 100 ng/ml) for 0, 4, 8, 12, 24, 48, 72 h in vitro. The effects of IL-18 on the cartilage-specific matrix protein collagen type II, the cytoskeletal protein vinculin, the cell matrix signal transduction receptor ß-integrin, key signalling proteins of the MAPKinase pathway (such as SHC (Sarc Homology Collagen) and activated MAPKinase [ERK-1/-2]), the pro-inflammatory enzyme cyclo-oxygenase-2 (COX-2) and the apoptosis marker activated caspase-3 were evaluated by Western blot analysis and immunofluorescence labelling. Morphological features of IL-18 stimulated chondrocytes were estimated by transmission electron microscopy.
IL-18 lead to inhibition of collagen type II-deposition, decreased ß-integrin receptor and vinculin synthesis, SHC and MAPKinase activation, increased COX-2 synthesis and activation of caspase-3 in chondrocytes in a time- and dose-dependent manner. Furthermore, chondrocytes treated with IL-18 exhibited typical morphological features of apoptosis as revealed by transmission electron microscopy.
Taken together, the results of the present study underline key catabolic events mediated by IL-18 signalling in chondrocytes such as loss of cartilage-specific matrix and apoptosis. Inhibition of MAPKinase signalling is hypothesized to contribute to these features. Future therapeutics targeting IL-18 signalling pathways may be beneficial in rheumatoid arthritis and osteoarthritis therapy. Histol Histopathol 22, 469-482 (2007)
Key words: IL-18, Apoptosis, Chondrocyte, COX-2, MAPKinase, Matrix proteins, Osteoarthritis
DOI: 10.14670/HH-22.469