Rheumatology Advance Access originally published online on September 14, 2004
Rheumatology 2005 44(1):32-39; doi:10.1093/rheumatology/keh406
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Rheumatology Vol. 44 No. 1 © British Society for Rheumatology 2004; all rights reserved
PAPER |
Extracellular cytochrome c, a mitochondrial apoptosis-related protein, induces arthritis
Department of Rheumatology and Inflammation Research, Sahlgrenska University Hospital, University of Göteborg, Sweden.
Correspondence to: R. Pullerits, Department of Rheumatology and Inflammation Research, Sahlgrenska University Hospital, Guldhedsgatan 10A, 41346, Göteborg, Sweden. E-mail: rille.pullerits{at}rheuma.gu.se
Objectives. The aim of the study was to assess the role of extracellular cytochrome c as an inducer of joint inflammation and to examine its levels in sera and synovial fluids of rheumatoid arthritis (RA) patients.
Methods. Mice were injected intra-articularly with different doses of cytochrome c and joints were evaluated histopathologically and immunohistochemically 3 and 10 days later. In addition, mouse spleen cells were stimulated with different concentrations of cytochrome c, followed by assessment of NF-
B activation and cytokine production. Sera and synovial fluid from RA patients and sera from healthy individuals were assessed with respect to cytochrome c levels by an enzyme-linked immunoassay technique.
Results. Histopathological signs of arthritis were evident in 75% of animals following intra-articular injection of cytochrome c. Synovitis was characterized by influx of Mac-1+ cells. In vivo depletion of neutrophils and monocytes led to abrogation of arthritis. Stimulation of mouse spleen cells in vitro with cytochrome c resulted in activation of NF-
B and release of proinflammatory cytokines and chemokines. Cytochrome c levels in RA patients sera were significantly lower than in healthy controls. Further, cytochrome c levels in synovial fluid were significantly lower than in corresponding blood samples.
Conclusions. Our findings demonstrate that extracellular cytochrome c displays direct proinflammatory properties mediated by activation of NF-
B and causing neutrophil and monocyte triggered inflammation. We hypothesize that decreased levels of cytochrome c in RA patients reflect consumption of this molecule in the synovial tissue, decreasing apoptosis and shifting the balance towards inflammation.
KEY WORDS: Cytochrome c, Arthritis, Inflammation, NF-
B, Cytokine, Chemokine