Extracellular cytochrome c, a mitochondrial apoptosis-related protein, induces arthritis.
OBJECTIVE
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-kappaB 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-kappaB 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-kappaB 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.
Pullerits
R
R
Department of Rheumatology and Inflammation Research, Sahlgrenska University Hospital, Guldhedsgatan 10A, 41346, Göteborg, Sweden. rille.pullerits@rheuma.gu.se
Bokarewa
M
M
Jonsson
I-M
IM
Verdrengh
M
M
Tarkowski
A
A
D000328:Adult; D000368:Aged; D000818:Animals; D017209:Apoptosis; D001169:Arthritis, Experimental / Q000139:chemically induced* / Q000473:pathology; D001172:Arthritis, Rheumatoid / Q000378:metabolism*; D002478:Cells, Cultured; D018925:Chemokines / Q000096:biosynthesis; D045304:Cytochromes c / Q000032:analysis / Q000494:pharmacology / Q000633:toxicity*; D024202:Electrophoretic Mobility Shift Assay; D045604:Extracellular Fluid / Q000378:metabolism; D005260:Female; D006801:Humans; D007270:Injections, Intra-Articular; D051379:Mice; D008807:Mice, Inbred BALB C; D008875:Middle Aged; D016328:NF-kappa B / Q000378:metabolism; D009504:Neutrophils / Q000502:physiology; D013154:Spleen / Q000166:cytology / Q000187:drug effects / Q000276:immunology; D013582:Synovial Fluid / Q000737:chemistry
D018925:Chemokines; D016328:NF-kappa B; D045304:Cytochromes c