Rheumatology Advance Access originally published online on September 7, 2004
Rheumatology 2004 43(12):1496-1503; doi:10.1093/rheumatology/keh395
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Rheumatology Vol. 43 No. 12 © British Society for Rheumatology 2004; all rights reserved
PAPER |
Gene expression relevant to osteoclastogenesis in the synovium and bone marrow of mature rats with collagen-induced arthritis
Department of Orthopedic Surgery and 1 Division of Molecular Medical Zoology, Department of Microbiology and Pathology, Faculty of Medicine, Tottori University, Yonago, Japan.
Correspondence to: Y. Kishimoto, Department of Orthopedic Surgery, Faculty of Medicine, Tottori University, Yonago, Tottori 683-8504, Japan. E-mail: yu2{at}grape.med.tottori-u.ac.jp
Objectives. To investigate gene expression relevant to osteoclastogenesis in the synovium and bone marrow during the development of collagen-induced arthritis (CIA) in mature rats.
Methods. Total messenger RNAs (mRNAs) were obtained from CIA synovium and bone marrow after immunization. First, reverse transcriptasepolymerase chain reactions (RT-PCR) were carried out to detect the mRNA encoding receptor activator of NF-
B (RANK), RANK ligand (RANKL), osteoprotegerin (OPG), tumour necrosis factor-
(TNF-
), interleukin (IL)-1ß, IL-6 and the osteoclast markers tartrate-resistant acid phosphatase (TRAP) and cathepsin K. Secondly, the genes detected clearly by RT-PCR were quantified using real-time PCR.
Results. In the synovium, expression of all genes was confirmed by specific single bands in RT-PCR. In real-time PCR, the expression levels of TNF-
, IL-1ß, IL-6, RANKL, TRAP and cathepsin K mRNA increased, whereas the expression levels of RANK and OPG were unchanged and decreased respectively. RANKL expression was highly correlated with the two osteoclast markers. In the bone marrow, RT-PCR did not clearly detect the expression of IL-6, RANKL or OPG mRNA. Quantitative real-time PCR showed that TNF-
, RANK and TRAP mRNA expression did not change significantly with time, and that IL-1ß and cathepsin K changed slightly compared with those in the synovium.
Conclusions. In the early stages of arthritis, synovial RANKL is closely involved in osteoclastogenesis, and various changes in synovial cytokines, including down-regulation of OPG, probably accelerate osteoclast formation. In contrast, cytokine mRNA in the bone marrow showed little fluctuation. We suggest that synovial cytokines affect osteoclastogenesis not only in the synovium but in the bone marrow.
KEY WORDS: Osteoclastogenesis, Collagen-induced arthritis, Synovium, Bone marrow, RANKL/RANK/OPG, Inflammatory cytokines