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* Division of Molecular Life Sciences, Pohang University of Science and Technology, Pohang, Korea;
Department of Internal Medicine, Catholic University of Korea, Seoul, Korea
Serum amyloid A (SAA) is a major acute-phase reactant, and has been demonstrated to mediate proinflammatory cellular responses. Although SAA has been used as an indicator for a variety of inflammatory diseases, the role of SAA in synovial hyperplasia and proliferation of endothelial cells, a pathological hallmark of rheumatoid arthritis (RA), has yet to be elucidated. In this study, we have demonstrated that SAA promotes the proliferation of human fibroblast-like synoviocytes (FLS). In addition, SAA protects RA FLS against the apoptotic death induced by serum starvation, anti-Fas IgM, and sodium nitroprusside. The activity of SAA appears to be mediated by the formyl peptide receptor-like 1 (FPRL1) receptor, as it was mimicked by the WKYMVm peptide, a specific ligand for FPRL1, but completely abrogated by down-regulating the FPRL1 transcripts with short interfering RNA. The effect of SAA on FLS hyperplasia was shown to be caused by an increase in the levels of intracellular calcium, as well as the activation of ERK and Akt, which resulted in an elevation in the expression of cyclin D1 and Bcl-2. Moreover, SAA stimulated the proliferation, migration, and tube formation of endothelial cells in vitro, and enhanced the sprouting activity of endothelial cells ex vivo and neovascularization in vivo. These observations indicate that the binding of SAA to FPRL1 may contribute to the destruction of bone and cartilage via the promotion of synoviocyte hyperplasia and angiogenesis, thus providing a potential target for the control of RA.
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1 This work was supported by a grant from the Ministry of Science and Technology/Korea Science and Engineering Foundation to the National Core Research Center for Systems Bio-Dynamics and the 21st Frontier Proteome Research of the Ministry of Science and Technology in the Republic of Korea.
2 Address correspondence and reprint requests to Dr. Wan-Uk Kim, Department of Internal Medicine, Division of Rheumatology, School of Medicine, Catholic University of Korea, St. Vincent’s Hospital, 93 Chi-Dong, Suwon 442-723, South Korea; E-mail address: wan725{at}catholic.ac.kr or Dr. Sung Ho Ryu, Division of Molecular Life Sciences, Pohang University of Science and Technology, Pohang 790-784, South Korea. E-mail address: sungho{at}postech.ac.kr
3 Abbreviations used in this paper: RA, rheumatoid arthritis; SAA, serum amyloid A; FPRL1, formyl peptide receptor-like 1; OA, osteoarthritis; FLS, fibroblast-like synoviocyte; SNP, sodium nitroprusside; VEGF, vascular endothelial growth factor; siRNA, short interfering RNA; [Ca2+]i, intracellular Ca2+ concentration.
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