The Rheumatism Research Center, Catholic Research Institute of Medical Science, The Catholic University of Korea, Seoul, South Korea.
Immunol Lett. 2011 Sep 30;139(1-2):42-51. doi: 10.1016/j.imlet.2011.04.013. Epub 2011 May 19.
Osteoclastogenesis plays an important role in joint destruction in rheumatoid arthritis (RA). IL-15 is a pleiotropic proinflammatory cytokine that appears to help mediate the pathological bone loss. This study was undertaken to explore the signaling molecules essential for osteoclastogenesis mediated by IL-15 in rheumatoid synovial fibroblasts. Expression of phospholipase D1 (PLD1) and osteoclast-related gene expression in synovial tissues and their modulation by treatment with IL-15 and different inhibitors in synovial fibroblasts of RA patients were evaluated using immunohistochemistry and quantitative polymerase chain reaction. The levels of IL-15 in serum and synovial fluid were measured by ELISA. The effects of IL-15 and phosphatidic acid (PA) on osteoclast formation were evaluated in cocultures of rheumatoid synovial fibroblasts and peripheral blood monocytes or monocytes alone in the presence of M-CSF and RANKL. The levels of RANKL and PLD1 but not PLD2 were upregulated significantly by IL-15, and the RANKL level was significantly upregulated by PA in rheumatoid synovial fibroblasts. Blocking PA production with 1-butanol and siRNA against PLD1 significantly inhibited the IL-15-stimulated expression of RANKL and PLD1. IL-15 levels were significantly higher in serum and synovial fluid from patients with RA than in osteoarthritis patients and healthy controls. IL-15 and PA induced osteoclast formation through the mitogen-activated protein kinases (MAPKs) and NF-κB signaling pathways. Activation of PLD1 contributes to IL-15-mediated osteoclastogenesis via the MAPKs and NF-κB signaling pathways in rheumatoid synovial fibroblasts. Our data suggest that PLD1 might be an efficient therapeutic strategy for preventing bone destruction in rheumatoid arthritis.
破骨细胞生成在类风湿关节炎（RA）的关节破坏中起着重要作用。白细胞介素 15（IL-15）是一种多效前炎性细胞因子，似乎有助于介导病理性骨质流失。本研究旨在探讨 IL-15 介导的类风湿滑膜成纤维细胞破骨细胞生成所必需的信号分子。采用免疫组织化学和定量聚合酶链反应评估磷脂酶 D1（PLD1）在滑膜组织中的表达和 RA 患者滑膜成纤维细胞中受 IL-15 和不同抑制剂处理后的破骨细胞相关基因表达，并通过 ELISA 测定血清和滑液中 IL-15 的水平。在存在 M-CSF 和 RANKL 的情况下，将类风湿滑膜成纤维细胞和外周血单核细胞或单核细胞单独进行共培养，评估 IL-15 和磷脂酸（PA）对破骨细胞形成的影响。结果显示，IL-15 显著上调了 RANKL 和 PLD1 的水平，但 PLD2 的水平没有显著上调，而 PA 则显著上调了类风湿滑膜成纤维细胞中的 RANKL 水平。用 1-丁醇和针对 PLD1 的 siRNA 阻断 PA 产生可显著抑制 IL-15 刺激的 RANKL 和 PLD1 的表达。与骨关节炎患者和健康对照组相比，RA 患者血清和滑液中的 IL-15 水平显著升高。IL-15 和 PA 通过丝裂原活化蛋白激酶（MAPKs）和 NF-κB 信号通路诱导破骨细胞形成。PLD1 的激活通过 MAPKs 和 NF-κB 信号通路促进了类风湿滑膜成纤维细胞中 IL-15 介导的破骨细胞生成。我们的数据表明，PLD1 可能是预防类风湿关节炎骨破坏的有效治疗策略。
