Suda Koji, Udagawa Nobuyuki, Sato Nobuaki, Takami Masamichi, Itoh Kanami, Woo Je-Tae, Takahashi Naoyuki, Nagai Kazuo
Department of Bioengineering, Tokyo Institute of Technology, Yokohama, Japan.
J Immunol. 2004 Feb 15;172(4):2504-10. doi: 10.4049/jimmunol.172.4.2504.
LPS is a potent stimulator of bone resorption in inflammatory diseases. The mechanism by which LPS induces osteoclastogenesis was studied in cocultures of mouse osteoblasts and bone marrow cells. LPS stimulated osteoclast formation and PGE(2) production in cocultures of mouse osteoblasts and bone marrow cells, and the stimulation was completely inhibited by NS398, a cyclooxygenase-2 inhibitor. Osteoblasts, but not bone marrow cells, produced PGE(2) in response to LPS. LPS-induced osteoclast formation was also inhibited by osteoprotegerin (OPG), a decoy receptor of receptor activator of NF-kappaB ligand (RANKL), but not by anti-mouse TNFR1 Ab or IL-1 receptor antagonist. LPS induced both stimulation of RANKL mRNA expression and inhibition of OPG mRNA expression in osteoblasts. NS398 blocked LPS-induced down-regulation of OPG mRNA expression, but not LPS-induced up-regulation of RANKL mRNA expression, suggesting that down-regulation of OPG expression by PGE(2) is involved in LPS-induced osteoclast formation in the cocultures. NS398 failed to inhibit LPS-induced osteoclastogenesis in cocultures containing OPG knockout mouse-derived osteoblasts. IL-1 also stimulated PGE(2) production in osteoblasts and osteoclast formation in the cocultures, and the stimulation was inhibited by NS398. As seen with LPS, NS398 failed to inhibit IL-1-induced osteoclast formation in cocultures with OPG-deficient osteoblasts. These results suggest that IL-1 as well as LPS stimulates osteoclastogenesis through two parallel events: direct enhancement of RANKL expression and suppression of OPG expression, which is mediated by PGE(2) production.
脂多糖（LPS）是炎症性疾病中骨吸收的强效刺激物。在小鼠成骨细胞与骨髓细胞的共培养体系中研究了LPS诱导破骨细胞生成的机制。LPS刺激小鼠成骨细胞与骨髓细胞共培养体系中破骨细胞的形成及前列腺素E2（PGE2）的产生，且这种刺激被环氧化酶-2抑制剂NS398完全抑制。成骨细胞而非骨髓细胞在LPS刺激下产生PGE2。骨保护素（OPG），一种核因子κB受体活化因子配体（RANKL）的诱饵受体，也可抑制LPS诱导的破骨细胞形成，但抗小鼠肿瘤坏死因子受体1（TNFR1）抗体或白细胞介素-1（IL-1）受体拮抗剂则无此作用。LPS可诱导成骨细胞中RANKL mRNA表达增加及OPG mRNA表达降低。NS398可阻断LPS诱导的OPG mRNA表达下调，但不能阻断LPS诱导的RANKL mRNA表达上调，提示PGE2介导的OPG表达下调参与了共培养体系中LPS诱导的破骨细胞形成。NS398不能抑制含OPG基因敲除小鼠来源成骨细胞的共培养体系中LPS诱导的破骨细胞生成。IL-1也可刺激成骨细胞产生PGE2及共培养体系中破骨细胞的形成，且这种刺激被NS398抑制。与LPS情况类似，NS398不能抑制与OPG缺陷成骨细胞共培养体系中IL-1诱导的破骨细胞形成。这些结果提示，IL-1以及LPS通过两个平行事件刺激破骨细胞生成：直接增强RANKL表达及抑制OPG表达，后者由PGE2产生介导。
