Regulatory mechanism of expression of ODF and OCIF genes in P.gingivalis LPS-induced bone resorption.

脂多糖是一种在炎症反应中发挥多功能作用的细菌细胞成分，其中之一就是强大的骨吸收刺激因子。内源性CD_(14)在内毒素诱导的骨吸收中起重要作用，内源性CD_(14)通过IL-1、β和IL-6介导内毒素诱导的骨吸收。然而，内毒素刺激骨吸收的机制尚不清楚。在本研究中，我们利用ST-2细胞具有支持破骨细胞形成的能力，证明了内毒素诱导ST-2细胞破骨细胞分化因子(ODF)基因表达是由内源性IL-6通过CD14-TLR4介导的。我们观察到内毒素能明显刺激ST-2细胞ODF基因的表达。抗小鼠IL-6抗体可明显中和脂多糖诱导的ODF基因表达。此外，IL-6还能诱导ST-2细胞ODF基因表达。提示内毒素诱导的ST-2细胞ODF基因表达是通过内源性IL-6的间接作用实现的。而在ST-2细胞中，CD14和Toll样受体4呈结构性表达。PI-PLC处理能明显抑制脂多糖诱导的IL-6基因的表达，PI-PLC是一种从蜡样芽孢杆菌中特异切割CD14的GPI锚点的酶。此外，在高表达TLR4的ST-2细胞中，内毒素可明显刺激ODF和IL-6基因的表达。这些结果提示CD14和TLR4在ST-2细胞内毒素应答中的功能作用。因此，本研究明确了内源性IL-6通过CD14-TLR4信号通路在内毒素刺激的小鼠基质ST-2细胞ODF基因表达中的作用。

Lipopolysaccharid (LPS) is a bacterial cell component that plays multifunctional roles in inflammatory reactions, and one of these roles is a powerful stimulator of bone resorption. We have shown that endogenous CD14 plays an important role in LPS-stimulated bone resorption that is mediatedby IL-1β and IL-6 induced by the toxin. However, the mechanism by which LPS stimulates bone resorption is not yet understood. In the present study, we show using ST-2 cells having a supporting ability of osteoclast formation that LPS-induced osteoclast differentiation factor (ODF) gene expression in ST-2 cells is mediated by endogenous IL-6 via CD14-TLR4. We observed that LPS obviously stimulated expression of ODF gene in ST-2 cells. The LPS-induced expression of ODF gene was markedly neutralized by anti-mouse IL-6 antibody treatment. In addition, IL-6 was able to induce expression of ODF gene in ST-2 cells. These observations suggest that LPS-induced expression of ODF gene in ST-2 cells was mediated by indirect action of endogenous IL-6. On the other hand, ST-2 cells exhibited constitutive expression of CD14 and Toll-like receptor 4. The LPS-induced expression of IL-6 gene was clearly inhibited by PI-PLC treatment which was an enzyme from B.cereus which specifically cleaves the GPI anchor of CD14. In addition, LPS induction of ODF and IL-6 gene expressions was clearly stimulated in the TLR4-overexpressed ST-2 cells. These results suggested the functional role of CD14 and TLR4 in LPS responsibility of ST-2 cells. The present study thus clearly demonstrates a functional role of endogenous IL-6 via CD14-TLR4 signaling in LPS-stimulated expression of ODF gene.In conclusion, our present study suggests that LPS induce expression of ODF/RANKL/TRANCE/OPGL gene in mouse stromal ST-2 cells via CD14-TLR4 dependent endogenous IL-6.