Differentiation-inducing signals in osteoblasts and its application for development of bone anabolic therapy

(1) AP-1/IL-11信号通路分析体外液体剪切应力（FSS）诱导成骨细胞表达deltafosB，这是一种AP-1家族转录因子，在转基因小鼠体内过表达时能够刺激骨形成。进一步的机制研究表明，FSS以依赖于钙、ERK和CREB的方式促进fosB/deltafosB基因的转录，这些转录是通过小鼠fosB基因上游调控区存在的CREB样序列起作用的。AP-1和SmadsSmall之间的串扰是一种转录因子，作用于BMP-2的下游，BMP-2是一种众所周知的骨形成诱导剂。我们发现fss激活的AP-1与Smad1在物理上相互作用并在功能上协同诱导白细胞介素(IL)-11基因转录。(2) IL-11在糖皮质激素性骨质疏松症（GIO）中的致病作用IL-11PTH和IL-11的抗凋亡作用抑制地塞米松和依托泊苷诱导的成骨细胞凋亡50%。细胞凋亡诱导因子Bcl-2表达下调，PTH或IL-11可使Bcl-2表达恢复。PTH的作用部分被抗il -11中和抗体阻断。地塞米松epth抑制IL-11基因转录，诱导IL-11基因转录，而这种诱导被地塞米松阻断。我们发现这些作用很大程度上依赖于IL-11启动子中的AP-1结合位点。综上所述，这些结果表明IL-11在地塞米松的促凋亡作用和PTH的抗凋亡作用中都起作用。

(1)Analysis of the AP-1/IL-11 signaling pathway1.Transcriptional induction of fosB/deltafosB geneFluid shear stress (FSS) in vitro induced osteoblast expression of deltafosB, an AP-1 family transcription factor that is able to stimulate bone formation in vivo when over-expressed in transgenic mice. Further mechanistic studies revealed that FSS promoted fosB/deltafosB gene transcription in a manner dependent on calcium, ERK, and CREB, which acted via CRE-like sequences present in the mouse fosB gene upstream regulatory region.2.Crosstalk between AP-1 and SmadsSmall is a transcription factor that act downstream of BMP-2, a well-known inducer of bone formation. We found that FSS-activated AP-1 physically interacted and functionally cooperated with Smad1 to induce interleukin (IL)-11 gene transcription.(2)Pathogenic roles of IL-11 in glucocorticoid-induced osteoporosis (GIO)1.Anti-apoptotic effects of IL-11PTH as well as IL-11 suppressed dexamethasone- and etoposide-induced osteoblast apoptosis by 50 %. Expression of Bcl-2, an anti-apoptotic factor, was down-regulated by these apoptosis inducers, which was restored by PTH or IL-11. And the effect of PTH was partially blocked by an anti-IL-11 neutralizing antibody2.Transcriptional repression of IL-11 gene by dexamethasonePTH induced IL-11 gene transcription, and this induction was blocked by dexamethasone. We found that these effects were both largely dependent on the AP-1 binding site in the IL-11 promoter.Collectively, these results suggest that IL-11 plays a role in both pro-apoptotic effects of dexamethasone and anti-apoptotic effects of PTH in osteoblasts.