COLONY STIMULATING FACTOR 1 REGULATION AND ROLE IN BONE

成骨细胞介导骨形成的确切机制 再吸收不清楚。 一个被广泛接受的假设是， 成骨细胞分泌细胞因子，直接或间接影响 破骨细胞形成或功能。 虽然这些假定的性质 细胞因子是未知的，引人注目的体内和体外数据已经出现 支持集落刺激因子-1（CSF-1）作为一种 成骨细胞衍生因子参与破骨细胞的形成。 因此在 在体内，OP/OP骨硬化小鼠中CSF-1的缺乏导致 体外破骨细胞形成和骨吸收的失败 研究表明，CSF-1对增殖至关重要， 和破骨细胞祖细胞的分化，CSF-1刺激 骨吸收在胎鼠掌骨试验，和CSF-1 受体存在于破骨细胞上。 CSF-I作为可溶性的 或者细胞表面蛋白质，虽然我们知道成骨细胞合成 两种形式的CSF-1 I组成性地和响应于骨诱导性的 代理，很少有人知道他们的生理意义，在骨 重塑此外，虽然我们知道两种关键的骨诱导剂， 甲状旁腺激素（PTH）和肿瘤坏死因子（TNF）增加 CSF-1基因在成骨细胞中的表达， 他们这样做是不清楚的。 最后， CSF-1在体内骨重建中的作用尚不清楚。这一长期目标 因此，建议是：1. 来定义细胞的生理功能 骨中CSF-1的表面和可溶形式，通过检查 细胞表面CSF-1对体外破骨细胞信号传导的影响， 两种基因改变的小鼠，每一种都有一种缺陷， CSF-II同种型; 2. 来描述细胞机制， TNF和PTH通过以下方式增加成骨细胞中CSF-1的转录： 表征介导TNF诱导的CSF-1的NF-κ B蛋白 基因表达，并通过鉴定和表征CSF-1启动子 PTH介导这种反应的元件;和3. 分析 CSF-1在体内骨重建中的作用， 体外建立CSF-1靶向过表达转基因小鼠模型 在成骨细胞中。 这些研究将有助于阐明调节和作用， 细胞因子，这是破骨细胞发展的关键，并将改善 我们对生理性骨吸收机制的理解， 由骨诱导剂引起的。

The precise mechanism whereby osteoblasts mediate osteoclastic bone resorption is unclear. One widely-held hypothesis is that activated osteoblasts secrete cytokines that directly or indirectly influence osteoclast formation or function. Although the nature of these putative cytokines is unknown, compelling in vivo and in vitro data have emerged to support a role for colony-stimulating factor-1 (CSF-1) as an osteoblast-derived factor involved in osteoclast formation. Thus, in vivo, deficiency of CSF-1 in the op/op osteopetrotic mouse causes a failure of osteoclast formation and bone resorption while in vitro studies have demonstrated that CSF-1 is critical for the proliferation and differentiation of osteoclast progenitors, that CSF-1 stimulates bone resorption in the fetal mouse metacarpal assay, and that CSF-1 receptors are present on osteoclasts. CSF-1 is synthesized as a soluble or cell surface protein, and while we know that osteoblasts synthesize both forms of CSF-1 I constitutively and in response to osteotropic agents, little is known of their physiologic significance in bone remodeling. Additionally, while we know that two key osteotropic agents, parathyroid hormone (PTH) and tumor necrosis factor (TNF) increase expression of the CSF-1 gene in osteoblasts, the precise mechanism by which they do so is unclear. Finally, the precise physiologic role of CSF-1 in bone remodeling in vivo is unknown. The long term goals of this proposal are therefore: 1. to define the physiologic roles of the cell- surface and soluble forms of CSF-1 in bone, by examining the effects of cell-surface CSF-1 on osteoclast signaling in vitro, and by generating two lines of genetically-altered mice that are each deficient in one of the CSF-1 I isoforms; 2. to characterize the cellular mechanisms by which TNF and PTH increase CSF-1 transcription in osteoblasts by characterizing the NF-kappaB proteins that mediate TNF-induced CSF-1 gene expression and by identifying and characterizing the CSF-1 promoter elements by which PTH mediates this response; and 3. to analyze the role of CSF-1 in bone remodeling in vivo by characterizing in vivo and in vitro a transgenic mouse model with targeted overexpression of CSF-1 in osteoblasts. These studies will help to elucidate the regulation and role of a cytokine which is critical in osteoclast development, and will improve our understanding of the mechanisms of physiologic bone resorption, and that induced by osteotropic agents.