EFFECTS OF GLUCOCORTICOIDS AND IGF 1 ON BONE FORMATION

骨质疏松症通常是糖皮质激素治疗的结果， 内源性糖皮质激素水平 都升高了 糖皮质激素引起的骨质疏松症是由于 骨吸收增加和骨形成减少。 糖皮质激素是骨形成的重要调节剂， 尽管它们的效果往往是矛盾的。 虽然生理 糖皮质激素浓度促进成骨细胞分化 在颅骨和骨髓基质细胞的原代培养物中， 药理学浓度抑制骨形成， 降低成骨细胞的更新和功能。 胰岛素样生长 然而，因子I（IGF-I）是骨形成的合成代谢。 这才 先前已经证明IGF-I可以阻止抑制性的 糖皮质激素对胎鼠颅骨器官培养的影响。 在 根据这项建议，我们将利用转基因方法， 设计新的和更明确的战略来评估影响， 以及Gcs和IGF-I在骨形成中的相互作用。 一是 假设骨中IGF-I过表达将增加 骨形成和防止抑制作用 体内的糖皮质激素。 第二，建议IGF-I无效 小鼠将具有骨形成缺陷， 糖皮质激素对骨形成的抑制作用。 三是 假设体内糖皮质激素会限制 骨髓基质细胞体外成骨分化 通过耗尽祖细胞的骨髓来培养。这些假设 将通过以下模型解决： 将开发一种独特的转基因小鼠，其中IGF-I 通过COL 1A 1启动子特异性靶向骨表达 在骨中高度表达但在大多数其他组织中不表达的片段 组织中 将来自胎儿IGF-I缺失小鼠的颅盖的器官培养物 被研究。 最后，用糖皮质激素治疗小鼠， 骨髓基质细胞的体内和体外分化 在体外检查培养物。 这些研究将提供见解， 糖皮质激素和IGF-I在骨上的相互作用， 小鼠中靶向生长因子表达是否 防止糖皮质激素对骨的抑制作用 阵

Osteoporosis is often a consequence of glucocorticoid therapy and pathological conditions in which endogenous glucocorticoid level are elevated. Glucocorticoid induced osteoporosis is due to an increase of bone resorption and a decrease in bone formation. Glucocorticoids are important regulators of bone formation, although, their effects are often paradoxical. While physiologic concentrations of glucocorticoids promote osteoblast differentiation in primary cultures of calvarial and bone marrow stromal cells, pharmacological concentrations inhibit bone formation by decreasing osteoblast renewal and function. Insulin-like growth factor I (IGF-I), however, is anabolic for bone formation. It been have previously shown that IGF-I can prevent the inhibitory effects of glucocorticoids in organ cultures of fetal rat calvaria. In this proposal, we will take advantage of transgenic approaches to design new and more definitive strategies for assessing the effects and interactions of Gcs and IGF-I on bone formation. First, it is hypothesize that overexpression of IGF-I in bone will increase bone formation and prevent the inhibitory effects of glucocorticoids in vivo. Second, it is suggested that IGF-I null mice will have defects in bone formation and will be susceptible to the inhibitory effects glucocorticoids on bone formation. Third, it is hypothesized that in vivo glucocorticoids willlimit the osteogenic differentiation of ex vivo bone marrow stromal cell cultures by depleting the marrow of progenitors. These hypotheses will be addressed will be addressed with the following models: A unique trans-genic mouse will be developed in which IGF-I expression is specifically targeted to bone by a COL1A1 promoter fragment that is highly expressed in bone but not most other tissues. Organ cultures of calvaria from fetal IGF-I null mice will be studied. Finally, mice with be treated with glucocorticoids in vivo and the differentiation of ex vivo bone marrow stromal cell cultures examined in vitro. These studies will provide insights in to the interactions of glucocorticoids and IGF-I on bone and show whether or not targeted growth factor expression in mice will prevent the inhibitory effects of glucocorticoids on bone formation.