Regulated Tissue Specific BMP Function in Bone Repair

骨形态发生蛋白（BMPs）是一种有效的形态因子，已被证明可促进软骨和成骨分化。这已经在体外、间充质干细胞模型系统中以及在体内被植入或注射到异位、异位或正位部位的重组bmp中得到了证明。bmp在骨修复的所有阶段都有较高水平的表达，并且外源性给药可以增强愈合反应。假设：bmp在骨折愈合的所有阶段都起着关键的调节作用。为了验证这一假设，本应用程序中提出的研究将产生转基因小鼠，其中采用了一种新的实验策略

Bone morphogenetic proteins (BMPs) are potent morphogens that have been shown to promote chondrogenic and osteogenic differentiation. This has been demonstrated in vitro, within model systems of mesenchymal stem cells, and in vivo when recombinant BMPs have been implanted or injected into ectopic, heterotopic or orthotopic sites. BMPs are also expressed at elevated levels throughout all stages of bone repair and have been shown, when exogenously administered, to enhance the healing response. Hypothesis: BMPs are critical in the regulation of all phases of fracture healing. In order to test this hypothesis, the studies proposed in this application will generate transgenic mice in which a novel experimental strategy is employed that restricts the expression of a transgene to either cartilage or bone and allows for the exogenous regulation of that transgene through systemic administration of a small molecule. Transgenic animals will be engineered to contain an artificial transcription factor encoded in two proteins, a novel DNA binding domain and an activation domain. The expression of these domains will be driven by a tissue-specific promoter (type II collagen for cartilage or osteocalcin for bone). The transcription factor will be activated by the exogenous administration of a dimerizing agent (rapamycin analog), which brings these domains into proximity. When activated, it will recognize a unique promoter which will drive the overexpression of BMP-2 or antagonize BMP function by overexpressing Noggin. Using this strategy, transgenic animals will undergo normal embryological development and fractures (or, in the case of Project 1, distraction osteogensis) will be carried out in the presence of normal skeletal function. Only upon introduction of the dimerizing agent will loss or gain of function states be induced through the overexpression of these transgenes. Fracture healing will then be analyzed in specific tissues and at specific times under conditions in which BMP function is altered. These studies will provide extensive new data concerning the specific roles that BMPs play at critical stages of fracture healing and establish a powerful model system for investigating a wide array of molecules and their effects on skeletal function.