Mechanisms of Cortisol and Notch Action in Bone

描述（由申请人提供）：我们实验室先前的研究表明，Notch由成骨细胞表达，其合成受糖皮质激素调节。Notch在成骨细胞发生中起关键作用，其缺失导致严重的发育缺陷和新生儿死亡。其在骨骼中的过度表达导致继发于成骨细胞生成抑制作用的骨质减少。尽管经典Notch信号通路的激活诱导了毛状分裂增强子（HES）-1的表达，但HES-1的过度表达并不能概括Notch的所有作用，并且替代信号（如HEY-1）也在成骨细胞系中Notch的抑制作用中发挥作用。Notch抑制作用的核心是抑制Wnt/β-连环蛋白信号传导途径。拟定研究的目的是了解Notch和HES-1在体内和体外骨中的功能，并确定相关机制。为此，我们将使用在骨环境中过表达Notch或HES-1的转基因小鼠品系，以及携带Notch 1和2或hes-1条件性缺失的小鼠。我们的具体目标是：1）探索Notch在成骨细胞谱系中的作用机制，特别是其对Wnt/<$-连环蛋白的抑制作用机制; 2）通过在I型胶原启动子控制下转基因过表达HES-1和通过靶向hes-1条件性缺失来确定HES-1的体内功能。将错误表达HES-1的小鼠的骨骼表型与野生型小鼠的骨骼表型进行比较，并通过组织形态计量学、接触放射照相术、密度测定法和显微CT扫描进行测定;以及3）确定HES-1的体外作用机制和负责其对成骨细胞生成的影响的信号。将确定Notch和HES-1对骨重建的影响和相关机制。这些研究应阐明Notch和HES-1在骨细胞功能中的作用。公共卫生相关性：该项目将提供有关调节骨形成细胞功能的细胞内蛋白质的新信息，并与我们对骨质疏松症机制的理解和这种疾病新疗法的开发有关。

DESCRIPTION (provided by applicant): Previous investigations from our laboratory revealed that Notch is expressed by osteoblasts and its synthesis is regulated by glucocorticoids. Notch plays a critical role in osteoblastogenesis and its deletion results in serious developmental defects and neonatal lethality. Its over expression in the skeleton causes osteopenia secondary to an inhibitory effect on osteoblastogenesis. Although the activation of the canonical Notch signaling pathway induces the expression of hairy enhancer of split (HES)-1, HES-1 over expression does not recapitulate all the effects of Notch, and alternate signals, such as HEY-1 also play a role in the inhibitory effects of Notch in cells of the osteoblastic lineage. Central to the inhibitory actions of Notch is the suppression of the Wnt/¿-catenin signaling pathway. The aim of the proposed studies is to understand the function of Notch and HES-1 in bone in vivo and in vitro and define mechanisms involved. For this purpose, we will use transgenic mouse lines over expressing Notch or HES-1 in the bone environment, and mice carrying conditional deletions of notch1 and 2 or hes-1. Our specific aims are: 1) To explore the mechanism of action of Notch in cells of the osteoblastic lineage, particularly mechanisms involved in its inhibitory effects on Wnt/¿-catenin; 2) To determine the function of HES-1 in vivo by transgenic over expression of HES-1 under the control of the type I collagen promoter, and by targeted hes-1 conditional deletion. The skeletal phenotype of mice misexpressing HES-1 will be compared to that of wild type mice and determined by histomorphometry, contact radiography, densitometry and micro CT scanning; and 3) To determine the mechanism of action of HES-1 in vitro and signals responsible for its effects on osteoblastogenesis. The impact of Notch and HES-1 on bone remodeling and mechanisms involved will be determined. These investigations should clarify the role of Notch and HES-1 in bone cell function. PUBLIC HEALTH RELEVANCE: This project will provide novel information on intracellular proteins that regulate the function of bone forming cells, and is relevant to our understanding of mechanisms involved in osteoporosis and developments of new therapies for this disease.