Elucidating the Relationship Between Notch and WNT Signaling in Bone Formation

描述（由申请人提供）：在胚胎发生期间，Notch/RBPjk和Wnt/2-连环蛋白信号通路调节不同的细胞命运决定。成骨细胞是负责产生骨基质的主要细胞类型，并且不仅是骨发育所必需的，而且是骨重建和体内平衡所必需的。成骨细胞分化的缺陷导致骨质疏松症，这是一种以骨量显著减少为特征的疾病。在成骨细胞发育过程中，Notch/RBPjk信号通过抑制成骨细胞分化来维持骨髓间充质祖细胞。相反，Wnt/2-catenin信号促进成骨细胞分化。这两种途径的不同作用是明确的，Notch抑制分化，而Wnt促进分化。然而，Notch抑制成骨细胞发育的确切阶段尚未确定，尽管我们的初步研究表明，Notch可能会阻碍Runx 2阳性细胞的进一步发展。此外，成骨细胞分化过程中Wnt和Notch通路之间的遗传关系尚不清楚。因此，该提议的目标是检验Notch抑制Runx 2阳性细胞的进一步分化以及Notch至少部分地通过抑制Wnt/β-连环蛋白信号传导而起作用的假设。为了验证这个假设，我提出了两个具体的目标。目标1。确定成骨细胞分化过程中Runx 2阳性细胞中Notch/RBPjk信号传导的作用我将使用一种新的小鼠系以强力霉素诱导的方式删除Runx 2阳性细胞中的RBPjk，并评估潜在的骨表型。本研究将为Notch/RBPjk信号通路对成骨细胞分化的阶段特异性调控提供遗传学证据。目标二。评价成骨细胞发育过程中RBPjk和β-连环蛋白之间的遗传关系我将研究β-连环蛋白去除（单个或两个等位基因）对间充质祖细胞中RBPjk缺失引起的高骨量表型的影响。本研究将检验Notch/RBPjk在成骨细胞分化过程中在Wnt/β-catenin信号传导的遗传上游发挥作用的假设。 总的来说，这些研究将加强目前对Notch抑制成骨细胞分化的理解，并阐明成骨细胞发育过程中两个相反信号Notch和Wnt之间的功能关系。

DESCRIPTION (provided by applicant): During embryogenesis, the Notch/RBPjk and Wnt/2-catenin signaling pathways regulate diverse cell fate decisions. Osteoblasts are the primary cell type responsible for producing bone matrix and are necessary not only for bone development but also bone remodeling and homeostasis. Deficiency in osteoblast differentiation results in osteoporosis, a disease characterized by significant decreases in bone mass. During osteoblast development, Notch/RBPjk signaling maintains bone marrow mesenchymal progenitors by suppressing osteoblast differentiation. Conversely, Wnt/2-catenin signaling promotes osteoblast differentiation. The disparate effects of these two pathways are clear, with Notch inhibiting differentiation while Wnt promoting it. However, the exact stage at which Notch inhibits osteoblast development has not been defined, although our preliminary studies indicate that Notch likely impedes further progression of Runx2- positive cells. Moreover, the genetic relationship between Wnt and Notch pathways during osteoblast differentiation is not known. As such, the goal of this proposal is to test the hypothesis that Notch suppresses further differentiation of Runx2-positive cells and that Notch functions at least in part by inhibiting Wnt/ -catenin signaling. To test this hypothesis I have developed two specific aims. Aim 1. Determine the role of Notch/RBPjk signaling in Runx2-positive cells during osteoblast differentiation I will use a novel mouse line to delete RBPjk in Runx2-positive cells in a doxycycline-inducible manner and to assess the potential bone phenotype. This study will provide genetic evidence about the stage-specific regulation of osteoblast differentiation by Notch/RBPjk signaling. Aim 2. Evaluate the genetic relationship between RBPjk and -catenin during osteoblast development I will examine the effect of -catenin removal (single or both alleles) on the high-bone-mass phenotype caused by RBPjk deletion in mesenchymal progenitors. This study will test the hypothesis that Notch/RBPjk functions genetically upstream of Wnt/ -catenin signaling during osteoblast differentiation. Overall, these studies will enhance the current understanding about Notch inhibition of osteoblast differentiation, and shed light on the functional relationship between two opposing signals, Notch and Wnt, during osteoblast development.