Elucidating the Relationship Between Notch and WNT Signaling in Bone Formation

描述(申请人提供)：在胚胎发育过程中，Notch/RBPjk和Wnt/2-catenin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，不仅对骨发育是必需的，而且对骨重建和内稳态也是必需的。成骨细胞分化不足导致骨质疏松症，骨质疏松症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信号通路通过抑制成骨细胞分化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。这两条途径的不同作用是显而易见的，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还没有确定，尽管我们的初步研究表明Notch可能阻碍Runx2阳性细胞的进一步发展。此外，在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，这项建议的目标是验证Notch抑制Runx2阳性细胞的进一步分化以及Notch至少部分通过抑制Wnt/-catenin信号发挥作用的假设。为了检验这一假设，我提出了两个具体目标。目的1.确定Notch/RBPjk信号在Runx2阳性细胞成骨分化过程中的作用。我将利用一种新的小鼠株系，以多西环素诱导的方式删除Runx2阳性细胞中的RBPjk，并评估其潜在的骨表型。本研究将为Notch/RBPjk信号对成骨细胞分化的阶段性调控提供遗传学证据。目的2.探讨RBPjk与-catenin在成骨细胞发育过程中的遗传关系我将检测-catenin的去除(单等位基因或双等位基因)对RBPjk缺失导致的间充质祖细胞高骨量表型的影响。这项研究将验证Notch/RBPjk在成骨细胞分化过程中在Wnt/-catenin信号的遗传上游发挥作用的假设。总体而言，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.