Notch Signaling in Cartilage Development

描述（由申请人提供）：信号通路组分如Ihh/Pthrp、TGF β、BMP、Wnt/β-连环蛋白、FGF和Sox相关蛋白代表软骨形成和发育的重要调节剂。这些相同的信号通路和相关分子被靶向用于软骨损伤和疾病（骨关节炎、类风湿性关节炎和骨折修复）的临床治疗和软骨组织工程应用（间充质祖细胞（MPC）的维持和操作）。我们提供了原始的，未发表的数据表明，Notch信号通路是MPC分化和软骨细胞成熟的另一个重要调节因子，导致有关Notch控制这些过程的机制的问题。为了开始解决这些问题，我们建议测试新的假设，RBPj？依赖性Notch信号通过与稳定的β-连环蛋白相互作用以调节Hes 1并最终调节Sox 9来抑制MPC分化和软骨形成，并且随后需要通过软骨特异性调节Hes 1和Runx 2活性来促进软骨细胞成熟。为了检验这些假设，我们将讨论两个具体目标。特定目标1中的实验将使用肢体间充质特异性条件性功能丧失和遗传拯救小鼠模型研究Hes 1是否是MPC分化和软骨形成所需的，或者是Notch介导的MPC分化抑制。其次，我们将确定Wnt/β-catenin信号通路是否是Notch介导的Hes 1诱导和MPC分化抑制所必需和充分的。最后，我们将确定Hes 1是否通过直接调节Sox 9表达来抑制MPC分化。具体目标2将首先检查RBPJ？使用各种组织特异性Notch功能获得和丧失小鼠模型，研究了依赖性和非依赖性Notch信号传导在促进软骨细胞成熟中的作用。此外，我们将使用原代软骨细胞培养物进行体外实验，以鉴定RBPJ？依赖性Notch靶点调节软骨细胞成熟，并检查Notch是否在此过程中介导Wnt/β-连环蛋白或BMP信号传导。其次，我们将使用两种不同的条件性Hes 1突变小鼠模型来确定Hes 1是否是软骨细胞成熟的主要RBPJK依赖性Notch调节因子。最后，将进行体外研究，以确定Hes 1是否通过与相互辅阻遏物Groucho相关基因（Grg 1）的竞争性相互作用促进Runx 2活性和软骨细胞成熟。这些目标的完成将确定Notch信号传导机制在调节MPC维持和扩增以及软骨细胞成熟中的重要性。这些分子将可能作为软骨损伤或疾病的治疗靶点，并为我们提供用于软骨组织工程应用的潜在工具。

DESCRIPTION (provided by applicant): Signaling pathway components such as Ihh/Pthrp, TGF¿, BMPs, Wnt/¿-catenin, FGFs, and Sox-related proteins represent important regulators of cartilage formation and development. These same signaling pathways and related molecules are being targeted for clinical treatment of cartilage injuries and diseases (osteoarthritis, rheumatoid arthritis, and fracture repair) and cartilage tissue engineering applications (maintenance and manipulation of mesenchymal progenitor cells (MPCs)). We provide original, unpublished data indicating that the Notch signaling pathway is another important regulator of MPC differentiation and chondrocyte maturation, leading to questions regarding the mechanisms by which Notch controls these processes. To begin addressing these questions, we propose to test the novel hypothesis that RBPj?-dependent Notch signaling suppresses MPC differentiation and chondrogenesis by interacting with stabilized ¿-catenin to regulate Hes1 and ultimately Sox9, and is later required to promote chondrocyte maturation via cartilage specific regulation of Hes1 and Runx2 activities. To test these hypotheses, we will address two Specific Aims. Experiments in Specific Aim 1 will investigate whether Hes1 is required for MPC differentiation and chondrogenesis or the Notch-mediated suppression of MPC differentiation using limb mesenchyme specific conditional loss-of-function and genetic rescue mouse models. Secondly, we will determine whether the Wnt/beta-catenin signaling pathway is necessary and sufficient for Notch mediated induction of Hes1 and suppression of MPC differentiation. Finally, we will determine whether Hes1 suppresses MPC differentiation by directly regulating Sox9 expression. Specific Aim 2 will first examine the potential roles for both RBPJ?- dependent and -independent Notch signaling in promoting chondrocyte maturation using various tissue specific Notch gain- and loss-of-function mouse models. Additionally, we will perform in vitro experiments using primary chondrocyte cultures to identify RBPJ?-dependent Notch targets that regulate chondrocyte maturation and examine whether Notch mediates Wnt/beta-catenin or BMP signaling during this process. Secondly, we will use two different conditional Hes1 mutant mouse models to determine whether Hes1 is the primary RBPJk-dependent Notch regulator of chondrocyte maturation. Finally, in vitro studies will be performed to determine whether Hes1 promotes Runx2 activity and chondrocyte maturation via competitive interactions with the mutual co-repressor, Groucho related gene (Grg1). Completion of these aims will identify the Notch signaling mechanisms important in regulating MPC maintenance and expansion, as well as, chondrocyte maturation. These molecules will likely serve as therapeutic targets for cartilage injuries or diseases and provide us with potential tools for use in cartilage tissue engineering applications.