Role of PTPN11 in Cartilage Stem Cells and Tumorigenesis

 描述（由申请人提供）：腕关节疾病仍然是最昂贵的肌肉骨骼疾病之一，其治疗仍然是一个重大的临床挑战。缺乏足够的知识，关于调节软骨形成的分子和细胞机制，主要导致这种情况。该提案的目标试图通过研究软骨的发育和稳态如何受到新鉴定的表达组织蛋白酶K（Ctsk）的软骨样祖细胞（CCP）和细胞质蛋白酪氨酸磷酸酶SHP 2（由PTPN 11编码）的调节来填补这一知识空白。 在最近的一项旨在表征在表达Ctsk的细胞中缺乏SHP 2的小鼠的骨骼表型的研究中，我们做出了两个重要且相互关联的发现（Nature，2013. 499：491-5）。首先，我们发现了一个新的CCP群体，主要存在于朗维尔软骨膜沟，也稀疏地分散在关节和生长板软骨。CCP表达间充质干细胞（MSC）表面标志物，似乎在软骨发育和体内平衡中发挥作用。其次，我们发现SHP 2在软骨中起肿瘤抑制剂的作用：小鼠CCP中的SHP 2缺失产生了惊人的骨骼表型，其特征是骨软骨瘤和内生软骨瘤的生长。这些骨骼疾病概括了异软骨瘤病的临床特征，异软骨瘤病是一种人类软骨肿瘤综合征，其中已鉴定出杂合SHP 2功能丧失（LOF）突变。我们的研究结果强烈表明，CCP是一个表型和功能不同的软骨干细胞库，而SHP 2是软骨形成过程中CCP和可能其他软骨样细胞的关键调节剂。 与大量关于蛋白酪氨酸激酶信号传导的文献相比，SHP 2在软骨形成和软骨稳态中的调节作用知之甚少。我们假设CCP是软骨干细胞; SHP 2通过影响主软骨形成转录因子SOX 9的表达和转录活性来调节CCP和软骨形成的命运决定。SHP 2缺陷导致的SOX 9表达和转录活性的改变可导致细胞过度增殖、分化和软骨性肿瘤。该提案的具体目标是确定CCP在多大程度上是真正的软骨干细胞;以及SHP 2如何调节软骨发生和SHP 2杂合性缺失突变如何导致软骨肿瘤发生。我们的长期目标是通过动员CCP和/或修饰SHP 2调节的信号通路来开发抑制软骨退变并促进其再生和稳态的策略。这项研究的结果将为开发新的治疗方法和再生方法来治疗从肿瘤到骨关节炎的一系列软骨疾病提供新的思路。

 DESCRIPTION (provided by applicant): Cartilage diseases remain among the most costly musculoskeletal disorders, their treatment continues to be a major clinical challenge. Lack of adequate knowledge regarding the molecular and cellular mechanisms that regulate chondrogenesis primarily causes this scenario. The goal of this proposal attempts to fill this knowledge gap by studying how the development and homeostasis of cartilage are regulated by the newly identified population of cathepsin K (Ctsk)-expressing chondroid progenitors (CCP) and by the cytoplasmic protein tyrosine phosphatase SHP2 (encoded by PTPN11). In a recent study aimed at characterizing the skeletal phenotype of mice lacking SHP2 in Ctsk- expressing cells, we made two important and interrelated discoveries (Nature, 2013. 499:491-5). First, we identified a novel population of CCP which primarily reside in the perichondrial groove of Ranvier and also sparsely scatter in articular and growth plate cartilage. CCP express mesenchymal stem cell (MSC) surface markers and appear to play a role in cartilage development and homeostasis. Second, we found that SHP2 functions as a tumor suppressor in cartilage: SHP2 deletion in CCP in mice yields a striking skeletal phenotype, featuring the growth of osteochondromas and enchondromas in bone. These skeletal diseases recapitulate the clinical features of metachondromatosis, a cartilage tumor syndrome in humans in which heterozygous SHP2 loss-of-function (LOF) mutations have been identified. Our findings strongly suggest that CCP are a phenotypically and functionally distinct pool of cartilage stem cells, and SHP2 is a key modulator of CCP and possibly other chondroid cells during chondrogenesis. Little is known about the regulatory role of SHP2 in chondrogenesis and cartilage homeostasis, in contrast to the vast literature regarding protein tyrosine kinase signaling in this context. We hypothesize that CCP are cartilage stem cells; SHP2 regulates fate decisions of CCP and chondrogenesis by influencing the expression and transcriptional activity of the master chondrogenic transcription factor SOX9. Altered SOX9 expression and transcriptional activity as a result of SHP2 deficiency can cause excessive cell proliferation, differentiation and cartilaginous neoplasm. The specific objectives of this proposal are to determine CCP, to what extent, are truly cartilage stem cells; and mechanistically how SHP2 regulates chondrogenesis and SHP2 loss-of-heterozygosity mutations cause cartilage tumorigenesis. Our long-term objective is to develop strategies to inhibit cartilage degeneration and promote its regeneration and homeostasis by mobilizing CCP and/or modifying SHP2-regulated signaling pathway(s). The outcome of this study will shed new light on the development of novel therapeutics and regenerative approaches to a spectrum of cartilage diseases, from tumors to osteoarthritis.