Beta-Catenin Signaling and Pathogenesis of Osteoarthritis

描述(申请人提供)：骨关节炎(OA)是一种退行性关节疾病，其发病机制尚不清楚。关节软骨细胞是关节软骨中唯一的细胞类型，负责维持关节软骨组织的适当结构和功能。关节软骨细胞的功能受多种生长因子的调节，其中包括WNT家族成员。最近的人类遗传学研究表明，Wnt信号抑制因子分泌的卷曲相关蛋白3(SFRP3)突变(Arg324Gly替换)的患者容易发生骨性关节炎。我们还知道，sFRP3的突变会导致β-连环蛋白信号的激活。这些发现提示，规范的Wnt/β-连环蛋白信号通路可能在骨性关节炎的发生发展过程中起着关键作用。然而，直接的遗传学和分子证据表明-连环蛋白在骨性关节炎的发生发展中的作用以前还没有报道。在初步研究中，我们证明了-连环蛋白条件性激活(CACT)小鼠出现了严重的OA样表型。我们还发现，半月板损伤和机械损伤经常导致骨关节炎的发展，激活了关节软骨细胞中典型的Wnt/？-catenin信号。这一建议的基本假设是：1)规范的Wnt/β-catenin信号在检测关节软骨细胞半月板损伤和机械损伤的变化中起关键作用，并且是必需的，其异常激活将导致关节软骨细胞β-catenin信号的关键下游靶基因BMP2和MMP13的发展；2)BMP2和MMP13是关节软骨细胞β-catenin信号的关键下游靶基因，这些基因的缺失将显著逆转CACT小鼠β-catenin中观察到的OA样表型。在具体目标1中，我们将分析-catenin CACT小鼠，并确定成年-catenin CACT小鼠年龄相关的OA样表型。将在3个月、6个月、9个月和12个月大的CACT小鼠身上检测关节软骨结构和形态以及关节软骨细胞功能的变化。此外，我们还将确定成年CACT小鼠是否更容易受到化学或关节损伤诱导的骨关节炎的影响。在特定的目标2中，我们将确定半月板损伤或机械损伤在连环蛋白信号的激活和骨性关节炎发生发展中的作用。我们将确定关节软骨细胞的半月板损伤或机械损伤诱导的类骨关节炎表型是否需要规范的Wnt/？-catenin信号的激活。在特定的目标3中，我们将确定BMP2和MMP13是否是成年连环蛋白CACT小鼠骨性关节炎发生发展过程中连环蛋白信号的关键下游介质。我们将在-catenin基因过度表达的关节软骨细胞中删除BMP2或MMP-13基因，并确定它们的缺失是否会显著逆转在-catenin CACT小鼠中观察到的OA样表型。我们提出的研究将为连环蛋白信号在关节软骨细胞功能和骨关节炎发病机制中的作用提供新的和明确的证据。公共卫生相关性：骨关节炎(OA)是一种退行性关节疾病，其发病机制尚不清楚。最近的人类遗传学研究表明，连环蛋白信号转导可能在骨性关节炎的发生发展中起关键作用。在拟议的研究中，我们将使用分子遗传学方法和不同的小鼠骨性关节炎模型来研究连环蛋白在骨性关节炎发病机制中的作用。在成年小鼠的关节软骨细胞中，-catenin基因将被特异性激活或缺失。我们的研究将为连环蛋白在骨性关节炎发生中的作用提供直接的遗传学证据。

DESCRIPTION (provided by applicant): Osteoarthritis (OA) is a degenerative joint disease and the mechanism of this disease is poorly understood. The articular chondrocyte is the only cell type in articular cartilage and these cells are responsible for maintaining the appropriate structure and function of the articular cartilage tissue. The function of articular chondrocytes is regulated by a variety of growth factors, including Wnt family members. Recent human genetic studies demonstrate that patients with a mutation (Arg324Gly substitution) in the secreted frizzled-related protein 3 (sFRP3), a Wnt signaling inhibitor, have a predisposition for the development of OA. It is also known that the mutation of sFRP3 causes activation of ¿-catenin signaling. These findings suggest that the canonical Wnt/¿-catenin signaling pathway may play a critical role during the development of OA. However, direct genetic and molecular evidence for the role of ¿-catenin in the development of OA has not been reported before. In preliminary studies, we demonstrated that ¿-catenin conditional activation (cAct) mice developed a severe OA-like phenotype. We also found that meniscus injury and mechanical injury, which often lead to the development of OA, activate canonical Wnt/¿-catenin signaling in articular chondrocytes. The underlying hypotheses of this proposal are that 1) canonical Wnt/¿-catenin signaling plays a key role and is required for sensing changes in meniscus injury and mechanical injury in articular chondrocytes and its abnormal activation will lead to the development of an OA-like phenotype; and 2) Bmp2 and Mmp13 are key downstream target genes of ¿-catenin signaling in articular chondrocytes and deletion of these genes will significantly reverse the OA-like phenotype observed in ¿-catenin cAct mice. In Specific Aim 1, we will analyze ¿-catenin cAct mice and determine the age-dependent OA-like phenotype in adult ¿-catenin cAct mice. Changes in articular cartilage structure and morphology and articular chondrocyte function will be examined in 3-, 6-, 9-, and 12-month-old ¿-catenin cAct mice. In addition, we will also determine if adult ¿-catenin cAct mice are more susceptible to chemically- or joint injury-induced OA. In Specific Aim 2, we will determine the role of meniscus injury or mechanical injury in activation of ¿-catenin signaling and the development of OA. We will determine if activation of the canonical Wnt/¿-catenin signaling is required for the meniscus injury- or mechanical injury-induced OA-like phenotype in articular chondrocytes. In Specific Aim 3, we will determine if Bmp2 and Mmp-13 are key downstream mediators of ¿-catenin signaling during the development of OA in adult ¿-catenin cAct mice. We will delete the Bmp2 or Mmp-13 gene in articular chondrocytes where the ¿-catenin gene is over expressed and determine if their deletion will significantly reverse the OA-like phenotype observed in ¿-catenin cAct mice. Our proposed studies will provide novel and definitive evidence about the role of ¿-catenin signaling in articular chondrocyte function and OA pathogenesis. PUBLIC HEALTH RELEVANCE: Osteoarthritis (OA) is a degenerative joint disease and the mechanism of this disease is poorly understood. Recent human genetic studies demonstrated that ¿-catenin signaling may play a key role in OA development. In the proposed studies, we will use molecular genetic approach and different mouse OA models to investigate the role of ¿-catenin in OA pathogenesis. The ¿-catenin gene will be specifically activated or deleted in articular chondrocytes in adult mice. Our studies will provide direct genetic evidence on the function of ¿-catenin in OA development.