Notch Signaling in Joint Cartilage Maintenance and Arthritis

描述（由申请人提供）：在小鼠或人类骨关节炎（OA）的发病机制中，很少有信号分子或细胞外基质（ECM）基因被鉴定为关节软骨维持的关键调节因子。最近，我们已经确定了Notch信号通路作为一种新的和关键的调节骨骼祖细胞分化在早期肢体发育，以及，软骨细胞增殖和成熟在endochondrial骨发育过程中的一个不可或缺的介质。在这里，我们提出了额外的突破性发现，确定Notch信号效应，RBPjk，作为一种新的和关键的调节正常关节软骨和关节维护。具体而言，我们发现几乎所有关节细胞中RBPjk的缺失（Prx 1Cre; RBPjkf/f）导致1）关节软骨的纤维化和变性以及ECM组分的显著缺失，2）半月板纤维化和变性，3）软骨下骨硬化，4）骨赘形成，以及5）表达Prg 4（润滑素）的浅表关节软骨的进行性缺失。基于这些新发现，我们假设软骨细胞特异性RBPjk依赖性Notch信号传导是关节软骨和关节维护所需的，通过ECM相关分子的调节，最终控制PRG 4（LUBRICIN）在关节软骨内的表达、定位和功能。为了验证这一假设，我们开发了三个特定的目标，旨在揭示RBPjk依赖性Notch信号传导维持关节软骨的细胞和分子机制。我们将生成几种小鼠遗传模型和体外关节软骨细胞培养或外植体模型，以测试是否：A）软骨特异性RBPjk依赖性Notch信号传导控制关节软骨维持，B）RBPjk依赖性Notch信号传导是维持正常PRG 4表达、定位和功能所必需的，C）RBPjk和PRG 4在关节软骨维持期间在遗传上和功能上相互作用，D）PRG 4过表达可以挽救Prx 1Cre; RBPjkf/f突变小鼠的OA表型，E）RBPjk单倍不足加速创伤性关节损伤后的OA进展，和F）短暂Notch激活可以抑制创伤性关节损伤后的OA进展。该提案产生的数据可能会将RBPjk依赖性Notch途径确定为开发疾病修饰骨关节炎药物（DMOAD）的潜在靶点。

DESCRIPTION (provided by applicant): Few signaling molecules or extracellular matrix (ECM) genes have been identified as critical regulators of joint cartilage maintenance in the pathogenesis of osteoarthritis (OA) in mice or humans. Recently, we have identified the Notch signaling pathway as a novel and critical regulator of skeletal progenitor cell differentiation during early limb development, as well as, an integral mediator of chondrocyte proliferation and maturation during endochondral bone development. Here we present additional breakthrough discoveries identifying the Notch signaling effector, RBPjk, as a novel and critical regulator of normal articular cartilage and joint maintenance. Specifically, we have discovered that loss of RBPjk in nearly all cells of the joints (Prx1Cre; RBPjkf/f) results in 1) fibrosis and degenerationof the articular cartilage with a significant loss in ECM components, 2) meniscus fibrosis and degeneration, 3) subchondral bone sclerosis, 4) osteophyte formation, and 5) a progressive loss of the Prg4 (lubricin) expressing superficial articular cartilage. Based on these novel findings, w hypothesize that chondrocyte-specific RBPjk-dependent Notch signaling is required for articular cartilage and joint maintenance via regulation of ECM-related molecules, which ultimately controls PRG4 (LUBRICIN) expression, localization, and function within the articular cartilage. To test this hypothesis we have developed three specific aims geared at uncovering the cellular and molecular mechanisms by which RBPjk- dependent Notch signaling maintains articular cartilage. We will generate several mouse genetic models and in vitro articular chondrocyte culture or explant models to test whether: A) cartilage-specific RBPjk-dependent Notch signaling controls articular cartilage maintenance, B) RBPjk-dependent Notch signaling is required to maintain normal PRG4 expression, localization, and function, C) RBPjk and PRG4 genetically and functionally interact during articular cartilage maintenance, D) PRG4 overexpression can rescue the OA phenotype of Prx1Cre; RBPjkf/f mutant mice, E) RBPjk haploinsufficiency accelerates OA progression following traumatic joint injury, and F) transient Notch activation can suppress OA progression following traumatic joint injury. Data generated by this proposal wil likely identify the RBPjk-dependent Notch pathway as a potential target for developing disease modifying osteoarthritis drugs (DMOADs).