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）发病过程中，很少有信号分子或细胞外基质（ECM）基因被确定为关节软骨维持的关键调节因子。最近，我们发现Notch信号通路是早期肢体发育过程中骨骼祖细胞分化的一个新的关键调节因子，也是软骨内骨发育过程中软骨细胞增殖和成熟的一个完整介质。在这里，我们提出了额外的突破性发现，确定Notch信号效应物RBPjk是正常关节软骨和关节维持的一种新的关键调节因子。具体来说，我们发现几乎所有关节细胞（Prx1Cre; RBPjkf/f）中RBPjk的缺失导致1)关节软骨纤维化和变性，伴有ECM成分的显著缺失，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Prg4（润滑素）的关节表面软骨的进行性缺失。基于这些新发现，我们假设软骨细胞特异性rbpjk依赖的Notch信号是关节软骨和关节维持所必需的，通过调节ecm相关分子，最终控制PRG4（润滑剂）在关节软骨中的表达、定位和功能。为了验证这一假设，我们制定了三个特定的目标，旨在揭示依赖RBPjk的Notch信号维持关节软骨的细胞和分子机制。我们将建立几个小鼠遗传模型和体外关节软骨细胞培养或外植体模型来测试：A)软骨特异性RBPjk依赖的Notch信号是否控制关节软骨的维持，B) RBPjk依赖的Notch信号是否需要维持正常的PRG4表达、定位和功能，C) RBPjk和PRG4在关节软骨维持过程中的遗传和功能相互作用，D) PRG4过表达可以挽救Prx1Cre的OA表型；RBPjkf/f突变小鼠，E) RBPjk单倍体功能不全加速创伤性关节损伤后OA进展，f)瞬时Notch激活可抑制创伤性关节损伤后OA进展。该提案产生的数据可能会确定rbpjk依赖性Notch通路作为开发疾病修饰性骨关节炎药物（DMOADs）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).