The Role of Creb5 in Maintaining Synovial Joint Homeostasis

项目摘要/摘要。 这个项目的长期目标是对监管网络有一个全面的了解。 它调节着关节软骨的分化和维持，而关节软骨在维持 关节空间的低摩擦环境。事实上，构成关节软骨的细胞的一个标志是 它们的蛋白多糖的表达，如由Prg4基因编码的蛋白润滑素，可以润滑 对关节有保护作用，防止关节炎的发展。Prg4专门表达在最肤浅的 关节软骨层。拉萨实验室和其他实验室的研究结果表明，Prg4的表达 关节软骨表层的细胞(胚胎和出生后早期的小鼠)可作为干细胞。 成人关节软骨的所有深层区域。此外，在人类和小鼠身上 缺乏Prg4(编码润滑素)，关节软骨表面就会受损和早熟 发生关节故障。值得注意的是，在手术诱导后观察到润滑剂水平下降。 绵羊的骨性关节炎，以及骨关节炎或类风湿性关节炎患者的滑液中。 此外，老化过程中润滑剂表达的减少与老化膝盖的敏感性增加有关。 导致软骨退化。因此，Lassar实验室的一个关键目标是识别组织特异性转录 调节Prg4和其他在表面特异表达的基因的表达的因子 关节软骨区。Lassar实验室最近的发现表明，转录因子Creb5是 仅在浅层关节软骨细胞中表达(与深层关节软骨细胞表达相反 软骨细胞和生长板软骨细胞)，是Prg4表达的关键调节因子。最值得注意的是，异类 深部区牛关节软骨细胞(不表达Prg4)中Creb5的表达可激活转化生长因子-b2 和EGFR信号诱导Prg4在这些细胞中的表达，达到与表面区表达相同的水平 关节软骨细胞。这些发现表明，Creb5在软骨细胞中建立了一种胜任状态 表达Prg4以响应这些信号通路。此外，拉萨实验室还发现，通过基因工程改造的小鼠 缺乏功能的Creb5不能形成大量的滑膜关节。综上所述，这些发现表明，Creb5 在滑膜关节的形成中起着关键作用，并且是一种新的和关键的调节因子 Prg4/润滑素在关节软骨细胞中的表达。该项目将确定Creb5在维护 成熟滑膜关节中所有组织的健康状况；将决定Creb5在 关节软骨细胞或滑膜成纤维细胞在衰老过程中或在骨关节炎过程中会减弱，最终会 确定外源性Creb5在滑膜关节持续表达是否能促进润滑素的表达 并在衰老过程中或在创伤后骨关节炎的小鼠模型中阻止这种组织的降解。

Project Summary/Abstract. The broad, long-term goal of this project is to develop a comprehensive understanding of the regulatory network that regulates the differentiation and maintenance of articular cartilage, which plays a central role in maintaining the low-friction environment of the joint space. Indeed, a hallmark of cells comprising the articular cartilage is their expression of proteoglycans, such as the protein lubricin, encoded by the Prg4 gene, that lubricates the joint and protects against the development of arthritis. Prg4 is specifically expressed in the superficial-most layer of the articular cartilage. Findings by both the Lassar lab and others have established that Prg4-expressing cells in the superficial zone of articular cartilage (in embryonic and early post-natal mice) serve as a stem cell population for all deeper regions of the articular cartilage in the adult. Furthermore, in both humans and mice lacking Prg4 (which encodes lubricin), the surface of the articular cartilage becomes damaged and precocious joint failure occurs. Notably, decreased levels of lubricin have been observed following surgically induced osteoarthritis in sheep, and in synovial fluid from patients with either osteoarthritis or rheumatoid arthritis. Furthermore, a decrease in lubricin expression during aging, correlates with increasing sensitivity of aged knees to cartilage degradation. Thus, a key objective of the Lassar lab has been to identify tissue-specific transcription factors that regulate the expression of both Prg4 and other genes that are specifically expressed in the superficial zone of the articular cartilage. Recent findings in the Lassar lab indicate that the transcription factor Creb5 is uniquely expressed in superficial zone articular chondrocytes (as opposed to both deeper zone articular chondrocytes and growth plate chondrocytes) and is a crucial regulator of Prg4 expression. Most notably, ectopic expression of Creb5 in deep zone bovine articular chondrocytes (which do not expression Prg4) enabled TGF-b2 and EGFR signals to induce Prg4 expression in these cells, to a level equal to that expressed by superficial zone articular chondrocytes. These findings suggest that Creb5 establishes a competent state in chondrocytes to express Prg4 in response to these signaling pathways. In addition, the Lassar lab has found that mice engineered to lack functional Creb5 fail to form many synovial joints. Taken together, these findings indicate that Creb5 plays a critical role in both the formation of synovial joints and is a both a novel and crucial regulator of Prg4/lubricin expression in articular chondrocytes. This project will determine the role of Creb5 in maintaining the health of all tissues in the mature synovial joint; will determine whether expression of Creb5 in either articular chondrocytes or synovial fibroblasts is attenuated during aging or during osteoarthritis; and finally will determine whether sustained expression of exogenous Creb5 in the synovial joint can boost lubricin expression and block degradation of this tissue either during aging or in a murine model for post-traumatic osteoarthritis.