CCN proteins in cartilage formation and maintenance

CCN家族的成员是疾病过程的关键介体。CCN2/CTGF(结缔组织 生长因子)是迄今为止研究的所有纤维化条件下细胞外基质过度合成的主要介质，以及 CCN1/Cyr61在肿瘤进展过程中具有很强的促血管生成活性。这些蛋白质被认为是作为 基质细胞蛋白，由ECM-整合素与其他途径相互作用所介导的协调信号。 然而，这些蛋白质的许多体外活性中，哪些与生理相关尚不清楚， 因为它们在正常组织发育/维持中的功能尚未确定。靶向小鼠的研究 证明CCN2/CTGF在软骨形成中是必需的。CCN2是否通过作用来调节其效应 作为整合素的配体，影响ECM及其调节剂的合成，和/或改变 软骨中的信号通路将在目标一中进行研究。Ccn2基因缺失对基因的影响 将研究生长板离散区域中的表达，以检验Ccn2具有的假设 对ECM含量的全局影响，并测试特定信号通路的输出是否受到损失的影响 CCN2。控制软骨中CCN2表达的信号通路将在目标2中确定。AS Ccn2-L-小鼠与Sox9+/-小鼠有惊人的相似之处，Ccn2是否为SOX因子的直接靶标将 被调查。作为Ccn2-/-小鼠的主要表型之一，是缺陷小鼠所致的菌落减少症 这些研究还将阐明对软骨细胞肥大至关重要的信号通路。 肥大的软骨，以控制随后的骨形成。关于角色的一个关键问题 基质细胞蛋白是指它们完成重叠功能的程度。体外研究表明， CCNS也有类似的活动。然而，在任何情况下都没有证明CCN1和CCN2有重叠 功能。通过对CCN1的分析，揭示了CCN1在软骨形成和关节形成中的独特作用 零老鼠。在目标三中，研究了这种独特的关节表型，并使用CCN1等位基因来定义 CCN1在软骨中的作用。对双重和复合突变体的分析将直接检验 CCN1和CCN2具有重叠功能。最后，有令人信服的证据表明，多个CCN 家庭成员对成人关节软骨的维护至关重要。Ccn2是最多的 成人关节软骨中有丰富的转录本，关节软骨细胞对CCN2有反应，导致 关节损伤的修复。在人类中，相关基因CCN6的丢失会导致进行性 假性风湿性样异型增生，一种严重的关节炎形式，表明CCN的主要共同功能 蛋白质是维持关节软骨的。我们检验了CCN2对维持心脏功能至关重要的假设 使用花环状Ccn2等位基因和他莫昔芬诱导的Cre重组酶的成人软骨。

Members of the CCN family are key mediators of disease processes. CCN2/CTGF (Connective Tissue Growth Factor) is the major mediator of excess ECM synthesis in all fibrotic conditions studied to date, and CCN1/Cyr61 has potent proangiogenic activities in tumor progression. These proteins are proposed to act as matricellular proteins, coordinating signals mediated by ECM-integrin interactions with otherpathways. However, which of the many in vitro activities of these proteins are physiologicallyrelevant isunknown, because their functions in normal tissue development /maintenance are undefined. Studies of targeted mice demonstrate that CCN2/CTGF is essential for chondrogenesis. Whether CCN2 mediates its effects by acting as a ligand for integrins, affecting synthesis of ECM and its modulators, and/or altering the outputs of signaling pathways in cartilage will be investigated in aim one. The consequences of loss of Ccn2 on gene expression in discrete regions of the growth plate will be investigated to test the hypotheses that Ccn2 has global effects on ECM content, and to test whether output of specific signaling pathways is impacted by loss of CCN2. Signaling pathways controlling CCN2 expression in cartilage will be identified in aim two. As Ccn2-l- mice bear a striking resemblance to Sox9+/- mice, whether CCN2 is a direct target of Sox factors will be investigated. As one of the major phenptypes of Ccn2-/- mice is psteopenia as a result of defective chondrocyte hypertrophy, these studies will also shed light on signaling pathways essential for the ability of hypertrophic cartilage to control subsequent bone formation. A key question regarding the roles of matricellular proteins is the extent to which they fulfill overlapping functions. In vitro studies suggest broadly similar activities for CCNs. However, in no case has it been shown that CCN1 and CCN2 have overlapping functions. A unique role of CCN1 in chondrogenesis and in joint formation is revealed by analysis of Ccn1 null mice. In aim three this unique joint phenotype is investigated and a Ccn1 floxed allele is used to define the role of CCN1 in cartilage. Analysis of double and compound mutants will test directly the degree to which CCN1 and 2 fulfill overlapping functions. Finally, there is compelling evidence implicating multiple CCN family members as essential for the maintenance of adult articular cartilage. Ccn2 is one of the most abundant transcripts in adult articular cartilage, and articular chondrocytes respond to CCN2, leading to repair of articular defects. In humans, loss of a related gene, CCN6, leads to a progressive pseudorheumatoid dysplasia, a severe form of arthritis, suggesting that a major shared function for CCN proteins is to maintain articular cartilage. We test the hypothesis that CCN2 is vital for the maintenance of adult cartilage using a floxed Ccn2 allele and a tamoxifen-inducible Cre recombinase.