Strategy for Therapy of the Pseudoachondroplasia (PSACH) Phenotype: Understanding

软骨寡聚基质蛋白(COMP)突变导致两种骨骼发育不良， 假性软骨发育不良(PSACH)和多发性骨骺发育不良(MED/EDM1) 与慢性关节异常有关。这项研究的重点是确定 软骨突变是否对细胞病理造成显性负效应 寡聚基质蛋白(COMP)可以逆转。在我们之前的工作中，我们已经展示了 CoMP的突变阻碍了蛋白质折叠所需的钙结合。不适当地 折叠突变的comp与IX型胶原、matrlin-3一起保留在扩大的小池中 和众多的伴侣蛋白。这种保留具有下游影响，即导致 缺乏这些蛋白质的细胞外基质，一种严重紊乱的基质，最终 软骨细胞死亡。相比之下，CoMP缺失的小鼠是正常的，这表明CoMP不是 对于软骨和骨骼的发育和动态平衡来说是必要的。我们假设移除 突变的COMP将逆转和建立PSACH细胞表型并恢复 软骨细胞功能和正常基质形成。为了检验这一假设，我们现在将 通过使用可诱导的启动子确定病理的时间路径及其解析 系统。我们已经成功地在3D培养系统中过表达了突变的comp 概述正常人类软骨细胞的疾病病理。四环素(Tet) 可诱导启动子和表达Tet激活转录因子(RTTA)的DMA将被用来诱导细胞表型和抑制突变comp的产生。这些 实验将在人类原代生长板软骨细胞和转基因 老鼠。这些研究将使我们能够确定表型发育的时间以及 这种表型是可逆的，这是朝着开发治疗方法迈出的重要一步。 对这些衰弱的骨科侏儒症的干预。

Mutations in cartilage oligomeric matrix protein (COMP) cause two skeletal dysplasias, pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED/EDM1) both of which are associated with chronic joint abnormalities. The focus of this research is to determine whether the cellular pathology caused by the dominant negative effects of mutations in cartilage oligomeric matrix protein (COMP) can be reversed. In our previous work, we have demonstrated that mutations in COMP impede calcium-binding which is required for protein folding. Improperly folded mutant COMP is retained in enlarged rERcisternae along with type IX collagen, matrillin-3 and numerous chaperone proteins. This retention has the downstream effect of causing an extracellular matrix that is deficient in these proteins, a grossly disorganized matrix and eventual chondrocyte death. In contrast COMP null mice are normal suggesting that COMP is not necessary for cartilage and bone development and homeostasis. We hypothesize that removal of mutant COMP will reverse and established PSACH cellular phenotype and restore chondrocyte function and normal matrix formation. To test this hypothesis, we will now define the temporal pathway of the pathology and its resolution by using an inducible promoter system. We have successfully over-expressed mutant COMP in a 3-D culture system to recapitulate the disease pathology in normal human chondrocytes. The tetracycline (TET) inducible promoter and DMA expressing the TET-activated transcription factor (rtTA) will be used to both induce the cellular phenotype and to repress the production of mutant COMP. These experiments will be conducted in human primary growth plate chondrocytes and in transgenic mice. These studies will allow us to determine the timing of phenotype development and whether the phenotype is reversible, which is an important step towards toward developing a treatment intervention for these debilitating orthopedic dwarfing conditions.