Consequences of Mutant COMP Expression and Therapeutic Approaches in Transgenic M

描述（由申请人提供）：两种骨骼发育不良，假性软骨发育不全（PSACH）和多发性骨骺发育不良（MED/EDM1）是由内质网（ER）中突变型COMP （MT-COMP）在细胞内大量滞留导致骨发育过程中软骨细胞过早死亡引起的。本研究的重点是确定MT- COMP促进软骨细胞病理的细胞机制，并确定各种药物是否抑制或逆转病理。在之前的研究中，我们已经证明：1)COMP突变导致骨骼发育不良，2)突变的COMP干扰COMP以及IX型胶原和matrilin-3蛋白向细胞外基质的输出，3)细胞内基质在巨大的rER池中不适当地组装，4)PSACH软骨基质缺乏ECM蛋白，5)细胞内COMP滞留导致软骨细胞过早死亡。虽然我们的体外软骨细胞模型系统表明突变的COMP不会被细胞质量控制机制降解，但缺乏动物模型系统限制了对MT-COMP导致细胞病理的分子机制的研究。重要的是，我们创建了一个转基因小鼠模型，其中诱导的软骨细胞特异性MT-COMP表达再现了PSACH软骨细胞病理。该MT-COMP小鼠在体内表现为细胞内生长板病理，软骨细胞可以分离并用于体外研究。在这些研究中，我们将利用这只新颖而独特的转基因小鼠来集中我们的努力：1)确定未折叠蛋白反应（UPR）和细胞凋亡激活在体内对MT-COMP保留在软骨细胞中的作用；2)测试不同药物对抑制或逆转MT-COMP在细胞内保留的功效；3)表征MT-COMP对小鼠关节软骨形态和功能的影响。MT-COMP小鼠模型使我们能够验证从内质网中去除MT-COMP将使软骨细胞恢复正常功能的假设。这是迈向治疗干预的第一步，这将是向前迈出的重要一步，因为目前只有对症治疗可用于与PSACH和MED相关的疼痛性骨关节炎。总之，这项工作的结果将提供重要的信息，最终将导致对PSACH、MED/EDM1和骨关节炎患者的更好护理。

DESCRIPTION (provided by applicant): Two skeletal dysplasias, pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED/EDM1) result from massive intracellular retention of mutant COMP (MT-COMP) in the endoplasmic reticulum (ER) which causes premature chondrocyte death during bone development. The focus of this research is to determine the cellular mechanism by which MT- COMP promotes the chondrocyte cellular pathology and to determine whether various pharmacologic agents inhibit or reverse the pathology. In previous studies, we have shown that: 1) mutations in COMP cause skeletal dysplasias, 2) mutant COMP interferes with the export of COMP as well as type IX collagen and matrilin-3 proteins to the extracellular matrix, 3) intracellular matrix is inappropriately assembled in giant rER cisternae, 4) the PSACH cartilage matrix is deficient in ECM proteins and 5) the intracellular retention of COMP causes premature chondrocyte cell death. While our in vitro chondrocyte model system indicates that mutant COMP is not degraded by the cellular quality control machinery, the lack of an animal model system has limited studies to define the molecular mechanisms that result in the cellular pathology created by MT-COMP. Importantly and critical for this proposal, we have created a transgenic mouse model in which inducible chondrocyte-specific MT-COMP expression recapitulates the PSACH chondrocyte pathology. This MT-COMP mouse shows intracellular growth plate pathology in vivo and the chondrocytes can be isolated and utilized for in vitro studies. In these studies, we will use this novel and unique transgenic mouse to focus our efforts on: 1) defining the role of the Unfolded Protein Response (UPR) and activation of apoptosis in response to MT-COMP retention in chondrocytes in vivo, 2) testing the efficacy of different pharmacologic agents on inhibiting or reversing the intracellular retention of MT-COMP and 3) characterizing the effect of MT-COMP on articular cartilage morphology and function in mice throughout life. The MT-COMP mouse model allows us to test the hypothesis that removal of MT-COMP from the ER will return the chondrocyte to normal functionality. This is a first step towards a therapeutic intervention which will be a significant step forward as only symptomatic treatment is currently available for the painful osteoarthritis that is associated with PSACH and MED. Altogether, the results of this work will provide important information that will ultimately lead to better care of individuals with PSACH, MED/EDM1 and osteoarthritis. PUBLIC HEALTH RELEVANCE: The goals of the proposed studies are to understand the debilitating pathophysiology caused by mutations in cartilage oligomeric matrix protein (COMP) that leads to pseudoachondroplasia (PSACH), a severe dwarfing condition and to test therapeutic interventions to reverse this process. We have an inducible mouse model that mimics the human cellular process and this model will allow definition of the cellular mechanisms causing the disease. In addition, we can test pharmacologic agents that reduce cellular stress, thereby reducing the premature loss of growth plate chondrocytes that are needed for limb growth. This research will ultimately lead to treatments for the chronic life long problems related to severe short stature in PSACH and premature osteoarthritis.