Mechanism of growth deficiency in dominant forms of osteogenesis imperfecta

项目摘要 成骨不全（OI），被称为脆骨病，是一种遗传性疾病，通常由以下原因引起： 编码I型胶原蛋白的两个基因之一（Col 1）中的常染色体显性突变。除了骨 脆弱性、生长缺陷是OI的关键肌肉骨骼问题。没有治愈OI。而 双膦酸盐是强化骨骼的标准治疗，但没有可靠有效的治疗方法。 生长障碍阻碍这种治疗发展的主要障碍之一是， Col 1突变如何导致生长缺陷的机制尚未阐明。鉴于 改善成骨细胞功能的治疗对解决骨长度不足、细胞类型 除成骨细胞外，其他细胞也可能参与成骨细胞生长迟缓。我们和其他人发现 生长板，发生纵向骨生长的地方，包括总高度增加，软骨细胞减少， 营业额和更少的增殖软骨细胞，这表明突变的Col 1以某种方式影响软骨细胞， 生长板。因此，了解软骨细胞缺陷的机制对于开发 治疗OI生长缺陷。在本提案中，我们将使用G610 C小鼠专注于显性OI 因为85-90%的OI是常染色体显性形式，所以携带Col 1突变。我们的数据表明， HC随着成熟沿着扩大的内质网（ER）开始表达Col 1，提示 与成骨细胞相似，OI HC暴露于更高的ER应力。我们的初步研究表明 G610 C OI软骨细胞在颗粒培养中表达肥大表型的能力较低， ER应激减轻剂改善了这一缺陷，表明ER应激不仅可能导致功能障碍， 成骨细胞中也有，但在成骨细胞中也有。事实上，已经表明，在HC中诱导ER应激导致HC 功能障碍并导致生长缺陷。总的来说，这些发现为我们的研究提供了严格的前提。 一个高度创新的假设，即由ER应激诱导的HC功能障碍在生长缺陷中起着关键作用 占主导地位。这个假设将通过支持以下具体目标的实验来解决：（1） 表征G610 C OI小鼠中HC中发生的ER应激，（2）确定G610 C OI中HC功能障碍 小鼠，和（3）以确定ER应激在HC从显性OI患者与不同的突变。完成 这些目标将确定显性OI中的生长缺陷是否是HC功能障碍的结果 是由内质网应激引起的这个创新项目的成果有可能改变我们对开放式创新的理解 通过重新定义OI不仅是“骨疾病”，而且是“软骨疾病”， 在开发生长治疗策略时，专注于软骨细胞，而不是成骨细胞或破骨细胞 损伤。

PROJECT SUMMARY Osteogenesis imperfecta (OI), known as a brittle bone disease, is a genetic disorder typically caused by autosomal dominant mutations in one of the two genes that encode type l collagen (Col1). In addition to bone fragility, growth deficiency is a critical musculoskeletal issue in OI. There is no cure for OI. While bisphosphonates are the standard treatment to strengthen bones, there is no reliably effective treatment for growth impairment. One of the major hurdles preventing the development of such treatments is that the mechanism of how a mutation in Col1 causes growth deficiency has not been elucidated. Given that treatments to improve osteoblast function were not effective for resolving bone length deficiency, cell types other than osteoblasts might be involved in OI growth retardation. We and others found abnormalities in the growth plate, where longitudinal bone growth occurs, including increased total height, decreased chondrocyte turnover and fewer proliferating chondrocytes, suggesting that mutated Col1 somehow affects chondrocytes in the growth plate. Thus, understanding the mechanism underlying chondrocyte defects is critical to develop treatments for OI growth deficiency. In this proposal, we will focus on dominant OI using G610C mice harboring Col1 mutation because 85-90% of OI are autosomal dominant forms. Our data demonstrated that OI HCs began to express Col1 as they mature along with the enlarged endoplasmic reticulum (ER), suggesting that OI HCs are exposed to higher ER stress similar to OI osteoblasts. Our preliminary studies demonstrated that G610C OI chondrocytes had a lower ability to express hypertrophic phenotypes in pellet cultures and an ER stress reducer ameliorated this defect, suggesting that ER stress may cause dysfunction not only in osteoblasts but also in HCs in OI. Indeed, it has been shown that induction of ER stress in HCs causes HC dysfunction and results in growth deficiency. Collectively, these findings provide rigorous premises for our highly innovative hypothesis that HC dysfunction induced by ER stress plays a pivotal role in growth deficiency of dominant OI. This hypothesis will be addressed by experiments supporting the following specific aims: (1) to characterize ER stress occurring in HCs in G610C OI mice, (2) to determine HC dysfunction in G610C OI mice, and (3) to determine ER stress in HCs from dominant OI patients with distinct mutations. The completion of these aims will determine whether growth deficiency in dominant OI is a consequence of HC dysfunction caused by ER stress. The outcome of this innovative project has potential to change our understanding of OI by redefining OI not only as “bone disease” but also as “cartilage disease”, and by providing approaches focused on chondrocytes, rather than osteoblasts or osteoclasts in developing therapeutic strategies for growth impairment in OI.