Heparan Sulfate in Skeletal Development and Diseases

描述（由申请人提供）：此竞争性修订申请是对NOT-OD-09-058的回应：NIH宣布竞争性修订申请的恢复法案资金的可用性。硫酸乙酰肝素（HS）在多种组织的发育中起重要作用。了解HS在骨骼发育过程中的作用具有重要的临床意义。遗传性多发性外生骨瘤（HME）是一种以形成多发性骨软骨瘤（“外生骨瘤”）为特征的遗传性疾病，在美国影响着数千人。患有HME的个体携带EXT1或EXT2的杂合突变，它们共同编码HS生物合成所必需的糖基转移酶。尽管已确定其致病基因，但HME的发病机制仍有许多未解之谜。最令人困惑的问题之一是人类HME表现与携带相同基因型的小鼠表型之间的明显差异。最重要的是，Ext1和Ext2杂合小鼠（它们被认为是忠实地模仿人类HME）都能抵抗外生骨瘤的发展，尤其是长骨。我们最近做了一个令人惊讶的观察，我们的新Ext1条件敲除小鼠（Col2a1- CreERT;Ext1flox/flox），这是基于一小部分软骨细胞中随机纯合的Ext1缺失，在长骨中以100%的外显率出现外骨骼增生，并且在以前的任何突变小鼠中都没有见过人类HME的其他骨骼缺陷。这一竞争性修订提议增加第四个目标（利用新型HME小鼠模型研究HME的遗传和细胞机制）来表征这些突变小鼠。通过这些研究，我们希望建立Col2a1-CreERT；Ext1flox/flox小鼠作为首个与HME直接相关的小鼠模型，确定杂合子缺失在HME发病机制中的重要意义，为未来研究阐明骨软骨瘤发展背后的信号缺陷获得基线信息。

DESCRIPTION (provided by applicant): This competitive revision application is in response to NOT-OD-09-058: NIH Announces the Availability of Recovery Act Funds for Competitive Revision Applications. Heparan sulfate (HS) plays essential roles in development of various tissues. To understand how HS functions during skeletal development is of a great clinical importance. Hereditary multiple exostoses (HME) is a genetic disorder characterized by the formation of multiple osteochondromas ("exostoses"), which affects several thousands of people in the US. Individuals with HME carry heterozygous mutations of EXT1 or EXT2, which jointly encode a glycosyltransferase essential for the biosynthesis of HS. Despite the identification of its causative genes, there are a number of enigmas and unanswered questions on the pathogenic mechanism of HME. One of the most puzzling questions is the stark discrepancy between human HME manifestations and the phenotype of mice carrying the same genotype. Most importantly, both Ext1 and Ext2 heterozygous mice, which are supposed to mimic human HME faithfully, are resistant to the development of exostoses, especially in long bones. We have recently made a surprising observation that our new Ext1 conditional knockout mice (Col2a1- CreERT;Ext1flox/flox), which is based on stochastic homozygous Ext1 deletion in a small fraction of chondrocytes, develop exostoses in long bones at a 100% penetrance and phenocopy other skeletal defects of human HME to a degree not seen in any of the previous mutant mice. This competitive revision proposes to add the fourth aim (Investigate the genetic and cellular mechanisms of HME using novel HME mouse models) to characterize these mutant mice. By these studies, we wish to establish the Col2a1-CreERT;Ext1flox/flox mouse as the first mouse model directly relevant to HME, determine the significance of loss-of-heterozygocity in the pathogenesis of HME, and obtain baseline information for the future study to elucidate the signaling defects underlying osteochondroma development. PUBLIC HEALTH RELEVANCE: Heparan sulfate is essential for normal bone development, as illustrated by the existence of the human genetic bone disorder hereditary multiple exostosis (HME), which is caused by mutations of genes essential for heparan sulfate biosynthesis. In this competitive revision, we will characterize our novel conditional knockout mouse model that exhibits unprecedented levels of phenotypic similarities with human HME. The proposed studies will establish a novel mouse model for HME and generate new insights into the pathogenic mechanism of this human disorder.