Heparan Sulfate in Skeletal Development and Diseases

描述（由申请人提供）：本竞争性修订申请是对NOT-OD-09 - 058的回应：NIH宣布为竞争性修订申请提供恢复法案资金。硫酸乙酰肝素（HS）在各种组织的发育中起重要作用。了解HS在骨骼发育过程中的功能具有重要的临床意义。遗传性多发性外生骨疣（HME）是一种遗传性疾病，其特征是形成多发性骨软骨瘤（"外生骨疣"），在美国影响数千人。患有HME的个体携带EXT1或EXT2的杂合突变，其共同编码HS生物合成所必需的糖基转移酶。尽管HME的致病基因已被确定，但其致病机制仍存在许多未解之谜。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杂合子小鼠，应该忠实地模仿人类HME，对外生骨疣的发展有抵抗力，特别是在长骨中。我们最近做了一个令人惊讶的观察，我们的新的Ext1条件性敲除小鼠（Col2a1-CreERT; Ext1flox/flox），这是基于随机纯合Ext1缺失的一小部分软骨细胞，发展外生骨疣在长骨中的100%骨转移率和表型其他骨骼缺陷的人HME的程度上没有看到在任何以前的突变小鼠。该竞争性修订建议增加第四个目标（使用新型HME小鼠模型研究HME的遗传和细胞机制），以表征这些突变小鼠。通过这些研究，我们希望建立Col2a1-CreERT; Ext1 flox/flox小鼠作为第一个与HME直接相关的小鼠模型，确定杂合性缺失在HME发病机制中的重要性，并为未来的研究获得基线信息，以阐明骨软骨瘤发生的信号缺陷。 公共卫生相关性：硫酸乙酰肝素对于正常骨发育是必需的，如人类遗传性骨病遗传性多发性外生骨疣（HME）的存在所示，其由硫酸乙酰肝素生物合成必需的基因突变引起。在这次竞争性修订中，我们将描述我们新的条件性敲除小鼠模型，该模型与人类HME表现出前所未有的表型相似性。这些研究将为HME建立一种新的小鼠模型，并对这种人类疾病的致病机制产生新的见解。

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.