Heparan Sulfate in Skeletal Development and Diseases

描述(申请人提供)：多发性遗传性外生性骨病(MHE)是一种常染色体显性遗传性骨病，由EXT1或EXT2杂合突变引起，这两个基因共同编码硫酸乙酰肝素生物合成所必需的糖基转移酶。MHE是最常见的遗传性骨发育不良，被认为影响了数千美国人。在当前的资金周期中，我们阐明了一个长期存在的关于MHE遗传机制的谜题。具体地说，我们证明了通过随机条件基因敲除建模的杂合性丢失导致了基本上所有人类MHE表型的重述。基于这一成就和这些研究揭示的新问题，我们将进一步探索这种令人衰弱的疾病，目的是了解其完整的致病机制，并寻找新的生物标志物和潜在的治疗靶点。我们提出了以下目标。1.确定骨软骨瘤的起源：虽然我们的研究阐明了骨软骨瘤形成的遗传学机制，但少数Ext1缺失细胞发展成骨软骨瘤的细胞机制几乎完全不清楚。关键问题之一是骨软骨瘤是起源于生长板软骨细胞还是来自软骨膜。为了解决这个问题，我们将进行软骨膜特异的Ext1基因敲除和对缺乏Ext1的软骨膜前体细胞的分析。2.确定影响骨软骨瘤形成的关键信号通路：另一个关键问题是直接导致骨软骨瘤形成的信号通路缺陷是什么。基于强有力的初步证据，我们将重点研究BMP途径，并确定BMP信号异常是否是导致该病的主要分子原因。3.骨软骨瘤转录组的全基因组分析：我们将进行一项最先进的生物信息学研究，以确定定义骨软骨瘤的转录变化。通过对RNA微阵列数据集进行加权基因共表达网络分析，我们将识别区分骨软骨瘤和正常软骨细胞的分子特征，以及潜在的遗传生物标志物，以预测MHE患者骨软骨瘤的未来严重程度和复发。

DESCRIPTION (provided by applicant): Multiple hereditary exostoses (MHE) is an autosomal dominant bone disorder caused by heterozygous mutations of EXT1 or EXT2, which jointly encode a glycosyltransferase essential for heparan sulfate biosynthesis. MHE is the most common genetic bone dysplasia and thought to affect several thousand Americans. During the current funding cycle, we elucidated a long- standing puzzle concerning the genetic mechanism of MHE. Specifically, we demonstrated that loss of heterozygosity modeled via stochastic conditional knockout results in the recapitulation of essentially all human MHE phenotypes. Based on this achievement and novel questions revealed by these studies, we will explore further this debilitating disease, with goals of understanding its complete pathogenic mechanism and identifying novel biomarkers and potential therapeutic targets. We propose the following aims. 1. Determine the origin of osteochondroma: While our studies elucidated the genetic mechanisms of osteochondromatogenesis, the cellular mechanisms by which a small number of Ext1 null cells develop into osteochondromas remains almost entirely elusive. One of the critical issues is whether osteochondromas are originated either from growth plate chondrocytes or from the perichondrium. We will perform perichondrium-specific Ext1 knockout and the analysis of perichondrial progenitor cells lacking Ext1 to address this issue. 2. Determine the affected signaling pathway that is critical for osteochondromatogenesis: Another critical issue is what is the defective signaling pathway directly responsible for osteochondromatogenesis. Based on strong preliminary evidence, we will focus on the BMP pathway and determine whether aberrant BMP signaling is the main molecular culprit underlying the disease. 3. Genome-wide analysis of osteochondroma transcriptome: We will perform a state-of-the-art bioinformatics study to determine transcriptomic changes that define osteochondroma. By applying the weighted gene coexpression network analysis on RNA microarray data sets, we will identify molecular signatures that distinguish osteochondroma from normal chondrocytes and potential genetic biomarkers to predict the future severity and recurrence of osteochondroma in MHE patients.