Heparan Sulfate in Skeletal Development and Diseases

描述（由申请人提供）：多发性遗传性外生骨病（MHE）是一种常染色体显性骨疾病，由EXT1或EXT2的杂合突变引起，这两个基因共同编码硫酸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，据信影响了数千名美国人。在当前的资助周期中，我们阐明了一个长期存在的谜题，即MHE的遗传机制。具体来说，我们证明了通过随机条件敲除建模的杂合性损失导致基本上所有人类MHE表型的再现。基于这一成果和这些研究揭示的新问题，我们将进一步探索这种使人衰弱的疾病，以了解其完整的致病机制，并确定新的生物标志物和潜在的治疗靶点。我们提出以下目标。1. 确定骨软骨瘤的起源：虽然我们的研究阐明了骨软骨瘤发生的遗传机制，但少数Ext1零细胞发展成骨软骨瘤的细胞机制仍然几乎完全难以捉摸。其中一个关键问题是骨软骨瘤是起源于生长板软骨细胞还是起源于软骨膜。我们将进行软骨膜特异性的Ext1敲除和分析缺乏Ext1的软骨膜祖细胞来解决这个问题。2. 确定影响骨软骨瘤发生的关键信号通路：另一个关键问题是直接导致骨软骨瘤发生的有缺陷的信号通路是什么。基于强有力的初步证据，我们将关注BMP通路，并确定异常BMP信号是否是该疾病的主要分子罪魁祸首。3. 骨软骨瘤转录组全基因组分析：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组变化。通过对RNA微阵列数据集应用加权基因共表达网络分析，我们将识别区分骨软骨瘤与正常软骨细胞的分子特征和潜在的遗传生物标志物，以预测MHE患者未来骨软骨瘤的严重程度和复发。

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.