Pathogenic Mechanisms in Hereditary Multiple Exostoses Syndrome

遗传性多发性外生骨疣综合征的发病机制

• 批准号: 8475565
• 负责人: EIKI KOYAMA
• 金额: $ 48.26万
• 依托单位: CHILDREN'S HOSP OF PHILADELPHIA
• 依托单位国家: 美国
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-07-01 至 2016-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8475565
• 关键词: Adolescent; Adverse effects; Affect; Binding; Biochemical; Biomedical Research; Blood Vessels; Cartilage; Cartilaginous exostosis; Cells; Child; Chondrocytes; Chondrogenesis; Communities; Defect; Deformity; Degenerative polyarthritis; Developmental Process; Disease; EXT1 gene; EXT2 gene; Elements; Epiphysial cartilage; Erinaceidae; Exostoses; Family; Family member; Fatigue; Genes; Genetic; Growth; Heparitin Sulfate; Hereditary Multiple Exostoses; Impairment; Incidence; Infiltration; Life; Malignant - descriptor; Malignant Bone Neoplasm; Mesenchymal; Mesenchymal Differentiation; Methods; Molecular; Motion; Mus; Mutation; Nerve compression syndrome; Operative Surgical Procedures; Organ; Pain; Palliative Care; Pathogenesis; Patients; Physiological Processes; Procedures; Production; Protein Binding; Proteins; Proteoglycan; Reporter; Role; Severities; Signal Pathway; Signal Transduction; Signaling Protein; Stem cells; Structure; Syndrome; Tendon structure; Testing; Therapeutic; Tissues; base; bone; drug candidate; early onset; effective therapy; glycosyltransferase; in vitro Model; in vivo; insight; interest; liquid chromatography mass spectrometry; loss of function mutation; mutant; neglect; prevent; research study; skeletal; skeletal dysplasia; sulfation; translational medicine; tumor

DESCRIPTION (provided by applicant): Hereditary Multiple Exostoses (HME) is an autosomal dominant disorder that affects about 1 in 20,000 children. HME is characterized by cartilage-capped outgrowths that form adjacent to the growth plates, protrude into surrounding tissues and organs, and cause growth retardation, compression of nerves and early onset osteoarthritis. They become malignant in about 5% of the patients. Current therapies are palliative, and patients struggle with pain and limited mobility and undergo multiple surgeries through life. The genes responsible for HME cases are EXT1 and EXT2 that encode glycosyltransferases responsible for heparan sulfate (HS) synthesis. Patients are heterozygous for EXT1 or EXT2 loss-of-function mutations and their cells produce lower HS amounts. HS-rich proteoglycans regulate key physiologic processes by various mechanisms and most notably by restricting the topographical distribution and action of hedgehog, BMPs and other signaling factors within tissues, but it is not known whether defects in these mechanisms subtend HME. In ongoing studies, we found that HS deficiency in growth plate leads to re-distribution of Indian hedgehog (Ihh), its infiltration over the entire perichondrium and formation of exostosis-like cartilaginous masses within perichondrium itself. A similar ectopic action of Ihh was seen in mouse growth plates deficient in HS N- sulfation. We found also that interference with HS function greatly stimulates differentiation of mesenchymal cells into chondrocytes. Thus, our central hypothesis is that the HS deficiency in HME (i) causes re-distribution of hedgehog and other pro-chondrogenic factors from growth plate to perichondrium and (ii) enhances responsiveness of perichondrial cells to these and other local factors. As a result of this combination of mechanisms, growth plate and perichondrium would mis-communicate, and perichondrial cells would lose their normal character, become chondrogenic and give rise to exostoses. To test our hypotheses, we will analyze the mechanisms of exostosis formation by creating conditional Ext-deficient mice in growth plate and/or perichondrium and determining roles of pro-chondrogenic signaling pathways (Aim 1). We will determine the mechanisms for increased chondrogenic capacity of HS-deficient cells will test their responsiveness to signaling factors and assess structure and protein binding capabilities of their HS chains (Aim 2). We will then carry out proof-of-principle experiments to determine whether pharmacologic antagonists of pro-chondrogenic signaling pathways block exostosis formation (Aim 3). The project will provide fundamentally new insights into the cellular and molecular mechanisms of HME pathogenesis and will test possible rational therapies based on those insights. The project thus has significant importance for both basic biomedical research and translational medicine in HME and related growth plate-based skeletal dysplasias. The number of HME patients is small, but the community of their families is large. This project will thus provide a renewed sense of hope to patients and families alike that this neglected disease will actively be studied and a cure may one day be found.

描述（由申请人提供）：遗传性多发性外生骨疣 (HME) 是一种常染色体显性遗传疾病，影响大约两万分之一的儿童。 HME 的特点是生长板附近形成软骨帽增生，突出到周围组织和器官，导致生长迟缓、神经受压和早发性骨关节炎。大约 5% 的患者会变成恶性。目前的治疗方法都是姑息疗法，患者一生都在与疼痛和活动受限作斗争，并接受多次手术。导致 HME 病例的基因是 EXT1 和 EXT2，它们编码负责硫酸乙酰肝素 (HS) 合成的糖基转移酶。患者是 EXT1 或 EXT2 功能丧失突变的杂合子，并且他们的细胞产生较低的 HS 量。富含 HS 的蛋白聚糖通过各种机制调节关键的生理过程，最显着的是通过限制 hedgehog、BMP 和组织内其他信号因子的拓扑分布和作用，但尚不清楚这些机制的缺陷是否会导致 HME。在正在进行的研究中，我们发现生长板中的 HS 缺陷导致印度刺猬 (Ihh) 的重新分布，其渗透到整个软骨膜并在软骨膜本身内形成外生骨疣样软骨肿块。在缺乏 HS N-硫酸化的小鼠生长板中观察到 Ihh 的类似异位作用。我们还发现，干扰 HS 功能会极大地刺激间充质细胞分化为软骨细胞。因此，我们的中心假设是，HME 中的 HS 缺陷（i）导致刺猬因子和其他促软骨形成因子从生长板重新分布到软骨膜，以及（ii）增强软骨膜细胞对这些和其他局部因子的反应性。由于这种机制的结合，生长板和软骨膜会发生错误通讯，软骨膜细胞会失去其正常特性，变成软骨并产生外生骨疣。为了检验我们的假设，我们将通过在生长板和/或软骨膜中创建条件性 Ext 缺陷小鼠并确定促软骨信号通路的作用来分析外生骨疣形成的机制（目标 1）。我们将确定 HS 缺陷细胞软骨形成能力增加的机制，测试其对信号因子的反应性，并评估其 HS 链的结构和蛋白质结合能力（目标 2）。然后，我们将进行原理验证实验，以确定促软骨信号通路的药理学拮抗剂是否可以阻止外生骨疣的形成（目标 3）。该项目将为 HME 发病机制的细胞和分子机制提供全新的见解，并将根据这些见解测试可能的合理疗法。因此，该项目对于 HME 和相关生长板骨骼发育不良的基础生物医学研究和转化医学具有重要意义。 HME患者人数虽少，但其家庭社区规模很大。因此，该项目将为患者和家属带来新的希望，即这种被忽视的疾病将得到积极研究，有一天可能会找到治愈方法。