Pathogenic Mechanisms in Hereditary Multiple Exostoses Syndrome

遗传性多发性骨软骨病(HME)是一种罕见的常染色体显性遗传病，每50,000人中就有1人患病 世界各地的儿童。HME的特征是软骨瘤，称为外骨瘤，形成于软骨膜。 细胞沿着生长板向周围组织突起。因此，外生骨可能会导致骨骼 约5%的患者出现畸形、神经和血管受压、慢性疼痛和恶变 病人。目前的治疗方法是有限的，患者与疼痛和有限的活动作斗争，并接受 一生中做过多次手术。大多数HME患者携带EXT1或EXT2杂合突变，这些突变 负责硫酸乙酰肝素(HS)的合成，从而导致部分全身性HS缺乏。房协链条- 而它们所在的蛋白多糖部分地调节和明显地调节许多过程。值得注意的是，他们 与成纤维细胞生长因子相互作用并通过成纤维细胞生长因子刺激信号，但通过骨骼相互作用并抑制信号传递 形态发生蛋白。FGFs和BMPs一般分别发挥抑制和促进软骨形成的作用。 然而，目前尚不清楚HS部分减少是否足以形成外生骨疣，HS是否丢失 逆转这些信号活动--从而减少成纤维细胞生长因子和增加骨形态发生蛋白信号--以及是否 变化会导致外生骨疣的形成。在上一次筹资期间，我们取得了重大进展。我们创造了 Ext1+/-、双ext1+/-、ext2+/-和条件性ext1缺失小鼠。虽然单个HET小鼠基本上是正常的， 双HETS和条件性缺失小鼠(两者产生的HS都要少得多)表现出多个外突并被模仿 人类的HME。局部成纤维细胞生长因子信号转导水平降低先于外生性骨软骨瘤的发展 PMEK/PERK和BMP信号介质pSmad1/5/8水平的增加。体外研究加强了这些 调查结果。与直觉相反的是，HS缺乏也刺激了内源性乙酰肝素酶的表达，可能 进一步促进软骨生成。事实上，重组乙酰肝素酶的治疗刺激了BMP 信号转导和软骨形成，而乙酰肝素酶抑制剂Roneparstat阻止了这两个过程。我们的中央 假说是：(I)HS局部严重缺乏；(Ii)成纤维细胞生长因子减少，导致外生骨疣的形成。 信号和增加的BMP信号；和(Iii)突变细胞中软骨形成潜力的增加 软骨-软骨膜边界。我们还假设，外生骨软骨瘤的形成可以通过药物治疗来预防。这个 该项目将继续提供对细胞和分子机制的根本新见解 外生骨软骨瘤的形成及其对正常软骨膜中这些机制正常功能的影响 和生长板细胞。它还将根据这些见解测试可能的治疗方法，因此具有强大的基础 研究价值和转化医学的意义。HME患者的数量相对较少，但 他们的家庭社区很大。因此，这个项目将给患者带来新的希望， 家庭都相信，将继续积极研究这种被忽视的疾病，有一天可能会找到治疗方法。

Hereditary Multiple Exostoses (HME) is a rare autosomal dominant disorder that affects about 1 in 50,000 children worldwide. HME is characterized by cartilaginous tumors called exostoses that form in perichondrial cells along the growth plates and protrude into surrounding tissues. The exostoses can thus cause skeletal deformities, compression of nerves and blood vessels, chronic pain, and become malignant in about 5% of the patients. Current therapies are limited, and patients struggle with pain and limited mobility and undergo multiple surgeries through life. Most HME patients bear a heterozygous mutation in EXT1 or EXT2 that are responsible for heparan sulfate (HS) synthesis, thus causing a partial systemic HS deficiency. The HS chains - and the proteoglycans of which they are part- regulate and distinctly modulate many processes. Notably, they interact with and stimulate signaling by fibroblast growth factors, but interact and inhibit signaling by bone morphogenetic proteins. FGFs and BMPs generally exert anti- and pro-chondrogenic roles, respectively. However, it was unclear whether HS partial decrease is sufficient for exostosis formation, whether HS loss reverses those signaling activities –thus decreasing FGF and increasing BMP signaling-, and whether such changes induce exostosis formation. In the previous funding period, we made significant progress. We created Ext1+/-, double Ext1+/-;Ext2+/- and conditional Ext1-null mice. While single het mice were largely normal, double hets and conditional-null mice (both producing far less HS) displayed multiple exostoses and mimicked human HME. Exostosis development was preceded by local decreased levels of FGF signal transducers pMEK/pERK and increased levels of BMP signaling mediators pSmad1/5/8. In vitro studies reinforced these findings. Counter-intuitively, the HS deficiency also stimulated endogenous heparanase expression, likely enhancing chondrogenesis even further. Indeed, treatment with recombinant heparanase stimulated BMP signaling and chondrogenesis, while the heparanase inhibitor Roneparstat blocked both. Our central hypothesis is that exostosis formation is caused by: (i) a steep local deficiency in HS; (ii) decreased FGF signaling and increased BMP signaling; and (iii) a boost in chondrogenic potentials in mutant cells along the chondro-perichondrial border. We posit also that exostosis formation is preventable by drug treatment. The project will continue to provide fundamentally new insights into the cellular and molecular mechanisms of exostosis formation and by extension on the normal functioning of these mechanisms in normal perichondrial and growth plate cells. It will also test possible therapies based on those insights and thus has strong basic research value and translational medicine implications. The number of HME patients is relatively 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 continue to be actively studied and a cure may one day be found.