Mechanisms of Vertebral Bone Disease in Mucopolysaccharidosis VII

摘要 粘多糖病(MPS)是一种以酶缺乏为特征的溶酶体储存障碍 会降解糖胺多聚糖(GAG)。MPS VII的特征是缺乏β-葡萄糖苷酸酶活性， 导致全身堆积未完全降解的软骨素、肝素和硫酸皮肤素。 虽然疾病表现在多个器官系统，但脊柱疾病尤其严重，包括 椎间盘和椎骨的形态异常，导致脊髓受压 和脊椎侧弯畸形。目前还没有治疗方法，无论是临床上的还是实验性的，都不能矫正脊柱 MPS VII中的疾病。我们已经证明MPS VII犬的脊椎有较大的软骨病变 影响椎间关节生物力学稳定性的身体。这些损伤是 在出生后发育过程中软骨向骨的转化失败。潜在的分子 导致MPS VII软骨内骨化失败的机制尚不清楚。在.期间 正常的脊椎骨形成，软骨残片形成了后续骨化的模板。这个 填充在这些雏形中的软骨细胞经历了不同的分化阶段，受高度 精心编排的信号通路模式。印度刺猬是软骨细胞的关键调节因子 差异化。GAG在调节IHH的稳定性、分布和结合方面发挥着关键作用 软骨内骨化。在试点工作中，我们已经证明了关键的IHH途径分子的表达是 从出生后早期起，MPS VII犬的骨骺软骨与正常狗相比发生了变化。 我们的总体假设是MPS VII中异常的GAG积聚破坏了软骨细胞 通过干扰细胞的合成、稳定性、分布和结合促进细胞的增殖和分化 IHH，阻止正常软骨向骨的转化。在目标1中，我们将调查特定地区和年龄- MPS VII椎体发育过程中依赖的细胞内外GAG蓄积模式，并建立 这些GAG堆积模式如何与软骨细胞成熟的不同阶段相对应。在AIM 2 我们将确定IHH及其相关调控因子的表达和分布随年龄的差异 正常和MPS VII椎体的软骨细胞增殖和肥大分化的研究。在AIM 3中 我们将直接评估细胞对IHH的反应，确定外源性酶是否可以 挽救这些细胞的健康表型，并评估小分子IHH的治疗潜力 途径激动剂。这项工作的长期目标是为MPS VII确定新的治疗靶点 11 MPS家族疾病的酶缺乏，以及其他遗传性肌肉骨骼疾病 涉及异常的GAG合成或周转。

Summary The mucopolysaccharidoses (MPS) are lysosomal storage disorders characterized by deficiencies in enzymes that degrade glycosaminoglycans (GAG). MPS VII is characterized by deficient beta-glucuronidase activity, leading to systemic accumulation of incompletely degraded chondroitin, heparan and dermatan sulfate GAGs. While disease is manifested in multiple organ systems, spine disease is particularly severe and includes morphological abnormalities in the intervertebral discs and vertebral bones, leading to spinal cord compression and kypho-scoliotic deformity. Currently there are no treatments, clinical or experimental, which correct spine disease in MPS VII. We have shown that MPS VII dogs have large, cartilaginous lesions in the vertebral bodies that compromise biomechanical stability of the intervertebral joint. These lesions are the result of failed conversion of cartilage to bone during postnatal development. The underlying molecular mechanisms that lead to this failure of endochondral ossification in MPS VII are unknown. During normal vertebral bone formation, cartilaginous rudiments form the template for subsequent ossification. The chondrocytes that populate these rudiments undergo distinct stages of differentiation, regulated by a highly orchestrated pattern of signaling pathways. Indian hedgehog (IHH) is a key regulator of chondrocyte differentiation. GAGs perform critical roles regulating the stability, distribution and binding of IHH during endochondral ossification. In pilot work we have shown that expression of key IHH pathway molecules is altered in the epiphyseal cartilage of MPS VII dogs compared to normals from early in postnatal development. Our overall hypothesis is that abnormal GAG accumulation in MPS VII disrupts chondrocyte proliferation and differentiation by interfering with the synthesis, stability, distribution and binding of IHH, preventing normal cartilage to bone conversion. In Aim 1 we will investigate region-specific and age- dependent intra- and extracellular GAG accumulation patterns in developing MPS VII vertebrae, and establish how these patterns of GAG accumulation correspond to different stages of chondrocyte maturation. In Aim 2 we will identify age-dependent differences in the expression and distribution of IHH and associated regulators of chondrocyte proliferation and hypertrophic differentiation between normal and MPS VII vertebrae. In Aim 3 we will directly evaluate the cellular response to IHH, determine if exogenous enzyme administration can rescue the healthy phenotype of these cells, and evaluate the therapeutic potential of a small molecule IHH pathway agonist. The long-term goal of this work is to identify new therapeutic targets for MPS VII, for the other 11 enzyme deficiencies of the MPS family of disorders, and for other genetic musculoskeletal disorders that involve abnormal GAG synthesis or turnover.