Mechanisms of Vertebral Bone Disease in Mucopolysaccharidosis VII

描述(申请人提供)：粘多糖症(MPS)是一种溶酶体储存障碍，其特征是降解糖胺聚糖(GAG)的酶缺乏。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，导致脊髓受压和脊柱后凸畸形。目前还没有临床或实验方法来纠正MPS VII中的脊柱疾病。我们已经证明MPS VII中的狗在椎体中有较大的软骨损伤，损害了椎间关节的生物力学稳定性。这些损伤是出生后发育过程中颈动脉向骨转化失败的结果。导致MPS VII软骨内成骨失败的潜在分子机制尚不清楚。在正常的脊椎骨形成过程中，软骨残片形成了后续骨化的模板。构成这些雏形的软骨细胞经历了不同的分化阶段，受到高度协调的信号通路模式的调控。印度刺猬(IHH)是软骨细胞分化的关键调节因子。在软骨内成骨过程中，GAG对IHH的稳定性、分布和结合起着重要的调节作用。在先导性工作中，我们已经表明，与正常犬相比，MPS VII犬从出生后早期起，关键的IHH途径分子的表达就发生了变化。我们的总体假设是，MPS VII中异常的GAG积聚通过干扰IHH的合成、稳定、分布和结合来扰乱软骨细胞的增殖和分化，阻止正常的软骨向骨的转化。在目标1中，我们将研究发育中的MPS VII椎体中特定区域和年龄相关的细胞内外GAG积累模式，并建立这些GAG积累模式如何与软骨细胞成熟的不同阶段相对应。在目标2中，我们将确定IHH在正常和MPS VII椎体之间的表达和分布以及与软骨细胞增殖和肥大分化相关的调节因子的年龄差异。在目标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途径激动剂的治疗潜力。这项工作的长期目标是为MPS VII、MPS家族疾病的其他11种酶缺陷以及涉及异常GAG合成或转换的其他遗传性肌肉骨骼疾病确定新的治疗靶点。

DESCRIPTION (provided by applicant): 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 cartilae 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.