Mechanisms of Vertebral Bone Disease in Mucopolysaccharidosis VII

描述（由申请方提供）：粘多糖贮积症（MPS）是一种以降解糖胺聚糖（GAG）的酶缺乏为特征的溶酶体贮积症。MPS VII的特征在于β-葡萄糖醛酸酶活性不足，导致不完全降解的软骨素、乙酰肝素和硫酸皮肤素GAG全身蓄积。虽然疾病表现为多个器官系统，但脊柱疾病特别严重，包括椎间盘和椎骨的形态异常，导致脊髓压迫和脊柱后凸畸形。目前没有临床或实验性治疗方法可以纠正MPS VII中的脊柱疾病。我们已经证明MPS VII犬的椎体中存在大的软骨病变，这会损害椎间关节的生物力学稳定性。这些病变是出生后发育过程中软骨向骨转化失败的结果。导致MPS VII中软骨内骨化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，软骨雏形形成了随后骨化的模板。这些软骨细胞在高度协调的信号通路的调控下经历不同的分化阶段。Indian hedgehog（IHH）是软骨细胞分化的关键调节因子。GAG在软骨内骨化过程中起着调节IHH稳定性、分布和结合的关键作用。在试点工作中，我们已经表明，与出生后发育早期的正常人相比，MPS VII犬的骺软骨中关键IHH途径分子的表达发生了变化。我们的总体假设是，MPS VII中的异常GAG蓄积通过干扰IHH的合成、稳定性、分布和结合来破坏软骨细胞增殖和分化，从而阻止正常的软骨向骨转化。在目的1中，我们将研究发育中的MPS VII椎骨中区域特异性和年龄依赖性的细胞内和细胞外GAG蓄积模式，并确定这些GAG蓄积模式如何对应于软骨细胞成熟的不同阶段。在目标2中，我们将确定正常和MPS VII椎骨之间IHH和软骨细胞增殖和肥大分化的相关调节因子的表达和分布的年龄依赖性差异。在目标3中，我们将直接评估对IHH的细胞应答，确定外源酶施用是否可以拯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确定MPS VII、MPS家族疾病的其他11种酶缺乏症以及涉及异常GAG合成或转换的其他遗传性肌肉骨骼疾病的新治疗靶点。

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.