Pathogenesis and Treatment of Bone Disease in the Mucopolysaccharidoses

摘要 粘多糖贮积症（MPS）是一个遗传性溶酶体贮积症家族，其特征在于 缺乏降解糖胺聚糖（GAG）的酶。MPS患者遭受瘫痪 对当前治疗无反应的骨骼异常。MPS VII表现出特别严重的 骨骼表型，患者表现出进行性脊柱后凸畸形和脊髓压迫 导致慢性疼痛和瘫痪MPS VII是由β-葡萄糖醛酸酶活性缺乏引起的，导致 多种GAG类型的累积。将这种GAG积累与细胞内的 功能障碍和骨骼疾病的了解很少，阻碍了有效治疗的发展。我们 该实验室使用临床相关的、自然发生的MPS VII犬模型， 发生在人类患者中的骨骼疾病的进展。在以前的工作中，我们证明了MPS VII 狗在椎骨中具有软骨损伤，这损害了椎间关节的稳定性。这些 损伤是由出生后生长期间软骨向骨的转化失败引起的。在初步研究中，我们 当异常骨化首次出现在MPS VII犬中时， 并且这可以追溯到驻留的软骨细胞不能通过肥大成熟而进展。 我们还表明，从早期开始，MPS VII骺软骨中存在异常的GAG积聚。 年龄，并且，使用全转录组测序，Wnt/β-catenin信号转导存在失调 在疾病发展的这个关键时刻。Wnt生长因子是 软骨细胞分化和GAG已知是Wnt分布和活性的重要调节剂， 表明GAG积累和该途径的失调之间的联系。这一目标 建议研究MPS VII中骨形成失败的机制，并建立改进的 使用临床相关犬模型的治疗范例。我们的核心假设是 GAG在MPS VII骺软骨中的积累破坏了 启动和维持软骨细胞肥大分化。此外，我们假设， 有效治疗MPS VII中的骨病，必须使GAG转换正常化， 激活骺软骨中必要的成骨信号通路。在目标1中，我们将定义时间 和GAG积累和骨骺软骨细胞分化潜力之间的空间关系， MPS VII犬从出生到骨骼成熟的骨病进展关键阶段。在目标2中， 确定Wnt/β-catenin信号失调在MPS延迟骨骺骨形成中的关键作用 七只狗。在目标3中，我们将确定Wnt/β-连环蛋白信号传导的治疗靶点，单独或联合 与酶替代疗法，可以增强MPS VII犬的骨形成。

Abstract The mucopolysaccharidoses (MPS) are a family of genetic, lysosomal storage disorders characterized by deficiencies in enzymes that degrade glycosaminoglycans (GAGs). Patients with MPS suffer from crippling skeletal abnormalities that are unresponsive to current treatments. MPS VII presents with a particularly severe skeletal phenotype, where patients exhibit progressive kyphoscoliotic deformity and spinal cord compression resulting in chronic pain and paralysis. MPS VII is caused by deficient beta-glucuronidase activity, leading to accumulation of multiple GAG types. The molecular mechanisms linking this GAG accumulation to cellular dysfunction and skeletal disease are poorly understood, impeding development of effective therapies. Our laboratory uses a clinically-relevant, naturally-occurring canine model of MPS VII that closely mimics the progression of skeletal disease that occurs in human patients. In previous work we demonstrated that MPS VII dogs have cartilaginous lesions in the vertebrae that compromise the stability of the intervertebral joint. These lesions are caused by failed conversion of cartilage to bone during postnatal growth. In preliminary studies, we have identified the precise developmental window when abnormal ossification first manifests in MPS VII dogs and that this can be traced to a failure of resident chondrocytes to progress through hypertrophic maturation. We have also shown that there is abnormal GAG accumulation in MPS VII epiphyseal cartilage from an early age, and, using whole transcriptome sequencing, that there is dysregulation of the Wnt/β-catenin signaling pathway at this crucial juncture in the disease progression. Wnt growth factors are critical regulators of chondrocyte differentiation, and GAGs are known to be important regulators of Wnt distribution and activity, suggesting a link between GAG accumulation and dysregulation of this pathway. The objectives of this proposal are to investigate mechanisms of failed bone formation in MPS VII and establish improved treatment paradigms using a clinically-relevant canine model. Our central hypothesis is that abnormal accumulation of GAGs in MPS VII epiphyseal cartilage disrupts the signaling pathways necessary to initiate and sustain chondrocyte hypertrophic differentiation. Further, we hypothesize that to effectively treat bone disease in MPS VII, it will be necessary to both normalize GAG turnover and activate requisite osteogenic signaling pathways in epiphyseal cartilage. In Aim 1 we will define temporal and spatial relationships between GAG accumulation and epiphyseal chondrocyte differentiation potential at key stages of bone disease progression in MPS VII dogs, from birth to skeletal maturity. In Aim 2 we will establish the critical role of Wnt/β-catenin signaling dysregulation in delayed epiphyseal bone formation in MPS VII dogs. In Aim 3 we will establish if therapeutic targeting of Wnt/β-catenin signaling, alone and in combination with enzyme replacement therapy, can enhance bone formation in MPS VII dogs.