Carbohydrate Deficient Glycoprotein Syndromes: Models and Therapy

描述(申请人提供)：先天性糖基化障碍(CDG)是一种罕见的遗传性糖链(糖链)合成缺陷及其与蛋白质的结合。所有14种类型(不同基因)的CDG-I患者都有不同基因的突变，但有一个共同的病变：缺乏完整的N-糖基化位点。同样，患者有许多共同的症状，但在不同类型之间和不同类型之间表现出广泛的临床差异。目前还没有针对这些疾病的脊椎动物模型，只有一种类型-CDG-Ib有治疗方法。在这里，我们建议分析第一个可存活的CDG-I小鼠模型，评估已知的单一疗法，并将该疗法应用于目前无法治疗的CDG类型。CDG-Ib患者存在磷酸甘露糖异构酶(MPI，Fru-6-P_&GT；Man-6-P)活性不足，并出现肝功能障碍、纤维化、生长不全、蛋白丢失性肠病和凝血功能障碍。然而，补充甘露糖可以通过一个较小的生物合成途径(人-6-P)增加甘露糖的流量，从而绕过这一缺陷，从而缓解几乎所有的症状。缺乏PMM2(Man-6-P`Man-1-P)的CDG-Ia患者对甘露糖治疗没有反应，因为他们通过强大的MPI分解Man-6-P。请注意，PMM2和MPI竞争相同的关键底物Man-6-P，它们的比例决定了它的代谢流量。我们设计了一个亚形的MPI等位基因，建立了第一个可行的潜在CDG-I小鼠模型。到目前为止，对这些小鼠的分析表明，进展的肝脏病理和增加的肠道蛋白丢失。在目标1中，我们将确定这些小鼠是否表现出对CDG-Ib患者的病理模拟。目标2将确定亚形线如何对环境压力做出反应。目的3将确定甘露糖是否拯救(防止和/或逆转)低形态小鼠对病理的易感性，特别是蛋白质丢失性肠病和肝脏病理。由于各种类型的CDG具有许多共同的病理基础，一种类型的成功治疗可能会建立一种治疗其他类型的范例。因此，在目标4中，我们将用目前在子宫中死亡的Pmm2缺陷小鼠培育MPI亚型小鼠。基于非常令人鼓舞的初步数据，我们预测，在PMM2缺陷小鼠中提供甘露糖和遗传降低MPI活性将通过增加Man-6-P进入枯竭糖基化途径的代谢流量来挽救致命的表型。如果成功，这种方法将表明将甘露糖通量重定向到耗尽的糖基化途径具有治疗潜力，并将使高通量筛选搜索几种类型的CDG甘露糖通量增强型化合物成为可能。

DESCRIPTION (provided by applicant): Congenital Disorders of Glycosylation (CDG) are rare inherited defects in sugar chain (glycan) synthesis and their addition to protein. All 14 types (different genes) of CDG-I patients have mutations in different genes, but share a common lesion: lack of full N-glycosylation site occupancy. Likewise, patients share many symptoms, but show broad clinical variations both within and between different types. There are no vertebrate animal models for these disorders and only one Type, CDG-Ib, has a therapy. Here we propose to analyze the first viable CDG-I mouse model, evaluate the single known therapy, and apply that therapy to currently untreatable types of CDG. CDG-Ib patients have insufficient phosphomannose isomerase (MPI, Fru-6-P_>Man-6-P) activity and develop liver dysfunction, fibrosis, failure to thrive, protein-losing enteropathy and coagulopathy. However, dietary supplements of mannose bypass the defect by increasing the flux of Mannose through a minor biosynthetic pathway (Man`Man-6-P) thus relieving nearly all symptoms. CDG-Ia patients, who are deficient in PMM2 (Man-6-P`Man-1-P), do not respond to mannose therapy because they catabolize Man-6-P via robust MPI. Note that PMM2 and MPI compete for the same critical substrate, Man-6-P, and their ratio determines its metabolic flux. We engineered a hypomorphic Mpi allele to create the first viable potential CDG-I mouse model. Analysis of these mice to date shows progressive hepatopathology and increased enteric protein loss. In Aim 1 we will determine whether these mice show pathology modeling CDG-Ib patients. Aim 2 will determine how hypomorphic lines respond to environmental stresses. Aim 3 will determine whether mannose rescues (prevents and/or reverses) the susceptibility of hypomorphic mice to pathology, specifically, protein-losing enteropathy and hepatic pathology. Since the various CDG types share many of the pathologies, successful treatment of one type may establish a paradigm to treat others. Therefore, in Aim 4 we will breed our Mpi-hypomorphic mice with Pmm2-deficient mice that currently die in utero. Based on highly encouraging preliminary data, we predict that providing mannose and genetically reducing Mpi activity in Pmm2-deficient mice will rescue the lethal phenotype by increasing the metabolic flux of Man-6-P into the depleted glycosylation pathway. If successful, this approach will show that redirecting mannose flux into the depleted glycosylation pathway has therapeutic potential and would empower high-throughput screening search for mannose flux-enhancing compounds for several types of CDG.