Pathophysiology and potential therapy for a childhood neurodegenerative disease

描述（由申请人提供）：约40溶酶体贮积病（lsd）是幼儿神经退行性变的最常见原因。其中一种没有治疗方法的破坏性lsd是IV型粘脂病（MLIV）。MLIV患者通常在大约1-3岁时被诊断出来，并表现出严重的运动功能缺陷、智力迟钝和视网膜变性。MLIV患者溶酶体活性缺陷并不局限于中枢神经系统，而是存在于大多数器官和组织中。MLIV临床特征的发病机制尚不清楚。MLIV是由人类MCOLN1基因的功能缺失突变引起的，这种突变会破坏Mucolipin1 （TRPML1）蛋白。TRPML1属于瞬时受体电位（TRP）阳离子通道超家族，该家族在蠕虫（cup-5）、苍蝇（trpml）和小鼠（Mcoln1或TRPML1）中有同源物。在两种无脊椎动物模型中，破坏TRPML1同源物功能的突变都会破坏溶酶体功能。最近，对果蝇trpml基因敲除的分析表明，进行性神经变性和运动障碍是由于大脑中早期凋亡神经元的去除缺陷引起的，这导致晚期凋亡神经元的积累，细胞毒性细胞内容物的释放和邻近细胞的细胞死亡。巨噬细胞中野生型trpml+基因的表达抑制了这种旁观者效应导致的进行性神经退行性变以及随之而来的运动缺陷。在这里，我建议将重点放在MLIV小鼠模型上，以测试我们从果蝇模型中收集到的有关神经变性发病机制的概念。此外，我建议测试骨髓移植是否会降低表型的严重程度。这个建议是可行的，因为我已经获得了最近生成的概括MLIV临床表现的小鼠模型（TRPML1-/-）。此外，我开始描述TRPML1-/-小鼠的特征，发现它们在大脑中表现出进行性神经变性和运动缺陷。目的一是验证TRPML1-/-小鼠的造血吞噬细胞在内吞作用和溶酶体依赖性降解方面存在缺陷的假设。目的二是验证TRPML1-/-敲除小鼠表现出慢性神经炎症，从而导致神经毒性的假设。我认为我提出的研究将为神经炎症如何促进广泛的神经退行性疾病的进展提供见解。第三个也是最重要的目的是验证骨髓移植中TRPML1-/-敲除会抑制神经退行性变严重程度的假设。如果是这样，这将提高骨髓移植可能成为MLIV治疗方法的可能性。最后，在小鼠MLIV模型上提出的研究结果可能为深入了解具有广泛神经退行性疾病特征的进行性神经元细胞死亡的机制提供见解。

DESCRIPTION (provided by applicant): The ~40 lysosomal storage diseases (LSDs) account for the most common cause of neurodegeneration in young children. One of these devastating LSDs, for which there is no treatment, is mucolipidosis type IV (MLIV). Patients with MLIV are diagnosed typically at about 1-3 years of age and display severe motor function deficits, mental retardation and retinal degeneration. The defects in lysosomal activity in MLIV patients are not exclusive to the central nervous system (CNS), but are observed in most organs and tissues. The pathogenesis underlying the clinical characteristics of MLIV is not clearly understood. MLIV arises from loss-of-function mutations in the human MCOLN1 gene, which disrupt the Mucolipin1 (TRPML1) protein. TRPML1 belongs to the Transient Receptor Potential (TRP) superfamily of cation channels, which include homologs in worms (cup-5), flies (trpml) and mice (Mcoln1 or TRPML1). Mutations that disrupt the function of the TRPML1 homolog in both invertebrate models disrupt lysosomal function. Most recently, analysis of the Drosophila trpml knockout demonstrates that the progressive neurodegeneration and motor impairment result from a defect in the removal of early apoptotic neurons in the brain, which leads to accumulation of late apoptotic neurons, release of cytotoxic cellular contents and cell death in the adjacent cells. The progressive neurodegeneration, due to this bystander effect, and the ensuing motor defects are suppressed by expression of the wild-type trpml+ gene in macrophages. Here, I propose to focus on a MLIV mouse model to test concepts concerning the pathogenesis of neurodegeneration, which we have gleaned from the Drosophila model. In addition, I propose to test whether bone marrow transplantation will reduce the severity of the phenotype. This proposal is feasible since I have obtained the recently generated mouse model (TRPML1-/-) that recapitulates clinical manifestations of MLIV. Moreover, I started characterizing the TRPML1-/- mice and found that they display progressive neurodegeneration in the brain and motor defects. Aim one is to test the hypothesis that the hematopoietic phagocytes in the TRPML1-/- mice are defective in endocytosis and lysosomal dependent degradation. Aim two is to test the hypotheses that the TRPML1-/- knockout mice display chronic neuroinflammation, which contributes to neurotoxicity. I suggest that my proposed study will provide insight into how neuroinflammation contributes to the progression of a broad range of neurodegenerative conditions. The third and most important aim is to test the hypothesis that bone marrow transplantation in the TRPML1-/- knockout will suppress the severity of the neurodegeneration. If so, this would raise the possibility that bone marrow transplantation may be a treatment for MLIV. Finally, the findings from the proposed study on the mouse MLIV model may provide insights into the mechanisms underlying the progressive neuronal cell death that characterize a broad range of neurodegenerative diseases. PUBLIC HEALTH RELEVANCE: The proposed research is aimed at understanding the cellular mechanisms that are involved in MLIV neurodegeneration. MLIV is a devastating childhood disease which lacks any treatment for the disease, I am testing BMT as a viable treatment for suppressing neurodegeneration in MLIV patients. This proposed work is relevant to the understanding and treatment of MLIV, and to improving the lives of MLIV patients.