Mechanistic basis for endosomal dysfunction in frontotemporal dementia linked to

描述（由申请方提供）：额颞叶痴呆（FTD）是第二常见的早发性神经退行性疾病伴认知障碍，几乎一半的FTD病例被认为是家族性的。与3号染色体（FTD 3）连锁的FTD为常染色体显性，与CHMP 2B基因突变密切相关，该基因编码转运蛋白-III（ESCRT-III）所需的内体分选复合物亚基。在晚期内体，ESCRT-III通过其组装过程催化膜断裂反应，而CHMP 2B通过刺激催化ESCRT-III分解的ATP酶来维持这种活性，从而补充重复轮复合物组装的亚基的可用性。在FTD 3患者中，一个基因组CHMP 2B位点的点突变导致其编码序列截短，这消除了ATP酶结合位点，同时消除了自抑制区域。截短的CHMP 2B表达导致ESCRT-III膜断裂活性的遗传显性抑制，但这种功能障碍的机制基础尚不清楚，也不清楚它如何导致晚期内体和自噬体的积累，这是FTD 3中的主要细胞病理学。本研究的长期目标是使用芽殖酵母酿酒酵母作为模型系统来理解FTD 3中晚期内体功能障碍的机制基础。中心假设是CHMP 2B截短抑制晚期内体和自噬体与溶酶体的融合，这通常阻止这些细胞器积聚。这项研究将研究杂合二倍体酵母，其中一个拷贝的CHMP 2B基因直系同源物被截断的方式在一个大型丹麦家族FTD 3折磨。所使用的方法包括蛋白质生物化学，定位研究，表达谱分析和功能测定，以研究FTD 3截短如何影响ESCRT-III和调节溶酶体融合活性的机制。这项研究的基本原理是，这些参数必须确定，以制定一项战略，定义关键的蛋白质相互作用和特定的调控元件，连接内溶酶体融合ESCRT-III功能。使用酵母作为模型系统来理解这种关系与人类健康直接相关，因为内溶酶体融合和ESCRT-III功能的机制是高度保守的。关于预期的结果，预计这项研究的完成将揭示FTD 3中ESCRT-III功能障碍的性质，以及它如何导致晚期内体和自噬体的积累。这些结果预计将产生重要的积极影响，因为它们将产生对内吞途径中一个知之甚少的调控步骤的基本见解，揭示预防和治疗FTD 3的潜在靶点，并激发新的创新方法来了解内体功能障碍的机制，这些机制是许多其他神经退行性疾病的特征。

DESCRIPTION (provided by applicant): Frontotemporal dementia (FTD) is the second most common early-onset neurodegenerative disease with cognitive impairment, and almost one half of FTD cases are thought to be familial. FTD linked to chromosome 3 (FTD3) is autosomal dominant and strongly linked to mutations in the CHMP2B gene, which encodes a subunit of the endosomal sorting complex required for transport-III (ESCRT-III). At late endosomes, ESCRT-III catalyzes membrane scission reactions through its assembly process, and CHMP2B sustains this activity by stimulating the ATPase that catalyzes disassembly of ESCRT-III, thereby replenishing the availability of subunits for repeated rounds of complex assembly. In FTD3 patients, point-mutation of one genomic CHMP2B locus results in truncation of its coding sequence, which eliminates the ATPase-binding site and simultaneously removes an autoinhibitory region. Truncated CHMP2B expression results in genetic-dominant inhibition of ESCRT-III membrane scission activity, but the mechanistic basis for this dysfunction is unknown, nor is it understood how it results in the accumulation of late endosomes and autophagosomes, which is the predominant cellular pathology in FTD3. The long-term objective of this research is to understanding the mechanistic basis for late endosomal dysfunction in FTD3 using the budding yeast Saccharomyces cerevisiae as a model system. The central hypothesis is that CHMP2B truncation inhibits the fusion of late endosomes and autophagosomes with lysosomes, which normally prevents these organelles from accumulating. This research will study heterozygous diploid yeast in which one copy of the CHMP2B gene ortholog is truncated in a manner homologous to that described in a large Danish kindred afflicted with FTD3. The methodology to be used includes protein biochemistry, localization studies, expression profiling, and functional assays to study how the FTD3 truncation affects ESCRT-III and the machinery that regulates lysosomal fusion activity. The rationale for this research is that these parameters must be determined in order to develop a strategy for defining the critical protein interactions and specific regulatory elements that link endolysosomal fusion to ESCRT-III function. Using yeast as a model system to understand this relationship is directly relevant to human health because the mechanisms of endolysosomal fusion and ESCRT-III function are highly conserved. With respect to expected outcomes, it is anticipated that completion of this research will reveal the nature of ESCRT-III dysfunction in FTD3 and how it results in accumulation of late endosomes and autophagosomes. Such results are expected to have an important positive impact because they will yield fundamental insight into a poorly understood regulatory step in the endocytic pathway, reveal potential targets for the prevention and treatment of FTD3, and inspire new and innovative approaches to understand the mechanisms of endosomal dysfunction that characterize many other neurodegenerative diseases.