Defining mechanisms underlying C9orf72-associated frontotemporal dementia with C. elegans and mammalian models

额颞叶痴呆（FTD）是继阿尔茨海默氏症之后第二种最常见的遗传性痴呆 疾病FTD是由额叶和颞叶细胞的进行性神经变性引起的， 大脑皮层在C9 orf 72基因的第一内含子中的GGGGCC（G4 C2）序列的扩增是最多的。 是FTD的常见遗传原因，约占病例的25%。扩张的机制 导致特定神经元神经变性G4 C2序列还不完全清楚。G4C2 RNA 在正义和反义方向转录，两条RNA链都可以经历一种不寻常的类型， 重复相关非AG依赖翻译（RANT）。正义和反义的RANT G4 C2 RNA产生五种不同的二肽重复蛋白（DPRs），其中两种（PR和GR）赋予强的 多模型系统中的毒性。为了更好地了解C9 orf 72介导的FTD的发病机制，我们 生成C.表达纯DPR的线虫模型。PR和GR对蠕虫都有毒性， 神经变性为了确定导致毒性的基因和途径，我们进行了无偏倚的遗传学分析。 抑制子筛选，发现了几个高度保守的基因，阻断PR 50的毒性。一个高度 保守的抑制子是核E3连接酶接头SPOP。自SPOP以来，SPOP在癌症中被广泛研究 错义突变是前列腺癌和子宫内膜癌的主要遗传原因。然而，SPOP从未 与神经退行性疾病有关SPOP在DPR毒性中的作用是保守的，因为 SPOP基因敲低和SPOP小分子抑制剂均阻断哺乳动物原发性 神经元癌症中的一个主要SPOP靶标是BRD 2/3/4，其是含溴结构域的转录调控蛋白。 调节蛋白我们发现，抑制BRD同系物bet-1抑制SPOP突变体的能力， 以防止DPR毒性。基于这些发现，我们假设SPOP途径， 目前被靶向用于治疗癌症，也可能是C9神经退行性病变的基础。 疾病为了验证这一假设，我们将：1）确定DPR是否直接与SPOP相互作用以调节 已知的病理途径，如有缺陷的核转运和应激颗粒形成; 2）描绘 SPOP、BRD和可能的其他底物介导DPR毒性的机制;以及3）确定SPOP是否 是哺乳动物神经元中针对DPR的神经保护的“可用药”靶点。我们的研究将审问一个 使用多种方法和实验模型系统研究与C9疾病相关的新途径。 这种新型泛素化系统的发现可能会为这种无法治愈的疾病带来新的治疗见解。 痴呆

Frontotemporal dementia (FTD) is the second most common type of inherited dementia following Alzheimer’s disease. FTD is caused by the progressive neurodegeneration of cells in the frontal and temporal lobe of the cerebral cortex. Expansion of a GGGGCC (G4C2) sequence in the first intron of the C9orf72 gene is the most common genetic cause of FTD and is responsible for ~25% of cases. The mechanisms by which expansion of the G4C2 sequence lead to neurodegeneration of specific neurons is incompletely understood. G4C2 RNA is transcribed in both sense and antisense directions and both RNA strands can undergo an unusual type of translation called Repeat Associated non-AG dependent translation (RANT). RANT of the sense and antisense G4C2 RNA produces five distinct dipeptide repeat proteins (DPRs), two of which (PR and GR) confer strong toxicity in multiple model systems. To better understand the pathogenesis of C9orf72-mediated FTD, we generated C. elegans models expressing pure DPRs. Both PR and GR were toxic in worms and caused neurodegeneration. To define genes and pathways causing toxicity, we performed an unbiased genetic suppressor screen and discovered several highly conserved genes that blocked PR50 toxicity. One highly conserved suppressor is the nuclear E3 ligase adaptor SPOP. SPOP is widely studied in cancer since SPOP missense mutations are a major genetic cause of prostate and endometrial cancer. However, SPOP has never been linked to a neurodegenerative disease until now. The role of SPOP in DPR toxicity is conserved, since both SPOP genetic knockdown and an SPOP small molecule inhibitor blocks DPR toxicity in mammalian primary neurons. One major SPOP target in cancer is BRD2/3/4, which are bromodomain-containing transcriptional regulatory proteins. We found that inhibition of the BRD homolog bet-1 suppresses the ability of SPOP mutants to protect against DPR toxicity. Based on these findings, we hypothesize that the SPOP pathway, which is currently being targeted for the treatment of cancer, may also underlie neurodegenerative pathology in C9 disease. To test this hypothesis, we will: 1) determine whether DPRs directly interact with SPOP to modulate known pathological pathways, such as defective nuclear transport and stress granule formation; 2) delineate the mechanism by which SPOP, BRD, and possibly other substrates mediate DPR toxicity; and 3) determine if SPOP is a ‘druggable’ target for neuroprotection against DPRs in mammalian neurons. Our studies will interrogate a novel pathway associated with C9 disease using a diversity of approaches and experimental model systems. The discovery of this novel ubiquitination system could lead to new therapeutic insights for this incurable form of dementia.