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

额颞性痴呆(FTD)是仅次于阿尔茨海默病的第二大遗传性痴呆类型 疾病。FTD是由额叶和颞叶细胞进行性神经变性引起的。 大脑皮层。C9orf72基因第一内含子中GGGGCC(G4C2)序列的扩展是最多的 FTD的常见遗传原因，约25%的病例是由该基因引起的。企业扩张的机制 G4C2序列导致特定神经元的神经退行性变尚不完全清楚。G4C2 RNA是 在正义和反义方向上转录，两条RNA链都可以经历一种不寻常的类型的 翻译称为重复关联非AG依赖翻译(RANT)。正义与反义的咆哮 G4C2 RNA产生五种不同的二肽重复蛋白(Dprs)，其中两种(PR和GR)提供强大的 多个模型系统的毒性。为了更好地了解C9orf72介导的FTD的发病机制，我们 生成了表达纯dprs的线虫模型。PR和GR对蠕虫都有毒性，并引起 神经退行性变。为了确定导致毒性的基因和途径，我们进行了一项无偏见的遗传 抑制者筛选，发现了几个高度保守的基因，阻断了PR50的毒性。一位高度 保守的抑制子是核E3连接酶适配器SPOP。自从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从来没有 到目前为止一直与一种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基因敲除和SPOP小分子抑制剂均可阻断DPR对哺乳动物的毒性 神经元。癌症中的一个主要SPOP靶点是BRD2/3/4，它们是含有溴域的转录产物 调节蛋白。我们发现，抑制BRD同源基因bet-1会抑制SPOP突变体的能力 以防止DPR的毒性。基于这些发现，我们假设SPOP途径，即 目前被作为治疗癌症的靶点，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dprs是否直接与spop相互作用以调节 已知的病理途径，如核运输缺陷和应激颗粒形成；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对抗dprs的神经保护的可用药靶点。我们的研究将询问一位 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。 这种新的泛素化系统的发现可能会为这种不治之症带来新的治疗见解。 痴呆症。

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.