ATXN2-CAG42 Sequesters PABPC1 into Insolubility and Induces FBXW8 in Cerebellum of Old Ataxic Knock-In Mice
ATXN2-CAG42 Sequesters PABPC1 into Insolubility and Induces FBXW8 in Cerebellum of Old Ataxic Knock-In Mice
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DOI：
10.1371/journal.pgen.1002920
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发表时间：
2012-08-01
期刊：
影响因子：
4.5
通讯作者：
Auburger, Georg
中科院分区：
文献类型：
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作者：
Damrath, Ewa;Heck, Melanie V.;Auburger, Georg
脊髓小脑型共济失调2型(SCA2)是由编码三联体重复序列的多聚谷氨酰胺在人类ATXN2基因Beyond(CAG)(31)中的扩增引起的。这被认为是通过蛋白质聚集来调节有毒的功能获得，并影响RNA的处理，导致退化过程优先影响小脑神经元。作为一个忠实的动物模型，我们产生了一只敲入小鼠，用常见的患者基因CAG42取代了小鼠Atxn2的单一CAG。这一扩张规模是稳定遗传的。小鼠表现出体重减轻和后来的运动不协调的表型。尽管大脑中的ATXn2基因表达水平升高，但随着时间的推移，可溶的ATXN2蛋白水平降低，这可能解释了部分功能丧失的影响。可溶性ATXN_2蛋白的缺失与不溶性ATXN_2的出现有关，这是小脑的一种进行性特征，可能反映了毒性功能的获得。由于在体外过表达ATXN2已知会降低其蛋白相互作用因子PABPC1的水平，因此我们研究了对PABPC1的扩张效应。在大脑皮层，PABPC1转录本、可溶性蛋白和不溶性蛋白水平升高。在更脆弱的小脑中，PABPC1的进行性不溶性伴随着可溶性蛋白水平的下降，PABPC1mRNA没有显示出代偿性增加。在人类细胞培养中，验证了通过ATXN2功能增益将PABPC1隔离到不溶性中。为了了解对mRNA处理的影响，研究了三个不同组织在中年和老年时的转录组谱，并证明了Fbxw8在老年小脑中的选择性诱导。Fbxw8编码在Atxn2基因附近，体外研究表明它能降低ATXn2蛋白的表达水平。总之，我们的数据支持这一概念，即扩展的ATXN2经历进行性不溶性，并通过具有组织特异性效应的毒性功能获得机制影响PABPC1，这种机制可能被FBXW8的诱导部分缓解。
Spinocerebellar Ataxia Type 2 (SCA2) is caused by expansion of a polyglutamine encoding triplet repeat in the human ATXN2 gene beyond (CAG)(31). This is thought to mediate toxic gain-of-function by protein aggregation and to affect RNA processing, resulting in degenerative processes affecting preferentially cerebellar neurons. As a faithful animal model, we generated a knock-in mouse replacing the single CAG of murine Atxn2 with CAG42, a frequent patient genotype. This expansion size was inherited stably. The mice showed phenotypes with reduced weight and later motor incoordination. Although brain Atxn2 mRNA became elevated, soluble ATXN2 protein levels diminished over time, which might explain partial loss-of-function effects. Deficits in soluble ATXN2 protein correlated with the appearance of insoluble ATXN2, a progressive feature in cerebellum possibly reflecting toxic gains-of-function. Since in vitro ATXN2 overexpression was known to reduce levels of its protein interactor PABPC1, we studied expansion effects on PABPC1. In cortex, PABPC1 transcript and soluble and insoluble protein levels were increased. In the more vulnerable cerebellum, the progressive insolubility of PABPC1 was accompanied by decreased soluble protein levels, with PABPC1 mRNA showing no compensatory increase. The sequestration of PABPC1 into insolubility by ATXN2 function gains was validated in human cell culture. To understand consequences on mRNA processing, transcriptome profiles at medium and old age in three different tissues were studied and demonstrated a selective induction of Fbxw8 in the old cerebellum. Fbxw8 is encoded next to the Atxn2 locus and was shown in vitro to decrease the level of expanded insoluble ATXN2 protein. In conclusion, our data support the concept that expanded ATXN2 undergoes progressive insolubility and affects PABPC1 by a toxic gain-of-function mechanism with tissue-specific effects, which may be partially alleviated by the induction of FBXW8.