RNA Dysfunction in Selectively Vulnerable Populations in SCA7 Mice

项目摘要/摘要： 脊髓小脑型共济失调7型(SCA7)是一种常染色体显性遗传性神经退行性疾病，由 在ataxin-7基因的编码区遗传CAG重复扩增，导致聚谷氨酰胺 (PolyQ)扩展突变蛋白。SCA7具有与其他神经退行性疾病相同的特征 由多聚Q扩张性突变引起，如亨廷顿病。其中一个特征就是退化 发生在选择性脆弱的神经群体中。在SCA7中，退化的种群包括浦肯野人 细胞(PC)、Bergmann Glia(BG)和下橄榄(IO)神经元将攀升纤维轴突发送到 PC树突上的突触。利用SCA7的动物模型，我们已经证明了疾病基因的表达 特别是在BG，PC和IO神经元影响SCA7疾病的表型。有趣的是，使用带牙线的- PolyQ-ataxin-7小鼠SCA7模型观察Cre重组酶在三种细胞类型中表达 显著延迟了症状的出现。综上所述，这些发现支持了突变株 在这三种细胞类型中，Aaxin-7的表达导致了功能障碍的细胞相互作用，并且是一个关键的 SCA7小脑变性的介体。不幸的是，导致SCA7的分子机制 这3种特殊细胞类型的病理尚未确定。我们还观察到， 在症状出现后抑制突变基因的表达可以阻止疾病的进展，但不能逆转 PC或BG中的病理学。然而，在SCA7中，小脑的IO输入既减少又重新分配 老鼠。IO-PC突触病理是唯一可检测到的异常，可通过抑制突变来防止 症状出现后基因表达，提示IO-PC突触丢失与SCA7病有关 进步。由于SCA7小脑病理涉及特定细胞类型之间的相互作用改变， 存在于中枢神经系统的不同区域，这是研究基因表达或蛋白质变化的标准方法 内容不能区分与病理机制有关的细胞类型的具体变化 随着选择性脆弱细胞的退化而发生的过程和反应性变化。至 为了解决这个问题，我们已经开发了从三个细胞中专门分离RNA的技术 已知会影响小脑病理和运动行为的人群。在这个项目中，我们将使用这些 处理编码和非编码RNA中的细胞类型特定变化导致 在SCA7小鼠小脑中观察到的特殊细胞功能障碍模式。我们将进一步确定 在可诱导的Cre-7抑制突变的ataxin-7表达后，哪些RNA变化是可逆的 重组酶。这些由发现驱动的实验风险很高，但有可能产生关键的 关于多Q紊乱中选择性易损性的分子机制的信息。

Project Summary/Abstract: Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant neurodegenerative disorder caused by inheriting a CAG repeat expansion in the coding region of the ataxin-7 gene, resulting in a polyglutamine (polyQ) expanded mutant protein. SCA7 has features in common with other neurodegenerative disorders caused by polyQ expansion mutations such as Huntington's Disease. One such feature is that degeneration occurs in selectively vulnerable neural populations. In SCA7 the populations that degenerate include Purkinje cells (PCs), Bergmann Glia (BG) and neurons of the inferior olive (IO) which send climbing fiber axons to synapse on PC dendrites. Using animal models of SCA7, we have shown that disease gene expression specifically in BG, PCs and IO neurons influence the SCA7 disease phenotype. Interestingly, using a floxed- polyQ ataxin-7 mouse model of SCA7 we observed that expression of Cre recombinase in all three cell types dramatically delayed symptom onset. Taken together, these findings support the hypothesis that mutant ataxin-7 expression in these three cell types contributes to dysfunctional cellular interactions and is a critical mediator of SCA7 cerebellar degeneration. Unfortunately, the molecular mechanisms responsible for SCA7 pathology in these 3 specific cell types have not yet been determined. We have also observed that suppression of mutant gene expression after symptom onset halts disease progression, but does not reverse pathology in PCs or BG. However, IO inputs to the cerebellum are both decreased and redistributed in SCA7 mice. IO-PC synapse pathology was the only detectable abnormality prevented by suppression of mutant gene expression after symptom onset, suggesting that loss of IO-PC synapses contributes to SCA7 disease progression. Since SCA7 cerebellar pathology involves altered interactions between specific cell types that reside in distinct regions of the CNS, standard approaches to the study of altered gene expression or protein content cannot distinguish between cell type specific changes mechanistically involved in the pathologic process and reactive changes that develop in response to the degeneration of selectively vulnerable cells. To address this issue, we have developed techniques to isolate RNA specifically from the three cellular populations known to impact cerebellar pathology and motor behavior. In this project, we will employ these methods to address the hypothesis that cell type specific changes in both coding and non-coding RNAs lead to the specific pattern of cellular dysfunction observed in the cerebellum of SCA7 mice. We will further identify which RNA changes are reversible following suppression of mutant ataxin-7 expression by inducible Cre- recombinase. These discovery driven experiments are high-risk, but have the potential to yield critical information regarding the molecular mechanisms responsible for selective vulnerability in a polyQ disorder.