RNA Dysfunction in Selectively Vulnerable Populations in SCA7 Mice

项目概要/摘要： 脊髓小脑性共济失调7型（SCA 7）是一种常染色体显性遗传的神经退行性疾病， 遗传性共济失调蛋白-7基因编码区的CAG重复扩增，导致多聚谷氨酰胺 （polyQ）扩增的突变体蛋白。SCA 7与其他神经退行性疾病具有共同特征 由polyQ扩增突变引起，如亨廷顿病。其中一个特征是， 发生在选择性脆弱的神经群体中。在SCA 7中，退化的种群包括Purkinje 细胞（PC），Bergmann胶质细胞（BG）和下橄榄（IO）的神经元，它们将攀爬纤维轴突发送到 突触在PC树突上。使用SCA 7的动物模型，我们已经表明疾病基因表达 特别是在BG中，PC和IO神经元影响SCA 7疾病表型。有趣的是，使用floxed- 我们在SCA 7的polyQ共济失调蛋白-7小鼠模型中观察到Cre重组酶在所有三种细胞类型中的表达 显著延迟了症状发作。综上所述，这些发现支持了突变体 在这三种细胞类型中，共济失调蛋白-7的表达有助于功能失调的细胞相互作用， SCA 7小脑变性的介质。不幸的是，SCA 7的分子机制 这3种特定细胞类型的病理学尚未确定。我们还注意到， 症状发作后抑制突变基因表达可阻止疾病进展，但不能逆转 PC或BG中的病理学。然而，在SCA 7中，小脑的IO输入减少并重新分配 小鼠IO-PC突触病理学是通过抑制突变体而防止的唯一可检测的异常。 症状发作后的基因表达，表明IO-PC突触的丢失有助于SCA 7疾病 进展由于SCA 7小脑病理学涉及特定细胞类型之间改变的相互作用， 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改变的标准方法。 内容不能区分病理学中涉及的细胞类型特异性变化， 过程和反应性的变化，发展在应对选择性脆弱细胞的退化。到 为了解决这个问题，我们已经开发了从三种细胞中特异性分离RNA的技术， 已知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 方法来解决这一假设，即细胞类型特异性变化的编码和非编码RNA导致 在SCA 7小鼠小脑中观察到的细胞功能障碍的特定模式。我们将进一步确定 其RNA变化在通过诱导型Cre抑制突变型共济失调蛋白-7表达后是可逆的。 重组酶这些发现驱动的实验是高风险的，但有可能产生关键的 关于负责polyQ障碍中的选择性脆弱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.