Evaluation of the role of RNA toxicity in SCA2 pathogenesis using genome editing in patient iPSCs

脊髓小脑型共济失调2(Sca2)是一种由cag重复引起的破坏性神经退行性疾病。 基因ataxin-2(ATXN2)的扩增。CAG重复序列被翻译成聚谷氨酰胺(PolyQ)链。 具有神经毒性特性的突变型ATXN2蛋白。目前的治疗努力集中在抑制 表达突变的ATXN2蛋白，或靶向神经毒性的下游途径。我们和其他人 已经表明，突变的CAG/CTG重复序列转录本也参与了几种 重复疾病，包括亨廷顿病(HD)、亨廷顿病样2(HDL2)和脊髓小脑 共济失调3型和8型(SCA3和SCA8)。因此，除了靶向突变蛋白的神经毒性外， 成功的治疗可能需要靶向突变转录本和/或突变下游的通路 成绩单。我们的初步证据支持这一观点，即在SCA2中，除了有毒的ATXN2蛋白外，两者都 正义ATXN2RNA和含有扩展CUG重复序列的ATXN2反义转录本(ATXN2AS)， 参与了SCA2的发病机制。因此，我们建议使用基因组编辑的方法来修改正常和 将sca2 ipsc转化为新的等基因ipsc系，模拟sca2的蛋白质或RNA诱导的机制 发病机制。这些品系将被用来(1)进一步检验sca2的新假说，突变体 ATXN_2/ATXN_2-AS转录产物干扰SCA2中的RNA加工，包括RNA输出、rRNA代谢和 剪接，以及(2)确定RNA神经毒性在SCA2发病中的相对贡献。结果是 这项研究不仅有助于我们了解日益复杂的糖尿病发病机制。 SCA2，也包括其他CAG/CTG重复疾病，在这些疾病中，双向编码的转录本和 蛋白质对病理有贡献。这一结果将有助于指导SCA2治疗的未来发展，以及 其他微卫星重复扩张性疾病的治疗。

Spinocerebellar ataxia type 2 (SCA2) is a devastating neurodegenerative disease caused by a CAG repeat expansion in the gene ataxin-2 (ATXN2). The CAG repeat is translated into a polyglutamine (polyQ) tract in the mutant ATXN2 protein that has neurotoxic properties. Current therapeutic efforts are focused at suppressing the expression of the mutant ATXN2 protein, or targeting downstream pathways of neurotoxicity. We and others have shown that mutant CAG/CTG repeat-containing transcripts also contribute to pathogeneses of several repeat diseases, including Huntington's disease (HD), Huntington's disease-like 2 (HDL2) and spinocerebellar ataxia type 3 and 8 (SCA3 and SCA8). Therefore, in addition to targeting the neurotoxicity of mutant proteins, a successful therapy may require targeting the mutant transcripts and/or pathways downstream of the mutant transcripts. Our preliminary evidence supports the idea that in SCA2, in addition to toxic ATXN2 protein, both sense ATXN2 RNA and a transcript antisense to ATXN2 (ATXN2-AS) containing an expanded CUG repeat, contribute to SCA2 pathogenesis. We therefore propose to use genome editing approach to modify normal and SCA2 iPSC line into novel, isogenic iPSC lines that model either protein or RNA-induced mechanisms of SCA2 pathogenesis. These lines will be used to (1) further test the novel hypothesis of SCA2 by which mutant ATXN2/ATXN2-AS transcripts disrupt RNA processing in SCA2, including RNA export, rRNA metabolism and splicing, and (2) determine the relative contribution of RNA neurotoxicity to SCA2 pathogenesis. The results obtained from this study will not only facilitate our understanding of the increasingly complex pathogenesis of SCA2, but also that of other CAG/CTG repeat diseases in which both bi-directionally encoded transcripts and protein contribute to pathology. The results will help guide future development of SCA2 therapy, as well as therapies of other microsatellite repeat expansion diseases.