Spinocerebellar ataxia type 12 iPSCs and PP2A dysregulation

 描述（由申请人提供）：脊髓小脑共济失调12型（SCA 12）是一种进行性、常染色体显性、神经退行性疾病，由染色体5 q32上CAG/CTG三核苷酸重复扩增引起;我们的研究组最初描述了疾病表型和致病突变（Holmes et al，1999）。虽然这种疾病是印度最常见的SCA形式之一，并且已经在世界各地检测到了分散的SCA 12家系，但SCA 12最有趣的方面可能是重复福尔斯落在PPP 2 R2 B的推定启动子中，PPP 2 R2 B是编码三聚体酶磷酸酶2A（PP 2A）的α调节亚基的基因。功能性PP 2A由一个结构单元、两个催化单元之一和约30个调节亚基之一组成，调节亚基的N-末端区域用于将全酶靶向特定的细胞内位点。PP 2A的失调与阿尔茨海默病中的tau过度磷酸化以及多种其他神经退行性疾病直接相关。基于来自细胞过表达模型的初步数据，我们假设SCA 12重复扩增导致PPP 2 R2 B亚型B β 1表达增加，并且这种过表达导致PP 2A活性失调和神经毒性。然而，还不可能证实这些观察结果，因为人SCA 12脑材料不可用，并且PPP 2 R2 B不在白细胞或淋巴母细胞中表达。为了检验我们的假设，我们将使用来自SCA 12患者皮肤活检的成纤维细胞来产生诱导多能干细胞（iPSC）（目的1）。然后，我们将确定突变对成纤维细胞和分化为前脑神经元的IPSC中PPP 2 R2 B表达和其他细胞特性的影响（目的2）。该项目的潜在公共卫生益处有三个方面：1）更好地了解重复DNA如何影响基因表达，2）更好地了解SCA 12发病机制，具有检测治疗药物靶点的潜力，以及3）对PP 2A在神经退行性疾病发病机制中的作用的新见解。

 DESCRIPTION (provided by applicant): Spinocerebellar ataxia type 12 (SCA12) is a progressive, autosomal dominant, neurodegenerative disorder caused by an expansion of a CAG/CTG trinucleotide repeat on chromosome 5q32; both the disease phenotype and the causative mutation were initially described by our group (Holmes et al, 1999). While the disease is one of most common forms of SCA in India, and scattered SCA12 pedigrees have been detected around the world, perhaps the most intriguing aspect of SCA12 is that the repeat falls in a putative promoter of PPP2R2B, a gene encoding ß regulatory subunits of the trimeric enzyme phosphatase 2A (PP2A). Functional PP2A consists of a structural unit, one of two catalytic units, and one of ~30 regulatory subunits, with the N-terminal region of the regulatory subunits serving to target the holoenzyme to specific intracellular sites. Dysregulation of PP2A has been directly linked to tau hyperphosphorylation in Alzheimer's disease, and to multiple other neurodegenerative diseases. We hypothesize, based on preliminary data from cell overexpression models, that the SCA12 repeat expansion leads to increased expression of PPP2R2B isoform Bß1, and that this overexpression leads to dysregulation of PP2A activity and neurotoxicity. However, it has not been possible to confirm these observations, as human SCA12 brain material is not available and PPP2R2B Is not expressed in leukocytes or lymphoblasts. To test our hypothesis, we will use fibroblasts from skin biopsies of patients with SCA12 to generate induced pluripotent stem cells (iPSCs)(Aim 1). We will then determine the effect of the mutation on PPP2R2B expression and other cellular properties in the fibroblasts and in the IPSCs differentiated into forebrain neurons (Aim 2). The potential public health benefits of this project are three fold: 1) a better understanding of how repetitive DNA can influence gene expression, 2) a better understanding of SCA12 pathogenesis, with the potential of detecting targets for therapeutic agents, and 3) new insight into the role of PP2A in the pathogenesis of neurodegenerative disease.