第十七型脊髓小腦運動失調症：遺傳檢測暨細胞模式之氧化壓力與細胞毒性研究

Spinocerebellar ataxia type 17: genetic testing and oxidative stress and cytotoxicity studies using SCA17 lymphoblastoid and HEK-293 cell models

林佩瑛(Pei-Ying Lin)

指導教授 ： 李桂楨

國立臺灣師範大學/理學院/生命科學研究所/碩士(2007年)

摘要

第十七型脊髓小腦運動失調症（SCA17）為體染色體顯性遺傳的神經退化性疾病，起因於位在染色體 6q27 位置上的 TATA-binding protein（TBP）基因之 CAG/CAA 三核?酸重複擴增，轉譯出帶有不正常的聚麩醯胺鏈（polyQ tract）的蛋白質產物，造成蛋白質構形改變而產生錯誤摺疊與聚集，導致疾病。目前SCA17致病機轉尚未完全瞭解，且尚無有效治療方法，加上疾病進程發展及變異極大，因此瞭解 TBP 基因 CAG 三核?酸重複在族群中的分佈情形及探討可能致病機轉，將對發展疾病治療策略有所助益。本論文即以 SCA17 為主題，首先進行臺灣地區正常人族群、帕金森氏症患者族群、原發性顫抖症患者族群與其它神經退化性疾病患者族群的 TBP 基因CAG 三核?酸重複遺傳分析，發現 CAG/CAA 重複次數的頻率主要集中在 36 個重複序列，並於 OPMD 及 TICS 疾病中發現有兩名不正常擴增的例子（44 and 45 repeats），顯示 TBP 基因重複擴增序列可能與其它神經疾病相關。另一部分利用年齡與性別配對的 SCA17 淋巴細胞株及建立誘導式 SCA17 細胞模式，檢視氧化壓力與熱休克蛋白在 SCA17 上扮演的角色。氧化劑 TBH 處理後兩種細胞模式皆顯示帶有 polyQ 擴增的細胞對氧化壓力的耐受性顯著差於帶有正常 TBP 的細胞，推論氧化壓力可能參與 SCA17 致病機轉。此外，在 SCA17 淋巴細胞株或誘導式 SCA17 細胞模式觀察到 HSPA8 與 HSPB1 表現量的改變，暗示此兩種熱休克蛋白亦可能參與 SCA17 致病機轉。最後，組蛋白去乙醯?抑制劑 valproate 可增加帶有 polyQ 擴增細胞的存活率的發現，將有利於找出 SCA17 治療策略的目標。

關鍵字

第十七型脊髓小腦運動失調症 ； 氧化壓力 ； 細胞毒性

並列摘要

Spinocerebellar ataxia 17 (SCA17) is an inherited progressive neurodegenerative disease. It is caused by an expanded polyglutamine (polyQ) tract in the TATA-box binding protein (TBP), a general transcription initiation factor, which is crucial for most gene transcription. The expanded polyQ causes a conformational change leading to protein misfolding and aggregation. However, it remains unclear how the polyQ tract affects cellular protein function and induces selective loss of neurons. In this study, we examined the CAG/CAA repeat size range in TBP allele in Taiwanese control subjects and in patients with Parkinson’s disease, essential tremor, and other neurological disorders by SCA17 genotyping. The most common TBP allele contains 36 repeats and two expanded (44 and 45 repeats) alleles were found in patients with OPMD and TICS. Using age- and gender-matched lymphoblastoid and stably induced HEK-293 cells with expanded polyQ, we examined the roles of oxidative stress and chaperones in the pathogenesis of SCA17. In both cell models the relative cell death ratio in cells expressed expanded TBP is significantly higher than that in cells expressed normal TBP upon prooxidant TBH (tert-butyl hydroperoxide) treatment. The results suggest that oxidative stress may be involved in SCA17 pathogenesis. In addition, altered HSPA8 and HSPB1 expressions were observed in lymphoblastoid model or stably induced HEK-293 model, suggesting that HSPA8 and HSPB1 may be involved in SCA17 pathogenesis. Finally, the finding that treatment of histone deacetylases inhibitor valproate increases the viability of cells expressing expanded TBP may help to identify potential targets of SCA17 therapies.

並列關鍵字

Spinocerebellar ataxia type 17 ； oxidative stress ； cytotoxicity

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