第十七型脊髓小腦共濟失調症(SCA17)細胞模式的新穎化合物篩檢及氧化壓力研究

Abstract

第十七型脊髓小腦運動失調症(spinocerebellar ataxias 17，簡稱SCA17)是起因於TATA-box binding protein (TBP)基因上的CAG三核苷重複序列重複擴增，導致轉譯出異常的polyQ蛋白。在正常人族群中polyQ蛋白重複的數目約25到42之間，而SCA17疾病的患者polyQ蛋白重複數目擴增至43到66之間。polyQ蛋白擴增會造成多胜肽的構型改變，促使蛋白質錯誤摺疊和聚集(aggregation)，並進ㄧ步形成不溶性的蛋白包涵體(inclusion)。隨著對疾病致病機轉的瞭解增加，也使疾病治療的發展有很大的進展。本論文即建立表現EGFP標記、polyQ擴增的TBP N端蛋白的293細胞，處理合成的indole、quinoxaline化合物(由化學系姚清發和陳焜銘老師所提供)，藉計算包含聚集物的細胞的比例，及不溶性TBP-EGFP融合蛋白定量，來檢測化合物對抑制polyQ蛋白聚集的效果。結果顯示338化合物降低融合蛋白聚集的程度比SAHA略好(64.3% vs. 66.1%；70.7% vs. 77.4%)。而且338的IC50 (396 μM)遠高於SAHA (31.4 μM)，可能作為未來發展治療SCA17疾病的參考藥物。此外，由於擴增的polyQ蛋白會造成氧化壓力，增加粒線體功能損傷，本研究亦利用年齡與性別配對的淋巴細胞株，來檢測氧化壓力在SCA17疾病上扮演的角色，結果發現SCA17病人細胞較正常人細胞對氧化壓力的耐受性差。

關鍵字：第十七型脊髓小腦運動失調症、polyQ蛋白、氧化壓力

Spinocerebellar ataxias 17 (SCA17) has been attributed to CAG repeat expansions in human TATA-box binding protein (TBP) gene. The CAG repeats code for polyglutamine (polyQ) tract. The polyQ tract contains 25~42 polyQ in normal population while expanded 43~66 polyQ is linked to SCA17. The polyQ expansions cause a conformational change in the polypeptide to promote misfolding and aggregation of the disease protein, which ultimately forms insoluble protein inclusions. Accompanying increasing insights into the pathophysiology of repeat expansion, much progress has been made to develop therapeutics. In this study, the 293 cells expressing EGFP-tagged polyQ-expanded N-terminal TBP were established and treated with the synthesized indole and quinoxaline compounds (provided by Drs Ching-Fa Yao and Kwunmin Chen). The effects of compounds on inhibiting polyQ aggregation were examined by counting aggregates numbers and quantifying insoluble nTBP-EGFP levels on EGFP-positive cells. The results illustrate that compounds 338 reduce aggregation to a level slightly better than that of SAHA (64.3% vs. 66.1%；70.7% vs. 77.4%). Among them, the IC50 of compound 338 (396 μM) is much higher than that of SAHA (31.4 μM), indicating that 338 may be a lead compound for SCA17 therapeutic development. As the polyQ expansions can induce reactive oxygen species (ROS) to lead to mitochondria impairment, age- and gender-matched lymphoblastoid cells were used to examine the roles of oxidative stress in SCA17 pathogenesis. The results demonstrate oxidative vulnerability of cells carrying expanded TBP.

Key words: SCA 17, polyglutamine (polyQ), oxidative stress