脊髓小腦萎縮症第十七型基因轉殖小鼠之分子特性探討

Abstract

TATA binding protein (TBP)為細胞中一種主要的轉錄因子，其在主導基因轉錄的起始過程中扮演著重要的角色。人類TBP基因位於染色體6q27，其5’端包含一段CAG三核苷酸重複序列，轉譯出的蛋白質N端上會形成一段多麩醯胺(polyglutamine, polyQ)的片段。SCA17為一種體染色體顯性遺傳之神經退化性疾病，目前已知SCA17致病原因與TBP基因之CAG重複序列擴增有關，為了探討TBP基因Ｎ端CAG三核苷重複擴增與神經退化的關係，我們之前已經利用小腦Purkinje細胞專一性表現之Pcp2/L7啟動子，建立了帶有109個CAG重複之TBP基因之轉殖小鼠，作為研究SCA17之疾病動物模式。由外觀及分子生物之分析中，我們已確認此基因轉殖小鼠有步態不穩、小腦中Purkinjecells明顯退化及缺失之病徵。在目前的研究中，我們進一步發現此基因轉殖小鼠小腦中與Purkinjecells相鄰的Bergmann glia有增加之現象，此結果與之前研究看到的小腦中astrocyte之增加有類似之意義，代表神經退化之結果。此外，進行微陣列實驗並分析資料後，我們發現有許多與鈣離子調控相關之基因表現量改變，經由西方墨點法進一步確認，發現基因轉殖小鼠小腦中calbindin、Inositol1,4,5-Triphosphate Receptor 1 (IP3R1)及Cacnα1G表現量明顯較正常小鼠為低。

TATA binding protein (TBP) is a general transcription factor that plays an important role in initiation of transcription. TBP gene is located in chromosome 6q27 and contains a CAG/CAA trinucleotide repeat region in its 5’ end, which encodes a polyglutamine (polyQ) tract. Spinocerebellar ataxias type 17(SCA17) is an autosomal dominant cerebellar ataxia caused by TBP gene with an expanded polyQ tract correlated to the disease onset and progression. To investigate the TBP trinucleotide expansion effect on neurodegeneration, we have generated transgenic mice expressing the human TBP gene with expandedCAA/CAG tracts under the control of Purkinje cell-specific promoter, Pcp2/L7 promoter. Our previous studies have shown that these hTBP109Q transgenic mice had ataxia and severe Purkinje cell loss in the cerebellum. In the present study, we found Bergmann glia surrounding the Purkinje cells were also increased as astrocytes that was identified in our previous study and suggesting a neurodegeneration occurred in the mouse cerebella. According to the result of cDNA microarray analysis, we found several calcium regulatory protein expression were differentiated expressed in the transgenic mouse cerebella. We further conducted western analysis and confirmed that the expressions of calbindin, inositol 1, 4,5-triphosphate receptor 1 (IP3R1) and Cacnα1G were downregulated in the SCA17 mouse cerebellum.We suggest that hTBP109Q mutant protein in the mouse brain might result in the impairment of calcium homeostasis.