在果蠅模式中探討 Tau 蛋白經轉譯後修飾與 其所引發的神經毒性之關係

Post-translational modifications of Tau-linked neurodegenerative disorders in a Drosophila model

徐仁慧(Ren-Huei Shiu)

指導教授 ： 桑自剛

國立清華大學/生命科學院/生物科技研究所/碩士(2013年)

摘要

Tauopathies為神經退化性疾病的其中一類，與tau蛋白不正常的聚合堆積有關。Tau蛋白是與微管相關的一種蛋白，主要表達於神經細胞，其功能為穩定由微管組成的細胞骨架和調節微管蛋白的動態平衡。
近年來的研究指出， tau蛋白進行過磷酸化、去磷酸化或是進行截斷作用(truncation)都與tau蛋白引起的細胞毒性有關。然而，磷酸化與否以及截斷作用究竟何者對於tau造成的毒性扮演著較重要的角色至今仍然在爭論中。為了研究何者扮演著較重要的角色，我們修飾tau蛋白上的磷酸化和裂解作用的位置，製造出基因轉殖果蠅，以闡釋tau蛋白經轉譯後修飾，其神經毒性可能會產生的影響。我們發現，長度全長並且過磷酸化或去磷酸化的tau蛋白都對眼睛造成毒性。有趣的是，過磷酸化並且裂解後缺少羧酸基端(C端)至少20個胺基酸的tau蛋白，可改善tau蛋白引起的果蠅眼睛神經退化；由此，我們進一步推測tau蛋白的C端對於tau蛋白所引起的毒性可能是一重要關鍵。根據tau蛋白之C端，我們找出含有酪蛋白激酶(casein kinase)以及醣基化的作用區，於是我們將藉由調控酪蛋白激酶的活性和醣基化相關的酵素活性，以驗證tau蛋白介導的病理機轉。我們的實驗結果顯示，酪蛋白激酶可能對tau造成的毒性扮演重要角色。
這項研究提供與tau蛋白相關的神經退化性疾病之致病機轉，對未來人們治療神經退化性疾病將有莫大的助益。

關鍵字

Tau蛋白

並列摘要

Tauopathies are a class of neurodegenerative diseases associated with the pathological aggregation of tau. Tau is a microtubule-associated protein predominantly expressed in nerve cells and its main function is to stabilize the microtubules and to regulate the dynamic of tubulin assembly. Accumulated studies have demonstrated that Tau hyperphosphorylation, nonphosphorylation and truncation play important roles for Tau-induced cytotoxicity. However, the question of whether Tau truncation or phosphorylation linking to the underlying pathogenic mechanism of tauopathies is under debates. To investigate which event is more critical for Tau-induced pathology, we generated transgenic flies with modified phosphorylation and truncation sites, and employed fly eye as a model to elucidate the effect of post-translational modification in tau-mediated toxicity in vivo. We found that hTau-E14FL and hTau-APFL have eye phenotype and further speculate that both hyperphosphorylated and nonphosphorylated full length hTau have detrimental effect. Interestingly, our data indicate that expressing truncated and psudophosphorylated hTau without the least twenty amino acids (hTau-E14421) only showed mild eye degeneration. Hence, we suggest that posttranslational modification of Tau C-terminus may be critical for Tau-induced pathology. Since the aforementioned C-terminal fragment contains a putative casein kinase site and a glycosylation site, we further manipulated casein kinase activity and glycosylated enzyme activity to validate the significance of the potential modifications. Based on the genetic data, we suggest that casein kinase may play a crucial role for tau-mediated neurotoxicity. This study may provide a mechanistic insight for developing the therapeutic targets for mitigating pathogenic tau-related neurodegeneration.

並列關鍵字

Tau ； Tauopathies

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