評估海藻糖對第十七型脊髓小腦萎縮症小鼠及組織切片培養之作用

Abstract

脊髓小腦萎縮症 (Spinocerebellar ataxia, SCA) 是一種體染色體顯性的遺傳性疾病，患有 SCA 的患者會因為小腦和脊髓的神經細胞發生退化，而導致病人有運動失調等症狀出現。現在已知導致 SCA 的原因多半是因特定基因某些重複核苷片段過度擴增所致。SCA17 是眾多 SCA 的其中一亞型，研究發現導致 SCA17發病的原因為染色體 6q27 位置上的 TATA-Box Binding Protein (TBP) 基因CAG 過度擴增，而導致 TBP N-terminal的Polyglutamine (polyQ) 過長，使得 TBP 在細胞內形成不溶性的聚集物 (detergent-insoluble aggregate)，令神經細胞功能異常而退化，然而 SCA17 的整體病理路徑至今仍未十分清楚。小腦組織切片培養 (Cerebellar organotyptic culture) 是一種可以觀察小腦神經細胞發育、神經細胞排列狀況以及神經細胞存活率的有效平台。由於SCA17的病人多在中年後發病，但神經細胞退化的情形在明顯的外顯病徵前就已經開始進行，因此我們試圖以 SCA17 基因轉殖小鼠之小腦組織切片培養作為一分析平台，利用此模式可直接觀察在 SCA1 7發病前神經細胞的發展，除了可進一步了解 SCA17 的致病成因外，並可作為藥物測試之初步模式。海藻糖被報導出在許多疾病中具有預防蛋白質降解和防止蛋白質聚集 (aggregation) 的情形，例如阿茲海默氏症 (Alzheimer’s disease, AD) 杭丁頓氏舞蹈症 (Huntington’s diseases, HD)，脊髓小腦萎縮症第十四型 (SCA 14) 和其他的poly Q 神經退化性疾病。在本研究中，我們運用小腦組織切片培養來評估海藻糖對於 SCA17 的治療效果。我們的結果顯示出 TBP aggregation 會在小腦組織切片培養中的 Purkinje cell 中在體外培養第三天 (DIV3 )發生，而聚集的情形會在 SCA17 的 DIV7 小腦組織切片培養中越來越明顯。然而，我們發現在加入海藻糖後，TBP aggregation的情形有明顯下降的現象。為了要了解海藻糖在體內的治療效果，我們將海藻糖加入 SCA17 基因轉殖小鼠的飲用水中，並藉由行為實驗和病理分析來了解海藻糖對於 SCA17的療效。結果發現，飲用有加入海藻糖的 SCA17 基因轉殖小鼠，其 rota-rod 的平衡能力，footprint的檢測實驗都有顯著回復的情形，而且飲用有加入海藻飲用水的基因轉殖小鼠，其神經膠細胞的發炎反應亦有回復的情形。綜合上述結果，顯示海藻糖應該是一對於 SCA17 具有療效的潛力藥物。

Spinocerebellar ataxia (SCA) is an autosomal dominant and progressive neurodegenerative disease chartered by ataxia, parkinsonism, dementia and seizures. Although there remains lots unclarified mechanism in SCA17, it is believed that the mutation on the TATA box binding protein (TBP) is responsible for the disease. The CAG repeat expansion of TBP gene leads to the reduced solubility of polyglutamine (polyQ) TBP and induces aggregate formation. For TBP plays an important role in transcription initiation, the abnormal aggregate is believed to cause neuron degeneration especially in the cerebellar Purkinje cells. Cerebellar organotypic culture is a system which could provide research evidence on tissue level. In addition, the cerebellar organotypic culture could provide the normal interaction between Purkinje cells and the other cells in vitro. We have established this system to study and monitor the cerebellar cell development, neuron survival, Purkinje cell aggregate forming and death and for a drug screening platform. Trehalose is reported to prevent protein degradation and aggregate formation in several disease models, including Huntington’s diseases, Alzheimer's disease, SCA14 and some other neurodegenerative diseases caused by polyQ expansion. In this study, we evaluated the therapeutic effect of trehalose using SCA17 cerebellar organotypic culture system. Our results showed that TBP aggregation formed in the Purkinje cells at in vitro day 3 (DIV3) and became more obvious at DIV7 in the SCA17 cerebellar slice culture. Furthermore, we found that the TBP aggregation significant decreased in our slice culture at DIV7 after treatment with trehalose. To identify the effect of trehalose in vivo, trehalose supplied in the drinking water of SCA17 transgenic mice was conducted. In the behavior test, we found that mice drinking trehalose ameliorated their hyperactivity and improved their coordination in rotarod test. Furthermore, we confirmed that the calbindin expression level was upregulated in the trehalose treatment mouse cerebellum. In addition, the cerebellum size in trehalose treatment mouse is bigger than that of vehicle treatment mouse. In our 4% trehalose treatment study, we found the gait behavior and motor coordination of SCA17 mice were rescued in the footprint and rotarod task, respectively. We also could observe the astrocyte gliosis performance was downregulated after trehalose treatment. However, the microglia cell was activated especially in transgenic trehalose treatment group. Furthermore, the MnSOD was also upregulated after trehalose treatment. These data suggest that trehalose could be a potential non-toxic treatment for SCA17.