以基因轉殖小鼠模式評估SCA17之神經治療藥物

Abstract

第十七型小腦脊隨萎縮症 (SCA17)是一種體染色體顯性遺傳的神經退化性疾病，患者通常會有共濟失調、肌張力不全、震顫麻痺、癡呆或癲癇等症狀。此疾病的發生主要是由於TATA box 結合蛋白(TBP)基因上CAG/CAA 三核苷酸過度擴增所致，此過度擴增會轉譯出多麩醯胺酸(polyglutamine)使TBP形成難溶性的不正常蛋白堆積在細胞中，進而造成細胞毒性，而這些不正常的蛋白也會造成TBP失去其正常功能，最終導致神經退化及死亡。為了研究此疾病，我們實驗室建立了SCA17基因轉殖小鼠，希望透過此動物模式來評估對SCA17有潛力的治療方式。組織切片培養是一種半活體系統，有別於一般的細胞培養，其可有效的模擬一個器官或組織中不同細胞之間交互作用的情形。我們透過SCA17基因轉殖小鼠的小腦組織切片培養來篩選對於SCA17有治療潛力的藥物。在篩選了二十一種藥物之後，我們發現四個藥物可以降低切片培養中Purkinje cell內不正常TBP之聚集，其中包括兩種植物萃取物NTNU312及NTNU319、一種組蛋白去乙醯化酶抑制劑(HDACi) splitomicin和由師大化學系姚清發老師合成的化合物NC004-6，這四種藥物均各具特色。近年來越來越多植物萃取物都被證實具有神經保護的功能；再者SCA17因TBP之突變導致細胞內轉錄功能異常，HDACi可藉由抑制組蛋白去乙醯化酶的活性調節組蛋白乙醯化的程度進而增加DNA的轉錄效率；而NC004-6是以黃酮的結構為基礎修飾而成的化合物，黃酮已經被證實具有抗氧化、抗發炎等功效，而氧化壓力與發炎亦正是不正常蛋白堆積所造成之致病機制之一。在初步的小量動物行為實驗中我們發現NC004-6、NTNU312及NTNU319皆能稍微改善SCA17小鼠的運動協調能力，此外，在病理分析上我們也看到給予NC004-6的組別，其小鼠的小腦重量有明顯的增加，表示NC004-6可能具有保護小腦避免萎縮的功效；我們也發現在給予NTNU319的組別其pRSK的表現量有明顯的增加，pRSK是ERK訊息傳遞的下游，能夠促進細胞存活。因此我們選擇了NC004-6、NTNU312及NTNU319這三支藥物進入大量動物實驗。我們發現給予了NC004-6的組別，在滾輪實驗及步態分析中皆能有效的改善運動行為能力及步態協調性，而給予了NTNU312及NTNU319的組別也能有效的改善SCA17小鼠在步態分析中的行為缺失。因此我們認為這三支藥物可能是具有潛力的治療藥物。Spinocerebellar ataxia 17 (SCA17) is an autosomal dominant and progressive neurodegenerative disease showing phenotypes with ataxia, dystonia, parkinsonism, dementia and seizures. SCA17 is caused by CAG/CAA excessive expansion in TATA box binding protein (TBP) gene, and the ploy-glutamine (polyQ)-expanded mutant TBP proteins form detergent-insoluble aggregates accumulate in Purkinje cells (PC) that may cause TBP lose its normal function and contribute to PC degeneration. To investigate the pathogenesis of SCA17, our lab has generated SCA17 mouse model and used it for potential therapeutic evaluation. Organotypic slice culture is a good semi-in vivo system because it can well mimic the interaction between different cell types within an organ. Through SCA17 mouse cerebellar slice culture system, we have screened 21 compounds/plant extracts and identified 4 potential ones that can reduce TBP aggregation, including two plant extracts, NTNU312 and NTNU319; one histone deacetylase inhibitor (HDACi), splitomicin; and one chemical compound, NC004-6, synthesized by Dr. Yao (Department of chemistry, NTNU). These 4 extracts/compounds have their own specific features. First of all, recent researches show plant extracts have benefits on neurodegenerative disease through neuron protective effect. In addition, transcription dysfunction caused by mutant TBP can be improved through HDACi regulating the acetylation of histones and increasing transcription efficiency. Moreover, inflammation and oxidation are two of the pathomechanism caused by mutant protein aggregation. NC004-6 was derived from the basis of flavone which is reported to have anti-inflammatory and antioxidative properties. In the pilot study, we found that NC004-6, NTNU312 and NTNU319 treatments could slightly improve motor coordination of SCA17 transgenic mice. Moreover, NC004-6 treatment protect cerebellum from atrophy while NTNU319 treatment upregulated pRSK expression level. pRSK is a downstream target of ERK pathway and promote cell survival. We therefore evaluate these three drugs in large scale test and found that NC004-6 could significantly rescue motor and coordination defects through both rotarod and footprint test, while NTNU312 and NTNU319 could also improve coordination deficiency in footprint test in SCA17 mice. We suggest these three drugs may be potential therapeutics for SCA17 disease.