建立楓糖尿症的果蠅模型

Abstract

在台灣患有罕見疾病的嬰兒中，有大部分是屬於「先天性代謝異常疾病」，這類的疾病包括醣類和胺基酸代謝異常，較為有名的分別是半乳糖血症、肝糖屯積症、糖尿病、楓糖尿症以及苯酮尿症等，因為對於這些疾病的致病機制並不完全了解，所以對於這些疾病的治療方式比較傾向飲食控制，藉由控制攝入的食物來抑制病情發作。在這篇論文中，以果蠅為模式生物，建立患有楓糖尿症的病理模型，未來可以藉此探討楓糖尿症病患體內的支鏈甲型酮脫氫酵素複合物的異常，以及可能的治療方式。在果蠅基因中，CG1673、CG5599以及CG8199分別對照人類支鏈甲型酮脫氫酵素複合物中的支鏈氨基酸轉氨酶、二氫硫辛酰胺支鏈酰基轉移酶和3-甲基-2-氧代丁酸脫氫酶；首先，使用CRISPR / CAS 9的方法，來產生分別帶有三種基因突變的果蠅。接著確認了血淋巴多支鏈胺基酸含量在這些突變果蠅中有上升的現象，同時導致果蠅有腦部病變、行動力下降等病徵，而這些病徵和哺乳動物的楓糖尿症類似。同時在這項研究中，這些酵素的異常會導致果蠅脂肪內的三酸甘油脂無法儲存，而脂肪代謝與楓糖尿症間的關係在果蠅模型中尚未有明確的報導；此外，餵食果蠅含有雷帕黴素的食物可以延長楓糖尿症果蠅的壽命並且改善其爬行能力；同時，藉由這些果蠅，更進一步的了解microRNA-277和BCAA代謝酵素之間的關聯性。因此透過建立此果蠅模型，可以對於楓糖尿症的致病機制、併發症以及上下游的交互影響，提供一個快速的篩藥的方法來治療這種疾病。

The congenital metabolic disorder disease is a very common disease in Taiwan infant. This disease group includes the alteration of carbohydrates and amino acid metabolisms, such as galactosemia, glycogen storage disease, phenylketonuria, diabetes mellitus and maple syrup urine disease. Because the pathogenesis is not clear, diet control is the most common therapy strategy for patients. Patients control their food intakes to prevent these disease outbreak. In this research, Drosophila was used as animal models to mimic the symptoms of branched-chain α-keto acid dehydrogenase complex (BCKAD complex) dysfunction which correlates with the maple syrup urine disease (MSUD) to find the cure strategy. In Drosophila, three Branch-Chain amino acid (BCAA) catabolic enzymes called CG1673, CG5599, and CG8199. These three enzymes are homologs with branch chain aminotransferase, dihydro lipoyl transacylase (E2) and branched-chain alpha-keto acid decarboxylase (E1) in human were selected. Using CRISPR/Cas9 technology, three kinds of gene mutation flies were established. The results showed that the branched chain amino acids in hemolymph in mutant flies were higher than wild type. And their brain damage and climbing ability defect were more serious than wild type. In the experiment, fat storage problem was observed in these flies which had never been reported yet. At the same time, feeding rapamycin could rescue their lifespan and climbing abilities defect in mutant flies. Finally, the microRNA-277 which was one of the upstream controllers of BCAA catabolism pathway also be found in this research. Because of these reasons, these Drosophila models help us to know more about MSUD mechanisms, complications, the upstream and downstream of BCAA catabolic and even drug test more quickly.