氏 名 大沼
ｵ ｵ ﾇ ﾏ康
ｺ ｳ平
ﾍ ｲ学 位 の 種 類 博士（理学）
学 位 記 番 号 理工博 第
330号 学位授与の日付 令和
2年
7月
16日
課程・論文の別 学位規則第４条第２項該当
学 位 論 文 題 名
Functional analyses of novel genes associated with mitochondrial diseases using Drosophila modelsショウジョウバエを用いた新規ミトコンドリア病関連遺伝子の機能 解析（英文）
論 文 審 査 委 員 主査 教授 相垣 敏郎 委員 教授 酒井 貴臣 委員 准教授 安藤 香奈絵
【論文の内容の要旨】
Mitochondria are essential for energy producing pathways including oxidative phosphorylation, fatty acid oxidation and Krebs cycle. Dysfunction of mitochondria causes rare, but serious physiological state, collectively called “mitochondrial diseases”, and can manifest with a wide range and complex symptoms involving various organs due to deficiency of cellular energy production. The heterogeneity in clinical presentation of the diseases makes it difficult to diagnose and manage them. Therefore, genetic testing is essential for definitive diagnosis for mitochondrial diseases. “Whole Exome Sequencing (WES)” has been increasingly used as a time and cost-effective method to discover nonsynonymous single nucleotide variations associated with diseases. To date, a number of candidate genes have been identified to be responsible for mitochondrial diseases. However, experimental verification is necessary to establish the pathogenicity of the variations/mutations in the candidate genes. In this thesis, I used Drosophila melanogaster as a model to investigate the function of novel candidate genes
for mitochondrial diseases.
Kohda et al. (2016) has performed WES for the patients diagnosed with mitochondrial diseases and identified 57 genes, each of which had a novel nonsynonymous variation associated with the disease. Among these candidates, I analyzed the functions of three genes, Ndufb11, mRpS23, and TTC37, using Drosophila models; RNAi-mediated gene knock down or loss-of-function mutant flies. First, I knocked down ndufb11 encoding NADH:ubiquinone oxidoreductase subunit B11, a complex I component of the mitochondrial respiratory chain and characterized their pathophysiological phenotypes. They showed decreased locomotor activity, oxygen consumption, short lifespan, increased levels of lactate and pyruvate, biomarker of mitochondrial dysfunction. The ndufb11 knockdown flies disrupted mitochondrial respiratory chain complex I assembly, indicating that the function of ndufb11 is required for the formation of mitochondrial respiratory complex I. Second, I showed that loss-of-function mutations in mRpS23 encoding mitochondrial ribosomal protein S23 were lethal, and that knock down of the gene reduced viability and the adult flies had decreased body weight with aberrant levels of metabolites in glycolysis and the TCA cycle. The knockdown flies were sensitive to rotenone, an inhibitor of mitochondrial respiratory complex I, and a translation inhibitor (chloramphenicol), suggesting that knockdown of mRpS23 impairs the translation system in mitochondria. Finally, I demonstrated that loss of ski3, a homolog of TTC37 (Tetratricopeptide Repeat Domain 37) caused pupal lethality, and the mutant larvae showed growth retardation, heart arrhythmia and hyperlipidemia with significant impacts on the levels of metabolic intermediates in glycolysis and the TCA cycle. The mutants were unable to maintain mitochondrial membrane potential and had reduced activities of mitochondrial
respiratory complexes. TTC37 is known as a causative gene of Tricho-Hepato-Enteric syndrome (THES) which has a variety of symptoms with multiple organs. Mitochondrial dysfunction caused by loss of ski3/TTC37 may underlie the pathophysiology of THES.
In conclusion, I have demonstrated that reduction or loss of Ndufb11,mRpS23, or ski3/TTC37 impairs mitochondrial functions in Drosophila. Mutations or deficiencies of these genes are most likely to cause symptoms of mitochondrial diseases.
