以果蠅為模式動物探討UQCR-C1調控巴金森氏症之機制

Abstract

UQCR-C1 是電子傳遞鏈上ubiquinol-cytochrome c reductase complex 的蛋白質。我們合作團隊尚未發表之研究利用次世代全外顯子定序技術 (whole exome sequencing)，發現在一個巴金森氏症顯性遺傳家族中帶有UQCR-C1 點突變基因。為瞭解其功能，我以果蠅為模式動物，利用RNA干擾技術 (RNAi) 抑制其同源基因表現以及基因編輯術建立無效突變體 (null mutant)。全身性抑制果蠅UQCR-C1會使個體發育延遲且因此死亡；此現象可以被過表達人類的UQCR-C1所回復，代表UQCR-C1的功能在演化上具有保守性。只在成年時於肌肉抑制UQCR-C1會導致肌肉退化；而在神經中抑制UQCR-C1會導致神經傳導異常。在運動神經元中抑制UQCR-C1會降低果蠅攀爬能力，且在突觸後神經元之粒腺體數量減少。與RNA干擾術的結果相似，我發現果蠅UQCR-C1無效突變同樣會導致個體死亡，而全身性表達人類或是果蠅UQCR-C1 的cDNA能使這個現象回復，代表UQCR-C1是維持生命所必須的基因。 為瞭解 UQCR-C1 導致帕金森氏症的致病機轉，我們於果蠅檢測UQCR-C1和兩個常見的帕金森氏症基因突變，pink1 以及 parkin，之間的交互作用。在神經過表達parkin 無法改變抑制UQCR-C1所造成的損害；然而，在神經過表達UQCR-C1能夠部分回復失去pink1所造成的攀爬能力下降以及肌肉退化。因此，UQCR-C1和pink1 在遺傳學上似乎有所連結。已知pink1會調控粒腺體自噬 (mitophagy)，因此我們未來會檢測UQCR-C1對粒腺體自噬的調控。

UQCR-C1 is a component of the ubiquinol-cytochrome c reductase complex of the mitochondrial respiratory chain. Unpublished data from our collaborator suggest that point mutations in UQCR-C1 associate with parkinsonism in patients. However, the function of UQCR-C1 remains unknown. To investigate its endogenous function, I utilized both RNAi knockdown and CRIPSR/cas9-mediated knockout approaches in the model organism Drosophila. Ubiquitous knockdown of UQCR-C1 caused developmental delay that can be rescued by expressing human UQCR-C1, suggesting the essential role of UQCR-C1 in organismic viability is evolutionarily conserved. Tissue-specific knockdown of UQCR-C1 in indirect flight muscle at adult stage resulted in muscle degeneration in aged fly; whereas neuronal reduction of UQCR-C1 led to impairment in both neurotransmission and neuronal maintenance. Specifically, knockdown of UQCR-C1 in motor neuron led to both functional decline, as shown in climbing assay, and morphological defects, as indicated in the number of mitochondria in postsynaptic boutons. To verify the phenotypes of RNAi knockdown of UQCR-C1, we generated the UQCR-C1 knockout fly by deleting the whole open reading frame of UQCR-C1 locus. The mutant is homozygously lethal which can be rescued by ubiquitous expression of UQCR-C1, indicating that UQCR-C1 is essential for cellular homeostasis. To further investigate the role of UQCR-C1 in parkinsonism, we focus on its interaction between pink1 and parkin, both of which are linked to recessive Parkinson’s disease. Expression of Parkin in neurons could not rescue the neurotransmission defects where UQCR-C1 was knocked down. However, UQCR-C1 rescued the climbing defects and muscle degeneration in pink1 mutants. Since PINK1 regulates mitophagy to maintain mitochondrial function, in the future we will focus on the role of UQCR-C1 in mitophagy.