Maurice Wohl Clinical Neuroscience Institute, King's College London, 5 Cutcombe Road, London SE5 9RX, UK.
Department of Medicine, Biochemistry and Molecular Genetics, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.
Biol Open. 2024 Feb 15;13(2). doi: 10.1242/bio.060278. Epub 2024 Feb 28.
Mutations in genes that affect mitochondrial function cause primary mitochondrial diseases. Mitochondrial diseases are highly heterogeneous and even patients with the same mitochondrial disease can exhibit broad phenotypic heterogeneity, which is poorly understood. Mutations in subunits of mitochondrial respiratory complex I cause complex I deficiency, which can result in severe neurological symptoms and death in infancy. However, some complex I deficiency patients present with much milder symptoms. The most common nuclear gene mutated in complex I deficiency is the highly conserved core subunit NDUFS1. To model the phenotypic heterogeneity in complex I deficiency, we used RNAi lines targeting the Drosophila NDUFS1 homolog ND-75 with different efficiencies. Strong knockdown of ND-75 in Drosophila neurons resulted in severe behavioural phenotypes, reduced lifespan, altered mitochondrial morphology, reduced endoplasmic reticulum (ER)-mitochondria contacts and activation of the unfolded protein response (UPR). By contrast, weak ND-75 knockdown caused much milder behavioural phenotypes and changes in mitochondrial morphology. Moreover, weak ND-75 did not alter ER-mitochondria contacts or activate the UPR. Weak and strong ND-75 knockdown resulted in overlapping but distinct transcriptional responses in the brain, with weak knockdown specifically affecting proteosome activity and immune response genes. Metabolism was also differentially affected by weak and strong ND-75 knockdown including gamma-aminobutyric acid (GABA) levels, which may contribute to neuronal dysfunction in ND-75 knockdown flies. Several metabolic processes were only affected by strong ND-75 knockdown including the pentose phosphate pathway and the metabolite 2-hydroxyglutarate (2-HG), suggesting 2-HG as a candidate biomarker of severe neurological mitochondrial disease. Thus, our Drosophila model provides the means to dissect the mechanisms underlying phenotypic heterogeneity in mitochondrial disease.
影响线粒体功能的基因突变会导致原发性线粒体疾病。线粒体疾病高度异质，即使是患有相同线粒体疾病的患者也表现出广泛的表型异质性，这一点尚未得到很好的理解。线粒体呼吸复合物 I 的亚基突变会导致复合物 I 缺陷，从而导致严重的神经症状和婴儿期死亡。然而，一些复合物 I 缺陷患者的症状要轻得多。复合物 I 缺陷中最常见的突变核基因是高度保守的核心亚基 NDUFS1。为了模拟复合物 I 缺陷中的表型异质性，我们使用靶向果蝇 NDUFS1 同源物 ND-75 的不同效率的 RNAi 线进行研究。在果蝇神经元中强烈敲低 ND-75 会导致严重的行为表型、寿命缩短、线粒体形态改变、内质网 (ER)-线粒体接触减少和未折叠蛋白反应 (UPR) 的激活。相比之下，弱 ND-75 敲低只会导致更轻微的行为表型和线粒体形态改变。此外，弱 ND-75 不会改变 ER-线粒体接触或激活 UPR。弱和强 ND-75 敲低会导致大脑中重叠但不同的转录反应，弱敲低特异性影响蛋白酶体活性和免疫反应基因。代谢也受到弱和强 ND-75 敲低的不同影响，包括γ-氨基丁酸 (GABA) 水平，这可能导致 ND-75 敲低果蝇的神经元功能障碍。几种代谢过程仅受到强 ND-75 敲低的影响，包括戊糖磷酸途径和代谢物 2-羟基戊二酸 (2-HG)，这表明 2-HG 是严重神经线粒体疾病的候选生物标志物。因此，我们的果蝇模型为剖析线粒体疾病表型异质性的机制提供了手段。
