NAD+ regeneration rescues lifespan but not ataxia in a mouse model of brain mitochondrial complex I dysfunction

Mitochondrial complex I regenerates NAD+ and proton pumps for TCA cycle function and ATP production, respectively. Mitochondrial complex I dysfunction has been implicated in many brain pathologies including Leigh Syndrome and Parkinson's disease. We sought to determine whether NAD+ regeneration or proton pumping is the dominant function of mitochondrial complex I in protection from brain pathology. We generated a mouse that conditionally expresses the yeast NDI1 protein, a single enzyme that can replace the NAD+ regeneration capability of the 45-subunit mammalian mitochondrial complex I without proton pumping. NDI1 expression was sufficient to dramatically prolong lifespan without significantly improving motor function in a mouse model of Leigh Syndrome. Therefore, mitochondrial complex I activity in the brain supports organismal survival through its NAD+ regeneration capacity, while optimal motor control requires the bioenergetic function of mitochondrial complex I. RNA sequencing of mouse cerebellum tissue, 24 total samples, 3 male and 3 female biological replicates for 4 different genotype groups. Cre control mice, NDI1 expressing control mice, cKO mice, and cKO+NDI1 mice.线粒体复合物I（mitochondrial complex I）可分别介导烟酰胺腺嘌呤二核苷酸（nicotinamide adenine dinucleotide，NAD+）再生与质子泵功能：前者支撑三羧酸循环（tricarboxylic acid cycle，简称TCA）的正常运转，后者为三磷酸腺苷（adenosine triphosphate，ATP）的合成提供能量支持。线粒体复合物I功能异常与多种脑部病理过程密切相关，涵盖利氏综合征（Leigh Syndrome）与帕金森病（Parkinson's disease）等病症。本研究旨在明确：在抵御脑部病理损伤的过程中，线粒体复合物I的核心功能究竟为NAD+再生，还是质子泵功能。我们构建了可条件性表达酵母源NDI1蛋白的小鼠模型，该单一酶可替代由45个亚基组成的哺乳动物线粒体复合物I的NAD+再生功能，且不具备质子泵活性。在利氏综合征小鼠模型中，仅通过NDI1的表达即可显著延长小鼠的生存期，但无法有效改善其运动功能。由此可见，脑部线粒体复合物I可通过其NAD+再生能力维持机体存活，而精准的运动控制则依赖于线粒体复合物I的生物能量功能。本研究对小鼠小脑组织开展了RNA测序，共计24个样本；4种不同基因型组别各设置3只雄性与3只雌性生物学重复，4个组别分别为：Cre对照小鼠、表达NDI1的对照小鼠、条件性敲除（conditional knockout，cKO）小鼠以及cKO+NDI1小鼠。