Regulation of mitochondrial function by folate enzyme ALDH1L2 in health and disease

2010年，PI的实验室发现了线粒体叶酸酶ALDH1L2，其生理作用尚不清楚。该酶催化N aDP++10-甲酰基四氢叶酸→NADPH+Co2+四氢叶酸的反应，该反应对线粒体叶酸结合的单碳基氧化生成NADPH具有重要作用。为了支持这一功能，我们最近的基因敲除实验表明，Aldh1l2基因的缺失会导致小鼠氧化应激增加。此外，Aldh1l2-/-小鼠出现溃疡性皮炎，脾高度增大(4倍)，代谢型广泛改变。这些表型背后的机制基础目前尚不清楚，但具有临床意义，因为最近发现了ALDH1L2突变患者，他们被诊断为一种罕见的神经皮肤病或自闭症谱系障碍。我们对患者成纤维细胞的代谢组学分析发现，细胞脂质代谢发生了戏剧性的变化，这种结果很可能是由线粒体CoA依赖的脂肪酸代谢障碍引起的。这会导致线粒体功能障碍，表现为能量产生不足和氧化应激。进一步支持这一机制的是，ALDH1L2缺陷患者的成纤维细胞线粒体碎裂，并显示出脂滴的积累。重要的是，这些成纤维细胞中ALDH1L2酶的修复挽救了表型和代谢型，使这些细胞类似于健康个体的成纤维细胞。基于这些发现，我们假设ALDH1L2在细胞中具有不同的代谢功能，通过与叶酸循环相关的线粒体NADPH的产生来维持氧化还原状态。ALDH1L2的缺失导致线粒体功能障碍、能量失衡和氧化应激。因此，ALDH1L2基因的有害突变是与线粒体相关的人类疾病/疾病的根本原因。这项提议将确定ALDH1L2在细胞代谢中的作用，并将通过以下目的将其突变与人类疾病的致病因素联系起来：(1)检验ALDH1L2维持线粒体氧化还原平衡并控制辅酶A生物合成和脂肪酸氧化的假设。(2)确定ALDH1L2在一碳基团在能量产生或线粒体到细胞质穿梭之间的分配中的作用。(3)确定ALDH1L2缺乏是人类罕见遗传性疾病的原因，并探索其潜在机制。现在清楚的是，线粒体功能障碍是许多以前没有发现的疾病的病理生理学的重要组成部分。ALDH1L2在维持线粒体功能中的作用，以及在线粒体相关疾病中的作用，在很大程度上尚不清楚。这项建议将填补这一知识空白，并将提供对ALDH1L2在人类疾病中的作用的机械性洞察。

The physiological role of the mitochondrial folate enzyme ALDH1L2, discovered by the PI's lab in 2010, is not well understood. This enzyme catalyzes the reaction: NADP+ + 10-formyltetrahydrofolate → NADPH + CO2 + tetrahydrofolate, which can be important for the mitochondrial NADPH production from the oxidation of folate- bound one-carbon groups. In support of this function, our recent gene knockout experiments show that deletion of Aldh1l2 in mice causes increased oxidative stress. Furthermore, Aldh1l2-/- mice develop ulcerative dermatitis, and have highly enlarged (4-fold) spleen and extensively altered metabotype. The mechanistic basis underlying these phenotypes is currently unknown but has clinical relevance given the recent identification of patients with ALDH1L2 mutations who were diagnosed with a rare neurocutaneous disease or autistic spectrum disorder. Our metabolomics analysis of patient's fibroblasts identified dramatic changes in the cellular lipid repertoire, the outcome most likely caused by the impairment of mitochondrial CoA-dependent fatty acid metabolism. This leads to mitochondrial dysfunction, which is manifested as insufficient energy production and oxidative stress. In further support of this mechanism, fibroblasts from ALDH1L2-deficient patients have fragmented mitochondria and show the accumulation of lipid droplets. Importantly, the restoration of the ALDH1L2 enzyme in these fibroblasts rescues the phenotype and metabotype, making these cells similar to fibroblasts from healthy individuals. Based on these findings, we hypothesize that ALDH1L2 serves distinct metabolic function in the cell, the maintenance of redox state through the mitochondrial NADPH generation linked to the folate cycle. The loss of ALDH1L2 leads to mitochondrial dysfunction, energy disbalance and oxidative stress. Thus, deleterious mutations in the ALDH1L2 gene are underlying cause of mitochondria-related human disorders/diseases. This proposal will determine the role of ALDH1L2 in cellular metabolism and will link its mutations as causative factor of human diseases through the following aims: (1) Test the hypothesis that ALDH1L2 maintains mitochondrial redox balance and controls coenzyme A biosynthesis and fatty acid oxidation. (2) Define the role of ALDH1L2 in partitioning of one-carbon groups between energy production or mitochondria to cytoplasm shuttling. (3) Establish ALDH1L2 deficiency as the cause of rare genetic disorders in humans and explore underlying mechanisms. It is now clear that mitochondrial dysfunction is an important component in the pathophysiology of numerous diseases that had not been previously identified. The role of ALDH1L2 in maintenance of mitochondrial function, as well as in mitochondria-related diseases, is largely unexplored. This proposal will fill this knowledge gap and will provide mechanistic insight into the role of ALDH1L2 in human diseases.