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

PI实验室在2010年发现的线粒体叶酸酶ALDH 1 L2的生理作用还没有得到很好的理解。这种酶催化反应：NADP++10-甲酰四氢叶酸→ NADPH + CO2 +四氢叶酸，这对于由叶酸结合的一碳基团氧化产生线粒体NADPH可能是重要的。为了支持这一功能，我们最近的基因敲除实验表明，小鼠中Aldh 1 l2的缺失会导致氧化应激增加。此外，Aldh 1 l2-/-小鼠发生溃疡性皮炎，脾脏高度增大（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，但鉴于最近发现的ALDH 1 L2突变患者被诊断患有罕见的神经皮肤疾病或自闭症谱系障碍，因此具有临床相关性。我们对患者成纤维细胞的代谢组学分析确定了细胞脂质谱的显著变化，结果最有可能是由线粒体CoA依赖性脂肪酸代谢受损引起的。这导致线粒体功能障碍，表现为能量产生不足和氧化应激。为了进一步支持这种机制，来自ALDH 1 L2缺陷患者的成纤维细胞具有破碎的线粒体并显示脂滴的积累。重要的是，这些成纤维细胞中ALDH 1 L2酶的恢复挽救了表型和代谢型，使这些细胞与健康个体的成纤维细胞相似。基于这些发现，我们假设ALDH 1 L2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生成来维持氧化还原状态。ALDH 1 L2的缺失导致线粒体功能障碍、能量失衡和氧化应激。因此，ALDH 1 L2基因中的有害突变是与Escherichia相关的人类病症/疾病的潜在原因。本研究将通过以下目的确定ALDH 1 L2在细胞代谢中的作用，并将其突变与人类疾病的致病因素联系起来：（1）检验ALDH 1 L2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)定义ALDH 1 L2在能量产生或线粒体到细胞质穿梭之间的一碳基团分配中的作用。(3)确定ALDH 1 L2缺乏是人类罕见遗传疾病的原因，并探索潜在的机制。现在很清楚，线粒体功能障碍是许多以前未被确定的疾病的病理生理学中的重要组成部分。ALDH 1 L2在维持线粒体功能以及与线粒体相关的疾病中的作用在很大程度上未被探索。该提案将填补这一知识空白，并将为ALDH 1 L2在人类疾病中的作用提供机制性见解。

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.