ENU mutagenesis identifies mice with mitochondrial branched-chain aminotransferase deficiency resembling human maple syrup urine disease
ENU mutagenesis identifies mice with mitochondrial branched-chain aminotransferase deficiency resembling human maple syrup urine disease
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DOI：
10.1172/jci200419574
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发表时间：
2004-02-01
影响因子：
15.9
通讯作者：
Chen, YT
中科院分区：
文献类型：
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作者：
Wu, JY;Kao, HJ;Chen, YT
应用串联质谱法检测了N-乙基-N-亚硝基脲（ENU）处理小鼠的氨基酸和脂肪酸代谢途径的紊乱。我们发现小鼠血液支链氨基酸（BCAAs）显著升高，酮酸尿症，临床特征类似于人类枫糖浆尿病（MSUD），一种严重的遗传代谢紊乱引起的缺乏支链α-酮酸脱氢酶（BCKD）复合物。然而，BCKD基因和酶活性正常。支链氨基转移酶基因（Bcat）的测序结果显示，在胞质亚型（Bcat-1）没有突变，但在线粒体亚型（Bcat-2）中发现了一个纯合剪接位点突变。该突变导致外显子2缺失，BCAT-2 mRNA显著降低，BCAT-2蛋白及其酶活性缺乏。受影响的小鼠对BCAA限制饮食有反应，临床症状改善，氨基酸模式正常化。我们的结论是，BCAT-2缺乏症的小鼠可能会导致一种疾病，模仿人类MSUD。这些小鼠为研究支链氨基酸代谢及其毒性提供了重要的动物模型。代谢组学引导的筛选，加上ENU诱变，是一个强大的方法，在发现新的酶的缺陷和识别遗传代谢紊乱的重要途径。
Tandem mass spectrometry was applied to detect derangements in the pathways of amino acid and fatty acid metabolism in N-ethyl-N-nitrosourea-treated (ENU-treated) mice. We identified mice with marked elevation of blood branched-chain amino acids (BCAAs), ketoaciduria, and clinical features resembling human maple syrup urine disease (MSUD), a severe genetic metabolic disorder caused by the deficiency of branched-chain a-keto acid dehydrogenase (BCKD) complex. However, the BCKD genes and enzyme activity were normal. Sequencing of branched-chain aminotransferase genes (Bcat) showed no mutation in the cytoplasmic isoform (Bcat-1) but revealed a homozygous splice site mutation in the mitochondrial isoform (Bcat-2). The mutation caused a deletion of exon 2, a marked decrease in Bcat-2 mRNA, and a deficiency in both BCAT-2 protein and its enzyme activity. Affected mice responded to a BCAA-restricted diet with amelioration of the clinical symptoms and normalization of the amino acid pattern. We conclude that BCAT-2 deficiency in the mouse can cause a disease that mimics human MSUD. These mice provide an important animal model for study of BCAA metabolism and its toxicity. Metabolomics-guided screening, coupled with ENU mutagenesis, is a powerful approach in uncovering novel enzyme deficiencies and recognizing important pathways of genetic metabolic disorders.