ENU mutagenesis identifies mice with mitochondrial branched-chain aminotransferase deficiency resembling human maple syrup urine disease.
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 alpha-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.
Wu
Jer-Yuarn
JY
Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan, Republic of China.
Kao
Hsiao-Jung
HJ
Li
Sing-Chung
SC
Stevens
Robert
R
Hillman
Steven
S
Millington
David
D
Chen
Yuan-Tsong
YT
D000595:Amino Acid Sequence; D000597:Amino Acids, Branched-Chain / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D004195:Disease Models, Animal; D005038:Ethylnitrosourea / Q000494:pharmacology; D006801:Humans; D008375:Maple Syrup Urine Disease / Q000201:enzymology* / Q000235:genetics; D013058:Mass Spectrometry; D051379:Mice; D008928:Mitochondria / Q000201:enzymology* / Q000378:metabolism; D008969:Molecular Sequence Data; D009153:Mutagens / Q000494:pharmacology; D009154:Mutation; D000637:Transaminases / Q000172:deficiency* / Q000187:drug effects / Q000235:genetics
D000597:Amino Acids, Branched-Chain; D009153:Mutagens; D000637:Transaminases; C019798:branched-chain-amino-acid transaminase; D005038:Ethylnitrosourea