Mutations in mitochondrial enzyme GPT2 cause metabolic dysfunction and neurological disease with developmental and progressive features

Qing Ouyang, Tojo Nakayama, Ozan Baytas, Shawn M. Davidson, Chendong Yang, Michael Schmidt, Sofia B. Lizarraga, Sasmita Mishra, Malak Ei-Quessny, Saima Niaz, Mirrat Gul Butt, Syed Imran Murtaza, Afzal Javed, Haroon Rashid Chaudhry, Dylan J. Vaughan, R. Sean Hill, Jennifer N. Partlow, Seung Yun Yoo, Anh Thu N Lam, Ramzi NasirMuna Al-Saffar, A. James Barkovich, Matthew Schwede, Shailender Nagpal, Anna Rajab, Ralph J. DeBerardinis, David E. Housman, Ganeshwaran H. Mochida, Eric M. Morrow

Research output: Contribution to journalArticle

18 Scopus citations

Abstract

Mutations that cause neurological phenotypes are highly informative with regard to mechanisms governing human brain function and disease. We report autosomal recessive mutations in the enzyme glutamate pyruvate transaminase 2 (GPT2) in large kindreds initially ascertained for intellectual and developmental disability (IDD). GPT2 [also known as alanine transaminase 2 (ALT2)] is one of two related transaminases that catalyze the reversible addition of an amino group from glutamate to pyruvate, yielding alanine and α-ketoglutarate. In addition to IDD, all affected individuals show postnatal microcephaly and ∼80% of those followed over time show progressive motor symptoms, a spastic paraplegia. Homozygous nonsense p.Arg404∗ and missense p.Pro272Leu mutations are shown biochemically to be loss of function. The GPT2 gene demonstrates increasing expression in brain in the early postnatal period, and GPT2 protein localizes to mitochondria. Akin to the human phenotype, Gpt2-null mice exhibit reduced brain growth. Through metabolomics and direct isotope tracing experiments, we find a number of metabolic abnormalities associated with loss of Gpt2. These include defects in amino acid metabolism such as low alanine levels and elevated essential amino acids. Also, we find defects in anaplerosis, the metabolic process involved in replenishing TCA cycle intermediates. Finally, mutant brains demonstrate misregulated metabolites in pathways implicated in neuroprotective mechanisms previously associated with neurodegenerative disorders. Overall, our data reveal an important role for the GPT2 enzyme in mitochondrial metabolism with relevance to developmental as well as potentially to neurodegenerative mechanisms.

Original languageEnglish (US)
Pages (from-to)E5598-E5607
JournalProceedings of the National Academy of Sciences of the United States of America
Volume113
Issue number38
DOIs
StatePublished - Sep 20 2016

Keywords

  • GPT2
  • Intellectual and developmental disability
  • Metabolomics
  • Mitochondria
  • Spastic paraplegia

ASJC Scopus subject areas

  • General

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    Ouyang, Q., Nakayama, T., Baytas, O., Davidson, S. M., Yang, C., Schmidt, M., Lizarraga, S. B., Mishra, S., Ei-Quessny, M., Niaz, S., Butt, M. G., Murtaza, S. I., Javed, A., Chaudhry, H. R., Vaughan, D. J., Hill, R. S., Partlow, J. N., Yoo, S. Y., Lam, A. T. N., ... Morrow, E. M. (2016). Mutations in mitochondrial enzyme GPT2 cause metabolic dysfunction and neurological disease with developmental and progressive features. Proceedings of the National Academy of Sciences of the United States of America, 113(38), E5598-E5607. https://doi.org/10.1073/pnas.1609221113