1581-P: Systemic Alteration of Amino Acids Metabolism in Glutamate Dehydrogenase Gain-of-Function Mutation Knockin Mice

Abstract

Patients with gain-of-function (GoF) mutations of glutamate dehydrogenase (GDH) have protein-sensitive hypoglycemia, hyperammonemia, epilepsy, and intellectual disability (HI/HA syndrome). Studies of mouse models with a beta-cell specific expression of H454Y hGDH suggest that the mechanisms of HI are caused by increased glutaminolysis induced by GDH GoF in islets. However, the mechanism of hyperammonemia is still unknown. In order to study the systemic effects of GDH GoF, H454Y GDH knockin mice (H454Y-GDH-KI) were created. Enzyme kinetic of GDH in the brain, kidney and liver confirmed that H454Y was successfully expressed with impaired GTP inhibition. H454Y-GDH-KI mice have a ~2.5-fold elevation of plasma ammonia and fasting hypoglycemia, similar to HI/HA patients. Tissues (brain, liver and kidney) and plasma amino acids profiles were determined by LC-MS. Compared to wildtype, the amino acids profile in the kidney was unaltered in KI mice. In contrast, KI liver had 60% lower glutamine, unchanged glutamate and aspartate, increased branch chain amino acids, etc. The glutamine of KI brain was 40% lower than the wildtype, glutamate and GABA was unchanged. Interestingly, plasma glutamine in KI mice was 30% higher compared to controls. A similar phenomenon has also been observed in HI/HA patients. We hypothesize that hyperammonemia is mainly caused by the increased glutaminolysis in KI liver. Higher plasma glutamine can be explained by the increased activity of tissue glutamine synthetase (GS). GS and glutamine serve as an ammonia sink, which is the main mechanism for the removal of increased ammonia in KI mice. We therefore applied the GS inhibitor, methionine sulfoximine (MSO) to KI mice. MSO significantly increased ammonia levels in KI mice after a single dose of injection. These studies in H454Y-GDH-KI mice suggest that GDH GoF in the liver is the main cause of hyperammonemia. GS plays an important role in ammonia removal. Disclosure C.Su: None. D.Han: Employee; Nanjing AscendRare Pharmaceutical Technology. S.Meng: Employee; Nanjing AscendRare Pharmaceutical Technology. Q.Zhu: Employee; Nanjing AscendRare Pharmaceutical Technology. X.Zhou: Employee; Nanjing AscendRare Pharmaceutical Technology. H.Jiang: None. J.Li: None. C.Gong: None. C.Li: Employee; Hua Medicine, Nanjing AscendRare Pharmaceutical Technology. Funding Beijing Natural Science Foundation (L212037)