Overexpression of constitutively activated glutamate dehydrogenase induces insulin secretion through enhanced glutamate oxidation

Takatoshi Anno, Shunsuke Uehara, Hideki Katagiri, Yasuharu Ohta, Kohei Ueda, Hiroyuki Mizuguchi, Yoshinori Moriyama, Yoshitomo Oka, Yukio Tanizawa

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

Glutamate dehydrogenase (GDH) catalyzes reversible oxidative deamination of L-glutamate to α-ketoglutarate. Enzyme activity is regulated by several allosteric effectors. Recognition of a new form of hyperinsulinemic hypoglycemia, hyperinsulinism/hyperammonemia (HI/HA) syndrome, which is caused by gain-of-function mutations in GDH, highlighted the importance of GDH in glucose homeostasis. GDH266C is a constitutively activated mutant enzyme we identified in a patient with HI/HA syndrome. By overexpressing GDH266C in MIN6 mouse insulinoma cells, we previously demonstrated unregulated elevation of GDH activity to render the cells responsive to glutamine in insulin secretion. Interestingly, at low glucose concentrations, basal insulin secretion was exaggerated in such cells. Herein, to clarify the role of GDH in the regulation of insulin secretion, we studied cellular glutamate metabolism using MIN6 cells overexpressing GDH266C (MIN6-GDH266C). Glutamine-stimulated insulin secretion was associated with increased glutamine oxidation and decreased intracellular glutamate content. Similarly, at 5 mmol/1 glucose without glutamine, glutamine oxidation also increased, and glutamate content decreased with exaggerated insulin secretion. Glucose oxidation was not altered. Insulin secretion profiles from GDH266C-overexpressing isolated rat pancreatic islets were similar to those from MIN6-GDH266C, suggesting observation in MIN6 cells to be relevant in native [β-cells. These results demonstrate that, upon activation, GDH oxidizes glutamate to α-ketoglutarate, thereby stimulating insulin secretion by providing the TCA cycle with a substrate. No evidence was obtained supporting the hypothesis that activated GDH produced glutamate, a recently proposed second messenger of insulin secretion, by the reverse reaction, to stimulate insulin secretion.

Original languageEnglish
Pages (from-to)E280-E285
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Volume286
Issue number2 49-2
DOIs
Publication statusPublished - 2004 Feb

Keywords

  • Hyperinsulinism/hyperammonemia syndrome
  • Hypoglycemia
  • Islet of Langerhans

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Physiology
  • Physiology (medical)

Fingerprint Dive into the research topics of 'Overexpression of constitutively activated glutamate dehydrogenase induces insulin secretion through enhanced glutamate oxidation'. Together they form a unique fingerprint.

  • Cite this