Glutamate is an essential mediator in glutamine-amplified insulin secretion

Guirong Han, Harumi Takahashi, Naoya Murao, Ghupurjan Gheni, Norihide Yokoi, Yoshiyuki Hamamoto, Shun ichiro Asahara, Yutaka Seino, Yoshiaki Kido, Susumu Seino

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)

Abstract

Aims/Introduction: Glutamine is the most abundant amino acid in the circulation. In this study, we investigated cell signaling in the amplification of insulin secretion by glutamine. Materials and Methods: Clonal pancreatic β-cells MIN6-K8, wild-type B6 mouse islets, glutamate dehydrogenase (GDH) knockout clonal β-cells (Glud1KOβCL), and glutamate-oxaloacetate transaminase 1 (GOT1) knockout clonal β-cells (Got1KOβCL) were studied. Insulin secretion from these cells and islets was examined under various conditions, and intracellular glutamine metabolism was assessed by metabolic flux analysis. Intracellular Ca2+ concentration ([Ca2+]i) was also measured. Results: Glutamine dose-dependently amplified insulin secretion in the presence of high glucose in both MIN6-K8 cells and Glud1KOβCL. Inhibition of glutaminases, the enzymes that convert glutamine to glutamate, dramatically reduced the glutamine-amplifying effect on insulin secretion. A substantial amount of glutamate was produced from glutamine through direct conversion by glutaminases. Glutamine also increased [Ca2+]i at high glucose, which was abolished by inhibition of glutaminases. Glutamic acid dimethylester (dm-Glu), a membrane permeable glutamate precursor that is converted to glutamate in cells, increased [Ca2+]i as well as induced insulin secretion at high glucose. These effects of glutamine and dm-Glu were dependent on calcium influx. Glutamine also induced insulin secretion in clonal β-cells MIN6-m14, which otherwise exhibit no insulin secretory response to glucose. Conclusions: Glutamate converted from glutamine is an essential mediator that enhances calcium signaling in the glutamine-amplifying effect on insulin secretion. Our data also suggest that glutamine exerts a permissive effect on glucose-induced insulin secretion.

Original languageEnglish
Pages (from-to)920-930
Number of pages11
JournalJournal of Diabetes Investigation
Volume12
Issue number6
DOIs
Publication statusPublished - 06-2021

All Science Journal Classification (ASJC) codes

  • Internal Medicine
  • Endocrinology, Diabetes and Metabolism

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