Amino Acid-Stimulated Alpha Cell Proliferation Requires Glutaminase Activity

Interrupted glucagon signaling reduces hyperglycemia. However, interrupted glucagon signaling increases serum amino acid and glucagon levels and stimulates amino acid-dependent alpha cell proliferation as part of an endocrine feedback loop, the liver-alpha cell axis. Our previous studies showed that glutamine and SLC38A5, a transporter of glutamine and other amino acids, are required for amino acid-stimulated alpha cell proliferation. To understand the mechanism of glutamine-stimulated proliferation, we analyzed published transcriptomics data for enzymes involved in the glutamine metabolism pathway and found 3-fold greater gene expression of glutaminase (Gls/GLS) in mouse and human alpha cells than in other pancreatic endocrine cells, while Gls2/GLS2 expression was extremely low in islet cells. Immunohistochemical analyses of mouse and human pancreata showed greater protein expression of GLS in islets versus the surrounding exocrine tissue. Within islets, both human and mouse alpha cells had higher expression than beta cells, suggesting that alpha cells may have increased capacity for glutamine metabolism. This expression pattern was also observed in individuals with either type 1 or type 2 diabetes. To examine the role of GLS activity in alpha cell proliferation, we treated the αTC1-6 mouse glucagonoma cell line with a competitive GLS inhibitor CB-839. GLS inhibition resulted in a 1.6-fold decrease in cell count over an 8-day cell growth assay (DMSO: (9.7 ± 1.3)x105, 10 μM CB-839: (6.2 ± 1.4)x105; n=2-4). In isolated mouse islets cultured in high glutamine and amino acid containing media, GLS inhibition inhibited alpha cell proliferation (DMSO: 7.6 ± 2.2%, 0.1 μM CB-839: 0.11 ± 0.05%**, 1.0 μM: 0.04 ± 0.02**, 10 μM: 0.02 ± 0.01%**, n=3-4, p<0.01). These data indicate that glutamine metabolism through GLS is critical for amino acid-dependent alpha cell proliferation in mice and support that alpha cells are unique amino acid sensors playing a critical role in amino acid homeostasis. Disclosure W. Siv: None. K. Sellick: None. A. Reuter: None. M. Shou: None. J. Stanley: None. E. Spears: None. W. Chen: None. D. Dean: None. Funding National Institutes of Health (DK117969, DK117147, DK020593); JDRF (2-SRA-2016-149-Q-R)