RF04 | PSUN135 Genetic Inactivation of Glutaminase Reduces Amino Acid Induced Alpha Cell Proliferation

Abstract Glucagon stimulates glycogenolysis and gluconeogenesis in liver resulting in increased hepatic glucose output. Thus, interrupting glucagon signaling in liver reduces blood glucose levels in animal models and individuals with diabetes. However, interrupting glucagon signaling also leads to hyperaminoacidemia and proliferation of glucagon secreting alpha cells, evidence of an endocrine liver-alpha cell axis. Among the high amino acids, we previously identified high glutamine levels are required for alpha cell proliferation. We recently found that glutaminase (GLS) is expressed in alpha cells at much higher levels than any other pancreatic endocrine cells. Additionally, mouse pancreatic islets cultured in high amino acid containing media and treated with the small molecule inhibitor of GLS (CB839) have reduced alpha cell proliferation (Vehicle: 7.6 ± 2.2%, 0.1µM CB839: 0.11 ± 0.05%**, 10µM: 0.02 ± 0.01%**; n=3-4, **p < 0.01). To further characterize the role of glutamine metabolism in glutamine-induced alpha cell proliferation, GLS activity was specifically knocked out in mouse alpha cells by breeding Gcg-CRE ERT2 with Glsflox mice (aGlsKO). Targeted deletion of Gls expression in most alpha cells was confirmed by staining for GLS and glucagon (aGlsWT: 95% GLS+, aGlsKO: 18% GLS+). Mice were treated with a glucagon receptor monoclonal antibody (GCGR mAb/mAb-4) for 10 days or with isotype control IgG. aGlsWT mice treated with GCGR mAb have robust alpha cell proliferation while aGlsKO mice treated with GCGR mAb for 10 days showed a 4.5-fold decrease in alpha cell proliferation and were similar to mice treated with the control IgG (aGlsWT Ab: 15.7 ± 3.6% alpha cell proliferation, aGlsWT IgG: 1.0 ± 0.4%***, aGlsKO Ab: 3.4 ± 0.6%**; n=4-6, ***p < 0.001). In addition, aGlsWT mice treated with GCGR mAb showed a robust activation of mTOR in alpha cells as measured by phospho-S6 expression while this was lost in aGlsKO mice treated with GCGR mAb. Induced expression of the mTOR-dependent glutamine transporter SLC38A5 was also lost (aGlsWT Ab: 25.0 ± 4.8% alpha cell SLC38A5 expression, aGlsWT IgG: 0.40 ± 0.27%***, aGlsKO Ab: 3.7 ± 3.5%***, n= 2-4, ***p < 0.001). Similar results on proliferation and mTOR activation in alpha cells were observed after 4 weeks of GCGR mAb treatment. Together these data suggest a critical role for glutamine metabolism via glutaminase in alpha cell proliferation. Presentation: Saturday, June 11, 2022 1:36 p.m. - 1:41 p.m., Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.