Interruption Of Glucagon Signaling Increases Pancreas Mass

Interruption of glucagon signaling by glucagon receptor gene inactivation or treatment with a glucagon receptor blocking monoclonal antibody (GCGR-Ab) stimulates alpha cell proliferation and expansion. Surprisingly, pancreas weight is also increased in mice with GCG gene inactivation. To investigate mechanisms linking glucagon signaling and pancreas size, we treated C57BL/6J mice with GCGR-Ab or a control IgG. Eight weeks of treatment (N=4-15 mice/treatment) increased absolute pancreas weight (0.42±0.013 vs. 0.32±0.008; p<0.0001), pancreas weight normalized to body weight (1.39±0.03% vs. 1.11±0.02%; p<0.0001), and serum levels of 15 amino acids (AA), including glutamine (1.7-4.67 fold, p<0.0001). GCGR-Ab treatment promoted acinar cell proliferation (Ki67+, 0.65±0.14% vs. 0.20±0.03%; p=0.0058), increased acinar cell size (peri-islet region: 438.4±12.77 vs. 341.7±22.05μm2; p=0.0045; peripheral region: 431.1±9.34 vs. 334.2±25μm2, p=0.0055; central region: 437.0±10.45 vs. 338.7±13.6 μm2, p=0.0006), and increased pancreas protein content (248.3±9.84 vs. 194±8.67μg/mg tissue; p=0.0003). By electron microscopy, GCGR-Ab treatment increased acinar cell zymogen granule number (129±9 vs. 49±6; p<0.0001; n=28-37 cells/treatment) and led to acinar cell ER dilatation, but did not induce pancreatitis or alter acinar cell apoptosis or pancreatic macrophage number. Serum cholecystokinin and total glucagon-like peptide-1, trophic hormones linked to exocrine growth, were not changed by GCGR-Ab treatment. GCGR-Ab treatment upregulated mRNA and protein levels of the glutamine transporter, Slc38a3, and increased mTOR-related ribosomal protein S6 phosphorylation in acinar cells. Together, these data indicate that interruption of glucagon signaling increases pancreas mass by inducing acinar cell hyperplasia and hypertrophy and activates protein synthesis and mTOR signaling; whether this is mediated by elevated glutamine or AA levels is not known. Disclosure C. Dai: None. A. Bradley: None. K.C. Coate: None. G. Poffenberger: None. E. Spears: None. J.J. Wright: None. S. Shrestha: None. D. Dean: None. M. Brissova: None. A.C. Powers: None. Funding National Institutes of Health (DK117147)