Increased SLC38A4 Amino Acid Transporter Expression in Human Pancreatic α-Cells After Glucagon Receptor Inhibition.

Plasma amino acids and their transporters constitute an important part of the feedback loop between the liver and pancreatic alpha-cell function, and glucagon regulates hepatic amino acid turnover. Disruption of hepatic glucagon receptor action activates the loop and results in high plasma amino acids and hypersecretion of glucagon associated with alpha-cell hyperplasia. In the present study, we report a technique to rescue implanted human pancreatic islets from the mouse kidney capsule. Using this model, we have demonstrated that expression of the amino acid transporter SLC38A4 increases in alpha-cells after administration of a glucagon receptor blocking antibody. The increase in SLC38A4 expression and associated alpha-cell proliferation was dependent on mechanistic target of rapamycin pathway. We confirmed increased alpha-cell proliferation and expression of SLC38A4 in pancreas sections from patients with glucagon cell hyperplasia and neoplasia (GCHN) with loss-of-function mutations in the glucagon receptor. Collectively, using a technique to rescue implanted human islets from the kidney capsule in mice and pancreas sections from patients with GCHN, we found that expression of SLC38A4 was increased under conditions of disrupted glucagon receptor signaling. These data provide support for the existence of a liver-human alpha-cell endocrine feedback loop.