Fibroblast growth factor 21 (FGF21) and glucagon-like peptide 1 contribute to diabetes resistance in glucagon receptor-deficient mice

Abstract

Mice genetically deficient in the glucagon receptor (Gcgr-/-) show improved glucose tolerance, insulin sensitivity, and a-cell hyperplasia. In addition, Gcgr-/- mice do not develop diabetes after chemical destruction of β-cells. Since fibroblast growth factor 21 (FGF21) has insulin-independent glucose-lowering properties, we investigated whether FGF21 was contributing to diabetes resistance in insulin-deficient Gcgr-/- mice. Plasma FGF21 was 25-fold higher in Gcgr-/- mice than in wild-type mice. FGF21 was found to be expressed in pancreatic b- and a-cells, with high expression in the hyperplastic a-cells of Gcgr-/- mice. FGF21 expression was also significantly increased in liver and adipose tissue of Gcgr-/- mice. To investigate the potential antidiabetic actions of FGF21 in insulindeficient Gcgr-/- mice, an FGF21-neutralizing antibody was administered prior to oral glucose tolerance tests (OGTTs). FGF21 neutralization caused a decline in glucose tolerance in insulindeficient Gcgr-/- mice during the OGTT. Despite this decline, insulin-deficient Gcgr-/- mice did not develop hyperglycemia. Glucagon-like peptide 1 (GLP-1) also has insulin-independent glucoselowering properties, and an elevated circulating level of GLP-1 is a known characteristic of Gcgr-/- mice. Neutralization of FGF21, while concurrently blocking the GLP-1 receptor with the antagonist Exendin 9-39 (Ex9-39), resulted in significant hyperglycemia in insulin-deficient Gcgr-/- mice, while blocking with Ex9-39 alone did not. In conclusion, FGF21 acts additively with GLP-1 to prevent insulinopenic diabetes in mice lacking glucagon action. © 2014 by the American Diabetes Association.