Glucagon receptor blockage inhibits ß-cell dedifferentiation through FoxO1.

ABSTRACT

Glucagon-secreting pancreatic α-cells play pivotal roles in the development of diabetes. Glucagon promotes insulin secretion from ß-cells. However, the long-term effect of glucagon on the function and phenotype of ß-cells had remained elusive. In this study, we found that long-term glucagon intervention or glucagon intervention with the presence of palmitic acid downregulated ß-cell-specific markers and inhibited insulin secretion in cultured ß-cells. These results suggested that glucagon induced ß-cell dedifferentiation under pathological conditions. Glucagon blockage by a glucagon receptor (GCGR) monoclonal antibody (mAb) attenuated glucagon-induced ß-cell dedifferentiation. In primary islets, GCGR mAb treatment upregulated ß-cell-specific markers and increased insulin content, suggesting that blockage of endogenous glucagon-GCGR signaling inhibited ß-cell dedifferentiation. To investigate the possible mechanism, we found that glucagon decreased FoxO1 expression. FoxO1 inhibitor mimicked the effect of glucagon, whereas FoxO1 overexpression reversed the glucagon-induced ß-cell dedifferentiation. In db/db mice and ß-cell lineage-tracing diabetic mice, GCGR mAb lowered glucose level, upregulated plasma insulin level, increased ß-cell area, and inhibited ß-cell dedifferentiation. In aged ß-cell-specific FoxO1 knockout mice (with the blood glucose level elevated as a diabetic model), the glucose-lowering effect of GCGR mAb was attenuated and the plasma insulin level, ß-cell area, and ß-cell dedifferentiation were not affected by GCGR mAb. Our results proved that glucagon induced ß-cell dedifferentiation under pathological conditions, and the effect was partially mediated by FoxO1. Our study reveals a novel cross talk between α- and ß-cells and is helpful to understand the pathophysiology of diabetes and discover new targets for diabetes treatment.NEW & NOTEWORTHY Glucagon-secreting pancreatic α-cells can interact with ß-cells. However, the long-term effect of glucagon on the function and phenotype of ß-cells has remained elusive. Our new finding shows that long-term glucagon induces ß-cell dedifferentiation in cultured ß-cells. FoxO1 inhibitor mimicks whereas glucagon signaling blockage by GCGR mAb reverses the effect of glucagon. In type 2 diabetic mice, GCGR mAb increases ß-cell area, improves ß-cell function, and inhibits ß-cell dedifferentiation, and the effect is partially mediated by FoxO1.