Glucagon-Like Peptide 1 Inhibits Cell Apoptosis and Improves Glucose Responsiveness of Freshly Isolated Human Islets

Abstract

The peptide hormone, glucagon-like peptide 1 (GLP-1), has been shown to increase glucose-dependent insulin secretion, enhance insulin gene transcription, expand islet cell mass, and inhibit beta-cell apoptosis in animal models of diabetes. The aim of the present study was to evaluate whether GLP-1 could improve function and inhibit apoptosis in freshly isolated human islets. Human islets were cultured for 5 d in the presence, or absence, of GLP-1 (10 nm, added every 12 h) and studied for viability and expression of proapoptotic (caspase-3) and antiapoptotic factors (bcl-2) as well as glucose-dependent insulin production. We observed better-preserved three-dimensional islet morphology in the GLP-1-treated islets, compared with controls. Nuclear condensation, a feature of cell apoptosis, was inhibited by GLP-1. The reduction in the number of apoptotic cells in GLP-1-treated islets was particularly evident at d 3 (6.1% apoptotic nuclei in treated cultures vs. 15.5% in controls; P < 0.01) and at d 5 (8.9 vs. 18.9%; P < 0.01). The antiapoptotic effect of GLP-1 was associated with the down-regulation of active caspase-3 (P < 0.001) and the up-regulation of bcl-2 (P < 0.01). The effect of GLP-1 on the intracellular levels of bcl-2 and caspase-3 was observed at the mRNA and protein levels. Intracellular insulin content was markedly enhanced in islets cultured with GLP-1 vs. control (P < 0.001, at d 5), and there was a parallel GLP-1-dependent potentiation of glucose-dependent insulin secretion (P < 0.01 at d 3; P < 0.05 at d 5). Our findings provide evidence that GLP-1 added to freshly isolated human islets preserves morphology and function and inhibits cell apoptosis.