325-OR: ß-Arrestin 1 Regulates Glucagon-Like Peptide-1 Receptor Mediated Insulin Secretion in a Ligand-Dependent Manner

Incretin-based drugs are widely thought to act via a Gα_s/adenylate cyclase (AC)/cAMP pathway in β-cells. This model has been challenged by data demonstrating various glucagon-like peptide 1 receptor (GLP-1R) ligands differentially activate multiple signaling pathways including Gα_s, Gq, ERK, and β-arrestins. This ligand-mediated signaling bias implicates an array of intracellular mechanisms that regulate GLP-1R action and raises the possibility GLP-1R agonists can be optimized to enhance insulin secretion. We tested the hypothesis that β-arrestin 1 (βarr1), a critical GPCR effector, is necessary for the full insulinotropic action of GLP-1R agonists. The β-cell βarr1 knockout mice (βarr1^βcell-/-) used here have reduced Arrb1 expression in the β-cell, but not α- or Δ-cells; Arrb2 expression was unaffected. Islets isolated from βarr1^βcell-/-micehave increased glucose stimulated insulin secretion (GSIS) compared to controls. The enhanced GSIS in the knockout islets was ablated by the GLP-1R antagonist exendin-9. In addition, βarr1^βcell-/-islets treated with GLP-1 or exendin 4 (Ex4) have increased insulin release compared to controls. Conversely, βarr1 deletion did not impact the insulinotropic actions of glucagon, which signals through both the GLP-1R and the glucagon receptor (GCGR). Moreover, control and βarr1^βcell-/- islets produced similar insulin secretion in response to a GCGR specific agonist that does not signaling through GLP-1R and to glucose-dependent insulinotropic polypeptide. Together, these results indicate that βarr1 in β-cells selectively dampens the insulinotropic actions of the GLP-1R, but not the GCGR or GIP receptor. Thus, there is a specific interaction between the GLP-1R and βarr1 that points to divergent regulation between the insulinotropic class B G-protein coupled receptors in β-cells. This data implies that GLP-1R agonists that bias away from βarr1 may be more effective at stimulating insulin secretion.