Regulation of GLP-1 and Glucagon Receptor Function by β-Arrestins in Metabolically Important Cell Types

Glucagon-like peptide-1 (GLP-1) and glucagon (GCG) are polypeptides derived from a common precursor (preproglucagon) that modulates the activity of numerous cell types involved in regulating glucose and energy homeostasis. GLP-1 and GCG exert their biological functions via binding to specific G protein-coupled receptors (GLP-1Rs and GCGRs). Ligand-activated GLP-1Rs and GCGRs preferentially activate the heterotrimeric G protein G_s, resulting in increased cytosolic cAMP levels. However, activation of the two receptors also leads to the recruitment of β-arrestin-1 and -2 (βarr1 and βarr2, respectively) to the intracellular surface of the receptor proteins. The binding of β-arrestins to the activated receptors contributes to the termination of receptor-stimulated G protein coupling. In addition, receptor-β-arrestin complexes can act as signaling nodes in their own right by modulating the activity of many intracellular signaling pathways. In this Review, we will discuss the roles of βarr1 and βarr2 in regulating key metabolic functions mediated by activated GLP-1Rs and GCGRs. During the past decade, GLP-1R agonists have emerged as highly efficacious antidiabetic and antiobesity drugs. Moreover, dual agonists that stimulate both GLP-1Rs and GCGRs are predicted to offer additional therapeutic benefits as compared to GLP-1R agonist monotherapy. We will summarize and try to synthesize a series of studies suggesting that the development of G protein-biased GLP-1R and/or GCGR agonists, which do not lead to the recruitment of β-arrestins, may lead to even more efficacious therapeutic agents.