Genetic and biased agonist-mediated reductions in β-arrestin recruitment prolong cAMP signalling at glucagon family receptors

Abstract

Receptors for the peptide hormones glucagon-like peptide-1 (GLP-1R), glucose-dependent insulinotropic polypeptide (GIPR) and glucagon (GCGR) are important regulators of insulin secretion and energy metabolism. GLP-1R agonists have been successfully deployed for the treatment of type 2 diabetes, but it has been suggested that their efficacy is limited by target receptor desensitisation and downregulation due to recruitment of β-arrestins. Indeed, recently described GLP-1R agonists with reduced β-arrestin-2 recruitment have delivered promising results in preclinical and clinical studies. We therefore aimed to determine if the same phenomenon could apply to the closely related GIPR and GCGR. In HEK293 cells depleted of both β-arrestin isoforms the duration of G protein-dependent cAMP/PKA signalling was increased in response to the endogenous ligand for each receptor. Moreover, in wild-type cells, “biased” GLP-1, GCG and GIP analogues with selective reductions in β-arrestin-2 recruitment led to reduced receptor endocytosis and increased insulin secretion over a prolonged stimulation period, although the latter effect was only seen at high agonist concentrations. Biased GCG analogues increased the duration of cAMP signalling, but this did not lead to increased glucose output from hepatocytes. Our study provides a rationale for development of GLP-1R, GIPR and GCGR agonists with reduced β-arrestin recruitment, but further work is needed to maximally exploit this strategy for therapeutic purposes.