Unimolecular peptides targeting the receptors for glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) and glucagon (GCG) have been shown to improve glycaemic management Show more
Unimolecular peptides targeting the receptors for glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) and glucagon (GCG) have been shown to improve glycaemic management in both mice and humans. Yet the identity of the downstream signalling events mediated by these peptides remain to be elucidated. Here, we aimed to assess the mechanisms by which a validated peptide triagonist for GLP-1/GIP/GCG receptors (IUB447) stimulates insulin secretion in murine pancreatic islets. Islets were isolated from wild-type (WT), Gipr-knockout (Gipr The triagonist promoted glucose-stimulated insulin secretion (GSIS) to a greater degree than co-administration of conventional mono-agonists in WT mouse islets. The triagonist-induced increase in GSIS was unchanged in the absence of either Gipr or Gcgr. However, the triagonist failed to enhance insulin secretion in islets lacking both Glp-1r and Gipr and upon treatment with the GLP-1 receptor-specific antagonist exendin-3 (9-39). Similarly, the specific blocking of Gαq signalling with YM254890 or transient receptor potential melastatin 5 (TRPM5) with triphenylphosphine oxide (TPPO) suppressed the triagonist-induced enhancement of GSIS. In vivo assessment of high-fat-fed Trpm5 Triagonist-induced augmentation of GSIS is primarily mediated through its interaction with the GLP-1 receptor and subsequent activation of the Gαq-TRPM5 signalling pathway. Given that Gαq is a key player in the amplification of GSIS, particularly under diabetic conditions, these findings highlight a GLP-1 receptor-centric pharmacological profile that underlies the potent effects of this multi-receptor agonist. Show less