The development of dual agonists for the glucagon-like peptide-1 receptor (GLP-1R) and glucose-dependent insulinotropic polypeptide receptor (GIPR) has been a landmark moment in the treatment of type 2 diabetes and obesity. However, for reasons that are incompletely understood, in preclinical and clinical studies, adding either a GIPR agonist or GIPR antagonist to GLP-1R agonism causes additional weight loss1. Here we show that distinct brain regions mediate the appetite-suppressing effects of GIPR agonists and the synergistic weight loss effects conferred by GIPR antagonists. We knock out Gipr in either the area postrema (AP) or hypothalamus of mice (GiprAP-KO and Giprhypo-KO, respectively) and compare body weight and food intake responses to GIPR agonists and antagonists, alone and in combination with the GLP-1R agonist liraglutide. GiprAP-KO mice exhibit partial protection against diet-induced obesity, reduced responsiveness to the appetite-suppressing effects of acyl-GIP and a reduced ability of acyl-GIP to prevent avoidance triggered by peptide YY. Weight loss effects of liraglutide are comparable in GiprAP-KO and control mice, and the co-administration of a GIPR antagonist peptide causes similar additional weight loss in both groups. Giprhypo-KO mice, by contrast, exhibit normal appetite suppression by acyl-GIP but enhanced weight loss on liraglutide compared with control mice. Giprhypo-KO also abolishes the synergistic effect of a GIPR antagonist when combined with liraglutide—an effect that is not mediated by nucleus tractus solitarius preproglucagon neurons. GIPR antagonism and Giprhypo-KO also sensitise to cagrilintide-induced weight loss. Overall, our results suggest that the AP is responsible for the appetite-suppressing effects of GIPR agonism but that GIP receptors in the hypothalamus underlie the ability of GIPR antagonism to enhance the weight loss effects of GLP-1R and amylin receptor agonists.
