Ashford, F. | Search bioRxiv

bioRxiv2021

Partial agonism improves the anti-hyperglycaemic efficacy of an oxyntomodulin-derived GLP-1R/GCGR co-agonist

ObjectiveGlucagon-like peptide-1 and glucagon receptor (GLP-1R/GCGR) co-agonism can maximise weight loss and improve glycaemic control in type 2 diabetes and obesity. In this study we investigated the cellular and metabolic effects of modulating the balance between G protein activation and {beta}-arrestin-2 recruitment at GLP-1R and GCGR using oxyntomodulin (OXM)-derived co-agonists. This strategy has been previously shown to improve the duration of action of GLP-1R mono-agonists by reducing target desensitisation and downregulation. MethodsDipeptidyl dipeptidase-4 (DPP-4)-resistant OXM analogues were generated and assessed for a variety of cellular readouts. Molecular dynamic simulations were used to gain insights into the molecular interactions involved. In vivo studies were performed in mice to identify effects on glucose homeostasis and weight loss. ResultsLigand-specific reductions in {beta}-arrestin-2 recruitment led to reduced GLP-1R internalisation and prolonged glucose-lowering action in vivo. The putative benefits of GCGR agonism were retained, with equivalent weight loss compared to the GLP-1R mono-agonist liraglutide in spite of a lesser degree of food intake suppression. The compounds tested showed only a minor degree of biased agonism between G protein and {beta}-arrestin-2 recruitment at both receptors and were best classified as partial agonists for the two pathways measured. ConclusionsDiminishing {beta}-arrestin-2 recruitment may be an effective way to increase the therapeutic efficacy of GLP-1R/GCGR co-agonists. These benefits can be achieved by partial rather than biased agonism.

pharmacology and toxicology↗

bioRxiv2020

Testosterone enhances GLP-1 efficacy at the plasma membrane and endosomes to augment insulin secretion in male pancreatic β cells

Male mice with elimination of the androgen receptor (AR) in islet {beta} cells ({beta}ARKO) exhibit blunted glucose-stimulated insulin secretion (GSIS), leading to hypoinsulinemia and hyperglycemia when challenged with a Western diet. Testosterone activation of an extranuclear AR in {beta} cells potentiates GSIS by amplifying the insulinotropic action of glucagon-like peptide-1 (GLP-1). Here, using a combination of {beta}ARKO and {beta} cell-selective GLP-1 receptor knockout mice and their islets, we show that AR activation in {beta} cells amplifies the insulinotropic effect of islet-derived GLP-1. In {beta} cell models expressing cAMP sensors, testosterone enhances the ability of GLP-1, but not that of glucose-dependent insulinotropic polypeptide or glucagon, to produce cAMP. Accordingly, testosterone selectively enhances the ability of GLP-1 to potentiate GSIS. Notably, testosterone enhances GLP-1 production of cAMP at the plasma membrane and endosomes. In male mouse and human islets, the insulinotropic effect of testosterone is abolished following inhibition of the membrane and endosomal cAMP-dependent protein kinase A and exchange protein activated by cAMP islet 2 pathways. Thus, membrane localization of AR enhances the ability of the GLP-1 receptor to produce cAMP, thus increasing glucose-stimulated insulin exocytosis. Significance StatementThis study reveals that testosterone, acting on the androgen receptor (AR) in insulin-producing {beta} cells amplifies the insulinotropic action of glucagon-like peptide-1 (GLP-1) by increasing GLP-1-mediated production of cAMP at the plasma membrane and endosomal compartments, to promote insulin vesicles exocytosis in human {beta} cells. This study establishes a novel biological paradigm in which membrane location of a steroid nuclear receptor enhances the ability of a G protein-coupled receptor to produce cAMP. It has exceptional clinical significance for targeted delivery of testosterone to {beta} cells in the large population of aging and androgen-deficient men who are at increased risk of diabetes.

physiology↗