ADGRL1 is a glucose receptor involved in mediating energy and glucose homeostasis

Abstract

Aims/hypothesis The brain is a major consumer of glucose as an energy source and regulates systemic glucose as well as energy balance. Although glucose transporters such as GLUT2 and sodium−glucose cotransporter 2 (SGLT2) are known to regulate glucose homeostasis and metabolism, the identity of a receptor that binds glucose to activate glucose signalling pathways in the brain is unknown. In this study, we aimed to discover a glucose receptor in the mouse hypothalamus. Methods Here we used a high molecular mass glucose–biotin polymer to enrich glucose-bound mouse hypothalamic neurons through cell-based affinity chromatography. We then subjected the enriched neurons to proteomic analyses and identified adhesion G-protein coupled receptor 1 (ADGRL1) as a top candidate for a glucose receptor. We validated glucose–ADGRL1 interactions using CHO cells stably expressing human ADGRL1 and ligand–receptor binding assays. We generated and determined the phenotype of global Adgrl1-knockout mice and hypothalamus-specific Adgrl1-deficient mice. We measured the variables related to glucose and energy homeostasis in these mice. We also generated an Adgrl1Cre mouse model to investigate the role of ADGRL1 in sensing glucose using electrophysiology. Results Adgrl1 is highly expressed in the ventromedial nucleus of the hypothalamus (VMH) in mice. Lack of Adgrl1 in the VMH in mice caused fasting hyperinsulinaemia, enhanced glucose-stimulated insulin secretion and insulin resistance. In addition, the Adgrl1-deficient mice had impaired feeding responses to glucose and fasting coupled with abnormal glucose sensing and decreased physical activity before development of obesity and hyperglycaemia. In female mice, ovariectomy was necessary to reveal the contribution of ADGRL1 to energy and glucose homeostasis. Conclusions/interpretation Altogether, our findings demonstrate that ADGRL1 binds glucose and is involved in energy as well as glucose homeostasis in a sex-dependent manner. Targeting ADGRL1 may introduce a new class of drugs for the treatment of type 2 diabetes and obesity. Graphical Abstract

A protocol to isolate, identify, and verify glucose- or carbohydrate-binding receptors

“…For in-depth analysis of carbohydrate–receptor interaction, we recommend the use of the SPR technique. We recently used both In-cell ELISA and SPR technique to validate glucose–ADGRL1 interactions [ 6 ].The SPR method not only allows to confirm glycan–receptor binding but also enables the user to determine the binding kinetics simultaneously. This is crucial to determine the affinity of the receptor toward glycan at low concentrations.…”

“…The isolation of glucose receptors has been challenging because currently available glucose conjugates such as biotin- or radio-labeled glucose reagents do not provide sufficient sensitivity and density for an affinity chromatography assay owing to their low molecular weight as described in our previous publication [ 6 ]. To overcome this limitation, we developed a protocol to isolate glucose- or carbohydrate-binding receptors using a high molecular weight 30 kDa glucose– (or other carbohydrate–) biotin–polyacrylamide (PAA) conjugate with mole fractions of 80:5:15% respectively.…”

“…Next, we describe how the binding of glucose to its receptor can be verified using an In-cell ELISA with CHO-K cells stably expressing the recently identified glucose receptor ADGRL1 [ 6 ]. Further, we demonstrate how to determine the binding kinetics and interaction between glucose and ADGRL1 using the surface plasmon resonance (SPR) technique.…”