Real-time trafficking and signaling of the glucagon-like peptide-1 receptor

Abstract

The glucagon-like peptide-1 incretin receptor (GLP-1R) of family B G protein-coupled receptors (GPCRs) is a major drug target in type-2-diabetes due to its regulatory effect on post-prandial blood-glucose levels. The mechanism(s) controlling GLP-1R mediated signaling are far from fully understood. A fundamental mechanism controlling the signaling capacity of GPCRs is the post-endocytic trafficking of receptors between recycling and degradative fates. Here, we combined microscopy with novel real-time assays to monitor both receptor trafficking and signaling in living cells. We find that the human GLP-1R internalizes rapidly and with similar kinetics in response to equipotent concentrations of GLP-1 and the stable GLP-1 analogues exendin-4 and liraglutide. Receptor internalization was confirmed in mouse pancreatic islets. GLP-1R is shown to be a recycling receptor with faster recycling rates mediated by GLP-1 as compared to exendin-4 and liraglutide. Furthermore, a prolonged cycling of ligand-activated GLP-1Rs was observed and is suggested to be correlated with a prolonged cAMP signal.

The pro-healing effect of exendin-4 on wounds produced by abrasion in normoglycemic mice

“…These changes might account for the finding indicating that, after 6 days, the wounds received Exe4 were more healed than those treated with NT, exendin-4(9-39) but also with Exendin-4(9-39) þExe4. Furthermore, we found, in line with that already described by Ishibashi et al (2011), myofibroblasts positive for GLP-1R immunostaining both at the plasma membrane and intracellular (Widmann et al, 1995;Roed et al, 2013). In addition, activation of the mitogenic ERK1/2, was described as part of the intracellular cascade activated by GLP-1R (Favaro et al, 2012).…”

“…Exe4 activates GLP-1 receptor (GLP-1R) thus mimicking most of GLP-1 effects including the ability to induce receptor phosphorylation and internalization (Roed et al, 2013), two mechanisms ensuring a continuous recycling from intracellular stores towards the plasma membrane (Widmann et al, 1995). Since the insulinotropic activity of GLP-1 was found dysregulated in diabetic patients (Meier and Nauck, 2010), a synthetic version of Exe4, exenatide, became recently part of an innovative anti-diabetic therapy (incretin analogues).…”

GLP-1 and Exendin-4 Transiently Enhance GABAA Receptor–Mediated Synaptic and Tonic Currents in Rat Hippocampal CA3 Pyramidal Neurons

“…Interestingly, in our experiments, 10 pmol/L GLP-1 and exendin-4 effectively enhanced the GABA-activated current response with a similar time constant of activation (2 min), an apparent synchrony with the lifetime of GLP-1 in plasma. Recently, Roed et al (23) determined the half-maximal concentration for activation (EC 50 ) of the GLP-1 receptor expressed in human embryonic kidney cells to be 9.8 6 1.0 pmol/L. They further determined the EC 50 of GLP-1 for inducing GLP-1 receptors internalization to be 12 6 5 nmol/L and showed that maximal internalization level occurred with supersaturating concentrations (1 mmol/L) within 15-20 min.…”

“…Exendin (9-39) (Ex9-39) is a competitive inhibitor of GLP-1 at the GLP-1 receptor (23). Since GLP-1 once bound to the GLP-1 receptor starts intracellular cascades leading to activation of various proteins, it is essential to apply the inhibitor first and only then coapply GLP-1 together with the inhibitor in order to prevent GLP-1 effects on neuronal function such as modulation of the GABA signaling.…”

“…The half-life of the peptides in plasma is very short, only about 1-2 min (13,19), due to degradation by the enzyme dipeptidyl peptidase-4 (13). In the pancreatic islets, the GLP-1 receptor is internalized after GLP-1-induced activation (20)(21)(22)(23) and passes through recycling endosomes before it appears in the plasma membrane again (23). The GLP-1 receptor is widely distributed in the brain (10, 16,24), including in the hippocampal CA3 pyramidal neurons (16,25), and GLP-1 and other agonists at the GLP-1 receptor have been reported to regulate food intake (26), be neuroprotective (27), anti-inflammatory (28), and modulate synaptic plasticity and memory formation (28)(29)(30)(31)(32).…”