Publications
71 results found
Manchanda Y, Bitsi S, Chen S, et al., 2023, Enhanced endosomal signaling and desensitization of GLP-1R versus GIPR in pancreatic beta cells, Endocrinology, Vol: 164, Pages: 1-15, ISSN: 0013-7227
The incretin receptors, glucagon-like peptide-1 receptor (GLP-1R) and glucose-dependent insulinotropic polypeptide receptor (GIPR), are prime therapeutic targets for the treatment of type 2 diabetes (T2D) and obesity. They are expressed in pancreatic beta cells where they potentiate insulin release in response to food intake. Despite GIP being the main incretin in healthy individuals, GLP-1R has been favored as a therapeutic target due to blunted GIPR responses in T2D patients and conflicting effects of GIPR agonists and antagonists in improving glucose tolerance and preventing weight gain. There is, however, a recently renewed interest in GIPR biology following the realization that GIPR responses can be restored after an initial period of blood glucose normalization and the recent development of dual GLP-1R/GIPR agonists with superior capacity for controlling blood glucose levels and weight. The importance of GLP-1R trafficking and subcellular signaling in the control of receptor outputs is well established, but little is known about the pattern of spatiotemporal signaling from the GIPR in beta cells. Here, we have directly compared surface expression, trafficking and signaling characteristics of both incretin receptors in pancreatic beta cells to identify potential differences that might underlie distinct pharmacological responses associated with each receptor. Our results indicate increased cell surface levels, internalization, degradation, and endosomal versus plasma membrane activity for the GLP-1R, while the GIPR is instead associated with increased plasma membrane recycling, reduced desensitization, and enhanced downstream signal amplification. These differences might have potential implications for the capacity of each incretin receptor to control beta cell function.
Thayabaran D, Tsui APT, Ebmeier S, et al., 2023, The effect of adjusting LDL-cholesterol for Lp(a)-cholesterol on the diagnosis of Familial Hypercholesterolaemia., J Clin Lipidol, ISSN: 1933-2874
BACKGROUND: Familial Hypercholesterolaemia (FH) diagnostic tools help prioritise patients for genetic testing and include LDL-C estimates commonly calculated using the Friedewald equation. However, cholesterol contributions from lipoprotein(a) (Lp(a)) can overestimate 'true' LDL-C, leading to potentially inappropriate clinical FH diagnosis. OBJECTIVE: To assess how adjusting LDL-C for Lp(a)-cholesterol affects FH diagnoses using Simon Broome (SB) and Dutch Lipid Clinic Network (DLCN) criteria. METHODS: Adults referred to a tertiary lipid clinic in London, UK were included if they had undergone FH genetic testing based on SB or DLCN criteria. LDL-C was adjusted for Lp(a)-cholesterol using estimated cholesterol contents of 17.3%, 30% and 45%, and the effects of these adjustments on reclassification to 'unlikely' FH and diagnostic accuracy were determined. RESULTS: Depending on the estimated cholesterol content applied, LDL-C adjustment reclassified 8-23% and 6-17% of patients to 'unlikely' FH using SB and DLCN criteria, respectively. The highest reclassification rates were observed following 45% adjustment in mutation-negative patients with higher Lp(a) levels. This led to an improvement in diagnostic accuracy (46% to 57% with SB, and 32% to 44% with DLCN following 45% adjustment) through increased specificity. However all adjustment factors led to erroneous reclassification of mutation-positive patients to 'unlikely' FH. CONCLUSION: LDL-C adjustment for Lp(a)-cholesterol improves the accuracy of clinical FH diagnostic tools. Adopting this approach would reduce unnecessary genetic testing but also incorrectly reclassify mutation-positive patients. Health economic analysis is needed to balance the risks of over- and under-diagnosis before LDL-C adjustments for Lp(a) can be recommended.
Padam P, Barton L, Wilson S, et al., 2022, Lipid-lowering with inclisiran: areal-world single-centre experience, Open Heart, Vol: 9, ISSN: 2053-3624
Objective The reduction in circulating low-density lipoprotein cholesterol (LDL-c) is the primary aim of lipid-lowering therapies as a method of atherosclerotic cardiovascular disease risk reduction. Inclisiran is a new and potent lipid-lowering drug that is shown to be effective in reducing LDL-c in randomised controlled trials, however, real-world data of its use are not yet known. We sought to analyse the early effects of this drug in a tertiary centre lipid and cardiovascular risk clinic.Methods We performed a retrospective analysis of the first 80 patients who received a single dose of inclisiran at our lipid clinic between 1 December 2021 and 1 September 2022. Data were collected using electronic healthcare records. Baseline blood tests were taken prior to start of treatment and were repeated at 2 months follow-up. Data on adverse events were also recorded.Results At 2 months after treatment initiation, mean baseline LDL-c fell from 3.5±1.1 mmol/L by 48.6% to 1.8±1.0 mmol/L and total cholesterol from 5.7±1.3 mmol/L by 33.3% to 3.8±1.1 mmol/L (both p<0.0001). Mean high-density lipoprotein-c rose by 7.7% to 1.4±0.4 mmol/L (p=0.02) and median triglycerides fell by 31.3% to 1.1 mmol/L (IQR 0.9–2) (p=0.001). Adverse events (injection site reaction, fatigue and headache) were recorded in three patients and all had self-resolved by time of follow-up.Conclusion Inclisiran use in line with National Institute for Health and Care Excellence guidelines led to significant lowering of LDL-c at 2 months, with efficacy similar to that reported in trials with good tolerability.
Hope D, Hinds C, Lopes T, et al., 2022, Hypoaminoacidemia underpins glucagon-mediated energy expenditure and weight loss, Cell Reports Medicine, Vol: 3, ISSN: 2666-3791
Glucagon analogues show promise as components of next-generation, multi-target, anti-obesity therapeutics. The biology of chronic glucagon treatment, in particular its ability to induce energy expenditure and weight loss, remains poorly understood. Using a long-acting glucagon analogue, G108, we demonstrate that glucagon-mediated body weight loss is intrinsically linked to the hypoaminoacidemia associated with its known amino acid catabolic action. Mechanistic studies reveal an energy-consuming response to low plasma amino acids in G108-treated mice, prevented by dietary amino acid supplementation and mimicked by a rationally designed low amino acid diet. Therefore, low plasma amino acids are a prerequisite for G108-mediated energy expenditure and weight loss. However, preventing hypoaminoacidemia with additional dietary protein does not affect the ability of G108 to improve glycemia or hepatic steatosis in obese mice. These studies provide a mechanism for glucagon-mediated weight loss and confirm the hepatic glucagon receptor as an attractive molecular target for metabolic disease therapeutics.
McGlone ER, Dunsterville C, Carling D, et al., 2022, Hepatocyte cholesterol content modulates glucagon receptor signalling, Molecular Metabolism, Vol: 63, ISSN: 2212-8778
ObjectiveTo determine whether glucagon receptor (GCGR) actions are modulated by cellular cholesterol levels.MethodsWe determined the effects of experimental cholesterol depletion and loading on glucagon-mediated cAMP production, ligand internalisation and glucose production in human hepatoma cells, mouse and human hepatocytes. GCGR interactions with lipid bilayers were explored using coarse-grained molecular dynamic simulations. Glucagon responsiveness was measured in mice fed a high cholesterol diet with or without simvastatin to modulate hepatocyte cholesterol content.ResultsGCGR cAMP signalling was reduced by higher cholesterol levels across different cellular models. Ex vivo glucagon-induced glucose output from mouse hepatocytes was enhanced by simvastatin treatment. Mice fed a high cholesterol diet had increased hepatic cholesterol and a blunted hyperglycaemic response to glucagon, both of which were partially reversed by simvastatin. Simulations identified likely membrane-exposed cholesterol binding sites on the GCGR, including a site where cholesterol is a putative negative allosteric modulator.ConclusionsOur results indicate that cellular cholesterol content influences glucagon sensitivity and indicate a potential molecular basis for this phenomenon. This could be relevant to the pathogenesis of non-alcoholic fatty liver disease, which is associated with both hepatic cholesterol accumulation and glucagon resistance.
Jones B, Burade V, Akalestou E, et al., 2022, In vivo and in vitro characterization of GL0034, a novel long-acting glucagon-like peptide-1 receptor agonist, DIABETES OBESITY & METABOLISM, Vol: 24, Pages: 2090-2101, ISSN: 1462-8902
Rossmann K, Akkaya KC, Poc P, et al., 2022, N-Methyl deuterated rhodamines for protein labelling in sensitive fluorescence microscopy, CHEMICAL SCIENCE, Vol: 13, Pages: 8605-8617, ISSN: 2041-6520
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Georgiadou E, Muralidharan C, Martinez M, et al., 2022, Mitofusins Mfn1 and Mfn2 are required to preserve glucose- but not incretin-stimulated beta cell connectivity and insulin secretion, Diabetes, Vol: 71, Pages: 1472-1489, ISSN: 0012-1797
Mitochondrial glucose metabolism is essential for stimulated insulin release from pancreatic beta cells. Whether mitofusin gene expression, and hence mitochondrial network integrity, is important for glucose or incretin signalling has not previously been explored. Here, we generated mice with beta cell-selective, adult-restricted deletion of the mitofusin genes Mfn1 and Mfn2 (βMfn1/2 dKO). βMfn1/2 dKO mice displayed elevated fed and fasted glycaemia and a >five-fold decrease in plasma insulin. Mitochondrial length, glucose-induced polarisation, ATP synthesis, cytosolic and mitochondrial Ca2+ increases were all reduced in dKO islets. In contrast, oral glucose tolerance was more modestly affected in βMfn1/2 dKO mice and GLP-1 or GIP receptor agonists largely corrected defective GSIS through enhanced EPAC-dependent signalling. Correspondingly, cAMP increases in the cytosol, as measured with an Epac-camps based sensor, were exaggerated in dKO mice. Mitochondrial fusion and fission cycles are thus essential in the beta cell to maintain normal glucose, but not incretin, sensing. These findings broaden our understanding of the roles of mitofusins in beta cells, the potential contributions of altered mitochondrial dynamics to diabetes development and the impact of incretins on this process.
Birke R, Ast J, Roosen DA, et al., 2022, Sulfonated red and far-red rhodamines to visualize SNAP- and Halo-tagged cell surface proteins, ORGANIC & BIOMOLECULAR CHEMISTRY, Vol: 20, Pages: 5967-5980, ISSN: 1477-0520
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Jones B, 2022, The therapeutic potential of GLP-1 receptor biased agonism, British Journal of Pharmacology, Vol: 179, Pages: 492-510, ISSN: 0007-1188
Glucagon-like peptide-1 (GLP-1) receptor agonists are effective treatments for type 2 diabetes as they stimulate insulin release and promote weight loss through appetite suppression. Their main side effect is nausea. All approved GLP-1 agonists are full agonists across multiple signalling pathways. However, selective engagement with specific intracellular effectors, or biased agonism, has been touted as a means to improve GLP-1 agonists therapeutic efficacy. In this review, I critically examine how GLP-1 receptor-mediated intracellular signalling is linked to physiological responses and discuss the implications of recent studies investigating the metabolic effects of biased GLP-1 agonists. Overall, there is little conclusive evidence that beneficial and adverse effects of GLP-1 agonists are attributable to distinct, nonoverlapping signalling pathways. Instead, G protein-biased GLP-1 agonists appear to achieve enhanced anti-hyperglycaemic efficacy by avoiding GLP-1 receptor desensitisation and downregulation, partly via reduced β-arrestin recruitment. This effect seemingly applies more to insulin release than to appetite regulation and nausea, possible reasons for which are discussed. At present, most evidence derives from cellular and animal studies, and more human data are required to determine whether this approach represents a genuine therapeutic advance.
Jones B, Sands C, Alexiadou K, et al., 2022, The metabolomic effects of tripeptide gut hormone infusion compared to Roux-en-Y gastric bypass and caloric restriction, Journal of Clinical Endocrinology and Metabolism, Vol: 107, Pages: e767-e782, ISSN: 0021-972X
Context: The gut-derived peptide hormones glucagon-like peptide-1 (GLP-1), oxyntomodulin (OXM), and peptide YY (PYY) are regulators of energy intake and glucose homeostasis, and are thought to contribute to the glucose-lowering effects of bariatric surgery. Objective: To establish the metabolomic effects of a combined infusion of GLP-1, OXM and PYY (tripeptide “GOP”) in comparison to a placebo infusion, Roux-en-Y gastric bypass (RYGB) surgery, and a very low-calorie diet (VLCD). Design and setting: Sub-analysis of a single-blind, randomised, placebo-controlled study of GOP infusion (ClinicalTrials.gov NCT01945840), including VLCD and RYGB comparator groups. Patients and interventions: 25 obese patients with type 2 diabetes or prediabetes were randomly allocated to receive a 4-week subcutaneous infusion of GOP (n=14) or 0.9% saline control (SAL; n=11). An additional 22 patients followed a VLCD, and 21 underwent RYGB surgery. Main outcome measures: Plasma and urine samples collected at baseline and 4 weeks into each intervention were subjected to cross-platform metabolomic analysis, followed by unsupervised and supervised modelling approaches to identify similarities and differences between the effects of each intervention. Results: Aside from glucose, very few metabolites were affected by GOP, contrasting with major metabolomic changes seen with VLCD and RYGB. Conclusions: Treatment with GOP provides a powerful glucose-lowering effect but does not replicate the broader metabolomic changes seen with VLCD and RYGB. The contribution of these metabolomic changes to the clinical benefits of RYGB remains to be elucidated.
Hinds CE, Owen BM, Hope DCD, et al., 2021, A glucagon analogue decreases body weight in mice via signalling in the liver., Scientific Reports, Vol: 11, Pages: 1-17, ISSN: 2045-2322
Glucagon receptor agonists show promise as components of next generation metabolic syndrome pharmacotherapies. However, the biology of glucagon action is complex, controversial, and likely context dependent. As such, a better understanding of chronic glucagon receptor (GCGR) agonism is essential to identify and mitigate potential clinical side-effects. Herein we present a novel, long-acting glucagon analogue (GCG104) with high receptor-specificity and potent in vivo action. It has allowed us to make two important observations about the biology of sustained GCGR agonism. First, it causes weight loss in mice by direct receptor signalling at the level of the liver. Second, subtle changes in GCG104-sensitivity, possibly due to interindividual variation, may be sufficient to alter its effects on metabolic parameters. Together, these findings confirm the liver as a principal target for glucagon-mediated weight loss and provide new insights into the biology of glucagon analogues.
McGlone ER, Manchanda Y, Jones B, et al., 2021, Receptor Activity-Modifying Protein 2 (RAMP2) alters glucagon receptor trafficking in hepatocytes with functional effects on receptor signalling, Molecular Metabolism, Vol: 53, Pages: 1-11, ISSN: 2212-8778
ObjectivesReceptor Activity-Modifying Protein 2 (RAMP2) is a chaperone protein which allosterically binds to and interacts with the glucagon receptor (GCGR). The aims of this study were to investigate the effects of RAMP2 on GCGR trafficking and signalling in the liver, where glucagon (GCG) is important for carbohydrate and lipid metabolism.MethodsSubcellular localisation of GCGR in the presence and absence of RAMP2 was investigated using confocal microscopy, trafficking and radioligand binding assays in human embryonic kidney (HEK293T) and human hepatoma (Huh7) cells. Mouse embryonic fibroblasts (MEFs) lacking Wiskott Aldrich Syndrome protein and scar homologue (WASH) complex and the trafficking inhibitor monensin were used to investigate the effect of a halt in recycling of internalised proteins on GCGR subcellular localisation and signalling in the absence of RAMP2. NanoBiT complementation and cyclic AMP assays were used to study the functional effect of RAMP2 on the recruitment and activation of GCGR signalling mediators. Response to hepatic RAMP2 up-regulation in lean and obese adult mice using a bespoke adeno-associated viral vector was also studied.ResultsGCGR is predominantly localised at the plasma membrane in the absence of RAMP2 and exhibits remarkably slow internalisation in response to agonist stimulation. Rapid intracellular accumulation of GCG-stimulated GCGR in cells lacking WASH complex or in the presence of monensin indicates that activated GCGRs undergo continuous cycles of internalisation and recycling despite apparent GCGR plasma membrane localisation up to 40 minutes post-stimulation. Co-expression of RAMP2 induces GCGR internalisation both basally and in response to agonist stimulation. The intracellular retention of GCGR in the presence of RAMP2 confers a bias away from β-arrestin-2 recruitment coupled to increased activation of Gαs proteins at endosomes. This is associated with increased short-term efficacy for glucagon-stimulated
Lucey M, Ashik T, Marzook A, et al., 2021, Acylation of the incretin peptide exendin-4 directly impacts GLP-1 receptor signalling and trafficking, Molecular Pharmacology, Vol: 100, Pages: 319-334, ISSN: 0026-895X
The glucagon-like peptide-1 receptor (GLP-1R) is a class B G protein-coupled receptor and mainstay therapeutic target for the treatment of type 2 diabetes and obesity. Recent reports have highlighted how biased agonism at the GLP-1R affects sustained glucose-stimulated insulin secretion through avoidance of desensitisation and downregulation. A number of GLP-1R agonists (GLP-1RAs) feature a fatty acid moiety to prolong their pharmacokinetics via increased albumin binding, but the potential for these chemical changes to influence GLP-1R function has rarely been investigated beyond potency assessments for cyclic adenosine monophosphate (cAMP). Here we directly compare the prototypical GLP-1RA exendin-4 with its C-terminally acylated analogue, exendin-4-C16. We examine relative propensities of each ligand to recruit and activate G proteins and β-arrestins, endocytic and post-endocytic trafficking profiles, and interactions with model and cellular membranes in HEK293 and HEK293T cells. Both ligands had similar cAMP potency but exendin-4-C16 showed ~2.5-fold bias towards G protein recruitment and a ~60% reduction in β-arrestin-2 recruitment efficacy compared to exendin-4, as well as reduced GLP-1R endocytosis and preferential targeting towards recycling pathways. These effects were associated with reduced movement of the GLP-1R extracellular domain measured using a conformational biosensor approach, and a ~70% increase in insulin secretion in INS-1 832/3 cells. Interactions with plasma membrane lipids were enhanced by the acyl chain. Exendin-4-C16 showed extensive albumin binding and was highly effective for lowering of blood glucose in mice over at least 72 hours. Our study highlights the importance of a broad approach to the evaluation of GLP-1RA pharmacology.
Pickford P, Lucey M, Rujan R-M, et al., 2021, Partial agonism improves the anti-hyperglycaemic efficacy of an oxyntomodulin-derived GLP-1R/GCGR co-agonist, Molecular Metabolism, Vol: 51, ISSN: 2212-8778
OBJECTIVE: Glucagon-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 and β-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. METHODS: Dipeptidyl 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. RESULTS: Ligand-specific reductions in β-arrestin-2 recruitment were associated with slower 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 β-arrestin-2 recruitment at both receptors and were best classified as partial agonists for the two pathways measured. CONCLUSIONS: Diminishing β-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.
Marzook A, Chen S, Pickford P, et al., 2021, Evaluation of efficacy- versus affinity-driven agonism with biased GLP-1R ligands P5 and exendin-F1, Biochemical Pharmacology, Vol: 190, Pages: 1-12, ISSN: 0006-2952
The glucagon-like peptide-1 receptor (GLP-1R) is an important regulator of glucose homeostasis and has been successfully targeted for the treatment of type 2 diabetes. Recently described biased GLP-1R agonists with selective reductions in β-arrestin versus G protein coupling show improved metabolic actions in vivo. However, two prototypical G protein-favouring GLP-1R agonists, P5 and exendin-F1, are reported to show divergent effects on insulin secretion. In this study we aimed to resolve this discrepancy by performing a side-by-side characterisation of these two ligands across a variety of in vitro and in vivo assays. Exendin-F1 showed reduced acute efficacy versus P5 for several readouts, including recruitment of mini-G proteins, G protein-coupled receptor kinases (GRKs) and β-arrestin-2. Maximal responses were also lower for both GLP-1R internalisation and the presence of active GLP-1R-mini-Gs complexes in early endosomes with exendin-F1 treatment. In contrast, prolonged insulin secretion in vitro and sustained anti-hyperglycaemic efficacy in mice were both greater with exendin-F1 than with P5. We conclude that the particularly low acute efficacy of exendin-F1 and associated reductions in GLP-1R downregulation appear to be more important than preservation of endosomal signalling to allow sustained insulin secretion responses. This has implications for the ongoing development of affinity- versus efficacy-driven biased GLP-1R agonists as treatments for metabolic disease.
Ast J, Novak AN, Podewin T, et al., 2021, An expanded LUXendin color palette for GLP1R detection and visualization in vitro and in vivo, Publisher: ChemRxiv
The glucagon-like peptide-1 receptor (GLP1R) is expressed in peripheral tissues and the brain, where it exerts pleiotropic actions on metabolic and inflammatory processes. Detection and visualization of GLP1R remains challenging, partly due to a lack of validated reagents. Previously, we generated LUXendins, antagonistic red and far-red fluorescent probes for specific labeling of GLP1R in live and fixed cells/tissue. We now extend this concept to the green and near-infrared color ranges by synthesizing and testing LUXendin492, LUXendin551, LUXendin615 and LUXendin762. All four probes brightly and specifically label GLP1R in cells and pancreatic islets. Further, LUXendin551 acts as chemical beta cell reporter in preclinical rodent models, while LUXendin762 allows non-invasive imaging, highlighting differentially-accessible GLP1R populations. We thus expand the color palette of LUXendins to seven different spectra, opening up a range of experiments using widefield microscopy available in most labs through super-resolution imaging and whole animal imaging. With this, we expect that LUXendins will continue to generate novel and specific insight into GLP1R biology.
Marzook A, Tomas A, Jones B, 2021, The interplay of glucagon-like peptide-1 receptor trafficking and signalling in pancreatic beta cells, Frontiers in Endocrinology, Vol: 12, Pages: 1-12, ISSN: 1664-2392
The glucagon-like peptide 1 receptor (GLP-1R) is a class B G protein-coupled receptor (GPCR) which mediates the effects of GLP-1, an incretin hormone secreted primarily from L-cells in the intestine and within the central nervous system. The GLP-1R, upon activation, exerts several metabolic effects including the release of insulin and suppression of appetite, and has, accordingly, become an important target for the treatment for type 2 diabetes (T2D). Recently, there has been heightened interest in how the activated GLP-1R is trafficked between different endomembrane compartments, controlling the spatial origin and duration of intracellular signals. The discovery of “biased” GLP-1R agonists that show altered trafficking profiles and selective engagement with different intracellular effectors has added to the tools available to study the mechanisms and physiological importance of these processes. In this review we survey early and recent work that has shed light on the interplay between GLP-1R signalling and trafficking, and how it might be therapeutically tractable for T2D and related diseases.
Arcones AC, Vila-Bedmar R, Mirasierra M, et al., 2021, GRK2 regulates GLP-1R-mediated early phase insulin secretion in vivo, BMC Biology, Vol: 19, ISSN: 1741-7007
BACKGROUND: Insulin secretion from the pancreatic β-cell is finely modulated by different signals to allow an adequate control of glucose homeostasis. Incretin hormones such as glucagon-like peptide-1 (GLP-1) act as key physiological potentiators of insulin release through binding to the G protein-coupled receptor GLP-1R. Another key regulator of insulin signaling is the Ser/Thr kinase G protein-coupled receptor kinase 2 (GRK2). However, whether GRK2 affects insulin secretion or if GRK2 can control incretin actions in vivo remains to be analyzed. RESULTS: Using GRK2 hemizygous mice, isolated pancreatic islets, and model β-cell lines, we have uncovered a relevant physiological role for GRK2 as a regulator of incretin-mediated insulin secretion in vivo. Feeding, oral glucose gavage, or administration of GLP-1R agonists in animals with reduced GRK2 levels (GRK2+/- mice) resulted in enhanced early phase insulin release without affecting late phase secretion. In contrast, intraperitoneal glucose-induced insulin release was not affected. This effect was recapitulated in isolated islets and correlated with the increased size or priming efficacy of the readily releasable pool (RRP) of insulin granules that was observed in GRK2+/- mice. Using nanoBRET in β-cell lines, we found that stimulation of GLP-1R promoted GRK2 association to this receptor and that GRK2 protein and kinase activity were required for subsequent β-arrestin recruitment. CONCLUSIONS: Overall, our data suggest that GRK2 is an important negative modulator of GLP-1R-mediated insulin secretion and that GRK2-interfering strategies may favor β-cell insulin secretion specifically during the early phase, an effect that may carry interesting therapeutic applications.
Manchanda Y, Bitsi S, Kang Y, et al., 2021, Spatiotemporal control of GLP-1 receptor activity, Current Opinion in Endocrine and Metabolic Research, Vol: 16, Pages: 19-27, ISSN: 2451-9650
Pleiotropic signalling by G protein–coupled receptors is subject to spatiotemporal regulation, which allows precise control over a diverse range of cellular outputs. The glucagon-like peptide-1 receptor (GLP-1R), a class B G protein–coupled receptor important in the control of blood glucose and energy homeostasis, is subject to redistribution within nanoregions of the plasma membrane and throughout the endocytic network, enabling complex patterns of signalling at different locations. Nanodomain segregation of GLP-1Rs promotes the formation of functionally important homo-oligomers and hetero-oligomers and increases proximity to cytosolic effectors. Persistent signalling from GLP-1Rs within the endosomal compartment has also been described. These processes can be dramatically altered by biased and/or modified orthosteric GLP-1R agonists and allosteric modulators. GLP-1R signalling is not a monotonic process and fine-tuning of cellular responses in space and time may provide a means to improve the therapeutic efficacy of GLP-1R agonists.
Jones B, McGlone ER, Fang Z, et al., 2021, Genetic and biased agonist-mediated reductions in β-arrestin recruitment prolong cAMP signalling at glucagon family receptors, Journal of Biological Chemistry, Vol: 296, Pages: 1-15, ISSN: 0021-9258
Receptors for the peptide hormones glucagon-like peptide-1 (GLP-1R), glucose-dependent insulinotropic polypeptide (GIPR) and glucagon (GCGR) are important regulators of insulin secretion and energy metabolism. GLP-1R agonists have been successfully deployed for the treatment of type 2 diabetes, but it has been suggested that their efficacy is limited by target receptor desensitisation and downregulation due to recruitment of β-arrestins. Indeed, recently described GLP-1R agonists with reduced β-arrestin-2 recruitment have delivered promising results in preclinical and clinical studies. We therefore aimed to determine if the same phenomenon could apply to the closely related GIPR and GCGR. In HEK293 cells depleted of both β-arrestin isoforms the duration of G protein-dependent cAMP/PKA signalling was increased in response to the endogenous ligand for each receptor. Moreover, in wild-type cells, “biased” GLP-1, GCG and GIP analogues with selective reductions in β-arrestin-2 recruitment led to reduced receptor endocytosis and increased insulin secretion over a prolonged stimulation period, although the latter effect was only seen at high agonist concentrations. Biased GCG analogues increased the duration of cAMP signalling, but this did not lead to increased glucose output from hepatocytes. Our study provides a rationale for development of GLP-1R, GIPR and GCGR agonists with reduced β-arrestin recruitment, but further work is needed to maximally exploit this strategy for therapeutic purposes.
Jones B, Fang Z, Chen S, et al., 2020, Ligand-specific factors influencing GLP-1 receptor post-endocytic trafficking and degradation in pancreatic beta cells, International Journal of Molecular Sciences, Vol: 212, Pages: 1-24, ISSN: 1422-0067
The glucagon-like peptide-1 receptor (GLP-1R) is an important regulator of blood glucose homeostasis. Ligand-specific differences in membrane trafficking of the GLP-1R influence its signalling properties and therapeutic potential in type 2 diabetes. Here, we have evaluated how different factors combine to control the post-endocytic trafficking of GLP-1R to recycling versus degradative pathways. Experiments were performed in primary islet cells, INS-1 832/3 clonal beta cells and HEK293 cells, using biorthogonal labelling of GLP-1R to determine its localisation and degradation after treatment with GLP-1, exendin-4 and several further GLP-1R agonist peptides. We also characterised the effect of a rare GLP1R coding variant, T149M, and the role of endosomal peptidase endothelin-converting enzyme-1 (ECE-1), in GLP1R trafficking. Our data reveal how treatment with GLP-1 versus exendin-4 is associated with preferential GLP-1R targeting towards a recycling pathway. GLP-1, but not exendin-4, is a substrate for ECE-1, and the resultant propensity to intra-endosomal degradation, in conjunction with differences in binding affinity, contributes to alterations in GLP-1R trafficking behaviours and degradation. The T149M GLP-1R variant shows reduced signalling and internalisation responses, which is likely to be due to disruption of the cytoplasmic region that couples to intracellular effectors. These observations provide insights into how ligand- and genotype-specific factors can influence GLP-1R trafficking.
Ast J, Arvaniti A, Fine NHF, et al., 2020, Author Correction: Super-resolution microscopy compatible fluorescent probes reveal endogenous glucagon-like peptide-1 receptor distribution and dynamics., Nature Communications, Vol: 11, Pages: 1-1, ISSN: 2041-1723
Correction to: Nature Communications https://doi.org/10.1038/s41467-020-14309-w, published online 24 January 2020.
Anand U, Jones B, Korchev Y, et al., 2020, CBD effects on TRPV1 signaling pathways in cultured DRG neurons, Journal of Pain Research, Vol: 2020, Pages: 2269-2278, ISSN: 1178-7090
Introduction: Cannabidiol (CBD) is reported to produce pain relief, but the clinically relevant cellular and molecular mechanisms remain uncertain. The TRPV1 receptor integrates noxious stimuli and plays a key role in pain signaling. Hence, we conducted in vitro studies, to elucidate the efficacy and mechanisms of CBD for inhibiting neuronal hypersensitivity in cultured rat sensory neurons, following activation of TRPV1. Methods: Adult rat dorsal root ganglion (DRG) neurons were cultured, and supplemented with the neurotrophic factors NGF and GDNF, in an established model of neuronal hypersensitivity. 48 h after plating, neurons were stimulated with CBD (Adven 150, EMMAC Life Sciences) at 1, 10, 100 nMol/L and 1, 10 and 50 µMol/L. In separate experiments, DRG neurons were also stimulated with capsaicin with or without CBD (1 nMol/L to10 µMol/L), in a functional calcium imaging assay. The effects of the adenylyl cyclase activator forskolin and the calcineurin inhibitor cyclosporin were determined. We also measured forskolin-stimulated cAMP levels, without and after treatment with CBD, using a homogenous time resolved fluorescence (HTRF) assay. The results were analysed using Student’s t-test. Results: DRG neurons treated with 10 and 50 µMol/L CBD showed calcium influx, but not at lower doses. Neurons treated with capsaicin demonstrated robust calcium influx, which was dose-dependently reduced in the presence of low dose CBD (IC50 = 100 nMol/L). The inhibition or desensitization by CBD was reversed in the presence of forskolin and cyclosporin. Forskolin stimulated cAMP levels were significantly reduced in CBD treated neurons.Conclusions: CBD at low doses corresponding to plasma concentrations observed physiologically, inhibits or desensitizes neuronal TRPV1 signalling by inhibiting the adenylyl cyclase – cAMP pathway, which is essential for maintaining TRPV1 phosphorylation and sensitization. CBD also facilitated calcineurin-med
Pickford P, Lucey M, Fang Z, et al., 2020, Signalling, trafficking and glucoregulatory properties of glucagon-like peptide-1 receptor agonists exendin-4 and lixisenatide., British Journal of Pharmacology, Vol: 177, Pages: 3905-3923, ISSN: 0007-1188
BACKGROUND AND PURPOSE: Amino acid substitutions at the N-termini of glucagon-like peptide-1 receptor agonist (GLP-1RA) peptides result in distinct patterns of intracellular signalling, sub-cellular trafficking and efficacy in vivo. Here we aimed to determine whether sequence differences at the ligand C-termini of clinically approved GLP-1RAs exendin-4 and lixisenatide lead to similar phenomena. EXPERIMENTAL APPROACH: Exendin-4, lixisenatide, and N-terminally substituted analogues with biased signalling characteristics were compared across a range of in vitro trafficking and signalling assays in different cell types. Fluorescent ligands and new time-resolved FRET approaches were developed to study agonist behaviours at the cellular and sub-cellular level. Anti-hyperglycaemic and anorectic effects of each parent ligand, and their biased derivatives, were assessed in mice. KEY RESULTS: Lixisenatide and exendin-4 showed equal binding affinity, but lixisenatide was 5-fold less potent for cAMP signalling. Both peptides induced extensive GLP-1R clustering in the plasma membrane and were rapidly endocytosed, but the GLP-1R recycled more slowly to the cell surface after lixisenatide treatment. These combined deficits resulted in reduced maximal sustained insulin secretion and reduced anti-hyperglycaemic and anorectic effects in mice with lixisenatide. N-terminal substitution of His1 by Phe1 to both ligands had favourable effects on their pharmacology, resulting in improved insulin release and lowering of blood glucose. CONCLUSION AND IMPLICATIONS: Changes to the C-terminus of exendin-4 affect signalling potency and GLP-1R trafficking via mechanisms unrelated to GLP-1R occupancy. These differences were associated with changes in their ability to control blood glucose and therefore may be therapeutically relevant.
Poc P, Gutzeit VA, Ast J, et al., 2020, Interrogating surfaceversusintracellular transmembrane receptor populations using cell-impermeable SNAP-tag substrates, Chemical Science, Vol: 11, Pages: 7871-7883, ISSN: 2041-6520
Employing self-labelling protein tags for the attachment of fluorescent dyes has become a routine and powerful technique in optical microscopy to visualize and track fused proteins. However, membrane permeability of the dyes and the associated background signals can interfere with the analysis of extracellular labelling sites. Here we describe a novel approach to improve extracellular labelling by functionalizing the SNAP-tag substrate benzyl guanine (“BG”) with a charged sulfonate (“SBG”). This chemical manipulation can be applied to any SNAP-tag substrate, improves solubility, reduces non-specific staining and renders the bioconjugation handle impermeable while leaving its cargo untouched. We report SBG-conjugated fluorophores across the visible spectrum, which cleanly label SNAP-fused proteins in the plasma membrane of living cells. We demonstrate the utility of SBG-conjugated fluorophores to interrogate class A, B and C G protein-coupled receptors (GPCRs) using a range of imaging approaches including nanoscopic superresolution imaging, analysis of GPCR trafficking from intra- and extracellular pools, in vivo labelling in mouse brain and analysis of receptor stoichiometry using single molecule pull down.
Jones B, Pickford P, Lucey M, et al., 2020, Disconnect between signalling potency and in vivo efficacy of pharmacokinetically optimised biased glucagon-like peptide-1 receptor agonists, Molecular Metabolism, Vol: 37, ISSN: 2212-8778
ObjectiveThe objective of this study was to determine how pharmacokinetically advantageous acylation impacts on glucagon-like peptide-1 receptor (GLP-1R) signal bias, trafficking, anti-hyperglycaemic efficacy, and appetite suppression.MethodsIn vitro signalling responses were measured using biochemical and biosensor assays. GLP-1R trafficking was determined by confocal microscopy and diffusion-enhanced resonance energy transfer. Pharmacokinetics, glucoregulatory effects, and appetite suppression were measured in acute, sub-chronic, and chronic settings in mice.ResultsA C-terminally acylated ligand, [F1,K⁴⁰.C16 diacid]exendin-4, was identified that showed undetectable β-arrestin recruitment and GLP-1R internalisation. Depending on the cellular system used, this molecule was up to 1000-fold less potent than the comparator [D3,K⁴⁰.C16 diacid]exendin-4 for cyclic AMP signalling, yet was considerably more effective in vivo, particularly for glucose regulation.ConclusionsC-terminal acylation of biased GLP-1R agonists increases their degree of signal bias in favour of cAMP production and improves their therapeutic potential.
Jones B, McGlone ER, Fang Z, et al., 2020, Signal bias at glucagon family receptors: rationale and downstream impacts
<jats:title>Abstract</jats:title><jats:p>Receptors for the peptide hormones glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) and glucagon (GCG) are important regulators of insulin secretion and energy metabolism. Recently described GLP-1 receptor agonists showing signal bias in favour of cyclic AMP over β-arrestin-2 recruitment have delivered promising results in preclinical studies. Here we first sought to establish the role of β-arrestins in the control of intracellular signalling and trafficking responses at the closely related GLP-1, GIP and GCG receptors, through studies performed in cells depleted of both β-arrestin isoforms. We also generated analogues of GLP-1, GCG and GIP which in some cases showed selective reduction in β-arrestin-2 recruitment <jats:italic>versus</jats:italic> cAMP signalling compared to the parent peptide. Despite reduced acute signalling potency and/or efficacy, some biased GLP-1 and GIP analogues increased maximal sustained insulin secretion from INS-1 832/3 clonal beta cells, although only at high agonist concentrations. Biased GCG analogues did not affect maximal insulin release, or glucose output in hepatocytes.</jats:p>
Ma Y, Ratnasabapathy R, De Backer I, et al., 2020, Glucose in the hypothalamic paraventricular nucleus regulates GLP-1 release, JCI insight, Vol: 5, ISSN: 2379-3708
Glucokinase (GK) is highly expressed in the hypothalamic paraventricular nucleus (PVN); however, its role is currently unknown. We found that GK in the PVN acts as part of a glucose-sensing mechanism within the PVN that regulates glucose homeostasis by controlling glucagon-like peptide 1 (GLP-1) release. GLP-1 is released from enteroendocrine L cells in response to oral glucose. Here we identify a brain mechanism critical to the release of GLP-1 in response to oral glucose. We show that increasing expression of GK or injection of glucose into the PVN increases GLP-1 release in response to oral glucose. On the contrary, decreasing expression of GK or injection of nonmetabolizable glucose into the PVN prevents GLP-1 release. Our results demonstrate that gluco-sensitive GK neurons in the PVN are critical to the response to oral glucose and subsequent release of GLP-1.
Fang Z, Chen S, Pickford P, et al., 2020, The influence of peptide context on signaling and trafficking of glucagon-like peptide-1 receptor biased agonists, ACS Pharmacology & Translational Science, Vol: 3, Pages: 345-360, ISSN: 2575-9108
Signal bias and membrane trafficking have recently emerged as important considerations in the therapeutic targeting of the glucagon-like peptide-1 receptor (GLP-1R) in type 2 diabetes and obesity. In the present study, we have evaluated a peptide series with varying sequence homology between native GLP-1 and exendin-4, the archetypal ligands on which approved GLP-1R agonists are based. We find notable differences in agonist-mediated cyclic AMP signaling, recruitment of β-arrestins, endocytosis, and recycling, dependent both on the introduction of a His → Phe switch at position 1 and the specific midpeptide helical regions and C-termini of the two agonists. These observations were linked to insulin secretion in a beta cell model and provide insights into how ligand factors influence GLP-1R function at the cellular level.
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