Publications
109 results found
Manchanda Y, Ben J, Carrat G, et al., 2021, Binding Kinetics, Bias, Receptor Internalization, and Effects on Insulin Secretion for a Novel GLP1R-GIPR Dual Agonist, HISHS-2001, Publisher: AMER DIABETES ASSOC, ISSN: 0012-1797
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- Citations: 2
Bitsi S, Suba K, Mohamed N, et al., 2021, β-arrestin-2 Deletion Influences GLP-1 Receptor Signaling in Pancreatic β Cells In Vivo, 81st Virtual Scientific Sessions of the American-Diabetes-Association (ADA), Publisher: AMER DIABETES ASSOC, ISSN: 0012-1797
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.
Cheung R, Pizza G, Chabosseau P, et al., 2021, miR-125b impairs beta cell function <i>in vivo</i> by targeting lysosomal and mitochondrial genes, Publisher: WILEY, ISSN: 0742-3071
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.
Georgiadou E, Muralidharan C, Martinez M, et al., 2021, Mitofusins Mfn1 and Mfn2 are required to preserve glucose-but not incretin- stimulated beta cell connectivity and insulin secretion, bioRxiv
Aims/hypothesis Mitochondrial glucose metabolism is essential for stimulated insulin release from pancreatic beta cells. Whether mitochondrial networks may be important for glucose or incretin sensing has yet to be determined.Methods Here, we generated mice with beta cell-selective, adult-restricted deletion of the mitofusin genes Mfn1 and Mfn2 (βMfn1/2 dKO). Whole or dissociated pancreatic islets were used for live beta cell fluorescence imaging of cytosolic or mitochondrial Ca2+ concentration and ATP production or GSIS in response to increasing glucose concentrations or GLP-1 receptor agonists. Serum and blood samples were collected to examine oral and i.p. glucose tolerance.Results βMfn1/2 dKO mice displayed elevated fed and fasted glycaemia (p<0.01, p<0.001) and a >five-fold decrease (p<0.0001) in plasma insulin. Mitochondrial length, glucose-induced polarisation, ATP synthesis and cytosolic Ca2+ increases were all reduced (p<0.05,p<0.01,p<0.0001) in dKO islets, and beta cell Ca2+ dynamics were suppressed in vivo (p<0.001). In contrast, oral glucose tolerance was near normal in βMfn1/2 dKO mice (p<0.05, p<0.01) and GLP-1 or GIP receptor agonists largely corrected defective GSIS from isolated islets through an EPAC-dependent signalling activation.Conclusions/interpretation Mitochondrial fusion and fission cycles are thus essential in the beta cell to maintain normal glucose, but not incretin, sensing. Defects in these cycles in some forms of diabetes might therefore provide opportunities for novel incretin-based or other therapies.Impact of Mfn1/2 deletion on glucose and incretin stimulated-insulin secretion in beta cells. (A) In control animals, glucose is taken up by beta cells through GLUT2 and metabolised by mitochondria (elongated structure) through the citrate (TCA) cycle, leading to an increased mitochondrial proton motive force (hyperpolarised Δψm), accelerated
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.
Lagou V, Jiang L, Ulrich A, et al., 2021, Random glucose GWAS in 493,036 individuals provides insights into diabetes pathophysiology, complications and treatment stratification, medRxiv
Homeostatic control of blood glucose requires different physiological responses in the fasting and post-prandial states. We reasoned that glucose measurements under non-standardised conditions (random glucose; RG) may capture diverse glucoregulatory processes more effectively than previous genome-wide association studies (GWAS) of fasting glycaemia or after standardised glucose loads. Through GWAS meta-analysis of RG in 493,036 individuals without diabetes of diverse ethnicities we identified 128 associated loci represented by 162 distinct signals, including 14 with sex-dimorphic effects, 9 discovered through trans-ethnic analysis, and 70 novel signals for glycaemic traits. Novel RG loci were particularly enriched in expression in the ileum and colon, indicating a prominent role for the gastrointestinal tract in the control of blood glucose. Functional studies and molecular dynamics simulations of coding variants of GLP1R, a well-established type 2 diabetes treatment target, provided a genetic framework for optimal selection of GLP-1R agonist therapy. We also provided new evidence from Mendelian randomisation that lung function is modulated by blood glucose and that pulmonary dysfunction is a diabetes complication. Thus, our approach based on RG GWAS provided wide-ranging insights into the biology of glucose regulation, diabetes complications and the potential for treatment stratification.Competing Interest StatementAlejandra Tomas has received grant funding from Sun Pharmaceuticals. Ivan R Corrêa, Jr is an employee of New England Biolabs, Inc., a manufacturer and vendor of reagents for life science research. Mark J Caulfield is Chief Scientist for Genomics England, a UK Government company. The views expressed in this article are those of the author(s) and not necessarily those of the NHS, the NIHR, or the Department of Health. Mark McCarthy has served on advisory panels for Pfizer, NovoNordisk and Zoe Global, has received honoraria from Merck, Pfizer, Novo No
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.
Carrat GR, Haythorne E, Tomas A, et al., 2020, The type 2 diabetes gene product STARD10 is a phosphoinositide-binding protein that controls insulin secretory granule biogenesis, Molecular Metabolism, Vol: 40, ISSN: 2212-8778
OBJECTIVE: Risk alleles for type 2 diabetes at the STARD10 locus are associated with lowered STARD10 expression in the β-cell, impaired glucose-induced insulin secretion, and decreased circulating proinsulin:insulin ratios. Although likely to serve as a mediator of intracellular lipid transfer, the identity of the transported lipids and thus the pathways through which STARD10 regulates β-cell function are not understood. The aim of this study was to identify the lipids transported and affected by STARD10 in the β-cell and the role of the protein in controlling proinsulin processing and insulin granule biogenesis and maturation. METHODS: We used isolated islets from mice deleted selectively in the β-cell for Stard10 (βStard10KO) and performed electron microscopy, pulse-chase, RNA sequencing, and lipidomic analyses. Proteomic analysis of STARD10 binding partners was executed in the INS1 (832/13) cell line. X-ray crystallography followed by molecular docking and lipid overlay assay was performed on purified STARD10 protein. RESULTS: βStard10KO islets had a sharply altered dense core granule appearance, with a dramatic increase in the number of "rod-like" dense cores. Correspondingly, basal secretion of proinsulin was increased versus wild-type islets. The solution of the crystal structure of STARD10 to 2.3 Å resolution revealed a binding pocket capable of accommodating polyphosphoinositides, and STARD10 was shown to bind to inositides phosphorylated at the 3' position. Lipidomic analysis of âStard10KO islets demonstrated changes in phosphatidylinositol levels, and the inositol lipid kinase PIP4K2C was identified as a STARD10 binding partner. Also consistent with roles for STARD10 in phosphoinositide signalling, the phosphoinositide-binding proteins Pirt and Synaptotagmin 1 were amongst the differentially expressed genes in βStard10KO islets. CONCLUSION: Our data indicate that STARD10 binds to, and may transp
Rutter GA, Georgiadou E, Rodriguez T, et al., 2020, Pancreatic beta cell-selective deletion of themitofusins 1 and 2 (Mfn1 and Mfn2) impairs glucose-stimulated insulin secretion in vitro and in vivo, 56th Annual Meeting of the European-Association-for-the-Study-of-Diabetes (EASD), Publisher: SPRINGER, Pages: S6-S7, ISSN: 0012-186X
Carrat G, Haataja L, Arvan P, et al., 2020, The type 2 diabetes-associated lipid-binding protein STARD10 could bind phosphatidylinositides and affect islet lipid composition, Publisher: WILEY, Pages: 39-39, ISSN: 0742-3071
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.
Ali UT, Suba K, Bitsi S, et al., 2020, Improving islet transplantation success by increasing expression of the epidermal growth factor receptor (EGFR), Publisher: WILEY, Pages: 36-36, ISSN: 0742-3071
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.
Salem V, Ali U, Suba K, et al., 2020, Upregulation of Pancreatic Islet EGF Receptor Improves Beta-Cell Identity and In Vivo Vascularisation in a Directly Observed Transplant Model, 80th Scientific Sessions of the American-Diabetes-Association (ADA), Publisher: AMER DIABETES ASSOC, ISSN: 0012-1797
Carrat G, Nguyen-Tu M-S, Leclerc I, et al., 2020, Binding Kinetics, GLP-1 Receptor Internalization, and Effects on Insulin Secretion for GL0034 and Related GLP-1R Agonists, 80th Scientific Sessions of the American-Diabetes-Association (ADA), Publisher: AMER DIABETES ASSOC, ISSN: 0012-1797
Georgiadou E, Chabosseau PL, Tomas A, et al., 2020, Deletion of the Mitofusins 1 and 2 (Mfn1 and Mfn2) in the Pancreatic Beta Cell Disrupts Mitochondrial Structure and Function In Vitro and Strongly Impairs Glucose-Stimulated Insulin Secretion In Vivo, 80th Scientific Sessions of the American-Diabetes-Association (ADA), Publisher: AMER DIABETES ASSOC, ISSN: 0012-1797
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.
Carrat GR, Haythorne E, Tomas A, et al., 2020, The type 2 diabetes gene product STARD10 is a phosphoinositide binding protein that controls insulin secretory granule biogenesis
<jats:title>Abstract</jats:title><jats:sec><jats:title>Objective</jats:title><jats:p>Risk alleles for type 2 diabetes at the<jats:italic>STARD10</jats:italic>locus are associated with lowered<jats:italic>STARD10</jats:italic>expression in the β-cell, impaired glucose-induced insulin secretion and decreased circulating proinsulin:insulin ratios. Although likely to serve as a mediator of intracellular lipid transfer, the identity of the transported lipids, and thus the pathways through which STARD10 regulates β-cell function, are not understood. The aim of this study was to identify the lipids transported and affected by STARD10 in the β-cell and its effect on proinsulin processing and insulin granule biogenesis and maturation.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>We used isolated islets from mice deleted selectively in the β-cell for<jats:italic>Stard10</jats:italic>(β<jats:italic>StarD10</jats:italic>KO) and performed electron microscopy, pulse-chase, RNA sequencing and lipidomic analyses. Proteomic analysis of STARD10 binding partners was executed in INS1 (832/13) cell line. X-ray crystallography followed by molecular docking and lipid overlay assay were performed on purified STARD10 protein.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>β<jats:italic>StarD10</jats:italic>KO islets had a sharply altered dense core granule appearance, with a dramatic increase in the number of “rod-like” dense cores. Correspondingly, basal secretion of proinsulin was increased. Amongst the differentially expressed genes in β<jats:italic>StarD10</jats:italic>KO islets, expression of the phosphoinositide binding proteins<jats:italic>Pirt</jats:italic>and<jats:italic>Synaptotagmin 1</jats:
Tomas A, Jones B, Leech C, 2020, New insights into beta cell GLP-1 receptor and cAMP signaling, Journal of Molecular Biology, Vol: 432, Pages: 1347-1366, ISSN: 0022-2836
Harnessing the translational potential of the GLP-1/GLP-1R system in pancreatic beta cells has led to the development of established GLP-1R-based therapies for the long-term preservation of beta cell function. In this review, we discuss recent advances in the current research on the GLP-1/GLP-1R system in beta cells, including the regulation of signaling by endocytic trafficking as well as the application of concepts such as signal bias, allosteric modulation, dual agonism, polymorphic receptor variants, spatial compartmentalization of cAMP signaling and new downstream signaling targets involved in the control of beta cell function.
Khan R, Tomas A, Rutter GA, 2020, Effects on pancreatic Beta and other Islet cells of the glucose-dependent insulinotropic polypeptide, PEPTIDES, Vol: 125, ISSN: 0196-9781
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Ast J, Arvaniti A, Fine NHF, et al., 2020, Super-resolution microscopy compatible fluorescent probes reveal endogenous glucagon-like peptide-1 receptor distribution and dynamics, Nature Communications, Vol: 11, ISSN: 2041-1723
The glucagon-like peptide-1 receptor (GLP1R) is a class B G protein-coupled receptor (GPCR) involved in metabolism. Presently, its visualization is limited to genetic manipulation, antibody detection or the use of probes that stimulate receptor activation. Herein, we present LUXendin645, a far-red fluorescent GLP1R antagonistic peptide label. LUXendin645 produces intense and specific membrane labeling throughout live and fixed tissue. GLP1R signaling can additionally be evoked when the receptor is allosterically modulated in the presence of LUXendin645. Using LUXendin645 and LUXendin651, we describe islet, brain and hESC-derived β-like cell GLP1R expression patterns, reveal higher-order GLP1R organization including membrane nanodomains, and track single receptor subpopulations. We furthermore show that the LUXendin backbone can be optimized for intravital two-photon imaging by installing a red fluorophore. Thus, our super-resolution compatible labeling probes allow visualization of endogenous GLP1R, and provide insight into class B GPCR distribution and dynamics both in vitro and in vivo.
Lakić B, Avignone FT, Betz M, et al., 2020, IAXO-the future axion helioscope, Pages: 115-118
International Axion Observatory (IAXO) is a new generation axion helioscope aiming to search for axions and axion-like particles with a sensitivity to the axion-photon coupling that is 1 to 1.5 orders of magnitude beyond the one achieved by currently the most sensitive axion helioscope, CAST. IAXO relies on large improvements in magnetic field volume, X-ray focusing optics and detector backgrounds with respect to CAST. Additional IAXO searches would include electron-coupled axions, relic axions, and other more generic axion-like particles.
Xu W, Ashford FB, Bitsi S, et al., 2020, Testosterone enhances GLP-1 efficacy at the plasma membrane and endosomes to augment insulin secretion in male pancreatic β cells, bioRxiv
Male mice with elimination of the androgen receptor (AR) in islet β cells (βARKO) 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 β cells potentiates GSIS by amplifying the insulinotropic action of glucagon-like peptide-1 (GLP-1). Here, using a combination of βARKO and β cell-selective GLP-1 receptor knockout mice and their islets, we show that AR activation in β cells amplifies the insulinotropic effect of islet-derived GLP-1. In β 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 Statement This study reveals that testosterone, acting on the androgen receptor (AR) in insulin-producing β 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 β 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 β cells in the large popul
Fremaux J, Venin C, Mauran L, et al., 2019, Ureidopeptide GLP-1 analogues with prolonged activity in vivo via signal bias and altered receptor trafficking, Chemical Science, Vol: 42, Pages: 9872-9879, ISSN: 2041-6520
The high demand of the pharmaceutical industry for new modalities to address the diversification of biological targets with large surfaces of interaction led us to investigate the replacement of α-amino acid residues with ureido units at selected positions in peptides to improve potency and generate effective incretin mimics. Based on molecular dynamics simulations, N-terminally modified GLP-1 analogues with a ureido residue replacement at position 2 were synthesized and showed preservation of agonist activity while exhibiting a substantial increase in stability. This enabling platform was applied to exenatide and lixisenatide analogues to generate two new ureidopeptides with antidiabetic properties and longer duration of action. Further analyses demonstrated that the improvement was due mainly to differences in signal bias and trafficking of the GLP-1 receptor. This study demonstrates the efficacy of single α-amino acid substitution with ureido residues to design long lasting peptides.
Bitsi S, Buenaventura T, Laughlin WE, et al., 2019, GLP-1R translocation to plasma membrane nanodomains and downstream signalling are modulated by agonist-dependent receptor palmitoylation, 55th Annual Meeting of the European-Association-for-the-Study-of-Diabetes (EASD), Publisher: SPRINGER, Pages: S215-S215, ISSN: 0012-186X
Buenaventura T, Bitsi S, Laughlin WE, et al., 2019, Agonist-induced membrane nanodomain clustering drives GLP-1 receptor responses in pancreatic beta cells., PLoS Biology, Vol: 17, Pages: 1-40, ISSN: 1544-9173
The glucagon-like peptide-1 receptor (GLP-1R), a key pharmacological target in type 2 diabetes (T2D) and obesity, undergoes rapid endocytosis after stimulation by endogenous and therapeutic agonists. We have previously highlighted the relevance of this process in fine-tuning GLP-1R responses in pancreatic beta cells to control insulin secretion. In the present study, we demonstrate an important role for the translocation of active GLP-1Rs into liquid-ordered plasma membrane nanodomains, which act as hotspots for optimal coordination of intracellular signaling and clathrin-mediated endocytosis. This process is dynamically regulated by agonist binding through palmitoylation of the GLP-1R at its carboxyl-terminal tail. Biased GLP-1R agonists and small molecule allosteric modulation both influence GLP-1R palmitoylation, clustering, nanodomain signaling, and internalization. Downstream effects on insulin secretion from pancreatic beta cells indicate that these processes are relevant to GLP-1R physiological actions and might be therapeutically targetable.
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