TY - JOUR

T1 - GLP-1 metabolite GLP-1(9–36) is a systemic inhibitor of mouse and human pancreatic islet glucagon secretion

AU - Gandasi, Nikhil R.

AU - Gao, Rui

AU - Kothegala, Lakshmi

AU - Pearce, Abigail

AU - Santos, Cristiano

AU - Acreman, Samuel

AU - Basco, Davide

AU - Benrick, Anna

AU - Chibalina, Margarita V.

AU - Clark, Anne

AU - Guida, Claudia

AU - Harris, Matthew

AU - Johnson, Paul R.V.

AU - Knudsen, Jakob G.

AU - Ma, Jinfang

AU - Miranda, Caroline

AU - Shigeto, Makoto

AU - Tarasov, Andrei I.

AU - Yeung, Ho Yan

AU - Thorens, Bernard

AU - Asterholm, Ingrid W.

AU - Zhang, Quan

AU - Ramracheya, Reshma

AU - Ladds, Graham

AU - Rorsman, Patrik

N1 - Funding Information: Studies in Göteborg were covered by a Wallenberg Scholars Fellowship (PR), an International Recruitment Award (538-2013-7107) and project grants from the (2020-01463 and 2020-02485) from the Swedish Research Council (Vetenskapsrådet). NRG’s work in Göteborg was supported by a grant from the Novo Nordisk Foundation (NRG). Initial stages of the project were supported by Diabetes UK RD Lawrence Fellowship (RR and QZ), a Novo Nordisk University of Oxford postdoctoral fellowship (CG) and a project grant from the Rosetrees Trust (PR). The isolation of human islets was funded by the National Institute for Health Research (NIHR) Oxford Biomedical Research Centre (BRC) (PRVJ and PR). The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health. Studies in Cambridge were supported by the Rosetrees foundation (to HYY and GL) and an international scholarship from the Cambridge Trust (HYY). Work in Lausanne (BT) was supported by grants from the Swiss National Science Foundation and the European Research Council. Publisher Copyright: © 2023, The Author(s).

PY - 2024

Y1 - 2024

N2 - Aims/hypothesis: Diabetes mellitus is associated with impaired insulin secretion, often aggravated by oversecretion of glucagon. Therapeutic interventions should ideally correct both defects. Glucagon-like peptide 1 (GLP-1) has this capability but exactly how it exerts its glucagonostatic effect remains obscure. Following its release GLP-1 is rapidly degraded from GLP-1(7–36) to GLP-1(9–36). We hypothesised that the metabolite GLP-1(9–36) (previously believed to be biologically inactive) exerts a direct inhibitory effect on glucagon secretion and that this mechanism becomes impaired in diabetes. Methods: We used a combination of glucagon secretion measurements in mouse and human islets (including islets from donors with type 2 diabetes), total internal reflection fluorescence microscopy imaging of secretory granule dynamics, recordings of cytoplasmic Ca2+ and measurements of protein kinase A activity, immunocytochemistry, in vivo physiology and GTP-binding protein dissociation studies to explore how GLP-1 exerts its inhibitory effect on glucagon secretion and the role of the metabolite GLP-1(9–36). Results: GLP-1(7–36) inhibited glucagon secretion in isolated islets with an IC50 of 2.5 pmol/l. The effect was particularly strong at low glucose concentrations. The degradation product GLP-1(9–36) shared this capacity. GLP-1(9–36) retained its glucagonostatic effects after genetic/pharmacological inactivation of the GLP-1 receptor. GLP-1(9–36) also potently inhibited glucagon secretion evoked by β-adrenergic stimulation, amino acids and membrane depolarisation. In islet alpha cells, GLP-1(9–36) led to inhibition of Ca2+ entry via voltage-gated Ca2+ channels sensitive to ω-agatoxin, with consequential pertussis-toxin-sensitive depletion of the docked pool of secretory granules, effects that were prevented by the glucagon receptor antagonists REMD2.59 and L-168049. The capacity of GLP-1(9–36) to inhibit glucagon secretion and reduce the number of docked granules was lost in alpha cells from human donors with type 2 diabetes. In vivo, high exogenous concentrations of GLP-1(9–36) (>100 pmol/l) resulted in a small (30%) lowering of circulating glucagon during insulin-induced hypoglycaemia. This effect was abolished by REMD2.59, which promptly increased circulating glucagon by >225% (adjusted for the change in plasma glucose) without affecting pancreatic glucagon content. Conclusions/interpretation: We conclude that the GLP-1 metabolite GLP-1(9–36) is a systemic inhibitor of glucagon secretion. We propose that the increase in circulating glucagon observed following genetic/pharmacological inactivation of glucagon signalling in mice and in people with type 2 diabetes reflects the removal of GLP-1(9–36)’s glucagonostatic action. Graphical Abstract: [Figure not available: see fulltext.]

AB - Aims/hypothesis: Diabetes mellitus is associated with impaired insulin secretion, often aggravated by oversecretion of glucagon. Therapeutic interventions should ideally correct both defects. Glucagon-like peptide 1 (GLP-1) has this capability but exactly how it exerts its glucagonostatic effect remains obscure. Following its release GLP-1 is rapidly degraded from GLP-1(7–36) to GLP-1(9–36). We hypothesised that the metabolite GLP-1(9–36) (previously believed to be biologically inactive) exerts a direct inhibitory effect on glucagon secretion and that this mechanism becomes impaired in diabetes. Methods: We used a combination of glucagon secretion measurements in mouse and human islets (including islets from donors with type 2 diabetes), total internal reflection fluorescence microscopy imaging of secretory granule dynamics, recordings of cytoplasmic Ca2+ and measurements of protein kinase A activity, immunocytochemistry, in vivo physiology and GTP-binding protein dissociation studies to explore how GLP-1 exerts its inhibitory effect on glucagon secretion and the role of the metabolite GLP-1(9–36). Results: GLP-1(7–36) inhibited glucagon secretion in isolated islets with an IC50 of 2.5 pmol/l. The effect was particularly strong at low glucose concentrations. The degradation product GLP-1(9–36) shared this capacity. GLP-1(9–36) retained its glucagonostatic effects after genetic/pharmacological inactivation of the GLP-1 receptor. GLP-1(9–36) also potently inhibited glucagon secretion evoked by β-adrenergic stimulation, amino acids and membrane depolarisation. In islet alpha cells, GLP-1(9–36) led to inhibition of Ca2+ entry via voltage-gated Ca2+ channels sensitive to ω-agatoxin, with consequential pertussis-toxin-sensitive depletion of the docked pool of secretory granules, effects that were prevented by the glucagon receptor antagonists REMD2.59 and L-168049. The capacity of GLP-1(9–36) to inhibit glucagon secretion and reduce the number of docked granules was lost in alpha cells from human donors with type 2 diabetes. In vivo, high exogenous concentrations of GLP-1(9–36) (>100 pmol/l) resulted in a small (30%) lowering of circulating glucagon during insulin-induced hypoglycaemia. This effect was abolished by REMD2.59, which promptly increased circulating glucagon by >225% (adjusted for the change in plasma glucose) without affecting pancreatic glucagon content. Conclusions/interpretation: We conclude that the GLP-1 metabolite GLP-1(9–36) is a systemic inhibitor of glucagon secretion. We propose that the increase in circulating glucagon observed following genetic/pharmacological inactivation of glucagon signalling in mice and in people with type 2 diabetes reflects the removal of GLP-1(9–36)’s glucagonostatic action. Graphical Abstract: [Figure not available: see fulltext.]

KW - GLP-1

KW - Glp1r

KW - Glucagon

KW - Glucagon receptor antagonist

KW - Granule docking

KW - Pancreatic alpha cell

KW - Type 2 diabetes

U2 - 10.1007/s00125-023-06060-w

DO - 10.1007/s00125-023-06060-w

M3 - Journal article

C2 - 38127123

AN - SCOPUS:85180215840

VL - 67

SP - 528

EP - 546

JO - Diabetologia

JF - Diabetologia

SN - 0012-186X

ER -