Differential Stimulation of Insulin Secretion by GLP-1 and Kisspeptin-10

PLOS ONE, Dec 2019

β-cells in the pancreatic islet respond to elevated plasma glucose by secreting insulin to maintain glucose homeostasis. In addition to glucose stimulation, insulin secretion is modulated by numerous G-protein coupled receptors (GPCRs). The GPCR ligands Kisspeptin-10 (KP) and glucagon-like peptide-1 (GLP-1) potentiate insulin secretion through Gq and Gs-coupled receptors, respectively. Despite many studies, the signaling mechanisms by which KP and GLP-1 potentiate insulin release are not thoroughly understood. We investigated the downstream signaling pathways of these ligands and their affects on cellular redox potential, intracellular calcium activity ([Ca2+]i), and insulin secretion from β-cells within intact murine islets. In contrast to previous studies performed on single β-cells, neither KP nor GLP-1 affect [Ca2+]i upon stimulation with glucose. KP significantly increases the cellular redox potential, while no effect is observed with GLP-1, suggesting that KP and GLP-1 potentiate insulin secretion through different mechanisms. Co-treatment with KP and the Gβγ-subunit inhibitor gallein inhibits insulin secretion similar to that observed with gallein alone, while co-treatment with gallein and GLP-1 does not differ from GLP-1 alone. In contrast, co-treatment with the Gβγ activator mSIRK and either KP or GLP-1 stimulates insulin release similar to mSIRK alone. Neither gallein nor mSIRK alter [Ca2+]i activity in the presence of KP or GLP-1. These data suggest that KP likely alters insulin secretion through a Gβγ-dependent process that stimulates glucose metabolism without altering Ca2+ activity, while GLP-1 does so, at least partly, through a Gα-dependent pathway that is independent of both metabolism and Ca2+.

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Differential Stimulation of Insulin Secretion by GLP-1 and Kisspeptin-10

Citation: Schwetz TA, Reissaus CA, Piston DW ( Differential Stimulation of Insulin Secretion by GLP-1 and Kisspeptin-10 Tara A. Schwetz 0 Christopher A. Reissaus 0 David W. Piston 0 G. William Wong, Johns Hopkins University School of Medicine, United States of America 0 1 Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville , Tennessee, United States of America, 2 Department of Physics, Vanderbilt University , Nashville , Tennessee, United States of America, 3 Department of Chemical and Biomolecular Engineering, Vanderbilt University , Nashville, Tennessee , United States of America b-cells in the pancreatic islet respond to elevated plasma glucose by secreting insulin to maintain glucose homeostasis. In addition to glucose stimulation, insulin secretion is modulated by numerous G-protein coupled receptors (GPCRs). The GPCR ligands Kisspeptin-10 (KP) and glucagon-like peptide-1 (GLP-1) potentiate insulin secretion through Gq and Gscoupled receptors, respectively. Despite many studies, the signaling mechanisms by which KP and GLP-1 potentiate insulin release are not thoroughly understood. We investigated the downstream signaling pathways of these ligands and their affects on cellular redox potential, intracellular calcium activity ([Ca2+]i), and insulin secretion from b-cells within intact murine islets. In contrast to previous studies performed on single b-cells, neither KP nor GLP-1 affect [Ca2+]i upon stimulation with glucose. KP significantly increases the cellular redox potential, while no effect is observed with GLP-1, suggesting that KP and GLP-1 potentiate insulin secretion through different mechanisms. Co-treatment with KP and the Gbc-subunit inhibitor gallein inhibits insulin secretion similar to that observed with gallein alone, while co-treatment with gallein and GLP-1 does not differ from GLP-1 alone. In contrast, co-treatment with the Gbc activator mSIRK and either KP or GLP-1 stimulates insulin release similar to mSIRK alone. Neither gallein nor mSIRK alter [Ca2+]i activity in the presence of KP or GLP-1. These data suggest that KP likely alters insulin secretion through a Gbc-dependent process that stimulates glucose metabolism without altering Ca2+ activity, while GLP-1 does so, at least partly, through a Ga-dependent pathway that is independent of both metabolism and Ca2+. - Funding: Experiments were performed in part through use of the Vanderbilt University Cell Imaging Shared Resource (supported by National Institutes of Health (NIH) grants P30DK020593, P30DK058404, and U24DK059637). This work was funded by NIH through grants F32DK091181 (TAS) and R01DK085064 (CAR, DWP), and by Vanderbilt University through the Louise B. McGavock Chair. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Insulin secretion is tightly regulated to maintain glucose homeostasis. During glucose stimulated insulin secretion (GSIS) from pancreatic b-cells, glucose is metabolized to increase the ATP/ADP ratio, which inhibits the ATP-sensitive inward rectifying potassium (KATP) channel. The b-cell is subsequently depolarized, which activates voltage-gated calcium channels (VGCC) and stimulates insulin secretion [1]. Beyond GSIS, multiple G-protein coupled receptor (GPCR) ligands also play a large role in the modulation of insulin release [2]. Since GPCRs are common therapeutic targets and constitute about 50% of drugs on the market [3], a thorough understanding of the mechanisms by which GPCR ligands modulate insulin release is crucial. Originally identified as a metastasis suppressor gene in breast cancer and melanoma cell lines, the KISS1 gene products kisspeptins have been identified as the endogenous ligands for GPR-54, expression of which has been detected in pancreatic islets. Specifically, mRNA expression of kisspeptin (KP) and GPR54 has been observed in mouse and human islets and both colocalize with murine insulin and glucagon positive cells [4,5]. Activation of GPR-54, a Gq-coupled receptor that stimulates the phospholipase-c (PLC) pathway, has been shown to potentiate insulin release from human and mouse islets [6,7] although this effect remains debated [8,9]. GLP-1 is a potent stimulator of insulin secretion. GLP-1 is an incretin hormone secreted by the L-cells of the distal intestine, and it binds to the Gs coupled GLP-1 receptor, GLP-1R [10]. GLP-1 has been shown to induce effects on multiple organ systems, including the heart, brain, and liver [11]. In the pancreas, GLP-1 stimulates insulin gene expression and proinsulin biosynthesis, in addition to its potentiation of GSIS. GLP-1 also has proliferative and anti-apoptotic effects on the b-cell [12,13]. Patients with type 2 diabetes mellitus (T2DM) display impaired GLP-1 secretion and/or responses. Because of GLP-19s modulation of pancreatic hormones (in (...truncated)


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Tara A. Schwetz, Christopher A. Reissaus, David W. Piston. Differential Stimulation of Insulin Secretion by GLP-1 and Kisspeptin-10, PLOS ONE, 2014, Volume 9, Issue 11, DOI: 10.1371/journal.pone.0113020