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Skelin Klemen M, Dolenšek J, Križančić Bombek L, Pohorec V, Gosak M, Slak Rupnik M, Stožer A. The effect of forskolin and the role of Epac2A during activation, activity, and deactivation of beta cell networks. Front Endocrinol (Lausanne) 2023; 14:1225486. [PMID: 37701894 PMCID: PMC10494243 DOI: 10.3389/fendo.2023.1225486] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/19/2023] [Accepted: 08/08/2023] [Indexed: 09/14/2023] Open
Abstract
Beta cells couple stimulation by glucose with insulin secretion and impairments in this coupling play a central role in diabetes mellitus. Cyclic adenosine monophosphate (cAMP) amplifies stimulus-secretion coupling via protein kinase A and guanine nucleotide exchange protein 2 (Epac2A). With the present research, we aimed to clarify the influence of cAMP-elevating diterpene forskolin on cytoplasmic calcium dynamics and intercellular network activity, which are two of the crucial elements of normal beta cell stimulus-secretion coupling, and the role of Epac2A under normal and stimulated conditions. To this end, we performed functional multicellular calcium imaging of beta cells in mouse pancreas tissue slices after stimulation with glucose and forskolin in wild-type and Epac2A knock-out mice. Forskolin evoked calcium signals in otherwise substimulatory glucose and beta cells from Epac2A knock-out mice displayed a faster activation. During the plateau phase, beta cells from Epac2A knock-out mice displayed a slightly higher active time in response to glucose compared with wild-type littermates, and stimulation with forskolin increased the active time via an increase in oscillation frequency and a decrease in oscillation duration in both Epac2A knock-out and wild-type mice. Functional network properties during stimulation with glucose did not differ in Epac2A knock-out mice, but the presence of Epac2A was crucial for the protective effect of stimulation with forskolin in preventing a decline in beta cell functional connectivity with time. Finally, stimulation with forskolin prolonged beta cell activity during deactivation, especially in Epac2A knock-out mice.
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Affiliation(s)
- Maša Skelin Klemen
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
| | - Jurij Dolenšek
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
- Faculty of Natural Sciences and Mathematics, University of Maribor, Maribor, Slovenia
| | | | - Viljem Pohorec
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
| | - Marko Gosak
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
- Faculty of Natural Sciences and Mathematics, University of Maribor, Maribor, Slovenia
- Alma Mater Europaea, European Center Maribor, Maribor, Slovenia
| | - Marjan Slak Rupnik
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
- Alma Mater Europaea, European Center Maribor, Maribor, Slovenia
- Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Andraž Stožer
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
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2
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Jakhar K, Vaishnavi S, Kaur P, Singh P, Munshi A. Pharmacogenomics of GLP-1 receptor agonists: Focus on pharmacological profile. Eur J Pharmacol 2022; 936:175356. [PMID: 36330902 DOI: 10.1016/j.ejphar.2022.175356] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2022] [Revised: 10/11/2022] [Accepted: 10/21/2022] [Indexed: 02/08/2023]
Abstract
Type 2 Diabetes mellitus (T2DM) is a multifactorial metabolic disorder also known as a silent killer disease. Macrovascular and microvascular complications associated with diabetes worsen the condition leading to higher comorbidity and mortality rate. Currently, available treatment strategies for diabetes include biguanides, sulfonylureas, alpha-glucosidase inhibitors, thiazolidinediones, insulin and its analogs, DPP-4 (dipeptidyl-peptidase-4) inhibitors, SGLT-2 inhibitors, and Glucagon Like Peptide-1 receptor agonists (GLP-1RAs). Synthetic agonists of GLP-1 hormone, GLP-1RAs are an emerging class of anti-diabetic drugs which target the pathophysiology of diabetes through various mechanisms and at multiple sites. They promote insulin secretion from beta cells, and the proliferation of beta cells inhibits glucagon secretion, delays gastric emptying and induces satiety. However, treatment is reported to be associated with inter-individual variations and adverse drug reactions, which are also influenced by genetic variations. There have been a few pharmacogenetic studies have been carried out on this drug class. This review discusses all the available GLP-1RAs, their pharmacokinetics, pharmacodynamics and genetic variation affecting the inter-individual variation.
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Affiliation(s)
- Kalpna Jakhar
- Department of Human Genetics and Molecular Medicine, Central University of Punjab, Bathinda, 151401, India
| | - Swetha Vaishnavi
- Department of Human Genetics and Molecular Medicine, Central University of Punjab, Bathinda, 151401, India
| | - Prabhsimran Kaur
- Department of Human Genetics and Molecular Medicine, Central University of Punjab, Bathinda, 151401, India
| | | | - Anjana Munshi
- Department of Human Genetics and Molecular Medicine, Central University of Punjab, Bathinda, 151401, India.
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3
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Epac activation ameliorates tubulointerstitial inflammation in diabetic nephropathy. Acta Pharmacol Sin 2022; 43:659-671. [PMID: 34103688 PMCID: PMC8888565 DOI: 10.1038/s41401-021-00689-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Accepted: 04/26/2021] [Indexed: 02/05/2023] Open
Abstract
Tubulointerstitial inflammation plays an important role in the progression of diabetic nephropathy (DN), and tubular epithelial cells (TECs) are crucial promoters of the inflammatory cascade. Exchange protein activated by cAMP (Epac) has been shown to suppress the angiotensin II (Ang-II)-induced release of inflammatory cytokines in tubular cells. However, the role of Epac in TEC-mediated tubulointerstitial inflammation in DN remains unknown. We found that administering the Epac agonist 8-pCPT-2'-O-Me-cAMP (8-O-cAMP) to db/db mice inhibited tubulointerstitial inflammation characterized by macrophage infiltration and increased inflammatory cytokine release and consequently alleviated tubulointerstitial fibrosis in the kidney. Furthermore, 8-O-cAMP administration restored CCAAT/enhancer binding protein β (C/EBP-β) expression and further upregulated the expression of Suppressor of cytokine signaling 3 (SOCS3), while inhibiting p-STAT3, MCP-1, IL-6, and TNF-α expression in the kidney cortex in db/db mice. And in vitro study showed that macrophage migration and MCP-1 expression induced by high glucose (HG, 30 mM) were notably reduced by 8-O-cAMP in human renal proximal tubule epithelial (HK-2) cells. In addition, 8-O-cAMP treatment restored C/EBP-β expression in HK-2 cells and promoted C/EBP-β translocation to the nucleus, where it transcriptionally upregulated SOCS3 expression, subsequently inhibiting STAT3 phosphorylation. Under HG conditions, siRNA-mediated knockdown of C/EBP-β or SOCS3 in HK-2 cells partially blocked the inhibitory effect of Epac activation on the release of MCP-1. In contrast, SOCS3 overexpression inhibited HG-induced activation of STAT3 and MCP-1 expression in HK-2 cells. These findings indicate that Epac activation via 8-O-cAMP ameliorates tubulointerstitial inflammation in DN through the C/EBP-β/SOCS3/STAT3 pathway.
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Cabrera O, Ficorilli J, Shaw J, Echeverri F, Schwede F, Chepurny OG, Leech CA, Holz GG. Intra-islet glucagon confers β-cell glucose competence for first-phase insulin secretion and favors GLP-1R stimulation by exogenous glucagon. J Biol Chem 2022; 298:101484. [PMID: 34896391 PMCID: PMC8789663 DOI: 10.1016/j.jbc.2021.101484] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2021] [Revised: 12/07/2021] [Accepted: 12/07/2021] [Indexed: 02/07/2023] Open
Abstract
We report that intra-islet glucagon secreted from α-cells signals through β-cell glucagon and GLP-1 receptors (GcgR and GLP-1R), thereby conferring to rat islets their competence to exhibit first-phase glucose-stimulated insulin secretion (GSIS). Thus, in islets not treated with exogenous glucagon or GLP-1, first-phase GSIS is abolished by a GcgR antagonist (LY2786890) or a GLP-1R antagonist (Ex[9-39]). Mechanistically, glucose competence in response to intra-islet glucagon is conditional on β-cell cAMP signaling because it is blocked by the cAMP antagonist prodrug Rp-8-Br-cAMPS-pAB. In its role as a paracrine hormone, intra-islet glucagon binds with high affinity to the GcgR, while also exerting a "spillover" effect to bind with low affinity to the GLP-1R. This produces a right shift of the concentration-response relationship for the potentiation of GSIS by exogenous glucagon. Thus, 0.3 nM glucagon fails to potentiate GSIS, as expected if similar concentrations of intra-islet glucagon already occupy the GcgR. However, 10 to 30 nM glucagon effectively engages the β-cell GLP-1R to potentiate GSIS, an action blocked by Ex[9-39] but not LY2786890. Finally, we report that the action of intra-islet glucagon to support insulin secretion requires a step-wise increase of glucose concentration to trigger first-phase GSIS. It is not measurable when GSIS is stimulated by a gradient of increasing glucose concentrations, as occurs during an oral glucose tolerance test in vivo. Collectively, such findings are understandable if defective intra-islet glucagon action contributes to the characteristic loss of first-phase GSIS in an intravenous glucose tolerance test that is diagnostic of type 2 diabetes in the clinical setting.
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Affiliation(s)
- Over Cabrera
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA.
| | - James Ficorilli
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA
| | - Janice Shaw
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA
| | | | - Frank Schwede
- Biolog Life Science Institute GmbH & Co KG, Bremen, Germany
| | - Oleg G Chepurny
- Department of Medicine, State University of New York (SUNY) Upstate Medical University, Syracuse, New York, USA
| | - Colin A Leech
- Department of Medicine, State University of New York (SUNY) Upstate Medical University, Syracuse, New York, USA
| | - George G Holz
- Department of Medicine, State University of New York (SUNY) Upstate Medical University, Syracuse, New York, USA; Department of Pharmacology, State University of New York (SUNY) Upstate Medical University, Syracuse, New York, USA.
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Mkaouar R, Abdallah LCB, Naouali C, Lahbib S, Turki Z, Elouej S, Bouyacoub Y, Somai M, Mcelreavey K, Bashamboo A, Abdelhak S, Messaoud O. Oligogenic Inheritance Underlying Incomplete Penetrance of PROKR2 Mutations in Hypogonadotropic Hypogonadism. Front Genet 2021; 12:665174. [PMID: 34539727 PMCID: PMC8446458 DOI: 10.3389/fgene.2021.665174] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2021] [Accepted: 07/05/2021] [Indexed: 11/17/2022] Open
Abstract
The role of the prokineticin 2 pathway in human reproduction, olfactory bulb morphogenesis, and gonadotropin-releasing hormone secretion is well established. Recent studies have highlighted the implication of di/oligogenic inheritance in this disorder. In the present study, we aimed to identify the genetic mechanisms that could explain incomplete penetrance in hypogonadotropic hypogonadism (HH). This study involved two unrelated Tunisian patients with HH, which was triggered by identifying a homozygous p.(Pro290Ser) mutation in the PROKR2 gene in a girl (HH1) with Kallmann syndrome (KS). The functional effect of this variant has previously been well demonstrated. Unexpectedly, her unaffected father (HH1P) and brother (HH1F) also carried this genetic variation at a homozygous state. In the second family, we identified a heterozygous p.(Lys205del) mutation in PROKR2, both in a male patient with normosmic idiopathic IHH (HH12) and his asymptomatic mother. Whole-exome sequencing in the three HH1 family members allowed the identification of additional variants in the prioritized genes. We then carried out digenic combination predictions using the oligogenic resource for variant analysis (ORVAL) software. For HH1, we found the highest number of disease-causing variant pairs. Notably, a CCDC141 variant (c.2803C > T) was involved in 18 pathogenic digenic combinations. The CCDC141 variant acts in an autosomal recessive inheritance mode, based on the digenic effect prediction data. For the second patient (HH12), prediction by ORVAL allowed the identification of an interesting pathogenic digenic combination between DUSP6 and SEMA7A genes, predicted as “dual molecular diagnosis.” The SEMA7A variant p.(Glu436Lys) is novel and predicted as a VUS by Varsome. Sanger validation revealed the absence of this variant in the healthy mother. We hypothesize that disease expression in HH12 could be induced by the digenic transmission of the SEMA7A and DUSP6 variants or a monogenic inheritance involving only the SEMA7A VUS if further functional assays allow its reclassification into pathogenic. Our findings confirm that homozygous loss-of-function genetic variations are insufficient to cause KS, and that oligogenism is most likely the main transmission mode involved in Congenital Hypogonadotropic Hypogonadism.
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Affiliation(s)
- Rahma Mkaouar
- Laboratoire de Génomique Biomédicale et Oncogénétique, Institut Pasteur de Tunis, Tunis, Tunisia.,Faculté des Sciences Mathématiques, Physiques et Naturelles de Tunis, Université de Tunis El Manar, Tunis, Tunisia
| | | | - Chokri Naouali
- Laboratoire de Génomique Biomédicale et Oncogénétique, Institut Pasteur de Tunis, Tunis, Tunisia
| | - Saida Lahbib
- Laboratoire de Génomique Biomédicale et Oncogénétique, Institut Pasteur de Tunis, Tunis, Tunisia
| | - Zinet Turki
- Département d'Endocrinologie et de Technologie Alimentaire, Institut de Nutrition, Tunis, Tunisia
| | - Sahar Elouej
- Laboratoire de Génomique Biomédicale et Oncogénétique, Institut Pasteur de Tunis, Tunis, Tunisia
| | - Yosra Bouyacoub
- Laboratoire de Génomique Biomédicale et Oncogénétique, Institut Pasteur de Tunis, Tunis, Tunisia
| | - Maali Somai
- Département d'Endocrinologie et de Technologie Alimentaire, Institut de Nutrition, Tunis, Tunisia
| | | | - Anu Bashamboo
- Génétique du Développement Humain, Institut Pasteur, Paris, France
| | - Sonia Abdelhak
- Laboratoire de Génomique Biomédicale et Oncogénétique, Institut Pasteur de Tunis, Tunis, Tunisia
| | - Olfa Messaoud
- Laboratoire de Génomique Biomédicale et Oncogénétique, Institut Pasteur de Tunis, Tunis, Tunisia
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6
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Reverte-Salisa L, Sanyal A, Pfeifer A. Role of cAMP and cGMP Signaling in Brown Fat. Handb Exp Pharmacol 2019; 251:161-182. [PMID: 29633180 DOI: 10.1007/164_2018_117] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Cold-induced activation of brown adipose tissue (BAT) is mediated by norepinephrine and adenosine that are released during sympathetic nerve activation. Both signaling molecules induce an increase in intracellular levels of 3',5'-cyclic adenosine monophosphate (cAMP) in murine and human BAT. In brown adipocytes, cAMP plays a central role, because it activates lipolysis, glucose uptake, and thermogenesis. Another well-studied intracellular second messenger is 3',5'-cyclic guanosine monophosphate (cGMP), which closely resembles cAMP. Several studies have shown that intact cGMP signaling is essential for normal adipogenic differentiation and BAT-mediated thermogenesis in mice. This chapter highlights recent observations, demonstrating the physiological significance of cyclic nucleotide signaling in BAT as well as their potential to induce browning of white adipose tissue (WAT) in mice and humans.
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Affiliation(s)
- Laia Reverte-Salisa
- Institute of Pharmacology and Toxicology, University Hospital Bonn, University of Bonn, Bonn, Germany
| | - Abhishek Sanyal
- Institute of Pharmacology and Toxicology, University Hospital Bonn, University of Bonn, Bonn, Germany
| | - Alexander Pfeifer
- Institute of Pharmacology and Toxicology, University Hospital Bonn, University of Bonn, Bonn, Germany.
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7
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Veluthakal R, Chepurny OG, Leech CA, Schwede F, Holz GG, Thurmond DC. Restoration of Glucose-Stimulated Cdc42-Pak1 Activation and Insulin Secretion by a Selective Epac Activator in Type 2 Diabetic Human Islets. Diabetes 2018; 67:1999-2011. [PMID: 29986926 PMCID: PMC6152341 DOI: 10.2337/db17-1174] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Accepted: 06/29/2018] [Indexed: 12/20/2022]
Abstract
Glucose metabolism stimulates cell division control protein 42 homolog (Cdc42)-p21-activated kinase (Pak1) activity and initiates filamentous actin (F-actin) cytoskeleton remodeling in pancreatic β-cells so that cytoplasmic secretory granules can translocate to the plasma membrane where insulin exocytosis occurs. Since glucose metabolism also generates cAMP in β-cells, the cross talk of cAMP signaling with Cdc42-Pak1 activation might be of fundamental importance to glucose-stimulated insulin secretion (GSIS). Previously, the type-2 isoform of cAMP-regulated guanine nucleotide exchange factor 2 (Epac2) was established to mediate a potentiation of GSIS by cAMP-elevating agents. Here we report that nondiabetic human islets and INS-1 832/13 β-cells treated with the selective Epac activator 8-pCPT-2'-O-Me-cAMP-AM exhibited Cdc42-Pak1 activation at 1 mmol/L glucose and that the magnitude of this effect was equivalent to that which was measured during stimulation with 20 mmol/L glucose in the absence of 8-pCPT-2'-O-Me-cAMP-AM. Conversely, the cAMP antagonist Rp-8-Br-cAMPS-pAB prevented glucose-stimulated Cdc42-Pak1 activation, thereby blocking GSIS while also increasing cellular F-actin content. Although islets from donors with type 2 diabetes had profound defects in glucose-stimulated Cdc42-Pak1 activation and insulin secretion, these defects were rescued by the Epac activator so that GSIS was restored. Collectively, these findings indicate an unexpected role for cAMP as a permissive or direct metabolic coupling factor in support of GSIS that is Epac2 and Cdc42-Pak1 regulated.
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Affiliation(s)
- Rajakrishnan Veluthakal
- Department of Molecular and Cellular Endocrinology, Diabetes and Metabolism Research Institute, Beckman Research Institute of City of Hope, Duarte, CA
| | - Oleg G Chepurny
- Department of Medicine, State University of New York, Upstate Medical University, Syracuse, NY
| | - Colin A Leech
- Department of Medicine, State University of New York, Upstate Medical University, Syracuse, NY
- Department of Surgery, State University of New York, Upstate Medical University, Syracuse, NY
| | | | - George G Holz
- Department of Medicine, State University of New York, Upstate Medical University, Syracuse, NY
- Department of Pharmacology, State University of New York, Upstate Medical University, Syracuse, NY
| | - Debbie C Thurmond
- Department of Molecular and Cellular Endocrinology, Diabetes and Metabolism Research Institute, Beckman Research Institute of City of Hope, Duarte, CA
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8
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Robichaux WG, Cheng X. Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development. Physiol Rev 2018; 98:919-1053. [PMID: 29537337 PMCID: PMC6050347 DOI: 10.1152/physrev.00025.2017] [Citation(s) in RCA: 138] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Revised: 09/05/2017] [Accepted: 09/06/2017] [Indexed: 12/13/2022] Open
Abstract
This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.
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Affiliation(s)
- William G Robichaux
- Department of Integrative Biology and Pharmacology, Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center , Houston, Texas
| | - Xiaodong Cheng
- Department of Integrative Biology and Pharmacology, Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center , Houston, Texas
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9
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Tengholm A, Gylfe E. cAMP signalling in insulin and glucagon secretion. Diabetes Obes Metab 2017; 19 Suppl 1:42-53. [PMID: 28466587 DOI: 10.1111/dom.12993] [Citation(s) in RCA: 130] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/27/2017] [Revised: 04/24/2017] [Accepted: 04/26/2017] [Indexed: 01/24/2023]
Abstract
The "second messenger" archetype cAMP is one of the most important cellular signalling molecules with central functions including the regulation of insulin and glucagon secretion from the pancreatic β- and α-cells, respectively. cAMP is generally considered as an amplifier of insulin secretion triggered by Ca2+ elevation in the β-cells. Both messengers are also positive modulators of glucagon release from α-cells, but in this case cAMP may be the important regulator and Ca2+ have a more permissive role. The actions of cAMP are mediated by protein kinase A (PKA) and the guanine nucleotide exchange factor Epac. The present review focuses on how cAMP is regulated by nutrients, hormones and neural factors in β- and α-cells via adenylyl cyclase-catalysed generation and phosphodiesterase-mediated degradation. We will also discuss how PKA and Epac affect ion fluxes and the secretory machinery to transduce the stimulatory effects on insulin and glucagon secretion. Finally, we will briefly describe disturbances of the cAMP system associated with diabetes and how cAMP signalling can be targeted to normalize hypo- and hypersecretion of insulin and glucagon, respectively, in diabetic patients.
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Affiliation(s)
- Anders Tengholm
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
| | - Erik Gylfe
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
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Emery AC, Xu W, Eiden MV, Eiden LE. Guanine nucleotide exchange factor Epac2-dependent activation of the GTP-binding protein Rap2A mediates cAMP-dependent growth arrest in neuroendocrine cells. J Biol Chem 2017; 292:12220-12231. [PMID: 28546426 DOI: 10.1074/jbc.m117.790329] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2017] [Revised: 05/23/2017] [Indexed: 11/06/2022] Open
Abstract
First messenger-dependent activation of MAP kinases in neuronal and endocrine cells is critical for cell differentiation and function and requires guanine nucleotide exchange factor (GEF)-mediated activation of downstream Ras family small GTPases, which ultimately lead to ERK, JNK, and p38 phosphorylation. Because there are numerous GEFs and also a host of Ras family small GTPases, it is important to know which specific GEF-small GTPase dyad functions in a given cellular process. Here we investigated the upstream activators and downstream effectors of signaling via the GEF Epac2 in the neuroendocrine NS-1 cell line. Three cAMP sensors, Epac2, PKA, and neuritogenic cAMP sensor-Rapgef2, mediate distinct cellular outputs: p38-dependent growth arrest, cAMP response element-binding protein-dependent cell survival, and ERK-dependent neuritogenesis, respectively, in these cells. Previously, we found that cAMP-induced growth arrest of PC12 and NS-1 cells requires Epac2-dependent activation of p38 MAP kinase, which posed the important question of how Epac2 engages p38 without simultaneously activating other MAP kinases in neuronal and endocrine cells. We now show that the small GTP-binding protein Rap2A is the obligate effector for, and GEF substrate of, Epac2 in mediating growth arrest through p38 activation in NS-1 cells. This new pathway is distinctly parcellated from the G protein-coupled receptor → Gs → adenylate cyclase → cAMP → PKA → cAMP response element-binding protein pathway mediating cell survival and the G protein-coupled receptor → Gs → adenylate cyclase → cAMP → neuritogenic cAMP sensor-Rapgef2 → B-Raf → MEK → ERK pathway mediating neuritogenesis in NS-1 cells.
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Affiliation(s)
- Andrew C Emery
- Section on Molecular Neuroscience, National Institute of Mental Health Intramural Research Program, Bethesda, Maryland 20892
| | - Wenqin Xu
- Section on Molecular Neuroscience, National Institute of Mental Health Intramural Research Program, Bethesda, Maryland 20892
| | - Maribeth V Eiden
- Office of the Scientific Director, National Institute of Mental Health Intramural Research Program, Bethesda, Maryland 20892
| | - Lee E Eiden
- Section on Molecular Neuroscience, National Institute of Mental Health Intramural Research Program, Bethesda, Maryland 20892.
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11
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Simvastatin Impairs Insulin Secretion by Multiple Mechanisms in MIN6 Cells. PLoS One 2015; 10:e0142902. [PMID: 26561346 PMCID: PMC4641640 DOI: 10.1371/journal.pone.0142902] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2015] [Accepted: 10/28/2015] [Indexed: 01/17/2023] Open
Abstract
Statins are widely used in the treatment of hypercholesterolemia and are efficient in the prevention of cardiovascular disease. Molecular mechanisms explaining statin-induced impairment in insulin secretion remain largely unknown. In the current study, we show that simvastatin decreased glucose-stimulated insulin secretion in mouse pancreatic MIN6 β-cells by 59% and 79% (p<0.01) at glucose concentration of 5.5 mmol/l and 16.7 mmol/l, respectively, compared to control, whereas pravastatin did not impair insulin secretion. Simvastatin induced decrease in insulin secretion occurred through multiple targets. In addition to its established effects on ATP-sensitive potassium channels (p = 0.004) and voltage-gated calcium channels (p = 0.004), simvastatin suppressed insulin secretion stimulated by muscarinic M3 or GPR40 receptor agonists (Tak875 by 33%, p = 0.002; GW9508 by 77%, p = 0.01) at glucose level of 5.5 mmol/l, and inhibited calcium release from the endoplasmic reticulum. Impaired insulin secretion caused by simvastatin treatment were efficiently restored by GPR119 or GLP-1 receptor stimulation and by direct activation of cAMP-dependent signaling pathways with forskolin. The effects of simvastatin treatment on insulin secretion were not affected by the presence of hyperglycemia. Our observation of the opposite effects of simvastatin and pravastatin on glucose-stimulated insulin secretion is in agreement with previous reports showing that simvastatin, but not pravastatin, was associated with increased risk of incident diabetes.
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12
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Zhang Y, Wang H, Guo Q, Li X, Gao J, Liu Y, Yang C, Niu L, Yang J. PI3K is involved in P2Y receptor-regulated cAMP /Epac/Kv channel signaling pathway in pancreatic β cells. Biochem Biophys Res Commun 2015; 465:714-8. [PMID: 26296468 DOI: 10.1016/j.bbrc.2015.08.057] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Accepted: 08/13/2015] [Indexed: 12/20/2022]
Abstract
P2Y receptors (P2YR) are a family of purinergic G protein-coupled receptors, which could be stimulated by extracellular nucleotides. In pancreatic β cells, activation of P2YR has long been shown to stimulate insulin secretion in a glucose-dependent manner. Previously, we reported that P2YR-modulated insulin secretion is mediated by a cAMP/Epac/Kv channel pathway. However, the interaction between Epac and the Kv channel in P2YR-modulated insulin secretion remains unclear. In this study, we used patch-clamp technique and insulin secretion assay to investigate the potential molecules that may link Epac to Kv channel inhibition induced by P2YR activation. We identified that phosphatidylinositide 3-kinase, which mediates P2YR-regulated insulin secretion, is a critical mediator between Epac and the Kv channel.
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Affiliation(s)
- Yi Zhang
- Department of Pharmacology, Shanxi Medical University, Taiyuan, China.
| | - Hui Wang
- Department of Pharmacology, Shanxi Medical University, Taiyuan, China.
| | - Qing Guo
- Department of Pharmacology, Shanxi Medical University, Taiyuan, China.
| | - Xiaodong Li
- Department of Pharmacology, Shanxi Medical University, Taiyuan, China.
| | - Jingying Gao
- Department of Pharmacology, Shanxi Medical University, Taiyuan, China.
| | - Yunfeng Liu
- Department of Endocrinology, The First Hospital of Shanxi Medical University, Shanxi Medical University, Taiyuan, China.
| | - Caihong Yang
- Department of Pharmacology, Shanxi Medical University, Taiyuan, China.
| | - Longgang Niu
- Department of Pharmacology, Shanxi Medical University, Taiyuan, China.
| | - Jing Yang
- Department of Endocrinology, The First Hospital of Shanxi Medical University, Shanxi Medical University, Taiyuan, China.
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13
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Parnell E, Smith BO, Yarwood SJ. The cAMP sensors, EPAC1 and EPAC2, display distinct subcellular distributions despite sharing a common nuclear pore localisation signal. Cell Signal 2015; 27:989-96. [PMID: 25683912 PMCID: PMC4372255 DOI: 10.1016/j.cellsig.2015.02.009] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2014] [Accepted: 02/08/2015] [Indexed: 11/22/2022]
Abstract
We have identified a conserved nuclear pore localisation signal (NPLS; amino acids 764-838 of EPAC1) in the catalytic domains of the cAMP-sensors, EPAC1 and EPAC2A. Consequently, EPAC1 is mainly localised to the nuclear pore complex in HEK293T cells where it becomes activated following stimulation with cAMP. In contrast, structural models indicate that the cAMP-binding domain of EPAC2A (CNBD1) blocks access to the conserved NPLS in EPAC2A, reducing its ability to interact with nuclear binding sites. Consequently, a naturally occurring EPAC2 isoform, EPAC2B, which lacks CNBD1 is enriched in nuclear fractions, similar to EPAC1. Structural differences in EPAC isoforms may therefore determine their intracellular location and their response to elevations in intracellular cAMP.
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Affiliation(s)
- Euan Parnell
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, G12 8QQ, UK
| | - Brian O Smith
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, G12 8QQ, UK
| | - Stephen J Yarwood
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, G12 8QQ, UK.
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14
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Zhang Y, Guo Q, Li X, Gao J, Liu Y, Yang J, Li Q. P2Y purinergic receptor-regulated insulin secretion is mediated by a cAMP/Epac/Kv channel pathway. Biochem Biophys Res Commun 2015; 460:850-6. [PMID: 25839655 DOI: 10.1016/j.bbrc.2015.03.121] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2015] [Accepted: 03/21/2015] [Indexed: 10/23/2022]
Abstract
Enhancement of insulin secretion is a major therapeutic approach for type 2 diabetes (T2D). Activation of P2Y purinergic receptor (P2YR) causes potentiation of insulin secretion in a glucose-dependent manner, making it a promising therapeutic target for T2D. Here we show that activation of P2YR to potentiate insulin secretion is mediated by adenylyl cyclase/cyclic AMP (cAMP) and the downstream effector, exchange protein directly activated by cAMP (Epac), leading to inhibition of voltage-dependent potassium (Kv) channels. P2YR-mediated Kv channel inhibition results in prolongation of action potential duration, and in turn elevates intracellular Ca(2+) level and insulin secretion. Taken together, the data indicate that cAMP/Epac/Kv channel pathway mediates P2YR-regulated insulin secretion, which may have important therapeutic implications for T2D.
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Affiliation(s)
- Yi Zhang
- Department of Pharmacology, Shanxi Medical University, Taiyuan 030001, China.
| | - Qing Guo
- Department of Pharmacology, Shanxi Medical University, Taiyuan 030001, China.
| | - Xiaodong Li
- Department of Pharmacology, Shanxi Medical University, Taiyuan 030001, China.
| | - Jingying Gao
- Department of Pharmacology, Shanxi Medical University, Taiyuan 030001, China.
| | - Yunfeng Liu
- Department of Endocrinology, the First Hospital of Shanxi Medical University, Shanxi Medical University, Taiyuan, China.
| | - Jing Yang
- Department of Endocrinology, the First Hospital of Shanxi Medical University, Shanxi Medical University, Taiyuan, China.
| | - Qingshan Li
- School of Pharmaceutical Sciences, Shanxi Medical University, Taiyuan, China.
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15
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Henquin JC, Nenquin M. Activators of PKA and Epac distinctly influence insulin secretion and cytosolic Ca2+ in female mouse islets stimulated by glucose and tolbutamide. Endocrinology 2014; 155:3274-87. [PMID: 24977470 PMCID: PMC4255079 DOI: 10.1210/en.2014-1247] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Amplification of insulin secretion by cAMP is mediated by protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac). Using selective activators, we determined how each effector influences the cytosolic free Ca(2+) concentration ([Ca(2+)]c) and insulin secretion in mouse islets. Alone PKA activator amplified glucose- and tolbutamide-induced insulin secretion, with a greater impact on second than first phase. Epac activator strongly amplified both phases in response to either secretagogue. Amplification was even greater when activators were combined. Although both activators similarly amplified glucose-induced insulin secretion, Epac activator was particularly efficient on tolbutamide-induced insulin secretion. That greater efficacy is attributed to higher [Ca(2+)]c rather than interaction of tolbutamide with Epac, because it was also observed during KCl stimulation. Moreover, in contrast to Epac activator, tolbutamide was inactive when insulin secretion was increased by gliclazide, and its effect on glucose-induced insulin secretion was unaffected by an inhibitor of Epac2. PKA activator increased [Ca(2+)]c during acute or steady-state glucose stimulation, whereas Epac activator had no effect alone or in combination. Neither activator affected [Ca(2+)]c response to tolbutamide or KCl. Metabolic (glucose-mediated) amplification of insulin secretion was unaffected by PKA activator. It was attenuated when insulin secretion was augmented by Epac activator but insensitive to Epac2 inhibitor, which suggests distinct although somewhat overlapping mechanisms. In conclusion, activators of PKA and Epac amplify insulin secretion by augmenting the action of Ca(2+) on exocytosis and, for PKA only, slightly increasing glucose-induced [Ca(2+)]c rise. The influence of Epac seems more important than that of PKA during first phase.
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Affiliation(s)
- Jean-Claude Henquin
- Unit of Endocrinology and Metabolism, Faculty of Medicine, Université Catholique de Louvain, B-1200 Brussels, Belgium
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16
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Almahariq M, Mei FC, Cheng X. Cyclic AMP sensor EPAC proteins and energy homeostasis. Trends Endocrinol Metab 2014; 25:60-71. [PMID: 24231725 PMCID: PMC3946731 DOI: 10.1016/j.tem.2013.10.004] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Revised: 09/30/2013] [Accepted: 10/11/2013] [Indexed: 12/16/2022]
Abstract
The pleiotropic second-messenger cAMP plays a crucial role in mediating the effects of various hormones on metabolism. The major intracellular functions of cAMP are transduced by protein kinase A (PKA) and by exchange proteins directly activated by cAMP (EPACs). The latter act as guanine-nucleotide exchange factors for the RAS-like small G proteins Rap1 and Rap2. Although the role of PKA in regulating energy balance has been extensively studied, the impact of EPACs remains relatively enigmatic. This review summarizes recent genetic and pharmacological studies concerning EPAC involvement in glucose homeostasis and energy balance via the regulation of leptin and insulin signaling pathways. In addition, the development of small-molecule EPAC-specific modulators and their therapeutic potential for the treatment of diabetes and obesity are discussed.
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Affiliation(s)
- Muayad Almahariq
- Department of Pharmacology and Toxicology, The University of Texas Medical Branch, Galveston, Texas 77555-0615, USA
| | - Fang C Mei
- Department of Pharmacology and Toxicology, The University of Texas Medical Branch, Galveston, Texas 77555-0615, USA; Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center, Houston, Texas 77030, USA
| | - Xiaodong Cheng
- Department of Pharmacology and Toxicology, The University of Texas Medical Branch, Galveston, Texas 77555-0615, USA; Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center, Houston, Texas 77030, USA.
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17
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VMAT2 identified as a regulator of late-stage β-cell differentiation. Nat Chem Biol 2013; 10:141-8. [PMID: 24316738 DOI: 10.1038/nchembio.1410] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2012] [Accepted: 10/15/2013] [Indexed: 02/06/2023]
Abstract
Cell replacement therapy for diabetes mellitus requires cost-effective generation of high-quality, insulin-producing, pancreatic β cells from pluripotent stem cells. Development of this technique has been hampered by a lack of knowledge of the molecular mechanisms underlying β-cell differentiation. The present study identified reserpine and tetrabenazine (TBZ), both vesicular monoamine transporter 2 (VMAT2) inhibitors, as promoters of late-stage differentiation of Pdx1-positive pancreatic progenitor cells into Neurog3 (referred to henceforth as Ngn3)-positive endocrine precursors. VMAT2-controlled monoamines, such as dopamine, histamine and serotonin, negatively regulated β-cell differentiation. Reserpine or TBZ acted additively with dibutyryl adenosine 3',5'-cyclic AMP, a cell-permeable cAMP analog, to potentiate differentiation of embryonic stem (ES) cells into β cells that exhibited glucose-stimulated insulin secretion. When ES cell-derived β cells were transplanted into AKITA diabetic mice, the cells reversed hyperglycemia. Our protocol provides a basis for the understanding of β-cell differentiation and its application to a cost-effective production of functional β cells for cell therapy.
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18
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Song WJ, Mondal P, Li Y, Lee SE, Hussain MA. Pancreatic β-cell response to increased metabolic demand and to pharmacologic secretagogues requires EPAC2A. Diabetes 2013; 62:2796-807. [PMID: 23578994 PMCID: PMC3717830 DOI: 10.2337/db12-1394] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Incretin hormone action on β-cells stimulates in parallel two different intracellular cyclic AMP-dependent signaling branches mediated by protein kinase A and exchange protein activated by cAMP islet/brain isoform 2A (EPAC2A). Both pathways contribute toward potentiation of glucose-stimulated insulin secretion (GSIS). However, the overall functional role of EPAC2A in β-cells as it relates to in vivo glucose homeostasis remains incompletely understood. Therefore, we have examined in vivo GSIS in global EPAC2A knockout mice. Additionally, we have conducted in vitro studies of GSIS and calcium dynamics in isolated EPAC2A-deficient islets. EPAC2A deficiency does not impact GSIS in mice under basal conditions. However, when mice are exposed to diet-induced insulin resistance, pharmacologic secretagogue stimulation of β-cells with an incretin hormone glucagon-like peptide-1 analog or with a fatty acid receptor 1/G protein-coupled receptor 40 selective activator, EPAC2A is required for the increased β-cell response to secretory demand. Under these circumstances, EPAC2A is required for potentiating the early dynamic increase in islet calcium levels after glucose stimulation, which is reflected in potentiated first-phase insulin secretion. These studies broaden our understanding of EPAC2A function and highlight its significance during increased secretory demand or drive on β-cells. Our findings advance the rationale for developing EPAC2A-selective pharmacologic activators for β-cell-targeted pharmacotherapy in type 2 diabetes.
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Affiliation(s)
- Woo-Jin Song
- Department of Pediatrics, Johns Hopkins University, Baltimore, Maryland
| | - Prosenjit Mondal
- Department of Pediatrics, Johns Hopkins University, Baltimore, Maryland
| | - Yuanyuan Li
- Department of Pediatrics, Johns Hopkins University, Baltimore, Maryland
| | - Suh Eun Lee
- Department of Pediatrics, Johns Hopkins University, Baltimore, Maryland
| | - Mehboob A. Hussain
- Department of Pediatrics, Johns Hopkins University, Baltimore, Maryland
- Department of Medicine, Johns Hopkins University, Baltimore, Maryland
- Department of Biological Chemistry, Johns Hopkins University, Baltimore, Maryland
- Corresponding author: Mehboob A. Hussain,
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19
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Yang SK, Xiao L, Li J, Liu F, Sun L, Kanwar YS. Role of guanine-nucleotide exchange factor Epac in renal physiology and pathophysiology. Am J Physiol Renal Physiol 2013; 304:F831-9. [PMID: 23364803 PMCID: PMC3625846 DOI: 10.1152/ajprenal.00711.2012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2012] [Accepted: 01/28/2013] [Indexed: 12/13/2022] Open
Abstract
Exchange proteins directly activated by cAMP [Epac(s)] were discovered more than a decade ago as new sensors for the second messenger cAMP. The Epac family members, including Epac1 and Epac2, are guanine nucleotide exchange factors for the Ras-like small GTPases Rap1 and Rap2, and they function independently of protein kinase A. Given the importance of cAMP in kidney homeostasis, several molecular and cellular studies using specific Epac agonists have analyzed the role and regulation of Epac proteins in renal physiology and pathophysiology. The specificity of the functions of Epac proteins may depend upon their expression and localization in the kidney as well as their abundance in the microcellular environment. This review discusses recent literature data concerning the involvement of Epac in renal tubular transport physiology and renal glomerular cells where various signaling pathways are known to be operative. In addition, the potential role of Epac in kidney disorders, such as diabetic kidney disease and ischemic kidney injury, is discussed.
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Affiliation(s)
- Shi-kun Yang
- Department of Nephrology, The Second Xiangya Hospital, Kidney Institute of Nephrology, Central South University, Changsha, Hunan Province, China
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20
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Schmidt M, Dekker FJ, Maarsingh H. Exchange protein directly activated by cAMP (epac): a multidomain cAMP mediator in the regulation of diverse biological functions. Pharmacol Rev 2013; 65:670-709. [PMID: 23447132 DOI: 10.1124/pr.110.003707] [Citation(s) in RCA: 203] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Since the discovery nearly 60 years ago, cAMP is envisioned as one of the most universal and versatile second messengers. The tremendous feature of cAMP to tightly control highly diverse physiologic processes, including calcium homeostasis, metabolism, secretion, muscle contraction, cell fate, and gene transcription, is reflected by the award of five Nobel prizes. The discovery of Epac (exchange protein directly activated by cAMP) has ignited a new surge of cAMP-related research and has depicted novel cAMP properties independent of protein kinase A and cyclic nucleotide-gated channels. The multidomain architecture of Epac determines its activity state and allows cell-type specific protein-protein and protein-lipid interactions that control fine-tuning of pivotal biologic responses through the "old" second messenger cAMP. Compartmentalization of cAMP in space and time, maintained by A-kinase anchoring proteins, phosphodiesterases, and β-arrestins, contributes to the Epac signalosome of small GTPases, phospholipases, mitogen- and lipid-activated kinases, and transcription factors. These novel cAMP sensors seem to implement certain unexpected signaling properties of cAMP and thereby to permit delicate adaptations of biologic responses. Agonists and antagonists selective for Epac are developed and will support further studies on the biologic net outcome of the activation of Epac. This will increase our current knowledge on the pathophysiology of devastating diseases, such as diabetes, cognitive impairment, renal and heart failure, (pulmonary) hypertension, asthma, and chronic obstructive pulmonary disease. Further insights into the cAMP dynamics executed by the Epac signalosome will help to optimize the pharmacological treatment of these diseases.
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Affiliation(s)
- Martina Schmidt
- Department of Molecular Pharmacology, Groningen Research Institute for Pharmacy, University of Groningen, 9713 AV Groningen, The Netherlands.
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21
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Meloni AR, DeYoung MB, Lowe C, Parkes DG. GLP-1 receptor activated insulin secretion from pancreatic β-cells: mechanism and glucose dependence. Diabetes Obes Metab 2013; 15:15-27. [PMID: 22776039 PMCID: PMC3556522 DOI: 10.1111/j.1463-1326.2012.01663.x] [Citation(s) in RCA: 225] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/30/2012] [Revised: 06/19/2012] [Accepted: 07/05/2012] [Indexed: 12/18/2022]
Abstract
The major goal in the treatment of type 2 diabetes mellitus is to control the hyperglycaemia characteristic of the disease. However, treatment with common therapies such as insulin or insulinotrophic sulphonylureas (SU), while effective in reducing hyperglycaemia, may impose a greater risk of hypoglycaemia, as neither therapy is self-regulated by ambient blood glucose concentrations. Hypoglycaemia has been associated with adverse physical and psychological outcomes and may contribute to negative cardiovascular events; hence minimization of hypoglycaemia risk is clinically advantageous. Stimulation of insulin secretion from pancreatic β-cells by glucagon-like peptide 1 receptor (GLP-1R) agonists is known to be glucose-dependent. GLP-1R agonists potentiate glucose-stimulated insulin secretion and have little or no activity on insulin secretion in the absence of elevated blood glucose concentrations. This 'glucose-regulated' activity of GLP-1R agonists makes them useful and potentially safer therapeutics for overall glucose control compared to non-regulated therapies; hyperglycaemia can be reduced with minimal hypoglycaemia. While the inherent mechanism of action of GLP-1R agonists mediates their glucose dependence, studies in rats suggest that SUs may uncouple this dependence. This hypothesis is supported by clinical studies showing that the majority of events of hypoglycaemia in patients treated with GLP-1R agonists occur in patients treated with a concomitant SU. This review aims to discuss the current understanding of the mechanisms by which GLP-1R signalling promotes insulin secretion from pancreatic β-cells via a glucose-dependent process.
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Affiliation(s)
- A R Meloni
- Amylin Pharmaceuticals, Inc., San Diego, CA 92121, USA.
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22
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Abstract
Insulin secretion from pancreatic β-cells is tightly regulated by glucose and other nutrients, hormones, and neural factors. The exocytosis of insulin granules is triggered by an elevation of the cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) and is further amplified by cyclic AMP (cAMP). Cyclic AMP is formed primarily in response to glucoincretin hormones and other G(s)-coupled receptor agonists, but generation of the nucleotide is critical also for an optimal insulin secretory response to glucose. Nutrient and receptor stimuli trigger oscillations of the cAMP concentration in β-cells. The oscillations arise from variations in adenylyl cyclase-mediated cAMP production and phosphodiesterase-mediated degradation, processes controlled by factors like cell metabolism and [Ca(2+)](i). Protein kinase A and the guanine nucleotide exchange factor Epac2 mediate the actions of cAMP in β-cells and operate at multiple levels to promote exocytosis and pulsatile insulin secretion. The cAMP signaling system contains important targets for pharmacological improvement of insulin secretion in type 2 diabetes.
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Affiliation(s)
- Anders Tengholm
- Department of Medical Cell Biology, Uppsala University, Biomedical Centre , Box 571, SE-751 23 Uppsala, Sweden.
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Coupling of metabolic, second messenger pathways and insulin granule dynamics in pancreatic beta-cells: a computational analysis. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2011; 107:293-303. [PMID: 21920379 DOI: 10.1016/j.pbiomolbio.2011.09.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2011] [Revised: 08/26/2011] [Accepted: 09/01/2011] [Indexed: 12/26/2022]
Abstract
Insulin secretory responses to nutrient stimuli and hormonal modulators in pancreatic beta-cells are controlled by a variety of secondary messengers. We have analyzed numerous mechanisms responsible for regulated exocytosis in these cells and present an integrated mathematical model of cytosolic Ca²⁺, cAMP and granule dynamics. The insulin-containing granules in the beta-cell were divided into four classes: a large "reserve" granule pool, a smaller pool of the morphologically docked granules that is chemically 'primed' for release or the "readily releasable pool", and a pool of "restless newcomer granules" that undergoes preferential exocytosis. The model incorporates glucose and other aspects of metabolism, the cAMP amplifying pathway, insulin granule dynamics and the exocyst concept for granule binding. The values of most of the model parameters were inferred from available experimental data. The model can generate both the fast first phase and slow biphasic insulin secretion found experimentally in response to a step increase of membrane potential or of glucose. The numerical simulations have also reproduced a variety of experimental conditions, such as periodic stimulation by high K⁺ and the potentiation induced in islets by pre-incubation with cAMP pathway activators. The explicit incorporation of Ca²⁺ channels, Ca²⁺ and cAMP dynamics allows the model to be further connected to current models for calcium and metabolic dynamics and provides an interpretation of the roles of the triggering and amplifying pathways of glucose-stimulated insulin secretion. The model may be important in the identification of pharmacological targets for improving insulin secretion in type 2 diabetes.
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Leech CA, Dzhura I, Chepurny OG, Kang G, Schwede F, Genieser HG, Holz GG. Molecular physiology of glucagon-like peptide-1 insulin secretagogue action in pancreatic β cells. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2011; 107:236-47. [PMID: 21782840 DOI: 10.1016/j.pbiomolbio.2011.07.005] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2011] [Accepted: 07/08/2011] [Indexed: 10/18/2022]
Abstract
Insulin secretion from pancreatic β cells is stimulated by glucagon-like peptide-1 (GLP-1), a blood glucose-lowering hormone that is released from enteroendocrine L cells of the distal intestine after the ingestion of a meal. GLP-1 mimetics (e.g., Byetta) and GLP-1 analogs (e.g., Victoza) activate the β cell GLP-1 receptor (GLP-1R), and these compounds stimulate insulin secretion while also lowering levels of blood glucose in patients diagnosed with type 2 diabetes mellitus (T2DM). An additional option for the treatment of T2DM involves the administration of dipeptidyl peptidase-IV (DPP-IV) inhibitors (e.g., Januvia, Galvus). These compounds slow metabolic degradation of intestinally released GLP-1, thereby raising post-prandial levels of circulating GLP-1 substantially. Investigational compounds that stimulate GLP-1 secretion also exist, and in this regard a noteworthy advance is the demonstration that small molecule GPR119 agonists (e.g., AR231453) stimulate L cell GLP-1 secretion while also directly stimulating β cell insulin release. In this review, we summarize what is currently known concerning the signal transduction properties of the β cell GLP-1R as they relate to insulin secretion. Emphasized are the cyclic AMP, protein kinase A, and Epac2-mediated actions of GLP-1 to regulate ATP-sensitive K⁺ channels, voltage-dependent K⁺ channels, TRPM2 cation channels, intracellular Ca⁺ release channels, and Ca⁺-dependent exocytosis. We also discuss new evidence that provides a conceptual framework with which to understand why GLP-1R agonists are less likely to induce hypoglycemia when they are administered for the treatment of T2DM.
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Affiliation(s)
- Colin A Leech
- Department of Medicine, State University of New York Upstate Medical University, Syracuse, NY, USA.
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25
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Dzhura I, Chepurny OG, Leech CA, Roe MW, Dzhura E, Xu X, Lu Y, Schwede F, Genieser HG, Smrcka AV, Holz GG. Phospholipase C-ε links Epac2 activation to the potentiation of glucose-stimulated insulin secretion from mouse islets of Langerhans. Islets 2011; 3:121-8. [PMID: 21478675 PMCID: PMC3116928 DOI: 10.4161/isl.3.3.15507] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells is potentiated by cAMP-elevating agents, such as the incretin hormone glucagon-like peptide-1 (GLP-1), and cAMP exerts its insulin secretagogue action by activating both protein kinase A (PKA) and the cAMP-regulated guanine nucleotide exchange factor designated as Epac2. Although prior studies of mouse islets demonstrated that Epac2 acts via Rap1 GTPase to potentiate GSIS, it is not understood which downstream targets of Rap1 promote the exocytosis of insulin. Here, we measured insulin secretion stimulated by a cAMP analog that is a selective activator of Epac proteins in order to demonstrate that a Rap1-regulated phospholipase C-epsilon (PLC-ε) links Epac2 activation to the potentiation of GSIS. Our analysis demonstrates that the Epac activator 8-pCPT-2'-O-Me-cAMP-AM potentiates GSIS from the islets of wild-type (WT) mice, whereas it has a greatly reduced insulin secretagogue action in the islets of Epac2 (-/-) and PLC-ε (-/-) knockout (KO) mice. Importantly, the insulin secretagogue action of 8-pCPT-2'-O-Me-cAMP-AM in WT mouse islets cannot be explained by an unexpected action of this cAMP analog to activate PKA, as verified through the use of a FRET-based A-kinase activity reporter (AKAR3) that reports PKA activation. Since the KO of PLC-ε disrupts the ability of 8-pCPT-2'-O-Me-cAMP-AM to potentiate GSIS, while also disrupting its ability to stimulate an increase of β-cell [Ca2+]i, the available evidence indicates that it is a Rap1-regulated PLC-ε that links Epac2 activation to Ca2+-dependent exocytosis of insulin.
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Affiliation(s)
- Igor Dzhura
- Department of Medicine, State University of New York, Upstate Medical University, Syracuse, NY, USA
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26
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Epac2-dependent rap1 activation and the control of islet insulin secretion by glucagon-like peptide-1. VITAMINS AND HORMONES 2011; 84:279-302. [PMID: 21094904 DOI: 10.1016/b978-0-12-381517-0.00010-2] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Glucagon-like peptide-1 (GLP-1) binds its Class II G protein-coupled receptor to stimulate cyclic adenosine monophosphate (cAMP) production and to potentiate the glucose metabolism-dependent secretion of insulin from pancreatic β cells located within the islets of Langerhans. Prior clinical studies demonstrate that this cAMP-mediated action of GLP-1 to potentiate glucose-stimulated insulin secretion (GSIS) is of major therapeutic importance when evaluating the abilities of GLP-1 receptor (GLP-1R) agonists to lower levels of blood glucose in type 2 diabetic subjects. Surprisingly, recent in vitro studies of human or rodent islets of Langerhans provide evidence for the existence of a noncanonical mechanism of β cell cAMP signal transduction, one that may explain how GLP-1R agonists potentiate GSIS. What these studies demonstrate is that a cAMP-regulated guanine nucleotide exchange factor designated as Epac2 couples β cell cAMP production to the protein kinase A-independent stimulation of insulin exocytosis. Provided here is an overview of the Epac2 signal transduction system in β cells, with special emphasis on Rap1, a Ras-related GTPase that is an established target of Epac2.
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27
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Dzhura I, Chepurny OG, Kelley GG, Leech CA, Roe MW, Dzhura E, Afshari P, Malik S, Rindler MJ, Xu X, Lu Y, Smrcka AV, Holz GG. Epac2-dependent mobilization of intracellular Ca²+ by glucagon-like peptide-1 receptor agonist exendin-4 is disrupted in β-cells of phospholipase C-ε knockout mice. J Physiol 2010; 588:4871-89. [PMID: 21041529 DOI: 10.1113/jphysiol.2010.198424] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Calcium can be mobilized in pancreatic β-cells via a mechanism of Ca(2+)-induced Ca(2+) release (CICR), and cAMP-elevating agents such as exendin-4 facilitate CICR in β-cells by activating both protein kinase A and Epac2. Here we provide the first report that a novel phosphoinositide-specific phospholipase C- (PLC-) is expressed in the islets of Langerhans, and that the knockout (KO) of PLC- gene expression in mice disrupts the action of exendin-4 to facilitate CICR in the β-cells of these mice. Thus, in the present study, in which wild-type (WT) C57BL/6 mouse β-cells were loaded with the photolabile Ca(2+) chelator NP-EGTA, the UV flash photolysis-catalysed uncaging of Ca(2+) generated CICR in only 9% of the β-cells tested, whereas CICR was generated in 82% of the β-cells pretreated with exendin-4. This action of exendin-4 to facilitate CICR was reproduced by cAMP analogues that activate protein kinase A (6-Bnz-cAMP-AM) or Epac2 (8-pCPT-2'-O-Me-cAMP-AM) selectively. However, in β-cells of PLC- KO mice, and also Epac2 KO mice, these test substances exhibited differential efficacies in the CICR assay such that exendin-4 was partly effective, 6-Bnz-cAMP-AM was fully effective, and 8-pCPT-2'-O-Me-cAMP-AM was without significant effect. Importantly, transduction of PLC- KO β-cells with recombinant PLC- rescued the action of 8-pCPT-2'-O-Me-cAMP-AM to facilitate CICR, whereas a K2150E PLC- with a mutated Ras association (RA) domain, or a H1640L PLC- that is catalytically dead, were both ineffective. Since 8-pCPT-2'-O-Me-cAMP-AM failed to facilitate CICR in WT β-cells transduced with a GTPase activating protein (RapGAP) that downregulates Rap activity, the available evidence indicates that a signal transduction 'module' comprised of Epac2, Rap and PLC- exists in β-cells, and that the activities of Epac2 and PLC- are key determinants of CICR in this cell type.
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Affiliation(s)
- Igor Dzhura
- Department of Medicine, State University of New York Upstate Medical University, Syracuse, NY, USA
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Leech CA, Dzhura I, Chepurny OG, Schwede F, Genieser HG, Holz GG. Facilitation of ß-cell K(ATP) channel sulfonylurea sensitivity by a cAMP analog selective for the cAMP-regulated guanine nucleotide exchange factor Epac. Islets 2010; 2:72-81. [PMID: 20428467 PMCID: PMC2860288 DOI: 10.4161/isl.2.2.10582] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Clinical studies demonstrate that combined administration of sulfonylureas with exenatide can induce hypoglycemia in type 2 diabetic subjects. Whereas sulfonylureas inhibit ß-cell K(ATP) channels by binding to the sulfonylurea receptor-1 (SUR1), exenatide binds to the GLP-1 receptor, stimulates ß-cell cAMP production and activates both PKA and Epac. In this study, we hypothesized that the adverse in vivo interaction of sulfonylureas and exenatide to produce hypoglycemia might be explained by Epac-mediated facilitation of K(ATP) channel sulfonylurea sensitivity. We now report that the inhibitory action of a sulfonylurea (tolbutamide) at K(ATP) channels was facilitated by 2’-O-Me-cAMP, a selective activator of Epac. Thus, under conditions of excised patch recording, the dose-response relationship describing the inhibitory action of tolbutamide at human ß-cell or rat INS-1 cell K(ATP) channels was left-shifted in the presence of 2’-O-Me-cAMP, and this effect was abolished in INS-1 cells expressing a dominant-negative Epac2. Using an acetoxymethyl ester prodrug of an Epac-selective cAMP analog (8-pCP T-2’-O-Me-cAMP-AM), the synergistic interaction of an Epac activator and tolbutamide to depolarize INS-1 cells and to raise [Ca²(+)](i) was also measured. This effect of 8-pCP T-2’-O-Me-cAMP-AM correlated with its ability to stimulate phosphatidylinositol 4,5-bisphosphate hydrolysis that might contribute to the changes in K(ATP) channel sulfonylurea-sensitivity reported here. On the basis of such findings, we propose that the adverse interaction of sulfonylureas and exenatide to induce hypoglycemia involves at least in part, a functional interaction of these two compounds to close K(ATP) channels, to depolarize ß-cells and to promote insulin secretion.
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Affiliation(s)
- Colin A Leech
- Department of Medicine, State University of New York, Syracuse, USA.
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Chepurny OG, Kelley GG, Dzhura I, Leech CA, Roe MW, Dzhura E, Li X, Schwede F, Genieser HG, Holz GG. PKA-dependent potentiation of glucose-stimulated insulin secretion by Epac activator 8-pCPT-2'-O-Me-cAMP-AM in human islets of Langerhans. Am J Physiol Endocrinol Metab 2010; 298:E622-33. [PMID: 20009023 PMCID: PMC2838523 DOI: 10.1152/ajpendo.00630.2009] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Potential insulin secretagogue properties of an acetoxymethyl ester of a cAMP analog (8-pCPT-2'-O-Me-cAMP-AM) that activates the guanine nucleotide exchange factors Epac1 and Epac2 were assessed using isolated human islets of Langerhans. RT-QPCR demonstrated that the predominant variant of Epac expressed in human islets was Epac2, although Epac1 was detectable. Under conditions of islet perifusion, 8-pCPT-2'-O-Me-cAMP-AM (10 microM) potentiated first- and second-phase 10 mM glucose-stimulated insulin secretion (GSIS) while failing to influence insulin secretion measured in the presence of 3 mM glucose. The insulin secretagogue action of 8-pCPT-2'-O-Me-cAMP-AM was associated with depolarization and an increase of [Ca(2+)](i) that reflected both Ca(2+) influx and intracellular Ca(2+) mobilization in islet beta-cells. As expected for an Epac-selective cAMP analog, 8-pCPT-2'-O-Me-cAMP-AM (10 microM) failed to stimulate phosphorylation of PKA substrates CREB and Kemptide in human islets. Furthermore, 8-pCPT-2'-O-Me-cAMP-AM (10 microM) had no significant ability to activate AKAR3, a PKA-regulated biosensor expressed in human islet cells by viral transduction. Unexpectedly, treatment of human islets with an inhibitor of PKA activity (H-89) or treatment with a cAMP antagonist that blocks PKA activation (Rp-8-CPT-cAMPS) nearly abolished the action of 8-pCPT-2'-O-Me-cAMP-AM to potentiate GSIS. It is concluded that there exists a permissive role for PKA activity in support of human islet insulin secretion that is both glucose dependent and Epac regulated. This permissive action of PKA may be operative at the insulin secretory granule recruitment, priming, and/or postpriming steps of Ca(2+)-dependent exocytosis.
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Affiliation(s)
- Oleg G Chepurny
- Departments of Medicine, State University of New York, Syracuse, 13210, USA
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