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Suckert C, Zosel C, Schaefer M. Simultaneous TIRF imaging of subplasmalemmal Ca 2+ dynamics and granule fusions in insulin-secreting INS-1 cells reveals coexistent synchronized and asynchronous release. Cell Calcium 2024; 120:102883. [PMID: 38643716 DOI: 10.1016/j.ceca.2024.102883] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2024] [Revised: 03/21/2024] [Accepted: 03/29/2024] [Indexed: 04/23/2024]
Abstract
The basal and glucose-induced insulin secretion from pancreatic beta cells is a tightly regulated process that is triggered in a Ca2+-dependent fashion and further positively modulated by substances that raise intracellular levels of adenosine 3',5'-cyclic monophosphate (cAMP) or by certain antidiabetic drugs. In a previous study, we have temporally resolved the subplasmalemmal [Ca2+]i dynamics in beta cells that are characterized by trains of sharply delimited spikes, reaching peak values up to 5 µM. Applying total internal reflection fluorescence (TIRF) microscopy and synaptopHluorin to visualize fusion events of individual granules, we found that several fusion events can coincide within 50 to 150 ms. To test whether subplasmalemmal [Ca2+]i microdomains around single or clustered Ca2+ channels may cause a synchronized release of insulin-containing vesicles, we applied simultaneous dual-color TIRF microscopy and monitored Ca2+ fluctuations and exocytotic events in INS-1 cells at high frame rates. The results indicate that fusions can be triggered by subplasmalemmal Ca2+ spiking. This, however, does account for a minority of fusion events. About 90 %-95 % of fusion events either happen between Ca2+ spikes or incidentally overlap with subplasmalemmal Ca2+ spikes. We conclude that only a fraction of exocytotic events in glucose-induced and tolbutamide- or forskolin-enhanced insulin release from INS-1 cells is tightly coupled to Ca2+ microdomains around voltage-gated Ca2+ channels.
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Affiliation(s)
- Charlotte Suckert
- Leipzig University, Rudolf-Boehm-Institute of Pharmacology and Toxicology, Härtelstraße 16-18, Leipzig 04107, Germany
| | - Carolin Zosel
- Leipzig University, Rudolf-Boehm-Institute of Pharmacology and Toxicology, Härtelstraße 16-18, Leipzig 04107, Germany
| | - Michael Schaefer
- Leipzig University, Rudolf-Boehm-Institute of Pharmacology and Toxicology, Härtelstraße 16-18, Leipzig 04107, Germany.
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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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Ramanadham S, Turk J, Bhatnagar S. Noncanonical Regulation of cAMP-Dependent Insulin Secretion and Its Implications in Type 2 Diabetes. Compr Physiol 2023; 13:5023-5049. [PMID: 37358504 PMCID: PMC10809800 DOI: 10.1002/cphy.c220031] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/27/2023]
Abstract
Impaired glucose tolerance (IGT) and β-cell dysfunction in insulin resistance associated with obesity lead to type 2 diabetes (T2D). Glucose-stimulated insulin secretion (GSIS) from β-cells occurs via a canonical pathway that involves glucose metabolism, ATP generation, inactivation of K ATP channels, plasma membrane depolarization, and increases in cytosolic concentrations of [Ca 2+ ] c . However, optimal insulin secretion requires amplification of GSIS by increases in cyclic adenosine monophosphate (cAMP) signaling. The cAMP effectors protein kinase A (PKA) and exchange factor activated by cyclic-AMP (Epac) regulate membrane depolarization, gene expression, and trafficking and fusion of insulin granules to the plasma membrane for amplifying GSIS. The widely recognized lipid signaling generated within β-cells by the β-isoform of Ca 2+ -independent phospholipase A 2 enzyme (iPLA 2 β) participates in cAMP-stimulated insulin secretion (cSIS). Recent work has identified the role of a G-protein coupled receptor (GPCR) activated signaling by the complement 1q like-3 (C1ql3) secreted protein in inhibiting cSIS. In the IGT state, cSIS is attenuated, and the β-cell function is reduced. Interestingly, while β-cell-specific deletion of iPLA 2 β reduces cAMP-mediated amplification of GSIS, the loss of iPLA 2 β in macrophages (MØ) confers protection against the development of glucose intolerance associated with diet-induced obesity (DIO). In this article, we discuss canonical (glucose and cAMP) and novel noncanonical (iPLA 2 β and C1ql3) pathways and how they may affect β-cell (dys)function in the context of impaired glucose intolerance associated with obesity and T2D. In conclusion, we provide a perspective that in IGT states, targeting noncanonical pathways along with canonical pathways could be a more comprehensive approach for restoring β-cell function in T2D. © 2023 American Physiological Society. Compr Physiol 13:5023-5049, 2023.
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Affiliation(s)
- Sasanka Ramanadham
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Alabama, USA
- Comprehensive Diabetes Center, University of Alabama at Birmingham, Alabama, USA
| | - John Turk
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Sushant Bhatnagar
- Comprehensive Diabetes Center, University of Alabama at Birmingham, Alabama, USA
- Department of Medicine, University of Alabama at Birmingham, Alabama, USA
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Virwani PD, Cai L, Yeung PKK, Qian G, Chen Y, Zhou L, Wong JWH, Wang Y, Ho JWK, Lau KK, Qian PY, Chung SK. Deficiency of exchange protein directly activated by cAMP (EPAC)-1 in mice augments glucose intolerance, inflammation, and gut dysbiosis associated with Western diet. MICROBIOME 2022; 10:187. [PMID: 36329549 PMCID: PMC9635209 DOI: 10.1186/s40168-022-01366-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/06/2022] [Accepted: 09/05/2022] [Indexed: 06/16/2023]
Abstract
BACKGROUND Gut microbiota (GM) dysregulation, known as dysbiosis, has been proposed as a crucial driver of obesity associated with "Western" diet (WD) consumption. Gut dysbiosis is associated with increased gut permeability, inflammation, and insulin resistance. However, host metabolic pathways implicated in the pathophysiology of gut dysbiosis are still elusive. Exchange protein directly activated by cAMP (Epac) plays a critical role in cell-cell junction formation and insulin secretion. Here, we used homozygous Epac1-knockout (Epac1-/-), Epac2-knockout (Epac2-/-), and wild-type (WT) mice to investigate the role of Epac proteins in mediating gut dysbiosis, gut permeability, and inflammation after WD feeding. RESULTS The 16S rRNA gene sequencing of fecal DNA showed that the baseline GM of Epac2-/-, but not Epac1-/-, mice was represented by a significantly higher Firmicutes to Bacteroidetes ratio and significant alterations in several taxa compared to WT mice, suggesting that Epac2-/- mice had gut dysbiosis under physiological conditions. However, an 8-week WD led to a similar gut microbiome imbalance in mice regardless of genotype. While Epac1 deficiency modestly exacerbated the WD-induced GM dysbiosis, the WD-fed Epac2-/- mice had a more significant increase in gut permeability than corresponding WT mice. After WD feeding, Epac1-/-, but not Epac2-/-, mice had significantly higher mRNA levels of tumor necrosis factor-alpha (TNF-α) and F4/80 in the epididymal white adipose tissue (EWAT), increased circulating lipocalin-2 protein and more severe glucose intolerance, suggesting greater inflammation and insulin resistance in WD-fed Epac1-/- mice than corresponding WT mice. Consistently, Epac1 protein expression was significantly reduced in the EWAT of WD-fed WT and Epac2-/- mice. CONCLUSION Despite significantly dysregulated baseline GM and a more pronounced increase in gut permeability upon WD feeding, WD-fed Epac2-/- mice did not exhibit more severe inflammation and glucose intolerance than corresponding WT mice. These findings suggest that the role of gut dysbiosis in mediating WD-associated obesity may be context-dependent. On the contrary, we demonstrate that deficiency of host signaling protein, Epac1, drives inflammation and glucose intolerance which are the hallmarks of WD-induced obesity. Video abstract.
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Affiliation(s)
- Preeti Dinesh Virwani
- School of Biomedical Sciences, Li Ka Shing (LKS) Faculty of Medicine, The University of Hong Kong, Hong Kong S.A.R., China
- Department of Medicine, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong S.A.R., China
| | - Lin Cai
- Department of Ocean Science and Division of Life Science, Hong Kong University of Science and Technology, Kowloon, Hong Kong S.A.R. China
| | - Patrick Ka Kit Yeung
- School of Biomedical Sciences, Li Ka Shing (LKS) Faculty of Medicine, The University of Hong Kong, Hong Kong S.A.R., China
| | - Gordon Qian
- School of Biomedical Sciences, Li Ka Shing (LKS) Faculty of Medicine, The University of Hong Kong, Hong Kong S.A.R., China
- Laboratory of Data Discovery for Health Limited (D24H), Hong Kong Science Park, Hong Kong S.A.R., China
| | - Yingxian Chen
- School of Biomedical Sciences, Li Ka Shing (LKS) Faculty of Medicine, The University of Hong Kong, Hong Kong S.A.R., China
| | - Lei Zhou
- School of Biomedical Sciences, Li Ka Shing (LKS) Faculty of Medicine, The University of Hong Kong, Hong Kong S.A.R., China
| | - Jason Wing Hon Wong
- School of Biomedical Sciences, Li Ka Shing (LKS) Faculty of Medicine, The University of Hong Kong, Hong Kong S.A.R., China
| | - Yu Wang
- Department of Pharmacology and Pharmacy, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong S.A.R., China
- State Key Laboratory of Pharmaceutical Biotechnology, The University of Hong Kong, Hong Kong S.A.R., China
| | - Joshua Wing Kei Ho
- School of Biomedical Sciences, Li Ka Shing (LKS) Faculty of Medicine, The University of Hong Kong, Hong Kong S.A.R., China
- Laboratory of Data Discovery for Health Limited (D24H), Hong Kong Science Park, Hong Kong S.A.R., China
| | - Kui Kai Lau
- Department of Medicine, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong S.A.R., China
- State Key Laboratory of Brain and Cognitive Sciences, The University of Hong Kong, Hong Kong S.A.R., China
| | - Pei-Yuan Qian
- Department of Ocean Science and Division of Life Science, Hong Kong University of Science and Technology, Kowloon, Hong Kong S.A.R. China
- Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, 511458 China
| | - Sookja Kim Chung
- Faculty of Medicine; Faculty of Innovation Engineering, Macau University of Science and Technology, Macau Special Administrative Region (S.A.R.), China
- School of Biomedical Sciences, Li Ka Shing (LKS) Faculty of Medicine, The University of Hong Kong, Hong Kong S.A.R., China
- State Key Laboratory of Pharmaceutical Biotechnology, The University of Hong Kong, Hong Kong S.A.R., China
- Dr. Neher’s Biophysics Laboratory for Innovative Drug Discovery, Macau University of Science and Technology, Macau S.A.R., China
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Cornman RS, Cryan PM. Positively selected genes in the hoary bat ( Lasiurus cinereus) lineage: prominence of thymus expression, immune and metabolic function, and regions of ancient synteny. PeerJ 2022; 10:e13130. [PMID: 35317076 PMCID: PMC8934532 DOI: 10.7717/peerj.13130] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2021] [Accepted: 02/25/2022] [Indexed: 01/12/2023] Open
Abstract
Background Bats of the genus Lasiurus occur throughout the Americas and have diversified into at least 20 species among three subgenera. The hoary bat (Lasiurus cinereus) is highly migratory and ranges farther across North America than any other wild mammal. Despite the ecological importance of this species as a major insect predator, and the particular susceptibility of lasiurine bats to wind turbine strikes, our understanding of hoary bat ecology, physiology, and behavior remains poor. Methods To better understand adaptive evolution in this lineage, we used whole-genome sequencing to identify protein-coding sequence and explore signatures of positive selection. Gene models were predicted with Maker and compared to seven well-annotated and phylogenetically representative species. Evolutionary rate analysis was performed with PAML. Results Of 9,447 single-copy orthologous groups that met evaluation criteria, 150 genes had a significant excess of nonsynonymous substitutions along the L. cinereus branch (P < 0.001 after manual review of alignments). Selected genes as a group had biased expression, most strongly in thymus tissue. We identified 23 selected genes with reported immune functions as well as a divergent paralog of Steep1 within suborder Yangochiroptera. Seventeen genes had roles in lipid and glucose metabolic pathways, partially overlapping with 15 mitochondrion-associated genes; these adaptations may reflect the metabolic challenges of hibernation, long-distance migration, and seasonal variation in prey abundance. The genomic distribution of positively selected genes differed significantly from background expectation by discrete Kolmogorov-Smirnov test (P < 0.001). Remarkably, the top three physical clusters all coincided with islands of conserved synteny predating Mammalia, the largest of which shares synteny with the human cat-eye critical region (CECR) on 22q11. This observation coupled with the expansion of a novel Tbx1-like gene family may indicate evolutionary innovation during pharyngeal arch development: both the CECR and Tbx1 cause dosage-dependent congenital abnormalities in thymus, heart, and head, and craniodysmorphy is associated with human orthologs of other positively selected genes as well.
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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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7
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Jones B. The therapeutic potential of GLP-1 receptor biased agonism. Br J Pharmacol 2022; 179:492-510. [PMID: 33880754 PMCID: PMC8820210 DOI: 10.1111/bph.15497] [Citation(s) in RCA: 27] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2021] [Revised: 04/03/2021] [Accepted: 04/06/2021] [Indexed: 12/20/2022] Open
Abstract
Glucagon-like peptide-1 (GLP-1) receptor agonists are effective treatments for type 2 diabetes as they stimulate insulin release and promote weight loss through appetite suppression. Their main side effect is nausea. All approved GLP-1 agonists are full agonists across multiple signalling pathways. However, selective engagement with specific intracellular effectors, or biased agonism, has been touted as a means to improve GLP-1 agonists therapeutic efficacy. In this review, I critically examine how GLP-1 receptor-mediated intracellular signalling is linked to physiological responses and discuss the implications of recent studies investigating the metabolic effects of biased GLP-1 agonists. Overall, there is little conclusive evidence that beneficial and adverse effects of GLP-1 agonists are attributable to distinct, nonoverlapping signalling pathways. Instead, G protein-biased GLP-1 agonists appear to achieve enhanced anti-hyperglycaemic efficacy by avoiding GLP-1 receptor desensitisation and downregulation, partly via reduced β-arrestin recruitment. This effect seemingly applies more to insulin release than to appetite regulation and nausea, possible reasons for which are discussed. At present, most evidence derives from cellular and animal studies, and more human data are required to determine whether this approach represents a genuine therapeutic advance. LINKED ARTICLES: This article is part of a themed issue on GLP1 receptor ligands (BJP 75th Anniversary). To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.4/issuetoc.
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Affiliation(s)
- Ben Jones
- Section of Endocrinology and Investigative MedicineImperial College LondonLondonUK
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8
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Daniel PV, Kamthan M, Thakur S, Mondal P. Molecular pathways dysregulated by Pb 2+ exposure prompts pancreatic beta-cell dysfunction. Toxicol Res (Camb) 2022; 11:206-214. [PMID: 35237425 PMCID: PMC8882803 DOI: 10.1093/toxres/tfab121] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2021] [Revised: 11/28/2021] [Accepted: 11/30/2021] [Indexed: 01/24/2023] Open
Abstract
Type 2 diabetes mellitus (T2DM) is a metabolic disease characterized by reduced insulin sensitivity and dysfunction of β-cells. Although the increasing prevalence of diabetes worldwide is largely attributed to genetic predisposition or lifestyle factors (insufficient physical activity), and caloric intake. Environmental factors, exposure to xenobiotics and heavy metals have also been reported to be causative factors of T2DM. At this juncture, we, through our work unveil a plausible link between Pb2+ exposure and diabetes mellitus, and delineated a comprehensive understanding of the potential mechanisms of Pb2+-induced β-cells dysfunction. In our in vivo observations, we found that Pb2+ exposure strongly reduced glucose-stimulated insulin secretion and diminished functional pancreatic β-cell mass. Mechanistically, we found that Pb2+ downregulates intracellular cAMP level via hyper-activating Ca2+/calmodulin-dependent 3',5'-cyclic nucleotide phosphodiesterase 1C and thereby reduces glucose-stimulated insulin secretion. Further, we report that Pb2+ inhibited mitochondrial adenosine triphosphate production and also identified Pb2+ as a negative regulator of β-cell proliferation via Ca2+/calmodulin-dependent protein kinase kinases-pAMPK-pRaptor axis. Together, our findings strongly reinforce Pb2+ to hijack the physiological role of calcium ions, by mimicking Ca2+ within pancreatic β-cell and thereby stands as a diabetogenic xenobiotic.
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Affiliation(s)
- P Vineeth Daniel
- School of Basic Sciences, Indian Institute of Technology Mandi, Mandi, Himachal Pradesh 175001, India
| | - Mohan Kamthan
- Department of Biochemistry, School of Chemical and Life Sciences Jamia Hamdard, New Delhi, India
| | - Shilpa Thakur
- School of Basic Sciences, Indian Institute of Technology Mandi, Mandi, Himachal Pradesh 175001, India
| | - Prosenjit Mondal
- Correspondence address. School of Basic Sciences, Indian Institute of Technology, Mandi, Himachal Pradesh 175001, India. Tel: (91)1950267262;
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9
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Siehler J, Blöchinger AK, Meier M, Lickert H. Engineering islets from stem cells for advanced therapies of diabetes. Nat Rev Drug Discov 2021; 20:920-940. [PMID: 34376833 DOI: 10.1038/s41573-021-00262-w] [Citation(s) in RCA: 45] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/22/2021] [Indexed: 12/20/2022]
Abstract
Diabetes mellitus is a metabolic disorder that affects more than 460 million people worldwide. Type 1 diabetes (T1D) is caused by autoimmune destruction of β-cells, whereas type 2 diabetes (T2D) is caused by a hostile metabolic environment that leads to β-cell exhaustion and dysfunction. Currently, first-line medications treat the symptomatic insulin resistance and hyperglycaemia, but do not prevent the progressive decline of β-cell mass and function. Thus, advanced therapies need to be developed that either protect or regenerate endogenous β-cell mass early in disease progression or replace lost β-cells with stem cell-derived β-like cells or engineered islet-like clusters. In this Review, we discuss the state of the art of stem cell differentiation and islet engineering, reflect on current and future challenges in the area and highlight the potential for cell replacement therapies, disease modelling and drug development using these cells. These efforts in stem cell and regenerative medicine will lay the foundations for future biomedical breakthroughs and potentially curative treatments for diabetes.
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Affiliation(s)
- Johanna Siehler
- Institute of Stem Cell Research, Helmholtz Zentrum München, Neuherberg, Germany.,Technical University of Munich, Medical Faculty, Munich, Germany.,German Center for Diabetes Research (DZD), Neuherberg, Germany
| | - Anna Karolina Blöchinger
- Technical University of Munich, Medical Faculty, Munich, Germany.,German Center for Diabetes Research (DZD), Neuherberg, Germany.,Institute of Diabetes and Regeneration Research, Helmholtz Zentrum München, Neuherberg, Germany
| | - Matthias Meier
- Technical University of Munich, Medical Faculty, Munich, Germany.,Helmholtz Pioneer Campus, Helmholtz Zentrum München, Neuherberg, Germany
| | - Heiko Lickert
- Institute of Stem Cell Research, Helmholtz Zentrum München, Neuherberg, Germany. .,Technical University of Munich, Medical Faculty, Munich, Germany. .,German Center for Diabetes Research (DZD), Neuherberg, Germany. .,Institute of Diabetes and Regeneration Research, Helmholtz Zentrum München, Neuherberg, Germany.
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10
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Stožer A, Paradiž Leitgeb E, Pohorec V, Dolenšek J, Križančić Bombek L, Gosak M, Skelin Klemen M. The Role of cAMP in Beta Cell Stimulus-Secretion and Intercellular Coupling. Cells 2021; 10:1658. [PMID: 34359828 PMCID: PMC8304079 DOI: 10.3390/cells10071658] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Revised: 06/18/2021] [Accepted: 06/28/2021] [Indexed: 12/22/2022] Open
Abstract
Pancreatic beta cells secrete insulin in response to stimulation with glucose and other nutrients, and impaired insulin secretion plays a central role in development of diabetes mellitus. Pharmacological management of diabetes includes various antidiabetic drugs, including incretins. The incretin hormones, glucagon-like peptide-1 and gastric inhibitory polypeptide, potentiate glucose-stimulated insulin secretion by binding to G protein-coupled receptors, resulting in stimulation of adenylate cyclase and production of the secondary messenger cAMP, which exerts its intracellular effects through activation of protein kinase A or the guanine nucleotide exchange protein 2A. The molecular mechanisms behind these two downstream signaling arms are still not fully elucidated and involve many steps in the stimulus-secretion coupling cascade, ranging from the proximal regulation of ion channel activity to the central Ca2+ signal and the most distal exocytosis. In addition to modifying intracellular coupling, the effect of cAMP on insulin secretion could also be at least partly explained by the impact on intercellular coupling. In this review, we systematically describe the possible roles of cAMP at these intra- and inter-cellular signaling nodes, keeping in mind the relevance for the whole organism and translation to humans.
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Affiliation(s)
- Andraž Stožer
- Institute of Physiology, Faculty of Medicine, University of Maribor, SI-2000 Maribor, Slovenia; (A.S.); (E.P.L.); (V.P.); (J.D.); (L.K.B.); (M.G.)
| | - Eva Paradiž Leitgeb
- Institute of Physiology, Faculty of Medicine, University of Maribor, SI-2000 Maribor, Slovenia; (A.S.); (E.P.L.); (V.P.); (J.D.); (L.K.B.); (M.G.)
| | - Viljem Pohorec
- Institute of Physiology, Faculty of Medicine, University of Maribor, SI-2000 Maribor, Slovenia; (A.S.); (E.P.L.); (V.P.); (J.D.); (L.K.B.); (M.G.)
| | - Jurij Dolenšek
- Institute of Physiology, Faculty of Medicine, University of Maribor, SI-2000 Maribor, Slovenia; (A.S.); (E.P.L.); (V.P.); (J.D.); (L.K.B.); (M.G.)
- Faculty of Natural Sciences and Mathematics, University of Maribor, SI-2000 Maribor, Slovenia
| | - Lidija Križančić Bombek
- Institute of Physiology, Faculty of Medicine, University of Maribor, SI-2000 Maribor, Slovenia; (A.S.); (E.P.L.); (V.P.); (J.D.); (L.K.B.); (M.G.)
| | - Marko Gosak
- Institute of Physiology, Faculty of Medicine, University of Maribor, SI-2000 Maribor, Slovenia; (A.S.); (E.P.L.); (V.P.); (J.D.); (L.K.B.); (M.G.)
- Faculty of Natural Sciences and Mathematics, University of Maribor, SI-2000 Maribor, Slovenia
| | - Maša Skelin Klemen
- Institute of Physiology, Faculty of Medicine, University of Maribor, SI-2000 Maribor, Slovenia; (A.S.); (E.P.L.); (V.P.); (J.D.); (L.K.B.); (M.G.)
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11
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White MA, Tsalkova T, Mei FC, Cheng X. Conformational States of Exchange Protein Directly Activated by cAMP (EPAC1) Revealed by Ensemble Modeling and Integrative Structural Biology. Cells 2019; 9:cells9010035. [PMID: 31877746 PMCID: PMC7016869 DOI: 10.3390/cells9010035] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2019] [Revised: 12/16/2019] [Accepted: 12/18/2019] [Indexed: 02/08/2023] Open
Abstract
Exchange proteins directly activated by cAMP (EPAC1 and EPAC2) are important allosteric regulators of cAMP-mediated signal transduction pathways. To understand the molecular mechanism of EPAC activation, we performed detailed Small-Angle X-ray Scattering (SAXS) analysis of EPAC1 in its apo (inactive), cAMP-bound, and effector (Rap1b)-bound states. Our study demonstrates that we can model the solution structures of EPAC1 in each state using ensemble analysis and homology models derived from the crystal structures of EPAC2. The N-terminal domain of EPAC1, which is not conserved between EPAC1 and EPAC2, appears folded and interacts specifically with another component of EPAC1 in each state. The apo-EPAC1 state is a dynamic mixture of a compact (Rg = 32.9 Å, 86%) and a more extended (Rg = 38.5 Å, 13%) conformation. The cAMP-bound form of EPAC1 in the absence of Rap1 forms a dimer in solution; but its molecular structure is still compatible with the active EPAC1 conformation of the ternary complex model with cAMP and Rap1. Herein, we show that SAXS can elucidate the conformational states of EPAC1 activation as it proceeds from the compact, inactive apo conformation through a previously unknown intermediate-state, to the extended cAMP-bound form, and then binds to its effector (Rap1b) in a ternary complex.
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Affiliation(s)
- Mark Andrew White
- Sealy Center for Structural Biology and Molecular Biophysics, The University of Texas Medical Branch, Galveston, TX 77555, USA
- Department of Biochemistry and Molecular Biology, The University of Texas Medical Branch, Galveston, TX 77555, USA
- Correspondence: (M.A.W.); (X.C.); Tel.: +409-747-4747 (M.A.W.); +713-500-7487 (X.C.)
| | - Tamara Tsalkova
- Department of Pharmacology and Toxicology, The University of Texas Medical Branch, Galveston, TX 77555, USA;
| | - Fang C. Mei
- Department of Integrative Biology & Pharmacology, University of Texas Health Science Center at Houston, Houston, TX 77030, USA;
- Texas Therapeutics Institute, Institute of Molecular Medicine, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| | - Xiaodong Cheng
- Department of Integrative Biology & Pharmacology, University of Texas Health Science Center at Houston, Houston, TX 77030, USA;
- Texas Therapeutics Institute, Institute of Molecular Medicine, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
- Correspondence: (M.A.W.); (X.C.); Tel.: +409-747-4747 (M.A.W.); +713-500-7487 (X.C.)
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12
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EPAC1 and EPAC2 promote nociceptor hyperactivity associated with chronic pain after spinal cord injury. NEUROBIOLOGY OF PAIN 2019; 7:100040. [PMID: 31890991 PMCID: PMC6926371 DOI: 10.1016/j.ynpai.2019.100040] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/04/2019] [Revised: 11/15/2019] [Accepted: 11/20/2019] [Indexed: 12/19/2022]
Abstract
Chronic pain following spinal cord injury (SCI) is associated with electrical hyperactivity (spontaneous and evoked) in primary nociceptors. Cyclic adenosine monophosphate (cAMP) signaling is an important contributor to nociceptor excitability, and knockdown of the cAMP effector, exchange protein activated by cAMP (EPAC), has been shown to relieve pain-like responses in several chronic pain models. To examine potentially distinct roles of each EPAC isoform (EPAC1 and 2) in maintaining chronic pain, we used rat and mouse models of contusive spinal cord injury (SCI). Pharmacological inhibition of EPAC1 or 2 in a rat SCI model was sufficient to reverse SCI-induced nociceptor hyperactivity, indicating that EPAC1 and 2 signaling activity are complementary, with both required to maintain hyperactivity. However, EPAC activation was not sufficient to induce similar hyperactivity in nociceptors from naïve rats, and we observed no change in EPAC protein expression after SCI. In the mouse SCI model, inhibition of both EPAC isoforms through a combination of pharmacological inhibition and genetic deletion was required to reverse SCI-induced nociceptor hyperactivity. This was consistent with our finding that neither EPAC1-/- nor EPAC2-/- mice were protected against SCI-induced chronic pain as assessed with an operant mechanical conflict test. Thus, EPAC1 and 2 activity may play a redundant role in mouse nociceptors, although no corresponding change in EPAC protein expression levels was detected after SCI. Despite some differences between these species, our data demonstrate a fundamental role for both EPAC1 and EPAC2 in mechanisms maintaining nociceptor hyperactivity and chronic pain after SCI.
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13
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Sivertsen Åsrud K, Pedersen L, Aesoy R, Muwonge H, Aasebø E, Nitschke Pettersen IK, Herfindal L, Dobie R, Jenkins S, Berge RK, Henderson NC, Selheim F, Døskeland SO, Bakke M. Mice depleted for Exchange Proteins Directly Activated by cAMP (Epac) exhibit irregular liver regeneration in response to partial hepatectomy. Sci Rep 2019; 9:13789. [PMID: 31551444 PMCID: PMC6760117 DOI: 10.1038/s41598-019-50219-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Accepted: 09/06/2019] [Indexed: 02/07/2023] Open
Abstract
The exchange proteins directly activated by cAMP 1 and 2 (Epac1 and Epac2) are expressed in a cell specific manner in the liver, but their biological functions in this tissue are poorly understood. The current study was undertaken to begin to determine the potential roles of Epac1 and Epac2 in liver physiology and disease. Male C57BL/6J mice in which expression of Epac1 and/or Epac2 are deleted, were subjected to partial hepatectomy and the regenerating liver was analyzed with regard to lipid accumulation, cell replication and protein expression. In response to partial hepatectomy, deletion of Epac1 and/or Epac2 led to increased hepatocyte proliferation 36 h post surgery, and the transient steatosis observed in wild type mice was virtually absent in mice lacking both Epac1 and Epac2. The expression of the protein cytochrome P4504a14, which is implicated in hepatic steatosis and fibrosis, was substantially reduced upon deletion of Epac1/2, while a number of factors involved in lipid metabolism were significantly decreased. Moreover, the number of Küpffer cells was affected, and Epac2 expression was increased in the liver of wild type mice in response to partial hepatectomy, further supporting a role for these proteins in liver function. This study establishes hepatic phenotypic abnormalities in mice deleted for Epac1/2 for the first time, and introduces Epac1/2 as regulators of hepatocyte proliferation and lipid accumulation in the regenerative process.
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Affiliation(s)
| | - Line Pedersen
- Department of Biomedicine, The University of Bergen, Bergen, Norway
| | - Reidun Aesoy
- Department of Clinical Science, The University of Bergen, Bergen, Norway
| | - Haruna Muwonge
- Department of Biomedicine, The University of Bergen, Bergen, Norway
| | - Elise Aasebø
- Department of Clinical Science, The University of Bergen, Bergen, Norway
- Department of Biomedicine, The Proteomic Unit at The University of Bergen (PROBE), University of Bergen, 5009, Bergen, Norway
| | | | - Lars Herfindal
- Department of Clinical Science, The University of Bergen, Bergen, Norway
| | - Ross Dobie
- Centre for Inflammation Research, The Queen's Medical Research Institute, The University of Edinburgh, Edinburgh, UK
| | - Stephen Jenkins
- Centre for Inflammation Research, The Queen's Medical Research Institute, The University of Edinburgh, Edinburgh, UK
| | - Rolf Kristian Berge
- Department of Clinical Science, The University of Bergen, Bergen, Norway
- Department of Heart Disease, Haukeland University Hospital, Bergen, Norway
| | - Neil Cowan Henderson
- Centre for Inflammation Research, The Queen's Medical Research Institute, The University of Edinburgh, Edinburgh, UK
| | - Frode Selheim
- Department of Biomedicine, The University of Bergen, Bergen, Norway
- Department of Clinical Science, The University of Bergen, Bergen, Norway
| | | | - Marit Bakke
- Department of Biomedicine, The University of Bergen, Bergen, Norway
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14
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Wang Z, Feng M, Awe O, Ma Y, Shen M, Xue P, Ahima R, Wolfe A, Segars J, Wu S. Gonadotrope androgen receptor mediates pituitary responsiveness to hormones and androgen-induced subfertility. JCI Insight 2019; 5:127817. [PMID: 31393859 DOI: 10.1172/jci.insight.127817] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Many women with hyperandrogenemia suffer from irregular menses and infertility. However, it is unknown whether androgens directly affect reproduction. Since animal models of hyperandrogenemia-induced infertility are associated with obesity, which may impact reproductive function, we have created a lean mouse model of elevated androgen using implantation of low dose dihydrotestosterone (DHT) pellets to separate the effects of elevated androgen from obesity. The hypothalamic-pituitary-gonadal axis controls reproduction. While we have demonstrated that androgen impairs ovarian function, androgen could also disrupt neuroendocrine function at the level of brain and/or pituitary to cause infertility. To understand how elevated androgens might act on pituitary gonadotropes to influence reproductive function, female mice with disruption of the androgen receptor (Ar) gene specifically in pituitary gonadotropes (PitARKO) were produced. DHT treated control mice with intact pituitary Ar (Con-DHT) exhibit disrupted estrous cyclicity and fertility with reduced pituitary responsiveness to GnRH at the level of both calcium signaling and LH secretion. These effects were ameliorated in DHT treated PitARKO mice. Calcium signaling controls GnRH regulation of LH vesicle exotocysis. Our data implicated upregulation of GEM (a voltage-dependent calcium channel inhibitor) in the pituitary as a potential mechanism for androgen's pathological effects. These results demonstrate that gonadotrope AR, as an extra-ovarian regulator, plays an important role in reproductive pathophysiology.
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Affiliation(s)
- Zhiqiang Wang
- Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Mingxiao Feng
- Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Olubusayo Awe
- Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Yaping Ma
- Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Department of Pediatrics, Affiliated Hospital of Jiangnan University, Wuxi, China
| | - Mingjie Shen
- Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Department of Gynecology and Obstetrics, Shuguang Hospital Affiliated with Shanghai University of Traditional Chinese Medicine, Shanghai, China
| | - Ping Xue
- Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | | | - Andrew Wolfe
- Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Department of Molecular and Cellular Physiology, and
| | - James Segars
- Department of Gynecology and Obstetrics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Sheng Wu
- Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Department of Molecular and Cellular Physiology, and.,Department of Gynecology and Obstetrics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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15
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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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16
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Xu H, Yang Y, Chen Y, Mueller U, Iyer S, Presland J, Yang R, Kariv I. Determination of EPAC2 function using EPAC2 null Min6 sublines generated through CRISPR-Cas9 technology. Mol Cell Endocrinol 2018; 473:114-123. [PMID: 29407196 DOI: 10.1016/j.mce.2018.01.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/07/2017] [Revised: 01/16/2018] [Accepted: 01/17/2018] [Indexed: 11/21/2022]
Abstract
Min6 cells, a mouse β cell line derived from transgenic mouse expressing the large T-antigen of SV40 in pancreatic beta cells, are commonly utilized as an in vitro cellular model for investigating targets involved in insulin secretion. Epac2, an exchange protein that can be directly activated by cyclic AMP (cAMP), is critical for pharmacologic stimuli-induced insulin secretion and has been hypothesized to be a direct target of sulfonylurea. Previous loss of function studies only specifically knocked out EPAC2 isoform A, leaving the other two isoforms intact. In this study, we investigated the function of EPAC2 in Min6 cells by generating EPAC2 knock-out sublines using CRISPR-Cas9 technology, by removing all three isoforms of EPAC2. Our results indicate that Min6 cells can be successfully cloned from a single cell after electroporation with plasmids expressing EPAC2 specific guide RNA, Cas9 and GFP, followed by sorting for GFP expressing single cells. Two clones were found to have a single nucleotide deletion in targeted site of EPAC2 gene by sequencing, therefore creating a frame shift in exon 13. The EPAC2 null clones have an unexpectedly increased secretion of insulin at basal level and an elevated total intracellular insulin content. However, EPAC2 deficiency impaires glucose and sulfonylurea induced insulin secretion without affecting sulfonylurea binding to cells. Potassium chloride induced insulin secretion remains intact. Interestingly, cAMP levels remained unchanged in EPAC2 null cells during these processes. To understand the global function of EPAC2, RNA Seq study was performed, which reveals that EPAC2 deficiency affects expression of multiple previously unrecognized genes, suggesting that EPAC2 can function through multiple pathways in addition to being a cAMP sensor.
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Affiliation(s)
- Haiyan Xu
- Department of Early Discovery Pharmacology, Cellular Pharmacology, Merck & Co., Inc., 33 Ave. Louis Pasteur, Boston, MA 02115, USA.
| | - Yi Yang
- Department of Early Discovery Pharmacology, Cellular Pharmacology, Merck & Co., Inc., 33 Ave. Louis Pasteur, Boston, MA 02115, USA
| | - Yiping Chen
- Department of Early Discovery Pharmacology, Cellular Pharmacology, Merck & Co., Inc., 33 Ave. Louis Pasteur, Boston, MA 02115, USA
| | - Uwe Mueller
- Department of Early Discovery Pharmacology, Cellular Pharmacology, Merck & Co., Inc., 33 Ave. Louis Pasteur, Boston, MA 02115, USA
| | - Sharanya Iyer
- Department of Early Discovery Pharmacology, Cellular Pharmacology, Merck & Co., Inc., 33 Ave. Louis Pasteur, Boston, MA 02115, USA
| | - Jeremy Presland
- Department of Early Discovery Pharmacology, Cellular Pharmacology, Merck & Co., Inc., 33 Ave. Louis Pasteur, Boston, MA 02115, USA
| | - Ruojing Yang
- Department of Early Discovery Pharmacology, Cellular Pharmacology, Merck & Co., Inc., 33 Ave. Louis Pasteur, Boston, MA 02115, USA
| | - Ilona Kariv
- Department of Early Discovery Pharmacology, Cellular Pharmacology, Merck & Co., Inc., 33 Ave. Louis Pasteur, Boston, MA 02115, USA
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17
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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: 140] [Impact Index Per Article: 23.3] [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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18
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Kaneko K, Xu P, Cordonier EL, Chen SS, Ng A, Xu Y, Morozov A, Fukuda M. Neuronal Rap1 Regulates Energy Balance, Glucose Homeostasis, and Leptin Actions. Cell Rep 2017; 16:3003-3015. [PMID: 27626668 DOI: 10.1016/j.celrep.2016.08.039] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Revised: 06/30/2016] [Accepted: 08/11/2016] [Indexed: 10/21/2022] Open
Abstract
The CNS contributes to obesity and metabolic disease; however, the underlying neurobiological pathways remain to be fully established. Here, we show that the small GTPase Rap1 is expressed in multiple hypothalamic nuclei that control whole-body metabolism and is activated in high-fat diet (HFD)-induced obesity. Genetic ablation of CNS Rap1 protects mice from dietary obesity, glucose imbalance, and insulin resistance in the periphery and from HFD-induced neuropathological changes in the hypothalamus, including diminished cellular leptin sensitivity and increased endoplasmic reticulum (ER) stress and inflammation. Furthermore, pharmacological inhibition of CNS Rap1 signaling normalizes hypothalamic ER stress and inflammation, improves cellular leptin sensitivity, and reduces body weight in mice with dietary obesity. We also demonstrate that Rap1 mediates leptin resistance via interplay with ER stress. Thus, neuronal Rap1 critically regulates leptin sensitivity and mediates HFD-induced obesity and hypothalamic pathology and may represent a potential therapeutic target for obesity treatment.
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Affiliation(s)
- Kentaro Kaneko
- Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Pingwen Xu
- Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Elizabeth L Cordonier
- Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Siyu S Chen
- Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Amy Ng
- Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Yong Xu
- Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA; Department of Molecular and Cellular Biology, Baylor College of Medicine, 1 Baylor Plaza, Houston, TX 77030, USA
| | - Alexei Morozov
- Unit on Behavioral Genetics, Laboratory of Molecular Pathophysiology, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892, USA; Virginia Tech Carilion Research Institute, Roanoke, VA 24016, USA
| | - Makoto Fukuda
- Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA.
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19
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Mondal P, Prasad A, Girdhar K. Interventions to improve β-cell mass and function. ANNALES D'ENDOCRINOLOGIE 2017; 78:469-477. [PMID: 28870707 DOI: 10.1016/j.ando.2016.11.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Revised: 10/18/2016] [Accepted: 11/09/2016] [Indexed: 01/09/2023]
Abstract
Diabetes mellitus (T2DM) has become an epidemiologically important disease worldwide and is also becoming a great matter of concern due to the effects associated with it like: high morbidity, elevated health care cost and shortened life span. T2DM is a chronic metabolic disease characterized by insulin resistance as well as β-cell dysfunction. It is widely accepted that in the face of insulin resistance, euglycemia can be maintained by increase in pancreatic β-cell mass and insulin secretion. This compensation is largely due to enhanced secretion of insulin by the β-cell mass, which is present initially, and thereby subsequent increases in β-cell mass provide additional insulin secretion. However, the mechanism by which β-cell anatomical plasticity and functional plasticity for insulin secretion is coordinated and executed in different physiological and pathophysiological states is complex and has been poorly understood. As the incidence of T2DM continues to increase at an alarming rate, it is becoming imperative to shift the research focus towards the β-cell physiology where identification of novel pathways that influence the β-cell proliferation and/or contribute to increase insulin secretion has the potential to lead to new therapies for preventing or delaying onset of disease.
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Affiliation(s)
- Prosenjit Mondal
- School of Basic Sciences, BioX, Indian Institute of Technology, Mandi, HP 175005, India.
| | - Amit Prasad
- School of Basic Sciences, BioX, Indian Institute of Technology, Mandi, HP 175005, India
| | - Khyati Girdhar
- School of Basic Sciences, BioX, Indian Institute of Technology, Mandi, HP 175005, India
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20
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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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21
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Zhu Y, Mei F, Luo P, Cheng X. A cell-based, quantitative and isoform-specific assay for exchange proteins directly activated by cAMP. Sci Rep 2017; 7:6200. [PMID: 28740152 PMCID: PMC5524698 DOI: 10.1038/s41598-017-06432-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2017] [Accepted: 06/13/2017] [Indexed: 12/17/2022] Open
Abstract
Extensive functional studies of the exchange protein directly activated by cAMP (EPAC) family of signaling molecules have demonstrated that EPAC proteins play a fundamental role in several physiological and pathophysiological responses, therefore are attractive drug targets. In this report, the development of a cell-based, medium to high throughput screening assay that is capable of monitoring EPAC-mediated activation of cellular Rap1 in an isoform-specific manner is described. This assay adapts a conventional ELISA format with immobilized RalGDS-RBD as a bait to selectively capture GTP-bound active Rap1. As a result, it fills an urgent need for a cell-based EPAC assay that can be conveniently performed using microtiter plates for the discovery and/or validation of isoform-specific EPAC agonists and antagonists.
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Affiliation(s)
- Yingmin Zhu
- Department of Integrative Biology and Pharmacology, Texas Therapeutics Institute, University of Health Science Center, Houston, Texas, USA
| | - Fang Mei
- Department of Integrative Biology and Pharmacology, Texas Therapeutics Institute, University of Health Science Center, Houston, Texas, USA
| | - Pei Luo
- Department of Integrative Biology and Pharmacology, Texas Therapeutics Institute, University of Health Science Center, Houston, Texas, USA
| | - Xiaodong Cheng
- Department of Integrative Biology and Pharmacology, Texas Therapeutics Institute, University of Health Science Center, Houston, Texas, USA.
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22
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Zhu L, Almaça J, Dadi PK, Hong H, Sakamoto W, Rossi M, Lee RJ, Vierra NC, Lu H, Cui Y, McMillin SM, Perry NA, Gurevich VV, Lee A, Kuo B, Leapman RD, Matschinsky FM, Doliba NM, Urs NM, Caron MG, Jacobson DA, Caicedo A, Wess J. β-arrestin-2 is an essential regulator of pancreatic β-cell function under physiological and pathophysiological conditions. Nat Commun 2017; 8:14295. [PMID: 28145434 PMCID: PMC5296650 DOI: 10.1038/ncomms14295] [Citation(s) in RCA: 58] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2016] [Accepted: 12/15/2016] [Indexed: 01/06/2023] Open
Abstract
β-arrestins are critical signalling molecules that regulate many fundamental physiological functions including the maintenance of euglycemia and peripheral insulin sensitivity. Here we show that inactivation of the β-arrestin-2 gene, barr2, in β-cells of adult mice greatly impairs insulin release and glucose tolerance in mice fed with a calorie-rich diet. Both glucose and KCl-induced insulin secretion and calcium responses were profoundly reduced in β-arrestin-2 (barr2) deficient β-cells. In human β-cells, barr2 knockdown abolished glucose-induced insulin secretion. We also show that the presence of barr2 is essential for proper CAMKII function in β-cells. Importantly, overexpression of barr2 in β-cells greatly ameliorates the metabolic deficits displayed by mice consuming a high-fat diet. Thus, our data identify barr2 as an important regulator of β-cell function, which may serve as a new target to improve β-cell function. Beta-arrestins have key roles in development and metabolic functions as euglycaemic control and insulin sentitivity. Here Zhu et al. show that beta-arrestin-2 regulates insulin secretion and glucose tolerance in mice by promoting CAMKII functions in beta cells.
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Affiliation(s)
- Lu Zhu
- Molecular Signaling Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892, USA
| | - Joana Almaça
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida 33136, USA
| | - Prasanna K Dadi
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee 37232, USA
| | - Hao Hong
- Molecular Signaling Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892, USA.,Key Laboratory of Acupuncture and Medicine Research of Ministry of Education, Nanjing University of Chinese Medicine, Nanjing, Jiangsu 210023, China
| | - Wataru Sakamoto
- Molecular Signaling Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892, USA
| | - Mario Rossi
- Molecular Signaling Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892, USA
| | - Regina J Lee
- Molecular Signaling Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892, USA
| | - Nicholas C Vierra
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee 37232, USA
| | - Huiyan Lu
- Mouse Transgenic Core Facility, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892, USA
| | - Yinghong Cui
- Molecular Signaling Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892, USA
| | - Sara M McMillin
- Molecular Signaling Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892, USA
| | - Nicole A Perry
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee 37232, USA
| | - Vsevolod V Gurevich
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee 37232, USA
| | - Amy Lee
- Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, Iowa 52242, USA
| | - Bryan Kuo
- Laboratory of Bioengineering and Physical Science, National Institute of Biomedical Imaging and Bioengineering, Bethesda, Maryland 20892, USA
| | - Richard D Leapman
- Laboratory of Bioengineering and Physical Science, National Institute of Biomedical Imaging and Bioengineering, Bethesda, Maryland 20892, USA
| | - Franz M Matschinsky
- Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, Pennslvania 19104, USA
| | - Nicolai M Doliba
- Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, Pennslvania 19104, USA
| | - Nikhil M Urs
- Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA
| | - Marc G Caron
- Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA
| | - David A Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee 37232, USA
| | - Alejandro Caicedo
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida 33136, USA
| | - Jürgen Wess
- Molecular Signaling Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892, USA
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Guerra ML, Kalwat MA, McGlynn K, Cobb MH. Sucralose activates an ERK1/2-ribosomal protein S6 signaling axis. FEBS Open Bio 2017; 7:174-186. [PMID: 28174684 PMCID: PMC5292669 DOI: 10.1002/2211-5463.12172] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2016] [Revised: 10/13/2016] [Accepted: 11/28/2016] [Indexed: 12/20/2022] Open
Abstract
The sweetener sucralose can signal through its GPCR receptor to induce insulin secretion from pancreatic β cells, but the downstream signaling pathways involved are not well‐understood. Here we measure responses to sucralose, glucagon‐like peptide 1, and amino acids in MIN6 β cells. Our data suggest a signaling axis, whereby sucralose induces calcium and cAMP, activation of ERK1/2, and site‐specific phosphorylation of ribosomal protein S6. Interestingly, sucralose acted independently of mTORC1 or ribosomal S6 kinase (RSK). These results suggest that sweeteners like sucralose can influence β‐cell responses to secretagogues like glucose through metabolic as well as GPCR‐mediated pathways. Future investigation of novel sweet taste receptor signaling pathways in β cells will have implications for diabetes and other emergent fields involving these receptors.
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Affiliation(s)
- Marcy L Guerra
- Department of Pharmacology UT Southwestern Medical Center Dallas TX USA; Present address: Stem Synergy Therapeutics Nashville TN USA
| | - Michael A Kalwat
- Department of Pharmacology UT Southwestern Medical Center Dallas TX USA
| | - Kathleen McGlynn
- Department of Pharmacology UT Southwestern Medical Center Dallas TX USA
| | - Melanie H Cobb
- Department of Pharmacology UT Southwestern Medical Center Dallas TX USA
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24
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Hwang M, Go Y, Park JH, Shin SK, Song SE, Oh BC, Im SS, Hwang I, Jeon YH, Lee IK, Seino S, Song DK. Epac2a-null mice exhibit obesity-prone nature more susceptible to leptin resistance. Int J Obes (Lond) 2016; 41:279-288. [PMID: 27867203 PMCID: PMC5309344 DOI: 10.1038/ijo.2016.208] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/11/2016] [Revised: 10/07/2016] [Accepted: 10/30/2016] [Indexed: 02/08/2023]
Abstract
BACKGROUND The exchange protein directly activated by cAMP (Epac), which is primarily involved in cAMP signaling, has been known to be essential for controlling body energy metabolism. Epac has two isoforms: Epac1 and Epac2. The function of Epac1 on obesity was unveiled using Epac1 knockout (KO) mice. However, the role of Epac2 in obesity remains unclear. METHODS To evaluate the role of Epac2 in obesity, we used Epac2a KO mice, which is dominantly expressed in neurons and endocrine tissues. Physiological factors related to obesity were analyzed: body weight, fat mass, food intake, plasma leptin and adiponectin levels, energy expenditure, glucose tolerance, and insulin and leptin resistance. To determine the mechanism of Epac2a, mice received exogenous leptin and then hypothalamic leptin signaling was analyzed. RESULTS Epac2a KO mice appeared to have normal glucose tolerance and insulin sensitivity until 12 weeks of age, but an early onset increase of plasma leptin levels and decrease of plasma adiponectin levels compared with wild-type mice. Acute leptin injection revealed impaired hypothalamic leptin signaling in KO mice. Consistently, KO mice fed a high-fat diet (HFD) were significantly obese, presenting greater food intake and lower energy expenditure. HFD-fed KO mice were also characterized by greater impairment of hypothalamic leptin signaling and by weaker leptin-induced decrease in food consumption compared with HFD-fed wild-type mice. In wild-type mice, acute exogenous leptin injection or chronic HFD feeding tended to induce hypothalamic Epac2a expression. CONCLUSIONS Considering that HFD is an inducer of hypothalamic leptin resistance and that Epac2a functions in pancreatic beta cells during demands of greater work load, hypothalamic Epac2a may have a role in facilitating leptin signaling, at least in response to higher metabolic demands. Thus, our data indicate that Epac2a is critical for preventing obesity and thus Epac2a activators may be used to manage obesity and obesity-mediated metabolic disorders.
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Affiliation(s)
- M Hwang
- Department of Physiology and Obesity-mediated Disease Research Center, Keimyung University School of Medicine, Daegu, Korea
| | - Y Go
- Department of Internal Medicine, Kyungpook National University School of Medicine, Daegu, Korea
| | - J-H Park
- Department of Physiology and Obesity-mediated Disease Research Center, Keimyung University School of Medicine, Daegu, Korea
| | - S-K Shin
- Department of Physiology and Obesity-mediated Disease Research Center, Keimyung University School of Medicine, Daegu, Korea
| | - S E Song
- Department of Physiology and Obesity-mediated Disease Research Center, Keimyung University School of Medicine, Daegu, Korea
| | - B-C Oh
- Laboratory of Molecular and Cellular Biochemistry, Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Korea
| | - S-S Im
- Department of Physiology and Obesity-mediated Disease Research Center, Keimyung University School of Medicine, Daegu, Korea
| | - I Hwang
- Department of Physiology and Obesity-mediated Disease Research Center, Keimyung University School of Medicine, Daegu, Korea
| | - Y H Jeon
- Department of Internal Medicine, Kyungpook National University School of Medicine, Daegu, Korea
| | - I-K Lee
- Department of Internal Medicine, Kyungpook National University School of Medicine, Daegu, Korea
| | - S Seino
- Division of Molecular and Metabolic Medicine, Department of Physiology and Cell Biology, Kobe University Graduate School of Medicine, Kobe, Japan
| | - D-K Song
- Department of Physiology and Obesity-mediated Disease Research Center, Keimyung University School of Medicine, Daegu, Korea
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25
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Levine JA, Kaihara KA, Layden BT, Wicksteed B. Long-term activation of PKA in β-cells provides sustained improvement to glucose control, insulin sensitivity and body weight. Islets 2016; 8:125-34. [PMID: 27340937 PMCID: PMC5029204 DOI: 10.1080/19382014.2016.1198457] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Type 2 diabetes is associated with obesity, insulin resistance and β-cell failure. Therapeutic aims are to reduce adiposity, improve insulin sensitivity and enhance β-cell function. However, it has been proposed that chronically increasing insulin release leads to β-cell exhaustion and failure. We previously developed mice to have increased activity of the cAMP-dependent protein kinase (PKA), specifically in β-cells (β-caPKA mice). β-caPKA mice have enhanced acute phase insulin release, which is the primary determinant of the efficacy of glucose clearance. Here these mice were used to determine the sustainability of enhanced insulin secretion, and to characterize peripheral effects of enhanced β-cell function. Increased PKA activity was induced by tamoxifen administration at 10 weeks of age. Male mice were aged to 12 months of age and female mice to 16 months. Glucose control in both male and female β-caPKA mice was significantly improved relative to littermate controls with ad libitum feeding, upon refeeding after fasting, and in glucose tolerance tests. In female mice insulin release was both greater and more rapid than in controls. Female mice were more insulin sensitive than controls. Male and female β-caPKA mice had lower body weights than controls. DEXA analysis of male mice revealed that this was due to reduced adiposity and not due to changes in lean body mass. This study indicates that targeting β-cells to enhance insulin release is sustainable, maintains insulin sensitivity and reduces body weight. These data identify β-cell PKA activity as a novel target for obesity therapies.
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Affiliation(s)
- Joshua A. Levine
- Division of Endocrinology, Metabolism and Molecular Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | - Kelly A. Kaihara
- Committee for Molecular Metabolism and Nutrition, The University of Chicago, Chicago, IL, USA
- Bio-Rad Laboratories, Hercules, CA, USA
| | - Brian T. Layden
- Division of Endocrinology, Metabolism and Molecular Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
- Jesse Brown Veterans Affairs Medical Center, Chicago, IL, USA
| | - Barton Wicksteed
- Division of Endocrinology, Metabolism and Molecular Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
- Committee for Molecular Metabolism and Nutrition, The University of Chicago, Chicago, IL, USA
- CONTACT Barton Wicksteed Division of Endocrinology, Metabolism and Molecular Medicine, Tarry Building 15-735 300 East Superior St., Chicago, IL 60611-3008, USA
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26
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Chen C, Chmelova H, Cohrs CM, Chouinard JA, Jahn SR, Stertmann J, Uphues I, Speier S. Alterations in β-Cell Calcium Dynamics and Efficacy Outweigh Islet Mass Adaptation in Compensation of Insulin Resistance and Prediabetes Onset. Diabetes 2016; 65:2676-85. [PMID: 27207518 DOI: 10.2337/db15-1718] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Accepted: 04/05/2016] [Indexed: 11/13/2022]
Abstract
Emerging insulin resistance is normally compensated by increased insulin production of pancreatic β-cells, thereby maintaining normoglycemia. However, it is unclear whether this is achieved by adaptation of β-cell function, mass, or both. Most importantly, it is still unknown which of these adaptive mechanisms fail when type 2 diabetes develops. We performed longitudinal in vivo imaging of β-cell calcium dynamics and islet mass of transplanted islets of Langerhans throughout diet-induced progression from normal glucose homeostasis, through compensation of insulin resistance, to prediabetes. The results show that compensation of insulin resistance is predominated by alterations of β-cell function, while islet mass only gradually expands. Hereby, functional adaptation is mediated by increased calcium efficacy, which involves Epac signaling. Prior to prediabetes, β-cell function displays decreased stimulated calcium dynamics, whereas islet mass continues to increase through prediabetes onset. Thus, our data reveal a predominant role of islet function with distinct contributions of triggering and amplifying pathway in the in vivo processes preceding diabetes onset. These findings support protection and recovery of β-cell function as primary goals for prevention and treatment of diabetes and provide insight into potential therapeutic targets.
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Affiliation(s)
- Chunguang Chen
- Paul Langerhans Institute Dresden, Helmholtz Center Munich, University Clinic Carl Gustav Carus, Technische Universität Dresden, Helmholtz Zentrum München, Neuherberg, Germany German Research Foundation-Center for Regenerative Therapies Dresden (CRTD), Faculty of Medicine, Technische Universität Dresden, Dresden, Germany German Center for Diabetes Research (DZD), München-Neuherberg, Germany
| | - Helena Chmelova
- Paul Langerhans Institute Dresden, Helmholtz Center Munich, University Clinic Carl Gustav Carus, Technische Universität Dresden, Helmholtz Zentrum München, Neuherberg, Germany German Research Foundation-Center for Regenerative Therapies Dresden (CRTD), Faculty of Medicine, Technische Universität Dresden, Dresden, Germany German Center for Diabetes Research (DZD), München-Neuherberg, Germany
| | - Christian M Cohrs
- Paul Langerhans Institute Dresden, Helmholtz Center Munich, University Clinic Carl Gustav Carus, Technische Universität Dresden, Helmholtz Zentrum München, Neuherberg, Germany German Research Foundation-Center for Regenerative Therapies Dresden (CRTD), Faculty of Medicine, Technische Universität Dresden, Dresden, Germany German Center for Diabetes Research (DZD), München-Neuherberg, Germany
| | - Julie A Chouinard
- Paul Langerhans Institute Dresden, Helmholtz Center Munich, University Clinic Carl Gustav Carus, Technische Universität Dresden, Helmholtz Zentrum München, Neuherberg, Germany German Research Foundation-Center for Regenerative Therapies Dresden (CRTD), Faculty of Medicine, Technische Universität Dresden, Dresden, Germany German Center for Diabetes Research (DZD), München-Neuherberg, Germany
| | - Stephan R Jahn
- Paul Langerhans Institute Dresden, Helmholtz Center Munich, University Clinic Carl Gustav Carus, Technische Universität Dresden, Helmholtz Zentrum München, Neuherberg, Germany German Research Foundation-Center for Regenerative Therapies Dresden (CRTD), Faculty of Medicine, Technische Universität Dresden, Dresden, Germany German Center for Diabetes Research (DZD), München-Neuherberg, Germany
| | - Julia Stertmann
- Paul Langerhans Institute Dresden, Helmholtz Center Munich, University Clinic Carl Gustav Carus, Technische Universität Dresden, Helmholtz Zentrum München, Neuherberg, Germany German Research Foundation-Center for Regenerative Therapies Dresden (CRTD), Faculty of Medicine, Technische Universität Dresden, Dresden, Germany German Center for Diabetes Research (DZD), München-Neuherberg, Germany
| | - Ingo Uphues
- Boehringer Ingelheim Pharma GmbH & Co. KG, Ingelheim, Germany
| | - Stephan Speier
- Paul Langerhans Institute Dresden, Helmholtz Center Munich, University Clinic Carl Gustav Carus, Technische Universität Dresden, Helmholtz Zentrum München, Neuherberg, Germany German Research Foundation-Center for Regenerative Therapies Dresden (CRTD), Faculty of Medicine, Technische Universität Dresden, Dresden, Germany German Center for Diabetes Research (DZD), München-Neuherberg, Germany
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27
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Yamada H, Yoshida M, Ito K, Dezaki K, Yada T, Ishikawa SE, Kakei M. Potentiation of Glucose-stimulated Insulin Secretion by the GPR40-PLC-TRPC Pathway in Pancreatic β-Cells. Sci Rep 2016; 6:25912. [PMID: 27180622 PMCID: PMC4867641 DOI: 10.1038/srep25912] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2016] [Accepted: 04/25/2016] [Indexed: 01/04/2023] Open
Abstract
G protein-coupled receptors (GPCRs) are expressed in pancreatic beta-cells. G protein-coupled receptor 40 (GPR40) contributes to medium- or long-chain fatty acid-induced amplification of glucose-stimulated insulin secretion (GSIS), and GPR40 agonists are promising therapeutic targets in type 2 diabetes. Recently, we demonstrated that glucagon-like peptide 1, a ligand of pancreatic GPCR, activates a class of nonselective cation channels (NSCCs) and enhances GSIS. The aim of the current study was to determine whether the GPR40 signal interacts with NSCCs. A GPR40 agonist (fasiglifam) potentiated GSIS at 8.3 and 16.7 mM glucose but not 2.8 mM glucose. The NSCC current was activated by fasiglifam at 5.6 mM glucose with 100 μM tolbutamide (−70 mV), and this activation was prevented by the presence of pyrazole-3 (transient receptor potential canonical; a TRPC3 channel blocker). Inhibitors of phospholipase C or protein kinase C (PKC) inhibited the increases in GSIS and the NSCC current induced by GPR40 stimulation. The present study demonstrates a novel mechanism for the regulation of insulin secretion by GPR40 agonist in pancreatic beta-cells. The stimulation of the GPR40–PLC/PKC–TRPC3 channel pathway potentiates GSIS by the depolarization of the plasma membrane in pancreatic beta-cell.
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Affiliation(s)
- Hodaka Yamada
- First Department of Comprehensive Medicine, Jichi Medical University Saitama Medical Center, Amanuma, Omiya 1-847, Saitama 330-8503, Japan
| | - Masashi Yoshida
- First Department of Comprehensive Medicine, Jichi Medical University Saitama Medical Center, Amanuma, Omiya 1-847, Saitama 330-8503, Japan
| | - Kiyonori Ito
- First Department of Comprehensive Medicine, Jichi Medical University Saitama Medical Center, Amanuma, Omiya 1-847, Saitama 330-8503, Japan
| | - Katsuya Dezaki
- Division of Integrative Physiology, Department of physiology, Jichi Medical University School of Medicine, Yakushiji 3311-1, Shimotsuke, Tochigi 329-0498, Japan
| | - Toshihiko Yada
- Division of Integrative Physiology, Department of physiology, Jichi Medical University School of Medicine, Yakushiji 3311-1, Shimotsuke, Tochigi 329-0498, Japan
| | - San-E Ishikawa
- First Department of Comprehensive Medicine, Jichi Medical University Saitama Medical Center, Amanuma, Omiya 1-847, Saitama 330-8503, Japan
| | - Masafumi Kakei
- First Department of Comprehensive Medicine, Jichi Medical University Saitama Medical Center, Amanuma, Omiya 1-847, Saitama 330-8503, Japan
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28
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Mondal P, Song WJ, Li Y, Yang KS, Hussain MA. Increasing β-cell mass requires additional stimulation for adaptation to secretory demand. Mol Endocrinol 2016; 29:108-20. [PMID: 25387052 DOI: 10.1210/me.2014-1265] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Type 2 diabetes mellitus (T2DM) is caused by relative insulin deficiency, subsequent to both reduced β-cell mass and insufficient insulin secretion, and both augmenting β-cell mass and β-cell function are therapeutic strategies for treating T2DM. However, the relative significance of increasing β-cell mass vs improving β-cell stimulus secretion coupling remains unclear. We have developed a mouse model that allows proliferation of β-cells in adult mice without affecting β-cell function by inducible expression of the positive cell cycle regulator cyclin A2 specifically in β-cells. In these mice, when kept on a standard diet, doubling of β-cell mass does not result in altered glucose tolerance or glucose-stimulated circulating insulin levels. Notably, a doubling of β-cell mass also does not confer improved glycemic control and ability of β-cells to respond to diabetogenic high-fat diet-induced glucose intolerance. However, in high-fat diet-exposed mice, an increase in endogenous β-cell mass confers increased potentiation of in vivo glucose-stimulated rise in circulating insulin in response to acute pharmacologic treatment with the incretin glucagon-like peptide-1 receptor agonist exendin-4. These observations indicate that increasing endogenous β-cell mass may not be sufficient to improve glycemic control in T2DM without additional strategies to increase β-cell stimulus secretion coupling.
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Affiliation(s)
- Prosenjit Mondal
- Departments of Medicine (M.A.H.), Pediatrics (P.M., W.-J.S., Y.L., K.S.Y., M.A.H.), and Biological Chemistry (M.A.H.), Johns Hopkins University, Baltimore, Maryland 21287
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29
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30
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Lewis AE, Aesoy R, Bakke M. Role of EPAC in cAMP-Mediated Actions in Adrenocortical Cells. Front Endocrinol (Lausanne) 2016; 7:63. [PMID: 27379015 PMCID: PMC4904129 DOI: 10.3389/fendo.2016.00063] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/15/2016] [Accepted: 05/30/2016] [Indexed: 12/31/2022] Open
Abstract
Adrenocorticotropic hormone regulates adrenal steroidogenesis mainly via the intracellular signaling molecule cAMP. The effects of cAMP are principally relayed by activating protein kinase A (PKA) and the more recently discovered exchange proteins directly activated by cAMP 1 and 2 (EPAC1 and EPAC2). While the intracellular roles of PKA have been extensively studied in steroidogenic tissues, those of EPACs are only emerging. EPAC1 and EPAC2 are encoded by the genes RAPGEF3 and RAPGEF4, respectively. Whereas EPAC1 is ubiquitously expressed, the expression of EPAC2 is more restricted, and typically found in endocrine tissues. Alternative promoter usage of RAPGEF4 gives rise to three different isoforms of EPAC2 that vary in their N-termini (EPAC2A, EPAC2B, and EPAC2C) and that exhibit distinct expression patterns. EPAC2A is expressed in the brain and pancreas, EPAC2B in steroidogenic cells of the adrenal gland and testis, and EPAC2C has until now only been found in the liver. In this review, we discuss current knowledge on EPAC expression and function with focus on the known roles of EPAC in adrenal gland physiology.
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Affiliation(s)
- Aurélia E. Lewis
- Department of Molecular Biology, University of Bergen, Bergen, Norway
- *Correspondence: Aurélia E. Lewis,
| | - Reidun Aesoy
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | - Marit Bakke
- Department of Biomedicine, University of Bergen, Bergen, Norway
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31
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Schwede F, Chepurny OG, Kaufholz M, Bertinetti D, Leech CA, Cabrera O, Zhu Y, Mei F, Cheng X, Manning Fox JE, MacDonald PE, Genieser HG, Herberg FW, Holz GG. Rp-cAMPS Prodrugs Reveal the cAMP Dependence of First-Phase Glucose-Stimulated Insulin Secretion. Mol Endocrinol 2015; 29:988-1005. [PMID: 26061564 DOI: 10.1210/me.2014-1330] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
cAMP-elevating agents such as the incretin hormone glucagon-like peptide-1 potentiate glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells. However, a debate has existed since the 1970s concerning whether or not cAMP signaling is essential for glucose alone to stimulate insulin secretion. Here, we report that the first-phase kinetic component of GSIS is cAMP-dependent, as revealed through the use of a novel highly membrane permeable para-acetoxybenzyl (pAB) ester prodrug that is a bioactivatable derivative of the cAMP antagonist adenosine-3',5'-cyclic monophosphorothioate, Rp-isomer (Rp-cAMPS). In dynamic perifusion assays of human or rat islets, a step-wise increase of glucose concentration leads to biphasic insulin secretion, and under these conditions, 8-bromoadenosine-3',5'-cyclic monophosphorothioate, Rp-isomer, 4-acetoxybenzyl ester (Rp-8-Br-cAMPS-pAB) inhibits first-phase GSIS by up to 80%. Surprisingly, second-phase GSIS is inhibited to a much smaller extent (≤20%). Using luciferase, fluorescence resonance energy transfer, and bioluminescence resonance energy transfer assays performed in living cells, we validate that Rp-8-Br-cAMPS-pAB does in fact block cAMP-dependent protein kinase activation. Novel effects of Rp-8-Br-cAMPS-pAB to block the activation of cAMP-regulated guanine nucleotide exchange factors (Epac1, Epac2) are also validated using genetically encoded Epac biosensors, and are independently confirmed in an in vitro Rap1 activation assay using Rp-cAMPS and Rp-8-Br-cAMPS. Thus, in addition to revealing the cAMP dependence of first-phase GSIS from human and rat islets, these findings establish a pAB-based chemistry for the synthesis of highly membrane permeable prodrug derivatives of Rp-cAMPS that act with micromolar or even nanomolar potency to inhibit cAMP signaling in living cells.
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Affiliation(s)
- Frank Schwede
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Oleg G Chepurny
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Melanie Kaufholz
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Daniela Bertinetti
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Colin A Leech
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Over Cabrera
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Yingmin Zhu
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Fang Mei
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Xiaodong Cheng
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Jocelyn E Manning Fox
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Patrick E MacDonald
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Hans-G Genieser
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Friedrich W Herberg
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - George G Holz
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
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Kaihara KA, Dickson LM, Ellenbroek JH, Orr CMD, Layden BT, Wicksteed B. PKA Enhances the Acute Insulin Response Leading to the Restoration of Glucose Control. Diabetes 2015; 64:1688-97. [PMID: 25475437 PMCID: PMC4407848 DOI: 10.2337/db14-1051] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/07/2014] [Accepted: 11/24/2014] [Indexed: 12/18/2022]
Abstract
Diabetes arises from insufficient insulin secretion and failure of the β-cell mass to persist and expand. These deficits can be treated with ligands to Gs-coupled G-protein-coupled receptors that raise β-cell cAMP. Here we studied the therapeutic potential of β-cell cAMP-dependent protein kinase (PKA) activity in restoring glucose control using β-caPKA mice. PKA activity enhanced the acute insulin response (AIR) to glucose, which is a primary determinant of the efficacy of glucose clearance. Enhanced AIR improved peripheral insulin action, leading to more rapid muscle glucose uptake. In the setting of pre-established glucose intolerance caused by diet-induced insulin resistance or streptozotocin-mediated β-cell mass depletion, PKA activation enhanced β-cell secretory function to restore glucose control, primarily through augmentation of the AIR. Enhanced AIR and improved glucose control were maintained through 16 weeks of a high-fat diet and aging to 1 year. Importantly, improved glucose tolerance did not increase the risk for hypoglycemia, nor did it rely upon hyperinsulinemia or β-cell hyperplasia, although PKA activity was protective for β-cell mass. These data highlight that improving β-cell function through the activation of PKA has a large and underappreciated capacity to restore glucose control with minimal risk for adverse side effects.
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Affiliation(s)
- Kelly A Kaihara
- Kovler Diabetes Center, The University of Chicago, Chicago, IL Committee for Molecular Metabolism and Nutrition, The University of Chicago, Chicago, IL Section of Adult and Pediatric Endocrinology, Diabetes, and Metabolism, Department of Medicine, The University of Chicago, Chicago, IL
| | - Lorna M Dickson
- Kovler Diabetes Center, The University of Chicago, Chicago, IL Section of Adult and Pediatric Endocrinology, Diabetes, and Metabolism, Department of Medicine, The University of Chicago, Chicago, IL
| | - Johanne H Ellenbroek
- Kovler Diabetes Center, The University of Chicago, Chicago, IL Section of Adult and Pediatric Endocrinology, Diabetes, and Metabolism, Department of Medicine, The University of Chicago, Chicago, IL
| | - Caitlin M D Orr
- Kovler Diabetes Center, The University of Chicago, Chicago, IL Committee for Molecular Metabolism and Nutrition, The University of Chicago, Chicago, IL Section of Adult and Pediatric Endocrinology, Diabetes, and Metabolism, Department of Medicine, The University of Chicago, Chicago, IL
| | - Brian T Layden
- Division of Endocrinology, Metabolism, and Molecular Medicine, Northwestern University Feinberg School of Medicine, Chicago, IL Jesse Brown Veterans Affairs Medical Center, Chicago, IL
| | - Barton Wicksteed
- Kovler Diabetes Center, The University of Chicago, Chicago, IL Committee for Molecular Metabolism and Nutrition, The University of Chicago, Chicago, IL Section of Adult and Pediatric Endocrinology, Diabetes, and Metabolism, Department of Medicine, The University of Chicago, Chicago, IL
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33
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Takahashi H, Shibasaki T, Park JH, Hidaka S, Takahashi T, Ono A, Song DK, Seino S. Role of Epac2A/Rap1 signaling in interplay between incretin and sulfonylurea in insulin secretion. Diabetes 2015; 64:1262-72. [PMID: 25315008 DOI: 10.2337/db14-0576] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Incretin-related drugs and sulfonylureas are currently used worldwide for the treatment of type 2 diabetes. We recently found that Epac2A, a cAMP binding protein having guanine nucleotide exchange activity toward Rap, is a target of both incretin and sulfonylurea. This suggests the possibility of interplay between incretin and sulfonylurea through Epac2A/Rap1 signaling in insulin secretion. In this study, we examined the combinatorial effects of incretin and various sulfonylureas on insulin secretion and activation of Epac2A/Rap1 signaling. A strong augmentation of insulin secretion by combination of GLP-1 and glibenclamide or glimepiride, which was found in Epac2A(+/+) mice, was markedly reduced in Epac2A(-/-) mice. In contrast, the combinatorial effect of GLP-1 and gliclazide was rather mild, and the effect was not altered by Epac2A ablation. Activation of Rap1 was enhanced by the combination of an Epac-selective cAMP analog with glibenclamide or glimepiride but not gliclazide. In diet-induced obese mice, ablation of Epac2A reduced the insulin secretory response to coadministration of the GLP-1 receptor agonist liraglutide and glimepiride. These findings clarify the critical role of Epac2A/Rap1 signaling in the augmenting effect of incretin and sulfonylurea on insulin secretion and provide the basis for the effects of combination therapies of incretin-related drugs and sulfonylureas.
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Affiliation(s)
- Harumi Takahashi
- Division of Molecular and Metabolic Medicine, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Japan
| | - Tadao Shibasaki
- Division of Cellular and Molecular Medicine, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Japan
| | - Jae-Hyung Park
- Department of Physiology, Keimyung University School of Medicine, Dalseo-Gu, Daegu, Korea
| | - Shihomi Hidaka
- Division of Molecular and Metabolic Medicine, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Japan
| | - Toshimasa Takahashi
- Division of Molecular and Metabolic Medicine, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Japan Division of Diabetes and Endocrinology, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Japan
| | - Aika Ono
- Division of Cellular and Molecular Medicine, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Japan
| | - Dae-Kyu Song
- Department of Physiology, Keimyung University School of Medicine, Dalseo-Gu, Daegu, Korea
| | - Susumu Seino
- Division of Molecular and Metabolic Medicine, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Japan
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Sukma Rita R, Dezaki K, Kurashina T, Kakei M, Yada T. Partial blockade of Kv2.1 channel potentiates GLP-1's insulinotropic effects in islets and reduces its dose required for improving glucose tolerance in type 2 diabetic male mice. Endocrinology 2015; 156:114-23. [PMID: 25337656 DOI: 10.1210/en.2014-1728] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Glucagon-like peptide-1 (GLP-1)-based medicines have recently been widely used to treat type 2 diabetic patients, whereas adverse effects of nausea and vomiting have been documented. Inhibition of voltage-gated K(+) channel subtype Kv2.1 in pancreatic β-cells has been suggested to contribute to mild depolarization and promotion of insulin release. This study aimed to determine whether the blockade of Kv2.1 channels potentiates the insulinotropic effect of GLP-1 agonists. Kv2.1 channel blocker guangxitoxin-1E (GxTx) and GLP-1 agonist exendin-4 at subthreshold concentrations, when combined, markedly increased the insulin release and cytosolic Ca(2+) concentration ([Ca(2+)]i) in a glucose-dependent manner in mouse islets and β-cells. Exendin-4 at subthreshold concentration alone increased islet insulin release and β-cell [Ca(2+)]i in Kv2.1(+/-) mice. The [Ca(2+)]i response to subthreshold exendin-4 and GxTx in combination was attenuated by pretreatment with protein kinase A inhibitor H-89, indicating the protein kinase A dependency of the cooperative effect. Furthermore, subthreshold doses of GxTx and GLP-1 agonist liraglutide in combination markedly increased plasma insulin and improved glucose tolerance in diabetic db/db mice and NSY mice. These results demonstrate that a modest suppression of Kv2.1 channels dramatically raises insulinotropic potency of GLP-1-based drugs, which opens a new avenue to reduce their doses and associated adverse effects while achieving the same glycemic control in type 2 diabetes.
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Affiliation(s)
- Rauza Sukma Rita
- Division of Integrative Physiology (R.S.R., K.D., T.K., T.Y.), Department of Physiology, Jichi Medical University School of Medicine, Shimotsuke, Tochigi 329-0498, Japan; Department of Internal Medicine (M.K.), Saitama Medical Center, Jichi Medical University School of Medicine, Saitama 337-8503, Japan; and Department of Development Physiology (T.Y.), Division of Adaptation Development, National Institute for Physiological Sciences, Okazaki, Aichi 444-8585, Japan
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Yosida M, Dezaki K, Uchida K, Kodera S, Lam NV, Ito K, Rita RS, Yamada H, Shimomura K, Ishikawa SE, Sugawara H, Kawakami M, Tominaga M, Yada T, Kakei M. Involvement of cAMP/EPAC/TRPM2 activation in glucose- and incretin-induced insulin secretion. Diabetes 2014; 63:3394-403. [PMID: 24824430 DOI: 10.2337/db13-1868] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
In pancreatic β-cells, closure of the ATP-sensitive K(+) (K(ATP)) channel is an initial process triggering glucose-stimulated insulin secretion. In addition, constitutive opening of background nonselective cation channels (NSCCs) is essentially required to effectively evoke depolarization as a consequence of K(ATP) channel closure. Thus, it is hypothesized that further opening of NSCC facilitates membrane excitability. We identified a class of NSCC that was activated by exendin (ex)-4, GLP-1, and its analog liraglutide at picomolar levels. This NSCC was also activated by increasing the glucose concentration. NSCC activation by glucose and GLP-1 was a consequence of the activated cAMP/EPAC-mediated pathway and was attenuated in TRPM2-deficient mice. The NSCC was not activated by protein kinase A (PKA) activators and was activated by ex-4 in the presence of PKA inhibitors. These results suggest that glucose- and incretin-activated NSCC (TRPM2) works in concert with closure of the KATP channel to effectively induce membrane depolarization to initiate insulin secretion. The current study reveals a new mechanism for regulating electrical excitability in β-cells and for mediating the action of glucose and incretin to evoke insulin secretion, thereby providing an innovative target for the treatment of type 2 diabetes.
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Affiliation(s)
- Masashi Yosida
- Internal Medicine, Saitama Medical Center, Jichi Medical University, Saitama, Japan
| | - Katsuya Dezaki
- Integrative Physiology, Jichi Medical University, Shimotsuke, Japan
| | | | - Shiho Kodera
- Internal Medicine, Saitama Medical Center, Jichi Medical University, Saitama, Japan
| | - Nien V Lam
- Internal Medicine, Saitama Medical Center, Jichi Medical University, Saitama, Japan
| | - Kiyonori Ito
- Internal Medicine, Saitama Medical Center, Jichi Medical University, Saitama, Japan
| | - Rauza S Rita
- Integrative Physiology, Jichi Medical University, Shimotsuke, Japan
| | - Hodaka Yamada
- Internal Medicine, Saitama Medical Center, Jichi Medical University, Saitama, Japan
| | - Kenju Shimomura
- Integrative Physiology, Jichi Medical University, Shimotsuke, Japan
| | - San-e Ishikawa
- Internal Medicine, Saitama Medical Center, Jichi Medical University, Saitama, Japan
| | - Hitoshi Sugawara
- Internal Medicine, Saitama Medical Center, Jichi Medical University, Saitama, Japan
| | - Masanobu Kawakami
- Internal Medicine, Saitama Medical Center, Jichi Medical University, Saitama, Japan Nerima Hikarigaoka Hospital, Nerima, Japan
| | - Makoto Tominaga
- National Institute for Physiological Sciences, Okazaki, Japan
| | - Toshihiko Yada
- Integrative Physiology, Jichi Medical University, Shimotsuke, Japan National Institute for Physiological Sciences, Okazaki, Japan
| | - Masafumi Kakei
- Internal Medicine, Saitama Medical Center, Jichi Medical University, Saitama, Japan
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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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37
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Holz GG, Leech CA, Chepurny OG. New insights concerning the molecular basis for defective glucoregulation in soluble adenylyl cyclase knockout mice. Biochim Biophys Acta Mol Basis Dis 2014; 1842:2593-600. [PMID: 24980705 DOI: 10.1016/j.bbadis.2014.06.023] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Revised: 06/17/2014] [Accepted: 06/18/2014] [Indexed: 01/09/2023]
Abstract
Recently published findings indicate that a knockout (KO) of soluble adenylyl cyclase (sAC, also known as AC-10) gene expression in mice leads to defective glucoregulation that is characterized by reduced pancreatic insulin secretion and reduced intraperitoneal glucose tolerance. Summarized here are current concepts regarding the molecular basis for this phenotype, with special emphasis on the potential role of sAC as a determinant of glucose-stimulated insulin secretion. Highlighted is new evidence that in pancreatic beta cells, oxidative glucose metabolism stimulates mitochondrial CO₂production that in turn generates bicarbonate ion (HCO(3)(-)). Since HCO(3)(-) binds to and directly stimulates the activity of sAC, we propose that glucose-stimulated cAMP production in beta cells is mediated not simply by transmembrane adenylyl cyclases (TMACs), but also by sAC. Based on evidence that sAC is expressed in mitochondria, there exists the possibility that beta-cell glucose metabolism is linked to mitochondrial cAMP production with consequent facilitation of oxidative phosphorylation. Since sAC is also expressed in the cytoplasm, sAC catalyzed cAMP production may activate cAMP sensors such as PKA and Epac2 to control ion channel function, intracellular Ca²⁺ handling, and Ca²⁺-dependent exocytosis. Thus, we propose that the existence of sAC in beta cells provides a new and unexpected explanation for previously reported actions of glucose metabolism to stimulate cAMP production. It seems possible that alterations of sAC activity might be of importance when evaluating new strategies for the treatment of type 2 diabetes (T2DM), or when evaluating why glucose metabolism fails to stimulate insulin secretion in patients diagnosed with T2DM. This article is part of a Special Issue entitled: The role of soluble adenylyl cyclase in health and disease.
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Affiliation(s)
- George G Holz
- Department of Medicine, State University of New York (SUNY), Upstate Medical University, Syracuse, NY 13210, USA; Department of Pharmacology, State University of New York (SUNY), Upstate Medical University, Syracuse, NY 13210, USA.
| | - Colin A Leech
- Department of Medicine, State University of New York (SUNY), Upstate Medical University, Syracuse, NY 13210, USA
| | - Oleg G Chepurny
- Department of Medicine, State University of New York (SUNY), Upstate Medical University, Syracuse, NY 13210, USA
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38
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Liu S, Moayeri M, Leppla SH. Anthrax lethal and edema toxins in anthrax pathogenesis. Trends Microbiol 2014; 22:317-25. [PMID: 24684968 DOI: 10.1016/j.tim.2014.02.012] [Citation(s) in RCA: 144] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2013] [Revised: 02/23/2014] [Accepted: 02/26/2014] [Indexed: 10/25/2022]
Abstract
The pathophysiological effects resulting from many bacterial diseases are caused by exotoxins released by the bacteria. Bacillus anthracis, a spore-forming bacterium, is such a pathogen, causing anthrax through a combination of bacterial infection and toxemia. B. anthracis causes natural infection in humans and animals and has been a top bioterrorism concern since the 2001 anthrax attacks in the USA. The exotoxins secreted by B. anthracis use capillary morphogenesis protein 2 (CMG2) as the major toxin receptor and play essential roles in pathogenesis during the entire course of the disease. This review focuses on the activities of anthrax toxins and their roles in initial and late stages of anthrax infection.
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Affiliation(s)
- Shihui Liu
- Microbial Pathogenesis Section, Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA.
| | - Mahtab Moayeri
- Microbial Pathogenesis Section, Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA.
| | - Stephen H Leppla
- Microbial Pathogenesis Section, Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA.
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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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Nadkarni P, Chepurny OG, Holz GG. Regulation of glucose homeostasis by GLP-1. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2014. [PMID: 24373234 DOI: 10.1016/b978-0-12-800101-1.00002-8.] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 10/01/2022]
Abstract
Glucagon-like peptide-1(7-36)amide (GLP-1) is a secreted peptide that acts as a key determinant of blood glucose homeostasis by virtue of its abilities to slow gastric emptying, to enhance pancreatic insulin secretion, and to suppress pancreatic glucagon secretion. GLP-1 is secreted from L cells of the gastrointestinal mucosa in response to a meal, and the blood glucose-lowering action of GLP-1 is terminated due to its enzymatic degradation by dipeptidyl-peptidase-IV (DPP-IV). Released GLP-1 activates enteric and autonomic reflexes while also circulating as an incretin hormone to control endocrine pancreas function. The GLP-1 receptor (GLP-1R) is a G protein-coupled receptor that is activated directly or indirectly by blood glucose-lowering agents currently in use for the treatment of type 2 diabetes mellitus (T2DM). These therapeutic agents include GLP-1R agonists (exenatide, liraglutide, lixisenatide, albiglutide, dulaglutide, and langlenatide) and DPP-IV inhibitors (sitagliptin, vildagliptin, saxagliptin, linagliptin, and alogliptin). Investigational agents for use in the treatment of T2DM include GPR119 and GPR40 receptor agonists that stimulate the release of GLP-1 from L cells. Summarized here is the role of GLP-1 to control blood glucose homeostasis, with special emphasis on the advantages and limitations of GLP-1-based therapeutics.
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Affiliation(s)
- Prashant Nadkarni
- Department of Medicine, State University of New York (SUNY), Upstate Medical University, Syracuse, New York, USA; Joslin Diabetes Center, State University of New York (SUNY), Upstate Medical University, Syracuse, New York, USA
| | - Oleg G Chepurny
- 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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Nadkarni P, Chepurny OG, Holz GG. Regulation of glucose homeostasis by GLP-1. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2014; 121:23-65. [PMID: 24373234 DOI: 10.1016/b978-0-12-800101-1.00002-8] [Citation(s) in RCA: 156] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Glucagon-like peptide-1(7-36)amide (GLP-1) is a secreted peptide that acts as a key determinant of blood glucose homeostasis by virtue of its abilities to slow gastric emptying, to enhance pancreatic insulin secretion, and to suppress pancreatic glucagon secretion. GLP-1 is secreted from L cells of the gastrointestinal mucosa in response to a meal, and the blood glucose-lowering action of GLP-1 is terminated due to its enzymatic degradation by dipeptidyl-peptidase-IV (DPP-IV). Released GLP-1 activates enteric and autonomic reflexes while also circulating as an incretin hormone to control endocrine pancreas function. The GLP-1 receptor (GLP-1R) is a G protein-coupled receptor that is activated directly or indirectly by blood glucose-lowering agents currently in use for the treatment of type 2 diabetes mellitus (T2DM). These therapeutic agents include GLP-1R agonists (exenatide, liraglutide, lixisenatide, albiglutide, dulaglutide, and langlenatide) and DPP-IV inhibitors (sitagliptin, vildagliptin, saxagliptin, linagliptin, and alogliptin). Investigational agents for use in the treatment of T2DM include GPR119 and GPR40 receptor agonists that stimulate the release of GLP-1 from L cells. Summarized here is the role of GLP-1 to control blood glucose homeostasis, with special emphasis on the advantages and limitations of GLP-1-based therapeutics.
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Affiliation(s)
- Prashant Nadkarni
- Department of Medicine, State University of New York (SUNY), Upstate Medical University, Syracuse, New York, USA; Joslin Diabetes Center, State University of New York (SUNY), Upstate Medical University, Syracuse, New York, USA
| | - Oleg G Chepurny
- 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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Affiliation(s)
- George G Holz
- Department of Medicine, State University of New York Upstate Medical University, Syracuse, New York, USA.
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