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Dienelt A, Keller KC, zur Nieden NI. High glucose impairs osteogenic differentiation of embryonic stem cells via early diversion of beta-catenin from Forkhead box O to T cell factor interaction. Birth Defects Res 2022; 114:1056-1074. [PMID: 36164276 PMCID: PMC9708100 DOI: 10.1002/bdr2.2085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2022] [Revised: 08/18/2022] [Accepted: 08/19/2022] [Indexed: 11/10/2022]
Abstract
BACKGROUND Diabetes, which is characterized by an increase in blood glucose concentration, is accompanied by low bone turnover, increased fracture risk, and the formation of embryonic skeletal malformations. Yet, there are few studies elucidating the underlying alterations in signaling pathways leading to these osteogenic defects. We hypothesized here that bone formation deficiencies in a high glucose environment result from altered activity of beta-catenin (CTNNB1), a key contributor to osteogenic differentiation, dysregulation of which has also been implicated in the development of diabetes. METHODS To test this hypothesis, we used a previously established embryonic stem cell (ESC) model of differentiation that mimics the diabetic environment of the developing embryo. We differentiated murine ESCs within osteogenic-inducing media containing either high (diabetic) or low (physiological) levels of D-glucose and performed time course analyses to study the influence of high glucose on early and late bone cell differentiation. RESULTS Endpoint measures for osteogenic differentiation were reduced in a glucose-dependent manner and expression of precursor-specific markers altered at multiple time points. Furthermore, transcriptional activity of the lymphoid enhancer factor (LEF)/T cell factor (TCF) transcription factors during precursor formation stages was significantly elevated while levels of CTNNB1 complexed with Forkhead box O 3a (FOXO3a) declined. Modulation of AKT, a known upstream regulator of both LEF/TCF and FOXO3a, as well as CTNNB1 rescued some of the reductions in osteogenic output seen in the high glucose condition. CONCLUSIONS Within our in vitro model, we found a clear involvement of LEF/TCF and FOXO3a signaling pathways in the regulation of osteogenic differentiation, which may account for the skeletal deficiencies found in newborns of diabetic mothers.
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Affiliation(s)
- Anke Dienelt
- Department of Cell Therapy, Applied Stem Cell Technologies Unit, Fraunhofer Institute for Cell Therapy and Immunology, Leipzig, Germany
| | - Kevin C. Keller
- Department of Molecular, Cell and Systems Biology & Stem Cell Center, College of Natural and Agricultural Sciences, University of California Riverside, Riverside, CA, USA
| | - Nicole I. zur Nieden
- Department of Cell Therapy, Applied Stem Cell Technologies Unit, Fraunhofer Institute for Cell Therapy and Immunology, Leipzig, Germany
- Department of Molecular, Cell and Systems Biology & Stem Cell Center, College of Natural and Agricultural Sciences, University of California Riverside, Riverside, CA, USA
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2
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Rachdaoui N, Polo-Parada L, Ismail-Beigi F. Prolonged Exposure to Insulin Inactivates Akt and Erk 1/2 and Increases Pancreatic Islet and INS1E β-Cell Apoptosis. J Endocr Soc 2018; 3:69-90. [PMID: 30697602 PMCID: PMC6344346 DOI: 10.1210/js.2018-00140] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/09/2018] [Accepted: 10/29/2018] [Indexed: 12/18/2022] Open
Abstract
Chronic hyperinsulinemia, in vivo, increases the resistance of peripheral tissues to insulin by desensitizing insulin signaling. Insulin, in a heterologous manner, can also cause IGF-1 resistance. The aim of the current study was to investigate whether insulin-mediated insulin and IGF-1 resistance develops in pancreatic β-cells and whether this resistance results in β-cell decompensation. Chronic exposure of rat islets or INS1E β-cells to increasing concentrations of insulin decreased AktS473 phosphorylation in response to subsequent acute stimulation with 10 nM insulin or IGF-1. Prolonged exposure to high insulin levels not only inhibited AktS473 phosphorylation, but it also resulted in a significant inhibition of the phosphorylation of P70S6 kinase and Erk1/2 phosphorylation in response to the acute stimulation by glucose, insulin, or IGF-1. Decreased activation of Akt, P70S6K, and Erk1/2 was associated with decreased insulin receptor substrate 2 tyrosine phosphorylation and insulin receptor β-subunit abundance; neither IGF receptor β-subunit content nor its phosphorylation were affected. These signaling impairments were associated with decreased SERCA2 expression, perturbed plasma membrane calcium current and intracellular calcium handling, increased endoplasmic reticulum stress markers such as eIF2αS51 phosphorylation and Bip (GRP78) expression, and increased islet and β-cell apoptosis. We demonstrate that prolonged exposure to high insulin levels induces not only insulin resistance, but in a heterologous manner causes resistance to IGF-1 in rat islets and insulinoma cells resulting in decreased cell survival. These findings suggest the possibility that chronic exposure to hyperinsulinemia may negatively affect β-cell mass by increasing β-cell apoptosis.
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Affiliation(s)
- Nadia Rachdaoui
- Division of Clinical and Molecular Endocrinology, Department of Medicine, Case Western Reserve University, Cleveland, Ohio
| | - Luis Polo-Parada
- Department of Medical Pharmacology and Physiology, Dalton Cardiovascular Research Center, University of Missouri-Columbia, Columbia, Missouri
| | - Faramarz Ismail-Beigi
- Division of Clinical and Molecular Endocrinology, Department of Medicine, Case Western Reserve University, Cleveland, Ohio
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Somvanshi RK, Jhajj A, Heer M, Kumar U. Characterization of somatostatin receptors and associated signaling pathways in pancreas of R6/2 transgenic mice. Biochim Biophys Acta Mol Basis Dis 2018; 1864:359-373. [DOI: 10.1016/j.bbadis.2017.11.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2017] [Revised: 10/22/2017] [Accepted: 11/01/2017] [Indexed: 01/12/2023]
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McClelland Descalzo DL, Satoorian TS, Walker LM, Sparks NRL, Pulyanina PY, Zur Nieden NI. Glucose-Induced Oxidative Stress Reduces Proliferation in Embryonic Stem Cells via FOXO3A/β-Catenin-Dependent Transcription of p21(cip1). Stem Cell Reports 2017; 7:55-68. [PMID: 27411103 PMCID: PMC4945584 DOI: 10.1016/j.stemcr.2016.06.006] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2015] [Revised: 06/08/2016] [Accepted: 06/09/2016] [Indexed: 11/17/2022] Open
Abstract
Embryonic stem cells (ESCs), which are derived from a peri-implantation embryo, are routinely cultured in medium containing diabetic glucose (Glc) concentrations. While pregnancy in women with pre-existing diabetes may result in small embryos, whether such high Glc levels affect ESC growth remains uncovered. We show here that long-term exposure of ESCs to diabetic Glc inhibits their proliferation, thereby mimicking in vivo findings. Molecularly, Glc exposure increased oxidative stress and activated Forkhead box O3a (FOXO3a), promoting increased expression and activity of the ROS-removal enzymes superoxide dismutase and catalase and the cell-cycle inhibitors p21cip1 and p27kip1. Diabetic Glc also promoted β-catenin nuclear localization and the formation of a complex with FOXO3a that localized to the promoters of Sod2, p21cip1, and potentially p27kip1. Our results demonstrate an adaptive response to increases in oxidative stress induced by diabetic Glc conditions that promote ROS removal, but also result in a decrease in proliferation. Exposure of ESCs to diabetic glucose (Glc) induces oxidative stress ESCs fight oxidative stress via FOXO3a-mediated transcription of Sod2 FOXO3a activation promotes p21cip1 and p27kip1 expression and cell-cycle inhibition Glc regulates FOXO3a/β-catenin co-occupation of the p21 and Sod2 promoters
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Affiliation(s)
- Darcie L McClelland Descalzo
- Department of Cell Biology & Neuroscience and Stem Cell Center, College of Natural and Agricultural Sciences, University of California Riverside, 1113 Biological Sciences Building, Riverside, CA 92521, USA
| | - Tiffany S Satoorian
- Department of Cell Biology & Neuroscience and Stem Cell Center, College of Natural and Agricultural Sciences, University of California Riverside, 1113 Biological Sciences Building, Riverside, CA 92521, USA
| | - Lauren M Walker
- Department of Cell Biology & Neuroscience and Stem Cell Center, College of Natural and Agricultural Sciences, University of California Riverside, 1113 Biological Sciences Building, Riverside, CA 92521, USA
| | - Nicole R L Sparks
- Department of Cell Biology & Neuroscience and Stem Cell Center, College of Natural and Agricultural Sciences, University of California Riverside, 1113 Biological Sciences Building, Riverside, CA 92521, USA
| | - Polina Y Pulyanina
- Department of Cell Biology & Neuroscience and Stem Cell Center, College of Natural and Agricultural Sciences, University of California Riverside, 1113 Biological Sciences Building, Riverside, CA 92521, USA
| | - Nicole I Zur Nieden
- Department of Cell Biology & Neuroscience and Stem Cell Center, College of Natural and Agricultural Sciences, University of California Riverside, 1113 Biological Sciences Building, Riverside, CA 92521, USA.
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5
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Mezza T, Shirakawa J, Martinez R, Hu J, Giaccari A, Kulkarni RN. Nuclear Export of FoxO1 Is Associated with ERK Signaling in β-Cells Lacking Insulin Receptors. J Biol Chem 2016; 291:21485-21495. [PMID: 27535223 DOI: 10.1074/jbc.m116.735738] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Revised: 08/06/2016] [Indexed: 12/17/2022] Open
Abstract
The insulin/insulin-like growth factor (IGF) signaling pathway plays a critical role in the regulation of islet cell biology. However, the signaling pathway(s) utilized by insulin to directly modulate β-cells is unclear. To interrogate whether insulin exerts endocrine effects in regulating proteins in the insulin/IGF-1 signaling cascade in vivo in physiological states via the insulin receptor, we designed two experimental approaches: 1) glucose gavage and 2) hyperinsulinemic intravenous infusion, for studies in either β-cell specific insulin receptor knock-out (βIRKO) or control mice. Immunostaining of sections of pancreas (collected immediately after glucose gavage or insulin infusion) from controls showed significant increases in pAKT+, p-p70S6K+, and pERK+ β-cells and a significant decrease in % nuclear FoxO1+ β-cells compared with corresponding vehicle-treated groups. In contrast, in βIRKOs, we observed no significant changes in pAKT+ or p-p70S6K+ β-cells in either experiment; however, pERK+ β-cells were significantly increased, and an attenuated decrease in % nuclear FoxO1+ β cells was evident in response to glucose gavage or insulin infusion. Treatment of control and βIRKO β-cell lines with glucose or insulin showed significantly decreased % nuclear FoxO1+ β-cells suggesting direct effects. Furthermore, blocking MAPK signaling had virtually no effect on FoxO1 nuclear export in controls, in contrast to attenuated export in βIRKO β-cells. These data suggest insulin acts on β-cells in an endocrine manner in the normal situation; and that in β-cells lacking insulin receptors, insulin and glucose minimally activate the Akt pathway, while ERK phosphorylation and FoxO1 nuclear export occur independently of insulin signaling.
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Affiliation(s)
- Teresa Mezza
- From the Islet Cell and Regenerative Biology, Joslin Diabetes Center, Department of Medicine, Brigham and Women's Hospital, Harvard Stem Cell Institute, Harvard Medical School, Boston, Massachusetts 02215 and.,Center for Endocrine and Metabolic Diseases, Policlinico Gemelli, Università Cattolica del Sacro Cuore, 00168 Rome, Italy
| | - Jun Shirakawa
- From the Islet Cell and Regenerative Biology, Joslin Diabetes Center, Department of Medicine, Brigham and Women's Hospital, Harvard Stem Cell Institute, Harvard Medical School, Boston, Massachusetts 02215 and
| | - Rachael Martinez
- From the Islet Cell and Regenerative Biology, Joslin Diabetes Center, Department of Medicine, Brigham and Women's Hospital, Harvard Stem Cell Institute, Harvard Medical School, Boston, Massachusetts 02215 and
| | - Jiang Hu
- From the Islet Cell and Regenerative Biology, Joslin Diabetes Center, Department of Medicine, Brigham and Women's Hospital, Harvard Stem Cell Institute, Harvard Medical School, Boston, Massachusetts 02215 and
| | - Andrea Giaccari
- Center for Endocrine and Metabolic Diseases, Policlinico Gemelli, Università Cattolica del Sacro Cuore, 00168 Rome, Italy
| | - Rohit N Kulkarni
- From the Islet Cell and Regenerative Biology, Joslin Diabetes Center, Department of Medicine, Brigham and Women's Hospital, Harvard Stem Cell Institute, Harvard Medical School, Boston, Massachusetts 02215 and
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Stamateris RE, Sharma RB, Kong Y, Ebrahimpour P, Panday D, Ranganath P, Zou B, Levitt H, Parambil NA, O'Donnell CP, García-Ocaña A, Alonso LC. Glucose Induces Mouse β-Cell Proliferation via IRS2, MTOR, and Cyclin D2 but Not the Insulin Receptor. Diabetes 2016; 65:981-95. [PMID: 26740601 PMCID: PMC5314707 DOI: 10.2337/db15-0529] [Citation(s) in RCA: 75] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2015] [Accepted: 12/29/2015] [Indexed: 12/21/2022]
Abstract
An important goal in diabetes research is to understand the processes that trigger endogenous β-cell proliferation. Hyperglycemia induces β-cell replication, but the mechanism remains debated. A prime candidate is insulin, which acts locally through the insulin receptor. Having previously developed an in vivo mouse hyperglycemia model, we tested whether glucose induces β-cell proliferation through insulin signaling. By using mice lacking insulin signaling intermediate insulin receptor substrate 2 (IRS2), we confirmed that hyperglycemia-induced β-cell proliferation requires IRS2 both in vivo and ex vivo. Of note, insulin receptor activation was not required for glucose-induced proliferation, and insulin itself was not sufficient to drive replication. Glucose and insulin caused similar acute signaling in mouse islets, but chronic signaling differed markedly, with mammalian target of rapamycin (MTOR) and extracellular signal-related kinase (ERK) activation by glucose and AKT activation by insulin. MTOR but not ERK activation was required for glucose-induced proliferation. Cyclin D2 was necessary for glucose-induced β-cell proliferation. Cyclin D2 expression was reduced when either IRS2 or MTOR signaling was lost, and restoring cyclin D2 expression rescued the proliferation defect. Human islets shared many of these regulatory pathways. Taken together, these results support a model in which IRS2, MTOR, and cyclin D2, but not the insulin receptor, mediate glucose-induced proliferation.
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Affiliation(s)
- Rachel E Stamateris
- Diabetes Center of Excellence, Department of Medicine, University of Massachusetts Medical School, Worcester, MA
| | - Rohit B Sharma
- Diabetes Center of Excellence, Department of Medicine, University of Massachusetts Medical School, Worcester, MA
| | - Yahui Kong
- Diabetes Center of Excellence, Department of Medicine, University of Massachusetts Medical School, Worcester, MA
| | - Pantea Ebrahimpour
- Diabetes Center of Excellence, Department of Medicine, University of Massachusetts Medical School, Worcester, MA
| | - Deepika Panday
- Diabetes Center of Excellence, Department of Medicine, University of Massachusetts Medical School, Worcester, MA
| | - Pavana Ranganath
- Diabetes Center of Excellence, Department of Medicine, University of Massachusetts Medical School, Worcester, MA
| | - Baobo Zou
- Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA
| | - Helena Levitt
- Division of Endocrinology, University of Pittsburgh School of Medicine, Pittsburgh, PA
| | | | - Christopher P O'Donnell
- Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA
| | - Adolfo García-Ocaña
- Diabetes, Obesity and Metabolism Institute, Division of Endocrinology, Diabetes and Bone Disease, The Mindich Child Health and Development Institute, Icahn School of Medicine at Mount Sinai, New York, NY
| | - Laura C Alonso
- Diabetes Center of Excellence, Department of Medicine, University of Massachusetts Medical School, Worcester, MA
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Beneficial effects of growth hormone-releasing hormone agonists on rat INS-1 cells and on streptozotocin-induced NOD/SCID mice. Proc Natl Acad Sci U S A 2015; 112:13651-6. [PMID: 26474831 DOI: 10.1073/pnas.1518540112] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Agonists of growth hormone-releasing hormone (GHRH) have been previously reported to promote growth, function, and engraftment of islet cells following transplantation. Here we evaluated recently synthesized GHRH agonists on the proliferation and biological functions of rat pancreatic β-cell line (INS-1) and islets. In vitro treatment of INS-1 cells with GHRH agonists increased cell proliferation, the expression of cellular insulin, insulin-like growth factor-1 (IGF1), and GHRH receptor, and also stimulated insulin secretion in response to glucose challenge. Exposure of INS-1 cells to GHRH agonists, MR-356 and MR-409, induced activation of ERK and AKT pathways. Agonist MR-409 also significantly increased the levels of cellular cAMP and the phosphorylation of cAMP response element binding protein (CREB) in INS-1 cells. Treatment of rat islets with agonist, MR-409 significantly increased cell proliferation, islet size, and the expression of insulin. In vivo daily s.c. administration of 10 μg MR-409 for 3 wk dramatically reduced the severity of streptozotocin (STZ)-induced diabetes in nonobese diabetic severe combined immunodeficiency (NOD/SCID) mice. The maximal therapeutic benefits with respect to the efficiency of engraftment, ability to reach normoglycemia, gain in body weight, response to high glucose challenge, and induction of higher levels of serum insulin and IGF1 were observed when diabetic mice were transplanted with rat islets preconditioned with GHRH agonist, MR-409, and received additional treatment with MR-409 posttransplantation. This study provides an improved approach to the therapeutic use of GHRH agonists in the treatment of diabetes mellitus.
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8
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Riopel M, Li J, Trinder M, Fellows GF, Wang R. Fibrin supports human fetal islet-epithelial cell differentiation via p70(s6k) and promotes vascular formation during transplantation. J Transl Med 2015; 95:925-36. [PMID: 26006020 DOI: 10.1038/labinvest.2015.74] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2014] [Revised: 03/11/2015] [Accepted: 04/06/2015] [Indexed: 12/23/2022] Open
Abstract
The human fetal pancreas expresses a variety of extracellular matrix (ECM) binding receptors known as integrins. A provisional ECM protein found in blood clots that can bind to integrin receptors and promote β cell function and survival is fibrin. However, its role in support of human fetal pancreatic cells is unknown. We investigated how fibrin promotes human fetal pancreatic cell differentiation in vitro and in vivo. Human fetal pancreata were collected from 15 to 21 weeks of gestation and collagenase digested. Cells were then plated on tissue-culture polystyrene, or with 2D or 3D fibrin gels up to 2 weeks, or subcutaneously transplanted in 3D fibrin gels. The human fetal pancreas contained rich ECM proteins and expressed integrin αVβ3. Fibrin-cultured human fetal pancreatic cells had significantly increased expression of PDX-1, glucagon, insulin, and VEGF-A, along with increased integrin αVβ3 and phosphorylated FAK and p70(s6k). Fibrin-cultured cells treated with rapamycin, the mTOR pathway inhibitor, had significantly decreased phospho-p70(s6k) and PDX-1 expression. Transplanting fibrin-mixed cells into nude mice improved vascularization compared with collagen controls. These results suggest that fibrin supports islet cell differentiation via p70(s6k) and promotes vascularization in human fetal islet-epithelial clusters in vivo.
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Affiliation(s)
- Matthew Riopel
- 1] Children's Health Research Institute, London, Ontario, Canada [2] Department of Pathology, Western University, London, Ontario, Canada
| | - Jinming Li
- 1] Children's Health Research Institute, London, Ontario, Canada [2] Department of Physiology and Pharmacology, Western University, London, Ontario, Canada
| | - Mark Trinder
- 1] Children's Health Research Institute, London, Ontario, Canada [2] Department of Physiology and Pharmacology, Western University, London, Ontario, Canada
| | - George F Fellows
- Department of Obstetrics and Gynecology, Western University, London, Ontario, Canada
| | - Rennian Wang
- 1] Children's Health Research Institute, London, Ontario, Canada [2] Department of Physiology and Pharmacology, Western University, London, Ontario, Canada [3] Department of Medicine, Western University, London, Ontario, Canada
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SALVATIERRA CRISTIANAS, REIS SÍLVIAR, PESSOA ANAF, SOUZA LETÍCIAMDE, STOPPIGLIA LUIZF, VELOSO ROBERTOV, REIS MARISEA, CARNEIRO EVERARDOM, BOSCHERO ANTONIOC, COLODEL EDSONM, ARANTES VANESSAC, LATORRACA MÁRCIAQ. Short-term low-protein diet during pregnancy alters islet area and protein content of phosphatidylinositol 3-kinase pathway in rats. ACTA ACUST UNITED AC 2015; 87:1007-18. [DOI: 10.1590/0001-3765201520140251] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2014] [Accepted: 12/15/2014] [Indexed: 12/31/2022]
Abstract
The phosphatidylinositol 3-kinase and mitogen-activated protein kinase pathways mediate β cell growth, proliferation, survival and death. We investigated whether protein restriction during pregnancy alters islet morphometry or the expression and phosphorylation of several proteins involved in the phosphatidylinositol 3-kinase and mitogen-activated protein kinase pathways. As controls, adult pregnant and non-pregnant rats were fed a normal-protein diet (17%). Pregnant and non-pregnant rats in the experimental groups were fed a low-protein diet (6%) for 15 days. Low protein diet during pregnancy increased serum prolactin level, reduced serum corticosterone concentration and the expression of both protein kinase B/AKT1 (AKT1) and p70 ribosomal protein S6 kinase (p70S6K), as well as the islets area, but did not alter the insulin content of pancreatic islets. Pregnancy increased the expression of the Src homology/collagen (SHC) protein and the extracellular signal-regulated kinases 1/2 (ERK1/2) independent of diet. ERK1/2 phosphorylation (pERK1/2) was similar in islets from pregnant and non-pregnant rats fed a low-protein diet, and was higher in islets from pregnant rats than in islets from non-pregnant rats fed a normal-protein diet. Thus, a short-term, low-protein diet during pregnancy was sufficient to reduce the levels of proteins in the phosphatidylinositol 3-kinase pathway and affect islet morphometry.
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Rajan S, Dickson LM, Mathew E, Orr CMO, Ellenbroek JH, Philipson LH, Wicksteed B. Chronic hyperglycemia downregulates GLP-1 receptor signaling in pancreatic β-cells via protein kinase A. Mol Metab 2015; 4:265-76. [PMID: 25830090 PMCID: PMC4354925 DOI: 10.1016/j.molmet.2015.01.010] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/12/2015] [Revised: 01/21/2015] [Accepted: 01/26/2015] [Indexed: 02/07/2023] Open
Abstract
Objective Glucagon-like peptide 1 (GLP-1) enhances insulin secretion and protects β-cell mass. Diabetes therapies targeting the GLP-1 receptor (GLP-1R), expressed in numerous tissues, have diminished dose-response in patients with type 2 diabetes compared with healthy human controls. The aim of this study was to determine the mechanistic causes underlying the reduced efficacy of GLP-1R ligands. Methods Using primary mouse islets and the β-cell line MIN6, outcomes downstream of the GLP-1R were analyzed: Insulin secretion; phosphorylation of the cAMP-response element binding protein (CREB); cAMP responses. Signaling systems were studied by immunoblotting and qRT-PCR, and PKA activity was assayed. Cell surface localization of the GLP-1R was studied by confocal microscopy using a fluorescein-tagged exendin-4 and GFP-tagged GLP-1R. Results Rodent β-cells chronically exposed to high glucose had diminished responses to GLP-1R agonists including: diminished insulin secretory response; reduced phosphorylation of (CREB); impaired cAMP response, attributable to chronically increased cAMP levels. GLP-1R signaling systems were affected by hyperglycemia with increased expression of mRNAs encoding the inducible cAMP early repressor (ICER) and adenylyl cyclase 8, reduced PKA activity due to increased expression of the PKA-RIα subunit, reduced GLP-1R mRNA expression and loss of GLP-1R from the cell surface. To specifically examine the loss of GLP-1R from the plasma membrane a GLP-1R-GFP fusion protein was employed to visualize subcellular localization. Under low glucose conditions or when PKA activity was inhibited, GLP-1R-GFP was found at the plasma membrane. Conversely high glucose, expression of a constitutively active PKA subunit, or exposure to exendin-4 or forskolin led to GLP-1R-GFP internalization. Mutation of serine residue 301 of the GLP-1R abolished the glucose-dependent loss of the receptor from the plasma membrane. This was associated with a loss of an interaction between the receptor and the small ubiquitin-related modifier (SUMO), an interaction that was found to be necessary for internalization of the receptor. Conclusions These data show that glucose acting, at least in part, via PKA leads to the loss of the GLP-1R from the cell surface and an impairment of GLP-1R signaling, which may underlie the reduced clinical efficacy of GLP-1R based therapies in individuals with poorly controlled hyperglycemia.
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Affiliation(s)
- Sindhu Rajan
- Kovler Diabetes Center, The University of Chicago, USA ; Department of Medicine, Section of Adult and Pediatric Endocrinology, Diabetes and Metabolism, The University of Chicago, USA
| | - Lorna M Dickson
- Kovler Diabetes Center, The University of Chicago, USA ; Department of Medicine, Section of Adult and Pediatric Endocrinology, Diabetes and Metabolism, The University of Chicago, USA
| | - Elizabeth Mathew
- Kovler Diabetes Center, The University of Chicago, USA ; Department of Medicine, Section of Adult and Pediatric Endocrinology, Diabetes and Metabolism, The University of Chicago, USA
| | - Caitlin M O Orr
- Kovler Diabetes Center, The University of Chicago, USA ; Department of Medicine, Section of Adult and Pediatric Endocrinology, Diabetes and Metabolism, The University of Chicago, USA ; Committee on Molecular Metabolism and Nutrition, The University of Chicago, USA
| | - Johanne H Ellenbroek
- Kovler Diabetes Center, The University of Chicago, USA ; Department of Medicine, Section of Adult and Pediatric Endocrinology, Diabetes and Metabolism, The University of Chicago, USA
| | - Louis H Philipson
- Kovler Diabetes Center, The University of Chicago, USA ; Department of Medicine, Section of Adult and Pediatric Endocrinology, Diabetes and Metabolism, The University of Chicago, USA ; Committee on Molecular Metabolism and Nutrition, The University of Chicago, USA
| | - Barton Wicksteed
- Kovler Diabetes Center, The University of Chicago, USA ; Department of Medicine, Section of Adult and Pediatric Endocrinology, Diabetes and Metabolism, The University of Chicago, USA ; Committee on Molecular Metabolism and Nutrition, The University of Chicago, USA
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Ryall CL, Viloria K, Lhaf F, Walker AJ, King A, Jones P, Mackintosh D, McNeice R, Kocher H, Flodstrom-Tullberg M, Edling C, Hill NJ. Novel role for matricellular proteins in the regulation of islet β cell survival: the effect of SPARC on survival, proliferation, and signaling. J Biol Chem 2014; 289:30614-30624. [PMID: 25204658 DOI: 10.1074/jbc.m114.573980] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Understanding the mechanisms regulating islet growth and survival is critical for developing novel approaches to increasing or sustaining β cell mass in both type 1 and type 2 diabetes patients. Secreted protein acidic and rich in cysteine (SPARC) is a matricellular protein that is important for the regulation of cell growth and adhesion. Increased SPARC can be detected in the serum of type 2 diabetes patients. The aim of this study was to investigate the role of SPARC in the regulation of β cell growth and survival. We show using immunohistochemistry that SPARC is expressed by stromal cells within islets and can be detected in primary mouse islets by Western blot. SPARC is secreted at high levels by pancreatic stellate cells and is regulated by metabolic parameters in these cells, but SPARC expression was not detectable in β cells. In islets, SPARC expression is highest in young mice, and is also elevated in the islets of non-obese diabetic (NOD) mice compared with controls. Purified SPARC inhibits growth factor-induced signaling in both INS-1 β cells and primary mouse islets, and inhibits IGF-1-induced proliferation of INS-1 β cells. Similarly, exogenous SPARC prevents IGF-1-induced survival of primary mouse islet cells. This study identifies the stromal-derived matricellular protein SPARC as a novel regulator of islet survival and β cell growth.
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Affiliation(s)
- Claire L Ryall
- Diabetes and Cardiovascular Research Group, Kingston University, Kingston upon Thames, United Kingdom
| | - Katrina Viloria
- Diabetes and Cardiovascular Research Group, Kingston University, Kingston upon Thames, United Kingdom
| | - Fadel Lhaf
- Diabetes and Cardiovascular Research Group, Kingston University, Kingston upon Thames, United Kingdom
| | - Anthony J Walker
- School of Life Sciences, and Kingston University, Kingston upon Thames, United Kingdom
| | - Aileen King
- Diabetes Research Group, Division of Reproduction & Endocrinology, King's College London, London, United Kingdom
| | - Peter Jones
- Diabetes Research Group, Division of Reproduction & Endocrinology, King's College London, London, United Kingdom
| | - David Mackintosh
- Diabetes and Cardiovascular Research Group, Kingston University, Kingston upon Thames, United Kingdom
| | - Rosemary McNeice
- School of Mathematics, Kingston University, Kingston upon Thames, United Kingdom
| | - Hemant Kocher
- Barts Cancer Institute, and Queen Mary University of London, London, United Kingdom
| | - Malin Flodstrom-Tullberg
- Center for Infectious Medicine, Department of Medicine, Karolinska Institutet, Stockholm, Sweden
| | - Charlotte Edling
- Blizard Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom, and
| | - Natasha J Hill
- Diabetes and Cardiovascular Research Group, Kingston University, Kingston upon Thames, United Kingdom.
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12
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Kim JH, Park YK, Kim JE, Lee SP, Kim BC, Jang BC. Crude extract of Ceriporia lacerata has a protective effect on dexamethasone-induced cytotoxicity in INS-1 cells via the modulation of PI3K/PKB activity. Int J Mol Med 2013; 32:179-86. [PMID: 23624822 DOI: 10.3892/ijmm.2013.1364] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2012] [Accepted: 12/14/2012] [Indexed: 11/05/2022] Open
Abstract
Excessive and/or long-term glucocorticoid therapy reduces β-cell mass and induces hyperglycemia, which contribute to the development of steroid‑induced diabetes. Ceriporia (C.) lacerata is one of the white‑rot fungi and has been used in bioremediations, such as lignocellulose degradation, in nature. The pharmacologic effect of C. lacerata on steroid-induced β-cell toxicity is not known. In this study, we evaluated the effect of a crude extract from a submerged cultivation of C. lacerata on the survival and apoptosis of INS-1 rat insulin-secreting cells exposed to dexamethasone (Dex), a synthetic diabetogenic glucocorticoid. Treatment with the C. lacerata crude extract (CLCE) largely blocked the Dex-induced reduction in survival and apoptosis of INS-1 cells. Moreover, CLCE treatment inhibited Dex-induced protein kinase B (PKB) dephosphorylation without affecting Dex-induced extracellular signal-regulated protein kinase-1/2 dephosphorylation and MKP-1 upregulation. Importantly, the protective effect of CLCE on Dex-induced cytotoxicity in INS-1 cells was attenuated by LY294002, an inhibitor of PI3K/PKB. CLCE treatment, however, did not protect the INS-1 cells from the cytotoxic effects triggered by other insults, such as interleukin-1β (an inflammatory cytokine), streptozotocin (a diabetogenic drug), thapsigargin (a calcium mobilizing agent), and tunicamycin (an ER stress inducer). Collectively, these findings demonstrate for the first time the ability of CLCE to specifically protect INS-1 cells from Dex-induced cytotoxicity through the modulation of the PI3K/PKB pathway. It is suggested that CLCE may be applied for the prevention and/or treatment of steroid diabetes in which reduction of β-cell survival and induction of β-cell apoptosis play pathogenic roles.
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Affiliation(s)
- Ji-Hye Kim
- Department of Medical Genetic Engineering, Keimyung University School of Medicine, Dalseo-gu, Daegu 704-701, Republic of Korea
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13
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Abstract
β-Cell failure coupled with insulin resistance is a key factor in the development of type 2 diabetes. Changes in circulating levels of adipokines, factors released from adipose tissue, form a significant link between excessive adiposity in obesity and both aforementioned factors. In this review, we consider the published evidence for the role of individual adipokines on the function, proliferation, death and failure of β-cells, focusing on those reported to have the most significant effects (leptin, adiponectin, tumour necrosis factor α, resistin, visfatin, dipeptidyl peptidase IV and apelin). It is apparent that some adipokines have beneficial effects whereas others have detrimental properties; the overall contribution to β-cell failure of changed concentrations of adipokines in the blood of obese pre-diabetic subjects will be highly dependent on the balance between these effects and the interactions between the adipokines, which act on the β-cell via a number of intersecting intracellular signalling pathways. We emphasise the importance, and comparative dearth, of studies into the combined effects of adipokines on β-cells.
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Affiliation(s)
- Simon J Dunmore
- Diabetes and Metabolic Disease Research Group, Research Institute in Healthcare Science, University of Wolverhampton, Wolverhampton WV1 1LY, UK.
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14
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Lavezzi JR, Thorn SR, O'Meara MC, LoTurco D, Brown LD, Hay WW, Rozance PJ. Increased fetal insulin concentrations for one week fail to improve insulin secretion or β-cell mass in fetal sheep with chronically reduced glucose supply. Am J Physiol Regul Integr Comp Physiol 2012; 304:R50-8. [PMID: 23135788 DOI: 10.1152/ajpregu.00413.2012] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Maternal undernutrition during pregnancy and placental insufficiency are characterized by impaired development of fetal pancreatic β-cells. Prolonged reduced glucose supply to the fetus is a feature of both. It is unknown if reduced glucose supply, independent of other complications of maternal undernutrition and placental insufficiency, would cause similar β-cell defects. Therefore, we measured fetal insulin secretion and β-cell mass following prolonged reduced fetal glucose supply in sheep. We also tested whether restoring physiological insulin concentrations would correct any β-cell defects. Pregnant sheep received either a direct saline infusion (CON = control, n = 5) or an insulin infusion (HG = hypoglycemic, n = 5) for 8 wk in late gestation (75 to 134 days) to decrease maternal glucose concentrations and reduce fetal glucose supply. A separate group of HG fetuses also received a direct fetal insulin infusion for the final week of the study with a dextrose infusion to prevent a further fall in glucose concentration [hypoglycemic + insulin (HG+I), n = 4]. Maximum glucose-stimulated insulin concentrations were 45% lower in HG fetuses compared with CON fetuses. β-Cell, pancreatic, and fetal mass were 50%, 37%, and 40% lower in HG compared with CON fetuses, respectively (P < 0.05). Insulin secretion and β-cell mass did not improve in the HG+I fetuses. These results indicate that chronically reduced fetal glucose supply is sufficient to reduce pancreatic insulin secretion in response to glucose, primarily due to reduced pancreatic and β-cell mass, and is not correctable with insulin.
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Affiliation(s)
- Jinny R Lavezzi
- Perinatal Research Center, Section of Neonatology, Department of Pediatrics, University of Colorado Denver School of Medicine, Aurora, USA
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15
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Kim HS, Tian L, Lin S, Cha JH, Jung HS, Park KS, Moon WK. Magnetic labeling of pancreaticβ-cells modulates the glucose- and insulin-induced phosphorylation of ERK1/2 and AKT. CONTRAST MEDIA & MOLECULAR IMAGING 2012; 8:20-6. [DOI: 10.1002/cmmi.1490] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Affiliation(s)
- Hoe Suk Kim
- Department of Radiology; Seoul National University Hospital; 101 Daehangno, Jongno-gu Seoul 110-744 Korea
- Institute of Radiation Medicine, Medical Research Center; Seoul National University; 101 Daehangno, Jongno-gu Seoul 110-744 Korea
| | - Lianji Tian
- Department of Radiology; Seoul National University Hospital; 101 Daehangno, Jongno-gu Seoul 110-744 Korea
- Department of Biomedical Science, College of Medicine; Seoul National University; Seoul, 101 Daehangno, Jongno-gu Seoul 110-744 Korea
| | - Shunmei Lin
- Department of Radiology; Seoul National University Hospital; 101 Daehangno, Jongno-gu Seoul 110-744 Korea
| | - Joo Hee Cha
- Department of Radiology; Seoul National University Hospital; 101 Daehangno, Jongno-gu Seoul 110-744 Korea
| | - Hye Seung Jung
- Department of Internal Medicine; Seoul National University Hospital; 101 Daehangno, Jongno-gu Seoul 110-744 Korea
| | - Kyong Soo Park
- Department of Internal Medicine; Seoul National University Hospital; 101 Daehangno, Jongno-gu Seoul 110-744 Korea
| | - Woo Kyung Moon
- Department of Radiology; Seoul National University Hospital; 101 Daehangno, Jongno-gu Seoul 110-744 Korea
- Institute of Radiation Medicine, Medical Research Center; Seoul National University; 101 Daehangno, Jongno-gu Seoul 110-744 Korea
- Department of Biomedical Science, College of Medicine; Seoul National University; Seoul, 101 Daehangno, Jongno-gu Seoul 110-744 Korea
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16
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Liu S, Liu R, Chiang YT, Song L, Li X, Jin T, Wang Q. Insulin detemir enhances proglucagon gene expression in the intestinal L cells via stimulating β-catenin and CREB activities. Am J Physiol Endocrinol Metab 2012; 303:E740-51. [PMID: 22811470 PMCID: PMC3468432 DOI: 10.1152/ajpendo.00328.2011] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Insulin therapy using insulin detemir (d-INS) has demonstrated weight-sparing effects compared with other insulin formulations. Mechanisms underlying these effects, however, remain largely unknown. Here we postulate that the intestinal tissues' selective preference allows d-INS to exert enhanced action on proglucagon (Gcg) expression and the production of glucagon-like peptide (GLP)-1, an incretin hormone possessing both glycemia-lowering and weight loss effects. To test this hypothesis, we used obese type 2 diabetic db/db mice and conducted a 14-day intervention with daily injection of a therapeutic dose of d-INS or human insulin (h-INS) in these mice. The body weight of the mice after 14-day daily injection of d-INS (5 IU/kg) was decreased significantly compared with those injected with the same dose of h-INS or saline. The weight-sparing effect of d-INS was associated with significantly elevated circulating levels of total GLP-1 and reduced food intake. Histochemistry analysis demonstrated that d-INS induced rapid phosphorylation of protein kinase B (Akt) in the gut L cells of normal mice. Western blotting showed that d-INS stimulated Akt activation in a more rapid and enhanced fashion in the mouse distal ileum compared with those by h-INS. In vitro investigation in primary fetal rat intestinal cell (FRIC) cultures showed that d-INS increased Gcg mRNA expression as determined by Northern blotting and real-time RT-PCR. Consistent with these in vivo investigations, d-INS significantly increased GLP-1 secretion in FRIC cultures. Consistently, d-INS was also shown to induce rapid phosphorylation of Akt in the clonal gut cell line GLUTag. Furthermore, d-INS increased β-catenin phosphorylation, its nuclear translocation, and enhanced cAMP response element-binding protein (CREB) phosphorylation in a phosphatidylinositol 3-kinase and/or mitogen-activated protein kinase kinase/extracellular signal-regulated kinase-sensitive manner. We suggest that the weight-sparing benefit of d-INS in mice is related to its intestinal tissues preference that leads to profound stimulation of Gcg expression and enhanced GLP-1 secretion in intestinal L cells, potentially involving the activation of insulin/β-catenin/CREB signaling pathways.
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MESH Headings
- Animals
- Cells, Cultured
- Cyclic AMP Response Element-Binding Protein/agonists
- Cyclic AMP Response Element-Binding Protein/metabolism
- Diabetes Mellitus, Type 2/complications
- Diabetes Mellitus, Type 2/drug therapy
- Diabetes Mellitus, Type 2/metabolism
- Diabetes Mellitus, Type 2/pathology
- Fetus/cytology
- Gene Expression Regulation/drug effects
- Glucagon-Like Peptide 1/blood
- Glucagon-Like Peptide 1/metabolism
- Hypoglycemic Agents/pharmacology
- Hypoglycemic Agents/therapeutic use
- Insulin Detemir
- Insulin, Long-Acting/pharmacology
- Insulin, Long-Acting/therapeutic use
- Intestinal Mucosa/drug effects
- Intestinal Mucosa/metabolism
- Intestinal Mucosa/pathology
- L Cells
- Mice
- Mice, Mutant Strains
- Obesity/complications
- Obesity/prevention & control
- Organ Specificity
- Phosphorylation/drug effects
- Proglucagon/genetics
- Proglucagon/metabolism
- Protein Processing, Post-Translational/drug effects
- RNA, Messenger/metabolism
- Rats
- Rats, Wistar
- beta Catenin/agonists
- beta Catenin/metabolism
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Affiliation(s)
- Shenghao Liu
- Division of Endocrinology and Metabolism, the Keenan Research Centre in the Li Ka Shing Knowledge Institute, St. Michael’s Hospital, Toronto, Ontario, Canada
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17
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Wang X, Liu Y, Yang Z, Zhang Z, Zhou W, Ye Z, Zhang W, Zhang S, Yang Z, Feng X, Chen F, Hu R. Glucose metabolism-related protein 1 (GMRP1) regulates pancreatic beta cell proliferation and apoptosis via activation of Akt signalling pathway in rats and mice. Diabetologia 2011; 54:852-63. [PMID: 21267538 DOI: 10.1007/s00125-011-2048-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2010] [Accepted: 12/10/2010] [Indexed: 12/31/2022]
Abstract
AIMS/HYPOTHESIS We attempted to elucidate the impacts on and possible mechanisms by which glucose metabolism-related protein 1 (GMRP1) affects beta cell survival. METHODS Adenovirus-mediated GMRP1 overproduction and siRNA-mediated knockdown were performed in INS-1E cells and rat islets, after which cell proliferation or apoptosis were determined, and phosphorylation of Akt and BCL2-associated agonist of cell death (BAD) investigated. INS-1E cells and rat islets were cultured at 5.6 (low) or 25 mmol/l (high) glucose for 24 or 48 h, and cell proliferation or apoptosis and GMRP1 levels were investigated. INS-1E cells were treated for 24 h with 0, 10, 50 and 100 nmol/l insulin, and GMRP1 levels were determined. After INS-1E cells were transfected with siRNA for 72 h, high glucose-induced cell proliferation and insulin-stimulated Akt phosphorylation were investigated. Glucose-infused rat models were established and beta cell proliferation and mass were evaluated. Levels of GMRP1, and phosphorylation of Akt and BAD were determined in glucose-infused islets. The GMRP1-mediated Akt pathway was also investigated in db/db mice. RESULTS Overproduction of GMRP1 promoted beta cell proliferation via increased phosphorylation of Akt. Knockdown of Gmrp1 (also known as Btbd10) reduced phosphorylation of Akt with enhanced beta cell apoptosis. High glucose increased GMRP1 levels and cell proliferation in INS-1E cells and islet cells. Knockdown of Gmrp1 decreased high glucose-induced cell proliferation and insulin-stimulated Akt phosphorylation. Increased GMRP1 levels were involved in the enhancement of beta cell proliferation and mass in glucose-infused islets. Decreased GMRP1 levels may participate in beta cell apoptosis of db/db mice. CONCLUSIONS/INTERPRETATION GMRP1 regulates pancreatic beta cell proliferation and apoptosis via activation of Akt signalling pathway.
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Affiliation(s)
- X Wang
- Department of Endocrinology, Huashan Hospital, Shanghai Medical College, Fudan University, 12 Wulumuqi Road Middle, Shanghai 200040, People's Republic of China.
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18
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Leen JLS, Izzo A, Upadhyay C, Rowland KJ, Dubé PE, Gu S, Heximer SP, Rhodes CJ, Storm DR, Lund PK, Brubaker PL. Mechanism of action of glucagon-like peptide-2 to increase IGF-I mRNA in intestinal subepithelial fibroblasts. Endocrinology 2011; 152:436-46. [PMID: 21159855 PMCID: PMC3384785 DOI: 10.1210/en.2010-0822] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
IGF-I, a known secretory product of intestinal subepithelial myofibroblasts (ISEMFs), is essential for the intestinotropic effects of glucagon-like peptide-2 (GLP-2). Furthermore, GLP-2 increases IGF-I mRNA transcript levels in vitro in heterogeneous fetal rat intestinal cultures, as well as in vivo in the rodent small intestine. To determine the mechanism underlying the stimulatory effect of GLP-2 on intestinal IGF-I mRNA, murine ISEMF cells were placed into primary culture. Immunocytochemistry showed that the ISEMF cells appropriately expressed α-smooth muscle actin and vimentin but not desmin. The cells also expressed GLP-2 receptor and IGF-I mRNA transcripts. Treatment of ISEMF cells with (Gly2)GLP-2 induced IGF-I mRNA transcripts by up to 5-fold of basal levels after treatment with 10(-8) m GLP-2 for 2 h (P < 0.05) but did not increase transcript levels for other intestinal growth factors, such as ErbB family members. Immunoblot revealed a 1.6-fold increase in phospho (p)-Akt/total-(t)Akt with 10(-8) m GLP-2 treatment (P < 0.05) but no changes in cAMP, cAMP-dependent β-galactosidase expression, pcAMP response element-binding protein/tcAMP response element-binding protein, pErk1/2/tErk1/2, or intracellular calcium. Furthermore, pretreatment of ISEMF cells with the phosphatidylinositol 3 kinase (PI3K) inhibitors, LY294002 and wortmannin, abrogated the IGF-I mRNA response to GLP-2, as did overexpression of kinase-dead Akt. The role of PI3K/Akt in GLP-2-induced IGF-I mRNA levels in the murine jejunum was also confirmed in vivo. These findings implicate the PI3K/Akt pathway in the stimulatory effects of GLP-2 to enhance intestinal IGF-I mRNA transcript levels and provide further evidence in support of a role for IGF-I produced by the ISEMF cells in the intestinotropic effects of GLP-2.
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Affiliation(s)
- Jason L S Leen
- Department of Physiology,University of Toronto, Toronto, Ontario, Canada
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19
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Oldham S. Obesity and nutrient sensing TOR pathway in flies and vertebrates: Functional conservation of genetic mechanisms. Trends Endocrinol Metab 2011; 22:45-52. [PMID: 21216618 PMCID: PMC3035994 DOI: 10.1016/j.tem.2010.11.002] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/09/2010] [Revised: 11/12/2010] [Accepted: 11/15/2010] [Indexed: 12/19/2022]
Abstract
The global prevalence of obesity has grown to epidemic proportions, and 400 million people are now considered to be obese. Excessive accumulation of dietary lipids (obesity) is a known risk factor for the development of deleterious metabolic conditions and has been strongly linked to the progression of heart disease and type 2 diabetes. Investigating the origin and effects of high-fat diet (HFD)-induced obesity and its genetic mediators is an important step in understanding the mechanisms that contribute to obesity. However, the mechanisms that underlie HFD pathophysiology have yet to be elucidated fully. Here we describe recent work in a Drosophila model to investigate the origin and genetic mechanisms that could underlie HFD-induced obesity, type 2 diabetes and cardiac dysfunction.
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Affiliation(s)
- Sean Oldham
- Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA.
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20
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Brown LD, Green AS, Limesand SW, Rozance PJ. Maternal amino acid supplementation for intrauterine growth restriction. Front Biosci (Schol Ed) 2011; 3:428-44. [PMID: 21196387 DOI: 10.2741/s162] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Maternal dietary protein supplementation to improve fetal growth has been considered as an option to prevent or treat intrauterine growth restriction. However, in contrast to balanced dietary supplementation, adverse perinatal outcomes in pregnant women who received high amounts of dietary protein supplementation have been observed. The responsible mechanisms for these adverse outcomes are unknown. This review will discuss relevant human and animal data to provide the background necessary for the development of explanatory hypotheses and ultimately for the development therapeutic interventions during pregnancy to improve fetal growth. Relevant aspects of fetal amino acid metabolism during normal pregnancy and those pregnancies affected by IUGR will be discussed. In addition, data from animal experiments which have attempted to determine mechanisms to explain the adverse responses identified in the human trials will be presented. Finally, we will suggest new avenues for investigation into how amino acid supplementation might be used safely to treat and/or prevent IUGR.
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Affiliation(s)
- Laura D Brown
- Department of Pediatrics, University of Colorado Denver; Aurora, CO 80045, USA
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21
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Soleimanpour SA, Crutchlow MF, Ferrari AM, Raum JC, Groff DN, Rankin MM, Liu C, De León DD, Naji A, Kushner JA, Stoffers DA. Calcineurin signaling regulates human islet {beta}-cell survival. J Biol Chem 2010; 285:40050-9. [PMID: 20943662 DOI: 10.1074/jbc.m110.154955] [Citation(s) in RCA: 114] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The calcium-regulated phosphatase calcineurin intersects with both calcium and cAMP-mediated signaling pathways in the pancreatic β-cell. Pharmacologic calcineurin inhibition, necessary to prevent rejection in the setting of organ transplantation, is associated with post-transplant β-cell failure. We sought to determine the effect of calcineurin inhibition on β-cell replication and survival in rodents and in isolated human islets. Further, we assessed whether the GLP-1 receptor agonist and cAMP stimulus, exendin-4 (Ex-4), could rescue β-cell replication and survival following calcineurin inhibition. Following treatment with the calcineurin inhibitor tacrolimus, human β-cell apoptosis was significantly increased. Although we detected no human β-cell replication, tacrolimus significantly decreased rodent β-cell replication. Ex-4 nearly normalized both human β-cell survival and rodent β-cell replication when co-administered with tacrolimus. We found that tacrolimus decreased Akt phosphorylation, suggesting that calcineurin could regulate replication and survival via the PI3K/Akt pathway. We identify insulin receptor substrate-2 (Irs2), a known cAMP-responsive element-binding protein target and upstream regulator of the PI3K/Akt pathway, as a novel calcineurin target in β-cells. Irs2 mRNA and protein are decreased by calcineurin inhibition in both rodent and human islets. The effect of calcineurin on Irs2 expression is mediated at least in part through the nuclear factor of activated T-cells (NFAT), as NFAT occupied the Irs2 promoter in a calcineurin-sensitive manner. Ex-4 restored Irs2 expression in tacrolimus-treated rodent and human islets nearly to baseline. These findings reveal calcineurin as a regulator of human β-cell survival in part through regulation of Irs2, with implications for the pathogenesis and treatment of diabetes following organ transplantation.
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Affiliation(s)
- Scott A Soleimanpour
- Division of Endocrinology, Department of Medicine and the Institute for Diabetes, Obesity, and Metabolism, the University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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22
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Belibi FA, Edelstein CL. Metastatic Renal Cancer: What Role for Everolimus? CLINICAL MEDICINE REVIEWS IN ONCOLOGY 2010; 2:4. [PMID: 24771995 DOI: 10.4137/cmro.s1551] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Metastatic renal cell carcinoma is uncommon (only 3% of cancers worldwide) but of poor prognosis. Renal cell carcinoma has traditionally been treated with cytokines (interferon-α or interleukin-2). More recently, a more clear understanding of the molecular and cellular mechanisms of the disease, involving the VEGF receptor and mTOR, has led to the discovery of novel therapies. Therapeutic options in patients with advanced RCC include the VEGF receptor inhibitors Sunitinib and Sorafenib, the anti-VEGF monoclonal antibody Bevacizumab and the mTORC1 inhibitors Temsirolimus and Everolimus. In 2009, Everolimus was FDA-approved for the treatment of patients with advanced clear cell RCC which had progressed within 6 months of stopping treatment with Sunitinib or sorafenib, or both drugs. Everolimus resulted in a 70% reduction in the risk of disease recurrence or death. The purpose of this review is to update on the current knowledge of the role of Everolimus in metastatic renal cell carcinoma.
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Affiliation(s)
- Franck A Belibi
- Division of Renal Diseases and Hypertension, University of Colorado Denver, Aurora, CO, USA
| | - Charles L Edelstein
- Division of Renal Diseases and Hypertension, University of Colorado Denver, Aurora, CO, USA
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23
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Liu S, Okada T, Assmann A, Soto J, Liew CW, Bugger H, Shirihai OS, Abel ED, Kulkarni RN. Insulin signaling regulates mitochondrial function in pancreatic beta-cells. PLoS One 2009; 4:e7983. [PMID: 19956695 PMCID: PMC2776992 DOI: 10.1371/journal.pone.0007983] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2009] [Accepted: 10/26/2009] [Indexed: 12/18/2022] Open
Abstract
Insulin/IGF-I signaling regulates the metabolism of most mammalian tissues including pancreatic islets. To dissect the mechanisms linking insulin signaling with mitochondrial function, we first identified a mitochondria-tethering complex in β-cells that included glucokinase (GK), and the pro-apoptotic protein, BADS. Mitochondria isolated from β-cells derived from β-cell specific insulin receptor knockout (βIRKO) mice exhibited reduced BADS, GK and protein kinase A in the complex, and attenuated function. Similar alterations were evident in islets from patients with type 2 diabetes. Decreased mitochondrial GK activity in βIRKOs could be explained, in part, by reduced expression and altered phosphorylation of BADS. The elevated phosphorylation of p70S6K and JNK1 was likely due to compensatory increase in IGF-1 receptor expression. Re-expression of insulin receptors in βIRKO cells partially restored the stoichiometry of the complex and mitochondrial function. These data indicate that insulin signaling regulates mitochondrial function and have implications for β-cell dysfunction in type 2 diabetes.
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Affiliation(s)
- Siming Liu
- Department of Medicine, Harvard Medical School, Boston, Massachusetts, United States of America
- Research Division, Joslin Diabetes Center, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Terumasa Okada
- Department of Medicine, Harvard Medical School, Boston, Massachusetts, United States of America
- Research Division, Joslin Diabetes Center, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Anke Assmann
- Department of Medicine, Harvard Medical School, Boston, Massachusetts, United States of America
- Research Division, Joslin Diabetes Center, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Jamie Soto
- Division of Endocrinology, Metabolism and Diabetes and Program in Molecular Medicine, University of Utah School of Medicine, Salt Lake City, Utah, United States of America
| | - Chong Wee Liew
- Department of Medicine, Harvard Medical School, Boston, Massachusetts, United States of America
- Research Division, Joslin Diabetes Center, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Heiko Bugger
- Division of Endocrinology, Metabolism and Diabetes and Program in Molecular Medicine, University of Utah School of Medicine, Salt Lake City, Utah, United States of America
| | - Orian S. Shirihai
- Department of Medicine, Boston University School of Medicine, Boston, Massachusetts, United States of America
| | - E. Dale Abel
- Division of Endocrinology, Metabolism and Diabetes and Program in Molecular Medicine, University of Utah School of Medicine, Salt Lake City, Utah, United States of America
| | - Rohit N. Kulkarni
- Department of Medicine, Harvard Medical School, Boston, Massachusetts, United States of America
- Research Division, Joslin Diabetes Center, Harvard Medical School, Boston, Massachusetts, United States of America
- * E-mail:
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24
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Lieberthal W, Levine JS. The role of the mammalian target of rapamycin (mTOR) in renal disease. J Am Soc Nephrol 2009; 20:2493-502. [PMID: 19875810 DOI: 10.1681/asn.2008111186] [Citation(s) in RCA: 224] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that plays a pivotal role in mediating cell size and mass, proliferation, and survival. mTOR has also emerged as an important modulator of several forms of renal disease. mTOR is activated after acute kidney injury and contributes to renal regeneration and repair. Inhibition of mTOR with rapamycin delays recovery of renal function after acute kidney injury. Activation of mTOR within the kidney also occurs in animal models of diabetic nephropathy and other causes of progressive kidney disease. Rapamycin ameliorates several key mechanisms believed to mediate changes associated with the progressive loss of GFR in chronic kidney disease. These include glomerular hypertrophy, intrarenal inflammation, and interstitial fibrosis. mTOR also plays an important role in mediating cyst formation and enlargement in autosomal dominant polycystic kidney disease. Inhibition of mTOR by rapamycin or one of its analogues represents a potentially novel treatment for autosomal dominant polycystic kidney disease. Finally, inhibitors of mTOR improve survival in patients with metastatic renal cell carcinoma.
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Affiliation(s)
- Wilfred Lieberthal
- Stony Brook Medical Center, Health Sciences Center, 16-081B Nicholls Road, Stony Brook, NY 11794-8166, USA.
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25
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Fontés G, Semache M, Hagman DK, Tremblay C, Shah R, Rhodes CJ, Rutter J, Poitout V. Involvement of Per-Arnt-Sim Kinase and extracellular-regulated kinases-1/2 in palmitate inhibition of insulin gene expression in pancreatic beta-cells. Diabetes 2009; 58:2048-58. [PMID: 19502418 PMCID: PMC2731539 DOI: 10.2337/db08-0579] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
OBJECTIVE Prolonged exposure of pancreatic beta-cells to simultaneously elevated levels of fatty acids and glucose (glucolipotoxicity) impairs insulin gene transcription. However, the intracellular signaling pathways mediating these effects are mostly unknown. This study aimed to ascertain the role of extracellular-regulated kinases (ERKs)1/2, protein kinase B (PKB), and Per-Arnt-Sim kinase (PASK) in palmitate inhibition of insulin gene expression in pancreatic beta-cells. RESEARCH DESIGN AND METHODS MIN6 cells and isolated rat islets were cultured in the presence of elevated glucose, with or without palmitate or ceramide. ERK1/2 phosphorylation, PKB phosphorylation, and PASK expression were examined by immunoblotting and real-time PCR. The role of these kinases in insulin gene expression was assessed using pharmacological and molecular approaches. RESULTS Exposure of MIN6 cells and islets to elevated glucose induced ERK1/2 and PKB phosphorylation, which was further enhanced by palmitate. Inhibition of ERK1/2, but not of PKB, partially prevented the inhibition of insulin gene expression in the presence of palmitate or ceramide. Glucose-induced expression of PASK mRNA and protein levels was reduced in the presence of palmitate. Overexpression of wild-type PASK increased insulin and pancreatic duodenal homeobox-1 gene expression in MIN6 cells and rat islets incubated with glucose and palmitate, whereas overexpression of a kinase-dead PASK mutant in rat islets decreased expression of insulin and pancreatic duodenal homeobox-1 and increased C/EBPbeta expression. CONCLUSIONS Both the PASK and ERK1/2 signaling pathways mediate palmitate inhibition of insulin gene expression. These findings identify PASK as a novel mediator of glucolipotoxicity on the insulin gene in pancreatic beta-cells.
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Affiliation(s)
- Ghislaine Fontés
- Montreal Diabetes Research Center, CRCHUM, University of Montréal, Québec, Canada
- Department of Medicine, University of Montréal, Québec, Canada
| | - Meriem Semache
- Montreal Diabetes Research Center, CRCHUM, University of Montréal, Québec, Canada
| | - Derek K. Hagman
- Montreal Diabetes Research Center, CRCHUM, University of Montréal, Québec, Canada
- Department of Medicine, University of Montréal, Québec, Canada
| | - Caroline Tremblay
- Montreal Diabetes Research Center, CRCHUM, University of Montréal, Québec, Canada
| | - Ramila Shah
- Kovler Diabetes Center, University of Chicago, Chicago, Illinois
| | | | - Jared Rutter
- Division of Endocrinology, University of Utah School of Medicine, Salt Lake City, Utah
| | - Vincent Poitout
- Montreal Diabetes Research Center, CRCHUM, University of Montréal, Québec, Canada
- Department of Medicine, University of Montréal, Québec, Canada
- Corresponding author: Vincent Poitout,
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Widenmaier SB, Sampaio AV, Underhill TM, McIntosh CHS. Noncanonical activation of Akt/protein kinase B in {beta}-cells by the incretin hormone glucose-dependent insulinotropic polypeptide. J Biol Chem 2009; 284:10764-73. [PMID: 19233842 DOI: 10.1074/jbc.m809116200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Therapeutics based on the actions of the incretin hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), have recently been introduced for the treatment of type 2 diabetes mellitus. The serine/threonine kinase Akt is a major mediator of incretin action on the pancreatic islet, increasing beta-cell mass and function and promoting beta-cell survival. The mechanisms underlying incretin activation of Akt are thought to involve an essential phosphoinositide 3-kinase-mediated phosphorylation of threonine 308, similar to the prototypical Akt activator, insulin-like growth factor-I (IGF-I). In this study, using activity assays on immunoprecipitated Akt, we discovered that GIP and GLP-1 were capable of stimulating Akt in the INS-1 beta-cell line and isolated mouse islets via a mechanism that did not require phosphoinositide 3-kinase or phosphorylation of Thr(308) and Ser(473), and this pathway involved the production of cAMP. Furthermore, we found that GIP stimulated anti-apoptotic signaling via this alternate mode of Akt activation. We conclude that incretins can activate Akt via a novel noncanonical mechanism that may provide an alternative therapeutic target for the treatment of type 2 diabetes mellitus and have broader implications for Akt physiology in human health and disease.
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Affiliation(s)
- Scott B Widenmaier
- Department of Cellular and Physiological Sciences and the Diabetes Research Group, Life Sciences Institute, University of British Columbia, Vancouver V6T 1Z3, Canada
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Lim GE, Huang GJ, Flora N, LeRoith D, Rhodes CJ, Brubaker PL. Insulin regulates glucagon-like peptide-1 secretion from the enteroendocrine L cell. Endocrinology 2009; 150:580-91. [PMID: 18818290 PMCID: PMC5393261 DOI: 10.1210/en.2008-0726] [Citation(s) in RCA: 126] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Insulin resistance and type 2 diabetes mellitus are associated with impaired postprandial secretion of glucagon-like peptide-1 (GLP-1), a potent insulinotropic hormone. The direct effects of insulin and insulin resistance on the L cell are unknown. We therefore hypothesized that the L cell is responsive to insulin and that insulin resistance impairs GLP-1 secretion. The effects of insulin and insulin resistance were examined in well-characterized L cell models: murine GLUTag, human NCI-H716, and fetal rat intestinal cells. MKR mice, a model of chronic hyperinsulinemia, were used to assess the function of the L cell in vivo. In all cells, insulin activated the phosphatidylinositol 3 kinase-Akt and MAPK kinase (MEK)-ERK1/2 pathways and stimulated GLP-1 secretion by up to 275 +/- 58%. Insulin resistance was induced by 24 h pretreatment with 10(-7) m insulin, causing a marked reduction in activation of Akt and ERK1/2. Furthermore, both insulin-induced GLP-1 release and secretion in response to glucose-dependent insulinotropic peptide and phorbol-12-myristate-13-acetate were significantly attenuated. Whereas inhibition of phosphatidylinositol 3 kinase with LY294002 potentiated insulin-induced GLP-1 release, secretion was abrogated by inhibiting the MEK-ERK1/2 pathway with PD98059 or by overexpression of a kinase-dead MEK1-ERK2 fusion protein. Compared with controls, MKR mice were insulin resistant and displayed significantly higher fasting plasma insulin levels. Furthermore, they had significantly higher basal GLP-1 levels but displayed impaired GLP-1 secretion after an oral glucose challenge. These findings indicate that the intestinal L cell is responsive to insulin and that insulin resistance in vitro and in vivo is associated with impaired GLP-1 secretion.
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Affiliation(s)
- Gareth E Lim
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
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Fred RG, Welsh N. The importance of RNA binding proteins in preproinsulin mRNA stability. Mol Cell Endocrinol 2009; 297:28-33. [PMID: 18621093 DOI: 10.1016/j.mce.2008.06.007] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/08/2008] [Revised: 06/12/2008] [Accepted: 06/12/2008] [Indexed: 11/26/2022]
Abstract
A dynamic production of insulin is necessary for proper glucose homeostasis. In order to generate enough insulin available for exocytosis in response to the demands of the organism, the level of preproinsulin mRNA in the pancreatic beta-cell needs to fluctuate. In animal models for type 2 diabetes the contents of preproinsulin mRNA are lowered, which might suggest that an impaired metabolism of preproinsulin mRNA contributes to the development of glucose intolerance and diabetes. Thus, it is of importance to understand the mechanisms by which preproinsulin mRNA levels are regulated. Although extensively studied, there are aspects of the regulation of insulin gene expression that still remain enigmatic. Our understanding of insulin gene transcription has improved considerably the last 20 years, but less effort has been invested into the control of preproinsulin mRNA stability. The preproinsulin mRNA has a long half-life and changes in preproinsulin mRNA stability, induced by glucose, are likely to be regulated through specific mechanisms. Recent findings indicate that the polypyrimidine tract-binding protein (PTB), also named hnRNP I, by binding to the 3'-UTR (untranslated region) of the preproinsulin mRNA molecule, stabilizes the messenger, thereby participating in the glucose-induced increase in preproinsulin mRNA. This review will focus both on recent findings pertinent to PTB function in general, and on the specific role of PTB on the production of insulin in beta-cells. We will also discuss the putative co-operativity between PTB and other proteins in the control of preproinsulin mRNA stability, and review beta-cell signaling events that may control the mRNA stabilizing effect of PTB.
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Affiliation(s)
- Rikard G Fred
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
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Aronovitz A, Josefson J, Fisher A, Newman M, Hughes E, Chen F, Moons DS, Kiyokawa H, Lowe WL. Rapamycin inhibits growth factor-induced cell cycle regulation in pancreatic beta cells. J Investig Med 2009; 56:985-96. [PMID: 19105244 DOI: 10.2310/jim.0b013e31818ce763] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
A progressive decline in islet function is a major obstacle to success of islet transplantation. The cause of this decline is islet function is unclear, but immunosuppressive agents may contribute. Insulin-like growth factor-I (IGF-I) and betacellulin are important for islet cell survival and/or proliferation. In the present study, we performed studies of IGF-I and betacellulin on progression of islet cells through the cell cycle and the impact of immunosuppressive agents. Treatment of INS-1 cells for 24 hours with 20 ng/mL betacellulin or 50 ng/mL IGF-1 increased cells in S phase by ~2-fold. Treatment of INS-1 cells with IGF-I or betacellulin also increased cyclin D1 expression and nuclear exclusion of the cyclindependent kinase inhibitors p21(Cip1) and p27(Kip1). In INS-1 cells and islets, betacellulin- and IGF-I increased the increase in p70(s6 kinase) phosphorylation stimulated by betacellulin- and IGF-I in INS-1 cells. Rapamycin also inhibited betacellulin- and IGF-I IN IGF-1 cells. Rapamycin also inhibited betacellulin- and IGF-I-induced entry of cells into S phase and 5'-Bromo-2'-deoxyuridine incorporation as well as the effect of betacellulin and IGF-I on cyclin D1 expression and nuclear exclusion of p21(Cip1) and p(27Kip1). Together, these data suggest that the effect of betacellulin and IGF-I on islet cell growth and proliferation is mediated, in part, via signaling through mammalian target of rapamycin. As rapamycin is used to treat islet transplant recipients, these results suggest that rapamycin could have deleterious effects on islet proliferation and function over time.
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Affiliation(s)
- Amy Aronovitz
- Department of Medicine, Division of Endocrinology, Metabolism and Molecular Medicine, Northwestern University Feinberg School of Medicine, chicago, IL 60611, USA
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Sinclair EM, Yusta B, Streutker C, Baggio LL, Koehler J, Charron MJ, Drucker DJ. Glucagon receptor signaling is essential for control of murine hepatocyte survival. Gastroenterology 2008; 135:2096-106. [PMID: 18809404 DOI: 10.1053/j.gastro.2008.07.075] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/03/2007] [Revised: 06/27/2008] [Accepted: 07/24/2008] [Indexed: 12/02/2022]
Abstract
BACKGROUND & AIMS Glucagon action in the liver is essential for control of glucose homeostasis and the counterregulatory response to hypoglycemia. Because receptors for the related peptides glucagon-like peptide-1 and glucagon-like peptide-2 regulate beta-cell and enterocyte apoptosis, respectively, we examined whether glucagon receptor (Gcgr) signaling modulates hepatocyte survival. METHODS The importance of the Gcgr for hepatocyte cell survival was examined using Gcgr+/+ and Gcgr-/- mice in vivo, and murine hepatocyte cultures in vitro. RESULTS Gcgr-/- mice showed enhanced susceptibility to experimental liver injury induced by either Fas Ligord activation or a methionine- and choline-deficient diet. Restoration of hepatic Gcgr expression in Gcgr-/- mice attenuated the development of hepatocellular injury. Furthermore, exogenous glucagon administration reduced Jo2-induced apoptosis in wild-type mice and decreased caspase activation in fibroblasts expressing a heterologous Gcgr and in primary murine hepatocyte cultures. The anti-apoptotic actions of glucagon were independent of protein kinase A, phosphatidylinositol-3K, and mitogen-activated protein kinase, and were mimicked by the exchange protein directly activated by the cyclic AMP agonist 8-(4-chloro-phenylthio)-2'-O-methyladenosine-3', 5'-cyclic monophosphate-cAMP. CONCLUSIONS These findings extend the essential actions of the Gcgr beyond the metabolic control of glucose homeostasis to encompass the regulation of hepatocyte survival.
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Affiliation(s)
- Elaine M Sinclair
- Department of Medicine, Mt. Sinai Hospital, Samuel Lunenfeld Research Institute, Toronto, Ontario, Canada
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31
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Fei H, Zhao B, Zhao S, Wang Q. Requirements of calcium fluxes and ERK kinase activation for glucose- and interleukin-1β-induced β-cell apoptosis. Mol Cell Biochem 2008; 315:75-84. [DOI: 10.1007/s11010-008-9791-8] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2007] [Accepted: 05/06/2008] [Indexed: 10/22/2022]
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Abstract
The healthy beta-cell has an enormous capacity to adapt to conditions of higher insulin demand (e.g. in obesity, pregnancy, cortisol excess) to maintain normoglycaemia with an increase in its functional beta-cell mass. This compensates in 80-90% of individuals for insulin resistance. However, in 10-20% of individuals, the beta-cells are unable to match the demands of insulin resistance and insulin levels are relatively insufficient to maintain normal glycaemic control. This eventually leads to glucose intolerance and type 2 diabetes (T2DM). Accordingly, preservation of functional beta-cell mass has become central in the treatment of type 1 diabetes as well as T2DM. The purpose of this review is to summarize the recently described mechanisms of beta-cell death in T2DM and to postulate possible new targets for treatment.
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Affiliation(s)
- Kathrin Maedler
- Department of Medicine, Larry L. Hillblom Islet Research Center, University of California at Los Angeles, Los Angeles, CA 90095-7345, USA.
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33
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Liu Z, Tanabe K, Bernal-Mizrachi E, Permutt MA. Mice with beta cell overexpression of glycogen synthase kinase-3beta have reduced beta cell mass and proliferation. Diabetologia 2008; 51:623-31. [PMID: 18219478 DOI: 10.1007/s00125-007-0914-7] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/03/2007] [Accepted: 11/23/2007] [Indexed: 01/21/2023]
Abstract
AIMS/HYPOTHESIS Glycogen synthase kinase-3 (GSK3) has been implicated in the pathophysiology of several prevalent diseases, including diabetes. However, despite recent progress in our understanding of the role of GSK3 in the regulation of glucose metabolism in peripheral tissues, the involvement of GSK3 in islet beta cell growth and function in vivo is unknown. We therefore sought to determine whether over-activation of GSK3beta would lead to alterations in islet beta cell mass and/or function. METHODS Transgenic mice overexpressing a constitutively active form of human GSK3beta (S9A) under the control of the rat insulin promoter (RIP-GSK3betaCA) were created. Studies using mouse insulinoma cells (MIN6) were conducted to investigate the regulation of GSK3beta activity and its impact on pancreas/duodenum homeobox protein-1 (PDX-1) levels. RESULTS We demonstrated that phosphorylation of GSK3beta was decreased, indicating increased GSK3beta activity in two animal models of diabetes, Lepr(-/- ) mice and Ins2 (Akita/+) mice. In MIN6 cells, the activity of GSK3beta was regulated by glucose, in a fashion largely dependent on phosphatidylinositol 3-kinase. RIP-GSK3betaCA transgenic mice showed impaired glucose tolerance after 5 months of age. Histological studies revealed that transgenic mice had decreased beta cell mass and decreased beta cell proliferation, with a 50% decrease (p<0.05) in the level of PDX-1. CONCLUSIONS/INTERPRETATION We showed direct evidence that GSK3beta activity is associated with beta cell failure in diabetic mouse models and that its overactivation resulted in decreased pancreatic beta cell proliferation and mass. GSK3 modulates PDX-1 stability in both cultured insulinoma cells and islets in vivo. These results may ultimately facilitate the development of potential therapeutic interventions targeting type 2 diabetes and/or islet transplantation.
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Affiliation(s)
- Z Liu
- Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine, Washington University School of Medicine, 660 S. Euclid Ave., Campus Box 8127, St Louis, MO 63110, USA
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Impaired insulin secretion and decreased expression of the nutritionally responsive ribosomal kinase protein S6K-1 in pancreatic islets from malnourished rats. Life Sci 2008; 82:542-8. [DOI: 10.1016/j.lfs.2007.12.012] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2007] [Revised: 09/25/2007] [Accepted: 12/15/2007] [Indexed: 11/21/2022]
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Fiaschi-Taesch N, Stewart AF, Garcia-Ocaña A. Improving islet transplantation by gene delivery of hepatocyte growth factor (HGF) and its downstream target, protein kinase B (PKB)/Akt. Cell Biochem Biophys 2007; 48:191-9. [PMID: 17709889 DOI: 10.1007/s12013-007-0024-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/1999] [Revised: 11/30/1999] [Accepted: 11/30/1999] [Indexed: 12/31/2022]
Abstract
Clinical studies have demonstrated that islet transplantation may be a useful procedure to replace beta cell function in patients with Type 1 diabetes. Islet transplantation faces many challenges, including complications associated with the procedure itself, the toxicity of immunosuppression regimens, and to the loss of islet function and insulin-independence with time. Despite the current successes, and residual challenges, these studies have pointed out an enormous scarcity of islet tissue that precludes the use of islet transplantation in a clinical setting on a wider scale. To address this problem, many research groups are trying to identify different islet growth factors and intracellular molecules capable of improving islet graft survival and function, therefore reducing the number of islets needed for successful transplantation. Among these growth factors, hepatocyte growth factor (HGF), a factor known to improve transplantation of a variety of organs/cells, has shown promising results in increasing islet graft survival and reducing the number of islets needed for successful transplantation in four different rodent models of islet transplantation. Protein kinase B (PKB)/Akt, a pro-survival intracellular signaling molecule is known to be activated in the beta cell by several different growth factors, including HGF. PKB/Akt has also shown promising results for improving human islet graft survival and function in a minimal islet mass model of islet transplantation in diabetic SCID mice. Increasing our knowledge on how HGF, PKB/Akt and other emerging molecules work for improving islet transplantation may provide substrate for future therapeutic approaches aimed at increasing the number of patients in which beta cell function can be successfully replaced.
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Vasavada RC, Wang L, Fujinaka Y, Takane KK, Rosa TC, Mellado-Gil JMD, Friedman PA, Garcia-Ocaña A. Protein kinase C-zeta activation markedly enhances beta-cell proliferation: an essential role in growth factor mediated beta-cell mitogenesis. Diabetes 2007; 56:2732-43. [PMID: 17686945 DOI: 10.2337/db07-0461] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE Diabetes results from a deficiency of functional beta-cells. Previous studies have identified hepatocyte growth factor (HGF) and parathyroid hormone-related protein (PTHrP) as two potent beta-cell mitogens. The objective of this study is to determine 1) whether HGF and PTHrP have additive/synergistic effects on beta-cell growth and proliferation; 2) the signaling pathways through which these growth factors mediate beta-cell mitogenesis; and 3) whether activation of this/these signaling pathway(s) enhances human beta-cell replication. RESEARCH DESIGN AND METHODS We generated and phenotypically analyzed doubly transgenic mice overexpressing PTHrP and HGF in the beta-cell. INS-1 and primary mouse and human islet cells were used to identify mitogenic signaling pathways activated by HGF and/or PTHrP. RESULTS Combined overexpression of HGF and PTHrP in the beta-cell of doubly transgenic mice did not result in additive/synergistic effects on beta-cell growth and proliferation, suggesting potential cross-talk between signaling pathways activated by both growth factors. Examination of these signaling pathways in INS-1 cells revealed atypical protein kinase C (PKC) as a novel intracellular target activated by both HGF and PTHrP in beta-cells. Knockdown of PKC zeta, but not PKC iota/lambda, expression using specific small-interfering RNAs blocked growth factor-induced INS-1 cell proliferation. Furthermore, adenovirus-mediated delivery of kinase-dead PKC zeta completely inhibited beta-cell proliferation in primary islet cells overexpressing PTHrP and/or HGF. Finally, adenovirus-mediated delivery of constitutively active PKC zeta in mouse and human primary islet cells significantly enhanced beta-cell proliferation. CONCLUSIONS PKC zeta is essential for PTHrP- and HGF-induced beta-cell proliferation. PKC zeta activation could be useful in therapeutic strategies for expanding beta-cell mass in vitro and in vivo.
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Affiliation(s)
- Rupangi C Vasavada
- Department of Medicine, Division of Endocrinology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA
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Podcheko A, Northcott P, Bikopoulos G, Lee A, Bommareddi SR, Kushner JA, Farhang-Fallah J, Rozakis-Adcock M. Identification of a WD40 repeat-containing isoform of PHIP as a novel regulator of beta-cell growth and survival. Mol Cell Biol 2007; 27:6484-96. [PMID: 17636024 PMCID: PMC2099606 DOI: 10.1128/mcb.02409-06] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The pleckstrin homology domain-interacting protein (PHIP) was originally identified as a 902-amino-acid (aa) protein that regulates insulin receptor-stimulated GLUT4 translocation in skeletal-muscle cells. Immunoblotting and immunohistological analyses of pancreatic beta-cells reveal prominent expression of a 206-kDa PHIP isoform restricted to the nucleus. Herein, we report the cloning of this larger, 1,821-aa isoform of PHIP (PHIP1), which represents a novel WD40 repeat-containing protein. We demonstrate that PHIP1 overexpression stimulates insulin-like growth factor 1-dependent and -independent proliferation of beta-cells, an event which correlates with transcriptional upregulation of the cyclin D2 promoter and the accumulation of cyclin D2 protein. RNA interference knockdown of PHIP1 in INS-1 cells abrogates insulin receptor substrate 2 (IRS2)-mediated DNA synthesis, providing for a specific role for PHIP1 in the enhancement of IRS2-dependent signaling responses leading to beta-cell growth. Finally, we provide evidence that PHIP1 overexpression blocks free fatty acid-induced apoptosis in INS-1 cells, which is accompanied by marked activation of phosphoprotein kinase B (PKB)/AKT and the concomitant inhibition of caspase-9 and caspase-3 cleavage. Our finding that the restorative effect of PHIP1 on beta-cell lipotoxicity can be attenuated by the overexpression of dominant-negative PKB suggests a key role for PKB in PHIP1-mediated cytoprotection. Taken together, these findings provide strong support for PHIP1 as a novel positive regulator of beta-cell function. We suggest that PHIP1 may be involved in the induction of long-term gene expression programs to promote beta-cell mitogenesis and survival.
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Affiliation(s)
- Alexey Podcheko
- Department of Laboratory Medicine and Pathobiology, 1 King's College Circle, Room 6238, University of Toronto, Toronto, Canada M5S 1A8
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Yoshida K, Murao K, Imachi H, Cao WM, Yu X, Li J, Ahmed RAM, Kitanaka N, Wong NCW, Unterman TG, Magnuson MA, Ishida T. Pancreatic glucokinase is activated by insulin-like growth factor-I. Endocrinology 2007; 148:2904-13. [PMID: 17317782 DOI: 10.1210/en.2006-1149] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Glucokinase (GK) plays a key role in the regulation of glucose use and glucose-stimulated insulin secretion in pancreatic islet cells. Gene targeting of the IGF-I receptor down-regulated pancreatic islet GK activity. That finding prompted us to examine the potential mechanism that may control GK gene activity using an islet cell line, INS-1, known to express IGF-I receptor. Exposure of these cells to IGF-I induced GK protein expression and activity of the enzyme in a dose-dependent manner. In addition, IGF-I induced activity of a reporter construct containing the GK promoter in parallel with the effect on endogenous GK mRNA levels. The stimulatory effect of IGF-I on GK promoter activity was abrogated by wortmannin and LY294002, specific inhibitors of phosphatidylinositol 3-kinase. Exposure of cells to IGF-I elicited a rapid phosphorylation of Akt and FoxO1, a known target of Akt signaling. Constitutively active Akt stimulates the activity of the GK promoter, and a dominant-negative mutant of Akt or mutagenesis of a FoxO1 response element in the GK promoter abolished the ability of IGF-I to stimulate the promoter activity. Furthermore, cell knockdown of FoxO1 with small interfering RNA disrupted the effect of IGF-I on GK expression. These results demonstrate that the phosphatidylinositol 3-kinase/Akt/FoxO1 pathway contributes to the regulation of GK gene expression in response to IGF-I stimulation.
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Affiliation(s)
- Kazuya Yoshida
- Division of Endocrinology and Metabolism, Department of Internal Medicine, Faculty of Medicine, Kagawa University, 1750-1 Miki-cho, Kita-gun, Kagawa 761-0793, Japan
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Fernández E, Martín MA, Fajardo S, Escrivá F, Alvarez C. Increased IRS-2 content and activation of IGF-I pathway contribute to enhance beta-cell mass in fetuses from undernourished pregnant rats. Am J Physiol Endocrinol Metab 2007; 292:E187-95. [PMID: 16912057 DOI: 10.1152/ajpendo.00283.2006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
We have previously shown that fetuses from undernourished (U) pregnant rats exhibited an increased beta-cell mass probably related to an enhanced IGF-I replicative response. Because IGF-I signaling pathways have been implicated in regulating beta-cell growth, we investigated in this study the IGF-I transduction system in U fetuses. To this end, an in vitro model of primary fetal islets was developed to characterize glucose/IGF-I-mediated signaling that specially influences beta-cell proliferation. We found that U fetal islets showed a greater replicative response to glucose and IGF-I than controls. Furthermore, insulin receptor substrate (IRS)-2 protein and its association with p85 were also increased. In the complete absence of IGF-I or stimulatory glucose, U islets presented an increased basal phosphorylation of downstream signals of the phosphatidylinositol 3-kinase (PI3K) pathway such as PKB, glycogen synthase kinase (GSK)3alpha/beta, PKCzeta, and mammalian target of rapamycin (mTOR). Similarly, phosphorylation of these proteins (except GSK3alpha/beta) by glucose and IGF-I was augmented even though total protein content remained unchanged. Downstream of PKB, direct glucose activation of mTOR was increased as well. In contrast, ERK1/2 phosphorylation was unaffected by undernutrition, but ERK activation seemed to be required to induce a higher proliferative response in U islets. In conclusion, we have demonstrated that fetal U islets show increased IRS-2 content and an enhancement in both basal and glucose/IGF-I activations of the IRS-2/PI3K/PKB pathway. These molecular changes may be responsible for the greater glucose/IGF-I islet replication and contribute to the increased beta-cell mass found in these fetuses.
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Affiliation(s)
- Elisa Fernández
- Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia, Universidad Complutense, Ciudad Universitaria, 28040 Madrid, Spain
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Aikin R, Hanley S, Maysinger D, Lipsett M, Castellarin M, Paraskevas S, Rosenberg L. Autocrine insulin action activates Akt and increases survival of isolated human islets. Diabetologia 2006; 49:2900-9. [PMID: 17053882 DOI: 10.1007/s00125-006-0476-0] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2006] [Accepted: 09/08/2006] [Indexed: 12/31/2022]
Abstract
AIMS/HYPOTHESIS The phosphatidylinositol 3-kinase (PI3K)/Akt pathway plays a critical role in promoting the survival of pancreatic beta cells. Akt becomes activated in isolated human islets following overnight culture despite significant levels of cell death. The aim of the current study was to identify the cause of the observed increase in Akt phosphorylation in isolated islets. We hypothesised that a factor secreted by the islets in culture was acting in an autocrine manner to activate Akt. METHODS In order to identify the stimulus of the PI3K/Akt pathway in culture, we examined the effects of different culture conditions on Akt phosphorylation and islet survival during the immediate post-isolation period. RESULTS We demonstrated that islet-conditioned medium induced Akt phosphorylation in freshly isolated human islets, whereas frequent medium replacement decreased Akt phosphorylation. Following overnight culture, islet-conditioned medium contained significantly elevated levels of insulin, indicating that insulin may be responsible for the observed increase in Akt phosphorylation. Indeed, treatment with an anti-insulin antibody or with inhibitors of insulin receptor/IGF receptor 1 kinase activity suppressed Akt phosphorylation, leading to decreased islet survival. In addition, dispersion of islets into single cells also suppressed Akt phosphorylation and induced islet cell death, indicating that islet integrity is also required for maximal Akt phosphorylation. CONCLUSIONS/INTERPRETATION Our findings demonstrate that insulin acts in an autocrine manner to activate Akt and mediate the survival of isolated human islets. These findings provide new information on how culturing islets prior to transplantation may be beneficial to their survival by allowing for autocrine activation of the pro-survival Akt pathway.
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Affiliation(s)
- R Aikin
- Department of Surgery, McGill University, Montreal, QC, Canada
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41
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Päth G, Opel A, Gehlen M, Rothhammer V, Niu X, Limbert C, Romfeld L, Hügl S, Knoll A, Brendel MD, Bretzel RG, Seufert J. Glucose-dependent expansion of pancreatic beta-cells by the protein p8 in vitro and in vivo. Am J Physiol Endocrinol Metab 2006; 291:E1168-76. [PMID: 16822955 DOI: 10.1152/ajpendo.00436.2005] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
p8 protein expression is known to be upregulated in the exocrine pancreas during acute pancreatitis. Own previous work revealed glucose-dependent p8 expression also in endocrine pancreatic beta-cells. Here we demonstrate that glucose-induced INS-1 beta-cell expansion is preceded by p8 protein expression. Moreover, isopropylthiogalactoside (IPTG)-induced p8 overexpression in INS-1 beta-cells (p8-INS-1) enhances cell proliferation and expansion in the presence of glucose only. Although beta-cell-related gene expression (PDX-1, proinsulin I, GLUT2, glucokinase, amylin) and function (insulin content and secretion) are slightly reduced during p8 overexpression, removal of IPTG reverses beta-cell function within 24 h to normal levels. In addition, insulin secretion of p8-INS-1 beta-cells in response to 0-25 mM glucose is not altered by preceding p8-induced beta-cell expansion. Adenovirally transduced p8 overexpression in primary human pancreatic islets increases proliferation, expansion, and cumulative insulin secretion in vitro. Transplantation of mock-transduced control islets under the kidney capsule of immunosuppressed streptozotocin-diabetic mice reduces blood glucose and increases human C-peptide serum concentrations to stable levels after 3 days. In contrast, transplantation of equal numbers of p8-transduced islets results in a continuous decrease of blood glucose and increase of human C-peptide beyond 3 days, indicating p8-induced expansion of transplanted human beta-cells in vivo. This is underlined by a doubling of insulin content in kidneys containing p8-transduced islet grafts explanted on day 9. These results establish p8 as a novel molecular mediator of glucose-induced pancreatic beta-cell expansion in vitro and in vivo and support the notion of existing beta-cell replication in the adult organism.
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Affiliation(s)
- Günter Päth
- Division of Endocrinology and Diabetology, Dept. of Internal Medicine II, University Hospital of Freiburg, 79106 Freiburg, Germany
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42
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Kaido T, Yebra M, Cirulli V, Rhodes C, Diaferia G, Montgomery AM. Impact of defined matrix interactions on insulin production by cultured human beta-cells: effect on insulin content, secretion, and gene transcription. Diabetes 2006; 55:2723-9. [PMID: 17003336 DOI: 10.2337/db06-0120] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The impact of extracellular matrix on insulin production needs to be understood both to optimize the derivation of functional beta-cells for transplantation and to understand mechanisms controlling islet neogenesis and glucose homeostasis. In this study, we present evidence that adhesion to some common matrix constituents has a profound impact on the transcription, secretion, and storage of insulin by human beta-cells. The integrin-dependent adhesion of fetal beta-cells to both collagen IV and vitronectin induces significant glucose-independent insulin secretion and a substantial reciprocal decline in insulin content. Collagen IV, but not vitronectin, induces comparable responses in adult beta-cells. Inhibition of extracellular signal-regulated kinase activation abrogates matrix-induced insulin secretion and effectively preserves the insulin content of adherent beta-cells. Using real-time PCR, we demonstrate that adhesion of both fetal and adult beta-cells to collagen IV and vitronectin also results in the marked suppression of insulin gene transcription. Based on these findings, we contend that integrin-dependent adhesion and signaling in response to certain matrices can have a significant negative impact on insulin production by primary human beta-cells. Such responses were not found to be associated with cell death but may precede beta-cell dedifferentiation.
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Affiliation(s)
- Thomas Kaido
- Islet Research Laboratory at the Whittier Institute for Diabetes, Department of Pediatrics, University of California at San Diego, 9894 Genesee Ave., La Jolla, CA 92037, USA
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43
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Marzban L, Rhodes CJ, Steiner DF, Haataja L, Halban PA, Verchere CB. Impaired NH2-terminal processing of human proislet amyloid polypeptide by the prohormone convertase PC2 leads to amyloid formation and cell death. Diabetes 2006; 55:2192-201. [PMID: 16873681 DOI: 10.2337/db05-1566] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Islet amyloid, formed by aggregation of islet amyloid polypeptide (IAPP; amylin), is a pathological characteristic of the pancreas in type 2 diabetes and may contribute to the progressive loss of beta-cells in this disease. We tested the hypothesis that impaired processing of the IAPP precursor proIAPP contributes to amyloid formation and cell death. GH3 cells lacking the prohormone convertase 1/3 (PC1/3) and IAPP and with very low levels of prohormone convertase 2 (PC2) were transduced with adenovirus (Ad) expressing human or rat (control) proIAPP linked to green fluorescent protein, with or without Ad-PC2 or Ad-PC1/3. Expression of human proIAPP increased the number of transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells 96 h after transduction (+hIAPP 8.7 +/- 0.4% vs. control 3.0 +/- 0.4%; P < 0.05). COOH-terminal processing of human proIAPP by PC1/3 increased (hIAPP+PC1/3 10.4 +/- 0.7%; P < 0.05), whereas NH(2)-terminal processing of proIAPP by addition of PC2 markedly decreased (hIAPP+PC2 5.5 +/- 0.5%; P < 0.05) the number of apoptotic GH3 cells. Islets from mice lacking PC2 and with beta-cell expression of human proIAPP (hIAPP(+/+)/PC2(-/-)) developed amyloid associated with beta-cell death during 2-week culture. Rescue of PC2 expression by ex vivo transduction with Ad-PC2 restored NH(2)-terminal processing to mature IAPP and decreased both the extent of amyloid formation and the number of TUNEL-positive cells (-PC2 26.5 +/- 4.1% vs. +PC2 16.1 +/- 4.3%; P < 0.05). These findings suggest that impaired NH(2)-terminal processing of proIAPP leads to amyloid formation and cell death and that accumulation of the NH(2)-terminally extended human proIAPP intermediate may be a critical initiating step in amyloid formation.
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Affiliation(s)
- Lucy Marzban
- Deparment of Pathology and Laboratory Medicine and Child and Family Research Institute, University of British Columbia, Vancouver, BC, Canada.
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44
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Martinez SC, Cras-Méneur C, Bernal-Mizrachi E, Permutt MA. Glucose regulates Foxo1 through insulin receptor signaling in the pancreatic islet beta-cell. Diabetes 2006; 55:1581-91. [PMID: 16731820 DOI: 10.2337/db05-0678] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Glucose controls islet beta-cell mass and function at least in part through the phosphatidylinositol 3-kinase (PI3K)/Akt pathway downstream of insulin signaling. The Foxo proteins, transcription factors known in other tissues to be negatively regulated by Akt activation, affect proliferation and metabolism. In this study, we tested the hypothesis that glucose regulates Foxo1 activity in the beta-cell via an autocrine/paracrine effect of released insulin on its receptor. Mouse insulinoma cells (MIN6) were starved overnight for glucose (5 mmol/l) then refed with glucose (25 mmol/l), resulting in rapid Foxo1 phosphorylation (30 min, P < 0.05 vs. untreated). This glucose response was demonstrated to be time (0.5-2 h) and dose (5-30 mmol/l) dependent. The use of inhibitors demonstrated that glucose-induced Foxo1 phosphorylation was dependent upon depolarization, calcium influx, and PI3K signaling. Additionally, increases in glucose concentration over a physiological range (2.5-20 mmol/l) resulted in nuclear to cytoplasmic translocation of Foxo1. Phosphorylation and translocation of Foxo1 following glucose refeeding were eliminated in an insulin receptor knockdown cell line, indicating that the glucose effects are mediated primarily through the insulin receptor. Activity of Foxo1 was observed to increase with decreased glucose concentrations, assessed by an IGF binding protein-1 promoter luciferase assay. Starvation of MIN6 cells identified a putative Foxo1 target, Chop, and a Chop-promoter luciferase assay in the presence of cotransfected Foxo1 supported this hypothesis. The importance of these observations was that nutritional alterations in the beta-cell are associated with changes in Foxo1 transcriptional activity and that these changes are predominantly mediated through glucose-stimulated insulin secretion acting through its own receptor.
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Affiliation(s)
- Sara C Martinez
- Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, 660 S. Euclid Ave., Campus Box 8127, St. Louis, MO 63110, USA
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45
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Verbeke P, Welter-Stahl L, Ying S, Hansen J, Häcker G, Darville T, Ojcius DM. Recruitment of BAD by the Chlamydia trachomatis vacuole correlates with host-cell survival. PLoS Pathog 2006; 2:e45. [PMID: 16710454 PMCID: PMC1463014 DOI: 10.1371/journal.ppat.0020045] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2005] [Accepted: 04/10/2006] [Indexed: 12/02/2022] Open
Abstract
Chlamydiae replicate intracellularly in a vacuole called an inclusion. Chlamydial-infected host cells are protected from mitochondrion-dependent apoptosis, partly due to degradation of BH3-only proteins. The host-cell adapter protein 14-3-3β can interact with host-cell apoptotic signaling pathways in a phosphorylation-dependent manner. In Chlamydia trachomatis-infected cells, 14-3-3β co-localizes to the inclusion via direct interaction with a C. trachomatis-encoded inclusion membrane protein. We therefore explored the possibility that the phosphatidylinositol-3 kinase (PI3K) pathway may contribute to resistance of infected cells to apoptosis. We found that inhibition of PI3K renders C. trachomatis-infected cells sensitive to staurosporine-induced apoptosis, which is accompanied by mitochondrial cytochrome c release. 14-3-3β does not associate with the Chlamydia pneumoniae inclusion, and inhibition of PI3K does not affect protection against apoptosis of C. pneumoniae-infected cells. In C. trachomatis-infected cells, the PI3K pathway activates AKT/protein kinase B, which leads to maintenance of the pro-apoptotic protein BAD in a phosphorylated state. Phosphorylated BAD is sequestered via 14-3-3β to the inclusion, but it is released when PI3K is inhibited. Depletion of AKT through short-interfering RNA reverses the resistance to apoptosis of C. trachomatis-infected cells. BAD phosphorylation is not maintained and it is not recruited to the inclusion of Chlamydia muridarum, which protects poorly against apoptosis. Thus, sequestration of BAD away from mitochondria provides C. trachomatis with a mechanism to protect the host cell from apoptosis via the interaction of a C. trachomatis-encoded inclusion protein with a host-cell phosphoserine-binding protein. Chlamydia trachomatis is the most common cause of sexually transmitted bacterial infections in humans. These bacteria survive and replicate within a vacuole in the infected cell called an inclusion, producing up to a thousand bacteria per inclusion within a day of infection. Despite the large size of the inclusion, the infected cell survives long enough for the pathogens to complete their infection cycle and then infect new host cells. The researchers describe a novel mechanism for protection of the host cell by Chlamydia, namely activation of enzymes involved in host-cell survival. These enzymes, called kinases, cause the phosphorylation and inactivation of a protein, BAD, which can promote “cell suicide” (apoptosis) of uninfected cells. BAD phosphorylation is accompanied by recruitment of BAD to the chlamydial inclusion, where BAD binds to a cellular adapter protein, 14-3-3β. The adapter protein, in turn, is attracted to the inclusion by a membrane protein produced by Chlamydia. Thus, the chlamydial inclusion sequesters BAD away from mitochondria, where BAD could induce host-cell apoptosis. The cross talk between chlamydiae and host-cell signaling pathways demonstrates a novel mechanism of pathogen modulation of host-cell biology, and represents a potential therapeutic target for blocking infection by this prevalent pathogen.
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Affiliation(s)
- Philippe Verbeke
- Institut Jacques Monod, Université Paris—Denis Diderot, Paris, France
| | - Lynn Welter-Stahl
- Institut Jacques Monod, Université Paris—Denis Diderot, Paris, France
| | - Songmin Ying
- Institute for Medical Microbiology, Technische Universität München, Munich, Germany
| | - Jon Hansen
- Institut Jacques Monod, Université Paris—Denis Diderot, Paris, France
| | - Georg Häcker
- Institute for Medical Microbiology, Technische Universität München, Munich, Germany
| | - Toni Darville
- Department of Microbiology and Immunology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States of America
| | - David M Ojcius
- Institut Jacques Monod, Université Paris—Denis Diderot, Paris, France
- School of Natural Sciences, University of California Merced, Merced, California, United States of America
- * To whom correspondence should be addressed. E-mail:
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46
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Elghazi L, Balcazar N, Bernal-Mizrachi E. Emerging role of protein kinase B/Akt signaling in pancreatic β-cell mass and function. Int J Biochem Cell Biol 2006. [DOI: 10.1016/j.biocel.2006.01.005] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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47
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Guillen C, Navarro P, Robledo M, Valverde AM, Benito M. Differential mitogenic signaling in insulin receptor-deficient fetal pancreatic beta-cells. Endocrinology 2006; 147:1959-68. [PMID: 16396989 DOI: 10.1210/en.2005-0831] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Insulin receptor (IR) may play an essential role in the development of beta-cell mass in the mouse pancreas. To further define the function of this signaling system in beta-cell development, we generated IR-deficient beta-cell lines. Fetal pancreata were dissected from mice harboring a floxed allele of the insulin receptor (IRLoxP) and used to isolate islets. These islets were infected with a retrovirus to express simian virus 40 large T antigen, a strategy for establishing beta-cell lines (beta-IRLoxP). Subsequently, these cells were infected with adenovirus encoding cre recombinase to delete insulin receptor (beta-IR(-/-)). beta-Cells expressed insulin and Pdx-1 mRNA in response to glucose. In beta-IRLoxP beta-cells, p44/p42 MAPK and phosphatidylinositol 3 kinase pathways, mammalian target of rapamycin (mTOR), and p70S(6)K phosphorylation and beta-cell proliferation were stimulated in response to insulin. Wortmannin or PD98059 had no effect on insulin-mediated mTOR/p70S(6)K signaling and the corresponding mitogenic response. However, the presence of both inhibitors totally impaired these signaling pathways and mitogenesis in response to insulin. Rapamycin completely blocked insulin-activated mTOR/p70S(6)K signaling and mitogenesis. Interestingly, in beta-IR(-/-) beta-cells, glucose failed to stimulate phosphatidylinositol 3 kinase activity but induced p44/p42 MAPKs and mTOR/p70S(6)K phosphorylation and beta-cell mitogenesis. PD98059, but not wortmannin, inhibited glucose-induced mTOR/p70S(6)K signaling and mitogenesis in those cells. Finally, rapamycin blocked glucose-mediated mitogenesis of beta-IR(-/-) cells. In conclusion, independently of glucose, insulin can mediate mitogenesis in fetal pancreatic beta-cell lines. However, in the absence of the insulin receptor, glucose induces beta-cell mitogenesis.
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Affiliation(s)
- C Guillen
- Institute of Biochemistry/Department of Biochemistry and Molecular Biology, Joint Center Consejo Superior Investigacion Cientifica/Universidad Complutense, School of Pharmacy, Complutense University, Madrid, Spain
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48
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Lingohr MK, Briaud I, Dickson LM, McCuaig JF, Alárcon C, Wicksteed BL, Rhodes CJ. Specific regulation of IRS-2 expression by glucose in rat primary pancreatic islet beta-cells. J Biol Chem 2006; 281:15884-92. [PMID: 16574657 DOI: 10.1074/jbc.m600356200] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Insulin receptor substrate 2 (IRS-2) plays a critical role in pancreatic beta-cells. Increased IRS-2 expression promotes beta-cell growth and survival, whereas decreased IRS-2 levels lead to apoptosis. It was found that IRS-2 turnover in rat islet beta-cells was rapid, with mRNA and protein half-lives of approximately 90 min and approximately 2 h, respectively. However, this was countered by specific glucose-regulated IRS-2 expression mediated at the transcriptional level. Glucose (> or = 6 mM) increased IRS-2 mRNA and protein levels in a dose-dependent manner, reaching a maximum 4-fold increase in IRS-2 mRNA and a 5-6-fold increase in IRS-2 protein levels at > or = 12 mM glucose (p < or = 0.01). Glucose (15 mM) regulation of islet beta-cell IRS-2 gene expression was rapid, with a significant increase in IRS-2 mRNA levels within 2 h that reached a maximum 4-fold increase by 4 h. IRS-2 protein expression in beta-cells followed that of IRS-2 mRNA. Glucose metabolism was necessary for increased IRS-2 expression in beta-cells. Moreover, inhibition of a glucose-induced rise in islet beta-cell cytosolic [Ca2+]i prevented an increase in IRS-2 expression, indicating this was Ca2+-dependent. The glucose-induced rise in IRS-2 levels correlated with increased IRS-2 tyrosine phosphorylation and downstream activation of protein kinase B. These data indicate that fluctuations of glucose in the normal physiological range (5-15 mM) promote beta-cell survival via regulation of IRS-2 expression and a subsequent parallel protein kinase B activation. Given that the onset of type-2 diabetes is marked by loss of beta-cells, these data further the idea that controlled IRS-2 expression in beta-cells could be a therapeutic means to promote beta-cell survival and delay the onset of the disease.
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Affiliation(s)
- Melissa K Lingohr
- The Pacific Northwest Research Institute, Seattle, Washington 98122, USA
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49
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Tamarina NA, Kuznetsov A, Rhodes CJ, Bindokas VP, Philipson LH. Inositol (1,4,5)-trisphosphate dynamics and intracellular calcium oscillations in pancreatic beta-cells. Diabetes 2005; 54:3073-81. [PMID: 16249428 DOI: 10.2337/diabetes.54.11.3073] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Glucose-stimulated insulin secretion is associated with transients of intracellular calcium concentration ([Ca2+]i) in the pancreatic beta-cell. We tested the hypothesis that inositol (1,4,5)-trisphosphate [Ins(1,4,5)P3] [Ca2+]i release is incorporated in glucose-induced [Ca2+]i oscillations in mouse islets and MIN6 cells. We found that depletion of intracellular Ca2+ stores with thapsigargin increased the oscillation frequency by twofold and inhibited the slow recovery phase of [Ca2+]i oscillations. We employed a pleckstrin homology domain-containing fluorescent biosensor, phospholipase C partial differential pleckstrin homology domain-enhanced green fluorescent protein, to visualize Ins(1,4,5)P3 dynamics in insulin-secreting MIN6 cells and mouse islets in real time using a video-rate confocal system. In both types of cells, stimulation with carbamoylcholine (CCh) and depolarization with KCl results in an increase in Ins(1,4,5)P3 accumulation in the cytoplasm. When stimulated with glucose, the Ins(1,4,5)P3 concentration in the cytoplasm oscillates in parallel with oscillations of [Ca2+]i. Maximal accumulation of Ins(1,4,5)P3 in these oscillations coincides with the peak of [Ca2+]i and tracks changes in frequencies induced by the voltage-gated K+ channel blockade. We show that Ins(1,4,5)P3 release in insulin-secreting cells can be stimulated by depolarization-induced Ca2+ flux. We conclude that Ins(1,4,5)P3 concentration oscillates in parallel with [Ca2+]i in response to glucose stimulation, but it is not the driving force for [Ca2+]i oscillations.
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Affiliation(s)
- Natalia A Tamarina
- Department of Medicine, MC 1027, University of Chicago, Chicago, IL 60637, USA
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50
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Vasavada RC, Gonzalez-Pertusa JA, Fujinaka Y, Fiaschi-Taesch N, Cozar-Castellano I, Garcia-Ocaña A. Growth factors and beta cell replication. Int J Biochem Cell Biol 2005; 38:931-50. [PMID: 16168703 DOI: 10.1016/j.biocel.2005.08.003] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2005] [Revised: 07/20/2005] [Accepted: 08/10/2005] [Indexed: 01/08/2023]
Abstract
Recent studies have demonstrated that human islet allograft transplantation can be a successful therapeutic option in the treatment of patients with Type I diabetes. However, this impressive recent advance is accompanied by a very important constraint. There is a critical paucity of pancreatic islets or pancreatic beta cells for islet transplantation to become a large-scale therapeutic option in patients with diabetes. This has prompted many laboratories around the world to invigorate their efforts in finding ways for increasing the availability of beta cells or beta cell surrogates that potentially could be transplanted into patients with diabetes. The number of studies analyzing the mechanisms that govern beta cell proliferation and growth in physiological and pathological conditions has increased exponentially during the last decade. These studies exploring the role of growth factors, intracellular signaling molecules and cell cycle regulators constitute the substrate for future strategies aimed at expanding human beta cells in vitro and/or in vivo after transplantation. In this review, we describe the current knowledge on the effects of several beta cell growth factors that have been shown to increase beta cell proliferation and expand beta cell mass in vitro and/or in vivo and that they could be potentially deployed in an effort to increase the number of patients transplanted with islets. Furthermore, we also analyze in this review recent studies deciphering the relevance of these specific islet growth factors as physiological and pathophysiological regulators of beta cell proliferation and islet growth.
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Affiliation(s)
- Rupangi C Vasavada
- Division of Endocrinology, University of Pittsburgh, BST-E1140, PA 15261, USA
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