151
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Hambrock A, de Oliveira Franz CB, Hiller S, Grenz A, Ackermann S, Schulze DU, Drews G, Osswald H. Resveratrol binds to the sulfonylurea receptor (SUR) and induces apoptosis in a SUR subtype-specific manner. J Biol Chem 2006; 282:3347-56. [PMID: 17138562 DOI: 10.1074/jbc.m608216200] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Sulfonylurea receptors (SURs) constitute the regulatory subunits of ATP-sensitive K+ channels (K(ATP) channels). SUR binds nucleotides and synthetic K(ATP) channel modulators, e.g. the antidiabetic sulfonylurea glibenclamide, which acts as a channel blocker. However, knowledge about naturally occurring ligands of SUR is very limited. In this study, we show that the plant phenolic compound trans-resveratrol can bind to SUR and displace binding of glibenclamide. Electrophysiological measurements revealed that resveratrol is a blocker of pancreatic SUR1/K(IR)6.2 K(ATP) channels. We further demonstrate that, like glibenclamide, resveratrol induces enhanced apoptosis. This was shown by analyzing different apoptotic parameters (cell detachment, nuclear condensation and fragmentation, and activities of different caspase enzymes). The observed apoptotic effect was specific to cells expressing the SUR1 isoform and was not mediated by the electrical activity of K(ATP) channels, as it was observed in human embryonic kidney 293 cells expressing SUR1 alone. Enhanced susceptibility to resveratrol was not observed in pancreatic beta-cells from SUR1 knock-out mice or in cells expressing the isoform SUR2A or SUR2B or the mutant SUR1(M1289T). Resveratrol was much more potent than glibenclamide in inducing SUR1-specific apoptosis. Treatment with etoposide, a classical inducer of apoptosis, did not result in SUR isoform-specific apoptosis. In conclusion, resveratrol is a natural SUR ligand that can induce apoptosis in a SUR isoform-specific manner. Considering the tissue-specific expression patterns of SUR isoforms and the possible effects of SUR mutations on susceptibility to apoptosis, these observations could be important for diabetes and/or cancer research.
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MESH Headings
- ATP-Binding Cassette Transporters/drug effects
- ATP-Binding Cassette Transporters/genetics
- ATP-Binding Cassette Transporters/physiology
- Animals
- Apoptosis/drug effects
- Apoptosis/physiology
- Caspases/drug effects
- Caspases/metabolism
- Cell Adhesion/drug effects
- Cell Line
- Etoposide/pharmacology
- Female
- Humans
- Hypoglycemic Agents/pharmacology
- Islets of Langerhans/cytology
- Islets of Langerhans/drug effects
- Islets of Langerhans/metabolism
- Islets of Langerhans/physiology
- Kidney
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Potassium Channels/deficiency
- Potassium Channels/drug effects
- Potassium Channels/genetics
- Potassium Channels/physiology
- Potassium Channels, Inwardly Rectifying/deficiency
- Potassium Channels, Inwardly Rectifying/drug effects
- Potassium Channels, Inwardly Rectifying/genetics
- Potassium Channels, Inwardly Rectifying/physiology
- Receptors, Drug/deficiency
- Receptors, Drug/drug effects
- Receptors, Drug/genetics
- Receptors, Drug/physiology
- Recombinant Proteins/drug effects
- Recombinant Proteins/metabolism
- Resveratrol
- Stilbenes/pharmacokinetics
- Stilbenes/pharmacology
- Sulfonylurea Receptors
- Transfection
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Affiliation(s)
- Annette Hambrock
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstrasse 56, D-72074 Tübingen, Germany.
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152
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Geoffrey R, Jia S, Kwitek AE, Woodliff J, Ghosh S, Lernmark A, Wang X, Hessner MJ. Evidence of a Functional Role for Mast Cells in the Development of Type 1 Diabetes Mellitus in the BioBreeding Rat. THE JOURNAL OF IMMUNOLOGY 2006; 177:7275-86. [PMID: 17082646 DOI: 10.4049/jimmunol.177.10.7275] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Human type 1 diabetes mellitus (T1DM) arises through autoimmune destruction of pancreatic beta cells and is modeled in many respects by the lymphopenic and spontaneously diabetic BioBreeding (BB) DRlyp/lyp rat. Previously, preonset expression profiling of whole DRlyp/lyp pancreatic lymph nodes (PLN) revealed innate immune activity, specifically that of mast cells and eosinophils. Furthermore, we observed that pancreatic islets of DRlyp/lyp rats as well as those of diabetes-inducible BB DR(+/+) rats potentially recruit innate cells through eotaxin expression. Here we determine that lifelong eotaxin expression begins before 40 days of life and is localized specifically to beta cells. In this report, we find that PLN mast cells are more abundant in DRlyp/lyp compared with related BB DR(+/+) rats (2.1 +/- 0.9% vs 0.9 +/- 0.4% of total cells, p < 0.0001). DRlyp/lyp PLN mast cell gene expression profiling revealed an activated population and included significant overrepresentation of transcripts for mast cell protease 1, cationic trypsinogen, carboxypeptidase A, IL-5, and phospholipase Cgamma. In the DR(+/+) rat, which develops T1DM upon depletion of T regulator cells, mast cells displayed gene expression consistent with the negative regulation of degranulation, including significant overrepresentation of transcripts encoding tyrosine phosphatase SHP-1, lipid phosphatase SHIP, and E3 ubiquitin ligase c-Cbl. To recapitulate the negative mast cell regulation observed in the DR(+/+) rats, we treated DRlyp/lyp rats with the mast cell "stabilizer" cromolyn, which significantly (p < 0.05) delayed T1DM onset. These findings are consistent with a growing body of evidence in human and animal models, where a role for mast cells in the initiation and progression of autoimmune disease is emerging.
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Affiliation(s)
- Rhonda Geoffrey
- Max McGee National Research Center for Juvenile Diabetes, Department of Pediatrics at the Medical College of Wisconsin, and Children's Research Institute of the Children's Hospital of Wisconsin, Milwaukee, WI 53226, USA
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153
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Yusta B, Baggio LL, Estall JL, Koehler JA, Holland DP, Li H, Pipeleers D, Ling Z, Drucker DJ. GLP-1 receptor activation improves beta cell function and survival following induction of endoplasmic reticulum stress. Cell Metab 2006; 4:391-406. [PMID: 17084712 DOI: 10.1016/j.cmet.2006.10.001] [Citation(s) in RCA: 326] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/04/2006] [Revised: 08/16/2006] [Accepted: 10/06/2006] [Indexed: 01/09/2023]
Abstract
Perturbation of endoplasmic reticulum (ER) homeostasis impairs insulin biosynthesis, beta cell survival, and glucose homeostasis. We show that a murine model of diabetes is associated with the development of ER stress in beta cells and that treatment with the GLP-1R agonist exendin-4 significantly reduced biochemical markers of islet ER stress in vivo. Exendin-4 attenuated translational downregulation of insulin and improved cell survival in purified rat beta cells and in INS-1 cells following induction of ER stress in vitro. GLP-1R agonists significantly potentiated the induction of ATF-4 by ER stress and accelerated recovery from ER stress-mediated translational repression in INS-1 beta cells in a PKA-dependent manner. The effects of exendin-4 on the induction of ATF-4 were mediated via enhancement of ER stress-stimulated ATF-4 translation. Moreover, exendin-4 reduced ER stress-associated beta cell death in a PKA-dependent manner. These findings demonstrate that GLP-1R signaling directly modulates the ER stress response leading to promotion of beta cell adaptation and survival.
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Affiliation(s)
- Bernardo Yusta
- Department of Medicine, Banting and Best Diabetes Centre, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada
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154
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Yang SN, Berggren PO. The role of voltage-gated calcium channels in pancreatic beta-cell physiology and pathophysiology. Endocr Rev 2006; 27:621-76. [PMID: 16868246 DOI: 10.1210/er.2005-0888] [Citation(s) in RCA: 175] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Voltage-gated calcium (CaV) channels are ubiquitously expressed in various cell types throughout the body. In principle, the molecular identity, biophysical profile, and pharmacological property of CaV channels are independent of the cell type where they reside, whereas these channels execute unique functions in different cell types, such as muscle contraction, neurotransmitter release, and hormone secretion. At least six CaValpha1 subunits, including CaV1.2, CaV1.3, CaV2.1, CaV2.2, CaV2.3, and CaV3.1, have been identified in pancreatic beta-cells. These pore-forming subunits complex with certain auxiliary subunits to conduct L-, P/Q-, N-, R-, and T-type CaV currents, respectively. beta-Cell CaV channels take center stage in insulin secretion and play an important role in beta-cell physiology and pathophysiology. CaV3 channels become expressed in diabetes-prone mouse beta-cells. Point mutation in the human CaV1.2 gene results in excessive insulin secretion. Trinucleotide expansion in the human CaV1.3 and CaV2.1 gene is revealed in a subgroup of patients with type 2 diabetes. beta-Cell CaV channels are regulated by a wide range of mechanisms, either shared by other cell types or specific to beta-cells, to always guarantee a satisfactory concentration of Ca2+. Inappropriate regulation of beta-cell CaV channels causes beta-cell dysfunction and even death manifested in both type 1 and type 2 diabetes. This review summarizes current knowledge of CaV channels in beta-cell physiology and pathophysiology.
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Affiliation(s)
- Shao-Nian Yang
- The Rolf Luft Research Center for Diabetes and Endocrinology L1:03, Karolinska University Hospital Solna, SE-171 76 Stockholm, Sweden.
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155
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Johnson JD, Ford EL, Bernal-Mizrachi E, Kusser KL, Luciani DS, Han Z, Tran H, Randall TD, Lund FE, Polonsky KS. Suppressed insulin signaling and increased apoptosis in CD38-null islets. Diabetes 2006; 55:2737-46. [PMID: 17003338 DOI: 10.2337/db05-1455] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
CD38 is a multifunctional enzyme capable of generating metabolites that release Ca2+ from intracellular stores, including nicotinic acid adenine dinucleotide phosphate (NAADP). A number of studies have led to the controversial proposal that CD38 mediates an alternate pathway for glucose-stimulated insulin release and contributes to the pathogenesis of diabetes. It has recently been shown that NAADP mediates Ca2+ mobilization by insulin in human pancreatic beta-cells. In the present study, we report altered Ca2+ homeostasis and reduced responsiveness to insulin, but not glucose, in Cd38-/- beta-cells. In keeping with the antiapoptotic role of insulin signaling, Cd38-/- islets were significantly more susceptible to apoptosis compared with islets isolated from littermate controls. This finding correlated with disrupted islet architecture and reduced beta-cell mass in Cd38-/- mice, both in the context of a normal lab diet and a high-fat diet. Nevertheless, we did not find robust differences in glucose homeostasis in vivo or glucose signaling in vitro in Cd38-/- mice on the C57BL/6 genetic background, in contrast to previous studies by others of Cd38 knockout mice on the ICR background. Thus, our results suggest that CD38 plays a role in novel antiapoptotic signaling pathways but does not directly control glucose signaling in pancreatic beta-cells.
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Affiliation(s)
- James D Johnson
- Division of Metabolism, Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri, USA.
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156
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Knight JD, Hebda JA, Miranker AD. Conserved and cooperative assembly of membrane-bound alpha-helical states of islet amyloid polypeptide. Biochemistry 2006; 45:9496-508. [PMID: 16878984 DOI: 10.1021/bi060579z] [Citation(s) in RCA: 259] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The conversion of soluble protein into beta-sheet-rich amyloid fibers is the hallmark of a number of serious diseases. Precursors for many of these systems (e.g., Abeta from Alzheimer's disease) reside in close association with a biological membrane. Membrane bilayers are reported to accelerate the rate of amyloid assembly. Furthermore, membrane permeabilization by amyloidogenic peptides can lead to toxicity. Given the beta-sheet-rich nature of mature amyloid, it is seemingly paradoxical that many precursors are either intrinsically alpha-helical or transiently adopt an alpha-helical state upon association with membrane. In this work, we investigate these phenomena in islet amyloid polypeptide (IAPP). IAPP is a 37-residue peptide hormone which forms amyloid fibers in individuals with type II diabetes. Fiber formation by human IAPP (hIAPP) is markedly accelerated by lipid bilayers despite adopting an alpha-helical state on the membrane. We further show that IAPP partitions into monomeric and oligomeric helical assemblies. Importantly, it is this latter state which most strongly correlates to both membrane leakage and accelerated fiber formation. A sequence variant of IAPP from rodents (rIAPP) does not form fibers and is reputed not to permeabilize membranes. Here, we report that rIAPP is capable of permeabilizing membranes under conditions that permit rIAPP membrane binding. Sequence and spectroscopic comparisons of rIAPP and hIAPP enable us to propose a general mechanism for the helical acceleration of amyloid formation in vitro. As rIAPP cannot form amyloid fibers, our results show that fiber formation need not be directly coupled to toxicity.
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Affiliation(s)
- Jefferson D Knight
- Department of Pharmacology, Yale University, 260 Whitney Avenue, New Haven, Connecticut 06520-8114, USA
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157
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Maedler K, Schumann DM, Schulthess F, Oberholzer J, Bosco D, Berney T, Donath MY. Aging correlates with decreased beta-cell proliferative capacity and enhanced sensitivity to apoptosis: a potential role for Fas and pancreatic duodenal homeobox-1. Diabetes 2006; 55:2455-62. [PMID: 16936193 DOI: 10.2337/db05-1586] [Citation(s) in RCA: 131] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Type 2 diabetes is characterized by a deficit in beta-cell mass, and its incidence increases with age. Here, we analyzed beta-cell turnover in islets from 2- to 3- compared with 7- to 8-month-old rats and in human islets from 53 organ donors with ages ranging from 17 to 74 years. In cultured islets from 2- to 3-month-old rats, the age at which rats are usually investigated, increasing glucose from 5.5 to 11.1 mmol/l decreased beta-cell apoptosis, which was augmented when glucose was further increased to 33.3 mmol/l. In parallel, beta-cell proliferation was increased by both 11.1 and 33.3 mmol/l glucose compared with 5.5 mmol/l. In contrast, in islets from 7- to 8-month-old rats and from adult humans, increasing glucose concentrations from 5.5 to 33.3 mmol/l induced a linear increase in beta-cell death and a decrease in proliferation. Additionally, in cultivated human islets, age correlated positively with the sensitivity to glucose-induced beta-cell apoptosis and negatively to baseline proliferation. In rat islets, constitutive expression of Fas ligand and glucose-induced Fas receptor expression were observed only in 7- to 8-month-old but not in 2- to 3-month-old islets, whereas no age-dependent changes in the Fas/Fas ligand system could be detected in human islets. However, pancreatic duodenal homeobox (PDX)-1 expression decreased with age in pancreatic tissue sections of rats and humans. Furthermore, older rat islets were more sensitive to the high-glucose-mediated decrease in PDX-1 expression than younger islets. Therefore, differences in glucose sensitivity between human and 2- to 3-month-old rat islets may be due to both differences in age and in the genetic background. These data provide a possible explanation for the increased incidence of type 2 diabetes at an older age and support the use of islets from older rats as a more appropriate model to study glucose-induced beta-cell apoptosis.
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Affiliation(s)
- Kathrin Maedler
- Larry L. Hillblom Islet Research Center, University of California, Los Angeles, USA
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158
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Zaitseva II, Sharoyko V, Størling J, Efendic S, Guerin C, Mandrup-Poulsen T, Nicotera P, Berggren PO, Zaitsev SV. RX871024 reduces NO production but does not protect against pancreatic beta-cell death induced by proinflammatory cytokines. Biochem Biophys Res Commun 2006; 347:1121-8. [PMID: 16870144 DOI: 10.1016/j.bbrc.2006.06.197] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2006] [Accepted: 06/30/2006] [Indexed: 11/19/2022]
Abstract
The imidazoline compound RX871024 reduces IL-1beta-induced NO production thereby protecting against IL-1beta-induced beta-cell apoptosis. The aim of this study was to evaluate whether imidazolines RX871024 and efaroxan protect beta-cells against death in the presence of a combination of the cytokines IL-1beta, IFNgamma, and TNFalpha. To address this issue, experiments involving different methods for detection of cell death, different concentrations of the cytokines, and a variety of conditions of preparation and culturing of ob/ob mouse islets and beta-cells have been carried out. Thoroughly performed experiments have not been able to demonstrate a protective effect of RX871024 and efaroxan on beta-cell death induced by the combination of cytokines. However, the inhibitory effect of RX871024 on NO production in ob/ob mouse islets and beta-cells was still observed in the presence of all three cytokines and correlated with the decrease in p38 MAPK phosphorylation. Conversely, efaroxan did not affect cytokine-induced NO production. Our data indicate that a combination of pro-inflammatory cytokines IL-1beta, IFNgamma, and TNFalpha, conditions modelling those that take place in type 1 diabetes, induces pancreatic beta-cell death that does not directly correlate with NO production and cannot be counteracted with imidazoline compounds.
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Affiliation(s)
- Irina I Zaitseva
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, SE-171 76 Stockholm, Sweden
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159
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Choi SE, Min SH, Shin HC, Kim HE, Jung MW, Kang Y. Involvement of calcium-mediated apoptotic signals in H2O2-induced MIN6N8a cell death. Eur J Pharmacol 2006; 547:1-9. [PMID: 16934799 DOI: 10.1016/j.ejphar.2006.06.016] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2006] [Revised: 06/05/2006] [Accepted: 06/12/2006] [Indexed: 01/11/2023]
Abstract
Reactive oxygen species are believed to be the central mediators of beta-cell destruction that leads to type 1 and 2 diabetes, and calcium has been reported to be an important mediator of beta cell death. In the present study, the authors investigated whether Ca(2+) plays a role in hydrogen peroxide (H(2)O(2))-induced MIN6N8a mouse beta cell death. Treatment with low concentration H(2)O(2) (50 microM) was found to be sufficient to reduce MIN6N8a cell viability by 55%, largely via apoptosis. However, this H(2)O(2)-induced cell death was near completely blocked by pretreatment with BAPTA/AM (5 microM), a chelator of intracellular Ca(2+). Moreover, the intracellular calcium store channel blockers, such as, xestospongin c and ryanodine, significant protected cells from 50 microM H(2)O(2)-induced cell death and under extracellular Ca(2+)-free conditions, 50 microM H(2)O(2) elicited transient [Ca(2+)](i) increases. In addition, pharmacologic inhibitors of calpain, calcineurin, and calcium/calmodulin-dependent protein kinase II were found to have a protective effect on H(2)O(2)-induced death. Moreover, H(2)O(2)-induced apoptotic signals, such as c-JUN N-terminal kinase activation, cytochrome c release, caspase 3 activation, and poly (ADP-ribose) polymerase cleavage were all down-regulated by the intracellular Ca(2+) chelation. These findings show that [Ca(2+)](i) elevation, possibly due to release from intracellular calcium stores and the subsequent activation of Ca(2+)-mediated apoptotic signals, critically mediates low concentration H(2)O(2)-induced MIN6N8a cell death. These findings suggest that a breakdown of calcium homeostasis by low level of reactive oxygen species may be involved in beta cell destruction during diabetes development.
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Affiliation(s)
- Sung-E Choi
- Institute for Medical Science, Ajou University School of Medicine,442-749, Suwon, Kyunggi-do, Republic of Korea
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160
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Abstract
Type 2 diabetes is characterized by hyperglycemia resulting from insulin resistance in the setting of inadequate beta-cell compensation. Currently available therapeutic agents lower blood glucose through multiple mechanisms but do not directly reverse the decline in beta-cell mass. Glucagon-like peptide-1 (GLP-1) receptor agonists, exemplified by Exenatide (exendin-4), not only acutely lower blood glucose but also engage signaling pathways in the islet beta-cell that lead to stimulation of beta-cell replication and inhibition of beta-cell apoptosis. Similarly, glucose-dependent insulinotropic polypeptide (GIP) receptor activation stimulates insulin secretion, enhances beta-cell proliferation, and reduces apoptosis. Moreover, potentiation of the endogenous postprandial levels of GLP-1 and GIP via inhibition of dipeptidyl peptidase-IV (DPP-IV) also expands beta-cell mass via related mechanisms. The thiazolidinediones (TZDs) enhance insulin sensitivity, reduce blood glucose levels, and also preserve beta-cell mass, although it remains unclear whether TZDs affect beta-cell mass via direct mechanisms. Complementary approaches to regeneration of beta-cell mass involve combinations of factors, exemplified by epidermal growth factor and gastrin, which promote islet neogenesis and ameliorate diabetes in rodent studies. Considerable preclinical data support the concept that one or more of these therapeutic approaches, alone or in combination, may potentially reverse the decline in beta-cell mass that is characteristic of the natural history of type 2 diabetes.
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Affiliation(s)
- Laurie L Baggio
- Department of Medicine, Toronto General Hospital, Banting and Best Diabetes Center, University of Toronto, Toronto, Ontario, Canada M5S 2S2
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161
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Abstract
Sulfonylureas are still largely used for treatment of type 2 diabetic patients, and they still occupy a central position in many international therapy guidelines. More recently concern has been raised with respect to possible adverse effects associated with the use of these agents. Sulfonylureas are, indeed, believed to favor the development of hypoglycemia, to accelerate beta cell apoptosis and beta-cell exhaustion, and to impair endothelial function with increased risk for ischemic complications. However, because of the intrinsic pathogenetic heterogeneity of type 2 diabetes, sulfonylureas are likely to remain a therapeutic option. Careful choice of a specific sulfonylurea should be made on the basis of efficacy, safety, convenience, tissue specificity, and neutrality with respect to the beta cell. In this review the advantage:disadvantage ratio of available sulfonylureas is analyzed with the purpose of providing a critical clinical appraisal of the role of sulfonylureas in the modern treatment of type 2 diabetes.
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Affiliation(s)
- Stefano Del Prato
- Department of Endocrinology and Metabolism, Section of Diabetes and Metabolic Diseases, University of Pisa, Italy.
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162
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Simmons RA. Developmental origins of diabetes: the role of oxidative stress. Free Radic Biol Med 2006; 40:917-22. [PMID: 16540386 DOI: 10.1016/j.freeradbiomed.2005.12.018] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/06/2005] [Revised: 12/14/2005] [Accepted: 12/16/2005] [Indexed: 12/13/2022]
Abstract
The "thrifty phenotype" hypothesis proposes that the fetus adapts to an adverse intrauterine milieu by optimizing the use of a reduced nutrient supply to ensure survival, but, by favoring the development of certain organs over that of others, this leads to persistent alterations in the growth and function of developing tissues. This concept has been somewhat controversial; however, recent epidemiological, clinical, and animal studies provide support for the developmental origins of disease hypothesis. Underlying mechanisms include reprogramming of the hypothalamic-pituitary-adrenal axis, islet development, and insulin signaling pathways. Emerging data suggest that oxidative stress and mitochondrial dysfunction may also play critical roles in the pathogenesis of type 2 diabetes in individuals who were growth retarded at birth.
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Affiliation(s)
- Rebecca A Simmons
- Department of Pediatrics, Children's Hospital Philadelphia and University of Pennsylvania, Philadelphia, PA 19104, USA.
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163
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Affiliation(s)
- Rebecca Simmons
- Department of Pediatrics, Children's Hospital of Philadelphia, Philadelphia, PA, USA.
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164
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Chen J, Jeppesen PB, Abudula R, Dyrskog SEU, Colombo M, Hermansen K. Stevioside does not cause increased basal insulin secretion or β-cell desensitization as does the sulphonylurea, glibenclamide: Studies in vitro. Life Sci 2006; 78:1748-53. [PMID: 16260001 DOI: 10.1016/j.lfs.2005.08.012] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2005] [Accepted: 08/10/2005] [Indexed: 10/25/2022]
Abstract
We have shown that stevioside (SVS) enhances insulin secretion and thus may have a potential role as antihyperglycemic agent in the treatment of type 2 diabetes mellitus. However, whether SVS stimulates basal insulin secretion (BIS) and/or cause desensitization of beta cells like sulphonylureas (SU), e.g. glibenclamide (GB), is not known. To explore and compare the effects of SVS pretreatment with those of GB and glucagon-like peptide-1 (GLP-1), we exposed isolated mouse islets to low or high glucose for 1 h after short-term (2 h) or long-term (24 h) pretreatment with SVS, GB or GLP-1, respectively. BIS at 3.3 or 5.5 mM glucose were not changed after short-term pretreatment with SVS (10(-7) M), while it increased about three folds after pretreatment with GB (10(-7) M). Glucose stimulated insulin secretion (GSIS) (16.7 mM) increased dose-dependently after long-term pretreatment with SVS at concentrations from 10(-7) to 10(-5) M. Pretreatment for 24 h with GB (10(-7) M) increased the subsequent BIS (3.3 mM glucose) (p < 0.001), but decreased GSIS (16.7 mM glucose) (p < 0.001). In contrast SVS (10(-7) M) and GLP-1 (10(-7) M) did not stimulate BIS but both enhanced the subsequent GSIS (16.7 mM glucose) (p < 0.05 and p < 0.05, respectively). While SVS pretreatment increased the intracellular insulin content, GB pretreatment decreased the insulin content. Our study suggests that SVS pretreatment does not cause a stimulation of BIS and does not desensitize beta-cells, i.e. SVS seems to have advantageous characteristics to GB as a potential treatment of type 2 diabetes.
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Affiliation(s)
- Jianguo Chen
- Department of Endocrinology and Metabolism, Aarhus Sygehus THG, Aarhus University Hospital, Tage-Hansens Gade 2, DK-8000 Aarhus C, Denmark.
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165
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Johansen A, Jensen DP, Bergholdt R, Mortensen HB, Pociot F, Nerup J, Hansen T, Pedersen O. IRS1, KCNJ11, PPARgamma2 and HNF-1alpha: do amino acid polymorphisms in these candidate genes support a shared aetiology between type 1 and type 2 diabetes? Diabetes Obes Metab 2006; 8:75-82. [PMID: 16367885 DOI: 10.1111/j.1463-1326.2005.00471.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
AIMS Type 1 diabetes mellitus (T1DM) is a chronic disorder primarily triggered by environmental and immunological factors in genetically susceptible individuals. Despite the fact that there are indications of common aetiological features of T1DM and type 2 diabetes (T2DM), variation in genes involved in insulin secretion and insulin signalling has to a large extent been ignored as potential modifiers in the pathogenesis of T1DM. Recent studies suggest, however, that proven T2DM susceptibility gene variants may be involved in the pathogenesis of T1DM. The objective of this study was to estimate the impact of four selected amino acid polymorphisms -IRS-1 Gly972Arg, Kir6.2 Glu23Lys, HNF-1alpha Ala98Val and PPARgamma2 Pro12Ala in a Danish population of T1DM families. METHODS All variants were genotyped in 490 simplex- and multiplex-T1DM families applying polymerase chain reaction-restriction fragment length polymorphism, and results were evaluated by means of a transmission disequilibrium test (TDT) analysis. RESULTS TDT analysis revealed that the Arg972 IRS-1, the Lys23 Kir6.2 and the Val98 HNF-1alpha variants were transmitted from heterozygous parents to affected probands at frequencies of 49.1%, 47.0% and 54.1%, respectively (p > 0.05 for all). This was similar to the rate of transmission to unaffected siblings. The transmission rate of the Ala12 PPARgamma2 variant to affected probands was 46.5% (p > 0.05) which differed significantly from the transmission to unaffected offspring (p = 0.024). A combined analysis of the present and published pertinent data of 1691 transmissions showed a significantly decreased transmission of the PPARgamma2 Ala12 allele to affected probands (p = 0.0045). CONCLUSIONS The Pro12Ala variant of PPARgamma2 is associated with T1DM, the minor Ala allele conferring a reduced risk. This same finding has been reported in patients with T2DM.
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Affiliation(s)
- A Johansen
- Steno Diabetes Center and Hagedorn Research Institute, Gentofte, Copenhagen, Denmark.
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166
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Donath MY, Ehses JA, Maedler K, Schumann DM, Ellingsgaard H, Eppler E, Reinecke M. Mechanisms of beta-cell death in type 2 diabetes. Diabetes 2005; 54 Suppl 2:S108-13. [PMID: 16306327 DOI: 10.2337/diabetes.54.suppl_2.s108] [Citation(s) in RCA: 328] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
A decrease in the number of functional insulin-producing beta-cells contributes to the pathophysiology of type 2 diabetes. Opinions diverge regarding the relative contribution of a decrease in beta-cell mass versus an intrinsic defect in the secretory machinery. Here we review the evidence that glucose, dyslipidemia, cytokines, leptin, autoimmunity, and some sulfonylureas may contribute to the maladaptation of beta-cells. With respect to these causal factors, we focus on Fas, the ATP-sensitive K+ channel, insulin receptor substrate 2, oxidative stress, nuclear factor-kappaB, endoplasmic reticulum stress, and mitochondrial dysfunction as their respective mechanisms of action. Interestingly, most of these factors are involved in inflammatory processes in addition to playing a role in both the regulation of beta-cell secretory function and cell turnover. Thus, the mechanisms regulating beta-cell proliferation, apoptosis, and function are inseparable processes.
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Affiliation(s)
- Marc Y Donath
- Division of Endocrinology and Diabetes, Department of Medicine, University Hospital, CH-8091 Zurich, Switzerland.
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167
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Hambrock A, de Oliveira Franz CB, Hiller S, Osswald H. Glibenclamide-induced apoptosis is specifically enhanced by expression of the sulfonylurea receptor isoform SUR1 but not by expression of SUR2B or the mutant SUR1(M1289T). J Pharmacol Exp Ther 2005; 316:1031-7. [PMID: 16306272 DOI: 10.1124/jpet.105.097501] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Sulfonylurea receptor 1 (SUR1) is the regulatory subunit of the pancreatic ATP-sensitive K+ channel (K(ATP) channel), which is essential for triggering insulin secretion via membrane depolarization. Sulfonylureas, such as glibenclamide and tolbutamide, act as K(ATP) channel blockers and are widely used in diabetes treatment. These antidiabetic substances are known to induce apoptosis in pancreatic beta-cells or beta-cell lines under certain conditions. However, the precise molecular mechanisms of this sulfonylurea-induced apoptosis are still unidentified. To investigate the role of SUR in apoptosis induction, we tested the effect of glibenclamide on recombinant human embryonic kidney 293 cells expressing either SUR1, the smooth muscular isoform SUR2B, or the mutant SUR1(M1289T) at which a single amino acid in transmembrane helix 17 (TM17) was exchanged by the corresponding amino acid of SUR2. By analyzing cell detachment, nuclear condensation, DNA fragmentation, and caspase-3-like activity, we observed a SUR1-specific enhancement of glibenclamide-induced apoptosis that was not seen in SUR2B, SUR1(M1289T), or control cells. Coexpression with the pore-forming Kir6.2 subunit did not significantly alter the apoptotic effect of glibenclamide on SUR1 cells. In conclusion, expression of SUR1, but not of SUR2B or SUR1(M1289T), renders cells more susceptible to glibenclamide-induced apoptosis. Therefore, SUR1 as a pancreatic protein could be involved in specific variation of beta-cell mass and might also contribute to the regulation of insulin secretion at this level. According to our results, TM17 is essentially involved in SUR1-mediated apoptosis. This effect does not require the presence of functional Kir6.2-containing K(ATP) channels, which points to additional, so far unknown functions of SUR.
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Affiliation(s)
- Annette Hambrock
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Tübingen, Germany.
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168
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Konarkowska B, Aitken JF, Kistler J, Zhang S, Cooper GJS. Thiol reducing compounds prevent human amylin-evoked cytotoxicity. FEBS J 2005; 272:4949-59. [PMID: 16176268 DOI: 10.1111/j.1742-4658.2005.04903.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Human amylin (hA) is a small fibrillogenic protein that is the major constituent of pancreatic islet amyloid, which occurs in most subjects with type-2 diabetes mellitus (T2Dm). There is growing evidence that hA toxicity towards islet beta-cells is responsible for their gradual loss of function in T2Dm. Preventing hA-mediated cytotoxicity has been proposed as a route to halt the progression of this disease, although this has not yet been demonstrated in vivo. The aim of our studies, in which we show that a small number of hA-treated cells exhibit intracellular accumulation of reactive oxygen species (ROS), was to evaluate the role of oxidative stress in the mechanism of hA-mediated cytotoxicity. Here we report that catalase and n-propyl gallate, antioxidants that are thought to act mainly as free radical scavengers, afford RINm5F cells only limited protection against hA-mediated toxicity. By contrast, the thiol antioxidants, N-acetyl-L-cysteine (NAC), GSH and dithiothreitol, which not only react with ROS, but also modulate the cellular redox potential by increasing intracellular levels of GSH and/or by acting as thiol reducing agents, afford almost complete protection and inhibit the progression of hA-evoked apoptosis. We also show that hA treatment is not associated with changes in intracellular GSH levels and that inhibition of GSH biosynthesis has no effect on either hA-mediated cytotoxicity or NAC-mediated protection. These results indicate that, in addition to the induction of oxidative stress, hA appears to mediate cytotoxicity through signalling pathways that are sensitive to the actions of thiol antioxidants.
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169
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Mellado-Gil JM, Aguilar-Diosdado M. Assay for high glucose-mediated islet cell sensitization to apoptosis induced by streptozotocin and cytokines. Biol Proced Online 2005; 7:162-71. [PMID: 16281079 PMCID: PMC1280327 DOI: 10.1251/bpo113] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2005] [Revised: 10/10/2005] [Accepted: 10/11/2005] [Indexed: 12/24/2022] Open
Abstract
Pancreatic beta-cell apoptosis is known to participate in the beta-cell destruction process that occurs in diabetes. It has been described that high glucose level induces a hyperfunctional status which could provoke apoptosis. This phenomenon is known as glucotoxicity and has been proposed that it can play a role in type 1 diabetes mellitus pathogenesis. In this study we develop an experimental design to sensitize pancreatic islet cells by high glucose to streptozotocin (STZ) and proinflammatory cytokines [interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma]-induced apoptosis. This method is appropriate for subsequent quantification of apoptotic islet cells stained with Tdt-mediated dUTP Nick-End Labeling (TUNEL) and protein expression assays by Western Blotting (WB).
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Affiliation(s)
- Jose M. Mellado-Gil
- Endocrinology Service and Research Unit, Puerta del Mar Hospital. Cadiz. Spain
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170
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Ansar MM, Ansari M. Nitric oxide involvement in pancreatic beta cell apoptosis by glibenclamide. Nitric Oxide 2005; 14:39-44. [PMID: 16256381 DOI: 10.1016/j.niox.2005.09.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2005] [Revised: 09/04/2005] [Accepted: 09/09/2005] [Indexed: 01/09/2023]
Abstract
Glibenclamide as a second-generation compound of sulfonylurea has widely been used in the treatment of type 2 diabetes patients. It has been shown that it induces apoptosis in beta cells, which is partially mediated by Ca(2+) influx. Here, we investigated the role of nitric oxide (NO) and nitric oxide synthase (NOS) isoforms on glibenclamide-induced apoptosis in rat insulinoma cells. Our results showed that glibenclamide induces NO generation (measured as nitrite) that is accompanied with decrease of cell viability in a defined concentration of glibenclamide. The effects of glibenclamide on cell viability were partially inhibited after treatment with N(G)-nitro-L-arginine methyl ester (L-NAME), inhibitor more selective for constitutive nitric oxide synthase, and in the presence of D600--a blocker of voltage-gated L-type Ca(2+) channels inhibited Ca(2+) influx into beta cells, whereas aminoguanidine (AG), a preferential inhibitor of inducible NOS, was significantly less effective. Analysis of DNA fragmentation by electrophoresis and staining with Hoechest 33342 and propidium iodide showed that L-NAME, but not AG, prevented DNA fragmentation and decreased the number of cells with condensed and fragmented nuclei. It revealed that the effects of glibenclamide on apoptosis were partially inhibited by treatment with L-NAME. In conclusion, we have shown that NO production in glibenclamide treated cells may be involved in the induction of apoptotic cell death in pure beta cell line and it may be due to Ca(2+) dependent activation of constitutive NOS isoforms.
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Affiliation(s)
- Malek Moien Ansar
- Department of Clinical Biochemistry, Faculty of Medicine, Tehran University of Medical Sciences, Iran.
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171
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Abstract
Congenital hyperinsulinism is a cause of persistent hypoglycaemia in the neonatal period. It is a heterogeneous disease with respect to clinical presentation, molecular biology, genetic aetiology and response to medical therapy. The clinical heterogeneity may range from severe life-threatening disease to very mild clinical symptoms. Recent advances have begun to clarify the molecular pathophysiology of this disease, but despite these advances treatment options remain difficult and there are many long-term complications. So far mutations in five different genes have been identified in patients with congenital hyperinsulinism. Most cases are caused by mutations in genes coding for either of the two subunits of the beta-cell K(ATP) channel (ABCC8 and KCNJ11). Two histological subtypes of the disease - diffuse and focal - have been described. The preoperative histological differentiation of these two subtypes is now mandatory as surgical management will be radically different. The ability to distinguish diffuse from focal lesions has profound implications for therapeutic approaches, prognosis and genetic counselling.
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Affiliation(s)
- K Hussain
- The Institute of Child Health, Unit of Biochemistry, Endocrinology and Metabolism, University College London, 30 Guilford Street, London WC1N 1EH, UK.
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172
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Størling J, Zaitsev SV, Kapelioukh IL, Karlsen AE, Billestrup N, Berggren PO, Mandrup-Poulsen T. Calcium has a permissive role in interleukin-1beta-induced c-jun N-terminal kinase activation in insulin-secreting cells. Endocrinology 2005; 146:3026-36. [PMID: 15831571 DOI: 10.1210/en.2005-0036] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The c-jun N-terminal kinase (JNK) signaling pathway mediates IL-1beta-induced apoptosis in insulin-secreting cells, a mechanism relevant to the destruction of pancreatic beta-cells in type 1 and 2 diabetes. However, the mechanisms that contribute to IL-1beta activation of JNK in beta-cells are largely unknown. In this study, we investigated whether Ca(2+) plays a role for IL-1beta-induced JNK activation. In insulin-secreting rat INS-1 cells cultured in the presence of 11 mm glucose, combined pharmacological blockade of L- and T-type Ca(2+) channels suppressed IL-1beta-induced in vitro phosphorylation of the JNK substrate c-jun and reduced IL-1beta-stimulated activation of JNK1/2 as assessed by immunoblotting. Inhibition of IL-1beta-induced in vitro kinase activity toward c-jun after collective L- and T-type Ca(2+) channel blockade was confirmed in primary rat and ob/ob mouse islets and in mouse betaTC3 cells. Ca(2+) influx, specifically via L-type but not T-type channels, contributed to IL-1beta activation of JNK. Activation of p38 and ERK in response to IL-1beta was also dependent on L-type Ca(2+) influx. Membrane depolarization by KCl, exposure to high glucose, treatment with Ca(2+) ionophore A23187, or exposure to thapsigargin, an inhibitor of sarco(endo)plasmic reticulum Ca(2+) ATPase, all caused an amplification of IL-1beta-induced JNK activation in INS-1 cells. Finally, a chelator of intracellular free Ca(2+) [bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid-acetoxymethyl], an inhibitor of calmodulin (W7), and inhibitors of Ca(2+)/calmodulin-dependent kinase (KN62 and KN93) partially reduced IL-1beta-stimulated c-jun phosphorylation in INS-1 or betaTC3 cells. Our data suggest that Ca(2+) plays a permissive role in IL-1beta activation of the JNK signaling pathway in insulin-secreting cells.
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Affiliation(s)
- Joachim Størling
- Laboratory for Beta-Cell Biology, Steno Diabetes Center, Niels Steensensvej 8, NSPP, DK-2820 Gentofte, Denmark.
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173
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Maedler K, Donath MY. Beta-cells in type 2 diabetes: a loss of function and mass. HORMONE RESEARCH 2005; 62 Suppl 3:67-73. [PMID: 15539803 DOI: 10.1159/000080503] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Type 2 diabetes mellitus manifests itself in individuals who lose the ability to produce sufficient amounts of insulin to maintain normoglycaemia in the face of insulin resistance. The ability to secrete adequate amounts of insulin depends on beta-cell function and mass. Chronic hyperglycaemia is detrimental to pancreatic beta-cells, causing impaired insulin secretion and playing an essential role in the regulation of beta-cell turnover. This paper will address the effect of chronically elevated glucose levels on beta-cell turnover and function. In previous studies we have shown that elevated glucose concentrations induce apoptosis in human beta-cells due to an interaction between constitutively expressed Fas ligand and upregulated Fas. Human beta-cells produce interleukin (IL)-1beta in response to high glucose concentrations, independently of an immune-mediated process. This was antagonized by the IL-1 receptor antagonist (IL-1Ra), a naturally occurring anti-inflammatory cytokine also found in the beta-cell. Therefore the balance of IL-1beta and IL-1Ra may play a crucial role in the pathogenesis of diabetes. Inhibition of glucotoxicity represents a promising therapeutic stratagem in diabetes therapy to preserve functional beta-cell mass.
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Affiliation(s)
- K Maedler
- Division of Endocrinology and Diabetes, University Hospital Zürich, Switzerland.
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174
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Simmons RA, Suponitsky-Kroyter I, Selak MA. Progressive accumulation of mitochondrial DNA mutations and decline in mitochondrial function lead to beta-cell failure. J Biol Chem 2005; 280:28785-91. [PMID: 15946949 DOI: 10.1074/jbc.m505695200] [Citation(s) in RCA: 160] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
A key adaptation enabling the fetus to survive in a limited energy environment may be the reprogramming of mitochondrial function, which can have deleterious effects. Critical questions are whether mitochondrial dysfunction progressively declines after birth, and if so, what mechanism might underlie this process. To address this, we developed a model of intrauterine growth retardation (IUGR) in the rat that leads to diabetes in adulthood. Reactive oxygen species (ROS) production and oxidative stress gradually increased in IUGR islets. ATP production was impaired and continued to deteriorate with age. The activities of complex I and III of the electron transport chain progressively declined in IUGR islets. Mitochondrial DNA point mutations accumulated with age and were associated with decreased mitochondrial DNA content and reduced expression of mitochondria-encoded genes in IUGR islets. Mitochondrial dysfunction resulted in impaired insulin secretion. These results demonstrate that IUGR induces mitochondrial dysfunction in the fetal beta-cell, leading to increased production of ROS, which in turn damage mitochondrial DNA. A self-reinforcing cycle of progressive deterioration in mitochondrial function leads to a corresponding decline in beta-cell function. Finally, a threshold in mitochondrial dysfunction and ROS production is reached, and diabetes ensues.
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Affiliation(s)
- Rebecca A Simmons
- Department of Pediatrics Children's Hospital Philadelphia and University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
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175
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Hussain K, Cosgrove KE. From congenital hyperinsulinism to diabetes mellitus: the role of pancreatic beta-cell KATP channels. Pediatr Diabetes 2005; 6:103-13. [PMID: 15963039 DOI: 10.1111/j.1399-543x.2005.00109.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Pancreatic beta-cell adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channels play a pivotal role in linking glucose metabolism to regulated insulin secretion. K(ATP) channels are hetero-octameric complexes comprising two subunits Kir6.2 and sulfonylurea receptor 1 (SUR1). Changes in the intracellular concentration of nucleotides (ATP) cause alterations in the resting and opening state of the K(ATP) channels. Loss-of-function mutations in the genes encoding the two subunits of K(ATP) channels lead to the most common form of congenital hyperinsulinism (CHI). This causes persistent and severe hypoglycemia in the neonatal and infancy period. CHI can cause mental retardation and epilepsy if not treated properly. On the other hand, now there is evidence of an association between polymorphisms in the Kir6.2 gene and type 2 diabetes mellitus, mutations in the Kir6.2 gene and neonatal diabetes mellitus, and mutations in the SUR1 gene and diabetes mellitus. Interestingly, for reasons that are unclear at present, mice knockout models of K(ATP) channels are different from the human phenotype of CHI. This article is a review focusing on how abnormalities in the pancreatic beta-cell K(ATP) channels can lead to severe hypoglycemia on the one hand and diabetes mellitus on the other.
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Affiliation(s)
- Khalid Hussain
- The London Centre for Paediatric Endocrinology and Metabolism, Great Ormond Street Hospital for Children NHS Trust, London, UK.
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176
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Elouil H, Cardozo AK, Eizirik DL, Henquin JC, Jonas JC. High glucose and hydrogen peroxide increase c-Myc and haeme-oxygenase 1 mRNA levels in rat pancreatic islets without activating NFkappaB. Diabetologia 2005; 48:496-505. [PMID: 15739117 DOI: 10.1007/s00125-004-1664-4] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/12/2004] [Accepted: 11/12/2004] [Indexed: 01/09/2023]
Abstract
AIMS/HYPOTHESIS Hyperglycaemia and the pro-inflammatory cytokine IL-1beta induce similar alterations of beta cell gene expression, including up-regulation of c-Myc and haeme-oxygenase 1. These effects of hyperglycaemia may result from nuclear factor-kappa B (NFkappaB) activation by oxidative stress. To test this hypothesis, we compared the effects of IL-1beta, high glucose, and hydrogen peroxide, on NFkappaB DNA binding activity and target gene mRNA levels in cultured rat islets. METHODS Rat islets were pre-cultured for 1 week in serum-free RPMI medium containing 10 mmol/l glucose, and further cultured in glucose concentrations of 5-30 mmol/l plus various test substances. Islet NFkappaB activity was measured by ELISA and gene mRNA expression was measured by RT-PCR. RESULTS IL-1beta consistently increased islet NFkappaB activity and c-Myc, haeme-oxygenase 1, inducible nitric oxide synthase (iNOS), Fas, and inhibitor of NFkappaB alpha (IkappaBalpha) mRNA levels. In comparison, 1- to 7-day culture in 30 mmol/l instead of 10 mmol/l glucose stimulated islet c-Myc and haeme-oxygenase 1 expression without affecting NFkappaB activity or iNOS and IkappaBalpha mRNA levels. Fas mRNA levels only increased after 1 week in 30 mmol/l glucose. Overnight exposure to hydrogen peroxide mimicked the effects of 30 mmol/l glucose on haeme-oxygenase 1 and c-Myc mRNA levels without activating NFkappaB. On the other hand, the antioxidant N-acetyl-L-cysteine inhibited the stimulation of haeme-oxygenase 1 and c-Myc expression by 30 mmol/l glucose and/or hydrogen peroxide. CONCLUSIONS/INTERPRETATION In contrast to IL-1beta, high glucose and hydrogen peroxide do not activate NFkappaB in cultured rat islets. It is suggested that the stimulation of islet c-Myc and haeme-oxygenase 1 expression by 30 mmol/l glucose results from activation of a distinct, probably oxidative-stress-dependent signalling pathway.
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Affiliation(s)
- H Elouil
- Endocrinology and Metabolism, Université Catholique de Louvain (UCL), 55.30, Avenue Hippocrate, 55, 1200, Brussels, Belgium
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177
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Abstract
The beta-cell is equipped with at least six voltage-gated Ca2+ (CaV) channel alpha1-subunits designated CaV1.2, CaV1.3, CaV2.1, CaV2.2, CaV2.3, and CaV3.1. These principal subunits, together with certain auxiliary subunits, assemble into different types of CaV channels conducting L-, P/Q-, N-, R-, and T-type Ca2+ currents, respectively. The beta-cell shares customary mechanisms of CaV channel regulation with other excitable cells, such as protein phosphorylation, Ca2+-dependent inactivation, and G protein modulation. However, the beta-cell displays some characteristic features to bring these mechanisms into play. In islet beta-cells, CaV channels can be highly phosphorylated under basal conditions and thus marginally respond to further phosphorylation. In beta-cell lines, CaV channels can be surrounded by tonically activated protein phosphatases dominating over protein kinases; thus their activity is dramatically enhanced by inhibition of protein phosphatases. During the last 10 years, we have revealed some novel mechanisms of beta-cell CaV channel regulation under physiological and pathophysiological conditions, including the involvement of exocytotic proteins, inositol hexakisphosphate, and type 1 diabetic serum. This minireview highlights characteristic features of customary mechanisms of CaV channel regulation in beta-cells and also reviews our studies on newly identified mechanisms of beta-cell CaV channel regulation.
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Affiliation(s)
- Shao-Nian Yang
- The Rolf Luft Center for Diabetes Research, Karolinska Diabetes Center, Department of Molecular Medicine, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
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178
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Kaiser N, Yuli M, Uçkaya G, Oprescu AI, Berthault MF, Kargar C, Donath MY, Cerasi E, Ktorza A. Dynamic changes in {beta}-cell mass and pancreatic insulin during the evolution of nutrition-dependent diabetes in psammomys obesus: impact of glycemic control. Diabetes 2005; 54:138-45. [PMID: 15616021 DOI: 10.2337/diabetes.54.1.138] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Recent studies ascribe a major role to pancreatic beta-cell loss in type 2 diabetes. We investigated the dynamics of beta-cell mass during diabetes evolution in Psammomys obesus, a model for nutrition-dependent type 2 diabetes, focusing on the very early and the advanced stages of the disease. P. obesus fed a high-calorie diet for 26 days developed severe hyperglycemia, beta-cell degranulation, and markedly reduced pancreatic insulin content. Reducing calories for 7 days induced normoglycemia in 90% of the animals, restoring beta-cell granulation and insulin content. To dissociate effects of diet from blood glucose reduction, diabetic animals received phlorizin for 2 days, which normalized glycemia and increased the pancreatic insulin reserve to 50% of control, despite a calorie-rich diet. During diabetes progression, beta-cell mass decreased initially but recovered spontaneously to control levels, despite persistent hyperglycemia. Strikingly, however, beta-cell mass did not correlate with degree of hyperglycemia or pancreatic insulin content. We conclude that reduced insulin reserve is the main cause of diabetes progression, whereas irreversible beta-cell mass reduction is a late event in P. obesus. The rapid recovery of the pancreas by phlorizin-induced normoglycemia implies a causal relationship between hyperglycemia and islet dysfunction. Similar mechanisms could be operative during the evolution of type 2 diabetes in humans.
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Affiliation(s)
- Nurit Kaiser
- Endocrinology and Metabolism Service, Department of Medicine, Hadassah-Hebrew University Medical Center, P.O. Box 12000, Jerusalem 91120, Israel.
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179
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Abstract
Insufficient pancreatic beta-cell mass is fundamental to the pathogenesis of both types 1 and 2 diabetes and constitutes the basis for the goal of beta-cell replacement therapy. Current methods for isolating islets from organ donor pancreases do not come close to supplying all in need, thus providing a compelling need to find new sources of insulin-producing cells. Possible sources include generation of cells from embryonic stem cells (ESC), adult stem/precursor cells, transdifferentiation of other cell types and xenodonors. Bioengineering can be used to improve secretory performance and strengthen cells to better withstand the challenges of transplantation. Strategies include protection against hypoxia, inflammation, and immune attack.
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Affiliation(s)
- Gordon C Weir
- Section on Islet Transplantation and Cell Biology, Joslin Diabetes Center, Harvard Medical School, One Joslin Place, Boston, MA 02215, USA.
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180
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Rustenbeck I, Wienbergen A, Bleck C, Jörns A. Desensitization of insulin secretion by depolarizing insulin secretagogues. Diabetes 2004; 53 Suppl 3:S140-50. [PMID: 15561902 DOI: 10.2337/diabetes.53.suppl_3.s140] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Prolonged stimulation of insulin secretion by depolarization and Ca2+ influx regularly leads to a reversible state of decreased secretory responsiveness to nutrient and nonnutrient stimuli. This state is termed "desensitization." The onset of desensitization may occur within 1 h of exposure to depolarizing stimuli. Desensitization by exposure to sulfonylureas, imidazolines, or quinine produces a marked cross-desensitization against other ATP-sensitive K+ channel (KATP channel)-blocking secretagogues. However, desensitized beta-cells do not necessarily show changes in KATP channel activity or Ca2+ handling. Care has to be taken to distinguish desensitization-induced changes in signaling from effects due to the persisting presence of secretagogues. The desensitization by depolarizing secretagogues is mostly accompanied by a reduced content of immunoreactive insulin and a marked reduction of secretory granules in the beta-cells. In vitro recovery from a desensitization by the imidazoline efaroxan was nearly complete after 4 h. At this time point the depletion of the granule content was partially reversed. Apparently, recovery from desensitization affects the whole lifespan of a granule from biogenesis to exocytosis. There is, however, no direct relation between the beta-cell granule content and the secretory responsiveness. Even though a prolonged exposure of isolated islets to depolarizing secretagogues is often associated with the occurrence of ultrastructural damage to beta-cells, we could not find a cogent link between depolarization and Ca2+ influx and apoptotic or necrotic beta-cell death.
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Affiliation(s)
- Ingo Rustenbeck
- Institute of Pharmacology and Toxicology, University of Braunschweig, Mendelssohnstr. 1, D-38106 Braunschweig, Germany.
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181
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Briaud I, Dickson LM, Lingohr MK, McCuaig JF, Lawrence JC, Rhodes CJ. Insulin receptor substrate-2 proteasomal degradation mediated by a mammalian target of rapamycin (mTOR)-induced negative feedback down-regulates protein kinase B-mediated signaling pathway in beta-cells. J Biol Chem 2004; 280:2282-93. [PMID: 15537654 DOI: 10.1074/jbc.m412179200] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Regulation of insulin receptor substrate (IRS)-2 expression is critical to beta-cell survival, but the mechanisms that control this are complex and undefined. Here in pancreatic beta-cells (INS-1), chronic exposure (>8 h) to 15 mm glucose and/or 5 nm IGF-1, increased Ser/Thr phosphorylation of IRS-2, which correlated with decreased IRS-2 levels. This glucose/IGF-1-induced decrease in IRS-2 levels was prevented by the proteasomal inhibitor, lactacystin. In addition, the glucose/IGF-1-induced increase in Ser/Thr phosphorylation of IRS-2 and the subsequent decrease in INS-1 cell IRS-2 protein levels was thwarted by the mammalian target of rapamycin(mTOR) inhibitor, rapamycin. Moreover, adenoviral-mediated expression of constitutively active mTOR (mTORDelta) further increased glucose/IGF-1-induced Ser/Thr phosphorylation of IRS-2 and decreased IRS-2 protein levels, whereas adenoviral-mediated expression of "kinase-dead" mTOR (mTOR-KD) conversely reduced Ser/Thr phosphorylation of IRS-2 and maintained IRS-2 protein levels. In adenoviral-infected beta-cells expressing mTORDelta, the decrease in IRS-2 protein levels was also prevented by rapamycin or lactacystin, further indicating a proteasomal mediated degradation of IRS-2 mediated via mTOR-induced Ser/Thr phosphorylation of IRS-2. Finally, we found that chronic activation of mTOR leading to decreased levels of IRS-2 in INS-1 cells led to a significant decrease in PKB activation and consequently increased beta-cell apoptosis. Thus, chronic activation of mTOR by glucose (and/or IGF-1) in beta-cells leads to increased Ser/Thr phosphorylation of IRS-2 that targets it for proteasomal degradation, resulting in decreased IRS-2 expression and increased beta-cell apoptosis. This may be a contributing mechanism as to how beta-cell mass is decreased by chronic hyperglycemia in the pathogenesis of type-2 diabetes.
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Affiliation(s)
- Isabelle Briaud
- Pacific Northwest Research Institute, and Department of Pharmacology, University of Washington, Seattle, Washington 98122, USA
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182
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Topp BG, McArthur MD, Finegood DT. Metabolic adaptations to chronic glucose infusion in rats. Diabetologia 2004; 47:1602-10. [PMID: 15349726 DOI: 10.1007/s00125-004-1493-5] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/06/2004] [Accepted: 05/14/2004] [Indexed: 12/17/2022]
Abstract
AIMS/HYPOTHESIS Several studies have employed the chronic glucose infusion protocol to quantify the metabolic adaptations associated with a prolonged glucose challenge. However, the limited number of indices and time points reported by these studies has generated an incomplete picture of this process. In this study we aimed to generate an integrative and dynamic picture of the physiological adaptations that occur during chronic glucose infusion. METHODS Sprague-Dawley rats were infused with either 50% dextrose or saline (2 ml/h) for a period of between 0 and 6 days. Glucose, insulin and NEFA dynamics were determined from daily blood samples. Subsets of animals were killed daily for histological determination of beta cell mass, size and replication rates. The mathematical model of coupled beta cell mass, insulin and glucose (the betaIG model) was used to estimate insulin sensitivity, beta cell function and net neogenesis from this data. RESULTS Glucose-infused rats displayed transient hyperglycaemia, persistent hyperinsulinaemia and unchanged NEFA levels. Insulin sensitivity decreased by approximately 80% during the first day of glucose infusion, but had returned to pre-infusion levels by Day 3. Beta cell function was four to six times higher than in control rats throughout the experiment. Beta cell mass doubled over the 6 days of glucose infusion due to three phases of adaptation: (i) neogenesis; (ii) hypertrophy and hyperplasia; and (iii) continued hyperplasia coupled to a second wave of neogenesis. CONCLUSIONS/INTERPRETATION Contrary to the results reported for perfused pancreas and in vitro experiments, we found that chronic glucose infusion elevated beta cell function. The prediction of a second wave of beta cell neogenesis, coupled with our previous report of "focal areas" on Day 3, suggests the existence of delayed acinar-to-islet transdifferentiation.
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Affiliation(s)
- B G Topp
- Diabetes Research Laboratory, School of Kinesiology, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada V5A 1S6
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183
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Chang I, Cho N, Kim S, Kim JY, Kim E, Woo JE, Nam JH, Kim SJ, Lee MS. Role of calcium in pancreatic islet cell death by IFN-gamma/TNF-alpha. THE JOURNAL OF IMMUNOLOGY 2004; 172:7008-14. [PMID: 15153522 DOI: 10.4049/jimmunol.172.11.7008] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We studied the intracellular events associated with pancreatic beta cell apoptosis by IFN-gamma/TNF-alpha synergism. IFN-gamma/TNF-alpha treatment of MIN6N8 insulinoma cells increased the amplitude of high voltage-activated Ca(2+) currents, while treatment with IFN-gamma or TNF-alpha alone did not. Cytosolic Ca(2+) concentration ([Ca(2+)](c)) was also increased by IFN-gamma/TNF-alpha treatment. Blockade of L-type Ca(2+) channel by nifedipine abrogated death of insulinoma cells by IFN-gamma/TNF-alpha. Diazoxide that attenuates voltage-activated Ca(2+) currents inhibited MIN6N8 cell death by IFN-gamma/TNF-alpha, while glibenclamide that accentuates voltage-activated Ca(2+) currents augmented insulinoma cell death. A protein kinase C inhibitor attenuated MIN6N8 cell death and the increase in [Ca(2+)](c) by IFN-gamma/TNF-alpha. Following the increase in [Ca(2+)](c), calpain was activated, and calpain inhibitors decreased insulinoma cell death by IFN-gamma/TNF-alpha. As a downstream of calpain, calcineurin was activated and the inhibition of calcineurin activation by FK506 diminished insulinoma cell death by IFN-gamma/TNF-alpha. BAD phosphorylation was decreased by IFN-gamma/TNF-alpha because of the increased calcineurin activity, which was reversed by FK506. IFN-gamma/TNF-alpha induced cytochrome c translocation from mitochondria to cytoplasm and activation of caspase-9. Effector caspases such as caspase-3 or -7 were also activated by IFN-gamma/TNF-alpha treatment. These results indicate that IFN-gamma/TNF-alpha synergism induces pancreatic beta cell apoptosis by Ca(2+) channel activation followed by downstream intracellular events such as mitochondrial events and caspase activation and also suggest the therapeutic potential of Ca(2+) modulation in type 1 diabetes.
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Affiliation(s)
- Inik Chang
- Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
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184
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Khaldi MZ, Guiot Y, Gilon P, Henquin JC, Jonas JC. Increased glucose sensitivity of both triggering and amplifying pathways of insulin secretion in rat islets cultured for 1 wk in high glucose. Am J Physiol Endocrinol Metab 2004; 287:E207-17. [PMID: 15100093 DOI: 10.1152/ajpendo.00426.2003] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Chronic hyperglycemia has been shown to induce either a lack of response or an increased sensitivity to glucose in pancreatic beta-cells. We reinvestigated this controversial issue in a single experimental model by culturing rat islets for 1 wk in 10 or 30 mmol/l glucose (G10, Controls; or G30, High-glucose islets) before testing the effect of stepwise glucose stimulation from G0.5 to G20 on key beta-cell stimulus-secretion coupling events. Compared with Controls, the glucose sensitivity of High-glucose islets was markedly increased, leading to maximal stimulation of oxidative metabolism and both triggering and amplifying pathways of insulin secretion in G6 rather than G20, hence to loss of glucose effect above G6. This enhanced glucose sensitivity occurred despite an approximately twofold increase in islet uncoupling protein 2 mRNA expression. Besides this increased glucose sensitivity, the maximal glucose stimulation of insulin secretion in High-glucose islets was reduced by approximately 50%, proportionally to the reduction of insulin content. In High-glucose islets, changes in (45)Ca(2+) influx induced by glucose and diazoxide were qualitatively similar but quantitatively smaller than in Control islets and, paradoxically, did not lead to detectable changes in the intracellular Ca(2+) concentration measured by microspectrofluorimetry (fura PE 3). In conclusion, after 1 wk of culture in G30, the loss of glucose stimulation of insulin secretion in the physiological range of glucose concentrations (G5-G10) results from the combination of an increased sensitivity to glucose of both triggering and amplifying pathways of insulin secretion and an approximately 50% reduction in the maximal glucose stimulation of insulin secretion.
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Affiliation(s)
- M Z Khaldi
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, Brussels, Belgium
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185
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Abstract
Insulin remains the most effective and durable drug in the armamentarium for the treatment of advanced-stage diabetes. Nevertheless, clinical studies have shown that even on insulin treatment, a significant percentage of patients fail to attain lasting glycemic control. Well-recognized reasons for this failure include issues related to patients' noncompliance with an injectable drug and the late stage at which insulin is prescribed, but less explicit reasons related to the nonphysiological way insulin is currently administered are equally important. Parenteral insulin targets peripheral tissue rather than the liver with pharmacokinetics that do not replicate the normal dynamics of endogenous insulin release. Oral insulin is one of several alternative methods of insulin administration that are in clinical stages of development. The oral route of insulin delivery takes advantage of the portal-hepatic route of absorption. A review of relevant physiology is herewith provided.
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Affiliation(s)
- Ehud Arbit
- Emisphere Technologies, Inc., Tarrytown, New York 10591, USA.
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186
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Chae SY, Kim YY, Kim SW, Bae YH. Prolonged Glucose Normalization of Streptozotocin-Induced Diabetic Mice by Transplantation of Rat Islets Coencapsulated with Crosslinked Hemoglobin. Transplantation 2004; 78:392-7. [PMID: 15316367 DOI: 10.1097/01.tp.0000128617.14309.26] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
BACKGROUND Facilitated oxygen transport by crosslinked hemoglobin (Hb-C) in islet microcapsules may promote transplanted graft function by improving islet functionality and viability. METHODS This study investigated the in vivo efficacy of Hb-C as an oxygen carrier on the functionality and viability of microencapsulated rat islets. Hb-C by poly(ethylene glycol) was introduced into rat islet microcapsules (alginate-poly[L-lysine]-alginate microcapsule), and 500 suboptimal encapsulated islets were xenotransplanted into each streptozotocin-induced diabetic BALB/c mouse. The graft efficacy over time was evaluated by measuring nonfasting blood glucose level, body weight, and glucose tolerance. RESULTS Mice that received Hb-C-containing microcapsules maintained normoglycemia for at least 8 weeks with normal glucose clearance, determined by intraperitoneal glucose tolerance test. However, the mice that received the conventional control islet microcapsule (without Hb-C) transplant showed graft failure in 4 weeks, exhibited by hyperglycemia, weight loss, and deteriorated glucose tolerance. Severe central necrosis of retrieved islets was observed for the control islet capsule graft after 8 weeks. CONCLUSION The present study revealed that the incorporation of Hb-C in islet microcapsules promotes graft function for a longer period of time than the conventional islet capsules. Therefore, Hb-C coencapsulation is a potential approach for prolonging graft function of islet microcapsules and reducing the number of islets required for normoglycemia.
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Affiliation(s)
- Su Young Chae
- Department of Pharmaceutics and Pharmaceutical Chemistry, University of Utah, Salt Lake City, USA
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187
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Maedler K, Størling J, Sturis J, Zuellig RA, Spinas GA, Arkhammar POG, Mandrup-Poulsen T, Donath MY. Glucose- and interleukin-1beta-induced beta-cell apoptosis requires Ca2+ influx and extracellular signal-regulated kinase (ERK) 1/2 activation and is prevented by a sulfonylurea receptor 1/inwardly rectifying K+ channel 6.2 (SUR/Kir6.2) selective potassium channel opener in human islets. Diabetes 2004; 53:1706-13. [PMID: 15220194 DOI: 10.2337/diabetes.53.7.1706] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Increasing evidence indicates that a progressive decrease in the functional beta-cell mass is the hallmark of both type 1 and type 2 diabetes. The underlying causes, beta-cell apoptosis and impaired secretory function, seem to be partly mediated by macrophage production of interleukin (IL)-1beta and/or high-glucose-induced beta-cell production of IL-1beta. Treatment of type 1 and type 2 diabetic patients with the potassium channel opener diazoxide partially restores insulin secretion. Therefore, we studied the effect of diazoxide and of the novel potassium channel opener NN414, selective for the beta-cell potassium channel SUR1/Kir6.2, on glucose- and IL-1beta-induced apoptosis and impaired function in human beta-cells. Exposure of human islets for 4 days to 11.1 and 33.3 mmol/l glucose, 2 ng/ml IL-1beta, or 10 and 100 micromol/l of the sulfonylurea tolbutamide induced beta-cell apoptosis and impaired glucose-stimulated insulin secretion. The deleterious effects of glucose and IL-1beta were blocked by 200 micromol/l diazoxide as well as by 3 and 30 micromol/l NN414. By Western blotting with phosphospecific antibodies, glucose and IL-1beta were shown to activate the extracellular signal-regulated kinase (ERK) 1/2, an effect that was abrogated by 3 micromol/l NN414. Similarly, 1 micromol/l of the mitogen-activated protein kinase/ERK kinase 1/2 inhibitor PD098059 or 1 micromol/l of the l-type Ca(2+) channel blocker nimodipine prevented glucose- and IL-1beta-induced ERK activation, beta-cell apoptosis, and impaired function. Finally, islet release of IL-1beta in response to high glucose could be abrogated by nimodipine, NN414, or PD098059. Thus, in human islets, glucose- and IL-1beta-induced beta-cell secretory dysfunction and apoptosis are Ca(2+) influx and ERK dependent and can be prevented by the beta-cell selective potassium channel opener NN414.
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Affiliation(s)
- Kathrin Maedler
- Division of Endocrinology and Diabetes, Department of Medicine, University Hospital, CH-8091 Zurich, Switzerland
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188
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Butler AE, Jang J, Gurlo T, Carty MD, Soeller WC, Butler PC. Diabetes due to a progressive defect in beta-cell mass in rats transgenic for human islet amyloid polypeptide (HIP Rat): a new model for type 2 diabetes. Diabetes 2004; 53:1509-16. [PMID: 15161755 DOI: 10.2337/diabetes.53.6.1509] [Citation(s) in RCA: 203] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The islet in type 2 diabetes is characterized by a deficit in beta-cell mass, increased beta-cell apoptosis, and impaired insulin secretion. Also, islets in type 2 diabetes often contain deposits of islet amyloid derived from islet amyloid polypeptide (IAPP), a 37-amino acid protein cosecreted with insulin by beta-cells. Several lines of evidence suggest that proteins with a capacity to develop amyloid fibrils may also form small toxic oligomers that can initiate apoptosis. The amino acid sequence of IAPP in rats and mice is identical and differs from that in humans by substitution of proline residues in the amyloidogenic sequence so that the protein no longer forms amyloid fibrils or is cytotoxic. In the present study, we report a novel rat model for type 2 diabetes: rats transgenic for human IAPP (the HIP rat). HIP rats develop diabetes between 5 and 10 months of age, characterized by an approximately 60% deficit in beta-cell mass that is due to an increased frequency of beta-cell apoptosis. HIP rats develop islet amyloid, but the extent of amyloid was not related to the frequency of beta-cell apoptosis (r = 0.10, P = 0.65), whereas the fasting blood glucose was (r = 0.77, P < 0.001). The frequency of beta-cell apoptosis was related to the frequency of beta-cell replication (r = 0.97, P < 0.001) in support of the hypothesis that replicating cells are more vulnerable to apoptosis than nondividing cells. The HIP rat provides additional evidence in support of the potential role of IAPP oligomer formation toward the increased frequency of apoptosis in type 2 diabetes, a process that appears to be compounded by glucose toxicity when hyperglycemia supervenes.
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Affiliation(s)
- Alexandra E Butler
- Larry Hillblom Islet Research Center, UCLA David Geffen School of Medicine, 24-130 Warren Hall, 900 Veteran Ave., Los Angeles, CA 90095-7073, USA.
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189
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Sesti G, Marini MA, Cardellini M, Sciacqua A, Frontoni S, Andreozzi F, Irace C, Lauro D, Gnasso A, Federici M, Perticone F, Lauro R. The Arg972 variant in insulin receptor substrate-1 is associated with an increased risk of secondary failure to sulfonylurea in patients with type 2 diabetes. Diabetes Care 2004; 27:1394-8. [PMID: 15161794 DOI: 10.2337/diacare.27.6.1394] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
OBJECTIVE The aim of this study was to investigate whether diabetic patients carrying the Arg(972) insulin receptor substrate-1 (IRS-1) variant are at increased risk for secondary failure to sulfonylurea. RESEARCH DESIGN AND METHODS A total of 477 unrelated Caucasian type 2 diabetic patients were recruited according to the following criteria: onset of diabetes after age 35 years, absence of ketonuria at diagnosis, and anti-GAD(-) antibody. Type 2 diabetes was diagnosed according to the American Diabetes Association criteria. Patients with secondary sulfonylurea failure were defined as those requiring insulin due to uncontrolled hyperglycemia (fasting plasma glucose >300 mg/dl) despite sulfonylurea-metformin combined therapy, appropriate diet, and absence of any conditions causing hyperglycemia. RESULTS Of the total patients, 53 (11.1%) were heterozygous for the Arg(972) IRS-1 variant, 1 (0.2%) was homozygous, and the remainder (88.7%) were homozygous for the wild-type allele. The genotype frequency of the Arg(972) IRS-1 variant was 8.7% among diabetic patients well controlled with oral therapy and 16.7% among patients with secondary failure to sulfonylurea (odds ratio 2.1 [95% CI 1.18-3.70], P = 0.01). Adjustment for age, sex, BMI, metabolic control, age at diagnosis, duration of diabetes, and Pro12Ala polymorphism of peroxisome proliferator-activated receptor-gamma2 gene in a logistic regression analysis with secondary failure to sulfonylurea as a dependent variable did not change this association (2.0 [1.38-3.86], P = 0.038). CONCLUSIONS These data demonstrate that the Arg(972) IRS-1 variant is associated with increased risk for secondary failure to sulfonylurea, thus representing a potential example of pharmacogenetics in type 2 diabetes.
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Affiliation(s)
- Giorgio Sesti
- Dipartimento di Medicina Sperimentale e Clinica, Università Magna Graecia di Catanzaro-Via Tommaso Campanella, 115 88100 Catanzaro, Italy.
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190
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Maedler K, Sergeev P, Ehses JA, Mathe Z, Bosco D, Berney T, Dayer JM, Reinecke M, Halban PA, Donath MY. Leptin modulates beta cell expression of IL-1 receptor antagonist and release of IL-1beta in human islets. Proc Natl Acad Sci U S A 2004; 101:8138-43. [PMID: 15141093 PMCID: PMC419570 DOI: 10.1073/pnas.0305683101] [Citation(s) in RCA: 199] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
High concentrations of glucose induce beta cell production of IL-1beta, leading to impaired beta cell function and apoptosis in human pancreatic islets. IL-1 receptor antagonist (IL-1Ra) is a naturally occurring antagonist of IL-1beta and protects cultured human islets from glucotoxicity. Therefore, the balance of IL-1beta and IL-1Ra may play a crucial role in the pathogenesis of diabetes. In the present study, we observed expression of IL-1Ra in human pancreatic beta cells of nondiabetic individuals, which was decreased in tissue sections of type 2 diabetic patients. In vitro, chronic exposure of human islets to leptin, a hormone secreted by adipocytes, decreased beta cell production of IL-1Ra and induced IL-1beta release from the islet preparation, leading to impaired beta cell function, caspase-3 activation, and apoptosis. Exogenous addition of IL-1Ra protected cultured human islets from the deleterious effects of leptin. Antagonizing IL-1Ra by introduction of small interfering RNA to IL-1Ra into human islets led to caspase-3 activation, DNA fragmentation, and impaired beta cell function. Moreover, siIL-1Ra enhanced glucose-induced beta cell apoptosis. These findings demonstrate expression of IL-1Ra in the human beta cell, providing localized protection against leptin- and glucose-induced islet IL-1beta.
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Affiliation(s)
- Kathrin Maedler
- Division of Endocrinology and Diabetes, University Hospital, CH8091 Zurich, Switzerland
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191
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Rustenbeck I, Krautheim A, Jörns A, Steinfelder HJ. β-Cell toxicity of ATP-sensitive K+ channel-blocking insulin secretagogues. Biochem Pharmacol 2004; 67:1733-41. [PMID: 15081872 DOI: 10.1016/j.bcp.2004.01.016] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2003] [Accepted: 01/16/2004] [Indexed: 11/27/2022]
Abstract
A prolonged exposure of isolated pancreatic islets to insulin secretagogues, the imidazolines phentolamine, alinidine and idazoxan (100microM each), the sulfonylurea tolbutamide (500microM), or the alkaloid quinine (100microM) resulted in morphological damage of 4-18% of beta-cells compared to less than 2% in controls. Thus, the question arose whether K(ATP) channel-blocking insulin secretagogues are beta-cell toxic as has already been suggested for sulfonylureas. The concentration- and time-dependency of the secretagogue-associated toxicity was documented by viability assays in insulin-secreting HIT T15 cells. Treatment for 24h with idazoxan reduced MTT conversion by 50% at 100microM and by 98% at 1000microM. Phentolamine and quinine reduced viability comparably at 1000microM, but were less toxic at 100microM. On the other hand, the imidazoline alinidine and the sulfonylurea tolbutamide were only moderately toxic (less than 40% viability loss at 1000microM). The imidazoline efaroxan appeared even to be non-toxic. Apoptotic DNA fragmentation and DEVD-caspase activation was observed at 100microM of idazoxan and phentolamine, whereas at 1000microM signs of necrosis predominated. Alinidine, tolbutamide and quinine treatment did not increase markers of apoptotic cell death. Blocking Ca(2+) influx by D600 did not diminish secretagogue-associated toxicity. Electron microscopy confirmed the validity of these observations for beta-cells in intact mouse islets. In summary, beta-cell toxicity of the tested insulin secretagogues varied widely and did not depend on a prolonged Ca(2+) influx via L-type Ca(2+) channels. Thus, secretagogue-mediated closure of K(ATP) channels is apparently not per se beta-cell toxic.
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Affiliation(s)
- Ingo Rustenbeck
- Institute of Pharmacology and Toxicology, Technical University of Braunschweig, D-38106 Braunschweig, Germany.
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192
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Buteau J, El-Assaad W, Rhodes CJ, Rosenberg L, Joly E, Prentki M. Glucagon-like peptide-1 prevents beta cell glucolipotoxicity. Diabetologia 2004; 47:806-15. [PMID: 15095038 DOI: 10.1007/s00125-004-1379-6] [Citation(s) in RCA: 234] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/03/2003] [Accepted: 01/16/2004] [Indexed: 12/31/2022]
Abstract
AIMS/HYPOTHESIS We have provided evidence that glucagon-like peptide-1, a potential therapeutic agent in the treatment of diabetes, activates phosphatidylinositol-3 kinase/protein kinase B signalling in the pancreatic beta cell. Since this pathway promotes cell survival in a variety of systems, we tested whether glucagon-like peptide-1 protects beta cells against cell death induced by elevated glucose and/or non-esterified fatty acids. METHODS Human islets and INS832/13 cells were cultured at glucose concentrations of 5 or 25 mmol/l in the presence or absence of palmitate. Apoptosis was evaluated by monitoring DNA fragmentation and chromatin condensation. Wild-type and protein kinase B mutants were overexpressed in INS832/13 cells using adenoviruses. Nuclear factor-kappa B DNA binding was assayed by electrophoretic mobility shift assay. RESULTS In human pancreatic beta cells and INS832/13 cells, glucagon-like peptide-1 prevented beta cell apoptosis induced by elevated concentrations of (i) glucose (glucotoxicity), (ii) palmitate (lipotoxicity) and (iii) both glucose and palmitate (glucolipotoxicity). Overexpression of a dominant-negative protein kinase B suppressed the anti-apoptotic action of glucagon-like peptide-1 in INS832/13 cells, whereas a constitutively active protein kinase B prevented beta cell apoptosis induced by elevated glucose and palmitate. Glucagon-like peptide-1 enhanced nuclear factor-kappa B DNA binding activity and stimulated the expression of inhibitor of apoptosis protein-2 and Bcl-2, two anti-apoptotic genes under the control of nuclear factor-kappa B. Inhibition of nuclear factor-kappa B by BAY 11-7082 abolished the prevention of glucolipotoxicity by glucagon-like peptide-1. CONCLUSIONS/INTERPRETATION The results demonstrate a potent protective effect of glucagon-like peptide-1 on beta cell gluco-, lipo- and glucolipotoxicity. This effect is mediated via protein kinase B activation and possibly its downstream target nuclear factor-kappa B.
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Affiliation(s)
- J Buteau
- Molecular Nutrition Unit, Department of Nutrition, University of Montreal, CR-CHUM, Pavillon de Sève, Montreal, PQ, Canada
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193
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Tomimoto S, Hashimoto H, Shintani N, Baba A. [Transgenic mice overexpressing PACAP in pancreatic beta-cells: acute and chronic effects on insulin and glucose homeostasis]. Nihon Yakurigaku Zasshi 2004; 123:261-6. [PMID: 15056941 DOI: 10.1254/fpj.123.261] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
PACAP belongs to the vasoactive intestinal polypeptide (VIP)/secretin/glucagon superfamily, which also includes glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP). PACAP shares an insulinotropic property with the latter two peptides; for instance, it stimulates insulin secretion from islets in a glucose-dependent manner at femtomolar concentrations. However, the pathophysiological significance of PACAP in diabetes remains largely unknown, for several reasons, including a lack of low-molecular weight PACAP ligands and a lack of suitable animal models. As an approach to understanding PACAP's pancreatic function in vivo, we have recently generated transgenic mice overexpressing PACAP in islet beta cells under the control of human insulin promoter (Tg mice). As a consequence, it has been demonstrated that in addition to stimulating insulin secretion, PACAP has long-term effects on pancreatic endocrine cells, including proliferation of beta cells during streptozotocin-induced diabetes development as well as aging. These observations provide additional information to support the possibility that drugs associated with PACAP-signaling pathways might be of therapeutic value for the treatment of diabetes. In this review, we briefly summarize these previous studies using Tg mice and also focus on the physiological and pathophysiological roles mediated by PACAP during diabetes development.
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Affiliation(s)
- Shuhei Tomimoto
- Laboratory of Molecular Neuropharmacology, Graduate School of Pharmaceutical Sciences, Osaka University, Suita, Japan
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194
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D'Alessandris C, Andreozzi F, Federici M, Cardellini M, Brunetti A, Ranalli M, Del Guerra S, Lauro D, Del Prato S, Marchetti P, Lauro R, Sesti G. IncreasedO‐glycosylation of insulin signaling proteins results in their impaired activation and enhanced susceptibility to apoptosis in pancreatic β‐cells. FASEB J 2004; 18:959-61. [PMID: 15059979 DOI: 10.1096/fj.03-0725fje] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Because adverse effects of glucose were attributed to its increased routing through the hexosamine pathway (HBP), we inquired whether HBP activation affects pancreatic beta-cell survival. Exposure of human islets to high glucose resulted in increased apoptosis of beta-cells upon serum deprivation that was reversed by azaserine. Also, glucosamine, a direct precursor of the downstream product of the HBP, increased human beta-cells apoptosis upon serum deprivation, which was reversed by benzyl-2-acetamido-2-deoxy-alpha-d-galactopyranoside (BADGP), an inhibitor of protein O-glycosylation. These results were reproduced in RIN rat beta-cells. Glucosamine treatment resulted in inhibition of tyrosine-phosphorylation of the insulin receptor (IR), IRS-1, and IRS-2, which was associated with increased O-glycosylation. These changes caused impaired activation of the PI 3-kinase/Akt survival signaling that resulted in reduced GSK-3 and FOXO1a inactivation. BADGP reversed the glucosamine-induced reduction in insulin-stimulated phosphorylation of IR, IRS-1, IRS-2, Akt, GSK-3, and FOXO1a. Impaired FOXO1a inactivation sustained expression of the pro-apoptotic protein Bim, without affecting Bad, Bcl-XL, or Bcl-2 expression. These results indicate that hyperglycemia may increase susceptibility to apoptosis of human and rat beta-cell through activation of the HBP. Increased routing of glucose through this metabolic pathway results in impaired activation of the IR/IRSs/PI3-kinase/Akt survival pathway by induction of O-glycosylation of signaling molecules.
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Affiliation(s)
- Cristina D'Alessandris
- Laboratory of Molecular Medicine, Department of Internal Medicine, University of Rome-Tor Vergata, Rome, Italy
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195
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Ishida H, Takizawa M, Ozawa S, Nakamichi Y, Yamaguchi S, Katsuta H, Tanaka T, Maruyama M, Katahira H, Yoshimoto K, Itagaki E, Nagamatsu S. Pioglitazone improves insulin secretory capacity and prevents the loss of beta-cell mass in obese diabetic db/db mice: Possible protection of beta cells from oxidative stress. Metabolism 2004; 53:488-94. [PMID: 15045697 DOI: 10.1016/j.metabol.2003.11.021] [Citation(s) in RCA: 116] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In order to assess the beneficial effect of the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist pioglitazone on reduction of mass and alteration of function of pancreatic beta cells under diabetic conditions, diabetic C57BL/KsJ db/db mice were treated with pioglitazone for 6 weeks, and insulin secretory capacity and insulin content of isolated pancreatic islets were evaluated. In addition, the expression of oxidative stress markers, 4-hydroxy-2-nonenal (HNE)-modified proteins and heme oxygenase-1, in endocrine pancreas was examined to measure reduction of oxidative stress in pancreatic beta cells. The capacity for glucose-induced insulin secretion from isolated islets and their insulin content were improved by pioglitazone treatment (P <.01). When beta cells were stained with anti-insulin antibodies, those of db/db mice treated with pioglitazone exhibited strong staining, as also observed in their lean littermates. The density of immunostaining for oxidative stress markers was significantly reduced in pancreatic islets of pioglitazone-treated db/db mice (P <.05). This study clearly demonstrates the benefit of long-term treatment with pioglitazone in decreasing hyperglycemia and improving glucose-induced insulin secretory capacity in diabetic db/db mice. The results of immunocytochemical examination suggest that this treatment reduces oxidative stress and thereby preserves beta-cell mass. Treatment with pioglitazone thus protects against beta-cell damage and would be useful for restoration of insulin secretory capacity in obese diabetes individuals.
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Affiliation(s)
- Hitoshi Ishida
- Third Department of Internal Medicine, Kyorin University School of Medicine, Tokyo, Japan
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196
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Welters HJ, Tadayyon M, Scarpello JHB, Smith SA, Morgan NG. Mono-unsaturated fatty acids protect against beta-cell apoptosis induced by saturated fatty acids, serum withdrawal or cytokine exposure. FEBS Lett 2004; 560:103-8. [PMID: 14988006 DOI: 10.1016/s0014-5793(04)00079-1] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2003] [Revised: 01/09/2004] [Accepted: 01/19/2004] [Indexed: 01/09/2023]
Abstract
Long-chain saturated fatty acids are cytotoxic to pancreatic beta-cells while shorter-chain saturated and long-chain unsaturated molecules are better tolerated. Mono-unsaturated fatty acids are not, however, inert since they inhibit the pro-apoptotic effects of saturated molecules. In the present work we show that the mono-unsaturates palmitoleate (C16:1) or oleate (C18:1) also cause marked inhibition of apoptosis induced by exposure of clonal BRIN-BD11 beta-cells to serum withdrawal or a combination of interleukin-1beta plus interferon-gamma. This response was dose-dependent and not accompanied by changes in NO formation. Taken together, the results suggest that mono-unsaturated fatty acids regulate a distal step common to several apoptotic pathways in pancreatic beta-cells.
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Affiliation(s)
- Hannah J Welters
- Institute of Biomedical and Clinical Science, Peninsula Medical School, Room N32, ITTC Building, Tamar Science Park, Plymouth, PL6 8BX, UK
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197
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Kaminski A, Gao H, Morgan NG. Involvement of the cGMP signalling pathway in the regulation of viability in insulin-secreting BRIN-BD11 cells. FEBS Lett 2004; 559:118-24. [PMID: 14960318 DOI: 10.1016/s0014-5793(04)00048-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2003] [Accepted: 12/21/2003] [Indexed: 01/01/2023]
Abstract
We have evaluated the hypothesis that cGMP may serve as an intracellular messenger regulating the viability of pancreatic beta-cells. A direct activator of soluble guanylyl cyclase, YC-1, caused a time- and dose-dependent loss of viability in clonal BRIN-BD11 beta-cells. This was accompanied by a rise in cGMP and was antagonised by Rp-8-pCPT-cGMPS, a selective inhibitor of protein kinase G (PKG). Reverse transcription polymerase chain reaction analysis confirmed that BRIN-BD11 cells (and human islets) express all three known isoforms of PKG (PKG-Ialpha, -Ibeta and II). Cell death induced by YC-1 was not sensitive to cell-permeable caspase inhibitors and was not accompanied by oligonucleosomal DNA fragmentation. The response was, however, inhibited by actinomycin D, suggesting that a transcription-dependent pathway of programmed cell death is involved in the actions of cGMP.
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Affiliation(s)
- Anna Kaminski
- Endocrine Pharmacology Group, Institute of Biomedical and Clinical Science, Peninsula Medical School, Room N32, ITTC Building, Tamar Science Park, Plymouth, Devon PL6 8BX, UK
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198
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Johnson JD, Han Z, Otani K, Ye H, Zhang Y, Wu H, Horikawa Y, Misler S, Bell GI, Polonsky KS. RyR2 and calpain-10 delineate a novel apoptosis pathway in pancreatic islets. J Biol Chem 2004; 279:24794-802. [PMID: 15044459 DOI: 10.1074/jbc.m401216200] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Cells are programmed to die when critical signaling and metabolic pathways are disrupted. Inhibiting the type 2 ryanodine receptor (RyR2) in human and mouse pancreatic beta-cells markedly increased apoptosis. This mode of programmed cell death was not associated with robust caspase-3 activation prompting a search for an alternative mechanism. Increased calpain activity and calpain gene expression suggested a role for a calpain-dependent death pathway. Using a combination of pharmacological and genetic approaches, we demonstrated that the calpain-10 isoform mediated ryanodine-induced apoptosis. Apoptosis induced by the fatty acid palmitate and by low glucose also required calpain-10. Ryanodine-induced calpain activation and apoptosis were reversed by glucagon-like peptide or short-term exposure to high glucose. Thus RyR2 activity seems to play an essential role in beta-cell survival in vitro by suppressing a death pathway mediated by calpain-10, a type 2 diabetes susceptibility gene with previously unknown function.
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Affiliation(s)
- James D Johnson
- Department of Internal Medicine, Washington University, St. Louis, Missouri 63110, USA
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199
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Van de Casteele M, Kefas BA, Cai Y, Heimberg H, Scott DK, Henquin JC, Pipeleers D, Jonas JC. Prolonged culture in low glucose induces apoptosis of rat pancreatic beta-cells through induction of c-myc. Biochem Biophys Res Commun 2004; 312:937-44. [PMID: 14651961 DOI: 10.1016/j.bbrc.2003.11.013] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Prolonged culture in low-glucose concentrations (</=5mM) induces apoptosis in pancreatic beta-cells by a poorly defined mechanism. We now show that, in both purified rat beta-cells and isolated rat islets, culture in the presence of 3 or 5mM (G3-G5) instead of 10mM glucose (G10) induces a large increase in c-myc expression before onset of a caspase-dependent apoptosis. These effects were prevented by addition of leucine and glutamine to G3 and G5, and were mimicked by addition of the mitochondrial poison azide to G10. In contrast, inhibition of Ca(2+) influx and insulin secretion with diazoxide under control conditions did not stimulate islet c-myc expression nor beta-cell apoptosis. In rat beta-cells, adenovirus-mediated c-myc overexpression increased their rate of apoptosis, whereas antisense-c-myc expression reduced low-glucose-induced apoptosis by approximately 50%. In the insulin producing MIN6 cell line, apoptosis induction by either low glucose or an activator of AMP-activated protein kinase (AMPK) was associated with c-myc mRNA and protein upregulation. In conclusion, stimulation of beta-cell apoptosis by prolonged culture at low glucose partly results from early and sustained induction of beta-cell c-myc expression. These effects may be due to sustained restriction in nutrient-derived metabolic signals.
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200
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Donath MY, Halban PA. Decreased beta-cell mass in diabetes: significance, mechanisms and therapeutic implications. Diabetologia 2004; 47:581-589. [PMID: 14767595 DOI: 10.1007/s00125-004-1336-4] [Citation(s) in RCA: 294] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/18/2003] [Revised: 12/17/2003] [Indexed: 12/25/2022]
Abstract
Increasing evidence indicates that decreased functional beta-cell mass is the hallmark of both Type 1 and Type 2 diabetes. This underlies the absolute or relative insulin insufficiency in both conditions. In this For Debate, we consider the possible mechanisms responsible for beta-cell death and impaired function and their relative contribution to insulin insufficiency in diabetes. Beta-cell apoptosis and impaired proliferation consequent to hyperglycaemia is one pathway that could be operating in all forms of diabetes. Autoimmunity and other routes to beta-cell death are also considered. Recognition of decreased functional beta-cell mass and its overlapping multifactorial aetiology in diabetic states, leads us to propose a unifying classification of diabetes.
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Affiliation(s)
- M Y Donath
- Division of Endocrinology and Diabetes, Department of Medicine, University Hospital, 8091, Zurich, Switzerland.
| | - P A Halban
- Department of Genetic Medicine and Development, University Medical Centre, Geneva, Switzerland
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