101
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Gupta D, Jetton TL, Mortensen RM, Duan SZ, Peshavaria M, Leahy JL. In vivo and in vitro studies of a functional peroxisome proliferator-activated receptor gamma response element in the mouse pdx-1 promoter. J Biol Chem 2008; 283:32462-70. [PMID: 18718916 PMCID: PMC2583321 DOI: 10.1074/jbc.m801813200] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2008] [Revised: 08/01/2008] [Indexed: 01/03/2023] Open
Abstract
We reported that peroxisome proliferator-activated receptor gamma (PPARgamma) transcriptionally regulates the beta-cell differentiation factor pancreatic duodenal homeobox (PDX)-1 based on in vitro RNA interference studies. We have now studied mice depleted of PPARgamma within the pancreas (PANC PPARgamma(-/-)) created by a Cre/loxP recombinase system, with Cre driven by the pdx-1 promoter. Male PANC PPARgamma(-/-) mice were hyperglycemic at 8 weeks of age (8.1+/-0.2 mM versus 6.4+/-0.3 mM, p=0.009) with islet cytoarchitecture and pancreatic mass of islet beta-cells that were indistinguishable from the controls. Islet PDX-1 mRNA (p=0.001) and protein levels (p=0.003) were lowered 60 and 40%, respectively, in tandem with impaired glucose-induced insulin secretion and loss of thiazolidinedione-induced increase in PDX-1 expression. We next identified a putative PPAR-response element (PPRE) in the mouse pdx-1 promoter with substantial homology to the corresponding region of the human PDX-1 promoter. Electrophoretic mobility supershift assays with nuclear extracts from beta-cell lines and mouse islets, also in vitro translated PPARgamma and retinoid X receptor, and chromatin immunoprecipitation analysis demonstrated specific binding of PPARgamma and retinoid X receptor to the human and mouse pdx-1 x PPREs. Transient transfection assays of beta-cells with reporter constructs of mutated PPREs showed dramatically reduced pdx-1 promoter activity. In summary, we have presented in vivo and in vitro evidence showing PPARgamma regulation of pdx-1 transcription in beta-cells, plus our results support an important regulatory role for PPARgamma in beta-cell physiology and thiazolidinedione pharmacology of type 2 diabetes.
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Affiliation(s)
- Dhananjay Gupta
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, University of Vermont, Burlington, Vermont 05405, USA
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102
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Leibowitz G, Cerasi E, Ketzinel-Gilad M. The role of mTOR in the adaptation and failure of beta-cells in type 2 diabetes. Diabetes Obes Metab 2008; 10 Suppl 4:157-69. [PMID: 18834443 DOI: 10.1111/j.1463-1326.2008.00952.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Mammalian target of rapamycin (mTOR) is an important nutrient sensor that plays a critical role in cellular metabolism, growth, proliferation and apoptosis and in the cellular response to oxidative stress. In addition, mTOR-raptor complex, also called mammalian target of rapamycin complex 1 (mTORC1), generates an inhibitory feedback loop on insulin receptor substrate proteins. It was suggested that nutrient overload leads to insulin/insulin-like growth factor 1 resistance in peripheral insulin-responsive tissues and in the beta-cells through sustained activation of mTORC1. In this review, we summarize the literature on the regulation and function of mTOR, its role in the organism's response to nutrients and its potential impact on lifespan, insulin resistance and the metabolic adaptation to hyperglycaemia in type 2 diabetes. We also propose a hypothesis based on data in the literature as well as data generated in our laboratory, which assigns a central positive role to mTOR in the maintenance of beta-cell function and mass in the diabetic environment.
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Affiliation(s)
- G Leibowitz
- Endocrinology and Metabolism Service, Department of Medicine, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.
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103
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Affiliation(s)
- Jack L Leahy
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Vermont, Burlington, Vermont, USA.
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104
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Bates HE, Sirek A, Kiraly MA, Yue JTY, Riddell MC, Matthews SG, Vranic M. Adaptation to intermittent stress promotes maintenance of beta-cell compensation: comparison with food restriction. Am J Physiol Endocrinol Metab 2008; 295:E947-58. [PMID: 18713962 DOI: 10.1152/ajpendo.90378.2008] [Citation(s) in RCA: 11] [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
Intermittent restraint stress delays hyperglycemia in ZDF rats better than pair feeding. We hypothesized that intermittent stress would preserve beta-cell mass through distinct mechanisms from food restriction. We studied temporal effects of intermittent stress on beta-cell compensation during pre-, early, and late diabetes. Six-week-old obese male ZDF rats were restraint-stressed 1 h/day, 5 days/wk for 0, 3, 6, or 13 wk and compared with age-matched obese ZDF rats that had been food restricted for 13 wk, and 19-wk-old lean ZDF rats. Thirteen weeks of stress and food restriction lowered cumulative food intake 10-15%. Obese islets were fibrotic and disorganized and not improved by stress or food restriction. Obese pancreata had islet hyperplasia and showed evidence of neogenesis, but by 19 wk old beta-cell mass was not increased, and islets had fewer beta-cells that were hypertrophic. Both stress and food restriction partially preserved beta-cell mass at 19 wk old via islet hypertrophy, whereas stress additionally lowered alpha-cell mass. Concomitant with maintenance of insulin responses to glucose, stress delayed the sixfold decline in beta-cell proliferation and reduced beta-cell hypertrophy, translating into 30% more beta-cells per islet after 13 wk. In contrast, food restriction did not improve insulin responses or beta-cell hyperplasia, exacerbated beta-cell hypertrophy, and resulted in fewer beta-cells and greater alpha-cell mass than with stress. Thus, preservation of beta-cell mass with adaptation to intermittent stress is related to beta-cell hyperplasia, maintenance of insulin responses to glucose, and reductions in alpha-cell mass that do not occur with food restriction.
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Affiliation(s)
- Holly E Bates
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada.
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105
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Di Nardo F, Burattini R, Cogo CE, Faelli E, Ruggeri P. Age-related analysis of insulin resistance, body weight and arterial pressure in the Zucker fatty rat. Exp Physiol 2008; 94:162-8. [PMID: 18820002 DOI: 10.1113/expphysiol.2008.044529] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The evolution with ageing of insulin resistance, body weight (BW) and mean arterial pressure (MAP) was studied in a group of Zucker fatty rats (ZFRs, n = 22), between 7 and 16 weeks of age, compared with an age-matched control group of Zucker lean rats (ZLRs, n = 22). The minimal model of glucose kinetics was applied to estimate glucose effectiveness, S(G), and insulin sensitivity, S(I), from insulinaemia and glycaemia measured during a 70 min intravenous glucose tolerance test. No correlation was found between S(G) and age in both ZFR and ZLR groups. No significant changes in mean S(G) between the two groups indicated no alteration of glucose-mediated glucose disposal. Estimates of S(I) from individual ZFRs were independent of age and, on average, showed 83% reduction (P < 0.001) compared with the ZLR group. Despite the lack of alteration of S(I) with age, the ZFR group showed an age-related increase of MAP, which correlated with increasing BW (r = 0.71 and P < 0.001). These results support the hypothesis that in our ZFRs, as a suitable genetic model of obesity and hypertension, insulin resistance is fully established at the age of 7 weeks and remains practically unaltered until at least the sixteenth week. An age-related increase in arterial pressure, observed in this strain, relates more properly to increasing BW, rather than insulin resistance. Development of hypertension with increasing age and BW may result from an enhanced insulin-mediated activity of the sympathetic nervous system, as observed in our previously reported study.
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Affiliation(s)
- Francesco Di Nardo
- Department of Biomedical, Electronics and Telecommunication Engineering, Polytechnic University of Marche, 60131 Ancona, Italy
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106
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Wang XD, Vatamaniuk MZ, Wang SK, Roneker CA, Simmons RA, Lei XG. Molecular mechanisms for hyperinsulinaemia induced by overproduction of selenium-dependent glutathione peroxidase-1 in mice. Diabetologia 2008; 51:1515-24. [PMID: 18560803 DOI: 10.1007/s00125-008-1055-3] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/21/2008] [Accepted: 04/30/2008] [Indexed: 01/11/2023]
Abstract
AIMS/HYPOTHESIS We previously observed hyperglycaemia, hyperinsulinaemia, insulin resistance and obesity in Gpx1-overexpressing mice (OE). Here we determined whether these phenotypes were eliminated by diet restriction, subsequently testing whether hyperinsulinaemia was a primary effect of Gpx1 overexpression and caused by dysregulation of pancreatic duodenal homeobox 1 (PDX1) and uncoupling protein-2 (UCP2) in islets. METHODS First, 24 male OE and wild-type (WT) mice (2 months old) were given 3 g (diet-restricted) or 5 g (full-fed) feed per day for 4 months to compare their glucose metabolism. Thereafter, several mechanistic experiments were conducted with pancreas and islets of the two genotypes (2 or 6 months old) to assay for beta cell mass, reactive oxygen species (ROS) levels, mitochondrial membrane potential (Deltapsi(m)) and expression profiles of regulatory proteins. A functional assay of islets was also performed. RESULTS Diet restriction eliminated obesity but not hyperinsulinaemia in OE mice. These mice had greater pancreatic beta cell mass (more than twofold) and pancreatic insulin content (40%) than the WT, along with an enhanced Deltapsi(m) and glucose-stimulated insulin secretion in islets. With diminished ROS production, the OE islets displayed hyperacetylation of H3 and H4 histone in the Pdx1 promoter, elevated PDX1 and decreased UCP2. CONCLUSIONS/INTERPRETATION Overproduction of the major antioxidant enzyme, glutathione peroxidase 1, caused seemingly beneficial changes in pancreatic PDX1 and UCP2, but eventually led to chronic hyperinsulinaemia by dysregulating islet insulin production and secretion.
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Affiliation(s)
- X D Wang
- Department of Animal Science, Cornell University, 252 Morrison Hall, Ithaca, NY 14853, USA
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107
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Abstract
BAD, a proapoptotic member of the Bcl-2 family of proteins, is regulated by phosphorylation. A recent study (Danial et al., 2008) suggests a phosphorylation-state-dependent bifunctional role of BAD in the regulation of glucose-stimulated insulin secretion and beta cell mass.
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108
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Jetton TL, Everill B, Lausier J, Roskens V, Habibovic A, LaRock K, Gokin A, Peshavaria M, Leahy JL. Enhanced beta-cell mass without increased proliferation following chronic mild glucose infusion. Am J Physiol Endocrinol Metab 2008; 294:E679-87. [PMID: 18230696 DOI: 10.1152/ajpendo.00569.2007] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
The physiological mechanisms underlying pancreatic beta-cell mass (BCM) homeostasis are complex and not fully resolved. Here we examined the factors contributing to the increased BCM following a mild glucose infusion (GI) whereby normoglycemia was maintained through 96 h. We used morphometric and immunochemical methods to investigate enhanced beta-cell growth and survival in Sprague-Dawley rats. BCM was elevated >2.5-fold over saline-infused control rats by 48 h and increased modestly thereafter. Unexpectedly, increases in beta-cell proliferation were not observed at any time point through 4 days. Instead, enhanced numbers of insulin(+) cell clusters and small islets (400-12,000 microm(2); approximately 23- to 124-microm diameter), mostly scattered among the acini, were observed in the GI rats by 48 h despite no difference in the numbers of medium to large islets. We previously showed that increased beta-cell growth in rodent models of insulin resistance and pancreatic regeneration involves increased activated Akt/PKB, a key beta-cell signaling intermediate, in both islets and endocrine cell clusters. GI in normal rats also leads to increased Akt activation in islet beta-cells, as well as in insulin(+) and insulin(-) cells in the common duct epithelium and endocrine clusters. This correlated with strong Pdx1 expression in these same cells. These results suggest that mechanisms other than proliferation underlie the rapid beta-cell growth response following a mild GI in the normal rat and involve Akt-regulated enhanced beta-cell survival potential and neogenesis from epithelial precursors.
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Affiliation(s)
- Thomas L Jetton
- Division of Endocrinology, Diabetes, and Metabolism, University of Vermont, Burlington, VT 05405, USA.
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109
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Hagman DK, Latour MG, Chakrabarti SK, Fontes G, Amyot J, Tremblay C, Semache M, Lausier JA, Roskens V, Mirmira RG, Jetton TL, Poitout V. Cyclical and alternating infusions of glucose and intralipid in rats inhibit insulin gene expression and Pdx-1 binding in islets. Diabetes 2008; 57:424-31. [PMID: 17991758 PMCID: PMC2979006 DOI: 10.2337/db07-1285] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE Prolonged exposure of isolated islets of Langerhans to elevated levels of fatty acids, in the presence of high glucose, impairs insulin gene expression via a transcriptional mechanism involving nuclear exclusion of pancreas-duodenum homeobox-1 (Pdx-1) and loss of MafA expression. Whether such a phenomenon also occurs in vivo is unknown. Our objective was therefore to ascertain whether chronic nutrient oversupply inhibits insulin gene expression in vivo. RESEARCH DESIGN AND METHODS Wistar rats received alternating 4-h infusions of glucose and Intralipid for a total of 72 h. Control groups received alternating infusions of glucose and saline, saline and Intralipid, or saline only. Insulin and C-peptide secretion were measured under hyperglycemic clamps. Insulin secretion and gene expression were assessed in isolated islets, and beta-cell mass was quantified by morphometric analysis. RESULTS Neither C-peptide secretion nor insulin sensitivity was different among infusion regimens. Insulin content and insulin mRNA levels were lower in islets isolated from rats infused with glucose plus Intralipid. This was associated with reduced Pdx-1 binding to the endogenous insulin promoter, and an increased proportion of Pdx-1 localized in the cytoplasm versus the nucleus. In contrast, MafA mRNA and protein levels and beta-cell mass and proliferation were unchanged. CONCLUSIONS Cyclical and alternating infusions of glucose and Intralipid in normal rats inhibit insulin gene expression without affecting insulin secretion or beta-cell mass. We conclude that fatty acid inhibition of insulin gene expression, in the presence of high glucose, is an early functional defect that may contribute to beta-cell failure in type 2 diabetes.
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Affiliation(s)
- Derek K. Hagman
- Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l’Université de Montréal, Montréal, Quebec, Canada
| | - Martin G. Latour
- Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l’Université de Montréal, Montréal, Quebec, Canada
| | - Swarup K. Chakrabarti
- Department of Medicine and the Diabetes Center, University of Virginia, Charlottesville, Virginia
| | - Ghislaine Fontes
- Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l’Université de Montréal, Montréal, Quebec, Canada
| | - Julie Amyot
- Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l’Université de Montréal, Montréal, Quebec, Canada
| | - Caroline Tremblay
- Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l’Université de Montréal, Montréal, Quebec, Canada
| | - Meriem Semache
- Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l’Université de Montréal, Montréal, Quebec, Canada
| | - James A. Lausier
- Division of Endocrinology, Diabetes and Metabolism, University of Vermont College of Medicine, Burlington, Vermont
| | - Violet Roskens
- Division of Endocrinology, Diabetes and Metabolism, University of Vermont College of Medicine, Burlington, Vermont
| | - Raghavendra G. Mirmira
- Department of Medicine and the Diabetes Center, University of Virginia, Charlottesville, Virginia
| | - Thomas L. Jetton
- Division of Endocrinology, Diabetes and Metabolism, University of Vermont College of Medicine, Burlington, Vermont
| | - Vincent Poitout
- Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l’Université de Montréal, Montréal, Quebec, Canada
- Departments of Medicine, Nutrition, and Biochemistry, Université de Montréal, Montréal, Quebec, Canada
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110
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Király MA, Bates HE, Kaniuk NA, Yue JTY, Brumell JH, Matthews SG, Riddell MC, Vranic M. Swim training prevents hyperglycemia in ZDF rats: mechanisms involved in the partial maintenance of beta-cell function. Am J Physiol Endocrinol Metab 2008; 294:E271-83. [PMID: 18029442 DOI: 10.1152/ajpendo.00476.2007] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Exercise improves glucose tolerance in obese rodent models and humans; however, effects with respect to mechanisms of beta-cell compensation remain unexplained. We examined exercise's effects during the progression of hyperglycemia in male Zucker diabetic fatty (ZDF) rats until 19 wk of age. At 6 wk old, rats were assigned to 1) basal--euthanized for baseline values; 2) exercise--swam individually for 1 h/day, 5 days/wk; and 3) controls (n = 8-10/group). Exercise (13 wk) resulted in maintenance of fasted hyperinsulinemia and prevented increases in fed and fasted glucose (P < 0.05) compared with sham-exercised and sedentary controls (P < 0.05). Beta-cell function calculations indicate prolonged beta-cell adaptation in exercised animals alone. During an intraperitoneal glucose tolerance test (IPGTT), exercised rats had lower 2-h glucose (P < 0.05) vs. controls. Area-under-the-curve analyses from baseline for IPGTT glucose and insulin indicate improved glucose tolerance with exercise was associated with increased insulin production and/or secretion. Beta-cell mass increased in exercised vs. basal animals; however, mass expansion was absent at 19 wk in controls (P < 0.05). Hypertrophy and replication contributed to expansion of beta-cell mass; exercised animals had increased beta-cell size and bromodeoxyuridine incorporation rates vs. controls (P < 0.05). The relative area of GLUT2 and protein kinase B was significantly elevated in exercised vs. sedentary controls (P < 0.05). Last, we show formation of ubiquitinated protein aggregates, a response to cellular/oxidative stress, occurred in nonexercised 19 wk-old ZDF rats but not in lean, 6 wk-old basal, or exercised rats. In conclusion, improved beta-cell compensation through increased beta-cell function and mass occurs in exercised but not sedentary ZDF rats and may be in part responsible for improved glucoregulation.
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Affiliation(s)
- Michael A Király
- Department of Physiology, University of Toronto, 1 King's College Circle, Toronto, Ontario, Canada
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111
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Dual role of proapoptotic BAD in insulin secretion and beta cell survival. Nat Med 2008; 14:144-53. [PMID: 18223655 DOI: 10.1038/nm1717] [Citation(s) in RCA: 246] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2007] [Accepted: 12/20/2007] [Indexed: 12/25/2022]
Abstract
The proapoptotic BCL-2 family member BAD resides in a glucokinase-containing complex that regulates glucose-driven mitochondrial respiration. Here, we present genetic evidence of a physiologic role for BAD in glucose-stimulated insulin secretion by beta cells. This novel function of BAD is specifically dependent upon the phosphorylation of its BH3 sequence, previously defined as an essential death domain. We highlight the pharmacologic relevance of phosphorylated BAD BH3 by using cell-permeable, hydrocarbon-stapled BAD BH3 helices that target glucokinase, restore glucose-driven mitochondrial respiration and correct the insulin secretory response in Bad-deficient islets. Our studies uncover an alternative target and function for the BAD BH3 domain and emphasize the therapeutic potential of phosphorylated BAD BH3 mimetics in selectively restoring beta cell function. Furthermore, we show that BAD regulates the physiologic adaptation of beta cell mass during high-fat feeding. Our findings provide genetic proof of the bifunctional activities of BAD in both beta cell survival and insulin secretion.
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112
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Menge BA, Tannapfel A, Belyaev O, Drescher R, Müller C, Uhl W, Schmidt WE, Meier JJ. Partial pancreatectomy in adult humans does not provoke beta-cell regeneration. Diabetes 2008; 57:142-9. [PMID: 17959931 DOI: 10.2337/db07-1294] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
OBJECTIVE beta-Cell regeneration has been proposed as a possible treatment for diabetes, but the capacity for new beta-cell formation in humans is yet unclear. In young rats, partial pancreatectomy prompts new beta-cell formation to restore beta-cell mass. We addressed the following questions: In adult humans: 1) Does partial pancreatectomy provoke new beta-cell formation and increased beta-cell mass? 2) Is beta-cell turnover increased after partial pancreatectomy? RESEARCH DESIGN AND METHODS Protocol 1: human pancreatic tissue was collected from 13 patients who underwent two consecutive partial pancreas resections, and markers of cell turnover were determined in both tissue samples, respectively. Protocol 2: pancreas volumes were determined from abdominal computer tomography scans, performed in 17 patients on two separate occasions after partial pancreatectomy. RESULTS Protocol 1: fasting glucose concentrations increased significantly after the 50% pancreatectomy (P = 0.01), but the fractional beta-cell area of the pancreas remained unchanged (P = 0.11). beta-Cell proliferation, the overall replication index (Ki67 staining), and the percentage of duct cells expressing insulin were similar before and after the partial pancreatectomy. The overall frequency of apoptosis (terminal deoxynucleotidyl transferase biotin-dUTP nick-end labeling) was slightly increased following the partial pancreatectomy (P = 0.02). Protocol 2: pancreatic volume was approximately 50% reduced to 35.6 +/- 2.6 ccm(3) by the partial pancreatectomy. The total pancreatic volume was unchanged after an interval of 247 +/- 160 days (35.4 +/- 2.7 ccm(3); P = 0.51). CONCLUSIONS Unlike in rodents, a 50% pancreatectomy does not prompt beta-cell regeneration in adult humans. This explains the high incidence of diabetes after pancreatic resections. Such differences in beta-cell turnover between rodents and humans should be born in mind when evaluating new treatment options aiming to restore beta-cell mass in patients with diabetes.
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Affiliation(s)
- Bjoern A Menge
- Department of Medicine I, St. Josef-Hospital, Ruhr-University Bochum, Gudrunstr. 56, 44791 Bochum, Germany
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113
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Yano T, Liu Z, Donovan J, Thomas MK, Habener JF. Stromal cell derived factor-1 (SDF-1)/CXCL12 attenuates diabetes in mice and promotes pancreatic beta-cell survival by activation of the prosurvival kinase Akt. Diabetes 2007; 56:2946-57. [PMID: 17878289 DOI: 10.2337/db07-0291] [Citation(s) in RCA: 108] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
OBJECTIVE Diabetes is caused by a deficiency of pancreatic beta-cells that produce insulin. Approaches to enhance beta-cell mass by increasing proliferation and survival are desirable. We determined whether stromal cell-derived factor (SDF)-1/CXCL12 and its receptor, CX chemokine receptor (CXCR)4, are important for the survival of beta-cells. RESEARCH DESIGN AND METHODS Mouse pancreata and clonal beta-cells were examined for expression of SDF-1 and CXCR4, activation of AKT and downstream signaling pathways by SDF-1, and protection against apoptosis and diabetes induced by streptozotocin (STZ). RESULTS CXCR4 is expressed in beta-cells, and SDF-1 is expressed in microvascular endothelial cells within the islets and in surrounding interstitial stromal tissue. Transgenic mice overexpressing SDF-1 within their beta-cells (RIP-SDF-1 mice) are resistant to STZ-induced beta-cell apoptosis and diabetes. In MIN6 beta-cells, a CXCR4 antagonist (AMD3100) induces apoptosis, increases reactive oxygen species, decreases expression levels of the anti-apoptotic protein Bcl-2, and reduces phosphorylation of the proapoptotic protein Bad. Active phosphorylated prosurvival kinase Akt is increased both in the beta-cells of RIP-SDF-1 mice and in INS-1 cells treated with SDF-1 and sensitive to AMD3100. Inhibition of AKT expression by small interfering RNA attenuates the ameliorative effects of SDF-1 on caspase-dependent apoptosis induced by thapsigargin or glucose deprivation in INS-1 beta-cells. Specific inhibition of Akt activation by a soluble inhibitor (SH-5) reverses the anti-apoptotic effects of SDF-1 in INS-1 cells and mouse islets. CONCLUSIONS SDF-1 promotes pancreatic beta-cell survival via activation of Akt, suggesting that SDF-1 agonists may prove beneficial for treatment of diabetes.
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Affiliation(s)
- Tatsuya Yano
- Laboratory of Molecular Endocrinology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114, USA
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114
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Morioka T, Asilmaz E, Hu J, Dishinger JF, Kurpad AJ, Elias CF, Li H, Elmquist JK, Kennedy RT, Kulkarni RN. Disruption of leptin receptor expression in the pancreas directly affects beta cell growth and function in mice. J Clin Invest 2007; 117:2860-8. [PMID: 17909627 PMCID: PMC1994606 DOI: 10.1172/jci30910] [Citation(s) in RCA: 169] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2006] [Accepted: 07/06/2007] [Indexed: 12/13/2022] Open
Abstract
Obesity is characterized by hyperinsulinemia, hyperleptinemia, and an increase in islet volume. While the mechanisms that hasten the onset of diabetes in obese individuals are not known, it is possible that the adipose-derived hormone leptin plays a role. In addition to its central actions, leptin exerts biological effects by acting in peripheral tissues including the endocrine pancreas. To explore the impact of disrupting leptin signaling in the pancreas on beta cell growth and/or function, we created pancreas-specific leptin receptor (ObR) KOs using mice expressing Cre recombinase under the control of the pancreatic and duodenal homeobox 1 (Pdx1) promoter. The KOs exhibited improved glucose tolerance due to enhanced early-phase insulin secretion, and a greater beta cell mass secondary to increased beta cell size and enhanced expression and phosphorylation of p70S6K. Similar effects on p70S6K were observed in MIN6 beta cells with knockdown of the ObR gene, suggesting crosstalk between leptin and insulin signaling pathways. Surprisingly, challenging the KOs with a high-fat diet led to attenuated acute insulin secretory response to glucose, poor compensatory islet growth, and glucose intolerance. Together, these data provide direct genetic evidence, from a unique mouse model lacking ObRs only in the pancreas, for a critical role for leptin signaling in islet biology and suggest that altered leptin action in islets is one factor that contributes to obesity-associated diabetes.
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Affiliation(s)
- Tomoaki Morioka
- Research Division, Joslin Diabetes Center, Boston, Massachusetts, USA.
Laboratory of Molecular Genetics, The Rockefeller University, New York, New York, USA.
Departments of Chemistry and Pharmacology, University of Michigan, Ann Arbor, Michigan, USA.
Center for Hypothalamic Research and Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil
| | - Esra Asilmaz
- Research Division, Joslin Diabetes Center, Boston, Massachusetts, USA.
Laboratory of Molecular Genetics, The Rockefeller University, New York, New York, USA.
Departments of Chemistry and Pharmacology, University of Michigan, Ann Arbor, Michigan, USA.
Center for Hypothalamic Research and Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil
| | - Jiang Hu
- Research Division, Joslin Diabetes Center, Boston, Massachusetts, USA.
Laboratory of Molecular Genetics, The Rockefeller University, New York, New York, USA.
Departments of Chemistry and Pharmacology, University of Michigan, Ann Arbor, Michigan, USA.
Center for Hypothalamic Research and Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil
| | - John F. Dishinger
- Research Division, Joslin Diabetes Center, Boston, Massachusetts, USA.
Laboratory of Molecular Genetics, The Rockefeller University, New York, New York, USA.
Departments of Chemistry and Pharmacology, University of Michigan, Ann Arbor, Michigan, USA.
Center for Hypothalamic Research and Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil
| | - Amarnath J. Kurpad
- Research Division, Joslin Diabetes Center, Boston, Massachusetts, USA.
Laboratory of Molecular Genetics, The Rockefeller University, New York, New York, USA.
Departments of Chemistry and Pharmacology, University of Michigan, Ann Arbor, Michigan, USA.
Center for Hypothalamic Research and Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil
| | - Carol F. Elias
- Research Division, Joslin Diabetes Center, Boston, Massachusetts, USA.
Laboratory of Molecular Genetics, The Rockefeller University, New York, New York, USA.
Departments of Chemistry and Pharmacology, University of Michigan, Ann Arbor, Michigan, USA.
Center for Hypothalamic Research and Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil
| | - Hui Li
- Research Division, Joslin Diabetes Center, Boston, Massachusetts, USA.
Laboratory of Molecular Genetics, The Rockefeller University, New York, New York, USA.
Departments of Chemistry and Pharmacology, University of Michigan, Ann Arbor, Michigan, USA.
Center for Hypothalamic Research and Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil
| | - Joel K. Elmquist
- Research Division, Joslin Diabetes Center, Boston, Massachusetts, USA.
Laboratory of Molecular Genetics, The Rockefeller University, New York, New York, USA.
Departments of Chemistry and Pharmacology, University of Michigan, Ann Arbor, Michigan, USA.
Center for Hypothalamic Research and Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil
| | - Robert T. Kennedy
- Research Division, Joslin Diabetes Center, Boston, Massachusetts, USA.
Laboratory of Molecular Genetics, The Rockefeller University, New York, New York, USA.
Departments of Chemistry and Pharmacology, University of Michigan, Ann Arbor, Michigan, USA.
Center for Hypothalamic Research and Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil
| | - Rohit N. Kulkarni
- Research Division, Joslin Diabetes Center, Boston, Massachusetts, USA.
Laboratory of Molecular Genetics, The Rockefeller University, New York, New York, USA.
Departments of Chemistry and Pharmacology, University of Michigan, Ann Arbor, Michigan, USA.
Center for Hypothalamic Research and Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil
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115
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Park S, Hong SM, Lee JE, Sung SR. Exercise improves glucose homeostasis that has been impaired by a high-fat diet by potentiating pancreatic β-cell function and mass through IRS2 in diabetic rats. J Appl Physiol (1985) 2007; 103:1764-71. [PMID: 17761790 DOI: 10.1152/japplphysiol.00434.2007] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
In this study, we investigated the effects of a high-fat diet and exercise on pancreatic β-cell function and mass and its molecular mechanism in 90% pancreatectomized male rats. The pancreatectomized diabetic rats were given control diets (20% energy) or a high-fat (HF) diet (45% energy) for 12 wk. Half of each group was given regular exercise on an uphill treadmill at 20 m/min for 30 min 5 days/wk. HF diet lowered first-phase insulin secretion with glucose loading, whereas exercise training reversed this decrease. However, second-phase insulin secretion did not differ among the groups. Exercise increased pancreatic β-cell mass. This resulted from stimulated β-cell proliferation and reduced apoptosis, which is associated with potentiated insulin or IGF-I signaling through insulin receptor substrate-2 (IRS2) induction. Although the HF diet resulted in decreased proliferation and accelerated apoptosis by weakened insulin and IGF-I signaling from reduction of IRS2 protein, β-cell mass was maintained in HF rats just as much as in control rats via increased individual β-cell size and neogenesis from precursor cells. Consistent with the results of β-cell proliferation, pancreas duodenal homeobox-1 expression increased in the islets of rats in the exercise groups, and it was reduced the most in rats fed the HF diet. In conclusion, exercise combined with a moderate fat diet is a good way to maximize β-cell function and mass through IRS2 induction to alleviate the diabetic condition. This study suggests that dietary fat contents and exercise modulate β-cell function and mass to overcome insulin resistance in two different pathways.
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Affiliation(s)
- Sunmin Park
- Dept. of Food and Nutrition, College of Natural Science, Institutes of Basic Sciences, Hoseo Univ., 165 Sechul-Ri Baebang-Myun Asan-Si, Chungnam-Do, 336-795, Korea.
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116
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Ballian N, Hu M, Liu SH, Brunicardi FC. Proliferation, hyperplasia, neogenesis, and neoplasia in the islets of Langerhans. Pancreas 2007; 35:199-206. [PMID: 17895838 DOI: 10.1097/mpa.0b013e318074c6ed] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Pancreatic disease is responsible for significant morbidity and mortality as a result of pancreatic carcinoma and diabetes mellitus. Regulation of endocrine cell mass is thought to have a central role in the pathogenesis of both these diseases. Islet cell proliferation, hypertrophy, neogenesis, and apoptosis are the main determinants of endocrine cell mass in the pancreas, and their understanding has been improved by new clues of their genetic and molecular basis. Beta cells have attracted most research interest because of potential implications in the treatment of diabetes mellitus and hypoglycemic disorders. The processes that operate during pancreatic adaptation to a changing hormonal milieu are important in pancreatic carcinogenesis. There is evidence that somatostatin and its receptors are fundamental regulators of endocrine cell mass and are involved in islet tumorigenesis.
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Affiliation(s)
- Nikiforos Ballian
- Department of Surgery, The Johns Hopkins Hospital, Baltimore, MD, USA
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117
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Babu DA, Deering TG, Mirmira RG. A feat of metabolic proportions: Pdx1 orchestrates islet development and function in the maintenance of glucose homeostasis. Mol Genet Metab 2007; 92:43-55. [PMID: 17659992 PMCID: PMC2042521 DOI: 10.1016/j.ymgme.2007.06.008] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/29/2007] [Revised: 06/14/2007] [Accepted: 06/15/2007] [Indexed: 01/30/2023]
Abstract
Emerging evidence over the past decade indicates a central role for transcription factors in the embryonic development of pancreatic islets and the consequent maintenance of normal glucose homeostasis. Pancreatic and duodenal homeobox 1 (Pdx1) is the best studied and perhaps most important of these factors. Whereas deletion or inactivating mutations of the Pdx1 gene causes whole pancreas agenesis in both mice and humans, even haploinsufficiency of the gene or alterations in its expression in mature islet cells causes substantial impairments in glucose tolerance and the development of a late-onset form of diabetes known as maturity onset diabetes of the young. The study of Pdx1 has revealed crucial phenotypic interrelationships of the varied cell types within the pancreas, particularly as these impinge upon cellular differentiation in the embryo and neogenesis and regeneration in the adult. In this review, we describe the actions of Pdx1 in the developing and mature pancreas and attempt to unify these actions with its known roles in modulating transcriptional complex formation and chromatin structure at the molecular genetic level.
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Affiliation(s)
- Daniella A. Babu
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908 USA
| | - Tye G. Deering
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908 USA
| | - Raghavendra G. Mirmira
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908 USA
- Diabetes Center, Department of Medicine, University of Virginia, Charlottesville, VA 22908 USA
- To whom correspondence should be addressed: University of Virginia Health System, 450 Ray C. Hunt Drive, Box 801407, Charlottesville, VA 22908. E-mail: , Telephone: 434-924-9416, Fax: 434-982-3796
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118
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Park S, Jang JS, Hong SM. Long-term consumption of caffeine improves glucose homeostasis by enhancing insulinotropic action through islet insulin/insulin-like growth factor 1 signaling in diabetic rats. Metabolism 2007; 56:599-607. [PMID: 17445533 DOI: 10.1016/j.metabol.2006.12.004] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/01/2006] [Accepted: 12/20/2006] [Indexed: 11/16/2022]
Abstract
Our previous study demonstrated that long-term cola consumption reduced body weight and improved insulin sensitivity in healthy male rats. In this study, we investigated the effect and mechanism of caffeine and sucrose, major components of cola, on glucose metabolism in 90% pancreatectomized diabetic rats. After a 12-week administration of 0.01% caffeine solution, the rats exhibited reduced body weight, fats, and insulin resistance, without a change in food intake, regardless of an 11% sucrose solution supplementation. In addition, caffeine enhanced glucose-stimulated first- and second-phase insulin secretion and beta-cell hyperplasia. This insulinotropic action was explained by potentiating an insulin/insulin-like growth factor 1 (IGF-1) signaling cascade via induction of insulin receptor substrate 2 in islets. In contrast, sucrose supplementation deteriorated insulin sensitivity and attenuated insulin/IGF-1 signaling in islets, which reduced the number of beta cells. Caffeine nullified the adverse effect of sucrose on glucose homeostasis. These findings indicate that long-term caffeine consumption can help alleviate diabetic symptoms by enhancing insulin sensitivity and beta-cell function through improved insulin/IGF-1 signaling via induction of insulin receptor substrate 2 in mildly diabetic rats.
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Affiliation(s)
- Sunmin Park
- Department of Food and Nutrition, College of Natural Science and Institute of Basic Sciences, Hoseo University, Asan-Si, South Korea.
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119
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Latour MG, Alquier T, Oseid E, Tremblay C, Jetton TL, Luo J, Lin DCH, Poitout V. GPR40 is necessary but not sufficient for fatty acid stimulation of insulin secretion in vivo. Diabetes 2007; 56:1087-94. [PMID: 17395749 PMCID: PMC1853382 DOI: 10.2337/db06-1532] [Citation(s) in RCA: 212] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Long-chain fatty acids amplify insulin secretion from the pancreatic beta-cell. The G-protein-coupled receptor GPR40 is specifically expressed in beta-cells and is activated by fatty acids; however, its role in acute regulation of insulin secretion in vivo remains unclear. To this aim, we generated GPR40 knockout (KO) mice and examined glucose homeostasis, insulin secretion in response to glucose and Intralipid in vivo, and insulin secretion in vitro after short- and long-term exposure to fatty acids. Our results show that GPR40 KO mice have essentially normal glucose tolerance and insulin secretion in response to glucose. Insulin secretion in response to Intralipid was reduced by approximately 50%. In isolated islets, insulin secretion in response to glucose and other secretagogues was unaltered, but fatty acid potentiation of insulin release was markedly reduced. The Galpha(q/11) inhibitor YM-254890 dose-dependently reduced palmitate potentiation of glucose-induced insulin secretion. Islets from GPR40 KO mice were as sensitive to fatty acid inhibition of insulin secretion upon prolonged exposure as islets from wild-type animals. We conclude that GPR40 contributes approximately half of the full acute insulin secretory response to fatty acids in mice but does not play a role in the mechanisms by which fatty acids chronically impair insulin secretion.
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Affiliation(s)
- Martin G. Latour
- Montréal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l’Université de Montréal, Montréal, QC, Canada
| | - Thierry Alquier
- Montréal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l’Université de Montréal, Montréal, QC, Canada
| | | | - Caroline Tremblay
- Montréal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l’Université de Montréal, Montréal, QC, Canada
| | - Thomas L. Jetton
- Division of Endocrinology, Diabetes and Metabolism, University of Vermont College of Medicine, Burlington, VT
| | | | | | - Vincent Poitout
- Montréal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l’Université de Montréal, Montréal, QC, Canada
- Departments of Medicine, Nutrition, and Biochemistry, University of Montréal, Montréal, QC, Canada
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120
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Kien CL, Blauwiekel R, Bunn JY, Jetton TL, Frankel WL, Holst JJ. Cecal infusion of butyrate increases intestinal cell proliferation in piglets. J Nutr 2007; 137:916-22. [PMID: 17374654 PMCID: PMC1949321 DOI: 10.1093/jn/137.4.916] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The effects of colon-derived butyrate on intestinal cell proliferation are controversial. In vitro studies suggest an inhibitory effect, and in vivo studies suggest the opposite, but neither type of study has been based on a physiologically relevant, intracolonic supply of butyrate. In this study, piglets (n = 24) were fed sow's milk replacement formula and randomized into 4 equal groups: 1) control; 2) cecal butyrate infusion at a rate equal to that produced in the colon; 3) inulin supplementation at a concentration previously found to lower cecal cell proliferation; and 4) butyrate infusion plus inulin supplementation. After 6 d of oral feeding, cecal butyrate infusions were initiated for a period of 4 d. Cecal, distal colonic, jejunal, and ileal cell proliferation, apoptosis, and morphology were evaluated and serum concentration of glucagon-like peptide-2 (GLP-2) was measured. Butyrate or inulin did not affect GLP-2, weight gain, apoptosis, intestinal injury scores, cecal or colon crypt depth, and jejunal or ileal villus height. For cell proliferation, there was a significant interaction between inulin, butyrate, and tissue (P = 0.007). Inulin modified the effect of butyrate (butyrate x inulin interaction in cecum, P = 0.001; in distal colon, P = 0.018; in ileum, P = 0.001; and in jejunum, P = 0.003). In the absence of inulin, butyrate caused a 78- 119% increase in cell proliferation in the ileum, distal colon, jejunum, and cecum (P < or = 0.002). Thus, at an entry rate into the colon within the physiological range, butyrate caused increased intestinal cell proliferation, but inulin tended to block this effect. Thus, intracolonic butyrate may enhance intestinal growth during infancy.
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Affiliation(s)
- C Lawrence Kien
- Department of Pediatrics, College of Medicine, University of Vermont, Burlington, VT 05405, USA.
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121
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Mussmann R, Geese M, Harder F, Kegel S, Andag U, Lomow A, Burk U, Onichtchouk D, Dohrmann C, Austen M. Inhibition of GSK3 promotes replication and survival of pancreatic beta cells. J Biol Chem 2007; 282:12030-7. [PMID: 17242403 DOI: 10.1074/jbc.m609637200] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Recent developments indicate that the regeneration of beta cell function and mass in patients with diabetes is possible. A regenerative approach may represent an alternative treatment option relative to current diabetes therapies that fail to provide optimal glycemic control. Here we report that the inactivation of GSK3 by small molecule inhibitors or RNA interference stimulates replication of INS-1E rat insulinoma cells. Specific and potent GSK3 inhibitors also alleviate the toxic effects of high concentrations of glucose and the saturated fatty acid palmitate on INS-1E cells. Furthermore, treatment of isolated rat islets with structurally diverse small molecule GSK3 inhibitors increases the rate beta cell replication by 2-3-fold relative to controls. We propose that GSK3 is a regulator of beta cell replication and survival. Moreover, our results suggest that specific inhibitors of GSK3 may have practical applications in beta cell regenerative therapies.
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Affiliation(s)
- Rainer Mussmann
- DeveloGen AG, Marie-Curie-Strasse 7, Göttingen 37079, Germany
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122
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Peshavaria M, Larmie BL, Lausier J, Satish B, Habibovic A, Roskens V, Larock K, Everill B, Leahy JL, Jetton TL. Regulation of pancreatic beta-cell regeneration in the normoglycemic 60% partial-pancreatectomy mouse. Diabetes 2006; 55:3289-98. [PMID: 17130472 DOI: 10.2337/db06-0017] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
beta-Cell mass is determined by a dynamic balance of proliferation, neogenesis, and apoptosis. The precise mechanisms underlying compensatory beta-cell mass (BCM) homeostasis are not fully understood. To evaluate the processes that maintain normoglycemia and regulate BCM during pancreatic regeneration, C57BL/6 mice were analyzed for 15 days following 60% partial pancreatectomy (Px). BCM increased in Px mice from 2 days onwards and was approximately 68% of the shams by 15 days, partly due to enhanced beta-cell proliferation. A transient approximately 2.8-fold increase in the prevalence of beta-cell clusters/small islets at 2 days post-Px contributed substantially to BCM augmentation, followed by an increase in the number of larger islets at 15 days. To evaluate the signaling mechanisms that may regulate this compensatory growth, we examined key intermediates of the insulin signaling pathway. We found insulin receptor substrate (IRS)2 and enhanced-activated Akt immunoreactivity in islets and ducts that correlated with increased pancreatic duodenal homeobox (PDX)1 expression. In contrast, forkhead box O1 expression was decreased in islets but increased in ducts, suggesting distinct PDX1 regulatory mechanisms in these tissues. Px animals acutely administered insulin exhibited further enhancement in insulin signaling activity. These data suggest that the IRS2-Akt pathway mediates compensatory beta-cell growth by activating beta-cell proliferation with an increase in the number of beta-cell clusters/small islets.
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Affiliation(s)
- Mina Peshavaria
- University of Vermont College of Medicine, Department of Medicine, Given C331, Burlington, VT 05405, USA.
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123
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Abstract
The major focus of this Review is on the mechanisms of islet beta cell failure in the pathogenesis of obesity-associated type 2 diabetes (T2D). As this demise occurs within the context of beta cell compensation for insulin resistance, consideration is also given to the mechanisms involved in the compensation process, including mechanisms for expansion of beta cell mass and for enhanced beta cell performance. The importance of genetic, intrauterine, and environmental factors in the determination of "susceptible" islets and overall risk for T2D is reviewed. The likely mechanisms of beta cell failure are discussed within the two broad categories: those with initiation and those with progression roles.
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Affiliation(s)
- Marc Prentki
- Molecular Nutrition Unit and Montreal Diabetes Research Center, University of Montreal and Centre Hospitalier de l’Université de Montréal, Montreal, Quebec, Canada.
Department of Endocrinology and Diabetes, The Canberra Hospital, and Medical School, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Christopher J. Nolan
- Molecular Nutrition Unit and Montreal Diabetes Research Center, University of Montreal and Centre Hospitalier de l’Université de Montréal, Montreal, Quebec, Canada.
Department of Endocrinology and Diabetes, The Canberra Hospital, and Medical School, Australian National University, Canberra, Australian Capital Territory, Australia
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124
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Wente W, Efanov AM, Brenner M, Kharitonenkov A, Köster A, Sandusky GE, Sewing S, Treinies I, Zitzer H, Gromada J. Fibroblast growth factor-21 improves pancreatic beta-cell function and survival by activation of extracellular signal-regulated kinase 1/2 and Akt signaling pathways. Diabetes 2006; 55:2470-8. [PMID: 16936195 DOI: 10.2337/db05-1435] [Citation(s) in RCA: 378] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Fibroblast growth factor-21 (FGF-21) is a recently discovered metabolic regulator. Here, we investigated the effects of FGF-21 in the pancreatic beta-cell. In rat islets and INS-1E cells, FGF-21 activated extracellular signal-regulated kinase 1/2 and Akt signaling pathways. In islets isolated from healthy rats, FGF-21 increased insulin mRNA and protein levels but did not potentiate glucose-induced insulin secretion. Islets and INS-1E cells treated with FGF-21 were partially protected from glucolipotoxicity and cytokine-induced apoptosis. In islets isolated from diabetic rodents, FGF-21 treatment increased islet insulin content and glucose-induced insulin secretion. Short-term treatment of normal or db/db mice with FGF-21 lowered plasma levels of insulin and improved glucose clearance compared with vehicle after oral glucose tolerance testing. Constant infusion of FGF-21 for 8 weeks in db/db mice nearly normalized fed blood glucose levels and increased plasma insulin levels. Immunohistochemistry of pancreata from db/db mice showed a substantial increase in the intensity of insulin staining in islets from FGF-21-treated animals as well as a higher number of islets per pancreas section and of insulin-positive cells per islet compared with control. No effect of FGF-21 was observed on islet cell proliferation. In conclusion, preservation of beta-cell function and survival by FGF-21 may contribute to the beneficial effects of this protein on glucose homeostasis observed in diabetic animals.
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Affiliation(s)
- Wolf Wente
- Lilly Research Laboratories, Essener Bogen 7, D-22419 Hamburg, Germany
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125
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Robertson K, Kopchick JJ, Liu JL. Growth hormone receptor gene deficiency causes delayed insulin responsiveness in skeletal muscles without affecting compensatory islet cell overgrowth in obese mice. Am J Physiol Endocrinol Metab 2006; 291:E491-8. [PMID: 16621895 DOI: 10.1152/ajpendo.00378.2005] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Growth hormone (GH), acting through its receptor (GHR), is essential for somatic growth and development and maintaining metabolic homeostasis. GHR gene-deficient (GHR(-/-)) mice exhibit drastically diminished insulin-like growth factor-I (IGF-I) levels, proportional growth retardation, elevated insulin sensitivity, and reduced islet beta-cell mass. Unlike the liver, which is mostly unaffected by changes in IGF-I level, skeletal muscles express high levels of IGF-I receptor (IGF-IR). The net result of a concurrent deficiency in the actions of both GH and IGF-I, which exert opposite influences on insulin responsiveness, has not been evaluated. We studied insulin-stimulated early responses in the insulin receptor (IR), insulin receptor substrate-1 (IRS-1), and p85 subunit of phosphatidylinositol 3-kinase. Upon in vivo insulin stimulation, skeletal muscles of GHR(-/-) mice exhibit transient delayed responses in IR and IRS-1 phosphorylation but normal levels of p85 association with IRS-1. This is in contrast to normal/elevated insulin responses in hepatocytes and indicates tissue-specific effects of GHR gene deficiency. In addition to stimulating normal islet cell growth, GH may participate in islet cell overgrowth, which compensates for insulin resistance induced by obesity. To determine whether the islet cell overgrowth is dependent on GH signaling, we studied the response of male GHR(-/-) mice to high-fat diet (HFD)-induced obesity. After 17 wk on a HFD, GHR(-/-) mice became more significantly obese than wild-type mice and exhibited increased beta-cell mass to a slightly higher extent. These data demonstrate that GH signaling is not required for compensatory islet growth. Thus, in both muscle insulin responsiveness and islet growth compensation, normal levels of GH signals do not seem to play a dominant role.
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Affiliation(s)
- Katie Robertson
- Fraser Laboratories for Diabetic Research, Department of Medicine, McGill University Health Center, Montreal, QC, Canada
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126
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Perera HK, Caldwell ME, Hayes-Patterson D, Teng L, Peshavaria M, Jetton TL, Labosky PA. Expression and shifting subcellular localization of the transcription factor, Foxd3, in embryonic and adult pancreas. Gene Expr Patterns 2006; 6:971-7. [PMID: 16750430 DOI: 10.1016/j.modgep.2006.04.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2006] [Revised: 03/08/2006] [Accepted: 04/05/2006] [Indexed: 11/27/2022]
Abstract
Multipotent progenitor cells self renew throughout an animal's lifetime and can differentiate to give rise to different cell types. Before we can fully understand the developmental potential of progenitor cells and control their differentiation both in vivo and in vitro as stem cells, identification and characterization of the genes that control stem cell fate must first be obtained. Foxd3, a member of the forkhead family of transcriptional regulators, is required for the maintenance of embryonic stem cells and trophoblast stem cells of the early mouse embryo. We describe here the expression of this protein in the developing pancreas. Foxd3 is expressed in most beta cells and infrequently in alpha and PP cells but is not expressed in somatostatin cells. The subcellular localization of Foxd3 varies with fat content in the diet; with a high fat diet the protein is found primarily in the cytoplasm while a low fat diet results in nuclear localization. Foxd3 is differentially localized in a rat model of diabetes: it is nuclear in ZDF rats but cytoplasmic in their lean counterparts. Foxd3 is nuclear in Lep(Ob/Ob) mice.
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Affiliation(s)
- Hemashi K Perera
- Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia, PA 19104-6058, USA
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127
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Masiello P. Animal models of type 2 diabetes with reduced pancreatic beta-cell mass. Int J Biochem Cell Biol 2005; 38:873-93. [PMID: 16253543 DOI: 10.1016/j.biocel.2005.09.007] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2005] [Revised: 09/02/2005] [Accepted: 09/08/2005] [Indexed: 12/31/2022]
Abstract
Type 2 diabetes is increasingly viewed as a disease of insulin deficiency due not only to intrinsic pancreatic beta-cell dysfunction but also to reduction of beta-cell mass. It is likely that, in diabetes-prone subjects, the regulated beta-cell turnover that adapts cell mass to body's insulin requirements is impaired, presumably on a genetic basis. We still have a limited knowledge of how and when this derangement occurs and what might be the most effective therapeutic strategy to preserve beta-cell mass. The animal models of type 2 diabetes with reduced beta-cell mass described in this review can be extremely helpful (a) to have insight into the mechanisms underlying the defective growth or accelerated loss of beta-cells leading to the beta-cell mass reduction; (b) to investigate in prospective studies the mechanisms of compensatory adaptation and subsequent failure of a reduced beta-cell mass. Furthermore, these models are of invaluable importance to test the effectiveness of potential therapeutic agents that either stimulate beta-cell growth or inhibit beta-cell death.
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Affiliation(s)
- Pellegrino Masiello
- Dipartimento di Patologia Sperimentale, Biotecnologie Mediche, Infettivologia ed Epidemiologia, University of Pisa, Scuola Medica, Italy.
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