| 1. |
- Abels, Mia, et al.
(author)
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CART is overexpressed in human type 2 diabetic islets and inhibits glucagon secretion and increases insulin secretion
- 2016
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In: Diabetologia. - : Springer Science and Business Media LLC. - 0012-186X .- 1432-0428. ; 59:9, s. 1928-1937
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Journal article (peer-reviewed)abstract
- Aims/hypothesis Insufficient insulin release and hyperglucagonaemia are culprits in type 2 diabetes. Cocaine- and amphetamine-regulated transcript (CART, encoded by Cartpt) affects islet hormone secretion and beta cell survival in vitro in rats, and Cart(-/-) mice have diminished insulin secretion. We aimed to test if CART is differentially regulated in human type 2 diabetic islets and if CART affects insulin and glucagon secretion in vitro in humans and in vivo in mice. Methods CART expression was assessed in human type 2 diabetic and non-diabetic control pancreases and rodent models of diabetes. Insulin and glucagon secretion was examined in isolated islets and in vivo in mice. Ca2+ oscillation patterns and exocytosis were studied in mouse islets. Results We report an important role of CART in human islet function and glucose homeostasis in mice. CART was found to be expressed in human alpha and beta cells and in a subpopulation of mouse beta cells. Notably, CART expression was several fold higher in islets of type 2 diabetic humans and rodents. CART increased insulin secretion in vivo in mice and in human and mouse islets. Furthermore, CART increased beta cell exocytosis, altered the glucose-induced Ca2+ signalling pattern in mouse islets from fast to slow oscillations and improved synchronisation of the oscillations between different islet regions. Finally, CART reduced glucagon secretion in human and mouse islets, as well as in vivo in mice via diminished alpha cell exocytosis. Conclusions/interpretation We conclude that CART is a regulator of glucose homeostasis and could play an important role in the pathophysiology of type 2 diabetes. Based on the ability of CART to increase insulin secretion and reduce glucagon secretion, CART-based agents could be a therapeutic modality in type 2 diabetes.
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| 2. |
- Anvari, Ebrahim, et al.
(author)
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The H-1-Receptor Antagonist Cetirizine Protects Partially Against Cytokine- and Hydrogen Peroxide-Induced beta-TC6 Cell Death In Vitro
- 2014
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In: Pancreas. - 0885-3177 .- 1536-4828. ; 43:4, s. 624-629
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Journal article (peer-reviewed)abstract
- Objective It has been proposed that the histamine 1 (H-1) receptor not only promotes allergic reactions but also modulates autoimmune diseases, such as type 1 diabetes. In line with this, it has recently been reported that the H-1-receptor antagonist cetirizine can counteract the activation of signals/factors pertinent to the pathogenesis of type 1 diabetes and cytokine-induced beta-cell destruction. Therefore, the overall aim of this study was to determine whether H-1-receptor antagonists affect cytokine-induced beta-cell death and signaling in vitro. Methods The insulin-producing cell line beta-TC6 was exposed to the proinflammatory cytokines interleukin 1 beta(+) interferon gamma, or hydrogen peroxide. The H-1-receptor antagonists desloratadine and cetirizine were added to the cell cultures and cell viability; macrophage inhibitory factor levels, c-Jun N-terminal kinase phosphorylation, c-Jun expression, and beta-catenin levels were analyzed by flow cytometry, real-time polymerase chain reaction, and immunoblotting. Results Cetirizine protected partially against both cytokine- and hydrogen peroxide-induced cell death. This effect was paralleled by an inhibition of cytokine-induced c-Jun N-terminal kinase phosphorylation, c-Jun induction, and a restoration of macrophage inhibitory factor contents. Cetirizine also increased the beta-TC6 cell contents of beta-catenin at basal conditions. Conclusions Our results indicate a protective effect of a specific H-1-receptor antagonist.
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| 3. |
- Ejdesjö, Andreas, 1978-, et al.
(author)
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Receptor for Advanced Glycation End products (RAGE) knockout reduces fetal dysmorphogenesis in murine diabetic pregnancy
- 2016
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In: Reproductive Toxicology. - : Elsevier BV. - 0890-6238 .- 1873-1708. ; 62, s. 62-70
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Journal article (other academic/artistic)abstract
- Background & Aim: The receptor for Advanced Glycation End products (RAGE) is implicated in the pathogenesis of diabetic complications, but its importance for the induction of congenital malformations in diabetic pregnancy is unclear. The aim of the present study was to investigate a possible role of RAGE activation in the induction of diabetic embryopathy.Methods: Female non-diabetic and diabetic wildtype (WT) C57Bl/6 mice and RAGE knockout C57Bl/6 (RAGE‑/-) mice were mated with males of the same genotype. Diabetes was induced by daily streptozotocin (STZ) injections (50 mg/kg STZ i.p.) on five consecutive days. On gestational day 18, pregnant mice were anesthetized and blood was drawn from the heart to measure maternal metabolic parameters. Fetuses and placentas were excised, weighed, and examined for morphological anomalies, and fetal livers were analyzed for 8‑iso‑PGF2α levels.Results: There were no malformations in non-diabetic WT or non-diabetic RAGE‑/- mice. However, resorption rates were higher in non-diabetic WT (10%) than in non-diabetic RAGE‑/- mice (4%). Diabetic WT mice had higher malformation (22%) and resorption (43%) rates than diabetic RAGE‑/- mice (3% malformations and 21% resorptions). Maternal diabetes decreased fetal weight more in WT fetuses (44%) than in RAGE‑/- fetuses (36%). There were no differences in plasma glucose levels between the diabetic WT and RAGE‑/- mice, but plasma levels of triglycerides and cholesterol were lower in diabetic WT mice than in diabetic RAGE-/- mice. Diabetes increased maternal plasma levels of methylglyoxal in WT and RAGE‑/- mice, and increased fetal hepatic levels of 8-iso-PGF2α in WT fetuses, but not in RAGE‑/- fetuses. Discussion: Knockout of RAGE diminished the rates of fetal malformations and resorptions, despite similar levels of hyperglycemia in pregnant diabetic mice. An anti-teratogenic effect was present in RAGE‑/- mice despite having a more severe diabetic state than diabetic WT mice. As 8-iso-PGF2α, a marker of oxidative stress, only increased in diabetic WT offspring, this suggested a pivotal role of RAGE activation and oxidative stress in the pathogenesis of diabetic embryopathy.
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| 4. |
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| 5. |
- Fred, Rikard G, et al.
(author)
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High glucose suppresses human islet insulin biosynthesis by inducing miR-133a leading to decreased polypyrimidine tract binding protein-expression
- 2010
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In: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 5:5, s. e10843-
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Journal article (peer-reviewed)abstract
- BACKGROUND:Prolonged periods of high glucose exposure results in human islet dysfunction in vitro. The underlying mechanisms behind this effect of high glucose are, however, unknown. The polypyrimidine tract binding protein (PTB) is required for stabilization of insulin mRNA and the PTB mRNA 3'-UTR contains binding sites for the microRNA molecules miR-133a, miR-124a and miR-146. The aim of this study was therefore to investigate whether high glucose increased the levels of these three miRNAs in association with lower PTB levels and lower insulin biosynthesis rates.METHODOLOGY/PRINCIPAL FINDINGS:Human islets were cultured for 24 hours in the presence of low (5.6 mM) or high glucose (20 mM). Islets were also exposed to sodium palmitate or the proinflammatory cytokines IL-1beta and IFN-gamma, since saturated free fatty acids and cytokines also cause islet dysfunction. RNA was then isolated for real-time RT-PCR analysis of miR-133a, miR-124a, miR-146, insulin mRNA and PTB mRNA contents. Insulin biosynthesis rates were determined by radioactive labeling and immunoprecipitation. Synthetic miR-133a precursor and inhibitor were delivered to dispersed islet cells by lipofection, and PTB was analyzed by immunoblotting following culture at low or high glucose. Culture in high glucose resulted in increased islet contents of miR-133a and reduced contents of miR-146. Cytokines increased the contents of miR-146. The insulin and PTB mRNA contents were unaffected by high glucose. However, both PTB protein levels and insulin biosynthesis rates were decreased in response to high glucose. The miR-133a inhibitor prevented the high glucose-induced decrease in PTB and insulin biosynthesis, and the miR-133a precursor decreased PTB levels and insulin biosynthesis similarly to high glucose.CONCLUSION:Prolonged high-glucose exposure down-regulates PTB levels and insulin biosynthesis rates in human islets by increasing miR-133a levels. We propose that this mechanism contributes to hyperglycemia-induced beta-cell dysfunction.
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| 6. |
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| 7. |
- Fred, Rikard G., et al.
(author)
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Imatinib mesylate stimulates low-density lipoprotein receptor-related protein 1-mediated ERK phosphorylation in insulin-producing cells
- 2015
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In: Clinical Science. - 0143-5221 .- 1470-8736. ; 128:1, s. 17-28
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Journal article (peer-reviewed)abstract
- Low-density lipoprotein receptor-related protein 1 (LRP1) is an endocytic and multi-functional type I cell surface membrane protein, which is known to be phosphorylated by the activated platelet-derived growth factor receptor (PDGFR). The tyrosine kinase inhibitor imatinib, which inhibits PDGFR and c-Abl, and which has previously been reported to counteract beta-cell death and diabetes, has been suggested to reduce atherosclerosis by inhibiting PDGFR-induced LRP1 phosphorylation. The aim of the present study was to study LRP1 function in beta-cells and to what extent imatinib modulates LRP1 activity. LRP1 and c-Abl gene knockdown was performed by RNAi using rat INS-1 832/13 and human EndoC1-beta H1 cells. LRP1 was also antagonized by treatment with the antagonist low-density lipoprotein receptor-related protein associated protein 1 (LRPAP1). We have used PDGF-BB, a PDGFR agonist, and apolipoprotein E (ApoE), an LRP1 agonist, to stimulate the activities of PDGFR and LRP1 respectively. Knockdown or inhibition of LRP1 resulted in increased hydrogen peroxide (H2O2)(-) or cytokine-induced cell death, and glucose-induced insulin release was lowered in LRP1-silenced cells. These results indicate that LRP1 function is necessary for beta-cell function and that LRP1 is adversely affected by challenges to beta-cell health. PDGF-BB, or the combination of PDGF-BB+ApoE, induced phosphorylation of extracellular-signal-regulated kinase (ERK), Akt and LRP1. LRP1 silencing blocked this event. Imatinib blocked phosphorylation of LRP1 by PDGFR activation but induced phosphorylation of ERK. LRP1 silencing blocked imatinib-induced phosphorylation of ERK. Sunitinib also blocked LRP1 phosphorylation in response to PDGF-BB and induced phosphorylation of ERK, but this latter event was not affected by LRP1 knockdown. siRNA-mediated knockdown of the imatinib target c-Abl resulted in an increased ERK phosphorylation at basal conditions, with no further increase in response to imatinib. Imatinib-induced cell survival of tunicamycin-treated cells was partially mediated by ERK activation. We have concluded that imatinib promotes LRP1-dependent ERK activation, possibly via inhibition of c-Abl, and that this could contribute to the pro-survival effects of imatinib on beta-cells.
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| 8. |
- Fred, Rikard G, et al.
(author)
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Increased expression of polypyrimidine tract binding protein results in higher insulin mRNA levels
- 2005
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In: Biochemical and Biophysical Research Communications - BBRC. - : Elsevier BV. - 0006-291X .- 1090-2104. ; 328:1, s. 38-42
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Journal article (peer-reviewed)abstract
- The aim of this study was to further elucidate the role of the polypyrimidine tract binding protein (PTB) in the control of insulin mRNA stability. We observed that the glucose- or interleukin-1β-induced increase in insulin mRNA was paralleled by an increase in PTB mRNA. To further test the hypothesis that PTB controls insulin gene expression, βTC-6 cells were treated with a PTB-specific siRNA to modify the β-cell content of PTB. Surprisingly, we observed an increase in PTB mRNA and PTB protein levels in response to the siRNA treatment. In addition, the PTB-siRNA treatment also increased insulin mRNA. We conclude that expression of the PTB gene controls insulin production.
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| 9. |
- Fred, Rikard G, et al.
(author)
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PTB and TIAR binding to insulin mRNA 3'- and 5'UTRs; implications for insulin biosynthesis and messenger stability.
- 2016
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In: Heliyon. - : Elsevier BV. - 2405-8440. ; 2:9
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Journal article (peer-reviewed)abstract
- ObjectivesInsulin expression is highly controlled on the posttranscriptional level. The RNA binding proteins (RBPs) responsible for this result are still largely unknown.Methods and resultsTo identify RBPs that bind to insulin mRNA we performed mass spectrometry analysis on proteins that bound synthetic oligonucloetides mimicing the 5′- and the 3′-untranslated regions (UTRs) of rat and human insulin mRNA in vitro. We observed that the RBPs heterogeneous nuclear ribonucleoprotein (hnRNP) U, polypyrimidine tract binding protein (PTB), hnRNP L and T-cell restricted intracellular antigen 1-related protein (TIA-1-related protein; TIAR) bind to insulin mRNA sequences, and that the in vitro binding affinity of these RBPs changed when INS-1 cells were exposed to glucose, 3-isobutyl-1-methylxanthine (IBMX) or nitric oxide. High glucose exposure resulted in a modest increase in PTB and TIAR binding to an insulin mRNA sequence. The inducer of nitrosative stress DETAnonoate increased markedly hnRNP U and TIAR mRNA binding. An increased PTB to TIAR binding ratio in vitro correlated with higher insulin mRNA levels and insulin biosynthesis rates in INS-1 cells. To further investigate the importance of RNA-binding proteins for insulin mRNA stability, we decreased INS-1 and EndoC-βH1 cell levels of PTB and TIAR by RNAi. In both cell lines, decreased levels of PTB resulted in lowered insulin mRNA levels while decreased levels of TIAR resulted in increased insulin mRNA levels. Thapsigargin-induced stress granule formation was associated with a redistribution of TIAR from the cytosol to stress granules.ConclusionsThese experiments indicate that alterations in insulin mRNA stability and translation correlate with differential RBP binding. We propose that the balance between PTB on one hand and TIAR on the other participates in the control of insulin mRNA stability and utilization for insulin biosynthesis.
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| 10. |
- Fred, Rikard G., et al.
(author)
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Role of the AMP kinase in cytokine-induced human EndoC-beta H1 cell death
- 2015
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In: Molecular and Cellular Endocrinology. - : Elsevier BV. - 0303-7207 .- 1872-8057. ; 414:C, s. 53-63
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Journal article (peer-reviewed)abstract
- The aim of the present investigation was to delineate cytokine-induced signaling and death using the EndoC-beta H1 cells as a model for primary human beta-cells. The cytokines IL-1 beta and IFN-gamma induced a rapid and transient activation of NF-kappa B, STAT-1, ERK, JNK and eIF-2 alpha signaling. The EndoC-beta H1 cells died rapidly when exposed to IL-1 beta + IFN-gamma, and this occurred also in the presence of the actinomycin D. Inhibition of NF-kappa B and STAT-1 did not protect against cell death, nor did the cytokines activate iNOS expression. Instead, cytokines promoted a rapid decrease in EndoC-beta H1 cell respiration and ATP levels, and we observed protection by the AMPK activator AICAR against cytokine-induced cell death. It is concluded that EndoC-beta H1 cell death can be prevented by AMPK activation, which suggests a role for ATP depletion in cytokine-induced human beta-cell death.
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