| 1. |
- Fred, Rikard G, et al.
(författare)
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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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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 5:5, s. e10843-
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Abels, Mia, et al.
(författare)
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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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Ingår i: Diabetologia. - : Springer Science and Business Media LLC. - 0012-186X .- 1432-0428. ; 59:9, s. 1928-1937
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Anvari, Ebrahim, et al.
(författare)
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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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Ingår i: Pancreas. - 0885-3177 .- 1536-4828. ; 43:4, s. 624-629
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Ejdesjö, Andreas, 1978-, et al.
(författare)
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Receptor for Advanced Glycation End products (RAGE) knockout reduces fetal dysmorphogenesis in murine diabetic pregnancy
- 2016
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Ingår i: Reproductive Toxicology. - : Elsevier BV. - 0890-6238 .- 1873-1708. ; 62, s. 62-70
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)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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| 5. |
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| 6. |
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| 7. |
- Fred, Rikard G., et al.
(författare)
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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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Ingår i: Clinical Science. - 0143-5221 .- 1470-8736. ; 128:1, s. 17-28
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Increased expression of polypyrimidine tract binding protein results in higher insulin mRNA levels
- 2005
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Ingår i: Biochemical and Biophysical Research Communications - BBRC. - : Elsevier BV. - 0006-291X .- 1090-2104. ; 328:1, s. 38-42
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Tidskriftsartikel (refereegranskat)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.
(författare)
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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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Ingår i: Heliyon. - : Elsevier BV. - 2405-8440. ; 2:9
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Role of the AMP kinase in cytokine-induced human EndoC-beta H1 cell death
- 2015
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Ingår i: Molecular and Cellular Endocrinology. - : Elsevier BV. - 0303-7207 .- 1872-8057. ; 414:C, s. 53-63
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Tidskriftsartikel (refereegranskat)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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| 11. |
- Fred, Rikard G., et al.
(författare)
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The human insulin mRNA is partly translated via a cap- and eIF4A-independent mechanism
- 2011
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Ingår i: Biochemical and Biophysical Research Communications - BBRC. - : Elsevier BV. - 0006-291X .- 1090-2104. ; 412:4, s. 693-698
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to investigate whether cap-independent insulin mRNA translation occurs in human pancreatic islets at basal conditions, during stimulation at a high glucose concentration and at conditions of nitrosative stress. We also aimed at correlating cap-independent insulin mRNA translation with binding of the IRES trans-acting factor polypyrimidine tract binding protein (FTB) to the 5'-UTR of insulin mRNA. For this purpose, human islets were incubated for 2 h in the presence of low (1.67 mM) or high glucose (16.7 mM). Nitrosative stress was induced by addition of 1 mM DETA/NO and cap-dependent mRNA translation was inhibited with hippuristanol. Insulin biosynthesis rates were determined by radioactive labeling and immunoprecipitation. PTB affinity to insulin mRNA 5'-UTR was assessed by a magnetic micro bead pull-down procedure. We observed that in the presence of 1.67 mM glucose, approximately 70% of the insulin mRNA translation was inhibited by hippuristanol. Corresponding value from islets incubated at 16.7 mM glucose was 93%. DETA/NO treatment significantly decreased the translation of insulin by 85% in high glucose incubated islets, and by 50% at a low glucose concentration. The lowered insulin biosynthesis rates of DETA/NO-exposed islets were further suppressed by hippuristanol with 55% at 16.7 mM glucose but not at 1.67 mM glucose. Thus, hippuristanol-induced inhibition of insulin biosynthesis was less pronounced in DETA/NO-treated islets as compared to control islets. We observed also that PTB bound specifically to the insulin mRNA 5'-UTR in vitro, and that this binding corresponded well with rates of cap-independent insulin biosynthesis at the different conditions. In conclusion, our studies show that insulin biosynthesis is mainly cap-dependent at a high glucose concentration, but that the cap-independent biosynthesis of insulin can constitute as much as 40-100% of all insulin biosynthesis during conditions of nitrosative stress. These data suggest that the pancreatic beta-cell is able to uphold basal insulin synthesis at conditions of starvation and stress via a cap- and eIF4A-independent mechanism, possibly mediated by the binding of FIB to the 5'-UTR of the human insulin mRNA.
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| 12. |
- Fred, Rikard G., et al.
(författare)
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The importance of RNA binding proteins in preproinsulin mRNA stability
- 2009
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Ingår i: Molecular and Cellular Endocrinology. - : Elsevier BV. - 0303-7207 .- 1872-8057. ; 297:1-2, s. 28-33
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Forskningsöversikt (refereegranskat)abstract
- A dynamic production of insulin is necessary for proper glucose homeostasis. In order to generate enough insulin available for exocytosis in response to the demands of the organism, the level of preproinsulin mRNA in the pancreatic beta-cell needs to fluctuate. In animal models for type 2 diabetes the contents of preproinsulin mRNA are lowered, which might suggest that an impaired metabolism of preproinsulin mRNA contributes to the development of glucose intolerance and diabetes. Thus, it is of importance to understand the mechanisms by which preproinsulin mRNA levels are regulated. Although extensively studied, there are aspects of the regulation of insulin gene expression that still remain enigmatic. Our understanding of insulin gene transcription has improved considerably the last 20 years, but less effort has been invested into the control of preproinsulin mRNA stability. The preproinsulin mRNA has a long half-life and changes in preproinsulin mRNA stability, induced by glucose, are likely to be regulated through specific mechanisms. Recent findings indicate that the polypyrimidine tract-binding protein (PTB), also named hnRNP I, by binding to the 3'-UTR (untranslated region) of the preproinsulin mRNA molecule, stabilizes the messenger, thereby participating in the glucose-induced increase in preproinsulin mRNA. This review will focus both on recent findings pertinent to PTB function in general, and on the specific role of PTB on the production of insulin in beta-cells. We will also discuss the putative co-operativity between PTB and other proteins in the control of preproinsulin mRNA stability, and review beta-cell signaling events that may control the mRNA stabilizing effect of PTB.
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| 13. |
- Fred, Rikard G.
(författare)
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The Role of RNA Binding Proteins in Insulin Messenger Stability and Translation
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although the reason for insufficient release of insulin in diabetes mellitus may vary depending on the type and stage of the disease, it is of vital importance that an amplified insulin biosynthesis can meet the increased need during periods of hyperglycemia. The insulin mRNA is highly abundant in beta cells and changes in insulin mRNA levels are, at least in part, controlled by altered rates of mRNA degradation. Since the mechanisms behind the control of insulin messenger stability and translation are still largely obscure, the work presented in this thesis therefore aimed to further investigate the role of insulin mRNA binding proteins in the control of insulin mRNA break-down and utilization for insulin biosynthesis. To clarify how glucose regulates insulin mRNA stability and translation we studied the correlation between polypyrimidine tract binding protein (PTB) gene expression and insulin mRNA levels. It was found that an increase in PTB mRNA and protein levels is paralleled by an increase in insulin mRNA levels. It was also found that PTB binds to the 5’-untranslated region of the insulin mRNA and that insulin mRNA can be translated through a cap-independent mechanism in human islets of Langerhans, possibly due to the interaction with PTB. Further it was discovered that the suppressed insulin biosynthesis in human islets during glucotoxicity is partly due to an induction of the microRNA miR-133a. This induction leads to decreased levels of PTB and insulin biosynthesis rates in human islets. Finally, we were able to identify two proteins, hnRNP U and TIAR, that bind specifically to the insulin mRNA in vitro, and show that the stability and translation of insulin mRNA is oppositely affected by these proteins. In conclusion, insulin producing cells seem to be able to regulate insulin messenger stability and translation by a control mechanism in which the binding of specific proteins to the insulin messenger dictates the outcome. A better understanding of the events leading to insulin production may in the future aid in optimal diagnosis and treatment of type 2 diabetes.
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| 14. |
- Krizhanovskii, Camilla, et al.
(författare)
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Addition of exogenous sodium palmitate increases the IAPP/insulin mRNA ratio via GPR40 in human EndoC-beta H1 cells
- 2017
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Ingår i: Upsala Journal of Medical Sciences. - : Uppsala Medical Society. - 0300-9734 .- 2000-1967. ; 122:3, s. 149-159
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Tidskriftsartikel (refereegranskat)abstract
- Background: Enhanced IAPP production may contribute to islet amyloid formation in type 2 diabetes. The objective of this study was to determine the effects of the saturated fatty acid palmitate on IAPP levels in human beta-cells. Methods: EndoC-beta H1 cells and human islets were cultured in the presence of sodium palmitate. Effects on IAPP/insulin mRNA expression and secretion were determined using real-time qPCR/ELISA. Pharmacological activators and/or inhibitors and RNAi were used to determine the underlying mechanisms. Results: We observed that EndoC-beta H1 cells exposed to palmitate for 72 h displayed decreased expression of Pdx-1 and MafA and increased expression of thioredoxin-interacting protein (TXNIP), reduced insulin mRNA expression and glucose-induced insulin secretion, as well as increased IAPP mRNA expression and secretion. Further, these effects were independent of fatty acid oxidation, but abolished in response to GPR40 inhibition/downregulation. In human islets both a high glucose concentration and palmitate promoted increased IAPP mRNA levels, resulting in an augmented IAPP/insulin mRNA ratio. This was paralleled by elevated IAPP/insulin protein secretion and content ratios. Conclusions: Addition of exogenous palmitate to human beta-cells increased the IAPP/insulin expression ratio, an effect contributed to by activation of GPR40. These findings may be pertinent to our understanding of the islet amyloid formation process.
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| 15. |
- Mokhtari, Dariush, et al.
(författare)
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Imatinib mesilate-induced phosphatidylinositol 3-kinase signalling and improved survival in insulin-producing cells : role of Src homology 2-containing inositol 5'-phosphatase interaction with c-Abl
- 2013
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Ingår i: Diabetologia. - : Springer Science and Business Media LLC. - 0012-186X .- 1432-0428. ; 56:6, s. 1327-1338
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Tidskriftsartikel (refereegranskat)abstract
- AIMS/HYPOTHESIS: It is not clear how small tyrosine kinase inhibitors, such as imatinib mesilate, protect against diabetes and beta cell death. The aim of this study was to determine whether imatinib, as compared with the non-cAbl-inhibitor sunitinib, affects pro-survival signalling events in the phosphatidylinositol 3-kinase (PI3K) pathway. METHODS: Human EndoC-βH1 cells, murine beta TC-6 cells and human pancreatic islets were used for immunoblot analysis of insulin receptor substrate (IRS)-1, Akt and extracellular signal-regulated kinase (ERK) phosphorylation. Phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P3] plasma membrane concentrations were assessed in EndoC-βH1 and MIN6 cells using evanescent wave microscopy. Src homology 2-containing inositol 5'-phosphatase 2 (SHIP2) tyrosine phosphorylation and phosphatase and tensin homologue deleted on chromosome 10 (PTEN) serine phosphorylation, as well as c-Abl co-localisation with SHIP2, were studied in HEK293 and EndoC-βH1 cells by immunoprecipitation and immunoblot analysis. Gene expression was assessed using RT-PCR. Cell viability was measured using vital staining. RESULTS: Imatinib stimulated ERK(thr202/tyr204) phosphorylation in a c-Abl-dependent manner. Imatinib, but not sunitinib, also stimulated IRS-1(tyr612), Akt(ser473) and Akt(thr308) phosphorylation. This effect was paralleled by oscillatory bursts in plasma membrane PI(3,4,5)P3 levels. Wortmannin induced a decrease in PI(3,4,5)P3 levels, which was slower in imatinib-treated cells than in control cells, indicating an effect on PI(3,4,5)P3-degrading enzymes. In line with this, imatinib decreased the phosphorylation of SHIP2 but not of PTEN. c-Abl co-immunoprecipitated with SHIP2 and its binding to SHIP2 was largely reduced by imatinib but not by sunitinib. Imatinib increased total β-catenin levels and cell viability, whereas sunitinib exerted negative effects on cell viability. CONCLUSIONS/INTERPRETATION: Imatinib inhibition of c-Abl in beta cells decreases SHIP2 activity, which results in enhanced signalling downstream of PI3 kinase.
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