| 1. |
- Cen, Jing, et al.
(författare)
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Fatty acids stimulate insulin secretion from human pancreatic islets at fasting glucose concentrations via mitochondria-dependent and -independent mechanisms
- 2016
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Ingår i: Nutrition & Metabolism. - : Springer Science and Business Media LLC. - 1743-7075. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- Background: Free fatty acids (FFAs) acutely stimulate insulin secretion from pancreatic islets. Conflicting results have been presented regarding this effect at non-stimulatory glucose concentration, however. The aim of our study was to investigate how long-chain FFAs affect insulin secretion from isolated human pancreatic islets in the presence of physiologically fasting glucose concentrations and to explore the contribution of mitochondria to the effects on secretion. Methods: Insulin secretion from human pancreatic islets was measured from short-term static incubation or perfusion system at fasting glucose concentration (5.5 mM) with or without 4 different FFAs (palmitate, palmitoleate, stearate, and oleate). The contribution of mitochondrial metabolism to the effects of fatty acid-stimulated insulin secretion was explored. Results: The average increase in insulin secretion, measured from statically incubated and dynamically perifused human islets, was about 2-fold for saturated free fatty acids (SFAs) (palmitate and stearate) and 3-fold for mono-unsaturated free fatty acids (MUFAs) (palmitoleate and oleate) compared with 5.5 mmol/l glucose alone. Accordingly, MUFAs induced 50 % and SFAs 20 % higher levels of oxygen consumption compared with islets exposed to 5.5 mmol/l glucose alone. The effect was due to increased glycolysis. When glucose was omitted from the medium, addition of the FFAs did not affect oxygen consumption. However, the FFAs still stimulated insulin secretion from the islets although secretion was more than halved. The mitochondria-independent action was via fatty acid metabolism and FFAR1/GPR40 signaling. Conclusions: The findings suggest that long-chain FFAs acutely induce insulin secretion from human islets at physiologically fasting glucose concentrations, with MUFAs being more potent than SFAs, and that this effect is associated with increased glycolytic flux and mitochondrial respiration.
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| 2. |
- Cen, Jing, 1985-
(författare)
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Free fatty acids and insulin hypersecretion studied in human islets
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Free fatty acid (FFA) levels are increased in many obese subjects. High FFA levels stimulate the pancreatic beta-cells but have negative long-term effects. In obese children with high FFA levels circulating insulin concentration is high early in life but decline with age precipitating the development of type 2 diabetes mellitus (T2DM). The present study aims at preventing this development of T2DM by defining underlying mechanisms of insulin hypersecretion. Such mechanisms will be identified by studying regulation of insulin secretion from human pancreatic islets and human EndoC-βH1 cells exposed to elevated FFA levels.We found that elevated concentrations of FFAs acutely stimulate insulin from human pancreatic islets at fasting blood glucose level, with mono-unsatured being more potent than saturated fatty acids. Enhanced secretion was associated with increased glycolytic flux and mitochondrial respiration. Continued exposure to elevated palmitate levels for up to 2 days accentuated insulin secretion, whereas 7 days’ exposure caused secretory decline. Metformin prevented insulin hypersecretion from human islets treated with palmitate for 2 days by decreasing mitochondrial metabolism. In islets exposed to palmitate for 7 days metformin improved insulin secretion by enhancing calcium binding protein sorcin levels and thereby reducing ER stress and apoptosis. Downregulation of sorcin had negative effects on insulin secretion, mitochondrial metabolism and ER stress in human islets and EndoC-βH1 cells. Specific cellular pathways involved in insulin hypersecretion and secretory decline were identified by microarray expression analysis and subsequent bioinformatics in human islets cultured with palmitate for 0, 4, 12 hours, 1, 2, and 7 days.In conclusion, beta-cells respond to elevated levels of FFAs by initially augmenting insulin release followed by declining secretory levels after prolonged exposure. Metformin normalizes these secretory aberrations. Specific signaling pathways and proteins including sorcin contribute to the secretory alterations induced by palmitate. When developing strategies for prevention of T2DM in obese children with elevated FFA levels, metformin should be considered as well as novel strategies involving sorcin and the identified specific pathways.
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| 3. |
- Cen, Jing, et al.
(författare)
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Mechanisms of beneficial effects of metformin on fatty acid-treated human islets
- 2018
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Ingår i: Journal of Molecular Endocrinology. - 0952-5041 .- 1479-6813. ; 61:3, s. 91-99
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Tidskriftsartikel (refereegranskat)abstract
- Elevated levels of palmitate accentuate glucose-stimulated insulin secretion (GSIS) after short-term and cause beta-cell dysfunction after prolonged exposure. We investigated whether metformin, the first-line oral drug for treatment of T2DM, has beneficial effects on FFA-treated human islets and the potential mechanisms behind the effects. Insulin secretion, oxygen consumption rate (OCR), AMPK activation, endoplasmic reticulum (ER) stress and apoptosis were examined in isolated human islets after exposure to elevated levels of palmitate in the absence or presence of metformin. Palmitate exposure doubled GSIS after 2 days but halved after 7 days compared with control. Inclusion of metformin during palmitate exposure normalized insulin secretion both after 2 and 7 days. After 2-day exposure to palmitate, OCR and the marker of the adaptive arm of ER stress response (sorcin) were significantly raised, whereas AMPK phosphorylation, markers of pro-apoptotic arm of ER stress response (p-EIF2α and CHOP) and apoptosis (cleaved caspase 3) were not affected. Presence of metformin during 2-day palmitate exposure normalized OCR and sorcin levels. After 7-day exposure to palmitate, OCR and sorcin were not significantly different from control level, p-AMPK was reduced and p-EIF2α, CHOP and cleaved caspase 3 were strongly upregulated. Presence of metformin during 7-day culture with palmitate normalized the level of p-AMPK, p-EIF2α, CHOP and cleaved caspase 3 but significantly increased the level of sorcin. Our study demonstrates that metformin prevents early insulin hypersecretion and later decrease in insulin secretion from palmitate-treated human islets by utilizing different mechanisms.
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| 4. |
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| 5. |
- Cen, Jing, et al.
(författare)
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Sorcin counteracts lipotoxicity in palmitate-exposed human beta-cells
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In obese subjects elevated circulating levels of free fatty acids (FFAs) have been connected with hyperinsulinemia and development of type 2 diabetes. In human islets insulin secretion is accentuated when palmitate concentration is increased for short time periods. Our previous findings indicated that increased sorcin expression may delay development of ER stress in such human islets exposed to palmitate. In the present study we tested this hypothesis by using human islets and human EndoC-βH1 cells transfected with lenti-viral transduction particles of anti-sorcin. Human islets and EndoC-βH1 cells treated with palmitate for 2 days induced sorcin expression. The beta-cells showed enhanced glucose-stimulated insulin secretion (GSIS), mitochondrial respiration and glycolysis and no alterations in ER stress and apoptosis. When sorcin was knocked down, palmitate-induced upregulation of sorcin was reduced. The beta-cells showed reduced GSIS, mitochondrial respiration and glycolysis and increased ER stress and apoptosis. We conclude that enhanced sorcin levels play a role in preventing lipotoxicity in beta-cells exposed to elevated palmitate levels for prolonged time periods.
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| 6. |
- Elksnis, Andris, et al.
(författare)
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Imatinib protects against human beta-cell death via inhibition of mitochondrial respiration and activation of AMPK
- 2021
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Ingår i: Clinical Science. - : Portland Press. - 0143-5221 .- 1470-8736. ; 135:19, s. 2243-2263
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Tidskriftsartikel (refereegranskat)abstract
- The protein tyrosine kinase inhibitor imatinib is used in the treatment of various malignancies but may also promote beneficial effects in the treatment of diabetes. The aim of the present investigation was to characterize the mechanisms by which imatinib protects insulin producing cells. Treatment of non-obese diabetic (NOD) mice with imatinib resulted in increased beta-cell AMP-activated kinase (AMPK) phosphorylation. Imatinib activated AMPK also in vitro, resulting in decreased ribosomal protein S6 phosphorylation and protection against islet amyloid polypeptide (IAPP)-aggregation, thioredoxin interacting protein (TXNIP) up-regulation and beta-cell death. 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR) mimicked and compound C counteracted the effect of imatinib on beta-cell survival. Imatinib-induced AMPK activation was preceded by reduced glucose/pyruvate-dependent respiration, increased glycolysis rates, and a lowered ATP/AMP ratio. Imatinib augmented the fractional oxidation of fatty acids/malate, possibly via a direct interaction with the beta-oxidation enzyme enoyl coenzyme A hydratase, short chain, 1, mitochondrial (ECHS1). In non-beta cells, imatinib reduced respiratory chain complex I and II-mediated respiration and acyl-CoA carboxylase (ACC) phosphorylation, suggesting that mitochondrial effects of imatinib are not beta-cell specific. In conclusion, tyrosine kinase inhibitors modestly inhibit mitochondrial respiration, leading to AMPK activation and TXNIP down-regulation, which in turn protects against beta-cell death.
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| 7. |
- Elksnis, Andris, et al.
(författare)
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Pharmacological Inhibition of NOX4 Improves Mitochondrial Function and Survival in Human Beta-Cells
- 2021
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Ingår i: Biomedicines. - : MDPI. - 2227-9059. ; 9:12
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Tidskriftsartikel (refereegranskat)abstract
- Previous studies have reported beneficial effects of NADPH oxidase 4 (NOX4) inhibition on beta-cell survival in vitro and in vivo. The mechanisms by which NOX4 inhibition protects insulin producing cells are, however, not known. The aim of the present study was to investigate the effects of a pharmacological NOX4 inhibitor (GLX7013114) on human islet and EndoC-beta H1 cell mitochondrial function, and to correlate such effects with survival in islets of different size, activity, and glucose-stimulated insulin release responsiveness. We found that maximal oxygen consumption rates, but not the rates of acidification and proton leak, were increased in islets after acute NOX4 inhibition. In EndoC-beta H1 cells, NOX4 inhibition increased the mitochondrial membrane potential, as estimated by JC-1 fluorescence; mitochondrial reactive oxygen species (ROS) production, as estimated by MitoSOX fluorescence; and the ATP/ADP ratio, as assessed by a bioluminescent assay. Moreover, the insulin release from EndoC-beta H1 cells at a high glucose concentration increased with NOX4 inhibition. These findings were paralleled by NOX4 inhibition-induced protection against human islet cell death when challenged with high glucose and sodium palmitate. The NOX4 inhibitor protected equally well islets of different size, activity, and glucose responsiveness. We conclude that pharmacological alleviation of NOX4-induced inhibition of beta-cell mitochondria leads to increased, and not decreased, mitochondrial ROS, and this was associated with protection against cell death occurring in different types of heterogeneous islets. Thus, NOX4 inhibition or modulation may be a therapeutic strategy in type 2 diabetes that targets all types of islets.
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| 8. |
- 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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| 9. |
- Groebe, Karlfried, et al.
(författare)
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Palmitate-Induced Insulin Hypersecretion and Later Secretory Decline Associated with Changes in Protein Expression Patterns in Human Pancreatic Islets
- 2018
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Ingår i: Journal of Proteome Research. - : American Chemical Society (ACS). - 1535-3893 .- 1535-3907. ; 17:11, s. 3824-3836
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Tidskriftsartikel (refereegranskat)abstract
- In obese children with high circulating concentrations of free fatty acid palmitate, we have observed that insulin levels at fasting and in response to a glucose challenge were several times higher than in obese children with low concentrations of the fatty acid as well as in lean controls. Declining and even insufficient insulin levels were observed in obese adolescents with high levels of the fatty acid. In isolated human islets exposed to palmitate we have observed insulin hypersecretion after 2 days exposure. In contrast, insulin secretion from the islets was reduced after 7 days culture in the presence of the fatty acid. This study aims at identifying islet-related biological events potentially linked with the observed insulin hypersecretion and later secretory decline in these obese children and adolescents using the islet model. We analyzed protein expression data obtained from human islets exposed to elevated palmitate levels for 2 and 7 days by an improved methodology for statistical analysis of differentially expressed proteins. Protein profiling of islet samples by liquid chromatography-tandem mass spectrometry identified 115 differentially expressed proteins (DEPs). Several DEPs including sorcin were associated with increased glucose-stimulated insulin secretion in islets after 2 days of exposure to palmitate. Similarly, several metabolic pathways including altered protein degradation, increased autophagy, altered redox condition, and hampered insulin processing were coupled to the functional impairment of islets after 7 days of culture in the presence of palmitate. Such biological events, once validated in the islets, may give rise to novel treatment strategies aiming at normalizing insulin levels in obese children with high palmitate levels, which may reduce or even prevent obesity-related type 2 diabetes mellitus.
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| 10. |
- Huang, Zhen, et al.
(författare)
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Recurrent chromosome reshuffling and the evolution of neo-sex chromosomes in parrots
- 2022
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Parrots have undergone substantial karyotype evolution compared to most other birds. Here, Huang et al. analyze chromosome-level genome assemblies for four parrot species and elucidate the complex evolutionary history of parrot chromosomes. The karyotype of most birds has remained considerably stable during more than 100 million years' evolution, except for some groups, such as parrots. The evolutionary processes and underlying genetic mechanism of chromosomal rearrangements in parrots, however, are poorly understood. Here, using chromosome-level assemblies of four parrot genomes, we uncover frequent chromosome fusions and fissions, with most of them occurring independently among lineages. The increased activities of chromosomal rearrangements in parrots are likely associated with parrot-specific loss of two genes, ALC1 and PARP3, that have known functions in the repair of double-strand breaks and maintenance of genome stability. We further find that the fusion of the ZW sex chromosomes and chromosome 11 has created a pair of neo-sex chromosomes in the ancestor of parrots, and the chromosome 25 has been further added to the sex chromosomes in monk parakeet. Together, the combination of our genomic and cytogenetic analyses characterizes the complex evolutionary history of chromosomal rearrangements and sex chromosomes in parrots.
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