| 1. |
|
|
| 2. |
|
|
| 3. |
- Malmgren, Siri, et al.
(författare)
-
Coordinate changes in histone modifications, mRNA levels and metabolite profiles in clonal INS-1 832/13 β-cells accompany functional adaptations to lipotoxicity.
- 2013
-
Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 288:17, s. 11973-11987
-
Tidskriftsartikel (refereegranskat)abstract
- Lipotoxicity is a presumed pathogenetic process whereby elevated circulating and stored lipids in Type 2 Diabetes cause pancreatic β-cell failure. To resolve the underlying molecular mechanisms, we exposed clonal INS-1 832/13 β-cells to palmitate for 48 h. We observed elevated basal insulin secretion but impaired glucose-stimulated insulin secretion in palmitate-exposed cells. Glucose utilization was unchanged, palmitate oxidation increased, and oxygen consumption impaired. Removal of palmitate from the clonal INS-1 832/13 β-cells largely recovered all of the lipid-induced functional changes. Metabolite profiling revealed profound but reversible increases in cellular lipids. Glucose-induced increases in tricarboxylic acid cycle intermediates were attenuated by exposure to palmitate. Analysis of gene expression by microarray showed increased expression of 982 genes and decreased expression of 1032 genes after exposure to palmitate. Increases were seen in pathways for steroid biosynthesis, cell cycle, fatty acid metabolism, DNA replication, and biosynthesis of unsaturated fatty acids; decreases occurred in the aminoacyl-tRNA-synthesis pathway. The activity of histone-modifying enzymes and histone modifications of differentially expressed genes were reversibly altered upon exposure to palmitate. Thus, Insig1, Lss, Peci, Idi1, Hmgcs1 and Casr were subject to epigenetic regulation. Our analyses demonstrate that coordinate changes in histone modifications, mRNA levels and metabolite profiles accompanied functional adaptations of clonal β-cells to lipotoxicity. It is highly likely that these changes are pathogenetic, accounting for loss of glucose responsiveness and perturbed insulin secretion.
|
|
| 4. |
- Nagorny, Cecilia, et al.
(författare)
-
Distribution of melatonin receptors in murine pancreatic islets.
- 2011
-
Ingår i: Journal of Pineal Research. - 1600-079X. ; 50, s. 412-417
-
Tidskriftsartikel (refereegranskat)abstract
- Melatonin has multiple receptor-dependent and receptor-independent functions. At the cell membrane, melatonin interacts with its receptors MT1 and MT2, which are expressed in numerous tissues. Genome-wide association studies have recently shown that the MTNR1B/MT2 receptor may be involved in the pathogenesis of type 2 diabetes mellitus. In line with these findings, expression of melatonin receptors has been shown in mouse, rat, and human pancreatic islets. MT1 and MT2 are G-protein-coupled receptors and are proposed to exert inhibitory effects on insulin secretion. Here, we show by immunocytochemistry that these membrane melatonin receptors have distinct locations in the mouse islet. MT1 is expressed in α-cells while MT2 is located to the β-cells. These findings help to unravel the complex machinery underlying melatonin's role in the regulation of islet function.
|
|
| 5. |
- Nagorny, Cecilia
(författare)
-
Melatonin receptors in pancreatic islets - Linking a genetic variant to functional phenotype
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Defective insulin secretion and insulin resistance are the two hallmarks of Type 2 Diabetes (T2D). The pathophysiology of the disease is not fully understood but genetic susceptibility for the disease is a new major player in the understanding of the underlying mechanisms. T2D research has in recent years invested tremendous efforts in identifying new risk variants for the disease. It has proven to be a great success, with about 40 new risk loci identified. This thesis describes the discovery and functional phenotype of one of these risk variants: the melatonin receptor 2 (MT2; MTNR1B). The overall aim was to understand the link between this genetic variation and the functional phenotype. The initial finding of the risk variant in the MTNR1B gene was associated with increased fasting plasma glucose, impaired early insulin secretion, and increased risk of T2D. Also, risk variant carriers displayed increased mRNA expression of MTNR1B in islets, suggesting a direct inhibitory effect of melatonin on β-cells. The confirmation and further characterization of melatonin receptor expression in pancreatic islets was completed in study II. Here, we could show that murine pancreatic islets express MT2 in β-cells, whereas melatonin receptor 1 (MT1) is localized in α-cells. After an intravenous glucose challenge, glucose elimination was unaltered in MT2 whole body knock out animals. In contrast, insulin secretion was elevated, particularly the first phase of secretion. This could in part be explained by an increased amount of pancreatic islets in these animals. The two other knock out strains investigated – the MT1 knock out and the double knock out MT1/2 – displayed a more moderate phenotype. Whereas the MT1/2 mouse was very similar to wild type mice in all parameters of glucose homeostasis investigated, MT1 mice displayed a more diabetes-like phenotype, with elevated blood glucose levels after glucose challenge. Taken together, findings in the MT2 knock out mice supported the model of a gain-of-function mutation in MT2/MTNR1B in humans in T2D. This results in increased expression of the receptor in β-cells, where it exhibits a direct inhibition of insulin release. With this, we have substantiated a possible link between the genetic risk variant and the functional phenotype of MTNR1B.
|
|
| 6. |
|
|
| 7. |
- Nagorny, Cecilia, et al.
(författare)
-
Tired of Diabetes Genetics? Circadian Rhythms and Diabetes: The MTNR1B Story?
- 2012
-
Ingår i: Current Diabetes Reports. - : Springer Science and Business Media LLC. - 1539-0829 .- 1534-4827. ; 12:6, s. 667-672
-
Tidskriftsartikel (refereegranskat)abstract
- Circadian rhythms are ubiquitous in biological systems and regulate metabolic processes throughout the body. Misalliance of these circadian rhythms and the systems they regulate has a profound impact on hormone levels and increases risk of developing metabolic diseases. Melatonin, a hormone secreted by the pineal gland, is one of the major signaling molecules used by the master circadian oscillator to entrain downstream circadian rhythms. Several recent genetic studies have pointed out that a common variant in the gene that encodes the melatonin receptor 2 (MTNR1B) is associated with impaired glucose homeostasis, reduced insulin secretion, and an increased risk of developing type 2 diabetes. Here, we try to review the role of this receptor and its signaling pathways in respect to glucose homeostasis and development of the disease.
|
|
| 8. |
- Spégel, Peter, et al.
(författare)
-
Metabolomic analysis of a human oral glucose tolerance test reveals fatty acids as reliable indicators of regulated metabolism
- 2010
-
Ingår i: Metabolomics. - : Springer Science and Business Media LLC. - 1573-3882 .- 1573-3890. ; 6:1, s. 56-66
-
Tidskriftsartikel (refereegranskat)abstract
- Gas chromatography/mass spectrometry-based metabolomics was applied to investigate dynamic changes in the plasma metabolome upon an oral glucose tolerance test (OGTT). The OGTT is a frequently used diagnostic test of glucose homeostasis and diabetes. Diabetes is diagnosed either when glucose levels a parts per thousand yen7.0 mM in the fasting state or a parts per thousand yen11.0 mM at 2 h after oral glucose intake. The accuracy of the OGTT would, however, most likely improve if additional variables could be identified. In the present study, plasma samples were drawn every 15 min for 2 h after an oral glucose load of 75 g preceded by an overnight fast in healthy individuals. Blood plasma levels of more than 200 putative metabolites were measured. Multivariate modelling was used to distinguish metabolic regulation due to the glucose challenge from that of other variability. Two data scaling methods were applied, yielding similar results when evaluated by appropriate diagnostic tools. Fatty acid levels were found to be strongly decreased during the OGTT. Also, the levels of amino acids were shown to decrease. However, technical and uninduced biological variations were found to affect the amino acid levels to a greater extent than the fatty acid levels, making the fatty acids more reliable as indicators of metabolic regulation. Levels of several metabolites correlated with the quadratic glucose profile and two were found having an inverse correlation. Raw data plots of all identified significantly altered metabolites confirmed the excellent performance of the multivariate models. Using this approach, a better understanding of the metabolic response to an OGTT can be achieved, paving the way for inclusion of other variables describing appropriate metabolic control.
|
|
| 9. |
- Spégel, Peter, et al.
(författare)
-
Time-resolved metabolomics analysis of beta-cells implicates the pentose phosphate pathway in the control of insulin release
- 2013
-
Ingår i: Biochemical Journal. - 0264-6021. ; 450, s. 595-605
-
Tidskriftsartikel (refereegranskat)abstract
- Insulin secretion is coupled with changes in beta-cell metabolism. To define this process, 195 putative metabolites, mitochondrial respiration, NADP(+), NADPH and insulin secretion were measured within 15 mm of stimulation of clonal INS-1 832/13 beta-cells with glucose. Rapid responses in the major metabolic pathways of glucose occurred, involving several previously suggested metabolic coupling factors. The complexity of metabolite changes observed disagreed with the concept of one single metabolite controlling insulin secretion. The complex alterations in metabolite levels suggest that a coupling signal should reflect large parts of the beta-cell metabolic response. This was fulfilled by the NADPH/NADP(+) ratio, which was elevated (8-fold; P < 0.01) at 6 min after glucose stimulation. The NADPH/NADP+ ratio paralleled an increase in ribose 5-phosphate (>2.5-fold; P < 0.001). Inhibition of the pentose phosphate pathway by trans-dehydroepiandrosterone (DHEA) suppressed ribose 5-phosphate levels and production of reduced glutathione, as well as insulin secretion in INS-1 832/13 beta-cells and rat islets without affecting ATP production. Metabolite profiling of rat islets confirmed the glucose-induced rise in ribose 5-phosphate, which was prevented by DHEA. These findings implicate the pentose phosphate pathway, and support a role for NADPH and glutathione, in beta-cell stimulus-secretion coupling.
|
|
| 10. |
|
|
| 11. |
- Stamenkovic, Jelena, et al.
(författare)
-
Regulation of core clock genes in human islets.
- 2012
-
Ingår i: Metabolism, Clinical and Experimental. - : Elsevier BV. - 1532-8600. ; 61:7, s. 978-985
-
Tidskriftsartikel (refereegranskat)abstract
- Nearly all mammalian cells express a set of genes known as clock genes. These regulate the circadian rhythm of cellular processes by means of negative and positive autoregulatory feedback loops of transcription and translation. Recent genomewide association studies have demonstrated an association between a polymorphism near the circadian clock gene CRY2 and elevated fasting glucose. To determine whether clock genes could play a pathogenetic role in the disease, we examined messenger RNA (mRNA) expression of core clock genes in human islets from donors with or without type 2 diabetes mellitus. Microarray and quantitative real-time polymerase chain reaction analyses were used to assess expression of the core clock genes CLOCK, BMAL-1, PER1 to 3, and CRY1 and 2 in human islets. Insulin secretion and insulin content in human islets were measured by radioimmunoassay. The mRNA levels of PER2, PER3, and CRY2 were significantly lower in islets from donors with type 2 diabetes mellitus. To investigate the functional relevance of these clock genes, we correlated their expression to insulin content and glycated hemoglobin levels: mRNA levels of PER2 (ρ = 0.33, P = .012), PER3 (ρ = 0.30, P = .023), and CRY2 (ρ = 0.37, P = .0047) correlated positively with insulin content. Of these genes, expression of PER3 and CRY2 correlated negatively with glycated hemoglobin levels (ρ = -0.44, P = .0012; ρ = -0.28, P = .042). Furthermore, in an in vitro model mimicking pathogenetic conditions, the PER3 mRNA level was reduced in human islets exposed to 16.7 mmol/L glucose per 1 mmol/L palmitate for 48 hours (P = .003). Core clock genes are regulated in human islets. The data suggest that perturbations of circadian clock components may contribute to islet pathophysiology in human type 2 diabetes mellitus.
|
|
