| 1. |
- Malmgren, Siri, et al.
(author)
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Coordinate changes in histone modifications, mRNA levels and metabolite profiles in clonal INS-1 832/13 β-cells accompany functional adaptations to lipotoxicity.
- 2013
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In: Journal of Biological Chemistry. - 1083-351X. ; 288:17, s. 11973-11987
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Journal article (peer-reviewed)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.
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| 2. |
- Spégel, Peter, et al.
(author)
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Time-resolved metabolomics analysis of beta-cells implicates the pentose phosphate pathway in the control of insulin release
- 2013
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In: Biochemical Journal. - 0264-6021. ; 450, s. 595-605
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Journal article (peer-reviewed)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.
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