| 1. |
- Göhring, Isabel, et al.
(författare)
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Chronic high glucose and pyruvate levels differentially affect mitochondrial bioenergetics and fuel-stimulated insulin secretion from clonal INS-1 832/13 cells.
- 2014
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Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 289:6, s. 3786-3798
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Tidskriftsartikel (refereegranskat)abstract
- Glucotoxicity in pancreatic β-cells is a well-established pathogenetic process in Type 2 Diabetes. It has been suggested that metabolism-derived reactive oxygen species perturb the β-cell transcriptional machi-nery. Less is known about altered mitochondrial function in this condition. We used INS-1 832/13 cells cultured for 48 h in 2.8 mM glucose (low-G), 16.7 mM glucose (high-G) or 2.8 mM glucose plus 13.7 mM pyruvate (high-P) to identify metabolic perturbations. High-G cells showed decreased responsiveness, relative to low-G cells, with respect to mitochondrial membrane hyperpolarization, plasma membrane depolarization and insulin secretion, when stimulated acutely with 16.7 mM glucose or 10 mM pyruvate. In contrast, high-P cells were functionally unimpaired, eliminating chronic provision of saturating mitochondrial substrate as a cause of glucotoxicity. Although cellular insulin content was depleted in high-G cells, relative to low-G and high-P cells, cellular functions were largely recovered following a further 24 h culture in low-G medium. After 2 h at 2.8 mM glucose, high-G cells did not retain increased levels of glycolytic or TCA-cycle intermediates, but nevertheless displayed increased glycolysis, increased respiration and an increased mitochondrial proton leak relative to low-G and high-P cells. This notwithstanding, titration of low-G cells with low protonophore concen-trations, monitoring respiration and insulin secretion in parallel, showed that the perturbed insulin secretion of high-G cells could not be accounted for by increased proton leak. The present study supports the idea that glucose-induced disturbances of stimulus-secretion coupling by extra-mitochondrial metabolism upstream of pyruvate, rather than exhaustion from metabolic overload, underlie glucotoxicity in insulin-producing cells.
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| 2. |
- Göhring, Isabel, et al.
(författare)
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Glutamate dehydrogenase, insulin secretion and Type 2 Diabetes. A new means to protect the pancreatic β-cell?
- 2012
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Ingår i: Journal of Endocrinology. - 1479-6805. ; 212:3, s. 239-242
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Tidskriftsartikel (refereegranskat)abstract
- In this issue of Journal of Endocrinology, Dr Han and colleagues report a protective effect of the glutamate dehydrogenase-activator BCH under diabetes-like conditions that impair β-cell function in both a pancreatic β-cell line and in db/db mice. Based on these observations, the authors suggest that BCH could serve as novel treatment modality in Type 2 Diabetes. The present commentary discusses the importance of the findings. Some additional questions are raised, that may be addressed in future investigations, as is some concern regarding BCH treatment of β-cell failure.
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| 3. |
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| 4. |
- Sharoyko, Vladimir, et al.
(författare)
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Loss of TFB1M results in mitochondrial dysfunction that leads to impaired insulin secretion and diabetes.
- 2014
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Ingår i: Human Molecular Genetics. - : Oxford University Press (OUP). - 0964-6906 .- 1460-2083. ; 23:21, s. 5733-5749
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Tidskriftsartikel (refereegranskat)abstract
- We have previously identified Transcription Factor B1 Mitochondrial (TFB1M) as a Type 2 Diabetes (T2D) risk gene, using human and mouse genetics. To further understand the function of TFB1M and how it is associated with T2D we created a β-cell specific knockout of Tfb1 m, which gradually developed diabetes. Prior to the onset of diabetes, β-Tfb1 m(-/-) mice exhibited retarded glucose clearance due to impaired insulin secretion. β-Tfb1 m(-/-) islets released less insulin in response to fuels, contained less insulin and secretory granules, and displayed reduced β-cell mass. Moreover, mitochondria in Tfb1 m-deficient β-cells were more abundant with disrupted architecture. TFB1M is known to control mitochondrial protein translation by adenine-dimethylation of 12S ribosomal RNA (rRNA). Here, we found that levels of TFB1M and mitochondrial encoded proteins, mitochondrial 12S rRNA methylation, ATP production and oxygen consumption were reduced in β-Tfb1 m(-/-) islets. Furthermore, levels of reactive oxygen species in response to cellular stress were increased while induction of defense mechanisms was attenuated. We also show increased apoptosis and necrosis as well as infiltration of macrophages and CD4(+)-cells in the islets. Taken together, our findings demonstrate that Tfb1 m-deficiency in β-cells caused mitochondrial dysfunction and subsequently diabetes due to combined loss of β-cell function and mass. These observations reflect pathogenetic processes in human islets: using RNA sequencing, we found that the TFB1M risk variant exhibited a negative gene-dosage effect on islet TFB1M mRNA levels, as well as insulin secretion. Our findings highlight the role of mitochondrial dysfunction in impairments of β-cell function and mass, the hallmarks of T2D.
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| 5. |
- Spégel, Peter, et al.
(författare)
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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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Ingår i: Biochemical Journal. - 0264-6021. ; 450, s. 595-605
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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.
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| 6. |
- Spégel, Peter, et al.
(författare)
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Unique and Shared Metabolic Regulation in Clonal β-cells and Primary Islets Derived from Rat Revealed by Metabolomics Analysis.
- 2015
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Ingår i: Endocrinology. - : The Endocrine Society. - 0013-7227 .- 1945-7170. ; 156:6, s. 1995-2005
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Tidskriftsartikel (refereegranskat)abstract
- As models for β-cell metabolism, rat islets are, to some extent, a, heterogeneous cell-population stressed by the islet isolation procedure, while rat-derived clonal β-cells exhibit a tumor-like phenotype. To describe to what extent either of these models reflect normal cellular metabolism, we compared metabolite profiles and gene expression in rat islets and the INS-1 832/13 line, a widely used clonal β-cell model. We found that insulin secretion and metabolic regulation provoked by glucose were qualitatively similar in these β-cell models. However, rat islets exhibited a more pronounced glucose-provoked increase of glutamate, glycerol-3-phosphate, succinate and lactate levels while INS-1 832/13 cells showed a higher glucose-elicited increase in glucose-6-phosphate, alanine, isocitrate, and α-ketoglutarate levels. Glucose induced a decrease in levels of γ-aminobutyrate (GABA) and aspartate in rat islets and INS-1 832/13 cells, respectively. Genes with cellular functions related to proliferation and the cell cycle were more highly expressed in the INS-1 832/13 cells. Most metabolic pathways that were differentially expressed included GABA metabolism, in line with altered glucose responsiveness of GABA. Also, lactate dehydrogenase A, which is normally expressed at low levels in mature β-cells, was more abundant in rat islets than in INS-1 832/13 cells, confirming the finding of elevated glucose-provoked lactate production in the rat islets. Overall, our results suggest that metabolism in rat islets and INS-1 832/13 cells is qualitatively similar, albeit with quantitative differences. Differences may be accounted for by cellular heterogeneity of islets and proliferation of the INS-1 832/13 cells.
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