| 1. |
- Barres, R., et al.
(författare)
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Non-CpG methylation of the PGC-1alpha promoter through DNMT3B controls mitochondrial density
- 2009
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Ingår i: Cell Metabolism. - : Elsevier BV. - 1550-4131 .- 1932-7420. ; 10:3, s. 189-98
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Tidskriftsartikel (refereegranskat)abstract
- Epigenetic modification through DNA methylation is implicated in metabolic disease. Using whole-genome promoter methylation analysis of skeletal muscle from normal glucose-tolerant and type 2 diabetic subjects, we identified cytosine hypermethylation of peroxisome proliferator-activated receptor gamma (PPARgamma) coactivator-1 alpha (PGC-1alpha) in diabetic subjects. Methylation levels were negatively correlated with PGC-1alpha mRNA and mitochondrial DNA (mtDNA). Bisulfite sequencing revealed that the highest proportion of cytosine methylation within PGC-1alpha was found within non-CpG nucleotides. Non-CpG methylation was acutely increased in human myotubes by exposure to tumor necrosis factor-alpha (TNF-alpha) or free fatty acids, but not insulin or glucose. Selective silencing of the DNA methyltransferase 3B (DNMT3B), but not DNMT1 or DNMT3A, prevented palmitate-induced non-CpG methylation of PGC-1alpha and decreased mtDNA and PGC-1alpha mRNA. We provide evidence for PGC-1alpha hypermethylation, concomitant with reduced mitochondrial content in type 2 diabetic patients, and link DNMT3B to the acute fatty-acid-induced non-CpG methylation of PGC-1alpha promoter.
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| 2. |
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| 3. |
- Dyachok, Oleg, 1965-, et al.
(författare)
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Glucose-induced cyclic AMP oscillations regulate pulsatile insulin secretion
- 2008
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Ingår i: Cell Metabolism. - : Cell Press. - 1550-4131 .- 1932-7420. ; 8:1, s. 26-37
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Tidskriftsartikel (refereegranskat)abstract
- Cyclic AMP (cAMP) and Ca2+ are key regulators of exocytosis in many cells, including insulin-secreting β-cells. Glucose-stimulated insulin secretion from β cells is pulsatile and involves oscillations of the cytoplasmic Ca2+ concentration ([Ca2+]i), but little is known about the detailed kinetics of cAMP signalling. Using evanescent-wave fluorescence imaging we found that glucose induces pronounced oscillations of cAMP in the sub-membrane space of single MIN6-cells and primary mouse β-cells. These oscillations were preceded and enhanced by elevations of [Ca2+]i. However, conditions raising cytoplasmic ATP could trigger cAMP elevations without accompanying [Ca2+]i rise, indicating that adenylyl cyclase activity may be controlled also by the substrate concentration. The cAMP oscillations correlated with pulsatile insulin release. Whereas elevation of cAMP enhanced secretion, inhibition of adenylyl cyclases suppressed both cAMP oscillations and pulsatile insulin release. We conclude that cell metabolism directly controls cAMP, and that glucose-induced cAMP oscillations regulate the magnitude and kinetics of insulin exocytosis.
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| 4. |
- Edgar, Daniel, et al.
(författare)
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Random point mutations with major effects on protein-coding genes are the driving force behind premature aging in mtDNA mutator mice.
- 2009
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Ingår i: Cell metabolism. - : Elsevier BV. - 1932-7420 .- 1550-4131. ; 10:2, s. 131-8
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Tidskriftsartikel (refereegranskat)abstract
- The mtDNA mutator mice have high levels of point mutations and linear deletions of mtDNA causing a progressive respiratory chain dysfunction and a premature aging phenotype. We have now performed molecular analyses to determine the mechanism whereby these mtDNA mutations impair respiratory chain function. We report that mitochondrial protein synthesis is unimpaired in mtDNA mutator mice consistent with the observed minor alterations of steady-state levels of mitochondrial transcripts. These findings refute recent claims that circular mtDNA molecules with large deletions are driving the premature aging phenotype. We further show that the stability of several respiratory chain complexes is severely impaired despite normal synthesis of the corresponding mtDNA-encoded subunits. Our findings reveal a mechanism for induction of aging phenotypes by demonstrating a causative role for amino acid substitutions in mtDNA-encoded respiratory chain subunits, which, in turn, leads to decreased stability of the respiratory chain complexes and respiratory chain deficiency.
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| 5. |
- Feldmann, Helena M., et al.
(författare)
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UCP1 ablation induces obesity and abolishes diet-induced thermogenesis in mice exempt from thermal stress by living at thermoneutrality.
- 2009
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Ingår i: Cell metabolism. - : Elsevier BV. - 1932-7420 .- 1550-4131. ; 9:2, s. 203-9
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Tidskriftsartikel (refereegranskat)abstract
- As original studies of UCP1-ablated mice failed to demonstrate an obesogenic effect, alternative mechanisms for adaptive adrenergic thermogenesis have been sought. However, we demonstrate here that in C57Bl6 mice exempt from thermal stress (i.e., kept at thermoneutrality), UCP1 ablation in itself induced obesity, even in mice fed control diet, and vastly augmented diet-induced obesity (high-fat diet); i.e., the mice exhibited increased metabolic efficiency. In wild-type mice, high-fat diet increased norepinephrine-induced thermogenesis; i.e., diet-induced thermogenesis was observed, but no such effect was observed in UCP1-ablated mice, demonstrating that diet-induced thermogenesis fully emanates from UCP1 activity. We conclude that ambient temperature is qualitatively determinative for the outcome of metabolic studies, that no other protein and no other mechanism can substitute for UCP1 in mediating diet-induced adrenergic thermogenesis, and that UCP1 activity can be determinative for obesity development in mice and possibly in humans.
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| 6. |
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| 7. |
- Li, Dai-Qing, et al.
(författare)
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Suppression of sulfonylurea- and glucose-induced insulin secretion in vitro and in vivo in mice lacking the chloride transport protein ClC-3.
- 2009
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Ingår i: Cell metabolism. - : Elsevier BV. - 1932-7420 .- 1550-4131. ; 10:4, s. 309-15
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Tidskriftsartikel (refereegranskat)abstract
- Priming of insulin secretory granules for release requires intragranular acidification and depends on vesicular Cl(-)-fluxes, but the identity of the chloride transporter/ion channel involved is unknown. We tested the hypothesis that the chloride transport protein ClC-3 fulfills these actions in pancreatic beta cells. In ClC-3(-/-) mice, insulin secretion evoked by membrane depolarization (high extracellular K(+), sulfonylureas), or glucose was >60% reduced compared to WT animals. This effect was mirrored by a approximately 80% reduction in depolarization-evoked beta cell exocytosis (monitored as increases in cell capacitance) in single ClC-3(-/-) beta cells, as well as a 44% reduction in proton transport across the granule membrane. ClC-3 expression in the insulin granule was demonstrated by immunoblotting, immunostaining, and negative immuno-EM in a high-purification fraction of large dense-core vesicles (LDCVs) obtained by phogrin-EGFP labeling. The data establish the importance of granular Cl(-) fluxes in granule priming and provide direct evidence for the involvement of ClC-3 in the process.
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| 10. |
- Solinas, Giovanni, et al.
(författare)
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JNK1 in hematopoietically derived cells contributes to diet-induced inflammation and insulin resistance without affecting obesity
- 2007
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Ingår i: Cell Metabolism. - 1550-4131 .- 1932-7420. ; 6:5, s. 386-397
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Tidskriftsartikel (refereegranskat)abstract
- Obesity-induced insulin resistance is a major factor in the etiology of type 2 diabetes, and Jun kinases (JNKs) are key negative regulators of insulin sensitivity in the obese state. Activation of JNKs (mainly JNK1) in insulin target cells results in phosphorylation of insulin receptor substrates (IRSs) at serine and threonine residues that inhibit insulin signaling. JNK1 activation is also required for accumulation of visceral fat. Here we used reciprocal adoptive transfer experiments to determine whether JNK1 in myeloid cells, such as macrophages, also contributes to insulin resistance and central adiposity. Our results show that deletion of Jnk1 in the nonhematopoietic compartment protects mice from high-fat diet (HFD)-induced insulin resistance, in part through decreased adiposity. By contrast, Jnk1 removal from hematopoietic cells has no effect on adiposity but confers protection against HFD-induced insulin resistance by decreasing obesity-induced inflammation.
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