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- Kizilkaya, Hüsün S., et al.
(author)
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Characterization of genetic variants of GIPR reveals a contribution of β-arrestin to metabolic phenotypes
- 2024
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In: Nature Metabolism. - 2522-5812. ; 6:7, s. 1268-1281
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Journal article (peer-reviewed)abstract
- Incretin-based therapies are highly successful in combatting obesity and type 2 diabetes1. Yet both activation and inhibition of the glucose-dependent insulinotropic polypeptide (GIP) receptor (GIPR) in combination with glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) activation have resulted in similar clinical outcomes, as demonstrated by the GIPR–GLP-1R co-agonist tirzepatide2 and AMG-133 (ref. 3) combining GIPR antagonism with GLP-1R agonism. This underlines the importance of a better understanding of the GIP system. Here we show the necessity of β-arrestin recruitment for GIPR function, by combining in vitro pharmacological characterization of 47 GIPR variants with burden testing of clinical phenotypes and in vivo studies. Burden testing of variants with distinct ligand-binding capacity, Gs activation (cyclic adenosine monophosphate production) and β-arrestin 2 recruitment and internalization shows that unlike variants solely impaired in Gs signalling, variants impaired in both Gs and β-arrestin 2 recruitment contribute to lower adiposity-related traits. Endosomal Gs-mediated signalling of the variants shows a β-arrestin dependency and genetic ablation of β-arrestin 2 impairs cyclic adenosine monophosphate production and decreases GIP efficacy on glucose control in male mice. This study highlights a crucial impact of β-arrestins in regulating GIPR signalling and overall preservation of biological activity that may facilitate new developments in therapeutic targeting of the GIPR system.
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| 4. |
- Parikh, Hemang, et al.
(author)
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TXNIP regulates peripheral glucose metabolism in humans
- 2007
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In: PLoS Medicine. - : Public Library of Science (PLoS). - 1549-1676. ; 4:5, s. 868-879
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Journal article (peer-reviewed)abstract
- Background Type 2 diabetes mellitus ( T2DM) is characterized by defects in insulin secretion and action. Impaired glucose uptake in skeletal muscle is believed to be one of the earliest features in the natural history of T2DM, although underlying mechanisms remain obscure. Methods and Findings We combined human insulin/glucose clamp physiological studies with genome-wide expression profiling to identify thioredoxin interacting protein ( TXNIP) as a gene whose expression is powerfully suppressed by insulin yet stimulated by glucose. In healthy individuals, its expression was inversely correlated to total body measures of glucose uptake. Forced expression of TXNIP in cultured adipocytes significantly reduced glucose uptake, while silencing with RNA interference in adipocytes and in skeletal muscle enhanced glucose uptake, confirming that the gene product is also a regulator of glucose uptake. TXNIP expression is consistently elevated in the muscle of prediabetics and diabetics, although in a panel of 4,450 Scandinavian individuals, we found no evidence for association between common genetic variation in the TXNIP gene and T2DM. Conclusions TXNIP regulates both insulin-dependent and insulin- independent pathways of glucose uptake in human skeletal muscle. Combined with recent studies that have implicated TXNIP in pancreatic beta-cell glucose toxicity, our data suggest that TXNIP might play a key role in defective glucose homeostasis preceding overt T2DM.
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| 6. |
- Gillberg, Linn, et al.
(author)
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Adipose tissue transcriptomics and epigenomics in low birthweight men and controls : role of high-fat overfeeding
- 2016
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In: Diabetologia. - : Springer Science and Business Media LLC. - 0012-186X .- 1432-0428. ; 59:4, s. 799-812
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Journal article (peer-reviewed)abstract
- Aims/hypothesis Individuals who had a low birthweight (LBW) are at an increased risk of insulin resistance and type 2 diabetes when exposed to high-fat overfeeding (HFO). We studied genome-wide mRNA expression and DNA methylation in subcutaneous adipose tissue (SAT) after 5 days of HFO and after a control diet in 40 young men, of whom 16 had LBW. Methods mRNA expression was analysed using Affymetrix Human Gene 1.0 ST arrays and DNA methylation using Illumina 450K BeadChip arrays. Results We found differential DNA methylation at 53 sites in SAT from LBW vs normal birthweight (NBW) men (false discovery rate < 5%), including sites in the FADS2 and CPLX1 genes previously associated with type 2 diabetes. When we used reference-free cell mixture adjustments to potentially adjust for cell composition, 4,323 sites had differential methylation in LBW vs NBW men. However, no differences in SAT gene expression levels were identified between LBW and NBW men. In the combined group of all 40 participants, 3,276 genes (16.5%) were differentially expressed in SAT after HFO (false discovery rate < 5%) and there was no difference between LBW men and controls. The most strongly upregulated genes were ELOVL6, FADS2 and NNAT; in contrast, INSR, IRS2 and the SLC27A2 fatty acid transporter showed decreased expression after HFO. Interestingly, SLC27A2 expression correlated negatively with diabetes- and obesity-related traits in a replication cohort of 142 individuals. DNA methylation at 652 CpG sites (including in CDK5, IGFBP5 and SLC2A4) was altered in SAT after overfeeding in this and in another cohort. Conclusions/interpretation Young men who had a LBW exhibit epigenetic alterations in their adipose tissue that potentially influence insulin resistance and risk of type 2 diabetes. Short-term overfeeding influences gene transcription and, to some extent, DNA methylation in adipose tissue; there was no major difference in this response between LBW and control participants.
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| 8. |
- Larsen, Claus M., et al.
(author)
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Interleukin-1-receptor antagonist in type 2 diabetes mellitus
- 2007
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In: New England Journal of Medicine. - 0028-4793 .- 1533-4406. ; 356:15, s. 1517-1526
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Journal article (peer-reviewed)abstract
- Background: The expression of interleukin-1-receptor antagonist is reduced in pancreatic islets of patients with type 2 diabetes mellitus, and high glucose concentrations induce the production of interleukin-1(beta) in human pancreatic beta cells, leading to impaired insulin secretion, decreased cell proliferation, and apoptosis. Methods: In this double-blind, parallel-group trial involving 70 patients with type 2 diabetes, we randomly assigned 34 patients to receive 100 mg of anakinra (a recombinant human interleukin-1-receptor antagonist) subcutaneously once daily for 13 weeks and 36 patients to receive placebo. At baseline and at 13 weeks, all patients underwent an oral glucose-tolerance test, followed by an intravenous bolus of 0.3 g of glucose per kilogram of body weight, 0.5 mg of glucagon, and 5 g of arginine. In addition, 35 patients underwent a hyperinsulinemic-euglycemic clamp study. The primary end point was a change in the level of glycated hemoglobin, and secondary end points were changes in beta-cell function, insulin sensitivity, and inflammatory markers. Results: At 13 weeks, in the anakinra group, the glycated hemoglobin level was 0.46 percentage point lower than in the placebo group (P=0.03); C-peptide secretion was enhanced (P=0.05), and there were reductions in the ratio of proinsulin to insulin (P=0.005) and in levels of interleukin-6 (P<0.001) and C-reactive protein (P=0.002). Insulin resistance, insulin-regulated gene expression in skeletal muscle, serum adipokine levels, and the body-mass index were similar in the two study groups. Symptomatic hypoglycemia was not observed, and there were no apparent drug-related serious adverse events. Conclusions: The blockade of interleukin-1 with anakinra improved glycemia and beta-cell secretory function and reduced markers of systemic inflammation.
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| 9. |
- Larsen, Claus M., et al.
(author)
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Sustained Effects of Interleukin-1 Receptor Antagonist Treatment in Type 2 Diabetes
- 2009
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In: Diabetes Care. - : American Diabetes Association. - 1935-5548 .- 0149-5992. ; 32:9, s. 1663-1668
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Journal article (peer-reviewed)abstract
- OBJECTIVE - Interleukin (IL)-1 impairs insulin secretion and induces P-cell apoptosis. Pancreatic beta-cell IL-1 expression is increased and interleukin-1 receptor antagonist (IL-1Ra) expression reduced in patients with type 2 diabetes. Treatment with recombinant IL-1Ra improves glycemia and P-cell function and reduces inflammatory markers in patients with type 2 diabetes. Here we investigated the durability of these responses. RESEARCH DESIGN AND METHODS - Among 70 ambulatory patients who had type 2 diabetes, A1C >7.5%, and BMI >27 kg/m(2) and were randomly assigned to receive 13 weeks of anakinra, a recombinant human IL-1Ra, or placebo, 67 completed treatment and were included in this double-blind 39-week follow-up study. Primary outcome was change in P-cell function after anakinra withdrawal. Analysis was done by intention to treat. RESULTS - Thirty-nine weeks after anakinra withdrawal, the proinsulin-to-insulin (PI/I) ratio but not stimulated C-peptide remained improved (by -0.07 [95% CI -0.14 to -0.02], P = 0.011) compared with values in placebo-treated patients. Interestingly, a subgroup characterized by genetically determined low baseline IL-1Ra serum levels maintained the improved stimulated C-peptide obtained by 13 weeks of IL-1Ra treatment. Reductions in C-reactive protein (-3.2 mg/l [-6.2 to -1.1], P = 0.014) and in IL-6 (-1.4 mg/l [-2.6 to -0.3], P = 0.036) were maintained until the end of study. CONCLUSIONS - IL-1 blockade with anakinra induces improvement of the PIA ratio and markers of systemic inflammation lasting 39 weeks after treatment withdrawal.
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| 10. |
- Nilsson, Emma A, et al.
(author)
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Altered DNA Methylation and Differential Expression of Genes Influencing Metabolism and Inflammation in Adipose Tissue From Subjects With Type 2 Diabetes
- 2014
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In: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 63:9, s. 2962-2976
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Journal article (peer-reviewed)abstract
- Genetics, epigenetics, and environment may together affect the susceptibility for type 2 diabetes (T2D). Our aim was to dissect molecular mechanisms underlying T2D using genome-wide expression and DNA methylation data in adipose tissue from monozygotic twin pairs discordant for T2D and independent case-control cohorts. In adipose tissue from diabetic twins, we found decreased expression of genes involved in oxidative phosphorylation; carbohydrate, amino acid, and lipid metabolism; and increased expression of genes involved in inflammation and glycan degradation. The most differentially expressed genes included ELOVL6, GYS2, FADS1, SPP1 (OPN), CCL18, and IL1RN. We replicated these results in adipose tissue from an independent case-control cohort. Several candidate genes for obesity and T2D (e.g., IRS1 and VEGFA) were differentially expressed in discordant twins. We found a heritable contribution to the genome-wide DNA methylation variability in twins. Differences in methylation between monozygotic twin pairs discordant for T2D were subsequently modest. However, 15,627 sites, representing 7,046 genes including PPARG, KCNQ1, TCF7L2, and IRS1, showed differential DNA methylation in adipose tissue from unrelated subjects with T2D compared with control subjects. A total of 1,410 of these sites also showed differential DNA methylation in the twins discordant for T2D. For the differentially methylated sites, the heritability estimate was 0.28. We also identified copy number variants (CNVs) in monozygotic twin pairs discordant for T2D. Taken together, subjects with T2D exhibit multiple transcriptional and epigenetic changes in adipose tissue relevant to the development of the disease.
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