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- Ahlqvist, Emma, et al.
(author)
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A link between GIP and osteopontin in adipose tissue and insulin resistance.
- 2013
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In: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 62:6, s. 2088-2094
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Journal article (peer-reviewed)abstract
- Low grade inflammation in obesity is associated with accumulation of the macrophagederived cytokine osteopontin in adipose tissue and induction of local as well as systemic insulin resistance. Since GIP (glucose-dependent insulinotropic polypeptide) is a strong stimulator of adipogenesis and may play a role in the development of obesity, we explored whether GIP directly would stimulate osteopontin (OPN) expression in adipose tissue and thereby induce insulin resistance. GIP stimulated OPN protein expression in a dose-dependent fashion in rat primary adipocytes. The level of OPN mRNA was higher in adipose tissue of obese individuals (0.13±}0.04 vs 0.04±}0.01, P<0.05) and correlated inversely with measures of insulin sensitivity (r=-0.24, P=0.001). A common variant of the GIP receptor (GIPR) (rs10423928) gene was associated with lower amount of the exon 9 containing isoform required for transmembrane activity. Carriers of the A-allele with a reduced receptor function showed lower adipose tissue OPN mRNA levels and better insulin sensitivity. Together, these data suggest a role for GIP not only as an incretin hormone, but also as a trigger of inflammation and insulin resistance in adipose tissue. Carriers of GIPR rs10423928 A-allele showed protective properties via reduced GIP effects. Identification of this unprecedented link between GIP and OPN in adipose tissue might open new avenues for therapeutic interventions.
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- Banasik, Karina, et al.
(author)
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The FOXO3A rs2802292 G-Allele Associates with Improved Peripheral and Hepatic Insulin Sensitivity and Increased Skeletal Muscle-FOXO3A mRNA Expression in Twins.
- 2011
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In: The Journal of clinical endocrinology and metabolism. - : The Endocrine Society. - 1945-7197 .- 0021-972X. ; 96, s. 119-124
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Journal article (peer-reviewed)abstract
- Objective: The minor G allele of FOXO3A rs2802292 has been associated with longevity. We aimed to investigate whether a phenotype related to healthy metabolic aging could be identified in individuals carrying the longevity-associated FOXO3A rs2802292 G allele. Research Design and Methods: rs2802292 was genotyped in a phenotypically well-characterized population of young and elderly twins (n = 190) and in the population-based Inter99 cohort (n = 5768). All participants underwent oral glucose tolerance tests, and the twin population was additionally examined with an iv glucose tolerance test and a hyperinsulinemic, euglycemic clamp. Basal and insulin-stimulated FOXO3A mRNA expression was assessed in skeletal muscle biopsies from the twin population. Results: In the twin sample, carriers of the minor G allele of rs2802292 showed reduced fasting plasma insulin [per allele effect (β) = -13% (-24; -1) (95% confidence interval), P = 0.03] and lower incremental area under the curve 0-120 min for insulin after an oral glucose load [β = -14% (-23; -), P = 0.005]. The G allele was associated with increased peripheral insulin action [glucose disposal rate clamp, β = 0.85 mg·kgfat-free mass(-1) · min(-1) (0.049; 1.64), P = 0.04] and lower hepatic insulin resistance index [β = -13% (-25; -1), P = 0.03]. Furthermore, carriers of the G allele had increased basal FOXO3A mRNA expression in skeletal muscle compared with T-allele carriers [β = 16% (0; 33), P = 0.047]. In the Inter99 sample, we found an association with reduced incremental area under the curve 0-120 min for insulin after an oral glucose load [β = -3% (-5; -0.07), P = 0.04], but this association was not significant after adjustment for body mass index. Conclusion: Our data indicate that the minor G allele of FOXO3A rs2802292 is associated with enhanced peripheral and hepatic insulin sensitivity in our small twin cohort, which may be mediated through increased FOXO3A mRNA expression, although no major metabolic impact of rs2802292 was found in the large Inter99 cohort.
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- Brøns, Charlotte, et al.
(author)
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Deoxyribonucleic Acid Methylation and Gene Expression of PPARGC1A in Human Muscle Is Influenced by High-Fat Overfeeding in a Birth-Weight-Dependent Manner.
- 2010
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In: The Journal of clinical endocrinology and metabolism. - : The Endocrine Society. - 1945-7197 .- 0021-972X. ; 95, s. 3048-3056
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Journal article (peer-reviewed)abstract
- Context: Low birth weight (LBW) and unhealthy diets are risk factors of metabolic disease including type 2 diabetes (T2D). Genetic, nongenetic, and epigenetic data propose a role of the key metabolic regulator peroxisome proliferator-activated receptor gamma, coactivator 1alpha (PPARGC1A) in the development of T2D. Objective: Our objective was to investigate gene expression and DNA methylation of PPARGC1A and coregulated oxidative phosphorylation (OXPHOS) genes in LBW and normal birth weight (NBW) subjects during control and high-fat diets. Design, Subjects, and Main Outcome Measures: Twenty young healthy men with LBW and 26 matched NBW controls were studied after 5 d high-fat overfeeding (+50% calories) and after a control diet in a randomized manner. Hyperinsulinemic-euglycemic clamps were performed and skeletal muscle biopsies excised. DNA methylation and gene expression were measured using bisulfite sequencing and quantitative real-time PCR, respectively. Results: When challenged with high-fat overfeeding, LBW subjects developed peripheral insulin resistance and reduced PPARGC1A and OXPHOS (P < 0.05) gene expression. PPARGC1A methylation was significantly higher in LBW subjects (P = 0.0002) during the control diet. However, PPARGC1A methylation increased in only NBW subjects after overfeeding in a reversible manner. DNA methylation of PPARGC1A did not correlate with mRNA expression. Conclusions: LBW subjects developed peripheral insulin resistance and decreased gene expression of PPARGC1A and OXPHOS genes when challenged with fat overfeeding. The extent to which our finding of a constitutively increased DNA methylation in the PPARGC1A promoter in LBW subjects may contribute needs to be determined. We provide the first experimental support in humans that DNA methylation induced by overfeeding is reversible.
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- Friedrichsen, Martin, et al.
(author)
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Dissociation between Skeletal Muscle Inhibitor-{kappa}B Kinase/Nuclear Factor-{kappa}B Pathway Activity and Insulin Sensitivity in Nondiabetic Twins.
- 2010
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In: Journal of Clinical Endocrinology and Metabolism. - : The Endocrine Society. - 1945-7197 .- 0021-972X. ; 95:1, s. 414-421
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Journal article (peer-reviewed)abstract
- Context: Several studies suggest a link between increased activity of the inflammatory inhibitor-kappaB kinase/nuclear factor-kappaB (IKK/NF-kappaB) pathway in skeletal muscle and insulin resistance. Objective: We aimed to study the regulation of skeletal muscle IKK/NF-kappaB pathway activity as well as the association with glucose metabolism and skeletal muscle insulin signaling. Methods: The study population included a metabolically well-characterized cohort of young and elderly predominantly nondiabetic twins (n = 181). Inhibitor-kappaBbeta (IkappaBbeta) protein levels are negatively associated with IKK/NF-kappaB pathway activity and were used to evaluate pathway activity with p65 levels included as loading control. This indirect measure for IKK/NF-kappaB pathway activity was validated by a p65 binding assay. Results: Evaluating the effects of heritability, age, sex, obesity, aerobic capacity, and several hormonal factors (eg insulin and TNF-alpha), only sex and age were significant predictors of IkappaBbeta to p65 ratio (28% decreased ratio in the elderly, P < 0.01, and 49% increased in males P < 0.01). IkappaBbeta to p65 ratio was unrelated to peripheral insulin sensitivity (P = 0.51) and in accordance with this also unrelated to proximal insulin signaling (P = 0.81). Although no association was seen with plasma glucose after oral glucose challenge, there was a tendency for lower IkappaBbeta to p65 ratio (adjusted for age and sex) in subjects with impaired as opposed to normal glucose tolerance (P = 0.055). Conclusions: Altogether the subtle elevated IKK/NF-kappaB pathway activity seen in glucose-intolerant subjects suggests that IKK/NF-kappaB pathway activation may be secondary to impaired glucose tolerance and that skeletal muscle IKK/NF-kappaB pathway activity is unlikely to play any major role in the control of skeletal muscle insulin action in nondiabetic subjects.
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- Grunnet, Louise G., et al.
(author)
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Regulation and Function of FTO mRNA Expression in Human Skeletal Muscle and Subcutaneous Adipose Tissue
- 2009
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In: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 58:10, s. 2402-2408
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Journal article (peer-reviewed)abstract
- OBJECTIVE-Common variants in FTO (the fat mass- and obesity-associated gene) associate with obesity and type 2 diabetes. The regulation and biological function of FTO mRNA expression in target tissue is unknown. We investigated the genetic and nongenetic regulation of FTO mRNA in skeletal muscle and adipose tissue and their influence on in vivo glucose and fat metabolism. RESEARCH DESIGN AND METHODS-The FTO rs9939609 polymorphism was genotyped in two twin cohorts: 1) 298 elderly twins aged 62-83 years with glucose tolerance ranging from normal to type 2 diabetes and 2) 196 young (25-32 years) and elderly (58-66 years) nondiabetic twins examined by a hyperinsulinemic-euglycemic clamp including indirect calorimetry. FTO mRNA expression was determined in subcutaneous adipose tissue (n = 226) and skeletal muscle biopsies (n = 158). RESULTS-Heritability of FTO expression in both tissues was low, and FTO expression was not influenced by FTO rs9939609 genotype. FTO mRNA expression in skeletal muscle was regulated by age and sex, whereas age and BMI were predictors of adipose tissue FTO mRNA expression. FTO mRNA expression in adipose tissue was associated with an atherogenic lipid profile. In skeletal muscle, FTO mRNA expression was negatively associated to fat and positively to glucose oxidation rates as well as positively correlated with expression of genes involved in oxidative phosphorylation including PGC1 alpha. CONCLUSIONS-The heritability of FTO expression in adipose tissue and skeletal muscle is low and not influenced by obesity-associated FTO genotype. The age-dependent decline in FTO expression is associated with peripheral defects of glucose and fat metabolism. Diabetes 58:2402-2408, 2009
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- Grunnet, Louise Groth, et al.
(author)
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The Triglyceride Content in Skeletal Muscle Is Associated with Hepatic But Not Peripheral Insulin Resistance in Elderly Twins.
- 2012
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In: The Journal of clinical endocrinology and metabolism. - : The Endocrine Society. - 1945-7197 .- 0021-972X.
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Journal article (peer-reviewed)abstract
- Context and Objective:Total muscle triglyceride (MT) content has been associated with insulin resistance. We investigated the predictors and impact of MT on relevant metabolic parameters including peripheral and hepatic insulin resistance in elderly twins.Design and Participants:Seventy-four elderly same-sex twins underwent hyperinsulinemic euglycemic clamps preceded by an iv glucose tolerance test. Aerobic capacity (VO(2max)) and body composition (dual-energy x-ray absorptiometry scan) were determined in all twins. A biopsy from the vastus lateralis muscle was excised in the fasting state. The muscle triacylglycerol content was analyzed by biochemical extraction from these biopsies.Results:The percentage of total body fat was the only independent predictor of MT content. After adjustment for trunk fat percentages and sex, MT level was significantly associated to fasting plasma levels of glucose and insulin as well as hepatic insulin resistance. However, the association was weakened after adjustment for total fat percentages. A 1 sd (34.5 mmol/kg dry weight) increase in MT content was associated with a 24% increase of hepatic insulin resistance. No association between MT content and peripheral insulin sensitivity was observed.Conclusion:MT content is associated with hepatic but not peripheral insulin resistance in elderly twins. We speculate that MT content may reflect the general ectopic accumulation of triglycerides, including fat in the liver.
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- Jacobsen, Stine C., et al.
(author)
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Young men with low birthweight exhibit decreased plasticity of genome-wide muscle DNA methylation by high-fat overfeeding
- 2014
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In: Diabetologia. - : Springer Science and Business Media LLC. - 1432-0428 .- 0012-186X. ; 57:6, s. 1154-1158
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Journal article (peer-reviewed)abstract
- Aims/hypothesis The association between low birthweight (LBW) and risk of developing type 2 diabetes may involve epigenetic mechanisms, with skeletal muscle being a prime target tissue. Differential DNA methylation patterns have been observed in single genes in muscle tissue from type 2 diabetic and LBW individuals, and we recently showed multiple DNA methylation changes during short-term high-fat overfeeding in muscle of healthy people. In a randomised crossover study, we analysed genome-wide DNA promoter methylation in skeletal muscle of 17 young LBW men and 23 matched normal birthweight (NBW) men after a control and a 5 day high-fat overfeeding diet. Methods DNA methylation was measured using Illumina's Infinium BeadArray covering 27,578 CpG sites representing 14,475 different genes. Results After correction for multiple comparisons, DNA methylation levels were found to be similar in the LBW and NBW groups during the control diet. Whereas widespread DNA methylation changes were observed in the NBW group in response to high-fat overfeeding, only a few methylation changes were seen in the LBW group (chi(2), p < 0.001). Conclusions/interpretation Our results indicate lower DNA methylation plasticity in skeletal muscle from LBW vs NBW men, potentially contributing to understanding the link between LBW and increased risk of type 2 diabetes.
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- Koeck, Thomas, et al.
(author)
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A common variant in TFB1M is associated with reduced insulin secretion and increased future risk of type 2 diabetes.
- 2011
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In: Cell Metabolism. - : Elsevier BV. - 1550-4131 .- 1932-7420. ; 13:1, s. 80-91
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Journal article (peer-reviewed)abstract
- Type 2 diabetes (T2D) evolves when insulin secretion fails. Insulin release from the pancreatic β cell is controlled by mitochondrial metabolism, which translates fluctuations in blood glucose into metabolic coupling signals. We identified a common variant (rs950994) in the human transcription factor B1 mitochondrial (TFB1M) gene associated with reduced insulin secretion, elevated postprandial glucose levels, and future risk of T2D. Because islet TFB1M mRNA levels were lower in carriers of the risk allele and correlated with insulin secretion, we examined mice heterozygous for Tfb1m deficiency. These mice displayed lower expression of TFB1M in islets and impaired mitochondrial function and released less insulin in response to glucose in vivo and in vitro. Reducing TFB1M mRNA and protein in clonal β cells by RNA interference impaired complexes of the mitochondrial oxidative phosphorylation system. Consequently, nutrient-stimulated ATP generation was reduced, leading to perturbed insulin secretion. We conclude that a deficiency in TFB1M and impaired mitochondrial function contribute to the pathogenesis of T2D.
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