White Adipose Tissue Insulin Sensitivity Research Articles

Adipocyte-specific FXR-deficiency protects adipose tissue from oxidative stress and insulin resistance and improves glucose homeostasis

ObjectiveObesity is associated with metabolic dysfunction of white adipose tissue (WAT). Activated adipocytes secrete pro-inflammatory cytokines resulting in the recruitment of pro-inflammatory macrophages, which contribute to WAT insulin resistance. The bile acid (BA)-activated nuclear Farnesoid X Receptor (FXR) controls systemic glucose and lipid metabolism. Here, we studied the role of FXR in adipose tissue function. MethodsWe first investigated the immune phenotype of epididymal WAT (eWAT) from high fat diet (HFD)-fed whole-body FXR-deficient (FXR−/−) mice by flow cytometry and gene expression analysis. We then generated adipocyte-specific FXR-deficient (Ad-FXR−/−) mice and analyzed systemic and eWAT metabolism and immune phenotype upon HFD feeding. Transcriptomic analysis was done on mature eWAT adipocytes from HFD-fed Ad-FXR−/− mice. ResultseWAT from HFD-fed whole-body FXR−/− and Ad-FXR−/− mice displayed decreased pro-inflammatory macrophage infiltration and inflammation. Ad-FXR−/− mice showed lower blood glucose concentrations, improved systemic glucose tolerance and WAT insulin sensitivity and oxidative stress. Transcriptomic analysis identified Gsta4, a modulator of oxidative stress in WAT, as the most upregulated gene in Ad-FXR−/− mouse adipocytes. Finally, chromatin immunoprecipitation analysis showed that FXR binds the Gsta4 gene promoter. ConclusionsThese results indicate a role for the adipocyte FXR-GSTA4 axis in controlling HFD-induced inflammation and systemic glucose homeostasis.

An Egg White-Derived Peptide Enhances Systemic Insulin Sensitivity and Modulates Markers of Non-Alcoholic Fatty Liver Disease in Obese, Insulin Resistant Mice

Non-alcoholic fatty liver disease (NAFLD), the hepatic manifestation of the metabolic syndrome, is a global health problem. Currently, no pharmacological treatment is approved for NAFLD. Natural health products, including bioactive peptides, are potential candidates to aid in the management of metabolic syndrome-related conditions, including insulin resistance and obesity. In this study, we hypothesized that an egg-white-derived bioactive peptide QAMPFRVTEQE (Peptide 2) would improve systemic and local white adipose tissue insulin sensitivity, thereby preventing high-fat diet-induced exacerbation of pathological features associated with NAFLD, such as lipid droplet size and number, inflammation, and hepatocyte hypertrophy in high-fat diet-fed mice. Similar to rosiglitazone, Peptide 2 supplementation improved systemic insulin resistance during the hyperinsulinemic-euglycemic clamp and enhanced insulin signalling in white adipose tissue, modulating ex vivo lipolysis. In the liver, compared with high-fat diet fed animals, Peptide 2 supplemented animals presented decreased hepatic cholesterol accumulation (p < 0.05) and area of individual hepatic lipid droplet by around 50% (p = 0.09) and reduced hepatic inflammatory infiltration (p < 0.05) whereas rosiglitazone exacerbated steatosis. In conclusion, Peptide 2 supplementation improved insulin sensitivity and decreased hepatic steatosis, unlike the insulin-sensitizing drug rosiglitazone.

Hyperbaric oxygen rapidly improves tissue-specific insulin sensitivity and mitochondrial capacity in humans with type 2 diabetes: a randomised placebo-controlled crossover trial

Aims/hypothesisHyperbaric oxygen (HBO) therapy may improve hyperglycaemia in humans with type 2 diabetes, but underlying mechanisms are unclear. Our objective was to examine the glucometabolic effects of HBO on whole-body glucose disposal in humans with type 2 diabetes.MethodsIn a randomised placebo-controlled crossover trial located at the German Diabetes Center, 12 male individuals with type 2 diabetes (age 18–75 years, BMI <35 kg/m2, HbA1c 42–75 mmol/mol [6–9%]), randomly allocated by one person, underwent 2-h HBO, once with 100% (240 kPa; HBO) and once with 21% oxygen (240 kPa; control, CON). Insulin sensitivity was assessed by hyperinsulinaemic–euglycaemic clamps with d-[6,6-2H2]glucose, hepatic and skeletal muscle energy metabolism were assessed by 1H/31P-magnetic resonance spectroscopy, while high-resolution respirometry measured skeletal muscle and white adipose tissue (WAT) mitochondrial capacity. All participants and people assessing the outcomes were blinded.ResultsHBO decreased fasting blood glucose by 19% and increased whole-body, hepatic and WAT insulin sensitivity about one-third (p<0.05 vs CON). Upon HBO, hepatic γ-ATP concentrations doubled, mitochondrial respiratory control doubled in skeletal muscle and tripled in WAT (p<0.05 vs CON). HBO increased myocellular insulin-stimulated serine-473/threonine-308 phosphorylation of Akt but decreased basal inhibitory serine-1101 phosphorylation of IRS-1 and endoplasmic reticulum stress (p<0.05 vs CON).Conclusions/interpretationHBO-mediated improvement of insulin sensitivity likely results from decreased endoplasmic reticulum stress and increased mitochondrial capacity, possibly leading to low-dose reactive oxygen species-mediated mitohormesis in humans with type 2 diabetes.Trial registrationClinicalTrials.gov NCT04219215FundingGerman Federal Ministry of Health, German Federal Ministry of Education and Research, North-Rhine Westfalia Ministry of Culture and Science, European-Regional-Development-Fund, German-Research-Foundation (DFG), Schmutzler StiftungGraphical abstract

Active integrins regulate white adipose tissue insulin sensitivity and brown fat thermogenesis

ObjectiveReorganization of the extracellular matrix is a prerequisite for healthy adipose tissue expansion, whereas fibrosis is a key feature of adipose dysfunction and inflammation. However, very little is known about the direct effects of impaired cell–matrix interaction in adipocyte function and insulin sensitivity. The objective of this study was to determine whether integrin activity can regulate insulin sensitivity in adipocytes and thereby systemic metabolism. MethodsWe characterized integrin activity in adipose tissue and its consequences on whole-body metabolism using adipose-selective deletion of β1 integrin (Itgb1adipo-cre) and Kindlin-2 (Kind2adipo-cre) in mice. ResultsWe demonstrate that integrin signaling regulates white adipocyte insulin action and systemic metabolism. Consequently, loss of adipose integrin activity, similar to loss of adipose insulin receptors, results in a lipodystrophy-like phenotype and systemic insulin resistance. However, brown adipose tissue of Kind2adipo-cre and Itgb1adipo-cre mice is chronically hyperactivated and has increased substrate delivery, reduced endothelial basement membrane thickness, and increased endothelial vesicular transport. ConclusionsThus, we establish integrin-extracellular matrix interactions as key regulators of white and brown adipose tissue function and whole-body metabolism.

1782-P: Mechanism of Lipid-Induced White Adipose Tissue Insulin Resistance

White adipose tissue (WAT), as an energy storage organ, plays a major role in regulating peripheral insulin resistance and hepatic gluconeogenesis, but the mechanism by which lipid induces insulin resistance in WAT is poorly understood. To examine the potential role of the diacylglycerol (DAG) - protein kinase Cε (PKCε) - insulin receptor (INSR) pathway in mediating lipid-induced WAT insulin resistance, we assessed insulin action in liver, muscle and WAT in 7-day high fat diet (HFD) and regular chow (RC) fed rats by hyperinsulinemic-euglycemic clamp (HEC) combined with [3-3H] glucose, [14C] deoxyglucose and [2H5]glycerol infusions. Using this approach, we found that HFD induced WAT insulin resistance as reflected by impaired suppression (∼20%, P&amp;lt;0.05 vs. RC) of WAT lipolysis during the HEC. WAT insulin resistance was associated with increased PKCε translocation (P&amp;lt;0.05 vs. RC) and increased phosphorylation of perilipin, HSL and ATGL (all P&amp;lt;0.05 vs. RC). To investigate if PKCε induced Thr1150phosphorylation mediates lipid-induced WAT insulin resistance by inhibiting INSR kinase activity, we studied mice with a threonine-to-alanine knockin mutation at INSR Thr1150(InsrT1150Amice). InsrT1150Amice were protected from HFD-induced WAT insulin resistance as reflected by normalization of insulin’s ability to suppress WAT lipolysis and normalization of insulin’s ability to stimulate INSR and Akt2 phosphorylation in WAT, as well as a restoration of insulin’s ability to suppress phosphorylation of perilipin, HSL and ATGL (all P&amp;lt;0.05 vs. WT). Conclusion: The DAG-PKCε-INSR Thr1150pathway plays a major role in mediating lipid-induced WAT insulin resistance and represents a potential therapeutic target to improve insulin sensitivity in WAT. Disclosure D. Zhang: None. K. Lyu: None. J.D. Song: None. X. Li: None. R.J. Perry: Research Support; Self; AstraZeneca. V. Samuel: None. G.I. Shulman: Advisory Panel; Self; AstraZeneca, Janssen Research &amp; Development, Merck &amp; Co., Inc. Advisory Panel; Spouse/Partner; Merck &amp; Co., Inc. Board Member; Self; Novo Nordisk A/S. Consultant; Self; Aegerion Pharmaceuticals, IMetabolic BioPharma Corporation, Longitude Capital, Nimbus Discovery, Inc., Staten Biotechnology B.V. Funding National Institutes of Health (R01DK116774)

272-LB: The Micropeptide ORF60 Modulates Insulin Sensitivity

Although long non-coding RNAs (lncRNAs) are non-protein-coding transcripts by definition, recent studies have shown that a number of putative small open reading frames within lncRNAs are translated. The biological significance of these hidden polypeptides is still unclear, although studies have demonstrated functional significance for some polypeptides. Recently, our lab discovered a novel micropeptide ORF60 encoded by a lncRNA. The micropeptide is conserved across species. Topology prediction indicates that the micropeptide is likely transmembrane. RNA transcript expression is nearly ubiquitous across tissues. In mice, ORF60 expression was found to be increased in the setting of high fat diet (HFD). Using CRISPR/Cas9 technology we developed ORF60 KO mice. In both mice feeding on normal chow diet and HFD, we observed impaired glucose tolerance in KO mice compared to wild type mice. ORF60 KO mice also demonstrated impaired response to insulin compared to WT mice on insulin tolerance testing (ITT), suggesting insulin resistance. Mouse tissue harvested under the condition of insulin infusion demonstrated insulin signaling attenuation in white adipose tissue (WAT) and brown adipose tissue (BAT). We are currently dissecting the molecular mechanism underlying ORF60’s influence on insulin signaling pathways. In summary, our results demonstrate that the conserved micropeptide ORF60 regulates insulin sensitivity in WAT and BAT in mice. Micropeptides involved in diabetes may serve as novel drug targets. Disclosure N. Gupta: None. Y. Shi: None. P. Li: None. H. Cao: None.

Chronic helminth infection and helminth-derived egg antigens promote adipose tissue M2 macrophages and improve insulin sensitivity in obese mice.

Chronic low-grade inflammation associated with obesity contributes to insulin resistance and type 2 diabetes. Helminth parasites are the strongest natural inducers of type 2 immune responses, and short-lived infection with rodent nematodes was reported to improve glucose tolerance in obese mice. Here, we investigated the effects of chronic infection (12 weeks) with Schistosoma mansoni, a helminth that infects millions of humans worldwide, on whole-body metabolic homeostasis and white adipose tissue (WAT) immune cell composition in high-fat diet-induced obese C57BL/6 male mice. Our data indicate that chronic helminth infection reduced body weight gain (-62%), fat mass gain (-89%), and adipocyte size; lowered whole-body insulin resistance (-23%) and glucose intolerance (-16%); and improved peripheral glucose uptake (+25%) and WAT insulin sensitivity. Analysis of immune cell composition by flow cytometry and quantitative PCR (qPCR) revealed that S. mansoni promoted strong increases in WAT eosinophils and alternatively activated (M2) macrophages. Importantly, injections with S. mansoni-soluble egg antigens (SEA) recapitulated the beneficial effect of parasite infection on whole-body metabolic homeostasis and induced type 2 immune responses in WAT and liver. Taken together, we provide novel data suggesting that chronic helminth infection and helminth-derived molecules protect against metabolic disorders by promoting a T helper 2 (Th2) response, eosinophilia, and WAT M2 polarization.

In adipose tissue, increased mitochondrial emission of reactive oxygen species is important for short-term high-fat diet-induced insulin resistance in mice.

Consuming a high-fat diet (HFD) induces insulin resistance in white adipose tissue (WAT) within 1week. However, little is known about the initiating events. One potential mechanism that has remained largely unexplored is excessive mitochondrial emission of reactive oxygen species (ROS). To determine the role of mitochondrial ROS emissions at the onset of insulin resistance, wild-type (WT) mice were placed on an HFD for 1week. WAT insulin sensitivity and inflammation were assessed by western blot. In addition, we optimised/validated a method to determine ROS emissions in permeabilised WAT. An HFD for 1week resulted in impaired insulin signalling, increased c-Jun NH2-terminal kinase (JNK) phosphorylation and an increase in oxidative stress. These changes were associated with an increase in fatty-acid-mediated mitochondrial ROS emissions without any change in mitochondrial respiration/content. To determine that mitochondrial ROS causes insulin resistance, we used transgenic mice that express human catalase in mitochondria (MCAT) as a model of upregulated mitochondrial antioxidant enzyme capacity. MCAT mice displayed attenuated mitochondrial ROS emission, preserved insulin signalling and no inflammatory response following an HFD. Findings from this study suggest that elevated mitochondrial ROS emission contributes to HFD-induced WAT insulin resistance.

Effect of dietary fat modification on subcutaneous white adipose tissue insulin sensitivity in patients with metabolic syndrome.

To determine whether the insulin resistance that exists in metabolic syndrome (MetS) patients is modulated by dietary fat composition. Seventy-five patients were randomly assigned to one of four diets for 12 wk: high-saturated fatty acids (HSFAs), high-MUFA (HMUFA), and two low-fat, high-complex carbohydrate (LFHCC) diets supplemented with long-chain n-3 (LFHCC n-3) PUFA or placebo. At the end of intervention, the LFHCC n-3 diet reduced plasma insulin, homeostasis model assessment of insulin resistance, and nonsterified fatty acid concentration (p < 0.05) as compared to baseline Spanish habitual (BSH) diet. Subcutaneous white adipose tissue (WAT) analysis revealed decreased EH-domain containing-2 mRNA levels and increased cbl-associated protein gene expression with the LFHCC n-3 compared to HSFA and HMUFA diets, respectively (p < 0.05). Moreover, the LFHCC n-3 decreased gene expression of glyceraldehyde-3-phosphate dehydrogenase with respect to HMUFA and BSH diets (p < 0.05). Finally, proteomic characterization of subcutaneous WAT identified three proteins of glucose metabolism downregulated by the LFHCC n-3 diet, including annexin A2. RT-PCR analysis confirmed the decrease of annexin A2 (p = 0.027) after this diet. Our data suggest that the LFHCC n-3 diet reduces systemic insulin resistance and improves insulin signaling in subcutaneous WAT of MetS patients compared to HSFA and BSH diets consumption.

Sex dimorphism in the onset of the white adipose tissue insulin sensitivity impairment associated with age.

The aim of this study was to investigate the time-course response of retroperitoneal white adipose tissue (WAT) insulin and adiponectin signaling pathway intermediates in relation to the systemic age-associated impairment of insulin sensitivity in male and female rats. The main markers of the insulin and adiponectin signaling pathways of the retroperitoneal WAT, as well as of the systemic insulin sensitivity profile of 3-, 9- and 18-month old Wistar rats of both sexes were determined. Our results indicate that age leads to a decrease in the insulin sensitivity in both sexes that agrees with the decline in the levels of the WAT insulin signaling pathway intermediates, the increase in the adiposity index and the rise in the serum insulin resistance markers. This is accompanied by a sex-dimorphism that involves a gradual insulin signaling pathway decrease in female rats and an earlier and acute decrease in males and suggests a better insulin responsiveness in female rats at any age group. Our results confirm the idea that in rats, the insulin signaling pathway of WAT is altered at earlier ages than that of skeletal muscle and also provides further evidence of the impairment of the WAT adiponectin signaling pathway.

Fish Oil Improves White Adipose Tissue Function And Protects Against Atherosclerosis

Fish oil (FO) is known to reduce triglyceride synthesis and improve insulin sensitivity in liver which may account for its anti-atherogenic effects. The objective of this study was to investigate the role of white adipose tissue (WAT), another important insulin responsive tissue, in mediating the anti-atherogenic effect of FO. Female LDL receptor-deficient mice were fed a high fat diet enriched with 6% olive oil (control) or 6% menhaden oil (FO) for 12 weeks. FO feeding led a to a significant (47%) reduction in atherosclerotic lesion formation. In addition to improving serum and liver lipid profiles, FO-feeding also led to a significant decrease in cholesteryl ester, phospholipid and free fatty acid levels in WAT. FO-fed animals showed a significant reduction in expression of inflammatory mediators in WAT, which could be attributed to a reduction in activation of mitogen activated protein kinases. Insulin sensitivity in WAT of FO-fed mice was improved, as indicated by increased phosphorylation of the insulin receptor. Finally, we found that FO reduced the formation of F2 isoprostanes in both liver and WAT with a concomitant increase in the formation of the protective EPA and DHA-derived F3 and F4 isoprostanes; providing evidence that FO-feeding also improves oxidative stress. Taken together, these data clearly suggest that in addition to playing a role in hepatic lipid homeostasis, FO could also exert its anti-atherogenic effect by improving WAT function (supported in part by grants from the NIH (P01 ES013125), the American Diabetes Association (1-04-JF-20) and the American Heart Association (0330011N).