GLUT4 Expression In Adipose Tissue Research Articles

SAT386 Constitutive Overexpression Of Microrna-93 As A Cause Of Metabolic Dysfunction And Hyperandrogenism In Polycystic Ovary Syndrome (PCOS): Evidence From A Transgenic (Mir-93+) Murine Model

Abstract Disclosure: Y. Chen: None. H. Wu: None. B.A. Gower: None. R. Azziz: Advisory Board Member; Self; Arora Forge. Consulting Fee; Self; Fortress Biotech, Spruce Biosciences, Core Access Surgical Technologies, Rani Therapeutics. Grant Recipient; Self; Ferring Pharmaceuticals, Foundation for Research and Education Excellence. Stock Owner; Self; Martin Imaging. Background: PCOS appears to result from enhanced stimuli, either increased LH or insulin, and exaggerated responsiveness of ovarian theca cell androgen biosynthesis to these stimuli. However, the etiology of the enhanced stimuli remains unclear. We previously reported that a specific microRNA, miR-93, regulates GLUT4 content in adipocytes; and that in PCOS miR-93 overexpression in adipocytes results in suppressed GLUT4 expression and insulin-meditated glucose uptake in these cells, and is associated with whole-body insulin resistance (IR). These data suggest that constitutive miR-93 overexpression may underly the metabolic dysfunction and, possibly, the hyperandrogenism of PCOS. Objective: To test the hypothesis in a transgenic murine model that miR-93 overexpression results in the metabolic and hyperandrogenic features of PCOS. Materials and methods: We generated a novel miR-93 overexpressed (miR-93+) mouse model in collaboration with InGenious Targeting Laboratory (Ronkonkoma, NY). The mouse miR-93 sequence with the R26/CAG promoter was inserted immediately downstream of loxP flanked stop cassette in intron 1 of ROSA26 locus. miR-93 insertion was not expected to cause unwanted phenotypes resulting from modification of the Rosa26 locus. When mating miR-93+ transgenic mice to whole body Cre mice (The Jackson Lab) the stop code is removed, and miR-93 is overexpressed systemically. Results: In miR-93+ mice, miR-93 was overexpressed in adipose tissue (AT), muscle, liver, heart, kidneys, and ovaries. Phenotypically, miR-93+ mice had reduced GLUT4 expression in AT, and higher fasting serum insulin, higher fasting serum glucose, and higher testosterone levels. In PCOS women, increased CYP17A1 expression in theca cells is associated with excess androgen production. Consistent with this PCOS phenotype, Cyp17a1 expression in miR-93+ mice ovaries were also increased. In addition, the ovaries of miR-93+ mice had reduced expression of Cdkn1a, similar to that observed in granulosa cells from PCOS patients. miR-93+ mice gained more weight and epididymal AT than controls. miR-93+ mice also demonstrated a lesser response to insulin during an insulin tolerance test (ITT) and exhibited altered estrous cycles as compared to wild type. Conclusion: We successfully developed a miR-93 overexpressed (miR93+) murine model, which demonstrates IR, hyperandrogenemia, exaggerated ovarian Cyp17a1 expression, increased weight gain, and abnormal estrous (ovulatory) cyclicity, mimicking the PCOS phenotype. These results provide further evidence to support the role for constitutive overexpression of miR-93 in the metabolic and hyperandrogenic features of PCOS. These data also suggest a potential model to study the mechanisms mediating the effect of miR-93 overexpression on IR and on the PCOS phenotype in tissues and conditions not readily accessible in human subjects. Presentation Date: Saturday, June 17, 2023

Evaluation of the effect of co-administration of irak inhibitor and pioglitazone on ppar-γ, glut-4, tnf-α, and leptin genes expression in adipose tissue of insulin-resistant mice

Background: The worldwide prevalence of diabetes is increasing. Diabetes is a complex disease that results from impaired secretion of insulin or insulin resistance. In adipose tissue, insulin increases glucose uptake by stimulating the transfer of glucose transporter type 4 (GLUT-4) to the plasma membrane. In this study, the effect of IRAK inhibitor (IRAKi) and pioglitazone on genes expression in adipose tissue of insulin resistant mice was evaluated. Methods: Mice were randomly divided into 6 groups (n= 8 each), five groups of which were fed a high-fat diet and one group received a normal diet for 12 weeks. The treatment with pioglitazone and IRAKi was performed for 2 weeks. At the end of the study, the animals were sacrificed and the adipose tissue and blood samples were collected. The expression of GLUT4, TNF-I±, peroxisome proliferator-activated receptor gamma (PPARI³), and Lepin were determined by real-time PCR in the adipose tissue. The malondialdehyde (MDA) level and total antioxidant capacity (TAC) in serum were measured. Results were analyzed by SPSS 22. Results: The data showed that the combination of IRAKi and pioglitazone increased PPARI³ expression, leptin and TAC levels in serum, and reduced TNF-I± expression and MDA levels. The GLUT4 expression in adipose tissue was not significant between studied groups. Pioglitazone and IRAKi improved insulin function by inhibiting inflammation signaling. Conclusion: According to the results of this study, IRAKi may be an appropriate target for inhibiting inflammation and related disorders, including insulin resistance. © 2021 The Author(s); Published by Kerman University of Medical Sciences.

Exercise serum increases GLUT4 in human adipocytes

What is the central question of this study? Do circulating factors mediate exercise-induced effects on adipose tissue GLUT4 expression? What is the main finding and its importance? Serum (10%) obtained from human volunteers immediately after a single exercise bout increased GLUT4 protein levels in human adipocytes in culture. This result suggests that circulating factors might mediate the effects of exercise on adipose tissue GLUT4 and prompts further effort to identify the specific factor(s) and tissue(s) of origin. In this study, we tested the hypothesis that circulating factors generated during exercise increase adipose tissue GLUT4 expression. Serum was obtained from eight healthy subjects before and after 60min of cycling exercise, and primary adipocytes were cultured from stromal vascular fractions that were isolated from subcutaneous abdominal adipose tissue samples from one healthy, male volunteer. A 48h exposure of human primary adipocytes to 10% serum obtained after exercise increased GLUT4 protein expression, on average, by 12% compared with exposure to 10% serum obtained at rest, before exercise. GLUT4 mRNA levels were increased after 12h of exposure to exercise serum but were unchanged after 6 and 24h of exposure. Our results suggest that circulating factors might mediate the effects of exercise on adipose tissue GLUT4 expression and encourage further efforts to identify the potential factor(s), tissue(s) of origin and physiological relevance.

Exercise and GLUT4 in human subcutaneous adipose tissue.

To examine the effect of acute and chronic exercise on adipose tissue GLUT4 expression, a total of 20 healthy, male subjects performed one of two studies. Ten subjects performed cycle ergometer exercise for 60 min at 73 ± 2% VO 2 peak and abdominal adipose tissue samples were obtained immediately before and after exercise and after 3 h of recovery. Another 10 subjects completed 10 days of exercise training, comprising a combination of six sessions of 60 min at 75% VO 2 peak and four sessions of 6 × 5 min at 90% VO 2 peak, separated by 3 min at 40% VO 2 peak. Abdominal adipose tissue and vastus lateralis muscle samples were obtained before training and 24 h after the last training session. A single bout of exercise did not change adipose tissue GLUT4 mRNA; however, there was a small, but significant, reduction in adipose tissue GLUT4 protein expression 3 h after exercise. There were no changes in adipose tissue GLUT4 or COX‐IV expression following exercise training. In contrast, skeletal muscle GLUT4 and COX‐IV were increased by 47% and 44%, respectively following exercise training. The exercise training‐induced increase in GLUT4 expression was similar in both type I and type IIa single muscle fibers. Our results indicate that neither a single exercise bout, nor 10 days of exercise training, increased adipose tissue GLUT4, in contrast with the increases observed in skeletal muscle GLUT4 expression.

NaoXinTong Capsules inhibit the development of diabetic nephropathy in db/db mice

NaoXinTong Capsule (NXT), a Chinese medicine, is currently used to treat patients with cardiovascular and cerebrovascular diseases. Clinical observations indicate its anti-diabetic functions with unclear mechanisms. Herein, we report the effect of NXT on diabetic nephropathy (DN). Type 2 diabetic db/db mice were treated with NXT for 14 weeks. In the course of treatment, NXT reduced diabetes-increased glucose levels and improved renal functions. At the end of treatment, we found that NXT ameliorated serum lipid profiles and other biochemical parameters. In the kidney, NXT inhibited mesangial matrix expansion, expression of vascular endothelial growth factor A, fibronectin, advanced glycation end product and its receptor. Meanwhile, it reduced the diabetes-induced podocyte injury by increasing WT1 and nephrin expression. In addition, NXT inhibited accumulation of extracellular matrix proteins by increasing MMP2/9 expression through inactivation of TGFβ/Smad pathway and CTGF expression. Mechanically, NXT activated insulin signaling pathway by increasing expression of INSR, IRS and FGF21, phosphorylation of Akt and AMPKα in the liver, INSR phosphorylation in the kidney, and FGF21 and GLUT4 expression in adipose tissue and skeletal muscle. Taken together, our study demonstrates that NXT inhibits DN by ameliorating glucose/lipid metabolism, maintaining tissue structure integrity, and correcting diabetes-induced renal dysfunctions.

Effect of iron supplementation on glucose transporter 4 expression in adipose tissue and skeletal muscle of pregnant rats

Objective: The main goal of the present study was to investigate the effect of iron supplementation on glucose transporter 4 expressions in adipose tissue and skeletal muscle in female rats during pregnancy. Methods: Twenty-four pregnant Sprague-Dawley rats were randomly divided into 2 groups: a control group with a standard diet (containing iron 150 mg/kg) and an iron-supplementation group with a high-iron diet (containing iron 700 mg/kg) from day 0 to day 21 of pregnancy. Intraperitoneal glucose tolerance test was performed on gestational day 19. On gestational day 21, all of the pregnant rats from each group were sacrificed. The mean neonatal weights were measured and samples of maternal intraabdominal adipose tissue and skeletal muscle were taken to measure the expression of Glucose Transporter 4 (GLUT4) mRNA and protein. Results: Glucose tolerance decreased significantly in the iron supplementation group compared to the control group. The mean neonatal weights in the iron supplementation group were higher than that in the control group. Levels of GLUT4 mRNA in the adipose tissue were reduced by the administrations of high-iron diet. The skeletal muscle GLUT4 mRNA levels were not changed significantly by iron supplementation. Expression of GLUT4 protein both in the adipose tissue and skeletal muscle reduced significantly. Conclusion: These results suggest that iron supplementation during pregnancy would increase neonatal weights and could decrease maternal glucose tolerance by interfering GLUT4 expression in adipose tissue and skeletal muscle of rats.

A novel ChREBP isoform in adipose tissue regulates systemic glucose metabolism

SummaryThe prevalence of obesity and type 2-diabetes is increasing worldwide and threatens to shorten lifespan. Impaired insulin action in peripheral tissues is a major pathogenic factor. Insulin stimulates glucose uptake in adipose tissue through the Glut4-glucose transporter and alterations in adipose-Glut4 expression or function regulate systemic insulin sensitivity. Downregulation of adipose tissue-Glut4 occurs early in diabetes development. Here we report that adipose tissue-Glut4 regulates the expression of carbohydrate responsive-element binding protein (ChREBP), a transcriptional regulator of lipogenic and glycolytic genes. Furthermore, adipose-ChREBP is a major determinant of adipose tissue fatty acid synthesis and systemic insulin sensitivity. We discovered a new mechanism for glucose-regulation of ChREBP: Glucose-mediated activation of the canonical ChREBP isoform (ChREBPα) induces expression of a novel, potent isoform (ChREBPβ) that is transcribed from an alternative promoter. ChREBPβ expression in human adipose tissue predicts insulin sensitivity indicating that it may be an effective target for treating diabetes.

Exercise training increases adipose tissue GLUT4 expression in patients with type 2 diabetes

We investigated the effects of exercise training on adipose tissue and skeletal muscle GLUT4 expression in patients with type 2 diabetes (T2D). Muscle and adipose tissue samples were obtained before and after 4-weeks of exercise training in seven patients with T2D [47 ± 2 years, body mass index (BMI) 28 ± 2]. Seven control subjects (54 ± 4, BMI 30 ± 2) were recruited for baseline comparison. Adipose tissue GLUT4 protein expression was 43% lower (p < 0.05) in patients with T2D compared with control subjects and exercise training increased (p < 0.05) adipose tissue GLUT4 expression by 36%. Skeletal muscle GLUT4 protein expression was not different between control subjects and patients with T2D. Exercise training increased (p < 0.05) skeletal muscle GLUT4 protein expression by 20%. In conclusion, 4-weeks of exercise training increased GLUT4 expression in adipose tissue and skeletal muscle of patients with T2D, although the functional benefits of this adaptation appear to be dependent on an optimal β-cell function.

The frequency of daily ethanol consumption influences the effect of ethanol on insulin sensitivity in rats fed a high-fat diet

The different effects of ethanol on insulin sensitivity may be due to complex reasons. Here, we focus on the various daily ethanol consumption frequencies in rats fed a high-fat (HF) diet and explore the possible mechanism mediated by adiponectin and AMP-activated protein kinase (AMPK). A total of thirty-six male Wistar rats were fed a HF diet and were randomly divided into three groups: those that received tap water (C); those that received ethanol via a gastric tube twice per d (E1); those that received free access to ethanol for drinking (E2). The total daily ethanol dosage in groups E1 and E2 were the same (5 g/kg per d). At the end of 18 weeks, insulin sensitivity was evaluated. Adiponectin AMPK and GLUT4 levels were determined. We found that the different administration frequencies led to markedly different plasma ethanol concentrations and there were intimate relationships between plasma ethanol concentration and insulin sensitivity. Insulin resistance was markedly improved in group E1, whereas only a slight improvement was observed in group E2. Accordingly, adiponectin, phosphorylated AMPK and GLUT4 levels were significantly increased in group E1. Based on these findings, we propose that ethanol concentration might be the major influencing factor mediating the effect of ethanol on insulin sensitivity. At a total daily dosage of 5 g/kg per d, twice daily administration of ethanol was more beneficial than continuous drinking. The protective effect of ethanol might be mediated by increased adiponectin levels, which subsequently improve the activation of AMPKα and GLUT4 expression in adipose tissue.

Altered estrogen receptor expression in skeletal muscle and adipose tissue of female rats fed a high-fat diet

Estrogen receptors (ERs) are expressed in adipose tissue and skeletal muscle, with potential implications for glucose metabolism and insulin signaling. Previous studies examining the role of ERs in glucose metabolism have primarily used knockout mouse models of ERα and ERβ, and it is unknown whether ER expression is altered in response to an obesity-inducing high-fat diet (HFD). The purpose of the current study was to determine whether modulation of glucose metabolism in response to a HFD in intact and ovariectomized (OVX) female rats is associated with alterations in ER expression. Our results demonstrate that a 6-wk HFD (60% calories from fat) in female rats induces whole body glucose intolerance with tissue-specific effects isolated to the adipose tissue, and no observed differences in insulin-stimulated glucose uptake, GLUT4, or ERα protein expression levels in skeletal muscle. In chow-fed rats, OVX resulted in decreased ERα with a trend toward decreased GLUT4 expression in adipose tissue. Sham-treated and OVX rats fed a HFD demonstrated a decrease in ERα and GLUT4 in adipose tissue. The HFD also increased activation of stress kinases (c-jun NH₂-terminal kinase and inhibitor of κB kinase β) in the sham-treated rats and decreased expression of the protective heat shock protein 72 (HSP72) in both sham-treated and OVX rats. Our findings suggest that decreased glucose metabolism and increased inflammation in adipose tissue with a HFD in female rats could stem from a significant decrease in ERα expression.

Tissue-specific Alterations of Glucose Transport and Molecular Mechanisms of Intertissue Communication in Obesity and Type 2 Diabetes

Insulin resistance plays a major role in the pathogenesis of type 2 diabetes. Insulin regulates blood glucose levels primarily by promoting glucose uptake from the blood into multiple tissues and by suppressing glucose production from the liver. The glucose transporter, GLUT4, mediates insulin-stimulated glucose uptake in muscle and adipose tissue. Decreased GLUT4 expression in adipose tissue is a common feature of many insulin resistant states. GLUT4 expression is preserved in skeletal muscle in many insulin resistant states. However, functional defects in the intracellular trafficking and plasma membrane translocation of GLUT4 result in impaired insulin-stimulated glucose uptake in muscle. Tissue-specific genetic knockout of GLUT4 expression in adipose tissue or muscle of mice has provided new insights into the pathogenesis of insulin resistance. We recently determined that the expression of serum retinol binding protein (RBP4) is induced in adipose tissue as a consequence of decreased GLUT4 expression. We found that RBP4 is elevated in the serum of insulin resistant humans and mice. Furthermore, we found that increasing serum RBP4 levels by transgenic overexpression or by injection of purified RBP4 protein into normal mice causes insulin resistance. Therefore, RBP4 appears to play an important role in mediating adipose tissue communication with other insulin target tissues in insulin resistant states.

Age related obesity-induced shortening of GLUT4 mRNA poly(A) tail length in rat gastrocnemius skeletal muscle

Obese insulin resistant animals and humans have shown reduced GLUT4 gene expression. Yet, in skeletal muscle, discrepancy between mRNA and protein regulation has been frequently observed, suggesting a post-transcriptional modulation. We investigated the GLUT4 expression in adipose tissue and muscle of obese 12-month-old (12-mo) rats, comparing with lean 2-month-old (2-mo) animals. Obesity was accompanied by insulin resistance, and 65% reduction ( P < 0.01) in GLUT4 mRNA and protein in adipose tissue. However, in muscle, despite increased ( P < 0.05) mRNA content, GLUT4 protein was unchanged. RNase H and poly(A) test assays showed a reduction ( P < 0.01) of ∼80 adenines in the GLUT4 mRNA poly(A) tail of muscle from 12-mo rats, recognizing that the poly(A) tail length correlates with translation efficiency. Concluding, age related obesity of 12-mo rats involves suppression of GLUT4 expression in adipose tissue; however, in muscle, GLUT4 mRNA content increases, but with a shorter poly(A) tail, thus unchanging the protein content.

Novel findings regarding Glut-4 expression in adipose tissue and muscle in horses – A preliminary report

One of the hallmarks of insulin resistance is a reduction in glucose transporter-4 (Glut-4) expression in adipose tissue but not in skeletal muscle. However, while Glut-4 has been demonstrated in skeletal and cardiac muscles in horses it has not been demonstrated in adipose tissue. The initial objectives of the present study were: (1) to test the hypothesis that Glut-4 expression would vary between selected key skeletal muscles; (2) to test the hypothesis that it would also vary between representative adipose tissue depots, and (3) to see whether expression would be greater in adipose tissue compared to muscle. Glut-4 expression was determined by Western blot using samples obtained from post mortem biopsies obtained from four muscles (gluteus medius, semitendinosus, heart, and diaphragm), and four adipose tissues (subcutaneous, retroperitoneal, mesenteric, and omental) in three horses. There were no differences (P>0.05) in Glut-4 protein expression between the muscles sampled. Likewise there were no differences (P>0.05) in Glut-4 protein expression between fat depots. There was a significant difference (P=0.03) when pooled means for Glut-4 expression in muscle (58.8±2.5 densitometry units) were compared with adipose tissue (115.8±15.7). This difference in Glut-4 expression in these two tissues with distinctly different metabolic reasons for taking up glucose may warrant further investigation to see if there are more pronounced differences in Glut-4 expression in muscle and adipose tissue in various populations of horses.

Retinol-Binding Protein 4 in Human Obesity

Studies in mice suggest that adipocytes serve as glucose sensors and regulate systemic glucose metabolism through release of serum retinol-binding protein 4 (RBP4). This model has not been validated in humans. RBP4 was highly expressed in isolated mature human adipocytes and secreted by differentiating human adipocytes. In contrast to the animal data, RBP4 mRNA was downregulated in subcutaneous adipose tissue of obese women, and circulating RBP4 concentrations were similar in normal weight, overweight, and obese women (n = 74). RBP4 was positively correlated with GLUT4 expression in adipose tissue, independent of any obesity-associated variable. Five percent weight loss slightly decreased adipose RBP4 expression but did not influence circulating RBP4. In another set of experiments, we stratified patients (n = 14) by low or high basal fasting interstitial glucose concentrations, as determined by the microdialysis technique. Venous glucose concentrations were similar throughout oral glucose tolerance testing, and basal RBP4 expression in adipose tissue and serum RBP4 concentrations were similar in the groups with higher and lower interstitial glucose levels. Our findings point to profound differences between rodents and humans in the regulation of adipose or circulating RBP4 and challenge the notion that glucose uptake by adipocytes has a dominant role in the regulation of RBP4.

Adipocyte Insensitivity to Insulin in Growth Hormone-Transgenic Mice

Growth hormone (GH) has an inhibitory effect on adipogenesis, and its effect is associated with insulin action in obesity. In this study, the relationship between GH effect on insulin sensitivity and adipocyte differentiation in vivo was investigated. Transgenic (TG) female mice expressing porcine GH had reduced body weights and weights of retroperitoneal and parametrial fat depots. Insulin treatment increased PPARγ and GLUT4 expression in adipose tissue of WT mice but had no effect in TG mice. Content of transcription factors, PPARγ and C/EBPα and β, was higher in adipose tissue of WT mice, and for C/EBPα and PPARγ, the difference occurred primarily in 24-, compared to 12-week-old, mice. Expression of preadipocyte factor-1 was higher in adipose tissue of TG mice, and expression of TNF-α and leptin was reduced in adipose tissue of 24-week-old TG mice. Our results suggest that increased expression of GH reduces adipogenesis by inducing adipocyte resistance to the adipogenic effect of insulin.