Insulin-stimulated Muscle Glucose Uptake Research Articles

Chromium chloride increases insulin-stimulated glucose uptake in the perfused rat hindlimb.

To determine the effect of chromium chloride (CrCl3 ) on healthy skeletal muscle glucose uptake in the absence and presence of submaximal insulin using the rat hindlimb perfusion technique. Sprague-Dawley rats were randomly assigned to an experimental group: basal (Bas), chromium chloride (Cr), submaximal insulin (sIns) or chromium chloride plus submaximal insulin (Cr-sIns). Insulin significantly increased [H(3)]-2 deoxyglucose (2-DG) uptake in the gastrocnemius muscles. Additionally, Cr-sIns displayed greater rates of 2-DG uptake than sIns (Cr-sIns 6.86 ± 0.74 μmol g h(-1) vs. sIns 4.83 ± 0.42 μmol g h(-1)). There was no difference between Cr and Bas treatment groups. It has been speculated that chromium works to increase glucose uptake by increasing insulin signalling. We found that Akt and AS160 phosphorylation was increased in the sINS treatment group, while chromium treatment had no additional effect on Akt or AS160 phosphorylation in the absence or presence of insulin. Cr-sIns significantly increased plasma membrane GLUT4 concentration above that of sIns (Cr-sIns 72.22 ± 12.7%, sIns 53.4 ± 6.1%), but in the absence of insulin, chromium had no effect. Exposure of healthy skeletal muscle to chromium may increase skeletal muscle insulin-stimulated GLUT4 translocation and glucose uptake. However, these effects do not appear to result from enhanced insulin signalling proximal to AS160.

Deletion of Both Rab-GTPase–Activating Proteins TBC1D1 and TBC1D4 in Mice Eliminates Insulin- and AICAR-Stimulated Glucose Transport

The Rab-GTPase–activating proteins TBC1D1 and TBC1D4 (AS160) were previously shown to regulate GLUT4 translocation in response to activation of AKT and AMP-dependent kinase [corrected]. However, knockout mice lacking either Tbc1d1 or Tbc1d4 displayed only partially impaired insulin-stimulated glucose uptake in fat and muscle tissue. The aim of this study was to determine the impact of the combined inactivation of Tbc1d1 and Tbc1d4 on glucose metabolism in double-deficient (D1/4KO) mice. D1/4KO mice displayed normal fasting glucose concentrations but had reduced tolerance to intraperitoneally administered glucose, insulin, and AICAR. D1/4KO mice showed reduced respiratory quotient, indicating increased use of lipids as fuel. These mice also consistently showed elevated fatty acid oxidation in isolated skeletal muscle, whereas insulin-stimulated glucose uptake in muscle and adipose cells was almost completely abolished. In skeletal muscle and white adipose tissue, the abundance of GLUT4 protein, but not GLUT4 mRNA, was substantially reduced. Cell surface labeling of GLUTs indicated that RabGAP deficiency impairs retention of GLUT4 in intracellular vesicles in the basal state. Our results show that TBC1D1 and TBC1D4 together play essential roles in insulin-stimulated glucose uptake and substrate preference in skeletal muscle and adipose cells.

Targeting steroid receptor coactivator 1 with antisense oligonucleotides increases insulin-stimulated skeletal muscle glucose uptake in chow-fed and high-fat-fed male rats.

The steroid receptor coactivator 1 (SRC1) regulates key metabolic pathways, including glucose homeostasis. SRC1(-/-) mice have decreased hepatic expression of gluconeogenic enzymes and a reduction in the rate of endogenous glucose production (EGP). We sought to determine whether decreasing hepatic and adipose SRC1 expression in normal adult rats would alter glucose homeostasis and insulin action. Regular chow-fed and high-fat-fed male Sprage-Dawley rats were treated with an antisense oligonucleotide (ASO) against SRC1 or a control ASO for 4 wk, followed by metabolic assessments. SRC1 ASO did not alter basal EGP or expression of gluconeogenic enzymes. Instead, SRC1 ASO increased insulin-stimulated whole body glucose disposal by ~30%, which was attributable largely to an increase in insulin-stimulated muscle glucose uptake. This was associated with an approximately sevenfold increase in adipose expression of lipocalin-type prostaglandin D2 synthase, a previously reported regulator of insulin sensitivity, and an approximately 70% increase in plasma PGD2 concentration. Muscle insulin signaling, AMPK activation, and tissue perfusion were unchanged. Although GLUT4 content was unchanged, SRC1 ASO increased the cleavage of tether-containing UBX domain for GLUT4, a regulator of GLUT4 translocation. These studies point to a novel role of adipose SRC1 as a regulator of insulin-stimulated muscle glucose uptake.

A Rab10:RalA G protein cascade regulates insulin-stimulated glucose uptake in adipocytes.

Insulin-stimulated glucose uptake in fat and muscle is mediated by the major facilitative glucose transporter Glut4. Insulin controls the trafficking of Glut4 to the plasma membrane via regulation of a series of small G proteins, including RalA and Rab10. We demonstrate here that Rab10 is a bona fide target of the GTPase-activating protein AS160, which is inhibited after phosphorylation by the protein kinase Akt. Once activated, Rab10 can increase the GTP binding of RalA by recruiting the Ral guanyl nucleotide exchange factor, Rlf/Rgl2. Rab10 and RalA reside in the same pool of Glut4-storage vesicles in untreated cells, and, together with Rlf, they ensure maximal glucose transport. Overexpression of membrane-tethered Rlf compensates for the loss of Rab10 in Glut4 translocation, suggesting that Rab10 recruits Rlf to membrane compartments for RalA activation and that RalA is downstream of Rab10. Together these studies identify a new G protein cascade in the regulation of insulin-stimulated Glut4 trafficking and glucose uptake.

Beta2-adrenoceptor stimulation has no effect on skeletal muscle glucose uptake.

Blockade of the β-adrenergic receptor induces insulin resistance and chronic β-adrenoceptor stimulation improves insulin sensitivity in animals. We tested whether acute β2-adrenoceptor stimulation increased insulin-induced glucose uptake in human forearm skeletal muscle. During a hyperinsulinemic euglycemic clamp procedure, forearm glucose uptake was calculated by multiplying the arteriovenous glucose gradient and forearm blood flow before and during local infusion of the β2-adrenoceptor salbutamol into the brachial artery. β2-Adrenergic stimulation had no effect on insulin-stimulated glucose uptake in human forearm skeletal muscle.

Loss of ovarian estrogens causes only mild deterioration of glucose homeostasis in female ZDF rats preventable by voluntary running exercise.

Studies on normoglycemic ovariectomized Sprague-Dawley rats have provided insights about the effects of estrogen deficiency on insulin resistance in lean individuals. It is not completely clear if subjects with pre-established obesity and insulin resistance are at greater risk of developing type 2 diabetes when ovarian estrogens are no longer secreted, and if physical activity can protect against this susceptibility. Contrasting with their male counterparts, obese and insulin resistant female ZDF (Zucker diabetic fatty) rats do not become hyperglycemic when fed a standard diet. The aim of the study was to evaluate the hypothesis that withdrawal of ovarian estrogens in insulin resistant female ZDF rats would trigger overt hyperglycemia, provided they remain physically inactive. Female ZDF rats underwent either an ovariectomy (OVX) or a simulated surgery (SHAM). Thereafter, OVX rats engaged either in voluntary wheel cage running (OVX-Active), or like the Sham rats, remained sedentary (OVX-Sed) for 6 weeks. Fasting glycemia, insulinemia, and glucose tolerance were not altered in OVX-Sed as compared to SHAM-Sed rats. However, OVX-Sed rats showed altered liver triglyceride and glycogen contents, increased pancreatic insulin content and reduced insulin-stimulated muscle pAKT as compared to SHAM-Sed rats. Physical activity in OVX rats lowered fasting glucose and insulin levels, improved glucose tolerance and insulin-stimulated skeletal muscle glucose uptake as compared to OVX-Sed rats. OVX-induced alterations in pancreatic insulin content and liver glycogen and triglyceride contents were significantly improved by physical activity. Loss of ovarian estrogens did not cause overt hyperglycemia in insulin-resistant female ZDF rats. Physical activity improved glucose homeostasis despite estrogen deficiency.

Feeding butter with elevated content of trans-10, cis-12 conjugated linoleic acid to lean rats does not impair glucose tolerance or muscle insulin response.

BackgroundNumerous studies have investigated the effects of isolated CLA supplementation on glucose homeostasis in humans and rodents. However, both the amount and relative abundance of CLA isomers in supplemental form are not representative of what is consumed from natural sources. No study to date has examined the effects of altered CLA isomer content within a natural food source. Our goal was to increase the content of the insulin desensitizing CLAt10,c12 isomer relative to the CLAc9,t11 isomer in cow’s milk by inducing subacute rumenal acidosis (SARA), and subsequently investigate the effects of this milk fat on parameters related to glucose and insulin tolerance in rats.MethodsWe fed female rats (~2.5 to 3 months of age) CLA t10,c12 –enriched (SARA) butter or non-SARA butter based diets for 4 weeks in either low (10% of kcal from fat; 0.18% total CLA by weight) or high (60% of kcal from fat; 0.55% total CLA by weight) amounts. In an effort to extend these findings, we then fed rats high (60% kcal) amounts of SARA or non-SARA butter for a longer duration (8 weeks) and assessed changes in whole body glucose, insulin and pyruvate tolerance in comparison to low fat and 60% lard conditions.ResultsThere was a main effect for increased fasting blood glucose and insulin in SARA vs. non-SARA butter groups after 4 weeks of feeding (p < 0.05). However, blood glucose and insulin concentration, and maximal insulin-stimulated glucose uptake in skeletal muscle were similar in all groups. Following 8 weeks of feeding, insulin tolerance was impaired by the SARA butter, but not glucose or pyruvate tolerance. The non-SARA butter did not impair tolerance to glucose, insulin or pyruvate.ConclusionsThis study suggests that increasing the consumption of a naturally enriched CLAt10,c12 source, at least in rats, has minimal impact on whole body glucose tolerance or muscle specific insulin response.

A common Greenlandic TBC1D4 variant confers muscle insulin resistance and type 2 diabetes

The Greenlandic population, a small and historically isolated founder population comprising about 57,000 inhabitants, has experienced a dramatic increase in type 2 diabetes (T2D) prevalence during the past 25 years. Motivated by this, we performed association mapping of T2D-related quantitative traits in up to 2,575 Greenlandic individuals without known diabetes. Using array-based genotyping and exome sequencing, we discovered a nonsense p.Arg684Ter variant (in which arginine is replaced by a termination codon) in the gene TBC1D4 with an allele frequency of 17%. Here we show that homozygous carriers of this variant have markedly higher concentrations of plasma glucose (β = 3.8 mmol l(-1), P = 2.5 × 10(-35)) and serum insulin (β = 165 pmol l(-1), P = 1.5 × 10(-20)) 2 hours after an oral glucose load compared with individuals with other genotypes (both non-carriers and heterozygous carriers). Furthermore, homozygous carriers have marginally lower concentrations of fasting plasma glucose (β = -0.18 mmol l(-1), P = 1.1 × 10(-6)) and fasting serum insulin (β = -8.3 pmol l(-1), P = 0.0014), and their T2D risk is markedly increased (odds ratio (OR) = 10.3, P = 1.6 × 10(-24)). Heterozygous carriers have a moderately higher plasma glucose concentration 2 hours after an oral glucose load than non-carriers (β = 0.43 mmol l(-1), P = 5.3 × 10(-5)). Analyses of skeletal muscle biopsies showed lower messenger RNA and protein levels of the long isoform of TBC1D4, and lower muscle protein levels of the glucose transporter GLUT4, with increasing number of p.Arg684Ter alleles. These findings are concomitant with a severely decreased insulin-stimulated glucose uptake in muscle, leading to postprandial hyperglycaemia, impaired glucose tolerance and T2D. The observed effect sizes are several times larger than any previous findings in large-scale genome-wide association studies of these traits and constitute further proof of the value of conducting genetic association studies outside the traditional setting of large homogeneous populations.

SHR3824, a novel selective inhibitor of renal sodium glucose cotransporter 2, exhibits antidiabetic efficacy in rodent models.

The sodium glucose cotransporter 2 (SGLT2) plays an important role in renal glucose reabsorption, thus serves as a new target for the treatment of diabetes. The purpose of this study was to evaluate SHR3824 as a novel selective SGLT2 inhibitor and to characterize its in vivo effects on glucose homeostasis. The effects of chronic administration of SHR3824 on peripheral insulin sensitivity and pancreatic β-cell function were also investigated. The in vitro potency and selectivity of SHR3824 were assessed in HEK293 cells transfected with human SGLT2 or SGLT1. Acute and multi-dose studies were performed on ICR mice, GK rats and db/db mice to assess the ability of SHR3824 to enhance urinary glucose excretion and improve blood glucose levels. 2-Deoxyglucose uptake and insulin immunohistochemical staining were performed in the soleus muscle and pancreas, respectively, of db/db mice. A selective SGLT2 inhibitor BMS512148 (dapagliflozin) was taken as positive control. SHR3824 potently inhibited human SGLT2 in vitro, but exerted much weak inhibition on human SGLT1 (the IC50 values of SHR3824 against human SGLT2 and SGLT1 were 2.38 and 4324 nmol/L, respectively). Acute oral administration of SHR3824 (0.3, 1.0, 3.0 mg/kg) dose-dependently improved glucose tolerance in ICR mice, and reduced hyperglycemia by increasing urinary glucose excretion in GK rats and db/db mice. Chronic oral administration of SHR3824 (0.3, 1.0, 3.0 mg·kg(-1)·d(-1)) dose-dependently reduced blood glucose and HbA1c levels in GK rats and db/db mice, and significantly increased insulin-stimulated glucose uptake in the soleus muscles and enhanced insulin staining in the islet cells of db/db mice. SHR3824 is a potent and selective SGLT2 inhibitor and exhibits antidiabetic efficacy in several rodent models, suggesting its potential as a new therapeutic agent for the treatment of type 2 diabetes.

Effects of AMPK Activation on Insulin Sensitivity and Metabolism in Leptin-Deficient ob/ob Mice

AMP-activated protein kinase (AMPK) is a heterotrimeric complex, composed of a catalytic subunit (α) and two regulatory subunits (β and γ), which act as a metabolic sensor to regulate glucose and lipid metabolism. A mutation in the γ3 subunit (AMPKγ3(R225Q)) increases basal AMPK phosphorylation, while concomitantly reducing sensitivity to AMP. AMPKγ3(R225Q) (γ3(R225Q)) transgenic mice are protected against dietary-induced triglyceride accumulation and insulin resistance. We determined whether skeletal muscle-specific expression of AMPKγ3(R225Q) prevents metabolic abnormalities in leptin-deficient ob/ob (ob/ob-γ3(R225Q)) mice. Glycogen content was increased, triglyceride content was decreased, and diacylglycerol and ceramide content were unaltered in gastrocnemius muscle from ob/ob-γ3(R225Q) mice, whereas glucose tolerance was unaltered. Insulin-stimulated glucose uptake in extensor digitorum longus muscle during the euglycemic-hyperinsulinemic clamp was increased in lean γ3(R225Q) mice, but not in ob/ob-γ3(R225Q) mice. Acetyl-CoA carboxylase phosphorylation was increased in gastrocnemius muscle from γ3(R225Q) mutant mice independent of adiposity. Glycogen and triglyceride content were decreased after leptin treatment (5 days) in ob/ob mice, but not in ob/ob-γ3(R225Q) mice. In conclusion, metabolic improvements arising from muscle-specific expression of AMPKγ3(R225Q) are insufficient to ameliorate insulin resistance and obesity in leptin-deficient mice. Central defects due to leptin deficiency may override any metabolic benefit conferred by peripheral overexpression of the AMPKγ3(R225Q) mutation.

De novo duplication of 17p13.1–p13.2 in a patient with intellectual disability and obesity

17p13.1 Deletion encompassing TP53 has been described as a syndrome characterized by intellectual disability and dysmorphic features. Only one case with a 17p13.1 duplication encompassing TP53 has been reported in a patient with intellectual disability, seizures, obesity, and diabetes mellitus. Here, we present a patient with a 17p13.1 duplication who exhibited obesity and intellectual disability, similar to the previous report. The 9-year-old proposita was referred for the evaluation of intellectual disability and obesity. She also exhibited insulin resistance and liver dysfunction. She had wide palpebral fissures, upturned nostrils, a long mandible, short and slender fingers, and skin hyperpigmentation. Array comparative genomic hybridization (array CGH) detected a 3.2 Mb duplication of 17p13.1-p13.2 encompassing TP53, FXR2, NLGN2, and SLC2A4, which encodes the insulin-responsive glucose transporter 4 (GLUT4) associated with insulin-stimulated glucose uptake in adipocytes and muscle. We suggest that 17p13.1 duplication may represent a clinically recognizable condition characterized partially by a characteristic facial phenotype, developmental delay, and obesity.

Two weeks of metformin treatment induces AMPK-dependent enhancement of insulin-stimulated glucose uptake in mouse soleus muscle

Metformin-induced activation of the 5'-AMP-activated protein kinase (AMPK) has been associated with enhanced glucose uptake in skeletal muscle, but so far no direct causality has been examined. We hypothesized that an effect of in vivo metformin treatment on glucose uptake in mouse skeletal muscles is dependent on AMPK signaling. Oral doses of metformin or saline treatment were given to muscle-specific kinase dead (KD) AMPKα2 mice and wild-type (WT) littermates either once or chronically for 2 wk. Soleus and extensor digitorum longus muscles were used for measurements of glucose transport and Western blot analyses. Chronic treatment with metformin enhanced insulin-stimulated glucose uptake in soleus muscles of WT (∼45%, P < 0.01) but not of AMPK KD mice. Insulin signaling at the level of Akt protein expression or Thr(308) and Ser(473) phosphorylation was not changed by metformin treatment. Insulin signaling at the level of Akt and TBC1D4 protein expression as well as Akt Thr(308)/Ser(473) and TBC1D4 Thr(642)/Ser(711) phosphorylation were not changed by metformin treatment. Also, protein expressions of Rab4, GLUT4, and hexokinase II were unaltered after treatment. The acute metformin treatment did not affect glucose uptake in muscle of either of the genotypes. In conclusion, we provide novel evidence for a role of AMPK in potentiating the effect of insulin on glucose uptake in soleus muscle in response to chronic metformin treatment.

Trying to understand gestational diabetes

Women with normal glucose tolerance pre-gravid and developing gestational diabetes in late gestation have subclinical metabolic dysfunction prior to conception compared with women with normal glucose tolerance. Because of the 60% decrease in insulin sensitivity with normal pregnancy, these women develop clinical hyperglycaemia/gestational diabetes in late gestation. The metabolic dysfunction includes impaired insulin response, decreased hepatic suppression of glucose production during insulin infusion and decreased insulin-stimulated glucose uptake in skeletal muscle, i.e. peripheral insulin resistance. The insulin resistance in normal glucose tolerance pregnancy is related to a decrease in the post-receptor insulin signalling cascade, specifically decreased insulin receptor substrate 1 tyrosine phosphorylation. In women with normal glucose tolerance this is reversed post-partum. In contrast, in gestational diabetes, in addition to the decrease in insulin receptor substrate 1 tyrosine phosphorylation, there is an additional decrease in tyrosine phosphorylation of the intracellular portion of the insulin receptor that is not related to the insulin receptor protein content. Post-partum women with gestational diabetes, who had retention of gestational weight gain, had no significant improvement in insulin sensitivity and increased inflammation expressed as increased plasma and skeletal muscle tumour necrosis factor alpha. The increased inflammation or meta-inflammation is a hallmark of obesity and during pregnancy develops in both white adipose tissue and placenta. Last gene array studies of placenta were associated with alterations in gene expression relating primarily to lipid in contrast to glucose metabolic pathways in gestational diabetes compared with Type 1 diabetes. Future studies are directed at decreasing inflammation prior to and during pregnancy using various lifestyle and nutritional interventions.

Development of overweight and obesity in mid-age women from the Australian Longitudinal on Women Health Study

uptake, but increased insulin-stimulated (30 nM, 30min) glucose uptake by 51.0± 18.7% vs. empty vector control cells (p < 0.05). BRSK1 knockdown decreased basal glucose uptake by 21.3± 5.7% (p < 0.05) and insulin-stimulated glucose uptake by 22.8± 6.9%, (p < 0.05)when compared to scrambled shRNA. To study the role of BRSK1 in vivo, short form Brsk1 was expressed in tibialis anterior (TA) muscles by in vivo gene injection and electroporation. Similar to L6 cells, wild type BRSK1 over-expression increased insulin-stimulated glucose uptake in TA (77.7± 12.0%, p < 0.05), with no effect of the mutant BRSK1. In summary, short form BRSK1 over-expression increases insulin-stimulated glucose uptake in L6 myotubes and skeletal muscle, and BRSK1 knockdown in L6 cells decreases basal and insulin-stimulated glucose uptake. The short form of BRSK1, an AMPK-related Kinase, is highly expressed in skeletal muscle and may function to regulate insulin action.

Akt and Rac1 signaling are jointly required for insulin-stimulated glucose uptake in skeletal muscle and downregulated in insulin resistance

Skeletal muscle plays a major role in regulating whole body glucose metabolism. Akt and Rac1 are important regulators of insulin-stimulated glucose uptake in skeletal muscle. However the relative role of each pathway and how they interact are not understood. Here we delineate how Akt and Rac1 pathways signal to increase glucose transport independently of each other and are simultaneously downregulated in insulin resistant muscle.Pharmacological inhibition of Rac1 and Akt signaling was used to determine the contribution of each pathway to insulin-stimulated glucose uptake in mouse muscles. The actin filament-depolymerizing agent LatrunculinB was combined with pharmacological inhibition of Rac1 or Akt, to examine whether either pathway mediates its effect via the actin cytoskeleton. Akt and Rac1 signaling were investigated under each condition, as well as upon Akt2 knockout and in ob/ob mice, to uncover whether Akt and Rac1 signaling are independent and whether they are affected by genetically-induced insulin resistance.While individual inhibition of Rac1 or Akt partially decreased insulin-stimulated glucose transport by ~40% and ~60%, respectively, their simultaneous inhibition completely blocked insulin-stimulated glucose transport. LatrunculinB plus Akt inhibition blocked insulin-stimulated glucose uptake, while LatrunculinB had no additive effect on Rac1 inhibition. In muscles from severely insulin-resistant ob/ob mice, Rac1 and Akt signaling were severely dysregulated and the increment in response to insulin reduced by 100% and 90%, respectively.These findings suggest that Rac1 and Akt regulate insulin-stimulated glucose uptake via distinct parallel pathways, and that insulin-induced Rac1 and Akt signaling are both dysfunctional in insulin resistant muscle. There may thus be multiple treatment targets for improving insulin sensitivity in muscle.

Identification and Association of SNPs in &amp;lt;italic&amp;gt;TBC1D1&amp;lt;/italic&amp;gt; Gene with Growth Traits in Two Rabbit Breeds

The TBC1D1 plays a key role in body energy homeostasis by regulating the insulin-stimulated glucose uptake in skeletal muscle. The present study aimed to identify the association between genetic polymorphisms of TBC1D1 and body weight (BW) in rabbits. Among the total of 12 SNPs detected in all 20 exons, only one SNP was non-synonymous (c.214G>A. p.G72R) located in exon 1. c.214G>A was subsequently genotyped among 491 individuals from two rabbit breeds by the high-resolution melting method. Allele A was the predominant allele with frequencies of 0.7780 and 0.6678 in European white rabbit (EWR, n = 205) and New Zealand White rabbit (NZW, n = 286), respectively. The moderate polymorphism information content (0.25<PIC<0.50) was present in both breeds. The association analysis revealed that genotypes GA and AA had higher 35 d body weight (BW) than genotype GG in both EWR (p<0.01) and NEW (p<0.05). For the 56 d BW and 70 d BW traits, genotypes AA and GA were higher than genotype GG in both two breeds, the difference was not significant (p>0.05). Our results implied that the c.214G>A of TBC1D1 gene might be one of the candidate loci affecting the trait of 35 d BW in the rabbit.

Angiotensin 1–7 improves insulin sensitivity by increasing skeletal muscle glucose uptake in vivo

The renin–angiotensin system (RAS) regulates skeletal muscle insulin sensitivity through different mechanisms. The overactivation of the ACE (angiotensin-converting enzyme)/Ang (angiotensin) II/AT1R (Ang II type 1 receptor) axis has been associated with the development of insulin resistance, whereas the stimulation of the ACE2/Ang 1–7/MasR (Mas receptor) axis improves insulin sensitivity. The in vivo mechanisms by which this axis enhances skeletal muscle insulin sensitivity are scarcely known. In this work, we investigated whether rat soleus muscle expresses the ACE2/Ang 1–7/MasR axis and determined the effect of Ang 1–7 on rat skeletal muscle glucose uptake in vivo. Western blot analysis revealed the expression of ACE2 and MasR, while Ang 1–7 levels were detected in rat soleus muscle by capillary zone electrophoresis. The euglycemic clamp exhibited that Ang 1–7 by itself did not promote glucose transport, but it increased insulin-stimulated glucose disposal in the rat. In a similar manner, captopril (an ACE inhibitor) enhanced insulin-induced glucose uptake and this effect was blocked by the MasR antagonist A-779. Our results show for the first time that rat soleus muscle expresses the ACE2/Ang 1–7/MasR axis of the RAS, and Ang 1–7 improves insulin sensitivity by enhancing insulin-stimulated glucose uptake in rat skeletal muscle in vivo. Thus, endogenous (systemic and/or local) Ang 1–7 could regulate insulin-mediated glucose transport in vivo.

Insulin signaling in skeletal muscle of HIV-infected patients in response to endurance and strength training

Human immunodeficiency virus (HIV)-infected patients with lipodystrophy have decreased insulin-stimulated glucose uptake. Both endurance and resistance training improve insulin-stimulated glucose uptake in skeletal muscle of HIV-infected patients, but the mechanisms are unknown. This study aims to identify the molecular pathways involved in the beneficial effects of training on insulin-stimulated glucose uptake in skeletal muscle of HIV-infected patients. Eighteen sedentary male HIV-infected patients underwent a 16 week supervised training intervention, either resistance or strength training. Euglycemic–hyperinsulinemic clamps with muscle biopsies were performed before and after the training interventions. Fifteen age- and body mass index (BMI)-matched HIV-negative men served as a sedentary baseline group. Phosphorylation and total protein expression of insulin signaling molecules as well as glycogen synthase (GS) activity were analyzed in skeletal muscle biopsies in relation to insulin stimulation before and after training. HIV-infected patients had reduced basal and insulin-stimulated GS activity (%fractional velocity, [FV]) as well as impaired insulin-stimulated Aktthr308 phosphorylation. Despite improving insulin-stimulated glucose uptake, neither endurance nor strength training changed the phosphorylation status of insulin signaling proteins or affected GS activity. However; endurance training markedly increased the total Akt protein expression, and both training modalities increased hexokinase II (HKII) protein. HIV-infected patients with lipodystrophy have decreased insulin-stimulated glucose uptake in skeletal muscle and defects in insulin-stimulated phosphorylation of Aktthr308. Endurance and strength training increase insulin-stimulated glucose uptake in these patients, and the muscular training adaptation is associated with improved capacity for phosphorylation of glucose by HKII, rather than changes in markers of insulin signaling to glucose uptake or glycogen synthesis.

Exercise training favors increased insulin-stimulated glucose uptake in skeletal muscle in contrast to adipose tissue: a randomized study using FDG PET imaging

Physical exercise increases peripheral insulin sensitivity, but regional differences are poorly elucidated in humans. We investigated the effect of aerobic exercise training on insulin-stimulated glucose uptake in five individual femoral muscle groups and four different adipose tissue regions, using dynamic (femoral region) and static (abdominal region) 2-deoxy-2-[¹⁸F]fluoro-d-glucose (FDG) PET/CT methodology during steady-state insulin infusion (40 mU·m⁻²·min⁻¹). Body composition was measured by dual X-ray absorptiometry and MRI. Sixty-one healthy, sedentary [V(O2max) 36(5) ml·kg⁻¹·min⁻¹; mean(SD)], moderately overweight [BMI 28.1(1.8) kg/m²], young [age: 30(6) yr] men were randomized to sedentary living (CON; n = 17 completers) or moderate (MOD; 300 kcal/day, n = 18) or high (HIGH; 600 kcal/day, n = 18) dose physical exercise for 11 wk. At baseline, insulin-stimulated glucose uptake was highest in femoral skeletal muscle followed by intraperitoneal visceral adipose tissue (VAT), retroperitoneal VAT, abdominal (anterior + posterior) subcutaneous adipose tissue (SAT), and femoral SAT (P < 0.0001 between tissues). Metabolic rate of glucose increased similarly (~30%) in the two exercise groups in femoral skeletal muscle (MOD 24[9, 39] μmol·kg⁻¹·min⁻¹, P = 0.004; HIGH 22[9, 35] μmol·kg⁻¹·min⁻¹, P = 0.003) (mean[95% CI]) and in five individual femoral muscle groups but not in femoral SAT. Standardized uptake value of FDG decreased ~24% in anterior abdominal SAT and ~20% in posterior abdominal SAT compared with CON but not in either intra- or retroperitoneal VAT. Total adipose tissue mass decreased in both exercise groups, and the decrease was distributed equally among subcutaneous and intra-abdominal depots. In conclusion, aerobic exercise training increases insulin-stimulated glucose uptake in skeletal muscle but not in adipose tissue, which demonstrates some interregional differences.

Effects of alternate-day fasting on high-fat diet-induced insulin resistance in rat skeletal muscle

AimsThe purpose of this study was to investigate the effects of alternate-day fasting (ADF) on insulin-stimulated glucose transport activity in skeletal muscle in rats fed a high-fat diet. Main methodsMale Wistar rats were placed on a high-fat diet (n=24) or standard chow diet (Chow, n=12) for 10weeks. Rats fed the high-fat diet were separated into two groups after 4weeks. One group was subjected to ADF for the subsequent 6weeks (HF-ADF, n=12), and the other group was maintained on an ad libitum diet (HF-AL, n=12). After the 10-week dietary intervention, measurements of insulin-stimulated glucose uptake and insulin tolerance test (ITT) were performed. Key findingsWhereas the total intra-abdominal fat mass in the HF-AL group was significantly higher than in the Chow and HF-ADF groups, there was no significant difference between the Chow and HF-ADF groups. However, insulin-stimulated glucose uptake in skeletal muscles was significantly lower in both high-fat fed groups than in the Chow group. Muscle GLUT-4 protein content in HF-AL is significantly lower (~30%) than in Chow, and further reduction (~42%) was observed in the HF-ADF group rats. The HF-ADF and HF-AL group rats had less reduction in glycemia than did the Chow group rats during ITT. SignificanceADF was unable to eliminate high-fat diet-induced muscle insulin resistance, despite a substantial decrease in total intra-abdominal fat mass. This might have resulted from a reduction in GLUT-4 protein in both HF-AL and HF-ADF rats compared to the Chow group.