Disassociation of muscle insulin signaling and insulin-stimulated glucose uptake during endotoxemia

Lipopolysaccharide (LPS) elicits a strong immune response, which leads to the release of inflammatory cytokines. Increased cytokine production has been shown to impair insulin-mediated glucose disposal. LPS can alter other factors, such as muscle blood flow and insulin signaling in the myocyte, that can influence glucose disposal. We hypothesize that LPS induced impairments in cardiovascular function contribute to the associated impairments in insulin action in vivo. Male wild-type C57BL/6J mice had a catheter implanted in the jugular vein for infusions and the carotid artery for sampling 5 days prior to the hyperinsulinemic-euglycemic clamp. Mice were treated with vehicle, low- (1 ug/gBW) or high-dose (10 ug/gBW) LPS 4 hours prior to the clamp. Muscle glucose uptake (MGU) was assessed using [2-(14)C] deoxyglucose. While both low- and high-dose LPS inhibited insulin-stimulated MGU compared to vehicle-treated mice, the impairment was more significant with the high-dose treatment (～25% in soleus and ～70% in both gastrocnemius and vastus lateralis). Interestingly, insulin signaling through the PI3-kinase pathway in the muscle was not affected by this treatment suggesting that the decrease in MGU is not directly due to impairments in muscle insulin action. Echocardiography demonstrated that high-dose LPS treatment significantly decreased stroke volume (～30%), heart rate (～35%), and cardiac output (～50%). These observations were not seen with vehicle or low-dose LPS treatment. High-dose LPS treatment also significantly decreased muscle blood flow (～70%) and whole body oxygen consumption (～50%). Thus, in vivo acute endotoxemia does not impair insulin signaling through the PI3-kinase pathway in skeletal muscle and decreased tissue blood flow likely plays a central role in the impairment of glucose uptake in the muscle.     

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.     

Impaired insulin signaling in endothelial cells reduces insulin-induced glucose uptake by skeletal muscle

In obese patients with type 2 diabetes, insulin delivery to and insulin-dependent glucose uptake by skeletal muscle are delayed and impaired. The mechanisms underlying the delay and impairment are unclear. We demonstrate that impaired insulin signaling in endothelial cells, due to reduced Irs2 expression and insulin-induced eNOS phosphorylation, causes attenuation of insulin-induced capillary recruitment and insulin delivery, which in turn reduces glucose uptake by skeletal muscle. Moreover, restoration of insulin-induced eNOS phosphorylation in endothelial cells completely reverses the reduction in capillary recruitment and insulin delivery in tissue-specific knockout mice lacking Irs2 in endothelial cells and fed a high-fat diet. As a result, glucose uptake by skeletal muscle is restored in these mice. Taken together, our results show that insulin signaling in endothelial cells plays a pivotal role in the regulation of glucose uptake by skeletal muscle. Furthermore, improving endothelial insulin signaling may serve as a therapeutic strategy for ameliorating skeletal muscle insulin resistance.     

Limitations to basal and insulin-stimulated skeletal muscle glucose uptake in the high-fat-fed rat

Rats fed a high-fat diet display blunted insulin-stimulated skeletal muscle glucose uptake. It is not clear whether this is due solely to a defect in glucose transport, or if glucose delivery and phosphorylation are also impaired. To determine this, rats were fed standard chow (control rats) or a high-fat diet (HF rats) for 4 wk. Experiments were then performed on conscious rats under basal conditions or during hyperinsulinemic euglycemic clamps. Rats received primed constant infusions of 3-O-methyl-[(3)H]glucose (3-O-MG) and [1-(14)C]mannitol. Total muscle glucose concentration and the steady-state ratio of intracellular to extracellular 3-O-MG concentration [which distributes based on the transsarcolemmal glucose gradient (TSGG)] were used to calculate glucose concentrations at the inner and outer sarcolemmal surfaces ([G](im) and [G](om), respectively) in soleus. Total muscle glucose was also measured in two fast-twitch muscles. Muscle glucose uptake was markedly decreased in HF rats. In control rats, hyperinsulinemia resulted in a decrease in soleus TSGG compared with basal, due to increased [G](im). In HF rats during hyperinsulinemia, [G](im) also exceeded zero. Hyperinsulinemia also decreased muscle glucose in HF rats, implicating impaired glucose delivery. In conclusion, defects in extracellular and intracellular components of muscle glucose uptake are of major functional significance in this model of insulin resistance.     

Mechanotransduction and the regulation of mTORC1 signaling in skeletal muscle

Mechanical stimuli play a major role in the regulation of skeletal muscle mass, and the maintenance of muscle mass contributes significantly to disease prevention and issues associated with the quality of life. Although the link between mechanical signals and the regulation of muscle mass has been recognized for decades, the mechanisms involved in converting mechanical information into the molecular events that control this process remain poorly defined. Nevertheless, our knowledge of these mechanisms is advancing and recent studies have revealed that signaling through a protein kinase called the mammalian target of rapamycin (mTOR) plays a central role in this event. In this review we will, (1) discuss the evidence which implicates mTOR in the mechanical regulation of skeletal muscle mass, (2) provide an overview of the mechanisms through which signaling by mTOR can be regulated, and (3) summarize our current knowledge of the potential mechanisms involved in the mechanical activation of mTOR signaling.     

Chemerin enhances insulin signaling and potentiates insulin-stimulated glucose uptake in 3T3-L1 adipocytes

To explore a novel adipokine, we screened adipocyte differentiation-related gene and found that TIG2/chemerin was strongly induced during the adipocyte differentiation. Chemerin was secreted by the mature 3T3-L1 adipocytes and expressed abundantly in adipose tissue in vivo as recently described. Intriguingly, the expression of chemerin was differently regulated in the liver and adipose tissue in db/db mice. In addition, serum chemerin concentration was decreased in db/db mice. Chemerin and its receptor/ChemR23 were expressed in mature adipocytes, suggesting its function in autocrine/paracrine fashion. Finally, chemerin potentiated insulin-stimulated glucose uptake concomitant with enhanced insulin signaling in the 3T3-L1 adipocytes. These data establish that chemerin is a novel adipokine that regulates adipocyte function.     

miR-135a targets IRS2 and regulates insulin signaling and glucose uptake in the diabetic gastrocnemius skeletal muscle

Although aberrant miRNA signatures are associated with diabetes, yet, the status and role of altered miRNAs in the diabetic skeletal muscle is currently poorly understood. Here, we report that 41 miRNAs are altered in the diabetic gastrocnemius skeletal muscle and of these, miR-135a that is identified as a critical regulator of myogenesis, is significantly up-regulated. IRS2 is predicted as its potential putative target and its levels are down-regulated in the diabetic gastrocnemius skeletal muscle. In C2C12 cells, while miR-135a levels decreased during differentiation, IRS2 levels were up-regulated. miR-135a significantly reduced IRS2 protein levels and its 3′UTR luciferase reporter activity and these were blunted by the miR-135a inhibitor and mutation in the miR-135a binding site. Knock-down of endogenous miR-135a levels increased IRS2 at the mRNA and protein levels. miR-135a also attenuated insulin stimulated phosphorylation and activation of PI3Kp85α and Akt and glucose uptake. miR-135a levels were also found to be elevated in the human diabetic skeletal muscle. In-vivo silencing of miR-135a alleviated hyperglycemia, improved glucose tolerance and significantly restored the levels of IRS2 and p-Akt in the gastrocnemius skeletal muscle of db/db mice without any effect on their hepatic levels. These suggest that miR-135a targets IRS2 levels by binding to its 3′UTR and this interaction regulates skeletal muscle insulin signaling.     

Different effects of IGF-I on insulin-stimulated glucose uptake in adipose tissue and skeletal muscle

The effect of insulin-like growth factor I (IGF-I) on insulin-stimulated glucose uptake was studied in adipose and muscle tissues of hypophysectomized female rats. IGF-I was given as a subcutaneous infusion via osmotic minipumps for 6 or 20 days. All hypophysectomized rats received L-thyroxine and cortisol replacement therapy. IGF-I treatment increased body weight gain but had no effect on serum glucose or free fatty acid levels. Serum insulin and C-peptide concentrations decreased. Basal and insulin-stimulated glucose incorporation into lipids was reduced in adipose tissue segments and isolated adipocytes from the IGF-I-treated rats. In contrast, insulin treatment of hypophysectomized rats for 7 days increased basal and insulin-stimulated glucose incorporation into lipids in isolated adipocytes. Pretreatment of isolated adipocytes in vitro with IGF-I increased basal and insulin-stimulated glucose incorporation into lipids. These results indicate that the effect of IGF-I on lipogenesis in adipose tissue is not direct but via decreased serum insulin levels, which reduce the capacity of adipocytes to metabolize glucose. Isoproterenol-stimulated lipolysis, but not basal lipolysis, was enhanced in adipocytes from IGF-I-treated animals. In the soleus muscle, the glycogen content and insulin-stimulated glucose incorporation into glycogen were increased in IGF-I-treated rats. In summary, IGF-I has opposite effects on glucose uptake in adipose tissue and skeletal muscle, findings which at least partly explain previous reports of reduced body fat mass, increased body cell mass, and increased insulin responsiveness after IGF-I treatment.     

Increased submaximal insulin-stimulated glucose uptake in mouse skeletal muscle after treadmill exercise.

The primary purpose of this study was to determine the effect of prior exercise on insulin-stimulated glucose uptake with physiological insulin in isolated muscles of mice. Male C57BL/6 mice completed a 60-min treadmill exercise protocol or were sedentary. Paired epitrochlearis, soleus, and extensor digitorum longus (EDL) muscles were incubated with [3H]-2-deoxyglucose without or with insulin (60 microU/ml) to measure glucose uptake. Insulin-stimulated glucose uptake for paired muscles was calculated by subtracting glucose uptake without insulin from glucose uptake with insulin. Muscles from other mice were assessed for glycogen and AMPK Thr172 phosphorylation. Exercised vs. sedentary mice had decreased glycogen in epitrochlearis (48%, P < 0.001), soleus (51%, P < 0.001), and EDL (41%, P < 0.01) and increased AMPK Thr172 phosphorylation (P < 0.05) in epitrochlearis (1.7-fold), soleus (2.0-fold), and EDL (1.4-fold). Insulin-independent glucose uptake was increased 30 min postexercise vs. sedentary in the epitrochlearis (1.2-fold, P < 0.001), soleus (1.4-fold, P < 0.05), and EDL (1.3-fold, P < 0.01). Insulin-stimulated glucose uptake was increased (P < 0.05) approximately 85 min after exercise in the epitrochlearis (sedentary: 0.266 +/- 0.045 micromol x g(-1) x 15 min(-1); exercised: 0.414 +/- 0.051) and soleus (sedentary: 0.102 +/- 0.049; exercised: 0.347 +/- 0.098) but not in the EDL. Akt Ser473 and Akt Thr308 phosphorylation for insulin-stimulated muscles did not differ in exercised vs. sedentary. These results demonstrate enhanced submaximal insulin-stimulated glucose uptake in the epitrochlearis and soleus of mice 85 min postexercise and suggest that it will be feasible to probe the mechanism of enhanced postexercise insulin sensitivity by using genetically modified mice.     

Hydroxylamine enhances glucose uptake in C2C12 skeletal muscle cells through the activation of insulin receptor substrate 1

Diabetes mellitus is a global disease, and the number of patients with it is increasing. Of various agents for treatment, those that directly act on muscle are currently attracting attention because muscle is one of the main tissues in the human body, and its metabolism is decreased in type II diabetes. In this study, we found that hydroxylamine (HA) enhances glucose uptake in C2C12 myotubes. Analysis of HA’s mechanism revealed the involvement of IRS1, PI3 K and Akt that is related to the insulin signaling pathway. Further investigation about the activation mechanism of insulin receptor or IRS1 by HA may provide a way to develop a novel anti-diabetic agent alternating to insulin.     

Role of Akt2 in contraction-stimulated cell signaling and glucose uptake in skeletal muscle

The serine/threonine kinase Akt/PKB plays diverse roles in cells, and genetic studies have indicated distinct roles for the three Akt isoforms expressed in mammalian cells and tissues. Akt2 is a key signaling intermediate for insulin-stimulated glucose uptake and glycogen synthesis in skeletal muscle. Akt2 has also been shown to be activated by exercise and muscle contraction in both rodents and humans. In this study, we used Akt2 knockout mice to explore the role of Akt2 in exercise-stimulated glucose uptake and glycogen synthesis as well as intracellular signaling pathways that regulate glycogen metabolism in skeletal muscle. We found that Akt2 deficiency does not affect basal or exercise-stimulated glucose uptake or intracellular glycogen content in the soleus muscle. In addition, lack of Akt2 did not result in alterations in basal Akt Thr(308) or basal and contraction-stimulated glycogen synthase kinase-3beta (GSK-3beta) Ser(9) phosphorylation, glycogen synthase phosphorylation, or glycogen synthase activity. In contrast, in situ contraction failed to elicit normal increases in Akt T-loop Thr(308) phosphorylation and GSK-3alpha Ser(21) phosphorylation in tibialis anterior muscles from Akt2-deficient animals. Our data establish a key role for Akt2 in the regulation of GSK-3alpha Ser(21) phosphorylation with contraction and add genetic evidence to support the separation of the intracellular pathways regulated by insulin and exercise that converge on glucose uptake and glycogen synthesis in skeletal muscle.     

Ceramide inhibits insulin-stimulated Akt phosphorylation through activation of Rheb/mTORC1/S6K signaling in skeletal muscle

Ceramide is a negative regulator of insulin activity. At the molecular level, it causes a decrease in insulin-stimulated Akt Ser473 phosphorylation in C2C12 myotubes. Interestingly, we found that the phosphorylation of S6K at Thr389 was increased under the same conditions. Utilizing both rapamycin to inhibit mTORC1 activity and shRNA to knock down Rheb, we demonstrated that the decrease in Akt Ser473 phosphorylation stimulated by insulin after C2-ceramide incubation can be prevented. The mechanism by which C2-ceramide impairs signaling would seem to involve a negative feedback of activated S6K via phosphorylation of insulin receptor substrate-1 at Ser636/639, since S6K inhibitor can block this phenomenon. Finally, rapamycin treatment was found not to affect C2-ceramide-induced PKCζ activation, suggesting that the pathway revealed in this study is parallel to the one involving PKCζ activation. We proposed a novel pathway/mechanism involving Rheb/mTORC1/S6K signaling to explain how C2-ceramide impairs insulin signaling via Akt phosphorylation. The existence of multiple pathways involved in insulin signaling impairment by C2-ceramide treatment implies that different strategies might be needed to ameliorate insulin resistance caused by C2-ceramide.     

Insulin signaling and glucose transport in insulin resistant human skeletal muscle

Insulin increases glucose uptake and metabolism in skeletal muscle by signal transduction via protein phosphorylation cascades. Insulin action on signal transduction is impaired in skeletal muscle from Type 2 diabetic subjects, underscoring the contribution of molecular defects to the insulin resistant phenotype. This review summarizes recent work to identify downstream intermediates in the insulin signaling pathways governing glucose homeostasis, in an attempt to characterize the molecular mechanism accounting for skeletal muscle insulin resistance in Type 2 diabetes. Furthermore, the effects of pharmaceutical treatment of Type 2 diabetic patients on insulin signaling and glucose uptake are discussed. The identification and characterization of pathways governing insulin action on glucose metabolism will facilitate the development of strategies to improve insulin sensitivity in an effort to prevent and treat Type 2 diabetes mellitus.     

Leucine promotes glucose uptake in skeletal muscles of rats

Soleus muscles isolated from normal rats were incubated to evaluate whether or not leucine promotes glucose uptake under insulin-free conditions, using a labeled 2-deoxyglucose uptake assay. Glucose uptake was promoted by 2mM leucine. A metabolite of leucine, alpha-ketoisocaproic acid (alpha-KIC), also exhibited a similar stimulatory effect, although this was not as potent as leucine. Stimulation of glucose uptake by leucine was completely canceled by pre-treatment with either 10 microM LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (PI3-kinase), or 6 microM GF109203X, a specific inhibitor of protein kinase C (PKC). No significant change was observed by pre-treatment with 1 microM rapamycin, a specific inhibitor of mammalian target of rapamycin (mTOR). These results suggest that leucine stimulates glucose transport in skeletal muscle via PI3-kinase and PKC pathways independently of the mammalian target of mTOR. They also suggest that leucine stimulates glucose transport by an insulin-independent mechanism.     

Leucine stimulates protein synthesis in skeletal muscle of neonatal pigs by enhancing mTORC1 activation

Skeletal muscle in the neonate grows at a rapid rate due in part to an enhanced sensitivity to the postprandial rise in amino acids, particularly leucine. To elucidate the molecular mechanism by which leucine stimulates protein synthesis in neonatal muscle, overnight-fasted 7-day-old piglets were treated with rapamycin [an inhibitor of mammalian target of rapamycin (mTOR) complex (mTORC)1] for 1 h and then infused with leucine for 1 h. Fractional rates of protein synthesis and activation of signaling components that lead to mRNA translation were determined in skeletal muscle. Rapamycin completely blocked leucine-induced muscle protein synthesis. Rapamycin markedly reduced raptor-mTOR association, an indicator of mTORC1 activation. Rapamycin blocked the leucine-induced phosphorylation of mTOR, S6 kinase 1 (S6K1), and eukaryotic initiation factor (eIF)4E-binding protein-1 (4E-BP1) and formation of the eIF4E.eIF4G complex and increased eIF4E.4E-BP1 complex abundance. Rapamycin had no effect on the association of mTOR with rictor, a crucial component for mTORC2 activation, or G protein beta-subunit-like protein (GbetaL), a component of mTORC1 and mTORC2. Neither leucine nor rapamycin affected the phosphorylation of AMP-activated protein kinase (AMPK), PKB, or tuberous sclerosis complex (TSC)2, signaling components that reside upstream of mTOR. Eukaryotic elongation factor (eEF)2 phosphorylation was not affected by leucine or rapamycin, although current dogma indicates that eEF2 phosphorylation is mTOR dependent. Together, these in vivo data suggest that leucine stimulates muscle protein synthesis in neonates by enhancing mTORC1 activation and its downstream effectors.     

Limitations to exercise- and maximal insulin-stimulated muscle glucose uptake

The hypothesisof this investigation was that insulin and muscle contraction, byincreasing the rate of skeletal muscle glucose transport, would biascontrol so that glucose delivery to the sarcolemma (and t tubule) andphosphorylation of glucose intracellularly would exert more influenceover glucose uptake. Because of the substantial increases in blood flow(and hence glucose delivery) that accompany exercise, we predicted thatglucose phosphorylation would become more rate determining duringexercise. The transsarcolemmal glucose gradient (TSGG; the glucoseconcentration difference across the membrane) is inversely related tothe degree to which glucose transport determines the rate of glucoseuptake. The TSGG was determined by using isotopic methods in consciousrats during euglycemic hyperinsulinemia [Ins; 20 mU/(kg · min); n = 7], during treadmill exercise (Ex,n = 6), and in sedentary,saline-infused rats (Bas, n = 13).Rats received primed, constant intravenous infusions of trace3-O-[³H]methyl-D-glucoseand [U-¹⁴C]mannitol.Then2-deoxy-[³H]glucosewas infused for the calculation of a glucose metabolic index(R_g). At the end of experiments,rats were anesthetized, and soleus muscles were excised. Total soleusglucose concentration and the steady-state ratio of intracellular toextracellular3-O-[³H]methyl-D-glucose(which distributes on the basis of the TSGG) were used to calculateranges of possible glucose concentrations ([G]) at theinner and outer sarcolemmal surfaces([G]_im and[G]_om, respectively).Soleus R_g was increased in Ins andfurther increased in Ex. In Ins, total soleus glucose,[G]_om, and the TSGGwere decreased compared with Bas, while[G]_im remained near 0. In Ex, total soleus glucose and[G]_im were increasedcompared with Bas, and there was not a decrease in[G]_om as was observedin Ins. In addition, accumulation of intracellular free2-deoxy-[³H]glucoseoccurred in soleus in both Ex and Ins. Taken together, these dataindicate that, in Ex, glucose phosphorylation becomes an importantlimitation to soleus glucose uptake. In Ins, both glucose delivery andglucose phosphorylation influence the rate of soleus glucose uptakemore than under basal conditions.

     

Preventing the calorie restriction-induced increase in insulin-stimulated Akt2 phosphorylation eliminates calorie restriction's effect on glucose uptake in skeletal muscle

Calorie restriction (CR; ~60% of ad libitum, AL, consumption) improves insulin-stimulated glucose uptake in skeletal muscle. The precise cellular mechanism for this healthful outcome is unknown, but it is accompanied by enhanced insulin-stimulated activation of Akt. Previous research using Akt2-null mice demonstrated that Akt2 is essential for the full CR-effect on insulin-stimulated glucose uptake by muscle. However, because Akt2-null mice were completely deficient in Akt2 in every cell throughout life, it would be valuable to assess the efficacy of transient, muscle-specific Akt inhibition for attenuation of CR-effects on glucose uptake. Accordingly, we used a selective Akt inhibitor (MK-2206) to eliminate the CR-induced elevation in insulin-stimulated Akt2 phosphorylation and determined the effects on Akt substrates and glucose uptake. We incubated isolated epitrochlearis muscles from 9-month-old AL and CR (~60-65% of AL intake for 6months) rats with or without MK-2206 and measured insulin-stimulated (1.2nM) glucose uptake and phosphorylation of the insulin receptor (Tyr1162/1163), pan-Akt (Thr308 and Ser473), Akt2 (Thr308 and Ser473), AS160/TBC1D4 (Thr642), and Filamin C (Ser2213). Incubation of isolated skeletal muscles with a dose of a selective Akt inhibitor that eliminated the CR-induced increases in Akt2 phosphorylation prevented CR's effects on insulin-stimulated glucose uptake, pAS160(Thr642) and pFilamin C(Ser2213) without altering pIR(Tyr1162/1163). These data provide compelling new evidence linking the CR-induced increase in insulin-stimulated Akt2 phosphorylation to CR's effects on insulin-mediated phosphorylation of Akt substrates and glucose uptake in skeletal muscle.     

Uncarboxylated osteocalcin decreases insulin-stimulated glucose uptake without affecting insulin signaling and regulators of mitochondrial biogenesis in myotubes

Uncarboxylated osteocalcin (uOC) is a circulating bone matrix protein, which has previously been shown to regulate glucose uptake and systemic metabolism. However, the cellular mechanism by which uOC acts has yet to be elucidated. C2C12 mouse myotubes were treated for 72 h with uOC (1–100 ng/mL). Cellular metabolism was analyzed using oxygen consumption and extracellular acidification rate. Metabolic gene and protein expression were measured via quantitative real-time polymerase chain reaction and Western blot, respectively. Additionally, C2C12 myotubes were treated with 10 ng/mL uOC to examine glucose uptake and activation of insulin signaling with or without insulin resistance. Finally, cellular lipid content was measured via Oil Red O and Nile Red staining. uOC treatment resulted in dose-dependent alterations of oxygen consumption with little effect on regulators of mitochondrial metabolism. Basal expression of regulators of glucose uptake were unaffected by uOC treatment. However, insulin-stimulated glucose uptake was blunted by uOC treatment with no concurrent alterations in insulin signaling. While chronic insulin treatment resulted in suppressed activation of Akt, concurrent uOC treatment was unable to prevent these detrimental effects on insulin signaling. uOC treatment had no effect on markers of lipogenesis and cellular lipid content. These findings suggest that 72-h uOC treatment may alter oxygen consumption without effect on regulators of mitochondrial biogenesis. Additionally, uOC treatment suppressed insulin-stimulated glucose uptake in cultured myotubes but had little effect on insulin signaling or regulators of cellular metabolism and was unable to mitigate insulin resistance.