Natural compounds regulate glycolysis in hypoxic tumor microenvironment.

In the early twentieth century, Otto Heinrich Warburg described an elevated rate of glycolysis occurring in cancer cells, even in the presence of atmospheric oxygen (the Warburg effect). Recently it became a therapeutically interesting strategy and is considered as an emerging hallmark of cancer. Hypoxia inducible factor-1 (HIF-1) is one of the key transcription factors that play major roles in tumor glycolysis and could directly trigger Warburg effect. Thus, how to inhibit HIF-1-depended Warburg effect to assist the cancer therapy is becoming a hot issue in cancer research. In fact, HIF-1 upregulates the glucose transporters (GLUT) and induces the expression of glycolytic enzymes, such as hexokinase, pyruvate kinase, and lactate dehydrogenase. So small molecules of natural origin used as GLUT, hexokinase, or pyruvate kinase isoform M2 inhibitors could represent a major challenge in the field of cancer treatment. These compounds aim to suppress tumor hypoxia induced glycolysis process to suppress the cell energy metabolism or enhance the susceptibility of tumor cells to radio- and chemotherapy. In this review, we highlight the role of natural compounds in regulating tumor glycolysis, with a main focus on the glycolysis under hypoxic tumor microenvironment.

Transcriptional regulation of urate transportosome member SLC2A9 by nuclear receptor HNF4α.

Renal tubular handling of urate is realized by a network of uptake and efflux transporters, including members of drug transporter families such as solute carrier proteins and ATP-binding cassette transporters. Solute carrier family 2, member 9 (SLC2A9), is one key factor of this so called "urate transportosome." The aim of the present study was to understand the transcriptional regulation of SLC2A9 and to test whether identified factors might contribute to a coordinated transcriptional regulation of the transporters involved in urate handling. In silico analysis and cell-based reporter gene assays identified a hepatocyte nuclear factor (HNF)4α-binding site in the promoter of SLC2A9 isoform 1, whose activity was enhanced by transient HNF4α overexpression, whereas mutation of the binding site diminished activation. HNF4α overexpression induced endogenous SLC2A9 expression in vitro. The in vivo role of HNF4α in the modulation of renal SLC2A9 gene expression was supported by findings of quantitative real-time RT-PCR analyses and chromatin immunoprecipitation assays. Indeed, mRNA expression of SLC2A9 and HNF4α in human kidney samples was significantly correlated. We also showed that in renal clear cell carcinoma, downregulation of HNF4α mRNA and protein expression was associated with a significant decline in expression of the transporter. Taken together, our data suggest that nuclear receptor family member HNF4α contributes to the transcriptional regulation of SLC2A9 isoform 1. Since HNF4α has previously been assumed to be a modulator of several urate transporters, our findings support the notion that there could be a transcriptional network providing synchronized regulation of the functional network of the urate transportosome.

Glucose starvation-induced turnover of the yeast glucose transporter Hxt1.

BACKGROUND: The budding yeast Saccharomyces cerevisiae possesses multiple glucose transporters with different affinities for glucose that enable it to respond to a wide range of glucose concentrations. The steady-state levels of glucose transporters are regulated in response to changes in the availability of glucose. This study investigates the glucose regulation of the low affinity, high capacity glucose transporter Hxt1. METHODS AND RESULTS: Western blotting and confocal microscopy were performed to evaluate glucose regulation of the stability of Hxt1. Our results show that glucose starvation induces endocytosis and degradation of Hxt1 and that this event requires End3, a protein required for endocytosis, and the Doa4 deubiquitination enzyme. Mutational analysis of the lysine residues in the Hxt1 N-terminal domain demonstrates that the two lysine residues, K12 and K39, serve as the putative ubiquitin-acceptor sites by the Rsp5 ubiquitin ligase. We also demonstrate that inactivation of PKA (cAMP-dependent protein kinase A) is needed for Hxt1 turnover, implicating the role of the Ras/cAMP-PKA glucose signaling pathway in the stability of Hxt1. CONCLUSION AND GENERAL SIGNIFICANCE: Hxt1, most useful when glucose is abundant, is internalized and degraded when glucose becomes depleted. Of note, the stability of Hxt1 is regulated by PKA, known as a positive regulator for glucose induction of HXT1 gene expression, demonstrating a dual role of PKA in regulation of Hxt1.

High glucose condition suppresses neurosphere formation by human periodontal ligament-derived mesenchymal stem cells.

D-Glucose serves many roles in cellular functions, but its role in human periodontal ligament-derived mesenchymal stem cells (hPSLSCs) is yet unknown. Here, the roles of high glucose concentration on neurogenic differentiation by hPDLSCs were investigated. Two-stage neurogenic induction protocol was employed. Cells were maintained in normal neurogenic induction medium, high glucose condition, or high mannose condition. The results showed that high glucose attenuated neurosphere formation efficiency by hPDLSCs in terms of morphology, neurogenic marker expression, without a deleterious effect on cell viability. Contrastingly, neurosphere-derived cells matured in high glucose condition exhibited normal neuronal characteristics compared to the control. During neurosphere formation in high glucose, glucose transporters (GLUTs) mRNA levels were significantly decreased, corresponding with the deprivation of cellular glucose uptake. Further, a glucose uptake inhibitor, cytochalasin B, was used to confirm the deleterious effects of glucose uptake deprivation during neurosphere formation. The results demonstrated that deprivation of glucose uptake attenuated neurosphere formation efficiency by hPDLSCs. Together, the results illustrated that high glucose condition attenuated the efficiency of neurosphere formation but not neuronal maturation, which may occur through the downregulation of GLUTs and the reduction of glucose uptake.

Control of Sertoli cell metabolism by sex steroid hormones is mediated through modulation in glycolysis-related transporters and enzymes.

Sertoli cells (SCs) glucose metabolism is crucial for spermatogenesis since developing germ cells consume lactate produced by SCs as their main energy source. Recently, androgens and estrogens have been implicated in SCs energy metabolism modulation, although the molecular mechanisms remained undisclosed. Here, we report the effect of sex steroid hormones on key points of cultured rat SCs glycolytic pathway. We used primary cultures of immature rat SCs treated with 17ß-estradiol (E2) or 5α-dihydrotestosterone (DHT). The transcript levels of glucose transporters (GLUTs), phosphofructokinase 1 (PFK-1) and lactate dehydrogenase C (LDH C) were analyzed after 25 and 50 h of culture by qPCR. Protein levels of GLUTs, PFK-1, LDH and monocarboxylate transporter 4 (MCT4) after 25 and 50 h were determined by western blot and LDH activity was also assessed. Our results show that both E2 and DHT downregulated the transcript levels of PFK-1, GLUT1 and GLUT3 after 50 h. However, only DHT-treated cells presented a downregulation of LDH C transcript levels. Interestingly, the protein levels of these enzymes and transporters remained unaltered except in DHT-treated cells that presented a significant decrease on GLUT1 protein levels evidencing a possible site for the regulation of SCs glucose metabolism by androgens. Taken together, our results provide evidence that sex steroid hormones action in SCs energy metabolism is mediated through modulation in glycolysis-related transporters and enzymes, particularly at the transcriptional level. DHT decreased GLUT1 protein levels and increased LDH activity after 25 h, evidencing key points for this hormone action in the regulation of SCs metabolism.

CCL2/CCR2 augments the production of transforming growth factor-beta1, type 1 collagen and CCL2 by human CD45-/collagen 1-positive cells under high glucose concentrations.

BACKGROUND: The migration and activation of circulating profibrotic cells including fibrocytes by the action of the chemokine/chemokine receptor system has been implicated in pathological fibrogenesis. In the present study, the involvement of collagen 1 (Col1)-producing cells, CD45-positive/collagen-1-positive (CD45(+)/Col1(+)) cells originally named as fibrocytes via CC chemokine receptor 2 (CCR2), a cognate receptor of CCL2/monocyte chemoattractant protein, was examined in diabetic conditions. METHODS: Human CD45(+)/Col1(+) cells originating from the peripheral blood of healthy volunteers were incubated with high concentrations of D-glucose or D-mannitol as an osmotic control for 12, 24 or 48 h. In addition, these cells were preincubated with CCL2 under high glucose concentrations. We also examined the effects of the inhibitors of glucose transporters (GLUTs), reactive oxygen species or CCR2 on the expression of transforming growth factor beta1 (TGF-ß1), pro-α1 chain of Col1 (COL1A1), and CCL2. RESULTS: Stimulation of CD45(+)/Col1(+) cells with high glucose concentrations increased the mRNA and protein levels of TGF-ß1 and CCL2 and those of pro-COL1A1, and this effect was mediated in part by increased osmolality. Preincubation of the cells with cytochalasin B (a GLUT inhibitor) or N-acetylcysteine (an antioxidant) blocked the stimulatory effect of high glucose concentrations on these profibrotic molecules. In addition, preincubation of the cells with CCL2 enhanced the high glucose-induced upregulation of TGF-ß1, pro-COL1A1 and CCL2 and migration of the cells, and this effect was partly inhibited by treatment with CCR2 inhibitors. CONCLUSION: These results suggest that CD45(+)/Col1(+) cells may be directly involved, in part through CCL2/CCR2 signaling, in the fibrotic process under diabetic conditions.

1-deoxynojirimycin inhibits glucose absorption and accelerates glucose metabolism in streptozotocin-induced diabetic mice.

We investigated the role of 1-deoxynojirimycin (DNJ) on glucose absorption and metabolism in normal and diabetic mice. Oral and intravenous glucose tolerance tests and labeled (13)C6-glucose uptake assays suggested that DNJ inhibited intestinal glucose absorption in intestine. We also showed that DNJ down-regulated intestinal SGLT1, Na(+)/K(+)-ATP and GLUT2 mRNA and protein expression. Pretreatment with DNJ (50 mg/kg) increased the activity, mRNA and protein levels of hepatic glycolysis enzymes (GK, PFK, PK, PDE1) and decreased the expression of gluconeogenesis enzymes (PEPCK, G-6-Pase). Assays of protein expression in hepatic cells and in vitro tests with purified enzymes indicated that the increased activity of glucose glycolysis enzymes was resulted from the relative increase in protein expression, rather than from direct enzyme activation. These results suggest that DNJ inhibits intestinal glucose absorption and accelerates hepatic glucose metabolism by directly regulating the expression of proteins involved in glucose transport systems, glycolysis and gluconeogenesis enzymes.

Fructose consumption and cancer: is there a connection?

PURPOSE OF REVIEW: Cancer cell metabolism is characterized by high rates of glucose uptake and anaerobic glycolysis. Sugar consumption has increased dramatically in the industrialized world, with refined fructose intake skyrocketing upwards in the USA over the past 30 years. Fructose provides an alternative carbon source for glycolysis, entering downstream of glucose and bypassing two key rate-limiting steps. Considering that glycolysis is the major pathway which fuels cancer growth, this review will focus on regulation and flux of glucose versus fructose through this pathway, and consider whether epidemiologic and experimental data support a mechanism whereby fructose might potentiate cancer growth in transformed cells.(Figure is included in full-text article.) RECENT FINDINGS: Fructose intake is associated with increased risk of pancreatic and small intestinal cancers, and possibly others. Fructose promotes flux through the pentose phosphate, which enhances protein synthesis and may indirectly increase tumor growth. Fructose treatment is associated with more aggressive cancer behavior and may promote metastasis. SUMMARY: Whereas glucose favors overall growth kinetics, fructose enhances protein synthesis and appears to promote a more aggressive cancer phenotype. Fructose has become ubiquitous in our food supply, with the highest consumers being teens and young adults. Therefore, understanding the potential health consequences of fructose and its role in chronic disease development is of critical importance.

Changes in glucose transporter expression in monocytes of periparturient dairy cows.

The transition period of dairy cows is characterized by dramatic changes in metabolism and immune cell function that contributes to increased susceptibility to several economically important diseases. Monocyte and macrophage populations increase in blood and tissues of cows during the transition period and have enhanced inflammatory responses that may contribute to increased severity of disease. Glucose is a major energy source for activated monocytes and glucose uptake is facilitated by glucose transporters (GLUT). The objective of this study was to determine how bovine monocyte GLUT expression changes during lactogenesis and in response to proinflammatory stimulation. Blood samples were collected from 10 dairy cows approximately 5 wk before calving and during the first week of lactation. Monocytes were isolated from total peripheral blood mononuclear cells, and expression of GLUT1, GLUT3, and GLUT4 isoforms was assessed in resting cells and following endotoxin stimulation. In general, the onset of lactation served to decrease overall GLUT expression. Gene and protein expression of GLUT1 was significantly decreased after parturition, and GLUT3 and GLUT4 cell surface expression was also significantly decreased postcalving. Endotoxin stimulation, however, increased gene expression of GLUT3 and GLUT4, and gene expression for all GLUT isoforms was positively correlated to production of tumor necrosis factor-α. This study identified, for the first time, the presence of GLUT isoforms in bovine monocytes. Alterations in monocyte GLUT expression at the onset of lactation warrant further investigation to ascertain how changes in glucose uptake may contribute to periparturient inflammatory dysfunction.

Proinflammatory mediators disrupt glucose homeostasis in airway surface liquid.

The glucose concentration of the airway surface liquid (ASL) is much lower than that in blood and is tightly regulated by the airway epithelium. ASL glucose is elevated in patients with viral colds, cystic fibrosis, chronic obstructive pulmonary disease, and asthma. Elevated ASL glucose is also associated with increased incidence of respiratory infection. However, the mechanism by which ASL glucose increases under inflammatory conditions is unknown. The aim of this study was to investigate the effect of proinflammatory mediators (PIMs) on the mechanisms governing airway glucose homeostasis in polarized monolayers of human airway (H441) and primary human bronchial epithelial (HBE) cells. Monolayers were treated with TNF-α, IFN-γ, and LPS during 72 h. PIM treatment led to increase in ASL glucose concentration and significantly reduced H441 and HBE transepithelial resistance. This decline in transepithelial resistance was associated with an increase in paracellular permeability of glucose. Similar enhanced rates of paracellular glucose flux were also observed across excised trachea from LPS-treated mice. Interestingly, PIMs enhanced glucose uptake across the apical, but not the basolateral, membrane of H441 and HBE monolayers. This increase was predominantly via phloretin-sensitive glucose transporter (GLUT)-mediated uptake, which coincided with an increase in GLUT-2 and GLUT-10 abundance. In conclusion, exposure of airway epithelial monolayers to PIMs results in increased paracellular glucose flux, as well as apical GLUT-mediated glucose uptake. However, uptake was insufficient to limit glucose accumulation in ASL. To our knowledge, these data provide for the first time a mechanism to support clinical findings that ASL glucose concentration is increased in patients with airway inflammation.

Inhibition of glycolytic enzymes mediated by pharmacologically activated p53: targeting Warburg effect to fight cancer.

Unique sensitivity of tumor cells to the inhibition of glycolysis is a good target for anticancer therapy. Here, we demonstrate that the pharmacologically activated tumor suppressor p53 mediates the inhibition of glycolytic enzymes in cancer cells in vitro and in vivo. We showed that p53 binds to the promoters of metabolic genes and represses their expression, including glucose transporters SLC2A12 (GLUT12) and SLC2A1 (GLUT1). Furthermore, p53-mediated repression of transcription factors c-Myc and HIF1α, key drivers of ATP-generating pathways in tumors, contributed to ATP production block. Inhibition of c-Myc by p53 mediated the ablation of several glycolytic genes in normoxia, whereas in hypoxia down-regulation of HIF1α contributed to this effect. We identified Sp1 as a transcription cofactor cooperating with p53 in the ablation of metabolic genes. Using different approaches, we demonstrated that glycolysis block contributes to the robust induction of apoptosis by p53 in cancer cells. Taken together, our data suggest that tumor-specific reinstatement of p53 function targets the "Achilles heel" of cancer cells (i.e. their dependence on glycolysis), which could contribute to the tumor-selective killing of cancer cells by pharmacologically activated p53.

Expression and prognostic value of glucose transporters and hexokinases in tonsil and mobile tongue squamous cell carcinoma.

The aim of this study was to assess the expression pattern and prognostic value of the high affinity glucose transporters GLUT-1, 3, 4, 8 and 9, SGLT-1 and of hexokinases (HK) I, II and III in squamous cell carcinoma of the tonsil and mobile tongue (TTSCC) by means of immunohistochemistry. Seventy-one consecutive patients suffering from TTSCC were included. The intensity and amount of positive tumour cells in the immunoreaction (histology score (H-score)) for GLUT-1, 3, 4, 8 and 9 as well as for HK-I, II and III were assessed independently by two experienced observers, blinded to the clinical results. H-scores as well as clinical variables were related to patient outcome. Median follow-up time was 49 months (range 1-123 months). Mean H-scores for GLUT expression in decreasing order of magnitude were respectively 10.99 for GLUT-1 (sd 3.9), 5.7 for GLUT-8 (sd 4.0), 5.4 for GLUT-3 (sd 3.7), 1.0 for GLUT-4 (sd 2.0), 1.1 (sd 1.3) for SGLT-1, and 0.4 for GLUT-9 (sd 0.6); GLUT-1 > GLUT-8 = GLUT-3 > GLUT-4 = GLUT-9 = SGLT-1 (with > meaning significantly (p<0.05 on ANOVA + posthoc Bonferroni correction) higher than and =, meaning not significantly different from). Mean H-scores for hexokinase expression were respectively 5.8 for HK-I (sd 3.5), 4.6 for HK-II (sd 3.0) and 2.0 for HK-III (sd 2.0); HK-I > HK-II > HK-III. Finally high H-scores for GLUT-4 were favourably related to disease-free and overall survival on multivariate analysis. To conclude, TTSCC expresses a wide variety of glucose transporter systems and hexokinase enzymes with the "housekeeping" GLUT-1 and HK-I being the most intensely expressed. GLUT-4 over-expression appears to confer a favourable prognosis in squamous cell carcinoma of the tonsil and mobile tongue. Additional studies confirming this finding in larger cohorts of patients are mandatory.

Role of curcumin-dependent modulation of tumor microenvironment of a murine T cell lymphoma in altered regulation of tumor cell survival.

Using a murine model of a T cell lymphoma, in the present study, we report that tumor growth retarding action of curcumin involves modulation of some crucial parameters of tumor microenvironment regulating tumor progression. Curcumin-administration to tumor-bearing host caused an altered pH regulation in tumor cells associated with alteration in expression of cell survival and apoptosis regulatory proteins and genes. Nevertheless, an alteration was also observed in biophysical parameters of tumor microenvironment responsible for modulation of tumor growth pertaining to hypoxia, tumor acidosis, and glucose metabolism. The study thus sheds new light with respect to the antineoplastic action of curcumin against a tumor-bearing host with progressively growing tumor of hematological origin. This will help in optimizing application of the drug and anticancer research and therapy.

Low-volume interval training improves muscle oxidative capacity in sedentary adults.

INTRODUCTION: High-intensity interval training (HIT) increases skeletal muscle oxidative capacity similar to traditional endurance training, despite a low total exercise volume. Much of this work has focused on young active individuals, and it is unclear whether the results are applicable to older less active populations. In addition, many studies have used "all-out" variable-load exercise interventions (e.g., repeated Wingate tests) that may not be practical for all individuals. We therefore examined the effect of a more practical low-volume submaximal constant-load HIT protocol on skeletal muscle oxidative capacity and insulin sensitivity in middle-aged adults, who may be at a higher risk for inactivity-related disorders. METHODS: Seven sedentary but otherwise healthy individuals (three women) with a mean ± SD age, body mass index, and peak oxygen uptake (VO(2peak)) of 45 ± 5 yr, 27 ± 5 kg·m(-2), and 30 ± 3 mL·kg(-1)·min(-1) performed six training sessions during 2 wk. Each session involved 10 × 1-min cycling at ∼60% of peak power achieved during a ramp VO(2peak) test (eliciting ∼80%-95% of HR reserve) with 1 min of recovery between intervals. Needle biopsy samples (vastus lateralis) were obtained before training and ∼72 h after the final training session. RESULTS: Muscle oxidative capacity, as reflected by the protein content of citrate synthase and cytochrome c oxidase subunit IV, increased by ∼35% after training. The transcriptional coactivator peroxisome proliferator-activated receptor γ coactivator 1α was increased by ∼56% after training, but the transcriptional corepressor receptor-interacting protein 140 remained unchanged. Glucose transporter protein content increased ∼260%, and insulin sensitivity, on the basis of the insulin sensitivity index homeostasis model assessment, improved by ∼35% after training. CONCLUSIONS: Constant-load low-volume HIT may be a practical time-efficient strategy to induce metabolic adaptations that reduce the risk for inactivity-related disorders in previously sedentary middle-aged adults.

The relationship between fetal growth restriction and small placenta in 6-mercaptopurine exposed rat.

In order to investigate the effect of placental size on fetal intrauterine growth retardation (IURG), we examined the morphology and alterations in the expression of glucose transporter in the placentas of rats exposed to 6-mercaptopurine (6-MP). 6-MP was administered orally at 0 and 60 mg/kg/day on gestation day (GD) 9, 11, 13 or 15, and the placentas were sampled on GDs 17 and 21. The main findings in the treated groups were small placenta caused by mitotic inhibition and apoptosis, fetal resorption and IUGR with or without some malformations. The most sensitive period to 6-MP-induced fetal mortality was found to be in the GD9-treated group, and the small placenta and fetal abnormalities in the GD11-treated group, respectively. However, the litters in a quarter of the dams with the treatment on GD 11 had no fetotoxicity despite 25% decline in the placental weight. Histopathologically, the expression of glucose transporter GLUT3 was increased in the trophoblastic septa in all treated groups, particularly remarkable with proliferation of trophoblasts in the above litters, where the fetal-placental weight ratio was increased. Thus, we consider that the normal fetal growth and development can be maintained caused by adaptive change, even if the placental weight decreased by approximately 25% in 6-MP exposed rats.

Glucose-transporter-mediated positive inotropic effects in human myocardium of diabetic and nondiabetic patients.

Insulin causes inotropic effects via Ca(2+)-dependent and Ca(2+)-independent pathways. The latter one is potentially glucose dependent. We examined inotropic responses and signal transduction of insulin in human atrial myocardium of diabetic and nondiabetic patients to test for the role of glucose transporters. Experiments were performed in isolated atrial myocardium of 88 patients undergoing cardiac surgery and 28 ventricular muscle samples of explanted hearts. Influence of insulin (0.02 micromol/L) on isometric twitch force was examined with and without blocking glucose transporter (GLUT) 4 translocation (latrunculin), sodium-coupled glucose transporter (SGLT) 1 (phlorizin, T-1095A), or PI3-kinase (wortmannin). Experiments were performed in Tyrode solution containing glucose or pyruvate as energetic substrate. Messenger RNA expression of glucose transporters (GLUT1, GLUT4, SGLT1, SGLT2) was analyzed in atrial and ventricular myocardium of both diabetic and nondiabetic patients. Developed force increases after insulin (to 117.8% +/- 2.4% and 115.8% +/- 1.9%) in trabeculae from patients with and without diabetes. Inotropic effect was reduced after displacing glucose with pyruvate as well as after PI3-kinase inhibition (to 103% +/- 2%) or inhibition of glucose transporters GLUT4 (to 105% +/- 2%) and SGLT1 (phlorizin to 106% +/- 2%, T-1095A to 105% +/- 2%), without differences between the 2 groups. In glucose-free pyruvate-containing solution, only inhibition of PI3-kinase but not blocking glucose transporters resulted in further inhibitory effects. Messenger RNA expression did not show significant differences between patients with or without diabetes. Insulin exerts positive inotropic effects in human atrial myocardium. These effects are mediated via a PI3-kinase-sensitive and a glucose-transport-sensitive pathway. Differences in functional effects or messenger RNA expression of glucose transporters were not detectable between patients with and without diabetes.

GLUT1 as a therapeutic target in hepatocellular carcinoma.

Primary hepatocellular carcinoma (HCC) is one of the most fatal cancers in humans with rising incidence in many regions around the world. Currently, no satisfactory curative pharmacological treatment is available, and the outcome is mostly poor. Recently, we have shown that the glucose transporter GLUT1 is increased in a subset of patients with HCC and functionally affects tumorigenicity. GLUT1 is a rate-limiting transporter for glucose uptake, and its expression correlates with anaerobic glycolysis. This phenomenon is also known as the Warburg effect and recently became of great interest, since it affects not only glucose uptake and utilization but also has an influence on tumorigenic features like metastasis, chemoresistance and escape from immune surveillance. Consistent with this, RNA-interference-mediated inhibition of GLUT1 expression in HCC cells resulted in reduced tumorigenicity. Together, these findings indicate that GLUT1 is a novel and attractive therapeutic target for HCC. This review summarizes our current knowledge on the expression and function of GLUT1 in HCC, available drugs/strategies to inhibit GLUT1 expression or function, and potential side effects of such therapeutic strategies.

Estrogen-related receptor alpha inverse agonist enhances basal glucose uptake in myotubes through reactive oxygen species.

Estrogen-related receptors alpha (ERRalpha) and peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha) function coordinately to regulate mitochondrial biogenesis and oxidative phosphorylation particularly in muscle tissue. In this study, we addressed the consequences of suppressing the activity of ERRalpha in L6 myotubes using an ERRalpha inverse agonist XCT-790. We found that treating differentiated L6 myotubes with XCT-790 reduced the expression of PGC-1alpha and suppressed mitochondrial biogenesis. Additionally, XCT-790 increased the production of reactive oxygen species (ROS) which in turn induced the expressions of glucose transporters 1, 2, and 5 leading to an increase in glucose uptake and uncoupling protein 3 leading to a reduction of mitochondrial membrane potential. Thus, suppressing the activity of ERRalpha which is primarily responsible for controlling beta-oxidation would nonetheless indirectly affect glucose uptake in a ROS-dependent manner.

Molecular mechanisms involved in Sertoli cell adaptation to glucose deprivation.

Sertoli cells provide the physical support and the necessary environment for germ cell development. Among the products secreted by Sertoli cells, lactate, the preferred energy substrate for spermatocytes and spermatids, is present. Considering the essential role of lactate on germ cell metabolism, it is supposed that Sertoli cells must ensure its production even in adverse conditions, such as those that would result from a decrease in glucose levels in the extracellular milieu. The aim of the present study was to investigate 1) a possible effect of glucose deprivation on glucose uptake and on the expression of glucose transporters in rat Sertoli cells and 2) the participation of different signal transduction pathways in the above-mentioned regulation. Results obtained show that decreasing glucose levels in Sertoli cell culture medium provokes 1) an increase in glucose uptake accompanied by only a slight decrease in lactate production, 2) an increase in GLUT1 and a decrease in GLUT3 expression, and 3) an activation of AMP-activated protein kinase (AMPK)-, phosphatidylinositol 3-kinase (PI3K)/PKB-, and p38 MAPK-dependent pathways. Additionally, by using specific inhibitors of these pathways, a possible participation of AMPK- and p38MAPK-dependent pathways in the regulation of glucose uptake and GLUT1 expression is shown. These results suggest that Sertoli cells adapt to conditions of glucose deprivation to ensure an adequate lactate concentration in the microenvironment where germ cell development occurs.

Select nutrients in the ovine uterine lumen. ii. glucose transporters in the uterus and peri-implantation conceptuses.

Total glucose in ovine uterine lumenal fluid increases 6-fold between Days 10 and 15 of gestation, but not the estrous cycle; however, mechanisms for glucose transport into the uterine lumen and uptake by conceptuses (embryo/fetus and associated membranes) are not established. This study determined the effects of the estrous cycle, pregnancy, progesterone (P4), and interferon tau (IFNT) on expression of both facilitative (SLC2A1, SLC2A3, and SLC2A4) and sodium-dependent (SLC5A1 and SLC5A11) glucose transporters in ovine uterine endometria from Days 10 to 16 of the estrous cycle and Days 10 to 20 of pregnancy, as well as in conceptuses from Days 10 to 20 of pregnancy. The SLC2A1 and SLC5A1 mRNAs and proteins were most abundant in uterine luminal epithelia and superficial glandular epithelia (LE/sGE), whereas SLC2A4 was present in stromal cells and glandular epithelia (GE). SLC5A11 mRNA was most abundant in endometrial GE, whereas SLC2A3 mRNA was not detectable in endometria. SLC2A1, SLC2A3, SLC2A4, SLC5A1, and SLC5A11 were expressed in the trophectoderm and endoderm of conceptuses. Steady-state levels of SLC2A1, SLC5A1, and SLC5A11 mRNAs, but not SLC2A4 mRNA, were greater in endometria from pregnant than from cyclic ewes. Progesterone increased SLC2A1, SLC5A11, and SLC2A4 mRNAs in the LE/sGE and SLC5A1 in the GE of ovariectomized ewes. Expression of SLC5A1 was inhibited by ZK136,317 (progesterone receptor antagonist), and the combination of ZK136,317 and IFNT further decreased expression in GE. In constrast, P4 induced and IFNT stimulated expression of SLC2A1 and SLC5A11, and these effects were blocked by ZK136,317. Results of this study indicate differential expression of facilitative and sodium-dependent glucose transporters in ovine uteri and conceptuses for transport and uptake of glucose, and that P4 or P4 and IFNT regulate their expression during the peri-implantation period of pregnancy.