OBJECTIVE: To explore the effect of sodium tungstate on glucose metabolism in adipocytes and its mechanism. METHODS: After 3T3-L1 preadipocytes were differentiated into adipocytes, these adipocytes were incubated with sodium tungstate (0, 150, 300, 500, and 700 micromol/L) for 48 h, and then glucose consumption of the adipocytes was detected by glucose-oxidase assay. Glucose transport was determined by the uptake of 2-deoxy-[3H]-D-glucose, and the expression of glucose transport-4 (GLUT-4) mRNA was identified by semi-quantitative RT-PCR. RESULTS: Sodium tungstate (150 approximately 700 micromol/L) could significantly increase the glucose consumption and glucose transport with a concentration dependent-effect. Sodium tungstate could increase GLUT-4 mRNA expression. CONCLUSION Sodium tungstate can enhance the glucose metabolism of adipocytes by up-regulating the expression of GLUT-4 mRNA.
3T3-L1 Cells ; Adipocytes ; metabolism ; Animals ; Glucose ; metabolism ; Glucose Transporter Type 4 ; biosynthesis ; genetics ; Hypoglycemic Agents ; pharmacology ; Mice ; RNA, Messenger ; biosynthesis ; genetics ; Tungsten Compounds ; pharmacology ; Up-Regulation

Swine is an ideal model for diabetes studies. Insulin and insulin resistance are closely related with diabetes. To investigate the effect of SOCS-3 in insulin resistance, porcine primary adipocyte was treated with insulin (100 nmol/L) and dexamethasone (300 nmol/L) to induce insulin resistance. The simi-quantitative PCR results suggested that insulin increased GLUT4, PPARgamma and SOCS-3 gene expression in primary culture porcine adipocytes and no change of OB gene expression. Under insulin resistance conditions, SOCS-3 and OB gene expression were up-regulated, whereas GLUT4 and PPARgamma gene expression were down-regulated in primary porcine adipocytes. The overexpression of PPARgamma gene resulted in the increase of GLUT4 expression by insulin. Different expression levels of SOCS-3 determined the inhibitory effects of insulin signaling. Induction of insulin resistance by dexamethasone was not only due to inhibition of glucose transportation, but also repression of insulin signaling. SOCS-3 might be a potential gene to block the insulin resistance.
Adipocytes ; cytology ; metabolism ; Animals ; Cells, Cultured ; Dexamethasone ; pharmacology ; Glucose Transporter Type 4 ; biosynthesis ; genetics ; Insulin ; pharmacology ; Insulin Resistance ; Leptin ; biosynthesis ; genetics ; PPAR gamma ; biosynthesis ; genetics ; Suppressor of Cytokine Signaling 3 Protein ; Suppressor of Cytokine Signaling Proteins ; biosynthesis ; genetics ; Swine

AMP-activated protein kinase, AMPK, is responsible for regulation of exercise-induced GLUT4 gene expression in skeletal muscle. But the molecular mechanisms for this regulation and key protein in this signaling pathway are obscure. There has been growing recognition that histone acetylation probably represents a central mechanism for regulation of gene transcription, and recent studies showed that numerous gene expressions are regulated by nucleosomal histone acetylation, which is modulated through histone acetyltransferases (HATs) and histone deacetylases (HDACs). So we have a hypothesis that the AMPK regulates GLUT4 gene through recruiting HDACs. Skeletal muscle cells cultured with normal (5 mmol/L) and high (20 mmol/L) glucose concentration were incubated with AICAR, and then total and nuclear AMPKalpha2, HDAC5 protein and GLUT4 mRNA were measured. The results show that the AICAR activated AMPKalpha2, reduced nuclear HDAC5,and increased GLUT4 mRNA in skeletal muscle cells; in contrast, the effect evoked by AICAR was blunted in cultured skeletal muscle cells with high glucose. Therefore, the changes of GLUT4 gene expression under different glucose concentration are closely related to the changes of AMPKalpha2 and HDAC5 protein in skeletal muscle cells. This result demonstrates that HDAC5 plays an important role in regulating GLUT4 gene transcription by AMPK signaling pathway skeletal muscle cells.
AMP-Activated Protein Kinases ; metabolism ; Cells, Cultured ; Glucose Transporter Type 4 ; biosynthesis ; genetics ; Histone Deacetylases ; metabolism ; Humans ; Muscle, Skeletal ; cytology ; enzymology ; metabolism ; RNA, Messenger ; biosynthesis ; genetics ; Signal Transduction ; Transcription, Genetic

It is well known that exercise can have beneficial effects on insulin resistance by activation of glucose transporter. Following up our previous report that caveolin-1 plays an important role in glucose uptake in L6 skeletal muscle cells, we examined whether exercise alters the expression of caveolin-1, and whether exercise-caused changes are muscle fiber and exercise type specific. Fifity week-old Sprague Dawley (SD) rats were trained to climb a ladder and treadmill for 8 weeks and their soleus muscles (SOL) and extensor digitorum longus muscles (EDL) were removed after the last bout of exercise and compared with those from non-exercised animals. We found that the expression of insulin related proteins and caveolins did not change in SOL muscles after exercise. However, in EDL muscles, the expression of insulin receptor beta (IRbeta) and glucose transporter-4 (GLUT-4) as well as phosphorylation of AKT and AMPK increased with resistance exercise but not with aerobic exercise. Also, caveolin-1 and caveolin-3 increased along with insulin related proteins only in EDL muscles by resistance exercise. These results suggest that upregulation of caveolin-1 in the skeletal muscle is fiber specific and exercise type specific, implicating the requirement of the specific mode of exercise to improve insulin sensitivity.
AMP-Activated Protein Kinases ; Animals ; Caveolin 1/*biosynthesis ; Caveolin 3/metabolism ; Female ; Glucose Transporter Type 4/biosynthesis ; Insulin/*physiology ; Multienzyme Complexes/metabolism ; Muscle Fibers, Skeletal/*metabolism ; Muscle, Skeletal/metabolism/*physiology ; Phosphorylation ; *Physical Conditioning, Animal ; Protein-Serine-Threonine Kinases/metabolism ; Proto-Oncogene Proteins c-akt/metabolism ; Rats ; Rats, Sprague-Dawley ; Receptor, Insulin/biosynthesis ; Up-Regulation

The specific inhibition of angiotensin II action at AT(1) receptors by losartan has been shown to decrease peripheral insulin resistance in type 2 diabetic patients and animal models. We examined the effect of losartan on the expression of insulin receptor substrate 1 (IRS-1), protein kinase B (PKB) and glucose transporter 4 (GLUT4), as well as the phosphorylation status of IRS-1 and the association between IRS-1 and phosphatidylinositol (PI) 3-kinase in skeletal muscle from fat-fed and-streptozotocin (STZ)-treated rats, an animal model of type 2 diabetes mellitus. In addition, the effects of losartan on GLUT4 translocation in muscle cells and on insulin sensitivity were also evaluated. Muscle tissues were isolated from male losartan-treated and untreated normal or non-insulin-dependent diabetes mellitus (NIDDM) rats with a dose of 4 mg/kg per day for 6 weeks. Oral administration of losartan improved insulin sensitivity, which was determined by an oral glucose tolerance test (OGTT). In skeletal muscles, the protein levels of IRS-1, PKB and GLUT4 in NIDDM rats were not significantly different from those of the control rats, and they were not affected by losartan. The levels of IRS-1 tyrosine phosphorylation, PI 3-kinase activity associated with IRS-1 and PKB activation after stimulation with insulin in muscle tissue of NIDDM rats were significantly decreased (P<0.01) compared with those in the control rats, while they were not increased by losartan. Losartan had a major effect on GLUT4 translocation in myocytes, as it significantly increased (P<0.05) the insulin-induced amounts of GLUT4 in plasma membrane (PM) and T-tubules (TT) in myocytes from NIDDM rats. Consistent with these results, the plasma glucose level in losartan-treated NIDDM rats was decreased (P<0.05) compared with that in untreated NIDDM rats. Our results suggest that losartan may exert beneficial effects on insulin resistance by increasing the translocation of GLUT4 in muscle tissue, which is probably associated with a non-PI 3-kinase-dependent mechanism.
Animals ; Diabetes Mellitus, Experimental ; blood ; drug therapy ; Diabetes Mellitus, Type 2 ; blood ; drug therapy ; physiopathology ; Glucose Transporter Type 4 ; Insulin Receptor Substrate Proteins ; Insulin Resistance ; Losartan ; pharmacology ; therapeutic use ; Male ; Monosaccharide Transport Proteins ; biosynthesis ; genetics ; Muscle Proteins ; biosynthesis ; genetics ; Muscle, Skeletal ; metabolism ; Phosphoproteins ; biosynthesis ; genetics ; Protein-Serine-Threonine Kinases ; biosynthesis ; genetics ; Proto-Oncogene Proteins ; biosynthesis ; genetics ; Proto-Oncogene Proteins c-akt ; Rats ; Rats, Sprague-Dawley

The present study was undertaken to evaluate the influence of the methanolic fruit extract of Momordica cymbalaria (MFMC) on PPARγ (Peroxisome Proliferator Activated Receptor gamma) and GLUT-4 (Glucose transporter-4) with respect to glucose transport. Various concentrations of MFMC ranging from 62.5 to 500 μg·mL(-1) were evaluated for glucose uptake activity in vitro using L6 myotubes, rosiglitazone was used as a reference standard. The MFMC showed significant and dose-dependent increase in glucose uptake at the tested concentrations, further, the glucose uptake activity of MFMC (500 μg·mL(-1)) was comparable with rosigilitazone. Furthermore, MFMC has shown up-regulation of GLUT-4 and PPARγ gene expressions in L6 myotubes. In addition, the MFMC when incubated along with cycloheximide (CHX), which is a protein synthesis inhibitor, has shown complete blockade of glucose uptake. This indicates that new protein synthesis is required for increased GLUT-4 translocation. In conclusion, these findings suggest that MFMC is enhancing the glucose uptake significantly and dose dependently through the enhanced expression of PPARγ and GLUT-4 in vitro.
Biological Transport ; Dose-Response Relationship, Drug ; Fruit ; Gene Expression ; drug effects ; Glucose ; metabolism ; Glucose Transporter Type 4 ; metabolism ; Hypoglycemic Agents ; pharmacology ; In Vitro Techniques ; Insulin ; metabolism ; Momordica ; Muscle Fibers, Skeletal ; drug effects ; PPAR gamma ; metabolism ; Plant Extracts ; pharmacology ; Protein Biosynthesis ; Protein Synthesis Inhibitors ; pharmacology ; Rosiglitazone ; Thiazolidinediones ; pharmacology ; Up-Regulation