Selenium-enriched exopolysaccharides (EPS) produced by Enterobacter cloacae Z0206 have been proven to possess effect on reducing blood glucose level in diabetic mice. To investigate the specific mechanism, we studied the effects of oral supply with EPS on skeletal muscle glucose transportation and consumption in high-fat-diet-induced diabetic KKAy mice. We found that EPS supplementation increased expressions of glucose transporter 4 (Glut4), hexokinase 2 (hk2), phosphorylation of AMP-activated kinase subunit α2 (pAMPKα2), and peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), and increased expression of characteristic protein of oxidative fibers such as troponin I and cytochrome c (Cytc). Furthermore, we found that EPS increased glucose uptake and expressions of pAMPKα2 and PGC-1α in palmitic acid (PA)-induced C2C12 cells. However, while EPS inhibited AMPKα2 with interference RNA (iRNA), effects of EPS on the improvement of glucose uptake diminished. These results indicated that EPS may improve skeletal muscle glucose uptake of diabetic KKAy mice through AMPKα2-PGC-1α pathway.
Abstract. Polysaccharides belong to a structurally diverse class of macromolecules, with the necessary flexibility for the precise regulatory mechanisms and high capacity for carrying biological information. On the basis of a previous study regarding the administration of selenium-enriched exopolysaccharides (Se-ECZ-EPS) produced by Enterobacter cloacae (E. cloacae) Z0206 which resulted in a reduction of blood glucose levels and showed significant anti-inflammatory and anti-diabetic effects, the present study was conducted to evaluate the effects and mechanism of EPS on the alleviation of fat inflammation in high-fat-diet (HFD) induced-diabetic KKAy mice. The HFD induced-diabetic KKAy mice were gavaged once daily with EPS (0.2 mg/g body weight) or distilled water, while the C57BL/6J mice were gavaged with distilled water. Six weeks later visceral adipose tissue (VAT) was collected for quantified polymerase chain reaction (qPCR) and western blot (WB) analysis. The results showed that following supplementation with EPS, interleukin (IL) 6, IL1β and tumor necrosis factor (TNF) α mRNA expression in VAT were significantly reduced, while Glut4, pAMPK and SirT1 protein expression were markedly increased when compared with KKAy mice gavaged with water. Furthermore, ATGL and HSL mRNA were also significantly decreased. Subsequently, 3T3-L1 adipocytes were treated with insulin to induce insulin resistance to determine the mechanism by which EPS affects inflammation. Following the treatment of adipocytes with 100 nM insulin for 8 h, IL6 and TNFα mRNA expression were significantly increased, while the content of glucose uptake and Glut4 protein expression were significantly decreased. When treated with 100 nM insulin and 0.1 mg/ml EPS, no significant change in IL6 and TNFα mRNA expression or glucose uptake were observed. However, when SirT1-siRNA or AMPKα1-siRNA was tranfected into the 3T3-L1 adipocytes prior to treatment with insulin and EPS, there was a significant increase in IL6 and TNFα mRNA abundance. In conclusion, VAT inflammation and lipolysis in HFD-induced KKAy mice were significantly decreased following EPS usage. Moreover, EPS may alleviate VAT inflammation primarily through the AMPK/SirT1 pathway.
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