Synergistic suppression of IRS-1 expression by ET-1 and cAMP is mediated by AP-2β in 3T3-L1 adipocytes
| Autor: | Pu-Hung Kao, 高浦宏 |
|---|---|
| Rok vydání: | 2013 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 101 【Abstract】 ET-1 is a 21-amino acid polypeptide. infusion of ET-1 into healthy humans and rats was shown to cause insulin resistance. Moreover, ET-1 was shown to inhibit insulin-stimulated glucose uptake in 3T3-L1 adipocytes. β-Adrenergic agonists have been well known for impairing insulin action and their inhibitory effects seem to be mediated by cyclic AMP. In our preliminary studys, while ET-1 alone had only a minor non-significant inhibitory influence and 8-bromo cAMP permealte(analogue of cyclic AMP) alone only exerted significant inhibitory effect at 48 h, a combination of ET-1 and 8-bromo cAMP significantly inhibited insulin-stimulated glucose uptake at a much faster pace and this inhibition was getting stronger with time. We also found ET-1 and cAMP had a synergistic effect on IL-6 secretion, attributable to their synergistic effect on IL-6 expression. ET-1 and cAMP also interact cooperatively to attenuate IRS-1 expression and consequently, insulin signaling and insulin-stimulated glucose uptake. The inhibition evoked by ET-1 and cAMP on insulin-stimulated PKB phosphorylation and insulin-stimulated glucose uptake was no longer observed in the presence of neutralizing anti-IL-6 antibody. The effect of ET-1 and cAMP on IRS-1 protein or mRNA levels, on the other hand, was not affected by anti-IL-6 antibody. In this study, We found that ET-1 and 8-bromo cAMP increased AP-2β protein by MAPK pathway, and AP-2β binding to the AP-2β binding site on IRS-1 promoter (-362/-351), caused the inhibitory of ET-1 and cAMP on IRS-1 transcription. To further validate this notion, we knocked down AP-2β by RNAi and determined IRS-1 protein levels in cells exposed to ET-1 plus cAMP. We found that shRNA against AP-2β greatly reversed the decrease in IRS-1 quantity. In addition, knocked down AP-2β also reduced the induction of IL-6 by ET-1 and cAMP, and restore the insulin-stimulated PKB phosphorylation and insulin-stimulated glucose uptake. Furthermore, ET-1 and cAMP synergistic inhibited leptin and adiponectin mRNA expression, and knocking down AP-2β reversed the decrease in leptin, but not adiponectin. Taken together, the suppression of IRS-1 expression by ET-1 and cAMP appears to be mediated by AP-2β. AP-2βalso up-regulate IL-6 expression, impairing insulin-stimulated PKB phosphorylation and insulin-stimulated glucose uptake. In conclusion, ET-1 and β-adrenergic agonists (via cAMP) may act synergistically to induce insulin resistance, primarily mediated by AP-2β. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
| Externí odkaz: |
|