The Effect Of Dexamethasone On Glucose Transport And The Signaling Proteins In 3T3-L1 Adipocyte

Objective: To study the effects of dexamethasone (DEX) on the glucose transport system, glucose transporer(Glut1 and Glut4), the PI-3K/AKT and p38 MAPK insulin signaling pathways in 3T3-L1 adipocytes, investigate the possible mechanism in glucocorticoid induced insulin resistance.Methods: 1. The 3T3-L1 adipocytes were exposed to DEX for 48h and incubated for an additional 30 min with or without 100 nmol/L insulin, the basal and insulin-stimulated glucose uptake were measured by detecting the glucose content in cell culture supernatants. Then the expression of Glut1 and Glut4 in total cell lysates was measured with western blotting. The expression of Glut4 in separated plasma membrance was also detected to evaluate the insulin-induced traslocation of Glut4. 2. After the 3T3-L1 adipocytes were exposed to DEX, the insulin signaling proteins Akt, phospho-Akt, p38 MAPK, phospho-p38 MAPK were measured with western blotting.Results: 1. DEX inhibited both basal and insulin stimulated glucose transport capacity of 3T3-L1 adipocytes in a dose-dependent manner. 1μmol/L DEX impired both basal and insulin stimulated glucose uptake by 80% and 75%(P<0.05).In 3T3-L1 adipocytes treated with DEX, the Glut1 protein expression level was decreased by 41%(P<0.01). DEX did not alter the amount of Glut4 protein in total cell lysates but attenuated the insulin-stimulated Glut4 translocation to the plasma membrane by 34%(P<0.01). 2. In 3T3-L1 adipocytes treated with DEX, DEX did not alter the expression of Akt and p38 MAPK, but significantly inhibited insulin stimulated phosphorylation of Akt, p38 MAPK by 35% and 57%(P<0.01).Conclusions: 1.These results suggest that DEX impaired both basal and insulin stimulated glucose transport capacity. DEX ruduced Glut1 abundance possibly caused decreased basal glucose uptake. DEX inhibited insulin stimulated Glut4 translocation, which may contribute to impair insulin stimulated glucose uptake. 2. DEX impaired glucose transport capacity in 3T3-L1 adipocytes was mediated via attenuated insulin stimulated activation of PI-3K/AKT and p38 MAPK pathways, reduced insulin stimulated Glut4 translocation and transport activity. These may lead to insulin resistance in 3T3-L1 adipocytes.