Abstract
Exposure of insulin-sensitive tissues to free fatty acids can impair glucose disposal through inhibition of carbohydrate oxidation and glucose transport. However, certain fatty acids and their derivatives can also act as endogenous ligands for peroxisome proliferator-activated receptor gamma (PPARgamma), a nuclear receptor that positively modulates insulin sensitivity. To clarify the effects of externally delivered fatty acids on glucose uptake in an insulin-responsive cell type, we systematically examined the effects of a range of fatty acids on glucose uptake in 3T3-L1 adipocytes. Of the fatty acids examined, arachidonic acid (AA) had the greatest positive effects, significantly increasing basal and insulin-stimulated glucose uptake by 1.8- and 2-fold, respectively, with effects being maximal at 4 h at which time membrane phospholipid content of AA was markedly increased. The effects of AA were sensitive to the inhibition of protein synthesis but were unrelated to changes in membrane fluidity. AA had no effect on total cellular levels of glucose transporters, but significantly increased levels of GLUT1 and GLUT4 at the plasma membrane. While the effects of AA were insensitive to cyclooxygenase inhibition, the lipoxygenase inhibitor, nordihydroguaiaretic acid, substantially blocked the AA effect on basal glucose uptake. Furthermore, adenoviral expression of a dominant-negative PPARgamma mutant attenuated the AA potentiation of basal glucose uptake. Thus, AA potentiates basal and insulin-stimulated glucose uptake in 3T3-L1 adipocytes by a cyclooxygenase-independent mechanism that increases the levels of both GLUT1 and GLUT4 at the plasma membrane. These effects are at least partly dependent on de novo protein synthesis, an intact lipoxygenase pathway and the activation of PPARgamma with these pathways having a greater role in the absence than in the presence of insulin.
Highlights
Exposure of insulin-sensitive tissues to free fatty acids can impair glucose disposal through inhibition of carbohydrate oxidation and glucose transport
arachidonic acid (AA) potentiates basal and insulin-stimulated glucose uptake in 3T3-L1 adipocytes by a cyclooxygenase-independent mechanism that increases the levels of both GLUT1 and GLUT4 at the plasma membrane
The recently established fact that certain fatty acids and their metabolites can act as endogenous ligands for the nuclear hormone receptor PPAR␥ provides a potential mechanism [15]
Summary
Materials—2-Deoxy-D-[2,6-3H]glucose, [1-14C]AA, and the enhanced chemiluminescence (ECL) kit were purchased from Amersham Pharmacia Biotech. This solution was diluted 1:10 into serum-free DMEM (containing 25 mM glucose and 2 mM glutamine) for studies with up to 4-h incubation times, or into DMEM/FBS for studies with Ͼ4-h incubation times This gives a final concentration of 8 ϫ 10Ϫ4 M fatty acid and 0.4% ethanol. In the time course experiment, incubations of 48 and h were commenced on days 7 and 8 of differentiation, respectively, and on day 9 cells were serum-starved in DMEM (containing mM glucose and 2 mM glutamine) for 2 h prior to the assay. 3T3-L1 adipocytes (day 9) in six-well plates were supplemented with 2 ml of medium containing 0.05 Ci of [1-14C]AA per well for 2, 4, 6, 8, and 10 h At these time points, media was removed and cells were washed twice with PBS. Statistical significance of treatments was determined using the paired Student’s t test (*, p Ͻ 0.05; **, p Ͻ 0.01; ***, p Ͻ 0.001)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
