Oleic Acid Stimulates Glucose Uptake Into Adipocytes by Enhancing Insulin Receptor Signaling

The present study investigated cis-unsaturated free fatty acid (FFA)-regulated glucose uptake. In the cell-free assay of protein tyrosine phosphatase 1B (PTP1B), cis-unsaturated FFAs such as linoleic, linolenic, and oleic acid significantly suppressed PTP1B activity in a concentration (1 - 100 mu M)-dependent manner, with the highest potential for oleic acid. Oleic acid (1 mu M) stimulated insulin (0.1 nM)-induced phosphorylation of the insulin receptor at Tyr1185 and increased insulin (0.1 nM)-induced phosphorylation of Akt at Thr308 and Ser473 in differentiated 3T3-L1-GLUT4myc adipocytes. In the foerster resonance energy transfer analysis, oleic acid activated Racl in PC-12 cells, which is inhibited by the phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin, the 3-phosphoinositide-dependent protein kinase-1 (PDK1) inhibitor BX912, or the Akt inhibitor MK2206. Oleic acid (1 mu M) significantly increased insulin (0.1 nM)stimulated glucose uptake in 3T3-L1-GLUT4myc adipocytes, although oleic acid by itself had no effect on the glucose uptake. Taken together, the results of the present study show that oleic acid enhances insulin receptor signaling through a pathway along an insulin receptor/PI3K/PDK1/Akt/Racl axis in association with PTP1B inhibition and facilitates insulin-induced glucose uptake into adipocytes.