Background— In the endothelium, insulin promotes nitric oxide (NO) production, through the insulin receptor/IRS-1/PI3-Kinase/Akt/eNOS signaling pathway. An inhibitor of insulin action, TRIB3, has recently been identified which affects insulin action by binding to and inhibiting Akt phosphorylation. We have recently described a Q84R gain-of-function polymorphism of TRIB3 with the R84 variant being associated with insulin resistance and an earlier age at myocardial infarction.

Methods and Results— To investigate the TRIB3 R84 variant impact on endothelial insulin action, we cultured human umbilical vein endothelial cells (HUVECs) naturally carrying different TRIB3 genotypes (QQ-, QR-, or RR-HUVECs). TRIB3 inhibitory activity on insulin-stimulated Akt phosphorylation and the amount of protein which was coimmunoprecipitable with Akt were significantly greater in QR- and RR- as compared to QQ- HUVECs. After insulin stimulation, Akt and eNOS activation as well as NO production were markedly decreased in QR- and RR- as compared to QQ-HUVECs. TRIB3 molecular modeling analysis provided insights into the structural changes related to the polymorphisms potentially determining differences in protein-protein interaction with Akt.

Conclusions— Our data demonstrate that the TRIB3 R84 variant impairs insulin signaling and NO production in human endothelial cells. This finding provides a plausible biological background for the deleterious role of TRIB3 R84 on genetic susceptibility to coronary artery disease.