TNF-alpha inhibits flow and insulin signaling leading to NO production in aortic endothelial cells

Endothelial cells release nitric oxide(NO) acutely in response to increased "flow" or fluid shear stress(FSS), and the increase in NO production is correlated with enhancedphosphorylation and activation of endothelial nitric oxide synthase(eNOS). Both vascular endothelial growth factor and FSS activateendothelial protein kinase B (PKB) by way of incompletely understoodpathway(s), and, in turn, PKB phosphorylates eNOS at Ser-1179, causingits activation. In this study, we found that either FSS or insulinstimulated insulin receptor substrate-1 (IRS-1) tyrosine and serinephosphorylation and increased IRS-1-associated phosphatidylinositol3-kinase activity, phosphorylation of PKB Ser-473, phosphorylation ofeNOS Ser-1179, and NO production. Brief pretreatment of bovine aorticendothelial cells with tumor necrosis factor- (TNF-) inhibitedthe above described FSS- or insulin-stimulated protein phosphorylationevents and almost totally inhibited FSS- or insulin-stimulated NOproduction. These data indicate that FSS and insulin regulate eNOSphosphorylation and NO production by overlapping mechanisms. This studysuggests one potential mechanism for the development of endothelialdysfunction in disease states with alterations in insulin regulationand increased TNF- levels.