Phosphatidylinositol 3-kinase/protein kinase Akt negatively regulates plasminogen activator inhibitor type 1 expression in vascular endothelial cells

Abstract

Plasminogen activator inhibitor type 1 (PAI-1) regulates fibrinolytic activity and mediates vascular atherothrombotic disease. Endothelial cells (ECs) synthesize and secrete PAI-1, but the intracellular signaling pathways that regulate PAI-1 expression are not entirely known. We hypothesize that the phosphatidylinositol 3-kinase (PI3K)/protein kinase Akt pathway, which regulates endothelial function, could modulate PAI-1 expression in ECs. Cultured bovine aortic and human saphenous vein ECs were stimulated with TNF-alpha, ANG II, insulin, or serum, and PAI-1 expression was determined by Northern and Western analyses. Inhibition of PI3K with wortmannin or LY-294002 enhanced PAI-1 expression induced by these extracellular stimuli. Similarly, overexpression of a dominant-negative mutant of PI3K or Akt increased TNF-alpha- and insulin-induced PAI-1 expression. The increase in PAI-1 was due to transcriptional and posttranscriptional mechanisms as PI3K inhibitors increased PAI-1 promoter activity and mRNA stability. The induction of PAI-1 by TNF-alpha and insulin is mediated, in part, by ERK and p38 MAPK. PI3K inhibitors augmented TNF-alpha- and insulin-induced phosphorylation of these MAPKs. Simvastatin, a 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor, which is known to activate PI3K/Akt, blocks TNF-alpha- and insulin-induced PAI-1 expression. Treatment with PI3K inhibitors reversed the inhibitor effects of simvastatin on TNF-alpha- and insulin-induced PAI-1 expression. These findings indicate that the PI3K/Akt pathway acts as a negative regulator of PAI-1 expression in ECs, in part, through the downregulation of MAPK pathways. These results suggest that factors that activate the PI3K/Akt pathway in ECs may have therapeutic benefits for atherothrombotic vascular disease.