Fluid shear stress induces upregulation of COX-2 and PGI release in endothelial cells via a pathway involving PECAM-1, PI3K, FAK, and p38.

Vascular endothelial cells play an important role in the regulation of vascular function in response to mechanical stimuli in both healthy and diseased states. Prostaglandin I (PGI) is an important antiatherogenic prostanoid and vasodilator produced in endothelial cells through the action of the cyclooxygenase (COX) isoenzymes COX-1 and COX-2. However, the mechanisms involved in sustained, shear-induced production of COX-2 and PGI have not been elucidated but are determined in the present study. We used cultured endothelial cells exposed to steady fluid shear stress (FSS) of 10 dyn/cm for 5 h to examine shear stress-induced induction of COX-2/PGI Our results demonstrate the relationship between the mechanosensor platelet endothelial cell adhesion molecule-1 (PECAM-1) and the intracellular mechanoresponsive molecules phosphatidylinositol 3-kinase (PI3K), focal adhesion kinase (FAK), and mitogen-activated protein kinase p38 in the FSS induction of COX-2 expression and PGI release. Knockdown of PECAM-1 (small interference RNA) expression inhibited FSS-induced activation of αβ-integrin, upregulation of COX-2, and release of PGI in both bovine aortic endothelial cells (BAECs) and human umbilical vein endothelial cells (HUVECs). Furthermore, inhibition of the PI3K pathway (LY294002) substantially inhibited FSS activation of αβ-integrin, upregulation of COX-2 gene and protein expression, and release of PGI in BAECs. Inhibition of integrin-associated FAK (PF573228) and MAPK p38 (SB203580) also inhibited the shear-induced upregulation of COX-2. Finally, a PECAM-1 mouse model was characterized by reduced COX-2 immunostaining in the aorta and reduced plasma PGI levels compared with wild-type mice, as well as complete inhibition of acute flow-induced PGI release compared with wild-type animals. In this study we determined the major mechanotransduction pathway by which blood flow-driven shear stress activates cyclooxygenase-2 (COX-2) and prostaglandin I (PGI) release in endothelial cells. Our work has demonstrated for the first time that COX-2/PGI mechanotransduction is mediated by the mechanosensor platelet endothelial cell adhesion molecule-1 (PECAM-1).