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Fluid shear stress induces upregulation of COX‐2 and PGI2 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 I2 (PGI2) is an important anti‐atherogenic prostanoid and vasodilator produced in endothelial cells through the action of cyclooxygenase (COX) isoenzymes COX‐1 and COX‐2. However, the mechanisms involved in shear‐induced production of COX‐2 and PGI2 have not been elucidated. We used cultured endothelial cells exposed to steady fluid shear stress (FSS) of 10 dyn/cm2 for 5‐hrs to examine shear stress induced induction of COX‐2/PGI2. Our results demonstrate the relationship between mechanosensor platelet endothelial cell adhesion molecule‐1 (PECAM‐1) and intracellular mechano‐responsive molecules phosphatidylinositol 3‐kinase (PI3K), focal adhesion kinase (FAK), and mitogen‐activated protein kinase p38, in the FSS induction of COX‐2 expression and PGI2 release. Knockdown of PECAM‐1 (small interference RNA) expression inhibited FSS‐induced activation of α5β1 integrin, upregulation of COX‐2 and release of PGI2 in both bovine aortic endothelial cells (BAECs) and human umbilical cord endothelial cells (HUVECs). Furthermore, inhibition of the PI3K pathway (LY294002)substantially inhibited FSS activation of α5β1 integrin, upregulation of COX‐2 gene and protein expression and release of PGI2 in BAECs, while we showed that inhibition of integrin associated FAK (PF573228), and MAPK p38 (SB203580) also inhibited the shear induced up‐regulation of COX‐2. Finally, a PECAM‐1 −/− mouse model was characterized by reduced COX‐2 immunostaining in the aorta and reduced plasma PGI2 levels compared to wild type mice, as well as complete inhibition of acute flow‐induced PGI2 release compared to wild type animals.