Oscillatory Shear Stress Stimulates Endothelial Production of O ₂^- from p47^phox-dependent NAD(P)H Oxidases, Leading to Monocyte Adhesion

Arterial regions exposed to oscillatory shear (OS) in branched arteries are lesion-prone sites of atherosclerosis, whereas those of laminar shear (LS) are relatively well protected. Here, we examined the hypothesis that OS and LS differentially regulate production of O₂^- from the endothelial NAD(P)H oxidase, which, in turn, is responsible for their opposite effects on a critical atherogenic event, monocyte adhesion. We used aortic endothelial cells obtained from C57BL6 (MAE-C57) and p47^phox-/- (MAE-p47^-/-) mice, which lack a component of NAD(P)H oxidase. O ₂^- production was determined by dihydroethidium staining and an electron spin resonance using an electron spin trap methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine. Chronic exposure (18 h) to an arterial level of OS (± 5 dynes/cm²) increased O ₂^- (2-fold) and monocyte adhesion (3-fold) in MAE-C57 cells, whereas chronic LS (15 dynes/cm², 18 h) significantly decreased both monocyte adhesion and O₂^- compared with static conditions. In contrast, neither LS nor OS were able to induce O ^2- production and monocyte adhesion to MAE-p47 ^-/-. Treating MAE-C57 with a cell-permeable superoxide dismutase compound, polyethylene glycol-superoxide dismutase, also inhibited OS-induced monocyte adhesion. In addition, over-expressing p47^phox in MAE ^-/-p47^-/- restored OS-induced O₂^- production and monocyte adhesion. These results suggest that chronic exposure of endothelial cells to OS stimulates O₂^- and/or its derivatives produced from p47^phox-dependent NAD(P)H oxidase, which, in turn, leads to monocyte adhesion, an early and critical atherogenic event.