REACTIVE OXYGEN SPECIES ARE INVOLVED IN SHEAR STRESS-INDUCED INTERCELLULAR-ADHESION MOLECULE-1 EXPRESSION IN ENDOTHELIAL-CELLS

Vascular endothelial cells (ECs) are constantly subjected to flow-indu ced shear stress. Although the effects of shear stress on ECs are well known, the intracellular signal mechanisms remain largely unclear. Re active oxygen species (ROS) have recently been suggested to act as int racellular second messengers. The potential role of ROS in shear-induc ed gene expression was examined in the present study by subjecting ECs to a shear force using a parallel-plate flow chamber system. ECs unde r shear flow increased their intracellular ROS as indicated by superox ide production. This superoxide production was maintained at an elevat ed level as shear flow remained. Sheared ECs, similar to TNFalpha-, PM A-, or H2O2-treated cells, increased their intercellular adhesion mole cule-1 (ICAM-1) mRNA levels in a time-dependent manner. Pretreatment o f ECs with an antioxidant, N-acetyl-cysteine (NAC) or catalase, inhibi ted this shear-induced or oxidant-induced ICAM-1 expression. ROS that were involved in the shear-induced ICAM-1 gene expression were further substantiated by functional analysis using a chimera containing the I CAM-1 promoter region (-850 bp) and the reporter gene luciferase. Shea r-induced promoter activities were attenuated by pretreating sheared E Cs with NAC and catalase. Flow cytometric analysis and monocytic adhes ion assay confirmed the inhibitory effect of NAC and catalase on the s hear-induced ICAM-1 expression on ECs. These results clearly demonstra te that shear flow to ECs can induce intracellular ROS generation that may result in an increase of ICAM-1 mRNA levels via transcriptional e vents. Our findings thus support the importance of intracellular ROS i n modulating hemodynamically induced endothelial responses.