NO Modulates Monocyte Chemotactic Protein-1 Expression in Endothelial Cells Under Cyclic Strain

Endothelial cells (ECs) under hemodynamic forces increase intracellular reactive oxygen species (ROS) that modulate gene expression. We previously showed that NO attenuated the shear flow–induced gene level. The present study explored the role of endothelial NO in cyclic strain–treated ECs. Treatment of ECs with S-nitroso-N-acetylpenicillamine (SNAP), an NO donor, reduced cyclic strain–induced monocyte chemotactic protein (MCP)-1 expression. Conversely, exposure of ECs to an NO synthase inhibitor augmented MCP-1 mRNA levels. NO attenuated the binding of activator protein-1 to the 12-O-tetradecanoylphobol-13-acetate–responsive element (TRE) in the MCP-1 promoter region. ECs overexpressed with endothelial NO synthase (eNOS) inhibited cyclic strain–induced MCP-1 expression and MCP-1 promoter (−540 bp) activity. Consistently, ECs treated with SNAP or infected with adenovirus carrying eNOS reduced strain-induced superoxide levels. These strain-induced superoxide and MCP-1 expressions were greatly blunted by treating ECs with an NADPH oxidase inhibitor, diphenyleneiodonium chloride or apocynine, but not with a xanthine oxidase inhibitor. ECs infected with adenovirus carrying the dominant-negative mutant of Rac (RacN17), a component of NADPH oxidase, reduced the strain-induced superoxide and MCP-1 expression. In contrast, ECs transfected with a constitutively active Rac (RacV12) increased MCP-1 and 4× TRE promoter activities. However, ECs cotransfected with eNOS and RacV12 reduced those promoter activities. Consistently, the increases of superoxide levels and MCP-1 expression by overexpression of RacV12 were abolished after infecting ECs with eNOS. Our results show that NO from eNOS-inhibiting redox-sensitive MCP-1 expression is mediated via Rac-dependent NADPH oxidase by reducing ROS. This study provides a molecular basis to support the notion that endothelial NO acts as an antioxidant by negatively regulating redox-sensitive gene expression in ECs constantly under hemodynamic influence.