Shear stress induces iNOS expression in cultured smooth muscle cells: role of oxidative stress.

After deendothelialization, the most luminal smooth muscle cells of the neointima are in contact with blood flow and express inducible nitric oxide synthase (iNOS) in vivo. We hypothesized that shear stress may be a stimulus for this iNOS overexpression. We have thus submitted smooth muscle cells to laminar shear and measured the iNOS expression. Shear stress (20 dyn/cm(2)) induced iNOS mRNA and protein expression, whereas brain NOS mRNA expression was decreased. Conversely, nitrite production was increased. This production was blocked by a selective iNOS inhibitor. Pyrrolidine dithiocarbamate, an antioxidant molecule, and BXT-51072, a gluthation peroxidase mimic, both inhibited the shear-induced iNOS expression. Shear stress also increased the expression of both membrane subunits of NADPH oxidase p22(phox) and Mox-1. Shear stress activated the redox-sensitive nuclear translocation of the transcription nuclear factor-kappaB (NF-kappaB) and stimulated the degradation of both cytosolic inhibitors kappaB alpha and beta. These results show that shear stress can induce iNOS expression and nitrite production in smooth muscle cells and suggest that this regulation is probably mediated by oxidative stress-induced NF-kappaB activation.