Objective—Macrophage foam cells are characterized by increased oxidative stress. Macrophage urokinase plasminogen activator (uPA) was shown to contribute to atherosclerosis progression. We hypothesized that uPA atherogenicity is related to its ability to increase macrophage oxidative stress. Increased macrophage oxidative stress in turn was shown to enhance PON2 expression. In the present study we investigated the effect of uPA on macrophage PON2 expression in relation to cellular oxidative stress.

Methods and Results—uPA increased PON2 expression in THP-1 macrophages in a dose-dependent manner. This effect required uPA/uPAR interaction and was abolished by cell treatment with antioxidants. uPA increased macrophage oxidative stress, measured by increased lipid peroxides, reactive oxygen species formation, superoxide anion release, and cell-mediated LDL oxidation. These effects were related to uPA-mediated activation of NADPH oxidase, and could not be reproduced in mouse peritoneal macrophages (MPM) harvested from p47^phox-/- mice, suggesting a causal relationship between NADPH oxidase activation and the effects of uPA on macrophage oxidative stress and PON2 expression. Finally, MPM from PON2^-/- mice were more susceptible to uPA-induced cellular oxidative stress than wild-type MPM, suggesting that PON2 protects against uPA-stimulated macrophage oxidative stress.

Conclusions—Upregulation of macrophage PON2 may provide a compensatory protective mechanism against uPA-stimulation of macrophage oxidative stress during atherogenesis.