Reactive oxygen species mediate cyclooxygenase-2 induction during monocyte to macrophage differentiation : critical role of NADPH oxidase

OBJECTIVE: The objective of this study was to explore the relationship between monocyte differentiation into macrophages and cyclooxygenase-2 (Cox-2) expression, based upon the observation that high amounts of this enzyme, colocalizing mainly with macrophages, have been found in human atherosclerotic lesions. Moreover, the hypothesis that reactive oxygen species (ROS) could be important as mediators of Cox-2 expression during monocyte differentiation was verified. Although ROS are known as modulators of gene expression profile, their involvement in monocyte differentiation has not been explored previously. METHODS: Human adherent monocytes and the promonocytic cell line U937 were differentiated into macrophages by phorbol ester (PMA). Cox-2 was evaluated in terms of protein, mRNA and activity. Intracellular ROS formation was measured by the oxidant sensitive dye 2',7'-dichlorofluorescein diacetate. NADPH oxidase subunit p47(phox) was evaluated by Western blot analysis. RESULTS: Functionally active Cox-2 is expressed during PMA-induced monocyte transition into macrophages and ROS driven by the NADPH oxidase play a critical role in this event. CONCLUSION: Monocyte differentiation into macrophages, possibly triggered by unquenched ROS, may contribute to the increased inflammatory response within atheromata.