Downregulation of catalase by reactive oxygen species via PI 3 kinase/Akt signaling in mesangial cells

Reactive oxygen species (ROS) contribute to many glomerular diseases by targeting mesangial cells. ROS have been shown to regulate expression of many antioxidant enzymes including catalase. The mechanism by which the expression of catalase protein is regulated by ROS is not precisely known. Here we report that increased intracellular ROS level by hydrogen peroxide (H₂O ₂) reduced the expression of catalase. H₂O₂ increased phosphorylation of Akt kinase in a dose-dependent and sustained manner with a concomitant increase in the phosphorylation of FoxO1 transcription factor. Further analysis revealed that H₂O₂ promoted rapid activation of phosphatidylinositol (PI) 3 kinase. The PI 3 kinase inhibitor Ly294002 and expression of tumor suppressor protein PTEN inhibited Akt kinase activity, resulting in the attenuation of FoxO1 phosphorylation and preventing the down regulating effect of H₂O₂ on catalase protein level. Dominant negative Akt attenuated the inhibitory effect of H ₂O₂ on expression of catalase. Constitutively active FoxO1 increased the expression of catalase. However, dominant negative FoxO1 inhibited catalase protein level. Catalase transcription was reduced by H ₂O₂ treatment. Furthermore, expression of dominant negative Akt and constitutively active FoxO1 increased catalase transcription, respectively. These results demonstrate that ROS downregulatethe expression of catalase in mesangial cells by PI 3 kinase/Akt signaling via FoxO1 as a target.