Both the NADPH oxidase and the mitochondrial respiratory chain regulate chemokine gene expression.

Abstract

Alveolar macrophages are involved in the pathogenesis of immune and inflammatory disorders of the lung. One hallmark of the cellular response to inflammation is the recruitment of neutrophils to sites of inflammation. The generation of chemotactic proteins, such as MIP-2, triggers neutrophil recruitment. We have previously shown that alveolar macrophages spontaneously generate high levels of ROS, especially O2.−-, and their high catalase and glutathione peroxidase activity limits the effectiveness of H2O2 to act as a signaling mediator. In this study, we ask if O2.− generation in alveolar macrophages had a role in the expression of inflammatory genes. Specifically, we hypothesized that O2.− generation is necessary for MIP-2 gene expression in alveolar macrophages after TNF-α stimulation. We found that TNF-α increased O2.− generation by activating both NADPH oxidase and the mitochondrial respiratory chain in alveolar macrophages. TNF-α-induced O2.− generation was necessary for MIP-2 gene expression because inhibition of NADPH oxidase, the mitochondrial respiratory chain, or over expression of SOD significantly inhibited expression of MIP-2. In addition, TNF-α-induced NADPH oxidase and mitochondrial respiratory chain activity were necessary for ERK MAP kinase activation, and ERK activity was essential for MIP-2 gene expression. Furthermore, over expression of a constitutive active MEK1, the upstream kinase that activates ERK, significantly increased TNF-α-induced chemokine gene expression. These results suggest that in alveolar macrophages, O2.− generation from both NADPH oxidase and the mitochondrial respiratory chain mediates MIP-2 gene expression after TNF-α stimulation in an ERK-dependent manner.