TGF-β/SMAD4 mediated UCP2 downregulation contributes to Aspergillus protease-induced inflammation in primary bronchial epithelial cells

Abstract

Elevated levels of mitochondrial reactive oxygen species (ROS) can lead to the development of airway inflammation. In this study, we investigated the role of Aspergillus proteases—which contribute to the pathogenesis of Aspergillus-induced diseases such as allergic bronchopulmonary aspergillosis, hypersensitivity pneumonitis, and atopic asthma—and their mechanisms of action in airway inflammation using primary human bronchial epithelial cells, and evaluated the inflammatory responses mediated by mitochondrial ROS. We found that Aspergillus proteases regulated the expression of multifunctional inflammatory cytokines such as interleukin (IL)− 1β, − 6, and − 8, and transforming growth factor (TGF)-β, which stimulated cytokine production and chemokines involved in leukocyte migration and activated an inflammatory cascade. Expression of these factors and activator protein (AP)− 1 were decreased by treatment with the mitochondrial ROS scavenger Mito-TEMPO, suggesting that mitochondria are important sources of ROS in the context of inflammatory response by Aspergillus protease. The regulation of mitochondrial ROS influenced the production of proinflammatory mediators by preventing mitochondrial ROS-induced AP-1 activation in airway epithelial cells. In addition, Aspergillus protease-mediated mitochondrial ROS production was associated with downregulation of uncoupling protein (UCP)− 2 expression by TGF-β-SMAD4 signaling, which may play a regulatory role in mitochondrial ROS formation during fungal protease-mediated epithelial inflammation. This improved understanding of the allergenic fungal protease-induced inflammatory mechanism in the bronchial epithelium will help in developing intervention strategies for the regulation of inflammatory response in allergic airway diseases. Keywords: Aspergillus protease, Airway epithelial cells, Mitochondrial ROS, UCP-2, TGF-β-SMAD4 signaling