Lung fibrosis is the primary pathology in idiopathic pulmonary fibrosis and is considered to result from an increase in reactive oxygen species (ROS) levels in alveolar epithelial cells. However, the exact mechanism underlying lung fibrosis remains unclear and there is no effective therapy. The hydroxyl radical (•OH) has the strongest oxidizing potential among ROS. Recently, •OH localized to the cytoplasm (cyto •OH) was reported to induce cellular senescence, while mitochondria-localized •OH (mt •OH) was reported to induce apoptosis. We developed the cyto •OH- and mt •OH-scavenging antioxidants TA293 and mitoTA293 to evaluate the effects of cyto •OH and mt •OH in a bleomycin (BLM)-induced pulmonary fibrosis model. Treatment of BLM-induced pulmonary fibrosis mice with TA293 suppressed the induction of cellular senescence and fibrosis, as well as inflammation in the lung, but mitoTA293 exacerbated these. Furthermore, in BLM-stimulated primary alveolar epithelial cells, TA293 suppressed the activation of the p-ATMser1981/p-p53ser15/p21, p-HRI/p-eIF2ser51/ATF4/p16, NLRP3 inflammasome/caspase-1/IL-1β/IL1R/p-p38 MAPK/p16, and p21 pathways and the induction of cellular senescence. However, mitoTA293 suppressed the induction of mitophagy, enhanced the activation of the NLRP3 inflammasome/caspase-1/IL1β/IL1R/p-p38 MAPK/p16 and p21 pathways, and exacerbated cellular senescence, inflammation, and fibrosis. Our findings may help develop new strategies to treat idiopathic pulmonary fibrosis.
Keywords: cellular senescence; cytoplasmic hydroxyl radical; hydroxyl radical; inflammation; mitochondrial hydroxyl radical; pulmonary fibrosis.