A role of Romo1-derived mitochondrial reactive oxygen species in lung injury

Abstract

Reactive oxygen species (ROS) modulator 1 (Romo1) is localized in the outer membrane of mitochondria and increases mitochondrial ROS production through complex III mitochondrial electron transport chain. However, the role of Romo1-mediated mitochondrial ROS production in lung epithelial cell apoptosis and lung injury has not been identified yet. In this study, we investigated the role of Romo1 as a mediator in mitochondrial ROS production and apoptotic cell death induced by oxidative stress in lung epithelial cells.H2O2 treatment increased cellular ROS levels and Romo1 expression. Romo1 knockdown blocked H2O2-induced ROS production. H2O2 treatment induced death of BEAS-2B cells in a time- and a dose-dependent manner, and it was inhibited by Romo1 knockdown. The terminal deoxynucleotidyl transferase–mediated dUTP nick end labeling (TUNEL)-stained apoptotic bodies were significantly less in the BEAS-2B cells transfected with Romo1 siRNA compared with control siRNA transfected cells. The Romo1 knockdown inhibited expression of cleaved PARP and γH2AX, which were induced by H2O2 treatment. These findings suggest that Romo1 is an important mediator of apoptotic cell death induced by H2O2 treatment. The TUNEL-positive alveolar epithelial cells were detected in most idiopathic pulmonary fibrosis (IPF) tissues, whereas not observed in normal appearing lung tissues. Also, Romo1 overexpression of alveolar epithelial cells were detected in most IPF tissue, but not observed in normal controls. In conclusion, Romo1 knockdown suppressed the cellular ROS levels increased by exogenous H2O2 in lung epithelial cells. We observed that decreased ROS levels by Romo1 knockdown inhibited cell death by oxidative stress with exogenous H2O2. These results suggest that Romo1-induced ROS play an important role in cell death mechanism in lung epithelial cells.