Parkin-mediated mitophagy is involved in cigarette smoke extract (CSE)-induced cellular senescence in human bronchial epithelial cells (HBEC)

Introduction: Cigarette smoke-induced cellular senescence has been implicated in the pathogenesis of chronic obstructive pulmonary disease (COPD). Damaged mitochondria are a primary source of reactive oxygen species (ROS), which is thought to play an important role in cellular senescence. Mitophagy, the selective degradation of mitochondria, may play a pivotal role for removal of CSE-induced damaged mitochondria, while Parkin, an E3 ubiquitin ligase, mediates ubiquitination that is critical for mitophagic recognition. Methods: Using HBEC, senescence associated beta-galactosidase staining and western blotting (WB) of p21 were performed to evaluate cellular senescence. To characterize autophagy and mitochondrial damage, WB of p62 and ubiquitin, fluorescence microscopy of MitoTracker and electron microscopy were performed. Intracellular ROS production was evaluated by dichlorodihydrofluorescein and MitoSOX. Results: CSE induced senescence and increase of damaged mitochondria was observed. A mitochondria-targeted antioxidant showed mitochondrial oxidative stress was mainly responsible for CSE-induced senescence. Bafilomycin A, an autophagy inhibitor, enhanced CSE-induced ubiquitination and accumulation of p62 in the mitochondria. Parkin knockdown decreased CSE-induced ubiquitination and accumulation of p62, and also enhanced mitochondrial oxidative stress accompanied by acceleration of cellular senescence. Decreased Parkin levels were detected in lung homogenates from COPD patients. Conclusion: Parkin-mediated mitophagy plays a key role in CSE-induced oxidative stress and cellular senescence through the degradation of damaged mitochondria in HBEC.