Involvement of mitochondrial fragmentation in cigarette smoke induced-bronchial epithelial cell senescence

Rationale: Mitochondria are dynamic organelles that are essential for cellular metabolic functions. The proper regulation of dynamics is crucial for their functions. Disruption of dynamics induces excessive reactive oxygen species (ROS) production. Oxidative stress and accelerated cellular senescence are implicated in the pathogenesis of chronic obstructive pulmonary disease (COPD). Accordingly, we investigated the involvement of mitochondrial dynamics in cigarette smoke extract (CSE)-induced cellular senescence in human bronchial epithelial cells (HBEC). Methods: SA-β-gal staining and p21 western blotting of primary HBEC were performed to evaluate cellular senescence. Fluorescence microscopic analysis of mitochondrial morphology was performed by TOM20 staining. Mitochondrial specific superoxide production was measured by MitoSOX staining. Mitochondrial fragmentation was induced by knockdown of mitochondrial fusion proteins. N-acetylcysteine (NAC) and MitoTEMPO were used as antioxidants. Results: CSE induced mitochondrial fragmentation and mitochondrial oxidative stress, which were responsible for acceleration of cellular senescence in HBEC. Both mitochondrial fragmentation and mitochondrial oxidative stress induced by CSE treatment were inhibited in the presence of NAC or Mito TEMPO. Mitochondrial fragmentation induced by knockdown of fusion proteins also increased mitochondrial ROS production and percentages of senescent cells. Conclusions: CSE-induced mitochondrial fragmentation is involved in cellular senescence through the mechanism of mitochondrial ROS production. Hence, disruption of mitochondrial dynamics may be a part of the pathogenic sequence of COPD development.