Involvement of NCOA4-mediated ferritinophagy in cigarette smoke-induced ferroptosis in COPD pathogenesis

Introduction: Labile iron pool accompanied by excessive oxidative stress has been implicated in COPD pathogenesis. Our previous findings showed potential involvement of free iron-dependent regulated cell death, ferroptosis, in cigarette smoke(CS)-induced cell death. Autophagic degradation of ferritin has been participated in free iron accumulation associated with ferroptosis. Ferritin selective autophagy, termed ferritinophagy, depends on a selective cargo receptor NCOA4 (nuclear receptor coactivatior 4). Therefore, we explored the mechanisms for CS-induced ferroptosis with respect to NCOA4-mediated ferritinophagy. Method: Normal and COPD lung tissues were obtained. Primary human bronchial epithelial cells (HBEC) were isolated from airway. Iron concentration was measured by using ICP-MS. Cell death was evaluated by LDH release assay and TUNEL assay. Result: Although CS extract (CSE) treatment transiently increased ferritin expression, subsequent decline accompanied by up-regulation of NCOA4 was demonstrated in HBEC. Confocal microscopic evaluation of immunofluorescence staining showed colocalization of ferritin and LC3-GFP by CSE exposure in BEAS2B cells. NCOA4 knockdown experiments clarified involvement of NCOA4-mediated ferritinophagy in regulating free iron concentration and ferroptosis induction during CSE exposure in HBEC. NCOA4 expression levels in COPD lung tissues were significantly elevated than those in normal lung tissues, and were negatively correlated with %FEV1. Conclusion: These findings suggest that alteration of iron homeostasis by CS-induced ferritinophagy and subsequent ferroptosis is involved in COPD pathogenesis.