PRKN Ser131 phosphorylation promotes cigarette smoke-induced mitophagy impairment and epithelial cell senescence via MKK3/p38 MAPK activation: An in vitro and in vivo study

INTRODUCTION: Cigarette smoke (CS) exposure impairs mitochondrial function and promotes senescence in airway epithelial cells, contributing to the pathogenesis of chronic obstructive pulmonary disease (COPD). However, the molecular mechanisms linking mitophagy dysfunction to cellular senescence remain poorly understood. Parkin (PRKN) is a key regulator of mitophagy, but whether PRKN Ser131 phosphorylation contributes to CS-induced impairment of mitophagy and senescence remains unclear. Therefore, this study aimed to investigate the role of PRKN Ser131 phosphorylation in CS-induced impairment of mitophagy and epithelial cell senescence, and to explore the underlying mechanism. METHODS: This laboratory-based experimental study utilized human bronchial epithelial BEAS-2B cells exposed to cigarette smoke extract (CSE) and a mouse model of CS-induced emphysema. Molecular interventions included mutation of PRKN at Ser131, and knockdown of mitogen-activated protein kinase kinase 3 (MKK3) to modulate the downstream p38 mitogen-activated protein kinase (p38 MAPK) pathway. Mitophagy activity, mitochondrial reactive oxygen species (ROS), and senescence markers were evaluated. RESULTS: Exposure to cigarette smoke extract (CSE) increased MKK3 expression and activated the p38 MAPK pathway, leading to phosphorylation of PRKN at Ser131. This phosphorylation was accompanied by reduced mitophagy-related readouts and increased mitochondrial ROS. Both MKK3 knockdown and modulation of mitochondrial quality-control pathways were associated with improved mitophagy-related readouts and reduced senescence markers under CSE exposure. Moreover, cells expressing the PRKN S131A mutant exhibited significantly improved mitophagy flux, reduced ROS levels, and attenuated senescence compared to wild-type PRKN. In vivo, emphysematous lungs showed increased MKK3 and senescence markers alongside decreased PRKN and PTEN-induced kinase 1 (PINK1) expression. CONCLUSIONS: Our findings suggest that the MKK3/p38 MAPK-PRKN Ser131 axis contributes to CS-induced mitophagy impairment and epithelial senescence. Additional studies are needed to strengthen the evidence and evaluate the translational potential of targeting this pathway in COPD.