MLKL regulates intracellular trafficking of neutrophil elastase to promote lung epithelial cell senescence.

Neutrophil elastase (NE) is a key contributor to the pathogenesis of chronic obstructive pulmonary disease (COPD), driving airway inflammation and tissue destruction. While the receptor-interacting protein kinase 3 (RIPK3)/mixed lineage kinase domain-like protein (MLKL)-mediated necroptosis has been implicated in cigarette smoke-induced COPD, its role in NE-mediated lung injury remains undefined. In this study, we demonstrate that NE does not induce necroptosis in lung epithelial cells in vitro. Although genetic deletion of RIPK3 or MLKL did not prevent NE-induced apoptosis, the absence of MLKL significantly reduced NE-induced cellular senescence. Mechanistically, we found that after NE is internalized into endosomes, MLKL facilitates its escape into the cytoplasm and subsequent translocation to the nucleus, where it induces DNA damage and senescence. In contrast, MLKL deficiency retains NE within endosomes, promoting its degradation via lysosomal trafficking. Furthermore, Mlkl knockout mice were protected from porcine pancreatic elastase-induced emphysema, highlighting the pathological relevance of this mechanism. Collectively, our findings reveal a novel, necroptosis-independent function of MLKL in regulating intracellular NE trafficking, suggesting a new therapeutic target for protease-driven lung injury in COPD.