The neutrophil-NETs-elastase axis drives pulmonary lymphatic endothelial injury and aggravates acute lung injury.

Acute lung injury (ALI) is a severe lung disease marked by strong neutrophil-related inflammation and pulmonary edema. However, how activated neutrophils damage pulmonary lymphatic function during ALI remains unclear. In this study, we used an LPS-induced ALI mouse model, pulmonary lymphatic tracing, neutrophil depletion, NET degradation, NE inhibition, LEC experiments, RNA sequencing, and molecular analyses to examine this question. We found that LPS-induced ALI caused progressive pulmonary lymphatic injury and impaired lymphatic drainage. These changes were closely associated with neutrophil accumulation, NET formation, and NE release. Neutrophil depletion improved pulmonary lymphatic structure and drainage function. It also reduced pulmonary edema, tissue injury, and respiratory dysfunction. In vitro, LPS alone caused limited injury to LECs, whereas NETs and NE disrupted endothelial junctions, increased DNA damage, and promoted apoptosis. DNase I or sivelestat treatment reduced pulmonary lymphatic injury and lung injury, with the combined treatment showing the strongest effect. RNA sequencing showed changes in inflammation-, stress-, and apoptosis-related pathways. In conclusion, activated neutrophils damage pulmonary lymphatic endothelium through NETs and NE, leading to impaired lymphatic drainage and worsened ALI.