Ficolin-A/2 aggravated severe lung injury through NETs mediated by GSDMD-induced pyroptosis

Neutrophil extracellular traps (NETs) and pyroptosis are critical events in lung injury. We aimed to investigate whether Ficolin-A influences NET formation through pyroptosis to exacerbate lipopolysaccharides (LPS)-induced lung injury. The expression of Ficolin-A/2, NETs, and pyroptosis-related molecules was investigated in animal and cell models. Knockout and knockdown (recombinant protein) methods were employed to elucidate regulatory mechanisms. Pearson's correlation coefficient was utilized to analyze the correlation between Ficolins and pyroptosis- and NET-related markers in clinical samples. In this study, Ficolin-2 (similar to Ficolin-A) showed significant overexpression in patients with acute respiratory distress syndrome (ARDS). In vivo, knockout of Ficolin-A, but not Ficolin-B, attenuated lung inflammation and inhibited NET formation in LPS-induced mouse model. DNaseI further alleviated lung inflammation and NET formation in Ficolin-A knockout mice. In vitro, neutrophils derived from Fcna-/- mice exhibited less pyroptosis and necroptosis than those from the control group after LPS stimulation. Additionally, gasdermin D (GSDMD) knockdown or Nod-like receptor protein 3 (NLRP3) inhibitor reduced NET formation. Addition of recombinant Ficolin-2 protein to human peripheral blood neutrophils promoted NET formation and pyroptosis after LPS stimulation, whereas Ficolin-2 knockdown had opposite effects. ARDS patients exhibited increased levels of pyroptosis- and NET-related markers, which were positively correlated with Ficolin-2 levels. In conclusion, these results suggested that Ficolin-A/2 exacerbated NET formation and LPS-induced lung injury via the GSDMD-mediated pyroptosis.