Neutrophil extracellular traps (NETs) are DNA scaffolds coated with granule proteins that are released by neutrophils to ensnare and kill bacteria. NET formation occurs in response to many stimuli through independent molecular pathways. Although NET release has been equated to a form of lytic cell death, live neutrophils can rapidly release antimicrobial NETs. Gasdermin D (GSDMD), which causes pyroptotic death in macrophages, is thought to be required for NET formation by neutrophils. Through experiments with known physiological activators of NET formation and ligands that activate canonical and noncanonical inflammasome signaling pathways, we demonstrated that Gsdmd -deficient mouse neutrophils were as competent as wild-type mouse neutrophils in producing NETs. Furthermore, GSDMD was not cleaved in wild-type neutrophils during NET release in response to inflammatory mediators. We found that activation of both canonical and noncanonical inflammasome signaling pathways resulted in GSDMD cleavage in wild-type neutrophils but was not associated with cell death. Moreover, NET formation as a result of either pathway of inflammasome activation did not require GSDMD. Together, these data suggest that NETs can be formed by viable neutrophils after inflammasome activation and that this function does not require GSDMD.
The formation of neutrophil extracellular traps requires neither cell death nor the pore-forming protein gasdermin D.
Neutrophil extracellular traps (NETs) are formed by neutrophils in response to various microbial agents and noninfectious stimuli and bind to and kill microbes. Both defective and exaggerated NET formation contribute to various disorders, making it critical to better understand the mechanisms underlying NET formation. Stojkov et al . found that agonists that induced NET formation independently of multiprotein complexes called inflammasomes did not require the protein gasdermin D (GSDMD) and did not cause cell lysis, contrary to previous studies. Furthermore, the authors found that although canonical and noncanonical inflammasome activation caused GSDMD processing, it was not required for NET release. These data suggest that the mechanisms leading to NET formation require further study and should be distinguished from those that lead to cell death.—JFF