Gasdermin D Exerts Anti-Inflammatory Effects by Promoting Neutrophil Death

Gasdermin D (GSDMD) is considered a pro-inflammatory factor that mediates lytic pyroptotic cell death in macrophages to protect hosts from intracellular bacteria (He et al., 2015; Kayagaki et al., 2015; Shi et al., 2015a). However, GSDMD’s role in clearing extracellular pathogens has not been directly examined. Here we reveal that GSDMD deficiency unexpectedly and paradoxically augmented host responses to extracellular Escherichia coli, mainly by delaying neutrophil death, for the first time establishing GSDMD as a negative regulator of innate immunity. The levels of pro-inflammatory cytokines in the peritoneal cavity were significantly elevated in GSDMD-deficient mice, suggesting that the production of these cytokines was not mainly mediated by macrophage pyroptosis. This further confirmed that in E.coli-induced peritonitis GSDMD acted as an anti-inflammatory factor. In contrast to its activation in macrophages, in which activated inflammatory caspases cleave GSDMD to produce an N-terminal fragment (GSDMD-cNT) to trigger pyroptosis, GSDMD cleavage and activation in neutrophils was caspase independent and mediated by a neutrophil-specific serine protease, neutrophil elastase (ELANE), released from cytoplasmic granules into the cytosol during neutrophil death. ELANE-mediated GSDMD cleavage was upstream of the caspase cleavage site and produced a fully active ELANE-derived Nterminal fragment (GSDMD-eNT) that induced lytic cell death as efficiently as GSDMD-cNT. This is the first description of GSDMD’s role in neutrophil death and the negative regulation of neutrophil-mediated innate immunity. Thus, GSDMD is pleiotropic, exerting both pro- and anti-inflammatory effects that make it a unique target for novel anti-bacterial and anti-inflammatory therapies.