Gasdermin D Exerts Anti-inflammatory Effects by Promoting Neutrophil Death

Abstract

SUMMARY Gasdermin D (GSDMD) is considered a proinflammatory factor that mediates pyroptosis in macrophages to protect hosts from intracellular bacteria. Here, we reveal that GSDMD deficiency paradoxically augmented host responses to extracellular Escherichia coli, mainly by delaying neutrophil death, which established GSDMD as a negative regulator of innate immunity. 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. It was mediated by a neutrophil-specific serine protease, neutrophil elastase (ELANE), released from cytoplasmic granules into the cytosol in aging neutrophils. ELANE-mediated GSDMD cleavage was upstream of the caspase cleavage site and produced a fully active ELANE-derived NT fragment (GSDMD-eNT) that induced lytic cell death as efficiently as GSDMD-cNT. Thus, GSDMD is pleiotropic, exerting both pro- and anti-inflammatory effects that make it a potential target for antibacterial and anti-inflammatory therapies.

Gasdermins and their role in immunity and inflammation

“…Of these three caspases, caspase-1 appears to be the strongest driver of GSDMD cleavage and caspase-8 the weakest, perhaps acting more as a backup measure in situations where other caspases are impaired (Ramirez et al, 2018). Finally, in addition to the caspases above, both the neutrophil specific elastase (ELANE) and cathepsin G have been shown to cleave GSDMD upstream of the canonical caspase cleavage site (Kambara et al, 2018; Burgener et al, 2019).…”

Beyond inflammasomes: emerging function of gasdermins during apoptosis and NETosis

“…Although GSDMD was initially identified as a substrate of inflammatory caspases, two recent studies documented that GSDMD is also processed by the serine protease, neutrophil elastase, in neutrophils (Fig ; Kambara et al , ; Sollberger et al , ). Although neutrophil elastase cleaves GSDMD several amino acids upstream of the canonical caspase cleavage site, this did not affect the ability of the GSDMD N‐terminal fragment to oligomerise and induce lytic cell death upon overexpression in HEK 293T cells, in line with the observation that the membrane insertion and lytic properties of GSDMD N‐terminal fragment lie within the first 243 amino acid (Shi et al , ).…”

“…In one study, neutrophil elastase‐dependent GSDMD cleavage was proposed to trigger cell death in ageing neutrophils. Consequently, when challenged intraperitoneally with E. coli K12, Gsdmd ‐deficient mice accumulated more neutrophils at the site of infection and were more resistant to infection than wild‐type animals (Kambara et al , ). However, whether GSDMD promotes spontaneous neutrophil cell death is controversial, as other studies documented similar rate of spontaneous neutrophil death in wild‐type versus Gsdmd‐ deficient neutrophils (Chen et al , ; Burgener et al , ).…”

Inflammasome activation: Neutrophils go their own way

“…Although it is already known that serine proteases, including PR3 and NE, can process pro‐IL‐1β into IL‐1β, a connection between RIPK3 and neutrophil serine proteases signaling pathways is unexpected. Recently, NE released from cytosolic granules into the cytosol in aging neutrophils has been implicated in the cleavage of GSDMD, whereas Caspase‐1 has not . Although the cleavage site of the GSDMD by Caspase‐1 and NE differs, cleavage by both enzymes produces a N‐terminal GSDMD fragment forming pores at the plasma membrane .…”

“…Recently, NE released from cytosolic granules into the cytosol in aging neutrophils has been implicated in the cleavage of GSDMD, whereas Caspase‐1 has not . Although the cleavage site of the GSDMD by Caspase‐1 and NE differs, cleavage by both enzymes produces a N‐terminal GSDMD fragment forming pores at the plasma membrane . Thus, GSDMD cleavage by cytosolic NE leads to lytic cell death of neutrophils with NET release.…”