NLRP3 inflammasome activation triggers gasdermin D-independent inflammation

Abstract

NOD-like receptor (NLR), family pyrin domain containing 3 (NLRP3) assembles a protein complex known as the NLRP3 inflammasome upon sensing certain pathogen products or sterile danger signals. Gain-of-function mutations such as the D301N substitution in NLRP3, which cause its constitutive activation (NLRP3^CA) also results in inflammasome assembly. This inflammasome processes pro–interleukin-1 β (pro–IL-1β) and pro–IL-18 into bioactive IL-1β and IL-18, respectively, and cleaves gasdermin D (GSDMD). GSDMD amino-terminal fragments form plasma membrane pores that facilitate the secretion of IL-1β and IL-18 and lead to the inflammatory cell death pyroptosis. Accordingly, GSDMD inactivation results in negligible spontaneous inflammation in various experimental models such as in Nlrp3^CA/+ mice lacking GSDMD (Nlrp3^CA/+;Gsdmd^−/− mice). Here, we found that Nlrp3^CA/+;Gsdmd^−/− mice, when challenged with LPS or TNF-α, still secreted IL-1β and IL-18, indicating inflammasome activation independent of GSDMD. Accordingly, Gsdmd^−/− macrophages failed to secrete IL-1β and undergo pyroptosis when briefly exposed to NLRP3 inflammasome activators but released these cytokines when persistently activated. Sustained NLRP3 inflammasome induced caspase-8/-3 and GSDME cleavage and IL-1β maturation in vitro in Gsdmd^−/− macrophages. Thus, a salvage inflammatory pathway involving caspase-8/-3–GSDME was activated after NLRP3 activation when the canonical NLRP3-GSDMD signaling was blocked. Consistent with genetic data, the active metabolite of FDA-approved disulfiram CuET, which inhibited GSDMD and GSDME cleavage in macrophages, reduced the severe inflammation and tissue damage that occurred in the Nlrp3^CA/+ mice. Thus, NLRP3 inflammasome activation overwhelms the protection afforded by GSDMD deficiency, rewiring signaling cascades through mechanisms that include GSDME to propagate inflammation.