The colonic pathogen Entamoeba histolytica activates caspase-4/1 that cleaves the pore-forming protein gasdermin D to regulate IL-1β secretion

Abstract

A hallmark ofEntamoeba histolytica(Eh) invasion in the gut is acute inflammation dominated by the secretion of pro-inflammatory cytokines TNF-α and IL-1β. This is initiated whenEhin contact with macrophages in the lamina propria activates caspase-1 by recruiting the NLRP3 inflammasome complex in a Gal-lectin andEhCP-A5-dependent manner resulting in the maturation and secretion of IL-1β and IL-18. Here, we interrogated the requirements and mechanisms forEh-induced caspase-4/1 activation in the cleavage of gasdermin D (GSDMD) to regulate bioactive IL-1β release in the absence of cell death in human macrophages. Unlike caspase-1, caspase-4 activation occurred as early as 10 min that was dependent onEhGal-lectin andEhCP-A5 binding to macrophages. By utilizing CRISPR-Cas9 gene editedCASP4/1,NLRP3 KOand ASC-def cells, caspase-4 activation was found to be independent of the canonical NLRP3 inflammasomes. In CRISPR-Cas9 gene editedCASP1macrophages, caspase-4 activation was significantly up regulated that enhanced the enzymatic cleavage of GSDMD at the same cleavage site as caspase-1 to induce GSDMD pore formation and sustained bioactive IL-1β secretion.Eh-induced IL-1β secretion was independent of pyroptosis as revealed by pharmacological blockade of GSDMD pore formation and in CRISPR-Cas9 gene editedGSDMD KOmacrophages. This was in marked contrast to the potent positive control, lipopolysaccharide + Nigericin that induced high expression of predominantly caspase-1 that efficiently cleaved GSDMD with high IL-1β secretion/release associated with massive cell pyroptosis. These results reveal thatEhtriggered “hyperactivated macrophages” allowed caspase-4 dependent cleavage of GSDMD and IL-1β secretion to occur in the absence of pyroptosis that may play an important role in disease pathogenesis.