Gasdermin D Protects from Melioidosis through Pyroptosis and Direct Killing of Bacteria

Abstract

Gasdermin D (GSDMD) cleavage by caspase-1 or caspase-11 inflammasomes triggers pyroptosis, a lytic form of cell death protective against intracellular bacteria. In this study, we examine the role of GSDMD in a mouse model of melioidosis. <i>Gsdmd^-/-</i> mice were more susceptible than wild-type mice to intranasal infection with <i>Burkholderia thailandensis</i> Production of IL-18, but not IL-1β, was decreased in <i>Gsdmd^-/-</i> infected mice. Despite lower IL-18, IFN-γ was produced in similar amounts in wild-type and <i>Gsdmd^-/-</i> mice. In vitro, secretion of both IL-1β and IL-18 by macrophages or dendritic cells infected with <i>B. thailandensis</i> was dependent on GSDMD. Surprisingly, wild-type or GSDMD-deficient neutrophils secreted similar amounts of IL-1β, suggesting these cells may be the source of the GSDMD-independent IL-1β detected in vivo. Recombinant GSDMD was able to directly kill <i>B. thailandensis</i> in vitro upon processing by active caspase-1. Moreover, bacteria harvested from wild-type, but not <i>Gsdmd^-/-</i> , macrophages were more susceptible to the microbicidal effect of hydrogen peroxide or human β-defensin-3. Finally, we provide evidence that pyroptosis of in vitro infected macrophages is directly microbicidal. Taken together, these results indicate that the protective action of GSDMD in melioidosis is primarily due to induction of pyroptosis and direct killing of bacteria rather than production of cytokines.