<i>Clostridium septicum</i> α-toxin activates the NLRP3 inflammasome by engaging GPI-anchored proteins

Abstract

<i>Clostridium</i> species are a group of Gram-positive bacteria that cause diseases in humans, such as food poisoning, botulism, and tetanus. Here, we analyzed 10 different <i>Clostridium</i> species and identified that <i>Clostridium septicum</i>, a pathogen that causes sepsis and gas gangrene, activates the mammalian cytosolic inflammasome complex in mice and humans. Mechanistically, we demonstrate that α-toxin secreted by <i>C. septicum</i> binds to glycosylphosphatidylinositol (GPI)-anchored proteins on the host plasma membrane, oligomerizing and forming a membrane pore that is permissive to efflux of magnesium and potassium ions. Efflux of these cytosolic ions triggers the activation of the innate immune sensor NLRP3, inducing activation of caspase-1 and gasdermin D, secretion of the proinflammatory cytokines interleukin-1β and interleukin-18, pyroptosis, and plasma membrane rupture via ninjurin-1. Furthermore, α-toxin of <i>C. septicum</i> induces rapid inflammasome-mediated lethality in mice and pharmacological inhibition of the NLRP3 inflammasome using MCC950 prevents <i>C. septicum</i>-induced lethality. Overall, our results reveal that cytosolic innate sensing of α-toxin is central to the recognition of <i>C. septicum</i> infection and that therapeutic blockade of the inflammasome pathway may prevent sepsis and death caused by toxin-producing pathogens.