SLO induced inflammasome activation is triggered by pore-formation instead of membrane repair (INM6P.337)

Abstract

Abstract Macrophages activate membrane repair and the inflammasome in response to bacterial pore-forming toxins like streptolysin O (SLO). SLO mutants that are more easily resisted by repair processes produce increased amounts of IL-1β. This suggests that membrane repair may influence inflammasome activation, though it is not clear whether pore-formation or triggering repair pathways directly activates the inflammasome. In order to determine the relationship between membrane repair and the inflammasome, we first determined the mechanism of membrane repair in macrophages. Dose-dependent cytotoxicity of SLO is lower in macrophages than in either 3T3 or HeLa cell lines, indicating increased repair efficiency in macrophages. This was not due to decreased SLO binding to macrophages. Macrophages challenged with sublytic doses of SLO shed microvesicles similar to HeLa and 3T3 cells. Although pore-formation was necessary for inflammasome activation, the pore-dead SLO N402E still promoted microvesicle shedding. However, a second SLO pore-dead mutant, SLO G395V/G396V failed to promote shedding. This suggests that membrane binding and the extent of oligomerization, rather than pore-formation, is necessary to trigger membrane repair. Since pore-formation is necessary for IL-1β secretion, these data suggest that membrane repair itself does not promote inflammasome activation. Instead membrane repair preserves the cell long enough to execute its inflammatory program.