Staphylococcus aureus a-toxin induces inflammatory cytokines via lysosomal acid sphingomyelinase and ceramide
In summary, our study demonstrates how S. aureus α-toxin mediates a new pathway for inflammasome activation: we demonstrate that α-toxin leads to acid sphingomyelinase activation and induction of lysosomal ceramide. The acid sphingomyelinase - ceramide system causes changes in lysosomal membrane permeability, resulting in the release of cathepsin B/D from the lysosome into the cytosol. Cathepsin B associates with Nlrc4 and Asc and mediates inflammasome activation finally leading to the formation and release of IL-1β. Genetic deficiency of the acid sphingomyelinase or pharmacologcial inhibition of the acid sphingomyelinase or cathepsin B prevent these events. The acid sphingomyelinase is also activated by S. aureus α-toxin to trigger the formation and release of TNF-α, independent of cathepsin B/D. Taken together these results indicate that the acid sphingomyelinase - ceramide system plays a key role in the expression of cytokines caused by infection. These data link the lysosomal acid sphingomyelinase - ceramide system to the regulation of cytokines that are central for the regulation of inflammation in many human diseases.