The pro-inflammatory effect of Staphylokinase contributes to community-associated Staphylococcus aureus pneumonia

Pneumonia caused by community-associated Staphylococcus aureus (CA-SA) has high morbidity and mortality, but its pathogenic mechanism remains to be further investigated. Herein, we identify that staphylokinase (SAK) is significantly induced in CA-SA and inhibits biofilm formation in a plasminogen-dependent manner. Importantly, SAK can enhance CA-SA-mediated pneumonia in both wild-type and cathelicidins-related antimicrobial peptide knockout (CRAMP^-/-) mice, suggesting that SAK exacerbates pneumonia in a CRAMP-independent manner. Mechanistically, SAK induces pro-inflammatory effects, especially in the priming step of NLRP3 inflammasome activation. Moreover, we demonstrate that SAK can increase K⁺ efflux, production of reactive oxygen species production, and activation of NF-κB signaling. Furthermore, the NLRP3 inflammasome inhibitor can counteract the effective of SAK induced CA-SA lung infection in mice. Taken together, we speculate that SAK exacerbates CA-SA-induced pneumonia by promoting NLRP3 inflammasome activation, providing new insights into the pathogenesis of highly virulent CA-SA and emphasizes the importance of controlling inflammation in acute pneumonia.