PSMalpha Activates Early Growth Response 1 to Recruit Neutrophils to Protect the Host against Staphylococcus aureus pneumonia via Aerosolized Inhalational Infection

Staphylococcus aureus (S. aureus) produces several virulence factors, including alpha-toxin, enterotoxins, leukocidins, and phenol-soluble modulins (PSMs). PSMalpha play a crucial role in the pathogenesis of S. aureus due to its potent biological functions. However, the precise role of PSMalpha in S. aureus pneumonia remains unknown. Here, we aimed to investigate the impact of PSMalpha on S. aureus pneumonia. We compared the mortality and pathological changes in mice challenged by aerosolized inhalational infection with the wild type S. aureus strain MW2 (USA400) or its isogenic PSMalpha deletion mutant strain. In this pneumonia model, mice inoculated with S. aureus MW2 had higher mortality rates and more neutrophil infiltration in the lungs than those inoculated with the PSMalpha deletion mutant. Subsequently, we compared cDNA profiles of mouse lungs infected with S. aureus MW2 or the PSMalpha deletion mutant at 4 hours post-infection (hpi) and 6 hpi. RNA sequencing (RNA-seq) analysis revealed the identification of 793 differentially expressed genes (DEGs) at 4 hpi and 2461 DEGs at 6 hpi. We identified 229 overlapping DEGs by comparing the DEGs at 4 hpi and 6 hpi. From these overlapping DEGs, we screened the top 20 hub genes (IL6, Csf2, IL17a, Mmp9, Cd80, Cd3e, Cd8a, Cxcl1, Cxcl2, Fos, Thy1, Ccl20, Csf3, Ly6c2, Egr1, Dusp1, Hspa1b, Cd209a, Cd3g, Itgb2l). We demonstrated that PSMalpha activate Egr1 during S. aureus pneumonia. After aerosolized inhalational infection with S. aureus MW2, we observed lower survival rates, higher bacterial loads, and lower numbers of immigrated neutrophils in Early Growth Response 1 (Egr1) conditional knockout mice compared to control mice, and this difference was not observed when mice were infected with the PSMalpha deletion mutant. Overall our findings suggest that PSMalpha activate Egr1, which plays a critical role in the recruitment of neutrophils against S. aureus pneumonia.