PSMα contributes to Egr1-dependent early neutrophil recruitment and host defense in a murine model of Staphylococcus aureus pneumonia

Abstract

Abstract Background Staphylococcus aureus ( S. aureus ) pneumonia is associated with substantial morbidity and mortality. Neutrophils play a central role in host defense against bacterial infection and are significantly increased in the lungs during S. aureus pneumonia. However, the precise mechanisms underlying neutrophil accumulation in the lungs during S. aureus pneumonia remain poorly understood. Methods We compared mortality and lung pathological changes in mice challenged with wild-type S. aureus MW2 or its isogenic phenol-soluble modulin α (PSMα) deletion mutant (Δ psmα ) via non-invasive intratracheal aerosolization. RNA sequencing was then performed to investigate the regulatory role of PSMα during S. aureus pneumonia. Early growth response 1 ( Egr1 ) was identified as a candidate hub gene by bioinformatics analysis. To determine its functional role, myeloid cell-specific Egr1 conditional knockout ( Egr1 cKO) mice were generated using the Cre/LoxP system. Survival, bacterial load in the lungs, and pulmonary neutrophil infiltration were compared between Egr1 cKO and control mice. Results In our murine model, mice challenged with S. aureus MW2 showed higher mortality and more pronounced pulmonary neutrophil infiltration than mice challenged with Δ psmα . RNA-seq identified 793 and 2,461 differentially expressed genes (DEGs) at 4 and 6 h post-infection (hpi), respectively. Gene Ontology (GO) analysis indicated that genes differentially regulated at 4 hpi were mainly enriched in leukocyte migration, leukocyte chemotaxis, myeloid leukocyte migration, leukocyte cell-cell adhesion, and cell chemotaxis. Among the overlapping hub genes identified from the 4- and 6-hpi datasets, Egr1 was selected for further investigation. We found that PSMα contributes to the upregulation of Egr1 during S. aureus pneumonia. Following challenge with S. aureus MW2, Egr1 cKO mice exhibited reduced survival, higher pulmonary bacterial burdens, and decreased pulmonary neutrophil infiltration compared with control mice. These genotype-dependent differences were not observed when mice were challenged with Δ psmα . Conclusions Our study indicates that PSMα contributes to enhanced Egr1 expression in the lung during S. aureus pneumonia, and myeloid Egr1 plays an important role in early pulmonary neutrophil recruitment and host defense.