Gene Expression Profiles

We recently reported that Rickettsia australis supports its infection in macrophages by modulating an Atg5-dependent autophagic response, which is characterized by accumulated LC3 puncta with unaltered levels of SQSTM1/p62. In the present study, we sought to investigate how rickettsiae modulate autophagy and its effect on host innate immunity. We found that R. australis activated mTORC1 in bone marrow-derived macrophages (BMMs), as evidenced by significantly increased expression levels of phosphorylated mTOR and P70S6K. Compared to untreated controls, pharmacological inhibition of mTORC1 in R. australis-infected BMMs resulted in increased LC3 puncta and reduced expression levels of SQSTM1, which are characteristics of autophagy flux. Through RNA sequencing and Ingenuity Pathway Analysis, we showed that a significant number of genes were differentially regulated by R. australis in BMMs in an Atg5-dependent manner, including genes in the molecular networks of IL-1 family cytokines and PI3K-Akt-mTOR. The
production levels of IL-1α, IL-18, TNF-α, and IL-6 by R. australis-infected Atg5flox/flox Lyz-Cre
BMMs were significantly greater compared to Atg5flox/flox BMMs. Interestingly, the systemic levels
of IFN-γ and G-CSF in R. australis-infected Atg5 flox/flox Lyz-Cre mice were significantly less
accompanied by the lower rickettsial loads in tissues, compared to Atg5 flox/flox mice. These results highlight that R. australis modulates an autophagic response in association with activation of mTORC1 signaling in macrophages. Overall, we demonstrate that R. australis-modified autophagic response contributes to counteracting host innate immunity against rickettsial diseases.