Loss of mitochondrial protein FUS1 augments host resistance to Acinetobacter baumannii infection.

Fus1 is a tumor suppressor protein with recently described immunoregulatory functions. While its role in sterile inflammation is being elucidated, its role in regulating immune responses to infectious agents has not been examined. Here we employ a murine model of Acinetobacter baumannii pneumonia to identify the role of Fus1 in antibacterial host defenses. We found that loss of Fus1 in mice results in significantly increased resistance to A. baumannii pneumonia. We observed earlier and more robust recruitment of neutrophils and macrophages to the lungs of infected Fus1(-/-) mice, with a concomitant increase in phagocytosis of invading bacteria and more rapid clearance. Such a prompt and enhanced immune response to bacterial infection in Fus1(-/-) mice stems from early activation of pro-inflammatory pathways (NFkB and PI3K/Akt/mTOR), most likely due to significantly increased mitochondrial membrane potential and mitochondrial reactive oxygen species production. Significant early up-regulation of IL-17 in Fus1(-/-) immune cells was also observed, together with significant down-regulation of IL-10. Depletion of neutrophils eliminates the enhanced antibacterial defenses of the Fus1(-/-) mice, suggesting that ultimately it is the enhanced immune cell recruitment that mediates the increased resistance of Fus1(-/-) mice to A. baumannii pneumonia. Taken together, our data define the novel role for Fus1 in the immune response to A. baumannii pneumonia and highlight new avenues for immune modulating therapeutic targets for this treatment-resistant nosocomial pathogen.