1. The Role of ExoS in Dissemination of Pseudomonas aeruginosa during Pneumonia
- Author
-
Alan R. Hauser, Stephanie M. Rangel, Claire A. Knoten, Maureen H. Diaz, and Angelica Zhang
- Subjects
lcsh:Immunologic diseases. Allergy ,Phagocytosis ,Immunology ,Bacterial Toxins ,Iatrogenic Disease ,Bacteremia ,Biology ,medicine.disease_cause ,Microbiology ,Flow cytometry ,Mice ,Virology ,Genetics ,medicine ,Pneumonia, Bacterial ,Animals ,Secretion ,Pseudomonas Infections ,Type-I Pneumocytes ,Molecular Biology ,lcsh:QH301-705.5 ,Type-I Pneumocyte ,ADP Ribose Transferases ,Mice, Inbred BALB C ,medicine.diagnostic_test ,Effector ,Pseudomonas aeruginosa ,Correction ,medicine.disease ,Flow Cytometry ,3. Good health ,Disease Models, Animal ,lcsh:Biology (General) ,Disease Progression ,Parasitology ,Female ,lcsh:RC581-607 ,Pneumonia (non-human) ,Research Article - Abstract
Hospital-acquired pneumonia is associated with high rates of morbidity and mortality, and dissemination to the bloodstream is a recognized risk factor for particularly poor outcomes. Yet the mechanism by which bacteria in the lungs gain access to the bloodstream remains poorly understood. In this study, we used a mouse model of Pseudomonas aeruginosa pneumonia to examine this mechanism. P. aeruginosa uses a type III secretion system to deliver effector proteins such as ExoS directly into the cytosol of eukaryotic cells. ExoS, a bi-functional GTPase activating protein (GAP) and ADP-ribosyltransferase (ADPRT), inhibits phagocytosis during pneumonia but has also been linked to a higher incidence of dissemination to the bloodstream. We used a novel imaging methodology to identify ExoS intoxicated cells during pneumonia and found that ExoS is injected into not only leukocytes but also epithelial cells. Phagocytic cells, primarily neutrophils, were targeted for injection with ExoS early during infection, but type I pneumocytes became increasingly injected at later time points. Interestingly, injection of these pneumocytes did not occur randomly but rather in discrete regions, which we designate ““fields of cell injection” (FOCI). These FOCI increased in size as the infection progressed and contained dead type I pneumocytes. Both of these phenotypes were attenuated in infections caused by bacteria secreting ADPRT-deficient ExoS, indicating that FOCI growth and type I pneumocyte death were dependent on the ADPRT activity of ExoS. During the course of infection, increased FOCI size was associated with enhanced disruption of the pulmonary-vascular barrier and increased bacterial dissemination into the blood, both of which were also dependent on the ADPRT activity of ExoS. We conclude that the ADPRT activity of ExoS acts upon type I pneumocytes to disrupt the pulmonary-vascular barrier during P. aeruginosa pneumonia, leading to bacterial dissemination., Author Summary Dissemination to the bloodstream is a poor prognostic sign in patients with hospital-acquired pneumonia, yet the mechanism by which this occurs is poorly understood. To begin to address this issue, we have used a mouse model of P. aeruginosa pneumonia to study the mechanism by which the type-III-secreted effector protein ExoS enhances bacterial dissemination. We show that intoxication of type I pneumocytes by ExoS leads to cell death and disruption of the pulmonary-vascular barrier, allowing bacterial dissemination into the bloodstream. These effects required the ADP-ribosyltransferase activity of ExoS, as strains secreting an ExoS variant lacking this activity demonstrated reduced type I pneumocytes death and pulmonary-vascular breakdown. This study indicates that inhibitors of the ADP-ribosyltransferase activity of ExoS could serve as novel therapeutics for the prevention of bacteremic pneumonia.
- Published
- 2015