The Gram-negative bacteria, which include Pseudomonas aeruginosa, cause substantial morbidity and mortality: bacterial pneumonia, septicemia and chronic disease account for ~15% of the total deaths in the USA. Therefore, it is imperative that we develop a better cellular and molecular understanding of the host interactions with bacterial pathogens, how bacteria avoid or manipulate the host's response, and to develop new strategies to prevent disease and improve patient care. Bacterial swimming motility, conferred by their flagella, has been recognized for over 25 years to influence the ability of bacteria to infect and colonize a host. Importantly, motility is required to initially infect the host, but bacteria must become non-motile to persist during clinical chronic infection. A well-described example is that the loss of P. aeruginosa motility directly correlates with increased bacterial burdens and increased disease severity in Cystic Fibrosis patients. However the underlying reasons for why and how changes in bacterial motility alter the course of infection and disease are unknown. We have recently provided the first formal demonstration that it is loss of bacterial motility, rather than loss of flagellar expression, that confers an advantage towards evasion of immune responses. Specifically, we have shown that loss of bacterial motility, in a variety of bacterial genera, results in bacterial resistance to phagocytosis in vitro and in vivo. Thus motility represents a novel and widespread mechanism by which the innate immune system recognizes and responds to bacteria ? and is a mechanism by which bacteria successfully elude immune responses during chronic infection. Therefore this proposal has the central goal of identifying the mechanisms by which immune cells respond to bacterial motility. Our recent finding that phagocyte PI3K and Akt activity are responsive to bacterial flagellar motility identifies novel regulation of an intracellular pathway that determines the phagocytic fate of Pa. We have leveraged this finding to identify two new critical molecular links in this motility-induced signal transduction pathway. Based on our preliminary data, in Specific Aim 1 our working hypothesis is that the Pa motility-stimulated phagocytic signal is transduced through a CIN85/src-family kinase pathway to PI3K/Akt. Our working hypothesis for Specific Aim 2 is that the c-Abl pathway is also responsive to, and required for, motility-induced phagocytosis. Therefore we propose to identify the c-Abl molecule(s) that contribute to motility-induced phagocytosis, and how this pathway functionally intersects with the PI3K/Akt axis. Achievement of these Aims will provide a mechanistic understanding of how loss of bacterial motility enables immune evasion and persistence of infection, and will identify molecular targets which can potentially be targeted to effect the therapeutic clearance of the non-motile, antibiotic-resistant bacteria present in chronic infections.

Public Health Relevance

Attachment Bacterial infections result in pneumonia, septicemia and chronic respiratory diseases that are major causes of death and mortality in the USA; the rates of infection are even higher in less developed countries. Specific to this grant proposal, Pseudomonas aeruginosa is a bacterial species that continues to cause substantial morbidity and mortality. Thus it is evident and imperative that we develop a better understanding of the host interactions with bacterial pathogens, how bacteria avoid or manipulate the host's response, and to develop new strategies to prevent disease and improve patient care. Therefore this proposal focuses on the identification of novel host/pathogen interactions, and therapeutic interventions into these interactions, that can be clinically utilized to improve public health.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Exploratory/Developmental Grants (R21)
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Special Emphasis Panel (ZRG1-IMM-M (90))
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Taylor, Christopher E,
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Dartmouth College
Schools of Medicine
United States
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Torres, Iviana M; Patankar, Yash R; Berwin, Brent (2018) Acidosis exacerbates in vivo IL-1-dependent inflammatory responses and neutrophil recruitment during pulmonary Pseudomonas aeruginosa infection. Am J Physiol Lung Cell Mol Physiol 314:L225-L235
Demirdjian, Sally; Hopkins, Daniel; Sanchez, Hector et al. (2018) Phosphatidylinositol-(3,4,5)-Trisphosphate Induces Phagocytosis of Nonmotile Pseudomonas aeruginosa. Infect Immun 86:
Demirdjian, Sally; Schutz, Kristin; Wargo, Matthew J et al. (2017) The effect of loss of O-antigen ligase on phagocytic susceptibility of motile and non-motile Pseudomonas aeruginosa. Mol Immunol 92:106-115
Torres, Iviana M; Demirdjian, Sally; Vargas, Jennifer et al. (2017) Acidosis increases the susceptibility of respiratory epithelial cells to Pseudomonas aeruginosa-induced cytotoxicity. Am J Physiol Lung Cell Mol Physiol 313:L126-L137