Pseudomonas expression of an oxygen sensing prolyl hydroxylase homologue regulates neutrophil host responses and in vitro in vivo [ version 1 ; referees : awaiting peer review ]

Pseudomonas species are adapted to evade innate immune responses Background: and can persist at sites of relative tissue hypoxia, including the mucus-plugged airways of patients with cystic fibrosis and bronchiectasis. The ability of these bacteria to directly sense and respond to changes in local oxygen availability is in part consequent upon expression of the 2-oxoglutarate oxygenase, prolyl Pseudomonas hydroxylase (PPHD), which acts on elongation factor Tu (EF-Tu), and is homologous with the human hypoxia inducible factor (HIF) prolyl hydroxylases. We report that PPHD expression regulates the neutrophil response to acute pseudomonal infection. co-culture experiments were performed with human neutrophils Methods: In vitro and PPHD-deficient and wild-type bacteria and supernatants, with viable neutrophil counts determined by flow cytometry. consequences of infection with PPHD In vivo deficient were determined in an acute pneumonia mouse model P. aeruginosa following intra-tracheal challenge. Supernatants of PPHD-deficient bacterial cultures contained higher Results: concentrations of the phenazine exotoxin pyocyanin and induced greater acceleration of neutrophil apoptosis than wild-type PAO1 supernatants infection in vitro. In vivo with PPHD mutants compared to wild-type PAO1 controls resulted in increased levels of neutrophil apoptosis and impaired control of infection, with higher numbers of P. recovered from the lungs of mice infected with the PPHD-deficient strain. aeruginosa This resulted in an overall increase in mortality in mice infected with the PPHD-deficient strain. Our data show that expression of its prolyl hydroxylase Conclusions: Pseudomonas influences the outcome of host-pathogen interactions and , in vitro in vivo demonstrating the importance of considering how both host and pathogen adaptations to hypoxia together define outcomes of infection. Given that inhibitors for the HIF prolyl hydroxylases are in late stage trials for the treatment of anaemia and that the active sites of PPHD and human HIF prolyl hydroxylases are closely related, the results are of current clinical interest. 1 1 1 1