Background: Pseudomonas species are adapted to evade innate immune responses 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, Pseudomonas
prolyl 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. Methods:In vitro co-culture experiments were performed with human neutrophils and
PPHD-deficient and wild-type bacteria and supernatants, with viable neutrophil counts determined by flow cytometry. In vivo consequences of
infection with
PPHD deficient P. aeruginosa were determined in an acute
pneumonia mouse model following intra-tracheal challenge. Results: Supernatants of
PPHD-deficient bacterial cultures contained higher concentrations of the
phenazine exotoxin pyocyanin and induced greater acceleration of neutrophil apoptosis than wild-type PAO1 supernatants in vitro. In vivo
infection 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. aeruginosa recovered from the lungs of mice infected with the
PPHD-deficient strain. This resulted in an overall increase in mortality in mice infected with the
PPHD-deficient strain. Conclusions: Our data show that Pseudomonas expression of its
prolyl hydroxylase influences the outcome of host-pathogen interactions in vitro and 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.