title: Hypoxia-mediated impairment of the mitochondrial respiratory chain inhibits the bactericidal activity of macrophages.
abstract: In infected tissues oxygen tensions are low. As innate immune cells have to operate under these conditions, we analyzed the ability of macrophages (Mφ) to kill Escherichia coli or Staphylococcus aureus in a hypoxic microenvironment. Oxygen restriction did not promote intracellular bacterial growth but did impair the bactericidal activity of the host cells against both pathogens. This correlated with a decreased production of reactive oxygen intermediates (ROI) and reactive nitrogen intermediates. Experiments with phagocyte NADPH oxidase (PHOX) and inducible NO synthase (NOS2) double-deficient Mφ revealed that in E. coli- or S. aureus-infected cells the reduced antibacterial activity during hypoxia was either entirely or partially independent of the diminished PHOX and NOS2 activity. Hypoxia impaired the mitochondrial activity of infected Mφ. Inhibition of the mitochondrial respiratory chain activity during normoxia (using rotenone or antimycin A) completely or partially mimicked the defective antibacterial activity observed in hypoxic E. coli- or S. aureus-infected wild-type Mφ, respectively. Accordingly, inhibition of the respiratory chain of S. aureus-infected, normoxic PHOX(-/-) NOS2(-/-) Mφ further raised the bacterial burden of the cells, which reached the level measured in hypoxic PHOX(-/-) NOS2(-/-) Mφ cultures. Our data demonstrate that the reduced killing of S. aureus or E. coli during hypoxia is not simply due to a lack of PHOX and NOS2 activity but partially or completely results from an impaired mitochondrial antibacterial effector function. Since pharmacological inhibition of the respiratory chain raised the generation of ROI but nevertheless phenocopied the effect of hypoxia, ROI can be excluded as the mechanism underlying the antimicrobial activity of mitochondria.
authors.affiliation: Microbiology Institute–Clinical Microbiology, Immunology, and Hygiene, University Hospital of Erlangen and Friedrich-Alexander University, Erlangen-Nuremberg, Germany.
authors.forename: Melanie
authors.initials: M
authors.lastname: Wiese
authors.forename: Roman G
authors.initials: RG
authors.lastname: Gerlach
authors.forename: Isabel
authors.initials: I
authors.lastname: Popp
authors.forename: Jasmin
authors.initials: J
authors.lastname: Matuszak
authors.forename: Mousumi
authors.initials: M
authors.lastname: Mahapatro
authors.forename: Kirstin
authors.initials: K
authors.lastname: Castiglione
authors.forename: Dipshikha
authors.initials: D
authors.lastname: Chakravortty
authors.forename: Carsten
authors.initials: C
authors.lastname: Willam
authors.forename: Michael
authors.initials: M
authors.lastname: Hensel
authors.forename: Christian
authors.initials: C
authors.lastname: Bogdan
authors.forename: Jonathan
authors.initials: J
authors.lastname: Jantsch
mesh_terms: D000818:Animals; D015687:Cell Hypoxia; D004579:Electron Transport; D004926:Escherichia coli / Q000254:growth & development / Q000276:immunology*; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism* / Q000382:microbiology; D053078:Membrane Potential, Mitochondrial; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008928:Mitochondria / Q000378:metabolism*; D019255:NADPH Oxidases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering; D026361:Reactive Nitrogen Species / Q000096:biosynthesis / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013211:Staphylococcus aureus / Q000254:growth & development / Q000276:immunology*
chemical_list: D034741:RNA, Small Interfering; D026361:Reactive Nitrogen Species; D017382:Reactive Oxygen Species; D052247:Nitric Oxide Synthase Type II; D019255:NADPH Oxidases