Titel: Hypoxia-induced citrate limitation results in C. burnetii containment in macrophages
Art: Abstractautor
Session: Workshop 01
Virulence Principles in Respiratory Tract Infections (FG MP)

Referent: Inaya Hayek (Erlangen)

Abstract - Text

Introduction: Coxiella burnetii is the causative agent of the zoonotic disease Q fever. Apart from acute Q fever, around 2-5% of C. burnetii infected humans will develop chronic Q fever, which mainly manifests as endocarditis years after exposure to the pathogen. Usually, humans get infected through the inhalation of contaminated aerosols, often discharged from infected ruminants. Alveolar macrophages are the first line of defense against inhaled C. burnetii. They replicate within a unique lysosome-derived vacuole, called the coxiella containing vacuole. Details about how C. burnetii are fought by host macrophages and how they escape the immune system and persist for years inside the host are not fully established yet.

Materials and methods: Murine bone marrow-derived macrophages (MΦs) were infected with C. burnetii under normoxia or hypoxia. Samples for western blots, DNA/RNA isolation and citrate measurements were taken.

Results: Our experiments revealed that under normoxic conditions, C. burnetii replicate in macrophages and fail to induce robust accumulation of hypoxia-inducible factor 1α (HIF1α). Exposure to hypoxia, in contrast, stabilizes HIF1α which is essential for inhibiting C. burnetii replication. This was proven in murine MΦs and human (PBMC) derived macrophages. Mechanistically, HIF1α impairs the activity of signal transducer and activator of transcription 3 (STAT3), reduces the intracellular citrate level and thereby prevents C. burnetii replication. Interestingly, hypoxic MΦs also restrict intracellular replication of Legionella pneumophila, another intracellular pathogen. However, while HIF1α mediated limitation of citrate prevents C. burnetii replication under hypoxia, this seems not to be the case in the context of L. pneumophila infection. Furthermore, viable C. burnetii induce less HIF1α stabilization than heat-killed or a T4SS-defective mutant, suggesting that C. burnetii manipulate HIF1α in a T4SS-dependent manner. Molecular details and consequences of this activity are under investigation.

Conclusion: Our data suggest that regulation of citrate levels by HIF1α represents a novel principle of nutritional pathogen-containment which might be C. burnetii specific.