Abstract
BackgroundCoxiella burnetii is an intracellular bacterial pathogen that causes acute and chronic disease in humans. Bacterial replication occurs within enlarged parasitophorous vacuoles (PV) of eukaryotic cells, the biogenesis and maintenance of which is dependent on C. burnetii protein synthesis. These observations suggest that C. burnetii actively subverts host cell processes, however little is known about the cellular biology mechanisms manipulated by the pathogen during infection. Here, we examined host cell gene expression changes specifically induced by C. burnetii proteins during infection.ResultsWe have identified 36 host cell genes that are specifically regulated when de novo C. burnetii protein synthesis occurs during infection using comparative microarray analysis. Two parallel sets of infected and uninfected THP-1 cells were grown for 48 h followed by the addition of chloramphenicol (CAM) to 10 μg/ml in one set. Total RNA was harvested at 72 hpi from all conditions, and microarrays performed using Phalanx Human OneArray™ slides. A total of 784 (mock treated) and 901 (CAM treated) THP-1 genes were up or down regulated ≥2 fold in the C. burnetii infected vs. uninfected cell sets, respectively. Comparisons between the complementary data sets (using >0 fold), eliminated the common gene expression changes. A stringent comparison (≥2 fold) between the separate microarrays revealed 36 host cell genes modulated by C. burnetii protein synthesis. Ontological analysis of these genes identified the innate immune response, cell death and proliferation, vesicle trafficking and development, lipid homeostasis, and cytoskeletal organization as predominant cellular functions modulated by C. burnetii protein synthesis.ConclusionsCollectively, these data indicate that C. burnetii proteins actively regulate the expression of specific host cell genes and pathways. This is in addition to host cell genes that respond to the presence of the pathogen whether or not it is actively synthesizing proteins. These findings indicate that C. burnetii modulates the host cell gene expression to avoid the immune response, preserve the host cell from death, and direct the development and maintenance of a replicative PV by controlling vesicle formation and trafficking within the host cell during infection.
Highlights
Coxiella burnetii is an intracellular bacterial pathogen that causes acute and chronic disease in humans
spacious PV (SPV) morphology within CAM treated C. burnetii infected THP-1 cells As the transient inhibition of C. burnetii protein synthesis within infected THP-1 cells using CAM is pivotal to testing our hypothesis, we sought to confirm that morphological changes occur to the parasitophorous vacuoles (PV) of infected THP-1 cells after transient CAM treatment in a manner consistent with that observed in other cell types [35]
Using phase contrast and immunofluorescent antibody (IFA) microscopy analysis, we assessed the effect of bacteriostatic levels of CAM (10 μg/ml) on infected THP-1 cells during the log growth phase of the C. burnetii infectious cycle in order to coincide with subsequent microarray analysis
Summary
Coxiella burnetii is an intracellular bacterial pathogen that causes acute and chronic disease in humans. Bacterial replication occurs within enlarged parasitophorous vacuoles (PV) of eukaryotic cells, the biogenesis and maintenance of which is dependent on C. burnetii protein synthesis. These observations suggest that C. burnetii actively subverts host cell processes, little is known about the cellular biology mechanisms manipulated by the pathogen during infection. Human infection occurs via inhalation of metabolically active large cell variants (LCVs). They are not environmentally stable, LCVs are infectious in laboratory settings and pose a risk of causing disease. LCV replication is accompanied by a remarkable expansion of the PV, which eventually occupies the majority of the host cell [2,7]
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