Prior infection with Type A Francisella tularensis antagonizes the pulmonary transcriptional response to an aerosolized Toll-like receptor 4 agonist.
BACKGROUND
Francisella infection attenuates immune cell infiltration and expression of selected pro-inflammatory cytokines in response to endogenous LPS, suggesting the bacteria is actively antagonizing at least some part of the response to Toll-like receptor 4 (TLR4) engagement. The ability of different Francisella strains to inhibit the ability of E. coli LPS to induce a pulmonary inflammatory response, as measured by gene expression profiling, was examined to define the scope of modulation and identify of inflammatory genes/pathways that are specifically antagonized by a virulent F. tularensis infection.


RESULTS
Prior aerosol exposure to F. tularensis subsp. tularensis, but not the live attenuated strain (LVS) of F. tularensis subsp. holarctica or F. novicida, significantly antagonized the transcriptional response in the lungs of infected mice exposed to aerosolized E. coli LPS. The response to E. coli LPS was not completely inhibited, suggesting that the bacteria is targeting further downstream of the TLR4 molecule. Analysis of the promotors of LPS-responsive genes that were perturbed by Type A Francisella infection identified candidate transcription factors that were potentially modulated by the bacteria, including multiple members of the forkhead transcription factor family (FoxA1, Foxa2, FoxD1, Foxd3, Foxf2, FoxI1, Fox03, Foxq1), IRF1, CEBPA, and Mef2. The annotated functional roles of the affected genes suggested that virulent Francisella infection suppressed cellular processes including mRNA processing, antiviral responses, intracellular trafficking, and regulation of the actin cytoskeleton. Surprisingly, despite the broad overall suppression of LPS-induced genes by virulent Francisella, and contrary to what was anticipated from prior studies, Type A Francisella did not inhibit the expression of the majority of LPS-induced cytokines, nor the expression of many classic annotated inflammatory genes.


CONCLUSIONS
Collectively, this analysis demonstrates clear differences in the ability of different Francisella strains to modulate TLR4 signaling and identifies genes/pathways that are specifically targeted by virulent Type A Francisella.
Institute for Systems Biology, 401 Terry Ave. N, Seattle, WA, 98109, USA. Kathie.Walters@systemsbiology.org.
Kathie-Anne
KA
Walters
Division of Pulmonary and Critical Care Medicine, University of Washington, Seattle, WA, 98104, USA. rachael.olsufka@uky.edu.
Rachael
R
Olsufka
Institute for Systems Biology, 401 Terry Ave. N, Seattle, WA, 98109, USA. Rolf.Kuestner@systemsbiology.org.
Rolf E
RE
Kuestner
Institute for Systems Biology, 401 Terry Ave. N, Seattle, WA, 98109, USA. Xiagang.Wu@systemsbiology.org.
Xiagang
X
Wu
Institute for Systems Biology, 401 Terry Ave. N, Seattle, WA, 98109, USA. Kai.Wang@systemsbiology.com.
Kai
K
Wang
Division of Pulmonary and Critical Care Medicine, University of Washington, Seattle, WA, 98104, USA. shawn@u.washington.edu.
Shawn J
SJ
Skerrett
Institute for Systems Biology, 401 Terry Ave. N, Seattle, WA, 98109, USA. aozinsky@systemsbiology.org.
Adrian
A
Ozinsky
D000336:Aerosols; D000818:Animals; D005260:Female; D005604:Francisella tularensis / Q000276:immunology*; D008070:Lipopolysaccharides / Q000276:immunology*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000819:agonists*; D014406:Tularemia / Q000276:immunology*
D000336:Aerosols; D008070:Lipopolysaccharides; D051197:Toll-Like Receptor 4