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Phillip S Coburn, Frederick Christian Miller, Craig Land, Austin L LaGrow, Michelle Callegan; Cereolysin O influences TLR4-dependent retinal gene expression during Bacillus cereus endophthalmitis. Invest. Ophthalmol. Vis. Sci. 2016;57(12):2344.
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© ARVO (1962-2015); The Authors (2016-present)
To determine whether cereolysin O, a member of the bacterial cholesterol-dependent cytolysin family, alters TLR4-dependent retinal gene expression in response to B. cereus infection early during the course of experimental murine endophthalmitis.
C57BL/6J or TLR4-/- mice were intravitreally injected with 100 CFU of B. cereus ATCC 14579 or an isogenic cereolysin O mutant. Fellow eyes served as uninfected controls. At 4 h post-infection, total RNA was isolated from retinas and subjected to qPCR. The threshold cycle (CT) was used to determine relative amounts of transcripts between RNA samples from infected and uninfected eyes. Fold increases were calculated by subtracting CT values of infected samples from CT values of uninfected samples. That value as a power of 2 yielded the fold increase of the transcript from infected samples relative to uninfected samples.
We previously identified a subset of genes related to the acute inflammatory response, inflammatory cell recruitment, cytokine signaling, photoreceptor survival, and pathogen recognition and clearance which were significantly upregulated 5-fold or greater in B. cereus-infected retinas at 4 h post-infection. These included CXCL1, CXCL2, CXCL10, CCL2, and CCL3, IL6, ICAM-1, SOCS3, LIF, PTGS2/COX-2, and PTX3. Analysis of the 4-h transcriptome in B. cereus-infected TLR4-/- retinas showed no change in the expression of these genes. Intravitreal infection of C57BL/6J mice with the isogenic cereolysin O mutant of B. cereus ATCC 14579 resulted in significantly reduced expression of CXCL1, CXCL2, CXCL10, CCL2, and CCL3, IL6, ICAM-1, and LIF. There were no changes in the expression of SOCS3 and PTX3, and PTGS2/COX-2 was downregulated 2-fold relative to uninfected mice.
These results suggest that cereolysin O plays a role in the activation of TLR4-dependent genes important for the acute inflammatory response and neutrophil recruitment, as well as genes related to photoreceptor survival and pathogen recognition and clearance. Future studies will evaluate the retinal and global ocular inflammatory responses over the course of B. cereus endophthalmitis to identify pathway-based anti-inflammatory targets, specifically those that are regulated by TLR4, and to determine whether cereolysin O/TLR4 interactions contribute to the uniquely explosive course of B. cereus endophthalmitis.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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