Krt5+ expressing urothelial cells appear responsible for IL-6 responsiveness in UTI through the IL-6 receptor
Sudipti Gupta, PhD, Brian Becknell, MD PhD, Ashley Jackson, PhD, John Spencer, MD, Christina Ching, MD.
Nationwide Children's Hospital, Columbus, OH, USA.
BACKGROUND: IL-6 is a cytokine expressed in response to UTI and been shown to be responsible for altered susceptibility to UTI in experimental models of UTI. We tried to identify the urinary tract cell population responsive to IL-6 signaling in UTI. We hypothesized this would be a basalar population of urothelial cells via the IL-6 receptor (IL-6R). METHODS: 6-8 week old female mice of various genotypes (C57BL/6J, Krt5icre+; Il6rafl/fl, Upk2icre+; Il6rafl/fl) were transurethrally infected with uropathogenic Escherichia coli. Urinary IL-6 expression was evaluated with ELISA. Bladder and urine bacterial burden was assessed by dilution plating at various time points after infection. Bladder tissue was also collected and prepared for immunofluorescent (IF) staining or in situ hybridization. Lastly, to evaluate for enrichment of IL-6R in different urothelial cell populations, we performed fluorescence-activated cell sorting (FACS) on urothelium harvested from Krt5CreERT2/+; R26 zsGreen/+;Upk1bRFP/+ mouse bladders after tamoxifen induction of fluorescent labeling in the respective cell populations. PCR was performed for IL-6R gene expression. Results were compared using Mann-Whitney U test with p <0.05 being significant. RESULTS: Experimental UTI in wild-type mice resulted in urinary IL-6 expression and Stat3 phosphorylation in the Krt5+ population of urothelial cells on IF. In situ hybridization localized IL-6R to the more basal cells in the urothelium; FACs showed enrichment of IL-6R in Krt5+ versus Krt5- urothelial cells on PCR. Loss of IL-6R in Krt5+ as opposed to Upk2+ cells showed increased UTI susceptibility early in infection (FIGURE).
CONCLUSIONS: Krt5+ expressing cells of the basal compartment of the urothelium appear necessary and sufficient for innate protection from UTI. 
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