The Polycomb Repressive Complex 2-dependent Epigenetic Program Regulates Urothelial Proliferation and Inflammatory Responses to Uropathogenic E. coli Infection
Zarine Balsara, MD PhD, Chunming Guo, PhD, X. Sean Li, PhD.
Boston Children's Hospital, Boston, MA, USA.
Urinary tract infections (UTI) cause considerable morbidity among children and adults with recurrence being common. Genetic factors only partially account for differences in host susceptibility to chronic or recurrent UTI. Emerging evidence suggests that uropathogenic E. coli (UPEC) infection may result in lasting changes to the host epigenetic landscape, which may influence host response to infection. Based on our preliminary findings, we hypothesized that the polycomb repressive complex (PRC) 2-dependent epigenetic program modulates clearance of UPEC infection, urothelial regeneration and host inflammatory response, and ultimately host susceptibility to recurrent infection.
Using a conditional gene knockout (cKO) strategy, we generated mice in which Eed, the obligatory component of PRC2, was deleted in all urothelial cells. Control and Eed cKO animals were transurethrally inoculated with 108 colony-forming units (CFU) of the prototypic E. coli cystitis strain, UTI89. The number of CFU in urine and/or bladders was measured over the course of 1 week to determine whether loss of the PRC2-dependent epigenetic program alters establishment and/or clearance of UPEC. Likewise, urothelial regeneration and proliferation were assessed by immunohistochemistry, and early cytokine responses at 2 hours and 24 hours post-infection (hpi) were analyzed by qRT-PCR.
Control and Eed cKO mice established similar levels of UPEC infection within the urine and bladder at 24 hours. However, Eed cKO mice displayed significantly reduced urothelial proliferation in response to UPEC, as assessed by the mitotic marker phospho-histone H3. This observation is consistent with PRC2’s known role in regulating cell cycle inhibitors including Cdkn2a/p16. Additionally, the mutants exhibited a blunted early pro-inflammatory response to infection with significant reductions in expression of IL-6, IL-1α, IL-1β, TNF-α, as well as the chemokine receptors CXCR2, CCR2, and CCR4. Nevertheless, despite the diminished inflammatory response to UPEC in the absence of PRC2, Eed cKO mice were still able to spontaneously clear bacteria within 7 dpi.
While loss of PRC2 does not significantly modify initial establishment or clearance of UPEC infection in the bladder, it does lead to a reduction in both urothelial proliferation and the pro-inflammatory response to infection, suggesting that PRC2 regulates host susceptibility and/or resistance to future infections. Because the majority of dysregulated genes belong to the NF-κB signaling pathway, we are testing whether the PRC2-dependent epigenetic program directly modulates host responses to UTI via the NF-κB signaling pathway.
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