Molecular Basis of UropathogenicEscherichia coliEvasion of the Innate Immune Response in the Bladder

Abstract

In the urinary tract, the innate immune system detects conserved bacterial components and responds to infection by activating the proinflammatory transcription factor NF-B, resulting in cytokine secretion and neutrophil recruitment. Uropathogenic Escherichia coli (UPEC), however, has been shown to evade the host innate immune response by suppressing NF-B activation in urothelial cells, which results in decreased cytokine secretion and increased urothelial apoptosis. To understand the molecular basis of UPEC modulation of inflammation, we performed a genetic screen with UPEC strain NU14 to identify genes which are required for modulation of urothelial cytokine secretion. Disruption of ampG (peptidoglycan permease), waaL (lipopolysaccharide O antigen ligase), or alr (alanine racemase) resulted in increased urothelial interleukin-8 (IL-8) and IL-6 release from urothelial cell cultures. Targeted deletion of these genes also resulted in elevated urothelial cytokine production during UPEC infection. Conditioned media from bacterial cultures of NU14 ⌬ampG and NU14 ⌬waaL contained a heat-stable factor(s) which stimulated greater urothelial IL-8 secretion than that in NU14-conditioned medium. In a mouse model of urinary tract infection, NU14 ⌬ampG, NU14 ⌬waaL, and NU14 ⌬alr were attenuated compared to wild-type NU14 and showed reduced fitness in competition experiments. Instillation of NU14 ⌬ampG or NU14 ⌬waaL increased bladder neutrophil recruitment, indicating that enhanced urothelial cytokine secretion during urinary tract infection results in an altered host response. Thus, UPEC evasion of innate immune detection of bacterial components, such as lipopolysaccharide and peptidoglycan fragments, is likely an important factor in the ability of UPEC to colonize the urinary tract.The host innate immune system utilizes a family of pattern recognition receptors (PRRs) that detect invading pathogens by recognition of evolutionarily conserved components. Recognition of these pathogen-associated molecular patterns (PAMPs) through PRR family members, including the Tolllike receptors (TLRs) and nucleotide binding and oligomerization domain-like receptors, results in activation of antimicrobial responses, such as the production of antimicrobial peptides and secretion of proinflammatory cytokines (18,29,45). Many bacterial pathogens, however, have evolved strategies for subverting the host innate immune system by evading detection by PRRs and/or disruption of the downstream cellular signaling pathways (8,30,38).Infection of the urinary tract by uropathogenic Escherichia coli (UPEC), the most frequent cause of urinary tract infection (UTI), is associated with a robust innate immune response characterized by the production of inflammatory cytokines and chemokines by the urothelium. The production of inflammatory cytokines and chemokines results in the rapid recruitment of neutrophils into the bladder lumen and in bacterial clearance (21,22,41). The activation of the innate immune response in the urinary tract is dependent upon PRR re...

Cytotoxic Necrotizing Factor 1 and Hemolysin from Uropathogenic Escherichia coli Elicit Different Host Responses in the Murine Bladder

“…We did not observe suppression of cytokine expression and/or neutrophil recruitment by our UPEC strains, regardless of HlyA1 production, by 6 h (data not shown) or 24 h after inoculation, as has previously been reported by others (46,(54)(55)(56)(57)(58). These groups measured the cytokine IL-6 and/or IL-8 after infection of different strains of bladder epithelial cell lines with clinical isolates (NU14, F11, UTI89) or with laboratory strains (HB101, MG1655) and showed that the laboratory strains induced significantly more cytokine release than the clinical isolates (54)(55)(56)(57).…”

“…Lipid A, a TLR4 ligand that is well-known to elicit a very strong innate immune response, is more accessible on rough strains than it is on smooth strains. Billips et al and Hunstad et al demonstrated that UPEC strains that contain mutations in genes involved in LPS biosynthesis, particularly O-and core-polysaccharide antigen synthesis, induced more IL-6 and IL-8 from urothelial cells in vitro than the isogenic smooth parent strains (46,57). Thus, though they and others found that the type of LPS expressed by the challenge strain (rough versus smooth) was not the only factor that contributed to immune suppression, rough LPS expressed by the more immune-stimulatory laboratory strains clearly played a role.…”

Uropathogenic E. coli infection provokes epigenetic downregulation of CDKN2A (p16INK4A) in uroepithelial cells

“…Several studies reported suppression of cytokine production in response to UPEC in vitro infection. 35,64,65 This discrepancy with our results is likely due to differences in post-infection incubation time and is therefore reflecting differences between acute and persistent phase of infection.…”

Safety of ProbioticEscherichia coliStrain Nissle 1917 Depends on Intestinal Microbiota and Adaptive Immunity of the Host

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