Aim: Here we investigated the role of complement activation in phagocytosis and the release of cytokines and chemokines in response to two clinical isolates: Borrelia afzelii K78, which is resistant to complement-mediated lysis, and Borrelia garinii LU59, which is complement-sensitive. Methods: Borrelia spirochetes were incubated in hirudin plasma, or hirudin-anticoagulated whole blood. Complement activation was measured as the generation of C3a and sC5b-9. Binding of the complement components C3, factor H, C4, and C4BP to the bacterial surfaces was analyzed. The importance of complement activation on phagocytosis, and on the release of cytokines and chemokines, was investigated using inhibitors acting at different levels of the complement cascade. Results: 1) Borrelia garinii LU59 induced significantly higher complement activation than did Borrelia afzelii K78. 2) Borrelia afzelii K78 recruited higher amounts of factor H resulting in significantly lower C3 binding. 3) Both Borrelia strains were efficiently phagocytized by granulocytes and monocytes, with substantial inhibition by complement blockade at the levels of C3 and C5. 4) The release of the pro-inflammatory cytokines and chemokines IL-1 beta, IL-6, TNF, CCL20, and CXCL8, together with the anti-inflammatory IL-10, were increased the most (by>10-fold after exposure to Borrelia). 5) Both strains induced a similar release of cytokines and chemokines, which in contrast to the phagocytosis, was almost totally unaffected by complement blockade. Conclusions: Our results show that complement activation plays an important role in the process of phagocytosis but not in the subsequent cytokine release in response to live Borrelia spirochetes.

The recent recognition of receptor-mediated ATP signalling as a pathway of epithelial pro-inflammatory cytokine release challenges the ubiquitous role of the TLR4 pathway during urinary tract infection. The aim of this study was to compare cellular responses of renal epithelial cells infected with uropathogenic Escherichia coli (UPEC) strain IA2 to stimulation with ATP-gamma-S. A498 cells were infected or stimulated in the presence or absence of apyrase, that degrades extracellular ATP, or after siRNA-mediated knockdown of ATP-responding P2Y(2) receptors. Cellular IL-8 release and global gene expression were analysed. Both IA2 and A498 cells per se released ATP, which increased during infection. IA2 and ATP-gamma-S caused a similar to 5-fold increase in cellular release of IL-8 and stimulations performed in the presence of apyrase or after siRNA knockdown of P2Y(2) receptors resulted in attenuation of IA2-mediated IL-8 release. Microarray results show that both IA2 and ATP-gamma-S induced marked changes in gene expression of renal cells. Thirty-six genes were in common between both stimuli, and many of these are key genes belonging to classical response pathways of bacterial infection. Functional analysis shows that 88 biological function-annotated cellular pathways were identical between IA2 and ATP-gamma-S stimuli. Results show that UPEC-induced release of IL-8 is dependent on P2Y(2) signalling and that cellular responses elicited by UPEC and ATP-gamma-S have many identical features. This indicates that renal epithelial responses elicited by bacteria could be mediated by bacteria- or host-derived ATP, thus defining a key role of ATP during infection.

Suppressor of cytokine signalling (SOCS) proteins inhibit pro-inflammatory signalling mediated by Janus-activated kinase (JAK)-signal transducer and activator of transcription (STAT) pathways. To evade the immune response some pathogens appear to modify the host SOCS proteins. Uropathogenic Escherichia coli (UPEC) are able to subvert the host response evoked by bladder epithelial cells, but the mechanisms are not fully understood. The objective of this study was to investigate whether UPEC can modify the host SOCS and STAT3 response. Real time RT-PCR studies demonstrated an increased SOCS1 and SOCS3 expression in the isolated human bladder epithelial cell lines (RT-4 and 5637) in response to cytokines. UPEC strain IA2 increased SOCS3, but not SOCS1, mRNA levels with a peak at 6h after infection. The increase of SOCS3 was confirmed at the protein level by Western blotting. The UPEC strain IA2 caused a time-dependent decrease in the phosphorylation of STAT3. This study demonstrates that UPEC are able to affect SOCS3 and STAT3 signalling in human uroepithelial cells. The finding that UPEC are able to induce mediators involved in suppression of host cytokine signalling may help to elucidate how UPEC may circumvent the host response during urinary tract infection.

PURPOSE: We characterized and identified the uroepithelial P2 receptor responsible for adenosine triphosphate mediated release of the cytokines interleukin-8 and 6.

MATERIALS AND METHODS: The human renal epithelial cell line A498 (ATCC™) was cultured and stimulated with different purinergic agonists with or without prior inhibition with different antagonists or signaling pathway inhibitors. Supernatant was analyzed for interleukin-8 and 6 by enzyme-linked immunosorbent assay. P2 receptor mRNA expression was assessed by real-time reverse transcriptase-polymerase chain reaction. The candidate receptor was knocked down with siRNA technology. Interleukin-8 and 6 responses were measured after purinergic stimulation of knocked down cells.

RESULTS: ATP and ATP-γ-S (Roche Diagnostics, Mannheim, Germany) were equipotent as inducers of interleukin-8 and 6 release. Agonist profile experiments using different P2 receptor agonists indicated that P2Y(2) was the main contributor to this release, although P2Y(11) and P2X(7) activation could not be excluded. Signaling pathway experiments showed that interleukin-8 release involved phospholipase C and inositol trisphosphate mediated signaling, indicating a P2Y receptor subtype. Antagonist experiments indicated P2Y(2) as the responsible receptor. Gene expression analysis of P2 receptors showed that strong expression of P2Y(2) receptor and subsequent knockdown of P2Y(2) receptor mRNA for 72 and 96 hours abrogated interleukin-8 and 6 release after purinergic stimulation with adenosine triphosphate-γ-S.

CONCLUSIONS: Interleukin-8 and 6 release after purinergic stimulation in uroepithelial A498 cells is mediated through P2Y(2) receptor activation.

Background/Aims: Increased nitric oxide (NO) production or inducible form of NO synthase activity have been documented in patients suffering from urinary tract infection (UTI), but the role of NO in this infection is unclear. We investigated whether NO can affect the host response in human renal epithelial cells by modulating IL-6 production and mRNA expression. Methods: The human renal epithelial cell line A498 was infected with a uropathogenic Escherichia coli (UPEC) strain and/or the NO donor DETA/NO. The IL-6 production and mRNA expression were evaluated by ELISA and real-time RT-PCR. IL-6 mRNA stability was evaluated by analyzing mRNA degradation by real-time RT-PCR. Results: DETA/NO caused a significant (p < 0.05) increase in IL-6 production. Inhibitors of p38 MAPK and ERK1/2 signaling, but not JNK, were shown to significantly suppress DETA/NO-induced IL-6 production. UPEC-induced IL-6 production was further increased (by 73 +/- 23%, p < 0.05) in the presence of DETA/NO. The IL-6 mRNA expression increased 2.1 +/- 0.17-fold in response to DETA/NO, while the UPEC-evoked increase was pronounced (20 +/- 4.5-fold). A synergistic effect of DETA/NO on UPEC-induced IL-6 expression was found (33 +/- 7.2-fold increase). The IL-6 mRNA stability studies showed that DETA/NO partially attenuated UPEC-induced degradation of IL-6 mRNA. Conclusions: NO was found to stimulate IL-6 in renal epithelial cells through p38 MAPK and ERK1/2 signaling pathways and also to increase IL-6 mRNA stability in UPEC-infected cells. This study proposes a new role for NO in the host response during UTI by modulating the transcription and production of the cytokine IL-6. Copyright (C) 2012 S. Karger AG, Basel

Adenosine has been identified as a significant inhibitor of inflammation by acting on adenosine A(2A) receptors. In this study, we examined the role of adenosine and A(2A) receptors in the transmigration of human neutrophils across an in vitro model of the transitional bladder urothelium. Human uroepithelial cells (UROtsa) were grown on transwell inserts; uropathogenic Escherichia coli (UPEC) and neutrophils were added to the transwell system; and the number of migrating neutrophils was evaluated. Reverse transcription-PCR (RT-PCR), immunohistochemistry, and flow cytometry were used to investigate the expression of adenosine receptors, the epithelial adhesion molecule ICAM-1, and the neutrophil integrin CD11b. Levels of proinflammatory interleukin-8 (IL-8) and phosphorylated I kappa B alpha were measured by enzyme-linked immunosorbent assays (ELISA) and Luminex assays, respectively. The neutrophils expressed all four adenosine receptor subtypes (A(1), A(2A), A(2B), and A(3) receptors), but A(3) receptors were not expressed by UROtsa cells. UPEC stimulated neutrophil transuroepithelial migration, which was significantly decreased in response to the specific A(2A) receptor agonist CGS 21680. The inhibitory effect of CGS 21680 on neutrophil migration was reversed by the A(2A) receptor antagonist SCH 58261. The production of chemotactic IL-8 and the expression of the adhesion molecule ICAM-1 or CD11b were not significantly affected by CGS 21680. However, a significant decrease in the level of phosporylated I kappa B alpha was revealed in response to CGS 21680. In conclusion, UPEC infection in vitro evoked neutrophil migration through a multilayered human uroepithelium. The UPEC-evoked neutrophil transmigration decreased in response to A(2A) receptor activation, possibly through inhibition of NF-kappa B signaling pathways.

Aims: Adenosine A(2A) and A(2B) receptor subtypes have both been implicated in the modulation of inflammation. We examined adenosine A(2A) and A(2B) receptor expression, signaling pathways and the effect of adenosine A(2A) and A(2B) receptor activation on the uropathogenic Escherichia coli (UPEC)-stimulated IL-8 response in human uroepithelial cells (UROtsa). Methods: Receptor expression was examined by RT-PCR and Western blot, and IL-8 production, intracellular cAMP levels and phosphoproteins were measured by ELISA, EIA and multiplex immunoassay, respectively. Results: The adenosine A(1), A(2A) and A(2B) receptor subtypes were detected in UROtsa cells. The adenosine A(2A) receptor agonist CGS 21680 did not stimulate cAMP production but CREB phosphorylation was slightly increased. The adenosine A(2) receptor agonist CPCA induced a pronounced cAMP and CREB response. Furthermore, CGS 21680 but not CPCA decreased ERK 1/2 and STAT3 phosphorylation. UPEC infection stimulated the host IL-8 production but CPCA or CGS 21680 did not affect UPEC-evoked IL-8 production. Conclusions: Our data identified differences in signaling pathways evoked by adenosine A(2A) and A(2B) receptor activation. Activation of the adenosine A(2A) receptor inhibited STAT3 and ERK 1/2 phosphorylation, while the cAMP-CREB pathway was induced by adenosine A(2B) receptor activation. No anti-or proinflammatory effects were found for uroepithelial adenosine A(2A) or A(2B) receptors. Copyright (C) 2010 S. Karger AG, Basel

Extracellular ATP can be released by many cell types under conditions of cellular stress and signals through activation of purinergic receptors. Bladder uroepithelial cells grown in vitro have previously been shown to release ATP in response to stretch. In the present study, we investigated ATP release from uroepithelial cells infected with bacteria and the effect of ATP on the host cell proinflammatory interleukin 8 (IL-8) response. The human kidney epithelial cell line A498 and the human uroepithelial cell line UROtsa were grown in culture and stimulated by the uropathogenic Escherichia coli (UPEC) IA2 strain or the stable ATP analogue ATP-gamma-S. ATP and IL-8 levels were measured in cell culture medium with a luciferin-luciferase assay and enzyme-linked immunosorbent assay (ELISA), respectively. The results showed that UPEC infection of uroepithelial cells for 1 h significantly increased (P < 0.01) the extracellular ATP levels. ATP-gamma-S (10 and 100 mu M) stimulated release of IL-8 from UROtsa and A498 cells after 6 and 24 h. Experiments with different purinoceptor agonists suggested that P2Y receptors, and not P2X receptors, were responsible for the ATP-gamma-S-induced IL-8 release. The potency profile further suggested involvement of P2Y(1), P2Y(2), and/or P2Y(11) receptors, and reverse transcription-PCR (RT-PCR) studies confirmed that the cells expressed these receptors. The amount of IL-8 released increased 12-fold in UPEC-infected cells, and apyrase, an enzyme that degrades ATP, reduced this increase by approximately 50%. The present study suggests that enhanced ATP release and P2Y receptor activation during urinary tract infection may represent a novel, non-TLR4-mediated mechanism for production of proinflammatory IL-8 in human urinary tract epithelial cells.

During the course of urinary tract infection (UTI) nitric oxide (NO) is generated as part of the host response. This study investigates the significance of the NO-detoxifying enzyme flavohemoglobin (Hmp) in protection of uropathogenic Escherichia coli (UPEC) against nitrosative stress. An hmp (J96Δhmp) knockout mutant of UPEC strain J96 was constructed using single-gene deletion. The viability of J96Δhmp was significantly reduced (P < 0.001) compared to the wild-type strain after exposure to the NO-donor DETA/NO. The NO consumption in J96Δhmp was significantly (P < 0.001) impaired compared to J96wt. Screening UPEC isolates from patients with UTI revealed increased hmp expression in all patients. In a competition-based mouse model of UTI, the hmp mutant strain was significantly (P < 0.05) out-competed by the wild-type strain. This study demonstrates, for the first time, that Hmp contributes to the protection of UPEC against NO-mediated toxicity in vitro. In addition, hmp gene expression occurs in UPEC isolates from the infected human urinary tract and UPEC that were hmp-deficient had a reduced ability to colonize the mouse urinary tract. Taken together the results suggest that NO detoxification by Hmp may be a fitness advantage factor in UPEC, and a potentially interesting target for development of novel treatment concepts for UTI.

OBJECTIVES

To examine the effect of nitric oxide (NO), an endogenous component of the host defence in urinary tract infection, on the adherence of P-fimbriated uropathogenic Escherichia coli (UPEC) to human renal epithelial cells.

MATERIALS AND METHODS

Two wild-type UPEC strains (AD110 and IA2) and the P-fimbriated recombinant strain HB101pPIL-75 were used. Bacteria were allowed to adhere to the human renal epithelial cell line A498 and attachment was evaluated in the absence or presence of the NO donor DETA/NONOate (1 mm). Total RNA was extracted from NO-exposed bacteria in static urine cultures, followed by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis of the papG gene that encodes the P-fimbriae adhesin PapG.

RESULTS

Bacterial adherence to A498 cells was fimbriae-dependent and the ability to agglutinate human P₁ positive erythrocytes confirmed that the used strains were P-fimbriated. UPEC strains AD110 and IA2 attached by a mean of 8 bacteria/cell and 20 bacteria/cell, respectively. In the presence of DETA/NONOate, the attachment of AD110 and IA2 to A498 cells was significantly reduced by a mean (sem) of 34 (3.9)% and 45 (14)%, respectively. The expression of papG was decreased after DETA/NONOate exposure as shown by semiquantitative RT-PCR.

CONCLUSION

NO disrupted functional adhesion of P-fimbriated UPEC to kidney epithelial cells, suggesting that NO-production from epithelial cells in the urinary tract may limit bacterial colonization at the mucosal surface. The reduced adherence may involve transcriptional effects of NO on papG expression, but further studies are needed to establish the underlying mechanisms.