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Escherichia coli-induced inducible nitric oxide synthase and cyclooxygenase expression in the mouse bladder and
M Poljakovic1, M L Svensson, C Svanborg
1Department of Clinical Pharmacology, Lund University Hospital, Lund, Sweden.
Background:
The host response to urinary tract infection includes the production of different inflammatory mediators. We investigated the cellular localization and time course of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX-2) expression in the mouse bladder and kidney after bacterial infection.
Methods:
Experimental urinary tract infection in mice was established by intravesical inoculation of a clinical uropathogen Escherichia coli (E. coli) AD 110. Urine was collected at 6-, 12-, 24-, and 72-hours postinstillation, and the nitrite concentration was determined. The induction of iNOS and COX-2 was studied by immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR).
Results:
Nitrite levels in the urine had increased threefold at 6 and 12 hours postbacterial instillation. Bladders from mice instilled with AD 110, but not with phosphate-buffered saline, showed a large number of iNOS-- and COX-2--expressing inflammatory cells. The inflammatory cell activation peaked at 6 and 12 hours postinstillation and had vanished by 72 hours. iNOS expression was detected in some urothelial cells after 24 and 72 hours, but COX-2 expression was not detected. In the kidney, infection activated an iNOS and COX-2 response, as shown by immunoreactivity in inflammatory cells at all time points. A strong epithelial iNOS response was observed in the renal pelvis at 12, 24, and 72 hours postinstillation, but COX-2 was not detected. Enhanced tissue expression of iNOS and COX-2 after bacterial instillation was also demonstrated by RT-PCR.
Conclusions:
E. coli AD 110 induced expression of iNOS and COX-2 in the urinary tract. Inflammatory cells expressed both iNOS-and COX-2, but epithelial cells expressed only iNOS and with a later onset than in the inflammatory cells. This suggests that the epithelial iNOS response is not caused by direct bacterial activation, but more likely is by mediators involved in the inflammatory response.
Insights
This study shows that Escherichia coli infection induces inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in the mouse urinary tract. Inflammatory cells express both, while epithelial cells express only iNOS, suggesting indirect activation.
Area of Science:
- Urology
- Immunology
- Microbiology
Background:
- Urinary tract infections (UTIs) trigger host inflammatory responses involving various mediators.
- Investigated the expression patterns of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in response to bacterial infection.
Purpose of the Study:
- To determine the cellular localization and temporal expression of iNOS and COX-2 in the mouse bladder and kidney following a UTI.
- To understand the host's molecular response to uropathogenic Escherichia coli (E. coli).
Main Methods:
- Experimental UTI induced in mice via intravesical inoculation of E. coli AD 110.
- Nitrite levels measured in urine; iNOS and COX-2 expression analyzed using immunohistochemistry and RT-PCR.
Main Results:
- Nitrite levels significantly increased within 6-12 hours post-infection.
- Both iNOS and COX-2 were expressed by inflammatory cells in the bladder and kidney, peaking at 6-12 hours.
- Epithelial cells showed iNOS expression later (24-72 hours), but not COX-2, suggesting indirect activation.
Conclusions:
- E. coli infection upregulates iNOS and COX-2 expression in the urinary tract.
- Inflammatory cells are key expressors of both mediators, while urothelial and renal pelvis epithelial cells primarily express iNOS.
- The delayed epithelial iNOS response indicates it's likely mediated by inflammatory signals rather than direct bacterial contact.