Human renal epithelial cells express iNOS in response to cytokines but not bacteria.
BACKGROUND
Epithelial cells form the mucosal barriers that prevent the entry of mucosal pathogens, and respond to bacterial infections by producing various host defense molecules. In this study, we examined the inducible nitric oxide synthase (iNOS) response of primary human renal tubular epithelial cells (HRTEC) following infection with uropathogenic Escherichia coli Hu734, or stimulation with lipopolysaccharide (LPS) or cytokines.


METHODS
Induction of iNOS was examined by RT-PCR, Western blot, immunohistochemistry and nitrite measurements. The effects of endogenously produced nitric oxide (NO), and exogenously applied DETA/NO, SIN-1 and H2O2 on cell viability were analyzed using a respiration assay.


RESULTS
HRTEC did not produce NO following infection with E. coli Hu734, LPS alone, or in combination with interferon-gamma (IFN-gamma), even though these agents caused a marked increase in iNOS expression by RAW 264.7, a macrophage cell line. In contrast, iNOS protein and mRNA expression by HRTEC increased after exposure to a cytokine mixture consisting of interleukin (IL)-1beta, tumor necrosis factor-alpha (TNF-alpha) and IFN-gamma. This was due to the combination of IL-1beta and IFN-gamma, but the individual cytokines had no effect. Inducible NOS-expressing cell cultures showed reduced viability, and this effect was inhibited with the NOS inhibitor L-NMMA in RAW 264.7 cells, but not in HRTEC. HRTEC were more sensitive to oxidative stress induced by H2O2 than to nitrogen stress induced by DETA/NO.


CONCLUSIONS
We conclude that uropathogenic E. coli that attach to HRTEC fail to directly activate iNOS expression, and that iNOS expression during bacterial infection is more likely to result from stimulation by local cytokines such as IL-1beta and IFN-gamma.
Poljakovic
Mirjana
M
Department of Clinical Pharmacology, Lund University Hospital, Lund, Sweden.
Karpman
Diana
D
Svanborg
Catharina
C
Persson
Katarina
K
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D002648:Child; D016207:Cytokines / Q000494:pharmacology*; D004847:Epithelial Cells / Q000187:drug effects / Q000201:enzymology* / Q000382:microbiology; D004927:Escherichia coli Infections / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000276:immunology; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007371:Interferon-gamma / Q000494:pharmacology; D007375:Interleukin-1 / Q000494:pharmacology; D007684:Kidney Tubules / Q000166:cytology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000166:cytology / Q000276:immunology; D051379:Mice; D008981:Molsidomine / Q000031:analogs & derivatives* / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000235:genetics* / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D009573:Nitrites / Q000378:metabolism; D016877:Oxidants / Q000494:pharmacology; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D014552:Urinary Tract Infections / Q000378:metabolism
D000970:Antineoplastic Agents; D016207:Cytokines; D007375:Interleukin-1; D008070:Lipopolysaccharides; D020030:Nitric Oxide Donors; D009573:Nitrites; D016877:Oxidants; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; C002385:linsidomine; D007371:Interferon-gamma; D006861:Hydrogen Peroxide; D008981:Molsidomine; C496319:NOS2 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse