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ová
ík
Institutes of Physiology and
1 Microbiology, Czech Academy of Sciences, Vídenská 1083, CZ-142 20 Prague 4, Czech Republic
(Requests for offprints should be addressed to J Pácha; Email: pacha{at}biomed.cas.cz)
| Abstract |
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| Introduction |
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(TNF-
) and interleukin-1 (IL-1), have been shown to link inflammation with glucocorticoid production by stimulating the hypothalamicpituitaryadrenal axis and elevating thereby the plasma glucocorticoid concentration (Besedovsky & del Rey 1996). However, the biological activity of glucocorticoids depends not only on their plasma concentration, the number of receptors, and the responsiveness of the target cell, but also on the local metabolism of glucocorticoids catalyzed by 11ß-hydroxysteroid dehydrogenase (11HSD), which can change the concentration of active glucocorticoids within tissues and/or target cells.
Two isoforms of 11HSD have been characterized. Isoform 2 (11HSD2) is a high-affinity NAD+-dependent enzyme that operates exclusively as an oxidase inactivating biologically active glucocorticoids cortisol and corticosterone to their 11-oxo derivatives cortisone and 11-dehydrocorticosterone respectively (Stewart & Krozowski 1999). In contrast, 11HSD1 is a low-affinity NADP(H)-dependent oxidoreductase whose reductase activity has been found in various intact cells (Seckl & Walker 2001), but alterations in the NADP+/NADPH redox potential governed by the metabolism of glucose-6-phosphate via hexose-6-phosphate dehydrogenase seem to determine whether 11HSD1 operates as a reductase or an oxidase (Hewitt et al. 2005). Thus, 11HSD2 decreases the local concentration of active gluco-corticoids, whereas 11HSD1 increases it due to regeneration of biologically active steroids from the circulating inactive 11-oxo metabolites or decreases it due to oxidation of active glucocorticoids (Stewart & Krozowski 1999, Seckl & Walker 2001, Hewitt et al. 2005). Exposure to pro-inflammatory stimuli such as TNF-
and IL-1ß increases 11HSD1 expression and enzymatic activity in some cells, while inducing a decrease of 11HSD2 in others (Cai et al. 2001, Cooper et al. 2001, Heiniger et al. 2001, Thieringer et al. 2001, Tomlinson et al. 2001). The biological significance of this process was shown recently (Escher et al. 1997, Thieringer et al. 2001, Zhang et al. 2005).
With regard to the colon, 11HSD2 is expressed in epithelial cells, whereas 11HSD1 is localized in the cells of lamina propria (Whorwood et al. 1994). This matches with the findings of 11HSD1 in fibroblasts (Hammami & Siiteri 1991), macrophages (Thieringer et al. 2001), and lymphocytes (Zhang et al. 2005). Consistent with the effect of TNF-
and IL-1ß on 11HSD1 and 11HSD2, we have shown in a rat model of colitis that 11HSD1 mRNA expression and 11-reductase activity increased, whereas 11HSD2 mRNA expression and 11-oxidase activity decreased during intestinal inflammation (Bryndová et al. 2004). Considering that colitis is accompanied by activation of mucosal immune cells and increased recruitment of leucocytes from the vascular space (Elson et al. 1995), one can hypothesize that the link between the upregulation of colonic 11HSD1 mRNA and the increased ability of the tissue to reduce 11-dehydrocorticosterone to corticosterone might be the cells of the intestinal immune system. To address this question, we used the dextran sulfate model of murine colitis and studied the changes of 11HSD1 in colon and immune cells during intestinal inflammation.
| Materials and Methods |
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Female 3-month-old mice Balb/c (Velaz, Prague, Czech Republic) were used in this study. Experimental colitis was induced by adding 3% (w/v) dextran sulfate sodium (DSS, MW 36 00050 000; ICN Biomedicals Inc., Cleveland, Ohio, USA) in drinking water (Okayasu et al. 1990). Mice were treated with DSS for 7 days and subsequently killed. Control animals received only tap water. The mice were killed by decapitation and the colon, spleen, and mesenteric lymph nodes were excised. Macrophages were collected by a peritoneal lavage and intraepithelial lymphocytes (IEL) as originally described by Lefrancois (1992) with some modifications. Briefly, the inflamed part of colon was dissected and the lumen gently flushed with cold physiological saline (4 °C). The intestine was then incised longitudinally and cut into 5 mm pieces. The pieces were incubated in flasks containing RPMI-1640 medium supplemented with fetal bovine serum (12.5%) for 20 min at 37 °C with stirring. The incubation step was repeated thrice, the supernatants were combined, and IEL were separated from epithelial cells by discontinuous Percoll gradient at the interface 67%/44%. The harvested cells were washed in RPMI medium and used for further analysis.
The animal study was approved by the Animal Care and Use Review Committee of the Czech Academy of Sciences.
Evaluation of colitis
The clinical assessment of DSS-treated animals included body weight, colon length, evaluation of stool consistency, and the presence of blood in the stool. A clinical disease activity index representing the sum of separate scores ranging from 0 to 4 was calculated using the following parameters: body weight decrease (0, less than 5% decrease; 1, 510%; 2, 1020%; 4, more than 20%), stool consistency (solid 0, loose 2, diarrhea 3), and bleeding (none 0, macroscopic in colon 2, blood adhering to the anus 4) as described previously (Bendjelloul et al. 2000).
Quantitative analysis of 11HSD and cytokine RNA
Total RNA from the colon was extracted by the guanidinium thiocyanate method. The isolated RNA was treated with DNase (Promega) to remove potential contamination by genomic DNA as mentioned earlier (Mazancová et al. 2003). Total RNA from the spleen, mesenteric lymph nodes, macrophages, and IEL was obtained using GeneElute Mammalian Total RNA Miniprep Kit (Sigma). cDNA was synthesized from 5 µg RNA and M-MLV Reverse Transcriptase reagents (Invitrogen GmbH). Amplification of the target cDNA was performed in the LightCycler (Roche) as previously reported (Mazancová et al. 2005) using QuantiTect Sybr Green PCR Kit (Qiagen GmbH) and the primers given in Table 1
. Results were analyzed with LightCycler software using the second derivative maximum method to set CP. For the quantification of the target genes 11HSD1, 11HSD2, TNF-
, and IL-1ß, we performed the quantitative comparison of several candidate reference genes to select the most stable genes for gene normalization. The panel of five reference genes generally used in many physiological and pathophysiological conditions, such as ß-actin (ACTB), hypoxanthine phosphoribosyltransferase 1 (HPRT1), ribosomal protein L13a (RPL13A), elongation factor 1
(EF1A), and peptidylpropyl isomerase B (cyclophilin B; PPIB), were tested (Table 1
). Because of the high concentration of ß-actin and 11HSD2, the samples were diluted 1/1000 before analyses of these RNA species. For other analyses, 1/10 pre-diluted cDNA was used as a template for PCR. Calibration curves were generated for each pair of primers from serial dilutions of standard cDNA. After statistical analysis of reference genes, the data of target gene expression were normalized according to the normalization factor calculated by the geNorm applet (Vandesompele et al. 2002).
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Enzyme activity assays
Colon homogenates were prepared in ice-cold buffers containing 10 mM Tris, 250 mM sucrose (pH 8.5; 11HSD2 assay) or 10 mM Tris, 5 mM EDTA, 0.5% Triton X-100 (pH 7.5; 11HSD1 assay). After centrifugation at 500 g for 15 min, the supernatant was obtained and protein concentration was measured using the Bradford technique (Bradford, 1976). 11HSD1 and 11HSD2 activities were measured as NADP+-and NAD+-dependent 11ß-oxidation of corticosterone according to Livingstone & Walker (2003) and Gomez-Sanchez et al.(2003). 11HSD1 activity was measured in incubation buffer containing 50 mM Tris, 100 mM KCl, 1 mM NADP+, 480 nM corticosterone, and 20 nM 1,2,6,7-[3H]corticosterone (pH 7.5). 11HSD2 activity was determined in a similar way, with 50 mM Tris, 100 mM KCl, 1 mM NAD+, and 20 nM 1,2,6,7-[3H]corticosterone (pH 8.5). The amounts of protein and the incubation times were determined in preliminary experiments to establish the optimal conditions, in order to work in the linear portion of the enzyme reaction. Steroids were extracted from the incubation buffer by SepPak cartridges (Waters, Milford, MA, USA) and separated by HPLC with on-line detection using a flow-cell detector (Radiomatic 150TR, Canberra Packard, Meriden, CT, USA). The separation was performed in a C18 column using a water methanol gradient (for details see Pácha et al. 2004).
Data analysis
All data are expressed as means ± S.E.M. or medians with 25th75th percentile values. The distributionfitting procedure according to ShapiroWilks W-test of normality was applied and the comparison between the control animals and the mice with colitis was analyzed using unpaired Students t-test or MannWhitney U-test. The values P<0.05 were considered statistically significant. For stability comparison of candidate reference genes and the calculation of normalization factor, the geNorm program was applied after conversion of CP values into relative quantities (Vandesompele et al. 2002). Using this approach, the normalization factor based on two candidate reference genes was calculated. Statistical analysis was performed using the statistical software Statistica v.6 (StatSoft Inc., Tulsa, OK, USA).
| Results |
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These genes displayed a relatively wide range of CP (Fig. 1
). Using the unpaired Students t-test or MannWhitney U-test, significant differences in gene expression between healthy and inflamed colon were observed for EF1A and RPL13A. The geNorm program was then used to calculate the gene expression stability measure M of the remaining genes and the normalization factor based on the geometric average of the two reference genes (Vandesompele et al. 2002). We found ACTB and PPIB to be the most convenient reference genes and thus these two genes were used for normalization of mRNA expression levels.
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and IL-1ß mRNAs. As shown in Table 3
transcript was changed much less, in a similar way as in the study of Egger et al.(2000) and Kwon et al.(2005).
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| Discussion |
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The exact mechanism of inflammation induced by DSS is not yet fully elucidated, but the pathogenesis seems to depend on the interaction between local immune reaction and environmental factors because animal models of inflammatory bowel disease reared in germfree conditions did not develop the disease (Tlaskalová-Hogenová 1997, Hudcovic et al. 2001, Elson & Cong 2002). Drinking of DSS generates in murine colon the upregulation of pro-inflammatory cytokines as well as reactive oxygen and nitrogen species and infiltration by polymorphonuclear and mononuclear cells (Okayasu et al. 1990, Kojouharoff et al. 1997, Arai et al. 1998). Previous data and our findings suggest that these processes are accompanied by upregulation of 11HSD1 in the cells of gut-associated lymphatic tissue. First, activated macrophages and lymphocytes acquire increased capacity of glucocorticoid reactivation via 11HSD1 (Zhang et al. 2005, Gilmour et al. 2006). Secondly, our data show that NADP+-dependent but not NAD+-dependent activity is increased in inflamed colon. Thirdly, the level of 11HSD1 transcript is increased not only in inflamed colon but also in IEL and in mesenteric lymphatic nodes. This upregulation of 11HSD1 is presumably induced by the pro-inflammatory cytokines, whose levels of transcript and protein are increased in colon of DSS-treated mice (Arai et al. 1998, Egger et al. 2000, Obermeier et al. 2002, Kwon et al. 2005). The cytokines TNF-
and IL-1ß are known to increase 11HSD1 mRNA and 11-reductase activity in various cell types, such as glomerular mesangial cells (Escher et al. 1997), osteoblasts (Cooper et al. 2001), adipocytes (Tomlinson et al. 2001), and aortic smooth muscle cells (Cai et al. 2001). In addition, pro-inflammatory cytokines are important inducers of nitric oxide generation in macrophages and intestinal epithelial cells, and the interaction between the NO system and the 11HSDs has recently been demonstrated (Kolios et al. 1996, Saito & Nakano 1996, Sun et al. 1997, Ruschitzka et al. 2001).
It is well recognized that glucocorticoids effectively modulate a number of immunological processes, including positive or negative regulation of cytokine production (Hennebold et al. 1996, Ashwell et al. 2000). Therefore, changes in the metabolism of glucocorticoids within peripheral lymphatic organs and in immune cells could modulate not only the suppression of cell activation by pro-inflammatory cytokines but also other immunomodulatory processes (Elenkov & Chrousos 1999, McKay & Cidlowski 1999). Using glomerular mesangial cells exposed to IL-1ß and TNF-
, it was demonstrated that the release of phospholipase A2, a key enzyme producing inflammatory mediators, is decreased by 11HSD1 activity (Escher et al. 1997). Similarly, the pharmacological inhibition of 11HSD in vivo greatly enhanced the susceptibility to progressive bacterial diseases and these changes in resistance following 11HSD inhibition correlated with changes in the patterns of inducible cytokines in lymphocytes and macrophages (Hennebold et al. 1997). Given the central role of 11HSD1 in glucocorticoid action, we can speculate that the increased expression of this enzyme may serve to enhance the exposure of immune cells to active glucocorticoids via the paracrine and/or intracrine pathway.
In summary, our observations are consistent with the notion that inflammation is associated with changes in 11HSD1. Although the mechanism and accurate function of 11HSD1 upregulation is equivocal, the findings suggest that the bioavailability of glucocorticoids in inflamed colon differs from the healthy tissue.
| Acknowledgements |
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Received in final form 25 July 2006
Accepted 11 August 2006
Made available online as an Accepted Preprint 12 September 2006
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