Role and regulation of 11β-hydroxysteroid dehydrogenase in lung inflammation
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Yang2010.doc (32.89Mb)
Date
2010Author
Yang, Fu
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Abstract
Glucocorticoids are steroid hormones that have potent anti-inflammatory actions.
Endogenous glucocorticoid action is modulated by 11β-hydroxysteroid
dehydrogenase (11β-HSD) which catalyses the interconversion of active
glucocorticoids (cortisol, corticosterone) and intrinsically inert forms (cortisone,
11-dehydrocorticosterone). There are 2 isozymes; 11β-HSD type 1 regenerates active
glucocorticoids in vivo whereas 11β-HSD type 2 inactivates glucocorticoids.
Although 11β-HSD1 is highly expressed in the lung, its role there has been little
explored. In this study, the expression and localization of 11β-HSD1 mRNA in lung
was confirmed by in situ hybridization. Immunohistochemical staining of mouse
lung localized 11β-HSD1 to the cytoplasm of fusiform cells in alveolar walls, in a
multivesicular pattern characteristic of interstitial fibroblasts. A lung fibrosis model
of inflammation was used to test the role and regulation of 11β-HSD1. The results
suggest that levels of 11β-HSD1 mRNA and enzyme were not changed during
bleomycin-induced lung inflammation. However, 11β-HSD1-deficient mice showed
a more severe inflammatory response than congenic wild-type controls, with greater
inflammatory cell infiltration into the lung, and increased levels of HO-1 and iNOS
mRNA 14 days following bleomycin installation into lung. Picrosirius red staining of
lung sections suggested more collagen deposition in 11β-HSD1-deficient mice than
in wild-type controls during the course of the lung inflammatory response. Moreover,
whereas naïve 11β-HSD1-deficient mice had significantly lower collagen content in
lung (84% of WT levels, p<0.05). 28d after bleomycin there was no significant
difference between genotypes (KO having 94% of WT levels, p=0.42) confirming
more collagen production in 11β-HSD1-deficient mice following bleomycin. Fibroblasts are critical in the regulation of inflammatory responses and are essential
in the model of bleomycin-induced lung injury. Lung fibroblasts may have a different
transcriptional regulation of 11β-HSD1 compared to other tissues. In the majority of
tissues, 11β-HSD1 can be transcribed from 2 promoters; the P1 promoter is the main
promoter used in lung, with other tissues mainly using the P2 promoter. To address
the relevance of the P1 promoter in lung and to identify the cell type using the P1
promoter, mouse lungs were collagenase-digested to isolate primary fibroblast and
epithelial cells. Isolated lung fibroblasts highly expressed 11β-HSD1, predominantly
from the P1 promoter. During passage, primary lung fibroblasts switched promoter
usage from P1 to P2. In fibroblast primary culture, treatment with TGF-β for 72h
markedly decreased 11β-HSD1 expression to 38% of untreated levels, an effect
which was reversed by SB431542, a TGF-β receptor antagonist. Whilst TGF-β
reduced levels of mRNA initiating at the P2 promoter, initiation from the P1
promoter was completely repressed. Treatment with TGF-β receptor antagonist
increased levels of P1-initiated 11β-HSD1 mRNA by 6.6-fold compared to untreated
cells. These data suggest that the switch in 11β-HSD1 promoter usage may be
regulated by TGF-β during an inflammatory response. Furthermore, as the P1 and P2
promoters are differentially regulated (e.g. by C/EBPβ, a cytokine-responsive
transcription factor), the promoter switch may place 11β-HSD1 under a different
transcriptional regulation during inflammation. Taken together, these results suggest
that 11β-HSD1 deficiency worsens lung inflammation and results in greater lung
fibrosis. Therefore, amplification of intracellular glucocorticoids levels, by
11β-HSD1, may represent an important mechanism to limit the inflammatory
response and shape fibroblast function, limiting subsequent collagen production and
fibrosis.