Dexamethasone attenuates methacholine‐mediated aquaporin 5 downregulation in human nasal epithelial cells via suppression of NF‐κB activation |
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Authors: | Yung‐Lung Chang PhD Kai Ren Jian BS Chun‐Shu Lin MD Hsing‐Won Wang MD PhD Shao‐Cheng Liu MD PhD |
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Affiliation: | 1. Department of Biochemistry, National Defense Medical Center, Taipei, Taiwan, Republic of China;2. Department of Radiation Oncology, Tri‐Service General Hospital, National Defense Medical Center, Taipei, Taiwan, Republic of China;3. Department of Otolaryngology–Head and Neck Surgery, Tri‐Service General HospitalNational Defense Medical Center;4. Department of Otolaryngology–Head and Neck Surgery, Shuang Ho Hospital, Taipei, Taiwan, Republic of China |
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Abstract: | Background Cholinergic stimulation plays a major role in inflammatory airway diseases. However, its role in airway surface liquid homeostasis and aquaporin 5 (AQP5) regulation remains unclear. In this study we sought to determine the effects of methacholine and dexamethasone on AQP5 expression in human nasal epithelial cells (HNEpC). Methods HNEpC were cultured with methacholine or dexamethasone at 4 concentrations in vitro. The subcellular distribution of AQP5 was explored using immunocytochemistry. The pharmacologic effects of methacholine and dexamethasone on the expression of the phosphorylation of cyclic adenosine monophosphate–responsive element binding protein (p‐CREB), AQP5, and nuclear factor‐kappaB (NF‐κB) were examined using Western blotting. Results AQP5 was found to be located in cell membrane and cytoplasm and present in every group without a statistically significant difference. Methacholine inhibited expression of AQP5 and p‐CREB in HNEpC, whereas dexamethasone increased these protein levels dose‐dependently in a statistically significant manner. In turn, HNEpC treated with methacholine and dexamethasone showed the same trends as those intervened separately with these 2 drugs. Moreover, dexamethasone had the ability to reverse the inhibitory effect of methacholine. Western blotting revealed that, after incubation with 10?4 mol/L methacholine, NF‐κB increased significantly, by 186.67%, compared with the untreated control group. Again, such an increase could be significantly reversed after dexamethasone treatment. Conclusion NF‐κB activation is important for inhibition of p‐CREB/AQP5 expression after methacholine intervention, and dexamethasone adjusts it to the opposite side. This observation could provide additional insight into the anti‐inflammatory effects of glucocorticoids that contribute to maintaining airway surface liquid and mucosal defense. |
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Keywords: | AQP5 CREB dexamethasone methacholine nasal mucosa NF‐κ B |
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