Hypoxia down-regulates glucocorticoid receptor alpha and attenuates the anti-inflammatory actions of dexamethasone in human alveolar epithelial A549 cells.
OBJECTIVE
Glucocorticoids (GCs) are frequently used to treat various pulmonary diseases, which are typically accompanied by hypoxia. Whether hypoxia influences the effects of GCs on human airway cells remains unclear. The aim of the present study was to characterize changes in the expression levels of two isoforms of the glucocorticoid receptor (GR) and to evaluate the anti-inflammatory actions of GCs under hypoxic conditions in A549 cells.


METHODS
A549 cells were exposed to normoxic or hypoxic conditions for 24, 48 and 72 h. Morphological alterations of cells were captured using a differential interference contrast microscope (DIC), and cell cycle distribution was estimated by flow cytometry. Real-time quantitative polymerase chain reaction and western blot were used to determine the mRNA and protein expression levels of GRalpha and GRbeta. Radioimmunoassay (RIA) for interleukin (IL)-8 was used to assess the anti-inflammatory actions of GCs after cells were stimulated with lipopolysaccharide (LPS).


RESULTS
After cells were exposed to hypoxic conditions for 48 h, visible morphological alterations in the cells were observed. Cell cycle analysis showed that the number of cells in G1 phase increased significantly under hypoxia compared to the normoxic conditions. Hypoxia caused a time-dependent decrease in both mRNA and protein expression levels for GRalpha, but not GRbeta. Furthermore, when exposed to hypoxia for 48 h, the inhibitory effects of dexamethasone on LPS-stimulated IL-8 release were attenuated.


CONCLUSIONS
These results indicate that hypoxia impairs the anti-inflammatory actions of GCs in A549 cells, which could be attributed to down-regulation of GRalpha expression under hypoxic conditions.
Huang
Yan
Y
Department of Pulmonary Anhui Geriatric Institute, the First Affiliated Hospital of Anhui Medical University, Jixi Road 218, Hefei 230022, Anhui, China.
Zhao
Ji-Jing
JJ
Lv
Yuan-Yuan
YY
Ding
Pei-Shan
PS
Liu
Rong-Yu
RY
D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D002460:Cell Line; D049109:Cell Proliferation; D003907:Dexamethasone / Q000494:pharmacology*; D015536:Down-Regulation; D006801:Humans; D000860:Hypoxia / Q000378:metabolism* / Q000473:pathology; D016209:Interleukin-8 / Q000037:antagonists & inhibitors / Q000378:metabolism; D020033:Protein Isoforms / Q000096:biosynthesis; D011650:Pulmonary Alveoli / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D011965:Receptors, Glucocorticoid / Q000096:biosynthesis*; D020545:Respiratory Mucosa / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology
D000893:Anti-Inflammatory Agents; D016209:Interleukin-8; D020033:Protein Isoforms; D011965:Receptors, Glucocorticoid; C411470:glucocorticoid receptor alpha; C121943:glucocorticoid receptor beta; D003907:Dexamethasone