Dexamethasone and The Long Acting β₂-Adrenergic Receptor Agonist, R,R-formoterrol (RF), Upregulate CCAAT Enhancer Binding Protein (C/EBP) Gene Expression and Induce Production of The Immunoprotective Surfactant Protein D (SP-D) in Alveolar Epithelial Cells

Article Outline

• Rationale
• Methods
• Results
• Conclusion
• Copyright

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Rationale 

The innate immune molecule SP-D is thought to exert an essential protective function during the allergic airway response. The regulation of this lung collectin is unclear but there are indications that corticosteroids and cAMP are necessary for expression of SP-D. We hypothesized that the immunosuppressive actions of dexamethasone and the long acting β₂-adrenergic receptor agonist, RF, are mediated at least partly, by induction of SP-D production in the airways.

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Methods 

Alveolar Type II epithelial cells were isolated from rat lungs and cultured with the combinations of dexamethasone, cAMP and isobutylmethylxanthine (DCI) or with varying concentrations of RF (Sigma) for 4 days. Cells treated with DCI+interleukin-4 (IL-4) were used as positive control. SP-D protein levels in culture supernatants were assessed by Western Blot. Total RNA was isolated, C/EBPβ and SP-D gene expression were studied by real-time PCR.

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Results 

SP-D protein levels were significantly increased in supernatants by treatment with either RF or dexamethasone alone in comparison to the untreated cells. The enhancing effects of RF were dose-dependant between 1 and 100 nM. Furthermore, cells cultured with RF, showed greater SP-D production than the DCI, DCI+IL-4 or dexamethasone-treated cells. Elevation of SP-D mRNA paralleled increases in protein levels. Interestingly, both dexamethasone and RF treatment resulted in upregulation of C/EBPβ gene expression in vitro.

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Conclusion 

Since C/EBPβ activation is an important inducer of SP-D transcription we speculate that RF and dexamethasone may elicit production of SP-D in airway and alveolar epithelial cells through enhancement of expression of this transcription regulator.