| dc.description.abstract | Interleukin-1 receptor antagonist (IL-1Ra) is a member of the IL-1 cytokine family that binds to IL-1 receptors and subsequently prevents IL-1 from triggering a signal in the cell. IL-1Ra can be produced by a variety of cell types in response to inflammatory stimuli. Accumulating evidences indicates that IL-1Ra functions as an anti-inflammatory cytokine that can block LPS-induced TNF-a and IL-1β production in inflammatory cells. Moreover, the human recombinant IL-1Ra is currently used as a therapeutic agent for rheumatoid arthritis. In this study, we demonstrated that stimulation of Raw 264.7 cells and mouse peritoneal macrophages with LPS increased IL-1Ra release in a time- and dose-dependent manner. The cAMP-specific phosphodiestrase PDE4 inhibitor Rolipram, a cAMP-elevating agent, significantly enhanced the LPS-stimulated IL-1Ra release with the EC50 of approx. 0.3~1 uM. This induction of IL-1Ra by LPS and Rolipram was also observed at the transcriptional level. Moreover, the increase in the IL-1Ra release was mimicked by the treatment of the cells with the PKA activator 6-Bnz-cAMP, whereas the Epac activator 8-pCPT-2’-O-Me-cAMP did not produce the similar effect. In addition, the Rolipram-enhanced IL-1Ra production was reversed by the PKA inhibitor Rp-8-CPT-cAMPS. These results indicated that the effect of Rolipram was mediated by activation of the cAMP/PKA signal pathway. To further dissect among the four PDE4 subtypes (PDE4A, 4B, 4C, 4D) which one is responsible for the regulation of the IL-1Ra production, PDE4-deficient peritoneal macrophages were employed. The results showed that ablation of PDE4B enhanced LPS-stimulated IL-1Ra release to the level similar to that produced by the WT cells treated with both LPS and Rolipram, indicating the effect of Rolipram was mediated by inhibition of PDE4B. Additionally, using anti-IL-1Ra antibody to deplete IL-1Ra in the culture medium, our results indicated that in the presence of LPS alone the TNF-a release could be suppressed by the release of IL-1Ra in the medium. However, the Rolipram-enhanced IL-1Ra release was not responsible for the inhibition of TNF-a release caused by Rolipram. Taken together, these findings suggested that ablation or inhibition of PDE4B activates cAMP/PKA signaling and leads to upregulation of LPS-stimulated IL-1Ra production, which however does not contribute to its down-regulation of TNF-a release in mouse macrophages.
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