Macrophages activate the production of cytokines and chemokines in response to LPS through signaling cascades downstream from TLR4. Lipid mediators such as PGE(2), which are produced during inflammatory responses, have been shown to suppress MyD88-dependent gene expression upon TLR4 activation in macrophages. The study reported here investigated the effect of PGE(2) on TLR3- and TLR4-dependent, MyD88-independent gene expression in murine J774A.1 macrophages, as well as the molecular mechanism underlying such an effect. We demonstrate that PGE(2) strongly suppresses LPS-induced IFN-beta production at the mRNA and protein levels. Poly (I:C)-induced IFN-beta and LPS-induced CCL5 production were also suppressed by PGE(2). The inhibitory effect of PGE(2) on LPS-induced IFN-beta expression is mediated through PGE(2) receptor subtypes EP(2) and EP(4), and mimicked by the cAMP analog 8-Br-cAMP as well as by the adenylyl cyclase activator forskolin. The downstream effector molecule responsible for the cAMP-induced suppressive effect is exchange protein directly activated by cAMP (Epac) but not protein kinase A. Moreover, data demonstrate that Epac-mediated signaling proceeds through PI3K, Akt, and GSK3beta. In contrast, PGE(2) inhibits LPS-induced TNF-alpha production in these cells through a distinct pathway requiring protein kinase A activity and independent of Epac/PI3K/Akt. In vivo, administration of a cyclooxygenase inhibitor before LPS injection resulted in enhanced serum IFN-beta concentration in mice. Collectively, data demonstrate that PGE(2) is a negative regulator for IFN-beta production in activated macrophages and during endotoxemia.
Animals Cell Line