To investigate whether PDE4B regulates the expression of additional inflammatory mediators other than TNF-a and whether inhibition of PDE4B is sufficient to block these responses in macrophages, in this study we used two-dimensional (2D) gel electrophoresis to screen the secreted proteins that are modulated by the PDE4 inhibitor rolipram in LPS-stimulated Raw 264.7 cells.
The generation of mice deficient in PDE4A, PDE4B, and PDE4D has been described previously.
Contrarily, LPS-induced CCL3 production was significantly decreased in PDE4B[sup]−/− macrophages ( P < 0.01), exerting 62% decrease compared to the PDE4B [sup]+/+ macrophages.
[sup] To determine whether these signal pathways mediate the effect of PDE4 inhibitors or PDE4B ablation on CCL3 production, mouse peritoneal macrophages were stimulated with LPS in the presence of the cAMP analog dibutyryl-cAMP (db-cAMP), the Epac activator 8-pCPT-2′-O-Me-cAMP or the PKA activator 6-Bnz-cAMP.
Of the three proteins identified, TNF-a regulation by PDE4B has been studied extensively, [sup],,,, whereas the information on CCL3 and IL-1Ra regulation by PDE4 subtypes remains largely unclear.
Using PDE4-deficient macrophages and their wild-type counterparts, we demonstrated that the pharmacological effect of rolipram on LPS-induced CCL3 production is exerted mainly through inhibition of PDE4B, one of the three PDE4 subtypes expressed in macrophages.
Like its impact on TNF-a production, ablation or inactivation of PDE4B also suppressed LPS-induced CCL3 production in macrophages.