Specific role of phosphodiesterase 4B in lipopolysaccharide-induced signaling in mouse macrophages.

Cyclic nucleotide signaling functions as a negative modulator of inflammatory cell responses, and type 4 phosphodiesterases (PDE4) are important regulators of this pathway. In this study, we provide evidence that only one of the three PDE4 genes expressed in mouse peritoneal macrophages is involved in the control of TLR signaling. In these cells, LPS stimulation of TLR caused a major up-regulation of PDE4B but not the paralogs PDE4A or PDE4D. Only ablation of PDE4B impacted LPS signaling and TNF-alpha production. TNF-alpha mRNA and protein were decreased by >50% in PDE4B-/-, but not in PDE4A-/- or PDE4D-/- macrophages. The PDE4 selective inhibitors rolipram and roflumilast had no additional inhibitory effect in macrophages deficient in PDE4B, but suppressed the TNF-alpha response in the other PDE4 null cells. The inhibition of TNF-alpha production that follows either genetic ablation or acute inhibition of PDE4B is cAMP-dependent and requires protein kinase A activity. However, no global changes in cAMP concentration were observed in the PDE4B-/- macrophages. Moreover, ablation of PDE4B protected mice from LPS-induced shock, suggesting that altered TLR signaling is retained in vivo. These findings demonstrate the highly specialized function of PDE4B in macrophages and its critical role in LPS signaling. Moreover, they provide proof of concept that a PDE4 inhibitor with subtype selectivity retains useful pharmacological effects.