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-α production. TNF-α 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-α response in the other PDE4 null cells. The inhibition of TNF-α 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.

␤ adrenoceptor (␤AR) signaling is finely regulated to mediate the sympathetic nervous system control of cardiovascular function. In neonatal cardiac myocytes, ␤1AR activates the conventional Gs͞ cAMP pathway, whereas ␤2AR sequentially activates both the Gs and Gi pathways to regulate the myocyte contraction rate. Here, we show that phosphodiesterase 4D (PDE4D) selectively impacts signaling by ␤2AR in neonatal cardiac myocytes, while having little or no effect on ␤1AR signaling. Although ␤2AR activation leads to an increase in cAMP production, the cAMP generated does not have access to the protein kinase A-dependent signaling pathways by which the ␤1AR regulates the contraction rate. However, this restricted access is lost in the presence of PDE4 inhibitors or after ablation of PDE4D. These results not only suggest that PDE4D is an integral component of the ␤2AR signaling complex, but also underscore the critical role of subcellular cAMP regulation in the complex control of receptor signaling. They also illustrate a mechanism for fine-tuned ␤AR subtype signaling specificity and intensity in the cardiac system. cAMP ͉ heart ͉ knockout

␤-Arrestins are pleiotropic molecules that mediate signal desensitization, G-protein-independent signaling, scaffolding of signaling molecules, and chemotaxis. Protease-activated receptor-2 (PAR-2), a G␣ q/11 -coupled receptor, which has been proposed as a therapeutic target for inflammation and cancer, requires the scaffolding function of ␤-arrestins for chemotaxis. We hypothesized that PAR-2 can trigger specific responses by differential activation of two pathways, one through classic G␣ q /Ca 2؉ signaling and one through ␤-arrestins, and we proposed that the latter involves scaffolding of proteins involved in cell migration and actin assembly. Here we demonstrate the following.

CD47 exerts different effects on disease in distinct cell types and locations and during different stages of experimental autoimmune encephalomyelitis.