A regulatory loop involving the cytochrome P450-soluble epoxide hydrolase axis and TGF-b signaling

Fatty acid metabolites generated by the sequential actions of cytochrome P450 enzymes and the soluble epoxide hydrolase (sEH) regulate inflammation. Here we report that the TGF--induced polarization of macrophages to a pro-resolving phenotype requires the activation of Alk5 and Smad2 to increase sEH expression and activity. Macrophages lacking sEH failed to fully repolarize, were less efficient at phagocytosis, and retained a pro-inflammatory gene expression profile. 11,12-Epoxyeicosatrienoic acid (EET) was one of the fatty acid metabolites altered in sEH-/- macrophages and was able to reproduce the effect of sEH deletion on gene expression. Importantly, 11,12-EET also attenuated the expression of Alk5 to inhibit the TGF--induced phosphorylation of Smad2 by eliciting the cytosolic translocation of the E3 ligase Smurf2. These results indicate that the expression of sEH is not only controlled by TGF- but that the activity of the enzyme, which keeps 11,12-EET levels low, actually promotes TGF- signaling by preventing the proteolytic degradation of Alk5. Thus, an autocrine loop between the sEH/11,12-EET and TGF-1 determines macrophage function.