Carboxylesterase 1 contributes to the human macrophage alternative activation response to Th2 cytokine interleukin-4.

Carboxylesterase 1 (CES1) is a hydrolytic enzyme with roles in xenobiotic and lipid metabolism. Our previous studies suggested a novel role for CES1 in the regulation of macrophage gene expression following exposure to inflammatory molecules. The nuclear receptor PPARγ has an important role in the M(IL-4) polarization response. Here, we investigated CES1 in human primary macrophages and THP-1 macrophages during M(IL-4) polarization. We hypothesized that ablating CES1's activity would decrease ligand signaling through PPARγ, thereby reducing the M2 polarization response. Inhibition of CES1's activity by small-molecule inhibitors (WWL113 or WWL229) attenuated the mRNA expression of several IL-4-induced M2 markers, including ALOX15. Similar results were found in macrophages in which CES1 or PPARg expression was silenced. Immunoblot and mass spectrometric analyses indicated that IL-4-induced ALOX15 and its enzymatic product, 15-hydroxyeicosatetraenoic acid, were both reduced by CES1 inhibition. Further, a PPARγ antagonist (GW9662) also altered the profile of IL-4-induced M2 markers. The M(IL-4)-induced increase in endogenous PPARγ ligands was augmented by WWL113. Surprisingly, PPARγ agonist "add-back" strengthened the WWL113-mediated repression of IL-4-induced ALOX15 expression, whereas IL-4-induced FABP4 mRNA levels were augmented. Collectively, these results suggest that CES1 has a complex role in driving the alternative activation phenotype in response to IL-4, possibly through an ability to influence PPARγ. These findings are consistent with previous work in which CES1 appeared to hold in check the inflammatory response of innate immune cells. The significance of our findings is that CES1 appears to contribute to the integration of extracellular signals that shape macrophage phenotypes.