Soluble Epoxide Hydrolase Regulates Macrophage Phagocytosis and Lung Bacterial Clearance of Streptococcus Pneumoniae

Authors

• H Li
• JA Bradbury
• ML Edin
• JP Graves
• A Gruzdev
• J Cheng
• SL Hoopes
• LM DeGraff
• MB Fessler
• S Garantiziotis
• SH Schurman
• DC Zeldin

Abstract

Epoxyeicosatrienoic acids (EETs) have potent anti-inflammatory properties. The hydrolysis of EETs by soluble epoxide hydrolase (Ephx2) to biologically less active diols attenuates this anti-inflammatory effect. Macrophage activation is critical to many inflammatory responses; however, the role of EETs and Ephx2 in regulating macrophage function remains unknown. Lung bacterial clearance of the gram-positive bacteria S. pneumoniae, but not the gram-negative bacteria K. pneumoniae, was impaired in Ephx2-/- mice that have increased EET levels. Induction of Tnfα, Il-6 and Il-1β expression was attenuated in Ephx2-/- macrophages compared to wild-type after stimulation with peptidoglycan (PGN), but not after stimulation with lipopolysaccharide (LPS), mannan or zymosan. Consistent with this observation, there was reduced phagocytosis by Ephx2-/- macrophages of S. pneumoniae, but not K. pneumoniae. Rac1/2 and Cdc42 activation was decreased in Ephx2-/- macrophages stimulated with PGN. Similarly, exogenous EETs inhibited phagocytosis as well as expression of Il-1, Il-6, and Tnfα genes in macrophages stimulated with PGN and S. pneumoniae. Genetic disruption of Ephx2, Ephx2 inhibitor treatment, or addition of exogenous EETs attenuated Tlr2 and Pgylrp1 receptor upregulation in PGN-stimulated macrophages. Pglyrp1 siRNA reduced macrophage phagocytosis of S. pneumoniae. Phosphorylation of ERK, p38, AKT and IκBα after PGN stimulation was also attenuated in Ephx2-/- macrophages. Heterologous overexpression of TLR2 and PGLYRP1 in Ephx2-/- macrophages restored macrophage activation and phagocytosis. Defining the role of EETs in macrophage function may lead to development of new therapeutic approaches for bacterial diseases.

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