Lipoxin A4 attenuates LPS-induced mouse acute lung injury via Nrf2-mediated E-cadherin expression in airway epithelial cells

A fundamental element of acute lung injury (ALI) is the inflammation that is part of the body's immune response to a variety of local or systemic stimuli. Lipoxins (LXs) are important endogenous lipids that mediate resolution of inflammation. Previously, we demonstrated that LXA(4) reduced the LPS inhalation-induced pulmonary edema, neutrophil infiltration and TNIF-oc production in mice. With the same model, the current investigation focused on the role of the airway epithelium, a first-line barrier and a prime target of inhaled toxicants. We report that LXA(4) strongly inhibited LPS-induced ALI in mice, in part by protecting the airway epithelium and preserving the E-cadherin expression and airway permeability. Using a cryo-imaging assay and fluorescence detection, LXA(4) was shown to block LPS-induced ROS generation and preserve mitochondrial redox status both in vivo and in vitro. To further assess whether and how NF-E2-related factor 2 (Nrf2) was involved in the protective effect of LXA(4), fluorescence resonance energy transfer (FRET) analysis was employed in human epithelial cell line (16HBE), to determine the relative distance between Nrf2 and its negative regulator or cytosolic inhibitor, Kelch-like ECH-associated protein 1 (Keapl). It provided us the evidence that LXA(4) further promoted the dissociation of Nrf2 and Keapl in LPS-treated 16HBE cells. The results also showed that LXA(4) activates Nrf2 by phosphorylating it on Ser40 and triggering its nuclear translocation. Moreover, when the plasmid expression dominant negative mutation of Nrf2 was transfected as an inhibitor of wild-type Nrf2, the protective effect of LXA(4) on E-cadherin expression was almost completely blocked. These results provide a new mechanism by which LXA(4) inhibits LPS-induced ALI through Nrf2-mediated E-cadherin expression. (C) 2016 Elsevier Inc. All rights reserved.