Physiological levels of lipoxin A ₄ inhibit ENaC and restore airway surface liquid height in cystic fibrosis bronchial epithelium

Abstract

In cystic fibrosis (CF), the airway surface liquid (ASL) is depleted. We previously demonstrated that lipoxin A ₄ (LXA ₄) can modulate ASL height (ASLh) through actions on Cl ⁻ transport. Here, we report novel effects of lipoxin on the epithelial Na ⁺ channel ENaC in this response. ASL dynamics and ion transport were studied using live‐cell confocal microscopy and short‐circuit current measurements in CF (CuFi‐1) and non‐CF (NuLi‐1) cell cultures. Low physiological concentrations of LXA4 in the picomolar range produced an increase in ASLh which was dependent on inhibition of an amiloride‐sensitive Na ⁺ current and stimulation of a bumetanide‐sensitive Cl ⁻ current. These ion transport and ASLh responses to LXA ₄ were blocked by Boc‐2 an inhibitor of the specific LXA4 receptor ALX/FPR2. LXA ₄ affected the subcellular localization of its receptor and enhanced the localization of ALX/FPR2 at the apical membrane of CF cells. Our results provide evidence for a novel effect of low physiological concentrations of LXA ₄ to inhibit airway epithelial Na ⁺ absorption that results in an ASL height increase in CF airway epithelia.

Abstract

LXA4 induced apical membrane ALX/FPR2 localization in CuFi‐1 monolayers. LXA4 induced an apical increase of ALX/FPR2 (green) expression (B). Primary rabbit anti‐ALX/FPR2 antibody and secondary Alexa‐Fluor 488 anti‐rabbit were used to label the ALX/FPR2 receptor. Localization of the receptor at the apical surface is shown in the merged fluorochrome images in yellow (A). Rhodamine‐phalloidin was used to stain f‐actin and DAPI used to stain the nuclei (C).