The pulmonary microvascular endothelial barrier function is controlled by the PGE2-EP4 signaling axis
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KeywordsEndothelial Monolayer Electric Cell Substrate Impedance Sensing Pulmonary Microvascular Endothelial Cell Adenylyl Cyclase Inhibitor Human Pulmonary Microvascular Endothelial Cell
Endothelial cells, like gate-keepers of the vascular bed, can actively protect against the inflammatory process. Prostaglandin E2 (PGE2) could be one of the mediators that can promote the barrier function of endothelial cells. PGE2 exerts its cellular effects by binding to four different E-prostanoid receptors (EP1–4) that belong to the family of G protein-coupled receptors. This project aimed at characterizing the barrier-protective properties of PGE2 and especially EP4 receptor on human pulmonary microvascular endothelial cells (HMVEC-L).
The endothelial barrier properties were analyzed by measurements of transendothelial electrical resistance (TEER) by Endohm and by ECIS (Electric Cell substrate Impedance Sensing) devices. Morphological studies were performed with immunofluorescence microscopy. Different protein expressions were detected by flow cytometry. Leukocyte diapedesis was studied by performing transendothelial migration assays of neutrophils and eosinophils.
We found that the EP4 receptor is expressed on HMVEC-L. PGE2 and the selective EP4 receptor agonist (ONO-AE1-329) prevented the barrier-disrupting effect of thrombin on the endothelial monolayer, as it was visualized by VE-cadherin staining. Selective blocking of EP4 receptors (EP4 antagonist ONO-AE3-208) inhibited the protective effect of PGE2 on endothelial monolayers. PGE2 and the EP4 agonist enhanced the regeneration of electrically wounded endothelial monolayers. The specificity of EP4 receptor involvement was proven by using the EP4 receptor antagonist and selective agonists for EP2 and EP3 receptors. PGE2 and the EP4 receptor agonist attenuated the TNF-α-induced up-regulation of E-selectin. Surprisingly, this effect was not affected by an adenylyl cyclase inhibitor, but inhibition of PKC activity reversed the effect of the EP4 receptor agonist and PGE2 at reducing the E-selectin expression. In the cell interaction assays, thrombin or TNF-α increased the permeability of endothelial monolayers which also enhanced the transmigration of neutrophils and eosinophils, respectively. These effects were prevented by the selective activation of EP4 receptors.
Our data support the hypothesis that endothelial cells, as gate-keepers of the vessel wall can actively participate in the inflammatory process. We have shown that PGE2, via activating EP4 receptors, enhances the barrier function of the endothelium by protecting the endothelial adherent junctional network and preventing leukocyte diapedesis. Therefore, EP4 agonists might be promising new therapeutic tools in treating inflammatory diseases.
This article is published under license to BioMed Central Ltd.