Role of EP4 receptor and prostaglandin transporter in prostaglandin E2-induced alteration in colonic epithelial barrier integrity

Abstract

Prostaglandin E2 (PGE2) is a proinflammatory lipid mediator produced in excess in inflammatory bowel disease (IBD). PGE2 couples to and signals via four different E-prostanoid (EP) receptors, namely EP1, EP2, EP3, and EP4. In this study, we determined a role for PGE2 and EP4 receptors in altering colonic epithelial barrier integrity. In healthy colonic mucosa, EP4 receptors were localized on apical plasma membrane of epithelial cells at the tip of mucosal folds, whereas, in patients with IBD and in rats with dextran sodium sulfate (DSS)-induced colitis, they were diffusely overexpressed throughout the mucosa. Similarly, expression of EP4 receptor was polarized in T84 colonic epithelial monolayer and mimics the normal epithelium. Apical exposure of T84 monolayer with high levels of PGE2 decreased barrier integrity, which was abrogated by an EP4 receptor antagonist. To reveal the mechanism of vectorial transport of basally produced PGE2 toward apical EP4 receptors, we identified prostaglandin transporters (PGT) in human colonic epithelia. PGT were least expressed on epithelial cells at the colonic mucosal folds of control subjects but overexpressed in epithelial cells of patients with IBD or animals with DSS-induced colitis. T84 monolayer also expressed PGT, which increased twofold following stimulation with TNF-α. Importantly, in T84 monolayer stimulated with TNF-α, there was a corresponding increase in the uptake and vectorial transport of 3H-PGE2 to the apical surface. Knockdown or pharmacological inhibition of PGT significantly decreased vectorial transport of 3H-PGE2. These studies unravel a mechanism whereby EP4 receptor and PGT play a role in PGE2-induced alteration of epithelial barrier integrity in colitis.