Prostaglandin E2 Produced by Entamoeba histolytica Signals via EP4 Receptor and Alters Claudin-4 to Increase Ion Permeability of Tight Junctions

Entamoeba histolytica is a protozoan parasite that causes amebic dysentery characterized by severe watery diarrhea. Unfortunately, the parasitic factors involved in the pathogenesis of diarrhea are poorly defined. Prostaglandin E2 (PGE2) is a host lipid mediator associated with diarrheal diseases. Intriguingly, E. histolytica produces and secretes this inflammatory molecule. We investigated the mechanism whereby ameba-derived PGE2 induces the onset of diarrhea by altering ion permeability of paracellular tight junctions (TJs) in colonic epithelia. PGE2 decreased barrier integrity of TJs in a dose- and time-dependent manner, as measured by transepithelial resistance. PGE2 signals were selectively transduced via the EP4 receptor. Furthermore, PGE2 signaling decreased TJ integrity, as revealed by EP receptor-specific agonist and antagonist studies. Loss of mucosal barrier integrity corresponded with increased ion permeability across TJs. Subcellular fractionation and confocal microscopy studies highlighted a significant spatial alteration of an important TJ protein, claudin-4, that corresponded with increased sodium ion permeability through TJs toward the lumen. Moreover, PGE2-induced luminal chloride secretion was a prerequisite for alterations at TJs. Thus, the gradient of NaCl created across epithelia could serve as a trigger for osmotic water flow that leads to diarrhea. Our results highlight a pathological role for E. histolytica-derived PGE2 in the onset of diarrhea.