Prostaglandin E₂Produced byEntamoeba histolyticaBinds to EP4 Receptors and Stimulates Interleukin-8 Production in Human Colonic Cells

Abstract

Entamoeba histolytica pathogenesis in the colon occurs in a stepwise fashion. It begins with colonization of the mucin layer, which is followed by stimulation of a proinflammatory response that causes nonspecific tissue damage that may facilitate parasite invasion of the underlying colonic mucosa. Unfortunately, the parasite and/or host factors that stimulate a proinflammatory response in the gut are poorly understood. In this study, we found that live E. histolytica or secretory or proteins (SP) and soluble ameba components (SAP) can markedly increase interleukin-8 (IL-8) mRNA expression and protein production in colonic epithelial cells. The IL-8-stimulating molecule produced by live amebae was identified as prostaglandin E 2 (PGE 2 ) as trophozoites treated with cyclooxygenase inhibitors inhibited the biosynthesis of PGE 2 and eliminated IL-8 production induced by live parasites or ameba components. Moreover, using specific prostaglandin EP2 and EP4 receptor agonists and antagonists, we found that PGE 2 binds exclusively through EP4 receptors in colonic epithelial cells to stimulate IL-8 production. Silencing of EP4 receptors with EP4 small interfering RNA completely eliminated SP-and SAP-induced IL-8 production. These studies identified bioactive PGE 2 as a one of the major virulence factors produced by E. histolytica that can stimulate the potent neutrophil chemokine and activator IL-8, which can trigger an acute host inflammatory response. Thus, the induction of IL-8 production in response to E. histolytica-derived PGE 2 may be a mechanism that explains the initiation and amplification of acute inflammation associated with intestinal amebiasis.Entamoeba histolytica is an enteric protozoan parasite and the fourth leading cause of death due to a parasite (26). Humans are the only known host for E. histolytica, and about 50 million people are affected worldwide each year. The pathogenesis of amebiasis is believed to be a multistep and multifactorial process. Although a large number of studies have attempted to unravel the factors or molecules responsible for the pathogenesis of amebiasis, the processes involved in pathogenesis are not well understood. In most infected individuals, E. histolytica trophozoites exist as commensals. However, in a small percentage of infections, amebae can elude luminal and epithelial barrier host defense mechanisms and invade the intestinal mucosa, causing ulcers and amebic colitis. Even though host inflammatory responses play an important role in the onset and progression of invasive amebiasis, little is known about the parasite factors that initiate this event. Even less is known about the parasite components that are secreted or released in the gut and can modulate colonic epithelial cell functions.

Kinetics of Serum and Local Leukotriene B<sub>4</sub> Response in Experimental Intravaginal Trichomoniasis by <i>T. vaginalis</i> Isolates from Symptomatic and Asymptomatic Women

“…On other hand, LTB 4 down-regulate IL-12, and up-regulate IL-10 by dendritic cells leading to immune tolerance [48]. These results also correlated well with the earlier reports conducted in experimental animals whereby Increase in LTB 4 in intestine has been demonstrated in other nematode-infected animals [49] [50] and other protozoan parasite as Entamoeba histolytica [51]. Experimental studies conducted on Strongyloides venezuelensis indicated greater LTB 4 release in the lungs, duodena and serum than that seen in the tissue of uninfected animals.…”

The Prostanoid EP4 Receptor and Its Signaling Pathway

“…These data suggest that PGE 2 coupling through EP4 and EP2 receptors can therefore act in an opposing manner to either promote (EP4) or decrease (EP2) IL-8 expression, even though both receptors use the same second messenger, cAMP. Since Chadee's laboratory has reported that PGE 2 promotes IL-8 production in the human colonic epithelial cell lines Caco-2 and T84 through both the PKA and PI3K pathways (Dey and Chadee, 2008;Dey et al, 2009;Srivastava et al, 2012), it appears that EP4 contributes to IL-8 production.…”

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

“…COX inhibitors were removed by centrifugation, followed by 2 hours of incubation in fresh HBSS for collecting SP as described previously. 18 In another experiment, 100 mol/L AA was added to trophozoites in HBSS at the start of the 2-hour incubation and SP was collected.…”

“…We have recently shown that E. histolytica PGE 2 signals via the host epithelial EP4 receptors to induce robust IL-8 secretion that could augment inflammation. 18 Because PGE 2 is strongly associated with various diarrheal diseases, however, we reasoned that ameba-derived PGE 2 might play a major role in the onset of diarrhea during acute amebic colitis.…”