Activation of prostaglandin EP4 receptor attenuates the induction of cyclooxygenase‐2 expression by EP2 receptor activation in human amnion fibroblasts: implications for parturition

Abstract

Human amnion fibroblasts produce abundant prostaglandin E2 (PGE2), which plays a crucial role in parturition by stimulating not only myometrial contraction and cervical ripening but also the expression of the rate‐limiting enzyme in PGE2 synthesis—namely, cyclooxygenase‐2 (COX‐2). This feed‐forward induction of COX‐2 expression by PGE2 is mediated via its receptors coupled with the cAMP and PKA pathway and subsequent phosphorylation of the transcription factors cAMP‐response element binding protein (CREB) and signal transducer and activator of transcription 3 (STAT3). Although prostaglandin E receptor (EP)‐2 and EP4 for PGE2 are coupled with activation of the cAMP and PKA pathway, the exact roles of these 2 receptors in the regulation of COX‐2 expression in amnion fibroblasts remain to be determined. Here, we clarify this issue by employing human amnion tissue and fibroblasts with the long‐term objective of specific targeting of prostaglandin synthesis in prevention of preterm birth. We find that an EP2 agonist caused long‐lasting increases in CREB phosphorylation and COX‐2 expression, whereas an EP4 agonist induced only transient increases in CREB phosphorylation and COX‐2 expression in amnion fibroblasts. Moreover, only EP2 stimulation increased STAT3 phosphorylation, whereas only EP4 stimulation increased PI3K activity. EP4 antagonist or inhibition of PI3K enhanced the induction of CREB and STAT3 phosphorylation and COX‐2 expression by PGE2 or EP2 stimulation, which was attenuated by EP4 overexpression. Of interest, PGE2 and Cortisol, both well‐demonstrated stimulants of COX‐2 expression in amnion fibroblasts, increased EP2 but decreased EP4 receptor expression. Furthermore, increased EP2 but decreased EP4 abundance were observed in amnion tissue at parturition. We conclude that EP2 and EP4 receptors play different roles in the regulation of COX‐2 expression in human amnion fibroblasts. EP2 is the dominant PGE2 receptor mediating the induction of COX‐2 at parturition, which can be attenuated by simultaneous activation of PI3K coupled to the EP4 receptor.—Lu, J.‐W., Wang, W.‐S., Zhou, Q., Gan, X.‐W., Myatt, L., Sun, K. Activation of prostaglandin EP4 receptor attenuates the induction of cyclooxygenase‐2 expression by EP2 receptor activation in human amnion fibroblasts: implications for parturition. FASEB J. 33, 8148–8160 (2019). http://www.fasebj.org

Wnt signaling enhances macrophage responses to IL-4 and promotes resolution of atherosclerosis

“…Our data further suggest that STAT3 is activated following Wnt stimulation via PGE , since the latter is produced by Wnt3a treated BMDMs ( Figure 8A) and has been shown to promote the phosphorylation of STAT3 in various cell types [46][47][48][49] . Wnt signaling promotes the production of PGE through transcriptional regulation of Ptgs2 50,51 , with similar results shown in Figure 8C.…”

“…Of the upregulated metabolites we focused on PGE 2 because of its function as an amplifier of IL-4 responses 29,[43][44][45] (Figure 8 figure supplement 1C) and its role as a STAT3 activator in various cell types [46][47][48][49] Figure 8B), despite marked differences in the IL-4 concentrations used in these experiments (0.1ng/mL and 20ng/mL , respectively).…”

C/EBPδ drives key endocrine signals in the human amnion at parturition

“…19,27,28 Of interest, in addition to COX-2, glucocorticoids also induce the expression of its own regenerating enzyme 11β-HSD1 in amnion fibroblasts so that a feedforward reaction for glucocorticoid regeneration and PG production is ensured toward the end of gestation in the fetal membranes in preparation for the onset of parturition. 29,30 Apart from the induction of 11β-HSD1 and COX-2 expression by glucocorticoids, [31][32][33][34] a number of other factors pertinent to parturition such as PGs and proinflammatory cytokines have also been shown to induce the expression of both 11β-HSD1 and COX-2 in amnion fibroblasts, 29,[35][36][37][38] which further illustrates the crucial roles of these genes in parturition.…”

Cortisol Regeneration in the Fetal Membranes, A Coincidental or Requisite Event in Human Parturition?

“…We set out to delineate this paradoxical mechanism and it turned out to be a very complicated mechanism. It is revealed that glucocorticoids induce cPLA2 and COX-2 expression through stimulation of the cAMP/PKA pathway with subsequent activation of multiple transcription factors including CREB and STAT3, and so on (Zhu et al, 2009;Guo et al, 2010;Wang et al, 2015;Lu et al, 2017Lu et al, , 2019a. Interestingly, the classical inflammatory transcription factor, nuclear factor κB, is nevertheless inhibited by glucocorticoids (Guo, 2010), which is responsible for the inhibition of proinflammatory cytokine expression in human amnion fibroblasts, a situation resembling most of non-gestational tissues.…”