Responsivity to PGE2 labor induction involves concomitant differential prostaglandin E receptor gene expression in cervix and myometrium.

Prostaglandin E2 (dinoprostone) is largely used for labor induction. However, one-third of patients do not respond to treatment. One cause of this poor response may be associated with changes in regulation of prostaglandin E receptors (EP1-4). In this study, we investigated EP mRNA expression in the uterine cervix and lower uterine segment myometrium for term births. Biopsies were obtained from women with successful (responders) and failed (non-responders) dinoprostone labor induction, while women that underwent spontaneous labor were included as controls. EP1 mRNA was upregulated in the cervical tissue of women who did not respond to dinoprostone induction. In addition, in the myometrium, significantly higher levels of EP3 mRNA were observed in women treated with dinoprostone, independent of their responsiveness. Dinoprostone-responders presented 3.6-fold higher levels of EP3 mRNA expression than the spontaneous labor group. Significantly higher levels of EP3 mRNA in the myometrium of the dinoprostone-treated group indicated that dinoprostone may regulate the EP3 gene on the transcriptional level. These results highlight the relationship between EP gene expression and delivery and indicate that understanding the regulation of prostaglandin E receptors may lead to improved labor induction.

Evidence for prostaglandin E2 receptor expression in the intramural ganglia of the guinea pig urinary bladder.

Intramural ganglia are present in the bladder wall of several species including human, pig, and guinea-pig. It has been suggested that there is a network of intramural ganglia in the bladder of these species that may be part of a motor-sensory system and receive afferent input. Prostaglandins (PG) have been suggested to play a role in this afferent signalling mechanism. To investigate the distribution of the prostaglandin E2 receptors EP1 and EP2 in and around intramural ganglia of the guinea pig, bladders of 6 guinea pigs were dissected, and processed for immunohistochemistry. Sections were examined for prostaglandin E2 receptor EP1- and EP2-immuno-reactivity and co-stained for vimentin, a marker for interstitial cells (IC) and cyclo-oxygenase 1 (COX I), the enzyme responsible for PG synthesis. Immunoreactivities for EP1 and EP2 were found in intramural ganglion cells. These cells were observed in between muscle bundles and on, or close to the serosal surface of the bladder. Furthermore, COX I was present in interstitial cells close to ganglion cells, indicating the possibility of a local synthesis of prostaglandins near the ganglia. The co-staining of EP1 or EP2 with vimentin showed that processes of interstitial cells run through the ganglia, often encircling or ensheathing cells. Therefore, it can be concluded that there is a close relationship between the intramural ganglia and the network of interstitial cells in the muscular layers of the bladder. EP1 and EP2 receptors are expressed on the ganglia and this arrangement suggests that intramural ganglia are involved in (pre)processing afferent information.

PGE2 maintains the tone of the guinea pig trachea through a balance between activation of contractile EP1 receptors and relaxant EP2 receptors.

BACKGROUND AND PURPOSE: The guinea pig trachea (GPT) is commonly used in airway pharmacology. The aim of this study was to define the expression and function of EP receptors for PGE(2) in GPT as there has been ambiguity concerning their role. EXPERIMENTAL APPROACH: Expression of mRNA for EP receptors and key enzymes in the PGE(2) pathway were assessed by real-time PCR using species-specific primers. Functional studies of GPT were performed in tissue organ baths. KEY RESULTS: Expression of mRNA for the four EP receptors was found in airway smooth muscle. PGE(2) displayed a bell-shaped concentration-response curve, where the initial contraction was inhibited by the EP(1) receptor antagonist ONO-8130 and the subsequent relaxation by the EP(2) receptor antagonist PF-04418948. Neither EP(3) (ONO-AE5-599) nor EP(4) (ONO-AE3-208) selective receptor antagonists affected the response to PGE(2). Expression of COX-2 was greater than COX-1 in GPT, and the spontaneous tone was most effectively abolished by selective COX-2 inhibitors. Furthermore, ONO-8130 and a specific PGE(2) antibody eliminated the spontaneous tone, whereas the EP(2) antagonist PF-04418948 increased it. Antagonists of other prostanoid receptors had no effect on basal tension. The relaxant EP(2) response to PGE(2) was maintained after long-term culture, whereas the contractile EP(1) response showed homologous desensitization to PGE(2), which was prevented by COX-inhibitors. CONCLUSIONS AND IMPLICATIONS: Endogenous PGE(2), synthesized predominantly by COX-2, maintains the spontaneous tone of GPT by a balance between contractile EP(1) receptors and relaxant EP(2) receptors. The model may be used to study interactions between EP receptors.

Immunolocalization of adipocytes and prostaglandin E2 and its four receptor proteins EP1, EP2, EP3, and EP4 in the caprine cervix during spontaneous term labor.

The mechanisms of cervical ripening and dilation in mammals remain obscure. Information is lacking about the localization of prostaglandin E(2) (PGE(2))-producing cells and PGE(2) receptors (EP) in intrapartum cervix and whether cervical dilation at parturition is an active process. To reveal these mechanisms, immunolocalization of EP1-EP4 (official gene symbols PTGER1-PTGER4) and PGE(2)-producing cells in caprine cervix during nonpregnancy, pregnancy, and parturition was assayed by immunohistochemistry (IHC); the mRNA expression levels of PTGS2, PTGER2 (EP2), and PTGER4 (EP4) were determined using quantitative PCR; and the existence of adipocytes in the cervix at various stages was demonstrated with Oil Red O staining and IHC of perilipin A. The results suggested that in intrapartum caprine cervix staining of the PGE(2) was observed in the overall tissues, for example, blood vessels, canal or glandular epithelia, serosa, circular and longitudinal muscles, and stroma in addition to adipocytes; EP2 was detectable in all the tissues other than glandular epithelia; EP4 was strongly expressed in all the tissues other than serosa; EP1 was detected mainly in arterioles and canal or glandular epithelia; and EP3 was poorly expressed only in stroma, canal epithelia, and circular muscles. Little or no expression of EP2, EP3, and EP4 as well as PGE(2) in all cervical tissues was observed during nonpregnancy and pregnancy except for the strong expression of EP1 in canal or glandular epithelia during pregnancy. The mRNA expression levels of PTGS2, PTGER2, and PTGER4 were significantly higher in intrapartum than nonpregnant and midpregnant cervices (P < 0.01). Adipocytes appear only in the intrapartum cervix. These results support the concept that PGE(2) modulates specific functions in various anatomical structures of the caprine cervix at labor and the appearance of adipocytes at labor is likely related to caprine cervical dilation.

Function of prostaglandin E2 EP receptors in the acute outcome of rodent hypoxic ischemic encephalopathy.

Neonatal hypoxic-ischemic encephalopathy (HIE) is a leading cause of severe and permanent neurologic disability after birth. The inducible cyclooxygenase COX-2, which along with COX-1 catalyzes the first committed step in prostaglandin (PG) synthesis, elicits significant brain injury in models of cerebral ischemia; however its downstream PG receptor pathways trigger both toxic and paradoxically protective effects. Here, we investigated the function of PGE(2) E-prostanoid (EP) receptors in the acute outcome of hypoxic-ischemic (HI) injury in the neonatal rat. We determined the temporal and cellular expression patterns of the EP1-4 receptors before and after HIE and tested whether modulation of EP1-4 receptor function could protect against cerebral injury acutely after HIE. All four EP receptors were expressed in forebrain neurons and were induced in endothelial cells after HIE. Inhibition of EP1 signaling with the selective antagonist SC-51089 or co-activation of EP2-4 receptors with the agonist misoprostol significantly reduced HIE cerebral injury 24 h after injury. These receptor ligands also protected brain endothelial cells subjected to oxygen glucose deprivation, suggesting that activation of EP receptor signaling is directly cytoprotective. These data indicate that the G-protein coupled EP receptors may be amenable to pharmacologic targeting in the acute setting of neonatal HIE.

The relationship between prostaglandin E receptor 1 and cyclooxygenase I expression in guinea pig bladder interstitial cells: proposition of a signal propagation system.

PURPOSE: We explored the structural relationship between enzymes producing prostaglandin (cyclooxygenase I) and 1 of the receptor families that respond to prostaglandin (prostaglandin E receptor 1) in the bladder muscle. MATERIALS AND METHODS: Nine male guinea pigs were sacrificed by cervical dislocation. Bladders were removed and fixed in 4% paraformaldehyde in phosphate buffered saline. Frozen sections (10 µm) were cut and stained with antibodies to prostaglandin E receptor type 1, cyclooxygenase I and vimentin. RESULTS: Prostaglandin E receptors 1 was identified on smooth muscle cells, and vimentin positive surface muscle and intramuscular interstitial cells. Muscle staining was less intense than on interstitial cells and had a punctuate appearance. Prostaglandin E receptor 1 expression on interstitial cells was highly localized. Discrete regions of intense staining were noted on interstitial cell processes. Cyclooxygenase I was also expressed in muscle interstitial cells. Cyclooxygenase I positive interstitial cells were more prevalent in the muscle bundles of the inner muscle than in the outer muscle layers. Cyclooxygenase I staining was noted on discrete regions of the cell or cell processes. Double staining with prostaglandin E receptor 1 and cyclooxygenase I suggested that cell regions expressing the former are different from those expressing the latter. CONCLUSIONS: The discovered arrangement of prostaglandin E receptor 1 and cyclooxygenase I may have the potential to facilitate the propagation of signals in the interstitial cell network. Such a signaling system may have a role in coordinating events, as in bladder pathology, facilitating the global coordinated changes associated with bladder wall remodeling.

Prostaglandin E receptor EP1 suppresses breast cancer metastasis and is linked to survival differences and cancer disparities.

Cyclooxygenase-2 is frequently overexpressed and associated with poor prognosis in breast cancer. The cyclooxygenase-2 product prostaglandin E(2) elicits cellular responses through four G-protein-coupled receptors, designated EP1 to EP4, coupled to distinct intracellular signaling pathways. EP4, expressed on malignant breast cells, promotes metastasis; however, a role for EP1 in metastasis has not been investigated. Using a murine model of metastatic breast cancer, we now show that pharmacologic antagonism of EP1 with SC19220 or AH6809 promoted lung colonization of mammary tumor cells by 3.7- to 5.4-fold. Likewise, reducing EP1 gene expression by shRNA also increased metastatic capacity relative to cells transfected with nonsilencing vector but did not affect the size of transplanted tumors. Examination of invasive ductal carcinomas by immunohistochemistry shows that EP1 was detected in both the cytoplasm and nucleus of benign ducts as well as malignant cells in some samples, but was absent or limited to either the nucleus or cytoplasm in other malignant samples. Overall survival for women with tumors that were negative for nuclear EP1 was significantly worse than for women with EP1 expression (P = 0.008). There was no difference in survival for women with differences in cytoplasmic EP1 expression (P = 0.46). Comparing EP1 mRNA in breast tumors from African American and European American women revealed that many more African American breast tumors lacked detectable EP1 mRNA (P = 0.04). These studies support the hypothesis that EP1 functions as a metastasis suppressor and that loss of nuclear EP1 is associated with poorer overall survival and may contribute to disparities in outcome in different populations.