EP Receptor Subtypes Research Articles

Stimulation of gastroduodenal HCO3- secretion by lubiprostone mediated by different prostaglandin EP receptor subtypes

We examined the stimulatory effects of lubiprostone, a bicyclic fatty acid derived from prostaglandin E1 and a chloride channel type-2 opener (ClC-2), on HCO3- secretion in the rat stomach and duodenum, with a focus on the EP receptor subtypes involved in this action. Under urethane anesthesia, an ex-vivo chambered stomach or a duodenal loop was perfused with saline, and HCO3- secretion was measured at pH 7.0 using a pH stat-method. Lubiprostone (0.1–30 μM) was perfused in the chamber or loop for 10 min. Indomethacin, ONO-8711 (an EP1 antagonist), or AE5-599 (an EP3 antagonist) was given s.c. 1 h before the lubiprostone treatment, while AE3-208 (an EP4 antagonist) or CFTRinh-172 (a cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor) was given i.p. 30 min before. Lubiprostone dose-dependently and significantly increased HCO3- secretion in both the stomach (≥ 10 μM) and duodenum (≥ 1 μM). The stimulatory effect in the stomach was significantly abrogated by a pretreatment with the EP1 antagonist, but not the EP3/EP4 antagonists or CFTR inhibitor, while that in the duodenum was significantly attenuated by the EP3/EP4 antagonists as well as the CFTR inhibitor. Indomethacin had no effect on the response of either tissue to lubiprostone. These results suggest that lubiprostone stimulated HCO3- secretion in the stomach and duodenum in a manner that was mediated by different EP receptor subtypes; the former was mediated by EP1 receptors, while the latter was mediated by both EP3 and EP4 receptors. CFTR/ClC-2 may be involved in the response observed in the duodenum, but not in the stomach.

Discovery and Characterization of 1H-1,2,3-Triazole Derivatives as Novel Prostanoid EP4 Receptor Antagonists for Cancer Immunotherapy.

The prostanoid EP4 receptor is one of the key receptors associated with inflammatory mediator PGE2-elicited immunosuppression in the tumor microenvironment. Blockade of EP4 signaling to enhance immunity-mediated tumor elimination has recently emerged as a promising strategy for cancer immunotherapy. In our efforts to discover novel subtype-selective EP4 antagonists, we designed and synthesized a class of 1H-1,2,3-triazole-based ligands that display low nanomolar antagonism activity toward the human EP4 receptor and excellent subtype selectivity. The most promising compound 59 exhibits single-digit nanomolar potency in the EP4 calcium flux and cAMP-response element reporter assays and effectively suppresses the expression of multiple immunosuppression-related genes in macrophage cells. On the basis of its favorable ADMET properties, compound 59 was chosen for further in vivo biological evaluation. Oral administration of compound 59 significantly inhibited tumor growth in the mouse CT26 colon carcinoma model accompanied by enhanced infiltration of cytotoxic T lymphocytes in the tumor tissue.

Role of the PGE2 receptor subtypes EP1, EP2, and EP3 in repetitive traumatic brain injury.

AimsThe goal was to explore the signaling pathways of PGE2 to investigate therapeutic effects against secondary injuries following TBI.MethodsYoung (4.9 ± 1.0 months) and aged (20.4 ± 1.4 months) male wild type (WT) C57BL/6 and PGE2 EP1, 2, and 3 receptor knockout mice were selected to either receive sham or repetitive concussive head injury. Immunohistochemistry protocols with Iba1 and GFAP were performed to evaluate microgliosis and astrogliosis in the hippocampus, two critical components of neuroinflammation. Passive avoidance test measured memory function associated with the hippocampus.ResultsNo differences in hippocampal microgliosis were found when aged EP2−/− and EP3−/− mice were compared with aged WT mice. However, the aged EP1−/− mice had 69.2 ± 7.5% less hippocampal microgliosis in the contralateral hemisphere compared with WT aged mice. Compared with aged EP2−/− and EP3−/−, EP1−/− aged mice had 78.9 ± 5.1% and 74.7 ± 6.2% less hippocampal microgliosis in the contralateral hemisphere. Within the EP1−/− mice, aged mice had 90.7 ± 2.7% and 81.1 ± 5.6% less hippocampal microgliosis compared with EP1−/− young mice in the contralateral and ipsilateral hemispheres, respectively. No differences were noted in all groups for astrogliosis. There was a significant difference in latency time within EP1−/−, EP2−/−, and EP3−/− on day 1 and day 2 in aged and young mice.ConclusionThese findings demonstrate that the PGE2 EP receptors may be potential therapeutic targets to treat repetitive concussions and other acute brain injuries.

Prostaglandin E2 receptor EP3 subtype in the paraventricular hypothalamic nucleus mediates corticotropin-releasing factor-induced elevation of plasma noradrenaline levels in rats

Corticotropin-releasing factor (CRF) plays an important role in sympathetic regulation. Centrally administered CRF elevates plasma catecholamine levels, resulting in CRF-dependent hypertension and tachycardia. We previously reported that brain thromboxane A2 mediates CRF-induced elevation of plasma adrenaline levels, whereas prostanoids other than thromboxane A2 mediate elevations in plasma noradrenaline levels. However, the mechanism by which CRF induces elevations in plasma noradrenaline levels remains unknown. Previous studies have revealed that brain prostaglandin (PG) E2, but not other PGs, causes sympathetic activation. In this study, we examined the roles of brain PGE2 and its receptors in CRF-induced elevation of plasma noradrenaline levels in rats. Our results showed that intracerebroventricular pretreatment with an antagonist of the PGE2 receptor EP3 subtype, but not other subtypes, suppressed CRF-induced elevations in plasma noradrenaline levels. We also examined the role of PGE2 and EP3 receptors in the paraventricular hypothalamic nucleus (PVN), the major integrative center for sympathetic regulation, in CRF-induced elevation of plasma noradrenaline levels. Centrally administered CRF increased PGE2 levels in PVN microdialysates, and microinjection of an EP3 receptor agonist into the PVN elevated plasma noradrenaline levels. Bilateral blockade of EP3 receptors in the PVN suppressed the elevation of plasma noradrenaline levels evoked by intracerebroventricular administration and PVN-microinjection of CRF. Our results suggest that CRF stimulates PGE2 release into the PVN that activates EP3 receptors in the PVN, resulting in the elevation of plasma noradrenaline levels.

Abstract 488: Overexpression of the Prostaglandin E2 EP3 Receptor Reduces Cardiac Function in an Angiotensin II Model of Hypertension

Prostaglandin E2 (PGE2) EP receptor subtypes EP3 and EP4 are present in the heart and signal via decreased and increased cAMP production, respectively. Previously we reported that cardiomyocyte-specific EP4 KO mice develop a phenotype of dilated cardiomyopathy with reduced ejection fraction, that PGE2 decreases contractility via EP3 in vivo, in vitro and ex vivo; and that EP3 expression in the heart increases when mice are subjected to Angiotensin (Ang) II-hypertension (HTN). We therefore hypothesized that overexpression of EP3 in the heart would exacerbate Ang II-HTN. To test this hypothesis, we used 10-12 week old male EP3 transgenic (Tg) mice with EP3 overexpression in cardiomyocytes and their wild type (WT) controls infused with either vehicle or 1.4 mg/kg/d Ang II for 2 weeks. Echocardiography was performed on conscious mice at the end of the experiment and systolic blood pressure (SBP) was measured every 2 days by tail cuff. Results: Table 1. All data are reported as means ± SEM. N= 3-6 mice per group. Statistical significance: * and *** p < 0.05 and p < 0.005 vs WT + vehicle, ++ p < 0.01 vs WT + Ang II, §§§ p < 0.005 vs Tg + vehicle. As shown in the table, cardiac function was unaffected in WT mice after Ang II infusion. Baseline cardiac function was reduced in EP3 Tg mice receiving vehicle and in contrast to WT mice, was further diminished after Ang II infusion. These differences were not due to altered systolic blood pressure. In conclusion, EP3 Tg mice present with reduced cardiac function at baseline and in support of our hypothesis, exhibit an enhanced response to Ang II. Antagonism of the EP3 receptor may be a novel treatment for heart failure associated with hypertension.

Beraprost Upregulates KV Channel Expression and Function via EP4 Receptor in Pulmonary Artery Smooth Muscle Cells Obtained from Rats with Hypoxia-Induced Pulmonary Hypertension

The reduced expression and function of voltage-dependent potassium (K_V) channels have been involved in the pathogenesis of hypoxia-induced pulmonary hypertension (HPH), leading to pulmonary vasoconstriction and vascular remodeling, while the upregulation of K_V channels is of therapeutic significance for pulmonary hypertension. Beraprost sodium (BPS) has been shown to be effective in patients with pulmonary hypertension. However, the effect of BPS on O₂-sensitive K_V channels in pulmonary artery smooth muscle cells (PASMCs) remains unclear. In the present study, the effect of BPS on rats with HPH was observed, and the influence of BPS on the expression and function of O₂-sensitive K_V channels in PASMCs was investigated. The results revealed that BPS reduced mean pulmonary artery pressure, suppressed right ventricular hypertrophy, and attenuated the remodeling of pulmonary arteries in rats exposed to discontinuous hypoxia for 4 weeks (8 h/day). This was accompanied with the significantly upregulated expression of K_V channel α-subunits (K_V1.2, K_V1.5 and K_V2.1) and O₂-sensitive voltage-gated K⁺ (K_V) channel current (I_K(V)) in small pulmonary arteries in HPH model rats, as well as in hypoxia-induced PASMCs. Furthermore, in vitrostudies have revealed that the upregulation of BPS on O₂-sensitive K_V channels was significantly inhibited after treatment with prostaglandin E₂ receptor subtype EP₄ antagonist GW627368X. Taken together, these results suggest that BPS attenuates the development of HPH through the upregulation of O₂-sensitive K_V channels, which was probably via the EP₄ receptor-related pathway.

Prostaglandin F2α Facilitates Platelet Activation by Acting on Prostaglandin E2 Receptor Subtype EP3 and Thromboxane A2 Receptor TP in Mice.

Platelets play an important role in both physiological hemostasis and pathological thrombosis. Thromboxane (TX) A2 and prostaglandin (PG) I2 are well known as a potent stimulator and an inhibitor of platelet function, respectively. Recently, PGE2 has also been reported to regulate platelet function via PGE2 receptor subtypes. However, the effect of PGF2α on platelet function remains to be determined. The aim of the present study was to clarify the effect of PGF2α on murine platelet function both in vitro and in vivo. Platelets prepared from wild-type mice (WT platelets) expressed several types of prostanoid receptors, including the PGE2 receptor subtype EP3 and the TXA2 receptor TP, while expression of the PGF2α receptor FP was not detected. In WT platelets, PGF2α potentiated adenosine diphosphate-induced aggregation in a concentration-dependent manner, while PGF2α alone did not induce aggregation. In platelets prepared from mice lacking FP, however, PGF2α-induced potentiation was not significantly different from that in WT platelets. Interestingly, the potentiation was significantly blunted in platelets lacking EP3 or TP and disappeared completely in platelets lacking both EP3 and TP. Accordingly, PGF2α decreased the cyclic adenosine monophosphate level via EP3 and increased the inositol triphosphate level via TP in WT platelets. Intravenously administered PGF2α significantly shortened the bleeding time and aggravated arachidonic acid-induced acute thromboembolism in WT mice, suggesting that PGF2α works as a platelet stimulator also in vivo. In conclusion, PGF2α potentiates platelet aggregation in vitro via EP3 and TP but not FP. Accordingly, PGF2α facilitates hemostasis and thromboembolism in vivo.

Roles of multiple lipid mediators in stress and depression

Prolonged or excessive stress may induce emotional and cognitive disturbances, and is a risk factor for mental illnesses. Using rodent chronic stress models of depression, roles of multiple lipid mediators related to inflammation have been revealed in chronic stress-induced emotional alterations. Prostaglandin (PG) E2, an arachidonic acid (AA)-derived lipid mediator, and its receptor subtype EP1 mediate depression-like behavior induced by repeated social defeat stress through attenuating prefrontal dopaminergic activity. Repeated social defeat stress activates microglia through innate immune receptors, and induces PGE2 synthesis through cyclooxygenase-1, a prostaglandin synthase enriched in microglia. PGD2, another AA-derived lipid mediator, has been implicated in depression induced by chronic stress, although either pro-depressive or anti-depressive actions have been reported. Chronic stress up-regulates hippocampal expression of 5-lipoxygenase, hence synthesis of cysteinyl leukotrienes, thereby inducing depression through their receptors. Consistent with beneficial effects of n-3 fatty acids in the diet of depressive patients, resolvins-a novel class of pro-resolving lipid mediators-in the brain attenuate neuroinflammation-associated depression. These findings in animal models of depression offer lipid mediators and related molecules as novel therapeutic targets for treating depression. To translate these findings into clinics, translational biomarkers to visualize lipid mediator profiles in depressive patients need to be established.

Suppressing pro-inflammatory prostaglandin signaling attenuates excitotoxicity-associated neuronal inflammation and injury

Glutamate receptor-mediated excitotoxicity is a common pathogenic process in many neurological conditions including epilepsy. Prolonged seizures induce elevations in extracellular glutamate that contribute to excitotoxic damage, which in turn can trigger chronic neuroinflammatory reactions, leading to secondary damage to the brain. Blocking key inflammatory pathways could prevent such secondary brain injury following the initial excitotoxic insults. Prostaglandin E2 (PGE2) has emerged as an important mediator of neuroinflammation-associated injury, in large part via activating its EP2 receptor subtype. Herein, we investigated the effects of EP2 receptor inhibition on excitotoxicity-associated neuronal inflammation and injury in vivo. Utilizing a bioavailable and brain-permeant compound, TG6-10-1, we found that pharmacological inhibition of EP2 receptor after a one-hour episode of kainate-induced status epilepticus (SE) in mice reduced seizure-promoted functional deficits, cytokine induction, reactive gliosis, blood-brain barrier impairment, and hippocampal damage. Our preclinical findings endorse the feasibility of blocking PGE2/EP2 signaling as an adjunctive strategy to treat prolonged seizures. The promising benefits from EP2 receptor inhibition should also be relevant to other neurological conditions in which excitotoxicity-associated secondary damage to the brain represents a pathogenic event.

Crystal structure of the endogenous agonist-bound prostanoid receptor EP3.

Prostanoids are a series of bioactive lipid metabolites that function in an autacoid manner via activation of cognate G-protein-coupled receptors (GPCRs). Here, we report the crystal structure of human prostaglandin (PG) E receptor subtype EP3 bound to endogenous ligand PGE2 at 2.90 Å resolution. The structure reveals important insights into the activation mechanism of prostanoid receptors and provides a molecular basis for the binding modes of endogenous ligands.

Calcium Signal Pathway is Involved in Prostaglandin E2 Induced Cardiac Fibrosis in Cardiac Fibroblasts.

The present study was designed to explore the effects of PGE2 on cardiac fibrosis and the involved mechanism. We used western blot analysis, real-time quantitative PCR and immunostaining etc. to testify the mechanism. Our data showed that in cultured adult rat cardiac fibroblasts (CFs), PGE2 effectively promoted the expression of α-smooth muscle actin (α-SMA), connective tissue growth factor (CTGF)，fibronectin (FN), Collagen I and induced [Ca2+]i increase. Besides, calcium increase evoked by PGE2 is mediated by virtue of EP1 activation. Instead of EP3 or EP4, inhibition of EP1 attenuated PGE2-stimulated upregulation of α-SMA，CTGF, FN, collagen I and [Ca2+]i, as well as the nuclear factor of activated T cell cytoplasmic 4 protein (NFATc4) translocation. PGE2 may promote cardiac fibrosis via EP1receptor and calcium signal pathway.

Identification of a Selective, Non-Prostanoid EP2 Receptor Agonist for the Treatment of Glaucoma: Omidenepag and its Prodrug Omidenepag Isopropyl.

EP2 receptor agonists are expected to be effective ocular hypotensive agents; however, it has been suggested that agonism to other EP receptor subtypes may lead to undesirable effects. Through medicinal chemistry efforts, we identified a scaffold bearing a (pyridin-2-ylamino)acetic acid moiety as a promising EP2-selective receptor agonist. (6-((4-(Pyrazol-1-yl)benzyl)(pyridin-3-ylsulfonyl)aminomethyl)pyridin-2-ylamino)acetic acid 13ax (omidenepag, OMD) exerted potent and selective activity toward the human EP2 receptor (h-EP2). Low doses of omidenepag isopropyl (OMDI), a prodrug of 13ax, lowered intraocular pressure (IOP) in ocular normotensive monkeys. OMDI was selected as a clinical candidate for the treatment of glaucoma.

PGE2 enhanced TNFα-mediated IL-8 induction in monocytic cell lines and PBMC

Background & purposeRecent studies suggested a role of prostaglandin E2 (PGE2) in the expression of the chemokine IL-8 by monocytes. The function of EP4 receptor for TNFα-induced IL-8 expression was studied in monocytic cell lines. Experimental approachIL-8 mRNA and protein induction as well as IL-8 promoter activity and transcription factor activation were assessed in monocytic cell lines, primary blood mononuclear cells (PBMC) and transgenic HEK293 cells expressing the EP4 receptor. Key resultsIn monocytic cell lines THP-1, MonoMac and U937 PGE2 had only a marginal impact on IL-8 induction but strongly enhanced TNFα-induced IL-8 mRNA and protein synthesis. Similarly, in PBMC IL-8 mRNA induction was larger by simultaneous stimulation with TNFα and PGE2 than by either stimulus alone. The EP4 receptor subtype was the most abundant EP receptor in all three cell lines and in PBMC. Stimulation of THP-1 cells with an EP4 specific agonist enhanced TNFα-induced IL-8 mRNA and protein formation to the same extent as PGE2. In HEK293 cells expressing EP4, but not in wild type HEK293 cells lacking EP4, PGE2 enhanced TNFα-induced IL-8 protein and mRNA synthesis. In THP-1 cells, the enhancement of TNFα-mediated IL-8 mRNA induction by PGE2 was mimicked by a PKA-activator. Furthermore in these cells PGE2 induced expression of transcription factor C/EBPß, enhanced NF-κB activation by TNFα and inhibited TNFα-mediated AP-1 activation. PGE2 and TNFα synergistically activated transcription factor CREB, induced C/EBPß expression and enhanced the activity of an IL-8 promoter fragment containing -223 bp upstream of the transcription start site. Conclusions and implicationsThese findings suggest that a combined stimulation of TNFα and PGE2/EP4 signal chains in monocytic cells leads to maximal IL-8 promoter activity, as well as IL-8 mRNA and protein induction, by activating the PKA/CREB/C/EBPß as well as NF-κB signal chains.

Inhibition of the Prostaglandin E2 EP3 Receptor Does Not Affect Beta Adrenergic Signaling in the Heart

High blood pressure is a major risk factor for cardiovascular disease. Prostaglandin E2 (PGE2) is a metabolite of arachidonic acid and is known to mediate inflammation and blood pressure regulation. Previous data from our lab have shown that PGE2 reduces contractility when signaling via its EP3 receptor subtype and that EP3 expression increases in the Angiotensin II (Ang II) model of hypertension. Furthermore, we demonstrated in vivo that the hypertensive effect of Ang II could be abrogated using an EP3 inhibitor (EP3i), suggesting an interaction between the two pathways. Since stimulation of the sympathetic nervous system increases Ang II and is an important regulator of cardiovascular function, we therefore hypothesized that inhibition of EP3 would also antagonize beta adrenergic signaling. To test our hypothesis, we studied 4 groups of male 10–12 wk. old C57Bl/6 mice receiving: (1) vehicle, (2) the beta adrenergic agonist Isoproterenol, ISO 30 mg/kg/d S.C., (3) the EP3i L798,106 40 μg/kg/d, (4) ISO + L798,106 for 10 days. ISO or its vehicle were given via osmotic mini pump and L798,106 or its vehicle were administered via daily injections S.C. Systolic blood pressure (BP) was measured every 2 days via tail cuff and cardiac function was assessed by echo at the end of the study period. At baseline, there were no differences in BP between the 4 groups. As expected, ISO infusion significantly increased both BP (105 ± 3.4 mmHg vs. 130 ± 4.1 mmHg, p<0.01) and heart rate (600 ± 21 bpm vs. 749 ± 16 bpm, p<0.005) at end of study, however, there was no difference in BP between the ISO group and the ISO + EP3i group (130 ± 4.1 mmHg vs 125 ± 6.1 mmHg, respectively) nor heart rate (749 ± 16 bpm vs 729 ± 26 bpm). Consistent with the blood pressure data, myocyte cross sectional area increased with ISO infusion from 195.5 ± 9.1 μm2 to 234.0 ± 10.4 μm2, p < 0.05 and this was unchanged at 219.9 ± 13.1 μm2 in the ISO+EP3i group. Similar results were noted in the heart weight to body weight ratios. Echocardiography in conscious animals demonstrated no significant differences in either ejection fraction (EF), shortening fraction, or left ventricle dimensions between the ISO group and the ISO + EP3i group. In conclusion, our data suggest that contrary to our hypothesis, there is no interaction between the EP3 receptor signaling pathway and the beta adrenergic pathway after ten days of ISO infusion. Thus, EP3 receptor signaling appears to be uniquely linked to the angiotensin II pathway.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Desensitization of PGE2‐stimulated cAMP Signaling Due to Upregulated Phosphodiesterase Activity in Human Lung Fibroblasts

Pulmonary fibroblasts play an essential role in maintaining the structure and function of the lung. In idiopathic pulmonary fibrosis, fibroblast cells persist in an activated form and produce excessive fibrous material, leading to loss of alveolar structure. PGE2, which specifically activates EP2 and EP4 receptor subtypes, is a cAMP elevating agent and thus has anti‐fibrotic potential, since cAMP has been shown to have anti‐fibrotic properties. Although PGE2 levels are increased in the bronchoalveolar lavage fluid of patients with idiopathic pulmonary fibrosis (and in animal models of pulmonary fibrosis), it does not prevent pulmonary fibrosis. One hypothesis is that PGE2 effects are self‐limiting because of desensitization caused by prolonged exposure. To test this hypothesis, we pretreated HFL‐1 fibroblasts with PGE2 and other cAMP‐elevating agents then measured PGE2‐stimulated cAMP levels using the downward cAMP difference detector in situ (cADDis) cAMP sensor (Montana Molecular, Bozeman MT). After 24‐hour pretreatment with 100 nM PGE2, we changed the media and measured cAMP kinetics in response to various concentrations of PGE2. Pretreatment with PGE2 shifted the concentration‐response curve of PGE2 rightward approximately 50‐fold. Neither 100 nM isoproterenol or 1μM forskolin pretreatment for 24 hours altered PGE2 response, implying that other cAMP elevating agents do not induce desensitization. We sought to uncover the underlying mechanism responsible for PGE2 desensitization. Desensitization could result from either receptor internalization through the GRK/β‐arrestin mediated pathway or via increase PDE activity. To determine if PGE2 pretreatment increases PDE activity, we used the PDE3 inhibitor, cilostazol, and the PDE4 inhibitor, rolipram after PGE2 pretreatment. Rolipram, increased both the EC50 and Emax of PGE2 in vehicle pretreated HFL‐1 fibroblasts. In cells pretreated with PGE2, rolipram partially reversed the desensitization, indicating that PDE4 may be induced by long term PGE2 exposure. Cilostazol had minimal effects on either control or desensitized PGE2 responses, implying that PDE3 is not involved. Examination of PDE isoform mRNA levels via quantitative RT‐PCR, show that PGE2 treatment upregulates PDE3A, PDE4C and PDE4D, while pretreatment with isoproterenol or forskolin only upregulated PDE4D. Taken together, these results show that long‐term exposure to PGE2 causes desensitization of EP receptor‐stimulated cAMP signaling, partly through the increased expression of a PDE4 isoform. Defining the precise PDE isoform involved in the desensitization of PGE2 responses may lead to new therapeutic strategies for treating pulmonary fibrosis.Support or Funding InformationThis work was supported by NIH grant GM107094 (RO)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Discovery of 2-Piperidinyl Phenyl Benzamides and Trisubstituted Pyrimidines as Positive Allosteric Modulators of the Prostaglandin Receptor EP2.

Prostaglandin E2 (PGE2) via its Gαs-coupled EP2 receptor protects cerebral cortical neurons from excitotoxic and anoxic injury, though EP2 receptor activation can also cause secondary neurotoxicity in chronic inflammation. We performed a high-throughput screen of a library of 292 000 small molecules and identified several compounds that have a 2-piperidinyl phenyl benzamide or trisubstituted pyrimidine core as positive modulators for human EP2 receptor. The most active compounds increased the potency of PGE2 on EP2 receptor 4-5-fold at 20 μM without altering efficacy, indicative of an allosteric mechanism. These compounds did not augment the activity of the other Gαs-coupled PGE2 receptor subtype EP4 and showed neuroprotection against N-methyl-d-aspartate (NMDA)-induced excitotoxicity. These newly developed compounds represent second-generation allosteric potentiators for EP2 receptor and shed light on a promising neuroprotective strategy. They should prove valuable as molecular tools to achieve a better understanding of the dichotomous action of brain EP2 receptor activation.

Prostaglandin E receptor subtype EP1 deficiency elicits AD/HD-like behavior correlated with a dysfunction of dopamine D1 receptor-ERK signaling in the prefrontal cortex

Prostaglandin E receptor subtype EP1 deficiency elicits AD/HD-like behavior correlated with a dysfunction of dopamine D1 receptor-ERK signaling in the prefrontal cortex

Investigation on the regulatory effect of PGE2 on ESCC cells through the trans-activation of EGFR by EP2 and the relevant mechanism.

To determine whether the combination of prostaglandin E2 (PGE2) and EP2, the subtype receptor of PGE2, could trans-activate the epidermal growth factor receptor (EGFR). In this experiment, we selected epithelial cells from normal esophageal mucosa as the negative control group, and the ESCC EC109 and TE-1 cell strain as the observation group. Real-time PCR and Western-blotting were used to detect the expression of EP2, EGFR and phosphorylated EGFR (p-EGFR). The pre-treatment of ESCC cell strains was carried out using Butaprost (special agonist of PGE2 and EP2) and RNAi of EP2, and we observed the expression of EP2, EGFR, and p-EGFR. WST-8 (CCK-8) was applied for the detection of the cell proliferation rate. The transwell invasion experiment was conducted for the detection of the invasion capability of cells. The expression of MMP-9 (matrix metalloproteinase-9), VEGF (vascular endothelial growth factor), pro-inflammatory factors (IL-6 and TNF-α) in the cell supernatant were detected using ELISA. The high mRNA and protein expression of EP2, EGFR, and p-EGFR were found in the EC109 and TE-1 cell strains in the observation group, which were higher than those in the control group (p < 0.05). After the intervention of PGE2, EP2 expression was decreased and the p-EGFR expression was increased (p < 0.05). There was no variation found in the expression of EGFR (p > 0.05). After cells were intervened using Butaprost, the expressions of EP2 and p-EGFR were increased (p < 0.05), and there were no changes identified in the expression of EGFR (p > 0.05). After the intervention of RNAi, the expression of EP2 and p-EGFR was decreased (p < .05), and no changes were identified in the expression of EGFR (p > 0.05). After the intervention of PGE2 and Butaprost, great increases were seen in the cell proliferation rate, invasion capability, and the expression of MMP-9, VEGF, IL-6, and TNF-α in EC109 and TE-1 cell strains (p < 0.05), however, the intervention of RNAi could reduce above indexes (p < 0.05). Through cell experiments, we verified that the combination of prostaglandin E2 (PGE2) and EP2, the subtype receptor of PGE2, could trans-activate the epidermal growth factor receptor (EGFR) to regulate the proliferation and invasion capability of esophageal squamous cell carcinoma (ESCC) cells, and secrete and express multiple cytokines, thus discovering the pathological mechanism of inflammation to carcinoma transition in the occurrence of ESCC, and providing the experimental evidence for the search of new target in the treatment of ESCC. ESCC cells can highly express the receptor subtype EP2 of PGE2 that can transactivate the EGFR, through which PGE2 is involved in the transition mechanism from inflammation to cancer.

Prostaglandin E2 in the Regulation of Water Transport in Renal Collecting Ducts.

The kidney plays a central role in the regulation of the body water balance. The process of targeting the water channel aquaporin-2 (AQP2) on the apical plasma membrane of the collecting duct (CD) principal cells is mainly regulated by the antidiuretic peptide hormone arginine vasopressin (AVP), which is responsible for the maintenance of water homeostasis. Recently, much attention has been focused on the local factors modulating renal water reabsorption by AQP2 in the collecting ducts, especially prostaglandin E2 (PGE2). PGE2 is a lipid mediator involved in a variety of physiological and pathophysiological processes in the kidney. The biological function of PGE2 is mainly mediated by four G-protein-coupled receptors, namely EP1-4, which couple to drive separate intracellular signaling pathways. Increasing evidence demonstrates that PGE2 is essential for renal water transport regulation via multiple mechanisms. Each EP receptor plays a unique role in regulating water reabsorption in renal collecting ducts. This brief review highlights the role of PGE2 in the regulation of water reabsorption and discusses the involvement of each EP receptor subtype in renal collecting duct. A better understanding of the role of PGE2 in renal water transport process may improve disease management strategies for water balance disorders, including nephrogenic diabetes insipidus.

Activating prostaglandin E2 receptor subtype EP4 increases secreted mucin from airway goblet cells

Prostaglandin E2 (PGE2) is a ligand of the E-type prostanoid receptors, EP1-4. PGE2 secretion is increased in the airways of patients with asthma by secretory phospholipases A2, which also increases MUC5AC mucin in goblet cells. We hypothesized that PGE2 would also increase MUC5AC mRNA and secreted protein through specific EP receptor activation. We sought to assess the effect of specific EP receptor activation on MUC5AC secretion from ciliated-enriched cells or goblet-enriched cells induced by IL-13. We develop an enriched goblet cell epithelium by growing normal human bronchial epithelial cells at air liquid interface for 14 days in the presence of IL-13. We examined exposure to 4 specific EP receptor agonists at 24 h and 14 days in cells grown with or without IL-13 exposure, and measured MUC5AC mRNA and secreted protein, as well as airway culture morphology, and EP receptor expression. In ciliated-enriched cells grown in the absence of IL-13, the EP4 receptor agonist modestly increased both MUC5AC mRNA and secretion (p < 0.001, 241% increase of transcripts and p < 0.01, 86% increase of secreted protein) but did not visibly change cell morphology. In goblet-enriched cells grown in the presence of IL-13, the EP4 receptor agonist greatly increased both MUC5AC mRNA and protein (p < 0.001, 315% increase of transcripts and 92% increase of secreted protein). Specific activation of the other EP receptor had no effect on secreted mucin. EP4 receptor mRNA and protein were significantly increased in goblet-enriched cells, while the other receptor mRNA were decreased. We conclude that PGE2 stimulates airway mucin production predominantly by EP4 receptor activation in association with increased EP4 receptor expression. This may contribute to mucus hypersecretion as seen in severe asthma.