Activated ß-catenin in Foxp3+ regulatory T cells links inflammatory environments to autoimmunity.

Foxp3+ regulatory T cells (Treg cells) are the central component of peripheral immune tolerance. Whereas a dysregulated Treg cytokine signature has been observed in autoimmune diseases, the regulatory mechanisms underlying pro- and anti-inflammatory cytokine production are elusive. Here, we identify an imbalance between the cytokines IFN-γ and IL-10 as a shared Treg signature present in patients with multiple sclerosis and under high-salt conditions. RNA-sequencing analysis on human Treg subpopulations revealed ß-catenin as a key regulator of IFN-γ and IL-10 expression. The activated ß-catenin signature was enriched in human IFN-γ+ Treg cells, as confirmed in vivo with Treg-specific ß-catenin-stabilized mice exhibiting lethal autoimmunity with a dysfunctional Treg phenotype. Moreover, we identified prostaglandin E receptor 2 (PTGER2) as a regulator of IFN-γ and IL-10 production under a high-salt environment, with skewed activation of the ß-catenin-SGK1-Foxo axis. Our findings reveal a novel PTGER2-ß-catenin loop in Treg cells linking environmental high-salt conditions to autoimmunity.

Peripheral Myeloid Cell EP2 Activation Contributes to the Deleterious Consequences of Status Epilepticus.

A multidimensional inflammatory response ensues after status epilepticus (SE), driven partly by cyclooxygenase-2-mediated activation of prostaglandin EP2 receptors. The inflammatory response is typified by astrocytosis, microgliosis, erosion of the blood-brain barrier (BBB), formation of inflammatory cytokines, and brain infiltration of blood-borne monocytes. Our previous studies have shown that inhibition of monocyte brain invasion or systemic administration of an EP2 receptor antagonist relieves multiple deleterious consequences of SE. Here we identify those effects of EP2 antagonism that are reproduced by conditional ablation of EP2 receptors in immune myeloid cells and show that systemic EP2 antagonism blocks monocyte brain entry in male mice. The induction of hippocampal IL-6 after pilocarpine SE was nearly abolished in EP2 conditional KO mice. Serum albumin levels in the cortex, a measure of BBB breakdown, were significantly higher after SE in EP2-sufficient mice but not in EP2 conditional KOs. EP2 deficiency in innate immune cells accelerated the recovery from sickness behaviors following SE. Surprisingly, neurodegeneration was not alleviated in myeloid conditional KOs. Systemic EP2 antagonism prevented monocyte brain infiltration and provided broader rescue of SE-induced effects than myeloid EP2 ablation, including neuroprotection and broader suppression of inflammatory mediators. Reporter expression indicated that the cellular target of CD11b-driven Cre was circulating myeloid cells but, unexpectedly, not microglia. These findings indicate that activation of EP2 receptors on immune myeloid cells drives substantial deficits in behavior and disrupts the BBB after SE. The benefits of systemic EP2 antagonism can be attributed, in part, to blocking brain recruitment of blood-borne monocytes.SIGNIFICANCE STATEMENT Unabated seizures reduce quality of life, promote the development of epilepsy, and can be fatal. We previously identified activation of prostaglandin EP2 receptors as a driver of undesirable consequences of seizures. However, the relevant EP2-expressing cell types remain unclear. Here we identify peripheral innate immune cells as a driver of the EP2-related negative consequences of seizures. Removal of EP2 from peripheral immune cells was beneficial, abolishing production of a key inflammatory cytokine, accelerating weight regain, and limiting behavioral deficits. These findings provide evidence that EP2 engagement on peripheral immune and brain endothelia contributes to the deleterious effects of SE, and will assist in the development of beneficial therapies to enhance quality of life in individuals who suffer prolonged seizures.

PGE2 deficiency predisposes to anaphylaxis by causing mast cell hyperresponsiveness.

BACKGROUND: Reduced levels of prostaglandin E2 (PGE2) contribute to aspirin-induced hypersensitivity. COX inhibitors are also frequent cofactors in anaphylaxis. Whether alterations in the PGE2 system contribute to anaphylaxis independently of COX inhibitor intake is unclear. OBJECTIVE: Our aim was to test the hypothesis that relative PGE2 deficiency predisposes to anaphylaxis. METHODS: Sera from 48 patients with anaphylaxis and 27 healthy subjects were analyzed for PGE2 levels and correlated against severity; 9α,11ß-PGF2 and PGI2 metabolites were measured for control purposes. PGE2 stabilization by 15-hydroxyprostaglandin dehydrogenase inhibitor or EP2 or EP4 receptor agonists were used in a murine model of passive systemic anaphylaxis. FcεRI-triggered mediator release was determined in bone marrow-derived cultured mast cells (MCs) and human skin-derived MCs. Signaling was studied by Western blot analysis. RESULTS: Patients with anaphylaxis were characterized by markedly reduced PGE2 levels vis-à-vis healthy subjects, whereas prostacyclin metabolite levels were diminished only weakly, and 9α,11ß-PGF2 levels conversely increased. PGE2 was negatively correlated with severity. Lower PGE2 levels and higher susceptibility to anaphylaxis were also found in C57BL/6 mice vis-à-vis in Balb/c mice. Stabilization of PGE2 level by 15-hydroxyprostaglandin dehydrogenase inhibitor protected mice against anaphylaxis. Exogenous PGE2 attenuated bone marrow-derived cultured MC activation through EP2 and EP4 receptors. EP2 and EP4 agonism also curbed FcεRI-mediated degranulation of human MCs. Mechanistically, PGE2 interfered with the phosphorylation of phospholipase C gamma-1 and extracellular signal-regulated kinase. CONCLUSIONS: Homeostatic levels of PGE2 attenuate MC activation via EP2/EP4 and protect against anaphylaxis. Relative deficiency of PGE2 predisposes to anaphylaxis in humans and mice, whereas PGE2 stabilization protects against anaphylactic reactions.

The Endocannabinoid Metabolite Prostaglandin E2 (PGE2)-Glycerol Inhibits Human Neutrophil Functions: Involvement of Its Hydrolysis into PGE2 and EP Receptors.

The endocannabinoids 2-arachidonoyl-glycerol and N-arachidonoyl-ethanolamine mediate an array of pro- and anti-inflammatory effects. These effects are related, in part, to their metabolism by eicosanoid biosynthetic enzymes. For example, N-arachidonoyl-ethanolamine and 2-arachidonoyl-glycerol can be metabolized by cyclooxygenase-2 into PG-ethanolamide (PG-EA) and PG-glycerol (PG-G), respectively. Although PGE2 is a recognized suppressor of neutrophil functions, the impact of cyclooxygenase-derived endocannabinoids such as PGE2-EA or PGE2-G on neutrophils is unknown. This study's aim was to define the effects of these mediators on neutrophil functions and the underlying cellular mechanisms involved. We show that PGE2-G, but not PGE2-EA, inhibits leukotriene B4 biosynthesis, superoxide production, migration, and antimicrobial peptide release. The effects of PGE2-G were prevented by EP1/EP2 receptor antagonist AH-6809 but not the EP4 antagonist ONO-AE2-227. The effects of PGE2-G required its hydrolysis into PGE2, were not observed with the non-hydrolyzable PGE2-serinol amide, and were completely prevented by methyl-arachidonoyl-fluorophosphate and palmostatin B, and partially prevented by JZL184 and WWL113. Although we could detect six of the documented PG-G hydrolases in neutrophils by quantitative PCR, only ABHD12 and ABHD16A were detected by immunoblot. Our pharmacological data, combined with our protein expression data, did not allow us to pinpoint one PGE2-G lipase, and rather support the involvement of an uncharacterized lipase and/or of multiple hydrolases. In conclusion, we show that PGE2-G inhibits human neutrophil functions through its hydrolysis into PGE2, and by activating the EP2 receptor. This also indicates that neutrophils could regulate inflammation by altering the balance between PG-G and PG levels in vivo.

Peripherally Restricted, Highly Potent, Selective, Aqueous-Soluble EP2 Antagonist with Anti-Inflammatory Properties.

The prostaglandin E2 receptor, EP2, plays an important role in physiology and in a variety of pathological conditions. Studies indicate that EP2 is pro-inflammatory in chronic peripheral and central nervous system disease and cancer models. Thus, targeting the EP2 receptor with small molecules could be a therapeutic strategy for treating inflammatory diseases and cancer. We recently reported a novel class of competitive antagonists of the EP2 receptor. However, earlier leads displayed low selectivity against the DP1 prostanoid receptor, moderate plasma half-life, and low aqueous solubility, which renders them suboptimal for testing in animal models of disease. We now report a novel compound TG8-69, which has suitable drug-like properties. We present synthesis, lead-optimization studies, pharmacological characterization, and anti-inflammatory properties of this compound that support its use in chronic peripheral inflammatory diseases, including rheumatoid arthritis, endometriosis, and cancer, in which EP2 appears to play a pathogenic role.

Dimethyl fumarate activates the prostaglandin EP2 receptor and stimulates cAMP signaling in human peripheral blood mononuclear cells.

Dimethyl fumarate (DMF) was recently approved by the FDA for the treatment of relapsing remitting MS. The pathology of MS is a result of both immune dysregulation and oxidative stress induced damage, and DMF is believed to have therapeutic effects on both of these processes. However, the mechanisms of action of DMF are not fully understood. To determine if DMF is able to activate signaling cascades that affect immune dysregulation, we treated human peripheral blood mononuclear cells with DMF. We discovered that DMF stimulates cyclic adenosine monophosphate (cAMP) production after 1 min treatment in vitro. cAMP is a small molecule second messenger that has been shown to modulate immune response. Using pharmacological inhibitors, we determined that adenylyl cyclase mediates DMF induced cAMP production; DMF activated the prostaglandin EP2 receptor to produce cAMP. This response was not due to increased endogenous production of prostaglandin E2 (PGE2), but was enhanced by addition of exogenous PGE2. Furthermore, we determined that the bioactive metabolite of DMF, monomethyl fumarate (MMF), also stimulates cAMP production. These novel findings suggest that DMF may provide protection against MS by inhibiting immune cell function via the cAMP signaling pathway.

Activation of the Prostaglandin E2 receptor EP2 prevents house dust mite-induced airway hyperresponsiveness and inflammation by restraining mast cells' activity.

BACKGROUND: Prostaglandin E2 (PGE2 ) has been proposed to exert antiasthmatic effects in patients, to prevent antigen-induced airway pathology in murine models, and to inhibit mast cells (MC) activity in vitro. OBJECTIVE: To assess in a murine model whether the protective effect of PGE2 may be a consequence of its ability to activate the E-prostanoid (EP)2 receptor on airway MC. METHODS: Either BALB/c or C57BL/6 mice were exposed intranasally (i.n.) to house dust mite (HDM) aeroallergens. Both strains were given PGE2 locally (0.3 mg/kg), but only BALB/c mice were administered butaprost (EP2 agonist: 0.3 mg/kg), or AH6809 (EP2 antagonist; 2.5 mg/kg) combined with the MC stabilizer sodium cromoglycate (SCG: 25 mg/kg). Airway hyperresponsiveness (AHR) and inflammation, along with lung MC activity, were evaluated. In addition, butaprost's effect was assessed in MC-mediated passive cutaneous anaphylaxis (PCA) in mice challenged with 2,4-dinitrophenol (DNP). RESULTS: Selective EP2 agonism attenuated aeroallergen-caused AHR and inflammation in HDM-exposed BALB/c mice, and this correlated with a reduced lung MC activity. Accordingly, the blockade of endogenous PGE2 by means of AH6809 worsened airway responsiveness in sensitive BALB/c mice, and such worsening was reversed by SCG. The relevance of MC to PGE2 -EP2 driven protection was further highlighted in MC-dependent PCA, where butaprost fully prevented MC-induced ear swelling. Unlike in BALB/c mice, PGE2 did not protect the airways of HDM-sensitized C57BL/6 animals, a strain in which we showed MC to be irrelevant to aeroallergen-driven AHR and inflammation. CONCLUSIONS & CLINICAL RELEVANCE: The beneficial effect of both exogenous and endogenous PGE2 in aeroallergen-sensitized mice may be attributable to the activation of the EP2 receptor, which in turn acts as a restrainer of airway MC activity. This opens a path towards the identification of therapeutic targets against asthma along the 'EP2 -MC-airway' axis.

Prostaglandin E2 deficiency uncovers a dominant role for thromboxane A2 in house dust mite-induced allergic pulmonary inflammation.

Prostaglandin E(2) (PGE(2)) is an abundant lipid inflammatory mediator with potent but incompletely understood anti-inflammatory actions in the lung. Deficient PGE(2) generation in the lung predisposes to airway hyperresponsiveness and aspirin intolerance in asthmatic individuals. PGE(2)-deficient ptges(-/-) mice develop exaggerated pulmonary eosinophilia and pulmonary arteriolar smooth-muscle hyperplasia compared with PGE(2)-sufficient controls when challenged intranasally with a house dust mite extract. We now demonstrate that both pulmonary eosinophilia and vascular remodeling in the setting of PGE(2) deficiency depend on thromboxane A(2) and signaling through the T prostanoid (TP) receptor. Deletion of TP receptors from ptges(-/-) mice reduces inflammation, vascular remodeling, cytokine generation, and airway reactivity to wild-type levels, with contributions from TP receptors localized to both hematopoietic cells and tissue. TP receptor signaling ex vivo is controlled heterologously by E prostanoid (EP)(1) and EP(2) receptor-dependent signaling pathways coupling to protein kinases C and A, respectively. TP-dependent up-regulation of intracellular adhesion molecule-1 expression is essential for the effects of PGE(2) deficiency. Thus, PGE(2) controls the strength of TP receptor signaling as a major bronchoprotective mechanism, carrying implications for the pathobiology and therapy of asthma.

Prostaglandin E2 suppresses allergic sensitization and lung inflammation by targeting the E prostanoid 2 receptor on T cells.

BACKGROUND: Endogenous prostanoids have been suggested to modulate sensitization during experimental allergic asthma, but the specific role of prostaglandin (PG) E2 or of specific E prostanoid (EP) receptors is not known. OBJECTIVE: Here we tested the role of EP2 signaling in allergic asthma. METHODS: Wild-type (WT) and EP2(-/-) mice were subjected to ovalbumin sensitization and acute airway challenge. The PGE2 analog misoprostol was administered during sensitization in both genotypes. In vitro culture of splenocytes and flow-sorted dendritic cells and T cells defined the mechanism by which EP2 exerted its protective effect. Adoptive transfer of WT and EP2(-/-) CD4 T cells was used to validate the importance of EP2 expression on T cells. RESULTS: Compared with WT mice, EP2(-/-) mice had exaggerated airway inflammation in this model. Splenocytes and lung lymph node cells from sensitized EP2(-/-) mice produced more IL-13 than did WT cells, suggesting increased sensitization. In WT but not EP2(-/-) mice, subcutaneous administration of misoprostol during sensitization inhibited allergic inflammation. PGE2 decreased cytokine production and inhibited signal transducer and activator of transcription 6 phosphorylation by CD3/CD28-stimulated CD4(+) T cells. Coculture of flow cytometry-sorted splenic CD4(+) T cells and CD11c(+) dendritic cells from WT or EP2(-/-) mice suggested that the increased IL-13 production in EP2(-/-) mice was due to the lack of EP2 specifically on T cells. Adoptive transfer of CD4(+) EP2(-/-) T cells caused greater cytokine production in the lungs of WT mice than did transfer of WT CD4(+) T cells. CONCLUSION: We conclude that the PGE2-EP2 axis is an important endogenous brake on allergic airway inflammation and primarily targets T cells and that its agonism represents a potential novel therapeutic approach to asthma.

Myeloid-derived suppressor cell function is diminished in aspirin-triggered allergic airway hyperresponsiveness in mice.

BACKGROUND: Myeloid-derived suppressor cells (MDSCs) have recently been implicated in the pathogenesis of asthma, but their regulation in patients with aspirin-intolerant asthma (AIA) remains unclear. OBJECTIVE: We sought to characterize MDSC accumulation and pathogenic functions in allergic airway inflammation mediated by COX-1 deficiency or aspirin treatment in mice. METHODS: Allergic airway inflammation was induced in mice by means of ovalbumin challenge. The distribution and function of MDSCs in mice were analyzed by using flow cytometry and pharmacologic/gene manipulation approaches. RESULTS: CD11b(+)Gr1(high)Ly6G(+)Ly6C(int) MDSCs (polymorphonuclear MDSCs [PMN-MDSCs]) recruited to the lungs are negatively correlated with airway inflammation in allergen-challenged mice. Aspirin-treated and COX-1 knockout (KO) mice showed significantly lower accumulation of PMN-MDSCs in the inflamed lung and immune organs accompanied by increased TH2 airway responses. The TH2-suppressive function of PMN-MDSCs was notably impaired by COX-1 deletion or inhibition, predominantly through downregulation of arginase-1. COX-1-derived prostaglandin E2 promoted PMN-MDSC generation in bone marrow through E prostanoid 2 and 4 receptors (EP2 and EP4), whereas the impaired arginase-1 expression in PMN-MDSCs in COX-1 KO mice was mediated by dysregulation of the prostaglandin E2/EP4/cyclic AMP/protein kinase A pathway. EP4 agonist administration alleviated allergy-induced airway hyperresponsiveness in COX-1 KO mice. Moreover, the immunosuppressive function of PMN-MDSCs from patients with AIA was dramatically decreased compared with that from patients with aspirin-tolerant asthma. CONCLUSION: The immunosuppressive activity of PMN-MDSCs was diminished in both allergen-challenged COX-1 KO mice and patients with AIA, probably through an EP4-mediated signaling pathway, indicating that activation of PMN-MDSCs might be a promising therapeutic strategy for asthma, particularly AIA.

Semen promotes the differentiation of tolerogenic dendritic cells.

Seminal plasma is not just a carrier for spermatozoa. It contains high concentrations of cytokines, chemokines, and other biological compounds that are able to exert potent effects on the immune system of the receptive partner. Previous studies have shown that semen induces an acute inflammatory response at the female genital mucosa after coitus. Moreover, it induces regulatory mechanisms that allow the fetus (a semiallograft) to grow and develop in the uterus. The mechanisms underlying these regulatory mechanisms, however, are poorly understood. In this study, we show that seminal plasma redirects the differentiation of human dendritic cells (DCs) toward a regulatory profile. DCs differentiated from human monocytes in the presence of high dilutions of seminal plasma did not express CD1a but showed high levels of CD14. They were unable to develop a fully mature phenotype in response to LPS, TNF-α, CD40L, Pam2CSK4 (TLR2/6 agonist), or Pam3CSK4 (TLR1/2 agonist). Upon activation, they produced low amounts of the inflammatory cytokines IL-12p70, IL-1ß, TNF-α, and IL-6, but expressed a high ability to produce IL-10 and TGF-ß. Inhibition of the PG receptors E-prostanoid receptors 2 and 4 prevented the tolerogenic effect induced by seminal plasma on the phenotype and function of DCs, suggesting that E-series PGs play a major role. By promoting a tolerogenic profile in DCs, seminal plasma might favor fertility, but might also compromise the capacity of the receptive partner to mount an effective immune response against sexually transmitted pathogens.

Modulation of the cAMP response by Gαi and Gßγ: a computational study of G protein signaling in immune cells.

Cyclic AMP is important for the resolution of inflammation, as it promotes anti-inflammatory signaling in several immune cell lines. In this paper, we present an immune cell specific model of the cAMP signaling cascade, paying close attention to the specific isoforms of adenylyl cyclase (AC) and phosphodiesterase that control cAMP production and degradation, respectively, in these cells. The model describes the role that G protein subunits, including Gαs, Gαi, and Gßγ, have in regulating cAMP production. Previously, Gαi activation has been shown to increase the level of cAMP in certain immune cell types. This increase in cAMP is thought to be mediated by ßγ subunits which are released upon Gα activation and can directly stimulate specific isoforms of AC. We conduct numerical experiments in order to explore the mechanisms through which Gαi activation can increase cAMP production. An important conclusion of our analysis is that the relative abundance of different G protein subunits is an essential determinant of the cAMP profile in immune cells. In particular, our model predicts that limited availability of ßγ subunits may both (i) enable immune cells to link inflammatory Gαi signaling to anti-inflammatory cAMP production thereby creating a balanced immune response to stimulation with low concentrations of PGE2, and (ii) prohibit robust anti-inflammatory cAMP signaling in response to stimulation with high concentrations of PGE2.

Prostanoid receptor 2 signaling protects T helper 2 cells from BALB/c mice against activation-induced cell death.

T helper 2 (Th2) cells play a central role in the progression of many diseases such as allergic airway inflammation, autoimmune diseases, and infections caused by intracellular pathogens. Consequently, animals such as BALB/c mice, which exhibit a propensity for generating Th2 responses, are susceptible to allergic airway inflammation, type-II autoimmune diseases, and various infections induced by intracellular pathogens, namely, Leishmania. In contrast, C3H/OuJ mice have a tendency for generating T helper 1 (Th1) responses and show resistance to these diseases. Here, we show that prostaglandin endoperoxide E(2) selectively inhibits activation-induced cell death of Th2 cells by signaling through its receptor E-prostanoid receptor 2 (EP2). Consequently, Th2 cells derived from BALB/c mice expressed very high levels of EP2. On the other hand, Th2 cells derived from C3H/OuJ mice expressed very low levels of EP2, which failed to support the survival of Th2 cells. Furthermore, we found that this effect of EP2 on Th2 cells from BALB/c mice was executed by a granzyme B-mediated mechanism. EP2 belongs to a group of G-protein-coupled receptors that are amenable to therapeutic targeting. Our findings therefore identify EP2 as a promising target for small molecule-directed immunomodulation.

Prostaglandin E2 modulates IL-8 expression through formation of a multiprotein enhanceosome in human colonic epithelial cells.

Gastrointestinal inflammation is mediated by the pro-inflammatory mediators interleukin-8 (IL-8) and prostaglandin E(2) (PGE(2) ). PGE(2) binding and coupling through EP2/4 receptor subtypes on colonic epithelial cells stimulates cyclic adenosine monophosphate (cAMP) and IL-8 production. Here we determined the mechanisms whereby PGE(2) regu-lates IL-8 in Caco2 colonic epithelial cells and in cells over-expressing the EP2/4 receptors (EP2S/EP4S). PGE(2) coupling through EP2 activated the transcription factor inducible cAMP early repressor (ICER), whereas coupling through EP4 receptors activated the cyclic AMP-responsive element-binding protein (CREB). Activation of CREB in Caco2/EP2S was protein kinase A (PKA) dependent, whereas in EP4S cells, activation of CREB occurred through the PKA and phosphatidylinositol 3-kinase pathways. Since ICER lacks the transactivation domain, it functions as a transcription repressor as opposed to CREB. PGE(2) coupling through EP2/4 receptors can therefore acts in an opposing manner to either decrease (EP2) or promote IL-8 expression by recruiting CREB-binding protein (CBP) (EP4), which formed a multiprotein IL-8 enhanceosome. A novel half CRE (167CRE) and a composite NFAT1-AP1-like site in the IL-8 promoter participated in binding and complex formation as confirmed by mutagenesis and expression studies. These data unravel the mechanisms by which expression of IL-8 is controlled by different signalling pathways that are activated by PGE(2) but acting through different EP receptors.

An important role of prostanoid receptor EP2 in host resistance to Mycobacterium tuberculosis infection in mice.

Mycobacterium tuberculosis, the causative agent of tuberculosis, resides and replicates within susceptible hosts by inhibiting host antimicrobial mechanisms. Prostaglandin E(2) (PGE(2)), produced by M. tuberculosis-infected macrophages, exerts a variety of immunomodulatory functions via 4 receptors (EP1-EP4), each mediating distinct PGE(2) functions. Here, we show that M. tuberculosis infection selectively upregulates EP2 messenger RNA expression in CD4(+) T cells. We found that EP2 deficiency in mice increases susceptibility to M. tuberculosis infection, which correlated with reduced antigen-specific T-cell responses and increased levels of CD4(+)CD25(+)Foxp3(+) T-regulatory cells. These findings have revealed an important role for EP2 in host immune defense against tuberculosis. As a G protein-coupled receptor, EP2 could serve as a target for immunotherapy of tuberculosis.

Potential therapeutic interventions via EP2/EP4 prostaglandin receptors.

Prevention and treatment of pathological inflammatory processes requires application of various classes of immune suppressors, such as calcineurin inhibitors, steroids and non-steroid inhibitors of prostaglandin synthesis. However, each type of these immune suppressors causes less or more serious adverse side-effects. Exploration of the role played by prostanoids in the immune response and identification of functionally distinct prostaglandin E receptors (EP1-EP4) opened new perspectives in therapy of inflammation, autoimmunity and prevention of graft rejection. The EP4 receptor appeared to be an attractive target to affect manifestations of various pathological states by application of either agonists or antagonists of the receptor. This article presents a short overview of experimental approaches aimed at manipulation of signaling via EP2 and EP4 receptors that could have therapeutic utility.

mPGES-1-Mediated Production of PGE2 and EP4 Receptor Sensing Regulate T Cell Colonic Inflammation.

PGE2 is a lipid mediator of the initiation and resolution phases of inflammation, as well as a regulator of immune system responses to inflammatory events. PGE2 is produced and sensed by T cells, and autocrine or paracrine PGE2 can affect T cell phenotype and function. In this study, we use a T cell-dependent model of colitis to evaluate the role of PGE2 on pathological outcome and T-cell phenotypes. CD4+ T effector cells either deficient in mPGES-1 or the PGE2 receptor EP4 are less colitogenic. Absence of T cell autocrine mPGES1-dependent PGE2 reduces colitogenicity in association with an increase in CD4+RORγt+ cells in the lamina propria. In contrast, recipient mice deficient in mPGES-1 exhibit more severe colitis that corresponds with a reduced capacity to generate FoxP3+ T cells, especially in mesenteric lymph nodes. Thus, our research defines how mPGES-1-driven production of PGE2 by different cell types in distinct intestinal locations impacts T cell function during colitis. We conclude that PGE2 has profound effects on T cell phenotype that are dependent on the microenvironment.

Up-regulation of EP2 and EP3 receptors in human tolerogenic dendritic cells boosts the immunosuppressive activity of PGE2.

Dendritic cells (DCs) are APCs essential in regulating the immune response. PGE2, produced during inflammation, has a pivotal role in the maturation of DCs and, therefore, is vital for the immune response. The large variety of biologic functions governed by PGE2 is mediated by its signaling through 4 distinct E-type prostanoid (EP) receptors. Immunogenic DCs express EP2 and EP4, which mediate the PGE2 signaling. However, the expression and function of EP receptors in human tolerogenic DCs (tol-DCs), which present an inhibitory phenotype, have not yet, to our knowledge, been assessed. To clarify the role of EP receptors in tol-DCs, we examined the expression of different EP receptors and their effect using selective agonists in human cells. We find that EP2 and EP3 expression are up-regulated in in vitro-generated tol-DCs compared with mature DCs (mDCs). Activation of EP2-EP4 has a direct effect on the surface expression of costimulatory molecules and maturation receptors, such as CD80, CD83, and CD86 or MHCII and CCR7 in tol-DCs, the latter being exclusively modulated by PGE2-EP4 signaling. Importantly, we find that EP2 and EP3 receptors are involved in tolerance induction through IL-10 production by tol-DCs. These results are in sharp contrast with the inflammatory role of EP4 Moreover, we show that DCs generated in the presence of agonists for EP receptors, induce naive T cell differentiation toward polarized Th1/Th17 cells. Given the differential effects of EP receptors, our results suggest that EP receptor agonist/antagonists might become relevant novel drug templates to modulate immune response.

Curcumin Ameliorates the Reduction Effect of PGE2 on Fibrillar ß-Amyloid Peptide (1-42)-Induced Microglial Phagocytosis through the Inhibition of EP2-PKA Signaling in N9 Microglial Cells.

Inflammatory activation of microglia and ß amyloid (Aß) deposition are considered to work both independently and synergistically to contribute to the increased risk of Alzheimer's disease (AD). Recent studies indicate that long-term use of phenolic compounds provides protection against AD, primarily due to their anti-inflammatory actions. We previously suggested that phenolic compound curcumin ameliorated phagocytosis possibly through its anti-inflammatory effects rather than direct regulation of phagocytic function in electromagnetic field-exposed N9 microglial cells (N9 cells). Here, we explored the prostaglandin-E2 (PGE2)-related signaling pathway that involved in curcumin-mediated phagocytosis in fibrillar ß-amyloid peptide (1-42) (fAß42)-stimulated N9 cells. Treatment with fAß42 increased phagocytosis of fluorescent-labeled latex beads in N9 cells. This increase was attenuated in a dose-dependent manner by endogenous and exogenous PGE2, as well as a selective EP2 or protein kinase A (PKA) agonist, but not by an EP4 agonist. We also found that an antagonist of EP2, but not EP4, abolished the reduction effect of PGE2 on fAß42-induced microglial phagocytosis. Additionally, the increased expression of endogenous PGE2, EP2, and cyclic adenosine monophosphate (AMP), and activation of vasodilator-stimulated phosphoprotein, cyclic AMP responsive element-binding protein, and PKA were depressed by curcumin administration. This reduction led to the amelioration of the phagocytic abilities of PGE2-stimulated N9 cells. Taken together, these data suggested that curcumin restored the attenuating effect of PGE2 on fAß42-induced microglial phagocytosis via a signaling mechanism involving EP2 and PKA. Moreover, due to its immune modulatory effects, curcumin may be a promising pharmacological candidate for neurodegenerative diseases.