Prostanoids such as prostaglandins (PGs) and thromboxanes exert a wide variety of actions via nine types of G protein-coupled receptors, including four PGE2 receptors (EPs) and two PGD2 receptors (DPs). Recent studies have revealed that prostanoids trigger or modulate acute inflammation in the skin via multiple mechanisms involving distinct receptors and molecules; PGE2 elicits vascular permeability and edema formation via EP3 receptor on mast cells, and PGE2 increases blood flow by eliciting vasodilatation via EP2/EP4 receptors on smooth muscle cells. PGD2-DP1 signaling plays a role in mast cell maturation and mast cell-mediated inflammation. Therefore, the local inhibition of specific prostanoid receptor signaling is expected to be an effective strategy for the prevention and treatment of acute inflammation.
It remains largely unclear how antigen-presenting cells (APCs) encounter effector or memory T cells efficiently in the periphery. Here we used a mouse contact hypersensitivity (CHS) model to show that upon epicutaneous antigen challenge, dendritic cells (DCs) formed clusters with effector T cells in dermal perivascular areas to promote in situ proliferation and activation of skin T cells in a manner dependent on antigen and the integrin LFA-1. We found that DCs accumulated in perivascular areas and that DC clustering was abrogated by depletion of macrophages. Treatment with interleukin 1? (IL-1?) induced production of the chemokine CXCL2 by dermal macrophages, and DC clustering was suppressed by blockade of either the receptor for IL-1 (IL-1R) or the receptor for CXCL2 (CXCR2). Our findings suggest that the dermal leukocyte cluster is an essential structure for elicitating acquired cutaneous immunity.
Alzheimer's disease (AD) is a neurodegenerative process involving amyloid-? (A?) peptide deposition, neuroinflammation, and progressive memory loss. Here, we evaluated whether oral administration of retinoic acid receptor (RAR)?,? agonist Am80 (tamibarotene) or specific retinoid X receptor (RXR) pan agonist HX630 or their combination could improve deficits in an AD model, 8.5-month-old amyloid-? protein precursor 23 (A?PP23) mice. Co-administration of Am80 (0.5 mg/kg) and HX630 (5 mg/kg) for 17 days significantly improved memory deficits (Morris water maze) in A?PP23 mice, whereas administration of either agent alone produced no effect. Only co-administration significantly reduced the level of insoluble A? peptide in the brain. These results thus indicate that effective memory improvement via reduction of insoluble A? peptide in 8.5-month-old A?PP23 mice requires co-activation of RAR?,? and RXRs. RAR?-positive microglia accumulated A? plaques in the A?PP23 mice. Rat primary microglia co-treated with Am80/HX630 showed increased degradation activity towards 125I-labeled oligomeric A?1-42 peptide in an insulin-degrading enzyme (IDE)-dependent manner. The co-administration increased mRNA for IDE and membrane-associated IDE protein in vivo, suggesting that IDE contributes to A? clearance in Am80/HX630-treated A?PP23 mice. Am80/HX630 also increased IL-4R? expression in microglial MG5 cells. The improvement in memory of Am80/HX630-treated A?PP23 mice was correlated with the levels and signaling of hippocampal interleukin-4 (IL-4). Therefore, Am80/HX630 may promote differentiation of IL-4-responsive M2-like microglia and increase their activity for clearance of oligomeric A? peptides by restoring impaired IL-4 signaling in A?PP23 mice. Combination treatment with RAR and RXR agonists may be an effective approach for AD therapy.
Resolution of inflammation is critical to restoration of tissue function after an inflammatory response. We previously demonstrated that 12/15-lipoxygenase (12/15-LOX)-expressing eosinophils contribute to this process in murine zymosan-induced peritonitis. In this study, eosinophils promoted resolution by regulating expression of macrophage CXCL13. Microarray analysis revealed that eosinophils significantly increased (?3-fold) the expression of macrophage CXCL13 by a 12/15-LOX-dependent mechanism. CXCL13 depletion caused a resolution defect, with the reduced appearance of phagocytes carrying engulfed zymosan in the draining lymph nodes. Inflamed lymph node hypertrophy, a critical feature of the resolution process, was reduced by ?60% in eosinophil-deficient mice, and adoptive transfer of eosinophils or administration of CXCL13 corrected this defect. Administration of the 12/15-LOX-derived mediator lipoxin A4 (LXA4) increased the expression of CXCL13 and restored the defect of lymph node hypertrophy in eosinophil-deficient mice. These results demonstrate that eosinophils control the resolution of inflammation and draining lymph node hypertrophy through proresolving lipid mediators and the CXCL13 pathway in mice.-Tani, Y., Isobe, Y., Imoto, Y., Segi-Nishida, E., Sugimoto, Y., Arai, H., Arita, M. Eosinophils control the resolution of inflammation and draining lymph node hypertrophy through the proresolving mediators and CXCL13 pathway in mice.
Leukotriene B4 (LTB4) receptor type 2 (BLT2) is a G protein-coupled receptor (GPCR) for 12(S)-hydroxyheptadeca-5Z,8E,10E-trienoic acid (12-HHT) and LTB4. Despite the well-defined proinflammatory roles of BLT1, the in vivo functions of BLT2 remain elusive. As mouse BLT2 is highly expressed in epidermal keratinocytes, we investigated the role of the 12-HHT/BLT2 axis in skin wound healing processes. 12-HHT accumulated in the wound fluid in mice, and BLT2-deficient mice exhibited impaired re-epithelialization and delayed wound closure after skin punching. Aspirin administration reduced 12-HHT production and resulted in delayed wound closure in wild-type mice, which was abrogated in BLT2-deficient mice. In vitro scratch assay using primary keratinocytes and a keratinocyte cell line also showed that the 12-HHT/BLT2 axis accelerated wound closure through the production of tumor necrosis factor ? (TNF) and matrix metalloproteinases (MMPs). A synthetic BLT2 agonist accelerated wound closure in cultured cells as well as in C57BL/6J and diabetic mice. These results identify a novel mechanism underlying the action of the 12-HHT/BLT2 axis in epidermal keratinocytes and accordingly suggest the use of BLT2 agonists as therapeutic agents to accelerate wound healing, particularly for intractable wounds, such as diabetic ulcers.
Prostaglandin E2 (PGE2) is one of the most typical lipid mediators produced from arachidonic acid (AA) by cyclooxygenase (COX) as the rate-limiting enzyme, and acts on four kinds of receptor subtypes (EP1-EP4) to elicit its diverse actions including pyrexia, pain sensation, and inflammation. Recently, the molecular mechanisms underlying the PGE2 actions mediated by each EP subtype have been elucidated by studies using mice deficient in each EP subtype as well as several compounds highly selective to each EP subtype, and their findings now enable us to discuss how PGE2 initiates and exacerbates inflammation at the molecular level. Here, we review the recent advances in PGE2 receptor research by focusing on the activation of mast cells via the EP3 receptor and the control of helper T cells via the EP2/4 receptor, which are the molecular mechanisms involved in PGE2-induced inflammation that had been unknown for many years. We also discuss the roles of PGE2 in acute inflammation and inflammatory disorders, and the usefulness of anti-inflammatory therapies that target EP receptors. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: Analysis and biological relevance".
PGE2 has long been known as a potentiator of acute inflammation, but its mechanisms of action still remain to be defined. In this study, we employed inflammatory swelling induced in mice by arachidonate and PGE2 as models and dissected the role and mechanisms of action of each EP receptor at the molecular level. Arachidonate- or PGE2-induced vascular permeability was significantly reduced in EP3-deficient mice. Intriguingly, the PGE2-induced response was suppressed by histamine H1 antagonist treatment, histidine decarboxylase deficiency, and mast cell deficiency. The impaired PGE2-induced response in mast cell-deficient mice was rescued upon reconstitution with wild-type mast cells but not with EP3-deficient mast cells. Although the number of mast cells, protease activity, and histamine contents in ear tissues in EP3-deficient mice were comparable to those in wild-type mice, the histamine contents in ear tissues were attenuated upon PGE2 treatment in wild-type but not in EP3-deficient mice. Consistently, PGE2-EP3 signaling elicited histamine release in mouse peritoneal and bone marrow-derived mast cells, and it exerted degranulation and IL-6 production in a manner sensitive to pertussis toxin and a PI3K inhibitor and dependent on extracellular Ca(2+) ions. These results demonstrate that PGE2 triggers mast cell activation via an EP3-Gi/o-Ca(2+) influx/PI3K pathway, and this mechanism underlies PGE2-induced vascular permeability and consequent edema formation.
Elastic fiber formation begins in mid-gestation and increases dramatically during the last trimester in the great arteries, providing elasticity and thus preventing vascular wall structure collapse. However, the ductus arteriosus (DA), a fetal bypass artery between the aorta and pulmonary artery, exhibits lower levels of elastic fiber formation, which promotes vascular collapse and subsequent closure of the DA after birth. The molecular mechanisms for this inhibited elastogenesis in the DA, which is necessary for the establishment of adult circulation, remain largely unknown.
Electroconvulsive therapy is an effective and rapid treatment for depression. In patients with depression, the function of the paraventricular nucleus of the hypothalamus (PVN) is frequently altered. Electroconvulsive seizure (ECS), which is a model of electroconvulsive therapy, upregulates the expression of c-fos in the PVN of animal models. Therefore, we hypothesized that ECS alters gene expression and function in the PVN. The PVN was microdissected from mouse brain sections following ECS treatment, and total RNA was analyzed by microarray. Two hours after ECS, the levels of expression of 2.6% (589 genes) of the genes showed a greater than 2-fold decrease and 0.9% (205 genes) showed a greater than 2-fold increase. Among these genes, 72 of the downregulated genes and 12 of the upregulated genes have been proposed to be associated with psychiatric disorders, such as depression, by knowledge database analyses. The groups of downregulated genes included neuropeptides (Cck), kinases (Prkcb, Camk2a), transcription factors (Tcf4), and transporters (Aqp4), and these have been suggested to be associated with psychiatric disorders and/or PVN function. The results of the present study indicated that ECS treatment could modulate PVN functions through altered gene expression, which may contribute to its antidepressant effects.
Prostanoids comprising prostaglandins (PGs) and thromboxanes (TXs) have been shown to play physiological and pathological roles in zebrafish. However, the molecular basis of zebrafish prostanoid receptors has not been established. Here, we demonstrate that there exist at least five contractile (Ca(2+)-mobilizing) and one inhibitory (Gi-coupled) prostanoid receptors in zebrafish; five contractile receptors consisting of two PGE2 receptors (EP1a and EP1b), two PGF2? receptors (FP1 and FP2), and one TXA2 receptor TP, and one inhibitory receptor, the PGE2 receptor EP3. [(3)H]PGE2 specifically bound to the membranes of cells expressing zebrafish EP1a, EP1b and EP3 with a Kd of 4.8, 1.8 and 13.6nM, respectively, and [(3)H]PGF2? specifically bound to the membranes of cells expressing zebrafish FP1 and FP2, with a Kd of 6.5 and 1.6nM, respectively. U-46619, a stable agonist for human and mouse TP receptors, significantly increased the specific binding of [(35)S]GTP?S to membranes expressing the zebrafish TP receptor. Upon agonist stimulation, all six receptors showed an increase in intracellular Ca(2+) levels, although the increase was very weak in EP1b, and pertussis toxin abolished only the EP3-mediated response. Zebrafish EP3 receptor also suppressed forskolin-induced cAMP formation in a pertussis toxin-sensitive manner. In association with the low structural conservation with mammalian receptors, most agonists and antagonists specific for mammalian EP1, EP3 and TP failed to work on each corresponding zebrafish receptor. This work provides further insights into the diverse prostanoid actions mediated by their receptors in zebrafish.
Mast cells are the major sources of histamine, which is released in response to immunological stimulations. The synthesis of histamine is catalyzed by histidine decarboxylase (HDC). Previous studies have shown that Hdc(-/-) mast cells exhibit aberrant granule morphology with severely decreased granule content. Here, we investigated whether the histamine synthesized in mast cells regulates the granule maturation of murine mast cells. Several genes, including those encoding granule proteases and enzymes involved in heparin biosynthesis, were downregulated in Hdc(-/-) peritoneal mast cells. Impaired granule maturation was also found in Hdc(-/-) BM-derived cultured mast cells when they were cocultured with fibroblasts in the presence of c-kit ligand. Exogenous application of histamine and several H4 receptor agonists restored the granule maturation of Hdc(-/-) cultured mast cells. However, the maturation of granules was largely normal in Hrh4(-/-) peritoneal mast cells. Depletion of cellular histamine with tetrabenazine, an inhibitor of vesicular monoamine transporter-2, did not affect granule maturation. In vivo experiments with mast cell deficient Kit(W) /Kit(W-v) mice indicated that the expression of the Hdc gene in mast cells is required for granule maturation. These results suggest that histamine promotes granule maturation in mast cells and acts as an proinflammatory mediator.
Prostanoids comprising prostaglandins (PGs) and thromboxanes have been shown to play physiological and pathological roles in zebrafish. However, the molecular basis of zebrafish prostanoid receptors has not been characterized to date. Here, we demonstrate that there exist at least six relaxant (Gs-coupled) prostanoid receptors in zebrafish; one PGI2 receptor IP and five PGE2 receptors comprising two EP2 (EP2a and EP2b), and three EP4 receptors (EP4a, EP4b and EP4c). In contrast, we failed to find a zebrafish PGD2 receptor with any structure and/or character similarities to the mammalian DP1 receptor. [(3)H]iloprost, a stable IP radioligand, specifically bound to the membrane of cells expressing zebrafish IP with a Kd of 42nM, and [(3)H]PGE2 specifically bound to the membranes of cells expressing zebrafish EP2a, EP2b, EP4a, EP4b and EP4c with a Kd of 6.9, 6.0, 1.4, 3.3 and 1.2nM, respectively. Upon agonist stimulation, the relaxant prostanoid receptors showed intracellular cAMP accumulation. The responsiveness of these zebrafish receptors to subtype-specific agonists correlated with their structural conservation to the corresponding receptor in mammals. RT-PCR analysis revealed that the six zebrafish prostanoid receptors show unique tissue distribution patterns; each receptor gene may hence be under unique transcriptional regulation. This work provides further insights into the diverse functions of prostanoids in zebrafish.
Although the mechanisms underlying the spatial pattern formation of sensory maps have been extensively investigated, those triggering sensory map formation during development are largely unknown. Here we show that the birth of pups instructively and selectively regulates the initiation of barrel formation in the somatosensory cortex by reducing serotonin concentration. We found that preterm birth accelerated barrel formation, whereas it did not affect either barreloid formation or barrel structural plasticity. We also found that serotonin was selectively reduced soon after birth and that the reduction of serotonin was triggered by birth. The reduction of serotonin was necessary and sufficient for the effect of birth on barrel formation. Interestingly, the regulatory mechanisms described here were also found to regulate eye-specific segregation in the visual system, suggesting that they are utilized in various brain regions. Our results shed light on roles of birth and serotonin in sensory map formation.
Microenvironment-based alterations in phenotypes of mast cells influence the susceptibility to anaphylaxis, yet the mechanisms underlying proper maturation of mast cells toward an anaphylaxis-sensitive phenotype are incompletely understood. Here we report that PLA2G3, a mammalian homolog of anaphylactic bee venom phospholipase A2, regulates this process. PLA2G3 secreted from mast cells is coupled with fibroblastic lipocalin-type PGD2 synthase (L-PGDS) to provide PGD2, which facilitates mast-cell maturation via PGD2 receptor DP1. Mice lacking PLA2G3, L-PGDS or DP1, mast cell-deficient mice reconstituted with PLA2G3-null or DP1-null mast cells, or mast cells cultured with L-PGDS-ablated fibroblasts exhibited impaired maturation and anaphylaxis of mast cells. Thus, we describe a lipid-driven PLA2G3-L-PGDS-DP1 loop that drives mast cell maturation.
The ventromedial nucleus of the hypothalamus (VMH) plays an important role in feeding and energy homeostasis. Electroconvulsive seizure (ECS) therapy is highly effective in the treatment of several psychiatric diseases, including depression, but may also have beneficial effects in other neurological diseases. Although it has been reported that the neurons of the VMH are strongly activated by ECS stimulation, the specific effects of ECS in this hypothalamic subnucleus remain unknown. To address this issue, we investigated the changes in gene expression in microdissected-VMH samples in response to ECS in mice, and examined the behavioral effects of ECS on feeding behavior. ECS significantly induced the expression of immediate-early genes such as Fos, Fosb, and Jun, as well as Bdnf, Adcyap1, Hrh1, and Crhr2 in the VMH. Given that signals of these gene products are suggested to have anorexigenic roles in the VMH, we also examined the effect of ECS on food intake and body weight. Repeated ECS had a suppressive effect on food intake and body weight gain under both regular and high-fat diet conditions. Furthermore, gold-thioglucose-induced hypothalamic lesions, including the VMH and the arcuate nucleus, abolished the anorexigenic effects of ECS, indicating the requirement for the activation of the hypothalamus. Our data show an effect of ECS on increased expression of anorexigenic factors in the VMH, and suggest a role in the regulation of energy homeostasis by ECS.
The prostaglandin (PG) receptors EP4 and FP have the potential to exert negative effects on adipogenesis, but the exact contribution of endogenous PG-driven receptor signaling to this process is not fully understood. In this study, we employed an adipocyte differentiation system from mouse embryonic fibroblasts (MEF) and compared the effects of each PG receptor-deficiency on adipocyte differentiation. In wild-type (WT) MEF cells, inhibition of endogenous PG synthesis by indomethacin augmented the differentiation, whereas exogenous PGE?, as well as an FP agonist, reversed the effect of indomethacin. In EP4-deficient cells, basal differentiation was upregulated to the levels in indomethacin-treated WT cells, and indomethacin did not further enhance differentiation. Differentiation in FP-deficient cells was equivalent to WT and was still sensitive to indomethacin. PGE? or indomethacin treatment of WT MEF cells for the first two days was enough to suppress or enhance transcription of the Pparg2 gene as well as the subsequent differentiation, respectively. Differentiation stimuli induced COX-2 gene and protein expression, as well as PGE? production, in WT MEF cells. These results suggest that PGE?-EP4 signaling suppresses adipocyte differentiation by affecting Pparg2 expression in an autocrine manner and that FP-mediated inhibition is not directly involved in adipocyte differentiation in the MEF system.
The gonadal primordium first emerges as a thickening of the embryonic coelomic epithelium, which has been thought to migrate mediodorsally to form the primitive gonad. However, the early gonadal development remains poorly understood. Mice lacking the paired-like homeobox gene Emx2 display gonadal dysgenesis. Interestingly, the knockout (KO) embryonic gonads develop an unusual surface accompanied by aberrant tight junction assembly. Morphological and in vitro cell fate mapping studies showed an apparent decrease in the number of the gonadal epithelial cells migrated to mesenchymal compartment in the KO, suggesting that polarized cell division and subsequent cell migration are affected. Microarray analyses of the epithelial cells revealed significant up-regulation of Egfr in the KO, indicating that Emx2 suppresses Egfr gene expression. This genetic correlation between the two genes was reproduced with cultured M15 cells derived from mesonephric epithelial cells. Epidermal growth factor receptor signaling was recently shown to regulate tight junction assembly through sarcoma viral oncogene homolog tyrosine phosphorylation. We show through Emx2 KO analyses that sarcoma viral oncogene homolog tyrosine phosphorylation, epidermal growth factor receptor tyrosine phosphorylation, and Egfr expression are up-regulated in the embryonic gonad. Our results strongly suggest that Emx2 is required for regulation of tight junction assembly and allowing migration of the gonadal epithelia to the mesenchyme, which are possibly mediated by suppression of Egfr expression.
Histamine and prostaglandins (PGs) play a variety of physiological roles as autacoids, which function in the vicinity of their sources and maintain local homeostasis in the body. They stimulate target cells by acting on their specific receptors, which are coupled to trimeric G proteins. For the precise understanding of the physiological roles of histamine and PGs, it is necessary to clarify the molecular mechanisms involved in their synthesis as well as their receptor-mediated responses. We cloned the cDNAs for mouse L-histidine decarboxylase (HDC) and 6 mouse prostanoid receptors (4 PGE(2) receptors, PGF receptor, and PGI receptor). We then characterized the expression patterns and functions of these genes. Furthermore, we established gene-targeted mouse strains for HDC and PG receptors to explore the novel pathophysiological roles of histamine and PGs. We have here summarized our research, which should contribute to progress in the molecular biology of HDC and PG receptors.
It is widely accepted that the inhibition of gastric motor activity as well as the maintenance of gastric mucosal blood flow and mucous secretion are important for the homeostasis of the gastric mucosa. The present study was performed to ascertain whether or not endogenous PGs, which can protect the stomach from noxious stimuli, affect gastric motor activity and emptying. The myoelectrical activity of rat gastric smooth muscle was increased at intragastric pressures of over 2 cmH(2)O. Replacement of intragastric physiological saline with 1 M NaCl solution significantly increased PGI(2) and PGE(2) in stomach and suppressed the myoelectrical activity under a pressure of 2 cmH(2)O by 70%. Indomethacin inhibited the suppression of myoelectrical activity by 1 M NaCl. The myoelectrical activity under a pressure of 2 cmH(2)O was suppressed by continuous infusion of a selective EP1 agonist (ONO-DI-004, 3-100 nmol·kg(-1)·min(-1)) into the gastric artery in a dose-dependent manner, but not by that of the PGI receptor agonist beraprost sodium (100 nmol·kg(-1)·min(-1)). Suppression of myoelectrical activity with 1 M NaCl was inhibited by continuous infusion of a selective EP1 antagonist (ONO-8711, 100 nmol·kg(-1)·min(-1)) into the gastric artery. Furthermore, gastric emptying was tested in EP1 knockout mice and their wild-type counterparts. Gastric emptying was strongly suppressed with intragastric 1 M NaCl in wild-type mice, but this 1 M NaCl-induced suppression was not seen in EP1 knockout mice. These results suggest that PGE(2)-EP1 signaling has crucial roles in suppression of myoelectrical activity of gastric smooth muscles and inhibition of gastric emptying and that EP1 is an obvious target for drugs that control gastric emptying.
To understand the role of prostaglandin (PG) receptor EP2 (Ptger2) signaling in ovulation and fertilization, we investigated time-dependent expression profiles in wild-type (WT) and Ptger2(-/-) cumuli before and after ovulation by using microarrays. We prepared cumulus cells from mice just before and 3, 9 and 14 h after human chorionic gonadotropin injection. Key genes including cAMP-related and epidermal growth factor (EGF) genes, as well as extracellular matrix- (ECM-) related and chemokine genes were up-regulated in WT cumuli at 3 h and 14 h, respectively. Ptger2 deficiency differently affected the expression of many of the key genes at 3 h and 14 h. These results indicate that the gene expression profile of cumulus cells greatly differs before and after ovulation, and in each situation, PGE(2)-EP2 signaling plays a critical role in cAMP-regulated gene expression in the cumulus cells under physiological conditions.
Bone marrow (BM)-derived hematopoietic cells, which are major components of tumor stroma, determine the tumor microenvironment and regulate tumor phenotypes. Cyclooxygenase (COX)-2 and endogenous prostaglandins are important determinants for tumor growth and tumor-associated angiogenesis; however, their contributions to stromal formation and angiogenesis remain unclear. In this study, we observed that Lewis lung carcinoma cells implanted in wild-type mice formed a tumor mass with extensive stromal formation that was markedly suppressed by COX-2 inhibition, which reduced the recruitment of BM cells. Notably, COX-2 inhibition attenuated CXCL12/CXCR4 expression as well as expression of several other chemokines. Indeed, in a Matrigel model, prostaglandin (PG) E2 enhanced stromal formation and CXCL12/CXCR4 expression. In addition, a COX-2 inhibitor suppressed stromal formation and reduced expression of CXCL12/CXCR4 and a fibroblast marker (S100A4) in a micropore chamber model. Moreover, stromal formation after tumor implantation was suppressed in EP3-/- mice and EP4-/- mice, in which stromal expression of CXCL12/CXCR4 and S100A4 was reduced. The EP3 or EP4 knockout suppressed S100A4+ fibroblasts, CXCL12+, and/or CXCR4+ stromal cells as well. Immunofluorescent analyses revealed that CXCL12+CXCR4+S100A4+ fibroblasts mainly comprised stromal cells and most of these were recruited from the BM. Additionally, either EP3- or EP4-specific agonists stimulated CXCL12 expression by fibroblasts in vitro. The present results address the novel activities of COX-2/PGE2-EP3/EP4 signaling that modulate tumor biology and show that CXCL12/CXCR4 axis may play a crucial role in tumor stromal formation and angiogenesis under the control of prostaglandins.
We previously demonstrated that prostaglandin EP3 receptor augments EP2-elicited cAMP formation in COS-7 cells in a G(i/o)-insensitive manner. The purpose of our current study was to identify the signaling pathways involved in EP3-induced augmentation of receptor-stimulated cAMP formation. The enhancing effect of EP3 receptor was irrespective of the C-terminal structure of the EP3 isoform. This EP3 action was abolished by treatment with inhibitors for phospholipase C and intracellular Ca(2+)-related signaling molecules such as U73122, staurosporine, 2-APB and SK&F 96365. Indeed, an EP3 agonist stimulated IP(3) formation and intracellular Ca(2+) mobilization, which was blocked by U73122, but not by pertussis toxin. The enhancing effect by EP3 on cAMP formation was mimicked by both a Ca(2+) ionophore and the activation of a typical G(q)-coupled receptor. Moreover, EP3 was exclusively localized to the raft fraction in COS-7 cells and EP3-elicited augmentation of cAMP formation was abolished by cholesterol depletion and introduction of a dominant negative caveolin-1 mutant. These results suggest that EP3 elicits adenylyl cyclase superactivation via G(q)/phospholipase C activation and intracellular Ca(2+) mobilization in a lipid raft microdomain-dependent manner.
Cyclooxygenase (COX)-2 is known to correlate with poor cancer prognosis and to contribute to tumor metastasis. However, the precise mechanism of this phenomenon remains unknown. We have previously reported that host stromal prostaglandin E(2) (PGE(2))-prostaglandin E2 receptor (EP)3 signaling appears critical for tumor-associated angiogenesis and tumor growth. Here we tested whether the EP3 receptor has a critical role in tumor metastasis. Lewis lung carcinoma (LLC) cells were intravenously injected into WT mice and mice treated with the COX-2 inhibitor NS-398. The nonselective COX inhibitor aspirin reduced lung metastasis, but the COX-1 inhibitor SC560 did not. The expression of matrix metalloproteinases (MMP)-9 and vascular endothelial growth factor (VEGF)-A was suppressed in NS-398-treated mice compared with PBS-treated mice. Lungs containing LLC colonies were markedly reduced in EP3 receptor knockout (EP3(-/-)) mice compared with WT mice. The expression of MMP-9 and VEGF-A was downregulated in metastatic lungs of EP3(-/-) mice. An immunohistochemical study revealed that MMP-9-expressing endothelial cells were markedly reduced in EP3(-/-) mice compared with WT mice. When HUVEC were treated with agonists for EP1, EP2, EP3, or EP4, only the EP3 agonist enhanced MMP-9 expression. These results suggested that EP3 receptor signaling on endothelial cells is essential for the MMP-9 upregulation that enhances tumor metastasis and angiogenesis. An EP3 receptor antagonist may be useful to protect against tumor metastasis.
Amyloid-beta (Abeta) peptides, generated by the proteolysis of beta-amyloid precursor protein by beta- and gamma-secretases, play an important role in the pathogenesis of Alzheimer disease. Inflammation is also important. We recently reported that prostaglandin E(2) (PGE(2)), a strong inducer of inflammation, stimulates the production of Abeta through EP(2) and EP(4) receptors, and here we have examined the molecular mechanism. Activation of EP(2) and EP(4) receptors is coupled to an increase in cellular cAMP levels and activation of protein kinase A (PKA). We found that inhibitors of adenylate cyclase and PKA suppress EP(2), but not EP(4), receptor-mediated stimulation of the Abeta production. In contrast, inhibitors of endocytosis suppressed EP(4), but not EP(2), receptor-mediated stimulation. Activation of gamma-secretase was observed with the activation of EP(4) receptors but not EP(2) receptors. PGE(2)-dependent internalization of the EP(4) receptor was observed, and cells expressing a mutant EP(4) receptor lacking the internalization activity did not exhibit PGE(2)-stimulated production of Abeta. A physical interaction between the EP(4) receptor and PS-1, a catalytic subunit of gamma-secretases, was revealed by immunoprecipitation assays. PGE(2)-induced internalization of PS-1 and co-localization of EP(4), PS-1, and Rab7 (a marker of late endosomes and lysosomes) was observed. Co-localization of PS-1 and Rab7 was also observed in the brain of wild-type mice but not of EP(4) receptor null mice. These results suggest that PGE(2)-stimulated production of Abeta involves EP(4) receptor-mediated endocytosis of PS-1 followed by activation of the gamma-secretase, as well as EP(2) receptor-dependent activation of adenylate cyclase and PKA, both of which are important in the inflammation-mediated progression of Alzheimer disease.
Two distinct helper T (TH) subsets, TH1 and TH17, mediate tissue damage and inflammation in animal models of various immune diseases such as multiple sclerosis, rheumatoid arthritis, inflammatory bowel diseases and allergic skin disorders. These experimental findings, and the implication of these TH subsets in human diseases, suggest the need for pharmacological measures to manipulate these TH subsets. Here we show that prostaglandin E2 (PGE2) acting on its receptor EP4 on T cells and dendritic cells not only facilitates TH1 cell differentiation but also amplifies interleukin-23-mediated TH17 cell expansion in vitro. Administration of an EP4-selective antagonist in vivo decreases accumulation of both TH1 and TH17 cells in regional lymph nodes and suppresses the disease progression in mice subjected to experimental autoimmune encephalomyelitis or contact hypersensitivity. Thus, PGE2-EP4 signaling promotes immune inflammation through TH1 differentiation and TH17 expansion, and EP4 antagonism may be therapeutically useful for various immune diseases.
Cumulus cells surround the oocyte and regulate the production and assembly of the extracellular matrix (ECM) around the cumulus-oocyte complex for its timely interaction with sperm in the oviduct. We recently found that C-C chemokines such as CCL2, CCL7, and CCL9 are produced and stimulate integrin-mediated ECM assembly in the postovulatory cumulus to protect eggs and that prostaglandin E(2)-EP2 signaling in the cumulus cells facilitates fertilization by suppressing this chemokine signaling, which otherwise results in fertilization failure by preventing sperm penetration through the cumulus ECM. However, it remains unknown as to what mechanisms underlie chemokine-induced cumulus ECM assembly. Here we report that inhibition of EP2 signaling or addition of CCL7 augments RhoA activation and induces the surface accumulation of integrin and the contraction of cumulus cells. Enhanced surface accumulation of integrin then stimulates the formation and assembly of fibronectin fibrils as well as induces cumulus ECM resistance to hyaluronidase and sperm penetration. These changes in the cumulus ECM as well as cell contraction are relieved by the addition of Y27632 or blebbistatin. These results suggest that chemokines induce integrin engagement to the ECM and consequent ECM remodeling through the RhoA/Rho kinase/actomyosin pathway, making the cumulus ECM barrier resistant to sperm penetration. Based on these results, we propose that prostaglandin E(2)-EP2 signaling negatively regulates chemokine-induced Rho/ROCK signaling in cumulus cells for successful fertilization.
Prostaglandin E(2) (PGE(2)) and prostaglandin E (EP) receptor signaling pathways have been implicated in the promotion of tumor growth and angiogenesis. However, little is known about their roles in lymphangiogenesis during tumor development. The present study evaluates whether endogenous PGE(2) exhibits a critical role in tumor-associated lymphangiogenesis. Treatment of male C57BL/6 mice with a cyclooxygenase-2 inhibitor, celecoxib, for seven days resulted in a 52.4% reduction in tumor size induced by subcutaneous injection of murine Lewis lung cells. Celecoxib treatment down-regulated the expression of vascular endothelial growth factor receptor (VEGFR)-3 in stromal tissues by 73.9%, and attenuated expression of podoplanin, a marker for lymphatic endothelial cells. To examine the role of host PGE receptor signaling, we tested four kinds of EP receptor knockout mice. At Day 7 after tumor cell implantation, EP3 receptor knockout mice, but not EP receptor knockout mice lacking EP1, EP2, or EP4, exhibited a 53.3% reduction in tumor weight, which was associated with a 74.5% reduction in VEGFR-3 mRNA expression in tumor stromal tissues. At Day 14, VEGFR-3 expression in EP3-/- mice remained significantly lower than that of their wild-type (WT) counterparts. The expression of VEGF-C in the tumor stromal tissues in EP3-/- mice were also reduced by 22.1% (Day 7) and 44.1% (Day 14), respectively. In addition, the level of immunoreactive podoplanin in the tumor tissues from EP3-/- mice was less than that of WT. These results suggest that host EP3 receptor signaling regulates tumor-associated lymphangiogenesis by up-regulating expression of VEGF-C and its receptor, VEGFR-3, in tumor stromal tissues. Host EP3 blockade together with COX-2 inhibition may be a novel therapeutic strategy to suppress tumor-associated lymphangiogenesis.
Recent results suggest that bone marrow (BM)-derived hematopoietic cells are major components of tumor stroma and play crucial roles in tumor growth and angiogenesis. An E-type prostaglandin is known to regulate angiogenesis. We examined the role of BM-derived cells expressing an E-type prostaglandin receptor subtype (EP3) in tumor-induced angiogenesis and tumor growth. The replacement of wild-type (WT) BM with BM cells (BMCs) from green fluorescent protein (GFP) transgenic mice revealed that the stroma developed via the recruitment of BMCs. Selective knockdown of EP3 by recruitment of genetically modified BMCs lacking EP3 receptors was performed by transplantation of BMCs from EP3 knockout (EP3(-/-)) mice. Tumor growth and tumor-associated angiogenesis were suppressed in WT mice transplanted with BMCs from EP3(-/-) mice, but not in mice transplanted with BMCs from either EP1(-/-), EP2(-/-), or EP4(-/-) mice. Immunohistochemical analysis revealed that vascular endothelial growth factor (VEGF) expression was suppressed in the stroma of mice transplanted with BMCs from EP3(-/-) mice. EP3 signaling played a significant role in the recruitment of VEGFR-1- and VEGFR-2-positive cells from the BM to the stroma. These results indicate that the EP3 signaling expressed in bone marrow-derived cells has a crucial role in tumor-associated angiogenesis and tumor growth with upregulation of the expression of the host stromal VEGF together with the recruitment of VEGFR-1/VEGFR-2-positive. The present study suggests that the blockade of EP3 signaling and the recruitment of EP3-expressing stromal cells may become a novel strategy to treat solid tumors.
Despite extensive attempts to develop cyclooxygenase (COX)-2 imaging radiotracers, no suitable positron emission tomography (PET)/single photon emission computed tomography (SPECT) tracers are currently available for in vivo imaging of COX-2 expression. The aims of this study were to synthesize and evaluate a radioiodinated derivative of lumiracoxib, 2-[(2-fluoro-6-iodophenyl)-amino]-5-methylphenylacetic acid (FIMA), which is structurally distinct from other drugs in the class and has weakly acidic properties, as a SPECT tracer for imaging COX-2 expression.
By using the recently established culture system that reproduces the terminal differentiation process of connective tissue-type mast cells, we found significant transcriptional induction of CD44. As CD44 is a primary receptor for hyaluronan (HA), which is one of the major extracellular matrix components, we investigated the role of CD44 in cutaneous mast cells. When co-cultured with fibroblasts, mouse bone marrow-derived cultured mast cells (BMMCs) were found to form clusters in an HA-dependent manner. As compared with BMMCs derived from the wild-type mice, those from the CD44(-/-) mice exhibited impaired growth during the co-cultured period. Furthermore, in the peritoneal cavities and ear tissues, mature mast cells were fewer in number in the CD44(-/-) mice than in the wild-type mice. We investigated roles of CD44 in mast cell proliferation by reconstituting BMMCs into the tissues of mast cell-deficient, Kit(W)/Kit(W-v) mice, and found that the number of metachromatic cells upon acidic toluidine blue staining in the tissues transplanted with CD44(-/-) BMMCs was not significantly changed for 10 weeks, whereas that in the tissues transplanted with the CD44(+/+) BMMCs was significantly increased. These results suggest that CD44 plays a crucial role in the regulation of the cutaneous mast cell number.
Mast cells (MCs) play pivotal roles in allergy and innate immunity and consist of heterogenous subclasses. However, the molecular basis determining the different characteristics of these multiple MC subclasses remains unclear.
Contact dermatitis is an inflammatory skin disease caused by toxic factors that activate the skin innate immunity (irritant contact dermatitis) or by a T cell-mediated hypersensitivity reaction (allergic contact dermatitis). These inflammatory skin diseases are sometimes still not easy to control. Therefore, the development of new effective drugs with fewer side effects is anticipated. In the skin under pathophysiological conditions, multiple prostaglandins are produced and their receptors are expressed in time- and/or cell-dependent manners. However, the precise role of prostaglandins and their receptors in contact dermatitis has not been fully understood. Recently, studies using mice with a disruption of each prostaglandin receptor gene, as well as receptor-selective compounds revealed that prostaglandin receptors have manifold functions, sometimes resulting in opposite outcomes. Here, we review new advances in the roles of prostaglandin receptors in contact hypersensitivity as a cutaneous immune response model, and also discuss the clinical potentials of receptor-selective drugs.
Aortic aneurysm is a common but life-threatening disease among the elderly, for which no effective medical therapy is currently available. Activation of prostaglandin E(2) (PGE(2)) is known to increase the expression of matrix metalloproteinase (MMP) and the release of inflammatory cytokines, and may thus exacerbate abdominal aortic aneurysm (AAA) formation. We hypothesized that selective blocking of PGE(2), in particular, EP4 prostanoid receptor signaling, would attenuate the development of AAA.
Inflammatory responses in the kidney lead to tubulointerstitial fibrosis, a common feature of chronic kidney diseases. Here we examined the role of prostaglandin E(2) (PGE(2)) in the development of tubulointerstitial fibrosis. In the kidneys of wild-type mice, unilateral ureteral obstruction leads to progressive tubulointerstitial fibrosis with macrophage infiltration and myofibroblast proliferation. This was accompanied by an upregulation of COX-2 and PGE(2) receptor subtype EP(4) mRNAs. In the kidneys of EP(4) gene knockout mice, however, obstruction-induced histological alterations were significantly augmented. In contrast, an EP(4)-specific agonist significantly attenuated these alterations in the kidneys of wild-type mice. The mRNAs for macrophage chemokines and profibrotic growth factors were upregulated in the kidneys of wild-type mice after ureteral obstruction. This was significantly augmented in the kidneys of EP(4)-knockout mice and suppressed by the EP(4) agonist but only in the kidneys of wild-type mice. Notably, COX-2 and MCP-1 proteins, as well as EP(4) mRNA, were localized in renal tubular epithelial cells after ureteral obstruction. In cultured renal fibroblasts, another EP(4)-specific agonist significantly inhibited PDGF-induced proliferation and profibrotic connective tissue growth factor production. Hence, an endogenous PGE(2)-EP(4) system in the tubular epithelium limits the development of tubulointerstitial fibrosis by suppressing inflammatory responses.
Appropriate culture models for tissue mast cells are required to determine how they are involved in regulation of local immune responses. We previously established a culture model for cutaneous mast cells, in which bone marrow-derived immature mast cells were co-cultured with Swiss 3T3 fibroblasts in the presence of stem cell factor. In this study, we focused on the roles of hyaluronan, which is produced by the feeder fibroblasts and forms the extracellular matrix during the co-culture period. Hyaluronan synthesis was found to be mediated by hyaluronan synthase 2 (HAS2) expressed in Swiss 3T3 cells. A decreases in the amount of hyaluronan, which was achieved by retroviral expression of short hairpin RNA for Has2 or by addition of hyaluronidase, significantly enhanced the proliferation of the cultured mast cells without any obvious effects on their maturation. Although we previously demonstrated that CD44 is required for proliferation of cutaneous mast cells, the deficiency of hyaluronan did not affect the proliferation of the cultured mast cells that lack CD44. These findings suggest that the extracellular matrix containing hyaluronan may have a potential to restrict proliferation of cutaneous mast cells in a CD44-independent manner.
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