Impaired febrile response in mice lacking the prostaglandin E receptor subtype EP3

Cyclooxygenase-2-derived Prostaglandin E2 Directs Oocyte Maturation by Differentially Influencing Multiple Signaling Pathways

The process of oocyte maturation, which impacts ovulation and fertilization, is complex and requires an integration of the endocrine, paracrine, juxtacrine, and autocrine signaling pathways. This process involves an intimate interaction between the oocyte and encircling cumulus cells within a follicle, a unique venue for somatic and germ cell communication. Cumulus cell expansion and resumption of meiosis with germinal vesicle breakdown are major events in oocyte maturation. Cyclooxygenase-2 (COX-2)-derived prostaglandin E(2) (PGE(2)) is a known critical mediator of oocyte maturation, but the diverse function of this lipid mediator in oocyte maturation, ovulation, and fertilization has not been fully appreciated. We show here that gonadotropins in coordination with PGE(2) signaling via its cell surface G-protein-coupled EP2 and EP4 receptor subtypes direct cumulus cell expansion and survival and oocyte meiotic maturation by differentially impacting cAMP-dependent protein kinase, MAPK, NF-kappaB, and phosphatidylinositol 3-kinase/Akt pathways. This study is unique in the sense that it provides evidence for new site- and event-specific involvement of these signaling pathways under the influence of COX-2-derived PGE(2) during the critical stages of this somatic-germ cell interaction, an absolute requirement for oocyte maturation.

Recruitment of a prostaglandin E receptor subtype, EP3-expressing bone marrow cells is crucial in wound-induced angiogenesis

E-type prostaglandins have been reported to be proangiogenic in vivo. Thus, we examined prostaglandin receptor signaling relevant to wound-induced angiogenesis. Full-thickness skin wounds were created on the backs of mice, and angiogenesis in wound granulation tissues was estimated. Wound closure and re-epithelization in EP3 receptor knockout mice (EP3-/-) were significantly delayed compared with their wild-type (WT) mice, whereas those in EP1-/-, EP2-/-, and EP4-/- were not delayed. Wound-induced angiogenesis estimated with CD31 immunohistochemistry in EP3-/- mice was significantly inhibited compared with that in WT mice. Immunoreactive vascular endothelial growth factor (VEGF) in wound granulation tissues in EP3-/- mice was markedly less than that in WT mice. Wound closure in WT mice was delayed significantly by VEGF neutralizing antibody compared with control IgG. Wound-induced angiogenesis and wound closure were significantly suppressed in EP3-/- bone marrow transplantation mice compared with those in WT bone marrow transplantation mice. These were accompanied with the reductions in accumulation of VEGF-expressing cells in wound granulation tissues and in mobilization of VEGF receptor 1-expressing leukocytes in peripheral circulation. These results indicate that the recruitment of EP3-expressing cells to wound granulation tissues is critical for surgical wound healing and angiogenesis via up-regulation of VEGF.

The IOP-lowering effects and mechanism of action of tafluprost in prostanoid receptor-deficient mice

AIM

To clarify the intraocular pressure (IOP)-lowering profile of tafluprost, a newly synthesised prostaglandin F(2alpha) analogue, in mice.

METHODS

C57BL/6J, and EP1, EP2, EP3 and postaglandin F (FP) receptor-deficient wild-type (WT), EP1KO, EP2KO, EP3KO and FPKO, respectively mice were bred and acclimatised under a 12-h (6:00-18:00) light-dark cycle. To evaluate effects of tafluprost (0.002%) on IOP at night, a single 3 microl drop of tafluprost solution was applied topically at 18:00 once into one eye in each mouse. IOP was measured 3 h after the application with a microneedle method. To clarify whether endogenous prostaglandin is concerned with the tafluprost-induced IOP reduction, we applied 0.1% diclofenac Na, a cyclo-oxygenase inhibitor or PBS 30 min before the application of tafluprost in WT and EP3KO mice and measured IOP 3 h after the tafluprost application. We also determined whether animals responded predictably to 0.1% bunazosin HCl, a drug known to increase uveoscleral outflow.

RESULTS

3 h after the application of 0.0015% tafluprost, mean (SEM) IOP reductions were 25.8 (2.1)% 26.3 (0.8)% 24.2 (1.4)% 16.5 (1.7)% and -0.9 (1.5)% in WT, EP1KO, EP2KO, EP3KO and FPKO mice, respectively. IOP reductions in EP3KO and FPKO mice were significantly smaller than in WT mice. Pretreatment with diclofenac Na significantly attenuated the IOP lowering effect of tafluprost in WT mice but not in EP3KO mice. Bunazosin HCl lowered IOP significantly in all genotypes by the same amount.

CONCLUSION

We conclude that tafluprost lowers IOP through the prostanoid FP receptor. A part of ocular hypotensive effect of tafluprost is attributed to FP receptor-mediated prostaglandin production acting through the prostanoid EP3 receptor.

Modulation of ocular inflammatory responses by EP1 receptors in mice

The purpose of the study was to investigate the role of EP1 receptors in intraocular inflammation and to determine possible interplay between EP1, EP2 and EP4 receptors. The eyes of separate groups of EP1 receptor knockout and wild type mice were: 1) treated topically with prostaglandin E2 (PGE2) or the EP2 receptor selective agonist, butaprost; 2) given intravitreal injection of LPS; or 3) paracentesis performed. Another group of knockout mice were pretreated topically with an EP4 receptor selective antagonist prior to paracentesis or LPS treatment. Results demonstrated a significant increase (50% or more) in the protein levels of aqueous humor of the EP1 knockout mice in response to PGE2, paracentesis or LPS. The leukocyte infiltration in the aqueous humor of the knockout mice was 47% higher when compared with that in the wild type controls in response to LPS injection. No significant change was observed in the protein levels in response to butaprost. Pretreating the knockout mice with an EP4 receptor antagonist prior to paracentesis and LPS treatment substantially reduced the aqueous humor protein levels. Also, the leukocyte count in the aqueous humor of the knockout mice in response to LPS was reduced 4 fold after pretreatment with EP4 receptor antagonist when compared with the findings in knockout mice receiving LPS only. We concluded that EP1 receptor has no modulatory effect on EP2 receptors but there is definitely cross-talk between EP1 and EP4 receptors.

Activation of prostaglandin E receptor EP4 subtype suppresses food intake in mice

Prostaglandin (PG) E2, a bioactive lipid produced in the brains of various mammals, decreases food intake after central administration. We examined which of four distinct subtypes of PGE2 receptors (EP1-EP4) mediated the anorexigenic action of PGE2 using highly selective ligands. PGE2 at a dose of 0.1-10 nmol/mouse decreased food intake after intracerebroventricular (i.c.v.) administration in a dose-dependent manner in fasted mice. A centrally administered EP4 agonist, ONO-AE1-329 at a dose of 1-10 nmol/mouse mimicked the anorexigenic action by PGE2. The anorexigenic action of PGE2 or EP4 agonist was ameliorated by EP4 antagonist ONO-AE3-208 at a dose of 10 nmol/mouse. Thus, activation of PGE2-EP4 signaling in the central nervous system suppresses food intake. The EP4 agonist at a dose of 10 nmol/mouse delayed gastric emptying and elevated blood glucose.

Deletion of microsomal prostaglandin E synthase-1 augments prostacyclin and retards atherogenesis

Prostaglandin (PG) E(2) is formed from PGH(2) by a series of PGE synthase (PGES) enzymes. Microsomal PGES-1(-/-) (mPGES-1(-/-)) mice were crossed into low-density lipoprotein receptor knockout (LDLR(-/-)) mice to generate mPGES-1(-/-) LDLR(-/-)s. Urinary 11alpha-hydroxy-9, 15-dioxo-2,3,4,5-tetranor-prostane-1,20-dioic acid (PGE-M) was depressed by mPGES-1 deletion. Vascular mPGES-1 was augmented during atherogenesis in LDLR(-/-)s. Deletion of mPGES-1 reduced plaque burden in fat-fed LDLR(-/-)s but did not alter blood pressure. mPGES-1(-/-) LDLR(-/-) plaques were enriched with fibrillar collagens relative to LDLR(-/-), which also contained small and intermediate-sized collagens. Macrophage foam cells were depleted in mPGES-1(-/-) LDLR(-/-) lesions, whereas the total areas rich in vascular smooth muscle cell (VSMC) and matrix were unaltered. mPGES-1 deletion augmented expression of both prostacyclin (PGI(2)) and thromboxane (Tx) synthases in endothelial cells, and VSMCs expressing PGI synthase were enriched in mPGES-1(-/-) LDLR(-/-) lesions. Stimulation of mPGES-1(-/-) VSMC and macrophages with bacterial LPS increased PGI(2) and thromboxane A(2) to varied extents. Urinary PGE-M was depressed, whereas urinary 2,3-dinor 6-keto PGF(1alpha), but not 2,3-dinor-TxB(2), was increased in mPGES-1(-/-) LDLR(-/-)s. mPGES-1-derived PGE(2) accelerates atherogenesis in LDLR(-/-) mice. Disruption of this enzyme retards atherogenesis, without an attendant impact on blood pressure. This may reflect, in part, rediversion of accumulated PGH(2) to augment formation of PGI(2). Inhibitors of mPGES-1 may be less likely than those selective for cyclooxygenase 2 to result in cardiovascular complications because of a divergent impact on the biosynthesis of PGI(2).

Cyclooxygenases, lipoxygenases, and epoxygenases in CNS: Their role and involvement in neurological disorders

Three enzyme systems, cyclooxygenases that generate prostaglandins, lipoxygenases that form hydroxy derivatives and leukotrienes, and epoxygenases that give rise to epoxyeicosatrienoic products, metabolize arachidonic acid after its release from neural membrane phospholipids by the action of phospholipase A(2). Lysophospholipids, the other products of phospholipase A(2) reactions, are either reacylated or metabolized to platelet-activating factor. Under normal conditions, these metabolites play important roles in synaptic function, cerebral blood flow regulation, apoptosis, angiogenesis, and gene expression. Increased activities of cyclooxygenases, lipoxygenases, and epoxygenases under pathological situations such as ischemia, epilepsy, Alzheimer's disease, Parkinson disease, amyotrophic lateral sclerosis, and Creutzfeldt-Jakob disease produce neuroinflammation involving vasodilation and vasoconstriction, platelet aggregation, leukocyte chemotaxis and release of cytokines, and oxidative stress. These are closely associated with the neural cell injury which occurs in these neurological conditions. The metabolic products of docosahexaenoic acid, through these enzymes, generate a new class of lipid mediators, namely docosatrienes and resolvins. These metabolites antagonize the effect of metabolites derived from arachidonic acid. Recent studies provide insight into how these arachidonic acid metabolites interact with each other and other bioactive mediators such as platelet-activating factor, endocannabinoids, and docosatrienes under normal and pathological conditions. Here, we review present knowledge of the functions of cyclooxygenases, lipoxygenases, and epoxygenases in brain and their association with neurodegenerative diseases.

Analgesic strategies beyond the inhibition of cyclooxygenases

Blocking the formation of prostaglandins with cyclooxygenase (COX) inhibitors has been the treatment of choice for inflammatory pain for more than a century. Although these agents provide profound pain relief, their long-term use is hampered by severe side-effects, mainly ulceration of the upper gastrointestinal tract. The development of COX-2-selective inhibitors ("coxibs") has significantly reduced gastrointestinal toxicity, but evidence from controlled clinical trials and experimental studies indicates that the use of coxibs has a significant cardiovascular risk. Recently, signalling elements downstream of COX-2 inhibition have been identified, which offer a great diversity of possible targets. This review focuses on prostaglandin E synthases, prostaglandin receptors and downstream effectors of prostaglandins in the PNS and CNS, including transient receptor potential channels, tetrodotoxin-resistant Na(+) channels and inhibitory glycine receptors. These novel targets should enable inflammatory pain to be treated with improved specificity and, possibly, fewer side-effects.

IL-1beta and LPS induce anorexia by distinct mechanisms differentially dependent on microsomal prostaglandin E synthase-1

Recent work demonstrated that the febrile response to peripheral immune stimulation with proinflammatory cytokine IL-1beta or bacterial wall lipopolysaccharide (LPS) is mediated by induced synthesis of prostaglandin E(2) by the terminal enzyme microsomal prostaglandin E synthase-1 (mPGES-1). The present study examined whether a similar mechanism might also mediate the anorexia induced by these inflammatory agents. Transgenic mice with a deletion of the Ptges gene, which encodes mPGES-1, and wild-type controls were injected intraperitoneally with IL-1beta, LPS, or saline. Mice were free fed, and food intake was continuously monitored with an automated system for 12 h. Body weight was recorded every 24 h for 4 days. The IL-1beta induced anorexia in wild-type but not knock-out mice, and so it was almost completely dependent on mPGES-1. In contrast, LPS induced anorexia of the same magnitude in both phenotypes, and hence it was independent of mPGES-1. However, when the mice were prestarved for 22 h, LPS induced anorexia and concomitant body weight loss in the knock-out animals that was attenuated compared with the wild-type controls. These data suggest that IL-1beta and LPS induce anorexia by distinct immune-to-brain signaling pathways and that the anorexia induced by LPS is mediated by a mechanism different from the fever induced by LPS. However, nutritional state and/or motivational factors also seem to influence the pathways for immune signaling to the brain. Furthermore, both IL-1beta and LPS caused reduced meal size but not meal frequency, suggesting that both agents exerted an anhedonic effect during these experimental conditions.

New role of the trigeminal nerve as a neuronal pathway signaling brain in acute periodontitis: participation of local prostaglandins

The systemic induction of cytokines and prostaglandins plays a key role in the development of fever. However, whether fever is triggered by local injection of lipopolysaccharide (LPS) and the involvement of locally produced prostaglandins in periodontal tissue has never been assessed. Thus, we tested the hypothesis that the trigeminal nerve is a neuronal pathway that signals the brain during acute periodontitis, and this response involves prostaglandin induction. Rats were given a gingival intra-pouch injection of sterile saline or Escherichia coli lipopolysaccharide, at doses of 10 and 100 microg/kg. Some animals were pre-treated with the local anesthetic mepivacaine or had the peripheral branches of the trigeminal nerves transected. Another group of animals were pre-treated (locally or systemically) with the nonselective inhibitor of cyclooxygenases diclofenac. Body core temperature (T (b)) was measured by means of biotelemetry before and after injections. LPS elicited a dose-dependent increase in T (b), which was abolished by mepivacaine, bilateral transection of the peripheral branches of the trigeminal nerve, or local treatment with diclofenac. The results indicate that there is an activation of periodontal nerves to induce fever by LPS. It also shows that local formation of prostaglandins plays a role in fever development. Moreover, immunohistochemistry detected c-fos expression in the subnucleus caudalis of spinal trigeminal nucleus and in the preoptic area of the hypothalamus 2 and 3 h after LPS injection, further confirming the role of trigeminal nerve signaling brain in acute periodontitis.

Cyclooxygenase 2 induced by Kaposi's sarcoma-associated herpesvirus early during in vitro infection of target cells plays a role in the maintenance of latent viral gene expression

Infection of human dermal microvascular endothelial (HMVEC-d) cells and human foreskin fibroblast (HFF) cells in vitro by Kaposi's sarcoma-associated herpesvirus (KSHV) provides an excellent in vitro model system to study viral latency. KSHV infection is characterized by the induction of preexisting host signal cascades; sustained expression of the latency-associated open reading frame 73 (ORF73) (LANA-1), ORF72, and K13 genes; transient expression of a limited number of lytic genes, including the lytic cycle switch ORF50 (replication and transcription activator) gene; and reprogramming of host transcriptional machinery regulating a variety of cellular processes, including several proinflammatory responses. The cyclooxygenase 2 (COX-2) gene was one of the host cell genes that was highly up-regulated at 2 and 4 h postinfection (p.i.) of HMVEC-d and HFF cells (P. P. Naranatt, H. H. Krishnan, S. R. Svojanovsky, C. Bloomer, S. Mathur, and B. Chandran, Cancer Res. 64:72-84, 2004). Since COX-2 is an important mediator of inflammatory and angiogenic responses, here, using real-time PCR, Western blot, and immunofluorescence assays, we characterized the COX-2 stimulation and its role in KSHV infection. KSHV induced a robust COX-2 expression, which reached a maximum at 2 h p.i. in HMVEC-d cells and at 8 h p.i. in HFF cells, and significantly higher levels were continuously detected for up to 72 h p.i. Constitutive COX-1 protein levels were not modulated by KSHV infection. Moderate levels of COX-2 were also induced by UV-irradiated KSHV and by envelope glycoproteins gB and gpK8.1A; however, viral gene expression appears to be essential for the increased COX-2 induction. High levels of prostaglandin E(2) (PGE(2)), a COX-2 product, were released in the culture supernatant medium of infected cells. PGE(2) synthase, catalyzing the biosynthesis of PGE(2), also increased upon infection and inhibition of COX-2 by NS-398, and indomethacin drastically reduced the levels of PGE(2) and PGE(2) synthase. COX-2 inhibition did not affect KSHV binding, internalization of virus, or the trafficking to the infected cell nuclei. However, latent ORF73 gene expression and ORF73 promoter activity were significantly reduced by COX-2 inhibitors, and this inhibition was relieved by exogenous supplementation with PGE(2). In contrast, lytic ORF50 gene expression and ORF50 promoter activity were unaffected. These studies demonstrate that COX-2 and PGE(2) play roles in facilitating latent viral gene expression and the establishment and maintenance of latency and suggest that KSHV has evolved to utilize the inflammatory responses induced during infection of endothelial cells for the maintenance of viral latent gene expression.

Molecular Aspects of Fever and Hyperthermia

A rise in core temperature during fever usually results from change in the thermocontroller characteristics, resulting in an elevation of the set point of body temperature. Time course and extent of natural fevers are variable, but an upper limit (41 degrees C in humans), at which core temperature is maintained for some time and reduced when the set point of body temperature returns to its normal level, rarely is exceeded. Although any rise in body temperature may result from fever, those rises that are not accompanied by supportive changes in thermoeffector activities are termed hyperthermia.

Endotoxic fever: New concepts of its regulation suggest new approaches to its management

Endotoxic fever is regulated by endogenous factors that provide pro- and anti-pyretic signals at different points along the febrigenic pathway, from the periphery to the brain. Current evidence indicates that the febrile response to invading Gram-negative bacteria and their products is initiated upon their arrival in the liver via the circulation and their uptake by Kupffer cells (Kc). These pathogens activate the complement cascade on contact, hence generating complement component 5a. It, in turn, very rapidly stimulates Kc to release prostaglandin (PG)E2. Pyrogenic cytokines (TNF-alpha, etc.) are produced later and are no longer considered to be the immediate triggers of fever. The Kc-generated PGE2 either (1) may be transported by the bloodstream to the ventromedial preoptic-anterior hypothalamus (POA, the locus of the temperature-regulating center), presumptively diffusing into it and acting on thermoregulatory neurons; PGE2 is thus taken to be the final, central fever mediator. Or (2) it may activate hepatic vagal afferents projecting to the medulla oblongata, thence to the POA via the ventral noradrenergic bundle. Norepinephrine consequently secreted stimulates alpha1-adrenoceptors on thermoregulatory neurons, rapidly evoking an initial rise in core temperature (Tc) not associated with any change in POA PGE2; this neural, PGE2-independent signaling pathway is quicker than the blood-borne route. Elevated POA PGE2 and a secondary Tc rise occur later, consequent to alpha2 stimulation. Endogenous counter-regulatory factors are also elaborated peripherally and centrally at different points during the course of the febrile response; they are, therefore, anti-pyretic. These multiple interacting pathways are the subject of this review.

Physiology of temperature regulation: comparative aspects

Few environmental factors have a larger influence on animal energetics than temperature, a fact that makes thermoregulation a very important process for survival. In general, endothermic species, i.e., mammals and birds, maintain a constant body temperature (Tb) in fluctuating environmental temperatures using autonomic and behavioural mechanisms. Most of the knowledge on thermoregulatory physiology has emerged from studies using mammalian species, particularly rats. However, studies with all vertebrate groups are essential for a more complete understanding of the mechanisms involved in the regulation of Tb. Ectothermic vertebrates-fish, amphibians and reptiles-thermoregulate essentially by behavioural mechanisms. With few exceptions, both endotherms and ectotherms develop fever (a regulated increase in Tb) in response to exogenous pyrogens, and regulated hypothermia (anapyrexia) in response to hypoxia. This review focuses on the mechanisms, particularly neuromediators and regions in the central nervous system, involved in thermoregulation in vertebrates, in conditions of euthermia, fever and anapyrexia.

Expression of prostaglandin E2 synthases in mouse postnatal cortical neurons

Eicosanoids and the enzymes associated with their metabolism play an active role in the neuroinflammatory process that is often a hallmark of neurodegenerative disorders. Cerebral cortical neurons constitute a highly affected cell population in neurologic disorders. To obtain a cellular model to analyze prostaglandin action and metabolism in cortical neurons, we developed postnatal neuronal cultures from mouse cortex in a serum-free medium. Cultured cortical cells were highly enriched in neurons containing only 5 +/- 2% glial cells. The cultures were assayed for expression of several protein markers of neuronal maturity: synaptic markers (synapsin I and synaptophysin) and glutamate receptor subunits (NMDA receptor 1 and glutamate receptor 1). The protein expression of eicosanoid-metabolizing enzymes, including cyclooxygenase-2 and microsomal and cytosolic PGE2 synthases, was investigated as well. Postnatal neurons successfully survived for a long term (up to 40 days) in vitro in serum-free media, as characterized by the expression of synapsin I, synaptophysin, and microtubule-associated protein 2. Glutamate receptor subunit expression increased over time in cultures, with the highest levels at 15 days. Enzymes involved in the eicosanoid metabolism followed a distinct pattern of expression, suggesting potential regulation of PGE2 synthesis with time in cultures under basal conditions. Use of postnatal brain cultures offers several advantages, especially regarding degree of neuronal maturation, use of postnatal pups instead of pregnant mice, and potentially increased clinical relevance in models of neuroinflammation processes and prostanoid cellular neurobiology.

Pharmacological separation between peripheral and central functions of cyclooxygenase-2 with CIAA, a novel cyclooxygenase-2 inhibitor

There are many reports concerning the physiological and pathological involvement of cyclooxygenase (COX)-2 in the central nervous system and peripheral tissue cells. Selective COX-2 inhibitors that mainly distribute peripherally have not been reported thus far. Therefore central and peripheral roles of COX-2 remain classified pharmacologically. In this study, in vivo pharmacological profiles of CIAA ([6-chloro-2-(4-chlorobenzoyl)-1H-indol-3-yl]acetic acid), a novel selective COX-2 inhibitor which distributes at higher concentrations in plasma than in brain, were compared with those of well-known selective COX-2 inhibitors, celecoxib and rofecoxib. Additionally, the possibility of pharmacological separation between peripheral and central actions of COX-2 with the inhibitors was investigated. CIAA selectively inhibited COX-2 activity compared with COX-1 in in vitro assays with rat whole blood. The compound exhibited lower brain penetration and higher plasma concentration (the brain/plasma concentration ratio was approximately 0.02) than celecoxib and rofecoxib after oral administration. Therefore, CIAA is mainly expected to act peripherally. Edema and prostaglandin E2 (PGE2) production in Carrageenan-injected rat paws, and pyrexia and PGE2 production in the brain in lipopolysaccharide (LPS)-injected rats were measured in in vivo experiments. CIAA exhibited lower ratios of anti-pyretic/anti-edematous activities and of inhibitory activities of PGE2 production in brain/paw than those of celecoxib and rofecoxib, and these ratios well-reflected brain/plasma concentration ratios. In conclusion, we discovered a novel selective COX-2 inhibitor, CIAA, which distributes at higher concentrations in plasma than in brain, which would make possible the pharmacological separation of the peripheral and central functions of COX-2.

Characteristics of acid extrusion from Chinese hamster ovary cells expressing different prostaglandin EP receptors

Acid extrusion responses to prostaglandin E2 were investigated in Chinese hamster ovary (CHO) cells heterologously expressing human EP1, EP2, and EP3I receptors (hEP1, hEP2 and hEP3I) by using a microphysiometer that detected small pH changes in the extracellular microenvironment. In the cells expressing hEP1, which is known to increase intracellular Ca2+, prostaglandin E2 (1 and 10 nM) slowly accelerated acid extrusion, but at higher concentrations an initial transient phase (approximately 5 times greater than the basal acidification) overlapped the slowly developing phase. In contrast, the cells expressing hEP2, which evokes cAMP production, showed dual responses to prostaglandin E2: an initial reduction followed by an acceleration of acid extrusion. In the cells expressing hEP3I, which is known to produce both a decrease in cAMP and a modest increase in intracellular Ca2+, acid extrusion was gradually accelerated by prostaglandin E2 and reached a plateau at around 2 min. Elimination of extracellular Ca2+ diminished the responses to prostaglandin E2 in hEP1 cells, but had little effect on the responses in hEP2 and hEP3I cells. Forskolin mimicked the dual effects of prostaglandin E2 observed in the hEP2 cells. Pretreatment with pertussis toxin inhibited the response to prostaglandin E2 in hEP3I cells, but the responses in hEP1 and hEP2 cells were not affected. Na+/H+ exchanger (NHE) inhibitors (EIPA and HOE642) suppressed all the responses induced by prostaglandin E2 in hEP1, hEP2, and hEP3I cells. These results suggest that EP receptor subtypes regulate acid extrusion mainly via NHE-1 through distinct signal transduction pathways in CHO cells.

The differential role of prostaglandin E2 receptors EP3 and EP4 in regulation of fever

The innate immune system of mammals is able to detect bacteria when they infect local tissue or enter the blood stream, and initiate an immediate immune response. Prostaglandin (PG) E2 is considered as the most important link between the peripheral immune system and the brain. Due to four PGE2 receptors (EP receptors) and their differential expression in various areas of the hypothalamus and brain stem, PGE2 mediates different components of the acute phase reaction. A fever model is discussed in which the preoptic area contains the mechanisms for both hyperthermic and hypothermic responses and EP receptors in the median preoptic area (MnPO) modulate the thermogenic system. The neuron-specific modulation of EP receptors in the MnPO can be critically tested by using Cre-recombinase-mediated DNA recombination in genetically engineered mice. A concept for mice with conditional expression of EP3R and EP4R to investigate the different roles of those receptors in lipopolysaccharide (LPS)-induced fever is presented.

Effects of LPS stimulation on the expression of prostaglandin carriers in the cells of the blood-brain and blood-cerebrospinal fluid barriers

Prostaglandins produced in cerebral endothelial cells (CECs) are the final signal transduction mediators from the periphery to the brain during fever response. However, prostaglandins are organic anions at physiological pH, and they enter cells poorly using simple diffusion. Several transporters have been described that specifically transport prostaglandins across cell membranes. We examined the expression of the two principal prostaglandin carriers, prostaglandin transporter (PGT), and multidrug resistance-associated protein 4 (MRP4) in cells of the blood-brain barrier and in choroid epithelial cells in vitro as well as in vivo in rat brain in control conditions and after lipopolysaccharide (LPS) challenge. We detected PGT in primary cultures of rat CECs, astrocytes, pericytes, and choroid epithelial cells. LPS stimulation had no effect on the expression level of PGT in these cells; however, after LPS stimulation the polarized, dominantly luminal, expression pattern of PGT significantly changed. MRP4 is also expressed in CECs, and its level was not influenced by LPS treatment. In rat brain, PGT was highly expressed in the supraoptic and paraventricular nuclei of the hypothalamus, in the ependymal cell layer of the third ventricle, and in the choroid plexus. LPS treatment increased the expression of PGT in the supraoptic and paraventricular nuclei. Our results suggest that PGT and MRP4 likely play a role in transporting prostaglandins through the blood-brain and blood-cerebrospinal fluid barriers and may be involved in the maintenance of prostaglandin homeostasis in the brain and in the initiation of fever response.

Cyclooxygenase-2 expression and effect of celecoxib in flurothyl-induced neonatal seizure

Endogenous PGE(2) dynamically regulates membrane excitability, synaptic transmission and plasticity. Neonatal seizures are associated with a number of activity-dependent changes in brain development including altered synaptogenesis and synaptic plasticity as well as reduction in neurogenesis. Thus, it is reasonable to hypothesize that alteration of cyclooxygenase-2 (COX-2) expression induced by neonatal seizure may influence brain development. We evaluated the expression of COX-2 and microsomal prostaglandin E synthase (mPGES) by Western blot analysis and immnohistochemistry in flurothyl-induced neonatal seizure and also studied the effect of celecoxib on seizure induction. Seven to 10 days old Sprague-Dawley rats were used for control (n = 18) and experimental group (n = 30). Recurrent seizure group showed more increased level of COX-2 expression than control group. However, the level of mPGES-2 expression was similar in both groups, and mPGES-1 was not detected. Hippocampus of control rats showed endogenous COX-2 expression, which was localized mainly in CA3 region. This localization pattern was similar in recurrent seizure rats, but intensity of COX-2 expression was more increased than in control rats. Celecoxib treatment significantly delayed the seizure attack and also reduced COX-2 expression. In conclusion, this study suggests that COX-2 expression is related to epileptogenesis in flurothyl-induced neonatal seizure model and shows the possibility that its inhibition lessens functional impairments that occurred in neonatal seizure.

Ceramide mediates the rapid phase of febrile response to IL-1beta

IL-1beta was identified after a long search for the endogenous pyrogen. It acts by inducing synthesis of prostaglandin E2, which mediates the late phase of IL-1beta-induced fever. Here we show by radiotelemetry that the early phase of the fever response to IL-1beta is mediated by ceramide. Hypothalamic application of the cell-penetrating C2-ceramide mimics the rapid phase of the IL-1beta-induced fever. Inhibition of ceramide synthesis blocks the rapid phase of fever but does not affect the slower prostaglandin E2-dependent phase, which is blocked by indomethacin or by null mutation of the EP3 prostanoid receptor. Electrophysiological experiments on preoptic area/anterior hypothalamic neurons show that C2-ceramide, but not dihydroceramide, mimics the rapid hyperpolarizing effects of IL-1beta on the activity of warm-sensitive hypothalamic neurons. IL-1beta-mediated hyperpolarization is blocked by PP2, the selective inhibitor of the protein tyrosine kinase Src, which is known to be activated by ceramide. These in vivo and in vitro data suggest that ceramide fulfills the criteria for an endogenous pyrogen.

Roles of cyclooxygenase-2 and prostacyclin/IP receptors in mucosal defense against ischemia/reperfusion injury in mouse stomach

We examined the roles of cyclooxygenase (COX) isozymes, prostaglandins (PGs), and their receptors in the mucosal defense against ischemia/reperfusion (I/R)-induced gastric lesions in mice. Male C57BL/6 mice, including wild-type animals and those lacking prostaglandin E(2) (EP)1, EP3, or prostaglandin I(2) (IP) receptors, were used after 18 h of fasting. Under urethane anesthesia, the celiac artery was clamped (ischemia) for 30 min, and then reperfusion was achieved for 60 min through the removal of the clamp, and the stomach was examined for lesions. I/R produced hemorrhagic gastric lesions in wild-type mice. The severity of lesions was significantly increased by pretreatment with indomethacin (a nonselective COX inhibitor) and rofecoxib (a selective COX-2 inhibitor) but not 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole (SC-560; a selective COX-1 inhibitor). The expression of COX-2 mRNA was up-regulated in the stomach following I/R but not by sham operation or ischemia alone. The ulcerogenic response was markedly aggravated in IP receptor knockout mice but not those lacking EP1 or EP3 receptors. I/R increased the levels of 6-keto-PGF(1alpha) and PGE(2) in the stomach of wild-type mice, and this response was attenuated by indomethacin and rofecoxib but not SC-560. Pretreatment of wild-type mice with iloprost, a prostacyclin (PGI(2)) analog, significantly prevented the I/R-induced gastric lesions in the absence and presence of indomethacin or rofecoxib. PGE(2) also reduced the severity of I/R-induced gastric lesions, yet the effect was much less pronounced than that of iloprost. These results suggest that endogenous PGs derived from COX-2 play a crucial role in gastric mucosal defense during I/R, and this action is mainly mediated by PGI(2) through the activation of IP receptors.

Prostacyclin-IP signaling and prostaglandin E2-EP2/EP4 signaling both mediate joint inflammation in mouse collagen-induced arthritis

Prostaglandin (PG)I₂ (prostacyclin [PGI]) and PGE₂ are abundantly present in the synovial fluid of rheumatoid arthritis (RA) patients. Although the role of PGE₂ in RA has been well studied, how much PGI₂ contributes to RA is little known. To examine this issue, we backcrossed mice lacking the PGI receptor (IP) to the DBA/1J strain and subjected them to collagen-induced arthritis (CIA). IP-deficient (IP^−/−) mice exhibited significant reduction in arthritic scores compared with wild-type (WT) mice, despite anti-collagen antibody production and complement activation similar to WT mice. IP^−/− mice also showed significant reduction in contents of proinflammatory cytokines, such as interleukin (IL)-6 in arthritic paws. Consistently, the addition of an IP agonist to cultured synovial fibroblasts significantly enhanced IL-6 production and induced expression of other arthritis-related genes. On the other hand, loss or inhibition of each PGE receptor subtype alone did not affect elicitation of inflammation in CIA. However, a partial but significant suppression of CIA was achieved by the combined inhibition of EP2 and EP4. Our results show significant roles of both PGI₂-IP and PGE₂-EP2/EP4 signaling in the development of CIA, and suggest that inhibition of PGE₂ synthesis alone may not be sufficient for suppression of RA symptoms.

Interleukin-1 beta-induced expression of the prostaglandin E-receptor subtype EP3 in U373 astrocytoma cells depends on protein kinase C and nuclear factor-kappaB

Both interleukin-1beta (IL-1beta) and prostaglandins (PGs) are important mediators of physiological and pathophysiological processes in the brain. PGE2 exerts its effects by binding to four different types of PGE2 receptors named EP1-EP4. EP3 has found to be expressed in neurons, whereas expression of EP3 in glial cells has not been reported in the brain yet. Here we describe IL-1beta-induced EP3 receptor expression in human astrocytoma cells, primary astrocytes of rat and human origin and in rat brain. Using western blot, we found a marked up-regulation of EP3 receptor synthesis in human and rat primary glial cells. Intracerebroventricular administration of IL-1beta stimulated EP3 receptor synthesis in rat hippocampus. The analysis of involved signal transduction pathways by pathway-specific inhibitors revealed an essential role of protein kinase C and nuclear factor-kappaB in astrocytic IL-1beta-induced EP3 synthesis. Our data suggest that PGE2 signaling in the brain may be altered after IL-1beta release due to up-regulation of EP3 receptors. This might play an important role in acute and chronic conditions such as cerebral ischemia, traumatic brain injury, HIV-encephalitis, Alzheimer's disease and prion diseases in which a marked up-regulation of IL-1beta is followed by a prolonged increase of PGE2 levels in the brain.

Cyclooxygenase inhibition in early onset of tumor growth and related angiogenesis evaluated in EP1 and EP3 knockout tumor-bearing mice

It is well established that prostanoids are essential for local inflammation including cell proliferation and apoptosis. Accordingly, prostaglandin E2 (PGE(2)) is a critical factor in wound healing, tumor invasiveness and progression. Therefore, the aim of the present work was to evaluate effects by PGE(2) on tumor vascular density at early onset of tumor growth where hypoxia is limited. Wild-type mice (C57Bl, C3H/HeN) bearing either MCG-101 tumors or a malignant melanoma (K1735-M2) with either high or insignificant PGE(2) production and subsequently different in sensitivity to cyclooxygenase (COX) inhibition were used. Tumor angiogenesis was estimated by intravital microscopy and immune histochemical analysis in wild type and EP(1) or EP(3) subtype receptor knockout mice (C57Bl). Both MCG-101 and K1735-M2 tumor cells stimulated early outgrowth of tumor vessels in proportion to intrinsic growth rate of tumor cells. Indomethacin had no effects on tumor growth or tumor related vascular area in K1735-M2 bearing mice. By contrast, indomethacin decreased tumor cell proliferation and increased apoptosis in MCG-101 tumors with subsequent adaptation in tumor vascular density. Effects of indomethacin on early growth of MCG-101 tumors were not related to tumor content of bFGF protein, while our earlier studies on long-term tumor growth have shown decreased mRNA levels of bFGF during indomethacin treatment. Early onset of tumor growth was significantly promoted in EP(3)- but not in EP(1)-knockouts, although long-term tumor growth is attenuated in EP(1)-knockouts as reported elsewhere. Our results demonstrate that tumor production of PGE(2) promotes primarily net growth of tumor cells with subsequent adaptations in development of the tumor vasculature. Therefore, it is likely that angiogenesis is not a limiting step at the early onset of tumor growth.

A Ser/Thr cluster within the C-terminal domain of the rat prostaglandin receptor EP3alpha is essential for agonist-induced phosphorylation, desensitization and internalization

Two isoforms of the rat prostaglandin E(2) receptor, rEP3alpha-R and rEP3beta-R, differ only in their C-terminal domain. To analyze the function of the rEP3-R C-terminal domain in agonist induced desensitization, a cluster of Ser/Thr residues in the C-terminal domain of the rEP3alpha-R was mutated to Ala and both isoforms and the receptor mutant (rEP3alpha-ST341-349A-R) were stably expressed in HEK293 cells. All rEP3-R receptors showed a similar ligand-binding profile. They were functionally coupled to Gi and reduced forskolin-induced cAMP-formation. Repeated exposure of cells expressing the rEP3alpha-R isoform to PGE(2) reduced the agonist induced inhibition of forskolin-stimulated cAMP-formation by 50% and led to internalization of the receptor to intracellular endocytotic vesicles. By contrast, Gi-response as well as plasma membrane localization of the rEP3beta-R and the rEP3alpha-ST341-349A-R were not affected by prior agonist-stimulation. Agonist-stimulation of HEK293-rEP3alpha-R cells induced a time- and dose-dependent phosphorylation of the receptor most likely by G protein-coupled receptor kinases and not by protein kinase A or protein kinase C. By contrast, upon agonist-stimulation the rEP3beta-R was not phosphorylated and the rEP3alpha-ST341-349A-R was phosphorylated only weakly. These results led to the hypothesis that agonist-induced desensitization of the rEP3alpha-R isoform is mediated most likely by a GRK-dependent phosphorylation of Ser/Thr residues 341-349. Phosphorylation then initiates uncoupling of the receptor from Gi protein and receptor internalization.

A subsidiary fever center in the medullary raphé?

In fever, as in normal thermoregulation, signals from the preoptic area drive both cutaneous vasoconstriction and thermogenesis by brown adipose tissue (BAT). Both of these responses are mediated by sympathetic nerves whose premotor neurons are located in the medullary raphé. EP3 receptors, key prostaglandin E2(PGE2) receptors responsible for fever induction, are expressed in this same medullary raphé region. To investigate whether PGE2in the medullary raphé might contribute to the febrile response, we tested whether direct injections of PGE2into the medullary raphé could drive sympathetic nerve activity (SNA) to BAT and cutaneous (tail) vessels in anesthetized rats. Microinjections of glutamate (50 mM, 60–180 nl) into the medullary raphé activated both tail and BAT SNA, as did cooling the trunk skin. PGE2injections (150–500 ng in 300–1,000 nl) into the medullary raphé had no effect on tail SNA, BAT SNA, body temperature, or heart rate. By contrast, 150 ng PGE2injected into the preoptic area caused large increases in both tail and BAT SNA (+60 ± 17 spikes/15 s and 1,591 ± 150% of control, respectively), increased body temperature (+1.8 ± 0.2°C), blood pressure (+17 ± 2 mmHg), and heart rate (+124 ± 19 beats/min). These results suggest that despite expression of EP3 receptors, neurons in the medullary raphé are unable to drive febrile responses of tail and BAT SNA independently of the preoptic area. Rather, they appear merely to transmit signals for heat production and heat conservation originating from the preoptic area.

In vivo reopening of the neonatal ductus arteriosus by a prostanoid EP4-receptor agonist in the rat

Prostaglandin E1 is used to reopen the constricted ductus arteriosus in neonates with ductus-dependent circulation. To clarify possible prostanoid receptor agonists that can reopen the neonatal ductus with fewer side effects, we studied in vivo reopening of the neonatal ductus arteriosus by AE1-329, a prostanoid EP4-receptor agonist, in the rat. Neonatal rats were incubated at 33 degrees C. The inner diameter of the ductus was measured with a microscope and a micrometer following rapid whole-body freezing. Intraesophageal pressure was measured with a Millar micro-tip transducer. The ductus arteriosus constricted quickly after birth, and the inner diameter was 0.80 and 0.08 mm at 0 and 60 min after birth. PGE1 and AE1-329, injected subcutaneously at 60 min after birth, dilated the ductus dose-dependently. Thirty minutes after injection of 10 ng/g of PGE1 and AE1-329, the ductus diameter was 0.52 and 0.65 mm, respectively. The ductus-dilating effect of PGE1 was maximal at 15-30 min, and disappeared at 2 h. The ductus-dilating effect of AE1-329 was prolonged, the ductus was widely open at 6 h, and closed at 12 h after injection of 10 ng/g AE1-329. AE1-259-01 (EP2 agonist) (100 ng/g) did not dilate the neonatal ductus. Respiration was depressed by PGE1, but not by AE1-329. These results indicate the major role of EP4 in the neonatal ductus and that AE1-329, an EP4 agonist, can be used to dilate the neonatal constricted ductus without the side effects shown by EP3, including apnea.

Direct pyrogenic input from prostaglandin EP3 receptor-expressing preoptic neurons to the dorsomedial hypothalamus

Fever is induced by a neuronal mechanism in the brain. Prostaglandin (PG) E2 acts as a pyrogenic mediator in the preoptic area (POA) probably through the EP3 subtype of PGE receptor expressed on GABAergic neurons, and this PGE2 action triggers neuronal pathways for sympathetic thermogenesis in peripheral effector organs including brown adipose tissue (BAT). To explore pyrogenic efferent pathways from the POA, we determined projection targets of EP3 receptor-expressing POA neurons with a special focus on rat hypothalamic regions including the dorsomedial hypothalamic nucleus (DMH), which is known as a center for autonomic responses to stress. Among injections of cholera toxin b-subunit (CTb), a retrograde tracer, into hypothalamic regions at the rostrocaudal level of the DMH, injections into the DMH, lateral hypothalamic area (LH) and dorsal hypothalamic area (DH) resulted in EP3 receptor immunolabelling in substantial populations of CTb-labeled neurons in the POA. Bilateral microinjections of muscimol, a GABA(A) receptor agonist, into the DMH and a ventral region of the DH, but not those into the LH, inhibited thermogenic (BAT sympathetic nerve activity, BAT temperature, core body temperature and expired CO2) and cardiovascular (arterial pressure and heart rate) responses to an intra-POA PGE2 microinjection. Further immunohistochemical observations revealed a close association of POA-derived GABAergic axon swellings with DMH neurons projecting to the medullary raphe regions where sympathetic premotor neurons for febrile and thermoregulatory responses are localized. These results suggest that a direct projection of EP3 receptor-expressing POA neurons to the DMH/DH region mediates febrile responses via a GABAergic mechanism.

Thermoregulatory responses to lipopolysaccharide in the mouse: dependence on the dose and ambient temperature

Most published studies of thermoregulatory responses of mice to LPS involved a stressful injection of LPS, were run at a poorly controlled and often subneutral ambient temperature (Ta), and paid little attention to the dependence of the response on the LPS dose. These pitfalls have been overcome in the present study. Male C57BL/6 mice implanted with jugular vein catheters were kept in an environmental chamber at a tightly controlled Ta. The relationship between the Tas used and the thermoneutral zone of the mice was verified by measuring tail skin temperature, either by infrared thermography or thermocouple thermometry. Escherichia coli LPS in a wide dose range (100-104μg/kg) was administered through an extension of the jugular catheter from outside the chamber. The responses observed were dose dependent. At a neutral Ta, low (just suprathreshold) doses of LPS (100-101μg/kg) caused a monophasic fever. To a slightly higher dose (101.5μg/kg), the mice responded with a biphasic fever. To even higher doses (101.75-104μg/kg), they responded with a polyphasic fever, of which three distinct phases were identified. The dose dependence and dynamics of LPS fever in the mouse appeared to be remarkably similar to those seen in the rat. However, the thermoregulatory response of mice to LPS in a subthermoneutral environment is remarkably different from that of rats. Although very high doses of LPS (104μg/kg) did cause a late (latency, ∼3 h) hypothermic response in mice, the typical early (latency, 10–30 min) hypothermic response seen in rats did not occur. The present investigation identifies experimental conditions to study LPS-induced mono-, bi-, and polyphasic fevers and late hypothermia in mice and provides detailed characteristics of these responses.

Prostaglandin E receptor EP1 controls impulsive behavior under stress

Animals under stress take adaptive actions that may lead to various types of behavioral disinhibition. Such behavioral disinhibition, when expressed excessively and impulsively, can result in harm in individuals and cause a problem in our society. We now show that, under social or environmental stress, mice deficient in prostaglandin E receptor subtype EP1 (Ptger1(-/-)) manifest behavioral disinhibition, including impulsive aggression with defective social interaction, impaired cliff avoidance, and an exaggerated acoustic startle response. This phenotype was reproduced in wild-type mice by administration of an EP1-selective antagonist, whereas administration of an EP1-selective agonist suppressed electric-shock-induced impulsive aggression. Dopamine turnover in the frontal cortex and striatum was increased in Ptger1(-/-) mice, and administration of dopaminergic antagonists corrected their behavioral phenotype. These results suggest that prostaglandin E(2) acts through EP1 to control impulsive behavior under stress, a finding potentially exploitable for development of drugs that attenuate impulsive behavior in humans.

Augmentation of bone morphogenetic protein-induced bone mass by local delivery of a prostaglandin E EP4 receptor agonist

Recombinant human bone morphogenetic protein (rhBMP) is viewed as a therapeutic cytokine because of its ability to induce bone. However, the high doses of rhBMP required for bone induction in humans remain a major hurdle for the therapeutic application of this protein. The development of a methodology that would effectively overcome the weak responsiveness to human BMP is highly desired. In the present study, we investigate the ability of a prostaglandin E EP4 receptor selective agonist (EP4A) to augment the bone-inducing ability of BMP in a biodegradable delivery system. A block copolymer composed of poly-D,L-lactic acid with random insertion of p-dioxanone and polyethylene glycol (PLA-DX-PEG, polymer) was used as the delivery system. Polymer discs containing rhBMP-2 and EP4A were implanted into the left dorsal muscle pouch of mice to examine the dose-dependent effects of EP4A. Fifty mice were divided into 5 groups based on the contents of rhBMP and EP4 in the polymer (group 1; BMP 5 microg EP4A 0 microg, group 2; BMP 5 microg EP4 3 microg, group 3; BMP 5 microg EP4 30 microg, group 4; BMP 5 microg EP4 300 microg, group 5; BMP 0 microg EP4 30 microg, n=10 each). All implants were harvested, examined radiologically, and processed for histological analysis 3 weeks after surgery. On dual-energy X-ray absorptiometry (DXA) analysis, the bone mineral content (BMC) of the ossicles was 6.52+/-0.80 (mg), 9.36+/-1.89, 14.21+/-1.27, and 18.75+/-2.31 in groups 1, 2, 3, and 4 respectively. In terms of BMC, the values of groups 3 and 4 were significantly higher than those of group 1. The mean BMC value of group 4 was approximately 3 times higher than that of group 1. No significant difference in body weight was noted among the groups during the experimental period. In summary, the presence of a prostaglandin E EP4 receptor selective agonist in the carrier polymer enhanced the bone-inducing capacity of rhBMP-2 with no apparent systemic adverse effects.

Mechanisms underlying capsaicin-stimulated secretion in the stomach: comparison with mucosal acidification

The effects of capsaicin and mucosal acidification on gastric HCO3(-) secretion were compared in wild-type and prostacyclin (PGI2) IP receptor or prostaglandin E receptor EP1 or EP3 knockout C57BL/6 mice as well as rats. Under urethane anesthesia, the stomach was mounted on an ex vivo chamber, perfused with saline, and the secretion of HCO3(-) was measured at pH 7.0 using the pH-stat method. Capsaicin or 200 mM HCl was applied to the chamber for 10 min. Capsaicin increased the secretion of HCO3(-) in rats and wild-type mice, the response at 0.3 mg/ml being equivalent to that induced by acidification. This effect of capsaicin in rats was abolished by ablation of capsaicin-sensitive afferent neurons and attenuated by indomethacin, N(G)-nitro-L-arginine methylester (L-NAME), and capsazepine [transient receptor potential vanilloid type 1 (TRPV1) antagonist] but not FR172357 [3-bromo-8-[2,6-dichloro-3-[N[(E)-4-(N,N-dimethylcarbamoyl) cinnamidoacetyl]-N-methylamino]benzyloxy]-2-metylimidazo[1,2-a]pyridine; bradykinin B2 antagonist] or the EP1 antagonist. The acid-induced HCO3(-) secretion was attenuated by indomethacin, L-NAME, the EP1 antagonist, and sensory deafferentation, but not affected by capsazepine or FR172357. Prostaglandin E2 (PGE2), NOR-3 [(+/-)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamine] (NO donor), and bradykinin stimulated the secretion of HCO3(-), and the effect of bradykinin was blocked by indomethacin and L-NAME as well as FR172357. The stimulatory effect of capsaicin disappeared in IP (-/-) mice, whereas that of acidification disappeared in EP1 (-/-) mice. Intragastric application of capsaicin increased mucosal PGI2 but not PGE2 levels in the rat stomach. These results suggested that both capsaicin and acid increase gastric HCO3(-) secretion via a common pathway, involving PG and NO as well as capsaicin-sensitive afferent neurons, yet their responses differ concerning TRPV1 or prostanoid receptor dependence.

An automated multistep high-throughput screening assay for the identification of lead inhibitors of the inducible enzyme mPGES-1

Prostaglandin E2 synthase (mPGES-1), the enzyme which catalyzes the synthesis of PGE2, is induced during the inflammatory response. For this reason, mPGES-1 could be a potential therapeutic target. A high-throughput screening assay was developed to identify potential inhibitors of mPGES-1. The assay consisted of a 30-s mPGES-1 enzymatic reaction followed by the detection of PGE2 by enzyme immunoassay (EIA). The enzymatic reaction was performed in a batch mode because the instability of the substrate (10 min) limited the number of plates assayed within a working day. The detection of the product by EIA was performed on 3 instruments requiring 14 different steps for complete automation. The authors describe here the optimization and implementation of a 2-part assay on a Thermo CRS robotic system. More than 315,000 compounds were tested, and a hit rate of 0.84% was obtained for this assay. Although the entire assay required multiple steps, the assay was successfully miniaturized and automated for a high-throughput screening campaign.

Dominant role of prostaglandin E2 EP4 receptor in furosemide-induced salt-losing tubulopathy: a model for hyperprostaglandin E syndrome/antenatal Bartter syndrome

Increased formation of prostaglandin E2 (PGE2) is a key part of hyperprostaglandin E syndrome/antenatal Bartter syndrome (HPS/aBS), a renal disease characterized by NaCl wasting, water loss, and hyperreninism. Inhibition of PGE2 formation by cyclo-oxygenase inhibitors significantly lowers patient mortality and morbidity. However, the pathogenic role of PGE2 in HPS/aBS awaits clarification. Chronic blockade of the Na-K-2Cl co-transporter NKCC2 by diuretics causes symptoms similar to HPS/aBS and provides a useful animal model. In wild-type (WT) mice and in mice lacking distinct PGE2 receptors (EP1-/-, EP2-/-, EP3-/-, and EP4-/-), the effect of chronic furosemide administration (7 d) on urine output, sodium and potassium excretion, and renin secretion was determined. Furthermore, furosemide-induced diuresis and renin activity were analyzed in mice with defective PGI2 receptors (IP-/-). In all animals studied, furosemide stimulated a rise in diuresis and electrolyte excretion. However, this effect was blunted in EP1-/-, EP3-/-, and EP4-/- mice. Compared with WT mice, no difference was observed in EP2-/- and IP-/- mice. The furosemide-induced increase in plasma renin concentration was significantly decreased in EP4-/- mice and to a lesser degree also in IP-/- mice. Pharmacologic inhibition of EP4 receptors in furosemide-treated WT mice with the specific antagonist ONO-AE3-208 mimicked the changes in renin mRNA expression, plasma renin concentration, diuresis, and sodium excretion seen in EP4-/- mice. The GFR in EP4-/- mice was not changed compared with that in WT mice, which indicated that blunted diuresis and salt loss seen in EP4-/- mice were not a consequence of lower GFR. In summary, these findings demonstrate that the EP4 receptor mediates PGE2-induced renin secretion and that EP1, EP3, and EP4 receptors all contribute to enhanced PGE2-mediated salt and water excretion in the HPS/aBS model.

Prostaglandin E receptor EP3 deficiency modifies tumor outcome in mouse two-stage skin carcinogenesis

We have recently shown that the prostaglandin E(2) (PGE(2)) receptor EP(3) plays an important role in suppression of colon cancer cell proliferation and that its deficiency enhances late stage colon carcinogenesis. Here we examined the effects of EP(3)-deficiency on two-stage skin carcinogenesis. 7,12-Dimethylbenz[a]anthracene (50 microg/200 microl of acetone) was thus applied to the back skin of female EP(3)-knockout and wild-type mice at 8 weeks of age, followed by treatment with 12-O-tetradecanoylphorbol-13-acetate (5 microg/200 microl of acetone) twice a week for 25 weeks. First tumor appearance was observed in EP(3)-knockout mice at week 10, which was 3 weeks later than in EP(3) wild-type mice, and multiplicity observed at week 11 was significantly lower in the EP(3)-knockout case. However, histological examination showed that the tumor incidence and multiplicity at week 25 were not significantly changed in knockout mice and wild-type mice (incidence, 19/19 versus 23/24; multiplicity, 3.58 +/- 0.51 versus 3.17 +/- 0.63, respectively). Interestingly, there were no squamous cell carcinomas (SCCs) in the EP(3)-knockout mice, while SCCs were observed in 3 out of 24 wild-type mice. Furthermore, benign keratoacanthomas only developed in EP(3)-knockout mice (6/19 versus 0/24, P < 0.01). The results suggest that PGE(2) receptor EP(3) signaling might contribute to development of SCCs in the skin.

Activation of lipid metabolism contributes to interleukin-8 production during Chlamydia trachomatis infection of cervical epithelial cells

Chlamydia trachomatis infection is the most common cause of bacterial sexually transmitted diseases. Infection of the urogenital tract by C. trachomatis causes chronic inflammation and related clinical complications. Unlike other invasive bacteria that induce a rapid cytokine/chemokine production, chlamydial infection induces delayed inflammatory response and proinflammatory chemokine production that is dependent on bacterial growth. We present data here to show that the lipid metabolism required for chlamydial growth contributes to Chlamydia-induced proinflammatory chemokine production. By gene microarray profiling, validated with biochemical studies, we found that C. trachomatis LGV2 selectively upregulated PTGS2 (COX2) and PTGER4 (EP4) in cervical epithelial HeLa 229 cells. COX2 is an enzyme that catalyzes the rate-limiting step of arachidonic acid conversion to prostaglandins, including prostaglandin E2 (PGE2) and other eicosanoids, whereas EP4 is a subtype of cell surface receptors for PGE2. We show that Chlamydia infection induced COX2 protein expression in both epithelial cells and peripheral blood mononuclear cells and promoted PGE2 release. Exogenous PGE2 was able to induce interleukin-8 release in HeLa 229 epithelial cells. Finally, we demonstrated that interleukin-8 induction by Chlamydia infection or PGE2 treatment was dependent on extracellular signal-regulated kinase/mitogen-activated protein activity. Together, these data demonstrate that the host lipid remodeling process required for chlamydial growth contributes to proinflammatory chemokine production. This study also highlights the importance of maintaining a balanced habitat for parasitic pathogens as obligate intracellular organisms.

Prostaglandin E and prostacyclin receptor expression in tumor and host tissues from MCG 101-bearing mice: a model with prostanoid-related cachexia

Preclinical and clinical studies in our laboratory have suggested that prostaglandin (PG) E2 is involved in anorexia and cachexia development, although the role of COX pathways on the pathogenesis of cancer cachexia remains to be clarified. Expressions of PGE (EP1, EP2, EP3alpha,beta,gamma and EP4) and PGI (IP) receptors in the central nervous system (brain cortex, hypothalamus and brain stem), in peripheral (liver, white adipose tissue and skeletal muscle) and tumor tissue from MCG-101-bearing mice with and without indomethacin treatment were investigated by RT-PCR and immunohistochemistry. Expression of EP1 in the liver and EP4 receptor in white adipose tissue were upregulated and responded to indomethacin treatment, while downregulated expression of EP3 in skeletal muscle from tumor-bearing mice was unresponsive to indomethacin treatment despite improved carcass weight. Expression of EP and IP receptors in brain and tumor tissue from tumor-bearing mice were neither related nor responsive to systemic PGE2 levels including increased IL-1beta, IL-6 and TNF-alpha host activities. The expression IP receptor in CNS, peripheral tissue and tumor tissue was unchanged by cachexia development. Our results suggest that transcription of EP receptors in liver, fat and skeletal muscle tissue may be a control level for host metabolic alterations during tumor progression, while overall EP and IP receptor expression in CNS did not indicate an important control level for appetite regulation in MCG 101-bearing mice despite prostanoid related anorexia.

Augmented cardiac hypertrophy in response to pressure overload in mice lacking the prostaglandin I2 receptor

BACKGROUND

In the heart, the expressions of several types of prostanoid receptors have been reported. However, their roles in cardiac hypertrophy in vivo remain unknown. We intended to clarify the roles of these receptors in pressure overload-induced cardiac hypertrophy using mice lacking each of their receptors.

METHODS AND RESULTS

We used a model of pressure overload-induced cardiac hypertrophy produced by banding of the transverse aorta in female mice. In wild-type mice subjected to the banding, cardiac hypertrophy developed during the observation period of 8 weeks. In mice lacking the prostaglandin (PG) I2 receptor (IP(-/-)), however, cardiac hypertrophy and cardiomyocyte hypertrophy were significantly greater than in wild-type mice at 2 and 4 weeks but not at 8 weeks, whereas there was no such augmentation in mice lacking the prostanoid receptors other than IP. In addition, cardiac fibrosis observed in wild-type hearts was augmented in IP(-/-) hearts, which persisted for up to 8 weeks. In IP(-/-) hearts, the expression level of mRNA for atrial natriuretic peptide, a representative marker of cardiac hypertrophy, was significantly higher than in wild-type hearts. In vitro, cicaprost, an IP agonist, reduced platelet-derived growth factor-induced proliferation of wild-type noncardiomyocytes, although it could not inhibit cardiotrophin-1-induced hypertrophy of cardiomyocytes. Accordingly, cicaprost increased cAMP concentration efficiently in noncardiomyocytes.

CONCLUSIONS

IP plays a suppressive role in the development of pressure overload-induced cardiac hypertrophy via the inhibition of both cardiomyocyte hypertrophy and cardiac fibrosis. Both effects have been suggested as originating from the action on noncardiomyocytes rather than cardiomyocytes.

Spinal inflammatory hyperalgesia is mediated by prostaglandin E receptors of the EP2 subtype

Blockade of prostaglandin (PG) production by COX inhibitors is the treatment of choice for inflammatory pain but is also prone to severe side effects. Identification of signaling elements downstream of COX inhibition, particularly of PG receptor subtypes responsible for pain sensitization (hyperalgesia), provides a strategy for better-tolerated analgesics. Here, we have identified PGE2 receptors of the EP2 receptor subtype as key signaling elements in spinal inflammatory hyperalgesia. Mice deficient in EP2 receptors (EP2-/- mice) completely lack spinal PGE2-evoked hyperalgesia. After a peripheral inflammatory stimulus, EP2-/- mice exhibit only short-lasting peripheral hyperalgesia but lack a second sustained hyperalgesic phase of spinal origin. Electrophysiological recordings identify diminished synaptic inhibition of excitatory dorsal horn neurons as the dominant source of EP2 receptor-dependent hyperalgesia. Our results thus demonstrate that inflammatory hyperalgesia can be treated by targeting of a single PG receptor subtype and provide a rational basis for new analgesic strategies going beyond COX inhibition.

Spinal inflammatory hyperalgesia is mediated by prostaglandin E receptors of the EP2 subtype

Blockade of prostaglandin (PG) production by COX inhibitors is the treatment of choice for inflammatory pain but is also prone to severe side effects. Identification of signaling elements downstream of COX inhibition, particularly of PG receptor subtypes responsible for pain sensitization (hyperalgesia), provides a strategy for better-tolerated analgesics. Here, we have identified PGE2 receptors of the EP2 receptor subtype as key signaling elements in spinal inflammatory hyperalgesia. Mice deficient in EP2 receptors (EP2-/- mice) completely lack spinal PGE2-evoked hyperalgesia. After a peripheral inflammatory stimulus, EP2-/- mice exhibit only short-lasting peripheral hyperalgesia but lack a second sustained hyperalgesic phase of spinal origin. Electrophysiological recordings identify diminished synaptic inhibition of excitatory dorsal horn neurons as the dominant source of EP2 receptor-dependent hyperalgesia. Our results thus demonstrate that inflammatory hyperalgesia can be treated by targeting of a single PG receptor subtype and provide a rational basis for new analgesic strategies going beyond COX inhibition.

Experimental study of bone formation around a titanium rod with beta-tricalcium phosphate and prostaglandin E2 receptor agonists

beta-Tricalcium phosphate (beta-TCP) is an excellent bone-filling material that is completely absorbed by the body and replaced by autologous bone. Unfortunately, its mechanical strength is low, rendering its application at loaded regions difficult. The purpose of this study is to evaluate the histological and mechanical effects of single and combined use of beta-TCP and EP4 agonist on bone formation around a titanium rod. beta-TCP was loaded into the femoral bone marrow from the distal end of the femur, where the titanium implants were inserted, and the animals received twice-daily subcutaneous injections of EP4 agonist. Group I received the rod only and was designated the control group; group II received EP4 agonist only; group III received beta-TCP only; and group IV received both beta-TCP and EP4 agonist. Examination of decalcified specimens revealed favorable bone formation in all treatment groups compared with that in group I, with the most active bone formation seen in group IV. Mechanical evaluation revealed significant differences in maximum pull-out force compared with group I at weeks 4 and 8. There were no differences between groups II and III at either week 4 or 8, but the values seen in group IV at weeks 4 and 8 were significantly higher compared with the other groups. Combined use of beta-TCP and EP4 agonist is expected to compensate for bone defects resulting from revision total joint arthroplasty and to achieve stability at an early stage.

Cytokines, PGE2 and endotoxic fever: a re-assessment

The innate immune system serves as the first line of host defense against the deleterious effects of invading infectious pathogens. Fever is the hallmark among the defense mechanisms evoked by the entry into the body of such pathogens. The conventional view of the steps that lead to fever production is that they begin with the biosynthesis of pyrogenic cytokines by mononuclear phagocytes stimulated by the pathogens, their release into the circulation and transport to the thermoregulatory center in the preoptic area (POA) of the anterior hypothalamus, and their induction there of cyclooxygenase (COX)-2-dependent prostaglandin (PG)E(2), the putative final mediator of the febrile response. But data accumulated over the past 5 years have gradually challenged this classical concept, due mostly to the temporal incompatibility of the newer findings with this concatenation of events. Thus, the former studies generally overlooked that the production of cytokines and the transduction of their pyrogenic signals into fever-mediating PGE(2) proceed at relatively slow rates, significantly slower certainly than the onset latency of fever produced by the i.v. injection of bacterial endotoxic lipopolysaccharides (LPS). Here, we review the conflicts between the earlier and the more recent findings and summarize new data that reconcile many of the contradictions. A unified model based on these data explicating the generation and maintenance of the febrile response is presented. It postulates that the steps in the production of LPS fever occur in the following sequence: the immediate activation by LPS of the complement (C) cascade, the stimulation by the anaphylatoxic C component C5a of Kupffer cells, their consequent, virtually instantaneous release of PGE(2), its excitation of hepatic vagal afferents, their transmission of the induced signals to the POA via the ventral noradrenergic bundle, and the activation by the thus, locally released norepinephrine (NE) of neural alpha(1)- and glial alpha(2)-adrenoceptors. The activation of the first causes an immediate, PGE(2)-independent rise in core temperature (T(c)) [the early phase of fever; an antioxidant-sensitive PGE(2) rise, however, accompanies this first phase], and of the second a delayed, PGE(2)-dependent T(c) rise [the late phase of fever]. Meanwhile-generated pyrogenic cytokines and their consequent upregulation of blood-brain barrier cells COX-2 also contribute to the latter rise. The consecutive steps that initiate the febrile response to LPS would now appear, therefore, to occur in an order different than conceived originally.

Mechanism of action of paracetamol

Paracetamol (acetaminophen) is generally considered to be a weak inhibitor of the synthesis of prostaglandins (PGs). However, the in vivo effects of paracetamol are similar to those of the selective cyclooxygenase-2 (COX-2) inhibitors. Paracetamol also decreases PG concentrations in vivo, but, unlike the selective COX-2 inhibitors, paracetamol does not suppress the inflammation of rheumatoid arthritis. It does, however, decrease swelling after oral surgery in humans and suppresses inflammation in rats and mice. Paracetamol is a weak inhibitor of PG synthesis of COX-1 and COX-2 in broken cell systems, but, by contrast, therapeutic concentrations of paracetamol inhibit PG synthesis in intact cells in vitro when the levels of the substrate arachidonic acid are low (less than about 5 mumol/L). When the levels of arachidonic acid are low, PGs are synthesized largely by COX-2 in cells that contain both COX-1 and COX-2. Thus, the apparent selectivity of paracetamol may be due to inhibition of COX-2-dependent pathways that are proceeding at low rates. This hypothesis is consistent with the similar pharmacological effects of paracetamol and the selective COX-2 inhibitors. COX-3, a splice variant of COX-1, has been suggested to be the site of action of paracetamol, but genomic and kinetic analysis indicates that this selective interaction is unlikely to be clinically relevant. There is considerable evidence that the analgesic effect of paracetamol is central and is due to activation of descending serotonergic pathways, but its primary site of action may still be inhibition of PG synthesis. The action of paracetamol at a molecular level is unclear but could be related to the production of reactive metabolites by the peroxidase function of COX-2, which could deplete glutathione, a cofactor of enzymes such as PGE synthase.

Thromboxane A2 and prostaglandin F2alpha mediate inflammatory tachycardia

Systemic inflammation induces various adaptive responses including tachycardia. Although inflammation-associated tachycardia has been thought to result from increased sympathetic discharge caused by inflammatory signals of the immune system, definitive proof has been lacking. Prostanoids, including prostaglandin (PG) D(2), PGE(2), PGF(2alpha), PGI(2) and thromboxane (TX) A(2), exert their actions through specific receptors: DP, EP (EP(1), EP(2), EP(3), EP(4)), FP, IP and TP, respectively. Here we have examined the roles of prostanoids in inflammatory tachycardia using mice that lack each of these receptors individually. The TXA(2) analog I-BOP and PGF(2alpha) each increased the beating rate of the isolated atrium of wild-type mice in vitro through interaction with TP and FP receptors, respectively. The cytokine-induced increase in beating rate was markedly inhibited in atria from mice lacking either TP or FP receptors. The tachycardia induced in wild-type mice by injection of lipopolysaccharide (LPS) was greatly attenuated in TP-deficient or FP-deficient mice and was completely absent in mice lacking both TP and FP. The beta-blocker propranolol did not block the LPS-induced increase in heart rate in wild-type animals. Our results show that inflammatory tachycardia is caused by a direct action on the heart of TXA(2) and PGF(2alpha) formed under systemic inflammatory conditions.

Suppression of allergic inflammation by the prostaglandin E receptor subtype EP3

Prostaglandins, including PGD(2) and PGE(2), are produced during allergic reactions. Although PGD(2) is an important mediator of allergic responses, aspirin-like drugs that inhibit prostaglandin synthesis are generally ineffective in allergic disorders, suggesting that another prostaglandin-mediated pathway prevents the development of allergic reactions. Here we show that such a pathway may be mediated by PGE(2) acting at the prostaglandin E receptor EP3. Mice lacking EP3 developed allergic inflammation that was much more pronounced than that in wild-type mice or mice deficient in other prostaglandin E receptor subtypes. Conversely, an EP3-selective agonist suppressed the inflammation. This suppression was effective when the agonist was administered 3 h after antigen challenge and was associated with inhibition of allergy-related gene expression. Thus, the PGE(2)-EP3 pathway is an important negative modulator of allergic reactions.

Redirection of Eicosanoid Metabolism in mPGES-1-deficient Macrophages

Microsomal prostaglandin E synthase (mPGES)-1 is one of several prostaglandin E synthases involved in prostaglandin H2 (PGH2) metabolism. In the present report, we characterize the contribution of mPGES-1 to cellular PGH2 metabolism in murine macrophages by studying the synthesis of eicosanoids and expression of eicosanoid metabolism enzymes in wild type and mPGES-1-deficient macrophages. Thioglycollate-elicited macrophages isolated from mPGES-1-/- animals and genetically matched wild type controls were stimulated with diverse pro-inflammatory stimuli. Prostaglandins were released in the following order of decreasing abundance from wild type macrophages stimulated with lipopolysaccharide: prostaglandin E2 (PGE2)>thromboxane B2 (TxB2)>6-keto prostaglandin F1alpha (PGF1alpha), prostaglandin F(2alpha) (PGF2alpha), and prostaglandin D2 (PGD2). In contrast, we detected in mPGES-1-/- macrophages a >95% reduction in PGE2 production resulting in the following altered prostaglandin profile: TxB2>6-keto PGF1alpha and PGF2alpha>PGE2, despite the comparable release of total prostaglandins. No significant change in expression pattern of key prostaglandin-synthesizing enzymes was detected between the genotypes. We then further profiled genotype-related differences in the eicosanoid profile using macrophages pre-stimulated with lipopolysaccharide followed by a 10-min incubation with 10 microm [3H]arachidonic acid. Eicosanoid products were subsequently identified by reverse phase high pressure liquid chromatography. The dramatic reduction in [3H]PGE2 formation from mPGES-1-/- macrophages compared with controls resulted in TxB2 and 6-keto PGF1alpha becoming the two most abundant prostaglandins in these samples. Our results also suggest a 5-fold increase in 12-[3H]hydroxyheptadecatrienoic acid release in mPGES-1-/- samples. Our data support the hypothesis that mPGES-1 induction in response to an inflammatory stimulus is essential for PGE2 synthesis. The redirection of prostaglandin production in mPGES-1-/- cells provides novel insights into how a cell processes the unstable endoperoxide PGH2 during the inactivation of a major metabolic outlet.