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

Expression of prostaglandin E synthase mRNA is induced in beta-amyloid treated rat astrocytes

Deposition of beta-amyloid (A beta) in the brain is considered to be one of the most critical events in the onset of Alzheimer's disease (AD). In order to identify factors involved in the exacerbation of AD, we investigated transcriptionally A beta-induced genes using a cDNA subtraction technique in rat astrocytes. One gene obtained was rat prostaglandin (PG) E synthase. In this report, we present the deduced sequence for rat PGE synthase for the first time and demonstrate the induction of PGE synthase mRNA by treatment of cells with A beta. Our results suggest a possibly significant role of this enzyme in the progression of AD.

The role of prostaglandin E receptor subtypes (EP1, EP2, EP3, and EP4) in bone resorption: an analysis using specific agonists for the respective EPs

PGE2 functions as a potent stimulator of bone resorption. The action of PGE2 is thought to be mediated by some PGE receptor subtypes present in osteoblastic cells. In this study, we examined the involvement of PGE receptor subtypes, EP1, EP2, EP3, and EP4, in PGE2-induced bone resorption using specific agonists for the respective EPs. In mouse calvaria cultures, EP4 agonist markedly stimulated bone resorption, but its maximal stimulation was less than that induced by PGE2. EP2 agonist also stimulated bone resorption, but only slightly. EP1 and EP3 agonists did not stimulate it at all. RT-PCR showed that osteoblastic cells isolated from newborn mouse calvaria expressed all of the EPs messenger RNA (mRNA). Both EP2 agonist and EP4 agonist induced cAMP production and the expression of osteoclast differentiation factor (ODF) mRNA in osteoblastic cells. Simultaneous addition of EP2 and EP4 agonists cooperatively induced cAMP production and ODF mRNA expression. In mouse bone marrow cultures, EP2 and EP4 agonists moderately induced osteoclast formation, but the simultaneous addition of the two agonists cooperatively induced it, similar to that by PGE2. In calvaria culture from EP4 knockout mice, a marked reduction in bone resorption to PGE2 was found. In EP4 knockout mice, EP4 agonist failed to induce bone resorption, but EP2 agonist slightly, but significantly, induced bone resorption. These findings suggest that PGE2 stimulates bone resorption by a mechanism involving cAMP and ODF, which is mediated mainly by EP4 and partially by EP2.

The roles of prostaglandin E receptor subtypes in the cytoprotective action of prostaglandin E2 in rat stomach

AIM

To investigate the EP receptor subtype involved in the gastroprotective action of prostaglandin (PG) E2 using various EP receptor agonists in rats, and using knockout mice lacking EP1 or EP3 receptors.

METHODS

Male SD rats and C57BL/6 mice were used after an 18-h fast. Gastric lesions were induced by oral administration of HCl/ethanol (150 mM HCl in 60% ethanol). Rats were given various EP agonists i.v. 10 min before HCl/ethanol: PGE2, sulprostone (EP1/EP3 agonist), butaprost (EP2 agonist), 17-phenyl-omega-trinorPGE2 (17-phenylPGE2: EP1 agonist), ONO-NT012 (EP3 agonist) and 11-deoxyPGE1 (EP3/EP4 agonist). In a separate study, the effect of PGE2 on HCl/ethanol lesions was examined in EP1- and EP3-receptor knockout mice.

RESULTS

Gastric lesions induced by HCl/ethanol were dose dependently prevented by PGE2: this effect was mimicked by sulprostone and 17-phenylPGE2 and was significantly antagonized by ONO-AE-829, an EP1 antagonist. Neither butaprost, ONO-NT012 nor 11-deoxyPGE1 exhibited any protective activity against HCl/ethanol-induced gastric lesions. PGE2 caused an inhibition of gastric motility as well as an increase of mucosal blood flow and mucus secretion, the effects being mimicked by prostanoids activating EP1 receptors, EP2/EP3/EP4 receptors and EP4 receptors, respectively. On the other hand, although HCl/ethanol caused similar damage in both wild-type mice and knockout mice lacking EP1 or EP3 receptors, the cytoprotective action of PGE2 observed in wild-type and EP3-receptor knockout mice totally disappeared in mice lacking EP1 receptors.

CONCLUSION

The gastric cytoprotective action of PGE2 is mediated by activation of EP1 receptors. This effect may be functionally associated with inhibition of gastric motility but not with increased mucosal blood flow or mucus secretion.

Genetic analysis of fetal development and parturition control in the mouse

The application of targeted gene inactivation methodologies to the study of late fetal development and control of the timing for parturition in mice has yielded insight into the mechanisms that enhance fetal survival. An essential role for glucocorticoids in promoting lung maturation sufficient for viability ex utero before the onset of normal parturition has been demonstrated in corticotropin-releasing hormone-deficient mice. In contrast, maternal deficiency in the prostaglandin synthetic enzyme cyclooxygenase-1 results in the markedly delayed onset of labor and fetal demise because of postdates gestation. The complex interplay of factors that govern the onset of labor is highlighted by mice deficient in both cyclooxygenase-1 and oxytocin. Whereas mice deficient in oxytocin demonstrate normal parturition, simultaneous cyclooxygenase-1 and oxytocin deficiency rescues the delayed onset of labor found in cyclooxygenase-1 knockout mice but results in the prolonged duration of labor. The consequences of complete deficiency of molecules involved in parturition in mice suggest novel interventions for human preterm labor.

Molecular signaling in uterine receptivity for implantation

Successful implantation is the result of an intimate 'cross-talk' between the blastocyst and uterus in a temporal and cell-specific manner. Thus, both the uterine and embryonic events must be examined to better understand this process. Although various aspects and molecules associated with these events have been explored, a comprehensive understanding of the implantation process is still very limited. In this review, we have highlighted the importance of the blastocyst's activity state and the receptive state of the uterus in determining the 'window' of implantation. In this context, we provide a testable scheme that signifies the important roles of various key molecules in embryo-uterine interactions during implantation.

Prolonged gestation does not extend survival of uterine natural killer lymphocytes in mice deleted in the receptor for prostaglandin F2alpha

During decidualization in mice and women, expansion of the Natural Killer (NK) cell lineage occurs within the uterus. In rodents, peak numbers of uterine (u)NK cells are reached at mid-gestation. The population then declines and residual cells are shed with the placenta. Decidualization, but not a fetus, is required to induce division and maturation of uNK cells. Mechanisms regulating the decline in uNK cells are unknown. To determine if the conceptus or its products have regulatory roles on uNK cell survival during normal gestation, a histological time course study was undertaken of implantation sites in mice ablated in the gene for the Prostaglandin F2alpha receptor (PGF2alphaR). These females experience normal gestation but fail to initiate labour and delivery. Their pregnancies extend a further 4-7 days before onset of maternal compromise. Large numbers of uNK cells were present in PGF2alphaR null mice by gestational day (gd) 10 and numbers had begun to decline at gd 14. By gd 18, very few uNK cells remained and no uNK cells were found at day 22 of extended gestation. Thus, the population history of uNK cells in PGF2alphaR null mice resembles that of uNK cells in normal mice, suggesting that the placenta, its products, the fetus and PGF2alpha are not factors that influence the rate of uNK cell decline in late gestation.

In vivo evidence that activation of tyrosine kinase is a trigger for lipopolysaccharide-induced fever in rats

We measured the rectal temperature of free-moving, conscious rats after intracerebroventricular (i.c.v.) injections of lipopolysaccharide (LPS) and interleukin-1beta (IL-1beta) with or without various antagonists to investigate the mechanisms involved in LPS-induced fever. LPS (3 microg) elicited significant increases in rectal temperature, which lasted from 0.5 h to more than 8 h after administration. This febrile response was inhibited by pretreatment with L-nitro-arginine (LNA), indomethacin (IND), genistein (GEN), tyrphostin 46 and anti-rat IL-1beta antibody (anti-IL-1beta Ab), but was not inhibited by pretreatment with daidzein or chelerythrine (CHE) into the ventricle. LPS (0.3 microg) following orthovanadate (i.c.v.) produced fever, although the small amount of LPS (0.3 microg) or orthovanadate alone showed no effect on rectal temperature. I.c.v. injections of IL-1beta also induced fever of approximately 4-h duration. This effect was inhibited by pretreatment with IND and anti-IL-1beta Ab, but was not inhibited by pretreatment with LNA, GEN or CHE into the ventricle. These findings demonstrate that in the central nervous system, LPS increases IL-1beta production after activation of tyrosine kinase and NO synthase, and IL-1beta promotes prostaglandin production resulting in increased rectal temperature. Activation of tyrosine kinase in the central nervous system is probably a trigger for the febrile response induced by LPS.

Angiotensin AT1 receptors in the preoptic area negatively modulate the cardiovascular and ACTH responses induced in rats by intrapreoptic injection of prostaglandin E2

We previously reported that brain angiotensin II type 2 (AT2) receptors contribute to the hyperthermia induced by intrahypothalamic (intrapreoptic (i.p.o.)) administration of prostaglandin E2 (PGE2) in rats. The present study was carried out to investigate the role of angiotensin II (ANG II) receptors in the cardiovascular and adrenocorticotropic hormone (ACTH) responses induced in rats by i.p.o. injection of PGE2. PGE2 (100 ng) produced marked increases in blood pressure, heart rate, and plasma ACTH concentration. These changes were significantly enhanced by i.p.o. treatment with an AT1-receptor antagonist, losartan, while an AT2-receptor antagonist, CGP 42112A, had no effect. In contrast, losartan, but not CGP 42112A, reduced the pressor and ACTH responses to i.p.o. injection of a large dose of "exogenous" ANG II (25 ng). These results suggest that while "endogenous" ANG II exerts inhibitory effects on both the cardiovascular and the ACTH responses to i.p.o. PGE2 by way of preoptic AT1-receptors, a large dose of exogenous ANG II produces effects opposite to those induced by the endogenous ANG II that is released locally and in small amounts by i.p.o. PGE2.

How the blood talks to the brain parenchyma and the paraventricular nucleus of the hypothalamus during systemic inflammatory and infectious stimuli

There are exciting new developments regarding the molecular mechanisms involved in the influence of circulating proinflammatory molecules within cells of the blood-brain barrier (BBB) during systemic immune challenges. These molecules, when present in the circulation, have the ability to trigger a series of events in cascade, leading to either the mitogen-activated protein (MAP) kinases/nuclear factor kappa B (NF-kappaB) or the janus kinase (JAK)/signal transducer and activator of transcription (STAT) transduction pathways in vascular-associated cells of the central nervous system (CNS). The brain blood vessels exhibit both constitutive and induced expression of receptors for different proinflammatory ligands that have the ability to stimulate these signaling molecules. Depending on the challenges and the cytokines involved, the transduction signal(s) solicited in cells of the BBB may orient the neuronal activity in a very specific manner in activating the transcription and production of soluble factors, such as prostaglandins (PGs). It is interesting to note that cytokines as well as systemic localized inflammation stimulate the cells of the BBB in a nonselective manner (i.e., within both large blood vessels and small capillaries across the brain). This nonselectivity raises several questions with regard to the localized neuronal activation induced by different experimental models of inflammation and cytokines. It is possible that the selectivity of the neuronal response is a consequence of the fine interaction between nonparenchymal synthesis of soluble mediators and expression of specific receptors for these ligands within parenchymal elements of different brain nuclei. This review will present the recent developments on this concept and the mechanisms that take place in cells of the BBB, which lead to the neuronal circuits involved in restoring the body's homeostasis during systemic immunogenic challenges. The induction of fever, the hypothalamic-pituitary adrenal (HPA) axis, and other autonomic functions are among the physiological outcomes necessary for the protection of the mammalian organism in the presence of foreign material.

COX-2 and iNOS, good targets for chemoprevention of colon cancer

Cyclooxygenase (COX)-2 has been suggested to play an important role in colon carcinogenesis. We found that the COX-2 selective inhibitor, nimesulide, reduces azoxymethane (AOM)-induced aberrant crypt foci (ACF) in rats and colon carcinogenesis in mice, as well as formation of intestinal polyps in Min mice. Thus, selective inhibitors of COX-2, which catalyzes the synthesis of prostanoids, could be good candidates as chemopreventive agents against colon cancer. Examination of the effect of prostanoid receptor deficiency and a selective antagonist of prostanoid receptor on the development of AOM-induced ACF in mice revealed the involvement of the EP1 receptor. Moreover, a selective EP1 antagonist reduced the number of intestinal polyps in Min mice. These results suggest that PGE2 contributes to colon carcinogenesis through binding to the EP1 receptor. Nitric oxide synthase (NOS) is known to be overexpressed in colon cancers of humans and rats, and a NOS inhibitor, L-NG-nitroarginine methyl ester, was found to inhibit the development of AOM-induced ACF in rats. Thus, NOS including iNOS could also be a good target for chemoprevention of colon cancer, as in the COX-2 case.

Prostaglandin receptors: their role in regulating renal function

Renal cyclooxygenase-1 and cyclooxygenase-2 actively metabolize arachidonate to metabolism five primary prostanoids: prostaglandin E2, prostaglandin F2a, prostaglandin I2, thromboxane A2, and prostaglandin D2. These lipid mediators interact with a family of distinct G-protein-coupled prostanoid receptors designated EP, FP, IP, TP, and DP, respectively, which exert important regulatory effects on renal function. The intrarenal distribution of these prostanoid receptors has been mapped and the consequences their activation are being characterized. The FP, TP, and EP1 receptors preferentially couple to increased cell Ca2+. EP2, EP4, DP, and IP receptors stimulate cyclic adenosine monophosphate, whereas the EP3 receptor preferentially couples to Gi, inhibiting cyclic adenosine monophosphate generation. EP1 and EP3 messenger RNA expression predominate in the collecting duct and thick limb, respectively, where their stimulation reduces sodium chloride and water absorption, promoting natriuresis and diuresis. Interestingly, only a mild change in renal water handling is seen in the EP3 receptor knockout mouse. Although only low levels EP2 receptor messenger RNA are detected in kidney and its precise intrarenal localization is uncertain, mice with targeted disruption of the EP2 receptor display salt-sensitive hypertension, suggesting it also plays an important role in salt excretion. In contrast, EP4 messenger RNA is readily detected in the glomerulus where it may contribute to the regulation of renin release and decrease glomerular resistance. TP receptors are also highly expressed in the glomerulus, where they may increase glomerular vascular resistance. The IP receptor messenger RNA is most highly expressed in the afferent arteriole and it may also modulate renal arterial resistance and renin release. At present there is little evidence for DP receptor expression in the kidney. Together these receptors act as physiologic buffers that protect the kidney from excessive functional changes during periods of physiologic stress. Loss of the combined effects of these receptors contributes to the side effects seen in the setting of nonsteroidal anti-inflammatory drug administration, whereas selective antagonists for these receptors may provide new therapeutic approaches in disease.

Relation between complement and the febrile response of guinea pigs to systemic endotoxin

We reported recently that the complement (C) system may play a role in the febrile response of guinea pigs to intravenous lipopolysaccharide (LPS) administration because C depletion abolished the LPS-induced rise in core temperature (T(c)). The present study was designed to investigate further the relation between C reduction [induced by cobra venom factor (CVF); 20, 50, 100, and 200 U/animal iv] and the fever of adult, conscious guinea pigs produced by LPS injected intravenously (2 microg/kg) or intraperitoneally (8, 16, 32 microg/kg) 18 h after CVF; control animals received pyrogen-free saline. Serum C levels were measured as total hemolytic C activity before and 18 h after CVF injection and expressed as CH(100) units. In other experiments, serum C levels were determined at various intervals after the intravenous and intraperitoneal injections at different doses of LPS alone. LPS produced fevers generally of similar heights but of different onset latencies and durations, depending on the dose and route of administration. CVF caused dose-related reductions in serum C, from approximately 1,136 U to below detection. These reductions proportionately attenuated the fevers induced by intraperitoneal LPS, but not by intravenous LPS. Intravenous and intraperitoneal LPS per se caused reductions in serum C of 25 and 40%, respectively, indicating activation of the C cascade. These decreases were transient, however, occurring early during the febrile rise approximately 30 min after LPS injection. These data thus support the notion that the C system may be critically involved in the febrile response of guinea pigs to systemic, particularly intraperitoneal, LPS.

Insight into prostaglandin, leukotriene, and other eicosanoid functions using mice with targeted gene disruptions

In recent years, there has been an exponential increase in the number of targeted gene disruptions performed in mice. At least 18 different gene knockouts have now been reported that have direct relevance to eicosanoid biology. These include genes that influence substrate availability (phospholipases), metabolism to eicosanoids (e.g., prostaglandin H synthases, lipoxygenases), and eicosanoid action (e.g., receptors for various prostaglandins). This minireview will outline the phenotype of these knockout mice and what has been learned about eicosanoid functions through use of this novel methodology.

Prostaglandin E2 inhibits spontaneous inhibitory postsynaptic currents in rat supraoptic neurones via presynaptic EP receptors

Prostaglandin E2 (PGE2) has been implicated in the excitatory regulation of magnocellular neurones in the supraoptic nucleus (SON). We have recently reported that PGE2 excited SON neurones by directly activating postsynaptic PGE2 receptors (EP receptors) of a subclass other than EP1-3, but did not affect excitatory postsynaptic currents (EPSCs). In the present study, we examined presynaptic effects of PGE2 on rat SON neurones by measuring spontaneous inhibitory postsynaptic currents (IPSCs) by a slice patch-clamp technique. PGE2 inhibited spontaneous IPSCs in a dose-dependent and reversible manner. PGE2 selectively suppressed the frequency of IPSCs without affecting the amplitude of IPSCs in the presence of tetrodotoxin, a blocker of Na+ channels, indicating that the effects were presynaptic. The inhibitory effects of PGE2 on the frequency of IPSCs were mimicked by the EP1/EP3 agonists, 17PT-PGE2 and sulprostone, and the EP2/EP3 agonist, misoprostol, whereas the EP2 agonist, butaprost, or the FP agonist, fluprostenol, had little effect. The effects of PGE2 on IPSCs were unaffected by the selective EP1 antagonist, SC-51322. They were unaffected also by antagonists of GABAB and alpha2 adrenergic receptors, which are present at presynaptic terminals of GABA neurones in the SON and cause suppression of spontaneous IPSCs. The inhibitor of PG synthesis, indomethacin, had little effect on spontaneous IPSCs and on the inhibitory effects of PGE2 as well as of the GABAB agonist, baclofen, and noradrenaline. These results suggest that PGE2 inhibits release of GABA from the GABAergic terminals innervating SON neurones by activating presynaptic EP receptors, presumably of the EP3 subclass, and that such a presynaptic mechanism may play a role in the excitatory regulation of SON neurones by PGE2.

Impaired duodenal bicarbonate secretion and mucosal integrity in mice lacking prostaglandin E-receptor subtype EP(3)

BACKGROUND & AIMS

To examine the involvement of EP(3) receptors in physiological regulation of duodenal HCO(3)(-) secretion, we disrupted the gene encoding EP receptors in mice by homologous recombination and evaluated acid-induced HCO(3)(-) secretion, which is physiologically important in the mucosal defense against acid injury, using EP(1)- and EP(3)-receptor knockout mice.

METHODS

The experiments were performed in the following 3 groups of mice after 18 hours of fasting: wild-type [WT (+/+)] mice, EP(1)-receptor knockout [EP(1) (-/-)] mice, and EP(3)-receptor knockout [EP(3) (-/-)] mice. Under urethane anesthesia, the proximal duodenal loop was perfused with saline that was gassed with 100% O(2), heated at 37 degrees C, and kept in a reservoir, and HCO(3)(-) secretion was measured at pH 7.0 using a pH-stat method and by adding 5 mmol/L HCl.

RESULTS

The duodenum of WT (+/+) mice increased HCO(3)(-) secretion in response to luminal perfusion of prostaglandin E(2) and forskolin as well as mucosal acidification. The latter effect was significantly inhibited by prior administration of indomethacin. HCO(3)(-) response to acid was observed in EP(1) (-/-) mice but disappeared totally in EP(3) (-/-) animals, although the acidification increased mucosal PGE(2) generation by similar degrees in all groups. The HCO(3)(-) stimulatory action of PGE(2) was also absent in EP(3) (-/-) but not EP(1) (-/-) mice, but forskolin effect was observed in both groups of animals, similar to WT (+/+) mice. Perfusion of the duodenum with 20 mmol/L HCl for 4 hours caused severe damage in EP(3) (-/-) mice and WT (+/+) animals pretreated with indomethacin, but not in EP(1) (-/-) mice.

CONCLUSIONS

The presence of EP(3)-receptors is essential for maintaining duodenal HCO(3)(-) secretion and mucosal integrity against luminal acid.

Developmental changes in prostaglandin E(2) receptor subtypes in porcine ductus arteriosus. Possible contribution in altered responsiveness to prostaglandin E(2)

BACKGROUND

Prostaglandin E(2) (PGE(2)) is important in ductus arteriosus (DA) patency, but the types of functional PGE(2) receptors (EP) in the developing DA are not known. We postulated that age-dependent alterations in EP and/or their subtypes may possibly contribute to the reduced responsiveness of the newborn DA to PGE(2).

METHODS AND RESULTS

We determined PGE(2) receptor subtypes by competition binding and immunoblot studies on the DA of fetal ( approximately 75% and 90% gestation) and newborn (<45 minutes old) pigs. We studied the effects of EP receptor stimulation on cAMP signaling in vitro and on term newborn (<3 hours old) DA patency in vivo. Fetal pig DA expressed EP(2), EP(3), and EP(4) receptors equivalently, but not EP(1). In neonatal DA, EP(1), EP(3), and EP(4) were undetectable, whereas EP(2) density was similar in fetus and newborn. Prostaglandin-induced changes in cAMP mirrored binding data. 16,16-Dimethyl PGE(2) and 11-deoxy PGE(1) (EP(2)/EP(3)/EP(4) agonist) produced more cAMP in fetus than newborn, but butaprost (selective EP(2) agonist) caused similar cAMP increases in both; EP(3) and EP(4) ligands (M&B28767 and AH23848B, respectively) affected cAMP production only in fetus. After birth, administration of butaprost alone was as effective as 11-deoxy PGE(1) and 16,16-dimethyl PGE(2) in dilating DA in vivo.

CONCLUSIONS

The data reveal fewer PGE(2) receptors in the DA of the newborn than in that of the fetus; this may contribute to the decreased responsiveness of the DA to PGE(2) in newborn. Because EP(2) receptors seem to mediate the effects of PGE(2) on the newborn DA, one may propose that a selective EP(2) agonist may be preferred as a pharmacological agent to maintain DA patency in infants with certain congenital heart diseases.

Prostanoid receptors: structures, properties, and functions

Prostanoids are the cyclooxygenase metabolites of arachidonic acid and include prostaglandin (PG) D(2), PGE(2), PGF(2alpha), PGI(2), and thromboxne A(2). They are synthesized and released upon cell stimulation and act on cells in the vicinity of their synthesis to exert their actions. Receptors mediating the actions of prostanoids were recently identified and cloned. They are G protein-coupled receptors with seven transmembrane domains. There are eight types and subtypes of prostanoid receptors that are encoded by different genes but as a whole constitute a subfamily in the superfamily of the rhodopsin-type receptors. Each of the receptors was expressed in cultured cells, and its ligand-binding properties and signal transduction pathways were characterized. Moreover, domains and amino acid residues conferring the specificities of ligand binding and signal transduction are being clarified. Information also is accumulating as to the distribution of these receptors in the body. It is also becoming clear for some types of receptors how expression of their genes is regulated. Furthermore, the gene for each of the eight types of prostanoid receptor has been disrupted, and mice deficient in each type of receptor are being examined to identify and assess the roles played by each receptor under various physiological and pathophysiological conditions. In this article, we summarize these findings and attempt to give an overview of the current status of research on the prostanoid receptors.

Temperature and hemodynamic changes associated with increased neural damage to global hemispheric hypoxic ischemia by prior prostaglandin E2, D2 and F2alpha administration

Experiments compared the hemispheric neural damage resulting from global hemispheric hypoxic ischemia (GHHI, ligation of right common carotid artery plus 35 min of 12% O2) in groups of anesthetized, male Long Evans rats, 9-10 weeks of age, kept at 37 degrees C, and previously given an intracerebroventricular (i.c.v., 2.5 microl) injection of 28 or 70 pmoles of PGE2, PGF2alpha or PGD2 or sterile saline (SS) 30 min beforehand. Mean arterial pressure (MAP), ipsilateral cortical capillary blood flow (CBF), colonic (Tc), ipsilateral (Tipsi) and contralateral (Tcontra), temporalis muscle temperatures were measured before, during and for 15 min after GHHI. Necrotic neural damage was assessed 7 days post-GHHI. All groups given GHHI + PGs showed increased ipsilateral hemispheric damage to GHHI especially due to enhanced neocortical damage, compared to the saline control group given the same insult. PGD2 was the most potent PG to cause further damage to the global insult. Tc, Tipsi, Tcontra and MAP increased following the i.c.v. injection of PGE2. I.c.v. PGF2alpha transiently decreased MAP, PGD2 tended to decrease cerebral blood flow and neither evoked changes in temperature compared to respective pre-injection control values. Results demonstrate increased neural damage to GHHI with prior i.c.v. PGE2, PGF2alpha or PGD2 administration.

Induction of ferritin and heat shock proteins by prostaglandin A1 in human monocytes. Evidence for transcriptional and post-transcriptional regulation

Prostaglandins of the A type (PGA) exert a cytoprotective activity during hyperthermia and virus infection. This effect is associated with induction of heat shock proteins (HSP) in mammalian cells. We now report that, in human monocytes, PGA1 is able to induce the synthesis of the iron-binding, redox-regulated protein ferritin. L-chain ferritin induction is consequent to a substantial increase in the accumulation of L-chain ferritin transcripts in PGA1-treated cells, whereas H-chain ferritin is regulated post-transcriptionally, consequently to reduction of iron-regulatory protein binding to iron-responsive elements in ferritin mRNA. Ferritin induction is specific for cyclopentenone prostaglandins (PGA1, PGA2, PGJ2, Delta12-PGJ2), whereas other arachidonic acid (AA) metabolites have no effect. In human monocytes, PGA1 also induces heat shock gene transcription via heat shock factor activation, as well as the synthesis of the oxidative-stress protein heme oxygenase (HOS). Differently from HSP, the induction of ferritin by PGA1 is specific for monocytes. Monocytes/macrophages play a pivotal role in inflammation, controlling iron metabolism and releasing a variety of mediators, including proinflammatory reactive oxygen species (ROS), cytokines and AA metabolites. As ferritin, together with hsp70 and HO, plays a key role in protection from oxidant damage, these results suggest that PGA1 may have cytoprotective activity also during oxidative injury.

Abortive expansion of the cumulus and impaired fertility in mice lacking the prostaglandin E receptor subtype EP(2)

Female mice lacking the gene encoding the prostaglandin (PG) E(2) receptor subtype EP(2) (EP(2)(-/-)) become pregnant and deliver their pups at term, but with a much reduced litter size. A decrease in ovulation number and a much reduced fertilization rate were observed in EP(2)(-/-) females without difference of the uterus to support implantation of wild-type embryos. Treatment with gonadotropins induced EP(2) mRNA expression in the cumulus cells of ovarian follicles of wild-type mice. The immature cumuli oophori from wild-type mice expanded in vitro in response to both follicle-stimulating hormone and PGE(2), but the response to PGE(2) was absent in those from EP(2)(-/-) mice. Cumulus expansion proceeded normally in preovulatory follicles but became abortive in a number of ovulated complexes in EP(2)(-/-) mice, indicating that EP(2) is involved in cumulus expansion in the oviduct in vivo. No difference in the fertilization rate between wild-type and EP(2)(-/-) mice was found in in vitro studies using cumulus-free oocytes. These results indicate that PGE(2) cooperates with gonadotropin to complete cumulus expansion for successful fertilization.

Distribution, regulation and colocalization of the genes encoding the EP2- and EP4-PGE2 receptors in the rat brain and neuronal responses to systemic inflammation

It is currently believed that prostaglandin (PG) of E2 type plays a crucial role in transferring the information received from circulating immune factors to brain parenchymal cells. Although PGE2 is synthesized quite essentially by cells of the blood-brain barrier, the organization and regulation of its receptor subtypes within neuronal elements remain unknown. In this study, intravenous (i.v.) injection of the endotoxin lipopolysaccharide (LPS) or recombinant rat interleukin-1beta (IL-1beta), and intramuscular (i.m.) injection of turpentine were used as different models of systemic immune stimuli. Rats were perfused at various times after the insults (30 min to 24 h), their brains cut and hybridized with full-length rat cRNA probes. Double-labelling procedures were accomplished to determine the cellular phenotype and activity. A very distinct distribution of both EP2 and EP4 receptors was found across the brain under basal conditions; the hybridization signal for the type 2 was detected in the bed nucleus of the stria terminalis (BNST), lateral septum, subfornical organ (SFO), ventromedial hypothalamic nucleus (VMH), central nucleus of the amygdala (CeA), locus coeruleus (LC) and the area postrema (AP), whereas the ventral septal/anterior preoptic area, the magnocellular paraventricular nucleus (PVN), supraoptic nucleus, parabrachial nucleus, LC, the nucleus of the solitary tract (NTS) and the ventrolateral medulla (VLM) exhibited moderate to strong levels for the EP4 mRNA under basal conditions. Upregulation of the genes encoding EP2 and EP4 receptors was detected in selective regions and neuronal populations during systemic inflammatory challenges. The most dramatic one being the robust transcriptional activation of the EP4 subtype within corticotropin-releasing factor (CRF) neurons of the parvocellular PVN following i.v. LPS and IL-1beta injection, and the localized i.m. aggression. These neurons of the endocrine hypothalamus as well as those of numerous autonomic-related nuclei were activated by the proinflammatory cytokine, as they were immunoreactive (ir) to Fos nuclear protein. The EP4 transcript was also present in activated catecholaminergic neurons of the LC, NTS and VLM, although only the A1 cell group exhibited an increase in EP4 transcription in response to circulating IL-1beta. Moreover, the systemic immunogenic insults caused a significant increase in the EP2 mRNA levels in the CeA, SFO, AP and the leptomeninges. These data provide a distinct pattern of EP2 and EP4 expression throughout the rat brain under both basal and immune-challenged conditions, and underlie the possible role of the EP4 subtype in mediating the effects of PGE2 on different autonomic and neuroendocrine functions. The presence of Fos-ir nuclei in various populations of EP4 neurons of IL-1beta-treated animals clearly supports this concept and suggests that the selectivity of the neuronal response during systemic inflammation may depend on the expression of specific PGE2 receptors in key structures of the brain.

Identification of human prostaglandin E synthase: a microsomal, glutathione-dependent, inducible enzyme, constituting a potential novel drug target

Human prostaglandin (PG) E synthase (EC 5.3.99.3) is a member of a recently recognized protein superfamily consisting of membrane associated proteins involved in eicosanoid and glutathione metabolism (the MAPEG family). Previous designations of the protein are PIG12 and MGST1-L1. PGE synthase was expressed in Escherichia coli, and both cytosolic and membrane fractions were prepared. Western blot analysis specifically detected a 15- to 16-kDa protein in the membrane fraction. Both fractions were incubated with prostaglandin H2 in the presence or absence of reduced glutathione. The membrane but not the cytosolic fraction was found to possess high glutathione-dependent PGE synthase activity (0.25 micromol/min/mg). The human tissue distribution was analyzed by Northern blot analysis. High expression of PGE synthase mRNA was detected in A549 and HeLa cancer cell lines. Intermediate level of expression was demonstrated in placenta, prostate, testis, mammary gland, and bladder whereas low mRNA expression was observed in several other tissues. A549 cells have been used as a model system to study cyclooxygenase-2 induction by IL-1beta. If A549 cells were grown in the presence of IL-1beta, a significant induction of the PGE synthase was observed by Western blot analysis. Also, Western blot analysis specifically detected a 16-kDa protein in sheep seminal vesicles. In summary, we have identified a human membrane bound PGE synthase. The enzyme activity is glutathione-dependent, and the protein expression is induced by the proinflammatory cytokine IL-1beta. PGE synthase is a potential novel target for drug development.

Cyclo-oxygenase-2-derived prostacyclin mediates embryo implantation in the mouse via PPARdelta

We have demonstrated previously that cyclo-oxygenase-2 (COX2), the rate-limiting enzyme in the biosynthesis of prostaglandins (PGs), is essential for blastocyst implantation and decidualization. However, the candidate PG(s) that participates in these processes and the mechanism of its action remain undefined. Using COX2-deficient mice and multiple approaches, we demonstrate herein that COX2-derived prostacyclin (PGI2) is the primary PG that is essential for implantation and decidualization. Several lines of evidence suggest that the effects of PGI2 are mediated by its activation of the nuclear hormone receptor PPARdelta, demonstrating the first reported biologic function of this receptor signaling pathway.

The febrile response to lipopolysaccharide is blocked in cyclooxygenase-2(-/-), but not in cyclooxygenase-1(-/-) mice

Various lines of evidence have implicated inducible cyclooxygenase-2 (COX-2) in fever production. Thus, its expression is selectively enhanced in brain after peripheral exogenous (e.g., lipopolysaccharide [LPS]) or endogenous (e.g., interleukin-1) pyrogen administration, while selective COX-2 inhibitors suppress the fever induced by these pyrogens. In this study, we assessed the febrile response to LPS of congenitally constitutive COX-1 (COX-1-/-) and COX-2 (COX-2-/-)-deficient C57BL/6J-derived mice. COX-1+/- and COX-2+/- mice were also evaluated; controls were wild-type C57BL/6J mice (Jackson Labs.). All the animals were pretrained daily for two weeks to the experimental procedures. LPS was injected intraperitoneally at 1 microgram/mouse; pyrogen-free saline (PFS) was the vehicle and control solution. Core temperatures (Tcs) were recorded using thermocouples inserted 2 cm into the colon. The presence of the COX isoforms was determined in cerebral blood vessels immunocytochemically after the experiments, without knowledge of the functional results. The data showed that the wild-type, COX-1+/-, and COX-1-/- mice all responded to LPS with a 1 degrees C rise in Tc within 1 h; the fever gradually abated over the next 4 h. By contrast, COX-2+/- and COX-2-/- mice displayed no Tc rise after LPS. PFS did not affect the Tc of any animal. It would appear therefore that COX-2 is necessary for LPS-induced fever production.

Immunocytochemical localization of prostaglandin EP3 receptor in the rat hypothalamus

A rabbit antibody against an N-terminal portion of rat prostaglandin EP3 receptor (EP3R) was produced to examine the distribution of EP3R in the rat hypothalamus. The antibody specifically recognized EP3R proteins in rat brain extract, in membrane fractions of rat kidney, and in membrane fractions of EP3R-expressing culture cells. Intense EP3R-like immunoreactivity was observed in the median preoptic nucleus, medial preoptic area, parastrial nucleus, compact part of the dorsomedial hypothalamic nucleus, and dorsal part of the premammillary nucleus. These results suggest that prostaglandin E2 mediates various actions in the hypothalamus, such as fever induction in the preoptic area, through EP3R.

Radically novel prostaglandins in animals and plants: the isoprostanes

Animal prostaglandins and plant jasmonates are well-known enzymatically formed cyclopentanoic lipids that have regulatory functions and serve as inducible mediators of host defense reactions. A novel group of prostaglandin-like compounds, the isoprostanes, generated in animals and plants by a nonenzymatic, free radical-catalyzed process, are now suspected to be mediators of oxidant injury in vivo.