Manganese exposure caused reproductive toxicity of male mice involving activation of GnRH secretion in the hypothalamus by prostaglandin E2 receptors EP1 and EP2

Exposure to manganese (Mn) can cause male reproductive damage and lead to abnormal secretion of sex hormones. Gonadotropin-releasing hormone (GnRH) plays an important role in the neuromodulation of vertebrate reproduction. Astrocytes can indirectly regulate the secretion of GnRH by binding paracrine prostaglandin E₂ (PGE₂) specifically to the EP1 and EP2 receptors on GnRH neurons. Prior studies assessed the abnormal secretion of GnRH caused by Mn exposure, but the specific mechanism has not been reported in detail. This study investigated the effects of Mn exposure on the reproductive system of male mice to clarify the role of PGE₂ in the abnormal secretion of GnRH in the hypothalamus caused by exposure to Mn. Our data demonstrate that antagonizing the EP1 and EP2 receptors of PGE₂ can restore abnormal levels of GnRH caused by Mn exposure. Mn exposure causes reduced sperm count and sperm shape deformities. These findings suggest that EP1 and EP2, the receptors of PGE₂, may be the key to abnormal GnRH secretion caused by Mn exposure. Antagonizing the PGE₂ receptors may reduce reproductive damage caused by Mn exposure.

The epinephrine-induced PGE2 reduces Na+/K+ ATPase activity in Caco-2 cells via PKC, NF-κB and NO

We showed previously an epinephrine-induced inhibition of the Na⁺/K⁺ ATPase in Caco-2 cells mediated via PGE2. This work is an attempt to further elucidate mediators downstream of PGE2 and involved in the observed inhibitory effect. The activity of the Na⁺/K⁺ ATPase was assayed by measuring the amount of inorganic phosphate liberated in presence and absence of ouabain, a specific inhibitor of the enzyme. Changes in the protein expression of the Na⁺/K⁺ ATPase were investigated by western blot analysis which revealed a significant decrease in the abundance of the ATPase in plasma membranes. Treating the cells with epinephrine or PGE2 in presence of SC19220, a blocker of EP1 receptors abolished completely the effect of the hormone and the prostaglandin while the effect was maintained unaltered in presence of antagonists to all other receptors. Treatment with calphostin C, PTIO, ODQ or KT5823, respective inhibitors of PKC, NO, soluble guanylate cyclase and PKG, abrogated completely the effect of epinephrine and PGE2, suggesting an involvement of these mediators. A significant inhibition of the ATPase was observed when cells were treated with PMA, an activator of PKC or with 8-Br-cGMP, a cell permeable cGMP analogue. PMA did reduce the protein expression of IκB, as shown by western blot analysis, and its effect on the ATPase was not manifested in presence of an inhibitor of NF-κB while that of SNAP, a nitric oxide donor, was not affected. The results infer that NF-κB is downstream PKC and upstream NO. The data support a pathway in which epinephrine induces the production of PGE2 which binds to EP1 receptors and activates PKC and NF-κB leading to NO synthesis. The latter activates soluble guanylate cyclase resulting in cGMP production and activation of PKG which through direct or indirect phosphorylation inhibits the Na⁺/K⁺ ATPase by inducing its internalization.

Cyclooxygenase-2 expression is associated with initiation of hepatocellular carcinoma, while prostaglandin receptor-1 expression predicts survival

AIM

To determine whether cyclooxygenase-2 (COX-2) and prostaglandin E1 receptor (EP₁) contribute to disease and whether they help predict prognosis.

METHODS

We retrospectively reviewed the records of 116 patients with hepatocellular carcinoma (HCC) who underwent surgery between 2008 and 2011 at our hospital. Expression of COX-2 and EP₁ receptor was examined by immunohistochemistry of formalin-fixed, paraffin-embedded tissues using polyclonal antibodies. Possible associations between immunohistochemical scores and survival were determined.

RESULTS

Factors associated with poor overall survival (OS) were alpha-fetoprotein > 400 ng/mL, tumor size ≥ 5 cm, and high EP₁ receptor expression, but not high COX-2 expression. Disease-free survival was not significantly different between patients with low or high levels of COX-2 or EP₁. COX-2 immunoreactivity was significantly higher in well-differentiated HCC tissues (Edmondson grade I-II) than in poorly differentiated tissues (Edmondson grade III-IV) (P = 0.003). EP₁ receptor immunoreactivity was significantly higher in poorly differentiated tissue than in well-differentiated tissue (P = 0.001).

CONCLUSION

COX-2 expression appears to be linked to early HCC events (initiation), while EP₁ receptor expression may participate in tumor progression and predict survival.

PGE2 Modulates GABAA Receptors via an EP1 Receptor-Mediated Signaling Pathway

AIMS

PGE2 is one of the most abundant prostanoids in mammalian tissues, but its effect on neuronal receptors has not been well investigated. This study examines the effect of PGE2 on GABAA receptor currents in rat cerebellar granule neurons.

METHODS

GABAA currents were recorded using a patch-clamp technique. Cell surface and total protein of GABAA β1/2/3 subunits was carried out by Western blot analysis.

RESULTS

Upon incubation of neurons with PGE2 (1 μM) for 60 minutes, GABAA currents were significantly potentiated. This PGE2-driven effect could be blocked by PKC or CaMKII inhibitors as well as EP1 receptor antagonist, and mimicked by PMA or EP1 receptor agonist. Furthermore, Western blot data showed that PGE2 did not increase the total expression level of GABAA receptors, but significantly increased surface levels of GABAA β1/2/3 subunits after 1 h of treatment. Consistently, both PKC and CaMKII inhibitors were able to reduce PGE2-induced increases in cell surface expression of GABAA receptors.

CONCLUSION

Activation of either the PKC or CaMKII pathways by EP1 receptors mediates the PGE2-induced increase in GABAA currents. This suggests that upregulation of postsynaptic GABAA receptors by PGE2 may have profound effects on cerebellar functioning under physiological and pathological conditions.

Validation of EP1 Antibody Clone for Estrogen Receptor Immunohistochemistry for Breast Cancer

BACKGROUND

SP1 Rabbit monoclonal antibody to estrogen receptor (ER) has long been the standard for determination of ER status in breast cancer but has been replaced by the rabbit EP1 clone.

AIM

To validate the EP1 antibody clone for use in determination of breast cancer ER status in a large clinical population against the previous standard SP1.

MATERIALS AND METHODS

ER immunohistochemistry was assessed in 523 consecutive cases from a clinical setting using tissue microarrays.

RESULTS

The kappa statistic showed that the agreement of ER status between SP1 and EP1 was considered to be almost perfect (kappa=0.97, 95% confidence interval=0.94-1.00). Sensitivity was 99.3%, specificity was 98.6% and overall agreement was 99.2%.

CONCLUSION

The EP1 antibody was herein validated regarding its use in breast cancer with almost perfect agreement with the previously used standard SP1 antibody.

Apigenin inhibits COX-2, PGE2, and EP1 and also initiates terminal differentiation in the epidermis of tumor bearing mice

Non-melanoma skin cancer (NMSC) is the most prevalent cancer in the United States. NMSC overexpresses cyclooxygenase-2 (COX-2). COX-2 synthesizes prostaglandins such as PGE2 which promote proliferation and tumorigenesis by engaging G-protein-coupled prostaglandin E receptors (EP). Apigenin is a bioflavonoid that blocks mouse skin tumorigenesis induced by the chemical carcinogens, 7,12-dimethylbenz[a]anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA). However, the effect of apigenin on the COX-2 pathway has not been examined in the DMBA/TPA skin tumor model. In the present study, apigenin decreased tumor multiplicity and incidence in DMBA/TPA-treated SKH-1 mice. Analysis of the non-tumor epidermis revealed that apigenin reduced COX-2, PGE2, EP1, and EP2 synthesis and also increased terminal differentiation. In contrast, apigenin did not inhibit the COX-2 pathway or promote terminal differentiation in the tumors. Since fewer tumors developed in apigenin-treated animals which contained reduced epidermal COX-2 levels, our data suggest that apigenin may avert skin tumor development by blocking COX-2.

Loss of the PGE2 receptor EP1 enhances bone acquisition, which protects against age and ovariectomy-induced impairments in bone strength

PGE2 exerts anabolic and catabolic effects on bone through the discrete actions of four prostanoid receptors (EP1-4). We have previously demonstrated that loss EP1 accelerates fracture repair by enhancing bone formation. In the present study we defined the role of EP1 in bone maintenance and homeostasis during aging and in response to ovariectomy. The femur and L4 vertebrae of wild type (WT) and EP1(-/-) mice were examined at 2-months, 6-months, and 1-year of age, and in WT and EP1(-/-) mice following ovariectomy (OVX) or sham surgery. Bone volume fraction, trabecular architecture and mechanical properties were maintained during aging in EP1(-/-) mice to a greater degree than age-matched WT mice. Moreover, significant increases in bone formation rate (BFR) (+60%) and mineral apposition rate (MAR) (+50%) were observed in EP1(-/-), relative to WT, while no change in osteoclast number and osteoclast surface were observed. Following OVX, loss of EP1 was protective against bone loss in both femur and L4 vertebrae, with increased bone volume/total volume (BV/TV) (+32% in femur) and max load at failure (+10% in femur) relative to WT OVX, likely resulting from the increased bone formation rate that was observed in these mice. Taken together these studies identify inhibition of EP1 as a potential therapeutic approach to suppress bone loss in aged or post-menopausal patients.

Cloning and expression of prostaglandin E2 receptor subtype 1 (ep 1 ) in Bostrichthys sinensis

Our previous studies suggested that prostaglandin E2 (PGE2) is a putative sex pheromone in Chinese black sleeper Bostrichthys sinensis, a fish species that inhabits intertidal zones and mates and spawns inside a muddy burrow. We found immunoreactivities of PGE2 receptor subtypes (Ep1-3) expressed in the olfactory sac, but only Ep1 presented higher density of immunoreactivity in mature fish than that in immature fish in both sexes. To gain a better understanding of the underlying molecular mechanism for the detection of PGE2 in the olfactory system, we cloned an ep 1 cDNA from the adult olfactory sac. The open-reading frame of the ep 1 consisted of 1,134-bp nucleotides that encoded a 378-amino acid-long protein with a seven-transmembrane domain, typical for the G protein-coupled receptors superfamily. Expression of ep 1 mRNA was observed in all tissues examined, with higher levels obtained in the olfactory sacs and testes. The expression of ep 1 mRNA in the olfactory sacs and gonads was significantly higher in both sexes of mature fish than in those of immature ones. Taken together, our results suggested that Ep1, which is highly expressed in the olfactory sacs and gonads of mature fish, is important for the control of reproduction and may be involved in PGE2-initiated spawning behavior in B. sinensis.

Functional and molecular characterization of hyposensitive underactive bladder tissue and urine in streptozotocin-induced diabetic rat

Background

The functional and molecular alterations of nerve growth factor (NGF) and Prostaglandin E2 (PGE2) and its receptors were studied in bladder and urine in streptozotocin (STZ)-induced diabetic rats.

Methodology/Principal Findings

Diabetes mellitus was induced with a single dose of 45 mg/kg STZ Intraperitoneally (i.p) in female Sprague-Dawley rats. Continuous cystometrogram were performed on control rats and STZ treated rats at week 4 or 12 under urethane anesthesia. Bladder was then harvested for histology, expression of EP receptors and NGF by western blotting, PGE2 levels by ELISA, and detection of apoptosis by TUNEL staining. In addition, 4-hr urine was collected from all groups for urine levels of PGE2, and NGF assay. DM induced progressive increase of bladder weight, urine production, intercontraction interval (ICI) and residual urine in a time dependent fashion. Upregulation of Prostaglandin E receptor (EP)1 and EP3 receptors and downregulation of NGF expression, increase in urine NGF and decrease levels of urine PGE2 at week 12 was observed. The decrease in ICI by intravesical instillation of PGE2 was by 51% in control rats and 31.4% in DM group at week 12.

Conclusions/Significance

DM induced hyposensitive underactive bladder which is characterized by increased inflammatory reaction, apoptosis, urine NGF levels, upregulation of EP1 and EP3 receptors and decreased bladder NGF and urine PGE2. The data suggest that EP3 receptor are potential targets in the treatment of diabetes induced underactive bladder.

Prostaglandin E2 induces apoptosis in cultured rat microglia

Prostaglandin E2 (PGE2) plays a critical role in the modulation of microglial function including migration and phagocytosis through EP2, which increases intracellular cyclic adenosine monophosphate (AMP) concentration. In the present study, we found that PGE2 reduces cell viability in microglia. PGE2 decreased 3-(4,5-dimethylthiazol-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) reduction and increased lactate dehydrogenase release, deoxyribonucleic acid fragmentation, and poly(ADP-ribose) polymerase cleavage after 24h incubation, suggesting that PGE2 induces apoptosis in these cells. An EP2 agonist, butaprost, and an EP4 agonist, PGE1 alcohol, also induced apoptosis, while an EP1 agonist, 17-phenyl trinor PGE2, or an EP3 agonist, sulprostone, at 10(-6)M did not. On the other hand, EP1-EP4 antagonists, SC-51322, AH6809, L-798106, or GW627368X, up to 10(-5)M did not affect the decrease in MTT reduction by PGE2. Intracellular cyclic AMP accumulation was induced by butaprost, but not 17-phenyl trinor PGE2, sulprostone, or PGE1 alcohol at 10(-6)M. Additionally, we previously reported that PGE2-induced intracellular cyclic AMP accumulation was reversed by AH6809. Besides EP receptors, one of other targets was thought to be prostaglandin transporter, but its inhibitors, bromocresol green or U-46619 up to 10(-5)M did not affect the decrease in MTT reduction by PGE2. These results suggest that PGE2 induces apoptosis in microglia independent of intracellular cyclic AMP concentration, and there are different mechanisms between PGE2-induced apoptosis and the modulation of microglial function.

Hormonal therapy deregulates prostaglandin-endoperoxidase synthase 2 (PTGS2) expression in endometriotic tissues

CONTEXT

Endometriosis is a common gynecologic condition characterized by an important inflammatory process mediated by the prostaglandin pathway. Oral contraceptives are the treatment of choice for symptomatic endometriotic women. However the effects of oral contraceptives use and prostaglandin pathway in endometriotic women are actually still unknown.

OBJECTIVE

To investigate the expression of prostaglandin pathway key genes in endometriotic tissue, affected or not by hormonal therapy, as compared with healthy endometrial tissue.

DESIGN

This was a comparative laboratory study.

SETTING

This study was conducted in a tertiary-care university hospital.

PATIENTS

Seventy-six women, with (n = 46) and without (n = 30) histologically proven endometriosis.

MAIN OUTCOME MEASURES

Prostaglandin-endoperoxidase synthase (PTGS)1, PTGS2, prostaglandin E receptor (PTGER)1, PTGER2, PTGER3, and PTGER4 mRNA levels in endometrium of disease-free women and in eutopic and ectopic endometrium of endometriosis-affected women. PTGS2 expression was further investigated by immunohistochemistry, using specific monoclonal antibodies. PTGS2 expression was analyzed at mRNA and protein levels and correlated with taking hormonal treatment.

RESULTS

PTGS2 expression was significantly increased in eutopic and ectopic endometrium as compared with healthy tissue (induction of 9.6- and 6.3-fold, respectively; P = .001). PTGS2 immunoreactivity increased gradually from normal endometrium to eutopic and ectopic endometrium (h-score of 96.7 ± 55.0, 128.3 ± 66.1, and 226.7 ± 62.6, respectively, P < .001). PTGER2, PTGER3, and PTGER4 expression increased significantly and gradually from normal to eutopic and ectopic endometrium, whereas PTGER1 remained unchanged. Patients under hormonal treatment had a higher PTGS2 expression at transcriptional and protein levels as compared with those without treatment (P = .002 and P = .025, respectively).

CONCLUSIONS

Prostaglandin pathway is strongly deregulated in eutopic and ectopic endometrium of women suffering from endometriosis for the benefit of an increased PTGS2 expression. We show for the first time that hormonal treatment appears to enhance even more PTGS2 expression. These results contribute to explain why medical treatment could fail to control endometriosis progression.

Role of PGE2 in the colonic motility: PGE2 generates and enhances spontaneous contractions of longitudinal smooth muscle in the rat colon

The aim of this study was to determine which PGE2 receptors (EP1-4 receptors) influence colonic motility. Mucosa-free longitudinal smooth muscle strips of the rat middle colon spontaneously induced frequent phasic contractions (giant contractions, GCs) in vitro, and the GCs were almost completely abolished by a cyclooxygenase inhibitor, piroxicam, and by an EP3 receptor antagonist, ONO-AE3-240, but enhanced by tetrodotoxin (TTX). In the presence of piroxicam, exogenous PGE2, both ONO-AE-248 (EP3 agonist), and ONO-DI-004 (EP1 agonist) induced GC-like contractions, and increased the frequency and amplitude. These effects of EP receptor agonists were insensitive to TTX and ω-conotoxins. In immunohistochemistry, the EP1 and EP3 receptors were expressed in the longitudinal smooth muscle cells. These results suggest that the endogenous PGE2 spontaneously generates and enhances the frequent phasic contractions directly activating the EP1 and EP3 receptors expressed on longitudinal smooth muscle cells in the rat middle colon.

Prostaglandin E2-EP3 axis in fine-tuning excessive skin inflammation by restricting dendritic cell functions

Prostaglandin E₂ (PGE₂) is produced in the skin and is suggested to play a role in the regulation of cutaneous immune homeostasis and responses. However, the multifaceted functions of PGE₂ continue to elude our understanding, especially because of the multiplicity of PGE₂ receptors—EP1, EP2, EP3, and EP4. While cAMP-elevating EP4 is known to activate the functions of cutaneous dendritic cells (DCs), including Langerhans cells (LCs) and dermal DCs, the role of cAMP-suppressing EP3 in this process remains unknown. Here we demonstrated that an EP3 receptor selective agonist, ONO-AE-248, inhibited chemotaxis and co-stimulatory molecule expressions of DCs in vitro. A suboptimal dose of antigen was sufficient to induce contact hypersensitivity in EP3-deficient mice. Intriguingly, EP3 deficiency did not impair skin inflammation at all when the antigen dose was sufficiently high. EP3 limited the functions of cutaneous DCs only when the antigen dose was low. In contrast to EP4, the observed unappreciated function of EP3 may stabilize the cutaneous DCs to halt the impetuous response to a suboptimal dose of antigen. Taken together, PGE₂-EP3 signaling is essential for fine-tuning excessive skin inflammation by restricting DC functions.

Development of an in vivo active, dual EP1 and EP3 selective antagonist based on a novel acyl sulfonamide bioisostere

Recent preclinical studies demonstrate a role for the prostaglandin E(2) (PGE(2)) subtype 1 (EP1) receptor in mediating, at least in part, the pathophysiology of hypertension and diabetes mellitus. A series of amide and N-acylsulfonamide analogs of a previously described picolinic acid-based human EP1 receptor antagonist (7) were prepared. Each analog had improved selectivity at the mouse EP1 receptor over the mouse thromboxane receptor (TP). A subset of analogs gained affinity for the mouse PGE(2) subtype 3 (EP3) receptor, another potential therapeutic target. One analog (17) possessed equal selectivity for EP1 and EP3, displayed a sufficient in vivo residence time in mice, and lacked the potential for acyl glucuronide formation common to compound 7. Treatment of mice with 17 significantly attenuated the vasopressor activity resulting from an acute infusion of EP1 and EP3 receptor agonists. Compound 17 represents a potentially novel therapeutic in the treatment of hypertension and diabetes mellitus.

Tumor-associated stromal cells expressing E-prostanoid 2 or 3 receptors in prostate cancer: correlation with tumor aggressiveness and outcome by angiogenesis and lymphangiogenesis

OBJECTIVE

To clarify the detailed pathologic roles of prostaglandin E(2) in prostate cancer tissues, the present study investigated the clinical significance and prognostic roles of the density of tumor-associated stromal cells expressing specific receptors for prostaglandin E2, termed "E-prostanoid (EP)1-4 receptors (EP1R-4Rs)."

METHODS

The expression of each receptor was immunohistochemically examined in 114 formalin-fixed biopsy specimens. Correlations with clinicopathologic features were investigated in these specimens. Angiogenesis and lymphangiogenesis were measured by the percentage of CD34-stained vessels (microvessel density) and D2-40-stained vessels (lymph vessel density). The relationships between the density of each EPR-stained cells and the microvessel density or lymph vessel density were evaluated in 62 prostate cancer tissues obtained by radical surgery for more detailed analysis in a wider area of prostate cancer tissue.

RESULTS

The density of tumor-associated cells with EP2R expression was positively associated with the N (P<.001) and M (P=.002) stages. Similarly, EP3R-positive stromal cell density was significantly associated with the N (P=.033) and M (P=.026) stages. The density of EP2R- and EP3R-stained cells correlated with the microvessel density (r=0.42, P<.001) and lymph vessel density (r=0.36, P=.012), respectively. A greater density of EP2R-stained cells was recognized as an independent predictor of progression (hazard ratio 7.26, P=.002) on multivariate analysis.

CONCLUSION

EP2R- and EP3R-stained cells might play important roles in tumor progression, angiogenesis, and lymphangiogenesis in prostate cancer. The density of EP2R-stained stromal cells could offer a useful predictor of biochemical recurrence after radical surgery.

Molecular characterization of prostaglandin F receptor (FP) and E receptor subtype 1 (EP₁) in zebrafish

Prostaglandins E (PGE) and F (PGF) mediate diverse physiological functions via their cell surface receptors - prostaglandin E receptor (EP) subtypes 1, 2, 3 and 4 (EP(1); EP(2); EP(3); EP(4)) and F receptor (FP). In teleost fishes, PGE was implicated in gill epithelium ion transport, while both PGE and PGF were involved in oocyte maturation, follicular rupture and coordination of reproductive behaviors. However, little is known about the mechanisms behind their actions. In present study, we first identified the full-length ORF cDNA clones of three zebrafish prostaglandin E receptor subtype 1 (zEP(1)) isoforms - zEP(1a), zEP(1b) and zEP(1c) - and FP (zFP) from adult ovary. RT-PCR showed that zEP(1a), zEP(1b) and zFP are widely expressed in adult tissues, while zEP(1c) mRNA expression is mainly confined in brain and kidney. Using a pGL3-NFAT-RE luciferase reporter system, both zEP(1a) and zEP(1b) expressed in DF-1 cells were shown to be activated by PGE(2) potently while zEP(1c) and zFP were activated by PGF(2a) effectively, suggesting that the four receptors are functionally coupled to intracellular Ca(2+)-signaling pathway. Furthermore, EP1a and EP1b, but not EP1c were suggested to couple to cAMP-PKA signaling pathway using a pGL3-CRE luciferase reporter assay. Although zEP(1c) might originate as a paralog to zEP(1a) and zEP(1b), its functional coupling to PGF(2α) instead of PGE(2) suggested that zEP(1) isoforms might have sub-functionalized in their ligand binding and G protein coupling specificity, in addition to differential tissue distribution. Characterization of these receptors undoubtedly furthered our understanding on the diverse yet highly target-specific responses of prostaglandins in teleosts.

The roles of prostaglandin EP 1 and 3 receptors in the control of human myometrial contractility

CONTEXT

Prostaglandins are central to the processes of human labor. Prostaglandin E(2) (PGE(2)) synthesized within the uterus mediates cervical ripening and uterine contractions. PGE receptors, EP1 and EP3, may each mediate contractions, and represent potential therapeutic targets in the management of preterm labor. Studies of the expression and function of EP1 and EP3 in pregnant myometrium are inconsistent.

OBJECTIVE

The objective of the study was to determine the relative importance of EP1 and EP3 in human myometrial contractility.

DESIGN

We studied the expression of EP1 and EP3 in upper- and lower-segment myometrium at term in vivo and the effects of specific inhibitors on contractions in vitro.

PATIENTS

Myometrial biopsies for both in vivo and in vitro studies were taken at cesarean section at term before or in labor in uncomplicated pregnancies.

RESULTS

We found no differences in the expression of EP1 or EP3 at mRNA or protein level between the upper and lower segment myometrium and no overall changes associated with the onset of labor. Upon labor, EP1, but not EP3, was found to relocalize to the nucleus. In studies of contractility, we found no differences in spontaneous or PGE(2)-induced contractility between the upper- and lower-segment samples. Spontaneous contractions were inhibited by acetylsalicylic acid and were rescued by PGE(2). Although an EP1 antagonist, ZD6416, had no effect, an EP3 antagonist, L798106, inhibited both spontaneous and PGE(2)-induced contractions.

CONCLUSIONS

EP3 is the primary receptor subtype that mediates PGE(2) induced contractility in human pregnant myometrium at term and represents a possible therapeutic target.

EP1 receptor within the ventrolateral periaqueductal grey controls thermonociception and rostral ventromedial medulla cell activity in healthy and neuropathic rat

The aim of this study was to investigate the expression of prostaglandin EP1 receptor within the ventrolateral periaqueductal grey (VL PAG). The role of VL PAG EP1 receptor in controlling thermonociception and rostral ventromedial medulla (RVM) activity in healthy and neuropathic rats was also examined. EP1 receptor was indeed found to be expressed within the VL PAG and co-localized with vesicular GABA transporter. Intra-VL PAG microinjection of ONO-DI-004, a selective EP1 receptor agonist, dose-dependently reduced tail flick latency as well as respectively increasing and decreasing the spontaneous activity of ON and OFF cells. Furthermore, it increased the ON cell burst and OFF cell pause. Intra-VL PAG prostaglandin E2 (PGE2) behaved similarly to ONO-DI-004. The effects of ONO-DI-004 and PGE2 were antagonized by intra-VL PAG L335677, a selective EP1 receptor antagonist. L335677 dose-dependently increased the tail flick latency and ongoing activity of the OFF cells, while reducing the ongoing ON cell activity. It also decreased the ON cell burst and OFF cell pause. In neuropathic rats using spare nerve injury (SNI) of the sciatic nerve model, EP1 receptor expression decreased in the VL PAG. However, ONO-DI-004 and L335677 were able to alter pain responses and ON and OFF cell activity, as they did in healthy animals. Collectively, these data show that within the VL PAG, EP1 receptor has a facilitatory effect on the nociceptive response and consistently affects RVM neuron activity. Thus, the blockade of EP1 receptor in the VL PAG leads to antinociception in neuropathic pain conditions, despite its down-regulation. The expression of EP1 receptor on GABAergic neurons is consistent with an EP1 receptor blockade-induced disinhibition of the antinociceptive descending pathway at VL PAG level.

Purinergic signaling induces cyclooxygenase-1-dependent prostanoid synthesis in microglia: roles in the outcome of excitotoxic brain injury

Cyclooxygenases (COX) are prostanoid synthesizing enzymes constitutively expressed in the brain that contribute to excitotoxic neuronal cell death. While the neurotoxic role of COX-2 is well established and has been linked to prostaglandin E(2) synthesis, the role of COX-1 is not clearly understood. In a model of N-Methyl-D-aspartic acid (NMDA) induced excitotoxicity in the mouse cerebral cortex we found a distinctive temporal profile of COX-1 and COX-2 activation where COX-1, located in microglia, is responsible for the early phase of prostaglandin E(2) synthesis (10 minutes after NMDA), while both COX-1 and COX-2 contribute to the second phase (3-24 hours after NMDA). Microglial COX-1 is strongly activated by ATP but not excitatory neurotransmitters or the Toll-like receptor 4 ligand bacterial lipopolysaccharide. ATP induced microglial COX-1 dependent prostaglandin E(2) synthesis is dependent on P2X7 receptors, extracellular Ca(2+) and cytoplasmic phospholipase A2. NMDA receptor activation induces ATP release from cultured neurons leading to microglial P2X7 receptor activation and COX-1 dependent prostaglandin E(2) synthesis in mixed microglial-neuronal cultures. Pharmacological inhibition of COX-1 has no effect on the cortical lesion produced by NMDA, but counteracts the neuroprotection exerted by inhibition of COX-2 or observed in mice lacking the prostaglandin E(2) receptor type 1. Similarly, the neuroprotection exerted by the prostaglandin E(2) receptor type 2 agonist butaprost is not observed after COX-1 inhibition. P2X7 receptors contribute to NMDA induced prostaglandin E(2) production in vivo and blockage of P2X7 receptors reverses the neuroprotection offered by COX-2 inhibition. These findings suggest that purinergic signaling in microglia triggered by neuronal ATP modulates excitotoxic cortical lesion by regulating COX-1 dependent prostanoid production and unveil a previously unrecognized protective role of microglial COX-1 in excitotoxic brain injury.

Central PGE2 exhibits anxiolytic-like activity via EP1 and EP4 receptors in a manner dependent on serotonin 5-HT1A, dopamine D1 and GABAA receptors

We found that centrally administered prostaglandin (PG) E(2) exhibited anxiolytic-like activity in the elevated plus-maze and open field test in mice. Agonists selective for EP(1) and EP(4) receptors, among four receptor subtypes for PGE(2), mimicked the anxiolytic-like activity of PGE(2). The anxiolytic-like activity of PGE(2) was blocked by an EP(1) or EP(4) antagonist, as well as in EP(4) but not EP(1) knockout mice. Central activation of either EP(1) or EP(4) receptors resulted in anxiolytic-like activity. The PGE(2)-induced anxiolytic-like activity was inhibited by antagonists for serotonin 5-HT(1A), dopamine D(1) and GABA(A) receptors. Taken together, PGE(2) exhibits anxiolytic-like activity via EP(1) and EP(4) receptors, with downstream involvement of 5-HT(1A), D(1) and GABA(A) receptor systems.

Prostaglandin E2 increases cardiac fibroblast proliferation and increases cyclin D expression via EP1 receptor

PGE(2) affects growth of many cell types. Thus, we hypothesized that PGE(2) would stimulate growth of cardiac fibroblasts. To test our hypothesis we used neonatal rat ventricular fibroblasts (NVF). RT-PCR demonstrated the presence of all 4 PGE(2) receptor (EPs) mRNAs in NVF. Using flow cytometry, we found that PGE(2) decreased the percentage of cells in G0/G1 and increased the number of cells in S phase. PGE(2) also increased expression of cyclin D3, a known regulator of the cell cycle and this effect was mimicked by the EP1/EP3 agonist sulprostone. Next, we found that treatment of NVF with PGE(2) increased phosphorylation of p42/44 MAPK and Akt and that PGE(2)-stimulation of cyclin D3 was antagonized with both a MEK inhibitor and a PI3 kinase inhibitor. In conclusion, PGE(2) stimulates cardiac fibroblast proliferation via EP1 and/or EP3, p42/44 MAPK and Akt-regulation of cyclin D3. These results may be relevant to cardiac fibrosis.

Anti-pigmentary activity of fucoxanthin and its influence on skin mRNA expression of melanogenic molecules

OBJECTIVES

Carotenoids and retinoic acid derivatives are topically applied for sun-protective and whitening purposes. Fucoxanthin is a carotenoid derived from edible sea algae, but its effect on melanogenesis has not been established. Therefore, we examined the effect of fucoxanthin on melanogenesis.

METHODS

Inhibitory effects on tyrosinase activity, melanin formation in B16 melanoma and skin pigmentation in UVB-irradiated guinea-pigs were evaluated. To elucidate the action of fucoxanthin on melanogenesis, its effect on skin melanogenic mRNA expression was evaluated in UVB-irradiated mice. Fucoxanthin was given topically or orally to mice once a day and UVB irradiation was applied for 14 days. The effect of fucoxanthin on skin melanogenic mRNA expression was evaluated by real time reverse transcription polymerase chain reaction.

KEY FINDINGS

Fucoxanthin inhibited tyrosinase activity, melanogenesis in melanoma and UVB-induced skin pigmentation. Topical application of fucoxanthin (1%) significantly suppressed mRNA expression of cyclooxygenase (COX)-2, endothelin receptor A, p75 neurotrophin receptor (NTR), prostaglandin E receptor 1 (EP1), melanocortin 1 receptor (MC1R) and tyrosinase-related protein 1. The suppression of p75NTR, EP1 and MC1R expressions was observed at 0.01% application. Also, oral application of fucoxanthin (10 mg/kg) significantly suppressed expression of COX-2, p75NTR, EP1 and MC1R.

CONCLUSIONS

These results suggest that fucoxanthin exhibits anti-pigmentary activity by topical or oral application in UVB-induced melanogenesis. This effect of fucoxanthin may be due to suppression of prostaglandin (PG) E(2) synthesis and melanogenic stimulant receptors (neurotrophin, PGE(2) and melanocyte stimulating hormone expression).

EP4 upregulation of Ras signaling and feedback regulation of Ras in human colon tissues and cancer cells

Previous studies indicate that COX-2 and prostaglandin E(2) (PGE(2)) receptor subtypes are involved in intestinal carcinogenesis and activation of downstream pathways. In this report, we try to understand the association of PGE(2) receptor and K-ras cellular mechanism during the development of colorectal cancer. We collected 21 colorectal cancer patients and compared the protein expression of tumor tissues and normal mucosa tissues by using immunoblot. Furthermore, we transferred empty vector and pcDNA-K-ras into Ras-HT29 colon cancer cells. Result showed that phosphorylation of Akt and EP(1)/EP(4) were over-expressed in the colorectal tumor tissue. K-ras induces HT29 cells proliferation through the expressions of COX-2, EP1/EP4, pAkt, GSK3beta and increases Tcf transcriptional factor activation. Additionally, Ras protein was suppressed when treated with EP(4) inhibitor in Ras-HT29 cell. In cell cycle assay, K-ras mutation causing cell cycle S phase was prolonged with an increase in the G2/M phase ratio. In conclusion, we suggested that Ras overexpression leads to cell proliferation through activating Ras/PI3K/GSK3beta/EP(4) PGE(2) receptor signals and caused a feedback regulation of Ras by EP4 in colorectal tumor progression.