Prostaglandin E2 reduces extracellular ATP-induced migration in cultured rat microglia

Prostaglandin E2 increases the expression of cyclooxygenase-2 in cultured rat microglia

Prostaglandin E₂ (PGE₂) plays pivotal roles in controlling microglial activation with the EP₂ receptor, a PGE₂ receptor subtype. Activated microglia are often reported to increase cyclooxygenase (COX)-2 expression, followed by PGE₂ production, but it is unclear whether extracellular PGE₂ is involved in microglial PGE₂ synthesis. In the present study, we report that PGE₂ increases COX-2 protein in microglia. In a culture system, PGE₂ at 10^-6 M for 3 h increased COX-2 and microsomal PGE synthase (mPGES)-1 mRNA levels, and reduced mPGES-2, but did not affect COX-1 or cytosolic PGE synthase (cPGES) in microglia. PGE₂ at 10^-6 M for 3 h also increased the COX-2 protein level, but did not affect COX-1, mPGES-1, mPGES-2, or cPGES. An EP₂ agonist, ONO-AE1-259-01, also increased COX-2 and mPGES-1 mRNA levels, and reduced mPGES-2, but did not affect COX-1 or cPGES, whereas an EP₁ agonist, ONO-DI-004, an EP₃ agonist, ONO-AE-248, and an EP₄ agonist, ONO-AE1-329, had no effect. Similar to PGE₂, ONO-AE1-259-01 increased the COX-2 protein level, but did not affect COX-1, mPGES-1, mPGES-2, or cPGES. In addition, the effects of PGE₂ were inhibited by an EP₂ antagonist, PF-04418948, but not by an EP₁ antagonist, ONO-8713, an EP₃ antagonist, ONO-AE3-240, or an EP₄ antagonist, ONO-AE3-208, at 10^-6 M. On the other hand, lipopolysaccharide (LPS) increased PGE₂ production, but the LPS-induced PGE₂ production was not affected by ONO-8713, PF-04418948, ONO-AE3-240, or ONO-AE3-208. These results indicate that PGE₂ increases COX-2 protein in microglia through the EP₂ receptor supporting the idea that extracellular PGE₂ has a triggering aspect for microglial activation.

Late endosomes promote microglia migration via cytosolic translocation of immature protease cathD

Organelle transport requires dynamic cytoskeleton remodeling, but whether cytoskeletal dynamics are, in turn, regulated by organelles remains elusive. Here, we demonstrate that late endosomes, a type of prelysosomal organelles, facilitate actin-cytoskeleton remodeling via cytosolic translocation of immature protease cathepsin D (cathD) during microglia migration. After cytosolic translocation, late endosome-derived cathD juxtaposes actin filaments at the leading edge of lamellipodia. Suppressing cathD expression or blocking its cytosolic translocation impairs the maintenance but not the initiation of lamellipodial extension. Moreover, immature cathD balances the activity of the actin-severing protein cofilin to maintain globular-actin (G-actin) monomer pool for local actin recycling. Our study identifies cathD as a key lysosomal molecule that unconventionally contributes to actin cytoskeleton remodeling via cytosolic translocation during adenosine triphosphate-evoked microglia migration.

AH6809 decreases production of inflammatory mediators by PGE2 - EP2 - cAMP signaling pathway in an experimentally induced pure cerebral concussion in rats

Increasing evidence suggests that PGE₂ metabolic pathway is involved in pathological changes of the secondary brain injury after traumatic brain injury. However, the underlying mechanisms, in particular, the correlation between various key enzymes and the brain injury, has remained to be fully explored. More specifically, it remains to be ascertained whether AH6809 (an EP2 receptor antagonist) would interfere with the downstream of the PGE₂, regulate the inflammatory mediators and improve neuronal damage in the hippocampus by PGE₂ - EP2 - cAMP signaling pathway. The expression and pathological changes of cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), microsomal prostaglandin-E synthase-1 (mPGES-1), E-prostanoid receptor 2 (EP2), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and inducible nitricoxide synthase (iNOS) in the CA1 area of hippocampus were evaluated by immunohistochemistry, Western blot and RT-PCR after pure cerebral concussion (PCC) induced by a metal pendulum closed brain injury in rats followed by AH6809 treatment. The morphology and number of neurons in CA1 region were analyzed by cresyl violet staining. The concentration of prostaglandin E₂ (PGE₂) and cyclic adenosine monophosphate (cAMP) was assayed by ELISA. Many neurons in hippocampal CA1 area appeared to undergo necrosis and the number of neurons was concomitantly reduced after PCC injury. With the passage of time, the protein and mRNA expression of various key enzymes including COX-1, COX-2 and mPGES-1, EP2 receptor, and inflammatory mediators including TNF-α, IL-1β and iNOS was increased; meanwhile, the concentration of PGE₂ and cAMP was enhanced. After PCC injury given AH6809 intervention, injury of neurons in hippocampal CA1 area was attenuated. The protein and mRNA expression of COX-1, COX-2, mPGES-1, EP2, TNF-α, IL-1β and iNOS was decreased, this was coupled with reduction of PGE₂ and cAMP. The results suggest that PGE₂ metabolic pathway is involved in secondary pathological changes of PCC. AH6809 improves the recovery of injured neurons in the hippocampal CA1 area and downregulates the inflammatory mediators by PGE₂ - EP2 - cAMP signaling pathway.

Prostaglandin E2 potentiates interferon-γ-induced nitric oxide production in cultured rat microglia

Prostaglandin E₂ (PGE₂ ) plays crucial roles in managing microglial activation through the prostanoid EP₂ receptor, a PGE₂ receptor subtype. In this study, we report that PGE₂ enhances interferon-γ (IFN-γ)-induced nitric oxide production in microglia. IFN-γ increased the release of nitrite, a metabolite of nitric oxide, which was augmented by PGE₂ , although PGE₂ by itself slightly affects nitrite release. The potentiating effect of PGE₂ was positively associated with increased expression of inducible nitric oxide synthase. In contrast to nitrite release induced by IFN-γ, lipopolysaccharide-induced nitrite release was not affected by PGE₂ . An EP₂ agonist, ONO-AE1-259-01 also augmented IFN-γ-induced nitrite release, while an EP₁ agonist, ONO-DI-004, an EP₃ agonist, ONO-AE-248, or an EP₄ agonist, ONO-AE1-329, did not. In addition, the potentiating effect of PGE₂ was inhibited by an EP₂ antagonist, PF-04418948, but not by an EP₁ antagonist, ONO-8713, an EP₃ antagonist, ONO-AE3-240, or an EP₄ antagonist, ONO-AE3-208, at 10^-6  M. Among the EP agonists, ONO-AE1-259-01 alone was able to accumulate cyclic adenosine monophosphate (AMP), and among the EP antagonists, PF-04418948 was the only one able to inhibit PGE₂ -increased intracellular cyclic AMP accumulation. On the other hand, IFN-γ promoted phosphorylation of signal transducer and activator of transcription 1, which was not affected by PGE₂ . Furthermore, other prostanoid receptor agonists, PGD₂ , PGF_2α , iloprost, and U-46119, slightly affected IFN-γ-induced nitrite release. These results indicate that PGE₂ potentiates IFN-γ-induced nitric oxide production in microglia through the EP₂ receptor, which may shed light on one of the pro-inflammatory aspects of PGE₂ .

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.

Prostaglandin receptor EP2 in the crosshairs of anti-inflammation, anti-cancer, and neuroprotection

Modulation of a specific prostanoid synthase or receptor provides therapeutic alternatives to nonsteroidal anti-inflammatory drugs (NSAIDs) for treating pathological conditions governed by cyclooxygenase-2 (COX-2 or PTGS2). Among the COX-2 downstream signaling pathways, the prostaglandin E2 (PGE2) receptor EP2 subtype (PTGER2) is emerging as a crucial mediator of many physiological and pathological events. Genetic ablation strategies and recent advances in chemical biology provide tools for a better understanding of EP2 signaling. In the brain, the EP2 receptor modulates some beneficial effects, including neuroprotection, in acute models of excitotoxicity, neuroplasticity, and spatial learning via cAMP-PKA signaling. Conversely, EP2 activation accentuates chronic inflammation mainly through the cAMP-Epac pathway, likely contributing to delayed neurotoxicity. EP2 receptor activation also engages β-arrestin in a G-protein-independent pathway that promotes tumor cell growth and migration. Understanding the conditions under which multiple EP2 signaling pathways are engaged might suggest novel therapeutic strategies to target this key inflammatory prostaglandin receptor.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

A novel role of prostaglandin E2 in neuropathic pain: blockade of microglial migration in the spinal cord

Neuropathic pain produced by damage to or dysfunction of the nervous system is a common and severely disabling state that affects millions of people worldwide. Recent evidence indicates that activated microglia are key cellular intermediaries in the pathogenesis of neuropathic pain and that ATP serves as the mediator. However, the in vivo mechanism underlying the retention of activated microglia in the injured region has not yet been completely elucidated. Prostaglandin E(2) (PGE(2)) is the principal proinflammatory prostanoid and plays versatile roles by acting via four PGE receptor subtypes, EP1-EP4. In the present study, we investigated the role of PGE(2) in spinal microglial activation in relation to neuropathic pain by using genetic and pharmacological methods. Mice deficient in microsomal prostaglandin E synthase-1 impaired the activation of microglia and the NMDA-nitric oxide (NO) cascade in spinal neurons in the dorsal horn and did not exhibit mechanical allodynia after peripheral nerve injury. The intrathecal injection of indomethacin, a nonsteroidal anti-inflammatory drug, ONO-8713, a selective EP1 antagonist, or 7-nitroindole, a neuronal NO synthase inhibitor, attenuated mechanical allodynia and the increase in activated microglia observed in the established neuropathic-pain state. We further demonstrated that ATP-induced microglial migration was blocked in vitro by PGE(2) via EP2 and by S-nitrosoglutathione, an NO donor. Taken together, the present study suggests that PGE(2) participated in the maintenance of neuropathic pain in vivo not only by activating spinal neurons, but also by retaining microglia in the central terminals of primary afferent fibers via EP2 subtype and via EP1-mediated NO production.

Long-lasting post-mortem activity of spinal microglia in situ in mice

As CNS macrophages, microglia show a high spontaneous motility of their processes, continuously surveying their microenvironment. Upon CNS injury, microglia react by immediate cellular polarization and process extension toward the lesion site as well as by subsequent amoeboid lesion-directed migration and phagocytosis. To determine the ability of microglia to fulfill their role within distinctively lesioned tissue in the absence of life support, we investigated microglial activity and responsiveness to laser-induced axonal injuries in the spinal dorsal columns in situ after cardiac and respiratory arrest, i.e., post-mortem, in the progressively degrading nervous tissue. For this purpose, we used time-lapse two-photon laser scanning microscopy in double transgenic mice expressing enhanced green fluorescent protein in microglia and enhanced yellow fluorescent protein in projection neurons. Depending on the premortal condition of the animal, microglial activity and responsiveness remain for up to5-10 hr post-mortem. Thereby, the continuously decreasing glial reaction is independent of oxygen and glucose supply but requires residual ATP, suggesting a parasitic form of energy, such as a transmembrane uptake of ATP released from injured nervous tissue. Even though initially microglia are able to detect axonal injury after disruption of the blood supply, the later aspects of glial reaction, for example amoeboid conversion and migration, are absent post- mortem, corresponding to the failure of microglia to prevent secondary damage after injury of nervous tissue.

Prostaglandin E2 reduces amyloid beta-induced phagocytosis in cultured rat microglia

Treatment with amyloid beta(1-42) (Abeta(1-42)) at 1microM for 60min increased phagocytosis of latex beads by cultured rat microglia. This increase was reduced dose-dependently by prostaglandin E(2) (PGE(2)), but PGD(2), PGF(2alpha), iloprost, or U-46619 had no effects. PGE(2) also reduced the phagocytosis of fluorescent-labeled Abeta(1-42). Abeta(1-42)-induced phagocytosis was reduced by butaprost but not by 17-phenyl trinor PGE(2), sulprostone, or PGE(1) alcohol. The reduction effect of PGE(2) on phagocytosis was reversed by AH6809, an E-prostanoid receptor 2 (EP2) antagonist, which inhibited cyclic adenosine monophosphate (AMP) accumulation induced by PGE(2). Butaprost, but not 17-phenyl trinor PGE(2), sulprostone, or PGE(1) alcohol increased intracellular cyclic AMP accumulation. In western blotting analysis, EP2-like immunoreactivity was detected in the crude membrane fraction of microglia. On the other hand, Abeta(1-42)-induced phagocytosis was not affected by SC-560, a cyclooxygenase-1 (COX-1) inhibitor, NS-398, a COX-2 inhibitor, or ibuprofen, a non-specific COX inhibitor. Abeta(1-42) or PGE(2) had little effect on the expression levels of COX-1 or COX-2. These results indicate that Abeta(1-42)-induced microglial phagocytosis is reduced by PGE(2) through EP2.

Expression of cyclooxygenase-1/-2, microsomal prostaglandin-E synthase-1 and E-prostanoid receptor 2 and regulation of inflammatory mediators by PGE(2) in the amoeboid microglia in hypoxic postnatal rats and murine BV-2 cells

This study aimed to investigate the effect of hypoxia on the expression of cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), microsomal prostaglandin-E synthase (mPGES-1), E-prostanoid receptor 2 (EP2) in microglia; and the roles of EP2-cyclic adenosine monophosphate (cAMP) signaling pathway in the prostaglandin E(2) (PGE(2)) regulation of inflammatory mediators released by hypoxic BV-2 cells. Immunoexpression of COX-1, COX-2, mPGES-1 and EP2 was localized in the amoeboid microglial cells (AMC), a nascent brain macrophage in the developing brain, as confirmed by double labeling with OX-42 and lectin, specific markers of microglia. AMC emitted a more intense immunofluorescence in hypoxic rats when compared with the matching controls. In postnatal rats subjected to hypoxia, mRNA and protein expression levels of COX-1, COX-2 and mPGES-1 along with tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), inducible nitric-oxide synthase (iNOS) and PGE(2) product in the callosal tissue were significantly increased. The results were shared in the BV-2 cells except for COX-1 mRNA and protein whose levels remained unaltered. Interestingly, treatment with EP2 antagonist AH-6809 resulted in suppression of hypoxia induced EP2, IL-1beta and iNOS mRNA and protein expression, TNF-alpha protein expression and intracellular cAMP level in BV-2 cells. It is suggested that PGE(2) may regulate above inflammatory mediators in the activated microglia via EP2-cAMP signaling pathway in hypoxic conditions.