Prostaglandin EP1 receptor contributes to excitotoxicity and focal ischemic brain damage

Arachidonic acid metabolism in health and disease

Arachidonic acid (AA), an n-6 essential fatty acid, is a major component of mammalian cells and can be released by phospholipase A2. Accumulating evidence indicates that AA plays essential biochemical roles, as it is the direct precursor of bioactive lipid metabolites of eicosanoids such as prostaglandins, leukotrienes, and epoxyeicosatrienoic acid obtained from three distinct enzymatic metabolic pathways: the cyclooxygenase pathway, lipoxygenase pathway, and cytochrome P450 pathway. AA metabolism is involved not only in cell differentiation, tissue development, and organ function but also in the progression of diseases, such as hepatic fibrosis, neurodegeneration, obesity, diabetes, and cancers. These eicosanoids are generally considered proinflammatory molecules, as they can trigger oxidative stress and stimulate the immune response. Therefore, interventions in AA metabolic pathways are effective ways to manage inflammatory-related diseases in the clinic. Currently, inhibitors targeting enzymes related to AA metabolic pathways are an important area of drug discovery. Moreover, many advances have also been made in clinical studies of AA metabolic inhibitors in combination with chemotherapy and immunotherapy. Herein, we review the discovery of AA and focus on AA metabolism in relation to health and diseases. Furthermore, inhibitors targeting AA metabolism are summarized, and potential clinical applications are discussed.

Cross-talk between bioactive lipid mediators and the unfolded protein response in ischemic stroke

Ischemic cerebral stroke is a severe medical condition that affects about 15 million people every year and is the second leading cause of death and disability globally. Ischemic stroke results in neuronal cell death and neurological impairment. Current therapies may not adequately address the deleterious metabolic changes and may increase neurological damage. Oxygen and nutrient depletion along with the tissue damage result in endoplasmic reticulum (ER) stress, including the Unfolded Protein Response (UPR), and neuroinflammation in the affected area and cause cell death in the lesion core. The spatio-temporal production of lipid mediators, either pro-inflammatory or pro-resolving, decides the course and outcome of stroke. The modulation of the UPR as well as the resolution of inflammation promotes post-stroke cellular viability and neuroprotection. However, studies about the interplay between the UPR and bioactive lipid mediators remain elusive and this review gives insights about the crosstalk between lipid mediators and the UPR in ischemic stroke. Overall, the treatment of ischemic stroke is often inadequate due to lack of effective drugs, thus, this review will provide novel therapeutical strategies that could promote the functional recovery from ischemic stroke.

EP1 receptor: Devil in emperors coat

EP1 receptor belongs to prostanoid receptors and is activated by prostaglandin E2. The receptor performs contrasting functions in central nervous system (CNS) and other tissues. Although the receptor is neurotoxic and proapoptotic in CNS, it has also been reported to act in an antiapoptotic manner by modulating cell survival, proliferation, invasion, and migration in different types of cancers. The receptor mediates its neurotoxic effects by increasing cytosolic Ca2+ levels, leading to the activation of its downstream target, protein kinase C, in different neurological disorders including Alzheimer's disease, Parkinson's disease, stroke, amyotrophic lateral sclerosis, and epilepsy. Antagonists ONO-8713, SC51089, and SC51322 against EP1 receptor ameliorate the neurotoxic effect by attenuating the neuroinflammation. The receptor also shows increased expression in different types of cancers and has been found to activate different signaling pathways, which lead to the development, progression, and metastasis of different cancers. The receptor stimulates the cell survival pathway by phosphorylating the AKT and PTEN (phosphatase and tensin homolog deleted on chromosome 10) signaling pathways. Although there are limited studies about this receptor and not a single clinical trial has been targeting the EP1 receptor for different neurological disorders or cancer, the receptor is appearing as a potential candidate for therapeutic targets. The aim of this article is to review the recent progress in understanding the pathogenic roles of EP1 receptors in different pathological conditions.

Neuroinflammatory mediators in acquired epilepsy: an update

Epilepsy is a group of chronic neurological disorders that have diverse etiologies but are commonly characterized by spontaneous seizures and behavioral comorbidities. Although the mechanisms underlying the epileptic seizures mostly remain poorly understood and the causes often can be idiopathic, a considerable portion of cases are known as acquired epilepsy. This form of epilepsy is typically associated with prior neurological insults, which lead to the initiation and progression of epileptogenesis, eventually resulting in unprovoked seizures. A convergence of evidence in the past two decades suggests that inflammation within the brain may be a major contributing factor to acquired epileptogenesis. As evidenced in mounting preclinical and human studies, neuroinflammatory processes, such as activation and proliferation of microglia and astrocytes, elevated production of pro-inflammatory cytokines and chemokines, blood-brain barrier breakdown, and upregulation of inflammatory signaling pathways, are commonly observed after seizure-precipitating events. An increased knowledge of these neuroinflammatory processes in the epileptic brain has led to a growing list of inflammatory mediators that can be leveraged as potential targets for new therapies of epilepsy and/or biomarkers that may provide valued information for the diagnosis and prognosis of the otherwise unpredictable seizures. In this review, we mainly focus on the most recent progress in understanding the roles of these inflammatory molecules in acquired epilepsy and highlight the emerging evidence supporting their candidacy as novel molecular targets for new pharmacotherapies of acquired epilepsy and the associated behavioral deficits.

Alpha-Synuclein, cyclooxygenase-2 and prostaglandins-EP2 receptors as neuroinflammatory biomarkers of autism spectrum disorders: Use of combined ROC curves to increase their diagnostic values

BACKGROUND

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impairments in social interaction and restricted and repetitive behaviors. Neuroinflammation and abnormal lipid mediators have been identified in multiple investigations as an acknowledged etiological mechanism of ASD that can be targeted for therapeutic intervention.

METHODS

In this study, multiple regression and combined receiver operating characteristic (ROC) curve analyses were used to determine the relationship between the neuroinflammatory marker α-synuclein and lipid mediator markers related to inflammation induction, such as cyclooxygenase-2 and prostaglandin-EP2 receptors, in the etiology of ASD. Additionally, the study aimed to determine the linear combination that maximizes the partial area under ROC curves for a set of markers. Forty children with ASD and 40 age- and sex-matched controls were enrolled in the study. Using ELISA, the levels of α-synuclein, cyclo-oxygenase-2, and prostaglandin-EP2 receptors were measured in the plasma of both groups. Statistical analyses using ROC curves and multiple and logistic regression models were performed.

RESULTS

A remarkable increase in the area under the curve was observed using combined ROC curve analyses. Moreover, higher specificity and sensitivity of the combined markers were reported.

CONCLUSIONS

The present study indicates that measurement of the predictive value of selected biomarkers related to neuroinflammation and lipid metabolism in children with ASD using a ROC curve analysis should lead to a better understanding of the etiological mechanism of ASD and its link with metabolism. This information may facilitate early diagnosis and intervention.

Effect of Experimental Ischemic Stroke and PGE2 EP1 Selective Antagonism in Alzheimer's Disease Mouse Models

BACKGROUND

Neuroinflammation has been recognized as an important factor in the pathogenesis of Alzheimer's disease (AD). One of the most recognized pathways in mediating neuroinflammation is the prostaglandin E2-EP1 receptor pathway.

OBJECTIVE

Here, we examined the efficacy of the selective EP1 antagonist ONO-8713 in limiting amyloid-β (Aβ), lesion volumes, and behavioral indexes in AD mouse models after ischemic stroke.

METHODS

Transgenic APP/PS1, 3xTgAD, and wildtype (WT) mice were subjected to permanent distal middle cerebral artery occlusion (pdMCAO) and sham surgeries. Functional outcomes, memory, anatomical outcomes, and Aβ concentrations were assessed 14 days after surgery.

RESULTS

pdMCAO resulted in significant deterioration in functional and anatomical outcomes in the transgenic mice compared with the WT mice. No relevant differences were observed in the behavioral tests when comparing the ONO-8713 and vehicle-treated groups. Significantly lower cavitation (p = 0.0373) and percent tissue loss (p = 0.0247) were observed in APP/PS1 + ONO-8713 mice compared with the WT + ONO-8713 mice. However, the percent tissue injury was significantly higher in APP/PS1 + ONO-8713 mice compared with the WT + ONO-8713 group (p = 0.0373). Percent tissue loss was also significantly lower in the 3xTgAD + ONO-8713 mice than in the WT + ONO-8713 mice (p = 0.0185). ONO-8713 treatment also attenuated cortical microgliosis in APP/PS1 mice as compared with the vehicle (p = 0.0079); however, no differences were observed in astrogliosis across the groups. Finally, APP/PS1 mice presented with characteristic Aβ load in the cortex while 3xTgAD mice exhibited very low Aβ levels.

CONCLUSION

In conclusion, under the experimental conditions, EP1 receptor antagonist ONO-8713 showed modest benefits in anatomical outcomes after stroke, mainly in APP/PS1 mice.

Bioactive Lipid Mediators in the Initiation and Resolution of Inflammation after Spinal Cord Injury

Neuroinflammation is a prominent feature of the response to CNS trauma. It is also an important hallmark of various neurodegenerative diseases in which inflammation contributes to the progression of pathology. Inflammation in the CNS can contribute to secondary damage and is therefore an excellent therapeutic target for a range of neurological conditions. Inflammation in the nervous system is complex and varies in its fine details in different conditions. It involves a wide variety of secreted factors such as chemokines and cytokines, cell adhesion molecules, and different cell types that include resident cell of the CNS, as well as immune cells recruited from the peripheral circulation. Added to this complexity is the fact that some aspects of inflammation are beneficial, while other aspects can induce secondary damage in the acute, subacute and chronic phases. Understanding these aspects of the inflammatory profile is essential for developing effective therapies. Bioactive lipids constitute a large group of molecules that modulate the initiation and the resolution of inflammation. Dysregulation of these bioactive lipid pathways can lead to excessive acute inflammation, and failure to resolve this by specialized pro-resolution lipid mediators can lead to the development of chronic inflammation. The focus of this review is to discuss the effects of bioactive lipids in spinal cord trauma and their potential for therapies.

Arachidonic Acid Derivatives and Neuroinflammation

Neuroinflammation is characterized by dysregulated inflammatory responses localized within the brain and spinal cord. Neuroinflammation plays a pivotal role in the onset of several neurodegenerative disorders and is considered a typical feature of these disorders. Microglia perform primary immune surveillance and macrophage-like activities within the central nervous system. Activated microglia are predominant players in the central nervous system response to damage related to stroke, trauma, and infection. Moreover, microglial activation per se leads to a proinflammatory response and oxidative stress. During the release of cytokines and chemokines, cyclooxygenases and phospholipase A2 are stimulated. Elevated levels of these compounds play a significant role in immune cell recruitment into the brain. Cyclic phospholipase A2 plays a fundamental role in the production of prostaglandins by releasing arachidonic acid. In turn, arachidonic acid is biotransformed through different routes into several mediators that are endowed with pivotal roles in the regulation of inflammatory processes. Some experimental models of neuroinflammation exhibit an increase in cyclic phospholipase A2, leukotrienes, and prostaglandins such as prostaglandin E2, prostaglandin D2, or prostacyclin. However, findings on the role of the prostacyclin receptors have revealed that their signalling suppresses Th2-mediated inflammatory responses. In addition, other in vitro evidence suggests that prostaglandin E2 may inhibit the production of some inflammatory cytokines, attenuating inflammatory events such as mast cell degranulation or inflammatory leukotriene production. Based on these conflicting experimental data, the role of arachidonic acid derivatives in neuroinflammation remains a challenging issue.

Small molecules targeting cyclooxygenase/prostanoid cascade in experimental brain ischemia: Do they translate?

Acute brain ischemia accounts for most of stroke cases and constitutes a leading cause of deaths among adults and permanent disabilities in survivors. Currently, the intravenous thrombolysis is the only available medication for ischemic stroke; mechanical thrombectomy is an emerging alternative treatment for occlusion of large arteries and has shown some promise in selected subsets of patients. However, the overall narrow treatment window and potential risks largely limit the patient eligibility. New druggable targets are needed to innovate the treatment of brain ischemia. As the rate-limiting enzyme in the biosyntheses of prostanoids, cyclooxygenase (COX), particularly the inducible isoform COX-2, has long been implicated in mechanisms of acute stroke-induced brain injury and inflammation. However, the notion of therapeutically targeting COX has been diminished over the past two decades due to significant complications of the cardiovascular and cerebrovascular systems caused by long-term use of COX-2 inhibitor drugs. New treatment strategies targeting the downstream prostanoid signaling receptors regulating the deleterious effects of COX cascade have been proposed. As such, a large number of selective small molecules that negatively or positively modulate these important inflammatory regulators have been evaluated for neuroprotection and other beneficial effects in various animal models of brain ischemia. These timely preclinical studies, though not yet led to clinical innovation, provided new insights into the regulation of inflammatory reactions in the ischemic brain and could guide drug discovery efforts aiming for novel adjunctive strategies, along with current reperfusion therapy, to treat acute brain ischemia with higher specificity and longer therapeutic window.

Prostaglandin E receptors as targets for ischemic stroke: Novel evidence and molecular mechanisms of efficacy

Over the past two decades the interest has waned in therapeutically targeting cyclooxygenase-2 (COX-2) due to growing concerns over the potential cardiovascular and cerebrovascular toxicities of the long-term use of COX-2 inhibitors. Attention thus has recently been shifted downstream to the prostaglandin signaling pathways for new druggable anti-inflammatory targets aiming for higher therapeutic specificity. Prostaglandin E2 (PGE₂) is robustly synthesized in the ischemic cortex by quickly induced COX-2 and microsomal prostaglandin E synthase-1 (mPGES-1) following cerebral ischemia. The elevated PGE₂, in turn, divergently regulates the excitotoxic injury and neuroinflammation by acting on four membrane-bound G protein-coupled receptors (GPCRs), namely, EP1-EP4. Markedly, all four EP receptors have been implicated in the excitotoxicity-associated brain inflammation and injury in animal models of cerebral ischemia. However promising, these preclinical studies have not yet led to a clinical trial targeting any PGE₂ receptor for ischemic stroke. The goal of this article is to review the recent progress in understanding the pathogenic roles of PGE₂ in cerebral ischemia as well as to provide new mechanistic insights into the PGE₂ signaling via these four GPCRs in neuronal excitotoxicity and inflammation. We also discuss the feasibility of targeting EP1-EP4 receptors as an emerging delayed treatment, together with the first-line reperfusion strategy, to manage acute ischemic stroke with potentially extended window as well as improved specificity.

International Union of Basic and Clinical Pharmacology. CIX. Differences and Similarities between Human and Rodent Prostaglandin E2 Receptors (EP1-4) and Prostacyclin Receptor (IP): Specific Roles in Pathophysiologic Conditions

Prostaglandins are derived from arachidonic acid metabolism through cyclooxygenase activities. Among prostaglandins (PGs), prostacyclin (PGI2) and PGE2 are strongly involved in the regulation of homeostasis and main physiologic functions. In addition, the synthesis of these two prostaglandins is significantly increased during inflammation. PGI2 and PGE2 exert their biologic actions by binding to their respective receptors, namely prostacyclin receptor (IP) and prostaglandin E2 receptor (EP) 1-4, which belong to the family of G-protein-coupled receptors. IP and EP1-4 receptors are widely distributed in the body and thus play various physiologic and pathophysiologic roles. In this review, we discuss the recent advances in studies using pharmacological approaches, genetically modified animals, and genome-wide association studies regarding the roles of IP and EP1-4 receptors in the immune, cardiovascular, nervous, gastrointestinal, respiratory, genitourinary, and musculoskeletal systems. In particular, we highlight similarities and differences between human and rodents in terms of the specific roles of IP and EP1-4 receptors and their downstream signaling pathways, functions, and activities for each biologic system. We also highlight the potential novel therapeutic benefit of targeting IP and EP1-4 receptors in several diseases based on the scientific advances, animal models, and human studies. SIGNIFICANCE STATEMENT: In this review, we present an update of the pathophysiologic role of the prostacyclin receptor, prostaglandin E2 receptor (EP) 1, EP2, EP3, and EP4 receptors when activated by the two main prostaglandins, namely prostacyclin and prostaglandin E2, produced during inflammatory conditions in human and rodents. In addition, this comparison of the published results in each tissue and/or pathology should facilitate the choice of the most appropriate model for the future studies.

Role of the PGE2 receptor subtypes EP1, EP2, and EP3 in repetitive traumatic brain injury

Aims

The goal was to explore the signaling pathways of PGE₂ to investigate therapeutic effects against secondary injuries following TBI.

Methods

Young (4.9 ± 1.0 months) and aged (20.4 ± 1.4 months) male wild type (WT) C57BL/6 and PGE₂ EP1, 2, and 3 receptor knockout mice were selected to either receive sham or repetitive concussive head injury. Immunohistochemistry protocols with Iba1 and GFAP were performed to evaluate microgliosis and astrogliosis in the hippocampus, two critical components of neuroinflammation. Passive avoidance test measured memory function associated with the hippocampus.

Results

No differences in hippocampal microgliosis were found when aged EP2^−/− and EP3^−/− mice were compared with aged WT mice. However, the aged EP1^−/− mice had 69.2 ± 7.5% less hippocampal microgliosis in the contralateral hemisphere compared with WT aged mice. Compared with aged EP2^−/− and EP3^−/−, EP1^−/− aged mice had 78.9 ± 5.1% and 74.7 ± 6.2% less hippocampal microgliosis in the contralateral hemisphere. Within the EP1^−/− mice, aged mice had 90.7 ± 2.7% and 81.1 ± 5.6% less hippocampal microgliosis compared with EP1^−/− young mice in the contralateral and ipsilateral hemispheres, respectively. No differences were noted in all groups for astrogliosis. There was a significant difference in latency time within EP1^−/−, EP2^−/−, and EP3^−/− on day 1 and day 2 in aged and young mice.

Conclusion

These findings demonstrate that the PGE₂ EP receptors may be potential therapeutic targets to treat repetitive concussions and other acute brain injuries.

Neuroinflammation: friend and foe for ischemic stroke

Stroke, the third leading cause of death and disability worldwide, is undergoing a change in perspective with the emergence of new ideas on neurodegeneration. The concept that stroke is a disorder solely of blood vessels has been expanded to include the effects of a detrimental interaction between glia, neurons, vascular cells, and matrix components, which is collectively referred to as the neurovascular unit. Following the acute stroke, the majority of which are ischemic, there is secondary neuroinflammation that both promotes further injury, resulting in cell death, but conversely plays a beneficial role, by promoting recovery. The proinflammatory signals from immune mediators rapidly activate resident cells and influence infiltration of a wide range of inflammatory cells (neutrophils, monocytes/macrophages, different subtypes of T cells, and other inflammatory cells) into the ischemic region exacerbating brain damage. In this review, we discuss how neuroinflammation has both beneficial as well as detrimental roles and recent therapeutic strategies to combat pathological responses. Here, we also focus on time-dependent entry of immune cells to the ischemic area and the impact of other pathological mediators, including oxidative stress, excitotoxicity, matrix metalloproteinases (MMPs), high-mobility group box 1 (HMGB1), arachidonic acid metabolites, mitogen-activated protein kinase (MAPK), and post-translational modifications that could potentially perpetuate ischemic brain damage after the acute injury. Understanding the time-dependent role of inflammatory factors could help in developing new diagnostic, prognostic, and therapeutic neuroprotective strategies for post-stroke inflammation.

Isosteviol sodium injection improves outcomes by modulating TLRs/NF-κB-dependent inflammatory responses following experimental traumatic brain injury in rats

Supplemental Digital Content is available in the text.

Previous studies have shown that isosteviol sodium (STVNa) protects against permanent cerebral ischemia injury by inhibition of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB)-mediated inflammatory responses. Overwhelming evidence shows that toll-like receptors (TLRs) are the upstream regulators of NF-κB. On the basis of the similarity of the pathology caused by traumatic brain injury (TBI) and stroke, we speculated that STVNa may have a therapeutic effect against TBI through regulation of the TLRs/NF-κB signaling-mediated inflammatory response. Thus, we studied the potential therapeutic effects of STVNa and the underlying mechanisms. Male rats, subjected to controlled cortical impact (CCI) injury, were injected intraperitoneally with STVNa (5, 10, 20, 40, and 80 mg/kg, daily for 3 or 7 days) after trauma. Neurobehavioral scores, relative numbers of cortical lesions, and histology were examined. We also measured the mRNA and protein expression levels of TLRs/NF-κB signaling pathway-related genes including TLR2, TLR4, and NF-κB by quantitative real-time-PCR and western blotting, respectively, and concentrations of tumor necrosis factor-α and interleukin-1β by an enzyme-linked immunosorbent assay. The results indicated that STVNa (20 mg/kg) showed significant neuroprotective effects 3 and 7 days after TBI, including the reduction of cortical lesions, improvement of the neurological severity score, significantly increased number of restored neurons, decreased number of astrocytes, and lower concentrations of tumor necrosis factor-α and interleukin-1β. Results from quantitative real-time-PCR and western blotting also show that the mRNA and protein expression levels of TLR2, TLR4, and NF-κB were significantly lower in STVNa-treated rats compared with the vehicle-treated rats. The administration of STVNa attenuates the TLR/NF-κB signaling pathway-mediated inflammatory responses in the injured rat brain, and this may be the mechanism by which STVNa improves the outcome following TBI.

Bioactive Lipids in Inflammation After Central Nervous System Injury

Despite the progress made over the last decades to understand the mechanisms underlying tissue damage and neurological deficits after neurotrauma, there are currently no effective treatments in the clinic. It is well accepted that the inflammatory response in the CNS after injury exacerbates tissue loss and functional impairments. Unfortunately, the use of potent anti-inflammatory drugs, such as methylprednisolone, fails to promote therapeutic recovery and also gives rise to several undesirable side effects related to immunosuppression. The injury-induced inflammatory response is complex, and understanding the mechanisms that regulate this inflammation is therefore crucial in the quest to develop effective treatments. Bioactive lipids have emerged as potent molecules in controlling the initiation, coordination, and resolution of inflammation and in promoting tissue repair and recovery of homeostasis. These bioactive lipids are produced by cells involved in the inflammatory response, and their defective synthesis leads to persistent chronic inflammation, tissue damage, and fibrosis. The present chapter discusses recent evidence for the role of some of these bioactive lipids, in particular, eicosanoid and pro-resolving lipid mediators, in the regulation of inflammation after neurotrauma and highlights the therapeutic potential of some of these lipids in enhancing neurological outcomes after CNS injuries.

Genetic Deletion of PGF2α-FP Receptor Exacerbates Brain Injury Following Experimental Intracerebral Hemorrhage

Background: The release of inflammatory molecules such as prostaglandins (e.g., PGF_2α) is associated with brain damage following an intracerebral hemorrhagic (ICH) stroke; however, the role of PGF_2α and its cognate FP receptor in ICH remains unclear. This study focused on investigating the role of the FP receptor as a target for novel neuroprotective drugs in a preclinical model of ICH, aiming to investigate the contribution of the PGF_2α-FP axis in modulating functional recovery and anatomical outcomes following ICH.

Results: Neurological deficit scores in FP^−/− mice were significantly higher compared to WT mice 72 h after ICH (6.1 ± 0.7 vs. 3.1 ± 0.8; P < 0.05). Assessing motor skills, the total time mice stayed on the rotating rod was significantly less in FP^−/−mice compared to WT mice 24 h after ICH (27.0 ± 7.5 vs. 52.4 ± 11.2 s; P < 0.05). Using grip strength to quantify forepaw strength, results showed that the FP^−/− mice had significantly less strength compared to WT mice 72 h after ICH (96.4 ± 17.0 vs. 129.6 ± 5.9 g; P < 0.01). In addition to the behavioral outcomes, histopathological measurements were made. In Cresyl violet stained brain sections, the FP^−/− mice showed a significantly larger lesion volume compared to the WT (15.0 ± 2.2 vs. 3.2 ± 1.7 mm³; P < 0.05 mice.) To estimate the presence of ferric iron in the peri-hematoma area, Perls' staining was performed, which revealed that FP^−/− mice had significantly greater staining than the WT mice (186.3 ± 34.4% vs. 86.9 ± 13.0% total positive pixel counts, P < 0.05). Immunoreactivity experiments on brain sections from FP^−/− and WT mice post-ICH were performed to monitor changes in microgliosis and astrogliosis using antibodies against Iba1 and GFAP respectively. These experiments showed that FP^−/− mice had a trend toward greater astrogliosis than WT mice post-ICH.

Conclusion: We showed that deletion of the PGF_2α FP receptor exacerbates behavioral impairments and increases lesion volumes following ICH compared to WT-matched controls.Detailed mechanisms responsible for these novel results are actively being pursued.

Expression of NR1 and apoptosis levels in the hippocampal cells of mice treated with MK‑801

The aim of the present study was to investigate the characteristics of N‑methyl‑D‑aspartate receptor R1 (NR1) expression and apoptosis in the nerve cells of the hippocampus in schizophrenia‑like mice. C57BL/6 mice were randomly allocated to the following groups: i) Blank group; ii) MK‑801 group; iii) MK‑801+NMDA group, according to body weight. The NMDAR antagonist, MK‑801 (0.6 mg/kg/d) was intraperitoneally injected daily for 14 days to induce a schizophrenia‑like phenotype mouse model, and the effect of the NMDA injection via the lateral ventricle was observed. The results demonstrated that the number of NR1 positive cells in the MK‑801 group increased in the CA1 and DG regions, indicating that NMDA may reverse this change. The level of damage decreased in the MK‑801 treated group when compared with the blank group in the CA3 region. The protein expression of NR1 increased however, at the mRNA expression level, NR1 was lower in the MK‑801 treated group when compared to the blank group; NMDA also reversed this change. In addition, early and total apoptosis detected in the hippocampal nerve cells was significantly increased in the MK‑801 group when compared with the blank group, which was reversible following treatment with NMDA. These results indicated that NMDA may regulate the expression of NR1 and suppress apoptosis in hippocampal nerve cells in schizophrenia‑like mice. Thus, NR1 may be a promising therapeutic target for the treatment of schizophrenia.

EP2 receptor agonist ONO-AE1-259-01 attenuates pentylenetetrazole- and pilocarpine-induced seizures but causes hippocampal neurotoxicity

Epilepsy is a common and devastating neurological disease affecting more than 50 million people worldwide. Accumulating experimental and clinical evidence suggests that inflammatory pathways contribute to the development of seizures in various forms of epilepsy. In this context, while the activation of the PGE₂ EP2 receptor causes early neuroprotective and late neurotoxic effects, the role of EP2 receptor in seizures remains unclear. We investigated whether the systemic administration of the highly selective EP2 agonist ONO-AE1-259-01 prevented acute pentylenetetrazole (PTZ)- and pilocarpine-induced seizures. The effect of ONO-AE1-259-01 on cell death in the hippocampal formation of adult male mice seven days after pilocarpine-induced status epilepticus (SE) was also evaluated. ONO-AE1-259-01 (10μg/kg, s.c.) attenuated PTZ- and pilocarpine-induced seizures, evidenced by the increased latency to seizures, decreased number and duration of seizures episodes and decreased mean amplitude of electrographic seizures. ONO-AE1-259-01 and pilocarpine alone significantly increased the number of pyknotic cells per se in all hippocampal subfields. The EP2 agonist also additively increased pilocarpine-induced pyknosis in the pyramidal cell layer of CA1 but reduced pilocarpine-induced pyknosis in the granule cell layer of the dentate gyrus (DG). Although the systemic administration of ONO-AE1-259-01 caused a significant anticonvulsant effect in our assays, this EP2 agonist caused extensive cell death. These findings limit the likelihood of EP2 receptor agonists being considered as novel potential anticonvulsant drugs.

Ischemia-responsive protein 94 is a key mediator of ischemic neuronal injury-induced microglial activation

Neuroinflammation, especially activation of microglia, the key immune cells in the brain, has been proposed to contribute to the pathogenesis of ischemic stroke. However, the dynamics and the potential mediators of microglial activation following ischemic neuronal injury are not well understood. In this study, using oxygen/glucose deprivation and reoxygenation with neuronal and microglial cell cultures as an in vitro model of ischemic neuronal injury, we set out to identify neuronal factors released from injured neurons that are capable of inducing microglial activation. Conditioned media (CM) from hippocampal and cortical neurons exposed to oxygen/glucose deprivation and reoxygenation induced significant activation of microglial cells as well as primary microglia, evidenced by up-regulation of inducible nitric oxide synthase, increased production of nitrite and reactive oxygen species, and increased expression of microglial markers. Mechanistically, neuronal ischemia-responsive protein 94 (Irp94) was a key contributor to microglial activation since significant increase in Irp94 was detected in the neuronal CM following ischemic insult and immunodepletion of Irp94 rendered ischemic neuronal CM ineffective in inducing microglial activation. Ischemic insult-augmented oxidative stress was a major facilitator of neuronal Irp94 release, and pharmacological inhibition of NADPH oxidase significantly reduced the ischemic injury-induced neuronal reactive oxygen species production and Irp94 release. Taken together, these results indicate that neuronal Irp94 may play a pivotal role in the propagation of ischemic neuronal damage. Continued studies may help identify Irp94 and/or related proteins as potential therapeutic targets and/or diagnostic/prognostic biomarkers for managing ischemia-associated brain disorders.

White Matter Tract Integrity in Alzheimer's Disease vs. Late Onset Bipolar Disorder and Its Correlation with Systemic Inflammation and Oxidative Stress Biomarkers

Background: Late Onset Bipolar Disorder (LOBD) is the development of Bipolar Disorder (BD) at an age above 50 years old. It is often difficult to differentiate from other aging dementias, such as Alzheimer's Disease (AD), because they share cognitive and behavioral impairment symptoms.

Objectives: We look for WM tract voxel clusters showing significant differences when comparing of AD vs. LOBD, and its correlations with systemic blood plasma biomarkers (inflammatory, neurotrophic factors, and oxidative stress).

Materials: A sample of healthy controls (HC) (n = 19), AD patients (n = 35), and LOBD patients (n = 24) was recruited at the Alava University Hospital. Blood plasma samples were obtained at recruitment time and analyzed to extract the inflammatory, oxidative stress, and neurotrophic factors. Several modalities of MRI were acquired for each subject,

Methods: Fractional anisotropy (FA) coefficients are obtained from diffusion weighted imaging (DWI). Tract based spatial statistics (TBSS) finds FA skeleton clusters of WM tract voxels showing significant differences for all possible contrasts between HC, AD, and LOBD. An ANOVA F-test over all contrasts is carried out. Results of F-test are used to mask TBSS detected clusters for the AD > LOBD and LOBD > AD contrast to select the image clusters used for correlation analysis. Finally, Pearson's correlation coefficients between FA values at cluster sites and systemic blood plasma biomarker values are computed.

Results: The TBSS contrasts with by ANOVA F-test has identified strongly significant clusters in the forceps minor, inferior longitudinal fasciculus, inferior fronto-occipital fasciculus, and cingulum gyrus. The correlation analysis of these tract clusters found strong negative correlation of AD with the nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) blood biomarkers. Negative correlation of AD and positive correlation of LOBD with inflammation biomarker IL6 was also found.

Conclusion: TBSS voxel clusters tract atlas localizations are consistent with greater behavioral impairment and mood disorders in LOBD than in AD. Correlation analysis confirms that neurotrophic factors (i.e., NGF, BDNF) play a great role in AD while are absent in LOBD pathophysiology. Also, correlation results of IL1 and IL6 suggest stronger inflammatory effects in LOBD than in AD.

Prostaglandin E2 Produced by Alginate-Encapsulated Mesenchymal Stromal Cells Modulates the Astrocyte Inflammatory Response

Astroglia are well known for their role in propagating secondary injury following brain trauma. Modulation of this injury cascade, including inflammation, is essential to repair and recovery. Mesenchymal stromal cells (MSCs) have been demonstrated as trophic mediators in several models of secondary CNS injury, however, there has been varied success with the use of direct implantation due to a failure to persist at the injury site. To achieve sustained therapeutic benefit, we have encapsulated MSCs in alginate microspheres and evaluated the ability of these encapsulated MSCs to attenuate neuro-inflammation. In this study, astroglial cultures were administered lipopolysaccharide (LPS) to induce inflammation and immediately co-cultured with encapsulated or monolayer human MSCs. Cultures were assayed for the pro-inflammatory cytokine tumor necrosis factor alpha (TNF-α) produced by astroglia, MSC-produced prostaglandin E2, and expression of neurotrophin-associated genes. We found that encapsulated MSCs significantly reduced TNF-α produced by LPS-stimulated astrocytes, more effectively than monolayer MSCs, and this enhanced benefit commences earlier than that of monolayer MSCs. Furthermore, in support of previous findings, encapsulated MSCs constitutively produced high levels of PGE2, while monolayer MSCs required the presence of inflammatory stimuli to induce PGE2 production. The early, constitutive presence of PGE2 significantly reduced astrocyte-produced TNF-α, while delayed administration had no effect. Finally, MSC-produced PGE2 was not only capable of modulating inflammation, but appears to have an additional role in stimulating astrocyte neurotrophin production. Overall, these results support the enhanced benefit of encapsulated MSC treatment, both in modulating the inflammatory response and providing neuroprotection.

Anti-Inflammatory and Neuroprotective Effects of PGE2 EP4 Signaling in Models of Parkinson's Disease

Inflammation is a ubiquitous factor accompanying normal aging and neurodegeneration, and recent studies indicate a major contribution of inducible cyclooxygenase (COX-2) and its downstream prostaglandin signaling pathways in modulating neuroinflammatory responses and neuronal function. We have previously shown that the prostaglandin PGE₂ receptor EP4 suppresses innate immune responses in models of systemic inflammation. Here we investigated the role of the EP4 receptor in models of Parkinson's disease (PD). Systemic co-administration of the EP4 agonist ONO-AE1-329 with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) prevented loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) without significant changes in glial activation, suggesting a potent neuroprotective effect of EP4 signaling in this acute model of DA neuronal loss. Cell-specific conditional ablation of EP4 in Cd11bCre;EP4^lox/lox mice exacerbated MPTP-associated glial activation and T-cell infiltration in SNpc, consistent with anti-inflammatory functions of microglial EP4 signaling. In vitro, in primary microglia stimulated with oligomeric α-synuclein, EP4 receptor activation suppressed generation of pro-inflammatory and oxidative stress factors. Taken together, these findings suggest a dual neuroprotective and anti-inflammatory mechanism of action by the EP4 receptor in models of PD.

3,4-methylenedioxymethamphetamine increases excitability in the dentate gyrus: role of 5HT2A receptor-induced PGE2 signaling

3,4-methylenedioxymethamphetamine (MDMA) is a widely abused psychostimulant, which causes release of serotonin in various forebrain regions. Recently, we reported that MDMA increases extracellular glutamate concentrations in the dentate gyrus, via activation of 5HT2A receptors. We examined the role of prostaglandin signaling in mediating the effects of 5HT2A receptor activation on the increases in extracellular glutamate and the subsequent long-term loss of parvalbumin interneurons in the dentate gyrus caused by MDMA. Administration of MDMA into the dentate gyrus of rats increased PGE2 concentrations which was prevented by coadministration of MDL100907, a 5HT2A receptor antagonist. MDMA-induced increases in extracellular glutamate were inhibited by local administration of SC-51089, an inhibitor of the EP1 prostaglandin receptor. Systemic administration of SC-51089 during injections of MDMA prevented the decreases in parvalbumin interneurons observed 10 days later. The loss of parvalbumin immunoreactivity after MDMA exposure coincided with a decrease in paired-pulse inhibition and afterdischarge threshold in the dentate gyrus. These changes were prevented by inhibition of EP1 and 5HT2A receptors during MDMA. Additional experiments revealed an increased susceptibility to kainic acid-induced seizures in MDMA-treated rats, which could be prevented with SC51089 treatments during MDMA exposure. Overall, these findings suggest that 5HT2A receptors mediate MDMA-induced PGE2 signaling and subsequent increases in glutamate. This signaling mediates parvalbumin cell losses as well as physiologic changes in the dentate gyrus, suggesting that the lack of the inhibition provided by these neurons increases the excitability within the dentate gyrus of MDMA-treated rats. We hypothesized that the widely abused psychostimulant MDMA causes a loss of parvalbumin (PV) cells and increases excitability in the dentate gyrus. MDMA increases serotonin (5HT) release and activates 5HT2A receptors. The increased activation of 5HT2A receptors promotes the production of prostaglandin E2 (PGE2) and subsequent activation of EP1 receptors in the dentate gyrus. EP1 receptor activation leads to eventual excitotoxicity and loss of PV interneurons resulting in reduced inhibition and lowered seizure threshold resulting in increased seizure susceptibility.

Animal Models of Posttraumatic Seizures and Epilepsy

Posttraumatic epilepsy (PTE) is one of the most common and devastating complications of traumatic brain injury (TBI). Currently, the etiopathology and mechanisms of PTE are poorly understood and as a result, there is no effective treatment or means to prevent it. Antiepileptic drugs remain common preventive strategies in the management of TBI to control acute posttraumatic seizures and to prevent the development of PTE, although their efficacy in the latter case is disputed. Different strategies of PTE prophylaxis have been showing promise in preclinical models, but their translation to the clinic still remains elusive due in part to the variability of these models and the fact they do not recapitulate all complex pathologies associated with human TBI. TBI is a multifaceted disorder reflected in several potentially epileptogenic alterations in the brain, including mechanical neuronal and vascular damage, parenchymal and subarachnoid hemorrhage, subsequent toxicity caused by iron-rich hemoglobin breakdown products, and energy disruption resulting in secondary injuries, including excitotoxicity, gliosis, and neuroinflammation, often coexisting to a different degree. Several in vivo models have been developed to reproduce the acute TBI cascade of events, to reflect its anatomical pathologies, and to replicate neurological deficits. Although acute and chronic recurrent posttraumatic seizures are well-recognized phenomena in these models, there is only a limited number of studies focused on PTE. The most used mechanical TBI models with documented electroencephalographic and behavioral seizures with remote epileptogenesis include fluid percussion, controlled cortical impact, and weight-drop. This chapter describes the most popular models of PTE-induced TBI models, focusing on the controlled cortical impact and the fluid percussion injury models, the methods of behavioral and electroencephalogram seizure assessments, and other approaches to detect epileptogenic properties, and discusses their potential application for translational research.

DJ-1 mutation decreases astroglial release of inflammatory mediators

Mutations in DJ-1, reactive gliosis and concomitant inflammatory processes are implicated in the pathogenesis and progression of Parkinson's disease (PD). To study the physiological consequences of DJ-1 mutation in the context of neuroinflammatory insult, primary cortical astrocytes were isolated from DJ-1 knockout mice. Astrocytes were exposed to 1μg/mL lipopolysaccharide (LPS) for 24h following 2h pre-exposure to inhibitors of MEK (U0126), JNK (JNK inhibitor II) or p38 (SB203580). Real-time PCR was used to assess the LPS-induced expression of pro-inflammatory mediators cyclooxygenase 2 (COX2), inducible nitric oxide synthetase (NOS2), and tumor necrosis factor α (TNFα). LPS-induced expression of COX2 decreased similarly in DJ-1(+/+) and DJ-1(-/-) astrocytes in response to inhibition of p38, but was unaffected by inhibition of MEK or JNK. No significant alterations in NOS2 expression were observed in any inhibitor-treated cells. The inhibitors did not affect expression of TNFα; however, DJ-1(-/-) astrocytes had consistently lower expression compared to DJ-1(+/+) counterparts. Secretion of TNFα and prostaglandin E2 (PGE2) into the culture medium was significantly decreased in DJ-1(-/-) astrocytes, and inhibition of p38 decreased this secretion in both genotypes. In conclusion, DJ-1(-/-) astrocytes may provide decreased neuroprotection to surrounding neurons due to alterations in pro-inflammatory mediator expression.

Detrimental role of the EP1 prostanoid receptor in blood-brain barrier damage following experimental ischemic stroke

Cyclooxygenase-2 (COX-2) is activated in response to ischemia and significantly contributes to the neuroinflammatory process. Accumulation of COX-2-derived prostaglandin E₂ (PGE₂) parallels the substantial increase in stroke-mediated blood-brain barrier (BBB) breakdown. Disruption of the BBB is a serious consequence of ischemic stroke, and is mainly mediated by matrix metalloproteinases (MMPs). This study aimed to investigate the role of PGE₂ EP1 receptor in neurovascular injury in stroke. We hypothesized that pharmacological blockade or genetic deletion of EP1 protects against BBB damage and hemorrhagic transformation by decreasing the levels and activity of MMP-3 and MMP-9. We found that post-ischemic treatment with the EP1 antagonist, SC-51089, or EP1 genetic deletion results in a significant reduction in BBB disruption and reduced hemorrhagic transformation in an experimental model of transient focal cerebral ischemia. These neurovascular protective effects of EP1 inactivation are associated with a significant reduction in MMP-9/-3, less peripheral neutrophil infiltration, and a preservation of tight junction proteins (ZO-1 and occludin) composing the BBB. Our study identifies the EP1 signaling pathway as an important link between neuroinflammation and MMP-mediated BBB breakdown in ischemic stroke. Targeting the EP1 receptor could represent a novel approach to diminish the devastating consequences of stroke-induced neurovascular damage.

Inflammatory Cyclooxygenase Activity and PGE2 Signaling in Models of Alzheimer's Disease

The inflammatory response is a fundamental driving force in the pathogenesis of Alzheimer’s disease (AD). In the setting of accumulating immunogenic Aß peptide assemblies, microglia, the innate immune cells of the brain, generate a non-resolving immune response and fail to adequately clear accumulating Aß peptides, accelerating neuronal and synaptic injury. Pathological, biomarker, and imaging studies point to a prominent role of the innate immune response in AD development, and the molecular components of this response are beginning to be unraveled. The inflammatory cyclooxygenase-PGE₂ pathway is implicated in pre-clinical development of AD, both in epidemiology of normal aging populations and in transgenic mouse models of Familial AD. The cyclooxygenase-PGE₂ pathway modulates the inflammatory response to accumulating Aß peptides through actions of specific E-prostanoid G-protein coupled receptors.

Intracerebral hemorrhage outcomes following selective blockade or stimulation of the PGE2 EP1 receptor

Background

Inflammation following intracerebral hemorrhage (ICH) significantly contributes to secondary brain damage and poor outcomes. Prostaglandin E₂ (PGE₂) is known to modulate neuroinflammatory responses and is upregulated in response to brain injury as a result of changes in inducible cyclooxygenase 2 (COX-2) and the membrane-bound type of PGE synthase. Inhibition of COX-2 activity has been reported to attenuate ICH-induced brain injury; however, the clinical utility of such drugs is limited due to the potential for severe side effects. Therefore, it is now important to search for downstream targets capable of preferentially modulating PGE₂ signaling, and the four E prostanoid receptors, EP1-4, which are the main targets of PGE₂, remain a viable therapeutic option. We have previously shown that EP1 receptor deletion aggravates ICH-induced brain injury and impairs functional recovery, thus the current study aimed to elaborate on these results by including a pharmacologic approach targeting the EP1 receptor.

Results

Chronic post-treatment with the selective EP1 receptor antagonist, SC-51089, increased lesion volume by 30.1 ± 14.5% (p < 0.05) and treatment with the EP1 agonist, 17-pt-PGE₂, improved neuromuscular functional recovery on grip strength (p < 0.01) and hanging wire (p < 0.05) behavioral testing. To begin identifying the mechanisms involved in EP1-mediated neuroprotection after ICH, histology was performed to assess ferric iron content, neuroinflammation, leukocyte transendothelial migratory potential, and peripheral neutrophil and immunoglobulin infiltration. Following ICH, mice treated with the antagonist displayed increased ferric iron (p < 0.05) and cortical microgliosis (p < 0.05), whereas treatment with the agonist decreased cortical (p < 0.01) and striatal (p < 0.001) astrogliosis, leukocyte transendothelial migratory potential (p < 0.01), neutrophil infiltration (p < 0.05), and blood brain barrier breakdown (p < 0.05).

Conclusions

In agreement with our previous results, selective antagonism of the EP1 receptor aggravated ICH-induced brain injury. Furthermore, EP1 receptor agonism improved anatomical outcomes and functional recovery. Thus, the present data continues to reinforce a putative role for EP1 as a new and more selective therapeutic target for the treatment of ICH that could reduce the side effects associated with COX-2 inhibition while still exploiting the beneficial effects.

The role of the prostaglandin E2 receptors in vulnerability of oligodendrocyte precursor cells to death

Background

Activity of cyclooxygenase 2 (COX-2) in mouse oligodendrocyte precursor cells (OPCs) modulates vulnerability to excitotoxic challenge. The mechanism by which COX-2 renders OPCs more sensitive to excitotoxicity is not known. In the present study, we examined the hypothesis that OPC excitotoxic death is augmented by COX-2-generated prostaglandin E2 (PGE₂) acting on specific prostanoid receptors which could contribute to OPC death.

Methods

Dispersed OPC cultures prepared from mice brains were examined for expression of PGE₂ receptors and the ability to generate PGE₂ following activation of glutamate receptors with kainic acid (KA). OPC death in cultures was induced by either KA, 3′-O-(Benzoyl) benzoyl ATP (BzATP) (which stimulates the purinergic receptor P2X7), or TNFα, and the effects of EP3 receptor agonists and antagonists on OPC viability were examined.

Results

Stimulation of OPC cultures with KA resulted in nearly a twofold increase in PGE₂. OPCs expressed all four PGE receptors (EP1–EP4) as indicated by immunofluorescence and Western blot analyses; however, EP3 was the most abundantly expressed. The EP3 receptor was identified as a candidate contributing to OPC excitotoxic death based on pharmacological evidence. Treatment of OPCs with an EP1/EP3 agonist 17 phenyl-trinor PGE₂ reversed protection from a COX-2 inhibitor while inhibition of EP3 receptor protected OPCs from excitotoxicity. Inhibition with an EP1 antagonist had no effect on OPC excitotoxic death. Moreover, inhibition of EP3 was protective against toxic stimulation with KA, BzATP, or TNFα.

Conclusion

Therefore, inhibitors of the EP3 receptor appear to enhance survival of OPCs following toxic challenge and may help facilitate remyelination.

Genetic deletion of the prostaglandin E2 E prostanoid receptor subtype 3 improves anatomical and functional outcomes after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a stroke subtype associated with high mortality and morbidity. Following ICH, excitotoxicity and inflammation significantly contribute to secondary brain injury and poor outcomes. Prostaglandin E2 (PGE2 ) levels rise locally with insult to the nervous system, and PGE2 is known to modulate these processes mainly through its E prostanoid (EP) receptors, EP1-4. EP receptor subtype 3 (EP3) is the most abundant EP receptor in the brain and we have previously shown that signaling through the PGE2 -EP3 axis exacerbates excitotoxicity and ischemic stroke outcomes. This study aimed to investigate the contribution of this pathway in modulating anatomical outcomes and functional recovery following ICH. Genetic deletion of EP3 resulted in 48.2 ± 7.3% less ICH-induced brain injury (P < 0.005) and improved functional recovery (P < 0.05), as identified by neurological deficit scoring. To start investigating the mechanisms involved in neuroprotection with impaired PGE2 -EP3 signaling, histological staining was performed to evaluate blood and ferric iron accumulation, neuroinflammation, blood-brain barrier dysfunction, and peripheral neutrophil infiltration. After ICH, EP3 knockout mice demonstrated 49.5 ± 8.8% and 42.8 ± 13.1% less blood (P < 0.01) and ferric iron (P < 0.05), respectively. Furthermore, EP3 knockout mice had significantly reduced astrogliosis, microglial activation, blood-brain barrier breakdown, and neutrophil infiltration. Collectively, these results suggest an injurious role for the PGE2 -EP3 signaling axis in modulating brain injury, inflammation, and neurological functional recovery after ICH. Modulation of the PGE2 -EP3 signaling axis may represent a putative therapeutic avenue for the treatment of ICH.

Toxic role of prostaglandin E2 receptor EP1 after intracerebral hemorrhage in mice

Inflammatory mechanisms mediated by prostaglandins may contribute to the progression of intracerebral hemorrhage (ICH)-induced brain injury, but they are not fully understood. In this study, we examined the effect of prostaglandin E2 receptor EP1 (EP1R) activation and inhibition on brain injury in mouse models of ICH and investigated the underlying mechanism of action. ICH was induced by injecting collagenase, autologous blood, or thrombin into the striatum of middle-aged male and female mice and aged male mice. Effects of selective EP1R agonist ONO-DI-004, antagonist SC51089, and nonspecific Src family kinase inhibitor PP2 were evaluated by a combination of histologic, magnetic resonance imaging (MRI), immunofluorescence, molecular, cellular, and behavioral assessments. EP1R was expressed primarily in neurons and axons but not in astrocytes or microglia after ICH induced by collagenase. In middle-aged male mice subjected to collagenase-induced ICH, EP1R inhibition mitigated brain injury, brain edema, cell death, neuronal degeneration, neuroinflammation, and neurobehavioral deficits, whereas its activation exacerbated these outcomes. EP1R inhibition also was protective in middle-aged female mice and aged male mice after collagenase-induced ICH and in middle-aged male mice after blood- or thrombin-induced ICH. EP1R inhibition also reduced oxidative stress, white matter injury, and brain atrophy and improved functional outcomes. Histologic results were confirmed by MRI. Src kinase phosphorylation and matrix metalloproteinase-9 activity were increased by EP1R activation and decreased by EP1R inhibition. EP1R regulated matrix metalloproteinase-9 activity through Src kinase signaling, which mediated EP1R toxicity after collagenase-induced ICH. We conclude that prostaglandin E2 EP1R activation plays a toxic role after ICH through mechanisms that involve the Src kinases and the matrix metalloproteinase-9 signaling pathway. EP1R inhibition could be a novel therapeutic strategy to improve outcomes after ICH.

Astrocyte physiopathology: At the crossroads of intercellular networking, inflammation and cell death

Recent breakthroughs in neuroscience have led to the awareness that we should revise our traditional mode of thinking and studying the CNS, i.e. by isolating the privileged network of "intelligent" synaptic contacts. We may instead need to contemplate all the variegate communications occurring between the different neural cell types, and centrally involving the astrocytes. Basically, it appears that a single astrocyte should be considered as a core that receives and integrates information from thousands of synapses, other glial cells and the blood vessels. In turn, it generates complex outputs that control the neural circuitry and coordinate it with the local microcirculation. Astrocytes thus emerge as the possible fulcrum of the functional homeostasis of the healthy CNS. Yet, evidence indicates that the bridging properties of the astrocytes can change in parallel with, or as a result of, the morphological, biochemical and functional alterations these cells undergo upon injury or disease. As a consequence, they have the potential to transform from supportive friends and interactive partners for neurons into noxious foes. In this review, we summarize the currently available knowledge on the contribution of astrocytes to the functioning of the CNS and what goes wrong in various pathological conditions, with a particular focus on Amyotrophic Lateral Sclerosis, Alzheimer's Disease and ischemia. The observations described convincingly demonstrate that the development and progression of several neurological disorders involve the de-regulation of a finely tuned interplay between multiple cell populations. Thus, it seems that a better understanding of the mechanisms governing the integrated communication and detrimental responses of the astrocytes as well as their impact towards the homeostasis and performance of the CNS is fundamental to open novel therapeutic perspectives.

Prostaglandin E2 EP2 receptor deletion attenuates intracerebral hemorrhage-induced brain injury and improves functional recovery

Intracerebral hemorrhage (ICH) is a devastating type of stroke characterized by bleeding into the brain parenchyma and secondary brain injury resulting from strong neuroinflammatory responses to blood components. Production of prostaglandin E₂ (PGE₂) is significantly upregulated following ICH and contributes to this inflammatory response in part through its E prostanoid receptor subtype 2 (EP2). Signaling through the EP2 receptor has been shown to affect outcomes of many acute and chronic neurological disorders; although, not yet explored in the context of ICH. Wildtype (WT) and EP2 receptor knockout (EP2^−/−) mice were subjected to ICH, and various anatomical and functional outcomes were assessed by histology and neurobehavioral testing, respectively. When compared with age-matched WT controls, EP2^−/− mice had 41.9 ± 4.7% smaller ICH-induced brain lesions and displayed significantly less ipsilateral hemispheric enlargement and incidence of intraventricular hemorrhage. Anatomical outcomes correlated with improved functional recovery as identified by neurological deficit scoring. Histological staining was performed to begin investigating the mechanisms involved in EP2-mediated neurotoxicity after ICH. EP2^−/− mice exhibited 45.5 ± 5.8% and 41.4 ± 8.1% less blood and ferric iron accumulation, respectively. Furthermore, significantly less striatal and cortical microgliosis, striatal and cortical astrogliosis, blood–brain barrier breakdown, and peripheral neutrophil infiltration were seen in EP2^−/− mice. This study is the first to suggest a deleterious role for the PGE₂-EP2 signaling axis in modulating brain injury, inflammation, and functional recovery following ICH. Targeting the EP2 G protein-coupled receptor may represent a new therapeutic avenue for the treatment of hemorrhagic stroke.

Neuroprotective role of prostaglandin PGE2 EP2 receptor in hemin-mediated toxicity

Heme (Fe(2+) protoporphyrin IX) and hemin (Fe(3+)), the prosthetic group of hemoprotein, are cytotoxic due to their ability to contribute to the production of reactive oxygen species, increased intracellular calcium levels, and stimulate glutamate-mediated excitotoxicity. Previous work by our group showed that blockade of the prostaglandin E2 (PGE2)-EP1 receptor reduced hemin-induced cytotoxicity in primary cortical neuronal cultures. However, the role of the prostaglandin E2 (PGE2)-EP2 receptor in hemin neurotoxicity remains unclear. Activation of the EP2 receptor in neurons results in increased cyclic AMP (cAMP) and protein kinase A signaling; therefore, we hypothesized that the activation of the EP2 receptor decreases hemin neurotoxicity. Using postnatal primary cortical neurons cultured from wildtype-control (WT) and EP2(-/-) mice, we investigated the role of the EP2 receptor in hemin neurotoxicity by monitoring cell survival with the Calcein-AM live-cell and lactate dehydrogenase assays. MitoTracker staining was also performed to determine how mitochondria were affected by hemin. Hemin neurotoxicity in EP2(-/-) neurons was 37.2 ± 17.0% greater compared to WT neurons. Of interest, cotreatment with the EP2 receptor agonist, butaprost (1 and 10 μM), significantly attenuated hemin neurotoxicity by 55.7 ± 21.1% and 60.1 ± 14.8%, respectively. To further investigate signaling mechanisms related to EP2 receptor mediating cytoprotection, neurons were cotreated with hemin and activators/inhibitors of both the cAMP-protein kinase A/exchange protein directly activated by cAMP (Epac) pathways. Forskolin, a cAMP activator, and 8-pCPT-cAMP, an Epac activator, both attenuated hemin neurotoxicity by 78.8 ± 22.2% and 58.4 ± 9.8%, respectively, as measured using the lactate dehydrogenase assay. Together, the results reveal that activation of the EP2 receptor is protective against hemin neurotoxicity in vitro and these findings suggest that neuroprotection occurs through the cAMP-Epac pathway in neuronal cultures. Therefore, activation of the EP2 receptor could be used to minimize neuronal damage following exposure to supraphysiological levels of hemin.

Role of the prostaglandin E2 EP1 receptor in traumatic brain injury

Brain injuries promote upregulation of so-called proinflammatory prostaglandins, notably prostaglandin E₂ (PGE₂), leading to overactivation of a class of its cognate G-protein-coupled receptors, including EP1, which is considered a promising target for treatment of ischemic stroke. However, the role of the EP1 receptor is complex and depends on the type of brain injury. This study is focused on the investigation of the role of the EP1 receptor in a controlled cortical impact (CCI) model, a preclinical model of traumatic brain injury (TBI). The therapeutic effects of post-treatments with a widely studied EP1 receptor antagonist, SC-51089, were examined in wildtype and EP1 receptor knockout C57BL/6 mice. Neurological deficit scores (NDS) were assessed 24 and 48 h following CCI or sham surgery, and brain immunohistochemical pathology was assessed 48 h after surgery. In wildtype mice, CCI resulted in an obvious cortical lesion and localized hippocampal edema with an associated significant increase in NDS compared to sham-operated animals. Post-treatments with the selective EP1 receptor antagonist SC-51089 or genetic knockout of EP1 receptor had no significant effects on cortical lesions and hippocampal swelling or on the NDS 24 and 48 h after CCI. Immunohistochemistry studies revealed CCI-induced gliosis and microglial activation in selected ipsilateral brain regions that were not affected by SC-51089 or in the EP1 receptor-deleted mice. This study provides further clarification on the respective contribution of the EP1 receptor in TBI and suggests that, under this experimental paradigm, the EP1 receptor would have limited effects in modulating acute neurological and anatomical pathologies following contusive brain trauma. Findings from this protocol, in combination with previous studies demonstrating differential roles of EP1 receptor in ischemic, neurotoxic, and hemorrhagic conditions, provide scientific background and further clarification of potential therapeutic application of prospective prostaglandin G-protein-coupled receptor drugs in the clinic for treatment of TBI and other acute brain injuries.

The prostaglandin EP1 receptor potentiates kainate receptor activation via a protein kinase C pathway and exacerbates status epilepticus

Prostaglandin E2 (PGE2) regulates membrane excitability, synaptic transmission, plasticity, and neuronal survival. The consequences of PGE2 release following seizures has been the subject of much study. Here we demonstrate that the prostaglandin E2 receptor 1 (EP1, or Ptger1) modulates native kainate receptors, a family of ionotropic glutamate receptors widely expressed throughout the central nervous system. Global ablation of the EP1 gene in mice (EP1-KO) had no effect on seizure threshold after kainate injection but reduced the likelihood to enter status epilepticus. EP1-KO mice that did experience typical status epilepticus had reduced hippocampal neurodegeneration and a blunted inflammatory response. Further studies with native prostanoid and kainate receptors in cultured cortical neurons, as well as with recombinant prostanoid and kainate receptors expressed in Xenopus oocytes, demonstrated that EP1 receptor activation potentiates heteromeric but not homomeric kainate receptors via a second messenger cascade involving phospholipase C, calcium and protein kinase C. Three critical GluK5 C-terminal serines underlie the potentiation of the GluK2/GluK5 receptor by EP1 activation. Taken together, these results indicate that EP1 receptor activation during seizures, through a protein kinase C pathway, increases the probability of kainic acid induced status epilepticus, and independently promotes hippocampal neurodegeneration and a broad inflammatory response.

Prostaglandin E2 EP1 receptor antagonist improves motor deficits and rescues memory decline in R6/1 mouse model of Huntington's disease

In this study, we evaluated the potential beneficial effects of antagonizing prostaglandin E2 (PGE2) EP1 receptor on motor and memory deficits in Huntington's disease (HD). To this aim, we implanted an osmotic mini-pump system to chronically administrate an EP1 receptor antagonist (SC-51089) in the R6/1 mouse model of HD, from 13 to 18 weeks of age, and used different paradigms to assess motor and memory function. SC-51089 administration ameliorated motor coordination and balance dysfunction in R6/1 mice as analyzed by rotarod, balance beam, and vertical pole tasks. Long-term memory deficit was also rescued after EP1 receptor antagonism as assessed by the T-maze spontaneous alternation and the novel object recognition tests. Additionally, treatment with SC-51089 improved the expression of specific synaptic markers and reduced the number of huntingtin nuclear inclusions in the striatum and hippocampus of 18-week-old R6/1 mice. Moreover, electrophysiological studies showed that hippocampal long-term potentiation was significantly recovered in R6/1 mice after EP1 receptor antagonism. Altogether, these results show that the antagonism of PGE2 EP1 receptor has a strong therapeutic effect on R6/1 mice and point out a new therapeutic candidate to treat motor and memory deficits in HD.

Prostaglandin F2α FP receptor antagonist improves outcomes after experimental traumatic brain injury

BACKGROUND

Injuries to the brain promote upregulation of prostaglandins, notably the proinflammatory PGF2α, and overactivation of their cognate G-protein-coupled FP receptor, which could exacerbate neuronal damage. Our study is focused on investigation of the FP receptor as a target for novel neuroprotective drugs in a preclinical animal traumatic brain injury (TBI) model.

METHODS

Accordingly, the effects of acute intraperitoneal post-treatment with selective FP antagonist AL-8810 were studied in wildtype (WT) and FP receptor knockout (FP-/-) mice after controlled cortical impact (CCI). Neurological impairments were evaluated using neurological deficit scores (NDS) and the grip strength test. Cortical lesions and overall brain pathology were assessed using immunohistochemistry.

RESULTS

Morphological analyses of cerebral vasculature and anastomoses revealed no differences between WT and FP-/- mice. CCI produced cortical lesions characterized by cavitation, neuronal loss, and hematoma with a volume of 20.0 ± 1.0 mm(3) and significant hippocampal swelling (146.5 ± 7.4% of contralateral) compared with sham (P < 0.05). Post-treatment with AL-8810 (1 to 10 mg/kg) had no significant effect on cortical lesions, which suggests the irreversible effect of primary CCI injury, but significantly reduced hippocampal swelling to a size not significantly different from the sham group. Post-treatment with AL-8810 at a dose of 10 mg/kg significantly improved NDS at 24 and 48 hours after CCI (P < 0.001 and P < 0.01, respectively). In the AL-8810 group, CCI-induced decrease in grip strength was three-fold (2.93 ± 1.71) less and significantly different than in the saline-treated group. The FP-/- mice had significantly less hippocampal swelling, but not NDS, compared with WT mice. In addition, immunohistochemistry showed that pharmacologic blockade and genetic deletion of FP receptor led to attenuation of CCI-induced gliosis and microglial activation in selected brain regions.

CONCLUSION

This study provides, for the first time, demonstration of the unique role of the FP receptor as a potential target for disease-modifying CNS drugs for treatment of acute traumatic injury.

Contribution of PGE2 EP1 receptor in hemin-induced neurotoxicity

Although hemin-mediated neurotoxicity has been linked to the production of free radicals and glutamate excitotoxicity, the role of the prostaglandin E₂ (PGE₂)-EP1 receptor remains unclear. Activation of the EP1 receptor in neurons results in increased intracellular calcium levels; therefore, we hypothesize that the blockade of the EP1 receptor reduces hemin neurotoxicity. Using postnatal primary cortical neurons cultured from wild-type (WT) and EP1^−/− mice, we investigated the EP1 receptor role in hemin neurotoxicity measured by lactate dehydrogenase (LDH) cell survival assay. Hemin (75 μM) induced greater release of LDH in WT (34.7 ± 4.5%) than in EP1^−/− (27.6 ± 3.3%) neurons. In the presence of the EP1 receptor antagonist SC-51089, the hemin-induced release of LDH decreased. To further investigate potential mechanisms of action, we measured changes in the intracellular calcium level [Ca²⁺]_i following treatment with 17-phenyl trinor PGE₂ (17-pt-PGE₂) a selective EP1 agonist. In the WT neurons, 17-pt-PGE₂ dose-dependently increased [Ca²⁺]_i. However, in EP1^−/− neurons, [Ca²⁺]_i was significantly attenuated. We also revealed that hemin dose-dependently increased [Ca²⁺]_i in WT neurons, with a significant decrease in EP1^−/− neurons. Both 17-pt-PGE₂ and hemin-induced [Ca²⁺]_i were abolished by N-methyl-D-aspartic (NMDA) acid receptor and ryanodine receptor blockers. These results suggest that blockade of the EP1 receptor may be protective against hemin neurotoxicity in vitro. We speculate that the mechanism of hemin neuronal death involves [Ca²⁺]_i mediated by NMDA acid receptor-mediated extracellular Ca²⁺ influx and EP1 receptor-mediated intracellular release from ryanodine receptor-operated Ca²⁺ stores. Therefore, blockade of the EP1 receptor could be used to minimize neuronal damage following exposure to supraphysiological levels of hemin.

Prostaglandin E2 type 1 receptors contribute to neuronal apoptosis after transient forebrain ischemia

Cyclooxygenase-2-derived prostaglandin E2 (PGE2) contributes to excitotoxic and ischemic neuronal cell death by engaging neuronal PGE2 type 1 receptors (EP1R). Our previous studies have shown that EP1R signaling resulted in disturbances of intracellular Ca(2+) homeostasis and suppression of the pro-survival protein kinase AKT. The aim of this study was to investigate whether these pathophysiological mechanism have a role in the neuronal cell death after transient forebrain ischemia. Mice were subjected to ischemia/reperfusion by bilateral common carotid artery occlusion. Hippocampal cornu ammonis area 1 (CA1) neuronal cell death was determined 5 days after reperfusion. Animals treated with the EP1R antagonist SC51089 or EP1R-deficient mice (EP1(-/-)) showed significantly less neuronal injury as compared to vehicle-treated wild-type controls. Benefits of EP1R blockage were still evident 14 days after injury. Better neuronal survival was correlated with reduced neuronal caspase-3 activity and decreased nuclear translocation of the apoptosis-inducing factor . Neuroprotection could be reverted by intracerebroventricular administration of the phosphoinositide 3-kinase inhibitor LY294002 and was not further increased by the calcineurin inhibitor FK506. These data implicate EP1R in postischemic neuronal apoptosis possibly by facilitating AKT inhibition.

Role of PGE₂ EP1 receptor in intracerebral hemorrhage-induced brain injury

Prostaglandin E₂ (PGE₂) has been described to exert beneficial and detrimental effects in various neurologic disorders. These conflicting roles of PGE₂ could be attributed to its diverse receptor subtypes, EP1-EP4. At present, the precise role of EP1 in intracerebral hemorrhage (ICH) is unknown. Therefore, to elucidate its possible role in ICH, intrastriatal injection of collagenase was given in randomized groups of adult male wildtype (WT) and EP1 receptor knockout (EP1⁻/⁻)C57BL/6 mice. Functional outcomes including neurologic deficits, rotarod performance, open field activity, and adhesive removal performance were evaluated at 24, 48, and 72 h post-ICH. Lesion volume, cell survival and death, were assessed using Cresyl Violet, and Fluoro-Jade staining, respectively. Microglial activation and phagocytosis were estimated using Iba1 immunoreactivity and fluorescently-labeled microspheres. Following 72 h post-ICH, EP1⁻/⁻ mice showed deteriorated outcomes compared to the WT control mice. These outcomes were demonstrated by elevated neurological deficits, exacerbated lesion volume, and significantly worsened sensorimotor functions. Fluoro-Jade staining showed significantly increased numbers of degenerating neurons and reduced neuronal survival in EP1⁻/⁻ compared to WT mice. To assess in vivo phagocytosis, the number of microspheres phagocytosed by Iba1-positive cells was 145.4 ± 15.4 % greater in WT compared to EP1⁻/⁻ mice. These data demonstrate that EP1 deletion exacerbates neuro-behavioral impairments following ICH, potentially by slowing down/impairing microglial phagocytosis. A better understanding of this EP1 mechanism could lead to improved intervention strategies for hemorrhagic stroke.

PGE2 EP1 receptor deletion attenuates 6-OHDA-induced Parkinsonism in mice: old switch, new target

Recent experimental data on Parkinson's disease (PD) predicts the critical role of inflammation in the progression of neurodegeneration and the promising preventive effects of nonsteroidal anti-inflammatory drugs (NSAIDs). Previous studies suggest that NSAIDs minimize cyclooxygenase-2 (COX-2) activity and thereby attenuate free radical generation. Prostaglandin E2 (PGE2) is an important product of COX activity and plays an important role in various physiologic and pathophysiologic conditions through its EP receptors (EP1-EP4). Part of the toxic effect of PGE2 in the central nervous system has been reported to be through the EP1 receptor; however, the effect of the EP1 receptor in PD remains elusive. Therefore, in our pursuit to determine if deletion of the PGE2 EP1 receptor will attenuate 6-hydroxy dopamine (6-OHDA)-induced Parkinsonism, mice were given a unilateral 6-OHDA injection into the medial forebrain bundle. We found that apomorphine-induced contralateral rotations were significantly attenuated in the 6-OHDA-lesioned EP1(-/-) mice compared with the 6-OHDA-lesioned WT mice. Quantitative analysis showed significant protection of dopaminergic neurons in the substantia nigra pars compacta of the 6-OHDA-lesioned EP1(-/-) mice. To the best of our knowledge, this is the first in vivo study to implicate the PGE2 EP1 receptor in toxin-induced Parkinsonism. We propose the PGE2 EP1 receptor as a new target to better understand some of the mechanisms leading to PD.

Putative role of prostaglandin receptor in intracerebral hemorrhage

Each year, approximately 795,000 people experience a new or recurrent stroke. Of all strokes, 84% are ischemic, 13% are intracerebral hemorrhage (ICH) strokes, and 3% are subarachnoid hemorrhage strokes. Despite the decreased incidence of ischemic stroke, there has been no change in the incidence of hemorrhagic stroke in the last decade. ICH is a devastating disease 37–38% of patients between the ages of 45 and 64 die within 30 days. In an effort to prevent ischemic and hemorrhagic strokes we and others have been studying the role of prostaglandins and their receptors. Prostaglandins are bioactive lipids derived from the metabolism of arachidonic acid. They sustain homeostatic functions and mediate pathogenic mechanisms, including the inflammatory response. Most prostaglandins are produced from specific enzymes and act upon cells via distinct G-protein coupled receptors. The presence of multiple prostaglandin receptors cross-reactivity and coupling to different signal transduction pathways allow differentiated cells to respond to prostaglandins in a unique manner. Due to the number of prostaglandin receptors, prostaglandin-dependent signaling can function either to promote neuronal survival or injury following acute excitotoxicity, hypoxia, and stress induced by ICH. To better understand the mechanisms of neuronal survival and neurotoxicity mediated by prostaglandin receptors, it is essential to understand downstream signaling. Several groups including ours have discovered unique roles for prostaglandin receptors in rodent models of ischemic stroke, excitotoxicity, and Alzheimer disease, highlighting the emerging role of prostaglandin receptor signaling in hemorrhagic stroke with a focus on cyclic-adenosine monophosphate and calcium (Ca²⁺) signaling. We review current ICH data and discuss future directions notably on prostaglandin receptors, which may lead to the development of unique therapeutic targets against hemorrhagic stroke and brain injuries alike.

Prostanoid EP₁ receptors mediate up-regulation of the orphan nuclear receptor Nurr1 by cAMP-independent activation of protein kinase A, CREB and NF-κB

BACKGROUND AND PURPOSE

Prostaglandin E(2) (PGE(2)) stimulation of the G protein-coupled prostanoid EP(1) receptor was found to up-regulate the expression of Nur-related factor 1 (Nurr1) (NR4A2), a transcription factor in the NR4A subfamily of nuclear receptors. The present studies characterize the molecular mechanism of this up-regulation.

EXPERIMENTAL APPROACH

The expression of Nurr1 was examined by immunoblot analysis, the polymerase chain reaction and reporter gene assays in human embryonic kidney (HEK) cells stably expressing the recombinant EP(1) receptor and in SH-SY5Y neuroblastoma cells expressing endogenous EP(1) receptors. Signalling pathway inhibitors were used to examine the roles of Rho, PKA, the cAMP response element binding protein (CREB) and NF-κB on the PGE(2) stimulated up-regulation of Nurr1. CREB and NF-κB signalling were also examined by immunoblot analysis and reporter gene assays.

KEY RESULTS

The EP(1) receptor mediated up-regulation of Nurr1 was blocked with inhibitors of Rho, PKA, NF-κB and CREB; but PGE(2) failed to significantly stimulate intracellular cAMP formation. PGE(2) stimulation of the EP1 receptor induced the phosphorylation and activation of CREB and NF-κB, which could be blocked by inhibition of PKA.

CONCLUSIONS AND IMPLICATIONS

PGE(2) stimulation of the human EP(1) receptor up-regulates the expression of Nurr1 by a mechanism involving the sequential activation of the Rho, PKA, CREB and NF-κB signalling pathways. EP(1) receptors are implicated in tumorigenesis and the up-regulation of Nurr1 may underlie the anti-apoptotic effects of PGE(2) .

Role of phospholipase A2s and lipid mediators in secondary damage after spinal cord injury

Inflammation is considered to be an important contributor to secondary damage after spinal cord injury (SCI). This secondary damage leads to further exacerbation of tissue loss and functional impairments. The immune responses that are triggered by injury are complex and are mediated by a variety of factors that have both detrimental and beneficial effects. In this review, we focus on the diverse effects of the phospholipase A(2) (PLA(2)) superfamily and the downstream pathways that generate a large number of bioactive lipid mediators, some of which have pro-inflammatory and demyelinating effects, whereas others have anti-inflammatory and pro-resolution properties. For each of these lipid mediators, we provide an overview followed by a discussion of their expression and role in SCI. Where appropriate, we have compared the latter with their role in other neurological conditions. The PLA(2) pathway provides a number of targets for therapeutic intervention for the treatment of SCI and other neurological conditions.

PGE2 EP1 receptor exacerbated neurotoxicity in a mouse model of cerebral ischemia and Alzheimer's disease

Stroke and Alzheimer's disease (AD) are major age-related neurodegenerative diseases that may worsen the prognosis of each other. Our study was designed to delineate the prostaglandin E(2) EP1 receptor role in AD and in the setting of cerebral ischemia. Genetic deletion of the prostaglandin EP1 receptor significantly attenuated the more severe neuronal damage (38.5 ± 10.6%) and memory loss induced by ischemic insult observed in AD transgenic mice (percentage of viable hippocampal CA1 neurons: 11.2 ± 2.9%) when compared with wild type mice (45.1 ± 9.1%). In addition, we found that the amyloid plaques were reduced in EP1 deleted AD mice. β-amyloid-induced toxicity (18.0 ± 7.1%) and Ca(2+) response (91.8 ± 12.9%) were also reduced in EP1(-/-) neurons compared with control neurons in in vitro. Hence, EP1 might mediate most of the toxicity associated with cyclooxygenase-2 and contribute substantially to the cell death pathways in AD and stroke. Exploring potential therapeutic agent targeting EP1 receptor could potentially benefit treatments for stroke and AD patients.

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.