15d-Prostaglandin J2 Enhancement of Nerve Growth Factor–Induced Neurite Outgrowth Is Blocked by the Chemoattractant Receptor– Homologous Molecule Expressed on T-Helper Type 2 Cells (CRTH2) Antagonist CAY10471 in PC12 Cells

Lipocalin-type prostaglandin D synthase regulates light-induced phase advance of the central circadian rhythm in mice

We previously showed that mice lacking pituitary adenylate cyclase-activating polypeptide (PACAP) exhibit attenuated light-induced phase shift. To explore the underlying mechanisms, we performed gene expression analysis of laser capture microdissected suprachiasmatic nuclei (SCNs) and found that lipocalin-type prostaglandin (PG) D synthase (L-PGDS) is involved in the impaired response to light stimulation in the late subjective night in PACAP-deficient mice. L-PGDS-deficient mice also showed impaired light-induced phase advance, but normal phase delay and nonvisual light responses. Then, we examined the receptors involved in the response and observed that mice deficient for type 2 PGD₂ receptor DP2/CRTH2 (chemoattractant receptor homologous molecule expressed on Th2 cells) show impaired light-induced phase advance. Concordant results were observed using the selective DP2/CRTH2 antagonist CAY10471. These results indicate that L-PGDS is involved in a mechanism of light-induced phase advance via DP2/CRTH2 signaling.

Kawaguchi et al. show that mice deficient in lipocalin-type prostaglandin (PG) D synthase (L-PGDS) exhibit impaired light-induced phase advance, but normal phase delay and nonvisual light responses. This study suggests the role of L-PGDS for the light-induced phase advance possibly via a chemoattractant receptor DP2/CRTH2.

The Molecular Mechanisms Underlying Prostaglandin D2-Induced Neuritogenesis in Motor Neuron-Like NSC-34 Cells

Prostaglandins are a group of physiologically active lipid compounds derived from arachidonic acid. Our previous study has found that prostaglandin E2 promotes neurite outgrowth in NSC-34 cells, which are a model for motor neuron development. However, the effects of other prostaglandins on neuronal differentiation are poorly understood. The present study investigated the effect of prostaglandin D2 (PGD2) on neuritogenesis in NSC-34 cells. Exposure to PGD2 resulted in increased percentages of neurite-bearing cells and neurite length. Although D-prostanoid receptor (DP) 1 and DP2 were dominantly expressed in the cells, BW245C (a DP1 agonist) and 15(R)-15-methyl PGD2 (a DP2 agonist) had no effect on neurite outgrowth. Enzyme-linked immunosorbent assay demonstrated that PGD2 was converted to 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) under cell-free conditions. Exogenously applied 15d-PGJ2 mimicked the effect of PGD2 on neurite outgrowth. GW9662, a peroxisome proliferator-activated receptor-gamma (PPARγ) antagonist, suppressed PGD2-induced neurite outgrowth. Moreover, PGD2 and 15d-PGJ2 increased the protein expression of Islet-1 (the earliest marker of developing motor neurons), and these increases were suppressed by co-treatment with GW9662. These results suggest that PGD2 induces neuritogenesis in NSC-34 cells and that PGD2-induced neurite outgrowth was mediated by the activation of PPARγ through the metabolite 15d-PGJ2.

Integrated communications between cyclooxygenase-2 and Alzheimer's disease

Elevated levels of cyclooxygenase-2 (COX-2) and prostaglandins (PGs) are involved in the pathogenesis of Alzheimer's disease (AD), which is characterized by the accumulation of β-amyloid protein (Aβ) and tau hyperphosphorylation. However, the gaps in our knowledge of the roles of COX-2 and PGs in AD have not been filled. Here, we summarized the literature showing that COX-2 dysregulation obviously influences abnormal cleavage of β-amyloid precursor protein, aggregation and deposition of Aβ in β-amyloid plaques and the inclusion of phosphorylated tau in neurofibrillary tangles. Neuroinflammation, oxidative stress, synaptic plasticity, neurotoxicity, autophagy, and apoptosis have been assessed to elucidate the mechanisms of COX-2 regulation of AD. Notably, an imbalance of these factors ultimately produces cognitive decline. The current review substantiates our understanding of the mechanisms of COX-2-induced AD and establishes foundations for the design of feasible therapeutic strategies to treat AD.-Guan, P.-P., Wang, P. Integrated communications between cyclooxygenase-2 and Alzheimer's disease.

The therapeutic potential of CRTH2/DP2 beyond allergy and asthma

Prostaglandin (PG) D₂ has been in the focus of research for quite a long time, but its biological effects and its roles in human disease are still not fully characterized. When in 2001 a second major PGD₂ receptor termed chemoattractant receptor homologue expressed on Th2 cells (CRTH2; alternative name DP2) was discovered, diverse investigations started to shed more light on the complex and often controversial actions of the prostaglandin. With various immunomodulating effects, such as induction of migration, activation, and cytokine release of leukocytes observed both in vivo and in vitro, CRTH2 has emerged as a promising target for the treatment of allergic diseases. However, with more and more research being performed on CRTH2, it has also become clear that its biological actions are far more diverse than expected at the beginning. In this review, we aim to summarize the roles that PGD₂ - and CRTH2 in particular - might play in diseases of the central nervous system, kidney, intestine, lung, hair and skin, bone and cartilage, and in cancer. Based on current data we propose that blocking CRTH2 might be a potential therapeutic approach to numerous conditions beyond classical allergic diseases and asthma.

15-Deoxy-Δ12,14-prostaglandin J2 induced neurotoxicity via suppressing phosphoinositide 3-kinase

15-Deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) induces neuronal cell death via apoptosis independently of its receptors. 15d-PGJ₂ inhibits growth factor-induced cell proliferation of primary astrocytes via down-regulating phosphoinositide 3-kinase (PI3K)-Akt pathway. Although 15d-PGJ₂-reduced cell viability is accompanied with attenuation of the PI3K signaling in neuroblastoma, it has not been sufficiently clarified how 15d-PGJ₂ induces cell death in primary neurons. Here, we found that 15d-PGJ₂ exhibited neurotoxicity via inhibiting the PI3K signaling in the primary culture of rat cortical neurons. A PI3K inhibitor induced neuronal cell death regardless serum throughout maturation, confirming that PI3K is required for neuronal cell survival. The inhibitor disrupted neuronal cell bodies, shortened neurites thinly, damaged plasma membranes and activated caspase-3 similarly to 15d-PGJ₂. Little additive or synergistic neurotoxicity was detected between 15d-PGJ₂ and the PI3K inhibitor. A PI3K activator prevented neurons from undergoing the 15d-PGJ₂-induced cell death in vitro. In vivo, the PI3K signaling is required for contextual memory retrieval, which was impaired by bilateral injection of 15d-PGJ₂ into hippocampus. The activator suppressed the 15d-PGJ₂-impaired memory retrieval significantly. In neurons as well as primary astrocytes and neuroblastomas, 15d-PGJ₂ exhibited cytotoxicity via suppressing the PI3K-Akt pathway in vivo and in vitro.

Identification of a prostaglandin D2 metabolite as a neuritogenesis enhancer targeting the TRPV1 ion channel

Mast cells play important roles in allergic inflammation by secreting various mediators. In the present study, based on the finding that the medium conditioned by activated RBL-2H3 mast cells enhanced the nerve growth factor (NGF)-induced neuritogenesis of PC12 cells, we attempted to isolate an active compound from the mast cell conditioned culture medium. Our experiment identified 15-deoxy-Δ(12,14)-PGJ2 (15d-PGJ2), one of the PGD2 metabolites, as a potential enhancer of neuritogenesis. 15d-PGJ2 strongly enhanced the neuritogenesis elicited by a low-concentration of NGF that alone was insufficient to induce the neuronal differentiation. This 15d-PGJ2 effect was exerted in a Ca(2+)-dependent manner, but independently of the NGF receptor TrkA. Importantly, 15d-PGJ2 activated the transient receptor potential vanilloid-type 1 (TRPV1), a non-selective cation channel, leading to the Ca(2+) influx. In addition, we observed that (i) NGF promoted the insertion of TRPV1 into the cell surface membrane and (ii) 15d-PGJ2 covalently bound to TRPV1. These findings suggest that the NGF/15d-PGJ2-induced neuritogenesis may be regulated by two sets of mechanisms, one for the translocation of TRPV1 into the cell surface by NGF and one for the activation of TRPV1 by 15d-PGJ2. Thus, there is most likely a link between allergic inflammation and activation of the neuronal differentiation.

Prostaglandin D2 elicits the reversible neurite retraction in hypothalamic cell line

Prostaglandins (PGs) play important roles in diverse physiological processes in the central nervous system. PGD2 is the most abundant PG in the brain and acts through specific receptors, DP1 and CRTH2. We investigated the effects of PGD2 on the morphology of the hypothalamic cell line mHypoE-N37 (N37). In N37 cells, serum starvation induced neurite outgrowth and PGD2 elicited neurite retraction, although we failed to detect transcripts for DP1 and CRTH2. Such an effect of PGD2 was efficiently mimicked by its metabolite, 15-deoxy-Δ(12,14)-prostaglandin J2. N-acetyl cysteine completely abolished the effect of PGD2, and reactive oxygen species (ROS) were considered to be important. Notably, neurite outgrowth was restored by PGD2 removal. These results suggest that PGD2 induces reversible neurite retraction in a ROS-mediated mechanism that does not involve any known receptor.

Localization of 14-3-3δ/ξ on the neuronal cell surface

14-3-3 proteins are intracellularly expressed as ubiquitous adaptor proteins. Here, we found localization of 14-3-3δ/ξ on the neuronal cell surface. 14-3-3δ/ξ was identified as a membrane target for 15-deoxy-Δ(12,14)-prostaglandin J2 (15d-PGJ2). 15d-PGJ2 is a pathological mediator of neurodegenerative diseases including Alzheimer's disease (AD). A causative peptide for AD, amyloid β, is one of binding partner of 14-3-3δ/ξ. Non-permeabilized neurons were used to avoid the intracellular effects of anti-14-3-3δ/ξ antibody in the present study. The plasmalemmal 14-3-3δ/ξ, but not the cytosolic one, was stimulated by its specific antibody, resulting in neuronal cell death. The neurotoxicity of anti-14-3-3δ/ξ antibody was suppressed by an antioxidant, catalase. Catalase prevented neurons from anti-14-3-3δ/ξ antibody-generating neurotoxic H2O2. The neuroprotective effect of catalase was also detected with the post-treatment of neurons after the application of anti-14-3-3δ/ξ antibody. Activation of mitogen-activated protein kinase signaling cascade is a down-stream consequence of H2O2 exposure. A c-Jun N-terminal kinase inhibitor suppressed anti-14-3-3δ/ξ antibody-induced neuronal cell death. To my knowledge, this is the first report that the antibody-stimulated plasmalemmal 14-3-3δ/ξ induced neuronal cell death. Furthermore, H2O2 and JNK contributed to the neurotoxicity of anti-14-3-3δ/ξ antibody as well as those of amyloid β and 15d-PGJ2.

Activin A prevents neuron-like PC12 cell apoptosis after oxygen-glucose deprivation

In this study, PC12 cells were induced to differentiate into neuron-like cells using nerve growth factor, and were subjected to oxygen-glucose deprivation. Cells were treated with 0, 10, 20, 30, 50, 100 ng/mL exogenous Activin A. The 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide assay and Hoechst 33324 staining showed that the survival percentage of PC12 cells significantly decreased and the rate of apoptosis significantly increased after oxygen-glucose deprivation. Exogenous Activin A significantly increased the survival percentage of PC12 cells in a dose-dependent manner. Reverse transcription-PCR results revealed a significant increase in Activin receptor IIA, Smad3 and Smad4 mRNA levels, which are key sites in the Activin A/Smads signaling pathway, in neuron-like cells subjected to oxygen-glucose deprivation, while mRNA expression of the apoptosis-regulation gene caspase-3 decreased. Our experimental findings indicate that exogenous Activin A plays an anti-apoptotic role and protects neurons by means of activating the Activin A/Smads signaling pathway.

Central CRTH2, a second prostaglandin D2 receptor, mediates emotional impairment in the lipopolysaccharide and tumor-induced sickness behavior model

Chemoattractant receptor-homologous molecule expressed on T helper type 2 cells (CRTH2) is a second prostaglandin D2 receptor involved in mediating the allergic response; however, its central function is not yet known. Here, we demonstrate that central CRTH2 mediates emotional impairment. Lipopolysaccharide (LPS)-induced decreases in social interaction and novel exploratory behavior were observed in wild-type (CRTH2(+/+)) mice but not CRTH2-deficient (CRTH2(-/-)) mice, but both genotypes showed hypolocomotion and anorexia following LPS injection. Tumor (colon 26) inoculation, a more pathologically relevant model, induced decreases in social interaction and novel exploratory behavior in CRTH2(+/+), but not CRTH2(-/-) mice. In addition, the CRTH2 antagonists including clinically available ramatroban reversed impaired social interaction and novel exploratory behavior after either LPS or tumor inoculation in CRTH2(+/+) mice. Finally, LPS-induced c-Fos expression in the hypothalamic paraventricular nucleus (PVN) and central amygdala (CeA) was selectively abolished in CRTH2(-/-) mice. These results show that CRTH2 participates in LPS-induced emotional changes and activation in the PVN and CeA. Our study provides the first evidence that central CRTH2 regulates specific emotional behaviors, and that CRTH2 antagonism has potential as a therapeutic target for behavioral symptoms associated with tumors and infectious diseases.

15-deoxy-Δ¹²,¹⁴-PGJ₂ promotes inflammation and apoptosis in cardiomyocytes via the DP2/MAPK/TNFα axis

Background

Prostaglandins (PGs), lipid autacoids derived from arachidonic acid, play a pivotal role during inflammation. PGD₂ synthase is abundantly expressed in heart tissue and PGD₂ has recently been found to induce cardiomyocyte apoptosis. PGD₂ is an unstable prostanoid metabolite; therefore the objective of the present study was to elucidate whether its final dehydration product, 15-deoxy-Δ^12,14-PGJ₂ (15d-PGJ₂, present at high levels in ischemic myocardium) might cause cardiomyocyte damage.

Methods and results

Using specific (ant)agonists we show that 15d-PGJ₂ induced formation of intracellular reactive oxygen species (ROS) and phosphorylation of p38 and p42/44 MAPKs via the PGD₂ receptor DP2 (but not DP1 or PPARγ) in the murine atrial cardiomyocyte HL-1 cell line. Activation of the DP2-ROS-MAPK axis by 15d-PGJ₂ enhanced transcription and translation of TNFα and induced apoptosis in HL-1 cardiomyocytes. Silencing of TNFα significantly attenuated the extrinsic (caspase-8) and intrinsic apoptotic pathways (bax and caspase-9), caspase-3 activation and downstream PARP cleavage and γH2AX activation. The apoptotic machinery was unaffected by intracellular calcium, transcription factor NF-κB and its downstream target p53. Of note, 9,10-dihydro-15d-PGJ₂ (lacking the electrophilic carbon atom in the cyclopentenone ring) did not activate cellular responses. Selected experiments performed in primary murine cardiomyocytes confirmed data obtained in HL-1 cells namely that the intrinsic and extrinsic apoptotic cascades are activated via DP2/MAPK/TNFα signaling.

Conclusions

We conclude that the reactive α,β-unsaturated carbonyl group of 15d-PGJ₂ is responsible for the pronounced upregulation of TNFα promoting cardiomyocyte apoptosis. We propose that inhibition of DP2 receptors could provide a possibility to modulate 15d-PGJ₂-induced myocardial injury.

Prostaglandin D2 toxicity in primary neurons is mediated through its bioactive cyclopentenone metabolites

Prostaglandin D2 (PGD2) is the most abundant prostaglandin in brain but its effect on neuronal cell death is complex and not completely understood. PGD2 may modulate neuronal cell death via activation of DP receptors or its metabolism to the cyclopentenone prostaglandins (CyPGs) PGJ2, Δ(12)-PGJ2 and 15-deoxy-Δ(12,14)-PGJ2, inducing cell death independently of prostaglandin receptors. This study aims to elucidate the effect of PGD2 on neuronal cell death and its underlying mechanisms. PGD2 dose-dependently induced cell death in rat primary neuron-enriched cultures in concentrations of ≥10μM, and this effect was not reversed by treatment with either DP1 or DP2 receptor antagonists. Antioxidants N-acetylcysteine (NAC) and glutathione which contain sulfhydryl groups that can bind to CyPGs, but not ascorbate or tocopherol, attenuated PGD2-induced cell death. Conversion of PGD2 to CyPGs was detected in neuronal culture medium; treatment with these CyPG metabolites alone exhibited effects similar to those of PGD2, including apoptotic neuronal cell death and accumulation of ubiquitinated proteins. Disruption of lipocalin-type prostaglandin D synthase (L-PGDS) protected neurons against hypoxia. These results support the hypothesis that PGD2 elicits its cytotoxic effects through its bioactive CyPG metabolites rather than DP receptor activation in primary neuronal culture.

Sprouty2 and Spred1-2 proteins inhibit the activation of the ERK pathway elicited by cyclopentenone prostanoids

Sprouty and Spred proteins have been widely implicated in the negative regulation of the fibroblast growth factor receptor-extracellular regulated kinase (ERK) pathway. In considering the functional role of these proteins, we explored their effects on ERK activation induced by cyclopentenone prostanoids, which bind to and activate Ras proteins. We therefore found that ectopic overexpression in HeLa cells of human Sprouty2, or human Spred1 or 2, inhibits ERK1/2 and Elk-1 activation triggered by the cyclopentenone prostanoids PGA₁ and 15d-PGJ₂. Furthermore, we found that in HT cells that do not express Sprouty2 due to hypermethylation of its gene-promoter, PGA₁-provoked ERK activation was more intense and sustained compared to other hematopoietic cell lines with unaltered Sprouty2 expression. Cyclopentenone prostanoids did not induce Sprouty2 tyrosine phosphorylation, in agreement with its incapability to activate tyrosine-kinase receptors. However, Sprouty2 Y55F, which acts as a defective mutant upon tyrosine-kinase receptor stimulation, did not inhibit cyclopentenone prostanoids-elicited ERK pathway activation. In addition, Sprouty2 did not affect the Ras-GTP levels promoted by cyclopentenone prostanoids. These results unveil both common and differential features in the activation of Ras-dependent pathways by cyclopentenone prostanoids and growth factors. Moreover, they provide the first evidence that Sprouty and Spred proteins are negative regulators of the ERK/Elk-1 pathway activation induced not only by growth-factors, but also by reactive lipidic mediators.