Coupling between cyclooxygenases and terminal prostanoid synthases

Deficiency of long-chain acyl-CoA synthetase 4 leads to lipopolysaccharide-induced mortality in a mouse model of septic shock

Long-chain acyl-CoA synthetase 4 (ACSL4) converts free highly unsaturated fatty acids (HUFAs) into their acyl-CoA esters and is important for HUFA utilization. HUFA-containing phospholipids produced via ACSL4-dependent reactions are involved in pathophysiological events such as inflammatory responses and ferroptosis as a source for lipid mediators and/or a target of oxidative stress, respectively. However, the in vivo role of ACSL4 in inflammatory responses is not fully understood. This study sought to define the effects of ACSL4 deficiency on lipopolysaccharide (LPS)-induced systemic inflammatory responses using global Acsl4 knockout (Acsl4 KO) mice. Intraperitoneal injection of LPS-induced more severe symptoms, including diarrhea, hypothermia, and higher mortality, in Acsl4 KO mice within 24 h compared with symptoms in wild-type (WT) mice. Intestinal permeability induced 3 h after LPS challenge was also enhanced in Acsl4 KO mice compared with that in WT mice. In addition, plasma levels of some eicosanoids in Acsl4 KO mice 6 h post-LPS injection were 2- to 9-fold higher than those in WT mice. The increased mortality observed in LPS-treated Acsl4 KO mice was significantly improved by treatment with the general cyclooxygenase inhibitor indomethacin with a partial reduction in the severity of illness index for hypothermia, diarrhea score, and intestinal permeability. These results suggest that ACSL4 deficiency enhances susceptibility to endotoxin at least partly through the overproduction of cyclooxygenase-derived eicosanoids.

Enzymes Present in Neutrophil Extracellular Traps May Stimulate the Fibrogenic PGF2α Pathway in the Mare Endometrium

Simple Summary

Endometrosis is a fibrotic disease in mare endometrium whose pathological mechanisms remain obscure. Prostaglandin (PG)F_2α, despite modulating reproductive physiological processes, may also provoke local pathological collagen deposition (fibrogenesis). Neutrophil extracellular traps (NETs) released during inflammation have been linked to fibrogenesis in several tissues. We have previously shown that enzymes found in NETs increase in vitro collagen production in mare endometrium. In this study, activation of PGF_2α-pathway in equine endometrial explants challenged in vitro by enzymes found in NETs is shown. Our results indicate that both endocrine microenvironment (estrous cycle phase) and healthy or pathological conditions of endometrial tissues play an important role in PGF_2α-pathway activation. In the endometrium of the follicular phase, we have observed both high production of PGF_2α and/or PGF2α receptor gene transcription under the action of enzymes found in NETs, both conditions associated with fibrogenesis in other tissues. Nevertheless, transcription of the PGF_2α receptor gene does not appear to be hormone-dependent, albeit their levels seem to be dependent on endometrial category in the mid-luteal phase. This study suggests that enzymes existing in NETs may instigate changes on PGF_2α mediators, which may become an additional mechanism of fibrogenesis in mare endometrium.

Abstract

Endometrosis, a fibrotic disease of mare endometrium, impairs uterine function. Prostaglandins (PG), despite modulating reproductive physiological functions, may also cause local pathological collagen deposition (fibrogenesis). We have previously shown that neutrophil extracellular traps (NETs) may also favor mare endometrosis. The aim of this study was to investigate the effect of enzymes present in NETs on PGF_2α-pathway activation. Kenney and Doig’s type I/IIA and IIB/III mare endometria, from follicular phase (FLP) and mid-luteal (MLP) phase, were cultured in vitro in the presence of NETs enzymes (elastase, cathepsin-G or myeloperoxidase). Production of PGF_2α (EIA) and transcription (qPCR) of its synthases (PTGS2, AKR1C3) and receptor (PTGFR) genes were evaluated. PGF_2α and PTGFR were influenced by endometrial category and estrous cycle phase. In FLP endometrium, NETs enzymes induced both high PGF_2α production and/or PTGFR transcription. In MLP type I/IIA tissues, down-regulation of PTGFR transcripts occurred. However, in MLP type IIB/III endometrium, high levels of PTGFR transcripts were induced by NETs enzymes. As PGF2α-pathway activation facilitates fibrogenesis in other tissues, PGF2α may be involved in endometrosis pathogenesis. In the mare, the endocrine microenvironment of healthy and pathological endometrium might modulate the PGF_2α pathway, as well as fibrosis outcome on endometrium challenged by NETs enzymes.

The key contribution of platelet and vascular arachidonic acid metabolism to the pathophysiology of atherothrombosis

Arachidonic acid is one of the most abundant and ubiquitous ω-6 polyunsaturated fatty acid, present in esterified form in the membrane phospholipids of all mammalian cells and released from phospholipids by several phospholipases in response to various activating or inhibitory stimuli. Arachidonic acid is the precursor of a large number of enzymatically and non-enzymatically derived, biologically active autacoids, including prostaglandins (PGs), thromboxane (TX) A2, leukotrienes, and epoxyeicosatetraenoic acids (collectively called eicosanoids), endocannabinoids and isoprostanes, respectively. Eicosanoids are local modulators of the physiological functions and pathophysiological roles of blood vessels and platelets. For example, the importance of cyclooxygenase (COX)-1-derived TXA2 from activated platelets in contributing to primary haemostasis and atherothrombosis is demonstrated in animal and human models by the bleeding complications and cardioprotective effects associated with low-dose aspirin, a selective inhibitor of platelet COX-1. The relevance of vascular COX-2-derived prostacyclin (PGI2) in endothelial thromboresistance and atheroprotection is clearly shown by animal and human models and by the adverse cardiovascular effects exerted by COX-2 inhibitors in humans. A vast array of arachidonic acid-transforming enzymes, downstream synthases and isomerases, transmembrane receptors, and specificity in their tissue expression make arachidonic acid metabolism a fine-tuning system of vascular health and disease. Its pharmacological regulation is central in human cardiovascular diseases, as demonstrated by biochemical measurements and intervention trials.

Lipid Profile of Activated Macrophages and Contribution of Group V Phospholipase A2

Macrophages activated by Interleukin (IL)-4 (M2) or LPS+ Interferon (IFN)γ (M1) perform specific functions respectively in type 2 inflammation and killing of pathogens. Group V phospholipase A₂ (Pla2g5) is required for the development and functions of IL-4-activated macrophages and phagocytosis of pathogens. Pla2g5-generated bioactive lipids, including lysophospholipids (LysoPLs), fatty acids (FAs), and eicosanoids, have a role in many diseases. However, little is known about their production by differentially activated macrophages. We performed an unbiased mass-spectrometry analysis of phospholipids (PLs), LysoPLs, FAs, and eicosanoids produced by Wild Type (WT) and Pla2g5-null IL-4-activated bone marrow-derived macrophages (IL-4)BM-Macs (M2) and (LPS+IFNγ)BM-Macs (M1). Phosphatidylcholine (PC) was preferentially metabolized in (LPS+IFNγ)BM-Macs and Phosphatidylethanolamine (PE) in (IL-4)BM-Macs, with Pla2g5 contributing mostly to metabolization of selected PE molecules. While Pla2g5 produced palmitic acid (PA) in (LPS+IFNγ)BM-Macs, the absence of Pla2g5 increased myristic acid (MA) in (IL-4)BM-Macs. Among eicosanoids, Prostaglandin E₂ (PGE₂) and prostaglandin D₂ (PGD₂) were significantly reduced in (IL-4)BM-Macs and (LPS+IFNγ)BM-Macs lacking Pla2g5. Instead, the IL-4-induced increase in 20-carboxy arachidonic acid (20CooH AA) was dependent on Pla2g5, as was the production of 12-hydroxy-heptadecatrienoic acid (12-HHTrE) in (LPS+IFNγ)BM-Macs. Thus, Pla2g5 contributes to PE metabolization, PGE₂ and PGD₂ production independently of the type of activation, while in (IL-4)BM-Macs, Pla2g5 regulates selective lipid pathways and likely novel functions.

The Role(s) of Eicosanoids and Exosomes in Human Parturition

The roles that eicosanoids play during pregnancy and parturition are crucial to a successful outcome. A better understanding of the regulation of eicosanoid production and the roles played by the various end products during pregnancy and parturition has led to our view that accurate measurements of a panel of those end products has exciting potential as diagnostics and prognostics of preterm labor and delivery. Exosomes and their contents represent an exciting new area for research of movement of key biological factors circulating between tissues and organs akin to a parallel endocrine system but involving key intracellular mediators. Eicosanoids and enzymes regulating their biosynthesis and metabolism as well as regulatory microRNAs have been identified within exosomes. In this review, the regulation of eicosanoid production, abundance and actions during pregnancy will be explored. Additionally, the functional significance of placental exosomes will be discussed.

Effects of prostaglandin E2 on gap junction protein alpha 1 in the rat epididymis

Gap junctions are responsible for intercellular communication. In the adult mammalian epididymis, gap junction protein alpha 1 (GJA1) is localized between basal and either principal or clear cells. GJA1 levels and localization change during the differentiation of basal cells. The present objective was to determine the role of basal cells and prostaglandin E2 (PGE2) on GJA1 in the rat epididymis. Prior to basal cell differentiation, GJA1 is colocalized with TJP1 at the apical lateral margins between adjacent epithelial cells. When basal cells are present, GJA1 becomes associated between basal and principal cells, where it is primarily immunolocalized until adulthood. Basal cells express TP63, differentiate from epithelial cells, and produce prostaglandin-endoperoxide synthase 1 by 21 days of age. Prior to day 21, GJA1and TP63 are not strongly associated at the apical region. However, by day 28, TP63-positive basal cells migrate to the base of the epithelium, and also express GJA1. To assess effects of PGE2 on GJA1, rat caput epididymal (RCE) cells were exposed to PGE2 (50 μM) for 3 h. PGE2 increased levels of Gja1 mRNA in RCE cells, while levels of Gjb1, Gjb2, Gjb4, and GjB5 were unaltered. Furthermore, PGE2 increased protein levels of GJA1, phospho-GJA1, phospho-AKT, CTNNB1, and phospho-CTNNB1. Total AKT and the tight junction protein claudin1 were also not altered by PGE2. Data suggest that development of the epididymal epithelium and differentiation of epididymal basal cells regulate the targeting of GJA1, and that this appears to be mediated by PGE2.

Druggable Prostanoid Pathway

Prostanoids (prostaglandins, prostacyclin and thromboxane) belong to the oxylipin family of biologically active lipids generated from arachidonic acid (AA). Protanoids control numerous physiological and pathological processes. Cyclooxygenase (COX) is a rate-limiting enzyme involved in the conversion of AA into prostanoids. There are two COX isozymes: the constitutive COX-1 and the inducible COX-2. COX-1 and COX-2 have similar structures, catalytic activities, and subcellular localizations but differ in patterns of expression and biological functions. Non-selective COX-1/2 or traditional, non-steroidal anti-inflammatory drugs (tNSAIDs) target both COX isoforms and are widely used to relieve pain, fever and inflammation. However, the use of NSAIDs is associated with various side effects, particularly in the gastrointestinal tract. NSAIDs selective for COX-2 inhibition (coxibs) were purposefully designed to spare gastrointestinal toxicity, but predisposed patients to increased cardiovascular risks. These health complications from NSAIDs prompted interest in the downstream effectors of the COX enzymes as novel drug targets. This chapter describes various safety issues with tNSAIDs and coxibs, and discusses the current development of novel classes of drugs targeting the prostanoid pathway, including nitrogen oxide- and hydrogen sulfide-releasing NSAIDs, inhibitors of prostanoid synthases, dual inhibitors, and prostanoid receptor agonists and antagonists.

Role of GluN2A NMDA receptor in homocysteine-induced prostaglandin E2 release from neurons

Hyperhomocysteinemia or systemic elevation of homocysteine is a metabolic condition that has been linked to multiple neurological disorders where inflammation plays an important role in the progression of the disease. However, it is unclear whether hyperhomocysteinemia contributes to disease pathology by inducing an inflammatory response. The current study investigates whether exposure of primary cultures from rat and mice cortical neurons to high levels of homocysteine induces the expression and release of the proinflammatory prostanoid, Prostaglandin E2 (PGE2). Using enzymatic assays and immunoblot analysis we show concurrent increase in the activity of cytosolic phospholipase A2 (cPLA2) and level of cyclooxygenase-2 (COX2), two enzymes involved in PGE2 biosynthesis. The findings also show an increase in PGE2 release from neurons. Pharmacological inhibition of GluN2A-containing NMDAR (GluN2A-NMDAR) with NVP-AAM077 significantly reduces homocysteine-induced cPLA2 activity, COX2 expression, and subsequent PGE2 release. Whereas, inhibition of GluN2B-containing NMDAR (GluN2A-NMDAR) with Ro 25-6981 has no effect. Complementary studies in neuron cultures obtained from wild type and GluN2A knockout mice show that genetic deletion of GluN2A subunit of NMDAR attenuates homocysteine-induced neuronal increase in cPLA2 activity, COX2 expression, and PGE2 release. Pharmacological studies further establish the role of both extracellular-regulated kinase/mitogen-activated protein kinase and p38 MAPK in homocysteine-GluN2A NMDAR-dependent activation of cPLA2-COX2-PGE2 pathway. Collectively, these findings reveal a novel role of GluN2A-NMDAR in facilitating homocysteine-induced proinflammatory response in neurons.

Systematic Understanding of Bioactive Lipids in Neuro-Immune Interactions: Lessons from an Animal Model of Multiple Sclerosis

Bioactive lipids, or lipid mediators, are utilized for intercellular communications. They are rapidly produced in response to various stimuli and exported to extracellular spaces followed by binding to cell surface G protein-coupled receptors (GPCRs) or nuclear receptors. Many drugs targeting lipid signaling such as non-steroidal anti-inflammatory drugs (NSAIDs), prostaglandins, and antagonists for lipid GPCRs are in use. For example, the sphingolipid analog, fingolimod (also known as FTY720), was the first oral disease-modifying therapy (DMT) for relapsing-remitting multiple sclerosis (MS), whose mechanisms of action (MOA) includes sequestration of pathogenic lymphocytes into secondary lymphoid organs, as well as astrocytic modulation, via down-regulation of the sphingosine 1-phosphate (S1P) receptor, S1P₁, by in vivo-phosphorylated fingolimod. Though the cause of MS is still under debate, MS is considered to be an autoimmune demyelinating and neurodegenerative disease. This review summarizes the involvement of bioactive lipids (prostaglandins, leukotrienes, platelet-activating factors, lysophosphatidic acid, and S1P) in MS and the animal model, experimental autoimmune encephalomyelitis (EAE). Genetic ablation, along with pharmacological inhibition, of lipid metabolic enzymes and lipid GPCRs revealed that each bioactive lipid has a unique role in regulating immune and neural functions, including helper T cell (T_H1 and T_H17) differentiation and proliferation, immune cell migration, astrocyte responses, endothelium function, and microglial phagocytosis. A systematic understanding of bioactive lipids in MS and EAE dredges up information about understudied lipid signaling pathways, which should be clarified in the near future to better understand MS pathology and to develop novel DMTs.

Up-regulation of COX-2 and mPGES-1 by 27-hydroxycholesterol and 4-hydroxynonenal: A crucial role in atherosclerotic plaque instability

Atherosclerosis is currently understood to be mainly the consequence of a complicated inflammatory process at the different stages of plaque development. Among the several inflammatory molecules involved, up-regulation of the functional cyclooxygenase 2/membrane-bound prostaglandin E synthase 1 (COX-2/mPGES-1) axis plays a key role in plaque development. Excessive production of oxidized lipids, following low-density lipoprotein (LDL) oxidation, is a characteristic feature of atherosclerosis. Among the oxidized lipids of LDLs, the oxysterol 27-hydroxycholesterol (27-OH) and the aldehyde 4-hydroxynonenal (HNE) substantially accumulate in the atherosclerotic plaque, contributing to its progression and instability through a variety of processes. This study shows that 27-OH and HNE promote up-regulation of both the inducible enzymes COX-2 and mPGES-1, leading to increased production of prostaglandin (PG) E₂ and inducible nitric oxide synthase, and the subsequent release of nitric oxide in human promonocytic U937 cells. The study also examined the potential involvement of the functionally coupled COX-2/mPGES-1 in enhancing the production of certain pro-inflammatory cytokines and of matrix metalloproteinase 9 by U937 cells. This enhancement is presumably due to the induction of PGE₂ synthesis, as a result of the up-regulation of the COX-2/mPGES-1, stimulated by the two oxidized lipids, 27-OH and HNE. Induction of PGE₂ synthesis might thus be a mechanism of plaque instability and eventual rupture, contributing to matrix metalloproteinase production by activated macrophages.

Raging the War Against Inflammation With Natural Products

Over the last few decade Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) are the drugs of choice for treating numerous inflammatory diseases including rheumatoid arthritis. The NSAIDs produces anti-inflammatory activity via inhibiting cyclooxygenase enzyme, responsible for the conversation of arachidonic acid to prostaglandins. Likewise, cyclooxegenase-2 inhibitors (COX-2) selectively inhibit the COX-2 enzyme and produces significant anti-inflammatory, analgesic, and anti-pyretic activity without producing COX-1 associated gastrointestinal and renal side effects. In last two decades numerous selective COX-2 inhibitors (COXIBs) have been developed and approved for various inflammatory conditions. However, data from clinical trials have suggested that the prolong use of COX-2 inhibitors are also associated with life threatening cardiovascular side effects including ischemic heart failure and myocardial infection. In these scenario secondary metabolites from natural product offers a great hope for the development of novel anti-inflammatory compounds. Although majority of the natural product based compounds exhibit more selectively toward COX-1. However, the data suggest that slight structural modification can be helpful in developing COX-2 selective secondary metabolites with comparative efficacy and limited side effects. This review is an effort to highlight the secondary metabolites from terrestrial and marine source with significant COX-2 and COX-2 mediated PGE2 inhibitory activity, since it is anticipated that isolates with ability to inhibit COX-2 mediated PGE2 production would be useful in suppressing the inflammation and its classical sign and symptoms. Moreover, this review has highlighted the potential lead compounds including berberine, kaurenoic acid, α-cyperone, curcumin, and zedoarondiol for further development with the help of structure-activity relationship (SAR) studies and their current status.

Kinetic effect of oestrogen on secretion of prostaglandins E2 and F2α in bovine oviduct epithelial cells

This study aimed to investigate the effect of oestrogen on prostaglandin E2 (PGE₂) and prostaglandin F2α (PGF_2α) secretion in bovine oviduct epithelial cells. Bovine oviduct epithelial cells were obtained from the lumen of fresh bovine oviducts. Quantitative real-time polymerase chain reaction and in-cell western assays were used to measure PGE₂ and PGF_2α synthase activity and enzyme-linked immunosorbent assays were used to detect the concentrations of the two prostaglandins in extracellular fluid. We observed that oestradiol caused a short-term increase in cyclo-oxygenase-2 (COX-2), which stimulated PGE₂ and PGF_2α secretion, and that a subsequent decrease in COX-2 and an increase in cyclo-oxygenase-1 (COX-1) produced a high PGE₂:PGF_2α ratio. These findings reflect the dynamic change in PGE₂ and PGF_2α levels under the influence of oestrogen, which may be essential for fertilisation.

The Neurokinin-1 Receptor Contributes to the Early Phase of Lipopolysaccharide-Induced Fever via Stimulation of Peripheral Cyclooxygenase-2 Protein Expression in Mice

Neurokinin (NK) signaling is involved in various inflammatory processes. A common manifestation of systemic inflammation is fever, which is usually induced in animal models with the administration of bacterial lipopolysaccharide (LPS). A role for the NK1 receptor was shown in LPS-induced fever, but the underlying mechanisms of how the NK1 receptor contributes to febrile response, especially in the early phase, have remained unknown. We administered LPS (120 µg/kg, intraperitoneally) to mice with the Tacr1 gene, i.e., the gene encoding the NK1 receptor, either present (Tacr1^+/+ ) or absent (Tacr1^-/- ) and measured their thermoregulatory responses, serum cytokine levels, tissue cyclooxygenase-2 (COX-2) expression, and prostaglandin (PG) E₂ concentration. We found that the LPS-induced febrile response was attenuated in Tacr1^-/- compared to their Tacr1^+/+ littermates starting from 40 min postinfusion. The febrigenic effect of intracerebroventricularly administered PGE₂ was not suppressed in the Tacr1^-/- mice. Serum concentration of pyrogenic cytokines did not differ between Tacr1^-/- and Tacr1^+/+ at 40 min post-LPS infusion. Administration of LPS resulted in amplification of COX-2 mRNA expression in the lungs, liver, and brain of the mice, which was statistically indistinguishable between the genotypes. In contrast, the LPS-induced augmentation of COX-2 protein expression was attenuated in the lungs and tended to be suppressed in the liver of Tacr1^-/- mice compared with Tacr1^+/+ mice. The Tacr1^+/+ mice responded to LPS with a significant surge of PGE₂ production in the lungs, whereas Tacr1^-/- mice did not. In conclusion, the NK1 receptor is necessary for normal fever genesis. Our results suggest that the NK1 receptor contributes to the early phase of LPS-induced fever by enhancing COX-2 protein expression in the periphery. These findings advance the understanding of the crosstalk between NK signaling and the "cytokine-COX-2-prostaglandin E₂" axis in systemic inflammation, thereby open up the possibilities for new therapeutic approaches.

Fever and hypothermia in systemic inflammation

Systemic inflammation-associated syndromes (e.g., sepsis and septic shock) often have high mortality and remain a challenge in emergency medicine. Systemic inflammation is usually accompanied by changes in body temperature: fever or hypothermia. In animal studies, systemic inflammation is often modeled by administering bacterial lipopolysaccharide, which triggers autonomic and behavioral thermoeffector responses and causes either fever or hypothermia, depending on the dose and ambient temperature. Fever and hypothermia are regulated changes of body temperature, which correspond to mild and severe forms of systemic inflammation, respectively. Mediators of fever and hypothermia are called endogenous pyrogens and cryogens; they are produced when the innate immune system recognizes an infectious pathogen. Upon an inflammatory challenge, hepatic and pulmonary macrophages (and later brain endothelial cells) start to release lipid mediators, of which prostaglandin (PG) E₂ plays the key role, and cytokines. Blood PGE₂ enters the brain and triggers fever. At later stages of fever, PGE₂ synthesized within the blood-brain barrier maintains fever. In both cases, PGE₂ is synthesized by cyclooxygenase-2 and microsomal PGE₂synthase-1. Mediators of hypothermia are not well established. Both fever and hypothermia are beneficial host defense responses. Based on evidence from studies in laboratory animals and clinical trials in humans, fever is beneficial for fighting mild infection. Based mainly on animal studies, hypothermia is beneficial in severe systemic inflammation and infection.

Flipping the cyclooxygenase (Ptgs) genes reveals isoform-specific compensatory functions

Two prostaglandin (PG) H synthases encoded by Ptgs genes, colloquially known as cyclooxygenase (COX)-1 and COX-2, catalyze the formation of PG endoperoxide H2, the precursor of the major prostanoids. To address the functional interchangeability of these two isoforms and their distinct roles, we have generated COX-2>COX-1 mice whereby Ptgs2 is knocked in to the Ptgs1 locus. We then "flipped" Ptgs genes to successfully create the Reversa mouse strain, where knock-in COX-2 is expressed constitutively and knock-in COX-1 is lipopolysaccharide (LPS) inducible. In macrophages, flipping the two Ptgs genes has no obvious impact on COX protein subcellular localization. COX-1 was shown to compensate for PG synthesis at high concentrations of substrate, whereas elevated LPS-induced PG production was only observed for cells expressing endogenous COX-2. Differential tissue-specific patterns of expression of the knock-in proteins were evident. Thus, platelets from COX-2>COX-1 and Reversa mice failed to express knock-in COX-2 and, therefore, thromboxane (Tx) production in vitro and urinary Tx metabolite formation in COX-2>COX-1 and Reversa mice in vivo were substantially decreased relative to WT and COX-1>COX-2 mice. Manipulation of COXs revealed isoform-specific compensatory functions and variable degrees of interchangeability for PG biosynthesis in cells/tissues.

Effect of estrogen on prostaglandin synthetase in bovine oviduct smooth muscle

Gamete and embryo transport is an important function of the oviduct. This type of transport involves both smooth muscle contraction and epithelial cell secretions, and the former is mediated by prostaglandins (PGs) and their receptors. Our objective was to study the regulation of prostaglandin synthetase (prostaglandin-endoperoxide synthase-1 (PTGS1), prostaglandin-endoperoxide synthase-2 (PTGS2), mPGES-1, mPGES-2, cPGES, and PGFS) by estradiol (E₂) in bovine oviduct smooth muscle. Prostaglandin synthetase mRNA and protein expression were investigated using real-time RT-PCR and Western blot analyses, respectively. Prostaglandin synthetase mRNA and protein expression were increased in oviductal smooth muscle tissue after treatment with different concentrations of estradiol for various time periods. The results indicated that there was no increase in expression observed after treatment with fulvestrant, a selective antagonist of the E₂ receptor, indicating that E₂ interacts with specific E₂ nuclear receptors to upregulate PTGS1, PTGS2, mPGES-1, and PGFS expression. In conclusion, E₂ increases PTGS1, mPGES-1, and PGFS mRNA and protein expression in bovine oviductal smooth muscle when added for different periods of time and at different concentrations. Additionally, E₂ is transported intracellularly and interacts with specific E₂ nuclear receptors to increase PTGS1, PTGS2, mPGES-1 and PGFS expression.

Eicosanoid storm in infection and inflammation

Controlled immune responses to infection and injury involve complex molecular signalling networks with coordinated and often opposing actions. Eicosanoids and related bioactive lipid mediators derived from polyunsaturated fatty acids constitute a major bioactive lipid network that is among the most complex and challenging pathways to map in a physiological context. Eicosanoid signalling, similar to cytokine signalling and inflammasome formation, has primarily been viewed as a pro-inflammatory component of the innate immune response; however, recent advances in lipidomics have helped to elucidate unique eicosanoids and related docosanoids with anti-inflammatory and pro-resolution functions. This has advanced our overall understanding of the inflammatory response and its therapeutic implications. The induction of a pro-inflammatory and anti-inflammatory eicosanoid storm through the activation of inflammatory receptors by infectious agents is reviewed here.

Multiple roles of the prostaglandin D2 signaling pathway in reproduction

Prostaglandins signaling molecules are involved in numerous physiological processes. They are produced by several enzyme-limited reactions upon fatty acids, which are catalyzed by two cyclooxygenases and prostaglandin synthases. In particular, the prostaglandins E2(PGE2), D2(PGD2), and F2(PGF2α) have been shown to be involved in female reproductive mechanisms. Furthermore, widespread expression of lipocalin- and hematopoietic-PGD2synthases in the male reproductive tract supports the purported roles of PGD2in the development of both embryonic and adult testes, sperm maturation, and spermatogenesis. In this review, we summarize the putative roles of PGD2signaling and the roles of both PGD2synthases in testicular formation and function. We review the data reporting the involvement of PGD2signaling in the differentiation of Sertoli and germ cells of the embryonic testis. Furthermore, we discuss the roles of lipocalin-PGD2synthase in steroidogenesis and spermatogenesis, in terms of lipid molecule transport and PGD2production. Finally, we discuss the hypothesis that PGD2signaling may be affected in certain reproductive diseases, such as infertility, cryptorchidism, and testicular cancer.

Modeling of eicosanoid fluxes reveals functional coupling between cyclooxygenases and terminal synthases

Eicosanoids, including prostaglandins (PG) and leukotrienes, are lipid mediators derived from arachidonic acid. A quantitative and biochemical level understanding of eicosanoid metabolism would aid in understanding the mechanisms that govern inflammatory processes. Here, we present a combined experimental and computational approach to understanding the biochemical basis of eicosanoid metabolism in macrophages. Lipidomic and transcriptomic measurements and analyses reveal temporal and dynamic changes of the eicosanoid metabolic network in mouse bone marrow-derived macrophages (BMDM) upon stimulation of the Toll-like receptor 4 with Kdo2-Lipid A (KLA) and stimulation of the P2X7 purinergic receptor with adenosine 5'-triphosphate. Kinetic models were developed for the cyclooxygenase (COX) and lipoxygenase branches of arachidonic acid metabolism, and then the rate constants were estimated with a data set from ATP-stimulated BMDM, using a two-step matrix-based approach employing a constrained least-squares method followed by nonlinear optimization. The robustness of the model was validated through parametric sensitivity, uncertainty analysis, and predicting an independent dataset from KLA-primed ATP-stimulated BMDM by allowing the parameters to vary within the uncertainty range of the calculated parameters. We analyzed the functional coupling between COX isozymes and terminal enzymes by developing a PGH2-divided model. This provided evidence for the functional coupling between COX-2 and PGE2 synthase, between COX-1/COX-2 and PGD2 synthase, and also between COX-1 and thromboxane A2 synthase. Further, these functional couplings were experimentally validated using COX-1 and COX-2 selective inhibitors. The resulting fluxomics analysis demonstrates that the "multi-omics" systems biology approach can define the complex machinery of eicosanoid networks.

Celecoxib attenuates hepatic cirrhosis through inhibition of epithelial-to-mesenchymal transition of hepatocytes

BACKGROUND AND AIM

The epithelial-mesenchymal transition (EMT) of hepatocytes is a key step for hepatic fibrosis and cirrhosis. Long-term administration of celecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor, can ameliorate hepatic fibrosis. This research aimed to examine the effect of celecoxib on the EMT of hepatocytes during the development of liver cirrhosis.

METHODS

Cirrhotic liver model of rat was established by peritoneal injection of thiacetamide (TAA). Thirty-six rats were randomly assigned to control, TAA, and TAA + celecoxib groups. Hepatic expressions of tumor necrosis factor-α (TNF-α), interleukin 6 (IL-6), COX-2, prostaglandin E2 (PGE2 ), matrix metalloproteinase (MMP)-2 and -9, transforming growth factor-β1 (TGF-β1), Phospho-Smad2/3, Snail1, α-smooth muscle actin (α-SMA), vimentin, collagen I, fibroblast-specific protein (FSP-1), E-cadherin and N-cadherin were quantitated. Hepatic fibrosis was assessed by the visible hepatic fibrotic areas and Ishak's scoring system.

RESULTS

Exposed to TAA treatment, hepatocytes underwent the process of EMT during hepatic fibrosis. Compared with those in TAA group, celecoxib significantly downregulated the hepatic expressions of TNF-α, IL-6, COX-2, PGE2 , MMP-2, MMP-9, TGF-β1, Phospho-Smad2/3, Snail1, α-SMA, FSP-1, and vimentin while greatly restoring the levels of E-cadherin. The fibrotic areas and collagen I levels of TAA + celecoxib group were much lower than those in TAA group.

CONCLUSIONS

Celecoxib could ameliorate hepatic fibrosis and cirrhosis in TAA-rat model through suppression of the mesenchymal biomarkers in the hepatocytes while restoring the levels of their epithelial biomarkers. The inhibitory effect of celecoxib on the EMT of hepatocytes is associated with reduction of intrahepatic inflammation, preservation of normal basement matrix, and inhibition of TGF-β1/Smad pathway.

Lipopolysaccharide-induced neuronal activation in the paraventricular and dorsomedial hypothalamus depends on ambient temperature

Systemic inflammatory response syndrome is associated with either fever or hypothermia, but the mechanisms responsible for switching from one to the other are unknown. In experimental animals, systemic inflammation is often induced by bacterial lipopolysaccharide (LPS). To identify the diencephalic and brainstem structures involved in the fever-hypothermia switch, we studied the expression of c-Fos protein, a marker of neuronal activation, in rats treated with the same high dose of LPS (0.5 mg/kg, intravenously) either in a thermoneutral (30 °C) or cool (24 °C) environment. At 30 °C, LPS caused fever; at 24 °C, the same dose caused profound hypothermia. Both fever and hypothermia were associated with the induction of c-Fos in many brain areas, including several structures of the anterior preoptic, paraventricular, lateral, and dorsal hypothalamus, the bed nucleus of the stria terminalis, the posterior pretectal nucleus, ventrolateral periaqueductal gray, lateral parabrachial nucleus, area postrema, and nucleus of the solitary tract. Every brain area studied showed a comparable response to LPS at the two different ambient temperatures used, with the exception of two areas: the dorsomedial hypothalamic nucleus (DMH), which we studied together with the adjacent dorsal hypothalamic area (DA), and the paraventricular hypothalamic nucleus (PVH). Both structures had much stronger c-Fos expression during LPS hypothermia than during fever. We propose that PVH and DMH/DA neurons are involved in a circuit, which - depending on the ambient temperature - determines whether the thermoregulatory response to bacterial LPS will be fever or hypothermia.

Cyclooxygenase-2, prostaglandin E2 glycerol ester and nitric oxide are involved in muscarine-induced presynaptic enhancement at the vertebrate neuromuscular junction

Previous work has demonstrated that activation of muscarinic acetylcholine receptors at the lizard neuromuscular junction (NMJ) induces a biphasic modulation of evoked neurotransmitter release: an initial depression followed by a delayed enhancement. The depression is mediated by the release of the endocannabinoid 2-arachidonylglycerol (2-AG) from the muscle and its binding to cannabinoid type 1 receptors on the motor nerve terminal. The work presented here suggests that the delayed enhancement of neurotransmitter release is mediated by cyclooxygenase-2 (COX-2) as it converts 2-AG to the glycerol ester of prostaglandin E2 (PGE2-G). Using immunofluorescence, COX-2 was detected in the perisynaptic Schwann cells (PSCs) surrounding the NMJ. Pretreatment with either of the selective COX-2 inhibitors, nimesulide or DuP 697, prevents the delayed increase in endplate potential (EPP) amplitude normally produced by muscarine. In keeping with its putative role as a mediator of the delayed muscarinic effect, PGE2-G enhances evoked neurotransmitter release. Specifically, PGE2-G increases the amplitude of EPPs without altering that of spontaneous miniature EPPs. As shown previously for the muscarinic effect, the enhancement of evoked neurotransmitter release by PGE2-G depends on nitric oxide (NO) as the response is abolished by application of either N(G)-nitro-l-arginine methyl ester (l-NAME), an inhibitor of NO synthesis, or carboxy-PTIO, a chelator of NO. Intriguingly, the enhancement is not prevented by AH6809, a prostaglandin receptor antagonist, but is blocked by capsazepine, a TRPV1 and TRPM8 receptor antagonist. Taken together, these results suggest that the conversion of 2-AG to PGE2-G by COX-2 underlies the muscarine-induced enhancement of neurotransmitter release at the vertebrate NMJ.

Microsomal prostaglandin E synthase type 2 (mPGES2) is a glutathione-dependent heme protein, and dithiothreitol dissociates the bound heme to produce active prostaglandin E2 synthase in vitro

An x-ray study indicated that microsomal prostaglandin E synthase type 2 (mPGES2) is a heme-bound protein and catalyzes prostaglandin (PG) H2 degradation, but not PGE2 formation (Yamada, T., and Takusagawa, F. (2007) Biochemistry 46, 8414-8424). In response to the x-ray study, Watanabe et al. claimed that mPGES2 is a heme-free protein and that both the heme-free and heme-bound proteins have PGE2 synthesis activity in the presence of dithiothreitol (Watanabe, K., Ito, S., and Yamamoto, S. (2008) Biochem. Biophys. Res. Commun. 367, 782-786). To resolve the contradictory results, the heme-binding scheme of mPGES2 was further characterized in vivo and in vitro by absorption and fluorescence spectroscopies. A substantial amount of heme-bound mPGES2 was detected in cell extracts. The heme content in mPGES2 was increased along with an increase in Fe(3+) in the culture medium. Heme-free mPGES2 was converted to the heme-bound form by mixing it with pig liver extract, indicating that mPGES2 is capable of forming a complex with heme in mammalian cells. Heme binds to mPGES2 only in the presence of glutathione. The newly determined heme dissociation constant (2.9 nM) supports strongly that mPGES2 is a heme-bound protein in vivo. The bound heme was not dissociated by oxidation by H2O2 or reduction by glutathione or 2-mercaptoethanol. However, reduction by dithiothreitol (an artificial reducing compound) induced the bound heme to dissociate from mPGES2 and released heme-free mPGES2, which exhibited PGE2 synthesis activity in vitro. Imidazole bound to mPGES2 by stacking on the bound heme and inhibited heme oxidation by H2O2 and reduction by dithiothreitol.

Eicosanoids in skin inflammation

Eicosanoids play an integral part in homeostatic mechanisms related to skin health and structural integrity. They also mediate inflammatory events developed in response to environmental factors, such as exposure to ultraviolet radiation, and inflammatory and allergic disorders, including psoriasis and atopic dermatitis. This review article discusses biochemical aspects related to cutaneous eicosanoid metabolism, the contribution of these potent autacoids to skin inflammation and related conditions, and considers the importance of nutritional supplementation with bioactives such as omega-3 and omega-6 polyunsaturated fatty acids and plant-derived antioxidants as means of addressing skin health issues.

Synergistic suppression of early phase of adipogenesis by microsomal PGE synthase-1 (PTGES1)-produced PGE2 and aldo-keto reductase 1B3-produced PGF2α

We recently reported that aldo-keto reductase 1B3-produced prostaglandin (PG) F_2α suppressed the early phase of adipogenesis. PGE₂ is also known to suppress adipogenesis. In this study, we found that microsomal PGE₂ synthase (PGES)-1 (mPGES-1; PTGES1) acted as the PGES in adipocytes and that PGE₂ and PGF_2α synergistically suppressed the early phase of adipogenesis. PGE₂ production was detected in preadipocytes and transiently enhanced at 3 h after the initiation of adipogenesis of mouse adipocytic 3T3-L1 cells, followed by a quick decrease; and its production profile was similar to the expression of the cyclooxygenase-2 (PTGS2) gene. When 3T3-L1 cells were transfected with siRNAs for any one of the three major PTGESs, i.e., PTGES1, PTGES2 (mPGES-2), and PTGES3 (cytosolic PGES), only PTGES1 siRNA suppressed PGE₂ production and enhanced the expression of adipogenic genes. AE1-329, a PTGER4 (EP4) receptor agonist, increased the expression of the Ptgs2 gene with a peak at 1 h after the initiation of adipogenesis. PGE₂-mediated enhancement of the PTGS2 expression was suppressed by the co-treatment with L-161982, a PTGER4 receptor antagonist. Moreover, AE1-329 enhanced the expression of the Ptgs2 gene by binding of the cyclic AMP response element (CRE)-binding protein to the CRE of the Ptgs2 promoter; and its binding was suppressed by co-treatment with L-161982, which was demonstrated by promoter luciferase and chromatin immunoprecipitation assays. Furthermore, when 3T3-L1 cells were caused to differentiate into adipocytes in medium containing both PGE₂ and PGF_2α, the expression of the adipogenic genes and the intracellular triglyceride level were decreased to a greater extent than in medium containing either of them, revealing that PGE₂ and PGF_2α independently suppressed adipogenesis. These results indicate that PGE₂ was synthesized by PTGES1 in adipocytes and synergistically suppressed the early phase of adipogenesis of 3T3-L1 cells in cooperation with PGF_2α through receptor-mediated activation of PTGS2 expression.

Involvement of PGE2 and the cAMP signalling pathway in the up-regulation of COX-2 and mPGES-1 expression in LPS-activated macrophages

PG (prostaglandin) E2 plays an important role in the modulation of the immune response and the inflammatory process. In the present study, we describe a PGE2 positive feedback for COX (cyclo-oxygenase)-2 and mPGES-1 [microsomal PGES (PGE synthase)-1] expression in the macrophage cell line RAW 264.7. Our results show that PGE2 induces COX-2 and mPGES-1 expression, an effect mimicked by dbcAMP (dibutyryl-cAMP) or forskolin. Furthermore, the cAMP signalling pathway co-operates with LPS (lipopolysaccharide) in the induction of COX-2 and mPGES-1 transcriptional activation. Analysis of the involvement of PGE receptors [EPs (E-prostanoids)] showed that incubation with EP2 agonists up-regulated both COX2 and mPGES-1 mRNA levels. Moreover, EP2 receptor overexpression enhanced the transcriptional activation of COX2 and mPGES-1 promoters. This induction was repressed by the PKA (protein kinase A) inhibitor H89. Activation of the PGE2/EP2/PKA signalling pathway induced the phosphorylation of CREB [CRE (cAMP-response element)-binding protein] in macrophages and stimulated the specific binding of this transcription factor to COX2 and mPGES-1 promoters. Deletion or mutation of potential CRE sites in both promoters diminished their transcriptional activity. In summary, the results of the present study demonstrate that activation of PKA/CREB signalling through the EP2 receptor by PGE2 plays a key role in the expression of COX-2 and mPGES-1 in activated macrophages.

Cyclooxygenase-2 contributes to VX-induced cell death in cultured cortical neurons

The link between cell death and increased cyclooxygenases-2 (COX-2) activity has not been clearly established. In this study, we examined whether COX-2 activation contributed to the mechanism of neurotoxicity produced by an organophosphorous nerve agent in cultured rat cortical neurons. Exposure of neuronal cells to the nerve agent, VX resulted in an increase in COX enzyme activity in the culture media. A concentration dependent increase in the activity levels of COX-2 enzyme was observed while there was little to no effect on COX-1. In addition, COX-2 mRNA and protein levels increased several hours post-VX exposure. Pre-treatment of the cortical cells with the COX-2 selective inhibitor, NS 398 resulted in a decrease in both the enzyme activity and prostaglandin (PGE(2) and PGF(2α)) release, as well as in a reduction in cell death. These findings indicate that the increase in COX-2 activity may contribute to the mechanism of VX-induced neurotoxicity in cultured rat cortical neuron.

Role of PGE2 in asthma and nonasthmatic eosinophilic bronchitis

Eosinophilic bronchitis is a common cause of chronic cough, which like asthma is characterized by sputum eosinophilia, but unlike asthma there is no variable airflow obstruction or airway hyperresponsiveness. Several studies suggest that prostaglandins may play an important role in orchestrating interactions between different cells in several inflammatory diseases such as asthma. PGE₂ is important because of the multiplicity of its effects on immune response in respiratory diseases; however, respiratory system appears to be unique in that PGE₂ has beneficial effects. We described that the difference in airway function observed in patients with eosinophilic bronchitis and asthma could be due to differences in PGE₂ production. PGE₂ present in induced sputum supernatant from NAEB patients decreases BSMC proliferation, probably due to simultaneous stimulation of EP2 and EP4 receptors with inhibitory activity. This protective effect of PGE₂ may not only be the result of a direct action exerted on airway smooth-muscle proliferation but may also be attributable to the other anti-inflammatory actions.

Lipidomics of polyunsaturated-fatty-acid-derived oxygenated metabolites

Nutritionally important PUFAs (polyunsaturated fatty acids) mediate some of their bioactivities through formation of oxygenated metabolites. These bioactive lipids are formed by COX (cyclo-oxygenase), LOX (lipoxygenase) and cytochrome-P450-catalysed reactions, as well as non-enzymatic lipid peroxidation. These reactions produce numerous species, some of which can be formed through more than one pathway. MS-based lipidomics offers the selectivity and sensitivity required for qualitative and quantitative analysis of multiple lipid species, in a variety of biological systems, and can facilitate the study of these mediators.

Inhibition of cyclooxygenase-2 reduces hypothalamic excitation in rats with adriamycin-induced heart failure

BACKGROUND

The paraventricular nucleus (PVN) of the hypothalamus plays an important role in the progression of heart failure (HF). We investigated whether cyclooxygenase-2 (COX-2) inhibition in the PVN attenuates the activities of sympathetic nervous system (SNS) and renin-angiotensin system (RAS) in rats with adriamycin-induced heart failure.

METHODOLOGY/PRINCIPAL FINDING

Heart failure was induced by intraperitoneal injection of adriamycin over a period of 2 weeks (cumulative dose of 15 mg/kg). On day 19, rats received intragastric administration daily with either COX-2 inhibitor celecoxib (CLB) or normal saline. Treatment with CLB reduced mortality and attenuated both myocardial atrophy and pulmonary congestion in HF rats. Compared with the HF rats, ventricle to body weight (VW/BW) and lung to body weight (LW/BW) ratios, heart rate (HR), left ventricular end-diastolic pressure (LVEDP), left ventricular peak systolic pressure (LVPSP) and maximum rate of change in left ventricular pressure (LV±dp/dtmax) were improved in HF+CLB rats. Angiotensin II (ANG II), norepinephrine (NE), COX-2 and glutamate (Glu) in the PVN were increased in HF rats. HF rats had higher levels of ANG II and NE in plasma, higher level of ANG II in myocardium, and lower levels of ANP in plasma and myocardium. Treatment with CLB attenuated these HF-induced changes. HF rats had more COX-2-positive neurons and more corticotropin releasing hormone (CRH) positive neurons in the PVN than did control rats. Treatment with CLB decreased COX-2-positive neurons and CRH positive neurons in the PVN of HF rats.

CONCLUSIONS

These results suggest that PVN COX-2 may be an intermediary step for PVN neuronal activation and excitatory neurotransmitter release, which further contributes to sympathoexcitation and RAS activation in adriamycin-induced heart failure. Treatment with COX-2 inhibitor attenuates sympathoexcitation and RAS activation in adriamycin-induced heart failure.

Production of prostaglandin e(2) and i(2) is coupled with cyclooxygenase-2 in human follicular dendritic cells

Background

Prostaglandins (PGs) play pathogenic and protective roles in inflammatory diseases. The novel concept of PGs as immune modulators is being documented by several investigators. By establishing an in vitro experimental model containing human follicular dendritic cell-like cells, HK cells, we reported that HK cells produce prostaglandin E₂ (PGE₂) and prostaglandin I₂ (PGI₂) and that these PGs regulate biological functions of T and B cells.

Methods

To investigate the respective contribution of cyclooxygenase-1 (COX-1) and COX-2 to PGE₂ and PGI₂ production in HK cells, we performed siRNA technology to knock down COX enzymes and examined the effect on PG production.

Results

Both PGE₂ and PGI₂ productions were almost completely inhibited by the depletion of COX-2. In contrast, COX-1 knockdown did not significantly affect PG production induced by lipopolysaccharide (LPS).

Conclusion

The current results suggest that mPGES-1 and PGIS are coupled with COX-2 but not with COX-1 in human follicular dendritic cell (FDC) and may help understand the potential effects of selective COX inhibitors on the humoral immunity.

Prostaglandin E(2) potentiates methylmalonate-induced seizures

PURPOSE

Methylmalonic acidemias are inherited metabolic disorders characterized by methylmalonate (MMA) accumulation and neurologic dysfunction, including seizures. It is known that metabolic crises in affected patients are precipitated by infections. Although growing evidence supports that inflammation facilitates seizures, it is not known whether inflammatory mediators facilitate MMA-induced seizures. Therefore, in this study we investigate the involvement of cyclooxygenase-2 (COX-2) and prostaglandin E(2) (PGE(2)) in MMA-induced seizures.

METHODS

Adult male Wistar rats were implanted with electrodes over the parietal cortex for electroencephalography (EEG) recording and a cannula in the right lateral ventricle. Animals were injected with PGE(2) (100 ng/2 μl, i.c.v.) or phosphate-buffered saline (PBS) (2 μl, i.c.v.), 15 min before MMA (2.5 μmol/2.5 μl, i.c.v.) or NaCl (2.5 μmol/2.5 μl, i.c.v.). The anticonvulsant effect of celecoxib (0.2; 2 or 20 mg/kg, p.o., 60 min before MMA) on MMA-induced seizures, and whether PGE(2) (10 or 100 ng/2 μl, i.c.v.) prevented the anticonvulsant effect of celecoxib (2 mg/kg, p.o.) were also investigated.

KEY FINDINGS

PGE(2) decreased the latency to MMA-induced jerks and generalized seizures, and increased the amplitude of generalized seizure EEG recordings. The selective COX-2 inhibitor celecoxib at the dose 2 mg/kg, but not at the dose 20 mg/kg, completely prevented MMA-induced seizures. The protective effect of celecoxib (2 mg/kg) against MMA-induced seizures was prevented by PGE(2).

SIGNIFICANCE

These results support a role for PGE(2) in the seizures elicited by MMA, which is in agreement with the view that infections may precipitate and exacerbate neurologic dysfunction in patients with MMA acidemic.

Rapid degradation of cyclooxygenase-1 and hematopoietic prostaglandin D synthase through ubiquitin-proteasome system in response to intracellular calcium level

Cyclooxygenase (COX)-1 and hematopoietic prostaglandin (PG) D synthase (H-PGDS) proteins, which are both involved in the arachidonate cascade, were stable in human megakaryocytic MEG-01 cells. In contrast, once the intracellular calcium level was increased by treatment with a calcium ionophore, both protein levels rapidly decreased with a half-life of less than 30 and 120 min for COX-1 and H-PGDS, respectively. In the presence of a proteasome inhibitor, COX-1 and H-PGDS proteins accumulated within 10 and 30 min, respectively, and concurrently appeared as the high-molecular-mass ubiquitinated proteins within 30 and 60 min, respectively, after an increase in the intracellular calcium level. The ubiquitination of these proteins was also observed when ADP, instead of a calcium ionophore, was used as an inducer to elevate the intracellular calcium level. When the entry of calcium ion into the cells was inhibited by ethylene glycol tetraacetic acid (EGTA), the ubiquitination of COX-1 and H-PGDS was clearly suppressed; and the addition of CaCl(2) to the medium cleared the EGTA-mediated suppression of the ubiquitination. These results indicate that COX-1 and H-PGDS were rapidly ubiquitinated and degraded through the ubiquitin-proteasome system in response to the elevation of the intracellular calcium level.

Inhibition of aldose reductase prevents endotoxin-induced inflammation by regulating the arachidonic acid pathway in murine macrophages

The bacterial endotoxin lipopolysaccharide (LPS) is known to induce release of arachidonic acid (AA) and its metabolic products, which play important roles in the inflammatory process. We have shown earlier that LPS-induced signals in macrophages are mediated by aldose reductase (AR). Here we have investigated the role of AR in LPS-induced release of AA metabolites and their modulation using a potent pharmacological inhibitor, fidarestat, and AR siRNA ablation in RAW264.7 macrophages and AR-knockout mouse peritoneal macrophages and heart tissue. Inhibition or genetic ablation of AR prevented the LPS-induced synthesis and release of AA metabolites such as PGE2, TXB, PGI2, and LTBs in macrophages. LPS-induced activation of cPLA2 was also prevented by AR inhibition. Similarly, AR inhibition also prevented the calcium ionophore A23187-induced cPLA2 and LTB4 in macrophages. Further, AR inhibition by fidarestat prevented the expression of AA-metabolizing enzymes such as COX-2 and LOX-5 in RAW264.7 cells and AR-knockout mouse-derived peritoneal macrophages. LPS-induced expression of AA-metabolizing enzymes and their catalyzed metabolic products was significantly lower in peritoneal macrophages and heart tissue from AR-knockout mice. LPS-induced activation of redox-sensitive signaling intermediates such as MAPKs, transcription factor NF-κB, and EGR-1, a transcriptional regulator of mPGES-1, which in collaboration with COX-2 leads to the production of PGE2, was also significantly prevented by AR inhibition. Taken together, our results indicate that AR mediates LPS-induced inflammation by regulating the AA-metabolic pathway and thus provide a novel role for AR inhibition in preventing inflammatory complications such as sepsis.

Specificity of eicosanoid production depends on the TLR-4-stimulated macrophage phenotype

Eicosanoid metabolism differs in profile and quantity between macrophages of different tissue origin and method of elicitation, as well as between primary and immortalized macrophages after activation with inflammatory stimuli. Using a lipidomic approach, we comprehensively analyzed the eicosanoids made by murine RPMs, TGEMs, BMDM, and the macrophage-like cell line RAW after stimulation with the TLR-4-specific agonist KLA. Direct correlation among total COX metabolites, COX side-products (11-HETE, 15-HETE), COX-2 mRNA, and protein at 8 h was found when comparing each cell type. Comprehensive qPCR analysis was used to compare relative transcript levels between the terminal prostanoid synthases themselves as well as between each cell type. Levels of PGE(2), PGD(2), and TxB(2) generally correlated with enzyme transcript expression of PGES, PGDS, and TBXS, providing evidence of comparable enzyme activities. PGIS transcript was expressed only in RPM and TGEM macrophages and at an exceptionally low level, despite high metabolite production compared with other synthases. Presence of PGIS in RPM and TGEM also lowered the production of PGE(2) versus PGD(2) by approximately tenfold relative to BMDM and RAW cells, which lacked this enzyme. Our results demonstrate that delayed PG production depends on the maximal level of COX-2 expression in different macrophages after TLR-4 stimulation. Also, the same enzymes in each cell largely dictate the profile of eicosanoids produced depending on the ratios of expression between them, with the exception of PGIS, which appears to have much greater synthetic capacity and competes selectively with mPGES-1.

Platelets participate in synovitis via Cox-1-dependent synthesis of prostacyclin independently of microparticle generation

In addition to the well-described role of platelets in thrombosis, a growing body of evidence implicates platelets in diverse inflammatory responses. We recently showed platelets can contribute to the pathophysiology of inflammatory arthritis via IL-1- containing microparticles. In this study, we demonstrate that platelets, and not platelet microparticles, actively contribute to synovitis via production of proinflammatory prostacyclin in an autoimmune arthritis model. Using both genetic and pharmacologic approaches, we establish that paracrine production of prostacyclin proceeds in the absence of cyclooxygenase-2. Furthermore, we also demonstrate that prostacyclin generation can arise via transcellular collaboration between platelets and fibroblast-like synoviocytes. In addition to shedding light on an unappreciated pathway of lipid synthesis in arthritis, we further delineate a novel effector activity by which platelets can contribute to inflammatory disease.

Hematopoietic-Prostaglandin D2 synthase through PGD2 production is involved in the adult ovarian physiology

Background

The prostaglandin D2 (PGD2) pathway is involved in numerous biological processes and while it has been identified as a partner of the embryonic sex determining male cascade, the roles it plays in ovarian function remain largely unknown. PGD2 is secreted by two prostaglandin D synthases (Pgds); the male-specific lipocalin (L)-Pgds and the hematopoietic (H)-Pgds.

Methods

To study the expression of the Pgds in the adult ovary, in situ hybridization were performed. Then, to evaluate the role of H-Pgds produced PGD2 in the ovarian physiology, adult female mice were treated with HQL-79, a specific inhibitor of H-Pgds enzymatic activity. The effects on expression of the gonadotrophin receptors FshR and LhR, steroidogenic genes Cyp11A1, StAR and on circulating progesterone and estradiol, were observed.

Results

We report the localization of H-Pgds mRNA in the granulosa cells from the primary to pre-ovulatory follicles. We provide evidence of the role of H-Pgds-produced PGD2 signaling in the FSH signaling through increased FshR and LhR receptor expression. This leads to the activation of steroidogenic Cyp11A1 and StAR gene expression leading to progesterone secretion, independently on other prostanoid-synthetizing mechanisms. We also identify a role whereby H-Pgds-produced PGD2 is involved in the regulation of follicular growth through inhibition of granulosa cell proliferation in the growing follicles.

Conclusions

Together, these results show PGD2 signaling to interfere with FSH action within granulosa cells, thus identifying an important and unappreciated role for PGD2 signaling in modulating the balance of proliferation, differentiation and steroidogenic activity of granulosa cells.

Comprehensive expression analysis of prostanoid enzymes and receptors in the human endometrium across the menstrual cycle

Prostanoids are well-described primary mediators of inflammatory processes and are essential for the normal physiological function of the female reproductive system. The aim of this study was to determine the temporal expression of the prostanoid biosynthetic enzymes (PTGS1, PTGS2, PTGES, PTGES2, PTGES3, AKR1B1, AKR1C3, CBR1, HPGDS, PTGDS, PTGIS, TBXAS1 and HPGD) and the prostanoid receptors (PTGER1, PTGER2, PTGER3, PTGER4, PTGFR, PTGDR, GPR44, PTGIR and TBXA2R) in the human endometrium throughout the menstrual cycle. The analysis identified PTGFR to have a distinct expression profile compared with other components of the prostanoid system, as expression is maximal during the proliferative phase. Immunohistochemical analysis for PTGER1 suggests a dual function for this receptor depending on its temporal (proliferative versus secretory) and spatial (nuclear versus cell membrane) expression. The expression profiles of the PGF(2α) synthases identified AKR1B1 and CBR1 as the likely regulators of PGF(2α) production during the menstrual phase. Immunohistochemical analysis for AKR1B1, CBR1 and AKR1C3 suggest expression to be in the glandular epithelium and vasculature. This study represents the first comprehensive analysis of the components of prostanoid biosynthetic and signalling pathway in the human endometrium. The expression profiles described have the potential to identify specific prostanoid components that may be dysregulated in inflammatory-associated disorders of the endometrium.

Enhanced pressor response to acute Ang II infusion in mice lacking membrane-associated prostaglandin E2 synthase-1

AIM

To examine the contribution of vascular membrane-associated prostaglandin E2 synthase-1 (mPGES-1) to acute blood pressure homeostasis.

METHODS

Angiotensin II (AngII, 75 pmol·kg⁻¹·min⁻¹) was continuously infused via the jugular vein into wild-type and mPGES-1(-/-) mice for 30 min, and blood pressure was measured by carotid arterial catheterization. RT-PCR and immunohistochemistry were performed to detect the expression and localization of mPGES-1 in the mouse arterial vessels. Mesenteric arteries were dissected from mice of both genotypes to study vessel tension and measure vascular PGE2 levels.

RESULTS

Wild-type and mPGES-1(-/-) mice showed similar blood pressure levels at baseline, and the acute intravenous infusion of AngII caused a greater increase in mean arterial pressure in the mPGES-1(-/-) group, with a similar diuretic and natriuretic response in both groups. mPGES-1 was constitutively expressed in the aortic and mesenteric arteries and vascular smooth muscle cells of wild-type mice. Strong staining was detected in the smooth muscle layer of arterial vessels. Ex vivo treatment of mesenteric arteries with AngII produced more vasodilatory PGE2 in wild-type than in mPGES-1(-/-) mice. In vitro tension assays further revealed that the mesenteric arteries of mPGES-1(-/-) mice exhibited a greater vasopressor response to AngII than those arteries of wild-type mice.

CONCLUSION

Vascular mPGES-1 acts as an important tonic vasodilator, contributing to acute blood pressure regulation.

Mitochondrial dysfunction and reduced prostaglandin synthesis in skeletal muscle of Group VIB Ca2+-independent phospholipase A2gamma-deficient mice

Group VIB Ca(2+)-independent phospholipase A(2)γ (iPLA(2)γ) is a membrane-bound iPLA(2) enzyme with unique features, such as the utilization of distinct translation initiation sites and the presence of mitochondrial and peroxisomal localization signals. Here we investigated the physiological functions of iPLA(2)γ by disrupting its gene in mice. iPLA(2)γ-knockout (KO) mice were born with an expected Mendelian ratio and appeared normal and healthy at the age of one month but began to show growth retardation from the age of two months as well as kyphosis and significant muscle weakness at the age of four months. Electron microscopy revealed swelling and reduced numbers of mitochondria and atrophy of myofilaments in iPLA(2)γ-KO skeletal muscles. Increased lipid peroxidation and the induction of several oxidative stress-related genes were also found in the iPLA(2)γ-KO muscles. These results provide evidence that impairment of iPLA(2)γ causes mitochondrial dysfunction and increased oxidative stress, leading to the loss of skeletal muscle structure and function. We further found that the compositions of cardiolipin and other phospholipid subclasses were altered and that the levels of myoprotective prostanoids were reduced in iPLA(2)γ-KO skeletal muscle. Thus, in addition to maintenance of homeostasis of the mitochondrial membrane, iPLA(2)γ may contribute to modulation of lipid mediator production in vivo.

Acyl chain-dependent effect of lysophosphatidylcholine on endothelial prostacyclin production

Previously we identified palmitoyl-lysophosphatidylcholine (16:0 LPC), linoleoyl-LPC (18:2 LPC), arachidonoyl-LPC (20:4 LPC), and oleoyl-LPC (18:1 LPC) as the most prominent LPC species generated by the action of endothelial lipase (EL) on high-density lipoprotein. In the present study, the impact of those LPC on prostacyclin (PGI(2)) production was examined in vitro in primary human aortic endothelial cells (HAEC) and in vivo in mice. Although 18:2 LPC was inactive, 16:0, 18:1, and 20:4 LPC induced PGI(2) production in HAEC by 1.4-, 3-, and 8.3-fold, respectively. LPC-elicited 6-keto PGF1α formation depended on both cyclooxygenase (COX)-1 and COX-2 and on the activity of cytosolic phospholipase type IVA (cPLA2). The LPC-induced, cPLA2-dependent (14)C-arachidonic acid (AA) release was increased 4.5-fold with 16:0, 2-fold with 18:1, and 2.7-fold with 20:4 LPC, respectively, and related to the ability of LPC to increase cytosolic Ca(2+) concentration. In vivo, LPC increased 6-keto PGF(1α) concentration in mouse plasma with a similar order of potency as found in HAEC. Our results indicate that the tested LPC species are capable of eliciting production of PGI(2), whereby the efficacy and the relative contribution of underlying mechanisms are strongly related to acyl-chain length and degree of saturation.

Uptake of dihomo-gamma-linolenic acid by murine macrophages increases series-1 prostaglandin release following lipopolysaccharide treatment

Administration of dihomo-gamma-linolenic acid is useful for atopic dermatitis and atherosclerosis in mice; however, the metabolites of dihomo-gamma-linolenic acid have been little studied. We employed a method which enabled simultaneous analysis of nine prostaglandins using liquid chromatography-tandem mass spectrometry, and determined the concentrations of prostaglandins in the supernatants of cultures of mouse peritoneal macrophages stimulated with lipopolysaccharide after pre-incubation with dihomo-gamma-linolenic acid, arachidonic acid, or eicosapentaenoic acid. Accumulated prostaglandin concentrations from mouse macrophages with dihomo-gamma-linolenic acid uptake increased in a dihomo-gamma-linolenic acid concentration-dependent fashion. These increases were mainly due to prostaglandin D(1) and prostaglandin E(1). The order of accumulated prostaglandin concentrations was dihomo-gamma-linolenic acid>arachidonic acid>eicosapentaenoic acid in supernatants with the same concentration of polyunsaturated fatty acid. Since mouse macrophages can clearly produce series-1 prostaglandins, they must be formed in vivo. These findings suggest that the effects of dihomo-gamma-linolenic acid on diseases may be due to series-1 prostaglandins.