Quick viewing(Text Mode)

Lipid Mediators in Life Science

Lipid Mediators in Life Science

Exp. Anim. 60(1), 7–20, 2011

—Review— Review Series: Frontiers of Model Animals for Human Diseases Lipid Mediators in Life Science

Makoto Murakami1, 2)

1)Biomembrane Signaling Project, The Tokyo Metropolitan Institute of Medical Science, 2–1–6 Kamikitazawa, Setagaya-ku, Tokyo 156-8506 and 2)Department of Health Chemistry, School of Pharmaceutical Science, Showa University, 1–5–8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan

Abstract: “Lipid mediators” represent a class of bioactive lipids that are produced locally through specific biosynthetic pathways in response to extracellular stimuli. They are exported extracellularly, bind to their cognate G protein-coupled receptors (GPCRs) to transmit signals to target cells, and are then sequestered rapidly through specific enzymatic or non-enzymatic processes. Because of these properties, lipid mediators can be regarded as local hormones or autacoids. Unlike proteins, whose information can be readily obtained from the genome, we cannot directly read out the information of lipids from the genome since they are not genome-encoded. However, we can indirectly follow up the dynamics and functions of lipid mediators by manipulating the genes encoding a particular set of proteins that are essential for their biosynthesis (enzymes), transport (transporters), and signal transduction (receptors). Lipid mediators are involved in many physiological processes, and their dysregulations have been often linked to various diseases such as , infertility, atherosclerosis, ischemia, metabolic syndrome, and cancer. In this article, I will give an overview of the basic knowledge of various lipid mediators, and then provide an example of how research using mice, gene-manipulated for a lipid mediator-biosynthetic enzyme, contributes to life science and clinical applications. Key words: , knockout mouse, lipid mediator, lysophospholipid,

Introduction non-lipidologists. These primarily arose because of the many difficulties of working with bioactive lipids, which Although it has been decades since the term “bioactive are hydrophobic (water-insoluble), unstable, structur- lipids” was broadly defined as changes in lipid levels ally variable, and typically present only in small amounts. that result in functional consequences, it has only start- Now, it has become increasingly difficult to find events ed to gain traction in the past 20 years. Now, it prom- in medical biology in which lipids do not play important, ises to occupy center stage in biological research in the if not central, roles as signaling and regulatory molecules. 21st century. This delayed recognition has its roots in Imbalance of lipid mediator signaling pathways clearly classic ideas about exclusive roles for lipids as a nutrient contributes to disease progression in inflammation, au- source of energy and as a main component of cell mem- toimmunity, allergy, cancer, atherosclerosis, hyperten- branes, which prevented general recognition of lipids by sion, metabolic syndrome, and degenerative diseases,

(Received 7 May 2010 / Accepted 23 July 2010) Address corresponding: M. Murakami, Biomembrane Signaling Project, The Tokyo Metropolitan Institute of Medical Science, 2–1–6 Kamikitazawa, Setagaya-ku, Tokyo 156-8506, Japan 8 M. Murakami among others. In this article, I will provide an overview tively, were identified. In 1982, Samuelsson and Berg- of the classification and roles of various lipid mediators, strom (Sweden) who had discovered PGs and LTs, and such as , lysophospholipids, sphingolipids, Vane (UK) who had found that exerts its anti- and endocannabinoids. In the latter part, I will focus on inflammatory action through inhibiting COX, were a particular enzyme that produces the most intensively awarded the Nobel Prize. Thousands of studies involv- studied lipid mediator, PGE2. On the bases of cell bio- ing biochemical, pharmacological and gene knockout logical and clinical studies, together with recent analyses strategies have delineated the regulatory actions of in- of mice with manipulation of its gene, PGE2 synthase dividual PGs, LTs and other related eicosanoids in a wide (PGES) now attracts much attention as a potential target variety of physiological and pathological systems, and for a new class of anti-inflammatory, analgesic and anti- many compounds that can block the eicosanoid pathway cancer drugs which are currently being developed. are currently in clinical use. The major eicosanoid path- ways are illustrated in Fig. 1. Lipid Mediators So far, five major bioactive that act on

their cognate GPCRs, namely PGE2, PGD2, PGF2α, PGI2

Lipid mediators can be historically and structurally and (TXA2), are known. They are pro- grouped into three categories. Class 1 includes well- duced through three sequential enzymatic steps: release known (AA)-derived eicosanoids in- of AA from membrane glycerophospholipids by various cluding (PGs), leukotrienes (LTs) and A2 (PLA2) subtypes, oxygenated conver- their relatives [4, 56]. Class 2 includes lysophospholip- sion of AA to PGG2 and then to PGH2 by either constitu- ids or their derivatives such as platelet-activating factor tive COX-1 or inducible COX-2, and finally isomeriza-

(PAF), (LPA) and sphingosine-1- tion of PGH2 to individual bioactive prostanoids by phosphate (S1P), which possess either glycerol or sphin- specific terminal PG synthases [56]. On the basis of gosine backbone [9, 21, 78]. Endocannabinoids can also analyses of mice gene-manipulated for the biosynthetic be categorized in this class, since the hallmark endocan- enzymes and receptors, together with pharmacological nabinoid, 2-arachidonoyl-glycerol, has a glycerol back- studies using enzyme inhibitors and agonists/ bone and since endocannabinoid receptors cluster in antagonists, many physiological and pathological func- close proximity to lysophospholipid receptors on the tions have been assigned to each . For in- phylogenetic tree [11]. Class 3 represents newly identi- stance, sleep, allergy and adiposity are regulated by fied anti-inflammatory lipid mediators derived fromω -3 PGD2, parturition and fibrosis by PGF2α, anti-thrombo- polyunsaturated fatty acids (PUFAs), such as sis and arthritis by PGI2, and thrombosis and atheroscle-

[derived from (EPA)] and protec- rosis by TXA2. PGE2 is the most pleiotropic prostanoid tins [derived from (DHA)] [2], that is produced by a variety of cell types and controls whose biosynthetic enzymes and receptors are not yet many pathological events, such as inflammation, fever, fully understood. In addition, given the recent findings pain, and cancer, through its receptors EP1 to EP4 [76]. of a few unique GPCRs that recognize medium- to long- Aspirin and related non-steroidal anti-inflammatory chain fatty acids [75], it is conceivable that some nutri- drugs (NSAIDs), which inhibit COX enzymes and ent lipids abundantly present in the circulation or tissues thereby shut off the synthesis of all prostanoids, are could exhibit lipid mediator-like actions and be regard- among the most commonly used drugs worldwide. How- ed as another class of lipid mediators. ever, since one prostanoid often counteracts another, blocking a specific prostanoid pathway, rather than mul- Class 1: eicosanoids tiple pathways altogether, would provide a more effica- It was about half a century ago when the first (or clas- cious strategy for drug development. For instance, sical) class of lipid mediators, eicosanoids (PGs and PGD2, a major prostanoid produced by mast cells, exerts LTs), which are produced from AA via the cyclooxyge- its pro-allergic action through the two receptors DP1 and nase (COX) and lipoxygenase (LOX) pathways, respec- DP2 [46], whereas PGE2 produced from stromal cells Overview of lipid mediators 9

Fig. 1. Lipid mediator pathways. PLA2 hydrolyzes membrane phospholipids to liberate PUFAs (e.g., arachidonic acid, EPA, and DHA) and lysophospholipids (e.g., LPC). Of approximately 30 members of the PLA2 fam- 2+ ily, cytosolic Ca -dependent PLA2 (cPLA2) is responsible for the release of arachidonic acid in a wide va- 2+ riety of cells. Some Ca -independent PLA2 (iPLA2) and secreted PLA2 (sPLA2) enzymes can also participate in the release of PUFAs and LPC in cell type- and stimulus-specific manners. In the COX pathway, arachi- donic acid is converted to PGH2 by COX-1 or COX-2 and then to bioactive prostanoids (PGD2, PGE2, PGF2a, PGI2 and TXA2) by various terminal PG synthases: hematopoietic and lipocalin-type PGD synthases (H- and L-PGDS), cytosolic and membrane-bound PGE synthases (cPGES, mPGES-1 and mPGES-2), PGF synthase, PGI synthase and TX synthase. In the 5-LOX pathway, arachidonic acid is converted to LTA4 by 5-LOX and FLAP and then to bioactive LTs by LTA4 hydrolase (LTA4H) or LTC4 synthase (LTC4S) (5-LOX path- way). Arachidonic acid, EPA and DHA are converted by 5-LOX and 12-LOX to the anti-inflammatory lipid mediators A4 (LXA4), resolving E1 (RevE1) and protectin D1 (PD1). LPC is converted to PAF by LPCAT2 or to LPA by autotaxin. Individual lipid mediators thus produced act on their cognate GPCRs on the target cell membrane.

exerts an anti-allergic action through EP3 [36]. Accord- release by PLA2, metabolism of AA to LTA4 by 5-LOX ingly, application of NSAIDs, which block both the pro- in concert with 5-LOX activating protein (FLAP), and allergic PGD2 and anti-allergic PGE2 pathways, has no conversion of this unstable intermediate to LTB4 and therapeutic effect on allergic asthma, or even exacerbates LTC 4 by LTA4 hydrolase and LTC4 synthase, respec- the disease, likely because the precursor AA shunts into tively [4]. LTC4, which is synthesized by conjugation the biosynthetic arm of LTs, which are potently pro-al- of LTA4 with glutathione by perinuclear LTC4 synthase, lergic. The development of a novel anti-asthmatic drug is exported extracellularly by an ABC transporter, and which specifically ablates the PGD2 pathway without rapidly metabolized into LTD4 and then into LTE4. The affecting the PGE2 pathway is desirable. actions of cys-LTs are mediated by their receptors Cys-

Bioactive LTs, including LTB4 and cysteinyl LTs (cys- LT1 (an LTD4 receptor) and CysLT2 (an LTC4 receptor).

LTs; which include LTC4, LTD4, and LTE4), represent Accordingly, mice deficient in 5-LOX, FLAP, or LTC4 critical lipid mediators of asthma. As in the case of PGs, synthase are all highly resistant to asthmatic challenge LTs are produced through three sequential reactions: AA [14, 31], and an antagonist of CysLT1 is now clinically 10 M. Murakami used as an anti-asthmatic drug worldwide. In addition, pathophysiological roles await future studies [44]. LPC it has been recently shown that CysLT1 and CysLT2 can also exhibits immune-regulatory actions through G2A form a heterodimer, that GPR17 counteracts the CysLT1 (probably indirectly), a GPCR belonging to the proton- signaling, and that , a purinergic GPCR, is impor- sensing GPCR family [23]. tant for the biological action of LTE4, the most stable S1P, a bioactive lysophospholipid structurally similar and abundant cys-LT in biological fluid [43, 62]. The to LPA, has a sphingosine (instead of glycerol) backbone first LTB4 receptor, BLT1, is a fundamental TH1 and TH2 and exerts its actions through S1P1 to S1P5 receptors, immune regulator which acts through recruitment of T which share homology with the LPA receptors LPA1 to lymphocytes [80]. BLT2, originally regarded as a sec- LPA 3 [78]. S1P also regulates a number of biological ond, low-affinity LTB4 receptor, is now considered to be processes such as developmental vascular integrity, ana- a high-affinity (and probably physiological) receptor for phylaxis, cancer, and lymphocyte egress from the lym- 12(S)-hydroxyheptadecatrienoic acid (12-HHT), a by- phoid organs [78]. FYT720 is a powerful immune sup- product of the COX-1/TXA2 synthase pathway [58]. pressant that blocks lymphocyte egress by down-

regulating S1P1 [45]. S1P levels are tightly controlled Class 2: lysophosholipids and their derivatives through synthesis with sphingosine kinases and inactiva- The first recognized lysophospholipid-type lipid me- tion by S1P phosphatase and S1P lyase [5]. A recent diator was PAF. Biosynthesis of PAF involves produc- study using zebrafish has identified a multipass trans- tion of 1-O-alkyl-lysophosphatidylcholine (LPC) by membrane protein, Spns2, which plays a role in S1P

PLA2, followed by its acetylation by LPC acyltransferase export from the cell [28]. S1P stimulates the induction 2 (LPCAT2) [70]. Analyses of PAF receptor (PAFR)- of COX-2, while ceramide-1-phosphate, another sphin- deficient mice have revealed important roles for this golipid mediator, is important for PLA2 activation at the particular lipid mediator in inflammation and allergy [21, Golgi membrane, delineating the functional crosstalk 29, 54]. Since PAFR also recognizes PAF-like oxidized between sphingolipid and eicosanoid pathways [38]. phospholipids [71], some of the implied biological ac- N-Acylethanolamines (NAEs) are endocannabinoids tions of PAF might actually be ascribed to some oxidized that transmit signals through the cannabinoid receptors phospholipids. PAF undergoes rapid inactivation by (central CB1 and peripheral CB2) and probably through plasma-type and intracellular PAF acetylhydrolases, other less understood mechanisms [11]. N-Arachidonoyl- which represent a special group of the PLA2 family ethanolamine (anandamide) is a representative NAE that [1]. exerts anti-nociceptive and anti-inflammatory effects LPA is produced extracellularly from LPC or other through cannabinoid receptors. Development of inhibi- lysophospholipids by autotaxin (ATX; lysophospholi- tors for the NAE-degrading enzymes, fatty acid amide pase D) and is degraded by a class of lipid phosphatases hydrolase and NAE-hydrolyzing acid amidase, has un- [85]. Currently, at least six LPA receptors have been veiled the functions of endocannabinoids, which are identified (named LPA1 to LPA6) [9]. From studies of otherwise promptly degraded in vivo, in various bio- knockout mice and hereditary diseases associated with logical processes [11]. N-Palmitoyl-ethanolamine, an these LPA receptors, it is now clear that LPA is involved NAE that is abundantly present in the body, is gaining in various physiological processes such as brain develop- attention as an important analgesic, anti-inflammatory ment, embryo implantation and hair growth, as well as and neuroprotective mediator, and N-palmitoyl-etha- pathological conditions such as neuropathic pain and nolamine itself, its analogs, or agents that inhibit its pulmonary fibrosis [63, 77]. Biosynthetic pathways for degradation may lead to the development of new thera- lysophospholipid-type mediators are illustrated in Fig. peutic strategies for the treatment of pathological condi- 1. Accumulating evidence suggests that other lysophos- tions [65]. N-Oleoyl-ethanolamine, another NAE, is pholipids also act as lipid mediators. Specifically, LPC, produced in the gut after feeding and acts on the hypo- lysophosphatidylserine and lysophosphatidylinositol act thalamus as an anorexigenic mediator [37]. 2-Arachi- on GPR119, GPR34 and GPR55, respectively, whose donoyl-glycerol, a more potent Overview of lipid mediators 11

agonist than NAEs, is produced by diacylglycerol lipase [81]. As evidenced by gene targeting of the four PGE2

α, and is now considered to be a major CB1 that receptors EP1 to EP4 [76], it is evident that PGE2 is a regulates the retrograde suppression of neurotransmis- major prostanoid that mediates various pathological sion at central synapses [79]. events, and many of the pharmacological effects of

NSAIDs can be attributed to the inhibition of PGE2 bio-

Class 3: ω-3 PUFA derivatives synthesis. However, since PGE2 is also involved in Recent advances in lipidomic techniques have allowed several homeostatic processes such as gastrointestinal the identification of new class of lipid mediators derived mucosal protection, renal blood flow, airway homeosta- from ω-3 PUFA (e.g., EPA and DHA) [2]. Pioneered by sis, and female reproduction, their adverse effects includ- Serhan and Bazan, these ω-3 lipid mediators such as ing gastric ulcer and renal damage often limit their long- resolvins, protectins and maresins, as well as term use. In view of the concurrent concept that derived from ω-6 AA, have recently attracted consider- pathogenic PGE2 is produced by inducible COX-2, while able attention as critical mediators of the resolution of homeostatic PGE2 is produced by constitutive COX-1, inflammation [6, 68]. Biosynthesis of these anti-inflam- a novel class of NSAIDs that selectively inhibits COX- matory lipid mediators from PUFAs involves 12/15-LOX 2 in marked preference to COX-1 has been developed and other enzymes acting upstream and downstream of over the past decade. Even though COX-2-specific in- 12/15-LOX that have not yet been fully identified. Also, hibitors exhibit less gastrointestinal toxicity than tradi- although several GPCRs have been proposed to act as tional NSAIDs that inhibit both COX-1 and COX-2, they receptors for the anti-inflammatory lipid mediators, such still have a serious adverse effect, namely cardiovascu- as ALX for lipoxin A4, ChemR23 for E1, and lar toxicity [33]. This is likely because specific inhibi-

ALX and GPR32 for resolvin D1 [3, 34], their in vivo tion of COX-2 affects the balance between platelet-de- relevance awaits future studies using knockout mice of rived pro-thrombotic TXA2 and endothelium-derived these receptor candidates. anti-thrombotic PGI2, leading to an increase in the risk of thrombosis due to altered vascular tone. Theoreti-

PGE2 Synthase cally, a specific blockade of the PGE2-biosynthetic path- way, more specifically a step of PGES, could decrease

Here, I highlight the pathophysiological roles played the pathogenic PGE2 production while sparing other by one of the best-studied lipid mediators, i.e., PGE2, by prostanoids, and this is indeed the reason why microsom- focusing on mPGES-1, an enzyme that specifically con- al PGES (mPGES-1), a major and inducible subtype of verts the intermediate prostanoid PGH2 into PGE2 [51]. PGES enzymes, has attracted much attention as a novel

The reasons why I focus on PGE2 here are that it is one drug target. In support of this, a number of cell studies of the most pleiotropic lipid mediators, that its patho- have demonstrated that mPGES-1 is induced by pro- logical and physiological roles, regulation of its biosyn- inflammatory stimuli, couples with COX-2 in preference thesis, and signal transduction via its receptors have been to COX-1, and is responsible for a large fraction of PGE2 well documented on the basis of numerous cell biologi- synthesis. Gene targeting of mPGES-1 (Ptges–/–) have cal, pharmacological and genetic approaches, and that it provided unequivocal evidence that mPGES-1 does play represents a good example of how analyses of lipid me- a role in pain, fever, inflammation and cancer [50]. Us- diators, through integration of the pathways from bio- ing research results from Ptges–/– mice, I will next give synthetic enzymes to receptors, are linked to basic biol- an overview of the functions of mPGES-1-driven PGE2 ogy and drug development. in pathophysiology. I will also describe recent efforts Clinically, NSAIDs (COX inhibitors) are very effec- toward the development of a small molecule mPGES-1 tive at treating patients with inflammation, fever and inhibitor and note the concerns on whether such an pain. In addition, the regular use of NSAIDs has been mPGES-1-targeted strategy can avoid the adverse effects shown in clinical trials to markedly reduce the relative associated with NSAIDs. risk of developing colorectal cancer by up to 40–50% 12 M. Murakami

Inflammation Pain, fever, and nerve injury Migration of after peritoneal injection of Peripheral pain nociception, as assessed by the acetic thioglycollate or pleural injection of carrageenan is strik- acid writhing test, is markedly reduced in Ptges–/– mice ingly reduced in Ptges–/– mice relative to replicate wild- [27]. This phenotype is particularly evident when the type mice [27]. The formation of inflammatory granula- animals are primed with LPS, which induces simultane- tion tissue and attendant angiogenesis in the dorsum ous induction of COX-2 and mPGES-1. The basal pain induced by subcutaneous implantation of a cotton thread response is also partially reduced in Ptges–/– mice [82], are significantly reduced in Ptges–/– mice as compared in which the COX-1-mPGES-1 coupling provides noci- –/– with wild-type mice [27]. In this model, mPGES-1 de- ceptive PGE2 to its receptor EP1 [74]. Ptges mice are ficiency is associated with reduced induction of vascular also refractory to mechanical allodynia or thermal hy- endothelial cell growth factor (VEGF) in the granulation peralgesia in a spinal nerve transection model, implying tissue, implying that mPGES-1-derived PGE2, in coop- the role of mPGES-1-driven PGE2 in neuropathic pain. eration with VEGF, contributes to inflammation-associ- Given that spinal inflammatory hyperalgesia is mediated ated angiogenesis and thereby to tissue remodeling. by the EP2 subtype of PGE receptors [66], the spinal In collagen-induced or collagen antibody-induced COX-2/mPGES-1/EP2 axis controls neuropathic pain in arthritis models (a mouse model of rheumatoid arthritis), the CNS. –/– Ptges mice are protected from joint inflammation [27, PGE2 is a critical mediator of fever during infectious 32, 82]. Similar phenotypes have been observed in mice and inflammatory conditions, but not of circadian and lacking COX-2 [53] or the PGE receptor EP4 [18], thus psychological temperature regulation. LPS-induced revealing a metabolic flow of the COX-2/mPGES-1/EP4 febrile response is blunted in mice deficient in mPGES-1 pathway in the development of inflammatory arthritis. as well as those deficient in COX-2 or the PGE receptor In addition to the synovial symptoms, defective genera- EP3 [13, 39, 86]. Cerebral vascular endothelial cells tion of the humoral immune response is associated with express COX-2 and mPGES-1 enabling pro-inflamma- –/– reduced incidence and severity of arthritis in Ptges tory cytokines to stimulate the synthesis of PGE2, whose mice [32], indicating that mPGES-1 also participates in small size and lipophilic property allow it to pass across adaptive immunity. In addition, mPGES-1-mediated the blood-brain barrier into CNS neurons, where the

PGE2 production by osteoblasts plays a critical role in PGE2/EP3 signaling elicits Gi/o activation in preoptic LPS-induced bone loss associated with inflammation thermocenter neurons by decreasing preoptic GABA type [20]. Moreover, mPGES-1 deficiency is associated with A receptor expression [84]. impaired fracture healing in mouse models of skeletal mPGES-1 expression is induced in neurons, microglia, disorders [90], indicating its role in bone metabolism. and endothelial cells in the cerebral cortex after transient –/– In experimental autoimmune encephalomyelitis (EAE), focal ischemia. In Ptges mice, postischemic PGE2 a mouse model of multiple sclerosis that is the most production in the cortex is completely absent, and infarc- prevalent TH1/TH17-mediator autoimmune disorder of the tion, edema, apoptotic cell death, and caspase-3 activa- CNS with neurological symptoms caused by inflamma- tion in the cortex after ischemia are all reduced compared tion and demyelination, Ptges–/– mice show less severe with those in wild-type mice [19]. Furthermore, the symptoms of EAE and lower production of IL-17 and behavioral neurological dysfunctions observed after

IFN-γ than wild-type mice [30]. PGE2, acting on its ischemia in wild-type mice are significantly ameliorated –/– receptor EP4 on T cells and dendritic cells, facilitates in Ptges mice. Thus, mPGES-1-driven PGE2 is a

TH1 cell differentiation and amplifies IL-23-mediated critical determinant of postischemic neurological dys-

TH17 cell expansion, and administration of an EP4-selec- functions. tive antagonist in vivo decreases accumulation of both

TH1 and TH17 cells in regional lymph nodes and sup- Cardiovascular disease presses the disease progression in mice subjected to EAE The selective inhibition, knockout, or mutation of or contact hypersensitivity [91]. COX-2, or the deletion of the receptor for COX-2-de- Overview of lipid mediators 13

rived PGI2, accelerates thrombogenesis and elevates dothelial growth factor, and activity of matrix metallo- blood pressure in mice, whereas these responses are at- proteinase-2 [26]. On the other hand, implantation of tenuated by COX-1 knockdown, which mimics the ben- mPGES-1-overexpressed lung carcinoma cells results in eficial effects of low-dose aspirin [92]. The deletion of increased lung metastasis (Fig. 2E). mPGES-1 in mice reduces PGE2 and increases PGI2 in Experimental observations made in cell culture stud- the circulation, has no effect on TXA2 biosynthesis, and ies, together with the well-recognized role of COX-2- affects neither thrombogenesis nor blood pressure [8]. dependent PGE2 during tumor promotion, have led to In mice with a low-density lipoprotein receptor knockout several recent in vivo studies focused on the impact of background, the deletion of mPGES-1 retards athero- mPGES-1 on tumorigenesis. Ptges–/– mice exhibit a sclerosis development without an attendant impact on significant reduction in the number and size of intestinal blood pressure [87], and protects against abdominal aor- tumors generated on an Apc mutant background [55]. tic aneurysm formation induced by angiotensin II [88]. Interestingly, mPGES-1 deficiency is associated with a These results suggest that inhibitors of mPGES-1 may disorganized vascular pattern within primary adenomas, retain their anti-inflammatory or anti-atherosclerotic ef- confirming a key role for PGE2 in tumor angiogenesis. ficacy by depressing PGE2, while avoiding the adverse mPGES-1 deletion also results in both reduced size and cardiovascular consequences associated with COX-2- numbers of pre-neoplastic aberrant crypt foci following mediated PGI2 suppression. However, another study treatment with the colon carcinogen azoxymethane [55]. showed that the deletion of mPGES-1 leads to eccentric Importantly, protection of the colonic mucosa is accom- cardiac myocyte hypertrophy, left ventricular dilation, panied by a marked suppression of nuclear β-catenin and impaired left ventricular contractile function after translocation, a finding that confirms an earlier study in acute myocardial infarction [10], suggesting a cardio- which PGE2 stimulated colon cancer cell growth through protective role of mPGES-1-driven PGE2. the COX-2/mPGES-1/EP2/Axin/GSK3β/β-catenin axis [7]. Furthermore, lung carcinoma cells implanted into Cancer Ptges–/– mice show reduced tumor expansion and lung PGE2 is widely recognized as a bioactive lipid me- metastasis [26], suggesting the contribution of mPGES-1 tabolite with potent tumor promotion properties, and the in host stroma cells to tumor development. Finally, in vivo roles of COX-2 [59] and EP receptors [52, 72] in transgenic mice overexpressing both COX-2 and mPG- tumor development have been established by studies ES-1 are susceptible to gastric carcinogenesis, a process using their knockout mice. Clinical studies have shown that is prevented by treatment of the animals with anti- increased levels of COX-2 and mPGES-1 which are biotics [60], suggesting the influence of gut microbial directly associated with increased PGE2 production in a flora and associated inflammation in the initiation of the number of human cancers [49] (Fig. 2A). The func- tumor. The roles of mPGES-1-driven PGE2 are sum- tional role of mPGES-1 in cancer has also been sup- marized in Fig. 2F. Despite this evidence, one study has ported by results from cell culture systems. For instance, reported that Ptges–/– display accelerated, rather than co-transfection of COX-2 and mPGES-1 facilitates pro- decreased, intestinal tumorigenesis in ApcMin/+ mice [12]. liferation of HEK293 cells, which form large, well- Although the reason for this discrepancy is unknown, it vascularized tumors when injected into the flanks of nude may be a reflection of the shunting of intermediate PGH2 mice [25]. In several cancer cell lines, mPGES-1 knock- toward another pro-tumorigenic prostanoid pathway; for down reduces cell growth, clonogenic capacity, motility, example, the potential contribution of the TXA2/TP path- and matrix invasiveness [26], whereas mPGES-1 over- way to tumor progression has been reported in several expression accelerates these events (Fig. 2B–D). Fur- cancers [48]. thermore, mPGES-1-silenced lung carcinoma cell xeno- grafts show decreased propagation and metastasis, with Metabolic syndrome concomitant decreases in the density of microvascular PGE2 negatively regulates adipogenesis via its recep- networks, expression of pro-angiogenic vascular en- tor EP4 [83]. mPGES-1 expression is down-regulated 14 M. Murakami

Fig. 2. Tumorigenic role of mPGES-1, a PGE2-biosynthetic enzyme. (A) Immunohistochemical staining of mPGES-1 in various human cancers. Human tumor sections were obtained by surgery at Toho University Ohmori Hospital (Tokyo, Japan) following approval from the ethical committee of the Faculty and receipt of informed consent from the patients. (B) Overexpression of mPGES-1 facilitates the migration of tumor cells. mPGES-1- or mock-transfected mouse lung carcinoma cells were seeded on Matrigel matrix (8 µm pore size) in the upper chamber, which was filled with serum-free medium, and placed on the lower chamber contain- ing medium with 10% fetal calf serum. After culture for 16 h, the cells which had invaded the lower chamber were fixed and stained with crystal violet. More mPGES-1-transfected cells than mock-transfected cells were found in the lower chamber, indicating increased matrix invasiveness due to overexpression of mPGES-1. The cell migration was suppressed by the COX-2 inhibitor NS-398, suggesting the dependence of the migration on PGE2. (C) Quantification of the cell migration assay shown in (B) (mean ± SD, n=4, *P<0.05). (D) Cell motility assay. mPGES-1- or mock-transfected mouse lung carcinoma cells were cultured in Petri dishes to near confluency, and then a portion of the cell monolayer was scratched off with a tip. After culture for 16 h, the cells were fixed with crystal violet. More mPGES-1-transfected cells than mock-transfected cells were found in the scratched area, suggesting that cell motility was increased by overexpression of mPGES-1. (E) Lung metastasis assay. mPGES-1-transfected and mock-transfected cells were injected intravenously into BALB/c mice. After 20 days, the mice were sacrificed and metastatic foci in the lung (arrowheads) were visualized by Bouin staining (left panel). The numbers of the lung metastatic foci were counted (right panel) (mean ± SD, n=4, *P<0.05). All procedures involving animals were performed in accordance with protocols approved by the Institutional Animal Care and Use Committee of Showa University, in accordance with Standards Relating to the Care and Management of Experimental Animals in Japan. (F) Summary of the roles of mPGES-1-driven PGE2 in tumor development. PGE2 produced by both cancer cell-associated and host stromal mPGES-1 contributes to tumor growth, migration, invasion, metastasis and angiogenesis. PGE2 may also contribute to cellular transformation in the presence of other cancer-promoting factors. Overview of lipid mediators 15

in visceral adipose tissue of obese mice given a high-fat worsen the disease by inhibiting PGE2 synthesis [69]. diet [16]. Mice with pancreatic β-cell-specific trans- Ptges–/– mice display exacerbated dextran sulfate-induced genic overexpression of both COX-2 and mPGES-1 colitis compared with replicate wild-type mice, accom- show severe hyperglycemia [61]. In these mice, the panied with increased fecal bleeding and diarrhea, de- relative number of β-cells to the total islet cell numbers creased hematocrit scores, shortened colon (an indication was markedly reduced compared with wild-type mice, of colon inflammation), splenomegaly, increased col- in accordance with a decreased proliferation rate in the orectal ulceration, and elevated expression of pro-in- islets. Thus, it is possible that increased PGE2 signaling flammatory cytokines [15]. An example of the worsened contributes to a reduction of pancreatic β-cell mass colorectal ulceration and stool bleeding in Ptges–/– mice through inhibition of proliferation, thereby aggravating treated with 7% dextran sulfate is shown in Fig. 3A and diabetes. Metabolic syndrome accompanies chronic, 3B. These observations are in agreement with the fact low-grade inflammation in the hypothalamic arcuate that mice deficient in COX-2 or EP4 are more sensitive nucleus, and PGE2 decreases feeding behaviors via its to dextran sulfate-induced colitis [24, 47], and imply the receptor, EP3 [67]. IL-1β induces anorexia in normal protective role of the COX-2/mPGES-1/EP4 axis in mu- mice, whereas it fails to decrease food intake in Ptges–/– cosal homeostasis and integrity. Third, in mouse models mice [64]. Thus, the central mPGES-1/EP3 axis is in- of allergic airway inflammation induced by a house dust volved in feeding control and is essential for immune mite, Ptges–/– mice show marked increases in the num- anorexic behavior, and thus may constitute a potential bers of vascular smooth muscle cells and the thickness therapeutic target. of intrapulmonary vessels as well as modestly enhanced eosinophil infiltration compared with control mice [42]. Tissue homeostasis This observation indicates that mPGES-1 and its product,

Many of the above studies suggest mPGES-1 as a new PGE2, possibly through EP3 [36], protect the pulmonary drug target which would yield anti-inflammatory, anti- vasculature from remodeling during allergen-induced pyretic, analgesic and anti-tumor effects, while having pulmonary inflammation, which agrees with the view little or no cardiovascular toxicity. Furthermore, while that NSAIDs often exacerbate airway inflammation. mice deficient in COX-2 or EP2 show defective female Therefore, drugs targeting mPGES-1 may still have un- reproduction [17, 40] and mice deficient in both COX-1 desired side effects on the kidney, gut and lung. The and COX-2 or EP4 show neonatal lethality due to failure pathological and physiological roles of mPGES-1 are of ductus arteriosus closure [41, 57], mice deficient in summarized in Fig. 3C. mPGES-1 do not show any abnormality in these pro- cesses [35]. Hence, an mPGES-1 inhibitor may stand Drug discovery with mPGES-1 as a molecular target out as a better prospective tool than the currently used Despite the above criticisms, selective drugs targeting COX inhibitors for the management of pregnant women mPGES-1 may be safe relative to COX-inhibiting as well as premature infants with persistent ductus. NSAIDs, since much of the cardiovascular toxicity as- However, accumulating lines of evidence suggest that sociated with COX-2 inhibition can potentially be cir- the inhibition of mPGES-1 cannot fully avoid the side cumvented. A compound that has been developed by effects of classical NSAIDs. Merck, MF63 [2-(6-chloro-1H-phenanthro[9,10-d]imi- First, Ptges–/– mice develop progressive hypertension dazol-2-yl)-isophthalonitrile], is a selective mPGES-1 with an inappropriate increase in sodium balance when inhibitor that potently inhibits human mPGES-1 (IC50 fed a high-salt diet [22], and also exhibit an impaired of 1.3 nM), with a high degree (>1,000-fold) of selectiv- ability to excrete an acute water load [73]. These obser- ity over other prostanoid synthases [89]. MF63 retains vations indicate that mPGES-1-driven PGE2 is important NSAID-like efficacy at inhibiting LPS-induced pyresis, for renal homeostasis. Second, PGE2 is increased in hyperalgesia, and iodoacetate-induced osteoarthritic pain inflammatory bowel diseases, including Crohn’s disease in rodents. In addition, MF63 does not cause NSAID- and ulcerative colitis, and traditional NSAIDs trigger or like gastrointestinal toxic effects, such as mucosal ero- 16 M. Murakami

Conclusion and Perspectives

Lipid signaling cascades are complex, often redundant and highly interconnected, and counter-regulatory in some cases. Nevertheless, enzymes and receptors in- volved in lipid mediator signaling have been and are still being targeted pharmacologically to alleviate the symp- toms of various diseases. If the modulation of one lipid mediator pathway does not suffice therapeutically, a combination of targeting two or more pathways could be effective. At present, however, the tools that are avail- able to follow the dynamics of individual lipid mediators and to monitor their precise modification and spatiotem- poral localization in situ are still technically limited and thus hamper a more comprehensive description of these pathways and their crosstalk. Unlike proteins, the func- tions of which can largely be addressed individually, lipid actions are frequently masked by the large steady- state mass of the structural lipids in membranes, which make it difficult to detect the transient lipid signal. Fur- Fig. 3. mPGES-1 in the gastrointestinal mucosa protects against ther advances in this field and their integration into dextran sulfate-induced colitis. (A) Dextran sulfate 5000 therapeutic use are likely to benefit from improved, time- (DSS) at a 7% (w/v) concentration in drinking water was given to 8–12 week-old male Ptges–/– (KO) and Ptges+/+ and space-resolved lipidomics technology for monitoring (WT) mice on the C57BL/6J background. On day 4, colon individual lipid mediators within tissue niches. Clearly, sections were stained with hematoxylin and eosin. The more research is required to elucidate each of the many crypt epithelium remained intact in Ptges+/+ mice (panel a), whereas it was considerably lost in Ptges–/– mice (pan- regulated pathways of bioactive lipids and define the el b). In magnified views of the Ptges–/– colon (panels c regulatory mechanisms of their enzymes, the roles of the and d), crypt abscesses and ulcers were frequently found pathways in specific cell responses, and the mechanisms (arrowheads), accompanied by infiltration of (asterisk). Original magnifications: × 100 (panels a and by which individual lipid mediators mediate their ac- b) and × 200 (panels c and d). (B) Fecal bleeding score of tions. Ptges KO and WT mice with (+) or without (–) treatment with 7% dextran sulfate (mean ± SD, n=4, *P<0.05). DSS- treated KO mice showed more fecal bleeding than replicate Acknowledgments WT mice. The results shown in (A) and (B) indicate that mPGES-1 plays a protective role in the colon. (C) Sum- I would like to thank Y. Taketomi (The Tokyo Metro- mary of the pathological and physiological roles of mPG- ES-1 and its product, PGE2. mPGES-1-driven PGE2 par- politan Institute of Medical Science, Tokyo, Japan) and ticipates in pathologies such as inflammation, atheroscle- D. Kamei and S. Hara (Showa University, Tokyo, Japan) rosis, pain, fever, and cancer, and in physiologies such as for preparing illustrations. In the interest of brevity, I gastrointestinal mucosal protection, renal function, and airway homeostasis. For details, please see text. have referenced other reviews whenever possible and apologize to the authors of the numerous primary papers that were not explicitly cited. sions or leakage in mice and even in non-human pri- This work was supported by grants-in aid for Scien- mates. Thus, mPGES-1 inhibition leads to effective tific Research from the Ministry of Education, Culture, relief of both pyresis and inflammatory pain in preclini- Sports, Science and Technology of Japan. cal models of inflammation and may be a useful approach for treating inflammatory diseases. Overview of lipid mediators 17

References understanding their pathophysiological roles through mouse genetic models. Biochimie (in press). 1. arai, H. 2002. Platelet-activating factor acetylhydrolase. 16. Hétu, P.O. and Riendeau, D. 2007. Down-regulation of Prostaglandins Other Lipid Mediat. 68–69: 83–94. microsomal synthase-1 in adipose tissue 2. ariel, A. and Serhan, C.N. 2007. Resolvins and protectins by high-fat feeding. Obesity (Silver Spring) 15: 60–68. in the termination program of acute inflammation. Trends 17. Hizaki, H., Segi, E., Sugimoto, Y., Hirose, M., Saji, T., Immunol. 28: 176–183. Ushikubi, F., Matsuoka, T., Noda,Y., Tanaka, T., Yoshida, 3. Arita, M., Bianchini, F., Aliberti, J., Sher, A., Chiang, N., N., Narumiya, S., and Ichikawa, A. 1999. Abortive expansion Hong, S., Yang, R., Petasis, N.A., and Serhan, C.N. 2005. of the cumulus and impaired fertility in mice lacking the Stereochemical assignment, antiinflammatory properties, prostaglandin E receptor subtype EP2. Proc. Natl. Acad. Sci.

and receptor for the omega-3 lipid mediator resolvin E1. J. U.S.A. 96: 10501–10506. Exp. Med. 201: 713–722. 18. Honda, T., Segi-Nishida, E., Miyachi, Y., and Narumiya, S. 4. austen, K.F. 2008. The cysteinyl leukotrienes: where do 2006. -IP signaling and prostaglandin E2-EP2/ they come from? What are they? Where are they going? Nat. EP4 signaling both mediate joint inflammation in mouse Immunol. 9: 113–115. collagen-induced arthritis. J. Exp. Med. 203: 325–335. 5. Bandhuvula, P. and Saba, J.D. 2007. Sphingosine-1- 19. ikeda-Matsuo, Y., Hirayama, Y., Ota, A., Uematsu, S., Akira, phosphate lyase in immunity and cancer: silencing the siren. S., and Sasaki, Y. 2010. Microsomal prostaglandin E Trends Mol. Med. 13: 210–217. synthase-1 and cyclooxygenase-2 are both required for

6. Bazan, N.G. 2009. Neuroprotectin D1-mediated anti- ischaemic excitotoxicity. Br. J. Pharmacol. 159: 1174– inflammatory and survival signaling in stroke, retinal 1186. degenerations, and Alzheimer’s disease. J. Lipid Res. 50: 20. inada, M., Matsumoto, C., Uematsu, S., Akira, S., and S400–405. Miyaura, C. 2006. Membrane-bound prostaglandin E 7. Castellone, M.D., Teramoto, H., Williams, B.O., Druey, synthase-1-mediated prostaglandin E2 production by

K.M., and Gutkind, J.S. 2005. Prostaglandin E2 promotes osteoblast plays a critical role in lipopolysaccharide-induced colon cancer cell growth through a Gs-axin-β-catenin bone loss associated with inflammation. J. Immunol. 177: signaling axis. Science 310: 1504–1510. 1879–1885. 8. Cheng, Y., Wang, M., Yu, Y., Lawson, J., Funk, C.D., and 21. ishii, S., Nagase, T., and Shimizu, T. 2002. Platelet-activating Fitzgerald, G.A. 2006. Cyclooxygenases, microsomal factor receptor. Prostaglandins Other Lipid Mediat. 68–69: prostaglandin E synthase-1, and cardiovascular function. J. 599–609. Clin. Invest. 116: 1391–1399. 22. Jia, Z., Zhang, A., Zhang, H., Dong, Z., and Yang, T. 2006. 9. Choi, J.W., Herr, D.R., Noguchi, K., Yung, Y.C., Lee, C.W., Deletion of microsomal prostaglandin E synthase-1 increases Mutoh, T., Lin, M.E., Teo, S.T., Park, K.E., Mosley, A.N., sensitivity to salt loading and angiotensin II infusion. Circ. and Chun, J. 2010. LPA receptors: subtypes and biological Res. 99: 1243–1251. actions. Annu. Rev. Pharmacol. Toxicol. 50: 157–186. 23. kabarowski, J.H. 2009. G2A and LPC: regulatory functions 10. Degousee, N., Fazel, S., Angoulvant, D., Stefanski, E., in immunity. Prostaglandins Other Lipid Mediat. 89: 73– Pawelzik, S.C., Korotkova, M., Arab, S., Liu, P., Lindsay, 81. T.F., Zhuo, S., Butany, J., Li, R.K., Audoly, L., Schmidt, R., 24. kabashima, K., Saji, T., Murata, T., Nagamachi, M., Angioni, C., Geisslinger, G., Jakobsson, P.J., and Rubin, Matsuoka, T., Segi, E., Tsuboi, K., Sugimoto, Y., Kobayashi,

B.B. 2008. Microsomal prostaglandin E2 synthase-1 deletion T., Miyachi, Y., Ichikawa, A., and Narumiya, S. 2002. The leads to adverse left ventricular remodeling after myocardial EP4 suppresses colitis, mucosal infarction. Circulation 117: 1701–1710. damage and CD4 cell activation in the gut. J. Clin. Invest. 11. Di Marzo, V. 2009. The endocannabinoid system: its general 109: 883–893. strategy of action, tools for its pharmacological manipulation 25. kamei, D., Murakami, M., Nakatani, Y., Ishikawa, Y., Ishii, and potential therapeutic exploitation. Pharmacol. Res. 60: T., and Kudo, I. 2003. Potential role of microsomal 77–84. prostaglandin E synthase-1 in tumorigenesis. J. Biol. Chem. 12. Elander, N., Ungerbäck, J., Olsson, H., Uematsu, S., Akira, 278: 19396–19405. S., and Söderkvist, P. 2008. Genetic deletion of mPGES-1 26. kamei, D., Murakami, M., Sasaki, Y., Nakatani,Y., Majima, accelerates intestinal tumorigenesis in APCMin/+ mice. M., Ishikawa, Y., Ishii, T., Uematsu, S., Akira, S., Hara, S., Biochem. Biophys. Res. Commun. 372: 249–253. and Kudo, I. 2009. Microsomal prostaglandin E synthase-1 13. Engblom, D., Saha, S., Engström, L., Westman, M., Audoly, in both cancer cells and hosts contributes to tumour growth, L.P., Jakobsson, P.J., and Blomqvist, A. 2003. Microsomal invasion and metastasis. Biochem. J. 425: 361–371. prostaglandin E synthase-1 is the central switch during 27. kamei, D., Yamakawa, K., Takegoshi, Y., Mikami-Nakanishi, immune-induced pyresis. Nat. Neurosci. 6: 1137–1138. M., Nakatani, Y., Oh-Ishi, S., Yasui, H., Azuma, Y., Hirasawa, 14. Funk, C.D., Chen, X.S., Johnson, E.N., and Zhao, L. 2002. N., Ohuchi, K., Kawaguchi, H., Ishikawa, Y., Ishii, T., Lipoxygenase genes and their targeted disruption. Uematsu, S., Akira, S., Murakami, M., and Kudo, I. 2004. Prostaglandins Other Lipid Mediat. 68–69: 303–312. Reduced pain hypersensitivity and inflammation in mice 15. Hara, S., Kamei, D., Sasaki, Y., Tanemoto, A., Nakatani, Y., lacking microsomal prostaglandin E synthase-1. J. Biol. and Makatani, Y. 2010. Prostaglandin E synthases: Chem. 279: 33684–33695. 18 M. Murakami

28. kawahara, A., Nishi, T., Hisano, Y., Fukui, H., Yamaguchi, Cell 91: 197–208. A., and Mochizuki, N. 2009. The sphingolipid transporter 41. Loftin, C.D., Trivedi, D.B., and Langenbach, R. 2002. spns2 functions in migration of zebrafish myocardial Cyclooxygenase-1-selective inhibition prolongs gestation precursors. Science 323: 524–527. in mice without adverse effects on the ductus arteriosus. J. 29. kihara, Y., Ishii, S., Kita, Y., Toda, A., Shimada, A., and Clin. Invest. 110: 549–557. Shimizu, T. 2005. Dual phase regulation of experimental 42. Lundequist, A., Nallamshetty, S.N., Xing, W., Feng, C., allergic encephalomyelitis by platelet-activating factor. J. Laidlaw, T.M., Uematsu, S., Akira, S., and Boyce, J.A. 2010.

Exp. Med. 202: 853–863. Prostaglandin E2 exerts homeostatic regulation of pulmonary 30. kihara, Y., Matsushita, T., Kita, Y., Uematsu, S., Akira, S., vascular remodeling in allergic airway inflammation. J. Kira, J., Ishii, S., and Shimizu, T. 2009. Targeted lipidomics Immunol. 184: 433–441.

reveals mPGES-1-PGE2 as a therapeutic target for multiple 43. Maekawa, A., Balestrieri, B., Austen, K.F., and Kanaoka, Y. sclerosis. Proc. Natl. Acad. Sci. U.S.A. 106: 21807–21812. 2009. GPR17 is a negative regulator of the cysteinyl

31. Kim, D.C., Hsu, F.I., Barrett, N.A., Friend, D.S., Grenningloh, leukotriene 1 receptor response to leukotriene D4. Proc. Natl. R., Ho, I.C., Al-Garawi, A., Lora, J.M., Lam, B.K., Austen, Acad. Sci. U.S.A. 106: 11685–11690. K.F., and Kanaoka, Y. 2006. Cysteinyl leukotrienes regulate 44. Makide, K., Kitamura, H., Sato, Y., Okutani, M., and Aoki, Th2 cell-dependent pulmonary inflammation. J. Immunol. J. 2009. Emerging lysophospholipid mediators, 176: 4440–4448. lysophosphatidylserine, lysophosphatidylthreonine, 32. kojima, F., Kapoor, M., Yang, L., Fleishaker, E.L., Ward, lysophosphatidylethanolamine and lysophosphatidylglycerol. M.R., Monrad, S.U., Kottangada, P.C., Pace, C.Q., Clark, Prostaglandins Other Lipid Mediat. 89: 135–139. J.A., Woodward, J.G., and Crofford, L.J. 2008. Defective 45. Mandala, S., Hajdu, R., Bergstrom, J., Quackenbush, E., generation of a humoral immune response is associated with Xie, J., Milligan, J., Thornton, R., Shei, G.J., Card, D., a reduced incidence and severity of collagen-induced Keohane, C., Rosenbach, M., Hale, J., Lynch, C.L., arthritis in microsomal prostaglandin E synthase-1 null mice. Rupprecht, K., Parsons, W., and Rosen, H. 2002. Alteration J. Immunol. 180: 8361–8368. of lymphocyte trafficking by sphingosine-1-phosphate 33. konstam, M.A., Weir, M.R., Reicin, A., Shapiro, D., receptor agonists. Science 296: 346–349. Sperling, R.S., Barr, E., and Gertz, B.J. 2001. Cardiovascular 46. Matsuoka, T., Hirata, M., Tanaka, H., Takahashi, Y., Murata, thrombotic events in controlled, clinical trials of . T., Kabashima, K., Sugimoto, Y., Kobayashi, T., Ushikubi, Circulation 104: 2280–2288. F., Aze, Y., Eguchi, N., Urade, Y., Yoshida, N., Kimura, K., 34. krishnamoorthy, S., Recchiuti, A., Chiang, N., Yacoubian, Mizoguchi, A., Honda, Y., Nagai, H., and Narumiya, S.

S., Lee, C.H., Yang, R., Petasis, N.A., and Serhan, C.N. 2000. as a mediator of allergic asthma. 2010. Resolvin D1 binds human phagocytes with evidence Science 287: 2013–2017. for proresolving receptors. Proc. Natl. Acad. Sci. U.S.A. 107: 47. Morteau, O., Morham, S.G., Sellon, R., Dieleman, L.A., 1660–1665. Langenbach, R., Smithies, O., and Sartor, R.B. 2000. 35. kubota, K., Kubota, T., Kamei, D., Murakami, M., Kudo, Impaired mucosal defense to acute colonic injury in mice I., Aso, T., and Morita, I. 2005. Change in prostaglandin E lacking cyclooxygenase-1 or cyclooxygenase-2. J. Clin. synthases (PGESs) in microsomal PGES-1 knockout mice Invest. 105: 469–478. in a preterm delivery model. J. Endocrinol. 187: 339–345. 48. Moussa, O., Ashton, A.W., Fraig, M., Garrett-Mayer, E., 36. kunikata, T., Yamane, H., Segi, E., Matsuoka, T., Sugimoto, Ghoneim, M.A., Halushka, P.V., and Watson, D.K. Novel Y., Tanaka, S., Tanaka, H., Nagai, H., Ichikawa, A., and role of thromboxane receptors beta isoform in bladder cancer Narumiya, S. 2005. Suppression of allergic inflammation pathogenesis. Cancer Res. 68: 4097–4104. by the prostaglandin E receptor subtype EP3. Nat. Immunol. 49. Murakami, M. and Kudo, I. 2006. Prostaglandin E synthase: 6: 524–531. a novel drug target for inflammation and cancer. Curr. 37. Lambert, D.M. and Muccioli, G.G. 2007. Endocannabinoids Pharm. Des. 12: 943–954. and related N-acylethanolamines in the control of appetite 50. Murakami, M., Nakatani, Y., Tanioka, T., and Kudo, I. and energy metabolism: emergence of new molecular Prostaglandin E synthase. 2002. Prostaglandins Other Lipid players. Curr. Opin. Clin. Nutr. Metab. Care. 10: 735– Mediat. 68–69: 383–399. 744. 51. Murakami, M., Naraba, H., Tanioka, T., Semmyo, N., 38. Lamour, N.F., Subramanian, P., Wijesinghe, D.S., Stahelin, Nakatani, Y., Kojima, F., Ikeda, T., Fueki, M., Ueno, A., R.V., Bonventre, J.V., and Chalfant, C.E. 2009. Ceramide Oh-ishi, S., and Kudo, I. 2000. Regulation of prostaglandin

1-phosphate is required for the translocation of group IVA E2 biosynthesis by inducible membrane-associated cytosolic phospholipase A2 and prostaglandin synthesis. J. prostaglandin E2 synthase that acts in concert with Biol. Chem. 284: 26897–26907. cyclooxygenase-2. J. Biol. Chem. 275: 32783–32792. 39. Li, S., Ballou, L.R., Morham, S.G., and Blatteis, C.M. 2001. 52. Mutoh, M., Watanabe, K., Kitamura, T., Shoji, Y., Takahashi, Cyclooxygenase-2 mediates the febrile response of mice to M., Kawamori, T., Tani, K., Kobayashi, M., Maruyama, T., interleukin-1β. Brain Res. 910: 163–173. Kobayashi, K., Ohuchida, S., Sugimoto, Y., Narumiya, S., 40. Lim, H., Paria, B.C., Das, S.K., Dinchuk, J.E., Langenbach, Sugimura, T., and Wakabayashi, K. 2002. Involvement of R., Trzaskos, J.M., and Dey, S.K. 1997. Multiple female prostaglandin E receptor subtype EP4 in colon carcinogenesis. reproductive failures in cyclooxygenase 2-deficient mice. Cancer Res. 62: 28–32. Overview of lipid mediators 19

53. Myers, L.K., Kang, A.H., Postlethwaite, A.E., Rosloniec, hyperalgesia is mediated by prostaglandin E receptors of E.F., Morham, S.G., Shlopov, B.V., Goorha, S., and Ballou, the EP2 subtype. J. Clin. Invest. 115: 673–679. L.R. 2000. The genetic ablation of cyclooxygenase 2 67. Sanchez-Alavez, M., Klein, I., Brownell, S.E., Tabarean, prevents the development of autoimmune arthritis. Arthritis I.V., Davis, C.N., Conti, B., and Bartfai, T. 2007. Night Rheum. 43: 2687–2693. eating and obesity in the EP3R-deficient mouse. Proc. Natl. 54. Nagase, T., Ishii, S., Kume, K., Uozumi, N., Izumi, T., Acad. Sci. U.S.A. 104: 3009–3014. Ouchi, Y., and Shimizu, T. 1999. Platelet-activating factor 68. Serhan, C.N., Yang, R., Martinod, K., Kasuga, K., Pillai, mediates acid-induced lung injury in genetically engineered P.S., Porter, T.F., Oh, S.F., and Spite, M. 2009. Maresins: mice. J. Clin. Invest. 104: 1071–1076. novel mediators with potent anti-inflammatory 55. Nakanishi, M., Montrose, D.C., Clark, P., Nambiar, P.R., and proresolving actions. J. Exp. Med. 206: 15–23. Belinsky, G.S., Claffey, K.P., Xu, D., and Rosenberg, D.W. 69. Sigthorsson, G., Tibble, J., Hayllar, J., Menzies, I., 2008. Genetic deletion of mPGES-1 suppresses intestinal Macpherson, A., Moots, R., Scott, D., Gumpel, M.J., and tumorigenesis. Cancer Res. 68: 3251–3259. Bjarnason, I. 1998. Intestinal permeability and inflammation 56. Narumiya, S. and FitzGerald, G.A. 2010. Genetic and in patients on NSAIDs. Gut 43: 506–511. pharmacological analysis of prostanoid receptor function. 70. Shindou, H., Hishikawa, D., Nakanishi, H., Harayama, T., J. Clin. Invest. 108: 25–30. Ishii, S., Taguchi, R., and Shimizu, T. 2007. A single enzyme 57. Nguyen, M., Camenisch, T., Snouwaert, J.N., Hicks, E., catalyzes both platelet-activating factor production and Coffman, T.M., Anderson, P.A., Malouf, N.N., and Koller, membrane biogenesis of inflammatory cells. Cloning and B.H. 1997. The prostaglandin receptor EP4 triggers characterization of acetyl-CoA:LYSO-PAF acetyltransferase. remodelling of the cardiovascular system at birth. Nature J. Biol. Chem. 282: 6532–6539. 390: 78–81. 71. Smiley, P.L., Stremler, K.E., Prescott, S.M., Zimmerman, 58. Okuno, T., Iizuka, Y., Okazaki, H., Yokomizo, T., Taguchi, G.A., and McIntyre, T.M. 1991. Oxidatively fragmented R., and Shimizu, T. 2008. 12(S)-Hydroxyheptadeca-5Z, 8E, activate human neutrophils through

10E-trienoic acid is a natural ligand for the receptor for platelet-activating factor. J. Biol. Chem. receptor 2. J. Exp. Med. 205: 759–766. 266: 11104–11110. 59. Oshima, H., Oshima, M., Inaba, K., and Taketo, M.M. 2004. 72. Sonoshita, M., Takaku, K., Sasaki, N., Sugimoto, Y., Hyperplastic gastric tumors induced by activated Ushikubi, F., Narumiya, S., Oshima, M., and Taketo, M.M. macrophages in COX-2/mPGES-1 transgenic mice. EMBO 2001. Acceleration of intestinal polyposis through J. 23: 1669–1678. prostaglandin receptor EP2 in Apc(Delta 716) knockout 60. Oshima, H., Taketo, M.M., and Oshima, M. 2006. Destruction mice. Nat. Med. 7: 1048–1051. of pancreatic β-cells by transgenic induction of prostaglandin 73. Soodvilai, S., Jia, Z., Wang, M.H., Dong, Z., and Yang, T.

E2 in the islets. J. Biol. Chem. 281: 29330–29336. 2009. mPGES-1 deletion impairs diuretic response to acute 61. Oshima, M., Dinchuk, J.E., Kargman, S.L., Oshima, H., water loading. Am. J. Physiol. Renal. Physiol. 296: Hancock, B., Kwong, E., Trzaskos, J.M., Evans, J.F., and F1129–1135. Taketo, M.M. 1996. Suppression of intestinal polyposis in 74. Stock, J.L., Shinjo, K., Burkhardt, J., Roach, M., Taniguchi, Apc delta716 knockout mice by inhibition of cyclooxygenase K., Ishikawa, T., Kim, H.S., Flannery, P.J., Coffman, T.M.,

2 (COX-2). Cell 87: 803–809. McNeish, J.D., and Audoly, LP. 2001. The prostaglandin E2 62. Paruchuri, S., Tashimo, H., Feng, C., Maekawa, A., Xing, EP1 receptor mediates pain perception and regulates blood W., Jiang, Y., Kanaoka,Y., Conley, P., and Boyce, J.A. 2009. pressure. J. Clin. Invest. 107: 325–331.

Leukotriene E4-induced pulmonary inflammation is mediated 75. Stoddart, L.A., Smith, N.J., and Milligan, G. 2008. by the P2Y12 receptor. J. Exp. Med. 206: 2543–2555. International Union of Pharmacology. LXXI. Free 63. Pasternack, S.M., von Kügelgen, I., Aboud, K.A., Lee, Y.A., fatty acid receptors FFA1, -2, and -3: pharmacology Rüschendorf, F., Voss, K., Hillmer, A.M., Molderings, G.J., and pathophysiological functions. Pharmacol. Rev. 60: Franz, T., Ramirez, A., Nürnberg, P., Nöthen, M.M., and 405–417. Betz, R.C. 2008. G protein-coupled receptor P2Y5 and its 76. Sugimoto, Y. and Narumiya, S. 2007. Prostaglandin E ligand LPA are involved in maintenance of human hair receptors. J. Biol. Chem. 282: 11613–11617. growth. Nat. Genet. 40: 329–334. 77. Tager, A.M., LaCamera, P., Shea, B.S., Campanella, G.S., 64. Pecchi, E., Dallaporta, M., Thirion, S., Salvat, C., Berenbaum, Selman, M., Zhao, Z., Polosukhin, V., Wain, J., Karimi-Shah, F., Jean, A., and Troadec, J.D. 2006. Involvement of central B.A., Kim, N.D., Hart, W.K., Pardo, A., Blackwell, T.S., microsomal prostaglandin E synthase-1 in IL-1β-induced Xu, Y., Chun, J., and Luster, A.D. 2008. The lysophosphatidic anorexia. Physiol. Genomics 25: 485–492. acid receptor LPA1 links pulmonary fibrosis to lung injury 65. Petrosino, S., Ligresti, A., and Di Marzo, V. 2009. by mediating fibroblast recruitment and vascular leak. Nat. Endocannabinoid chemical biology: a tool for the Med. 14: 45–54. development of novel therapies. Curr. Opin. Chem. Biol. 78. Takabe, K., Paugh, S.W., Milstien, S., and Spiegel, S. 2008. 13: 309–320. “Inside-out” signaling of sphingosine-1-phosphate: 66. Reinold, H., Ahmadi, S., Depner, U.B., Layh, B., Heindl, therapeutic targets. Pharmacol. Rev. 60: 181–195. C., Hamza, M., Pahl, A., Brune, K., Narumiya, S., Müller, 79. Tanimura, A., Yamazaki, M., Hashimotodani, Y., U., and Zeilhofer, H.U. 2005. Spinal inflammatory Uchigashima, M., Kawata, S., Abe, M., Kita, Y., Hashimoto, 20 M. Murakami

K., Shimizu, T., Watanabe, M., Sakimura, K., and Kano, M. 1998. Impaired febrile response in mice lacking the 2010. The endocannabinoid 2-arachidonoylglycerol prostaglandin E receptor subtype EP3. Nature 395: 281– produced by diacylglycerol lipase alpha mediates retrograde 284. suppression of synaptic transmission. Neuron 65: 320– 87. wang, M., Zukas, A.M., Hui,Y., Ricciotti, E., Puré, E., and 327. FitzGerald, G.A. 2006. Deletion of microsomal prostaglandin 80. Terawaki, K., Yokomizo, T., Nagase, T., Toda, A., Taniguchi, E synthase-1 augments prostacyclin and retards atherogenesis. M., Hashizume, K., Yagi, T., and Shimizu, T. 2005. Absence Proc. Natl. Acad. Sci. U.S.A. 103: 14507–14512.

of 1 confers resistance to airway 88. wang, M., Lee, E., Song, W., Ricciotti, E., Rader, D.J., hyperresponsiveness and Th2-type immune responses. J. Lawson, J.A., Puré, E., and FitzGerald, G.A. 2008. Immunol. 175: 4217–4225. Microsomal prostaglandin E synthase-1 deletion suppresses 81. Thun, M.J., Namboodiri, M.M., and Heath, C.W. Jr. 1991. oxidative stress and angiotensin II-induced abdominal aortic Aspirin use and reduced risk of fatal colon cancer. N. Engl. aneurysm formation. Circulation 117: 1302–1309. J. Med. 325: 1593–1596. 89. Xu, D., Rowland, S.E., Clark, P., Giroux, A., Côté, B., 82. Trebino, C.E., Stock, J.L., Gibbons, C.P., Naiman, B.M., Guiral, S., Salem, M., Ducharme, Y., Friesen, R.W., Méthot, Wachtmann, T.S., Umland, J.P., Pandher, K., Lapointe, J.M., N., Mancini, J., Audoly, L., and Riendeau, D. 2008. MF63 Saha, S., Roach, M.L., Carter, D., Thomas, N.A., Durtschi, [2-(6-chloro-1H-phenanthro[9,10-d]imidazol-2-yl)- B.A., McNeish, J.D., Hambor, J.E., Jakobsson, P.J., Carty, isophthalonitrile], a selective microsomal prostaglandin E T.J., Perez, J.R., and Audoly, L.P. 2003. Impaired inflammatory synthase-1 inhibitor, relieves pyresis and pain in preclinical and pain responses in mice lacking an inducible prostaglandin models of inflammation. J. Pharmacol. Exp. Ther. 326: E synthase. Proc. Natl. Acad. Sci. U.S.A. 100: 9044–9049. 754–763. 83. Tsuboi, H., Sugimoto, Y., Kainoh, T., and Ichikawa, A. 2004. 90. Yamakawa, K., Kamekura, S., Kawamura, N., Saegusa, M., Prostanoid EP4 receptor is involved in suppression of 3T3- Kamei, D., Murakami, M., Kudo, I., Uematsu, S., Akira, S., L1 adipocyte differentiation. Biochem. Biophys. Res. Chung, U.I., Nakamura, K., and Kawaguchi, H. 2008. Commun. 322: 1066–1072. Association of microsomal prostaglandin E synthase 1 84. Tsuchiya, H., Oka, T., Nakamura, K., Ichikawa, A., Saper, deficiency with impaired fracture healing, but not with bone

C.B., and Sugimoto, Y. 2008. Prostaglandin E2 attenuates loss or osteoarthritis, in mouse models of skeletal disorders. preoptic expression of GABAA receptors via EP3 receptors. Arthritis Rheum. 58: 172–183. J. Biol. Chem. 283: 11064–11071. 91. Yao, C., Sakata, D., Esaki, Y., Li, Y., Matsuoka, T., Kuroiwa, 85. umezu-Goto, M., Kishi, Y., Taira, A., Hama, K., Dohmae, K., Sugimoto, Y., and Narumiya, S. 2009. Prostaglandin

N., Takio, K., Yamori, T., Mills, G.B., Inoue, K., Aoki, J., E2-EP4 signaling promotes immune inflammation through and Arai, H. 2002. Autotaxin has lysophospholipase D Th1 cell differentiation and Th17 cell expansion. Nat. Med. activity leading to tumor cell growth and motility by 15: 633–640. lysophosphatidic acid production. J. Cell Biol. 158: 227– 92. Yu, Y., Cheng, Y., Fan, J., Chen, X.S., Klein-Szanto, A., 233. Fitzgerald, G.A., and Funk, C.D. 2005. Differential impact 86. ushikubi, F., Segi, E., Sugimoto, Y., Murata, T., Matsuoka, of prostaglandin H synthase 1 knockdown on platelets and T., Kobayashi, T., Hizaki, H., Tuboi, K., Katsuyama, M., parturition. J. Clin. Invest. 115: 986–995. Ichikawa, A., Tanaka, T., Yoshida, N., and Narumiya, S.

Top View