The orphan receptor GPR17 identified as a new dual uracil nucleotides/cysteinyl-leukotrienes receptor

Evolutionary aspects of lipoxygenases and genetic diversity of human leukotriene signaling

Leukotrienes are pro-inflammatory lipid mediators, which are biosynthesized via the lipoxygenase pathway of the arachidonic acid cascade. Lipoxygenases form a family of lipid peroxidizing enzymes and human lipoxygenase isoforms have been implicated in the pathogenesis of inflammatory, hyperproliferative (cancer) and neurodegenerative diseases. Lipoxygenases are not restricted to humans but also occur in a large number of pro- and eucaryotic organisms. Lipoxygenase-like sequences have been identified in the three domains of life (bacteria, archaea, eucarya) but because of lacking functional data the occurrence of catalytically active lipoxygenases in archaea still remains an open question. Although the physiological and/or pathophysiological functions of various lipoxygenase isoforms have been studied throughout the last three decades there is no unifying concept for the biological importance of these enzymes. In this review we are summarizing the current knowledge on the distribution of lipoxygenases in living single and multicellular organisms with particular emphasis to higher vertebrates and will also focus on the genetic diversity of enzymes and receptors involved in human leukotriene signaling.

Treatment with UDP-glucose, GDNF, and memantine promotes SVZ and white matter self-repair by endogenous glial progenitor cells in neonatal rats with ischemic PVL

Periventricular leukomalacia (PVL) is one of the foremost neurological conditions leading to long-term abnormalities in premature infants. Since it is difficult to prevent initiation of this damage in utero, promoting the innate regenerative potential of the brain after birth may provide a more feasible, prospective therapy for PVL. Treatment with UDP-glucose (UDPG), an endogenous agonist of G protein-coupled receptor 17 (GPR17) that may enhance endogenous self-repair potentiality, glial cell line-derived neurotrophic factor (GDNF), a neurotrophic factor associated with the growth and survival of nerve cells, and memantine, a noncompetitive antagonist of N-methyl-d-aspartate (NMDA) receptors that block ischemia-induced glutamate signal transduction, has been reported to achieve functional, neurological improvement in neonatal rats with PVL. The aim of the present study was to further explore whether UDPG, GDNF and/or memantine could promote corresponding self-repair of the subventricular zone (SVZ) and white matter (WM) in neonatal rats with ischemia-induced PVL. SVZ or WM tissue samples and cultured glial progenitor cells derived from a 5 day-old neonatal rat model of PVL were utilized for studying response to UDPG, GDNF and memantine in vivo and in vitro, respectively. Labeling with 5'-bromo-2'-deoxyuridine and immunofluorescent cell lineage markers after hypoxia-ischemia or oxygen-glucose deprivation (OGD) revealed that UDPG, GDNF and memantine each significantly increased glial progenitor cells and preoligodendrocytes (preOLs), as well as more differentiated immature and mature oligodendrocyte (OL), in both the SVZ and WM in vivo or in vitro. SVZ and WM glial cell apoptosis was also significantly reduced by UDPG, GDNF or memantine, both in vivo and in vitro. These results indicated that UDPG, GDNF or memantine may promote endogenous self-repair by stimulating proliferation of glial progenitor cells derived from both the SVZ and WM, activating their differentiation into more mature OLs, and raising the survival rate of these newly generated glial cells in neonatal rats with ischemic PVL.

Early phenotypic asymmetry of sister oligodendrocyte progenitor cells after mitosis and its modulation by aging and extrinsic factors

Oligodendrocyte progenitor cells (OPCs) persist in the adult central nervous system and guarantee oligodendrocyte turnover throughout life. It remains obscure how OPCs avoid exhaustion during adulthood. Similar to stem cells, OPCs could self-maintain by undergoing asymmetric divisions generating a mixed progeny either keeping a progenitor phenotype or proceeding to differentiation. To address this issue, we examined the distribution of stage-specific markers in sister OPCs during mitosis and later after cell birth, and assessed its correlation with distinct short-term fates. In both the adult and juvenile cerebral cortex a fraction of dividing OPCs gives rise to sister cells with diverse immunophenotypic profiles and short-term behaviors. Such heterogeneity appears as cells exit cytokinesis, but does not derive from the asymmetric segregation of molecules such as NG2 or PDGFRa expressed in the mother cell. Rather, rapid downregulation of OPC markers and upregulation of molecules associated with lineage progression contributes to generate early sister OPC asymmetry. Analyses during aging and upon exposure to physiological (i.e., increased motor activity) and pathological (i.e., trauma or demyelination) stimuli showed that both intrinsic and environmental factors contribute to determine the fraction of symmetric and asymmetric OPC pairs and the phenotype of the OPC progeny as soon as cells exit mitosis.

8-BuS-ATP derivatives as specific NTPDase1 inhibitors

BACKGROUND AND PURPOSE

Ectonucleotidases control extracellular nucleotide levels and consequently, their (patho)physiological responses. Among these enzymes, nucleoside triphosphate diphosphohydrolase-1 (NTPDase1), -2, -3 and -8 are the major ectonucleotidases responsible for nucleotide hydrolysis at the cell surface under physiological conditions, and NTPDase1 is predominantly located at the surface of vascular endothelial cells and leukocytes. Efficacious inhibitors of NTPDase1 are required to modulate responses induced by nucleotides in a number of pathological situations such as thrombosis, inflammation and cancer.

EXPERIMENTAL APPROACH

Here, we present the synthesis and enzymatic characterization of five 8-BuS-adenine nucleotide derivatives as potent and selective inhibitors of NTPDase1.

KEY RESULTS

The compounds 8-BuS-AMP, 8-BuS-ADP and 8-BuS-ATP inhibit recombinant human and mouse NTPDase1 by mixed type inhibition, predominantly competitive with Ki values <1 μM. In contrast to 8-BuS-ATP which could be hydrolyzed by other NTPDases, the other BuS derivatives were resistant to hydrolysis by either NTPDase1, -2, -3 or -8. 8-BuS-AMP and 8-BuS-ADP were the most potent and selective inhibitors of NTPDase1 expressed in human umbilical vein endothelial cells as well as in situ in human and mouse tissues. As expected, as a result of their inhibition of recombinant human NTPDase1, 8-BuS-AMP and 8-BuS-ADP impaired the ability of this enzyme to block platelet aggregation. Importantly, neither of these two inhibitors triggered platelet aggregation nor prevented ADP-induced platelet aggregation, in support of their inactivity towards P2Y1 and P2Y12 receptors.

CONCLUSIONS AND IMPLICATIONS

The 8-BuS-AMP and 8-BuS-ADP have therefore potential to serve as drugs for the treatment of pathologies regulated by NTPDase1.

Ticlopidine in its prodrug form is a selective inhibitor of human NTPDase1

Nucleoside triphosphate diphosphohydrolase-1 (NTPDase1), like other ectonucleotidases, controls extracellular nucleotide levels and consequently their (patho)physiological responses such as in thrombosis, inflammation, and cancer. Selective NTPDase1 inhibitors would therefore be very useful. We previously observed that ticlopidine in its prodrug form, which does not affect P2 receptor activity, inhibited the recombinant form of human NTPDase1 (K_i = 14 μM). Here we tested whether ticlopidine can be used as a selective inhibitor of NTPDase1. We confirmed that ticlopidine inhibits NTPDase1 in different forms and in different assays. The ADPase activity of intact HUVEC as well as of COS-7 cells transfected with human NTPDase1 was strongly inhibited by 100 µM ticlopidine, 99 and 86%, respectively. Ticlopidine (100 µM) completely inhibited the ATPase activity of NTPDase1 in situ as shown by enzyme histochemistry with human liver and pancreas sections. Ticlopidine also inhibited the activity of rat and mouse NTPDase1 and of potato apyrase. At 100 µM ticlopidine did not affect the activity of human NTPDase2, NTPDase3, and NTPDase8, nor of NPP1 and NPP3. Weak inhibition (10–20%) of NTPDase3 and -8 was observed at 1 mM ticlopidine. These results show that ticlopidine is a specific inhibitor of NTPDase1 that can be used in enzymatic and histochemistry assays.

Structure and putative signaling mechanism of Protease activated receptor 2 (PAR2) - a promising target for breast cancer

Experimental evidences have observed enhanced expression of protease activated receptor 2 (PAR2) in breast cancer consistently. However, it is not yet recognized as an important therapeutic target for breast cancer as the primary molecular mechanisms of its activation are not yet well-defined. Nevertheless, recent reports on the mechanism of GPCR activation and signaling have given new insights to GPCR functioning. In the light of these details, we attempted to understand PAR2 structure & function using molecular modeling techniques. In this work, we generated averaged representative stable models of PAR2, using protease activated receptor 1 (PAR1) as a template and selected conformation based on their binding affinity with PAR2 specific agonist, GB110. Further, the selected model was used for studying the binding affinity of putative ligands. The selected ligands were based on a recent publication on phylogenetic analysis of Class A rhodopsin family of GPCRs. This study reports putative ligands, their interacting residues, binding affinity and molecular dynamics simulation studies on PAR2-ligand complexes. The results reported from this study would be useful for researchers and academicians to investigate PAR2 function as its physiological role is still hypothetical. Further, this information may provide a novel therapeutic scheme to manage breast cancer.

Update on leukotriene, lipoxin and oxoeicosanoid receptors: IUPHAR Review 7

The endogenous ligands for the LT, lipoxin (LX) and oxoeicosanoid receptors are bioactive products produced by the action of the lipoxygenase family of enzymes. The LT receptors BLT1 and BLT2 , are activated by LTB4 and the CysLT1 and CysLT2 receptors are activated by the cysteinyl-LTs, whereas oxoeicosanoids exert their action through the OXE receptor. In contrast to these pro-inflammatory mediators, LXA4 transduces responses associated with the resolution of inflammation through the receptor FPR2/ALX (ALX/FPR2). The aim of the present review is to give a state of the field on these receptors, with focus on recent important findings. For example, BLT1 receptor signalling in cancer and the dual role of the BLT2 receptor in pro- and anti-inflammatory actions have added more complexity to lipid mediator signalling. Furthermore, a cross-talk between the CysLT and P2Y receptor systems has been described, and also the presence of novel receptors for cysteinyl-LTs, such as GPR17 and GPR99. Finally, lipoxygenase metabolites derived from ω-3 essential polyunsaturated acids, the resolvins, activate the receptors GPR32 and ChemR23. In conclusion, the receptors for the lipoxygenase products make up a sophisticated and tightly controlled system of endogenous pro- and anti-inflammatory signalling in physiology and pathology.

Expression of dual nucleotides/cysteinyl-leukotrienes receptor GPR17 in early trafficking of cardiac stromal cells after myocardial infarction

GPR17 is a G_i-coupled dual receptor activated by uracil-nucleotides and cysteinyl-leukotrienes. These mediators are massively released into hypoxic tissues. In the normal heart, GPR17 expression has been reported. By contrast, its role in myocardial ischaemia has not yet been assessed. In the present report, the expression of GPR17 was investigated in mice before and at early stages after myocardial infarction by using immunofluorescence, flow cytometry and RT-PCR. Before induction of ischaemia, results indicated the presence of the receptor in a population of stromal cells expressing the stem-cell antigen-1 (Sca-1). At early stages after ligation of the coronary artery, the receptor was expressed in Sca-1⁺ cells, and cells stained with Isolectin-B4 and anti-CD45 antibody. GPR17⁺ cells also expressed mesenchymal marker CD44. GPR17 function was investigated in vitro in a Sca-1⁺/CD31⁻ cell line derived from normal hearts. These experiments showed a migratory function of the receptor by treatment with UDP-glucose and leukotriene LTD4, two GPR17 pharmacological agonists. The GPR17 function was finally assessed in vivo by treating infarcted mice with Cangrelor, a pharmacological receptor antagonist, which, at least in part, inhibited early recruitment of GPR17⁺ and CD45⁺ cells. These findings suggest a regulation of heart-resident mesenchymal cells and blood-borne cellular species recruitment following myocardial infarction, orchestrated by GPR17.

Microglia is a key player in the reduction of stroke damage promoted by the new antithrombotic agent ticagrelor

The ADP-responsive P2Y12 receptor is expressed on both platelets and microglia. Clinical data show that ticagrelor, a direct-acting, reversibly binding P2Y12-receptor antagonist, reduces total cardiovascular events, including stroke. In our present study, we investigated the expression of P2Y12 receptors and the effects of ticagrelor on brain injury in Sprague-Dawley rats subjected to a permanent middle cerebral artery occlusion (MCAo). Rats were treated per os with ticagrelor 3 mg/kg or vehicle at 10 minutes, 22, and 36 hours after MCAo and killed after 48 hours. Immunofluorescence analysis showed an ischemia-related modulation of the P2Y12 receptor, which is constitutively expressed in Iba1(+) resting microglia. After MCAo, activated microglia was mainly concentrated around the lesion, with fewer cells present inside the ischemic core. Ticagrelor significantly attenuated the evolution of ischemic damage-evaluated by magnetic resonance imaging (MRI) at 2, 24, and 48 hours after MCAo-, the number of infiltrating cells expressing the microglia/monocyte marker ED-1, the cerebral expression of proinflammatory mediators (interleukin 1 (IL-1), monocyte chemoattractant protein 1 (MCP-1), nitric oxide synthase (iNOS)) and the associated neurologic impairment. In transgenic fluorescent reporter CX3CR1-green fluorescent protein (GFP) mice, 72 hours after MCAo, ticagrelor markedly reduced GFP(+) microglia and both early and late infiltrating blood-borne cells. Finally, in primary cultured microglia, ticagrelor fully inhibited ADP-induced chemotaxis (P<0.01). Our results show that ticagrelor is protective against ischemia-induced cerebral injury and this effect is mediated, at least partly, by inhibition of P2Y12-mediated microglia activation and chemotaxis.

Cysteinyl leukotrienes and their receptors; emerging concepts

Cysteinyl leukotrienes (cys-LTs) are potent mediators of inflammation derived from arachidonic acid through the 5-lipoxygenase/leukotriene C4 synthase pathway. The derivation of their chemical structures and identification of their pharmacologic properties predated the cloning of their classical receptors and the development of drugs that modify their synthesis and actions. Recent studies have revealed unanticipated insights into the regulation of cys-LT synthesis, the function of the cys-LTs in innate and adaptive immunity and human disease, and the identification of a new receptor for the cys-LTs. This review highlights these studies and summarizes their potential pathobiologic and therapeutic implications.

A rapid and efficient immunoenzymatic assay to detect receptor protein interactions: G protein-coupled receptors

G protein-coupled receptors (GPCRs) represent one of the largest families of cell surface receptors, and are the target of at least one-third of the current therapeutic drugs on the market. Along their life cycle, GPCRs are accompanied by a range of specialized GPCR-interacting proteins (GIPs), which take part in receptor proper folding, targeting to the appropriate subcellular compartments and in receptor signaling tasks, and also in receptor regulation processes, such as desensitization and internalization. The direction of protein-protein interactions and multi-protein complexes formation is crucial in understanding protein function and their implication in pathological events. Although several methods have been already developed to assay protein complexes, some of them are quite laborious, expensive, and, more important, they do not generate fully quantitative results. Herein, we show a rapid immunoenzymatic assay to quantify GPCR interactionswith its signaling proteins. The recently de-orphanized GPCR, GPR17, was chosen as a GPCR prototype to optimize the assay. In a GPR17 transfected cell line and primary oligodendrocyte precursor cells, GPR17 interaction with proteins involved in the typical GPCR regulation, such as desensitization and internalization machinery, was investigated. The obtained results were validated by co-immunoprecipitation experiments, confirming this new method as a rapid and quantitative assay to study protein-protein interactions.

Development of [(3)H]2-Carboxy-4,6-dichloro-1H-indole-3-propionic Acid ([(3)H]PSB-12150): A Useful Tool for Studying GPR17

The recently described synthetic GPR17 agonist 2-carboxy-4,6-dichloro-1H-indole-3-propionic acid (1) was prepared in tritium-labeled form by catalytic hydrogenation of the corresponding propenoic acid derivative 8 with tritium gas. The radioligand [(3)H]PSB-12150 (9) was obtained with a specific activity of 17 Ci/mmol (629 GBq/mmol). It showed specific and saturable binding to a single binding site in membrane preparations from Chinese hamster ovary cells recombinantly expressing the human GPR17. A competition assay procedure was established, which allows the determination of ligand binding affinities.

Intercellular Lipid Mediators and GPCR Drug Discovery

G-protein-coupled receptors (GPCR) are the largest superfamily of receptors responsible for signaling between cells and tissues, and because they play important physiological roles in homeostasis, they are major drug targets. New technologies have been developed for the identification of new ligands, new GPCR functions, and for drug discovery purposes. In particular, intercellular lipid mediators, such as, lysophosphatidic acid and sphingosine 1-phosphate have attracted much attention for drug discovery and this has resulted in the development of fingolimod (FTY-720) and AM095. The discovery of new intercellular lipid mediators and their GPCRs are discussed from the perspective of drug development. Lipid GPCRs for lysophospholipids, including lysophosphatidylserine, lysophosphatidylinositol, lysophosphatidylcholine, free fatty acids, fatty acid derivatives, and other lipid mediators are reviewed.

Restoration of oligodendrocyte pools in a mouse model of chronic cerebral hypoperfusion

Chronic cerebral hypoperfusion, a sustained modest reduction in cerebral blood flow, is associated with damage to myelinated axons and cognitive decline with ageing. Oligodendrocytes (the myelin producing cells) and their precursor cells (OPCs) may be vulnerable to the effects of hypoperfusion and in some forms of injury OPCs have the potential to respond and repair damage by increased proliferation and differentiation. Using a mouse model of cerebral hypoperfusion we have characterised the acute and long term responses of oligodendrocytes and OPCs to hypoperfusion in the corpus callosum. Following 3 days of hypoperfusion, numbers of OPCs and mature oligodendrocytes were significantly decreased compared to controls. However following 1 month of hypoperfusion, the OPC pool was restored and increased numbers of oligodendrocytes were observed. Assessment of proliferation using PCNA showed no significant differences between groups at either time point but showed reduced numbers of proliferating oligodendroglia at 3 days consistent with the loss of OPCs. Cumulative BrdU labelling experiments revealed higher numbers of proliferating cells in hypoperfused animals compared to controls and showed a proportion of these newly generated cells had differentiated into oligodendrocytes in a subset of animals. Expression of GPR17, a receptor important for the regulation of OPC differentiation following injury, was decreased following short term hypoperfusion. Despite changes to oligodendrocyte numbers there were no changes to the myelin sheath as revealed by ultrastructural assessment and fluoromyelin however axon-glial integrity was disrupted after both 3 days and 1 month hypoperfusion. Taken together, our results demonstrate the initial vulnerability of oligodendroglial pools to modest reductions in blood flow and highlight the regenerative capacity of these cells.

Cysteinyl leukotrienes and their receptors: Bridging inflammation and colorectal cancer

Long-standing inflammation has emerged as a hallmark of neoplastic transformation of epithelial cells and may be a limiting factor of successful conventional tumor therapies. A complex milieu composed of distinct stromal and immune cells, soluble factors and inflammatory mediators plays a crucial role in supporting and promoting various types of cancers. An augmented inflammatory response can predispose a patient to colorectal cancer (CRC). Common risk factors associated with CRC development include diet and lifestyle, altered intestinal microbiota and commensals, and chronic inflammatory bowel diseases. Cysteinyl leukotrienes are potent inflammatory metabolites synthesized from arachidonic acid and have a broad range of functions involved in the etiology of various pathologies. This review discusses the important role of cysteinyl leukotriene signaling in linking inflammation and CRC.

Improved synthesis of 4-/6-substituted 2-carboxy-1H-indole-3-propionic acid derivatives and structure–activity relationships as GPR17 agonists

Several tri- and tetra-substituted indole derivatives were synthesized and evaluated as human GPR17 agonists. Steep structure–activity relationships were observed.

The Concise Guide to PHARMACOLOGY 2013/14: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. G protein-coupled receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

Patent Highlights

Snapshot of key developments in the patent literature accompanied by explanatory synopses

Enigmatic GPCR finds a stimulating drug

GPR17 is an orphan G protein-coupled receptor involved in orchestration of oligodendrocyte differentiation and myelination in the central nervous system. In this issue of Science Signaling, Hennen et al. used a signaling pathway-unbiased screen to identify two small molecule activators of this receptor. One of these, MDL29951, was carried forward to illustrate GPR17-dependent activation of Gαi- and Gαq-promoted signaling pathways in cell lines expressing recombinant GPR17, whereas no effect was observed with previously proposed but dubitable agonists (uracil nucleotides and cysteinyl leukotrienes) of this receptor. Conversely, MDL29951 did not activate any of the known uracil or adenine nucleotide-activated P2Y receptors or cysteinyl leukotriene receptors. Gαi- and Gαq-dependent signaling responses also were observed in primary rat oligodendrocytes in the presence of MDL29951. Moreover, MDL29951 diminished myelination in primary oligodendrocytes isolated from heterozygous mice but had no effect on myelination in oligodendrocytes from GPR17 knockout mice. Effects of a small-molecule GPR17 agonist observed during oligodendrocyte differentiation support the idea that development of antagonists of GPR17 is a rational goal for elaboration of pharmacotherapies in demyelinating diseases.

Decoding signaling and function of the orphan G protein-coupled receptor GPR17 with a small-molecule agonist

Replacement of the lost myelin sheath is a therapeutic goal for treating demyelinating diseases of the central nervous system (CNS), such as multiple sclerosis (MS). The G protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptor (GPCR) GPR17, which is phylogenetically closely related to receptors of the "purinergic cluster," has emerged as a modulator of CNS myelination. However, whether GPR17-mediated signaling positively or negatively regulates this critical process is unresolved. We identified a small-molecule agonist, MDL29,951, that selectively activated GPR17 even in a complex environment of endogenous purinergic receptors in primary oligodendrocytes. MDL29,951-stimulated GPR17 engaged the entire set of intracellular adaptor proteins for GPCRs: G proteins of the Gα(i), Gα(s), and Gα(q) subfamily, as well as β-arrestins. This was visualized as alterations in the concentrations of cyclic adenosine monophosphate and inositol phosphate, increased Ca²⁺ flux, phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/2), as well as multifeatured cell activation recorded with label-free dynamic mass redistribution and impedance biosensors. MDL29,951 inhibited the maturation of primary oligodendrocytes from heterozygous but not GPR17 knockout mice in culture, as well as in cerebellar slices from 4-day-old wild-type mice. Because GPCRs are attractive targets for therapeutic intervention, inhibiting GPR17 emerges as therapeutic strategy to relieve the oligodendrocyte maturation block and promote myelin repair in MS.

Inhibition of P2X4 function by P2Y6 UDP receptors in microglia

ATP-gated P2X4 receptor channels expressed in spinal microglia actively participate in central sensitization, making their functional regulation a key process in chronic pain pathologies. P2Y6 metabotropic Gq -coupled receptors, also expressed in microglia, are involved in the initial response to nerve injury, triggering phagocytosis upon activation by UDP. It has been reported recently that expression of both P2X4 and P2Y6 is upregulated in activated microglia following nerve injury. We show here, in resting as well as LPS-activated primary microglia, that P2Y6 decreases P2X4-mediated calcium entry and inhibits the dilation of P2X4 channels into a large-conductance pore measured with a YO-PRO-1 uptake assay. Furthermore, P2Y6 activation modulates the ATP-dependent migration of microglia, a process likely involved in their shift from migratory to phagocytic phenotype. Reconstituting the P2X4-P2Y6 interaction in recombinant systems shows that P2Y6 activation decreases P2X4 current amplitude, activation and desensitization rates, and reduces P2X4 channel permeability to the large cation NMDG(+) . Phospholipase C-mediated hydrolysis of the phosphoinositide PI(4,5)P2 , a necessary cofactor for P2X4 channel function, underlies this inhibitory crosstalk. As extracellular levels of both ATP and UDP are increased in the spinal cord following nerve injury, the control of P2X4 activity by P2Y6 might play a critical role in regulating neuropathic pain-inducing microglial responses.

Is GPR17 a P2Y/leukotriene receptor? examination of uracil nucleotides, nucleotide sugars, and cysteinyl leukotrienes as agonists of GPR17

The orphan receptor GPR17 has been reported to be activated by UDP, UDP-sugars, and cysteinyl leukotrienes, and coupled to intracellular Ca(2+) mobilization and inhibition of cAMP accumulation, but other studies have reported either a different agonist profile or lack of agonist activity altogether. To determine if GPR17 is activated by uracil nucleotides and leukotrienes, the hemagglutinin-tagged receptor was expressed in five different cell lines and the signaling properties of the receptor were investigated. In C6, 1321N1, or Chinese hamster ovary (CHO) cells stably expressing GPR17, UDP, UDP-glucose, UDP-galactose, and cysteinyl leukotriene C4 (LTC4) all failed to promote inhibition of forskolin-stimulated cAMP accumulation, whereas both UDP and UDP-glucose promoted marked inhibition (>80%) of forskolin-stimulated cAMP accumulation in C6 and CHO cells expressing the P2Y14 receptor. Likewise, none of these compounds promoted accumulation of inositol phosphates in COS-7 or human embryonic kidney 293 cells transiently transfected with GPR17 alone or cotransfected with Gαq/i5, which links Gi-coupled receptors to the Gq-regulated phospholipase C (PLC) signaling pathway, or PLCε, which is activated by the Gα12/13 signaling pathway. Moreover, none of these compounds promoted internalization of GPR17 in 1321N1-GPR17 cells. Consistent with previous reports, coexpression experiments of GPR17 with cysteinyl leukotriene receptor 1 (CysLTR1) suggested that GPR17 acts as a negative regulator of CysLTR1. Taken together, these data suggest that UDP, UDP-glucose, UDP-galactose, and LTC4 are not the cognate ligands of GPR17.

siRNA Treatment: "A Sword-in-the-Stone" for Acute Brain Injuries

Ever since the discovery of small interfering ribonucleic acid (siRNA) a little over a decade ago, it has been highly sought after for its potential as a therapeutic agent for many diseases. In this review, we discuss the promising possibility of siRNA to be used as a drug to treat acute brain injuries such as stroke and traumatic brain injury. First, we will give a brief and basic overview of the principle of RNA interference as an effective mechanism to decrease specific protein expression. Then, we will review recent in vivo studies describing siRNA research experiments/treatment options for acute brain diseases. Lastly, we will discuss the future of siRNA as a clinical therapeutic strategy against brain diseases and injuries, while addressing the current obstacles to effective brain delivery.

Changes of the GPR17 receptor, a new target for neurorepair, in neurons and glial cells in patients with traumatic brain injury

Unveiling the mechanisms participating in the damage and repair of traumatic brain injury (TBI) is fundamental to develop new therapies. The P2Y-like GPR17 receptor has recently emerged as a sensor of damage and a key actor in lesion remodeling/repair in the rodent brain, but its role in humans is totally unknown. Here, we characterized GPR17 expression in brain specimens from seven intensive care unit TBI patients undergoing neurosurgery for contusion removal and from 28 autoptic TBI cases (and 10 control subjects of matched age and gender) of two university hospitals. In both neurosurgery and autoptic samples, GPR17 expression was strong inside the contused core and progressively declined distally according to a spatio-temporal gradient. Inside and around the core, GPR17 labeled dying neurons, reactive astrocytes, and activated microglia/macrophages. In peri-contused parenchyma, GPR17 decorated oligodendrocyte precursor cells (OPCs) some of which had proliferated, indicating re-myelination attempts. In autoptic cases, GPR17 expression positively correlated with death for intracranial complications and negatively correlated with patients' post-traumatic survival. Data indicate lesion-specific sequential involvement of GPR17 in the (a) death of irreversibly damaged neurons, (b) activation of microglia/macrophages remodeling the lesion, and (c) activation/proliferation of multipotent parenchymal progenitors (both reactive astrocytes and OPCs) starting repair processes. Data validate GPR17 as a target for neurorepair and are particularly relevant to setting up new therapies for TBI patients.

A review on leukotrienes and their receptors with reference to asthma

OBJECTIVE AND METHODS

Leukotrienes (LTs) including cysteinyl leukotrienes (CysLTs) and LTB4 are the most potent inflammatory lipid mediators and play a central role in the pathophysiology of asthma and other inflammatory diseases. These biological molecules mediate a plethora of contractile and inflammatory responses through specific interaction with distinct G protein-coupled receptors (GPCRs). The main objective of this review is to present an overview of the biological effects of CysLTs and their receptors, along with the current knowledge of mechanisms and role of LTs in the pathogenesis of asthma.

RESULTS

CysLTs including LTC4, LTD4 and LTE4 are ligands for CysLT1 and CysLT2 receptors, and LTB4 is the agonist for BLT1 and BLT2 receptors. The role of CysLT1 receptor is well established, and most of the pathophysiological effects of CysLTs in asthma are mediated by CysLT1 receptor. Several CysLT1 antagonists have been developed to date and are currently in clinical practice. Most common among them are classical CysLT1 receptor antagonists such as montelukast, zafirlukast, pranlukast, pobilukast, iralukast, cinalukast and MK571. The pharmacological role of CysLT2 receptor, however, is less defined and there is no specific antagonist available so far. The recent demonstration that mice lacking both known CysLT receptors exhibit full/augmented response to CysLT points to the existence of additional subtypes of CysLT receptors. LTB4, on the other hand, is another potent inflammatory leukotriene, which acts as a strong chemoattractant for neutrophils, but weaker for eosinophils. LTB4 is known to play an important role in the development of airway hyper-responsiveness in severe asthma. However there is no LTB4 antagonist available in clinic to date.

CONCLUSION

This review gives a recent update on the LTs including their biosynthesis, biological effects and the role of anti-LTs in the treatment of asthma. It also discusses about the possible existence of additional subtypes of CysLT receptors.

HAMI 3379, a CysLT2 receptor antagonist, attenuates ischemia-like neuronal injury by inhibiting microglial activation

The cysteinyl leukotrienes (CysLTs) are inflammatory mediators closely associated with neuronal injury after brain ischemia through the activation of their receptors, CysLT1R and CysLT2R. Here we investigated the involvement of both receptors in oxygen-glucose deprivation/recovery (OGD/R)-induced ischemic neuronal injury and the effect of the novel CysLT2R antagonist HAMI 3379 [3-({[(1S,3S)-3- carboxycyclohexyl]amino}carbonyl)-4-(3-{4-[4-(cyclo-hexyloxy)butoxy]phenyl}propoxy)benzoic acid] in comparison with the CysLT1R antagonist montelukast. In primary neurons, neither the nonselective agonist leukotriene D4 (LTD4) nor the CysLT2R agonist N-methyl-leukotriene C4 (NMLTC4) induced neuronal injury, and HAMI 3379 did not affect OGD/R-induced neuronal injury. However, in addition to OGD/R, LTD4 and NMLTC4 induced cell injury and neuronal loss in mixed cultures of cortical cells, and neuronal loss and necrosis in neuron-microglial cocultures. Moreover, they induced phagocytosis and cytokine release (interleukin-1β and tumor necrosis factor-α) from primary microglia, and conditioned medium from the treated microglia induced neuronal necrosis. HAMI 3379 inhibited all of these responses, and its effects were the same as those of CysLT2R interference by CysLT2R short hairpin RNA, indicating CysLT2R dependence. In comparison, montelukast moderately inhibited OGD/R-induced primary neuronal injury and most OGD/R- and LTD4-induced (but not NMLTC4-induced) responses in mixed cultures, cocultures, and microglia. The effects of montelukast were both dependent and independent of CysLT1Rs because interference by CysLT1R small interfering RNA had limited effects on neuronal injury in neuron-microglial cocultures and on cytokine release from microglia. Our findings indicated that HAMI 3379 effectively blocked CysLT2R-mediated microglial activation, thereby indirectly attenuating ischemic neuronal injury. Therefore, CysLT2R antagonists may represent a new type of therapeutic agent in the treatment of ischemic stroke.

International Union of Basic and Clinical Pharmacology. LXXXVIII. G protein-coupled receptor list: recommendations for new pairings with cognate ligands

In 2005, the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification (NC-IUPHAR) published a catalog of all of the human gene sequences known or predicted to encode G protein-coupled receptors (GPCRs), excluding sensory receptors. This review updates the list of orphan GPCRs and describes the criteria used by NC-IUPHAR to recommend the pairing of an orphan receptor with its cognate ligand(s). The following recommendations are made for new receptor names based on 11 pairings for class A GPCRs: hydroxycarboxylic acid receptors [HCA₁ (GPR81) with lactate, HCA₂ (GPR109A) with 3-hydroxybutyric acid, HCA₃ (GPR109B) with 3-hydroxyoctanoic acid]; lysophosphatidic acid receptors [LPA₄ (GPR23), LPA₅ (GPR92), LPA₆ (P2Y5)]; free fatty acid receptors [FFA4 (GPR120) with omega-3 fatty acids]; chemerin receptor (CMKLR1; ChemR23) with chemerin; CXCR7 (CMKOR1) with chemokines CXCL12 (SDF-1) and CXCL11 (ITAC); succinate receptor (SUCNR1) with succinate; and oxoglutarate receptor [OXGR1 with 2-oxoglutarate]. Pairings are highlighted for an additional 30 receptors in class A where further input is needed from the scientific community to validate these findings. Fifty-seven human class A receptors (excluding pseudogenes) are still considered orphans; information has been provided where there is a significant phenotype in genetically modified animals. In class B, six pairings have been reported by a single publication, with 28 (excluding pseudogenes) still classified as orphans. Seven orphan receptors remain in class C, with one pairing described by a single paper. The objective is to stimulate research into confirming pairings of orphan receptors where there is currently limited information and to identify cognate ligands for the remaining GPCRs. Further information can be found on the IUPHAR Database website (http://www.iuphar-db.org).

Cellular and molecular characterization of multipolar Map5-expressing cells: a subset of newly generated, stage-specific parenchymal cells in the mammalian central nervous system

Although extremely interesting in adult neuro-glio-genesis and promising as an endogenous source for repair, parenchymal progenitors remain largely obscure in their identity and physiology, due to a scarce availability of stage-specific markers. What appears difficult is the distinction between real cell populations and various differentiation stages of the same population. Here we focused on a subset of multipolar, polydendrocyte-like cells (mMap5 cells) expressing the microtubule associated protein 5 (Map5), which is known to be present in most neurons. We characterized the morphology, phenotype, regional distribution, proliferative dynamics, and stage-specific marker expression of these cells in the rabbit and mouse CNS, also assessing their existence in other mammalian species. mMap5 cells were never found to co-express the Ng2 antigen. They appear to be a population of glial cells sharing features but also differences with Ng2+progenitor cells. We show that mMap5 cells are newly generated, postmitotic parenchymal elements of the oligodendroglial lineage, thus being a stage-specific population of polydendrocytes. Finally, we report that the number of mMap5 cells, although reduced within the brain of adult/old animals, can increase in neurodegenerative and traumatic conditions.

UDP-glucose enhances outward K(+) currents necessary for cell differentiation and stimulates cell migration by activating the GPR17 receptor in oligodendrocyte precursors

In the developing and mature central nervous system, NG2 expressing cells comprise a population of cycling oligodendrocyte progenitor cells (OPCs) that differentiate into mature, myelinating oligodendrocytes (OLGs). OPCs are also characterized by high motility and respond to injury by migrating into the lesioned area to support remyelination. K(+) currents in OPCs are developmentally regulated during differentiation. However, the mechanisms regulating these currents at different stages of oligodendrocyte lineage are poorly understood. Here we show that, in cultured primary OPCs, the purinergic G-protein coupled receptor GPR17, that has recently emerged as a key player in oligodendrogliogenesis, crucially regulates K(+) currents. Specifically, receptor stimulation by its agonist UDP-glucose enhances delayed rectifier K(+) currents without affecting transient K(+) conductances. This effect was observed in a subpopulation of OPCs and immature pre-OLGs whereas it was absent in mature OLGs, in line with GPR17 expression, that peaks at intermediate phases of oligodendrocyte differentiation and is thereafter downregulated to allow terminal maturation. The effect of UDP-glucose on K(+) currents is concentration-dependent, blocked by the GPR17 antagonists MRS2179 and cangrelor, and sensitive to the K(+) channel blocker tetraethyl-ammonium, which also inhibits oligodendrocyte maturation. We propose that stimulation of K(+) currents is responsible for GPR17-induced oligodendrocyte differentiation. Moreover, we demonstrate, for the first time, that GPR17 activation stimulates OPC migration, suggesting an important role for this receptor after brain injury. Our data indicate that modulation of GPR17 may represent a strategy to potentiate the post-traumatic response of OPCs under demyelinating conditions, such as multiple sclerosis, stroke, and brain trauma.

The role of leukotrienes in immunopathogenesis of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disorder of joints for which there is no strict cure. However, conventional medications can reduce inflammation, relieve pain, and slow joint damage. Leukotrienes are a family of paracrine agents derived from oxidative metabolism of arachidonic acid. Synthesis of lipid mediators and subsequent induction of receptor activity are tightly regulated under normal physiological conditions, so that enzyme and/or receptor dysfunction can lead to a variety of clinical signs and symptoms of disease, such as local pain and tissue edema. In these tissues, immunocompetent cells accumulate at the site of injury, contributing to tissue damage and perpetuation of the disease process. Leukotrienes (often leukotriene B4) as potent chemotactic agents can provoke most signs and symptoms in rheumatoid arthritis by initiating, coordinating, sustaining, and amplifying the inflammatory response, through recruitment of leukocytes. A number of studies have reported that pharmacological modulation in this field can significantly attenuate clinical manifestations associated with different inflammatory pathologies.

A Strategy Combining Differential Low-Throughput Screening and Virtual Screening (DLS-VS) Accelerating the Discovery of new Modulators for the Orphan GPR34 Receptor

The DLS-VS strategy was developed as an integrated method for identifying chemical modulators for orphan GPCRs. It combines differential low-throughput screening (DLS) and virtual screening (VS). The two cascaded techniques offer complementary advantages and allow the experimental testing of a minimal number of compounds. First, DLS identifies modulators specific for the considered receptor among a set of receptors, through the screening of a small library with diverse chemical compounds. Then, an active molecular model of the receptor is built by homology to a validated template, and it is progressively refined by rotamers modification for key side-chains, by VS of the already screened library, and by iterative selection of the model generating the best enrichment. The refined active model is finally used for the VS of a large chemical library and the selection of a small set of compounds for experimental testing. Applied to the orphan receptor GPR34, the DLS-VS strategy combined the experimental screening of 20 000 compounds and the virtual screening of 1 250 000 compounds. It identified one agonist and eight inverse agonists, showing a high chemical diversity. We describe the method. The strategy can be applied to other GPCRs.

The leukotrienes: immune-modulating lipid mediators of disease

The leukotrienes are important lipid mediators with immune modulatory and proinflammatory properties. Classical bioactions of leukotrienes include chemotaxis, endothelial adherence, and activation of leukocytes, chemokine production, as well as contraction of smooth muscles in the microcirculation and respiratory tract. When formed in excess, these compounds play a pathogenic role in several acute and chronic inflammatory diseases, such as asthma, rheumatoid arthritis, and inflammatory bowel disease. An increasing number of diseases have been linked to inflammation implicating the leukotrienes as potential mediators. For example, recent investigations using genetic, morphological, and biochemical approaches have pointed to the involvement of leukotrienes in cardiovascular diseases including atherosclerosis, myocardial infarction, stroke, and abdominal aortic aneurysm. Moreover, new insights have changed our previous notion of leukotrienes as mediators of inflammatory reactions to molecules that can fine-tune the innate and adaptive immune response. Here, we review the most recent understanding of the leukotriene cascade with emphasis on recently identified roles in immune reactions and pathophysiology.

Cysteinyl leukotriene receptors, old and new; implications for asthma

The cysteinyl leukotrienes (cys-LTs) are three structurally similar, but functionally distinct lipid mediators of inflammation. The parent cys-LT, LTC(4) , is synthesized by and released from mast cells, eosinophils, basophils, and macrophages, and is converted to the potent constrictor LTD(4) and the stable metabolite, LTE(4) . While only two cys-LT-selective receptors (CysLTRs) have been identified, cloned, and characterized, studies dating back three decades predicted the existence of at least three functional CysLTRs, each with a characteristic physiological function in airways and other tissues. The recent demonstration that mice lacking both known CysLTRs exhibit full (and in some instances, augmented) physiological responses to cys-LTs verifies the existence of unidentified CysLTRs. Moreover, the ability to manipulate receptor expression in both whole animal and cellular systems reveals that the functions of CysLTRs are controlled at multiple levels, including receptor-receptor interactions. Finally, studies in transgenic mice have uncovered a potentially major role for cys-LTs in controlling the induction of Th(2) responses to common allergens. This review focuses on these recent findings and their potential clinical implications.

The regulated expression, intracellular trafficking, and membrane recycling of the P2Y-like receptor GPR17 in Oli-neu oligodendroglial cells

GPR17 is a G-protein-coupled receptor that is activated by two classes of molecules: uracil-nucleotides and cysteinyl-leukotrienes. GPR17 is required for initiating the differentiation of oligodendrocyte precursors but has to be down-regulated to allow cells to undergo terminal maturation. Although a great deal has been learned about GPR17 expression and signaling, no information is currently available about the trafficking of native receptors after the exposure of differentiating oligodendrocytes to endogenous agonists. Here, we demonstrate that neuron-conditioned medium induces the transcriptionally mediated, time-regulated expression of GPR17 in Oli-neu, an oligodendrocyte precursor cell line, making these cells suitable for studying the endocytic traffic of the native receptor. Agonist-induced internalization, intracellular trafficking, and membrane recycling of GPR17 were analyzed by biochemical and immunofluorescence assays using an ad hoc-developed antibody against the extracellular N-terminal of GPR17. Both UDP-glucose and LTD(4) increased GPR17 internalization, although with different efficiency. At early time points, internalized GPR17 co-localized with transferrin receptor, whereas at later times it partially co-localized with the lysosomal marker Lamp1, suggesting that a portion of GPR17 is targeted to lysosomes upon ligand binding. An analysis of receptor recycling and degradation demonstrated that a significant aliquot of GPR17 is recycled to the cell surface. Furthermore, internalized GPR17 displayed a co-localization with the marker of the "short loop" recycling endosomes, Rab4, while showing very minor co-localization with the "long loop" recycling marker, Rab11. Our results provide the first data on the agonist-induced trafficking of native GPR17 in oligodendroglial cells and may have implications for both physiological and pathological myelination.

Extrinsic purinergic regulation of neural stem/progenitor cells: implications for CNS development and repair

There has been tremendous progress in understanding neural stem cell (NSC) biology, with genetic and cell biological methods identifying sequential gene expression and molecular interactions guiding NSC specification into distinct neuronal and glial populations during development. Data has emerged on the possible exploitation of NSC-based strategies to repair adult diseased brain. However, despite increased information on lineage specific transcription factors, cell-cycle regulators and epigenetic factors involved in the fate and plasticity of NSCs, understanding of extracellular cues driving the behavior of embryonic and adult NSCs is still very limited. Knowledge of factors regulating brain development is crucial in understanding the pathogenetic mechanisms of brain dysfunction. Since injury-activated repair mechanisms in adult brain often recapitulate ontogenetic events, the identification of these players will also reveal novel regenerative strategies. Here, we highlight the purinergic system as a key emerging player in the endogenous control of NSCs. Purinergic signalling molecules (ATP, UTP and adenosine) act with growth factors in regulating the synchronized proliferation, migration, differentiation and death of NSCs during brain and spinal cord development. At early stages of development, transient and time-specific release of ATP is critical for initiating eye formation; once anatomical CNS structures are defined, purinergic molecules participate in calcium-dependent neuron-glia communication controlling NSC behaviour. When development is complete, some purinergic mechanisms are silenced, but can be re-activated in adult brain after injury, suggesting a role in regeneration and self-repair. Targeting the purinergic system to develop new strategies for neurodevelopmental disorders and neurodegenerative diseases will be also discussed.

Genetics of hypersensitivity to aspirin and nonsteroidal anti-inflammatory drugs

Various hypersensitivity reactions have been reported with aspirin and nonsteroidal anti-inflammatory drugs. Hypersensitivity can occur regardless of a chemical drug structure or its therapeutic potency. Allergic conditions include aspirin-exacerbated respiratory disease (AERD or aspirin-induced asthma), aspirin-induced urticaria/angioedema (AIU), and anaphylaxis. Several genetic studies on aspirin hypersensitivity have been performed to discover the genetic predisposition to aspirin hypersensitivity and to gain insight into the phenotypic diversity. This article updates data on the genetic mechanisms that govern AERD and AIU and summarizes recent findings on the molecular genetic mechanism of aspirin hypersensitivity.

G protein-coupled receptor deorphanizations

G protein-coupled receptors (GPCRs) are major regulators of intercellular interactions. They initiate these actions by being activated by a wide variety of natural ligands. Historically, ligands were discovered first, but the advent of molecular biology reversed this trend. Most GPCRs are identified on the basis of their DNA sequences and thus are initially unmatched to known natural ligands. They are termed orphan GPCRs. Discovering their ligands-i.e., "deorphanizing" the GPCRs-gave birth to the field of reverse pharmacology. This review discusses the present status of GPCR deorphanization, presents a few examples of successes and surprises, and highlights difficulties encountered in these efforts.

Periventricular leukomalacia long-term prognosis may be improved by treatment with UDP-glucose, GDNF, and memantine in neonatal rats

The therapeutic effects of UDP-glucose (UDPG), an endogenous agonist of GPR17 that may promote the self-repair of white matter, glial cell line-derived neurotrophic factor (GDNF), a neurotrophic factor correlated with the growth and survival of nerve cells, and memantine, an antagonist of NMDA receptors, were evaluated for functional improvement of neonatal rats with experimental periventricular leukomalacia (PVL). Five day-old neonatal rat pups were subjected to an ischemia-induced model of PVL. The pups were then randomly divided into sham, PVL, PVL plus UDPG, PVL plus GDNF, and PVL plus memantine groups. All pups were weighed and the age at first eye opening recorded. Pathological changes and myelin sheath formation in the white matter were assessed under both light and electron microscopy on day 7 and 21 after induction of PVL. Values of escape latency (EL) and swimming distance (SD) in Morris water maze test, and the modified inclined plane scores in Rivlin inclined plane test were recorded for rats on day 26. Pups in the PVL group were found to be significantly lower in weight (p<0.05), delayed in age at first eye opening (p<0.01), and impaired in their inclined plane (p<0.01) and Morris water maze (p<0.01) performance compared with those in the sham, UDPG, GDNF and memantine groups. Histopathological grading of the white matter classified all pups in the PVL group with significantly more severe injury (p<0.01), and the number and thickness of their myelin sheaths were significantly less (p<0.01), compared to the UDPG, GDNF, memantine, or sham groups. These results indicate that treatment with UDPG, GDNF, and memantine may significantly improve long-term prognosis in neonatal rats with cerebral white matter injury, characteristic of PVL.

Intracerebroventricular injection of HAMI 3379, a selective cysteinyl leukotriene receptor 2 antagonist, protects against acute brain injury after focal cerebral ischemia in rats

Cysteinyl leukotrienes (CysLTs) induce inflammatory responses by activating their receptors, CysLT(1)R and CysLT(2)R. We recently reported that CysLT(2)R is involved in neuronal injury, astrocytosis and microgliosis after focal cerebral ischemia in rats. Here, we determined whether HAMI 3379, a selective CysLT(2)R antagonist, protects against acute brain injury after focal cerebral ischemia in rats. We induced transient focal cerebral ischemia by 30 min of middle cerebral artery occlusion (MCAO), followed by 24h of reperfusion. HAMI 3379 (1, 10 or 100 ng) was injected intracerebroventricularly (i.c.v.) 30 min before MCAO, and the CysLT(1)R antagonist pranlukast (0.1mg/kg, i.p.) was used as a positive control. HAMI 3379 at 10 and 100 ng (but not at 1 ng) attenuated the neurological deficits, and reduced infarct volume, brain edema, IgG exudation, neuronal degeneration and neuronal loss. This protective effect was similar to that of pranlukast. Thus, HAMI 3339 at 10-100 ng i.c.v. is neuroprotective against acute brain injury after focal cerebral ischemia in rats. These findings suggest therapeutic potential for CysLT(2)R antagonists in the treatment of ischemic stroke.

Purinergic trophic signalling in glial cells: functional effects and modulation of cell proliferation, differentiation, and death

In the last decades, the discovery that glial cells do not only fill in the empty space among neurons or furnish them with trophic support but are rather essential participants to the various activities of the central and peripheral nervous system has fostered the search for the signalling pathways controlling their functions. Since the early 1990s, purines were foreseen as some of the most promising candidate molecules. Originally just a hypothesis, this has become a certainty as experimental evidence accumulated over years, as demonstrated by the exponentially growing number of articles related to the role of extracellular nucleotides and nucleosides in controlling glial cell functions. Indeed, as new functions for already known glial cells (for example, the ability of parenchymal astrocytes to behave as stem cells) or new subtypes of glial cells (for example, NG2(+) cells, also called polydendrocytes) are discovered also, new actions and new targets for the purinergic system are identified. Thus, glial purinergic receptors have emerged as new possible pharmacological targets for various acute and chronic pathologies, such as stroke, traumatic brain and spinal cord injury, demyelinating diseases, trigeminal pain and migraine, and retinopathies. In this article, we will summarize the most important and promising actions mediated by extracellular purines and pyrimidines in controlling the functions, survival, and differentiation of the various "classical" types of glial cells (i.e., astrocytes, oligodendrocytes, microglial cells, Müller cells, satellite glial cells, and enteric glial cells) but also of some rather new members of the family (e.g., polydendrocytes) and of other cells somehow related to glial cells (e.g., pericytes and spinal cord ependymal cells).

Cellular function and molecular structure of ecto-nucleotidases

Ecto-nucleotidases play a pivotal role in purinergic signal transmission. They hydrolyze extracellular nucleotides and thus can control their availability at purinergic P2 receptors. They generate extracellular nucleosides for cellular reuptake and salvage via nucleoside transporters of the plasma membrane. The extracellular adenosine formed acts as an agonist of purinergic P1 receptors. They also can produce and hydrolyze extracellular inorganic pyrophosphate that is of major relevance in the control of bone mineralization. This review discusses and compares four major groups of ecto-nucleotidases: the ecto-nucleoside triphosphate diphosphohydrolases, ecto-5'-nucleotidase, ecto-nucleotide pyrophosphatase/phosphodiesterases, and alkaline phosphatases. Only recently and based on crystal structures, detailed information regarding the spatial structures and catalytic mechanisms has become available for members of these four ecto-nucleotidase families. This permits detailed predictions of their catalytic mechanisms and a comparison between the individual enzyme groups. The review focuses on the principal biochemical, cell biological, catalytic, and structural properties of the enzymes and provides brief reference to tissue distribution, and physiological and pathophysiological functions.

FoxO1 target Gpr17 activates AgRP neurons to regulate food intake

Hypothalamic neurons expressing Agouti-related peptide (AgRP) are critical for initiating food intake, but druggable biochemical pathways that control this response remain elusive. Thus, genetic ablation of insulin or leptin signaling in AgRP neurons is predicted to reduce satiety but fails to do so. FoxO1 is a shared mediator of both pathways, and its inhibition is required to induce satiety. Accordingly, FoxO1 ablation in AgRP neurons of mice results in reduced food intake, leanness, improved glucose homeostasis, and increased sensitivity to insulin and leptin. Expression profiling of flow-sorted FoxO1-deficient AgRP neurons identifies G-protein-coupled receptor Gpr17 as a FoxO1 target whose expression is regulated by nutritional status. Intracerebroventricular injection of Gpr17 agonists induces food intake, whereas Gpr17 antagonist cangrelor curtails it. These effects are absent in Agrp-Foxo1 knockouts, suggesting that pharmacological modulation of this pathway has therapeutic potential to treat obesity.

Trichinella spiralis secreted enzymes regulate nucleotide-induced mast cell activation and release of mouse mast cell protease 1

Extracellular nucleotides are important triggers of innate immunity, acting on a wide variety of cells via signaling through purinergic receptors. Mucosal mast cells contribute to expulsion of a number of gastrointestinal nematode parasites, and mouse mast cell protease 1 has been shown to have a critical role in clearance of Trichinella spiralis from the intestinal tract. We show here that adenosine, ADP, ATP, UDP, and UTP all stimulate calcium mobilization in bone marrow-derived mast cells with a mucosal phenotype. Secreted proteins from T. spiralis infective larvae inhibit nucleotide-induced mast cell activation, and that induced by ADP and UDP is specifically blocked by parasite secretory 5'-nucleotidase. Release of mouse mast cell protease 1 is stimulated by ADP and ATP. Both parasite secreted products and the 5'-nucleotidase inhibit ADP-induced release of mast cell protease, whereas that stimulated by ATP is partially inhibited by secreted products alone. This indicates that the 5'-nucleotidase contributes to but is not solely responsible for inhibition of nucleotide-mediated effects on mast cell function. Secretion of nucleotide-metabolizing enzymes by parasitic nematodes most likely evolved as a strategy for suppression of innate immune responses and is discussed in this context.

Candidate pathways for promoting differentiation or quiescence of oligodendrocyte progenitor-like cells in glioma

Platelet-derived growth factor receptor alpha-positive oligodendrocyte progenitor cells (OPC) located within the mature central nervous system may remain quiescent, proliferate, or differentiate into oligodendrocytes. Human glioblastoma multiforme tumors often contain rapidly proliferating oligodendrocyte lineage transcription factor 2 (Olig2)-positive cells that resemble OPCs. In this study, we sought to identify candidate pathways that promote OPC differentiation or quiescence rather than proliferation. Gene expression profiling conducted in both normal murine OPCs and highly proliferative Olig2-positive glioma cells identified all the transcripts associated with the highly proliferative state of these cells and showed that among the various cell types found within the brain, Olig2-positive tumor cells are most similar to OPCs. We then subtracted OPC transcripts found in tumor samples from those found in normal brain samples and identified 28 OPC transcripts as candidates for promoting differentiation or quiescence. Systematic analysis of human glioma data revealed that these genes have similar expression profiles in human tumors and were significantly enriched in genomic deletions, suggesting an antiproliferative role. Treatment of primary murine glioblastoma cells with agonists of one candidate gene, Gpr17, resulted in a decreased number of neurospheres. Together, our findings show that comparison of the molecular phenotype of progenitor cells in tumors to the equivalent cells in the normal brain represents a novel approach for the identification of targeted therapies.

Activity of the leukotriene pathway in Barrett's metaplasia and oesophageal adenocarcinoma

OBJECTIVE

Leukotriene (LT) B(4) is a lipid inflammatory mediator implicated in tumorigenesis in animal models of Barrett's oesophagitis, but little is known about the cysteinyl-leukotrienes (LTC(4), LTD(4), LTE(4)), which have distinct inflammatory and tumorigenic actions in other tissues. We recently showed that the terminal enzymes for the synthesis of both LT families are highly expressed in human oesophageal adenocarcinoma (OA) tissues. This study therefore examined the capacity of Barrett's metaplasia (BM) and OA tissues to synthesise LTs in vitro.

SUBJECTS AND METHODS

Oesophageal biopsies from patients with BM (n = 14), high-grade dysplasia (n = 2), OA (n = 11), and squamous control tissues (n = 11) were cultured with calcium ionophore A32187 (2 μM) for 60 min. LTB(4) and cysteinyl-leukotrienes were extracted and measured by specific enzyme immunoassays.

RESULTS

Levels of LTB(4) and cysteinyl-leukotrienes were 8.6-fold (P < 0.01) and 2.4-fold (P < 0.02) higher, respectively, in OA tissues than in squamous control tissues, but levels in BM tissues (n = 14) were not altered. Production of the two LT families correlated across all tissue types (r = 0.62, p < 0.00005).

CONCLUSIONS

Increased synthesis of LTB(4) and cysteinyl-leukotrienes has not previously been shown in human OA tissue and our results may indicate a role of these lipids in Barrett's disease progression.