Purification and characterization of diacylglycerol lipase from human platelets

Roles of lipid mediators in early pregnancy events

Background

Early pregnancy events, including embryo implantation, are critical for maintaining a healthy pregnancy and facilitating childbirth. Despite numerous signaling pathways implicated in establishing early pregnancy, a comprehensive understanding of implantation remains elusive.

Methods

This paper provides a comprehensive review of the current research on lipids in the context of early pregnancy, with a particular focus on feto-maternal communications.

Main Findings

Embryo implantation entails direct interaction between uterine tissues and embryos. Introducing embryos triggers significant changes in uterine epithelial morphology and stromal differentiation, facilitating embryo implantation through communication with uterine tissue. Studies employing genetic models and chemical compounds targeting enzymes and receptors have elucidated the crucial roles of lipid mediators-prostaglandins, lysophosphatidic acid, sphingosine-1-phosphate, and cannabinoids-in early pregnancy events.

Conclusion

Given the high conservation of lipid synthases and receptors across species, lipid mediators likely play pivotal roles in rodents and humans. Further investigations into lipids hold promise for developing novel diagnostic and therapeutic approaches for infertility in humans.

Inhibition of Monoacylglycerol Lipase Decreases Angiogenic Features of Endothelial Cells via Release of Tissue Inhibitor of Metalloproteinase-1 from Lung Cancer Cells

Despite the well-described anticarcinogenic effects of endocannabinoids, the influence of the endocannabinoid system on tumor angiogenesis is still debated. In the present study, conditioned medium (CM) from A549 and H358 lung cancer cells treated with ascending concentrations of the monoacylglycerol lipase (MAGL) inhibitor JZL184 and 2-arachidonoylglycerol (2-AG), a prominent MAGL substrate, caused a concentration-dependent reduction in human umbilical vein endothelial cell (HUVEC) migration and tube formation compared with CM from vehicle-treated cancer cells. Comparative experiments with MAGL inhibitors JW651 and MJN110 showed the same results. On the other hand, the angiogenic properties of HUVECs were not significantly altered by direct stimulation with JZL184 or 2-AG or by exposure to CM of JZL184- or 2-AG-treated non-cancerous bronchial epithelial cells (BEAS-2B). Inhibition of HUVEC migration and tube formation by CM of JZL184- and 2-AG-treated A549 cells was abolished in the presence of the CB1 antagonist AM-251. Increased release of tissue inhibitor of metalloproteinase-1 (TIMP-1) from JZL184- or 2-AG-stimulated A549 or H358 cells was shown to exert an antiangiogenic effect on HUVECs, as confirmed by siRNA experiments. In addition, JZL184 caused a dose-dependent regression of A549 tumor xenografts in athymic nude mice, which was associated with a decreased number of CD31-positive cells and upregulation of TIMP-1-positive cells in xenograft tissue. In conclusion, our data suggest that elevation of 2-AG by MAGL inhibition leads to increased release of TIMP-1 from lung cancer cells, which mediates an antiangiogenic effect on endothelial cells.

The main Aflatoxin B1 degrading enzyme in Pseudomonas putida is thermostable lipase

Aflatoxin B1 is a carcinogenic and mutagenic mycotoxin mainly produced by Aspergillus flavus and A. parasiticus, and prevalent in food and feed. Microbial degradation is a promising strategy which can be performed in mild and environmental friendly condition. This work is a step towards identifying the enzyme responsible for biodegradation of AFB1 by P. putida. Experiments were performed with P. putida lysate and compared with commercial lipase to see the degradation efficiency and the temperature stability. The cell free lysate of P. putida efficiently degraded AFB1 in a range of temperature from 20 to 90 °C. The lysate is thermostable and could retain its activity on pre-incubation up to 90 °C. Highest rate of degradation was observed at 70 °C. These observations show that the P. putida lysate is not only stable at higher temperatures but its enzymatic activity increases after incubation. Similarly, the commercial lipase degraded AFB1 efficiently. However, both, the P. putida lysate and lipase ceased degradation in presence of a lipase inhibitor, HgCl₂. The Hill function accurately predicted enzyme activity at various times and temperatures. Like lipase, the lysate also hydrolyses the p-nitrophenyl palmitate to p-nitrophenol. Kinetic parameters such as V_max, K_m and n values are good measures to characterize the lysate response with respect to changing paranitro phenyl palmitate levels. The substrate specificity test of lipase showed linear correlation between the absorbance at 410 nm vs amount of product paranitro phenol. The value of Km, Vmax and n are 0.62 mM, 355.7 μmol min⁻¹ and 1.29, respectively. The lipase gene presence in P. putida was confirmed using PCR technique. These observations indicate that the main enzyme responsible for AFB1 degradation by P. putida is lipase. Thus, lipase as a multifunctional biocatalyst provides a promising future for a variety of industries and may also help to ensure the food safety by degrading the mycotoxins.

Characterization of L-amino Acid Oxidase Derived from Crotalus adamanteus Venom: Procoagulant and Anticoagulant Activities

Snake venom enzymes of the L-amino acid oxidase (LAAO) class are responsible for tissue hemorrhage, edema, and derangement of platelet function. However, what role, if any, these flavoenzymes play in altering plasmatic coagulation have not been well defined. Using coagulation kinetomic analyses (thrombelastograph-based), it was determined that the LAAO derived from Crotalus adamanteus venom displayed a procoagulant activity associated with weak clot strength (no factor XIII activation) similar to thrombin-like enzymes. The procoagulant activity was not modified in the presence of reduced glutathione, demonstrating that the procoagulant activity was likely due to deamination, and not hydrogen peroxide generation by the LAAO. Further, unlike the raw venom of the same species, the purified LAAO was not inhibited by carbon monoxide releasing molecule-2 (CORM-2). Lastly, exposure of the enzyme to phenylmethylsulfonyl fluoride (PMSF) resulted in the LAAO expressing anticoagulant activity, preventing contact activation generated thrombin from forming a clot. In sum, this investigation for the first time characterized the LAAO of a snake venom as both a fibrinogen polymerizing and an anticoagulant enzyme acting via oxidative deamination and not proteolysis as is the case with thrombin-like enzymes (e.g., serine proteases). Using this thrombelastographic approach, future investigation of purified enzymes can define their biochemical nature.

Cytosolic Phospholipase A2α Promotes Pulmonary Inflammation and Systemic Disease during Streptococcus pneumoniae Infection

Pulmonary infection by Streptococcus pneumoniae is characterized by a robust alveolar infiltration of neutrophils (polymorphonuclear cells [PMNs]) that can promote systemic spread of the infection if not resolved. We previously showed that 12-lipoxygenase (12-LOX), which is required to generate the PMN chemoattractant hepoxilin A₃ (HXA₃) from arachidonic acid (AA), promotes acute pulmonary inflammation and systemic infection after lung challenge with S. pneumoniae As phospholipase A₂ (PLA₂) promotes the release of AA, we investigated the role of PLA₂ in local and systemic disease during S. pneumoniae infection. The group IVA cytosolic isoform of PLA₂ (cPLA₂α) was activated upon S. pneumoniae infection of cultured lung epithelial cells and was critical for AA release from membrane phospholipids. Pharmacological inhibition of this enzyme blocked S. pneumoniae-induced PMN transepithelial migration in vitro Genetic ablation of the cPLA₂ isoform cPLA₂α dramatically reduced lung inflammation in mice upon high-dose pulmonary challenge with S. pneumoniae The cPLA₂α-deficient mice also suffered no bacteremia and survived a pulmonary challenge that was lethal to wild-type mice. Our data suggest that cPLA₂α plays a crucial role in eliciting pulmonary inflammation during pneumococcal infection and is required for lethal systemic infection following S. pneumoniae lung challenge.

Synthetic cannabinoids and potential reproductive consequences

Increases in emergency room visits due to abuse of designer drugs, popularly known by the street names "K2" and "Spice," are a cause for social, judicial, and clinical concerns. The psychoactive components in these herbal drugs mainly consist of different synthetic cannabinoids, and users of these street drugs are primarily within the age group of 12 to 20years old. The abusive use of synthetic cannabinoids results in anxiety, nausea, vomiting, tachycardia, elevated blood pressure, tremors, seizures, hallucinations, and paranoid behavior, but the effects of maternal use of synthetic cannabinoids during pregnancy are ambiguous due to limited studies in humans and a relative short history of the drugs. In this review, we discuss the known and potential adverse effects of synthetic cannabinoids on human pregnancy using knowledge gathered from studies in mice and limited studies in humans. In mice, multiple sites and stages of pregnancy are potential targets of synthetic cannabinoids, including preimplantation embryo development, oviductal embryo transport, implantation, placentation, and parturition. It is anticipated that maternal use of synthetic cannabinoids would result in severely compromised female fertility and pregnancy outcome.

Class specific peptide inhibitors for secretory phospholipases A2

Phospholipases A2 (PLA2) catalyze the hydrolytic cleavage of free fatty acids from the sn-2 OH-moiety of glycerophospholipids. These enzymes have a number of functions, from digestion to signaling and toxicity of several venoms. They have also been implicated in inflammation and are connected to diverse diseases, such as cancer, ischemia, atherosclerosis, and schizophrenia. Accordingly, there is a keen interest to develop selective inhibitors for therapeutic use. We recently proposed a novel mechanism for the control of PLA2 activity with highly active protofibrils of PLA2 existing transiently before conversion to inactive amyloid fibrils [19]. In keeping with the above mechanism several algorithms identified (85)KMYFNLI(91) and (17)AALSYGFYG(25) in bee venom (bv) and human lacrimal fluid (Lf) PLA2, respectively, as a regions potentially forming amyloid type aggregates. Interestingly, in keeping with the proposed role of these sequences in the control of the activity of these enzymes, preincubation of 2nM bvPLA2 with (85)KMYFNLI(91) caused complete inhibition of PLA2 activity while the scrambled control peptide YNFLIMK had no effect. Approximately 36% attenuation of the hydrolytic activity of LfPLA2 present in human lacrimal fluid was observed in the presence of 80nM (17)AALSYGFYG(25).

Role of Phospholipids in Endocytosis, Phagocytosis, and Macropinocytosis

Endocytosis, phagocytosis, and macropinocytosis are fundamental processes that enable cells to sample their environment, eliminate pathogens and apoptotic bodies, and regulate the expression of surface components. While a great deal of effort has been devoted over many years to understanding the proteins involved in these processes, the important contribution of phospholipids has only recently been appreciated. This review is an attempt to collate and analyze the rapidly emerging evidence documenting the role of phospholipids in clathrin-mediated endocytosis, phagocytosis, and macropinocytosis. A primer on phospholipid biosynthesis, catabolism, subcellular distribution, and transport is presented initially, for reference, together with general considerations of the effects of phospholipids on membrane curvature and charge. This is followed by a detailed analysis of the critical functions of phospholipids in the internalization processes and in the maturation of the resulting vesicles and vacuoles as they progress along the endo-lysosomal pathway.

The diacylglycerol lipases: structure, regulation and roles in and beyond endocannabinoid signalling

The diacylglycerol lipases (DAGLs) hydrolyse diacylglycerol to generate 2-arachidonoylglycerol (2-AG), the most abundant ligand for the CB(1) and CB(2) cannabinoid receptors in the body. DAGL-dependent endocannabinoid signalling regulates axonal growth and guidance during development, and is required for the generation and migration of new neurons in the adult brain. At developed synapses, 2-AG released from postsynaptic terminals acts back on presynaptic CB(1) receptors to inhibit the secretion of both excitatory and inhibitory neurotransmitters, with this DAGL-dependent synaptic plasticity operating throughout the nervous system. Importantly, the DAGLs have functions that do not involve cannabinoid receptors. For example, 2-AG is the precursor of arachidonic acid in a pathway that maintains the level of this essential lipid in the brain and other organs. This pathway also drives the cyclooxygenase-dependent generation of inflammatory prostaglandins in the brain, which has recently been implicated in the degeneration of dopaminergic neurons in Parkinson's disease. Remarkably, we still know very little about the mechanisms that regulate DAGL activity-however, key insights can be gleaned by homology modelling against other α/β hydrolases and from a detailed examination of published proteomic studies and other databases. These identify a regulatory loop with a highly conserved signature motif, as well as phosphorylation and palmitoylation as post-translational mechanisms likely to regulate function.

Assay and inhibition of diacylglycerol lipase activity

A series of N-formyl-α-amino acid esters of β-lactone derivatives structurally related to tetrahydrolipstatin (THL) and O-3841 were synthesized that inhibit human and murine diacylglycerol lipase (DAGL) activities. New ether lipid reporter compounds were developed for an in vitro assay to efficiently screen inhibitors of 1,2-diacyl-sn-glycerol hydrolysis and related lipase activities using fluorescence resonance energy transfer (FRET). A standardized thin layer chromatography (TLC) radioassay of diacylglycerol lipase activity utilizing the labeled endogenous substrate [1″-(14)C]1-stearoyl-2-arachidonoyl-sn-glycerol with phosphorimaging detection was used to quantify inhibition by following formation of the initial product [1″-(14)C]2-arachidonoylglycerol and further hydrolysis under the assay conditions to [1-(14)C]arachidonic acid.

Endocannabinoid signaling in female reproduction

Marijuana is a preparation of the flower, as well as the leaves and seeds, of the plant Cannabis sativa. Marijuana has been used for medicinal and recreational purposes for thousands of years due to its psychoactive effects including euphoria, sedation, and analgesia. Although it has been suspected for decades that marijuana has adverse effects on female fertility, the underlying molecular mechanism was not clear. The discovery of cannabinoid receptors and endocannabinoids has advanced studies if cannabinoid signaling. Since then, numerous studies have been published on cannabinoid signaling in female reproductive events, including preimplantation embryo development, oviductal embryo transport, embryo implantation, placentation, and parturition. This review focuses on various aspects of endocannabinoid signaling in female fertility.

Biosynthesis and degradation of the endocannabinoid 2-arachidonoylglycerol

2-Arachidonoylglycerol (2-AG) is a monoacylglycerol (MAG) molecule containing an esterified arachidonic acid chain at sn-2 position of the glycerol backbone. Together with structurally similar N-arachidonoylethanolamine (anandamide), 2-AG has been extensively studied as an endogenous ligand of cannabinoid receptors (an endocannabinoid) in brain and other mammalian tissues. Accumulating evidence demonstrates that the endocannabinoid system, including the central-type cannabinoid receptor CB1 and 2-AG, is responsible for synaptic retrograde signaling in the central nervous system. As 2-AG is rapidly formed from membrane phospholipids on cellular stimuli and degraded to arachidonic acid and glycerol, the enzymes catalyzing its biosynthesis and degradation are believed to play crucial roles in the regulation of its tissue levels. The major biosynthetic pathway appears to consist of sequential hydrolyses of inositol phospholipids via diacylglycerol (DAG) by β-type phospholipase C and DAG lipase, while MAG lipase is a principal enzyme in the degradation. In this short review, we will briefly outline rapid advances in enzymological research on the biosynthetic and degradative pathways of 2-AG.

Role of platelets in neuroinflammation: a wide-angle perspective

OBJECTIVES

This review summarizes recent developments in platelet biology relevant to neuroinflammatory disorders. Multiple sclerosis (MS) is taken as the "Poster Child" of these disorders but the implications are wide. The role of platelets in inflammation is well appreciated in the cardiovascular and cancer research communities but appears to be relatively neglected in neurological research.

ORGANIZATION

After a brief introduction to platelets, topics covered include the matrix metalloproteinases, platelet chemokines, cytokines and growth factors, the recent finding of platelet PPAR receptors and Toll-like receptors, complement, bioactive lipids, and other agents/functions likely to be relevant in neuroinflammatory diseases. Each section cites literature linking the topic to areas of active research in MS or other disorders, including especially Alzheimer's disease.

CONCLUSION

The final section summarizes evidence of platelet involvement in MS. The general conclusion is that platelets may be key players in MS and related disorders, and warrant more attention in neurological research.

Cannabinoid/Endocannabinoid signaling impact on early pregnancy events

It has been known for decades that marijuana and its major psychoactive component Δ⁹-tetrahydrocannabinol (THC) alter both male and female reproductive functions in humans and laboratory animals. The discovery of cannabinoid-like molecules (endocannabinoids), anandamide (AEA) and 2-arachidonylglycerol (2AG), as well as G-protein-coupled cannabinoid/endocannabinoid receptors CB₁ and CB₂, created an opportunity to study the adverse and beneficial effects of cannabinoids/endocannabinoids on fertility using molecular, physiological and genetic approaches. In fact, studies to explore the significance of cannabinoid/endocannabinoid signaling in reproduction have revealed some intriguing physiological roles in early pregnant events. This review summarizes some aspects of these signaling molecules in preimplantation and implantation biology utilizing genetically engineered mouse models.

Aspects of endocannabinoid signaling in periimplantation biology

Physiological roles of endocannabinoids, a group of endogenously produced cannabinoid-like lipid molecules that activate G protein-coupled cannabinoid receptors, are being increasingly appreciated in female reproduction. Adverse effects of cannabinoids on female fertility have been suspected for decades; however, underlying molecular and genetic bases by which they exert these effects were not clearly understood. The discovery of cannabinoid receptors (CB1 and CB2), endocannabinoid ligands (anandamide and 2-acylglycerol) as well as their key synthetic and hydrolytic pathways has helped to better understand the roles of cannabinoid/endocannabinoid signaling in preimplantation embryo development, oviductal embryo transport, embryo implantation and postimplantation embryonic growth. This review focuses on various aspects of the endocannabinoid system in female fertility based on studies that used knockout mouse models. The information generated from studies in mice is likely to shed deeper insight into fertility regulation in women.

Role of calcium-independent phospholipase A2 in cortex striatum thalamus cortex circuitry-enzyme inhibition causes vacuous chewing movements in rats

RATIONALE

High levels of calcium independent phospholipase A2 (iPLA2) are present in certain regions of the brain, including the cerebral cortex, striatum, and cerebellum (Ong et al. 2005).

OBJECTIVES

The present study was carried out to elucidate a possible role of the enzyme in the motor system.

METHODS

The selective iPLA2 inhibitor bromoenol lactone (BEL), the nonselective PLA2 inhibitor methyl arachidonyl fluorophosphonate (MAFP), and an antisense oligonucleotide were used to interfere with iPLA2 activity in various components of the motor system. Control animals received injections of carrier (phosphate buffered saline, PBS) at the same locations. The number of vacuous chewing movements (VCM) was counted from 1 to 14 days after injection.

RESULTS

Rats that received BEL and high-dose MAFP injections in the striatum, thalamus, and motor cortex, but not the cerebellum, showed significant increase in VCM, compared to those injected with PBS at these locations. BEL-induced VCM were blocked by intramuscular injections of the anticholinergic drug, benztropine. Increased VCM was also observed after intrastriatal injection of antisense oligonucleotide to iPLA2. The latter caused a decrease in striatal iPLA2 levels, confirming a role of decreased enzyme activity in the appearance of VCM.

CONCLUSIONS

These results suggest an important role for iPLA2 in the cortex-striatum-thalamus-cortex circuitry. It is postulated that VCM induced by iPLA2 inhibition may be a model of human parkinsonian tremor.

Regulation of Drosophila TRPC channels by protein and lipid interactions

The Drosophila TRPC channels TRP and TRPL are the founding members of the TRP superfamily of ion channels, proteins likely to be important components of calcium influx pathways. The activation of these channels in the context of fly phototransduction is one of the few in vivo models for TRPC channel activation and has served as a paradigm for understanding TRPC function. TRP and TRPL are activated by G-protein coupled PI(4,5)P(2) hydrolysis through a mechanism in which IP(3) receptor mediated calcium release seems dispensable. Recent analysis has provided compelling evidence that the accurate turnover of PI(4,5)P(2) generated lipid messengers in essential for regulating TRP and TRPL activity. TRP channels also appear to exist in the context of a macromolecular complex containing key components involved in activation such as phospholipase Cbeta and protein kinase C. This complex may be important for activation. The role of these protein and lipid elements in regulating TRP and TRPL activity is discussed in this review.

Serotonin 5-HT2Areceptor activation induces 2-arachidonoylglycerol release through a phospholipase c-dependent mechanism

To date, several studies have demonstrated that phospholipase C-coupled receptors stimulate the production of endocannabinoids, particularly 2-arachidonoylglycerol. There is now evidence that endocannabinoids are involved in phospholipase C-coupled serotonin 5-HT(2A) receptor-mediated behavioral effects in both rats and mice. The main objective of this study was to determine whether activation of the 5-HT(2A) receptor leads to the production and release of the endocannabinoid 2-arachidonoylglycerol. NIH3T3 cells stably expressing the rat 5-HT(2A) receptor were first incubated with [(3)H]-arachidonic acid for 24 h. Following stimulation with 10 mum serotonin, lipids were extracted from the assay medium, separated by thin layer chromatography, and analyzed by liquid scintillation counting. Our results indicate that 5-HT(2A) receptor activation stimulates the formation and release of 2-arachidonoylglycerol. The 5-HT(2A) receptor-dependent release of 2-arachidonoylglycerol was partially dependent on phosphatidylinositol-specific phospholipase C activation. Diacylglycerol produced downstream of 5-HT(2A) receptor-mediated phospholipase D or phosphatidylcholine-specific phospholipase C activation did not appear to contribute to 2-arachidonoylglycerol formation in NIH3T3-5HT(2A) cells. In conclusion, our results support a functional model where neuromodulatory neurotransmitters such as serotonin may act as regulators of endocannabinoid tone at excitatory synapses through the activation of phospholipase C-coupled G-protein coupled receptors.

Depolarization-induced retrograde synaptic inhibition in the mouse cerebellar cortex is mediated by 2-arachidonoylglycerol

Endocannabinoids acting on CB(1) cannabinoid receptors are involved in short- and long-term depression of synaptic transmission. The aim of the present study was to determine which endocannabinoid, anandamide or 2-arachidonoylglycerol (2-AG), is involved in depolarization-induced suppression of inhibition (DSI) in the cerebellar cortex, which is the most widely studied form of short-term depression. Depolarization of Purkinje cells in the mouse cerebellum led to an increase in intracellular calcium concentration and to suppression of the inhibitory input to these neurons (i.e. DSI occurred). Orlistat and RHC80267, two blockers of sn-1-diacylglycerol lipase, the enzyme catalysing 2-AG formation, abolished DSI by acting downstream of calcium influx. In contrast, DSI occurred also in the presence of a phospholipase C inhibitor. Intact operation of the calcium-dependent messengers calmodulin and Ca(2+)-calmodulin-dependent protein kinase II were necessary for DSI. DSI was potentiated by an inhibitor of the main 2-AG-degrading enzyme, monoacylglycerol lipase. Interference with the anandamide metabolizing enzyme, fatty acid amide hydrolase, did not modify DSI. Thus, three kinds of observations identified 2-AG as the endocannabinoid involved in DSI in the mouse cerebellum: DSI was abolished by diacylglycerol lipase inhibitors; DSI was potentiated by a monoglyceride lipase inhibitor; and DSI was not changed by an inhibitor of fatty acid amide hydrolase. Further experiments indicated that 2-AG is the endocannabinoid mediating short-term retrograde signalling also at other synapses: orlistat abolished DSI in the rat cerebellum, DSI in the mouse substantia nigra pars reticulata and depolarization-induced suppression of excitation in the mouse cerebellum.

Calcium-independent phospholipase A2 and apoptosis

Apoptosis or programmed cell death is associated with changes in glycerophospholipid metabolism. Cells undergoing apoptosis generally release free fatty acids including arachidonic acid, which parallels the reduction in cell viability. The involvement of cytosolic group IVA phospholipase A(2)alpha (cPLA(2)alpha) in apoptosis has been the subject of numerous studies but a clear picture of the role(s) played by this enzyme is yet to emerge. More recently, the importance of lipid products generated by the action of a second phospholipase A(2), the group VIA calcium-independent phospholipase A(2) (iPLA(2)-VIA) in apoptosis has begun to be unveiled. Current evidence suggests that iPLA(2)-VIA-derived lysophosphatidylcholine may play a prominent role in mediating the chemoattractant and recognition/engulfment signals that accompany the process of apoptotic cell death, and gives possibility to the efficient clearance of dying cells by circulating phagocytes. Other lines of evidence suggest that perturbations in the control of free arachidonic acid levels within the cells, a process that may implicate iPLA(2)-VIA as well, may provide important cellular signals for the onset of apoptosis.

Nuclear Transportation of Diacylglycerol Kinase γ and Its Possible Function in the Nucleus

Diacylglycerol kinases (DGKs) convert diacylglycerol (DG) to phosphatidic acid, and both lipids are known to play important roles in lipid signal transduction. Thereby, DGKs are considered to be a one of the key players in lipid signaling, but its physiological function remains to be solved. In an effort to investigate one of nine subtypes, we found that DGKgamma came to be localized in the nucleus with time in all cell lines tested while seen only in the cytoplasm at the early stage of culture, indicating that DGKgamma is transported from the cytoplasm to the nucleus. The nuclear transportation of DGKgamma didn't necessarily need DGK activity, but its C1 domain was indispensable, suggesting that the C1 domain of DGKgamma acts as a nuclear transport signal. Furthermore, to address the function of DGKgamma in the nucleus, we produced stable cell lines of wild-type DGKgamma and mutants, including kinase negative, and investigated their cell size, growth rate, and cell cycle. The cells expressing the kinase-negative mutant of DGKgamma were larger in size and showed slower growth rate, and the S phase of the cells was extended. These findings implicate that nuclear DGKgamma regulates cell cycle.

The diacylglycerol lipase inhibitor RHC-80267 potentiates the relaxation to acetylcholine in rat mesenteric artery by anti-cholinesterase action

The diacylglycerol lipase inhibitor 1,6-bis(cyclohexyloximinocarbonylamino) hexane (RHC-80267) was tested for its effect on acetylcholine-evoked relaxation in rat mesenteric artery. In artery contracted with either noradrenaline or KCl, RHC-80267 (0.1-10 muM) potentiated the relaxation evoked by acetylcholine. The effect of RHC-80267 was not affected by nitric oxide synthase inhibition or by inhibitors of protein kinase C or of phospholipase A(2). The diacylglycerol analogue 1-oleoyl-2-acetyl-sn-glycerol did not change the relaxation to acetylcholine. RHC-80267 did not affect the relaxation evoked by carbachol, by the nitric oxide donor SNAP (S-nitroso-N-acetylpenicillamine) or by the K(+) channel opener cromakalim. Neostigmine, a cholinesterase inhibitor, produced the same effect as RHC-80267 on acetylcholine-evoked relaxation. When tested on cholinesterase in brain homogenate, RHC-80267 concentration-dependently inhibited cholinesterase activity with an IC(50) of 4 muM. These results indicate that the potentiation of acetylcholine-evoked responses by RHC-80267 in rat mesenteric artery is caused by the inhibition of the cholinesterase activity in the vascular wall.

Proteinase-activated receptor-2-mediated relaxation in mouse tracheal and bronchial smooth muscle: signal transduction mechanisms and distinct agonist sensitivity

We characterized the tracheal and bronchial relaxation caused by proteinase-activated receptor-2 (PAR-2) activation in ddY mice and/or in wild-type and PAR-2-knockout mice of C57BL/6 background. Ser-Leu-Ile-Gly-Arg-Leu-amide (SLIGRL-NH(2)) and Thr-Phe-Leu-Leu-Arg-amide, PAR-2- and PAR-1-activating peptides, respectively, caused relaxation in the isolated ddY mouse trachea and main bronchus. The relaxation was abolished by specific inhibitors of cyclooxygenase (COX)-1, COX-2, mitogen-activated protein kinase kinase (MEK), and p38 MAP kinase. The MEK and p38 MAP kinase inhibitors did not affect prostaglandin E(2)-induced relaxation. Inhibitors of cytosolic Ca(2+)-dependent phospholipase A(2) (PLA), Ca(2+)-independent PLA(2), diacylglycerol lipase, tyrosine kinase, and protein kinase C exhibited no or only minor inhibitory effects on the PAR-mediated relaxation. Trypsin, a PAR-2 activator, and 2-furoyl-Leu-Ile-Gly-Arg-Leu-amide, a potent PAR-2-activating peptide, in addition to SLIGRL-NH(2), caused airway relaxation in wild-type C57BL/6 mice, as in ddY mice. In PAR-2-knockout mice, the peptide effects were absent and the potency of trypsin decreased. Desensitization of PAR-2 and/or PAR-1 greatly suppressed the relaxant effect of trypsin. The bronchial and tracheal tissues displayed distinct sensitivities toward trypsin and the PAR-2-activating peptides. Our data indicate an involvement of both COX-1 and COX-2, and the MEK-extracellular signal-regulated kinase and p38 MAP kinase signaling pathways in the PAR-2- and PAR-1-triggered relaxation of mouse airway tissue, and substantiate a role for PAR-2 in regulating both the trachea and bronchial responsiveness in the mouse lung.

P2X7 receptors control 2-arachidonoylglycerol production by microglial cells

Endogenous cannabinoid ligands (endocannabinoids) produced by neurons, astrocytes, and microglial cells activate cannabinoid receptors, the molecular target for marijuana's bioactive ingredient Delta(9)-tetrahydrocannabinol. The molecular mechanism underlying the production of the most abundant endocannabinoid, 2-arachidonoylglycerol (2-AG), is unclear. A prevalent hypothesis proposes that activation of metabotropic receptors coupled to the phosphatidylinositol-specific phospholipase C and diacylglycerol (DG) lipase pathway will systematically lead to increases in 2-AG production. Here, we show that ATP increases 2-AG production by cultured microglial cells in a phosphatidylinositol-specific phospholipase C and DG lipase-dependent manner. However, efficacious activation of metabotropic P2Y purinergic receptors coupled to phosphatidylinositol-specific phospholipase C does not increase 2-AG production. This suggests that ionotropic, and not metabotropic, purinergic receptors control 2-AG production at an unexpected enzymatic step of its metabolic pathway. We show that activation of P2X(7) ionotropic receptors, which are highly permeable to calcium, is necessary and sufficient to increase 2-AG production in microglial cells. We also show that the sustained rise in intracellular calcium induced by activation of P2X(7) receptors directly increases DG lipase activity while inhibiting the activity of monoacylglycerol lipase, the enzyme that degrades 2-AG. This inverse sensitivity of DG lipase and monoacylglycerol lipase to calcium constitutes an original and efficient modality for sustained accumulation of 2-AG. Because prolonged increases in 2-AG amounts in brain parenchyma are thought to orchestrate neuroinflammation, the enzymatic steps involved in 2-AG synthesis and degradation by microglial cells constitute appealing targets for therapy aimed at controlling exacerbated neuroinflammation.

Biosynthesis and degradation of anandamide and 2-arachidonoylglycerol and their possible physiological significance

N -arachidonoylethanolamine (anandamide) was the first endogenous cannabinoid receptor ligand to be discovered. Dual synthetic pathways for anandamide have been proposed. One is the formation from free arachidonic acid and ethanolamine, and the other is the formation from N -arachidonoyl phosphatidylethanolamine (PE) through the action of a phosphodiesterase. These pathways, however, do not appear to be able to generate a large amount of anandamide, at least under physiological conditions. The generation of anandamide from free arachidonic acid and ethanolamine is catalyzed by a degrading enzyme anandamide amidohydrolase/fatty acid amide hydrolase operating in reverse and requires large amounts of substrates. As for the second pathway, arachidonic acids esterified at the 1-position of glycerophospholipids, which are mostly esterified at the 2-position, are utilized for the formation of N -arachidonoyl PE, a stored precursor form of anandamide. In fact, the actual levels of anandamide in various tissues are generally low except in a few cases. 2-Arachidonoylglycerol (2-AG) was the second endogenous cannabinoid receptor ligand to be discovered. 2-AG is a degradation product of arachidonic acid-containing glycerophospholipids such as inositol phospholipids. Several investigators have demonstrated that 2-AG is produced in a variety of tissues and cells upon stimulation. 2-AG acts as a full agonist at the cannabinoid receptors (CB1 and CB2). Evidence is gradually accumulating and indicates that 2-AG is the most efficacious endogenous natural ligand for the cannabinoid receptors. In this review, we summarize the tissue levels, biosynthesis, degradation and possible physiological significance of two endogenous cannabimimetic molecules, anandamide and 2-AG.

Chlorpyrifos oxon potentiates diacylglycerol-induced extracellular signal-regulated kinase (ERK 44/42) activation, possibly by diacylglycerol lipase inhibition

Chlorpyrifos oxon (CPO) activates extracellular signal-regulated kinase (ERK 44/42) in Chinese hamster ovary (CHOK1) cells but the mechanism is not defined. This study tests the hypothesis that diacylglycerol (DAG) is the secondary messenger responsible for CPO-induced ERK 44/42 activation. It is known that DAG is sequentially hydrolyzed by DAG lipase and monoacylglycerol (MAG) lipase, both of which are organophosphate sensitive. Inhibition of these enzymes might therefore lead to the accumulation of DAG and MAG, of which only DAG is a secondary messenger. The experiments show that treatment of CHOK1 cells with CPO significantly inhibits DAG/MAG lipase activity and elevates cellular DAG levels. Pretreatment of CHOK1 cells with CPO or a carbamate known to be a DAG lipase inhibitor, followed by treatment with a cell-permeable DAG (1,2-dihexanoyl-sn-glycerol), results in synergistic activation of ERK 44/42. CPO-potentiated DAG-induced ERK 44/42 activation is both time and concentration dependent. This activation is blocked by inhibitors of protein kinase C and mitogen-activated protein kinase kinase, suggesting that these enzymes are important in CPO/DAG cellular signaling. Activation by a stable DAG analogue (phorbol ester) was not altered by CPO, suggesting that DAG metabolism is the probable target for CPO-potentiated DAG-induced ERK 44/42 activation. These observations support the hypothesis that CPO potentiates DAG signaling in CHOK1 cells by inhibiting a CPO-sensitive DAG lipase, thereby providing a potential mechanism of toxicity not associated with acetylcholinesterase inhibition.

Fatty Acid Amide Hydrolase Inhibition by Neurotoxic Organophosphorus Pesticides

Organophosphorus (OP) compound-induced inhibition of acetylcholinesterase (AChE) and neuropathy target esterase explains the rapid onset and delayed neurotoxic effects, respectively, for OP insecticides and related compounds but apparently not a third or intermediate syndrome with delayed onset and reduced limb mobility. This investigation tests the hypothesis that fatty acid amide hydrolase (FAAH), a modulator of endogenous signaling compounds affecting sleep (oleamide) and analgesia (anandamide), is a sensitive target for OP pesticides with possible secondary neurotoxicity. Chlorpyrifos oxon inhibits 50% of the FAAH activity (IC50 at 15 min, 25 degrees C, pH 9.0) in vitro at 40--56 nM for mouse brain and liver, whereas methyl arachidonyl phosphonofluoridate, ethyl octylphosphonofluoridate (EOPF), oleyl-4H-1,3,2-benzodioxaphosphorin 2-oxide (oleyl-BDPO), and dodecyl-BDPO give IC50s of 0.08--1.1 nM. These BDPOs and EOPF inhibit mouse brain FAAH in vitro with > or =200-fold higher potency than for AChE. Five OP pesticides inhibit 50% of the brain FAAH activity (ED50) at <30 mg/kg 4 h after ip administration to mice; while inhibition by chlorpyrifos, diazinon, and methamidophos occurs near acutely toxic levels, profenofos and tribufos are effective at asymptomatic doses. Two BDPOs (dodecyl and phenyl) and EOPF are potent inhibitors of FAAH in vivo (ED50 0.5--6 mg/kg). FAAH inhibition of > or =76% in brain depresses movement of mice administered anandamide at 30 mg/kg ip, often leading to limb recumbency. Thus, OP pesticides and related inhibitors of FAAH potentiate the cannabinoid activity of anandamide in mice. More generally, OP compound-induced FAAH inhibition and the associated anandamide accumulation may lead to reduced limb mobility as a secondary neurotoxic effect.

Further characterization of a novel triacylglycerol hydrolase activity (pH 6.0 optimum) from microvillous membranes from human term placenta

We recently identified the presence of two distinct triacylglycerol hydrolases with pH optima of 6.0 and 8.0 in human placental microvillous membranes (MVM). The TAG hydrolase with a pH optimum of 8.0 has properties similar to lipoprotein lipase, whereas TAG hydrolase with a pH optimum of 6.0 still to be fully characterized. In order to understand the functional and structural relationships between these two TAG hydrolases of MVM we have further investigated their biochemical and molecular properties. The presence of oleic acid inhibited TAG hydrolase activity with a pH optimum of 8.0 by 60 per cent whilst it had very little effect on the pH 6.0 TAG hydrolase activity. K(m)values for TAG hydrolases at pH 6.0 and pH 8. 0 optima were 170.6 and 9.83 nmol triolein, respectively, whereas the corresponding V(max)values were 0.32 and 0.037 nmol oleic acid/min mg/protein. Treatment of MVM with phenylmethylsulphonofluoride or protamine had no effect on TAG hydrolase at pH 6.0 whereas both decreased activity at pH 8.0, by 70 per cent and 52 per cent, respectively (P< 0.05), compared with control. p-Chloromercuribenzoate inhibited both TAG hydrolase activities by 25-30 per cent whereas iodoacetate inhibited TAG hydrolase activity with optimum pH 8.0 by 74 per cent and the activity at pH 6.0 by 28 per cent. Unlike the TAG hydrolase activity at pH 8.0, the activity at pH 6.0 was not affected by heparin. TAG hydrolase activity at pH 6.0 was significantly decreased compared with that of pH 8.0 optimum TAG hydrolase activity in smokers placenta. A threefold increase in pH 6.0 TAG hydrolase activity was observed following differentiation, whereas membrane associated TAG hydrolase activity with optimum pH 8.0 did not change. The TAG hydrolase with optimum pH 6.0 was subsequently purified from MVM to almost 1000-fold enrichment of the activity over the starting material. The final preparation however, still contained three distinct protein bands (90, 70 and 45 kDa). When extracted from non-denaturing polyacrylamide gels, the 70 kDa protein was the only protein to have TAG hydrolysing activity and had a pH optimum of 6.0. Labelling of samples with [(14)C]tetrahydrolipstatin also confirmed that the TAG hydrolase active protein was a 70 kDa protein. In conclusion, we report that there is a 70 kDa TAG hydrolase with optimum pH 6.0 in human placental MVM which is quite distinct from placental lipoprotein lipase.

2-Arachidonoylglycerol and the cannabinoid receptors

2-Arachidonoylglycerol (2-AG) is a unique molecular species of monoacylglycerol isolated from rat brain and canine gut as an endogenous cannabinoid receptor ligand (Sugiura, T., Kondo, S., Sukagawa, A., Nakane, S., Shinoda, A., Itoh, K., Yamashita, A., Waku, K., 1995. 2-Arachidonoylglycerol: a possible endogenous cannabinoid receptor ligand in brain. Biochem. Biophys. Res. Commun. 215, 89-97; Mechoulam, R., Ben-Shabat, S., Hanus, L., Ligumsky, M., Kaminski, N. E., Schatz, A.R., Gopher, A., Almog, S., Martin, B.R., Compton, D.R., Pertwee, R.G., Giffin, G., Bayewitch, M., Brag, J., Vogel, Z., 1995. Identification of an endogenous 2-monoglyceride, present in canine gut, that binds to cannabinoid receptors. Biochem. Pharmacol. 50, 83-90). 2-AG binds to the cannabinoid receptors (CB1 and CB2) and exhibits a variety of cannabimimetic activities in vitro and in vivo. Recently, we found that 2-AG induces Ca(2+) transients in NG108-15 cells, which express the CB1 receptor, and in HL-60 cells, which express the CB2 receptor, through a cannabinoid receptor- and Gi/Go-dependent mechanism. Based on the results of structure-activity relationship experiments, we concluded that 2-AG but not anandamide is the natural ligand for both the CB1 and the CB2 receptors and both receptors are primarily 2-AG receptors. Evidences are gradually accumulating that 2-AG is a physiologically essential molecule, although further detailed studies appear to be necessary to determine relative importance of 2-AG and anandamide in various animal tissues. In this review, we described mainly our previous and current experimental results, as well as those of others, concerning the tissue levels, bioactions and metabolism of 2-AG.

Inhibitors of tyrosine phosphatases block angiotensin II inhibition of Na(+) pump

To determine how angiotensin II inhibits the Na(+) pump (Na(+), K(+)-ATPase) in rat zona glomerulosa, we selectively blocked signaling proteins that could be activated by the angiotensin AT(1) receptor and known to affect Na(+) pump activity. Inhibitors of protein kinase C [calphostin C (1 microM); staurosporine (1 microM)], phospholipase A(2) [arachidonyl triflouromethyl ketone (25 microM); quinacrine (75 microM)], diacylgycerol lipase [RHC-80267 (5 microM)], and tyrosine phosphorylation [tyrphostin 47 (100 microM)] had no effect on angiotensin II inhibition of the Na(+) pump. On the other hand, inhibitors of tyrosine phosphatases [phenylarsine oxide (5 microM) and 4-bromotetramisole oxalate (100 microM)] blocked angiotensin II inhibition, where as inhibitors of serine/threonine phosphatases [okadaic acid (1 microM) and microcystin (1.5 microM)] did not. Thus, angiotensin II inhibition of the Na(+) pump may in part be mediated by a tyrosine phosphatase.

Subtype-specific translocation of diacylglycerol kinase alpha and gamma and its correlation with protein kinase C

We examined the translocation of diacylglycerol kinase (DGK) alpha and gamma fused with green fluorescent protein in living Chinese hamster ovary K1 cells (CHO-K1) and investigated temporal and spatial correlations between DGK and protein kinase C (PKC) when both kinases are overexpressed. DGKalpha and gamma were present throughout the cytoplasm of CHO-K1 cells. Tetradecanoylphorbol 13-acetate (TPA) induced irreversible translocation of DGKgamma, but not DGKalpha, from the cytoplasm to the plasma membrane. The (TPA)-induced translocation of DGKgamma was inhibited by the mutation of C1A but not C1B domain of DGKgamma and was not inhibited by staurosporine. Arachidonic acid induced reversible translocation of DGKgamma from the cytoplasm to the plasma membrane, whereas DGKalpha showed irreversible translocation to the plasma membrane and the Golgi network. Purinergic stimulation induced reversible translocation of both DGKgamma and alpha to the plasma membrane. The timing of the ATP-induced translocation of DGKgamma roughly coincided with that of PKCgamma re-translocation from the membrane to the cytoplasm. Furthermore, re-translocation of PKCgamma was obviously hastened by co-expression with DGKgamma and was blocked by an inhibitor of DGK (R59022). These results indicate that DGK shows subtype-specific translocation depending on extracellular signals and suggest that PKC and DGK are orchestrated temporally and spatially in the signal transduction.

Deacylation and reacylation of neural membrane glycerophospholipids

The deacylation-reacylation cycle is an important mechanism responsible for the introduction of polyunsaturated fatty acids into neural membrane glycerophospholipids. It involves four enzymes, namely acyl-CoA synthetase, acyl-CoA hydrolase, acyl-CoA: lysophospholipid acyltransferase, and phospholipase A2. All of these enzymes have been purified and characterized from brain tissue. Under normal conditions, the stimulation of neural membrane receptors by neurotransmitters and growth factors results in the release of arachidonic acid from neural membrane glycerophospholipids. The released arachidonic acid acts as a second messenger itself. It can be further metabolized to eicosanoids, a group of second messengers involved in a variety of neurochemical functions. A lysophospholipid, the second product of reactions catalyzed by phospholipase A2, is rapidly acylated with acyl-CoA, resulting in the maintenance of the normal and essential neural membrane glycerophospholipid composition. However, under pathological situations (ischemia), the overstimulation of phospholipase A2 results in a rapid generation and accumulation of free fatty acids including arachidonic acid, eicosanoids, and lipid peroxides. This results in neural inflammation, oxidative stress, and neurodegeneration. In neural membranes, the deacylation-reacylation cycle maintains a balance between free and esterified fatty acids, resulting in low levels of arachidonic acid and lysophospholipids. This is necessary for not only normal membrane integrity and function, but also for the optimal activity of the membrane-bound enzymes, receptors, and ion channels involved in normal signal-transduction processes.

The generation of localized calcium rises mediated by cell adhesion molecules and their role in neuronal growth cone motility

Neurite growth and guidance depends on the transduction of extracellular guidance cues into motile responses by the sensory apparatus at the tip of the neurite, the growth cone. Contact of the growth cone with extracellular ligands leads to the cytoskeletal reorganisation required for changes in rate of motility and direction of outgrowth. Differential adhesion mediated by cell adhesion molecules and signal transduction pathways mediated by growth cone receptors were once seen as separate but cooperative events in controlling growth cone motility. However, recent findings suggest that cell adhesion molecules can activate novel signalling pathways in the growth cone by the recruitment of fibroblast growth factor receptors leading to neurite outgrowth. This Review focuses on work by various laboratories centering on the intracellular consequences of the cell adhesion molecule-mediated activation of the fibroblast growth factor receptor. These include activation of a lipase cascade including phospholipase C and diacylglycerol lipase and culminating in the release of arachidonic acid. This release of arachidonic acid is proposed to activate the transient opening of voltage dependent ion-channels leading to localised rises in growth Ca(2+). Recent findings demonstrating this previously undetectable rise in Ca(2+) in the growth cone are discussed in light of the proposed roles and mechanisms of Ca(2+) in controlling neurite outgrowth. The Ca(2+) rises are thought to induce the activation of GAP43 and Ca(2+)/calmodulin-dependent kinase II, molecules implicated in the modulation of cytoskeletal remodelling. The evidence that this pathway may be involved in the guidance of retinal ganglion cells is evaluated.