5-Lipoxygenase is required for proliferation of immature cerebellar granule neurons in vitro

Antiplatelet strategies: past, present, and future

Antiplatelet therapy plays a critical role in the prevention and treatment of major cardiovascular diseases triggered by thrombosis. Since the 1900s, significant progress in reducing morbidity and death caused by cardiovascular diseases has been made. However, despite the development and approval of drugs that specifically target the platelet, including inhibitors for cycloxygenase-1, P2Y12 receptor, integrin αIIbβ3, phosphodiesterases, and protease-activated receptor 1, the risk of recurrent thrombotic events remains high, and the increased risk of bleeding is a major concern. Scientific advances in our understanding of the role of platelets in haemostasis and thrombosis have revealed novel targets, such as protease-activated receptor 4 (PAR4), glycoprotein Ib (GPIb)-V-IX complex, glycoprotein VI, and 12-lipoxygenase. The antithrombotic effects and safety of the pharmacologic inhibition of these targets are currently under investigation in clinical studies. This review provides an overview of drugs in early development to target the platelet and those in current use in clinical practice. Furthermore, it describes the emerging drug targets being developed and studied to reduce platelet activity and outlines potential novel therapeutic targets in the platelet.

5-lipoxygenase antagonist therapy: a new approach towards targeted cancer chemotherapy

Leukotrienes are the bioactive group of fatty acids and major constituents of arachidonic acid metabolism molded by the catalytic activity of 5-lipoxygenase (5-LOX). Evidence is accumulating in support of the direct involvement of 5-LOX in the progression of different types of cancer including prostate, lung, colon, and colorectal cancers. Several independent studies now support the correlation between the 5-LOX expression and cancer cell viability, proliferation, cell migration, invasion through extracellular matrix destruction, metastasis, and activation of anti-apoptotic signaling cascades. The involvement of epidermal growth factor receptor and 5-oxo-ETE receptor (OXER1) is the major talking point in the downstream of the 5-LOX pathway, which relates the cancer cells to the proliferative pathways. Antisense technology approaches and use of different kinds of blocker targeted to 5-LOX, FLAP (5-LOX-activating protein), and OXER1 have shown a greater efficiency in combating different cancer cell types. Lastly, suppression of 5-LOX activity that reduces the cell proliferation activity also induces intrinsic mitochondrial apoptotic pathway in either p53-dependent or independent manner. Pharmacological agents that specifically inhibit the LOX-mediated signaling pathways have been used during last few years to treat inflammatory diseases such as asthma and arthritis. Studies of these well-characterized agents are therefore warranted for their use as possible candidates for chemotherapeutic studies against the killer disease cancer.

Differential contribution of lipoxygenase isozymes to nigrostriatal vulnerability

The 5- and 12/15-lipoxygenase (LOX) isozymes have been implicated to contribute to disease development in CNS disorders such as Alzheimer's disease. These LOX isozymes are distinct in function, with differential effects on neuroinflammation, and the impact of the distinct isozymes in the pathogenesis of Parkinson's disease has not as yet been evaluated. To determine whether the isozymes contribute differently to nigrostriatal vulnerability, the effects of 5- and 12/15-LOX deficiency on dopaminergic tone under naïve and toxicant-challenged conditions were tested. In naïve mice deficient in 5-LOX expression, a modest but significant reduction (18.0% reduction vs. wildtype (WT)) in striatal dopamine (DA) was detected (n=6-8 per genotype). A concomitant decline in striatal tyrosine hydroxylase (TH) enzyme was also revealed in null 5-LOX vs. WT mice (26.2%); however, no changes in levels of DA or TH immunoreactivity were observed in null 12/15-LOX vs. WT mice. When challenged with the selective dopaminergic toxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), WT mice showed a marked reduction in DA (31.9%) and robust astrocytic and microglial activation as compared to saline-treated animals. In contrast, null 5-LOX littermates demonstrated no significant striatal DA depletion or astrogliosis (as noted by Western blot analyses for glial acidic fibrillary protein (GFAP) immunoreactivity). In naïve null 12/15-LOX mice, no significant change in striatal DA values was observed compared to WT, and following MPTP treatment, the transgenics revealed striatal DA reduction similar to the challenged WT mice. Taken together, these data provide the first evidence that: (i) LOX isozymes are involved in the maintenance of normal dopaminergic function in the striatum and (ii) the 5- and 12/15-LOX isozymes contribute differentially to striatal vulnerability in response to neurotoxicant challenge.

Cyclooxygenases and 5-lipoxygenase in Alzheimer's disease

Typically, cyclooxygenases (COXs) and 5-lipoxygenase (5-LOX), enzymes that generate biologically active lipid molecules termed eicosanoids, are considered inflammatory. Hence, their putative role in Alzheimer's disease (AD) has been explored in the framework of possible inflammatory mechanisms of AD pathobiology. More recent data indicate that these enzymes and the biologically active lipid molecules they generate could influence the functioning of the central nervous system and the pathobiology of neurodegenerative disorders such as AD via mechanisms different from classical inflammation. These mechanisms include the cell-specific localization of COXs and 5-LOX in the brain, the type of lipid molecules generated by the activity of these enzymes, the type and the localization of receptors selective for a type of lipid molecule, and the putative interactions of the COXs and 5-LOX pathways with intracellular components relevant for AD such as the gamma-secretase complex. Considering the importance of these multiple and not necessarily inflammatory mechanisms may help us delineate the exact nature of the involvement of the brain COXs and 5-LOX in AD and would reinvigorate the search for novel targets for AD therapy.

5-Lipoxygenase inhibitors induce potent anti-proliferative and cytotoxic effects in human tumour cells independently of suppression of 5-lipoxygenase activity

BACKGROUND AND PURPOSE

Certain 5-lipoxygenase (5-LO) inhibitors exhibit anti-carcinogenic activities against 5-LO overexpressing tumour types and cultured tumour cells. It has been proposed therefore that 5-LO products significantly contribute to tumour cell proliferation. To date, the relationship between the inhibitory mechanisms of 5-LO inhibitors, which vary widely, and tumour cell viability has not been evaluated. This study addresses the anti-proliferative and cytotoxic potency of a number of 5-LO inhibitors with different inhibitory mechanisms in 5-LO-positive and 5-LO-negative tumour cells.

EXPERIMENTAL APPROACH

Cell viability was measured by the WST-1 assay; cell proliferation was assessed using the bromodeoxyuridine (BrdU) incorporation assay. Cell death was analysed by annexin V staining, Western blot analysis of PARP (poly ADP-ribose polymerase) cleavage and a cytotoxicity assay. 5-LO product formation was quantified by a 5-LO activity assay.

KEY RESULTS

The common 5-LO inhibitors AA-861, Rev-5901 and MK-886 induced cytotoxic and anti-proliferative effects in 5-LO-positive Capan-2 pancreatic cancer cells; BWA4C and CJ-13,610 only caused anti-proliferative effects, while zileuton failed to impair cell viability. Moreover, the concentrations of the 5-LO inhibitors required to induce anti-proliferation and cytotoxicity highly exceeded those for suppression of 5-LO. Supplementation with mitogenic 5-LO products failed to protect Capan-2 cells from the effects of 5-LO inhibitors. Finally, the cytotoxic and anti-proliferative 5-LO inhibitors also potently reduced the viability of 5-LO-deficient tumour cell lines (HeLa, Panc-1 and U937).

CONCLUSIONS AND IMPLICATIONS

Certain 5-LO inhibitors cause cytotoxic and anti-proliferative effects independently of suppression of 5-LO activity. Thus, the role of 5-LO overexpression in tumour cell viability remains unclear and requires further elucidation.

Differential roles of phospholipases A2 in neuronal death and neurogenesis: implications for Alzheimer disease

The involvement of phospholipase A(2) (PLA(2)) in Alzheimer disease (AD) was first investigated nearly 15 years ago. Over the years, several PLA(2) isoforms have been detected in brain tissue: calcium-dependent secreted PLA(2) or sPLA(2) (IIA, IIC, IIE, V, X, and XII), calcium-dependent cytosolic PLA(2) or cPLA(2) (IVA, IVB, and IVC), and calcium-independent PLA(2) or iPLA(2) (VIA and VIB). Additionally, numerous in vivo and in vitro studies have suggested the role of different brain PLA(2) in both physiological and pathological events. This review aimed to summarize the findings in the literature relating the different brain PLA(2) isoforms with alterations found in AD, such as neuronal cell death and impaired neurogenesis process. The review showed that sPLA(2)-IIA, sPLA(2)-V and cPLA(2)-IVA are involved in neuronal death, whereas sPLA(2)-III and sPLA(2)-X are related to the process of neurogenesis, and that the cPLA(2) and iPLA(2) groups can be involved in both neuronal death and neurogenesis. In AD, there are reports of reduced activity of the cPLA(2) and iPLA(2) groups and increased expression of sPLA(2)-IIA and cPLA(2)-IVA. The findings suggest that the inhibition of cPLA(2) and iPLA(2) isoforms (yet to be determined) might contribute to impaired neurogenesis, whereas stimulation of sPLA(2)-IIA and cPLA(2)-IVA might contribute to neurodegeneration in AD.

5-Lipoxygenase in mouse cerebellar Purkinje cells

It has been suggested that the enzymatic pathway of 5-lipoxygenase (5-LOX) influences brain functioning and pathobiology. The mRNAs for both the enzyme 5-LOX and its activating protein FLAP have been found in the cerebellum. In this work, we investigated the cellular expression of 5-LOX in the adult mouse cerebellar cortex. We used the in situ mRNA hybridization assay, immunocytochemistry, laser capture microdissection, and our previously developed method for assaying the DNA methylation status of a putative mouse 5-LOX promoter. Since both 5-LOX mRNA in situ hybridization signal and FLAP immunoreactivity co-localize with calbindin 28 kD immunoreactivity (a Purkinje cell marker) but not with S-100β immunoreactivity (a Bergmann glia marker), the suggestion is that the 5-LOX pathway is expressed in cerebellar Purkinje cells. We found that methylation in the sites targeted by methylation-sensitive restriction endonucleases AciI and HinP1I but not BstUI and HpaII was greater in DNA samples obtained from a high-5-LOX-expressing cerebellar region (Purkinje cells) versus a low-5-LOX-expressing region (the molecular cell layer), suggesting a possible epigenetic contribution to the cell-specific 5-LOX expression in the cerebellum. We propose that Purkinje cell-localized 5-LOX and FLAP expression may be involved in the cerebellar synthesis of leukotrienes and/or could influence the Dicer-mediated microRNA formation and processes of neuroplasticity.

5-Lipoxygenase and epigenetic DNA methylation in aging cultures of cerebellar granule cells

5-Lipoxygenase (5-Lox), an enzyme involved in the metabolism of arachidonic acid participates in the modulation of the proliferation and differentiation of neural stem cells and cerebellar granule cell (CGC) precursors. Since epigenetic mechanisms including DNA methylation regulate 5-LOX expression and have been suggested as possible modulators of stem cell differentiation and aging, using primary cultures of mouse CGC (1, 5, 10, 14, 30 days in vitro; DIV), we studied DNA methylation patterns of the 5-LOX promoter and 5-LOX mRNA levels. We also measured the mRNA and protein content of the DNA methyltransferases DNMT1 and DNMT3a. 5-LOX, DNMT1, and DNMT3a mRNA levels were measured by real-time PCR. We observed that 5-LOX expression and the expression of maintenance DNMT1 is maximal at 1 DIV (proliferating neuronal precursors), whereas the expression of the de novo DNA methyltransferase DNMT3a mRNA increased in aging cultures. We analyzed the methylation status of the 5-LOX promoter using the methylation-sensitive restriction endonucleases AciI, BstUI, HpaII, and HinP1I, which digest unmethylated CpGs while leaving methylated CpGs intact. The 5-LOX DNA methylation increased with the age of the cells. Taken together, our data show that as cultured CGC mature and age in vitro, a decrease in 5-LOX mRNA content is accompanied by an increase in the methylation of the gene DNA. In addition, an increase in DNMT3a but not DNMT1 expression accompanies an increase of 5-LOX methylation during in vitro maturation.

Expression of enzymes and receptors of the leukotriene pathway in human neuroblastoma promotes tumor survival and provides a target for therapy

The metabolism of arachidonic acid by the cyclooxygenase (COX) or lipoxygenase (LO) pathways generates eicosanoids that have been implicated in the pathogenesis of a variety of human diseases, including cancer. In this study, we examined the expression and significance of components within the 5-LO pathway in human neuroblastoma, an embryonal tumor of the sympathetic nervous system. High expression of 5-LO, 5-LO-activating protein (FLAP), leukotriene A(4) hydrolase, leukotriene C(4) synthase, and leukotriene receptors was detected in a majority of primary neuroblastoma tumors and all cell lines investigated. Expression of 5-LO and FLAP was evident in tumor cells but not in nonmalignant adrenal medulla where neuroblastomas typically arise. Moreover, neuroblastoma cells produce leukotrienes, and stimulation of neuroblastoma cells with leukotrienes increased neuroblastoma cell viability. Inhibitors of 5-LO (AA-861), FLAP (MK-886), or the leukotriene receptor antagonist montelukast inhibited neuroblastoma cell growth by induction of G(1)-cell cycle arrest and apoptosis. Similarly, specific 5-LO and leukotriene receptor silencing by small interfering RNA decreased neuroblastoma cell growth. These findings provide new insights into the pathobiology of neuroblastoma, and the use of leukotriene pathway inhibitors as a novel adjuvant therapy for children with neuroblastoma warrants further consideration.

Melatonin signaling in mouse cerebellar granule cells with variable native MT1 and MT2 melatonin receptors

Although G protein-coupled MT1 and MT2 melatonin receptors are expressed in neurons of the mammalian brain including in humans, relatively little is known about the influence of native MT1 and MT2 melatonin receptors on neuronal melatonin signaling. Whereas human cerebellar granule cells (CGC) express only MT1 receptors, mouse CGC express both MT1 and MT2. To study the effects of altered neuronal MT1/MT2 receptors, we used CGC cultures prepared from immature cerebella of wild-type mice (MT1/MT2 CGC) and MT1- and MT2-knockout mice (MT2 and MT1 CGC, respectively). Here we report that in MT1/MT2 cultures, physiological (low nanomolar) concentrations of melatonin decrease the activity (phosphorylation) of extracellular-signal-regulated kinase (ERK) whereas a micromolar concentration was ineffective. Both MT1 and MT2 deficiencies transformed the melatonin inhibition of ERK into melatonin-induced ERK activation. In MT1/MT2 CGC, 1 nM melatonin inhibited serine/threonine kinase Akt, whereas in MT1 and MT2 CGC, this concentration was ineffective. Under these conditions, both MT1 and MT2 deficiencies prevented melatonin from inhibiting forskolin-stimulated cAMP levels and cFos immunoreactivity. We demonstrated that selective removal of native neuronal MT1 and MT2 receptors has a profound effect on the intracellular actions of low/physiological concentrations of melatonin. Since the expression of MT1 and MT2 receptors is cell-type-specific and species-dependent, we postulate that the pattern of expression of neuronal melatonin receptor types in different brain areas and cells could determine the capabilities of endogenous melatonin in regulating neuronal functioning.

Effects of salicylhydroxamic acid on the proliferation of Atriplex and murine neuroblastoma cells, and on Drosophila egg laying and development

Salicylhydroxamic acid (SHAM) inhibits the proliferation of cultured plant (Atriplex halimus) and murine neuroblastoma cells with IC50 of 90 and 250 microM, respectively. After 2 h of application, SHAM induces an acceleration of the neuroblastoma cell cycle from G1/S to G2 phases and, after 6 h, it induces an accumulation of the cells in S phase and a cell swelling. Up to 300 microM, SHAM is not cytotoxic and does not induce electrophysiological differentiation of neuroblastoma cells. When Drosophila females are grown in media containing 0.6-1.25 mM SHAM, the rate and number of laid eggs are increased. Furthermore, SHAM stimulates the different development stages from embryo to adult. A general interpretation of the effects of SHAM on cell proliferation and differentiation is proposed.

Dietary supplementation of arachidonic and docosahexaenoic acids improves cognitive dysfunction

Age-dependent increase of peroxidation of membrane fatty acids such as arachidonic acid (ARA) and docosahexaenoic acid (DHA) in neurons was reported to cause a decline of the hippocampal long-term potentiation (LTP) and cognitive dysfunction in rodents. Although supplementation of ARA and DHA can improve LTP and cognitive function in rodents, their effects in humans are unknown. The present work was undertaken to study whether ARA and DHA have beneficial effects in human amnesic patients. The subjects were 21 mild cognitive dysfunction (12 MCI-A with supplementation and 9 MIC-P with placebo), 10 organic brain lesions (organic), and 8 Alzheimer's disease (AD). The cognitive functions were evaluated using Japanese version of repeatable battery for assessment of neuropsychological status (RBANS) at two time points: before and 90 days after the supplementation of 240 mg/day ARA and DHA, or 240 mg/day of olive oil, respectively. MCI-A group showed a significant improvement of the immediate memory and attention score. In addition, organic group showed a significant improvement of immediate and delayed memories. However, there were no significant improvements of each score in AD and MCI-P groups. It is suggested from these data that ARA and DHA supplementation can improve the cognitive dysfunction due to organic brain damages or aging.

Minocycline protects PC12 cells against NMDA-induced injury via inhibiting 5-lipoxygenase activation

Recently, we have reported that minocycline, a semi-synthetic tetracycline with neuroprotective effects, inhibits the in vitro ischemic-like injury and 5-lipoxygenase (5-LOX) activation in PC12 cells. In the present study, we further determined whether minocycline protects PC12 cells from excitotoxicity via inhibiting 5-LOX activation. We used N-methyl-d-aspartate (NMDA, 200 microM) to induce early (exposure for 6 h) and delayed (exposure for 6 h followed by 24 h recovery) injuries. We found that NMDA receptor antagonist ketamine, 5-LOX inhibitor caffeic acid and minocycline concentration dependently attenuated NMDA-induced early and delayed cell injuries (viability reduction and cell death). However, only ketamine (1 microM) inhibited NMDA-evoked elevation of intracellular calcium. In addition, immunohistochemical analysis showed that NMDA induced 5-LOX translocation to the nuclear membrane after 1- to 6-h exposure which was confirmed by Western blotting, indicating that 5-LOX was activated. Ketamine, caffeic acid and minocycline (each at 1 microM) inhibited 5-LOX translocation after early injury. After delayed injury, PC12 cells were shrunk, and 5-LOX was translocated to the nuclei and nuclear membrane; ketamine, caffeic acid and minocycline inhibited both cell shrinking and 5-LOX translocation. As a control, 12-LOX inhibitor baicalein showed a weak effect on cell viability and death, but no effect on 5-LOX translocation. Therefore, we conclude that the protective effect of minocycline on NMDA-induced injury is partly mediated by inhibiting 5-LOX activation.

Expression patterns of 5-lipoxygenase in human brain with traumatic injury and astrocytoma

5-Lipoxygenase (5-LOX) is a key enzyme in the metabolism of arachidonic acid to leukotrienes. The levels of leukotrienes increase after brain injury and when tumors are present. It has been reported that 5-LOX is widely expressed in the brain and that 5-LOX inhibition provides neuroprotection. However, there is still no information available for the expression patterns of 5-LOX in human brain following trauma or with astrocytomas. We investigated its expression patterns by immunohistochemistry. We found that 5-LOX is normally expressed in neurons and glial cells. In neurons, it was expressed in two patterns: in the cytosol and nucleus or only in the cytosol. In traumatic brain injury, 5-LOX expression increased in glial cells and neutrophils. Double-labeling immunohistochemistry showed that part of the 5-LOX-positive glial cells were GFAP positive. No 5-LOX expression was found in brain microvessel endothelia, except in the regenerated endothelia of a patient 8 days following brain trauma. Furthermore, 5-LOX expression increased and showed a granular pattern in high-grade (grade III/IV) astrocytoma. These results indicate that 5-LOX has multiple expression patterns, and can be induced by brain injury, which implies that 5-LOX might have pathophysiological roles in the human brain.

The meaning of mammalian adult neurogenesis and the function of newly added neurons: the "small-world" network

Adult neurogenesis has been observed in mammalian brain including human but a question remains: how do new neurons become functional in the adult brain? We propose that the random addition of only a few new neurons functions as a maintenance system for the brain's "small-world" networks. In popular parlance, the small-world network phenomenon is described by the concept of "six degrees of separation", which postulates that everyone in the world is connected to everyone else through a chain of at most six mutual acquaintances. Randomly added to an orderly network, new links enhance signal propagation speed and synchronizability. Newly generated neurons are ideally suited to become such links: they are immature, form more new connections compared to mature ones, and their number but not their precise location may be maintained by continuous proliferation and dying off. Similarly, we envisage that the treatment of brain pathologies by cell transplantation would also create new random links in small-world networks and that even a small number of successfully incorporated new neurons may be functionally important.

A novel neurotrophic role of secretory phospholipases A2for cerebellar granule neurons

Cultured cerebellar granule neurons (CGNs) require membrane depolarization or neurotrophic factors for their survival in vitro and undergo apoptosis when deprived of these survival-promoting stimuli. Here, we show that secretory phospholipases A(2)s (sPLA(2)s) rescue CGNs from apoptosis after potassium deprivation. The neurotrophic effect required the enzymatic activity of sPLA(2)s, since catalytically inactive mutants of sPLA(2)s failed to protect CGNs from apoptosis. Consistently, the ability of sPLA(2)s to protect CGNs from apoptosis correlated with the extent of sPLA(2)-induced arachidonic acid release from live CGNs. The survival-promoting effect of sPLA(2) was inhibited by depletion of extracellular Ca(2+) or by the presence of L-type Ca(2+) channel blocker nicardipine, suggesting that Ca(2+) influx occurs upon sPLA(2) treatment. Among the mammalian sPLA(2)s tested, only group X sPLA(2), but not group IB nor IIA sPLA(2)s, displayed neurotrophic activity. These results suggest a novel, unexpected neurotrophin-like role of sPLA(2) in the nervous system.

Cysteinyl-leukotrienes are released from astrocytes and increase astrocyte proliferation and glial fibrillary acidic protein via cys-LT1 receptors and mitogen-activated protein kinase pathway

Cysteinyl-leukotrienes (cys-LTs), potent mediators in inflammatory diseases, are produced by nervous tissue, but their cellular source and role in the brain are not very well known. In this report we have demonstrated that rat cultured astrocytes express the enzymes (5'-lipoxygenase and LTC(4) synthase) required for cys-LT production, and release cys-LTs in resting condition and, to a greater extent, in response to calcium ionophore A23187, 1 h combined oxygen-glucose deprivation or 2-methyl-thioATP, a selective P2Y(1)/ATP receptor agonist. MK-886, a LT synthesis inhibitor, prevented basal and evoked cys-LT release. In addition, 2-methyl-thioATP-induced cys-LT release was abolished by suramin, a P2 receptor antagonist, or by inhibitors of ATP binding cassette proteins involved in cys-LT release. We also showed that astrocytes express cys-LT(1) and not cys-LT(2) receptors. The stimulation of these receptors by LTD(4) activated the mitogen-activated protein kinase (MAPK) pathway. This effect was: (i) insensitive to inhibitors of receptor-coupled Gi protein (pertussis toxin) or tyrosine kinase receptors (genistein); (ii) abolished by MK-571, a cys-LT(1) selective receptor antagonist, or PD98059, a MAPK inhibitor; (iii) reduced by inhibitors of calcium/calmodulin-dependent kinase II (KN-93), Ca(2+)-dependent and -independent (GF102903X) or Ca(2+)-dependent (Gö6976) protein kinase C isoforms. LTD(4) also increased astrocyte proliferation and glial fibrillary acidic protein content, which are considered hallmarks of reactive astrogliosis. Both effects were counteracted by cell pretreatment with MK-571 or PD98059. Thus, cys-LTs released from astrocytes might play an autocrine role in the induction of reactive astrogliosis that, in brain injuries, contributes to the formation of a reparative glial scar.

Minocycline protects PC12 cells from ischemic-like injury and inhibits 5-lipoxygenase activation

Minocycline protects animals against cerebral ischemia by inhibiting inflammation. To determine whether minocycline protects PC12 cells from in vitro ischemic-like injury and affects pro-inflammatory 5-lipoxygenase activation, the cell viability and 5-lipoxygenase translocation to nuclear membrane were observed after oxygen-glucose deprivation (OGD). We found that OGD reduced cell viability, which was attenuated by minocycline and 5-lipoxygenase inhibitor caffeic acid. 5-Lipoxygenase protein was detected in PC12 cells by immunohistochemical and Western blot analyses. OGD induced 5-lipoxygenase translocation to nuclear membranes, which was abolished by minocycline and caffeic acid. Thus, minocycline can protect PC12 cells from in vitro ischemic-like injury, and this effect may be partly related to the inhibition of 5-lipoxygenase activation.

Blockade of 12-lipoxygenase expression protects cortical neurons from apoptosis induced by β-amyloid peptide

The cyclo-oxygenase (COX) and lipoxygenase (LOX) pathways belong to the eicosanoid synthesis pathway, a major component of the chronic inflammatory process occurring in Alzheimer's disease (AD). Clinical studies reported beneficial effects of COX inhibitors, but little is known about the involvement of LOXs in AD pathogenesis. beta-amyloid peptide (A beta) accumulation contributes to neurodegeneration in AD, but mechanisms underlying A beta toxicity have not been fully elucidated yet. Here, using an antisense oligonucleotide-based strategy, we show that blockade of 12-LOX expression prevents both A beta-induced apoptosis and overexpression of c-Jun, a factor required for the apoptotic process, in cortical neurons. Conversely, the 12-LOX metabolite, 12(S)-HETE (12(S)-hydroxy-(5Z, 8Z, 10E, 14Z)-eicosatetraenoic acid), promoted c-Jun-dependent apoptosis. Specificity of the 12-LOX involvement was further supported by the observed lack of contribution of 5-LOX in this process. These data indicate that blockade of 12-LOX expression disrupts a c-Jun-dependent apoptosis pathway, and suggest that 12-LOX may represent a new target for the treatment of AD.

DNA methylation as an epigenetic regulator of neural 5-lipoxygenase expression: evidence in human NT2 and NT2-N cells

Increased expression of 5-lipoxygenase is associated with various neuropathologies and may be related to epigenetic gene regulation. DNA methylation in promoter regions is typically associated with gene silencing. We found that human NT2 cells, which differentiate into neuron-like NT2-N cells, express 5-lipoxygenase and we investigated the relationship between 5-lipoxygenase expression and the methylation state of the 5-lipoxygenase core promoter. We used the demethylating agent 5-aza-2'-deoxycytidine and the histone deacetylase inhibitor valproate to alter DNA methylation and to induce histone modifications. 5-Lipoxygenase expression and DNA methylation were assayed with RT-PCR and bisulfite genomic sequencing, respectively. Neuronal differentiation of proliferating NT2 precursors decreased 5-lipoxygenase expression. 5-Aza-2'-deoxycytidine increased 5-lipoxygenase mRNA levels only in proliferating cells, whereas valproate increased 5-lipoxygenase mRNA levels in a cell cycle-independent manner. In both precursors and differentiated cells, CpG dinucleotides of the promoter were poorly methylated. In precursors, both 5-aza-2'-deoxycytidine and valproate further reduced the number of methylated CpGs. Moreover, we found evidence for cytosine methylation in CpWpG (W=adenine or thymine) and other asymmetrical sequences; CpWpG methylation was reduced by valproate in NT2-N but not in NT2 cells. This is the first report demonstrating that the dynamics of DNA methylation relates to neural 5-lipoxygenase gene expression.

Inhibition of 5-lipoxygenase induces cell growth arrest and apoptosis in rat Kupffer cells: implications for liver fibrosis

The existence of an increased number of Kupffer cells is recognized as critical in the initiation of the inflammatory cascade leading to liver fibrosis. Because 5-lipoxygenase (5-LO) is a key regulator of cell growth and survival, in the current investigation we assessed whether inhibition of the 5-LO pathway would reduce the excessive number of Kupffer cells and attenuate inflammation and fibrosis in experimental liver disease. Kupffer cells were the only liver cell type endowed with a metabolically active 5-LO pathway (i.e., expressed mRNAs for 5-LO, 5-LO-activating protein [FLAP], and leukotriene [LT] C4 synthase and generated LTB4 and cysteinyl-LTs). Both the selective 5-LO inhibitor AA861 and the FLAP inhibitor BAY-X-1005 markedly reduced the number of Kupffer cells in culture. The antiproliferative properties of AA861 and BAY-X-1005 were associated with the occurrence of condensed nuclei, fragmented DNA, and changes in DNA content and cell cycle frequency distribution consistent with an apoptotic process. In vivo, in carbon tetrachloride-treated rats, BAY-X-1005 had a significant antifibrotic effect and reduced liver damage and the hepatic content of hydroxyproline. Together, these findings indicate a novel mechanism by which inactivation of the 5-LO pathway could disrupt the sequence of events leading to liver inflammation and fibrosis.

Valproate administration to mice increases histone acetylation and 5-lipoxygenase content in the hippocampus

Gene expression can be regulated by chromatin remodeling induced by the opposing actions of histone acetyltransferases and histone deacetylases (HDAC). HDAC inhibitors are considered putative anti-cancer drugs, but may also alter gene expression in the brain. Valproic acid (valproate; VPA), a drug used for treatment of bipolar disorder, has been characterized as a HDAC inhibitor. In neuronal cultures, VPA increases the expression of 5-lipoxygenase (5-LOX). Here we show that in vivo treatment of mice with intraperitoneal VPA injections increases the acetylation of histone H3 and the content of 5-LOX immunoreactive protein in the hippocampus. Since the extent of 5-LOX expression may alter mouse behavior, we suggest that VPA-altered chromatin remodeling and 5-LOX expression in the brain may be functionally important.

Lithium stimulates progenitor proliferation in cultured brain neurons

The number of neurons in the brain is controlled by production of new neurons and neuronal death. Neural progenitor proliferation in the developing and adult brain plays a prominent role in the production of new neurons. Here, we examined the effects of lithium, a mood-stabilizing drug, on neuronal proliferation in rat primary neuronal cultures. The incorporation of 5-bromo-2'-deoxyuridine (BrdU) into replicating DNA was used to label proliferating cells. BrdU incorporation was detected by immunocytochemistry in cerebellar granule cells prepared from postnatal rats and cerebral cortical cultures prepared from embryonic rats. Quantification of BrdU incorporation into cultures was performed by counting BrdU-positive cells and BrdU-coupled enzyme-linked immunosorbent assay. Both methods revealed that lithium increased BrdU incorporation in cerebellar granule cells and cerebral cortical cultures. Most BrdU-positive cells colocalized with nestin, a neuroblast cell marker, in cerebral cortical cultures. Blockade of DNA replication by cytosine arabinoside almost completely abolished BrdU incorporation, suggesting that lithium-induced BrdU incorporation was mainly due to enhanced DNA replication. Glutamate, glucocorticoids and haloperidol were found to markedly reduce neural progenitor proliferation in cerebellar granule cells. The presence of lithium prevented the loss of proliferation induced by these agents. Lithium-induced neural progenitor proliferation in vitro suggests that similar effects might occur in vivo and this action could also be related to its clinical efficacy. Cultured brain neurons may provide a valuable model for studying the molecular mechanisms underlying lithium-induced up-regulation of neural proliferation.

DNA hypomethylating agents 5-aza-2'-deoxycytidine and valproate increase neuronal 5-lipoxygenase mRNA

DNA methylation regulates gene expression. Neuronal 5-lipoxygenase expression increases during aging and during the proliferation of immature rat cerebellar granule neurons. In these cultures, we investigated the effects of hypomethylating agents 5-aza-2'-deoxycytidine (AdC) and valproate on 5-lipoxygenase mRNA. Both drugs increased 5-lipoxygenase mRNA in proliferating cells; only valproate was effective in differentiated neurons. We propose that neuronal 5-lipoxygenase expression can be affected by aging-altered DNA methylation and by hypomethylating drugs, such as the anticonvulsant valproate.