N18 Cells Research Articles

Cannabidiol's Upregulation of N-acyl Ethanolamines in the Central Nervous System Requires N-acyl Phosphatidyl Ethanolamine-Specific Phospholipase D.

Introduction: Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) are bioactive cannabinoids. We recently showed that acute THC administration drives region-dependent changes in the mouse brain lipidome. This study tested the hypothesis that cell lines representing cell types present in the central nervous system (CNS), neurons (N18 cells), astrocytes (C6 glioma cells), and microglia (BV2 cells) would respond differently to THC, CBD, or their combination. This experimental strategy also allowed us to test the hypothesis that THC and CBD are metabolized differently if presented in combination and to test the hypothesis that responses to CBD are not like the fatty acid amide hydrolase (FAAH) inhibitor URB597. Finally, we tested the hypothesis that CBD's CNS effects would differ in the N-acyl phosphatidyl ethanolamine-specific phospholipase D (NAPE-PLD) knockout (KO) compared to wild-type (WT) mice.Methods: N18, C6, and BV2 cells were stimulated with 1 μM THC, 1 μM CBD, 1 μM THC:CBD, 1 μM URB597, or vehicle for 2 h and lipids extracted. Adult female WT and NAPE-PLD KO mice were injected with 3 mg/kg CBD or vehicle i.p., brains collected 2 h later, eight brain regions dissected, and lipids extracted. Extracted lipids were characterized and quantified using high-pressure liquid chromatography coupled with tandem mass spectrometry (HPLC/MS/MS).Results: Lipid levels in each cell type were differentially affected by THC, CBD, or THC:CBD with a few exceptions. In all cell lines, THC increased levels of arachidonic acid and CBD increased levels of N-acyl ethanolamines (NAEs), including N-arachidonoyl ethanolamine. More THC remained when cells were coincubated with CBD; however, levels of THC metabolites were cell-type dependent. CBD and URB597 caused very different lipid profiles in the cell-based assays with the primary similarity being increases in NAEs. CBD increased levels of NAEs in the WT hippocampus, cerebellum, thalamus, cortex, midbrain, and brainstem; however, NAEs did not increase in any brain region after CBD in NAPE-PLD KO mice.Conclusions: CBD and THC differentially modify the lipidome of the brain and CNS-type cell lines. Increases in NAEs observed after CBD treatment had previously been attributed to FAAH inhibition; however, data here suggest the alternative hypothesis that CBD is activating NAPE-PLD to increase NAE levels.

The phospholipase A2 signaling as a new therapeutic biomarker of Alzheimer’s disease: modulation through phage display-derived peptides able to cross the blood-brain barrier

Event Abstract Back to Event The phospholipase A2 signaling as a new therapeutic biomarker of Alzheimer’s disease: modulation through phage display-derived peptides able to cross the blood-brain barrier Séverine André1*, Fatima Daldal1, Marine Lecomte1, Robert Muller1, 2, Luce Vander Elst1, Sophie Laurent1, 2 and Carmen Burtea1 1 University of Mons, General, Organic and Biomedical Chemistry, Belgium 2 Center for Microscopy and Molecular Imaging, Belgium Introduction The treatment of Alzheimer’s disease (AD) is a real challenge up to now. Phospholipase A2 (PLA2) signaling pathway was recently revealed to be involved in this pathology [1], its inhibition already showing neuron protection against apoptosis induced by amyloid beta (Aβ) [2]. Using the phage-display technology, we have identified a PLA2-targeted peptide (PLP25) aiming to limit the activation of PLA2. Furthermore, the blood-brain barrier (BBB) is a restrictive barrier protecting the brain against xenobiotics and limiting the access of most molecules, including potential therapeutic agents. Non-invasive crossing strategies are thus indispensable to deliver therapeutic agents to the central nervous system (CNS) without BBB disruption. Because of its involvement in LDL transcytosis [3], LDL receptor (LDLR) was targeted by phage display and the peptide LRP2 was identified as a new vector able to facilitate the crossing of this barrier. LRP2 will be thus used as vector of our therapeutic peptide aiming to improve its CNS delivery. Methods The specificity of both peptides PLP25 and LRP2 to their respective target was validated by immunofluorescence. The inhibitory potential of PLP25 targeting PLA2 was evaluated by the dosage of arachidonic acid (AA) released by human astrocytes (1321N1) and mouse neurons (N18) induced by H2O2 and glutamate respectively, known as PLA2 activators. The localization of PLA2 after its activation was evaluated on these same cells by immunofluorescence. The endocytosis mechanism of LDLR-targeted LRP2 was investigated in human brain endothelial cells ACBRI376, human astrocytes 1321N1 and mouse neurons N18(H) by immunofluorescence. The ability of LRP2 to accede the brain was assessed in vivo on NMRI mice by Magnetic Resonance Imaging (MRI) using LRP2-grafted Ultrasmall Superparamagnetic Particles of Iron Oxide (USPIO-LRP2). After brain collection, USPIO derivatives were detected by Perls’-DAB. Results and Prospects The AA released by 1321N1 and N18(H) cells was increased after PLA2 induction with H2O2 or glutamate respectively. On 1321N1, the pre-incubation with PLP25 before PLA2 stimulation allowed to decrease AA levels released by these cells, ranging from 20% to 60% as compared to induced cells, with a more potent effect at low concentration. On differentiated N18(H) cells, PLP25 produced the same effects. Generally, PLP25 restored PLA2 activity in the range of negative control both in astrocytes and neurons. In order to observe the effect of PLP25 on cellular localization of PLA2, this last one was detected in a first stage on 1321N1 by immunofluorescence. H2O2 stimulation resulted in the concentration of PLA2 at the plasma membrane and its processes, showed by a higher fluorescent labeling. A similar experiment performed on glutamate-induced N18(H) revealed the migration of PLA2 in filopodia of neuronal growth cones. These results agree with the known translocation of the induced PLA2 from the cytoplasm to cellular membranes, where it binds via its C2 domain to the enzymatic substrate, the phosphatidylcholine [4]. PLA2 is involved in the dynamics of actin cytoskeleton and filipodia formation in astrocytes and neurons, playing a key role in neuronal plasticity [5,6]. Being specific to the C2 domain of PLA2, PLP25 prevented the migration of PLA2 to cell membrane and filopodia, as suggested by the decreased fluorescent labeling of these structures. This effect was moreover facilitated when PLP25 was combined to LRP2. Concerning the crossing of the BBB, the peptide LRP2 is endocytosed via a caveolae-mediated non-degradation pathway in ACBRI376 cells, which compose the BBB, whereas the lysosome degradation is bypassed. Interestingly, LRP2 is also able to penetrate 1321N1 and N18(H) cells mostly via the caveolae pathway, even if a small proportion seems to taken by lysosomes. These results confirm that LRP2 could be used as vector through the BBB for the therapeutic agent. In vivo MRI experiments showed that USPIO-LRP2 (a negative contrast agent) induces a darkening of brains as compared to USPIO-NSP (nonspecific). These observations were confirmed by the increased negative contrast (%SNR) obtained by the analysis of signal intensity. The Perls’-DAB staining performed on brain slices of the injected mice, highlighting iron contained in USPIO, revealed an important brown staining for USPIO-LRP2, as opposed to USPIO-NSP or PBS that do not show any staining. The evaluation of peptide LRP2 coupled to the therapeutic peptide PLP25 is currently in progress. Acknowledgements This work is supported by the Rotary Foundation – Hope in Head campaign 2015, the FRMH (Fond pour la Recherche Médicale en Hainaut) and the grant “Actions de Recherche Concertée” financed by the Fédération Wallonie-Bruxelles, the Waloon Region, Feder, Interreg and COST actions.

In vitro growth, pathogenicity and serological characteristics of the Japanese encephalitis virus genotype V Muar strain.

The characteristics of genotype V Japanese encephalitis virus (GV JEV) remain poorly understood as only two strains have been isolated to date. In this study, we examined the effects of the GV JEV Muar strain on in vitro growth and pathogenicity in mice; we also evaluated the efficacy of inactivated JEV vaccines against the Muar strain. Although growth of the Muar strain in mouse neuroblastoma N18 cells was clearly worse than that of the GIII Beijing-1 and GI Mie/41/2002 strains, neuroinvasiveness of the Muar strain was similar to that of the Beijing-1 strain and significantly higher than that of the Mie/41/2002 strain. The results of a plaque reduction neutralization test suggested that the neutralization ability of the JEV vaccines against the Muar strain was reduced compared with the GI and GIII strains. However, the protection potency of the JEV vaccine against the Muar strain was similar to that for the Beijing-1 strain in mice. Our data indicate that GV JEV has unique growth, virulence and antigenicity features.

Glutamate release from astrocyte cell-line GL261 via alterations in the intracellular ion environment

Astrocytes modify and maintain neural activity and functions via gliotransmitter release such as, glutamate. They also change their properties and functions in response to alterations of ion environment resulting from neurotransmission; however, the direct evidence for whether intracellular ion alteration in astrocytes triggers gliotransmitter release is not indicated. Recent studies have reported that channelrhodopsin-2 (ChR2) is useful for alteration of intracellular ion environment in several types of cells with blue light exposure. Here, we show that ChR2-expressing GL261 (GLChR2) cells, clonal astrocytes, change their properties by photo-activation. Increased intracellular sodium and calcium ion concentrations and an altered membrane potential were observed in GLChR2 cells with blue light exposure. Alterations in the intracellular ion environment caused intracellular acidification and the inhibition of proliferation. In addition, it triggered glutamate release from GLChR2 cells. Glutamate from GLChR2 cells acted on N18 cells, clonal neuronal cells, as both a transmitter and neurotoxin depending on photo-activation. Our results show that the properties of ChR2-expressing astrocytes can be controlled by blue light exposure, and cation influx through photo-activated ChR2 might trigger functional cation influx via endogenous channels and result in the increase of glutamate release. Further, our results suggest that ChR2-expressing glial cells could become a useful tool in understanding the roles of glial cell activation and neural communication in the regulation of brain functions.

Ectopic Expression of Nolz-1 in Neural Progenitors Promotes Cell Cycle Exit/Premature Neuronal Differentiation Accompanying with Abnormal Apoptosis in the Developing Mouse Telencephalon

Nolz-1, as a murine member of the NET zinc-finger protein family, is expressed in post-mitotic differentiating neurons of striatum during development. To explore the function of Nolz-1 in regulating the neurogenesis of forebrain, we studied the effects of ectopic expression of Nolz-1 in neural progenitors. We generated the Cre-loxP dependent conditional transgenic mice in which Nolz-1 was ectopically expressed in proliferative neural progenitors. Ectopic expression of Nolz-1 in neural progenitors by intercrossing the Nolz-1 conditional transgenic mice with the nestin-Cre mice resulted in hypoplasia of telencephalon in double transgenic mice. Decreased proliferation of neural progenitor cells were found in the telencephalon, as evidenced by the reduction of BrdU−, Ki67− and phospho-histone 3-positive cells in E11.5–12.5 germinal zone of telencephalon. Transgenic Nolz-1 also promoted cell cycle exit and as a consequence might facilitate premature differentiation of progenitors, because TuJ1-positive neurons were ectopically found in the ventricular zone and there was a general increase of TuJ1 immunoreactivity in the telencephalon. Moreover, clusters of strong TuJ1-expressing neurons were present in E12.5 germinal zone. Some of these strong TuJ1-positive clusters, however, contained apoptotic condensed DNA, suggesting that inappropriate premature differentiation may lead to abnormal apoptosis in some progenitor cells. Consistent with the transgenic mouse analysis in vivo, similar effects of Nozl-1 over-expression in induction of apoptosis, inhibition of cell proliferation and promotion of neuronal differentiation were also observed in three different N18, ST14A and N2A neural cell lines in vitro. Taken together, our study indicates that ectopic expression of Nolz-1 in neural progenitors promotes cell cycle exit/premature neuronal differentiation and induces abnormal apoptosis in the developing telencephalon.

Atp8a1 deficiency is associated with phosphatidylserine externalization in hippocampus and delayed hippocampus‐dependent learning

The molecule responsible for the enzyme activity plasma membrane (PM) aminophospholipid translocase (APLT), which catalyzes phosphatidylserine (PS) translocation from the outer to the inner leaflet of the plasma membrane, is unknown in mammals. A Caenorhabditis elegans study has shown that ablation of transbilayer amphipath transporter-1 (TAT-1), which is an ortholog of a mammalian P-type ATPase, Atp8a1, causes PS externalization in the germ cells. We demonstrate here that the hippocampal cells of the dentate gyrus, and Cornu Ammonis (CA1, CA3) in mice lacking Atp8a1 exhibit a dramatic increase in PS externalization. Although their hippocampi showed no abnormal morphology or heightened apoptosis, these mice displayed increased activity and a marked deficiency in hippocampus-dependent learning, but no hyper-anxiety. Such observations indicate that Atp8a1 plays a crucial role in PM-APLT activity in the neuronal cells. In corroboration, ectopic expression of Atp8a1 but not its close homolog, Atp8a2, caused an increase in the population (V(max) ) of PM-APLT without any change in its signature parameter K(m) in the neuronal N18 cells. Conversely, expression of a P-type phosphorylation-site mutant of Atp8a1 (Atp8a1*) caused a decrease in V(max) of PM-APLT without significantly altering its K(m) . The Atp8a1*-expressing N18 cells also exhibited PS externalization without apoptosis. Together, our data strongly indicate that Atp8a1 plays a central role in the PM-APLT activity of some mammalian cells, such as the neuronal N18 and hippocampal cells.

The presence of double-stranded RNAs in Alternaria alternata Japanese pear pathotype is associated with morphological changes

Strains of the Japanese pear pathotype of Alternaria alternata were screened for double-stranded RNAs (dsRNAs). Four strains had several dsRNAs; strain N18 was associated with several dsRNAs and had impaired growth phenotypes such as irregular mycelium and abnormal pigmentation. We isolated dsRNA-cured isolates from strain N18 by single-conidium isolation. The dsRNA-cured isolates had recovered normal growth and pigmentation. Enlarged vesicles were observed in mycelial cells of the original dsRNA-carrying N18 strain. DAPI nuclear staining revealed regression of the nuclei in dsRNA-carrying N18 cells. These results indicate that the dsRNAs might have negative effects, such as apoptosis-like cell death, on the host fungus.

Expression of G protein-coupled receptors and related proteins in HEK293, AtT20, BV2, and N18 cell lines as revealed by microarray analysis

BackgroundG protein coupled receptors (GPCRs) are one of the most widely studied gene superfamilies. Thousands of GPCR research studies have utilized heterologous expression systems such as human embryonic kidney cells (HEK293). Though often treated as 'blank slates', these cell lines nevertheless endogenously express GPCRs and related signaling proteins. The outcome of a given GPCR study can be profoundly influenced by this largely unknown complement of receptors and/or signaling proteins. Little easily accessible information exists that describes the expression profiles of the GPCRs in cell lines. What is accessible is often limited in scope - of the hundreds of GPCRs and related proteins, one is unlikely to find information on expression of more than a dozen proteins in a given cell line. Microarray technology has allowed rapid analysis of mRNA levels of thousands of candidate genes, but though often publicly available, the results can be difficult to efficiently access or even to interpret.ResultsTo bridge this gap, we have used microarrays to measure the mRNA levels of a comprehensive profile of non-chemosensory GPCRs and over a hundred GPCR signaling related gene products in four cell lines frequently used for GPCR research: HEK293, AtT20, BV2, and N18.ConclusionsThis study provides researchers an easily accessible mRNA profile of the endogenous signaling repertoire that these four cell lines possess. This will assist in choosing the most appropriate cell line for studying GPCRs and related signaling proteins. It also provides a better understanding of the potential interactions between GPCRs and those signaling proteins.

Curcumin blocks migration and invasion of mouse-rat hybrid retina ganglion cells (N18) through the inhibition of MMP-2, -9, FAK, Rho A and Rock-1 gene expression.

Cancer metastasis involves multiple processes which may complicate clinical management and even lead to death. Matrix metalloproteinases (MMPs) play an important role in cancer cell invasion, metastasis and angiogenesis, depending on whether agents can inhibit MMPs which could lead to inhibition of the migration and invasion of cancer cells. Curcumin, the active constituent of the dietary spice turmeric, has potential for the prevention and therapy of cancer. However, there is no study to address the effects of curcumin on migration and invasion of mouse-rat hybrid retina ganglion cells (N18). This is the first study to explore the anti-migration and -invasion of curcumin in mouse-rat hybrid retina ganglion cells (N18) in vitro. Curcumin exerted a dose- and time-dependent inhibitory effect on the invasion and migration of N18 cells in vitro. Results from Western blotting showed that curcumin inhibited the protein levels of PKC, FAK, NF-kappaB p65 and Rho A leading to the inhibition of ERK1/2, MKK7, COX-2 and ROCK1, respectively, finally causing the inhibition of MMP-2 and -9 for the inhibition of migration and invasion of N18 cells. Moreover, this action was involved in the inhibition of gene expression of MMP-2 and -7, FAK, ROCK1 and Rho A. Overall, the above data show that the anticancer effect of curcumin also exists for the inhibition of migration and invasion in N18 cells, and that curcumin may be a powerful candidate for developing preventive agents for cancer metastasis.

Curcumin blocks migration and invasion of mouse-rat hybrid retina ganglion cells (N18) through the inhibition of MMP-2, -9, FAK, Rho A and Rock-1 gene expression

Cancer metastasis involves multiple processes which may complicate clinical management and even lead to death. Matrix metalloproteinases (MMPs) play an important role in cancer cell invasion, metastasis and angiogenesis, depending on whether agents can inhibit MMPs which could lead to inhibition of the migration and invasion of cancer cells. Curcumin, the active constituent of the dietary spice turmeric, has potential for the prevention and therapy of cancer. However, there is no study to address the effects of curcumin on migration and invasion of mouse-rat hybrid retina ganglion cells (N18). This is the first study to explore the anti-migration and -invasion of curcumin in mouse-rat hybrid retina ganglion cells (N18) in vitro. Curcumin exerted a dose- and time-dependent inhibitory effect on the invasion and migration of N18 cells in vitro. Results from Western blotting showed that curcumin inhibited the protein levels of PKC, FAK, NF-κB p65 and Rho A leading to the inhibition of ERK1/2, MKK7, COX-2 and ROCK1, respectively, finally causing the inhibition of MMP-2 and -9 for the inhibition of migration and invasion of N18 cells. Moreover, this action was involved in the inhibition of gene expression of MMP-2 and -7, FAK, ROCK1 and Rho A. Overall, the above data show that the anticancer effect of curcumin also exists for the inhibition of migration and invasion in N18 cells, and that curcumin may be a powerful candidate for developing preventive agents for cancer metastasis.

A single mutation in the Japanese encephalitis virus E protein (S123R) increases its growth rate in mouse neuroblastoma cells and its pathogenicity in mice

We previously reported that the Japanese encephalitis virus (JEV) strain Mie/41/2002 has weak pathogenicity compared with the laboratory strain Beijing-1. To identify the determinants of its growth nature and pathogenicity, we produced intertypic viruses, rJEV(EB1-M41), rJEV(nEB1-M41) and rJEV(cEB1-M41), which contained the entire, the N-terminal, and the C-terminal half, respectively, of the Beijing-1 E region in the Mie/41/2002 background. The growth of rJEV(EB1-M41) in mouse neuroblastoma N18 cells and virulence in mice were similar to those of Beijing-1. rJEV(nEB1-M41) propagated in N18 cells to the same extent as did Beijing-1. Furthermore, we produced mutant viruses with single amino acid substitutions in the N-terminal half of the Mie/41/2002 E region. A Ser-123-Arg mutation in the Mie/41/2002 E protein exhibited significantly increased growth rate in N18 cells and virulence in mice. These results indicate that the position 123 in the E protein is responsible for determining the growth properties and pathogenicity of JEV.

Curcumin induces apoptosis through FAS and FADD, in caspase-3-dependent and -independent pathways in the N18 mouse-rat hybrid retina ganglion cells

Curcumin, a naturally occurring yellow pigment isolated from turmeric, is a well known antioxidant with broad spectrum of anti-tumor activities against many human cancer cells. In this study, curcumin-induced cytotoxic effect of mouse-rat hybrid retina ganglion cells (N18) were investigated. For determining cell viability, the trypan blue exclusion and flow cytometric analysis were used. The curcumin-caused cell cycle arrest in N18 cells was examined by flow cytometry. Curcumin affect on the production of reactive oxygen species and Ca2+ and on the decrease of the level of mitochondria membrane potential (DeltaPsim) were also examined by flow cytometry. Curcumin-induced apoptosis was determined by DAPI staining and Western blotting was used for examining the apoptotic signaling proteins. Cell cycle analysis showed that G2/M phase arrest and sub-G1 occurs in N18 cells following 48 h exposure to curcumin. Curcumin also caused a marked increase in apoptosis, as characterized by DNA fragmentation (sub-G1 phase formation) and DAPI staining, and dysfunction of mitochondria, which was associated with the activation of caspase-8, -9 and -3. Curcumin also promoted the levels of Fas and FADD, Bax, cytochrome c release, but decreased the levels of Bcl-2 causing changes of DeltaPsim. Curcumin also induced endoplasmic reticulum stress in N18 cells which was based on the changes of GADD153 and GRP78 and caused Ca2+ release. Curcumin induced apoptosis through the intrinsic pathway and caspase-3-dependent and -independent pathways in N18 cells.

A genetic strategy involving a glycosyltransferase promoter and a lipid translocating enzyme to eliminate cancer cells

The most common therapeutic strategy for the treatment of cancer uses antimetabolites, which block uncontrolled division of cancer cells and kill them. However, such antimetabolites also kill normal cells, thus yielding detrimental side effects. This emphasizes the need for an alternative therapy, which would have little or no side effects. Our approach involves designing genetic means to alter surface lipid determinants that induce phagocytosis of cancer cells. The specific target of this strategy has been the enzyme activity termed aminophospholipid translocase (APLT) or flippase that causes translocation of phosphatidylserine (PS) from the outer to the inner leaflet of the plasma membrane in viable cells. Efforts to identify the enigmatic, plasma membrane APLT of mammalian cells have led investigators to some P-type ATPases, which have often proven to be the APLT of internal membranes rather than the plasma membrane. By measuring kinetic parameters for the plasma membrane APLT activity, we have shown that the P-type ATPase Atp8a1 is the plasma membrane APLT of the tumorigenic N18 cells, but not the non-tumorigenic HN2 (hippocampal neuron x N18) cells. Targeted knockdown of this enzyme causes PS externalization in the N18 cells, which would trigger phagocytic removal of these cells. But how would we specifically express the mutants or antisense Atp8a1 in the cancer cells? This has brought us to a glycosyltransferase, GnT-V, which is highly expressed in the transformed cells. By using the GnT-V promoter to drive a luciferase reporter gene we have demonstrated a dramatic increase in luciferase expression selectively in tumor cells. The described strategy could be tested for the removal of cancer cells without the use of antimetabolites that often kill normal cells.

Curcumin-Induced DNA Damage and Inhibited DNA Repair Genes Expressions in Mouse–Rat Hybrid Retina Ganglion Cells (N18)

Curcumin is reported to be a potent inhibitor of the initiation and promotion of many cancer cells. We investigated to examine whether or not curcumin induce DNA damage in mouse-rat hybrid retina ganglion cell line N18 cells. The Comet assay showed that incubation of N18 cells with 10, 25 and 30 microM of curcumin led to a longer DNA migration smear (Comet tail). The DNA gel electrophoresis showed that 20 microM of curcumin for 24 and 48 h treatment induced DNA damage and fragments in N18 cells. The real time PCR analysis showed that 20 microM of curcumin for 48 h treatment decreased ATM, ATR, BRCA1, 14-3-3sigma, DNA-PK and MGMT mRNA, and ATM and MGMT mRNA expression were inhibited in a time-dependent manner. Our results indicate that curcumin caused DNA damage and inhibited DNA repair genes which may be the factors for curcumin-inhibited cell growth.

Japanese encephalitis virus infection activates caspase-8 and -9 in a FADD-independent and mitochondrion-dependent manner

Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, replicates primarily at the endoplasmic reticulum and thereby triggers apoptosis of infected cells. This study investigated the hierarchical activation of the caspase network induced by JEV infection. It was found that JEV activated the initiators caspase-8 and -9, as well as effector caspase-3, in infected baby hamster kidney and mouse neuroblastoma (N18) cells. In neuronal N18 cells, JEV infection triggered cytochrome c release from mitochondria, which in turn activated caspase-9 and -3. Treatment of JEV-infected N18 cells with cyclosporin A or ruthenium red, which attenuate mitochondrial injuries, blocked activation of caspase-9 or -3, typifying that, in neuronal cells, this apoptosis involves the mitochondrial pathway. Alternatively, in caspase-3-deficient MCF-7 cells, JEV persisted and readily triggered a typical apoptotic response, including cytochrome c release and full activation of caspase-9 and -8 along with caspase-6, indicating that JEV did not require caspase-3 to manifest caspase-8 activation and apoptosis. Interestingly, a Fas-associated death-domain-containing protein (FADD) dominant-negative mutant, which interfered with transmission of the extracellular death signals into cells through the Fas/tumour necrosis factor (TNF) receptor, failed to block JEV-induced apoptosis and caspase-8 activation, implying that receptor oligomerization of the Fas/TNF pathway might not participate in JEV-induced apoptosis. Taken together, these results illustrate that JEV infection triggers caspase cascades involving the initiators caspase-8 and -9, probably through FADD-independent but mitochondrion-dependent pathways.

Baicalein-Induced Apoptosis via Endoplasmic Reticulum Stress Through Elevations of Reactive Oxygen Species and Mitochondria Dependent Pathway in Mouse–Rat Hybrid Retina Ganglion Cells (N18)

Studies were designed to investigate the effects of baicalein on mouse-rat hybrid retina ganglion cells (N18) to better understand its effect on apoptosis and apoptosis-related genes in vitro. Cell viability, reactive oxygen species (ROS), cytoplasmic Ca2+, mitochondrial membrane potential (MMP), apoptosis induction, and caspases-3 activity were examined by flow cytometric assay. Apoptosis-associated proteins such as p53, Bax, Bcl-2, cytochrome c, and caspase-3 were examined by Western blot. We demonstrated the increase in the levels of p53, Bax, and cytochrome c and decrease in the level of Bcl-2, which are associated with the induction of apoptotic cell death after 24 h treatment with baicalein in N18 cells. Baicalein induced an increase in the cytoplasmic levels of ROS and Ca2+ in 1 h and reached their peak at 3 h, and thereafter a loss of MMP by flow cytometry. We also demonstrated a release of the cytochrome c from mitochondria into cytosol and an activation of caspase-3, which led to the occurrence of apoptosis in N18 cells treated with baicalein by Western blot. Pretreatment was conducted with BAPTA (intracellular calcium chelator) in baicalein-treated cells, the decline of MMP was recovered, and the increase in the level of cytoplasmic Ca2+ was suppressed, and the proportion of apoptosis was also markedly diminished. In conclusion, our data suggests that oxidative stress and cellular Ca2+ modulates the baicalein-induced cell death via a Ca2+-dependent mitochondrial death pathway in N18 cells.

GMF overexpression causes apoptosis in neuroblastoma cells

In the present study we report that a replication‐defective adenovirus construct of GMF cDNA (GMF‐V) induced overexpression of GMF protein in neuroblastoma (N18) cells. Overexpression of GMF in N18 cells is correlated with the increase in toxicity and loss of cell viability. A significant increase in GSK‐3beta activity occurred after infection with GMF‐V compared to the no infection (mock) and lacZ controls. Overexpression of GMF also increased caspase‐3 activity, an early marker of apoptosis. Depletion of GMF mRNA by introducing GMF‐specific siRNA completely blocked GSK‐3beta and caspase‐3 activation whereas control scrambled siRNA had no effect. A cell‐permeable specific inhibitor of GSK‐3beta and lithium completely prevented GMF‐dependent activation of caspase‐3. Our results demonstrate that GMF is involved in the signaling leading to the activation of GSK‐3beta, caspase‐3 and inactivation of Akt in neuroblastoma cells and strongly suggest the involvement of GMF in neuro degeneration. This is the first study to demonstrate that GMF overexpression causes apoptosis through activation of the GSK‐caspase‐mediated signaling mechanism.

Glia maturation factor overexpression in neuroblastoma cells activates glycogen synthase kinase-3β and caspase-3

In the present study we report that a replication-defective adenovirus construct of GMF cDNA (GMF-V) induced overexpression of GMF protein in neuroblastoma (N18) cells caused cytotoxicity and loss of cell viability. A significant increase in activation of GSK-3β occurred after infection with GMF-V when compared with mock and lacZ controls. Overexpression of GMF also increased caspase-3 activity, an early marker of apoptosis. Depletion of GMF gene by introducing GMF-specific siRNA (GsiRNA) completely blocked both activation of GSK-3β and caspase-3 activation whereas a control scrambled siRNA (CsiRNA) had no effect. A cell-permeable peptide inhibitor of GSK-3β, and lithium completely prevented GMF-dependent activation of caspase-3. These results demonstrate that GSK-3 mediates activation of the death domain caspase by GMF overexpression. We also show that the phosphorylation of GSK-3-dependent site of Tau was a consequence of GMF-overexpression in N18 cells. Taken together our results imply that GMF is involved in the signaling leading to the activation of GSK-3β and caspase-3 in N18 cells and strongly suggest its involvement in neurodegeneration since GSK-3β is known to hyperphosphorylate tau which is associated with the neurotoxicity of neurofibrillary tangles in Alzheimer's disease.

The binding and phosphorylation of Thr231 is critical for Tau’s hyperphosphorylation and functional regulation by glycogen synthase kinase 3β

Neuropathological hallmarks of Alzheimer's disease are extracellular senile plaques and intracellular neurofibrillary lesions. The neurofibrillary lesions mainly consist of the hyperphosphorylated microtubule-associated protein Tau predominantly expressed in the axon of CNS neurons. Hyperphosphorylation of Tau negatively affects its binding to tubulin and decreases the capacity to promote microtubule assembly. Among a number of proline-directed kinases capable of phosphorylating paired helical filament-Tau, glycogen synthase kinase 3beta (GSK3beta) was first identified as a Tau protein kinase I and has been demonstrated to phosphorylate Tau both in vivo and in vitro. However, the phosphorylation mechanism of Tau by GSK3beta remained unclear. In this study, we show that the T231 is the primary phosphorylation site for GSK3beta and the Tau227-237 (AVVRTPPKSPS) derived from Tau containing T231P232 motif is identified as the GSK3beta binding site with high affinity of a Kd value 0.82 +/- 0.16 mumol/L. Our results suggest that direct binding and phosphorylation of T231P232 motif by GSK3beta induces conformational change of Tau and consequentially alters the inhibitory activity of its N-terminus that allows the phosphorylation of C-terminus of Tau by GSK3beta. Furthermore, hyperphosphorylation reduces Tau's ability to promote tubulin assembly and to form bundles in N18 cells. T231A mutant completely abolishes Tau phosphorylation by GSK3beta and retains the ability to promote tubulin polymerization and bundle formation. Taken together, these results suggest that phosphorylation of T231 by GSK3beta may play an important role in Tau's hyperphosphorylation and functional regulation.

The Role of Ca2+ on the DADS-induced Apoptosis in Mouse–Rat Hybrid Retina Ganglion Cells (N18)

Diallyl disulfide (DADS), a component of garlic, has been shown to induce growth inhibition and apoptosis in human cancer cell types. The present studies were designed to investigate the effects of DADS on mouse-rat hybrid retina ganglion cells (N18) to better understand its effect on apoptosis and apoptosis-related genes in vitro. Cell viability, cell cycle analysis, reactive oxygen species (ROS), Ca2+ production, mitochondria membrane potential, apoptosis induction, associated gene expression and caspases-3 activity were examined by flow cytometric assay and/or Western blot. After 24-h treatment with DADS, a dose- and time-dependent decrease in the viability of N18 cells was observed and the approximate IC50 was 27.6 microM. The decreased percentage of viable cells are associated with the production of ROS then followed by the production of Ca2+ which is induced by DADS. DADS induced apoptosis in N18 cells via the activation of caspase-3. DADS increased the protein levels of p53, cytochrome c and phosphated JNK within 24 h of treatment and it decreased the levels of Bcl-2 and those factors may have led to the mitochondria depolarization of N18 cells. DADS induced apoptosis were accompanied by increased levels of Ca2+ and decreased mitochondrial membrane potential which then led to release the cytochrome c, cleavage of pro-caspase-3. Deleted levels of Ca2+ by BAPTA-AM 10 microM (intracellular calcium chelator) then led to decrease DADS-induced apoptosis. Inhibition of caspase-3 activation by inhibitor (z-VAD-fmk) completely blocked DADS-induced apoptosis on N18 cells. The results indicated that oxidative stress modulates cell proliferation and Ca2+ modulates the cell death induced by DADS.