Primary Glial Cell Cultures Research Articles

Imipramine and fluoxetine inhibit LPS-induced activation and affect morphology of microglial cells in the rat glial culture

BackgroundRecent evidence has suggested that antidepressants evoke neuroprotective and immunomodulatory effects in the brain, partly at least, by inhibiting glia activation. This study has been conducted on the lipopolysaccharide (LPS)-stimulated primary rat mixed glial cell culture in order to better recognize the influence of imipramine (a tricyclic antidepressant) and fluoxetine (a selective serotonin reuptake inhibitor) on the important balance between pro- and anti-inflammatory cytokines produced by the glial cells. Moreover, microscopic observations were made to describe the morphological alterations in the studied cell cultures exposed to the drugs. MethodsThe effect of both antidepressants on TNF-α, IL-1β and IL-10 levels was determined by ELISA. The mRNA levels of mentioned cytokines were evaluated by qRT-PCR assay. Moreover, drug influence on the LPS-stimulated level of NF-κB p65 subunit in nuclear fraction was determined by the colorimetric transcription factor assay. ResultsAfter LPS-stimulation both drugs decreased concentration of TNF-α and IL-1β in culture medium and expression of TNF-α and IL-1β mRNAs in cellular extracts. They also diminished the LPS-induced nuclear translocation of NF-κB p65 subunit. In contrast, imipramine and fluoxetine induced a few-fold weaker suppressing effect on the levels of IL-10. Parallelly to the inhibition of the LPS-induced inflammatory response, the antidepressants prevented the morphological alterations of cells elicited by LPS. Moreover, in unstimulated cultures imipramine but not fluoxetine caused transformation of microglia cells into cells with neuron-like morphology. ConclusionsImipramine and fluoxetine, by modulating glia activation, may exert anti-inflammatory effects in the CNS. It also seems that microglia cells are important target particularly for imipramine.

Crosstalk between Phosphodiesterase 7 and Glycogen Synthase Kinase-3: Two Relevant Therapeutic Targets for Neurological Disorders

Chronic neuroinflammation has been increasingly recognized as a primary mechanism underlying acute brain injury and neurodegenerative diseases. Enhanced expression of diverse pro-inflammatory agents in glial cells has been shown to contribute to the cell death that takes place in these disorders. Previous data from our group have shown that different inhibitors of the cyclic adenosine monophosphate (cAMP) specific phosphodiesterase 7 (PDE7) and glycogen synthase kinase-3 (GSK-3) enzymes are potent anti-inflammatory agents in different models of brain injury. In this study, we investigated cross-talk between PDE7 and GSK-3, two relevant therapeutic targets for neurological disorders, using a chemical approach. To this end, we compared specific inhibitors of GSK-3 and PDE7 with dual inhibitors of both enzymes with regard to anti-inflammatory effects in primary cultures of glial cells treated with lipopolysaccharide. Our results show that the GSK-3 inhibitors act exclusively by inhibition of this enzyme. By contrast, PDE7 inhibitors exert their effects via inhibition of PDE7 to increase intracellular cAMP levels but also through indirect inhibition of GSK-3. Activation of protein kinase A by cAMP results in phosphorylation of Ser9 of GSK-3 and subsequent inhibition. Our results indicate that the indirect inhibition of GSK-3 by PDE7 inhibitors is an important mechanism that should be considered in the future development of pharmacological treatments.

Glial Cell Response to 3,4-(±)-Methylenedioxymethamphetamine and Its Metabolites

3,4-(±)-Methylenedioxymethamphetamine (MDMA) and 3,4-(±)-methylenedioxyamphetamine (MDA), a primary metabolite of MDMA, are phenylethylamine derivatives that cause serotonergic neurotoxicity. Although several phenylethylamine derivatives activate microglia, little is known about the effects of MDMA on glial cells, and evidence of MDMA-induced microglial activation remains ambiguous. We initially determined microglial occupancy status of the parietal cortex in rats at various time points following a single neurotoxic dose of MDMA (20mg/kg, SC). A biphasic microglial response to MDMA was observed, with peak microglial occupancy occurring 12- and 72-h post-MDMA administration. Because direct injection of MDMA into the brain does not produce neurotoxicity, the glial response to MDMA metabolites was subsequently examined in vivo and in vitro. Rats were treated with MDA (20mg/kg, SC) followed by ex vivo biopsy culture to determine the activation of quiescent microglia. A reactive microglial response was observed 72 h after MDA administration that subsided by 7 days. In contrast, intracerebroventricular (ICV) administration of MDA failed to produce a microglial response. However, thioether metabolites of MDA derived from α-methyldopamine (α-MeDA) elicited a robust microglial response following icv injection. We subsequently determined the direct effects of various MDMA metabolites on primary cultures of E18 hippocampal mixed glial and neuronal cells. 5-(Glutathion-S-yl)-α-MeDA, 2,5-bis-(glutathion-S-yl)-α-MeDA, and 5-(N-acetylcystein-S-yl)-α-MeDA all stimulated the proliferation of glial fibrillary acidic protein-positive astrocytes at a dose of 10 µM. The findings indicate that glial cells are activated in response to MDMA/MDA and support a role for thioether metabolites of α-MeDA in the neurotoxicity.

GLAST/EAAT1 regulation in cultured Bergmann glia cells: Role of the NO/cGMP signaling pathway

Glutamate, the major excitatory amino acid, activates a wide variety of signal transduction cascades. Ionotropic and metabotropic glutamate receptors are critically involved in long-term synaptic changes, although recent findings suggest that the electrogenic Na+-dependent glutamate transporters, responsible for its removal from the synaptic cleft participate in the signaling transactions triggered by this amino acid. Glutamate transporters are profusely expressed in glia therefore most of its uptake occurs in this cellular compartment. In the cerebellar cortex, Bergmann glial cells enwrap glutamatergic synapses and participate in the recycling of its neurotransmitter through the glutamate/glutamine shuttle. It has long been acknowledged that glutamatergic transmission in the cerebellar molecular layer results in cGMP accumulation within Bergmann glia cells. In this context, we decided to investigate a plausible role of the nitric oxide/cGMP-signaling pathway in the regulation of Bergmann glia glutamate transporters. To this end, the well-established model of primary cultures of chick cerebellar Bergmann glial cells was used. Confluent monolayers were exposed to the nitric oxide donor, sodium nitroprusside, or to the non-hydrolysable cGMP analog dbcGMP and the [3H] D-aspartate uptake activity measured. An increase in uptake activity, related to an augmentation in VMax, was detected with both treatments. The signaling cascade includes NO/cGMP/PKG and Ca2+ influx through the Na+/Ca2+ exchanger and might be related to the plasma membrane glutamate transporters turnover. Interestingly enough, an inhibitor of the cGMP dependent protein kinase was capable to abolish the sodium nitroprusside induced Ca2+ influx. These results provide an insight into the physiological role of cGMP in the cerebellum.

Prolonged Minocycline Treatment Impairs Motor Neuronal Survival and Glial Function in Organotypic Rat Spinal Cord Cultures

BackgroundMinocycline, a second-generation tetracycline antibiotic, exhibits anti-inflammatory and neuroprotective effects in various experimental models of neurological diseases, such as stroke, Alzheimer’s disease, amyotrophic lateral sclerosis and spinal cord injury. However, conflicting results have prompted a debate regarding the beneficial effects of minocycline.MethodsIn this study, we analyzed minocycline treatment in organotypic spinal cord cultures of neonatal rats as a model of motor neuron survival and regeneration after injury. Minocycline was administered in 2 different concentrations (10 and 100 µM) at various time points in culture and fixed after 1 week.ResultsProlonged minocycline administration decreased the survival of motor neurons in the organotypic cultures. This effect was strongly enhanced with higher concentrations of minocycline. High concentrations of minocycline reduced the number of DAPI-positive cell nuclei in organotypic cultures and simultaneously inhibited microglial activation. Astrocytes, which covered the surface of the control organotypic cultures, revealed a peripheral distribution after early minocycline treatment. Thus, we further analyzed the effects of 100 µM minocycline on the viability and migration ability of dispersed primary glial cell cultures. We found that minocycline reduced cell viability, delayed wound closure in a scratch migration assay and increased connexin 43 protein levels in these cultures.ConclusionsThe administration of high doses of minocycline was deleterious for motor neuron survival. In addition, it inhibited microglial activation and impaired glial viability and migration. These data suggest that especially high doses of minocycline might have undesired affects in treatment of spinal cord injury. Further experiments are required to determine the conditions for the safe clinical administration of minocycline in spinal cord injured patients.

Abstract 1442: PDGFRβ activation defines a subset of astrocytes in the neuroinflammatory microenvironment of breast cancer brain metastasis, inhibitable by pazopanib.

Abstract Brain metastases occur in approximately 35% of metastatic breast cancer patients whose tumors overexpress HER2. Brain colonization of cancer cells occurs in a unique environment, containing microglia, oligodendrocytes, astrocytes and neurons. While a neuroinflammatory response has been documented in brain metastasis, its contribution to cancer progression and therapy remains poorly understood. Using a model system to study experimental brain metastasis of breast cancer, we intensively characterized the brain metastatic microenvironment of a brain tropic, HER2-transfected MDA-MB-231 human breast carcinoma subline (231-BR-HER2). The 231-BR-HER2 cell line was injected into the left cardiac ventricle of immunocompromised mice; mice were treated with vehicle, 30mg/kg or 100mg/kg pazopanib twice a day beginning on day 3 post-injection, for 4 weeks. Pazopanib, a multispecific tyrosine kinase inhibitor targeting VEGFR-1, -2, and -3, PDGFR-α and β, and c-kit, directly targeted tumor cells through the disruption of B-Raf pathway, prevents the outgrowth of 231-BR-HER2 large brain metastases by 73% (p<0.0001). Here we evaluated the effect of pazopanib on the brain micro-environment microenvironment. A novel subpopulation of metastasis-associated astrocytes expressing phosphorylated (Y751) PDGFRβ was identified surrounding brain metastases. This subpopulation of p751-PDGFRβ + astrocytes was also identified in human brain metastases from five different craniotomy specimens. Expression of p751-PDGFRβ was studied in primary cultures of astrocyte-enriched glial cells. p751-PDGFRβ expression was increased in response to soluble factors from cultured breast cancer cells, and was inhibited by pazopanib treatment. In the mouse mode, pazopanib treatment resulted in a 70% (p=0.023) decrease of the p751-PDGFRβ+ astrocyte population, at the lowest dose of 30mg/kg, twice daily. In contrast, pazopanib did not have any effect on microglia expression. Collectively, the data identify a new subpopulation of activated astrocytes in the perivascular stage of subclinical brain metastases and demonstrate that they are inhibitable by pazopanib, suggesting its potential to prevent the development of brain metastases from breast cancer patients. Citation Format: Brunilde M. Gril, Diane Palmieri, Yong Qian, David J. Liewehr, Seth M. Steinberg, Talha Anwar, Zoraida Andreu, Daniel Masana, Patricia S. Steeg, Fernando Vidal-Vanaclocha. PDGFRβ activation defines a subset of astrocytes in the neuroinflammatory microenvironment of breast cancer brain metastasis, inhibitable by pazopanib. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1442. doi:10.1158/1538-7445.AM2013-1442

Pazopanib Inhibits the Activation of PDGFRβ-Expressing Astrocytes in the Brain Metastatic Microenvironment of Breast Cancer Cells

Brain metastases occur in more than one-third of metastatic breast cancer patients whose tumors overexpress HER2 or are triple negative. Brain colonization of cancer cells occurs in a unique environment, containing microglia, oligodendrocytes, astrocytes, and neurons. Although a neuroinflammatory response has been documented in brain metastasis, its contribution to cancer progression and therapy remains poorly understood. Using an experimental brain metastasis model, we characterized the brain metastatic microenvironment of brain tropic, HER2-transfected MDA-MB-231 human breast carcinoma cells (231-BR-HER2). A previously unidentified subpopulation of metastasis-associated astrocytes expressing phosphorylated platelet-derived growth factor receptor β (at tyrosine 751; p751-PDGFRβ) was identified around perivascular brain micrometastases. p751-PDGFRβ(+) astrocytes were also identified in human brain metastases from eight craniotomy specimens and in primary cultures of astrocyte-enriched glial cells. Previously, we reported that pazopanib, a multispecific tyrosine kinase inhibitor, prevented the outgrowth of 231-BR-HER2 large brain metastases by 73%. Here, we evaluated the effect of pazopanib on the brain neuroinflammatory microenvironment. Pazopanib treatment resulted in 70% (P = 0.023) decrease of the p751-PDGFRβ(+) astrocyte population, at the lowest dose of 30 mg/kg, twice daily. Collectively, the data identify a subpopulation of activated astrocytes in the subclinical perivascular stage of brain metastases and show that they are inhibitable by pazopanib, suggesting its potential to prevent the development of brain micrometastases in breast cancer patients.

Prenatal Cocaine Exposure Inhibits Neurite Outgrowth Through RAGE Pathway and Activates Altered Expression of Pro‐addictive Cytokines in Primary Neuronal and Glial Cell Cultures

BackgroundThe prevalence of neonates exposed to cociane continues to be an endemic within the U.S. An overwhelming amount of evidence has shown that prenatal cocaine exposure is associated with numerous neurological and behavioral abnormalities, as well as structural damage and a deficiency in neurodevelopment with no established underlying mechanisms.PurposeThe present study was designed to investigate biochemical events coupled to cocaine‐induced cytotoxicity of neurons and glial cells seen in exposed offspring.Research Approach:Time pregnant Sprague‐Dawley rats were treated with 40 mg/kg of cocaine HCl on gestational day (GD) 10–21. On postnatal day (PND) 3 the brain tissue of the pups was harvested to yield mixed neuronal and glial cell cultures. A cytokine antibody array determined a decrease in RAGE expression and an increase in TIMP‐1 expression in prenatally exposed pups. Immunocytochemistry (ICC) showed decreased neurite outgrowth in prenatally exposed neurons. ICC also determined there was an increase in dopamine (DA) in prenatally exposed primary cell cultures indicating the presence of DA receptors on astrocytes and oligodendrocytes.. Western Blot analysis quantitatively determined a variation of amphoterin (HMGB1) which is necessary for RAGE activation and pro‐inflammatory cytokine matrix metalloproteinase 9 (MMP‐9) protein expressions between the control and cocaine treated pups.ConclusionThrough in vivo and in vitro studies exposure to cocaine during gestation leads to marked alterations in morphology and function of primary neuronal and glial cell cultures. These findings suggest that exposure to cocaine in utero can ultimately increase the incidence of addiction and development of neurodegenerative diseases and neuropathologies in the affected offspring.

Expression and Function of Psoriasin (S100A7) and Koebnerisin (S100A15) in the Brain

The expression and function of psoriasin in the brain have been insufficiently characterized. Here, we show the induction of psoriasin expression in the central nervous system (CNS) after bacterial and viral stimulation. We used a pneumococcal meningitis in vivo model that revealed S100A15 expression in astrocytes and meningeal cells. These results were confirmed by a cell-based in vivo assay using primary rat glial and meningeal cell cultures. We investigated psoriasin expression in glial and meningeal cells using polyinosinic-polycytidylic acid, a synthetic analog of double-stranded RNA that mimics viral infection. Furthermore, previous results showed that antimicrobial peptides have not only bactericidal but also immunomodulatory functions. To test this statement, we used recombinant psoriasin as a stimulus. Glial and meningeal cells were treated with recombinant psoriasin at concentrations from 25 to 500 ng/ml. Treated microglia and meningeal cells showed phosphorylation of the extracellular signal-regulated kinase 1 (ERK1)/ERK2 (ERK1/2) signal transduction pathway. We demonstrated that this activation of ERK depends on RAGE, the receptor for advanced glycation end products. Furthermore, microglia cells treated with recombinant psoriasin change their phenotype to an enlarged shape. In conclusion, our results indicate an occurrence of psoriasin in the brain. An involvement of psoriasin as an antimicrobial protein that modulates the innate immune system after bacterial or viral stimulation is possible.

Cuprizone [Bis(Cyclohexylidenehydrazide)] is Selectively Toxic for Mature Oligodendrocytes

Cuprizone [bis(cyclohexylidenehydrazide)]-induced toxic demyelination is an experimental animal model commonly used to study de- and remyelination in the central nervous system. In this model, mice are fed with the copper chelator cuprizone which leads to oligodendrocyte death with subsequent demyelination. The underlying mechanisms of cuprizone-induced oligodendrocyte death are still unknown, and appropriate in vitro investigations to study these mechanisms are not available. Thus, we studied cuprizone effects on rat primary glial cell cultures and on the neuroblastoma cell line SH-SY5Y. Treatment of cells with different concentrations of cuprizone failed to show effects on the proliferation and survival of SH-SY5Y cells, microglia, astrocytes, and oligodendrocyte precursor cells (OPC). In contrast, differentiated mature oligodendrocytes (OL) were found to be significantly affected by cuprizone treatment. This was accompanied by a reduced mitochondrial potential in cuprizone-treated OL. These results demonstrate that the main toxic target for cuprizone is mature OL, whilst other glial cells including OPC are not or only marginally affected. This explains the selective demyelination induced by cuprizone in vivo.

Effects of IFN-γ, TNF-α, IL-10 and TGF-β on Neospora caninum infection in rat glial cells

Neospora caninum causes abortion in cattle and neurological disorders in dogs. The immunological response to this parasite has been described as predominantly of the Th1 type. However, infected primary glial cell cultures release IL-10 and IL-6 but not IFN-γ. This suggests a rather protective response of the glia to avoid inflammatory damage of the nervous tissue. In this study, we investigated the effects of pro-inflammatory cytokines in primary mixed cultures of rat astrocytes and microglia infected with N. caninum. The cells were treated with either IFN-γ, TNF-α, anti-IL-10 or anti-TGF-β antibodies and were infected with parasite tachyzoites 24h later. Trypan Blue exclusion and MTT assays were performed to test cell viability. It was observed that cytokines, antibody treatment and in vitro infection did not reveal significant cell death in the various culture conditions. Treatment with 50, 150 and 300 IU/mL of either IFN-γ or TNF-α reduced tachyzoites numbers in cultures by 36.7%, 54.8% and 63.8% for IFN-γ and by 27.6%, 38.4% and 29.7% for TNF-α, respectively. In the absence of IL-10 and TGF-β, tachyzoite numbers were reduced by 52.8% and 41.5%, respectively. While IFN-γ (150 and 300 IU/mL) increased the nitrite levels in uninfected cells, parasite infection seemed to reduce the nitrite levels, and this reduction was more expressive in IFN-γ-infected cells, thereby suggesting an inhibitory effect on its production. However, TNF-α, IL-10 and TGF-β did not affect the nitrite levels. Basal PGE(2) levels also increased by 17% and 25%; 78% and 13% in uninfected and infected cells treated with IFN-γ or anti-TGF-β, respectively. Nevertheless, the antibody neutralization of IL-10 reduced PGE(2) release significantly. These results highlight the possibility of a combined effect between the IFN-γ and parasite evasion strategies and show that the IFN-γ, TNF-α, IL-10 and TGF-β cytokines participate in parasite proliferation control mechanisms.

Asymmetric Production of Nitric Oxide in Mouse Primary Cortical Mixed Glial Cell Cultures Treated With Lipopolysaccharide

Activated glial cells produce many toxic molecules, including cytokines and nitric oxide (NO). There is evidence that excess NO production plays a key role in neuronal cell death. Previous research has demonstrated that cortical glial cells from the left and right cortices of the brain secrete cytokines asymmetrically. However, no evidence to date exists about whether glial cell-produced NO is produced asymmetrically as well. The results of this study show that NO production and inducible NO synthase gene expression are both significantly higher in the right hemisphere-derived mixed glial cell compared with cultures derived from the left.

Grafting of Cell-Penetrating Peptide to Receptor-Targeted Liposomes Improves their Transfection Efficiency and Transport across Blood–Brain Barrier Model

We report bifunctional liposomal delivery system, combining transferrin (Tf)-mediated receptor targeting and poly-L-arginine (PR)-facilitated cell penetration, which overcomes the drawback of saturation of delivery. PR was conjugated to the distal end of distearoyl phosphoethanolamine-polyethylene glycol (PEG) 2000 and was incorporated with other phospholipids in chloroform/methanol (2:1) to form PR liposomes using thin-film hydration technique. Tf-PEG phospholipid micelles were incorporated into PR liposomes using postinsertion technique to form Tf-PR liposomes. The bifunctional liposomes demonstrated significantly (p < 0.05) higher cellular uptake by brain endothelial cells (bEnd.3) and about eightfold higher transfection in primary culture of glial cells as compared with the Tf liposomes. Cell viabilities of Tf-conjugated and bifunctional liposomes were not markedly different; however, transport across in vitro blood-brain barrier model improved considerably after dual modification. The study underlines the potential of bifunctional liposomes as high-efficiency and low-toxicity gene delivery system for the treatment of central nervous system disorders.

Acetaminophen induces oligodendrocyte precursor cell death and reactive astroglia in a primary mixed glial cell culture

Brain damage in acetaminophen (AP) overdose is associated with liver failure but its direct effects has not been evaluated.AimTo study the effect of toxic and non‐toxic doses of AP on astrocyte and oligodendrocyte precursor cell (OPC) viability in a primary mixed glial cell culture.MYMPrimary cultures of mixed glial cells were carried out according to McCarthy and de Vellis (1980). Cells were treated with vehicle (DMSO) or AP (1 and 20 mM). After 48 hs cell viability was assessed; astrocyte marker (GFAP) and OPC marker (PDGFR‐alpha) expression was evaluated by western‐blot (WB) and immunocytochemistry.ResultsThe 1 mM dose of AP did not produce significant differences in cell viability, while 20 mM exposure decreased in 40% cell viability (P&lt;0.001). The 20 mM dose produced the death of the 90% of the OPC in the culture and a decrease of 89% of PDGFR‐alpha expression (P&lt;0.001) with an increase in GFAP optical density/cell and WB expression (47% and 97% respectively) (P&lt;0.05). The 1mM dose did not produce significant changes in GFAP but produce a 25% significant decreased in PDGFR‐alpha expression (p&lt;0.05).ConclusionAP produces direct toxic effects on glial cells characterized by oligodendrocyte death and the induction of reactive astroglia.

In vivo study: Developmental alterations in primary rat neuronal and glial cell cultures following prenatal cocaine exposure

Evidence has shown that prenatal cocaine exposure to the developing fetus is associated with neurological and behavioral abnormalities. These alterations are attributed to structural damage in the brain as well as neurodevelopment with no significant underlying mechanisms. Since the effects of prenatal cocaine exposure on glial and neuronal development are largely unclear, there is a need to establish an appropriate animal model to evaluate cocaine's antecedent role in the occurrence of neuronal and glial cell maturation. The present study addresses the hypothesis that chronic prenatal cocaine exposure alters the maturation and function of neurons and glial cells in the offspring. Timed pregnant Sprague‐Dawley rats were treated with 40 mg/kg of cocaine on gestational day 10–21. The brain tissue of the pups was harvested to yield pure neuronal and glial cell cultures. ICC analysis confirmed the successful isolation of primary neurons and glial cells, as well as morphological differences between the control and treatment pups among these cell types. Western Blot analysis determined a variation of protein expression. A cytokine array was used to identify cytokine expression levels. These studies suggest that cocaine alters growth, maturation, and function of growing neuronal and glial cell cultures. Excessive glial cell activation can cause harm to neurons in regards to their development and plasticity.

Multifunctionalized CMCht/PAMAM Dendrimer Nanoparticles Modulate the Cellular Uptake by Astrocytes and Oligodendrocytes in Primary Cultures of Glial Cells

The efficiency of the treatments involving CNS disorders is commonly diminished by the toxicity, reduced stability and lack of targeting of the administered neuroactive compounds. In this study, we have successfully multifunctionalized CMCht/PAMAM dendrimer nanoparticles by coupling the CD11b antibody and loading MP into the nanoparticles. The modification of the new antibody-conjugated nanoparticles was confirmed by S-TEM observation and (1) H NMR and FTIR spectroscopy. Cytotoxicity assays revealed that the conjugates did not affect the viability of both primary cultures of glial and microglial cells. Trace analyses of FITC-labelled nanoparticles revealed that the uptake of antibody-conjugated nanoparticles was conserved in microglial cells but significantly decreased in astrocytes and oligodendrocytes. Thus, this study demonstrates that antibody conjugation contributes to a modulation of the internalization of these nanocarriers by different cell types, which might be of relevance for specific targeting of CNS cell populations.

Normalization of Cholesterol Homeostasis by 2-Hydroxypropyl-β-cyclodextrin in Neurons and Glia from Niemann-Pick C1 (NPC1)-deficient Mice

Niemann-Pick C (NPC) disease is an inherited, progressive neurodegenerative disorder caused by mutations in the NPC1 or NPC2 gene that result in an accumulation of unesterified cholesterol in late endosomes/lysosomes (LE/L) and impaired export of cholesterol from LE/L to the endoplasmic reticulum (ER). Recent studies demonstrate that administration of cyclodextrin (CD) to Npc1(-/-) mice eliminates cholesterol sequestration in LE/L of many tissues, including the brain, delays neurodegeneration, and increases lifespan of the mice. We have now investigated cholesterol homeostasis in NPC1-deficient cells of the brain in response to CD. Primary cultures of neurons and glial cells from Npc1(-/-) mice were incubated for 24 h with 0.1 to 10 mm CD after which survival and cholesterol homeostasis were monitored. Although 10 mm CD was profoundly neurotoxic, and altered astrocyte morphology, 0.1 and 1 mm CD were not toxic but effectively mobilized stored cholesterol from the LE/L as indicated by filipin staining. However, 0.1 and 1 mm CD altered cholesterol homeostasis in opposite directions. The data suggest that 0.1 mm CD releases cholesterol trapped in LE/L of neurons and astrocytes and increases cholesterol availability at the ER, whereas 1 mm CD primarily extracts cholesterol from the plasma membrane and reduces ER cholesterol. These studies in Npc1(-/-) neurons and astrocytes establish a dose of CD (0.1 mm) that would likely be beneficial in NPC disease. The findings are timely because treatment of NPC disease patients with CD is currently being initiated.

Role of Retinal Glial Cell Glutamate Transporters in Retinal Ganglion Cell Survival Following Stimulation of NMDA Receptor

Purpose: To investigate the role of glutamate transporters (GLTs)in retinal glial cells that were treated with N-methyl-D-aspartate (NMDA), in retinal ganglion cell (RGC) survival.Methods: Primary cultures of retinal glial cells or RGCs from 3-day-old Sprague-Dawley rats were employed in the present study. Retinal glial cells were treated with NMDA and changes in GLT mRNA and protein expression were analyzed. The effects of pretreating retinal glial cells with the GLAST-specific inhibitor, rottlerin (ROT), and the GLT-1-specific inhibitor, dihydrokainic acid (DHK), on RGC survival were investigated under exposure to NMDA. The amount of glutamate in the culture medium of retinal glial cells was measured by high-performance liquid chromatography.Results: NMDA treatment increased GLAST and GLT-1 expression. GLAST and GLT-1 mRNA expression increased by 2.94-fold and 3.36-fold at 12 h after treatment with the highest concentration of NMDA (33 mM), and by 1.41-fold and 1.39-fold at 24 h, respectively. GLT-1 and GLAST protein expression also increased. MK801, an NMDA-receptor antagonist, inhibited the NMDA-induced upregulation of GLT mRNA expression. Co-culture with retinal glial cells increased the survival rate of RGCs. ROT decreased the survival rate of RGCs, whereas DHK significantly increased the survival rate of RGCs treated with 33 mM NMDA. NMDA treatment reduced the total amount of glutamate in the culture medium, particularly when 33 mM NMDA was added to the medium. ROT pretreatment increased the amount of glutamate in the culture medium, whereas DHK pretreatment decreased it.Conclusion: GLAST and GLT-1 may have different roles in the survival of RGCs mediated by retinal glial cells. These results suggest that the NMDA-associated induction of GLTs plays an important role in RGC survival.

Signaling through EAAT-1/GLAST in cultured Bergmann glia cells

Glutamate, the major excitatory amino acid, activates a wide variety of signal transduction cascades. Synaptic plasticity relies on activity-dependent differential protein expression. Ionotropic and metabotropic glutamate receptors have been critically involved in long-term synaptic changes, although recent findings suggest that the electrogenic Na +-dependent glutamate transporters, responsible of its removal from the synaptic cleft, participate in glutamate-induced signaling. Transporter proteins are expressed in neurons and glia cells albeit most of the glutamate uptake occurs in the glial compartment. Within the cerebellum, Bergmann glial cells are close to glutamatergic synapses and participate actively in the recycling of glutamate through the glutamate/glutamine shuttle. In this context, we decided to investigate a plausible role of Bergmann glia glutamate transporters as signaling entities. To this end, primary cultures of chick cerebellar Bergmann glial cells were exposed to d-aspartate ( d-Asp) and other transporter ligands and the serine 2448 phosphorylation pattern of the master regulator of protein synthesis, namely the mammalian target of rapamycin (mTOR), determined. An increase in mTOR phosphorylation and activity was detected. The signaling cascade included Ca 2+ influx, activation of the phosphatidylinositol 3-kinase and protein kinase B. Furthermore, transporter signaling resulted also in an increase in activator protein-1 (AP-1) binding to DNA and the up-regulation of the transcription of an AP-1 driven gene construct. These results add a novel mediator of the glutamate effects at the translational and transcriptional levels and further strengthen the notion of the critical involvement of glia cells in synaptic function.

Cannabinoid receptor agonists modulate oligodendrocyte differentiation by activating PI3K/Akt and the mammalian target of rapamycin (mTOR) pathways

The endogenous cannabinoid system participates in oligodendrocyte progenitor differentiation in vitro. To determine the effect of synthetic cannabinoids on oligodendrocyte differentiation, we exposed differentiating cultures of oligodendrocytes with cannabinoid CB(1), CB(2) and CB(1)/CB(2) receptor agonists and antagonists. The response of the PI3K/Akt and the mammalian target of rapamycin (mTOR) signalling pathways were studied as effectors of cannabinoid activity. Purified oligodendrocyte progenitor cells (OPC) obtained from primary mixed glial cell cultures were treated for 48 h with CB(1), CB(2) and CB(1) /CB(2) receptor agonists (ACEA, JWH133 and HU210, respectively) in the presence or absence of the antagonists AM281 (CB(1) receptor) and AM630 (CB(2) receptor). Moreover, inhibitors of the phosphatidylinositol 3-kinase (PI3K)/Akt and mTOR pathways (LY294002 and rapamycin, respectively) were used to study the involvement of these pathways on cannabinoid-induced OPC maturation. ACEA, JWH133 and HU-210 enhanced OPC differentiation as assessed by the expression of stage specific antigens and myelin basic protein (MBP). Moreover, this effect was blocked by the CB receptor antagonists. ACEA, JWH133 and HU210 induced a time-dependent phosphorylation of Akt and mTOR, whereas the inhibitors of PI3K/Akt (LY294002) or of mTOR (rapamycin) reversed the effects of HU-210 on oligodendrocyte differentiation and kinase activation. Activation of cannabinoid CB(1) or CB(2) receptors with selective agonists accelerated oligodendrocyte differentiation through the mTOR and Akt signalling pathways.