Ethanol alters astrocyte development: a study of critical periods using primary cultures

Astrocyte DNA damage and response upon acute exposure to ethanol and corticosterone

Introduction: Astrocytes are the glial cells responsible for brain homeostasis, but if injured, they could damage neural cells even deadly. Genetic damage, DNA damage response (DDR), and its downstream cascades are dramatic events poorly studied in astrocytes. Hypothesis and methods: We propose that 1 h of 400 mmol/L ethanol and/or 1 μmol/L corticosterone exposure of cultured hippocampal astrocytes damages DNA, activating the DDR and eliciting functional changes. Immunolabeling against γH2AX (chromatin DNA damage sites), cyclin D1 (cell cycle control), nuclear (base excision repair, BER), and cytoplasmic (anti-inflammatory functions) APE1, ribosomal nucleolus proteins together with GFAP and S100β plus scanning electron microscopy studies of the astrocyte surface were carried out. Results: Data obtained indicate significant DNA damage, immediate cell cycle arrest, and BER activation. Changes in the cytoplasmic signals of cyclin D1 and APE1, nucleolus number, and membrane-attached vesicles strongly suggest a reactivity like astrocyte response without significant morphological changes. Discussion: Obtained results uncover astrocyte genome immediate vulnerability and DDR activation, plus a functional response that might in part, be signaled through extracellular vesicles, evidencing the complex influence that astrocytes may have on the CNS even upon short-term aggressions.

Impact of alcohol exposure on neural development and network formation in human cortical organoids

Prenatal alcohol exposure is the foremost preventable etiology of intellectual disability and leads to a collection of diagnoses known as Fetal Alcohol Spectrum Disorders (FASD). Alcohol (EtOH) impacts diverse neural cell types and activity, but the precise functional pathophysiological effects on the human fetal cerebral cortex are unclear. Here, we used human cortical organoids to study the effects of EtOH on neurogenesis and validated our findings in primary human fetal neurons. EtOH exposure produced temporally dependent cellular effects on proliferation, cell cycle, and apoptosis. In addition, we identified EtOH-induced alterations in post-translational histone modifications and chromatin accessibility, leading to impairment of cAMP and calcium signaling, glutamatergic synaptic development, and astrocytic function. Proteomic spatial profiling of cortical organoids showed region-specific, EtOH-induced alterations linked to changes in cytoskeleton, gliogenesis, and impaired synaptogenesis. Finally, multi-electrode array electrophysiology recordings confirmed the deleterious impact of EtOH on neural network formation and activity in cortical organoids, which was validated in primary human fetal tissues. Our findings demonstrate progress in defining the human molecular and cellular phenotypic signatures of prenatal alcohol exposure on functional neurodevelopment, increasing our knowledge for potential therapeutic interventions targeting FASD symptoms.

Potential of Glial Cell Modulators in the Management of Substance Use Disorders

The pervasive and devastating nature of substance use disorders underlies the need for the continued development of novel pharmacotherapies. We now know that glia play a much greater role in neuronal processes than once believed.  The various types of glial cells (e.g., astrocytes, microglial, oligodendrocytes) participate in numerous functions that are crucial to healthy central nervous system function. Drugs of abuse have been shown to interact with glia in ways that directly contribute to the pharmacodynamic effects responsible for their abuse potential. Through their effect upon glia, drugs of abuse also alter brain function resulting in behavioral changes associated with substance use disorders. Therefore, drug-induced changes in glia and inflammation within the central nervous system (neuroinflammation) have been investigated to treat various aspects of drug abuse and dependence. This article presents a brief overview of the effects of each of the major classes of addictive drugs on glia. Next, the paper reviews the pre-clinical and clinical studies assessing the effects that glial modulators have on abuse-related behavioral effects, such as pleasure, withdrawal, and motivation. There is a strong body of pre-clinical literature demonstrating the general effectiveness of several glia-modulating drugs in models of reward and relapse. Clinical studies have also yielded promising results, though not as robust. There is still much to disentangle regarding the integration between addictive drugs and glial cells. Improved understanding of the relationship between glia and the pathophysiology of drug abuse should allow for more precise exploration in the development and testing of glial-directed treatments for substance use disorders.

Optic Nerve Hypoplasia in Fetal Alcohol Syndrome: An Update

Optic nerve hypoplasia was detected in up to one half of a group of Swedish children born to alcoholic mothers. Using an experimental model of pre- and postnatal alcohol exposure in rats fed a liquid diet, reduced optic nerve size from gestational day 21 (294 ± 26×102 μm2 vs 502 ± 16×102 μm2; n=6; p≤0.001) to later in development was observed as a result of the daily mean blood alcohol levels achieved in dams and their offspring. Altered glial cells and degenerating and atrophic optic axons, myelin sheaths and ganglion cells were frequent in the alcohol-exposed optic nerves.

Smaller optic nerve (1,918 ± 61×102 μm2 vs 2.195 ± 40×102 μm2; n=4; p≤0.001), reduced gaglion cell and axonal densities, and ultrastructural damage to the macroglial cells and myelin sheaths were also detected in the treated group. All these changes remained in the retina and optic nerve of the oldest rats, as a consequence of the long-lasting effects of prenatal alcohol exposure. In summary, alcohol as a major teratogenic agent may induce dysmorphogenesis and irremediable damage to the retina and optic nerve, which frequently manifests itself as hypoplastic optic nerve.

Glial and Neuroimmune Mechanisms as Critical Modulators of Drug Use and Abuse

Drugs of abuse cause persistent alterations in synaptic plasticity that may underlie addiction behaviors. Evidence suggests glial cells have an essential and underappreciated role in the development and maintenance of drug abuse by influencing neuronal and synaptic functions in multifaceted ways. Microglia and astrocytes perform critical functions in synapse formation and refinement in the developing brain, and there is growing evidence that disruptions in glial function may be implicated in numerous neurological disorders throughout the lifespan. Linking evidence of function in health and under pathological conditions, this review will outline the glial and neuroimmune mechanisms that may contribute to drug-abuse liability, exploring evidence from opioids, alcohol, and psychostimulants. Drugs of abuse can activate microglia and astrocytes through signaling at innate immune receptors, which in turn influence neuronal function not only through secretion of soluble factors (eg, cytokines and chemokines) but also potentially through direct remodeling of the synapses. In sum, this review will argue that neural-glial interactions represent an important avenue for advancing our understanding of substance abuse disorders.

Alcohol Teratogenesis: Mechanisms of Damage and Strategies for Intervention

There are multiple mechanisms by which alcohol can damage the developing brain, but the type of damage induced will depend on the amount and developmental timing of exposure, along with other maternal and genetic factors. This article reviews current perspectives on how ethanol can produce neuroteratogenic effects by its interactions with molecular regulators of brain development. The current evidence suggests that alcohol produces many of its damaging effects by exerting specific actions on molecules that regulate key developmental processes (e.g., L1 cell adhesion molecule, alcohol dehydrogenase, catalase), interfering with the early development of midline serotonergic neurons and disrupting their regulatory-signaling function for other target brain structures, interfering with trophic factors that regulate neurogenesis and cell survival, or inducing excessive cell death via oxidative stress or activation of caspase-3 proteases. The current understanding of pathogenesis mechanisms suggests several strategic approaches to develop rational molecular prevention. However, the development of behavioral and biologic treatments for alcohol-affected children is crucial because it is unlikely that effective delivery of preventative interventions can realistically be achieved in ways to prevent prenatal damage in at-risk pregnancies. Toward that end, behavioral training that promotes experience-dependent neuroplasticity has been effective in a rat model of cerebellar damage induced by alcohol exposure during the period of brain development that is comparable to that of the human third trimester.

Transient exposure to ethanol during zebrafish embryogenesis results in defects in neuronal differentiation: an alternative model system to study FASD

Background

The exposure of the human embryo to ethanol results in a spectrum of disorders involving multiple organ systems, including the impairment of the development of the central nervous system (CNS). In spite of the importance for human health, the molecular basis of prenatal ethanol exposure remains poorly understood, mainly to the difficulty of sample collection. Zebrafish is now emerging as a powerful organism for the modeling and the study of human diseases. In this work, we have assessed the sensitivity of specific subsets of neurons to ethanol exposure during embryogenesis and we have visualized the sensitive embryonic developmental periods for specific neuronal groups by the use of different transgenic zebrafish lines.

Methodology/Principal Findings

In order to evaluate the teratogenic effects of acute ethanol exposure, we exposed zebrafish embryos to ethanol in a given time window and analyzed the effects in neurogenesis, neuronal differentiation and brain patterning. Zebrafish larvae exposed to ethanol displayed small eyes and/or a reduction of the body length, phenotypical features similar to the observed in children with prenatal exposure to ethanol. When neuronal populations were analyzed, we observed a clear reduction in the number of differentiated neurons in the spinal cord upon ethanol exposure. There was a decrease in the population of sensory neurons mainly due to a decrease in cell proliferation and subsequent apoptosis during neuronal differentiation, with no effect in motoneuron specification.

Conclusion

Our investigation highlights that transient exposure to ethanol during early embryonic development affects neuronal differentiation although does not result in defects in early neurogenesis. These results establish the use of zebrafish embryos as an alternative research model to elucidate the molecular mechanism(s) of ethanol-induced developmental toxicity at very early stages of embryonic development.

Ethanol-induced transcriptional activation of programmed cell death 4 (Pdcd4) is mediated by GSK-3β signaling in rat cortical neuroblasts

Ingestion of ethanol (ETOH) during pregnancy induces grave abnormalities in developing fetal brain. We have previously reported that ETOH induces programmed cell death 4 (PDCD4), a critical regulator of cell growth, in cultured fetal cerebral cortical neurons (PCNs) and in the cerebral cortex in vivo and affect protein synthesis as observed in Fetal Alcohol Spectrum Disorder (FASD). However, the mechanism which activates PDCD4 in neuronal systems is unclear and understanding this regulation may provide a counteractive strategy to correct the protein synthesis associated developmental changes seen in FASD. The present study investigates the molecular mechanism by which ethanol regulates PDCD4 in cortical neuroblasts, the immediate precursor of neurons. ETOH treatment significantly increased PDCD4 protein and transcript expression in spontaneously immortalized rat brain neuroblasts. Since PDCD4 is regulated at both the post-translational and post-transcriptional level, we assessed ETOH's effect on PDCD4 protein and mRNA stability. Chase experiments demonstrated that ETOH does not significantly impact either PDCD4 protein or mRNA stabilization. PDCD4 promoter-reporter assays confirmed that PDCD4 is transcriptionally regulated by ETOH in neuroblasts. Given a critical role of glycogen synthase kinase 3β (GSK-3β) signaling in regulating protein synthesis and neurotoxic mechanisms, we investigated the involvement of GSK-3β and showed that multifunctional GSK-3β was significantly activated in response to ETOH in neuroblasts. In addition, we found that ETOH-induced activation of PDCD4 was inhibited by pharmacologic blockade of GSK-3β using inhibitors, lithium chloride (LiCl) and SB-216763 or siRNA mediated silencing of GSK-3β. These results suggest that ethanol transcriptionally upregulates PDCD4 by enhancing GSK-3β signaling in cortical neuroblasts. Further, we demonstrate that canonical Wnt-3a/GSK-3β signaling is involved in regulating PDCD4 protein expression. Altogether, we provide evidence that GSK-3β/PDCD4 network may represent a critical modulatory point to manage the protein synthetic anomalies and growth aberrations of neural cells seen in FASD.

LPS or ethanol triggers clathrin- and rafts/caveolae-dependent endocytosis of TLR4 in cortical astrocytes

Toll-like receptor 4 (TLR4) activation and signalling in glial cells play critical roles in neurological disorders and in alcohol-induced brain damage. TLR4 endocytosis upon lipopolysaccharide (LPS) stimulation regulates which signalling pathway is activated, the MyD88-dependent or the TIR-domain-containing adapter-inducing interferon-β (TRIF)-dependent pathway. However, it remains elusive whether ethanol-induced TLR4 signalling is associated with receptor internalization and trafficking, and which endocytic pathway(s) are used in cortical astrocytes. Using the adenoviral over-expression of TLR4(GFP) , confocal microscopy and the imagestream technique, we show that upon ethanol or LPS stimulation, TLR4 co-localizes with markers of the clathrin and caveolin endocytic pathways, and that this endocytosis is dependent on dynamin. Using chlorpromazin and filipin as inhibitors of the clathrin and rafts/caveolae endocytic pathways, respectively, we demostrate that TRIF-dependent signalling relies on an intact clathrin pathway, whereas disruption of rafts/caveolae inhibits the MyD88- and TRIF-dependent signalling pathways. Immunofluorescence studies also suggest that lipid rafts and clathrin cooperate for appropriate TLR4 internalization. We also show that ethanol can trigger similar endocytic pathways as LPS does, although ethanol delays clathrin internalization and alters TLR4 vesicular trafficking. Our results provide new insights into the effects of ethanol or LPS on TLR4 signalling in cortical astrocytes, events that may underlie neuroinflammation and brain damage. The results demonstrate that ethanol or lipopolysaccharide (LPS) triggers toll-like receptor 4 (TLR4) endocytosis by caveolae and clathrin-dependent pathways in astrocytes. We proposed that while clathrin is the protein responsible for TLR4 internalization, caveolin-1/lipid rafts membrane microdomains are required for TLR4 signaling. The results provide new insights into the effects of ethanol on TLR4 signalling in astrocytes, events that may underlie neuroinflammation.

Nuanced but significant: how ethanol perturbs avian cranial neural crest cell actin cytoskeleton, migration and proliferation

Children with fetal alcohol syndrome (FAS) display striking craniofacial abnormalities. These features are proposed to result from perturbations in the morphology and function of cranial neural crest cells (cNCCs), which contribute significantly to the craniofacial complex. While certain pathways by which this may occur have been suggested, precise teratogenic mechanisms remain intensely investigated, as does the question of the teratogenic dose. The present study focused on examining how avian cNCC actin cytoskeleton, migratory distance, and proliferation are affected ex vivo by exposure to ethanol concentrations that simulate maternal intoxication. Chick cNCCs were cultured in 0.2% and 0.4% v/v ethanol. Distances migrated by both ethanol-treated and control cells at 24 and 48 h were recorded. Following phalloidin immunocytochemistry, treated and control cNCCs were compared morphologically and quantitatively. Apoptosis and proliferation in control versus treated cNCCs were also studied. Chick cNCCs cultured in ethanol lost their spindle-like shapes and their ordered cytoskeleton. There was a significant stage-dependent effect on cNCC migration at 24 h (p = 0.035), which was greatest at stage 10 (HH). Ethanol treatment for 48 h revealed a significant main effect for ethanol, chiefly at the 0.4% level. There was also an interaction effect between ethanol dose and stage of development (stage 9 HH). Actin microfilament disruption was quantitatively increased by ethanol at the doses studied while cNCC proliferation was increased but not significantly. Ethanol had no effect on cNCC apoptosis. At ethanol levels likely to induce human FAS, avian cNCCs exhibit various subtle, potentially significant changes in morphology, migration, and proliferation, with possible consequences for fated structures.

Ethanol induces TLR4/TLR2 association, triggering an inflammatory response in microglial cells

Alcohol consumption can induce brain damage, demyelination, and neuronal death, although the mechanisms are poorly understood. Toll-like receptors are sensors of the innate immune system and their activation induces inflammatory processes. We have reported that ethanol activates and recruits Toll-like receptor (TLR)4 receptors within the lipid rafts of glial cells, triggering the production of inflammatory mediators and causing neuroinflammation. Since TLR2 can also participate in the glial response and in the neuroinflammation, we investigate the effects of ethanol on TLR4/TLR2 responses. Here, we demonstrate that ethanol up-regulates TLR4 and TLR2 expression in microglial cells, inducing the production of inflammatory mediators which triggers reactive oxygen species generation and neuronal apoptosis. Ethanol also promotes TLR4/TLR2 recruitment into lipid rafts-caveolae, mimicking their activation by their ligands, lipopolysaccharide, and lipoteichoic acid (LTA). Immunoprecipitation and confocal microscopy studies reveal that ethanol induces a physical association between TLR2 and TLR4 receptors, suggesting the formation of heterodimers. Using microglia from either TLR2 or TLR4 knockout mice, we show that TLR2 potentiates the effects of ethanol on the TLR4 response reflected by the activation of MAPKs and inducible NO synthase. In summary, we provide evidence for a mechanism by which ethanol triggers TLR4/TLR2 association contributing to the neuroinflammation and neurodegeneration associated with alcohol abuse.

Total sialic acid profile in regressing and remodelling organs during the metamorphosis of marsh frog (Pelophylax ridibundus Pallas 1771)

This study aimed to investigate the functional relationship of sialic acid in regressing and remodelling organs such as the tail, small intestine and liver during the metamorphosis of Pelophylax ridibundus. For this purpose, four groups were composed according to developmental periods by considering Gosner's criteria (1964). Our findings showed that the sialic acid content of the larval tail has an opposite profile to cell death process. Although the sialic acid content of the small intestine and liver did not change evidently during metamorphosis, it increased after the completion of metamorphosis. Frog tail extensively exhibited cell death process and decreased proliferative activity and underwent complete degeneration during metamorphic climax. In spite of increased apoptotic index, a decreased sialic acid level in the tail tissues during climax can be the indication of a death cell removal process. However, the intestine and the liver included both cell death and proliferative process and remodelling in their adult forms. Thus, their sialic acid profiles during metamorphosis were different from the tail's profile. These data show that sialic acid may be an indicator of the presence of some cellular events during metamorphosis and that it can have different roles in the developmental process depending on the organ's fate throughout metamorphosis.

Effects of ethanol during adolescence on the number of neurons and glia in the medial prefrontal cortex and basolateral amygdala of adult male and female rats

Human adolescents often consume alcohol in a binge-like manner at a time when changes are occurring within specific brain structures, such as the medial prefrontal cortex (mPFC) and the basolateral nucleus of the amygdala (BLN). In particular, the number of neurons and glia is changing in both of these areas in the rat between adolescence and adulthood (Markham et al., 2007; Rubinow and Juraska, 2009). The current study investigated the effects of ethanol exposure during adolescence on the number of neurons and glia in the adult mPFC and BLN in Long-Evans male and female rats. Saline or 3g/kg ethanol was administered between postnatal days (P) 35-45 in a binge-like pattern, with 2days of injections followed by 1 day without an injection. Stereological analyses of the ventral mPFC (prelimbic and infralimbic areas) and the BLN were performed on brains from rats at 100 days of age. Neuron and glia densities were assessed with the optical disector and then multiplied by the volume to calculate the total number of neurons and glia. In the adult mPFC, ethanol administration during adolescence resulted in a decreased number of glia in males, but not females, and had no effect on the number of neurons. Adolescent ethanol exposure had no effects on glia or neuron number in the BLN. These results suggest that glia cells in the prefrontal cortex are particularly sensitive to binge-like exposure to ethanol during adolescence in male rats only, potentially due to a decrease in proliferation in males or protective mechanisms in females.

Ethanol affects differentiation-related pathways and suppresses Wnt signaling protein expression in human neural stem cells

BACKGROUND

Prenatal exposure of the fetus to ethanol (EtOH) can be teratogenic. We previously showed that EtOH alters the cell fate of human neural stem cells (NSC). As Wnt signaling plays an important role in fetal brain development, we hypothesized that EtOH suppresses Wnt signaling protein expression in differentiating NSC and thereby contributes to fetal alcohol spectrum disorder.

METHODS

NSC isolated from fetal human brains were cultured in mitogenic media to induce neurospheres, which were dissociated into single-cell suspensions and used for all experiments. Equal numbers of NSC were cultured on lysine/laminin-coated plates for 96 hours in differentiating media containing 0, 20, or 100 mM EtOH. Total mRNA was isolated from samples containing 0 or 100 mM EtOH and changes in expression of 263 genes associated with neurogenesis and NSC differentiation were determined by Oligo GEArray technology. The biological impact of gene changes was estimated using a systems biology approach with pathway express software and KEGG database. Based on the pathways identified, expression of Wnt proteins (Wnt3a and Wnt5a), Wnt-receptor complex proteins (p-LRP6, LRP6, DVL2, and DVL3), Wnt antagonist Naked-2 (NKD-2), and downstream Wnt proteins (β-catenin, Tyr-p-GSK3β, Ser-p-GSK3β) were analyzed by Western blot.

RESULTS

Of the 263 genes examined, the expressions of 22 genes in differentiating NSC were either upwardly or downwardly affected by EtOH. These genes are associated with 5 pathways/cellular processes: axon guidance; hedgehog signaling; TGF-β signaling; cell adhesion molecules; and Wnt signaling. When compared to controls, EtOH, at both 20 and 100 mM concentrations, suppressed the expression of Wnt3a and Wnt5a, receptor complex proteins p-LRP6, LRP6 and DVL2, and cytoplasmic proteins Ser-p-GSK3β and β-catenin. Expression of NKD-2 and DVL3 remained unchanged and the expression of active Tyr-p-GSK3β increased significantly.

CONCLUSIONS

EtOH can significantly alter neural differentiation pathway-related gene expression and suppress Wnt signaling proteins in differentiating human NSC.

Comparison of ethanol and acetaldehyde toxicity in rat astrocytes in primary culture

This study compared the effects of toxicity of ethanol and its first metabolite acetaldehyde in rat astrocytes through cell viability and cell proliferation. The cells were treated with different concentrations of ethanol in the presence or absence of a catalase inhibitor 2-amino-1,2,4 triazole (AMT) or with different concentrations of acetaldehyde. Cell viability was assessed using the trypan blue test. Cell proliferation was assessed after 24 hours and after seven days of exposure to either ethanol or acetaldehyde.We showed that both ethanol and acetaldehyde decreased cell viability in a dose-dependent manner. In proliferation studies, after seven days of exposure to either ethanol or acetaldehyde, we observed a significant dose-dependent decrease in cell number. The protein content study showed biphasic dose-response curves, after 24 hours and seven days of exposure to either ethanol or acetaldehyde. Co-incubation in the presence of AMT significantly reduced the inhibitory effect of ethanol on cell proliferation.We concluded that long-term exposure of astrocytes to ethanol is more toxic than acute exposure. Acetaldehyde is a much more potent toxin than ethanol, and at least a part of ethanol toxicity is due to ethanol's first metabolite acetaldehyde.

Ethanol neurotoxicity and dentate gyrus development

Maternal alcohol ingestion during pregnancy adversely affects the developing fetus, often leading to fetal alcohol syndrome (FAS). One of the most severe consequences of FAS is brain damage that is manifested as cognitive, learning, and behavioral deficits. The hippocampus plays a crucial role in such abilities; it is also known as one of the brain regions most vulnerable to ethanol-induced neurotoxicity. Our recent studies using morphometric techniques have further shown that ethanol neurotoxicity appears to affect the development of the dentate gyrus in a region-specific manner; it was found that early postnatal ethanol exposure causes a transitory deficit in the hilus volume of the dentate gyrus. It is strongly speculated that such structural modifications, even transitory ones, appear to result in developmental abnormalities in the brain circuitry and lead to the learning disabilities observed in FAS children. Based on reports on possible factors deciding ethanol neurotoxicity to the brain, we review developmental neurotoxicity to the dentate gyrus of the hippocampal formation.

Ethanol mimics ligand-mediated activation and endocytosis of IL-1RI/TLR4 receptors via lipid rafts caveolae in astroglial cells

We have recently reported that ethanol-induced inflammatory processes in the brain and glial cells are mediated via the activation of interleukin-1 beta receptor type I (IL-1RI)/toll-like receptor type 4 (TLR4) signalling. The mechanism(s) by which ethanol activates these receptors in astroglial cells remains unknown. Recently, plasma membrane microdomains, lipid rafts, have been identified as platforms for receptor signalling and, in astrocytes, rafts/caveolae constitute an important integrators of signal events and trafficking. Here we show that stimulation of astrocytes with IL-1beta, lipopolysaccharide or ethanol (10 and 50 mM), triggers the translocation of IL-1RI and/or TLR4 into lipid rafts caveolae-enriched fractions, promoting the recruitment of signalling molecules (phospho-IL-1R-associated kinase and phospho-extracellular regulated-kinase) into these microdomains. With confocal microscopy, we further demonstrate that IL-1RI is internalized by caveolar endocytosis via enlarged caveosomes organelles upon IL-1beta or ethanol treatment, which sorted their IL-1RI cargo into the endoplasmic reticulum-Golgi compartment and into the nucleus of astrocytes. In short, our findings demonstrate that rafts/caveolae are critical for IL-1RI and TLR4 signalling in astrocytes, and reveal a novel mechanism by which ethanol, by interacting with lipid rafts caveolae, promotes IL-1RI and TLR4 receptors recruitment, triggering their endocytosis via caveosomes and downstream signalling stimulation. These results suggest that TLRs receptors are important targets of ethanol-induced inflammatory damage in the brain.

Ethanol affects calmodulin and the calmodulin-binding proteins neuronal nitric oxide synthase and alphaII-spectrin (alpha-fodrin) in the nucleus of growing and differentiated rat astrocytes in primary culture

The distribution of calmodulin (CaM) and the CaM-binding proteins neuronal nitric oxide synthase (nNOS) and alphaII-spectrin (alpha-fodrin) in the nucleus of growing and differentiated astrocytes was analysed using immunogold electronmicroscopy. We also analysed the effect of moderate ethanol exposure on these proteins. For this, female Wistar rat were fed with an alcoholic liquid diet and exposed to males after several weeks. Pregnant rats were fed with this diet and, after birth, the foetuses brains were used to establish primary cultures of astrocytes. Astrocytes from control and ethanol-exposed rats foetuses were cultured in the absence or presence of ethanol (30 mM) for 7 days (growing cells) and 21 days (differentiated astrocytes). Our results indicate that all the proteins studied appeared mainly on the condensed chromatin of both control- and alcohol-exposed cells and that there are significant variations in the amount of these proteins between quiescent and dividing astrocytes. Altogether, we have not found a co-localisation between CaM and the CaM-binding proteins.

Time-specific effects of ethanol exposure on cranial nerve nuclei: gastrulation and neuronogenesis

During the development of the central nervous system, neurons pass through critical periods or periods of vulnerability. We explored periods of vulnerability for cranial nerve nuclei by determining the effects of acute exposure to ethanol during development on the number of neurons in mature brainstem. Long-Evans rats were injected with 2.9 g ethanol/kg body weight on one day between gestational day (G) 7 and G13, inclusive. Two hours later, animals received a second injection of 1.45 g/kg. Controls were injected with equivalent volumes of saline. Brainstems of 31-day-old offspring were cryosectioned and stained with cresyl violet. Stereological methods were used to determine the volume and numerical density of neurons in three trigeminal sensory nuclei (the principal sensory nucleus of the trigeminal nerve, and the oral and interpolar subnuclei of the spinal trigeminal nuclear complex) and three motor nuclei (the trigeminal, facial, and hypoglossal nuclei). The numbers of neurons in most nuclei were lower following early (on G7 and/or G8) or later (on G12 and/or G13) exposure. Only the trigeminal interpolar nucleus was affected by neither early nor late ethanol exposure. Thus, prenatal exposure to ethanol affects the number of neurons in brainstem nuclei in a time-dependent manner. Windows of vulnerability coincide with gastrulation (G7/G8) and the period of neuronal generation (G12/G13).

Neural stem cell transplantation in a model of fetal alcohol effects

Neural stem cell (NSC) transplantation has been investigated and developed in areas such as brain injury, stroke and neurodegenerative diseases. Recently, emerging evidence suggest that many of clinical symptoms observed in psychiatric disease are likely related to neural network disruptions including neurogenesis dysfunction. In the present study, we transplanted NSCs into a model of fetal alchol effects (FAE) for the purpose of investigating the possibility of regenerative therapy for the FAE. We labeled NSCs with fluorescent dye and radioisotope which were transplanted into FAE rats by intravenous injection. The transplanted cells were detected in wide areas of brain and were greater in number in the brains of the FAE group compared to the control group. Furthermore NSC transplantation attenuated behavioral abnormalities in FAE animals. These results suggest NSC transplantation as a potental new therapy for human FAE.

Glial-derived neurotrophic factor (GDNF) prevents ethanol (EtOH) induced B92 glial cell death by both PI3K/AKT and MEK/ERK signaling pathways

We investigated the neuroprotective effect of glial-derived neurotrophic factor (GDNF) upon alcohol-exposed B92 cultures, as well as the role of the cytoskeleton and mitogen-activated protein kinase (MAPK) pathways in this effect. Ethanol (EtOH) was added to cultures, either alone or in combination with 30 ng/ml GDNF. Exposure to EtOH (86 and 172 mM; 60 and 120 min) increased the frequency of apoptotic cells identified by nuclear DNA staining with 4,6-diamidino-2-phenylindole (DAPI). Cultures treated with GDNF showed a decrease in ethanol-induced apoptosis. A jun N-terminal kinase (JNK) pathway is activated by EtOH and their pharmacological inhibition (by SP600125) neutralized ethanol-induced apoptosis, suggesting a role for JNK in EtOH neurotoxicity. Immunocytochemically detected phospho-JNK (p-JNK) showed an unusual filamental expression, and localized together with actin stress fibers. Examination of the cytoskeleton showed that EtOH depolymerized actin filaments, inducing p-JNK dissociation and translocation to the nucleus, which suggests that released p-JNK may contribute to glial cell death after EtOH exposure. Treatment with GDNF, in turn, may neutralize the ethanol-induced cell death pathway. Either a phosphatidylinositol 3-kinase (PI3K)/AKT pathway inhibitor (LY294002) or an inhibitor of the extracellular signal-regulated kinase (ERK) 1, 2 pathways (UO126) failed to neutralize GDNF protective effects. However, the simultaneous use of both inhibitors blocked the protective effect of GDNF, suggesting a role for both signaling cascades in the GDNF protection. These findings provide further insight into the mechanism involved in ethanol-induced apoptosis and the neurotrophic protection of glial cells.

GLYCOSYLATION IS ALTERED BY ETHANOL IN RAT HIPPOCAMPAL CULTURED NEURONS

AIMS

Glycoproteins, such as adhesion molecules and growth factors, participate in the regulation of nervous system development. Ethanol affects the synthesis, intracellular transport, distribution, and secretion of N-glycoproteins in different cell types, including astrocytes and hepatocytes, suggesting alterations in the glycosylation process. We analysed the effect of exposure to low doses of ethanol (30 mm, 7 days) on glycosylation in cultured hippocampal neurons.

METHODS

Neurons were incubated for short (5 min) and long (90 min) periods with the radioactively labelled carbohydrate precursors 2-deoxy-glucose, N-acetyl-D-mannosamine and mannose. The uptake and metabolism of these precursors, as well as the radioactivity distribution in protein gels, were analysed. The levels of the glucose transporters GLUT1 and GLUT3 were also determined.

RESULTS

Ethanol exposure reduces the synthesis of proteins, DNA and RNA and decreased the uptake of mannose, but not of 2-deoxy-glucose and N-acetyl-D-mannosamine, and it increased the protein levels of both glucose transporters. Moreover, it altered the carbohydrate moiety of several proteins. Finally, alcohol treatment results in an increment of cell surface glycoconjugates containing terminal non-reduced mannose.

CONCLUSIONS

Alcohol-induced alterations in glycosylation of proteins in neurons could be a key mechanism involved in the teratogenic effects of alcohol exposure on brain development.

A Systems-Based Computational Model for Dose-Response Comparisons of Two Mode of Action Hypotheses for Ethanol-Induced Neurodevelopmental Toxicity

Investigations into the potential mechanisms for ethanol-induced developmental toxicity have been ongoing for over 30 years since Fetal Alcohol Syndrome (FAS) was first described. Neurodevelopmental endpoints are particularly sensitive to in utero exposure to alcohol as suggested by the more prevalent alcohol-related neurodevelopmental disorder (ARND). The inhibition of proliferation during neurogenesis and the induction of apoptosis during the period of synaptogenesis have been identified as potentially important mechanisms for ARND. However, it is unclear how these two mechanisms quantitatively relate to the dose and timing of exposure. We have extended our model of neocortical neurogenesis to evaluate apoptosis during synaptogenesis. This model construct allows quantitative evaluation of the relative impacts on neuronal proliferation versus apoptosis during neocortical development. Ethanol-induced lengthening of the cell cycle of neural progenitor cells during rat neocortical neurogenesis (G13-G19) is used to compute the number of neurons lost after exposure during neurogenesis. Ethanol-induced dose-dependent increases in cell death rates are applied to our apoptosis model during rat synaptogenesis (P0-P14), when programmed cell death plays a major role in shaping the future neocortex. At a human blood ethanol concentration that occurs after 3-5 drinks ( approximately 150 mg/dl), our model predicts a 20-30% neuronal deficit due to inhibition of proliferation during neurogenesis, while a similar exposure during synaptogenesis suggests a 7-9% neuronal loss through induction of cell death. Experimental in vitro and in vivo dose-response research and stereological research on long-term neuronal loss after developmental exposure to ethanol is compared to our model predictions. Our computational model allows for quantitative, systems-level comparisons of mechanistic hypotheses for perturbations during specific neurodevelopmental periods.

Effect of Ethanol on the Growth and Differentiation of Spinal Motoneurons and Possibility of Correcting This Effect In Vitro

We studied the effect of ethanol on the growth and differentiation of spinal cells in 14-day chick embryos in vitro and the possibility of correcting the destructive changes with dolivin (antioxidant). Ethanol blocked migration of glial cells and growth of axons. Addition of dolivin into the nutrient medium together with ethanol prevented the effect of ethanol and stimulated axon growth and migration of glial cells.

RhoA and lysophosphatidic acid are involved in the actin cytoskeleton reorganization of astrocytes exposed to ethanol

Astroglial cells play an important role in maintaining neuronal function in the adult and in the developing nervous system. Ethanol exposure induces profound alterations in the astrogliogenesis process, affecting important cell functions, including intracellular protein trafficking. Because the actin cytoskeleton plays a crucial role in intracellular protein transport, the aim of the present study was to analyze the effects of ethanol on actin cytoskeleton organization and the involvement of the RhoA signaling pathway in these effects. We show that RhoA and lysophosphatidic acid (LPA), an upstream activator of RhoA, stimulate the formation of stress fibers and focal adhesion in cortical astrocytes in primary culture. Exposure of cultured astrocytes to different concentrations of ethanol profoundly disorganizes the actin cytoskeleton, leading to the formation of actin rings at the cell periphery and decreasing the content of focal adhesion proteins. Furthermore, LPA treatment or RhoA transfection revert the ethanol-induced actin alterations in astrocytes, whereas transfection with an inactive mutant of RhoA is unable to revert the actin ring organization. In addition, inhibition of endogenous RhoA by C3 exoenzyme effectively blocks ethanol-induced actin ring formation. These results suggest that the effects of alcohol on actin cytoskeleton organization are mediated by the RhoA signaling pathway. Disruptions in actin organization may impair important astrocyte functions, participating in ethanol-induced astroglial and brain damage during development.

Effects of ethanol and ipsapirone on the development of midline raphe glial cells and astrocytes

Previously, results of studies from our laboratory have shown that the offspring of ethanol-fed female rats have a significant decrease in serotonin (5-HT) neurons and glia that contain S100B, an essential trophic factor for the development of 5-HT neurons. The deficiency of S100B-immunopositive glia was detected during the vulnerable period in 5-HT neuron development and in brain areas proximal to these neurons. The reductions of both 5-HT neurons and S100B-positive glia were prevented by maternal treatment with a 5-HT(1A) agonist (i.e., ipsapirone or buspirone). In the current study, we investigated whether the offspring of ethanol-fed rats had a general decrease in the density of glial cells in the brain areas that contain 5-HT neurons, and we determined whether these changes were prevented by maternal treatment with ipsapirone between gestational days (GDs) 13 and 20. We estimated the density of vimentin-positive glia of the midline raphe glial structure (MRGS) at GD 20 and postnatal day (PND) 5 and of glial fibrillary acidic protein (GFAP)-positive astrocytes proximal to the dorsal and median raphe at PNDs 5 and 19. The results of this study provide evidence that in utero ethanol exposure is associated with a reduced density of GFAP-immunopositive astrocytes proximal to the dorsal and median raphe. Maternal ipsapirone treatment significantly increased astroglial density in the dorsal raphe at PNDs 5 and 19 and in the median raphe at PND 5, such that it either prevented (dorsal raphe, PNDs 5 and 19) or blunted (median raphe, PND 5) the effects of ethanol.

Effect of ethanol on the metabolism of primary astrocytes studied by (13)C- and (31)P-NMR spectroscopy

Nuclear magnetic resonance was used as the primary technique to investigate the effect of ethanol (40, 80, and 160 mM) on the levels of high-energy phosphates, glycolytic flux, anaplerotic and oxidative fluxes to the tricarboxylic acid (TCA) cycle, the contribution of the pentose phosphate pathway (PPP), and the uptake and release of amino acids on primary cultures of rat astrocytes. On line (31)P-NMR spectroscopy showed that long-term exposure to ethanol caused a drop in the levels of ATP and phosphocreatine. The ratio between the fluxes through the pyruvate dehydrogenase and pyruvate carboxylase reactions also decreased, whereas the glycolytic flux and the ratio between formation of lactate and glucose consumption increased when cells were exposed to acute doses of ethanol. Flux through the pentose phosphate pathway was not affected. The uptake of cysteine and the release of glutamine were stimulated by ethanol, whereas the release of methionine was inhibited. Moreover, the fractional enrichment in serine was enhanced. The changes in the amino acid metabolism are interpreted as a response to oxidative stress induced by ethanol.

Astrocyte-mediated trophic support of developing serotonin neurons: effects of ethanol, buspirone, and S100B

Previously, this laboratory demonstrated that the development of serotonin (5-HT) neurons and S100B-immunopositive glia proximal to these neurons is impaired in the offspring of ethanol-fed rats. However, maternal treatment with a 5-HT(1A) agonist, e.g., buspirone or ipsapirone, between gestational days 13 and 20 prevented most of the ethanol-associated changes to developing 5-HT neurons and S100B-immunopositive glia in offspring. The present in vitro studies examined the hypothesis that the protective effects of a 5-HT(1A) agonist on ethanol-exposed, developing 5-HT neurons are mediated in part by astrocyte-produced factors such as S100B. Primary cultures of fetal 5-HT neurons were maintained in conditioned medium (CM) that was obtained from ethanol- and buspirone-treated astrocytes. In order to assess the potential contribution of S100B to the protective effects of buspirone, a mouse monoclonal antibody to S100B was added to the CM to block the biological effects of this protein. These studies demonstrated that CM, obtained from ethanol-treated astrocytes, was unable to support normal development of 5-HT neurons; there was a significant reduction in the number of 5-HT neurons/well. However, CM that was obtained from astrocytes that were co-treated with buspirone and ethanol prevented the ethanol-associated reduction, and the protective effects of buspirone required S100B. We also investigated whether exogenous S100B could protect 5-HT neurons from damage caused by direct exposure to ethanol. Direct exposure of fetal brainstem neurons to ethanol in chemically-defined medium was associated with a significant reduction in the number of 5-HT immunopositive neurons/well. However, exogenous S100B protected 5-HT neurons from the ethanol-associated reduction. Our observations suggest that the protective effects of buspirone on ethanol-exposed, developing 5-HT neurons are mediated in part by the astrocyte-produced factor S100B.

Potential involvement of S100B in the protective effects of a serotonin-1a agonist on ethanol-treated astrocytes

Previously, this laboratory found that the offspring of rats that consumed ethanol on a chronic basis prior to parturition exhibited a significant reduction in serotonin (5-HT) neurons and in astrocytes proximal to these neurons. This laboratory also showed that maternal treatment with a 5-HT(1A) agonist during the latter part of gestation prevented the reduction of 5-HT neurons and most of the astrocyte abnormalities. The present in vitro studies extended our prior in vivo work by examining the potential involvement of S100B with the protective effects of a 5-HT(1A) agonist, i.e., buspirone, on astrocytes. Astrocyte cultures were either maintained in chemically defined media in the presence and absence of ethanol and buspirone or in conditioned media that was generated by ethanol- and buspirone-treated astrocytes. A mouse monoclonal antibody to S100B was used to assess the potential involvement of S100B with the protective effects of buspirone. Additional in vitro studies measured the direct effects of S100B and ethanol on astrocyte proliferation. These investigations demonstrate that in vitro ethanol exposure reduces the number of astrocytes, and that treatment with the 5-HT(1A) agonist buspirone prevents the ethanol-associated reduction in astrocyte number. The protective effects of buspirone appear to be mediated by factors that are secreted by astrocytes; such factors likely include S100B. In addition, added S100B prevents an ethanol-associated reduction in [(3)H]-thymidine incorporation into proliferating astrocytes.

Differential effects of ethanol on the expression of cyclo-oxygenase in cultured cortical astrocytes and neurons

The developing central nervous system is a primary target of ethanol toxicity. The teratogenic effect of ethanol may result from its action on prostaglandins. Prostaglandins are generated through the release of arachidonic acid (AA) by the action of cytosolic phospholipase A(2) (cPLA(2)) on membrane-bound phospholipids and the catalytic conversion of AA to prostaglandin E(2) (PGE(2)) by cyclo-oxygenase (COX). COX is expressed in two isoforms, constitutive COX1 and inducible COX2. Cultured astrocytes and neurons from immature cerebral cortex were used as in vitro models to investigate the effect of ethanol on PGE(2) synthesis. In both cell types, neither the activity nor the expression of cPLA(2) was affected by ethanol. PGE(2) was synthesized by astrocytes and neurons. Ethanol (200-400 mg/dL for 24 h) significantly increased PGE(2) production in both cell types and the ethanol-induced increase in PGE(2) accumulation in astrocytes was significantly greater than in neurons. These increases resulted from the effects of ethanol on COX. Overall COX activity was up-regulated by ethanol in astrocytes and neurons, and indomethacin, a nonselective blocker for COX, eliminated the ethanol-induced increases of COX activity in both cell types. Increased COX activity in astrocytes resulted from an increase in COX2 expression. NS-398, a selective COX2 blocker, completely inhibited ethanol-induced alterations in COX activity. In neurons, however, ethanol had a direct effect on COX activity in the absence of a change in COX expression. NS-398 only partially blocked ethanol-induced increases in neuronal COX activity. Thus, astrocytes are a primary target of ethanol and ethanol-induced increases in glial PGE(2) synthesis are mediated by COX, principally COX2. Ethanol toxicity may be mediated through PGE(2) in immature cortical cells.

Neural cell adhesion molecule is endocytosed via a clathrin-dependent pathway

Neural cell adhesion molecule (NCAM) constitutes a group of cell surface glycoproteins that regulate cell-cell interactions in the developing and adult brain. Endocytosis is a mechanism which dynamically controls the amount of cell surface NCAM expression and may involve the rapid changes occurring in NCAM expression under certain physiological or pathological conditions. However, the endocytic pathway of NCAM is presently unknown. Using astrocytes in culture and immunofluorescence we show that NCAM is internalized and that the immunolabelling presents a high degree of colocalization with clathrin, alpha-adaptin and transferrin, suggesting that NCAM is endocytosed by a clathrin-dependent pathway. Potassium depletion which disrupts clathrin-mediated endocytosis, inhibited internalization of NCAM. Electron microscopy and immunogold studies also demonstrate that the surface of clathrin-coated vesicles are also immunolabelled for both alpha-adaptin and PSA-NCAM, the highly sialylated isoform of NCAM. Furthermore, immunoprecipation studies demonstrate that NCAM is associated with both clathrin and alpha-adaptin, a component of adaptor complex AP-2, in brain, neurons and astrocytes. These findings indicate that NCAM is mainly endocytosed via clathrin-coated vesicles, suggesting a possible mechanism that may contribute to the rapid changes in NCAM expression at the cell surface.

Alcohol deters the outgrowth of serotonergic neurons at midgestation

We have previously demonstrated that treatment of pregnant C57BL mice from gestation days 8 to 14 with alcohol with 20% ethanol-derived calories (EDC) reduced the number of serotonin (5-HT) neurons and retarded their migration in the fetal brains. In the present study, we obtained similar results with the use of 25% EDC and extended our previous findings by demonstrating that besides the alteration of the number of 5-HT neurons, prenatal alcohol exposure also affects their projecting fibers in their early development. Pregnant C57BL mice were divided into an alcohol-exposed (ALC) group given 25% EDC (4.49%, v/v), a pair-fed group to the ethanol-fed group (PF) and a chow-fed group (Chow). The PF and Chow groups served as controls. Our results showed that in the ALC group, when compared with the control groups, prenatal alcohol exposure with 25% EDC reduced the number of 5-HT-immunoreactive neurons in both the median and dorsal raphe, and the amount of 5-HT-immunoreactive fibers in the medial forebrain bundle (MFB). The diameter of the 5-HT-immunoreactive MFB was also reduced as a result of treatment. No significant differences of the above parameters were found between the PF and Chow groups. The previous and present work confirmed that alcohol reduces the normal formation and growth of 5-HT neurons in the midbrain. Furthermore, the projection of 5-HT fibers, in density as well as in distribution, is reduced in the major trajectory bundle. This may affect the amount of 5-HT fibers available to the forebrain. In light of the importance of the 5-HT system in brain development, alcohol may affect the growth of the forebrain through its effect on 5-HT signaling.

Inhibition of insulin-like growth factor-1 receptor and IRS-2 signaling by ethanol in SH-SY5Y neuroblastoma cells

The effect of ethanol on insulin-like growth factor-1 (IGF-I)-mediated signal transduction and functional activation in neuronal cells was examined. In human SH-SY5Y neuroblastoma cells, ethanol inhibited tyrosine autophosphorylation of the IGF-I receptor. This corresponded to the inhibition of IGF-I-induced phosphorylation of p42/p44 mitogen-activated/extracellular signal-regulated protein kinase (MAPK) by ethanol. Insulin-related substrate-2 (IRS-2) and focal adhesion kinase phosphorylation were reduced in the presence of ethanol, which corresponded to the prevention of lamellipodia formation (30 min). By contrast, ethanol had no effect on Shc phosphorylation when measured up to 1 h, and did not affect the association of Grb-2 with Shc. Neurite formation at 24 h was similarly unaffected by ethanol. The data indicate that the IGF-I receptor is a target for ethanol in SH-SY5Y cells However, there is diversity in the sensitivity of signaling elements within the IGF-I receptor tyrosine kinase signaling cascades to ethanol, which can be related to the inhibition of specific functional events in neuronal activation.

Alcohol exposure alters the expression pattern of neural cell adhesion molecules during brain development

Neural cell adhesion molecules (NCAMs) play critical roles during development of the nervous system. The aim of this study is to investigate the possible effect of ethanol exposure on the pattern of expression and sialylation of NCAM isoforms during postnatal rat brain development because alterations in NCAM content and distribution have been associated with defects in cell migration, synapse formation, and memory consolidation, and deficits in these processes have been observed after in utero alcohol exposure. The expression of NCAM isoforms in the developing cerebral cortex of pups from control and alcohol-fed mothers was assessed by western blotting, ribonuclease protection assay, and immunocytochemistry. The highly sialylated form of NCAM [polysialic acid (PSA)-NCAM] is mainly expressed during the neonatal period and then is down-regulated in parallel with the appearance of NCAM 180 and NCAM 140. Ethanol exposure increases PSA-NCAM levels during the neonatal period, delays the loss of PSA-NCAM, decreases the amount of NCAM 180 and NCAM 140 isoforms, and reduces sialyltransferase activity during postnatal brain development. Neuraminidase treatment of ethanol-exposed neonatal brains leads to more intense band degradation products, suggesting a higher content of NCAM polypeptides carrying PSA in these samples. However, NCAM mRNA levels are not changed by ethanol. Immunocytochemical analysis demonstrates that ethanol triggers an increase in PSA-NCAM immunolabeling in the cytoplasm of astroglial cells, accompanied by a decrease in immunogold particles over the plasma membrane. These findings indicate that ethanol exposure during brain development alters the pattern of NCAM expression and suggest that modification of NCAM could affect neuronal-glial interactions that might contribute to the brain defects observed after in utero alcohol exposure.

Effects of in utero ethanol exposure and maternal treatment with a 5-HT(1A) agonist on S100B-containing glial cells

This laboratory previously showed that in utero ethanol exposure severely impairs the development of the cell bodies and projections of serotonin (5-HT) neurons, and that maternal treatment with a 5-HT(1A) agonist prevents many of these abnormalities. Others demonstrated that stimulation of fetal astroglial 5-HT(1A) receptors increases production and release of S100B, a glial trophic factor that is essential for the development of 5-HT neurons. The present study investigated a potential mechanism by which ethanol hinders development of 5-HT neurons, and by which maternal 5-HT(1A) agonist treatment prevents this damage. This study tested the hypothesis that in utero ethanol exposure reduces the number of S100B immunopositive glia and that maternal 5-HT(1A) agonist treatment prevents ethanol-associated changes in S100B. To test our hypothesis, we determined the effects of in utero ethanol exposure and maternal treatments with the 5-HT(1A) agonists ipsapirone and buspirone on S100B immunopositive glial cells. On gestation day 20 (G20), S100B immunopositive cells were quantified in the midline raphe glial structure (MRGS), a large transient structure that contains substantial numbers of S100B-positive glial cells and that spans the dorsal raphe, median raphe, and B9 complex of 5-HT neurons. S100B immunopositive glial cells were also determined in an area proximal to the dorsal raphe in postnatal day 2 (PN2) rats. In utero ethanol exposure significantly reduced S100B immunopositive glial cells in the MRGS at G20 and in the dorsal raphe at PN2. In addition, treatment of pregnant rats with a 5-HT(1A) agonist between G13 and G20 prevented the ethanol-associated reduction in S100B immunopositive glial cells. These studies demonstrated that part of ethanol's damaging effects on developing 5-HT neurons is mediated by a reduction of S100B and that some of the protective effects of maternal 5-HT(1A) agonist treatment are related to the actions of these drugs on glial cells.

Prenatal alcohol exposure increases TNFalpha-induced cytotoxicity in primary astrocytes

We examined the effect of prenatal alcohol exposure (PAE) on tumor necrosis factor-alpha-(TNFalpha) induced cell death in primary astrocyte cultures. Flow cytometry revealed that PAE increased the sensitivity of astrocytes to the cytotoxic effects of TNFalpha when compared to astrocytes prepared from pair-fed and chow-fed controls. In a number of cell types, TNFalpha regulates cell growth or death, in part, by the hydrolysis of sphingomyelin to ceramide and sphingosine-1-phosphate (SPP). Using a 3-(4. 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxic assay we found that PAE increased the sensitivity of astrocytes to the cytotoxic effects of TNFalpha, sphingomyelinase (SMase), and C(2)- and C(6)-ceramide. The increasing cellular concentrations of SPP, a sphingolipid metabolic that induces cell growth, protected the cells from TNFalpha-induced cell death. N, N-dimethylsphingosine (DMS), which inhibits SPP production, and N-oleoylethanolamine, which inhibits acid ceramidases, increased TNFalpha-induced cytotoxicity in astrocytes prepared from PAE rats. These studies suggest that PAE shifts the balance of sphingolipid metabolism in favor of a pathway that increases the susceptibility of astrocytes to the cytotoxic effect of TNFalpha.

Platelet-derived growth factor-mediated signal transduction underlying astrocyte proliferation: site of ethanol action

Platelet-derived growth factor (PDGF) is a critical regulator of cell proliferation. Because ethanol inhibits cell proliferation in vivo and in vitro, we hypothesize that ethanol-induced inhibition results from differential interference with signal transduction pathways activated by PDGF. Cultured cortical astrocytes were used to examine the effects of ethanol on PDGF-mediated signal transduction, on the expression of two PDGF monomers (A- and B-chains), and on the expression of two PDGF receptor subunits (PDGFalphar and PDGFbetar). PDGF-B chain homodimer (PDGF-BB), and to a lesser extent PDGF-A chain homodimer (PDGF-AA), stimulated the proliferation of astrocytes raised in a serum-free medium. Ethanol attenuated these actions in a concentration-dependent manner. Ethanol inhibited both PDGF-AA- and PDGF-BB-mediated phosphorylation of PDGFalphar, but it had little effect on PDGFbetar autophosphorylation. Likewise, ethanol abolished the association of PDGFalphar to Ras GTPase-activating protein (Ras-GAP), but it did not affect the binding of Ras-GAP to PDGFbetar. PDGF stimulated the activities of mitogen-activated protein kinase (MAPK) in protein kinase C (PKC) independent and dependent manners. Ethanol inhibited the PKC-independent, acute activation of MAPK; however, it stimulated the PKC-dependent, sustained activation of MAPK. The expression of neither ligand was altered by exposure to ethanol for 3 d. Moreover, such treatment specifically upregulated PDGFalphar expression in a concentration-dependent manner. It did not, however, affect the binding affinity of either receptor. Thus, the signal transduction pathways initiated by PDGF-AA and PDGF-BB were differentially affected by ethanol. This differential vulnerability resulted from the preferential effects of ethanol on PDGFalphar autophosphorylation. Hence, ethanol-induced alterations are transduced through specific receptors of mitogenic growth factors.

In utero ethanol exposure decreased the density of serotonin neurons. Maternal ipsapirone treatment exerted a protective effect

Prior studies from this laboratory showed that in utero ethanol exposure severely retards the development of the serotonin (5-HT) system; we demonstrated a reduced concentration of 5-HT and 5-HT reuptake sites and alterations in the concentration of 5-HT(1A) receptors in ethanol-exposed offspring. These investigations also found that maternal treatment with a 5-HT(1A) agonist, buspirone, prevented most of the ethanol-associated damage to the developing 5-HT system. In the present investigation, we investigated whether the ethanol-associated changes in the 5-HT system are due to a reduction of 5-HT neurons and whether any changes in the density of 5-HT neurons can be prevented by maternal treatment with another 5-HT(1A) agonist, ipsapirone. Using immunocytochemistry, we found that in utero ethanol exposure reduced the density of 5-HT immunopositive neurons in the dorsal raphe, median raphe and B9 neurons of postnatal day 5 (PN5) rats. In all three brain areas, the offspring of ethanol-fed, saline-treated dams exhibited a 28%-40% reduction in 5-HT neurons. Ipsapirone prevented the ethanol-induced reduction in 5-HT immunopositive neurons in the dorsal raphe, median raphe and B9 neurons. In the dorsal and median raphe of control offspring, ipsapirone did not alter the concentration of 5-HT neurons. However, this drug did reduce 5-HT neurons in the B9 region of the offspring of control-fed rats.

Effect of alcohol on energy storage of primary astrocytes and C6-glioma cells in vitro

The present experiments were conducted to investigate the direct effects of ethanol on the energy metabolism of astrocytes and C6-glioma cells. Primary astrocytes were prepared from cerebral cortices of neonatal rats, and C6-glioma cells were purchased from American Type Culture Collection (ATCC). These cells were exposed to different concentrations of alcohol (100 mM, 200 mM, and 300 mM) for 15 minutes and 24 hours. The amount of ATP and PCr was measured by the method of Lowry and Passonneau (1972). Following 15 minutes treatment with different doses of ethanol the amount of ATP and PCr increased, in both cell types. Only the increase of ATP concentration with varying doses of ethanol (100 mM, 200 mM, and 300 mM) was statistically significant. Following 24 hours treatment of astrocytes with different doses of ethanol the concentration of ATP and PCr decreased. The decrease in concentration of ATP was significant with all three doses of ethanol, but the decrease of PCr concentration was only statistically significant with 300 mM ethanol. Following 24 hours treatment of C6-glioma cells to varying doses of ethanol, the concentration of PCr and ATP decreased. The decrease of PCr was statistically significant with all three doses of ethanol and the decrease of ATP concentration was only significant with 300 mM ethanol.

Acetaldehyde cytotoxicity in cultured rat astrocytes

The effect of acetaldehyde on astrocytes have been investigated because not only do they play an important role in brain maturation but also recent reports have shown their delayed proliferation following both 'in vivo' and 'in vitro' ethanol exposure. Biochemical parameters related to apoptotic and necrotic processes were examined in primary cultures of rat astrocytes exposed for 4 days to acetaldehyde generated from ethanol by co-cultured alcohol dehydrogenase-transfected Chinese hamster ovary cells. Acetaldehyde levels in the culture media attained concentrations of approximately 450 microM. To study ethanol effects, alcohol oxidation was inhibited by 4-methylpyrazole (an inhibitor of alcohol dehydrogenase). Acetaldehyde but not ethanol increased intracellular calcium levels by 155%. Moreover, significant DNA fragmentation was detected using a random oligonucleotide primed synthesis assay, by flow cytometry and when using agar gel electrophoresis. Transglutaminase activity was elevated in the cells treated with acetaldehyde but when acetaldehyde formation was inhibited by 4-methylpyrazole the enzyme activity was unaffected. Nitrate levels in the culture media were unchanged. Additionally, microscopic examination of cell nuclei revealed chromatin condensation in astrocytes exposed to acetaldehyde. It can be concluded, that in 'in vitro' acetaldehyde exposed rat astrocytes apoptotic pathways are activated.

Transforming growth factor beta1-regulated cell proliferation and expression of neural cell adhesion molecule in B104 neuroblastoma cells: differential effects of ethanol

The expression and activity of factors influencing early neuronal development are altered by ethanol. Such factors include growth factors, for example, platelet-derived growth factor and basic fibroblast growth factor (for cell proliferation), and cell adhesion molecules (for neuronal migration). One agent, transforming growth factor beta1 (TGFbeta1), may affect both events. We tested the hypothesis that ethanol alters myriad TGFbeta1-mediated activities [i.e., cell proliferation and neural cell adhesion molecule (N-CAM) expression] using B104 neuroblastoma cells. TGFbeta1 inhibited the proliferation of B104 cells as evidenced by decreases in cell number and [3H]thymidine ([3H]dT) incorporation. TGFbeta1 induced sustained activation of extracellular signal-regulated kinases (ERKs), which are part of the family of mitogen-activated protein kinases (MAPKs). Treatment with PD98059 (a MAPK kinase blocker) abolished TGFbeta1-regulated inhibition of [3H]dT incorporation. TGFbeta1-mediated growth inhibition was potentiated by ethanol exposure. Ethanol also produced prolonged activation of ERK, an effect that was partially eliminated by treatment with PD98059. On the other hand, TGFbeta1 up-regulated N-CAM expression, and this up-regulation was not affected by treatment with PD98059. Ethanol inhibited the TGFbeta1-induced up-regulation of N-CAM expression in a concentration-dependent manner. Thus, TGFbeta1 affects ERK-dependent cell proliferation and ERK-independent N-CAM expression in B104 cells. Both activities are sensitive to ethanol and may underlie the ethanol-induced alterations in the proliferation and migration of CNS neurons.

The effect of ethanol and acetaldehyde on microsomal and mitochondrial membrane fatty acid profiles in cultured rat astroglia

It has been shown that free radical damage may be involved in ethanol-induced cytotoxicity in cultured neural cells. Since changes in oxidative metabolism and the resulting lipid peroxidation readily modify biological membranes and alter cell functions we studied the effect of ethanol and its metabolite acetaldehyde on rat astroglial fatty acids profiles in the most common lipid classes of mitochondrial and microsomal membranes, i.e. phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Rat astroglial cells were grown for 1 week in the presence of 50 m M or 100 m M ethanol. To examine acetaldehyde effects we used a 4-day co-culture model consisting of astroglial cells and alcohol dehydrogenase-transfected Chinese hamster ovary (CHO) cells. Acetaldehyde produced by these cells reached 172 mu M and 265 mu M, respectively, for ethanol concentrations of 10 and 20 m M. Mitochondrial and microsomal membranes were prepared by differential centrifugation, phosphatidylcholine and phosphatidylethanolamine were separated using thin layer chromatography and fatty acid quantitation was performed by GLC. Neither ethanol nor acetaldehyde changed the mitochondrial phosphatidylcholine or phosphatidylethanolamine profiles of total saturated, mono-unsaturated or polyunsaturated fatty acids. However, some significant alterations in particular fatty acids appeared especially after acetaldehyde but also after the highest ethanol dose. In microsomal phosphatidylcholine monounsaturated fatty acids were significantly increased after both, ethanol and acetaldehyde exposure. Among polyunsaturated fatty acids, arachidonic acid was found to be especially affected by both ethanol and acetaldehyde. Similar decreases were observed in adrenic, docosapentaenoic and docosahexaenoic acids in the groups treated with ethanol. In microsomal phosphatidylethanolamine, ethanol and acetaldehyde decreased monounsaturated and some polyunsaturated fatty acids. These data support the role of peroxidative processes in cultured rat astroglia exposed to ethanol and point to the role of acetaldehyde in this mechanism.

Neuroanatomical and neurophysiological mechanisms involved in central nervous system dysfunctions induced by prenatal alcohol exposure

One of the most severe consequences of maternal ethanol consumption is the damage to the developing central nervous system, which is manifested by long-term cognitive and behavioral deficits in the offspring. Prenatal exposure to ethanol affects many crucial neurochemical and cellular components of the developing brain. Ethanol interferes with all of the stages of brain development, and the severity of the damage depends on the amount of ethanol intake and level of exposure. Experimental observations also indicate that the toxic effects of ethanol are not uniform: some brain regions are more affected than others and, even within a given region, some cell populations are more vulnerable than others. The neocortex, the hippocampus, and the cerebellum are the regions in which the neurotoxic effects of ethanol have been associated with the behavioral deficits. At the cellular level, ethanol disrupts basic developmental processes, including interference with division and proliferation, cell growth, and differentiation and the migration of maturing cells. Alterations in astroglia development and in neuronal-glial interactions may also influence the development of the nervous system. An impairment of several neurotransmitter systems and/or their receptors, as well as changes in the endocrine environment during brain development, are also important factors involved in the behavioral dysfunctions observed after prenatal ethanol exposure. Finally, some molecular mechanisms of ethanol-induced behavioral dysfunctions will be discussed.

Ethanol potentiates the stimulatory effects of insulin and phosphocholine on mitogenesis by a zinc-dependent and rapamycin-sensitive mechanism in fibroblasts and JB6 cells

In most cellular systems ethanol inhibits growth factor-induced cell growth. Here we examined the effects of ethanol on DNA synthesis and cell proliferation induced by insulin and phosphocholine (PCho) in NIH3T3 fibroblasts, Swiss 3T3 fibroblasts and mouse epidermal JB6 cells. In serum-starved low (12-18) passage NIH3T3 fibroblasts, 60 mM ethanol enhanced the mitogenic effect of insulin in the absence or presence of 25 microM zinc about 2- or 12-fold, respectively. In contrast, in serum-starved high (30-47) passage NIH3T3 cells 60 mM ethanol had large (20-40-fold) potentiating effects on insulin-induced DNA synthesis even in the absence of zinc. Furthermore, ethanol also enhanced the effects of PCho on DNA synthesis in both the absence and presence of insulin. The potentiating effects of ethanol on insulin- and PCho-induced DNA synthesis were associated with 1.2-1.3-fold stimulation of cell proliferation. Rapamycin, an inhibitor of p70 S6 kinase action, strongly inhibited the potentiating effects of ethanol on insulin- and PCho-induced mitogenesis. Unexpectedly, ethanol inhibited synergistic activation of p42/p44 mitogen-activated protein kinases by insulin and PCho. In both Swiss 3T3 and JB6 cells, ethanol potentiated insulin-induced DNA synthesis only in the presence of zinc. In these cells, ethanol also increased the effects of PCho on both DNA synthesis and cell proliferation in the co-presence of either insulin or ATP. The results indicate that in various cell lines physiologically relevant concentrations of ethanol can increase the ability of insulin and PCho to induce DNA synthesis and, to smaller extents, cell proliferation. In low passage NIH3T3 cells as well as in Swiss 3T3 and JB6 cells potentiation of insulin-induced DNA synthesis by ethanol requires the presence of zinc.