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

Astrocytes and microglia in the coordination of CNS development and homeostasis

Glia have emerged as important architects of central nervous system (CNS) development and maintenance. While traditionally glial contributions to CNS development and maintenance have been studied independently, there is growing evidence that either suggests or documents that glia may act in coordinated manners to effect developmental patterning and homeostatic functions in the CNS. In this review, we focus on astrocytes, the most abundant glia in the CNS, and microglia, the earliest glia to colonize the CNS highlighting research that documents either suggestive or established coordinated actions by these glial cells in various CNS processes including cell and/or debris clearance, neuronal survival and morphogenesis, synaptic maturation, and circuit function, angio-/vasculogenesis, myelination, and neurotransmission. Some molecular mechanisms underlying these processes that have been identified are also described. Throughout, we categorize the available evidence as either suggestive or established interactions between microglia and astrocytes in the regulation of the respective process and raise possible avenues for further research. We conclude indicating that a better understanding of coordinated astrocyte-microglial interactions in the developing and mature brain holds promise for developing effective therapies for brain pathologies where these processes are perturbed.

Alterations in Neurotrophins in Alcohol-Addicted Patients during Alcohol Withdrawal

BACKGROUND

Alcohol use disorder (AUD) is related to mental and somatic disorders that result in alcohol withdrawal syndrome (AWS), with 30% of AWS cases leading to life-threatening delirium tremens (DTs). Currently, studies do not support using any one biomarker in DTs. Neurotrophins affect neuromodulation, playing a role in the pathogenesis of AUD, AWS, and DTs.

METHODS

This review aims to summarize experimental and clinical data related to neurotrophins and S100B in neuroplasticity, as well as neurodegeneration in the context of AUD, AWS, and DTs. This work used publications that were selected based on the protocol consistent with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement.

RESULTS

The BDNF level could be a good candidate biomarker for relapse susceptibility, as it is significantly reduced during consumption and gradually increases during abstinence. GDNF influences AUD through its integral role in the function of dopaminergic neurons and ablates the return to alcohol-drinking behavior. NGF protects neurons from ethanol-induced cytotoxic damage and affects recovery from cognitive deficits after brain damage. The NT-3 level is decreased after alcohol exposure and is involved in compensatory mechanisms for cognitive decline in AUD. NT-4 affects oxidative stress, which is associated with chronic alcohol consumption. S100B is used as a biomarker of brain damage, with elevated levels in serum in AUD, and can protect 5-HT neurons from the damage caused by alcohol.

CONCLUSIONS

BDNF, GDNF, NT-3, NT-4, NGF, and S100B may be valuable markers for withdrawal syndrome. In particular, the most relevant is their association with the development of delirium complications. However, there are few data concerning some neurotrophins in AWS and DTs, suggesting the need for further research.

Buspirone Enhances Cell Survival and Preserves Structural Integrity during Oxidative Injury to the Retinal Pigment Epithelium

Chronic oxidative stress impairs the normal functioning of the retinal pigment epithelium (RPE), leading to atrophy of this cell layer in cases of advance age-related macular degeneration (AMD). The purpose of our study was to determine if buspirone, a partial serotonin 1A (5-HT1A) receptor agonist, protected against oxidative stress-induced changes in the RPE. We exposed differentiated human ARPE-19 cells to paraquat to induce oxidative damage in culture, and utilized a mouse model with sodium iodate (NaIO3)-induced oxidative injury to evaluate the effect of buspirone. To investigate buspirone's effect on protective gene expression, we performed RT-PCR. Cellular toxicities and junctional abnormalities due to paraquat induction in ARPE-19 cells and buspirone's impact were assessed via WST-1 assays and ZO-1 immunostaining. We used spectral-domain optical coherence tomography (SD-OCT) and ZO-1 immunostaining of RPE/choroid for structural analysis. WST-1 assays showed dose-dependent protection of viability in buspirone-treated ARPE-19 cells in culture and preservation of RPE junctional integrity under oxidative stress conditions. In the NaIO3 model, daily intraperitoneal injection (i.p.) of buspirone (30 mg/kg) for 12 days improved the survival of photoreceptors compared to those of vehicle-treated eyes. ZO-1-stained RPE flat-mounts revealed the structural preservation of RPE from oxidative damage in buspirone-treated mice, as well as in buspirone-induced Nqo1, Cat, Sqstm1, Gstm1, and Sod2 genes in the RPE/choroid compared to untreated eyes. Since oxidative stress is implicated in the pathogenesis AMD, repurposing buspirone, which is currently approved for the treatment of anxiety, might be useful in treating or preventing dry AMD.

Lipopolysaccharide impairs neurodevelopment and induces changes in astroglial reactivity, antioxidant defenses and bioenergetics in the cerebral cortex of neonatal rats

Neonates have an immature immune system, which increases their vulnerability to infectious agents and inflammatory insults. The administration of the immunostimulatory agent lipopolysaccharide (LPS) has been shown to induce the expression of pro-inflammatory cytokines and cause behavior alterations in rodents at different ages. However, the effects of LPS administration during the neonatal period and its consequences during immune system maturation remain to be elucidated. We showed here that a single intraperitoneal administration of LPS in rats on postnatal day (PND) 7 caused early and variable alterations in TNF-α, S100B and GFAP levels in the cerebral cortex, CSF and serum of the animals, indicating long-term induction of neuroinflammation and astroglial reactivity. However, on PND 21, only GFAP levels were increased by LPS. Additionally, LPS induced oxidative stress and altered energy metabolism enzymes in the cerebral cortex on PND 21, and caused neurodevelopment impairment over time. These data suggest that neuroinflammation induction during the neonatal period induces glial reactivity, oxidative stress and bioenergetic disruption that may lead to neurodevelopment impairment and cognitive deficit in adult life.

Brain-derived neurotrophic factor and glutathione peroxidase as state biomarkers in alcohol use disorder patients undergoing detoxification

The pathophysiology of alcohol use disorder (AUD) is not totally clear. The aim of this study was to investigate the serum levels of brain-derived neurotrophic factor (BDNF) and oxidative stress markers in AUD patients during alcohol detoxification. Evaluation of changes in BDNF, glutathione peroxidase (GPX), catalase, superoxide dismutase, thiobarbituric acid reactive substances, 8-hydroxy 2'-deoxyguanosine, PCC and S100B were carried out.14 AUD inpatients and 20 healthy control subjects were recruited for this study. The serum BDNF, S100B and oxidative stress markers were measured with assay kits.Serum levels of catalase, GPX, PCC and 8-hydroxy 2'-deoxyguanosine were significantly higher in the AUD group subjects than in the controls (P < .05). However, BDNF levels were lower in the AUD group than in the controls (P < .05). After alcohol detoxification treatment, the GPX levels in the AUD group dropped (P < .05) and the BDNF levels rose (P < .05).The results suggest that serum BDNF and GPX levels might be state biomarkers for AUD patients undergoing alcohol detoxification.

Plasma Levels of Glial Cell Marker S100B in Children With Autism

Autism spectrum disorder (ASD) is a neurodevelopmental condition with increasing incidence. Recent evidences suggest glial cells involvement in autism pathophysiology. S100B is a calcium binding protein, mainly found in astrocytes and therefore used as a marker of their activity. In our study, children with autism had higher plasma concentrations of S100B compared to non-autistic controls. No association of S100B plasma levels with behavioral symptoms (ADI-R and ADOS-2 scales) was found. Plasma S100B concentration significantly correlated with urine serotonin, suggesting their interconnection. Correlation of plasma S100B levels with stool calprotectin concentrations was found, suggesting not only brain astrocytes, but also enteric glial cells may take part in autism pathogenesis. Based on our findings, S100B seems to have a potential to be used as a biomarker of human neurodevelopmental disorders, but more investigations are needed to clarify its exact role in pathomechanism of autism.

Aquaporin 4: A key player in Parkinson's disease

Parkinson's disease (PD) is one of the most prevalent neurodegenerative diseases which occur in aged people worldwide. Given that a sequence of cellular and molecular mechanisms, including oxidative stresses, apoptosis, inflammatory pathways, microglia, astrocyte activation, and aquaporin 4 (AQP4) are associated with initiation and the progression of PD. AQP4 may affect various pathways (i.e., α-synuclein, inflammatory pathways, and microglia and astrocyte activation). Few reports have evaluated the relationship between AQP4 and PD-related cellular and molecular pathways. Here, for the first time, we highlighted the relationship between AQP4 and molecular mechanisms involved in PD pathogenesis.

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.

Graphene Enhances Cellular Proliferation through Activating the Epidermal Growth Factor Receptor

Graphene has promising applications in food packaging, water purification, and detective sensors for contamination monitoring. However, the biological effects of graphene are not fully understood. It is necessary to clarify the potential risks of graphene exposure to humans through diverse routes, such as foods. In the present study, graphene, as the model nanomaterial, was used to test its potential effects on the cell proliferation based on multiple representative cell lines, including HepG2, A549, MCF-7, and HeLa cells. Graphene was characterized by Raman spectroscopy, particle size analysis, atomic force microscopy, and transmission electron microscopy. The cellular responses to graphene exposure were evaluated using flow cytometry, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, and alamarBlue assays. Rat cerebral astrocyte cultures, as the non-cancer cells, were used to assess the potential cytotoxicity of graphene as well. The results showed that graphene stimulation enhanced cell proliferation in all tested cell cultures and the highest elevation in cell growth was up to 60%. A western blot assay showed that the expression of epidermal growth factor (EGF) was upregulated upon graphene treatment. The phosphorylation of EGF receptor (EGFR) and the downstream proteins, ShC and extracellular regulating kinase (ERK), were remarkably induced, indicating that the activation of the mitogen-activated protein kinase (MAPK)/ERK signaling pathway was triggered. The activation of PI3 kinase p85 and AKT showed that the PI3K/AKT signaling pathway was also involved in graphene-induced cell proliferation, causing the increase of cell ratios in the G2/M phase. No influences on cell apoptosis were observed in graphene-treated cells when compared to the negative controls, proving the low cytotoxicity of this emerging nanomaterial. The findings in this study revealed the potential cellular biological effect of graphene, which may give useful hints on its biosafety evaluation and the further exploration of the bioapplication.

Electrophysiological Assessment of Serotonin and GABA Neuron Function in the Dorsal Raphe during the Third Trimester Equivalent Developmental Period in Mice

Alterations in the development of the serotonin system can have prolonged effects, including depression and anxiety disorders later in life. Serotonin axonal projections from the dorsal raphe undergo extensive refinement during the first 2 weeks of postnatal life in rodents (equivalent to the third trimester of human pregnancy). However, little is known about the functional properties of serotonin and GABA neurons in the dorsal raphe during this critical developmental period. We assessed the functional properties and synaptic connectivity of putative serotoninergic neurons and GABAergic neurons in the dorsal raphe during early [postnatal day (P) P5-P7] and late (P15-P17) stages of the third trimester equivalent period using electrophysiology. Our studies demonstrate that GABAergic neurons are hyperexcitable at P5-P7 relative to P15-P17. Furthermore, putative serotonin neurons exhibit an increase in both excitatory and GABAA receptor-mediated spontaneous postsynaptic currents during this developmental period. Our data suggest that GABAergic neurons and putative serotonin neurons undergo significant electrophysiological changes during neonatal development.

S100B Serum Levels Predict Treatment Response in Patients with Melancholic Depression

BACKGROUND

There is an ongoing search for biomarkers in psychiatry, for example, as diagnostic tools or predictors of treatment response. The neurotrophic factor S100 calcium binding protein B (S100B) has been discussed as a possible predictor of antidepressant response in patients with major depression, but also as a possible biomarker of an acute depressive state. The aim of the present study was to study the association of serum S100B levels with antidepressant treatment response and depression severity in melancholically depressed inpatients.

METHODS

After a wash-out period of 1 week, 40 inpatients with melancholic depression were treated with either venlafaxine or imipramine. S100B levels and Hamilton Depression Rating Scale (HAM-D) scores were assessed at baseline, after 7 weeks of treatment, and after 6 months.

RESULTS

Patients with high S100B levels at baseline showed a markedly better treatment response defined as relative reduction in HAM-D scores than those with low baseline S100B levels after 7 weeks (P=.002) and 6 months (P=.003). In linear regression models, S100B was a significant predictor for treatment response at both time points. It is of interest to note that nonresponders were detected with a predictive value of 85% and a false negative rate of 7.5%. S100B levels were not associated with depression severity and did not change with clinical improvement.

CONCLUSIONS

Low S100B levels predict nonresponse to venlafaxine and imipramine with high precision. Future studies have to show which treatments are effective in patients with low levels of S100B so that this biomarker will help to reduce patients' burden of nonresponding to frequently used antidepressants.

Enteroglial-derived S100B protein integrates bacteria-induced Toll-like receptor signalling in human enteric glial cells

OBJECTIVE

Enteric glial cells (EGC) have been suggested to participate in host-bacteria cross-talk, playing a protective role within the gut. The way EGC interact with microorganisms is still poorly understood. We aimed to evaluate whether: EGC participate in host-bacteria interaction; S100B and Toll-like receptor (TLR) signalling converge in a common pathway leading to nitric oxide (NO) production.

DESIGN

Primary cultures of human EGC were exposed to pathogenic (enteroinvasive Escherichia coli; EIEC) and probiotic (Lactobacillus paracasei F19) bacteria. Cell activation was assessed by evaluating the expression of cFos and major histocompatibility complex (MHC) class II molecules. TLR expression in EGC was evaluated at both baseline and after exposure to bacteria by real-time PCR, fluorescence microscopy and western blot analysis. S100B expression and NO release from EGC, following exposure to bacteria, were measured in the presence or absence of specific TLR and S100B pathway inhibitors.

RESULTS

EIEC activated EGC by inducing the expression of cFos and MHC II. EGC expressed TLR at baseline. Pathogens and probiotics differentially modulated TLR expression in EGC. Pathogens, but not probiotics, significantly induced S100B protein overexpression and NO release from EGC. Pretreatment with specific inhibitors of TLR and S100B pathways abolished bacterial-induced NO release from EGC.

CONCLUSIONS

Human EGC interact with bacteria and discriminate between pathogens and probiotics via a different TLR expression and NO production. In EGC, NO release is impaired in the presence of specific inhibitors of the TLR and S100B pathways, suggesting the presence of a novel common pathway involving both TLR stimulation and S100B protein upregulation.

S100B overexpression increases behavioral and neural plasticity in response to the social environment during adolescence

Genetic variants as well as increased serum levels of the neurotrophic factor S100B are associated with different psychiatric disorders. However, elevated S100B levels are also related to a better therapeutic outcome in psychiatric patients. The functional role of elevated S100B in psychiatric disorders is still unclear. Hence, this study was designed in order to elucidate the differential effects of S100B overexpression in interaction with chronic social stress during adolescence on emotional behavior and adult neurogenesis. S100B transgenic and wild-type mice were housed either in socially stable or unstable environments during adolescence, between postnatal days 28 and 77. In adulthood, anxiety-related behavior in the open field, dark-light, and novelty-induced suppression of feeding test as well as survival of proliferating hippocampal progenitor cells were assessed. S100B transgenic mice revealed significantly reduced anxiety-related behavior in the open field compared to wild-types when reared in stable social conditions. In contrast, when transgenic mice grew up in unstable social conditions, their level of anxiety-related behavior was comparable to the levels of wild-type mice. In addition, S100B overexpressing mice from unstable housing conditions displayed higher numbers of surviving newborn cells in the adult hippocampus which developed into mature neurons. In conclusion, elevated S100B levels increase the susceptibility to environmental stimuli during adolescence resulting in more variable behavioral and neural phenotypes in adulthood. In humans, this increased plasticity might lead to both, enhanced risk for psychiatric disorders in negative environments and improved therapeutic outcome in positive environments.

From research to practice: an integrative framework for the development of interventions for children with fetal alcohol spectrum disorders

Since fetal alcohol syndrome was first described over 35 years ago, considerable progress has been made in the delineation of the neurocognitive profile in children with prenatal alcohol exposure. Preclinical investigators have made impressive strides in elucidating the mechanisms of alcohol teratogenesis and in testing the effectiveness of pharmacological agents and dietary supplementation in the amelioration of alcohol-induced deficits. Despite these advances, only limited progress has been made in the development of evidence-based comprehensive interventions for functional impairment in alcohol-exposed children. Having performed a search in PubMed and PsycINFO using key words, interventions, treatment, fetal alcohol syndrome, prenatal alcohol exposure, and fetal alcohol spectrum disorders, we found only 12 papers on empirically-based interventions. Only two of these interventions had been replicated and none met the criteria of "well-established," as defined by Chambless and Hollon (Journal of Consulting and Clinical Psychology 66(1):7-18, 1998). There has been only limited cross-fertilization of ideas between preclinical and clinical research with regard to the development of interventions. Therefore, we propose a framework that allows integrating data from preclinical and clinical investigations to develop comprehensive intervention programs for children with fetal alcohol spectrum disorders. This framework underscores the importance of multi-level evaluations and interventions.

Effects of lipoic acid on antiapoptotic genes in control and ethanol-treated fetal rhombencephalic neurons

This laboratory showed that ethanol augments apoptosis in fetal rhombencephalic neurons and co-treatment with alpha-lipoic acid (LA) or one of several other antioxidants prevents ethanol-associated apoptosis. Because ethanol increases oxidative stress, which causes apoptosis, it is likely that some of the neuroprotective effects of LA and other antioxidants involve classical antioxidant actions. Considering the reported link of LA with pro-survival cell signaling, it is also possible that LA's neuroprotective effects involve additional mechanisms. The present study investigated the effects of LA on ethanol-treated fetal rhombencephalic neurons with regard to oxidative stress and up-regulation of the pro-survival genes Xiap and Bcl-2. We included parallel gene expression studies with N-acetyl cysteine (NAC) to determine whether LA's effects on Xiap and Bcl-2 were shared by other antioxidants. We also used enzyme inhibitors to determine which signaling pathway(s) might be involved with the effects of LA. The results of this investigation showed that LA treatment of ethanol-treated neurons exerted several pro-survival effects. LA blocked two pro-apoptotic changes, i.e., the ethanol-associated rise in ROS and caspase-3. LA also up-regulated the expression genes that encode the anti-apoptotic proteins Bcl-2 and Xiap by a mechanism that involves NF-κB. NAC also up-regulated Bcl-2 and Xiap. Thus, the neuroprotective effects of LA and NAC could involve up-regulation of pro-survival genes as well as their classical antioxidant actions.

A neurodevelopmental framework for the development of interventions for children with fetal alcohol spectrum disorders

Despite considerable data published on cognitive and behavioral disabilities in children with fetal alcohol spectrum disorders (FASD), relatively little information is available on behavioral or pharmacological interventions for alcohol-affected children. The main goals of this article, therefore, are to summarize published intervention studies of FASD and to present a neurodevelopmental framework, based on recent findings from a number of disciplines, for designing new therapies for alcohol-affected children. This framework assumes a neuroconstructionist view, which posits that reciprocal interactions between neural activity and the brain's hardware lead to the progressive formation of intra- and interregional neural connections. In this view, behavioral interventions can be conceptualized as a series of guided experiences that are designed to produce neural activation. Based on evidence from cognitive neuroscience, it is hypothesized that specific interventions targeting executive attention and self-regulation may produce greater generalizable results than those aimed at domain-specific skills in children with FASD. In view of reciprocal interactions between environmental effects and neural structures, the proposed framework suggests that the maximum effects of interventions can eventually be achieved by optimally combining behavioral methods and cognition-enhancing drugs.

Post-ischemic hypothermia for 24h in P7 rats rescues hippocampal neuron: association with decreased astrocyte activation and inflammatory cytokine expression

Hypothermia is an effective method for reducing the neuronal damage induced by hypoxia-ischemia (HI) but the underlying mechanism remains unclear. To investigate the effects of post-HI hypothermia on the developing brain, 7-day-old rats were subjected to left carotid artery ligation followed by 8% oxygen for 2h. They were divided into a hypothermia group (rectal temperature 32-33 degrees C for 24h) and a normothermia group (36-37 degrees C for 24h) immediately after hypoxia-ischemia. Animals were sacrificed at 12, 24 and 72 h for gene analysis and 0, 1, 3 and 7 days for protein analysis after HI. There was a significant decrease in infarct volume in the hypothermia group at 7 days after HI compared with that in the normothermia group. The hypothermia group had more neuronal nuclei (NeuN) positive neurons and lower levels of glial fibrillary acidic protein (GFAP) mRNA and immunoreactivity in the hippocampus CA1 region than the normothermia group. Real-time PCR showed no significant difference in glial cell line-derived neurotrophic factor (GDNF) mRNA expression in the hippocampus in the two groups at various time points after HI. However, GDNF protein level was significantly increased in the hypothermia group. On the other hand, mRNA and protein levels of the inflammatory cytokines tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6) were dramatically decreased in the hypothermia compared with the normothermia group. The present findings highlight an apparent association between inhibition of hippocampal neuron loss by hypothermia and decreased astrocytosis and inflammatory cytokine release after hypoxia-ischemia in the developing brain.

Antioxidants prevent ethanol-associated apoptosis in fetal rhombencephalic neurons

It is well known that ethanol damages the developing nervous system by augmenting apoptosis. Previously, this laboratory reported that ethanol augments apoptosis in fetal rhombencephalic neurons, and that the increased apoptosis is associated with reduced activity of the phosphatidylinositol 3-kinase pathway and downstream expression of pro-survival genes. Other laboratories have shown that another mechanism by which ethanol induces apoptosis in developing neurons is through the generation of reactive oxygen species (ROS) and the associated oxidative stress. The present study used an in vitro model to investigate the potential neuroprotective effects of several antioxidants against ethanol-associated apoptosis in fetal rhombencephalic neurons. The investigated antioxidants included three phenolics: (-)-epigallocatechin-3-gallate (EGCG), a flavanoid polyphenol found in green tea; curcumin, found in tumeric; and resveratrol (3,5,4'-trihydroxystilbene), a component of red wine. Additional antioxidants, including melatonin, a naturally occurring indole, and alpha-lipoic acid, a naturally occurring dithiol, were also investigated. These studies demonstrated that a 24-hour treatment of fetal rhombencephalic neurons with 75 mM ethanol caused a 3-fold increase in the percentage of apoptotic neurons. However, co-treatment of these cultures with any of the five different antioxidants prevented ethanol-associated apoptosis. Antioxidant treatment did not alter the extent of apoptosis in control neurons, i.e., those cultured in the absence of ethanol. These studies showed that several classes of antioxidants can exert neuroprotection against ethanol-associated apoptosis in fetal rhombencephalic neurons.

Enteric glial-derived S100B protein stimulates nitric oxide production in celiac disease

BACKGROUND & AIMS

Enteric glia participates to the homeostasis of the gastrointestinal tract. In the central nervous system, increased expression of astroglial-derived S100B protein has been associated with the onset and maintaining of inflammation. The role of enteric glial-derived S100B protein in gastrointestinal inflammation has never been investigated in humans. In this study, we evaluated the expression of S100B and its relationship with nitric oxide production in celiac disease.

METHODS

Duodenal biopsy specimens from untreated and on gluten-free diet patients with celiac disease and controls were respectively processed for S100B and inducible nitric oxide synthase (iNOS) protein expression and nitrite production. To evaluate the direct involvement of S100B in the inflammation, control biopsy specimens were exposed to exogenous S100B, and iNOS protein expression and nitrite production were measured. We also tested gliadin induction of S100B-dependent inflammation in cultured biopsy specimens deriving from on gluten-free diet patients in the absence or presence of the specific S100B antibody.

RESULTS

S100B messenger RNA and protein expression, iNOS protein expression, and nitrite production were significantly increased in untreated patients but not in on gluten-free diet patients vs controls. Addition of S100B to control biopsy specimens resulted in a significant increase of iNOS protein expression and nitrite production. In celiac disease patients but not in controls biopsy specimens, gliadin challenge significantly increased S100B messenger RNA and protein expression, iNOS protein expression, and nitrite production, but these effects were completely inhibited by S100B antibody.

CONCLUSIONS

Enteric glial-derived S100B is increased in the duodenum of patients with celiac disease and plays a role in nitric oxide production.

S100B-mediated protection against the pro-apoptotic effects of ethanol on fetal rhombencephalic neurons

Previously, this laboratory demonstrated that ethanol treatment significantly reduces the number of developing serotonin (5-HT) and other fetal rhombencephalic neurons in rats by augmenting apoptosis. Using a 5-HT(1A) agonist we were able to attenuate the ethanol-associated reduction and apoptosis of 5-HT and rhombencephalic neurons. The downstream pro-survival effects of 5-HT(1A) stimulation were associated with the activation of phosphatidylinositol 3'kinase (PI-3K) and its subsequent up-regulation of specific NF-kappaB-dependent pro-survival genes. Using an in vitro model, we investigated the hypothesis that S100B, a protein which is released from astrocytes following 5-HT(1A) agonist stimulation, can reduce apoptosis in ethanol-treated rat fetal rhombencephalic neurons. We also evaluated whether the anti-apoptotic effects of S100B on fetal rhombencephalic neurons were linked to the activation of the PI-3K-->pAkt pro-survival pathway and the expression of two NF-kappaB-dependent pro-survival genes: XIAP and Bcl-2. Moreover, we determined whether S100B's pro-survival effects were associated with mitogen activated protein kinase kinase (MAPKK)-->p42/p44 MAPK. The results of these investigations demonstrated that S100B treatment prevented ethanol-associated apoptosis of fetal rhombencephalic neurons. In addition, it appears that these neuroprotective effects are linked to activation of the PI-3K pathways, because the PI-3K inhibitor LY294002 blocks the neuroprotective effects of S100B. Moreover, S100B increases the formation of pAkt and the up-regulation of two downstream NF-kappaB-dependent pro-survival genes: XIAP and Bcl-2. Although the MAPKK inhibitor PD98059 reduced the number of surviving neurons in S100B-treated cultures, S100B did not activate MAPKK.

TNF alpha affects the expression of GFAP and S100B: implications for Alzheimer's disease

Neurodegenerative disorders such as Alzheimer's disease are characterized by increased intracellular and extracellular concentrations of the astrocytic proteins glial fibrillary acidic protein (GFAP) and S100B. The present study examined the potential contribution of tumor necrosis factor alpha (TNFalpha) to these changes by measuring astrocyte viability along with the intracellular and extracellular expression of GFAP and S100B following exposure to this cytokine. Although TNFalpha did not affect astrocyte viability, the extracellular levels of both proteins were increased three-fold with associated reductions in immunocytochemical labeling.

The effects of ethanol and the serotonin(1A) agonist ipsapirone on the expression of the serotonin(1A) receptor and several antiapoptotic proteins in fetal rhombencephalic neurons

Previously, this laboratory demonstrated that ethanol reduces the number of developing serotonin (5-HT)-containing neurons by increasing apoptosis. We also found that 5-HT(1A) agonists attenuate the proapoptotic effects of ethanol and the ethanol-mediated reduction of fetal 5-HT neurons. These neuroprotective effects are mediated in part by the ability of 5-HT(1A) agonists to activate the phosphatidyl 3'-kinase (PI-3K) prosurvival pathway. NF-kappaB is one of the downstream effectors activated by this pathway. In the present study, we used quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR) to determine the effects of 50mM ethanol and 100nM of ipsapirone, a 5-HT(1A) agonist, on the expression of several NF-kappaB-dependent antiapoptotic genes: X-linked inhibitor of apoptosis protein (XIAP), cIAP1, cIAP2, Bcl-2, and Bcl-xl. We also investigated the effects of ethanol and ipsapirone on the expression of the gene encoding the 5-HT(1A) receptor. The results demonstrate that ethanol reduces the expression of several prosurvival genes: XIAP, cIAP1, cIAP2, Bcl-2, and Bcl-xl. Importantly, the ethanol-mediated reduction in the expression of XIAP and Bcl-xl was prevented by co-treatment with ipsapirone. Thus, the damaging effects of ethanol are likely to involve a reduction in several prosurvival proteins. Moreover, the protective effects of ipsapirone on ethanol-treated neurons might involve their ability to prevent the reduction of XIAP and Bcl-xl. Although ipsapirone treatment decreased the expression of cIAP1, Bcl-2, and Bcl-xl in control neurons, our prior studies suggest that their survival is not reduced by ipsapirone. We also observed an increased expression of the 5-HT(1A) receptor in ipsapirone-treated control neurons.

Astrocytes induce hemeoxygenase-1 expression in microglia: a feasible mechanism for preventing excessive brain inflammation

Microglia are the major inflammatory cells in the brain, in which microglial inflammatory responses are modulated by interactions with other brain cells. Here, we show that astrocytes, the most abundant cells in the brain, can secrete one or more factors capable of modulating microglial activation by regulating the microglial levels of reactive oxygen species (ROS). Treatment of microglia with astrocyte culture-conditioned media (ACM) increased the expression level and activity of hemeoxygenase-1 (HO-1). ACM also induced nuclear translocation of the nuclear factor E2-related factor 2 transcription factor, increased the binding activity of the antioxidant response element (ARE), and enhanced HO-1 promoter activity in an ARE-dependent manner. Furthermore, treatment with ACM suppressed interferon-gamma (IFN-gamma)-induced ROS production, leading to reduced inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) release. In agreement with these results, mimickers of HO-1 products, such as bilirubin, ferrous iron, and a carbon monoxide-releasing molecule, reduced IFN-gamma-induced iNOS expression and/or NO release. Finally, we found that the active component(s) in ACM was heat labile and smaller than 3 kDa. Together, these results suggest that astrocytes could cooperate with microglia to prevent excessive inflammatory responses in the brain by regulating microglial expression of HO-1 and production of ROS.

The RhoA/ROCK-I/MLC pathway is involved in the ethanol-induced apoptosis by anoikis in astrocytes

Anoikis is a programmed cell death induced by loss of anchorage that is involved in tissue homeostasis and disease. Ethanol is an important teratogen that induces marked central nervous system (CNS) dysfunctions. Here we show that astrocytes exposed to ethanol undergo morphological changes associated with anoikis, including the peripheral reorganization of both focal adhesions and actin-myosin system, cell contraction, membrane blebbing and chromatin condensation. We found that either the small GTPase RhoA or its effector ROCK-I (Rho kinase), promotes membrane blebbing in astrocytes. Ethanol induces a ROCK-I activation that is mediated by RhoA, rather than by caspase-3 cleavage. Accordingly, the RhoA inhibitor C3, completely abolishes the ethanol-induced ROCK-I activation. Furthermore, inhibition of both RhoA and ROCK prevents the membrane blebbing induced by ethanol. Ethanol also promotes myosin light chain (MLC) phosphorylation, which might be involved in the actin-myosin contraction. All of these findings strongly support that ethanol-exposed astrocytes undergo apoptosis by anoikis and also that the RhoA/ROCK-I/MLC pathway participates in this process.

Rapid up-regulation of the neuronal serotoninergic phenotype by brain-derived neurotrophic factor and cyclic adenosine monophosphate: relations with raphe astrocytes

Up-regulation of the neuronal serotoninergic phenotype in relation to astrocytic population was studied in primary cultures of rat embryonic rostral raphe. Short treatments (18 hr at day in vitro 4) with brain-derived neurotrophic factor (BDNF) or dibutyryl-cAMP (dBcAMP) increased the number of serotoninergic neurons by approximately 80% and approximately 40%, respectively, and markedly enhanced the branching (by 11-fold and 5-fold, respectively) and total length (by 4-fold and 2.5-fold, respectively) of their neurites. Concomitantly, under BDNF treatment, the astrocyte population was decreased by half and became mostly protoplasmic-like. In contrast, dBcAMP treatment also reduced the astrocytic cell density (by one-third) but induced a stellate morphology. Similar short treatment with the astrocyte-derived S100beta factor induced no modification of the serotonin (5-HT) neuronal phenotype nor of astrocytes morphology. Both BDNF- and cAMP-induced effects were abolished by simultaneous treatment with the specific tyrosine kinase inhibitor genistein, suggesting a role for the high-affinity BDNF receptor tyrosine kinase (TrkB). These data suggest that BDNF and cAMP, but not S100beta, rapidly induce both an up-regulation of the 5-HT neuronal phenotype and modifications of the neighboring astrocytes in a TrkB-dependent manner.

Signaling pathways involved with serotonin1A agonist-mediated neuroprotection against ethanol-induced apoptosis of fetal rhombencephalic neurons

Previously, this laboratory demonstrated that developing serotonin (5-HT) neurons and other fetal rhombencephalic neurons are reduced by in vivo and in vitro exposure to ethanol, effects that are related to ethanol's augmentation of apoptosis. We also found that 5-HT1A agonists diminished the ethanol-associated reduction of 5-HT neurons and other fetal rhombencephalic neurons by attenuating the pro-apoptotic effects of ethanol. Presently, we investigated the hypothesis that the protective/anti-apoptotic effects of a 5-HT1A agonist on fetal rhombencephalic neurons are mediated by activation of the phosphatidylinositol 3' kinase (PI-3K) and/or the mitogen-activated protein kinase kinase (MAPKK) pathway. Apoptotic and non-apoptotic fetal rhombencephalic neurons were quantitated in primary cultures that were treated with 50 mM ethanol and with 100 nM of a 5-HT1A agonist such as 8-OH-DPAT [8-hydroxy 2-(di-n-propylamino)tetralin], ipsapirone, or buspirone. Analysis of neurons stained with Hoechst 33342 demonstrated the anti-apoptotic effects of 5-HT1A agonists and implicated the involvement of the PI-3K pathway and possibly the MAPKK pathway with the protective effects of these drugs. The protective effects were blocked by a 5-HT1A antagonist (WAY 100635), an inhibitor of PI-3K (LY294002), and an inhibitor of MAPKK (PD98059). Western blot analyses showed that ethanol treatment reduces basal pAkt levels. These analyses also provide support for the involvement of the PI-3K pathway; ipsapirone stimulated the phosphorylation of Akt in control and ethanol-treated neurons, and these effects were antagonized by LY294002.

Chronic gliosis induced by loss of S-100B: knockout mice have enhanced GFAP-immunoreactivity but blunted response to a serotonin challenge

Serotonin (5-HT) can induce a release of intraglial S-100B and produce a change in glial morphology. Because S-100B can inhibit polymerization of glial fibrillary acidic protein (GFAP), we hypothesize that glial reactivity may reflect the loss of intraglial S-100B. Adult male transgenic S-100B homozygous knockout (-/-) mice (KO) and wild-type CD-1 (WT) mice were studied. S-100B-immunoreactivity (IR) was seen in the brain tissue of WT (CD-1) but not S-100B KO (-/-) mice. GFAP-IR was seen in both WT (CD-1) and S-100B KO (-/-) glia cells, but S-100B KO (-/-) GFAP-IR cells appeared larger, darker, and more branched than in WT (CD-1). To compare the response of GFAP-IR cells to 5-HT in S-100B KO (-/-) and WT (CD-1) mice, we injected animals with para-chloroamphetamine (PCA) over 2 days (5 and 10 mg/ml). PCA is a potent 5-HT releaser which can induce gliosis in the rodent brain. In WT (CD-1) mice, the size, branching, and density of GFAP-IR cells were significantly increased after PCA injections. No increase in GFAP-IR activation was seen in the S-100B KO (-/-) after PCA injections. Cell-specific densitometry (set at a threshold of 0-150 based on a scale of 255) in these animals statistically showed an increase in GFAP-IR after PCA injections in WT (CD-1) but not S-100B KO (-/-) mice. These results are consistent with the hypothesis that 5-HT may modulate glial morphology by inducing a release of intracellular S-100B, and this pathway is inoperable in the S-100B KO (-/-).

S100b counteracts effects of the neurotoxicant trimethyltin on astrocytes and microglia

Central nervous system degenerative diseases are often characterized by an early, strong reaction of astrocytes and microglia. Both these cell types can play a double role, protecting neurons against degeneration through the synthesis and secretion of trophic factors or inducing degeneration through the secretion of toxic molecules. Therefore, we studied the effects of S100B and trimethyltin (TMT) on human astrocytes and microglia with two glial models, primary cultures of human fetal astrocytes and a microglia cell line. After treatment with 10(-5) M TMT, astrocytes showed morphological alterations associated with an increase in glial fibrillary acidic protein (GFAP) expression and changes in GFAP filament organization. Administration of S100B before TMT treatment prevented TMT-induced changes in morphology and GFAP expression. A decrease in inducible nitric oxide synthase expression was observed in astrocytes treated with TMT, whereas the same treatment induced iNOS expression in microglia. In both cases, S100B prevented TMT-induced changes. Tumor necrosis factor-alpha mRNA expression in astrocytes was not modified by TMT treatment, whereas it was increased in microglia cells. S100B pretreatment blocked the TMT-induced increase in TNF-alpha expression in microglia. To trace the mechanisms involved in S100B activity, the effect of BAY 11-7082, an inhibitor of nuclear factor-kappaB (NF-kappaB) activation, and of PD98059, an inhibitor of MEK-ERK1/2, were investigated. Results showed that the protective effects of S100B against TMT toxicity in astrocytes depend on NF-kappaB, but not on ERK1/2 activation. These results might help in understanding the role played by glial cells in brain injury after exposure to chemical neurotoxicants and support the view that S100B may protect brain cells in case of injury. (c) 2005 Wiley-Liss, Inc.

The serotonin-1A agonist ipsapirone prevents ethanol-associated death of total rhombencephalic neurons and prevents the reduction of fetal serotonin neurons

Previously, this laboratory showed that in utero and in vitro ethanol exposure significantly reduces developing serotonin (5-HT) neurons and that treatment with a 5-HT1A agonist such as buspirone or ipsapirone prevents the ethanol-associated loss. The present study investigated whether ethanol decreases fetal rhombencephalic neurons, including 5-HT neurons, by causing apoptosis. We also investigated whether ipsapirone prevents the ethanol-associated deficit of fetal rhombencephalic neurons by reducing apoptosis. The results of these studies strongly suggest that the ethanol-associated reduction in fetal rhombencephalic neurons that accompanies both in utero and in vitro exposure to physiological concentrations of ethanol is associated with increased apoptosis in these neurons. A physiological concentration of ethanol (i.e., 50 mM) increases apoptosis in fetal rhombencephalic neurons and decreases the number 5-HT neurons. It also appears that the 5-HT1A agonist ipsapirone provides neuroprotection to these neurons by reducing apoptosis. Another mechanism by which ethanol-associated apoptosis can be blocked is by including serum proteins in the media at a concentration of 1% or higher; this concentration of serum proteins is high in comparison to the protein concentration in cerebrospinal fluid.

Astrocyte apoptosis: implications for neuroprotection

Astrocytes, the most abundant glial cell types in the brain, provide metabolic and trophic support to neurons and modulate synaptic activity. Accordingly, impairment in these astrocyte functions can critically influence neuronal survival. Recent studies show that astrocyte apoptosis may contribute to pathogenesis of many acute and chronic neurodegenerative disorders, such as cerebral ischemia, Alzheimer's disease and Parkinson's disease. We found that incubation of cultured rat astrocytes in a Ca(2+)-containing medium after exposure to a Ca(2+)-free medium causes an increase in intracellular Ca(2+) concentration followed by apoptosis, and that NF-kappa B, reactive oxygen species, and enzymes such as calpain, xanthine oxidase, calcineurin and caspase-3 are involved in reperfusion-induced apoptosis. Furthermore, we demonstrated that heat shock protein, mitogen-activated protein/extracellular signal-regulated kinase, phosphatidylinositol-3 kinase and cyclic GMP phosphodiesterase are target molecules for anti-apoptotic drugs. This review summarizes (1) astrocytic functions in neuroprotection, (2) current evidence of astrocyte apoptosis in both in vitro and in vivo studies including its molecular pathways such as Ca(2+) overload, oxidative stress, NF-kappa B activation, mitochondrial dysfunction, endoplasmic reticulum stress, and protease activation, and (3) several drugs preventing astrocyte apoptosis. As a whole, this article provides new insights into the potential role of astrocytes as targets for neuroprotection. In addition, the advance in the knowledge of molecular mechanisms of astrocyte apoptosis may lead to the development of novel therapeutic strategies for neurodegenerative disorders.

Cytosine arabinofuranoside-induced activation of astrocytes increases the susceptibility of neurons to glutamate due to the release of soluble factors

Activation of astrocytes occurs during many forms of CNS injury, but its importance for neuronal survival is poorly understood. When hippocampal cultures of neurons and astrocytes were treated from day 2-4 in vitro (DIV 2-4) with 1 microM cytosine arabinofuranoside (AraC), we observed a stellation of astrocytes, an increase in glial fibrillary acidic protein (GFAP) level as well as a higher susceptibility of the neurons to glutamate compared with cultures treated from DIV 2-4 with vehicle. To find out whether factors released into the culture medium were responsible for the observed differences in glutamate neurotoxicity, conditioned medium of AraC-treated cultures (MCMAraC) was added to vehicle-treated cultures and conditioned medium of vehicle-treated cultures (MCMvh) was added to AraC-treated cultures 2 h before and up to 18 h after the exposure to 1mM glutamate for 1 h. MCMAraC increased glutamate neurotoxicity in vehicle-treated cultures and MCMvh reduced glutamate neurotoxicity in AraC-treated cultures. Heat-inactivation of MCMvh increased, whereas heat-inactivation of MCMAraC did not affect glutamate toxicity suggesting that heat-inactivation changed the proportion of factors in MCMvh inhibiting and exacerbating the excitotoxic injury. Similar findings were obtained using conditioned medium of pure astrocyte cultures of DIV 12 treated from DIV 2-4 with vehicle or 1 microM AraC suggesting that heat-sensitive factors in MCMvh were mainly derived from astrocytes. Treatment of hippocampal cultures with 1mM dibutyryl-cAMP for 3 days induced an activation of the astrocytes similar to AraC and increased neuronal susceptibility to glutamate. Our findings provide evidence that activation of astrocytes impairs their ability to protect neurons after excitotoxic injury due to changes in the release of soluble and heat-sensitive factors.

Effects of ethanol and 5-HT1A agonists on astroglial S100B

Previous studies from this and another laboratory demonstrated that in utero ethanol exposure reduces 5-HT neurons and S100B-immunopositive glia that are proximal to these neurons. Our laboratory also found that these effects are prevented by maternal treatment with a 5-HT(1A) agonist. Because of S100B's important role in the development of 5-HT neurons, the present study used both in vivo and in vitro models to investigate the potential involvement of S100B with the damaging effects of ethanol and with the protective effects of 5-HT(1A) agonists. We used in situ hybridization to address whether a 5-HT(1A) agonist could potentially affect S100B mRNA in vivo. Maternal treatment with buspirone between gestation days 13 and 20 significantly increased S100B mRNA in neuroepithelium of G20 offspring of control (40%) and ethanol-fed dams (20%). However, S100B mRNA was not altered in neuroepithelium from ethanol-exposed offspring. In astroglial cultures, we examined whether ethanol reduces the release of S100B and whether a 5-HT(1A) agonist could stimulate the release of this protein. We also evaluated the effects of ethanol and ipsapirone on astroglial content of S100B. Neither the concentration of S100B in astroglial media nor astroglial content of S100B were affected by ethanol. However, treatment with 100 nM ipsapirone, a 5-HT(1A) agonist, between the 6th and 7th day in vitro, increased astroglial release of S100B 2- to 3-fold. Thus, the protective effects of a 5-HT(1A) agonist on ethanol-treated 5-HT neurons might be associated with the ability of these drugs to release the neurotrophic factor S100B from astrocytes.