Regulation of serotonin transporter gene expression in human glial cells by growth factors

Wiring and Volume Transmission: An Overview of the Dual Modality for Serotonin Neurotransmission

Serotonin is a neurotransmitter involved in the modulation of a multitude of physiological and behavioral processes. In spite of the relatively reduced number of serotonin-producing neurons present in the mammalian CNS, a complex long-range projection system provides profuse innervation to the whole brain. Heterogeneity of serotonin receptors, grouped in seven families, and their spatiotemporal expression pattern account for its widespread impact. Although neuronal communication occurs primarily at tiny gaps called synapses, wiring transmission, another mechanism based on extrasynaptic diffusion of neuroactive molecules and referred to as volume transmission, has been described. While wiring transmission is a rapid and specific one-to-one modality of communication, volume transmission is a broader and slower mode in which a single element can simultaneously act on several different targets in a one-to-many mode. Some experimental evidence regarding ultrastructural features, extrasynaptic localization of receptors and transporters, and serotonin-glia interactions collected over the past four decades supports the existence of a serotonergic system of a dual modality of neurotransmission, in which wiring and volume transmission coexist. To date, in spite of the radical difference in the two modalities, limited information is available on the way they are coordinated to mediate the specific activities in which serotonin participates. Understanding how wiring and volume transmission modalities contribute to serotonergic neurotransmission is of utmost relevance for the comprehension of serotonin functions in both physiological and pathological conditions.

Impact of Solute Carrier Transporters in Glioma Pathology: A Comprehensive Review

Solute carriers (SLCs) are essential for brain physiology and homeostasis due to their role in transporting necessary substances across cell membranes. There is an increasing need to further unravel their pathophysiological implications since they have been proposed to play a pivotal role in brain tumor development, progression, and the formation of the tumor microenvironment (TME) through the upregulation and downregulation of various amino acid transporters. Due to their implication in malignancy and tumor progression, SLCs are currently positioned at the center of novel pharmacological targeting strategies and drug development. In this review, we discuss the key structural and functional characteristics of the main SLC family members involved in glioma pathogenesis, along with their potential targeting options to provide new opportunities for CNS drug design and more effective glioma management.

Age-Related Changes in Central Nervous System 5-Hydroxytryptamine Signalling and Its Potential Effects on the Regulation of Lifespan

Serotonin or 5-hydroxytryptamine (5-HT) is an important neurotransmitter in the central nervous system and the periphery. Most 5-HT (~99%) is found in the periphery where it regulates the function of the gastrointestinal (GI) tract and is an important regulator of platelet aggregation. However, the remaining 1% that is found in the central nervous system (CNS) can regulate a range of physiological processes such as learning and memory formation, mood, food intake, sleep, temperature and pain perception. More recent work on the CNS of invertebrate model systems has shown that 5-HT can directly regulate lifespan.This chapter will focus on detailing how CNS 5-HT signalling is altered with increasing age and the potential consequences this has on its ability to regulate lifespan.

Therapeutic targeting of membrane-associated proteins in central nervous system tumors

The activity of the most complex system, the central nervous system (CNS) is profoundly regulated by a huge number of membrane-associated proteins (MAP). A minor change stimulates immense chemical changes and the elicited response is organized by MAP, which acts as a receptor of that chemical or channel enabling the flow of ions. Slight changes in the activity or expression of these MAPs lead to severe consequences such as cognitive disorders, memory loss, or cancer. CNS tumors are heterogeneous in nature and hard-to-treat due to random mutations in MAPs; like as overexpression of EGFRvIII/TGFβR/VEGFR, change in adhesion molecules α5β3 integrin/SEMA3A, imbalance in ion channel proteins, etc. Extensive research is under process for developing new therapeutic approaches using these proteins such as targeted cytotoxic radiotherapy, drug-delivery, and prodrug activation, blocking of receptors like GluA1, developing viral vector against cell surface receptor. The combinatorial approach of these strategies along with the conventional one might be more potential. Henceforth, our review focuses on in-depth analysis regarding MAPs aiming for a better understanding for developing an efficient therapeutic approach for targeting CNS tumors.

Lactobacillus acidophilus and Bifidobacterium longum supernatants upregulate the serotonin transporter expression in intestinal epithelial cells

BACKGROUND/AIMS

Probiotics play a role in relieving irritable bowel syndrome (IBS); however, the underlying mechanism is yet unclear. The aim of the study was to investigate the effects of the supernatants of Lactobacillus acidophilus and Bifidobacterium longum on the expression of serotonin transporter (SERT) messenger ribonucleic acid (mRNA) and protein.

MATERIALS AND METHODS

HT-29 and Caco-2 cells were treated with different concentrations of L. acidophilus and B. longum supernatants for 12 h and 24 h, respectively. SERT mRNA and proteins levels were detected by real-time polymerase chain reaction (real-time PCR) and Western-blotting.

RESULTS

The mRNA levels of SERT in HT-29 and Caco-2 cells treated with different concentrations of L. acidophilus or B. longum supernatants for 12 h and 24 h, each, were higher than that in the control groups. In addition, the expression of the protein in both cells was also upregulated, which was approximately similar to that of the corresponding mRNA.

CONCLUSIONS

L. acidophilus and B. longum supernatants can upregulate SERT mRNA and protein levels in intestinal epithelial cells.

Regulatory Pathways of Monoamine Oxidase A during Social Stress

Social stress has a high impact on many biological systems in the brain, including serotonergic (5-HT) system-a major drug target in the current treatment for depression. Hyperactivity of hypothalamic-pituitary-adrenal (HPA) axis and monoamine oxidase A (MAO-A) are well-known stress responses, which are involved in the central 5-HT system. Although, many MAO-A inhibitors have been developed and used in the therapeutics of depression, effective management of depression by modulating the activity of MAO-A has not been achieved. Identifying the molecular pathways that regulate the activity of MAO-A in the brain is crucial for developing new drug targets for precise control of MAO-A activity. Over the last few decades, several regulatory pathways of MAO-A consisting of Kruppel like factor 11 (KLF11), Sirtuin1, Ring finger protein in neural stem cells (RINES), and Cell division cycle associated 7-like protein (R1) have been identified, and the influence of social stress on these regulatory factors evaluated. This review explores various aspects of these pathways to expand our understanding of the roles of the HPA axis and MAO-A regulatory pathways during social stress. The first part of this review introduces some components of the HPA axis, explains how stress affects them and how they interact with the 5-HT system in the brain. The second part summarizes the novel regulatory pathways of MAO-A, which have high potential as novel therapeutic targets for depression.

Down-regulation of serotonin and dopamine transporter genes in individual rats expressing a gambling-prone profile: A possible role for epigenetic mechanisms

Gambling Disorder (GD) is characterized by excessive gambling despite adverse consequences on individual functioning. In spite of some positive findings, it is difficult to draw any conclusion on the genetics of GD. Indeed, beyond DNA sequence variation, other regulatory mechanisms (like those that engage epigenetics) may explain gene alterations in this addictive disease. Wistar male rats underwent an operant task for the evaluation of individual propensity to gamble. Few rats, after having learnt to prefer nose-poking for a large over a small food reward, were sacrificed to obtain a baseline profile of gene expression at both central and peripheral levels. In the remaining rats, probability of occurrence of large-reward delivery decreased progressively to very low levels. Thus, rats were faced with temptation to "gamble", i.e. to nose-poke for a binge reward, whose delivery was omitted the majority of times. After 3weeks of testing, rats showing a clear-cut profile of either gambling proneness or aversion were selected and sacrificed after the last session. A selective down-regulation of i) serotonin transporter in prefrontal cortex, ii) tyrosine hydroxylase in ventral striatum, iii) dopamine transporter in lymphocytes was evidenced in "gambler" vs "non-gambler" rats. The exposure to such operant task (compared to home-cage alone) modulated ventrostriatal but not prefrontal genes. A consistent increase of DNA methylation, in one specific CpG site at serotonin transporter gene, was evident in prefrontal cortex of "gambler" rats. Elucidation of epigenetic changes occurring during GD progression may pave the way to the development of new therapeutic strategies through specific modulation of epigenetic factors.

Exposure to serotonin adversely affects oligodendrocyte development and myelination in vitro

Serotonin (5-hydroxytryptamine, 5-HT) has been implicated to play critical roles in early neural development. Recent reports have suggested that perinatal exposure to selective serotonin reuptake inhibitors (SSRIs) resulted in cortical network miswiring, abnormal social behavior, callosal myelin malformation, as well as oligodendrocyte (OL) pathology in rats. To gain further insight into the cellular and molecular mechanisms underlying SSRIs-induced OL and myelin abnormalities, we investigated the effect of 5-HT exposure on OL development, cell death, and myelination in cell culture models. First, we showed that 5-HT receptor 1A and 2A subtypes were expressed in OL lineages, using immunocytochemistry, Western blot, as well as intracellular Ca(2+) measurement. We then assessed the effect of serotonin exposure on the lineage development, expression of myelin proteins, cell death, and myelination, in purified OL and neuron-OL myelination cultures. For pure OL cultures, our results showed that 5-HT exposure led to disturbance of OL development, as indicated by aberrant process outgrowth and reduced myelin proteins expression. At higher doses, such exposure triggered a development-dependent cell death, as immature OLs exhibited increasing susceptibility to 5-HT treatment compared to OL progenitor cells (OPC). We showed further that 5-HT-induced immature OL death was mediated at least partially via 5-HT2A receptor, since cell death could be mimicked by 5-HT2A receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride, (±)-2,5-dimethoxy-4-iodoamphetamine hydrochloride, but atten-uated by pre-treatment with 5-HT2A receptor antagonist ritanserin. Utilizing a neuron-OL myelination co-culture model, our data showed that 5-HT exposure significantly reduced the number of myelinated internodes. In contrast to cell injury observed in pure OL cultures, 5-HT exposure did not lead to OL death or reduced OL density in neuron-OL co-cultures. However, abnormal patterns of contactin-associated protein (Caspr) clustering were observed at the sites of Node of Ranvier, suggesting that 5-HT exposure may affect other axon-derived factors for myelination. In summary, this is the first study to demonstrate that manipulation of serotonin levels affects OL development and myelination, which may contribute to altered neural connectivity noted in SSRIs-treated animals. The current in vitro study demonstrated that exposure to high level of serotonin (5-HT) led to aberrant oligodendrocyte (OL) development, cell injury, and myelination deficit. We propose that elevated extracellular serotonin levels in the fetal brain, such as upon the use of selective serotonin reuptake inhibitors (SSRIs) during pregnancy, may adversely affect OL development and/or myelination, thus contributing to altered neural connectivity seen in Autism Spectrum Disorders. OPC = oligodendrocyte progenitor cell.

Epidermal growth factor upregulates serotonin transporter and its association with visceral hypersensitivity in irritable bowel syndrome

AIM: To investigate the role of epidermal growth factor (EGF) in visceral hypersensitivity and its effect on the serotonin transporter (SERT).

METHODS: A rat model for visceral hypersensitivity was established by intra-colonic infusion of 0.5% acetic acid in 10-d-old Sprague-Dawley rats. The visceral sensitivity was assessed by observing the abdominal withdrawal reflex and recording electromyographic activity of the external oblique muscle in response to colorectal distension. An enzyme-linked immunosorbent assay was used to measure the EGF levels in plasma and colonic tissues. SERT mRNA expression was detected by real-time PCR while protein level was determined by Western blot. The correlation between EGF and SERT levels in colon tissues was analyzed by Pearson’s correlation analysis. SERT function was examined by tritiated serotonin (5-HT) uptake experiments. Rat intestinal epithelial cells (IEC-6) were used to examine the EGF regulatory effect on SERT expression and function via the EGF receptor (EGFR).

RESULTS: EGF levels were significantly lower in the rats with visceral hypersensitivity as measured in plasma (2.639 ± 0.107 ng/mL vs 4.066 ± 0.573 ng/mL, P < 0.01) and in colonic tissue (3.244 ± 0.135 ng/100 mg vs 3.582 ± 0.197 ng/100 mg colon tissue, P < 0.01) compared with controls. Moreover, the EGF levels were positively correlated with SERT levels (r = 0.820, P < 0.01). EGF displayed dose- and time-dependent increased SERT gene expressions in IEC-6 cells. An EGFR kinase inhibitor inhibited the effect of EGF on SERT gene upregulation. SERT activity was enhanced following treatment with EGF (592.908 ± 31.515 fmol/min per milligram vs 316.789 ± 85.652 fmol/min per milligram protein, P < 0.05) and blocked by the EGFR kinase inhibitor in IEC-6 cells (590.274 ± 25.954 fmol/min per milligram vs 367.834 ± 120.307 fmol/min per milligram protein, P < 0.05).

CONCLUSION: A decrease in EGF levels may contribute to the formation of visceral hypersensitivity through downregulation of SERT-mediated 5-HT uptake into enterocytes.

The pro-inflammatory cytokine TNF-α regulates the activity and expression of the serotonin transporter (SERT) in astrocytes

Pro-inflammatory cytokines have been implicated in the precipitation of depression and related disorders, and the antidepressant sensitive serotonin transporter (SERT) may be a major target for immune regulation in these disorders. Here, we focus on astrocytes, a major class of immune competent cells in the brain, to examine the effects of pro-longed treatment with tumor necrosis factor-alpha (TNF-α) on SERT activity. We first established that high-affinity serotonin uptake into C6 glioma cells occurs through a SERT-dependent mechanism. Functional SERT expression is also confirmed for primary astrocytes. In both cell types, exposure to TNF-α resulted in a dose- and time-dependent increase in SERT-mediated 5-HT uptake, which was sustained for at least 48 h post-stimulation. Further analysis in primary astrocytes revealed that TNF-α enhanced the transport capacity (Vmax) of SERT-specific 5-HT uptake, suggesting enhanced transporter expression, consistent with our observation of an increase in SERT mRNA levels. We confirmed that in both, primary astrocytes and C6 glioma cells, treatment with TNF-α activates the p38 mitogen-activated protein kinase (MAPK) signaling pathway. Pre-treatment with the p38 MAPK inhibitor SB203580 attenuated the TNF-α mediated stimulation of 5-HT transport in both, C6 glioma and primary astrocytes. In summary, we show that SERT gene expression and activity in astrocytes is subject to regulation by TNF-α, an effect that is at least in part dependent on p38 MAPK activation.

Disruption of the serotonergic system after neonatal hypoxia-ischemia in a rodent model

Identifying which specific neuronal phenotypes are vulnerable to neonatal hypoxia-ischemia, where in the brain they are damaged, and the mechanisms that produce neuronal losses are critical to determine the anatomical substrates responsible for neurological impairments in hypoxic-ischemic brain-injured neonates. Here we describe our current work investigating how the serotonergic network in the brain is disrupted in a rodent model of preterm hypoxia-ischemia. One week after postnatal day 3 hypoxia-ischemia, losses of serotonergic raphé neurons, reductions in serotonin levels in the brain, and reduced serotonin transporter expression are evident. These changes can be prevented using two anti-inflammatory interventions; the postinsult administration of minocycline or ibuprofen. However, each drug has its own limitations and benefits for use in neonates to stem damage to the serotonergic network after hypoxia-ischemia. By understanding the fundamental mechanisms underpinning hypoxia-ischemia-induced serotonergic damage we will hopefully move closer to developing a successful clinical intervention to treat neonatal brain injury.

Modulation of human serotonin transporter expression by 5-HTTLPR in colon cells

Serotonin (5-HT) is a monoamine neurotransmitter and plays important roles in several of the human body's systems. Known as a primary target for psychoactive drug development, the 5-HT transporter (5-HTT, SERT) plays a critical role in the regulation of serotonergic function by reuptaking 5-HT. The allelic variation of 5-HTT expression is caused by functional gene promoter polymorphism with two principal variant alleles, 5-HTT gene-linked polymorphic region (5-HTTLPR). It has been demonstrated that 5-HTTLPR is associated with numerous neuropsychiatric disorders. The functional roles of 5-HTTLPR have been reported in human choriocarcinoma (JAR), lymphoblast and raphe cells. To date, the significance of 5-HTTLPR in gastrointestinal tract-derived cells has never been elucidated. Thus, the impact of 5-HTTLPR on 5-HTT transcription was studied in SW480 human colon carcinoma cells, which were shown to express 5-HTT. We found 42-bp fragment in long (L) allele as compared to short (S) allele, and this allelic difference resulted in 2-fold higher transcriptional efficiency of L allele (P < 0.05) as demonstrated using a functional reporter gene assay. Nevertheless, the transcriptional effect of estrogen and glucocorticoid on 5-HTT expression via 5-HTTLPR was not found in this cell line. Our study was the first to demonstrate the molecular role of this allelic variation in gastrointestinal tract cells.

Adolescent escitalopram administration modifies neurochemical alterations in the hippocampus of maternally separated rats

Early life stress is a potential precursor of eventual neuropsychiatric diseases and may result in altered neurodevelopment and function of the hippocampus, which thus provides a site at which potential interventions to modify the effects of early life stress may act. In this study, Sprague-Dawley rat pups comprising male and female animals underwent maternal separation (MS) for 180 min from postnatal days (PND) 2 to 14, or were left with their dams. They subsequently received daily administration of saline (0.9%), escitalopram (10 mg/kg), or no treatment during adolescence (PND 43-60). All adult animals underwent brain magnetic resonance imaging (MRI) and bilateral hippocampal proton magnetic resonance spectroscopy ((1)H-MRS). Neither MS nor escitalopram treatment had a significant effect on hippocampal volume. Adult rats that experienced MS displayed significantly increased choline-containing compounds (Cho) and decreased N-acetylaspartate (NAA), glutamate (Glu) and Myo-inositol (MI) relative to the stable neurometabolite creatine (Cr) in hippocampus. Administration of escitalopram during adolescence could modify the alterations of NAA/Cr, Glu/Cr and MI/Cr. The effects of MS on hippocampal neurochemistry were most significant in the right hippocampus. These results indicate that MS in rats has long-term consequences on hippocampal neurochemistry reflective of neural density/functional integrity, especially on the right hippocampus, and adolescent administration with escitalopram can at least partially ameliorate these neurochemical alterations. Furthermore, these metabolite changes seem to be more sensitive indicators of the results from early life stress than volume changes.

The opioid antagonist, beta-funaltrexamine, inhibits chemokine expression in human astroglial cells

Emerging evidence indicates that neuroinflammatory responses in astroglia, including chemokine expression, are altered by opioids. Astroglial chemokines, such as CXCL10, are instrumental in response to many neuropathological insults. Opioid mediated disruption of astroglial CXCL10 expression may be detrimental in opioid abusers or patients receiving acute opioid therapy. We have characterized the in vitro effects of opioids on CXCL10 protein expression in human astroglial (A172) cells. The proinflammatory cytokine, tumor necrosis factor (TNF)alpha induced CXCL10 expression in A172 cells. Using MG-132, helenalin and SN50 [inhibitors of the transcription factor, nuclear factor (NF)-kappaB], we determined that NF-kappaB activation is instrumental in TNFalpha-induced CXCL10 expression in A172 astroglia. Morphine exposure during the 24 h TNFalpha stimulation period did not alter CXCL10 expression. However, fentanyl, a more potent mu-opioid receptor (MOR) agonist, inhibited TNFalpha-induced CXCL10 expression. Interestingly, neither the non-selective opioid receptor antagonist, naltrexone nor beta-funaltrexamine (beta-FNA), a highly selective MOR antagonist, blocked fentanyl mediated inhibition of TNFalpha-induced CXCL10 expression. Rather, beta-FNA dose-dependently inhibited TNFalpha-induced CXCL10 expression with a greater potency than that observed for fentanyl. Immunoblot analysis indicated that morphine, fentanyl and beta-FNA each reduced TNFalpha-induced nuclear translocation of NF-kappaB p65. These data show that beta-FNA and fentanyl inhibit TNFalpha-induced CXCL10 expression via a MOR-independent mechanism. Data also suggest that inhibition of TNFalpha-induced CXCL10 expression by fentanyl and beta-FNA is not directly related to a reduction in NF-kappaB p65 nuclear translocation. Further investigation is necessary in order to fully elucidate the mechanism through which these two opioid compounds inhibit CXCL10 expression. Understanding the mechanism by which chemokine expression is suppressed, particularly by the opioid antagonist, beta-FNA, may provide insights into the development of safe and effective treatments for neuroinflammation.

HIV-1 neuropathogenesis: glial mechanisms revealed through substance abuse

Neuronal dysfunction and degeneration are ultimately responsible for the neurocognitive impairment and dementia manifest in neuroAIDS. Despite overt neuronal pathology, HIV-1 does not directly infect neurons; rather, neuronal dysfunction or death is largely an indirect consequence of disrupted glial function and the cellular and viral toxins released by infected glia. A role for glia in HIV-1 neuropathogenesis is revealed in experimental and clinical studies examining substance abuse-HIV-1 interactions. Current evidence suggests that glia are direct targets of substance abuse and that glia contribute markedly to the accelerated neurodegeneration seen with substance abuse in HIV-1 infected individuals. Moreover, maladaptive neuroplastic responses to chronic drug abuse might create a latent susceptibility to CNS disorders such as HIV-1. In this review, we consider astroglial and microglial interactions and dysfunction in the pathogenesis of HIV-1 infection and examine how drug actions in glia contribute to neuroAIDS.

A role for serotonin (5-HT) in hepatic stellate cell function and liver fibrosis

Hepatic stellate cells (HSCs) are key cellular components of hepatic wound healing and fibrosis. There is emerging evidence that the fibrogenic function of HSCs may be influenced by neurochemical and neurotrophic factors. This study addresses the potential for the serotonin (5-HT) system to influence HSC biology. Rat and human HSCs express the 5-HT1B, 5-HT1F 5-HT2A 5-HT2B, and 5-HT7 receptors, with expression of 5-HT1B 5-HT2A and 5-HT2B being induced on HSC activation. Induction of 5-HT2A and 5-HT2B was 106+/-39- and 52+/-8.5-fold that of quiescent cells, respectively. 5-HT2B was strongly associated with fibrotic tissue in diseased rat liver. Treatment of HSCs with 5-HT2 antagonists suppressed proliferation and elevated their rate of apoptosis; by contrast 5-HT was protective against nerve growth factor-induced apoptosis. 5-HT synergized with platelet-derived growth factor to stimulate increased HSC proliferation. HSCs were shown to express a functional serotonin transporter and to participate in both active uptake and release of 5-HT. We conclude that HSCs express key regulatory components of the 5-HT system enabling them to store and release 5-HT and to respond to the neurotransmitter in a profibrogenic manner. Antagonists that selectively target the 5-HT class of receptors may be exploited as antifibrotic drugs.

Zinc: the new antidepressant?

Low serum zinc levels have been linked to major depression. Furthermore, zinc treatment has been shown to have an antidepressant effect. With the hope of understanding the role of zinc in mood disorders, recent work has begun to explore possible mechanisms of zinc action on serotonin uptake in the brain.

Initial conditions of psychotropic drug response: studies of serotonin transporter long promoter region (5-HTTLPR), serotonin transporter efficiency, cytokine and kinase gene expression relevant to depression and antidepressant outcome

The Hypothesis of Initial Conditions posits that differences in psychotropic drug response result from individual differences in receptor site kinetics, and differences in the sensitivity of downstream receptor-linked responses. This work examines data consistent with the hypothesis, specific to genetic and kinetic differences of the serotonin (5-HT) transporter (SERT), as they may be linked to divergent antidepressant response (ADR). The mechanisms for divergent ADR in association with different initial SERT function are considered within the context of SERT trafficking as sensitive to various different kinase and cytokine signals, some of which are dependent on the 5-HTTLPR polymorphism of the SERT gene. Pilot data suggest that human lymphocytes show kinase changes similar to those found in rat brain with ADT. These studies additionally suggest that ADT prompts a shift in cytokine gene expression toward a greater anti-inflammatory/inflammatory ratio. These latter findings are discussed within the context of a literature suggesting increased inflammatory cytokine levels in depression, and recent observations of increased temperature associated with depression. In sum, the data suggest the opportunity to identify response dependent protein (RDP) expression patterns that may differ with dichotomous ADR, and suggest new insights into understanding the mechanisms of psychotropic drug response through an understanding of initial differences in potential for psychotropic drug target regulation during therapy.

Ethanol increases nuclear factor-kappa B activity in human astroglial cells

Alcohol abuse adversely affects essentially all the organs of the body, either directly or indirectly. Ethanol may contribute to brain damage via inflammation. Ethanol may also alter CNS immunocompetence and further the progression of certain CNS infections. Nuclear factor (NF)-kappa B helps regulate inflammatory gene expression in glia. It is possible that ethanol effects on CNS pathology are partly a consequence of ethanol modulation of NF-kappa B-associated pathways in glia. We have assessed the effects of 0.5-6 h ethanol exposure on cytokine (5 ng/ml interleukin-1 beta + 100 ng/ml interferon gamma + 30 ng/ml tumor necrosis factor-alpha)-induced NF-kappa B activation in human A172 astroglial cells. Immunoblot analysis indicated that NF-kappa B p65 nuclear translocation occurred within 0.5 h after cytokine stimulation. Stimulation in the presence of ethanol resulted in increased nuclear p65 levels at 3 h, with 200 mM causing a greater increase than 50 mM ethanol. Gel shift assay data suggested that cytokine-induced NF-kappa B binding activity was greatest in cells exposed to 50 mM ethanol, followed by 200 and 0 mM ethanol exposed cells, respectively. Thus, in cytokine-stimulated cells, 200 mM ethanol resulted in greater nuclear p65 levels, yet, 50 mM ethanol exposure resulted in more pronounced DNA binding by NF-kappa B. These findings demonstrate that acute ethanol enhances p65 activity in human astroglia and further support the hypothesis that ethanol-mediated brain pathology involves modulation of NF-kappa B pathways. A better understanding of the mechanistic events involved in ethanol-induced CNS pathology should provide for therapeutic strategies to combat detrimental effects of alcohol on the CNS.

Activation of epidermal growth factor receptors directs astrocytes to organize in a network surrounding axons in the developing rat optic nerve

In postnatal developing optic nerves, astrocytes organize their processes in a cribriform network to group axons into bundles. In neonatal rat optic nerves in vivo, the active form of EGFR tyrosine kinase is abundantly present when the organization of astrocytes and axons is most actively occurring. Blocking activity of EGFR tyrosine kinase during the development of rat optic nerves in vivo inhibits astrocytes from extending fine processes to surround axons. In vitro, postnatal optic nerve astrocytes, stimulated by EGF, organize into cribriform structures which look remarkably like the in vivo structure of astrocytes in the optic nerve. In addition, when astrocytes are co-cultured with neonatal rat retinal explants in the presence of EGF, astrocytes that are adjacent to the retinal explants, re-organize to an astrocyte-free zone into which neurites grow out from the retinal tissue. We hypothesize that in the developing optic nerve, EGFR activity directs the formation of a histo-architectural structure of astrocytes which surrounds axons and provides a permissive environment for axon development.

Activation of epidermal growth factor receptor causes astrocytes to form cribriform structures

Epidermal growth factor receptor (EGFR) is expressed in reactive astrocytes following injury in the CNS. However, the effects of activation of the EGFR pathway in astrocytes are not well established. In the present study, we demonstrate that activation of EGFR causes optic nerve astrocytes, as well as brain astrocytes, to form cribriform structures with cavernous spaces. Formation of the cribriform structures is dependent on new protein synthesis and cell proliferation. Platelet-derived growth factor and basic fibroblast growth factor were not effective. Smooth muscle cells and epithelial cells do not form cribriform structures in response to EGFR activation. The formation of the cribriform structures appears to be related to a guided migration of astrocytes and the expression of integrin beta1 and extracellular fibronectin in response to activation of EGFR. The EGFR pathway may be a specific, signal transduction pathway that regulates reactive astrocytes to form cavernous spaces in the glial scars following CNS injury and in the compressed optic nerve in glaucomatous optic nerve neuropathy.

Chronic ethanol inhibits CXC chemokine ligand 10 production in human A172 astroglia and astroglial-mediated leukocyte chemotaxis

Astroglia are the most prevalent cell type in the human central nervous system (CNS) and perform important roles in normal tissue homeostasis, during pathological events and following trauma. Astroglial-derived chemokines have important neurotrophic effects and are important to CNS immunocompetence and response to injury, in part, due to their direct role in leukocyte and microglial cell recruitment. However, while ethanol is known to induce CNS pathologies and to be peripherally immunosuppressive, ethanol effects on chemokine expression in human astroglia are essentially unknown. We have demonstrated that chemotaxis of human U937 leukocytic cells, across a 0.5 microm pore polycarbonate transmembrane insert, is induced in response to culture media collected from 10 microg/ml lipopolysaccharide (LPS) + 10 ng/ml interleukin (IL)-1beta-stimulated A172 human astroglia cells. The involvement of the chemokine CXCL10 (also known as interferon-gamma inducible protein or IP-10) in astroglial-induced chemotaxis of U937 cells has been indicated, as chemotaxis can be reduced by an anti-CXCL10 neutralizing antibody. Interestingly, chemotaxis of U937 cells, in response to astroglial-exposed media, is reduced when astroglia are chronically (9 days) exposed to 50 mM ethanol before stimulation with LPS + IL-1beta. Furthermore, we observed that LPS + IL-1beta-stimulated CXCL10 production is inhibited in human A172 astroglia exposed to chronic 50 mM ethanol. Thus, alterations in astroglial CXCL10 expression may disrupt CNS immunocompetence and play an important role in ethanol-induced CNS pathologies.

Acute ethanol exposure modulates expression of inducible nitric-oxide synthase in human astroglia: evidence for a transcriptional mechanism

Astroglia are important in immunocompetence and response to injury within the CNS. Activated astroglia respond, in part, by expressing inducible nitric-oxide synthase (iNOS) and subsequent catalytic production of nitric oxide. Results from a previous study in our laboratory, in the human A172 astroglial cell line, revealed that induction of iNOS activity by tumor necrosis factor-alpha + interferon-gamma + interleukin-1 beta was inhibited by 24-h exposure to a high ethanol concentration (200 mM), but enhanced by 50 mM ethanol. In the work reported in this article, we tested the working hypothesis that ethanol acts transcriptionally to modulate cytokine-induced expression of the iNOS gene, NOS2A, in human astroglia. Ethanol, 50 or 200 mM, did not directly alter in vitro catalytic activity of the iNOS enzyme, indicating that ethanol does not affect the enzyme directly. Likewise, ethanol exposure after a 12-h cytokine-stimulation period had no effect on in vivo iNOS activity. However, when cells were simultaneously exposed to ethanol and cytokines for 12 h, in vivo iNOS activity was altered. That ethanol must be present during cytokine stimulation to influence iNOS activity is consistent with a transcriptional mechanism of action. In addition, steady-state expression of iNOS protein and NOS2A mRNA levels were modulated in a biphasic manner by ethanol similar to that noted previously for iNOS activity. These findings strongly support the suggestion that ethanol modulates cytokine-induced iNOS expression in A172 cells at a pretranslational site. These findings should be instrumental in the identification of the critical ethanol-sensitive elements involved in the regulation of NOS2A in human astroglia.

Glia as a putative target for antidepressant treatments

BACKGROUND

Since the early 1950s, various molecular mechanisms have been invoked to explain how antidepressants work. The most recent suggests that pharmacologically stimulated adult neurogenesis might be involved. Surprisingly, in the adult brain, an important source of new neurons and possibly mediators of neurogenesis appears to be glia, i.e., astrocytes. We have recently shown that protracted administration of the antidepressant fluoxetine to adult rats upregulated the astrocytic protein S100beta content and increased neurogenesis in the hippocampus.

METHODS

Rats were treated with fluoxetine for 21 days; before sacrifice bromodeoxyuridine (BrdU) was injected to label the proliferating cells. Immunofluorescence was used to identify proliferating BrdU-positive cells, and cells immunopositive for S100beta and its receptor receptor for advanced glycation end products (RAGE).

RESULTS

Typically, S100beta-positive cells were observed in the vicinity of BrdU-positive cells. On the other hand, we observed colocalization of RAGE receptors and BrdU immunoreactivities, suggesting that some proliferating cells express these receptors for S100beta. RAGE expression by neuronal cells or neuronal precursors and its activation by S100beta may promote their survival.

LIMITATIONS

The anatomical localization of hippocampal S100beta, its receptor RAGE, and BrdU-positive cells that we describe in this study is only indicative of a putative role for glia in antidepressant-stimulated neurogenesis. Functional in vitro and in vivo studies are needed to directly investigate this role; quantitative assays and time-course studies are also warranted.

CONCLUSION

We propose that a better understanding of glia functioning could establish its role as a target for novel antidepressant treatments.

Abnormal expression of epidermal growth factor and its receptor in the forebrain and serum of schizophrenic patients

Epidermal growth factor (EGF) comprises a structurally related family of proteins containing heparin-binding EGF-like growth factor (HB-EGF) and transforming growth factor alpha (TGFalpha) that regulates the development of dopaminergic neurons as well as monoamine metabolism. We assessed the contribution of EGF to schizophrenia by measuring EGF family protein levels in postmortem brains and in fresh serum of schizophrenic patients and control subjects. EGF protein levels were decreased in the prefrontal cortex and striatum of schizophrenic patients, whereas the levels of HB-EGF and TGFalpha were not significantly different in any of the regions examined. Conversely, EGF receptor expression was elevated in the prefrontal cortex. Serum EGF levels were markedly reduced in schizophrenic patients, even in young, drug-free patients. Chronic treatment of animals with the antipsychotic drug haloperidol had no influence on EGF levels in the brain or serum. These findings suggest that there is abnormal EGF production in various central and peripheral tissues of patients with both acute and chronic schizophrenia. EGF might thus provide a molecular substrate for the pathologic manifestation of the illness, although additional studies are required to determine a potential link between impaired EGF signaling and the pathology/etiology of schizophrenia.

Functional expression of the norepinephrine transporter in cultured rat astrocytes

We assessed the functional expression of the norepinephrine (NE) transporter (NET) in cultured rat cortical astrocytes. Specific [3H]NE uptake increased in a time-dependent manner, and this uptake involves temperature- and Na+-sensitive mechanisms. The Na+-dependent [3H]NE uptake was saturable, and the Km for the process was 539.3 +/- 55.4 nm and the Vmax was 1.41 +/- 0.03 pmol/mg protein/min. Ouabain, a Na+-K+ ATPase inhibitor, significantly inhibited Na+-dependent [3H]NE uptake. The selective NE uptake inhibitor nisoxetine, the tricyclic antidepressants desipramine and imipramine, and the serotonin and NE reuptake inhibitor (SNRI) milnacipran very potently inhibited Na+-dependent [3H]NE uptake. On the other hand, GBR-12935 (a selective dopamine uptake inhibitor), fluvoxamine (a selective serotonin reuptake inhibitor), venlafaxine (a SNRI) and cocaine had weaker inhibitory activities. RT-PCR demonstrated that astrocytes expressed mRNA for the cloned NET protein, which was characterized as neuronal NET. Western blots indicated that anti-NET polyclonal antibody recognized a major band of 80 kDa in astrocytes. These data indicate that the neuronal NET is functionally expressed in cultured rat astrocytes. Glial cells may exert significant control of noradrenergic activity by inactivating NE that escapes neuronal re-uptake in sites distant from terminals, and are thus cellular targets for antidepressant drugs that inhibit NE uptake.

Mechanisms of bFGF and NT-4 potentiation of necrotic neuronal death

The effects of neurotrophic factors on necrotic neuronal death are controversial. In this study we found that both neurotrophin-4 (NT-4) and basic fibroblast growth factor (bFGF) potentiated necrotic neuronal death caused by exposure to oxygen-glucose deprivation or iron-citrate (Fe) in cortical cultures. However, there were significant differences in the actions of the two neurotrophic factors. Neurotrophin-4 protected against apoptotic neuronal death, while bFGF had no effect on apoptotic death in these cultures. Furthermore, potentiation of oxygen-glucose deprivation induced necrotic death by NT-4 required pretreatment (24 h), while pretreatment with bFGF had no effect. However, acute treatment with bFGF during oxygen-glucose deprivation did potentiate neuronal death. Both neurotrophic factors potentiated free radical mediated necrotic neuronal death induced by exposure to Fe. However, the RNA synthesis inhibitor, actinomycin-D, blocked the injury potentiation by NT-4, but not that caused by bFGF. Also, NT-4, but not bFGF, potentiated Fe induced necrotic death in pure neuronal cultures. Expression of mRNA for FGF receptors FGFR1 and FGFR2 was observed at high levels in astrocytes. The results indicate that the injury enhancing effects of bFGF are acute, while those of NT-4 require prolonged exposure and new protein synthesis. Furthermore, the effects of bFGF appear to be mediated through actions on astrocytes, while NT-4 appears to act directly on neurons. The fact that neurotrophic factors from two distinct families can potentiate neuronal death by two different mechanisms suggests that such injury potentiation may be a common concern regarding the use of neurotrophic factors.