Glutathione metabolism in primary astrocyte cultures: flow cytometric evidence of heterogeneous distribution of GSH content

Generation of Human iPSC-Derived Astrocytes with a mature star-shaped phenotype for CNS modeling

The generation of astrocytes from human induced pluripotent stem cells has been hampered by either prolonged differentiation—spanning over two months—or by shorter protocols that generate immature astrocytes, devoid of salient mature astrocytic traits pivotal for central nervous system (CNS) modeling. We directed stable hiPSC-derived neuroepithelial stem cells to human iPSC-derived Astrocytes (hiAstrocytes) with a high percentage of star-shaped cells by orchestrating an astrocytic-tuned culturing environment in 28 days. We employed RT-qPCR and ICC to validate the astrocytic commitment of the neuroepithelial stem cells. To evaluate the inflammatory phenotype, we challenged the hiAstrocytes with the pro-inflammatory cytokine IL-1β (interleukin 1 beta) and quantitatively assessed the secretion profile of astrocyte-associated cytokines and the expression of intercellular adhesion molecule 1 (ICAM-1). Finally, we quantitatively assessed the capacity of hiAstrocytes to synthesize and export the antioxidant glutathione. In under 28 days, the generated cells express canonical and mature astrocytic markers, denoted by the expression of GFAP, AQP4 and ALDH1L1. In addition, the notion of a mature phenotype is reinforced by the expression of both astrocytic glutamate transporters EAAT1 and EAAT2. Thus, hiAstrocytes have a mature phenotype that encompasses traits critical in CNS modeling, including glutathione synthesis and secretion, upregulation of ICAM-1 and a cytokine secretion profile on a par with human fetal astrocytes. This protocol generates a multifaceted astrocytic model suitable for in vitro CNS disease modeling and personalized medicine.

Glutathione antioxidant system and methylmercury-induced neurotoxicity: An intriguing interplay

Methylmercury (MeHg) is a toxic chemical compound naturally produced mainly in the aquatic environment through the methylation of inorganic mercury catalyzed by aquatic microorganisms. MeHg is biomagnified in the aquatic food chain and, consequently, piscivorous fish at the top of the food chain possess huge amounts of MeHg (at the ppm level). Some populations that have fish as main protein's source can be exposed to exceedingly high levels of MeHg and develop signs of toxicity. MeHg is toxic to several organs, but the central nervous system (CNS) represents a preferential target, especially during development (prenatal and early postnatal periods). Though the biochemical events involved in MeHg-(neuro)toxicity are not yet entirely comprehended, a vast literature indicates that its pro-oxidative properties explain, at least partially, several of its neurotoxic effects. As result of its electrophilicity, MeHg interacts with (and oxidize) nucleophilic groups, such as thiols and selenols, present in proteins or low-molecular weight molecules. It is noteworthy that such interactions modify the redox state of these groups and, therefore, lead to oxidative stress and impaired function of several molecules, culminating in neurotoxicity. Among these molecules, glutathione (GSH; a major thiol antioxidant) and thiol- or selenol-containing enzymes belonging to the GSH antioxidant system represent key molecular targets involved in MeHg-neurotoxicity. In this review, we firstly present a general overview concerning the neurotoxicity of MeHg. Then, we present fundamental aspects of the GSH-antioxidant system, as well as the effects of MeHg on this system.

Glutathione-Dependent Detoxification Processes in Astrocytes

Astrocytes have a pivotal role in brain as partners of neurons in homeostatic and metabolic processes. Astrocytes also protect other types of brain cells against the toxicity of reactive oxygen species and are considered as first line of defence against the toxic potential of xenobiotics. A key component in many of the astrocytic detoxification processes is the tripeptide glutathione (GSH) which serves as electron donor in the GSH peroxidase-catalyzed reduction of peroxides. In addition, GSH is substrate in the detoxification of xenobiotics and endogenous compounds by GSH-S-transferases which generate GSH conjugates that are efficiently exported from the cells by multidrug resistance proteins. Moreover, GSH reacts with the reactive endogenous carbonyls methylglyoxal and formaldehyde to intermediates which are substrates of detoxifying enzymes. In this article we will review the current knowledge on the GSH metabolism of astrocytes with a special emphasis on GSH-dependent detoxification processes.

Beta-amyloidolysis and glutathione in Alzheimer's disease

In this review, we hypothesized the importance of the interaction between the brain glutathione (GSH) system, the proteolytic tissue plasminogen activator (t-PA)/plasminogen/ plasmin system, regulated by plasminogen activator inhibitor (PAI-1), and neuroserpin in the pathogenesis of Alzheimer’s disease. The histopathological characteristic hallmark that gives personality to the diagnosis of Alzheimer’s disease is the accumulation of neurofibroid tangles located intracellularly in the brain, such as the protein tau and extracellular senile plaques made primarily of amyloidal substance. These formations of complex etiology are intimately related to GSH, brain protective antioxidants, and the proteolytic system, in which t-PA plays a key role. There is scientific evidence that suggests a relationship between aging, a number of neurodegenerative disorders, and the excessive production of reactive oxygen species and accompanying decreased brain proteolysis. The plasminogen system in the brain is an essential proteolytic mechanism that effectively degrades amyloid peptides (“beta-amyloidolysis”) through action of the plasmin, and this physiologic process may be considered to be a means of prevention of neurodegenerative disorders. In parallel to the decrease in GSH levels seen in aging, there is also a decrease in plasmin brain activity and a progressive decrease of t-PA activity, caused by a decrease in the expression of the t-PA together with an increase of the PAI-1 levels, which rise to an increment in the production of amyloid peptides and a lesser clearance of them. Better knowledge of the GSH mechanism and cerebral proteolysis will allow us to hypothesize about therapeutic practices.

The undertow of sulfur metabolism on glutamatergic neurotransmission

Metabolic interdependence between specialized cells in an organ represents a strategy for energy economy by requiring expression of only a subset of pathway genes in a given cell type. In brain, sulfur metabolism exemplifies this principle of metabolic cooperation between glial and neuronal cells and furnishes three key reagents: S-adenosylmethionine, glutathione and taurine. The pathways for glutathione and taurine syntheses depend on metabolic integration between astrocytes and neurons and intersect with the glutamine-glutamate cycle, which underlies glutamatergic synaptic transmission and requires cooperation between these cell types. We propose that underlying waves of glutamate clearance by astrocytes are activation of cystine import and taurine efflux that result, respectively, from a shared transporter and an increase in solute concentration that triggers osmoregulatory responses.

Glutathione content as a potential mediator of the vulnerability of cultured fetal cortical neurons to ethanol-induced apoptosis

Ethanol ingestion during pregnancy elicits damage to the developing brain, some of which appears to result from enhanced apoptotic death of neurons. A consistent characteristic of this phenomenon is a highly differing sensitivity to ethanol within specific neuron populations. One possible explanation for this "selective vulnerability" could be cellular variations in glutathione (GSH) homeostasis. Prior studies have illustrated that ethanol elicits apoptotic death of neurons in the developing brain, that oxidative stress may be an underlying mechanism, and that GSH can be neuroprotective. In the present study, both multiphoton microscopy and flow cytometry demonstrate a striking heterogeneity in GSH content within cortical neuron populations. Ethanol differentially elicits apoptotic death and oxidative stress in these neurons. When neuron GSH content is reduced by treatment with butathione sulfoxamine, the ethanol-mediated enhancement of reactive oxygen species is exacerbated. Sorting of cells into high- and low-GSH populations further exemplifies ethanol-mediated oxidative stress whereby apoptotic indices are preferentially elevated in the low-GSH population. Western blot analysis of the low-GSH subpopulations shows higher ethanol-mediated expression of active caspase 3 and 24-kDa PARP-1 fragments compared with the high-GSH subpopulation. In addition, neuronal content of 4-hydroxynonenal adducts is higher in low-GSH neurons in response to ethanol. These studies suggest that GSH content is an important predictor of neuronal sensitivity to ethanol-mediated oxidative stress and subsequent cell death. The data support the proposition that the differences in proapoptotic responses to ethanol within specific neuron populations reflect a heterogeneity of neuron GSH content.

Impact of the gliotoxin l-serine-O-sulphate on cellular metabolism in cultured rat astrocytes

L-serine-O-sulphate is a member of a group of amino acids collectively called gliotoxins and is a substrate for the high affinity sodium-dependent glutamate transporters. Previous studies have shown that it is toxic to primary cultures of astrocytes but the mode of toxicity is unknown. The current study demonstrates that L-serine-O-sulphate, at a sub-toxic concentration (400 microM), causes significant disruption to glucose and alanine metabolism in cultures of rat cortical astrocytes. More specifically, using (13)C NMR spectroscopy a significant reduction in labelled end products from [1-(13)C]glucose and [3-(13)C]alanine was found in the presence of L-serine-O-sulphate. Additionally, using [2-(13)C]glycine a 27% reduction in de novo glutathione synthesis was observed in the presence of the gliotoxin. Incubation of the cells with L-serine-O-sulphate reduced the activity of alanine and aspartate aminotransferase by 53% and 67%, respectively. Collectively these results show that the gliotoxin, L-serine-O-sulphate, causes major disruptions to metabolic pathways in primary cultures of astrocytes.

Coordinate regulation of glutathione metabolism in astrocytes by Nrf2

The tripeptide glutathione (GSH) represents the major brain thiol and is essential for prevention of oxidative stress. Using monochlorobimane to label intracellular GSH in a glutathione S-transferase catalyzed reaction we have examined the kinetics of GSH metabolism including its rate of conjugation, total GSH content, synthesis, and efflux in astrocyte cultures under basal conditions and after induction of antioxidant response element (ARE)-mediated gene expression by the transcription factor Nrf2. In the presence of a cerebral spinal fluid-like salt solution astrocytes could not synthesize detectable levels of GSH. Addition of GSH precursors, cystine, glutamate, and glycine, rapidly restored GSH synthesis. Astrocytes were able to use either glutamate or glutamine as precursors equally for GSH synthesis. Using the small molecule chemical inducer tert-butylhydroqunione (tBHQ) we report that induction of ARE-mediated gene expression is associated with a coordinated increase in GSH content and synthesis rate with little effect on the rate of GSH conjugation or efflux. Consistent with the effect of the inducer, adenovirus-mediated overexpression of the transcription factor Nrf2 that mediates tBHQ's effects also increased GSH content, confirming that GSH metabolism can be regulated by the Nrf2 pathway.

Dynamics of sulfur amino acids in mammalian brain: assessment of the astrocytic-neuronal cysteine interaction by a mathematical hybrid model

A mathematically hybrid model was used to analyze three mechanisms by which cysteine could be produced in the brain to be used as preferential substrate in the synthesis of neuronal glutathione. In that way, the fluxes of sulfur-compounds at the brain-blood barrier were integrated with their transport in astrocytes and neurons, and with their metabolism in astrocytes. We concluded that cysteine, in contrast with its precursor cystine, would not be taken up from the blood at the blood-brain barrier, but instead it must be lost continuously from astrocytes. Cysteine efflux is produced because the uptake of cystine in astrocytes is much greater than their cysteine demand to synthesize glutathione, hypotaurine and taurine. Once in the interstitial parenchyma, cysteine would be taken for the neurons, as backwardly by the endothelial cells. Remarkably, a close sulfur-macro balance can be maintained only if the surplus of the produced cysteine is transferred from the endothelial cells to the blood together with significant amounts of other sulfur-compounds, probably taurine and hypotaurine. In addition, the results obtained shown that alternative mechanisms of cysteine generation (i.e., nonenzymatic-thiol-disulfide exchange reaction, enzymatic cleavage of the glutathione effluxed from astrocytes) are not quantitatively significant under physiological conditions, in situ.

Glutathione pathways in the brain

The antioxidant glutathione (GSH) is essential for the cellular detoxification of reactive oxygen species in brain cells. A compromised GSH system in the brain has been connected with the oxidative stress occuring in neurological diseases. Recent data demonstrate that besides intracellular functions GSH has also important extracellular functions in brain. In this respect astrocytes appear to play a key role in the GSH metabolism of the brain, since astroglial GSH export is essential for providing GSH precursors to neurons. Of the different brain cell types studied in vitro only astrocytes release substantial amounts of GSH. In addition, during oxidative stress astrocytes efficiently export glutathione disulfide (GSSG). The multidrug resistance protein 1 participates in both the export of GSH and GSSG from astrocytes. This review focuses on recent results on the export of GSH and GSSG from brain cells as well as on the functions of extracellular GSH in the brain. In addition, implications of disturbed GSH pathways in brain for neurodegenerative diseases will be discussed.

Zinc toxicity on neonatal cortical neurons: involvement of glutathione chelation

Several mechanisms have been implicated in pathological neuronal death including zinc neurotoxicity, calcium excitotoxicity and oxidative injury. Glutathione (GSH) serves to provide reducing equivalents for the maintenance of oxidant homeostasis, and also plays roles in intracellular and intercellular signaling in the brain. We investigated the role of GSH homeostasis in the neurotoxic action of zinc using both mixed cortical cultures containing neurons and glia, and cortical neurons prepared from 1-day-old rats. Zinc caused neuronal cell death in a concentration-dependent manner. In parallel, a high concentration of zinc depleted GSH, in a time-dependent manner, preceding the onset of neuronal damage. Depletion of GSH by diethylmaleate injured neurons and exacerbated zinc-induced death. In contrast, replenishment of GSH attenuated zinc neurotoxicity. The thiol-containing compounds N-acetylcysteine and GSH chemically chelated zinc leading to decreases in the influx of zinc, the fall in GSH level and neuronal death. Interestingly, the glycolytic substrate pyruvate, but not lactate, chelated zinc concentration dependently and prevented its toxicity. On the other hand, pyrrolidine dithiocarbamate, serving as a zinc chaperon, enhanced its entry and toxicity. The results suggest that zinc non-enzymatically depleted GSH, an intrinsic factor for neuron survival, leading to activation of the cellular death signal and eventually neuronal death.

Na+ dependent glutamate transporters (EAAT1, EAAT2, and EAAT3) in primary astrocyte cultures: effect of oxidative stress

The Na+ -dependent L-glutamate transporters EAAT1(GLAST), EAAT2 (GLT-1) and EAAT3 (EAAC1) are expressed in primary astrocyte cultures, showing that the EAAT3 transporter is not neuron-specific. The presence of these three transporters was evaluated by RT-PCR, immunoblotting, immunocytochemical techniques, and transport activity. When primary astrocyte cultures were incubated with L-buthionine-(S,R)-sulfoximine (BSO), a selective inhibitor of gamma-glutamylcysteine synthetase, the GSH concentration was significantly lower than in control cultures, but the expression and amount of protein of EAAT1, EAAT2 and EAAT3 and transport of L-glutamate was unchanged. Oxidative stress was created by adding H(2)O(2) or tert.-butyl hydroperoxide (t-bOOH) to the primary astrocyte cultures and cell damage was evaluated by measuring activity of lactate dehydrogenase. Under oxidative stress, GSH levels were significantly lower than in control astrocytes; but the expression and the amount of protein of the three transporters remained unchanged. However, L-glutamate uptake was significantly lower in astrocytes under oxidative conditions when compared to controls. L-Glutamate uptake was not changed in the presence of ascorbate, but was partially recovered in the presence of DTT and GSH ethyl ester. This report emphasizes that oxidative stress and not GSH depletion alters transporter activity without changing transporter expression.

Metabolism and functions of glutathione in brain

The tripeptide glutathione is the thiol compound present in the highest concentration in cells of all organs. Glutathione has many physiological functions including its involvement in the defense against reactive oxygen species. The cells of the human brain consume about 20% of the oxygen utilized by the body but constitute only 2% of the body weight. Consequently, reactive oxygen species which are continuously generated during oxidative metabolism will be generated in high rates within the brain. Therefore, the detoxification of reactive oxygen species is an essential task within the brain and the involvement of the antioxidant glutathione in such processes is very important. The main focus of this review article will be recent results on glutathione metabolism of different brain cell types in culture. The glutathione content of brain cells depends strongly on the availability of precursors for glutathione. Different types of brain cells prefer different extracellular glutathione precursors. Glutathione is involved in the disposal of peroxides by brain cells and in the protection against reactive oxygen species. In coculture astroglial cells protect other neural cell types against the toxicity of various compounds. One mechanism for this interaction is the supply by astroglial cells of glutathione precursors to neighboring cells. Recent results confirm the prominent role of astrocytes in glutathione metabolism and the defense against reactive oxygen species in brain. These results also suggest an involvement of a compromised astroglial glutathione system in the oxidative stress reported for neurological disorders.

Monochlorobimane fluorometric method to measure tissue glutathione

Glutathione (GSH) is the principal intracellular low-molecular-weight thiol and plays a critical role in the cellular defense against agents that impose oxidative stress. A common technique to measure GSH uses reversed-phase high-performance liquid chromatography (HPLC) following derivatization with 5, 5'-dithiobis(2-nitrobenzoic acid), a technique, although reliable and sensitive, that is time consuming and laborious. A common technique to measure GSH in cultured cells is to add monochlorobimane to the culture medium where it readily enters cells to form a fluorescent GSH-monochlorobimane adduct that can be measured fluorometrically. This reaction is catalyzed by glutathione S-transferase. We reasoned that adding glutathione S-transferase and monochlorobimane to tissue homogenates would allow a rapid reliable method to measure GSH. The accuracy of the new test was assessed in homogenates of rat livers. One-half of each homogenate was assayed for GSH using a HPLC approach while the other half was assayed using the monochlorobimane approach. The two methods were found to give identical results. We conclude that the monochlorobimane fluorescent method is sufficiently specific to reliably measure tissue GSH.

The detoxification of cumene hydroperoxide by the glutathione system of cultured astroglial cells hinges on hexose availability for the regeneration of NADPH

The ability of astroglia-rich primary cultures derived from the brains of newborn rats to detoxify exogenously applied cumene hydroperoxide (CHP) was analyzed as a model to study glutathione-mediated peroxide detoxification by astrocytes. Under the conditions used, 200 microM CHP disappeared from the incubation buffer with a half-time of approximately 10 min. The half-time of CHP in the incubation buffer was found strongly elevated (a) in cultures depleted of glutathione by a preincubation with buthionine sulfoximine, an inhibitor of glutathione synthesis, (b) in the presence of mercaptosuccinate, an inhibitor of glutathione peroxidase, and (c) in the absence of glucose, a precursor for the regeneration of NADPH. The involvement of glutathione peroxidase in the clearance of CHP was confirmed by the rapid increase in the level of GSSG after application of CHP. The restoration of the initial high ratio of GSH to GSSG depended on the presence of glucose during the incubation. The high capacity of astroglial cells to clear CHP and to restore the initial ratio of GSH to GSSG was fully maintained when glucose was replaced by mannose. In addition, fructose and galactose at least partially substituted for glucose, whereas exogenous isocitrate and malate were at best marginally able to replace glucose during peroxide detoxification and regeneration of GSH. These results demonstrate that CHP is detoxified rapidly by astroglial cells via the glutathione system. This metabolic process strongly depends on the availability of glucose or mannose as hydride donors for the regeneration of the NADPH that is required for the reduction of GSSG by glutathione reductase.

1,25-dihydroxyvitamin D3 regulates the synthesis of gamma-glutamyl transpeptidase and glutathione levels in rat primary astrocytes

Astrocytes play a pivotal role in CNS detoxification pathways, where glutathione (GSH) is involved in the elimination of oxygen and nitrogen reactive species such as nitric oxide. We have previously demonstrated that the specific activity of gamma-glutamyl transpeptidase (gamma-GT), an enzyme of central significance in GSH metabolism, is regulated in vivo in astrocytes by 1,25-dihydroxyvitamin D3 (1,25-D3). The aim of the present work was to investigate, in primary cultures of newborn rat astrocytes, the effects of this hormone on gamma-GT synthesis and on GSH and nitrite levels after lipopolysaccharide (LPS) treatment. This study demonstrates that both gamma-GT gene expression and specific activity, induced by LPS, are potentiated by 1,25-D3. In contrast, 1,25-D3 does not regulate the expression of other enzymes involved in astrocyte detoxification processes, such as superoxide dismutase or GSH peroxidase. In parallel, 1,25-D3 enhanced intracellular GSH pools and significantly reduced nitrite production induced by LPS. Taken together, these results suggest that gamma-GT, GSH, and 1,25-D3 play a fundamental role in astrocyte detoxification pathways.

Rapid clearance of tertiary butyl hydroperoxide by cultured astroglial cells via oxidation of glutathione

The ability of astroglial cells to detoxify exogenously applied tertiary butyl hydroperoxide (tBHP) was tested using astroglia-rich primary cultures derived from the brains of newborn rats. If 200 microM tBHP was applied, this compound disappeared from the incubation buffer with an apparent half-life of about 5 min. After 20 min incubation tBHP was not detectable any more. A decay of tBHP was found even in the absence of cells. Therefore, half-times for the cell-dependent tBHP clearance were corrected for the cell-independent decay of tBHP. The cell-dependent half-time of tBHP in the incubation buffer was found strongly elevated i) with increasing concentration of tBHP, ii) after decrease of the glutathione content of the cells by a preincubation with buthionine sulfoximine, an inhibitor of glutathione synthesis, iii) in the presence of mercaptosuccinate, an inhibitor of glutathione peroxidase, and iv) in the absence of glucose, the precursor for the generation of NADPH. Incubation of astroglial cells with 200 microM tBHP in the absence of glucose led to a 46% oxidation of the cellular glutathione within 30 s. Under these conditions the cells were unable to restore the original high ratio of the concentrations of GSH to GSSG within 30 min of incubation. In contrast, if glucose was present the level of GSSG encountered on incubation with tBHP was lower (32% of total glutathione after 30 s) and the original ratio of the levels of GSH to GSSG was essentially reestablished within 10 min. In the presence of 3 mM mercaptosuccinate oxidation of glutathione was almost completely inhibited. These results demonstrate that an exogenous hydroperoxide is detoxified rapidly by astroglial cells via the glutathione system.

Involvement of glutathione peroxidase and catalase in the disposal of exogenous hydrogen peroxide by cultured astroglial cells

The ability of astroglial cells to detoxify exogenously applied hydrogen peroxide (H2O2) was tested using astroglia-rich primary cultures derived from the brains of newborn rats. Incubation of astroglial cells with 100 microM H2O2 in the absence of glucose led to a 66% oxidation of the cellular glutathione within 30 s. Under these conditions, the cells were unable to re-establish the original high ratio of GSH/GSSG within 30 min of incubation. In contrast, if glucose was present the amount of GSSG produced on incubation with H2O2 was smaller (45% of total glutathione after 30 s) and the original ratio of GSH/GSSG was almost completely re-established within 10 min. If 100 microM H2O2 was applied, H2O2 disappeared from the incubation buffer with an apparent half-life of approximately 4 min. After 15 min of incubation, no H2O2 was detectable any more. The apparent half-life of H2O2 in the incubation buffer increased slightly but significantly with increasing concentration of H2O2 or when the cells were starved of glucose. A small reduction in the capacity of the cells to detoxify H2O2 was also observed after depletion of the glutathione content to 14% of control level by a 24 h pre-incubation of the cells in culture medium containing buthionine sulfoximine, an inhibitor of glutathione synthesis. Incubation of astroglial cells with mercaptosuccinate or 3-aminotriazole, inhibitors of glutathione peroxidase and catalase, respectively, only marginally reduced the rate of disappearance of H2O2 from the incubation buffer. In contrast, the rate of H2O2 clearance was strongly reduced in the presence of both inhibitors. These results demonstrate that glutathione peroxidase and catalase are involved in the detoxification of H2O2 by astroglial cells and that both enzymes are able to substitute for each other in the detoxification of H2O2.

Biosynthesis and maintenance of GSH in primary astrocyte cultures: role of L-cystine and ascorbate

We have studied the optimal conditions to maintain the astrocyte GSH levels under normal and oxidative stress conditions. The rate of GSH synthesis from L-methionine was statistically lower than from L-cystine or N-acetyl-cysteine in astrocytes treated with diethyl-maleate, which is a substrate of GSH S-transferases. This is in accordance with the fact that cystathionase activity was not detectable. The transport of L-cystine mediated by the Na(+)-independent system Xc- is the limiting step in GSH synthesis in astrocytes. Incubation with tert-butyl hydroperoxide (t-booH) reduced GSH concentration in astrocytes. This reduction was ameliorated in part by the addition of ascorbate or dehydroascorbate. When L-cystine and ascorbate were added together to the t-booH-treated astrocytes, the GSH concentration was indistinguishable from controls. Electron micrographs of astrocytes treated with t-booH showed an increased number of vacuoles and mitochondrial swelling. This was prevented by ascorbate and dehydroascorbate. The physiological implications of the availability of GSH precursors and ascorbate in the maintenance of GSH in astrocytes are discussed.

An in vivo study of the effect of 5-HT and sympathetic nerves on transferrin and transthyretin mRNA expression in rat choroid plexus and meninges

Brain expression of transferrin (Tf) and transthyretin (TTR) mRNA has been demonstrated in different species, TTR being found only in the choroid plexus. We report here that both these mRNAs are also expressed in the meninges. In vitro studies have shown that Tf secretion by the rat choroid plexus is stimulated by 5-hydroxytryptamine (5-HT) while sympathetic nerves regulate different transport functions in the same tissue. We have used various in vivo models to study the neuroendocrine regulation of Tf and TTR mRNA expression in the choroid plexus and meninges. Destruction of the serotonergic nerves in the brain by either raphe nuclei lesion or intraventricular injections of 5,7-dihydroxytryptamine (5,7-DHT), which both decreased brain 5-HT levels significantly, did not affect Tf or TTR mRNA levels in choroid plexus and meninges, but increased TTR mRNA in liver. Intraventricular injection of 10 or 100 pmol 5-HT did not change the expression of these proteins in any of the tissues studied. Removal of the sympathetic innervation to the choroid plexus by cervical sympathectomy did not affect Tf or TTR mRNA levels in choroid plexus and liver, nor the incorporation of radioactive leucine into protein in various parts of the brain. In conclusion, our results do not support a regulatory role in vivo for neuronally derived 5-HT or sympathetic nerve activity on Tf and TTR mRNA expression in rat choroid plexus and meninges.