Transferrin gene expression and secretion by rat brain cells in vitro

Transferrin Enhances Neuronal Differentiation

Although transferrin (Tf) is a glycoprotein best known for its role in iron delivery, iron-independent functions have also been reported. Here, we assessed apoTf (aTf) treatment effects on Neuro-2a (N2a) cells, a mouse neuroblastoma cell line which, once differentiated, shares many properties with neurons, including process outgrowth, expression of selective neuronal markers, and electrical activity. We first examined the binding of Tf to its receptor (TfR) in our model and verified that, like neurons, N2a cells can internalize Tf from the culture medium. Next, studies on neuronal developmental parameters showed that Tf increases N2a survival through a decrease in apoptosis. Additionally, Tf accelerated the morphological development of N2a cells by promoting neurite outgrowth. These pro-differentiating effects were also observed in primary cultures of mouse cortical neurons treated with aTf, as neurons matured at a higher rate than controls and showed a decrease in the expression of early neuronal markers. Further experiments in iron-enriched and iron-deficient media showed that Tf preserved its pro-differentiation properties in N2a cells, with results hinting at a modulatory role for iron. Moreover, N2a-microglia co-cultures revealed an increase in IL-10 upon aTf treatment, which may be thought to favor N2a differentiation. Taken together, these findings suggest that Tf reduces cell death and favors the neuronal differentiation process, thus making Tf a promising candidate to be used in regenerative strategies for neurodegenerative diseases.

Hepcidin attenuates the iron-mediated secondary neuronal injury after intracerebral hemorrhage in rats

Iron plays a key role in secondary neuronal injury after intracerebral hemorrhage (ICH), and hepcidin is able to reduce brain iron in iron-overloaded rats by down-regulating iron transport proteins including ferroportin 1 and transferrin receptor 1. These led us to hypothesize that hepcidin might reduce iron-mediated neurotoxicity by inhibiting iron accumulation in ICH brain. Here, we examined effects of Ad-hepcidin (hepcidin expression adenovirus) on the nonheme iron contents, expression of hepcidin, ferritin and iron transport proteins, neuronal cell survival, water contents in the brain and/or cerebrospinal fluid (CSF), and ICH-induced apoptosis, neurological deficit by RT-PCR, Western blot analysis, NeuN Immunofluorescence, TUNEL, Fluoro-Jade B staining, behavioral performance and Morris water-maze tests in 510 rats. We demonstrated that hepcidin could significantly suppress the ICH-induced increase in iron and ferritin in brain tissues and CSF by inhibiting expression of iron transport proteins, increase neuronal survival by attenuating ICH-induced apoptosis, reactive oxygen species, neurodegeneration and brain edema, as well as effectively improve ICH-induced behavioral and cognitive deficit in rats. The findings collectively showed that hepcidin could effectively attenuate iron-mediated secondary neuronal injury after ICH in rats. This naturally existing protein can potentially be developed into a therapeutic drug for the treatment of ICH patients.

Brain iron transport

Brain iron is a crucial participant and regulator of normal physiological activity. However, excess iron is involved in the formation of free radicals, and has been associated with oxidative damage to neuronal and other brain cells. Abnormally high brain iron levels have been observed in various neurodegenerative diseases, including neurodegeneration with brain iron accumulation, Alzheimer's disease, Parkinson's disease and Huntington's disease. However, the key question of why iron levels increase in the relevant regions of the brain remains to be answered. A full understanding of the homeostatic mechanisms involved in brain iron transport and metabolism is therefore critical not only for elucidating the pathophysiological mechanisms responsible for excess iron accumulation in the brain but also for developing pharmacological interventions to disrupt the chain of pathological events occurring in these neurodegenerative diseases. Numerous studies have been conducted, but to date no effort to synthesize these studies and ideas into a systematic and coherent summary has been made, especially concerning iron transport across the luminal (apical) membrane of the capillary endothelium and the membranes of different brain cell types. Herein, we review key findings on brain iron transport, highlighting the mechanisms involved in iron transport across the luminal (apical) as well as the abluminal (basal) membrane of the blood-brain barrier, the blood-cerebrospinal fluid barrier, and iron uptake and release in neurons, oligodendrocytes, astrocytes and microglia within the brain. We offer suggestions for addressing the many important gaps in our understanding of this important topic, and provide new insights into the potential causes of abnormally increased iron levels in regions of the brain in neurodegenerative disorders.

A blend containing docosahexaenoic acid, arachidonic acid, vitamin B12, vitamin B9, iron and sphingomyelin promotes myelination in an in vitro model

During the development of the central nervous system, oligodendrocytes (OLs) are responsible for myelination, the formation of the myelin sheath around axons. This process enhances neuronal connectivity and supports the maturation of emerging cognitive functions. In humans, recent evidence suggests that early life nutrition may affect myelination. In the present study, we investigated the impact of a blend containing docosahexaenoic acid, arachidonic acid, vitamin B12, vitamin B9, iron and sphingomyelin, or each of these nutrients individually, on oligodendrocyte precursor cells (OPCs) proliferation and maturation into OLs as well as their myelinating properties. By using an in vitro model, developed to study each step of myelination, we found that the nutrient blend increased the number of OPCs and promoted their differentiation and maturation into OLs, as measured by quantifying A2B5 positive cells, myelin-associated glycoprotein (MAG) positive cells and area, myelin binding protein (MBP) positive cells and area, respectively. Moreover, measuring myelination by quantifying the overlapping signal between neurofilament and either MAG or MBP revealed a positive effect of the blend on OLs myelinating properties. In contrast, treatment with each individual nutrient resulted in differential effects on the various readouts. This work suggests that dietary intake of these nutrients during early life, might be beneficial for myelination.

Enhancing Glioblastoma-Specific Penetration by Functionalization of Nanoparticles with an Iron-Mimic Peptide Targeting Transferrin/Transferrin Receptor Complex

Treatment of glioblastoma (GBM) remains to be the most formidable challenge because of the hindrance of the blood-brain barrier (BBB) along with the poor drug penetration into the glioma parenchyma. Nanoparticulate drug delivery systems (DDS) utilizing transferrin (Tf) as the targeting ligand to target the glioma-associated transferrin receptor (TfR) had met the problem of loss of specificity in biological environment due to the high level of endogenous Tf. Here we conjugated CRT peptide, an iron-mimicry moiety targeting the whole complex of Tf/TfR, to poly(ethylene glycol)-poly(l-lactic-co-glycolic acid) nanoparticles (CRT-NP), to open a new route to overcome such obstacle. High cellular associations, advanced transport ability through the BBB model, and penetration in 3-dimensional C6 glioma spheroids in vitro had preliminarily proved the advantages of CRT-NP over Tf-nanoparticle conjugates (Tf-NP). Compared with Tf-NP, NP, and Taxol, paclitaxel-loaded CRT-NP (CRT-NP-PTX) displayed a superior antiproliferation effect on C6 glioma cells and stronger inhibitory effect on glioma spheroids. Favored pharmacokinetics behavior and enhanced accumulation in glioma foci was observed, together with a much deeper distribution pattern in glioma parenchyma compared with unmodified nanoparticles and Tf-NP. Eventually, mice treated with CRT-NP-PTX showed a remarkably prolonged median survival compared to those treated with Taxol, NP, or Tf-NP. In conclusion, the modification of CRT to nanoparticles holds great promise for enhancement of antiglioma therapy.

Iron transport across the blood-brain barrier: development, neurovascular regulation and cerebral amyloid angiopathy

There are two barriers for iron entry into the brain: (1) the brain-cerebrospinal fluid (CSF) barrier and (2) the blood-brain barrier (BBB). Here, we review the literature on developmental iron accumulation by the brain, focusing on the transport of iron through the brain microvascular endothelial cells (BMVEC) of the BBB. We review the iron trafficking proteins which may be involved in the iron flux across BMVEC and discuss the plausible mechanisms of BMVEC iron uptake and efflux. We suggest a model for how BMVEC iron uptake and efflux are regulated and a mechanism by which the majority of iron is trafficked across the developing BBB under the direct guidance of neighboring astrocytes. Thus, we place brain iron uptake in the context of the neurovascular unit of the adult brain. Last, we propose that BMVEC iron is involved in the aggregation of amyloid-β peptides leading to the progression of cerebral amyloid angiopathy which often occurs prior to dementia and the onset of Alzheimer's disease.

Iron and intracerebral hemorrhage: from mechanism to translation

Intracerebral hemorrhage (ICH) is a leading cause of morbidity and mortality around the world. Currently, there is no effective medical treatment available to improve functional outcomes in patients with ICH due to its unknown mechanisms of damage. Increasing evidence has shown that the metabolic products of erythrocytes are the key contributor of ICH-induced secondary brain injury. Iron, an important metabolic product that accumulates in the brain parenchyma, has a detrimental effect on secondary injury following ICH. Because the damage mechanism of iron during ICH-induced secondary injury is clear, iron removal therapy research on animal models is effective. Although many animal and clinical studies have been conducted, the exact metabolic pathways of iron and the mechanisms of iron removal treatments are still not clear. This review summarizes recent progress concerning the iron metabolism mechanisms underlying ICH-induced injury. We focus on iron, brain iron metabolism, the role of iron in oxidative injury, and iron removal therapy following ICH, and we suggest that further studies focus on brain iron metabolism after ICH and the mechanism for iron removal therapy.

Impact of simulated microgravity on oligodendrocyte development: implications for central nervous system repair

We have recently established a culture system to study the impact of simulated microgravity on oligodendrocyte progenitor cells (OPCs) development. We subjected mouse and human OPCs to a short exposure of simulated microgravity produced by a 3D-Clinostat robot. Our results demonstrate that rodent and human OPCs display enhanced and sustained proliferation when exposed to simulated microgravity as assessed by several parameters, including a decrease in the cell cycle time. Additionally, OPC migration was examined in vitro using time-lapse imaging of cultured OPCs. Our results indicated that OPCs migrate to a greater extent after stimulated microgravity than in normal conditions, and this enhanced motility was associated with OPC morphological changes. The lack of normal gravity resulted in a significant increase in the migration speed of mouse and human OPCs and we found that the average leading process in migrating bipolar OPCs was significantly longer in microgravity treated cells than in controls, demonstrating that during OPC migration the lack of gravity promotes leading process extension, an essential step in the process of OPC migration. Finally, we tested the effect of simulated microgravity on OPC differentiation. Our data showed that the expression of mature oligodendrocyte markers was significantly delayed in microgravity treated OPCs. Under conditions where OPCs were allowed to progress in the lineage, simulated microgravity decreased the proportion of cells that expressed mature markers, such as CC1 and MBP, with a concomitant increased number of cells that retained immature oligodendrocyte markers such as Sox2 and NG2. Development of methodologies aimed at enhancing the number of OPCs and their ability to progress on the oligodendrocyte lineage is of great value for treatment of demyelinating disorders. To our knowledge, this is the first report on the gravitational modulation of oligodendrocyte intrinsic plasticity to increase their progenies.

White matter loss in a mouse model of periventricular leukomalacia is rescued by trophic factors

Periventricular leukomalacia (PVL) is the most frequent cause of cerebral palsy and other intellectual disabilities, and currently there is no treatment. In PVL, glutamate excitotoxicity (GME) leads to abnormal oligodendrocytes (OLs), myelin deficiency, and ventriculomegaly. We have previously identified that the combination of transferrin and insulin growth factors (TSC1) promotes endogenous OL regeneration and remyelination in the postnatal and adult rodent brain. Here, we produced a periventricular white matter lesion with a single intracerebral injection of N-methyl-d-aspartate (NMDA). Comparing lesions produced by NMDA alone and those produced by NMDA + TSC1 we found that: NMDA affected survival and reduced migration of OL progenitors (OLPs). In contrast, mice injected with NMDA + TSC1 proliferated twice as much indicating that TSC1 supported regeneration of the OLP population after the insult. Olig2-mRNA expression showed 52% OLP survival in mice receiving a NMDA injection and increased to 78% when TSC1 + NMDA were injected simultaneously and ventricular size was reduced by TSC1. Furthermore, in striatal slices TSC1 reduced the inward currents induced by NMDA in medium-sized spiny neurons, demonstrating neuroprotection. Thus, white matter loss after excitotoxicity can be partially rescued as TSC1 conferred neuroprotection to preexisting OLP and regeneration via OLP proliferation. Furthermore, we showed that early TSC1 administration maximizes neuroprotection.

Brain iron metabolism: neurobiology and neurochemistry

New findings obtained during the past years, especially the discovery of mutations in the genes associated with brain iron metabolism, have provided key insights into the homeostatic mechanisms of brain iron metabolism and the pathological mechanisms responsible for neurodegenerative diseases. The accumulated evidence demonstrates that misregulation in brain iron metabolism is one of the initial causes for neuronal death in some neurodegenerative disorders. The errors in brain iron metabolism found in these disorders have a multifactorial pathogenesis, including genetic and nongenetic factors. The disturbances of iron metabolism might occur at multiple levels, including iron uptake and release, storage, intracellular metabolism and regulation. It is the increased brain iron that triggers a cascade of deleterious events, leading to neuronal death in these diseases. In the article, the recent advances in studies on neurochemistry and neuropathophysiology of brain iron metabolism were reviewed.

Posterior capsular opacification in diabetic and nondiabetic canine patients following cataract surgery

Posterior capsular opacification (PCO) is the most common postoperative complication of contemporary cataract surgery. Limited information is available regarding PCO formation and factors that influence PCO development in the dog. Two hundred sixty-five eyes (144 from diabetic dogs and 121 from dogs with breed-related cataracts) were prospectively evaluated for PCO formation for up to 12 months postoperatively. The mean age of all dogs in the study was 7.77 years and diabetic dogs were significantly older than dogs with breed-related cataracts. There were 73 males (61 neutered, 12 intact) and 74 females (70 neutered, 4 intact) in the study. Statistical analysis was performed based on age, breed/size, gender, stage of cataract at the time of surgery, PCO score at each time point, breed-related vs. diabetic cataract, right eyes compared to left eyes, and presence/absence of uveitis. Age and gender did not significantly influence PCO formation. Small and medium-sized breeds developed significantly more PCO in comparison to the large/giant breeds at 2 weeks and 2-4 months postoperatively, but the differences were not significant at later time points. There was an overall significant increase in PCO formation in eyes with early immature cataracts when compared to other stages of cataract up to 4 months postoperatively but not at later time points. There were no statistical differences in PCO score at 6 months or at 1 year postoperatively in eyes with breed-related and diabetic cataracts. Right eyes did not differ from left eyes in PCO score. PCO score significantly increased over time in breed-related and diabetic groups and in the overall population. No difference was found in the degree of PCO formation in eyes with inflammation prior to or after surgery compared with those without inflammation. In summary, age, gender, presence of inflammation, and cause of cataract (breed-related vs. diabetes mellitus) do not influence the development of PCO in canine cataract dogs. Small and medium-sized breeds develop significant PCO earlier than larger breeds. It is important to note that all eyes from all dogs in this study developed PCO in a time dependent manner.

Constitutive secretion of protease nexin-1 by glial cells and its regulation by G-protein-coupled receptors

Extracellular serine proteases and their inhibitors (serpins) play a key role for synaptic plasticity in the developing and adult CNS. Serpins also counteract the extravasated proteases during brain injury. We studied the mechanisms by which one of the most important serpins, serpinE2 or protease nexin-1 (PN-1), is secreted by glial cells and how its secretion is regulated by extracellular signals. Using time-lapse videomicroscopy and biochemical methods, we demonstrate that PN-1 is constitutively secreted through small vesicles animated by a discontinuous movement using microtubules as tracks. The F-actin network underneath the plasma membrane acting as a barrier hindered PN-1 vesicle exocytosis. Vasointestinal/pituitary adenylate cyclase peptides and the G-protein activator mastoparan increased PN-1 secretion by disrupting the F-actin barrier. The receptor-mediated regulation of PN-1 constitutive secretion may be an important mechanism adapting extracellular proteolytic activity to synaptic activity.

Acute and chronic effects of developmental iron deficiency on mRNA expression patterns in the brain

Because of the multiple biochemical pathways that require iron, iron deficiency can impact brain metabolism in many ways. The goal of this study was to identify a molecular footprint associated with ongoing versus long term consequences of iron deficiency using microarray analysis. Rats were born to iron-deficient mothers, and were analyzed at two different ages: 21 days, while weaning and iron-deficient; and six months, after a five month iron-sufficient recovery period. Overall, the data indicate that ongoing iron deficiency impacts multiple pathways, whereas the long term consequences of iron deficiency on gene expression are more limited. These data suggest that the gene array profiles obtained at postnatal day 21 reflect a brain under development in a metabolically compromised setting that given appropriate intervention is mostly correctable. There are, however, long term consequences to the developmental iron deficiency that could underlie the neurological deficits reported for iron deficiency.

The Role of Iron in the Pathogenesis of Experimental Allergic Encephalomyelitis and Multiple Sclerosis

Multiple sclerosis (MS) and its animal model, experimental allergic encephalomyelitis (EAE), are autoimmune disorders resulting in demyelination in the central nervous system (CNS). Pathologically, the blood-brain barrier becomes damaged, macrophages and T cells enter into the CNS, oligodendrocytes and myelin are destroyed, astrocytes and microglia undergo gliosis, and axons become transected. Data from several biochemical and pharmacological studies indicate that free radicals participate in the pathogenesis of EAE, and iron has been implicated as the catalyst leading to their formation. The primary focus of this article is the examination of the role of iron in the pathogenesis of MS and EAE. Particular attention will be paid to the role and distribution of iron and proteins involved with iron metabolism (e.g., transferrin, ferritin, heme oxygenase-1, etc.) in normal and disease states of myelin. Furthermore, therapeutic interventions aimed at iron, iron-binding proteins, and substrates or products of iron-catalyzed reactions leading to free radical production will be discussed.

A direct contact between astrocyte and vitreous body is possible in the rabbit eye due to discontinuities in the basement membrane of the retinal inner limiting membrane

Different from most mammalian species, the optic nerve of the rabbit eye is initially formed inside the retina where myelination of the axons of the ganglion cells starts and vascularization occurs. Astrocytes are confined to these regions. The aforementioned nerve fibers known as medullated nerve fibers form two bundles that may be identified with the naked eye. The blood vessels run on the inner surface of these nerve fiber bundles (epivascularization) and, accordingly, the accompanying astrocytes lie mostly facing the vitreous body from which they are separated only by the inner limiting membrane of the retina. The arrangement of the astrocytes around blood vessels leads to the formation of structures known as glial tufts. Fragments (N = 3) or whole pieces (N = 3) of the medullated nerve fiber region of three-month-old male rabbits (Orictolagus cuniculus) were fixed in glutaraldehyde followed by osmium tetroxide, and their thin sections were examined with a transmission electron microscope. Randomly located discontinuities (up to a few micrometers long) of the basement membrane of the inner limiting membrane of the retina were observed in the glial tufts. As a consequence, a direct contact between the astrocyte plasma membrane and vitreous elements was demonstrated, making possible functional interactions such as macromolecular exchanges between this glial cell type and the components of the vitreous body.

Influence of iron-saturation of plasma transferrin in iron distribution in the brain

Based on the evidence that iron distribution in the peripheral tissues is changed by iron-saturation of plasma transferrin, the influence of iron-saturation of plasma transferrin in iron delivery to the brain was examined. Mouse plasma was pre-incubated with ferric chloride in citrate buffer to saturate transferrin and then incubated with (59)FeCl(3). Peak retention time of (59)Fe was transferred from the retention time of transferrin to that of mercaptalbumin, suggesting that iron may bind to albumin in the plasma in the case of iron-saturation of transferrin. When mice were intravenously injected with ferric chloride in citrate buffer 10 min before intravenous injection of (59)FeCl(3), 59Fe concentration in the plasma was remarkably low. (59)Fe concentration in the liver of iron-loaded mice was four times higher than in control, while 59Fe concentration in the brain of iron-loaded mice was approximately 40% of that of control mice. Twenty-four hours after intravenous injection of (59)FeCl(3), brain autoradiograms also showed that (59)Fe concentrations in the brain of iron-loaded mice were approximately 40-50% of those of control mice in all brain regions tested except the choroid plexus, in which (59)Fe concentration was equal. These results suggest that the fraction of non-transferrin-bound iron is engulfed by the liver, resulting in the reduction of iron available for iron delivery to the brain in iron-loaded mice. Transferrin-bound iron may be responsible for the fraction of iron in circulation that enters the brain.

Expression of transferrin mRNA in rat oligodendrocytes is iron-independent and changes with increasing age

As transferrin in the brain may originate principally from synthesis by three different cell types, i.e. hepatocytes, oligodendrocytes and choroid plexus, this study employed a morphological analysis to specifically address oligodendrocytic expression of transferrin mRNA in young (P17) and adult (P50) rats. In spite of a lowering of the concentration of brain iron by approximately 22% in the young iron deficient rats transferrin mRNA expression in oligodendrocytes was not affected when measured by quantitative densitometry. In adult rats, the baseline transferrin mRNA expression in oligodendrocytes was higher than in the young animals, but did not change in spite of a reduction in brain iron by approximately 19%. Brain iron and transferrin mRNA expression in oligodendrocytes were unaltered in iron overloaded rats when compared to age-matched controls. As transferrin expression was lower in the young rat, when constituents from the blood have a relatively higher concentration in the brain than during adulthood, it seems unlikely that blood-borne factors such as transition metals act as inducers of transferrin gene expression in oligodendrocytes. Instead, the higher but constitutive expression of transferrin mRNA at later ages, when the blood-brain barrier segregates the brain from other body parts, may indicate that molecules released from the brain interior are responsible for regulating transcription of the transferrin gene.

Distribution of divalent metal transporter 1 and metal transport protein 1 in the normal and Belgrade rat

Iron accumulation in the brain occurs in a number of neurodegenerative diseases. Two new iron transport proteins have been identified that may help elucidate the mechanism of abnormal iron accumulation. The Divalent Metal Transporter 1 (DMT1), is responsible for iron uptake from the gut and transport from endosomes. The Metal Transport Protein 1 (MTP1) promotes iron export. In this study we determined the cellular and regional expression of these two transporters in the brains of normal adult and Belgrade rats. Belgrade rats have a defect in DMT1 that is associated with lower levels of iron in the brain. In the normal rat, DMT1 expression is highest in neurons in the striatum, cerebellum, thalamus, ependymal cells lining the third ventricle, and vascular cells throughout the brain. The staining in the ependymal cells and endothelial cells suggests that DMT1 has an important role in iron transport into the brain. In Belgrade rats, there is generalized decrease in immunodetectable DMT1 compared to normal rats except in the ependymal cells. This decrease in immunoreactivity, however, was absent on immunoblots. The immunoblot analysis indicates that this protein did not upregulate to compensate for the chronic defect in iron transport. MTP1 staining is found in most brain regions. MTP1 expression in the brain is robust in pyramidal neurons of the cerebral cortex but is not detected in the vascular endothelial cells and ependymal cells. MTP1 staining in Belgrade rats was decreased compared to normal, but similar to DMT1 this decrease was not corroborated by immunoblotting. These results indicate that DMT1 and MTP1 are involved in brain iron transport and this involvement is regionally and cellularly specific.

Abnormal iron accumulation in the brain of neonatal hypotransferrinemic mice

Transferrin is a plasma protein involved in iron delivery to tissues. To study iron transport into the brain under a transferrin deficiency, iron concentration and 59Fe uptake in the brain were measured in neonatal hypotransferrinemic (HP) mice at 7 days of age. Brain iron concentration of the HP mice, in which iron concentration was relatively high in the cerebral cortex and cerebellum, was approximately three times higher than that of non-mutant mice, whereas serum iron concentration of HP mice was significantly lower than that of non-mutant mice. When 59FeCl3 was subcutaneously injected into HP and non-mutant mice, 59Fe was distributed highly in the choroid plexus in the ventricles of HP mice 24 h after injection. The 59Fe distribution in the brain was different between HP and non-mutant mice. On the other hand, the clearance of 59Fe from the blood was very high in HP mice and the hepatic 59Fe concentration of HP mice was more than ten times of that of non-mutant mice. The present findings demonstrate that iron distribution in the brain is changed by transferrin deficiency and that iron abnormally accumulates in the brain of HP mice. It is likely that the management of iron is different in the brain of HP mice.

Haptoglobin gene expression in human glioblastoma cell lines

Increases in cerebrospinal fluid (CSF) levels of the acute phase protein haptoglobin (Hp) occur in central nervous system (CNS) disorders such as Alzheimer's disease. To establish if Hp CSF level increases can be associated with Hp expression in brain, reverse transcription-polymerase chain reaction (RT-PCR) experiments were conducted to determine if the Hp mRNA transcript is expressed in human glioblastoma cells. Furthermore, Western blots and immunoprecipitations were performed to elucidate if Hp protein is synthesized and secreted by human glioblastoma cells. The Hp mRNA (alpha2beta) transcript (1155 bp) was detected both in U-87MG and U-138MG cells, and was positively verified by nested PCR in which a part of the beta sequence (482 bp) was targeted for amplification. Despite the presence of Hp mRNA, Hp protein was not secreted by U-87MG cells as compared to the hepatoma cell line, HepG2, where Hp protein (approximately 46 kDa) was detected in the media. The results suggest the expression of Hp protein by glioblastoma cells is possible since the Hp mRNA transcript exist, but whether or not Hp mRNA is contained in a storage pool requiring a specific signal for translation or is transiently expressed remains to be uncovered in future studies.

Alternative splicing prevents transferrin secretion during differentiation of a human oligodendrocyte cell line

Transferrin, the iron-transport protein of vertebrate serum, is synthesized mainly in the liver, from which it is secreted into the blood. Transferrin is also synthesized in oligodendrocytes and is an early marker of their differentiation. We have analyzed the regulation of transferrin expression in HOG cells, a human oligodendrocyte cell line. Transferrin expression was correlated with the appearance of oligodendrocyte differentiation markers when cells were exposed to differentiation medium. In contrast to the protein expressed in hepatocytes or in Sertoli cells, transferrin was secreted by neither HOG cells nor immature rat primary oligodendrocytes in vitro. Moreover, transferrin appears to be localized in the cytosol and not in the secretory compartment, as is expected for secreted proteins. This transferrin localization was correlated with the synthesis of a specific transcript, resulting from an alternative splicing, which leads to the elimination of the signal peptide sequence. These results suggest the existence of a functional difference between transferrin synthesized in the brain and in other organs such as liver and testis. They are in accordance with the hypothesis that transferrin plays a specific role, other than iron transport, in oligodendrocyte maturation and in the myelination process.

Transferrin and transferrin receptor function in brain barrier systems

1. Iron (Fe) is an essential component of virtually all types of cells and organisms. In plasma and interstitial fluids, Fe is carried by transferrin. Iron-containing transferrin has a high affinity for the transferrin receptor, which is present on all cells with a requirement for Fe. The degree of expression of transferrin receptors on most types of cells is determined by the level of Fe supply and their rate of proliferation. 2. The brain, like other organs, requires Fe for metabolic processes and suffers from disturbed function when a Fe deficiency or excess occurs. Hence, the transport of Fe across brain barrier systems must be regulated. The interaction between transferrin and transferrin receptor appears to serve this function in the blood-brain, blood-CSF, and cellular-plasmalemma barriers. Transferrin is present in blood plasma and brain extracellular fluids, and the transferrin receptor is present on brain capillary endothelial cells, choroid plexus epithelial cells, neurons, and probably also glial cells. 3. The rate of Fe transport from plasma to brain is developmentally regulated, peaking in the first few weeks of postnatal life in the rat, after which it decreases rapidly to low values. Two mechanisms for Fe transport across the blood-brain barrier have been proposed. One is that the Fe-transferrin complex is transported intact across the capillary wall by receptor-mediated transcytosis. In the second, Fe transport is the result of receptor-mediated endocytosis of Fe-transferrin by capillary endothelial cells, followed by release of Fe from transferrin within the cell, recycling of transferrin to the blood, and transport of Fe into the brain. Current evidence indicates that although some transcytosis of transferrin does occur, the amount is quantitatively insufficient to account for the rate of Fe transport, and the majority of Fe transport probably occurs by the second of the above mechanisms. 4. An additional route of Fe and transferrin transport from the blood to the brain is via the blood-CSF barrier and from the CSF into the brain. Iron-containing transferrin is transported through the blood-CSF barrier by a mechanism that appears to be regulated by developmental stage and iron status. The transfer of transferrin from blood to CSF is higher than that of albumin, which may be due to the presence of transferrin receptors on choroid plexus epithelial cells so that transferrin can be transported across the cells by a receptor-mediated process as well as by nonselective mechanisms. 5. Transferrin receptors have been detected in neurons in vivo and in cultured glial cells. Transferrin is present in the brain interstitial fluid, and it is generally assumed that Fe which transverses the blood-brain barrier is rapidly bound by brain transferrin and can then be taken up by receptor-mediated endocytosis in brain cells. The uptake of transferrin-bound Fe by neurons and glial cells is probably regulated by the number of transferrin receptors present on cells, which changes during development and in conditions with an altered iron status. 6. This review focuses on the information available on the functions of transferrin and transferrin receptor with respect to Fe transport across the blood-brain and blood-CSF barriers and the cell membranes of neurons and glial cells.

Transferrin is required for normal distribution of 59Fe and 54Mn in mouse brain

Hypotransferrinemia (hpx/hpx) is a genetic defect in mice resulting in <1% of normal plasma transferrin (Tf) concentrations; heterozygotes for this mutation (+/hpx) have low circulating Tf concentrations. These mice provide a unique opportunity to examine the role of Tf in Fe and Mn transport in the brain. Twenty weanling wild-type BALB/cJ mice, 15 +/hpx mice, and 12 hpx/hpx mice of both sexes were injected i.v. with either 54MnCl(2) or 59FeCl(3) either 1 h or 1 week before killing at 12 weeks of age. Total brain counts of 54Mn and 59Fe were measured, and regional brain distributions were assessed by autoradiography. Hypotransferrinemia did not affect total brain Mn uptake. However, 1 week after i.v. injection, hpx/hpx mice had less 54Mn in forebrain structures including cerebral cortex, corpus callosum, striatum, and substantia nigra. The +/hpx mice had the highest total brain 59Fe accumulation 1 h after i.v. injection. A striking effect of regional distribution of 59Fe was noted 1 week after injection; in hpx/hpx mice, 59Fe was located primarily in choroid plexus, whereas in +/+ and +/hpx mice 59Fe was widely distributed, with relatively high amounts in cerebral cortex and cerebellum. We interpret these data to mean that Tf is necessary for the transport of Fe but not Mn across the blood-brain barrier, and that there is a Tf-independent uptake mechanism for iron in the choroid plexus. Additionally, these data suggest that endogenous synthesis of Tf is necessary for Fe transport from the choroid plexus.

Existing and emerging mechanisms for transport of iron and manganese to the brain

The metals iron (Fe) and manganese (Mn) are essential for normal functioning of the brain. This review focuses on recent developments in the literature pertaining to Fe and Mn transport. These metals are treated together because they appear to share several transport mechanisms. In addition, several neurological diseases such as Alzheimer's Disease, Parkinson's Disease, and Huntington's Disease are all associated with Fe mismanagement in the brain, particularly in the striatum and basal ganglia. Similarly, Mn accumulation in brain also appears to target the same brain regions. Therefore, stringent regulation of the concentration of these metals in the brain is essential. The homeostatic mechanisms for these metals must be understood in order to design neurotoxicity prevention strategies.

Transferrin is an essential factor for myelination

It has been established that oligodendrocytes, the myelin forming cells, participate in iron homeostasis through the synthesis and secretion of transferrin. Here we investigated whether a correlation exists between myelination, the commonly studied function of oligodendrocytes, and that of transferrin synthesis and secretion. We used a proteolipid protein mutant, the myelin deficient rat, whose condition is characterized by severe hypomyelination. We compared the ontogenic profile for transferrin gene expression in mutants with that of unaffected rat pups through northern blot analysis and in situ hybridization. Surprisingly, transferrin synthesis was null in mutant oligodendrocytes. Next, we demonstrated that a single apo-transferrin intraparenchymal injection administered to P5 rat pups enabled mutant oligodendrocytes to synthesize myelin basic protein and to myelinate axons, indicating that transferrin effects mutant oligodendrocyte maturation regardless of its source. Thus, transferrin availability is essential for oligodendrocyte maturation and function, and oligodendrocytes are most vulnerable to transferrin deficiency during the premyelinating stage.

Kinetics and distribution of [59Fe-125I]transferrin injected into the ventricular system of the rat

We examined the kinetics and distribution of [59Fe-125I] rat Tf and unlabelled human Tf injected into a lateral cerebral ventricle (i.c. v. injection) in the rat. [56Fe-131I]Tf injected intravenously served as a control of blood-brain barrier (BBB) integrity. In CSF of adult rats, 59Fe and [125I]Tf decreased to only 2.5% of the dose injected after 4 h. In brain parenchyma, [125I]Tf had disappeared after 24 h, whereas approximately 18% of i.c.v.-injected 59Fe was retained even after 72 h. The elimination pattern of [125I]Tf from the CSF corresponded to that of [131I]albumin injected i.c.v., suggesting a nonselective washout of CSF proteins. [131I]Tf was hardly detectable in the brain, reflecting an unimpaired BBB during the experiments. Morphologically, 59Fe and i.c.v. injected human Tf were confined to the ventricular surface and meningeal areas, whereas grey matter regions at distances more than 2-3 mm from the ventricles and the subarachnoid space were unlabelled. However, accumulation of 59Fe was observed in the anterior thalamic and the medial habenular nuclei, and in brain regions with synaptic communications to these areas. In the newborn rats aged 7 days (P7) injected i.c.v. with [59Fe-125I]Tf and examined after 24 h, the amounts of [125I]Tf in CSF were approximately 3.5 times higher than in adult rats collected after the same time interval, whereas the amounts of 59Fe in CSF were at the same level in P7 and adult rats. In the brain tissue of the i.c.v. injected P7 rats, both [125I]Tf and 59Fe were retained to a significantly higher degree compared to that seen in adult brains. The rapid washout and lack of capability for i.c.v. injected [125I]Tf to penetrate deeply into the brain parenchyma of the adult brain question the importance of Tf of the CSF, and choroid plexus-derived Tf, for Fe neutralization and delivery of Fe-Tf to TfR-containing neurons and other cells in the CNS. However, it may serve these functions in young animals due to a lower rate of turnover of CSF.

Quantification of cerebrospinal fluid proteins in children by high-resolution agarose gel electrophoresis

Physiologic alterations in cerebrospinal fluid proteins occur inter alia with aging. Agarose gel electrophoresis discriminates many cerebrospinal fluid proteins and in addition quantifies concentration alterations. This study aimed to investigate the time course of these alterations in children and to establish normative values for cerebrospinal fluid protein properties. In 202 children without diseases known to alter cerebrospinal fluid, normative protein properties were quantified using nephelometry, ultrafiltration, high-resolution electrophoresis, and Gaussian curve fit densitometry. Total protein and protein concentrations (albumin and gamma-globulins) decreased from birth until 7 months age, and, from then on, increased slightly (transthyretin, albumin, and alpha2-proteins) or strongly (gamma-globulins). Protein proportions (transthyretin and transferrin) increased until about 3 years of age and decreased from then on. These normative values for children as quantified by high-resolution agarose gel electrophoresis are presented in a significance-structured percentile table. The time courses of these cerebrospinal fluid properties reflect physiologic alterations of the blood-brain barrier function during childhood.

Absence of neuronal and glial proteins in human and rat leptomeninges in situ

Human leptomeningeal (arachnoid and pia mater) cells in culture have been demonstrated in replicated studies to express typical neuronal proteins such as neurofilament protein and neuron-specific enolase. In addition, they can express glial fibrillary acidic protein. The present study examines the possibility that neuronal and glial proteins might be present in rat and human leptomeningeal cells in situ. The neuronal proteins 160 kDa and 200 kDa neurofilaments, neuron-specific enolase and microtubule-associated protein 2 were, however, not immunolocalized in either the pia mater or arachnoid. Glial fibrillary acidic protein and galactocerebroside were also not detected, while fibronectin and vimentin immunoreactivities were robust in all layers of the leptomeninges. Together with the previously reported expression of some neuronal and astroglial markers in cultured human leptomeninges, these observations suggest that culture alters the properties of leptomeningeal cells.

Distinct positive and negative regulatory elements control neuronal and hepatic transcription of the human transferrin gene

Transferrin (Tf), the iron-transport protein, plays an essential role in the central nervous system development, plasticity, and aging. As a first step toward elucidating the role of each transcription factor involved in the regulation of Tf gene expression, we have recently shown that similar promoter elements direct cell-type specific transcription in oligodendrocytes, epithelial choroid plexus cells, and in the neuronal cell line B103. Here we have analyzed the regulatory elements that control the level of expression of the Tf gene in neuronal cells. Transient expression experiments in B103 cells revealed that the -164/+1 promoter region is stimulated by a position-dependent -1140/-1000 upstream region. DNase I footprinting, gel retardation assays, and antibody reactivity data allowed us to characterize the nuclear factors interacting with this region. The upstream region I-binding protein (URI-BP) belongs to the steroid/retinoid receptor family, while URII-BP is a member of the nuclear factor I (NF-I) family. Interestingly, no enhancer nor silencer activity is detected in B103 cells. This contrasts with our findings in hepatoma cells, where the activity of the -125/+1 promoter can be repressed by a -1000/-819 upstream negative-acting region and stimulated by the -3600/-3300 enhancer. We demonstrate that the negative-acting region presents the characteristics of a silencer that interacts with a nuclear protein present in liver and absent in B103 cells. Similarly, B103 cells lack a nuclear protein able to bind to an essential site of the enhancer. This shows that in B103 cells, the inactivity of the silencer and the enhancer regions results from the absence of at least one essential nuclear protein.

Transcription of the human transferrin gene in neuronal cells

We have recently shown that a combination of three transcription factors governs the expression of the human transferrin gene in different brain cell types, oligodendrocytes, choroid plexus cells and neuronal cells. It was essential to elucidate the role of each factor in the regulation of transferrin gene transcription. Site-directed mutagenesis and co-transfection experiments in neuronal cells revealed that chicken ovalbumin upstream promoter transcription factor (COUP-TF), which binds to the promoter region I, acts as a repressor. Overexpression of the CCAAT/enhancer binding protein (C/EBP-alpha), which binds to the promoter region II, transactivates the -164/+1 promoter, even enables the -125/+1 region to promote transcription, and synergistically activates transcription in the presence of CREB. The C/EBP-alpha-mediated activation is antagonized by COUP-TF. The positive action of the cAMP response element-binding protein called CRI-BP is revealed by mutations of the central region I site which repress transcription. Moreover addition of dibutyryl cyclic AMP or overexpression of the catalytic subunit of protein kinase A increase transcription from the wild-type and not from the CRI mutant promoter, which shows that CRI-BP is responsible for mediating cAMP stimulation of Tf gene transcription.

Transferrin secretion by lens epithelial cells in culture

Transferrin (Tf), the plasma iron transport protein which supports cell proliferation and differentiation and has bacteriostatic, antioxidant and anti-inflammatory activity, has been found in relatively high concentrations in the intraocular fluids. Intraocular synthesis of Tf has recently been demonstrated, although the intraocular tissue(s) responsible have not been identified. We designed this study to determine whether certain ocular tissues can make and secrete transferrin. Transferrin content of aqueous and vitreous humors and whole lenses was determined by ELISA. Transferrin secretion by cultured epithelia from lens and ciliary body was also measured. In addition, Northern blots of RNA from cultured lens epithelial cells, ciliary body pigmented and non-pigmented epithelial cells, and from whole iris, ciliary body and retina were probed with riboprobes for Tf mRNA and 18S rRNA. Transferrin made up 23% and 16% of total canine aqueous and vitreous protein. All ocular tissues and cultured cells tested contained mRNA for Tf, however Tf was secreted into the bathing medium from lens epithelial cell cultures, but not from either the pigmented or non-pigmented epithelial cells of the ciliary body cultures, but not from either the pigmented or non-pigmented epithelial cells of the ciliary body Cycloheximide inhibited secretion of Tf from the lens epithelial cells. Lenses from inflamed eyes contained higher levels of Tf than their contralateral controls. This is the first experimental demonstration that an intraocular tissue can make and secrete Tf. Transferrin secretion by the lens may contribute significantly to the IOF content of this important intraocular protein.

The cerebral expression of plasma protein genes in different species

The cerebrospinal fluid (CSF) contains the same proteins as blood plasma, but with a different pattern of concentrations. Protein concentrations in CSF are much lower than those in blood. CSF proteins are derived from blood or synthesized within the brain. The choroid plexus is an important source of CSF proteins. Transthyretin is the protein most abundantly synthesized and secreted by choroid plexus. It determines the distribution of thyroxine in the cerebral compartment. Synthesis of transthyretin first evolved in the brain, then later it became a plasma protein synthesized in the liver. Other proteins secreted by choroid plexus are serum retinol-binding protein, transferrin, caeruloplasmin, insulin-like growth factors, insulin-like growth factor binding proteins, cystatin C, alpha 1-antichymotrypsin, alpha 2-macroglobulin, prothrombin, beta 2-microglobulin and prostaglandin D synthetase. Species differences in expression of the genes for these proteins are outlined, and their developmental pattern, regulation and roles in the cerebral extracellular compartment are discussed.

'Brain-type' N-glycosylation of asialo-transferrin from human cerebrospinal fluid

Asialo-transferrin from human cerebrospinal fluid was purified to homogeneity. Investigation of the structural characteristics of its oligosaccharides support our hypothesis of 'brain-type' glycosylation of intrathecally synthesized cerebrospinal fluid proteins. For carbohydrate structural analysis, high-pH anion-exchange chromatography, methylation analysis, liquid secondary ion- and matrix-assisted laser desorption/ ionization mass spectrometry of the permethylated derivatives were used. The major structure turned out to be a complex-type agalactodiantennary oligosaccharide with bisecting N-acetylglucosamine and proximal fucose. Analysis of a second transferrin preparation containing both asialo- and sialo-transferrin revealed another major glycan species derived from the sialylated transferrin variant which is galactosylated and lacks bisecting N-acetylglucosamine and fucose.

Glucocorticoids enhance the potency of Schwann cell mitogens

Previous studies have documented that cultured Schwann cells require serum-containing medium to respond maximally to mitogens. We now report that Schwann cells are able to proliferate to a mitogenic response in a serum-free defined medium termed oligodendrocyte defined media (ODM). Glucocorticoids are the essential component of ODM which allow Schwann cell proliferation in the serum-free medium. Charcoal treatment of the fetal calf serum decreases the mitogenic potency of the axolemma-enriched fraction (AEF) by 50%. The addition of 2 microM hydrocortisone to charcoal-treated fetal calf serum restores 75% of the lost mitogenicity. These observations are consistent with the view that glucocorticoids present in fetal calf serum are potent co-mitogens essential for AEF-induced Schwann cell proliferation. The synthetic glucocorticoid, dexamethasone, is a more potent co-mitogen than hydrocortisone, with a maximal effect at concentrations less than 10 nM. In contrast, other steroids including aldosterone, progesterone, testosterone, and 17 beta-estradiol have no effect on enhancing the mitogenic response of Schwann cells to the AEF. The glucocorticoid antagonists RU 486 and dehydroepiandrosterone (DHEA), but not the antiestrogenic compound tamoxifen, block AEF-induced Schwann cell proliferation. These results suggest that glucocorticoid-induced Schwann cell proliferation is mediated through a glucocorticoid receptor (GR) mechanism. We detected immunoreactivity to the GR in the cytoplasm, but not in the nuclei of Schwann cells grown in ODM lacking dexamethasone. The addition of 100 nM dexamethasone to these cultures resulted in immunoreactivity in the nucleus. This data suggests that glucocorticoids working through the GR are potent co-mitogens for Schwann cell proliferation.

Gene expression in astrocytes is affected by subculture

We have investigated the effects of cell passaging and time in culture on astrocyte morphology, transferrin expression and the expression of two main astrocyte markers, glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS: EC 6.3.1.2). When primary astrocytes were subcultured, giving rise to secondary and tertiary cultures, their morphology changed, regardless of the split ratio used to passage the cells. Correlating with this morphological change, a dramatic increase in the accumulation of GFAP and GS mRNAs was observed after cells had been passaged. This effect was in marked contrast to the moderate increase in the levels of GFAP and GS mRNAs observed over several weeks in primary culture. Hydrocortisone induction of GS gene expression was not affected by cell passage. Transferrin mRNA, which is not normally found in astrocytes in vivo, was expressed at a high level in primary cultures of astrocytes. However, transferring mRNA almost completely disappeared after the second passage. Astrocyte-conditioned media, or co-cultures with oligodendrocytes, modified transferrin gene expression. Taken together, these results show that subculturing of primary rat astrocytes leads to a dramatic change in the genetic expression of several proteins and provides a new approach to modify astrocyte differentiation in vitro.

Hemoglobin as a novel protein developmentally regulated in neurons

We have attempted to identify some novel genes which were found to be more highly expressed in the embryonic brain than in the adult brain. Consequently, one of these clones was identified as alpha-globin cDNA. Actually, alpha-globin mRNA was detected in the neurons. In addition, beta-globin mRNA was detected in the neurons as well. Both globin mRNAs were developmentally regulated in the same pattern. Subsequently, further examinations with antiserum to hemoglobin revealed the presence of hemoglobin in the neurons. Hemoglobin has, up to now, been known to be an important O2 transporter protein in erythrocytes. Moreover, hemoglobin is now considered to be also a very dangerous protein generating the toxic hydroxyl radical (.OH). We herein show the presence of hemoglobin and its regulation in the central nervous system, which may indicate the presence of a useful function regulating O2 homeostasis and a potential oxidative toxicity for neuronal cells.

Transferrin in the central nervous system of the shiverer mouse myelin mutant

Transferrin, the iron mobilization protein, and its mRNA are normally present in oligodendrocytes. Previous reports using myelin mutants have shown both a decrease in transferrin protein and mRNA when the oligodendrocyte population is compromised. In this study the shiverer mouse mutant in which the oligodendrocyte population is numerically normal, but has both quantitatively diminished and qualitatively abnormal myelin was used. This animal model was chosen to address the question whether expression of the transferrin message and/or protein correlated more closely to the number of oligodendrocytes (normal) or the amount of myelin (abnormally low). A 1/2 to 2/3 decrease in transferrin protein occurred in all brain regions examined except for the spinal cord in the shiverer group compared to both heterozygous littermates and wild type controls. Levels of transferrin transcripts in the brain are not affected by the shiverer mutation. These results taken with previous reports from this laboratory indicate that the presence of oligodendrocytes is a requirement for normal expression of transferrin mRNA in brain but is not sufficient for normal values of the protein. The level of Tf protein correlates more closely with the amount of myelin present than it does with the numbers of oligodendrocytes present. These data are consistent with previous reports from our laboratory that transferrin accumulation by oligodendrocytes is associated with myelin production by these cells. These data further suggest transferrin mRNA may be constitutively expressed by oligodendrocytes and that the protein expression is regulated at the level of translation.

Effects of interleukin-1 beta and tumor necrosis factor-alpha on the expression of glial fibrillary acidic protein and transferrin in cultured astrocytes

Recent evidence suggests that interleukin (IL)-1 and tumor necrosis factor (TNF) may play a role in astrogliosis following injury to the CNS. The short-term biochemical effects of these immune-related cytokines were determined on cultured rat polygonal and process-bearing astrocytes. Both IL-1 and TNF stimulated the rate of thymidine incorporation in polygonal astrocytes up to 137% and 215%, respectively, over the level observed in untreated controls. By contrast, thymidine incorporation was relatively unaffected by these cytokines in process-bearing astrocytes. The cytokines did not significantly affect the level of glial fibrillary acidic protein (GFAP) within polygonal astrocytes, even though they appeared to downregulate the expression of GFAP mRNA by as much as 62%. Both cytokines increased the intracellular expression of transferrin (Tf) within some polygonal astrocytes. In untreated control cultures, fewer than than 2% of polygonal astrocytes were immunoreactive for Tf. By contrast, approximately 30% of polygonal astrocytes treated with IL-1 or TNF-alpha became strongly immunoreactive for Tf. Neither IL-2 nor a number of other known growth factors appeared to alter the level of immunoreactive Tf in these cells. Process-bearing astrocytes were negative for Tf, regardless of the treatment used. Northern blot analysis demonstrated that the level of Tf mRNA in cultures of polygonal astrocytes increased 148% above the level observed in untreated controls following treatment with either IL-1 or TNF, whereas no change was observed following treatment with IL-2. These results suggest that increased levels of particular cytokines known to be present in injured CNS can produce pronounced biochemical alterations within a subtype of cultured astrocytes.

Characterization of "plasma proteins" secreted by cultured rat macroglial cells

The brain is isolated behind a blood-tissue barrier that restricts the access of circulating proteins to neural cells. There is evidence that some of these proteins are synthesized within the central nervous system. The present study examines the synthesis and secretion of such proteins by cultured macroglial cells. Primary glial cultures were derived from cortical and subcortical regions of neonatal rat brains, and subsequent secondary cultures were enriched in type-1 astrocytes, type-2 astrocytes, or oligodendrocytes. Newly synthesized proteins were immunoprecipitated from the culture media using antisera directed against whole rat serum. All three types of glial cells secreted a range of plasma proteins. In general, type-1 astrocytes secreted more of these proteins than did type-2 astrocytes or oligodendrocytes, although the one-dimensional polyacrylamide gel electrophoresis (PAGE) profiles were specific for each cell type. Anti-sera directed against specific plasma proteins identified three of the most abundant proteins secreted by type-1 astrocytes as transferrin, alpha-2-macroglobulin, and ceruloplasmin. Northern blot analysis of cellular RNA confirmed that type-1 astrocytes contained transferrin mRNA, and that it was more abundant in cultures derived from subcortical regions than from cortical regions. In situ hybridization studies revealed that virtually all type-1 and type-2 astrocytes contained transferrin mRNA. Since the proteins identified in this study have been proposed to have a variety of neurotrophic roles in the central nervous system, these data further extend the range of possible functions that glial cells may serve in the CNS.

Neuronal cell cultures: a tool for investigations in developmental neurobiology

The aim of this review is to describe environmental requirements for survival of neuronal cells in culture, and secondly to survey the complex interplay between hormones, neurotrophic factors, transport- and extracellular matrix- proteins, which characterize the developmental program of differentiating neurons. An overall reconsideration of the literature in this vast field is above the limits of the present paper; since progress and refinement in the techniques of neuronal cell cultures have paralleled the advancement in Developmental Neurobiology, we will run instead through the main steps which form the conceptual framework of neuronal cell cultures.

Rat brain creatine kinase messenger RNA levels are high in primary cultures of brain astrocytes and oligodendrocytes and low in neurons

Rat brain creatine kinase (CKB) gene expression is highest in the brain but is also detectable at lower levels in some other tissues. In the brain, the CKB enzyme is thought to be involved in the regeneration of ATP necessary for transport of ions and neurotransmitters. To understand the molecular events that lead to high CKB expression in the brain, we have determined the steady-state levels of CKB mRNA in homogeneous cultures of primary rat brain astrocytes, oligodendrocytes, and neurons. Northern blot analysis showed that whereas the 1.4-kb CKB mRNA was detectable in neurons, the level was about 17-fold higher in oligodendrocytes and 15-fold higher in astrocytes. The blots were hybridized with a CKB-specific 32P-antisense RNA probe, complementary to the 3' untranslated sequence of CKB, which hybridizes to CKB mRNA but not CKM mRNA. Also, the 5' and 3' ends of CKB mRNA from the glial cells were mapped, using exon-specific antisense probes in the RNase-protection assay, and were found to be the same in astrocytes and oligodendrocytes. This indicated that (a) the site of in vivo transcription initiation in astrocytes and oligodendrocytes was directed exclusively by the downstream, nonconcensus TTAA sequence at -25 bp in the CKB promoter that is also utilized by all other cell types that express CKB and (b) the 3' end of mature CKB mRNA was the same in astrocytes and oligodendrocytes. In addition, there was no detectable alternate splicing in exon 1, 2, or 8 of CKB mRNA in rat astrocytes and oligodendrocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Directed establishment of rat brain cell lines with the phenotypic characteristics of type 1 astrocytes

Interest in obtaining cell lines for use in studies on the development and biochemistry of the central nervous system has motivated efforts to establish cells from primary brain cultures by the use of oncogene-transfer techniques. In previous reports, cell lines derived from astrocytes in this way have had immature or abnormal phenotypes. We have explored the possibility of specifically "targeting" expression of exogenous oncogenes to differentiated astrocytes by using the promoter of the gene encoding glial fibrillary acidic protein, which is expressed almost exclusively in such cells. We report here that cell lines displaying the phenotypic characteristics of type 1 astrocytes can be established reproducibly in this manner. Given the heterogeneity of primary cultures, the availability of clonal cell lines displaying characteristics of type 1 astrocytes should greatly facilitate our understanding of the biology of these cells.

Uptake and distribution of iron and transferrin in the adult rat brain

Brain uptake of iron-59 and iodine-125-labelled transferrin from blood in the adult rat has been investigated using graphical analysis to determine the blood-brain barrier permeability to these tracers in experiments that lasted between 5 min and 8 days. The blood-brain barrier permeability (K(in)) to 59Fe was 89 x 10(-5) ml/min/g compared to the value of 7 x 10(-5) ml/min/g for 125I-transferrin, which is similar to that of albumin, a plasma marker. The autoradiographic distribution of these tracers in brain was also studied to determine any regional variation in brain uptake after the tracers had been administered either systemically or applied in vitro. No regional uptake was seen for 125I-transferrin even after 24 h of circulation. In contrast, 59Fe showed selective regional uptake by the choroid plexus and extra-blood-brain barrier structures 4 h after administration. After 24 h of circulation, 59Fe distribution in brain was similar to the transferrin receptor distribution, as determined in vitro, but was unlike the distribution of nonhaem iron determined histochemically. The data suggest that brain iron uptake does not involve any significant transcytotic pathway of transferrin-bound iron into brain. It is proposed that the uptake of iron into brain involves the entry of iron-loaded transferrin to the cerebral capillaries, deposition of iron within the endothelial cells, followed by recycling of apotransferrin to the circulation. The deposited iron is then delivered to brain-derived transferrin for extracellular transport within the brain, and subsequently taken up via transferrin receptors on neurones and glia for usage or storage.

Presence of low amounts of "neuronal" antigens in cultured human skin fibroblasts

To explore the utility of cultured skin fibroblasts in investigating diseases of the nervous system in which constituents characteristic of neurons are involved, sensitive immunochemical methods were used to test for the presence in skin fibroblasts of low amounts of proteins normally used as neuronal markers. The presence of each of the neurofilament triplet proteins and of neuron-specific enolase was demonstrated by immunoblotting and by immunocytochemistry, and of an 86-kDa synapsin-like material by immunoblotting. These observations agree with previous suggestions that readily available cultured fibroblasts may be useful in investigations of disorders in which molecules are involved which are typically associated with neurons in vivo, such as Alzheimer's disease.