bluuebunny/crossref_metadata_2025_split huggingface dataset:
The enhancement of glucose uptake caused by the collapse of gap junction communication is due to an increase in astrocyte proliferation
Authors: Tabernero Arantxa , Jiménez Cristina , Velasco Ana , Giaume Christian , Medina José M. 
Published: March 2003

We have previously shown that several gap junction uncouplers increase the uptake of glucose in astrocytes. The aim of the present work was to study whether the increase in glucose uptake was a consequence of the inhibition of gap junction communication and the purpose of this effect. Our results show that α‐glycyrrhetinic acid and endothelin‐1 increase the uptake of glucose in highly, but not in poorly, coupled astrocytes. This effect depended on connexin 43 levels and was abolished when the inhibition of gap junction communication was prevented by tolbutamide or ouabain. The inhibition of gap junctions increased the rate of glucose incorporation into DNA and RNA, which was inhibited by treatment with dehydroepiandrosterone, an inhibitor of glucose‐6‐phosphate dehydrogenase, the regulatory enzyme of the pentose phosphate pathway. The inhibition of gap junctions significantly increased astrocyte proliferation, which was counteracted by tolbutamide. These effects were not observed in poorly coupled astrocytes expressing low levels of connexin 43. The increase in astrocyte proliferation caused by gap junction inhibition was prevented when either glucose uptake or the pentose phosphate pathway were inhibited. We conclude that the inhibition of gap junction communication induces astrocyte proliferation, resulting in an enhancement of glucose uptake and its utilization through the pentose phosphate pathway to provide ribose‐5‐phosphate for the synthesis of nucleic acids.
Stress proteins in oligodendrocytes: differential effects of heat shock and oxidative stress
Authors: Goldbaum Olaf , Richter‐Landsberg Christiane 
Published: March 2003

Heat shock proteins (HSP) or stress proteins serve as biomarkers to identify the contribution of stress situations underlying the pathogenesis of degenerative diseases of the CNS. We have analyzed by immunoblot technique the constitutive and inducible occurance of stress proteins in cultured rat brain oligodendrocytes subjected to heat shock or oxidative stress exerted by hydrogen peroxide, or a combination of both. The data demonstrate that oligodendrocytes constitutively express HSP32, HSP60 and the cognate form of the HSP70 family of proteins, HSC70. After heat shock, HSP25, αB‐crystallin and HSP70 were up‐regulated, while after oxidative stress the specific induction of HSP32 and αB‐crystallin was observed. HSP32 represents heme oxygenase 1 (HO‐1), a small stress protein with enzymatic activity involved in the oxidative degradation of heme which participates in iron metabolism. The presence of the iron chelators phenanthroline or deferoxamine (DFO), which previously has been shown to protect oligodendrocytes from oxidative stress‐induced onset of apoptosis, caused a marked stimulation of HSP32 without affecting HSP70. This indicates that DFO possibly exerts its protective role by directly influencing the antioxidant capacity of HO‐1. In summary, HSP in oligodendrocytes are differentially stimulated by heat stress and oxidative stress. Heme oxygenase‐1 has been linked to inflammatory processes and oxidative stress, its specific up‐regulation after oxidative stress in oligodendrocytes suggests that it is an ideal candidate to investigate the involvement of oxidative stress in demyelinating diseases.
(1R,3S)‐1‐Aminocyclopentane‐1,3‐dicarboxylic acid (RS‐ACPD) reduces intracellular glutamate levels in astrocytes
Authors: Ye Zu‐Cheng , Ransom Bruce R. , Sontheimer Harald 
Published: March 2003

(+/–)‐1‐Aminocyclopentane‐trans‐1,3‐dicarboxylic acid (t‐ACPD) is an equimolar mixture of two enantiomers: (1S,3R)‐1‐Aminocyclopentane‐1,3‐dicarboxylic acid (SR‐ACPD) and 1R,3S‐1‐Aminocyclopentane‐1,3‐dicarboxylic acid (RS‐ACPD). t‐ACPD and SR‐ACPD have been commonly used as agonists for metabotropic glutamate receptors (mGluR). Here we demonstrated that RS‐ACPD, but not SR‐ACPD, is transported into astrocytes with a Km of 6.51 ± 2.38 mm and Vmax of 22.8 ± 3.4 nmol/mg/min. This low‐affinity transport is Na+‐dependent and is competitively blocked by glutamate or other substrates for the glutamate transporter. RS‐ACPD therefore is probably taken up by the glutamate transporter. Prolonged incubation with high levels of RS‐ACPD (> 500 µm) induced significant swelling of astrocytes. At lower concentrations (100 µm), RS‐ACPD reduced intracellular glutamate content ([Glu]i) by > 50% without obvious morphological changes. The reduction in [Glu]i was accompanied by an increase in [glutamine]i. The RS‐ACPD's effect on [Glu]i required glutamine and high levels of phosphate, suggesting that RS‐ACPD inhibited phosphate‐activated glutaminase (PAG). These data suggest that astrocytic PAG is actively involved in determining the equilibrium between intracellular glutamate and glutamine. By reducing [Glu]i, RS‐ACPD reduces the amount of glutamate available for release.
Insulin‐like growth factor‐1 effects on bovine retinal endothelial cell glucose transport: role of MAP kinase
Authors: DeBosch Brian J. , Deo Baljit K. , Kumagai Arno K. 
Published: March 2003

AbstractIn order to maintain normal metabolism, the neuroretina is completely dependent on the constant delivery of glucose across the retinal microvascular endothelial cells comprising the inner blood–retinal barrier. Glucose uptake into these cells is influenced by various stimuli, including hypoxia and growth factors. Recently, insulin‐like growth factor‐1 (IGF‐1) was shown to enhance retinal endothelial glucose transport in a process that is dependent on protein kinase C (PKC) and phosphatidylinositol‐3 kinase (PI3 kinase). In the current study, the role of mitogen‐activated protein kinase (MAP kinase) in regulating IGF‐1 effects on retinal endothelial cell glucose transport was investigated in a bovine retinal endothelial cell (BREC) culture model. IGF‐1 (25 ng/mL) caused a rapid increase in MAP‐kinase activity and ERK phosphorylation. Inhibition of MAP kinase with PD98059 (100 µm) blocked IGF‐1 enhancement of 2‐deoxyglucose uptake. In order to clarify the relationship between PKC, PI3 kinase and MAP kinase in IGF‐1 signaling in retinal endothelial cells, the effects of selective inhibitors of MAP kinase (PD98059), PKC (GF109203X), and PI3 kinase (wortmannin, LY294002) on signal transduction by IGF‐1 were studied. Inhibition of MAP kinase abolished IGF‐1 stimulation of PKC but had no effect on PI3 kinase activity, whereas inhibition of either PKC and PI3 kinase had no effect on MAP kinase phosphorylation or activity in IGF‐1‐treated cells. Taken together, these data demonstrate that IGF‐1 stimulation of BREC glucose transport requires activation of MAP kinase and that MAP kinase is upstream from PKC but is independent of PI3 kinase in mediating the actions of IGF‐1 on retinal endothelial cells.
Spermine modulation of the glutamatenmda receptor is differentially responsive to conantokins in normal and Alzheimer's disease human cerebral cortex
Authors: Ragnarsson Lotten , Mortensen Martin , Dodd Peter R. , Lewis Richard J. 
Published: March 2003

AbstractThe pharmacology of the N‐methyl‐d‐aspartate (NMDA) receptor site was examined in pathologically affected and relatively spared regions of cerebral cortex tissue obtained at autopsy from Alzheimer's disease cases and matched controls. The affinity and density of the [3H]MK‐801 binding site were delineated along with the enhancement of [3H]MK‐801 binding by glutamate and spermine. Maximal enhancement induced by either ligand was regionally variable; glutamate‐mediated maximal enhancement was higher in controls than in Alzheimer's cases in pathologically spared regions, whereas spermine‐mediated maximal enhancement was higher in controls in areas susceptible to pathological damage. These and other data suggest that the subunit composition of NMDA receptors may be locally variable. Studies with modified conantokin‐G (con‐G) peptides showed that Ala(7)–con‐G had higher affinity than Lys(7)–con‐G, and also defined two distinct binding sites in controls. Nevertheless, the affinity for Lys(7)–con‐G was higher overall in Alzheimer's brain than in control brain, whereas the reverse was true for Ala(7)–con‐G. Over‐excitation mediated by specific NMDA receptors might contribute to localized brain damage in Alzheimer's disease. Modified conantokins are useful for identifying the NMDA receptors involved, and may have potential as protective agents.
Activation of Ca2+/calmodulin‐dependent protein kinase I in cultured rat hippocampal neurons
Authors: Uezu Akiyoshi , Fukunaga Kohji , Kasahara Jiro , Miyamoto Eishichi 
Published: March 2003

AbstractWe have focused on activation mechanisms of calcium/calmodulin‐dependent protein kinase (CaM) kinase I in the hippocampal neurons and compared them with that of CaM kinase IV. Increased activation of CaM kinase I occurred by stimulation with glutamate and depolarization in cultured rat hippocampal neurons. Similar to CaM kinases II and IV, CaM kinase I was essentially activated by stimulation with the NMDA receptor. Although both CaM kinases I and IV seem to be activated by CaM kinase kinase, the activation of CaM kinase I was persistent during stimulation with glutamate in contrast to a transient activation of CaM kinase IV. In addition, CaM kinase I was activated in a lower concentration of glutamate than that of CaM kinase IV. Depolarization‐induced activation of CaM kinase I was also evident in the cultured neurons and was largely blocked by nifedipine. In the experiment with 32P‐labeled cells, phosphorylation of CaM kinase I was stimulated by glutamate treatment and depolarization. The glutamate‐ and depolarization‐induced phosphorylation was inhibited by the NMDA receptor antagonist and nifedipine, respectively. These results suggest that, although CaM kinases I and IV are activated bythe NMDA receptor and depolarization stimulation, these kinase activities are differently regulated in the hippocampal neurons.
Lack of up‐regulation of ferritin is associated with sustained iron regulatory protein‐1 binding activity in the substantia nigra of patients with Parkinson's disease
Authors: Faucheux Baptiste A. , Martin Marie‐Elise , Beaumont Carole , Hunot Stéphane , Hauw Jean‐Jacques , Agid Yves , Hirsch Etienne C. 
Published: March 2003

AbstractDopaminergic neurones degenerate during Parkinson's disease and cell loss is most extensive in the subpopulation of melanized neurones located in the substantia nigra pars compacta. Iron accumulation, together with a lack of up‐regulation of the iron‐storing protein, ferritin, has been reported and may contribute to increased oxidative stress in this region. We investigated the binding activity of iron regulatory protein‐1 (IRP1) to the iron‐responsive element that precludes ferritin mRNA translation, in the substantia nigra of a group of parkinsonian patients who presented a statistically significant reduction in the number of nigral melanized‐neurones and an increased iron content, together with unchanged H‐ferritin and L‐ferritin subunit levels as compared to matched controls. The levels of ferritin mRNAs and the binding activity of IRP1 to the iron‐responsive element of ferritin mRNA did not differ significantly between the two groups. Moreover, there was no detectable contribution of the iron regulatory protein‐2 (IRP2) binding activity. No change in IRP1 control of ferritin mRNA translation explains the lack of up‐regulation of ferritin expression in cytoplasmic extracts of SNpc that would be normally expected with cytosolic iron accumulation. The data of this study do not favor changes in transcription and post‐transcriptional regulation of ferritin expression in Parkinson's disease and suggest a ‘compartmentalized’ iron accumulation.
Presence of functionally active protease‐activated receptors 1 and 2 in myenteric glia
Authors: Garrido Rosario , Segura Bradley , Zhang Weizhen , Mulholland Michael 
Published: March 2003

AbstractProtease‐activated receptors (PARs) belong to the family of membrane receptors coupled to G‐proteins; their presence is reported in a wide variety of cells. The object of this study was to demonstrate the presence of PAR‐1 and PAR‐2 in myenteric glia of the guinea pig, and to elucidate the cellular mechanisms that are triggered upon receptor activation. Thrombin and PAR‐1 agonist peptide (PARP‐1) activate PAR‐1 with a maximum mean ± SEM change in intracellular calcium concentration with respect to basal level (Δ[Ca2+]i) of 183 ± 18 nm and 169 ± 6 nm, respectively. Trypsin and PAR‐2 agonist peptide (PARP‐2) activate PAR‐2 with a maximum Δ[Ca2+]i of 364 ± 28 nm and 239 ± 19 nm, respectively. Inhibition of phospholipase C by U73312 (1 µm) decreased the Δ[Ca2+]i due to PAR‐1 activation from 167 ± 10 nm to 87 ± 6 nm. The PAR‐2‐mediated Δ[Ca2+]i decreased from 193 ± 10 nm to 124 ± 8 nm when phospholipase C activity was inhibited. Blockade of sphingosine kinase with dimethylsphingosine (1 µm) decreased the Δ[Ca2+]i due to PAR‐2 activation from 149 ± 19 nm to 67 ± 1 nm, but did not influence the PAR‐1‐mediated Δ[Ca2+]i. PAR‐1 and PAR‐2 were localized in myenteric glia by immunolabeling. Our results indicate that PAR‐1 and PAR‐2 are present in myenteric glia of the guinea pig, and their activation leads to increases in intracellular calcium via different signal transduction mechanisms that involve activation of phospholipase C and sphingosine kinase.
Myelin proteolipid protein (Plp) intron 1 DNA is required to temporally regulate Plp gene expression in the brain
Authors: Li Shenyang , Moore Christopher L. , Dobretsova Anna , Wight Patricia A. 
Published: March 2003

AbstractThe myelin proteolipid protein (Plp) gene encodes the most abundant protein found in mature CNS myelin. Expression of the gene is regulated spatiotemporally, with maximal expression occurring in oligodendrocytes during the myelination period of CNS development. Plp gene expression is tightly controlled. Misregulation of the gene in humans can result in the dysmyelinating disorder Pelizaeus‐Merzbacher disease, and in transgenic mice carrying a null mutation or extra copies of the gene can result in a variety of conditions, from late onset demyelination and axonopathy, to severe early onset dysmyelination. In this study we have examined the effects of Plp intron 1 DNA in mediating proper developmental expression of Plp‐lacZ fusion genes in transgenic mice. Our results reveal the importance of Plp intron 1 sequences in instigating the expected surge in Plp‐lacZ gene activity during (and following) the active myelination period of brain development. Transgene expression was also detected in the testis (Leydig cells), however, the presence or absence of Plp intron 1 sequences had no effect on the temporal profile in the testis. Surprisingly, expression of the transgene missing Plp intron 1 DNA was always higher in the testis, ascompared to the brain, in all of the transgenic lines generated.
CNS neurons express two distinct plasma membrane electron transport systems implicated in neuronal viability
Authors: Wright M. V. , Kuhn T. B. 
Published: March 2003

Abstract Trans‐plasma membrane electron transport is critical for maintaining cellular redox balance and viability, yet few, if any, investigations have studied it in intact primary neurons. In this investigation, extracellular reduction of 2,6‐dichloroindophenol (DCIP) and ferricyanide (FeCN) were measured as indicators of trans‐plasma membrane electron transport by chick forebrain neurons. Neurons readily reduced DCIP, but not FeCN unless CoQ1, an exogenous ubiquinone analog, was added to the assays. CoQ1 stimulated FeCN reduction in a dose‐dependent manner but had no effect on DCIP reduction. Reduction of both substrates was totally inhibited by ε‐maleimidocaproic acid (MCA), a membrane‐impermeant thiol reagent, and slightly inhibited by superoxide dismutase. Diphenylene iodonium, a flavoenzyme inhibitor, completely inhibited FeCN reduction but had no affect on DCIP reduction, suggesting that these substrates are reduced by distinct redox pathways. The relationship between plasma membrane electron transport and neuronal viability was tested using the inhibitors MCA and capsaicin. MCA caused a dose‐dependent decline in neuronal viability that closely paralleled its inhibition of both reductase activities. Similarly capsaicin, a NADH oxidase inhibitor, induced a rapid decline in neuronal viability. These results suggest that trans‐plasma membrane electron transport helps maintain a stable redox environment required for neuronal viability.
Constitutive activation of the opioid receptor‐like (ORL1) receptor by mutation of Asn133 to tryptophan in the third transmembrane region
Authors: Kam Kenneth W. L. , New David C. , Wong Yung H. 
Published: March 2003

AbstractWe have introduced a series of point mutations into the human opioid receptor‐like (ORL1) receptor and characterized them for their ability to constitutively activate G protein‐coupled receptor signalling pathways. Among the 12 mutants generated, mutation at Asn133 (N133W) gave increased basal signalling through three separate pathways. N133W increased the basal activity of G14‐ and G16‐dependent pathways by two‐ to three‐fold. The constitutive activity of the mutant was confirmed by the finding that the enhanced activity is dependent on the level of receptor expression. In HEK‐293 cells stably expressing N133W, signalling through Gi/o‐dependent pathways was also observed. Radioligand binding studies revealed that the affinity for nociceptin of the wild‐type ORL1 receptor and the N133W mutant do not differ significantly, suggesting that the ligand binding and signalling functions of constitutively active mutants of G protein‐coupled receptors are not necessarily intrinsically linked. In conclusion, our results demonstrate that a mutation in the third transmembrane domain is able to increase the basal signalling activity of the human ORL1 receptor.
Spreading depression‐induced preconditioning in the mouse cortex: differential changes in the protein expression of ionotropic nicotinic acetylcholine and glutamate receptors
Authors: Chazot P. L. , Godukhin O. V. , McDonald A. , Obrenovitch T. P. 
Published: March 2003

AbstractPreconditioning of the cerebral cortex was induced in mice by repeated cortical spreading depression (CSD), and the major ionotropic glutamate (GluRs) and nicotinic acetylcholine receptor (nAChRs) subunits were compared by quantitative immunoblotting between sham‐ and preconditioned cortex, 24 h after treatment. A 30% reduction in α‐amino‐3‐hydroxy‐5‐methyl‐4‐iso‐ xazolepropionate (AMPA) GluR1 and 2 subunit immunoreactivities was observed in the preconditioned cortex (p < 0.03), but there was no significant change in the NMDA receptor subunits, NR1, NR2A and NR2B. A 12–15‐fold increase in α7 nAChR subunit expression following in vivo CSD (p < 0.001) was by far the most remarkable change associated with preconditioning. In contrast, the α4 nAChR subunit was not altered. These data point to the α7 nAChR as a potential new target for neuroprotection because preconditioning increases consistently the tolerance of the brain to acute insults such as ischaemia. These data complement recent studies implicating α7 nAChR overexpression in the amelioration of chronic neuropathologies, notably Alzheimer's disease (AD).
Region‐specific and epileptogenic‐dependent expression of six subtypes of α2,3‐sialyltransferase in the adult mouse brain
Authors: Matsuhashi Hitomi , Horii Yoichiro , Kato Keiko 
Published: March 2003

AbstractSialylated glycoconjugates play important roles in various biological functions. The structures are also observed in brains and it has been proposed that sialylation may affect neural plasticity. To clarify the effects of sialylation in the brain, particular neurons that exhibit sialylation should first be determined. Using in situ hybridization, we performed systematic surveys of the localization of mRNAs encoding the six α2,3‐sialyltransferases (ST3Gal I–VI) in the adult mouse brain with or without physiological stimulation. First, striking region‐specific patterns of expression were observed: While ST3Gal II, III, and V mRNAs were in neuronal cells throughout the brain, ST3Gal I, IV, and VI mRNAs were in restricted brain regions. Next, to assess whether the expression of the six mRNAs can be regulated, we examined the effect of kindling epileptogenesis on the six mRNA levels. Of the six subtypes, upregulation in the ST3Gal IV level in the thalamus was most pronounced; the number of ST3Gal IV‐expressing neurons in the anterior thalamic nuclei increased from 2% to 21% in a time‐dependent manner during epileptogenesis. Western blot analysis evaluated the increase of the end‐products in the thalamus. These findings provide a molecular basis to clarify when and where sialylated glycoconjugates function accompanied by neural plasticity.
Humanin rescues human cerebrovascular smooth muscle cells from Aβ‐induced toxicity
Authors: Jung Sonia S. , Van Nostrand William E. 
Published: March 2003

AbstractCerebral amyloid β‐protein (Aβ) angiopathy (CAA) is a key pathological feature of Alzheimer's disease (AD) and related disorders. We have used human cerebrovascular smooth muscle (HCSM) cells as an in vitro model system to investigate the pathogenic mechanisms of the pathology of CAA. It was previously demonstrated that certain pathogenic forms of Aβ induce several pathologic responses in these cells, including fibril assembly at the cell surface, increased levels of Aβ precursor, degradation of HCSM cell α‐actin and cell death. The recently discovered novel rescue factor humanin (HN) was shown to protect neuronal cells in culture from various AD‐relevant insults including treatment with Aβ. In this report we investigated whether the HN peptide could rescue HCSM cells from Aβ‐induced toxicity. We found that treatment of HCSM cells with 10 μm HN prevented pathogenic Aβ‐induced HCSM cell death using a fluorescent cell viability assay, and degradation of HCSM α‐actin was diminished shown by quantitative immunoblotting. However, Aβ deposition and fibril formation at the cell surface and increased levels of cell‐associated AβPP were not affected by treatment with HN as demonstrated by a thioflavin T fluorescence assay and immunochemical methods, respectively. These results suggest that the protective effects of HN occur downstream of these cell surface molecular events. This is the first demonstration of a rescue factor for HCSM cells from Aβ‐mediated cell death as well as being the first report to show that neuronal cells and HCSM cells may share a common downstream mechanism in the Aβ‐induced cell death pathway.