β-Amyloid 25-35 Peptide Reduces the Expression of Glutamine Transporter SAT1 in Cultured Cortical Neurons (original) (raw)
Related papers
2009
Alzheimer's disease is a major neurodegenerative disorder in which there is an overproduction and accumulation of amyloid-β (Aβ) peptides. During the initial stages of the disease, glutamate receptors are dysregulated by Aβ accumulation resulting in the disruption of glutamatergic synaptic transmission. We used rat cortical cell cultures to examine the effects of Aβ(25-35)-induced neurotoxicity on glutamine transporters involved in the glutamate cycle. In primary mixed cell cultures prepared from cerebral cortex, incubation with 10 µM Aβ(25-35) for 12 h, but not for 24 h, markedly suppressed system A transporter 1 (SAT1) mRNA expression. On the other hand, Aβ(25-35) had no effect on SAT1 mRNA level in neuronal cell cultures. Treatment of both types of cell cultures with Aβ(25-35) resulted in a significant decrease in cell survival in a concentration and time-dependent manner, as determined by MTT assay. These results indicated that Aβ may impair neuronal function and transmitter synthesis and perhaps reduce excitotoxicity through a reduction in neuronal glutamine uptake.
Alzheimer's disease is a major neurodegenerative disorder in which there is an overproduction and accumulation of amyloid- (A ) peptides. During the initial stages of the disease, glutamate receptors are dysregulated by A accumulation resulting in the disruption of glutamatergic synaptic transmission. We used rat cortical cell cultures to examine the effects of A (25-35)-induced neurotoxicity on glutamine transporters involved in the glutamate cycle. In primary mixed cell cultures prepared from cerebral cortex, incubation with 10 µM A (25-35) for 12 h, but not for 24 h, markedly suppressed system A transporter 1 (SAT1) mRNA expression. On the other hand, A (25-35) had no effect on SAT1 mRNA level in neuronal cell cultures. Treatment of both types of cell cultures with A (25-35) resulted in a significant decrease in cell survival in a concentration and time-dependent manner, as determined by MTT assay. These results indicated that A may impair neuronal function and transmitter sy...
Neurobiology of Disease, 2004
Glutamate transporters are vulnerable to oxidants resulting in reduced uptake function. We have studied the effects of B-amyloid 25-35 (BA 25-35) on [ 3 H]-glutamate uptake on cortical neuron or astrocyte cultures in comparison with a scrambled peptide (SCR) and dihydrokainic acid (DHK), a prototypic uptake inhibitor. BA 25-35 was more potent than DHK in inhibiting glutamate uptake and the effects of both were more marked on astrocytes than on neurons. At 24 h, BA 25-35 dose-dependently (0.5-15 MM) increased glutamate levels in media from neuron cultures. DHK only enhanced extracellular glutamate at the highest concentration tested (2500 AM). BA 25-35 induced gradual neurotoxicity (0.1-50 MM) over time. Exposure to BA 25-35 resulted in increased uptake in astrocytes (0.25-5 AM) and neurons (0.5-15 AM) surviving its toxic effects. However, exposure to DHK (2.5-2500 AM) did not induce neurotoxicity nor modulated uptake. These results indicate that, while inhibition of glutamate uptake may be involved in the neurotoxic effects of BA 25-35 , enhancement of uptake may be a survival mechanism following exposure to BA 25-35 .
Journal of Neurochemistry, 2002
Large numbers of neuritic plaques surrounded by reactive astrocytes are characteristic of Alzheimer's disease (AD). There is a large body of research supporting a causal role for the amyloid~3peptide (An), a main constituent of these plaques, in the neuropathology of AD. Several hypotheses have been proposed to explain the toxicity of A~3including free radical injury and excitotoxicity. It has been reported that treatment of neuronal/ astrocytic cultures with A~3increases the vulnerability of neurons to glutamate-induced cell death. One mechanism that may explain this finding is inhibition of the astrocyte glutamate transporter by A~9.The aim of the current study was to determine if A~3sinhibit astrocyte glutamate uptake and if this inhibition involves free radical damage to the transporter/astrocytes. We have previously reported that A/3 can generate free radicals, and this radical production was correlated with the oxidation of neurons in culture and inhibition of astrocyte glutamate uptake. In the present study, A~(25-35) significantly inhibited L-glutamate uptake in rat hippocampal astrocyte cultures and this inhibition was prevented by the antioxidant Trolox. Decreases in astrocyte function, in particular L-glutamate uptake, may contribute to neuronal degeneration such as that seen in AD. These results lead to a revised excitotoxicity/free radical hypothesis of A~3 toxicity involving astrocytes.
Neuroscience, 2008
Alzheimer's disease (AD) is a progressive neurodegenerative disorder primarily characterized by excessive deposition of amyloid- (A) peptides in the brain. One of the earliest neuropathological changes in AD is the presence of a high number of reactive astrocytes at sites of A deposition. Disturbance of glutamatergic neurotransmission and consequent excitotoxicity is also believed as implicated in the progression of this dementia. Therefore, the study of astrocyte responses to A, the main cellular type involved in the maintenance of synaptic glutamate concentrations, is crucial for understanding the pathogenesis of AD. This study aims to investigate the effect of A on the astrocytic glutamate transporters, glutamate transporter-1 (GLT-1) and glutamate-aspartate transporter (GLAST), and their relative participation to glutamate clearance. In addition we have also investigated the involvement of mitogen-activated protein (MAP) kinases in the modulation of GLT-1 and GLAST levels and activity and the putative contribution of oxidative stress induced by A to the astrocytic glutamate transport function. Therefore, we used primary cultures of rat brain astrocytes exposed to A synthetic peptides. The data obtained show that A 1-40 peptide decreased astroglial glutamate uptake capacity in a non-competitive mode of inhibition, assessed in terms of tritium radiolabeled D-aspartate (D-[ 3 H]aspartate) transport. The activity of GLT-1 seemed to be more affected than that of GLAST, and the levels of both transporters were decreased in A 1-40 -treated astrocytes. We demonstrated that MAP kinases, extracellular signal-regulated kinase (ERK), p38 and c-Jun N-terminal kinase, were activated in an early phase of A 1-40 treatment and the whole pathways differentially modulated the glutamate transporters activity/lev-els. Moreover it was shown that oxidative stress induced by A 1-40 may lead to the glutamate uptake impairment observed. Taken together, our results suggest that A peptide downregulates the astrocytic glutamate uptake capacity and this effect may be in part mediated by oxidative stress and the differential activity and complex balance between the MAP kinase signaling pathways.
Neuropharmacology, 2014
Alzheimer's disease (AD) is characterized phenotypically by memory impairment, neurochemically by accumulation of b-amyloid peptide (such as Ab 1e42 ) and morphologically by an initial loss of nerve terminals in cortical and hippocampal regions. However, it is not known what nerve terminals are mostly affected in early AD. We now used a mouse model of AD, based on the intra-cerebral administration of soluble Ab 1-42 , that leads to memory impairment and loss of nerve terminal markers within 2 weeks, to investigate which type of hippocampal nerve terminals was mostly affected in the hippocampus. Western blot analysis revealed a decrease of the density of vesicular glutamate transporters type 1 (vGluT1, a marker of glutamatergic terminals; À20.1 AE 3.6%) and of vesicular acetylcholine transporters (vAChT, a marker of cholinergic terminals; À27.2 AE 0.9%) but not of vesicular GABA transporters (vGAT, a marker of GABAergic terminals) in the hippocampus of Ab-injected mice. Immunocytochemical analysis of single hippocampal nerve terminals revealed that the decrease of the density of vGluT1 reflects a reduction of the number of vGluT1-immunopositive nerve terminals (À10.6 AE 3.6%), while no significant changes in the number of vAChT-or vGAT-immunopositive nerve terminals were observed. This pilot study shows that, in this Ab-based model of AD, there is an asymmetric loss of different synaptic markers with a predominant susceptibility of glutamatergic synapses.
Disturbed neurotransmitter transporter expression in Alzheimer's disease brain
Journal of Alzheimer's disease : JAD, 2011
Alzheimer's disease (AD) is a neurodegenerative disorder characterized by memory loss and behavioral and psychological symptoms of dementia. An imbalance of different neurotransmitters--glutamate, acetylcholine, dopamine, and serotonin--has been proposed as the neurobiological basis of behavioral symptoms in AD. The molecular changes associated with neurotransmission imbalance in AD are not clear. We hypothesized that altered reuptake of neurotransmitters by vesicular glutamate transporters (VGLUTs), excitatory amino acid transporters (EAATs), the vesicular acetylcholine transporter (VAChT), the serotonin reuptake transporter (SERT), or the dopamine reuptake transporter (DAT) are involved in the neurotransmission imbalance in AD. We tested this hypothesis by examining protein and mRNA levels of these transporters in postmortem prefrontal cortex from 10 AD patients and 10 matched non-AD controls. Compared with controls, protein and mRNA levels of VGLUTs, EAAT1-3, VAChT, and SERT ...
Journal of Alzheimer's Disease, 2007
Excitatory neurotransmitter dysfunction has been discussed to be involved in the pathophysiology of Alzheimer's disease (AD). In the current study we investigated gene and protein expression patterns of glutamatergic receptors and transporters in brains of AD patients in various stages of disease using gene chip arrays, real time PCR and immunohistochemistry. We found marked impairment in the expression of excitatory amino acid transporters (EAAT1 and EAAT 2) at both gene and protein levels in hippocampus and gyrus frontalis medialis of AD patients, already in early clinical stages of disease. The loss of EAAT immunoreactivity was particularly obvious in the vicinity of amyloid plaques. In contrast, EAAT expression was up-regulated in the cerebellum of these patients. Furthermore, a significant up-regulation of the glutamatergic kainate (GRIK4) receptor observed by gene arrays was confirmed by quantitative RT-PCR in late stages in the hippocampus of AD patients. Moreover, there were down-regulations of other glutamatergic receptors such as NMDA (GRINL1A) and AMPA (GRIA4) receptors. Our data show marked changes in the functional elements of the glutamatergic synapses such as glutamatergic receptors and transporters and indicate impaired glutamate clearing rendering neurons susceptible to excess extracellular glutamate and support further the involvement of excitotoxic mechanisms in the pathogenesis of AD.
2003
Malfunctioning of high-affinity glutamate transporters is believed to contribute to the accumulation of toxic concentrations of glutamate and, thus, trigger the cellular mechanisms of neurodegeneration. Emerging data point to the presence of excitotoxic component in Alzheimer's disease (AD) and aberrant expression of glutamate transporters in this neurodegenerative malady. Neuronal soluble factors are essential for differential expression and fine tuning of the astroglial glutamate transporters, GLT-1/EAAT2 and GLAST/EAAT1. However, the nature of factors specifically affecting glutamate uptake in AD is largely unknown. The overproduction of neurotoxic beta-amyloid peptide (A), a major constituent of amyloid plaques, and marked down-regulation of BDNF, a neuroprotective factor, are hallmarks of AD pathophysiology. None of these typically neuronal factors was capable of changing the pattern of glutamate transporter expression in undifferentiated rat astrocytes that predominantly expressed GLAST. In differentiated astrocytes, BDNF and, to a lesser extent, subtoxic concentrations of A 1-42 (1-5 M) induced the expression of GLT-1 and increased glutamate uptake, whereas the GLAST levels were unaltered by these factors. The BDNF-dependent up-regulation of GLT-1 in differentiated astrocytes was partially antagonized by the activation of metabotropic glutamate receptor 4 (mGluR4), but not by group I or II mGluRs. Activation of transcription factor NF-B appeared to be a shared essential, but not a sufficient molecular event in the BDNF-or A-dependent induction of GLT-1. The BDNF-dependent activation of NF-B and up-regulation of GLT-1 was critically dependent on the upstream activation of p42/p44 MAP kinase signaling, whereas the inhibition of these MAP kinases dramatically increased the A-dependent activation of NF-B and production of GLT-1. The capacity to up-regulate astroglial glutamate uptake system, that apparently represents a novel element in the neuroprotective repertoire of BDNF, can, however, provide adverse effect under certain insults when glutamate transporters start operating in reverse direction. The A-dependent up-regulation of GLT-1/EAAT2, more pronounced under the deficit of MAP kinase signaling, may attenuate synaptic efficacy and, thus contribute to the impairment of neuroplasticity in AD.
The secretion of amyloid β-peptides is inhibited in the tacrine-treated human neuroblastoma cells
Molecular Brain Research, 1998
The amyloid b-protein Ab is an approximately 4 kD secreted protein normally found in human plasma and cerebrospinal fluid. Ab Ž . is invariably deposited as insoluble amyloid fibrils in the brains of patients with Alzheimer's disease AD , and there is increasing evidence that Ab deposition plays an important role in AD pathogenesis. Ab is released from the larger b-amyloid precursor protein Ž . bAPP through cleavage on the amino and carboxyl side of Ab by proteolytic activities referred to as b and g secretase, respectively. bAPP is also cleaved at Ab16 by a third protease, a secretase, which may prevent amyloid deposition by bisecting the Ab peptide. Tacrine, a cholinesterase inhibitor, has been shown to improve memory and cognitive functions in some patients with AD, and we have Ž . previously demonstrated that it significantly reduces the levels of the secretion of soluble bAPP fragments sAPP in cultured cells. In this study, we extended our studies by analysis of Ab40 and Ab42 and report that in a human neuroblastoma cell line tacrine reduced the levels of total Ab, Ab40 and Ab42 in addition to sAPP. These inhibitory results cannot be attributed to a reduction in total bAPP synthesis as tacrine treatment did not cause a significant change in the rate of bAPP synthesis. Furthermore, significant toxicity was not Ž . observed in tacrine-treated cultures as determined by analysis of lactate dehydrogenase LDH in the conditioned media. Taken together, these results suggest that tacrine affects the processing of bAPP by alterations in bAPP trafficking andror increased intracellular proteolysis. This study raises the possibility that tacrine may aid in the treatment of AD due to its effects on bAPP processing as well as by its effects on the cholinergic pathway. q 1998 Elsevier Science B.V. All rights reserved.