PubMed Health⌕ Search

Biomedical subjects

S Shimohama

Publications and source records attributed to S Shimohama.

At least 37 records · Page 2Linked to original sources
PubMed2001

alpha 7 nicotinic receptor transduces signals to phosphatidylinositol 3-kinase to block A beta-amyloid-induced neurotoxicity.

Multiple lines of evidence, from molecular and cellular to epidemiological, have implicated nicotinic transmission in the pathogenesis of Alzheimer's disease (AD). Here we show the signal transduction mechanism involved in nicotinic receptor-mediated protection against beta-amyloid-enhanced glutamate neurotoxicity. Nicotine-induced protection was suppressed by an alpha7 nicotinic receptor antagonist (alpha-bungarotoxin), a phosphatidylinositol 3-kinase (PI3K) inhibitor (LY294002 and wortmannin), and a Src inhibitor (PP2). Levels of phosphorylated Akt, an effector of PI3K, and Bcl-2 were increased by nicotine. The alpha7 nicotinic receptor was physically associated with the PI3K p85 subunit and Fyn. These findings indicate that the alpha7 nicotinic receptor transduces signals to PI3K in a cascade, which ultimately contributes to a neuroprotective effect. This might form the basis of a new treatment for AD.

Amyloid beta-Peptides↗
PubMed2001

Protective effects of 1 alpha,25-(OH)(2)D(3) against the neurotoxicity of glutamate and reactive oxygen species in mesencephalic culture.

This study was undertaken to determine whether 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25-(OH)(2)D(3)], an active metabolite of vitamin D, protects dopaminergic neurons against the neurotoxic effects of glutamate and dopaminergic toxins using rat mesecephalic culture. Brief glutamate exposure elicited cytotoxicity in both dopaminergic and non-dopaminergic neurons. Pretreatment, but not co-administration, of 1 alpha,25-(OH)(2)D(3) protected both types of neurons against the cytotoxicity of glutamate in a concentration- and time-dependent manner. The neuroprotective effect of 1 alpha,25-(OH)(2)D(3) was inhibited by the protein synthesis inhibitor, cycloheximide. To investigate the mechanisms of these neuroprotective effects, we examined the effects of 1 alpha,25-(OH)(2)D(3) on neurotoxicity induced by calcium ionophore and reactive oxygen species (ROS). Pretreatment with 1 alpha,25-(OH)(2)D(3) protected both types of neurons against the cytotoxicity induced by A23187 in a concentration-dependent manner. Furthermore, 24-h pretreatment with 1 alpha,25-(OH)(2)D(3) concentration-dependently protected both types of neurons from ROS-induced cytotoxicity. A 24-h incubation with 1 alpha,25-(OH)(2)D(3) inhibited the increase in intracellular ROS level following H(2)O(2) exposure. A 24-h exposure to 1-methyl-4-phenylpyridium ion (MPP(+)) or 6-hydroxydopamine (6-OHDA) exerted selective neurotoxicity on dopaminergic neurons, and these neurotoxic effects were ameliorated by 1 alpha,25-(OH)(2)D(3). These results suggest that 1 alpha,25-(OH)(2)D(3) provides protection of dopaminergic neurons against cytotoxicity induced by glutamate and dopaminergic toxins by facilitating cellular functions that reduce oxidative stress.

1-Methyl-4-phenylpyridinium↗
PubMed2001

Activation of MKK6, an upstream activator of p38, in Alzheimer's disease.

Mitogen-activated protein kinase (MAPK) p38 has been implicated in the pathogenesis of Alzheimer's disease, but the upstream cascade leading to p38 activation has not been elucidated in the disease. In the present study, we focused on mitogen-activated protein kinase kinase 6 (MKK6), one of the upstream activators of p38 MAPK. We found that MKK6 was not only increased but also specifically associated with granular structures in the susceptible neurons in the hippocampus and cortex of Alzheimer's disease patients, but was only weakly diffuse in the cytoplasm in neurons in control cases. Immunoblot analysis demonstrated a significant increase of MKK6 level in Alzheimer's disease compared with age-matched controls. In this regard, in hippocampal and cortical regions of individuals with Alzheimer's disease, the activated phospho-MKK6 was localized exclusively in association with pathological alterations including neurofibrillary tangles, senile plaques, neuropil threads and granular structures, overlapping with activated p38 MAPK suggesting both a functional and mechanic link. By immunoblot analysis, phospho-MKK6 is also significantly increased in AD compared with control cases. Together, these findings lend further credence to the notion that the p38 MAPK pathway is dysregulated in Alzheimer's disease and also indicates an active role for this pathway in disease pathogenesis.

Adolescent↗
PubMed2001

The role of nitric oxide in amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by selective motor neuronal death. The cause of ALS is unclear, but accumulating evidence, such as the insufficient clearance of glutamate through the glutamate transporter, and the specific distribution of Ca2+-permeable AMPA receptors in spinal motor neurons, indicates that glutamate-induced neurotoxicity is involved in its pathogenesis. Interestingly, nitric oxide (NO), which has been identified as an endothelium-derived relaxing factor (EDRF), was found to be a pivotal inducer of glutamate-induced neuronal death. NO is generated by nitric oxide synthase (NOS), of which there are three subtypes: neuronal NOS expressed mainly in neurons, inducible NOS in astroglia, and endothelial NOS in vessels. NO-related toxicity is caused by peroxynitrite, formed by the reaction of NO with superoxide anions, resulting in the nitration of tyrosine residues in neurofilaments, irreversible inhibition of the mitochondrial respiratory chain, and inhibition of the glutamate transporter. Clinically, the axonal spheroids of motor neurons are reported to be immunoreactive to anti-nitrotyrosine antibody, and there are elevated levels of the metabolites of NO in the cerebrospinal fluid of ALS patients. Since physiologically normal motor neurons express limited amounts of neuronal NOS, the source of NO is considered to be non-motor neurons expressing neuronal NOS, astroglia expressing inducible NOS, or motor neurons themselves inducing neuronal NOS. Conversely, neurons containing neuronal NOS are known to be resistant to toxic stimuli, which raises the possibility that such neurons are protected by NO. Several mechanisms have been reported to mediate the NO-related neuroprotection, including cyclic guanosine 3',5'-monophosphate (cyclic GMP), a downstream product of NO generation. This review summarizes previous studies on NO, focusing on its dual functions of neurotoxicity or neuroprotection, and discusses the putative roles of NO in relation to the pathogenesis of ALS.

Amyotrophic Lateral Sclerosis↗
PubMed2001

Oxidative damage is the earliest event in Alzheimer disease.

Recently, we demonstrated a significant increase of an oxidized nucleoside derived from RNA, 8-hydroxyguanosine (8OHG), and an oxidized amino acid, nitrotyrosine in vulnerable neurons of patients with Alzheimer disease (AD). To determine whether oxidative damage is an early- or end-stage event in the process of neurodegeneration in AD, we investigated the relationship between neuronal 8OHG and nitrotyrosine and histological and clinical variables, i.e. amyloid-beta (A beta) plaques and neurofibrillary tangles (NFT), as well as duration of dementia and apolipoprotein E (ApoE) genotype. Our findings show that oxidative damage is quantitatively greatest early in the disease and reduces with disease progression. Surprisingly, we found that increases in A beta deposition are associated with decreased oxidative damage. These relationships are more significant in ApoE epsilon4 carriers. Moreover, neurons with NFT show a 40%-56% decrease in relative 8OHG levels compared with neurons free of NFT. Our observations indicate that increased oxidative damage is an early event in AD that decreases with disease progression and lesion formation. These findings suggest that AD is associated with compensatory changes that reduce damage from reactive oxygen.

Aged↗
PubMed2001

Analysis of the proteomic profiling of brain tissue in Alzheimer's disease.

In proteome analysis, it is necessary to separate proteins as a first step prior to characterization. Thus, the overall performance of the analysis depends strongly on the separation tool, which is usually two-dimensional electrophoresis (2DE). We have utilized 2DE to begin characterization of the complex pathologic processes in Alzheimer's disease (AD). In the present study, we show how a reliable 2-DE database of brain proteins in Alzheimer's disease was created, improving reproducibility by using an immobilized pH gradient (IPG) for the first dimension gel electrophoresis. The recent progress in this field, and future prospects in this area are also discussed. Preparation of brain proteins into a suitable solubilized state enabled us to separate over 1000 well-defined protein spots in each 2-DE. A comparison of the density of the spots identified on the reference map between the AD and control group, showed that 5 protein spots were significantly increased, 28 spots were significantly decreased and 7 spots were specifically detected in AD. Two spots among those significantly increased and one spot among those significantly decreased were identified as GFAP related. It is hoped that comparative studies to identify, quantitate, and characterize the proteins differentially expressed in normal brain versus diseased brain will give insight into the mechanisms of pathogenesis and allow the development of a strategy to control both the etiology and course of the diseases.

Aged↗
PubMed2001

Alterations of phospholipase C isozymes in rat cerebral cortex through hyperoxia.

The effect of hyperoxia on the level of three phospholipase C (PLC) isozymes (beta1, gamma1, delta1) was assessed in the rat cerebral cortex. When the rats were exposed to 100% oxygen for 60 h, there was a significant reduction in the catalytic activity of low molecular weight phosphotyrosine phosphatase, which was susceptible to activity loss under oxidative stress. The result suggests that oxidative stress is induced in the rat cerebral cortex through hyperoxia. The protein levels of PLC-beta1 and -delta1 were significantly increased in the cerebral cortex where oxidative stress had been induced, although that of PLC-gamma1 was not altered. There was no significant difference in the total PLC activity of the cerebral cortex between hyperoxia and control rats. Using gel filtration chromatography, it was revealed that the PLC-beta1 activity in the cerebral cortex of the hyperoxia rats was higher than that in the control rats, but the PLC-delta1 activity in the former did not differ from that in the latter, despite an increase in the PLC-delta1 protein level. These findings suggest that the PLC-beta1 and -delta1 protein levels of brain tissues are increased by oxidative stress, and that the increased PLC-delta1 molecule is less active.

Aerobiosis↗
PubMed2000

Distribution of the 4F2 light chain, LAT1, in the mouse brain.

LAT1 (the 4F2-light chain 1) is a component of the CD98 surface antigen which participates in multiple functions including amino acid transport, cell survival, cell fusion and integrin activation. We examined the distribution of LAT1 in the mouse brain using immunohistochemistry. LAT1 was expressed on the microvessels, the subfornical organ, the subcommissural organ, ventromedial nucleus of the hypothalamus, subgranular zone of the dentate gyrus, ependymal layer of the lateral ventricles, and the olfactory bulb. LAT1-positive cells incorporated bromodeoxyuridine in the latter three regions where neurogenesis occurs in adult mouse brain, indicating that LAT1 is involved in neuronal cell proliferation, as well as in amino acid transport in these regions.

Amino Acid Transport Systems↗
PubMed2000

Opposing effects of adenosine on the survival of glial cells exposed to chemical ischemia.

Extracellular adenosine (Ado) accumulates during brain ischemia. To investigate the pathophysiological role of Ado on glial cells under ischemic conditions, we examined the effect of Ado on the survival of C6 glial cells exposed to chemical ischemia (CI). Treatment with Ado during exposure to CI showed a marked protective effect, that was mediated via intracellular transport and conversion of Ado to inosine (Ino). In contrast, Ado exacerbated CI-mediated cell death when it was added during the recovery time after exposure to CI. Ado cytotoxicity was largely mediated via intracellular transport, but conversion of Ado to Ino abolished its toxicity. Ado-induced cell death was characteristic of apoptosis, and Ado increased the expression of a pro-apoptotic product Bax but decreased that of an anti-apoptotic product Bcl-2. Ado also suppressed the induction of two stress proteins HSC70 and HSP27. Furthermore, Ado induced cytochrome c release and increased caspase-3-like activity. These results indicate the dual opposing effects of Ado on glial cell survival. Intracellular accumulation of Ado can be both cytoprotective and cytotoxic, depending on its metabolic pathway.

Adenosine↗
PubMed2000

Protection of cultured spinal motor neurons by estradiol.

Estrogens have been reported to exert neuroprotection in the brain, but there have been no reports of such neuroprotection in spinal motor neurons, the neurons selectively involved in amyotrophic lateral sclerosis (ALS). In this study, we demonstrated that 17beta-estradiol and its biologically inactive stereoisomer, 17alpha-estradiol, prevented glutamate- and nitric oxide (NO)-induced selective motor neuronal death observed in primary cultures of the rat spinal cord. The dose of estradiols required for motor neuron protection was greatly reduced by co-administration with glutathione. The results of this study shows that estradiol protects spinal motor neurons from excitotoxic insults in vitro, and may have application as a treatment for ALS.

Animals↗
PubMed2000

The 4F2hc/LAT1 complex transports L-DOPA across the blood-brain barrier.

L-DOPA is transported across the blood-brain barrier (BBB) by an amino acid transporter, system L. Recently, it has been demonstrated that system L consists of two subunits, 4F2hc and either LAT1 or LAT2. 4F2hc/LAT1 and 4F2hc/LAT2 show different transport characteristics, while their distribution in the brain has not been determined. To clarify whether 4F2hc/LAT1 participates in L-DOPA transport across the BBB, we first examined the expression of 4F2hc/LAT1 in the mouse brain capillary endothelial cell line, MBEC4, as an in vitro BBB model. Northern hybridization and immunoblotting revealed that both 4F2hc and LAT1 are expressed and form a heterodimer in MBEC4 cells. To confirm whether 4F2hc/LAT1 acts as system L to transport L-DOPA, we characterized L-DOPA uptake into the cells. The uptake process was time-dependent, temperature-sensitive, and Na(+)-independent. Neutral amino acids with bulky side chains and a bicyclic amino acid, 2-aminobicyclo-[2, 2,1]-heptane-2-carboxylic acid (BCH), inhibited L-DOPA uptake into MBEC4 cells to a great extent, while an acidic amino acid, basic amino acids, and glycine had no effect. Other neutral amino acids, such as alanine, asparagine, glutamine, serine, and threonine inhibited L-DOPA uptake by 40-70% at most. These characteristics are more compatible with those of 4F2hc/LAT1, rather than those of 4F2hc/LAT2. Finally, immunohistochemistry with anti-LAT1 antibody demonstrated that LAT1 is predominantly expressed in the microvessels of the central nervous system. This is the first report showing that the 4F2hc/LAT1 complex participates in L-DOPA transport across the BBB.

Amino Acid Transport Systems↗
PubMed2000

Neuroprotective effect of cyclic GMP against radical-induced toxicity in cultured spinal motor neurons.

We have previously reported that nitric oxide-related cyclic guanosine-3',5'-monophosphate (GMP) protected spinal nonmotor neurons, but not motor neurons against chronic glutamate-induced toxicity, which is associated with selective motor neuronal death after glutamate stress. In this report, we investigated the effect of cyclic GMP against reactive oxygen species (ROS)-induced toxicity in cultured neurons from embryonic rat spinal cords. Pretreatment with a cGMP analogue, 8-bromoguanosine monophosphate (8br-cGMP), for 12-24 hours protected both spinal motor neurons and nonmotor neurons against injury induced by either hydrogen peroxide (H(2)O(2)), or a glutathione depletor, L-buthionine-[S,R]-sulfoximine (BSO). This protective effect was reversed by coadministration with the cGMP-dependent protein kinase (PKG) inhibitor Arg-Lys-Arg-Ala-Arg-Lys-Glu. Interestingly, when cultures were exposed to BSO for 24 hours to allow irreversible inhibition of glutathione synthesis, 8br-cGMP protected only nonmotor neurons. Our results indicate that cGMP attenuates oxidative injury to cultured spinal neurons, in a mechanism associated with glutathione synthesis.

Animals↗
PubMed2000

Activation of NADPH oxidase in Alzheimer's disease brains.

The present study is the first to show that superoxide (O(-)(2)) forming NADPH oxidase is activated in Alzheimer's disease (AD) brains by demonstrating the marked translocation of the cytosolic factors p47-phox and p67-phox to the membrane. In conjunction with a recent in vitro study showing that amyloid beta activates O(-)(2) forming NADPH oxidase in microglia, where these phox proteins are localized in this study, the present results suggest that, in AD, NADPH oxidase is activated in microglia, resulting in the formation of reactive oxygen species which can be toxic to neighboring neurons in AD.

Aged↗
PubMed2000

Increase in phospholipase C-delta1 protein levels in aluminum-treated rat brains.

The effect of administration of aluminum to rats on the level of three phospholipase C (PLC) isozymes (beta1, gamma1, and delta1) was assessed in a variety of brain tissues. After exposure to aluminum, a statistically significant increase in malondialdehyde, an index of lipid peroxidation, was observed. In addition, there was a significant reduction in the catalytic activity of low molecular weight phosphotyrosine phosphatase, which loses its activity during oxidative stress. This suggests that oxidative stress is induced in brain tissues exposed to aluminum. The protein level of PLC-delta1, but not that of PLC-beta1 or -gamma1, was significantly increased in brains where oxidative stress had been induced. The total PLC activity in aluminum-treated rat brains was significantly higher than that in control brains. These results suggest that PLC-delta1 protein levels in brain tissues are increased by the induction of oxidative stress, giving an explanation for its up-regulation in Alzheimer's disease.

Aluminum↗
PubMed2000

Phosphatidylinositol 3-kinase mediates neuroprotection by estrogen in cultured cortical neurons.

It has been shown that estrogen replacement in menopausal women is effective in slowing down the progression of cognitive impairment in Alzheimer's disease. Although recent studies have demonstrated the neuroprotective effects of estrogen, the precise mechanism of neuroprotection has not been elucidated. In the present study, we show that the phosphatidylinositol 3-kinase (PI3-K) cascade is involved in the neuroprotective mechanism stimulated by estrogen. Exposure to glutamate reduced the viability of rat primary cortical neurons. Pretreatment with 10 nM 17beta-estradiol significantly attenuated the glutamate-induced toxicity. This neuroprotective effect of 17beta-estradiol was blocked by co-administration with LY294002, a selective PI3-K inhibitor, but not by co-administration with PD98059, a selective mitogen activated protein kinase kinase inhibitor. Pretreatment with ICI182780, a specific estrogen receptor antagonist, also blocked the neuroprotection. Immunoblotting assay revealed that treatment with 17beta-estradiol induced the phosphorylation of Akt/PKB, an effector immediately downstream of PI3-K. These results suggest that PI3-K mediates the neuroprotective effect of 17beta-estradiol against glutamate-induced neurotoxicity.

Animals↗
PubMed2000

An IP3-assisted form of Ca2+-induced Ca2+ release in neocortical neurons.

Calcium increases induced by single action potentials in rat visual cortex layer II/III pyramidal neurons were shown to be augmented by muscarinic acetylcholine receptor (mAchR) stimulation. This augmentation was drastically reduced by intracellular injection of heparin but not ruthenium red, therefore involving inositol-1,4,5-trisphosphate (IP3)-sensitive rather than ryanodine-sensitive calcium stores. Only the calcium increase induced by the second or later spike of a spike train, but not that induced by the first spike, was augmented, indicating the requirement of both spike-induced calcium increase and mAchR activation. The calcium store depletor thapsigargin abolished this augmentation use-dependently. These findings suggest a neocortical occurrence of calcium-induced calcium release from IP3-sensitive calcium stores that have been sensitized beforehand by IP3 through mAchR-mediated mechanisms.

Action Potentials↗