Beta-amyloid-induced changes in cultured astrocytes parallel reactive astrocytosis associated with senile plaques in Alzheimer's disease

Chronic intracerebroventricular infusion of lipopolysaccharide: effects of ibuprofen treatment and behavioural and histopathological correlates

Twenty male Wistar rats were trained under an alternating-lever cyclic-ratio (ALCR) schedule of food reinforcement. When responding showed no trends, each subject was subcutaneously implanted with an Alzet osmotic mini-pump, connected to a chronic indwelling cannula extending into the lateral ventricle of the brain. The mini-pumps were primed to infuse 0.25 microl lipopolysaccharide (LPS) (1.0 microg/0.25 ml) or 0.25 microl artificial cerebrospinal fluid (aCSF) per hour and were implanted for 28 days. LPS infusion produced behavioural deficits which chronic ibuprofen treatment (40 mg/kg every 12 h) alleviated. Infusion of LPS induced R 1282-positive amyloid deposits, and activation of microglia and astrocytes. Ibuprofen treatment reduced the numbers of activated microglia, and withdrawal of ibuprofen resulted in an increase in activated microglia; however, ibuprofen treatment had no effect on numbers of activated astrocytes in the LPS-infused subjects.

Beta-amyloid-induced neuronal apoptosis involves c-Jun N-terminal kinase-dependent downregulation of Bcl-w

beta-Amyloid protein (Abeta) has been implicated as a key molecule in the neurodegenerative cascades of Alzheimer's disease (AD). Abeta directly induces neuronal apoptosis, suggesting an important role of Abeta neurotoxicity in AD neurodegeneration. However, the mechanism(s) of Abeta-induced neuronal apoptosis remain incompletely defined. In this study, we report that Abeta-induced neuronal death is preceded by selective alterations in expression of the Bcl-2 family of apoptosis-related genes. Specifically, we observe that Abeta significantly reduces expression of antiapoptotic Bcl-w and Bcl-x(L), mildly affects expression of bim, Bcl-2, and bax, but does not alter expression of bak, bad, bik, bid, or BNIP3.Abeta-induced downregulation of Bcl-w appears to contribute to the mechanism of apoptosis, because Abeta-induced neuronal death was significantly increased by Bcl-w suppression but significantly reduced by Bcl-w overexpression. Downstream of Bcl-w, Abeta-induced neuronal apoptosis is characterized by mitochondrial release of second mitochondrion-derived activator of caspase (Smac), an important precursor event to cell death. We observed that Smac release was potentiated by suppression of Bcl-w and reduced by overexpression of Bcl-w. Next, we investigated the upstream mediator of Abeta-induced Bcl-w downregulation and Smac release. We observed that Abeta rapidly activates c-Jun N-terminal kinase (JNK). Pharmacological inhibition of JNK effectively inhibited all measures of Abeta apoptosis: Bcl-w downregulation, Smac release, and neuronal death. Together, these results suggest that the mechanism of Abeta-induced neuronal apoptosis sequentially involves JNK activation, Bcl-w downregulation, and release of mitochondrial Smac, followed by cell death. Complete elucidation of the mechanism of Abeta-induced apoptosis promises to accelerate development of neuroprotective interventions for the treatment of AD.

Differential effects of oligomeric and fibrillar amyloid-β1–42 on astrocyte-mediated inflammation

Activated glia, as a result of chronic inflammation, are associated with amyloid-beta peptide (Abeta) deposits in the brain of Alzheimer's disease (AD) patients. In vitro, glia are activated by Abeta inducing secretion of pro-inflammatory molecules. Recent studies have focused on soluble oligomers (or protofibrils) of Abeta as the toxic species in AD. In the present study, using rat astrocyte cultures, oligomeric Abeta induced initial high levels of IL-1beta decreasing over time and, in contrast, fibrillar Abeta increased IL-1beta levels over time. In addition, oligomeric Abeta, but not fibrillar Abeta, induced high levels of iNOS, NO, and TNF-alpha. Our results suggest that oligomers induced a profound, early inflammatory response, whereas fibrillar Abeta showed less increase of pro-inflammatory molecules, consistent with a more chronic form of inflammation.

Astrocyte modulation of in vitro beta-amyloid neurotoxicity

In Alzheimer's disease brain, beta-amyloid (Abeta) deposition is accompanied by astrocyte activation, whose role in the pathogenesis of the disease is still unclear. To explore the subject, we compared Abeta neurotoxicity in pure hippocampal cultures and neuronal-astrocytic cocultures, where astrocytes conditioned neurons but were not in contact with them or Abeta. In the presence of astrocytes, neurons were protected from Abeta neurotoxicity. Neuritic dystrophy was reduced, synapses were partially preserved, and apoptosis was contrasted. The protection disappeared when astrocytes were also treated with Abeta, suggesting that Abeta-astrocyte interaction is deleterious for neurons. This was supported by comparing Abeta neurotoxicity in pure neurons and neurons grown on astrocytes. In this case, where astrocytes were also in contact with Abeta, neuritic damage was enhanced and expression of synaptic vesicle proteins decreased. Our results suggest that astrocytes can protect neurons from Abeta neurotoxicity, but when they interact with Abeta, the protection is undermined and neurotoxicity enhanced.

Astrocyte stellation induced by Rho kinase inhibitors in culture

To understand the role of Rho kinases in regulation of astrocyte morphology, we investigated the effects of Rho kinase inhibitors on the morphology of cultured rat cortical astrocytes. Cultured astrocytes exhibited flattened, polygonal morphology in the absence of stimulation, but changed into process-bearing stellate cells following treatment with the selective Rho kinase inhibitor Y-27632 (1-10 microM). The Y-27632-induced astrocyte stellation was abolished by treatment with colchicine, indicating that the response requires reorganization of cytoskeletal elements. The effect of Y-27632 was mimicked by another Rho kinase inhibitor HA1077, but not by the protein kinase C inhibitor GF-109203X or the protein kinase A inhibitor KT5720. These results suggest that Rho kinases are in an activated state in the absence of stimuli and contribute to the maintenance of polygonal morphology of cultured astrocytes.

Exercise increases the vulnerability of rat hippocampal neurons to kainate lesion

Available evidence suggests that regular, moderate-intensity exercise has beneficial effects on neural health, perhaps including neuroprotection. To evaluate this idea further, we compared the severity of kainate-induced neuronal loss in exercised versus sedentary female rats. Stereological estimations of neuron number revealed that rats in the exercise condition exhibited significantly greater neuron loss in hippocampal region CA2/3, suggesting that high levels of physical activity may increase neuronal vulnerability to excitotoxicity.

Amyloid beta peptide induces tau phosphorylation and loss of cholinergic neurons in rat primary septal cultures

The neuropathological features associated with Alzheimer's disease (AD) brain include the presence of extracellular neuritic plaques composed of amyloid beta protein (Abeta), intracellular neurofibrillary tangles containing phosphorylated tau protein and the loss of basal forebrain cholinergic neurons which innervate regions such as the hippocampus and the cortex. Studies of the pathological changes that characterize AD and several other lines of evidence indicate that Abeta accumulation in vivo may initiate phosphorylation of tau protein, which by disrupting neuronal network may trigger the process of neurodegeneration observed in AD brains. However, the underlying cause of degeneration of the basal forebrain cholinergic neurons and their association, if any, to Abeta peptides or phosphorylated tau remains mostly unknown. In the present study, using rat primary septal cultures, we have shown that aggregated Abeta peptides, in a time (18-96 h)- and concentration (0.7-60 microM)-dependent manner, induce toxicity and decrease choline acetyltransferase enzyme activity in cultured neurons. Using immunocytochemistry and immunoblotting, we have also demonstrated that Abeta treatment can significantly increase the phosphorylation of tau protein in septal cultures. At the cellular level, hyperphosphorylated tau is mostly apparent in the somatodendritic compartment of the neurons. Abeta peptide (10 microM), in addition to tau phosphorylation, also activates mitogen-activated protein kinase and glycogen synthase kinase-3beta, the two kinases which are known to be involved in the formation of hyperphosphorylated tau in the AD brain. Exposure to specific inhibitors of the mitogen-activated protein kinase (i.e. PD98059) or glycogen synthase kinase-3beta (i.e. LiCl) attenuated the hyperphosphorylation of the tau protein in cultured neurons. Given the evidence that tau phosphorylation can induce cell loss by disrupting neuronal cytoskeleton, it is likely that aggregated Abeta peptide triggers degeneration of septal neurons, including those expressing the cholinergic phenotype, by phosphorylation of the tau protein activated by mitogen-activated protein kinase and glycogen synthase kinase-3beta. These results, taken together, suggest that cultured septal cholinergic neurons are vulnerable to Abeta-mediated toxicity and tau phosphorylation may play an important role in Abeta-induced neurodegeneration.

Amyloid beta protein enhances the clearance of extracellular L-glutamate by cultured rat cortical astrocytes

To explore the impact of Alzheimer's disease amyloid beta protein (Abeta) on astrocyte functions, we investigated the effect of Abeta on glutamate clearance capacity of cultured rat cortical astrocytes. When L-glutamate (50-200 microM) was added to astrocyte cultures and incubated, the extracellular L-glutamate concentration declined with time. The time-dependent decline of extracellular L-glutamate was significantly faster in cultures treated with 10-20 microM Abeta for 24 h than in intact cultures, suggesting that Abeta enhances the L-glutamate clearance capacity of astrocytes. The effect of Abeta was not affected by antioxidants including catalase, propyl gallate or Trolox. Relatively long treatment time (8-48 h) was required for Abeta to exert this effect. Western blot analysis revealed that expression level of the glutamate transporter GLAST was increased by treatment with 10-20 microM Abeta for 8-48 h. These results suggest that Abeta upregulates a glutamate uptake system of astrocytes and enhances the clearance of extracellular L-glutamate.

Amyloid β Peptide Specifically Promotes Phosphorylation and Nuclear Translocation of the Extracellular Signal-Regulated Kinase in Cultured Rat Cortical Astrocytes

To explore cellular signaling molecules that respond to amyloid beta protein (A beta), we investigated the effect of A beta on tyrosine phosphorylation of cellular proteins in cultured rat cortical astrocytes. Western blotting with the phosphotyrosine-specific monoclonal antibody 4G10 demonstrated that exposure of cultured rat cortical astrocytes to 20 microM A beta 1-40 or A beta 25-35 for 24 h resulted in a prominent increase in the phosphotyrosine content of 44-kDa protein. The A beta-induced increase in tyrosine phosphorylation of 44-kDa protein was blocked by U0126, a specific inhibitor of the extracellular signal-regulated kinase (ERK) kinase MEK. Western blotting with anti-phospho-ERK1/2 antibody and anti-ERK1/2 antibody demonstrated that A beta 1-40 or A beta 25-35 induced an increase in the dually (tyrosine and threonine) phosphorylated form of ERK1 and ERK2, with no change in total ERK1/2 level. In addition, immunofluorescent staining with anti-ERK1/2 antibody revealed that A beta induced a significant increase in the number of cells expressing ERK1/2 mainly in the nucleus. These results suggest that A beta specifically promotes tyrosine phosphorylation and nuclear translocation of ERK in astrocytes.

Behavioural and histopathological analyses of ibuprofen treatment on the effect of aggregated Abeta(1-42) injections in the rat

It has been suggested that inflammatory processes may play a role in the development of Alzheimer's disease (AD), and that nonsteroidal anti-inflammatory drug treatments may provide protection against the onset of AD. In the current study male Wistar rats were trained in two-lever operant chambers under an alternating lever cyclic-ratio ratio (ALCR) schedule. When responding showed no trends, subjects were divided into groups. One group was bilaterally injected into the CA3 area of the hippocampus with 5 microl of aggregated beta-amyloid (Abeta) suspension, and one group was bilaterally injected into the CA3 area of the hippocampus with 5 microl of sterile saline. Subgroups were treated twice daily with 0.1 ml (40 mg/kg) ibuprofen administered orally. The results indicated that chronic administration of ibuprofen protected against detrimental behavioural effects following aggregated Abeta injections. Withdrawal of ibuprofen treatment from aggregated Abeta-injected subjects produced a decline in behavioural performance to the level of the non-treated aggregated Abeta-injected group. Ibuprofen treatment reduced the numbers of reactive astrocytes following aggregated Abeta injection, and withdrawal of ibuprofen resulted in an increase of reactive astrocytes. These results suggest that induced inflammatory processes may play a role in AD, and that ibuprofen treatment may protect against some of the symptoms seen in AD.

Beta-amyloid peptides decrease soluble guanylyl cyclase expression in astroglial cells

In astroglial cells beta-amyloid peptides (betaA) induce a reactive phenotype and increase expression of NO synthase. Here we show that treatment of rat brain astrocytes with betaA decreases their capacity to accumulate cyclic GMP (cGMP) in response to NO as a result of a decreased expression of soluble guanylyl cyclase (sGC) at the protein and mRNA levels. Potentiation of betaA-induced NO formation by interferon-gamma did not result in a larger decrease in cGMP formation and inhibition of NO synthase failed to reverse down-regulation of sGC, indicating that NO is not involved. The betaA effect was prevented by the protein synthesis inhibitor cycloheximide. Intracerebral betaA injection also decreased sGC beta1 subunit mRNA levels in adult rat hippocampus and cerebellum. A loss of sGC in reactive astrocytes surrounding beta-amyloid plaques could be a mechanism to prevent excess signalling via cGMP at sites of high NO production.

Association of CSF apolipoprotein E, Abeta42 and cognition in Alzheimer's disease

A significant association between CSF Abeta42 and cognition in patients with Alzheimer's disease (AD) homozygous for the epsilon3 allele of the apolipoprotein E (apoE) has been described. In this study we extended our observations on apoE, as another plaque component, and investigated the association between CSF apoE concentrations and cognitive performance after stratification for the apoE genotype in 62 patients with AD, 19 other forms of dementia and 18 controls. CSF Abeta42 and apoE concentrations were significantly and positively associated with Mini Mental State Examination (MMSE) score in AD (Abeta42: r = 0.332; P = 0.026; apoE: r = 0.386; P = 0.006). For Abeta42 this association was exclusively present in epsilon3 homozygotes (r = 0.44; P = 0.014), whereas apoE was correlated with MMSE in epsilon4 hetero- or homozygotes subjects (epsilon4/epsilonX: r = 0.638; P = 0.004: epsilon4/epsilon4; r = 0.812; P = 0.05). No association was observed between CSF concentrations of Abeta42 and apoE. The significant relationship between MMSE and CSF Abeta42 in epsilon3 homozygotes and apoE in epsilon4 hetero- and homozygotes respectively may suggest that both proteins may be associated independently from each other with cognitive decline.

Phenotypic and functional changes in glial cells as a function of age

Both in vivo and in vitro investigations point to an important role for the immune system in the development of age-related neurodegeneration. Microglia isolated from aged female F344 rats, 18-20 months, show a higher percentage of cells with an ameboid morphology indicative of activation, whereas, astrocytes had a quiescent morphology. The ability of astrocytes and microglia to attenuate toxin-induced neuronal injury was examined. Post-natal day 1-3 pup cells optimally rescued neurons from Abeta-induced toxicity, whereas mixed glial cells from 18-20 month old rats were unable to rescue neurons from Abeta-induced toxicity. Our results suggested the appearance of a neurotoxic co-factor, therefore we investigated the basal level of nitric oxide and pro-inflammatory cytokines to determine if altered levels of immune mediators play a role in the toxicity. Mitogen-stimulated nitric oxide production increased 10 fold with age of donor, whereas, only the pup cells expressed an increase in TNF-alpha production. Basal levels of pro-inflammatory cytokines, as measured by RNA protection assays, increased with age. In particular, IL-1beta was increased 2 fold between adult and aged glial cells. The elevated cytokine expression may contribute to enhanced susceptibility to neurodegenerative diseases.

Fibronectin modulation by A beta amyloid peptide (25-35) in cultured astrocytes of newborn rat cortex

Fibronectin appears to be present in Senile Plaques of Alzheimer's disease brains. These senile or neuritic plaques are surrounded by dystrophic neurites, activated microglia and reactive astrocytes. The purpose of this work was to establish if a direct correlation exists between the production of Fibronectin (FN) by astrocytes and the presence of amyloid, analysing the modification of this protein produced after the treatment of cultured astrocytes with amyloid peptide (25-35). Our data showed that the addition of previously polymerised A beta-peptide to cultured astrocytes induced a marked increase in FN immunoreactivity that is in part dependent on phosphatases 2A or phosphatase 1, since was partially inhibited by okadaic acid. The increased amount of FN did not appear to be associated to any specific single isoform of which are mainly present in the rat brain. Our data suggest that in vivo FN accumulated in senile plaques may be the result, at least in part, of the response of reactive astrocyte to the presence of amyloid peptide. The importance of FN up-regulation in vivo, as part of a 'positive' response of the astrocytes to produce molecules that favours neurite outgrowth, is discussed.

Expression of endothelial and inducible NOS-isoforms is increased in Alzheimer's disease, in APP23 transgenic mice and after experimental brain lesion in rat: evidence for an induction by amyloid pathology

The nitric oxide-synthesizing enzyme nitric oxide synthase (NOS) is present in the mammalian brain in three different isoforms, two constitutive enzymes (i.e., neuronal, nNOS, and endothelial eNOS) and one inducible enzyme (iNOS). All three isoforms are aberrantly expressed in Alzheimer's disease giving rise to elevated levels of nitric oxide apparently involved in the pathogenesis of this disease by various different mechanisms including oxidative stress and activation of intracellular signalling mechanisms. It still is a matter of debate, however, whether the abnormal expression of NOS isoforms has some primary importance in the pathogenetic chain and might thus be a potential therapeutic target or only reflects a secondary effect that occurs at more advanced stages of the disease process. To tackle this question, we analysed the expression of both eNOS and iNOS in patients with sporadic AD, in transgenic mice expressing human amyloid precursor protein (APP) with the Swedish double mutation under control of the Thy1 promotor (APP23 mice), and after electrolytic cortical lesion in rat, an experimental paradigm associated with elevated expression of APP. In all three conditions, an astrocytosis was induced accompanied by a strong increase of both iNOS and eNOS. Both NOS isoforms were frequently though not always colocalized. Thus, based on the expression pattern of NOS isoforms three types of astrocytes, expressing only one of the two isoforms or both together could be distinguished. In both AD and transgenic mice eNOS-expressing astrocytes exceeded iNOS-expressing astrocytes in number. Astrocytes with elevated levels of iNOS or eNOS were constantly seen in direct association with Abeta-deposits in AD and transgenic mice and were found in the vicinity of the lesion site in the rat cortex. The results of the present study show that expression of both iNOS and eNOS is increased in activated astrocytes under experimental conditions associated with elevated expression of APP (electrolytic brain lesion) or Abeta-deposition (APP23 transgenic mice). Therefore, it is suggested that altered expression of these NOS isoforms being part of AD pathology is secondary to the amyloid pathology and might not be primarily involved in the pathogenetic chain though it might contribute to the maintenance, self-perpetuation and progression of the neurodegenerative process.

The functions of the amyloid precursor protein gene

The amyloid precursor protein (APP) gene and its protein products have multiple functions in the central nervous system and fulfil criteria as neuractive peptides: presence, release and identity of action. There is increased understanding of the role of secretases (proteases) in the metabolism of APP and the production of its peptide fragments. The APP gene and its products have physiological roles in synaptic action, development of the brain, and in the response to stress and injury. These functions reveal the strategic importance of APP in the workings of the brain and point to its evolutionary significance.

L-glutamate suppresses astrocyte stellation induced by actin breakdown in culture

We have recently found that L-glutamate suppresses morphological changes of astrocytes induced by amyloid beta protein, adenosine 3',5'-cyclic monophosphate or phorbol ester in culture. To test the possibility that L-glutamate affects organization of the cytoskeleton, we investigated its effect on morphological changes induced by disruption of actin filaments with cytochalasin B. Cultured rat cortical astrocytes exhibited flat, polygonal morphology in the absence of stimulation, and changed into process-bearing stellate cells following treatment with cytochalasin B (50 microM). L-Glutamate strongly suppressed the stellation induced by cytochalasin B. The effect of L-glutamate was mimicked by D- and L-aspartate and transportable glutamate uptake inhibitors. These results suggest that glutamate transporter activity leads to cytoskeletal actin organization in astrocytes.

Astrocytes contribute to neuronal impairment in beta A toxicity increasing apoptosis in rat hippocampal neurons

Astrocytosis is a common feature of amyloid plaques, the hallmark of Alzheimer's disease (AD), along with activated microglia, neurofibrillary tangles, and beta-amyloid (beta A) deposition. However, the relationship between astrocytosis and neurodegeneration remains unclear. To assess whether beta A-stimulated astrocytes can damage neurons and contribute to beta A neurotoxicity, we studied the effects of beta A treatment in astrocytic/neuronal co-cultures, obtained from rat embryonic brain tissue. We found that in neuronal cultures conditioned by beta A-treated astrocytes, but not directly in contact with beta A, the number of apoptotic cells increased, doubling the values of controls. In astrocytes, beta A did not cause astrocytic cell death, nor did produce changes in nitric oxide or prostaglandin E(2) levels. In contrast, S-100 beta expression was remarkably increased. Our data show for the first time that beta A--astrocytic interaction produces a detrimental effect on neurons, which may contribute to neurodegeneration in AD.

A cell-based method for the detection of nanomolar concentrations of bioactive amyloid

A cell-based method for the detection of nanomolar concentrations of bioactive amyloid peptide is described. The method is based upon the observation that fibrillogenic amyloid peptides specifically and dramatically enhance the exocytosis of the intracellular vesicles that are involved in transporting the reduced tetrazolium dye 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT formazan), with the formation of unique formazan crystals on the cell surface. It is found that the ability of amyloid peptides to induce MTT formazan exocytosis is closely associated with both their neurotoxicity and their ability to activate glia cells, two biological activities of amyloid peptides that are believed to cause neurodegeneration. This simple assay for bioactive amyloid species can be of great value in the screening of anti-amyloid drugs and in the study of amyloid fibrillogenesis with a cell-based model.

Na+ and K+ dependence of L-glutamate-induced suppression of astrocyte stellation in culture

We have recently found that L-glutamate suppresses astrocyte stellation induced by various stimuli, and that this effect of L-glutamate is mimicked by transportable glutamate uptake inhibitors. To test the possible role of the glutamate transporter in the regulation of astrocyte morphology, we investigated the Na+ and K+ dependence of this effect of L-glutamate. In astrocyte cultures obtained from the cerebral cortex of neonatal rats, the L-glutamate-induced suppression of astrocyte stellation was significantly attenuated in a low- Na+/high- K+ medium and by the Na+ -K+ pump inhibitor ouabain. These results support that astrocyte morphology is affected by the activity of the Na+ -dependent glutamate transporter.

cAMP-induced stellation in primary astrocyte cultures with regional heterogeneity

It is well known that increased cAMP levels in cultured astrocytes can convert flat polygonal shaped astrocytes into process-bearing, stellate astrocytes. In this study, we have examined the possible existence of astrocyte regional heterogeneity in morphological changes in response to cAMP stimulation. Primary astrocyte cultures were prepared from six different regions of neonatal rat brains, including cerebral cortex, hippocampus, brain stem, mid brain, cerebellum, and hypothalamus. After about 2 weeks in culture, the astrocyte culture medium was changed to DMEM containing various concentrations of 8-CPT-cAMP, a membrane permeable cAMP analog, for 2 h. We found that 250 microM 8-CPT-cAMP produced a maximum effect causing >95% stellation in all regional astrocytes except hypothalamic astrocytes (56% stellation). At lower cAMP concentrations, cell stellation most effectively occurred in cerebellar astrocytes. To examine further the regional heterogeneity of astrocyte morphological changes, glutamate was added together with 8-CPT-cAMP to block cAMP-induced astrocyte stellation. Interestingly, glutamate blockage on cAMP-induced astrocyte stellation was brain region-specific in that cerebral and hippocampal astrocytes were effectively blocked by glutamate when compared to other regional astrocytes. Furthermore, glutamate inhibited isoproterenol-induced astrocyte stellation in a region-specific manner similarly as in cAMP-induced stellation. The present study demonstrates that astrocytes derived from different regions of the neonatal rat brain maintain different levels of morphological plasticity in culture.

Insulin-like growth factor-I and its receptor in the frontal cortex, hippocampus, and cerebellum of normal human and alzheimer disease brains

Assimilated evidence indicates that the neurotoxic potential of amyloid beta (Abeta) peptide and an alteration in the level of growth factor(s) may possibly be involved in the loss of neurons observed in the brain of patients suffering from Alzheimer disease (AD), the prevalent cause of dementia in the elderly. In the present study, using receptor binding assays and immunocytochemistry, we evaluated the pharmacological profile of insulin-like growth factor-I (IGF-I) receptors and the distribution of IGF-I immunoreactivity in the frontal cortex, hippocampus, and cerebellum of AD and age-matched control brains. In control brains, [(125)I]IGF-I binding was inhibited more potently by IGF-I than by Des(1-3)IGF-I, IGF-II or insulin. The IC(50) values for IGF-I in the frontal cortex, hippocampus, and cerebellum of the normal brain did not differ significantly from the corresponding regions of the AD brain. Additionally, neither K(D) nor B(max) values were found to differ in the hippocampus of AD brains from the controls. At the regional levels, [(125)I]IGF-I binding sites in the AD brain also remained unaltered compared to the controls. As for the peptide itself, IGF-I immunoreactivity, in normal control brains, was evident primarily in a subpopulation of astrocytes in the frontal cortex and hippocampus, and in certain Purkinje cells of the cerebellum. In AD brains, a subset of Abeta-containing neuritic plaques, apart from astrocytes, exhibit IGF-I immunoreactivity. These results, taken together, suggest a role for IGF-I in compensatory plasticity and/or survival of the susceptible neurons in AD brains.

Initiation and propagation of molecular cascades in human brain aging: insight from the canine model to promote successful aging

1. Normal aging is thought to proceed through two stages: initiation and propagation. Each of these phases is associated with different neuroanatomical events, vulnerabilities to injury and responsiveness to interventions. 2. The role of beta-amyloid (Abeta) in neuron dysfunction in the initiation stage may be mediated through alterations in signal transduction pathways involving cyclic AMP response element binding protein (CREB). CREB phosphorylation is associated with the expression of brain derived neurotrophic factor (BDNF), which promotes neuron health and survival. In primary neuronal cultures, Abeta decreases the phosphorylation of CREB, which results in up to a 31% decrease in BDNF levels. 3. In vivo studies also support a role for Abeta in neuron dysfunction since soluble Abeta levels correlate with the loss of synapses in brains of non-demented humans with high pathology. 4. The authors hypothesize that interventions during the initiation stage, when neuron dysfunction, but not overt pathology, is present, have the most promise to promote successful aging. The dog can serve as a useful model for interventions during the initiation stage since dogs develop neuropathology that closely resembles that observed in high pathology human brains.

Pathways of neurosteroid biosynthesis in cell lines from human brain: regulation of dehydroepiandrosterone formation by oxidative stress and beta-amyloid peptide

Neurosteroids in rodents can originate from peripheral tissues or be locally synthesized in specific brain areas. There is, as yet, no information about the synthesis and regulation of neurosteroids in human brain. We examined the ability of human brain cells to synthesize steroids from a radiolabeled precursor and the mRNA and protein expression of key components of peripheral steroidogenic machinery. Oligodendrocytes are the source of pregnenolone in human brain. Human astrocytes do not synthesize radiolabeled pregnenolone, nor do human neurons. There is potential for all three cell types to metabolize pregnenolone to other neurosteroids, including dehydroepiandrosterone. mRNA and protein for cytochrome P450 17alpha-hydroxylase were found in all cell types, although no activity could be demonstrated. We examined the ability of the cells to make dehydroepiandrosterone via an alternative pathway induced by treatment with Fe2+. Oligodendrocytes and astrocytes make dehydroepiandrosterone via this pathway, but neurons do not. In searching for a natural regulator of dehydroepiandrosterone formation, we observed that treating oligodendrocytes with beta-amyloid, which increases reactive oxygen species, also increased dehydroepiandrosterone formation. These effects of beta-amyloid were blocked by vitamin E. These results indicate that human brain makes steroids in a cell-specific manner and suggest that dehydroepiandrosterone synthesis can be regulated by intracellular free radicals.

L-glutamate suppresses amyloid beta-protein-induced stellation of cultured rat cortical astrocytes

Alzheimer's amyloid beta-protein (Abeta) has been reported to potentiate glutamate toxicity in neurons, but very little is known about interaction between Abeta and glutamate in astrocytes. Therefore, in the present study, we investigated the effects of Abeta and glutamate on morphology of astrocytes. Cultured rat cortical astrocytes exhibited polygonal morphology in the absence of stimulation and differentiated into process-bearing stellate cells following exposure to Abeta (20 microM). L-Glutamate (30-1,000 microM) had no effect on astrocyte morphology in the absence of stimulation but strongly suppressed Abeta-induced stellation. The suppressive effect of L-glutamate on Abeta-induced stellation was not mimicked by glutamate receptor agonists and not blocked by glutamate receptor antagonists. In contrast, the suppressive effect of L-glutamate was mimicked by D- and L-aspartate and transportable glutamate uptake inhibitors. These results suggest that Abeta-induced astrocyte stellation is suppressed by a mechanism related to glutamate transporters.

Enhanced BK-induced calcium responsiveness in PC12 cells expressing the C100 fragment of the amyloid precursor protein

Several lines of evidence have implicated the amyloid precursor protein (APP) and its metabolic products as key players in Alzheimer's disease (AD) pathophysiology. The approximately 100 amino acid C-terminal fragment (C100) of APP has been shown to accumulate intracellularly in neurons expressing familial AD (FAD) mutants of APP and to cause neurodegeneration when expressed in transfected neuronal cells. Transgenic animals expressing this fragment in the brain also exhibit some neuropathological and behavioral AD-like deficits. Here, we present evidence that PC12 cells expressing the C100 fragment either via stable transfections or herpes simplex virus-mediated infections show alterations in calcium handling that are similar to those previously shown in fibroblasts from AD patients. This alteration in calcium homeostasis may contribute to the deleterious effects of C100 in PC12 cells. Our data also lend support for a pathophysiological role for C100 since it induces an alteration thought to play an important role in AD pathology.

Glial-derived proteins activate cultured astrocytes and enhance beta amyloid-induced glial activation

A prominent feature of Alzheimer's disease (AD) pathology is an abundance of activated glia (astrocytes and microglia) in close proximity to the amyloid plaques. These activated glia overexpress a number of proteins that may participate in the progression of the disease, possibly by propagation of inflammatory and oxidative stress responses. The beta-amyloid peptide 1-42 (Abeta), a major constituent of neuritic plaques, can itself induce glial activation. However, little is known about whether other plaque components, especially the upregulated glial proteins, can induce glial activation or modulate the effects of Abeta on glia. In this study, we focused on four glial proteins that are abundant in amyloid plaques and/or that are known to interact with Abeta: alpha1-antichymotrypsin (ACT), interleukin-1beta (IL-1beta), S100beta, and butyrylcholinesterase (BChE). We examined the ability of these proteins to activate rat cortical astrocyte cultures and to influence the ability of Abeta to activate astrocytes. Treatment of astrocytes with ACT, IL-1beta, or S100beta resulted in glial activation, as assessed by reactive morphology, upregulation of IL-1beta, and production of inducible nitric oxide synthase and nitric oxide. The ability of Abeta to induce astrocyte activation was also enhanced in the presence of each of these three proteins. In contrast, BChE alone did not activate astrocytes and had no effect on Abeta-induced activation. These results suggest that certain proteins produced by activated glia may contribute to the chronic glial activation seen in AD through their ability to stimulate astrocytes directly or through their ability to modulate Abeta-induced activation.

Differential regulation of major histocompatibility complex class II expression and nitric oxide release by beta-amyloid in rat astrocyte and microglia

Astrocytes and microglial cells were examined for expression of two immunologically important molecules, major histocompatibility complex class II (MHC-II) and nitric oxide (NO) following treatment with IFN-gamma and beta-amyloid (betaA) peptides, betaA(1-42) and betaA(25-35). IFN-gamma is a potent inducer of both MHC-II gene expression and NO production. The induction of MHC-II was inhibited by both betaA peptides in astrocytes but they had little or no effect in microglia. betaA peptides had no effect on NO release in astrocytes but on microglia betaA(1-42) synergistically induced NO release with IFN-gamma. Transient transfection of astrocytes with 5' deletional mutants of MHC-II IAalpha promoter linked to the chloramphenicol acetyl transferase reporter gene (IAalpha-CAT), demonstrated that betaA acts at the transcriptional level to downregulate IFN-gamma induced MHC-II gene expression in astrocytes. In previous studies, the induction of MHC-II on glial cells were suggested to be involved in the pathogenesis of neurodegenerative diseases and MHC-II(+) microglial cells were observed at much higher frequency than astrocytes. This study provides information on the regulation of the MHC-II gene expression in astrocytes and in microglial cells by betaA and this pathway may be critically involved in the immune/inflammatory regulation within the central nervous system.

Estrogen modulates neuronal Bcl-xL expression and beta-amyloid-induced apoptosis: relevance to Alzheimer's disease

Recent findings indicate that estrogen is neuroprotective, a cellular effect that may contribute to its clinical benefits in delaying the development of Alzheimer's disease. In this report, we identify a novel neuronal action of estrogen that may contribute to its neuroprotective mechanism(s). Specifically, we report that estrogen significantly increases the expression of the antiapoptotic protein Bcl-xL in cultured hippocampal neurons. This effect presumably reflects classic estrogen transcriptional regulation, as we identified a putative estrogen response element in the bcl-x gene. Estrogen-induced enhancement of Bcl-xL is associated with a reduction in measures of beta-amyloid-induced apoptosis, including inhibition of both caspase-mediated proteolysis and neurotoxicity. A similar relationship between estrogen, Bcl-xL expression, and resistance to degeneration was also observed in human hippocampus. We report neuronal colocalization of estrogen receptor and Bcl-xL immunoreactivities that is most prominent in hippocampal subfield CA3, a region that shows relatively little immunoreactivity to paired helical filament-1, a marker of Alzheimer's disease neurodegeneration. These data suggest a novel mechanism of estrogen neuroprotection that may be relevant to estrogen's suggested ability to modulate neuronal viability across the life span, from neural sexual differentiation and development through age-related neurodegenerative conditions.

Glial fibrillary acidic protein is necessary for mature astrocytes to react to beta-amyloid

Upregulation of the glial fibrillary acidic protein (GFAP) in astrocytes is a hallmark of the phenomenon known as reactive gliosis and, yet, the function of GFAP in this process is largely unknown. Our previous studies have shown that mature astrocytes react vigorously to substrate bound beta-amyloid protein (BAP) in a variety of ways (i.e., increased GFAP, enhanced motility, unusual aggregation patterns, inhibitory ECM production). In order to uncover which, if any, of these phenomena are causally related to the function of GFAP, primary cortical astrocytes from transgenic mice lacking GFAP were cultured on BAP substrates at low or high density and at various lengths of time following in vitro maturation. Differences between mutant and control cells became progressively more obvious when cells were matured in vitro for two weeks or longer and especially in cultures that were at high density. Mature control astrocytes show a dramatic response to BAP by aggregating into a meshwork of rope-like structures that completely bridge over the peptide surface. In marked contrast, mature GFAP-null astrocytes initiate the response much more slowly and had a much reduced ability to aggregate tightly. Furthermore, we prepared hippocampal slice cultures from GFAP-/- and GFAP+/+ mice and compared their astrocytic responses to injected BAP. GFAP-/- astrocytes of hippocampal slice cultures failed to form a barrier-like structure around the edge of the BAP deposit as did GFAP+/+ astrocytes. Our data suggest that GFAP may be essential for mature astrocytes to constrain certain types of highly inflammatory lesions in the brain.

Intravascular infusions of soluble beta-amyloid compromise the blood-brain barrier, activate CNS glial cells and induce peripheral hemorrhage

Vascular wall levels of soluble beta-amyloid1-40 (Abeta1-40) are elevated in Alzheimer's disease (AD). Moreover, plasma Abeta levels are increased in familial AD, as well as in some cases of sporadic AD. To determine the histopathologic and behavioral consequences of elevated vascular Abeta levels, Abeta1-40 (50 micrograms in distilled water) or vehicle was intravenously infused twice daily into 3-month old male Sprague-Dawley rats for 2 weeks. Intravenous Abeta infusions impaired blood-brain barrier integrity, as indicated by substantial perivascular and parenchyma IgG immunostaining within the brain. Also evident in Abeta-infused animals was an increase in GFAP immunostaining around cerebral blood vessels, and an enhancement of OX-42 microglial immunostaining in brain white matter. Gross pulmonary hemorrhage was noted in most Abeta-infused animals. All the observed changes occurred in the absence of Congo red birefringence. No significant cognitive deficits were present in Abeta-infused animals during water maze acquisition and retention testing, which was conducted during the second week of treatment. These results indicate that circulating Abeta can: (1) induce vessel dysfunction/damage in both the brain and the periphery without complex Abeta fibril formation/deposition, and (2) induce an activation of brain astrocytes and microglia. Taken together, our results suggest that if circulating Abeta is elevated in AD, it is likely to have a pathophysiologic role.

Expression of calbindin-D28k in C6 glial cells stabilizes intracellular calcium levels and protects against apoptosis induced by calcium ionophore and amyloid beta-peptide

The calcium binding protein, calbindin-D28k is normally present in neurons. Recently we reported that brain injury and tumor necrosis factors (TNFs) induce calbindin-D28k in astrocytes. TNF-treated calbindin expressing astrocytes were resistant to acidosis and calcium ionophore toxicity, suggesting that calbindin may have a cytoprotective role in astrocytes in the injured brain (M.P. Mattson, B. Cheng, S.A. Baldwin, V.L. Smith-Swintosky, J. Keller, J. Geddes, Scheff, J.W., Christakos, S., Brain injury and tumor necrosis factors induce calbindin-D28k in astrocytes: evidence for a cytoprotective response, J. Neurosci. Res., 42 (1995) 257). In order to obtain direct evidence for a role of calbindin, using the eukaryotic expression vector pREP4, rat calbindin-D28k was stably expressed in C6 rat astocytoma glial cells. Cytotoxicity in response to calcium ionophore or amyloid beta-peptide (which accumulates in the brain in Alzheimer's disease and has been reported to be neurotoxic) was measured by MTT reduction in vector transfected cells and in calbindin transfected clones. Stably expressed calbindin resulted in increased cell survival in the presence of calcium ionophore (1-10 microM) or amyloid beta-peptide (10-100 microM). In addition, the calcium ionophore or amyloid beta-peptide mediated rise in intracellular calcium in vector transfected cells was significantly attenuated in calbindin expressing cells. Apoptotic cell death was detected by the Hoechst method in vector transfected C6 glial cells treated with calcium ionophore or beta-amyloid (34-36% apoptotic cells/culture). The number of apoptotic nuclei was significantly attenuated in similarly treated calbindin-D28k transfected clones (10-13% apoptotic cells/culture; p<0.01). Our results support the involvement of calcium fluxes in apoptosis and suggest that calbindin-D28k, by buffering calcium, can suppress death in apoptosis susceptible cells in the central nervous system.

Delayed behavioral effects following intrahippocampal injection of aggregated A beta (1-42)

Beta amyloid protein (A beta) is the major extracellular component of Alzheimer's disease (AD) plaques. In the current study, A beta (1-42) was aggregated in vitro using a method which produces A beta aggregates similar to those found in the AD brain. Twelve male Sprague-Dawley rats were trained in two-lever operant chambers under an alternating lever cyclic-ratio (ALCR) schedule. When performance was stable on the ALCR schedule, six subjects were injected (bilaterally into the CA3 area of the dorsal hippocampus) with 5.0 microliters aggregated A beta in suspension, and the remaining six subjects were injected with 5.0 microliters sterile water. Behavioral testing resumed 5 days after surgery and continued for 90 days post-injection. Aggregated A beta injection did not affect the number of lever switching errors made in a daily session but did affect the number of incorrect lever response perseverations. After approximately 30 days post-injection, aggregated A beta injection detrimentally affected ability to track the changing parameters of the schedule, and decreased the efficiency by which subjects obtained reinforcers. From approximately day 50 post-injection onward, A beta-injected subjects demonstrated significantly higher numbers of incorrect lever response perseverations than did sterile water-injected subjects. These effects appeared to be central rather than peripheral, as A beta injection did not decrease running response rates under the ALCR schedule. The delayed onset of behavioral effects seen in this and other behavioral studies may be a result of a cascade of potentially harmful responses induced through glial activation following aggregated A beta injection.

Fibroblast growth factor receptor-1 expression in the cortex and hippocampus in Alzheimer's disease

Localization of fibroblast growth receptor (FGFR)-1 immunoreactivity was investigated immunochemically in postmortem brain tissue of Alzheimer's disease (AD) and age-matched control cases using a rabbit polyclonal antibody and a mouse monoclonal antibody specific for FGFR-1. In control cases, FGFR-1 immunoreactivity was identified in astrocytes in white matter and in hippocampal pyramidal neurons. In AD cases, the immunoreactivity in reactive astrocytes surrounding senile plaques was increased. The pattern of FGFR-1 immunoreactivity was confirmed in selected cases by in situ hybridization for FGFR-1 mRNA. Immunoreactivity using a monoclonal antibody demonstrated a similar distribution pattern. The localization of FGFR-1 is consistent with previous reports on the involvement of FGF-1 and FGF-2 in AD.

The effects of beta/A4-amyloid and its fragments on calcium homeostasis, glial fibrillary acidic protein and S100beta staining, morphology and survival of cultured hippocampal astrocytes

Aggregated beta/A4-amyloid is known to increase intraneuronal calcium by various mechanisms and to lead eventually to the death of the cultured neuron. This study deals with the role of beta/A4-amyloid and several of its fragments in calcium homeostasis, glial fibrillary acid protein and S100beta staining, morphology and survival of cultured rat hippocampal astrocytes as determined by Fura imaging, indirect immunofluorescence and life/death assays. In contrast to cultured neurons, none of the 12 different beta/A4 fragments tested caused an increase in intra-astrocytic free calcium. However, among the compounds evaluated, the fragments 10-20mer, 25-35mer and the full-length peptides (1-40, 1-42 and 1-43mer), at 5 and 10 microM, decreased free intra-astrocytic calcium statistically significantly after the cells had been incubated for 48 and 72 h. This occurred both for astrocytes treated with vehicle alone or the reversed sequence of the 1-40mer, i.e. the 40-1mer. However, survival was not altered under the conditions examined, even when there was a change in free intracellular calcium. Concomitant with the decrease in intracellular free calcium, the shape of the astrocytes became more spider-like, normally an indication of activated astrocytes, and markedly more intense anti-S100beta and anti-glial fibrillary acidic protein staining was seen. The functional relevance of altered calcium homeostasis for apolipoprotein E secretion, potentially relevant for neuronal plasticity in general and in Alzheimer's disease, is discussed.

Amyloid beta protein inhibits cellular MTT reduction not by suppression of mitochondrial succinate dehydrogenase but by acceleration of MTT formazan exocytosis in cultured rat cortical astrocytes

Alzheimer's disease amyloid beta protein (Abeta) inhibits cellular reduction of the dye 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). Kaneko et al. have previously hypothesized that Abeta works by suppressing mitochondrial succinate dehydrogenase (SDH), but Liu and Schubert have recently demonstrated that Abeta decreases cellular MTT reduction by accelerating the exocytosis of MTT formazan in neuronal cells. To ask which is the case in astrocytes, we compared the effects of Abeta and 3-nitropropionic acid (3-NP), a specific SDH inhibitor, on MTT reduction in cultured rat cortical astrocytes. Treatment with 3-NP (10 mM) decreased cellular activity of MTT reduction, regardless of the time of incubation with MTT. On the other hand. Abeta-induced inhibition of cellular MTT reduction was dependent on the time of incubation with MTT. The cells treated with Abeta (0.1-1000 nM) exhibited normal capacity for MTT reduction at an early stage of incubation ( < 30 min), but ceased to reduce MTT at the late stage (> 1 h). Microscopic examination revealed that Abeta treatment accelerated the appearance of needle-like MTT formazan crystals at the cell surface. These observations support that Abeta accelerates the exocytosis of MTT formazan in astrocytes. In addition to inhibition of MTT reduction, Abeta is known to induce morphological changes in astrocytes. Following addition of Abeta (20 microM), polygonal astrocytes changed into process-bearing stellate cells. To explore a possible linkage between these two effects of Abeta, we tested if astrocyte stellation is induced by agents that mimic the effect of Abeta on MTT reduction. Cholesterol (5 5000 nM) and lysophosphatidic acid (0.2-20 microg/ml) were found to accelerate the exocytosis of MTT formazan in a similar manner to Abeta, but failed to induce astrocyte stellation. Therefore, Abeta-induced inhibition of MTT reduction is unlikely to be directly linked to its effect on astrocyte morphology.

Metallothioneins are highly expressed in astrocytes and microcapillaries in Alzheimer's disease

One of the neuropathological characteristics of Alzheimer's disease is the presence of a large number of reactive astrocytes, often, but not always, associated with senile plaques. The factors responsible for such an activation are as yet totally unknown. Other characteristic features of this disease such as betaA4 amyloid accumulation, senile plaques and neurofibrillary tangles represent well known pathological phenomena. Some studies suggest that betaA4 plays a major role in the reactive astrocytosis characteristic of Alzheimer's disease. In the normal human brain, metallothionein isoforms I and II are expressed in astrocytes but not in neurons. In the present study, we used anti-metallothionein antibodies to detect cells expressing metallothioneins isoforms I and II in normal and Alzheimer's disease (AD) brain sections. Results showed that expression of these proteins in the cortex, cerebral white matter and cerebellum is a relevant anatomopathological characteristic of Alzheimer's disease. Analysis of Alzheimer's disease brain sections revealed high expression of metallothioneins I/II in astrocytes and microcapillaries, and in the granular but not the molecular layer of the cerebellum. Furthermore, metallothionein expression can be used as a marker to identify subtypes of astrocytes.

Beta-amyloid plaques: stages in life history or independent origin?

Several types of discrete beta-amyloid (Abeta) deposit or senile plaque have been identified in the brains of individuals with Alzheimer's disease and Down's syndrome. The majority of these plaques can be classified into four morphological types: diffuse, primitive, classic and compact. Two hypotheses have been proposed to account for these plaques. Firstly, that the diffuse, primitive, classic and compact plaques develop in sequence and represent stages in the life history of a single plaque type. Secondly, that the different Abeta plaques develop independently and therefore, unique factors are involved in the formation of each type. To attempt to distinguish between these hypotheses, the morphology, ultrastructure, composition, and spatial distribution in the brain of the four types of plaque were compared. Although some primitive plaques may develop from diffuse plaques, the evidence suggests that a unique combination of factors is involved in the pathogenesis of each plaque type and, therefore, supports the hypothesis that the major types of Abeta plaque develop independently.

Fibrillar beta-amyloid induces microglial phagocytosis, expression of inducible nitric oxide synthase, and loss of a select population of neurons in the rat CNS in vivo

To determine the stability of beta-amyloid peptide (Abeta) and the glial and neuronal changes induced by Abeta in the CNS in vivo, we made single injections of fibrillar Abeta (fAbeta), soluble Abeta (sAbeta), or vehicle into the rat striatum. Injected fAbeta is stable in vivo for at least 30 d after injection, whereas sAbeta is primarily cleared within 1 d. After injection of fAbeta, microglia phagocytize fAbeta aggregates, whereas nearby astrocytes form a virtual wall between fAbeta-containing microglia and the surrounding neuropil. Similar glial changes are not observed after sAbeta injection. Microglia and astrocytes near the injected fAbeta show a significant increase in inducible nitric oxide synthase (iNOS) expression compared with that seen with sAbeta or vehicle injection. Injection of fAbeta but not sAbeta or vehicle induces a significant loss of parvalbumin- and neuronal nitric oxide synthase-immunoreactive neurons, whereas the number of calbindin-immunoreactive neurons remains unchanged. These data demonstrate that fAbeta is remarkably stable in the CNS in vivo and suggest that fAbeta neurotoxicity is mediated in large part by factors released from activated microglia and astrocytes, as opposed to direct interaction between Abeta fibrils and neurons.

Amyloid-beta peptide activates cultured astrocytes: morphological alterations, cytokine induction and nitric oxide release

A common feature of many neurodegenerative disorders is an abundance of activated glial cells (astrocytes and microglia). In Alzheimer's disease (AD), activated astrocytes are in close apposition to and surrounding the amyloid plaques. The mechanisms by which the astrocytes become activated in AD and the consequences of reactive astrocytosis to disease progression are not known. We examined the possibility that the amyloid-beta (Abeta) peptide, a major constituent of the amyloid plaque, could act as a stimulus leading to activation. We found that treatment of rat cortical astrocyte cultures with aggregated Abeta 1-42 peptide induces activation, as assessed by reactive morphological changes and upregulation of selective glial mRNA and proteins, such as the inflammatory cytokine interleukin-1beta. Abeta also stimulates inducible nitric oxide synthase (iNOS) mRNA levels and nitric oxide (NO) release. Abeta 1-42, a major form of amyloid associated with neurotoxicity, activated astrocytes in a time- and dose-dependent manner, whereas a scrambled Abeta 1-42 sequence or Abeta 17-42 had little or no effect. We also determined that the Abeta activity can be found in a supernatant fraction containing soluble Abeta oligomers. Our data suggest that Abeta plays a role in the reactive astrocytosis of AD and that the inflammatory response induced upon glial activation is a critical component of the neurodegenerative process.

The amyloid precursor protein gene: a neuropeptide gene with diverse functions in the central nervous system

The amyloid precursor protein (APP) is a member of a family of proteins found in the central nervous system with a fundamental role in the pathogenesis of Alzheimer's disease. This review describes the experimental evidence that has provided functional insights into this protein and emphasizes the importance of APP in many neurobiological processes.

Bilateral injections of amyloid-beta 25-35 into the amygdala of young Fischer rats: behavioral, neurochemical, and time dependent histopathological effects

To examine the time course of the histopathological effects of bilateral injections of amyloid-beta 25-35 (A beta) and to determine if these effects are associated with a reduction in choline acetyltransferase activity and behavioral impairments, we injected A beta (5.0 nmol) into the amygdala of young male Fischer rats. Control rats received vehicle infusions. For histological analysis, animals were sacrificed at 8, 32, 64, 96, and 128 days postoperatively (n = 21-33 per timepoint). A beta induced neuronal tau-2 staining in the right, but not the left amygdala and hippocampus. A beta also induced reactive astrocytosis and neuronal shrinkage within the right hippocampus and amygdala, respectively. As with tau-2, these same brain regions within the left hemisphere in the A beta-treated rats were significantly less affected. In addition, A beta appeared to induce microglial and neuronal interleukin-1beta staining. The histopathological effects of A beta peaked at 32 days postoperatively but were not associated with a reduction in amygdaloid choline acetyltransferase activity. In a separate experiment, behavioral effects of bilateral intra-amygdaloid injections of A beta were analyzed at 34-52 days postoperatively. In an open field test, the treatment groups differed only in the numbers of rears emitted (p = 0.016). There was no effect of A beta in the Morris water maze or in the acquisition and retention of a one-way conditioned avoidance response. These data suggest a laterality in the histopathological effects of A beta and that the effects of single injections are in part transient. These findings also suggest a direct association between plaque and tangle formation in Alzheimer's disease, and support the use of this rat model to screen drugs that may alter the initial pathological events associated with Alzheimer's disease, that occur before the manifestations of extensive behavioral impairments become evident.

Congo red reverses amyloid beta protein-induced cellular stress in astrocytes

An amyloid-binding dye Congo red has been reported to prevent the neurotoxic effect of Alzheimer's amyloid beta protein (Abeta). In the present study, we investigated the effect of Congo red in cultured rat cortical astrocytes. Abeta (1 nM-10 microM) did not cause cell death, but potently inhibited the cellular redox activity as determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay. Congo red (0.2-20 microM), when added together with or prior to Abeta, significantly blocked Abeta-induced inhibition of redox activity. Furthermore, when Congo red was added after treatment with Abeta, the inhibited redox activity was restored to normal, indicating that Congo red can reverse Abeta-induced cellular stress. The reversing effect of Congo red cannot be explained by the inhibition of Abeta fibril formation and suggests a novel aspect of the interaction of Congo red with Abeta.

Human amylin mimics amyloid beta protein-induced reactive gliosis and inhibition of cellular redox activity in cultured astrocytes

We have previously found that Alzheimer's disease amyloid beta protein (A beta) induces reactive gliosis and inhibits cellular redox activity of astrocytes. In the present study, human amylin, an amyloidogenic peptide with primary sequence dissimilar to A beta, mimicked the effects of A beta in cultured astrocytes. However, the non-amyloidogenic rat amylin showed no effect. These results suggest that amyloidogenic property is important for A beta to induce morphological and functional changes of astrocytes.

Apoptosis, neurotrophic factors and neurodegeneration

Apoptosis is an active process of cell death characterized by distinct morphological features, and is often the end result of a genetic programme of events, i.e. programmed cell death (PCD). There is growing evidence supporting a role for apoptosis in some neurodegenerative diseases. This conclusion is based on DNA fragmentation studies and findings of increased levels of pro-apoptotic genes in human brain and in in vivo and in vitro model systems. Additionally, there is some evidence for a loss of neurotrophin support in neurodegenerative diseases. In Alzheimer's disease, in particular, there is strong evidence from human brain studies, transgenic models and in vitro models to suggest that the mode of nerve cell death is apoptotic. In this review we describe the evidence implicating apoptosis in neurodegenerative diseases with a particular emphasis on Alzheimer's disease.

PrP and beta-amyloid fragments activate different neurotoxic mechanisms in cultured mouse cells

Alzheimer's disease and prion diseases such as Creutzfeldt-Jakob disease are caused by as yet undefined metabolic disturbances of normal cellular proteins, the amyloid precursor protein and the prion protein (PrP). Synthetic fragments of both proteins, beta-amyloid 25-35 (betaA25-35) and PrP106-126, have been shown to be toxic to neurons in culture. Cell death in both cases occurs by apoptosis. Here we show that there are considerable differences in the mechanisms involved. Thus, PrP106-126 is not toxic to cortical cell cultures of PrP knockout mouse neurons whereas betaA25-35 is. The toxicity of both peptides involves Ca2+ uptake through voltage-sensitive Ca2+ channels but only PrP106-126 toxicity involves the activity of NMDA receptors. The toxicity of betaA25-35, but not PrP106-126, is attenuated by the action of forskolin. These results indicate that PrP106-126 and PA25-35 induce neuronal apoptosis through different mechanisms.

Altered apolipoprotein E secretion in cytokine treated human astrocyte cultures

Apolipoprotein E (ApoE), postulated to be a major lipid carrier protein in brain, is synthesized and secreted primarily by astrocytes and is involved in brain development and repair. We have analyzed its secretion in primary cultures of older (high passage) slowly dividing and younger (lower passage) rapidly dividing fetal human astrocytes exposed to various inflammatory and anti-inflammatory cytokines, alone and in combination. ApoE secretion was reduced in high passage astrocytes when compared to lower passage astrocytes. A further reduction in ApoE secretion in high passage cells was consistently produced by the combination of cytokines interleukin 1 (IL-1) alpha and beta and interferon (IFN-gamma) cytokines or by the basic fibroblast growth factor (basic-FGF) alone. Epidermal growth factor (EGF) increased ApoE secretion. The combination of these cytokine effects in chronically degenerating brain regions of Alzheimer's disease and other neurodegenerative diseases could reduce the amount of ApoE available for neuronal regeneration. EGF, or agents inducing EGF, could ameliorate these ApoE deficiencies.