Early association of reactive astrocytes with senile plaques in Alzheimer's disease

Minocycline inhibits neuronal death and glial activation induced by ?-amyloid peptide in rat hippocampus

Minocycline, a second-generation tetracycline compound, has been examined as a neuroprotectant in beta-amyloid (A beta)-injected rat hippocampus. At 7 days post-injection, A beta(1-42) caused a significant loss of granule cell layer neurons (28% reduction) compared to control uninjected hippocampus. Hippocampal injection of A beta peptide also led to marked gliosis with numbers of microglia (increased by 26-fold) and immunoreactivity of astrocytes (increased by 11-fold) relative to control, as determined from immunohistochemical analysis. Intraperitoneal administration of minocycline significantly reduced neuronal loss induced by A beta(1-42) (by 80%) and also diminished numbers of microglia (by 69%) and astrocytes (by 36%) relative to peptide alone. Peptide injection increased expression of cyclooxygenase-2 (COX-2) in most (about 70%) of granule cells, a subset (about 20%) of microglia, but not in astrocytes; in the presence of minocycline, COX-2 immunostaining was abolished in microglia. The results from this study suggest that minocycline may have efficacy in the treatment of AD.

Nitric oxide in the cerebral cortex of amyloid-precursor protein (SW) Tg2576 transgenic mice

Changes in the amyloid-peptide (Abeta), neuronal and inducible nitric oxide (NO)synthase (nNOS, iNOS), nitrotyrosine, glial fibrillary acidic protein, and lectin from Lycopersicon esculentum (tomato) were investigated in the cerebral cortex of transgenic mice (Tg2576) to amyloid precursor protein (APP), by immunohistochemistry (bright light, confocal, and electron microscopy). The expression of nitrergic proteins and synthesis of nitric oxide were analyzed by immunoblotting and NOS activity assays, respectively. The cerebral cortex of these transgenic mice showed an age-dependent progressive increase in intraneuronal aggregates of Abeta-peptide and extracellular formation of senile plaques surrounded by numerous microglial and reactive astrocytes. Basically, no changes to nNOS reactivity or expression were found in the cortical mantle of either wild or transgenic mice. This reactivity in wild mice corresponded to numerous large type I and small type II neurons. The transgenic mice showed swollen, twisted, and hypertrophic preterminal and terminal processes of type I neurons, and an increase of the type II neurons. The calcium-dependent NOS enzymatic activity was higher in wild than in the transgenic mice. The iNOS reactivity, expression and calcium-independent enzymatic activity increased in transgenic mice with respect to wild mice, and were related to cortical neurons and microglial cells. The progressive elevation of NO production resulted in a specific pattern of protein nitration in reactive astrocytes. The ultrastructural study carried out in the cortical mantle showed that the neurons contained intracellular aggregates of Abeta-peptide associated with the endoplasmic reticulum, mitochondria, and Golgi apparatus. The endothelial vascular cells also contained Abeta-peptide deposits. This transgenic model might contribute to understand the role of the nitrergic system in the biological changes related to neuropathological progression of Alzheimer's disease.

Astroglial regulation of apolipoprotein E expression in neuronal cells. Implications for Alzheimer's disease

Although apolipoprotein (apo) E is synthesized in the brain primarily by astrocytes, neurons in the central nervous system express apoE, albeit at lower levels than astrocytes, in response to various physiological and pathological conditions, including excitotoxic stress. To investigate how apoE expression is regulated in neurons, we transfected Neuro-2a cells with a 17-kilobase human apoE genomic DNA construct encoding apoE3 or apoE4 along with upstream and downstream regulatory elements. The baseline expression of apoE was low. However, conditioned medium from an astrocytic cell line (C6) or from apoE-null mouse primary astrocytes increased the expression of both isoforms by 3-4-fold at the mRNA level and by 4-10-fold at the protein level. These findings suggest that astrocytes secrete a factor or factors that regulate apoE expression in neuronal cells. The increased expression of apoE was almost completely abolished by incubating neurons with U0126, an inhibitor of extracellular signal-regulated kinase (Erk), suggesting that the Erk pathway controls astroglial regulation of apoE expression in neuronal cells. Human neuronal precursor NT2/D1 cells expressed apoE constitutively; however, after treatment of these cells with retinoic acid to induce differentiation, apoE expression diminished. Cultured mouse primary cortical and hippocampal neurons also expressed low levels of apoE. Astrocyte-conditioned medium rapidly up-regulated apoE expression in fully differentiated NT2 neurons and in cultured mouse primary cortical and hippocampal neurons. Thus, neuronal expression of apoE is regulated by a diffusible factor or factors released from astrocytes, and this regulation depends on the activity of the Erk kinase pathway in neurons.

Acetylcholinesterase induces neuronal cell loss, astrocyte hypertrophy and behavioral deficits in mammalian hippocampus

Previous studies have demonstrated that acetylcholinesterase (AChE) promotes the assembly of amyloid-beta-peptides into neurotoxic amyloid fibrils and is toxic for chick retina neuronal cultures and neuroblastoma cells. Moreover, AChE is present in senile plaques in Alzheimer's disease (AD) brains. Here we have studied the effect of AChE on astrocytes and hippocampal neurons in vivo. Morphological as well as behavioral disturbances were analyzed after intrahippocampal injection of AChE. Rats were trained in the Morris water maze and assayed for behavioral parameters. Neuronal cell loss was found in the upper leaf of the dentate gyrus in rats injected with AChE in comparison with control animals. Glial fibrillary acidic protein immunoreactivity showed astrocytic hypertrophy and the magnitude of the response was associated with neuronal cell loss. Behavioral results show that injection of AChE produces cognitive impairment demonstrated by an altered water maze performance including (i) a higher escape latency score, (ii) a decreased spatial acuity and (iii) a shorter time of swimming in the platform quadrant. These findings indicate that a local increment in neuronal AChE concentration at the mammalian hippocampus, such as those present in amyloid deposits, may play a role in triggering neuropathological and behavioral changes such as those observed in AD brains.

1-40 Beta-amyloid protein fragment modulates the expression of CD44 and CD71 on the astrocytoma cell line in the presence of IL1beta and TNFalpha

The modulation of CD44, VCAM-1 and CD71 expression was analysed by flow cytometry in the 1321N1 astrocytoma cell line in the presence of interleukin-1beta (IL1beta), tumour necrosis factor-alpha (TNFalpha) and 1-40 or 25-35 beta-amyloid (Abeta) fragments. The percentage of 1321N1 astrocytoma cell line expressing these markers increased significantly after treatment with TNFalpha or IL1beta. The presence of Abeta 1-40 fragment, alone or in combination with IL1beta, induced an increase in the percentage of cells expressing CD44, but not VCAM-1. However, the concomitant presence of Abeta 1-40 fragment and of IL1beta or TNFalpha caused an increase in the percentage of CD71 positive cells. In contrast, the shorter Abeta 25-35 fragment was always inactive. These results indicates that Abeta 1-40 fragment, in association with cytokines, can activate this astrocyte-derived cell line and add further elements in favour of the hypothesis that beta-amyloid can act as immunological mediator.

Quantification of regional glial fibrillary acidic protein levels in Alzheimer's disease

OBJECTIVES

Our objectives were to quantify glial fibrillary acidic protein (GFAP) in brains of Alzheimer's disease (AD) cases, and non-AD controls to determine the regions with the most severe gliosis in AD.

MATERIAL AND METHODS

In a case control design, we used an enzyme-linked immunosorbent assay (ELISA) to quantify GFAP in frozen brain from four areas of neocortex in 10 AD cases, 10 age-matched controls, and 10 younger controls from the Honolulu-Asia Aging Study autopsy archive.

RESULTS

Median age at death was 83.5 years for cases and age-matched controls, and 77 years for younger controls. For the AD cases compared with the age-matched controls, levels of GFAP in occipital (P=0.01), parietal (P=0.028), and temporal lobes (P=0.004) (but not frontal) were significantly higher in the cases. The median GFAP excess in AD cases compared with age matched controls was highest in the temporal lobe.

CONCLUSIONS

Regional quantification of GFAP reveals that the glial response is most prominent in the temporal lobe in AD.

Targeting monocyte chemoattractant protein-1 signalling in disease

Monocyte chemoattractant protein-1 (MCP-1) has been implicated in many inflammatory and autoimmune diseases. The G-protein-coupled receptor CCR-2B is probably the most important MCP-1 receptor in vivo, and loss of MCP-1 effector function alone is sufficient to impair monocytic trafficking in inflammation models. MCP-1 signalling appears to be a relevant target, especially in rheumatoid arthritis (RA). In RA patients, MCP-1 is produced by synovial cells and infiltrating monocytes, plasma MCP-1 concentrations correlate with swollen joint count, and elevated serum MCP-1 concentrations were found in juvenile RA in patients with active disease. Modulation of MCP-1 signalling in experimental RA showed beneficial effects on inflammation and joint destruction. With respect to chronic neuroinflammation, a critical role for MCP-1 has been established in animal models for multiple sclerosis. In acute neuroinflammation, experimental evidence for a detrimental role of MCP-1 in stroke and excitotoxic injury has been found. Several selective small molecular weight CCR-2B antagonists and MCP-1-blocking antibodies have been described. The proof for the validity of targeting MCP-1 signalling in disease, however, has yet to be established in clinical trials.

Neurite outgrowth is impaired on HSP70-positive astrocytes through a mechanism that requires NF-kappaB activation

In the adult central nervous system (CNS), prominent reactive astrocytosis is seen in acute traumatic brain injury, neurodegenerative diseases and a variety of viral infections. Reactive astrocytes synthesize a number of factors that could play different roles in neuronal regeneration. In this study, the effects of thermal stress were evaluated on nuclear factor-kappaB (NF-kappaB) activation and proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) secretion in primary astrocytic cultures. The ability of HSP70-positive astrocytes to support or inhibit neurite outgrowth was investigated in neuron-astrocyte cocultures. Cultured astrocytes from cerebral cortex of rats were exposed to transient hyperthermia (42 degrees C/30 min) and incubated at 37 degrees C for different periods of recovery. During HSP70 accumulation, astrocytes extended large and thick processes associated to rearrangement of glial fibrillary acidic protein (GFAP) filaments and an increase in protein synthesis and GFAP, suggesting an astrogliosis event. A delay of NF-kappaB activation appeared closely related to TNF-alpha secretion by HSP70-positive astrocytes. These cells demonstrated a functional shift from neurite growth-promoting to non-permissive substrate. We also found that gliotoxin, a specific NF-kappaB inhibitor, partially abrogated the inhibitory ability of reactive astrocytes. These findings may suggest a involvement of NF-kappaB and TNF-alpha in modulating the failure of HSP70-positive astrocytes to provide functional support to neuritic outgrowth.

Chronic gliosis triggers Alzheimer's disease-like processing of amyloid precursor protein

Alzheimer's disease is a progressively dementing illness characterized by the extracellular accumulation and deposition of beta-amyloid. Early onset Alzheimer's disease is linked to mutations in three genes, all of which lead to increased beta-amyloid production. Inflammatory changes and gliosis may also play a role in the disease process, but the importance of these reactive events remains unclear. We recently reported that chronic cortical gliosis in heterotopic fetal rat cortical transplants is associated with significant changes in the levels of some of the proteins implicated in the pathogenesis of Alzheimer's disease. Because rodent beta-amyloid does not form extracellular amyloid deposits, we have now extended this model of chronic cortical gliosis to transgenic mice expressing the Swedish mutant form of human amyloid precursor protein. In addition, apolipoprotein E knockout mice were used to elucidate the role of this protein in reactive gliosis. The expression of mutant and murine proteins was assayed 6 or 10 months after transplantation using immunohistochemical and western blot methods. Heterotopic transplantation of fetal cortex onto the midbrain of neonatal mice consistently resulted in reactive gliosis, independent of apolipoprotein E status. In contrast, in homotopic cortex-to-cortex grafts there was little alteration in glial reactivity, a result similar to that obtained previously in rats. By 10 months post-transplantation the level of presenilin-1 expression was lower in heterotopic grafts than in host cortex and there was increased expression of transgenic amyloid precursor protein, but only in the gliotic cortex-to-midbrain grafts. Most importantly, increased levels of beta-amyloid, and particularly its precursor, C-99, were selectively found in these heterotopic transplants. Our results show that chronic gliosis is associated with altered processing of the amyloid precursor protein in vivo and thus may initiate or exacerbate pathological changes associated with Alzheimer's disease.

Effects of intrahippocampal CT105, a carboxyl terminal fragment of beta-amyloid precursor protein, alone/with inflammatory cytokines on working memory in rats

In this study, we examined the effects of a 105 amino acid carboxyl terminal fragment of beta-amyloid precursor protein (CT105) and inflammatory cytokines on working memory in rats, by using a three-panel runway set-up. CT105 at 10 nmol/side significantly impaired working memory when it was administered bilaterally into the hippocampus. Furthermore, to elucidate the interaction of CT105 with inflammatory cytokines, we co-administered tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) in combination with CT105. Concurrent injections of CT105 (1.0 nmol/side) and TNF-alpha (100 ng/side) produced a synergistic deficit of working memory, whereas IL-1beta (100 ng/side) combined with CT105 (1.0 nmol/side) did not affect the working memory performance. These results indicate that the CT105-induced impairment of working memory is strongly aggravated by an increase in the level of the inflammatory cytokine TNF-alpha, which may occur in the brains of patients with Alzheimer's disease.

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.

Generation of reactive oxygen species and activation of NF-kappaB by non-Abeta component of Alzheimer's disease amyloid

Non-amyloid beta (Abeta) component of Alzheimer's disease (AD) amyloid (NAC) coexists with Abeta protein in senile plaques. After exposure to NAC fibrils, cortical neurons of rat brain primary culture became apoptotic, while astrocytes were activated with extension of their processes. NAC fibrils decreased the activity of reducing 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) in cortical neurons more markedly (IC(50) = 5.6 microm) than in astrocytes (IC(50) approximately 50 microm). The neuron-specific toxicity of NAC fibrils was indicated also by an increased release of lactate dehydrogenase from the cells. Neuronal apoptosis was suppressed by pre-treatment with the antioxidants, propyl gallate (PG) and N-t-butyl-phenylnitrone (BPN), or overexpression of human Bcl-2. Exposure to NAC fibrils enhanced generation of reactive oxygen species (ROS) in neurons and less efficiently in astrocytes, as demonstrated by oxidation of 2',7'-dichlorofluorescin. The site of ROS generation was shown to be mitochondria by oxidation of chloromethyl-tetramethyl rosamine. Exposure to NAC fibrils increased also the nuclear translocation of nuclear factor kappa B (NF-kappaB) and enhanced its DNA-binding activity, which was inhibited by PG and BPN more efficiently in neurons than in astrocytes. These results suggest that NAC fibrils increase mitochondrial ROS generation and activate NF-kappaB, thereby causing a differential change in gene expression between neurons and astrocytes in the AD brain.

Aspects of neurodegeneration in the canine brain

The process of neurodegeneration displays some common morphological characteristics, most of which are jointly observed in the brains of most mammalian species. In the canine brain, neurodegeneration is frequently typified by an extensive beta-amyloid (A beta) deposition (mainly of the C-terminal A beta1-42 form) within the neurones and at the synaptic regions, in the early stages of the process. These deposits subsequently appear to give rise to the formation of senile plaques of the diffuse (non-beta-sheet) subtype, which tend to develop spontaneously but rarely proceed to form neuritic plaques. Additional features accompanying neurodegeneration include accumulations of the "aging pigment," lipofuscin, intraneuronal changes in the cytoskeleton, vascular changes in the cerebrum, cortical cerebral atrophy, enlargement of the ventricles and increased concentration of oxidative stress markers, many of which are perceived as cardinal features of extensive dysfunction in the protein turnover network. The involvement of ubiquitin is discrete but consistent in many of these molecular structures and seems to account for some critical aspects of the associated neuropathology. Irrespective of these, though, the degenerated canine brain seems to be devoid of neurofibrillary tangle formation, a manifestation commonly observed in the brain of both aged (cognitively normal) and Alzheimer-affected human subjects. The fact that canines exhibit clear symptoms of an age-related cognitive decline pertains to the concept of A beta playing a central role in age-related cognitive dysfunction and neurodegeneration.

Amyloid-beta-induced chemokine production in primary human macrophages and astrocytes

In Alzheimer's disease (AD), chemotaxis might be responsible for attracting glial cells towards the neuritic plaque. Using primary monocyte-derived macrophages and primary adult astrocytes as a model, amyloid-beta (Abeta) (1-42) was able to stimulate the production, as measured by RT-PCR, of MIP-1alpha and MIP-1beta mRNA in macrophages and MCP-1 in astrocytes. Cocultures showed in unstimulated as well as in Abeta-stimulated cells an increase in MIP-1alpha, MIP-1beta and MCP-1 mRNA. ELISAs of supernatant samples of stimulated macrophages and astrocytes also showed an increase in MIP-1alpha and MIP-1beta in macrophages and MCP-1 in astrocytes. Stimulated cocultures showed an increase in MIP-1alpha, MIP-1beta and MCP-1 protein levels in contrast to unstimulated cocultures.

Altered expression of apolipoprotein E, amyloid precursor protein and presenilin-1 is associated with chronic reactive gliosis in rat cortical tissue

A major characteristic feature of Alzheimer's disease is the formation of compact, extracellular deposits of beta-amyloid (senile plaques). These deposits are surrounded by reactive astrocytes, microglia and dystrophic neurites. Mutations in three genes have been implicated in early-onset familial Alzheimer's disease. However, inflammatory changes and astrogliosis are also believed to play a role in Alzheimer's pathology. What is unclear is the extent to which these factors initiate or contribute to the disease progression. Previous rat studies demonstrated that heterotopic transplantation of foetal cortical tissue onto the midbrain of neonatal hosts resulted in sustained glial reactivity for many months. Similar changes were not seen in cortex-to-cortex grafts. Using this model of chronic cortical gliosis, we have now measured reactive changes in the levels of the key Alzheimer's disease proteins, namely the amyloid precursor protein, apolipoprotein E and presenilin-1. These changes were visualised immunohistochemically and were quantified by western blot analysis. We report here that chronic cortical gliosis in the rat results in a sustained increase in the levels of apolipoprotein E and total amyloid precursor protein. Reactive astrocytes in heterotopic cortical grafts were immunopositive for both of these proteins. Using a panel of amyloid precursor protein antibodies we demonstrate that chronic reactive gliosis is associated with alternative cleavage of the peptide. No significant changes in apolipoprotein E or amyloid precursor protein expression were seen in non-gliotic cortex-to-cortex transplants. Compared to host cortex, the levels of both N-terminal and C-terminal fragments of presenilin-1 were significantly lower in gliotic heterotopic grafts.The changes described here largely mirror those seen in the cerebral cortex of humans with Alzheimer's disease and are consistent with the proposal that astrogliosis may be an important factor in the pathogenesis of this disease.

Brain energy metabolism in Alzheimer's disease: 99mTc-HMPAO SPECT imaging during verbal fluency and role of astrocytes in the cellular mechanism of 99mTc-HMPAO retention

The central hypothesis of the study which has been carried out as part of the NRP38 program, is that perturbations of brain energy metabolism are critically involved in the neurodegeneration occurring in Alzheimer's disease (AD) and that they may correlate with early cognitive dysfunctioning. In the present multidisciplinary study we set out to monitor brain energy metabolism using FDG-PET and HMPAO-SPECT imaging in a cohort of individuals over 65 years of age, drawn from the general population. HMPAO-SPECT imaging, which is a simpler and more widely accessible imaging procedure than FDG-PET, was performed under basal conditions and during the performance of a cognitive task (verbal fluency test). Three groups were studied. Two groups (groups I and II) included individuals age 65 or more, with no cognitive impairment and carrying an APOE4 positive or APOE4 negative phenotype, respectively; a third group (group III) included patients with clinical signs of AD. Each subject entering the study underwent an FDG-PET, an HMPAO-SPECT and an extensive battery of neuropsychological tests which assess various aspects of cognitive functioning, with a strong emphasis on working memory, divided attention and executive functions. A total of 101 participants were submitted to brain imaging and neuropsychological testing. Among these, 60 participants received the same set of imaging and neuropsychological tasks 24-36 months after the first set (phase II). In this article, we present a preliminary analysis performed on ten subjects from groups I and II and nine subjects from group III: activation (verbal fluency task) induced a specific pattern of increase in HMPAO retention (including BA 9/10, BA 18 bilaterally and right BA 17). In contrast to controls, in nine AD subjects no significant differences in HMPAO retention were observed when comparing activation and basal conditions. The cellular and molecular mechanisms that underlie the retention of HMPAO, the tracer used for single photon emission computed tomography (SPECT) imaging, has been studied in vitro in purified preparations of neurons and astrocytes with the aim of investigating the contribution of different cell types to hexamethyl-propyleneamineoxime labeled with technetium-99m (99mTc-HMPAO) retention in vitro. Results show that 99mTc-HMPAO retention predominates in astrocytes over neurons by a factor of approximately 2.5. Diethyl maleate, ethacrynic acid and buthionine sulfoximine, three agents which significantly reduce glutathione levels, also decreased 99mTc-HMPAO retention in both astrocytes and in neurons. Decrease did not always correlate with glutathione levels however, thus suggesting that other factors could be involved. The data presented indicate that astrocytes might constitute a prominent site of 99mTc-HMPAO retention and most likely contribute significantly to the SPECT signal. In addition, they also suggest that specific alterations in glial cell metabolism could explain flow-independent changes in 99mTc-HMPAO retention in the brain as observed by SPECT in certain pathologies (including Alzheimer's disease). In particular, these observations suggest a key role of astrocytes in the signal detected with the imaging procedure, which is altered in the Alzheimer's cohort subjected to the verbal fluency activation task.

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.

Neurodegenerative changes associated with beta-amyloid deposition in the brains of mice carrying mutant amyloid precursor protein and mutant presenilin-1 transgenes

Mutations of amyloid precursor protein (APP) and presenilin-1 (PS1) lead to an increase in beta-amyloid (Abeta) production. Despite the fact that a number of transgenic mice develop cerebral Abeta plaques, few have been subjected to ultrastructural investigation and the sequence of events leading to Abeta plaque formation is unclear. We therefore investigated the doubly transgenic (mutant APP(K670N,M671L)-mutant PS1(M146L)) mouse, which develops Abeta deposits much earlier than singly transgenic littermates. Widespread Abeta plaques with or without a distinct core were found in gray matter. Abeta plaques were also present in white matter. Astrocytosis was greater around gray matter plaques than around white matter plaques. In some plaques, Abeta cores were associated with cell profiles containing prominent endoplasmic reticulum and a homogeneous cytoplasm that appeared to be neuronal. The morphology and location of other profiles indicated them to be microglia or oligodendrocytes. Some Abeta fibrils appeared to lie within these profiles, but they may have been simply surrounded by the cell profile since the profile membrane was not always visible. Dark atrophic neurons, whose morphology suggested that they were apoptotic, were present around gray matter plaques. Cerebrovascular Abeta deposition was also observed in the brains of APP/PS1 transgenic mice. Thus, the amyloid deposition and neuropathology observed in APP/PS1 mouse brain are similar to those in Alzheimer's disease and they appear to develop earlier and become more severe than in the other transgenic models currently available.

Activation of human macrophages by amyloid-beta is attenuated by astrocytes

In Alzheimer's disease, neuritic amyloid-beta plaques along with surrounding activated microglia and astrocytes are thought to play an important role in the inflammatory events leading to neurodegeneration. Studies have indicated that amyloid-beta can be directly neurotoxic by activating these glial cells to produce oxygen radicals and proinflammatory cytokines. This report shows that, using primary human monocyte-derived macrophages as model cells for microglia, amyloid-beta(1-42) stimulate these macrophages to the production of superoxide anions and TNF-alpha. In contrast, astrocytes do not produce both inflammatory mediators when stimulated with amyloid-beta(1-42). In cocultures with astrocytes and amyloid-beta(1-42)-stimulated macrophages, decreased levels of both superoxide anion and TNF-alpha were detected. These decreased levels of potential neurotoxins were due to binding of amyloid-beta(1-42) to astrocytes since FACScan analysis demonstrated binding of FITC-labeled amyloid-beta(1-42) to astrocytoma cells and pretreatment of astrocytes with amyloid-beta(1-16) prevented the decrease of superoxide anion in cocultures of human astrocytes and amyloid-beta(1-42)-stimulated macrophages. To elucidate an intracellular pathway involved in TNF-alpha secretion, the activation state of NF-kappaB was investigated in macrophages and astrocytoma cells after amyloid-beta(1-42) treatment. Interestingly, although activation of NF-kappaB could not be detected in amyloid-beta-stimulated macrophages, it was readily detected in astrocytoma cells. These results not only demonstrate that amyloid-beta stimulation of astrocytes and macrophages result in different intracellular pathway activation but also indicate that astrocytes attenuate the immune response of macrophages to amyloid-beta(1-42) by interfering with amyloid-beta(1-42) binding to macrophages.

Regional distribution of amyloid-Bri deposition and its association with neurofibrillary degeneration in familial British dementia

Familial British dementia (FBD), pathologically characterized by cerebral amyloid angiopathy (CAA), amyloid plaques, and neurofibrillary degeneration, is associated with a stop codon mutation in the BRI gene resulting in the production of an amyloidogenic fragment, amyloid-Bri (ABri). The aim of this study was to assess the distribution of ABri fibrillar and nonfibrillar lesions and their relationship to neurofibrillary pathology, astroglial and microglial response using immunohistochemistry, confocal microscopy, and immunoelectron microscopy in five cases of FBD. Abnormal tau was studied with immunoblotting. We present evidence that ABri is deposited throughout the central nervous system in blood vessels and parenchyma where both amyloid (fibrillar) and pre-amyloid (nonfibrillar) lesions are formed. Ultrastructurally amyloid lesions appear as bundles of fibrils recognized by an antibody raised against ABri, whereas Thioflavin S-negative diffuse deposits consist of amorphous electron-dense material with sparse, dispersed fibrils. In contrast to nonfibrillar lesions, fibrillar ABri is associated with a marked astrocytic and microglial response. Neurofibrillary tangles and neuropil threads occurring mainly in limbic structures, are found in areas affected by all types of ABri lesions whereas abnormal neurites are present around amyloid lesions. Immunoblotting for tau revealed a triplet electrophoretic migration pattern. Our observations confirm a close link between ABri deposition and neurodegeneration in FBD.

nNOS expression in reactive astrocytes correlates with increased cell death related DNA damage in the hippocampus and entorhinal cortex in Alzheimer's disease

The immunocytochemical distribution of the neuronal form of nitric oxide synthase (nNOS) was compared with neuropathological changes and with cell death related DNA damage (as revealed by in situ end labeling, ISEL) in the hippocampal formation and entorhinal cortex of 12 age-matched control subjects and 12 Alzheimer's disease (AD) patients. Unlike controls, numerous nNOS-positive reactive astrocytes were found in AD patients around beta-amyloid plaques in CA1 and subiculum and at the places of clear and overt neuron loss, particularly in the entorhinal cortex layer II and CA4. This is the first evidence of nNOS-like immunoreactivity in reactive astrocytes in AD. In contrast to controls, in all but one AD subject, large numbers of ISEL-positive neuronal nuclei and microglial cells were found in the CA1 and CA4 regions and subiculum. Semiquantitative analysis showed that neuronal DNA fragmentation in AD match with the distribution of nNOS-expressing reactive astroglial cells in CA1 (r = 0.74, P < 0.01) and CA4 (r = 0.58, P < 0.05). A portion of the nNOS-positive CA2/CA3 pyramidal neurons was found to be spared even in the most affected hippocampi. A significant inverse correlation between nNOS expression and immunoreactivity to abnormally phosphorylated tau proteins (as revealed by AT8 monoclonal antibody) in perikarya of these CA2/3 neurons (r = -0.85, P < 0.01) suggests that nNOS expression may provide selective resistance to neuronal degeneration in AD. In conclusion, our results imply that an upregulated production of NO by reactive astrocytes may play a key role in the pathogenesis of AD.

Alzheimer's disease: transgenic mouse models and drug assessment

Alzheimer's disease (AD), characterized by neuritic plaques and neurofibrillary tangles of the brain, is experienced by more and more elderly people in a form of senile dementia. Four genes are closely linked with AD and are located on chromosomes 21, 19, 14 and 1. Transgenic technology enables the development of animal models for research into this human disease. Recently reported transgenic AD mouse models, which express AD-related mutant human genes, develop some significant aspects of AD-like pathology. The specific role of these mice in representing different targets, the consequent pathology of AD and the availability of this increasingly popular tool for investigating new therapeutic strategies for AD are reviewed.

Long-term evolution of local, proximal and remote astrocyte responses after diverse nucleus basalis lesioning (an experimental Alzheimer model): GFAP immunocytochemical study

A study on long-term astrocytic responses (from 1 day to 20 months after lesioning in 4-month-old rats, and from 1 day to 6 months in 20-month-old rats) to diverse unilateral damage of the nucleus basalis (nbM) by injection of 40 nmol of ibotenic acid, or 50 or 100 nmols of quisqualic acid was performed using a histochemical method (immunoreactivity against the glial fibrillary acidic protein GFAP). Glial reactivity (i.e., isolated or clustered hypertrophic and/or hyper-reactive astrocytes) was evaluated in several ipsilateral and contralateral brain regions: the 'local response' within the damaged nbM region; the 'proximal response' (a new concept proposed by us) in the non-damaged structures neighbouring the nbM; and the 'remote response' in the ipsilateral brain cortex and in the contralateral cortex and nbM. In 4-month-old animals, the remote cortical glial responses, independent of the involution of cortical cholinergic activity and randomly located in layers I-V of motor and somatosensory cortical regions, were similar in appearance over a long period (13-20 months), with the highest reactivity 45 days after lesioning. The proximal response lasted from 1 day to 13 months and afterwards tended to disappear. Contralateral reactivity and ipsilateral cortical scars were observed. The local (nbM) glial response was maintained throughout the period studied. Subsets of astrocytes of different reactivities were observed, most of their elements being highly intermeshed. In 20-month-old animals, nbM lesions produced less positive, but similar, glial reactive patterns. This glial reactivity was superposed onto the glial reactivity of old age. All these results are discussed. The maintenance of reactive astrocytes many months after lesioning suggests the existence of cellular factors other than those produced by damaged nbM neurons. Taking into account the role of glial cells under pathological conditions, it is possible that these reactive astrocytes in humans could promote neurodegenerative processes, such as amyloid plaque formation and neurodegeneration (Alzheimer's disease). Along this line, nbM cholinergic involution could then originate cortical involution through induced reactive astrocytosis.

The human astrocytoma cell line U373MG produces monocyte chemotactic protein (MCP)-1 upon stimulation with beta-amyloid protein

Astrocytes associated with beta-amyloid (Abeta) accumulate in senile plaques of Alzheimer's disease (AD). To investigate the biological effects of Abeta/astrocyte interaction, we examined chemokine production by the human astrocytoma cell line U373MG stimulated with Abeta peptides. Northern blot analysis and specific immunoassays demonstrate that Abeta [1-42] and Abeta [25-35] induce mRNA expression and release of monocyte chemotactic protein (MCP)-1 but not of gamma-interferon inducible protein (IP)-10 by U373MG cells. The observation that Abeta induces astrocyte production of the potent microglia chemoattractant MCP-1 contributes to understanding mechanism of damage exerted by Abeta in AD senile plaques.

Neuronal expression of glutamine synthetase in Alzheimer's disease indicates a profound impairment of metabolic interactions with astrocytes

A considerable body of evidence indicates that the activity of glutamine synthetase is decreased in the cerebral cortices of brains affected by Alzheimer's disease. It is difficult to discern the reason for this decrease because it is not known whether the cellular distribution of glutamine synthetase is altered in Alzheimer's disease. Therefore the present study has used immunocytochemistry to compare the cellular distributions of glutamine synthetase in the inferior temporal cortices of six Alzheimer's diseased brains and six age-matched, non-demented brains. Double-label immunocytochemistry has been used to examine whether the distribution of cellular glutamine synthetase is influenced by the distribution of senile plaques. It was found that glutamine synthetase expression in astrocytes is diminished in Alzheimer's disease, particularly in the vicinity of senile plaques. The most striking finding of the present study was that glutamine synthetase was expressed in a subpopulation of pyramidal neurons in all six Alzheimer's diseased brains, whereas glutamine synthetase was not observed in any neurons from control brains. The changed expression of glutamine synthetase may be triggered by toxic agents in senile plaques, a reduced noradrenergic supply to the cerebral cortex, and increased brain ammonia levels. That such dramatic changes occur in the distribution of this critical, and normally stable enzyme, suggests that the glutamate-glutamine cycle is profoundly impaired in Alzheimer's disease. This is significant because impairments of the glutamate-glutamine cycle are known to cause alterations of mood and behaviour, disturbance of sleeping patterns, amnesia, confusion and reduced awareness. Since these behavioural changes are also seen in Alzheimer's disease, it is speculated that they might be attributable to the reduced expression of glutamine synthetase or to impairments of the glutamate-glutamine cycle.

Roles of A beta and carboxyl terminal peptide fragments of amyloid precursor protein in Alzheimer disease

Several lines of evidence indicate that A beta may play an important role in the pathogenesis of AD. However, there are several discrepancies between the production of A beta and the development of the disease. Thus, A beta may not be the sole active fragment of beta-amyloid precursor protein (betaAPP) in the neurotoxicity assiciated with AD. We focused on the amyloidegenic carboxyl terminal fragments of betaAPP containing the full length of A beta (CT105). We synthesized a recombinant carboxyl-terminal 105 amino acid fragment of betaAPP and examined the effects of CT105 and A beta on cultured neurons, Ca++ uptake into rat brain microsomes, Na+-Ca++ exchange activity, ion channel forming activity in lipid bilayers and passive avoidance performance of mice. Our results suggest that the cytotoxic and channel inducing effects of CT105 are much more potent than that of A beta and toxic mechanisms of CT105 are different from those of A beta. Taken together, these lines of evidence postulate that CT is an alternative toxic element important in the generation of the symptoms common to AD.

Astrocytes, oligodendroglia, extracellular space volume and geometry in rat fetal brain grafts

Fetal neocortex or tectum transplanted to the midbrain or cortex of newborn rats develops various degrees of gliosis, i.e. increased numbers of hypertrophied, glial fibrillary acidic protein-positive astrocytes. In addition, there were patches or bundles of myelinated fibres positive for the oligodendrocyte and central myelin marker Rip, and increased levels of extracellular matrix molecules. Three diffusion parameters--extracellular space volume fraction alpha (alpha = extracellular volume/total tissue volume), tortuosity lambda (lambda = square root(D/ADC), where D is the free and ADC is the apparent tetramethylammonium diffusion coefficient) and non-specific uptake k'--were determined in vivo from extracellular concentration-time profiles of tetramethylammonium. Grafts were subsequently processed immunohistochemically to compare diffusion measurements with graft morphology. Comparisons were made between the diffusion parameters of host cortex and corpus callosum, fetal cortical or tectal tissue transplanted to host midbrain ("C- and T-grafts") and fetal cortical tissue transplanted to host cortex ("cortex-to-cortex" or C-C-grafts). In host cortex, alpha ranged from 0.20 +/- 0.01 (layer V) to 0.21 +/- 0.01 (layers III, IV and VI) and lambda from 1.59 +/- 0.03 (layer VI) to 1.64 +/- 0.02 (layer III) (mean +/- S.E.M., n = 15). Much higher values were found in "young" C-grafts (81-150 days post-transplantation), where alpha = 0.34 +/- 0.01 and lambda = 1.78 +/- 0.03 (n = 13), as well as in T-grafts, where alpha = 0.29 +/- 0.02 and lambda = 1.85 +/- 0.04 (n = 7). Further analysis revealed that diffusion in grafts was anisotropic and more hindered than in host cortex. The heterogeneity of diffusion parameters correlated with the structural heterogeneity of the neuropil, with the highest values of alpha in gray matter and the highest values of lambda in white matter bundles. Compared to "young" C-grafts, in "old" C-grafts (one year post-transplantation) both alpha and lambda were significantly lower, and there was a clear decrease in glial fibrillary acidic protein immunoreactivity throughout the grafted tissue. In C-C-grafts, alpha and lambda varied with the degree of graft incorporation into host tissue, but on average they were significantly lower (alpha = 0.24 +/- 0.01 and lambda = 1.66 +/- 0.02, n = 8) than in young C- and T-grafts. Well-incorporated grafts revealed less astrogliosis, and alpha and lambda values were not significantly higher than those in normal host cortex. The observed changes in extracellular space diffusion parameters could affect the movement and accumulation of neuroactive substances and thus impact upon neuron-glia communication, synaptic and extrasynaptic transmission in the grafts. The potential relevance of these observations to human neuropathological conditions associated with acute or chronic astrogliosis is considered.

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.

Activated isoforms of MMP-2 are induced in U87 human glioma cells in response to beta-amyloid peptide

Prior studies using rat primary hippocampal cultures indicated induction of matrix metalloproteinases (MMPs) in response to beta-amyloid (A beta). Hence, it was of interest to determine whether MMP activity in a human cell line is influenced by A beta. A beta, but not interleukin-1beta (IL-1beta) or lipopolysaccharide (LPS), stimulated an active form of MMP-2 in human U87 glioblastoma cells, as well as increased the expression of the well-known activator of MMP-2, membrane-type (MT)-MMP. Activation experiments carried out with amino phenyl mercuric acetate (APMA), immunoprecipitation, as well as immunoblotting, suggest that the lower molecular weight, gelatin-degrading activity was an activated form of MMP-2. Furthermore, it was demonstrated that a synthetic furin convertase inhibitor, decanoyl-Arg-Val-Lys-Arg-chloromethylketone, decreased the production of A beta-induced active MMP-2 in U87 cells. The induction of MMP-3 by cytokines, but not by A beta, suggests that the effect of A beta on MMP-2 is selective. Although A beta stimulated tissue inhibitor of metalloproteinase-1 (TIMP-1), there was no obvious effect of A beta on TIMP-2 production in U87 cells. These results demonstrate that A beta induces an active form of MMP-2 likely by increasing the expression of MT-MMP in a human glioblastoma cell line. Active MMP-2 may degrade A beta or act on ECM components critical in neuronal survival mechanisms and possibly play a role in Alzheimer's disease (AD) neuropathology.

The long term adenoviral expression of the human amyloid precursor protein shows different secretase activities in rat cortical neurons and astrocytes

Recombinant adenoviruses were used for the expression of human amyloid precursor protein (APP) of Alzheimer's disease in primary cultures of rat cortical neurons and astrocytes. The catabolic pathways of human APP were studied 3 to 4 days after infection, when the equilibrium of APP production was reached. Although the expression of human wild type APP (WtAPP) by rat neurons induced the production of both extracellular and intraneuronal amyloid peptide (Abeta), Abeta was not detected in the culture medium of rat astrocytes producing human WtAPP. Because a low beta-secretase activity was previously reported in rodent astrocytes, we wondered whether modifications of the APP amino acid sequence at the beta-secretase clipping site would modify the astrocytic production of Abeta. Interestingly, rat astrocytes produced high amounts of Abeta after expression of human APP carrying a double amino acid substitution responsible for Alzheimer's disease in a large Swedish family (SwAPP). In both rat cortical neurons and astrocytes, the beta-secretase cleavage of the human SwAPP occurred very early in the secretion process in a cellular compartment in which a different sorting of SwAPP and WtAPP seems unlikely. These results suggest that human WtAPP and SwAPP could be processed by different beta-secretase activities.

Glial reaction in aging and Alzheimer's disease

It is well-established that glial cells play an important role during injury and neurodegenerative processes in the central nervous system. In normal aging, no global glia proliferation is found morphologically, but reactive gliosis has been described in specific areas of the limbic system and neocortex that undergo selective neuronal or synaptic degeneration in nondemented elderly persons. In addition, there is an age-associated increase in the metabolic turnover of cellular proteins, such as glial fibrillary acidic protein, in human brain tissue, even without detectable signs of neurodegeneration. In contrast to the relatively moderate overall glial changes in normal aging, the close association of activated astrocytes and microglial cells with neuritic plaques and cells undergoing neurofibrillary degeneration in Alzheimer's disease (AD), the expression of receptors for complement by glial cells, and the release of soluble cytokines strongly suggest that inflammatory processes may play an important part in the complex pathophysiological interactions that occur in AD. Understanding the role of glia in age-associated neurodegenerative disorders may provide new insights into the neurobiology of glia-neuronal interaction and may allow the development of strategies to alter the disease process. This review aims to summarize some of the important aspects of glial cells in aging and dementia.

Brain injury and growth inhibitory factor (GIF)--a minireview

Growth inhibitory factor (GIF) is a small (7 kDa), heat-stable, acidic, hydrophilic metallothionein (MT)-like protein. GIF inhibits the neurotrophic activity in Alzheimer's disease (AD) brain extracts on neonatal rat cortical neurons in culture. GIF has been shown to be drastically reduced and down-regulated in AD brains. In neurodegenerative diseases in humans, GIF expression levels are reduced whereas GFAP expression levels are markedly induced in reactive astrocytes. Both GIF and GIF mRNA are present at high levels in reactive astrocytes following acute experimental brain injury. In chronological observations the level of GIF was found to increase more slowly and remain elevated for longer periods than that of glial fibrillary acidic protein (GFAP). These differential patterns and distribution of GIF and GFAP seem to be important in understanding the mechanism of brain tissue repair. The most important point concerning GIF in AD is not simply the decrease in the level of expression throughout the brain, but the drastic decrease in the level of expression in reactive astrocytes around senile plaques in AD. Although what makes the level of GIF decrease drastically in reactive astrocytes in AD is still unknown, supplements of GIF may be effective for AD, based on a review of current evidence. The processes of tissue repair following acute brain injury are considered to be different from those in AD from the viewpoint of reactive astrocytes.

Interaction of presenilins with the filamin family of actin-binding proteins

Mutations in presenilin genes PS1 and PS2 account for approximately 50% of early-onset familial Alzheimer's disease (FAD). The PS1 and PS2 genes encode highly homologous transmembrane proteins related to the Caenorhabditis elegans sel-12 and spe-4 gene products. A hydrophilic loop region facing the cytoplasmic compartment is likely to be functionally important because at least 14 mutations in FAD patients have been identified in this region. We report here that the loop regions of PS1 and PS2 interact with nonmuscle filamin (actin-binding protein 280, ABP280) and a structurally related protein (filamin homolog 1, Fh1). Overexpression of PS1 appears to modify the distribution of ABP280 and Fh1 proteins in cultured cells. A monoclonal antibody recognizing ABP280 and Fh1 binds to blood vessels, astrocytes, neurofibrillary tangles, neuropil threads, and dystrophic neurites in the AD brain. Detection of ABP280/Fh1 proteins in these structures suggests that these presenilin-interacting proteins may be involved in the development of AD and that interactions between presenilins and ABP280/Fh1 may be functionally significant. The ABP280 gene is located on the human X chromosome, whereas the newly identified Fh1 gene maps to human chromosome 3. These results provide a new basis for understanding the function of presenilin proteins and further implicate cytoskeletal elements in AD pathogenesis.

Astrocytes regulate microglial phagocytosis of senile plaque cores of Alzheimer's disease

We have developed an in vitro model in which isolated senile plaque (SP) cores are presented to rat microglial cells in culture. Microglia rapidly phagocytosed, broke apart, and cleared SP cores. However, when cocultured with astrocytes, microglial phagocytosis was markedly suppressed, allowing the SPs to persist. Suppression of phagocytosis by astrocytes appears to be a general phenomena since microglia in the presence of astrocytes showed reduced capacity to phagocytose latex beads as well. The astrocyte effect on microglia is related in part to a diffusible factor(s) since astrocyte- but not fibroblast-conditioned media also reduced phagocytosis. These results suggest that while microglia have the capacity to phagocytose and remove SPs, astrocytes which lie in close association to microglia may help prevent the efficient clearance of SP material allowing them to persist in Alzheimer's disease.

Effect of a carboxy-terminal fragment of the Alzheimer's amyloid precursor protein on expression of proinflammatory cytokines in rat glial cells

To explore factors involved in the induction of cytokines that may contribute to the pathogenesis of Alzheimer's disease (AD), the effect of a carboxy terminal 105 amino acid fragment (CT105) of the amyloid precursor protein (APP) on the gene expression of proinflammatory cytokines, IL-1beta and IL-6 was determined in cultured rat cortical glial cells in comparision to amyloid beta protein (A beta). Cells were incubated with 1 microM of insoluble CT105 aggregates or aged A beta1-40 peptide deposits which were mainly composed of stable monomeric and dimeric forms as assessed on Western blots. The levels of mRNAs were analyzed by reverse transcription polymerase chain reaction (RT-PCR). Highest levels of both IL-1beta and IL-6 transcripts were detected in the culture exposed to CT105 aggregates for 4 days. CT105 aggregates markedly increased IL-1beta mRNA level by 3.5 fold of the control level and this effect was more potent than that produced by aged A beta1-40 peptides. Furthermore, CT105 strongly induced accumulation of IL-6 mRNA level by 2 fold of the value potentiated by A beta1-40. Such induction was not observed with A beta 12-28 treatment. On the other hand, CT105 did not significantly alter either APP or glial fibrillary acidic protein (GFAP) mRNA levels. These results together imply that CT peptide besides its cytotoxic potency may act as a potent immunological component, strongly inducing both IL-1beta and IL-6 mRNA levels in the cultured glial cells. This CT peptide associated exacerbation of cytokine expression may be in part responsible for chronic inflammation linked to slowly progressive neurodegeneration characteristic to AD.

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.

Perivascular astrocytes within Alzheimer's disease plaques

The association of astrocytes with plaques is a well-established feature of Alzheimer's disease (AD) and has generally been interpreted as a secondary reaction to amyloid deposition or neuronal degeneration. Astrocytes in brain tissue from six non-demented controls and six patients with AD were investigated using enhanced immunohistochemistry for glial fibrillary acid protein (GFAP) in serial sections from cortex, basal forebrain, amygdala, putamen and diencephalon. Astrocytes colocalized with all diffuse and non-diffuse plaques in AD and control brain tissue. All plaque-associated astrocytes contacted microvessels, and despite having greater numbers of hypertrophic and fine calibre processes, the cells maintained the perivascular arrangement characteristic of control brain tissue. These observations suggest that plaques form at the site of microvascular aberrations followed by reactive and degenerative changes in perivascular astrocytes.

Nitric oxide synthase in reactive astrocytes adjacent to beta-amyloid plaques

This study provides the first evidence that nitric oxide is released by astrocytes surrounding beta-amyloid plaques. Nitric oxide is involved in many neuropathological conditions and can have either a neuroprotective or a neurotoxic function depending on its concentration and the redox state of the tissue. It is produced by the enzyme nitric oxide synthase, which can be located by a simple histochemical technique for demonstrating NADPH diaphorase. Using this method we examined tissue from 10 brains where there were varying numbers of beta-amyloid plaques in the cerebral cortex. In the 6 brains with moderate or high densities of plaques, primitive and cored plaques were associated with between 1 and 10 reactive astrocytes that contained NADPH diaphorase or were immunoreactive for the inducible form of nitric oxide synthase. In the 4 brains which had only low densities of plaques, the plaques were not associated with diaphorase-containing astrocytes. The percentage of plaques associated with 1 or more NADPH diaphorase-containing astrocyte varied between 1 and 21% and was correlated with the density of plaques. Astrocytes were the only form of NADPH diaphorase-positive glial cell associated with the plaques. There was no evidence of any nitric oxide synthase occurring in microglia.

Amyloid deposition is associated with c-Jun expression in Alzheimer's disease and amyloid angiopathy

Since the PAD gene (also called promoter of Alzheimer's disease amyloid A4 precursor gene or amyloid beta-protein precursor promoter) has two AP-1 consensus sequences, and members of the Fos and Jun families are the major components of the transcription factor activator protein-1 (AP-1), we have investigated the localization of c-Fos and c-Jun immunoreactivity and its relationship to beta-amyloid deposition in the brains of patients with Alzheimer's disease and amyloid angiopathy. c-Jun, but not c-Fos, immunoreactivity is observed in the muscular layer of meningeal and cerebral blood vessels with amyloid angiopathy, and in the soma of glial cells and cellular processes of unknown origin surrounding beta-amyloid deposits in the brain. These results show that c-Jun may participate in the cascade of events leading to increased beta-APP (beta-amyloid precursor protein) production and beta-amyloid deposition in the brains of patients with Alzheimer's disease and amyloid angiopathy.

beta-Amyloid converts an acute phase injury response to chronic injury responses

As the brain ages, amyloid deposits accumulate and, as these deposits condense into a beta-sheet conformation, they contribute to the organization of cellular responses and maintain a chronic level of stimulation and injury. Furthermore, accompanying reactions can lead to the production of additional beta-amyloid, the build up of additional fibrillar beta-amyloid, and prolongation of the response. As it accumulates, beta-amyloid appears to develop properties that drive many signal transduction processes in the classic injury cascade and also activate complement, which results in an amplified beta-amyloid AD cascade. In this way several mechanisms, although apparently independent, proceed in parallel, reinforce each other, and perpetuate pathology and structural damage to the brain. Specifically, we suggest that via the activation of complement, initiation, and perpetuation of other cascades, and its own direct toxic actions, beta-amyloid converts an acute response to injury into a chronic damaging inflammatory reaction thereby contributing to neuronal dysfunction and degeneration.

Amyloid in Alzheimer's disease and prion-related encephalopathies: studies with synthetic peptides

Deposition of amyloid-beta protein (beta A) in brain parenchyma and vessel walls is a major pathological feature of Alzheimer's disease (AD). In prion-related encephalopathies (PRE), too, an altered form of prion protein (PrPsc) forms amyloid fibrils and accumulates in the brain. In both conditions the amyloid deposition is accompanied by nerve cell loss, whose pathogenesis and molecular basis are not understood. Neuropathological, genetic and biochemical studies indicate a central role of beta A in the AD pathogenesis. Synthetic peptides homologous to beta A and its fragments contribute to investigate the mechanisms of beta A deposit formation and the role played by beta A in AD pathogenesis. The physicochemical studies on the beta-sheet conformation and self-aggregation properties of beta A peptides indicate the conditions and the factors influencing the formation of beta A deposits. The neurotoxic activity of beta A and its fragments support the causal relationship between beta A deposits and the neuropathological events in AD. Numerous studies were performed to clarify the mechanism of neuronal death induced by exposure to beta A peptides. A similar approach has been used to investigate the role of PrPsc in PRE; in these diseases, the association between accumulation of PrPsc and neuropathology is evident and numerous data indicate that PrPsc itself might be the infectious agent responsible for disease transmission. Thus, PrP peptides were used to investigate the pathogenic role of PrPsc in PRE and the conformational change responsible for the conversion PrPc to PrPsc that makes the molecule apparently infectious. In particular, we synthesized a peptide homologous to residues 106-126, an integral part of all abnormal PrP isoforms that accumulate in the brain of subjects' PRE. This peptide is fibrillogenic, has secondary structure largely composed of beta-sheet and proteinase-resistant properties, is neurotoxic and induces astrogliosis. In this review, we summarize and compare the data obtained with beta A and PrP peptides and analyze the significance in terms of amyloidogenic proteins and neurodegeneration.

Diffuse plaques contain C-terminal A beta 42 and not A beta 40: evidence from cats and dogs

Recent reports have suggested that beta-amyloid (A beta) species of variable length C-termini are differentially deposited within early and late-stage plaques and the cerebrovasculature. Specifically, longer C-terminal length A beta 42/3 fragments (i.e., A beta forms extending to residues 42 and/or 43) are thought to be predominant within diffuse plaques while both A beta 42/3 and A beta 40 (A beta forms terminating at residue 40) are present within a subset of neuritic plaques and cerebrovascular deposits. We sought to clarify the issue of differential A beta deposition using aged canines, a partial animal model of Alzheimer's disease that exhibits extensive diffuse plaques and frequent vascular amyloid, but does not contain neuritic plaques or neurofibrillary tangles. We examined the brains of 20 aged canines, 3 aged felines, and 17 humans for the presence of A beta immunoreactive plaques, using antibodies to A beta 1(-17), A beta 17(-24), A beta 1(-28), A beta 40, and A beta 42. We report that plaques within the canine and feline brain are immunopositive for A beta 42 but not A beta 40. This is the first observation of nascent AD pathology in the aged feline brain. Canine plaques also contained epitopes within A beta 1(-17), A beta 17(-24), and A beta 1(-28). In all species examined, vascular deposits were immunopositive for both A beta 40 and A beta 42. In the human brain, diffuse plaques were preferentially A beta 42 immunopositive, while neuritic plaques and vascular deposits were both A beta 40 and A beta 42 immunopositive. However, not all neuritic plaques contain A beta 40 epitopes.

The canine as an animal model of human aging and dementia

The aged canine displays many features that make it an excellent model for studying the progression of pathology in brain aging and linking these findings to learning, memory and other cognitive functions. Canines develop extensive beta-amyloid deposition within neurons and their synaptic fields, which appears to give rise to senile plaques. These plaques are primarily of the early diffuse subtype. Aged canines also exhibit accumulations of lipofuscin, cerebral vascular changes, dilation of the ventricles, and cytoskeletal changes. Neurofibrillary tangles (NFTs) are not present in the aged canine. Thus, the aged canine brain provides a suitable model for studying early degeneration normally considered to be pre-Alzheimer's. This supposition is also supported by behavioral data. We have found that the extent of beta-amyloid deposition correlates with a decline in select measures of cognitive function. These data provide the first evidence of a correlation between beta-amyloid accumulation and cognitive decline in the absence of NFTs. We summarize four lines of evidence that support using the aged canine as a model of human aging: (a) Aged canines develop aspects of neuropathology similar to that observed in aged humans; (b) Veterinarians have observed that many canines exhibit a clinical syndrome of age-related cognitive dysfunction; (c) Aged canines are deficient on a variety of neuropsychological tests of cognitive function; (d) The level of beta-amyloid accumulation correlates with cognitive dysfunction in the canine. These data indicate that the aged canine is a particularly useful model for studying age-related cognitive dysfunction (ARCD), early neuronal changes associated with aging, and the initial stages of senile plaque formation.

Immunoreactivity for Bcl-2 protein within neurons in the Alzheimer's disease brain increases with disease severity

Bcl-2 protein has been suggested to be one of the proteins preventing apoptosis in a variety of cell types. Recently, apoptosis has been suggested to have an important role in the pathogenesis of Alzheimer's disease (AD). We have utilized Bcl-2 immunohistochemical methods to examine Bcl-2 in the hippocampus and entorhinal cortex of AD patients ranging in clinical and neuropathological severity from mild to severe and compared these results to those obtained from age-matched controls. Immunoreactivity for Bcl-2 was predominantly found within neurons. Bcl-2 immunostaining within AD tissue was increased relative to controls in most neurons of the entorhinal cortex, subiculum, CA1, CA2, CA3, hilus and dentate gyrus. Relative Bcl-2 staining increased in parallel with increasing disease severity. However, neurons exhibiting immunoreactivity for markers of neurofibrillary tangle formation (AT8 and PHF-1) showed reduced Bcl-2 staining, suggesting that Bcl-2 may be down regulated in these degenerating neurons. Bcl-2 immunoreactivity within astrocytes and the vasculature was also increased in AD. These results suggest that Bcl-2 protein may have a role in compensation responses to AD pathology, perhaps affording to the remaining neurons a margin of protection from apoptosis.