Expression of small heat-shock protein hsp 27 in reactive gliosis in Alzheimer disease and other types of dementia

Immunohistochemical and immunoblotting analysis of brain tissue of Alzheimer's disease (AD) patients showed highly induced expression of the small heat-shock protein hsp 27 in affected cortex. Expression of hsp 27 was present in a large number of proliferating astrocytes. The highest expression was exhibited by degenerative astrocytes in the areas rich in senile plaques. Neurofibrillary tangles, Hirano bodies and some hippocampal neurons were also positive. Expression of hsp 27 increased with the severity of AD-specific morphological changes, and with the duration of dementia. In control brains immunoreaction was restricted to the vessels and to occasional astrocytes in the white matter. Similar patterns of immunoreactivity were present in cases without dementia (Parkinson disease, lacunar state, or focal ischemic necrosis). Patients suffering from other types of dementia (Parkinson/dementia complex, multi-infarct dementia, normal pressure hydrocephalus) showed less expression of hsp 27 in reactive astrocytes than AD, but more than controls. These results indicate that increased expression of hsp 27, especially in astrocytes showing klazmatodendrosis, is associated with AD pathology.Supported by a fellowship of the Royal Netherlands Academy of Arts and Sciences     

Astrocytes accumulate A beta 42 and give rise to astrocytic amyloid plaques in Alzheimer disease brains

beta-Amyloid(1-42) (A beta 42), a major component of amyloid plaques, accumulates within pyramidal neurons in the brains of individuals with Alzheimer's disease (AD) and Down syndrome. In brain areas exhibiting AD pathology, A beta 42-immunopositive material is observed in astrocytes. In the present study, single- and double-label immunohistochemistry were used to reveal the origin and fate of this material in astrocytes. Our findings suggest that astrocytes throughout the entorhinal cortex of AD patients gradually accumulate A beta 42-positive material and that the amount of this material correlates positively with the extent of local AD pathology. A beta 42-positive material within astrocytes appears to be of neuronal origin, most likely accumulated via phagocytosis of local degenerated dendrites and synapses, especially in the cortical molecular layer. The co-localization of neuron-specific proteins, alpha 7 nicotinic acetylcholine receptor and choline acetyltransferase, in A beta 42-burdened, activated astrocytes supports this possibility. Our results also suggest that some astrocytes containing A beta 42-positive deposits undergo lysis, resulting in the formation of astrocyte-derived amyloid plaques in the cortical molecular layer in brain regions showing moderate to advanced AD pathology. These astrocytic plaques can be distinguished from those arising from neuronal lysis by virtue of their smaller size, their nearly exclusive localization in the subpial portion of the molecular layer of the cerebrocortex, and by their intense glial fibrillary acidic protein immunoreactivity. Overall, A beta 42 accumulation and the selective lysis of A beta 42-burdened neurons and astrocytes appear to make a major contribution to the observed amyloid plaques in AD brains.     

Neuronal and nonneuronal quantitative BACE immunocytochemical expression in the entorhinohippocampal and frontal regions in Alzheimer's disease

In this study, we quantitatively investigated the expression of beta-site amyloid precursor protein cleaving enzyme (BACE) in the entorhinohippocampal and frontal cortex of Alzheimer's disease (AD) and old control subjects. The semiquantitative estimation indicated that the intensity of BACE overall immunoreactivity did not differ significantly between AD and controls, but that a significantly stronger staining was observed in the hippocampal regions CA3-4 compared to other regions in both AD patients and controls. The quantitative estimation confirmed that the number of BACE-positive neuronal profiles was not significantly decreased in AD. However, some degeneration of BACE-positive profiles was attested by the colocalization of neurons expressing BACE and exhibiting neurofibrillary tangles (NFT), as well as by a decrease in the surface area of BACE-positive profiles. In addition, BACE immunocytochemical expression was observed in and around senile plaques (SP), as well as in reactive astrocytes. BACE-immunoreactive astrocytes were localized in the vicinity or close to the plaques and their number was significantly increased in AD entorhinal cortex. The higher amount of beta-amyloid SP and NFT in AD was not correlated with an increase in BACE immunoreactivity. Taken together, these data accent that AD progression does not require an increased neuronal BACE protein level, but suggest an active role of BACE in immunoreactive astrocytes. Moreover, the strong expression in controls and regions less vulnerable to AD puts forward the probable existence of alternate BACE functions.     

Defined astrocytic expression of human amyloid precursor protein in Tg2576 mouse brain

Transgenic Tg2576 mice expressing human amyloid precursor protein (hAPP) with the Swedish mutation are among the most frequently used animal models to study the amyloid pathology related to Alzheimer's disease (AD). The transgene expression in this model is considered to be neuron-specific. Using a novel hAPP-specific antibody in combination with cell type-specific markers for double immunofluorescent labelings and laser scanning microscopy, we here report that—in addition to neurons throughout the brain—astrocytes in the corpus callosum and to a lesser extent in neocortex express hAPP. This astrocytic hAPP expression is already detectable in young Tg2576 mice before the onset of amyloid pathology and still present in aged Tg2576 mice with robust amyloid pathology in neocortex, hippocampus, and corpus callosum. Surprisingly, hAPP immunoreactivity in cortex is restricted to resting astrocytes distant from amyloid plaques but absent from reactive astrocytes in close proximity to amyloid plaques. In contrast, neither microglial cells nor oligodendrocytes of young or aged Tg2576 mice display hAPP labeling. The astrocytic expression of hAPP is substantiated by the analyses of hAPP mRNA and protein expression in primary cultures derived from Tg2576 offspring. We conclude that astrocytes, in particular in corpus callosum, may contribute to amyloid pathology in Tg2576 mice and thus mimic this aspect of AD pathology.     

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

The fibrillar β-amyloid protein (Aβ) Plaques of Alzheimer's disease (AD) are associated with reactive astrocytes and dystrophic neurites and have been suggested to contribute to neurodegenerative events in the disease. We recently reported parallel in vitro and in situ findings, suggesting that the adoption of a reactive phenotype and the colocalization of astrocytes with plaques in AD may be mediated in large part by aggregated Aβ. Thus, Aβ-mediated effects on astrocytes may directly affect disease progression by modifying the degenerative plaque environment. Alternatively, plaque-associated reactive astrocytosis may primarily represent a glial response to the neural injury associated with plaques and not significantly contribute to AD pathology. To investigate the validity of these two positions, we examined the differential colocalization of reactive astrocytes and dystrophic neurites with plaques. Hippocampal sections from AD brains—ranging in neuropathology from mild to severe—were triple-labeled with antibodies recognizing Aβ protein, reactive astrocytes, and dystrophic neurites. We observed not only plaques containing both or neither cell type, but also plaques containing (1) reactive astrocytes but not dystrophic neurites and (2) dystrophic neurites but not reactive astrocytes. The relative proportion of plaques colocalized with reactive astrocytes in the absence of dystrophic neurites is relatively high in mild AD but significantly decreases over the course of the disease, suggesting that plaque-associated astrocytosis may be an early and perhaps contributory event in AD pathology rather than merely a response to neuronal injury. These data underscore the potentially significant contributions of reactive astrocytosis in modifying the plaque environment in particular and disease progression in general.     

Expression of microsomal epoxide hydrolase is elevated in Alzheimer's hippocampus and induced by exogenous beta-amyloid and trimethyl-tin

The brain is a potential target for drugs and environmental toxins. Microsomal epoxide hydrolase (mEH) is one of several critical biotransformation enzymes in xenobiotic metabolism and detoxification. In the present study, we report that the expression of mEH is significantly elevated in the hippocampus and associated cortex, but not in the cerebellum, in Alzheimer's disease (AD) patients. A large proportion of the mEH-positive cells are located around beta-amyloid plaques. The mEH-positive-staining cells are astrocytes and pyramidal neurons. Western blotting analysis confirmed increased expression of mEH in AD hippocampal tissues. In primary hippocampal glial culture, beta-amyloid aggregation stimulated mEH expression in the astrocytes, which displayed a patchy distribution. An environmental neurotoxic agent, trimethyl-tin, also activated mEH expression in rat hippocampus and entorhinal cortex. The present study demonstrates a significant increase in mEH expression in the AD hippocampus, a region showing abundant neuropathology in AD. The expression of mEH could also be elevated by exposure to exogenous beta-amyloid in vitro and environmental toxins in vivo. Our studies suggest that mEH may play a role in pathogenesis of neurodegeneration in response to environmental stress.     

Accumulation of a repulsive axonal guidance molecule RGMa in amyloid plaques: a possible hallmark of regenerative failure in Alzheimer's disease brains

J. Satoh, H. Tabunoki, T. Ishida, Y. Saito and K. Arima (2013) Neuropathology and Applied Neurobiology 39, 109–120 Accumulation of a repulsive axonal guidance molecule RGMa in amyloid plaques: a possible hallmark of regenerative failure in Alzheimer's disease brains Aims: RGMa is a repulsive guidance molecule that induces the collapse of axonal growth cones by interacting with the receptor neogenin in the central nervous system during development. It remains unknown whether RGMa plays a role in the neurodegenerative process of Alzheimer's disease (AD). We hypothesize that RGMa, if it is concentrated on amyloid plaques, might contribute to a regenerative failure of degenerating axons in AD brains. Methods: By immunohistochemistry, we studied RGMa and neogenin (NEO1) expression in the frontal cortex and the hippocampus of 6 AD and 12 control cases. The levels of RGMa expression were determined by qRT‐PCR and Western blot in cultured human astrocytes following exposure to cytokines and amyloid beta (Aβ) peptides. Results: In AD brains, an intense RGMa immunoreactivity was identified on amyloid plaques and in the glial scar. In the control brains, the glial scar and vascular foot processes of astrocytes expressed RGMa immunoreactivity, while oligodendrocytes and microglia were negative for RGMa. In AD brains, a small subset of amyloid plaques expressed a weak NEO1 immunoreactivity, while some reactive astrocytes in both AD and control brains showed an intense NEO1 immunoreactivity. In human astrocytes, transforming growth factor beta‐1 (TGFβ₁), Aβ_1–40 or Aβ_1–42 markedly elevated the levels of RGMa, and TGFβ₁ also increased its own levels. Coimmunoprecipitation analysis validated the molecular interaction between RGMa and the C‐terminal fragment β of amyloid beta precursor protein (APP). Furthermore, recombinant RGMa protein interacted with amyloid plaques in situ. Conclusions: RGMa, produced by TGFβ‐activated astrocytes and accumulated in amyloid plaques and the glial scar, could contribute to the regenerative failure of degenerating axons in AD brains.     

Reduced expression of NO-sensitive guanylyl cyclase in reactive astrocytes of Alzheimer disease, Creutzfeldt-Jakob disease, and multiple sclerosis brains

In Alzheimer's disease (AD) brains increased NO synthase (NOS) expression is found in reactive astrocytes surrounding amyloid plaques. We have recently shown that treatment with beta-amyloid peptides or IL-1beta down-regulates NO-sensitive soluble guanylyl cyclase (sGC) in cultured astrocytes and in adult rat brain. In this work, we have examined sGC activity and expression in postmortem brain tissue of AD patients and matched controls. No significant alteration was observed in basal or NO-stimulated sGC activity, nor in sGC beta1 and alpha1 subunit levels in cortical extracts of AD brains. Immunohistochemistry showed intense and widespread labeling of sGC beta1 in cortical and hippocampal neurons and white matter fibrillar astrocytes, while grey matter astrocytes were faintly stained. In AD, expression of sGC in neurons and fibrillar astrocytes is not altered but is markedly reduced in reactive astrocytes surrounding amyloid plaques. Immunostaining for sGC beta1 was also lacking in reactive astrocytes in cortex and subcortical white matter in Creutzfeldt-Jakob disease brains and in subacute and chronic plaques in multiple sclerosis (MS) brains. Thus, induction of astrocyte reactivity is associated with decreased capacity to generate cGMP in response to NO both in vitro and in vivo. This effect may be related to the development of the astroglial inflammatory response.     

Ryanodine receptor-mediated [Ca(2+)](i) release in glomus cells is independent of natural stimuli and does not participate in the chemosensory responses of the rat carotid body

Advanced glycation endproducts (AGEs), protein-bound oxidation products of sugars, have been shown to be involved in the pathophysiological processes of Alzheimer’s disease (AD). AGEs induce the expression of various pro-inflammatory cytokines and the inducible nitric oxide synthase (iNOS) leading to a state of oxidative stress. AGE modification and resulting crosslinking of protein deposits such as amyloid plaques may contribute to the oxidative stress occurring in AD. The aim of this study was to immunohistochemically compare the localization of AGEs and β-amyloid (Aβ) with iNOS in the temporal cortex (Area 22) of normal and AD brains. In aged normal individuals as well as early stage AD brains (i.e. no pathological findings in isocortical areas), a few astrocytes showed co-localization of AGE and iNOS in the upper neuronal layers, compared with no astrocytes detected in young controls. In late AD brains, there was a much denser accumulation of astrocytes co-localized with AGE and iNOS in the deeper and particularly upper neuronal layers. Also, numerous neurons with diffuse AGE but not iNOS reactivity and some AGE and iNOS-positive microglia were demonstrated, compared with only a few AGE-reactive neurons and no microglia in controls. Finally, astrocytes co-localized with AGE and iNOS as well as AGE and were found surrounding mature but not diffuse amyloid plaques in the AD brain. Our results show that AGE-positive astrocytes and microglia in the AD brain express iNOS and support the evidence of an AGE-induced oxidative stress occurring in the vicinity of the characteristic lesions of AD. Hence activation of microglia and astrocytes by AGEs with subsequent oxidative stress and cytokine release may be an important progression factor in AD.     

Cyclooxygenase expression in microglia and neurons in Alzheimer's disease and control brain

Epidemiological studies suggest that non-steroidal anti-inflammatory drugs (NSAIDs) lower the risk of developing Alzheimer's disease (AD). Most NSAIDs act upon local inflammatory events by inhibiting the expression or activation of cylooxygenase (COX). In the present study the expression of COX-1 and COX-2 in AD and non-demented control temporal and frontal cortex was investigated using immunohistochemistry. COX-1 expression was detected in microglial cells, while COX-2 expression was found in neuronal cells. In AD brains, COX-1-positive microglial cells were primarily associated with amyloid beta plaques, while the number of COX-2-positive neurons was increased compared to that in control brains. No COX expression was detected in astrocytes. In vitro, primary human microglial and astrocyte cultures, and human neuroblastoma cells (SK-N-SH) were found to secrete prostaglandin E2 (PGE2), especially when stimulated. PGE2 synthesis by astrocytes and SK-N-SH cells was stimulated by interleukin-1beta. Microglial cell PGE2 synthesis was stimulated by lipopolysaccharide only. Although astrocytes are used in studies in vitro to investigate the role of COX in AD, there are no indications that these cells express COX-1 or COX-2 in vivo. The different distribution patterns of COX-1 and COX-2 in AD could implicate that these enzymes are involved in different cellular processes in the pathogenesis of AD.     

High selective expression of alpha7 nicotinic receptors on astrocytes in the brains of patients with sporadic Alzheimer's disease and patients carrying Swedish APP 670/671 mutation: a possible association with neuritic plaques

In the present study, we have investigated the expression of nicotinic acetylcholine receptors (nAChRs) on astrocytes and neurons in the hippocampus and temporal cortex of subjects carrying the Swedish amyloid precursor protein (APP) 670/671 mutation (APPswe), patients with sporadic Alzheimer's disease (AD), and age-matched control subjects. Significant increases in the total numbers of astrocytes and of astrocytes expressing the alpha7 nAChR subunit, along with significant decreases in the levels of alpha7 and alpha4 nAChR subunits on neurons, were observed in the hippocampus and temporal cortex of both APPswe and sporadic AD brains. Both of these phenomena were more pronounced in APPswe than sporadic AD cases. Furthermore, the number of [(125)I]alpha-BTX binding sites (alpha7 nAChR) in the temporal cortex of the APPswe brain was significant lower than in the younger control group, reflecting the lower neuronal level of alpha7 nAChR. The increase in the level of expression of alpha7 nAChR on astrocytes was positively correlated with the extent of neuropathological alternations, especially the number of neuritic plaques, in the AD brain. The elevated expression of alpha7 nAChR on astrocytes might participate in Abeta cascade and formation of neuritic plaques, thereby playing an important role in the pathogenesis of AD.     

LRP and senile plaques in Alzheimer's disease: colocalization with apolipoprotein E and with activated astrocytes

The low density lipoprotein receptor-related protein (LRP) is a multifunctional receptor which is present on senile plaques in Alzheimer's disease (AD). It is suggested to play an important role in the balance between amyloid beta (Abeta) synthesis and clearance mechanisms. One of its ligands, apolipoprotein E (apoE), is also present on senile plaques and has been implicated as a risk factor for AD, potentially affecting the deposition, fibrillogenesis and clearance of Abeta. Using immunohistochemistry we show that LRP was present only on cored, apoE-containing senile plaques, in both PDAPP transgenic mice and human AD brains. We detected strong LRP staining in neurons and in reactive astrocytes, and immunostaining of membrane-bound LRP showed colocalization with fine astrocytic processes surrounding senile plaques. LRP was not present in plaques in young transgenic mice or in plaques of APOE-knockout mice. As LRP ligands associated with Abeta deposits in AD brain may play an important role in inducing levels of LRP in both neurons and astrocytes, our findings support the idea that apoE might be involved in upregulation of LRP (present in fine astrocytic processes) and act as a local scaffolding protein for LRP and Abeta. The upregulation of LRP would allow increased clearance of LRP ligands as well as clearance of Abeta/ApoE complexes.     

Hematopoietic prostaglandin D synthase and DP1 receptor are selectively upregulated in microglia and astrocytes within senile plaques from human patients and in a mouse model of Alzheimer disease

Prostaglandin (PG) D2 is produced in activated microglia by the action of hematopoietic PGD synthase (HPGDS) and plays important roles in neuroinflammation. Because the fact that neuroinflammation accelerates progression of Alzheimer disease (AD) has been documented, we investigated whether PGD2 is also involved in the pathology of AD. Here, we report that the level of the mRNA of the receptor for PGD2 (DP1) was increased in AD brains compared with the level in non-AD brains. Immunocytochemical analysis showed HPGDS expression to be localized in the microglia surrounding senile plaques. In situ hybridization studies revealed that DP1 mRNA was specifically localized in microglia and reactive astrocytes within senile plaques of AD brains. In the brain of Tg2576 mice, a model of AD, HPGDS and DP1 proteins were mainly localized immunocytochemically in microglia and astrocytes in the plaques, and the levels of their mRNAs increased in parallel with amyloid beta deposition. These results indicate that PGD2 may act as a mediator of plaque-associated inflammation in AD brain and may explain the pharmacologic mechanisms underlying the favorable response of patients with AD to nonsteroidal anti-inflammatory drugs.     

Absence of brain-derived neurotrophic factor and trkB receptor immunoreactivity in glia of Alzheimer’s disease

Alterations in the neuronal expression of some neurotrophins have been shown in various neurodegenerative processes, particularly Alzheimer’s disease (AD). Glia may up-regulate neurotrophins and their high-affinity tyrosine kinase (trk) receptors in response to neural injury. In human immunodeficiency virus type 1 (HIV-1) encephalitis, activated microglia were shown to express brain-derived neurotrophic factor (BDNF), while reactive astrocytes expressed trkB receptor. This observation has suggested the existence of local neurotrophic regulation between different glial populations. To characterize the glial cellular distribution of BDNF and trkB receptor proteins in AD, we studied selected regions of postmortem brains from four AD and three age-matched control patients by double-immunofluorescence confocal microscopy. In both groups, BDNF immunoreactivity was distributed in neuronal perikarya and neuritic processes in the neocortex and hippocampus. No BDNF immunoreactivity was observed in microglia or astrocytes within and between senile plaques of AD. Catalytic trkB receptor immunoreactivity was present in neuronal perikarya in the neocortex and hippocampus. Reactive astrocytes and microglia were not immunoreactive for catalytic trkB. The absence of BDNF and trkB proteins in glia in AD patients is in contrast to the finding in patients with HIV-1 encephalitis. This difference suggests that glial expression of BDNF and trkB proteins may be characteristic of particular disease processes, rather than merely representing a stereotyped response to any type of neural injury. Received: 13 July 1998 / Revised, accepted: 25 February 1999     

Correlation between astrocyte apoptosis and Alzheimer changes in gray matter lesions in Alzheimer's disease

The relationships between astrocytic apoptosis and both senile plaques and neurofibrillary tangles (NFT) in gray matter lesions were examined quantitatively in Alzheimer's disease (AD) brains. Seven cortical regions were examined in seven AD brains by terminal dUTP nick end-labeling and immunolabeling with antibodies to glial fibrillary acidic protein, phosphorylated tau protein (AT180), apoptosis-related proteins (caspase-3, bcl-2, and CD95), and beta amyloid protein. Senile plaques showed the lowest density in the cornu ammonis. The density of apoptotic astrocytes was significantly correlated with the density of uncored and cored senile plaques. Neuronal caspase-3 and CD95 expression levels were too low to allow statistical assessment, but Bcl-2 was expressed strongly in the astrocytes and neurons with and without NFT. The correlation of the density of apoptotic astrocytes with apoptotic neurons and NFT was not statistically significant. The density of Bcl2-positive neurons correlated significantly with those of NFT and cored senile plaques, but Bcl2-positive astrocyte density showed no correlation with density of senile plaques or apoptotic astrocytes. These observations suggest that senile plaques may be a cause of astrocytic apoptosis in the gray matter, and that Bcl-2 protein is associated with NFT formation.     

Expression of intercellular adhesion molecule (ICAM)-1 by a subset of astrocytes in Alzheimer disease and some other degenerative neurological disorders

Summary Intercellular adhesion molecule-1 (ICAM-1) was localized immunohistochemically in postmortem brain tissue of Alzheimer's disease (AD), progressive supranuclear palsy, amyotrophic lateral sclerosis, Pick's disease, and controls. In controls, only capillaries were stained for ICAM-1. In affected areas of neurologically disease brains, a subset of reactive astrocytes was also strongly stained. In addition, there were irregular, diffuse patches of positive staining in the tissue matrix. In AD, many of these patches had dense cores which corresponded with senile plaques. Double immunostaining for glial fibrillary acidic protein and ICAM-1 indicated that some reactive astrocytes at the periphery of senile plaques were positive for ICAM-1. Within such plaques, microglial aggregates were stained intensely for leukocyte function-associated antigen-1 (LFA-1), the adhesion molecule for ICAM-1. The LFA-1/ICAM-1 system appears to play an important role in the interaction of astrocytes and microglia in several neurological diseases.Supported by grants from the Foundation for Total Health Promotion (HA), the Sasakawa Research Foundation (HA), the Alzheimer Society of B.C. and the MRC of Canada, as well as donations from individual British Columbians     

Transplanted astrocytes internalize deposited beta-amyloid peptides in a transgenic mouse model of Alzheimer's disease

Alzheimer's disease (AD) is one of the most devastating neurodegenerative disorders. The neuropathological hallmarks include extracellular senile plaques consisting of deposited beta-amyloid (Abeta) peptides and intraneuronal neurofibrillary tangles. Neuroinflammation and activation of astrocytes are also well-established features of AD neuropathology; however, the relationships between astrocytes and Abeta deposition remain unclear. Previous studies have shown that adult mouse astrocytes internalize and degrade Abeta deposits in brain sections prepared from human amyloid precursor protein (APP) transgenic mice. In the present study, we demonstrate that cultured adult, but not neonatal mouse astrocytes, respond morphologically and degrade Abeta deposits present in human AD brain. We also transplanted astrocytes isolated from enhanced green fluorescent protein expressing adult and neonatal mice into the hippocampi of human Abeta plaque-bearing transgenic APPSwe+PS1dE9 (APdE9) mice and their wild-type littermates and followed the migration and localization of these astrocytes by confocal microscopy upto 7 days after transplantation. Posttransplantation the astrocytes localized as aggregates or thin strings of many cells within the hippocampi of APdE9 and wild-type mice and showed limited migration from the injection site. Interestingly, most of the transplanted astrocytes were found near Abeta deposits in the hippocampi of APdE9 mice. In contrast to findings in ex vivo degradation assay, confocal microscopy revealed that both adult and neonatal transplanted astrocytes internalized human Abeta immunoreactive material in vivo. These results support the role of astrocytes as active Abeta clearing cells in the CNS that may have important implications for future development of therapeutic strategies for AD.     

Fas and Fas ligand expression in Alzheimer's disease

The Fas/Fas ligand (L) signaling system has been implicated in the control of cell death and cell survival of T and B lymphocytes and in a variety of cell types under particular pathological conditions. In the present study we examined the expression of Fas and Fas-L, by Western blotting and immunohistochemistry, in the human frontal cortex and hippocampus of individuals with advanced Alzheimer's disease (AD) and age-matched controls. Expression levels of Fas and Fas-L, as seen in Western blots, are preserved in the frontal cortex but decreased in the hippocampus in AD when compared with age-matched controls. Yet Fas and Fas-L immunoreactivity is found in remaining AD neurons in the frontal cortex and hippocampus. Moreover, Fas and Fas-L are expressed equally in tangle-bearing and non-tangle-bearing neurons, as revealed with double-labeling immunohistochemistry to Fas or Fas-L and tau or phosphorylated neurofilament epitopes. Dystrophic neurites of senile plaques are not stained with Fas and Fas-L antibodies. A moderate increase in Fas and a strong increase in Fas-L immunoreactivity occur in reactive astrocytes in AD. Yet there is no relationship between Fas or Fas-L expression and increased nuclear DNA vulnerability as revealed with double-labeling immunohistochemstry and in situ end-labeling of nuclear DNA fragmentation. Although the Fas/Fas-L system may have some effect in the control of reactive astrocytosis in AD, the present results show no evidence that Fas/Fas-L signals participate in specific processes of the disease, including neurofibrillary degeneration, dystrophic neurite formation, and cell death.