Fas antigen expression in brains of patients with Alzheimer-type dementia

Systematic review of human post-mortem immunohistochemical studies and bioinformatics analyses unveil the complexity of astrocyte reaction in Alzheimer's disease

AIMS

Reactive astrocytes in Alzheimer's disease (AD) have traditionally been demonstrated by increased glial fibrillary acidic protein (GFAP) immunoreactivity; however, astrocyte reaction is a complex and heterogeneous phenomenon involving multiple astrocyte functions beyond cytoskeletal remodelling. To better understand astrocyte reaction in AD, we conducted a systematic review of astrocyte immunohistochemical studies in post-mortem AD brains followed by bioinformatics analyses on the extracted reactive astrocyte markers.

METHODS

NCBI PubMed, APA PsycInfo and WoS-SCIE databases were interrogated for original English research articles with the search terms 'Alzheimer's disease' AND 'astrocytes.' Bioinformatics analyses included protein-protein interaction network analysis, pathway enrichment, and transcription factor enrichment, as well as comparison with public human -omics datasets.

RESULTS

A total of 306 articles meeting eligibility criteria rendered 196 proteins, most of which were reported to be upregulated in AD vs control brains. Besides cytoskeletal remodelling (e.g., GFAP), bioinformatics analyses revealed a wide range of functional alterations including neuroinflammation (e.g., IL6, MAPK1/3/8 and TNF), oxidative stress and antioxidant defence (e.g., MT1A/2A, NFE2L2, NOS1/2/3, PRDX6 and SOD1/2), lipid metabolism (e.g., APOE, CLU and LRP1), proteostasis (e.g., cathepsins, CRYAB and HSPB1/2/6/8), extracellular matrix organisation (e.g., CD44, MMP1/3 and SERPINA3), and neurotransmission (e.g., CHRNA7, GABA, GLUL, GRM5, MAOB and SLC1A2), among others. CTCF and ESR1 emerged as potential transcription factors driving these changes. Comparison with published -omics datasets validated our results, demonstrating a significant overlap with reported transcriptomic and proteomic changes in AD brains and/or CSF.

CONCLUSIONS

Our systematic review of the neuropathological literature reveals the complexity of AD reactive astrogliosis. We have shared these findings as an online resource available at www.astrocyteatlas.org.

Mechanistic insights and perspectives involved in neuroprotective action of quercetin

Neurodegenerative diseases (NDDs) are the primary cause of disabilities in the elderly people. Growing evidence indicates that oxidative stress, mitochondrial dysfunction, neuroinflammation and apoptosis are associated with aging and the basis of most neurodegenerative disorders. Quercetin is a flavonoid with significant pharmacological effects and promising therapeutic potential. It is widely distributed among plants and typically found in daily diets mainly in fruits and vegetables. It shows a number of biological properties connected to its antioxidant activity. Neuroprotection by quercetin has been reported in many in vitro as well as in in vivo studies. However, the exact mechanism of action is still mystery and similarly there are a number of hypothesis exploring the mechanism of neuroprotection. Quercetin enhances neuronal longevity and neurogenesis by modulating and inhibiting wide number of pathways. This review assesses the food sources of quercetin, its pharmacokinetic profile, structure activity relationship and its pathophysiological role in various NDDs and it also provides a synopsis of the literature exploring the relationship between quercetin and various downstream signalling pathways modulated by quercetin for neuroprotection for eg. nuclear factor erythroid 2-related factor 2 (Nrf2), Paraoxonase-2 (PON2), c-Jun N-terminal kinase (JNK), Tumour Necrosis Factor alpha (TNF-α), Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha (PGC-1α), Sirtuins, Mitogen-activated protein kinases (MAPKs) signalling cascades, CREB (Cyclic AMP response element binding protein) and Phosphoinositide 3- kinase(PI3K/Akt). Therefore, the aim of the present review was to elaborate on the cellular and molecular mechanisms of the quercetin involved in the protection against NDDs.

Studies on sporadic non-syndromic thoracic aortic aneurysms: 1. Deregulation of Jagged/Notch 1 homeostasis and selection of synthetic/secretor phenotype smooth muscle cells

Background

Sporadic non-syndromic thoracic aortic aneurysms (SNSTAAs) are less well understood than familial non-syndromic or syndromic ones. The study aimed at defining the peculiar morphologic and molecular changes occurring in the media layer of SNSTAAs.

Design

This study was based on a single centre design.

Methods

Media layer samples taken from seven carefully selected SNSTAAs and seven reference patients (controls) were investigated via quantitative polymerase chain reaction, proteomics-bioinformatics, immunoblotting, quantitative histology, and immunohistochemistry/immunofluorescence.

Results

In SNSTAAs media, aortic smooth muscle cells numbers were halved due to an apoptotic process coupled with a negligible cell proliferation. Cystathionine γ-lyase was diffusely up-regulated. Surviving aortic smooth muscle cells exhibited diverging phenotypes: in inner- and outer-media contractile cells prevailed, having higher contents of smooth-muscle-α-actin holoprotein (45-kDa) and of caspase-3-cleaved smooth-muscle-α-actin 25-kDa fragments; in mid-media, aortic smooth muscle cells exhibited a synthetic/secretor phenotype, down-regulating vimentin, but up-regulating glial fibrillary acidic protein, trans-Golgi network 46 protein, Jagged1 (172-kDa) holoprotein, and Jagged1’s receptor Notch1. Extracellular soluble Jagged1 (42-kDa) fragments accumulated.

Conclusions

In SNSTAAs, there is a relentless aortic smooth muscle cells attrition caused by the up-regulated cystathionine γ-lyase. In mid-media, synthetic/secretor aortic smooth muscle cells intensify Jagged1/NOTCH1 signalling in the attempt to counterbalance the weakened aortic wall, due to aortic smooth muscle cells net loss and mechanical stress. Synthetic/secretor aortic smooth muscle cells are apoptosis-prone, and the accruing thrombin-cleaved Jagged1 fragments counteract the otherwise useful effects of Jagged1/NOTCH1 signalling, thus hampering tissue homeostasis/remodelling, and aortic smooth muscle cells adhesion, differentiation, and migration.

Antidepressants, sertraline and paroxetine, increase calcium influx and induce mitochondrial damage-mediated apoptosis of astrocytes

The impacts of antidepressants on the pathogenesis of dementia remain unclear despite depression and dementia are closely related. Antidepressants have been reported may impair serotonin-regulated adaptive processes, increase neurological side-effects and cytotoxicity. An ‘astroglio-centric’ perspective of neurodegenerative diseases proposes astrocyte dysfunction is involved in the impairment of proper central nervous system functioning. Thus, defining whether antidepressants are harmful to astrocytes is an intriguing issue. We used an astrocyte cell line, primary cultured astrocytes and neuron cells, to identify the effects of 11 antidepressants which included selective serotonin reuptake inhibitors, a serotonin-norepinephrine reuptake inhibitor, tricyclic antidepressants, a tetracyclic antidepressant, a monoamine oxide inhibitor, and a serotonin antagonist and reuptake inhibitor. We found that treatment with 10 μM sertraline and 20 μM paroxetine significantly reduced cell viability. We further explored the underlying mechanisms and found induction of the [Ca²⁺]_i level in astrocytes. We also revealed that sertraline and paroxetine induced mitochondrial damage, ROS generation, and astrocyte apoptosis with elevation of cleaved-caspase 3 and cleaved-PARP levels. Ultimately, we validated these mechanisms in primary cultured astrocytes and neuron cells and obtained consistent results. These results suggest that sertraline and paroxetine cause astrocyte dysfunction, and this impairment may be involved in the pathogenesis of neurodegenerative diseases.

CSF tau is associated with impaired cortical plasticity, cognitive decline and astrocyte survival only in APOE4-positive Alzheimer's disease

In Alzheimer’s disease (AD) patients, apopoliprotein (APOE) polymorphism is the main genetic factor associated with more aggressive clinical course. However, the interaction between cerebrospinal fluid (CSF) tau protein levels and APOE genotype has been scarcely investigated. A possible key mechanism invokes the dysfunction of synaptic plasticity. We investigated how CSF tau interacts with APOE genotype in AD patients. We firstly explored whether CSF tau levels and APOE genotype influence disease progression and long-term potentiation (LTP)-like cortical plasticity as measured by transcranial magnetic stimulation (TMS) in AD patients. Then, we incubated normal human astrocytes (NHAs) with CSF collected from sub-groups of AD patients to determine whether APOE genotype and CSF biomarkers influence astrocytes survival. LTP-like cortical plasticity differed between AD patients with apolipoprotein E4 (APOE4) and apolipoprotein E3 (APOE3) genotype. Higher CSF tau levels were associated with more impaired LTP-like cortical plasticity and faster disease progression in AD patients with APOE4 but not APOE3 genotype. Apoptotic activity was higher when cells were incubated with CSF from AD patients with APOE4 and high tau levels. CSF tau is detrimental on cortical plasticity, disease progression and astrocyte survival only when associated with APOE4 genotype. This is relevant for new therapeutic approaches targeting tau.

Decreased cortical FADD protein is associated with clinical dementia and cognitive decline in an elderly community sample

BACKGROUND

FADD (Fas-associated death domain) adaptor is a crucial protein involved in the induction of cell death but also mediates non-apoptotic actions via a phosphorylated form (p-Ser194-FADD). This study investigated the possible association of FADD forms with age-related neuropathologies, cognitive function, and the odds of dementia in an elderly community sample.

METHODS

FADD forms were quantified by western blot analysis in dorsolateral prefrontal cortex (DLPFC) samples from a large cohort of participants in a community-based aging study (Memory and Aging Project, MAP), experiencing no-(NCI, n = 51) or mild-(MCI, n = 42) cognitive impairment, or dementia (n = 57).

RESULTS

Cortical FADD was lower in subjects with dementia and lower FADD was associated with a greater load of amyloid-β pathology, fewer presynaptic terminal markers, poorer cognitive function and increased odds of dementia. Together with the observations of FADD redistribution into tangles and dystrophic neurites within plaques in Alzheimer's disease brains, and its reduction in APP23 mouse cortex, the results suggest this multifunctional protein might participate in the mechanisms linking amyloid and tau pathologies during the course of the illness.

CONCLUSIONS

The present data suggests FADD as a putative biomarker for pathological processes associated with the course of clinical dementia.

Relationship between the FAS gene A-670G polymorphism and Alzheimer's disease: a meta-analysis

BACKGROUNDS AND AIMS

The pathogenetic mechanism of Alzheimer's disease (AD) is still unknown; however, gene polymorphism may play a critical role in the pathogenesis of AD. The aim of this meta-analysis was to evaluate the association between FAS gene A-670G polymorphism and AD.

METHODS

We searched all related subjects in PubMed, Embase, Cochrane Library, SinoMed, and the China Knowledge Resource Integrated Database and identified seven studies reporting a relationship between the A-670G polymorphism in the FAS gene and AD.

RESULTS

A total of 1512 cases and 1707 controls were included in the seven studies. The meta-analyses results suggested no significant association between the A-670G polymorphism and AD in any genetic models. When a subgroup analysis was conducted by ethnicity, the A-670G polymorphism was also not relevant to AD. However, when stratified by age, the GG genotype increased the risk of early-onset AD. We also found that the A-670G polymorphism was related to patients with AD who carried the apolipoprotein-E ε4 allele in three genetic models.

CONCLUSIONS

To sum up, our data suggested that the FAS gene A-670G polymorphism may not be associated with AD. When a subgroup analysis was conducted by ethnicity, the A-670G polymorphism was also not related with AD in Asian and Caucasian population. However, the FAS-670 GG genotype may increase the risk of AD in the younger population (age, ≤65 years). Furthermore, we found that the A-670G polymorphism was related to patients with AD who carried the APOE4 allele in dominant, allele and homozygous models.

Differences in abundances of cell-signalling proteins in blood reveal novel biomarkers for early detection of clinical Alzheimer's disease

BACKGROUND

In November 2007 a study published in Nature Medicine proposed a simple test based on the abundance of 18 proteins in blood to predict the onset of clinical symptoms of Alzheimer's Disease (AD) two to six years before these symptoms manifest. Later, another study, published in PLoS ONE, showed that only five proteins (IL-1, IL-3, EGF, TNF- and G-CSF) have overall better prediction accuracy. These classifiers are based on the abundance of 120 proteins. Such values were standardised by a Z-score transformation, which means that their values are relative to the average of all others.

METHODOLOGY

The original datasets from the Nature Medicine paper are further studied using methods from combinatorial optimisation and Information Theory. We expand the original dataset by also including all pair-wise differences of z-score values of the original dataset ("metafeatures"). Using an exact algorithm to solve the resulting Feature Set problem, used to tackle the feature selection problem, we found signatures that contain either only features, metafeatures or both, and evaluated their predictive performance on the independent test set.

CONCLUSIONS

It was possible to show that a specific pattern of cell signalling imbalance in blood plasma has valuable information to distinguish between NDC and AD samples. The obtained signatures were able to predict AD in patients that already had a Mild Cognitive Impairment (MCI) with up to 84% of sensitivity, while maintaining also a strong prediction accuracy of 90% on a independent dataset with Non Demented Controls (NDC) and AD samples. The novel biomarkers uncovered with this method now confirms ANG-2, IL-11, PDGF-BB, CCL15/MIP-1; and supports the joint measurement of other signalling proteins not previously discussed: GM-CSF, NT-3, IGFBP-2 and VEGF-B.

Regulator of calcineurin 1 (RCAN1) facilitates neuronal apoptosis through caspase-3 activation

Individuals with Down syndrome (DS) will inevitably develop Alzheimer disease (AD) neuropathology sometime after middle age, which may be attributable to genes triplicated in individuals with DS. The characteristics of AD neuropathology include neuritic plaques, neurofibrillary tangles, and neuronal loss in various brain regions. The mechanism underlying neurodegeneration in AD and DS remains elusive. Regulator of calcineurin 1 (RCAN1) has been implicated in the pathogenesis of DS. Our data show that RCAN1 expression is elevated in the cortex of DS and AD patients. RCAN1 expression can be activated by the stress hormone dexamethasone. A functional glucocorticoid response element was identified in the RCAN1 isoform 1 (RCAN1-1) promoter region, which is able to mediate the up-regulation of RCAN1 expression. Here we show that overexpression of RCAN1-1 in primary neurons activates caspase-9 and caspase-3 and subsequently induces neuronal apoptosis. Furthermore, we found that the neurotoxicity of RCAN1-1 is inhibited by knock-out of caspase-3 in caspase-3(-/-) neurons. Our study provides a novel mechanism by which RCAN1 functions as a mediator of stress- and Aβ-induced neuronal death, and overexpression of RCAN1 due to an extra copy of the RCAN1 gene on chromosome 21 contributes to AD pathogenesis in DS.

Experimental autoimmune encephalomyelitis (EAE) IN C57Bl/6 mice is not associated with astrogliosis

The C57Bl/6 mouse is the preferred host for the maintenance of gene deletion mutants and holds a unique place in investigations of cytokine/chemokine networks in neuroinflammation. It is also susceptible to experimental autoimmune encephalomyelitis (EAE), a multiple sclerosis (MS)-like disease commonly used to assess potential MS therapies. Investigations of glial reactivity in EAE have revealed hitherto undescribed astroglial responses in this model, characterized by progressively diminishing glial fibrillary acidic protein and aquaporin-4 immunostaining, from early disease. These observations show that astrocyte responses vary with the EAE paradigm and are an important pathological criterion for disease mapping and therapy evaluation.

Interaction of double-stranded RNA-dependent protein kinase (PKR) with the death receptor signaling pathway in amyloid beta (Abeta)-treated cells and in APPSLPS1 knock-in mice

For 10 years, research has focused on signaling pathways controlling translation to explain neuronal death in Alzheimer Disease (AD). Previous studies demonstrated in different cellular and animal models and AD patients that translation is down-regulated by the activation of double-stranded RNA-dependent protein kinase (PKR). Among downstream factors of PKR, the Fas-associated protein with a death domain (FADD) and subsequent activated caspase-8 are responsible for PKR-induced apoptosis in recombinant virus-infected cells. However, no studies have reported the role of PKR in death receptor signaling in AD. The aim of this project is to determine physical and functional interactions of PKR with FADD in amyloid-beta peptide (Abeta) neurotoxicity and in APP(SL)PS1 KI transgenic mice. In SH-SY5Y cells, results showed that Abeta42 induced a large increase in phosphorylated PKR and FADD levels and a physical interaction between PKR and FADD in the nucleus, also observed in the cortex of APP(SL)PS1 KI mice. However, PKR gene silencing or treatment with a specific PKR inhibitor significantly prevented the increase in pT(451)-PKR and pS(194)-FADD levels in SH-SY5Y nuclei and completely inhibited activities of caspase-3 and -8. The contribution of PKR in neurodegeneration through the death receptor signaling pathway may support the development of therapeutics targeting PKR to limit neuronal death in AD.

Fas antigen and sporadic Alzheimer's disease in Southern Italy: evaluation of two polymorphisms in the TNFRSF6 gene

Tumor Necrosis Factor Receptor Super Family 6 gene (TNFRSF6), also known as FAS, encodes the Fas antigen, a cell surface receptor mediating cell apoptosis, situated on chromosome 10q located near the region of linkage to sporadic Alzheimer's disease (sAD). FAS levels have been reported elevated in the brain of AD patients. Due to both positional and pathobiological criteria, the association of the FAS antigen with this pathology is of great interest. We have tested two SNPs in the FAS gene in 223 Italian patients with non-familial AD from Southern Italy (Calabria region) and 211 healthy control subjects. No significant differences in allelic and genotypic distributions were found between cases and controls, or late and early-onset AD patients, thus suggesting that these polymorphisms do not represent an AD risk factor in our population.

Constitutively active calcineurin mediates delayed neuronal death through Fas-ligand expression via activation of NFAT and FKHR transcriptional activities in mouse brain ischemia

We recently demonstrated that a constitutively active form of calcineurin (CaN) is generated by calpain-mediated limited proteolysis following brain ischemia. The calpain-induced CaN activation mediated delayed neuronal death through translocation of nuclear factor of activated T-cells (NFAT) into nuclei after brain ischemia. We also previously demonstrated that activation of forkhead in rhabdomyosarcoma (FKHR), a forkhead transcription factor and substrate of protein kinase-B (Akt), mediated ischemia-induced neuronal death through Fas-ligand expression in gerbil hippocampus. FKHR activation occurred through decreased Akt activity and concomitant dephosphorylation mediated by undefined phosphatases. In this study, we show that phosphorylated Ser-256 of FKHR is dephosphorylated by constitutively active CaN and that in turn FKHR forms a complex with CaN that is translocated into nuclei after brain ischemia. After nuclear translocation of NFAT and FKHR, both NFAT and FKHR stimulated expression of Fas-ligand by binding to its promoter region. Consistent with activation of the Fas-ligand promoter by FKHR dephosphorylation, Fas-ligand expression increased 2 days after ischemia/reperfusion, and treatment with the CaN inhibitor FK506 inhibited that expression. These results suggest that FKHR is a downstream target of CaN and that constitutively active CaN mediates delayed neuronal death through Fas-ligand expression via up-regulation of both NFAT and FKHR transcriptional activity in brain ischemia.

Polymorphisms of fas gene: relationship with Alzheimer's disease and cognitive decline

The Fas antigen (CD95) is a cell surface receptor that mediates cell apoptosis signalling. Recent investigations have shown that Fas-regulated apoptosis was linked to neurodegenerative lesions in the brain of patients with Alzheimer's disease (AD). Here data regarding the association of two polymorphisms of the Fas promoter region with AD patient's cognitive deterioration are reported. The polymorphism at position -1377 was associated with the risk of developing AD and with a differential rate of cognitive decline during a 2-year follow-up. The polymorphism at position -670 was not associated with the risk of AD and with the cognitive decline during the follow-up. Our data suggest that different genetic background in the Fas gene may influence the risk and clinical progression of the disease by affecting neurodegenerative processes leading to neuronal loss.

Changes in the immune system in depression and dementia: causal or coincidental effects?

Epidemiological studies show that there is a correlation between chronic depression and the likelihood of demential in later life. There is evidence that inflammatory changes in the brain are pathological features of both depression and dementia. This suggests that an increase in inflammation-induced apoptosis, together with a reductin in the synthesis of neurotrophic factors caused by a rise in brain glucocorticoids, may play a role in the pathology of these disorders. A reduction in the neuroprotective components of the kynurenine pathway, such as kynurenic acid, and an increase in the neurodegenerative components, 3-hydroxykynurenine and quinolinic acid, contribute to the pathological changes. Such changes are postulated t cause neuronal damage, and thereby predispose chronically depressed patients to demential.

The Fas gene A-670G polymorphism is not associated with sporadic Alzheimer disease in a Chinese Han population

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by excessive neuronal loss, intracellular neurofibrillary tangles and extracellular deposition of amyloid beta-peptide (Abeta). The Fas antigen is a cell surface receptor-mediating cell apoptosis. Several lines of evidence have made Fas/Fas ligand induced apoptosis play an important role in the pathogenesis of AD. Moreover, the Fas gene is located on chromosome 10q24.1, a region of linkage to late-onset AD. Several reports have investigated the association between a single nucleotide polymorphism (SNP) that is located at position -670 of Fas gene and AD, but yielded ambiguous results. To figure out the association of this SNP with sporadic AD in Chinese Han population, we have analyzed 509 patients with AD and 561 controls for the genetic association studies. Our results indicate that the distribution of the Fas genotypes (chi(2) = 0.66, P = 0.72) and alleles (chi(2) = 0.70, P = 0.40) did not differ significantly. The similar results were observed when AD and control groups were stratified by age/age at onset and sex (P > 0.10). The present data revealed no significant effect of the genotypes on the age of onset for developing AD, and no significant association between the genotypes and the severity of the disease.

Nell-1 induces acrania-like cranioskeletal deformities during mouse embryonic development

We previously reported NELL-1 as a novel molecule overexpressed during premature cranial suture closure in patients with craniosynostosis (CS). Nell-1 overexpression also results in premature suture closure/craniosynostosis in newborn transgenic mice. On a cellular level, increased levels of Nell-1 induce osteoblast differentiation and apoptosis. In this report, mice over-expressing Nell-1 were examined during embryonic development as well as shortly after birth for further analysis of craniofacial defects including neural tube defects (NTDs). The results demonstrated that overexpression of Nell-1 could induce acrania at relatively late gestation stage (E15.5) in mouse embryos, through massive apoptosis in calvarial osteoblasts and neural cells. The induced apoptosis was associated with an increase in Fas and Fas-L production. In addition, transgenic E15.5 and newborn transgenic mice with the CS phenotype displayed distortion of the chondrocranium associated with premature hypertrophy and increased apoptosis of chondrocytes. These findings were also verified in vitro with primary chondrocytes transduced with AdNell-1. In conclusion, Nell-1 overexpression can induce craniofacial anomalies associated with neural tube defects during embryonic development and may involve mechanisms of massive apoptosis associated with the Fas/Fas-L signaling pathway. NELL-1: used when describing the human gene; NELL-1: used when describing the human protein; Nell-1: used when describing the rodent gene; Nell-1: used when describing the rodent protein.

Fas/CD95/APO-1 can function as a death receptor for neuronal cells in vitro and in vivo and is upregulated following cerebral hypoxic-ischemic injury to the developing rat brain

Fas/CD95/Apo-1 is a cell surface receptor that transduces apoptotic death signals following activation and has been implicated in triggering apoptosis in infected or damaged cells in disease states. Apoptosis is a major mechanism of neuronal loss following hypoxic-ischemic injury to the developing brain, although the role of Fas in this process has not been studied in detail. In the present study, we have investigated the expression and function of Fas in neuronal cells in vitro and in vivo. Fas was found to be expressed in the 14 day old rat brain, with strongest expression in the cortex, hippocampus and cerebellum. Cross-linking of Fas induced neuronal apoptosis both in neuronal PC12 cells in culture and following intracerebral injection in vivo, indicating that neuronal Fas was functional as a death receptor. This death was shown to be caspase dependent in primary neuronal cultures and was blocked by the selective caspase 8 inhibitor IETD. Finally, cerebral hypoxia-ischemia resulted in a strong lateralised upregulation of Fas in the hippocampus, that peaked six to twelve hours after the insult and was greater on the side of injury. These results suggest that Fas may be involved in neuronal apoptosis following hypoxic-ischemic injury to the developing brain.

Caspase-cleaved amyloid precursor protein in Alzheimer's disease

Caspase-3 mediated cleavage of the amyloid precursor protein (APP) has been proposed as a putative mechanism underlying amyloidosis and neuronal cell death in Alzheimer's disease (AD). We utilized an antibody that selectively recognizes the neo epitope generated by caspase-3 mediated cleavage of APP (alphadeltaC(csp)-APP) to determine if this proteolytic event occurs in senile plaques in the inferior frontal gyrus and superior temporal gyrus of autopsied AD and age-matched control brains. Consistent with a role for caspase-3 activation in AD pathology, alphadeltaC(csp)-APP immunoreactivity colocalized with a subset of TUNEL-positive pyramidal neurons in AD brains. AlphadeltaC(csp)-APP immunoreactivity was found in neurons and glial cells, as well as in small- and medium-size particulate elements, resembling dystrophic terminals and condensed nuclei, respectively, in AD and age-matched control brains. There were a larger number of alphadeltaC(csp)-APP immunoreactive elements in the inferior frontal gyrus and superior temporal gyrus of subjects with AD pathology than age-matched controls. AlphadeltaC(csp)-APP immunoreactivity in small and medium size particulate elements were the main component colocalized with 30% of senile plaques in the inferior frontal gyrus and superior temporal gyrus of AD brains. In some control brains, alphadeltaC(csp)-APP immunoreactivity appeared to be associated with a clinical history of metabolic encephalopathy. Our results suggest that apoptosis contributes to cell death resulting from amyloidosis and plaque deposition in AD.

Stimulation of microglial metabotropic glutamate receptor mGlu2 triggers tumor necrosis factor alpha-induced neurotoxicity in concert with microglial-derived Fas ligand

Activated microglia may be detrimental to neuronal survival in a number of neurodegenerative diseases. Thus, strategies that reduce microglial neurotoxicity may have therapeutic benefit. Stimulation of group II metabotropic glutamate (mGlu) receptors on rat primary microglia with the specific group II agonist 2S,2'R,3'R-2-(2',3'-dicarboxy-cyclopropyl)glycine for 24 h induced microglial activation and resulted in a neurotoxic microglial phenotype. These effects were attributable to preferential mGlu2 stimulation, because N-acetyl-L-aspartyl-L-glutamate, a specific mGlu3 agonist, did not induce microglial activation or neurotoxicity. Stimulation of microglial mGlu2 but not mGlu3 induced caspase-3 activation in cerebellar granule neurons in culture, using microglial-conditioned media as well as cocultures. Stimulation of microglial mGlu2 induced tumor necrosis factor-alpha (TNFalpha) release, which contributed to microglial neurotoxicity mediated via neuronal TNF receptor 1 and caspase-3 activation. Stimulation of microglial group I or III mGlu receptors did not induce TNFalpha release. TNFalpha was only neurotoxic in the presence of microglia or microglial-conditioned medium. The toxicity of TNFalpha could be prevented by coexposure of neurons to conditioned medium from microglia stimulated by the specific group III agonist L-2-amino-4-phosphono-butyric acid. The neurotoxicity of TNFalpha derived from mGlu2-stimulated microglia was potentiated by microglial-derived Fas ligand (FasL), the death receptor ligand. FasL was constitutively expressed in microglia and shed after mGlu2 stimulation. Our data suggest that selective and inverse modulation of microglial mGlu2 and mGlu3 may prove a therapeutic target in neuroinflammatory diseases such as Alzheimer's disease and multiple sclerosis.

Modulation of sFas indicates apoptosis in human herpes simplex encephalitis

Herpes simplex encephalitis (HSE) is the most common cause of non-epidemic, acute and fatal viral encephalitis. A pronounced mortality and morbidity remains in HSE despite antiviral treatment. There is evidence of a vigorous intrathecal immune activity in acute phases of HSE and of persistently increased activity at follow-ups after years. The role of apoptosis of neuronal cells in HSE patients as a mechanism of damage has been brought up lately. We hypothesize that the severity and the progression of the cerebral injury resulting from HSE can be evaluated by quantitative measurement of a compartment of immune activation molecules i.e. soluble Fas (sFas) involved in apoptosis through the Fas/Fas Ligand pathway. Consecutive cerebrospinal fluid (CSF) samples from a prospectively followed cohort, included in an antiviral treatment trial in HSE, were enrolled for quantitative measurement of sFas using commercial capture ELISA. In total, CSF samples from 49 patients with HSE, 63 patients with non-HSE encephalitis and 18 healthy individuals were studied. High levels of sFas were expressed in CSF samples collected between days 0-45 after neurological onset in 41/49 (84%) HSE patients, whereas only 21/63 (33%) of non-HSE patients and none of 18 healthy controls demonstrated measurable levels of sFas. Following the consecutive CSF sFas levels over the time and considering the clinical state of patients at admission, their neurological or lethal outcome at 12 months, and antiviral treatment, we observed that HSE patients with severe neurological sequels revealed an increase in changes of CSF sFas as compared to patients with mild or moderate neurological outcome (57.6+/-55.6 pg/ml, n=10 versus 26.3+/-97.5 pg/ml, n=14; P=0.008). Also HSE patients undergoing vidarabine treatment expressed significantly higher levels of changes of CSF sFas when compared to acyclovir-treated patients (63.7+/-52.8 pg/ml, n=9 versus 26.1+/-98.4 pg/ml, n=14; P=0.003). Interestingly, regardless of the clinical state at admission, and subsequent disease progression of the HSE patients, we could not observe any significant differences in the CSF sFas levels during the first 7 days of neurological symptoms. These observations underline the role of immunological response throughout the course of HSV infection in the brain and the role of the Fas/FasL pathway in particular in disease progression of HSE. The findings further enforce the need of expanding the knowledge of the pathogenesis of HSE to direct to more effective, in particular not only antiviral but also anti-apoptotic or anti-inflammatory treatment.

Apoptotic signals within the basal forebrain cholinergic neurons in Alzheimer's disease

A relatively early and substantial loss of basal forebrain cholinergic neurons is a constant feature of Alzheimer's disease (AD). However, the mechanisms that contribute to the selective vulnerability of these neurons are not fully delineated. In the present series of experiments, we determined the possible contribution of apoptotic processes and other pathologic cascades to the degeneration of the cholinergic neurons of the nucleus basalis of Meynert (NBM) in AD. In contrast to neurons in the frontal cortex which showed prominent DNA fragmentation as detected by the TUNEL method, no DNA fragmentation was observed within the NBM in any of the AD or normal brains. Similarly, immunoreactivity for the apoptotic signals Fas, Fas-ligand, Bax, Bcl-x, caspase-8, caspase-9 and caspase-3 was absent from the NBM of AD and control brains. In contrast, a substantial subpopulation of cholinergic neurons within the NBM in AD displayed prominent immunoreactivity for the apoptotic signal Fas-associated death domain (FADD) in the form of tangles. FADD immunoreactivity was also present in dystrophic neurites. FADD-positive tangle-like structures were localized in neurons which contained immunoreactivity for the cholinergic marker choline acetyltransferase (ChAT) and the low affinity neurotrophin receptor p75NTR. While many of the NBM cholinergic neurons in control brains contained immunoreactivity for the calcium binding protein calbindin-D28K (CB), the NBM neurons in AD displayed a substantial loss of CB immunoreactivity. Importantly, most of FADD-immunoreactive cholinergic neurons were devoid of CB immunoreactivity, and, conversely, most CB-positive cholinergic neurons had no FADD immunoreactivity. FADD immunoreactivity within the basal forebrain was colocalized with phosphorylated tau immunoreactive tangles and dystrophic neurites. In contrast, FADD immunoreactivity did not appear to be related to the primarily diffuse amyloid-beta deposits intermingled between cholinergic neurons in AD NBM. Finally, many CD68-positive microglia were observed surrounding the NBM cholinergic neurons in AD. In conclusion, the findings of the present study indicate that, while the FADD apoptotic signaling pathway may be triggered within the basal forebrain cholinergic neurons in AD, the apoptotic cascade is most likely aborted as no DNA fragmentation was detected and the executioner caspase-3 was not up-regulated within these neurons. The findings also suggest possible relationships between loss of CB, FADD expression and phosphorylation of tau within the basal forebrain cholinergic neurons in AD.

Fas and activated caspase 8 in normal, Alzheimer and multiple infarct brains

Using immunohistochemistry, Fas and caspase 8 positive sites were localized in the brains of Alzheimer patients and those with multiple infarcts as well as age-matched normal. The frontal, occipital and hippocampal regions were dissected out from these patients and normal individuals shortly after death. Positive Fas neurons were found in all these regions of normal individuals and Alzheimer patients, but not in the brains of patients with multiple infarct. Activated caspase 8 protein was found only in the brains of Alzheimer patients and not in the other groups. Plaques in the Alzheimer patients were positive for Fas and activated caspase 8. The former was localized in the membrane and the inside of the plaque whereas activated caspase 8 was only present in the interior of the plaque, as revealed by confocal microscopy. Our study shows that caspase 8 was activated in the Alzheimer brain and the presence of Fas and activated caspase 8 points to a possibility that at least some plaques were of intracellular origin as Fas was a cell membrane receptor and caspase 8 was a intracellular enzyme downstream to Fas. Furthermore, we had confirmed that in most neurons Fas and caspase 8 did not exist concomitantly and that the glial cells (astrocytes) did not express caspase 8 in Alzheimer patients.

The Fas promoter polymorphism at position -670 is not associated with late-onset sporadic Alzheimer's disease

The Fas antigen is a cell surface receptor-mediating cell apoptosis. Recent studies have demonstrated that Fas-associated apoptosis is involved in the pathogenesis of Alzheimer's disease (AD). Moreover, the Fas gene is located on chromosome 10q24.1, a region of linkage to late-onset AD (LOAD). These two criteria, pathobiological and positional, make the Fas antigen an interesting candidate for an association with AD. We performed a case-control association study between the common A/G polymorphism at position -670 in the Fas gene (TNFSRF6) promoter and sporadic AD in Jews, investigating whether this locus acts as a risk factor or whether it has a modifying effect. An association has recently been detected by Feuk et al. in the Scottish population between this locus and the risk of early-onset AD (EOAD), but not of LOAD. In agreement with Feuk et al., we found no association between this locus and the risk of LOAD (n = 86). However, in our small sample of patients with EOAD (n = 19), no association was found either. No interactive effect was found between the Fas promoter polymorphism at position -670 and the known risk factor of LOAD, apolipoprotein E epsilon4, and no association was detected with disease progression. These findings show no evidence for an association between the Fas promoter polymorphism at position -670 and AD in our population.

The extracellular matrix, p53 and estrogen compete to regulate cell-surface Fas/Apo-1 suicide receptor expression in proliferating embryonic cerebral cortical precursors, and reciprocally, Fas-ligand modifies estrogen control of cell-cycle proteins

BACKGROUND

Apoptosis is important for normal cerebral cortical development. We previously showed that the Fas suicide receptor was expressed within the developing cerebral cortex, and that in vitro Fas activation resulted in caspase-dependent death. Alterations in cell-surface Fas expression may significantly influence cortical development. Therefore, in the following studies, we sought to identify developmentally relevant cell biological processes that regulate cell-surface Fas expression and reciprocal consequences of Fas receptor activation.

RESULTS

Flow-cytometric analyses identified two distinct neural sub-populations that expressed Fas on their cell surface at high (FasHi) or moderate (FasMod) levels. The anti-apoptotic protein FLIP further delineated a subset of Fas-expressing cells with potential apoptosis-resistance. FasMod precursors were mainly in G0, while FasHi precursors were largely apoptotic. However, birth-date analysis indicated that neuroblasts express the highest levels of cell-surface Fas at the end of S-phase, or after their final round of mitosis, suggesting that Fas expression is induced at cell cycle checkpoints or during interkinetic nuclear movements. FasHi expression was associated with loss of cell-matrix adhesion and anoikis. Activation of the transcription factor p53 was associated with induction of Fas expression, while the gonadal hormone estrogen antagonistically suppressed cell-surface Fas expression. Estrogen also induced entry into S-phase and decreased the number of Fas-expressing neuroblasts that were apoptotic. Concurrent exposure to estrogen and to soluble Fas-ligand (sFasL) suppressed p21/waf-1 and PCNA. In contrast, estrogen and sFasL, individually and together, induced cyclin-A expression, suggesting activation of compensatory survival mechanisms.

CONCLUSIONS

Embryonic cortical neuronal precursors are intrinsically heterogeneous with respect to Fas suicide-sensitivity. Competing intrinsic (p53, cell cycle, FLIP expression), proximal (extra-cellular matrix) and extrinsic factors (gonadal hormones) collectively regulate Fas suicide-sensitivity either during neurogenesis, or possibly during neuronal migration, and may ultimately determine which neuroblasts successfully contribute neurons to the differentiating cortical plate.

Fas ligand/Fas system in the brain: regulator of immune and apoptotic responses

Apoptosis, also known as programmed cell death, is the major type of cell death involved in normal development, regeneration, proliferation and pathologic degeneration in the central nervous system (CNS). The apoptotic process can be divided further into two pathways depending on the involvement of mitochondria and related biochemical cascades. The internal pathway of apoptosis is initiated by a variety of cytotoxic stimuli and mediated by the release of cytochrome c and subsequent activation of downstream caspases. The external pathway is mainly triggered by ligation of death receptors such as Fas, tumor necrosis factor (TNF)-related apoptosis inducing ligand-R1 (TRAIL-R1), TRAIL-R2 and TNFRp55, and mediated by direct activation of upstream caspases. The Fas-FasL system has been known as a prototypic inducer of extrinsic cell death responsible for cell-mediated cytotoxicity, peripheral immune regulation, immune privilege and "counterattack" of malignant tumor cells against the host immune system. Fas and FasL are expressed in the normal CNS, and expression increases in inflamed and degenerated brains. Like other specialized tissues such as the eye and testis, the Fas-FasL system is thought to be involved in immune suppressed status in the CNS. Expression of Fas and FasL is significantly elevated in a variety of the neurologic disorders, suggesting the possibility that this system may play roles in degenerative and inflammatory responses in the CNS. Therefore, the FasL-Fas system should be considered as a double-edged sword in the CNS: maintaining the immune suppressed status in normal brain and inducing neuronal cell death and inflammation in a variety of neurologic disorders.

A three amino acid peptide, Gly-Pro-Arg, protects and rescues cell death induced by amyloid β-peptide

Amyloid beta-peptide (Abeta) contributes to the pathogenesis of Alzheimer's disease (AD), causing neuronal death through apoptosis. In this study, the neuroprotective role of small peptides, Gly-Pro-Glu (GPE), Gly-Glu (GE), Gly-Pro-Asp (GPD), and Gly-Pro-Arg (GPR) were examined against Abeta-induced toxicity in cultured rat hippocampal neurons. We report here that GPR (10-100 microM) prevented Abeta-mediated increase in lactate dehydrogenase (LDH) release and Abeta inhibition of MTT reduction, even in neurons that were pre-exposed to Abeta for 24 or 48 h. Since GPR prevented Abeta inhibition of MTT reduction, the anti-apoptotic effect of GPR was studied by examining activation of caspase-3 and expression of p53 protein. Caspase-3 was significantly activated by 20 microM Abeta25-35 and 5 microM Abeta1-40, but GPR effectively prevented the Abeta-mediated activation of caspase-3. Similarly, Abeta increased numbers of p53-positive cells, but GPR prevented this Abeta effect. Our findings suggest that GPR can rescue cultured rat hippocampal neurons from Abeta-induced neuronal death by inhibiting caspase-3/p53-dependent apoptosis.

Protection against murine leukemia virus-induced spongiform myeloencephalopathy in mice overexpressing Bcl-2 but not in mice deficient for interleukin-6, inducible nitric oxide synthetase, ICE, Fas, Fas ligand, or TNF-R1 genes

Some murine leukemia viruses (MuLVs), among them Cas-Br-E and ts-1 MuLVs, are neurovirulent, inducing spongiform myeloencephalopathy and hind limb paralysis in susceptible mice. It has been shown that the env gene of these viruses harbors the determinant of neurovirulence. It appears that neuronal loss occurs by an indirect mechanism, since the target motor neurons have not been found to be infected. However, the pathogenesis of the disease remains unclear. Several lymphokines, cytokines, and other cellular effectors have been found to be aberrantly expressed in the brains of infected mice, but whether these are required for the development of the neurodegenerative lesions is not known. In an effort to identify the specific effectors which are indeed required for the initiation and/or development of spongiform myeloencephalopathy, we inoculated gene-deficient (knockout [KO]) mice with ts-1 MuLV. We show here that interleukin-6 (IL-6), inducible nitric oxide synthetase (iNOS), ICE, Fas, Fas ligand (FasL), and TNF-R1 KO mice still develop signs of disease. However, transgenic mice overexpressing Bcl-2 in neurons (NSE/Bcl-2) were largely protected from hind limb paralysis and had less-severe spongiform lesions. These results indicate that motor neuron death occurs in this disease at least in part by a Bcl-2-inhibitable pathway not requiring the ICE, iNOS, Fas/FasL, TNF-R1, and IL-6 gene products.

Fas/tumor necrosis factor receptor death signaling is required for axotomy-induced death of motoneurons in vivo

Activation of the Fas death receptor leads to the death of motoneurons in culture. To investigate the role of Fas in programmed cell death and pathological situations, we used several mutant mice deficient for Fas signaling and made a novel transgenic FADD-DN (FAS-associated death domain-dominant-negative) strain. In vitro, motoneurons from all of these mice were found to be resistant to Fas activation and to show a delay in trophic deprivation-induced death. During normal development in vivo, no changes in motoneuron survival were observed. However, the number of surviving motoneurons was twofold higher in animals deficient for Fas signaling after facial nerve transection in neonatal mice. These results reveal a novel role for Fas as a trigger of axotomy-induced death and suggest that the Fas pathway may be activated in pathological degeneration of motoneurons.

Tissue inhibitor of metalloproteinases-3 and matrix metalloproteinase-3 regulate neuronal sensitivity to doxorubicin-induced apoptosis

Metalloproteinase activity at the cell surface influences cellular sensitivity to extrinsic death vs. survival signals in a variety of cell types, through proteolytic shedding of cell surface signalling molecules. Tissue inhibitor of metalloproteinases-3 (TIMP-3) is a unique natural metalloproteinase inhibitor that plays a pro-apoptotic role through its ability to inhibit metalloproteinases that proteolytically cleave death receptors and their ligands from the cell surface. To study the convergence of metalloproteinase activity and death receptor signalling in neurons, we established an in vitro model of neuronal apoptosis utilizing the chemotherapeutic drug, doxorubicin (Dox). Primary cultures established from embryonic rat cerebral cortices displayed robust and selective neuronal apoptosis in response to Dox, an effect that was dependent on the activation of the death receptor, Fas. We demonstrate that both TIMP-3 and matrix metalloproteinase-3 (MMP-3) are constitutively expressed by primary cortical neurons in culture, and selectively modulated Fas-mediated neuronal apoptosis induced by Dox. Metalloproteinase inhibition by TIMP-3 was found to be necessary for Dox-induced neuronal death, whereas addition of active MMP-3 markedly attenuated apoptosis and diminished Fas-Fas ligand interaction at the cell surface. These observations implicate a physiological role for the balance of TIMP-3 and MMP-3 activity at the neuronal surface in regulating death receptor sensitivity. The convergence of metalloproteinase activity and death receptor signalling at the cell surface may influence neuronal cell death vs. survival decisions.

HIV-1 and IL-1 beta regulate Fas ligand expression in human astrocytes through the NF-kappa B pathway

Reactive astrogliosis is a prominent pathological feature of HIV-1-associated dementia (HAD). We hypothesized that in HAD, astrocytes activated with proinflammatory stimuli such as IL-1beta express Fas ligand (FasL), a death protein. IL-1beta and HIV-1-activated astrocytes expressed FasL mRNA and protein. Luciferase reporter constructs showed that IL-1beta and HIV-1 upregulated FasL promoter activity (p<0.001). The NF-kappaB pathway was involved as shown by inhibition with SN50 and dominant negative IkappaBalpha mutants. Brain extracts from HAD patients had significantly elevated FasL levels compared to HIV-seropositive (p<0.001) and seronegative individuals (p<0.01). We propose that astrocyte expression of FasL may participate in neuronal injury in HAD.

Fas and Fas ligand are associated with neuritic degeneration in the AD brain and participate in beta-amyloid-induced neuronal death

It has recently been suggested that neuronal cell death in response to many brain insults may be mediated by the upregulation of tumor necrosis factor receptor (TNFR) family members and their ligands. In the present study, we investigated whether the expression of the TNFR family death domain receptor, Fas, and its ligand, FasL, is altered in association with neuropathology and activated caspase markers in Alzheimer disease (AD) brain, and Abeta-induced neuronal cell death in vitro. To evaluate this hypothesis, we examined Fas and FasL expression in AD and control brain, and Abeta-treated primary neurons, using immunocytochemistry and Western blots. Neurons in both AD brain and Abeta-treated cultures exhibited FasL upregulation and changes in immunoreactivity for Fas receptor. Further, FasL expression was remarkably elevated in senile plaques and neurofilament-positive dystrophic neurites, and in association with caspase activation and neuritic apoptosis in AD brain. Based on these and previous data regarding protection of primary neuronal cultures from Abeta(1-42)-induced apoptosis by blockade of Fas-associated death domain signaling, we also tested the hypothesis that dynamic regulation of Fas and FasL may contribute to Abeta-mediated neuronal cell death. Accordingly, neuronal cultures derived from mice carrying inactivating mutations in Fas (Faslpr) or FasL (Fasgld) exhibited protection from Abeta(1-42)-induced cell death. These findings suggest that Fas-FasL interactions may contribute to mechanisms of neuronal loss and neuritic degeneration in AD.

Hypothesis for a common basis for neuroprotection in glaucoma and Alzheimer's disease: anti-apoptosis by alpha-2-adrenergic receptor activation

Recent studies have suggested glaucomatous loss of retinal ganglion cells and their axons in Alzheimer's disease. Amyloid beta peptides and phosphorylated tau protein have been implicated in the selective regional neuronal loss and protein accumulations characteristic of Alzheimer's disease. Similar protein accumulations are not present on glaucomatous retinal ganglion cells. Neurons die in both Alzheimer's disease and glaucoma by apoptosis, although the signaling pathways for neuronal degradation appear to differ in the two diseases. Alzheimer's disease features a loss of locus ceruleus noradrenergic neurons, which send axon terminals to the brain regions suffering neuronal apoptosis and results in reductions in noradrenaline in those regions. Activation of alpha-2 adrenergic receptors reduces neuronal apoptosis, in part through a protein kinase B (Akt)-dependent signaling pathway. Loss of noradrenaline innervation facilitates neuronal apoptosis in Alzheimer's disease models and may act similarly in glaucoma. Alpha-2 adrenergic receptor agonists offer the potential to slow the neuronal loss in both diseases by compensating for lost noradrenaline innervation.

Death receptors on reactive astrocytes: a key role in the fine tuning of brain inflammation?

Immune responses protect the CNS against pathogens. However, the fact that there is little dispensable tissue in the brain makes regulation necessary to avoid disastrous immune-mediated damage. Astrocytes respond vigorously to any brain injury (e.g., tumor, stroke, AD, MS, HIV) and are postulated to play an important role in the fine tuning of brain inflammation. The authors propose that astrocytes use death receptors to modulate pro- and anti-inflammatory effects.

Further evidence for role of a promoter variant in the TNFRSF6 gene in Alzheimer disease

The tumor necrosis factor receptor superfamily, member 6 gene (TNFRSF6) is situated on chromosome 10q, near the region indicated in several AD linkage studies. In a previous study a significant association was found between a promoter variant within the TNFRSF6 gene and Alzheimer disease (AD). To further investigate the TNFRSF6 region, 34 SNPs within 180 kb were first genotyped in an exploratory set of 121 early-onset dementia cases and 152 controls in order to establish the extent of linkage disequilibrium (LD) and the major haplotypes in the region. This analysis showed that the LD was clustered in two large blocks within each of which a limited number of haplotypes represented most of the diversity. Haplotype tagging markers were chosen and genotyped in an additional 204 late onset AD cases and 177 controls. Tests of association were performed for single markers for case/control status and for a quantitative measure of cognitive ability [Mini-Mental State Examination (MMSE) scores] within cases only. The previously associated marker, located in the promoter of TNFRSF6, now gave significant association with cognitive status in the Scottish early-onset dementia samples (p = 0.005) with the strongest signals being evident in the APOE-e4 carrier subgroup, thus providing a second independent positive result for this marker. The same marker was also significantly associated with cognitive performance in the Swedish APOE-e4 carriers (p = 0.014), providing a third independent signal. Association analysis was also performed using the major haplotypes in the region, employing both case/control status and MMSE scores. The haplotype analysis did not give further significant findings. These results together with previous data suggest that a promoter marker in TNFRSF6 plays a moderate but demonstrable role in AD etiology.

Decreased akt activity is associated with activation of forkhead transcription factor after transient forebrain ischemia in gerbil hippocampus

The authors recently reported that sodium orthovanadate rescues cells from delayed neuronal death in gerbil hippocampus after transient forebrain ischemia through phosphatidylinositol 3-kinase-protein kinase B (Akt) pathway (Kawano et al., 2001). In the current study, they demonstrated that the activation of FKHR, a Forkhead transcription factor and a substrate for Akt, preceded delayed neuronal death in CA1 regions after transient forebrain ischemia. Adult Mongolian gerbils were subjected to 5-minute forebrain ischemia. Immunoblotting analysis with anti-phospho-FKHR antibody showed that phosphorylation of FKHR at serine-256 in the CA1 region decreased immediately after and 0.5 and 1 hour after reperfusion. The dephosphorylation of FKHR was correlated with the decreased Akt activity. Intracerebroventricular injection of orthovanadate 30 minutes before ischemia inhibited dephosphorylation of FKHR after reperfusion, and blocked delayed neuronal death in the CA1 region. Gel mobility shift analysis using nuclear extracts from the CA1 region prepared immediately after reperfusion revealed increases in DNA binding activity for the FKHR-responsive element on the Fas ligand promoter. The orthovanadate injection administered before ischemia inhibited its binding activity. Two days after reperfusion, expression of Fas ligand increased in the CA1 region and the orthovanadate injection inhibited this increased expression. These results suggest that the inactivation of Akt results in the activation of FKHR and, in turn, relates to the expression of Fas ligand in the CA1 region after transient forebrain ischemia.

Apoptosis of astrocytes with enhanced lysosomal activity and oligodendrocytes in white matter lesions in Alzheimer's disease

Cerebral white matter lesions in Alzheimer's disease (AD) consist of subcortical degeneration and ischaemic-hypoxic changes. Glial changes are intimately associated with the white matter lesions, and regressive changes in astrocytes and loss of oligodendroglial cells have been reported. We quantitatively compared glial changes including apoptosis and enhanced lysosomal activity in the frontal and temporal white matter by using terminal dUTP nick end labelling (TUNEL) and immunohistochemistry for glial markers, lysosomes and apoptosis-regulating proteins in non-familial AD brains. The degree of myelin pallor and axonal loss varied considerably in both the frontal and temporal white matter but fibrillary gliosis in demyelinated lesions tended to be less prominent in the temporal white matter in AD cases. A morphometric study with planimetric methods for cross-sectional areas of frontal and temporal white matter revealed that the white matter of AD cases manifested atrophy with significant reduction in frontal (11.9%) and temporal (29.4%) white matter compared to normal controls. Double immunolabelling for glial fibrillary acidic protein (GFAP) and KP1 (CD68) revealed KP1-positive fragmented structures within the weakly GFAP-labelled astrocytes. These KP1-positive structures correspond to process fragmentation and cytoplasmic vacuoles, which in turn indicate enhanced lysosomal activity during regressive changes in astrocytes. The KP1-modified astrocytes were not found in Pick's disease and corticobasal degeneration. The density of apoptotic glial cells, largely oligodendroglial, was significantly higher in the temporal than in the frontal white matter, and most GFAP-positive astrocytes with regressive changes were apoptotic. GFAP-positive astrocyte density was statistically the same in the frontal and temporal white matter, but the density of KP1-modified astrocytes was higher in the temporal than in the frontal white matter. The rate of white matter shrinkage was significantly correlated with the density of apoptotic glial cells and the density of KP1-modified astrocytes in the temporal lobe in AD cases. An increase in apoptotic glial cell density was found to contribute to GFAP-positive astrocytes with regressive changes in temporal white matter, while apoptosis of vascular smooth muscle cells did not show topographical accentuation. Astrocytes labelled with beta amyloid protein were not apoptotic, and the density of apoptotic cells labelled with CD95 and caspase-3 was too low in both types of white matter to be statistically evaluated. Our results imply that regressive changes in astrocytes and glial apoptosis are, to some extent, associated with white matter lesions, particularly of the temporal lobe in AD brains. The presence of apoptotic astrocytes with evidence of regressive change could therefore be a histological hallmark for white matter degeneration in AD.

Increased serum levels of CD95 in Alzheimer's disease

There is growing evidence for a role of apoptosis in Alzheimer's disease (AD). Recent findings suggest an increased susceptibility of lymphocytes to apoptosis in AD. To prove the hypothesis of systemic alterations in the apoptotic balance in AD, serum and cerebrospinal fluid levels of soluble CD95, which is known to mediate apoptosis, were measured. In the serum, AD patients exhibited significantly higher levels of CD95 than the controls (p = 0.017), suggesting an involvement of peripheral markers in AD.

Fas (CD95/Apo-1)/Fas ligand expression in neonates with pontosubicular neuron necrosis

Pontosubicular neuron necrosis (PSN) represents an age-specific response to severe hypoxic-ischemic injury occurring in human neonates but not in older children or adults. Histologically, PSN is characterized by acute neuronal death in the pontine nuclei and the hippocampal subiculum bearing the hallmarks of apoptosis. In animal models of hypoxic-ischemic injury, induction of neuronal apoptosis can be triggered by Fas (CD95/Apo-1), a cell surface receptor of the tumor necrosis factor-alpha superfamily, which transduces apoptotic death signals when cross-linked by its natural ligand. Here, we have investigated the expression of Fas/Fas ligand in human autopsy material consisting of 13 PSN cases and 10 age-matched cases without PSN. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling, immunohistochemistry, and double labeling for Fas/Fas ligand and the astrocyte marker glial fibrillary acid protein, the microglia/macrophage specific marker KiM1P, and the neuronal marker NeuN were performed on formalin-fixed brain specimens. Although mainly neurons of both PSN and controls expressed Fas receptor, expression was significantly increased (p = 0.001) in PSN cases in which predominantly degenerating cells with signs of early apoptosis showed Fas expression. In contrast, Fas ligand expression was found mainly on astrocytes and microglial cells. There was no significant difference between cases with and without PSN. We conclude that in the developing human brain, cells expressing the Fas receptor may be susceptible to undergoing apoptosis in response to hypoxic-ischemic injury.

Prolonged intrathecal release of soluble Fas following severe traumatic brain injury in humans

The mechanisms underlying cell death following traumatic brain injury (TBI) are not fully understood. Apoptosis is believed to be one mechanism contributing to a marked and prolonged neuronal cell loss following TBI. Recent data suggest a role for Fas (APO-1, CD95), a type I transmembrane receptor glycoprotein of the nerve growth factor/tumor necrosis factor superfamily, and its ligand (Fas ligand, FasL) in apoptotic events in the central nervous system. A truncated form of the Fas receptor, soluble Fas (sFas) may indicate activation of the Fas/FasL system and act as a negative feedback mechanism, thereby inhibiting Fas mediated apoptosis. Soluble Fas was measured in cerebrospinal fluid (CSF) and serum of 10 patients with severe TBI (GCS< or =8) for up to 15 days post-trauma. No sFas was detected in CSF samples from patients without neurological pathologies. Conversely, after TBI 118 out of 120 CSF samples showed elevated sFas concentrations ranging from 56 to 4327 mU/ml. Paired serum samples showed above normal (8.5 U/ml) sFas concentrations in 5 of 10 patients. Serum levels of sFas were always higher than CSF levels. However, there was no correlation between concentrations measured in CSF and in serum (r(2)=0.078, p=0.02), suggesting that the concentrations in the two compartments are independently regulated. Also, no correlation was found between sFas in CSF and blood brain barrier (BBB) dysfunction as assessed by the albumin CSF/serum quotient (Q(A)), and concentrations of the cytotoxic cytokine tumor necrosis factor-alpha in CSF, respectively. Furthermore, there was no correlation with two markers of immune activation (soluble interleukin-2 receptor and neopterin) in CSF. Maximal CSF levels of sFas correlated significantly (r(2)=0.8191, p<0.001) with the early peaks of neuron-specific enolase in CSF (a marker for neuronal cell destruction), indicating that activation of the Fas mediated pathway of apoptosis may be in part the direct result of the initial trauma. However, the prolonged elevation of sFas in CSF may be caused by the ongoing inflammatory response to trauma and delayed apoptotic cell death.

Fas (CD95) may mediate delayed cell death in hippocampal CA1 sector after global cerebral ischemia

Cell death-regulatory genes like caspases and bcl-2 family genes are involved in delayed cell death in the CA1 sector of hippocampus after global cerebral ischemia, but little is known about the mechanisms that trigger their expression. The authors found that expression of Fas and Fas-ligand messenger ribonucleic acid and protein was induced in vulnerable CA1 neurons at 24 and 72 hours after global ischemia. Fas-associating protein with a novel death domain (FADD) also was upregulated and immunoprecipitated and co-localized with Fas. Caspase-10 was activated and interacted with FADD protein to an increasing extent as the duration of ischemia increased. Moreover, caspase-10 co-localized with both FADD and caspase-3. These findings suggest that Fas-mediated death signaling may play an important role in signaling hippocampal neuronal death in CA1 after global cerebral ischemia.

Activation of Fas and caspase 3 precedes PrP accumulation in 87V scrapie

The sequence of events involved in the neurodegeneration caused by transmissible spongiform encephalopathies is not yet known. Using a murine scrapie model in which neurodegeneration in the hippocampus is restricted to the CA2, we show an up-regulation of the proapoptotic markers Fas and caspase 3 early in the incubation period prior to disease-specific prion protein (PrP) deposition and clinical signs. These results suggest that activation of Fas and caspase 3 are involved in the early pathological sequence of events during murine scrapie, and that these proapoptotic markers may be a specific method for early detection of neurodegeneration.

Glial cells as targets for cytotoxic immune mediators

Oligodendrocytes and Schwann cells are the glia principally responsible for the synthesis and maintenance of myelin. Damage may occur to these cells in a number of conditions, but perhaps the most studied are the idiopathic inflammatory demyelinating diseases, multiple sclerosis in the CNS, and Guillain-Barré syndrome and its variants in the peripheral nervous system (PNS). This article explores the effects on these cells of cytotoxic immunological and inflammatory mediators: similarities are revealed, of which perhaps the most important is the sensitivity of both Schwann cells and oligodendrocytes to many such agents. This area of research is, however, characterised and complicated by numerous and often very substantial inter-observer discrepancies. Marked variability in cell culture techniques, and in assays of cell damage and death, provide artifactual explanations for some of this variability; true inter-species differences also contribute. Not the least important conclusion centres on the limited capacity of in vitro studies to reveal disease mechanisms: cell culture findings merely illustrate possibilities which must then be tested ex vivo using human tissue samples affected by the relevant disease.

Increased expression of Fas (CD95/APO-1) in adult rat brain after kainate-induced seizures

Fas (CD95/APO-1), a transmembrane glycoprotein and receptor for the Fas ligand, plays an important role in apoptosis. The present study examined whether excitotoxic cell death induces Fas expression in the adult rat brain. Although relatively light immunostaining was observed in control brain sections, significantly increased Fas immunoreactivity was seen from 4 h to 5 days after the onset of kainic acid-induced seizures. Increased expression of both Fas mRNA and protein were also evident by reverse transcription polymerase chain reaction and Western blotting, respectively. Fas induction was correlated with neuronal apoptosis as demonstrated by colocalization of Fas and terminal dT-mediated dUTP nick end-labeling (TUNEL). Cells with increased Fas-expression were also immunoreactive for tumor suppressor p53 and neuronal specific nuclear protein (NeuN). These results suggest that Fas receptor may contribute to excitotoxic neuronal death in cooperation with p53, and further implicates the Fas pathway in the pathophysiology of neurodegenerative diseases.