Von Economo neurons are part of a larger neuronal population that are selectively vulnerable in C9orf72 frontotemporal dementia.

AIMS: The behavioural variant of frontotemporal dementia with a C9orf72 expansion (C9-bvFTD) is characterised by early changes in social-emotional cognition that are linked to the loss of von Economo neurons (VENs). Together with a subset of neighbouring pyramidal neurons, VENs express the GABA receptor subunit theta (GABRQ). It is not known if the selective vulnerability of VENs in C9-bvFTD also includes this GABRQ-expressing population. METHODS: We quantified VENs and GABRQ immunopositive neurons in the anterior cingulate cortex (ACC) in C9-bvFTD (n = 16), controls (n = 12) and Alzheimer's disease (AD) (n = 7). Second, we assessed VENs and GABRQ-expressing populations in relation to the clinicopathological profiles. RESULTS: We found the number of VENs and GABRQ-expressing neurons and their ratio over the total layer 5 neuronal population was lower in C9-bvFTD compared to control and AD. C9-bvFTD donors with underlying TDP43 type A pathology in the ACC showed the highest loss of GABRQ-expressing neurons. C9-bvFTD donors that did not present with motor neuron disease (MND) symptoms in the first half of their disease course showed a prominent loss of GABRQ-expressing neurons compared to controls. C9-bvFTD donors with no symptoms of psychosis showed a higher loss compared to controls. Across all donors, the number of VENs correlated strongly with the number of GABRQ-expressing neurons. CONCLUSION: We show that VENs, together with GABRQ-expressing neurons, are selectively vulnerable in C9-bvFTD but are both spared in AD. This suggests they are related and that this GABRQ-expressing population of VENs and pyramidal neurons, is a key modulator of social-emotional functioning.

BRI2 ectodomain affects Aß42 fibrillation and tau truncation in human neuroblastoma cells.

Alzheimer's disease (AD) is pathologically characterized by the presence of misfolded proteins such as amyloid beta (Aß) in senile plaques, and hyperphosphorylated tau and truncated tau in neurofibrillary tangles (NFT). The BRI2 protein inhibits Aß aggregation via its BRICHOS domain and regulates critical proteins involved in initiating the amyloid cascade, which has been hypothesized to be central in AD pathogenesis. We recently detected the deposition of BRI2 ectodomain associated with Aß plaques and concomitant changes in its processing enzymes in early stages of AD. Here, we aimed to investigate the effects of recombinant BRI2 ectodomain (rBRI276-266) on Aß aggregation and on important molecular pathways involved in early stages of AD, including the unfolded protein response (UPR), phosphorylation and truncation of tau, as well as apoptosis. We found that rBRI276-266 delays Aß fibril formation, although less efficiently than the BRI2 BRICHOS domain (BRI2 residues 113-231). In human neuroblastoma SH-SY5Y cells, rBRI276-266 slightly decreased cell viability and increased up to two-fold the Bax/Bcl-2 ratio and the subsequent activity of caspases 3 and 9, indicating activation of apoptosis. rBRI276-266 upregulated the chaperone BiP but did not modify the mRNA expression of other UPR markers (CHOP and Xbp-1). Strikingly, rBRI276-266 induced the activation of GSK3ß but not the phosphorylation of tau. However, exposure to rBRI276-266 significantly induced the truncation of tau, indicating that BRI2 ectodomain can contribute to NFT formation. Since BRI2 can also regulate the metabolism of Aß, the current data suggests that BRI2 ectodomain is a potential nexus between Aß, tau pathology and neurodegeneration.

Plasma proteome profiling identifies changes associated to AD but not to FTD.

BACKGROUND: Frontotemporal dementia (FTD) is caused by frontotemporal lobar degeneration (FTLD), characterized mainly by inclusions of Tau (FTLD-Tau) or TAR DNA binding43 (FTLD-TDP) proteins. Plasma biomarkers are strongly needed for specific diagnosis and potential treatment monitoring of FTD. We aimed to identify specific FTD plasma biomarker profiles discriminating FTD from AD and controls, and between FTD pathological subtypes. In addition, we compared plasma results with results in post-mortem frontal cortex of FTD cases to understand the underlying process. METHODS: Plasma proteins (n = 1303) from pathologically and/or genetically confirmed FTD patients (n = 56; FTLD-Tau n = 16; age = 58.2 ± 6.2; 44% female, FTLD-TDP n = 40; age = 59.8 ± 7.9; 45% female), AD patients (n = 57; age = 65.5 ± 8.0; 39% female), and non-demented controls (n = 148; 61.3 ± 7.9; 41% female) were measured using an aptamer-based proteomic technology (SomaScan). In addition, exploratory analysis in post-mortem frontal brain cortex of FTD (n = 10; FTLD-Tau n = 5; age = 56.2 ± 6.9, 60% female, and FTLD-TDP n = 5; age = 64.0 ± 7.7, 60% female) and non-demented controls (n = 4; age = 61.3 ± 8.1; 75% female) were also performed. Differentially regulated plasma and tissue proteins were identified by global testing adjusting for demographic variables and multiple testing. Logistic lasso regression was used to identify plasma protein panels discriminating FTD from non-demented controls and AD, or FTLD-Tau from FTLD-TDP. Performance of the discriminatory plasma protein panels was based on predictions obtained from bootstrapping with 1000 resampled analysis. RESULTS: Overall plasma protein expression profiles differed between FTD, AD and controls (6 proteins; p = 0.005), but none of the plasma proteins was specifically associated to FTD. The overall tissue protein expression profile differed between FTD and controls (7-proteins; p = 0.003). There was no difference in overall plasma or tissue expression profile between FTD subtypes. Regression analysis revealed a panel of 12-plasma proteins discriminating FTD from AD with high accuracy (AUC: 0.99). No plasma protein panels discriminating FTD from controls or FTD pathological subtypes were identified. CONCLUSIONS: We identified a promising plasma protein panel as a minimally-invasive tool to aid in the differential diagnosis of FTD from AD, which was primarily associated to AD pathophysiology. The lack of plasma profiles specifically associated to FTD or its pathological subtypes might be explained by FTD heterogeneity, calling for FTD studies using large and well-characterize cohorts.

Always around, never the same: pathways of amyloid beta induced neurodegeneration throughout the pathogenic cascade of Alzheimer's disease.

There is an increasing amount of evidence showing the importance of intermediate aggregation species of amyloid beta (Abeta) in the pathogenic cascade of Alzheimer's disease (AD). Different Abeta assembly forms may mediate diverse toxic effects at different stages of the disease. Mouse models for AD suggest that intraneuronal accumulation of Abeta oligomers might be involved in AD pathogenesis at a very early stage of the disease. The detrimental effect of oligomeric Abeta on synaptic efficacy is suggested to be an early event in the pathogenic cascade. Also early neuronal responses as activation of the unfolded protein response are processes likely to be associated with the increased occurrence of oligomeric or low fibrillar Abeta in AD pathology. In later stages of AD pathology, the fibrillarity of Abeta increases, concomitantly with a neuroinflammatory response, followed by tau related neurofibrillary changes in end stage pathology. We will review recent findings in in vitro cell models, in vivo mouse models, and post mortem AD brain tissue in view of the effects of different Abeta peptide species on neurodegeneration during AD pathogenesis. Insight into the role of different Abeta species during AD pathogenesis is essential for the development of disease modifying drugs and therapeutical strategies.

Neuroinflammation and regeneration in the early stages of Alzheimer's disease pathology.

The initial stages of Alzheimer's disease pathology in the neocortex show upregulation of cell cycle proteins, adhesion and inflammation related factors, indicating the early involvement of inflammatory and regenerating pathways in Alzheimer's disease pathogenesis. These brain changes precede the neurofibrillary pathology and the extensive process of neurodestruction and (astro)gliosis. Amyloid beta deposition, inflammation and regenerative mechanisms are also early pathogenic events in transgenic mouse models harbouring the pathological Alzheimer's disease mutations, while neurodegenerative characteristics are not seen in these models. This review will discuss the relationship between neuroinflammation and neuroregeneration in the early stages of Alzheimer's disease pathogenesis.

Interleukin-1beta induced cyclooxygenase 2 expression and prostaglandin E2 secretion by human neuroblastoma cells: implications for Alzheimer's disease.

Non-steroidal anti-inflammatory drugs (NSAIDs) may decrease the risk of developing Alzheimer's disease (AD). Cyclooxygenase 2 (COX-2), one of the targets of NSAIDs, is increasingly expressed in neuronal cells in AD brain. In this study, of the cytokines that are found at increased levels in AD brain (interleukin (IL)-1alpha, IL-1beta, IL-6 and tumour necrosis factor (TNF)alpha), IL-1beta was found to induce COX-2 immunoreactivity and prostaglandin (PG) E2 secretion by human neuroblastoma cell line SK-N-SH. COX inhibitors indomethacin and BF389, as well as the glucocorticoid dexamethasone (DEX) and pyrrolidinedithiocarbamate, which is an inhibitor of nuclear factor kappaB as well as a potent antioxidant, inhibited IL-1beta induced PGE2 secretion. In addition, DEX reduced the IL-1beta induced COX-2 immunoreactivity in the same concentration as wherein it inhibited PGE2 secretion. Palmitoyl trifluormethyl ketone, an inhibitor of Ca(2+) independent phospholipase A2 (iPLA2) and a less potent inhibitor of cytosolic PLA2, dose-dependently reduced the IL-1beta induced PGE2 secretion. This suggests that the IL-1beta induced PGE2 secretion may depend on the availability of arachidonic acid. Although the physiological role of neuronal COX-2 still remains unclear, we suggest an interplay between glial derived IL-1 and neuronal upregulation of COX-2 expression in chronic neurodegenerative diseases, such as AD.

Establishment of microglial cell cultures derived from postmortem human adult brain tissue: immunophenotypical and functional characterization.

Cell cultures have become an integral part of the daily routine in most biological research laboratories. Because they are very dynamic and highly accessible, cell cultures permit direct experimental manipulations where cause-effect relations can be more definitely assayed. We have developed cultures of microglial cells from rapid autopsies (range 3-10 hours) of nondemented elderly patients and Alzheimer's disease patients. Cultures were derived from the subcortical white matter, corpus callosum, and frontal, temporal, and occipital cortex. The adherent microglial cells were immunoreactive for CD68, CD45, CD11c, and major histocompatibility complex (MHC) class II markers, and were not immunoreactive for astrocyte or oligodendrocyte markers. In addition, some functional characteristics of the isolated microglial cells were also studied. Upon stimulation with lipopolysaccharide (LPS), microglial cells secreted pro- and antiinflammatory mediators, i.e., interleukin- (IL)-6, prostaglandin E2 (PGE2), and IL-10, indicating the functional capacity of cultured microglia.

Immunological aspects of alzheimer's disease: therapeutic implications.

Alzheimer's disease (AD) is a chronic neurodegenerative disease causing progressive impairment of memory and cognitive function. The amyloid cascade hypothesis suggests that mismetabolism of the beta-amyloid (A beta) precursor protein (APP) followed by subsequent formation of non-fibrillar and fibrillar A beta deposits leads to glial activation and eventually to neurotoxicity, causing cognitive impairment. Several lines of evidence indicate that an inflammatory process contributes to the pathology of AD. First, inflammatory proteins have been identified as being associated with neuritic plaques and in glial cells surrounding these plaques. Second, certain polymorphisms of acute-phase proteins and cytokines associated with AD plaques increase the risk or predispose for earlier onset of developing AD. Third, epidemiological studies indicate that anti-inflammatory drugs can retard the development of AD. Several steps in the pathological cascade of AD have been identified as possible targets for actions of nonsteroidal anti-inflammatory drugs. For instance, microglia are considered a target because this cell type is closely involved in AD pathology through secretion of neurotoxic substances and by modulating a positive feedback loop of the inflammatory mechanism that may be involved in the pathological cascade in AD. On the basis of studies in APP transgenic mice, immunisation with A beta was recently suggested as a novel immunological approach for the treatment of AD. Immunisation elicits A beta-specific antibodies that could affect several early steps of the amyloid-driven cascade. Antibodies could prevent A beta from aggregating into fibrils and accelerate clearance of A beta by stimulating its removal by microglial cells. This review outlines the pathological and genetic evidence that an inflammatory mechanism is involved in AD and the therapeutic approaches based on inhibition or mediation of inflammation.

Soothing the inflamed brain: effect of non-steroidal anti-inflammatory drugs on Alzheimer's disease pathology.

Epidemiological studies suggest that systemic use of non-steroidal anti-inflammatory drugs (NSAIDs) can prevent or retard the development of Alzheimer's disease (AD). However, clinical trials investigating the effects of NSAIDs on AD progression have yielded mixed or inconclusive results. The aim of this review is to distinguish the role of inflammation and the molecular targets of NSAIDs in the different stages of AD pathology. AD brains are characterized by extracellular deposits of ß-amyloid protein and intraneuronal accumulation of hyperphosphorylated tau protein. Already in the early stages of AD pathology ß-amyloid protein deposits are associated with inflammatory proteins and microglia, the brain resident macrophages. Recently, two genome-wide association studies identified new genes that are associated with an increased risk of developing AD. These genes include CLU and CR1 which encode for clusterin and complement receptor 1 respectively. Both genes are involved in the regulation of inflammation. This strongly indicates that inflammation plays a central role in the aetiology of AD. In this review we will show that the primary targets of NSAIDs are involved in a pathological stage that precedes the clinical appearance of AD. The early, preclinical involvement of inflammation in AD explains why patients with clinical signs of AD do not benefit from anti-inflammatory treatment and suggests that NSAIDs, rather than having a direct therapeutic effect, may have preventive effects.

Removing protein aggregates: the role of proteolysis in neurodegeneration.

A common characteristic of neurodegenerative diseases like Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD) is the accumulation of protein aggregates. This reflects a severe disturbance of protein homeostasis, the proteostasis. Here, we review the involvement of the two major proteolytic machineries, the ubiquitin proteasome system (UPS) and the autophagy/lysosomal system, in the pathogenesis of neurodegenerative diseases. These proteolytic systems cooperate to maintain the proteostasis, as is indicated by intricate cross talk. In addition, the UPS and autophagy are regulated by stress pathways that are activated by disturbed proteostasis, like the unfolded protein response (UPR). We will specifically discuss how these proteolytic pathways are affected in neurodegenerative diseases. We will show that there is a differential involvement of the UPS and autophagy in different neurodegenerative disorders. In addition, the proteolytic impairment may be primary or secondary to the pathology. These differences have important implications for the design of therapeutic strategies. The opportunities and caveats of targeting the UPS and autophagy/lysosomal system as a therapeutic strategy in neurodegeneration will be discussed.

The early involvement of the innate immunity in the pathogenesis of late-onset Alzheimer's disease: neuropathological, epidemiological and genetic evidence.

The idea that an inflammatory process is involved in Alzheimer's disease (AD) was proposed already hundred years ago but only the past twenty years inflammation-related proteins have been identified within plaques. A number of acute-phase proteins colocalize with the extracellular amyloid fibrils, the so called Aß-associated proteins. Activated microglia and astrocytes surrounding amyloid deposits express receptors of innate immunity and secrete pro-inflammatory cytokines. In this paper we review the evidence for involvement of innate immunity in the early stages of the pathological cascade of AD. Diffuse plaques, the initial neuropathological lesion in the cerebral neocortex, contain next to Aß also apolipoprotein E, clusterin, α1-antichymotrypsin and activated complement proteins. Interestingly, genetic studies have shown gene-loci to be associated with AD for all these proteins, except α1-antichymotrpsin. Fibrillar Aß can, through stimulation of toll-like receptors and CD-14 on glial cells, activate pathways for increased production of pro-inflammatory cytokines. This pathway, inducing production of proinflammatory cytokines, is under genetic control. The finding that the responsiveness of the innate immunity is higher in offspring with a parental history of late-onset AD indicates heritable traits for AD that are related to inflammatory processes. Prospective epidemiological studies which report that higher serum levels of certain acute-phase proteins are associated with cognitive decline or dementia provide additional evidence for the early involvement of inflammation in AD pathogenesis. The reviewed neuropathological, epidemiological and genetic findings show evidence for involvement of the innate-immunity in the early stages of pathological cascade as well as for the hypothesis that the innate immunity contributes to the etiology of late-onset AD.

Endoplasmic reticulum stress activates autophagy but not the proteasome in neuronal cells: implications for Alzheimer's disease.

Protein folding stress in the endoplasmic reticulum (ER) may lead to activation of the unfolded protein response (UPR), aimed to restore cellular homeostasis via transcriptional and post-transcriptional mechanisms. ER stress is also reported to activate the ER overload response (EOR), which activates transcription via NF-κB. We previously demonstrated that UPR activation is an early event in pre-tangle neurons in Alzheimer's disease (AD) brain. Misfolded and unfolded proteins are degraded via the ubiquitin proteasome system (UPS) or autophagy. UPR activation is found in AD neurons displaying both early UPS pathology and autophagic pathology. Here we investigate whether activation of the UPR and/or EOR is employed to enhance the proteolytic capacity of neuronal cells. Expression of the immunoproteasome subunits ß2i and ß5i is increased in AD brain. However, expression of the proteasome subunits is not increased by the UPR or EOR. UPR activation does not relocalize the proteasome or increase overall proteasome activity. Therefore proteasomal degradation is not increased by ER stress. In contrast, UPR activation enhances autophagy and LC3 levels are increased in neurons displaying UPR activation in AD brain. Our data suggest that autophagy is the major degradational pathway following UPR activation in neuronal cells and indicate a connection between UPR activation and autophagic pathology in AD brain.

Cyclooxygenase-1 and -2 in the different stages of Alzheimer's disease pathology.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the deposition of beta amyloid (Abeta) protein and the formation of neurofibrillary tangles. In addition, there is an increase of inflammatory proteins in the brains of AD patients. Epidemiological studies, indicating that non-steroidal anti-inflammatory drugs (NSAIDs) decrease the risk of developing AD, have encouraged the study on the role of inflammation in AD. The best-characterized action of most NSAIDs is the inhibition of cyclooxygenase (COX). The expression of the constitutively expressed COX-1 and the inflammatory induced COX-2 has been intensively investigated in AD brain and different disease models for AD. Despite these studies, clinical trials with NSAIDs or selective COX-2 inhibitors showed little or no effect on clinical progression of AD. The expression levels of COX-1 and COX-2 change in the different stages of AD pathology. In an early stage, when low-fibrillar Abeta deposits are present and only very few neurofibrillary tangles are observed in the cortical areas, COX-2 is increased in neurons. The increased neuronal COX-2 expression parallels and colocalizes with the expression of cell cycle proteins. COX-1 is primarily expressed in microglia, which are associated with fibrillar Abeta deposits. This suggests that in AD brain COX-1 and COX-2 are involved in inflammatory and regenerating pathways respectively. In this review we will discuss the role of COX-1 and COX-2 in the different stages of AD pathology. Understanding the physiological and pathological role of cyclooxygenase in AD pathology may facilitate the design of therapeutics for the treatment or prevention of AD.

Rab6 is increased in Alzheimer's disease brain and correlates with endoplasmic reticulum stress.

Alzheimer's disease (AD) is characterized by deposits of aggregated proteins. Accumulation of aggregation-prone proteins activates protein quality control mechanisms, such as the unfolded protein response (UPR) in the endoplasmic reticulum (ER). We previously reported upregulation of the UPR marker BiP in AD brain. In this study, we investigated the small GTPase Rab6, which is involved in retrograde Golgi-ER trafficking and may function as a post-ER quality control system. Using immunohistochemistry and semiquantitative Western blotting, the expression of Rab6 was analysed in hippocampus, entorhinal and temporal cortex of 10 AD patients and six nondemented control subjects. Rab6 is upregulated in AD temporal cortex from Braak stage 3/4, the same stage that UPR activation is found. We observe increased neuronal Rab6 immunoreactivity in all brain areas examined. Although some neurones show colocalization of immunoreactivity for Rab6 and hyperphosphorylated tau, strong Rab6 staining does not colocalize with tangles. We find a highly significant correlation between the Rab6 and BiP levels. In vitro data show that Rab6 is not upregulated as a result of UPR activation or proteasome inhibition indicating an independent regulatory mechanism. Our data suggest that ER and post-ER protein quality control mechanisms are activated early in the pathology of AD.

Activation of the unfolded protein response in Parkinson's disease.

Parkinson's disease (PD) is, at the neuropathological level, characterized by the accumulation of misfolded proteins. The presence of misfolded proteins can trigger a cellular stress response in the endoplasmic reticulum (ER) called the Unfolded Protein Response (UPR). The UPR has been shown to be involved in cellular models for PD. In this study, we investigated UPR activation in the substantia nigra of control and PD patients. Immunoreactivity for the UPR activation markers phosphorylated pancreatic ER kinase (pPERK) and phosphorylated eukaryotic initiation factor 2alpha (peIF2alpha) is detected in neuromelanin containing dopaminergic neurons in the substantia nigra of PD cases but not in control cases. In addition, pPERK immunoreactivity is colocalized with increased alpha-synuclein immunoreactivity in dopaminergic neurons. These data show that the UPR is activated in PD and that UPR activation is closely associated with the accumulation and aggregation of alpha-synuclein.

The significance of neuroinflammation in understanding Alzheimer's disease.

The interest of scientists in the involvement of inflammation-related mechanisms in the pathogenesis of Alzheimer's disease (AD) goes back to the work of one of the pioneers of the study of this disease. About hundred years ago Oskar Fischer stated that the crucial step in the plaque formation is the extracellular deposition of a foreign substance that provokes an inflammatory reaction followed by a regenerative response of the surrounding nerve fibers. Eighty years later immunohistochemical studies revealed that amyloid plaques are indeed co-localized with a broad variety of inflammation-related proteins (complement factors, acute-phase proteins, pro-inflammatory cytokines) and clusters of activated microglia. These findings have led to the view that the amyloid plaque is the nidus of a non-immune mediated chronic inflammatory response locally induced by fibrillar A beta deposits. Recent neuropathological studies show a close relationship between fibrillar A beta deposits, inflammation and neuroregeneration in relatively early stages of AD pathology preceding late AD stages characterized by extensive tau-related neurofibrillary changes. In the present work we will review the role of inflammation in the early stage of AD pathology and particularly the role of inflammation in A beta metabolism and deposition. We also discuss the possibilities of inflammation-based therapeutic strategies in AD.

The unfolded protein response is activated in Alzheimer's disease.

Alzheimer's disease (AD) is, at the neuropathological level, characterized by the accumulation and aggregation of misfolded proteins. The presence of misfolded proteins in the endoplasmic reticulum (ER) triggers a cellular stress response called the unfolded protein response (UPR) that may protect the cell against the toxic buildup of misfolded proteins. In this study we investigated the activation of the UPR in AD. Protein levels of BiP/GRP78, a molecular chaperone which is up-regulated during the UPR, was found to be increased in AD temporal cortex and hippocampus as determined by Western blot analysis. At the immunohistochemical level intensified staining of BiP/GRP78 was observed in AD, which did not co-localize with AT8-positive neurofibrillary tangles. In addition, we performed immunohistochemistry for phosphorylated (activated) pancreatic ER kinase (p-PERK), an ER kinase which is activated during the UPR. p-PERK was observed in neurons in AD patients, but not in non-demented control cases and did not co-localize with AT8-positive tangles. Overall, these data show that the UPR is activated in AD, and the increased occurrence of BiP/GRP78 and p-PERK in cytologically normal-appearing neurons suggest a role for the UPR early in AD neurodegeneration. Although the initial participation of the UPR in AD pathogenesis might be neuroprotective, sustained activation of the UPR in AD might initiate or mediate neurodegeneration.

Neuroinflammation and Alzheimer disease: clinical and therapeutic implications.

In Alzheimer disease brains, the amyloid plaques are closely associated with a locally induced, nonimmune-mediated, chronic inflammatory response without any apparent influx of leukocytes from the blood. The present findings indicate that in cerebral A beta diseases (Alzheimer disease, Down syndrome, hereditary cerebral hemorrhage with amyloidosis-Dutch type), the clinical symptoms are determined to a great extent by the site of inflammatory response. It was found that the formation of the amyloid-microglia complex seems to be a relatively early pathogenic event that precedes the process of severe destruction of the neuropil. The idea that inflammation is implicated in Alzheimer pathology has received support from the epidemiologic studies indicating that the use of anti-inflammatory drugs can prevent or retard the Alzheimer disease process. In this contribution, we review the relationship between inflammation and clinical manifestation and the opportunities for anti-inflammatory treatments in Alzheimer disease.

Complement C1-inhibitor expression in Alzheimer's disease.

In situ and in vitro studies suggest that activation of locally produced complement factors may act as a mediator between amyloid deposits and neurodegenerative changes seen in Alzheimer's disease (AD). C1-esterase inhibitor (C1-Inh), which regulates activation of C1 of the complement classical pathway, can be detected immunohistochemically in its inactivated form in activated astrocytes and dystrophic neurites in AD plaque areas. In this study, designed to investigate the cellular source of C1-Inh, C1-Inh was found to be secreted in a functionally active form by astrocytes cultured from postmortem human brain specimens as well as by neuroblastoma cell lines. Recombinant human interferon-gamma (IFN-gamma), which stimulates C1-Inh synthesis in various cell types, several-fold stimulated C1-Inh protein secretion by cultured human astrocytes derived from different regions of the central nervous system and by one (SK-N-SH) of two neuroblastoma cell lines (SK-N-SH and IMR-32) included in this study. In contrast to IFN-gamma, other cytokines [interleukin (IL)-1beta, IL-6 and tumor necrosis factor (TNF)-alpha] that can be found in brain areas affected by AD, did not stimulate C1-Inh secretion by astrocytes or neuroblastomas in vitro. This inability to secrete C1-Inh is probably due to unresponsiveness at the transcriptional level, since C1-Inh secretion paralleled the expression of the 2.1-kb C1-Inh mRNA. In situ hybridization with a C1-Inh RNA antisense probe labeled neurons rather than astrocytes, suggesting a role for neurons as producers of complement regulatory proteins in vivo. Since IFN-gamma is apparently lacking in the brain parenchyma, and amyloid plaque-associated cytokines (IL-1beta, IL-6, TNF-alpha) do not stimulate C1-Inh expression in vitro, the nature of the stimulus responsible for neuronal C1-Inh expression in AD brains remains to be investigated.

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.