J. J. M. Hoozemans

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.

The significance of neuroinflammation in understanding Alzheimer’s disease

Summary.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 Aβ deposits. Recent neuropathological studies show a close relationship between fibrillar Aβ 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 Aβ metabolism and deposition. We also discuss the possibilities of inflammation-based therapeutic strategies in AD.

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

The initial stages of Alzheimers 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 Alzheimers disease pathogenesis. These brain changes precede the neurofibrillary pathology and the extensive process of neurodestruction and (astro)gliosis. Amyloid β deposition, inflammation and regenerative mechanisms are also early pathogenic events in transgenic mouse models harbouring the pathological Alzheimers 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 Alzheimers disease pathogenesis.

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 Alzheimers 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 Aβ-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 Aβ 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 Aβ 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.

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

Abstract Non-steroidal anti-inflammatory drugs (NSAIDs) may decrease the risk of developing Alzheimers 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)-1α, IL-1β, IL-6 and tumour necrosis factor (TNF)α), IL-1β 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 κB as well as a potent antioxidant, inhibited IL-1β induced PGE2 secretion. In addition, DEX reduced the IL-1β induced COX-2 immunoreactivity in the same concentration as wherein it inhibited PGE2 secretion. Palmitoyl trifluormethyl ketone, an inhibitor of Ca2+ independent phospholipase A2 (iPLA2) and a less potent inhibitor of cytosolic PLA2, dose-dependently reduced the IL-1β induced PGE2 secretion. This suggests that the IL-1β 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.

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.

DNA polymerase-beta is expressed early in neurons of Alzheimer's disease brain and is loaded into DNA replication forks in neurons challenged with beta-amyloid

Cultured neurons exposed to synthetic β-amyloid (Aβ) fragments reenter the cell cycle and initiate a pathway of DNA replication that involves the repair enzyme DNA polymerase-β (DNA pol-β) before undergoing apoptotic death. In this study, by performing coimmunoprecipitation experiments on cross-linked nucleoprotein fragments from Aβ-treated neurons, we demonstrate that DNA pol-β coimmunoprecipitates with cell division cycle 45 (Cdc45) and with DNA primase in short nucleoprotein fragments. This indicates that DNA pol-β is loaded into neuronal DNA replication forks after Aβ treatment. In response to Aβ the canonical DNA-synthesizing enzyme DNA pol-δ also was loaded into neuronal replication forks, but at later times than DNA pol-β. Methoxyamine, an inhibitor of the apurinic/apyrimidinic endonuclease that allows for the recruitment of DNA pol-β during the process of base excision repair (BER), failed to affect coimmunoprecipitation between DNA pol-β and Cdc45, indicating that DNA pol-β loading to the replication forks is independent of DNA breaks. However, methoxyamine reduced DNA replication and ensuing apoptosis in neurons exposed to Aβ, suggesting that an efficient BER process allows DNA replication to proceed up to the threshold for death. These data demonstrate that DNA pol-β is an essential component of the DNA replication machinery in Aβ-treated neurons and additionally support the hypothesis of a close association of cell cycle events with neuronal death in Alzheimers disease (AD). Accordingly, by investigating the neuronal expression of DNA pol-β, along with phosphorylated retinoblastoma protein and neurofibrillary changes in AD brain, we show an early involvement of DNA pol-β in the pathogenesis of AD.

The unfolded protein response affects neuronal cell cycle protein expression: implications for Alzheimer's disease pathogenesis

Alzheimers disease (AD) is 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). Previously, we have shown that the UPR is activated in AD neurons. In actively dividing cells, activation of the UPR is accompanied by decreased cell cycle protein expression and an arrest in the G1 phase of the cell cycle. Aberrant expression of cell cycle proteins has been observed in post mitotic neurons in AD and is suggested to be involved in neurodegeneration. In this study we show that the protein levels of BiP/GRP78, an ER-stress marker, is increased in Braak stages B and C for amyloid deposits. This is in contrast to the levels of cell cycle markers cyclin D1, cyclin E and phosphorylated retinoblastoma protein (ppRb) which are decreased in Braak stage C compared to Braak stage A for amyloid deposits. In addition, we report a negative correlation between neuronal expression of ppRb and expression levels of BiP/GRP78 in control and AD cases. Activation of the UPR in neuronal cells induces changes in cell cycle protein expression similar to these observed in AD brain. ER stress inducers tunicamycin and thapsigargin down-regulate cell cycle proteins ppRb and cyclin D1 in differentiated neuroblastoma cells. In contrast, protein levels of p27, a cyclin dependent kinase inhibitor, are increased after induction of ER-stress using tunicamycin. These data suggest that activation of the UPR affects cell cycle protein expression in neurons during neurodegeneration in AD.

Neuroinflammation in plaque and vascular beta-amyloid disorders: clinical and therapeutic implications.

Background: The cerebral β-amyloid (Aβ) disorders show a great variability in the distribution of parenchymal and vascular amyloid deposits. Objective: To study the relationship between amyloid deposition and inflammatory responses in three distinct subtypes of cerebral Aβ disorders. Methods: The distribution of inflammatory proteins and cells in vascular and plaque amyloid deposits was evaluated in postmortem brain tissue using immunohistochemistry. The effects of a mixture of Aβ peptides and inflammation-related Aβ-associated proteins were studied in postmortem obtained human microglia cell cultures. Results: The chronic inflammatory response is associated with amyloid plaques (but not with amyloid in the walls of larger vessels) in Alzheimer’s disease (AD), with amyloid in cerebral arteries in hereditary cerebral hemorrhage with amyloidosis-Dutch type and with amyloid microangiopathy in the vascular variant of AD. Aβ1–42 fibrils complexed with complement factor C1q and serum amyloid P component (the relevant amyloid-associated proteins) stimulate the production of proinflammatory cytokines in human microglia cell cultures and this production is attenuated by minocycline. Conclusion: The pattern of the chronic inflammatory response associated with fibrillar Aβ is strikingly different in the three studied types of Aβ disorders. The site of the fibrillar Aβ-induced chronic inflammatory response is closely related to clinical symptoms. Minocycline is a drug of interest to inhibit microglia-mediated neuroinflammatory response in Aβ brain disorders.

DIFFERENT PATHOLOGICAL DISTRIBUTION PATTERN OF PHOSPHORYLATED TAU AND MICROGLIA IN AMNESTIC AND NON-AMNESTIC ALZHEIMER’S DISEASE

have higher dementia prevalence, different genetic markers and higher vascular risk factors. However, pathological underpinnings are unknown. Methods:We included 111 AA demented autopsies and 444 random Caucasians autopsies and compared the two groups regarding demographics, cognition, apolipoprotein E (ApoE), comorbidities including cerebrovascular pathology and Lewy body disease (LBD), clinical and pathological diagnoses, neuropathological Alzheimer disease (AD) criteria, quantitative Ab and tau scales, neuropathological vascular findings and nonAlzheimer diseases. Results:When comparing AA and Caucasians the primary clinical diagnoses differed but the primary pathological diagnoses did not. Importantly, there is evidence that AA had more AD-related pathology, measured as meeting the NIA/Reagan and CERAD criteria and throughAD neuropathological features (Braak Stage, CERAD neuritic and diffuse plaque scores). ApoE 4 was more common in AA than Caucasians. There were significant differences vascular, LBD and TDP pathology. Conclusions: Primary pathological diagnosis does not differ between groups however AD, LBD and vascular pathology are more common in AA and TDP and Tau less common. ApoE accounts for most of the AD pathology scales differences. These similarities and differences are important in public policy.