Neuritic Plaques In Alzheimer's Disease Research Articles

Associations of Fully Automated CSF and Novel Plasma Biomarkers With Alzheimer Disease Neuropathology at Autopsy.

ObjectiveTo study CSF biomarkers of Alzheimer disease (AD) analyzed by fully automated Elecsys immunoassays compared to neuropathologic gold standards and to compare their accuracy to plasma phosphorylated tau (p-tau181) measured with a novel single molecule array method.MethodsWe studied antemortem Elecsys-derived CSF biomarkers in 45 individuals who underwent standardized postmortem assessments of AD and non-AD neuropathologic changes at autopsy. In a subset of 26 participants, we also analyzed antemortem levels of plasma p-tau181 and neurofilament light (NfL). Reference biomarker values were obtained from 146 amyloid-PET–negative healthy controls (HC).ResultsAll CSF biomarkers clearly distinguished pathology-confirmed AD dementia (n = 27) from HC (area under the curve [AUC] 0.86–1.00). CSF total tau (t-tau), p-tau181, and their ratios with β-amyloid1-42 (Aβ1-42) also accurately distinguished pathology-confirmed AD from non-AD dementia (n = 8; AUC 0.94–0.97). In pathology-specific analyses, intermediate to high Thal amyloid phases were best detected by CSF Aβ1-42 (AUC [95% confidence interval] 0.91 [0.81–1]), while intermediate to high scores for Consortium to Establish a Registry for Alzheimer's Disease neuritic plaques and Braak tau stages were best detected by CSF p-tau181 (AUC 0.89 [0.79–0.99] and 0.88 [0.77–0.99], respectively). Optimal Elecsys biomarker cutoffs were derived at 1,097, 229, and 19 pg/mL for Aβ1-42, t-tau, and p-tau181. In the plasma subsample, both plasma p-tau181 (AUC 0.91 [0.86–0.96]) and NfL (AUC 0.93 [0.87–0.99]) accurately distinguished those with pathology-confirmed AD (n = 14) from HC. However, only p-tau181 distinguished AD from non-AD dementia cases (n = 4; AUC 0.96 [0.88–1.00]) and showed a similar, although weaker, pathologic specificity for neuritic plaques (AUC 0.75 [0.52–0.98]) and Braak stage (AUC 0.71 [0.44–0.98]) as CSF p-tau181.ConclusionElecsys-derived CSF biomarkers detect AD neuropathologic changes with very high discriminative accuracy in vivo. Preliminary findings support the use of plasma p-tau181 as an easily accessible and scalable biomarker of AD pathology.Classification of EvidenceThis study provides Class II evidence that fully automated CSF t-tau and p-tau181 measurements discriminate between autopsy-confirmed AD and other dementias.

Deep Learning-Based Image Classification in Differentiating Tufted Astrocytes, Astrocytic Plaques, and Neuritic Plaques.

This study aimed to develop a deep learning-based image classification model that can differentiate tufted astrocytes (TA), astrocytic plaques (AP), and neuritic plaques (NP) based on images of tissue sections stained with phospho-tau immunohistochemistry. Phospho-tau-immunostained slides from the motor cortex were scanned at 20× magnification. An automated deep learning platform, Google AutoML, was used to create a model for distinguishing TA in progressive supranuclear palsy (PSP) from AP in corticobasal degeneration (CBD) and NP in Alzheimer disease (AD). A total of 1500 images of representative tau lesions were captured from 35 PSP, 27 CBD, and 33 AD patients. Of those, 1332 images were used for training, and 168 images for cross-validation. We tested the model using 100 additional test images taken from 20 patients of each disease. In cross-validation, precision and recall for each individual lesion type were 100% and 98.0% for TA, 98.5% and 98.5% for AP, and 98.0% and 100% for NP, respectively. In a test set, all images of TA and NP were correctly predicted. Only eleven images of AP were predicted to be TA or NP. Our data indicate the potential usefulness of deep learning-based image classification methods to assist in differential diagnosis of tauopathies.

Human Amyloid-β40 Kinetics after Intravenous and Intracerebroventricular Injections and Calcitriol Treatment in Rats In Vivo.

Amyloid-β peptides of 40 and 42 amino acid lengths, which are synthesized in neurons and degraded in the brain and liver, have the potential to aggregate and form neuritic plaques in Alzheimer disease. The kinetics of human amyloid-β (hAβ) 40 were examined in the rat pursuant to intravenous and intracerebroventricular administration after pretreatment with calcitriol, the active vitamin D receptor ligand (6.4 nmol·kg-1 in 0.3 ml corn oil every other day for four intraperitoneal doses) to induce P-glycoprotein (P-gp) and enhance hAβ40 brain efflux. The interference of hAβ40 by media matrix that suppressed absorbance readings in the ELISA assay was circumvented with use of different calibration curves prepared in Standard Dilution Buffer, undiluted, 10-10,000 or 5-fold diluted plasma, or artificial cerebrospinal fluid. Simultaneous fitting of hAβ40 plasma and cerebrospinal fluid (CSF) data after intravenous and intracerebroventricular administration were described by catenary-mammillary models comprising of a central and two peripheral compartments, the brain, and one to four CSF compartments. The model with only one CSF compartment (model I) best fitted the intravenous data that showed a faster plasma decay t1/2 and slower equilibration between plasma and brain/CSF. Calcitriol induction increased the brain efflux rate constant, k41 (1.8-fold), at the blood-brain barrier when compared with the control group, as confirmed by the 2-fold (P < 0.05) increase in brain P-gp relative protein expression. SIGNIFICANCE STATEMENT: An accurate description of the kinetic behavior of human amyloid-β (hAβ) 40 is needed in defining the toxic peptide as a biomarker of Alzheimer disease. Modeling of hAβ40 data after intravenous and intracerebroventricular administration to the rat revealed an initially faster plasma half-life that reflected faster peripheral distribution but slower equilibration between plasma and brain/cerebrospinal fluid even with calcitriol pretreatment that increased P-glycoprotein protein expression and enhanced efflux clearance from brain.

Clinician-judged hearing impairment and associations with neuropathologic burden.

To examine whether neuropathologic burden is associated with hearing impairment. We studied 2,755 autopsied participants ≥55 years of age from the National Alzheimer's Coordinating Center database. Participants had at least 1 clinical evaluation at US National Institute on Aging-funded Alzheimer's Disease Center no more than 2 years before death. Patients were classified as hearing impaired by clinician report at baseline. Common dementia neuropathologies included Alzheimer disease pathologic change (Consortium to Establish a Registry for Alzheimer's Disease neuritic plaque density, neurofibrillary degeneration Braak stage), Lewy body disease, gross infarcts, and microinfarcts. Logistic regression models predicted impaired hearing with adjustment for age at death, sex, race, education, center, and follow-up time. Relative risks were calculated with the use of marginal standardization. Impaired hearing was common (32%). In participants who were cognitively normal at baseline (n = 580), impaired hearing was associated with higher Braak stage (relative risk [RR] 1.33 per 2-stage increase, 95% confidence interval [CI] 1.06-1.66) but not other pathologies. In participants with dementia (n = 2,175), impaired hearing was positively associated with microinfarcts (RR 1.18, 95% CI 1.00-1.39) and inversely associated with neuritic plaque density (RR 0.91 per score increase, 95% CI 0.85-0.99). Development of impaired hearing in those with cognitive impairment was associated with neocortical Lewy bodies (1.26, 95% CI 1.02-1.55). Impaired hearing, reported before the onset of cognitive impairment, was associated with increased neurofibrillary tangle burden. Impaired hearing in those with cognitive impairment was associated with microinfarcts and neocortical Lewy bodies but not typical Alzheimer disease pathologic change. Functional hearing problems may be a preclinical marker of neurofibrillary neurodegeneration, although replication is needed.

Identification of rare RTN3 variants in Alzheimer's disease in Han Chinese.

Reticulon 3 (RTN3) is a neuronally-expressed reticulon family protein that was previously shown to negatively regulate BACE1, a protease that is required for the generation of β-amyloid peptides (Aβ) from amyloid precursor protein. Despite biochemical and morphological evidence that supports a role of RTN3 in the formation of neuritic amyloid plaques, no systematic analyses of RTN3 mutations in patients with Alzheimer's disease (AD) have yet been reported. RTN3 were targeted sequenced in 154 sporadic early-onset and 285 late-onset AD patients. Luciferase reporter assay and kymographs were performed to analysis the expression of RNT3 and BACE1-RFP particle mobility on cells transfected with wild-type or variants RTN3 constructs. We identified heterozygous variants such as c.-8G>T, c.17C>A, c.42C>T, and c.116C>T from patients in the early-onset AD group and c.-8G>T, c.17C>A, from patients in the late-onset AD group. Such variants of RTN3 were not observed in control individuals. Further biochemical studies show that the RTN3 c.-8G>T variant in the 5'-untranslated region appears to cause reduced expression of RTN3. The RTN3 c.116 C>T variant causes a change of codon T39 to M39 (T39M). Overexpression of RTN3 T39M in cultured neurons led to impaired axonal transport of BACE1. The variants found in this study are likely genetic modifiers for RTN3-mediated formation of neuritic plaques in AD.

Characterizing Apolipoprotein E ε4 Carriers and Noncarriers With the Clinical Diagnosis of Mild to Moderate Alzheimer Dementia and Minimal β-Amyloid Peptide Plaques.

β-Amyloid peptide (Aβ) plaques are a cardinal neuropathologic feature of Alzheimer disease (AD), yet more than one-third of apolipoprotein E ε4 (APOE4) noncarriers with the clinical diagnosis of mild to moderate Alzheimer dementia may not meet positron emission tomographic criteria for significant cerebral amyloidosis. To clarify the percentage of APOE4 carriers and noncarriers with the primary clinical diagnosis of mild to moderate Alzheimer dementia near the end of life and minimal Aβ plaques noted at autopsy and the extent to which these cases are associated with appreciable neurofibrillary degeneration or a primary neuropathologic diagnosis other than AD. Data on participants included in this study were obtained from the National Alzheimer Coordinating Center's Uniform Data Set, which comprises longitudinal clinical assessments performed at the AD centers funded by the National Institute on Aging. Neuropathology data are available for the subset of participants who died. A total of 100 APOE4 noncarriers and 100 APOE4 carriers had the primary clinical diagnosis of mild to moderate Alzheimer dementia at their last visit, known APOE4 genotype, died within the ensuing 24 months, and underwent neuropathologic evaluation on autopsy. The study was conducted from September 1, 2005, to September 1, 2012; analysis was performed from October 9, 2012, to March 20, 2015. Standardized histopathologic assessments of AD neuropathologic changes were the primary measures of interest in this study, specifically Consortium to Establish a Registry for Alzheimer's Disease neuritic plaque density score, diffuse plaque density score, and Braak stage for neurofibrillary degeneration. The distributions of scores for these measures were the primary outcomes. Of the 37 APOE4 noncarriers with minimal neuritic plaques, 16 individuals (43.2%) had Braak stages III to VI ratings, and 15 of the others (75.0%) met neuropathologic criteria for other dementia-related diseases. Of the 13 APOE4 carriers with minimal neuritic plaques, 6 individuals (46.2%) had Braak stages III to VI ratings and met neuropathologic criteria for other dementia-related diseases. Similarly, of the 7 APOE4 carriers with minimal neuritic plaques and Braak stages 0 to II, 4 participants (57.1%) were thought to have pathologic changes and alterations resulting from non-AD neuropathologic features. In this study, more than one-third of APOE4 noncarriers with the primary clinical diagnosis of mild to moderate Alzheimer dementia had minimal Aβ plaque accumulation in the cerebral cortex and, thus, may show limited or no benefit from otherwise effective anti-Aβ treatment. Almost half of the participants with a primary clinical diagnosis of mild to moderate Alzheimer dementia and minimal Aβ plaque accumulation had an extensive topographic distribution of neurofibrillary degeneration. Additional studies are needed to better understand and provide treatment for patients with this unexpectedly common cliniconeuropathologic condition.

Amyloid-Beta (1-40) and the Risk of Death From Cardiovascular Causes in Patients With Coronary Heart Disease

BackgroundThe amyloid beta peptide is the major protein constituent of neuritic plaques in Alzheimer disease and appears to play a central role in vascular inflammation pathophysiology. ObjectivesThis study sought to determine the clinical value of amyloid-beta 1-40 (Abeta40) measurement in predicting cardiovascular (CV) mortality in patients with coronary heart disease (CHD) and arterial stiffness progression in young healthy subjects. MethodsAbeta40 was retrospectively measured in blood samples collected from 3 independent prospective cohorts and 2 case-control cohorts (total N = 1,464). Major adverse cardiac events (MACE) were assessed in the 2 prospective cohorts (n = 877) followed for a median of 4.4 years. To look at effects on subclinical disease, arterial stiffness was evaluated at baseline and after 5-year follow-up (n = 107) in young healthy subjects. The primary endpoint was the predictive value of Abeta40 for CV mortality and outcomes in patients with CHD. ResultsIn Cox proportional hazards models adjusted for age, sex, estimated glomerular filtration rate, left ventricular ejection fraction, high-sensitivity C-reactive protein, and high-sensitivity troponin T, Abeta40 independently predicted CV death and MACE in patients with CHD (p < 0.05 for all). After multivariate adjustment, Abeta40 levels conferred a substantial enhancement of net reclassification index and integrated discrimination improvement of individuals at risk in the total combined CHD cohort over the best predictive model. Further cohort-based analysis revealed that Abeta40 levels were significantly and independently associated with arterial stiffness progression, incident subclinical atherosclerosis, and incident CHD. ConclusionsMeasuring blood levels of Abeta40 identified patients at high risk for CV death.

Disruption of cerebrospinal fluid flow through the olfactory system may contribute to Alzheimer's disease pathogenesis.

Plaques and tangles may be manifestations of a more substantial underlying cause of Alzheimer's disease (AD). Disease-related changes in the clearance of amyloid-β (Aβ) and other metabolites suggest this cause may involve cerebrospinal fluid (CSF) flow through the interstitial spaces of the brain, including an archaic route through the olfactory system that predates neocortical expansion by three hundred million years. This olfactory CSF conduit (OCC) runs from the medial temporal lobe (MTL) along the lateral olfactory stria, through the olfactory trigone, and down the olfactory tract to the olfactory bulb, where CSF seeps through the cribriform plate to the nasal submucosa. Olfactory dysfunction is common in AD and could be related to alterations in CSF flow along the OCC. Further, reductions in OCC flow may impact CSF hydrodynamics upstream in the MTL and basal forebrain, resulting in less efficient Aβ removal from those areas-among the first affected by neuritic plaques in AD. Factors that reduce CSF drainage across the cribriform plate and slow the clearance of metabolite-laden CSF could include aging-related bone changes, head trauma, inflammation of the nasal epithelium, and toxins that affect olfactory neuron survival and renewal, as well as vascular effects related to diabetes, obesity, and atherosclerosis-all of which have been linked to AD risk. Problems with CSF-mediated clearance could also provide a link between these seemingly disparate factors and familial AD mutations that induce plaque and tangle formation. I hypothesize that disruptions of CSF flow across the cribriform plate are important early events in AD, and I propose that restoring this flow will enhance the drainage of Aβ oligomers and other metabolites from the MTL.

Altered distribution of the EphA4 kinase in hippocampal brain tissue of patients with Alzheimer’s disease correlates with pathology

Synaptic dysfunction occurs early in the progression of Alzheimer’s disease (AD) and correlates with memory decline. There is emerging evidence that deregulation of Erythropoietin-producing hepatocellular (Eph) receptor tyrosine kinases (RTK) signaling contributes to the aberrant synaptic functions associated with neurodegeneration. The Eph receptor A4 is highly expressed in human adult hippocampal brain tissue and was previously linked to cognitive impairment in a transgenic mouse model for AD. Whether EphA4 levels are altered in AD brain remains elusive. Therefore we investigated the protein levels and localization of EphA4 in human hippocampus derived from AD (n = 29) as well as non-demented control cases (n = 19).The total EphA4 protein levels were not changed in AD patients compared to control cases. However, immunohistochemical localization of EphA4 revealed an altered distribution in AD compared to control hippocampus. EphA4 immunoreactivity was observed in plaque-like structures in AD cases. Double-labelling with phosphorylated tau and amyloid beta indicates that EphA4 co-localizes with neuritic plaques in AD. This altered distribution pattern was observed at early stages (Braak stage II) and correlates with the hallmarks of AD pathology suggesting a reduced availability of EphA4 that is likely to contribute to synaptic dysfunction that occurs early in AD.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-014-0079-9) contains supplementary material, which is available to authorized users.

Retinoic acid-induced upregulation of the metalloendopeptidase nardilysin is accelerated by co-expression of the brain-specific protein p42 IP4 (centaurin α1; ADAP1) in neuroblastoma cells

The mainly neuronally expressed protein p42 IP4 (centaurin α1; ADAP1), which interacts with the metalloendopeptidase nardilysin (NRD) was found to be localized in neuritic plaques in Alzheimer disease (AD) brains. NRD was shown to enhance the cleavage of the amyloid precursor protein (APP) by α-secretases, thereby increasing the release of neuroprotective sAPPα. We here investigated in vitro the biochemical interaction of p42 IP4 and NRD and studied the physiological interaction in SH-SY5Y cells. NRD is a member of the M16 family of metalloendopeptidases. Some members of this M16 family act bi-functionally, as protease and as non-enzymatic scaffold protein. Here, we show that p42 IP4 enhances the enzymatic activity of NRD 3–4 times. However, p42 IP4 is not a substrate for NRD. Furthermore, we report that differentiation of SH-SY5Y cells by stimulation with 10 μM retinoic acid (RA) results in upregulation of NRD protein levels, with a 6-fold rise after 15 days. NRD is expressed in the neurites of RA-stimulated SH-SY5Y cells, and localized in vesicular structures. Since p42 IP4 is not expressed in untreated SH-SY5Y cells, we could use this cell system as a model to find out, whether there is a functional interaction. Interestingly, SH-SY5Y cells, which we stably transfected with GFP-tagged-p42 IP4 showed an enhanced NRD protein expression already at an earlier time point after RA stimulation.

Age, Alzheimer's disease and dementia in the Baltimore Longitudinal Study of Ageing

Recent studies suggest that dementia in the most elderly (90 years of age and above) is only modestly related to Alzheimer's disease pathology. This raises the possibility that other, as yet unknown, disease processes may underlie dementia in this rapidly growing demographic group, and that efforts designed to combat Alzheimer's disease may not be appropriate for treating dementia in very elderly subjects. To study this question more closely, we examined the relationship between neocortical Alzheimer-type brain pathology and dementia in consecutive autopsies from 209 participants in the Baltimore Longitudinal Study of Ageing, a prospective longitudinal cohort study of the effect of ageing on cognition. Almost half of the cohort was older than 90 years of age at death. We found that several measures of neocortical Alzheimer's pathology, including the Consortium to Establish a Registry of Alzheimer's Disease neuritic plaque score and the Braak neurofibrillary tangle score, remained significant predictors of dementia, independent of age. In participants older than 90 years of age, intracranial atherosclerosis emerged as an important predictor of dementia in subjects with low Alzheimer's pathology scores, but did not mitigate the importance or population attributable risk of high Alzheimer's pathology scores on the odds of dementia. There was evidence that the threshold score for neurofibrillary pathology to cause dementia increased in the oldest subjects, but this was offset by an overall increase in neurofibrillary pathology in this age group. We conclude that neocortical Alzheimer's disease pathology remains significantly correlated with dementia, independent of age. In the most elderly, atherosclerosis also emerged as a cause of dementia in subjects with low Alzheimer's pathology scores. We found no evidence for a significant number of elderly subjects having dementia without an apparent cause.

TGF-β1 blockade of microglial chemotaxis toward Aβ aggregates involves SMAD signaling and down-regulation of CCL5

BackgroundOveractivated microglia that cluster at neuritic plaques constantly release neurotoxins, which actively contribute to progressive neurodegeneration in Alzheimer's disease (AD). Therefore, attenuating microglial clustering can reduce focal neuroinflammation at neuritic plaques. Previously, we identified CCL5 and CCL2 as prominent chemokines that mediate the chemotaxis of microglia toward beta-amyloid (Aβ)aggregates. Although transforming growth factor-β1 (TGF-β1) has been shown to down-regulate the expression of chemokines in activated microglia, whether TGF-β1 can reduce the chemotaxis of microglia toward neuritic plaques in AD remains unclear.MethodsIn the present study, we investigated the effects of TGF-β1 on Aβ-induced chemotactic migration of BV-2 microglia using time-lapse recording, transwell assay, real-time PCR, ELISA, and western blotting.ResultsThe cell tracing results suggest that the morphological characteristics and migratory patterns of BV-2 microglia resemble those of microglia in slice cultures. Using this model system, we discovered that TGF-β1 reduces Aβ-induced BV-2 microglial clustering in a dose-dependent manner. Chemotactic migration of these microglial cells toward Aβ aggregates was significantly attenuated by TGF-β1. However, these microglia remained actively moving without any reduction in migration speed. Pharmacological blockade of TGF-β1 receptor I (ALK5) by SB431542 treatment reduced the inhibitory effects of TGF-β1 on Aβ-induced BV-2 microglial clustering, while preventing TGF-β1-mediated cellular events, including SMAD2 phosphorylation and CCL5 down-regulation.ConclusionsOur results suggest that TGF-β1 reduces Aβ-induced microglial chemotaxis via the SMAD2 pathway. The down-regulation of CCL5 by TGF-β1 at least partially contributes to the clustering of microglia at Aβ aggregates. The attenuating effects of SB431542 upon TGF-β1-suppressed microglial clustering may be mediated by restoration of CCL5 to normal levels. TGF-β1 may ameliorate microglia-mediated neuroinflammation in AD by preventing activated microglial clustering at neuritic plaques.

Ultrastructural study of florid plaques in variant Creutzfeldt–Jakob disease: a comparison with amyloid plaques in kuru, sporadic Creutzfeldt–Jakob disease and Gerstmann–Sträussler–Scheinker disease

Although the histological features of the amyloid plaques in variant Creutzfeldt-Jakob disease (vCJD) are distinct from those in other forms of prion disease [kuru, sporadic Creutzfeldt-Jakob disease (sCJD) and Gerstmann-Sträussler-Scheinker disease (GSS)], their ultrastructural features have only been described in a single case report. To study vCJD plaques systematically and compare them with plaques in kuru, sCJD, GSS and Alzheimer disease (AD). Amyloid plaques were studied by transmission electron microscopy and image analysis in five cases of vCJD, three cases of GSS, two cases of sCJD, one case of kuru and five cases of AD. Immunohistochemistry was performed on paraffin sections from one case of vCJD, two cases of GSS, one case of kuru and two cases of sCJD. The florid plaques in vCJD were either compact or more diffuse; in both forms, the radiating fibrils were organized into thick 'tongues', in contrast to kuru plaques. Dystrophic neurites (DNs) containing lysosomal electron-dense bodies or vesicles surrounded florid plaques. Microglial cells were found within florid plaques; occasional amyloid fibrils were identified in membrane-bound pockets of microglial cells. In vCJD, there was significant tau immunoreactivity in DNs around florid plaques while, in sCJD, GSS and kuru, minimal tau immunoreactivity was observed around plaques. The ultrastructure of the florid plaques and DNs in vCJD is more reminiscent of neuritic plaques in AD than kuru or multicentric plaques. These findings may reflect differences both in the strains of the transmissible agents responsible for these disorders and in host factors.

Targets of Caspase-6 Activity in Human Neurons and Alzheimer Disease

Caspase-6 activation occurs early in Alzheimer disease and sometimes precedes the clinical manifestation of the disease in aged individuals. The active Caspase-6 is localized in neuritic plaques, in neuropil threads, and in neurofibrillary tangles containing neurons that are not morphologically apoptotic in nature. To investigate the potential consequences of the activation of Caspase-6 in neurons, we conducted a proteomics analysis of Caspase-6-mediated cleavage of human neuronal proteins. Proteins from the cytosolic and membrane subcellular compartments were treated with recombinant active Caspase-6 and compared with undigested proteins by two-dimensional gel electrophoresis. LC/MS/MS analyses of the proteins that were cleaved identified 24 different potential protein substrates. Of these, 40% were cytoskeleton or cytoskeleton-associated proteins. We focused on the cytoskeleton proteins because these are critical for neuronal structure and function. Caspase-6 cleavage of alpha-Tubulin, alpha-Actinin-4, Spinophilin, and Drebrin was confirmed. At least one Caspase-6 cleavage site was identified for Drebrin, Spinophilin, and alpha-Tubulin. A neoepitope antiserum to alpha-Tubulin cleaved by Caspase-6 immunostained neurons, neurofibrillary tangles, neuropil threads, and neuritic plaques in Alzheimer disease and co-localized with active Caspase-6. These results imply that the early and neuritic activation of Caspase-6 in Alzheimer disease could disrupt the cytoskeleton network of neurons, resulting in impaired neuronal structure and function in the absence of cell death. This study provides novel insights into the pathophysiology of Alzheimer disease.

Expression profiles for macrophage alternative activation genes in AD and in mouse models of AD

BackgroundMicroglia are associated with neuritic plaques in Alzheimer disease (AD) and serve as a primary component of the innate immune response in the brain. Neuritic plaques are fibrous deposits composed of the amyloid beta-peptide fragments (Abeta) of the amyloid precursor protein (APP). Numerous studies have shown that the immune cells in the vicinity of amyloid deposits in AD express mRNA and proteins for pro-inflammatory cytokines, leading to the hypothesis that microglia demonstrate classical (Th-1) immune activation in AD. Nonetheless, the complex role of microglial activation has yet to be fully explored since recent studies show that peripheral macrophages enter an "alternative" activation state.MethodsTo study alternative activation of microglia, we used quantitative RT-PCR to identify genes associated with alternative activation in microglia, including arginase I (AGI), mannose receptor (MRC1), found in inflammatory zone 1 (FIZZ1), and chitinase 3-like 3 (YM1).ResultsOur findings confirmed that treatment of microglia with anti-inflammatory cytokines such as IL-4 and IL-13 induces a gene profile typical of alternative activation similar to that previously observed in peripheral macrophages. We then used this gene expression profile to examine two mouse models of AD, the APPsw (Tg-2576) and Tg-SwDI, models for amyloid deposition and for cerebral amyloid angiopathy (CAA) respectively. AGI, MRC1 and YM1 mRNA levels were significantly increased in the Tg-2576 mouse brains compared to age-matched controls while TNFα and NOS2 mRNA levels, genes commonly associated with classical activation, increased or did not change, respectively. Only TNFα mRNA increased in the Tg-SwDI mouse brain. Alternative activation genes were also identified in brain samples from individuals with AD and were compared to age-matched control individuals. In AD brain, mRNAs for TNFα, AGI, MRC1 and the chitinase-3 like 1 and 2 genes (CHI3L1; CHI3L2) were significantly increased while NOS2 and IL-1β mRNAs were unchanged.ConclusionImmune cells within the brain display gene profiles that suggest heterogeneous, functional phenotypes that range from a pro-inflammatory, classical activation state to an alternative activation state involved in repair and extracellular matrix remodeling. Our data suggest that innate immune cells in AD may exhibit a hybrid activation state that includes characteristics of classical and alternative activation.

Distinct transcriptional regulation and function of the human BACE2 and BACE1 genes

Amyloid beta protein (Abeta) is the principal component of neuritic plaques in Alzheimer's disease (AD). Abeta is derived from beta amyloid precursor protein (APP) by beta- and gamma-secretases. Beta-site APP cleaving enzyme 1 (BACE1) has been identified as the major beta-secretase. BACE2 is the homolog of BACE1. The BACE2 gene is on chromosome 21 and has been implicated in the pathogenesis of AD. However, the function of BACE2 in Abeta generation is controversial. Some studies have shown that BACE2 cleaved APP at the beta-site whereas other studies showed it cleaved around the alpha-secretase site. To elucidate the involvement of BACE2 in AD pathogenesis, we compared BACE2 and BACE1 gene regulation and their functions in Abeta generation. We cloned and functionally characterized the human BACE2 promoter. The BACE2 gene is controlled by a TATA-less promoter. Though Sp1 can regulate both BACE1 and BACE2 genes, comparative sequence analysis and transcription factor prediction showed little similarity between the two promoters. BACE1 increased APP cleavage at the beta-site and Abeta production whereas BACE2 did not. Overexpression of BACE2 significantly increased sAPP levels in conditioned media but markedly reduced Abeta production. Knockdown of BACE2 resulted in increased APP C83. Our data indicate that despite being homologous in amino acid sequence, BACE2 and BACE1 have distinct functions and transcriptional regulation. BACE2 is not a beta-secretase, but processes APP within the Abeta domain at a site downstream of the alpha-secretase cleavage site. Our data argue against BACE2 being involved in the formation of neuritic plaques in AD.

The cholinergic hypothesis of age and Alzheimer's disease-related cognitive deficits: recent challenges and their implications for novel drug development.

The cholinergic hypothesis was initially presented over 20 years ago and suggests that a dysfunction of acetylcholine containing neurons in the brain contributes substantially to the cognitive decline observed in those with advanced age and Alzheimer's disease (AD). This premise has since served as the basis for the majority of treatment strategies and drug development approaches for AD to date. Recent studies of the brains of patients who had mild cognitive impairment or early stage AD in which choline acetyltransferase and/or acetylcholinesterase activity was unaffected (or even up-regulated) have, however, led some to challenge the validity of the hypothesis as well as the rationale for using cholinomimetics to treat the disorder, particularly in the earlier stages. These challenges, primarily based on assays of post mortem enzyme activity, should be taken in perspective and evaluated within the wide range of cholinergic abnormalities known to exist in both aging and AD. The results of both post mortem and antemortem studies in aged humans and AD patients, as well as animal experiments suggest that a host of cholinergic abnormalities including alterations in choline transport, acetylcholine release, nicotinic and muscarinic receptor expression, neurotrophin support, and perhaps axonal transport may all contribute to cognitive abnormalities in aging and AD. Cholinergic abnormalities may also contribute to noncognitive behavioral abnormalities as well as the deposition of toxic neuritic plaques in AD. Therefore, cholinergic-based strategies will likely remain valid as one approach to rational drug development for the treatment of AD other forms of dementia.

The Alzheimer's A beta -peptide is deposited at sites of complement activation in pathologic deposits associated with aging and age-related macular degeneration.

Age-related macular degeneration (AMD) is a leading cause of irreversible vision loss in older individuals worldwide. The disease is characterized by abnormal extracellular deposits, known as drusen, that accumulate along the basal surface of the retinal pigmented epithelium. Although drusen deposition is common in older individuals, large numbers of drusen and/or extensive areas of confluent drusen represent a significant risk factor for AMD. Widespread drusen deposition is associated with retinal pigmented epithelial cell dysfunction and degeneration of the photoreceptor cells of the neural retina. Recent studies have shown that drusen contain a variety of immunomodulatory molecules, suggesting that the process of drusen formation involves local inflammatory events, including activation of the complement cascade. Similar observations in Alzheimer's disease (AD) have lead to the hypothesis that chronic localized inflammation is an important element of AD pathogenesis, with significant neurodegenerative consequences. Accordingly, the amyloid beta (A beta) peptide, a major constituent of neuritic plaques in AD, has been implicated as a primary activator of complement in AD. Here we show that A beta is associated with a substructural vesicular component within drusen. A beta colocalizes with activated complement components in these "amyloid vesicles," thereby identifying them as potential primary sites of complement activation. Thus, A beta deposition could be an important component of the local inflammatory events that contribute to atrophy of the retinal pigmented epithelium, drusen biogenesis, and the pathogenesis of AMD.

Iron mediates gene expression in activated microglia

Microglia have diverse functions within the brain. Activation of microglia has been described in many neurological diseases and these activated microglia may contribute to the disease process. Following brain injury, activated microglia increase the expression of macrophage‐associated antigens and release neuroactive substances, including reactive oxygen and nitrogen molecules, inflammatory cytokines, and neurotoxins. Iron accumulation accompanies activation of microglia including those associated with neuritic plaques in Alzheimer Disease, infarcted brain areas in stroke, and within the vicinity of plaques in Multiple Sclerosis. The question is whether the effect of iron acummulation in microglia is enhances activation or limits function. To address this question, we examined the influence of iron on gene expression in the murine microglia (BV2) cell line during activation with lipopolysaccharide (LPS) using microarray analysis. The combined presence of LPS and iron resulted in the increased expression of an additional 48 genes and decreased expression of 76 genes compared to the LPS alone group. Among the genes that increased expression in the iron plus LPS group where CD38, CD83, caspase 11, IL15, Mip 1a, interferon alpha family, and Ras superfamily of regulatory GTPase. These results suggest that iron can influence the inflammatory response in microglia elicited by LPS and the removal of tissue debris during any reparative processes.

Fibril formation and neurotoxicity by a herpes simplex virus glycoprotein B fragment with homology to the Alzheimer's A beta peptide.

Despite significant progress in the elucidation of the genetic basis of early-onset familial Alzheimer's disease (AD), the etiology of sporadic cases remains elusive. Although certain genetic loci play a role in conferring susceptibility in some sporadic AD cases, it is likely that the etiology is multifactorial; hence, the majority of cases cannot be attributed to genetic factors alone, indicating that environmental factors may modulate the onset and/or progression of the disease. Head injury and infectious agents are environmental factors that have been periodically implicated, but no plausible mechanisms have been clearly identified. With regard to infectious agents, speculation has often centered on the neurotropic herpes viruses, with herpes simplex virus 1 (HSV1) considered a likely candidate. We report that an internal sequence of HSV1 glycoprotein B (gB) is homologous to the carboxyl-terminal region of the A beta peptide that accumulates in diffuse and neuritic plaques in AD. Synthetic peptides were generated and the biophysical and biological properties of the viral peptide compared to those of A beta. Here we show that this gB fragment forms beta-pleated sheets, self-assembles into fibrils that are thioflavin-positive and ultrastructurally indistinguishable from A beta, accelerates the formation of A beta fibrils in vitro, and is toxic to primary cortical neurons at doses comparable to those of A beta. These findings suggest a possible role for this infectious agent in the pathophysiology of sporadic cases of AD.