Marc Mercken

Macroautophagy—a novel β-amyloid peptide-generating pathway activated in Alzheimer's disease

Macroautophagy, which is a lysosomal pathway for the turnover of organelles and long-lived proteins, is a key determinant of cell survival and longevity. In this study, we show that neuronal macroautophagy is induced early in Alzheimers disease (AD) and before β-amyloid (Aβ) deposits extracellularly in the presenilin (PS) 1/Aβ precursor protein (APP) mouse model of β-amyloidosis. Subsequently, autophagosomes and late autophagic vacuoles (AVs) accumulate markedly in dystrophic dendrites, implying an impaired maturation of AVs to lysosomes. Immunolabeling identifies AVs in the brain as a major reservoir of intracellular Aβ. Purified AVs contain APP and β-cleaved APP and are highly enriched in PS1, nicastrin, and PS-dependent γ-secretase activity. Inducing or inhibiting macroautophagy in neuronal and nonneuronal cells by modulating mammalian target of rapamycin kinase elicits parallel changes in AV proliferation and Aβ production. Our results, therefore, link β-amyloidogenic and cell survival pathways through macroautophagy, which is activated and is abnormal in AD.

The Alzheimer's Association external quality control program for cerebrospinal fluid biomarkers.

The cerebrospinal fluid (CSF) biomarkers amyloid β (Aβ)‐42, total‐tau (T‐tau), and phosphorylated‐tau (P‐tau) demonstrate good diagnostic accuracy for Alzheimers disease (AD). However, there are large variations in biomarker measurements between studies, and between and within laboratories. The Alzheimers Association has initiated a global quality control program to estimate and monitor variability of measurements, quantify batch‐to‐batch assay variations, and identify sources of variability. In this article, we present the results from the first two rounds of the program.

Endogenous amyloid-β is necessary for hippocampal synaptic plasticity and memory

The goal of this study was to investigate the role of endogenous amyloid‐β peptide (Aβ) in healthy brain.

Increased expression of BIN1 mediates Alzheimer genetic risk by modulating tau pathology

Genome-wide association studies (GWAS) have identified a region upstream the BIN1 gene as the most important genetic susceptibility locus in Alzheimer’s disease (AD) after APOE. We report that BIN1 transcript levels were increased in AD brains and identified a novel 3u2009bp insertion allele ∼28u2009kb upstream of BIN1, which increased (i) transcriptional activity in vitro, (ii) BIN1 expression levels in human brain and (iii) AD risk in three independent case-control cohorts (Meta-analysed Odds ratio of 1.20 (1.14–1.26) (P=3.8 × 10−11)). Interestingly, decreased expression of the Drosophila BIN1 ortholog Amph suppressed Tau-mediated neurotoxicity in three different assays. Accordingly, Tau and BIN1 colocalized and interacted in human neuroblastoma cells and in mouse brain. Finally, the 3u2009bp insertion was associated with Tau but not Amyloid loads in AD brains. We propose that BIN1 mediates AD risk by modulating Tau pathology.

Extracellular amyloid formation and associated pathology in neural grafts

Amyloid precursor protein (APP) processing and the generation of β-amyloid peptide (Aβ) are important in the pathogenesis of Alzheimers disease. Although this has been studied extensively at the molecular and cellular levels, much less is known about the mechanisms of amyloid accumulation in vivo. We transplanted transgenic APP23 and wild-type B6 embryonic neural cells into the neocortex and hippocampus of both B6 and APP23 mice. APP23 grafts into wild-type hosts did not develop amyloid deposits up to 20 months after grafting. In contrast, both transgenic and wild-type grafts into young transgenic hosts developed amyloid plaques as early as 3 months after grafting. Although largely diffuse in nature, some of the amyloid deposits in wild-type grafts were congophilic and were surrounded by neuritic changes and gliosis, similar to the amyloid-associated pathology previously described in APP23 mice. Our results indicate that diffusion of soluble Aβ in the extracellular space is involved in the spread of Aβ pathology, and that extracellular amyloid formation can lead to neurodegeneration.

Tear gasses CN, CR, and CS are potent activators of the human TRPA1 receptor

The TRPA1 channel is activated by a number of pungent chemicals, such as allylisothiocyanate, present in mustard oil and thiosulfinates present in garlic. Most of the known activating compounds contain reactive, electrophilic chemical groups, reacting with cysteine residues in the active site of the TRPA1 channel. This covalent modification results in activation of the channel and has been shown to be reversible for several ligands. Commonly used tear gasses CN, CR and CS are also pungent chemicals, and in this study we show that they are extremely potent and selective activators of the human TRPA1 receptor. To our knowledge, these are the most potent TRPA1 agonists known to date. The identification of the molecular target for these tear gasses may open up possibilities to alleviate the effects of tear gasses via treatment with TRPA1 antagonists. In addition these results may contribute to the basic knowledge of the TRPA1 channel that is gaining importance as a pharmacological target.

Amyloid precursor protein mutation E682K at the alternative β‐secretase cleavage β′‐site increases Aβ generation

BACE1 cleaves the amyloid precursor protein (APP) at the β‐cleavage site (Met671–Asp672) to initiate the generation of amyloid peptide Aβ. BACE1 is also known to cleave APP at a much less well‐characterized β′‐cleavage site (Tyr681–Glu682). We describe here the identification of a novel APP mutation E682K located at this β′‐site in an early onset Alzheimers disease (AD) case. Functional analysis revealed that this E682K mutation blocked the β′‐site and shifted cleavage of APP to the β‐site, causing increased Aβ production. This work demonstrates the functional importance of APP processing at the β′‐site and shows how disruption of the balance between β‐ and β′‐site cleavage may enhance the amyloidogenic processing and consequentially risk for AD. Increasing exon‐ and exome‐based sequencing efforts will identify many more putative pathogenic mutations without conclusive segregation‐based evidence in a single family. Our study shows how functional analysis of such mutations allows to determine the potential pathogenic nature of these mutations. We propose to classify the E682K mutation as probable pathogenic awaiting further independent confirmation of its association with AD in other patients.

Characterization of Abeta11-40/42 peptide deposition in Alzheimer's disease and young Down's syndrome brains: implication of N-terminally truncated Abeta species in the pathogenesis of Alzheimer's disease

Senile plaques (SPs), one of two defining lesions of Alzheimer’s disease (AD), are composed of a mixture of full-length Aβ1-40/42, and N- or C-terminally truncated Aβ peptides, including Aβ11-40/42. Sequential proteolysis of amyloid precursor protein (APP) by β- and γ-secretases produces Aβ1-40/42, but β-site APP-cleaving enzyme 1 (BACE1), the major β-secretase, also generates Aβ11-40/42, and BACE1 overexpression in cultured cells results primarily in secretion of Aβ11-40/42. The ratio of Aβ11-40/42 to Aβ1-40/42 depends on the ratio of BACE1 to APP, and Aβ11-40/42 can be generated from both full-length APP and its carboxy-terminal fragment (C99). Here, we investigated the role of Aβ11-40/42 in the pathogenesis of AD and Down’s syndrome (DS) brains. We demonstrated significant amount of Aβ11-42 in DS brains by Western blots. While pyroAβ11-42-modified Aβ species existed predominantly in mature SP cores in AD brain sections, both unmodified free Aβ11-40 and pyro-modified Aβ11-40 are detected in vascular amyloid deposits by immunohistochemistry. Using novel ELISAs for quantifying free Aβ11-40/42 and pyroAβ11-40/42, we showed that insoluble Aβ11-42 predominated in extracts of AD and DS brains. This is the first systematic study of Aβ11-40/42 in neurodegenerative Aβ amyloidosis implicating Aβ11-40/42 in SP formation of AD and DS brains. The detection of Aβ11-42 in young DS brain suggests an early role for this N-terminally truncated Aβ peptide in the pathogenesis of SPs in AD and DS.

Chronic treatment with a novel γ-secretase modulator, JNJ-40418677, inhibits amyloid plaque formation in a mouse model of Alzheimer's disease

γ‐Secretase modulators represent a promising therapeutic approach for Alzheimers disease (AD) because they selectively decrease amyloid β 42 (Aβ42), a particularly neurotoxic Aβ species that accumulates in plaques in the brains of patients with AD. In the present study, we describe the in vitro and in vivo pharmacological properties of a potent novel γ‐secretase modulator, 2‐(S)‐(3,5‐bis(4‐(trifluoromethyl)phenyl)phenyl)‐4‐methylpentanoic acid (JNJ‐40418677).

Characterization of amyloid β peptides from brain extracts of transgenic mice overexpressing the London mutant of human amyloid precursor protein

Alzheimers disease (AD) is marked by the presence of neurofibrillary tangles and amyloid plaques in the brain of patients. To study plaque formation, we report on further quantitative and qualitative analysis of human and mouse amyloid β peptides (Aβ) from brain extracts of transgenic mice overexpressing the London mutant of human amyloid precursor protein (APP). Using enzyme‐linked immunosorbant assays (ELISAs) specific for either human or rodent Aβ, we found that the peptides from both species aggregated to form plaques. The ratios of deposited Aβ1–42/1–40 were in the order of 2–3 for human and 8–9 for mouse peptides, indicating preferential deposition of Aβ42. We also determined the identity and relative levels of other Aβ variants present in protein extracts from soluble and insoluble brain fractions. This was done by combined immunoprecipitation and mass spectrometry (IP/MS). The most prominent peptides truncated either at the carboxyl‐ or the amino‐terminus were Aβ1–38 and Aβ11–42, respectively, and the latter was strongly enriched in the extracts of deposited peptides. Taken together, our data indicate that plaques of APP‐London transgenic mice consist of aggregates of multiple human and mouse Aβ variants, and the human variants that we identified were previously detected in brain extracts of AD patients.