Association of β-Amyloid and Apolipoprotein E ε4 With Memory Decline in Preclinical Alzheimer Disease

Extracellular accumulation of β-amyloid peptide (Aβ) has been linked to the development of Alzheimer disease. The importance of intraneuronal Aβ has been recognized more recently. Although considerable evidence indicates that extracellular Aβ contributes to the intracellular pool of Aβ, the mechanisms involved in Aβ uptake by neurons are poorly understood. We examined the molecular mechanisms involved in Aβ-(1–42) internalization by primary neurons in the absence of apolipoprotein E. We demonstrated that Aβ-(1–42) is more efficiently internalized by axons than by cell bodies of sympathetic neurons, suggesting that Aβ-(1–42) uptake might be mediated by proteins enriched in the axons. Although the acetylcholine receptor α7nAChR, previously suggested to be involved in Aβ internalization, is enriched in axons, our results indicate that it does not mediate Aβ-(1–42) internalization. Moreover, receptors of the low density lipoprotein receptor family are not essential for Aβ-(1–42) uptake in the absence of apolipoprotein E because receptor-associated protein had no effect on Aβ uptake. By expressing the inactive dynamin mutant dynK44A and the clathrin hub we found that Aβ-(1–42) internalization is independent of clathrin but dependent on dynamin, which suggests an endocytic pathway involving caveolae/lipid rafts. Confocal microscopy studies showing that Aβ did not co-localize with the early endosome marker EEA1 further support a clathrin-independent mechanism. The lack of co-localization of Aβ with caveolin in intracellular vesicles and the normal uptake of Aβ by neurons that do not express caveolin indicate that Aβ does not require caveolin either. Instead partial co-localization of Aβ-(1–42) with cholera toxin subunit B and sensitivity to reduction of cellular cholesterol and sphingolipid levels suggest a caveolae-independent, raft-mediated mechanism. Understanding the molecular events involved in neuronal Aβ internalization might identify potential therapeutic targets for Alzheimer disease.

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β-amyloid and Alzheimer disease: recent progress

Academic Journal of Second Military Medical University ◽

10.3724/sp.j.1008.2010.01133 ◽

2010 ◽

Vol 30 (10) ◽

pp. 1133-1137

Author(s):

Tuo LI ◽

Zhong-xin ZHAO

Keyword(s):

Alzheimer Disease ◽

Recent Progress ◽

Β Amyloid

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Early stages of tau pathology and its associations with functional connectivity, atrophy and memory

Brain ◽

10.1093/brain/awab114 ◽

2021 ◽

Author(s):

David Berron ◽

Jacob W Vogel ◽

Philip S Insel ◽

Joana B Pereira ◽

Long Xie ◽

...

Keyword(s):

Functional Connectivity ◽

Entorhinal Cortex ◽

Temporal Lobe ◽

Medial Temporal Lobe ◽

Memory Impairment ◽

Memory Performance ◽

Hippocampal Atrophy ◽

Tau Pathology ◽

Β Amyloid ◽

With Memory

Abstract In Alzheimer’s disease, postmortem studies have shown that the first cortical site where neurofibrillary tangles appear is the transentorhinal region, a subregion within the medial temporal lobe that largely overlaps with area 35, and the entorhinal cortex. Here we used tau-PET imaging to investigate the sequence of tau pathology progression within the human medial temporal lobe and across regions in the posterior-medial system. Our objective was to study how medial temporal tau is related to functional connectivity, regional atrophy, and memory performance. We included 215 β-amyloid negative cognitively unimpaired, 81 β-amyloid positive cognitively unimpaired and 87 β-amyloid positive individuals with mild cognitive impairment, who each underwent [18]F-RO948 tau and [18]F-flutemetamol amyloid PET imaging, structural T1-MRI and memory assessments as part of the Swedish BioFINDER-2 study. First, event-based modelling revealed that the entorhinal cortex and area 35 show the earliest signs of tau accumulation followed by the anterior and posterior hippocampus, area 36 and the parahippocampal cortex. In later stages, tau accumulation became abnormal in neocortical temporal and finally parietal brain regions. Second, in cognitively unimpaired individuals, increased tau load was related to local atrophy in the entorhinal cortex, area 35 and the anterior hippocampus and tau load in several anterior medial temporal lobe subregions was associated with distant atrophy of the posterior hippocampus. Tau load, but not atrophy, in these regions was associated with lower memory performance. Further, tau-related reductions in functional connectivity in critical networks between the medial temporal lobe and regions in the posterior-medial system were associated with this early memory impairment. Finally, in patients with mild cognitive impairment, the association of tau load in the hippocampus with memory performance was partially mediated by posterior hippocampal atrophy. In summary, our findings highlight the progression of tau pathology across medial temporal lobe subregions and its disease-stage specific association with memory performance. While tau pathology might affect memory performance in cognitively unimpaired individuals via reduced functional connectivity in critical medial temporal lobe-cortical networks, memory impairment in mild cognitively impaired patients is associated with posterior hippocampal atrophy.

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