Cited by 208Alzheimer's disease research and treatmentsCerebrospinal fluid and hydrocephalusNeuroinflammation and Neurodegeneration Mechanisms

The DOI matches its Crossref record; 75 of the 75 references it cites were found in a registry or an index; none of the 45 sources its claims cite is checked for support yet.

Amyloid clearance defect in ApoE4 astrocytes is reversed by epigenetic correction of endosomal pH

Open access
Prasad, Hari, Rao, Rajini·2018·Proceedings of the National Academy of Sciences

Published version of a preprint

Abstract

Significance: Alzheimer’s disease is the most common cause of dementia in the elderly. Most cases occur sporadically, with 40–65% of patients carrying at least one copy of the E4 allele of Apolipoprotein E. Because no drug exists that can halt disease progress, there is strong interest in understanding the presymptomatic role of endosomes. We show that excessive endosomal acidification in ApoE4 astrocytes is caused by downregulation of the Na + /H + exchanger NHE6 and results in defective clearance of amyloid beta (Aβ) peptide by intracellular sequestration of the LRP1 receptor. Epigenetic modifiers restore NHE6 expression to alkalinize endosomal pH, increase surface expression of LRP1, and correct Aβ clearance in astrocytes. Thus, endosomal pH emerges as a target for the correction of amyloid disorders.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

In ApoE4 astrocytes, selective downregulation of the endosomal Na+/H+ exchanger NHE6 causes endosomal hyperacidification, trapping LRP1 intracellularly and impairing Aβ clearance. Restoring NHE6—by ectopic expression or broad-spectrum HDAC inhibitors—normalizes endosomal pH, increases surface LRP1, and rescues Aβ clearance to ApoE3-like levels.

Key findings

  • ApoE4 astrocytes showed 78% lower cell-associated Aβ than ApoE3 astrocytes, with lower Aβ at all time points (53% at 1 h, 59% at 4 h, 65% at 16 h), while transferrin uptake was 1.5–2-fold higher and dextran uptake did not differ.
  • Surface LRP1 was reduced in ApoE4 astrocytes by ~50% (biotinylation), ~43% (flow cytometry), and ~49% (confocal), and surface Aβ binding was 66% lower, despite no differences in LRP1 transcript or total protein.
  • Endosomal pH in ApoE4 astrocytes was reduced by ~0.84 pH unit, lysosomal pH was elevated by >1 pH unit, and monensin raised endosomal pH from 5.38±0.01 to 5.74±0.03 and restored Aβ clearance.
  • NHE6 transcript was ~56% lower in ApoE4 knock-in astrocytes; NHE6 KO mouse brains had elevated Aβ; ectopic NHE6 restored Aβ clearance and increased surface LRP1 (~2.5-fold by imaging, ~5.7-fold by biotinylation). Broad-spectrum HDAC inhibitors restored NHE6, with TSA and SAHA EC50 values of 6.50±0.36 µM and 6.81±0.53 µM, and corrected Aβ clearance up to 92.4% of ApoE3 levels (R²=0.7884 between Aβ clearance and NHE6 fold-change).

Methods

  • Isogenic ApoE3/ApoE4 knock-in immortalized astrocytes and ApoE KO astrocytes were used with fluorescent Aβ40 uptake/clearance assays, flow cytometry, confocal microscopy, surface biotinylation, pH-sensitive reporters, qPCR, Western blotting, lentiviral NHE6/NHE9 expression, and a nine-drug HDAC inhibitor panel.
  • Human bioinformatics included GSE5281 (15 LOAD, 12 controls), GSE15222 (n=363), and a meta-analysis of nine studies comprising 103 AD and 87 control post-mortem brains; NHE6 KO male mice (Slc9a6−/Y) versus wild-type male controls were used for brain Aβ40 ELISA, with on average five mice per genotype.
  • Statistical analysis used Student’s t test, ANOVA, and linear regression in GraphPad Prism; data are presented as mean ± SD.

Limitations

  • The paper states that the precise pH-mediated perturbation in trafficking remains to be determined, and that future work could test HDAC inhibitor efficacy on amyloid pathology in well-defined animal models.
  • Evident from the text: the mechanistic rescue experiments are primarily in immortalized astrocyte cell culture, while in vivo evidence is limited to elevated Aβ in NHE6 KO mouse brain rather than ApoE4-specific HDAC inhibitor treatment.
  • Evident from the text: human evidence for NHE6 downregulation in ApoE4 is based on transcriptomic datasets and post-mortem brain analyses, which are associative rather than direct causal tests in human tissue.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1073/pnas.1801612115

Cites

75 of 75 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Figures

Figure 1
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Figure 6
Figure 6 CC-BY-NC-ND · From the PDF

Verification

Claims the paper makes

52 Own result · 26 Sources not found · 21 Own interpretation · 4 Own method · 2 No basis given

Show all 78 claims

  • It may state two separate claims as one. 14
  • Probably not a substantial claim. 16
27 of 27
  • The paper relies on this without support.

    ApoE-isoform-expressing isogenic astrocytes produce, lipidate, package, and secrete ApoE in a brain-relevant physiological fashion, making them a valid model of human ApoE4 brain astrocytes.

    “Using ApoE-isoform-expressing isogenic astrocytes that produce, lipidate, package, and secrete ApoE in a brainrelevant physiological fashion”
  • The paper relies on this without support.

    Elevated brain Aβ in NHE6 KO mice reflects a role for NHE6 in amyloid pathology relevant to AD.

    “Consistent with a role in amyloid pathology, in vivo Aβ levels were found to be significantly higher in the brains of NHE6 KO mice.”
2 of 2

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Self-check

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Metadata

Authors
Prasad, H., & Rao, R.
Affiliations
Johns Hopkins University (US)
Venue
Proceedings of the National Academy of Sciences
Published
2018-06-26
Volume
115
Issue
28
Pages
E6640-E6649
ISSN
  • 0027-8424 (ISSN-L)
  • 1091-6490
OpenAlex
W2810838937
Cited by
207
References
73
Citations by year
2026: 19 · 2025: 26 · 2024: 30 · 2023: 25 · 2022: 34 · 2021: 32 · 2020: 23 · 2019: 14 · 2018: 4
FWCI
7.14
Type
journal article
Language
en
Open access
Locations
  • Proceedings of the National Academy of Sciences (publishedVersion)
  • bioRxiv (Cold Spring Harbor Laboratory) (acceptedVersion, cc-by-nc-nd)
  • Europe PMC (PubMed Central) (publishedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
Funders
  • HHS | National Institutes of Health (DK054214)
  • Johns Hopkins Medicine Discovery Fund (N/A)
Topics
  • Life Sciences › Neuroscience › Cellular and Molecular Neuroscience › Alzheimer's disease research and treatments
  • Health Sciences › Medicine › Clinical Neurology › Cerebrospinal fluid and hydrocephalus
  • Life Sciences › Neuroscience › Neurology › Neuroinflammation and Neurodegeneration Mechanisms
Keywords
Alzheimer's disease, APOE ε4, amyloid-beta clearance, astrocytes, endosomal acidification, endosomal pH, NHE6, Na+/H+ exchanger, epigenetic regulators, amyloidosis
MeSH terms
Alzheimer Disease, Animals, Astrocytes, Ataxia, Epilepsy, Histone Deacetylases, Humans, Hydrogen-Ion Concentration, Intellectual Disability, Microcephaly, Receptors, LDL, Endosomes, Ocular Motility Disorders, Amyloid beta-Peptides, Sodium-Hydrogen Exchangers, Mice, Knockout, Tumor Suppressor Proteins, Low Density Lipoprotein Receptor-Related Protein-1, Genetic Diseases, X-Linked, Epigenesis, Genetic, Mice, Apolipoprotein E4, Histone Deacetylase Inhibitors

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