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J Biol Chem. 2014 Nov 7;289(45):30990-1000. doi: 10.1074/jbc.M114.589069. Epub 2014 Sep 24.

Molecular mechanisms of Alzheimer disease protection by the A673T allele of amyloid precursor protein.

Author information

1
From the Departments of Neuroscience.
2
Protein Chemistry.
3
Biochemical and Cellular Pharmacology, and.
4
ITGR Diagnostics Discovery, Genentech, Inc., South San Francisco, California 94080.
5
From the Departments of Neuroscience, Protein Chemistry, jernst@gene.com.
6
From the Departments of Neuroscience, rwatts@gene.com.
7
From the Departments of Neuroscience, jatwal@gene.com.

Abstract

Pathogenic mutations in the amyloid precursor protein (APP) gene have been described as causing early onset familial Alzheimer disease (AD). We recently identified a rare APP variant encoding an alanine-to-threonine substitution at residue 673 (A673T) that confers protection against development of AD (Jonsson, T., Atwal, J. K., Steinberg, S., Snaedal, J., Jonsson, P. V., Bjornsson, S., Stefansson, H., Sulem, P., Gudbjartsson, D., Maloney, J., Hoyte, K., Gustafson, A., Liu, Y., Lu, Y., Bhangale, T., Graham, R. R., Huttenlocher, J., Bjornsdottir, G., Andreassen, O. A., Jönsson, E. G., Palotie, A., Behrens, T. W., Magnusson, O. T., Kong, A., Thorsteinsdottir, U., Watts, R. J., and Stefansson, K. (2012) Nature 488, 96-99). The Ala-673 residue lies within the β-secretase recognition sequence and is part of the amyloid-β (Aβ) peptide cleavage product (position 2 of Aβ). We previously demonstrated that the A673T substitution makes APP a less favorable substrate for cleavage by BACE1. In follow-up studies, we confirm that A673T APP shows reduced cleavage by BACE1 in transfected mouse primary neurons and in isogenic human induced pluripotent stem cell-derived neurons. Using a biochemical approach, we show that the A673T substitution modulates the catalytic turnover rate (V(max)) of APP by the BACE1 enzyme, without affecting the affinity (K(m)) of the APP substrate for BACE1. We also show a reduced level of Aβ(1-42) aggregation with A2T Aβ peptides, an observation not conserved in Aβ(1-40) peptides. When combined in a ratio of 1:9 Aβ(1-42)/Aβ(1-40) to mimic physiologically relevant mixtures, A2T retains a trend toward slowed aggregation kinetics. Microglial uptake of the mutant Aβ(1-42) peptides correlated with their aggregation level. Cytotoxicity of the mutant Aβ peptides was not dramatically altered. Taken together, our findings demonstrate that A673T, a protective allele of APP, reproducibly reduces amyloidogenic processing of APP and also mildly decreases Aβ aggregation. These effects could together have an additive or even synergistic impact on the risk of developing AD.

KEYWORDS:

Alzheimer Disease; Amyloid Precursor Protein (APP); Amyloid-β (AB); Neurobiology; Proteolytic Enzyme; β-Secretase 1 (BACE1)

PMID:
25253696
PMCID:
PMC4223305
DOI:
10.1074/jbc.M114.589069
[Indexed for MEDLINE]
Free PMC Article

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