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Behavioral and neural network abnormalities in human APP transgenic mice resemble those of App knock-in mice and are modulated by familial Alzheimer's disease mutations but not by inhibition of BACE1.

ABSTRACT: BACKGROUND:Alzheimer's disease (AD) is the most frequent and costly neurodegenerative disorder. Although diverse lines of evidence suggest that the amyloid precursor protein (APP) is involved in its causation, the precise mechanisms remain unknown and no treatments are available to prevent or halt the disease. A favorite hypothesis has been that APP contributes to AD pathogenesis through the cerebral accumulation of the amyloid-? peptide (A?), which is derived from APP through sequential proteolytic cleavage by BACE1 and ?-secretase. However, inhibitors of these enzymes have failed in clinical trials despite clear evidence for target engagement. METHODS:To further elucidate the roles of APP and its metabolites in AD pathogenesis, we analyzed transgenic mice overexpressing wildtype human APP (hAPP) or hAPP carrying mutations that cause autosomal dominant familial AD (FAD), as well as App knock-in mice that do not overexpress hAPP but have two mouse App alleles with FAD mutations and a humanized A? sequence. RESULTS:Although these lines of mice had marked differences in cortical and hippocampal levels of APP, APP C-terminal fragments, soluble A?, A? oligomers and age-dependent amyloid deposition, they all developed cognitive deficits as well as non-convulsive epileptiform activity, a type of network dysfunction that also occurs in a substantive proportion of humans with AD. Pharmacological inhibition of BACE1 effectively reduced levels of amyloidogenic APP C-terminal fragments (C99), soluble A?, A? oligomers, and amyloid deposits in transgenic mice expressing FAD-mutant hAPP, but did not improve their network dysfunction and behavioral abnormalities, even when initiated at early stages before amyloid deposits were detectable. CONCLUSIONS:hAPP transgenic and App knock-in mice develop similar pathophysiological alterations. APP and its metabolites contribute to AD-related functional alterations through complex combinatorial mechanisms that may be difficult to block with BACE inhibitors and, possibly, also with other anti-A? treatments.

SUBMITTER: Johnson ECB

PROVIDER: S-EPMC7489007 | biostudies-literature | 2020 Sep

REPOSITORIES: biostudies-literature

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Behavioral and neural network abnormalities in human APP transgenic mice resemble those of App knock-in mice and are modulated by familial Alzheimer's disease mutations but not by inhibition of BACE1.

Johnson Erik C B ECB Ho Kaitlyn K Yu Gui-Qiu GQ Das Melanie M Sanchez Pascal E PE Djukic Biljana B Lopez Isabel I Yu Xinxing X Gill Michael M Zhang Weiping W Paz Jeanne T JT Palop Jorge J JJ Mucke Lennart L

Molecular neurodegeneration 20200914 1

<h4>Background</h4>Alzheimer's disease (AD) is the most frequent and costly neurodegenerative disorder. Although diverse lines of evidence suggest that the amyloid precursor protein (APP) is involved in its causation, the precise mechanisms remain unknown and no treatments are available to prevent or halt the disease. A favorite hypothesis has been that APP contributes to AD pathogenesis through the cerebral accumulation of the amyloid-β peptide (Aβ), which is derived from APP through sequential ...[more]

PMID: 32921309

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Project description:BACKGROUND:The ?-secretase, BACE1, cleaves APP to initiate generation of the ?-amyloid peptide, A?, that comprises amyloid plaques in Alzheimer's disease (AD). Reducing BACE1 activity is an attractive therapeutic approach to AD, but complete inhibition of BACE1 could have mechanism-based side-effects as BACE1-/- mice show deficits in axon guidance, myelination, memory, and other neurological processes. Since BACE1+/- mice appear normal there is interest in determining whether 50% reduction in BACE1 is potentially effective in preventing or treating AD. APP transgenic mice heterozygous for BACE1 have decreased A? but the extent of reduction varies greatly from study to study. Here we assess the effects of 50% BACE1 reduction on the widely used 5XFAD mouse model of AD. RESULTS:50% BACE1 reduction reduces A?42, plaques, and BACE1-cleaved APP fragments in female, but not in male, 5XFAD/BACE1+/- mice. 5XFAD/BACE1+/+ females have higher levels of A?42 and steady-state transgenic APP than males, likely caused by an estrogen response element in the transgene Thy-1 promoter. We hypothesize that higher transgenic APP level in female 5XFAD mice causes BACE1 to no longer be in excess over APP so that 50% BACE1 reduction has a significant A?42 lowering effect. In contrast, the lower APP level in 5XFAD males allows BACE1 to be in excess over APP even at 50% BACE1 reduction, preventing lowering of A?42 in 5XFAD/BACE1+/- males. We also developed and validated a dot blot assay with an A?42-selective antibody as an accurate and cost-effective alternative to ELISA for measuring cerebral A?42 levels. CONCLUSIONS:50% BACE1 reduction lowers A?42 in female 5XFAD mice only, potentially because BACE1 is not in excess over APP in 5XFAD females with higher transgene expression, while BACE1 is in excess over APP in 5XFAD males with lower transgene expression. Our results suggest that greater than 50% BACE1 inhibition might be necessary to significantly lower A?, given that BACE1 is likely to be in excess over APP in the human brain. Additionally, in experiments using the 5XFAD mouse model, or other Thy-1 promoter transgenic mice, equal numbers of male and female mice should be used, in order to avoid artifactual gender-related differences.

Dataset Information

Behavioral and neural network abnormalities in human APP transgenic mice resemble those of App knock-in mice and are modulated by familial Alzheimer's disease mutations but not by inhibition of BACE1.

Publications

Behavioral and neural network abnormalities in human APP transgenic mice resemble those of App knock-in mice and are modulated by familial Alzheimer's disease mutations but not by inhibition of BACE1.

Similar Datasets

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