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Zinc and Copper Differentially Modulate Amyloid Precursor Protein Processing by ?-Secretase and Amyloid-? Peptide Production.

ABSTRACT: Recent evidence suggests involvement of biometal homeostasis in the pathological mechanisms in Alzheimer's disease (AD). For example, increased intracellular copper or zinc has been linked to a reduction in secreted levels of the AD-causing amyloid-? peptide (A?). However, little is known about whether these biometals modulate the generation of A?. In the present study we demonstrate in both cell-free and cell-based assays that zinc and copper regulate A? production by distinct molecular mechanisms affecting the processing by ?-secretase of its A? precursor protein substrate APP-C99. We found that Zn²⁺ induces APP-C99 dimerization, which prevents its cleavage by ?-secretase and A? production, with an IC₅₀ value of 15 ?m Importantly, at this concentration, Zn²⁺ also drastically raised the production of the aggregation-prone A?43 found in the senile plaques of AD brains and elevated the A?43:A?40 ratio, a promising biomarker for neurotoxicity and AD. We further demonstrate that the APP-C99 histidine residues His-6, His-13, and His-14 control the Zn²⁺-dependent APP-C99 dimerization and inhibition of A? production, whereas the increased A?43:A?40 ratio is substrate dimerization-independent and involves the known Zn²⁺ binding lysine Lys-28 residue that orientates the APP-C99 transmembrane domain within the lipid bilayer. Unlike zinc, copper inhibited A? production by directly targeting the subunits presenilin and nicastrin in the ?-secretase complex. Altogether, our data demonstrate that zinc and copper differentially modulate A? production. They further suggest that dimerization of APP-C99 or the specific targeting of individual residues regulating the production of the long, toxic A? species, may offer two therapeutic strategies for preventing AD.

SUBMITTER: Gerber H

PROVIDER: S-EPMC5339758 | biostudies-literature | 2017 Mar

REPOSITORIES: biostudies-literature

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Zinc and Copper Differentially Modulate Amyloid Precursor Protein Processing by γ-Secretase and Amyloid-β Peptide Production.

Gerber Hermeto H Wu Fang F Dimitrov Mitko M Garcia Osuna Guillermo M GM Fraering Patrick C PC

The Journal of biological chemistry 20170117 9

Recent evidence suggests involvement of biometal homeostasis in the pathological mechanisms in Alzheimer's disease (AD). For example, increased intracellular copper or zinc has been linked to a reduction in secreted levels of the AD-causing amyloid-β peptide (Aβ). However, little is known about whether these biometals modulate the generation of Aβ. In the present study we demonstrate in both cell-free and cell-based assays that zinc and copper regulate Aβ production by distinct molecular mechani ...[more]

PMID: 28096459

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Project description:INTRODUCTION: Inhibition of gamma-secretase presents a direct target for lowering A? production in the brain as a therapy for Alzheimer's disease (AD). However, gamma-secretase is known to process multiple substrates in addition to amyloid precursor protein (APP), most notably Notch, which has limited clinical development of inhibitors targeting this enzyme. It has been postulated that APP substrate selective inhibitors of gamma-secretase would be preferable to non-selective inhibitors from a safety perspective for AD therapy. METHODS: In vitro assays monitoring inhibitor potencies at APP ?-site cleavage (equivalent to A?40), and Notch ?-site cleavage, in conjunction with a single cell assay to simultaneously monitor selectivity for inhibition of A? production vs. Notch signaling were developed to discover APP selective gamma-secretase inhibitors. In vivo efficacy for acute reduction of brain A? was determined in the PDAPP transgene model of AD, as well as in wild-type FVB strain mice. In vivo selectivity was determined following seven days x twice per day (b.i.d.) treatment with 15 mg/kg/dose to 1,000 mg/kg/dose ELN475516, and monitoring brain A? reduction vs. Notch signaling endpoints in periphery. RESULTS: The APP selective gamma-secretase inhibitors ELN318463 and ELN475516 reported here behave as classic gamma-secretase inhibitors, demonstrate 75- to 120-fold selectivity for inhibiting A? production compared with Notch signaling in cells, and displace an active site directed inhibitor at very high concentrations only in the presence of substrate. ELN318463 demonstrated discordant efficacy for reduction of brain A? in the PDAPP compared with wild-type FVB, not observed with ELN475516. Improved in vivo safety of ELN475516 was demonstrated in the 7d repeat dose study in wild-type mice, where a 33% reduction of brain A? was observed in mice terminated three hours post last dose at the lowest dose of inhibitor tested. No overt in-life or post-mortem indications of systemic toxicity, nor RNA and histological end-points indicative of toxicity attributable to inhibition of Notch signaling were observed at any dose tested. CONCLUSIONS: The discordant in vivo activity of ELN318463 suggests that the potency of gamma-secretase inhibitors in AD transgenic mice should be corroborated in wild-type mice. The discovery of ELN475516 demonstrates that it is possible to develop APP selective gamma-secretase inhibitors with potential for treatment for AD.

Dataset Information

Zinc and Copper Differentially Modulate Amyloid Precursor Protein Processing by ?-Secretase and Amyloid-? Peptide Production.

Publications

Zinc and Copper Differentially Modulate Amyloid Precursor Protein Processing by γ-Secretase and Amyloid-β Peptide Production.

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