Phosphorylation of the Amyloid-Beta Peptide Inhibits Zinc-Dependent Aggregation, Prevents Na,K-ATPase Inhibition, and Reduces Cerebral Plaque Deposition.

Evgeny P. Barykin,Vladimir A. Mitkevich,Olga D. Lopina,Alexander A. Makarov,Georgy B. Telegin,Sergey A. Kozin,Sergey P. Radko,Alexander S. Chernov,Irina Y. Petrushanko

doi:10.3389/fnmol.2018.00302

Abstract

The triggers of late-onset sporadic Alzheimer’s disease (AD) are still poorly understood. Impairment of protein phosphorylation with age is well-known; however, the role of the phosphorylation in β-amyloid peptide (Aβ) is not studied sufficiently. Zinc-induced oligomerization of Aβ represents a potential seeding mechanism for the formation of neurotoxic Aβ oligomers and aggregates. Phosphorylation of Aβ by Ser8 (pS8-Aβ), localized inside the zinc-binding domain of the peptide, may significantly alter its zinc-induced oligomerization. Indeed, using dynamic light scattering, we have shown that phosphorylation by Ser8 dramatically reduces zinc-induced aggregation of Aβ, and moreover pS8-Aβ suppresses zinc-driven aggregation of non-modified Aβ in an equimolar mixture. We have further analyzed the effect of pS8-Aβ on the progression of cerebral amyloidosis with serial retro-orbital injections of the peptide in APPSwe/PSEN1dE9 murine model of AD, followed by histological analysis of amyloid burden in hippocampus. Unlike the non-modified Aβ that has no influence on the amyloidosis progression in murine models of AD, pS8-Aβ injections reduced the number of amyloid plaques in the hippocampus of mice by one-third. Recently shown inhibition of Na+,K+-ATPase activity by Aβ, which is thought to be a major contributor to neuronal dysfunction in AD, is completely reversed by phosphorylation of the peptide. Thus, several AD-associated pathogenic properties of Aβ are neutralized by its phosphorylation.

Highlights

The amyloid-beta peptide (Aβ) is a normal subnanomolar component of biological fluids (Masters and Selkoe, 2012); its deposition in the form of amyloid plaques is one of the hallmarks of Alzheimer’s disease (AD) (Selkoe and Hardy, 2016)
The results of the turbidity measurements support those of dynamic light scattering (DLS) experiments (Figure 1B): Ser8 phosphorylation substantially suppressed the propensity of β-amyloid peptide (Aβ) peptides for zinctriggered aggregation, which was manifested in the remarkably higher turbidity of the Aβ42/Zn2+ mixture than that of the pS8-Aβ42/Zn2+ mixture
To study a possible effect of pS8-Aβ42 on the zinc-induced aggregation of Aβ42, we determined the characteristic size of zincinduced aggregates in a series of pS8-Aβ42/Aβ42 mixtures with different molar ratios of the peptides (Figure 1C) at the 70-min time point

Summary

Introduction

The amyloid-beta peptide (Aβ) is a normal subnanomolar component of biological fluids (Masters and Selkoe, 2012); its deposition in the form of amyloid plaques is one of the hallmarks of AD (Selkoe and Hardy, 2016). The trigger of the pathologic Aβ aggregation in AD is unknown (Musiek and Holtzman, 2015); in animal models of AD, the conversion of a monomeric Aβ into fibrillar aggregates, through neurotoxic oligomers, is triggered by chemically and structurally modified Aβ species (Meyer-Luehmann et al, 2006; Prusiner, 2012; Jucker and Walker, 2013). Zinc-induced aggregation of Aβ is governed by its metal-binding domain (Aβ16), which comprises the N-terminal region (residues 1–16) of Aβ (Istrate et al, 2016). It has recently been shown that the metal-binding domain of Aβ containing isomerized Asp (isoD7-Aβ16) is more prone to zinc-induced oligomerization (Istrate et al, 2016), suggesting a role for Asp isomerization in the initiation of the pathological aggregation process. The ability of Aβ to form zinc-induced aggregates may correlate with its amyloidogenic and neurotoxic properties

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Conclusion