BackgroundAlzheimer’s disease (AD) is characterized by the deposition of insoluble amyloid plaques in the neuropil composed of highly stable, self-assembled Amyloid-beta (Aβ) fibrils. Copper has been implicated to play a role in Alzheimer’s disease. Dimers of Aβ have been isolated from AD brain and have been shown to be neurotoxic.ResultsWe have investigated the formation of dityrosine cross-links in Aβ42 formed by covalent ortho-ortho coupling of two tyrosine residues under conditions of oxidative stress with elevated copper and shown that dityrosine can be formed in vitro in Aβ oligomers and fibrils and that these links further stabilize the fibrils. Dityrosine crosslinking was present in internalized Aβ in cell cultures treated with oligomeric Aβ42 using a specific antibody for dityrosine by immunogold labeling transmission electron microscopy. Results also revealed the prevalence of dityrosine crosslinks in amyloid plaques in brain tissue and in cerebrospinal fluid from AD patients.ConclusionsAβ dimers may be stabilized by dityrosine crosslinking. These results indicate that dityrosine cross-links may play an important role in the pathogenesis of Alzheimer’s disease and can be generated by reactive oxygen species catalyzed by Cu2+ ions. The observation of increased Aβ and dityrosine in CSF from AD patients suggests that this could be used as a potential biomarker of oxidative stress in AD.

Amyloid β1-42 (Aβ1-42) plays a central role in Alzheimer’s disease. The link between structure, assembly and neuronal toxicity of this peptide is of major current interest but still poorly defined. Here, we explored this relationship by rationally designing a variant form of Aβ1-42 (vAβ1-42) differing in only two amino acids. Unlike Aβ1-42, we found that the variant does not self-assemble, nor is it toxic to neuronal cells. Moreover, while Aβ1-42 oligomers impact on synaptic function, vAβ1-42 does not. In a living animal model system we demonstrate that only Aβ1-42 leads to memory deficits. Our findings underline a key role for peptide sequence in the ability to assemble and form toxic structures. Furthermore, our non-toxic variant satisfies an unmet demand for a closely related control peptide for Aβ1-42 cellular studies of disease pathology, offering a new opportunity to decipher the mechanisms that accompany Aβ1-42-induced toxicity leading to neurodegeneration.

Protein synthesis is crucial for the maintenance of long-term memory-related synaptic plasticity. The cytoplasmic polyadenylation element-binding protein 3 (CPEB3) regulates the translation of several mRNAs important for long-term synaptic plasticity in the hippocampus. In previous studies, we found that the oligomerization and activity of CPEB3 are controlled by small ubiquitin-like modifier (SUMO)ylation. In the basal state, CPEB3 is SUMOylated; it is soluble and acts as a repressor of translation. Following neuronal stimulation, CPEB3 is de-SUMOylated; it now forms oligomers that are converted into an active form that promotes the translation of target mRNAs. To better understand how CPEB3 regulates the translation of its mRNA targets, we have examined CPEB3 subcellular localization. We found that basal, repressive CPEB3 is localized to membraneless cytoplasmic processing bodies (P bodies), subcellular compartments that are enriched in translationally repressed mRNA. This basal state is affected by the SUMOylation state of CPEB3. After stimulation, CPEB3 is recruited into polysomes, thus promoting the translation of its target mRNAs. Interestingly, when we examined CPEB3 recombinant protein in vitro, we found that CPEB3 phase separates when SUMOylated and binds to a specific mRNA target. These findings suggest a model whereby SUMO regulates the distribution, oligomerization, and activity of oligomeric CPEB3, a critical player in the persistence of memory.