Redox reactivities of membrane-bound amyloid-β-Cu complexes and their targeting by metallothionein-3.

Alzheimer's disease (AD) is characterized by the accumulation of amyloid-β peptide (Aβ) in the central nervous system (CNS). Copper coordination to Aβ triggers Aβ aggregation and promotes the catalytic generation of reactive oxygen species (ROS). Due to its amphiphilic nature, Aβ can interact with cell membranes and compromise their integrity. In this work, we characterized the insertion of Aβ into an artificial lipid bilayer system mimicking cell membranes and demonstrate that the Aβ-lipid interaction does not prevent the Cu coordination to Aβ. We performed a comparative analysis of the redox reactivities of membrane-bound Aβ (memAβ-Cu) with soluble Aβ-Cu establishing that membrane insertion leads to memAβ-Cu complexes featuring an enhanced detrimental catechol oxidase activity towards the neurotransmitter dopamine. Moreover, memAβ-Cu efficiently catalyzes Aβ di-tyrosine crosslinking and hydroxyl radical production in the presence of ascorbate. In addition, we establish that memAβ-Cu redox reactivity catalyzes polyunsaturated fatty acids (PUFAs) lipid peroxidation, leading to the generation of malondialdehyde (MDA) toxic end-product. This reactivity compromises the structural integrity of the lipid bilayers resulting in membrane leakage. Metallothioneins (MTs) are cysteine-rich metalloproteins central to neuronal and astrocytic metal homeostasis. MTs bind d metals (Cu and Zn) forming two metal thiolate clusters in their structure. In the CNS, the metallothionein-3 (MT-3) isoform possess a neuroprotective role, but it is downregulated in AD patients. MT-3 controls aberrant protein-Cu interactions and redox reactivities of amyloidogenic protein-Cu complexes, including soluble Aβ In this work, we unravel that the detrimental memAβ-Cu redox reactivities can also be efficiently silenced by MT-3 via metal swap reactions, by scavenging and reducing Cu to Cu in its β-domain using thiolates as electron source, forming the redox-inert CuZnMT-3 species. Consequently, MT-3 efficiently prevents lipid peroxidation and protects membrane structural integrity. New strategies targeting membrane-bound Aβ-Cu complexes as key players in AD etiology could be envisioned.