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 (Aβ1-40/42) in the central nervous system (CNS). Copper coordination to Aβ triggers Aβ1-40/42 aggregation and promotes the catalytic generation of reactive oxygen species (ROS). Due to its amphiphilic nature, Aβ1-40/42 can interact with cell membranes and compromise their integrity. In this work, we characterized the insertion of Aβ1-42 into an artificial lipid bilayer system mimicking cell membranes and demonstrate that the Aβ1-42-lipid interaction does not prevent the Cu2+ coordination to Aβ1-42. We performed a comparative analysis of the redox reactivities of membrane-bound Aβ1-42 (memAβ1-42-Cu2+) with soluble Aβ1-42-Cu2+ establishing that membrane insertion leads to memAβ1-42-Cu2+ complexes featuring an enhanced detrimental catechol oxidase activity towards the neurotransmitter dopamine. Moreover, memAβ1-42-Cu2+ efficiently catalyzes Aβ di-tyrosine crosslinking and hydroxyl radical production in the presence of ascorbate. In addition, we establish that memAβ1-42-Cu2+ 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 d10 metals (Cu+ and Zn2+) 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-Cu2+ interactions and redox reactivities of amyloidogenic protein-Cu2+ complexes, including soluble Aβ1-40. In this work, we unravel that the detrimental memAβ1-42-Cu2+ redox reactivities can also be efficiently silenced by MT-3 via metal swap reactions, by scavenging and reducing Cu2+ to Cu+ in its β-domain using thiolates as electron source, forming the redox-inert Cu+4Zn2+4MT-3 species. Consequently, MT-3 efficiently prevents lipid peroxidation and protects membrane structural integrity. New strategies targeting membrane-bound Aβ1-42-Cu2+ complexes as key players in AD etiology could be envisioned.