A novel mouse model for N-terminal truncated Aß2-x generation through meprin ß overexpression in astrocytes.

ABSTRACT

Neurotoxic amyloid-ß (Aß) peptides cause neurodegeneration in Alzheimer's disease (AD) patients' brains. They are released upon proteolytic processing of the amyloid precursor protein (APP) extracellularly at the ß-secretase site and intramembranously at the γ-secretase site. Several AD mouse models were developed to conduct respective research in vivo. Most of these classical models overexpress human APP with mutations driving AD-associated pathogenic APP processing. However, the resulting pattern of Aß species in the mouse brains differs from those observed in AD patients' brains. Particularly mutations proximal to the ß-secretase cleavage site (e.g., the so-called Swedish APP (APPswe) fostering Aß1-x formation) lead to artificial Aß production, as N-terminally truncated Aß peptides are hardly present in these mouse brains. Meprin ß is an alternative ß-secretase upregulated in brains of AD patients and capable of generating N-terminally truncated Aß2-x peptides. Therefore, we aimed to generate a mouse model for the production of so far underestimated Aß2-x peptides by conditionally overexpressing meprin ß in astrocytes. We chose astrocytes as meprin ß was detected in this cell type in close proximity to Aß plaques in AD patients' brains. The meprin ß-overexpressing mice showed elevated amyloidogenic APP processing detected with a newly generated neo-epitope-specific antibody. Furthermore, we observed elevated Aß production from endogenous APP as well as AD-related behavior changes (hyperlocomotion and deficits in spatial memory). The novel mouse model as well as the established tools and methods will be helpful to further characterize APP cleavage and the impact of different Aß species in future studies.