Meprin β elevates hippocampal soluble Aβ in the APP/V717I mouse model

The emergence of Alzheimer's disease (AD) pathology has been the focus of multiple hypotheses, with amyloid β (Aβ) playing a central role due to its presence in both familial and sporadic AD. Therefore, a crucial aspect of AD research is understanding the generation of different Aβ species. Aβ peptides result from the proteolytic processing of Amyloid Precursor Protein (APP) by β- and γ-secretases, with BACE1 being the most prominent β-secretase. However, BACE1-overexpressing mouse models exhibit disadvantages, making them limited for AD research. Importantly, N-terminally truncated Aβ species, which constitute up to 70 % of Aβ in AD brains, are not generated by BACE1. In recent years, alternative proteases capable of cleaving APP have been identified, bridging the gap between N-terminally truncated Aβ species and BACE1-derived Aβ. Among these novel players, the metalloprotease meprin β has emerged as a risk factor in AD pathology, generating both N-terminally truncated and full-length Aβ species. Our primary objective was to develop a mouse model that more accurately resembles the pathology of AD beyond BACE1-overexpressing models, while simultaneously confirming APP cleavage of meprin β in the hippocampus and cerebral cortex. Overexpression of meprin β led to a marked increase in soluble Aβ levels, particularly in the hippocampus, indicating a higher vulnerability or elevated meprin β activity in this region compared to the cerebral cortex. Notably, this biochemical change occurred without any observable behavioral deficits, suggesting a region-specific role of meprin β in AD pathology that may extend beyond immediate functional impairment.