Browsing by Author "Fricke, Merle"

Abstract Aims The aggregation and deposition of amyloid‐β (Aβ) peptides in the brain is thought to be the initial driver in the pathogenesis of Alzheimer's disease (AD). Aside from full‐length Aβ peptides starting with an aspartate residue in position 1, both N‐terminally truncated and elongated Aβ peptides are produced by various proteases from the amyloid precursor protein (APP) and have been detected in brain tissues and body fluids. Recently, we demonstrated that the particularly abundant N‐terminally truncated Aβ4–x peptides are generated by ADAMTS4, a secreted metalloprotease that is exclusively expressed in the oligodendrocyte cell population. In this study, we investigated whether ADAMTS4 might also be involved in the generation of N‐terminally elongated Aβ peptides. Methods We used cell‐free and cell‐based assays in combination with matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry (MALDI‐TOF) and electrochemiluminescence sandwich immunoassays to identify and quantify N‐terminally elongated Aβ peptide variants. Antibodies against these Aβ variants were characterised by peptide microarrays and employed for the immunohistochemical analyses of human brain samples. Results In this study, we discovered additional ADAMTS4 cleavage sites in APP. These were located N‐terminal to Asp‐(1) in the Aβ peptide sequence between residues Glu‐(‐7) and Ile‐(‐6) as well as Glu‐(‐4) and Val‐(‐3), resulting in the release of N‐terminally elongated Aβ‐6‐x and Aβ‐3‐x peptides, of which the latter serve as a component in a promising Aβ‐based plasma biomarker. Aβ‐6/‐3‐40 peptides were detected in supernatants of various cell lines and in the cerebrospinal fluid (CSF), and ADAMTS4 enzyme activity promoted the release of Aβ‐6/‐3‐x peptides. Furthermore, by immunohistochemistry, a subset of AD cases displayed evidence of extracellular and vascular localization of N‐terminally elongated Aβ‐6/‐3‐x peptides. Discussion The current findings implicate ADAMTS4 in both the pathological process of Aβ peptide aggregation and in the early detection of amyloid pathology in AD.

Senile plaques consisting of amyloid-beta (Aβ) peptides are a major pathological hallmark of Alzheimer’s disease (AD). Aβ peptides are heterogeneous regarding the exact length of their amino- and carboxy-termini. Aβ1-40 and Aβ1-42 are often considered to represent canonical “full-length” Aβ species. Using immunohistochemistry, we analyzed the distribution of Aβ1-x, Aβx-42 and Aβ4-x species in amyloid deposits in the subiculum, hippocampus and cortex in 5XFAD mice during aging. Overall plaque load increased in all three brain regions, with the subiculum being the area with the strongest relative plaque coverage. In the subiculum, but not in the other brain regions, the Aβ1-x load peaked at an age of five months and decreased thereafter. In contrast, the density of plaques positive for N-terminally truncated Aβ4-x species increased continuously over time. We hypothesize that ongoing plaque remodeling takes place, leading to a conversion of deposited Aβ1-x peptides into Aβ4-x peptides in brain regions with a high Aβ plaque burden.