The metalloprotease ADAMTS4 generates N-truncated Aβ4–x species and marks oligodendrocytes as a source of amyloidogenic peptides in Alzheimer’s disease

Abstract

Brain accumulation and aggregation of amyloid-β (Aβ) peptides is a critical step in the pathogenesis of Alzheimer's disease (AD). Full-length Aβ peptides (mainly Aβ1-40 and Aβ1-42) are produced through sequential proteolytic cleavage of the amyloid precursor protein (APP) by β-and γ-secretases. However, studies of autopsy brain samples from AD patients have demonstrated that a large fraction of insoluble Aβ peptides are truncated at the N-terminus, with Aβ4-x peptides being particularly abundant. Aβ4-x peptides are highly aggregation prone, but their origin and any proteases involved in their generation are unknown. We have identified a recognition site for the secreted metalloprotease ADAMTS4 (a disintegrin and metalloproteinase with thrombospondin motifs 4) in the Aβ peptide sequence, which facilitates Aβ4-x peptide generation. Inducible overexpression of ADAMTS4 in HEK293 cells resulted in the secretion of Aβ4-40 but unchanged levels of Aβ1-x peptides. In the 5xFAD mouse model of amyloidosis, Aβ4-x peptides were present not only in amyloid plaque cores and vessel walls, but also in white matter structures co-localized with axonal APP. In the ADAMTS4 −/− knockout background, Aβ4-40 levels were reduced confirming a pivotal role of ADAMTS4 in vivo. Surprisingly, in the adult murine brain, ADAMTS4 was exclusively expressed in oligodendrocytes. Cultured oligodendrocytes secreted a variety of Aβ species, but Aβ4-40 peptides were absent in cultures derived from ADAMTS4 −/− mice indicating that the enzyme was essential for Aβ4-x production in this cell type. These findings establish an enzymatic mechanism for the generation of Aβ4-x peptides. They further identify oligodendrocytes as a source of these highly amyloidogenic Aβ peptides.

N-Terminally Truncated Aß Peptide Variants in Alzheimer’s Disease

“…In vivo, the crossing of 5XFAD mice to ADAMTS4 knockout mice reduced Aβ 4-40 levels by 50%, but the overall amyloid plaque load and the distribution of Aβ 4-x peptides in amyloid plaque cores appeared to be unchanged, clearly suggesting that other mechanisms for Aβ 4-x generation beside ADAMTS4 must exist. Compellingly, abundant Aβ 4-x immunoreactivity was observed in white matter structures of 5XFAD mice, and this signal was entirely abolished in the ADAMTS4 knockout background (24). This could be of pathological relevance as numerous neuropathological, biochemical, and imaging studies have reported white matter abnormalities and oligodendrocyte dysfunction in AD patients (82,83).…”

“…The analysis of Aβ peptide species in brain samples using mass spectrometry revealed that most transgenic AD mouse models only partially reflect the Aβ spectrum in human sporadic AD. While the overall heterogeneity of N-terminal truncated Aβ species could be reproduced in mouse models such as APP/PS1KI (22) or 5XFAD (23,24), the ratio of full-length Aβ peptides to N-truncated variants is much different in human brain samples. While N-truncated variants such as Aβ pE3-x or Aβ 4-x might be present in comparable quantities compared to fulllength Aβ 1-40 or Aβ 1-42 species in human samples (16), full-length peptides comprise by far the majority of all Aβ peptides in transgenic AD models (23,25,26).…”

“…Most recently, it was shown that APP contains a cleavage site for the metalloprotease ADAMTS4 (a disintegrin-like and metalloprotease with thrombospondin type 1 motif) between Glu-3 and Phe-4 of the Aβ peptide sequence (24). ADAMTS proteases constitute a family of secreted Zn 2+ -metalloproteases that degrade or modify major components of the extracellular matrix (79).…”

“…In an important pathological process leading to osteoarthritis and rheumatoid arthritis, aggrecan is degraded by ADAMTS4 and the homologous family member ADAMTS5, leading to the exposure and subsequent degradation of collagen fibrils by collagenases (81). Co-expression of ADAMTS4 and APP in HEK293 cells resulted in the secretion of Aβ 4-40 peptides as measured by mass spectrometry and ELISA, while several species of Aβ 1-x peptides were not affected (24). Aβ 4-40 secretion was not blocked by treatment of the cells with a potent β-secretase inhibitor indicating that Aβ 4-x peptides were generated in a BACE1-independent fashion.…”

New Insights into ADAMTS Metalloproteases in the Central Nervous System

“…Finally, a recent study found a large fraction of insoluble Aβ peptides truncated at the N-terminus with Aβ4-x peptides in the brains of Alzheimer's patients (autopsies): this processing is carried out by ADAMTS-4. High levels of Aβ4-x peptides have been observed in animals deficient in ADAMTS-4 in an 5xFAD mice model, which was used as an amyloidosis model for the study of the accumulation of this peptide [134].…”