Distinct spatiotemporal accumulation of N-truncated and full-length amyloid-β42 in Alzheimer's disease

Accumulation of amyloid-beta peptides is a dominant feature in the pathogenesis of Alzheimer's disease; however, it is not clear how individual amyloid-beta species accumulate and affect other neuropathological and clinical features in the disease. Thus, we compared the accumulation of N-terminally truncated amyloid-beta and full-length amyloid-beta, depending on disease stage as well as brain area, and determined how these amyloid-beta species respectively correlate with clinicopathological features of Alzheimer's disease. To this end, the amounts of amyloid-beta species and other proteins related to amyloid-beta metabolism or Alzheimer's disease were quantified by enzyme-linked immunosorbent assays (ELISA) or theoretically calculated in 12 brain regions, including neocortical, limbic and subcortical areas from Alzheimer's disease cases (n = 19), neurologically normal elderly without amyloid-beta accumulation (normal ageing, n = 13), and neurologically normal elderly with cortical amyloid-beta accumulation (pathological ageing, n = 15). We observed that N-terminally truncated amyloid-beta(42) and full-length amyloid-beta(42) accumulations distributed differently across disease stages and brain areas, while N-terminally truncated amyloid-beta(40) and full-length amyloid-beta(40) accumulation showed an almost identical distribution pattern. Cortical N-terminally truncated amyloid-beta(42) accumulation was increased in Alzheimer's disease compared to pathological ageing, whereas cortical full-length amyloid-beta(42) accumulation was comparable between Alzheimer's disease and pathological ageing. Moreover, N-terminally truncated amyloid-beta(42) were more likely to accumulate more in specific brain areas, especially some limbic areas, while full-length amyloid-beta(42) tended to accumulate more in several neocortical areas, including frontal cortices. Immunoprecipitation followed by mass spectrometry analysis showed that several N-terminally truncated amyloid-beta(42) species, represented by pyroglutamylated amyloid-beta(11-42), were enriched in these areas, consistent with ELISA results. N-terminally truncated amyloid-beta(42) accumulation showed significant regional association with BACE1 and neprilysin, but not PSD95 that regionally associated with full-length amyloid-beta(42) accumulation. Interestingly, accumulations of tau and to a greater extent apolipoprotein E (apoE, encoded by APOE) were more strongly correlated with N-terminally truncated amyloid-beta(42) accumulation than those of other amyloid-beta species across brain areas and disease stages. Consistently, immunohistochemical staining and in vitro binding assays showed that apoE co-localized and bound more strongly with pyroglutamylated amyloid-beta(11-x) fibrils than full-length amyloid-beta fibrils. Retrospective review of clinical records showed that accumulation of N-terminally truncated amyloid-beta(42) in cortical areas was associated with disease onset, duration and cognitive scores. Collectively, N-terminally truncated amyloid-beta(42) species have spatiotemporal accumulation patterns distinct from full-length amyloid-beta(42), likely due to different mechanisms governing their accumulations in the brain. These truncated amyloid-beta species could play critical roles in the disease by linking other clinicopathological features of Alzheimer's disease.