Coordinated regional association of cathepsins and dipeptidyl peptidases with N-truncated Abeta42, Abeta40, and tau in Alzheimer's brain.

Regional distributions of amyloid-β (Aβ) and tau accumulation have provided important insights into the pathomechanisms of Alzheimer's disease (AD). While such analyses have typically been conducted through histochemical or clinical imaging studies, we previously reported unique regional associations among Aβ species, tau and other proteins by biochemically analyzing multiple postmortem brain regions. Here, using a new cohort and novel ELISAs, we investigated the regional relationships of Aβ species, tau, neuroglial markers, cathepsins and dipeptidyl peptidases (DPP) across AD stages. Despite a relatively small sample size, this study replicated key prior findings, including a strong regional association between Aβ1-42 and the postsynaptic maker PSD95 particularly in the early stage, distinct regional distributions of Aβ1-42 and N-terminally truncated Aβ42 (Aβt-42), and a significant association between Aβt-42 and tau in AD. Moreover, this study observed that Aβ1-42 was associated with other synaptic proteins, but not neurofilament proteins. Notably, several proteases, particularly cathepsin B, cathepsin D and DPPIV, exhibited strong regional correlations with total Aβx-42, Aβt-42, Aβx-40, and tau accumulations in AD, forming coordinated regional distribution patterns. Such strong regional associations with late-stage Aβ species and tau were not observed for neuroglial markers. At the microscopic level, these proteases displayed abnormal morphologies proximity to Aβ and tau pathologies. Their coordinated regional distributions with Aβt-42, Aβx-40, and tau may indicate that these proteases cooperatively promote neurodegenerative cascades in AD.