PYROGLUTAMATION OF AβX-42 AND Aβ1-40 DEPOSITION UNDERLIE AMYLOID PLAQUE POLYMORPHISM IN PROGRESSING ALZHEIMER’S DISEASE PATHOLOGY

Abstract

Amyloid β (Aβ) plaques display structural diversity between familial AD (fAD) and sporadic AD (sAD). Further, Aβ plaques are found in cognitively unaffected – amyloid positive (CU-AP) individuals. While Aβ plaques in CU-AP are mainly diffuse, plaques in sAD typically display a dense core/center. The relationship between these structural subtypes and their respective toxicity/neuroprotective roles remains unknown. The aim of this project is therefore to examine Aβ peptide composition in diffuse and cored Aβ plaques in sAD/CU-AP, to reveal molecular aggregation mechanisms behind structural plaque architecture variety. Brain tissue section from human sAD, CU-AP and transgenic APPSwe mice (12-, 18-months) were stained with conformational-sensitive fluorescent amyloid probes (LCO) that distinguish diffuse versus cored plaque. Hyperspectrally separated plaque populations were laser microdissected, enriched through immunoprecipitation and analyzed by mass spectrometry (IP-MS). Imaging mass spectrometry (MALDI-IMS) was employed to visualize Aβ peptides’ spatial distribution at a single plaque level. IP-MS revealed Aβ4-42 to be the most dominant peptide in all plaques. Aβ1-40 was exclusively found in cored sAD plaque. MALDI-IMS confirmed Aβ1-40 to be associated with plaque core. A relative increase in the pyroglutamation of Aβx-42 was found in diffuse and cored sAD plaques. MALDI-IMS revealed N-terminally truncated Aβx-40 and Aβx-42 following similar spatial distribution as full length peptides. APPSwe mice revealed an age-dependent increase in Aβ1-40. Pyroglutamation of Aβx-42 followed by Aβ1-40 deposition appear to underlie plaque polymorphism in progressing AD. Observations in APPSwe mice suggest this pattern to be associated with the maturation of individual Aβ plaques.