Divergent age-dependent conformational rearrangement within Aβ amyloid deposits in APP23, APPPS1, and AppNL-Fmice

Abstract

AbstractAmyloid plaques composed of fibrils of misfolded Aβ peptides are pathological hallmarks of Alzheimer’s disease (AD). Aβ fibrils are polymorphic in their tertiary and quaternary molecular structures. This structural polymorphism may carry different pathologic potency and can putatively contribute to clinical phenotypes of AD. Therefore, mapping of structural polymorphism of Aβ fibrils is valuable to understand disease mechanisms. Here, we investigated how Aβ fibril morphologyin situdiffers in Aβ plaque of different mouse models expressing familial mutations in the AβPP gene. We used a combination of conformation-sensitive luminescent conjugated oligothiophene (LCO) ligands, Aβ-specific antibodies, and different fluorescence microscopy techniques. LCO fluorescence mapping revealed that mouse models APP23, APPPS1, andAppNL-Fhave different fibril structures depending on AβPP-processing genotype. Co-staining of Aβ-specific antibodies showed that individual plaques from APP23 mice, expressing Swedish mutations (NL) have two distinct fibril polymorph regions of core and corona. The plaque core is predominantly composed of compact Aβ40 fibrils and the corona region is dominated by diffusely packed Aβ40 fibrils. On the other hand, the APP knock-in mouseAppNL-F, expressing Iberian mutation (F) along with Swedish mutation has tiny, cored plaques consisting mainly of compact Aβ42 fibrils, vastly different from APP23 even at elevated age up to 21 months. Age dependent polymorph maturation of plaque cores observed for APP23 and APPPS1 mice >12 months, was minuscule inAppNL-F. These structural studies of amyloid plaquesin situcan map disease-relevant fibril polymorph distributions to guide the design of diagnostic and therapeutic molecules.SignificanceAlzheimer’s disease (AD) is associated with the formation of deposits in the brain known as Aβ-amyloid plaques. AD can emerge as a sporadic disease or due to familial mutations in genes encoding for Aβ precursor and processing proteins. The Aβ-amyloid found in plaques displays different structures in sporadic AD and in various types of familial AD. We hypothesize that understanding plaque morphology and development is crucial for understanding the initiation and progression of AD. We here compared amyloid structures in three of the most used mouse models of human Aβ-plaque formation. Our findings suggest significant differences in plaque morphologies and structural maturation processes during aging. Our results emphasize that strain-like differences of Aβ-amyloids develop as a function of Aβ precursor protein-processing genetics and age.