Structural progression of amyloid-β Arctic mutant aggregation in cells revealed by multiparametric imaging

The 42-amino-acid beta-amyloid (A beta 42) is a critical causative agent in the pathology of Alzheimer's disease. The hereditary Arctic mutation of A beta 42 (E22G) leads to increased intracellular accumulation of beta-amyloid in early-onset Alzheimer's disease. However, it remains largely unknown how the Arctic mutant variant leads to aggressive protein aggregation and increased intracellular toxicity. Here, we constructed stable cell lines expressing fluorescent-tagged wildtype (WT) and E22G A beta 42 to study the aggregation kinetics of the Arctic A beta 42 mutant peptide and its heterogeneous structural forms. Arctic-mutant peptides assemble and form fibrils at a much faster rate than WT peptides. We identified five categories of intracellular aggregate-oligomers, single fibrils, fibril bundles, clusters, and aggresomes-that underline the heterogeneity of these A beta 42 aggregates and represent the progression of A beta 42 aggregation within the cell. Fluorescence-lifetime imaging (FLIM) and 3D structural illumination microscopy (SIM) showed that all aggregate species displayed highly compact structures with strong affinity between individual fibrils. We also found that aggregates formed by Arctic mutant A beta 42 were more resistant to intracellular degradation than their WT counterparts. Our findings uncover the structural basis of the progression of Arctic mutant A beta 42 aggregation in the cell.