Unique Molecular Signatures of Alzheimer's Disease Amyloid β Peptide Mutations and Deletion During Aggregate/Oligomer/Fibril Formation

The formation of amyloid (A) peptide aggregates, oligomers, and fibrils is a dynamic process; however, the kinetics of their formation is not well understood. This study compares the time course of aggregate/fibril formation by transmission electron microscopy (TEM) analyses with that of oligomer/fibril formation by Western blot analysis under native and denaturing conditions. Efforts to deaggregate/defibrillate these peptides by using hexafluoroisopropanol, ammonium hydroxide, or dimethylsulfoxide did not change the nondenaturing polyacrylamide gel electrophoresis (PAGE) footprints or drive the peptides to a monomeric species. Regardless of the pretreatment protocol, TEM analyses reveal that all A peptides (A40, A42, A39E22 [Osaka], A40E22G [Arctic], A40E22Q [Dutch], and A40A2T [Icelandic]) immediately formed nonfibrillar, amorphous aggregates when first placed into solution with the Osaka mutation, quickly forming early-stage fibrils. The extent of fibril formation for other A peptides is time dependent, with the Arctic mutation forming fibrils at 1 hr, the Dutch and Icelandic at 4 hr, A42 at 8 hr, and A40 at 24 hr. In contrast, nondenaturing PAGE revealed unique footprints for the different A species. The rapidity of aggregate formation and the rapid transition to fibrils, particularly for the Osaka deletion, suggest an important role for aggregates/fibrils of A in the development of neuronal degeneration. (c) 2014 Wiley Periodicals, Inc.