Real-time and Single Fibril Observation of the Formation of Amyloid β Spherulitic Structures

Tadato Ban,Kenichi Morigaki,Hisashi Yagi,Takashi Kawasaki,Atsuko Kobayashi,Shunsuke Yuba,Hironobu Naiki,Yuji Goto

doi:10.1074/jbc.m606072200

Abstract

In Alzheimer disease, amyloid beta, a 39-43-residue peptide produced by cleavage from a large amyloid precursor protein, undergoes conformational change to form amyloid fibrils and deposits as senile amyloid plaques in the extracellular cerebral cortices of the brain. However, the mechanism of how the intrinsically linear amyloid fibrils form spherical senile plaques is unknown. With total internal reflection fluorescence microscopy combined with the use of thioflavin T, an amyloid-specific fluorescence dye, we succeeded in observing the formation of the senile plaque-like spherulitic structures with diameters of around 15 microm on the chemically modified quartz surface. Real-time observation at a single fibrillar level revealed that, in the absence of tight contact with the surface, the cooperative and radial growth of amyloid fibrils from the core leads to a huge spherulitic structure. The results suggest the underlying physicochemical mechanism of senile plaque formation, essential for obtaining insight into prevention of Alzheimer disease.

Highlights

In Alzheimer disease, amyloid ␤ (A␤)3 peptide forms amyloid fibrils that deposit in the extracellular space of the brain as senile amyloid plaques, pathological hallmarks of Alzheimer disease, and in the walls of cerebral blood vessels [1,2,3,4,5]
We previously developed a unique approach to monitoring fibril growth in real time at the single fibril level [18, 19], in which TIRFM was combined with the use of thioflavin T, an amyloid-specific fluorescence dye [20]
The arrows indicate the direction of the upper side of the microscopic cell. This view focuses on the core face of various chemically modified regions, whereas peripheral regions with separated fibrils can be seen in the sectional images (Supplemental Movie 2)

Summary

Introduction

In Alzheimer disease, amyloid ␤ (A␤) peptide forms amyloid fibrils that deposit in the extracellular space of the brain as senile amyloid plaques, pathological hallmarks of Alzheimer disease, and in the walls of cerebral blood vessels [1,2,3,4,5]. The formation of A␤ amyloid fibrils is considered to be a nucleationdependent process in which A␤ peptides slowly associate to form a nucleus, which grows via an extension reaction involving the sequential incorporation of A␤ peptides, producing rigid and straight morphology consisting of several layers of cross-␤ sheets [6, 7]. This process is influenced by several fac-. We focused on the effects of the physicochemical properties of surface on the growth of amyloid fibrils of A␤

Results

Discussion

Conclusion