Differentiating Alzheimer's Aβ Isoforms Coaggregated in Cerebrospinal Fluid via Single-Particle Imaging

Area of Science:

• Neuroscience
• Biochemistry
• Biophysics

Background:

• Amyloid polymorphism correlates with Alzheimer's disease (AD) stages.
• Amyloid-beta (Aβ) peptides, specifically Aβ-40 and Aβ-42, are central to AD pathology.
• Cerebrospinal fluid (CSF) contains Aβ peptides whose aggregation patterns may indicate disease progression.

Purpose of the Study:

• To differentiate and characterize the morphology of Aβ-40 and Aβ-42 peptides in CSF.
• To investigate the inhibitory effect of Aβ-40 on Aβ-42 aggregation at a single-particle level.
• To explore the role of the CSF ionic environment in modulating Aβ coaggregation.

Main Methods:

• Utilized fluorescence-based super-resolution microscopy and atomic force microscopy (AFM) for detailed Aβ morphology studies.
• Employed molecular dynamics simulations to understand the mechanisms of Aβ coaggregation.
• Developed an isoform-specific imaging method for distinguishing Aβ aggregate types in patient CSF.

Main Results:

• Resolved the inhibitory effect of Aβ-40 on Aβ-42 aggregation, with Aβ-40 oligomers observed on Aβ-42 fibril backbones.
• Identified calcium ions in CSF as key mediators, forming bridges between Aβ-40 and Aβ-42 that stabilize fibrils and reduce elongation.
• Quantified nanoscopic differences in Aβ aggregate sizes (oligomers to fibrils) from AFM data in AD patient CSF.

Conclusions:

• The developed protein characterization method can fingerprint Aβ aggregates in CSF, irrespective of size or shape.
• This approach enables the distinction of Aβ-40 and Aβ-42 aggregates, offering insights into AD.
• Potential clinical application for monitoring Alzheimer's disease progression and related pathologies through CSF Aβ analysis.