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Imaging real-time aggregation of amyloid beta protein (1-42) by atomic force microscopy
Ashok Parbhu1, Hai Lin, Julian Thimm
1Neuroscience Research Institute, University of California, Santa Barbara, CA 93016, USA.
Abstract:
Amyloid beta protein (AbetaP) is the major fibrillar constituent of senile plaques. However, no causative role for AbetaP-fibers in Alzheimer's disease (AD) pathology is established. Globular AbetaPs are continuously released during normal cellular metabolism at pico- to nano-molar concentration. We used atomic force microscopy (AFM) to examine aggregation of freshly prepared AbetaP(1-42) and to examine the role of AbetaP concentration, imaging medium (air, water, or PBS) and agonists/antagonists on AbetaP-fibrillogenesis. At even very high and non-physiological AbetaP concentrations, 24-48 h of real-time AFM imaging (a) in water show only multiple layers of globular aggregates and no fibrils and (b) in PBS show mainly the globular structures and some short fibrils. On-line addition of Zn, an agonist for AbetaP-fibrillogenesis, induced a slow but non-fibrillar aggregation of globular AbetaPs. EDTA, a chelator of Zn and calcium (a modulator of AbetaP-mediated toxicity) induced a reversible change in the Zn-mediated aggregation. These results strongly suggest that no AbetaP-fibers are formed for the physiologically relevant concentration and thus the plaque-associated fibers may not account for the AD pathophysiology.
Insights
Amyloid beta protein (AbetaP) fibers, implicated in Alzheimer's disease (AD), are not formed at physiological concentrations. Globular AbetaP aggregates, not fibrils, dominate under relevant conditions, challenging the role of AbetaP fibers in AD.
Area of Science:
- Biochemistry
- Neuroscience
- Cell Biology
Background:
- Amyloid beta protein (AbetaP) forms fibrils in senile plaques, a hallmark of Alzheimer's disease (AD).
- The direct causative role of AbetaP fibrils in AD pathology remains unestablished.
- Globular AbetaPs are released during normal cellular metabolism at low concentrations.
Purpose of the Study:
- To investigate the aggregation of AbetaP(1-42) using atomic force microscopy (AFM).
- To determine the influence of AbetaP concentration, imaging medium, and agonists/antagonists on AbetaP fibrillogenesis.
Main Methods:
- Real-time atomic force microscopy (AFM) imaging of AbetaP(1-42) aggregation.
- Controlled imaging conditions including varying AbetaP concentrations, media (air, water, PBS), and addition of Zn or EDTA.
Main Results:
- At high, non-physiological concentrations, AbetaP formed globular aggregates in water and a mix of globular structures and short fibrils in PBS.
- No significant AbetaP fibril formation was observed under physiologically relevant conditions.
- Zinc (Zn) induced non-fibrillar aggregation of globular AbetaPs, with EDTA reversibly modulating this process.
Conclusions:
- AbetaP fibers are unlikely to form at physiologically relevant concentrations.
- The study challenges the established role of AbetaP fibers in Alzheimer's disease pathophysiology.
- Globular AbetaP aggregates may be more relevant to AD than previously thought.