Imaging real-time aggregation of amyloid beta protein (1–42) by atomic force microscopy

Abstract

Amyloid beta protein (AβP) is the major fibrillar constituent of senile plaques. However, no causative role for AβP-fibers in Alzheimer’s disease (AD) pathology is established. Globular AβPs 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 AβP 1–42 and to examine the role of AβP concentration, imaging medium (air, water, or PBS) and agonists/antagonists on AβP-fibrillogenesis. At even very high and non-physiological AβP 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 AβP-fibrillogenesis, induced a slow but non-fibrillar aggregation of globular AβPs. EDTA, a chelator of Zn and calcium (a modulator of AβP-mediated toxicity) induced a reversible change in the Zn-mediated aggregation. These results strongly suggest that no AβP-fibers are formed for the physiologically relevant concentration and thus the plaque-associated fibers may not account for the AD pathophysiology.