FIGURE 6.

Aβ42 protofibrils do not serve as efficient seeding nuclei for Aβ40 fibril formation. Fibril formation by 20 μm monomeric Aβ (Aβ40 and Aβ42) was induced at three different concentrations (1, 2, and 4 μm) of protofibrillar Aβ42. The addition of protofibrillar Aβ42 to monomeric Aβ42 abolishes the lag phase of fibril formation in a concentration-dependent fashion (A) and promotes fibril formation (C). In contrast, no seeding effect is observed when similar concentrations of protofibrillar Aβ42 are added to the solution containing monomeric Aβ40 (B), and predominantly curvilinear structures, reminiscent of protofibrils, are observed (D). Scale bar = 200 nm. ThT data were normalized by subtracting the ThT fluorescence values obtained from incubation of Aβ42 protofibrils (1, 2, and 4 μm) in isolation. M, monomeric Aβ; PF, protofibrillar Aβ42; 1× = 1 μm; 2× = 2 μm; 4× = 4 μm; a.u., arbitrary units.