There are several different neurodegenerative diseases, including prion disease, Alzheimer’s disease (AD), Parkinson’s disease and Huntington’s disease, in which a particular misfolded protein contributes to neurodegeneration in the brain [1]. In particular, the aggregation of amyloid-β (Aβ) peptides into protein fibres is one of the main neuropathological features of A. Imaging of such aggregation is extremely important for understanding pathology and in the development of aggregation inhibitors [2].
Unfortunately, potentially highly toxic, early Aβ aggregates are difficult to observe by current electron microscopy and atomic force microscopy (AFM) methods, due to low contrast and variability of peptide attachment to the substrate. In this paper we show that a poly-L-Lysine (PLL) surface can capture all protein components from monomers to fully formed fibres. We then use nanomechanical mapping via ultrasonic force microscopy (UFM), and scanning thermal microsopy (SThM) which marries high spatial resolution and contrast with the non-destructive nature of tapping mode AFM.
This approach provided profound contrast to small Aβ aggregates, and allowed the study of internal features of PF and MF fibres with a resolution comparable to that of transmission electron microscopy. Crucially we found that a population of oligomers and PF persists at least up to 72 h after commencement of aggregation, shedding the light on pathways of peptide aggregation. The new method has potential for studying much broader range of biopolymers, biomolecular assemblies and supramolecular structures.

1. Walsh, D.M. and D.J. Selkoe, A beta Oligomers - a decade of discovery. Journal of Neurochemistry, 2007. 101(5): p. 1172-1184.
2. Parthsarathy, V., et al., A Novel Retro-Inverso Peptide Inhibitor Reduces Amyloid Deposition, Oxidation and Inflammation and Stimulates Neurogenesis in the APPswe/PS1ΔE9 Mouse Model of Alzheimer’s Disease. PLoS ONE, 2013. 8(1): p. e54769.