WashU reveals details of amyloid aggregates

24 Jul 2024

Single-molecule localization microscopy assists understanding of neurodegenerative disease.

Accumulation of amyloid-beta (A-beta) peptides inhibiting normal brain function is a characteristic aspect of neurodegenerative disease, but how A-beta comes together and breaks apart as it does the damage remains poorly understood.

A project at Washington University in St. Louis (WashU) has now developed a microscopy technique able to view the orientations and movements of molecules as the A-beta builds up and takes shape. The results were published in Nano Letters.

"The way A-beta behaves in a variety of environments, including the human brain, is elusive,” commented Brian Sun from the WashU School of Medicine. "There's an understanding of growth and decay that isn't fully fleshed out."

The work promises to be a valuable addition to the study of how neurodegenerative disease develops, where new details are being uncovered regularly.

Earlier in 2024 a project at UC San Diego used a Raman-based imaging platform to explore the role of lipid droplets in Alzheimer's and similar diseases, tackling one "largely overlooked...important aspect of the disease," according to the researchers. Elsewhere a team at the University of Rochester has used correlative light electron microscopy to reveal the structural changes involved in Huntington’s disease and schizophrenia.

The new study at WashU aimed to study and monitor amyloid fibril beta-sheet assemblies, the underlying girders of the protein conglomeration, while they were changing. Previous high-resolution microscopy studies have only obtained static shots, according to the project.

Capturing this process in microscopy images needed the development of a suitable single-molecule localization method, analogous to previous localization techniques in which discrete molecular-scale events have been captured as a route to understanding protein structures.

Seeing the complexity of neurodegenerative change

WashU used single-molecule orientation-localization microscopy (SMOLM), one of a number of fluorescence techniques intended to augment the positional data acquired from single-molecule localization with added information about a molecule's orientation, derived from deeper analysis of the fluorescence signals emitted.

Time-lapse SMOLM imaging allowed the project to measure the orientations and rotational wobble of fluorescent Nile Blue marker molecules as they bonded transiently to fibrils of one A-beta peptide. This revealed the individual orientation of underlying beta-sheets, and the relationship between their organization to the amyloid protein's overall structure.

Some previously unknown details of A-beta's behavior were uncovered, including the several different ways A-beta structures remain stable, or grow and decay. These different kinds of remodeling have not been visible from previous diffraction-limited non-orientation imaging modalities, according to WashU, and understanding them could help development of therapies designed to inhibit the amyloid build-up.

"The individual proteins are always changing in response to their environment," said lead author Matthew Lew of WashU. "It is like having certain Lego bricks causing other bricks to change their shape. The changing architecture of the proteins and the assembled aggregates together leads to the complexity of neurodegenerative disease."