Amyloid-beta (A-beta) aggregates are protein tangles associated primarily with neurodegenerative diseases such as Alzheimer’s. However, despite their constant prominence, researchers have been unable to fully understand how A-beta binds and disintegrates.
“The way beta-amyloid behaves in a variety of environments, including the human brain, is difficult to understand,” said Brian Sun, an electrical systems and engineering alumnus at Washington University in St. Louis who is now a medical doctoral student at the School of Medicine.
“There is an understanding of growth and decline that is not fully developed,” he added.
That’s about to change, thanks to recently published research Sun co-authored with colleagues in the lab of Associate Professor Matthew Lew in the Preston M. Green Department of Electrical and Systems Engineering (ESE) in WashU’s McKelvey School of Engineering.
In a groundbreaking study, Sun and his colleagues were able to make measurements of the beta-sheet arrays of amyloid fibrils, the underlying beams of the protein conglomerate, as they changed. Previous studies using high-resolution microscopy had only obtained static images.
“We wanted to look specifically at the dynamics of the underlying structure of A-beta that might be responsible for the changes we’re seeing, not just changes in the overall shape,” Sun said.
Lew uses Lego as an analogy, pointing out that current imaging technology shows the complete Lego building but does not show how each individual brick is arranged.
“Individual proteins are constantly changing in response to their environment,” Lew said. “It’s as if certain Lego pieces cause other pieces to change shape. The changing architecture of proteins and the aggregates assembled together drive the complexity of neurodegenerative disease.”
Lew’s lab has developed a new type of imaging technology that allows them to see orientation and other minute details in previously invisible nanostructures of biological systems. Their technique, single-molecule orientation and localization microscopy (SMOLM), uses flashes of light from chemical probes to visualize the peptide sheets underlying Aβ42, a type of A-beta peptide.
Using SMOLM allows them to look at the individual orientation of the underlying beta sheets to see the relationship between their organization and how it relates to the overall structure of the amyloid protein.
Multiple ways to remodel
Aβ42 is constantly changing and the first step is to try to find a method for this madness, a model or pattern of action to predict the behavior of the protein.
Now that Lew’s lab can make these measurements, they’ve made some intuitive observations and found some hidden surprises in the architecture of amyloid beta.
As expected, stable Aβ42 structures tend to maintain stable underlying beta sheets; growing structures have underlying beta sheets that become more defined and rigid as growth continues. Decaying structures feature increasingly disordered and less rigid beta sheets. But they also found more than one way for Aβ42 to renew itself.
“There are many different ways for Aβ42 structures to remain stable or grow and break down,” Sun said.
The researchers also found that Aβ42 can grow and disintegrate in ways that defy expectations. For example, Aβ42 can grow and disintegrate in ways that preserve the underlying structure; sometimes there is growth where peptides simply pile up, but the underlying beta-sheet orientations do not change. In other cases, Aβ42 undergoes “stable disintegration,” where the opposite happens—that is, peptides leave, but the beta-sheet structure remains. Finally, the beta-sheets of Aβ42 sometimes rearrange and change orientation without immediate changes in overall shape. These nanostructural rearrangements may predispose to future large-scale remodeling.
“Since SMOLM can trace the underlying organization of Aβ42 and not just its shape, we can see different types of remodeling subtypes that are not visible to orientation-free and diffraction-limited imaging modalities,” Sun said.
If all of this sounds a little vague, keep in mind that this is the first step toward observing these ever-changing nanoscale structures. There was no previous work to compare notes on, which makes it all the more remarkable that Sun put together this work while juggling COVID-19 lockdown restrictions and his undergraduate course load at WashU, which he completed in three years. It paves the way for him and others to begin to really understand amyloid architecture.
He will likely end up researching these questions further during the postgraduate phase of his medical/PhD training, where he plans to design nanoscale imaging systems and sensors that could reveal hidden mechanisms of difficult-to-treat diseases.
Sun thanks WashU’s ESE department and the Lew lab for the rigorous training that made this study and academic path possible, as well as WashU’s MSTP for supporting his continued research after graduation. “I’m really glad I went through this experience,” he said.
Research reported in this publication was supported by the National Institute of General Medical Sciences of the National Institutes of Health under award number R35GM124858.