Alzheimer’s study separates two membrane-damaging protein forms
A peer-reviewed experimental study distinguished two transient forms of amyloid-beta, the protein associated with Alzheimer’s disease, by how they disrupted membranes. Both appeared in brain tissue from three people who had the disease. Their different routes of formation help describe the steps between individual proteins and the larger fibres found in plaques.
Science··Midday
Transient protein clusters
Amyloid-beta, a protein that accumulates in Alzheimer’s brain plaques, can pass through short-lived clusters before forming larger fibres. A peer-reviewed experimental study distinguished two main intermediate populations by their ability to damage membranes. The finding connects clusters studied in laboratory systems with patterns detected in donated human brain tissue.[1], [2]
To detect individual damaging events, the researchers used tiny lipid vesicles, sacs whose surfaces mimicked neuronal membranes. A calcium-sensitive dye inside each vesicle lit up when membrane damage let calcium enter. The selected vesicles measured 50–100 nanometres across. This fluorescence method separated events that would otherwise be mixed together in a measurement of the entire sample.[1]
Two routes through aggregation
The population called class A appeared early and showed stronger membrane disruption per event. Class B became more abundant later, during fibre growth. Modelling linked class B with secondary nucleation, in which existing fibre surfaces help new clusters form. Class A arose predominantly outside that fibre-forming route, although a small contribution to fibre formation could not be ruled out.[1]
Human tissue and experimental protection
Both main activity patterns appeared in postmortem brain samples from 3 patients: 2 women and 1 man aged 71–92. Their relative proportions varied between patients. The study also examined laboratory proteins, neurons derived from human stem cells and a mouse model of Alzheimer’s. In cellular experiments, the clusters injured neuronal projections, the extensions through which nerve cells connect with one another.[1]
An engineered protective protein domain called BRICHOS R221E reduced membrane-damaging activity and cellular injury in experimental systems. Brain tissue from mice treated in an earlier experiment also showed lower activity from both intermediate classes. The human component was a small postmortem sample rather than a treatment trial. Larger human cohorts and work with natural membranes are needed to establish how these transient forms vary through the disease.[1]
