Beta-amyloid (Aβ) aggregates are infamous for forming the toxic plaques in the brain of Alzheimer’s disease patients. The detrimental effects are fairly well studied, but the mechanism of formation remains largely a mystery.
Now, thanks to Ifor D. W. Samuel, J. Carlos Penedo and colleagues at University of St. Andrews and Glasgow University, researchers have a new fluorescent probe to study the process of Aβ aggregation. This paper was featured on the cover of the January 2014 issue of Molecular Biosystems.
The most common probe of Aβ currently in use is Thioflavin T (ThT), which has been very successful at detecting the presence of aggregates. However, this probe has a limited pH range where it can be used. Aggregate structures can form at low concentrations of Aβ, and in the slightly acidic (pH = 6) endosome, but both of these are beyond the detection limits of ThT. For maximum utility, a probe would be able to track Aβ formation under any biological conditions.
To address this disadvantage, Samuel & Penedo et al. have used a HiLyte Fluorescent probe attached to the N-terminal position of Aβ monomers. When monomers associate with each other, the probe undergoes fluorescence self-quenching (FSQ), a well-documented process where the presence of two probes proximal to each other will cause a decrease in the observed fluorescent signal. This decrease in signal can be monitored and correlated with the aggregation rate and type of Aβ structure formed.
First the researchers determined that the probe did not affect the final Aβstructures obtained by a TEM image comparison to ThT Aβ under various conditions (see Figure 1 below). They also showed that the rate of Aβ formation stayed the same. Because the HiLyte probe does not affect the normal Aβ function, they could then use the probe under biological conditions not accessible to ThT.
They found that they were able to detect fibrils under biological conditions (Figure 2a below), oligomers under endosomal conditions (Figure 2bbelow) and ADDLs (early precursor structures that occur at low Aβ concentrations). Each of these Aβ structures produced a different fluorescent signature, allowing them to be distinguished from each other. This ability to detect the different Aβ assembly rates will allow researchers to better characterize biological samples, hopefully leading to new treatment options for Alzheimer’s disease.
Read Samuel & Penedo et al’s HOT paper by following the link below!