Alzheimer’s and Parkinson’s disease are chronic, long-lasting, and so far, incurable neurodegenerative diseases. There are over 800,000 people living with dementia in the UK today, and this number is expected to rise rapidly as the population ages. Alzheimer’s disease is the most common cause of dementia, and according to figures published by the Alzheimer’s research trust, dementia costs the UK £23 billion per year, the vast majority of which is spent on care, rather than research.
The pathological hallmark of these diseases is the presence of insoluble protein deposits in the brain, which are formed when specific protein molecules mis-fold and aggregate (clump together) into highly ordered fibrils. In Alzheimer’s disease, the deposits are primarily made up of amyloid-beta, whereas in Parkinson’s, the major protein is alpha-synuclein. Rather than the fibrils themselves being toxic, much evidence now points towards the smaller, soluble oligomers formed in the initial stages of the process, as being the culprit. It is vitally important to characterise these oligomers and determine how they are formed, and more importantly, how they damage neurons.
During the aggregation process, the total concentration of oligomer may be much less than 1% of the total protein concentration. Therefore, in order to look at the oligomers, single molecule techniques must be used. Our methodology involves labelling half a population of the protein of interest (either alpha-synuclein, or amyloid-beta) with one colour, and the other half with another colour, and then observing the solution as the protein aggregates (within a test-tube). At the start, there will mainly be monomer and so each species will have only one colour dye. However, over time, the monomers will clump together to form oligomers, and so the species will be likely to have more than one colour. By looking at the progression of only the two-coloured species over time, it is possible to follow the oligomer formation process. The size/structure of the oligomers can also be determined by looking at the intensities of them. The conditions of the experiment can then be changed (i.e. by adding potential drugs, changing the biological environment etc.) and the effect on the aggregation observed.