IMPRiND

Alzheimer’s and Parkinson’s diseases are neurodegenerative disorders that affect 45 million and 10 million people worldwide respectively. There is currently no cure for these diseases, which place an immense burden on carers, many of whom are family members. Both diseases are characterised by the progressive loss of brain cells. Recent evidence suggests that this loss may be due to the release and uptake by brain cells of specific aggregated proteins (misfolded proteins which clump together leading to a progressive spreading of the degeneration). If these processes could be blocked, disease progression could be halted. However, the forces driving these processes are currently poorly understood. Working to change that was the IMPRiND project, which aimed to understand how these aggregated proteins are handled once inside brain cells and how they are moved from cell to cell.

If a brain protein folds the wrong way, it doesn’t affect that protein alone. There is a knock-on effect – one incorrectly folded protein directs other molecules of the same protein to also fold erroneously. The result is a chain reaction and the formation of assemblies (called fibrils) of these pathogenic, misfolded proteins in the brain which cause nerve cell damage as well as the symptoms of Alzheimer’s and Parkinson’s.

The IMPRiND project explored in detail the mechanisms by which the neuronal proteins tau and α-synuclein – whose misfolded forms cause Alzheimer’s and Parkinson’s – aggregate.  

Imaging techniques shed light on brain protein folding differences

To better understand how a brain protein filament is becoming misfolded and tangled, better imaging techniques were needed. In a world first, the IMPRiND project used electron cryo-microscopy (cooling brain samples down to extremely low temperatures and then using electron microscopy techniques to examine them) to show the first high-resolution structures of tau filaments in a person with Alzheimer’s disease. The results of this experiment were published in Nature.

The project then developed different models to study the propagation mechanisms of the pathogenic brain protein aggregates. Some aggregates gathered particularly aggressively and the researchers sought to understand what determined whether the misfolded protein aggregates would progress rapidly or slowly, and why they would assemble in different ways, resulting in different brain diseases. Using the new imaging and amplification techniques, the project improved visibility of these mechanisms and could investigate what was happening at the molecular level. 

The IMPRiND project illuminated that the tau protein folds in different ways and this is correlated with different diseases (termed tauopathies). For instance, one study (also published in Nature) showed that the tau protein structure in patients with Pick’s disease differed from the tau protein structure seen in Alzheimer’s disease. A unique disease-specific fold was also identified which was associated with corticobasal degeneration (CBD), a type of neurodegenerative disease involving the cerebral cortex and basal ganglia which results in dementia and affects movement. These findings lend support to the existence of structurally distinct aggregates or strains of the same protein, offering a molecular classification of tauopathies.

Other studies that IMPRiND researchers engaged in revealed that α-synuclein fibrils from the brains of people with Parkinson’s disease and dementia with Lewy bodies are thinner and less twisted than those from people with multiple system atrophy (MSA). This may have implications for identifying effective therapeutic targets for these diseases. For example, researchers at Oxford reported in Nature Communications that fibrils derived from MSA brain induced aggregates in human neurons that were more toxic than fibrils derived from Parkinson’s brains and this could be partly explained by differential interactions with intracellular proteins.  

The type of folds that are observed matter because since they result in different diseases, it’s possible that they arise in different ways through differential interactions with cellular proteins or membranes and this could mean that they need to be targeted distinctly when it comes to therapeutics.

New tools and methods aid scientists to delve deeper into brain protein structure

A significant breakthrough achieved by the project was the use of cell lines to perform CRISPR screens to identify genetic modifiers of tau and α-synuclein. More than fifty targets were selected and validated. These as-yet-unpublished results have been cross-validated in primary and neuronal models in vitro and will provide valuable insights into cellular pathways that regulate aggregation. Based on these results, an online tool is being developed through which people can access genetic information about tau and α-synuclein proteins based on the CRISPR analysis, which could aid the cross-validation of therapeutic targets in the field.

In another example, the fluorescent dye thioflavin T (ThT) has up until now been used routinely in laboratories to monitor α-synuclein aggregation. But researchers in Université de Bordeaux showed that some forms of α-synuclein structures were not detected by the ThT dye, even though they  seemed to be pathogenic. This suggested that additional methodologies are needed to detect all forms of α-synuclein aggregates.

Other results included a new model for investigating α-synuclein aggregates in mouse cultures or surgically-resected human brain slices and optimised readouts of pathology in yet-to-be-published animal and primate models.

Interrupting the disease-causing aggregation of brain proteins

The findings of IMPRiND could aid the development of future therapies that aim to halt or slow the progression of Alzheimer’s and Parkinson’s disease. If we can better understand the key determinants of tau or α-synuclein aggregation in disease-relevant cell types or models, then the hope is that we can design drugs that interrupt and stop this process.  

Legacy of the project

The IMPRiND project generated over 53 peer-reviewed publications by the end of 2023, several of which were in high-profile journals such as Nature. The results of the studies conducted by the project have led to new discoveries and new methodologies that will contribute the development of future drugs targeting the mechanism by which aggregates of pathogenic brain proteins form.