Tanz Centre research uncovers role of random protein formations in driving neurodegenerative disease

A new study from the University of Toronto suggests that different strains of a misfolded protein can arise randomly, even under identical conditions, driving the development of different neurodegenerative disease.

The study, published in Neuron, may influence how researchers use the protein, called alpha-synuclein, to study neurodegenerative diseases in lab settings.

“We hope that our paper stimulates researchers to consider these findings when they’re designing and interpreting their experiments and take into account that different strains of alpha-synuclein may be present,” said Joel Watts, a scientist at U of T’s Tanz Centre for Research in Neurodegenerative Diseases and associate professor in the department of biochemistry at the Temerty Faculty of Medicine.

“When we're making alpha-synuclein aggregates in a test tube, we need to make sure that the aggregates we’re using are the same for each experiment to ensure the best results,” Watts said.

The alpha-synuclein protein can misfold and form aggregates that are the hallmark of diseases such as Parkinson’s and multiple system atrophy. These aggregates act like “seeds” and induce misfolding in healthy alpha-synuclein protein, resulting in disease progression as more misfolded protein accumulates and damages brain cells.

Researchers have noticed that alpha-synuclein can misfold in different ways and hypothesized that these strains would lead to the development of different diseases. It wasn’t clear how the various strains of misfolding arose, but the prevailing idea was that alpha-synuclein misfolding would vary when kept in different buffer solutions.

Several years ago, however, Raphaella So — then a graduate student in the Watts lab who is now a postdoctoral fellow and first author on the current study — noticed that two different strains of misfolded alpha-synuclein formed under identical conditions. Instead of dismissing this observation as an error, she and the Watts team saw it as an opportunity.

They chose to examine what was behind the result, and to study the role of random variability in driving different alpha-synuclein diseases.

“That curiosity about whether there was some intrinsic randomness and variability in the strains that could form was really the genesis of this project,” said Watts. “We thought that maybe the random misfolding could be the initial driver that determines which type of aggregate forms, and that this might explain how different diseases arise.”

The research team examined both normal alpha-synuclein and a mutated form of the protein typically found in people with genetic Parkinson’s. They allowed aggregates of the protein to form under identical molecular conditions and inoculated mouse models with the aggregates to study which alpha-synuclein-related disease would develop.

They also collaborated with a research team in Germany that uses cryo-electron microscopy (cryo-EM), a high-resolution imaging technique that produces 3D images of individual molecules, to examine the structures of the aggregates.

The results showed there was more randomness in the system than expected. Evidence from both the cryo-EM imaging and the mouse models demonstrated that different strains of alpha-synuclein aggregates could arise under identical conditions, and these distinct strains could lead to different neurodegenerative diseases.

The research team also noticed that mutated alpha-synuclein drove the development of two different strains, while aggregates made of normal alpha-synuclein could lead to many different strains, including one that mimics Parkinson’s — suggesting that genetic mutations may limit the variability of alpha-synuclein strains that arise.

While the study provides some explanation for what drives the development of different alpha-synuclein diseases, Watts said the results are particularly relevant for researchers using lab-generated alpha-synuclein aggregates, given the effect that different strains of alpha-synuclein may have on results.

“The main finding of this work could have immediate impact on how research is done. We could identify aggregates of alpha-synuclein that drove the development of specific diseases, opening up new opportunities for using aggregates to understand Parkinson’s disease and develop therapeutics,” said Watts.

“These alpha-synuclein preparations are very useful research tools, but if we don’t consider their intrinsic variability, we might be missing something. Maybe a new therapeutic works against one strain, but its effect is diluted if other strains are present in the preparation. There’s a lot of opportunity in our finding to improve our research tools and, eventually, therapeutics for neurodegenerative diseases.”