Imaging protein oligomerization in neurodegeneration using bimolecular fluorescence complementation

Neurodegenerative disorders such as Alzheimer's, Parkinson's, Huntington's, or Prion diseases belong to a superfamily of pathologies known as protein misfolding disorders. The hallmark of these pathologies is the aberrant accumulation of specific proteins in beta sheet-rich amyloid aggregates either inside or outside cells. Current evidence suggests that oligomeric species, rather than mature protein aggregates, are the most toxic forms of the pathogenic proteins. This is due, at least in part, to their greater solubility and ability to diffuse between intracellular and extracellular compartments. Understanding how oligomerization occurs is essential for the development of new treatments for this group of diseases. Bimolecular fluorescence complementation assays (BiFC) have proved to be excellent systems to study aberrant protein-protein interactions, including those involved in neurodegenerative diseases. Here, we provide a detailed description of the rationale to develop and validate BiFC assays for the visualization of oligomeric species in living cells in the context of neurodegeneration. These systems could constitute powerful tools for the identification of genetic and pharmacological modifiers of protein misfolding and aggregation.