Preparation of stable tau oligomers for cellular and biochemical studies

Highlights

• The transient nature of tau aggregation makes it difficult to maintain the stability of preformed oligomers.

• Efficient labeling of tau K18 with Alexa Fluor-488-C5-maleimide or N-ethyl maleimide stabilizes the resulting oligomers.

• Oligomers applied exogenously are propagated intracellularly by cultured human iPSC neurons and neuroblastoma cells.

• Oligomer preparation by maleimide labeling allows mechanistic studies of tau aggregation and its link to neurodegeneration.

Abstract

Increasing evidence suggests that small oligomers are the principal neurotoxic species of tau in Alzheimer's disease and other tauopathies. However, mechanisms of tau oligomer-mediated neurodegeneration are poorly understood. The transience of oligomers due to aggregation can compromise the stability of oligomers prepared in vitro. Consequently, we sought to develop an efficient method which maintains the stability and globular conformation of preformed oligomers. This study demonstrates that labeling a single-cysteine form of the pro-aggregant tau four-repeat region (K18) with either Alexa Fluor 488-C5-maleimide or N-ethylmaleimide in reducing conditions stabilizes oligomers by impeding their further aggregation. Furthermore, the use of this approach to study the propagation of labeled extracellular tau K18 oligomers into human neuroblastoma cells and human stem cell-derived neurons is described. This method is potentially applicable for preparing stabilized oligomers of tau for diagnostic and biomarker tests, as well as for in vitro structure-activity relationship assays.