Pathologic tau conformer ensembles induce dynamic, liquid-liquid phase separation events at the nuclear envelope

Area of Science:

• Neuroscience
• Biochemistry
• Cell Biology

Background:

• Tau protein aggregates are hallmarks of tauopathies, a group of neurodegenerative diseases.
• A specific mutation (P301L) in the MAPT gene influences tau folding pathways, correlating with distinct clinical outcomes.
• Brain tau preparations exhibit complex unfolding profiles, suggesting an ensemble of different tau conformers.

Purpose of the Study:

• To investigate the progression of tau conformers and their relationship with liquid-like states.
• To understand how tau conformers perturb cellular processes.

Main Methods:

• Progressive chemical denaturation using guanidine hydrochloride (GdnHCl).
• Seeding reporter cells expressing tau fused to fluorescent proteins (GFP/YFP).
• Observing tau droplet formation, fusion, and intracellular localization using microscopy.

Main Results:

• Tau conformer ensembles from P301L mice induced liquid-like phase separation (LLPS) in reporter cells.
• These tau droplets exhibited fusion, movement, and recovery from photobleaching.
• Juxtanuclear tau assemblies disrupted nuclear transport and reduced cell viability.
• Thioflavin S (ThS) staining indicated a mass threshold for liquid-solid transitions in tau condensates.

Conclusions:

• Tau conformer ensembles can template the formation of dynamic, condensed droplets in living cells.
• These in vivo evolving species may represent an intermediate stage towards intracellular fibrillar tau inclusions in tauopathies.