The huntingtin inclusion is a dynamic phase-separated compartment

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Disordered protein inclusions characterize neurodegenerative diseases like Huntington's disease.
• Huntington's disease results from polyglutamine tract expansion in huntingtin protein, leading to unstable mutant huntingtin protein (mHtt) aggregation.
• mHtt accumulates in intracellular inclusions in affected individuals and in cellular models.

Purpose of the Study:

• To investigate the dynamics and intracellular trafficking of mutant huntingtin protein (mHtt) inclusions.
• To understand the mechanisms of mHtt inclusion formation and degradation.
• To explore the role of protein aggregation in Huntington's disease pathogenesis.

Main Methods:

• Utilized mHtt-GFP expressed in Saccharomyces cerevisiae to visualize and track inclusions.
• Employed pulse-chase studies with photoconverted mHtt-mEos2 to monitor protein turnover.
• Observed and tracked the movement of small mHtt-GFP particles.

Main Results:

• mHtt-GFP inclusions are dynamic, mobile, gel-like structures concentrating mHtt and Hsp104.
• Inclusions associate reversibly with the vacuolar membrane but are not endocytosed.
• mHtt is continuously removed directly from inclusion bodies, and small mHtt particles exhibit random movement.

Conclusions:

• Huntington's disease inclusions are not static but dynamic entities.
• mHtt is actively cleared from inclusions, suggesting a continuous degradation or removal process.
• Inclusion growth may occur through the collision and coalescence of smaller, mobile mHtt aggregates.