Glutamine missense suppressor transfer RNAs inhibit polyglutamine aggregation.

Area of Science:

• Genetics
• Molecular Biology
• Neuroscience

Background:

• Huntington's disease (HD) is characterized by polyglutamine (polyQ) expansions in the huntingtin gene.
• PolyQ protein aggregation is a critical step in HD pathogenesis.
• Translation fidelity influences protein aggregation, with mutations in glutamine (Gln) residues potentially reducing aggregation.

Purpose of the Study:

• To investigate if missense suppression of Gln codons by tRNA variants can reduce polyQ aggregate formation in cells.
• To assess the impact of serine and alanine mis-incorporation into polyQ on aggregation.

Main Methods:

• Utilized tRNA variants (tRNA^Ser _CUG and tRNA^Ala _CUG) to misread Gln codons in neuroblastoma cells.
• Quantified polyQ protein levels and aggregate formation (soluble and insoluble).
• Confirmed amino acid mis-incorporation using mass spectrometry and assessed cellular toxicity and global protein synthesis.

Main Results:

• tRNA^Ser _CUG reduced overall polyQ protein production and both soluble and insoluble aggregates.
• tRNA^Ala _CUG specifically decreased insoluble polyQ aggregates by twofold, with approximately 20% Ala mis-incorporation.
• Missense suppressor tRNAs were well-tolerated, showing no cytotoxicity or defects in growth or global protein synthesis.

Conclusions:

• Tandem repeat expansions in the huntingtin gene cause Huntington's disease.
• tRNA-dependent missense suppression of Gln codons is a viable strategy to reduce polyQ aggregation in mammalian cells.
• This approach demonstrates potential for mitigating the molecular pathology of Huntington's disease.