Distinct C9orf72-Associated Dipeptide Repeat Structures Correlate with Neuronal Toxicity.

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• Hexanucleotide repeat expansions in the C9orf72 gene are the leading inherited cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD).
• These expansions lead to toxic dipeptide repeat-containing proteins (DPRs) via repeat-associated non-AUG (RAN) translation.
• The structural properties and aggregation behaviors of these DPRs are not well understood.

Purpose of the Study:

• To investigate the structural characteristics and aggregation propensities of dipeptide units produced by C9orf72 RAN translation.
• To assess the relative toxicity of these dipeptides in primary cortical neurons.
• To correlate structural properties with observed toxicity.

Main Methods:

• Synthesis of three sense-strand dipeptide units from C9orf72 RAN translation.
• Structural analysis using circular dichroism, electron microscopy, and dye binding assays (Thioflavin T, Congo red).
• Assessment of neuronal toxicity and peptide internalization in primary cortical neurons.

Main Results:

• Short glycine-arginine (GR)3 peptides formed spherical aggregates and were toxic to neurons.
• Glycine-proline (GP)3 and glycine-alanine (GA)3 peptides showed different aggregation patterns.
• (GA)6 peptides formed beta-sheet rich aggregates, lacking typical amyloid morphology, with increased toxicity upon aging.
• Peptide toxicity correlated with cellular internalization.

Conclusions:

• C9orf72-related dipeptides possess distinct structural properties.
• These structural differences correlate with variations in their toxicity to neurons.
• Understanding these structure-toxicity relationships is crucial for C9orf72-related neurodegenerative diseases.