# C9orf72-derived arginine-containing dipeptide repeats associate with axonal transport machinery and impede microtubule-based motility

## TL;DR

This study shows that dipeptide repeats from a C9orf72 gene mutation disrupt axonal transport in neurons, contributing to ALS and FTD.

## Contribution

The study reveals that arginine-rich DPRs physically interact with and impair microtubule-based motor complexes in neurons.

## Key findings

- C9orf72 repeat expansions impair microtubule-based transport in patient-derived motor neurons.
- Arginine-rich DPRs inhibit axonal trafficking in both human neurons and Drosophila neurons.
- DPRs bind to motor complexes and microtubules, directly blocking motor protein movement.

## Abstract

Arginine-rich dipeptide repeats associated with ALS and FTD inhibit machinery for microtubule-based axonal cargo transport.

A hexanucleotide repeat expansion in the C9orf72 gene is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). How this mutation leads to these neurodegenerative diseases remains unclear. Here, we show using patient stem cell–derived motor neurons that the repeat expansion impairs microtubule-based transport, a process critical for neuronal survival. Cargo transport defects are recapitulated by treating neurons from healthy individuals with proline-arginine and glycine-arginine dipeptide repeats (DPRs) produced from the repeat expansion. Both arginine-rich DPRs similarly inhibit axonal trafficking in adult Drosophila neurons in vivo. Physical interaction studies demonstrate that arginine-rich DPRs associate with motor complexes and the unstructured tubulin tails of microtubules. Single-molecule imaging reveals that microtubule-bound arginine-rich DPRs directly impede translocation of purified dynein and kinesin-1 motor complexes. Collectively, our study implicates inhibitory interactions of arginine-rich DPRs with axonal transport machinery in C9orf72-associated ALS/FTD and thereby points to potential therapeutic strategies.