Effect of G ₄ C ₂ repeat expansions on the motion of lysosomes inside neurites

The G₄C₂hexanucleotide repeat expansion (HRE) in the c9orf72 locus is a mutation associated with amyotrophic lateral sclerosis. Recent evidence suggests a link with disrupted axonal trafficking in neurons. Here, using a neuronal-like cell line without or transfected with G₄C₂repeats, we characterize the motion of lysosomes inside neurites. The neurites grew either aligned to patterned lines, or oriented freely on a 2D-substrate. Implementing time-resolved (local) mean squared displacement analysis lysosome trajectories were split into sub-diffusive, diffusive, and super-diffusive parts. Our results suggest that in the presence of the G₄C₂repeats, lysosome trafficking is hampered, exhibiting overall decreased mean squared displacement and speed, more prominently inside aligned neurites. Moreover, a prominent effect in the super-diffusive drift velocity and diffusive motion diffusion coefficient was evident when the motion occurred inside aligned neurites. Trajectories which included super-diffusive motion, exhibited a varied ratio of anterograde/retrograde/neutral for both neurite geometries in the presence of G₄C₂repeats but a similar velocity decrease for both directions in each neurite geometry. Our findings support the hypothesis that impaired axonal trafficking emerges in the presence of the G₄C₂HRE, and demonstrate that this effect is more prominent when the neurites are aligned.