C9orf72-derived dipeptide repeat proteins poly-PR disrupt membrane excitability and synaptic function in cortical neurons

Amyotrophic lateral sclerosis (ALS) is one of the most fatal neurodegenerative disease, with the most common genetic form of the ALS is associated with hexanucleotide GGGGCC repeat expansions in the first intron of C9orf72 gene. Cortical hyperexcitability is one of the symptoms reported in several forms of ALS and implicated as a cause of neuronal death, however, the underlying mechanisms are still unclear. The dipeptide repeat (DPR) proteins produced from hexanucleotide repeat expansion have been shown toxic to neurons and induce cellular damages. In this study, we explore relationships between the membrane excitability of cortical neurons and the expression of one of the DPR proteins poly-proline-arginine (poly-PR). We found that expression of poly-PR in primary cultured cortical neurons induced an elevation of intrinsic membrane excitability and decreases in dendritic arborization and excitatory synaptic activity. The increased membrane excitability can be restored by Nav channel inhibitor riluzole and Kv7 channel activator retigabine. Our results suggest a rescuable ion channel-mediated hyperexcitability induced by poly-PR expression in cortical neurons, providing a foundation for developing targeted therapies for C9orf72 ALS.