Axonal Regeneration of ALS Patient iPSC-derived Motor Neurons

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease, characterized by degeneration of upper and lower motor neurons that leads to muscle weakness, paralysis, and death, usually 3-5 years following symptom onset. Current treatments only extend patient survival modestly. The failure of transgenic mice to faithfully replicate human disease processes, in addition to potentially confounding differences between human and mouse axonal regeneration and neuromuscular physiology, may contribute to lack of drug efficacy in human trials. The emergence of human induced pluripotent stem cell (iPSC)-derived motor neurons (hMNs) in ALS research is a promising avenue to develop more relevant models and platforms for target identification and drug development, but questions remain concerning the effects of distinct disease-causing mutations on hMNs. Though dying-back axonopathy is a hallmark of ALS and many other neurologic diseases, the effects of disease-causing mutations on hMN distal axon biology and axonal regeneration are poorly understood. Mutations in Superoxide Dismutase 1 (SOD1) were the first to be discovered in ALS patients. Mutations in many genes have been discovered since. Here, we investigated the effect of the SOD1A4V mutation on axonal regeneration of hMNs, utilizing compartmentalized microfluidic devices, which are powerful tools for studying the distal axons of hMNs. Surprisingly, SOD1+/A4V hMNs regenerated axons more quickly than SOD1+/+. Stathmin-2, a microtubule destabilizing protein that has been implicated in non-SOD1 ALS, appears to be increased in the growth cones of SOD1+/A4V regenerating axons. This unexpected result emphasizes the need to further characterize the effects of distinct disease-causing mutations on hMN axonal outgrowth and regeneration. We conclude that modeling the human neuromuscular circuit with hMNs and human-derived cell types may be critical for developing drugs that enhance axonal regeneration, sprouting, and reinnervation of NMJs