Motor neuron replacement therapy for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a motor neuron degenerative disease that is also known as Lou Gehrig's disease in the United States, Charcot's disease in France, and motor neuron disease in the UK. The loss of motor neurons causes muscle wasting, paralysis, and eventually death, which is commonly related to respiratory failure, within 3-5 years after onset of the disease. Although there are a limited number of drugs approved for amyotrophic lateral sclerosis, they have had little success at treating the associated symptoms, and they cannot reverse the course of motor neuron degeneration. Thus, there is still a lack of effective treatment for this debilitating neurodegenerative disorder. Stem cell therapy for amyotrophic lateral sclerosis is a very attractive strategy for both basic and clinical researchers, particularly as transplanted stem cells and stem cell-derived neural progenitor/precursor cells can protect endogenous motor neurons and directly replace the lost or dying motor neurons. Stem cell therapies may also be able to re-establish the motor control of voluntary muscles. Here, we review the recent progress in the use of neural stem cells and neural progenitor cells for the treatment of amyotrophic lateral sclerosis. We focus on MN progenitor cells derived from fetal central nervous system tissue, embryonic stem cells, and induced pluripotent stem cells. In our recent studies, we found that transplanted human induced pluripotent stem cell-derived motor neuron progenitors survive well, differentiate into motor neurons, and extend axons into the host white matter, not only in the rostrocaudal direction, but also along motor axon tracts towards the ventral roots in the immunodeficient rat spinal cord. Furthermore, the significant motor axonal extension after neural progenitor cell transplantation in amyotrophic lateral sclerosis models demonstrates that motor neuron replacement therapy could be a promising therapeutic strategy for amyotrophic lateral sclerosis, particularly as a variety of stem cell derivatives, including induced pluripotent stem cells, are being considered for clinical trials for various diseases.