Cell-replacement therapy with stem cells in neurodegenerative diseases.

In the past few years, research on stem cells has expanded greatly as a tool to develop potential therapies to treat incurable neurodegenerative diseases. Stem cell transplantation has been effective in several animal models, but the underlying restorative mechanisms are still unknown. Several mechanisms such as cell fusion, neurotrophic factor release, endogenous stem cell proliferation, and transdifferentiation may explain positive therapeutic results, in addition to replacement of lost cells. The biological issue needs to be clarified in order to maximize the potential for effective therapies. The absence of any effective pharmacological treatment and preliminary data both in experimental and clinical settings has recently identified Amyotrophic Lateral Sclerosis (ALS) as an ideal candidate disease for the development of stem cell therapy in humans. Preliminary stem transplantation trials have already been performed in patients. The review discusses relevant topics regarding the application of stem cell research to ALS but in general to other neurodegenerative diseases debating in particular the issue of transdifferentiation, endogenous neural stem cell, and factors influencing the stem cell fate.