Stem cells form the basis of regenerative medicine. Regeneration is when body tissue grows back after damage. Skin, for example, replaces itself, and the liver can regrow in a human adult.
Euro Stem Cell explain that omnipotent stem cells produce all the tissues that a body needs, but not all stem cells are omnipotent; there are different types of stem cells with different strategies for regeneration.
Scientists have been looking for ways to direct stem cells to replace functional cells damaged through trauma or by other causes, and the search is on to find the right kind of stem cell. The human corticospinal tract carries bundles of nerves from the cerebral cortex in the upper brain down into the spinal cord.
Successful regeneration of corticospinal axons
Previous experiments using stem cells have led to degrees of functional recovery in rats following spinal cord injury, but none of the studies involved regeneration of corticospinal axons. Humans need corticospinal axons to carry out voluntary movement. It was not thought that corticospinal neurons would have the internal mechanisms needed to allow for regeneration.
Researchers at the University of California-San Diego School of Medicine and Veterans Affairs San Diego Healthcare System, with colleagues in Japan and Wisconsin, collaborated to investigate the feasibility of using corticospinal neurons for this purpose.
They grafted multipotent neural progenitor cells into the injury sites of rats with spinal cord injury. Multipotent cells are stem cells that can regenerate into different types of cell. The team directed the cells to develop specifically as a spinal cord.
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The cells developed more successfully than the authors expected, replacing lost tissue and forming functional synapses that enabled the rats to move their forelimbs more than they could before.
Senior study author Dr. Mark Tuszynski, PhD, professor in the UC-San Diego School of Medicine Department of Neurosciences and director of the UC-San Diego Translational Neuroscience Institute, says:
"The corticospinal projection is the most important motor system in humans. It has not been successfully regenerated before. Many have tried, many have failed, including us, in previous efforts."
Still a long way to go
Dr. Tuszynski says that this was the first time for the team to use neural stem cells to find out whether they would support regeneration, where other cell types had not. He had been skeptical that therapies could be developed to improve function in humans, but the possibility of regenerating "the most important motor system for humans," now looks more likely. There is still a long way to go before stem cell therapies can be tested on humans or used in treatment. The first step is to carry out animal studies that demonstrate that such treatments can be used safely and with long-term functional benefit.
Then, says Dr. Tuszynski, scientists will need to use larger animal models to develop ways to transfer the technology to humans. They will also need to identify which is the best type of human neural stem cell to use.