This type of stem cell may form the basis for future therapies to help humans who have spinal cord injuries, suggest the findings of the UC Irvine Reeve-Irvine Research Center team.

New Myelin and Neurons

Brian Cummings, Aileen Anderson and colleagues injected adult human neural stem cells into mice that had limited mobility due to spinal cord injuries.

The transplanted stem cells differentiated into new oligodendrocyte cells that restored myelin around damaged mouse axons. The transplanted cells also differentiated into new neurons that formed synaptic connections with mouse neurons.

"We set out to find whether these cells would be able to respond to the injury in an appropriate and beneficial way on their own," Cummings said.

"We were excited to find that the cells responded to the damage by making appropriate new cells that could assist in repair. This study supports the possibility that formation of new myelin and new neurons may contribute to recovery," he added.

No Coaxing

Myelin -- the biological insulation for nerve fibers -- is critical for electrical conduction in the central nervous system. When myelin disease or injury destroys myelin, sensory and motor deficiencies result. In some cases, paralysis occurs.

Transplanting oligodendrocyte precursors derived from human embryonic stem cells was found to restore mobility in rats in earlier research conducted at Reeve-Irvine.

The latest study differs from the previous work with human embryonic stem cells in spinal cord injury, because the human neural stem cells were not coaxed into becoming specific cell types before transplantation.

Walking Ability Improved

Mice that received human neural stem cells nine days after spinal cord injury showed improvements in walking, compared to mice that received either no cells or a control transplant of human fibroblast cells (which cannot differentiate into nervous system cells).

There were behavioral improvements after either moderate or more severe injuries. The treated mice developed the ability to step using the hind paws and to coordinate stepping between paws, while the control mice were uncoordinated.

The cells survived, and the mice showed improved walking ability for at least sixteen weeks. At that point, the human cells were killed using diphtheria toxin (which is only toxic to the human cells, not the mouse). The improvements in walking disappeared, indicating that the human neural stem cells were the vital catalysts.

"This work is a promising first step, and supports the need to study multiple stem cell types for the possibility of treating of human neurological injury and disease," Anderson said.