Stem cells within the spinal cord that may soon be persuaded
to differentiate into more healing cells and fewer scarring cells following an
injury, researchers have revealed. This may lead to a new, non-surgical
treatment for debilitating spinal-cord injuries.
The findings of the study, conducted by Konstantinos Meletis, a postdoctoral fellow at MIT''s Picower Institute for Learning and Memory, and colleagues at the Karolinska Institute in Sweden, could lead to drugs that might restore some degree of mobility to the 30,000 people worldwide afflicted each year with spinal-cord injuries.
In a developing embryo, stem cells differentiate into all the specialized tissues of the body.
The tiny number of stem cells in the adult spinal cord proliferate slowly or rarely, and fail to promote regeneration on their own.
However, recent experiments showed that these same cells, grown in the lab and returned to the injury site, could restore some function in paralysed rodents and primates.
Researchers found that neural stem cells in the adult spinal cord are limited to a layer of cube- or column-shaped, cilia-covered cells called ependymal cells.
These cells make up the thin membrane lining the inner-brain ventricles and the connecting central column of the spinal cord.
"We have been able to genetically mark this neural stem cell population and then follow their behaviour. We find that these cells proliferate upon spinal cord injury, migrate toward the injury site and differentiate over several months," Meletis said.
The study uncovers the molecular mechanism underlying the tantalizing results of the rodent and primate and goes one step further: By identifying for the first time where this subpopulation of cells is found, they pave a path toward manipulating them with drugs to boost their inborn ability to repair damaged nerve cells.
"The ependymal cells'' ability to turn into several different cell types upon injury makes them very interesting from an intervention aspect: Imagine if we could regulate the behaviour of this stem cell population to repair damaged nerve cells," Meletis said.
When an injury occurs, ependymal cells proliferate and migrate to the injured area, producing a mass of scar-forming cells, plus fewer cells called oligodendrocytes.
The oligodendrocytes restore the myelin, or coating, on nerve cells'' long, slender, electrical impulse-carrying projections called axons.
Myelin is like the layer of plastic insulation on an electrical wire; without it, nerve cells don''t function properly.
"The limited functional recovery typically associated with central nervous system injuries is in part due to the failure of severed axons to regrow and reconnect with their target cells in the peripheral nervous system that extends to our arms, hands, legs and feet. The function of axons that remain intact after injury in humans is often compromised without insulating sheaths of myelin," Meletis said.
Researchers said that if scientists could genetically manipulate ependymal cells to produce more myelin and less scar tissue after a spinal cord injury, they could potentially avoid or reverse many of the debilitating effects of this type of injury.
The study is published in the July issue of the journal PloS Biology.