Researchers at the David Geffin School of Medicine at UCLA have made an interesting discovery regarding the glial scar tissue formed after a spinal injury, which may turn all future research in this area on its head.
Glial cells surround neurons in the central nervous system, and are responsible for the formation of scar tissue following an injury to the brain or spinal cord. Prior to these new findings, it was believed that it was necessary to remove the scarring caused by glial cells before any kind of repair could be made to the injured neurons. During the study, Dr. Michael Sofroniew and his colleagues discovered that this scar tissue, far from preventing cell regeneration, might actually encourage it to happen. This is significant as, for the last two decades, researchers have been trying to prevent this kind of scarring in the belief that it may promote the repair or regeneration of the fibres.
When the spinal cord is damaged, it’s unable to regrow axons in the injured part of the body. As these axons activate the muscles, it usually means that there is paralysis below the injury. Until now, doctors have believed that the scar tissue formed by astrocytes, a special type of glial cells, has been a barrier to regeneration, based on the fact that nerve fibres don’t grow past the scar tissue following an injury. Therefore, in the past, researchers have attempted to prevent or remove these scars.
The Study and the Results
Two sets of mice were used for the study: one in which specific genes could be switched on to prevent the scar formation; while the second set were genetically engineered to dissolve any such scars. By using fluorescent imaging, the team were able to trace individual axons to see what happened when they reached the site of the injury. In both sets of mice, there were no signs of the axons growing through the region, an observation that suggested that removing the scars wasn’t beneficial in the least.
As a result of this research, the team also found that glial scars had a positive role to play when the neurons were ‘softly flogged’ to encourage them to regenerate. This technique involved infusing neurotrophic growth factors at the site of the spinal injury, while apply additional lesions which are known to stimulate nerve growth. In the normal mice, this two-fold approach led to the spinal axons regrowing past the scars and through the injury site. However, there was no, or limited, regrowth in the mice that had been genetically modified to eliminate scars.
This discovery is likely to prompt a new approach to solving the problem of regenerating the spinal cord after traumatic injury, by shifting the focus from decreasing the activity of the glial cells to finding ways to exploit it to promote axon regeneration.