Previously injured nerve fibers, red, are shown regrowing through a dense astrocyte scar, in green, which scientists say was not expected before starting an experiment with mice. Photo by University of California Los Angeles
LOS ANGELES, March 31 (UPI) -- Doctors often try to prevent the formation of glial scar tissue in brain and spinal injuries because it was thought to impede healing but scientists at the University of California Los Angeles found in a recent study that may not be the case.
The scientists found glial scars may encourage nerves to regenerate, suggesting doctors that prevent or remove scar tissue could be impeding the regeneration of nerve fibers in the spine.
The spinal cord is a cable of nerve projects called axons that connect muscles to the brain, allowing for direction, movement and feedback to the brain. In peripheral nerve systems, the axons grow back, however that largely is not the case in the spine, leading to paralysis below the spinal injury.
The theory on scar tissue after spinal injuries was that glial cells called astrocytes impeded tissue growth because spinal nerve fibers appear not to grow past the scars. In mice in the recent study, scar tissue appeared to help healing and developed a concept for encouraging that healing, though the scientists caution the method used with mice in the study won't work in humans.
"This paper may encourage some to shift their focus away from trying to decrease astrocyte activity, in particular in scar formation, and toward how to exploit it as a way to promote regeneration," said Joshua Burda, a postdoctoral fellow at the University of California Los Angeles, in a press release.
For the study, published in the journal Nature, the scientists evaluated two sets of mice, one genetically modified to prevent the formation of scars and the other engineered to dissolve scars after they form. In both sets of mice, the scientists noted axons did not grow through the injury sites -- this, they said, shows eliminating the scars does not help healing.
Then the scientists instead injected neurotrophic growth factors to the injury site, and applied lesions known the stimulate nerve regrowth at the site. In normal mice, the axons grew past scars and through the injury site, while mice engineered to not generate scar tissue showed far less nerve regeneration.
Although Burda said scientists did not expect their results, he added that it's not surprising scar formation could offer a beneficial function to both healing and axon regeneration.
"Techniques used in mouse models cannot be applied today in patients," said Dr. Michael Sofroniew, a professor at UCLA. "But our work is an important scientific step toward developing strategies to get nerve fibers to regrow across severe spinal lesions. It opens the door to an area of research that has been inhibited by incorrect dogma."