Rather than being responsible for blocking neuronal regrowth, which has been commonly thought, astrocytes may actually be required for repair and regrowth following spinal cord injury.
This suggestion is the result of a recent study funded by the National Institutes of Health and published recently in Nature.
“At first, we were completely surprised when our early studies revealed that blocking scar formation after injury resulted in worse outcomes. Once we began looking specifically at regrowth, though, we became convinced that scars may actually be beneficial,” states Michael V. Sofroniew, MD, PhD, professor of neurobiology at the University of California, Los Angeles, and senior author of the study, in a media release from NIH/National Institute of Neurological Disorders and Stroke.
“Our results suggest that scars may be a bridge and not a barrier towards developing better treatments for paralyzing spinal cord injuries,” he adds.
Neurons communicate with one another by sending messages down long extensions called axons. When axons in the brain or spinal cord are severed, they do not grow back automatically. For example, damaged axons in the spinal cord can result in paralysis. When an injury occurs, astrocytes become activated and go to the injury site, along with cells from the immune system and form a scar. Scars have immediate benefits by decreasing inflammation at the injury site and preventing spread of tissue damage. However, long-term effects of the scars were thought to interfere with axon regrowth, the release explains.
In the study, Sofroniew and his team used three different mouse models to examine the effect of astrocyte scars on axonal regrowth. The team was able to remove the scars or prevent them from forming after a spinal cord injury. The results revealed that without astrocyte scars, there was no regrowth, according to the release.
Another experiment on spinal cord injury in mice involved growth factors. Here, Sofroniew and his team shuttled growth factors—specific molecules that stimulate axons to grow—to the injury site and discovered that there was robust regrowth through astrocyte scars. However, if the researchers prevented scar formation along the injury site, the regrowth was significantly reduced.
Genetic analyses revealed that astrocytes as well as non-astrocyte cells released a variety of chemicals involved in regrowth at the injury site. In this experiment, Sofroniew and his team found molecules that block regrowth along with molecules that support it, per the release.
“These preliminary findings established that axonal growth can occur in the presence of scars in mice. Eventually, we would like to see the regenerating axons grow far enough into healthy tissue to establish functional connections,” says Sofroniew in the release regarding he and his team’s future research plans.
[Source(s): NIH/National Institute of Neurological Disorders and Stroke, EurekAlert]