In a new study, researchers were astonished to discover that spinal cord injury scars could actually be helping and not hindering the regrowth of nerves across the site of injury.
Writing about their work in the journal Nature, the team from the University of California-Los Angeles explains how it used mice to show that “contrary to the prevailing dogma,” the formation of scar-forming cells called astrocytes aids rather than prevents the regrowth of nerve cells.
Senior author Michael V. Sofroniew, a professor of neurobiology, says when they first realized that blocking scar formation after spinal cord injury resulted in worse outcomes, they were “completely surprised,” but once they began looking more closely at what was happening in the regrowth, they became convinced that scars may actually be helping. He notes:
“Our results suggest that scars may be a bridge and not a barrier towards developing better treatments for paralyzing spinal cord injuries.”
Every year in the US, physical trauma causes about 12,500 people to suffer a spinal cord injury, and estimates suggest there are about 276,000 Americans living with the long-term effects.
The goal of spinal cord injury research is to find a way to regrow the connections across the site of injury, repair the spinal cord, and restore any function that has been lost.
Without astrocyte scars, there is no axon regrowth
The new study focuses on the role of astrocytes in the regrowth of axons, the long, thread-like extensions of nerve cells that carry messages to other nerve cells. When these are cut in spinal cord injury, they do not grow back automatically and can result in paralysis.
Astrocytes are specialized glial or support cells that outnumber neurons by over fivefold. When an injury occurs, they hasten to the injury site along with immune cells and begin to form a scar. Researchers are discovering that astrocytes reacting in this way have access to a vast arsenal of molecules.
Immediately, as scars form, they help to reduce inflammation and prevent spread of damage to surrounding tissue. However, for decades, it was thought that in the longer term, scars got in the way of axon regrowth.
Prof. Sofroniew and colleagues ran experiments in mice to find out what happens to axon regrowth when scars are prevented or removed at injury sites after spinal injury.
When they removed the scars or prevented them forming, they found that without astrocyte scars, there was no axon regrowth.
Then, they showed that ferrying growth factors to the injury site boosted axon regrowth through astrocyte scars, but if they prevented scars forming, there was significantly less axon regrowth.
Using a type of genetic analysis called RNA sequencing, the researchers found that astrocyte and non-astrocyte cells release a range of molecules that both block and encourage axon regrowth when they reach the injury site.
Prof. Sofroniew concludes:
“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.”
The team is now planning to study the mechanisms through which astrocyte scars support axon regrowth and how to boost them.
The study follows another that Medical News Today learned of recently, where stem cell therapy enabled spinal regrowth in rats, including the regeneration of corticospinal axons.