Pro-healing macrophages may help to regrow damaged nerves

In a study in the Proceedings of the National Academy of Sciences, researchers have shown that summoning these pro-healing macrophages can greatly help regrow severed nerves in rats.

“There’s been a long-held view that the best way to regrow severed nerves is to provide all sorts of matrix and growth proteins to coax repair,” says Ravi Bellamkonda, professor of biomedical engineering and Vinik Dean of the Pratt School of Engineering at Duke University.

“We’ve completely shifted that view by finding new players who have remained behind the scenes. We believe this approach will also have a major impact on regenerative medicine, even beyond this specific application.”

The peripheral nervous system includes nerves that run from the spinal cord to the rest of the body. It connects and controls movements, the digestive system, heart, lungs, and other organs. When these relatively long cells—which can stretch for a meter or more—are damaged or severed, the injury is not easily healed.

The current standard of care, called an autograft, involves surgically removing a less important nerve, like the one running down the back of the calf, and grafting it into the damaged area. But the treatment has several drawbacks.

A sensory neuron replacing a motor neuron is not a perfect replacement, painful neuromas can occur at the healing site, the patient loses the function of another nerve, and, in the case of extensive injuries, there are only so many semi-disposable nerves in the body to harvest.

Researchers have long been working on an alternative approach using “nerve bridges” to span these gaps. The idea is to introduce a tube filled with growth factors and other goodies across the gap to coax the regrowth of the existing nerve, like luring a dog out of a hiding place with treats. But despite efforts to find the optimal combination of tube material, growth factors, proteins, and other helpers, nothing has come close to matching the autograft’s success.

Bellamkonda and his group were traveling down this same road until some salamanders lost their tails.

“We saw a study showing that the early presence of macrophages were vital to a salamander’s ability to regenerate its tail,” says Nassir Mokarram, an assistant research professor of biomedical engineering. “We also knew that rare instances of nerve regeneration were accompanied by a surge of these cells right after the injury occurred. Those two observations gave us the inspiration to see if the same idea could be applied with nerve bridges.”

http://www.futurity.org/macrophages-damaged-nerves-1457202/