medicine : New nerves for old

One of the biggest challenges facing doctors and researchers today is how to help patients with spinal injuries. Many of these patients are permanently paralysed. How much of their body is affected depends on where in the spine the damage occurs. Although many advances have been made in minimizing the damage caused by spinal injuries and in helping those affected to live longer and happier lives, there is still no way to repair a damaged spinal cord.

There are, however, many potential treatments being investigated by researchers in the laboratory. Although none of these is yet in clinical use, some of them may be helpful in the future. John McDonald and colleagues, from the Washington University School of Medicine, St Louis, Missouri, report a promising new technique in Nature Medicine1.

One of the problems with treating spinal cord injuries is that the nerves in the central nervous system - the brain and spinal cord - do not regenerate in the same way as cells in the rest of the body. If you cut yourself, new skin cells develop, via cell division, to heal the cut. Cells in the spinal cord, however, do not divide or grow back, so injuries cannot be repaired in the same way.

In recent years, researchers have discovered that there are cells in the body called ‘stem cells’, which can be prompted to develop into any kind of cell - even nerve cells. McDonald and his team transplanted stem cells from mice into the damaged spinal cords of rats, in the hope that these impressionable cells would be able to repair the damage.

Importantly, the transplants took place nine days after the injuries. If any potential treatment were to be useful for the thousands of patients with existing spinal injuries, it would have to work on old injuries, not just in the period immediately after the damage occurred.

A month after the operation, the rats that had received the transplants were significantly better than those that had not. Although they were not able to walk normally, they did use their hind legs to support part of their weight and could, to an extent, coordinate hind-leg movement.

When the researchers looked at the injury sites several weeks after the surgery, they found that some of the mouse stem cells had survived and developed into nerve cells and the other kinds of cells found in the nervous system - supporting cells called ‘astrocytes’ and ‘oligodendrocytes’.

The results are very encouraging, say the researchers. Dennis Choi, another of the study’s authors, says, "This paper is the first to report a delayed treatment that promotes recovery". But further studies will be necessary to find out exactly what the transplanted cells are doing, and to try and increase the amount of improvement they confer, before researchers can consider applying the technique to humans.

    McDonald, J.W., Liu, X.-Z., Qu, Y., Liu, S., Mickey, S.K., Turetsky, D., Gottlied, D.I. & Choi, D.W. Transplanted embryonic stem cells survive, differentiate and promote recovery in injured rat spinal cord. Nature Medicine 5, 1410 (1999).