Stem cell scarring aids recovery from spinal cord injury

In a new study, researchers at Karolinska Institutet in Sweden show that the scar tissue formed by stem cells after a spinal cord injury does not impair recovery; in fact, stem cell scarring confines the damage. The findings, which are published in the scientific journal Science, indicate that scar tissue prevents the lesion from expanding and helps injured nerve cells survive.

Spinal cord injuries sever nerve fibres that conduct signals between the brain and the rest of the body, causing various degrees of paralysis depending on the site and extent of the injury. Functional impairment is often permanent, since the cut nerve fibres do not grow back. The lack of regeneration has been attributed to a blockage from that forms at the lesion. It has therefore been suggested that the nerve fibres could regenerate and that recovery could improve if scar formation is inhibited, and many proposed therapeutic strategies have been designed around this concept.

In the present study, the researchers focused on spinal cord , which are one of the main sources of the scar tissue that is formed after spinal cord injury. They found that when blocking scar formation by preventing the stem cells from forming new cells after an injury, the injury gradually expanded, and more were severed. They also observed that more spinal cord died in these mice compared to mice with intact stem cell function, which were able to form normal scar tissue.

"It turned out that scarring from stem cells was necessary for stabilising the injury and preventing it from spreading," says principal investigator Professor Jonas Frisén at the Department of Cell and Molecular Biology. "Scar tissue also facilitated the survival of damaged nerve cells. Our results suggest that more rather than less stem cell scarring could limit the consequences of a spinal cord injury."

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The animation shows a simplified view of lesion development after spinal cord injuries in mice, with and without the resident neural stem cell injury response. The neural stem cells (green) respond to injury by producing progeny that migrate to the lesion site where they contribute to the forming glial scar. Without the neural stem cell response, the injury gradually expands and more nerve fibers are cut off, suggesting that the neural stem cell-derived scar tissue prevents the lesion from expanding. The findings are published in Science, November 1, 2013 by Professor Jonas Frisén and colleagues at Karolinska Institutet in Sweden. Credit: Mattias Karlén

According to earlier animal studies, recovery can be improved by transplanting stem cells to the injured spinal cord. The new findings suggest that stimulating the 's own stem cells could offer an alternative to cell transplantation.

More information: 'Resident Neural Stem Cells Restrict Tissue Damage and Neuronal Loss After Spinal Cord Injury in Mice', Hanna Sabelström, Moa Stenudd, Pedro Réu, David O. Dias, Marta Elfineh, Sofia Zdunek, Peter Damberg, Christian Göritz, Jonas Frisén, Science, online 1 November 2013.

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