Damaged optic nerves – which run from the eye to the brain – have been regrown for the first time by scientists working with mice. The researchers believe the technique might one day restore sight to people whose optic nerves have been damaged by injury or glaucoma. It could even help regenerate other nerves in the body, they say.
A team led by Dong Feng Chen, at the Schepens Eye Research Institute in Boston, US, combined two genetic modifications to regrow the optic nerve after it was damaged. First they turned on a gene called BCL-2, which promotes growth and regeneration of the optic nerve in young mice. This gene is normally turned off shortly before birth. They then bred those animals with other mice carrying genetic mutations that reduce scar tissue in injured nerves. The researchers crushed the optic nerves shortly after birth, and found that in young mice – less than 14 days old – between 40% and 70% of the injured optic nerve fibres regrew to reach their target destinations in the brain. No regrowth was seen in injured mice without the genetic modifications. That suggests the mice may have regained some vision, Chen told New Scientist, although the study cannot prove it did.
However, the approach did not work on mice more than two weeks old. This may be because the effect of BCL-2 begins to weaken, and scarring – which takes time to set in – starts to inhibit healing. The study could offer some insight into why mammals tend to lose their ability to regrow nerves after a certain age – a phenomenon that remains largely a mystery, suggest the authors. “Unfortunately, the fountain of youth doesn’t last forever,” says Jerry Silver, a nerve regeneration expert at Case Western Reserve University in Ohio, US, who is not part of the team. “You can only give them two extra weeks” before the regeneration stops. But Silver was impressed by the breakthrough, saying the study had the potential to become a “classic” in the field.
Chen says the relatively simple structure of the optic nerve may shed light on how to repair damage to more complicated systems, such as the spinal cord. To apply the genetic technique to humans, a form of gene therapy would have to be developed, or drugs developed that manipulate gene expression. Chen and her colleagues have applied for two patents on the methods they have developed to stimulate neural cell regeneration and prevent degeneration.
Journal reference: Journal of Cell Science (March 2005 issue)
March 15, 2005
Original web page at New Scientist