Boston Life Sciences

Scientists 're-grow optic nerves'

February-2004.

Scientists believe they have taken a big step forward in their effort to be able to repair damaged nerves.

Researchers at Harvard Medical School say they have had some success trying to regenerate optic nerves in rats.

Writing in the Journal of Neuroscience they said while they were unable to restore sight they achieved three times more regeneration compared to others.

Finding a way to re-grow nerves could lead to cures for a wide range of conditions from blindness to paralysis.

Permanent damage

Any injuries that cause damage to nerves tend to be permanent. This is because nerve cells cannot regenerate or repair themselves.

Scientists around the world are working on projects aimed at finding a way to get nerves to re-grow.

One of the reasons nerves are unable to regenerate is that proteins in the outer layer of nerve fibres are programmed to stop re-growth.

Scientists have developed ways to turn these proteins off. However, this has not proved enough to make nerves regenerate.

Dr Larry Benowitz and colleagues tried a two-pronged approach to try to stimulate re-growth.

First, they damaged the lens in the eyes of a group of rats with optic nerve damage. This nerve links the retina to the part of the brain that enables them to see.

Damaging the lens stimulates an immune response - cells travel to the eye and release growth factors to try to repair the damage. This causes nerve fibres to grow into the optic nerve.

Dr Benowitz then used a gene therapy technique to try to boost this growth by injecting a gene designed to turn the proteins that are programmed to stop re-growth off.

"When we combined these two therapies - activating the growth programme in nerve cells and overcoming the inhibitory signalling - we got very dramatic regeneration," said Dr Benowitz.

However, the scientists were unable to get the nerve fibres from the retina and those from the brain to hook up properly.

"It's a mapping problem," said Dr Benowitz. "We have to retain the proper organisation of fibre projections to the brain."

Further research

The scientists are now planning further studies to try to overcome this problem.

Kevin Shakesheff, professor of tissue engineering at the University of Nottingham, said scientists were still years away from being able to use these techniques in humans.

"There has been a lot of progress in this area," he told BBC News Online.

"We have taken enough steps forward to indicate we can solve the problem. The science is really exciting.

"However, translating that excitement into clinical applications will take time."

May-2006.

Researchers at Children's Hospital Boston have discovered a naturally occurring but previously unrecognized growth factor that stimulates regeneration of injured nerve fibers (axons) in the central nervous system.

Normally, most axons in the mature central nervous system (brain, spinal cord and eye) cannot regrow after injury. The factor is described in an embargoed study in the May 14 online edition of Nature Neuroscience.

November-2008.

Optic nerve cell regrowth breakthrough could help the blind.Scientists have found a way to regrow damaged optic nerves, opening the door to possible new treatments for people who have lost their sight though injuries to the cells.

The discovery also raises hopes that spinal cord nerve cells could be made to fix themselves, improving the lives of people with serious back injuries.

By turning off proteins that keep nerve cell growth in check, researchers were able to stimulate regrowth in mice with damaged optic nerves.

"This is the first time it has been possible to see such significant regeneration by manipulating single molecules," Zhigang He of Children's Hospital Boston, whose study appears in the journal Science, said in a statement.

A separate team found that blocking a protein that discourages cell repairs allowed nerve cells in lab dishes to regenerate.

Taken together, the findings offer leads on ways to coax damaged nerves in the brain and spinal cord to fix themselves.

The studies focused on nerve fibres called axons that carry electrical signals throughout the body.

"In your arms and legs, if these fibres are severed, they can regrow back to the muscle," said Marc Tessier-Lavigne, executive vice president of research drug discovery at biotechnology firm Genentech Inc.

"Nerve fibres in the brain and spinal cord do not regenerate. When you have a spinal cord injury, the paralysis is usually permanent.

"The ambition of our field is to understand why it is the fibres don't regenerate in the central nervous system."

Scientists hope to use the new information to make drugs that allow nerve cells in the brain and spine to repair themselves