Injured optic nerves can regrow towards the brain if treated properly, according to scientists from the University of Connecticut.1

The findings on mice could lead to potential treatment for damage to the optic nerve caused by glaucoma, or trauma from car crashes and accidents, the researchers said.

Loss of vision from blunt trauma and glaucoma is usually permanent, as severed nerves rarely grow back.

Neuroscientist Dr Ephraim Trakhtenberg and members of his lab used an injectable peptide – a small piece of a larger protein – to get nerve cells in the severed optic nerves of mice to regrow from the damaged area all the way to the optic chiasm in the brain. The optic chiasm senses light and controls daily body rhythms. It is the first place in the brain the optic nerve touches.

It took the severed nerve cells about six weeks to regrow to the optic chiasm. It’s unknown how much further they would have grown if the experiment had gone on longer.

“We need to do longer trials, at least three months, to reach further targets in the brain,” Dr Trakhtenberg said in a university news release.2

FIBRONECTIN ENCOURAGES REGROWTH

The idea to encourage nerve cell regrowth by injecting peptides came from a series of experiments exploring the ways nerve cells regrow, or don’t, after trauma. It was well known that creating serious inflammation in the eye before nerve injury could induce some nerve cell regrowth afterward. But such a treatment is impractical for humans, both because it is impossible to anticipate a traumatic injury and because eye inflammation is generally undesirable.

Instead, Dr Trakhtenberg’s lab focussed on discovering what it is about inflammation that encourages nerves to regenerate. For example, inflammation draws in macrophages, which are immune cells that do many things, including secrete a large protein called fibronectin.

Over the course of many experiments, the researchers found that fibronectin seemed to encourage optic nerve cells to regrow.

But, in most people with optic nerve injuries, nerve cells don’t get a chance for much interaction with fibronectin due to its low levels around nerves. Most eye injuries don’t cause enough inflammation to attract macrophages. And doctors cannot inject fibronectin into the eye because it is too large a protein.

However, the Trakhtenberg lab team broke fibronectin up into pieces, short segments of protein called peptides, which are easily injectable. They then took the peptide that interacted most strongly with optic nerve cells, synthesised it, and injected it into the eyes of mice with injured optic nerves.

The results were dramatic, the university said.

Many more nerve cells survived in the mice that received the fibronectin peptide injection. And many of them began to regrow. In just six weeks, the optic nerves had dense regrowth through the spot of injury, and many nerve cells reached all the way to the optic chiasm in the brain. The best results were in mice that received gene therapy along with the fibronectin peptide injection, but the peptides alone also produced strong growth in the nerve fibres.

Dr Trakhtenberg said because “peptide is just a piece of protein, you can inject it. That gives it a therapeutic potential”.

The team is now running a longer trial in mice to see how far the regenerated nerve fibres grow, and whether they eventually reach the area of the brain responsible for sight. The lab also wants to experiment with combining other potential treatments with the peptides, to see if it further improves nerve regrowth.

References available at mivision.com.au.