- Title: UNITED KINGDOM: Retinal cell transplant restores vision to blind mice
- Date: 7th May 2012
- Summary: MOUSE WATCHING VIDEO SCREENS IN BOX
- Embargoed: 22nd May 2012 13:00
- Keywords:
- Location: United Kingdom
- Country: United Kingdom
- Topics: Health,Science
- Reuters ID: LVA3CVKH8AMZ11ZAU5QWW6X7CLQ4
- Story Text: British scientists have shown for the first time that transplanting light-sensitive photoreceptors into the eyes of visually impaired mice can restore their vision.
The research, published in Nature, suggests that transplanting photoreceptors - light-sensitive nerve cells that line the back of the eye - could form the basis of a new treatment to restore sight in people with degenerative eye diseases.
Scientists from the University College London (UCL) Institute of Ophthalmology injected cells from young healthy mice directly into the retinas of adult mice that lacked functional rod-photoreceptors, giving them so-called 'night blindness'.
Known medically as Nyctalopia, night blindness is a condition that affects sufferers' ability to see in relatively low light. A symptom of several eye diseases, it may exist from birth or be caused by injury or malnutrition. The most common cause of nyctalopia is retinitis pigmentosa, a disorder in which the rod cells in the retina gradually lose their ability to respond to the light. Patients suffering from this genetic condition have progressive nyctalopia and eventually their daytime vision may also be affected.
Loss of photoreceptors is the cause of blindness in many human eye diseases including age-related macular degeneration, retinitis pigmentosa and diabetes-related blindness, according to lead scientist Professor Robin Ali.
"The majority of blinding conditions, in the western world at least, are due to loss of photoreceptors, conditions such as age-related macular degeneration, the inherited retinal degeneration such as retinitis pigmentoza, diabetic retinopathy," said Ali. "The blindness in each of these conditions is caused by the loss of these photoreceptors and the only effective treatment once the photoreceptor cells have been lost - because they're not replaced - is to transplant new photoreceptors."
There are two types of photoreceptor in the eye - rods and cones. The cells transplanted into the mice were immature (or progenitor) rod-photoreceptor cells. Rod cells are especially important for seeing in the dark as they are extremely sensitive to even low levels of light.
After four to six weeks, the transplanted cells appeared to be functioning almost as well as normal rod-photoreceptor cells and had formed the connections needed to transmit visual information to the brain.
"We've shown for the first time that it's possible to transplant photoreceptors and improve vision. We've previously shown that we could transplant photoreceptor cells and they would integrate within the retina, and now we're able to show that these integrated photoreceptor cells make functional connections, not only within the retina, but that they make appropriate connections to the visual centres in the brain and as a result of this we can improve vision," said Ali.
The researchers also tested the vision of the treated mice in a dimly lit maze. Those mice with newly transplanted rod cells were able to use a visual cue to quickly find a hidden platform in the maze, whereas untreated mice were able to find it only by chance after extensive exploration of the maze.
Dr Rachael Pearson, from UCL Institute of Ophthalmology and first author of the paper, explained how the experiment was conducted.
She said: "The mice that we're using have.... their cones are fully functional, so that means that we can try them under bright light conditions and we train them to associate escape from the water with this visual signal. We can then turn the lights right down to the level at which the rods are normally operating, and the mice in the particular model that we're using they have non functional rods. So they've had a gene taken out, that means that their rods do not function. Those mice are unable to complete the task, so they just swim around in the water and they use physical cues, like the sides of the water maze to actually swim around and eventually find the escape from the water by chance."
The researchers demonstrated previously, in another study published in Nature, that it's possible to transplant photoreceptor cells into an adult mouse retina, provided the cells from the donor mouse are at a specific stage of development - when the retina is almost, but not fully, formed. In this study they optimised the rod transplantation procedure to increase the number of cells integrated into the recipient mice and so were able to restore vision.
Ali says human clinical trials are probably around five years away. He says that they must first prove their methods to be effective in a variety of models of visual degeneration, rather than just night blindness. They also need to be able to transplant human cone receptor cells, which Ali says his team are currently working on.
The research has possible implications for repairing nerves in other parts of the brain. "In principle what we've shown is that we can transplant nerves and have them make appropriate connections and that may have some far-reaching implications, that it might be possible eventually, it's going to be much more complicated, but it might be possible to transplant other types of nerves and perhaps repair other parts of the brain," said Ali.
The team's research was funded by Britain's Medical Research Council (MRC), the Wellcome Trust, the Royal Society, the British Retinitis Pigmentosa Society, Alcon Research Institute and The Miller's Trust. - Copyright Holder: REUTERS
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