The three blind mice might not have to stay that way much longer. British scientists have shown for the first time that they can improve vision in rodents—by transplanting light-sensitive cells into their eyes.
The research could lead to new treatments for millions of people suffering from common forms of blindness, such as retinitis pigmentosa and age-related macular degeneration, says Rachael Pearson, a Royal Society Research Fellow at University College London.The achievement was hailed by biologist Stephen Rose, chief research officer of the Foundation Fighting Blindness, a private nonprofit that raises money for inherited-retinal-disease research. “We are very happy with it,” he says. “We believe that it’s extremely good work.”
In a paper published on earlier this year in Nature, Pearson and her colleagues describe how they injected immature rods—the cells responsible for peripheral vision and the ability to see at night—into the eyes of mice that had been bred without functioning rods.
In these night-blind mice, the thousands of newly transplanted cells linked up with existing nerve cells in the retina, the layer of light-sensitive tissue in the back of the eye. The researchers had previously proved that transplantation could work; this time they greatly increased the number of transferred cells, boosting the number of apparently functional rod cells 20- to 30-fold. Then, they looked for evidence that the mice actually had better night vision.
Pearson and her team examined the transplanted cells to see whether they responded to light. They also measured electrical activity in the visual cortex of the mice, tracked the mice’s head movements to see whether they would react to patterns on a screen, and plopped them in a water tank to see if they’d swim toward a less than obvious exit. Despite the dim light, the transplanted mice were able to find their way out. “The mice who didn’t have the transplant swam around in circles,” Pearson says. “These mice can’t see in dim light, and so they can’t use any visual cues to escape.”
The trick to getting transplanted rods to function, Pearson says, is to harvest cells that are at just the right stage of development from donor mice. In people, it soon may be possible to cultivate a patient’s own stem cells and turn them into rods and cones. Meanwhile, Pearson and her colleagues are still trying to perfect the process of transplanting cones. “We demonstrated proof of principle a couple of years ago, but currently the numbers we can get to integrate are much lower than with the rods,” she says.
Age-related macular degeneration, the leading cause of blindness in people over 50, gradually damages the macula, the part of the retina responsible for central vision. A National Institutes of Health study estimates that nearly three million Americans will be affected by 2020. An additional 100,000 people in the U.S. suffer from retinitis pigmentosa, a group of inherited diseases that cause the retina to deteriorate.
Successful animal research doesn’t always translate into an effective treatment for humans, Rose cautions. “These are very carefully done studies, very well conducted,” he says. “There’s no reason to believe, from what I’ve seen, that it couldn’t work. But the proof of the pudding is the eating thereof.”