Blind Mice Regain Vision After Gene Insertion in Trials
Loss of vision is one of the trickier health issues to deal with and is permanent in most cases. But research done at the University of California Berkeley suggests that people who have lost their eyesight might one day be able to see again.
Using a technique described as rather easy, researchers succeeded in helping mice regain their eyesight by inserting a gene into their eyes. The animals were able to detect motion and patterns as well as avoid obstacles within a month of receiving treatment.
Around one in every 10 persons above the age of 55 suffers from age-related macular degeneration (AMD), according to estimates. Roughly 170 million people around the world have this disorder.
In addition, retinitis pigmentosa affects about 1.7 million people worldwide. Those who have this most-common form of inherited blindness typically become blind by age 40.
The best option currently available to people who have lost their vision is an electronic implant featuring a video camera. This is not only expensive but also does not deliver the finest results.
Researchers in the current study delivered a gene into the eyes of mice with the aid of an inactivated virus. This novel approach showed great promise of potentially being useful in the future to people with vision loss.
“You would inject this virus into a person’s eye and, a couple months later, they’d be seeing something,” said Ehud Isacoff, a professor of molecular and cell biology at UC Berkeley. “With neurodegenerative diseases of the retina, often all people try to do is halt or slow further degeneration. But something that restores an image in a few months — it is an amazing thing to think about.”
The research was reported in Nature Communications.
‘Simple’ fix for vision
It is a thorny affair trying to rectify the genetic flaw that results in the degeneration of the retina. This is mainly because there are hundreds of genetic mutations involved. These mutations ensure that the vast majority of light-converting receptor cells in the retina die off.
Isacoff and John Flannery, also a professor of molecular and cell biology at UC Berkeley, had tried a variety of complex approaches over the years to restore vision with limited success. One of the techniques involved the insertion of genetically-engineered neurotransmitter receptors and light-sensitive switches into surviving eye cells.
Finally, the research team settled for a simpler approach of inserting a gene.
The scientists turned to the light-sensitive green cone opsins of photoreceptor cells. They delivered the gene for an opsin into the eye with the aid of an adeno-associated virus (AAV), which infects ganglion cells in the eye.
Usually, ganglion cells are not sensitive to light in blind people. But, in this study, they became light-sensitive after the virus moved the gene into them. The cells became able to send signals to the brain, which translates them into sight.
The researchers succeeded in making 90 percent of ganglion cells in mice sensitive to light in their trials. The animals performed comparatively well, visually, as their healthy counterparts as a result.
“To the limits that we can test the mice, you can’t tell the optogenetically-treated mice’s behavior from the normal mice without special equipment,” said Flannery.
Applying to humans
In mice that regained their eyesight, the vision lasted for their entire lifetime, the research team said.
It remains to be seen, however, whether the results can be replicated in humans. Scientists would require many more virus particles to make this possible because the human eye contains way more ganglion cells.
Isacoff and Flannery did admit that some people might doubt whether opsins can function outside their specialized photoreceptor cells. It is thought that opsins would not work elsewhere without transplanting the enzyme system responsible for recharging them.
However, Isacoff theorized that an opsin would inevitably link to the retinal ganglion cells’ signaling system.
The researchers first tried rhodopsin in rods, being more light-sensitive than opsins in cones. This helped mice that were blind due to retinal degeneration to distinguish light from darkness. But rhodopsin failed in other aspects, including image recognition.
Finally, the team found that the green opsin in cones was 10 times more responsive than rhodopsin. It made the mice more sensitive that they could make out letters on an iPad.
The animals were able to make out and explore three-dimensional (3D) objects, a very common natural behavior. This means they could find their way around more easily.
The UC Berkeley team has fashioned a means of boosting viral delivery for possible use in humans. It aims to insert a light sensor into a high proportion of ganglion cells as done in the mice trials. The number of cells will be comparable to the incredibly high pixel count of a camera.
Isacoff and Flannery are trying to raise funds to assess the feasibility of this gene therapy in humans. They hope to be able to try it within three years in people who have lost their sight.