Restoring lost sight might sound like something from a sci-fi movie, but with new scientific advances, it’s becoming closer and closer to reality. Now, researchers have managed to restore sight in blind mice, using a gene therapy technique that could one day be applied to humans. Their findings are published in Nature.
The research revolves around cells in the retina called Müller glia. Their job is to maintain the functional and structural stability of other cells like nerve cells. Excitingly, the team found a way to get these cells to convert into a kind of cell that’s key to sight – rod cells.
Rod cells are retinal cells that detect light, and are therefore responsible for perceiving the brightness, shape, and size of the things that we see. As they are light-sensitive, they are particularly important for enabling us to see in the dark.
However, rod cells aren’t the only cells we use to see clearly. Another type of cell in the retina – cone cells – help us see fine details and color. They’re not great in low light, which is why you only see in different shades of gray when it’s dark – you’re relying on your light-sensitive rod cells, which don’t perceive color.
Obviously, if these photoreceptive cells get damaged through injury or disease, it’s not good news. Some non-mammalian animals, such as zebrafish, have the ability to replace lost light-sensitive cells using their Müller glia. These cells essentially become stem cells, before reprogramming to become rods and cones.
But sadly, us mammals don’t have this handy ability. Therefore, researchers from the National Institutes of Health decided to kickstart the process themselves.
During their study, they injected two lots of gene therapy into the retinas of blind mice. They also injected chemical tags that indicated to the scientists when cell division was taking place and whether new or not new rod cells had been formed.
They found that following the treatment, when a Müller glia divided, it would form one glia cell and one rod cell, thus replacing lost rods. The newly formed rod cells were found to produce the same proteins found in light-sensitive retinal cells.
The new rods reacted to light, and light-detection responses were observed in the primary visual cortices of the brains of the mice that had had the treatment. This was not seen in the controls.
However, while this new research is very exciting, it certainly comes with some caveats. First, it was only done in mice, which despite being useful model organisms are obviously not the same as humans, so it could be a very long time before this technique is clinically used in people, if at all.
Second, there aren’t very many Müller glia in the retina, so even if they can turn into rod cells, there may still not be enough of these cells to fully restore sight. Finally, so far we just know that the treated mice can detect light again, but that doesn’t mean they can see perfectly. The team plan on investigating how well the mice can see next.
Despite these limitations, this is the first time we've managed to reprogram Müller glia to become rod cells, and with some tweaking, it could pave the way for effective blindness treatments in future.