Researchers Make Progress On Retinal Regeneration

Diseases of the retina are one of the most common causes of blindness, and yet there is little that can be done to reverse their effects. Conditions such as macular degeneration – either due to aging or diabetes – can be slowed by using lasers to seal abnormal blood vessels in the retina, but areas of the retina that have already been damaged are largely untreatable. Even laser therapy only works for wet macular degeneration in a minority of cases – and is not effective for dry macular degeneration. Retinitis pigmentosa, a hereditary condition that likewise damages the retina over time, also has no cure – although there is some evidence that high doses of vitamin A can slow the disease somewhat. What is really needed is a breakthrough treatment that could be administered as easily as an ophthalmologist such as performs laser surgery today.

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Against this background, it is encouraging to see that researchers are starting to make some advances in treating retinal degeneration – even if it is only in mice. Recent progress has been made using embryonic stem cells to create new retinal structures and to repair existing retinas.

Back in 2011, researchers in Japan made a major breakthrough when they were able to grow new retinal tissue from mouse stem cells. This wasn’t just a set of cells such as photoreceptors – rods and cones – but instead a complete retinal structure that closely paralleled the multilayered retinal structure seen in embryonic mouse eyes. However, the problem with such an approach is that while the retina itself may have a functional structure, it is not connected back to the brain’s optical processing centers – there is no neural interface. Given the vast number of connections that run from the retina back to the brain, contemplating a surgical procedure to do this just wasn’t viable. What was needed was some way of having the retina make the connections by itself.

That is apparently what scientists at University College London have managed to do. Rather than growing an entire mouse retina, they instead grew light-sensitive retinal cells from embryonic mouse stem cells, and then implanted these back into the retina of a living mouse. Not only did the cells start to function alongside other cells in the retina, they also started to generate connections from the retina to the mouse’s optical processing centers in the brain.

While the use of embryonic cells has significant ethical implications when it comes to human therapy, their use as a model in mice poses no such problems. In addition, there has been significant progress with non-embryonic stem cells recently – although not specifically for retinal regeneration – and these may offer a way of sidestepping ethical debate. In fact, use of a patient’s own stem cells – or somatic cells that are induced to become stem cells – may have additional benefits such as avoiding tissue rejection.

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Of course, it is a long step from treating mice in the lab to having an approved human therapy, so we should not expect this within the next few months. However, researchers at UCL are fairly confident that they should be able to start human trials within five years.

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