Silencing a gene Nrl can prevent the loss of photoreceptor cells in a model of degenerative retinal disease
Many genetic retinal disease affect rod photoreceptor cells more than cone cells. Rod cells are responsible for vision in dim light, whereas cone cells deal with colour in vivid light. Both are important for vision, and cone cells are somewhat dependent on rod cells for support and nutrition; when rod cells die as a result of retinal disorders, this often causes cone cell death too. In the degenerative disease retinitis pigmentosa, rod cells are progressively loss which in turn leads to cone degeneration and blindness.
Can saving rod cells preserve sight?
Researchers at the National Eye Institute have been studying the gene Nrl, which plays an important role in determining rod or cone cell identity in development. A lack of Nrl expression appears to prevent rod development, but more curiously knocking our Nrl in rod cells with genetic mutations is able to protect them by coaxing them to have more 'cone-like' behaviour and features.
"The evidence suggested to us that coaxing rods into becoming more cone-like by knocking out Nrl was a potential strategy for overriding mutations that would otherwise lead to rod degeneration. Consequently, the neighboring cones would remain functional and viable"
Using the CRISPR system to selectively silence Nrl in wild-type mice and three different mouse models of retinal degeneration, the researchers discovered that Nrl loss did indeed protect rod cells by making them more cone-like. It's important to note that the deletion did not repair these cells' ability to detect light, but it did lead them to survive - ensuring the survival of neighbouring healthy cone cells and preserving vision. In all of the models tested the silencing of Nrl was able to slow or even prevent vision loss altogether in these degeneration diseases. The benefit was less pronounced in older animals, but still encouraging.
"Unlike conventional gene therapy, in which a normal gene is introduced to replace the defective gene, this approach could treat retinal degeneration caused by a variety of mutant genes"
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