Gene therapy of retinitis pigmentosa
Photosensitive protein saved mice from blindness
Anna Muravyeva, Naked Science
Biologists have embedded the gene of the light-sensitive protein MCO1 into the retinal neurons of blind mice and restored their vision. To do this, they packed the gene into a viral particle and injected it into the eyes of mice with retinitis pigmentosa. The new protein did not cause an inflammatory response and, unlike its predecessors, reacts to daylight, and mice learned to pass tests with visual cues. The study was published in the journal Gene Therapy (Batabyal et al., Sensitivity of ON-bipolar cells with ambient light activatable multi-characteristic opsin rescues vision in mice).
In the process of perception of visual information, light rays focus on the retina of the eye, in which photoreceptors are located: cones and rods. They contain photosensitive opsin proteins that react to the flow of photons and lead to the generation of a nerve impulse in the receptors. This impulse is transmitted to the bipolar neurons of the retina, and after the retina goes to the brain.
However, the retina does not work so well for everyone: in people with retinitis pigmentosa (and there are about one and a half million of them), rods and cones stop perceiving light due to mutations in the genes of photosensitive opsins. This hereditary disease leads to severe visual impairment, and often to complete blindness.
Medications for retinitis pigmentosa are now used only to preserve the function of the receptors that are still working: for example, vitamin A. Expensive retinal transplants and prostheses are now available to restore vision. But recently, optogenetics methods have been used to treat retinopathy: bypassing photoreceptors, scientists have embedded photosensitive proteins directly into retinal neurons, after which they began to respond to light. However, so far, genetically modified cells have responded only to a strong signal: this requires special devices to enhance daylight.
Researchers from Nanoscope Technologies, led by Samarendra Mohanty, have introduced a protein into bipolar neurons that reacts to daylight. First, scientists created a DNA fragment with the genes of multicharacteristic opsin 1 (MCO1) and a red fluorescent protein so that the opsin was illuminated in cells. This fragment was packed into a viral vector – a particle that has lost its pathogenic properties and is used to deliver and embed genetic constructs.
The viral vector was injected into the eye of each mouse, after which a DNA fragment from two genes was embedded in the bipolar neurons of the retina, and there MCO1 was synthesized with a luminous appendage. Using microscopy, scientists determined the level of luminescence and the amount of protein in the cells. It turned out that the genes reached the peak of work in the fourth week, after which they maintained a stable level.
Figure from the press release of the National Eye Institute Scientists use gene therapy and a novel light-sensing protein to restore vision in mice – VM.
To test the mice's eyesight after embedding, the scientists gave them tasks with a light maze: in a water pool in the dark, the mice had to find a dry platform that was illuminated. The test showed that mice actually begin to see the platform as early as 4-8 weeks after injections (p<0.05).
The researchers also confirmed that the level of inflammatory factors remained the same four weeks after the injection as before it. Analysis of mouse organs showed either complete absence or trace amounts of vector DNA outside the mice's eyes, and in the eyes the fluorescent protein was localized in bipolar neurons.
Perhaps the results of gene therapy of the retina of mice after clinical trials can be adapted for humans. Then, for the treatment of blindness, neither expensive operations nor devices for signal amplification will be required – but only one or several injections.
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