Researchers from the University of California are taking a new treatment path development for dealing with eye diseases. This includes retinitis pigmentosa (RP), a blinding disease that is caused by photoreceptor degeneration. The researchers think that reducing noise generated by nerve cells in the eye can bring images more sharply into view. This will help people with retinitis pigmentosa and other kinds of retinal degeneration such as age-related macular degeneration.
The research was done in Richard Kramer’s lab, a Ph.D. professor in the department of molecular and cell biology and published in Neuron on March 12th, 2019. Kramer said that it was not a cure for the disease but a treatment to help people see better. Also, he said that it would not put back photoreceptors that have died. It could, however, give people a few extra years of useful vision with the photoreceptors left.
Photoreceptors initiate light responses. Interneurons process the light responses and synaptically transmit them to retinal ganglion cells (RGCs) which send information to the brain. For years, researchers have known that photoreceptor degeneration does trigger the hyperactive firing of RGCs. This leads to obscuring light responses that surviving photoreceptors initiate.
Kramer and his team focused more on the role of retinoic acid (RA). It showed that signaling from its receptor (RAR) is the hyperactivity’s trigger. They discovered that RA floods the retina and stimulates the retinal ganglion cells to make more retinoic acid receptors. These receptors make ganglion cells hyperactive and create a constant buzz of activity. This submerges the visual scene preventing the brain from picking out noise signals.
Kramer said that once we inhibit the receptors for retinoic acid, we reverse the process shutting off the hyperactivity. People losing their hearing often get tinnitus. This is a ringing in the ears which worsens the situation. Kramer’s team found that retinoic acid does something similar in the retinal degeneration. Inhibiting the retinoic acid receptor makes it possible to decrease the noise while unmasking the signal.
A genetically encoded reporter from mouse RP models showed elevated RAR signaling in degenerated retinas. Enhancing RAR signaling in healthy retinas will mimic the pathophysiology of degenerating retinas.
The researchers searched for drugs that are known to block the receptor. They showed that treated mice saw better and behaved more like mice with normal vision. They tried gene therapy by inserting a gene for a defective retinoic acid receptor into ganglion cells. Once expressed, the defective receptor bullied out the normal receptor in the cells. This quieted their hyperactivity. The mice treated with gene therapy behaved like normal sighted mice too.
There is much excitement about emerging technologies addressing blinding diseases at the end-stage. However, the number of people who happen to be candidates for such a measure is relatively small. There are very many people with impaired vision. These experiments introduce new strategies to improve vision in these people.
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Liebert, M. A. (2019, 03 14). Genetic Engineering and Biotechnology News. Retrieved 04 30, 2019, from www.genengnews.com: https://www.genengnews.com/news/hyperactive-eye-cells-seen-as-view-new-treatments-for-vision-loss