Retinitis pigmentosa (RP) is a group of genetic disorders that involve a breakdown and loss of cells in the retina. Symptoms first appear in childhood and include difficulty getting around in the dark and having a hard time adjusting to changes from light to dark. This in turn leads to problems such as loss of peripheral vision, and eventually legal blindness. RP is rare: affecting only 1 in 4,000 persons in the U.S. Presently there is no cure, nor are there effective treatments except for wearing sunglasses to protect remaining vision.
Because of the serious nature of the disease, researchers are attacking the problem from all angles. What if something could be done to not just protect vision, but slow the vision loss? That is what researchers at the Columbia University Medical Center are studying.
These researchers, led by Stephen H. Tsang, MD, PhD, discovered that by ‘reprogramming’ the metabolism of photoreceptors, or light sensors, in the retina, vision loss can be slowed. Photoreceptors are the most active cells in the body. They convert up to 96 percent of glucose into lactic acid. Under normal conditions, the outer segments of the photoreceptors regenerate. Rods shuttle the glucose to help in this process. One of the signs of RP is the failure of the rods to develop properly and deliver the glucose.
Researchers were able to change this by inhibiting a transcription factor gene called Sirt6 in mice with RP. By inhibiting this gene, the rods did their job and photoreceptor survived longer in these mice when compared to mice in the control group. Still, even the mice with the particular gene change eventually experienced photoreceptor death. The next step is to figure out a way to extend the effects of the Sirt6 inhibition.
While this is a long way from being used on humans, this study shows that metabolic reprogramming can slow down the decline of the photoreceptor and eventually improve survival of the photoreceptors. Reprograming metabolism isn’t the only way to treat RP. Stem cells have shown promise, as well.
Work done by the lab of Henry Klassen, MD, PhD at the University of California Irvine, found that retinal stem cells can be used to protect and rejuvenate the photoreceptors. In fact, a clinical trial is currently taking place that tests the use of photoreceptor retinal progenitor cells made from retinal stem cells. The participants received an injection of cells under topical anesthesia and will be monitored for safety and efficacy over the course of 12 months.
If the clinical trial is successful, it will show that stem cells can be used to restore vision. These two research projects show that RP will become one more eye condition that can be successful treated. The more successful treatments there are for RP, the fewer number of people who will develop vision loss.