Saving Vision by Turning Rods into Cones

February 01, 2013
By genetically reprogramming rods to become like cones, researchers from the Washington University School of Medicine in St. Louis may have found an innovative way to treat vision-robbing retinal diseases like retinitis pigmentosa (RP). While their research is at an early stage in mice, it has revealed valuable clues about how to potentially save vision in people. Results of the study were published in a recent online edition of Proceedings of the National Academy of Sciences.

Most forms of RP are caused by genetic defects in rods, the retinal cells that provide peripheral and night vision. The progressive loss of rods eventually leads to loss of cones, the retinal cells responsible for daytime vision and the perception of colors and details.

In lab studies, several researchers have found that by saving rods in retinal diseases, through a drug or gene therapy, cones can also be preserved. But converting rods into cones is a new approach to saving vision.

Dr. Joseph Corbo
and his colleagues were able to partially convert rods into cones by shutting down a gene called Nrl. Reducing the number of rods significantly reduced the rate of retinal degeneration. Nrl is a gene that directs a cell to become a rod during retinal development. If that gene is not activated, the retinal cells develop into cones. Dr. Corbo notes that the rods’ partial conversion to cones worked in adult mice, providing some hope that the approach could work someday in adult humans.

“A significant benefit of this method is that we are using the patients’ resident retinal cells for the treatment,” says Dr. Corbo. “We are circumventing the complexities of transplanting stem cells or cells derived from other sources. We don’t have to worry about the challenges of cell integration or harmful immune reactions.”

In follow-up studies, the research team is looking for ways to more fully convert rods into cones. It is also planning to test the therapy in a variety of animal models of RP and at varying stages of degeneration.

Dr. Corbo believes that, once perfected, the treatment approach may also benefit people with Stargardt disease and age-related macular degeneration — conditions which often cause cone loss early on.