More than 100,000 Americans suffer from retinitis pigmentosis (RP), a suite of hereditary eye disorders that eventually culminate in blindness. Over the course of disease, the degeneration of light-detecting cells known as rods leads to the death of other light receptors called cones. How genetically coded rod death spurs the destruction of normal cone cells, however, has proved difficult to explain. Research reported in the November issue of the journal Nature Neuroscience offers new insight.
Duke University researcher Fulton Wong and his colleagues studied so-called rod bipolar cells in pigs and mice. These specialized nerve cells transmit information collected by the rods to the nerve cells that carry visual impulses to the brain. We found that as the rods die, the rod bipolar cells connected to them are still intact and want to communicate with other nerve cells, team member You-Wei Peng explains. Since they can no longer communicate with rod cells they do the next best thing--they start to connect to cone cells. It is a solution that Wong describes as an elegant example of Nature trying to make the best of a bad situation. The new connections grant another 10 years of vision in humans, but the barrage of inappropriate signals eventually leads to cone death.
The findings may impact research aimed at treating these disorders. Although there are many different mutations that could begin the process, our data demonstrate that there is a common downstream mechanism, Wong asserts. Practically it seems that these later steps in the disease process might be better targets for intervention than the individual gene mutations.