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Widening View of Vanishing Sight
September 20, 2012
Although retinitis pigmentosa (RP) is a leading cause of inherited blindness, some of its basic mechanisms remain a mystery. Now, research conducted at the Angiogenesis Laboratory at Massachusetts Eye and Ear has identified, for the first time, the mode of death of cone photoreceptor cells in an animal model of the disease —a key finding that points to a promising therapeutic target.
The groundbreaking study, led by Demetrios G. Vavvas, Harvard Medical School Assistant Professor of Ophthalmology, and including Joan W. Miller, chief of chief of ophthalmology at Massachusetts Eye and Ear/Mass General Hospital, chair of ophthalmology and Henry Willard Williams Professor of Ophthalmology at HMS, has further identified the receptor interacting protein (RIP) kinase pathway as a potential target for developing treatment for vision loss in patients with retinitis pigmentosa.
The study, published Aug. 20 in the Proceedings of the National Academy of Sciences, is titled “Receptor interacting protein kinase mediates necrotic cone but not rod cell death in a mouse model of inherited degeneration.”
Retinitis pigmentosa is an inherited condition that causes irreversible vision loss due to the degeneration of photoreceptor cells in the eye called rods and cones. Rods are responsible for night and peripheral vision, while cones are responsible for daylight and central vision. Vision loss from RP often begins with loss of night vision, due to death of rods, followed by loss of peripheral and central vision, due to additional death of rods and cones. Such vision loss can have a significant impact on people’s daily lives, such as affecting their ability to read or drive a car. RP affects more than 1 million people around the world.
Research conducted by Eliot L. Berson, William F. Chatlos Professor of Ophthalmology at HMS and at the Berman-Gund Laboratory for the Study of Retinal Degenerations at Massachusetts Eye and Ear, has shown that Vitamin A supplementation and an omega-3 rich diet can slow visual decline resulting from RP; they do not completely stop disease progression, however. For most patients, RP results in irreversible vision loss.
Previous studies have identified mutations in more than 50 genes that cause RP, but the mechanisms by which rods and cones die remain to be completely defined. Since many of the genes associated with RP produce proteins that are used specifically in rod cells, it is still a puzzle why and how cones, which in some cases do not use the mutant proteins, die after rods degenerate.
Using an animal model of RP, the investigators examined the role of RIP kinase mediated necrosis in the death of photoreceptor cells, finding for the first time that it is involved in cone degeneration and that a deficiency of RIP kinase reduced cone loss. Moreover, the study found that treatment with a drug that inhibits RIP kinase significantly delayed cone cell death and preserved cone photoreceptors.
“Though the precise mechanisms involved in RIP kinase inducing necrosis remain unknown, our finding that necrosis results in cone cell death puts us one step closer to understanding this disease and, more importantly, moves us one step closer to being able to provide novel therapies to millions of patients with vision loss,” said. Vavvas.
Adapted from a Massachusetts Eye and Ear news release.