Retinitis pigmentosa is a group of genetic diseases that affect sight. The disease is progressive, usually beginning with night blindness, then proceeding to night blindness and then complete blindness. The progression of the disease is somewhat slow, and many people retain some sight for the remainder of their lives, but others become completely blind.
Retinitis pigmentosa is caused by the death of retinal photoreceptor cells. The abnormalities originate in either the photoreceptors themselves, or the retinal epithelium behind the photoreceptors into which the photoreceptors are embedded.
Is there a way to replace dead photoreceptors? Yes there is, at least in mice. An international research team has used mouse embryonic stem cells to replace diseased retinal cells and restore sight in a mice with retinitis pigmentosa. The team, led by scientists at Columbia University Medical Center, made retinal cells and used them to replace the dead photoreceptors. They suggested that this regenerative strategy could potentially become a new treatment for retinitis pigmentosa, which is a leading cause of blindness that affects approximately one in 3,000 to 4,000 people, or 1.5 million people worldwide. This study will appear in the journal Transplantation in the March 27, 2010 print issue.
The retinal pigment epithelium cells are specialized retinal cells and they help maintain vision. Retinitis pigmentosa results from the death of these retinal cells on the periphery of the retina, which leads to “tunnel vision.” In people with tunnel vision, the field of vision is narrowed considerably and everything outside the “tunnel” appears blurred or wavy.
In this study, sight was restored in one-fourth of the mice that received the stem cells, but complications of benign tumors and retinal detachments were seen in some of the mice. Therefore there is a need to optimize these techniques to decrease these complications. One modification that might be to use cells other than embryonic stem cells that do not cause tumors.
For example, inside the eye and lining the back part of it is a layer of photoreceptors that detect light, color, and images. These photoreceptors convey this information to the brain with the help of several cells and assist them. Collectively, this layer is called the retina. Adjacent to the retina is a structure called the ciliary epithelium, which also harbors a stem cell population that divides and grows in response to retinal injury. Because of this, ciliary epithelium stem cells are also called retinal stem cells or RSCs. When grown in the laboratory, RSCs can differentiate into many of the cell types found in the retina (T.A. Reh and A. J. Fischer, Methods in Enzymology 2006;419:52-73). Discovery of this stem cell population offers the possibility of using them to repair retinal damage.
Because retinal damage and death are a major component of many diseases of the aged like macular degeneration and Stargardt disease, this procedure might provide some very exciting ways to treat blindness in older patients.