Therapeutic potential of Retinal Pigment Epithelial cell lines derived from hES cells for retinal degeneration.
Retinal degeneration represents a group of blinding diseases that are increasingly impacting the health and well being of Californians. It is estimated that by 2020, over 450,000 Californians will suffer from vision loss or blindness due to the age-related macular degeneration (AMD), the most common cause of retinal degeneration diseases in the elderly. Furthermore, retinitis pigmentosa is the leading cause of inherited blindness in younger people. Currently there are no cures for these diseases. A layer of cells at the back of the eye called the retinal pigment epithelium (RPE), provide support, protection, and nutrition to the light sensitive retina, and cooperate with other retinal cells to maintain normal visual function. The dysfunction and/or loss of these RPE cells play a critical role in the development of the previously described blinding diseases. We suggest that effective treatment of retinal degeneration could be achieved by the proper replacement of damaged RPE and retinal cells with healthy ones. However, lack of the reasonable supply of healthy human eye cells hampers the application of this therapeutic approach. Recent advances in knowledge and technology of embryonic stem cells brings new hope for the development of cell replacement treatment. Embryonic stem (ES) cells are capable of unlimited self-replication and production of different cell types. RPE cells derived from human ES cells (hES-RPE) are a potentially unlimited resource for the cell replacement approach. We hypothesize that the dysfunction and/or loss of RPE can be replenished and restored through the transplantation of functionally polarized RPE monolayers derived from human embryonic stem cells, and this transplantation can cure the retinal degeneration diseases caused by RPE dysfunction.We propose to: 1. Derive RPE cells from human ES cells; 2. Establish and characterize the functionally mature or polarized monolayer of hES-RPE cells that will be suitable for transplantation; 3. Rescue the retinal degeneration phenotype through the transplantation of functionally mature or polarized monolayer of hES-RPE cells in animal models. Our goal is to determine the feasibility of treating the retinal degeneration diseases caused by RPE dysfunction through the transplantation of a monolayer of polarized hES-RPE cell sheet. The knowledge and technology from our research can be used to develop new treatments for human retinal degeneration diseases.
Age-related macular degeneration (AMD) is the leading cause of severe vision loss or blindness among the elderly, and currently no cure for this disorder exists. Based on the fact that California is the most populated state, and that the population continues to age, it is estimated that over 450,000 of Californians will suffer from AMD with severe vision impairment by 2020. Studies have shown that the devastating consequences of AMD include the progressive loss of independence and productivity, and increased risks of falls, fractures, and depression among diseased population. So this is not only a problem of the individual quality of life, but also an issue of increasing public health burden and concern. In this study we will test the feasibility of treating AMD and other retinal degenerative diseases through the transplantation of human embryonic stem cells that have been treated to differentiate into retinal pigment epithelial cells (RPE); the cells known to primarily degenerate or die in AMD. If our experimentation with RPE replacement therapy is successful in animal models, the knowledge and techniques can be quickly used to develop novel treatments for human diseases. Hundreds of thousands of Californians with AMD and other retinal degeneration diseases could benefit from our research for better quality of life with reduced morbidity. The California economy may significantly benefit from this work through potential reduced costs for health care, social welfare, and the loss of labor force.
It is estimated that by 2020, over 450,000 Californians will suffer from vision loss or blindness due to the age-related macular degeneration (AMD), the most common cause of retinal degeneration in the elderly. A layer of cells at the back of the eye called the retinal pigment epithelium (RPE), provides support, protection, and nutrition to the light sensitive retina, and cooperates with other retinal cells to maintain normal visual function. The dysfunction and/or loss of these RPE cells play a critical role in the development of dry AMD, the most common form of that disease. RPE cells derived from human ES cells (hES-RPE) are a potentially unlimited resource for cell replacement therapy.
During this grant period we were able to develop methods to reproducibly derive RPE cells from established human ES (hES) cell lines.
Normal RPE cells have a polarized appearance, meaning that they have specialized appearances and functions on the top (retinal facing) and bottom of the cells. We were then able to induce the hES-derived RPE to develop a polarized appearance very similar to that found in the normal eye. These cells had specialized characteristics that were remarkable similar to normal RPE and showed ability to function like normal RPE cells. We then developed sheets of hES-derived RPE on substrates that could be used for surgical implantation into animal eyes.
We then performed studies to establish appropriate animal models in which to test the ability of hES-derived RPE to prevent or slow retinal degeneration in animal models that have some features of human AMD. We were not able to use standard mouse models of AMD because mouse eyes are too small to perform the surgical implantation of polarized RPE. We first looked at a rabbit model of RPE degeneration induced by a toxin (sodium iodate). We were able to establish reproducible RPE degeneration in these animals but whenever we tried to implant hES-derived RPE under the retinas of these animals, the RPE cells did not survive. We believe that the toxin that was used to induce this model was being taken up by the transplanted cells resulting in their death. We then tested a genetic model of retinal degeneration in rats (RCS rat). We were able to demonstrate reproducible retinal degeneration in these animals. When we transplanted hES-derived RPE under the retinas of these animals, we were able to show that the RPE were indeed human in origin and that they were able to survive for at least several weeks after transplantation. Importantly, we were able to show that in the areas where hES-derived RPE were transplanted, there was less retinal degeneration than in the areas in which there was no transplantation or "sham" transplantation.
Thus, in conclusion, we were able to show (1) the reproducible culture of RPE cells from human ES cell lines, (2) that these hES-derived RPE had the appearance and functional characterisitics of human RPE and could be grown on substrates as sheets or polarized cells, and (3) that when these sheets of polarized hES-derived RPE were implanted under the retinal of rats with retinal degeneration, that they were able to survive and showed the ability to slow the progression of retinal degeneration in these animals.
The results of this study suggest that hES cells may be an unlimited source of RPE cells suitable for transplantation into eyes with retinal degeneration and that subretinal implantation of polarized hES-derived RPE may represent a novel therapy for dry AMD.