Multipotential Stem Cells In The Neonatal Mammalian Eye
Lower vertebrates including frogs, lizards and fish have remarkable regenerative capacity, including the ability to completely regenerate a damaged retina. This regenerative power is due to retention of stem cells in adult tissues. By contrast, higher vertebrates lack a significant population of stem cells in the adult eye. This lack of functional stem cells means that humans are unable to repair damage caused by age-related macular degeneration (AMD), which destroys both photoreceptor cells in the retina and the retinal pigment epithelium (RPE) which is adjacent to the retina and required for photoreceptor survival. Effective therapeutic approaches to AMD must then be directed at restoration of both photoreceptors as well as RPE. Thus, if stem cell transplants are to be used, the cells must be multipotential and able to generate both photoreceptors as well as RPE. We have isolated a novel population of multipotential stem cells from the postnatal mouse retina that can differentiate into both photoreceptors and RPE, and we propose to begin assessing the potential of these cells to replace damaged photoreceptors and RPE in mouse models. But further, these stem cells express genes required for embryonic stem cell specification, suggesting that they may retain the ability to differentiate into multiple tissues like embryonic stem cells. Indeed, we demonstrate that the cells can differentiate to produce insulin and cardiac cells. Thus in the future, this novel population of eye stem cells may represent a postnatal source of cell lineages beyond those in the eye.
We are continuing our studies of stem cells in the eye and their ability to differentiate (change) into retinal cell lineages. In addition, we have discovered that we can effectively generate induced pluripotent stem (iPS) cells from skin fibroblasts using a novel cell culture technique, which does not require viral expression of stem cell genes (that can sometimes be associated with cancer risk). iPS cells are “adult” cells (in this case skin fibroblasts) reprogrammed to be more like embryonic stem cells by being forced to express proteins important for maintaining the "stemness" qualities, including the ability to change into other types of desired cells. We have been able in culture to differentiate these cells into various retinal lineages, suggesting their potential therapeutic use for replacing cells lost in various eye diseases, including macular degeneration. Together, we now have multiple potential sources for generation of retinal cell lineages.