| Retinal pigment epithelium (RPE) dysfunction has been linked to many devastating eye disorders, including age related macular degeneration, as well as hereditary disorders such as Stargardt's disease and retinitis pigmentosa. Attempts to repair the RPE include transplantation of RPE cells into the subretinal space. RPE transplantation in humans and animals, and macular relocation surgery have all shown that replacing diseased RPE with healthier RPE can rescue photoreceptors, prevent further visual loss or even promote visual improvement. Fetal or adult transplanted RPE cells attach to Bruch's membrane with poor efficiency and do not proliferate. These transplantation procedures are complex, associated with high complication rates, and often only result in short-term success. Other problems exist, including the immune rejection of transplanted homologous cells, and the difficulty finding autologous RPE cells for transplant.; In this body of work, an acute injury model of RPE damage was adopted using sodium iodate administration to test whether or not bone marrow-derived cells (BMDCs) can regenerate the RPE layer. This study was the first to demonstrate that donor cells assimilate to the host RPE layer, donor cells display key characteristics of RPE morphology, and display RPE melanin pigment. The pigment could only have been derived from the donor BMDCs because the recipient mice were albino and did not produce melanin. Fusion of donor and host cells was ruled out using sex mis-matched transplants and fluorescent in situ hybridization.; The mechanism in which the BMDCs are recruited into the RPE layer was also addressed. The RPE has been shown to constitutively express stromal derived factor 1alpha (SDF-1alpha) for the maintenance of the choroid. I tested the hypothesis that SDF-1alpha acts as a trophic factor to recruit bone marrow derived progenitor cells to the RPE. Immunohistochemistry was used to confirm the presence of SDF-1alpha after sodium iodate administration. These observations encouraged the further characterized the specific bone marrow derived progenitor cell population that was involved in regenerating the RPE layer. The BMDC population involved in regenerating the RPE expressed the receptor for SDF-1alpha (CXCR4) and were cKit+, a phenotypic receptor for early hematopoietic progenitor cells.; In addition to being CXCR4+ and cKit+, this population was also analyzed for the presence of human hematopoietic stem cell marker prominin 1, or CD133. Previous work has shown that point mutations in CD133 have been shown to display a retinal degenerative phenotype. Interestingly, CD133 expression has never been analyzed in the murine retina. This work shows CD133 expression to the outer segments of the neural retina, close to the RPE layer. In addition, the cKit+ transplanted BMDCs that have migrated and incorporated into the RPE layer express CD133. Flow cytometric analysis of the CD133+ population confirmed the presence of both cKit and CXCR4, in addition to the strong association to the monocytic hematopoietic lineage. Lastly, I demonstrated that CD34 + human cord blood cells also migrate and differentiate into RPE-like cells in a murine NOD/SCID xenotransplant model. Together these data display a promising potential for the use of cell-based therapy using autologous bone marrow hematopoietic cells to treat failing RPE. |
