| Popis: |
Human senses are specifically designed to recognize and understand the world that surrounds us. Even though we have five senses, vision alone is responsible for at least 30 % of the sensory input to our brain. The visual process is initiated in a highly specialized cell type, the photoreceptors. These are light-sensitive cells located in the retina, a layered nervous tissue situated at the back of the eye. Retinal degeneration diseases are a highly heterogeneous group of conditions that include mutations affecting the survival, maintenance and proper functioning of photoreceptors or the adjacent retinal pigment epithelium (RPE). Such mutations, alone or in combination with environmental factors, cause the loss of the affected cells, and therefore, impairment of the visual sense. Retinitis Pigmentosa and Age-related Macular Degeneration are typical examples of retinal degenerative diseases eventually leading to blindness. In the first one, rod photoreceptors degenerate and consequently also cone photoreceptors are lost. The second is characterized by malfunction and loss of both, RPE and photoreceptor cells. Many current therapeutic approaches for the treatment of retinal degenerative diseases focus on slowing down the progression of the disease, rather than restoring the visual function. Currently, new therapies with the potential to recover the visual signal are under development. Some of these therapeutic strategies have already reached clinical stages, including gene therapy or retinal prosthesis. However, gene therapy approaches require the presence of remaining photoreceptors and, furthermore, particular targeting of disease-related genes. Retinal prosthesis still require improvement in terms of long-term biocompatibility and relevant visual function recovery. An alternative strategy for vision restoration is cell replacement of the lost photoreceptors, which is potentially suitable for targeting late stages of retinal degeneration diseases, independently of the inherent cause of the disease. Human vision relies primarily on cone photoreceptors, which are the cells responsible for color and high acuity vision under daylight conditions. However, cones represent a minority of the photoreceptors within the retina, and so, due to the low availability of these cells, cone photoreceptor transplantation studies lag behind rod transplantation studies. Consequently, in this study, strategies to increase the numbers of cone photoreceptors within mouse embryonic stem cells (mESC)-derived retinal organoids, which represent a potential cell source for transplantation studies, were explored. In this regard, I manipulated developmental pathways known to be involved in retinal development, such as Notch signaling, through the addition of various compounds in the retinal organoid maturation media. However, early cone markers have not yet been definitively identified, complicating the detection and isolation of cone photoreceptor precursors within the organoids. Therefore, a new early cone-reporter mESC line was generated in the course of this study as a valuable tool with the potential to facilitate the development of novel cone photoreceptor replacement therapies. Equally important in the field of photoreceptor cell replacement is the understanding of how the transplanted donor cells interact with the host retina. Previous studies have shown that visual function improvement is possible after transplanting rod or cone-like photoreceptor precursors into the sub-retinal space of mouse models for retinal degeneration. For many years it has been assumed that the underlying mechanism for the observed vision improvement was the migration and structural integration of donor cells into the host outer nuclear layer, where they mature and establish synaptic connections with the host retinal circuitry. However, experiments performed in this study demonstrate, for the first time, that upon transplantation donor and host photoreceptors exchange cytoplasmic material rather than structurally integrate into the host outer nuclear layer. Furthermore, insights into the transferred cytoplasmic content are given, i.e. that mRNA, but not mitochondria are exchanged by donor and host photoreceptors. This novel way of photoreceptor-photoreceptor communication led to a paradigm change in the field of retinal transplantation, requiring a re-interpretation of former transplantation studies. In addition, the discovery of the material transfer phenomenon might serve as a starting point for the development of novel therapeutic strategies based on cell-cell support for the treatment of retinal degenerative diseases. This study generated new knowledge in two important topics related to the development of cell therapies for retinal degeneration diseases, including the development of tools for cone transplantation studies as well as elucidating the interaction between donor and host cells upon transplantation. |
