Examining collective behaviors or retinal progenitor cells to inform future retinal transplantation therapies
Creators: name: Markey, Miles W.
Publisher: name: No Publisher Supplied
Year: 2022

description: Retinal degenerative diseases, such as macular degeneration, diabetic retinopathy and retinitis pigmentosa, are leading causes of irreversible blindness worldwide for mature and aging adults. As neural degenerative disorders, these diseases are currently incurable, with current treatment options limited to those that slow disease progression and few available options at advanced stages of the disease. Many contemporary therapies have focused on retinogenesis, with the goal of developing cell replacement therapies that transplant stem-like cells able to mimic the conditions of retinal development to promote regeneration. Retinogenesis involves the migration and differentiation of retinal progenitor cells (RPCs), a multipotent cell type with the ability to differentiate into all sub-types of retinal neurons and glia. Complete understanding the mechanisms behind RPC migration and differentiation will greatly advance development of these cell replacement therapies. This thesis aims to further investigate an important but understudied component in RPC migration, collective chemotaxis, to help contribute to the knowledge base that will be used to realize full therapeutic potential for retinal cell replacement therapy. Collective chemotaxis occurs when a cohort of individual cells migrate as a single unit in response to external concentration gradients. This definition encompasses conditions from a pair of cells migrating in tandem to a population of communicating cells migrating in a specific direction. The size of the motile cohort depends largely on the type of cell involved, with certain cell types, such as metastasizing cancer cells, preferring small cluster migration and other cell types, such as endothelial cells during wound healing, preferring to migrate in large, coherent sheets. Regardless of the size of the motile cohort, intercellular junctions play an important role in, both, keeping cells together in coherent clusters and propagating pro-migratory signals between coherent cells. Cadherins, a class of homophilic intercellular junctions that are expressed in high levels in retinal progenitor cells, are known to play an important role in maintaining RPC cell-cell junctions. It is hypothesized that these cadherins also play an important role in coordinating RPC collective chemotaxis during development. This thesis will further explore the role of cadherins in coordinating collective chemotaxis of retinal progenitor cells during migration, shedding light on a potential therapeutic target that can be used to improve cellular integration for successful cell replacement therapies in retina. In this thesis, the collective behaviors of RPCs are analyzed under different pro-migratory conditions designed to replicate the conditions that these cells encounter in vivo. Novel microfluidic devices are utilized to create customizable micro-environments in which to study cell behaviors. One of these devices, the micro-Lane (μLane), was designed to study the migratory behaviors of Drosophila RPCs under time-dependent exogenous growth factor concentration gradients. Using this device, it was observed that Drosophila RPCs exhibit preferential migration as small clusters of 3-5 cells. Another device, the micro-Optic Stalk (μOS), was designed specifically to mimic the in vivo geometries of the developing Drosophila Optic Stalk, the developmental structure that the cells encounter in vivo, while establishing steady-state growth factor concentration gradients within the device microchannels. This allowed the migratory behaviors of these cells to be studied under conditions highly similar to those encountered during development in vivo. It was once again observed that Drosophila RPCs tended to migrate as small clusters of 3-5 cells in response to exogenous growth factor concentration gradients within this device. Finally, to further explore the collective behaviors of these cells, the expression of cadherins, the cell-cell cohesion molecule that plays a prominent role in RPC collective behaviors was quantified after exposure to an array of growth factors, in both Drosophila and Rodent RPCs. It was observed that certain growth factors linked to migration, namely FGF8 in Drosophila and SDF1- ? in Rodent, led to significant upregulation of cadherins in these RPCs, providing a potential mechanism to best replicate the developmental behaviors of transplanted RPCs and improve the efficacy of retinal cell replacement therapies.