Photoreceptor Renewal by Retinal Pigmented Epithelium Phagocytosis

Case Western Reserve University, Cleveland OH

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Abstract

DESCRIPTION (provided by applicant): The vertebrate retina has two main components, the neural retina, that employs specialized photoreceptor cells called rods and cones to collect light and transmit this information to the brain, and the retinal pigmented epithelium (RPE), which serves as part of the blood: retina barrier and performs several important functions. The RPE maintains retinal health by providing metabolites from the bloodstream, participating in the regeneration of the visual chromophore, and periodically removing the oldest portions of photoreceptor cells by phagocytosis. Photoreceptor cells maintain a virtually constant length by continuously generating new outer segments from their base while simultaneously releasing their mature outer segments at the tip in a circadian manner. Thus, post-mitotic RPE cells phagocytose an immense amount of material over a lifetime, disposing of cell waste required for photoreceptor survival and renewal. This function is required to maintain vision, as mutations in genes involved in RPE phagocytosis can lead to progressive retinal degeneration. Here, we propose a set of quantitative analyses to dissect the genetic factors underlying photoreceptor phagocytosis by the RPE. First, we will employ next generation massively parallel RNA-sequencing (RNA-Seq) to map the mouse eye transcriptome throughout the circadian timeline. Additionally, we will use quantitative proteomic approaches to gain a more complete picture of the signal transduction pathway leading to engulfment of shed photoreceptor outer segments. Lastly, we will grow primary RPE cells in culture and use newly developed techniques to discern second messenger signaling during RPE phagocytosis. These approaches will provide insights into the complex signaling networks responsible for RPE phagocytosis and potentially improve our understanding of phagocytic processes in general.