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.

Public Health Relevance

Retinal health and maintenance requires an intimate interaction between the neural retina and the retinal pigmented epithelium (RPE). This interaction provides nutrients and substrates to the neural retina, as well as a continuous process whereby the RPE engulfs the oldest portions of photoreceptors to permit their renewal. This study will increase our understanding of how RPE phagocytosis occurs and potentially provide answers to mechanistic questions pertaining to other phagocytic processes.

National Institute of Health (NIH)
National Eye Institute (NEI)
Research Project (R01)
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Neuhold, Lisa
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Case Western Reserve University
Schools of Medicine
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Maeda, Akiko; Palczewska, Grazyna; Golczak, Marcin et al. (2014) Two-photon microscopy reveals early rod photoreceptor cell damage in light-exposed mutant mice. Proc Natl Acad Sci U S A 111:E1428-37
Mustafi, Debarshi; Kevany, Brian M; Genoud, Christel et al. (2013) Photoreceptor phagocytosis is mediated by phosphoinositide signaling. FASEB J 27:4585-95
Mustafi, Debarshi; Kevany, Brian M; Bai, Xiaodong et al. (2013) Evolutionarily conserved long intergenic non-coding RNAs in the eye. Hum Mol Genet 22:2992-3002