Genetic and glial support mechanisms in acute and chronic models of photoreceptor degeneration - PROJECT SUMMARY Over 2 billion people suffer from vision impairment worldwide, largely due to chronic, age-associated retinal degenerative diseases. This presents a significant health and cost burden on our society. In addition, given that humans possess limited regenerative ability, there are currently no cures for these diseases. In contrast, zebrafish maintain a remarkable capacity to regenerate the retina following intense forms of acute damage, such as phototoxic ablation of photoreceptors, neurotoxicity by pharmacological agents, or even physical “pokes” using a wide-gauge needle. In 2008, resident Müller glia (MG) were identified as the stem cell source that were triggered to re-enter the cell cycle following these acute damage events. Since then, zebrafish MG have become a rich source to identify several genetic pathways involved in retinal regeneration. Despite these advances, most human retinal degenerative diseases are not acute, but instead manifest under slower, chronic stress conditions. The current work builds on two newly-established chronic models of photoreceptor degeneration: our chronic low light model and P23H mutant zebrafish that express a mutated Rhodopsin protein that is associated with retinitis pigmentosa in humans. Both models show a slow decay of rod photoreceptor outer segments and loss of ~50% rod photoreceptor nuclei. Interestingly, in neither model do we observe MG reactive gliosis or MG-mediated regeneration in this model. This differs substantially from our previously established acute light damage model, in which photoreceptors are rapidly destroyed and MG undergo two stages of reactive gliosis surrounding their cell-cycle re-entry. Here, we will compare the transcriptional, cellular, and functional changes that occur during chronic and acute photoreceptor damage, assessing 8 timepoints along a 28-day protocol. These data will provide the template for addressing photoreceptor degeneration and neuroprotection mechanisms (Aim 1), and MG reactivity to neuronal damage (Aim 2). This proposal aims to address a critical need to better understand genetic and glial support mechanisms in the context of chronic vs acute damage. Using state-of-the art bioinformatic approaches, cell sorting, pharmaceutical treatments, morpholino-mediated gene knockdown, and visually-evoked optokinetic responses, this proposal aims to directly test the relationship between acute and chronic photoreceptor stress, coupling cellular and morphological changes with transcriptomic and functional genetic studies.
