Inflammatory Signaling and Regeneration in Zebrafish models of Retinal Degeneration

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Project Summary Inherited retinal degenerations (IRDs) are genetic diseases that lead to the progressive loss of photoreceptors and the permanent loss of vision. Wild-type zebrafish regenerate photoreceptors after acute injury by reprogramming Müller glia into stem-like cells that produce retinal progenitors. This regenerative process fails to occur in zebrafish models of IRDs. This proposal will address the critical unanswered question as to why zebrafish mutants with chronic inflammation fail to regenerate. Our preliminary data show that Notch pathway inhibition can promote photoreceptor regeneration in the zebrafish cep290 and bbs2 models of progressive degeneration and that immunosuppression prevents photoreceptor loss. These results offer insight into the pathways that promote Müller glia- dependent regeneration and the role of inflammation in photoreceptor degeneration. Our central hypothesis is that in zebrafish models of retinal degeneration, chronic inflammation results in elevated Notch and NF-kB signaling that restricts the regenerative response to acute injury. Evidence from the literature and our preliminary data rigorously demonstrate that Notch signaling in Müller glia differs in response to acute injury or chronic degeneration. Understanding the link between pro-inflammatory signaling from microglia and Notch signaling in Müller glia has not been previously addressed. Furthermore, our current understanding of how inflammatory cytokines signal through the NF-kB pathway has only been studied in the context of wild-type animals. The proposed studies will provide critical insight into the relationship between microglia and Müller glia regeneration in chronic disease. We will use state-of-the-art sequencing technologies to identify Müller glia- and microglia-specific changes in gene expression in cep290 and bbs2 models in order to elucidate the relationship between inflammation and regeneration. We will also identify and test specific ligand-receptor pairs to identify the mechanisms that maintain Notch signaling in the zebrafish degeneration mutants and identify key factors that stimulate NF-kB signaling. Understanding the mechanisms that underpin retinal regeneration in multiple zebrafish disease models will generate novel hypotheses that can ultimately be translated into humans with retinal degenerative diseases.