The human retina is susceptible to many degenerative diseases, mainly Age-Related Macular Degeneration and Diabetic Retinopathy, and can be rendered nonfunctional as a result. Studying animal models that have the capacity to regenerate could provide clues on therapies for these devastating diseases. The embryonic chick is able to regenerate its retina via transdifferentiation of the Retinal Pigment Epithelium (RPE), a tissue located behind the retina, if an external source of Fibroblast Growth Factor 2 (FGF2) is present. In the process of RPE-to-retina transdifferentiation, RPE cells lose their identity, turning into progenitor like-cells and these reprogrammed cells then respond to differentiation signals and become retinal cells. Previous work from our lab has shown that the Sonic Hedgehog (SHH) pathway inhibits the process of FGF2 induced-transdifferentiation, protecting RPE phenotype. SHH signals via specific Gli transcriptional factors: Gli-1, 2 and 3. The aim of this study is to determine the mechanisms by which Gli-1 and Gli-3R modulate retina regeneration.<b> </b>Our results show that SHH activates Gli-1 to maintain the RPE phenotype. Over-expression of Gli-1 in retinectomized eyes, even in the presence of FGF2, results in up-regulation of RPE markers (MITF and OTX-2), and down-regulation of retinal marker Pax-6. In addition, inhibition of Gli-1 using morpholinos in retinectomized eyes, shows RPE depigmentation and expression of Pax6, thus confirming Gli-1’s role in maintaining the RPE phenotype. Gli-3R, on the other hand, has been shown in other biological systems to down-regulate Gli-1, and thus may play a significant role in transdifferentiation. To<b> </b>evaluate the role of Gli-3R, we electroporated a Gli-3R plasmid to retinectomized eyes, and are currently in the process of evaluating any changes histologically and by immunohistochemistry to determine if RPE or retina markers were regulated. Preliminary results show depigmentation of the RPE in retinectomized eyes overexpressing Gli-3R without FGF2. This suggests that Gli-3R may be inhibiting the actions of Gli-1. These results provide knowledge about the mechanisms that control the RPE cell identity and differentiation.

SHH transcription factors Gli-1 and Gli-3R: Modulators of retina regeneration

249th National Meeting (2015)

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