The Tgf Beta/Notch Axis Facilitates Muller Cell-To-Epithelial Transition To Ultimately Form A Chronic Glial Scar

Background: Contrasting with zebrafish, retinal regeneration from Muller cells (MCs) is largely limited in mammals, where they undergo reactive gliosis that consist of a hypertrophic response and ultimately results in vision loss. Transforming growth factor beta (TGF beta) is essential for wound healing, including both scar formation and regeneration. However, targeting TGF beta may affect other physiological mechanisms, owing its pleiotropic nature. The regulation of various cellular activities by TGF beta relies on its interaction with other pathways including Notch. Here, we explore the interplay of TGF beta with Notch and how this regulates MC response to injury in zebrafish and mice. Furthermore, we aimed to characterize potential similarities between murine and human MCs during chronic reactive gliosis.Methods: Focal damage to photoreceptors was induced with a 532 nm diode laser in TgBAC (gfap:gfap-GFP) zebrafish (ZF) and B6-Tg (Rlbp1-GFP) mice. Transcriptomics, immunofluorescence, and flow cytometry were employed for a comparative analysis of MC response to laser-induced injury between ZF and mouse. The laser-induced injury was paired with pharmacological treatments to inhibit either Notch (DAPT) or TGF beta (Pirfenidone) or TGF beta/Notch interplay (SIS3). To determine if the murine laser-induced injury model translates to the human system, we compared the ensuing MC response to human donors with early retinal degeneration.Results: Investigations into injury-induced changes in murine MCs revealed TGF beta/Notch interplay during reactive gliosis. We found that TGF beta 1/2 and Notch1/2 interact via Smad3 to reprogram murine MCs towards an epithelial lineage and ultimately to form a glial scar. Similar to what we observed in mice, we confirmed the epithelial phenotype of human Muller cells during gliotic response.Conclusion: The study indicates a pivotal role for TGF beta/Notch interplay in tuning MC stemness during injury response and provides novel insights into the remodeling mechanism during retinal degenerative diseases.