Discovery of Epigenetic Substances for the Treatment of FSGS Using Zebrafish Larvae as an In Vivo Model

Background: Podocytes are essential cells of the glomerulus that maintain the size selectivity of the glomerular filtration barrier. Injury to these postmitotic cells is a major cause of FSGS often resulting in end-stage kidney disease. To date, no specific drugs or compounds have been discovered to protect podocytes, underscoring the significant unmet need for drug development. Our group recently established a high-content in vivo screening assay to discover potential drugs and compounds to treat FSGS. For this purpose, we used zebrafish larvae that develop a filtering glomerulus within 4 days and we analyzed the effect of epigenetic substances after the induction of FSGS. Methods: A transgenic zebrafish screening strain expresses the bacterial enzyme nitroreductase as well as the fluorophore mCherry exclusively in podocytes. Furthermore, the expression of a circulating 78 kDa vitamin-D-binding fusion protein with eGFP provides a readout for the integrity of the glomerular filtration barrier in the vasculature. Addition of the prodrug Nifurpirinol (NFP) to the water results in a specific podocyte injury, a loss of mCherry in the glomerulus and a decreased eGFP fluorescence between 4 and 6 days post fertilization (dpf). After 6 dpf, larvae develop proteinuric edema and classical hallmarks of FSGS due to podocyte injury. These readouts were utilized in a rapid, imaging-based screening of an epigenetic drug library as reported in Schindler et al. 2023. Drugs and compounds that prevent a loss of fluorescence or the development of edema were further validated. Results: The screening of epigenetic drugs revealed that PTACH as well as the substances MN876 and MN119 showed a high potency to alleviate larval FSGS and exhibited a prolonged protective effect on podocytes. Conclusion: We have identified three promising new drugs/compounds for the treatment of FSGS in zebrafish larvae that are currently under validation in mammalian FSGS models. Funding: Private Foundation Support