Ex Vivo-Derived Human-Induced Pluripotent Stem Cell (hiPSC) Podocytes from a Patient with Genetic Focal Segmental Glomerulosclerosis with an INF2 Mutation

Background: Genetic focal segmental glomerulosclerosis (FSGS) is caused by mutations in podocyte genes related to slit diaphragm formation, actin cytoskeleton or cellular adhesion but knowledge on the consequences of these mutations is limited. Usually genetic FSGS is not responsive to immunosuppression even though partial responses have been documented in some mutations most likely due to direct effects of these agents on podocytes themselves. Patient-specific podocyte models that carry the patient’s mutation might help to further characterize the diseased podocyte phenotype and test response to potential treatment options ex vivo. Methods: Human induced pluripotent stem cell (hiPSC)-derived podocytes (hiPSC-Podocytes) were generated by reprogramming dermal fibroblasts, obtained from a human skin punch biopsy, into hiPSCs with subsequent differentiation into podocyte cell type. Healthy donor-derived hiPSC-Podocytes were compared to commonly used conditionally immortalized (ciPodocytes) by bulk RNA sequencing and electron microscopy. Patient-specific hiPSC-Podocytes holding an inverted formin 2 (INF2) mutation were used to assess phenotypical and functional alterations in a personalized manner ex vivo. Results: Compared to ciPodocytes, hiPSC-Podocytes had a higher developed phenotype with better podocyte marker expression, and foot processes. Patient-specific hiPSC-Podocytes showed unbranched and shorter protrusions, loss of podocyte-specific marker and decreased levels of filamentous actin. Furthermore, an increased actin depolymerization rate, altered INF2 cleavage, and other compensatory mechanisms were identified. First treatment experiments with immunosuppressive drugs and actin-modulating agents resulted in improvement of filamentous actin in patient-specific INF2 mutated hiPSC-Podocytes. Conclusion: Using a patient-specific hiPSC-based model enables investigation of the patient-specific diseased phenotype and response to treatment in vitro and allows further studies of podocyte mutations. This will provide valuable insights into patho-mechanisms and may help identify individualized therapeutic strategies. Moreover, patient-derived hiPSCs allow to create patient-specific 3D kidney organoids to study multi-cellular and -structural differences. Funding: Government Support – Non-U.S.