Focal segmental glomerulosclerosis (FSGS) is a kidney disease that produces scarring of glomeruli. It is particularly difficult to model the disease due to its high genetic diversity, potential requirement for environmental influences, and other factors. Interestingly, Rose et al. report on a personalized in vitro model of FSGS that may provide key insights for understanding and treating this disease. Preliminary studies involved characterizing an FSGS patient’s diseased tissue using histological and genetic analysis, and led to the identification of a mutation in inverted formin 2 (INF2), which is a type of actin-regulating formin protein. hiPSC-Podocytes were differentiated from hiPSCs that were reprogrammed from skin-biopsy fibroblasts from an INF2-FSGS patient or a healthy donor. Characterization for podocyte markers and morphology was performed, and the FSGS-hiPSC-podocytes showed reduced levels of podocyte markers, altered F-actin staining, and rounder cell bodies with shorter protrusions. RNA sequencing and gene analysis identified broader changes in cytoskeletal and adhesion proteins and pathways. Mechanistically, the group showed that INF2 total levels were decreased, but surprisingly, they also saw an increase in cathepsin-dependent proteolytic cleavage of the protein as well. This altered INF2 levels led to a marked increase in the rate of actin depolymerization while leaving the actin polymerization rate unchanged, and was likely a contributing factor to the dysfunctional morphology observed in the FSGS-hiPSC-podocytes. Cytoskeleton Inc.’s actin polymerization Biochem kit (Cat. # BK003) was an essential tool used to analyze changes in actin polymerization and depolymerization in response to factors in control versus FSGS-hiPSC-podocyte lysates. Further characterization found similarities between how these podocytes responded to therapeutic treatment and the patient’s response to steroids, and suggests that these personalized in vitro models may be valuable for investigating causes and treatments for FSGS.
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Product Used in Citation:
Actin Polymerization Biochem Kit (fluorescence format): rabbit skeletal muscle actin (Cat # BK003)
