*Purpose: Primary focal segmental glomerulosclerosis (FSGS) is a kidney disorder resulting in end-stage renal disease that is associated with an elevated rate of recurrence after renal transplantation. Etiology and pathogenesis of primary FSGS has not been well elucidated due to lack of appropriate preclinical models to study this complex disease, but different permeability factors circulating in plasma of patients with primary FSGS have been described. In recent years, procedures have been developed to differentiate human pluripotent stem cells (hPSCs) into renal tissues, which led us to investigate the effect of FSGS plasma during the development of kidney organoids.

*Methods: hPSCs were induced to differentiate into kidney progenitor cells by CHIR for 4 days, Activin for 3 days, and FGF 9 for 2 days. On day 9, progenitors were aggregated at the air-liquid interface and cultured in organoid media (containing BMP7, FGF9 and heparin) alone or in media containing 10% healthy plasma, recurrent FSGS plasma, non-recurrent FSGS plasma, or primary FSGS plasma. On day 16, organoids were evaluated under a stereomicroscope and stained for podocytes, CD44, and extracellular matrix (ECM) proteins produced by parietal epithelial cells (PECs).

*Results: Kidney organoids generated with organoid media or healthy plasma showed a typical developmental phenotype with intact and tightly packed tubular clusters, whereas organoids generated with FSGS plasma showed abnormal or damaged tubular clusters. Podocalyxin staining for podocytes showed that organoids generated in organoid media or healthy plasma had intact presumptive glomerular structures. Recurrent FSGS plasma treated organoids showed damaged presumptive glomerular structures, whereas non-recurrent or primary FSGS plasma treated organoids had a scattered podocalyxin staining pattern. Furthermore, a high ECM protein deposition and a high CD44 expression were observed in the glomerular basement membrane (GBM) of FSGS plasma treated organoids, whereas organoid media or healthy plasma led to a normal ECM protein expression and no expression of CD44 in their GBM.

*Conclusions: This study shows that primary FSGS plasma can trigger an abnormal kidney organoid development with a FSGS specific abnormality in glomerular structures and podocytes. Additionally, CD44⁺ activated glomerular PECs produce more ECM proteins that deposit on GBM and induce sclerotic glomerular development. In conclusion, the kidney organoid model could be a useful tool to study the pathophysiology and disease progression of primary FSGS.

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