Organoids derived from renal tissue stem cells (KS cells) isolated from the S3 segment of adult rat nephrons have previously been developed and evaluated. However, data regarding the histopathological evaluation of these organoids are limited. Therefore, in this study, we performed histopathological examinations of the properties of these organoids and evaluated the nephrotoxicity changes induced by cisplatin treatment. We observe that the tubular structure of the organoids was generally lined by a single layer of cells, in concordance with previous findings. Microvilli were exclusively observed under electron microscopy on the luminal side of this tubular structure.Moreover, the luminal side of the tubular structure was positive for aquaporin-1 (Aqp1), a marker of the proximal renal tubule. Cisplatin treatment induced cell death and degeneration, including cytoplasmic vacuolation, in cells within the tubular structure of the organoids. Cisplatin toxicity is associated with the induction of γ-H2AX (a marker of DNA damage) and the drop of phospho-histone H3 (a marker of cell division) levels. During the nephrotoxicity assessment, the kidney organoids displayed various features similar to those of the natural kidney, suggesting that it is possible to use these organoids in predicting nephrotoxicity. The histological evaluation of the organoids in this study provides insights into the mechanisms underlying nephrotoxicity.

Background The use of stem/ progenitor cellderived organoids to evaluate the toxicity of chemical substances has widely increased. Organoids with nephron-like structures (NLS) can be derived from rat adult kidney stem/ progenitor cells (rKS cells) using three-dimensional culture. In this study, we examined the effects of cisplatin, an anticancer drug that induces nephrotoxicity in vivo, on rKS cell-derived NLS. Methods Twelve organoids were simultaneously derived from three-dimensionally cultured rKS cells in Matrigel matrices. The surface area of each organoid was measured using microscopy-based imaging, and the morphological changes of NLS were monitored using an image analysis method. NLS were exposed to cisplatin, and their associated effects were assessed. Results NLS elongated over time. The surface areas of the 12 organoids were almost constant. Cisplatin exposure induced cell death in NLS and inhibited the increase in the surface area of the organoids. Conclusion Cisplatin exposure induces damage to NLS derived from rKS cells. Thus, the organoids may be valuable as an in vitro model to assess nephrotoxicity.