Phagocytosis model of calcium oxalate monohydrate crystals generated using human induced pluripotent stem cell-derived macrophages

Abstract Macrophages play a role in nephrolithiasis, offering the possibility of macrophage-mediated preventive therapies. To establish a system for screening drugs that could prevent the formation of kidney stones, we aimed to develop a model using human induced pluripotent stem cell (iPSC)-derived macrophages to study phagocytosis of calcium oxalate monohydrate (COM) crystals. Human iPSCs (201B7) were cultured. CD14 + monocytes were recovered using a stepwise process that involved the utilization of growth factors and cytokines. These cells were then allowed to differentiate into M1 and M2 macrophages. The macrophages were co-cultured with COM crystals and used in the phagocytosis experiments. Live cell imaging using a super-resolution microscope was used to visualize phagocytosis. Intracellular fluorescence intensity was measured using imaging cytometry to quantify phagocytosis. Human iPSCs successfully differentiated into M1 and M2 macrophages. M1 macrophages adhered to the culture plate and moved COM crystals from the periphery to the center of the cell over time, whereas M2 macrophages did not adhere to the culture plate and actively phagocytosed the surrounding COM crystals. Fluorescence assessment over a 24-h period showed that M2 macrophages exhibited higher intracellular fluorescence intensity (5.65 times that of M1 macrophages at 4.5 h) and maintained this advantage for 18 h. This study revealed that human iPSC-derived macrophages have the capacity to phagocytose COM crystals, presenting a new approach for studying urinary stone formation and highlighting the potential of iPSC-derived macrophages as a valuable tool to screen drugs related to nephrolithiasis.