Renal tubular epithelial cells treated with calcium oxalate up-regulate S100A8 and S100A9 expression in M1-polarized macrophages via interleukin 6

Objectives: Calgranulins S100A8 and S100A9 are common in renal stones and they are up-regulated in both urinary exosomes and kidneys of stone patients. Renal sources and important regulators for S100A8 and S100A9 in nephrolithiasis were explored in this study.

Materials and methods: We identified S100A8 and S100A9 abundance in various renal cells by searching the Single Cell Type Atlas. Macrophages were polarized from human myeloid leukemia mononuclear cells. Human proximal renal tubular epithelial cells (HK-2) were stimulated with calcium oxalate monohydrate (COM). Coculture experiments involving HK-2 cells and macrophages were conducted. qPCR, Western blotting, ELISA, and immunofluorescence were used for detecting interleukin 6 (IL6), S100A8, and S100A9.

Results: The Single Cell Type Atlas showed that S100A8 and S100A9 in human kidneys primarily originated from macrophages. M1 was the predominant macrophage type expressing S100A8 and S100A9. Direct culture with COM did not affect the expression of these two calgranulins in M1 macrophages but coculture with COM-treated HK-2 cells did. COM could promote HK-2 cells to secrete IL6. IL6 could up-regulate S100A8 and S100A9 expression in macrophages of M1 type. In addition, 0.5 μM SC144 (a kind of IL6 inhibitor) significantly prevented COM-treated HK-2 cells from up-regulating S100A8 and S100A9 expression in macrophages of M1 type.

Conclusion: M1-polarized macrophages were the predominant cell type expressing S100A8 and S100A9 in the kidneys of nephrolithiasis patients. CaOx crystals can promote renal tubular epithelial cells to secrete IL6 to up-regulate S100A8 and S100A9 expression in macrophages of M1 type.