Low-Dose FK-506 Contributes to Tubulointerstitial Fibrosis Through Epithelial-Stromal Interactions

FK-506 is a widely used immunosuppressive drug for renal transplantation, but has a common side effect of progressive tubulointerstitial fibrosis.Although fibroblasts have been receiving attention for the fibrogenesis, the roles of renal epithelial cells are remained to be further investigated.Therefore, we aimed to assess the responses of renal epithelial cells compared to the renal interstitial fibroblasts after FK-506 treatment for fibrogenesis.We adopted renal proximal tubule cells (NRK-52E) and interstitial fibroblast cells (NRK-49F) isolated from rats for the FK-506-induced renal fibrogenesis.The responses after FK-506 treatment were assessed by cell viability assay, spheroidogenesis, Western blotting, and immunocytochemistry.NRK-52E cells showed higher N-cadherin while NRK-49F cells showed higher E-cadherin, fibronectin, and alpha-smooth muscle actin (SMA).As compared to NRK-52E cells, NRK-49F cells showed higher sensitivity to FK-506 by cell viability and spheroidogenesis.Spheroidogenesis was induced by the increased fibronectin and vimentin in both cells, while cell adhesion molecules as well as SMA were decreased.The more sensitive NRK-49F cells showed a trend of increase in apoptosis after FK-506 treatment, but autophagy, ferroptosis, and cell cycle did not affect both cell lines.Low-dose FK-506 transiently increased SMA expression in NRK-52E cells, which was also confirmed by co-cultured NRK-52E cells as accompanied by fibronectin.Taken together, NRK-52E cells showed fibrogenic responses following low-dose FK-506 treatment with an increased SMA and fibronectin expression, which was disappeared after high-dose FK-506 treatment.As fibrogenesis markers were differentially expressed in various renal cell lines, further research through more detailed experimental design should be performed.