Tacrolimus Ameliorates Tubulointerstitial Inflammation in Diabetic Nephropathy via Inhibiting the NFATc1/TRPC6 Pathway

Background: Tubulointerstitial inflammation is crucial for the progression of diabetic nephropathy (DN), and tubular cells act as a driving force in the inflammatory cascade. Emerging data suggested that tacrolimus ameliorates podocyte injury and macrophage infiltration in STZ mice. However, the effect of tacrolimus on tubulointerstitial inflammation remains unknown. Methods: Macrophage infiltration and expression of proinflammatory and fibrosis proteins were observed in the kidneys of db/db mice treated with tacrolimus. NFATc1 and TRPC6 expression were assayed and the correlation with tubulointerstitial inflammation was analyzed. To explore the effect and mechanism of tacrolimus, HK-2 cells were treated with tacrolimus with or without NFATc1 siRNA and TRPC6 plasmid under high glucose (HG) conditions. Findings: Albuminuria and tubulointerstitial damage improved in db/db mice treated with tacrolimus. Macrophage inflitration and expression of IL-6, TNF-α, FN, Col-1 and cleaved-caspase 3 were inhibited. In addition, the expression of NFATc1 and TRPC6 was upregulated in the kidneys of DN patients, and correlated with tubular injury and inflammation. The expression of NFATc1 and TRPC6 also increased in the kidneys of db/db mice and HK-2 cells with HG, while tacrolimus inhibited these effects. HG-induced inflammatory markers and apoptosis were reversed by tacrolimus and NFATc1 siRNA in HK-2 cells, which was abolished by TRPC6 plasmid. Furthermore, HG-induced TRPC6 expression was inhibited by NFATc1 siRNA, while NFATc1 nuclear translocation was inhibited by tacrolimus, but was restored by TRPC6 plasmid in HK-2 cells under HG conditions. Interpretation: These findings suggest that tacrolimus ameliorates tubulointerstitial inflammation in DN through NFATc1/TRPC6 feedback loop. Funding Statement: This work was supported by the National Natural Science Foundation of China (81570658). Declaration of Interests: The authors declare that there are no conflicts of interest. Ethics Approval Statement: The human protocol was approved by the Ethics Committee of Second Xiangya Hospital, Central South University. The Animal Care and Use Committee of Second Xiangya Hospital of Central South University approved all animal procedures.