Introduction: The progression of diabetic kidney disease (DKD) is closely related to renal tubular epithelial- to-mesenchymal transition (EMT) and tubulointerstitial fibrosis. Tanshinone IIA (TSIIA), extracted from a traditional Chinese medicine named Salvia miltiorrhiza, has been proved to have anti-fibrosis effects. The aim of this study was to investigate the effect of TSIIA on high glucose-induced EMT in human proximal tubular cells (HK-2 cells) and its possible mechanism.
Material and methods: The proliferation of cells exposed to different concentrations of glucose was measured by light microscopy and CCK-8 test. The cells were stimulated with 30 mM glucose and different concentrations of TSIIA (5 μM or 10 μM) for 48 h. Vitamin D receptor (VDR)-siRNA was used to transfect cells, and high glucose and TSIIA treatment were further used to treat cells. The expression of alpha smooth muscle actin (a-SMA) mRNA was detected by qPCR to ensure successful induction of EMT, and the expression of VDR mRNA was detected by qPCR to ensure successful transfection of VDR-siRNA. Protein expression of a-SMA, E-cadherin, VDR, b-catenin and glycogen synthase kinase 3b (GSK-3b) was detected by Western blot analysis.
Results: The results showed that high glucose concentration inhibited cell proliferation and promoted EMT in HK-2 cells. TSIIA could reverse high glucose-induced EMT by increasing the level of VDR protein and inhibiting the levels of b-catenin and GSK-3b proteins suggestive of a negative correlation between VDR and the Wnt/b-catenin pathway. After VDR-siRNA transfection and incubation of cells at high glucose concentration, the inhibitory effect of VDR on the expression of b-catenin and GSK-3b of Wnt pathway was suppressed and the b-catenin pathway was activated. When VDR level was restored by TSIIA, the inhibitory effect of VDR on the pathway was also restored and the activation of the pathway was suppressed.
Conclusions: TSIIA was able to attenuate high glucose-induced EMT in HK-2 cells by up-regulating VDR levels, which might be related to the inhibitory effect of VDR on the Wnt pathway.
Keywords: HK-2 cells; VDR; Wnt/β-catenin pathway; epithelial-to-mesenchymal transition; tanshinone IIA.