This study evaluated effect of oxalate on epithelial mesenchymal transition (EMT) and potential anti-fibrotic property of epigallocatechin-3-gallate (EGCG). MDCK renal tubular cells were incubated with 0.5 mM sodium oxalate for 24-h with/without 1-h pretreatment with 25 μM EGCG. Microscopic examination, immunoblotting and immunofluorescence staining revealed that oxalate-treated cells gained mesenchymal phenotypes by fibroblast-like morphological change and increasing expression of vimentin and fibronectin, while levels of epithelial markers (E-cadherin, occludin, cytokeratin and ZO-1) were decreased. EGCG pretreatment could prevent all these changes and molecular mechanisms underlying the prevention by EGCG were most likely due to reduced production of intracellular ROS through activation of Nrf2 signaling and increased catalase anti-oxidant enzyme. Knockdown of Nrf2 by small interfering RNA (siRNA) abrogated all the effects of EGCG, confirming that the EGCG protection against oxalate-induced EMT was mediated via Nrf2. Taken together, our data indicate that oxalate turned on EMT of renal tubular cells that could be prevented by EGCG via Nrf2 pathway. These findings also shed light onto development of novel therapeutics or preventive strategies of renal fibrosis in the future.

Renal tubular cell injury can enhance calcium oxalate monohydrate (COM) crystal adhesion at the injured site and thus may increase the stone risk. Nevertheless, underlying mechanism of such enhancement remained unclear. In the present study, confluent MDCK renal tubular cell monolayers were scratched to allow cells to proliferate and repair the injured site. At 12-h post-scratch, the repairing cells had significant increases in crystal adhesion capacity and cell proliferation as compared to the control. Cell cycle analysis using flow cytometry demonstrated that the repairing cells underwent cell cycle shift from G0/G1 to S and G2/M phases. Cyclosporin A (CsA) and hydroxyurea (HU) at sub-toxic doses caused cell cycle shift mimicking that observed in the repairing cells. Crystal-cell adhesion assay confirmed the increased crystal adhesion capacity of the CsA-treated and HU-treated cells similar to that of the repairing cells. These findings provide evidence indicating that cell cycle shift from G0/G1 to S and G2/M phases is responsible, at least in part, for the increased adhesion of COM crystals on repairing renal tubular cells at the injured site.

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