Angiotensin AT1 receptor activation mediates high glucose-induced epithelial-mesenchymal transition in renal proximal tubular cells.

1. Renal tubular epithelial cells can undergo epithelial to mesenchymal transition (EMT) under hyperglycaemic conditions, which is associated with renal interstitial fibrosis. Activation of the renin-angiotensin system (RAS) is involved in diabetic nephropathy. The present study investigated the positive role of angiotensin AT1 receptors in high glucose-induced EMT in cultured tubular epithelial cells. 2. A rat kidney proximal tubular epithelial cell line (NRK-52E) was used in the present study. Levels of EMT makers, namely E-cadherin and vimentin, were estimated using fluorescence immunocytochemistry, mRNA levels of angiotensinogen (AGT), angiotensin-converting enzyme (ACE) and AT1 receptors were determined by real-time polymerase chain reaction, protein levels of E-cadherin, vimentin, fibronectin, matrix metallopeptidase (MMP)-9 and phosphorylated extracellular signal-regulated kinase (ERK) 1/2 were analysed by western blotting and the concentrations of angiotensin (Ang) II and transforming growth factor (TGF)-beta1 in the culture medium were determined by enzyme immunoassay and ELISA. 3. High glucose (30 mmol/L) induced EMT and increased the synthesis of fibronectin and MMP-9. Furthermore, high glucose increased AGT, ACE and AT(1) receptor mRNA levels, as well as AngII and TGF-beta1 concentrations in the culture medium and ERK1/2 phosphorylation. Pretreatment of cells for 15 min with the AT1 receptor antagonist losartan (10(-5) mol/L) attenuated high glucose-induced increases in TGF-beta1 and ERK1/2 phosphorylation and reduced EMT, as well as the consequent synthesis of fibronectin and MMP-9. 4. The results of the present study suggest that the activated local RAS mediates high glucose-induced EMT. By activating AT1 receptors and stimulating TGF-beta1 synthesis, the elevated local RAS participates in high glucose-induced EMT and increased extracellular matrix secretion.