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)‐β1 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 AT₁ receptor mRNA levels, as well as AngII and TGF‐β1 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‐β1 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‐β1 synthesis, the elevated local RAS participates in high glucose‐induced EMT and increased extracellular matrix secretion.