Protective effects of probucol on Ox-LDL-induced epithelial-mesenchymal transition in human renal proximal tubular epithelial cells via LOX-1/ROS/MAPK signaling

Oxidized low-density lipoprotein (Ox-LDL), as a strong oxidant, results in renal injury through multiple mechanisms. The aim of the present study was to determine the injury effects of Ox-LDL and the potential protective effects of the antioxidant reagent probucol on epithelial-mesenchymal transition (EMT) in human renal proximal tubular epithelial cells (HK-2) and to further explore the role and interrelation of lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), reactive oxygen species (ROS) and mitogen-activated protein kinase (MAPK) pathway. In the present study, concentrations of 0-100 mu g/ml Ox-LDL were used to induce HK-2 cell EMT. Then, probucol (20 mu mol/l) and the LOX-1 inhibitor, polyinosinic acid (250 mu g/ml), were also used to pretreat HK-2 cells. Intracellular ROS activity was evaluated using the specific probe 2,7-dichlorodihydrofluorescein diacetate (DCFH-DA). Concentration of nitric oxide (NO) was determined using a biochemical colorimetric method. Expression of E-cadherin, -smooth muscle actin (SMA), LOX-1, NADPH oxidase 4 (NOX4), cytochrome b-245 chain (p22phox), extracellular signal-regulated kinase (ERK), and p38 MAPK protein levels were examined by western blotting. The results revealed that Ox-LDL induced the expression of LOX-1 and -SMA and reduced the expression of E-cadherin in a dose-dependent manner, and these effects were inhibited by polyinosinic acid or probucol pretreatment. Stimulation with 50 mu g/ml Ox-LDL induced the expression of NOX4 and p22phox and increased intracellular ROS activity, but NO production in the cell supernatants was not affected. The Ox-LDL-mediated increases in Nox4 and p22phox expression and in ROS activity were inhibited by probucol pretreatment. Further investigations into the underlying molecular pathways demonstrated that ERK and p38 MAPK were activated by Ox-LDL stimulation and then inhibited by probucol pretreatment. The findings of the present study therefore suggest that Ox-LDL induced EMT in HK-2 cells, the mechanism of which may be associated with LOX-1-related oxidative stress via the ERK and p38 MAPK pathways. Notably, pretreatment with probucol inhibited the Ox-LDL-induced oxidative stress by reducing the expression of LOX-1, and blocked the progression of EMT.