Advanced oxidation protein products induce hypertrophy and epithelial-to-mesenchymal transition in human proximal tubular cells through induction of endoplasmic reticulum stress.

BACKGROUND: In chronic kidney disease (CKD), the accumulation of advanced oxidation protein products (AOPPs) is prevalent. Hypertrophy and epithelial-to-mesenchymal transition (EMT) of tubular cells are associated with the pathogenesis of CKD. However, whether AOPPs induce tubular-cell hypertrophy and EMT is unclear. In this study, we investigated the effect of AOPPs on human proximal tubular cells (HK-2 cells) and the mechanisms underlying tubular-cell hypertrophy and EMT in vitro. METHODS: The mRNA and protein expression of CCAAT/enhancer-binding protein-homologous protein (CHOP), glucose-regulated protein (GRP) 78, p27, α-smooth muscle actin (α-SMA) and E-cadherin were evaluated by quantitative real-time PCR and western blot, respectively. Cell cycle was detected by flow cytometry. Bicinchoninic acid method was performed to measure total protein content. RESULTS: AOPP treatment upregulated total protein expression, caused an increase in the percentage of G1-phase cells, and induced the overexpression of p27 and α-SMA, lowered the expression of E-cadherin. Furthermore, AOPP treatment induced the overexpression of GRP78 and CHOP. Moreover, the aforementioned effects were reversed following the treatment of cells with an NADPH oxidase inhibitor, a reactive oxygen species (ROS) scavenger, or salubrinal, which is an inhibitor of ER stress, whereas these effects were produced after exposure to thapsigargin, an inducer of ER stress. CONCLUSION: Our results suggest that AOPPs induced HK-2-cell hypertrophy and EMT by inducing ER stress, which was likely mediated by ROS. These findings could facilitate the development of novel therapeutic strategies for suppressing the progression of CKD.