Reactive oxygen species-evoked endoplasmic reticulum stress mediates albumin load-induced epithelial-mesenchymal transition in podocytes

Background Epithelial-mesenchymal transition (EMT) plays a significant role in cell migration and tissue fibrosis. Podocytes may undergo EMT after injury, leading to podocyte migration and detachment, which results ultimately in albuminuaria and renal fibrosis. The molecular mechanisms linking albuminuria to the progression of renal fibrosis is complex and not yet fully understood. Reactive oxygen species (ROS) and endoplasmic reticulum (ER) stress play significant roles in renal fibrosis. In this study, we evaluate whether albumin load induces podocyte EMT through ROS/ER stress pathways. Methods Podocytes were exposed to medium alone or to high concentrations of delipidated, endotoxin-free human serum albumin (HSA, 10 mg/ml) (albumin load) with or without antioxidant (N-acetylcysteine, NAC) and ER stress inhibitors (4-phenylbutyrate (4-PBA) and salubrinal (Sal)). Intracellular ROS generation was measured using the fluorescent indicator 20, 70-dichlorofluorescin diacetate (DCF-DA). Both mRNA and protein levels of the EMT biomarker (α-smooth muscle actin, α-SMA) and the protein levels of ER stress biomarkers (GRP78 and CHOP) were assessed by real-time PCR and Western blotting. Results After albumin load, intracellular albumin was increased in podocytes. In addition, the elevated ROS generation and protein levels of both GRP78 and CHOP were caused under albumin load, both of which could be reversed by NAC. Also, 4-PBA attenuated ROS generation induced by albumin load. Both mRNA and protein levels of α-SMA were up-regulated under albumin load. NAC alleviated albumin load-induced alterations in both mRNA and protein levels of α-SMA. Also, both 4-PBA and Sal ameliorated albumin load –triggered both mRNA and protein levels of α-SMA. Conclusion Our findings suggested that albumin load promoted podocyte EMT mainly via ROS-mediated ER stress. The ROS-ER stress related pathways might be a potential intervention target for albuminuria-caused renal fibrosis.