Endoplasmic Reticulum Stress as a Regulator of High Glucose-Induced Epithelial–Mesenchymal Transition in Human Lens Epithelial Cells

Purpose: Diabetic patients have been proven to have higher incidence of subcapsular cataract, and the subcapsular cataract formation has a closed link with epithelial-to-mesenchymal transition (EMT). EMT in numerous tissues can be regulated by the endoplasmic reticulum stress response (ER stress). In this study, we aim to explore the role of ER stress high glucose (HG)-induced EMT of human lens epithelial cells (HLECs). Methods: The human lens epithelial cell line SRA01/04 was treated under HG conditions, and 4-phenylbutyrate (PBA) or tauroursodeoxycholic acid (TUDCA) was used for 24 h to restore endoplasmic reticulum (ER) homeostasis under HG condition. The long axis and the aspect ratio of the cells were analyzed with ImageJ software to evaluate the morphology of the cells. Western blot analysis and immunofluorescence staining were applied to measure ER stress makers: glucose-regulated protein 78 (GRP78), phosphorylation of eukaryotic initiation factor-2α (P-eIf2α), activating transcription factor 6 (ATF6), phospho-inositol-requiring enzyme1 (P-IRE1α), and the EMT makers: fibronectin, vimentin, alpha-smooth muscle actin (α-SMA), and N-cadherin. Additionally, wound-healing assays were performed to evaluate the cell migration ability. Results: Under HG, the morphology of HLECs became elongated, accompanied by a significantly increased cellular aspect ratio. Both the expression of ER stress markers (GRP78, P-eIF2α, ATF6, and P-IRE1α) and the EMT markers (fibronectin, vimentin, αSMA, and N-cadherin) increased. Conversely, the expression of E-cadherin, a marker of epithelial cells, decreased, and wound-healing assays indicated enhanced cell migration ability. All of these alterations were inhibited by PBA or TUDCA treatment. Conclusions: ER stress regulates HG-induced EMT in lens epithelial cells.