Bit1-a potential positive regulator of epithelial-mesenchymal transition in lens epithelial cells

Posterior capsule opacification (PCO) is a common postoperative complication of cataract surgery. Epithelial-mesenchymal transition (EMT) of lens epithelial cells (LECs) is an important initial step of PCO pathogenesis. We have previously shown that Bit1 expresses in rat LECs. In this study, we aim to investigate the role of Bit1 in the EMT of human LECs. The expression of Bit1 was firstly detected in human PCO-attached LECs and human lens cell line SRA01/04 by real-time PCR and immunofluorescence staining. The proliferation and migration of Bit1 knockdown SRA01/04 cells were evaluated by cell counting, wound-healing assay, and transwell migration assay. The EMT of LECs was triggered by TGF-beta 2, and then the effect of Bit1 on EMT with a key biomarker of alpha-smooth muscle actin (alpha-SMA) was analyzed by siRNA knockdown assay, and the reversal of EMT was validated by real-time PCR and western blot. Bit1 was obviously augmented in LECs derived from PCO tissues and Bit1 expressed with high levels in the cytoplasm of cultured SRA01/04 cells. Cell proliferation, invasion, and migration, as well as alpha-SMA expression, were significantly decreased in Bit1 knockdown SRA01/04 cells. While TGF-beta 2 elevated Bit1 and alpha-SMA expression levels in a dose-dependent manner, with peak levels at 10 ng/ml of TGF-beta 2 treatment, suppression of Bit1 in SRA01/04 cells reversed the EMT process. TGF-beta 2 induced elevation of alpha-SMA expression level, as well as migration, and invasion abilities were all suppressed by Bit1 deficiency. These findings reveal that Bit1 promotes TGF-beta 2 induced alpha-SMA expression and acts as an positive regulator of EMT. Suppressing Bit1 inhibits the proliferation, migration, and EMT of LECs. Bit1 may be a potential novel therapeutic target for the prevention and treatment of PCO.