Objective:To explore whether thioredoin-2 (Trx-2) is involved in the development of cataract and to study the effect of Trx-2 on hydrogen peroxide (H2O2)-induced injury in human lens epithelial cells.Methods:A total of 10 volunteers (removing the lens due totraumatism) and 30 patients received phacoemulsification (age more than 60 years) were selected.The expression of Trx-2 protein in lens epithelial cells from cataract patients and volunteers were detected by the immunohistochemical streptavidin-peroxidase (SP) method.SRA01/04 cells were cultured and were divided into six groups according to different treatment:a control group,H2O2-treated groups at 20,50 or 100 μmol/L,a negative control group (transfected with pCMV6 plasmid plus 100 μmol/L H2O2),and a Trx-2 overexpression group (transfected with pCMV6-Trx-2 plasmid plus 100 μmol/L H2O2).Methyl thiazolyltetrazolium (MTT) assay and flow cytometry was performed to measure the cell viability and apoptosis for SRA01/04 cells,respectively.The activities of superoxide dismutase (SOD) and catalase (CAT),the content of glutathione (GSH) and malondialdehyde (MDA) in human lens epithelial cells were measured via chemical chromatometry.Western blot was used to measure the protein levels of Trx-2,B-cell lymphoma 2 protein (Bcl-2),Bcl-2 associated X protein (Bax) and caspase-3.Results:Compared with the volunteers,the expression of Trx-2 was significantly decreased in lens epithelial cells in patients with cataract (P＜0.05).Compared with the control group,the expression of Trx-2 protein in the 20,50 or 100 μmol/L H2O2 groups was decreased (all P＜0.05).Compared with the control group,the cell survival rates were decreased in the 100 μmol/L H2O2 group and the negative control group (both P＜0.05),along with enhanced apoptotic rates,inhibited cellular SOD activities and CAT activities,reduced GSH contents,augmented MDA contents,down-regulated Trx-2 and Bcl-2 expression and up-regulated Bax and caspase-3 expression (all P＜0.05).Compared with the negative control group,the cell survival rate was increased in the Trx-2 overexpression group (P＜0.05),along with suppressed apoptosis,increased SOD activities and CAT activities,elevated GSH contents,decreased MDA content,up-regulated Trx-2 and Bcl-2 expression and down-regulated Bax and caspase-3 expression (P＜0.05).Conclusion:Trx-2 might be involved in the apoptosis of lens epithelial cells in patients with cataract.The overexpression of Trx-2 obviously attenuated H2O2-induced injury of human lens epithelial cells,which might be associated with the inhibition of H2O2-mediated oxidative stress.