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AIM: To investigate the effects and mechanism of miR-138 in mediating the antioxidant function of lens epithelial cells affected by age-related cataracts. <p>METHODS: Real-time quantitative PCR(RT-qPCR)was used to detect miR-138 expression in the anterior lens capsules of healthy people, the anterior lens capsules of patients with age-related cataracts, and human epithelial cell line(SRA01/04)cells exposed to oxidative stress. A 2', 7'-dichloro-fluorescein diacetate(DCFH-DA)probe was used to measure the levels of endogenous reactive oxygen species(ROS)in human lens epithelial cells(hLECs)exposed to 400μmol/L H₂O₂ for 1h. SRA01/04 cells were transfected with either miR-138 mimics, mimic controls, miR-138 inhibitors or inhibitor controls. After 72h, these cells were exposed to 400μmol/L H₂O₂ for 1h, then p53 and Bax mRNA expression were measured using RT-qPCR. Expression of p53 and Bax protein were also measured by western blotting analysis. Finally, cell viability was assessed using an MTS assay. <p>RESULTS: Compared to the control group, expression of miR-138 in the anterior lens capsules of age-related cataract patients and in SRA01/04 cells exposed to oxidative stress significantly increased(<i>P</i><0.001). Levels of endogenous ROS were significantly elevated in hLECs exposed to oxidative stress(<i>P</i><0.001). Compared to the mimic control group, the hLECs in the miR-138 mimic group expressed significantly higher levels of p53 and Bax mRNA and protein while cell viability was significantly reduced(<i>P</i><0.001). Conversely, p53 and Bax mRNA and protein expression were significantly reduced in the miR-138 inhibitor group as compared to the control group, while the cells in this group had much higher levels of cell viability(<i>P</i><0.001). <p>CONCLUSION: The expression of miR-138 is upregulated in the anterior lens capsules of age-related cataract patients. MiR-138 decreases the anti-oxidative stress capacity of lens epithelial cells by upregulating p53 and Bax, while inhibiting cell proliferation and repair. This finding suggests that miR-138 may play a key role in the development of age-related cataracts.