Anti-oxidative stress effects of miR-125b on lens epithelial cells and its mechanism

Objective

To investigate the anti-oxidative stress effects of microRNA 125b (miR-125b) on lens epithelial cells (LECs) and its possible mechanism.

Methods

Twenty-four anterior capsule specimens were collected from 24 eyes of 24 age-related cataract patients during phacoemulsification and 20 normal anterior capsule specimens were obtained from 20 eyes of 20 donors in Henan Eye Hospital from July 2018 to March 2019 under the approval of a Medical Ethics Committee of Henan Eye Hospital (No.YKYY20193151).The reverse transcription PCR and Western blot assay were employed to detect and compare the relative expression levels of miR-125b and nuclear factor E2-related factor 2 (Nrf2) in different specimens.The human lens epithelial cell line HLEB-3 was divided into control group and oxidative stress model group.The oxidative stress models were established by coculture with different concentrations (100, 200, 400 μmol/L) of H₂O₂ for 24 hours, and the cells were cultured with normal medium without H₂O₂ in the control group.The reactive oxygen species (ROS) content was detected by DCFH-DA fluorescent probe, and the activities of total-antioxidative capability (T-AOC), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) as well as malondialdehyde (MDA) concentration were detected by ELISA, and compared among the groups.The expression levels of miR-125b and Nrf2 were detected by reverse transcription PCR and Western blot assay, respectively.The cells were transfected with miR-125b mimics, miR-125b control and miR-125b inhibitor for 24 hours, respectively, and ROS content was detected by DCFH-DA fluorescent probe and T-AOC, SOD and GSH-Px activities as well as MDA concentration were detected by ELISA and compared among different transfected groups.A dual luciferase reporter assay was used to assess an association between miR-125b and Nrf2.The expression level of Nrf2 protein was detected by Western blot assay and the expression levels of Nrf2 and Keap1 were assayed and located by immunofluorescence double staining.

Results

The relative expression levels of miR-125b and Nrf2 in the normal lens anterior capsule specimens were 0.21±0.03 and 0.27±0.06, which were significantly lower than 0.89±0.05 and 0.84±0.12 in the cataract specimens, respectively (t=15.355, P<0.05; t=18.647, P<0.05).The relative expression levels of miR-125b and Nrf2 were significantly increased in various H₂O₂ treated groups in comparison with the control group and were gradually elevated with the increase of H₂O₂ concentration (all at P<0.05).Compared with the control group, the T-AOC, SOD and GSH-Px activities were reduced, and ROS content and MDA concentration were significantly ascended (all at P<0.05).Compared with the miR-125b control group, the T-AOC, GSH-Px and SOD activities were increased, and ROS content and MDA concentration were decreased in the miR-125b mimics group (all at P<0.05).In addition, the T-AOC, GSH-Px and SOD activities were significantly weakened, and ROS content and MDA concentration were significantly increased in the miR-125b inhibitor group in comparison with the miR-125b control group (all at P<0.05).Dual luciferase reporter assay showed that miR-125b targeted to the expression of Nrf2 in the H₂O₂ model cells.The fluorescence of Nrf2 in the cytoplasm was the strongest with more nuclear transfer in the miR-125b mimics group, and the expression intensity of Keap1 in the cytoplasm was weaker.The expression of Nrf2 was the weakest with less nuclear transfer in the miR-125b inhibitor group, and the expression level of Keap1 in the cytoplasm was stronger.

Conclusions

MiR-125b can enhance the anti-oxidative stress of LECs in age-related cataractous eyes probably by upregulating the expression of Nrf2 and activating the Keap1/Nrf2 signaling pathway.