Association of light exposure with oxidative damage and apoptosis of human lens epithelial cells

Studies showed that light exposure induce the damage of lens epithelial cells (LECs), and this procedure is associated with the accumulation of reactive oxidative species (ROS) and apoptosis of LECs. However, the mechanism of light damage of LECs is below understood.

This study was to investigate the pathogenesis mechanism of light-induced LECs damage.

HLEB-3 strains were resuscitated and cultured and then divided into four groups. A light-emitting diode (LED) light source with the illuminance of 20 000 lx was set in a sealed culture box to irradiated the LECs for 6, 12 and 24 hours, and the cells were regularly cultured without light exposure in the normal control group. The mean fluorescence intensity (MFI) of ROS and apoptosis of the cells in different groups were tested by flow cytometry (FCM). The relative expressions of mRNA and protein of bax and transforming growth factor-β₂(TGF-β₂) in the cells of different groups were assayed by real-time PCR and Western blot, respectively. The growth and proliferation were assessed using MTT as absorbance (A₅₇₀) and compared between the normal control group and the light-exposure 24-hour group.

The cells grew well with the tight arrangement in the normal control group, but cellular swelling and intercellular space widening were seen in the light-exposure 24-hour group. The MFI of ROS in the normal control group, light-exposure 6-hour group, light-exposure 12-hour group and light-exposure 24-hour group was 2.85±0.14, 3.33±0.21, 5.82±1.69, 15.83±5.81, respectively, showing a significant increase in all the light-exposure groups (F=8.276, P=0.036). The early apoptosis rate was (0.17±0.13)%, (0.35±0.03)%, (0.74±0.27)%, (3.12±0.47)%, and the total apoptosis rate was (0.27±0.16)%, (0.58±0.14)%, (1.54±0.79)%, (5.22±1.63)% in the normal control group, light-exposure 6-hour group, light-exposure 12-hour group and light-exposure 24-hour group, respectively, with the significant elevation after light exposure (F=27.878, P=0.006; F=9.333, P=0.028). The expression of bax mRNA in the light-exposure 6-hour group, light-exposure 12-hour group and light-exposure 24-hour group were (1.45±0.33), (5.45±2.58) and (15.86±3.93) times more than that in the normal control group, and the expression of TGF-β₂ mRNA in the light-exposure 6-hour group, light-exposure 12-hour group and light-exposure 24-hour group was (1.22±0.12), (1.79±0.38) and (4.01±0.93) times more than that in the normal control group, showing significant differences among the four groups (F=13.320, P=0.024). The expressions of bax and TGF-β₂ protein in the light-exposure 24-hour group were about 1.85 times and 2 times higher than those in the normal control group respectively. The absorption luminosity value (A₅₇₀) was 0.959±0.058 in the normal control group, which was significantly higher than 0.897±0.093 in the light-exposure 24-hour group (t=-3.130, P=0.003).

Light-exposure with illumination of 20 000 lx results in oxidative damage and apoptosis of human LECs in vitro. Bax and TGF-β₂ probably participate in damage of LECs induced by light-exposure.