Flicker light can induce myopia, but its mechanism remains unclear. As one of immediate early genes, early growth response-1(Egr-1) gene can generate rapid response to visual stimulation, however, its effect on the formation and development of myopia is below understood.

This study was to investigate the dynamic expression of Egr-1 gene in retinas of flicker light-induced eyes (FL) and compare the results with form deprived eyes (FD).

One hundred and fifty 28-day-old C57BL/6J mice were randomly assigned to the normal control group, FD group and FL group. The right eyes of mice were occluded with a semitransparent hemispherical thin plastic shell for 2 weeks in the FD group, and the right eyes of mice were stimulated by 2 Hz flicker light for 2 weeks in the FL group, and then the mice were fed in the normal light environment for 1 week. The refractive state and axial length of the model eyes were measured by murine-specific eccentric infrared photorefraction and A-scan ultrasonography before modeling and 1 hour, 1 day, 1 week, 2 weeks after modeling as well as 1 week after termination, respectively. The mice were sacrificed in above-mentioned time points to isolate the retinas. The expressions and location of Egr-1 protein and mRNA in the retinas were detected by Western blot, and reverse transcription PCR (RT-PCR) and immunochemistry. The expressions of Egr-1 markers, neuron and protein kinase C (PKC)-α, in the retinas were assayed by using immunofluorescence. The care and use of the animals followed the administration regulations for experimental animals of Jiangsu Province.

Two weeks after modeling, the refraction of the FL group was (0.32±0.14)D, which was significantly lower than (-0.66±0.43)D in the FD group (t=6.78, P=0.00). One hour after modeling, The expression levels of Egr-1 mRNA in mouse retinas were 0.626±0.044 and 0.695±0.058 in the FD group and FL group, which were significantly declined in comparison with 1.009±0.089 of the normal group (t=14.81, P=0.01; t=9.15, P=0.03). In 2 weeks after modeling, the expression levels of Egr-1 mRNA were still lower in the FD group and FL group compared with the normal group (all at P<0.05). However, the expression levels were significantly elevated in the FD group and FL group compared with the normal group (t=4.13, P=0.01; t=4.26, P=0.01) at 1 week after termination. Western blot showed a dynamic decrease in the expressions of Egr-1 protein with lapse of time in the FD group and FL group with the lowest expressing level in the second week after modeling. In 1 week after termination of modeling, the expressing level was raised in the FD group or the FL group, but it was still lower than that in the normal group (t=6.32, P=0.00; t=5.45, P=0.01). Egr-1 protein was mainly expressed in the retinal ganglion cell (RGC) layer, inner nuclear layer and photoreceptor layer in the normal mice, and the expression intensity was obviously weaker in the FD mice and FL mice 2 weeks after modeling. However, the expression was enhanced in 1 week after termination of modeling. Neuron and PKC-α were strongly expressed in the RGCs and bipolar cells in the normal mice.

The eyes show a myopic trend after induce of flicker light in B6 mice. The expression level of Egr-1 gene in the retina down-regulates with the reduce of refraction in FL eyes, and its dynamic expressing change is consistent between the FD eyes and FL eyes.

Refraction, ocular/physiology; Myopia; Early growth response protein 1/genetics; Sensory deprivation; Light; Mice, inbred C57BL; Disease model, animal