Effect of light rhythm on the expression of cryptochrom 2 in retina / 中华实验眼科杂志

ABSTRACT

Background The cryptochrom 2 (Cry2)in mammalian retina is a main influential factor of circadian clock.Objective Purpose of this study was to investigate the effect of light exposure rhythm on expression of Cry2 in retina.Methods Thirty clean healthy Sprague Dawley(SD)rats were collected and divided into two groups randomly.The rats of the control group exposed to natural light with the normal rhythm for 30 days,but rats of the experimental group exposed to the artificial light (light dark =18 hours6 hours) for 3 months with the light intensity of(533± 16)lx.The histopathological change and ultrastructural alteration of rat retina in both groups were examined under the light microscope and transmission electron microscope at the end of the experiment.Expressions of Cry2 protein and its mRNA were assayed by immunohistochemistry and quantitative PCR(Q-PCR).Results The rat retinal morphology and ultrastructure were clear and order-arranged under the light microscope and transmission electron microscope in the control group.However,atrophy and disorganization of retina were found under the light microscope,and liquefaction and vacuole of outer segments of photoreceptors were observed.The vacuolar degeneration of mitochondria in the inner segments of photoreceptors,cellular nuclear shrinkage,chromatin margination,nuclear notch and destruction were seen in the outer nuclear layer under the transmission electron microscope.Immunohistochemistry showed that the expression of Cry2 protein located in cytoplasm and nuclei membrane of the retinal ganglion cell layer and inner nuclear layer in both normal rats and experimental rats.The scores of Cry2 protein expression were 0.833±0.197 in the experimental group,and 1.700±0.245 in the control group,with a significant difference between them (P=0.009).The quantities of Cry2 mRNA were 0.962 ± 0.125 in the control group and 0.615±0.100 in the experimental group,showing a significant difference between the two groups (P =0.006).Conclusions Long-term light exposure under the 533 lx leads to retinal structural and functional damage probably by down-regulating Cry2 expression in retina.Whether the regulation of Cry2 expression is helpful for stabilizing the biorhythm or not is a worthy question to explore.