Alterations in Per2 , Bcl2 gene expression, and oxidative status in aged rats liver after light pulse at night.

The aging process is characterized by circadian rhythm disruption, in physiology and behavior, which could result from weak entrainment. Light is the most potent cue that entrains the central circadian clock, which in turn synchronizes peripheral clocks in animal tissues. Period 2 (Per2 ) is one of the clock genes that respond to light. Moreover, oxidative stress could entrain the clock. Therefore, the present work aimed to investigate the role of light when applied late at night on the Per2 , B cell lymphoma 2 ( Bcl2 ) gene expression, and oxidative status in aged rats. Aged rats were divided into a control group and a group exposed to a 30-min light pulse applied daily during the subjective night at 5 am (ZT 22) for 4 weeks. Per2 and Bcl2 gene expression were quantified in liver tissue. To evaluate oxidative status, Glutathione (GSH), nitric oxide (NO), and malondialdehyde (MDA) were estimated. The light pulse reduced the expression levels of Per2 and Bcl2 mRNA. Although it diminished the levels of malondialdehyde (MDA), nitric oxide (NO) levels were elevated and the glutathione (GSH) levels were declined. In conclusion, the light pulse late at night abolished Per2 mRNA circadian rhythm and reduced its expression in the liver of the aged rat. Similarly, it diminished the anti-apoptotic gene expression, Bcl2 . Moreover, it might attenuate oxidative stress through the reduction in MDA levels.