Effects of bright light exposure during daytime on peripheral clock gene expression in humans
Light is the strongest synchronizer controlling circadian rhythms. The intensity and duration of light change throughout the year, thereby influencing body weight, food preferences, and melatonin secretion in humans and animals. Although the expression of clock genes has been examined using human samples, it currently remains unknown whether bright light during the daytime affects the expression of these genes in humans. Therefore, we herein investigated the effects of bright light exposure during the daytime on clock gene expression in the hair follicular and root cells of the human scalp. Seven healthy men (20.4 ± 2.2 years old; 172.3 ± 5.8 cm; 64.3 ± 8.5 kg; BMI 21.7 ± 3.1 kg/m2, mean ± SD) participated in this study. Subjects completed 3-day experimental sessions twice in 1 month during which they were exposed to bright and dim light conditions. The mRNA expression of Per1–3, Cry1–2, Rev-erb-α (Nr1d1), Rev-erb-β (Nr1d2), and Dec1 was analyzed using branched DNA probes. No significant changes were observed in the expression of Per1, Per2, Per3, Cry1, Cry2, Rev-erb-α (Nr1d1), or Dec1 following exposure to bright light conditions. However, the expression of Rev-erb-β (Nr1d2) tended to be stronger under bright light than dim light conditions. These results suggest that the bright light stimulus did not influence the expression of clock genes in humans. Long-lasting bright light exposure during the daytime may be required to change the expression of clock genes in humans.
KeywordsBright light Biological rhythm Hair follicular and root cells Clock genes Human
This research was partly supported by the Japan Society for the Promotion of Science grant no. 23370106 to TM. This work was also supported by a Grant-in-Aid for Scientific Research of Japan (MotohikoS) and the Toyoaki Scholarship Foundation (MotohikoS). We thank the Meijo University for loaning us the BioPlex 200 instrument to measure clock gene expression.
Compliance with ethical standards
All subjects gave written informed consent before the experiment, which was approved by the Ethics Committee, Fukuoka Women’s University, and adhered to the guidelines advocated by Chronobiology International.
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