Various biological processes show seasonal variations in humans, including important metabolic pathways. Seasonal changes in gene expression may affect annual differences in human immunity. We hypothesized that seasonal changes occur in clock gene expression levels that are associated with body mass index. Six non-obese men and five obese men participated in summer and winter. Two milliliters of saliva were collected, and total RNA was isolated from buccal epithelial cells in saliva. The clock gene expression levels of CLOCK, BMAL1, PER1, CRY2, REV-ERB-α, and REV-ERB-ß were examined by real-time PCR. Blood samples were measured HbA1c, glucose, insulin, adiponectin, IL-6, and TNF-α. Participants were asked about their sleeping hours and seasonal pattern. In the present study, CLOCK, BMAL1, and REV-ERB-β gene expression levels were significantly lower in winter than in summer; BMAL1 expression level was significantly lower in obese men than in non-obese. Concentrations of adiponectin and insulin were significantly different between obese and non-obese. No significant seasonal effects were observed in HbA1c, glucose, insulin, adiponectin, IL-6, or TNF-α concentrations. Sleep duration did not significantly differ between summer and winter. The short photoperiod during winter might contribute to seasonal alterations in the expression of clock genes in men. In the present results, revealed seasonal differences in clock gene expression levels might be associated with obesity. These results also showed the potential for measuring clock gene expression in a non-invasive manner using saliva samples.
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The authors wish to acknowledge the volunteers who participated in this study. We thank Dr. Yoshimi Niwa of Institute Transformative Bio-Molecules (ITbM), Nagoya University, for providing primer information. We also thank Institute of Comprehensive Medical Research, Division of Advanced Research Promotion at Aichi Medical University, for providing the equipment for the measurements.
This research was supported by the Japan Society for the Promotion of Science grants (no. 15K16529 and no. 18K06453) to Maki Sato.
Ethics approval and consent to participate
The present study was approved by the Ethics Committee of Aichi Medical University School of Medicine, Aichi, Japan, and was performed in accordance with the Declaration of Helsinki.
The authors declare no competing interests.
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Sato, M., Hayashi, H. & Kanikowska, D. Seasonal differences in clock gene expression levels in buccal epithelial cells of obese men: a pilot study. Int J Biometeorol (2021). https://doi.org/10.1007/s00484-021-02092-2