Effects of altered photoperiod on circadian clock and lipid metabolism in rats

ABSTRACT

Disruption of circadian clock timekeeping due to changes in the photoperiod enhances the risk of lipid metabolism disorders and metabolic syndrome. However, the effects of altered photoperiods on the circadian clock and lipid metabolism are not well understood. To explore the effects of altered photoperiods, we developed a rat model where rats were exposed to either short-day or long-day conditions. Our findings demonstrated that altered photoperiods mediated circadian clocks by partly disrupting rhythmicity and shifting phase values of clock genes. We also showed that compared to long-day conditions, rats under short-day conditions exhibited more photoperiodic changes in a variety of physiological outputs related to lipid metabolism, such as significant increases in serum triglyceride (TG), high-density lipoprotein, and leptin levels, as well as increased body weight, fat:weight ratio, and hepatic TG levels. These increments were gained possibly through upregulated expression of forkhead box O1 (FoxO1), which partly mediates the expression of peroxisome proliferator-activated receptorα (PPARα) to increase the expression of phosphoenolpyruvate carboxykinase (PEPCK), peroxisome proliferator-activated receptor-g coactivator-1β (PGC1β), and fatty acid synthase (Fasn). In addition, the oscillation rhythms of FoxO1, PEPCK, PGC1β, and Fasn expression levels in the livers of rats exposed to a short-day photoperiod were more robust than those exposed to a long-day photoperiod. These findings suggest that a change in photoperiod can partly disrupt the circadian rhythmcity of clock genes, impair lipid metabolism, and promote obesity.

KEYWORDS:

• Circadian clock
• light–dark cycle
• lipid metabolism
• obesity
• transcription factor

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.

Funding

This work was supported by a grant from National Natural Science Foundation of China (No. 31200890) and Program for Changjiang Scholars and Innovative Research Team in University (IRT_17R97).

Additional information

Funding

This work was supported by a grant from National Natural Science Foundation of China (No. 31200890) and Program for Changjiang Scholars and Innovative Research Team in University (IRT_17R97).