Aims: Clock genes that are synchronised to the light-dark cycle can influence cellular processes in the liver. We aimed to determine the effect of rapid alterations in the light-dark cycle on energy balance and liver metabolism.
Methods: 8wk old male C57BL/6 mice were separated into 4 groups (N=40/group, 2groups standard laboratory diet (SLD), 2groups high-fat diet (HFD)). After 4wks of 12:12hr light:dark, the light cycle was rotated twice a week for one group/diet for 8wks. 8 mice from each group were placed in metabolic monitoring cages. At 12wks mice were killed at 3 hour intervals (N=5/group/time point) starting at 1800hrs.
Results: SLD mice in a rotating light cycle (SLD-RL) gained more weight that SLD mice in a normal light cycle (SLD-NL). There was no difference in weight gain between HFD-NL and HFD-RL. Blood glucose levels were higher in RL compared to NL mice in both diet groups. RL mice accessed food more during the light phase (LP) compared to NL mice on both diets but not in the dark phase (DP). SLD-RL mice showed a greater meal size only during the LP compared to SLD-NL mice. HFD-RL mice did not show any difference in meal size compared to HFD-NL mice.
SLD-RL mice had decreased energy expenditure compared to SLD-NL mice during the DP. There was no difference in energy expenditure between HFD-NL and HFD-RL mice.
RL mice had increased hepatic triglycerides compared to NL mice on both diets. Hepatic mRNA expression of Glut2, insulin receptor-β, glycogen synthase 2, and Acetyl-CoA carboxylase showed circadian variation in SLD-NL and HFD-NL mice, with upregulation and phase shifts in SLD-RL rhythms. Rhythms were ablated in HFD-RL mice.
Conclusions: Rapid light cycle rotation causes increased body mass in SLD-RL mice combined with increased glucose uptake and increased fatty acid synthesis.