Diurnal variations of triglyceride accumulation in mouse and bovine adipocyte-derived cell lines

Several studies have suggested a strong interaction between the circadian clock and lipid metabolism in mammals. The circadian clock is driven by endogenous cyclic gene expression patterns, commonly referred to as clock genes, and transcription-translation negative feedback loops. Clock genes regulate the transcription of some lipid metabolism-related genes; however, the relationship between the circadian clock and triglyceride (TG) accumulation at the cellular level remains unclear. Here, we evaluated rhythms of intracellular TG accumulation levels as well as the expression of clock genes and lipid metabolism-related genes for 54 h in mouse and bovine adipose-derived cell cultures. To the best of our knowledge, this study represents the first report demonstrating that TG accumulation exhibits diurnal variations, with the pattern differing among cell types. Furthermore, we found that expression of clock genes and corresponding lipid metabolism-related genes exhibited circadian rhythms. Our results suggest that the cellular clock regulates lipid metabolism-related genes to relate circadian rhythms of TG accumulation in each cell type. We anticipate that the amount of fat stored depends on the timing of the supply of glucose-the precursor of fat. The findings of this study will contribute to the advancement of chrono-nutrition.