High-fat feeding exerts minimal effects on rhythmic mRNA expression of clock genes in mouse peripheral tissues

Recent studies have suggested that the impairment of the circadian molecular clock in peripheral tissues, including adipose tissue, is involved in the development of metabolic syndrome. Although the disorder is often caused by dietary obesity, it remains to be elucidated whether dietary obesity or high-caloric intake per se affects the molecular clock system. To address this issue, this study investigated the effect of high-fat feeding on the rhythmic mRNA expression of clock genes (Clock, Bmal1, Per1, Per2, Cry1, Cry2, and Dbp) in mouse visceral adipose tissue and liver. Mice fed a high-fat diet for 8 wks developed a mild but overt metabolic syndrome of obesity, hyperlipidemia, and hyperglycemia. However, the high-fat feeding had only minimal effects on the rhythmic expression of the clock genes examined in both tissues. On the other hand, daily rhythmicity in the transcript level of cholesterol 7alpha-hydroxylase, a hepatic enzyme controlling circadian cholesterol homeostasis, disappeared in the mice on high-fat chow. These results suggest that high-fat feeding and mild metabolic syndrome scarcely alter the molecular clock system in mouse peripheral tissues, and that physiological circadian rhythms could be affected without altering the system. Further studies are needed to better understand the role of the circadian molecular clock in the development of metabolic syndrome. The first two authors contributed equally to this study.