Loss of circadian rhythm of circulating insulin concentration induced by high-fat diet intake is associated with disrupted rhythmic expression of circadian clock genes in the liver.

OBJECTIVE: Peripheral clock genes show a circadian rhythm is correlated with the timing of feeding in peripheral tissues. It was reported that these clock genes are strongly regulated by insulin action and that a high-fat diet (HFD) intake in C57BL/6J mice for 21days induced insulin secretion during the dark phase and reduced the circadian rhythm of clock genes. In this study, we examined the circadian expression patterns of these clock genes in insulin-resistant animal models with excess secretion of insulin during the day. MATERIALS/METHODS: We examined whether insulin resistance induced by a HFD intake for 80days altered blood parameters (glucose and insulin concentrations) and expression of mRNA and proteins encoded by clock and functional genes in the liver using male ICR mice. RESULTS: Serum insulin concentrations were continuously higher during the day in mice fed a HFD than control mice. Expression of lipogenesis-related genes (Fas and Accß) and the transcription factor Chrebp peaked at zeitgeber time (ZT)24 in the liver of control mice. A HFD intake reduced the expression of these genes at ZT24 and disrupted the circadian rhythm. Expression of Bmal1 and Clock, transcription factors that compose the core feedback loop, showed circadian variation and were synchronously associated with Fas gene expression in control mice, but not in those fed a HFD. CONCLUSIONS: These results indicate that the disruption of the circadian rhythm of insulin secretion by HFD intake is closely associated with the disappearance of circadian expression of lipogenic and clock genes in the liver of mice.