Timed high-fat diet in the evening affects the hepatic circadian clock and PPARα-mediated lipogenic gene expressions in mice

Abstract

A long-term high-fat diet may result in a fatty liver. However, whether or not high-fat diets affect the hepatic circadian clock is controversial. The objective of this study is to investigate the effects of timed high-fat diet on the hepatic circadian clock and clock-controlled peroxisome proliferator-activated receptor (PPAR) α-mediated lipogenic gene expressions. Mice were orally administered high-fat milk in the evening for 4 weeks. The results showed that some hepatic clock genes, such as Clock, brain-muscle-Arnt-like 1 (Bmal1), Period 2 (Per2), and Cryptochrome 2 (Cry2) exhibited obvious changes in rhythms and/or amplitudes. Alterations in the expression of clock genes, in turn, further altered the circadian rhythm of PPARα expression. Among the PPARα target genes, cholesterol 7α-hydroxylase (CYP7A1), 3-hydroxy-3-methylglutaryl-coenzyme A reductase, low-density lipoprotein receptor, lipoprotein lipase, and diacylglycerol acyltransferase (DGAT) showed marked changes in rhythms and/or amplitudes. In particular, significant changes in the expressions of DGAT and CYP7A1 were observed. The effects of a high-fat diet on the expression of lipogenic genes in the liver were accompanied by increased hepatic cholesterol and triglyceride levels. These results suggest that timed high-fat diets at night could change the hepatic circadian expressions of clock genes Clock, Bmal1, Per2, and Cry2 and subsequently alter the circadian expression of PPARα-mediated lipogenic genes, resulting in hepatic lipid accumulation.

Fig. 1

Histopathological changes in mouse hepatic tissues (HE staining, ×40). No steatosis was observed in matched control mice (a) and 1/3 to 2/3 of hepatocytes filled with empty lipid vacuoles were seen in high-fat milk-fed mice (b)

Fig. 2

Hepatic TC, TG, and FFA contents in mice fed with high-fat milk in the evening for 4 weeks. White circles represent the matched control group, and black circles represent the high-fat milk-fed group. Values indicate the mean ± SD of n = 6 mice per group for each time point. ^#P < 0.05, ^##P < 0.01 versus the matched control group at the same time point

Fig. 3

Hepatic Clock, Bmal1, Per1, Per2, Cry1, and Cry2 mRNA expressions in mice fed with high-fat milk in the evening for 4 weeks. White circles represent the matched control group, and black circles represent the high-fat milk-fed group. C: the matched control group; HF: the high-fat milk group. Values indicate the mean ± SD of n = 6 mice per group for each time point. Gene bands were quantified relative to GAPDH. ^#P < 0.05 versus the matched control group at the same time point

Fig. 4

Hepatic PPARα and lipogenic genes CYP7A1, HMGCR, LDLR, LPL, DGAT, and FAS mRNA expressions in mice fed with high-fat milk in the evening for 4 weeks. White circles represent the matched control group, and black circles represent the high-fat milk-fed group. C: the matched control group; HF: the high-fat milk group. Values indicate the mean ± SD of n = 6 mice per group for each time point. Gene bands were quantified relative to GAPDH. ^#P < 0.05, ^##P < 0.01 versus the matched control group at the same time point