Effect of hyperlipidemia on the expression of circadian genes in apolipoprotein E knock-out atherosclerotic mice

Abstract

Background: Circadian patterns of cardiovascular vulnerability were well characterized, with a peak incidence of acute myocardial infarction and stroke secondary to atherosclerosis in the morning, which showed the circadian clock may take part in the pathological process of atherosclerosis induced by hyperlipidemia. Hence, the effect of hyperlipidemia on the expression of circadian genes was investigated in atherosclerotic mouse model.

Results: In apoE-/-mice on regular chow or high-fat diet, an atherosclerotic mouse model induced by heperlipidemia, we found that the peak concentration of serum lipids was showed four or eight hours later in apoE-/- mice, compared to C57BL/6J mice. During the artificial light period, a reduce in circulating level of serum lipids corresponded with the observed increase of the expression levels of some the transcription factors involved in lipid metabolism, such as PPARalpha and RXRalpha. Meanwhile, the expression of circadian genes was changed following with amplitude reduced or the peak mRNA level delayed.

Conclusions: Our studies indicated that heperlipidemia altered both the rhythmicity and expression of circadian genes. Diet-induced circadian disruption may affect the process of atherosclerosis and some acute cardiovascular disease.

Figure 1

Concentration of serum cholesterol, LDL-CHO and HDL-CHO in the serum of apoE-/- and C57BL/6J mice. (A)*P < 0.05 vs C57BL/6J mice and apoE-/-mice fed with regular chow; ^#P < 0.01 vs C57BL/6J mice fed with regular chow and apoE-/-mice fed with a high-fat diet. (B) *P < 0.05 vs CT16 in HF-fed apoE-/-mice; ^#P < 0.01 vs CT12 in apoE-/-mice on RC

Figure 2

Atherosclerotic plaques or foam cells showed by oil red O staining in frozen sections of aorta roots of the mice. (A) Atherosclerotic plaque formed in apoE-/- mouse aortas fed with a high-fat diet, ×100. (B) C57BL/6J mouse, ×100. (C) Foam cells were found in apoE-/- mouse aorta roots, ×100. (D) The rectangle in Fig C shows foam cells under the endothelium, ×400.

Figure 3

Diurnal variation of circaidan gene mRNA levels in SCN of C57BL/6J and apoE-/- mice. The experiment has been repeated three times with similar results. The data from three experiments was normalized to GAPDH mRNA and represented as fold increase over CT0 of C57BL/6J mice. (A) ^#P < 0.05 vs CT8 in C57BL/6J and apoE-/- mice fed with regular chow; *P < 0.05 vs CT8 in HF-fed apoE-/- mice. (B) ^#P < 0.05 vs CT4 in C57BL/6J and apoE-/- mice fed with regular chow; *P < 0.05 vs CT8 in HF-fed apoE-/- mice. (D) ^#P < 0.05 vs CT0 or CT20 in C57BL/6J and apoE-/- mice fed with regular chow; *P < 0.05 vs CT20 in HF-fed apoE-/- mice

Figure 4

Diurnal variation of circadian gene mRNA in hearts of C57BL/6J and apoE-/- mice. The experiment has been repeated three times with similar results. The data from three experiments was normalized to GAPDH mRNA and represented as fold increase over CT0 of C57BL/6J mice. (A)*P < 0.01 vs CT0, CT12 and CT16 in apoE-/- mice fed with regular chow or a high-fat diet. (B)^#P < 0.05 vs CT12 and CT16 in C57BL/6J and apoE-/- mice fed with regular chow. (D) *P < 0.05 vs CT0, CT4, CT12 and CT16 in apoE-/- mice on RC or HF diets

Figure 5

Diurnal variation of circadian gene mRNA in livers of C57BL/6J and apoE-/- mice. The experiment has been repeated three times with similar results. The data from three experiments was normalized to GAPDH mRNA and represented as fold increase over CT0 of C57BL/6J mice. (A)*P < 0.05 vs CT0, CT8, CT12 and CT20 in apoE-/- mice on RC or HF diets;^#P < 0.05 vs CT0, CT16 and CT20 in C57BL/6J mice and apoE-/-mice fed with regular chow (B)*P < 0.05 vs CT8, CT12, CT16 and CT20 in apoE-/- mice on RC or HF diets; ^#P < 0.05 vs CT20 in C57BL/6J mice and apoE-/-mice fed with regular chow (C)*P < 0.05 vs CT12 and CT16 in apoE-/- mice on RC or HF diet (D)*P < 0.05 vs CT0, CT8 and CT12 in apoE-/- mice on RC or HF diets

Figure 6

Diurnal variation of transcription factor Rev-erbα mRNA of C57BL/6J and apoE-/- mice. The experiment has been repeated three times with similar results. The data from three experiments was normalized to GAPDH mRNA and represented as fold increase over CT0 of C57BL/6J mice. (A)*P < 0.05 vs CT0 in apoE-/- mice on RC or HF diets. (B)*P < 0.05 vs CT0, CT8 and CT12 in apoE-/- mice on RC or HF diets. (C)*P < 0.01 vs CT0 in apoE-/- mice on RC or HF diets; ^#P < 0.05 vs CT8 in C57BL/6J and apoE-/- mice fed with regular chow;**P < 0.05 vs CT4 in C57BL/6J and HF-fed apoE-/- mice

Figure 7

Diurnal variation of transcription factors PPARα and RXRα mRNA of C57BL/6J and apoE-/- mice. The experiment has been repeated three times with similar results. The data from three experiments was normalized to GAPDH mRNA and represented as fold increase over CT0 of C57BL/6J mice. (A)*P < 0.01 vs CT0, CT4 and CT8 in C57BL/6J and apoE-/- mice fed with regular chow (B)*P < 0.01 vs CT0, CT4 and CT8 in C57BL/6J and apoE-/- mice fed with regular chow