Chronic environmental circadian disruption increases atherosclerosis and dyslipidemia in female, but not male, ApolipoproteinE-deficient mice.

Shift work chronically disrupts circadian rhythms and increases the risk of developing cardiovascular disease. However, the mechanisms linking shift work and cardiovascular disease are largely unknown. The goal of this study was to investigate the effects of chronically shifting the light-dark (LD) cycle, which models the disordered exposure to light that may occur during shift work, on atherosclerosis. Atherosclerosis is the progressive accumulation of lipid-filled lesions within the artery wall and is the leading cause of cardiovascular disease. We studied ApolipoproteinE-deficient (ApoE -/- ) mice that are a well-established model of atherosclerosis. Male and female ApoE -/- mice were housed in control 12L:12D or chronic LD shift conditions for 12 weeks and fed low-fat diet. In the chronic LD shift condition, the light-dark cycle was advanced by 6 h every week. We found that chronic LD shifts exacerbated atherosclerosis in female, but not male, ApoE -/- mice. In females, chronic LD shifts increased total serum cholesterol concentrations with increased atherogenic VLDL/LDL particles. Chronic LD shifts did not affect food intake, activity, or body weight in male or female ApoE -/- mice. We also examined eating behavior in female ApoE -/- mice since aberrant meal timing has been linked to atherosclerosis. The phases of eating behavior rhythms, like locomotor activity rhythms, gradually shifted to the new LD cycle each week in the chronic LD shift group, but there was no effect of the LD shift on the amplitudes of the eating rhythms. Moreover, the duration of fasting intervals was not different in control 12L:12D compared to chronic LD shift conditions. Together these data demonstrate that female ApoE -/- mice have increased atherosclerosis when exposed to chronic LD shifts due to increased VLDL/LDL cholesterol, independent of changes in energy balance or feeding-fasting cycles.

High-fat feeding disrupts daily eating behavior rhythms in obesity-prone but not in obesity-resistant male inbred mouse strains.

Abnormal meal timing, like skipping breakfast and late-night snacking, is associated with obesity in humans. Disruption of daily eating rhythms also contributes to obesity in mice. When fed a high-fat diet, male C57BL/6J mice have disrupted eating behavior rhythms and they become obese. In contrast to obesity-prone C57BL/6J mice, some inbred strains of mice are resistant to high-fat diet-induced obesity. In this study, we sought to determine whether there are distinct effects of high-fat feeding on daily eating behavior rhythms in obesity-prone and obesity-resistant male mice. Male obesity-prone (C57BL/6J and 129X1/SvJ) and obesity-resistant (SWR/J and BALB/cJ) mice were fed low-fat diet or high-fat diet for 6 wk. Consistent with previous studies, obesity-prone male mice gained more weight and adiposity during high-fat diet feeding than obesity-resistant male mice. The amplitude of the daily rhythm of eating behavior was markedly attenuated in male obesity-prone mice fed high-fat diet, but not in obesity-resistant males. In contrast, high-fat feeding did not differentially affect locomotor activity rhythms in obesity-prone and obesity-resistant male mice. Together, these data suggest that regulation of the daily rhythm of eating may underlie the propensity to develop diet-induced obesity in male mice.

Circadian disruption with constant light exposure exacerbates atherosclerosis in male ApolipoproteinE-deficient mice.

Disruption of the circadian system caused by disordered exposure to light is pervasive in modern society and increases the risk of cardiovascular disease. The mechanisms by which this happens are largely unknown. ApolipoproteinE-deficient (ApoE-/-) mice are studied commonly to elucidate mechanisms of atherosclerosis. In this study, we determined the effects of light-induced circadian disruption on atherosclerosis in ApoE-/- mice. We first characterized circadian rhythms of behavior, light responsiveness, and molecular timekeeping in tissues from ApoE-/- mice that were indistinguishable from rhythms in ApoE+/+ mice. These data showed that ApoE-/- mice had no inherent circadian disruption and therefore were an appropriate model for our study. We next induced severe disruption of circadian rhythms by exposing ApoE-/- mice to constant light for 12 weeks. Constant light exposure exacerbated atherosclerosis in male, but not female, ApoE-/- mice. Male ApoE-/- mice exposed to constant light had increased serum cholesterol concentrations due to increased VLDL/LDL fractions. Taken together, these data suggest that ApoE-/- mice are an appropriate model for studying light-induced circadian disruption and that exacerbated dyslipidemia may mediate atherosclerotic lesion formation caused by constant light exposure.