Lack of food intake during shift work alters the heart transcriptome and leads to cardiac tissue fibrosis and inflammation in rats.

BACKGROUND: Many epidemiological studies revealed that shift work is associated with an increased risk of a number of pathologies, including cardiovascular diseases. An experimental model of shift work in rats has additionally been shown to recapitulate aspects of metabolic disorders observed in human shift workers, including increased fat content and impaired glucose tolerance, and used to demonstrate that restricting food consumption outside working hours prevents shift work-associated obesity and metabolic disturbance. However, the way distinct shift work parameters, such as type of work, quantity, and duration, affect cardiovascular function and the underlying mechanisms, remains poorly understood. Here, we used the rat as a model to characterize the effects of shift work in the heart and determine whether they can be modulated by restricting food intake during the normal active phase. RESULTS: We show that experimental shift work reprograms the heart cycling transcriptome independently of food consumption. While phases of rhythmic gene expression are distributed across the 24-h day in control rats, they are clustered towards discrete times in shift workers. Additionally, preventing food intake during shift work affects the expression level of hundreds of genes in the heart, including genes encoding components of the extracellular matrix and inflammatory markers found in transcriptional signatures associated with pressure overload and cardiac hypertrophy. Consistent with this, the heart of shift worker rats not eating during work hours, but having access to food outside of shift work, exhibits increased collagen 1 deposition and displays increased infiltration by immune cells. While maintaining food access during shift work has less effects on gene expression, genes found in transcriptional signatures of cardiac hypertrophy remain affected, and the heart of shift worker rats exhibits fibrosis without inflammation. CONCLUSIONS: Together, our findings unraveled differential effects of food consumption on remodeled transcriptional profiles of the heart in shift worker rats. They also provide insights into how shift work affects cardiac function and suggest that some interventions aiming at mitigating metabolic disorders in shift workers may have adverse effects on cardiovascular diseases.

Manipulation of Rhythmic Food Intake in Mice Using a Custom-Made Feeding System.

Rhythmic gene expression is a hallmark of the circadian rhythm and is essential for driving the rhythmicity of biological functions at the appropriate time of day. Studies over the last few decades have shown that rhythmic food intake (i.e., the time at which organisms eat food during the 24 h day), significantly contributes to the rhythmic regulation of gene expression in various organs and tissues throughout the body. The effects of rhythmic food intake on health and physiology have been widely studied ever since and have revealed that restricting food intake for 8 h during the active phase attenuates metabolic diseases arising from a variety of obesogenic diets. These studies often require the use of controlled methods for timing the delivery of food to animals. This manuscript describes the design and use of a low-cost and efficient system, built in-house for measuring daily food consumption as well as manipulating rhythmic food intake in mice. This system entails the use of affordable raw materials to build cages suited for food delivery, following a user-friendly handling procedure. This system can be used efficiently to feed mice on different feeding regimens such as ad libitum, time-restricted, or arrhythmic schedules, and can incorporate a high-fat diet to study its effect on behavior, physiology, and obesity. A description of how wild-type (WT) mice adapt to the different feeding regimens is provided.

Clock-controlled rhythmic transcription: is the clock enough and how does it work?

Circadian clocks regulate the rhythmic expression of thousands of genes underlying the daily oscillations of biological functions. Here, we discuss recent findings showing that circadian clock rhythmic transcriptional outputs rely on additional mechanisms than just clock gene DNA binding, which may ultimately contribute to the plasticity of circadian transcriptional programs.

Rhythmic Food Intake Drives Rhythmic Gene Expression More Potently than the Hepatic Circadian Clock in Mice.

Every mammalian tissue exhibits daily rhythms in gene expression to control the activation of tissue-specific processes at the most appropriate time of the day. Much of this rhythmic expression is thought to be driven cell autonomously by molecular circadian clocks present throughout the body. By manipulating the daily rhythm of food intake in the mouse, we here show that more than 70% of the cycling mouse liver transcriptome loses rhythmicity under arrhythmic feeding. Remarkably, core clock genes are not among the 70% of genes losing rhythmic expression, and their expression continues to exhibit normal oscillations in arrhythmically fed mice. Manipulation of rhythmic food intake also alters the timing of key signaling and metabolic pathways without altering the hepatic clock oscillations. Our findings thus demonstrate that systemic signals driven by rhythmic food intake significantly contribute to driving rhythms in liver gene expression and metabolic functions independently of the cell-autonomous hepatic clock.

Tissue-specific BMAL1 cistromes reveal that rhythmic transcription is associated with rhythmic enhancer-enhancer interactions.

The mammalian circadian clock relies on the transcription factor CLOCK:BMAL1 to coordinate the rhythmic expression of thousands of genes. Consistent with the various biological functions under clock control, rhythmic gene expression is tissue-specific despite an identical clockwork mechanism in every cell. Here we show that BMAL1 DNA binding is largely tissue-specific, likely because of differences in chromatin accessibility between tissues and cobinding of tissue-specific transcription factors. Our results also indicate that BMAL1 ability to drive tissue-specific rhythmic transcription is associated with not only the activity of BMAL1-bound enhancers but also the activity of neighboring enhancers. Characterization of physical interactions between BMAL1 enhancers and other cis-regulatory regions by RNA polymerase II chromatin interaction analysis by paired-end tag (ChIA-PET) reveals that rhythmic BMAL1 target gene expression correlates with rhythmic chromatin interactions. These data thus support that much of BMAL1 target gene transcription depends on BMAL1 capacity to rhythmically regulate a network of enhancers.