The process of aging and circadian rhythms are intimately intertwined, but how peripheral clocks involved in metabolic homeostasis contribute to aging remains unknown. Importantly, caloric restriction (CR) extends lifespan in several organisms and rewires circadian metabolism. Using young versus old mice, fed ad libitum or under CR, we reveal reprogramming of the circadian transcriptome in the liver. These age-dependent changes occur in a highly tissue-specific manner, as demonstrated by comparing circadian gene expression in the liver versus epidermal and skeletal muscle stem cells. Moreover, de novo oscillating genes under CR show an enrichment in SIRT1 targets in the liver. This is accompanied by distinct circadian hepatic signatures in NAD-related metabolites and cyclic global protein acetylation. Strikingly, this oscillation in acetylation is absent in old mice while CR robustly rescues global protein acetylation. Our findings indicate that the clock operates at the crossroad between protein acetylation, liver metabolism, and aging.

Disruption of the circadian rhythm is a contributory factor to clinical and pathophysiological conditions, including cancer, the metabolic syndrome, and inflammation. Chronic and systemic inflammation are a potential trigger of type 2 diabetes and cardiovascular disease and are caused by the infiltration of large numbers of inflammatory macrophages into tissue. Although recent studies identified the circadian clock gene Rev-erbα, a member of the orphan nuclear receptors, as a key mediator between clockwork and inflammation, the molecular mechanism remains unknown. In this study, we demonstrate that Rev-erbα modulates the inflammatory function of macrophages through the direct regulation of Ccl2 expression. Clinical conditions associated with chronic and systemic inflammation, such as aging or obesity, dampened Rev-erbα gene expression in peritoneal macrophages from C57BL/6J mice. Rev-erbα agonists or overexpression of Rev-erbα in the murine macrophage cell line RAW264 suppressed the induction of Ccl2 following an LPS endotoxin challenge. We discovered that Rev-erbα represses Ccl2 expression directly through a Rev-erbα–binding motif in the Ccl2 promoter region. Rev-erbα also suppressed CCL2-activated signals, ERK and p38, which was recovered by the addition of exogenous CCL2. Further, Rev-erbα impaired cell adhesion and migration, which are inflammatory responses activated through the ERK- and p38-signaling pathways, respectively. Peritoneal macrophages from mice lacking Rev-erbα display increases in Ccl2 expression. These data suggest that Rev-erbα regulates the inflammatory infiltration of macrophages through the suppression of Ccl2 expression. Therefore, Rev-erbα may be a key link between aging- or obesity-associated impairment of clockwork and inflammation.

While the timing of food intake is important, it is unclear whether the effects of exercise on energy metabolism are restricted to unique time windows. As circadian regulation is key to controlling metabolism, understanding the impact of exercise performed at different times of the day is relevant for physiology and homeostasis. Using high-throughput transcriptomic and metabolomic approaches, we identify distinct responses of metabolic oscillations that characterize exercise in either the early rest phase or the early active phase in mice. Notably, glycolytic activation is specific to exercise at the active phase. At the molecular level, HIF1a, a central regulator of glycolysis during hypoxia, is selectively activated in a time-dependent manner upon exercise, resulting in carbohydrate exhaustion, usage of alternative energy sources, and adaptation of systemic energy expenditure. Our findings demonstrate that the time of day is a critical factor to amplify the beneficial impact of exercise on both metabolic pathways within skeletal muscle and systemic energy homeostasis.

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Time-restricted feeding (TRF) improves metabolism independent of dietary macronutrient composition or energy restriction. To elucidate mechanisms underpinning the effects of short-term TRF, we investigated skeletal muscle and serum metabolic and transcriptomic profiles from 11 men with overweight/obesity after TRF (8 h day−1) and extended feeding (EXF, 15 h day−1) in a randomised cross-over design (trial registration: ACTRN12617000165381). Here we show that muscle core clock gene expression was similar after both interventions. TRF increases the amplitude of oscillating muscle transcripts, but not muscle or serum metabolites. In muscle, TRF induces rhythmicity of several amino acid transporter genes and metabolites. In serum, lipids are the largest class of periodic metabolites, while the majority of phase-shifted metabolites are amino acid related. In conclusion, short-term TRF in overweight men affects the rhythmicity of serum and muscle metabolites and regulates the rhythmicity of genes controlling amino acid transport, without perturbing core clock gene expression.