Hepatic gene therapy rescues high-fat diet responses in circadian Clock mutant mice.

OBJECTIVE: Circadian Clock gene mutant mice show dampened 24-h feeding rhythms and an increased sensitivity to high-fat diet (HFD) feeding. Restricting HFD access to the dark phase counteracts its obesogenic effect in wild-type mice. The extent to which altered feeding rhythms are causative for the obesogenic phenotype of Clock mutant mice, however, remains unknown. METHODS: Metabolic parameters of wild-type (WT) and ClockΔ19 mutant mice (MT) were investigated under ad libitum and nighttime restricted HFD feeding. Liver circadian clock function was partially rescued by hydrodynamic tail vein delivery of WT-Clock DNA vectors in mutant mice and transcriptional, metabolic, endocrine and behavioral rhythms studied. RESULTS: Nighttime-restricted feeding restored food intake, but not body weight regulation in MT mice under HFD, suggesting Clock-dependent metabolic dysregulation downstream of circadian appetite control. Liver-directed Clock gene therapy partially restored liver circadian oscillator function and transcriptome regulation without affecting centrally controlled circadian behaviors. Under HFD, MT mice with partially restored liver clock function (MT-LR) showed normalized body weight gain, rescued 24-h food intake rhythms, and WT-like energy expenditure. This was associated with decreased nighttime leptin and daytime ghrelin levels, reduced hepatic lipid accumulation, and improved glucose tolerance. Transcriptome analysis revealed that hepatic Clock rescue in MT mice affected a range of metabolic pathways. CONCLUSION: Liver Clock gene therapy improves resistance against HFD-induced metabolic impairments in mice with circadian clock disruption. Restoring or stabilizing liver clock function might be a promising target for therapeutic interventions in obesity and metabolic disorders.

Tissue-Specific Dissociation of Diurnal Transcriptome Rhythms During Sleep Restriction in Mice.

Study objectives: Shortened or mistimed sleep affects metabolic homeostasis, which may in part be mediated by dysregulation of endogenous circadian clocks. In this study, we assessed the contribution of sleep disruption to metabolic dysregulation by analysing diurnal transcriptome regulation in metabolic tissues of mice subjected to a sleep restriction (SR) paradigm. Methods: Male mice were subjected to 2 × 5 days of SR with enforced waking during the first 6 hours of the light phase. SR and control mice were sacrificed at different time points of the day and RNA preparations from the mediobasal hypothalamus (MBH), liver, and epididymal white adipose tissue (eWAT) were subjected to whole-genome microarray hybridization. Transcriptional rhythms were associated with changes in behavioral and physiological parameters such as sleep, body temperature, and food intake. Rhythm detection was performed with CircWave and transcription profiles were compared by 2-way analysis of variance and t-tests with Benjamini-Hochberg corrections. Results: Clock gene rhythms were blunted in all tissues, while transcriptome regulation was associated with either clock gene expression, sleep patterns, or food intake in a tissue-specific manner. Clock gene expression was associated with apoptosis pathways in the MBH and with tumor necrosis factor alpha signalling in liver. Food intake-associated genes included cilium movement genes in the MBH and lipid metabolism-associated transcripts in liver. Conclusions: In mice, repeated SR profoundly alters behavioral and molecular diurnal rhythms, disrupting essential signalling pathways in MBH, liver, and eWAT, which may underlie the metabolic and cognitive disturbances observed in sleep-restricted humans such as shift workers.

Circadian regulation of lipid mobilization in white adipose tissues.

In mammals, a network of circadian clocks regulates 24-h rhythms of behavior and physiology. Circadian disruption promotes obesity and the development of obesity-associated disorders, but it remains unclear to which extent peripheral tissue clocks contribute to this effect. To reveal the impact of the circadian timing system on lipid metabolism, blood and adipose tissue samples from wild-type, ClockΔ19, and Bmal1(-/-) circadian mutant mice were subjected to biochemical assays and gene expression profiling. We show diurnal variations in lipolysis rates and release of free fatty acids (FFAs) and glycerol into the blood correlating with rhythmic regulation of two genes encoding the lipolysis pacemaker enzymes, adipose triglyceride (TG) lipase and hormone-sensitive lipase, by self-sustained adipocyte clocks. Circadian clock mutant mice show low and nonrhythmic FFA and glycerol blood content together with decreased lipolysis rates and increased sensitivity to fasting. Instead circadian clock disruption promotes the accumulation of TGs in white adipose tissue (WAT), leading to increased adiposity and adipocyte hypertrophy. In summary, circadian modulation of lipolysis rates regulates the availability of lipid-derived energy during the day, suggesting a role for WAT clocks in the regulation of energy homeostasis.

Circadian desynchrony promotes metabolic disruption in a mouse model of shiftwork.

Shiftwork is associated with adverse metabolic pathophysiology, and the rising incidence of shiftwork in modern societies is thought to contribute to the worldwide increase in obesity and metabolic syndrome. The underlying mechanisms are largely unknown, but may involve direct physiological effects of nocturnal light exposure, or indirect consequences of perturbed endogenous circadian clocks. This study employs a two-week paradigm in mice to model the early molecular and physiological effects of shiftwork. Two weeks of timed sleep restriction has moderate effects on diurnal activity patterns, feeding behavior, and clock gene regulation in the circadian pacemaker of the suprachiasmatic nucleus. In contrast, microarray analyses reveal global disruption of diurnal liver transcriptome rhythms, enriched for pathways involved in glucose and lipid metabolism and correlating with first indications of altered metabolism. Although altered food timing itself is not sufficient to provoke these effects, stabilizing peripheral clocks by timed food access can restore molecular rhythms and metabolic function under sleep restriction conditions. This study suggests that peripheral circadian desynchrony marks an early event in the metabolic disruption associated with chronic shiftwork. Thus, strengthening the peripheral circadian system by minimizing food intake during night shifts may counteract the adverse physiological consequences frequently observed in human shift workers.