B03

Adiponectin is an adipocyte-derived hormone with insulin-sensitizing and lipid-lowering effects. Its expression and circulating levels show pronounced variation across the day, which opens the possibility that adiponectin influences metabolic programs in target tissues, such as the liver in a time-of-day dependent manner. To test this, we compared liver circadian transcriptome profiles (with sampling at 4-h intervals) between adiponectin-deficient (ADQ-KO) and wild-type (ADQ-WT) mice. Adiponectin loss led to tonic (i.e. time-independent) transcriptional changes in the liver with 1,393 differentially expressed genes (518 up- and 875 downregulated). These included upregulation of chromatin and RNA processing pathways and downregulation of immune and mitochondrial metabolic genes. At the same time, circadian analysis identified a marked reprogramming of transcriptome rhythms in ADQ-KO livers with changes in MESOR (n = 3,369 transcripts), amplitude (n = 386), and phase of gene expression (n = 603). Genes associated with mitochondrial respiration and fatty acid metabolism showed reduced rhythm amplitude and MESOR, whereas glycolytic genes exhibited increased MESOR. One of the identified adiponectin candidate targets and a regulator of hepatic metabolism, Hif1a, was further studied by functional assays in murine hepatocytes. Pharmacological adiponectin receptor activation promoted glycolysis and mitochondrial respiration under normoxia, but these effects were attenuated under hypoxia mimicry, consistent with HIF1a-dependent interference. These findings suggest adiponectin as a regulator of liver circadian metabolism, modulating both the timing and magnitude of energy-related gene expression programs, potentially in part through a HIF1a-mediated mechanism.

Objective: The circadian clock anticipates daily repetitive events to adapt physiological processes. In mammals, the circadian system consists of a master clock in the suprachiasmatic nucleus (SCN), which synchronizes subordinate tissue clocks, including extra-SCN central nervous system (CNS) clocks involved in functions such as sleep and appetite regulation. Appetite is controlled by both homeostatic and non-homeostatic (hedonic) circuits. Homeostatic appetite addresses energy needs, while hedonic feeding targets cravings for palatable, calorie-dense foods. The adipokine leptin is a major appetite regulator, interacting with the circadian clock. Although leptin's role in satiation through its action in the mediobasal hypothalamus (MBH) is well established, its involvement in the circadian regulation of feeding remains poorly understood. We hypothesized that circadian gating of leptin signaling in the CNS controls homeostatic and hedonic appetite across the day.

Methods: We analyzed food intake rhythms in mice with a loss of leptin (ob/ob mice) or clock function (Per1/2 or Bmal1 KO) and in mice with specific disruption of leptin circadian gating in the CNS (ObRb.Bmal1).

Results: We found that in leptin-deficient mice hedonic appetite increases specifically in the early rest phase. In contrast, clock-deficient Per1/2 mutant mice exhibit blunted rhythms in both hedonic and homeostatic appetite control. Finally, when clock function is disrupted in leptin-sensitive neurons only, mice display a lower sensitivity to palatable food, along with reduced initial weight gain and adipose hypertrophy under obesogenic diet conditions.

Conclusions: Our data describe a local clock-controlled central leptin gating mechanism that modulates hedonic food intake rhythms and impacts metabolic homeostasis.

Physiological processes, including metabolism and immune responses, are generated by the circadian clock, driven by clock genes. Disrupting circadian rhythms through a high-fat diet promotes obesity and inflammation. Studies show that deleting the clock gene, brain, and muscle ARNT-like 1 (Bmal1) in adipose tissue leads to overeating and weight gain. We now show that Bmal1 deletion in neutrophils protects against diet-induced obesity and reduces inflammatory macrophage infiltration into epididymal white adipose tissue (eWAT), despite increased food intake over 20 weeks of a high-fat diet. This protection is linked to enhanced energy expenditure, increased UCP1 expression in iBAT, improved insulin sensitivity, and altered expression of genes encoding chemokine receptors CXCR2, CXCR4, and the ligand Cxcl2 in eWAT. Our findings reveal a key role of Bmal1 in neutrophils in regulating high-fat diet-induced adipose inflammation and emphasize circadian regulation's importance in immuno-metabolic function.

Circadian clocks are important regulators of physiology and behavior. In the brain, circadian clocks have been described in many centers of the central reward system. They affect neurotransmitter signaling, neuroendocrine circuits, and the sensitivity to external stimulation. Circadian disruption affects reward signaling, promoting the development of behavioral and substance use disorders. In this review, we summarize our current knowledge of circadian clock-reward crosstalk. We show how chronodisruption affects reward signaling in different animal models. We then translate these findings to circadian aspects of human reward (dys-) function and its clinical implications. Finally, we devise approaches to and challenges in implementing the concepts of circadian medicine in the therapy of substance use disorders.