bims-ciryme 2021-03-07 papers

Clocks Sleep. 2021 Feb 25. 3(1): 189-226

Circadian Rhythms of the Hypothalamus: From Function to Physiology.

The nearly ubiquitous expression of endogenous 24 h oscillations known as circadian rhythms regulate the timing of physiological functions in the body. These intrinsic rhythms are sensitive to external cues, known as zeitgebers, which entrain the internal biological processes to the daily environmental changes in light, temperature, and food availability. Light directly entrains the master clock, the suprachiasmatic nucleus (SCN) which lies in the hypothalamus of the brain and is responsible for synchronizing internal rhythms. However, recent evidence underscores the importance of other hypothalamic nuclei in regulating several essential rhythmic biological functions. These extra-SCN hypothalamic nuclei also express circadian rhythms, suggesting distinct regions that oscillate either semi-autonomously or independent of SCN innervation. Concurrently, the extra-SCN hypothalamic nuclei are also sensitized to fluctuations in nutrient and hormonal signals. Thus, food intake acts as another powerful entrainer for the hypothalamic oscillators' mediation of energy homeostasis. Ablation studies and genetic mouse models with perturbed extra-SCN hypothalamic nuclei function reveal their critical downstream involvement in an array of functions including metabolism, thermogenesis, food consumption, thirst, mood and sleep. Large epidemiological studies of individuals whose internal circadian cycle is chronically disrupted reveal that disruption of our internal clock is associated with an increased risk of obesity and several neurological diseases and disorders. In this review, we discuss the profound role of the extra-SCN hypothalamic nuclei in rhythmically regulating and coordinating body wide functions.

Keywords: circadian rhythm; clock genes; extra-SCN hypothalamic nuclei; food-entrainable oscillator; hypothalamus; metabolism; obesity

DOI: https://doi.org/10.3390/clockssleep3010012

Proc Natl Acad Sci U S A. 2021 Mar 09. pii: e2020646118. [Epub ahead of print]118(10):

Superoxide is promoted by sucrose and affects amplitude of circadian rhythms in the evening.

Ángela Román, Xiang Li, Dongjing Deng, John W Davey, Sally James, Ian A Graham, Michael J Haydon.

Plants must coordinate photosynthetic metabolism with the daily environment and adapt rhythmic physiology and development to match carbon availability. Circadian clocks drive biological rhythms which adjust to environmental cues. Products of photosynthetic metabolism, including sugars and reactive oxygen species (ROS), are closely associated with the plant circadian clock, and sugars have been shown to provide metabolic feedback to the circadian oscillator. Here, we report a comprehensive sugar-regulated transcriptome of Arabidopsis and identify genes associated with redox and ROS processes as a prominent feature of the transcriptional response. We show that sucrose increases levels of superoxide (O2 -), which is required for transcriptional and growth responses to sugar. We identify circadian rhythms of O2 --regulated transcripts which are phased around dusk and find that O2 - is required for sucrose to promote expression of TIMING OF CAB1 (TOC1) in the evening. Our data reveal a role for O2 - as a metabolic signal affecting transcriptional control of the circadian oscillator in Arabidopsis.

Keywords: ROS; circadian; redox; sugar; superoxide

DOI: https://doi.org/10.1073/pnas.2020646118

Front Physiol. 2021 ;12 634187

Impact of Time-Restricted Feeding to Late Night on Adaptation to a 6 h Phase Advance of the Light-Dark Cycle in Mice.

Baoyin Ren, Changxiao Ma, Lihong Chen, Garret A FitzGerald, Guangrui Yang.

In modern society, more and more people suffer from circadian disruption, which in turn affects health. But until now, there are no widely accepted therapies for circadian disorders. Rhythmic feeding behavior is one of the most potent non-photic zeitgebers, thus it has been suggested that it was important to eat during specific periods of time (time-restricted feeding, TRF) so that feeding is aligned with environmental cues under normal light/dark conditions. Here, we challenged mice with a 6 h advanced shift, combined with various approaches to TRF, and found that food restricted to the second half of the nights after the shift facilitated adaptation. This coincided with improved resilience to sepsis. These results raise the possibility of reducing the adverse responses to jet lag by subsequent timing of food intake.

Keywords: adaptation; behavior; jet lag; sepsis; time-restricted feeding

DOI: https://doi.org/10.3389/fphys.2021.634187