bims-ciryme Biomed News
on Circadian rhythms and metabolism
Issue of 2023–02–26
two papers selected by
Gabriela Da Silva Xavier, University of Birmingham
  1. Human glucose rhythms and subjective hunger anticipate meal timing.
  2. CLOCK and TIMELESS regulate rhythmic occupancy of the BRAHMA chromatin-remodeling protein at clock gene promoters.
  1. Curr Biol. 2023 Feb 15. pii: S0960-9822(23)00144-6. [Epub ahead of print]
    Human glucose rhythms and subjective hunger anticipate meal timing.
    Cheryl M Isherwood, Daan R van der Veen, Hana Hassanin, Debra J Skene, Jonathan D Johnston.
      Circadian rhythms, metabolism, and nutrition are closely linked.1 Timing of a three-meal daily feeding pattern synchronizes some human circadian rhythms.2 Despite animal data showing anticipation of food availability, linked to a food-entrainable oscillator,3 it is unknown whether human physiology predicts mealtimes and restricted food availability. In a controlled laboratory protocol, we tested the hypothesis that the human circadian system anticipates large meals. Twenty-four male participants undertook an 8-day laboratory study, with strict sleep-wake schedules, light-dark schedules, and food intake. For 6 days, participants consumed either hourly small meals throughout the waking period or two large daily meals (7.5 and 14.5 h after wake-up). All participants then undertook a 37-h constant routine. Interstitial glucose was measured every 15 min throughout the protocol. Hunger was assessed hourly during waking periods. Saliva melatonin was measured in the constant routine. During the 6-day feeding pattern, both groups exhibited increasing glucose concentration early each morning. In the small meal group, glucose concentrations continued to increase across the day. However, in the large meal group, glucose concentrations decreased from 2 h after waking until the first meal. Average 24-h glucose concentration did not differ between groups. In the constant routine, there was no difference in melatonin onset between groups, but antiphasic glucose rhythms were observed, with low glucose at the time of previous meals in the large meal group. Moreover, in the large meal group, constant routine hunger scores increased before the predicted meal times. These data support the existence of human food anticipation.
    Keywords:  appetite; chrononutrition; circadian clock; circadian rhythms; continuous glucose monitoring; food anticipation; hunger; meal timing; melatonin; peripheral clocks
    DOI:  https://doi.org/10.1016/j.cub.2023.02.005
  2. PLoS Genet. 2023 Feb 21. 19(2): e1010649
    CLOCK and TIMELESS regulate rhythmic occupancy of the BRAHMA chromatin-remodeling protein at clock gene promoters.
    Christine A Tabuloc, Yao D Cai, Rosanna S Kwok, Elizabeth C Chan, Sergio Hidalgo, Joanna C Chiu.
      Circadian clock and chromatin-remodeling complexes are tightly intertwined systems that regulate rhythmic gene expression. The circadian clock promotes rhythmic expression, timely recruitment, and/or activation of chromatin remodelers, while chromatin remodelers regulate accessibility of clock transcription factors to the DNA to influence expression of clock genes. We previously reported that the BRAHMA (BRM) chromatin-remodeling complex promotes the repression of circadian gene expression in Drosophila. In this study, we investigated the mechanisms by which the circadian clock feeds back to modulate daily BRM activity. Using chromatin immunoprecipitation, we observed rhythmic BRM binding to clock gene promoters despite constitutive BRM protein expression, suggesting that factors other than protein abundance are responsible for rhythmic BRM occupancy at clock-controlled loci. Since we previously reported that BRM interacts with two key clock proteins, CLOCK (CLK) and TIMELESS (TIM), we examined their effect on BRM occupancy to the period (per) promoter. We observed reduced BRM binding to the DNA in clk null flies, suggesting that CLK is involved in enhancing BRM occupancy to initiate transcriptional repression at the conclusion of the activation phase. Additionally, we observed reduced BRM binding to the per promoter in flies overexpressing TIM, suggesting that TIM promotes BRM removal from DNA. These conclusions are further supported by elevated BRM binding to the per promoter in flies subjected to constant light and experiments in Drosophila tissue culture in which the levels of CLK and TIM are manipulated. In summary, this study provides new insights into the reciprocal regulation between the circadian clock and the BRM chromatin-remodeling complex.
    DOI:  https://doi.org/10.1371/journal.pgen.1010649
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