Seasonal Light Hours Modulate Peripheral Clocks and Energy Metabolism in Mice

With the exception of latitudes close to the equator, seasonal variation in light hours can change dramatically between summer and winter. Yet, investigations into the interplay between energy metabolism and circadian rhythms typically use a 12 h light:12 h dark photoperiod corresponding to light duration at the equator. Here, we hypothesised that altering seasonal photoperiod affects both rhythmicity of peripheral tissue clocks as well as processes involved in energy storage and utilisation. Male mice were housed at one of three photoperiods representing light hours in summer, winter and the equinox. Mice housed at a winter photoperiod exhibited an increase in the amplitude of rhythmic lipid metabolism and a modest reduction in fat mass and liver triglyceride content. Comparing melatonin proficient and deficient mice, we provide evidence that the effect of seasonal light on energy metabolism is largely driven by differences in the rhythmicity of food intake, but not melatonin. Our results show that seasonal light impacts energy metabolism in mice and suggest that these effects are partly driven by modulating the timing of eating. Our work sets a course to integrate seasonal light duration in future circadian biology studies. RNAseq of livers from 32 male high fat diet fed C3H/HeNCrl mice, sampled every 6 hours over one full cycle, living in either short light or long light photoperiod, n = 4 per photoperiod per timepoint.除赤道附近纬度区域外，日照时长的季节变化在夏冬两季会呈现显著差异。然而，现有关于能量代谢与昼夜节律（circadian rhythms）相互作用的研究，通常采用12小时光照:12小时黑暗的光周期（photoperiod），该光周期对应赤道地区的日照时长。本研究提出假设：改变季节性光周期，会同时影响外周组织生物钟的节律性，以及参与能量储存与利用的生理过程。我们将雄性小鼠饲养于三种光周期环境中，分别对应夏季、冬季与二分日的日照时长。结果显示，饲养于冬季光周期的小鼠，其节律性脂质代谢的振幅有所升高，同时脂肪总量与肝脏甘油三酯含量出现小幅降低。通过比较褪黑素（melatonin）正常与缺陷型小鼠，我们证实季节性光照对能量代谢的影响主要由进食节律的差异介导，而非褪黑素本身。本研究结果表明，季节性光照会对小鼠的能量代谢产生影响，且此类效应部分通过调控进食时机实现。本研究为未来昼夜生物学研究中整合季节性光照时长提供了研究方向。本研究附带32只雄性高脂饮食（high fat diet）喂养的C3H/HeNCrl小鼠的肝脏RNA测序（RNAseq）数据：这些小鼠在完整采样周期内每6小时采集一次样本，分别饲养于短光照或长光照光周期环境中，每个光周期对应每个时间点的样本量为n=4。