Seasonal light hours modulate peripheral clocks and energy metabolism in mice

Except for 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 the light duration at the equator. We hypothesized that altering the seasonal photoperiod affects both the rhythmicity of peripheral tissue clocks and energy homeostasis. Mice were housed at photoperiods representing either light hours in summer, winter, or 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, the effect of seasonal light on energy metabolism was largely driven by differences in the rhythmicity of food intake and not melatonin. Together, these data indicate that seasonal light impacts energy metabolism by modulating the timing of eating. [Display omitted] •Seasonal light impacts energy metabolism by modulating the timing of eating•Photoperiod affects the rhythmicity of fasting-associated metabolites•Photoperiod alters the phase of core clock transcripts in peripheral tissues•These effects are largely independent of a functioning melatonergic system Circadian disruption influences energy metabolism in mammals; however, the impact of day length on non-seasonal animals is not well understood. Small et al. investigated the effect of different seasonal photoperiods on energy metabolism and diurnal rhythmicity and reported that seasonal light impacts energy metabolism by modulating the timing of eating.