External light dark cycle shapes gut microbiota through intrinsically photosensitive retinal ganglion cells

Gut microbiota has been shown to involve in many physiological functions such as metabolism, brain development, and neuron degeneration disease. Intriguingly, many microbes in the digestive tract do not maintain a constant level of their relative abundance but show daily oscillations under normal conditions. Recent evidence indicates that chronic jetlag, constant darkness, or deletion of the circadian core gene can alter the composition of gut microbiota and dampen the daily oscillation of gut microbes. These studies suggest that the interaction between the host circadian clock and the light-dark cycle plays an important role in gut homeostasis and microbiota. However, how or whether environmental factors such as the light-dark cycle could modulate gut microbiota is still poorly understood. Using genetic mouse models and 16s rRNA metagenomic analysis, we found that light-dark cycle information transmitted by the ipRGC-sympathetic circuit was essential for daily oscillations of gut microbes under temporal restricted high fat diet condition. Furthermore, aberrant light exposure such as dim light at night (dLAN), acting through intrinsically photosensitive retinal ganglion cells (ipRGCs), could alter the composition, relative abundance, and daily oscillations of gut microbiota. Together, our results indicate that external stimulation, such as light-dark cycle information, through the sensory system can modulate gut microbiota in the direction from the brain to the gut.