Abstract
The gut microbiome plays a critical role in regulating host immunity and can no longer be regarded as a bystander in human health and disease. In recent years, circadian (24 h) oscillations have been identified in the composition of the microbiota, its biophysical localization within the intestinal tract and its metabolic outputs. The gut microbiome and its key metabolic outputs, such as short chain fatty acids and tryptophan metabolites contribute to maintenance of intestinal immunity by promoting barrier function, regulating the host mucosal immune system and maintaining the function of gut-associated immune cell populations. Loss of rhythmic host-microbiome interactions disrupts host immunity and increases risk of inflammation and metabolic complications. Here we review factors that drive circadian variation in the microbiome, including meal timing, dietary composition and host circadian clocks. We also consider how host-microbiome interactions impact the core molecular clock and its rhythmic outputs in addition to the potential impact of this relationship on circadian control of immunity.
Highlights
The circadian clock is a critical regulator of immunity, including homeostatic processes and responses to immune challenge [1,2,3]
The intestinal microbiome is very well established as an influential component of immune-metabolic homeostasis
Whilst evidence is emerging of gut commensals with potential intrinsic rhythmic capacity, it is likely that these microbiome rhythms will be heavily reliant on entrainment derived largely from the host
Summary
The circadian clock is a critical regulator of immunity, including homeostatic processes and responses to immune challenge [1,2,3]. With the discovery of resident intestinal clocks [83,84,85] and rhythmicity in multiple immune cells, interest is growing in the circadian influence on host-microbiome interaction and immunity. Whilst feeding times clearly drive rhythms in the microbiome, the host circadian molecular clock plays a role, with studies evidencing the importance of the biological clock in regulating the composition of the microbial community as well as the rhythmicity.
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