Host circadian signaling, feeding, and the gut microbiome are tightly interconnected. Changes in the gut microbial community can affect the expression of core clock genes, but the specific metabolites and molecular mechanisms that mediate this relationship remain largely unknown. Here, we sought to identify gut microbial metabolites that impact circadian signaling. Through a phenotypic screen of a focused library of gut microbial metabolites, we identified a bile acid metabolite, lithocholic acid (LCA), as a circadian modulator. LCA lengthened the circadian period of core clock genetranscription in a dose-responsive manner in human colonic cells. We found evidence that LCA modulates the casein kinase 1 δ/ε (CK1δ/ε)-protein phosphatase 1 (PP1) feedback loop and stabilizes core clock protein cryptochrome 2 (CRY2). Furthermore, we showed that LCA feeding alters circadian transcription in mouse distal ileum and colon. Taken together, our work identifies LCA as a molecular link between host circadian biology and the microbiome. Because bile acids are secreted in response to feeding, our work provides potential mechanistic insight into the molecular nature of the food-entrainable oscillator (FEO) by which peripheral clocks adapt to the timing of food intake. Given the association between circadian rhythm, feeding, and metabolic disease, our insights may offer an avenue for modulating host health. hPer2
Circadian Biology