Gut Microbiota Mediates Oolong Tea Polyphenols Alleviation of Circadian Rhythm Disturbance
Authors: Yan Ruonan , Ho Chi-Tang , Liu Yanan , Zhang Ruilin , Wu Zufang , Weng Peifang , Zhang Xin 
Published: August 2021

Abstract
BackgroundTea polyphenols can be digested in the intestinal tract so as to promote the growth of helpful gut microbiota, and through the production of catechin, tryptophan, acetic acid and other active substances which involved in the modulation of circadian rhythms mechanism to improve the circadian rhythm disorders and neurological weakness, while its specific mechanism is still unclear. The interaction between host circadian rhythm and gut microbes through the gut-brain axis (GBA) provides new clues for tea polyphenols to improve host health. Our present research mainly investigated the metabolites of the gut microbiota and the heterogeneous expression of circadian rhythm genes in the liver and hypothalamic, and then revealed the modulatory role of oolong tea polyphenols (OTP) of circadian rhythm disorder via the GBA. We used 16S rDNA and untargeted metabolomics sequencing techniques to analyze the effects of OTP on intestinal flora diversity and abundance of specific flora in mice with diurnal disorders, and to screen out marker metabolites which may be involved in circadian rhythm regulation. Transcriptomics and 10X single-cell sequencing were used to evaluate the effects of OTP on circadian rhythm genes in liver and hypothalamus and hypothalamus cell types in mice with diurnal disorders. The Y maze and Morris water maze experiments were investigated the effects of OTP on long-term and short-term memory impairment.ResultsBy establishing a circadian rhythm disorder mouse model, our experimental results showed that OTP improved the structural disorder of the intestinal microbiota caused by continuous darkness, especially significantly decreased the ratio of Firmicutes/Bacteroidetes (F/B), thereby modulating the production of metabolites related to pyruvate metabolism, glycolysis/gluconeogenesis, and tryptophan metabolism to alleviate the steady-state imbalance caused by circadian rhythm disorders. In addition, OTP can significantly ameliorate the rhythm oscillation disorder of specific gut microbes and liver clock genes induced by continuous darkness, and made dysrhythmic mice perform well in cognitive behavior tests. Simultaneously, OTP intervention increased the number of rhythmic expression genes in the liver which in the CD group has 156, while in the OTP group has 208. Transplanting fecal microbiota from the OTP group into germ-free mice exhibited that OTP significantly increased the number of hypothalamus cell clusters, up-regulated the number of astrocytes and fibroblasts, and enhanced the expression of circadian rhythm genes Cry2, Per3, Bhlhe41, Nr1d1, Nr1d2, Dbp, and Rorb in hypothalamic cells. ConclusionsOur results confirmed that OTP reduced the F/B ratio, made the daily oscillation of the intestinal microbiota tended to be regular, actively improve the intestinal microecological status, the content of important metabolite closely associated with circadian rhythm such as Tryptophan, Glutamine, 2-indolecarboxylic acid and some others has been significantly increased, the poor expression of clock genes (such as Cry2, Per3, Bhlhe41, Nr1d1, Nr1d2, Dbp and Rorb) in liver and hypothalamus cells has been improved. These results indicated that OTP can significantly improve the metabolic imbalance and cognitive impairment caused by the circadian rhythm disorder, maintain the host's homeostasis, which with potential prebiotic functional characteristics to positively contribute to host health.