Guo et al. Translational Psychiatry (2021) 11:328 https://doi.org/10.1038/s41398-021-01443-2 Translational Psychiatry ARTICLE Open Access A diet high in sugar and fat influences neurotransmitter metabolism and then affects brainfunctionbyalteringthegutmicrobiota Yinrui Guo 1,XiangxiangZhu2,3,MiaoZeng2,4,LongkaiQi2, Xiaocui Tang2, Dongdong Wang2,MeiZhang4, Yizhen Xie2, Hongye Li3,XinYang5 and Diling Chen 2 Abstract Gut microbiota (GM) metabolites can modulate the physiology of the host brain through the gut–brain axis. We wished to discover connections between the GM, neurotransmitters, and brain function using direct and indirect methods. A diet with increased amounts of sugar and fat (high-sugar and high-fat (HSHF) diet) was employed to disturb the host GM. Then, we monitored the effect on pathology, neurotransmitter metabolism, transcription, and brain circularRNAs (circRNAs) profiles in mice. Administration of a HSHF diet-induced dysbacteriosis, damaged the intestinal tract, changed the neurotransmitter metabolism in the intestine and brain, and then caused changes in brain function and circRNA profiles. The GM byproduct trimethylamine-n-oxide could degrade some circRNAs. The basal level of the GM decided the conversion rate of choline to trimethylamine-n-oxide. A change in the abundance of a single bacterial strain could influence neurotransmitter secretion. These findings suggest that a new link between metabolism, brain circRNAs, and GM. Our data could enlarge the “microbiome–transcriptome” linkage library and provide more information on the gut–brain axis. Hence, our findings could provide more information on the interplay fi 1234567890():,; 1234567890():,; 1234567890():,; 1234567890():,; between the gut and brain to aid the identi cation of potential therapeutic markers and mechanistic solutions to complex problems encountered in studies of pathology, toxicology, diet, and nutrition development. Introduction sensory transduction of nutrients enables the gut to Gut microbiota (GM) metabolites can potentially inform the brain of all occurrences, and make sense of modulate nearly all aspects of host physiology1, from what has been eaten6. Recent studies have revealed that regulating immunity2 and metabolism3 in the gut to the GM is important in neurodegenerative diseases, shaping mood and behavior4. These metabolites can act including Alzheimer’s disease (AD)7,8 and Parkinson’s locally in the intestine or can accumulate up to millimolar disease (PD), and that targeting the GM or/GM metabo- concentrations in the serum and organs5. Studies have lites could be used to treat neurodegenerative diseases 9,10. shown that formation of a gut–brain neural circuit for An imbalanced diet that includes a high intake of sugar and fat and insufficient dietary fiber over a long time can cause enteric dysbacteriosis. The latter increases the Correspondence: Xin Yang ([email protected])or permeability of the intestinal mucosa, and results in Diling Chen ([email protected]) abnormalities in intestinal immunity and glucolipid 1 School of Basic Medical Science, Guangzhou University of Chinese Medicine, metabolism. At this time, the dominant bacteria can Guangdong, Guangzhou 510120, China 2State Key Laboratory of Applied Microbiology Southern China; Guangdong change readily. For example, Fujisaka and colleagues Provincial Key Laboratory of Microbial Culture Collection and Application; showed that the relative abundance of Bifidobacterium Guangdong Open Laboratory of Applied Microbiology; Institute of species and Bacillus species decreased in mice fed a high- Microbiology, Guangdong Academy of Sciences, Guangzhou 510070, China Full list of author information is available at the end of the article fat diet, whereas the abundance of Gram-negative bacteria These authors contributed equally: Yinrui Guo, Xiangxiang Zhu © The Author(s) 2021 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a linktotheCreativeCommons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Guo et al. Translational Psychiatry (2021) 11:328 Page 2 of 27 increased11. Recent studies have shown that obesity is not Microbiology (Guangzhou, China). All efforts were made necessary for dysfunction of the intestinal barrier. That is, to minimize the number of animals used. hyperglycemia is more likely to drive intestinal-barrier dysfunction and the risk of enteric infection. Hypergly- cemia increases the permeability of the intestinal barrier, Preparation and treatments of mice suffering from which provides microbes with more chances to enter the dysbacteriosis body and cause proliferation of pathogenic bacteria and Adult male KM mice (18–22 g, 6 weeks) were obtained focal shifts12. Studies have demonstrated that some bac- from the Center of Laboratory Animals of Guangdong teria can produce bioactive neurotransmitters13,14, and Province (certificate number: SCXK [Yue] 2008-0020, these neurotransmitters are thought to regulate the ner- SYXK [Yue] 2008-0085). They were pair-housed in plastic vous system activity and behavior of the host15,16. cages in a temperature-controlled (25 ± 2 °C) colony room Recently, O Donnell and coworkers revealed that the at a 12-h light–dark cycle. Food and water were available neuromodulator tyramine produced by commensal bac- ad libitum. teria of Providencia species (which colonize the gut) Mice were allocated randomly into two groups of 12: bypassed the requirement for host tyramine biosynthesis control and model. The mice in the control group were fed and manipulated a host sensory decision in Cae- a standard diet. The mice in the model groups were fed a norhabditis elegans17. However, how these bacteria HSHF diet. Water was available freely. These treatments release signals to activate the brain is not known. lasted for 3 months. Using animal models, several pathways of communica- The components of the HSHF diet were 20% sucrose, tion have been identified along the “gut–brain–axis”, 15% fat, 1.2% cholesterol, 0.2% of bile acid sodium, 10% including those driven by the immune system, vagus casein, 0.6% calcium hydrogen phosphate, 0.4% stone nerve, or by modulation of neuroactive compounds by the powder, 0.4% premix, and 52.2% basic feed. Heat ratio: microbiota18,19. In recent years, microbiota have been protein 17%, fat 17%, carbohydrate 46%. shown to produce and/or consume a wide range of mammalian neurotransmitters, including dopamine, nor- epinephrine, serotonin, or gamma-aminobutyric acid13,20. Preparation and treatment of SAMP8 mice and newborn KM Accumulating evidence in animals suggests that manip- mice ulation of these neurotransmitters by bacteria may have an Male SAMP8 mice (5 months; mean bodyweight, impact in host physiology. Preliminary clinical studies have 20 ± 5 g) were purchased from Beijing HFK Bioscience revealed that microbiota-based interventions can also alter (SCXK [Jing] 2014-0004). Adult KM mice (18–22 g, 16 neurotransmitter levels13. Nonetheless, substantially more females and 8 males, 8 weeks) were obtained from the work is required to determine if microbiota-mediated Center of Laboratory Animal of Guangdong Province manipulation of human neurotransmission has physiolo- (SCXK [Yue] 2008-0020, SYXK [Yue] 2008-0085). gical implications and, if so, how it may be exploited Allmicewerepair-housedinplasticcagesina therapeutically. temperature-controlled (25 ± 2 °C) colony room with a We chose a diet with increased amounts of sugar and fat 12-h light–dark cycle. Mice had free access to food (i.e., a high-sugar and high-fat (HSHF) diet) to disturb the and water. All animals were allowed to acclimatize to GM, then monitored the effect on pathology, neuro- their surroundings for ≥1weekbeforeinitiationof transmitters, metabolism, and transcription of circu- experimentation. larRNAs (circRNAs) in mice. We aimed to identify some associations between the functions of the GM, neuro- transmitters, and the brain. We also aimed to enlarge the Effects of TMA on Sprague–Dawley rats “microbiome–transcriptome” linkage library. This approach Twenty male Sprague–Dawley rats (180–220 g) would provide more information on the interplay between obtained from the Center of Laboratory Animal of the gut and brain to aid identification of potential ther- Guangdong Province (SCXK [Yue] 2008-0020, SYXK apeutic markers and mechanistic solutions to complex [Yue] 2008-0085). They were pair-housed in plastic cages problems encountered in studies on pathology, toxicology, in a temperature-controlled (25 ± 2 °C) colony room at a diets and nutrition development. 12-h light–dark cycle. Food and water were available ad libitum. Materials and methods Male Sprague–Dawley rats were divided into two Animals groups of 10: normal group, trimethylamine (TMA)- Ethical approval of the study protocol induced group (2 mL/kg/d of 2.5% TMA purchased from All experimental protocols