Mechanisms Of Flammulina Velutipes Polysaccharides Improve Learning And Memory Impairment By Modulating Gut Microbiota Composition

Flammulina velutipes is one of the most popular mushrooms in China.In 2017,the yields of Flammulina velutipes were more than 3' million tons,accounting for about 10%of the total domestic edible mushroom.Flammulina velutipes is not only nutritious,but also contains biologically active substances such as polysaccharides,proteins and sesquiterpenes.In our previous study,Flammulina velutipes polysaccharides have been proved to be effective in improving scopolamine-induced impairment of learning and memory in mice.However,the functional mechanism has not been elucidated.It has been debated whether mushroom polysaccharides have direct effects on brain function and behavior.There are increasing studies indicating that changes in gut microbiota composition can influence brain function and behavior.Hence,there is a pressing need to identify the underlying mechanism of FVP in delaying the impairment of learning and memory.In this study,the effect of FVP on the composition of gut microbiota was investigated.The functioning mechanisms of Flammulina velutipes polysaccharides improve learning and memory impairment by modulating gut microbiota composition was studied.More information of the present research was listed below:1.Flammulina velutipes polysaccharides(FVP)were prepared from freeze-dried Flammulina velutipes.The digestion and degradation of FVP were studied by simulating oral saliva,gastric juice,intestinal pancreatic juice and fecal fermentation in vitro.The purity of FVP is 92.39±2.24%.It mainly consists of five monosaccharides including glucose,mannose,xylose,fucose and galactose with the ratios of 48.4:15.4:14.6:11.8:9.9.The prepared Flammulina velutipes polysaccharide was a heteropolysaccharide with glucopyranose as the main chain.The molecular weight,free monosaccharide and reducing sugar of FVP did not change during saliva,simulated gastric juice and pancreatic juice digestion,indicating that FVP was not degraded in saliva,simulated gastric juice and pancreatic juice digestion stage.In the fermentation process of fecal bacteria,the molecular weight gradually decreased,and the small molecular weight substances appeared,the content of reducing sugar and total sugar decreased significantly(p<0.05),indicating that FVP can be degraded by the gut microbiota.Results indicated that the FVP can pass through the oral cavity,stomach and small intestine stage,and then reaches the colon area,which provides a possibility for regulating the structure of gut microbiota.2.We found that FVP can regulate the structure of fecal bacteria in vitro anaerobic fermentation model.In the level of phylum,the addition of FVP increased the abundance of Bacteroidetes and Actinobacteria reduced the abundance of Firmicutes and Proteobacteria(p<0.05).In the family level,FVP can significantly improve the abundance Bifidobacteriaceae and Bacteroidaceae(p<0.05),decreased Enterobacteriaceae abundance(p<0.05).In the genus level,FVP can significantly increase Bifidobacterium,Bacteroides and Clostridium abundance(p<0.05),decreased abundance Escherichia/Shigella's.FVP promoted the produce of short-chain fatty acids,including acetic acid,propionic acid,butyric,isobutyric acid,valeric acid and isovaleric acid and decreased the pH of the fermentation system.At the same time,FVP increased some metabolites such as tyrosine,N-acetylaspartate and sphingosine.By analyzing the biological functions of the gut microbiota and metabolites affected by FVP,these changes were closely related to the neurological health such as neurotransmitter production and signal transduction,especially neurodegenerative diseases.Results indicated that the structural and metabolic changes of gut microbiota regulated by FVP may be one of the reasons for its improvement in memory.3.The effects of FVP on gut microbiota were further studied by animal experiments.The results showed that the dominant bacteria of the mouse gut microbiota were mainly Bacteroidia,Clostridia,Erysipelotrichia,Bacilli,and Actinobacteria.The intake of FVP increased the abundance of Bacteroidia,Erysipelotrichia,Actinobacteria,Betaproteobacteria,and Gammaproteobacteria(p<0.05),and decreased the abundance of Clostridia,Bacilli,Deltapooteobacteria,and Verrucomicrobiae(p<0.05).Through the study of fecal microbiota transplantation(FMT)technology,it was found that the gut microbiota regulated by FVP can improve scopolamine-induced memory damage,and its effect is comparable to that of direct gavage of FVP(p>0.05).It can improve acetylcholine(ACh)in hippocampus.The production of neurotransmitters such as dopamine(DA),norepinephrine(NE),and serotonin(5-HT)were enhanced.Malondialdehyde(MDA),superoxide dismutase(SOD),catalase(CAT)activity and total antioxidant capacity(T-AOC)were increased.It inhibited the increase of inflammatory factors such as IL-6,IL-1? and TNF-? in serum.It can be preliminarily confirmed that the structure and metabolic changes of gut microbiota regulated by FVP have a causal relationship with the improvement of memory.4.The gut microbiota disorder model was prepared by using antibiotics that were not absorbed by the intestine.The effects and mechanism of gut microbiota on learning were systematically studied.At the same time,through the administration of FVP and natural recovery,memory improvement of FVP by regulating gut microbiota was confirmed again.The results showed that antibiotic treatment reduced the abundance and diversity of gut microbiota and caused disturbance.Gut microbiota disorder can lead to learning and memory dysfunction,reduce the expression of tight junction proteins Occludin and ZO-1 between intestinal epithelium,destroy the intestinal mucosal physical barrier,leading to increased intestinal permeability;The expression of SLC6A4 gene codes for the serotonin transporter and NPY1R and NPY2R codes for the receptors of neuropeptide Y were decreased.In addition,the loss of gut microbiota reduces the synthesis of tight junction proteins TJP1 and CLDN5 in the brain.Increase the permeability of the blood-brain barrier and reduce the production of brain-derived neurotrophic factor BDNF.These effects were not fully recovered after 14 days of stopping antibiotic treatment,but the gut microbiota and indicators as mentioned above were restored to normal by ingesting FVP.