Effects And Molecular Mechanisms Of Lactobacillus Plantarum PS128 On The Behavior Of Fmr1 Knockout Mice

The microbiome-gut-brain axis（MGBA）is a bidirectional interaction pathway between gut microbes and the brain,by which a class of microorganisms named psychobiotics improves the physical and mental health of hosts.Lactobacillus plantarum PS128（PS128）is known as a psychobiotics.It improves oppositional-defiant behaviors in children with autism spectrum disorder（ASD）,and together with oxytocin it ameliorates certain social defects of ASD patients,however,the molecular mechanism underlying this improvement is not known.ASD is a neurodevelopmental disorder with extreme genetic heterogeneity,which is characterized by communication impairments,social abnormalities,and stereotypic behaviors,accompanied by many complications,such as gastrointestinal problems and movement disorders.Excitation/inhibition imbalance of neurons in the central nervous system and abnormal microbial compositions are significant factors associated with ASD etiology.Fragile X Mental Retardation 1（Fmr1）knockout（KO）mice have been widely studied and used as a mouse model of ASD.Using systematic approaches,including metagenomics,behavioral studies,and Western blotting,we compared microbial profiles,behaviors,and abundance of specific protein targets before and after PS128supplement between 5-week-old and 2-month-old Fmr1 KO mice and their wild type littermates（WT mice）.The major findings are as follows:First,the gut microbial species diversity and species richness were both decreased in 2-month-old WT mice after PS128 supplement,but the relative abundance of Bifidobacteriaceae was increased in these mice.The 5-week-old Fmr1 KO mice have a higher abundance of bacteria that promote intestinal inflammation and a lower abundance of bacteria that produce short-chain fatty acids than their WT littermates.Gut microbial species diversity of 2-month-old Fmr1 KO mice was significantly lower than that of their WT littermates,but PS128 supplement significantly helped the KO mice to maintain a high abundance of Akkermansia species in the gut.Second,the stereotypic behaviors of 2-month-old Fmr1 KO mice with PS128supplement was significantly improved than that of their WT littermates without PS128supplement in the rotarod performance test.Social dominance of PS128-treated Fmr1KO mice was higher than that of WT mice in the tube test.In the three-chamber social choice task,PS128 supplement improved social defects of Fmr1 KO mice to a certain extent and adjusted the social environmental preference of mice.Third,the abundance of glutamate dehydrogenase（GAD65）in hippocampus and striatum of Fmr1 KO mice was higher than that of WT littermates,however,the expression levels of GAD65 were similar between PS128-treated Fmr1 KO mice and PS128-untreated WT littermates.In addition,the abundance of GABA_A receptorβ2subunit in the amygdala of Fmr1 KO mice was higher in PS128-trated group than in PS128-untreated group.Conclusively,we used a systematic approach to reveal that the microbial profiles of Fmr1 KO mice and their WT littermates were distinctively changed by PS128supplement and that PS128 supplement ameliorated part of autistic-like behaviors in Fmr1 KO mice.Molecular mechanisms underlining the behavior improvements might be involved in GABAergic nervous system adjusted by PS128 treatment that further ameliorated the excitation/inhibition imbalance of the neurons of Fmr1 KO mice.Our study provides novel insights in the use of psychobiotics as an adjuvant therapy for ASD.