Analysis Of The Effects And Mechanisms On DSS-Induced Colitis In Mice By Different Species Of Lactobacillus

IBD is a kind of gastrointestinal disease and prone to recur.The pathogenesis of IBD is still unclear.The medicines used for IBD are in limited efficacy with side effects.It's showed that probiotics have many functions including pathogenic bacteria resistant,anti-inflammation,intestinal barrier maintenance and gut microbiota regulation.Hence,probiotics have great potential for relieving or adjuvant treatment of IBD.Lactobacillus rhamnosus and L.reuteri are the two most common probiotics currently used in the research of IBD treatment.However,whether these two species of Lactobacillus have different effects on IBD is still unclear.This study aims to compare the different impacts on DSS-induced colitis in mice by strains of L.rhamnosus and L.reuteri,exploring the reasons for the difference between these two Lactobacillus species on alleviating colitis from the three aspects of intestinal barrier,shortchain fatty acids(SCFAs)and gut microbiota.What's more,based on genomic analysis,the relationship between the genome of strains and the effects towards colitis was initially explored.This study provides a theoretical basis for the application of different species of probiotics on the prevention or adjuvant treatment of IBD.The main results of this article are as follows:(1)Colitis mice model induced by DSS was established and the remission effects of probiotics in colitis was evaluated from body weight change,disease activity index,colon length,colon histopathology score,and colon MPO activity.The results showed that different strains have obvious strain-specific effects on colitis in mice.Among these 12 strains,8 strains of Lactobacillus are effective to improve DSS-induced colitis in mice.Re3 showed the best effect.Re4?Re5?Re6?R4?R5 showed slightly less relief effects on colitis.Re2?R1 were less effective in relieving colitis.Besides,R2?R3?R6?Re1 had no effect on colitis alleviation.In addition,it was showed that the improvement effects by L.reuteri on colitis were obviously better than those by L.rhamnosus.(2)The effects of two species of Lactobacillus on intestinal barrier was evaluated from the content of multiple pro-inflammatory cytokines in the colon and serum,the integrity of the colonic mucus layer,MUC2 transcription level in the colon,the content of Claudin-3 or Occludin and transcription levels of Claudin-3,Occludin,ZO1,ZO2 in colon,also the transcription level of Reg3 g,Reg3b and Lgr5.The results showed that L.reuteri exhibited higher capability in intestinal barrier improvement than that by L.rhamnosus,including(1)L.reuteri better improved the tight junction of intestinal epithelial cells,especially increased the transcription level of Claudin-3 to a greater extent than that by L.rhamnosus;(2)Increased the transcription levels of antibacterial peptides Reg3 g and Reg3 b to a greater extent than those by L.rhamnosus;(3)Increased the transcription level of intestinal stem cell marker Lgr5 to a higher extent than that by L.rhamnosus.(3)By measuring the content of SCFAs in feces,the effects of two species of Lactobacillus on SCFAs were evaluated.It was showed that L.rhamnosus increased the contents of acetate and total acids to a greater extent than those by L.reuteri.(4)The effects of two species of Lactobacillus on gut microbiota were evaluated from gut microbiota community diversity,species richness,?-diversity,abundance at phylum level and genus level.The results showed that L.reuteri better improved the community diversity,and the microbiota composition and structure in the group of L.reuteri treatment were closer to the control group.However,after the intervention of multiple strains of L.rhamnosus,an abnormal increase of genus of harmful bacteria was observed.(5)Genomic analysis revealed that there was no significant difference in the number of unique genes among different strains,and there was no obvious correlation between the evolutionary relationship and the remission ability of strains.Compared to R2,R4 and R5 which showed better alleviation effects on colitis had higher proportions of functional genes related to glycolysis or pentose phosphate pathway,which might result in a higher content of SCFAs.And compared to Re1,Re3 and Re5 with better colitis relief abilities had many functional genes related to phage.This suggests that Re3 and Re5 may obtain more specific functional genes through gene horizontal transfer.