Effect Of Protein Diets And Akkermansia Muciniphila On Intestinal Function In DSS-Induced Colitis Mice

Protein is one of the most important nutrients in human diets,the amino acid composition,structure and the digestibility can vary due to different protein sources.After being digested and absorbed in the intestine,the undigested portions from diets may differ in the large intestine,which could lead to alteration in microbiota composition and influence the capacity of anti-inflammatory.Colitis is a common inflammatory disease,and the effects of different sources of dietary proteins on the susceptibility of colitis and its mechanisms are unknown.Akkermansia muciniphila(A.muminiphila)was reported to promote mucus secretion and relieve colitis.The ability of A.muciniphila to repair inflammation in the recovery stage of colitis under different dietary protein feeding conditions remains to be further studied.In this study,six-week-old C57BL/6J mice were used to explore effects of protein diet and Akkermansia on the physiological,pathological and gut microbiota profile as well as the associated mechanisms by microbiome and molecular biological techniques.The main contents are listed as follows:1.Effect of dietary protein on the physiological and biochemical status of DSS induced colitis mice.Six-week-old C57BL/6J mice were fed with casein or chicken protein-based diet for27 days.2% DSS and A.muciniphila were used to treat the mice on day 14 and day 21,respectively.The effects of casein and chicken protein-based diets on body weight,food intake,spleen weight,colon length,DAI score,and serum inflammatory factors in DSS induced colitis mice at different stages were explored.The results showed that there was no significant difference in body weight,food intake and serum inflammatory factors between casein and chicken protein groups on day 14.After treatment of 2% DSS,body weight and colon length decreased,but spleen weight,DAI score,and serum inflammatory factor TNF-α,IL-6 and IFN-γ levels increased.Protein diets did not affect these parameters except the body weight.Oral gavage with A.muciniphila led to reduction in spleen weight and DAI score.Compared with the Ca-DSS-AKK group,weight of Ch-DSS-AKK group was lower,while DAI score was higher and colon was shorter.Therefore,oral gavage with A.muciniphila help the casein-diet-feed mice recover faster.2.Effects of dietary protein on susceptibility of colitis in miceAfter 2% DSS treatment for 7 days,the colonic tissue was taken for HE staining and RT-PCR.The colonic contents were collected for microbiota sequencing.After DSS treatment,the inflammatory cells were infiltrated in colonic tissue of mice,and the crypt structure destroyed with a lack of the goblet cells.The histological score was increased in all groups,but there was no significant difference between casein and chicken protein groups.RT-PCR showed that TNF-α and COX-2 were significantly upregulated by DSS treatment,while MUC1,MUC2,ZO-1,Claudin-1 and Occludin were significantly downregulated.The sequencing data showed that the diversity of gut microbiota decreased by DSS treatment.The relative abundance of Firmicutes and Actinobacteria significantly decreased,while the relative abundance of Proteobacteria increased.On the genus level,the relative abundance of Escherichia-Shigella in Ca-DSS group was significantly higher than that of Ch-DSS group,however,no significant differences were observed in other genera with higher relative abundance,such as Muribaculaceae＿norank,Ileibacterium,Faecalibaculum,Bacteroides,Dubosiella,Blautia,Klebsiella,and Akkermansia.Therefore,dietary proteins showed no significant different effect on the susceptibility of colitis in mice.3.Effects of dietary protein and A.muciniphila on recovery period in colitis miceHE staining,AB staining,immunofluorescence and high-throughput sequencing stretagies were applied to investigate the effects of dietary protein and A.muciniphila on recovery period of colitis mice.A.muciniphila was administrated by oral gavage.After 6days of recovery,the histological scores of DSS-induced colitis mice either gavage with A.muciniphila or not were higher than those in the control group.The histological score in casein group was lower than that in chicken protein group whether oral gavage with A.muciniphila or not,which suggested that the casein group was less inflammatory than the chicken protein group and recovered faster.The results further indicated that oral gavage with A.muciniphila could overall accelerate the recovery of colitis mice by increasing mucus thickness and MUC2 m RNA expression,decreasing TNF-α m RNA,as well as regulating the relative abundance of Ruminococcaceae NK4A214 group,Bifidobacterium,Ruminococcaceae UCG-014,Roseburia,Ruminiclostridium and Lachnospiraceae NK4A136 group.