Angiotensin Converting Enzyme 2 Alleviates Intestinal Barrier Dysfunction In Septic Mice

Background and PurposeSepsis is a multi-organ dysfunction caused by unbalanced immune response to infection.The compromised intestinal barrier is a starting factor in the occurrence of sepsis,which initiates intestinal symbiotic microbial translocation,bacteremia and aggravate the injury of extra-intestinal organs.Angiotensin converting enzyme 2(ACE2)is an important negative regulator of renin-angiotensin system(RASS).In recent years,it has been reported that ACE2 can play a role through RASSindependent pathway,such as cell membrane binding ACE2 can affect the expression of neutral amino acid transporter B0AT1 in intestinal epithelial cells,and ACE2 deficiency worsens microbial imbalance and intestinal inflammation in a model of colitis.However,the role and mechanism of ACE2 in sepsis is not clear,especially in intestinal injury.The study is to explore the effect of ACE2 on intestinal barrier function in septic mice and its potential mechanism.Methods the related clinical indexes of patients with sepsis were detected and recorded,and the level of serum ACE2 in patients with sepsis was detected by ELISA.The model of sepsis and related intestinal injury was established by cecal ligation and puncture(CLP).The organ damage of mice was evaluated by histology and molecular biology experiments.Pseudo-aseptic mice(ABX treatment)and fecal bacteria transplantation(FMT)were used to verify the role of intestinal microbiota in the process of sepsis.16srDNA sequencing and analysis were used to describe the differences of intestinal microbial diversity in mice.MethodRelevant clinical indicators of sepsis patients were detected and recorded.Serum ACE2 levels in sepsis patients were detected by ELISA.The model of sepsis and its associated intestinal injury was established by cecal ligation and perforation(CLP).Histology and molecular biology were used to evaluate the organ injury in mice.Pseudo-sterile mice(ABX treatment)and fecal bacteria transplantation(FMT)were used to investigate the role of intestinal microbes and metabolites in the course of sepsis.16srDNA sequencing and analysis were performed to delineate differences in intestinal microbial characteristics and diversities in mice.Results1.Compared with the serum levels of 18 healthy volunteers and 50 septic patients,the level of ACE2 in septic patients increased significantly.2.The level of serum ACE2 in septic mice increased,and small intestine might be a major source of the increased soluble ACE2(s-ACE2).3.Knockout of ACE2 decreased the survival rate of septic mice.4.Intestinal barrier function of ACE2 knockout mice was aggravated,bacterial translocation increased,lung injury and kidney injury aggravated in sepsis.5.The bacterial clearance test suggested that the protective effect of ACE2 on intestinal homeostasis and extra-intestinal organ injury partly depended on intestinal microbiota.6.The experiment of fecal bacteria transplantation showed that the wild-type mice transplanted with ACE2 knockout mouse feces were less tolerant to sepsis,and the intestinal barrier function and extra-intestinal organ damage were more severe.7.16srDNA sequencing of intestinal microbiota showed that there was a significant difference in intestinal microbiotaadiversity and β diversity between ACE2 knockout mice and wild-type mice.At the species level,the abundance of Akkermansia muciniphila and Ligiactobacillus murinus(Lactobacillus murinus)decreased significantly.Conclusion:This study shows that the level of serum ACE2 in patients with sepsis is significantly increased,which is positively correlated with the SOFA score of sepsis,and the circulating ACE2 might mainly come from the small intestine.ACE2 is very important for maintaining intestinal homeostasis,which can be achieved by intestinal microbiota.Therefore,ACE2 may be a candidate molecule for intestinal homeostasis protection and provide new ideas for clinical treatment.