Irradiation-induced Alteration Of Gut Microbiota And Its Role In Intestinal Injury

Exposure to short term high-dose irradiation(IR)or long-term low-dose IR leads to tissue damage,causing radiation syndrome,also known as radiation disease.Intestine is highly sensitive to IR.Radiation-induced intestinal injury can destroy the intestinal mucosal barrier,leading to severe intestinal infection and multiple organ dysfunction syndrome(MOSF),a critical condition resulting in the failure in rescueing acute radiation disease.In addition,intestinal damage in the course of radiotherapy for clinical malignant tumors becomes important.Thus,it is of great significance finding protective measures for radiation-induced intestinal injury.Recent studies have shown that transplantation of microbiota from healthy mice markedly alleviates radiation-induced gastrointestinal syndrome in mice after radiation,indicating that microbiota may be related to lessening radiation-induced intestinal injury.Moreover,intestinal flora imbalance can also affect the intestinal barrier function.However,it remains unknown whether the intestinal microbiota is disrupted by IR and which role of gut microbiota has played in the response to IR.More important,if the role of microbiota in IR-induced intestinal injury is confirmed,can agents that target microbiota be applied for the prevention and treatment of IR-induced intestinal injury? ObjectivesTo examine intestinal flora in mice with total body irradiation(IR),determine the potential role of gut microbiota in IR-induced intestinal injury,and evaluate Lactobacillus LGG and metformin,a diabetes therapeutic compound,in the protection of intestinal epithelial cells from irradiation-induced injury.Methods1.The outcome of TBI on intestinal damage was determined by measuring the survival rate,body weight and intestinal injury index of mice after IR.2.The impact of radiation on the diversity and composition of microbiota was analyzed by 16 s rDNA sequencing.3.Gut bacteria altered by TBI were identified by heat map.4.Lactobacillus,a class of bacteria depleted in the guts of mice with TBI,was applied into a sterile mouse model for validating the functional of microbiota correction in the protection from radiation-induced intestinal injury.5.After the mice were pretreated with metformin and irradiated,the ileum contents were sequenced to determine the effect of metformin on the diversity and composition of the intestinal flora.6.Gut bacteria manipulated by metformin in TBI mice were characterized with pie chart and heat map.7.In conventional and sterile mouse models,we evaluated the effects of metformin on the survival,body weight,and intestinal injury index of TBI mice and validated the role of metformin in the protection of radiation-induced intestinal damage by leveraging the composition and diversity of microbiota.8.Levels of FXR,FGF15 and ?-H2 AX in ileum tissues of TBI mice treated with metformin and lactobacillus were analyzed by immunohistochemistry staining.Results1.The survival rate and body and feces weight were substantially reduced and the ileum length of mice was significantly shortened in TBI mice.Disrupted villi of ileum,vanished crypts,and a weakened mucosa were observed in HE staining with intestinal tissues of TBI mice2.The diversity and abundance of intestinal flora were reduced and the composition was altered in TBI mice.3.The abundance of intestinal Lactobacillus,Streptococcus and Burkholderia was decreased,and the component of Escherichia,Candidatus and Enterococcus was increased in TBI mice.Lactobacillus was identified as the top listed gut genus depleted by TBI.4.Administration of LGG significantly rescued the weight loss of irradiated mice.The feces weight and ileum length were significantly increased,and the tissue damage was attenuated in LGG-applied TBI mice as compared with those with =TBI/vehicle treatment.5.Similarly,mice pretreated with metformin demonstrated an increased diversity and abundance of gut microbiota and an improved composition of the microbe after TBI.6.Metformin treatment led to the abundance of Lactobacillus,Akkermansia,Lactococcus,Streptococcus,Clostridium,and Burkholderia,and a tendency of decrease in Escherichia,Candidatus,Enterococcus in TBI mice.Lactobacillus was verified to be the mostly increased genus in gut microbiota7.In the conventional mouse model,metformin protected the intestine from IR-induced injury and significantly improved the survival rate and weight loss of TBI mice.No such observation was displayed in sterile mice pretreated with metformin and irradiated by TBI,suggesting the necessity of microbiota in metformin-induced intenstinal protection against TBI.8.FXR,FGF15 and ?-H2 AX were strikingly increased in ileal crypt cells by the IHC analysis in TBI mice treated with metformin or LGG.Conclusions1.TBI leads to the reduction of the diversity and abundance of intestinal flora in mice.The composition of gut microbiota is also altered in the TBI mice.2.Alterations of gut microbiota,in particular the reduction of Lactobacillus,play a critical role in TBI-induced intestinal injury.Administration of Lactobacillus to TBI mice substantially mitigates IR-induced intestinal injury and rescues the mice from IR-caused lethal.3.Metformin protects the mice from radioactive intestinal injury by improving the composition and diversity of intestinal flora,such as elevation of Lactobacillus,in the TBI mice.4.Enriched gut Lactobacillus activates the FXR-FGF15 signaling,and hence promotes DNA-damage repair of epithelial cells and mitigates TBI-induced intestinal injury.Application of metformin escalates the abundance of Lactobacillus and,thereby,activates the FXR-FGF15 axis and attenuates radiation-induced intestinal damage.