The Role Of Irisin In Ulcerative Colitis Mice And Its Possible Therapeutic Mechanism

Background:UC is a kind of chronic non-specific inflammatory bowel disease(IBD),with classic symptoms including pus and bloody stools with or without mucus,tenesmus and abdominal pain that can be relieved after cacation.With the development of economic level and the improvement of the quality of life,the prenalence of UC cases is 11.6/100 000 and the incidence has been increasing in China recently.Although the cause of UC is still unknown,more than 50 susceptibility loci and disease‐associated genes have been identifie.This has largely explained the genetic predisposition in the pathogenesis of UC.UC is a multifactorial disease that is triggered by several factors such as environment,immune ability,mental psychology,intestinal flora,genetic predisposition.One of the irreplacable factors leading to UC is the unique ecological environment formed by the intestinal flora.There are more than 100 trillion microbes in the human gut.Compared with normal intestinal flora,the microbial diversity of UC patients’ decreased,and the structure of flora changed by performing High-throughput sequencing.In some studies the application of beneficial bacteria can improve the symptoms of DSS-induced UC mice.Irisin is a newly discovered factor named after the Greek goddess Iris,which is released from skeletal muscle.It is a polypeptide consisting of 112 amino acids secreted by type III fibronectin 5(FNDC5).It has been confirmed that Irisin plays a role in the pathogenesis of various diseases such as diabetes,obesity,thyroid disease,cardiovascular disease,nervous system disease,chronic kidney disease,liver disease,autoimmune disease and so on.What’s more there is a high expression of Irisin in some tumor tissues.In the study of inflammatory,it is comfirmed that Irisin has an anti-inflammatory effect,but there is no uniform conclusion about the specific mechanism of action.Irisin has been studied in the inflammatory response of hepatitis and acute lung injury.There’s no research about Irisin related to ulcerative colitis(UC)until now.Objective:This study was to investigate the role of Irisin in the pathogenesis of UC,and the relationship between intestinal inflammation and changes in bacterial structure.We aimed to elucidate the possible mechanism of exogenous Irisin on the degree of UC inflammation and changes in bacterial structure.Methods:Collect normal human serum samples,colon tissue samples and stool samples from the physical examination center and clinical active UC patients’ data,serum samples,colon tissue samples and stool samples from ward in our hospital.Establish the DSS-induced UC mouse model.In this research,patients were divided into control group and UC group in clinical trials.In each group,the Mayo score,Baron grade,HE staining,and histopathological scores were calculated,erythrocyte sedimentation rate(ESR)and C-reactive protein(CRP)were tested by routine method,the levels of Irisin,IL-12 and IL-23 in serum were determined by ELISA kits,and the expression level of FNDC5 was measured through Western bolt,furthermore,the differential floras of feces were observed by the high-throughput sequence.In the animal part,6-8 weeks of mice were randomly divided into 4 groups,10 in each group.The mice with normal water and the mice with 4% DSS water were respectively set as the control group and UC group.The mice with normal water and subcutaneous injection of Irisin and the mice with 4% DSS water and subcutaneous injection of Irisin group were respectively set as Irisin group and UC+Irisin group.Macroscopic score and histological score were evaluated in each group,serum IL-12 and IL-23 levels were detected through ELISA kits,the number of macrophages was measured by immunofluorescence,and the feces were observed through the high-throughput sequence.Results:(1)Compared with the control group,the ESR(P<0.01)and the CPR(P<0.01)of active UC were increased,the Mayo score and the Baron grade increased evidently(P<0.01).The significant pathological changes in colon tissue can be observed(P<0.01),and the IL-12 and IL-23 in serum were increased(P<0.01).(2)While in serum of UC patients,Irisin level was significantly reduced(P<0.01),and the expression of FNDC5 was down-regulated(P<0.01).(3)The results of microbial diversity analysis showed that the most obvious five bacteria changed in the stool of active UC patients were Enterococcus,Lactobacillus,Bacteroides,Bifidobacterium,and Escherichia coli.(4)Correlation analysis revealed that Irisin level was negatively correlated with Baron grading(r=-0.813,P<0.01),the pathological scores(r=-0.735,P<0.01),and abundance of Enterococcus(r=-0.783,P<0.01),but positively correlated with Lactobacillus(r=0.376,P<0.01).(5)Animal experiments showed that the body weight of UC mice decreased significantly(P<0.05),while the spleen weight increased without statistical significance,macroscopic score and the histopathological score were increased(P<0.01).As was expected,the levels of IL-12 and IL-23 were elevated(P<0.05 or P<0.01),and the abundance of macrophages became strong.However,in Irisin-pretreated mice,there’s a tendency of decrease in spleen weight but without statistical significance,while the macroscopic score and the histological score were decreased(P<0.05 or P<0.01),and the macrophages expression in colonic tissue was down-regulated,in addition,the elevated IL-12 level was reversed by Irisin(P<0.05).The fecal bacteria in the UC group was significantly different from the control group and Irisin group,according to the principal component analysis(PCoA)and unweighted group averaging(UPGMA)cluster analysis,but partially overlapped with the Irisin pretreatment group.The analysis of the key bacterial heatmap showed that the control group and the Irisin group were similar in composition,and the UC group was significantly different from the two above,while the composition of the Irisin-pretreated mouse tends to be normal.In conclusion,Irisin plays an important role in the pathogenesis of UC and is closely related to the changes of intestinal flora.There’s obvious anti-inflammatory effect in Irisin,which mechanism may be related to the reduction of key factors and the improvement of intestinal flora.