Shewanella Algue Accelerates Colorectal Adenoma Growth In Apc^min/+ Mice Via IL-6/STAT3 Pathway

Research background and purposeColorectal adenoma is recognized as colon cancer precursors.Many studies have found that the occurrence and development of colorectal tumor is associated with gut microbiota.Metagenomics links colon cancer microbiome to colorectal adenoma-cancer,and indicating that gut microbiota plays an important role in the the occurrence and development of colorectal adenomas.APC（adenomatous polyposis coli）gene is a tumor suppressor genes,and mutations are prone to cause colon cancer.More than 70%of colorectal adenoma has APC gene mutation,and APC gene mutation is an early event in the multi-step process of colorectal cancer formation.This experiment mainly studies the effect of different intestinal bacteria on the growth of colorectal adenomas in Apc^min/+mice.MethodTwenty-eight 4-week-old Apc^min/+mice were randomly divided into four groups,which were Shewanella algae group,Lactobacillus casei group,Fusobacterium nucleatum group and blank control group.The Shewanella algae group was fed with Shewanella algae 10⁹ CFU every day.The Fusobacterium nucleatum group was fed with Fusobacterium nucleatum 10⁹ CFU every day.The Lactobacillus casei group was fed with Lactobacillus casei 10⁹ CFU every day,The control group was fed with PBS every day.The gavage volume was 0.2ml.Apc^min/+mice were sacrificed after 12 weeks,and the intestinal tumor size and number of Apc^min/+mice were recorded.The adenoma cell morphology of Apc^min/+mice in each group was observed by Hematoxylin-Eosin staining.The serum of mice was collected,and the content of TNF-α,IL-6,IL-17 was measured by ELISA,and the content of T TNF-α,IL-6,IL-17 m RNA in colorectal adenoma tissues was detected by RT-q PCR.The expression of Ki-67,p-STAT3 in colon tumors of Apc^min/+mice were measured by immunohistochemistry.The relative expression of STAT3 and p-STAT3 was detected by western blot.Result1.Gut microbiota promotes the development of colorectal adenomas.There were colorectal adenomas in both the experimental group and the control group.The number of colorectal adenomas in Fusobacterium nucleatum group and Shewanella algae group was higher than in the control group.Difference was statistically significant（P<0.05）。There was no significant difference in the number of colorectal adenomas in the Lactobacillus casei group compared with the control group.（P>0.05）。Hematoxylin-Eosin staining results showed that the intestinal epithelial structure of the mice in each group was disordered,appearing atypical hyperplasia,different cell sizes and morphologies,inconsistent gland sizes,disordered arrangement of glandular structures,and mitotic phase,suggesting adenomatous changes.Compared with the PBS control group,the Ki-67 positive cell rate was significantly increased in the Shewanella algae group（P<0.01）,Ki-67 positive cell rate increased significantly in the Fusobacterium nucleatum group.（P<0.01）.and there was no different in ki-67 positive cell rate in Lactobacillus casei group.2.Gut microbiota promotes the formation of inflammatory microenvironment in colorectal adenomasCompared with the control group,there was no significant change in serum TNF-α（P>0.05）,increased serum IL-6（P<0.05）,and increased serum change IL-17（P<0.05）in Shewanella algae group.Compared with the control group,there was no significant change in serum TNF-α（P>0.05）,increased serum IL-6（P<0.05）,and increased serum change IL-17（P<0.05）in Fusobacterium nucleatum group.Compared with the control group,there was no significant change in serum TNF-α（P>0.05）,no significant change in serum IL-6（P<0.05）,and no significant change IL-17（P<0.05）in Lactobacillus casei group.3.Gut microbiota promoted the expression of STAT3 in colorectal adenomaColon tumor tissues of each group were collected.RNA was extracted,and the content of STAT3 m RNA was detected by q PCR,and the expression of p-stat3 was detected by IHC and Western blot.Compared with the control group,the content of STAT3 m RNA in the colon tumor tissues of Shewanella algae group was increased（P<0.01）,and the expression of p-STAT3 protein was increased.Compared with the control group,the content of STAT3 m RNA in the colon tumor tissues of Fusobacterium nucleatum group was increased（P<0.01）,and the expression of p-STAT3 protein was increased.Compared with the control group,there was no significant change in the content of STAT3 m RNA in colon tumor tissue（P>0.05）,and no significant change in p-STAT3 protein.ConclusionThe Shewanella algae could promote the growth and development of colorectal adenomas in Apc^min/+mice.Feeding Shewanella algae could increase the level of IL-6and IL-17 in the colon of Apc^min/+mice and promote the formation of inflammatory microenvironment in the colon.The intestinal carcinogenic gut microbiota may promote the expression of related inflammatory factors downstream of STAT3 by upregulating the IL-6/STAT3 pathway,promote the formation of inflammatory microenvironment in the colon,and then promote the growth of intestinal adenomas in APC^min/+mice.