The Function And Mechanism Research Of FBW7 In Intestinal Inflammation

Intestinal inflammatory disease is a common intestinal disorder,which seriously plagues human life and health.It mainly manifests as digestive dysfunction,abdominal pain,diarrhea,and blood in the stool,and other clinical symptoms.Many external stimuli can cause intestinal inflammatory damage,such as chemical damage and radiation stimulation.In this article,the intestinal inflammatory diseases caused by chemical injury and irradiation were studied to explore the mechanism of its development and possible therapeutic targets.Inflammatory bowel disease（IBD）,which mainly includes Crohn’s disease and ulcerative colitis,is a group of chronic diseases that cause intestinal dysfunction.Although the exact etiology has not been fully understood,studies have found that IBD occurs when environmental factors are stimulated by factors that lead to an inappropriate host inflammatory response.Acute radiation syndrome is an acute sickness that occurs when the body got therapeutic or accidental exposed to high doses of ionizing radiation.In humans,due to the different radiation sensitivity of each organ,diverse radiation syndromes can occur at different doses of radiation.Villous epithelial cells and crypt stem cells have a very important influence on villus regeneration and epithelial cell integrity.When exposed to doses over 10 Gy in humans,these cells are inhibited or even killed,resulting in epithelial damage,impaired intestinal barrier function,inflammation,and even gut-derived sepsis.Severe gastrointestinal injury causes bacterial enteritis,malabsorption,diarrhea and loss of fluid,leading to the development of fatal gastrointestinal syndrome（GIS）.FBW7（F-box and WD repeat domain-containing7,FBW7）,also known as Fbxw7,hsel10,CDC4 and AGo,is an E3 ubiquitin ligase complex.FBW7 has been reported to target various proteins,functioning in tumorigenesis,tumor development and progression,for degradation,so Fbw7 is supposed to be an important tumor suppressor gene.FBW7gene mutations and deletions have been observed in a variety of tumors,such as leukemia,gastric cancer,rectal cancer,and ovarian cancer,and its role in tumorigenesis has been extensively studied.However,the role of FBW7 in the development of colitis and irradiation induced injury has not been studied.To explore the mechanism of FBW7 in colitis and irradiation induced injury,intestinal epithelial-specific Fbw7 conditional knockout mice(Vil-Cre;Fbw7^flox/flox,Fbw7^ΔG)were established using the Cre/LoxP system.Then,a model of colitis was induced by 3%DSS,and an irradiation induced intestinal injury model was established by giving the mice whole body radiation of 8 Gy ⁶⁰Go.Then we observed the effects of the intestinal specific deletion of FBW7 in the two animal models separately and explore the biological function of FBW7 in development and progression of the two diseases.Objective1.To determine the involvement and molecular mechanism of FBW7 in the pathological response of IBD.2.To explore the involvement and mechanism of FBW7 in the pathological process of GIS.Methods and Results1.Intestinal specific deletion of FBW7 aggravated the DSS-induced colitisWe established intestinal epithelial-specific Fbw7 conditional knockout mice(Vil-Cre;Fbw7^flox/flox,Fbw7^ΔG)using the Cre/LoxP system and constructed intestinal tract by drinking 5%DSS for 5 days inflammation model.Deletion of FBW7 aggravated the inflammatory response of DSS-induced colitis,including accelerated weight loss,increased blood in the stool and diarrhea,increased MPO expression in colonic cells,increased colonic length loss,and increased inflammatory damage in the colonic epithelium.There are 5 Fbw7^ΔG mice,while no WT mice,died during the experiment.In addition,DSS-induced upregulation of pro-inflammatory cytokines IL-1β,IL-6 and TNF-αwas observed in Fbw7^ΔG mice,which caused exacerbating intestinal damage.For the first time,our group found that deletion of FBW7 in intestine aggravated the DSS-induced colitis.2.Intestinal specific deletion of FBW7 activated NF-κB signaling pathwayOur group found that in the DSS-induced colitis model,intestinal specific deletion of FBW7 activated NF-κB signaling pathway.Immunofluorescence of NF-κB p65 showed that P65 expression was up-regulated and increased nucleus location of p65 in Fbw7^ΔGG mice.We then found that IKK,p-IκB p65 and p-p65 were up-regulated.The results demonstrated that p65 activates the NF-κB signaling pathway in DSS-induced colitis models,which up-regulated the expression of IL-1β,IL-6 and TNF-αand caused increased inflammatory damage to intestine.3.FBW7 deficiency in intestine protects mice against radiation-induced gastrointestinal syndromeContrary to the function of FBW7 deficiency in aggravating inflammatory bowel disease,deletion of FBW7 in intestine has been shown to protect mice against radiation-induced intestine damage.Mice were exposed to 8 dose of whole body irradiation to establish radiation-induced intestinal injury model.We found FBW7deficiency caused reduced mortality,increased mean survival time,milder weight loss and blood in the stool.Compared with the control group,the edema and hemorrhage in the jejunum of Fbw7^ΔG mice were milder,and the damage to intestinal villi and crypts were also alleviated.The expression of MPO in jejunum epithelial cells was decreased.Pro-inflammatory cytokines,such as IL-1β,IL-6 and TNF-αwere downregulated.4.Deficiency of FBW7 in intestine inhibited radiation-induced apoptosis and promoted intestinal repair.Our group tested the apoptosis and proliferation of jejunum epithelial cells in a model of radiation-induced intestinal injury.The results showed that the intestinal deficiency of FBW7 inhibited radiation-induced apoptosis and thus reduced intestinal damage and enhanced tolerance of radiation injury;Deficiency of FBW7 also promoted the proliferation of intestinal crypt cells,thereby enhancing intestinal repair capacity.ConclusionIn the DSS-induced colitis,deletion of FBW7 aggravates the inflammatory response,through activation of NF-κB signaling pathway.In the radiation-induced gastrointestinal injury,deficiency of FBW7 protects mice against radiation-induced gastrointestinal syndrome by inhibiting radiation-induced apoptosis and promoting the proliferation of intestinal crypt cells.We for the first time determined the distinct roles of FBW7 in the above two models and provided a new research idea for further study of colonic inflammation and reflex intestinal injury,providing a theoretical basis for finding new therapeutic approaches.At the same time,our research broadens the research field of FBW7 and provides a new perspective on the further research of FBW7.