| Background:Inflammatory bowel disease(IBD),including ulcerative colitis(UC)and Crohn’s disease(CD),is characterized by chronic,relapsing gastrointestinal inflammation.IBD is a world-wide health problem with sharply increasing prevalence among all populations.Patients with IBD suffer poor quality of life,and are at a 2-to 8-fold higher risk of colorectal cancer(termed colitis-associated colorectal cancer,CAC).However,due to unclear pathogenesis,the slow progress of related drugs and treatment methods has become the biggest obstacle to the effective treatment of IBD.Therefore,it is urgent to clarify the molecular mechanism of IBD and provide theoretical support for accelerating the development of effective therapeutic drugs.The immune response of intestinal mucosa imbalance is main cause of IBD.It has been confirmed that macrophages,dendritic cells and other pro-inflammatory cells are activated abnormally in the course of IBD,and the related cytokines such as IL-6,IL-1 β,TNF-α and IL-17 A are also abnormal.However,anti-inflammatory cells,such as regulatory T cells(Treg)and myeloid derived inhibitory cells(MDSCs),have defects in quantity or function.Therefore,study of the molecular regulatory mechanism of immune cells in colitis is the key to restore intestinal immune homeostasis and prevent IBD.In addition,there is abnormal histone modification in IBD,which is considered to be an important part of the pathogenesis of IBD.Enhancer of zeste homolog 2(EZH2),a major histone methyltransferase,plays an essential role in immune regulation via trimethylating lysine 27 on histone H3(H3K27Me3),and then silencing the downstream gene expression.EZH2 can regulate immune response in many ways: promote the self-renewal of hematopoietic stem cells(HSCs),maintain the quantity and function of peripheral Treg,Th1,Th2,Th17,and macrophages.The loss of EZH2 activity will significantly damage the development process of T and B cells,promote the differentiation and development of NK cell precursors,reduce the proportion of T and B cells in bone marrow and peripheral tissues,and increase the number of NK cells.Recently,EZH2 expression was abnormal in IBD patients.Interfering with the function of histone regulators may be an effective way to develop new therapeutic strategies.In view of the known role of immune cells in the pathogenesis of IBD and the involvement of EZH2 in the development,differentiation and function of immune cells,our task is to study whether inhibition of EZH2 methyltransferase activity can affect the progress of IBD by changing the intestinal immune response.Methods:1.Explore the effect of inhibition of EZH2 methyltransferase activity on experimental IBD.We first selected a widely used chemical reagent DSS to add into the drinking water for C57BL/6 mice,and then selected EZH2 methyltransferase inhibitors GSK343 for tail vein injection at different time points to establish the IBD prevention model and treatment model.The changes of pathology and symptoms were detected after the mice were treated for a set time.We extracted the protein in the distal colon and detected the related inflammatory factors by ELISA.2.Explore the effect of inhibition of EZH2 methyltransferase activity on CAC formation.The model of CAC induced by AOM and DSS was used and GSK343 was injected into caudal vein.We observed the tumor burden and morbidity in order to evaluate the effect of GSK343 on the formation of CAC.3.Explore the effect of inhibition of EZH2 methyltransferase activity on IBD intestinal immune cells.The IBD model of C57BL/6 mice was established by DSS,and GSK343 was injected into tail vein.The proportion and quantity of Th17,Treg,macrophage,dendritic cells,eosinophils and MDSC in colonic lamina propria(cLP)of GSK343 treated group and control group were compared by flow cytometry.Results:1.Inhibition of EZH2 methyltransferase activity can effectively prevent and treat IBD.Prophylactic treatment with GSK343 reduces DSS induced pathological and clinical symptoms,including body weight,DAI,colon length and histological score.At the same time,the levels of IL-6 and IL-1 β decreased significantly,while the levels of TNF-α and IL-17 A were not affected.When IBD is formed,GSK343 treatment can still achieve significant benefits.2.Inhibition of EZH2 methyltransferase activity can effectively reduce the prevalence and tumor load of CAC.By day 72,whereas 100% of control group mice developed CAC,only 50% of GSK343-treated mice did,and they had a reduced tumor burden.By day 84,although similar percentages of control and GSK343-treated mice developed CAC,GSK343-treated mice had a significantly reduced tumor burden.3.Inhibition of EZH2 methyltransferase activity is effective for IBD by increasing the number of MDSCs.Compared with the control group,the percentage and absolute number of Th17,Tregs,macrophages,dendritic cells and eosinophils in the cLP of GSK343 treatment group had no significant difference.However,the proportion of MDSC increased,and the number of Gr-1 positive cells increased.The protective effect of GSK343 on colitis can be significantly reversed by using specific Gr-1 antibody to clear MDSCs.Conclusion:EZH2 inhibitor GSK343 can prevent and treat experimental IBD induced by DSS.At the same time,due to the control of colonic inflammation,the incidence of CAC and tumor load have improved.This benefit may come from the inhibition of EZH2 methyltransferase activity to stimulate the increase of MDSCs. |
