Mast Cell Tryptase Promotes Inflammatory Bowel Disease-Induced Intestinal Fibrosis

Background Intestinal fibrosis is the final pathological outcome of chronic intestinal inflammation without specific therapeutic drugs,which leads to ileus and surgical intervention.Intestinal fibrosis is characterized by excessive deposition of extracellular matrix(ECM).Recent studies on intestinal fibrosis indicate that the activation and differentiation of fibroblasts,and the proliferation and migration of fibroblasts are the main factors driving intestinal fibrosis.Intestinal fibroblasts are activated to differentiate into myofibroblasts that express ?-smooth muscle aorta(?-SMA).Myofibroblasts mediate tissue repair by producing extracellular matrix components and physical contraction to promote wound healing and fibrosis.Mast cells(MCs)are members of the sentinel immune cell population.Research in recent years has found that MC is involved in inflammation and fibrosis of various organs by secreting tryptase,histamine and other mediators.However,the role and regulatory mechanism of MC and tryptase in intestinal fibrosis have not been reported.Methods In this study,we analyzed changes in MCs,tryptase and extracellular matrix components in human fibrotic and control intestine.We constructed dextran sodium sulfate-induced intestinal fibrosis models using wild-type mice,MC-deficient mice and MC-reconstruction mice to to explore the role and mechanism of MC and its tryptase in intestinal fibrosis.The effects of MC and tryptase on fibroblasts were evaluated using human MC lines(LAD-2 and HMC-1),commercial tryptase protein,tryptase inhibitor APC366,PAR-2 receptor antagonist ENMD-1068 and CCD-18 Co fibroblasts.Results Whether they are human colon samples or mouse colon samples,the fibrotic intestinal tissues have a greater number of MCs and higher expression of extracellular matrix component proteins or genes than the fibrotic control group.Compared with wildtype mice,MC-deficient mice significantly alleviated DSS-induced intestinal fibrosis.After MC reconstruction in MC-deficient mice,the alleviating effect disappeared.Tryptase,as a content stored in MC granules,was released into fibrotic intestinal tissues in the form of degranulation,resulting in increased expression of tryptase.Compared with the ethanol group,tryptase inhibition group(APC366 group)significantly alleviated intestinal fibrosis.CCD-18 Co fibroblasts,when co-cultured with MCs or treated with tryptase,were activated to express more ?-SMA protein and secrete extracellular matrix component proteins(such as collagen and fibronectin).PAR-2,as a known receptor of tryptase,activated the AKT / mTOR pathway of CCD-18 Co fibroblasts and promoted the activation and differentiation of intestinal fibroblasts when combined with tryptase.Conclusion MC tryptase promotes inflammatory bowel disease-induced intestinal fibrosis.The underlying mechanism is that tryptase promotes the differentiation of fibroblasts into fibrotic phenotype myofibroblasts by activating the PAR-2 / Akt / mTOR pathway of fibroblasts.