Discussion
UC is one of the main types of IBD which is affect the bowel5 and it could develop into colorectal cancer(CRC)7. EGCG is a major compound of tea9 and it could attenuate colitis in UC mice10. However, the mechanism of EGCG in the treatment of colitis should be further investigated. A previous study reported that regulation Notch signaling pathway could enhance intestinal barrier function in colitis mice4 and it could be a target of chronic inflammatory diseases, such as IBD6. In our previous studies, we reported that Notch is a receptor of EGCG11,17. In this study, we focused on the Notch signaling pathway which plays a role in the development of UC and aberrant activation of Notch1 was attributed to the severity of CRC18. Our results found that the inflammation state and Notch expression were altered by EGCG treatment in Caco-2 cell which induced by LPS. Furthermore, we also identified the mechanism is present in UC mice, which is induced by DSS in C57/BL6 mice. These results suggested that EGCG could play a role to against colitis by regulation Notch signaling pathway in UC mice.
Previous studies have been reported that Notch could regulation inflammation19,20 and modulates macrophages polarization21. Some studies also propose that targeting the Notch signaling pathway could be a potential therapeutic strategy to improve chronic inflammatory diseases6,22,23. A new research reported that the transcription levels of Notch1 and Hes-1 genes were significantly elevated in UC patients22 which reminder us to reflect on important of Notch in UC. And recent studies have revealed the unexpected importance of epithelial cells in the pathophysiology of IBD24. So, in this study, we take human epithelial colorectal adenocarcinoma Caco-2 cell line as inflammation model25 to assess the inflammatory responds with LPS treatment. Our research found that the inflammation responds was increased by LPS treatment in Caco-2 cell (figure 1A and 1B) or enhance intestinal immune response in DSS induced UC mice colon (figure3 and figure 4). And the levels of Notch1 and cleaved-Notch1 expression were also increase by LPS treatment in Caco-2 cell (figure 1D) or DSS induced UC mice colon. These results was similar to the previous study report22,26,27. And our finding also showed that Notch could be a target to therapy hyper-inflammatory respond and UC. Moreover, this research also proved that Notch activate could contribute to M1 macrophages accumulation. These founds suggest that activate Notch play a role to induced UC as other studies report7,8,22.
The effect of EGCG on perfect IBD has been reported in previous studies28,29. And our previous studies have been demonstration that Notch was a target of EGCG11,30 to attenuate inflammation responds or other chronic disease17. So, we think the Notch maybe was a target of EGCG to attenuate UC. In this study, we found that EGCG could decreased the cytokine level which induced by LPS in Caco-2 cell (figure 1A and 1B). The levels of Notch expression were increased and Notch was activation by LPS stimulation in cell, but, the phenomenon was disappeared by administration EGCG in vitro (figure 1D). Moreover, the inflammation state of colon and macrophages accumulation were also decreased by oral EGCG (figure 3 and figure 4). To further understand the mechanism of EGCG on attenuate colitis, we detected Notch signaling protein and found that the level of Notch expression, Notch activation, and downstream protein were also significance decreased by administration EGCG (figure 5). Our results revealed the effect of EGCG on UC and expound the mechanism.
In conclusion, our study provides direct evidence that EGCG reduces inflammatory response by targeting Notch and reveals the mechanism by which EGCG alleviates colitis in UC mice (Figure 6). EGCG suppressing inflammation may be a promising treatment option for chronic inflammatory diseases in patients with IBD.