1) Chronic Inflammation, Molecular Pathways involving Intestinal Stem/Progenitor Cell Activation
and Chemoprevention in Inflammatory Bowel Disease-Associated Colorectal Cancer.
Inflammatory bowel disease (IBD) is a longstanding inflammatory condition in the intestine and the risk for developing colorectal cancer is increased compared to the general population. Appropriately, then, patients, physician, and researchers are quite concerned about how to recognize (early detection) and prevent this fatal complication. Wnt/-catenin pathway is essential for intestinal homeostasis, including controlling intestinal stem cells (ISCs). In sporadic colorectal cancer, mutations (such as APC) that lead to activation of Wnt/-catenin pathway occur in most of cases. However, activation of Wnt/-catenin pathway by chronic inflammation such as IBD remains to be elucidated. My colleague and I proposed that chronic inflammation-mediated activation of PI3K/Akt signaling cooperated with Wnt to increase nuclear -catenin. We also demonstrated that Pi3k/Akt phosphorylated -catenin at Serine 552. Whereas N-terminal phosphorylation of -catenin triggers destruction, PI3k/Akt phosphorylation of -catenin near C-terminal causes nuclear translocation and increased transcription of target genes (cMyc, cyclinD1). PI3K inhibition in mice colitis-associated colon cancer model reduced epithelial Akt and -catenin activation, reduced stem/progenitor cell expansion, and reduced dysplasia. In conclusion, PI3K/Akt-mediated -catenin signaling is required for intestinal stem/progenitor activation during transformation from chronic colitis to colitis-associated colorectal cancer. Blocking PI3K pathway emerged as a biomarker of carcinogenesis and chemoprevention target in IBD-associated colorectal cancer from our results. A variety of pharmaceuticals which inhibit PI3K, Akt or the downstream target mTOR have been undergoing clinical trials in a variety of malignancies. Therefore we may soon see a move to combined endoscopic and biomarker- based surveillance that are able to identify those patient at high risk and even start chemopreventive drugs.
2) TNF medicates -catenin Activation in Intestinal Stem Cells in Inflammatory Bowel Disease.
TNF (tumor necrosis factor) is a cytokine, i.e., a cellular regulator that acts by triggering a specific cell-surface receptor (TNFR1 and TNFR2). TNF blockade by anti-TNF antibody in inflammatory bowel disease indicates that TNF is a central mediator of inflammation. TNF also alters cell proliferation and death. We hypothesized that TNF directly mediated ISC/progenitor responses in IBD through activation of Wnt/-catenin pathway. Data from human Crohn' show that anti-TNF reduces epithelial β-catenin and proliferation independent of inflammation. Data in intact and bone marrow chimera (BMC) Tnf-/- and Tnfr1/2-/- mice indicate that BM-derived TNF increases epithelial BrdU incorporation and β-catenin in crypt base-columnar (CBC) and transit amplifying cells and BAT-gal in CBC. TNF treatment of enteroid cultures increases ISC transcriptome including CD44 and Ascle2 mRNA and Ascl2 targets, Ets2 and TNFRSF19. TNF blockade abrogates colitis-induced dysplasia and limits epithelial BrdU and β-catenin levels in IL10-/- mice. The results are consistent with the model that TNF activates epithelial Wnt/β-catenin signaling and proliferation in IBD. These findings suggest that early anti-TNF therapy may attenuate the risk for dysplasia by reducing early stem cell activation during periods of severe mucosal inflammation.
3) Early Detection of Dysplasia in Inflammatory Bowel Disease.
Due to high risk for developing colorectal cancer in IBD, patient with long-standing IBD undergo surveillance colonoscopy. Surveillance colonoscopy involves taking random biopsies and sampling or removing suspicious lesions. The more samples taken, the better will be the sensitivity for detecting dysplasia because of “invisible” dysplasia by conventional colonoscopy. However, the more samples taken, the higher will be the pathology costs, the longer will be the time (and the associated costs) of the procedure, and the greater will be the morbidity of the colonoscopy. Hence, we presented data that florescence imaging of cathepsin activity correlated with dysplasia in mouse and human with inflammatory bowel disease. Cathepsins are lysosomal cysteine proteases that contribute to the proteolytic network in tumor microenvironments. The sensitivity and specificity for detecting dysplasia is 100% and 83%, respectively. This methodology presents unique advantages that may increase sensitivity and specificity of surveillance colonoscopy in patients with long-standing IBD.
4) Transepithelial Migration of Neutrophils in Inflammatory Bowel Disease.
The transepithelial migration (TEM) of neutrophils (PMN) is a histopathological hallmark of IBD, yet the mechanisms controlling PMN TEM remain poorly defined. The fucosylated, terminal glycan determinant Lewis X (Lex), expressed on the glycans of PMN surface glycoproteins (including MAC-1 and LFA-1), has previously been implicated in adhesive interactions between PMN and endothelium. However, little is known about the role of Lex in PMN function. Immunohistochemistry demonstrated robust expression of PMN-associated Lex within crypt abscesses in the colonic epithelium of individuals with IBD. Furthermore, engagement of Lex increased PMN adhesive interactions, both with other PMNs and with intestinal epithelial cells, blocking PMN chemotaxis and TEM. In addition to blocking PMN trafficking, targeting of Lex also altered post-migratory PMN functions, increasing both PMN phagocytosis of Salmonella enterica and release of primary granules.
Therefore, glycans expressing the Lex determinant represent a novel target for regulating both the trafficking of PMN into the intestinal lumen and PMN function. Further, given its robust expression in migrating PMN and during inflammation, Lex may be a rational target for modulating inflammation in IBD.
